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Sample records for stable p-heterocyclic carbenes

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

    PubMed

    Soleilhavoup, Michle; 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 ?-donor amino substituents of diaminocarbenes is replaced by a ?-donating but not ?-donating alkyl group. As a consequence, CAACs are more nucleophilic (?-donating) but also more electrophilic (?-accepting) than diaminocarbenes. Additionally, the presence of a quaternary carbon in the position ? 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 contrast to diaminocarbenes, the higher basicity of CAACs makes them poor leaving groups, and thus they cannot be used for classical organocatalysis. However, because of their superior electrophilicity and smaller singlet-triplet gap, CAACs can activate small molecules at room temperature, such as CO, H2, and P4, as well as enthalpically strong bonds, such as B-H, Si-H, N-H, and P-H. Lastly, excellent results have been obtained in palladium, ruthenium, and gold catalysis. CAAC-metal complexes are extremely thermally robust, which allows for their utilization in harsh conditions. This property has been used to perform a variety of gold-catalyzed reactions in the presence of basic amines, including ammonia and hydrazine, which usually deactivate catalysts. PMID:25515548

  2. Stable Cyclic Carbenes and Related Species beyond Diaminocarbenes

    PubMed Central

    Melaimi, Mohand; Soleilhavoup, Michle

    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 ?-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 ?-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. A carbene-carbene complex equilibrium.

    PubMed

    Moss, Robert A; Wang, Lei; Odorisio, Christina M; Krogh-Jespersen, Karsten

    2010-08-11

    Phenylchlorocarbene, generated by laser flash photolysis of phenylchlorodiazirine, formed highly stable pi-type complexes with 1,3,5-trimethoxybenzene in pentane. The carbene and carbene complexes were in equilibrium. We measured the equilibrium constant (K = 1264 M(-1) at 294 K) and, from its temperature dependence, extracted the associated thermodynamic parameters: DeltaH(o) = -7.1 kcal/mol, DeltaS(o) = -10.2 eu, and DeltaG(o) = -4.1 kcal/mol. The carbene complexes were characterized by UV-vis spectroscopy and computational analysis. PMID:20681697

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

    PubMed

    Mohapatra, Chandrajeet; Mondal, Kartik Chandra; Samuel, Prinson P; Keil, Helena; Nieptter, 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. PMID:26179976

  5. Formation and crystallographic elucidation of stable [4 + 2]-coordinate nickel(II) N,S-heterocyclic carbene (NSHC) complexes.

    PubMed

    Ding, Nini; Zhang, Jun; Hor, T S Andy

    2009-03-14

    A series of square-planar N,S-heterocyclic carbene (NSHC) complexes trans-[NiX(2)(N-RBzTh)(2)] (BzTh = benzothiazolin-2-ylidene) (R/X = Bz/Br; Me/I; Et/I; Pr(i)/I; Bu(i)/I) have been synthesized and characterized by X-ray single-crystal diffraction analysis. These are the first crystallographically established NSHC complexes of nickel in the literature. The N,S-heterocyclic carbene (NSHC) rings invariably twist away from co-planarity with the metal coordination plane such that the N-substituent moves on top and below the metal to facilitate electrostatic gamma-hydride interaction, thus giving an essentially [4 + 2] coordination at the Ni(ii) center. These compounds are active toward reductive Ullmann-type coupling reactions in Bu(4)NBr showing higher activities towards bromoanisole or bromotoluene than bromobenzene. The complex trans-[NiI(2)(N-Pr(i)BzTh)(2)] with the shortest NiH anagostic separation and a near-ideal orthogonal orientation between the carbene and metal planes gives the highest yields. PMID:19240921

