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Sample records for stable p-heterocyclic carbenes

  1. Cyclic (alkyl)(amino)carbenes (CAACs): stable carbenes on the rise.

    PubMed

    Soleilhavoup, Michèle; Bertrand, Guy

    2015-02-17

    CONSPECTUS: Carbenes are compounds that feature a divalent carbon atom with only six electrons in its valence shell. In the singlet state, they possess a lone pair of electrons and a vacant orbital and therefore exhibit Lewis acidic and Lewis basic properties, which explains their very high reactivity. Following the preparation by our group in 1988 of the first representative, a variety of stable carbenes are now available, the most popular being the cyclic diaminocarbenes. In this Account, we discuss another class of stable cyclic carbenes, namely, cyclic (alkyl)(amino)carbenes (CAACs), in which one of the electronegative and π-donor amino substituents of diaminocarbenes is replaced by a σ-donating but not π-donating alkyl group. As a consequence, CAACs are more nucleophilic (σ-donating) but also more electrophilic (π-accepting) than diaminocarbenes. Additionally, the presence of a quaternary carbon in the position α to the carbene center provides steric environments that differentiate CAACs dramatically from all other ligands. We show that the peculiar electronic and steric properties of CAACs allow for the stabilization of unusual diamagnetic and paramagnetic main group element species. As examples, we describe the preparation of room temperature stable phosphorus derivatives in which the heteroatom is in the zero oxidation state, nucleophilic boron compounds, and phosphorus-, antimony-, boron-, silicon-, and even carbon-centered neutral and cationic radicals. CAACs are also excellent ligands for transition metal complexes. The most recent application is their use for the stabilization of paramagnetic complexes, in which the metal is often in a formal zero oxidation state. Indeed, bis(CAAC)M complexes in which the metal is gold, copper, cobalt, iron, nickel, manganese, and zinc have been isolated. Depending on the metal, the majority of spin density can reside either on the metal or on the carbene carbons and the nitrogen atoms of the CAAC ligand. In

  2. Stable Cyclic Carbenes and Related Species beyond Diaminocarbenes

    PubMed Central

    Melaimi, Mohand; Soleilhavoup, Michèle

    2011-01-01

    The success of homogeneous catalysis can be attributed largely to the development of a diverse range of ligand frameworks that have been used to tune the behavior of various systems. Spectacular results in this area have been achieved using cyclic diaminocarbenes (NHCs) as a result of their strong σ-donor properties. Although it is possible to cursorily tune the structure of NHCs, any diversity is still far from matching their phosphorus-based counterparts, which is one of the great strengths of the latter. A variety of stable acyclic carbenes are known, but they are either reluctant to bind metals or they give rise to fragile metal complexes. During the last five years, new types of stable cyclic carbenes, as well as related carbon-based ligands (which are not NHCs), and which feature even stronger σ-donor properties have been developed. Their synthesis and characterization as well as the stability, electronic properties, coordination behavior, and catalytic activity of the ensuing complexes are discussed, and comparisons with their NHC cousins are made. PMID:20836099

  3. Direct arylations for study of the air-stable P-heterocyclic biradical: from wide electronic tuning to characterization of the localized radicalic electrons.

    PubMed

    Ito, Shigekazu; Ueta, Yasuhiro; Ngo, Trang Thi Thu; Kobayashi, Makoto; Hashizume, Daisuke; Nishida, Jun-ichi; Yamashita, Yoshiro; Mikami, Koichi

    2013-11-20

    We have developed methods for installing aryl substituents directly on the phosphino groups of the 1,3-diphosphacyclobutane-2,4-diyl system. The aryl substituents tuned the electronic and structural characteristics of the biradical unit both in solution and in the solid state. 1-tert-butyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobuten-4-yl anion, prepared from phosphaalkyne (Mes*C≡P; Mes* = 2,4,6-tBu3C6H2) and t-butyllithium, was allowed to react with an electron-deficient N-heterocyclic reagent. The corresponding N-heteroaryl-substituted P-heterocyclic biradicals were produced via SNAr reactions. Biradicals bearing perfluorinated pyridyl substituents exhibited photoabsorption properties comparable to those of previously reported derivatives because the highest occupied and lowest unoccupied molecular orbit levels were reduced by a similar amount. In contrast, the triazine substituent reduced the band gap of the biradical unit, and the large red shift in the visible absorption and high oxidation potential were further tuned via subsequent SNAr and Negishi coupling reactions. The amino-substituted triazine structure provided a strongly electron-donating biradical chromophore, which produced unique p-type semiconducting behavior even though there was no obvious π-overlap in the crystalline state. The single-electron transfer reaction involving Mes*C≡P, phenyllithium, and iodine afforded 1,3-diphenyl-2,4-bis(2,4,6-tri-tert-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyl via the intermediate P-heterocyclic monoradical. The tetraaryl-substituted symmetric biradical product was used to determine the electron density distribution from the X-ray diffraction data. The data show highly localized radicalic electrons around the skeletal carbon atoms, moderately polarized skeletal P-C bonds in the four-membered ring, and no covalent transannular interaction.

  4. Highly stable water-soluble platinum nanoparticles stabilized by hydrophilic N-heterocyclic carbenes.

    PubMed

    Baquero, Edwin A; Tricard, Simon; Flores, Juan Carlos; de Jesús, Ernesto; Chaudret, Bruno

    2014-11-24

    Controlling the synthesis of stable metal nanoparticles in water is a current challenge in nanochemistry. The strategy presented herein uses sulfonated N-heterocyclic carbene (NHC) ligands to stabilize platinum nanoparticles (PtNPs) in water, under air, for an indefinite time period. The particles were prepared by thermal decomposition of a preformed molecular Pt complex containing the NHC ligand and were then purified by dialysis and characterized by TEM, high-resolution TEM, and spectroscopic techniques. Solid-state NMR studies showed coordination of the carbene ligands to the nanoparticle surface and allowed the determination of a (13)C-(195)Pt coupling constant for the first time in a nanosystem (940 Hz). Additionally, in one case a novel structure was formed in which platinum(II) NHC complexes form a second coordination sphere around the nanoparticle.

  5. Ultra stable self-assembled monolayers of N-heterocyclic carbenes on gold

    NASA Astrophysics Data System (ADS)

    Crudden, Cathleen M.; Horton, J. Hugh; Ebralidze, Iraklii I.; Zenkina, Olena V.; McLean, Alastair B.; Drevniok, Benedict; She, Zhe; Kraatz, Heinz-Bernhard; Mosey, Nicholas J.; Seki, Tomohiro; Keske, Eric C.; Leake, Joanna D.; Rousina-Webb, Alexander; Wu, Gang

    2014-05-01

    Since the first report of thiol-based self-assembled monolayers (SAMs) 30 years ago, these structures have been examined in a huge variety of applications. The oxidative and thermal instabilities of these systems are widely known, however, and are an impediment to their widespread commercial use. Here, we describe the generation of N-heterocyclic carbene (NHC)-based SAMs on gold that demonstrate considerably greater resistance to heat and chemical reagents than the thiol-based counterparts. This increased stability is related to the increased strength of the gold-carbon bond relative to that of a gold-sulfur bond, and to a different mode of bonding in the case of the carbene ligand. Once bound to gold, NHCs are not displaced by thiols or thioethers, and are stable to high temperatures, boiling water, organic solvents, pH extremes, electrochemical cycling above 0 V and 1% hydrogen peroxide. In particular, benzimidazole-derived carbenes provide films with the highest stabilities and evidence of short-range molecular ordering. Chemical derivatization can be employed to adjust the surface properties of NHC-based SAMs.

  6. Cationic Silica-Supported N-Heterocyclic Carbene Tungsten Oxo Alkylidene Sites: Highly Active and Stable Catalysts for Olefin Metathesis.

    PubMed

    Pucino, Margherita; Mougel, Victor; Schowner, Roman; Fedorov, Alexey; Buchmeiser, Michael R; Copéret, Christophe

    2016-03-18

    Designing supported alkene metathesis catalysts with high activity and stability is still a challenge, despite significant advances in the last years. Described herein is the combination of strong σ-donating N-heterocyclic carbene ligands with weak σ-donating surface silanolates and cationic tungsten sites leading to highly active and stable alkene metathesis catalysts. These well-defined silica-supported catalysts, [(≡SiO)W(=O)(=CHCMe2 Ph)(IMes)(OTf)] and [(≡SiO)W(=O)(=CHCMe2 Ph)(IMes)(+) ][B(Ar(F) )4 (-) ] [IMes=1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene, B(Ar(F) )4 =B(3,5-(CF3 )2 C6 H3 )4 ] catalyze alkene metathesis, and the cationic species display unprecedented activity for a broad range of substrates, especially for terminal olefins with turnover numbers above 1.2 million for propene.

  7. Cationic Silica-Supported N-Heterocyclic Carbene Tungsten Oxo Alkylidene Sites: Highly Active and Stable Catalysts for Olefin Metathesis.

    PubMed

    Pucino, Margherita; Mougel, Victor; Schowner, Roman; Fedorov, Alexey; Buchmeiser, Michael R; Copéret, Christophe

    2016-03-18

    Designing supported alkene metathesis catalysts with high activity and stability is still a challenge, despite significant advances in the last years. Described herein is the combination of strong σ-donating N-heterocyclic carbene ligands with weak σ-donating surface silanolates and cationic tungsten sites leading to highly active and stable alkene metathesis catalysts. These well-defined silica-supported catalysts, [(≡SiO)W(=O)(=CHCMe2 Ph)(IMes)(OTf)] and [(≡SiO)W(=O)(=CHCMe2 Ph)(IMes)(+) ][B(Ar(F) )4 (-) ] [IMes=1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene, B(Ar(F) )4 =B(3,5-(CF3 )2 C6 H3 )4 ] catalyze alkene metathesis, and the cationic species display unprecedented activity for a broad range of substrates, especially for terminal olefins with turnover numbers above 1.2 million for propene. PMID:26928967

  8. A stable dimer of SiS2 arranged between two carbene molecules.

    PubMed

    Mohapatra, Chandrajeet; Mondal, Kartik Chandra; Samuel, Prinson P; Keil, Helena; Niepötter, Benedikt; Herbst-Irmer, Regine; Stalke, Dietmar; Dutta, Sayan; Koley, Debasis; Roesky, Herbert W

    2015-09-01

    The Me-cAAC:-stabilized dimer of silicon disulfide (SiS2 ) has been isolated in the molecular form as (Me-cAAC:)2 Si2 S4 (2) at room temperature [Me-cAAC:=cyclic alkyl(amino) carbene]. Compound 2 has been synthesized from the reaction of (Me-cAAC:)2 Si2 with elemental sulfur in a 1:4 molar ratio under oxidative addition. This is the smallest molecular unit of silicon disulfide characterized by X-ray crystallography, electron ionization mass spectrometry, and NMR spectroscopy. Structures with three sulfur atoms arranged around a silicon atom are known; however, 2 is the first structurally characterized silicon-sulfur compound containing one terminal and two bridging sulfur atoms at each silicon atom. Compound 2 shows no decomposition after storing for three months in an inert atmosphere at ambient temperature. The bonding of 2 has been further studied by theoretical calculations.

  9. Stable N-heterocyclic carbene (NHC)-palladium(0) complexes as active catalysts for olefin cyclopropanation reactions with ethyl diazoacetate.

    PubMed

    Martín, Carmen; Molina, Francisco; Alvarez, Eleuterio; Belderrain, Tomás R

    2011-12-23

    The Pd(0) complexes [(NHC)PdL(n)] (NHC=N-heterocyclic carbene ligand; L=styrene for n=2 or PR(3) for n=1) efficiently catalyse olefin cyclopropanation by using ethyl diazoacetate (EDA) as the carbene source with activities that improve on previously described catalytic systems based on this metal. Mechanistic studies have shown that all of these catalyst precursors deliver the same catalytic species in solution, that is, [(IPr)Pd(sty)], a 14e(-) unsaturated intermediate that further reacts with EDA to afford [(IPr)Pd(=CHCO(2)Et)(sty)], from which the cyclopropane is formed.

  10. Palladium-catalyzed carbene migratory insertion using conjugated ene-yne-ketones as carbene precursors.

    PubMed

    Xia, Ying; Qu, Shuanglin; Xiao, Qing; Wang, Zhi-Xiang; Qu, Peiyuan; Chen, Li; Liu, Zhen; Tian, Leiming; Huang, Zhongxing; Zhang, Yan; Wang, Jianbo

    2013-09-11

    Palladium-catalyzed cross-coupling reactions between benzyl, aryl, or allyl bromides and conjugated ene-yne-ketones lead to the formation of 2-alkenyl-substituted furans. This novel coupling reaction involves oxidative addition, alkyne activation-cyclization, palladium carbene migratory insertion, β-hydride elimination, and catalyst regeneration. Palladium (2-furyl)carbene is proposed as the key intermediate, which is supported by DFT calculations. The palladium carbene character of the key intermediate is validated by three aspects, including bond lengths, Wiberg bond order indices, and molecular orbitals, by comparison to those reported for stable palladium carbene species. Computational studies also revealed that the rate-limiting step is ene-yne-ketone cyclization, which leads to the formation of the palladium (2-furyl)carbene, while the subsequent carbene migratory insertion is a facile process with a low energy barrier (<5 kcal/mol). PMID:23947689

  11. Carbenes and Nitrenes

    ERIC Educational Resources Information Center

    Coyle, J. D.

    1974-01-01

    Summarizes the general methods for carbene and nitrene formation and the reactions in which carbenes and nitrenes are involved such as their reactions with transition metal atoms, alkenes of aromatic compounds, and uncharged oxygen or nitrogen nucleophiles. (CC)

  12. Arylation of rhodium(II) azavinyl carbenes with boronic acids.

    PubMed

    Selander, Nicklas; Worrell, Brady T; Chuprakov, Stepan; Velaparthi, Subash; Fokin, Valery V

    2012-09-12

    A highly efficient and stereoselective arylation of in situ-generated azavinyl carbenes affording 2,2-diaryl enamines at ambient temperatures has been developed. These transition-metal carbenes are directly produced from readily available and stable 1-sulfonyl-1,2,3-triazoles in the presence of a rhodium carboxylate catalyst. In several cases, the enamines generated in this reaction can be cyclized into substituted indoles employing copper catalysis. PMID:22913576

  13. Dihydrogen activation by frustrated carbene-borane Lewis pairs: an experimental and theoretical study of carbene variation.

    PubMed

    Kronig, Sabrina; Theuergarten, Eileen; Holschumacher, Dirk; Bannenberg, Thomas; Daniliuc, Constantin G; Jones, Peter G; Tamm, Matthias

    2011-08-01

    A variety of Lewis acid-base pairs consisting of tris(pentafluorophenyl)borane, B(C(6)F(5))(3), in combination with sterically demanding five- and six-membered N-heterocyclic carbenes (NHCs) of the imidazolin-2-ylidene, imidazolidin-2-ylidene, and tetrahydropyrimidin-2-ylidene types were investigated with respect to their potential to act as frustrated Lewis pairs (FLP) by reaction with dihydrogen (H(2)) and tetrahydrofuran (THF). A sufficient degree of "frustration" was usually established by introduction of a 1,3-di-tert-butyl or 1,3-diadamantyl carbene substitution pattern, which allows an unquenched acid-base reactivity and thus leads to heterolytic dihydrogen activation and ring-opening of THF. In contrast, 1,3-bis(2,6-diisopropylphenyl)-substituted carbenes showed ambiguous behavior, and the corresponding five-membered imidazolin-2-ylidene formed a stable carbene-B(C(6)F(5))(3) adduct, whereas fast C-F activation and formation of a zwitterionic pyrimidinium-fluoroborate was observed for the six-membered tetrahydropyrimidin-2-ylidene. A stable adduct was also isolated for the combination of the acyclic carbene bis(diisopropylamino)methylene with B(C(6)F(5))(3), and consequently no reactivity toward H(2) and THF was observed. To rationalize the reactivity of the carbene-borane Lewis pairs, the thermodynamics of adduct formation with B(C(6)F(5))(3) were calculated for 10 different carbenes; the stability (or instability) of these adducts can be used as a good measure of the degree of "frustration".

  14. Synthesis and Properties of Chelating N-Heterocyclic Carbene Rhodium(I) Complexes: Synthetic Experiments in Current Organometallic Chemistry

    ERIC Educational Resources Information Center

    Mata, Jose A.; Poyatos, Macarena; Mas-Marza, Elena

    2011-01-01

    The preparation and characterization of two air-stable Rh(I) complexes bearing a chelating N-heterocyclic carbene (NHC) ligand is described. The synthesis involves the preparation of a Ag(I)-NHC complex and its use as carbene transfer agent to a Rh(I) precursor. The so obtained complex can be further reacted with carbon monoxide to give the…

  15. Steroid Derived Mesoionic Gold and Silver Mono- and Polymetallic Carbenes.

    PubMed

    Frutos, María; de la Torre, María C; Sierra, Miguel A

    2015-12-01

    A two-step synthesis of gold mesoionic carbene complexes containing estrone moieties has been developed. The method uses the methylation of the triazole nucleus, followed by the treatment of the triazolium salt with Ag2O and transmetalation with [AuCl(SMe2)]. Mono-, bi-, tri-, and tetrametallic gold complexes can be obtained depending on the structure of the starting triazolium salts. Tetrametallic gold carbene embedded in a macrocylic stereoidal cavity containing four estrone nuclei has been also prepared. Additionally, the mono- and bimetallic silver carbene complexes containing triazole-steroid ligands have been isolated and characterized. These complexes resulted to be stable and have been characterized by spectroscopic and HRMS techniques. The gold and silver complexes having triazole-steroid ligands are unprecedented in the literature and the method reported here to access to these compounds is easy and efficient. Preliminary results regarding the catalytic activity of some of the gold-carbenes prepared in the insertion of diazoalkanes into alcohols are presented.

  16. Steroid Derived Mesoionic Gold and Silver Mono- and Polymetallic Carbenes.

    PubMed

    Frutos, María; de la Torre, María C; Sierra, Miguel A

    2015-12-01

    A two-step synthesis of gold mesoionic carbene complexes containing estrone moieties has been developed. The method uses the methylation of the triazole nucleus, followed by the treatment of the triazolium salt with Ag2O and transmetalation with [AuCl(SMe2)]. Mono-, bi-, tri-, and tetrametallic gold complexes can be obtained depending on the structure of the starting triazolium salts. Tetrametallic gold carbene embedded in a macrocylic stereoidal cavity containing four estrone nuclei has been also prepared. Additionally, the mono- and bimetallic silver carbene complexes containing triazole-steroid ligands have been isolated and characterized. These complexes resulted to be stable and have been characterized by spectroscopic and HRMS techniques. The gold and silver complexes having triazole-steroid ligands are unprecedented in the literature and the method reported here to access to these compounds is easy and efficient. Preliminary results regarding the catalytic activity of some of the gold-carbenes prepared in the insertion of diazoalkanes into alcohols are presented. PMID:26600185

  17. Substitution effects on the formation of T-shaped palladium carbene and thioketone complexes from Li/Cl carbenoids.

    PubMed

    Molitor, Sebastian; Feichtner, Kai-Stephan; Kupper, Claudia; Gessner, Viktoria H

    2014-08-18

    The preparation of palladium thioketone and T-shaped carbene complexes by treatment of thiophosphoryl substituted Li/Cl carbenoids with a Pd(0) precursor is reported. Depending on the steric demand, the anion-stabilizing ability of the silyl moiety (by negative hyperconjugation effects) and the remaining negative charge at the carbenic carbon atom, isolation of a three-coordinate, T-shaped palladium carbene complex is possible. In contrast, insufficient charge stabilization results in the transfer of the sulfur of the thiophosphoryl moiety and thus in the formation of a thioketone complex. While the thioketones are stable compounds the carbene complexes are revealed to be highly reactive and decompose under elimination of Pd metal. Computational studies revealed that both complexes are formed by a substitution mechanism. While the ketone turned out to be the thermodynamically favored product, the carbene is kinetically favored and thus preferentially formed at low reaction temperatures.

  18. N,N'-Diamidocarbenes: Isolable Divalent Carbons with Bona Fide Carbene Reactivity.

    PubMed

    Moerdyk, Jonathan P; Schilter, David; Bielawski, Christopher W

    2016-08-16

    Since the first reported isolation of a carbene just over a quarter century ago, the study of such compounds-including stable derivatives-has flourished. Indeed, N-heterocyclic carbenes (NHCs), of which imidazolylidenes and their derivatives are the most pervasive subclass, feature prominently in organocatalysis, as ligands for transition metal catalysts, and as stabilizers of reactive species. However, imidazolylidenes (and many other NHCs) typically lack the reactivity characteristic of electrophilic carbenes, including insertion into unactivated C-H bonds, participation in [2 + 1] cycloadditions, and reaction with carbon monoxide. This has led to debates over whether NHCs are truly carbenic in nature or perhaps better regarded as ylides. The fundamental and synthetic utility of transformations that involve electrophilic carbenes has motivated our group and others to expand the reactivity of NHCs and other stable carbenes to encompass electrophilic carbene chemistry. These efforts have led to the development of the diamidocarbenes (DACs), a stable and unique subset of the NHCs that feature carbonyl groups inserted into the N-heterocyclic scaffold. To date, crystalline five-, six-, and seven-membered DACs have been prepared and studied. Unlike imidazolylidenes, which are often designated as prototypical NHCs, the DACs exhibit a reactivity profile similar to that of bona fide carbenes, reactive species that are less "tamed" by heteroatom π conjugation. The DACs engage in [2 + 1] cycloadditions with electron-rich or -poor alkenes, aldehydes, alkynes, and nitriles, and doing so in a reversible manner in some cases. They also react with isonitriles, reversibly couple to CO, and mediate the dehydrogenation of hydrocarbons. Such rich chemistry may be rationalized in terms of their ambiphilicity: DACs are nucleophilic, as required for some of the reactions above, yet also have electrophilic character, as evidenced by their insertions into unactivated N-H and C-H bonds

  19. Gold Carbene or Carbenoid: Is There a Difference?

    PubMed Central

    Wang, Yahui; Muratore, Michael E; Echavarren, Antonio M

    2015-01-01

    By reviewing the recent progress on the elucidation of the structure of gold carbenes and the definitions of metal carbenes and carbenoids, we recommend to use the term gold carbene to describe gold carbene-like intermediates, regardless of whether the carbene or carbocation extreme resonance dominates. Gold carbenes, because of the weak metal-to-carbene π-back-donation and their strongly electrophilic reactivity, could be classified into the broader family of Fischer carbenes, although their behavior and properties are very specific. PMID:25786384

  20. Ruthenium Vinyl Carbene Intermediates in Enyne Metathesis

    PubMed Central

    Diver, Steven T.

    2009-01-01

    This review provides an overview of ruthenium vinyl carbene reactivity as it relates to enyne metathesis. Methods for the synthesis of metathesis-active and metathesis-inactive complexes are also summarized. Some of the early hypotheses about vinyl carbene intermediates in enyne metatheses were tested in the arena of synthetic chemistry and subsequently led to mechanistic studies. In these two areas, studies from the author's labs are described. There are still many unresolved questions in enyne metathesis that trace back to vinyl carbene reactivity. Hopefully this review will stimulate further investigation into vinyl carbene reactivity which should further refine our understanding of catalytic enyne metathesis. PMID:19590747

  1. Computational Chemistry Studies on the Carbene Hydroxymethylene

    ERIC Educational Resources Information Center

    Marzzacco, Charles J.; Baum, J. Clayton

    2011-01-01

    A density functional theory computational chemistry exercise on the structure and vibrational spectrum of the carbene hydroxymethylene is presented. The potential energy curve for the decomposition reaction of the carbene to formaldehyde and the geometry of the transition state are explored. The results are in good agreement with recent…

  2. N-Heterocyclic Carbene-Catalyzed Alcohol Acetylation: An Organic Experiment Using Organocatalysis

    ERIC Educational Resources Information Center

    Morgan, John P.; Shrimp, Jonathan H.

    2014-01-01

    Undergraduate students in the teaching laboratory have successfully used N-heterocyclic carbenes (NHCs) as organocatalysts for the acetylation of primary alcohols, despite the high water sensitivity of uncomplexed ("free") NHCs. The free NHC readily reacted with chloroform, resulting in an air- and moisture-stable adduct that liberates…

  3. A Three-Step Laboratory Sequence to Prepare a Carbene Complex of Silver(I) Chloride

    ERIC Educational Resources Information Center

    Canal, John P.; Ramnial, Taramatee; Langlois, Lisa D.; Abernethy, Colin D.; Clyburne, Jason A. C.

    2008-01-01

    We have developed a multistep inorganic synthesis experiment for our second-year undergraduate teaching laboratory that introduces students to modern organometallic chemistry. The ligands are prepared in two simple steps and the preparation of an air-stable silver carbene complex is accomplished in the third step. The students are introduced to…

  4. An Entry to Mixed NHC-Fischer Carbene Complexes and Zwitterionic Group 6 Metal Alkenyls.

    PubMed

    Sierra, Miguel A; Merinero, Alba D; Giner, Elena A; Gómez-Gallego, Mar; Ramírez de Arellano, Carmen

    2016-09-12

    The addition of NHCs to α,β-unsaturated Cr(0) and W(0) (Fischer) carbene complexes is strongly dependent on the electrophilicity of the carbene carbon. Electrophilic alkoxy-carbene complexes quantitatively react with NHCs to yield stable zwitterionic (racemic) Cr(0) - and W(0) -alkenyls with total regio- and E-stereoselectivity. Less electrophilic aminocarbenes react with NHCs to promote the displacement of a CO ligand and yield "mixed" NHC/Fischer biscarbenes in a process that is unprecedented in group 6 metal-carbene chemistry. In fact, the compounds prepared, are some of the scarce examples of Fischer bisylidenes reported in the literature. The electrochemistry of the zwitterionic Cr(0) - and W(0) -alkenylcomplexes made, show that these compounds have a strong reductor character, which is demonstrated in their reactions towards [Ph3 C][PF6 ]. The oxidation processes lead to new types of cationic Fischer mono- and biscarbene complexes having a charged NHC fragment in their structures, in a new example of the use of electron-transfer reactions as a method to prepare novel group 6 (Fischer) carbene complexes.

  5. An Entry to Mixed NHC-Fischer Carbene Complexes and Zwitterionic Group 6 Metal Alkenyls.

    PubMed

    Sierra, Miguel A; Merinero, Alba D; Giner, Elena A; Gómez-Gallego, Mar; Ramírez de Arellano, Carmen

    2016-09-12

    The addition of NHCs to α,β-unsaturated Cr(0) and W(0) (Fischer) carbene complexes is strongly dependent on the electrophilicity of the carbene carbon. Electrophilic alkoxy-carbene complexes quantitatively react with NHCs to yield stable zwitterionic (racemic) Cr(0) - and W(0) -alkenyls with total regio- and E-stereoselectivity. Less electrophilic aminocarbenes react with NHCs to promote the displacement of a CO ligand and yield "mixed" NHC/Fischer biscarbenes in a process that is unprecedented in group 6 metal-carbene chemistry. In fact, the compounds prepared, are some of the scarce examples of Fischer bisylidenes reported in the literature. The electrochemistry of the zwitterionic Cr(0) - and W(0) -alkenylcomplexes made, show that these compounds have a strong reductor character, which is demonstrated in their reactions towards [Ph3 C][PF6 ]. The oxidation processes lead to new types of cationic Fischer mono- and biscarbene complexes having a charged NHC fragment in their structures, in a new example of the use of electron-transfer reactions as a method to prepare novel group 6 (Fischer) carbene complexes. PMID:27459647

  6. Carbene formation upon reactive dissolution of metal oxides in imidazolium ionic liquids.

    PubMed

    Wellens, Sil; Brooks, Neil R; Thijs, Ben; Meervelt, Luc Van; Binnemans, Koen

    2014-03-01

    Metal oxides were found to dissolve in different imidazolium ionic liquids with a hydrogen atom in the C2 position of the imidazolium ring, but not if a methyl substituent was present in the C2 position. The crystal structure of the product that crystallised from an ionic liquid containing dissolved silver(i) oxide showed that this was a silver(i) carbene complex. The presence of carbenes in solution was proven by (13)C NMR spectroscopy and the reactions were also monitored by Raman spectroscopy. The dissolution of other metal oxides, namely copper(ii) oxide, zinc(ii) oxide and nickel(ii) oxide, was also studied in imidazolium ionic liquids and it was found that stable zinc(ii) carbenes were formed in solution, but these did not crystallise under the given experimental conditions. A crystalline nickel(ii) carbene complex could be obtained from a solution of nickel(ii) chloride dissolved in a mixture of 1-butyl-3-methylimidazolium and 1-ethyl-3-methylimidazolium acetate. PMID:24390601

  7. Metal-Ligand Cooperativity in a Methandiide-Derived Iridium Carbene Complex.

    PubMed

    Weismann, Julia; Waterman, Rory; Gessner, Viktoria H

    2016-03-01

    The synthesis, electronic structure, and reactivity of the first Group 9 carbene complex, [Cp*IrL] [L=C(Ph2 PS)(SO2 Ph)] (2), based on a dilithio methandiide are reported. Spectroscopic as well as computational studies have shown that, despite using a late transition-metal precursor, sufficient charge transfer occurred from the methandiide to the metal, resulting in a stable, nucleophilic carbene species with pronounced metal-carbon double-bond character. The potential of this iridium complex in the activation of a series of E-H bonds by means of metal-ligand cooperation has been tested. These studies have revealed distinct differences in the reactivity of 2 compared to a previously reported ruthenium analogue. Whereas attempts to activate the O-H bond in different phenol derivatives resulted in ligand cleavage, H-H and Si-H activation as well as dehydrogenation of isopropanol have been accomplished. These reactions are driven by the transformation of the carbene to an alkyl ligand. Contrary to a previously reported ruthenium carbene system, the dihydrogen activation has been found to proceed by a stepwise mechanism, with the activation first taking place solely at the metal. The activated products further reacted to afford a cyclometalated complex through liberation of the activated substrates. In the case of triphenylsilane, cyclometalation could thus be induced by a substoichiometric (i.e., catalytic) amount of silane. PMID:26748420

  8. Direct estimate of the internal π-donation to the carbene centre within N-heterocyclic carbenes and related molecules

    PubMed Central

    Andrada, Diego M; Holzmann, Nicole; Hamadi, Thomas

    2015-01-01

    Summary Fifteen cyclic and acylic carbenes have been calculated with density functional theory at the BP86/def2-TZVPP level. The strength of the internal X→p(π) π-donation of heteroatoms and carbon which are bonded to the C(II) atom is estimated with the help of NBO calculations and with an energy decomposition analysis. The investigated molecules include N-heterocyclic carbenes (NHCs), the cyclic alkyl(amino)carbene (cAAC), mesoionic carbenes and ylide-stabilized carbenes. The bonding analysis suggests that the carbene centre in cAAC and in diamidocarbene have the weakest X→p(π) π-donation while mesoionic carbenes possess the strongest π-donation. PMID:26877795

  9. Studies of coal structure using carbene chemistry

    SciTech Connect

    Not Available

    1990-01-01

    The object of this grant was to react coal, derivatized forms of coal, and solvent swelled coal with carbenes (divalent carbon species) under mild conditions. These carbenes were to be prepared by treating the coal with several diazo compounds and then thermally decomposing them at relatively low temperatures (80--130{degree}C). The carbenes were to be chosen to show varying selectively toward aromatic rings containing heteroatom functionalities and toward polynuclear aromatic systems. In some instances, where selectivities toward aromatic and heteroaromatic ring systems were not known, model studies were to be carried out. Because of the generally mild conditions employed and the good selectivity anticipated, and actually observed with one particular system, it was expected that this methodology would provide structural information about the coal, along with data on the extent of occurrence and type of aromatic systems. After carbene reactions, treatment of the coal samples was to include extractions and thermolysis. Physical studies included thermogravimetric analysis, diffuse reflectance FT-IR spectroscopy, NMR ({sup 1}H and {sup 13}C) spectroscopy, gas chromatography, GC/MS and GC/FT-IR. 7 figs., 10 tabs.

  10. Unusual solvation through both p-orbital lobes of a carbene carbon

    SciTech Connect

    Hadad, C. Z.; Jenkins, Samantha; Flórez, Elizabeth

    2015-03-07

    As a result of a configurational space search done to explain the experimental evidence of transient specific solvation of singlet fluorocarbene amide with tetrahydrofuran, we found that the most stable structures consist in a group in which each oxygen of two tetrahydrofuran molecules act as electron donor to its respective empty p-orbital lobe of the carbene carbon atom, located at each side of the carbene molecular plane. This kind of species, which to our knowledge has not been reported before, explains very well the particular experimental characteristics observed for the transient solvation of this system. We postulate that the simultaneous interaction to both p-orbital lobes seems to confer a special stability to the solvation complexes, because this situation moves away the systems from the proximity of the corresponding transition states for the ylide products. Additionally, we present an analysis of other solvation complexes and a study of the nature of the involved interactions.

  11. Quantitative assessment of the carbocation/carbene character of the gold-carbene bond.

    PubMed

    Azzopardi, Keith M; Bistoni, Giovanni; Ciancaleoni, Gianluca; Tarantelli, Francesco; Zuccaccia, Daniele; Belpassi, Leonardo

    2015-08-21

    The geometric perturbation of the cyclopropyl ring in [LAu(S)](n+) (S = cyclopropyl(methoxy)carbene) complexes has been recently proposed as an indirect experimental probe of the [LAu](n+) electron-donating power, but experimental data are available only for a phosphine ligand [Brooner et al., Chem. Commun., 2014, 50, 2420, L = P(t-Bu)2(o-biphenyl)]. We broaden the study through DFT geometry optimization of a large number of systems, including anionic, neutral and cationic ligands. We combine these results with the accurate calculation, through charge displacement analysis, of the Dewar-Chatt-Duncanson components of the Au-carbene bond. The results demonstrate a linear correlation between the distortion of the cyclopropyl ring (Δd) and the Au → C π back-donation, which enables us to confidently estimate back-donation from a simple geometry optimization or, when available, from experimental data such as X-ray crystal structures. Consequently, Δd can be reliably used to quantitatively determine the position of each system in the continuum between the carbocationic and carbene extremes and the percentage of back-donation that S is able to accept (Pback). In particular, Pback results to be vanishing with cationic ligands, between 18 and 27% with neutral phosphines and carbenes and around 50% with anionic ligands. Finally, we study the effect of the heteroatom on the substrate, showing that the absolute value of the back-donation is enhanced by around 25% when the methoxy is substituted by a methyl group. Despite this, since the absence of the heteroatom also enhances the maximum capacity of the carbene to accept back-donation, the position of the systems in the continuum moves only slightly toward the carbene end. PMID:26161587

  12. Divergent pathways in the reaction of Fischer carbenes and palladium.

    PubMed

    López-Alberca, María P; Mancheño, María J; Fernandez, Israel; Gómez-Gallego, Mar; Sierra, Miguel A; Torres, Rosario

    2007-04-26

    [reaction: see text] The Pd-catalyzed reaction of beta-arylaminochromium(0) carbene complexes produces by transmetalation the first isolated and X-ray structurally characterized bis-Pd(II) carbene complex, as well as other alternative reaction pathways, such as the oxidative addition-transmetalation sequence, not seen before in this chemistry.

  13. Synthesis in situ of gold nanoparticles by a dialkynyl Fischer carbene complex anchored to glass surfaces

    NASA Astrophysics Data System (ADS)

    Bertolino, María Candelaria; Granados, Alejandro Manuel

    2016-10-01

    In this work we present a detailed study of classic reactions such as "click reaction" and nucleophilic substitution reaction but on glass solid surface (slides). We used different reactive center of a dialkynylalcoxy Fischer carbene complex of tungsten(0) to be anchored to modified glass surface with amine, to obtain aminocarbene, and azide terminal groups. These cycloaddition reaction showed regioselectivity to internal triple bond of dialkynyl Fischer carbene complex without Cu(I) as catalyst. Anyway the carbene anchored was able to act as a reducing agent to produce in situ very stable gold nanoparticles fixed on surface. We showed the characterization of modified glasses by contact angle measurements and XPS. Synthesized nanoparticles were characterized by SEM, XPS, EDS and UV-vis. The modified glasses showed an important enhancement Raman-SERS. This simple, fast and robust method to create a polifunctional and hybrid surfaces can be valuable in a wide range of applications such as Raman-SERS substrates and other optical fields.

  14. New metathesis catalyst bearing chromanyl moieties at the N-heterocyclic carbene ligand

    PubMed Central

    Suchodolski, Szymon; Wojtkielewicz, Agnieszka; Morzycki, Jacek W

    2015-01-01

    Summary The synthesis of a new type of Hoveyda–Grubbs 2nd generation catalyst bearing a modified N-heterocyclic carbene ligands is reported. The new catalyst contains an NHC ligand symmetrically substituted with chromanyl moieties. The complex was tested in model CM and RCM reactions. It showed very high activity in CM reactions with electron-deficient α,β-unsaturated compounds even at 0 °C. It was also examined in more demanding systems such as conjugated dienes and polyenes. The catalyst is stable, storable and easy to purify. PMID:26877801

  15. Latent ruthenium–indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand

    PubMed Central

    Schmid, Thibault E; Modicom, Florian; Dumas, Adrien; Borré, Etienne; Toupet, Loic

    2015-01-01

    Summary A silver-free methodology was developed for the synthesis of unprecedented N-heterocyclic carbene ruthenium indenylidene complexes bearing a bidentate picolinate ligand. The highly stable (SIPr)(picolinate)RuCl(indenylidene) complex 4a (SIPr = 1,3-bis(2-6-diisopropylphenyl)imidazolidin-2-ylidene) demonstrated excellent latent behaviour in ring closing metathesis (RCM) reaction and could be activated in the presence of a Brønsted acid. The versatility of the catalyst 4a was subsequently demonstrated in RCM, cross-metathesis (CM) and enyne metathesis reactions. PMID:26425213

  16. New metathesis catalyst bearing chromanyl moieties at the N-heterocyclic carbene ligand.

    PubMed

    Hryniewicka, Agnieszka; Suchodolski, Szymon; Wojtkielewicz, Agnieszka; Morzycki, Jacek W; Witkowski, Stanisław

    2015-01-01

    The synthesis of a new type of Hoveyda-Grubbs 2(nd) generation catalyst bearing a modified N-heterocyclic carbene ligands is reported. The new catalyst contains an NHC ligand symmetrically substituted with chromanyl moieties. The complex was tested in model CM and RCM reactions. It showed very high activity in CM reactions with electron-deficient α,β-unsaturated compounds even at 0 °C. It was also examined in more demanding systems such as conjugated dienes and polyenes. The catalyst is stable, storable and easy to purify. PMID:26877801

  17. Latent ruthenium-indenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand.

    PubMed

    Schmid, Thibault E; Modicom, Florian; Dumas, Adrien; Borré, Etienne; Toupet, Loic; Baslé, Olivier; Mauduit, Marc

    2015-01-01

    A silver-free methodology was developed for the synthesis of unprecedented N-heterocyclic carbene ruthenium indenylidene complexes bearing a bidentate picolinate ligand. The highly stable (SIPr)(picolinate)RuCl(indenylidene) complex 4a (SIPr = 1,3-bis(2-6-diisopropylphenyl)imidazolidin-2-ylidene) demonstrated excellent latent behaviour in ring closing metathesis (RCM) reaction and could be activated in the presence of a Brønsted acid. The versatility of the catalyst 4a was subsequently demonstrated in RCM, cross-metathesis (CM) and enyne metathesis reactions. PMID:26425213

  18. Generating and trapping metalla-N-heterocyclic carbenes.

    PubMed

    Ruiz, Javier; García, Lucía; Vivanco, Marilín; Berros, Ángela; Van der Maelen, Juan Francisco

    2015-03-27

    By means of a combined experimental and theoretical approach, the electronic features and chemical behavior of metalla-N-heterocyclic carbenes (MNHCs, N-heterocyclic carbenes containing a metal atom within the heterocyclic skeleton) have been established and compared with those of classical NHCs. MNHCs are strongly basic (proton affinity and pK(a) values around 290 kcal mol(-1) and 36, respectively) with a narrow singlet-triplet gap (around 23 kcal mol(-1)). MNHCs can be generated from the corresponding metalla-imidazolium salts and trapped by addition of transition-metal complexes affording the corresponding heterodimetallic dicarbene derivatives, which can serve as carbene transfer agents.

  19. Fundamental spectroscopic studies of carbenes and hydrocarbon radicals

    SciTech Connect

    Thaddeus, P.; Gottlieb, C.

    1992-05-01

    This document details activities during this reporting period topics discussed are: The first spectroscopic identification of the HCCCO and DCCCO radicals; detection of new vibrationally excited states of the carbon chain radicals CCH and CCD and the three-membered carbene ring, cyclopropenylidene; determination of an accurate structure of the cumulene carbene H{sub 2}CCC; analysis the hyperfine structure in the SiC radical; and the undertaking of a systematic search for new sulfur bearing radicals.

  20. CPh3 as a functional group in P-heterocyclic chemistry: elimination of HCPh3 in the reaction of P-CPh3 substituted Li/Cl phosphinidenoid complexes with Ph2C=O.

    PubMed

    García, C Murcia; Ferao, A Espinosa; Schnakenburg, G; Streubel, R

    2016-02-14

    P-CPh3 substituted oxaphosphirane complexes 3 were prepared using Li/Cl phosphinidenoid complexes 2 (M = Cr, Mo, W) and benzaldehyde. Employing 2 and benzophenone resulted in the formation of oxaphospholane complexes 4 and 5, the former bearing a benzo[c]-1,2-oxaphospholane and the latter a novel pentacyclic P-ligand. According to DFT studies the latter P-heterocycle arises from formal dimerization of a transient benzofused 2-phosphafurane complex 8, one of the fragments undergoing water-catalyzed [1,3]H shift (4) and the other (11) formed via elimination of HCPh3.

  1. CPh3 as a functional group in P-heterocyclic chemistry: elimination of HCPh3 in the reaction of P-CPh3 substituted Li/Cl phosphinidenoid complexes with Ph2C=O.

    PubMed

    García, C Murcia; Ferao, A Espinosa; Schnakenburg, G; Streubel, R

    2016-02-14

    P-CPh3 substituted oxaphosphirane complexes 3 were prepared using Li/Cl phosphinidenoid complexes 2 (M = Cr, Mo, W) and benzaldehyde. Employing 2 and benzophenone resulted in the formation of oxaphospholane complexes 4 and 5, the former bearing a benzo[c]-1,2-oxaphospholane and the latter a novel pentacyclic P-ligand. According to DFT studies the latter P-heterocycle arises from formal dimerization of a transient benzofused 2-phosphafurane complex 8, one of the fragments undergoing water-catalyzed [1,3]H shift (4) and the other (11) formed via elimination of HCPh3. PMID:26751149

  2. Preparation and Use of Carbonyl-decorated Carbenes in the Activation of White Phosphorus

    PubMed Central

    Torres, Antonio J.; Dorsey, Christopher L.; Hudnall, Todd W.

    2014-01-01

    Here we present a protocol for the synthesis of two distinct carbonyl-decorated carbenes. Both carbenes can be prepared using nearly identical procedures in multi-gram scale quantities. The goal of this manuscript is to clearly detail how to handle and prepare these unique carbenes such that a synthetic chemist of any skill level can work with them. The two carbenes described are a diamidocarbene (DAC, carbene 1) and a monoamidoaminocarbene (MAAC 2). These carbenes are highly electron-deficient and as such display reactivity profiles that are atypical of more traditional N-heterocyclic carbenes. Additionally, these two carbenes only differ in their electrophilic character and not their steric parameters, making them ideal for studying how carbene electronics influence reactivity. To demonstrate this phenomenon, we are also describing the activation of white phosphorus (P4) using these carbenes. Depending on the carbene used, two very different phosphorus-containing compounds can be isolated. When the DAC 1 is used, a tris(phosphaalkenyl)phosphane can be isolated as the exclusive product. Remarkably however, when MAAC 2 is added to P4 under identical reaction conditions, an unexpected carbene-supported P8 allotrope of phosphorus is isolated exclusively. Mechanistic studies demonstrate that this carbene-supported P8allotrope forms via a [2+2] cycloaddition dimerization of a transient diphosphene which has been trapped by treatment with 2,3-dimethyl-1,3-butadiene. PMID:25350272

  3. How can a carbene be active in an ionic liquid?

    PubMed

    Thomas, Martin; Brehm, Martin; Hollóczki, Oldamur; Kirchner, Barbara

    2014-02-01

    The solvation of the carbene 1-ethyl-3-methylimidazole-2-ylidene in the ionic liquid 1-ethyl-3-methylimidazolium acetate was investigated by ab initio molecular dynamics simulations in order to reveal the interaction between these two highly important classes of materials: N-heterocyclic carbenes with superb catalytic activity and ionic liquids with advantageous properties as solvents and reaction media. In contrast to previously published data on analogous systems, no hydrogen bond is observed between the hypovalent carbon atom and the most acidic ring hydrogen atoms, as these interaction sites of the imidazolium ring are predominantly occupied by the acetate ions. Keeping the carbene away from the ring hydrogen atoms prevents stabilization of this reactive species, and hence any retarding effect on subsequent reactions, which explains the observed high reactivity of the carbene in acetate-based ionic liquids. Instead, the carbene exhibits a weaker interaction with the methyl group of the imidazolium cation by forming a hitherto unprecedented kind of C⋅⋅⋅H-C hydrogen bond. This unexpected finding not only indicates a novel kind of hydrogen bond for carbenes, but also shows that such interaction sites of the imidazolium cation are not limited to the ring hydrogen atoms. Thus, the results give the solute-solvent interactions within ionic liquids a new perspective, and provide a further, albeit weak, site of interaction to tune in order to achieve the desired environment for any dissolved active ingredient. PMID:24375892

  4. Poly(fluoroalkyl acrylate)-bound ruthenium carbene complex: a fluorous and recyclable catalyst for ring-closing olefin metathesis.

    PubMed

    Yao, Qingwei; Zhang, Yiliang

    2004-01-14

    The synthesis of a fluorous olefin metathesis catalyst derived from the Grubbs second-generation ruthenium carbene complex is described. The air stable fluorous polymer-bound ruthenium carbene complex 1 shows high reactivity in effecting the ring-closing metathesis of a broad spectrum of diene and enyne substrates leading to the formation of di-, tri-, and tetrasubstituted cyclic olefins in minimally fluorous solvent systems (PhCF3/CH2Cl2, 1:9-1:49 v/v). The catalyst can be readily separated from the reaction mixture by fluorous extraction with FC-72 and repeatedly reused. The practical advantage offered by the fluorous catalyst is demonstrated by its sequential use in up to five different metathesis reactions. PMID:14709066

  5. Poly(fluoroalkyl acrylate)-bound ruthenium carbene complex: a fluorous and recyclable catalyst for ring-closing olefin metathesis.

    PubMed

    Yao, Qingwei; Zhang, Yiliang

    2004-01-14

    The synthesis of a fluorous olefin metathesis catalyst derived from the Grubbs second-generation ruthenium carbene complex is described. The air stable fluorous polymer-bound ruthenium carbene complex 1 shows high reactivity in effecting the ring-closing metathesis of a broad spectrum of diene and enyne substrates leading to the formation of di-, tri-, and tetrasubstituted cyclic olefins in minimally fluorous solvent systems (PhCF3/CH2Cl2, 1:9-1:49 v/v). The catalyst can be readily separated from the reaction mixture by fluorous extraction with FC-72 and repeatedly reused. The practical advantage offered by the fluorous catalyst is demonstrated by its sequential use in up to five different metathesis reactions.

  6. A cyclic (alkyl)(amido)carbene: synthesis, study and utility as a desulfurization reagent.

    PubMed

    McCarty, Zachary R; Lastovickova, Dominika N; Bielawski, Christopher W

    2016-04-01

    The synthesis and study of a cyclic (alkyl)(amido)carbene is described. The carbene was found to undergo C-H insertion at low temperatures, formed cyclopropenes upon exposure to alkynes, and facilitated desulfurization reactions. Spectroscopic studies revealed that the carbene is strongly π-accepting but retains a complimentary degree of σ-donating properties. PMID:27010415

  7. Surveying sterically demanding N-heterocyclic carbene ligands with restricted flexibility for palladium-catalyzed cross-coupling reactions.

    PubMed

    Würtz, Sebastian; Glorius, Frank

    2008-11-18

    Heterocyclic carbenes (NHCs), especially monodentate ones, have become the ligand of choice for many transition-metal-catalyzed transformations. They generally form highly stable complexes, have strong sigma-donor character, and have a unique shape that can be used to generate sterically demanding ligands.In this Account, we survey recent developments in the design and synthesis of some sterically demanding NHCs with a particularly strong influence on the metal's coordination sphere. We show the successful and insightful application of these ligands in transition-metal catalysis. First, we discuss methods for determining and classifying the electronic and steric properties of NHCs. In addition, we present data on the most important NHC ligands.The selective variation of either electronic or steric parameters of NHCs, and therefore of the catalyst, allows for the optimization of the reaction. Thus, we prepared several series of differentially substituted NHC derivatives. However, because the substituents varied were not directly connected to the carbene carbon, it was difficult to induce a large electronic variation. In contrast, an independent variation of the ligands' steric properties was more straightforward. We highlight three different classes of very sterically demanding NHCs that allow this kind of a steric variation: imidazo[1,5-a]pyridine-3-ylidenes, bioxazoline-derived carbenes (IBiox), and cyclic (alkyl)(amino)carbenes (CAAC).These latter NHC ligands can facilitate a number of challenging cross-coupling reactions. Successful transformations often require a monoligated palladium complex as the catalytically active species, and the sterically demanding NHC ligand favors this monoligated complex. In addition, the electron-rich NHC facilitates difficult oxidative addition steps. Moreover, the conformational flexibility of the ligands can facilitate the formation of catalytically active species and hemilabile interactions, such as agostic or anagostic bonds

  8. Iron‐ and Cobalt‐Catalyzed Synthesis of Carbene Phosphinidenes

    PubMed Central

    Pal, Kuntal; Hemming, Oliver B.; Day, Benjamin M.; Pugh, Thomas; Evans, David J.

    2015-01-01

    Abstract In the presence of stoichiometric or catalytic amounts of [M{N(SiMe3)2}2] (M=Fe, Co), N‐heterocyclic carbenes (NHCs) react with primary phosphines to give a series of carbene phosphinidenes of the type (NHC)⋅PAr. The formation of (IMe4)⋅PMes (Mes=mesityl) is also catalyzed by the phosphinidene‐bridged complex [(IMe4)2Fe(μ‐PMes)]2, which provides evidence for metal‐catalyzed phosphinidene transfer. PMID:26643712

  9. Chirality and catalysis with aromatic N-fused heterobicyclic carbenes.

    PubMed

    Iglesias-Sigüenza, Javier; Izquierdo, Cristina; Díez, Elena; Fernández, Rosario; Lassaletta, José M

    2016-06-21

    The benzoannulation of the most common families of aromatic NHCs, imidazol-2-ylidenes and 1,2,4-triazol-3-ylidenes, results in heterobicyclic imidazo[1,5-a]pyridin-3-ylidenes ('s) and [1,2,4]triazolo[4,3-a]pyridin-3-ylidenes ('s), characterized by a bridged N atom. These are versatile platforms that offer multiple possibilities for the modulation of the steric and electronic properties of the carbene ligand and/or organocatalyst, and offer also diverse opportunities for the introduction of several types of chiralities. In this paper the different families of chiral and carbenes and their application in asymmetric catalysis will be discussed.

  10. Fundamental spectroscopic studies of carbenes and hydrocarbon radicals

    SciTech Connect

    1999-03-12

    Determination of bond dissociation energies and heats of formation of hydrocarbon radicals and carbenes requires knowledge of their structures, but this is not provided by standard mass spectrometric studies; what is needed is high-resolution spectroscopy, often best achieved at centimeter and millimeter wavelengths. Nearly 60 reactive organic molecules were investigated in the period from 1988--1998.

  11. Fundamental spectroscopic studies of carbenes and hydrocarbon radicals

    SciTech Connect

    Gottlieb, C.A.; Thaddeus, P.

    1993-12-01

    Highly reactive carbenes and carbon-chain radicals are studied at millimeter wavelengths by observing their rotational spectra. The purpose is to provide definitive spectroscopic identification, accurate spectroscopic constants in the lowest vibrational states, and reliable structures of the key intermediates in reactions leading to aromatic hydrocarbons and soot particles in combustion.

  12. Fischer and Schrock Carbene Complexes: A Molecular Modeling Exercise

    ERIC Educational Resources Information Center

    Montgomery, Craig D.

    2015-01-01

    An exercise in molecular modeling that demonstrates the distinctive features of Fischer and Schrock carbene complexes is presented. Semi-empirical calculations (PM3) demonstrate the singlet ground electronic state, restricted rotation about the C-Y bond, the positive charge on the carbon atom, and hence, the electrophilic nature of the Fischer…

  13. NHC-manganese(i) complexes as carbene transfer agents.

    PubMed

    Ruiz, Javier; Berros, Angela; Perandones, Bernabé F; Vivanco, Marilín

    2009-09-21

    Tautomerization of coordinated azoles to their corresponding N-heterocyclic carbenes (NHCs) has been carried out by reaction of complexes fac-[Mn(L)(CO)(3)(dppe)](+) (L = N-phenylimidazole) and fac-[Mn(L)(CO)(3)(bipy)](+) (L = N-methylbenzimidazole, benzoxazole, benzothiazole) with KO(t)Bu and subsequent protonation of the azolyl intermediates with NH(4)PF(6). Several NHC-manganese(i) complexes bearing an N-H residue of general formula fac-[Mn(NHC)(CO)(3)(dppe)](+) and fac-[Mn(NHC)(CO)(3)(bipy)](+) have been tested as carbene transfer agents to the gold fragments [Au(L)](+) (L = PPh(3), CNPh, CNXylyl), allowing isolation or spectroscopic detection of various Mn(i)/Au(i) heterometallic intermediates containing azolyl bridging ligands, which liberate the gold(i) carbene complexes [Au(NHC)(L)](+) by means of acid hydrolysis. By contrast, when using the silver(i) fragment [Ag(PPh(3))](+) as carbene acceptor no transmetallation process occurred but instead inverse tautomerization of the NHC to the corresponding imidazole ligand was observed.

  14. Group 1 and 2 cyclic (alkyl)(amino)carbene complexes.

    PubMed

    Turner, Zoë R; Buffet, Jean-Charles

    2015-08-01

    The first examples of cyclic (alkyl)(amino)carbene (CAAC) ligands bound to electropositive metal centres (K, Mg, Sr and Ba) have been isolated and characterised. Preliminary studies demonstrate that all complexes are active for polar monomer polymerisation under ambient conditions affording desirable hydroxyl-terminated telechelic polymers.

  15. Gold Sulfinyl Mesoionic Carbenes: Synthesis, Structure, and Catalytic Activity.

    PubMed

    Frutos, María; Avello, Marta G; Viso, Alma; Fernández de la Pradilla, Roberto; de la Torre, María C; Sierra, Miguel A; Gornitzka, Heinz; Hemmert, Catherine

    2016-08-01

    Gold mesoionic carbenes having a chiral sulfoxide group attached to the C4 position of the five membered ring have been prepared and tested as catalysts in the cycloisomerization of enynes. These new catalysts are very efficient, with the sulfoxide moiety playing a key role in their activity and the N1-substituent in control of the regioselectivity of these processes. PMID:27403763

  16. Gold Sulfinyl Mesoionic Carbenes: Synthesis, Structure, and Catalytic Activity.

    PubMed

    Frutos, María; Avello, Marta G; Viso, Alma; Fernández de la Pradilla, Roberto; de la Torre, María C; Sierra, Miguel A; Gornitzka, Heinz; Hemmert, Catherine

    2016-08-01

    Gold mesoionic carbenes having a chiral sulfoxide group attached to the C4 position of the five membered ring have been prepared and tested as catalysts in the cycloisomerization of enynes. These new catalysts are very efficient, with the sulfoxide moiety playing a key role in their activity and the N1-substituent in control of the regioselectivity of these processes.

  17. Access to Air-Stable 1,3-Diphosphacyclobutane-2,4-diyls by an Arylation Reaction with Arynes.

    PubMed

    Ueta, Yasuhiro; Mikami, Koichi; Ito, Shigekazu

    2016-06-20

    Tuning of the physicochemical properties of the 1,3-diphosphacyclobutane-2,4-diyl unit is attractive in view of materials applications. The use of arynes is shown to be effective for installing relatively electron rich aryl substituents into the open-shell singlet P-heterocyclic system. Treatment of the sterically encumbered 1,3-diphosphacyclobuten-4-yl anion with ortho-silylated aryl triflates in the presence of fluoride under appropriate conditions afforded the corresponding 1-aryl 1,3-diphosphacyclobutane-2,4-diyls. The air-stable open-shell singlet P-heterocycles exhibit considerable electron-donating character, and the aromatic substituent influences the open-shell character, which is thought to be related to the property of p-type semiconductivity. The P-arylated 1,3-diphosphacyclobutane-2,4-diyl systems can be further utilized as detectors of hydrogen fluoride (HF), which causes a remarkable change in their photoabsorption properties. PMID:27135439

  18. CAAC Boranes. Synthesis and characterization of cyclic (alkyl) (amino) carbene borane complexes from BF₃ and BH₃.

    PubMed

    Monot, Julien; Fensterbank, Louis; Malacria, Max; Lacôte, Emmanuel; Geib, Steven J; Curran, Dennis P

    2010-08-02

    In situ formation of two cyclic (alkyl) (amino) carbenes (CAACs) followed by addition of BF₃•Et₂O provided the first two examples of CAAC-BF₃ complexes: 1-(2,6-diisopropylphenyl)-3,5,5-trimethyl-3-phenylpyrrolidin-2-ylidene trifluoroborane, and 2-(2,6-diisopropylphenyl)-3,3-dimethyl-2-azaspiro[4.5]decan-1-ylidene trifluoroborane. These CAAC-BF₃ complexes are robust compounds that are stable to ambient laboratory conditions and silica gel chromatography. They were characterized by spectroscopy and X-ray crystallography. In contrast, a CAAC complex with borane (BH₃) was readily formed in situ according to ¹H and ¹¹B NMR analysis, but did not survive the workup conditions. These results set the stage for further studies of the chemistry of CAAC boranes.

  19. Copper and Silver Carbene Complexes without Heteroatom-Stabilization: Structure, Spectroscopy, and Relativistic Effects.

    PubMed

    Hussong, Matthias W; Hoffmeister, Wilhelm T; Rominger, Frank; Straub, Bernd F

    2015-08-24

    Salts of a copper and a silver carbene complex were prepared from dimesityl diazomethane, made possible by the steric shielding of the N-heterocyclic carbene (NHC) ancillary ligand IPr**. The mint-green complex [IPr**Ag=CMes2 ](+) [NTf2 ](-) is the first isolated silver carbene complex without heteroatom donor substituents. Single-crystal X-ray diffraction provides evidence for a predominant carbenoid character, and supports the postulation of such reactive species as intermediates in silver-catalyzed C-H activation reactions. The greenish yellow copper carbene complex [IPr**Cu=CMes2 ](+) [NTf2 ](-) has spectroscopic properties in between the isostructural silver complex and the already reported emerald green gold carbene complex. A comparison in the Group 11 series indicates that relativistic effects are responsible for the strong σ bond and the significant π back-bonding in the gold carbene moiety. PMID:26189567

  20. Fischer carbene complexes remain favourite targets, and vehicles for new discoveries.

    PubMed

    Raubenheimer, H G

    2014-12-01

    Exciting new variations in Fischer-type carbene complex composition and reactivity have been realised by following or modifying well-established synthetic approaches such as metal carbonyl functionalization and modification of existing carbene ligands. The formation of targeted complexes for organic synthesis, carbene-containing chelates, and polynuclear carbene complexes, by employing 'click chemistry', warrants discussion. Transmetallation and α,α-dehydrogenation of ethers and amines have come into their own as viable synthetic methods to access carbene complexes with unique properties and activities. Successful mediation of carbene complex formation with pincer ligands has proved its worth. Quantum chemistry has become essential for supporting or initiating mechanistic proposals, but heuristic approaches such as invoking the vinylology principle to describe substituted phenylcarbene complexes are still valuable in the interpretation of bonding properties and the classification of complex types. Electrochemical studies now also constitute a powerful part of the experimental characterization tool kit. PMID:25325879

  1. Computational chemistry insights in the REDOX Behaviour of Cr and W Fischer carbene complexes

    NASA Astrophysics Data System (ADS)

    Landman, Marile; Conradie, Jeanet; van Rooyen, Petrus H.

    2015-09-01

    An electrochemical study of a series of Fischer carbene complexes containing a hetero-aryl group showed that Cr and W carbenes exhibit different electrochemical behaviour. The Cr carbenes are oxidized in two one electron oxidation processes, namely Cr(0) to Cr(I) and Cr(I) to Cr(II). On the contrary, Fischer carbene complexes of tungsten are directly oxidized from W(0) to W(II). The first reduction process observed for both W- and Cr- carbenes, is a one electron process. A density functional theory (DFT) computational chemistry study of the electronic structure of the Cr- and W-carbenes, showed that the oxidation is metal based and the reduction is located on the carbene ligand. The DFT calculations further showed that the Cr(II) species is a triplet and the W(II) species a closed shell singlet. The DFT calculated energies of the HOMO and LUMO of the neutral carbenes relate linearly to the experimental oxidation and reduction potential, respectively. These mathematical relationships obtained can be used to predict experimentally measured potentials of related Fischer carbene complexes.

  2. Chirality and catalysis with aromatic N-fused heterobicyclic carbenes.

    PubMed

    Iglesias-Sigüenza, Javier; Izquierdo, Cristina; Díez, Elena; Fernández, Rosario; Lassaletta, José M

    2016-06-21

    The benzoannulation of the most common families of aromatic NHCs, imidazol-2-ylidenes and 1,2,4-triazol-3-ylidenes, results in heterobicyclic imidazo[1,5-a]pyridin-3-ylidenes ('s) and [1,2,4]triazolo[4,3-a]pyridin-3-ylidenes ('s), characterized by a bridged N atom. These are versatile platforms that offer multiple possibilities for the modulation of the steric and electronic properties of the carbene ligand and/or organocatalyst, and offer also diverse opportunities for the introduction of several types of chiralities. In this paper the different families of chiral and carbenes and their application in asymmetric catalysis will be discussed. PMID:27254732

  3. Cooperative Lewis acid/N-heterocyclic carbene catalysis

    PubMed Central

    Cohen, Daniel T.; Scheidt, Karl A.

    2015-01-01

    Lewis acid activation with N-heterocyclic carbene (NHC) catalysis has presented new opportunities for enantioselective reaction development. Recent findings illustrate that Lewis acids can play an important role in homoenolate annulations by: enhancement of the reactivity, reversal of the diastereo- or regioselectivity, and activation of previously inactive electrophiles. Additionally, the incorporation of a Lewis acid into Brønsted base-catalyzed conjugate addition allowed for an increase in yields. PMID:26413259

  4. Catalytic and Biocatalytic Iron Porphyrin Carbene Formation: Effects of Binding Mode, Carbene Substituent, Porphyrin Substituent, and Protein Axial Ligand

    PubMed Central

    2016-01-01

    Iron porphyrin carbenes (IPCs) are important intermediates in various chemical reactions catalyzed by iron porphyrins and engineered heme proteins, as well as in the metabolism of various xenobiotics by cytochrome P450. However, there are no prior theoretical reports to help understand their formation mechanisms and identify key information governing the binding mode, formation feasibility, and stability/reactivity. A systematic quantum chemical study was performed to investigate the effects of carbene substituent, porphyrin substituent, and axial ligand on IPC formation pathways. Results not only are consistent with available experimental data but also provide a number of unprecedented insights into electronic, steric, and H-bonding effects of various structural factors on IPC formation mechanisms. These results shall facilitate research on IPC and related systems for sustainable chemical catalysis and biocatalysis. PMID:26067900

  5. "Decarbonization" of an imino-N-heterocyclic carbene ligand via triple benzyl migration from hafnium.

    PubMed

    Prema, Dipesh; Mathota Arachchige, Yohan L N; Murray, Rex E; Slaughter, LeGrande M

    2015-04-21

    An imino-N-heterocyclic carbene underwent three sequential benzyl migrations upon reaction with tetrabenzylhafnium, resulting in complete removal of the carbene carbon from the ligand. The resulting eneamido-amidinato hafnium complex showed alkene polymerization activity comparable to that of a precatalyst containing the intact iminocarbene ligand.

  6. The Depolymerization of Poly(Ethylene Terephthalate) (PET) Using N-Heterocyclic Carbenes from Ionic Liquids

    ERIC Educational Resources Information Center

    Kamber, Nahrain E.; Tsujii, Yasuhito; Keets, Kate; Waymouth, Robert M.; Pratt, Russell C.; Nyce, Gregory W.; Hedrick, James L.

    2010-01-01

    The depolymerization of the plastic polyethylene terephthalate (PET or PETE) is described in this laboratory procedure. The transesterification reaction used to depolymerize PET employs a highly efficient N-heterocyclic carbene catalyst derived from a commercially available imidazolium ionic liquid. N-heterocyclic carbenes are potent nucleophilic…

  7. "Decarbonization" of an imino N-heterocyclic carbene via triple benzyl migration from hafnium

    Technology Transfer Automated Retrieval System (TEKTRAN)

    An imino N-heterocyclic carbene underwent three sequential benzyl migrations upon reaction with tetrabenzylhafnium, resulting in complete removal of the carbene carbon from the ligand. The resulting eneamido-amidinato hafnium complex showed alkene polymerization activity comparable to that of a prec...

  8. Simple direct formation of self-assembled N-heterocyclic carbene monolayers on gold and their application in biosensing.

    PubMed

    Crudden, Cathleen M; Horton, J Hugh; Narouz, Mina R; Li, Zhijun; Smith, Christene A; Munro, Kim; Baddeley, Christopher J; Larrea, Christian R; Drevniok, Benedict; Thanabalasingam, Bheeshmon; McLean, Alastair B; Zenkina, Olena V; Ebralidze, Iraklii I; She, Zhe; Kraatz, Heinz-Bernhard; Mosey, Nicholas J; Saunders, Lisa N; Yagi, Akiko

    2016-01-01

    The formation of organic films on gold employing N-heterocyclic carbenes (NHCs) has been previously shown to be a useful strategy for generating stable organic films. However, NHCs or NHC precursors typically require inert atmosphere and harsh conditions for their generation and use. Herein we describe the use of benzimidazolium hydrogen carbonates as bench stable solid precursors for the preparation of NHC films in solution or by vapour-phase deposition from the solid state. The ability to prepare these films by vapour-phase deposition permitted the analysis of the films by a variety of surface science techniques, resulting in the first measurement of NHC desorption energy (158±10 kJ mol(-1)) and confirmation that the NHC sits upright on the surface. The use of these films in surface plasmon resonance-type biosensing is described, where they provide specific advantages versus traditional thiol-based films. PMID:27585494

  9. Simple direct formation of self-assembled N-heterocyclic carbene monolayers on gold and their application in biosensing

    NASA Astrophysics Data System (ADS)

    Crudden, Cathleen M.; Horton, J. Hugh; Narouz, Mina R.; Li, Zhijun; Smith, Christene A.; Munro, Kim; Baddeley, Christopher J.; Larrea, Christian R.; Drevniok, Benedict; Thanabalasingam, Bheeshmon; McLean, Alastair B.; Zenkina, Olena V.; Ebralidze, Iraklii I.; She, Zhe; Kraatz, Heinz-Bernhard; Mosey, Nicholas J.; Saunders, Lisa N.; Yagi, Akiko

    2016-09-01

    The formation of organic films on gold employing N-heterocyclic carbenes (NHCs) has been previously shown to be a useful strategy for generating stable organic films. However, NHCs or NHC precursors typically require inert atmosphere and harsh conditions for their generation and use. Herein we describe the use of benzimidazolium hydrogen carbonates as bench stable solid precursors for the preparation of NHC films in solution or by vapour-phase deposition from the solid state. The ability to prepare these films by vapour-phase deposition permitted the analysis of the films by a variety of surface science techniques, resulting in the first measurement of NHC desorption energy (158+/-10 kJ mol-1) and confirmation that the NHC sits upright on the surface. The use of these films in surface plasmon resonance-type biosensing is described, where they provide specific advantages versus traditional thiol-based films.

  10. Simple direct formation of self-assembled N-heterocyclic carbene monolayers on gold and their application in biosensing.

    PubMed

    Crudden, Cathleen M; Horton, J Hugh; Narouz, Mina R; Li, Zhijun; Smith, Christene A; Munro, Kim; Baddeley, Christopher J; Larrea, Christian R; Drevniok, Benedict; Thanabalasingam, Bheeshmon; McLean, Alastair B; Zenkina, Olena V; Ebralidze, Iraklii I; She, Zhe; Kraatz, Heinz-Bernhard; Mosey, Nicholas J; Saunders, Lisa N; Yagi, Akiko

    2016-01-01

    The formation of organic films on gold employing N-heterocyclic carbenes (NHCs) has been previously shown to be a useful strategy for generating stable organic films. However, NHCs or NHC precursors typically require inert atmosphere and harsh conditions for their generation and use. Herein we describe the use of benzimidazolium hydrogen carbonates as bench stable solid precursors for the preparation of NHC films in solution or by vapour-phase deposition from the solid state. The ability to prepare these films by vapour-phase deposition permitted the analysis of the films by a variety of surface science techniques, resulting in the first measurement of NHC desorption energy (158±10 kJ mol(-1)) and confirmation that the NHC sits upright on the surface. The use of these films in surface plasmon resonance-type biosensing is described, where they provide specific advantages versus traditional thiol-based films.

  11. Simple direct formation of self-assembled N-heterocyclic carbene monolayers on gold and their application in biosensing

    PubMed Central

    Crudden, Cathleen M.; Horton, J. Hugh; Narouz, Mina R.; Li, Zhijun; Smith, Christene A.; Munro, Kim; Baddeley, Christopher J.; Larrea, Christian R.; Drevniok, Benedict; Thanabalasingam, Bheeshmon; McLean, Alastair B.; Zenkina, Olena V.; Ebralidze, Iraklii I.; She, Zhe; Kraatz, Heinz-Bernhard; Mosey, Nicholas J.; Saunders, Lisa N.; Yagi, Akiko

    2016-01-01

    The formation of organic films on gold employing N-heterocyclic carbenes (NHCs) has been previously shown to be a useful strategy for generating stable organic films. However, NHCs or NHC precursors typically require inert atmosphere and harsh conditions for their generation and use. Herein we describe the use of benzimidazolium hydrogen carbonates as bench stable solid precursors for the preparation of NHC films in solution or by vapour-phase deposition from the solid state. The ability to prepare these films by vapour-phase deposition permitted the analysis of the films by a variety of surface science techniques, resulting in the first measurement of NHC desorption energy (158±10 kJ mol−1) and confirmation that the NHC sits upright on the surface. The use of these films in surface plasmon resonance-type biosensing is described, where they provide specific advantages versus traditional thiol-based films. PMID:27585494

  12. Fe N-Heterocyclic Carbene Complexes as Promising Photosensitizers.

    PubMed

    Liu, Yizhu; Persson, Petter; Sundström, Villy; Wärnmark, Kenneth

    2016-08-16

    The photophysics and photochemistry of transition metal complexes (TMCs) has long been a hot field of interdisciplinary research. Rich metal-based redox processes, together with a high variety in electronic configurations and excited-state dynamics, have rendered TMCs excellent candidates for interconversion between light, chemical, and electrical energies in intramolecular, supramolecular, and interfacial arrangements. In specific applications such as photocatalytic organic synthesis, photoelectrochemical cells, and light-driven supramolecular motors, light absorption by a TMC-based photosensitizer and subsequent excited-state energy or electron transfer constitute essential steps. In this context, TMCs based on rare and expensive metals, such as ruthenium and iridium, are frequently employed as photosensitizers, which is obviously not ideal for large-scale implementation. In the search for abundant and environmentally benign solutions, six-coordinate Fe(II) complexes (Fe(II)L6) have been widely considered as highly desirable alternatives. However, not much success has been achieved due to the extremely short-lived triplet metal-to-ligand charge transfer ((3)MLCT) excited state that is deactivated by low-lying metal-centered (MC) states on a 100 fs time scale. A fundamental strategy to design useful Fe-based photosensitizers is thus to destabilize the MC states relative to the (3)MLCT state by increasing the ligand field strength, with special focus on making eg σ* orbitals on the Fe center energetically less accessible. Previous efforts to directly transplant successful strategies from Ru(II)L6 complexes unfortunately met with limited success in this regard, despite their close chemical kinship. In this Account, we summarize recent promising results from our and other groups in utilizing strongly σ-donating N-heterocyclic carbene (NHC) ligands to make strong-field Fe(II)L6 complexes with significantly extended (3)MLCT lifetimes. Already some of the first

  13. Reactions of Persistent Carbenes with Hydrogen-Terminated Silicon Surfaces.

    PubMed

    Zhukhovitskiy, Aleksandr V; Mavros, Michael G; Queeney, K T; Wu, Tony; Voorhis, Troy Van; Johnson, Jeremiah A

    2016-07-13

    Surface passivation has enabled the development of silicon-based solar cells and microelectronics. However, a number of emerging applications require a paradigm shift from passivation to functionalization, wherein surface functionality is installed proximal to the silicon surface. To address this need, we report here the use of persistent aminocarbenes to functionalize hydrogen-terminated silicon surfaces via Si-H insertion reactions. Through the use of model compounds (H-Si(TMS)3 and H-Si(OTMS)3), nanoparticles (H-SiNPs), and planar Si(111) wafers (H-Si(111)), we demonstrate that among different classes of persistent carbenes, the more electrophilic and nucleophilic ones, in particular, a cyclic (alkyl)(amino)carbene (CAAC) and an acyclic diaminocarbene (ADAC), are able to undergo insertion into Si-H bonds at the silicon surface, forming persistent C-Si linkages and simultaneously installing amine or aminal functionality in proximity to the surface. The CAAC (6) is particularly notable for its clean insertion reactivity under mild conditions that produces monolayers with 21 ± 3% coverage of Si(111) atop sites, commensurate with the expected maximum of ∼20%. Atomic force and transmission electron microscopy, nuclear magnetic resonance, X-ray photoelectron, and infrared spectroscopy, and time-of-flight secondary ion mass spectrometry provided evidence for the surface Si-H insertion process. Furthermore, computational studies shed light on the reaction energetics and indicated that CAAC 6 should be particularly effective at binding to silicon dihydride, trihydride, and coupled monohyride motifs, as well as oxidized surface sites. Our results pave the way for the further development of persistent carbenes as universal ligands for silicon and potentially other nonmetallic substrates. PMID:27366818

  14. Tailor-made N-heterocyclic carbenes for nanoparticle stabilization.

    PubMed

    Richter, Christian; Schaepe, Kira; Glorius, Frank; Ravoo, Bart Jan

    2014-03-25

    N-heterocyclic carbenes (NHCs) represent a leading class of ligands in organometallic chemistry, but have been rarely exploited as stabilizers for metal nanoparticles (NPs). We report the first example of NHC stabilized Pd-NPs that demonstrate long term stability. These NHC Pd-NPs were synthesized by a facile ligand exchange protocol using rationally designed long chained NHCs (LC-NHCs). Furthermore, we demonstrate that the surface modification of Pd-NPs results in significant chemoselectivity in a model reaction. PMID:24522886

  15. N-Heterocyclic carbene metal complexes: photoluminescence and applications.

    PubMed

    Visbal, Renso; Gimeno, M Concepción

    2014-05-21

    This review covers the advances made in the synthesis of luminescent transition metal complexes containing N-heterocyclic carbene (NHC) ligands. The presence of a high field strength ligand such as an NHC in the complexes gives rise to high energy emissions, and consequently, to the desired blue colour needed for OLED applications. Furthermore, the great versatility of NHC ligands for structural modifications, together with the use of other ancillary ligands in the complex, provides numerous possibilities for the synthesis of phosphorescent materials, with emission colours over the entire visible spectra and potential future applications in fields such as photochemical water-splitting, chemosensors, dye-sensitised solar cells, oxygen sensors, and medicine.

  16. Sterically (un)encumbered mer-tridentate N-heterocyclic carbene complexes of titanium(iv) for the copolymerization of cyclohexene oxide with CO2.

    PubMed

    Hessevik, Julie; Lalrempuia, Ralte; Nsiri, Hajar; Törnroos, Karl W; Jensen, Vidar R; Le Roux, Erwan

    2016-10-01

    Titanium(iv) complexes bearing an unsubstituted tridentate bis(phenolate) N-heterocyclic carbene (NHC) were synthesized and structurally identified. While sterically unencumbered NHC-Ti(iv) complexes bearing chloro and alkoxy co-ligands tend to dimerize in solution and in solid-state, the use of a bulky aryloxy as co-ligand favors the monomeric species. Upon activation by onium salts, all these complexes were found to be highly selective towards the copolymerization of cyclohexene oxide (CHO) with CO2 under mild conditions (PCO2 < 1 bar), albeit the sterically unencumbered NHC-Ti(iv) complexes are less stable and active than their structural analogues bearing bulkier substituents.

  17. Isolation of a non-heteroatom-stabilized gold-carbene complex.

    PubMed

    Hussong, Matthias W; Rominger, Frank; Krämer, Petra; Straub, Bernd F

    2014-08-25

    Gold-carbene complexes are essential intermediates in many gold-catalyzed organic-synthetic transformations. While gold-carbene complexes with direct, vinylogous, or phenylogous heteroatom substitution have been synthesized and characterized, the observation in the condensed phase of electronically non-stabilized gold-carbenes has so far remained elusive. The sterically extremely shielded, emerald-green complex [IPr**Au=CMes2](+)[NTf2](-) has now been synthesized, isolated, and fully characterized. Its absorption maximum at 642 nm, in contrast to 528 nm of the red-purple carbocation [Mes2CH](+), clearly demonstrates that gold is more than just a "soft proton". PMID:24953223

  18. Highly Regio- and Enantioselective Formal [3 + 2]-Annulation of Indoles with Electrophilic Enol Carbene Intermediates.

    PubMed

    Jing, Changcheng; Cheng, Qing-Qing; Deng, Yongming; Arman, Hadi; Doyle, Michael P

    2016-09-16

    Chiral cyclopentane-fused indolines are synthesized with high regio- and enantiocontrol by formal [3 + 2]-annulation reactions of indoles and electrophilic enol carbenes. High enantioselectivity and exclusive regiocontrol occurred with enoldiazoacetamides using a less sterically encumbered prolinate-ligated dirhodium(II) catalyst in reactions with N-substituted indoles without substituents at the 2- or 3-positions via a selective vinylogous addition process. In this transformation, donor-acceptor cyclopropenes generated from enoldiazoacetamides serve as the carbene precursors to form metal carbene intermediates. PMID:27589203

  19. Actinide metals with multiple bonds to carbon: synthesis, characterization, and reactivity of U(IV) and Th(IV) bis(iminophosphorano)methandiide pincer carbene complexes.

    PubMed

    Ma, Guibin; Ferguson, Michael J; McDonald, Robert; Cavell, Ronald G

    2011-07-18

    Treatment of ThCl(4)(DME)(2) or UCl(4) with 1 equiv of dilithiumbis(iminophosphorano) methandiide, [Li(2)C(Ph(2)P═NSiMe(3))(2)] (1), afforded the chloro actinide carbene complexes [Cl(2)M(C(Ph(2)P═NSiMe(3))(2))] (2 (M = Th) and 3 (M = U)) in situ. Stable PCP metal-carbene complexes [Cp(2)Th(C(Ph(2)P═NSiMe(3))(2))] (4), [Cp(2)U(C(Ph(2)P═NSiMe(3))(2))] (5), [TpTh(C(Ph(2)P═NSiMe(3))(2))Cl] (6), and [TpU(C(Ph(2)P═NSiMe(3))(2))Cl] (7) were generated from 2 or 3 by further reaction with 2 equiv of thallium(I) cyclopentadienide (CpTl) in THF to yield 4 or 5 or with 1 equiv of potassium hydrotris(pyrazol-1-yl) borate (TpK) also in THF to give 6 or 7, respectively. The derivative complexes were isolated, and their crystal structures were determined by X-ray diffraction. All of these U (or Th)-carbene complexes (4-7) possess a very short M (Th or U)═carbene bond with evidence for multiple bond character. Gaussian 03 DFT calculations indicate that the M═C double bond is constructed by interaction of the 5f and 6d orbitals of the actinide metal with carbene 2p orbitals of both π and σ character. Complex 3 reacted with acetonitrile or benzonitrile to cyclo-add C≡N to the U═carbon double bond, thereby forming a new C-C bond in a new chelated quadridentate ligand in the bridged dimetallic complexes (9 and 10). A single carbon-U bond is retained. The newly coordinated uranium complex dimerizes with one equivalent of unconverted 3 using two chlorides and the newly formed imine derived from the nitrile as three connecting bridges. In addition, a new crystal structure of [CpUCl(3)(THF)(2)] (8) was determined by X-ray diffraction.

  20. Characterizing a nonclassical carbene with coupled cluster methods: cyclobutylidene.

    PubMed

    Wang, Xiao; Agarwal, Jay; Schaefer Iii, Henry F

    2016-09-21

    Carbenes represent a special class of reactive compounds that possess a lone pair of electrons on a carbon atom. Among the myriad examples of carbenes in the literature, cyclobutylidene stands out as a unique nonclassical compound that includes transannular interaction between opposing C1 and C3 carbon atoms within a four-membered ring. On its lowest potential energy surface (X[combining tilde](1)A'), cyclobutylidene quickly rearranges, following three reaction paths: (i) 1,2-H migration; (ii) 1,2-C migration; and, (iii) 1,3-H migration. Herein, this reactivity is examined with high-level coupled-cluster methods [up to CCSDT(Q)]. At this level of theory, combined with extrapolation techniques to obtain energies at the complete basis set (CBS) limit, the long-standing disparity between theoretical and experimental results is resolved. Specifically, cyclobutylidene is predicted to prefer 1,2-C migration rather than 1,2-H migration. Rate constants for the three reaction paths are obtained from canonical variational transition state theory (CVT) and yield reasonable agreement with existing experimental results. Further characterization of cyclobutylidene is also reported: the singlet-triplet gap (ΔES-T) is found to be -9.3 kcal mol(-1) at the CCSDT(Q)/CBS level of theory, and anharmonic vibrational frequencies are determined with second-order vibrational perturbation theory (VPT2). PMID:27539444

  1. PEGylated N-Heterocyclic Carbene Anchors Designed To Stabilize Gold Nanoparticles in Biologically Relevant Media.

    PubMed

    MacLeod, Michelle J; Johnson, Jeremiah A

    2015-07-01

    N-Heterocyclic carbenes (NHCs) have emerged as versatile ligands for surface functionalization. Their ease of synthesis and ability to form strong bonds with a range of substrates provide a unique complement to traditional surface modification methods. Gold nanoparticles (NPs) are a particularly useful class of materials whose applications intimately depend on surface functionalization. Here we report the development of PEGylated-NHC ligands for Au-NP surfaces and the first example of NHC-functionalized NPs that are compatible with biologically relevant conditions. Our PEGylated-NHC-Au-NPs are stable toward aggregation in aqueous solutions in the pH range of 3-14, in <250 mM electrolyte solutions, at high and low temperatures (95 and -78 °C), in cell culture media, and in aqueous H2O2 solutions. This work demonstrates for the first time that NHCs can serve as anchors for water-soluble Au-NPs and opens the door to potential biomedical applications of NHC surface anchors. PMID:26081724

  2. Carbene supported dimer of heavier ketenimine analogue with p and si atoms.

    PubMed

    Roy, Sudipta; Dittrich, Birger; Mondal, Totan; Koley, Debasis; Stückl, A Claudia; Schwederski, Brigitte; Kaim, Wolfgang; John, Michael; Vasa, Suresh Kumar; Linser, Rasmus; Roesky, Herbert W

    2015-05-20

    A cyclic alkyl(amino) carbene (cAAC) stabilized dimer [(cAAC)Si(P-Tip)]2 (2) (Tip = 2,4,6-triisopropylphenyl) is reported. 2 can be considered as a dimer of the heavier ketenimine (R2C═C═N-R) analogue. The dark-red rod-shaped crystals of 2 were synthesized by reduction of the precursor, cAAC-dichlorosilylene-stabilized phosphinidene (cAAC)SiCl2→P-Tip with sodium napthalenide. The crystals of 2 are storable at room temperature for several months and stable up to 215 °C under an inert atmosphere. X-ray single-crystal diffraction revealed that 2 contains a cyclic nonplanar four-membered SiPSiP ring. Magnetic susceptibility measurements confirmed the singlet spin ground state of 2. Cyclic voltammetry of 2 showed a quasi-reversible one-electron reduction indicating the formation of the corresponding radical anion 2(•-), which was further characterized by EPR measurements in solution. The electronic structure and bonding of 2 and 2(•-) were studied by theoretical calculations. The experimentally obtained data are in good agreement with the calculated values.

  3. Air-persistent monomeric (amino)(carboxy) radicals derived from cyclic (alkyl)(amino) carbenes.

    PubMed

    Mahoney, Janell K; Martin, David; Thomas, Fabrice; Moore, Curtis E; Rheingold, Arnold L; Bertrand, Guy

    2015-06-17

    A series of monomeric (amino)(carboxy) radicals featuring carbonyl substituents with increasing electron-withdrawing properties (3a, phenyl; 3b, 3,5-bis(trifluoromethyl)phenyl; 3c, perfluorophenyl; 3d, heptafluoropropyl; 3e, 2H-pyrroliumyl) were synthesized in two or three steps from stable cyclic (alky)(amino)carbenes (CAACs). Although (amino)(carboxy) radicals had been previously considered as highly air-sensitive, some of these compounds feature half-lives of hours (3d), and even days (3c and 3e) in well-aerated solutions. DFT calculations show that (amino)(carboxy) radicals evolve from C-centered radical to ambidentate C,O-radicals when increasing the electron-withdrawing properties of the carbonyl substituent. This is paralleled with a destabilization of the peroxide resulting from the addition of dioxygen to the radical. This latter reaction is even predicted to be endothermic for substituents with Hammett constant σp > 0.2. PMID:26011769

  4. Cationic tungsten-oxo-alkylidene-N-heterocyclic carbene complexes: highly active olefin metathesis catalysts.

    PubMed

    Schowner, Roman; Frey, Wolfgang; Buchmeiser, Michael R

    2015-05-20

    The synthesis, structure, and olefin metathesis activity of the first neutral and cationic W-oxo-alkylidene-N-heterocyclic carbene (NHC) catalysts are reported. Neutral W-oxo-alkylidene-NHC catalysts can be prepared in up to 90% isolated yield. Depending on the ligands used, they possess either an octahedral (Oh) or trigonal bipyramidal ligand sphere. They can be activated with excess AlCl3 to form cationic olefin metathesis-active W-complexes; however, these readily convert into neutral chloro-complexes. Well-defined, stable cationic species can be prepared by stoichiometric substitution of one chloro ligand in the parent, neutral W-oxo-alkylidene-NHC complexes with Ag(MeCN)2B(Ar(F))4 or NaB(Ar(F))4; B(Ar(F))4 = B(3,5-(CF3)2-C6H3)4. They are highly active olefin metathesis catalysts, allowing for turnover numbers up to 10,000 in various olefin metathesis reactions including alkenes bearing nitrile, sec-amine, and thioether groups. PMID:25938340

  5. Cationic tungsten-oxo-alkylidene-N-heterocyclic carbene complexes: highly active olefin metathesis catalysts.

    PubMed

    Schowner, Roman; Frey, Wolfgang; Buchmeiser, Michael R

    2015-05-20

    The synthesis, structure, and olefin metathesis activity of the first neutral and cationic W-oxo-alkylidene-N-heterocyclic carbene (NHC) catalysts are reported. Neutral W-oxo-alkylidene-NHC catalysts can be prepared in up to 90% isolated yield. Depending on the ligands used, they possess either an octahedral (Oh) or trigonal bipyramidal ligand sphere. They can be activated with excess AlCl3 to form cationic olefin metathesis-active W-complexes; however, these readily convert into neutral chloro-complexes. Well-defined, stable cationic species can be prepared by stoichiometric substitution of one chloro ligand in the parent, neutral W-oxo-alkylidene-NHC complexes with Ag(MeCN)2B(Ar(F))4 or NaB(Ar(F))4; B(Ar(F))4 = B(3,5-(CF3)2-C6H3)4. They are highly active olefin metathesis catalysts, allowing for turnover numbers up to 10,000 in various olefin metathesis reactions including alkenes bearing nitrile, sec-amine, and thioether groups.

  6. The synthesis of pyrroles and oxazoles based on gold α-imino carbene complexes.

    PubMed

    Loy, Nicole S Y; Choi, Subin; Kim, Sunggak; Park, Cheol-Min

    2016-05-31

    Cationic gold complexes of α-oximimino carbenes have been identified to react with weak nucleophiles including enol ethers and nitriles. These findings allowed us to develop the highly efficient synthesis of pyrroles and oxazoles.

  7. Synthesis and structure of novel triphenylarsine-substituted tungsten(0) Fischer carbene complexes

    NASA Astrophysics Data System (ADS)

    Jansen van Rensburg, Armand; Landman, Marilé; van Rooyen, Petrus H.; Conradie, Marrigje M.; Conradie, Jeanet

    2016-02-01

    X-ray crystal structure determination, as well as IR and NMR spectroscopy of four novel triphenylarsine-substituted tetracarbonyl tungsten(0) Fischer carbene complexes of general formula [(CO)4(AsPh3)WC(OEt)(Ar)], with Ar = 2-thienyl (1), 2-furyl (2), 2-(N-methyl)pyrrolyl (3), 2,2‧-bithienyl (4), revealed a cis-configuration for the substituted AsPh3 group relative to the carbene ligand for all four novel complexes. All X-ray structures showed that the W-C bond trans AsPh3 < W-C bond trans carbene < W-C bond trans CO. DFT calculations on all possible conformations of each complex due to the different possible positions of the ligands and carbene substituents to each other, correlated with the experimental results.

  8. Copper-Carbene Intermediates in the Copper-Catalyzed Functionalization of O-H Bonds.

    PubMed

    Pereira, Ana; Champouret, Yohan; Martín, Carmen; Álvarez, Eleuterio; Etienne, Michel; Belderraín, Tomás R; Pérez, Pedro J

    2015-06-26

    Copper-carbene [Tp(x)Cu=C(Ph)(CO2Et)] and copper-diazo adducts [Tp(x)Cu{η(1)-N2C(Ph)(CO2Et)}] have been detected and characterized in the context of the catalytic functionalization of O-H bonds through carbene insertion by using N2=C(Ph)(CO2Et) as the carbene source. These are the first examples of these type of complexes in which the copper center bears a tridentate ligand and displays a tetrahedral geometry. The relevance of these complexes in the catalytic cycle has been assessed by NMR spectroscopy, and kinetic studies have demonstrated that the N-bound diazo adduct is a dormant species and is not en route to the formation of the copper-carbene intermediate.

  9. Copper-Carbene Intermediates in the Copper-Catalyzed Functionalization of O-H Bonds.

    PubMed

    Pereira, Ana; Champouret, Yohan; Martín, Carmen; Álvarez, Eleuterio; Etienne, Michel; Belderraín, Tomás R; Pérez, Pedro J

    2015-06-26

    Copper-carbene [Tp(x)Cu=C(Ph)(CO2Et)] and copper-diazo adducts [Tp(x)Cu{η(1)-N2C(Ph)(CO2Et)}] have been detected and characterized in the context of the catalytic functionalization of O-H bonds through carbene insertion by using N2=C(Ph)(CO2Et) as the carbene source. These are the first examples of these type of complexes in which the copper center bears a tridentate ligand and displays a tetrahedral geometry. The relevance of these complexes in the catalytic cycle has been assessed by NMR spectroscopy, and kinetic studies have demonstrated that the N-bound diazo adduct is a dormant species and is not en route to the formation of the copper-carbene intermediate. PMID:26014686

  10. Gold-Catalyzed Reactions via Cyclopropyl Gold Carbene-like Intermediates

    PubMed Central

    2015-01-01

    Cycloisomerizations of 1,n-enynes catalyzed by gold(I) proceed via electrophilic species with a highly distorted cyclopropyl gold(I) carbene-like structure, which can react with different nucleophiles to form a wide variety of products by attack at the cyclopropane or the carbene carbons. Particularly important are reactions in which the gold(I) carbene reacts with alkenes to form cyclopropanes either intra- or intermolecularly. In the absence of nucleophiles, 1,n-enynes lead to a variety of cycloisomerized products including those resulting from skeletal rearrangements. Reactions proceeding through cyclopropyl gold(I) carbene-like intermediates are ideally suited for the bioinspired synthesis of terpenoid natural products by the selective activation of the alkyne in highly functionalized enynes or polyenynes. PMID:26061916

  11. How Stable Is Stable?

    ERIC Educational Resources Information Center

    Baehr, Marie

    1994-01-01

    Provides a problem where students are asked to find the point at which a soda can floating in some liquid changes its equilibrium between stable and unstable as the soda is removed from the can. Requires use of Newton's first law, center of mass, Archimedes' principle, stable and unstable equilibrium, and buoyant force position. (MVL)

  12. Protonolysis of a Ruthenium-Carbene Bond and Applications in Olefin Metathesis

    PubMed Central

    Keitz, Benjamin K.; Bouffard, Jean; Bertrand, Guy; Grubbs, Robert H.

    2011-01-01

    The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Brønsted acid results in protonolysis of the Ru-MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicate a rate-determining protonation step to generate the metathesis active species. The NHC/MIC catalyst was found to have activity exceeding current commercial ruthenium catalysts. PMID:21574621

  13. Gold carbenes, gold-stabilized carbocations, and cationic intermediates relevant to gold-catalysed enyne cycloaddition.

    PubMed

    Harris, R J; Widenhoefer, R A

    2016-08-21

    Cationic gold complexes in which gold is bound to a formally divalent carbon atom, typically formulated as gold carbenes or α-metallocarbenium ions, have been widely invoked in a range of gold-catalyzed transformations, most notably in the gold-catalyzed cycloisomerization of 1,n-enynes. Although the existence of gold carbene complexes as intermediates in gold-catalyzed transformations is supported by a wealth of indirect experimental data and by computation, until recently no examples of cationic gold carbenes/α-metallocarbenium ions had been synthesized nor had any cationic intermediates generated via gold-catalyzed enyne cycloaddition been directly observed. Largely for this reason, there has been considerable debate regarding the electronic structure of these cationic complexes, in particular the relative contributions of the carbene (LAu(+)[double bond, length as m-dash]CR2) and α-metallocarbenium (LAu-CR2(+)) forms, which is intimately related to the extent of d → p backbonding from gold to the C1 carbon atom. However, over the past ∼ seven years, a number of cationic gold carbene complexes have been synthesized in solution and generated in the gas phase and cationic intermediates have been directly observed in the gold-catalyzed cycloaddition of enynes. Together, these advances provide insight into the nature and electronic structure of gold carbene/α-metallocarbenium complexes and the cationic intermediates generated via gold-catalyzed enyne cycloaddition. Herein we review recent advances in this area. PMID:27146712

  14. Synthesis and solvent dependent reactivity of chelating bis-N-heterocyclic carbene complexes of Fe(II) hydrides.

    PubMed

    Zlatogorsky, Sergey; Ingleson, Michael J

    2012-03-01

    The synthesis and isolation of low coordinate methylenebis-(N-DIPP-imidazole-2-ylidene)iron((II))hydrides, (((DIPP)C)(2)CH(2))FeH(2-y)I(y) ((DIPP = 2,6-di-isopropylphenyl, y = 1 or 0), was complicated by competitive reactions with solvent, rapid reductive elimination of H(2) and/or dissociation of the bis-N-heterocyclic carbene ligand. Addition of KH to (((DIPP)C)(2)CH(2))FeI(2) in THF/haloalkane mixtures enabled a short lived mono-hydride to be trapped by reaction with CH(2)Cl(2) or cyclo-heptylbromide to form (((DIPP)C)(2)CH(2))FeI(X) (X = Cl or Br, respectively). Toluene coordination stabilises iron-mono hydride complexes as (((DIPP)C)(2)CH(2))Fe(II)H{η(6)-(toluene)} species, which can be isolated in low yield from combination of borohydride salts and (((DIPP)C)(2)CH(2))FeI(2) in toluene, including an imidazole C4 deprotonated carbene-borane, methylene(N-DIPP-imidazole-2-ylidene)(N-DIPP-4-triethyl-borane-imidazole-2-ylidene)](hydrido)(η(6)-toluene)iron. In the absence of toluene, or at short reaction times compounds with empirical formula (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI (R = Et or sec-Bu) that function as a masked Fe((II))-dihydride are isolated. Whilst (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI was stable for days in Et(2)O, more polar solvents (MeCN, THF) led to formation of the carbene borane adducts (((DIPP)C)(2)CH(2))(BR(3))(2). The addition of CO or cyclo-heptylbromide to (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI formed (((DIPP)C)(2)CH(2))Fe(CO)(3) and (((DIPP)C)(2)CH(2))FeBr(2), respectively with BR(3) evolved from both reactions as a by-product.

  15. Solvent polarity effects on carbene/ether-O-ylide equilibria.

    PubMed

    Hoijemberg, Pablo A; Moss, Robert A; Krogh-Jespersen, Karsten

    2012-05-17

    p-Nitrophenylchlorocarbene (PNPCC) reacted reversibly with tetrahydrofuran (THF), tetrahydropyran (THP), 1,3-dioxane (1,3-D), and 1,4-dioxane (1,4-D) to form O-ylides 8, 9, 10, and 11, respectively. The O-ylides were visualized by their characteristic UV-vis spectroscopic signatures. Equilibrium constants (K) were determined spectroscopically, and studies of K as a function of pentane/1,2-dichloroethane (DCE) solvent blends illustrated the dependence of K on solvent polarity. Electronic structure calculations based on density functional theory provided carbene/ether O-ylide structures and energetics, as well as electronic spectroscopic parameters for use in the determination of K. Comparisons of the computed and experimental data were generally satisfactory. PMID:22564048

  16. New catalysts with unsymmetrical N-heterocyclic carbene ligands.

    PubMed

    Tornatzky, Johanna; Kannenberg, Axel; Blechert, Siegfried

    2012-07-21

    The importance of unsymmetrical N-heterocyclic carbenes (uNHCs) as ligands in metal-catalyzed reactions is undeniable. While uNHCs show similar properties as compared with symmetrical NHCs, dissymmetrization allows for further fine-tuning. The introduction of chelatization, hemilability, bifunctionality, shielding effects, and chirality-transfer influences the catalyst's stability, reactivity, and selectivity, thus offering access to tailor-made systems including mono- and multidentate uNHC ligands. Based on selected examples, the structure-reactivity relationship of uNHCs employed in metal catalysts is presented. The focus is on catalytically active complexes, which either offer access to new applications or lead to significantly improved results in metal-catalyzed reactions. PMID:22584913

  17. The carbene insertion methodology for the catalytic functionalization of unreactive hydrocarbons: no classical C-H activation, but efficient C-H functionalization.

    PubMed

    Díaz-Requejo, M Mar; Belderrain, Tomás R; Nicasio, M Carmen; Pérez, Pedro J

    2006-12-21

    This contribution intends to highlight the use of the metal-catalyzed functionalization of unreactive carbon-hydrogen bonds by the carbene insertion methodology, that employs diazo compounds as the carbene source.

  18. Computation Sheds Insight into Iron Porphyrin Carbenes' Electronic Structure, Formation, and N-H Insertion Reactivity.

    PubMed

    Sharon, Dina A; Mallick, Dibyendu; Wang, Binju; Shaik, Sason

    2016-08-01

    Iron porphyrin carbenes constitute a new frontier of species with considerable synthetic potential. Exquisitely engineered myoglobin and cytochrome P450 enzymes can generate these complexes and facilitate the transformations they mediate. The current work harnesses density functional theoretical methods to provide insight into the electronic structure, formation, and N-H insertion reactivity of an iron porphyrin carbene, [Fe(Por)(SCH3)(CHCO2Et)](-), a model of a complex believed to exist in an experimentally studied artificial metalloenzyme. The ground state electronic structure of the terminal form of this complex is an open-shell singlet, with two antiferromagnetically coupled electrons residing on the iron center and carbene ligand. As we shall reveal, the bonding properties of [Fe(Por)(SCH3)(CHCO2Et)](-) are remarkably analogous to those of ferric heme superoxide complexes. The carbene forms by dinitrogen loss from ethyl diazoacetate. This reaction occurs preferentially through an open-shell singlet transition state: iron donates electron density to weaken the C-N bond undergoing cleavage. Once formed, the iron porphyrin carbene accomplishes N-H insertion via nucleophilic attack. The resulting ylide then rearranges, using an internal carbonyl base, to form an enol that leads to the product. The findings rationalize experimentally observed reactivity trends reported in artificial metalloenzymes employing iron porphyrin carbenes. Furthermore, these results suggest a possible expansion of enzymatic substrate scope, to include aliphatic amines. Thus, this work, among the first several computational explorations of these species, contributes insights and predictions to the surging interest in iron porphyrin carbenes and their synthetic potential. PMID:27347808

  19. Computation Sheds Insight into Iron Porphyrin Carbenes' Electronic Structure, Formation, and N-H Insertion Reactivity.

    PubMed

    Sharon, Dina A; Mallick, Dibyendu; Wang, Binju; Shaik, Sason

    2016-08-01

    Iron porphyrin carbenes constitute a new frontier of species with considerable synthetic potential. Exquisitely engineered myoglobin and cytochrome P450 enzymes can generate these complexes and facilitate the transformations they mediate. The current work harnesses density functional theoretical methods to provide insight into the electronic structure, formation, and N-H insertion reactivity of an iron porphyrin carbene, [Fe(Por)(SCH3)(CHCO2Et)](-), a model of a complex believed to exist in an experimentally studied artificial metalloenzyme. The ground state electronic structure of the terminal form of this complex is an open-shell singlet, with two antiferromagnetically coupled electrons residing on the iron center and carbene ligand. As we shall reveal, the bonding properties of [Fe(Por)(SCH3)(CHCO2Et)](-) are remarkably analogous to those of ferric heme superoxide complexes. The carbene forms by dinitrogen loss from ethyl diazoacetate. This reaction occurs preferentially through an open-shell singlet transition state: iron donates electron density to weaken the C-N bond undergoing cleavage. Once formed, the iron porphyrin carbene accomplishes N-H insertion via nucleophilic attack. The resulting ylide then rearranges, using an internal carbonyl base, to form an enol that leads to the product. The findings rationalize experimentally observed reactivity trends reported in artificial metalloenzymes employing iron porphyrin carbenes. Furthermore, these results suggest a possible expansion of enzymatic substrate scope, to include aliphatic amines. Thus, this work, among the first several computational explorations of these species, contributes insights and predictions to the surging interest in iron porphyrin carbenes and their synthetic potential.

  20. Synthesis of the first radiolabeled 188Re N-heterocyclic carbene complex and initial studies on its potential use in radiopharmaceutical applications

    PubMed Central

    Wagner, Thomas; Zeglis, Brian M.; Groveman, Sam; Hille, Claudia; Pöthig, Alexander; Francesconi, Lynn C.; Herrmann, Wolfgang A.; Kühn, Fritz E.; Reiner, Thomas

    2015-01-01

    A novel approach towards the synthesis of radiolabeled organometallic rhenium complexes is presented. We successfully synthesized and analyzed the first 188Re-labeled N-heterocyclic biscarbene complex, trans-dioxobis(1,1′-methylene-bis(3,3′-diisopropylimidazolium-2-ylidene))188rhenium(V) hexafluorophosphate (188Re-4) via transmetalation using an air-stable and moisture-stable silver(I) biscarbene complex. In order to assess the viability of this complex as a potential lead structure for in vivo applications, the stability of the 188Re-NHC complex was tested in physiologically relevant media. Ultimately, our studies illustrate that the complex we synthesized dissociates rapidly and is therefore unsuitable for use in radiopharmaceuticals. However, it is clear that the transmetalation approach we have developed is a rapid, robust, and mild method for the synthesis of new 188Re-labeled carbene complexes. PMID:24889257

  1. Synthesis and application of a dual chiral [2.2]paracyclophane-based N-heterocyclic carbene in enantioselective β-boration of acyclic enones.

    PubMed

    Wang, Lei; Chen, Zhen; Ma, Manyuan; Duan, Wenzeng; Song, Chun; Ma, Yudao

    2015-11-21

    An enantioselective conjugate addition of boron to α,β-unsaturated ketones catalysed by either a N-heterocyclic carbene or a copper-carbene complex generated in situ from a new chiral bicyclic triazolium based on [2.2]paracyclophane is presented. The dual chiral carbene-copper catalyst has significant advantages over its carbene counterpart as an organocatalyst in asymmetric β-boration of acyclic enones, giving a variety of chiral β-boryl ketones in good yields and enantioselectivities. This is a successful example of employing the same N-heterocyclic carbene in one catalytic reaction as both an organocatalyst and a ligand for transition metal catalysis. PMID:26347490

  2. N-Heterocyclic Carbene Ligands for Au Nanocrystal Stabilization and Three-Dimensional Self-Assembly.

    PubMed

    Roland, Sylvain; Ling, Xiang; Pileni, Marie-Paule

    2016-08-01

    N-Heterocyclic carbenes (NHCs) have emerged as a new class of ligands for materials chemistry that appears particularly relevant for the stabilization and functionalization of metal nanoparticles (NPs). The particular properties and high synthetic flexibility of NHCs make them highly attractive tools for the development of new (nano)materials and the fundamental study of their properties. The relationships between the NHC structure and NP structure/properties, including physical, biological, and self-assembly properties, remain largely unknown. In the past decade, many efforts have been made to gain more fundamental understanding in this area. In this feature article, we present our contribution in this field focusing on the formation of NHC-coated Au nanocrystals (NCs), their stability, and their ability to self-assemble into 3D crystalline structures called supracrystals. First, the formation of NHC-stabilized Au NCs is discussed by comparing different NHC structures, NHC-based Au precursors, and synthesis methods. This study shows the major role of the NHC structure in obtaining both stable NHC-coated Au NCs and narrow size distributions. In a second part, a comparative study of the oxygen resistance of NHC- and thiol-coated NCs is presented, demonstrating the enhanced stability of NHC-coated Au NCs to oxygen-based treatments. Finally, the self-assembly of NHC-coated Au NCs into 3D Au superlattices is presented. The formation of large organized domains of several micrometers is described from the design of NHCs tailored with long alkyl chains. In these different contexts, efforts have been made to gain a more in-depth understanding of the behavior of NHC ligands at the surface of NCs. These results show that the NHC-based approach to nanomaterials has many assets for opening a new research area in the supracrystal world. PMID:27412075

  3. N-Heterocyclic Carbene Ligands for Au Nanocrystal Stabilization and Three-Dimensional Self-Assembly

    PubMed Central

    2016-01-01

    N-Heterocyclic carbenes (NHCs) have emerged as a new class of ligands for materials chemistry that appears particularly relevant for the stabilization and functionalization of metal nanoparticles (NPs). The particular properties and high synthetic flexibility of NHCs make them highly attractive tools for the development of new (nano)materials and the fundamental study of their properties. The relationships between the NHC structure and NP structure/properties, including physical, biological, and self-assembly properties, remain largely unknown. In the past decade, many efforts have been made to gain more fundamental understanding in this area. In this feature article, we present our contribution in this field focusing on the formation of NHC-coated Au nanocrystals (NCs), their stability, and their ability to self-assemble into 3D crystalline structures called supracrystals. First, the formation of NHC-stabilized Au NCs is discussed by comparing different NHC structures, NHC-based Au precursors, and synthesis methods. This study shows the major role of the NHC structure in obtaining both stable NHC-coated Au NCs and narrow size distributions. In a second part, a comparative study of the oxygen resistance of NHC- and thiol-coated NCs is presented, demonstrating the enhanced stability of NHC-coated Au NCs to oxygen-based treatments. Finally, the self-assembly of NHC-coated Au NCs into 3D Au superlattices is presented. The formation of large organized domains of several micrometers is described from the design of NHCs tailored with long alkyl chains. In these different contexts, efforts have been made to gain a more in-depth understanding of the behavior of NHC ligands at the surface of NCs. These results show that the NHC-based approach to nanomaterials has many assets for opening a new research area in the supracrystal world. PMID:27412075

  4. The influence of anionic ligands on stereoisomerism of Ru carbenes and their importance to efficiency and selectivity of catalytic olefin metathesis reactions.

    PubMed

    Torker, Sebastian; Khan, R Kashif M; Hoveyda, Amir H

    2014-03-01

    Investigations detailed herein provide insight regarding the mechanism of stereochemical inversion of stereogenic-at-Ru carbene complexes through a nonolefin metathesis-based polytopal rearrangement pathway. Computational analyses (DFT) reveal that there are two key factors that generate sufficient energy barriers that are responsible for the possibility of isolation and characterization of high-energy, but kinetically stable, intermediates: (1) donor-donor interactions that involve the anionic ligands and the strongly electron donating carbene groups and (2) dipolar effects arising from the syn relationship between the anionic groups (iodide and phenoxide). We demonstrate that a Brønsted acid lowers barriers to facilitate isomerization, and that the positive influence of a proton source is the result of its ability to diminish the repulsive electronic interactions originating from the anionic ligands. The implications of the present studies regarding a more sophisticated knowledge of the role of anionic units on the efficiency of Ru-catalyzed olefin metathesis reactions are discussed. The electronic basis for the increased facility with which allylic alcohols participate in olefin metathesis processes will be presented as well. Finally, we illustrate how a better understanding of the role of anionic ligands has served as the basis for successful design of Ru-based Z-selective catalysts for alkene metathesis. PMID:24533571

  5. The influence of anionic ligands on stereoisomerism of Ru carbenes and their importance to efficiency and selectivity of catalytic olefin metathesis reactions.

    PubMed

    Torker, Sebastian; Khan, R Kashif M; Hoveyda, Amir H

    2014-03-01

    Investigations detailed herein provide insight regarding the mechanism of stereochemical inversion of stereogenic-at-Ru carbene complexes through a nonolefin metathesis-based polytopal rearrangement pathway. Computational analyses (DFT) reveal that there are two key factors that generate sufficient energy barriers that are responsible for the possibility of isolation and characterization of high-energy, but kinetically stable, intermediates: (1) donor-donor interactions that involve the anionic ligands and the strongly electron donating carbene groups and (2) dipolar effects arising from the syn relationship between the anionic groups (iodide and phenoxide). We demonstrate that a Brønsted acid lowers barriers to facilitate isomerization, and that the positive influence of a proton source is the result of its ability to diminish the repulsive electronic interactions originating from the anionic ligands. The implications of the present studies regarding a more sophisticated knowledge of the role of anionic units on the efficiency of Ru-catalyzed olefin metathesis reactions are discussed. The electronic basis for the increased facility with which allylic alcohols participate in olefin metathesis processes will be presented as well. Finally, we illustrate how a better understanding of the role of anionic ligands has served as the basis for successful design of Ru-based Z-selective catalysts for alkene metathesis.

  6. Photochemistry of group 6 Fischer carbene complexes: beyond the photocarbonylation reaction.

    PubMed

    Fernández, Israel; Cossío, Fernando P; Sierra, Miguel A

    2011-07-19

    The seminal report by Hegedus in 1982, showing that alkoxychromium(0) carbenes reacted with imines under bright Colorado sunlight to yield β-lactams, marked the beginning of a key reaction in organometallic chemistry. Very little was known about the mechanism of this reaction. In fact, Hegedus proposed the reversible generation of a chromium-coordinated ketene, which would react with nucleophiles. This coordinated species would show all the advantages of ketenes without their shortcomings, namely, dimerization, formation of undesired adducts, and so forth. The quest for the detection of these species and the pursuit of the mechanism of the photocarbonylation (a reaction exclusive to Cr(0) and Mo(0) carbene complexes, not W(0) carbene complexes) remained unabated over the next 15 years. In fact, all attempts to experimentally determine the mechanism of this useful reaction have been fruitless. At the same time, the photocarbonylation of Cr(0) carbenes matured into a valuable synthetic reaction, allowing access to several families of organic compounds. Unfortunately, reactions other than photocarbonylation remained elusive. We used a combination of experimental and computational methodologies to study the photocarbonylation of Cr(0) carbene complexes and the subsequent reaction of the photogenerated ketenes with nucleophiles. In parallel, we discovered new photochemical processes and succeeded in making photoreactive the so-called "unreactive" W(0) carbene complexes. In this Account, we discuss the disentangling of the mechanisms of these transformations, thereby shedding some light onto the photochemistry of group 6 metal (Fischer) carbene complexes. The original designation of the electronic transitions of group 6 carbene complexes was reassigned, and the photocarbonylation step was analyzed again, resulting in the sequence S(0)-T(1)-S(0), which is far removed from conventional organic photochemistry. The T(1) species is a chromacyclopropanone; its unpaired

  7. Synthesis and characterisation of an N-heterocyclic carbene with spatially-defined steric impact.

    PubMed

    Shaw, Paul; Kennedy, Alan R; Nelson, David J

    2016-08-01

    The synthesis and co-ordination chemistry of a new 'bulky yet flexible' N-heterocyclic carbene ("IPaul") is reported. This carbene has spatially-defined steric impact; steric maps show that two quadrants are very bulky while the other two are quite open. The electronic properties of this carbene are very similar to those of other 1,3-diarylimidazol-2-ylidenes. Copper, silver, iridium, and nickel complexes of the new ligand have been prepared. In solution, the ligand adopts two different conformations, while X-ray crystallographic analyses of the transition metal complexes suggest that the syn-conformer is preferred in the solid state due to intermolecular interactions. The copper(i) chloride complex of this new ligand has been shown to be highly-active in the hydrosilylation of carbonyl compounds, when compared to the analogous IPr, IMes, IPr* and IPr*(OMe) complexes. PMID:27335266

  8. Homobimetallic Ruthenium-N-Heterocyclic Carbene Complexes For Olefin Metathesis

    NASA Astrophysics Data System (ADS)

    Sauvage, Xavier; Demonceau, Albert; Delaude, Lionel

    In this chapter, the synthesis and catalytic activity towards olefin metathesis of homobimetallic ruthenium (Ru)-alkylidene, -cyclodiene or -arene complexes bearing phosphine or N-heterocyclic carbene (NHC) ligands are reviewed. Emphasis is placed on the last category of bimetallic compounds. Three representatives of this new type of molecular scaffold were investigated. Thus, [(p-cymene)Ru(m-Cl)3RuCl (h2-C2H4)(L)] complexes with L = PCy3 (15a), IMes (16a), or IMesCl2 (16b) were prepared. They served as catalyst precursors for cross-metathesis (CM) of various styrene derivatives. These experiments revealed the outstanding aptitude of complex 16a (and to a lesser extent of 16b) to catalyze olefin metathesis reactions. Contrary to monometallic Ru-arene complexes of the [RuCl2(p-cymene)(L)] type, the new homobimetallic species did not require the addition of a diazo compound nor visible light illumination to initiate the ring-opening metathesis of norbornene or cyclooctene. When diethyl 2,2-diallylmalonate and N,N-diallyltosylamide were exposed to 16a,b, a mixture of cycloisomerization and ring-closing metathesis (RCM) products was obtained in a nonselective way. Addition of phenylacetylene enhanced the metathetical activity while completely repressing the cycloisomerization process.

  9. Ruthenium olefin metathesis catalysts featuring unsymmetrical N-heterocyclic carbenes.

    PubMed

    Paradiso, Veronica; Bertolasi, Valerio; Costabile, Chiara; Grisi, Fabia

    2016-01-14

    New ruthenium Grubbs' and Hoveyda-Grubbs' second generation catalysts bearing N-alkyl/N-isopropylphenyl N-heterocyclic carbene (NHC) ligands with syn or anti backbone configuration were obtained and compared in model olefin metathesis reactions. Different catalytic efficiencies were observed depending on the size of the N-alkyl group (methyl or cyclohexyl) and on the backbone configuration. The presence of an N-cyclohexyl substituent determined the most significant reactivity differences between catalysts with syn or anti phenyl groups on the backbone. In particular, anti catalysts proved highly efficient, especially in the ring-closing metathesis (RCM) of encumbered diolefins, while syn catalysts showed low efficiency in the RCM of less hindered diolefins. This peculiar behavior, rationalized through DFT studies, was found to be related to the high propensity of these catalysts to give nonproductive metathesis events. Enantiopure anti catalysts were also tested in asymmetric metathesis reactions, where moderate enantioselectivities were observed. The steric and electronic properties of unsymmetrical NHCs with the N-cyclohexyl group were then evaluated using the corresponding rhodium complexes. While steric factors proved unimportant for both syn and anti NHCs, a major electron-donating character was found for the unsymmetrical NHC with anti phenyl substituents on the backbone.

  10. {alpha},{beta}-Unsaturated Fischer carbene complexes as chemical multitalents

    SciTech Connect

    Meijere, A. de

    1995-12-31

    The well established reaction of {alpha},{beta}-unsaturated Fischer carbenechromium complexes 6(R{sup 1} = H) with alkynes normally proceeds with carbonyl insertion to yield 4-alkoxyphenols 9. Led by the incidental formation of a cyclopentadiene 3 from certain {beta}-aminosubstituted complexes 6(X = NR{sub 2}{sup 3}, R{sup 1} = cPr) the authors have studied the influences of the nature of substituents (R{sup 1}, X on 6; R{sub L}, R{sub S} in the alkyne; R{sup 3} in the amino group), solvents, and temperature on the outcome of the reaction. Imino substitution on complexes 6 leads to 2H-pyrroles 1, a free primary amino group (X = NH{sub 2}) to pyridines 5, and bulky substituents R{sup 1} to cyclopenta[b]pyrans 8 with double insertion of an alkyne. Eventually, appropriate conditions have been developed which permit to selectively prepare either 3-alkoxy-5-(dialkylamino)cyclopentadienes 3 (as synthetic equivalents of cyclopentenones 4), 5-(dialkylaminomethylene)cyclopent-2-enones 7, 3-alkoxy-2-(1{prime}-morpholino-1{prime}-alkenyl)cyclopent-2-enones 10, and 2-acyl-3-(dialkylamino)cyclopent-2-enones 11 from easily accessible carbene complexes 6 (X = NR{sub 2}{sup 3}) in high yields. Mechanistic aspects and implications of these novel transformations will be discussed.

  11. Ruthenium olefin metathesis catalysts featuring unsymmetrical N-heterocyclic carbenes.

    PubMed

    Paradiso, Veronica; Bertolasi, Valerio; Costabile, Chiara; Grisi, Fabia

    2016-01-14

    New ruthenium Grubbs' and Hoveyda-Grubbs' second generation catalysts bearing N-alkyl/N-isopropylphenyl N-heterocyclic carbene (NHC) ligands with syn or anti backbone configuration were obtained and compared in model olefin metathesis reactions. Different catalytic efficiencies were observed depending on the size of the N-alkyl group (methyl or cyclohexyl) and on the backbone configuration. The presence of an N-cyclohexyl substituent determined the most significant reactivity differences between catalysts with syn or anti phenyl groups on the backbone. In particular, anti catalysts proved highly efficient, especially in the ring-closing metathesis (RCM) of encumbered diolefins, while syn catalysts showed low efficiency in the RCM of less hindered diolefins. This peculiar behavior, rationalized through DFT studies, was found to be related to the high propensity of these catalysts to give nonproductive metathesis events. Enantiopure anti catalysts were also tested in asymmetric metathesis reactions, where moderate enantioselectivities were observed. The steric and electronic properties of unsymmetrical NHCs with the N-cyclohexyl group were then evaluated using the corresponding rhodium complexes. While steric factors proved unimportant for both syn and anti NHCs, a major electron-donating character was found for the unsymmetrical NHC with anti phenyl substituents on the backbone. PMID:26608162

  12. Co(III)-Carbene Radical Approach to Substituted 1H-Indenes.

    PubMed

    Das, Braja Gopal; Chirila, Andrei; Tromp, Moniek; Reek, Joost N H; Bruin, Bas de

    2016-07-20

    A new strategy for the catalytic synthesis of substituted 1H-indenes via metalloradical activation of o-cinnamyl N-tosyl hydrazones is presented, taking advantage of the intrinsic reactivity of a Co(III) carbene radical intermediate. The reaction uses readily available starting materials and is operationally simple, thus representing a practical method for the construction of functionalized 1H-indene derivatives. The cheap and easy to prepare low spin cobalt(II) complex [Co(II)(MeTAA)] (MeTAA = tetramethyltetraaza[14]annulene) proved to be the most active catalyst among those investigated, which demonstrates catalytic carbene radical reactivity for a nonporphyrin cobalt(II) complex, and for the first time catalytic activity of [Co(II)(MeTAA)] in general. The methodology has been successfully applied to a broad range of substrates, producing 1H-indenes in good to excellent yields. The metallo-radical catalyzed indene synthesis in this paper represents a unique example of a net (formal) intramolecular carbene insertion reaction into a vinylic C(sp(2))-H bond, made possible by a controlled radical ring-closure process of the carbene radical intermediate involved. The mechanism was investigated computationally, and the results were confirmed by a series of supporting experimental reactions. Density functional theory calculations reveal a stepwise process involving activation of the diazo compound leading to formation of a Co(III)-carbene radical, followed by radical ring-closure to produce an indanyl/benzyl radical intermediate. Subsequent indene product elimination involving a 1,2-hydrogen transfer step regenerates the catalyst. Trapping experiments using 2,2,6,6-tetra-methylpiperidine-1-oxyl (TEMPO) radical or dibenzoylperoxide (DBPO) confirm the involvement of cobalt(III) carbene radical intermediates. Electron paramagnetic resonance spectroscopic spin-trapping experiments using phenyl N-tert-butylnitrone (PBN) reveal the radical nature of the reaction. PMID

  13. Olefin Metathesis With Ruthenium-Arene Catalysts Bearing N-Heterocyclic Carbene Ligands

    NASA Astrophysics Data System (ADS)

    Delaude, Lionel; Demonceau, Albert

    In this chapter, we summarize the main results of our investigations on the ring-opening metathesis polymerization (ROMP) of cyclooctene catalyzed by various ruthenium (Ru)-arene complexes bearing imidazolin-2-ylidene, imidazolidin- 2-ylidene, or triazolin-5-ylidene ligands. Three major findings emerged from this study. First, we underscored the intervention of a photochemical activation step due to visible light illumination. Second, we established that the presence of an endocyclic double bond in the carbene ligand central heterocycle was not crucial to achieve high catalytic efficiencies. Third, we demonstrated that ortho-metallation of the N-heterocyclic carbene (NHC) ligand by the Ru center led to inactive catalysts.

  14. Gold(I) Carbenes by Retro-Buchner Reaction: Generation and Fate

    PubMed Central

    2013-01-01

    The fate of the aryl gold(I) carbenes generated by retro-Buchner reaction of ortho-substituted 7-aryl-1,3,5-cycloheptatrienes is dependent on the constitution of the ortho substituent. Indenes and fluorenes are obtained by intramolecular reaction of highly electrophilic gold(I) carbenes with alkenes and arenes. According to density functional theory calculations, the gold-catalyzed retro-Buchner process occurs stepwise, although the two carbon–carbon cleavages occur on a rather flat potential energy surface. PMID:24358986

  15. Stereoselective 1,3-Insertions of Rhodium(II) Azavinyl Carbenes

    PubMed Central

    Chuprakov, Stepan; Worrell, Brady T.; Selander, Nicklas; Sit, Rakesh K.; Fokin, Valery V.

    2014-01-01

    Rhodium(II) azavinyl carbenes, conveniently generated from 1-sulfonyl-1,2,3-triazoles, undergo a facile, mild and convergent formal 1,3-insertion into N–H and O–H bonds of primary and secondary amides, various alcohols, and carboxylic acids to afford a wide range of vicinally bis-functionalized Z-olefins with perfect regio- and stereoselectively. Utilizing the distinctive functionality installed through these reactions, a number of subsequent rearrangements and cyclizations expand the repertoire of valuable organic building blocks constructed by reactions of transition metal carbene complexes, including α-allenyl ketones and amino-substituted heterocycles. PMID:24295389

  16. Dual Catalysis: Proton/Metal-Catalyzed Tandem Benzofuran Annulation/Carbene Transfer Reaction.

    PubMed

    Ma, Jun; Chen, Kai; Fu, Hongguang; Zhang, Li; Wu, Wanqing; Jiang, Huanfeng; Zhu, Shifa

    2016-03-18

    An efficient proton/metal-catalyzed tandem benzofuran annulation/carbene transfer reaction for the synthesis of various benzofuryl-substituted cyclopropanes and cycloheptatrienes has been developed. The reaction was proposed to proceed through two key intermediates, o-quinone methide (o-QM) and benzofuryl carbene. The DFT-based computational studies indicated that the reaction was initiated through the dehydration of o-HBA via a Brønsted acid mediated proton shuttle transition state, forming the key intermediate o-QM. PMID:26950391

  17. Chemically Non-Innocent Cyclic (Alkyl)(Amino)Carbenes: Ligand Rearrangement, C-H and C-F Bond Activation.

    PubMed

    Turner, Zoë R

    2016-08-01

    A cyclic (alkyl)(amino)carbene (CAAC) was found to undergo unprecedented rearrangements and transformations of its core structure in the presence of Group 1 and 2 metals. Although the carbene was also found to be prone to intramolecular C-H activation, it was competent for intermolecular activation of a variety of sp-, sp(2) -, and sp(3) -hybridized C-H bonds. Double C-F activation of hexafluorobenzene was also observed in this work. These processes all hold relevance to the role of these carbenes in catalysis, as well as to their use in the synthesis of new and unusual main group or transition metal complexes. PMID:27363588

  18. Solvent mimicry with methylene carbene to probe protein topography.

    PubMed

    Gómez, Gabriela Elena; Monti, José Luis E; Mundo, Mariana Rocío; Delfino, José María

    2015-10-01

    The solvent accessible surface area (SASA) of the polypeptide chain plays a key role in protein folding, conformational change, and interaction. This fundamental biophysical parameter is elusive in experimental measurement. Our approach to this problem relies on the reaction of the minimal photochemical reagent diazirine (DZN) with polypeptides. This reagent (i) exerts solvent mimicry because its size is comparable to water and (ii) shows scant chemical selectivity because it generates extremely reactive methylene carbene. Methylation gives rise to the EM (extent of modification) signal, which is useful for scrutinizing the conformational change triggered by Ca(2+) binding to calmodulin (CaM). The increased EM observed for the full protein is dominated by the enhanced exposure of hydrophobic area in Ca(2+)-CaM. Fragmentation allowed us to quantify the methylene incorporation at specific sites. Peptide 91-106 reveals a major reorganization around the calcium 151 binding site, resulting in local ordering and a greater exposure of the hydrophobic surface. Additionally, this technique shows a high sensitivity to probe recognition between CaM and melittin (Mel). The large decrease in EM indicates the occlusion of a significant hydrophobic area upon complexation. Protection from labeling reveals a larger involvement of the N-terminal and central regions of CaM in this interaction. Despite its smaller size, Mel's differential exposure can also be quantified. Moreover, MS/MS fragmentation realizes the goal of extending the resolution of labeled sites at the amino acid level. Overall, DZN labeling emerges as a useful footprinting method capable of shedding light on physiological conformational changes and interactions. PMID:26348271

  19. Synthesis and reactivity of metal complexes with acyclic (amino)(ylide)carbene ligands.

    PubMed

    González-Fernández, Elisa; Rust, Jörg; Alcarazo, Manuel

    2013-10-18

    No cycle required: The straightforward synthesis of acyclic (amino)(ylide)carbene gold complexes was achieved by reaction of isocyanide gold complexes with phosphorus and arsenic ylides as well as electron-rich olefins. Their ability to form bimetallic species and to act as ligand-transfer reagents has also been established. PMID:24038894

  20. Synthesis and reactivity of metal complexes with acyclic (amino)(ylide)carbene ligands.

    PubMed

    González-Fernández, Elisa; Rust, Jörg; Alcarazo, Manuel

    2013-10-18

    No cycle required: The straightforward synthesis of acyclic (amino)(ylide)carbene gold complexes was achieved by reaction of isocyanide gold complexes with phosphorus and arsenic ylides as well as electron-rich olefins. Their ability to form bimetallic species and to act as ligand-transfer reagents has also been established.

  1. Copper N-Heterocyclic Carbene: A Catalyst for Aerobic Oxidation or Reduction Reactions.

    PubMed

    Zhan, Le-Wu; Han, Lei; Xing, Ping; Jiang, Biao

    2015-12-18

    Copper N-heterocyclic carbene complexes can be readily used as catalysts for both aerobic oxidation of alcohols to aldehydes and reduction of imines to amines. Our methodology is universal for aromatic substrates and shows versatile tolerance to potential cascade reactions. A one-pot tandem synthetic strategy could afford useful imines and secondary amines via an oxidation-reduction strategy.

  2. Electrochemical flow-reactor for expedient synthesis of copper-N-heterocyclic carbene complexes.

    PubMed

    Chapman, Michael R; Shafi, Yarseen M; Kapur, Nikil; Nguyen, Bao N; Willans, Charlotte E

    2015-01-25

    An electrochemical flow-cell for highly efficient and selective generation of Cu(I)-N-heterocyclic carbene complexes under neutral and ambient conditions is reported. The feasibility of the flow-cell is demonstrated through the electrochemical synthesis of [Cu(IMes)Cl] and subsequent in situ flow directly into hydrosilylation reactions, with equal efficiency to the purified catalyst.

  3. A comparison of the bonding in the second-row transition-metal oxides and carbenes

    NASA Astrophysics Data System (ADS)

    Siegbahn, Per E. M.

    1993-01-01

    Calculations including electron correlation of all valence electrons have been performed for the sequence of second-row transition-metal oxides and carbenes. For the atoms to the right the bond strengths of the carbenes and the oxides are similar while for the atoms to the left the oxide bond strengths are much larger. The origin of this difference is the interaction between the oxygen lone pairs and empty 4d orbitals on the metal. With the large donation of electrons from the oxygen lone pair to the metal for the atoms to the left, the bonding can almost be described as triple bond formation for YO, ZrO and NbO. For MoO, where a 4d π orbital is singly occupied on the metal, the bond strength is much smaller than for the oxides to the left. For the metal carbenes two covalent bonds are formed. The ground state spin for the oxides to the right is higher than for the corresponding carbenes, which can be explained by the presence of the π degeneracy for the oxides. The relevance of the present results for the epoxidation and the olefin metathesis reactions are discussed.

  4. Influence of bulky yet flexible N-heterocyclic carbene ligands in gold catalysis.

    PubMed

    Collado, Alba; Patrick, Scott R; Gasperini, Danila; Meiries, Sebastien; Nolan, Steven P

    2015-01-01

    Three new Au(I) complexes of the formula [Au(NHC)(NTf2)] (NHC = N-heterocyclic carbene) bearing bulky and flexible ligands have been synthesised. The ligands studied are IPent, IHept and INon which belong to the 'ITent' ('Tent' for 'tentacular') family of NHC derivatives. The effect of these ligands in gold-promoted transformations has been investigated.

  5. Copper N-Heterocyclic Carbene: A Catalyst for Aerobic Oxidation or Reduction Reactions.

    PubMed

    Zhan, Le-Wu; Han, Lei; Xing, Ping; Jiang, Biao

    2015-12-18

    Copper N-heterocyclic carbene complexes can be readily used as catalysts for both aerobic oxidation of alcohols to aldehydes and reduction of imines to amines. Our methodology is universal for aromatic substrates and shows versatile tolerance to potential cascade reactions. A one-pot tandem synthetic strategy could afford useful imines and secondary amines via an oxidation-reduction strategy. PMID:26633757

  6. Synthesis of α-Fluoroketones by Insertion of HF into a Gold Carbene.

    PubMed

    Zeng, Xiaojun; Liu, Shiwen; Shi, Zhenyu; Liu, Guangchang; Xu, Bo

    2016-08-16

    Reported is an efficient synthesis of α-fluoroketones by insertion of hydrogen fluoride (HF) into the gold carbene intermediate, generated from a cationic gold catalyzed addition of N-oxides to alkynes. This method results in excellent chemical yields for a wide range of alkyne substrates and demonstrates good functional-group tolerance. PMID:27436069

  7. Chemical functionalization of graphene by carbene cycloaddition: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Zan, Wenyan

    2014-08-01

    In this work, we have systematically studied the structural, energetic and electronic properties of graphene functionalized with carbene groups by using density functional theory. Introducing a low concentration of CCl2 group in graphene was studied in detail by DFT, and closed cyclopropane-like three-membered ring structure was formed, meanwhile, the potential candidate carbene groups CR2 (R = H, F, CH3, CN, NO2, OCH3, CCH, C6H5) were added to graphene sheet, and CR2 (R = H, NO2, CH3) groups were expected to be good reactive species to covalently modify graphene. The graphene functionalization with carbene groups above can open graphene's band gap. More CCl2 molecules were added to graphene, and different concentrations of CCl2 group can tune graphene's band gap. In addition, the addition of CCl2 group to graphene edges was investigated, and the stronger binding energy was found. Multiple CCl2 molecules preferred to be bound with the same edge of graphene nanoribbon. This work provides an insight into the detailed molecular mechanism of graphene functionalization with carbene groups.

  8. Synthesis and in vitro Efficacy Studies of Silver Carbene Complexes on Biosafety Level 3 Bacteria.

    PubMed

    Panzner, Matthew J; Deeraksa, Arpaporn; Smith, Alyssa; Wright, Brian D; Hindi, Khadijah M; Kascatan-Nebioglu, Aysegul; Torres, Alfredo G; Judy, Barbara M; Hovis, Christine E; Hilliard, Julia K; Mallett, Rebekah J; Cope, Emily; Estes, D Mark; Cannon, Carolyn L; Leid, Jeff G; Youngs, Wiley J

    2009-05-01

    A series of N-heterocyclic carbene silver complexes have been synthesized and tested against the select group of bio-safety level 3 bacteria Burkholderia pseudomallei, Burkholderia mallei, Bacillus anthracis, methicillin-resistant Staphylococcus aureus and Yersinia pestis. Minimal inhibitory concentrations, minimal bactericidal and killing assays demonstrated the exceptional efficacy of the complexes against these potentially weaponizable pathogens. PMID:20160993

  9. An abnormal N-heterocyclic carbene-carbon dioxide adduct from imidazolium acetate ionic liquids: the importance of basicity.

    PubMed

    Kelemen, Zsolt; Péter-Szabó, Barbara; Székely, Edit; Hollóczki, Oldamur; Firaha, Dzmitry S; Kirchner, Barbara; Nagy, József; Nyulászi, László

    2014-09-26

    In the reaction of 1-ethyl-3-methylimidazolium acetate [C2C1Im][OAc] ionic liquid with carbon dioxide at 125 °C and 10 MPa, not only the known N-heterocyclic carbene (NHC)-CO2 adduct I, but also isomeric aNHC-CO2 adducts II and III were obtained. The abnormal NHC-CO2 adducts are stabilized by the presence of the polarizing basic acetate anion, according to static DFT calculations and ab initio molecular dynamics studies. A further possible reaction pathway is facilitated by the high basicity of the system, deprotonating the initially formed NHC-CO2 adduct I, which can then be converted in the presence of the excess of CO2 to the more stable 2-deprotonated anionic abnormal NHC-CO2 adduct via the anionic imidazolium-2,4-dicarboxylate according to DFT calculations on model compounds. This suggests a generalizable pathway to abnormal NHC complex formation. PMID:25137312

  10. N-Heterocyclic carbene-catalyzed [3+3] cyclocondensation of bromoenals with aldimines: highly enantioselective synthesis of dihydropyridinones.

    PubMed

    Gao, Zhong-Hua; Chen, Xiang-Yu; Zhang, Han-Ming; Ye, Song

    2015-08-01

    The N-heterocyclic carbene-catalyzed [3+3] cyclocondensation of bromoenals and aldimines was developed to give the corresponding dihydropyridinones in good yields with excellent enantioselectivities. PMID:26121224

  11. An insight into the mechanism of the aerobic oxidation of aldehydes catalyzed by N-heterocyclic carbenes.

    PubMed

    Bortolini, O; Chiappe, C; Fogagnolo, M; Giovannini, P P; Massi, A; Pomelli, C S; Ragno, D

    2014-02-25

    N-Heterocyclic carbene catalysis for the aerobic oxidation and esterification of aromatic aldehydes was monitored by ESI-MS (MS/MS) and the key intermediates were intercepted and characterized using the charge-tag strategy. PMID:24413829

  12. Improving carbene-copper-catalyzed asymmetric synthesis of α-aminoboronic esters using benzimidazole-based precursors.

    PubMed

    Wen, Kun; Wang, Han; Chen, Jinbo; Zhang, He; Cui, Xiaodan; Wei, Chao; Fan, Erkang; Sun, Zhihua

    2013-04-01

    By using a benzimidazole core and N-substitutions to tune the electronic properties of the corresponding N-heterocyclic carbenes, a one-pot protocol for efficient synthesis of α-aminoboronic esters without the need of a glovebox was developed in this work. The starting materials for the transformation can also be extended from aldehydes to ketones. An alternative protocol with short reaction time using preformed carbene-copper chloride is also described. PMID:23461780

  13. Singlet-triplet energy differences in divalent five membered cyclic conjugated Arduengo-type carbenes XC2HN2M (M = C, Si, Ge, Sn, and Pb; X = F, Cl, Br, and I)

    NASA Astrophysics Data System (ADS)

    Vessally, Esmail; Dehbandi, Behnam; Ahmadi, Elaheh

    2016-09-01

    Singlet-triplet energy differences in Arduengo-type carbenes XC2HN2C compared and contrasted with their sila, germa, stana and plumba analogues; at B3LYP/6-311++G** level of theory. Free Gibbs energy differences between triplet (t) and singlet (s) states (Δ G(t-s)) change in the following order: plumbylenes > stannylenes > germylenes > silylenes > carbenes. The singlet states in XC2HN2C are generally more stable when the electron withdrawing groups such as-F was used at β-position. However, the singlet states in XC2N2HM (M = Si, Ge, Sn, and Pb) are generally more stable when the withdrawing groups such as-F was placed. The puckering energy is investigated for each the singlet and triplet states. The DFT calculations found the linear correlation to size of the group 14 divalent element (M), the ∠N-M-N angle, and the Δ(LUMO-HOMO) of XC2HN2M.

  14. Oxygen insertion reactions of mixed N-heterocyclic carbene-oxazolinylborato zinc alkyl complexes.

    PubMed

    Xu, Songchen; Everett, William C; Ellern, Arkady; Windus, Theresa L; Sadow, Aaron D

    2014-10-14

    We report the synthesis of a new mixed oxazoline-carbene scorpionate ligand, bis(4,4-dimethyl-2-oxazolinyl)(1-mesitylimidazolyl)phenylborate (PhB(Ox(Me2))2Im(Mes)). Reactions of the protonated form PhB(Ox(Me2))2(Im(Mes)H) with dialkylzinc compounds provide four-coordinate zinc alkyl complexes, and X-ray diffraction studies of the {PhB(Ox(Me2))2Im(Mes)}ZnR (R = Me, Et) compounds show significant structural distortions involving the R groups shifting away from the carbene donor. The reaction of {PhB(Ox(Me2))2Im(Mes)}ZnEt (3) and O2 provides an isolable mononuclear zinc alkylperoxide {PhB(Ox(Me2))2Im(Mes)}ZnOOEt (4), which has been characterized by single crystal X-ray diffraction and (17)O NMR spectroscopy.