  6. Aryl palladium carbene complexes and carbene-aryl coupling reactions.

    PubMed

    Albniz, Ana C; Espinet, Pablo; Manrique, Ral; Prez-Mateo, Alberto

    2005-02-18

    Transmetalation of an aminocarbene moiety from [W(CO)5{C(NEt2)R}] to palladium leads to isolable monoaminocarbene palladium aryl complexes [{Pd(mu-Br)Pf[C(NEt2)R]}2] (R = Me, Ph; Pf = C6F5). When [W(CO)5{C(OMe)R}] is used, the corresponding palladium carbenes cannot be isolated since these putative, more electrophilic carbenes undergo a fast migratory insertion process to give alkyl palladium complexes. These complexes could be stabilized in the eta3-allylic form for R = 2-phenylethenyl or in the less stable eta3-benzylic fashion for R = Ph. Hydrolysis products and a pentafluorophenylvinylic methyl ether (when R = Me) were also observed. The monoaminocarbenes slowly decompose through carbene-aryl coupling to produce the corresponding iminium salts and, depending on the reaction conditions, the corresponding hydrolysis products. The electrophilicity of the carbene carbon, which is mainly determined by the nature of the heteroatom group, controls the ease of evolution by carbene-aryl coupling. Accordingly, no carbene-aryl coupling was observed for a diaminocarbene palladium aryl complex. PMID:15662682

  7. A Strategy to Control the Reactivation of Frustrated Lewis Pairs from Shelf-Stable Carbene Borane Complexes

    PubMed Central

    Hoshimoto, Yoichi; Kinoshita, Takuya; Ohashi, Masato; Ogoshi, Sensuke

    2015-01-01

    N-Phosphine oxide substituted imidazolylidenes (PoxIms) have been synthesized and fully characterized. These species can undergo significant changes to the spatial environment surrounding their carbene center through rotation of the phosphine oxide moiety. Either classical Lewis adducts (CLAs) or frustrated Lewis pairs (FLPs) are thus formed with B(C6F5)3 depending on the orientation of the phosphine oxide group. A strategy to reactivate FLPs from CLAs by exploiting molecular motions that are responsive to external stimuli has therefore been developed. The reactivation conditions were successfully controlled by tuning the strain in the PoxImB(C6F5)3 complexes so that reactivation only occurred above ambient temperature. PMID:26315680

  8. Shape-Controllable Formation of Poly-imidazolium Salts for Stable Palladium N-Heterocyclic Carbene Polymers

    NASA Astrophysics Data System (ADS)

    Zhao, Huaixia; Li, Liuyi; Wang, Yangxin; Wang, Ruihu

    2014-06-01

    The imidazolium-based main-chain organic polymers are one of promising platforms in heterogeneous catalysis, the size and outer morphology of polymer particles are known to have important effects on their physical properties and catalytic applications, but main-chain ionic polymers usually generate amorphous or spherical particles. Herein, we presented a versatile and facile synthetic route for size- and shape-controllable synthesis of main-chain poly-imidazolium particles. The wire-shaped, spherical and ribbon-shaped morphologies of poly-imidazolium particles were readily synthesized through quaternization of bis-(imidazol-1-yl)methane and 2,4,6-tris(4-(bromomethyl)phenyl)-1,3,5-triazine, and the modification of their size and morphology were realized through adjusting solvent polarity, solubility, concentration and temperatures. The direct complexation of the particles with Pd(OAc)2 produced ionic polymers containing palladium N-heterocyclic carbene units (NHCs) with intactness of original morphologies. The particle morphologies have a significant effect on catalytic performances. Wire-shaped palladium-NHC polymer shows excellent catalytic activity and recyclabilty in heterogeneous Suzuki-Miyaura cross-coupling reaction.

  9. Carbene generation by cytochromes and electronic structure of heme-iron-porphyrin-carbene complex: a quantum chemical study.

    PubMed

    Taxak, Nikhil; Patel, Bhargav; Bharatam, Prasad V

    2013-05-01

    Carbene-heme-iron-porphyrin complexes generated from cytochrome P450 (CYP450)-mediated metabolism of compounds containing methylenedioxyphenyl (MDP) moiety lead to the mechanism-based inhibition (MBI) of CYPs. This coordination complex is termed as the metabolic-intermediate complex (MIC). The bioinorganic chemistry of MDP carbenes has been studied using quantum chemical methods employing density functional theory (B3LYP functional with implicit solvent corrections) to (i) analyze the characteristics of MDP-carbene in terms of singlet-triplet energy difference, protonation, and dimerization energies, etc.; (ii) determine the electronic structure and analyze the Fe-carbene interactions; and (iii) elucidate the potential reaction pathways for the generation of carbene, using Cpd I (iron(IV)-oxo-porphine with SH(-) as the axial ligand) as the model oxidant to mimic the activity of CYP450. The results show that MDP-carbenes are sufficiently stable and nucleophilic, leading to the formation of stable MIC (-40.35 kcal/mol) on the doublet spin state, formed via interaction between ?(LP) of carbene and empty dz(2) orbital of heme-iron. This was aided by the back-bonding between filled d(xz) orbital of heme-iron and the empty p orbital of carbene. The mechanistic pathway proposed in the literature for the generation of MDP-carbene (CH hydroxylation followed by water elimination) was studied, and observed to be unfavorable, owing to the formation of highly stable hydroxylated product (-57.12 kcal/mol). An intriguing pathway involving hydride ion abstraction and proton transfer followed by water elimination step was observed to be the most probable pathway. PMID:23560646