  15. Self-Supported N-Heterocyclic Carbenes and Their Use as Organocatalysts.

    PubMed

    Ma, Shuang; Toy, Patrick H

    2016-01-01

    The study of N-heterocyclic carbenes (NHCs) as organocatalysts has proliferated in recent years, and they have been found to be useful in a variety of reactions. In an attempt to further expand their utility and to study their recyclability, we designed and synthesized a series of self-supported NHCs in which the catalytic carbene groups form part of a densely functionalized polymer backbone, and studied them as organocatalysts. Of the self-Supported NHCs examined, a benzimidazole derived polymer with flexible linkers connecting the catalytic groups was found to be the most efficient organocatalyst in a model benzoin condensation reaction, and thus it was used in a variety of such reactions, including some involving catalyst recycling. Furthermore, it was also used to catalyze a set of redox esterification reactions involving conjugated unsaturated aldehydes. In all of these reactions the catalyst afforded good yield of the desired product and its polymeric nature facilitated product purification. PMID:27556435

  16. A Mesoionic Carbene as Neutral Ligand for Phosphorescent Cationic Ir(III) Complexes.

    PubMed

    Baschieri, Andrea; Monti, Filippo; Matteucci, Elia; Mazzanti, Andrea; Barbieri, Andrea; Armaroli, Nicola; Sambri, Letizia

    2016-08-15

    Two phosphorescent Ir(III) complexes bearing a mesoionic carbene ligand based on 1,2,3-triazolylidene are obtained for the first time. A silver-iridium transmetalation of the in situ-generated mesoionic carbene affords the cationic dichloro complex [Ir(trizpy)2Cl2](+) (3, trizpy = 1-benzyl-3-methyl-4-(pyridin-2-yl)-1H-1,2,3-triazolylidene) that reacts with a bis-tetrazolate (b-trz) dianionic ligand to give [Ir(trizpy)2(b-trz)](+) (5). The new compounds are fully characterized by NMR spectroscopy and mass spectrometry, and the X-ray structure of 3 is determined. The electrochemical behavior is somewhat different compared to most standard cationic iridium complexes. The first oxidation process is shifted to substantially higher potential in both 3 and 5, due to peculiar and different ligand-induced effects in the two cases, which stabilize the highest occupied molecular orbital; reduction processes are centered on the mesoionic carbene ligands. Both compounds exhibit a mostly ligand-centered luminescence band in the blue-green spectral region, substantially stronger in the case of 5 versus 3, both in CH3CN solution and in poly(methyl methacrylate) matrix at room temperature. Optimized geometries, orbital energies, spin densities, and electronic transitions are determined via density functional theory calculations, which support a full rationalization of the electrochemical and photophysical behavior. This work paves the way for the development of Ir-based emitters with neutral mesoionic carbene ligands and anionic ancillary ligands, a new concept in the area of cationic Ir(III) complexes.

  17. Charged bis-cyclometalated iridium(III) complexes with carbene-based ancillary ligands.

    PubMed

    Monti, Filippo; Kessler, Florian; Delgado, Manuel; Frey, Julien; Bazzanini, Federico; Accorsi, Gianluca; Armaroli, Nicola; Bolink, Henk J; Ortí, Enrique; Scopelliti, Rosario; Nazeeruddin, Md Khaja; Baranoff, Etienne

    2013-09-16

    Charged cyclometalated (C(^)N) iridium(III) complexes with carbene-based ancillary ligands are a promising family of deep-blue phosphorescent compounds. Their emission properties are controlled primarily by the main C(^)N ligands, in contrast to the classical design of charged complexes where N(^)N ancillary ligands with low-energy π* orbitals, such as 2,2'-bipyridine, are generally used for this purpose. Herein we report two series of charged iridium complexes with various carbene-based ancillary ligands. In the first series the C(^)N ligand is 2-phenylpyridine, whereas in the second one it is 2-(2,4-difluorophenyl)-pyridine. One bis-carbene (:C(^)C:) and four different pyridine-carbene (N(^)C:) chelators are used as bidentate ancillary ligands in each series. Synthesis, X-ray crystal structures, and photophysical and electrochemical properties of the two series of complexes are described. At room temperature, the :C(^)C: complexes show much larger photoluminescence quantum yields (ΦPL) of ca. 30%, compared to the N(^)C: analogues (around 1%). On the contrary, all of the investigated complexes are bright emitters in the solid state both at room temperature (1% poly(methyl methacrylate) matrix, ΦPL 30-60%) and at 77 K. Density functional theory calculations are used to rationalize the differences in the photophysical behavior observed upon change of the ancillary ligands. The N(^)C:-type complexes possess a low-lying triplet metal-centered ((3)MC) state mainly deactivating the excited state through nonradiative processes; in contrast, no such state is present for the :C(^)C: analogues. This finding is supported by temperature-dependent excited-state lifetime measurements made on representative N(^)C: and :C(^)C: complexes.

  18. Platinum(iv) N-heterocyclic carbene complexes: their synthesis, characterisation and cytotoxic activity.

    PubMed

    Bouché, M; Dahm, G; Wantz, M; Fournel, S; Achard, T; Bellemin-Laponnaz, S

    2016-07-28

    Platinum(ii) N-heterocyclic carbene complexes have been oxidized by bromine or iodobenzene dichloride to provide the fully characterised corresponding platinum(iv) NHC complexes. Antiproliferative activities of Pt(iv) NHC complexes were assayed against several cancer cell lines and the results were correlated with respect to their stability. Mechanistic investigations revealed that mitochondrial dysfunction and ROS production were associated with the cytotoxic process induced by these compounds. PMID:27331604

  19. N-heterocyclic carbene organocatalytic reductive β,β-coupling reactions of nitroalkenes via radical intermediates.

    PubMed

    Du, Yu; Wang, Yuhuang; Li, Xin; Shao, Yaling; Li, Guohui; Webster, Richard D; Chi, Yonggui Robin

    2014-11-01

    An unprecedented N-heterocyclic carbene catalytic reductive β,β-carbon coupling of α,β-nitroalkenes, by using an organic substrate to mimic the one-electron oxidation role of the pyruvate ferredoxin oxidoreductase (PFOR) in living systems, has been developed. The reaction goes through a radical anion intermediate generated under a catalytic redox process. For the first time, the presence of radical anion intermediate in NHC organocatalysis is observed and clearly verified. PMID:25343564

  20. Supported ruthenium-carbene catalyst on ionic magnetic nanoparticles for olefin metathesis.

    PubMed

    Chen, Shu-Wei; Zhang, Zhi-Cheng; Ma, Miaofeng; Zhong, Chong-Min; Lee, Sang-gi

    2014-10-01

    The Grubbs-Hoveyda ruthenium-carbene complex has been covalently immobilized on ionic magnetic nanoparticles utilizing an imidazolium salt linker. The supported catalyst exhibited excellent catalytic activity for ring-closing metathesis (RCM) and cross-metathesis (CM) in the presence of less than 1 mol % of ruthenium. The catalysts can easily be recovered magnetically and reused up to seven times with minimal leaching of ruthenium species. PMID:25215600

  1. Towards New Generations of Metathesis Metal-Carbene Pre-catalysts

    NASA Astrophysics Data System (ADS)

    Allaert, Bart; Dieltiens, Nicolai; Stevens, Chris; Drozdzak, Renata; Dragutan, Ileana; Dragutan, Valerian; Verpoort, Francis

    : A short general introduction combined with some historical milestones in the field of olefin metathesis is presented followed by an overview of recent representatives of metal carbene initiators. This paper attempts to relief the many superb contributions and overwhelming work invested in intelligent design and innovative synthesis in this area. Despites of recent advances there is still a great interest in the generation of new, better performing, and more environment friendly metathesis.

  2. Influence of bulky yet flexible N-heterocyclic carbene ligands in gold catalysis

    PubMed Central

    Collado, Alba; Patrick, Scott R; Gasperini, Danila; Meiries, Sebastien

    2015-01-01

    Summary Three new Au(I) complexes of the formula [Au(NHC)(NTf2)] (NHC = N-heterocyclic carbene) bearing bulky and flexible ligands have been synthesised. The ligands studied are IPent, IHept and INon which belong to the ‘ITent’ (‘Tent’ for ‘tentacular’) family of NHC derivatives. The effect of these ligands in gold-promoted transformations has been investigated. PMID:26664600

  3. Supported ruthenium-carbene catalyst on ionic magnetic nanoparticles for olefin metathesis.

    PubMed

    Chen, Shu-Wei; Zhang, Zhi-Cheng; Ma, Miaofeng; Zhong, Chong-Min; Lee, Sang-gi

    2014-10-01

    The Grubbs-Hoveyda ruthenium-carbene complex has been covalently immobilized on ionic magnetic nanoparticles utilizing an imidazolium salt linker. The supported catalyst exhibited excellent catalytic activity for ring-closing metathesis (RCM) and cross-metathesis (CM) in the presence of less than 1 mol % of ruthenium. The catalysts can easily be recovered magnetically and reused up to seven times with minimal leaching of ruthenium species.

  4. Alkyne-azide cycloaddition catalyzed by silver chloride and "abnormal" silver N-heterocyclic carbene complex.

    PubMed

    Ortega-Arizmendi, Aldo I; Aldeco-Pérez, Eugenia; Cuevas-Yañez, Erick

    2013-01-01

    A library of 1,2,3-triazoles was synthesized from diverse alkynes and azides using catalytic amounts of silver chloride instead of copper compounds. In addition, a novel "abnormal" silver N-heterocyclic carbene complex was tested as catalyst in this process. The results suggest that the reaction requires only 0.5% of silver complex, affording 1,2,3-triazoles in good yields. PMID:24307866

  5. Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

    PubMed Central

    Menon, Rajeev S; Biju, Akkattu T

    2016-01-01

    Summary N-Heterocyclic carbenes (NHCs) have emerged as a powerful class of organocatalysts that mediate a variety of organic transformations. The Benzoin reaction constitutes one of the earliest known carbon–carbon bond-forming reactions catalysed by NHCs. The rapid growth of NHC catalysis in general has resulted in the development of a variety of benzoin and benzoin-type reactions. An overview of such NHC-catalysed benzoin reactions is presented. PMID:27340440

  6. A Mesoionic Carbene as Neutral Ligand for Phosphorescent Cationic Ir(III) Complexes.

    PubMed

    Baschieri, Andrea; Monti, Filippo; Matteucci, Elia; Mazzanti, Andrea; Barbieri, Andrea; Armaroli, Nicola; Sambri, Letizia

    2016-08-15

    Two phosphorescent Ir(III) complexes bearing a mesoionic carbene ligand based on 1,2,3-triazolylidene are obtained for the first time. A silver-iridium transmetalation of the in situ-generated mesoionic carbene affords the cationic dichloro complex [Ir(trizpy)2Cl2](+) (3, trizpy = 1-benzyl-3-methyl-4-(pyridin-2-yl)-1H-1,2,3-triazolylidene) that reacts with a bis-tetrazolate (b-trz) dianionic ligand to give [Ir(trizpy)2(b-trz)](+) (5). The new compounds are fully characterized by NMR spectroscopy and mass spectrometry, and the X-ray structure of 3 is determined. The electrochemical behavior is somewhat different compared to most standard cationic iridium complexes. The first oxidation process is shifted to substantially higher potential in both 3 and 5, due to peculiar and different ligand-induced effects in the two cases, which stabilize the highest occupied molecular orbital; reduction processes are centered on the mesoionic carbene ligands. Both compounds exhibit a mostly ligand-centered luminescence band in the blue-green spectral region, substantially stronger in the case of 5 versus 3, both in CH3CN solution and in poly(methyl methacrylate) matrix at room temperature. Optimized geometries, orbital energies, spin densities, and electronic transitions are determined via density functional theory calculations, which support a full rationalization of the electrochemical and photophysical behavior. This work paves the way for the development of Ir-based emitters with neutral mesoionic carbene ligands and anionic ancillary ligands, a new concept in the area of cationic Ir(III) complexes. PMID:27483041

  7. Reversible Carbene Formation in the Ionic Liquid 1-Ethyl-3-Methylimidazolium Acetate by Vaporization and Condensation.

    PubMed

    Kar, Bishnu Prasad; Sander, Wolfram

    2015-12-01

    The role of N-heterocyclic carbenes in the chemistry of ionic liquids based on imidazolium salts has long been discussed. Here, we present experimental evidence that 1-ethyl-3-methylimidazolium-2-ylidene (EMIm) can coexist with its protonated imidazolium cation (EMImH(+) ) at low temperatures. If the vapor of the ionic liquid [EMImH(+) ][AcO(-) ] is trapped in solid argon or nitrogen at 9 K, only acetic acid (AcOH) and the carbene, but no ionic species, are found by IR spectroscopy. This indicates that during the evaporation of [EMImH(+) ][AcO(-) ] proton transfer occurs to form the neutral species. If the vapor of [EMImH(+) ][AcO(-) ] is trapped at 9 K as film in the absence of a host matrix, a solid consisting of EMImH(+) , EMIm, AcO(-) , and AcOH is formed. During warming to room temperature the proton transfer in the solid to form back the IL [EMImH(+) ][AcO(-) ] can be monitored by IR spectroscopy. This clearly demonstrates that evaporation and condensation of the IL [EMImH(+) ][AcO(-) ] results in a double proton transfer, and the carbene EMIm is only metastable even at low temperatures. PMID:26376583

  8. Masked N-Heterocyclic Carbene-Catalyzed Alkylation of Phenols with Organic Carbonates.

    PubMed

    Lui, Matthew Y; Yuen, Alexander K L; Masters, Anthony F; Maschmeyer, Thomas

    2016-09-01

    An easily prepared masked N-heterocyclic carbene, 1,3-dimethylimidazolium-2-carboxylate (DMI-CO2 ), was investigated as a "green" and inexpensive organocatalyst for the alkylation of phenols. The process made use of various low-toxicity and renewable alkylating agents, such as dimethyl- and diethyl carbonate, in a focused microwave reactor. DMI-CO2 was found to be a very active catalyst and excellent yields of a range of aryl alkyl ethers were obtained under relatively benign conditions. The observed difference in the conversion behavior of phenol methylation, in the presence of either the carbene or 1,8-diazabicycloundec-7-ene (DBU) catalyst, was rationalized on the basis of mechanistic investigations. The primary mode of action for the N-heterocyclic carbene is nucleophilic catalysis. Activation of the dialkyl carbonate electrophile results in concomitant evolution of an organo-soluble alkoxide, which deprotonates the phenolic starting material. In contrast, DBU is initially protonated by the phenol and thus consumed. Subsequent regeneration and participation in nucleophilic catalysis only becomes significant after some phenolate alkylation occurs. PMID:27528488

  9. Remote Control by π-Conjugation of the Emissive Properties of Fischer Carbene-BODIPY Dyads.

    PubMed

    Chu, Gong M; Guerrero-Martínez, Andrés; Ramírez de Arellano, Carmen; Fernández, Israel; Sierra, Miguel A

    2016-03-21

    The synthesis, structure, and complete characterization of mono- and bimetallic dyads joining Fischer carbene complexes and BODIPY chromophores are reported. In these organometallic species, the Fischer carbene complex is attached to the BODIPY moiety through a p-aminophenyl group linked at the C8 carbon atom of the BODIPY core. The photophysical properties, namely the corresponding UV/vis absorption and emission spectra of these new metal-carbene complexes, are analyzed and discussed. It is found that whereas the absorption of the considered dyads strongly resembles that of the parent 4-anilinyl-substituted BODIPY, the fluorescence emission is significantly reduced in these species, very likely as a result of a Förster-type energy transfer mechanism. At variance, the replacement of the pentacarbonyl-metal(0) fragment by a carbonyl group leads to high fluorescence emission intensity. In addition, the emissive properties of the BODIPY core in these organometallic dyads can be tuned by remote groups by means of π-conjugation, as supported by density functional theory calculations.

  10. In vitro antimicrobial studies of silver carbene complexes: activity of free and nanoparticle carbene formulations against clinical isolates of pathogenic bacteria

    PubMed Central

    Leid, Jeff G.; Ditto, Andrew J.; Knapp, Amanda; Shah, Parth N.; Wright, Brian D.; Blust, Robyn; Christensen, Lanette; Clemons, C. B.; Wilber, J. P.; Young, Gerald W.; Kang, Ae Gyeong; Panzner, Matthew J.; Cannon, Carolyn L.; Yun, Yang H.; Youngs, Wiley J.; Seckinger, Nicole M.; Cope, Emily K.

    2012-01-01

    Objectives Silver carbenes may represent novel, broad-spectrum antimicrobial agents that have low toxicity while providing varying chemistry for targeted applications. Here, the bactericidal activity of four silver carbene complexes (SCCs) with different formulations, including nanoparticles (NPs) and micelles, was tested against a panel of clinical strains of bacteria and fungi that are the causative agents of many skin and soft tissue, respiratory, wound, blood, and nosocomial infections. Methods MIC, MBC and multidose experiments were conducted against a broad range of bacteria and fungi. Time-release and cytotoxicity studies of the compounds were also carried out. Free SCCs and SCC NPs were tested against a panel of medically important pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistant Acinetobacter baumannii (MRAB), Pseudomonas aeruginosa, Burkholderia cepacia and Klebsiella pneumoniae. Results All four SCCs demonstrated strong efficacy in concentration ranges of 0.5–90 mg/L. Clinical bacterial isolates with high inherent resistance to purified compounds were more effectively treated either with an NP formulation of these compounds or by repeated dosing. Overall, the compounds were active against highly resistant bacterial strains, such as MRSA and MRAB, and were active against the biodefence pathogens Bacillus anthracis and Yersinia pestis. All of the medically important bacterial strains tested play a role in many different infectious diseases. Conclusions The four SCCs described here, including their development as NP therapies, show great promise for treating a wide variety of bacterial and fungal pathogens that are not easily killed by routine antimicrobial agents. PMID:21972270

  11. Fascinating frontiers of N/O-functionalized N-heterocyclic carbene chemistry: from chemical catalysis to biomedical applications.

    PubMed

    John, Alex; Ghosh, Prasenjit

    2010-08-21

    The in vogue N-heterocyclic carbenes (NHCs) have attracted attention largely for its new found popularity in chemical catalysis and also for displaying promising traits in biomedical applications. The current perspective provides an account of our efforts in exploring the utility of N/O-functionalized N-heterocyclic carbenes in these two areas. On the catalysis front, we have employed the N/O-functionalized N-heterocyclic carbene based precatalysts for the C-C and C-N bond forming reactions like the Suzuki-Miyaura, Sonogashira and Hiyama cross-couplings, the base-free Michael addition, the alkene and alkyne hydroamination reactions and the ring-opening polymerization (ROP) of L-lactides that produce biodegradable polylactide polymers while on the biomedical application front, the anticancer and antimicrobial properties of these N/O-functionalized N-heterocyclic carbene complexes were evaluated. Towards this objective, the N-heterocyclic carbene chemistry of a variety of transition metals like Ag, Au, Ni and Pd has been investigated. PMID:20495733

  12. Fascinating frontiers of N/O-functionalized N-heterocyclic carbene chemistry: from chemical catalysis to biomedical applications.

    PubMed

    John, Alex; Ghosh, Prasenjit

    2010-08-21

    The in vogue N-heterocyclic carbenes (NHCs) have attracted attention largely for its new found popularity in chemical catalysis and also for displaying promising traits in biomedical applications. The current perspective provides an account of our efforts in exploring the utility of N/O-functionalized N-heterocyclic carbenes in these two areas. On the catalysis front, we have employed the N/O-functionalized N-heterocyclic carbene based precatalysts for the C-C and C-N bond forming reactions like the Suzuki-Miyaura, Sonogashira and Hiyama cross-couplings, the base-free Michael addition, the alkene and alkyne hydroamination reactions and the ring-opening polymerization (ROP) of L-lactides that produce biodegradable polylactide polymers while on the biomedical application front, the anticancer and antimicrobial properties of these N/O-functionalized N-heterocyclic carbene complexes were evaluated. Towards this objective, the N-heterocyclic carbene chemistry of a variety of transition metals like Ag, Au, Ni and Pd has been investigated.

  13. A non-diazo approach to α-oxo gold carbenes via gold-catalyzed alkyne oxidation.

    PubMed

    Zhang, Liming

    2014-03-18

    For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, α-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C-H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds are the principle and most reliable strategy to access them. Unfortunately, the substrates contain a highly energetic diazo moiety and are potentially explosive. Moreover, chemists need to use energetic reagents to prepare them, putting further constrains on operational safety. In this Account, we show that the unique access to the gold carbene species in homogeneous gold catalysis offers an opportunity to generate α-oxo gold carbenes if both nucleophile and electrophile are oxygen. Hence, this approach would enable readily available and safer alkynes to replace hazardous α-diazo carbonyl compounds as precursors in the realm of gold carbene chemistry. For the past several years, we have demonstrated that alkynes can indeed effectively serve as precursors to versatile α-oxo gold carbenes. In our initial study, we showed that a tethered sulfoxide can be a suitable oxidant, which in some cases leads to the formation of α-oxo gold carbene intermediates. The

  14. A Non-Diazo Approach to α-Oxo Gold Carbenes via Gold-Catalyzed Alkyne Oxidation

    PubMed Central

    2015-01-01

    For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, α-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C–H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds are the principle and most reliable strategy to access them. Unfortunately, the substrates contain a highly energetic diazo moiety and are potentially explosive. Moreover, chemists need to use energetic reagents to prepare them, putting further constrains on operational safety. In this Account, we show that the unique access to the gold carbene species in homogeneous gold catalysis offers an opportunity to generate α-oxo gold carbenes if both nucleophile and electrophile are oxygen. Hence, this approach would enable readily available and safer alkynes to replace hazardous α-diazo carbonyl compounds as precursors in the realm of gold carbene chemistry. For the past several years, we have demonstrated that alkynes can indeed effectively serve as precursors to versatile α-oxo gold carbenes. In our initial study, we showed that a tethered sulfoxide can be a suitable oxidant, which in some cases leads to the formation of α-oxo gold carbene intermediates. The

  15. Cationic bis-N-heterocyclic carbene (NHC) ruthenium complex: structure and application as latent catalyst in olefin metathesis.

    PubMed

    Rouen, Mathieu; Queval, Pierre; Falivene, Laura; Allard, Jessica; Toupet, Loïc; Crévisy, Christophe; Caijo, Frédéric; Baslé, Olivier; Cavallo, Luigi; Mauduit, Marc

    2014-10-13

    An unexpected cationic bis-N-heterocyclic carbene (NHC) benzylidene ether based ruthenium complex (2 a) was prepared through the double incorporation of an unsymmetrical unsaturated N-heterocyclic carbene (U2 -NHC) ligand that bore an N-substituted cyclododecyl side chain. The isolation and full characterization (including X-ray diffraction studies) of key synthetic intermediates along with theoretical calculations allowed us to understand the mechanism of the overall cationization process. Finally, the newly developed complex 2 a displayed interesting latent behavior during ring-closing metathesis, which could be "switched on" under acidic conditions. PMID:25212827

  16. Spin transitions in bis(amidinato)-N-heterocyclic carbene iron(II) and iron(III) complexes.

    PubMed

    Drake, Jessica L; Kaplan, Hilan Z; Wilding, Matthew J T; Li, Bo; Byers, Jeffery A

    2015-10-14

    In contrast to high spin pyridyl diimine iron(ii) dichloride complexes, analogous bis(amidinato)-N-heterocyclic carbene iron(ii) and iron(iii) complexes demonstrate complex magnetic behaviour. In the solid state, they are best described as intermediate spin complexes at low temperatures that demonstrate gradual spin transitions beginning near or below room temperature. Treating the bis(amidinato)-N-heterocyclic carbene iron(ii) complex with an aryl azide revealed enhanced reactivity compared to analogous complexes supported by pyridyl diimine ligands.

  17. Cationic bis-N-heterocyclic carbene (NHC) ruthenium complex: structure and application as latent catalyst in olefin metathesis.

    PubMed

    Rouen, Mathieu; Queval, Pierre; Falivene, Laura; Allard, Jessica; Toupet, Loïc; Crévisy, Christophe; Caijo, Frédéric; Baslé, Olivier; Cavallo, Luigi; Mauduit, Marc

    2014-10-13

    An unexpected cationic bis-N-heterocyclic carbene (NHC) benzylidene ether based ruthenium complex (2 a) was prepared through the double incorporation of an unsymmetrical unsaturated N-heterocyclic carbene (U2 -NHC) ligand that bore an N-substituted cyclododecyl side chain. The isolation and full characterization (including X-ray diffraction studies) of key synthetic intermediates along with theoretical calculations allowed us to understand the mechanism of the overall cationization process. Finally, the newly developed complex 2 a displayed interesting latent behavior during ring-closing metathesis, which could be "switched on" under acidic conditions.

  18. N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis

    PubMed Central

    De Vreese, Rob

    2012-01-01

    Summary The interplay between metals and N-heterocyclic carbenes (NHCs) has provided a window of opportunities for the development of novel catalytic strategies within the past few years. The recent successful combination of Brønsted acids with NHCs has added a new dimension to the field of cooperative catalysis, enabling the stereoselective synthesis of functionalized pyrrolidin-2-ones as valuable scaffolds in heterocyclic chemistry. This Commentary will briefly highlight the concept of N-heterocyclic carbene/Brønsted acid cooperative catalysis as a new and powerful methodology in organic chemistry. PMID:22509208

  19. Pyridine versus acetonitrile coordination in rhodium-N-heterocyclic carbene square-planar complexes.

    PubMed

    Palacios, Laura; Di Giuseppe, Andrea; Castarlenas, Ricardo; Lahoz, Fernando J; Pérez-Torrente, Jesús J; Oro, Luis A

    2015-03-28

    Experimental and theoretical studies on the factors that control the coordination chemistry of N-donor ligands in square-planar complexes of the type RhCl(NHC)L(1)L(2) (NHC = N-heterocyclic carbene) are presented. The dinuclear complexes [Rh(μ-Cl)(IPr)(η(2)-olefin)]2 {IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-carbene} have been reacted with different combinations of ligands including pyridine, acetonitrile, 2-pyridylacetonitrile, triphenylphosphine, tricyclohexylphosphine, carbon monoxide or molecular oxygen. In addition, the reactivity of RhCl(IPr)(PPh3)2 has also been studied. Pyridine preferentially coordinates trans to the carbene ligand whereas π-acceptor ligands (olefin, CO or PPh3) are prone to bind cis to IPr and trans to chlorido, unless steric bulk hinders the coordination of the ligand (PCy3). In contrast, acetonitrile is more labile than pyridine but is able to form complexes coordinated cis-to-IPr. Molecular dioxygen also displaces the labile cyclooctene ligand in RhCl(IPr)(η(2)-coe)(py) to give a square-planar dioxygen adduct which can be transformed into a peroxo derivative by additional coordination of pyridine. Charge decomposition analysis (CDA) shows that σ-donation values are similar for coordination at cis- or trans-IPr positions, whereas efficient π-backbonding is significantly observed at cis position being the favoured coordination site for π-acceptor ligands. The Rh-IPr rotational barrier in a series of square-planar complexes has been analysed. It has been found that the main contribution is the steric hindrance of the ancillary ligand. The presence of a π-donor ligand such as chlorido slows down the dynamic process.

  20. Carboxylation of terminal alkynes with CO2 using novel silver N-heterocyclic carbene complexes.

    PubMed

    Li, Shanshan; Sun, Jing; Zhang, Zhizhi; Xie, Ruixia; Fang, Xiangchen; Zhou, Mingdong

    2016-06-28

    Four novel N-heterocyclic carbene (NHC) silver complexes, , have been synthesized and characterized. The single X-ray crystal diffraction data indicate a dinuclear solid-state structure for and and a mononuclear structure for and . These complexes have been successfully used as efficient catalysts for the C-H activating carboxylation of terminal alkynes with CO2. A wide range of substrates with various functional groups afforded the corresponding aryl or alkyl substituted propiolic acids in good yields under mild conditions. Moreover, the role of bases and the reaction mechanism is thoroughly discussed. PMID:27263977

  1. Synthesis of cyclic carbonates from diols and CO2 catalyzed by carbenes.

    PubMed

    Bobbink, Felix D; Gruszka, Weronika; Hulla, Martin; Das, Shoubhik; Dyson, Paul J

    2016-09-14

    The synthesis of cyclic carbonates from epoxides and CO2 is a well-established reaction, whereas the synthesis of cyclic carbonates from diols and CO2 is considerably more challenging, and few efficient catalysts are available. Here, we describe heterocyclic carbene catalysts, including one derived from a cheap and efficient thiazolium salt, for this latter reaction. The reaction proceeds at atmospheric pressure in the presence of an alkyl halide and Cs2CO3. Reaction mechanisms for the transformations involved are also proposed. PMID:27514459

  2. Methylpalladium complexes with pyrimidine-functionalized N-heterocyclic carbene ligands

    PubMed Central

    Meyer, Dirk

    2016-01-01

    Summary A series of methylpalladium(II) complexes with pyrimidine-NHC ligands carrying different aryl- and alkyl substituents R ([((pym)^(NHC-R))PdII(CH3)X] with X = Cl, CF3COO, CH3) has been prepared by transmetalation reactions from the corresponding silver complexes and chloro(methyl)(cyclooctadiene)palladium(II). The dimethyl(1-(2-pyrimidyl)-3-(2,6-diisopropylphenyl)imidazolin-2-ylidene)palladium(II) complex was synthesized via the free carbene route. All complexes were fully characterized by standard methods and in three cases also by a solid state structure. PMID:27559406

  3. Palladium-Catalyzed Intramolecular Carbene Insertion into C(sp(3) )-H Bonds.

    PubMed

    Solé, Daniel; Mariani, Francesco; Bennasar, M-Lluïsa; Fernández, Israel

    2016-05-23

    A palladium-catalyzed carbene insertion into C(sp(3) )-H bonds leading to pyrrolidines was developed. The coupling reaction can be catalyzed by both Pd(0) and Pd(II) , is regioselective, and shows a broad functional group tolerance. This reaction is the first example of palladium-catalyzed C(sp(3) )-C(sp(3) ) bond assembly starting from diazocarbonyl compounds. DFT calculations revealed that this direct C(sp(3) )-H bond functionalization reaction involves an unprecedented concerted metalation-deprotonation step.

  4. A Ruthenium Catalyst for Olefin Metathesis Featuring an Anti-Bredt N-Heterocyclic Carbene Ligand

    PubMed Central

    Martin, David; Marx, Vanessa M.

    2016-01-01

    A ruthenium complex bearing an “anti-Bredt” N-heterocyclic carbene was synthesized, characterized and evaluated as a catalyst for olefin metathesis. Good conversions were observed at room temperature for the formation of di- and tri-substituted olefins by ring-closing metathesis. It also allowed for the ring-opening metathesis polymerization of cyclooctadiene, as well as for the cross-metathesis of cis-1,4-diacetoxy-2-butene with allyl-benzene, with enhanced Z/E kinetic selectivity over classical NHC-based catalysts. PMID:27594819

  5. Electronic spectra of linear HC5H and cumulene carbene H2C5.

    PubMed

    Steglich, Mathias; Fulara, Jan; Maity, Surajit; Nagy, Adam; Maier, John P

    2015-06-28

    The 1(3)Σu (-)←X(3)Σg (-) transition of linear HC5H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC2n+1H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the 1(1)A1←X˜(1)A1 transition of the cumulene carbene pentatetraenylidene H2C5 (B). PMID:26133432

  6. Enantioselective conjugate addition of alkylboranes catalyzed by a copper-N-heterocyclic carbene complex.

    PubMed

    Yoshida, Mika; Ohmiya, Hirohisa; Sawamura, Masaya

    2012-07-25

    The first catalytic enantioselective conjugate addition of alkylboron compounds has been achieved. Reactions between alkylboranes and imidazol-2-yl α,β-unsaturated ketones proceeded with high enantioselectivity under the influence of a Cu(I) catalyst system, prepared in situ from CuCl, a new chiral imidazolium salt as a precursor for the N-heterocyclic carbene ligand, and PhOK. Alkylboranes are widely obtained via alkene hydroboration. A variety of functional groups are tolerated in alkylboranes and α,β-unsaturated ketones. PMID:22746339

  7. Enantioselective C-H carbene insertions with homogeneous and immobilized copper complexes.

    PubMed

    Fraile, José M; López-Ram-de-Viu, Pilar; Mayoral, José A; Roldán, Marta; Santafé-Valero, Jorge

    2011-09-01

    The efficiency of chiral bis(oxazoline)- and azabis(oxazoline)-copper complexes in the enantioselective carbene insertion into C-H bonds of cyclic ethers in homogeneous phase strongly depends on the structure of the substrate. The immobilization on laponite clay by electrostatic interactions not only allows the recovery and reuse of the heterogeneous catalysts, but in some cases also improves enantioselectivity and overall chemoselectivity, making possible reactions that do not take place or lead to low yields in solution, even with the commonly used Rh(2)[S-DOSP](4) catalyst. PMID:21750830

  8. Aminomethylation of enals through carbene and acid cooperative catalysis: concise access to β(2)-amino acids.

    PubMed

    Xu, Jianfeng; Chen, Xingkuan; Wang, Ming; Zheng, Pengcheng; Song, Bao-An; Chi, Yonggui Robin

    2015-04-20

    A convergent, organocatalytic asymmetric aminomethylation of α,β-unsaturated aldehydes by N-heterocyclic carbene (NHC) and (in situ generated) Brønsted acid cooperative catalysis is disclosed. The catalytically generated conjugated acid from the base plays dual roles in promoting the formation of azolium enolate intermediate, formaldehyde-derived iminium ion (as an electrophilic reactant), and methanol (as a nucleophilic reactant). This redox-neutral strategy is suitable for the scalable synthesis of enantiomerically enriched β(2) -amino acids bearing various substituents.

  9. Thermally Stable, Latent Olefin Metathesis Catalysts

    PubMed Central

    Thomas, Renee M.; Fedorov, Alexey; Keitz, Benjamin K.

    2011-01-01

    Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C, and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 hours. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C, and exhibited a long catalyst lifetime in solution at elevated temperatures. PMID:22282652

  10. Atmospheric Hydrogenation of Esters Catalyzed by PNP-Ruthenium Complexes with an N-Heterocyclic Carbene Ligand.

    PubMed

    Ogata, Osamu; Nakayama, Yuji; Nara, Hideki; Fujiwhara, Mitsuhiko; Kayaki, Yoshihito

    2016-08-01

    New pincer ruthenium complexes bearing a monodentate N-heterocyclic carbene ligand were synthesized and demonstrated as powerful hydrogenation catalysts. With an atmospheric pressure of hydrogen gas, aromatic, heteroaromatic, and aliphatic esters as well as lactones were converted into the corresponding alcohols at 50 °C. This reaction protocol offers reliable access to alcohols using an easy operational setup.

  11. Auranofin and N-heterocyclic carbene gold-analogs are potent inhibitors of the bacteria Helicobacter pylori.

    PubMed

    Owings, Joshua P; McNair, Nina N; Mui, Yiu Fung; Gustafsson, Tomas N; Holmgren, Arne; Contel, Maria; Goldberg, Joanna B; Mead, Jan R

    2016-07-01

    Auranofin is an FDA-approved gold-containing compound used for the treatment of rheumatoid arthritis. Recent reports of antimicrobial activity against protozoa and bacteria indicate that auranofin targets the reductive enzyme thioredoxin reductase (TrxR). We evaluated auranofin as well as five auranofin analogs containing N-heterocyclic carbenes (instead of the triethylphosphane present in auranofin) and five gold-carbene controls for their ability to inhibit or kill Helicobacter pylori in vitro Auranofin completely inhibited bacterial growth at 1.2 μM. Purified H. pylori TrxR was inhibited by auranofin in a cell-free assay (IC50 ∼88 nM). The most active gold(I)-N-heterocyclic carbene compounds exhibited MICs comparable to auranofin against H. pylori (2 μM), while also exhibiting lower toxicities for human embryonic kidney cells (HEK-293T cells). Median toxic concentrations (TC50) were 13-20-fold higher compared to auranofin indicating that they were less cytotoxic. The N-heterocyclic carbene analogs maybe well tolerated, but further evaluation is needed in vivo Finally, auranofin was synergistic with the antibiotic amoxicillin, suggesting that targeting both the reductive enzyme TrxR and cell wall synthesis may be effective against H. pylori infections. PMID:27279627

  12. Optimized Syntheses of Cyclopentadienyl Nickel Chloride Compounds Containing "N"-Heterocyclic Carbene Ligands for Short Laboratory Periods

    ERIC Educational Resources Information Center

    Cooke, Jason; Lightbody, Owen C.

    2011-01-01

    Experiments are described for the preparation of imidazolium chloride precursors to "N"-heterocyclic carbenes and their cyclopentadienyl nickel chloride derivatives. The syntheses have been optimized for second- and third-year undergraduate laboratories that have a maximum programmed length of three hours per week. The experiments are flexible and…

  13. Pd-N-Heterocyclic Carbene (NHC) Organic Silica: Synthesis and Application in Carbon-Carbon Coupling Reactions

    EPA Science Inventory

    The first Pd-N-heterocyclic carbene (NHC) complex in the form of organic silica was prepared using sol-gel method and its application in Heck and Suzuki reaction were demonstrated. These C-C coupling reactions proceeded efficiently under the influence of microwave irradiation, wi...

  14. Atmospheric Hydrogenation of Esters Catalyzed by PNP-Ruthenium Complexes with an N-Heterocyclic Carbene Ligand.

    PubMed

    Ogata, Osamu; Nakayama, Yuji; Nara, Hideki; Fujiwhara, Mitsuhiko; Kayaki, Yoshihito

    2016-08-01

    New pincer ruthenium complexes bearing a monodentate N-heterocyclic carbene ligand were synthesized and demonstrated as powerful hydrogenation catalysts. With an atmospheric pressure of hydrogen gas, aromatic, heteroaromatic, and aliphatic esters as well as lactones were converted into the corresponding alcohols at 50 °C. This reaction protocol offers reliable access to alcohols using an easy operational setup. PMID:27439106

  15. Selective Kumada biaryl cross-coupling reaction enabled by an iron(III) alkoxide-N-heterocyclic carbene catalyst system.

    PubMed

    Chua, Yi-Yuan; Duong, Hung A

    2014-08-01

    A catalyst system comprising Fe2(O(t)Bu)6 and an N-heterocyclic carbene ligand enables efficient syntheses of (hetero)biaryls from the reactions of aryl Grignard reagents with a diverse spectrum of (hetero)aryl chlorides. Amongst the alkoxide and amide counterions investigated, tert-butoxide was the most effective in inhibiting the homocoupling of arylmagnesiums. PMID:24947849

  16. The first examples of a meta-benzannulation from the reaction of Fischer carbene complexes with alkynes.

    PubMed

    Wang, Huan; Huang, Jie; Wulff, William D; Rheingold, Arnold L

    2003-07-30

    The intramolecular benzannulations of carbene complexes with alkynes are examined where the alkyne is tethered to the alpha-carbon of the vinyl carbene complex. These reactions are sensitive to the length of the tether and to the nature of the solvent. With a tether length of 16 methylenes, the reaction occurs in the same fashion as the intermolecular reactions to give a p-cyclophane. With intermediate tether lengths (n = 10, 13), the reaction gives an additional p-cyclophane in which the two oxygen substituents are meta on the arene ring. This type of product is unprecedented from the reaction of carbene complexes and alkynes and is quite surprising because the formation of this product requires that the carbon-carbon bond between the alpha- and beta-carbons of the vinyl carbene complex is broken. A mechanism is proposed to account for this process which involves the crossed intramolecular [2 + 2] cycloaddition of the alkene and a ketene in a conjugated dienyl ketene to give a benzvalenone paddalane intermediate.

  17. Reactivity studies of pincer bis-protic N-heterocyclic carbene complexes of platinum and palladium under basic conditions

    PubMed Central

    Marelius, David C; Moore, Curtis E; Rheingold, Arnold L

    2016-01-01

    Summary Bis-protic N-heterocyclic carbene complexes of platinum and palladium (4) yield dimeric structures 6 when treated with sodium tert-butoxide in CH2Cl2. The use of a more polar solvent (THF) and a strong base (LiN(iPr)2) gave the lithium chloride adducts monobasic complex 7 or analogous dibasic complex 8. PMID:27559382

  18. Reactivity studies of pincer bis-protic N-heterocyclic carbene complexes of platinum and palladium under basic conditions.

    PubMed

    Marelius, David C; Moore, Curtis E; Rheingold, Arnold L; Grotjahn, Douglas B

    2016-01-01

    Bis-protic N-heterocyclic carbene complexes of platinum and palladium (4) yield dimeric structures 6 when treated with sodium tert-butoxide in CH2Cl2. The use of a more polar solvent (THF) and a strong base (LiN(iPr)2) gave the lithium chloride adducts monobasic complex 7 or analogous dibasic complex 8. PMID:27559382

  19. Tandem olefin metathesis/hydrogenation at ambient temperature: activation of ruthenium carbene complexes by addition of hydrides.

    PubMed

    Schmidt, Bernd; Pohler, Michael

    2003-07-21

    Sodium hydride activates ruthenium carbene complexes to catalyze hydrogenation reactions subsequent to ring closing olefin metathesis. Under these conditions, hydrogenation of cyclopentenols proceeds smoothly at ambient temperature and under 1 atm of hydrogen in toluene. An alternative protocol was developed that involves the formation of hydrogen in situ by reaction of excess sodium hydride with protic functional groups and water. PMID:12956069

  20. Auranofin and N-heterocyclic carbene gold-analogs are potent inhibitors of the bacteria Helicobacter pylori.

    PubMed

    Owings, Joshua P; McNair, Nina N; Mui, Yiu Fung; Gustafsson, Tomas N; Holmgren, Arne; Contel, Maria; Goldberg, Joanna B; Mead, Jan R

    2016-07-01

    Auranofin is an FDA-approved gold-containing compound used for the treatment of rheumatoid arthritis. Recent reports of antimicrobial activity against protozoa and bacteria indicate that auranofin targets the reductive enzyme thioredoxin reductase (TrxR). We evaluated auranofin as well as five auranofin analogs containing N-heterocyclic carbenes (instead of the triethylphosphane present in auranofin) and five gold-carbene controls for their ability to inhibit or kill Helicobacter pylori in vitro Auranofin completely inhibited bacterial growth at 1.2 μM. Purified H. pylori TrxR was inhibited by auranofin in a cell-free assay (IC50 ∼88 nM). The most active gold(I)-N-heterocyclic carbene compounds exhibited MICs comparable to auranofin against H. pylori (2 μM), while also exhibiting lower toxicities for human embryonic kidney cells (HEK-293T cells). Median toxic concentrations (TC50) were 13-20-fold higher compared to auranofin indicating that they were less cytotoxic. The N-heterocyclic carbene analogs maybe well tolerated, but further evaluation is needed in vivo Finally, auranofin was synergistic with the antibiotic amoxicillin, suggesting that targeting both the reductive enzyme TrxR and cell wall synthesis may be effective against H. pylori infections.

  1. On the mechanism of imine elimination from Fischer tungsten carbene complexes

    PubMed Central

    Veit, Philipp

    2016-01-01

    Summary (Aminoferrocenyl)(ferrocenyl)carbene(pentacarbonyl)tungsten(0) (CO)5W=C(NHFc)Fc (W(CO) 5 ( E -2)) is synthesized by nucleophilic substitution of the ethoxy group of (CO)5W=C(OEt)Fc (M(CO) 5 (1 Et )) by ferrocenyl amide Fc-NH– (Fc = ferrocenyl). W(CO) 5 ( E -2) thermally and photochemically eliminates bulky E-1,2-diferrocenylimine (E -3) via a formal 1,2-H shift from the N to the carbene C atom. Kinetic and mechanistic studies to the formation of imine E -3 are performed by NMR, IR and UV–vis spectroscopy and liquid injection field desorption ionization (LIFDI) mass spectrometry as well as by trapping experiments for low-coordinate tungsten complexes with triphenylphosphane. W(CO) 5 ( E -2) decays thermally in a first-order rate-law with a Gibbs free energy of activation of ΔG ‡ 298K = 112 kJ mol−1. Three proposed mechanistic pathways are taken into account and supported by detailed (time-dependent) densitiy functional theory [(TD)-DFT] calculations. The preferred pathway is initiated by an irreversible CO dissociation, followed by an oxidative addition/pseudorotation/reductive elimination pathway with short-lived, elusive seven-coordinate hydrido tungsten(II) intermediates cis (N,H)-W(CO) 4 (H)( Z -15) and cis (C,H)-W(CO) 4 (H)( Z -15). PMID:27559381

  2. N-Heterocyclic Carbene-Phosphinidene Complexes of the Coinage Metals.

    PubMed

    Doddi, Adinarayana; Bockfeld, Dirk; Nasr, Alexandre; Bannenberg, Thomas; Jones, Peter G; Tamm, Matthias

    2015-11-01

    Coinage metal complexes of the N-heterocyclic carbene-phosphinidene adduct IPr⋅PPh (IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were prepared by its reaction with CuCl, AgCl, and [(Me2 S)AuCl], which afforded the monometallic complexes [(IPr⋅PPh)MCl] (M=Cu, Ag, Au). The reaction with two equivalents of the metal halides gave bimetallic [(IPr⋅PPh)(MCl)2 ] (M=Cu, Au); the corresponding disilver complex could not be isolated. [(IPr⋅PPh)(CuOTf)2 ] was prepared by reaction with copper(I) trifluoromethanesulfonate. Treatment of [(IPr⋅PPh)(MCl)2 ] (M=Cu, Au) with Na(BAr(F) ) or AgSbF6 afforded the tetranuclear complexes [(IPr⋅PPh)2 M4 Cl2 ]X2 (X=BAr(F) or SbF6 ), which contain unusual eight-membered M4 Cl2 P2 rings with short cuprophilic or aurophilic contacts along the chlorine-bridged M⋅⋅⋅M axes. Complete chloride abstraction from [(IPr⋅PPh)(AuCl)2 ] was achieved with two equivalents of AgSbF6 in the presence of tetrahydrothiophene (THT) to form [(IPr⋅PPh){Au(THT)}2 ][SbF6 ]2 . The cationic tetra- and dinuclear complexes were used as catalysts for enyne cyclization and carbene transfer reactions. PMID:26365325

  3. Surface Characterization and in situ Protein Adsorption Studies on Carbene-Modified Polymers.

    PubMed

    Nelson, Geoffrey W; Parker, Emily M; Singh, Kulveer; Blanford, Christopher F; Moloney, Mark G; Foord, John S

    2015-10-13

    Polystyrene thin films were functionalized using a facile two-step chemical protocol involving carbene insertion followed by azo-coupling, permitting the introduction of a range of chemical functional groups, including aniline, hexyl, amine, carboxyl, phenyl, phosphonate diester, and ethylene glycol. X-ray photoelectron spectroscopy (XPS) confirmed the success of the two-step chemical modification with a grafting density of at least 1/10th of the typical loading density (10(14)-10(15)) of a self-assembled monolayer (SAM). In situ, real-time quartz crystal microbalance with dissipation (QCM-D) studies show that the dynamics of binding of bovine serum albumin (BSA) are different at each modified surface. Mass, viscoelastic, and kinetic data were analyzed, and compared to cheminformatic descriptors (i.e., c log P, polar surface area) typically used for drug discovery. Results show that functionalities may either resist or adsorb BSA, and uniquely influence its adsorption dynamics. It is concluded that carbene-based surface modification can usefully influence BSA binding dynamics in a manner consistent with, and more robust than, traditional systems based on SAM chemistry. PMID:26391812

  4. On the mechanism of imine elimination from Fischer tungsten carbene complexes.

    PubMed

    Veit, Philipp; Förster, Christoph; Heinze, Katja

    2016-01-01

    (Aminoferrocenyl)(ferrocenyl)carbene(pentacarbonyl)tungsten(0) (CO)5W=C(NHFc)Fc (W(CO) 5 ( E -2)) is synthesized by nucleophilic substitution of the ethoxy group of (CO)5W=C(OEt)Fc (M(CO) 5 (1 (Et) )) by ferrocenyl amide Fc-NH(-) (Fc = ferrocenyl). W(CO) 5 ( E -2) thermally and photochemically eliminates bulky E-1,2-diferrocenylimine ( E -3) via a formal 1,2-H shift from the N to the carbene C atom. Kinetic and mechanistic studies to the formation of imine E -3 are performed by NMR, IR and UV-vis spectroscopy and liquid injection field desorption ionization (LIFDI) mass spectrometry as well as by trapping experiments for low-coordinate tungsten complexes with triphenylphosphane. W(CO) 5 ( E -2) decays thermally in a first-order rate-law with a Gibbs free energy of activation of ΔG (‡) 298K = 112 kJ mol(-1). Three proposed mechanistic pathways are taken into account and supported by detailed (time-dependent) densitiy functional theory [(TD)-DFT] calculations. The preferred pathway is initiated by an irreversible CO dissociation, followed by an oxidative addition/pseudorotation/reductive elimination pathway with short-lived, elusive seven-coordinate hydrido tungsten(II) intermediates cis (N,H)-W(CO) 4 (H)( Z -15) and cis (C,H)-W(CO) 4 (H)( Z -15).

  5. Stretch Out or Fold Back? Conformations of Dinuclear Gold(I) N-Heterocyclic Carbene Macrocycles.

    PubMed

    Kobialka, Stefanie; Müller-Tautges, Christina; Schmidt, Melanie T S; Schnakenburg, Gregor; Hollóczki, Oldamur; Kirchner, Barbara; Engeser, Marianne

    2015-07-01

    We report the synthesis and characterization of 12 new dinuclear gold(I) N-heterocyclic carbene (NHC) complexes and the corresponding imidazolium precursors. The focus lies in a systematic study of conformational changes and intra- and intermolecular gold-gold and π-π interactions of dinuclear gold(I) carbene complexes. Common to all members of the series of gold macrocycles are NHC ligands on the basis of imidazole with ethyl side chains and bromide as well as hexafluorophosphate counterions, respectively. The compounds vary in the length of a flexible alkyl linker between the NHC units. For the methylene and ethylene bridged macrocycles, a ring inversion movement can be observed by VT-NMR. In total, 11 molecular structures have been characterized by X-ray diffraction. Open ring conformations with intermolecular π-π and Au-Au interactions prevail, but a backfolded conformation with a short intramolecular Au-Au distance has been found for the ethylene-bridged species. The presence of Au-Au interactions could be proven by quantum chemical calculations. PMID:26087332

  6. Catalytic Transfer Hydrogenation with a Methandiide-Based Carbene Complex: An Experimental and Computational Study.

    PubMed

    Weismann, Julia; Gessner, Viktoria H

    2015-11-01

    The transfer hydrogenation (TH) reaction of ketones with catalytic systems based on a methandiide-derived ruthenium carbene complex was investigated and optimised. The complex itself makes use of the noninnocent behaviour of the carbene ligand (M=CR2 →MH-C(H)R2 ), but showed only moderate activity, thus requiring long reaction times to achieve sufficient conversion. DFT studies on the reaction mechanism revealed high reaction barriers for both the dehydrogenation of iPrOH and the hydrogen transfer. A considerable improvement of the catalytic activity could be achieved by employing triphenylphosphine as additive. Mechanistic studies on the role of PPh3 in the catalytic cycle revealed the formation of a cyclometalated complex upon phosphine coordination. This ruthenacycle was revealed to be the active species under the reaction conditions. The use of the isolated complex resulted in high catalytic activities in the TH of aromatic as well as aliphatic ketones. The complex was also found to be active under base-free conditions, suggesting that the cyclometalation is crucial for the enhanced activity. PMID:26403918

  7. Bis-mixed-carbene ruthenium-thiolate-alkylidene complexes: synthesis and olefin metathesis activity.

    PubMed

    Dahcheh, Fatme; Stephan, Douglas W

    2015-01-28

    A series of bis-carbene Ru-hydride species, including (IMes)(Im(OMe)2)(PPh3)RuHCl (1) and (SIMes)(Me2Im(OMe)2)(PPh3)RuHCl (2) were prepared and subsequently shown to react with aryl-vinyl-sulfides to give the bis-carbene-alkylidene complexes: Im(OMe)2(SIMes)RuCl(SR)(=CHCH3) (R = p-FC6H4 (3), p-(NO2)C6H4 (4)), Im(OMe)2(IMes)RuCl(=CHCH3)(SPh) (5), Me2Im(OMe)2(SIMes)RuCl(=CHCH3)(SPh) (6), Im(OMe)2(SIMes)(F5C6S)RuCl(=CHR) (R = C4H9 (9), C5H11 (10)). The activity of these species in the standard Grubbs' tests for ring-opening metathesis polymerization, ring-closing and cross-metathesis are reported. Although these thiolate derivatives are shown to exhibit modest metathesis activities, the reactivity is enhanced in the presence of BCl3. PMID:25462569

  8. First N-Heterocyclic Carbenes Relying on the Triazolone Structural Motif: Syntheses, Modifications and Reactivity.

    PubMed

    Jonek, Markus; Diekmann, Janina; Ganter, Christian

    2015-10-26

    4-Phenylsemicarbazide and 1,5-diphenylcarbazide are suitable starting materials for the syntheses of N-heterocyclic carbene (NHC) compounds with new backbone structures. In the first case, cyclisation and subsequent methylation leads to a cationic precursor whose deprotonation affords the triazolon-ylidene 2, which was converted to the corresponding sulfur and selenium adducts and a range of metal complexes. In contrast, cyclisation of diphenylcarbazide affords a neutral betain-type NHC-precursor 7, which is not in equilibrium with its carbene tautomer 7a. Precursor 7 can either be deprotonated to give the anionic NHC 8 or methylated at the N or O atom of the backbone resulting in two isomeric cationic species 16 and 20. Deprotonation of the latter two provides neutral NHC compounds with a carboxamide or carboximidate backbone, respectively. The ligand properties of the new NHC compounds were evaluated by IR and (77) Se NMR spectroscopy. Tolman electronic parameter (TEP) values range from 2050 to 2063 cm(-1) with the anionic NHC 8 being the best overall donor. PMID:26395132

  9. Bis-mixed-carbene ruthenium-thiolate-alkylidene complexes: synthesis and olefin metathesis activity.

    PubMed

    Dahcheh, Fatme; Stephan, Douglas W

    2015-01-28

    A series of bis-carbene Ru-hydride species, including (IMes)(Im(OMe)2)(PPh3)RuHCl (1) and (SIMes)(Me2Im(OMe)2)(PPh3)RuHCl (2) were prepared and subsequently shown to react with aryl-vinyl-sulfides to give the bis-carbene-alkylidene complexes: Im(OMe)2(SIMes)RuCl(SR)(=CHCH3) (R = p-FC6H4 (3), p-(NO2)C6H4 (4)), Im(OMe)2(IMes)RuCl(=CHCH3)(SPh) (5), Me2Im(OMe)2(SIMes)RuCl(=CHCH3)(SPh) (6), Im(OMe)2(SIMes)(F5C6S)RuCl(=CHR) (R = C4H9 (9), C5H11 (10)). The activity of these species in the standard Grubbs' tests for ring-opening metathesis polymerization, ring-closing and cross-metathesis are reported. Although these thiolate derivatives are shown to exhibit modest metathesis activities, the reactivity is enhanced in the presence of BCl3.

  10. Asymmetric intramolecular α-cyclopropanation of aldehydes using a donor/acceptor carbene mimetic

    PubMed Central

    Luo, Chaosheng; Wang, Zhen; Huang, Yong

    2015-01-01

    Enantioselective α-alkylation of carbonyl is considered as one of the most important processes for asymmetric synthesis. Common alkylation agents, that is, alkyl halides, are notorious substrates for both Lewis acids and organocatalysts. Recently, olefins emerged as a benign alkylating species via photo/radical mechanisms. However, examples of enantioselective alkylation of aldehydes/ketones are scarce and direct asymmetric dialkylation remains elusive. Here we report an intramolecular α-cyclopropanation reaction of olefinic aldehydes to form chiral cyclopropane aldehydes. We demonstrate that an α-iodo aldehyde can function as a donor/acceptor carbene equivalent, which engages in a formal [2+1] annulation with a tethered double bond. Privileged bicyclo[3.1.0]hexane-type scaffolds are prepared in good optical purity using a chiral amine. The synthetic utility of the products is demonstrated by versatile transformations of the bridgehead formyl functionality. We expect the concept of using α-iodo iminium as a donor/acceptor carbene surrogate will find wide applications in chemical reaction development. PMID:26644194

  11. On the mechanism of imine elimination from Fischer tungsten carbene complexes.

    PubMed

    Veit, Philipp; Förster, Christoph; Heinze, Katja

    2016-01-01

    (Aminoferrocenyl)(ferrocenyl)carbene(pentacarbonyl)tungsten(0) (CO)5W=C(NHFc)Fc (W(CO) 5 ( E -2)) is synthesized by nucleophilic substitution of the ethoxy group of (CO)5W=C(OEt)Fc (M(CO) 5 (1 (Et) )) by ferrocenyl amide Fc-NH(-) (Fc = ferrocenyl). W(CO) 5 ( E -2) thermally and photochemically eliminates bulky E-1,2-diferrocenylimine ( E -3) via a formal 1,2-H shift from the N to the carbene C atom. Kinetic and mechanistic studies to the formation of imine E -3 are performed by NMR, IR and UV-vis spectroscopy and liquid injection field desorption ionization (LIFDI) mass spectrometry as well as by trapping experiments for low-coordinate tungsten complexes with triphenylphosphane. W(CO) 5 ( E -2) decays thermally in a first-order rate-law with a Gibbs free energy of activation of ΔG (‡) 298K = 112 kJ mol(-1). Three proposed mechanistic pathways are taken into account and supported by detailed (time-dependent) densitiy functional theory [(TD)-DFT] calculations. The preferred pathway is initiated by an irreversible CO dissociation, followed by an oxidative addition/pseudorotation/reductive elimination pathway with short-lived, elusive seven-coordinate hydrido tungsten(II) intermediates cis (N,H)-W(CO) 4 (H)( Z -15) and cis (C,H)-W(CO) 4 (H)( Z -15). PMID:27559381

  12. Cyclometalated Palladium(II) N-Heterocyclic Carbene Complexes: Anticancer Agents for Potent In Vitro Cytotoxicity and In Vivo Tumor Growth Suppression.

    PubMed

    Fong, Tommy Tsz-Him; Lok, Chun-Nam; Chung, Clive Yik-Sham; Fung, Yi-Man Eva; Chow, Pui-Keong; Wan, Pui-Ki; Che, Chi-Ming

    2016-09-19

    Palladium(II) complexes are generally reactive toward substitution/reduction, and their biological applications are seldom explored. A new series of palladium(II) N-heterocyclic carbene (NHC) complexes that are stable in the presence of biological thiols are reported. A representative complex, [Pd(C^N^N)(N,N'-nBu2 NHC)](CF3 SO3 ) (Pd1 d, HC^N^N=6-phenyl-2,2'-bipyridine, N,N'-nBu2 NHC=N,N'-di-n-butylimidazolylidene), displays potent killing activity toward cancer cell lines (IC50 =0.09-0.5 μm) but is less cytotoxic toward a normal human fibroblast cell line (CCD-19Lu, IC50 =11.8 μm). In vivo anticancer studies revealed that Pd1 d significantly inhibited tumor growth in a nude mice model. Proteomics data and in vitro biochemical assays reveal that Pd1 d exerts anticancer effects, including inhibition of an epidermal growth factor receptor pathway, induction of mitochondrial dysfunction, and antiangiogenic activity to endothelial cells.

  13. Chelating bis-N-heterocyclic carbene complexes of iron(ii) containing bipyridyl ligands as catalyst precursors for oxidation of alcohols.

    PubMed

    Pinto, Mara F; Cardoso, Bernardo de P; Barroso, Sónia; Martins, Ana M; Royo, Beatriz

    2016-09-14

    Chelating bis-N-heterocyclic carbene (bis-NHC) complexes of iron(ii) containing pyridyl ligands have been prepared by the reaction of [FeCl2L] [L = bipy (1), phen (2)] with [LiN(SiMe3)2] and a bis(imidazolium) salt. The [Fe(bis-NHC)L(I)2] complexes were active pre-catalysts in the oxidation of 1-phenylethanol with tert-butyl hydroperoxide in neat conditions, affording a quantitative yield of acetophenone in 4.5 h. The catalyst could be reused up to six cycles giving a turnover number (TON) of 1500. Various secondary alcohols, both aromatic and aliphatic were selectivity oxidised to the corresponding ketones in excellent yields. Compound 1 is stable in acetonitrile solution for ca. 4 h, although after 16 h, it evolves to a mixture of [Fe(bis-NHC)(bipy)2]I2 (3), [Fe(bipy)3](2+) and bis-imidazolium salt. The molecular structure of 3 has been determined by X-ray diffraction studies. PMID:27506414

  14. Toward new organometallic architectures: synthesis of carbene-centered rhodium and palladium bisphosphine complexes. stability and reactivity of [PC(BIm)PRh(L)][PF6] pincers.

    PubMed

    Plikhta, Andriy; Pöthig, Alexander; Herdtweck, Eberhardt; Rieger, Bernhard

    2015-10-01

    In this article, we report the synthesis of a tridentate carbene-centered bisphosphine ligand precursor and its complexes. The developed four-step synthetic strategy of a new PC(BIm)P pincer ligand represents the derivatization of benzimidazole in the first and third positions by (diphenylphosphoryl)methylene synthone, followed by phosphine deprotection and subsequent insertion of a noncoordinating anion. The obtained ligand precursor undergoes complexation, with PdCl2 and [μ-OCH3Rh(COD)]2 smoothly forming the target organometallics [PC(BIm)PPdCl][PF6] and [PC(BIm)PRh(L)][PF6] under mild hydrogenation conditions. A more detailed study of the rhodium complexes [PC(BIm)PRh(L)][PF6] reveals significant thermal stability of the PC(BIm)PRh moiety in the solid state as well as in solution. The chemical behavior of 1,3-bis(diphenylphosphinomethylene)benzimidazol-2-ylrhodium acetonitrile hexafluorophosphate has been screened under decarbonylation, hydrogenation, and hydroboration reaction conditions. Thus, the PC(BIm)PRh(I) complex is a sufficiently stable compound, with the potential to be applied in catalysis.

  15. Rhenium(I)-Catalyzed Generation of α,β-Unsaturated Carbene Complex Intermediates from Propargyl Ethers for the Preparation of Cycloheptadiene Derivatives.

    PubMed

    Sogo, Hideyuki; Iwasawa, Nobuharu

    2016-08-16

    The rhenium(I)-catalyzed generation of α,β-unsaturated carbene complex intermediates from easily available propargyl ethers was achieved for the concise construction of cycloheptadiene derivatives through the formal [4+3] cycloaddition reaction with siloxydienes. PMID:27391557

  16. Efficient Room-Temperature, Au(+)-Mediated Coupling of a Carbene Ligand with Methane To Generate C2Hx (x = 4, 6).

    PubMed

    Zhou, Shaodong; Li, Jilai; Wu, Xiao-Nan; Schlangen, Maria; Schwarz, Helmut

    2016-01-01

    The thermal reactions of the closed-shell, "naked" gold-carbene complex [Au(CH2)](+) with methane have been explored by using FTICR mass spectrometry complemented by quantum chemical (QC) calculations at the CCSD(T)//BMK level of theory. Mechanistic aspects for this unprecedentedly efficient carbene insertion in the C-H bond of methane have been addressed and the origin of the counterintuitive high reactivity of [Au(CH2)](+) towards this most inert hydrocarbon is discussed. PMID:26577495

  17. Interaction of β-lactam carbenes with 3,6-diphenyltetrazines: a five-step cascade reaction for the direct construction of indeno[2,1-b]pyrrol-2-ones.

    PubMed

    Xing, Juan; Wang, Xiao-Rong; Yan, Cai-Xia; Cheng, Ying

    2011-06-01

    A study of the nucleophilic addition of β-lactam carbenes to 3,6-diphenyltetrazines is reported. Instead of the formation of pyrazole derivatives like most reactions between nucleophilic or ambiphilic carbenes and 3,6-disubstituted tetrazines, β-lactam carbenes reacted with 3,6-diphenyltetrazines to produce indeno[2,1-b]pyrrol-2-ones in good yields. The reaction proceeds most probably through a five-step cascade process. This work has not only provided a one-pot operation for the efficient construction of mutisubstituted indeno[2,1-b]pyrrol-2-ones but also revealed the nucleophilicity of β-lactam carbenes.

  18. Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

    PubMed Central

    Guan, Zong; Namyslo, Jan C; Drafz, Martin H H; Nieger, Martin

    2014-01-01

    Summary Deprotonation of indazolium salts at low temperatures gives N-heterocyclic carbenes of indazoles (indazol-3-ylidenes) which can be trapped as rhodium complexes (X-ray analysis). In the absence of Rh, the indazol-3-ylidenes spontaneously dimerize under ring cleavage of one of the N,N-bonds and ring closure to an indazole–indole spiro compound which possesses an exocyclic imine group. The E/Z isomers of the imines can be separated by column chromatography when methanol is used as eluent. We present results of a single crystal X-ray analysis of one of the E-isomers, which equilibrate in solution as well as in the solid state. Heating of the indazole–indole spiro compounds results in the formation of quinazolines by a ring-cleavage/ring-closure sequence (X-ray analysis). Results of DFT calculations are presented. PMID:24778738

  19. Cooperative Catalysis by Carbenes and Lewis Acids in a Highly Stereoselective Route to γ-Lactams

    PubMed Central

    Raup, Dustin E. A.; Cardinal-David, Benoit; Holte, Dane; Scheidt, Karl A.

    2010-01-01

    Enzymes are a continuing source of inspiration for the design of new chemical reactions that proceed with efficiency, high selectivity and minimal waste. In many biochemical processes, different catalytic species, such as Lewis acids and bases, are involved in precisely orchestrated interactions to activate reactants simultaneously or sequentially. Employing this type of cooperative catalysis, in which two or more catalytic cycles operate concurrently to achieve one overall transformation, has great potential to enhance known reactivity and drive the development of new chemical reactions with high value. In this disclosure, a cooperative N-heterocyclic carbene/Lewis acid catalytic system promotes the addition of homoenolate equivalents to hydrazones generating highly substituted γ-lactams in moderate to good yields and high levels of diastereo- and enantioselectivity. PMID:20729898

  20. Silver-catalyzed silicon-hydrogen bond functionalization by carbene insertion.

    PubMed

    Iglesias, M José; Nicasio, M Carmen; Caballero, Ana; Pérez, Pedro J

    2013-01-28

    The catalytic functionalization of silicon-hydrogen bonds by means of the insertion of carbene units :CHCO(2)Et from ethyl diazoacetate (EDA) has been achieved using a silver-based catalyst, constituting the first example of this metal to promote this transformation. Competition experiments have revealed that the relative reactivity of substituted silanes depends on the bond dissociation energy of the Si-H bond (tertiary > secondary > primary for ethyl substituted). In the presence of bulky substituents such order reverts to secondary > primary ≈ tertiary (for phenyl substituted). Screening with other diazo compounds has shown that N(2)C(Ph)CO(2)Et displays similar reactivity to that of EDA, whereas other N(2)C(R)CO(2)Et (R = Me, CO(2)Et) gave lower conversions.

  1. Silver-catalyzed silicon-hydrogen bond functionalization by carbene insertion.

    PubMed

    Iglesias, M José; Nicasio, M Carmen; Caballero, Ana; Pérez, Pedro J

    2013-01-28

    The catalytic functionalization of silicon-hydrogen bonds by means of the insertion of carbene units :CHCO(2)Et from ethyl diazoacetate (EDA) has been achieved using a silver-based catalyst, constituting the first example of this metal to promote this transformation. Competition experiments have revealed that the relative reactivity of substituted silanes depends on the bond dissociation energy of the Si-H bond (tertiary > secondary > primary for ethyl substituted). In the presence of bulky substituents such order reverts to secondary > primary ≈ tertiary (for phenyl substituted). Screening with other diazo compounds has shown that N(2)C(Ph)CO(2)Et displays similar reactivity to that of EDA, whereas other N(2)C(R)CO(2)Et (R = Me, CO(2)Et) gave lower conversions. PMID:23114570

  2. Isolation of neutral mononuclear copper complexes stabilized by two cyclic (alkyl)(amino)carbenes.

    PubMed

    Weinberger, David S; Amin Sk, Nurul; Mondal, Kartik Chandra; Melaimi, Mohand; Bertrand, Guy; Stückl, A Claudia; Roesky, Herbert W; Dittrich, Birger; Demeshko, Serhiy; Schwederski, Brigitte; Kaim, Wolfgang; Jerabek, Paul; Frenking, Gernot

    2014-04-30

    Two (cAAC)2Cu complexes, featuring a two-coordinate copper atom in the formal oxidation state zero, were prepared by reducing (Et2-cAAC)2Cu(+)I(-) with metallic sodium in THF, and by a one-pot synthesis using Me2-cAAC, Cu(II)Cl2, and KC8 in toluene in a molar ratio of 2:1:2, respectively. Both complexes are highly air and moisture sensitive but can be stored in the solid state for a month at room temperature. DFT calculations showed that in these complexes the copper center has a d(10) electronic configuration and the unpaired electron is delocalized over two carbene carbon atoms. This was further confirmed by the EPR spectra, which exhibit multiple hyperfine lines due to the coupling of the unpaired electron with (63,65)Cu isotopes, (14)N, and (1)H nuclei.

  3. Kinetic Selectivity of Olefin Metathesis Catalysts Bearing Cyclic (Alkyl)(Amino)Carbenes

    PubMed Central

    Anderson, Donde R.; Ung, Thay; Mkrtumyan, Garik; Bertrand, Guy; Grubbs, Robert H.; Schrodi, Yann

    2008-01-01

    The evaluation of ruthenium olefin metathesis catalysts 4–6 bearing cyclic (alkyl)(amino)carbenes (CAACs) in the cross-metathesis of cis-1,4-diacetoxy-2-butene (7) with allylbenzene (8) and the ethenolysis of methyl oleate (11) is reported. Relative to most NHC-substituted complexes, CAAC-substituted catalysts exhibit lower E/Z ratios (3:1 at 70% conversion) in the cross-metathesis of 7 and 8. Additionally, complexes 4–6 demonstrate good selectivity for the formation of terminal olefins versus internal olefins in the ethenolysis of 11. Indeed, complex 6 achieved 35 000 TONs, the highest recorded to date. CAAC-substituted complexes exhibit markedly different kinetic selectivity than most NHC-substituted complexes. PMID:18584055

  4. Cationic iridium(III) complexes with two carbene-based cyclometalating ligands: cis versus trans isomers.

    PubMed

    Monti, Filippo; La Placa, Maria Grazia I; Armaroli, Nicola; Scopelliti, Rosario; Grätzel, Michael; Nazeeruddin, Mohammad Khaja; Kessler, Florian

    2015-03-16

    A series of cationic iridium(III) complexes with two carbene-based cyclometalating ligands and five different N^N bipyridine and 1,10-phenanthroline ancillary ligands is presented. For the first time--in the frame of a rarely studied class of bis(heteroleptic) iridium complexes with two carbene-based cyclometalating ligands--a pair of cis and trans isomers has been isolated. All complexes (trans-1-5 and cis-3) were characterized by (1)H NMR, (13)C NMR, (31)P NMR, and HRMS (ESI-TOF); in addition, crystal structures of cis-3 and trans-4 are reported and discussed. Cyclic voltammetric studies show that the whole series exhibits highly reversible oxidation and reduction processes, suggesting promising potential for optoelectronic applications. Ground-state DFT and TD-DFT calculations nicely predict the blue shift experimentally observed in the room-temperature absorption and emission spectra of cis-3, compared to the trans complexes. In CH3CN, cis-3 displays a 4-fold increase in photoluminescence quantum yield (PLQY) with respect to trans-3, as a consequence of drastically slower nonradiative rate constant. By contrast, at 77 K, the emission properties of all the compounds, including the cis isomer, are much more similar, with a pronounced hypsochromic shift for the trans complexes. A similar behavior is found in solid state (1% w/w poly(methyl methacrylate) matrix), with all complexes displaying PLQY of ∼70-80%, comparable emission lifetimes (τ ≈ 1.3 μs), and a remarkable rigidochromic shift. To rationalize the more pronounced nonradiative deactivation (and smaller PLQY) observed for photoexcited trans complexes, comparative temperature-dependent emission studies in the range of 77-450 K for cis-3 and trans-3 were made in propylene glycol, showing that solvation effects are primarily responsible for the observed behavior.

  5. Synthesis, characterization and antimicrobial activities of novel silver(I) complexes with coumarin substituted N-heterocyclic carbene ligands.

    PubMed

    Karataş, Mert Olgun; Olgundeniz, Begüm; Günal, Selami; Özdemir, İlknur; Alıcı, Bülent; Çetinkaya, Engin

    2016-02-15

    Eight new coumarin substituted silver(I) N-heterocyclic carbene (NHC) complexes were synthesized by the interaction of the corresponding imidazolium or benzimidazolium chlorides and Ag2O in dichloromethane at room temperature. Structures of these complexes were established on the basis of elemental analysis, (1)H NMR, (13)C NMR, IR and mass spectroscopic techniques. The antimicrobial activities of carbene precursors and silver NHC complexes were tested against standard strains: Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and the fungi Candida albicans and Candida tropicalis. Results showed that all the compounds inhibited the growth of the all bacteria and fungi strains and some complexes performed good activities against different microorganisms. Among all the compounds, the most lipophilic complex bis[1-(4-methylene-6,8-dimethyl-2H-chromen-2-one)-3-(naphthalene-2-ylmethyl)benzimidazol-2-ylidene]silver(I) dichloro argentate (5e) was found out as the most active one.

  6. A search for thermal isomerization of olefins to carbenes: Thermal generations of the silicon-nitrogen double bond

    SciTech Connect

    Zhang, Xianping.

    1990-09-21

    The first part of this thesis will search for the thermal isomerization of olefins to carbenes which is predicted to be a high energy process by calculations and has only been observed in a few strained olefins. The possibility of thermal isomerization of simple olefins to carbenes will be explored. Substitution of a silyl group on the double bond of an olefin allows a potential intermediate which has a {beta}-radical to the silyl group during the cis-trans isomerization. The effects of a trimethylsilyl group on this isomerization are the subject of this study. The second part of this thesis will include the generation and chemistry of intermediates containing a silicon-nitrogen double bond. The isomerization of parent silanimine to the aminosilylene was calculated to be a high energy process. New approaches to the silicon-nitrogen double bond will also be presented. 92 refs., 12 figs., 11 tabs.

  7. Carbene-catalysed reductive coupling of nitrobenzyl bromides and activated ketones or imines via single-electron-transfer process

    NASA Astrophysics Data System (ADS)

    Li, Bao-Sheng; Wang, Yuhuang; Proctor, Rupert S. J.; Zhang, Yuexia; Webster, Richard D.; Yang, Song; Song, Baoan; Chi, Yonggui Robin

    2016-09-01

    Benzyl bromides and related molecules are among the most common substrates in organic synthesis. They are typically used as electrophiles in nucleophilic substitution reactions. These molecules can also be activated via single-electron-transfer (SET) process for radical reactions. Representative recent progress includes α-carbon benzylation of ketones and aldehydes via photoredox catalysis. Here we disclose the generation of (nitro)benzyl radicals via N-heterocyclic carbene (NHC) catalysis under reductive conditions. The radical intermediates generated via NHC catalysis undergo formal 1,2-addition with ketones to eventually afford tertiary alcohol products. The overall process constitutes a formal polarity-inversion of benzyl bromide, allowing a direct coupling of two initially electrophilic carbons. Our study provides a new carbene-catalysed reaction mode that should enable unconventional transformation of (nitro)benzyl bromides under mild organocatalytic conditions.

  8. Carbene-catalysed reductive coupling of nitrobenzyl bromides and activated ketones or imines via single-electron-transfer process

    PubMed Central

    Li, Bao-Sheng; Wang, Yuhuang; Proctor, Rupert S. J.; Zhang, Yuexia; Webster, Richard D.; Yang, Song; Song, Baoan; Chi, Yonggui Robin

    2016-01-01

    Benzyl bromides and related molecules are among the most common substrates in organic synthesis. They are typically used as electrophiles in nucleophilic substitution reactions. These molecules can also be activated via single-electron-transfer (SET) process for radical reactions. Representative recent progress includes α-carbon benzylation of ketones and aldehydes via photoredox catalysis. Here we disclose the generation of (nitro)benzyl radicals via N-heterocyclic carbene (NHC) catalysis under reductive conditions. The radical intermediates generated via NHC catalysis undergo formal 1,2-addition with ketones to eventually afford tertiary alcohol products. The overall process constitutes a formal polarity-inversion of benzyl bromide, allowing a direct coupling of two initially electrophilic carbons. Our study provides a new carbene-catalysed reaction mode that should enable unconventional transformation of (nitro)benzyl bromides under mild organocatalytic conditions. PMID:27671606

  9. Alkyne-Azide Cycloaddition Catalyzed by Silver Chloride and “Abnormal” Silver N-Heterocyclic Carbene Complex

    PubMed Central

    Ortega-Arizmendi, Aldo I.; Aldeco-Pérez, Eugenia; Cuevas-Yañez, Erick

    2013-01-01

    A library of 1,2,3-triazoles was synthesized from diverse alkynes and azides using catalytic amounts of silver chloride instead of copper compounds. In addition, a novel “abnormal” silver N-heterocyclic carbene complex was tested as catalyst in this process. The results suggest that the reaction requires only 0.5% of silver complex, affording 1,2,3-triazoles in good yields. PMID:24307866

  10. Preparation of a N-Heterocyclic Carbene Nickel(II) Complex: Synthetic Experiments in Current Organic and Organometallic Chemistry

    ERIC Educational Resources Information Center

    Ritleng, Vincent; Brenner, Eric; Chetcuti, Michael J.

    2008-01-01

    A four-part experiment that leads to the synthesis of a cyclopentadienyl chloro-nickel(II) complex bearing a N-heterocyclic carbene (NHC) ligand is presented. In the first part, the preparation of 1,3-bis-(2,4,6-trimethylphenyl)imidazolium chloride (IMes[middle dot]HCl) in a one-pot procedure by reaction of 2,4,6-trimethylaniline with…

  11. Rate and equilibrium constants for the addition of N-heterocyclic carbenes into benzaldehydes: a remarkable 2-substituent effect.

    PubMed

    Collett, Christopher J; Massey, Richard S; Taylor, James E; Maguire, Oliver R; O'Donoghue, AnnMarie C; Smith, Andrew D

    2015-06-01

    Rate and equilibrium constants for the reaction between N-aryl triazolium N-heterocyclic carbene (NHC) precatalysts and substituted benzaldehyde derivatives to form 3-(hydroxybenzyl)azolium adducts under both catalytic and stoichiometric conditions have been measured. Kinetic analysis and reaction profile fitting of both the forward and reverse reactions, plus onwards reaction to the Breslow intermediate, demonstrate the remarkable effect of the benzaldehyde 2-substituent in these reactions and provide insight into the chemoselectivity of cross-benzoin reactions.

  12. Catalytic boracarboxylation of alkynes with diborane and carbon dioxide by an N-heterocyclic carbene copper catalyst.

    PubMed

    Zhang, Liang; Cheng, Jianhua; Carry, Béatrice; Hou, Zhaomin

    2012-09-01

    By the use of an N-heterocyclic carbene copper(I) complex as a catalyst, the boracarboxylation of various alkynes (e.g., diaryl alkynes, aryl/alkyl alkynes, and phenylacetylene) with a diborane compound and carbon dioxide has been achieved for the first time, affording the α,β-unsaturated β-boralactone derivatives regio- and stereoselectively via a borylcupration/carboxylation cascade. Some important reaction intermediates were isolated and structurally characterized to clarify the reaction mechanism. PMID:22909063

  13. Formation and stability of N-heterocyclic carbenes in water: the carbon acid pKa of imidazolium cations in aqueous solution.

    PubMed

    Amyes, Tina L; Diver, Steven T; Richard, John P; Rivas, Felix M; Toth, Krisztina

    2004-04-01

    We report second-order rate constants kDO (M-1 s-1) for exchange for deuterium of the C(2)-proton of a series of simple imidazolium cations to give the corresponding singlet imidazol-2-yl carbenes in D2O at 25 degrees C and I = 1.0 (KCl). Evidence is presented that the reverse protonation of imidazol-2-yl carbenes by solvent water is limited by solvent reorganization and occurs with a rate constant of kHOH = kreorg = 10(11) s-1. The data were used to calculate reliable carbon acid pK(a)s for ionization of imidazolium cations at C(2) to give the corresponding singlet imidazol-2-yl carbenes in water: pKa = 23.8 for the imidazolium cation, pKa = 23.0 for the 1,3-dimethylimidazolium cation, pKa = 21.6 for the 1,3-dimethylbenzimidazolium cation, and pKa = 21.2 for the 1,3-bis-((S)-1-phenylethyl)benzimidazolium cation. The data also provide the thermodynamic driving force for a 1,2-hydrogen shift at a singlet carbene: K12 = 5 x 10(16) for rearrangement of the parent imidazol-2-yl carbene to give neutral imidazole in water at 298 K, which corresponds to a favorable Gibbs free energy change of 23 kcal/mol. We present a simple rationale for the observed substituent effects on the thermodynamic stability of N-heterocyclic carbenes relative to a variety of neutral and cationic derivatives that emphasizes the importance of the choice of reference reaction when assessing the stability of N-heterocyclic carbenes.

  14. Synthesis, structure and transmetalation of N-heterocyclic carbene complex of silver. Evidence of halogen exchange during the synthetic process.

    PubMed

    Xiao, Xu-Qiong; Jin, Guo-Xin

    2009-11-14

    Deprotonation of the bis(imidazolium) salt (1,1'-dimethyl-3,3'-ethylenediimidazolium dibromide, L x 2HBr) with silver oxide in a solution mixture of CH(2)Cl(2) and CH(3)OH affords a silver carbene complex [Ag(2)L(2)]Cl(2) (1, L = 1,1'-dimethyl-3,3'-ethylenediimidazol-2-ylidene). With CH(3)OH as the only solvent for the synthesis and after recrystallization in a chlorinated solvent in ambient condition, a polymeric silver complex [(L x 2H)(Ag(2)Br(4))](n) (2) was formed. The presence of chloride in complex 1 and bromide in complex 2 indicates that a halogen exchange reaction occurred unambiguously during the synthesis and not during recrystallization. The silver-carbene complex 1 undergoes a facile reaction with [(p-cymene)RuCl(2)](2) and (p-cymene)Ru[S(2)C(2)(B(10)H(10))] to yield the binuclear complexes [(p-cymene)RuCl(2)](2)L (3) and {(p-cymene)Ru[S(2)C(2)(B(10)H(10))]}(2)L (4). The latter compound contains a carbene ligand and a 1,2-dicarba-closo-dodecaborane ligand. Molecular structures of complexes 1-4 were confirmed by X-ray single-crystal analyses.

  15. Stable -ESiMe3 Complexes of Cu(I) and Ag(I) (E=S, Se) with NHCs: Synthons in Ternary Nanocluster Assembly.

    PubMed

    Azizpoor Fard, Mahmood; Levchenko, Tetyana I; Cadogan, Carolyn; Humenny, William J; Corrigan, John F

    2016-03-18

    As a part of efforts to prepare new "metallachalcogenolate" precursors and develop their chemistry for the formation of ternary mixed-metal chalcogenide nanoclusters, two sets of thermally stable, N-heterocyclic carbene metal-chalcogenolate complexes of the general formula [(IPr)Ag-ESiMe3] (IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene; E=S, 1; Se, 2) and [(iPr2-bimy)Cu-ESiMe3]2 (iPr2-bimy=1,3-diisopropylbenzimidazolin-2-ylidene; E=S, 4; Se, 5) are reported. These are prepared from the reaction between the corresponding carbene metal acetate, [(IPr)AgOAc] and [(iPr-bimy)CuOAc] respectively, and E(SiMe3 )2 at low temperature. The reaction of [(IPr)Ag-ESiMe3] 1 with mercury(II) acetate affords the heterometallic complex [{(IPr)AgS}2Hg] 3 containing two (IPr)Ag-S(-) fragments bonded to a central Hg(II), representing a mixed mercury-silver sulfide complex. The reaction of [(iPr2-bimy)Cu-SSiMe3]2, which contains a smaller N-heterocyclic-carbene, with mercuric(II) acetate affords the high nuclearity cluster, [(iPr2-bimy)6Cu10S8Hg3]6. The new N-heterocyclic carbene metal-chalcogenolate complexes 1, 2, 4, 5 and the ternary mixed-metal chalcogenolate complex 3 and cluster 6 have been characterized by multinuclear NMR spectroscopy ((1)H and (13)C), elemental analysis and single-crystal X-ray diffraction. PMID:26865473

  16. "Hummingbird" behaviour of N-heterocyclic carbenes stabilises out-of-plane bonding of AuCl and CuCl units.

    PubMed

    Teci, Matthieu; Brenner, Eric; Matt, Dominique; Gourlaouen, Christophe; Toupet, Loic

    2015-07-27

    An N-heterocyclic carbene substituted by two expanded 9-ethyl-9-fluorenyl groups was shown to bind an AuCl unit in an unusual manner, namely with the AuX rod sitting out of the plane defined by the heterocyclic carbene unit. As shown by X-ray studies and DFT calculations, the observed large pitch angle (21°) arises from an easy displacement of the gold(I) atom away from the carbene lone-pair axis, combined with the stabilisation provided by weak CH⋅⋅⋅Au interactions involving aliphatic and aromatic H atoms of the NHC wingtips. Weak, intermolecular Cl⋅⋅⋅H bonds are likely to cooperate with the H⋅⋅⋅Au interactions to stabilise the out-of-plane conformation. A general belief until now was that tilt angles in NHC complexes arise mainly from steric effects within the first coordination sphere.

  17. Methandiide as a non-innocent ligand in carbene complexes: from the electronic structure to bond activation reactions and cooperative catalysis.

    PubMed

    Becker, Julia; Modl, Tanja; Gessner, Viktoria H

    2014-09-01

    The synthesis of a ruthenium carbene complex based on a sulfonyl-substituted methandiide and its application in bond activation reactions and cooperative catalysis is reported. In the complex, the metal-carbon interaction can be tuned between a Ru-C single bond with additional electrostatic interactions and a Ru=C double bond, thus allowing the control of the stability and reactivity of the complex. Hence, activation of polar and non-polar bonds (O-H, H-H) as well as dehydrogenation reactions become possible. In these reactions the carbene acts as a non-innocent ligand supporting the bond activation as nucleophilic center in the 1,2-addition across the metal-carbon double bond. This metal-ligand cooperativity can be applied in the catalytic transfer hydrogenation for the reduction of ketones. This concept opens new ways for the application of carbene complexes in catalysis. PMID:25047390

  18. "Hummingbird" behaviour of N-heterocyclic carbenes stabilises out-of-plane bonding of AuCl and CuCl units.

    PubMed

    Teci, Matthieu; Brenner, Eric; Matt, Dominique; Gourlaouen, Christophe; Toupet, Loic

    2015-07-27

    An N-heterocyclic carbene substituted by two expanded 9-ethyl-9-fluorenyl groups was shown to bind an AuCl unit in an unusual manner, namely with the AuX rod sitting out of the plane defined by the heterocyclic carbene unit. As shown by X-ray studies and DFT calculations, the observed large pitch angle (21°) arises from an easy displacement of the gold(I) atom away from the carbene lone-pair axis, combined with the stabilisation provided by weak CH⋅⋅⋅Au interactions involving aliphatic and aromatic H atoms of the NHC wingtips. Weak, intermolecular Cl⋅⋅⋅H bonds are likely to cooperate with the H⋅⋅⋅Au interactions to stabilise the out-of-plane conformation. A general belief until now was that tilt angles in NHC complexes arise mainly from steric effects within the first coordination sphere. PMID:26130507

  19. Methandiide as a non-innocent ligand in carbene complexes: from the electronic structure to bond activation reactions and cooperative catalysis.

    PubMed

    Becker, Julia; Modl, Tanja; Gessner, Viktoria H

    2014-09-01

    The synthesis of a ruthenium carbene complex based on a sulfonyl-substituted methandiide and its application in bond activation reactions and cooperative catalysis is reported. In the complex, the metal-carbon interaction can be tuned between a Ru-C single bond with additional electrostatic interactions and a Ru=C double bond, thus allowing the control of the stability and reactivity of the complex. Hence, activation of polar and non-polar bonds (O-H, H-H) as well as dehydrogenation reactions become possible. In these reactions the carbene acts as a non-innocent ligand supporting the bond activation as nucleophilic center in the 1,2-addition across the metal-carbon double bond. This metal-ligand cooperativity can be applied in the catalytic transfer hydrogenation for the reduction of ketones. This concept opens new ways for the application of carbene complexes in catalysis.

  20. Effects of Phosphine-Carbene Substitutions on the Electrochemical and Thermodynamic Properties of Nickel Complexes

    SciTech Connect

    Galan, Brandon R.; Wiedner, Eric S.; Helm, Monte L.; Linehan, John C.; Appel, Aaron M.

    2014-05-12

    Nickel(II) complexes containing chelating N-heterocyclic carbene-phosphine ligands ([NiL2](BPh4)2, for which L = [MeIm(CH2)2PR2]) have been synthesized for the purpose of studying how this class of ligand effects the electrochemical properties compared to the nickel bis- diphosphine analogues. The nickel complexes were synthesized and characterized by x-ray crystallography and electrochemical methods. Based on the half wave potentials (E1/2), substitution of an NHC for one of the phosphines in a diphoshine ligand results in shifts in potential to 0.6 V to 1.2 V more negative than the corresponding nickel bis-diphosphine complexes. These quantitative results highlight the substantial effect that NHC ligands can have upon the electronic properties of the metal complexes. BRG, JCL, and AMA acknowledge the support by the US Department of Energy Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. MLH acknoledges the support of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  1. Biological Screening of Newly Synthesized BIAN N-Heterocyclic Gold Carbene Complexes in Zebrafish Embryos

    PubMed Central

    Farooq, Muhammad; Abu Taha, Nael; Butorac, Rachel R.; Evans, Daniel Anthony; Elzatahry, Ahmed A.; Elsayed, Elsayed Ahmed; Wadaan, Mohammad A. M.; Al-Deyab, Salem S.; Cowley, Alan H.

    2015-01-01

    N-Heterocyclic carbene (NHC) metal complexes possess diverse biological activities but have yet to be extensively explored as potential chemotherapeutic agents. We have previously reported the synthesis of a new class of NHC metal complexes N-heterocyclic with acetate [IPr(BIAN)AuOAc] and chloride [IPr(BIAN)AuCl] ligands. In the experiments reported herein, the zebrafish embryos were exposed to serial dilutions of each of these complexes for 10–12 h. One hundred percent mortality was observed at concentrations ≥50 µM. At sub-lethal concentrations (10–30 µM), both compounds influenced zebrafish embryonic development. However, quite diverse categories of abnormalities were found in exposed embryos with each compound. Severe brain deformation and notochord degeneration were evident in the case of [IPr(BIAN)AuOAc]. The zebrafish embryos treated with [IPr(BIAN)AuCl] exhibited stunted growth and consequently had smaller body sizes. A depletion of 30%–40% glutathione was detected in the treated embryos, which could account for one of the possible mechanism of neurotoxicity. The fact that these compounds are capable of both affecting the growth and also compromising antioxidant systems by elevating intracellular ROS production implies that they could play an important role as a new breed of therapeutic molecules. PMID:26501273

  2. Synthesis, crystal, and biological activity of a novel carbene silver(I) complex with imidazole derivative

    SciTech Connect

    Jiu-Fu, Lu Hong-Guang, Ge; Juan, Shi

    2015-12-15

    Reaction of 2-(1-methyl-1,2-dihydroimidazol-3-yl)acetonitrile tetrafluoroborate with silver oxide in dichloromethane readily yields [Ag(DIM){sub 2}]BF{sub 4}, where DIM is 2-(1-methyl-1, 2-dihydroimidazol-3-yl)acetonitrile, representing a carbene organic ligand. The title compound was characterized by elemental analysis, IR, MS and single crystal X-ray diffraction. The crystal is of monoclinic system, space group C2/c with a = 14.010(18), b = 8.303(11), c = 14.936(20) Å, β = 93.910(4)°, V = 1639(4) Å{sup 3}, Z = 4, D{sub x} = 1.771 g/cm{sup 3}, F (000) = 864, µ(MoK{sub α}) = 1.278 mm{sup –1}. The final R{sup 1} = 0.0711 and wR{sup 2} = 0.1903 for reflections with I > 2σ(I). In addition, the preliminary biological test showed that the title compound had anti-fungus yeast activity.

  3. Conformation analysis of triphenylphosphine in trans and cis triphenylphosphine-substituted Fischer carbene complexes

    NASA Astrophysics Data System (ADS)

    Landman, Marilé; Levell, Tamzyn; van Rooyen, Petrus H.; Conradie, Jeanet

    2014-05-01

    The synthesis and selected crystal structures of novel (M = Cr or Mo) and known (M = W) [(CO)4(PPh3)M = C(OEt)R] complexes, M = Cr, R = 2-thienyl (1), 2-furyl (2); M = Mo, R = 2-thienyl (3), 2-furyl (4); M = W, R = 2-thienyl (5), 2-furyl (6), are presented. Experimental crystal structures and DFT calculations of selected trans- and cis-triphenylphosphine-substituted Fischer carbene complexes, illustrate that the minimum energy conformation of triphenylphosphine (PPh3) in octahedral [(CO)4(PPh3)ML]-complexes generally have distinct features that can be described in terms of the "plane of nadir energy", a plane linking all points of minimum steric compression between the ligands. The generally observed orientation of PPh3 involves a correlated feathering of the phenyl groups with the PCipso bond of one phenyl group orientated near parallel to the nadir plane, and a meta carbon (Cm) of the other two phenyl groups orientated as near as possible to the nadir plane, orthogonal to the first. Although the orientation of PPh3 in 6-trans, [(CO)4(PPh3)W = C(OEt)2-furyl], deviates from this, DFT correctly calculated the unexpected and not generally observed PPh3 orientation.

  4. Probing Protein Surface with a Solvent Mimetic Carbene Coupled to Detection by Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Gómez, Gabriela E.; Mundo, Mariana R.; Craig, Patricio O.; Delfino, José M.

    2012-01-01

    Much knowledge into protein folding, ligand binding, and complex formation can be derived from the examination of the nature and size of the accessible surface area (SASA) of the polypeptide chain, a key parameter in protein science not directly measurable in an experimental fashion. To this end, an ideal chemical approach should aim at exerting solvent mimicry and achieving minimal selectivity to probe the protein surface regardless of its chemical nature. The choice of the photoreagent diazirine to fulfill these goals arises from its size comparable to water and from being a convenient source of the extremely reactive methylene carbene (:CH2). The ensuing methylation depends primarily on the solvent accessibility of the polypeptide chain, turning it into a valuable signal to address experimentally the measurement of SASA in proteins. The superb sensitivity and high resolution of modern mass spectrometry techniques allows us to derive a quantitative signal proportional to the extent of modification (EM) of the sample. Thus, diazirine labeling coupled to electrospray mass spectrometry (ESI-MS) detection can shed light on conformational features of the native as well as non-native states, not easily addressable by other methods. Enzymatic fragmentation of the polypeptide chain at the level of small peptides allows us to locate the covalent tag along the amino acid sequence, therefore enabling the construction of a map of solvent accessibility. Moreover, by subsequent MS/MS analysis of peptides, we demonstrate here the feasibility of attaining amino acid resolution in defining the target sites.

  5. Synthesis, crystal, and biological activity of a novel carbene silver(I) complex with imidazole derivative

    NASA Astrophysics Data System (ADS)

    Jiu-Fu, Lu; Hong-Guang, Ge; Juan, Shi

    2015-12-01

    Reaction of 2-(1-methyl-1,2-dihydroimidazol-3-yl)acetonitrile tetrafluoroborate with silver oxide in dichloromethane readily yields [Ag( DIM)2]BF4, where DIM is 2-(1-methyl-1, 2-dihydroimidazol-3-yl)acetonitrile, representing a carbene organic ligand. The title compound was characterized by elemental analysis, IR, MS and single crystal X-ray diffraction. The crystal is of monoclinic system, space group C2/ c with a = 14.010(18), b = 8.303(11), c = 14.936(20) Å, β = 93.910(4)°, V = 1639(4) Å3, Z = 4, D x = 1.771 g/cm3, F (000) = 864, µ(Mo K α) = 1.278 mm-1. The final R 1 = 0.0711 and wR 2 = 0.1903 for reflections with I > 2σ( I). In addition, the preliminary biological test showed that the title compound had anti-fungus yeast activity.

  6. Laser Spectroscopy of Radicals, Carbenes, and Ions in Superfluid Helium Droplets

    NASA Astrophysics Data System (ADS)

    Douberly, Gary E.

    2015-06-01

    The first beam of helium droplets was reported in the 1961 paper Strahlen aus kondensiertem Helium im Hochvakuum by Von E. W. Becker and co-workers. However, molecular spectroscopy of helium-solvated dopants wasn't realized until 30 years later in the laboratories of Scoles and Toennies. It has now been two decades since this early, seminal work on doped helium droplets, yet the field of helium droplet spectroscopy is still fresh with vast potential. Analogous in many ways to cryogenic matrix isolation spectroscopy, the helium droplet is an ideal environment to spectroscopically probe difficult to prepare molecular species, such as radicals, carbenes and ions. The quantum nature of helium at 0.35 K often results in molecular spectra that are sufficiently resolved to evoke an analysis of line shapes and fine-structure that is worthy of the International Symposium on Molecular Spectroscopy. The present talk will focus on our recent successful attempts to efficiently dope the title molecular species into helium droplets and probe their properties with infrared laser Stark and Zeeman spectroscopies. E. W. Becker, R. Klingelhöfer, P. Lohse, Z. Naturforsch. A 16A, 1259 (1961). S. Goyal, D. L. Schutt, G. Scoles, Phys. Rev. Lett. 69, 933 (1992). M. Hartmann, R. E. Miller, J. P. Toennies, A. F. Vilesov, Phys. Rev. Lett. 75, 1566, (1995).

  7. Recent advances in carbon dioxide capture, fixation, and activation by using N-heterocyclic carbenes.

    PubMed

    Yang, Longhua; Wang, Hongming

    2014-04-01

    In the last two decades, CO2 emission has caused a lot of environmental problems. To mitigate the concentration of CO2 in the atmosphere, various strategies have been implemented, one of which is the use of N-heterocyclic carbenes (NHCs) and related complexes to accomplish the capture, fixation, and activation of CO2 effectively. In this review, we summarize CO2 capture, fixation, and activation by utilizing NHCs and related complexes; homogeneous reactions and their reaction mechanisms are discussed. Free NHCs and NHC salts can capture CO2 in both direct and indirect ways to form imidazolium carboxylates, and they can also catalyze the reaction of aromatic aldehydes with CO2 to form carboxylic acids and derivatives. Moreover, associated with transition metals (TMs), NHCs can form NHC-TM complexes to transform CO2 into industrial acid or esters. Non-metal-NHC complexes can also catalyze the reactions of silicon and boron complexes with CO2 . In addition, catalytic cycloaddition of epoxides with CO2 is another effective function of NHC complexes, and NHC ionic liquids perform excellently in this aspect.

  8. Optimizing P,N-Bidentate Ligands for Oxidative Gold Catalysis: Highly Efficient Intermolecular Trapping of α-Oxo Gold Carbenes by Carboxylic Acids

    PubMed Central

    Ji, Kegong; Zhao, Yulong; Zhang, Liming

    2013-01-01

    Steric Bulk or Conformation Control? Optimization of P,N-bidentate ligands reveals the importance of conformation control in the development of highly efficient intermolecular trapping of reactive α-oxo gold carbene intermediates. While a pendant piperidine ring offers suitable steric bulk, fixing its conformation to provide better shielding to the highly electrophilic carbene center turned out to be crucial for the excellent reaction efficiency. A generally highly efficient and broadly applicable synthesis of carboxymethyl ketones from readily available carboxylic acids and terminal alkynes is developed under exceptionally mild reaction conditions. PMID:23640818

  9. Evidencing an inner-sphere mechanism for NHC-Au(I)-catalyzed carbene-transfer reactions from ethyl diazoacetate

    PubMed Central

    Fructos, Manuel R; Urbano, Juan

    2015-01-01

    Summary Kinetic experiments based on the measurement of nitrogen evolution in the reaction of ethyl diazoacetate (N2CHCO2Et, EDA) and styrene or methanol catalyzed by the [IPrAu]+ core (IPr = 1,3-bis(diisopropylphenyl)imidazole-2-ylidene) have provided evidence that the transfer of the carbene group CHCO2Et to the substrate (styrene or methanol) takes place in the coordination sphere of Au(I) by means of an inner-sphere mechanism, in contrast to the generally accepted proposal of outer-sphere mechanisms for Au(I)-catalyzed reactions. PMID:26664649

  10. Evidencing an inner-sphere mechanism for NHC-Au(I)-catalyzed carbene-transfer reactions from ethyl diazoacetate.

    PubMed

    Fructos, Manuel R; Urbano, Juan; Díaz-Requejo, M Mar; Pérez, Pedro J

    2015-01-01

    Kinetic experiments based on the measurement of nitrogen evolution in the reaction of ethyl diazoacetate (N2CHCO2Et, EDA) and styrene or methanol catalyzed by the [IPrAu](+) core (IPr = 1,3-bis(diisopropylphenyl)imidazole-2-ylidene) have provided evidence that the transfer of the carbene group CHCO2Et to the substrate (styrene or methanol) takes place in the coordination sphere of Au(I) by means of an inner-sphere mechanism, in contrast to the generally accepted proposal of outer-sphere mechanisms for Au(I)-catalyzed reactions.

  11. Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid

    PubMed Central

    Lamm, Vladimir; Pan, Xiangcheng

    2013-01-01

    Summary Acetic acid promotes the reduction of aldehydes and ketones by the readily available N-heterocyclic carbene borane, 1,3-dimethylimidazol-2-ylidene borane. Aldehydes are reduced over 1–24 h at room temperature with 1 equiv of acetic acid and 0.5 equiv of the NHC-borane. Ketone reductions are slower but can be accelerated by using 5 equiv of acetic acid. Aldehydes can be selectively reduced in the presence of ketones. On a small scale, products are isolated by evaporation of the reaction mixture and direct chromatography. PMID:23616812

  12. Enantioselective Nucleophilic β-Carbon-Atom Amination of Enals: Carbene-Catalyzed Formal [3+2] Reactions.

    PubMed

    Wu, Xingxing; Liu, Bin; Zhang, Yuexia; Jeret, Martin; Wang, Honglin; Zheng, Pengcheng; Yang, Song; Song, Bao-An; Chi, Yonggui Robin

    2016-09-26

    An enantioselective β-carbon amination for enals is disclosed. The nitrogen atom from a protected hydrazine with suitable electronic properties readily behaves as a nucleophile. Addition of the nitrogen nucleophile to a catalytically generated N-heterocyclic-carbene-bound α,β-unsaturated acyl azolium intermediate constructs a new carbon-nitrogen bond asymmetrically. The pyrazolidinone products from our catalytic reactions are common scaffolds in bioactive molecules, and can be easily transformed into useful compounds such as β(3) -amino-acid derivatives. PMID:27596365

  13. Computational Investigations of Potential Energy Function Development for Metal--Organic Framework Simulations, Metal Carbenes, and Chemical Warfare Agents

    NASA Astrophysics Data System (ADS)

    Cioce, Christian R.

    Metal-Organic Frameworks (MOFs) are three-dimensional porous nanomaterials with a variety of applications, including catalysis, gas storage and separation, and sustainable energy. Their potential as air filtration systems is of interest for designer carbon capture materials. The chemical constituents (i.e. organic ligands) can be functionalized to create rationally designed CO2 sequestration platforms, for example. Hardware and software alike at the bleeding edge of supercomputing are utilized for designing first principles-based molecular models for the simulation of gas sorption in these frameworks. The classical potentials developed herein are named PHAST --- Potentials with High Accuracy, Speed, and Transferability, and thus are designed via a "bottom-up" approach. Specifically, models for N2 and CH4 are constructed and presented. Extensive verification and validation leads to insights and range of applicability. Through this experience, the PHAST models are improved upon further to be more applicable in heterogeneous environments. Given this, the models are applied to reproducing high level ab initio energies for gas sorption trajectories of helium atoms in a variety of rare-gas clusters, the geometries of which being representative of sorption-like environments commonly encountered in a porous nanomaterial. This work seeks to push forward the state of classical and first principles materials modeling. Additionally, the characterization of a new type of tunable radical metal---carbene is presented. Here, a cobalt(II)---porphyrin complex, [Co(Por)], was investigated to understand its role as an effective catalyst in stereoselective cyclopropanation of a diazoacetate reagent. Density functional theory along with natural bond order analysis and charge decomposition analysis gave insight into the electronics of the catalytic intermediate. The bonding pattern unveiled a new class of radical metal---carbene complex, with a doublet cobalt into which a triplet carbene

  14. Synthesis and characterization of Pd(II)-methyl complexes with N-heterocyclic carbene-amine ligands.

    PubMed

    Warsink, Stefan; de Boer, Sandra Y; Jongens, Lianne M; Fu, Ching-Feng; Liu, Shiuh-Tzung; Chen, Jwu-Ting; Lutz, Martin; Spek, Anthony L; Elsevier, Cornelis J

    2009-09-21

    A number of palladium(ii) complexes with a heteroditopic NHC-amine ligand and their precursor silver(i) carbene complexes have been efficiently prepared and their structural features have been investigated. The heteroditopic coordination of this ligand class was unequivocally shown by NMR-spectroscopy and X-ray crystallographic analysis. The neutral and cationic cis-methyl-palladium(NHC) complexes are not prone to reductive elimination, which is normally a major degenerative pathway for this type of complex. In contrast, under carbon monoxide atmosphere rapid reductive elimination of the acyl-imidazolium salt was observed.

  15. Carboxylation of alkylboranes by N-heterocyclic carbene copper catalysts: synthesis of carboxylic acids from terminal alkenes and carbon dioxide.

    PubMed

    Ohishi, Takeshi; Zhang, Liang; Nishiura, Masayoshi; Hou, Zhaomin

    2011-08-22

    Caught in the act: N-Heterocyclic carbene copper(I) complexes (1; IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) serve as an excellent catalyst for the carboxylation of alkylboranes (2; R=alkyl) with CO(2) to afford a variety of functionalized carboxylic acids (3) in high yields. A novel copper methoxide/alkylborane adduct (A) and its subsequent CO(2) insertion product (B) have been isolated and shown to be true active catalyst species. PMID:21739544

  16. Bond Activation by Metal-Carbene Complexes in the Gas Phase.

    PubMed

    Zhou, Shaodong; Li, Jilai; Schlangen, Maria; Schwarz, Helmut

    2016-03-15

    "Bare" metal-carbene complexes, when generated in the gas phase and exposed to thermal reactions under (near) single-collision conditions, exhibit rather unique reactivities in addition to the well-known metathesis and cyclopropanation processes. For example, at room temperature the unligated [AuCH2](+) complex brings about efficient C-C coupling with methane to produce C2Hx (x = 4, 6), and the couple [TaCH2](+)/CO2 gives rise to the generation of the acetic acid equivalent CH2═C═O. Entirely unprecedented is the thermal extrusion of a carbon atom from halobenzenes (X = F, Cl, Br, I) by [MCH2](+) (M = La, Hf, Ta, W, Re, Os) and its coupling with the methylene ligand to deliver C2H2 and [M(X)(C5H5)](+). Among the many noteworthy C-N bond-forming processes, the formation of CH3NH2 from [RhCH2](+)/NH3, the generation of CH2═NH2(+) from [MCH2](+)/NH3 (M = Pt, Au), and the production of [PtCH═NH2](+) from [PtCH2](+)/NH3 are of particular interest. The latter species are likely to be involved as intermediates in the platinum-mediated large-scale production of HCN from CH4/NH3 (the DEGUSSA process). In this context, a few examples are presented that point to the operation of co-operative effects even at a molecular level. For instance, in the coupling of CH4 with NH3 by the heteronuclear clusters [MPt](+) (M = coinage metal), platinum is crucial for the activation of methane, while the coinage metal M controls the branching ratio between the C-N bond-forming step and unwanted soot formation. For most of the gas-phase reactions described in this Account, detailed mechanistic insight has been derived from extensive computational work in conjunction with time-honored labeling and advanced mass-spectrometry-based experiments, and often a coherent description of the experimental findings has been achieved. As for some transition metals, in particular those from the third row, the metal-carbene complexes can be formed directly from methane, coupling of the so

  17. Rhenium and technetium tricarbonyl complexes of N-heterocyclic carbene ligands.

    PubMed

    Chan, Chung Ying; Pellegrini, Paul A; Greguric, Ivan; Barnard, Peter J

    2014-10-20

    A strategy for the conjugation of N-heterocyclic carbene (NHC) ligands to biomolecules via amide bond formation is described. Both 1-(2-pyridyl)imidazolium or 1-(2-pyridyl)benzimidazolium salts functionalized with a pendant carboxylic acid group were prepared and coupled to glycine benzyl ester using 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide. A series of 10 rhenium(I) tricarbonyl complexes of the form [ReX(CO)3(ĈN)] (ĈN is a bidentate NHC ligand, and X is a monodentate anionic ligand: Cl(-), RCO2(-)) were synthesized via a Ag2O transmetalation protocol from the Re(I) precursor compound Re(CO)5Cl. The synthesized azolium salts and Re(I) complexes were characterized by elemental analysis and by (1)H and (13)C NMR spectroscopy, and the molecular structures for one imidazolium salt and seven Re(I) complexes were determined by single-crystal X-ray diffraction. (1)H NMR and mass spectrometry studies for an acetonitrile-d3 solution of [ReCl(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)] show that the monodentate chloride ligand is labile and exchanges with this solvent yielding a cationic acetonitrile adduct. For the first time the labeling of an NHC ligand with technetium-99m is reported. Rapid Tc-99m labeling was achieved by heating the imidazolium salt 1-(2-pyridyl)-3-methylimidazolium iodide and Ag2O in methanol, followed by the addition of fac-[(99m)Tc(OH2)3(CO)3](+). To confirm the structure of the (99m)Tc-labeled complex, the equivalent (99)Tc complex was prepared, and mass spectrometric studies showed that the formed Tc complexes are of the form [(99m/99)Tc(CH3CN)(CO)3(1-(2-pyridyl)-3-methylimidazolylidene)](+) with an acetonitrile molecule coordinated to the metal center.

  18. Chelated bis-N-heterocyclic carbene platinum and palladium units as tunable components of multinuclear complexes.

    PubMed

    Maeda, Yuri; Hashimoto, Hideki; Kinoshita, Isamu; Nishioka, Takanori

    2015-01-20

    Heterometallic trinuclear M2M' complexes (M = Rh, Ir; M' = Pt, Pd) containing a platinum or palladium moiety with chelated bis-N-heterocyclic carbene ligands, [(MCp*)2{M'(bisNHC-Cn-R)}(μ3-S)2](BPh4)2 (M = Rh, Ir; M' = Pt, Pd; bisNHC-Cn-R = methylene-, ethylene-, or propylene-bridged bis(N-alkyl-imidazolylidene)), were synthesized by reacting bis(hydrosulfido)platinum(II) or palladium(II) complexs with bisNHC-Cn-R and hydroxo-bridged dinuclear complexes [(MCp*)2(μ-OH)3](BPh4), whose dinuclear structures remained intact during the formation of the trinuclear complexes, which was confirmed by using electrospray mass spectrometry and NMR spectroscopy. The heterometallic trinuclear M2M' complexes with a variety of alkylene bridges in bisNHC-Cn-R showed two reversible reduction waves in the cyclic voltammogram, and the second reduction potentials were affected by the alkylene chain lengths, which caused different dihedral angles between the imidazolylidene rings and the coordination plane of the platinum or palladium center. The M2M' complexes, except for those containing the platinum unit with the ethylene-bridged bisNHC ligands, showed dynamic behavior in solution due to the flapping wing motion of the NHC ligand moieties. Although activation parameters obtained from line-shape analyses on variable-temperature NMR spectra of the complexes suggested that the flapping wing motion occurred without bond cleavage, large negative ΔS(‡) values were obtained for the complexes with the palladium unit with the ethylene-bridged ligand, suggesting that the Pd-Ccarbene bond cleavage, accompanied by coordination of solvent molecules, occurred.

  19. Synthesis of mixed silylene-carbene chelate ligands from N-heterocyclic silylcarbenes mediated by nickel.

    PubMed

    Tan, Gengwen; Enthaler, Stephan; Inoue, Shigeyoshi; Blom, Burgert; Driess, Matthias

    2015-02-01

    The Ni(II) -mediated tautomerization of the N-heterocyclic hydrosilylcarbene L(2) Si(H)(CH2 )NHC 1, where L(2) =CH(CCH2 )(CMe)(NAr)2 , Ar=2,6-iPr2 C6 H3 ; NHC=3,4,5-trimethylimidazol-2-yliden-6-yl, leads to the first N-heterocyclic silylene (NHSi)-carbene (NHC) chelate ligand in the dibromo nickel(II) complex [L(1) Si:(CH2 )(NHC)NiBr2 ] 2 (L(1) =CH(MeCNAr)2 ). Reduction of 2 with KC8 in the presence of PMe3 as an auxiliary ligand afforded, depending on the reaction time, the N-heterocyclic silyl-NHC bromo Ni(II) complex [L(2) Si(CH2 )NHCNiBr(PMe3 )] 3 and the unique Ni(0) complex [η(2) (Si-H){L(2) Si(H)(CH2 )NHC}Ni(PMe3 )2 ] 4 featuring an agostic SiH→Ni bonding interaction. When 1,2-bis(dimethylphosphino)ethane (DMPE) was employed as an exogenous ligand, the first NHSi-NHC chelate-ligand-stabilized Ni(0) complex [L(1) Si:(CH2 )NHCNi(dmpe)] 5 could be isolated. Moreover, the dicarbonyl Ni(0) complex 6, [L(1) Si:(CH2 )NHCNi(CO)2 ], is easily accessible by the reduction of 2 with K(BHEt3 ) under a CO atmosphere. The complexes were spectroscopically and structurally characterized. Furthermore, complex 2 can serve as an efficient precatalyst for Kumada-Corriu-type cross-coupling reactions.

  20. Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors

    PubMed Central

    Hans, Morgan; Lorkowski, Jan; Demonceau, Albert

    2015-01-01

    Summary The one-pot condensation of glyoxal, two equivalents of cyclohexylamine, and paraformaldehyde in the presence of aqueous HBF4 provided a straightforward access to 1,3-dicyclohexylimidazolium tetrafluoroborate (ICy·HBF4). 1,3-Dibenzylimidazolium tetrafluoroborate (IBn·HBF4) was obtained along the same lines. To synthesize 1,3-diarylmidazolium salts, it was necessary to isolate the intermediate N,N'-diarylethylenediimines prior to their cyclization. Although this additional step required more time and reagents, it led to a much more efficient overall process. It also proved very convenient to carry out the synthesis of imidazolinium salts in parallel to their imidazolium counterparts via the reduction of the diimines into diammonium salts. The critical assembly of the C2 precarbenic unit was best achieved with paraformaldehyde and chlorotrimethylsilane in the case of imidazolium derivatives, whereas the use of triethyl orthoformate under microwave irradiation was most appropriate for the fast and efficient synthesis of imidazolinium salts. This strategy was applied to the synthesis of six common N-heterocyclic carbene precursors, namely, 1,3-dimesitylimidazolium chloride (IMes·HCl), 1,3-dimesitylimidazolium tetrafluoroborate (IMes·HBF4), 1,3-dimesitylimidazolinium chloride (SIMes·HCl), 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride (IDip·HCl or IPr·HCl), 1,3-bis(2,6-diisopropylphenyl)imidazolinium chloride (SIDip·HCl or SIPr·HCl), and 1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazolium chloride (IDip*·HCl or IPr*·HCl). PMID:26734080

  1. Rhenium complexes of bidentate, bis-bidentate and tridentate N-heterocyclic carbene ligands.

    PubMed

    Chan, Chung Ying; Barnard, Peter J

    2015-11-28

    A series of eight Rhenium(I)-N-heterocyclic carbene (NHC) complexes of the general form [ReCl(CO)3(C^C)] (where C^C is a bis(NHC) bidentate ligand), [ReCl(CO)3(C^C)]2 (where C^C is a bis-bidentate tetra-NHC ligand) and [Re(CO)3(C^N^C)](+)[X](-) (where C^N^C is a bis(NHC)-amine ligand and the counter ion X is either the ReO4(-) or PF6(-)) have been synthesised using a Ag2O transmetallation protocol. The novel precursor imidazolium salts and Re(I) complexes were characterized by elemental analysis, (1)H and (13)C NMR spectroscopy and the molecular structures for two imidazolium salt and six Re(I) complexes were determined by single crystal X-ray diffraction. These NHC ligand systems are of interest for possible applications in the development of Tc-99m or Re-186/188 radiopharmaceuticals and as such the stability of two complexes of the form [ReCl(CO)3(C^C)] and [Re(CO)3(C^N^C)][ReO4] were evaluated in ligand challenge experiments using the metal binding amino acids L-histidine or L-cysteine. These studies showed that the former was unstable, with the chloride ligand being replaced by either cysteine or histidine, while no evidence for transchelation was observed for the latter suggesting that bis(NHC)-amine ligands of this type may be suitable for biological applications.

  2. Aerosolized Antimicrobial Agents Based on Degradable Dextran Nanoparticles Loaded with Silver Carbene Complexes

    PubMed Central

    Ornelas-Megiatto, Cátia; Shah, Parth N.; Wich, Peter R.; Cohen, Jessica L.; Tagaev, Jasur A.; Smolen, Justin A.; Wright, Brian D.; Panzner, Matthew J.; Youngs, Wiley J.; Fréchet, Jean M. J.; Cannon, Carolyn L.

    2012-01-01

    Degradable acetalated dextran (Ac-DEX) nanoparticles were prepared and loaded with a hydrophobic silver carbene complex (SCC) by a single-emulsion process. The resulting particles were characterized for morphology and size distribution using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The average particle size and particle size distribution were found to be a function of the ratio of the organic phase to the surfactant containing aqueous phase with a 1:5 volume ratio of Ac-DEX CH2Cl2 (organic): PBS (aqueous) being optimal for the formulation of nanoparticles with an average size of 100 ± 40 nm and a low polydispersity. The SCC loading was found to increase with an increase in the SCC quantity in the initial feed used during particle formulation up to 30% (w/w); however, the encapsulation efficiency was observed to be the best at a feed ratio of 20% (w/w). In vitro efficacy testing of the SCC loaded Ac-DEX nanoparticles demonstrated their activity against both Gram-negative and Gram-positive bacteria; the nanoparticles inhibited the growth of every bacterial species tested. As expected, a higher concentration of drug was required to inhibit bacterial growth when the drug was encapsulated within the nanoparticle formulations compared with the free drug illustrating the desired depot release. Compared with free drug, the Ac-DEX nanoparticles were much more readily suspended in an aqueous phase and subsequently aerosolized, thus providing an effective method of pulmonary drug delivery. PMID:23025592

  3. Inversion of the direction of stereoinduction in the coupling of chiral gamma,delta-unsaturated Fischer carbene complexes with o-ethynylbenzaldehyde.

    PubMed

    Ghorai, Binay K; Menon, Suneetha; Johnson, Dennis Lee; Herndon, James W

    2002-06-27

    [reaction: see text] A variety of gamma,delta-unsaturated carbene complexes that feature a stereogenic center at the beta-carbon couple with 2-ethynylbenzaldehyde to afford hydrophenanthrene derivatives with a high degree of stereoinduction. The direction of stereoinduction is opposite for examples where the stereogenic center is acyclic vs examples where it is within a ring.

  4. Hydrogen shuttling: synthesis and reactivity of a 14-electron iridium complex featuring a bis(alkyl) tethered N-heterocyclic carbene ligand.

    PubMed

    Tang, Christina Y; Phillips, Nicholas; Kelly, Michael J; Aldridge, Simon

    2012-12-21

    Solvent dependent double C-H activation in an Ir(NHC)(2) system generates an agostically stabilized 14-electron complex featuring a face-capping bis(alkyl) tethered NHC ligand [NHC = N-heterocyclic carbene]. These activation processes are reversible, and the resulting ligand-derived hydrogen shuttle can be applied to the dehydrogenation of BN-containing substrates. PMID:23128505

  5. Synthesis of Pd-N-heterocyclic carbene Pd-catalyst and its application in MW-assisted Heck and Suzuki reaction

    EPA Science Inventory

    The first Pd-N-heterocyclic carbene (NHC) complex in the form of organic silica is prepared using sol-gel method and its application in Heck and Suzuki reactions are demonstrated. These C-C coupling reactions proceeded efficiently under the influence of microwave irradiation, wit...

  6. Iridium(I) complexes with anionic N-heterocyclic carbene ligands as catalysts for the hydrogenation of alkenes in nonpolar media.

    PubMed

    Kolychev, Eugene L; Kronig, Sabrina; Brandhorst, Kai; Freytag, Matthias; Jones, Peter G; Tamm, Matthias

    2013-08-21

    A series of lithium complexes of anionic N-heterocyclic carbenes that contain a weakly coordinating borate moiety (WCA-NHC) was prepared in one step from free N-heterocyclic carbenes by deprotonation with n-butyl lithium followed by borane addition. The reaction of the resulting lithium-carbene adducts with [M(COD)Cl]2 (M = Rh, Ir; COD = 1,5-cyclooctadiene) afforded zwitterionic rhodium(I) and iridium(I) complexes of the type [(WCA-NHC)M(COD)], in which the metal atoms exhibit an intramolecular interaction with the N-aryl groups of the carbene ligands. For M = Rh, the neutral complex [(WCA-NHC)Rh(CO)2] and the ate complex (NEt4)[(WCA-NHC)Rh(CO)2Cl] were prepared, with the latter allowing an assessment of the donor ability of the ligand by IR spectroscopy. The zwitterionic iridium-COD complexes were tested as catalysts for the homogeneous hydrogenation of alkenes, which can be performed in the presence of nonpolar solvents or in the neat alkene substrate. Thereby, the most active complex showed excellent stability and activity in hydrogenation of alkenes at low catalyst loadings (down to 10 ppm).

  7. A new type of self-supported, polymeric Ru-carbene complex for homogeneous catalysis and heterogeneous recovery: synthesis and catalytic activities for ring-closing metathesis.

    PubMed

    Chen, Shu-Wei; Kim, Ju Hyun; Shin, Hyunik; Lee, Sang-Gi

    2008-08-01

    A novel 2nd generation Grubbs-type catalyst tethering an isopropoxystyrene has been synthesized and automatically polymerized in solution to form a self-supported polymeric Ru-carbene complex, which catalyzed ring-closing metathesis homogeneously, but was recovered heterogeneously.

  8. Electrophilic Reaction of 2,2,2-Trifluorodiazoethane with the in Situ Generated N-Heterocyclic Carbenes: Access to N-Aminoguanidines.

    PubMed

    Guo, Ran; Zheng, Yan; Ma, Jun-An

    2016-09-01

    A facile and efficient electrophilic reaction of 2,2,2-trifluorodiazoethane (CF3CHN2) with the in situ generated N-heterocyclic carbenes is reported. Under basic conditions, a series of trifluoromethylated N-aminoguanidines were obtained in good to high yields. Furthermore, this protocol was applied in the synthesis of the agrochemical Imidacloprid analogue. PMID:27540867

  9. "N"-Heterocyclic Carbene-Catalyzed Reaction of Chalcone and Cinnamaldehyde to Give 1,3,4-Triphenylcyclopentene Using Organocatalysis to Form a Homoenolate Equivalent

    ERIC Educational Resources Information Center

    Snider, Barry B.

    2015-01-01

    In this experiment, students carry out a modern organocatalytic reaction using IMes·HCl and NaOH to catalyze the formation of 1,3,4-triphenylcyclopentene from cinnamaldehyde and chalcone in water. Deprotonation of IMes·HCl with NaOH forms the "N"-heterocyclic carbene IMes that reacts with cinnamaldehyde to form a homoenolate equivalent…

  10. The fluxional amine gold(III) complex as an excellent catalyst and precursor of biologically active acyclic carbenes.

    PubMed

    Montanel-Pérez, Sara; Herrera, Raquel P; Laguna, Antonio; Villacampa, M Dolores; Gimeno, M Concepción

    2015-05-21

    A new amine gold(III) complex [Au(C6F5)2(DPA)]ClO4 with the di-(2-picolyl)amine (DPA) ligand has been synthesised. In the solid state the complex has a chiral amine nitrogen because the ligand coordinates to the gold centre through one nitrogen atom from a pyridine and through the NH moiety, whereas in solution it shows a fluxional behaviour with a rapid exchange between the pyridine sites. This complex can be used as an excellent synton to prepare new gold(III) carbene complexes by the reaction with isocyanide CNR. The resulting gold(III) derivatives have unprecedented bidentate C^N acyclic carbene ligands. All the complexes have been spectroscopically and structurally characterized. Taking advantage of the fluxional behaviour of the amine complex, its catalytic properties have been tested in several reactions with the formation of C-C and C-N bonds. The complex showed excellent activity with total conversion, without the presence of a co-catalyst, and with a catalyst loading as low as 0.1%. These complexes also present biological properties, and cytotoxicity studies have been performed in vitro against three tumour human cell lines, Jurkat (T-cell leukaemia), MiaPaca2 (pancreatic carcinoma) and A549 (lung carcinoma). Some of them showed excellent cytotoxic activity compared with the reference cisplatin.

  11. In Silico Olefin Metathesis with Ru-Based Catalysts Containing N-Heterocyclic Carbenes Bearing C60 Fullerenes.

    PubMed

    Martínez, Juan Pablo; Vummaleti, Sai Vikrama Chaitanya; Falivene, Laura; Nolan, Steven P; Cavallo, Luigi; Solà, Miquel; Poater, Albert

    2016-05-01

    Density functional theory calculations have been used to explore the potential of Ru-based complexes with 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) ligand backbone (A) being modified in silico by the insertion of a C60 molecule (B and C), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A, B, and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron-withdrawing N-heterocyclic carbene improves the performance of unannulated complex A. The efficiency of complex B is only surpassed by complex A when the backbone of the N-heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic-donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A. Overall, this study indicates that such Ru-based complexes B and C might have the potential to be effective olefin metathesis catalysts.

  12. In Silico Olefin Metathesis with Ru-Based Catalysts Containing N-Heterocyclic Carbenes Bearing C60 Fullerenes.

    PubMed

    Martínez, Juan Pablo; Vummaleti, Sai Vikrama Chaitanya; Falivene, Laura; Nolan, Steven P; Cavallo, Luigi; Solà, Miquel; Poater, Albert

    2016-05-01

    Density functional theory calculations have been used to explore the potential of Ru-based complexes with 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) ligand backbone (A) being modified in silico by the insertion of a C60 molecule (B and C), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A, B, and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron-withdrawing N-heterocyclic carbene improves the performance of unannulated complex A. The efficiency of complex B is only surpassed by complex A when the backbone of the N-heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic-donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A. Overall, this study indicates that such Ru-based complexes B and C might have the potential to be effective olefin metathesis catalysts. PMID:27059290

  13. Titanocene–Gold Complexes Containing N-Heterocyclic Carbene Ligands Inhibit Growth of Prostate, Renal, and Colon Cancers in Vitro

    PubMed Central

    2016-01-01

    We report on the synthesis, characterization, and stability studies of new titanocene complexes containing a methyl group and a carboxylate ligand (mba = −OC(O)-p-C6H4-S−) bound to gold(I)–N-heterocyclic carbene fragments through the thiolate group: [(η5-C5H5)2TiMe(μ-mba)Au(NHC)]. The cytotoxicities of the heterometallic compounds along with those of novel monometallic gold–N-heterocyclic carbene precursors [(NHC)Au(mbaH)] have been evaluated against renal, prostate, colon, and breast cancer cell lines. The highest activity and selectivity and a synergistic effect of the resulting heterometallic species was found for the prostate and colon cancer cell lines. The colocalization of both titanium and gold metals (1:1 ratio) in PC3 prostate cancer cells was demonstrated for the selected compound 5a, indicating the robustness of the heterometallic compound in vitro. We describe here preliminary mechanistic data involving studies on the interaction of selected mono- and bimetallic compounds with plasmid (pBR322) used as a model nucleic acid and the inhibition of thioredoxin reductase in PC3 prostate cancer cells. The heterometallic compounds, which are highly apoptotic, exhibit strong antimigratory effects on the prostate cancer cell line PC3. PMID:27182101

  14. Angina Pectoris (Stable Angina)

    MedlinePlus

    ... Pressure High Blood Pressure Tools & Resources Stroke More Angina Pectoris (Stable Angina) Updated:Aug 24,2016 You may have heard the term “angina pectoris” or “stable angina” in your doctor’s office, but ...

  15. N,N'-dialkylimidazolium chloroplatinate(II), chloroplatinate(IV), and chloroiridate(IV) salts and an N-heterocyclic carbene complex of platinum(II): synthesis in ionic liquids and crystal structures.

    PubMed

    Hasan, M; Kozhevnikov, I V; Siddiqui, M R; Femoni, C; Steiner, A; Winterton, N

    2001-02-12

    The first imidazole-type carbene complex of platinum(II), cis-(C2H4)(1-ethyl-3-methylimidazol-2-ylidene)PtCl2, has been obtained by reacting PtCl2 and PtCl4 with ethylene in the basic [EMIM]Cl/AlCl3 (1.3:1) ionic liquid (where [EMIM]+ = 1-ethyl-3-methylimidazolium) at 200 degrees C and structurally characterized (monoclinic P21/c space group, a = 10.416(2) A, b = 7.3421(9) A, c = 15.613(2) A, beta = 101.53(2) degrees, Z = 4). This complex can be regarded as a stable analogue of the pi-alkene-Pd(II)-carbene intermediate in the Heck reaction. In addition, a series of new N,N'-dialkylimidazolium salts of platinum group metals of the type [RMIM]2[MCln], where [RMIM+] = 1-alkyl-3-methylimidazolium and M = Pt(II), Pt(IV), or Ir(IV), have been prepared and characterized. The salts [EMIM]2[PtCl6] (1) and [EMIM]2[PtCl4] (2) were prepared in the ionic liquid [EMIM]Cl/AlCl3 and the salts [BMIM]2[PtCl4] (3) and [BMIM]2[PtCl6] (4) (where [BMIM]+ = 1-n-butyl-3-methylimidazolium) and [EMIM]2-[IrCl6] (5) in aqueous or acetonitrile media. From TGA measurements, salts 1-5 decompose in air in several steps eventually to form the corresponding metal, the onset of decomposition being observed at (degree C) 260 (1), 220 (2), 200 (3), 215 (4), and 210 (5). The structures of 1, 2, and 5 were determined by single-crystal X-ray analysis. The three salts crystallize in the monoclinic P21/n space group (1, a = 7.6433(9) A, b = 16.353(2) A, c = 9.213(1) A, beta = 113.56(1) degrees, Z = 2; 2, a = 8.601(1) A, b = 8.095(2) A, c = 13.977(2) A, beta = 91.75(2) degrees, Z = 2; 5, a = 10.353(2) A, b = 9.759(2) A, c = 10.371(2) A, beta = 92.98(3) degrees, Z = 2).

  16. Reactivity of cationic agostic and carbene structures derived from platinum(II) metallacycles.

    PubMed

    Campos, Jesús; Ortega-Moreno, Laura; Conejero, Salvador; Peloso, Riccardo; López-Serrano, Joaquín; Maya, Celia; Carmona, Ernesto

    2015-06-01

    This paper describes the formation of new platinacyclic complexes derived from the phosphine ligands PiPr2 Xyl, PMeXyl2 , and PMe2 Ar Xyl 2 (Xyl=2,6-Me2 C6 H3 and Ar Xyl 2=2,6-(2,6-Me2 C6 H3 )2 -C6 H3 ) as well as reactivity studies of the trans-[Pt(C^P)2 ] bis-metallacyclic complex 1 a derived from PiPr2 Xyl. Protonation of compound 1 a with [H(OEt2 )2 ][BArF ] (BArF =B[3,5-(CF3 )2 C6 H3 ]4 ) forms a cationic δ-agostic structure 4 a, whereas α-hydride abstraction employing [Ph3 C][PF6 ] produces a cationic platinum carbene trans-[Pt{PiPr2 (2,6-CH(Me)C6 H3 }{PiPr2 (2,6-CH2 (Me)C6 H3 }][PF6 ] (8). Compounds 4 a and 8 react with H2 to yield the same 1:3 equilibrium mixture of 4 a and trans-[PtH(PiPr2 Xyl)2 ][BArF ] (6), in which one of the phosphine ligands participates in a δ-agostic interaction. DFT calculations reveal that H2 activation by 8 occurs at the highly electrophilic alkylidene terminus with no participation of the metal. The two compounds 4 a and 8 experience C-C coupling reactions of a different nature. Thus, 4 a gives rise to complex trans-[PtH{(E)-1,2-bis(2-(PiPr2 )-3-MeC6 H3 )CHCH}] (7) that contains a tridentate diphosphine-alkene ligand, through agostic CH oxidative cleavage and C-C reductive coupling steps, whereas the C-C coupling reaction in 8 involves classical migratory insertion of its [PtCH] and [PtCH2 ] bonds promoted by platinum coordination of CO or CNXyl. The mechanisms of the CC bond-forming reactions have also been investigated by computational methods. PMID:25959723

  17. Reactivity of cationic agostic and carbene structures derived from platinum(II) metallacycles.

    PubMed

    Campos, Jesús; Ortega-Moreno, Laura; Conejero, Salvador; Peloso, Riccardo; López-Serrano, Joaquín; Maya, Celia; Carmona, Ernesto

    2015-06-01

    This paper describes the formation of new platinacyclic complexes derived from the phosphine ligands PiPr2 Xyl, PMeXyl2 , and PMe2 Ar Xyl 2 (Xyl=2,6-Me2 C6 H3 and Ar Xyl 2=2,6-(2,6-Me2 C6 H3 )2 -C6 H3 ) as well as reactivity studies of the trans-[Pt(C^P)2 ] bis-metallacyclic complex 1 a derived from PiPr2 Xyl. Protonation of compound 1 a with [H(OEt2 )2 ][BArF ] (BArF =B[3,5-(CF3 )2 C6 H3 ]4 ) forms a cationic δ-agostic structure 4 a, whereas α-hydride abstraction employing [Ph3 C][PF6 ] produces a cationic platinum carbene trans-[Pt{PiPr2 (2,6-CH(Me)C6 H3 }{PiPr2 (2,6-CH2 (Me)C6 H3 }][PF6 ] (8). Compounds 4 a and 8 react with H2 to yield the same 1:3 equilibrium mixture of 4 a and trans-[PtH(PiPr2 Xyl)2 ][BArF ] (6), in which one of the phosphine ligands participates in a δ-agostic interaction. DFT calculations reveal that H2 activation by 8 occurs at the highly electrophilic alkylidene terminus with no participation of the metal. The two compounds 4 a and 8 experience C-C coupling reactions of a different nature. Thus, 4 a gives rise to complex trans-[PtH{(E)-1,2-bis(2-(PiPr2 )-3-MeC6 H3 )CHCH}] (7) that contains a tridentate diphosphine-alkene ligand, through agostic CH oxidative cleavage and C-C reductive coupling steps, whereas the C-C coupling reaction in 8 involves classical migratory insertion of its [PtCH] and [PtCH2 ] bonds promoted by platinum coordination of CO or CNXyl. The mechanisms of the CC bond-forming reactions have also been investigated by computational methods.

  18. Ruthenium and osmium complexes of dihydroperimidine-based N-heterocyclic carbene pincer ligands.

    PubMed

    McQueen, Caitlin M A; Hill, Anthony F; Ma, Chenxi; Ward, Jas S

    2015-12-21

    The reactions of N,N'-bis(phosphinomethyl)dihydroperimidine pro-ligands H2C(NCH2PR2)2C10H6 (R = Cy 1a, R = Ph 1b) with [RuCl2(PPh3)3] give markedly different products. Chelate-assisted double C-H activation in the former affords the perimidinylidene-based N-heterocyclic carbene (per-NHC) pincer complex [RuCl2(OC4H8){κ(3)-P,C,P'-C(NCH2PCy2)2C10H6}] (2), while the latter reaction provides the asymmetric PNP-coordinated complex [RuCl2(PPh3){κ(3)-P,N,P'-CH2(NCH2PPh2)2C10H6}] (3), in which no C-H activation has occurred. Subsequent reactions of the per-NHC complex 2 with carbon monoxide and mesityl isocyanide readily displaced the labile THF ligand to afford the complexes [RuCl2(CA){κ(3)-P,C,P'-C(NCH2PCy2)2C10H6}] (A = O 4, A = NC6H2Me35). Double C-H activation of 1a and 1b was significantly more facile on reaction with [OsCl2(PPh3)3], providing the per-NHC complexes [OsHCl(PPh3){κ(3)-P,C,P'-C(NCH2PR2)2C10H6}] (R = Cy 7a, R = Ph 7b, respectively), each as two isomers. The reactions of 1b with [Ru2(μ-Cl)2Cl2(η-C6H3Me3)2] or [AuCl(THT)] (THT = tetrahydrothiophene) provide the bimetallic complexes [Ru2{μ-H2C(NCH2PPh2)2C10H6}Cl4(η-C6H3Me3)2] (8) and [Au2{μ-H2C(NCH2PPh2)2C10H6}Cl2] (9) without C-H activation occurring. PMID:26492361

  19. Accessible gold clusters using calix[4]arene N-heterocyclic carbene and phosphine ligands.

    PubMed

    Nigra, Michael M; Yeh, Alexander J; Okrut, Alexander; DiPasquale, Antonio G; Yeh, Sheila W; Solovyov, Andrew; Katz, Alexander

    2013-09-21

    We investigate the synthesis of accessible calix[4]arene-bound gold clusters consisting of open "coordinatively unsaturated" active sites, using a comparative approach that relies on calix[4]arene ligands with various upper- and lower-rim substituents. In contrast with a reported Au(I)-tert-butyl-calixarene phosphine complex, which exhibits a single cone conformer in solution, the H upper-rim analog exhibits multiple conformers in solution. This contrasts with observations of the tert-butyl upper-rim analog, which exhibits a single cone conformer in solution under similar conditions. In the solid state, as determined by single-crystal X-ray diffraction, both H and tert-butyl upper-rim analogs exhibit exclusively cone conformer. A detailed structural analysis of these two solid-state structures highlights a CH-π interaction involving a methoxy lower-rim substituent and phenyl substituent on P as the key feature that enforces a tight configuration of Au(I) atoms on the same side of the calix[4]arene lower-rim plane. We hypothesize that such a configuration promotes chelation of the ligand to a gold surface and facilitates the synthesis of small Au11-sized clusters after reduction of both complexes. The new cluster, like the one reported with the tert-butyl analog, has an extraordinary 25% of surface atoms that are open and accessible to a 2-NT (2-naphthalenethiol) probe in solution. We also investigated the effect of calix[4]arene lower-rim substituents that coordinate to the metal, by using N-heterocyclic carbene (NHC) functional groups rather than phosphines. Four small (<1.6 nm diameter) calix[4]arene NHC-bound gold clusters were synthesized, including three using novel calix[4]arene NHC ligands. The smallest calix[4]arene NHC-bound Au cluster consisted of a 1.2 nm gold core, and its number density of accessible and open surface sites was measured. This required development of a new titration method for open sites on gold clusters, using a SAMSA fluorescein dye

  20. Palladium/N-heterocyclic carbene catalysed regio and diastereoselective reaction of ketones with allyl reagents via inner-sphere mechanism

    PubMed Central

    Bai, Da-Chang; Yu, Fei-Le; Wang, Wan-Ying; Chen, Di; Li, Hao; Liu, Qing-Rong; Ding, Chang-Hua; Chen, Bo; Hou, Xue-Long

    2016-01-01

    The palladium-catalysed allylic substitution reaction is one of the most important reactions in transition-metal catalysis and has been well-studied in the past decades. Most of the reactions proceed through an outer-sphere mechanism, affording linear products when monosubstituted allyl reagents are used. Here, we report an efficient Palladium-catalysed protocol for reactions of β-substituted ketones with monosubstituted allyl substrates, simply by using N-heterocyclic carbene as ligand, leading to branched products with up to three contiguous stereocentres in a (syn, anti)-mode with excellent regio and diastereoselectivities. The scope of the protocol in organic synthesis has been examined preliminarily. Mechanistic studies by both experiments and density functional theory (DFT) calculations reveal that the reaction proceeds via an inner-sphere mechanism—nucleophilic attack of enolate oxygen on Palladium followed by C–C bond-forming [3,3']-reductive elimination. PMID:27283477

  1. Unexpected anion effect in the alkoxylation of alkynes catalyzed by N-heterocyclic carbene (NHC) cationic gold complexes.