  10. Carbene-dichlorosilylene stabilized phosphinidenes exhibiting strong intramolecular charge transfer transition.

    PubMed

    Roy, Sudipta; Stollberg, Peter; Herbst-Irmer, Regine; Stalke, Dietmar; Andrada, Diego M; Frenking, Gernot; Roesky, Herbert W

    2015-01-14

    The unstable species dichlorosilylene was previously stabilized by carbene. The lone pair of electrons on the silicon atom of (carbene)SiCl2 can form a coordinate bond with metal-carbonyls. Herein we report that (carbene)SiCl2 can stabilize a phosphinidene (Ar-P, a carbone analogue) with the general formula carbene?SiCl2?P-Ar (carbene = cyclic alkyl(amino) carbene (cAAC; 2) and N-heterocyclic carbene (NHC; 3)). Compounds 2 and 3 are stable, isolable, and storable at 0 C (2) to room temperature (3) under an inert atmosphere. The crystals of 2 and 3 are dark blue and red, respectively. The intense blue color of 2 arises due to the strong intramolecular charge transfer (ICT) transition from ?Si?P??*cAAC. The electronic structure and bonding of 2, 3 were studied by theoretical calculations. The HOMO of the molecule is located on the ?Si?P bond, while the LUMO is located at the carbene moiety (cAAC or NHC). The dramatic change in color of these compounds from red (3, NHC) to blue (2, cAAC) is ascribed to the difference in energy of the LUMO within the carbenes (cAAC/NHC) due to a lower lying LUMO of cAAC. PMID:25539016

  11. A persistent (amino)(ferrocenyl)carbene

    PubMed Central

    DeHope, Alan; Mendoza-Espinosa, Daniel; Donnadieu, Bruno

    2012-01-01

    Deprotonation of N,N-diisopropyl-C-ferrocenylaldiminium triflate 2 cleanly leads to the corresponding 1,2-diamino-1,2-diferrocenylethene 3, the dimer of the desired (amino)(ferrocenyl)carbene. Fulvene 6, obtained by addition of the lithium salt of tetramethylcyclopentadiene to methoxyformamidinium methylsulfate 5, reacts with dicarbonylcyclopentadienylbromoiron(II), and with a mixture of FeCl2 and Cp* lithium salt, affording the corresponding tetramethylferrocenylaldiminium salt 7, and nonamethylferrocenylaldiminium salt 8, respectively. Although the deprotonation of 7 gives a complex mixture of products, the treatment of 8 at ?78 C with sodium hexamethyldisilazide allowed for the isolation of the corresponding (amino)(ferrocenyl)carbene 9 as a yellow powder. However, even in the solid state, it is stable for less than 48 h at ?20 C. In addition to NMR spectroscopy, evidence for the carbene nature of 9 was found by a trapping experiment with sulfur that leads to the corresponding adduct 10, which was characterized by a single crystal X-ray diffraction study. PMID:22707878

  12. 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

  13. Bivalent Tin Analogues of Carbenes

    NASA Astrophysics Data System (ADS)

    Shiryaev, Vladimir I.; Mironov, Vladimir F.

    1983-02-01

    The structure and certain chemical and physicochemical properties of bivalent tin compounds (stannylenes) are examined and the electronic, structural and chemical similarity between these compounds and carbenes and their analogues bivalent compounds of Group IVB elements is demonstrated. The possibilities of stannylenes in the synthesis of organotin (IV) compounds as well as complexes in which stannylenes are electron-donating ligands, like carbenes, are analysed. The bibliography includes 457 references.