    PubMed

    Biasiolo, Luca; Trinchillo, Marina; Belanzoni, Paola; Belpassi, Leonardo; Busico, Vincenzo; Ciancaleoni, Gianluca; D'Amora, Angela; Macchioni, Alceo; Tarantelli, Francesco; Zuccaccia, Daniele

    2014-11-01

    The intermolecular alkoxylation of alkynes is the oldest application of cationic gold(I) catalysts; however, no systematic experimental data about the role of the anion are available. In this contribution, the role of the anion in this catalytic reaction as promoted by a N-heterocyclic carbene-based gold catalyst, [(NHC)AuX] (X=BARF(-) , BF4 (-) , OTf(-) , OTs(-) , TFA(-) , or OAc(-) ) is analyzed, through a combined experimental (NMR spectroscopy) and theoretical (DFT calculation) approach. The most important factor seems to be the ability to abstract the proton from the methanol during the nucleophilic attack, and such ability is related to the anion basicity. On the other hand, too high coordination power or basicity of the anion worsens the catalytic performance by preventing alkyne coordination or by forming too much free methoxide in solution, which poisons the catalyst. The intermediate coordinating power and basicity of the OTs(-) anion provides the best compromise to achieve efficient catalysis. PMID:25263571

  2. High-throughput screening of metal-N-heterocyclic carbene complexes against biofilm formation by pathogenic bacteria.

    PubMed

    Bernardi, Thierry; Badel, Stéphanie; Mayer, Pascal; Groelly, Jérome; de Frémont, Pierre; Jacques, Béatrice; Braunstein, Pierre; Teyssot, Marie-Laure; Gaulier, Christelle; Cisnetti, Federico; Gautier, Arnaud; Roland, Sylvain

    2014-06-01

    A set of molecules including a majority of metal-N-heterocyclic carbene (NHC) complexes (metal=Ag, Cu, and Au) and azolium salts were evaluated by high-throughput screening of their activity against biofilm formation associated with pathogenic bacteria. The anti-planktonic effects were compared in parallel. Representative biofilm-forming strains of various genera were selected (Listeria, Pseudomonas, Staphylococcus, and Escherichia). All the compounds were tested at 1 mg L(-1) by using the BioFilm Ring Test. An information score (IS, sum of the activities) and an activity score (AS, difference between anti-biofilm and anti-planktonic activity) were determined from normalized experimental values to classify the most active molecules against the panel of bacterial strains. With this method we identified lipophilic Ag(I) and Cu(I) complexes possessing aromatic groups on the NHC ligand as the most efficient at inhibiting biofilm formation. PMID:24729552

  3. Nitrenium ions and trivalent boron ligands as analogues of N-heterocyclic carbenes in olefin metathesis: a computational study.

    PubMed

    Pazio, A; Woźniak, K; Grela, K; Trzaskowski, B

    2015-12-14

    We used the density functional theory to evaluate the suitability of nitrenium ions and trivalent boron ligands as analogues of N-heterocyclic carbenes in ruthenium-based metathesis catalysts. We demonstrate that these analogues induce only minor structural changes in Hoveyda-Grubbs-like precatalysts, but have major impact on precatalyst initiation. Nitrenium ion-modified precatalysts are characterized by a weak Ru-N bond resulting in a relatively strong Ru-O bond and large free energy barriers for initiation, making them good candidates for efficient latent Ru-based catalysts. On the other hand the trivalent boron ligand, bearing a formal -1 charge, binds strongly to the ruthenium ion, weakening the Ru-O bond and facilitating its dissociation, to promote fast reaction initiation. We show that the calculated bond dissociation energy of the Ru-C/N/B bond may serve as an accurate indicator of the Ru-O bond strength and the rate of metathesis initiation.

  4. Synthesis of palladium(0) and -(II) complexes with chelating bis(N-heterocyclic carbene) ligands and their application in semihydrogenation.

    PubMed

    Sluijter, Soraya N; Warsink, Stefan; Lutz, Martin; Elsevier, Cornelis J

    2013-05-28

    A transmetallation route, using silver(I) precursors, to several zero- and di-valent palladium complexes with chelating bis(N-heterocyclic carbene) ligands bearing various N-substituents has been established. The resulting complexes have been characterized by NMR and mass spectroscopy. In addition, the structure of a representative compound, [Pd(0)(bis-(Mes)NHC)(η(2)-ma)] (3a), was confirmed by X-ray crystal structure determination. In contrast to the transfer semihydrogenation, in which only low activity was observed, complex 3a showed activity (TOF = 49 mol(sub) mol(cat)(-1) h(-1)) and selectivity comparable to its monodentate counterparts in the semihydrogenation of 1-phenyl-1-propyne with molecular hydrogen.

  5. Stereodivergent Intramolecular C(sp(3))-H Functionalization of Azavinyl Carbenes: Synthesis of Saturated Heterocycles and Fused N-Heterotricycles.

    PubMed

    Lindsay, Vincent N G; Viart, Hélène M-F; Sarpong, Richmond

    2015-07-01

    A general approach for the formation of five-membered saturated heterocycles by intramolecular C(sp(3))-H functionalization is reported. Using N-sulfonyltriazoles as Rh(II) azavinyl carbene equivalents, a wide variety of stereodefined cis-2,3-disubstituted tetrahydrofurans were obtained with good to excellent diastereoselectivity from readily available acyclic precursors. The reaction is shown to be amenable to gram scale, and judicious choice of reaction conditions allowed for stereodivergence, providing selective access to the trans diastereomer in good yield. The resulting products were shown to be valuable intermediates for the direct preparation of fused N-heterotricycles in one step by intramolecular C-H amination or Pictet-Spengler cyclization. PMID:26096731

  6. Grubbs-Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids.

    PubMed

    Koy, Maximilian; Altmann, Hagen J; Autenrieth, Benjamin; Frey, Wolfgang; Buchmeiser, Michael R

    2015-01-01

    The novel dicationic metathesis catalyst [(RuCl2(H2ITapMe2)(=CH-2-(2-PrO)-C6H4))(2+) (OTf(-))2] (Ru-2, H2ITapMe2 = 1,3-bis(2',6'-dimethyl-4'-trimethylammoniumphenyl)-4,5-dihydroimidazol-2-ylidene, OTf(-) = CF3SO3 (-)) based on a dicationic N-heterocyclic carbene (NHC) ligand was prepared. The reactivity was tested in ring opening metathesis polymerization (ROMP) under biphasic conditions using a nonpolar organic solvent (toluene) and the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM(+)][BF4 (-)]. The structure of Ru-2 was confirmed by single crystal X-ray analysis.

  7. N-Heterocyclic Carbene-Polyethylenimine Platinum Complexes with Potent in Vitro and in Vivo Antitumor Efficacy.

    PubMed

    Chekkat, Neila; Dahm, Georges; Chardon, Edith; Wantz, May; Sitz, Justine; Decossas, Marion; Lambert, Olivier; Frisch, Benoit; Rubbiani, Riccardo; Gasser, Gilles; Guichard, Gilles; Fournel, Sylvie; Bellemin-Laponnaz, Stéphane

    2016-08-17

    The current interest for platinum N-heterocyclic carbene complexes in cancer research stems from their impressive toxicity reported against a range of different human cancer cells. To date, the demonstration of their in vivo efficacy relative to that of established platinum-based drugs has not been specifically addressed. Here, we introduce an innovative approach to increase the NHC-Pt complex potency whereby multiple NHC-Pt(II) complexes are coordinated along a polyethylenimine polymer (PEI) chain. We show that such NHC-Pt(II)-PEI conjugates induce human cancer cell death in vitro and in vivo in a xenograft mouse model with no observable side effects in contrast to oxaliplatin. Additional studies indicate nucleus and mitochondria targeting and suggest various mechanisms of action compared to classical platinum-based anticancer drugs. PMID:27459208

  8. Grubbs–Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids

    PubMed Central

    Koy, Maximilian; Altmann, Hagen J; Autenrieth, Benjamin; Frey, Wolfgang

    2015-01-01

    Summary The novel dicationic metathesis catalyst [(RuCl2(H2ITapMe2)(=CH–2-(2-PrO)-C6H4))2+ (OTf−)2] (Ru-2, H2ITapMe2 = 1,3-bis(2’,6’-dimethyl-4’-trimethylammoniumphenyl)-4,5-dihydroimidazol-2-ylidene, OTf− = CF3SO3 −) based on a dicationic N-heterocyclic carbene (NHC) ligand was prepared. The reactivity was tested in ring opening metathesis polymerization (ROMP) under biphasic conditions using a nonpolar organic solvent (toluene) and the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM+][BF4 −]. The structure of Ru-2 was confirmed by single crystal X-ray analysis. PMID:26664582

  9. Grubbs-Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids.

    PubMed

    Koy, Maximilian; Altmann, Hagen J; Autenrieth, Benjamin; Frey, Wolfgang; Buchmeiser, Michael R

    2015-01-01

    The novel dicationic metathesis catalyst [(RuCl2(H2ITapMe2)(=CH-2-(2-PrO)-C6H4))(2+) (OTf(-))2] (Ru-2, H2ITapMe2 = 1,3-bis(2',6'-dimethyl-4'-trimethylammoniumphenyl)-4,5-dihydroimidazol-2-ylidene, OTf(-) = CF3SO3 (-)) based on a dicationic N-heterocyclic carbene (NHC) ligand was prepared. The reactivity was tested in ring opening metathesis polymerization (ROMP) under biphasic conditions using a nonpolar organic solvent (toluene) and the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM(+)][BF4 (-)]. The structure of Ru-2 was confirmed by single crystal X-ray analysis. PMID:26664582

  10. Understanding the mechanism of stereoselective synthesis of cyclopentenes via N-heterocyclic carbene catalyzed reactions of enals with enones.

    PubMed

    Domingo, Luis R; Zaragozá, Ramón J; Arnó, Manuel

    2010-11-01

    The N-heterocyclic carbene (NHC) catalyzed addition of enals to enones to yield trans-cyclopentenes has been investigated using DFT methods at B3LYP/6-31G** computational level. This NHC catalyzed reaction comprises several steps. The first one is the formation of a Breslow intermediate, which nucleophilically attacks to the conjugated position of the enone to yield an enol-enolate. This second step is responsible for the trans relationship at the final cyclopentene. An intramolecular aldolic condensation allows for the formation of the alkoxy cyclopentane intermediate, that by intramolecular nucleophilic attack on the carbonyl group yields a bicyclic ether. The extrusion of the NHC catalyst affords a bicyclic lactone, yielding by CO(2) elimination, the final trans-cyclopentene.

  11. Metal-metal interaction in Fischer carbene complexes: a study of ferrocenyl and biferrocenyl tungsten alkylidene complexes.

    PubMed

    van der Westhuizen, Belinda; Speck, J Matthäus; Korb, Marcus; Friedrich, Joachim; Bezuidenhout, Daniela I; Lang, Heinrich

    2013-12-16

    A series of ferrocenyl (Fc = ferrocenyl; fc = ferrocen-1,1'-diyl) and biferrocenyl (Bfc = 1',1″-biferrocenyl; bfc = 1',1″-biferrocen-1,1‴-diyl) mono- and biscarbene tungsten(0) complexes of the type [(CO)5W═C(OMe)R] (1, R = Fc; 3, R = Bfc) and [(CO)5W═C(OMe)-R'-(OMe)C═W(CO)5] (2, R' = fc; 4, R' = bfc) were synthesized according to the classical synthetic methodology by reacting W(CO)6 with LiR (R = Fc, fc, bfc), followed by a subsequent alkylation using methyl trifluoromethanesulfonate. Electrochemical investigations were carried out on these complexes to get a closer insight into the electronic properties of 1-4. The ferrocenyl and biferrocenyl moieties in 1-4 show reversible one-electron redox events. It was further found that the Fischer carbene unit is reducible in an electrochemical one-electron transfer process. For the tungsten carbonyl moieties, irreversible oxidation processes were found. In addition, charge transfer studies were performed on 1-4 using in situ UV-vis-NIR and infrared spectroelectrochemical techniques. During the UV-vis-NIR investigations, typical low energy transitions for the mixed-valent biferrocenyl unit were found. A further observed high energy NIR absorption is attributed to a metal-metal charge transfer transition between the tungsten carbonyl fragment and the ferrocenyl/biferrocenyl group in the corresponding oxidized states, which can be described as class II systems according to Robin and Day. This assignment was verified by infrared spectroelectrochemical studies. The electrochemical investigations are supported by density functional theory calculations. The structural properties of 1-4 in the solid state were investigated by single-crystal X-ray diffraction studies showing no substituent effects on bond lengths and angles. The biferrocenyl derivatives exhibit syn-conformation of the ferrocenyl and carbene building blocks.

  12. Carbene vs olefin products of C-H activation on ruthenium via competing alpha- and beta-H elimination.

    PubMed

    Kuznetsov, Vladimir F; Abdur-Rashid, Kamaluddin; Lough, Alan J; Gusev, Dmitry G

    2006-11-01

    Bulky pincer complexes of ruthenium are capable of C-H activation and H-elimination from the pincer ligand backbone to produce mixtures of olefin and carbene products. To characterize the products and determine the mechanisms of the C-H cleavage, reactions of [RuCl(2)(p-cymene)](2) with N,N'-bis(di-tert-butylphosphino)-1,3-diaminopropane (L1) and 1,3-bis(di-tert-butylphosphinomethyl)cyclohexane (L2) were studied using a combination of X-ray crystallography, NMR spectroscopy, and DFT computational techniques. The reaction of L1 afforded a mixture of an alkylidene, a Fischer carbene, and two olefin isomers of the 16-e monohydride RuHCl[(t)Bu(2)PNHC(3)H(4)NHPBu(t)(2)] (2), whereas the reaction of L2 gave two olefin and two alkylidene isomers of 16-e RuHCl[2,6-(CH(2)PBu(t)(2))(2)C(6)H(8)] (3), all resulting from dehydrogenations of the ligand backbone of L1 and L2. The key intermediates implicated in the C-H activation reactions were identified as 14-electron paramagnetic species RuCl(PCP), where PCP = cyclometalated L1 or L2. Thus the alpha- and beta-H elimination reactions of RuCl(PCP) involved spin change and were formally spin-forbidden. Hydrogenation of 2 and 3 afforded 16-electron dihydrides RuH(2)Cl(PCP) distinguished by a large quantum exchange coupling between the hydrides. PMID:17076513

  13. Well-defined N-heterocyclic carbenes-palladium(II) precatalysts for cross-coupling reactions.

    PubMed

    Marion, Nicolas; Nolan, Steven P

    2008-11-18

    Metal-catalyzed cross-coupling reactions, notably those permitting C-C bond formation, have witnessed a meteoritic development and are now routinely employed as a powerful synthetic tool both in academia and in industry. In this context, palladium is arguably the most studied transition metal, and tertiary phosphines occupy a preponderant place as ancillary ligands. Seriously challenging this situation, the use of N-heterocyclic carbenes (NHCs) as alternative ligands in palladium-catalyzed cross-coupling reactions is rapidly gaining in popularity. These two-electron donor ligands combine strong sigma-donating properties with a shielding steric pattern that allows for both stabilization of the metal center and enhancement of its catalytic activity. As a result, the number of well-defined NHC-containing palladium(II) complexes is growing, and their use in coupling reactions is witnessing increasing interest. In this Account, we highlight the advantages of this family of palladium complexes and review their synthesis and applications in cross-coupling chemistry. They generally exhibit high stability, allowing for indefinite storage and easy handling. The use of well-defined complexes permits a strict control of the Pd/ligand ratio (optimally 1/1), avoiding the use of excess costly ligand that usually requires end-game removal. Furthermore, it partly removes the "black box" character often associated with cross-coupling chemistry and catalyst formation. In the present Account, four main classes of NHC-containing palladium(II) complexes will be presented: palladium dimers with bridging halogens, palladacycles, palladium acetates and acetylacetonates, and finally pi-allyl complexes. These additional ligands are best described as a protecting shell that will be discarded going from the palladium(II) precatalyst to the palladium(0) true catalyst. The synthesis of all these precatalysts generally requires simple and short synthetic procedures. Their catalytic activity in

  14. On the mechanism of N-heterocyclic carbene-catalyzed reactions involving acyl azoliums.

    PubMed

    Mahatthananchai, Jessada; Bode, Jeffrey W

    2014-02-18

    Catalytic reactions promoted by N-heterocyclic carbenes (NHCs) have exploded in popularity since 2004 when several reports described new fundamental reactions that extended beyond the long-studied generation of acyl anion equivalents. These new NHC-catalyzed reactions allow chemists to generate unique reactive species from otherwise inert starting materials, all under simple, mild reaction conditions and with exceptional selectivities. In analogy to transition metal catalysis, the use of NHCs has introduced a new set of elementary steps that operate via discrete reactive species, including acyl anion, homoenolate, and enolate equivalents, usually generated by oxidation state reorganization ("redox neutral" reactions). Nearly all NHC-catalyzed reactions offer operationally simple reactions, proceed at room temperature without the need for stringent exclusion of air, and do not generate reaction byproducts. Variation of the catalyst or reaction conditions can profoundly influence reaction outcomes, and researchers can tune the desired selectivities through careful choice of NHC precursor and base. The catalytically generated homoenolate and enolate equivalents are nucleophilic species. In contrast, the catalytically generated acyl azolium and α,β-unsaturated acyl azoliums are electrophilic cationic species with unique and unprecedented chemistry. For example, when generated catalytically, these species transformed an α-functionalized aldehyde to an ester under redox neutral conditions without coupling reagents or waste. In addition to providing new approaches to catalytic esterifications, acyl azoliums offer unique reactivities that chemists can exploit for selective reactions. This Account focuses on the discovery and mechanistic investigation of the catalytic generation of acyl azoliums and α,β-unsaturated acyl azoliums. These chemical species are fascinating, and their catalytic generation is an important development. Studies of their unusual chemistry

  15. The development and catalytic uses of N-heterocyclic carbene gold complexes.

    PubMed

    Nolan, Steven P

    2011-02-15

    Gold has emerged as a powerful synthetic tool in the chemist's arsenal. From the early use of inorganic salts such as AuCl and AuCl(3) as catalysts, the field has evolved to explore ligands that fine-tune reactivity, stability, and, more recently, selectivity in gold-mediated processes. Substrates generally contain alkenes or alkynes, and they usually involve straightforward protocols in air with solvents that can often times be of technical grade. The actual catalytic species is the putative cationic gold(I) complex [Au(L)](+) (where L is a phosphorus-based species or N-heterocyclic carbene, NHC). The early gold systems bearing phosphine and phosphite ligands provided important transformations and served as useful mechanistic probes. More recently, the use of NHCs as ligands for gold has rapidly gained in popularity. These two-electron donor ligands combine strong σ-donating properties with a steric profile that allows for both stabilization of the metal center and enhancement of its catalytic activity. As a result, the gold-NHC complexes have been used as well-defined precatalysts and have permitted the isolation of reactive single-component systems that are now used instead of the initial [Au(L)Cl]/silver salt method. Because some are now commercially available, NHC-containing gold(I) complexes are gathering increasing interest. In this Account, we describe the chronological development of this chemistry in our laboratories, highlighting the advantages of this family of gold complexes and reviewing their synthesis and applications in catalysis. We first outline the syntheses, which are straightforward. The complexes generally exhibit high stability, allowing for indefinite storage and easy handling. We next consider catalysis, particularly examining efficacy in cycloisomerization, other skeletal rearrangements, addition of water to alkynes and nitriles, and C-H bond activation. These processes are quite atom-economical, and in the most recent C-H reactions the

  16. Alcohol-Induced C-N Bond Cleavage of Cyclometalated N-Heterocyclic Carbene Ligands with a Methylene-Linked Pendant Imidazolium Ring.

    PubMed

    Zhong, Wei; Fei, Zhaofu; Scopelliti, Rosario; Dyson, Paul J

    2016-08-16

    Reaction of the pentamethylcyclopentadienyl rhodium iodide dimer [Cp*RhI2 ]2 with 1,1'-diphenyl-3,3'-methylenediimidazolium diiodide in non-alcohol solvents, in the presence of base, led to the formation of bis-carbene complex [Cp*Rh(bis-NHC)I]I (bis-NHC=1,1'-diphenyl-4,4'-methylenediimidazoline-5,5'-diylidene). In contrast, when employing alcohols as the solvent in the same reaction, cleavage of a methylene C-N bond is observed, affording ether-functionalized (cyclometalated) carbene ligands coordinated to the metal center and the concomitant formation of complexes with a coordinated imidazole ligand. Studies employing other 1,1'-diimidazolium salts indicate that the cyclometalation step is a prerequisite for the activation/scission of the C-N bond and, based on additional experimental data, a SN 2 mechanism for the reaction is tentatively proposed. PMID:27412824

  17. Synthesis and anticancer activity of silver(I)-N-heterocyclic carbene complexes derived from the natural xanthine products caffeine, theophylline and theobromine.

    PubMed

    Mohamed, Heba A; Lake, Benjamin R M; Laing, Thomas; Phillips, Roger M; Willans, Charlotte E

    2015-04-28

    A new library of silver(I)-N-heterocyclic carbene complexes prepared from the natural products caffeine, theophylline and theobromine is reported. The complexes have been fully characterised using a combination of NMR spectroscopy, mass spectrometry, elemental analysis and X-ray diffraction analysis. Furthermore, the hydrophobicity of the complexes has been measured. The silver(I)-N-heterocyclic carbenes have been evaluated for their antiproliferative properties against a range of cancer cell lines of different histological types, and compared to cisplatin. The data shows different profiles of response when compared to cisplatin in the same panel of cells, indicating a different mechanism of action. Furthermore, it appears that the steric effect of the ligand and the hydrophobicity of the complex both play a role in the chemosensitivity of these compounds, with greater steric bulk and greater hydrophilicity delivering higher cytotoxicity.

  18. An Electronic Rationale for Observed Initiation Rates in Ruthenium-Mediated Olefin Metathesis: Charge Donation in Phosphine And N-Heterocyclic Carbene Ligands

    SciTech Connect

    Getty, K.; Delgado-Jaime, M.U.; Kennepohl, P.

    2009-06-01

    Ru K-edge XAS data indicate that second generation ruthenium-based olefin metathesis precatalysts (L = N-heterocyclic carbene) possess a more electron-deficient metal center than in the corresponding first generation species (L = tricyclohexylphosphine). This surprising effect is also observed from DFT calculations and provides a simple rationale for the slow phosphine dissociation kinetics previously noted for second-generation metathesis precatalysts.

  19. Catalytic functionalization of low reactive C(sp(3))-H and C(sp(2))-H bonds of alkanes and arenes by carbene transfer from diazo compounds.

    PubMed

    Caballero, Ana; Díaz-Requejo, M Mar; Fructos, Manuel R; Olmos, Andrea; Urbano, Juan; Pérez, Pedro J

    2015-12-21

    The direct functionalization of low reactive C(sp(3))-H and C(sp(2))-H bonds of alkanes and arenes, respectively, by metal-induced carbene transfer from diazo compounds is reviewed. To date, this methodology has enabled the incorporation of CR(1)R(2) moieties from N2[double bond, length as m-dash]CR(1)R(2) in a chemo, regio, enantio or diastereoselective manner in those substrates with the appropriate selection of metal and ligands.

  20. An N-Heterocyclic Carbene-Catalyzed Oxidative γ-Aminoalkylation of Saturated Carboxylic Acids through in Situ Activation Strategy: Access to δ-Lactam.

    PubMed

    Que, Yonglei; Xie, Yuanwei; Li, Tuanjie; Yu, Chenxia; Tu, Shujiang; Yao, Changsheng

    2015-12-18

    An N-Heterocyclic Carbene (NHC)-catalyzed oxidative formal [4 + 2] annulation of acylhydrazones with saturated carboxylic acids bearing γ-H to assemble δ-lactams featuring a chiral carbon stereogenic center was developed through an in situ activation strategy. The ready availability of the starting materials, excellent enantioselectivity, facile assembly, high yields, and potential biological significance of the final products make this protocol an attractive alternative for the construction of the pyridinone scaffold. PMID:26646554

  1. Metal-ligand bifunctional reactivity and catalysis of protic N-heterocyclic carbene and pyrazole complexes featuring β-NH units.

    PubMed

    Kuwata, Shigeki; Ikariya, Takao

    2014-11-28

    Metal-ligand bifunctional cooperation has attracted much attention because it offers a powerful methodology to realize a number of highly efficient and selective catalysts. In this article, recent developments in the metal-ligand cooperative reactions of protic N-heterocyclic carbene (NHC) and pyrazole complexes bearing an acidic NH group at the position β to the metal are surveyed. Protic 2-pyridylidenes as related cooperating non-innocent ligands are also described.

  2. Luminescent Ruthenium(II) Complex Bearing Bipyridine and N-Heterocyclic Carbene-based C∧N∧C Pincer Ligand for Live-Cell Imaging of Endocytosis

    NASA Astrophysics Data System (ADS)

    Tsui, Wai-Kuen; Chung, Lai-Hon; Wong, Matthew Man-Kin; Tsang, Wai-Him; Lo, Hoi-Shing; Liu, Yaxiang; Leung, Chung-Hang; Ma, Dik-Lung; Chiu, Sung-Kay; Wong, Chun-Yuen

    2015-03-01

    Luminescent ruthenium(II)-cyanide complex with N-heterocyclic carbene pincer ligand C∧N∧C = 2,6-bis(1-butylimidazol-2-ylidene)pyridine and 2,2'-bipyridine (bpy) shows minimal cytotoxicity to both human breast carcinoma cell (MCF-7) and human retinal pigmented epithelium cell (RPE) in a wide range of concentration (0.1-500 μM), and can be used for the luminescent imaging of endocytosis of the complex in these cells.

  3. Copper-Catalyzed Enantioselective Allyl-Allyl Coupling between Allylic Boronates and Phosphates with a Phenol/N-Heterocyclic Carbene Chiral Ligand.

    PubMed

    Yasuda, Yuto; Ohmiya, Hirohisa; Sawamura, Masaya

    2016-08-26

    Copper-catalyzed enantioselective allyl-allyl coupling between allylboronates and either Z-acyclic or cyclic allylic phosphates using a new chiral N-heterocyclic carbene ligand, bearing a phenolic hydroxy, is reported. This reaction occurs with exceptional SN 2'-type regioselectivities and high enantioselectivities to deliver chiral 1,5-diene derivatives with a tertiary stereogenic center at the allylic/homoallylic position. PMID:27467163

  4. Iridium(I) Compounds as Prospective Anticancer Agents: Solution Chemistry, Antiproliferative Profiles and Protein Interactions for a Series of Iridium(I) N-Heterocyclic Carbene Complexes.

    PubMed

    Gothe, Yvonne; Marzo, Tiziano; Messori, Luigi; Metzler-Nolte, Nils

    2016-08-22

    A series of structurally related mono- and bis-NHC-iridium(I) (NHC: N-heterocyclic carbene) complexes have been investigated for their suitability as potential anticancer drugs. Their spectral behaviour in aqueous buffers under physiological-like conditions and their cytotoxicity against the cancer cell lines MCF-7 and HT-29 are reported. Notably, almost all complexes exhibit significant cytotoxic effects towards both cancer cell lines. In general, the cationic bis-carbene complexes show higher stability and greater anticancer activity than their neutral mono-carbene analogues with IC50 values in the high nanomolar range. Furthermore, to gain initial mechanistic insight, the interactions of these iridium(I)-NHC complexes with two model proteins, namely lysozyme and cytochrome c, were explored by HR-ESI-MS analyses. The different protein metalation patterns of the complexes can be roughly classified into two distinct groups. Those interactions give us a first idea about the possible mechanism of action of this class of compounds. Overall, our findings show that iridium(I)-NHC complexes represent very interesting candidates for further development as new metal-based anticancer drugs.

  5. Iridium(I) Compounds as Prospective Anticancer Agents: Solution Chemistry, Antiproliferative Profiles and Protein Interactions for a Series of Iridium(I) N-Heterocyclic Carbene Complexes.

    PubMed

    Gothe, Yvonne; Marzo, Tiziano; Messori, Luigi; Metzler-Nolte, Nils

    2016-08-22

    A series of structurally related mono- and bis-NHC-iridium(I) (NHC: N-heterocyclic carbene) complexes have been investigated for their suitability as potential anticancer drugs. Their spectral behaviour in aqueous buffers under physiological-like conditions and their cytotoxicity against the cancer cell lines MCF-7 and HT-29 are reported. Notably, almost all complexes exhibit significant cytotoxic effects towards both cancer cell lines. In general, the cationic bis-carbene complexes show higher stability and greater anticancer activity than their neutral mono-carbene analogues with IC50 values in the high nanomolar range. Furthermore, to gain initial mechanistic insight, the interactions of these iridium(I)-NHC complexes with two model proteins, namely lysozyme and cytochrome c, were explored by HR-ESI-MS analyses. The different protein metalation patterns of the complexes can be roughly classified into two distinct groups. Those interactions give us a first idea about the possible mechanism of action of this class of compounds. Overall, our findings show that iridium(I)-NHC complexes represent very interesting candidates for further development as new metal-based anticancer drugs. PMID:27443984

  6. Synthesis and in vitro antitumor activity of water soluble sulfonate- and ester-functionalized silver(I) N-heterocyclic carbene complexes.

    PubMed

    Gandin, Valentina; Pellei, Maura; Marinelli, Marika; Marzano, Cristina; Dolmella, Alessandro; Giorgetti, Marco; Santini, Carlo

    2013-12-01

    The novel N-heterocyclic carbene ligand precursor NaHIm(PrSO3) (sodium 3,3'-(1H-imidazole-3-ium-1,3-diyl)dipropane-1-sulfonate) and the related silver carbene complex [Na4(Im(PrSO3))2]AgCl have been synthesized and characterized. Recrystallization of the analogous [Im(AcEt)]AgCl complex allowed the development of X-ray analysis which led to achieve relevant structural information concerning this silver(I) derivative. Both sulfonate- and ester-functionalized silver(I) N-heterocyclic carbenes (NHCs) were evaluated for their antiproliferative activities in a wide panel of human cancer cells. Complex [Na4(Im(PrSO3))2]AgCl showed a significant in vitro antiproliferative activity that was correlated with its strong ability to inhibit thioredoxin reductase. The inhibition of this selenoenzyme determined an alteration of the cellular redox environment thus leading to the induction of the apoptotic cell death through the activation of the ASK-1 pathway. PMID:24121303

  7. How stable are the 'stable ancient shields'?

    NASA Astrophysics Data System (ADS)

    Viola, Giulio; Mattila, Jussi

    2014-05-01

    "Archean cratons are relatively flat, stable regions of the crust that have remained undeformed since the Precambrian, forming the ancient cores of the continents" (King, EPSL, 2005). While this type of statement is supported by a wealth of constraints in the case of episodes of thoroughgoing ductile deformation affecting shield regions of Archean and also Peleoproterozoic age, a growing amount of research indicates that shields are not nearly as structurally stable within the broad field of environmental conditions leading to brittle deformation. In fact, old crystalline basements usually present compelling evidence of long brittle deformation histories, often very complex and challenging to unfold. Recent structural and geochronological studies point to a significant mechanical instability of the shield areas, wherein large volumes of 'stable' rocks actually can become saturated with fractures and brittle faults soon after regional cooling exhumes them to below c. 300-350° C. How cold, rigid and therefore strong shields respond to applied stresses remains, however, still poorly investigated and understood. This in turn precludes a better definition of the shallow rheological properties of large, old crystalline blocks. In particular, we do not yet have good constraints on the mechanisms of mechanical reactivation that control the partial (if not total) accommodation of new deformational episodes by preexisting structures, which remains a key to untangle brittle histories lasting several hundred Myr. In our analysis, we use the Svecofennian Shield (SS) as an example of a supposedly 'stable' region with Archean nucleii and Paleoproterozoic cratonic areas to show how it is possible to unravel the details of brittle histories spanning more than 1.5 Gyr. New structural and geochronological results from Finland are integrated with a review of existing data from Sweden to explore how the effects of far-field stresses are partitioned within a shield, which was growing

  8. Transient Palladadiphosphanylcarbenes: Singlet Carbenes with an “Inverse” Electronic Configuration (pπ2 instead of σ2) and Unusual Transannular Metal–Carbene Interactions (πC→pd Donation and σPd→C Back-donation)

    PubMed Central

    Vignolle, Joan; Gornitzka, Heinz; Maron, Laurent; Schoeller, Wolfgang W.; Bourissou, Didier; Bertrand, Guy

    2008-01-01

    Upon treatment with [PdCl(allyl)]2, asymmetrically substituted α, α′-diphosphanyl diazo compounds eliminate dinitrogen to afford C-chlorodiphosphanylmethanide complexes in high yields. In the presence of a chloride-abstracting agent, such as sodium tetraphenylborate, the C-chlorodiphosphanylmethanide complexes react with pyridine and trimethylphosphine, readily affording the corresponding nitrogen and phosphorus ylides. The postulated intermediate in this process, namely palladadiphosphanylcarbenes, could not be spectroscopically characterized, but their transient formation was chemically supported further by a Lewis base exchange reaction between pyridine and 4-dimethylaminopyridine. This hypothesis has also been substantiated by computing the corresponding dissociation energy using two model systems featuring methyl groups at the phosphorus. Of particular interest, density functional theory calculations reveal that these palladadiphosphanylcarbenes have a singlet ground state with an “inverse” pπ2 electronic configuration and a distorted geometry associated with unusual transannular metal–carbene interactions (πC→Pd donation and σPd→C back-donation). PMID:17243835

  9. Palladium/N-heterocyclic carbene catalysed regio and diastereoselective reaction of ketones with allyl reagents via inner-sphere mechanism

    DOE PAGESBeta

    Bai, Da -Chang; Yu, Fei -Le; Wang, Wan -Ying; Chen, Di; Li, Hao; Liu, Qing -Rong; Ding, Chang -Hua; Chen, Bo; Hou, Xue -Long

    2016-06-10

    The palladium-catalysed allylic substitution reaction is one of the most important reactions in transition-metal catalysis and has been well-studied in the past decades. Most of the reactions proceed through an outer-sphere mechanism, affording linear products when monosubstituted allyl reagents are used. Here, we report an efficient Palladium-catalysed protocol for reactions of beta-substituted ketones with monosubstituted allyl substrates, simply by using N-heterocyclic carbene as ligand, leading to branched products with up to three contiguous stereocentres in a (syn, anti)-mode with excellent regio and diastereoselectivities. The scope of the protocol in organic synthesis has been examined preliminarily. As a result, mechanistic studiesmore » by both experiments and density functional theory ( DFT) calculations reveal that the reaction proceeds via an inner-sphere mechanism-nucleophilic attack of enolate oxygen on Palladium followed by C-C bond-forming [3,3']-reductive elimination.« less

  10. Addition of N-heterocyclic carbenes to a ruthenium(VI) nitrido polyoxometalate: a new route to cyclic guanidines.

    PubMed

    Besson, Claire; Mirebeau, Jean-Hugues; Renaudineau, Séverine; Roland, Sylvain; Blanchard, Sébastien; Vezin, Hervé; Courillon, Christine; Proust, Anna

    2011-03-21

    The scope of N-atom transfer from the electrophilic ruthenium(VI) nitrido containing polyoxometalate [PW(11)O(39)Ru(VI)N](4-) has been extended to the N-heterocyclic carbene {CH(2)(Mes)N}(2)C and the coupling product {CH(2)(Mes)N}(2)CNH(2)(+) characterized by (1)H NMR and high-resolution mass spectrometry. Because guanidines display many fields of applications ranging from biology to supramolecular chemistry, this could afford an original route to the synthesis of cyclic guanidines. This also enlarges the potential of nitrido complexes in the synthesis of heterocycles, mainly illustrated in the literature through the formation of aziridines through N-atom transfer to alkenes. In the course of the reaction, the ruthenium(III)-containing polyoxometallic intermediate [PW(11)O(39)Ru(III){NC{N(Mes)CH(2)}(2)}](5-) has been thoroughly characterized by continuous-wave and pulsed electron paramagnetic resonance, which nicely confirms the presence of the organic moiety on the polyoxometallic framework, Ru K-edge X-ray absorption near-edge structure, and electrochemistry.

  11. A curious interplay in the films of N-heterocyclic carbene PtII complexes upon deposition of alkali metals

    PubMed Central

    Makarova, Anna A.; Grachova, Elena V.; Niedzialek, Dorota; Solomatina, Anastasia I.; Sonntag, Simon; Fedorov, Alexander V.; Vilkov, Oleg Yu.; Neudachina, Vera S.; Laubschat, Clemens; Tunik, Sergey P.; Vyalikh, Denis V.

    2016-01-01

    The recently synthesized series of PtII complexes containing cyclometallating (phenylpyridine or benzoquinoline) and N-heterocyclic carbene ligands possess intriguing structures, topologies, and light emitting properties. Here, we report curious physicochemical interactions between in situ PVD-grown films of a typical representative of the aforementioned PtII complex compounds and Li, Na, K and Cs atoms. Based on a combination of detailed core-level photoelectron spectroscopy and quantum-chemical calculations at the density functional theory level, we found that the deposition of alkali atoms onto the molecular film leads to unusual redistribution of electron density: essential modification of nitrogen sites, reduction of the coordination PtII centre to Pt0 and decrease of electron density on the bromine atoms. A possible explanation for this is formation of a supramolecular system “Pt complex-alkali metal ion”; the latter is supported by restoration of the system to the initial state upon subsequent oxygen treatment. The discovered properties highlight a considerable potential of the PtII complexes for a variety of biomedical, sensing, chemical, and electronic applications. PMID:27151364

  12. Emission properties and Cu(i)-Cu(i) interaction in 2-coordinate dicopper(i)-bis(N-heterocyclic)carbene complexes.

    PubMed

    Nishikawa, Michihiro; Sano, Taichi; Washimi, Masaya; Takao, Koichiro; Tsubomura, Taro

    2016-07-26

    The synthesis, characterization, and emission properties of 2-coordinate dicopper(i) complexes bearing two trimethylene-bridged bis-NHC ligands, [Cu2(L3Me)2](PF6)2 (1), [Cu2(L3Et)2](PF6)2 (2), [Cu2(L3Bu)2](PF6)2 (3), [Cu2(L3MeOPh)2](PF6)2 (4) and [Cu2(L3Mes)2](PF6)2 (5), where L3R denotes trimethylene-bridged bis(N-heterocyclic)carbene (NHC) ligand substituted by two R groups at the nitrogen atoms of NHC, have been investigated. The quantum yield, Φ, and the lifetime, τ, of the emission of 2, are 0.21 and 25 μs, respectively in methanol, which is a well-known solvent for quenching the luminescence of many copper(i) complexes. The 8-shaped geometry of the dicopper(i) complexes brings a considerable copper(i)-copper(i) interaction which affects the luminescent properties. Additionally, we find that methoxyphenyl and mesityl groups substituted at the nitrogen atom of the NHC moiety drastically stabilize the bis(NHC) copper(i) complexes even in air-saturated acetone-d6. PMID:27399152

  13. A curious interplay in the films of N-heterocyclic carbene Pt(II) complexes upon deposition of alkali metals.

    PubMed

    Makarova, Anna A; Grachova, Elena V; Niedzialek, Dorota; Solomatina, Anastasia I; Sonntag, Simon; Fedorov, Alexander V; Vilkov, Oleg Yu; Neudachina, Vera S; Laubschat, Clemens; Tunik, Sergey P; Vyalikh, Denis V

    2016-01-01

    The recently synthesized series of Pt(II) complexes containing cyclometallating (phenylpyridine or benzoquinoline) and N-heterocyclic carbene ligands possess intriguing structures, topologies, and light emitting properties. Here, we report curious physicochemical interactions between in situ PVD-grown films of a typical representative of the aforementioned Pt(II) complex compounds and Li, Na, K and Cs atoms. Based on a combination of detailed core-level photoelectron spectroscopy and quantum-chemical calculations at the density functional theory level, we found that the deposition of alkali atoms onto the molecular film leads to unusual redistribution of electron density: essential modification of nitrogen sites, reduction of the coordination Pt(II) centre to Pt(0) and decrease of electron density on the bromine atoms. A possible explanation for this is formation of a supramolecular system "Pt complex-alkali metal ion"; the latter is supported by restoration of the system to the initial state upon subsequent oxygen treatment. The discovered properties highlight a considerable potential of the Pt(II) complexes for a variety of biomedical, sensing, chemical, and electronic applications. PMID:27151364

  14. CO2 and Sn(II) adducts of N-heterocyclic carbenes as delayed-action catalysts for polyurethane synthesis.

    PubMed

    Bantu, Bhasker; Pawar, Gajanan Manohar; Decker, Ulrich; Wurst, Klaus; Schmidt, Axel M; Buchmeiser, Michael R

    2009-01-01

    Catalytic rivals: Both CO(2)-protected tetrahydropyrimidin-2-ylidene-based N-heterocyclic carbenes (NHCs) and Sn(II)-1,3-dimesitylimidazol-2-ylidene, as well as Sn(II)-1,3-dimesitylimidazolin-2-ylidene complexes (example displayed), have been identified as truly latent catalysts for polyurethane (PUR) synthesis rivaling all existing systems both in activity and latency.A series of CO(2)-protected pyrimidin-2-ylidenes as well as 1,3-dimesitylimidazol-2-ylidene and dimesitylimidazolin-2-ylidene complexes of Sn(II) have been prepared. Selected single-crystal X-ray structures are reported. The new compounds were investigated for their catalytic behavior in polyurethane (PUR) synthesis. All compounds investigated showed excellent catalytic activity, rivaling the industrially most relevant catalyst dibutyltin dilaurate. Even more important, all compounds displayed pronounced latent behavior, in selected cases rivaling and exceeding the industrially relevant latent catalyst phenylmercury neodecanoate both in terms of latency and catalytic activity. This allows for creating one-component PUR systems with improved pot lifetimes. Pseudo-second-order kinetics were found for both CO(2)-protected tetrahyropyrimidin-2-ylidenes and for [SnCl(2)(1,3-dimesityldihydroimidazol-2-ylidene)], indicating a fast pre-catalyst decomposition prior to polyurethane formation. 1,3-Di(2-propyl)tetrahydropyrimidin-2-ylidene was additionally found to be active in the cyclotrimerization of various isocyanates, offering access to a broad variability in polymer structure, that is, creating both urethane and isocyanurate moieties within the same polymer. PMID:19212991

  15. A monotopic aluminum telluride with an Al=Te double bond stabilized by N-heterocyclic carbenes

    PubMed Central

    Franz, Daniel; Szilvási, Tibor; Irran, Elisabeth; Inoue, Shigeyoshi

    2015-01-01

    Aluminum chalcogenides are mostly encountered in the form of bulk aluminum oxides that are structurally diverse but typically consist of networks with high lattice energy in which the chalcogen atoms bridge the metal centres. This makes their molecular congeners difficult to synthesize because of a pronounced tendency for oligomerization. Here we describe the isolation of the monotopic aluminum chalcogenide (LDipN)AlTe(LEt)2 (LDip=1,3-(2,6-diisopropylphenyl)-imidazolin-2-imine, LEt=1,3-diethyl-4,5-dimethyl-imidazolin-2-ylidene). Unique features of (LDipN)AlTe(LEt)2 are the terminal position of the tellurium atom, the shortest aluminum–tellurium distance hitherto reported for a molecular complex and the highest bond order reported for an interaction between these elements, to the best of our knowledge. At elevated temperature (LDipN)AlTe(LEt)2 equilibrates with dimeric {(LDipN)AlTe(LEt)}2 in which the chalcogen atoms assume their common role as bridges between the metal centres. These findings demonstrate that (LDipN)AlTe(LEt)2 comprises the elusive Al=Te double bond in the form of an N-heterocyclic carbene-stabilized species. PMID:26612781

  16. Traditional and ion-pair halogen-bonded complexes between chlorine and bromine derivatives and a nitrogen-heterocyclic carbene.

    PubMed

    Donoso-Tauda, Oscar; Jaque, Pablo; Elguero, José; Alkorta, Ibon

    2014-10-01

    A theoretical study of the halogen-bonded complexes (A-X···C) formed between halogenated derivatives (A-X; A = F, Cl, Br, CN, CCH, CF3, CH3, H; and X = Cl, Br) and a nitrogen heterocyclic carbene, 1,3-dimethylimidazole-2-ylidene (MeIC) has been performed using MP2/aug'-cc-pVDZ level of theory. Two types of A-X:MeIC complexes, called here type-I and -II, were found and characterized. The first group is described by long C-X distances and small binding energies (8-54 kJ·mol(-1)). In general, these complexes show the traditional behavior of systems containing halogen-bonding interactions. The second type is characterized by short C-X distances and large binding energies (148-200 kJ·mol(-1)), and on the basis of the topological analysis of the electron density, they correspond to ion-pair halogen-bonded complexes. These complexes can be seen as the interaction between two charged fragments: A(-) and (+)[X-CIMe] with a high electrostatic contribution in the binding energy. The charge transfer between lone pair A(LP) to the σ* orbital of C-X bond is also identified as a significant stabilizing interaction in type-II complexes.

  17. Stoichiometric sensitivity and structural diversity in click-active copper(I) N,S-heterocyclic carbene complexes.

    PubMed

    Han, Xiaoyan; Weng, Zhiqiang; Young, David James; Jin, Guo-Xin; Hor, T S Andy

    2014-01-21

    A series of novel Cu(I) N,S-heterocyclic carbene (NSHC) complexes [Cu(μ-Br)(NSHC)]2, [Cu(μ-X)(NSHC)]4 (X = Br or I), [(NSHC)2Cu(μ-Br)2Cu(NSHC)], and [(NSHC)2CuBr] have been isolated from in situ generated CuO(t)Bu and N-substituted benzothiazolium halides and characterized by X-ray crystallography. Five structural motifs were observed, viz. M(x)L(y) where x : y = 2 : 2, 4 : 4, 2 : 3, 1 : 2 and 2 : 4, with Cu···Cu separation traversing over a wide range of 2.5626(7) to 3.4725(7) Å distances. A preliminary investigation of the catalytic activity of these compounds indicated that the unusual mononuclear complex 6 [(NSHC)2CuBr] is an active catalyst for the Huisgen 1,3-dipolar cycloaddition of azide and alkynes while complexes 1-5 and 7 were marginally less active. PMID:24192930

  18. Nitrenium ions and trivalent boron ligands as analogues of N-heterocyclic carbenes in olefin metathesis: a computational study.

    PubMed

    Pazio, A; Woźniak, K; Grela, K; Trzaskowski, B

    2015-12-14

    We used the density functional theory to evaluate the suitability of nitrenium ions and trivalent boron ligands as analogues of N-heterocyclic carbenes in ruthenium-based metathesis catalysts. We demonstrate that these analogues induce only minor structural changes in Hoveyda-Grubbs-like precatalysts, but have major impact on precatalyst initiation. Nitrenium ion-modified precatalysts are characterized by a weak Ru-N bond resulting in a relatively strong Ru-O bond and large free energy barriers for initiation, making them good candidates for efficient latent Ru-based catalysts. On the other hand the trivalent boron ligand, bearing a formal -1 charge, binds strongly to the ruthenium ion, weakening the Ru-O bond and facilitating its dissociation, to promote fast reaction initiation. We show that the calculated bond dissociation energy of the Ru-C/N/B bond may serve as an accurate indicator of the Ru-O bond strength and the rate of metathesis initiation. PMID:26525899

  19. A curious interplay in the films of N-heterocyclic carbene PtII complexes upon deposition of alkali metals

    NASA Astrophysics Data System (ADS)

    Makarova, Anna A.; Grachova, Elena V.; Niedzialek, Dorota; Solomatina, Anastasia I.; Sonntag, Simon; Fedorov, Alexander V.; Vilkov, Oleg Yu.; Neudachina, Vera S.; Laubschat, Clemens; Tunik, Sergey P.; Vyalikh, Denis V.

    2016-05-01

    The recently synthesized series of PtII complexes containing cyclometallating (phenylpyridine or benzoquinoline) and N-heterocyclic carbene ligands possess intriguing structures, topologies, and light emitting properties. Here, we report curious physicochemical interactions between in situ PVD-grown films of a typical representative of the aforementioned PtII complex compounds and Li, Na, K and Cs atoms. Based on a combination of detailed core-level photoelectron spectroscopy and quantum-chemical calculations at the density functional theory level, we found that the deposition of alkali atoms onto the molecular film leads to unusual redistribution of electron density: essential modification of nitrogen sites, reduction of the coordination PtII centre to Pt0 and decrease of electron density on the bromine atoms. A possible explanation for this is formation of a supramolecular system “Pt complex-alkali metal ion” the latter is supported by restoration of the system to the initial state upon subsequent oxygen treatment. The discovered properties highlight a considerable potential of the PtII complexes for a variety of biomedical, sensing, chemical, and electronic applications.

  20. N-Heterocyclic Carbene-Ytterbium Amide as a Recyclable Homogeneous Precatalyst for Hydrophosphination of Alkenes and Alkynes.

    PubMed

    Yuan, Jia; Hu, Hongfan; Cui, Chunming

    2016-04-11

    The N-heterocyclic carbene-ytterbium(II) amides (NHC)2Yb[N(SiMe3)2]2 (1: NHC: 1,3,4,5-tetramethylimidazo-2-ylidene (IMe4); 2: NHC: 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (IiPr)) and the NHC-stabilized rare-earth phosphide (IMe4)3Yb(PPh2)2 (3) have been synthesized and fully characterized. Complexes 1-3 are active precatalysts for the hydrophosphination of alkenes, alkynes, and dienes and exhibited much superior catalytic activity to that of the NHC-free amide (THF)2Yb[N(SiMe)2]2. Complex 1 is the most active precursor among the three complexes. In particular, complex 1 can be recycled and recovered from the reaction media after the catalytic reactions. Furthermore, it was found that complex 3 could catalyze the polymerization of styrene to yield atactic polystyrenes with low molecular weights. To the best of our knowledge, complex 1 represents the first rare-earth complex that can be recovered after catalytic reactions. PMID:26934571

  1. The Stable Pairing Problem

    ERIC Educational Resources Information Center

    Greenwell, Raymond N.; Seabold, Daniel E.

    2014-01-01

    The Gale-Shapley stable marriage theorem is a fascinating piece of twentieth-century mathematics that has many practical applications--from labor markets to school admissions--yet is accessible to secondary school mathematics students. David Gale and Lloyd Shapley were both mathematicians and economists who published their work on the Stable…

  2. Stable Ejection Seat

    NASA Technical Reports Server (NTRS)

    Hirsch, R. S.

    1986-01-01

    Drogue chute for ejection seat slows down seat in more stable fashion than conventional parachutes and thus improves chances for survival. Square drogue linked to seat from its corners suppresses tendency of seat to rotate in pitch and yaw. New parachute expected to reduce dynamic forces on ejected person and extend maximum possible ejection altitude by 50 percent. Used at high or low speeds.

  3. Stable Unhappy Marriages.

    ERIC Educational Resources Information Center

    Heaton, Tim B.; Albrecht, Stan L.

    1991-01-01

    Examined prevalence and determinants of stable unhappy marriage using data from national survey. Results indicated age, lack of prior marital experience, commitment to marriage as an institution, low social activity, lack of control over one's life, and belief that divorce would detract from happiness were all predictive of stability in unhappy…

  4. Stable isotope studies

    SciTech Connect

    Ishida, T.

    1992-01-01

    The research has been in four general areas: (1) correlation of isotope effects with molecular forces and molecular structures, (2) correlation of zero-point energy and its isotope effects with molecular structure and molecular forces, (3) vapor pressure isotope effects, and (4) fractionation of stable isotopes. 73 refs, 38 figs, 29 tabs.

  5. Detailed analysis of pro-apoptotic signaling and metabolic adaptation triggered by a N-heterocyclic carbene-gold(I) complex.

    PubMed

    Holenya, Pavlo; Can, Suzan; Rubbiani, Riccardo; Alborzinia, Hamed; Jünger, Anja; Cheng, Xinlai; Ott, Ingo; Wölfl, Stefan

    2014-09-01

    Due to their broad spectrum of biological activity and antiproliferative effect on different human cancer cell lines, gold compounds have been in the focus of drug research for many years. Gold(I)-N-heterocyclic carbene complexes are of particular interest, because of their stability, ease of derivatization and clear cytotoxicity in cancer cells. To obtain a more detailed view of the molecular mechanisms underlying their cellular activity, we used a novel gold(I)-N-heterocyclic carbene complex, [triphenylphosphane-(1,3-diethyl-5-methoxy-benzylimidazol-2-ylidene)]gold(I) iodide and investigated changes in cellular signaling pathways using quantitative signal transduction protein microarray analysis. We also analyzed changes in cell metabolism in a time-dependent manner by on-line metabolic measurements and used isolated mitochondria to elucidate the direct effects on this cell organelle. We found strong cytotoxic effects in cancer cells, accompanied by an immediate and irreversible loss of mitochondrial respiration as well as by a crucial imbalance of the intracellular redox state, resulting in apoptotic cell death. ELISA microarray analysis of signal transduction pathways revealed a time-dependent up-regulation of pro-apoptotic signaling proteins, e.g. p38 and JNK, whereas pro-survival signals that are directly linked to the thioredoxin system were down-regulated, which pinpoints to thioredoxin reductase as a central target of the compound. Further results suggest that DNA is an indirect target of the compound. Based on our findings, we outline a signaling model for the molecular mechanism underlying the antiproliferative activity of the gold(I)-N-heterocyclic carbene complex investigated, which provides a good general model for the known pattern of cell death induced by this class of substances.

  6. Handbook of stable strontium

    SciTech Connect

    Skoryna, S.C.

    1981-01-01

    This book presents information on the following topics: chemistry of strontium; biogeochemistry of strontium; uptake of stable strontium by plants and effects on plant growth; divalent cation-dependent deposits in paramecium; effects of strontium ion on the hydrolysis of ATP; stronium ions and membranes - screening versus binding at charged surfaces; mitochondrial granules in the liver of rats kept on stable strontium supplementation; divalent cations and regulation of cyclic nucleotides in nervous systems; strontium as the substitute for calcium in the excitation-contraction coupling of crayfish muscle fibers; hemodynamic effects of strontium in the dog; some mechanical characteristics of strontium-mediated contractions in heart muscle; effects of calcium, magnesium, and strontium on drug-receptor interactions; strontium and histamine secretion; and effects of strontium in human dental enamel.

  7. Stable glow discharge detector

    DOEpatents

    Koo, Jackson C.; Yu, Conrad M.

    2004-05-18

    A highly sensitive electronic ion cell for the measurement of trace elements in He carrier gas which involves glow discharge. A constant wave (CW) stable glow discharge detector which is controlled through a biased resistor, can detect the change of electron density caused by impurities in the He carrier gas by many orders of magnitude larger than that caused by direct ionization or electron capture. The stable glow discharge detector utilizes a floating pseudo-electrode to form a probe in or near the plasma and a solid rod electrode. By using this probe, the large variation of electron density due to trace amounts of impurities can be directly measured. The solid rod electrode provides greater stability and thus easier alignment.

  8. Stable isotopes in mineralogy

    USGS Publications Warehouse

    O'Neil, J.R.

    1977-01-01

    Stable isotope fractionations between minerals are functions of the fundamental vibrational frequencies of the minerals and therefore bear on several topics of mineralogical interest. Isotopic compositions of the elements H, C, O, Si, and S can now be determined routinely in almost any mineral. A summary has been made of both published and new results of laboratory investigations, analyses of natural materials, and theoretical considerations which bear on the importance of temperature, pressure, chemical composition and crystal structure to the isotopic properties of minerals. It is shown that stable isotope studies can sometimes provide evidence for elucidating details of crystal structure and can be a powerful tool for use in tracing the reaction paths of mineralogical reactions. ?? 1977 Springer-Verlag.

  9. Stable local oscillator module.

    SciTech Connect

    Brocato, Robert Wesley

    2007-11-01

    This report gives a description of the development of a Stable Local Oscillator (StaLO) multi-chip module (MCM). It is a follow-on report to SAND2006-6414, Stable Local Oscillator Microcircuit. The StaLO accepts a 100MHz input signal and produces output signals at 1.2, 3.3, and 3.6 GHz. The circuit is built as a multi-chip module (MCM), since it makes use of integrated circuit technologies in silicon and lithium niobate as well as discrete passive components. This report describes the development of an MCM-based version of the complete StaLO, fabricated on an alumina thick film hybrid substrate.

  10. Stable Charged Cosmic Strings

    SciTech Connect

    Weigel, H.; Quandt, M.; Graham, N.

    2011-03-11

    We study the quantum stabilization of a cosmic string by a heavy fermion doublet in a reduced version of the standard model. We show that charged strings, obtained by populating fermionic bound state levels, become stable if the electroweak bosons are coupled to a fermion that is less than twice as heavy as the top quark. This result suggests that extraordinarily large fermion masses or unrealistic couplings are not required to bind a cosmic string in the standard model. Numerically we find the most favorable string profile to be a simple trough in the Higgs vacuum expectation value of radius {approx_equal}10{sup -18} m. The vacuum remains stable in our model, because neutral strings are not energetically favored.

  11. Stable charged cosmic strings.

    PubMed

    Weigel, H; Quandt, M; Graham, N

    2011-03-11

    We study the quantum stabilization of a cosmic string by a heavy fermion doublet in a reduced version of the standard model. We show that charged strings, obtained by populating fermionic bound state levels, become stable if the electroweak bosons are coupled to a fermion that is less than twice as heavy as the top quark. This result suggests that extraordinarily large fermion masses or unrealistic couplings are not required to bind a cosmic string in the standard model. Numerically we find the most favorable string profile to be a simple trough in the Higgs vacuum expectation value of radius ≈10(-18)  m. The vacuum remains stable in our model, because neutral strings are not energetically favored. PMID:21469786

  12. Highly Unsaturated Platinum and Palladium Carbenes PtC3 and PdC3 Isolated and Characterized in the Gas Phase

    PubMed Central

    Bittner, Dror M.; Zaleski, Daniel P.; Tew, David P.

    2016-01-01

    Abstract Carbenes of platinum and palladium, PtC3 and PdC3, were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and ab initio calculations confirm that both molecules are linear. The geometry of PtC3 was accurately determined by fitting to the experimental moments of inertia of twenty‐six isotopologues. The results are consistent with the proposal of an autogenic isolobal relationship between O, Au+, and Pt atoms. PMID:27478275

  13. Highly Unsaturated Platinum and Palladium Carbenes PtC3 and PdC3 Isolated and Characterized in the Gas Phase

    PubMed Central

    Bittner, Dror M.; Zaleski, Daniel P.; Tew, David P.

    2016-01-01

    Abstract Carbenes of platinum and palladium, PtC3 and PdC3, were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and ab initio calculations confirm that both molecules are linear. The geometry of PtC3 was accurately determined by fitting to the experimental moments of inertia of twenty‐six isotopologues. The results are consistent with the proposal of an autogenic isolobal relationship between O, Au+, and Pt atoms. PMID:26879473

  14. A general and regioselective synthesis of cyclopentenone derivatives through nickel(0)-mediated [3 + 2] cyclization of alkenyl Fischer carbene complexes and internal alkynes.

    PubMed

    Barluenga, José; Barrio, Pablo; Riesgo, Lorena; López, Luis A; Tomás, Miguel

    2007-11-21

    A broad range of substituted 2-cyclopentenone derivatives 3-6 are synthesized by the nickel(0)-mediated [3 + 2] cyclization reaction of chromium alkenyl(methoxy)carbene complexes 1 and internal alkynes 2. The reaction takes place with complete regioselectivity with both unactivated alkynes and activated alkynes (electron-withdrawing and electron-donating substituted alkynes). Representative cycloadducts containing boron and tin substituents are further demonstrated to be active partners in classical Pd-catalyzed C-C coupling processes to allow the production of 2-aryl- and 2-alkynyl-substituted cyclopentenones 9-13.

  15. N-Heterocyclic Carbenes as Promotors for the Rearrangement of Phosphaketenes to Phosphaheteroallenes: A Case Study for OCP to OPC Constitutional Isomerism.

    PubMed

    Li, Zhongshu; Chen, Xiaodan; Benkő, Zoltán; Liu, Liu; Ruiz, David A; Peltier, Jesse L; Bertrand, Guy; Su, Chen-Yong; Grützmacher, Hansjörg

    2016-05-10

    The concept of isomerism is essential to chemistry and allows defining molecules with an identical composition but different connectivity (bonds) between their atoms (constitutional isomers) and/or a different arrangement in space (stereoisomers). The reaction of phosphanyl ketenes, (NHP)-P=C=O (NHP=N-heterocyclic phosphenium) with N-heterocyclic carbenes (NHCs) leads to phosphaheteroallenes (NHP)-O-P=C=NHC in which the PCO unit has been isomerized to OPC. Based on the isolation of several intermediates and DFT calculations, a mechanism for this fundamental isomerisation process is proposed. PMID:27060924

  16. Highly Unsaturated Platinum and Palladium Carbenes PtC3 and PdC3 Isolated and Characterized in the Gas Phase

    DOE PAGESBeta

    Bittner, Dror M.; Zaleski, Daniel P.; Tew, David P.; Walker, Nicholas R.; Legon, Anthony C.

    2016-02-16

    Carbenes of platinum and palladium, PtC3 and PdC3 , were generated in the gas phase through laser vaporization of a metal target in the presence of a low concentration of a hydrocarbon precursor undergoing supersonic expansion. Rotational spectroscopy and abinitio calculations confirm that both molecules are linear. The geometry of PtC3 was accurately determined by fitting to the experimental moments of inertia of twenty-six isotopologues. In conclusion, the results are consistent with the proposal of an autogenic isolobal relationship between O, Au+ , and Ptatoms.

  17. Bulky N-Phosphino-Functionalized N-Heterocyclic Carbene Ligands: Synthesis, Ruthenium Coordination Chemistry, and Ruthenium Alkylidene Complexes for Olefin Metathesis.

    PubMed

    Brown, Christopher C; Rominger, Frank; Limbach, Michael; Hofmann, Peter

    2015-11-01

    Ruthenium chemistry and applications in catalytic olefin metathesis based on N-phosphino-functionalized N-heterocyclic carbene ligands (NHCPs) are presented. Alkyl NHCP Ru coordination chemistry is described, and access to several potential synthetic precursors for ruthenium alkylidene complexes is outlined, incorporating both trimethylsilyl and phenyl alkylidenes. The Ru alkylidene complexes are evaluated as potential olefin metathesis catalysts and were shown to behave in a latent fashion. They displayed catalytic activity at elevated temperatures for both ring closing metathesis and ring opening metathesis polymerization.

  18. α,β-Unsaturated Gold(I) Carbenes by Tandem Cyclization and 1,5-Alkoxy Migration of 1,6-Enynes: Mechanisms and Applications.

    PubMed

    Calleja, Pilar; Pablo, Óscar; Ranieri, Beatrice; Gaydou, Morgane; Pitaval, Anthony; Moreno, María; Raducan, Mihai; Echavarren, Antonio M

    2016-09-12

    1,6-Enynes bearing OR groups at the propargyl position generate α,β-unsaturated gold(I)-carbenes/ gold(I) stabilized allyl cations that can be trapped by alkenes to form cyclopropanes or 1,3-diketones to give products of α-alkylation. The best migrating group is p-nitrophenyl ether, which leads to the corresponding products without racemization. Thus, an improved formal synthesis of (+)-schisanwilsonene A has been accomplished. The different competitive reaction pathways have been delineated computationally.

  19. Anti-Markovnikov hydroheteroarylation of unactivated alkenes with indoles, pyrroles, benzofurans, and furans catalyzed by a nickel-N-heterocyclic carbene system.

    PubMed

    Schramm, York; Takeuchi, Makoto; Semba, Kazuhiko; Nakao, Yoshiaki; Hartwig, John F

    2015-09-30

    We report the catalytic addition of C-H bonds at the C2 position of heteroarenes, including pyrroles, indoles, benzofurans, and furans, to unactivated terminal and internal alkenes. The reaction is catalyzed by a combination of Ni(COD)2 and a sterically hindered, electron-rich N-heterocyclic carbene ligand or its analogous Ni(NHC)(arene) complex. The reaction is highly selective for anti-Markovnikov addition to α-olefins, as well as for the formation of linear alkylheteroarenes from internal alkenes. The reaction occurs with substrates containing ketones, esters, amides, boronate esters, silyl ethers, sulfonamides, acetals, and free amines. PMID:26334367

  20. Anti-Markovnikov hydroheteroarylation of unactivated alkenes with indoles, pyrroles, benzofurans, and furans catalyzed by a nickel-N-heterocyclic carbene system.

    PubMed

    Schramm, York; Takeuchi, Makoto; Semba, Kazuhiko; Nakao, Yoshiaki; Hartwig, John F

    2015-09-30

    We report the catalytic addition of C-H bonds at the C2 position of heteroarenes, including pyrroles, indoles, benzofurans, and furans, to unactivated terminal and internal alkenes. The reaction is catalyzed by a combination of Ni(COD)2 and a sterically hindered, electron-rich N-heterocyclic carbene ligand or its analogous Ni(NHC)(arene) complex. The reaction is highly selective for anti-Markovnikov addition to α-olefins, as well as for the formation of linear alkylheteroarenes from internal alkenes. The reaction occurs with substrates containing ketones, esters, amides, boronate esters, silyl ethers, sulfonamides, acetals, and free amines.

  1. Bulky N-Phosphino-Functionalized N-Heterocyclic Carbene Ligands: Synthesis, Ruthenium Coordination Chemistry, and Ruthenium Alkylidene Complexes for Olefin Metathesis.

    PubMed

    Brown, Christopher C; Rominger, Frank; Limbach, Michael; Hofmann, Peter

    2015-11-01

    Ruthenium chemistry and applications in catalytic olefin metathesis based on N-phosphino-functionalized N-heterocyclic carbene ligands (NHCPs) are presented. Alkyl NHCP Ru coordination chemistry is described, and access to several potential synthetic precursors for ruthenium alkylidene complexes is outlined, incorporating both trimethylsilyl and phenyl alkylidenes. The Ru alkylidene complexes are evaluated as potential olefin metathesis catalysts and were shown to behave in a latent fashion. They displayed catalytic activity at elevated temperatures for both ring closing metathesis and ring opening metathesis polymerization. PMID:26479425

  2. Luminescent Ruthenium(II) Complex Bearing Bipyridine and N-Heterocyclic Carbene-based C∧N∧C Pincer Ligand for Live-Cell Imaging of Endocytosis

    PubMed Central

    Tsui, Wai-Kuen; Chung, Lai-Hon; Wong, Matthew Man-Kin; Tsang, Wai-Him; Lo, Hoi-Shing; Liu, Yaxiang; Leung, Chung-Hang; Ma, Dik-Lung; Chiu, Sung-Kay; Wong, Chun-Yuen

    2015-01-01

    Luminescent ruthenium(II)-cyanide complex with N-heterocyclic carbene pincer ligand C∧N∧C = 2,6-bis(1-butylimidazol-2-ylidene)pyridine and 2,2′-bipyridine (bpy) shows minimal cytotoxicity to both human breast carcinoma cell (MCF-7) and human retinal pigmented epithelium cell (RPE) in a wide range of concentration (0.1–500 μM), and can be used for the luminescent imaging of endocytosis of the complex in these cells. PMID:25765974

  3. α,β-Unsaturated Gold(I) Carbenes by Tandem Cyclization and 1,5-Alkoxy Migration of 1,6-Enynes: Mechanisms and Applications.