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

    PubMed

    Frutos, Mara; de la Torre, Mara 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

  15. Synthesis and reactivity of a CAAC-aminoborylene adduct: a hetero-allene or an organoboron isoelectronic with singlet carbenes.

    PubMed

    Dahcheh, Fatme; Martin, David; Stephan, Douglas W; Bertrand, Guy

    2014-11-24

    A one-electron reduction of a cyclic (alkyl)(amino)carbene (CAAC)-bis(trimethylsilyl)aminodichloroborane adduct leads to a stable aminoboryl radical. A second one-electron reduction gives rise to a CAAC-aminoborylene adduct, which features an allenic structure. However, in manner similar to that of stable electrophilic singlet carbenes, this compound activates small molecules, such as CO and H2. PMID:25267591

  16. Betaine-carbene interconversions. From N-ylides to zwitterionic N-heterocyclic carbene-borane adducts.

    PubMed

    Pidlypnyi, Nazar; Namyslo, Jan C; Drafz, Martin H H; Nieger, Martin; Schmidt, Andreas

    2013-02-01

    In the presence of NBS 3-methylindole reacted with various imidazoles to give the (indol-2-yl)imidazolium salts 21a-f, which were converted in aqueous solution into the 2-(imidazolium-3-yl)-3-methylindolates 22a-f by base. These conjugated ylides--which represent a subclass of mesomeric betaines--are the exclusively detectable form in the NMR spectra taken in DMSO-d(6). A DFT calculation revealed that the betaine 22a is -9.3 kJ/mol more stable than the tautomeric N-heterocyclic carbene 23a and that the energy for the betaine-carbene interconversion is ?G() = 66.4 kJ/mol. The N-heterocyclic carbenes (3-methyl-indol-2-yl)imidazol-2-ylidenes, however, can be trapped by sulfur, triethylborane, and triphenylborane. Whereas the first trapping reaction yielded the expected imidazolethiones, the borates gave the first representatives of new zwitterionic borane adducts, imidazo[2',1':3,4][1,4,2]diazaborolo[1,5-a]indolium-11-ides 26a-h. We performed DFT calculations on the structures of mesomeric betaine 22a, the carbene 23a, and the mechanisms of the borane adduct formation to 26a-h, NMR spectroscopic investigations including (15)N, (7)Li, and (11)B NMR spectroscopy, and an X-ray single-crystal analysis of one of the borane adducts. PMID:23305205

  17. 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

  18. Continuous-Flow N-Heterocyclic Carbene Generation and Organocatalysis.

    PubMed

    Di Marco, Lorenzo; Hans, Morgan; Delaude, Lionel; Monbaliu, Jean-Christophe M

    2016-03-18

    Two methods were assessed for the generation of common N-heterocyclic carbenes (NHCs) from stable imidazol(in)ium precursors using convenient and straightforward continuous-flow setups with either a heterogeneous inorganic base (Cs2 CO3 or K3 PO4 ) or a homogeneous organic base (KN(SiMe3 )2 ). In-line quenching with carbon disulfide revealed that the homogeneous strategy was most efficient for the preparation of a small library of NHCs. The generation of free nucleophilic carbenes was next telescoped with two benchmark NHC-catalyzed reactions; namely, the transesterification of vinyl acetate with benzyl alcohol and the amidation of N-Boc-glycine methyl ester with ethanolamine. Both organocatalytic transformations proceeded with total conversion and excellent yields were achieved after extraction, showcasing the first examples of continuous-flow organocatalysis with NHCs. PMID:26880372

  19. Lewis Base Catalysts 6: Carbene Catalysts

    PubMed Central

    Moore, Jennifer L.

    2013-01-01

    The use of N-heterocyclic carbenes as catalysts for organic transformations has received increased attention in the past 10 years. A discussion of catalyst development and nucleophilic characteristics precedes a description of recent advancements and new reactions using N-heterocyclic carbenes in catalysis. PMID:21494949

  20. 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

  1. Direct estimate of the internal ?-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(?) ?-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(?) ?-donation while mesoionic carbenes possess the strongest ?-donation.