    PubMed

    Calleja, Pilar; Pablo, Óscar; Ranieri, Beatrice; Gaydou, Morgane; Pitaval, Anthony; Moreno, María; Raducan, Mihai; Echavarren, Antonio M

    2016-09-12

    1,6-Enynes bearing OR groups at the propargyl position generate α,β-unsaturated gold(I)-carbenes/ gold(I) stabilized allyl cations that can be trapped by alkenes to form cyclopropanes or 1,3-diketones to give products of α-alkylation. The best migrating group is p-nitrophenyl ether, which leads to the corresponding products without racemization. Thus, an improved formal synthesis of (+)-schisanwilsonene A has been accomplished. The different competitive reaction pathways have been delineated computationally. PMID:27527611

  4. Unexpected reactivity of diaryl α-diketones with thiazolium carbenes: discovery of a novel multicomponent reaction for the facile synthesis of 1,4-thiazin-3-ones.

    PubMed

    Bertolasi, Valerio; Bortolini, Olga; Donvito, Adelaide; Fantin, Giancarlo; Fogagnolo, Marco; Giovannini, Pier Paolo; Massi, Alessandro; Pacifico, Salvatore

    2012-08-28

    Diaryl α-diketones do not undergo polarity reversal in the presence of (benzo)thiazolium carbenes but are engaged in a novel multicomponent reaction with water to efficiently give medicinally relevant 1,4-thiazin-3-one heterocycles. Three different sets of conditions have been optimized to furnish the title compounds in fair to excellent yields depending on the electronic properties of α-diketone aromatic substituents and thiazolium or benzothiazolium substrate. A plausible reaction mechanism is also proposed based on the isolation and characterization of the postulated key intermediate and isotopic labeling experiments. PMID:22766681

  5. Thermally stable laminating resins

    NASA Technical Reports Server (NTRS)

    Jones, R. J.; Vaughan, R. W.; Burns, E. A.

    1972-01-01

    Improved thermally stable laminating resins were developed based on the addition-type pyrolytic polymerization. Detailed monomer and polymer synthesis and characterization studies identified formulations which facilitate press molding processing and autoclave fabrication of glass and graphite fiber reinforced composites. A specific resin formulation, termed P10P was utilized to prepare a Courtaulds HMS reinforced simulated airfoil demonstration part by an autoclave molding process.

  6. Forensic Stable Isotope Biogeochemistry

    NASA Astrophysics Data System (ADS)

    Cerling, Thure E.; Barnette, Janet E.; Bowen, Gabriel J.; Chesson, Lesley A.; Ehleringer, James R.; Remien, Christopher H.; Shea, Patrick; Tipple, Brett J.; West, Jason B.

    2016-06-01

    Stable isotopes are being used for forensic science studies, with applications to both natural and manufactured products. In this review we discuss how scientific evidence can be used in the legal context and where the scientific progress of hypothesis revisions can be in tension with the legal expectations of widely used methods for measurements. Although this review is written in the context of US law, many of the considerations of scientific reproducibility and acceptance of relevant scientific data span other legal systems that might apply different legal principles and therefore reach different conclusions. Stable isotopes are used in legal situations for comparing samples for authenticity or evidentiary considerations, in understanding trade patterns of illegal materials, and in understanding the origins of unknown decedents. Isotope evidence is particularly useful when considered in the broad framework of physiochemical processes and in recognizing regional to global patterns found in many materials, including foods and food products, drugs, and humans. Stable isotopes considered in the larger spatial context add an important dimension to forensic science.

  7. Synthesis of a Bent 2-Silaallene with a Perturbed Electronic Structure from a Cyclic Alkyl(amino) Carbene-Diiodosilylene.

    PubMed

    Li, Yan; Chan, Yuk-Chi; Li, Yongxin; Purushothaman, Indu; De, Susmita; Parameswaran, Pattiyil; So, Cheuk-Wai

    2016-09-01

    The cyclic alkyl(amino) carbene (cAAC) 1 reacted with SiI4 in toluene, affording the cAAC-silicon tetraiodide complex [(cAACMe)SiI4] (2, cAACMe = :C(CH2)(CMe2)2NAr, Ar = 2,6-iPr2C6H3). It further reacted with two equivalents of KC8 in toluene at room temperature to afford the first cAAC-diiodosilylene [(cAACMe)SiI2] (3). DFT calculations show that the Ccarbene-Si bond in 3 is formed by the donation of the lone pair of electrons on the Ccarbene atom to the SiI2 moiety, while the π-back-bonding of the lone pair of electrons on the Si atom to the Ccarbene atom is negligible. The presence of the lone pair of electrons on the silicon atom in 3 is also evidenced by its reaction with N3SiMe3 to form the cAAC-silaimine complex [(cAACMe)Si(NSiMe3)I2] (4). Compound 3 reacted with IiPrMe (:C{N(iPr)CMe}2) in n-hexane to form the NHC-cAAC-silyliumylidene iodide [cAACMe(SiI)IiPrMe]I (5), which was then reacted with two equivalents of KC8 in toluene to furnish [cAACMeSi(IiPrMe)] (6). The experimental and theoretical studies suggest that 6 can be described as a bent silaallene with a perturbed electronic structure, which can be attributed to the different donor-acceptor properties of cAACMe and IiPrMe. Compounds 3-6 were elucidated by NMR spectroscopy, X-ray crystallography, and theoretical studies. PMID:27560615

  8. Tunable and Efficient White Light Phosphorescent Emission Based on Single Component N-Heterocyclic Carbene Platinum(II) Complexes.

    PubMed

    Bachmann, Michael; Suter, Dominik; Blacque, Olivier; Venkatesan, Koushik

    2016-05-16

    A new class of cyclometalated pyridine N-heterocyclic carbene (NHC) Pt(II) complexes with electronically different alkyne derivatives (C≡CR; R = C6H4C(CH3)3 (1), C6H5 (2), C6H4F (3), C6H3(CF3)2 (4)) as ancillary ligands were synthesized, and the consequences of the electronic properties of the different substituted phenylacetylene ligands on the phosphorescent emission efficiencies were studied, where C≡CC6H4C(CH3)3 = 4-tert-butylphenylacetylene, C≡CC6H5 = phenylacetylene, C≡CC6H4F = 4-fluorophenylacetylene, and C≡CC6H3(CF3)2 = 3,5-bis(trifluoromethyl)phenylacetylene. Structural characterization, electrochemistry, and photophysical investigations were performed for all four compounds. Moreover, the emission quantum efficiencies and wavelength emission intensities of the complexes were also recorded in different weight percents in poly(methyl methacrylate) films (PMMA) and evaluated in the CIE-1931 chromaticity diagram. The square planar coordination geometry with the alkynyl ligands was corroborated for complexes 1, 2, and 3 by single crystal X-ray diffraction studies. These complexes show tunable monomeric high energy triplet emission and an additional concentration-dependent low-energy excimer-based phosphorescence. While adopting weight percent concentrations between 15 and 25%, the two emission bands covering the entire visible spectrum were obtained with these particular complexes displaying the properties of an efficient white light triplet emitter with excellent CIE-1931 coordinates (0.31, 0.33). On the basis of the high luminescent quantum efficiency of over 50% for white light emission, these compounds could be potentially useful for white organic light-emitting diodes (WOLEDs) based applications.

  9. Tunable and Efficient White Light Phosphorescent Emission Based on Single Component N-Heterocyclic Carbene Platinum(II) Complexes.

    PubMed

    Bachmann, Michael; Suter, Dominik; Blacque, Olivier; Venkatesan, Koushik

    2016-05-16

    A new class of cyclometalated pyridine N-heterocyclic carbene (NHC) Pt(II) complexes with electronically different alkyne derivatives (C≡CR; R = C6H4C(CH3)3 (1), C6H5 (2), C6H4F (3), C6H3(CF3)2 (4)) as ancillary ligands were synthesized, and the consequences of the electronic properties of the different substituted phenylacetylene ligands on the phosphorescent emission efficiencies were studied, where C≡CC6H4C(CH3)3 = 4-tert-butylphenylacetylene, C≡CC6H5 = phenylacetylene, C≡CC6H4F = 4-fluorophenylacetylene, and C≡CC6H3(CF3)2 = 3,5-bis(trifluoromethyl)phenylacetylene. Structural characterization, electrochemistry, and photophysical investigations were performed for all four compounds. Moreover, the emission quantum efficiencies and wavelength emission intensities of the complexes were also recorded in different weight percents in poly(methyl methacrylate) films (PMMA) and evaluated in the CIE-1931 chromaticity diagram. The square planar coordination geometry with the alkynyl ligands was corroborated for complexes 1, 2, and 3 by single crystal X-ray diffraction studies. These complexes show tunable monomeric high energy triplet emission and an additional concentration-dependent low-energy excimer-based phosphorescence. While adopting weight percent concentrations between 15 and 25%, the two emission bands covering the entire visible spectrum were obtained with these particular complexes displaying the properties of an efficient white light triplet emitter with excellent CIE-1931 coordinates (0.31, 0.33). On the basis of the high luminescent quantum efficiency of over 50% for white light emission, these compounds could be potentially useful for white organic light-emitting diodes (WOLEDs) based applications. PMID:27135529

  10. Estimation of σ-Donation and π-Backdonation of Cyclic Alkyl(amino) Carbene-Containing Compounds.

    PubMed

    Mondal, Kartik Chandra; Roy, Sudipta; Maity, Bholanath; Koley, Debasis; Roesky, Herbert W

    2016-01-01

    Herein, we present a general method for a reliable estimation of the extent of π-backdonation (CcAAC←E) of the bonded element (E) to the carbene carbon atom and CcAAC→E σ-donation. The CcAAC←E π-backdonation has a significant effect on the electronic environments of the (15)N nucleus. The estimation of the π-backdonation has been achieved by recording the chemical shift values of the (15)N nuclei via two-dimensional heteronuclear multiple-bond correlation spectroscopy. The chemical shift values of the (15)N nuclei of several cAAC-containing compounds and/or complexes were recorded. The (15)N nuclear magnetic resonance chemical shift values are in the range from -130 to -315 ppm. When the cAAC forms a coordinate σ-bond (CcAAC→E), the chemical shift values of the (15)N nuclei are around -160 ppm. In case the cAAC is bound to a cationic species, the numerical chemical shift value of the (15)N nucleus is downfield-shifted (-130 to -148 ppm). The numerical values of the (15)N nuclei fall in the range from -170 to -200 ppm when σ-donation (CcAAC→E) of cAAC is stronger than CcAAC←E π-backacceptance. The π-backacceptance of cAAC is stronger than σ-donation, when the chemical shift values of the (15)N nuclei are observed below -220 ppm. Electron density and charge transfer between CcAAC and E are quantified using natural bonding orbital analysis and charge decomposition analysis techniques. The experimental results have been correlated with the theoretical calculations. They are in good agreement.

  11. N-heterocyclic carbene gold(I) catalyzed transformation of N-tethered 1,5-bisallenes to 6,7-dimethylene-3-azabicyclo[3.1.1]heptanes.

    PubMed

    Kim, Soo Min; Park, Ji Hoon; Kang, Youn Kyung; Chung, Young Keun

    2009-01-01

    Tying up loose ends: The reaction of bisallenes tethered with N-(p-tolylsulfonamide) in the presence of a cationic gold N-heterocyclic carbene catalyst gave new cycloisomerization products, 6,7-dimethyleneazabicyclo[3.1.1]heptanes, in high yields (see scheme; IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). PMID:19437519

  12. Synthesis of Well-Defined Copper "N"-Heterocyclic Carbene Complexes and Their Use as Catalysts for a "Click Reaction": A Multistep Experiment that Emphasizes the Role of Catalysis in Green Chemistry

    ERIC Educational Resources Information Center

    Ison, Elon A.; Ison, Ana

    2012-01-01

    A multistep experiment for an advanced synthesis lab course that incorporates topics in organic-inorganic synthesis and catalysis and highlights green chemistry principles was developed. Students synthesized two "N"-heterocyclic carbene ligands, used them to prepare two well-defined copper(I) complexes and subsequently utilized the complexes as…

  13. Tungsten(VI) Carbyne/Bis(carbene) Tautomerization Enabled by N-Donor SBA15 Surface Ligands: A Solid-State NMR and DFT Study.

    PubMed

    Bendjeriou-Sedjerari, Anissa; Sofack-Kreutzer, Julien; Minenkov, Yury; Abou-Hamad, Edy; Hamzaoui, Bilel; Werghi, Baraa; Anjum, Dalaver H; Cavallo, Luigi; Huang, Kuo-Wei; Basset, Jean-Marie

    2016-09-01

    Designing supported well-defined bis(carbene) complexes remains a key challenge in heterogeneous catalysis. The reaction of W(≡CtBu)(CH2 tBu)3 with amine-modified mesoporous SBA15 silica, which has vicinal silanol/silylamine pairs [(≡SiOH)(≡SiNH2 )], leads to [(≡SiNH2 -)(≡SiO-)W(≡CHtBu)(CH2 tBu)2 ] and [(≡SiNH2 -)(≡SiO-)W(=CHtBu)2 (CH2 tBu). Variable temperature, (1) H-(1) H 2D double-quantum, (1) H-(13) C HETCOR, and HETCOR with spin diffusion solid-state NMR spectroscopy demonstrate tautomerization between the alkyl alkylidyne and the bis(alkylidene) on the SBA15 surface. Such equilibrium is possible through the coordination of W to the surface [(≡Si-OH)(≡Si-NH2 )] groups, which act as a [N,O] pincer ligand. DFT calculations provide a rationalization for the surface-complex tautomerization and support the experimental results. This direct observation of such a process shows the strong similarity between molecular mechanisms in homogeneous and heterogeneous catalysis. In propane metathesis (at 150 °C), the tungsten bis(carbene) tautomer is favorable, with a turnover number (TON) of 262. It is the highest TON among all the tungsten alkyl-supported catalysts.

  14. Tungsten(VI) Carbyne/Bis(carbene) Tautomerization Enabled by N-Donor SBA15 Surface Ligands: A Solid-State NMR and DFT Study.

    PubMed

    Bendjeriou-Sedjerari, Anissa; Sofack-Kreutzer, Julien; Minenkov, Yury; Abou-Hamad, Edy; Hamzaoui, Bilel; Werghi, Baraa; Anjum, Dalaver H; Cavallo, Luigi; Huang, Kuo-Wei; Basset, Jean-Marie

    2016-09-01

    Designing supported well-defined bis(carbene) complexes remains a key challenge in heterogeneous catalysis. The reaction of W(≡CtBu)(CH2 tBu)3 with amine-modified mesoporous SBA15 silica, which has vicinal silanol/silylamine pairs [(≡SiOH)(≡SiNH2 )], leads to [(≡SiNH2 -)(≡SiO-)W(≡CHtBu)(CH2 tBu)2 ] and [(≡SiNH2 -)(≡SiO-)W(=CHtBu)2 (CH2 tBu). Variable temperature, (1) H-(1) H 2D double-quantum, (1) H-(13) C HETCOR, and HETCOR with spin diffusion solid-state NMR spectroscopy demonstrate tautomerization between the alkyl alkylidyne and the bis(alkylidene) on the SBA15 surface. Such equilibrium is possible through the coordination of W to the surface [(≡Si-OH)(≡Si-NH2 )] groups, which act as a [N,O] pincer ligand. DFT calculations provide a rationalization for the surface-complex tautomerization and support the experimental results. This direct observation of such a process shows the strong similarity between molecular mechanisms in homogeneous and heterogeneous catalysis. In propane metathesis (at 150 °C), the tungsten bis(carbene) tautomer is favorable, with a turnover number (TON) of 262. It is the highest TON among all the tungsten alkyl-supported catalysts. PMID:27514022

  15. Stable predictive control horizons

    NASA Astrophysics Data System (ADS)

    Estrada, Raúl; Favela, Antonio; Raimondi, Angelo; Nevado, Antonio; Requena, Ricardo; Beltrán-Carbajal, Francisco

    2012-04-01

    The stability theory of predictive and adaptive predictive control for processes of linear and stable nature is based on the hypothesis of a physically realisable driving desired trajectory (DDT). The formal theoretical verification of this hypothesis is trivial for processes with a stable inverse, but it is not for processes with an unstable inverse. The extended strategy of predictive control was developed with the purpose of overcoming methodologically this stability problem and it has delivered excellent performance and stability in its industrial applications given a suitable choice of the prediction horizon. From a theoretical point of view, the existence of a prediction horizon capable of ensuring stability for processes with an unstable inverse was proven in the literature. However, no analytical solution has been found for the determination of the prediction horizon values which guarantee stability, in spite of the theoretical and practical interest of this matter. This article presents a new method able to determine the set of prediction horizon values which ensure stability under the extended predictive control strategy formulation and a particular performance criterion for the design of the DDT generically used in many industrial applications. The practical application of this method is illustrated by means of simulation examples.

  16. Polypyrrole-functionalized ruthenium carbene catalysts as efficient heterogeneous systems for olefin epoxidation.

    PubMed

    Dakkach, Mohamed; Fontrodona, Xavier; Parella, Teodor; Atlamsani, Ahmed; Romero, Isabel; Rodríguez, Montserrat

    2014-07-14

    New Ru complexes containing the bpea-pyr ligand (bpea-pyr stands for N,N-bis(pyridin-2-ylmethyl)-3-(1H-pyrrol-1-yl)propan-1-amine), with the formula [RuCl2(bpea-pyr)(dmso)] (isomeric complexes 2a and 2b) or [Ru(CN-Me)(bpea-pyr)X)](n+) (CN-Me = 3-methyl-1-(pyridin-2-yl)-1H-imidazol-3-ium-2-ide; X = Cl, 3, or X = H2O, 4), have been prepared and fully characterized. Complexes 3 and 4 have been anchored onto an electrode surface through electropolymerization of the attached pyrrole group, yielding stable polypyrrole films. The electrochemical behaviour of 4, which displays a bielectronic Ru(IV/II) redox pair in solution, is dramatically affected by the electropolymerization process leading to the occurrence of two monoelectronic Ru(IV/III) and Ru(III/II) redox pairs in the heterogeneous system. A carbon felt modified electrode containing complex 4 (C-felt/poly-4) has been evaluated as a heterogeneous catalyst in the epoxidation of various olefin substrates using PhI(OAc)2 as an oxidant, displaying TON values of several thousands in all cases and good selectivity for the epoxide product.

  17. Stable lepton mass matrices

    NASA Astrophysics Data System (ADS)

    Domcke, Valerie; Romanino, Andrea

    2016-06-01

    We study natural lepton mass matrices, obtained assuming the stability of physical flavour observables with respect to the variations of individual matrix elements. We identify all four possible stable neutrino textures from algebraic conditions on their entries. Two of them turn out to be uniquely associated to specific neutrino mass patterns. We then concentrate on the semi-degenerate pattern, corresponding to an overall neutrino mass scale within the reach of future experiments. In this context we show that i) the neutrino and charged lepton mixings and mass matrices are largely constrained by the requirement of stability, ii) naturalness considerations give a mild preference for the Majorana phase most relevant for neutrinoless double- β decay, α ˜ π/2, and iii) SU(5) unification allows to extend the implications of stability to the down quark sector. The above considerations would benefit from an experimental determination of the PMNS ratio | U 32 /U 31|, i.e. of the Dirac phase δ.

  18. Stable local oscillator microcircuit.

    SciTech Connect

    Brocato, Robert Wesley

    2006-10-01

    This report gives a description of the development of a Stable Local Oscillator (StaLO) Microcircuit. The StaLO accepts a 100MHz input signal and produces output signals at 1.2, 3.3, and 3.6 GHz. The circuit is built as a multi-chip module (MCM), since it makes use of integrated circuit technologies in silicon and lithium niobate as well as discrete passive components. The StaLO uses a comb generator followed by surface acoustic wave (SAW) filters. The comb generator creates a set of harmonic components of the 100MHz input signal. The SAW filters are narrow bandpass filters that are used to select the desired component and reject all others. The resulting circuit has very low sideband power levels and low phase noise (both less than -40dBc) that is limited primarily by the phase noise level of the input signal.

  19. Bi-stable optical actuator

    DOEpatents

    Holdener, Fred R.; Boyd, Robert D.

    2000-01-01

    The present invention is a bi-stable optical actuator device that is depowered in both stable positions. A bearing is used to transfer motion and smoothly transition from one state to another. The optical actuator device may be maintained in a stable position either by gravity or a restraining device.

  20. Uranium-Carbene-Imido Metalla-Allenes: Ancillary-Ligand-Controlled cis-/trans-Isomerisation and Assessment of trans Influence in the R2 C=U(IV) =NR' Unit (R=Ph2 PNSiMe3 ; R'=CPh3 ).

    PubMed

    Lu, Erli; Cooper, Oliver J; Tuna, Floriana; Wooles, Ashley J; Kaltsoyannis, Nikolas; Liddle, Stephen T

    2016-08-01

    Uranium(IV)-carbene-imido complexes [U(BIPM(TMS) )(NCPh3 )(κ(2) -N,N'-BIPY)] (2; BIPM(TMS) =C(PPh2 NSiMe3 )2 ; BIPY=2,2-bipyridine) and [U(BIPM(TMS) )(NCPh3 )(DMAP)2 ] (3; DMAP=4-dimethylamino-pyridine) that contain unprecedented, discrete R2 C=U=NR' units are reported. These complexes complete the family of E=U=E (E=CR2 , NR, O) metalla-allenes with feasible first-row hetero-element combinations. Intriguingly, 2 and 3 contain cis- and trans-C=U=N units, respectively, representing rare examples of controllable cis/trans isomerisation in f-block chemistry. This work reveals a clear-cut example of the trans influence in a mid-valent uranium system, and thus a strong preference for the cis isomer, which is computed in a co-ligand-free truncated model-to isolate the electronic trans influence from steric contributions-to be more stable than the trans isomer by approximately 12 kJ mol(-1) with an isomerisation barrier of approximately 14 kJ mol(-1) . PMID:27405793

  1. Construct validity of Stable-2000 and Stable-2007 scores.

    PubMed

    Nunes, Kevin L; Babchishin, Kelly M

    2012-02-01

    We addressed the construct validity of Stable-2000 and Stable-2007 scores by examining correlations between selected items and validated independent measures of relevant constructs in samples of convicted sex offenders. In Study 1, the Child Molester Attitudes item of the Stable-2000 shared 23% of the variance with a self-report measure of beliefs supportive of child molestation, r(19) = .48. The Deviant Sexual Interests items of the Stable-2000 and Stable-2007 shared 7% to 66% of the variance, respectively, with an offense-history-based measure of pedophilic interests, r(18) = .27 for the Stable-2000 and r(11) = .81 for the Stable-2007. In Study 2, the Lovers/Intimate Partners, General Social Rejection/Loneliness, Rapist Attitudes, and Child Molester Attitudes items of the Stable-2000 shared 4% to 19% of the variance with self-report measures of, respectively, intimacy, r(90) = -.44; loneliness, r(88) = .34; beliefs supportive of rape, r(72) = .21; and beliefs supportive of child molestation, r(78) = .36. The results generally suggest that the Stable items examined are associated with measures of similar constructs; however, the degree of convergence was lower than expected. More systematic and comprehensive research is needed to examine convergence of the Stable items with other relevant measures and additional aspects of construct validity. Such efforts will provide a clearer understanding of dynamic risk factors, appropriate areas of focus for treatment efforts, and, more generally, why some sex offenders recidivate.

  2. Dimers of N-heterocyclic carbene copper, silver, and gold halides: probing metallophilic interactions through electron density based concepts.

    PubMed

    Pinter, Balazs; Broeckaert, Lies; Turek, Jan; Růžička, Aleš; De Proft, Frank

    2014-01-13

    Homobimetallic metallophilic interactions between copper, silver, and gold-based [(NHC)MX]-type complexes (NHC=N-heterocyclic carbene, i.e, 1,3,4-trimethyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene; X=F, Cl, Br, I) were investigated by means of ab initio interaction energies, Ziegler-Rauk-type energy-decomposition analysis, the natural orbital for chemical valence (NOCV) framework, and the noncovalent interaction (NCI) index. It was found that the dimers of these complexes predominantly adopt a head-to-tail arrangement with typical M⋅⋅⋅M distance of 3.04-3.64 Å, in good agreement with the experimental X-ray structure determined for [{(NHC)AuCl}2 ], which has an Au⋅⋅⋅Au distance of 3.33 Å. The interaction energies between silver- and gold-based monomers are calculated to be about -25 kcal mol(-1) , whereas that for the Cu congener is significantly lower (-19.7 kcal mol(-1) ). With the inclusion of thermal and solvent contributions, both of which are destabilizing, by about 15 and 8 kcal mol(-1) , respectively, an equilibrium process is predicted for the formation of dimer complexes. Energy-decomposition analysis revealed a dominant electrostatic contribution to the interaction energy, besides significantly stabilizing dispersion and orbital interactions. This electrostatic contribution is rationalized by NHC(δ(+) )⋅⋅⋅halogen(δ(-) ) interactions between monomers, as demonstrated by electrostatic potentials and derived charges. The dominant NOCV orbital indicates weakening of the π backdonation in the monomers on dimer formation, whereas the second most dominant NOCV represents an electron-density deformation according to the formation of a very weak M⋅⋅⋅M bond. One of the characteristic signals found in the reduced density gradient versus electron density diagram corresponds to the noncovalent interactions between the metal centers of the monomers in the NCI plots, which is the manifestation of metallophilic interaction. PMID

  3. Stable face representations

    PubMed Central

    Jenkins, Rob; Burton, A. Mike

    2011-01-01

    Photographs are often used to establish the identity of an individual or to verify that they are who they claim to be. Yet, recent research shows that it is surprisingly difficult to match a photo to a face. Neither humans nor machines can perform this task reliably. Although human perceivers are good at matching familiar faces, performance with unfamiliar faces is strikingly poor. The situation is no better for automatic face recognition systems. In practical settings, automatic systems have been consistently disappointing. In this review, we suggest that failure to distinguish between familiar and unfamiliar face processing has led to unrealistic expectations about face identification in applied settings. We also argue that a photograph is not necessarily a reliable indicator of facial appearance, and develop our proposal that summary statistics can provide more stable face representations. In particular, we show that image averaging stabilizes facial appearance by diluting aspects of the image that vary between snapshots of the same person. We review evidence that the resulting images can outperform photographs in both behavioural experiments and computer simulations, and outline promising directions for future research. PMID:21536553

  4. Stable electroosmotically driven actuators

    NASA Astrophysics Data System (ADS)

    Sritharan, Deepa; Motsebo, Mylene; Tumbic, Julia; Smela, Elisabeth

    2013-04-01

    We have previously presented "nastic" actuators based on electroosmotic (EO) pumping of fluid in microchannels using high electric fields for potential application in soft robotics. In this work we address two challenges facing this technology: applying EO to meso-scale devices and the stability of the pumping fluid. The hydraulic pressure achieved by EO increases with as 1/d2, where d is the depth of the microchannel, but the flow rate (which determines the stroke and the speed) is proportional to nd, where n is the number of channels. Therefore to get high force and high stroke the device requires a large number of narrow channels, which is not readily achievable using standard microfabrication techniques. Furthermore, for soft robotics the structure must be soft. In this work we present a method of fabricating a three-dimensional porous elastomer to serve as the array of channels based on a sacrificial sugar scaffold. We demonstrate the concept by fabricating small pumps. The flexible devices were made from polydimethylsiloxane (PDMS) and comprise the 3D porous elastomer flanked on either side by reservoirs containing electrodes. The second issue addressed here involves the pumping fluid. Typically, water is used for EO, but water undergoes electrolysis even at low voltages. Since EO takes place at kV, these systems must be open to release the gases. We have recently reported that propylene carbonate (PC) is pumped at a comparable rate as water and is also stable for over 30 min at 8 kV. Here we show that PC is, however, degraded by moisture, so future EO systems must prevent water from reaching the PC.

  5. Hirshfeld and DFT analysis of the N-heterocyclic carbene proligand methylenebis(N-butylimidazolium) as the acetonitrile-solvated diiodide salt.

    PubMed

    Cebollada, Andrea; Vellé, Alba; Sanz Miguel, Pablo J

    2016-06-01

    N-Heterocyclic carbene (NHC) based systems are usually exploited in the exploration of catalytic mechanisms and processes in organocatalysis, and homo- and heterogeneous catalysis. However, their molecular structures have not received adequate attention. The NHC proligand methylenebis(N-butylimidazolium) has been synthesized as the acetonitrile solvate of the diiodide salt, C15H26N4(2+)·2I(-)·CH3CN [1,1'-methylenebis(3-butylimidazolium) diiodide acetonitrile monosolvate], and fully characterized. An interesting cation-anion connection pattern has been identified in the crystal lattice, in which three iodide anions interact simultaneously with the cisoid-oriented cation. A Hirshfeld surface analysis reveals the predominance of hydrogen bonding over anion-π interactions. This particular arrangement is observed in different methylene-bridged bis(imidazolium) cations bearing chloride or bromide counter-anions. Density functional theory (DFT) calculations with acetonitrile as solvent reproduce the geometry of the title cation.

  6. Ruthenium-porphyrin-catalyzed diastereoselective intramolecular alkyl carbene insertion into C-H bonds of alkyl diazomethanes generated in situ from N-tosylhydrazones.

    PubMed

    Reddy, Annapureddy Rajasekar; Zhou, Cong-Ying; Guo, Zhen; Wei, Jinhu; Che, Chi-Ming

    2014-12-15

    With a ruthenium-porphyrin catalyst, alkyl diazomethanes generated in situ from N-tosylhydrazones efficiently underwent intramolecular C(sp(3))-H insertion of an alkyl carbene to give substituted tetrahydrofurans and pyrrolidines in up to 99% yield and with up to 99:1 cis selectivity. The reaction displays good tolerance of many functionalities, and the procedure is simple without the need for slow addition with a syringe pump. From a synthetic point of view, the C-H insertion of N-tosylhydrazones can be viewed as reductive coupling between a C=O bond and a C-H bond to form a new C-C bond, since N-tosylhydrazones can be readily prepared from carbonyl compounds. This reaction was successfully applied in a concise synthesis of (±)-pseudoheliotridane.

  7. Theoretical study on cooperative effects between X⋯N and X⋯Carbene halogen bonds (X = F,Cl,Br and I).

    PubMed

    Esrafili, Mehdi D; Mohammdain-Sabet, Fariba; Esmailpour, Parvin

    2013-11-01

    Quantum chemical calculations are performed to study the interplay between halogen⋯nitrogen and halogen⋯carbene interactions in NCX⋯NCX⋯CH2 complexes, where X = F, Cl, Br and I. Molecular geometries and interaction energies of dyads and triads are investigated at the MP2/aug-cc-pVTZ level of theory. It is found that the X⋯N and X⋯Ccarbene interaction energies in the triads are larger than those in the dyads, indicating that both the halogen bonding interactions are enhanced. The estimated values of cooperative energy E coop are all negative with much larger E coop in absolute value for the systems including iodine. The nature of halogen bond interactions of the complexes is analyzed using parameters derived from the quantum theory atoms in molecules methodology and energy decomposition analysis. PMID:24013450

  8. Reaction of an N-heterocyclic carbene-stabilized silicon(II) monohydride with alkynes: [2+2+1] cycloaddition versus hydrogen abstraction.

    PubMed

    Eisenhut, Carsten; Szilvási, Tibor; Breit, Nora C; Inoue, Shigeyoshi

    2015-01-26

    An in depth study of the reactivity of an N-heterocyclic carbene (NHC)-stabilized silylene monohydride with alkynes is reported. The reaction of silylene monohydride 1, tBu3 Si(H)Si←NHC, with diphenylacetylene afforded silole 2, tBu3 Si(H)Si(C4 Ph4 ). The density functional theory (DFT) calculations for the reaction mechanism of the [2+2+1] cycloaddition revealed that the NHC played a major part stabilizing zwitterionic transition states and intermediates to assist the cyclization pathway. A significantly different outcome was observed, when silylene monohydride 1 was treated with phenylacetylene, which gave rise to supersilyl substituted 1-alkenyl-1-alkynylsilane 3, tBu3 Si(H)Si(CHCHPh)(CCPh). Mechanistic investigations using an isotope labelling technique and DFT calculations suggest that this reaction occurs through a similar zwitterionic intermediate and subsequent hydrogen abstraction from a second molecule of phenylacetylene. PMID:25413306

  9. The antimicrobial efficacy of sustained release silver–carbene complex-loaded l-tyrosine polyphosphate nanoparticles: Characterization, in vitro and in vivo studies

    PubMed Central

    Hindi, Khadijah M.; Ditto, Andrew J.; Panzner, Matthew J.; Medvetz, Douglas A.; Han, Daniel S.; Hovis, Christine E.; Hilliard, Julia K.; Taylor, Jane B.; Yun, Yang H.; Cannon, Carolyn L.; Youngs, Wiley J.

    2009-01-01

    The pressing need to treat multi-drug resistant bacteria in the chronically infected lungs of cystic fibrosis (CF) patients has given rise to novel nebulized antimicrobials. We have synthesized a silver–carbene complex (SCC10) active against a variety of bacterial strains associated with CF and chronic lung infections. Our studies have demonstrated that SCC10-loaded into l-tyrosine polyphosphate nanoparticles (LTP NPs) exhibits excellent antimicrobial activity in vitro and in vivo against the CF relevant bacteria Pseudomonas aeruginosa. Encapsulation of SCC10 in LTP NPs provides sustained release of the antimicrobial over the course of several days translating into efficacious results in vivo with only two administered doses over a 72 h period. PMID:19395021

  10. Even the normal is abnormal: N-heterocyclic carbene C(2) binding to a phosphaalkene without breaking the P=C π-bond.

    PubMed

    Majhi, Paresh Kumar; Chow, Keith C F; Hsieh, Tom H H; Bowes, Eric G; Schnakenburg, Gregor; Kennepohl, Pierre; Streubel, Rainer; Gates, Derek P

    2016-01-18

    The reaction of MesP=CPh2 with the least sterically demanding N-heterocyclic carbene (NHC = IMe) results in formation of the 'abnormal' (C(4)-substituted) 4-phosphino-NHC (1). In contrast, reaction with Me2IMe gives the unprecedented 'normal' C(2) adduct, Me2IMe → P(Mes)=CPh2 (2). Particularly striking is the asymmetric and weak bonding of the NHC to the P=C moiety in 2. DFT calculations indicate that the P=C natural bond order in 2 (1.54) still reflects significant π-character to the bond (cf. MesP=CPh2: NBO = 1.98). Further computational analysis suggests that π-delocalization into the remote C-phenyl substituents is key to stabilizing the NHC adduct. PMID:26592925

  11. Rational exploration of N-heterocyclic carbene (NHC) palladacycle diversity: a highly active and versatile precatalyst for Suzuki-Miyaura coupling reactions of deactivated aryl and alkyl substrates.

    PubMed

    Peh, Guang-Rong; Kantchev, Eric Assen B; Er, Jun-Cheng; Ying, Jackie Y

    2010-04-01

    As less attention has been focussed on the design of highly efficient palladium precatalysts to ensure the smooth formation of the active catalyst for metal-mediated cross coupling reactions, we herein demonstrate that combining the bulky N-heterocyclic carbene (NHC) 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) with cyclopalladated acetanilide as the optimal palladium precatalyst leads to superior catalytic activity compared with the state-of-the-art NHC-Pd catalysts. The complex was discovered through the evaluation of a small, rationally designed library of NHC-palladacycles prepared by a novel, practical and atom-economic method, the direct reaction of IPrHCl with palladacycle acetate dimers. PMID:20175159

  12. Correlation between functionality preference of Ru carbenes and exo/endo product selectivity for clarifying the mechanism of ring-closing enyne metathesis.

    PubMed

    Lee, Ok Suk; Kim, Kyung Hwan; Kim, Jinwoo; Kwon, Kuktae; Ok, Taedong; Ihee, Hyotcherl; Lee, Hee-Yoon; Sohn, Jeong-Hun

    2013-09-01

    Functionality preferences of metathesis Ru carbenes to various alkenes and alkynes with electronic and steric diversity were determined by using time-dependent fluorescence quenching. The functionality preferences depend not only on the properties of multiple bonds but also on the ligands on Ru. There was a good correlation between functionality preference and the metathesis reaction outcome. The correlation between functionality preference and exo/endo product ratio offers a solution to resolve the mechanistic issue related with alkene- vs alkyne-initiated pathway in ring-closing enyne metathesis. The correlation indicates the preference is likely to dictate the reaction pathway and eventually the outcome of the reaction. The Ru catalyst favoring alkyne over alkene provides more endo product, indicating that the reaction mainly initiates at the alkyne. By changing the substitution pattern, the preference can be reversed to give an exclusive exo product.

  13. Luminescent cyclometalated alkynylplatinum(II) complexes with a tridentate pyridine-based N-heterocyclic carbene ligand: synthesis, characterization, electrochemistry, photophysics, and computational studies.

    PubMed

    Leung, Sammual Yu-Lut; Lam, Elizabeth Suk-Hang; Lam, Wai Han; Wong, Keith Man-Chung; Wong, Wing-Tak; Yam, Vivian Wing-Wah

    2013-07-29

    A new class of luminescent alkynylplatinum(II) complexes with a tridentate pyridine-based N-heterocyclic carbene (2,6-bis(1-butylimidazol-2-ylidenyl)pyridine) ligand, [Pt(II)(C^N^C)(C≡CR)][PF6], and their chloroplatinum(II) precursor complex, [Pt(II)(C^N^C)Cl][PF6], have been synthesized and characterized. One of the alkynylplatinum(II) complexes has also been structurally characterized by X-ray crystallography. The electrochemistry, electronic absorption and luminescence properties of the complexes have been studied. Nanosecond transient absorption (TA) spectroscopy has also been performed to probe the nature of the excited state. The origin of the absorption and emission properties has been supported by computational studies. PMID:23788216

  14. The effect of substituted moiety on the optoelectronic and photophysical properties of tris (phenylbenzimidazolinato) Ir (III) carbene complexes and the OLED performance: a theoretical study

    NASA Astrophysics Data System (ADS)

    Srivastava, Ruby

    2015-06-01

    Density functional theory (DFT) and time-dependent density functional theory (TDDFT) are used to analyse theoretically the optoelectronic, photophysical properties and organic light-emitting diode performance of a series of fac-mer blue-emitting Iridium (III) carbene complexes. Swain-Lupton constant is used to discuss the substituents effect. 5d-orbital splitting and d-d* transitions are calculated to assess the efficiency of the studied complexes. The reorganisation energies (λ), transfer integrals, mobilities, radiative decay rate (kr), and triplet exciton generation fraction (χT) are also calculated. Due to the higher χT of these complexes, the formation of triplet exciton will be more and it will cause a faster intersystem crossing. Two host materials are proposed and host-guest match (Dexter-Förster energy) is also discussed. We hope that this unified work will surely help to design new blue-emitting phosphorescent materials in future.

  15. Visible-light photoredox catalysis: selective reduction of carbon dioxide to carbon monoxide by a nickel N-heterocyclic carbene-isoquinoline complex.

    PubMed

    Thoi, V Sara; Kornienko, Nikolay; Margarit, Charles G; Yang, Peidong; Chang, Christopher J

    2013-09-25

    The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene-amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni((Pr)bimiq1)](2+) (1c, where (Pr)bimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (E(cat) = -1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s(-1), respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion.

  16. Visible-Light Photoredox Catalysis: Selective Reduction of Carbon Dioxide to Carbon Monoxide by a Nickel N-Heterocyclic Carbene-Isoquinoline Complex

    SciTech Connect

    Thoi, VanSara; Kornienko, Nick; Margarit, C; Yang, Peidong; Chang, Christopher

    2013-06-07

    The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO. Systematic changes in the carbene and amine donors of the ligand have been surveyed, and [Ni(Prbimiq1)]2+ (1c, where Prbimiq1 = bis(3-(imidazolyl)isoquinolinyl)propane) emerges as a catalyst for electrochemical reduction of CO2 with the lowest cathodic onset potential (Ecat = 1.2 V vs SCE). Using this earth-abundant catalyst with Ir(ppy)3 (where ppy = 2-phenylpyridine) and an electron donor, we have developed a visible-light photoredox system for the catalytic conversion of CO2 to CO that proceeds with high selectivity and activity and achieves turnover numbers and turnover frequencies reaching 98,000 and 3.9 s1, respectively. Further studies reveal that the overall efficiency of this solar-to-fuel cycle may be limited by the formation of the active Ni catalyst and/or the chemical reduction of CO2 to CO at the reduced nickel center and provide a starting point for improved photoredox systems for sustainable carbon-neutral energy conversion.

  17. Mixed N-Heterocyclic Carbene-Bis(oxazolinyl)borato Rhodium and Iridium Complexes in Photochemical and Thermal Oxidative Addition Reactions

    SciTech Connect

    Xu, Songchen; Manna, Kuntal; Ellern, Arkady; Sadow, Aaron D

    2014-12-08

    In order to facilitate oxidative addition chemistry of fac-coordinated rhodium(I) and iridium(I) compounds, carbene–bis(oxazolinyl)phenylborate proligands have been synthesized and reacted with organometallic precursors. Two proligands, PhB(OxMe2)2(ImtBuH) (H[1]; OxMe2 = 4,4-dimethyl-2-oxazoline; ImtBuH = 1-tert-butylimidazole) and PhB(OxMe2)2(ImMesH) (H[2]; ImMesH = 1-mesitylimidazole), are deprotonated with potassium benzyl to generate K[1] and K[2], and these potassium compounds serve as reagents for the synthesis of a series of rhodium and iridium complexes. Cyclooctadiene and dicarbonyl compounds {PhB(OxMe2)2ImtBu}Rh(η4-C8H12) (3), {PhB(OxMe2)2ImMes}Rh(η4-C8H12) (4), {PhB(OxMe2)2ImMes}Rh(CO)2 (5), {PhB(OxMe2)2ImMes}Ir(η4-C8H12) (6), and {PhB(OxMe2)2ImMes}Ir(CO)2 (7) are synthesized along with ToMM(η4-C8H12) (M = Rh (8); M = Ir (9); ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate). The spectroscopic and structural properties and reactivity of this series of compounds show electronic and steric effects of substituents on the imidazole (tert-butyl vs mesityl), effects of replacing an oxazoline in ToM with a carbene donor, and the influence of the donor ligand (CO vs C8H12). The reactions of K[2] and [M(μ-Cl)(η2-C8H14)2]2 (M = Rh, Ir) provide {κ4-PhB(OxMe2)2ImMes'CH2}Rh(μ-H)(μ-Cl)Rh(η2-C8H14)2 (10) and {PhB(OxMe2)2ImMes}IrH(η3-C8H13) (11). In the former compound, a spontaneous oxidative addition of a mesityl ortho-methyl to give a mixed-valent dirhodium species is observed, while the iridium compound forms a monometallic allyl hydride. Photochemical reactions of dicarbonyl compounds 5 and 7 result in C–H bond oxidative addition providing the compounds {κ4-PhB(OxMe2)2ImMes'CH2}RhH(CO) (12) and {PhB(OxMe2)2ImMes}IrH(Ph)CO (13). In 12, oxidative addition results in cyclometalation of the mesityl ortho-methyl similar to 10, whereas the iridium compound reacts with the benzene solvent to give a rare crystallographically characterized cis

  18. Bis-N-heterocyclic carbene (NHC) stabilized η6-arene iron(0) complexes: synthesis, structure, reactivity, and catalytic activity.

    PubMed

    Blom, Burgert; Tan, Gengwen; Enthaler, Stephan; Inoue, Shigeyoshi; Epping, Jan Dirk; Driess, Matthias

    2013-12-01

    Reaction of FeCl2 with the chelating bis-N-heterocyclic carbene (NHC) bis-(N-Dipp-imidazole-2-ylidene)methylene (abbreviated {((Dipp)C:)2CH2}) (Dipp = 2,6-di-isopropylphenyl) affords the complex [FeCl2{((Dipp)C:)2CH2}] (1) in high yield. Reduction of complex 1 with excess KC8 with a 10-fold molar excess of PMe3 affords the Fe(II) complex [FeH{((Dipp)C:)2CH2}(PMe3)(η(2)-PMe2CH2)] (2) as a mixture of three stereoisomers. Complex 2, the first example of any iron(II) complex bearing mutually an NHC and PMe3 ligand, is likely obtained from the in situ, reductively generated 16 VE Fe(0) complex, [Fe{((Dipp)C:)2CH2}(PMe3)2] (2'), following intramolecular C-H activation of one of the phosphorus-bound CH3 groups. Complex 2 is unstable in aromatic solvents and forms, via a novel synthetic transformation involving intramolecular reductive elimination and concomitant PMe3 elimination, the Fe (0) arene complex [Fe{((Dipp)C:)2CH2}(η(6)-C6D6)] (4-d6) in C6D6. Complex 4-d6 represents the first example of an NHC stabilized iron (0) arene complex. The transformation from 2 to 4-d6 can be accelerated at higher temperature and at 60 °C forms immediately. Alternatively, the reduction of 1 in the presence of toluene or benzene affords the complexes [Fe{((Dipp)C:)2CH2}(η(6)-C7H8)] (3) and [Fe{((Dipp)C:)2CH2}(η(6)-C6H6)] (4), selectively and in good yields. DFT calculations characterizing the bonding situation in 3 and 4 reveal similar energies of the HOMO and LUMO orbitals, with the LUMO orbital of both complexes located on the Dipp rings of the bis-NHC. The HOMO orbital reflects a π-back-bonding interaction between the Fe(0) center and the chelating NHC ligand, while the HOMO-1 is associated with the arene interaction with the Fe(0) site. The calculations do not suggest any noninnocence of the coordinated arene in either complex. Moreover, the (57)Fe Mössbauer spectrum of 4 at 80K exhibits parameters (δ = 0.43 mm·s(-1); ΔEQ = 1.37 mm·s(-1)) which are consistent with a five

  19. Tris(carbene)borate ligands featuring imidazole-2-ylidene, benzimidazol-2-ylidene and 1,3,4-triazol-2-ylidene donors. Evaluation of donor properties in four-coordinate {NiNO}10 complexes

    PubMed Central

    Muñoz, Salvador B.; Foster, Wallace K.; Lin, Hsiu-Jung; Margarit, Charles G.; Dickie, Diane A.

    2012-01-01

    The synthesis and characterization of new tris(carbene)borate ligand precursors containing substituted benzimidazol-2-ylidene and 1,3,4-triazol-2-ylidene donor groups, as well as a new tris(imidazol-2-ylidene)borate ligand precursor are reported. The relative donor strength of the tris(carbene)borate ligands have been evaluated by the position of ν(NO) in four-coordinate {NiNO}10 complexes, and follows the order: imidazol-2-ylidene > benzimidazol-2-ylidene > 1,3,4-triazol-2-ylidene. There is a large variation in ν(NO), suggesting these ligands to have a wide range of donor strengths while maintaining a consistent ligand topology. All ligands are stronger donors than Tp* and Cp*. PMID:23140462

  20. Tempered stable Lévy motion driven by stable subordinator

    NASA Astrophysics Data System (ADS)

    Gajda, Janusz; Wyłomańska, Agnieszka

    2013-08-01

    In this article we propose a new model for financial data description. Combining two independent mechanisms, namely the tempered stable process and inverse stable subordinator, we obtain a new model which captures not only the tempered stable character of the underlying data but also such a property as periods in which the values of an asset stay on the same level. Moreover, we classify our system to the family of subdiffusive processes and investigate its tail behavior. We describe in detail testing and estimation procedures for the proposed model. In the last step we calibrate our model to the real data.

  1. New N^C^N-coordinated Pd(ii) and Pt(ii) complexes of a tridentate N-heterocyclic carbene ligand featuring a 6-membered central ring: synthesis, structures and luminescence.

    PubMed

    Moussa, Jamal; Haddouche, Kamel; Chamoreau, Lise-Marie; Amouri, Hani; Gareth Williams, J A

    2016-08-01

    We describe Pd(ii) and Pt(ii) complexes of an N^C^N-coordinating pincer-like ligand featuring two lateral pyridine rings and a 6-membered carbene core. Their crystal structures display 1-dimensional chains with short π-π and M(ii)M(ii) interactions. Such interactions also impact on the photophysical properties, with the Pt(ii) complex being luminescent in the solid state at room temperature. PMID:27465432

  2. Tempering the Reactivities of Postulated α-Oxo Gold Carbenes by Bidentate Ligands: Implication of Tricoordinated Gold Intermediates and the Development of an Expedient Bimolecular Assembly of 2,4-Disubstituted Oxazoles

    PubMed Central

    Luo, Yingdong; Ji, Kegong; Li, Yuxue

    2012-01-01

    2,4-Oxazole is an important structural motif in various natural products. An efficient modular synthesis of this structure is achieved via a [3+2] annulation between a terminal alkyne and a carboxamide by using a gold-catalyzed oxidation strategy. The postulated reactive intermediate, a terminal α-oxo gold carbene, previously known to be highly electrophilic and hence impropable to be trapped by stoichiometric external nucleophiles, is coerced to react smoothly with a carboxamide en route to the oxazole ring by a P,N- or P,S-bidentate ligand such as Mor-DalPhos; in stark contrast, often used ligands including monodentate phosphines and NHCs are totally ineffective. The role of these bidentate phosphines in this reaction is attributed to the formation of a tricoordinated gold carbene intermediate, which is less electrophilic and hence more chemoselective when reacting with nucleophiles. The success in using bidentate phosphine ligands to temper the reactivities of in-situ generated gold carbenes would likely open many new opportunities to apply the oxidative gold catalysis to the development of novel methods, and the implication of tricoordinated gold intermediates in homogeneous gold catalysis should stimulate further advance in gold catalysis. PMID:23039251

  3. Stable isotopes in obesity research.

    PubMed

    Dolnikowski, Gregory G; Marsh, Julian B; Das, Sai Krupa; Welty, Francine K

    2005-01-01

    Obesity is recognized as a major public health problem. Obesity is a multifactorial disease and is often associated with a wide range of comorbidities including hypertension, non-insulin dependent (Type II) diabetes mellitus, and cardiovascular disease, all of which contribute to morbidity and mortality. This review deals with stable isotope mass spectrometric methods and the application of stable isotopes to metabolic studies of obesity. Body composition and total energy expenditure (TEE) can be measured by mass spectrometry using stable isotope labeled water, and the metabolism of protein, lipid, and carbohydrate can be measured using appropriate labeled tracer molecules.

  4. Earthquakes in Stable Continental Crust.

    ERIC Educational Resources Information Center

    Johnston, Arch C.; Kanter, Lisa R.

    1990-01-01

    Discussed are some of the reasons for earthquakes which occur in stable crust away from familiar zones at the ends of tectonic plates. Crust stability and the reactivation of old faults are described using examples from India and Australia. (CW)

  5. Shelf-Stable Food Safety

    MedlinePlus

    ... process of packing meat and poultry in glass bottles, corking them, and submerging them in boiling water. ... fsis.usda.gov. [ Top of Page ] Are any egg products shelf stable? Pasteurized, dried egg products can ...

  6. Stable Multibubble Sonoluminescence Bubble Patterns

    SciTech Connect

    Posakony, Gerald J.; Greenwood, Lawrence R.; Ahmed, Salahuddin

    2006-06-30

    Multibubble standing wave patterns can be generated from a flat piezoceramic transducer element propagating into water. By adding a second transducer positioned at 90 degrees from the transducer generating the standing wave, a 3-dimensional volume of stable single bubbles can be established. Further, the addition of the second transducer stabilizes the bubble pattern so that individual bubbles may be studied. The size of the bubbles and the separation of the standing waves depend on the frequency of operation. Two transducers, operating at frequencies above 500 kHz, provided the most graphic results for the configuration used in this study. At these frequencies stable bubbles exhibit a bright sonoluminescence pattern. Whereas stable SBSL is well-known, stable MBSL has not been previously reported. This paper includes discussions of the acoustic responses, standing wave patterns, and pictorial results of the separation of individual bubble of sonoluminescence in a multibubble sonoluminescence environment.

  7. Distributed Weighted Stable Marriage Problem

    NASA Astrophysics Data System (ADS)

    Amira, Nir; Giladi, Ran; Lotker, Zvi

    The Stable Matching problem was introduced by Gale and Shapley in 1962. The input for the stable matching problem is a complete bipartite K n,n graph together with a ranking for each node. Its output is a matching that does not contain a blocking pair, where a blocking pair is a pair of elements that are not matched together but rank each other higher than they rank their current mates. In this work we study the Distributed Weighted Stable Matching problem. The input to the Weighted Stable Matching problem is a complete bipartite K n,n graph and a weight function W. The ranking of each node is determined by W, i.e. node v prefers node u 1 over node u 2 if W((v,u 1)) > W((v, u 2)). Using this ranking we can solve the original Stable Matching problem. We consider two different communication models: the billboard model and the full distributed model. In the billboard model, we assume that there is a public billboard and each participant can write one message on it in each time step. In the distributed model, we assume that each node can send O(logn) bits on each edge of the K n,n . In the billboard model we prove a somewhat surprising tight bound: any algorithm that solves the Stable Matching problem requires at least n - 1 rounds. We provide an algorithm that meets this bound. In the distributed communication model we provide an algorithm named intermediation agencies algorithm, in short (IAA), that solves the Distributed Weighted Stable Marriage problem in O(sqrt{n}) rounds. This is the first sub-linear distributed algorithm that solves some subcase of the general Stable Marriage problem.

  8. Hadamard Factorization of Stable Polynomials

    NASA Astrophysics Data System (ADS)

    Loredo-Villalobos, Carlos Arturo; Aguirre-Hernández, Baltazar

    2011-11-01

    The stable (Hurwitz) polynomials are important in the study of differential equations systems and control theory (see [7] and [19]). A property of these polynomials is related to Hadamard product. Consider two polynomials p,q ∈ R[x]:p(x) = anxn+an-1xn-1+...+a1x+a0q(x) = bmx m+bm-1xm-1+...+b1x+b0the Hadamard product (p × q) is defined as (p×q)(x) = akbkxk+ak-1bk-1xk-1+...+a1b1x+a0b0where k = min(m,n). Some results (see [16]) shows that if p,q ∈R[x] are stable polynomials then (p×q) is stable, also, i.e. the Hadamard product is closed; however, the reciprocal is not always true, that is, not all stable polynomial has a factorization into two stable polynomials the same degree n, if n> 4 (see [15]).In this work we will give some conditions to Hadamard factorization existence for stable polynomials.

  9. Stable Degeneracies for Ising Models

    NASA Astrophysics Data System (ADS)

    Knauf, Andreas

    2016-10-01

    We introduce and consider the notion of stable degeneracies of translation invariant energy functions, taken at spin configurations of a finite Ising model. By this term we mean the lack of injectivity that cannot be lifted by changing the interaction. We show that besides the symmetry-induced degeneracies, related to spin flip, translation and reflection, there exist additional stable degeneracies, due to more subtle symmetries. One such symmetry is the one of the Singer group of a finite projective plane. Others are described by combinatorial relations akin to trace identities. Our results resemble traits of the length spectrum for closed geodesics on a Riemannian surface of constant negative curvature. There, stable degeneracy is defined w.r.t. Teichmüller space as parameter space.

  10. Multi-stable cylindrical lattices

    NASA Astrophysics Data System (ADS)

    Pirrera, Alberto; Lachenal, Xavier; Daynes, Stephen; Weaver, Paul M.; Chenchiah, Isaac V.

    2013-11-01

    We present a cylindrical lattice structure that mimics the behaviour of the virus bacteriophage T4 in having two (or more) stable states which differ in their radii and length. While the virus achieves bistability through molecular mechanisms we use composite materials to exploit the interplay between pre-stress, material properties and structural geometry. We demonstrate (computationally) that multi-stability is a robust phenomenon. We also show (analytically) that it is possible to choose the design variables so that the energy is independent of the radius, thus resulting in every state of the structure being stable.

  11. Metal Stable Isotopes in Paleoceanography

    NASA Astrophysics Data System (ADS)

    Anbar, Ariel D.; Rouxel, Olivier

    2007-05-01

    Considered esoteric only a few years ago, research into the stable isotope geochemistry of transition metals is moving into the geoscience mainstream. Although initial attention focused on the potential use of some of these nontraditional isotope systems as biosignatures, they are now emerging as powerful paleoceanographic proxies. In particular, the Fe and Mo isotope systems are providing information about changes in oxygenation and metal cycling in ancient oceans. Zn, Cu, Tl, and a number of other metals and metalloids also show promise. Here we review the basis of stable isotope fractionation as it applies to these elements, analytical considerations, and the current status and future prospects of this rapidly developing research area.

  12. Determining the Impact of Ligand and Alkene Substituents on Bonding in Gold(I)-Alkene Complexes Supported by N-Heterocyclic Carbenes: A Computational Study.

    PubMed

    York, John T

    2016-08-01

    The nature of the gold(I)-alkene bond in [(NHC)Au(alkene)](+) complexes (where NHC is the N-heterocyclic carbene 1,3-bis(2,6-dimethylphenyl)imidazole-2-ylidine and its derivatives) has been studied using density functional theory. By utilization of a series of electron-withdrawing and electron-donating substituents ranging from -NO2 to -NH2, an examination of substituent effects has been undertaken with 4-substituted NHC ligands, monosubstituted ethylene derivatives, and 4-substituted styrene derivatives. Natural population, natural bond orbital (NBO), molecular orbital, and bond energy decomposition analysis (EDA) methods have been used to quantify a number of important parameters, including the charge of the coordinated alkenes and the magnitude of alkene→[(NHC)Au](+) and [(NHC)Au](+)→alkene electron donation. EDA methods have also been used to quantify the strength of the [(NHC)Au](+)-(alkene) bond and the impact of both ligand and alkene substitution on different components of the interaction, including polarization, orbital, electrostatic, and Pauli repulsive contributions. Finally, molecular orbital analysis has been used to understand the activation of the alkenes in terms of orbital composition and stabilization within the [(NHC)Au(alkene)](+) complexes relative to the free alkenes. These results provide important insight into the fundamental nature of gold(I)-alkene bonding and the impact of both ligand and alkene substitution on the electronic structure of these complexes. PMID:27455390

  13. Stepwise strategy to cyclometallated Pt(II) complexes with N-heterocyclic carbene ligands: a luminescence study on new β-diketonate complexes.

    PubMed

    Fuertes, Sara; García, Hector; Perálvarez, Mariano; Hertog, Wim; Carreras, Josep; Sicilia, Violeta

    2015-01-19

    The imidazolium salt 3-methyl-1-(naphthalen-2-yl)-1H-imidazolium iodide (2) has been treated with silver(I) oxide and [{Pt(μ-Cl)(η(3)-2-Me-C3H4)}2] (η(3)-2-Me-C3H4 = η(3)-2-methylallyl) to give the intermediate N-heterocyclic carbene complex [PtCl(η(3)-2-Me-C3H4)(HCC*-κC*)] (3) (HCC*-κC* = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene). Compound 3 undergoes regiospecific cyclometallation at the naphthyl ring of the NHC ligand to give the five-membered platinacycle compound [{Pt(μ-Cl)(CC*)}2] (4). Chlorine abstraction from 4 with β-diketonate Tl derivatives rendered the corresponding neutral compounds [Pt(CC*)(L-O,O')] {L = acac (HL = acetylacetone) 5, phacac (HL = 1,3-diphenyl-1,3-propanedione) 6, hfacac (HL = hexafluoroacetylacetone) 7}. All of the compounds (3-7) were fully characterized by standard spectroscopic and analytical methods. X-ray diffraction studies were performed on 5-7, revealing short Pt-Pt and π-π interactions in the solid-state structure. The influence of the R-substituents of the β-diketonate ligand on the photophysical properties and the use of the most efficient emitter, 5, as phosphor converter has also been studied.

  14. Cytotoxicity and biodistribution studies of luminescent Au(i) and Ag(i) N-heterocyclic carbenes. Searching for new biological targets.

    PubMed

    Visbal, Renso; Fernández-Moreira, Vanesa; Marzo, Isabel; Laguna, Antonio; Gimeno, M Concepción

    2016-10-14

    A range of fluorescent and biologically compatible gold(i)-N-heterocyclic carbenes bearing acridine as a wingtip group and either a 2-mercaptopyridine or a tetra-O-acetyl-1-thio-β-d-glucopyranoside as an ancillary ligand has been synthesised. Their luminescence, cytotoxicity and biodistribution have been investigated together with those of analogous gold(i) and silver(i) chloride- and bis-NHC complexes. All complexes displayed emissions based on IL transitions centred on the acridine moiety. The cytotoxic activity measured in lung, A549, and pancreatic, MiaPaca2, carcinoma cell lines revealed a general cytotoxicity pattern (thiolate > biscarbene > chloride derivatives) and flow cytometry assays pointed towards apoptosis as the cell death mechanism. Moreover, fluorescence cell microscopy disclosed an unusual biodistribution behavior, being mainly localised in lysosomes and to a lesser extent in the nucleus. Preliminary DNA interaction experiments suggested the metal fragment and not the acridine moiety as responsible for such biodistribution, which widen the scope for new biological targets.

  15. Determining the Impact of Ligand and Alkene Substituents on Bonding in Gold(I)-Alkene Complexes Supported by N-Heterocyclic Carbenes: A Computational Study.

    PubMed

    York, John T

    2016-08-01

    The nature of the gold(I)-alkene bond in [(NHC)Au(alkene)](+) complexes (where NHC is the N-heterocyclic carbene 1,3-bis(2,6-dimethylphenyl)imidazole-2-ylidine and its derivatives) has been studied using density functional theory. By utilization of a series of electron-withdrawing and electron-donating substituents ranging from -NO2 to -NH2, an examination of substituent effects has been undertaken with 4-substituted NHC ligands, monosubstituted ethylene derivatives, and 4-substituted styrene derivatives. Natural population, natural bond orbital (NBO), molecular orbital, and bond energy decomposition analysis (EDA) methods have been used to quantify a number of important parameters, including the charge of the coordinated alkenes and the magnitude of alkene→[(NHC)Au](+) and [(NHC)Au](+)→alkene electron donation. EDA methods have also been used to quantify the strength of the [(NHC)Au](+)-(alkene) bond and the impact of both ligand and alkene substitution on different components of the interaction, including polarization, orbital, electrostatic, and Pauli repulsive contributions. Finally, molecular orbital analysis has been used to understand the activation of the alkenes in terms of orbital composition and stabilization within the [(NHC)Au(alkene)](+) complexes relative to the free alkenes. These results provide important insight into the fundamental nature of gold(I)-alkene bonding and the impact of both ligand and alkene substitution on the electronic structure of these complexes.

  16. Ruthenium(II) and osmium(II) 1,2,3-triazolylidene organometallics: a preliminary investigation into the biological activity of 'click' carbene complexes.

    PubMed

    Kilpin, Kelly J; Crot, Stéphanie; Riedel, Tina; Kitchen, Jonathan A; Dyson, Paul J

    2014-01-21

    Taking advantage of the facile and versatile synthetic properties of 'click' 1,2,3-triazolylidene N-heterocyclic carbenes (tzNHC's), a range of new organometallic Ru(II) and Os(II) arene complexes containing functionalised tzNHC ligands, [M(η(6)-p-cymene)(tzNHC)Cl2] [M = Ru(II), Os(II)], have been synthesised and fully characterised, including the X-ray crystal structure of one of the Os(II) complexes. The tzNHC ligands remain coordinated to the metal centres under relevant physiological conditions, and following binding to the model protein, ubiquitin. The in vitro cytotoxicity of the compounds towards human ovarian cancer cells is dependent on the substituent on the tzNHC ligand but is generally <50 μM and in some cases <1 μM, whilst still retaining a high degree of selectivity towards cancer cells over healthy cells (1.85 μM in A2780 ovarian cancer cells versus 435 μM in human embryonic kidney cells in one case).

  17. Macrophage and colon tumor cells as targets for a binuclear silver(I) N-heterocyclic carbene complex, an anti-inflammatory and apoptosis mediator.

    PubMed

    Iqbal, Muhammad Adnan; Umar, Muhammad Ihtisham; Haque, Rosenani A; Khadeer Ahamed, Mohamed B; Asmawi, Mohd Zaini Bin; Majid, Amin Malik Shah Abdul

    2015-05-01

    Chronic inflammation intensifies the risk for malignant neoplasm, indicating that curbing inflammation could be a valid strategy to prevent or cure cancer. Cancer and inflammation are inter-related diseases and many anti-inflammatory agents are also used in chemotherapy. Earlier, we have reported a series of novel ligands and respective binuclear Ag(I)-NHC complexes (NHC=N-heterocyclic carbene) with potential anticancer activity. In the present study, a newly synthesized salt (II) and respective Ag(I)-NHC complex (III) of comparable molecular framework were prepared for a further detailed study. Preliminarily, II and III were screened against HCT-116 and PC-3 cells, wherein III showed better results than II. Both the compounds showed negligible toxicity against normal CCD-18Co cells. In FAM-FLICA caspase assay, III remarkably induced caspase-3/7 in HCT-116 cells most probably by tumor necrosis factor-alpha (TNF-α) independent intrinsic pathway and significantly inhibited in vitro synthesis of cytokines, interleukin-1 (IL-1) and TNF-α in human macrophages (U937 cells). In a cell-free system, both the compounds inhibited cyclooxygenase (COX) activities, with III being more selective towards COX-2. The results revealed that III has strong antiproliferative property selectively against colorectal tumor cells which could be attributed to its pro-apoptotic and anti-inflammatory abilities. PMID:25699476

  18. A comparison between nickel and palladium precatalysts of 1,2,4-triazole based N-heterocyclic carbenes in hydroamination of activated olefins.

    PubMed

    Dash, Chandrakanta; Shaikh, Mobin M; Butcher, Ray J; Ghosh, Prasenjit

    2010-03-14

    A comparison is drawn between the nickel and palladium precatalysts of 1,2,4-triazole based N-heterocyclic carbenes in the hydroamination of activated olefins. Though all of the newly designed nickel and palladium precatalysts, trans-[1-i-propyl-4-R-1,2,4-triazol-5-ylidene](2)MBr(2) [R = Et, M = Ni (1b); R = Et, M = Pd (1c); R = CH(2)CH=CH(2), M = Ni (2b) and R = CH(2)CH=CH(2), M = Pd (2c)], are moderately active for hydroamination reaction of a variety of secondary amines viz. morpholine, piperidine, pyrrolidine and diethylamine with activated olefins like, acrylonitrile, methyl acrylate, ethyl acrylate and t-butyl acrylate at room temperature in 1 hour, the nickel complexes (1b and 2b) exhibited superior activity compared to its palladium counterparts (1c and 2c). The better performance of the nickel complexes has been correlated to the more electron deficient metal center in the nickel 1b and 2b complexes than in the palladium 1c and 2c analogs based on the density functional theory studies. The 1b-c and 2b-c complexes were synthesized by the reaction of 1-i-propyl-4-R-1,2,4-triazolium bromide [R = Et (1a) and R = CH(2)CH=CH(2) (2a)] with MCl(2) [M = Ni, Pd] in presence of NEt(3) as a base. PMID:20179844

  19. Bayesian stable isotope mixing models

    EPA Science Inventory

    In this paper we review recent advances in Stable Isotope Mixing Models (SIMMs) and place them into an over-arching Bayesian statistical framework which allows for several useful extensions. SIMMs are used to quantify the proportional contributions of various sources to a mixtur...

  20. Stable Black Families. Final Report.

    ERIC Educational Resources Information Center

    Gary, Lawrence E.; And Others

    This document is the final report of a study conducted to determine what factors contribute to strong Black family life and how these strong families solve problems, in order to add to the knowledge base on stable families so as to enhance practical intervention with families in need, and to identify models of self-help strategies used by stable…

  1. Synthesis of thermally stable polymers

    NASA Technical Reports Server (NTRS)

    Butler, G. B.

    1978-01-01

    The reaction of bis triazo linediones with divinyl esters and substituted styrenes was investigated. Twenty new polymers were derived via reaction of two previously synthesized bis triazol linediones and four new bis atriazol linediones with eight styrenes. The structure and polymer properties of these thermally stable polymers was examined. The reaction of triazo linediones with enol esters was also considered.

  2. Comproportionation of Cationic and Anionic Tungsten Complexes Having an N -Heterocyclic Carbene Ligand To Give the Isolable 17-Electron Tungsten Radical CpW(CO) 2 (IMes)

    SciTech Connect

    Roberts, John A. S.; Franz, James A.; van der Eide, Edwin F.; Walter, Eric D.; Petersen, Jeffrey L.; DuBois, Daniel L.; Bullock, R. Morris

    2011-09-21

    A series consisting of a tungsten anion, radical and cation, supported by the N-heterocyclic carbene IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and spanning formal oxidation states W(0), W(I) and W(II), has been synthesized, isolated, and characterized. Reaction of the hydride CpW(CO)2(IMes)H with KH and 18 crown 6 gives the tungsten anion [CpW(CO)2(IMes)]-[K(18 crown 6)]+. The crystal structure of this complex shows that the K+ interacts not only with the oxygen atoms in the crown ether, but also with the carbonyl oxygens. The electrochemical oxidation of [CpW(CO)2(IMes)]- in acetonitrile is fully reversible (E½ = -1.65 V vs Cp2Fe+•/0) at all scan rates, indicating that CpW(CO)2(IMes)• is a persistent radical. Hydride transfer from CpW(CO)2(IMes)H to Ph3C+PF6 affords [cis-CpW(CO)2(IMes)(MeCN)]+PF6 . Comproportionation of [CpW(CO)2(IMes)]- with [CpW(CO)2(IMes)(MeCN)]+ gives the 17-electron tungsten radical CpW(CO)2(IMes)•. This complex shows paramagnetically shifted resonances in 1H NMR spectra and has been characterized by IR spectroscopy, low-temperature EPR spectroscopy, and X-ray diffraction. CpW(CO)2(IMes)• is very stable with respect to disproportionation and dimerization. NMR studies of degenerate electron transfer between CpW(CO)2(IMes)• and [CpW(CO)2(IMes)]- are reported. DFT calculations were carried out on CpW(CO)2(IMes)H, as well as on related complexes bearing NHC ligands with N,N´ substituents Me [CpW(CO)2(IMe)H] or H [CpW(CO)2(IH)H] to compare to the experimentally studied IMes complexes with mesityl substituents. These calculations reveal W H homolytic bond dissociation energies (BDEs) to decrease with increasing steric bulk of the NHC ligand, from 67 for CpW(CO)2(IH)H to 64 for CpW(CO)2(IMe)H to 63 kcal/mol for CpW(CO)2(IMes)H. The calculated spin density at W for CpW(CO)2(IMes)• is 0.63. The W radicals CpW(CO)2(IMe)• and CpW(CO)2(IH)• are calculated to form weak W W bonds. The weakly bonded complexes [CpW(CO)2(IMe)]2

  3. Stable continuous-time autoregressive process driven by stable subordinator

    NASA Astrophysics Data System (ADS)

    Wyłomańska, Agnieszka; Gajda, Janusz

    2016-02-01

    In this paper we examine the continuous-time autoregressive moving average process driven by α-stable Lévy motion delayed by inverse stable subordinator. This process can be applied to high-frequency data with visible jumps and so-called "trapping-events". Those properties are often visible in financial time series but also in amorphous semiconductors, technical data describing the rotational speed of a machine working under various load regimes or data related to indoor air quality. We concentrate on the main characteristics of the examined subordinated process expressed in the language of the measures of dependence which are main tools used in statistical investigation of real data. However, because the analyzed system is based on the α-stable distribution therefore we cannot consider here the correlation (or covariance) as a main measure which indicates at the dependence inside the process. In the paper we examine the codifference, the more general measure of dependence defined for wide class of processes. Moreover we present the simulation procedure of the considered system and indicate how to estimate its parameters. The theoretical results we illustrate by the simulated data analysis.

  4. Phase stable RF transport system

    DOEpatents

    Curtin, Michael T.; Natter, Eckard F.; Denney, Peter M.

    1992-01-01

    An RF transport system delivers a phase-stable RF signal to a load, such as an RF cavity of a charged particle accelerator. A circuit generates a calibration signal at an odd multiple frequency of the RF signal where the calibration signal is superimposed with the RF signal on a common cable that connects the RF signal with the load. Signal isolating diplexers are located at both the RF signal source end and load end of the common cable to enable the calibration to be inserted and extracted from the cable signals without any affect on the RF signal. Any phase shift in the calibration signal during traverse of the common cable is then functionally related to the phase shift in the RF signal. The calibration phase shift is used to control a phase shifter for the RF signal to maintain a stable RF signal at the load.

  5. Stable maps and Quot schemes

    NASA Astrophysics Data System (ADS)

    Popa, Mihnea; Roth, Mike

    2003-06-01

    In this paper we study the relationship between two different compactifications of the space of vector bundle quotients of an arbitrary vector bundle on a curve. One is Grothendieck's Quot scheme, while the other is a moduli space of stable maps to the relative Grassmannian. We establish an essentially optimal upper bound on the dimension of the two compactifications. Based on that, we prove that for an arbitrary vector bundle, the Quot schemes of quotients of large degree are irreducible and generically smooth. We precisely describe all the vector bundles for which the same thing holds in the case of the moduli spaces of stable maps. We show that there are in general no natural morphisms between the two compactifications. Finally, as an application, we obtain new cases of a conjecture on effective base point freeness for pluritheta linear series on moduli spaces of vector bundles.

  6. Advanced Thermally Stable Jet Fuels

    SciTech Connect

    A. Boehman; C. Song; H. H. Schobert; M. M. Coleman; P. G. Hatcher; S. Eser

    1998-01-01

    The Penn State program in advanced thermally stable jet fuels has five components: 1) development of mechanisms of degradation and solids formation; 2) quantitative measurement of growth of sub-micrometer and micrometer-sized particles during thermal stressing; 3) characterization of carbonaceous deposits by various instrumental and microscopic methods; 4) elucidation of the role of additives in retarding the formation of carbonaceous solids; and 5) assessment of the potential of producing high yields of cycloalkanes and hydroaromatics from coal.

  7. LP based approach to optimal stable matchings

    SciTech Connect

    Teo, Chung-Piaw; Sethuraman, J.

    1997-06-01

    We study the classical stable marriage and stable roommates problems using a polyhedral approach. We propose a new LP formulation for the stable roommates problem. This formulation is non-empty if and only if the underlying roommates problem has a stable matching. Furthermore, for certain special weight functions on the edges, we construct a 2-approximation algorithm for the optimal stable roommates problem. Our technique uses a crucial geometry of the fractional solutions in this formulation. For the stable marriage problem, we show that a related geometry allows us to express any fractional solution in the stable marriage polytope as convex combination of stable marriage solutions. This leads to a genuinely simple proof of the integrality of the stable marriage polytope. Based on these ideas, we devise a heuristic to solve the optimal stable roommates problem. The heuristic combines the power of rounding and cutting-plane methods. We present some computational results based on preliminary implementations of this heuristic.

  8. How Stable Is Stable? Function versus Community Composition

    PubMed Central

    Fernández, Ana; Huang, Suiying; Seston, Sherry; Xing, Jian; Hickey, Robert; Criddle, Craig; Tiedje, James

    1999-01-01

    The microbial community dynamics of a functionally stable, well-mixed, methanogenic reactor fed with glucose were analyzed over a 605-day period. The reactor maintained constant pH and chemical oxygen demand removal during this period. Thirty-six rrn clones from each of seven sampling events were analyzed by amplified ribosomal DNA restriction analysis (ARDRA) for the Bacteria and Archaea domains and by sequence analysis of dominant members of the community. Operational taxonomic units (OTUs), distinguished as unique ARDRA patterns, showed reproducible distribution for three sample replicates. The highest diversity was observed in the Bacteria domain. The 16S ribosomal DNA Bacteria clone library contained 75 OTUs, with the dominant OTU accounting for 13% of the total clones, but just 21 Archaea OTUs were found, and the most prominent OTU represented 50% of the clones from the respective library. Succession in methanogenic populations was observed, and two periods were distinguished: in the first, Methanobacterium formicicum was dominant, and in the second, Methanosarcina mazei and a Methanobacterium bryantii-related organism were dominant. Higher variability in Bacteria populations was detected, and the temporal OTU distribution suggested a chaotic pattern. Although dominant OTUs were constantly replaced from one sampling point to the next, phylogenetic analysis indicated that inferred physiologic changes in the community were not as dramatic as were genetic changes. Seven of eight dominant OTUs during the first period clustered with the spirochete group, although a cyclic pattern of substitution occurred among members within this order. A more flexible community structure characterized the second period, since a sequential replacement of a Eubacterium-related organism by an unrelated deep-branched organism and finally by a Propionibacterium-like species was observed. Metabolic differences among the dominant fermenters detected suggest that changes in carbon and

  9. Bis-N-Heterocyclic Carbene Palladium(IV) Tetrachloride Complexes: Synthesis, Reactivity and Mechanisms of Direct Chlorinations and Oxidations of Organic Substrates

    PubMed Central

    McCall, A. Scott; Wang, Hongwang; Desper, John M.; Kraft, Stefan

    2014-01-01

    This paper describes the preparation and isolation of novel octahedral CH2-bridged bis-(N-heterocyclic carbene)palladium(IV) tetrachlorides of the general formula LPdIVCl4 [L = (NHC)CH2(NHC)] from LPdIICl2 and Cl2. In intermolecular, non-chelation controlled transformations LPdIVCl4 reacted with alkenes and alkynes to 1,2-dichlorination adducts. Aromatic, benzylic, and aliphatic CH-bonds were converted into C-Cl bonds. Detailed mechanistic investigations in the dichlorinations of alkenes were conducted on the 18VE PdIV-complex. Positive solvent effects as well as kinetic measurements probing the impact of cyclohexene- and chloride concentrations on the rate of alkene chlorination, support a PdIV-Cl ionization in the first step. Product stereochemistry and product distributions from various alkenes also support Cl+-transfer from the pentacoordinated PdIV-intermediate LPdIVCl3+ to olefins. 1-hexene/3-hexene competition experiments rule out both the formation of π-complexes along the reaction coordinate as well as in situ generated Cl2 from a reductive elimination process. Instead, a ligand-mediated direct Cl+-transfer from LPdIVCl3+ to the π-system is likely to occur. Similarly, C-H bond chlorinations proceed via an electrophilic process with in situ formed LPdIVCl3+. The presence of a large excess of added Cl− slows down cyclohexene chlorination while the presence of stoichiometric amounts of chloride accelerates both PdIV-Cl ionization and Cl+-transfer from LPdIVCl3+. 1H NMR titrations, T1 relaxation time measurements, binding isotherms and Job plot analysis point to the formation of a trifurcated Cl−…H-C bond in the NHC-ligand periphery as a supramolecular cause for the accelerated chemical events involving the metal center. PMID:21247150

  10. Luminescent Iridium(III) Complexes Supported by N-Heterocyclic Carbene-based C^C^C-Pincer Ligands and Aromatic Diimines

    NASA Astrophysics Data System (ADS)

    Chung, Lai-Hon; Lo, Hoi-Shing; Ng, Sze-Wing; Ma, Dik-Lung; Leung, Chung-Hang; Wong, Chun-Yuen

    2015-10-01

    Iridium(III) hydrido complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-butylimidazolin-2-ylidene)phenyl anion (C1^C^C1) or 1,3-bis(3-butylbenzimidazolin-2-ylidene)phenyl anion (C2^C^C2) and aromatic diimine (2,2‧-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4‧-dimethyl-2,2‧-bipyridine (Me2bpy), or dipyrido-[3,2-f:2‧,3‧-h]-quinoxaline (dpq)) in the form of [Ir(C^C^C)(N^N)(H)]+ have been prepared. Crystal structures for these complexes show that the Ir-CNHC distances are 2.043(5)-2.056(5) Å. The hydride chemical shifts for complexes bearing C1^C^C1 (-20.6 to -20.3 ppm) are more upfield than those with C2^C^C2 (-19.5 and -19.2 ppm), revealing that C1^C^C1 is a better electron donor than C2^C^C2. Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (λ = 340-530 nm (ɛ ≤ 103 dm3 mol-1 cm-1)) originate from a dπ(IrIII) → π*(N^N) metal-to-ligand charge transfer transition, where the dπ(IrIII) level contain significant contribution from the C^C^C ligands. All these complexes are emissive in the yellow-spectral region (553-604 nm in CH3CN and CH2Cl2) upon photo-excitation with quantum yields of 10-3-10-1.

  11. Emissive osmium(II) complexes supported by N-heterocyclic carbene-based C^C^C-pincer ligands and aromatic diimines.

    PubMed

    Chung, Lai-Hon; Chan, Siu-Chung; Lee, Wing-Chun; Wong, Chun-Yuen

    2012-08-20

    Osmium(II) complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-methylimidazolin-2-ylidene)phenyl anion (C(1)^C^C(1)) or 1,3-bis(3-methylbenzimidazolin-2-ylidene)phenyl anion (C(2)^C^C(2)) and aromatic diimine (2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), or 4,4'-diphenyl-2,2'-bipyridine (Ph(2)bpy)) in the form of [Os(C^C^C)(N^N)(CO)](+) have been prepared. Crystal structures for these complexes show that the Os-C(NHC) bonds are essentially single (Os-C(NHC) distances = 2.079(5)-2.103(7) Å). Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (λ(max) = 493-536 nm, ε(max) = (5-10) × 10(3) dm(3) mol(-1) cm(-1), solvent = CH(3)CN) originate from a d(π)(Os(II)) → π*(N^N) metal-to-ligand charge transfer transition, where the d(π)(Os(II)) and π*(N^N) levels contain significant contribution from the C^C^C ligands. All these complexes are emissive in the red-spectral region (674-731 nm) with quantum yields of 10(-4)-10(-2) and emission lifetimes of around 1-6 μs. Transient absorption spectroscopy and spectroelectrochemical measurements have also been used to probe the nature of the emissive excited-states. Overall, this joint experimental and theoretical investigation reveals that the C^C^C ligands can be used to modulate the photophysical properties of a [Os(N^N)] core via the formation of the hybrid [Os + C^C^C] frontier orbitals. PMID:22873818

  12. Luminescent Iridium(III) Complexes Supported by N-Heterocyclic Carbene-based C^C^C-Pincer Ligands and Aromatic Diimines

    PubMed Central

    Chung, Lai-Hon; Lo, Hoi-Shing; Ng, Sze-Wing; Ma, Dik-Lung; Leung, Chung-Hang; Wong, Chun-Yuen

    2015-01-01

    Iridium(III) hydrido complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-butylimidazolin-2-ylidene)phenyl anion (C1^C^C1) or 1,3-bis(3-butylbenzimidazolin-2-ylidene)phenyl anion (C2^C^C2) and aromatic diimine (2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4′-dimethyl-2,2′-bipyridine (Me2bpy), or dipyrido-[3,2-f:2′,3′-h]-quinoxaline (dpq)) in the form of [Ir(C^C^C)(N^N)(H)]+ have been prepared. Crystal structures for these complexes show that the Ir–CNHC distances are 2.043(5)–2.056(5) Å. The hydride chemical shifts for complexes bearing C1^C^C1 (−20.6 to −20.3 ppm) are more upfield than those with C2^C^C2 (−19.5 and −19.2 ppm), revealing that C1^C^C1 is a better electron donor than C2^C^C2. Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (λ = 340–530 nm (ε ≤ 103 dm3 mol−1 cm−1)) originate from a dπ(IrIII) → π*(N^N) metal-to-ligand charge transfer transition, where the dπ(IrIII) level contain significant contribution from the C^C^C ligands. All these complexes are emissive in the yellow-spectral region (553–604 nm in CH3CN and CH2Cl2) upon photo-excitation with quantum yields of 10−3–10−1. PMID:26487542

  13. Stable vices and trailer problems.

    PubMed

    Houpt, K A

    1986-12-01

    Stable vices include oral vices such as cribbing, wood chewing, and coprophagia, as well as stall walking, weaving, pawing, and stall kicking. Some of these behaviors are escape behaviors; others are forms of self-stimulation. Most can be eliminated by pasturing rather than stall confinement. Trailering problems include failure to load, scrambling in the moving trailer, struggling in the stationary trailer, and refusal to unload. Gradual habituation to entering the trailer, the presence of another horse, or a change in trailer type can be used to treat these problems. PMID:3492249

  14. Stable Hemiaminals: 2-Aminopyrimidine Derivatives.

    PubMed

    Kwiecień, Anna; Ciunik, Zbigniew

    2015-01-01

    Stable hemiaminals can be obtained in the one-pot reaction between 2-aminopyrimidine and nitrobenzaldehyde derivatives. Ten new hemiaminals have been obtained, six of them in crystal state. The molecular stability of these intermediates results from the presence of both electron-withdrawing nitro groups as substituents on the phenyl ring and pyrimidine ring, so no further stabilisation by intramolecular interaction is required. Hemiaminal molecules possess a tetrahedral carbon atom constituting a stereogenic centre. As the result of crystallisation in centrosymmetric space groups both enantiomers are present in the crystal structure. PMID:26258772

  15. Persistence Length of Stable Microtubules

    NASA Astrophysics Data System (ADS)

    Hawkins, Taviare; Mirigian, Matthew; Yasar, M. Selcuk; Ross, Jennifer

    2011-03-01

    Microtubules are a vital component of the cytoskeleton. As the most rigid of the cytoskeleton filaments, they give shape and support to the cell. They are also essential for intracellular traffic by providing the roadways onto which organelles are transported, and they are required to reorganize during cellular division. To perform its function in the cell, the microtubule must be rigid yet dynamic. We are interested in how the mechanical properties of stable microtubules change over time. Some ``stable'' microtubules of the cell are recycled after days, such as in the axons of neurons or the cilia and flagella. We measured the persistence length of freely fluctuating taxol-stabilized microtubules over the span of a week and analyzed them via Fourier decomposition. As measured on a daily basis, the persistence length is independent of the contour length. Although measured over the span of the week, the accuracy of the measurement and the persistence length varies. We also studied how fluorescently-labeling the microtubule affects the persistence length and observed that a higher labeling ratio corresponded to greater flexibility. National Science Foundation Grant No: 0928540 to JLR.

  16. Stable Imaging for Astronomy (SIA)

    NASA Astrophysics Data System (ADS)

    Beaulieu, Mathilde; Ottogalli, Sebastien; Preis, Olivier; Bresson, Yves; Rivet, Jean-Pierre; Abe, Lyu; Vakili, Farrokh

    2014-07-01

    One of the most challenging fields of astronomical instrumentation is probably high-contrast imaging since it ultimately combines ultra-high sensitivity at low flux and the ability to cope with photon flux contrasts of several hundreds of millions or even more. These two aspects implicitly require that high-contrast instruments should be highly stable in the sense of the reproducibility of their measurements at different times, but also, continuously stable over time. In most high contrast instruments or experiments, their sensitivity is broken after at most tens of minutes of operation due to uncontrolled and unknown behaviour of the whole experiment regarding the environmental conditions. In this paper, we introduce a general approach of an exhaustive stability study for high-contrast imaging that has been initiated at Lagrange Laboratory, Observatoire de la Côte d'Azur (OCA). On a practical ground, one of the fundamental issues of this study is the metrology, which is the basis of all reproducible measurements. We describe a small experiment designed to understand the behaviour of one of our ultra-precise metrology tools (a commercial sub-nanometric 3-way interferometer) and derive the conditions under which its operation delivers reliable results. The approach will apply to the high-contrast imaging test-bench SPEED, under development at OCA.

  17. Paleoproxies: Heavy Stable Isotope Perspectives

    NASA Astrophysics Data System (ADS)

    Nagler, T. F.; Hippler, D.; Siebert, C.; Kramers, J. D.

    2002-12-01

    Recent advances in isotope ratio mass spectrometry, namely multiple collector ICP-MS and refined TIMS techniques, will significantly enhance the ability to measure heavy stable isotope fractionation, which will lead to the development of a wide array of process-identifying (bio)-geochemical tools. Thus far research in this area is not easily assessable to scientists outside the isotope field. This is due to the fact that analyzing heavy stable isotopes does not provide routine numbers which are per se true (the preciser the truer) but is still a highly experimental field. On the other hand resolving earth science problems requires specialists familiar with the environment being studied. So what is in there for paleoceanographers? In a first order approach, relating isotope variations to physical processes is straightforward. A prominent example are oxygen isotope variations with temperature. The total geological signal is of course far more complicated. At low temperatures, heavy stable isotopes variations have been reported for e.g. Ca, Cr, Fe, Cu, Zn, Mo and Tl. Fractionation mechanisms and physical parameters responsible for the observed variations are not yet resolved for most elements. Significant equilibrium isotope fractionation is expected from redox reactions of transition metals. However a difference in coordination number between two coexisting speciations of an element in the same oxidation state can also cause fractionation. Protonation of dissolved Mo is one case currently discussed. For paleoceanography studies, a principal distinction between transition metals essential for life (V to Zn plus Mo) or not will be helpful. In case of the former group, distinction between biogenic and abiogenic isotope fractionation will remain an important issue. For example, abiotic Fe redox reactions result in isotope fractionations indistinguishable in direction and magnitude from microbial effects. Only a combination of different stable isotope systems bears the

  18. Palladium complexes of abnormal N-heterocyclic carbenes as precatalysts for the much preferred Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium.

    PubMed

    John, Alex; Shaikh, Mobin M; Ghosh, Prasenjit

    2009-12-21

    A series of new PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed precatalysts of abnormal N-heterocyclic carbenes for the highly desirable Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium is reported. Specifically, the PEPPSI themed (NHC)PdI2(pyridine) type precatalysts, 1b-4b, efficiently carried out the highly convenient Cu-free and amine-free Sonogashira coupling of aryl bromides and iodides with terminal acetylenes in air in a mixed aqueous medium. Complexes, 1b-4b, were synthesized by the direct reaction of the corresponding imidazo[1,2-a]pyridinium iodide salts, 1a-4a, with PdCl2 in pyridine in the presence of K2CO3 as a base while the imidazo[1,2-a]pyridinium iodide salts, 1a-4a, were in turn synthesized by the alkylation reactions of the respective imidazo[1,2-a]pyridine derivatives with alkyl iodides. The density functional theory (DFT) studies revealed that these imidazol-3-ylidene[1,2-a]pyridine derived abnormal carbenes are strongly sigma-donating and consequently significantly weaken the catalytically important labile trans pyridine ligand in 1b-4b.

  19. Mixture of Skewed α-Stable Distributions

    NASA Astrophysics Data System (ADS)

    Shojaei, S. R. Hosseini; Nassiri, V.; Mohammadian, Gh. R.; Mohammadpour, A.

    2011-03-01

    Expectation maximization (EM) algorithm and the Bayesian techniques are two approaches for statistical inference of mixture models [3, 4]. By noting the advantages of the Bayesian methods, practitioners prefer them. However, implementing Markov chain Monte Carlo algorithms can be very complicated for stable distributions, due to the non-analytic density or distribution function formulas. In this paper, we introduce a new class of mixture of heavy-tailed distributions, called mixture of skewed stable distributions. Skewed stable distributions belongs to the exponential family and they have analytic density representation. It is shown that skewed stable distributions dominate skew stable distribution functions and they can be used to model heavy-tailed data. The class of skewed stable distributions has an analytic representation for its density function and the Bayesian inference can be done similar to the exponential family of distributions. Finally, mixture of skewed stable distributions are compared to the mixture of stable distributions through a simulations study.

  20. Super-stable Poissonian structures

    NASA Astrophysics Data System (ADS)

    Eliazar, Iddo

    2012-10-01

    In this paper we characterize classes of Poisson processes whose statistical structures are super-stable. We consider a flow generated by a one-dimensional ordinary differential equation, and an ensemble of particles ‘surfing’ the flow. The particles start from random initial positions, and are propagated along the flow by stochastic ‘wave processes’ with general statistics and general cross correlations. Setting the initial positions to be Poisson processes, we characterize the classes of Poisson processes that render the particles’ positions—at all times, and invariantly with respect to the wave processes—statistically identical to their initial positions. These Poisson processes are termed ‘super-stable’ and facilitate the generalization of the notion of stationary distributions far beyond the realm of Markov dynamics.

  1. Stable density stratification solar pond

    NASA Technical Reports Server (NTRS)

    Lansing, F. L. (Inventor)

    1985-01-01

    A stable density-stratification solar pond for use in the collection and storage of solar thermal energy including a container having a first section characterized by an internal wall of a substantially cylindrical configuration and a second section having an internal wall of a substantially truncated conical configuration surmounting the first section in coaxial alignment therewith, the second section of said container being characterized by a base of a diameter substantially equal to the diameter of the first section and a truncated apex defining a solar energy acceptance opening is discussed. A body of immiscible liquids is disposed within the container and comprises a lower portion substantially filling the first section of the container and an upper portion substantially filling the second section of the container, said lower portion being an aqueous based liquid of a darker color than the upper portion and of a greater density. A protective cover plate is removably provided for covering the acceptance opening.

  2. A stable perfluorochemical blood substitute.

    PubMed

    Mukherji, B; Sloviter, H A

    1991-05-01

    A stable emulsion of perfluorodecalin, made up of 34 percent (vol/vol) perfluorodecalin dispersed by sonication in isotonic Tyrode's buffer (pH 7.4) containing egg yolk lecithin, has been developed. The viscosity of the emulsion is the same as that of human blood, and the particle size is 0.2 microns in diameter. On storage at 5 degrees C, there was no change in viscosity for up to 60 weeks. At 21 degrees C, viscosity increased after 20 weeks of storage; this increase was considerably diminished by the presence of tocopherol in the emulsion. The accumulation of malondialdehyde indicated that there was continuous slow oxidation of the lecithin on storage of the emulsion at either 5 or 21 degrees C; this oxidation was markedly reduced by the presence of tocopherol. PMID:2020995

  3. Dimensionally stable metallic hydride composition

    DOEpatents

    Heung, Leung K.

    1994-01-01

    A stable, metallic hydride composition and a process for making such a composition. The composition comprises a uniformly blended mixture of a metal hydride, kieselguhr, and a ballast metal, all in the form of particles. The composition is made by subjecting a metal hydride to one or more hydrogen absorption/desorption cycles to disintegrate the hydride particles to less than approximately 100 microns in size. The particles are partly oxidized, then blended with the ballast metal and the kieselguhr to form a uniform mixture. The mixture is compressed into pellets and calcined. Preferably, the mixture includes approximately 10 vol. % or more kieselguhr and approximately 50 vol. % or more ballast. Metal hydrides that can be used in the composition include Zr, Ti, V, Nb, Pd, as well as binary, tertiary, and more complex alloys of La, Al, Cu, Ti, Co, Ni, Fe, Zr, Mg, Ca, Mn, and mixtures and other combinations thereof. Ballast metals include Al, Cu and Ni.

  4. Stable line defects in silicene

    NASA Astrophysics Data System (ADS)

    Ghosh, Dibyajyoti; Parida, Prakash; Pati, Swapan K.

    2015-11-01

    Line defects in two-dimensional (2D) materials greatly modulate various properties of their pristine form. Using ab initio molecular dynamics (AIMD) simulations, we investigate the structural reconstructions of different kinds of grain boundaries in the silicene sheets. It is evident that depending upon the presence of silicon adatoms and edge shape of grain boundaries (i.e., armchair or zigzag), stable extended line defects (ELDs) can be introduced in a controlled way. Further studies show the stability of these line-defects in silicene, grown on Ag(111) surface at room-temperature. Importantly, unlike most of the 2D sheet materials such as graphene and hexagonal boron nitride, 5-5-8 line defects modify the nonmagnetic semimetallic pristine silicene sheet to spin-polarized metal. As ferromagnetically ordered magnetic moments remain strongly localized at the line defect, a one-dimensional spin channel gets created in silicene. Interestingly, these spin channels are quite stable because, unlike the edge of nanoribbons, structural reconstruction or contamination cannot destroy the ordering of magnetic moments here. Zigzag silicene nanoribbons with a 5-5-8 line defect also exhibit various interesting electronic and magnetic properties depending upon their width as well as the nature of the magnetic coupling between edge and defect spin states. Upon incorporation of other ELDs, such as 4-4-4 and 4-8 defects, 2D sheets and nanoribbons of silicene show a nonmagnetic metallic or semiconducting ground state. Highlighting the controlled formation of ELDs and consequent emergence of technologically important properties in silicene, we propose new routes to realize silicene-based nanoelectronic and spintronic devices.

  5. Uses of stable isotopes in fish ecology

    EPA Science Inventory

    Analyses of fish tissues (other than otoliths) for stable isotope ratios can provide substantial information on fish ecology, including physiological ecology. Stable isotopes of nitrogen and carbon frequently are used to determine the mix of diet sources for consumers. Stable i...

  6. Stable bound orbits around black rings

    SciTech Connect

    Igata, Takahisa; Ishihara, Hideki; Takamori, Yohsuke

    2010-11-15

    We examine bound orbits of particles around singly rotating black rings. We show that there exist stable bound orbits in toroidal spiral shape near the 'axis' of the ring, and also stable circular orbits on the axis as special cases. The stable bound orbits can have arbitrary large size if the thickness of the ring is less than a critical value.

  7. On nonstable and stable population momentum.

    PubMed

    Espenshade, Thomas J; Olgiati, Analia S; Levin, Simon A

    2011-11-01

    This article decomposes total population momentum into two constituent and multiplicative parts: "nonstable" momentum and "stable" momentum. Nonstable momentum depends on deviations between a population's current age distribution and its implied stable age distribution. Stable momentum is a function of deviations between a population's implied stable and stationary age distributions. In general, the factorization of total momentum into the product of nonstable and stable momentum is a very good approximation. The factorization is exact, however, when the current age distribution is stable or when observed fertility is already at replacement. We provide numerical illustrations by calculating nonstable, stable, and total momentum for 176 countries, the world, and its major regions. In short, the article brings together disparate strands of the population momentum literature and shows how the various kinds of momentum fit together into a single unifying framework.

  8. A stable monomeric nickel borohydride.

    PubMed

    Desrochers, Patrick J; LeLievre, Stacey; Johnson, Rosemary J; Lamb, Brian T; Phelps, Andrea L; Cordes, A W; Gu, Weiwei; Cramer, Stephen P

    2003-12-01

    A stable discrete nickel borohydride complex (Tp*NiBH(4) or Tp*NiBD(4)) was prepared using the nitrogen-donor ligand hydrotris(3,5-dimethylpyrazolyl)borate (Tp*-). This complex represents one of the best characterized nickel(II) borohydrides to date. Tp*NiBH(4) and Tp*NiBD(4) are stable toward air, boiling water, and high temperatures (mp > 230 degrees C dec). X-ray crystallographic measurements for Tp*NiBH(4) showed a six-coordinate geometry for the complex, with the nickel(II) center facially coordinated by three bridging hydrogen atoms from borohydride and a tridentate Tp(-) ligand. For Tp*NiBH(4), the empirical formula is C(15)H(26)B(2)N(6)Ni, a = 13.469(9) A, b = 7.740(1) A, c = 18.851(2) A, beta = 107.605(9) degrees, the space group is monoclinic P2(1)/c, and Z = 4. Infrared measurements confirmed the presence of bridging hydrogen atoms; both nu(B[bond]H)(terminal) and nu(B[bond]H)(bridging) are assignable and shifted relative to nu(B-D) of Tp*NiBD(4) by amounts in agreement with theory. Despite their hydrolytic stability, Tp*NiBH(4) and Tp*NiBD(4) readily reduce halocarbon substrates, leading to the complete series of Tp*NiX complexes (X = Cl, Br, I). These reactions showed a pronounced hydrogen/deuterium rate dependence (k(H)/k(D) approximately 3) and sharp isosbestic points in progressive electronic spectra. Nickel K-edge X-ray absorption spectroscopy (XAS) measurements of a hydride-rich nickel center were obtained for Tp*NiBH(4), Tp*NiBD(4), and Tp*NiCl. X-ray absorption near-edge spectroscopy results confirmed the similar six-coordinate geometries for Tp*NiBH(4) and Tp*NiBD(4). These contrasted with XAS results for the crystallographically characterized pseudotetrahedral Tp*NiCl complex. The stability of Tp*Ni-coordinated borohydride is significant given this ion's accelerated decomposition and hydrolysis in the presence of transition metals and simple metal salts. PMID:14632512

  9. Addition of Small Electrophiles to N-Heterocyclic-Carbene-Stabilized Disilicon(0): A Revisit of the Isolobal Concept in Low-Valent Silicon Chemistry.

    PubMed

    Arz, Marius I; Straßmann, Martin; Geiß, Daniel; Schnakenburg, Gregor; Filippou, Alexander C

    2016-04-01

    Protonation and alkylation of (Idipp)Si═Si(Idipp) (1) afforded the mixed-valent disilicon(I)-borates [(Idipp)(R)Si(II)═Si(0)(Idipp)][B(Ar(F))4] (1R[B(Ar(F))4]; R = H, Me, Et; Ar(F) = C6H3-3,5-(CF3)2; Idipp = C[N(C6H3-2,6-iPr2)CH]2) as red to orange colored, highly air-sensitive solids, which were characterized by single-crystal X-ray diffraction, IR spectroscopy and multinuclear NMR spectroscopy. Dynamic NMR studies in solution revealed a degenerate isomerization (topomerization) of the "σ-bonded" tautomers of 1H[B(Ar(F))4], which proceeds according to quantum chemical calculations via a NHC-stabilized (NHC = N-heterocyclic carbene) disilahydronium ion ("π-bonded" isomer) and is reminiscent of the degenerate rearrangement of carbenium ions formed upon protonation of olefins. The topomerization of 1H[B(Ar(F))4] provides the first example of a reversible 1,2-H migration along a Si═Si bond observed in a molecular system. In contrast, 1Me[B(Ar(F))4] adopts a "rigid" structure in solution due to the higher energy required for the interconversion of the "σ-bonded" isomer into a putative NHC-stabilized disilamethonium ion. Addition of alkali metal borates to 1 afforded the alkali metal disilicon(0) borates 1M[BAr4] (M = Li, Ar = C6F5; M = Na, Ar = Ar(F)) as brown, air-sensitive solids. Single-crystal X-ray diffraction analyses and NMR spectroscopic studies of 1M[BAr4] suggest in concert with quantum chemical calculations that encapsulation of the alkali metal cations in the cavity of 1 predominantly occurs via electrostatic cation-π interactions with the Si═Si π-bond and the peripheral NHC aryl rings. Displacement of the [Si(NHC)] fragments by the isolobal fragments [PR] and [SiR](-) interrelates the cations [(NHC)(R)Si═Si(NHC)](+) to a series of familiar, multiply bonded Si and P compounds as verified by analyses of their electronic structures.

  10. Neutral and Cationic Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes: Reactivity in Selected Olefin Metathesis Reactions and Immobilization on Silica.

    PubMed

    Sen, Suman; Schowner, Roman; Imbrich, Dominik A; Frey, Wolfgang; Hunger, Michael; Buchmeiser, Michael R

    2015-09-21

    The synthesis and single-crystal X-ray structures of the novel molybdenum imido alkylidene N-heterocyclic carbene complexes [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf)2] (3), [Mo(N-2,6-Me2C6H3)(IMes)(CHCMe2Ph)(OTf)2] (4), [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf){OCH(CF3)2}] (5), [Mo(N-2,6-Me2C6H3)(CH3CN)(IMesH2)(CHCMe2Ph)(OTf)](+)BArF(-) (6), [Mo(N-2,6-Cl2C6H3)(IMesH2)(CHCMe3)(OTf)2] (7) and [Mo(N-2,6-Cl2C6H3)(IMes)(CHCMe3)(OTf)2] (8) are reported (IMesH2=1,3-dimesitylimidazolidin-2-ylidene, IMes=1,3-dimesitylimidazolin-2-ylidene, BArF(-)=tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate, OTf=CF3SO3(-)). Also, silica-immobilized versions I1 and I2 were prepared. Catalysts 3-8, I1 and I2 were used in homo-, cross-, and ring-closing metathesis (RCM) reactions and in the cyclopolymerization of α,ω-diynes. In the RCM of α,ω-dienes, in the homometathesis of 1-alkenes, and in the ethenolysis of cyclooctene, turnover numbers (TONs) up to 100,000, 210,000 and 30,000, respectively, were achieved. With I1 and I2, virtually Mo-free products were obtained (<3 ppm Mo). With 1,6-hepta- and 1,7-octadiynes, catalysts 3, 4, and 5 allowed for the regioselective cyclopolymerization of 4,4-bis(ethoxycarbonyl)-1,6-heptadiyne, 4,4-bis(hydroxymethyl)-1,6-heptadiyne, 4,4-bis[(3,5-diethoxybenzoyloxy)methyl]-1,6-heptadiyne, 4,4,5,5-tetrakis(ethoxycarbonyl)-1,7-octadiyne, and 1,6-heptadiyne-4-carboxylic acid, underlining the high functional-group tolerance of these novel Group 6 metal alkylidenes. PMID:26249141

  11. Organocatalytic conjugate-addition polymerization of linear and cyclic acrylic monomers by N-heterocyclic carbenes: mechanisms of chain initiation, propagation, and termination.

    PubMed

    Zhang, Yuetao; Schmitt, Meghan; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Chen, Eugene Y-X

    2013-11-27

    This contribution presents a full account of experimental and theoretical/computational investigations into the mechanisms of chain initiation, propagation, and termination of the recently discovered N-heterocyclic carbene (NHC)-mediated organocatalytic conjugate-addition polymerization of acrylic monomers. The current study specifically focuses on three commonly used NHCs of vastly different nucleophilicity, 1,3-di-tert-butylimidazolin-2-ylidene (I(t)Bu), 1,3-dimesitylimidazolin-2-ylidene (IMes), and 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene (TPT), and two representative acrylic monomers, the linear methyl methacrylate (MMA) and its cyclic analog, biomass-derived renewable γ-methyl-α-methylene-γ-butyrolactone (MMBL). For MMA, there exhibits an exquisite selectivity of the NHC structure for the three types of reactions it promotes: enamine formation (single-monomer addition) by IMes, dimerization (tail-to-tail) by TPT, and polymerization by I(t)Bu. For MMBL, all three NHCs promote no dimerization but polymerization, with the polymerization activity being highly sensitive to the NHC structure and the solvent polarity. Thus, I(t)Bu is the most active catalyst of the series and converts quantitatively 1000-3000 equiv of MMBL in 1 min or 10,000 equiv in 5 min at room temperature to MMBL-based bioplastics with a narrow range of molecular weights of M(n) = 70-85 kg/mol, regardless of the [MMBL]/[I(t)Bu] ratio employed. The I(t)Bu-catalyzed MMBL polymerization reaches an exceptionally high turnover frequency up to 122 s(-1) and a high initiator efficiency value up to 1600%. Unique chain-termination mechanisms have been revealed, accounting for the production of relative high-molecular-weight linear polymers and the catalytic nature of this NHC-mediated conjugate-addition polymerization. Computational studies have provided mechanistic insights into reactivity and selectivity between two competing pathways for each NHC-monomer zwitterionic adduct, namely

  12. Addition of Small Electrophiles to N-Heterocyclic-Carbene-Stabilized Disilicon(0): A Revisit of the Isolobal Concept in Low-Valent Silicon Chemistry.

    PubMed

    Arz, Marius I; Straßmann, Martin; Geiß, Daniel; Schnakenburg, Gregor; Filippou, Alexander C

    2016-04-01

    Protonation and alkylation of (Idipp)Si═Si(Idipp) (1) afforded the mixed-valent disilicon(I)-borates [(Idipp)(R)Si(II)═Si(0)(Idipp)][B(Ar(F))4] (1R[B(Ar(F))4]; R = H, Me, Et; Ar(F) = C6H3-3,5-(CF3)2; Idipp = C[N(C6H3-2,6-iPr2)CH]2) as red to orange colored, highly air-sensitive solids, which were characterized by single-crystal X-ray diffraction, IR spectroscopy and multinuclear NMR spectroscopy. Dynamic NMR studies in solution revealed a degenerate isomerization (topomerization) of the "σ-bonded" tautomers of 1H[B(Ar(F))4], which proceeds according to quantum chemical calculations via a NHC-stabilized (NHC = N-heterocyclic carbene) disilahydronium ion ("π-bonded" isomer) and is reminiscent of the degenerate rearrangement of carbenium ions formed upon protonation of olefins. The topomerization of 1H[B(Ar(F))4] provides the first example of a reversible 1,2-H migration along a Si═Si bond observed in a molecular system. In contrast, 1Me[B(Ar(F))4] adopts a "rigid" structure in solution due to the higher energy required for the interconversion of the "σ-bonded" isomer into a putative NHC-stabilized disilamethonium ion. Addition of alkali metal borates to 1 afforded the alkali metal disilicon(0) borates 1M[BAr4] (M = Li, Ar = C6F5; M = Na, Ar = Ar(F)) as brown, air-sensitive solids. Single-crystal X-ray diffraction analyses and NMR spectroscopic studies of 1M[BAr4] suggest in concert with quantum chemical calculations that encapsulation of the alkali metal cations in the cavity of 1 predominantly occurs via electrostatic cation-π interactions with the Si═Si π-bond and the peripheral NHC aryl rings. Displacement of the [Si(NHC)] fragments by the isolobal fragments [PR] and [SiR](-) interrelates the cations [(NHC)(R)Si═Si(NHC)](+) to a series of familiar, multiply bonded Si and P compounds as verified by analyses of their electronic structures. PMID:26978031

  13. Neutral and Cationic Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes: Reactivity in Selected Olefin Metathesis Reactions and Immobilization on Silica.

    PubMed

    Sen, Suman; Schowner, Roman; Imbrich, Dominik A; Frey, Wolfgang; Hunger, Michael; Buchmeiser, Michael R

    2015-09-21

    The synthesis and single-crystal X-ray structures of the novel molybdenum imido alkylidene N-heterocyclic carbene complexes [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf)2] (3), [Mo(N-2,6-Me2C6H3)(IMes)(CHCMe2Ph)(OTf)2] (4), [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf){OCH(CF3)2}] (5), [Mo(N-2,6-Me2C6H3)(CH3CN)(IMesH2)(CHCMe2Ph)(OTf)](+)BArF(-) (6), [Mo(N-2,6-Cl2C6H3)(IMesH2)(CHCMe3)(OTf)2] (7) and [Mo(N-2,6-Cl2C6H3)(IMes)(CHCMe3)(OTf)2] (8) are reported (IMesH2=1,3-dimesitylimidazolidin-2-ylidene, IMes=1,3-dimesitylimidazolin-2-ylidene, BArF(-)=tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate, OTf=CF3SO3(-)). Also, silica-immobilized versions I1 and I2 were prepared. Catalysts 3-8, I1 and I2 were used in homo-, cross-, and ring-closing metathesis (RCM) reactions and in the cyclopolymerization of α,ω-diynes. In the RCM of α,ω-dienes, in the homometathesis of 1-alkenes, and in the ethenolysis of cyclooctene, turnover numbers (TONs) up to 100,000, 210,000 and 30,000, respectively, were achieved. With I1 and I2, virtually Mo-free products were obtained (<3 ppm Mo). With 1,6-hepta- and 1,7-octadiynes, catalysts 3, 4, and 5 allowed for the regioselective cyclopolymerization of 4,4-bis(ethoxycarbonyl)-1,6-heptadiyne, 4,4-bis(hydroxymethyl)-1,6-heptadiyne, 4,4-bis[(3,5-diethoxybenzoyloxy)methyl]-1,6-heptadiyne, 4,4,5,5-tetrakis(ethoxycarbonyl)-1,7-octadiyne, and 1,6-heptadiyne-4-carboxylic acid, underlining the high functional-group tolerance of these novel Group 6 metal alkylidenes.

  14. Synthesis and Characterization of Amphiphilic Cyclic Diblock Copolypeptoids from N-Heterocyclic Carbene-Mediated Zwitterionic Polymerization of N-Substituted N-carboxyanhydride

    PubMed Central

    Lee, Chang-Uk; Smart, Thomas P.; Guo, Li; Epps, Thomas H.; Zhang, Donghui

    2011-01-01

    N-Heterocyclic carbene (NHC)-mediated ring-opening polymerization of N-decylN-carboxylanhydride monomer (De-NCA) has been shown to occur in a controlled manner, yielding cyclic poly(N-decyl-glycine)s (c-PNDGs) with polymer molecular weights (MW) between 4.8 and 31 kg·mol−1 and narrow molecular weight distributions (PDI < 1.15). The reaction exhibits pseudo-first order kinetics with respect to monomer concentration. The polymer MW increases linearly with conversion, consistent with a living polymerization. ESI MS and SEC analysesconfirm the cyclic architectures of the forming polymers. DSC and WAXS studies reveal that the c-PNDG homopolymers are highly crystalline with two prominent first order transitions at 72–79°C (Tm,1) and 166–177°C (Tm,2), which have been attributed to the side chain and main chain melting respectively. A series of amphiphilic cyclic diblock copolypeptoids [i.e.,poly(N-methyl-glycine)-b-poly(N-decyl-glycine) (c-PNMG-b-PNDG)] with variable molecular weight and composition was synthesized by sequential NHC-mediated polymerization of the corresponding N-methyl N-carboxyanhydride (Me-NCA) and De-NCA monomers. 1H NMR analysis reveals that adjusting the initial monomer to NHC molar ratio can readily control the block copolymer chain length and composition. Time-lapsed light scattering and cryogenic transmission electron microscopy (cryo-TEM) analysis of c-PNDG-b-PNMG samples revealed that the amphiphilic cyclic block copolypeptoids self-assemble into spherical micelles that reorganize into micron-long cylindrical micelles with uniform diameter in room temperature methanol over the course of several days. An identical morphological transition has also been noted for the linear analogs, which occurs more rapidly than for the cyclic copolypeptoids. We tentatively attribute this difference to the different crystallization kinetics of the solvophobic block (i.e., PNDG) in the cyclic and linear block copolypeptoids. PMID:22247571

  15. Evolutionary routes to stable ownership.

    PubMed

    Hare, D; Reeve, H K; Blossey, B

    2016-06-01

    Ownership can evolve in potentially any species. Drawing on insights from across disciplines, we distinguish between possession and ownership and present species-neutral criteria for ownership, defined as respect for possession. We use a variant of the tug-of-war evolutionary game to demonstrate how ownership can evolve in the form of a new, biologically realistic strategy, Restraint With Retaliation (RWR). In our game, resource holding potential (RHP) is assumed to be equal between interactants, and resource holding asymmetry determines whether ownership is adaptive. RWR will be evolutionarily stable when the ratio of resource holdings between interactants is relatively low, but not when this ratio is sufficiently high. We offer RWR as one evolutionary route to ownership among many, and discuss how ownership unites previously described behavioural phenomena across taxa. We propose that some but not all mechanisms of territory formation and maintenance can be considered ownership, and show that territories are not the only resources that can be owned. We argue that ownership can be a powerful cooperative solution to tragedies of the commons and problems of collective action throughout the biological world. We advance recent scholarship that has begun to investigate the biological importance of ownership, and we call for a comprehensive account of its evolutionary logic and taxonomic distribution. We propose that ownership should be considered a fundamental, unifying biological phenomenon. PMID:26991035

  16. Evolutionary routes to stable ownership.

    PubMed

    Hare, D; Reeve, H K; Blossey, B

    2016-06-01

    Ownership can evolve in potentially any species. Drawing on insights from across disciplines, we distinguish between possession and ownership and present species-neutral criteria for ownership, defined as respect for possession. We use a variant of the tug-of-war evolutionary game to demonstrate how ownership can evolve in the form of a new, biologically realistic strategy, Restraint With Retaliation (RWR). In our game, resource holding potential (RHP) is assumed to be equal between interactants, and resource holding asymmetry determines whether ownership is adaptive. RWR will be evolutionarily stable when the ratio of resource holdings between interactants is relatively low, but not when this ratio is sufficiently high. We offer RWR as one evolutionary route to ownership among many, and discuss how ownership unites previously described behavioural phenomena across taxa. We propose that some but not all mechanisms of territory formation and maintenance can be considered ownership, and show that territories are not the only resources that can be owned. We argue that ownership can be a powerful cooperative solution to tragedies of the commons and problems of collective action throughout the biological world. We advance recent scholarship that has begun to investigate the biological importance of ownership, and we call for a comprehensive account of its evolutionary logic and taxonomic distribution. We propose that ownership should be considered a fundamental, unifying biological phenomenon.

  17. High Frequency Stable Oscillate boiling

    NASA Astrophysics Data System (ADS)

    Li, Fenfang; Gonzalez-Avila, Silvestre Roberto; Ohl, Claus Dieter

    2015-11-01

    We present an unexpected regime of resonant bubble oscillations on a thin metal film submerged in water, which is continuously heated with a focused CW laser. The oscillatory bubble dynamics reveals a remarkably stable frequency of several 100 kHz and is resolved from the side using video recordings at 1 million frames per second. The emitted sound is measured simultaneously and shows higher harmonics. Once the laser is switched on the water in contact with the metal layer is superheated and an explosively expanding cavitation bubble is generated. However, after the collapse a microbubble is nucleated from the bubble remains which displays long lasting oscillations. Generally, pinch-off from of the upper part of the microbubble is observed generating a continuous stream of small gas bubbles rising upwards. The cavitation expansion, collapse, and the jetting of gas bubbles are detected by the hydrophone and are correlated to the high speed video. We find the bubble oscillation frequency is dependent on the bubble size and surface tension. A preliminary model based on Marangoni flow and heat transfer can explain the high flow velocities observed, yet the origin of bubble oscillation is currently not well understood.

  18. Advanced thermally stable jet fuels

    SciTech Connect

    Schobert, H.H.

    1999-01-31

    The Pennsylvania State University program in advanced thermally stable coal-based jet fuels has five broad objectives: (1) Development of mechanisms of degradation and solids formation; (2) Quantitative measurement of growth of sub-micrometer and micrometer-sized particles suspended in fuels during thermal stressing; (3) Characterization of carbonaceous deposits by various instrumental and microscopic methods; (4) Elucidation of the role of additives in retarding the formation of carbonaceous solids; (5) Assessment of the potential of production of high yields of cycloalkanes by direct liquefaction of coal. Future high-Mach aircraft will place severe thermal demands on jet fuels, requiring the development of novel, hybrid fuel mixtures capable of withstanding temperatures in the range of 400--500 C. In the new aircraft, jet fuel will serve as both an energy source and a heat sink for cooling the airframe, engine, and system components. The ultimate development of such advanced fuels requires a thorough understanding of the thermal decomposition behavior of jet fuels under supercritical conditions. Considering that jet fuels consist of hundreds of compounds, this task must begin with a study of the thermal degradation behavior of select model compounds under supercritical conditions. The research performed by The Pennsylvania State University was focused on five major tasks that reflect the objectives stated above: Task 1: Investigation of the Quantitative Degradation of Fuels; Task 2: Investigation of Incipient Deposition; Task 3: Characterization of Solid Gums, Sediments, and Carbonaceous Deposits; Task 4: Coal-Based Fuel Stabilization Studies; and Task 5: Exploratory Studies on the Direct Conversion of Coal to High Quality Jet Fuels. The major findings of each of these tasks are presented in this executive summary. A description of the sub-tasks performed under each of these tasks and the findings of those studies are provided in the remainder of this volume

  19. On Nonstable and Stable Population Momentum

    PubMed Central

    Olgiati, Analia S.; Levin, Simon A.

    2014-01-01

    This article decomposes total population momentum into two constituent and multiplicative parts: “nonstable” momentum and “stable” momentum. Nonstable momentum depends on deviations between a population’s current age distribution and its implied stable age distribution. Stable momentum is a function of deviations between a population’s implied stable and stationary age distributions. In general, the factorization of total momentum into the product of nonstable and stable momentum is a very good approximation. The factorization is exact, however, when the current age distribution is stable or when observed fertility is already at replacement. We provide numerical illustrations by calculating nonstable, stable, and total momentum for 176 countries, the world, and its major regions. In short, the article brings together disparate strands of the population momentum literature and shows how the various kinds of momentum fit together into a single unifying framework. PMID:21948106

  20. Magnetic properties of 1 : 4 complexes of CoCl2 and pyridines carrying carbenes (S(0) = 4/2, 6/2, and 8/2) in diluted frozen solution; influence of carbene multiplicity on heterospin single-molecule magnets.

    PubMed

    Karasawa, Satoru; Nakano, Kimihiro; Tanokashira, Jun-ichi; Yamamoto, Noriko; Yoshizaki, Takahito; Koga, Noboru

    2012-11-28

    The microcrystalline sample of a parent complex, [CoCl(2)(py)(4)], showed a single-molecule magnet (SMM) behavior with an effective activation barrier, U(eff)/k(B), of 16 K for reversal of the magnetism in the presence of a dc field of 3 kOe. Pyridine ligands having 2-4 diazo moieties, DYpy; Y = 2, 3l, 3b, and 4, were prepared and confirmed to be quintet, septet, septet, and nonet in the ground state, respectively, after irradiation. The 1 : 4 complexes, CoCl(2)(DYpy)(4); Y = 2, 3l, 3b, and 4 in frozen solutions after irradiation showed the magnetic behaviors of SMMs with total spin multiplicity, S(total) = 17/2, 25/2, 25/2, and 33/2, respectively. Hysteresis loops depending on the temperature were observed and the values of coercive force, H(c), at 1.9 K were 12, 8.4, 11, and 8.1 kOe for CoCl(2)(CYpy)(4); Y = 2, 3l, 3b, and 4, respectively. In dynamic magnetic susceptibility experiments, ac magnetic susceptibility data obeyed the Arrhenius law to give U(eff)/k(B) values of 94, 92, 93, and 87 K for CoCl(2)(CYpy)(4); Y = 2, 3l, 3b, and 4, respectively, while the relaxation times for CoCl(2)(CYpy)(4); Y = 2 and 3l, obtained by dc magnetization decay in the range of 3.5-1.9 K slightly deviated downward from Arrhenius plots on cooling. The dynamic magnetic behaviors for CoCl(2)(CYpy)(4) including [CoCl(2)(py)(4)] and CoCl(2)(C1py)(4) suggested that the generated carbenes interacted with the cobalt ion to increase the relaxation time, τ(q), due to the spin quantum tunneling magnetization, which became larger with increasing S(total) of the complex.

  1. Concerted Amidation of Activated Esters: Reaction Path and Origins of Selectivity in the Kinetic Resolution of Cyclic Amines via N-Heterocyclic Carbenes and Hydroxamic Acid Cocatalyzed Acyl Transfer

    PubMed Central

    2015-01-01

    The N-heterocyclic carbene and hydroxamic acid cocatalyzed kinetic resolution of cyclic amines generates enantioenriched amines and amides with selectivity factors up to 127. In this report, a quantum mechanical study of the reaction mechanism indicates that the selectivity-determining aminolysis step occurs via a novel concerted pathway in which the hydroxamic acid plays a key role in directing proton transfer from the incoming amine. This modality was found to be general in amide bond formation from a number of activated esters including those generated from HOBt and HOAt, reagents that are broadly used in peptide coupling. For the kinetic resolution, the proposed model accurately predicts the faster reacting enantiomer. A breakdown of the steric and electronic control elements shows that a gearing effect in the transition state is responsible for the observed selectivity. PMID:25050843

  2. H-D exchange in metal carbene complexes: Structure of cluster (μ-H)(μ-OCD3)Os3(CO)9{:C(CD3)NC2H8O}

    NASA Astrophysics Data System (ADS)

    Savkov, Boris; Maksakov, Vladimir; Kuratieva, Natalia

    2015-10-01

    X-ray and spectroscopic data for the new complex (μ-H)(μ-OCH3)Os3(CO)9{:C(CD3)NC2H8O} (2) obtained in the reaction of the (μ-H)(μ-Cl)Os3(CO)9{:C(CH3)NC2H8O} (1) with NaOCD3 in CD3OD solution are reported. It is shown that cluster 1 has the property of CH-acidity inherent of Fisher type carbenes. This had demonstrated using hydrogen deuterium exchange reaction in the presence of a strong base. Bridging chlorine to metoxide ligand substitution takes place during the reaction. The molecular structure of 2 is compared with known analogues.

  3. Blood feeding behavior of the stable fly

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Stable fly is a fly that looks similar to a house fly but both sexes are blood feeders. Blood is required for successful fertilization and development of eggs. Bites are painful but there is usually no pain after the fly stops feeding. The stable fly is a persistent feeder and will continue trying t...

  4. Structure of acid-stable carmine.

    PubMed

    Sugimoto, Naoki; Kawasaki, Yoko; Sato, Kyoko; Aoki, Hiromitsu; Ichi, Takahito; Koda, Takatoshi; Yamazaki, Takeshi; Maitani, Tamio

    2002-02-01

    Acid-stable carmine has recently been distributed in the U.S. market because of its good acid stability, but it is not permitted in Japan. We analyzed and determined the structure of the major pigment in acid-stable carmine, in order to establish an analytical method for it. Carminic acid was transformed into a different type of pigment, named acid-stable carmine, through amination when heated in ammonia solution. The features of the structure were clarified using a model compound, purpurin, in which the orientation of hydroxyl groups on the A ring of the anthraquinone skeleton is the same as that of carminic acid. By spectroscopic means and the synthesis of acid-stable carmine and purpurin derivatives, the structure of the major pigment in acid-stable carmine was established as 4-aminocarminic acid, a novel compound. PMID:11998314

  5. Facile Thermal W–W Bond Homolysis in the N-Heterocyclic Carbene Containing Tungsten Dimer [CpW(CO) 2 (IMe)] 2

    SciTech Connect

    van der Eide, Edwin F.; Liu, Tianbiao; Camaioni, Donald M.; Walter, Eric D.; Bullock, R. Morris

    2012-03-12

    The thermal W-W bond homolysis in [CpW(CO)2(IMe)]2 (IMe = 1,3-dimethylimidazol-2-ylidene) was investigated and was found to occur to a large extent compared to other tungsten dimers such as [CpW(CO)3]2. CpW(CO)2(IMe)H was prepared by heating a solution of [IMeH]+[CpW(CO)2(PMe3)]-, and exists in solution as a mixture of interconverting cis and trans isomers. The carbene rotation in CpW(CO)2(IMe)H was explored by DFT calculations, and low enthalpic barriers (< 3.5 kcal mol-1) are predicted. CpW(CO)2(IMe)H has pKaMeCN = 31.5(3) and deprotonation with KH gives K+[CpW(CO)2(IMe)]- (• MeCN). Hydride abstraction from CpW(CO)2(IMe)H with Ph3C+PF6- in the presence of a coordinating ligand L (MeCN or THF) gives [CpW(CO)2(IMe)(L)]+PF6-. Electrochemical measurements on the anion [CpW(CO)2(IMe)]- in MeCN, together with digital simulations, give an E1/2 of -1.54(2) V vs Cp2Fe+/0 for the [CpW(CO)2(IMe)]•/- couple. A thermochemical cycle provides the solution bond dissociation free energy of the W-H bond of CpW(CO)2(IMe)H as 61.3(6) kcal mol-1. In the electrochemical oxidation of [CpW(CO)2(IMe)]-, reversible dimerization of the electrogenerated radical CpW(CO)2(IMe)• occurs, and digital simulation provides kinetic and thermodynamic parameters for the monomer-dimer equilibrium: kdimerization ~ 2.5 x 104 M-1 s-1, khomolysis ~ 0.5 s-1 (i.e., Kdim ~ 5 x 104 M-1). Reduction of [CpW(CO)2(IMe)(MeCN)]+PF6- with cobaltocene gives the dimer [CpW(CO)2(IMe)]2, which in solution exists as a mixture of anti and gauche rotomers. As expected from the electrochemical experiments, the dimer is in equilibrium with detectable amounts of CpW(CO)2(IMe)•. This species was observed by IR spectroscopy, and its presence in solution is also in accordance with the observed reactivity toward 2,6-di-tert-butyl-1,4-benzoquinone, chloroform and dihydrogen. This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences

  6. Computing Stable Outcomes in Hedonic Games

    NASA Astrophysics Data System (ADS)

    Gairing, Martin; Savani, Rahul

    We study the computational complexity of finding stable outcomes in symmetric additively-separable hedonic games. These coalition formation games are specified by an undirected edge-weighted graph: nodes are players, an outcome of the game is a partition of the nodes into coalitions, and the utility of a node is the sum of incident edge weights in the same coalition. We consider several natural stability requirements defined in the economics literature. For all of them the existence of a stable outcome is guaranteed by a potential function argument, so local improvements will converge to a stable outcome and all these problems are in PLS. The different stability requirements correspond to different local search neighbourhoods. For different neighbourhood structures, our findings comprise positive results in the form of polynomial-time algorithms for finding stable outcomes, and negative (PLS-completeness) results.

  7. Polymeric foams stable at high temperatures

    NASA Technical Reports Server (NTRS)

    Riccitiello, S. R.; Harrison, E. S.; Delano, C. B.

    1976-01-01

    Crosslinked poly(N-arylenebenzimidazoles) are stable up to 370 C. Polymers are made by mixing appropriate stoichiometric amounts of tetramine and aromatic dicarboxylic acid anhydride with phenol or alkyl-substituted phenol.

  8. Thermally Stable Piezoelectric and Pyroelectric Polymers

    NASA Technical Reports Server (NTRS)

    Simpson, Joycelyn O.; St. Clair, Terry L.

    2006-01-01

    A class of thermally stable piezoelectric and pyroelectric polymers, and an improved method of making them, have been invented. These polymers can be used as substrates for a wide variety of electromechanical transducers, sensors, and actuators.

  9. DNA modifications: Another stable base in DNA

    NASA Astrophysics Data System (ADS)

    Brazauskas, Pijus; Kriaucionis, Skirmantas

    2014-12-01

    Oxidation of 5-methylcytosine has been proposed to mediate active and passive DNA demethylation. Tracking the history of DNA modifications has now provided the first solid evidence that 5-hydroxymethylcytosine is a stable epigenetic modification.

  10. Stable Isotope Signatures for Microbial Forensics

    SciTech Connect

    Kreuzer, Helen W.

    2012-01-03

    The isotopic distribution of the atoms composing the molecules of microorganisms is a function of the substrates used by the organisms. The stable isotope content of an organism is fixed so long as no further substrate consumption and biosynthesis occurs, while the radioactive isotopic content decays over time. The distribution of stable isotopes of C, N, O and H in heterotrophic microorganisms is a direct function of the culture medium, and therefore the stable isotope composition can be used to associate samples with potential culture media and also with one another. The 14C content depends upon the 14C content, and therefore the age, of the organic components of the culture medium, as well as on the age of the culture itself. Stable isotope signatures can thus be used for sample matching, to associate cultures with specific growth media, and to predict characteristics of growth media.

  11. Mechanically and thermally stable maser cavity resonator

    NASA Technical Reports Server (NTRS)

    Vessot, R. F. C.; Hoffman, T. E.; Levine, M. W.

    1972-01-01

    New type cavity resonator is designed for hydrogen maser. Resonator consists of three pieces of glass-ceramic material having extremely low thermal coefficient of expansion and provides very stable mechanical tuning.

  12. Evolutionary origin of asymptotically stable consensus.

    PubMed

    Tang, Chang-Bing; Wu, Bin; Wang, Jian-Bo; Li, Xiang

    2014-01-01

    Consensus is widely observed in nature as well as in society. Up to now, many works have focused on what kind of (and how) isolated single structures lead to consensus, while the dynamics of consensus in interdependent populations remains unclear, although interactive structures are everywhere. For such consensus in interdependent populations, we refer that the fraction of population adopting a specified strategy is the same across different interactive structures. A two-strategy game as a conflict is adopted to explore how natural selection affects the consensus in such interdependent populations. It is shown that when selection is absent, all the consensus states are stable, but none are evolutionarily stable. In other words, the final consensus state can go back and forth from one to another. When selection is present, there is only a small number of stable consensus state which are evolutionarily stable. Our study highlights the importance of evolution on stabilizing consensus in interdependent populations. PMID:24699444

  13. Stable Isotope Enrichment Capabilities at ORNL

    SciTech Connect

    Egle, Brian; Aaron, W Scott; Hart, Kevin J

    2013-01-01

    The Oak Ridge National Laboratory (ORNL) and the US Department of Energy Nuclear Physics Program have built a high-resolution Electromagnetic Isotope Separator (EMIS) as a prototype for reestablishing a US based enrichment capability for stable isotopes. ORNL has over 60 years of experience providing enriched stable isotopes and related technical services to the international accelerator target community, as well as medical, research, industrial, national security, and other communities. ORNL is investigating the combined use of electromagnetic and gas centrifuge isotope separation technologies to provide research quantities (milligram to several kilograms) of enriched stable isotopes. In preparation for implementing a larger scale production facility, a 10 mA high-resolution EMIS prototype has been built and tested. Initial testing of the device has simultaneously collected greater than 98% enriched samples of all the molybdenum isotopes from natural abundance feedstock.

  14. High-Order Energy Stable WENO Schemes

    NASA Technical Reports Server (NTRS)

    Yamaleev, Nail K.; Carpenter, Mark H.

    2008-01-01

    A new third-order Energy Stable Weighted Essentially NonOscillatory (ESWENO) finite difference scheme for scalar and vector linear hyperbolic equations with piecewise continuous initial conditions is developed. The new scheme is proven to be stable in the energy norm for both continuous and discontinuous solutions. In contrast to the existing high-resolution shock-capturing schemes, no assumption that the reconstruction should be total variation bounded (TVB) is explicitly required to prove stability of the new scheme. A rigorous truncation error analysis is presented showing that the accuracy of the 3rd-order ESWENO scheme is drastically improved if the tuning parameters of the weight functions satisfy certain criteria. Numerical results show that the new ESWENO scheme is stable and significantly outperforms the conventional third-order WENO finite difference scheme of Jiang and Shu in terms of accuracy, while providing essentially nonoscillatory solutions near strong discontinuities.

  15. Concentration of stable elements in food products

    SciTech Connect

    Montford, M.A.; Shank, K.E.; Hendricks, C.; Oakes, T.W.

    1980-01-01

    Food samples were taken from commercial markets and analyzed for stable element content. The concentrations of most stable elements (Ag, Al, As, Au, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Cu, Fe, Hf, I, K, La, Mg, Mn, Mo, Na, Rb, Sb, Sc, Se, Sr, Ta, Th, Ti, V, Zn, Zr) were determined using multiple-element neutron activation analysis, while the concentrations of other elements (Cd, Hg, Ni, Pb) were determined using atomic absorption. The relevance of the concentrations found are noted in relation to other literature values. An earlier study was extended to include the determination of the concentration of stable elements in home-grown products in the vicinity of the Oak Ridge National Laboratory. Comparisons between the commercial and local food-stuff values are discussed.

  16. Low work function, stable thin films

    DOEpatents

    Dinh, Long N.; McLean, II, William; Balooch, Mehdi; Fehring, Jr., Edward J.; Schildbach, Marcus A.

    2000-01-01

    Generation of low work function, stable compound thin films by laser ablation. Compound thin films with low work function can be synthesized by simultaneously laser ablating silicon, for example, and thermal evaporating an alkali metal into an oxygen environment. For example, the compound thin film may be composed of Si/Cs/O. The work functions of the thin films can be varied by changing the silicon/alkali metal/oxygen ratio. Low work functions of the compound thin films deposited on silicon substrates were confirmed by ultraviolet photoelectron spectroscopy (UPS). The compound thin films are stable up to 500.degree. C. as measured by x-ray photoelectron spectroscopy (XPS). Tests have established that for certain chemical compositions and annealing temperatures of the compound thin films, negative electron affinity (NEA) was detected. The low work function, stable compound thin films can be utilized in solar cells, field emission flat panel displays, electron guns, and cold cathode electron guns.

  17. High-Order Energy Stable WENO Schemes

    NASA Technical Reports Server (NTRS)

    Yamaleev, Nail K.; Carpenter, Mark H.

    2009-01-01

    A third-order Energy Stable Weighted Essentially Non-Oscillatory (ESWENO) finite difference scheme developed by Yamaleev and Carpenter was proven to be stable in the energy norm for both continuous and discontinuous solutions of systems of linear hyperbolic equations. Herein, a systematic approach is presented that enables 'energy stable' modifications for existing WENO schemes of any order. The technique is demonstrated by developing a one-parameter family of fifth-order upwind-biased ESWENO schemes; ESWENO schemes up to eighth order are presented in the appendix. New weight functions are also developed that provide (1) formal consistency, (2) much faster convergence for smooth solutions with an arbitrary number of vanishing derivatives, and (3) improved resolution near strong discontinuities.

  18. Stable isotope and elemental analysis in ants.

    PubMed

    Smith, Chris R; Tillberg, Chadwick V

    2009-07-01

    Over the past 20 yr, the use of stable isotopes to infer feeding ecology and the examination of how energetic and elemental exchanges are affected by and affect life (ecological stoichiometry) have gained momentum. The ecological diversity of ants makes them interesting models to explore dietary ecology and their role in food webs. Moreover, their ecological dominance in most habitats facilitates sampling. The protocol described here will produce samples adequate for submission to most labs that specialize in high-throughput analysis of stable isotopes; one should check with any particular lab for specific submission instructions. Note, however, that this protocol is designed specifically for the quantification of the natural abundance of stable isotopes; it does not cover the preparation of trace samples. PMID:20147207

  19. Effects of oral supplementation with stable strontium

    PubMed Central

    Skoryna, Stanley C.

    1981-01-01

    The biologic effects of stable strontium, a naturally occurring trace element in the diet and the body, have been little investigated. This paper discusses the effects of oral supplementation with stable strontium in laboratory studies and clinical investigations. The extent of intestinal absorption of various doses of orally administered strontium was estimated by determining serum and tissue levels with atomic absorption spectrophotometry. The central observation is that increased oral intake produces a direct increase in serum levels and intracellular uptake of strontium. The results of these studies, as well as those of other investigators, demonstrate that a moderate dosage of stable strontium does not adversely affect the level of calcium either in the serum or in soft tissues. In studies of patients receiving 1 to 1.5 g/d of strontium gluconate, a sustained increase in the serum level of strontium produced a 100-fold increase in the strontium:calcium ratio. In rats, studies indicate that an increase in intracellular strontium content following supplementation may exert a protective effect on mitochondrial structure, probably by means of a stabilizing effect of strontium on membranes. The strontium:calcium ratio in animals receiving a standard diet is higher in the cell than in the extracellular fluid; this may be of physiologic significance. An increase in density that corresponded to the deposition of stable strontium was observed in areas of bone lesions due to metastatic cancer in patients receiving stable strontium supplementation. This suggests the possibility of using strontium to mineralize osteophenic areas and to relieve bone pain. Also, because of reports of an inverse relation between the incidence of dental caries and a high strontium content in drinking water, the use of natural water containing relatively high levels of stable strontium should be considered. In each of these instances it is important to maintain a normal dietary intake of

  20. Effects of oral supplementation with stable strontium.

    PubMed

    Skoryna, S C

    1981-10-01

    The biologic effects of stable strontium, a naturally occurring trace element in the diet and the body, have been little investigated. This paper discusses the effects of oral supplementation with stable strontium in laboratory studies and clinical investigations. The extent of intestinal absorption of various doses of orally administered strontium was estimated by determining serum and tissue levels with atomic absorption spectrophotometry. The central observation is that increased oral intake produces a direct increase in serum levels and intracellular uptake of strontium. The results of these studies, as well as those of other investigators, demonstrate that a moderate dosage of stable strontium does not adversely affect the level of calcium either in the serum or in soft tissues. In studies of patients receiving 1 to 1.5 g/d of strontium gluconate, a sustained increase in the serum level of strontium produced a 100-fold increase in the strontium:calcium ratio. In rats, studies indicate that an increase in intracellular strontium content following supplementation may exert a protective effect on mitochondrial structure, probably by means of a stabilizing effect of strontium on membranes. The strontium:calcium ratio in animals receiving a standard diet is higher in the cell than in the extracellular fluid; this may be of physiologic significance.An increase in density that corresponded to the deposition of stable strontium was observed in areas of bone lesions due to metastatic cancer in patients receiving stable strontium supplementation. This suggests the possibility of using strontium to mineralize osteophenic areas and to relieve bone pain. Also, because of reports of an inverse relation between the incidence of dental caries and a high strontium content in drinking water, the use of natural water containing relatively high levels of stable strontium should be considered. In each of these instances it is important to maintain a normal dietary intake of

  1. Stable isotope labeling methods for DNA.

    PubMed

    Nelissen, Frank H T; Tessari, Marco; Wijmenga, Sybren S; Heus, Hans A

    2016-08-01

    NMR is a powerful method for studying proteins and nucleic acids in solution. The study of nucleic acids by NMR is far more challenging than for proteins, which is mainly due to the limited number of building blocks and unfavorable spectral properties. For NMR studies of DNA molecules, (site specific) isotope enrichment is required to facilitate specific NMR experiments and applications. Here, we provide a comprehensive review of isotope-labeling strategies for obtaining stable isotope labeled DNA as well as specifically stable isotope labeled building blocks required for enzymatic DNA synthesis. PMID:27573183

  2. Stable isotopes in Lithuanian bioarcheological material

    NASA Astrophysics Data System (ADS)

    Skipityte, Raminta; Jankauskas, Rimantas; Remeikis, Vidmantas

    2015-04-01

    Investigation of bioarcheological material of ancient human populations allows us to understand the subsistence behavior associated with various adaptations to the environment. Feeding habits are essential to the survival and growth of ancient populations. Stable isotope analysis is accepted tool in paleodiet (Schutkowski et al, 1999) and paleoenvironmental (Zernitskaya et al, 2014) studies. However, stable isotopes can be useful not only in investigating human feeding habits but also in describing social and cultural structure of the past populations (Le Huray and Schutkowski, 2005). Only few stable isotope investigations have been performed before in Lithuanian region suggesting a quite uniform diet between males and females and protein intake from freshwater fish and animal protein. Previously, stable isotope analysis has only been used to study a Stone Age population however, more recently studies have been conducted on Iron Age and Late medieval samples (Jacobs et al, 2009). Anyway, there was a need for more precise examination. Stable isotope analysis were performed on human bone collagen and apatite samples in this study. Data represented various ages (from 5-7th cent. to 18th cent.). Stable carbon and nitrogen isotope analysis on medieval populations indicated that individuals in studied sites in Lithuania were almost exclusively consuming C3 plants, C3 fed terrestrial animals, and some freshwater resources. Current investigation demonstrated social differences between elites and country people and is promising in paleodietary and daily life reconstruction. Acknowledgement I thank prof. dr. G. Grupe, Director of the Anthropological and Palaeoanatomical State Collection in Munich for providing the opportunity to work in her laboratory. The part of this work was funded by DAAD. Antanaitis-Jacobs, Indre, et al. "Diet in early Lithuanian prehistory and the new stable isotope evidence." Archaeologia Baltica 12 (2009): 12-30. Le Huray, Jonathan D., and Holger

  3. MHD stable regime of the tokamak

    SciTech Connect

    Cheng, C.Z.; Furth, H.P.; Boozer, A.H.

    1986-10-01

    A broad family of tokamak current profiles is found to be stable against ideal and resistive MHD kink modes for 1 less than or equal to q(0), with q(a) as low 2. For 0.5 less than or equal to q(0) < and q(a) > 1, current profiles can be found that are unstable only to the m = 1, n = 1 mode. A specific ''optimal'' tokamak profile can be selected from the range of stable solutions, by imposing a common upper limit on dj/dr - corresponding in ohmic equilibrium to a limitation of dT/sub e//dr by anomalous transport.

  4. UNCERTAINTY IN SOURCE PARTITIONING USING STABLE ISOTOPES

    EPA Science Inventory

    Stable isotope analyses are often used to quantify the contribution of multiple sources to a mixture, such as proportions of food sources in an animal's diet, C3 vs. C4 plant inputs to soil organic carbon, etc. Linear mixing models can be used to partition two sources with a sin...

  5. Dynamically stable magnetic suspension/bearing system

    DOEpatents

    Post, R.F.

    1996-02-27

    A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium. However, owing to the limitations imposed by Earnshaw`s Theorem, the magnetic bearing systems to be described do not possess a stable equilibrium at zero rotational speed. Therefore, mechanical stabilizers are provided, in each case, to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. The magnetic forces exerted by these elements, when taken together, levitate the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations. At the same time, this equilibrium is made stable against displacements of the rotating object from its equilibrium position by using combinations of elements that possess force derivatives of such magnitudes and signs that they can satisfy the conditions required for a rotating body to be stably supported by a magnetic bearing system over a finite range of those displacements. 32 figs.

  6. Dynamically stable magnetic suspension/bearing system

    DOEpatents

    Post, Richard F.

    1996-01-01

    A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium. However, owing to the limitations imposed by Earnshaw's Theorem, the magnetic bearing systems to be described do not possess a stable equilibrium at zero rotational speed. Therefore, mechanical stabilizers are provided, in each case, to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. The magnetic forces exerted by these elements, when taken together, levitate the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations. At the same time, this equilibrium is made stable against displacements of the rotating object from its equilibrium position by using combinations of elements that possess force derivatives of such magnitudes and signs that they can satisfy the conditions required for a rotating body to be stably supported by a magnetic bearing system over a finite range of those displacements.

  7. Conditional flux analysis and stable isotopes

    NASA Astrophysics Data System (ADS)

    Zeeman, M. J.; Knohl, A.; Sturm, P.; Buchmann, N. C.; Thomas, C. K.

    2009-12-01

    We propose to investigate to what extend conditional flux analysis can benefit from the addition of stable isotope information. Stable isotopes have been recognized for their potential as process tracer, and could add an extra dimension to the conditional flux concept, which aims at directly quantifying component fluxes and identifying their sources. Differences in 13C abundance in carbon dioxide can be used to distinguish assimilation or respiration sources, whereas the 18O abundance expresses differences in water exchange, for instance between canopy and soil. Lending to recent advances in measurement technology, stable isotopes can now be measured at high temporal resolutions (10Hz) required for commonly applied micrometeorological methods such as the eddy-covariance technique, or related conditional flux methods. We will present current ideas on how the conditional flux method, as recently proposed and evaluated by Thomas et al. (2008), Scanlon & Sahu (2008), to perform daytime flux partitioning at the ecosystem level, can be refined by stable isotope analysis (13C and 18O) of carbon dioxide as additional dimension for identification of fluxes.

  8. Substitution of stable isotopes in Chlorella

    NASA Technical Reports Server (NTRS)

    Flaumenhaft, E.; Katz, J. J.; Uphaus, R. A.

    1969-01-01

    Replacement of biologically important isotopes in the alga Chlorella by corresponding heavier stable isotopes produces increasingly greater deviations from the normal cell size and changes the quality and distribution of certain cellular components. The usefulness of isotopically altered organisms increases interest in the study of such permuted organisms.

  9. Insights into Stereoselective Aminomethylation Reaction of α,β-Unsaturated Aldehyde with N,O-Acetal via N-Heterocyclic Carbene and Brønsted Acid/Base Cooperative Organocatalysis.

    PubMed

    Wang, Yang; Tang, Mingsheng; Wang, Yanyan; Wei, Donghui

    2016-07-01

    A theoretical investigation has been performed to interrogate the mechanism and stereoselectivities of aminomethylation reaction of α,β-unsaturated aldehyde with N,O-acetal, which is initiated by N-heterocyclic carbene and Brønsted acid (BA). The calculated results disclose that the reaction contains several steps, i.e., formation of the actual catalysts NHC and Brønsted acid Et3N·H(+) coupled with activation of C-O bond of N,O-acetal, nucleophilic attack of NHC on α,β-unsaturated aldehyde, formation of Breslow intermediate, β-protonation for the formation of enolate intermediate, nucleophilic addition on the Re/Si face to enolate by the activated iminium cation, esterification coupled with regeneration of Et3N·H(+), and dissociation of NHC from product. Addition on the prochiral face of enolate should be the stereocontrolling step, in which the chiral α-carbon is formed. Furthermore, NBO, GRI, and FMO analyses have been performed to explore the roles of catalysts and origin of stereoselectivity. Surprisingly, the added Brønsted base (BB) Et3N plays an indispensable role in the esterification process, indicating the reaction proceeds under NHC-BA/BB multicatalysis rather than NHC-BA dual catalysis proposed in the experiment. This theoretical work provides a case on the exploration of the special roles of the multicatalysts in NHC chemistry, which is valuable for rational design on new cooperative organocatalysis.

  10. Insights into Stereoselective Aminomethylation Reaction of α,β-Unsaturated Aldehyde with N,O-Acetal via N-Heterocyclic Carbene and Brønsted Acid/Base Cooperative Organocatalysis.

    PubMed

    Wang, Yang; Tang, Mingsheng; Wang, Yanyan; Wei, Donghui

    2016-07-01

    A theoretical investigation has been performed to interrogate the mechanism and stereoselectivities of aminomethylation reaction of α,β-unsaturated aldehyde with N,O-acetal, which is initiated by N-heterocyclic carbene and Brønsted acid (BA). The calculated results disclose that the reaction contains several steps, i.e., formation of the actual catalysts NHC and Brønsted acid Et3N·H(+) coupled with activation of C-O bond of N,O-acetal, nucleophilic attack of NHC on α,β-unsaturated aldehyde, formation of Breslow intermediate, β-protonation for the formation of enolate intermediate, nucleophilic addition on the Re/Si face to enolate by the activated iminium cation, esterification coupled with regeneration of Et3N·H(+), and dissociation of NHC from product. Addition on the prochiral face of enolate should be the stereocontrolling step, in which the chiral α-carbon is formed. Furthermore, NBO, GRI, and FMO analyses have been performed to explore the roles of catalysts and origin of stereoselectivity. Surprisingly, the added Brønsted base (BB) Et3N plays an indispensable role in the esterification process, indicating the reaction proceeds under NHC-BA/BB multicatalysis rather than NHC-BA dual catalysis proposed in the experiment. This theoretical work provides a case on the exploration of the special roles of the multicatalysts in NHC chemistry, which is valuable for rational design on new cooperative organocatalysis. PMID:27267585

  11. The 1:1 co-crystallization of enantiomers of an arene-tethered and ortho-metallated N-heterocyclic carbene ruthenium(II) half-sandwich complex: Synthesis, structural characterization and theoretical study

    NASA Astrophysics Data System (ADS)

    Karabıyık, Hasan; Kılınçarslan, Rafet; Aygün, Muhittin; Çetinkaya, Bekir; García-Granda, Santiago

    2008-01-01

    The reaction of [RuCl 2( p-cymene)] 2 with in situ deprotonated NHC precursor 1,3-bis(biphenyl-2-yl)imidazolinium chloride was carried out in p-xylene at 140 °C to produce ?2, in which the NHC moiety acts as a tridentate C,C',C''-ligand. The complex 2 was characterized by NMR spectroscopy and X-ray crystallographic study. Crystallographic analysis combined with computational study regarding the compound, 1-[η 6-(2'-biphenyl)]-3-[2-phenyl-1,2-phenylene]imidazolidin-2-ylidenechlororuthenium(II), 2, reveals that its metal-centered enantiomers are co-crystallized in 1:1 ratio and NHC frame possessing a tridentate coordination mode consists of σ-donation of the carbene carbon, η 6-arene tethering of terminal biaryl and η 1-coordination of the biphenyl ring at 2-position. Enantiomers of the complex are packed as asymmetric dimers in solid state formed by C-H⋯Cl type weak H-bonds and C-H⋯π type interactions giving rise to asymmetric chains. Both interactions serve to stabilization of the extended structure.

  12. Uranium Metalla-Allenes with Carbene Imido R2 C=U(IV) =NR' Units (R=Ph2 PNSiMe3 ; R'=CPh3 ): Alkali-Metal-Mediated Push-Pull Effects with an Amido Auxiliary.

    PubMed

    Lu, Erli; Tuna, Floriana; Lewis, William; Kaltsoyannis, Nikolas; Liddle, Stephen T

    2016-08-01

    We report uranium(IV)-carbene-imido-amide metalla-allene complexes [U(BIPM(TMS) )(NCPh3 )(NHCPh3 )(M)] (BIPM(TMS) =C(PPh2 NSiMe3 )2 ; M=Li or K) that can be described as R2 C=U=NR' push-pull metalla-allene units, as organometallic counterparts of the well-known push-pull organic allenes. The solid-state structures reveal that the R2 C=U=NR' units adopt highly unusual cis-arrangements, which are also reproduced by gas-phase theoretical studies conducted without the alkali metals to remove their potential structure-directing roles. Computational studies confirm the double-bond nature of the U=NR' and U=CR2 interactions, the latter increasingly attenuated by potassium then lithium when compared to the hypothetical alkali-metal-free anion. Combined experimental and theoretical data show that the push-pull effect induced by the alkali metal cations and amide auxiliary gives a fundamental and tunable structural influence over the C=U(IV) =N units. PMID:27403746

  13. Metal-free catalytic enantioselective C-B bond formation: (pinacolato)boron conjugate additions to α,β-unsaturated ketones, esters, Weinreb amides, and aldehydes promoted by chiral N-heterocyclic carbenes.

    PubMed

    Wu, Hao; Radomkit, Suttipol; O'Brien, Jeannette M; Hoveyda, Amir H

    2012-05-16

    The first broadly applicable metal-free enantioselective method for boron conjugate addition (BCA) to α,β-unsaturated carbonyls is presented. The C-B bond forming reactions are promoted in the presence of 2.5-7.5 mol % of a readily accessible C(1)-symmetric chiral imidazolinium salt, which is converted, in situ, to the catalytically active diastereo- and enantiomerically pure N-heterocyclic carbene (NHC) by the common organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (dbu). In addition to the commercially available bis(pinacolato)diboron [B(2)(pin)(2)], and in contrast to reactions with the less sterically demanding achiral NHCs, the presence of MeOH is required for high efficiency. Acyclic and cyclic α,β-unsaturated ketones, as well as acyclic esters, Weinreb amides, and aldehydes, can serve as suitable substrates; the desired β-boryl carbonyls are isolated in up to 94% yield and >98:2 enantiomer ratio (er). Transformations are often carried out at ambient temperature. In certain cases, such as when the relatively less reactive unsaturated amides are used, elevated temperatures are required (50-66 °C); nonetheless, reactions remain highly enantioselective. The utility of the NHC-catalyzed method is demonstrated through comparison with the alternative Cu-catalyzed protocols; in cases involving a polyfunctional substrate, unique profiles in chemoselectivity are exhibited by the metal-free approach (e.g., conjugate addition vs reaction with an alkyne, allene, or aldehyde). PMID:22559866

  14. Synthesis and characterization of various ruthenium small molecules and metallopolymers for potential use in photovoltaic devices and luminescence properties of N-heterocyclic carbenes and trifluoro methylated tris(pyrazolyl)borate silver (I) acid-base adducts

    NASA Astrophysics Data System (ADS)

    Chitikuri, Shylaja

    This thesis with its 66 pages, 1 table, 29 figures and 47 references, deals with two major topics involving structure and properties of selected metal complexes and their use in electronic devices. The first chapter discusses the development of ruthenium-based metallopolymer and small molecular complexes toward possible utilization as active materials for solar cells. Such complexes have been found to be good "black absorbers" with solid-state absorption that spans the entire visible region into the near-infrared, representing an impressive overlap with the solar radiation that is more favorable than common molecular solar cell active materials. The second chapter includes photophysical studies of different metallo N-heterocyclic carbenes and acid-base adducts comprising fluorinated tris(pyrazolyl)borate silver(I) complexes coordinated to different solvent and aromatic molecules. These species have been investigated and found to exhibit unusual photophysical properties, including metal-free phosphorescence at room temperature with high quantum yield, multi-color emission from a single compound, and selective sensing of temperature and hazardous vapors.

  15. Development of a Safety Management Web Tool for Horse Stables.

    PubMed

    Leppälä, Jarkko; Kolstrup, Christina Lunner; Pinzke, Stefan; Rautiainen, Risto; Saastamoinen, Markku; Särkijärvi, Susanna

    2015-01-01

    Managing a horse stable involves risks, which can have serious consequences for the stable, employees, clients, visitors and horses. Existing industrial or farm production risk management tools are not directly applicable to horse stables and they need to be adapted for use by managers of different types of stables. As a part of the InnoEquine project, an innovative web tool, InnoHorse, was developed to support horse stable managers in business, safety, pasture and manure management. A literature review, empirical horse stable case studies, expert panel workshops and stakeholder interviews were carried out to support the design. The InnoHorse web tool includes a safety section containing a horse stable safety map, stable safety checklists, and examples of good practices in stable safety, horse handling and rescue planning. This new horse stable safety management tool can also help in organizing work processes in horse stables in general. PMID:26569319

  16. Development of a Safety Management Web Tool for Horse Stables.

    PubMed

    Leppälä, Jarkko; Kolstrup, Christina Lunner; Pinzke, Stefan; Rautiainen, Risto; Saastamoinen, Markku; Särkijärvi, Susanna

    2015-11-12

    Managing a horse stable involves risks, which can have serious consequences for the stable, employees, clients, visitors and horses. Existing industrial or farm production risk management tools are not directly applicable to horse stables and they need to be adapted for use by managers of different types of stables. As a part of the InnoEquine project, an innovative web tool, InnoHorse, was developed to support horse stable managers in business, safety, pasture and manure management. A literature review, empirical horse stable case studies, expert panel workshops and stakeholder interviews were carried out to support the design. The InnoHorse web tool includes a safety section containing a horse stable safety map, stable safety checklists, and examples of good practices in stable safety, horse handling and rescue planning. This new horse stable safety management tool can also help in organizing work processes in horse stables in general.

  17. Strategies for stable composite structural design

    NASA Astrophysics Data System (ADS)

    Brand, Richard A.

    1992-12-01

    Advanced composites have been effectively used in space applications such as telescopes, optical benches, and metering structures. As the sophistication of optics and instrumentation increases, the need for near-zero outgassing and extremely dimensionally stable composites becomes of paramount importance. Continuing improvements in resin and reinforcing fiber technology have resulted in a wider selection of materials for the composite designer of dimensionally stable structures. Additional improvements in metal sealing techniques promise unprecedented long-term environmental stability. These new options allow the designer to develop a dimensional stability strategy which conforms to design requirements and yields an optimum, cost-effective composite design approach. This paper addresses the major stability issues in composites and how stability can be predicted for long-term applications, along with design options to achieve program goals. Low-moisture-absorbing composites based on cyanate esters, metal sealing techniques, and long-range stability are also addressed.

  18. Unstable-stable resonators with toroidal mirrors.

    PubMed

    Borghese, A; Canevari, R; Donati, V; Garifo, L

    1981-10-15

    A resonator with toroidal mirrors is described. This resonator behaves like an off-axis unstable confocal resonator in one transverse dimension and like an on-axis concave-convex stable resonator in the other orthogonal dimension. Some experimental results are reported for a fast flow high power cw-CO(2) laser whose transverse cross section is restricted in the stable-resonator direction. These cavities allow an output laser beam with a fully illuminated cross section which is well suited for focusing. Moreover, the fraction of the available laser power which may be concentrated in the central lobe of the focal plane intensity distribution is 2.5-4.5 times higher than other unstable resonators with similarly restricted modal volumes. Finally the alignment requirements are examined. PMID:20372215

  19. A stable Ti-based quasicrystal

    SciTech Connect

    Kelton, K.F.; Kim, W.J.; Stroud, R.M.

    1997-06-01

    The thermal stability of the icosahedral phase (i phase) in Ti{sub 45}Zr{sub 38}Ni{sub 17} alloys is demonstrated. As-cast alloys containing initially only the C14 hexagonal Laves and {alpha}-solid-solution phases transformed primarily to the icosahedral phase upon annealing in vacuum for 64 h at 570{degree}C. This confirms previous evidence for i-phase stability and firmly establishes this quasicrystal as the first nonaluminum stable icosahedral phase. Diffraction data show that this stable i phase is primitive; energy dispersive x-ray spectroscopy measurements place its composition near Ti{sub 41.5}Zr{sub 41.5}Ni{sub 17}. These and other results suggest that the structure of this i phase is similar to that of i(AlLiCu). {copyright} {ital 1997 American Institute of Physics.}

  20. Compact and stable multibeam fiber injector

    SciTech Connect

    Collins, L. F., LLNL

    1998-07-01

    A compact and stable 20-beam injector was built for launching laser light into fibers for Fabry Perot velocity measurements of shock-driven surfaces. The fiber injector uses commercial mounts on mini-rails. Dielectric-coated beamsplitters provide accurate amplitude division. Minimal adjustments for stable operation are permitted by the use of a real-time video-viewer. The video system includes a non-linear camera for CW alignment and a linearized camera with a frame grabber for pulsed measurement and analysis. All 20-injection points are displayed on a single monitor. Optical requirements are given for image relay and magnification. Stimulated Brillouin scattering limitations on high-power are quantified.

  1. Thermally Stable, Piezoelectric and Pyroelectric Polymeric Substrates

    NASA Technical Reports Server (NTRS)

    Simpson, Joycely O. (Inventor); St.Clair, Terry L. (Inventor)

    1999-01-01

    A thermally stable, piezoelectric and pyroelectric polymeric substrate was prepared. This thermally stable, piezoelectric and pyroelectric polymeric substrate may be used to prepare electromechanical transducers, thermomechanical transducers, accelerometers. acoustic sensors, infrared sensors, pressure sensors, vibration sensors, impact sensors, in-situ temperature sensors, in-situ stress/strain sensors, micro actuators, switches, adjustable fresnel lenses, speakers, tactile sensors. weather sensors, micro positioners, ultrasonic devices, power generators, tunable reflectors, microphones, and hydrophones. The process for preparing these polymeric substrates includes: providing a polymeric substrate having a softening temperature greater than 1000 C; depositing a metal electrode material onto the polymer film; attaching a plurality of electrical leads to the metal electrode coated polymeric substrate; heating the metal electrode coated polymeric substrate in a low dielectric medium; applying a voltage to the heated metal electrode coated polymeric substrate to induce polarization; and cooling the polarized metal electrode coated polymeric electrode while maintaining a constant voltage.

  2. Unexpected Stable Stoichiometries of Sodium Chlorides

    NASA Astrophysics Data System (ADS)

    Zhang, Weiwei; Oganov, Artem R.; Goncharov, Alexander F.; Zhu, Qiang; Boulfelfel, Salah Eddine; Lyakhov, Andriy O.; Stavrou, Elissaios; Somayazulu, Maddury; Prakapenka, Vitali B.; Konôpková, Zuzana

    2013-12-01

    Sodium chloride (NaCl), or rocksalt, is well characterized at ambient pressure. As a result of the large electronegativity difference between Na and Cl atoms, it has highly ionic chemical bonding (with 1:1 stoichiometry dictated by charge balance) and B1-type crystal structure. By combining theoretical predictions and diamond anvil cell experiments, we found that new materials with different stoichiometries emerge at high pressures. Compounds such as Na3Cl, Na2Cl, Na3Cl2, NaCl3, and NaCl7 are theoretically stable and have unusual bonding and electronic properties. To test this prediction, we synthesized cubic and orthorhombic NaCl3 and two-dimensional metallic tetragonal Na3Cl. These experiments establish that compounds violating chemical intuition can be thermodynamically stable even in simple systems at nonambient conditions.

  3. Stable freestanding thin films of pure water

    SciTech Connect

    Weon, B. M.; Je, J. H.; Hwu, Y.; Margaritondo, G.

    2008-03-10

    Obtaining water microstructures is very difficult because of low viscosity and high surface tension. We produced stable freestanding thin films of pure water by x-ray bombardment of small liquid volumes in capillary tubes. A detailed characterization with phase-contrast radiology demonstrated a lifetime beyond 1 h with no chemical stabilizer for micron-thickness films with half-millimeter-level diameter. This can be attributed to the interplay of two x-ray effects: water evaporation and surface charging.

  4. Quantifying uncertainty in stable isotope mixing models

    NASA Astrophysics Data System (ADS)

    Davis, Paul; Syme, James; Heikoop, Jeffrey; Fessenden-Rahn, Julianna; Perkins, George; Newman, Brent; Chrystal, Abbey E.; Hagerty, Shannon B.

    2015-05-01

    Mixing models are powerful tools for identifying biogeochemical sources and determining mixing fractions in a sample. However, identification of actual source contributors is often not simple, and source compositions typically vary or even overlap, significantly increasing model uncertainty in calculated mixing fractions. This study compares three probabilistic methods, Stable Isotope Analysis in R (SIAR), a pure Monte Carlo technique (PMC), and Stable Isotope Reference Source (SIRS) mixing model, a new technique that estimates mixing in systems with more than three sources and/or uncertain source compositions. In this paper, we use nitrate stable isotope examples (δ15N and δ18O) but all methods tested are applicable to other tracers. In Phase I of a three-phase blind test, we compared methods for a set of six-source nitrate problems. PMC was unable to find solutions for two of the target water samples. The Bayesian method, SIAR, experienced anchoring problems, and SIRS calculated mixing fractions that most closely approximated the known mixing fractions. For that reason, SIRS was the only approach used in the next phase of testing. In Phase II, the problem was broadened where any subset of the six sources could be a possible solution to the mixing problem. Results showed a high rate of Type I errors where solutions included sources that were not contributing to the sample. In Phase III some sources were eliminated based on assumed site knowledge and assumed nitrate concentrations, substantially reduced mixing fraction uncertainties and lowered the Type I error rate. These results demonstrate that valuable insights into stable isotope mixing problems result from probabilistic mixing model approaches like SIRS. The results also emphasize the importance of identifying a minimal set of potential sources and quantifying uncertainties in source isotopic composition as well as demonstrating the value of additional information in reducing the uncertainty in calculated

  5. Stable localized patterns in thin liquid films

    NASA Technical Reports Server (NTRS)

    Deissler, Robert J.; Oron, Alexander

    1991-01-01

    We study a 2-D nonlinear evolution equation which describes the 3-D spatiotemporal behavior of the air-liquid interface of a thin liquid film lying on the underside of a cooled horizontal plate. We show that the Marangoni effect can stabilize the destabilizing effect of gravity (the Rayleigh-Taylor instability) allowing for the existence of stable localized axisymmetric solutions for a wide range of parameter values. Various properties of these structures are discussed.

  6. Detonation of Meta-stable Clusters

    SciTech Connect

    Kuhl, Allen; Kuhl, Allen L.; Fried, Laurence E.; Howard, W. Michael; Seizew, Michael R.; Bell, John B.; Beckner, Vincent; Grcar, Joseph F.

    2008-05-31

    We consider the energy accumulation in meta-stable clusters. This energy can be much larger than the typical chemical bond energy (~;;1 ev/atom). For example, polymeric nitrogen can accumulate 4 ev/atom in the N8 (fcc) structure, while helium can accumulate 9 ev/atom in the excited triplet state He2* . They release their energy by cluster fission: N8 -> 4N2 and He2* -> 2He. We study the locus of states in thermodynamic state space for the detonation of such meta-stable clusters. In particular, the equilibrium isentrope, starting at the Chapman-Jouguet state, and expanding down to 1 atmosphere was calculated with the Cheetah code. Large detonation pressures (3 and 16 Mbar), temperatures (12 and 34 kilo-K) and velocities (20 and 43 km/s) are a consequence of the large heats of detonation (6.6 and 50 kilo-cal/g) for nitrogen and helium clusters respectively. If such meta-stable clusters could be synthesized, they offer the potential for large increases in the energy density of materials.

  7. Deformed Palmprint Matching Based on Stable Regions.

    PubMed

    Wu, Xiangqian; Zhao, Qiushi

    2015-12-01

    Palmprint recognition (PR) is an effective technology for personal recognition. A main problem, which deteriorates the performance of PR, is the deformations of palmprint images. This problem becomes more severe on contactless occasions, in which images are acquired without any guiding mechanisms, and hence critically limits the applications of PR. To solve the deformation problems, in this paper, a model for non-linearly deformed palmprint matching is derived by approximating non-linear deformed palmprint images with piecewise-linear deformed stable regions. Based on this model, a novel approach for deformed palmprint matching, named key point-based block growing (KPBG), is proposed. In KPBG, an iterative M-estimator sample consensus algorithm based on scale invariant feature transform features is devised to compute piecewise-linear transformations to approximate the non-linear deformations of palmprints, and then, the stable regions complying with the linear transformations are decided using a block growing algorithm. Palmprint feature extraction and matching are performed over these stable regions to compute matching scores for decision. Experiments on several public palmprint databases show that the proposed models and the KPBG approach can effectively solve the deformation problem in palmprint verification and outperform the state-of-the-art methods.

  8. Deformed Palmprint Matching Based on Stable Regions.

    PubMed

    Wu, Xiangqian; Zhao, Qiushi

    2015-12-01

    Palmprint recognition (PR) is an effective technology for personal recognition. A main problem, which deteriorates the performance of PR, is the deformations of palmprint images. This problem becomes more severe on contactless occasions, in which images are acquired without any guiding mechanisms, and hence critically limits the applications of PR. To solve the deformation problems, in this paper, a model for non-linearly deformed palmprint matching is derived by approximating non-linear deformed palmprint images with piecewise-linear deformed stable regions. Based on this model, a novel approach for deformed palmprint matching, named key point-based block growing (KPBG), is proposed. In KPBG, an iterative M-estimator sample consensus algorithm based on scale invariant feature transform features is devised to compute piecewise-linear transformations to approximate the non-linear deformations of palmprints, and then, the stable regions complying with the linear transformations are decided using a block growing algorithm. Palmprint feature extraction and matching are performed over these stable regions to compute matching scores for decision. Experiments on several public palmprint databases show that the proposed models and the KPBG approach can effectively solve the deformation problem in palmprint verification and outperform the state-of-the-art methods. PMID:26390453

  9. A stable snow-atmosphere coupled mode

    NASA Astrophysics Data System (ADS)

    Zhao, Liang; Zhu, Yuxiang; Liu, Haiwen; Liu, Zhongfang; Liu, Yanju; Li, Xiuping; Chen, Zhou

    2016-10-01

    Snow is both an important lower boundary forcing of the atmosphere and a response to atmospheric forcing in the extratropics. It is still unclear whether a stable snow-atmosphere coupled mode exists in the extratropics, like the ENSO in the tropics. Using Sliding Correlation analysis over Any Window, the present study quantitatively evaluates the stability of coupling relationships between the major modes of winter snow over the Northern Hemisphere and the winter atmospheric Arctic Oscillation (AO), the Antarctic Oscillation (AAO) and the Siberian High over the period 1872-2010, and discusses their possible relationships for different seasons. Results show that the first mode of the winter snow cover fraction and the winter AO together constitute a stable snow-atmosphere coupled mode, the SNAO. The coupled mode is stronger during recent decades than before. The snow anomaly over Europe is one key factor of the SNAO mode due to the high stability there, and the polar vortex anomaly in the atmosphere is its other key factor. The continuity of signals in the SNAO between autumn and winter is weaker than that between winter and spring. The second winter snow mode is generally stably correlated with the winter AAO and was more stable before the 1970s. The AAO signal with boreal snow has a strong continuity in seasonal transition. Generally, through these coupled modes, snow and atmosphere can interact in the same season or between different seasons: autumn snow can influence the winter atmosphere; the winter atmosphere can influence spring snow.

  10. Stable solid-phase Rh antigen.

    PubMed

    Yared, M A; Moise, K J; Rodkey, L S

    1997-12-01

    Numerous investigators have attempted to isolate the Rh antigens in a stable, immunologically reactive form since the discovery of the Rh system over 56 years ago. We report here a successful and reproducible approach to solubilizing and adsorbing the human Rh antigen(s) to a solid-phase matrix in an antigenically active form. Similar results were obtained with rabbit A/D/F red blood cell antigens. The antigen preparation was made by dissolution of the red blood cell membrane lipid followed by fragmentation of the residual cytoskeleton in an EDTA solution at low ionic strength. The antigenic activity of the soluble preparations was labile in standard buffers but was stable in zwitterionic buffers for extended periods of time. Further studies showed that the antigenic activity of these preparations was enhanced, as was their affinity for plastic surfaces, in the presence of acidic zwitterionic buffers. Adherence to plastic surfaces at low pH maintained antigenic reactivity and specificity for antibody was retained. The data show that this approach yields a stable form of antigenically active human Rh D antigen that could be used in a red blood cell-free assay for quantitative analysis of Rh D antibody and for Rh D antibody immunoadsorption and purification.

  11. Overview and first results from Project STABLE (Stable Boundary Layer Experiment)

    NASA Astrophysics Data System (ADS)

    Weber, A. H.; Kurzeja, R. J.

    The STABLE project (STAble Boundary Layer Experiment) is a multiyear research effort conceived in 1984 by the Savannah River Laboratory (SRL) and planned by several research groups to study turbulence and diffusion in the stable boundary layer (SBL). The program was jointly planned by Department of Energy (DOE) affiliated laboratories and universities including SRL, Atmospheric Turbulence and Diffusion Division (ATDD) of the National Oceanic and Atmospheric Administration (NOAA), Argonne National Laboratory (ANL), North Carolina State University (NCSU), and The Pennsylvania State University. STABLE's goals are to determine the spatial and temporal distribution of turbulent events during the nighttime, to determine the validity of present models and theories in describing the structure and evolution of the SBL, to determine the role of waves and intermittent turbulence in dispersing chemicals, and to determine better parameterization for describing the mean state and intermittent events in the SBL. By taking advantage of special facility, the program seeks to economize effort and cost.

  12. Overview and first results from project STABLE (STAble Boundary Layer Experiment)

    SciTech Connect

    Weber, A.H.; Kurzeja, R.J.

    1988-01-01

    The STABLE project (STAble Boundary Layer Experiment) is a multiyear research effort conceived in 1984 by the Savannah River Laboratory (SRL) and planned by several research groups to study turbulence and diffusion in the stable boundary layer (SBL). The program was jointly planned by Department of Energy (DOE) affiliated laboratories and universities including SRL, Atmospheric Turbulence and Diffusion Division (ATDD) of the National Oceanic and Atmospheric Administration (NOAA), Argonne National Laboratory (ANL), North Carolina State University (NCSU), and The Pennsylvania State University. STABLE's goals are to determine the spatial and temporal distribution of turbulent events during the nighttime, to determine the validity of present models and theories in describing the structure and evolution of the SBL, to determine the role of waves and intermittent turbulence in dispersing chemicals, and to determine better parameterization for describing the mean state and intermittent events in the SBL. By taking advantage of special facility, the program seeks to economize effort and cost. 1 ref., 7 figs.

  13. Development of a Safety Management Web Tool for Horse Stables

    PubMed Central

    Leppälä, Jarkko; Kolstrup, Christina Lunner; Pinzke, Stefan; Rautiainen, Risto; Saastamoinen, Markku; Särkijärvi, Susanna

    2015-01-01

    Simple Summary A new web tool for equine activities, InnoHorse, was developed to support horse stable managers in business, safety, pasture and manure management. The aim of the safety section of the web tool was to raise awareness of safety issues in daily horse stable activities. This section contains a safety checklist, stable safety map and good practices to support human health and horse welfare and to prevent injuries in horse-related activities. Reviews of the literature and statistics, empirical horse stable case studies, expert panel workshops and stakeholder interviews were utilized in designing the web tool. Abstract Managing a horse stable involves risks, which can have serious consequences for the stable, employees, clients, visitors and horses. Existing industrial or farm production risk management tools are not directly applicable to horse stables and they need to be adapted for use by managers of different types of stables. As a part of the InnoEquine project, an innovative web tool, InnoHorse, was developed to support horse stable managers in business, safety, pasture and manure management. A literature review, empirical horse stable case studies, expert panel workshops and stakeholder interviews were carried out to support the design. The InnoHorse web tool includes a safety section containing a horse stable safety map, stable safety checklists, and examples of good practices in stable safety, horse handling and rescue planning. This new horse stable safety management tool can also help in organizing work processes in horse stables in general. PMID:26569319

  14. Highly photoluminescent copper carbene complexes based on prompt rather than delayed fluorescence† †Electronic supplementary information (ESI) available. CCDC 1469283 (for 1a), 1469285 (for 1b) and 1469284 (for 1c). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6cc02349e Click here for additional data file. Click here for additional data file.

    PubMed Central

    Romanov, Alexander S.; Di, Dawei; Yang, Le; Fernandez-Cestau, Julio; Becker, Ciaran R.; James, Charlotte E.; Zhu, Bonan

    2016-01-01

    Linear two-coordinate copper complexes of cyclic (alkyl)(amino)carbenes (CAAC)CuX (X = halide) show photoluminescence with solid-state quantum yields of up to 96%; in contrast to previously reported Cu photoemitters the emission is independent of temperature over the range T = 4–300 K and occurs very efficiently by prompt rather than delayed fluorescence, with lifetimes in the sub-nanosecond range. PMID:27087532

  15. Quantifying uncertainty in stable isotope mixing models

    DOE PAGESBeta

    Davis, Paul; Syme, James; Heikoop, Jeffrey; Fessenden-Rahn, Julianna; Perkins, George; Newman, Brent; Chrystal, Abbey E.; Hagerty, Shannon B.

    2015-05-19

    Mixing models are powerful tools for identifying biogeochemical sources and determining mixing fractions in a sample. However, identification of actual source contributors is often not simple, and source compositions typically vary or even overlap, significantly increasing model uncertainty in calculated mixing fractions. This study compares three probabilistic methods, SIAR [Parnell et al., 2010] a pure Monte Carlo technique (PMC), and Stable Isotope Reference Source (SIRS) mixing model, a new technique that estimates mixing in systems with more than three sources and/or uncertain source compositions. In this paper, we use nitrate stable isotope examples (δ15N and δ18O) but all methods testedmore » are applicable to other tracers. In Phase I of a three-phase blind test, we compared methods for a set of six-source nitrate problems. PMC was unable to find solutions for two of the target water samples. The Bayesian method, SIAR, experienced anchoring problems, and SIRS calculated mixing fractions that most closely approximated the known mixing fractions. For that reason, SIRS was the only approach used in the next phase of testing. In Phase II, the problem was broadened where any subset of the six sources could be a possible solution to the mixing problem. Results showed a high rate of Type I errors where solutions included sources that were not contributing to the sample. In Phase III some sources were eliminated based on assumed site knowledge and assumed nitrate concentrations, substantially reduced mixing fraction uncertainties and lowered the Type I error rate. These results demonstrate that valuable insights into stable isotope mixing problems result from probabilistic mixing model approaches like SIRS. The results also emphasize the importance of identifying a minimal set of potential sources and quantifying uncertainties in source isotopic composition as well as demonstrating the value of additional information in reducing the uncertainty in calculated

  16. Stable isotopic analyses in paleoclimatic reconstruction

    SciTech Connect

    Wigand, P.E.

    1995-09-01

    Most traditional paleoclimatic proxy data have inherent time lags between climatic input and system response that constrain their use in accurate reconstruction of paleoclimate chronology, scaling of its variability, and the elucidation of the processes that determine its impact on the biotic and abiotic environment. With the exception of dendroclimatology, and studies of short-lived organisms and pollen recovered from annually varved lacustrine sediments, significant periods of time ranging from years, to centuries, to millennia may intervene between climate change and its first manifestation in paleoclimatic proxy data records. Reconstruction of past climate through changes in plant community composition derived from pollen sequences and plant remains from ancient woodrat middens, wet environments and dry caves all suffer from these lags. However, stable isotopic analyses can provide more immediate indication of biotic response to climate change. Evidence of past physiological response of organisms to changes in effective precipitation as climate varies can be provided by analyses of the stable isotopic content of plant macrofossils from various contexts. These analyses consider variation in the stable isotopic (hydrogen, oxygen and carbon) content of plant tissues as it reflects (1) past global or local temperature through changes in meteoric (rainfall) water chemistry in the case of the first two isotopes, and (2) plant stress through changes in plant respiration/transpiration processes under differing water availability, and varying atmospheric CO, composition (which itself may actually be a net result of biotic response to climate change). Studies currently being conducted in the Intermountain West indicate both long- and short-term responses that when calibrated with modem analogue studies have the potential of revealing not only the timing of climate events, but their direction, magnitude and rapidity.

  17. Quantitative microbial ecology through stable isotope probing.

    PubMed

    Hungate, Bruce A; Mau, Rebecca L; Schwartz, Egbert; Caporaso, J Gregory; Dijkstra, Paul; van Gestel, Natasja; Koch, Benjamin J; Liu, Cindy M; McHugh, Theresa A; Marks, Jane C; Morrissey, Ember M; Price, Lance B

    2015-11-01

    Bacteria grow and transform elements at different rates, and as yet, quantifying this variation in the environment is difficult. Determining isotope enrichment with fine taxonomic resolution after exposure to isotope tracers could help, but there are few suitable techniques. We propose a modification to stable isotope probing (SIP) that enables the isotopic composition of DNA from individual bacterial taxa after exposure to isotope tracers to be determined. In our modification, after isopycnic centrifugation, DNA is collected in multiple density fractions, and each fraction is sequenced separately. Taxon-specific density curves are produced for labeled and nonlabeled treatments, from which the shift in density for each individual taxon in response to isotope labeling is calculated. Expressing each taxon's density shift relative to that taxon's density measured without isotope enrichment accounts for the influence of nucleic acid composition on density and isolates the influence of isotope tracer assimilation. The shift in density translates quantitatively to isotopic enrichment. Because this revision to SIP allows quantitative measurements of isotope enrichment, we propose to call it quantitative stable isotope probing (qSIP). We demonstrated qSIP using soil incubations, in which soil bacteria exhibited strong taxonomic variations in (18)O and (13)C composition after exposure to [(18)O]water or [(13)C]glucose. The addition of glucose increased the assimilation of (18)O into DNA from [(18)O]water. However, the increase in (18)O assimilation was greater than expected based on utilization of glucose-derived carbon alone, because the addition of glucose indirectly stimulated bacteria to utilize other substrates for growth. This example illustrates the benefit of a quantitative approach to stable isotope probing.

  18. Quantifying uncertainty in stable isotope mixing models

    SciTech Connect

    Davis, Paul; Syme, James; Heikoop, Jeffrey; Fessenden-Rahn, Julianna; Perkins, George; Newman, Brent; Chrystal, Abbey E.; Hagerty, Shannon B.

    2015-05-19

    Mixing models are powerful tools for identifying biogeochemical sources and determining mixing fractions in a sample. However, identification of actual source contributors is often not simple, and source compositions typically vary or even overlap, significantly increasing model uncertainty in calculated mixing fractions. This study compares three probabilistic methods, SIAR [Parnell et al., 2010] a pure Monte Carlo technique (PMC), and Stable Isotope Reference Source (SIRS) mixing model, a new technique that estimates mixing in systems with more than three sources and/or uncertain source compositions. In this paper, we use nitrate stable isotope examples (δ15N and δ18O) but all methods tested are applicable to other tracers. In Phase I of a three-phase blind test, we compared methods for a set of six-source nitrate problems. PMC was unable to find solutions for two of the target water samples. The Bayesian method, SIAR, experienced anchoring problems, and SIRS calculated mixing fractions that most closely approximated the known mixing fractions. For that reason, SIRS was the only approach used in the next phase of testing. In Phase II, the problem was broadened where any subset of the six sources could be a possible solution to the mixing problem. Results showed a high rate of Type I errors where solutions included sources that were not contributing to the sample. In Phase III some sources were eliminated based on assumed site knowledge and assumed nitrate concentrations, substantially reduced mixing fraction uncertainties and lowered the Type I error rate. These results demonstrate that valuable insights into stable isotope mixing problems result from probabilistic mixing model approaches like SIRS. The results also emphasize the importance of identifying a minimal set of potential sources and quantifying uncertainties in source isotopic composition as well as demonstrating the value of additional information in reducing the

  19. Stable water layers on solid surfaces.

    PubMed

    Hong, Ying-Jhan; Tai, Lin-Ai; Chen, Hung-Jen; Chang, Pin; Yang, Chung-Shi; Yew, Tri-Rung

    2016-02-17

    Liquid layers adhered to solid surfaces and that are in equilibrium with the vapor phase are common in printing, coating, and washing processes as well as in alveoli in lungs and in stomata in leaves. For such a liquid layer in equilibrium with the vapor it faces, it has been generally believed that, aside from liquid lumps, only a very thin layer of the liquid, i.e., with a thickness of only a few nanometers, is held onto the surface of the solid, and that this adhesion is due to van der Waals forces. A similar layer of water can remain on the surface of a wall of a microchannel after evaporation of bulk water creates a void in the channel, but the thickness of such a water layer has not yet been well characterized. Herein we showed such a water layer adhered to a microchannel wall to be 100 to 170 nm thick and stable against surface tension. The water layer thickness was measured using electron energy loss spectroscopy (EELS), and the water layer structure was characterized by using a quantitative nanoparticle counting technique. This thickness was found for channel gap heights ranging from 1 to 5 μm. Once formed, the water layers in the microchannel, when sealed, were stable for at least one week without any special care. Our results indicate that the water layer forms naturally and is closely associated only with the surface to which it adheres. Our study of naturally formed, stable water layers may shed light on topics from gas exchange in alveoli in biology to the post-wet-process control in the semiconductor industry. We anticipate our report to be a starting point for more detailed research and understanding of the microfluidics, mechanisms and applications of gas-liquid-solid systems. PMID:26856872

  20. Inducing stable reversion to achieve cancer control.

    PubMed

    Powers, Scott; Pollack, Robert E

    2016-04-01

    How can we stop cancer progression? Current strategies depend on modelling progression as the balanced outcome of mutations in, and expression of, tumour suppressor genes and oncogenes. New treatments emerge from successful attempts to tip that balance, but secondary mutational escape from those treatments has become a major impediment because it leads to resistance. In this Opinion article, we argue for a return to an earlier stratagem: tumour cell reversion. Treatments based on selection and analysis of stable revertants could create more durable remissions by reducing the selective pressure that leads to rapid drug resistance. PMID:27458638

  1. Medical management of chronic stable angina.

    PubMed

    Wee, Yong; Burns, Kylie; Bett, Nicholas

    2015-08-01

    Stable angina pectoris is characterised by typical exertional chest pain that is relieved by rest or nitrates. Risk stratification of patients is important to define prognosis, to guide medical management and to select patients suitable for revascularisation. Medical treatment aims to relieve angina and prevent cardiovascular events. Beta blockers and calcium channel antagonists are first-line options for treatment. Short-acting nitrates can be used for symptom relief. Low-dose aspirin and statins are prescribed to prevent cardiovascular events. PMID:26648642

  2. Stable, Electroinactive Wetting Agent For Fuel Cells

    NASA Technical Reports Server (NTRS)

    Prakash, Surya G.; Olah, George A.; Narayanan, Sekharipuram R.; Surampudi, Subbarao; Halpert, Gerald

    1994-01-01

    Straight-chain perfluorooctanesulfonic acid (C8 acid) identified as innocuous and stable wetting agent for use with polytetrafluoroethylene-containing electrodes in liquid-feed direct-oxidation fuel cells suggested for use in vehicles and portable power supplies. C8 acid in small concentrations in aqueous liquid solutions of methanol, trimethoxymethane, dimethoxymethane, and trioxane enables oxidation of these substances by use of commercially available electrodes of type designed originally for use with gases. This function specific to C8 acid molecule and not achieved by other related perfluorolkanesulfonic acids.

  3. Phase-stable, microwave FEL amplifier

    SciTech Connect

    Carlsten, B.E.; Fazio, M.V.; Haynes, W.B.; May, L.; Potter, M.

    1995-07-01

    Free-electron laser (FEL) amplifiers have demonstrated high efficiency and high output power for microwave wavelengths. However, using present technology, microwave FEL amplifiers are not phase stable enough to be suitable for driving linear accelerators, where several much amplifiers need to be phase locked. The growing wave`s phase sensitivity to the beam voltage in the small-signal gain regime is responsible for the largest contribution to this phase instability. We discuss a scheme that reduces the phase sensitivity to the beam voltage by operating off synchronism and matching the phase variation resulting from the desynchronism to the phase variation from the reduced plasma wavenumber as the beam voltage changes.

  4. Stable metallization for diamond and other materials

    NASA Technical Reports Server (NTRS)

    Bachli, Andreas (Inventor); Kolawa, Elzbieta (Inventor); Nicolet, Marc-Aurele (Inventor); Vandersande, Jan W. (Inventor)

    2000-01-01

    An adherent and metallurgically stable metallization system for diamond is presented. The big improvement in metallurgical stability is attributed to the use of a ternary, amorphous Ti--Si--N diffusion barrier. No diffusion between the layers and no delamination of the metallization was observed after annealing the schemes at 400.degree. C. for 100 hours and at 900.degree. C. for 30 minutes. Thermal cycling experiments in air from -65 to 155.degree. C. and adhesion tests were performed. Various embodiments are disclosed.

  5. Stable localized patterns in thin liquid films

    NASA Technical Reports Server (NTRS)

    Deissler, Robert J.; Oron, Alexander

    1992-01-01

    A two-dimensional nonlinear evolution equation is studied which describes the three-dimensional spatiotemporal behavior of the air-liquid interface of a thin liquid film lying on the underside of a cooled horizontal plate. It is shown that the equation has a Liapunov functional, and this fact is exploited to demonstrate that the Marangoni effect can stabilize the destabilizing effect of gravity (the Rayleigh-Taylor instability), allowing for the existence of stable localized axisymmetric solutions for a wide range of parameter values. Various properties of these structures are discussed.

  6. A computational study on the N-heterocyclic carbene-catalyzed Csp(2)-Csp(3) bond activation/[4+2] cycloaddition cascade reaction of cyclobutenones with imines: a new application of the conservation principle of molecular orbital symmetry.

    PubMed

    Wang, Yang; Wu, Bohua; Zhang, Haoyang; Wei, Donghui; Tang, Mingsheng

    2016-07-20

    A comprehensive density functional theory (DFT) investigation has been performed to interrogate the mechanisms and stereoselectivities of the Csp(2)-Csp(3) single bond activation of cyclobutenones and their [4+2] cycloaddition reaction with imines via N-heterocyclic carbene (NHC) organocatalysis. According to our calculated results, the fundamental reaction pathway contains four steps: nucleophilic addition of NHC to cyclobutenone, C-C bond cleavage for the formation of an enolate intermediate, [4+2] cycloaddition of the enolate intermediate with isatin imine, and the elimination of the NHC catalyst. In addition, the calculated results also reveal that the second reaction step is the rate-determining step, whereas the third step is the regio- and stereo-selectivity determining step. For the regio- and stereo-selectivity determining step, all four possible attack modes were considered. The addition of the C[double bond, length as m-dash]N bond in isatin imine to the dienolate intermediate is more energy favorable than the addition of the C[double bond, length as m-dash]O bond to a dienolate intermediate. Moreover, the Re face addition of the C[double bond, length as m-dash]N bond in isatin imine to the Re face of the dienolate intermediate leading to the SS configuration N-containing product was demonstrated to be most energy favorable, which is mainly due to the stronger second-order perturbation energy value in the corresponding transition state. Furthermore, by tracking the frontier molecular orbital (FMO) changes in the rate-determining C-C bond cleavage step, we found that the reaction obeys the conservation principle of molecular orbital symmetry. We believe that the present work would provide valuable insights into this kind of reaction.

  7. N-Heterocyclic Carbene-Copper-Catalyzed Group-, Site-, and Enantioselective Allylic Substitution with a Readily Accessible Propargyl(pinacolato)boron Reagent: Utility in Stereoselective Synthesis and Mechanistic Attributes.

    PubMed

    Shi, Ying; Jung, Byunghyuck; Torker, Sebastian; Hoveyda, Amir H

    2015-07-22

    The first instances of catalytic allylic substitution reactions involving a propargylic nucleophilic component are presented; reactions are facilitated by 5.0 mol % of a catalyst derived from a chiral N-heterocyclic carbene (NHC) and a copper chloride salt. A silyl-containing propargylic organoboron compound, easily prepared in multigram quantities, serves as the reagent. Aryl- and heteroaryl-substituted disubstituted alkenes within allylic phosphates and those with an alkyl or a silyl group can be used. Functional groups typically sensitive to hard nucleophilic reagents are tolerated, particularly in the additions to disubstituted alkenes. Reactions may be performed on the corresponding trisubstituted alkenes, affording quaternary carbon stereogenic centers. Incorporation of the propargylic group is generally favored (vs allenyl addition; 89:11 to >98:2 selectivity); 1,5-enynes can be isolated in 75-90% yield, 87:13 to >98:2 SN2'/SN2 (branched/linear) selectivity and 83:17-99:1 enantiomeric ratio. Utility is showcased by conversion of the alkynyl group to other useful functional units (e.g., homoallenyl and Z-homoalkenyl iodide), direct access to which by other enantioselective protocols would otherwise entail longer routes. Application to stereoselective synthesis of the acyclic portion of antifungal agent plakinic acid A, containing two remotely positioned stereogenic centers, by sequential use of two different NHC-Cu-catalyzed enantioselective allylic substitution (EAS) reactions further highlights utility. Mechanistic investigations (density functional theory calculations and deuterium labeling) point to a bridging function for an alkali metal cation connecting the sulfonate anion and a substrate's phosphate group to form the branched propargyl addition products as the dominant isomers via Cu(III) π-allyl intermediate complexes. PMID:26172476

  8. N-Heterocyclic Carbene-Copper-Catalyzed Group-, Site-, and Enantioselective Allylic Substitution with a Readily Accessible Propargyl(pinacolato)boron Reagent: Utility in Stereoselective Synthesis and Mechanistic Attributes.

    PubMed

    Shi, Ying; Jung, Byunghyuck; Torker, Sebastian; Hoveyda, Amir H

    2015-07-22

    The first instances of catalytic allylic substitution reactions involving a propargylic nucleophilic component are presented; reactions are facilitated by 5.0 mol % of a catalyst derived from a chiral N-heterocyclic carbene (NHC) and a copper chloride salt. A silyl-containing propargylic organoboron compound, easily prepared in multigram quantities, serves as the reagent. Aryl- and heteroaryl-substituted disubstituted alkenes within allylic phosphates and those with an alkyl or a silyl group can be used. Functional groups typically sensitive to hard nucleophilic reagents are tolerated, particularly in the additions to disubstituted alkenes. Reactions may be performed on the corresponding trisubstituted alkenes, affording quaternary carbon stereogenic centers. Incorporation of the propargylic group is generally favored (vs allenyl addition; 89:11 to >98:2 selectivity); 1,5-enynes can be isolated in 75-90% yield, 87:13 to >98:2 SN2'/SN2 (branched/linear) selectivity and 83:17-99:1 enantiomeric ratio. Utility is showcased by conversion of the alkynyl group to other useful functional units (e.g., homoallenyl and Z-homoalkenyl iodide), direct access to which by other enantioselective protocols would otherwise entail longer routes. Application to stereoselective synthesis of the acyclic portion of antifungal agent plakinic acid A, containing two remotely positioned stereogenic centers, by sequential use of two different NHC-Cu-catalyzed enantioselective allylic substitution (EAS) reactions further highlights utility. Mechanistic investigations (density functional theory calculations and deuterium labeling) point to a bridging function for an alkali metal cation connecting the sulfonate anion and a substrate's phosphate group to form the branched propargyl addition products as the dominant isomers via Cu(III) π-allyl intermediate complexes.

  9. A computational study on the N-heterocyclic carbene-catalyzed Csp(2)-Csp(3) bond activation/[4+2] cycloaddition cascade reaction of cyclobutenones with imines: a new application of the conservation principle of molecular orbital symmetry.

    PubMed

    Wang, Yang; Wu, Bohua; Zhang, Haoyang; Wei, Donghui; Tang, Mingsheng

    2016-07-20

    A comprehensive density functional theory (DFT) investigation has been performed to interrogate the mechanisms and stereoselectivities of the Csp(2)-Csp(3) single bond activation of cyclobutenones and their [4+2] cycloaddition reaction with imines via N-heterocyclic carbene (NHC) organocatalysis. According to our calculated results, the fundamental reaction pathway contains four steps: nucleophilic addition of NHC to cyclobutenone, C-C bond cleavage for the formation of an enolate intermediate, [4+2] cycloaddition of the enolate intermediate with isatin imine, and the elimination of the NHC catalyst. In addition, the calculated results also reveal that the second reaction step is the rate-determining step, whereas the third step is the regio- and stereo-selectivity determining step. For the regio- and stereo-selectivity determining step, all four possible attack modes were considered. The addition of the C[double bond, length as m-dash]N bond in isatin imine to the dienolate intermediate is more energy favorable than the addition of the C[double bond, length as m-dash]O bond to a dienolate intermediate. Moreover, the Re face addition of the C[double bond, length as m-dash]N bond in isatin imine to the Re face of the dienolate intermediate leading to the SS configuration N-containing product was demonstrated to be most energy favorable, which is mainly due to the stronger second-order perturbation energy value in the corresponding transition state. Furthermore, by tracking the frontier molecular orbital (FMO) changes in the rate-determining C-C bond cleavage step, we found that the reaction obeys the conservation principle of molecular orbital symmetry. We believe that the present work would provide valuable insights into this kind of reaction. PMID:27400324

  10. Stable isotope enrichment using a plasma centrifuge

    NASA Astrophysics Data System (ADS)

    Krishnan, Mahadevan; Bures, Brian; Madden, Robert

    2012-10-01

    A primary goal of the Department of Energy's Isotope Development and Production for Research and Applications Program (Isotope Program) within the Office of Nuclear Physics (NP) is to produce isotopes that are in short supply in the U.S. and of which there exists no or insufficient domestic commercial production capability. A vacuum arc plasma centrifuge is a rigid rotor column of metal plasma in which centrifugal forces re-distribute ions radially according to their mass/charge ratio. Early work demonstrated rotation at 2 million rpm and separation of various stable isotopes. The spinning plasma column had a Gaussian flux profile, peaked on the rigid rotor axis. This work adopts a more efficient approach, with the plasma created as a hollow column, wherein the flux is concentrated at larger radii where the centrifugal action is highest. By tailoring the vacuum arc discharge geometry, the rotation rate can also be increased to ˜10 million rpm. Data from Cu, Al and other metal plasmas will be presented and discussed in light of enriched stable isotopes needed for research and medicine.

  11. Fast and stable electrical discharge machining (EDM)

    NASA Astrophysics Data System (ADS)

    Wu, Jianyang; Zhou, Ming; Xu, Xiaoyi; Yang, Jianwei; Zeng, Xiangwei; Xu, Donghui

    2016-05-01

    In order to improve EDM performances, the most important issue is to develop a highly stable control system. As a serious defect in EDM adaptive control system by minimum-variance control law, the occasional instability deterred its full applications in industries. This paper focuses on stabilizing EDM process by establishing a new minimum-variance and pole-placement coupled control law. Based on real-time estimation of EDM process model parameters, this adaptive control system directly controls electrode discharging cycle not only to follow a specified gap state for fast machining but also to track the dynamical response of a reference model for stabilizing EDM process. Confirmation experiment demonstrates that this control system can timely adjust electrode discharging cycle in terms of different machining situations quantified as a series of varied gap states to maintain a stable and fast fabrication. The adaptive control system by this newly developed control law exhibits its superior machining ability and capability of stabilizing sparking process to those of the adaptive control system by minimum-variance control law. The adaptive system has actually theoretically and technically solved the stability issue puzzled EDM circle for decades.

  12. Color stable manganese-doped phosphors

    DOEpatents

    Lyons, Robert Joseph; Setlur, Anant Achyut; Deshpande, Anirudha Rajendra; Grigorov, Ljudmil Slavchev

    2012-08-28

    A process for preparing color stable Mn.sup.+4 doped phosphors includes providing a phosphor of formula I; A.sub.x[MF.sub.y]:Mn.sup.+4 I and contacting the phosphor in particulate form with a saturated solution of a composition of formula II in aqueous hydrofluoric acid; A.sub.x[MF.sub.y]; II wherein A is Li, Na, K, Rb, Cs, NR.sub.4 or a combination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; R is H, lower alkyl, or a combination thereof; x is the absolute value of the charge of the [MF.sub.y] ion; and y is 5, 6 or 7. In particular embodiments, M is Si, Ge, Sn, Ti, Zr, or a combination thereof. A lighting apparatus capable of emitting white light includes a semiconductor light source; and a phosphor composition radiationally coupled to the light source, and which includes a color stable Mn.sup.+4 doped phosphor.

  13. Highly stable electrochemical immunosensor for carcinoembryonic antigen.

    PubMed

    Sun, Xiaobin; Ma, Zhanfang

    2012-05-15

    The long-term stability of sensing interfaces is an important issue in biosensor fabrication. A novel stable gold nanoparticle (AuNP)-modified glassy carbon (GC) electrode interface (GC-Ph-AuNP)-based biosensor for detecting carcinoembryonic antigen (CEA) was developed. GC electrodes were modified with 1,4-phenylenediamine to form a stable layer, and then AuNPs were bound onto the GC electrodes through CAu bonds. Anti-CEA was directly adsorbed on AuNPs fixed on the GC electrode. The linear range of the immunosensor was from 10 fg to 100 ng mL(-1) with a detection limit of 3 fg mL(-1) (S/N=3). The current of the immunosensor was increased by 4% after one month. The GC-Ph-AuNP immunosensor showed high sensitivity, a wide linear range, low detection limit, and good selectivity and stability. The immobilization method of the immunosensor could be widely applied to construct other immunosensors.

  14. Prediction of new thermodynamically stable aluminum oxides

    PubMed Central

    Liu, Yue; Oganov, Artem R.; Wang, Shengnan; Zhu, Qiang; Dong, Xiao; Kresse, Georg

    2015-01-01

    Recently, it has been shown that under pressure, unexpected and counterintuitive chemical compounds become stable. Laser shock experiments (A. Rode, unpublished) on alumina (Al2O3) have shown non-equilibrium decomposition of alumina with the formation of free Al and a mysterious transparent phase. Inspired by these observations, we have explored the possibility of the formation of new chemical compounds in the system Al-O. Using the variable-composition structure prediction algorithm USPEX, in addition to the well-known Al2O3, we have found two extraordinary compounds Al4O7 and AlO2 to be thermodynamically stable in the pressure ranges 330-443 GPa and above 332 GPa, respectively. Both of these compounds at the same time contain oxide O2− and peroxide O22− ions, and both are insulating. Peroxo-groups are responsible for gap states, which significantly reduce the electronic band gap of both Al4O7 and AlO2. PMID:25830780

  15. Stable Lithium Argon compounds under high pressure

    PubMed Central

    Li, Xiaofeng; Hermann, Andreas; Peng, Feng; Lv, Jian; Wang, Yanchao; Wang, Hui; Ma, Yanming

    2015-01-01

    High pressure can fundamentally alter the bonding patterns of chemical elements. Its effects include stimulating elements thought to be “inactive” to form unexpectedly stable compounds with unusual chemical and physical properties. Here, using an unbiased structure search method based on CALYPSO methodology and density functional total energy calculations, the phase stabilities and crystal structures of Li−Ar compounds are systematically investigated at high pressure up to 300 GPa. Two unexpected LimArn compounds (LiAr and Li3Ar) are predicted to be stable above 112 GPa and 119 GPa, respectively. A detailed analysis of the electronic structure of LiAr and Li3Ar shows that Ar in these compounds attracts electrons and thus behaves as an oxidizing agent. This is markedly different from the hitherto established chemical reactivity of Ar. Moreover, we predict that the P4/mmm phase of Li3Ar has a superconducting transition temperature of 17.6 K at 120 GPa. PMID:26582083

  16. Stable magnesium peroxide at high pressure.

    PubMed

    Lobanov, Sergey S; Zhu, Qiang; Holtgrewe, Nicholas; Prescher, Clemens; Prakapenka, Vitali B; Oganov, Artem R; Goncharov, Alexander F

    2015-09-01

    Rocky planets are thought to comprise compounds of Mg and O as these are among the most abundant elements, but knowledge of their stable phases may be incomplete. MgO is known to be remarkably stable to very high pressure and chemically inert under reduced condition of the Earth's lower mantle. However, in exoplanets oxygen may be a more abundant constituent. Here, using synchrotron x-ray diffraction in laser-heated diamond anvil cells, we show that MgO and oxygen react at pressures above 96 GPa and T = 2150 K with the formation of I4/mcm MgO2. Raman spectroscopy detects the presence of a peroxide ion (O2(2-)) in the synthesized material as well as in the recovered specimen. Likewise, energy-dispersive x-ray spectroscopy confirms that the recovered sample has higher oxygen content than pure MgO. Our finding suggests that MgO2 may be present together or instead of MgO in rocky mantles and rocky planetary cores under highly oxidized conditions.

  17. Stable magnesium peroxide at high pressure

    NASA Astrophysics Data System (ADS)

    Lobanov, Sergey S.; Zhu, Qiang; Holtgrewe, Nicholas; Prescher, Clemens; Prakapenka, Vitali B.; Oganov, Artem R.; Goncharov, Alexander F.

    2015-09-01

    Rocky planets are thought to comprise compounds of Mg and O as these are among the most abundant elements, but knowledge of their stable phases may be incomplete. MgO is known to be remarkably stable to very high pressure and chemically inert under reduced condition of the Earth’s lower mantle. However, in exoplanets oxygen may be a more abundant constituent. Here, using synchrotron x-ray diffraction in laser-heated diamond anvil cells, we show that MgO and oxygen react at pressures above 96 GPa and T = 2150 K with the formation of I4/mcm MgO2. Raman spectroscopy detects the presence of a peroxide ion (O22-) in the synthesized material as well as in the recovered specimen. Likewise, energy-dispersive x-ray spectroscopy confirms that the recovered sample has higher oxygen content than pure MgO. Our finding suggests that MgO2 may be present together or instead of MgO in rocky mantles and rocky planetary cores under highly oxidized conditions.

  18. Stable extramarital affairs are breaking the heart.

    PubMed

    Fisher, A D; Bandini, E; Corona, G; Monami, M; Cameron Smith, M; Melani, C; Balzi, D; Forti, G; Mannucci, E; Maggi, M

    2012-02-01

    The relationship between extramarital affairs and cardiovascular risk is still not completely clarified. The aim of this study was to investigate whether extramarital affairs have a protective effect on cardiovascular risk or, conversely, a deleterious one. Among patients studied, 91.8% of the whole sample reported no or occasional extramarital affairs, while 8.2% declared a stable secondary relationship. During a median follow-up of 4 [0-8] years, 95 major adverse cardiovascular events (MACE), eight of which were fatal, were observed. Cox analysis, after adjustment for confounding factors, showed that presence of stable extramarital affair was associated with a higher incidence of MACE (HR = 2.13 [1.12; 4.07], p = 0.023). The introduction in the Cox model of patient perceived partner's hypoactive sexual desire (PPPHSD) attenuates the association (HR 1.86 [0.93; 3.70], p = 0.078). The sample was therefore divided according to PPPHSD. We observed that unadjusted incidence of MACE was significantly associated with presence of extramarital affairs only in men reporting a primal partner without PPPHSD. This association was also confirmed in a Cox regression model, after adjusting for confounders (HR = 2.87 [1.81; 6.98], p = 0.020). We can conclude that to be unfaithful represents an independent risk factor for MACE. Therefore, infidelity induces not only heart trouble in the betrayed partners, but seems to be also able to increase the betrayer's heart-related events.

  19. Thermodynamically stable superstructures in binary alloys

    NASA Astrophysics Data System (ADS)

    Nelson, Lance

    2009-10-01

    Adding a second metal to another can induce the formation of ordered superstructures. These ordered phases have properties that are desireable in many industrial, manufacturing and technological applications. Our goal is to find which of the thousands of possible superstructures are thermodynamically stable through the use of computational tools. Owing to the many superstructures that are possible, as well as the complex nature of some of these, DFT calculations become impractical for searching for these superstructures. We employ a cluster expansion method, which uses energy information from a relatively small number of structures and fits that information to a set of interaction types. Because the resulting expansion provides a fast way to compute energies, we can use it to calculate the energies of the thousands of other superstructures. Specifically, I discuss the use of the cluster expansion on two binary alloys: AgPd and MgZn. Palladium alloys are of interest in the fabrication of jewelry, and a stable ordered phase at some concentrations would be a breakthrough for the jewelry manufacturers. Magnesium alloys are of interest because of their strength and light weight. They are being used increasingly in the manufacturing of things such as airplanes and automobiles. A cheap alloying agent that promotes the formation of an ordered structure would be a breakthrough.

  20. Stable magnesium peroxide at high pressure.

    PubMed

    Lobanov, Sergey S; Zhu, Qiang; Holtgrewe, Nicholas; Prescher, Clemens; Prakapenka, Vitali B; Oganov, Artem R; Goncharov, Alexander F

    2015-01-01

    Rocky planets are thought to comprise compounds of Mg and O as these are among the most abundant elements, but knowledge of their stable phases may be incomplete. MgO is known to be remarkably stable to very high pressure and chemically inert under reduced condition of the Earth's lower mantle. However, in exoplanets oxygen may be a more abundant constituent. Here, using synchrotron x-ray diffraction in laser-heated diamond anvil cells, we show that MgO and oxygen react at pressures above 96 GPa and T = 2150 K with the formation of I4/mcm MgO2. Raman spectroscopy detects the presence of a peroxide ion (O2(2-)) in the synthesized material as well as in the recovered specimen. Likewise, energy-dispersive x-ray spectroscopy confirms that the recovered sample has higher oxygen content than pure MgO. Our finding suggests that MgO2 may be present together or instead of MgO in rocky mantles and rocky planetary cores under highly oxidized conditions. PMID:26323635