  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. 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…

  4. 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

  5. The reactivity game: theoretical predictions for heavy atom tunneling in adamantyl and related carbenes.

    PubMed

    Kozuch, S

    2014-05-01

    The possibility of carbon atom tunneling at cryogenic temperatures for carbene-based ring expansion of adamantane analogues calls for a delicate balance of reactivity to experimentally detect the transpiring reaction. An overly reactive carbene will precipitously decay; an excessively stable carbene will not tunnel. Nevertheless, the factors that affect the quantum-mechanical tunneling (QMT) reactivity - mass, barrier height and width - are strikingly different from the classical "over the barrier" thermal mechanism. Herein, comparisons with experimental values and predictions on measurable rate constants for novel carbene systems are presented by way of small curvature tunneling (SCT) computations. Adamantane, noradamantane and bisnoradamantane have a significantly different C-C bond strain and reactivity, which can be modulated by tinkering with the carbene substituent atom (H, Cl or F) to obtain an observable lifetime of the reactant. The influence of barrier heights and widths, kinetic isotope effects (KIEs), the detection of the tunneling-determining atoms (TDA) and the comparisons with hydrogen-based reactions are discussed with the objective of finding the physical limits for QMT. PMID:24590008

  6. A Triatomic Silicon(0) Cluster Stabilized by a Cyclic Alkyl(amino) Carbene.

    PubMed

    Mondal, Kartik Chandra; Roy, Sudipta; Dittrich, Birger; Andrada, Diego M; Frenking, Gernot; Roesky, Herbert W

    2016-02-01

    Reduction of the neutral carbene tetrachlorosilane adduct (cAAC)SiCl4 (cAAC=cyclic alkyl(amino) carbene :C(CMe2 )2 (CH2 )N(2,6-iPr2 C6 H3 ) with potassium graphite produces stable (cAAC)3 Si3 , a carbene-stabilized triatomic silicon(0) molecule. The Si-Si bond lengths in (cAAC)3 Si3 are 2.399(8), 2.369(8) and 2.398(8)?, which are in the range of Si-Si single bonds. Each trigonal pyramidal silicon atom of the triangular molecule (cAAC)3 Si3 possesses a lone pair of electrons. Its bonding, stability, and electron density distributions were studied by quantum chemical calculations. PMID:26821613

  7. A DFT and structural investigation of the conformations of Fischer carbene complexes

    NASA Astrophysics Data System (ADS)

    Landman, Maril

    2015-09-01

    A set of different Fischer carbene complexes of group VI and VII metals, with varied heteroatom and heteroaromatic substituents on the carbene carbon atom, was studied. Density functional theory as well as single crystal diffraction techniques were employed to investigated the most stable conformation of these complexes. The complexes studied, [M(CO)4L{C(X)Z}], with L = PPh3 or CO, X = ethoxy (-OCH2CH3) or amino (-NH2 or NHCy) substituents as the heteroatom carbene substituents, Z = 2-furyl (-C4H3O), 2-thienyl (-C4H3S), 2-(N-methyl)pyrrolyl (-C4H3NCH3) as the second carbene substituent had their substituents varied systematically to give all the possible conformations of these complexes. The conformations of the complexes, in particular the relative orientations of the heteroatoms in the molecule (syn vs. anti), E/Z isomerism in the aminocarbene complexes and cis/trans isomerism in the ligand substituted complexes as well as various combinations of these aspects, were studied. In general, it was found that the most stable conformation theoretically as well as in the solid state for most of the complexes preferred the syn conformation. The Z-isomer is generally preferred over the E isomer while the cis is more predominant than the trans isomer. Using DFT and NBO calculations, explanations for the preferred conformations were explored. It was concluded that both steric and electronic factors influence the conformations of the carbene complexes, with the extent of contribution of these two factors varying for each of the different carbene substituents.

  8. Crystalline Cyclic (Alkyl)(amino)carbene-tetrafluoropyridyl Radical.

    PubMed

    Styra, Steffen; Melaimi, Mohand; Moore, Curtis E; Rheingold, Arnold L; Augenstein, Timo; Breher, Frank; Bertrand, Guy

    2015-06-01

    A stable cyclic (alkyl)(amino)carbene (CAAC) 1 inserts into the para-CF bond of pentafluoropyridine, and after fluoride abstraction, the iminium-pyridyl adduct [3](+) was isolated. A cyclic voltammetry study shows a reversible three-state redox system involving [3](+) , [3](?) , and [3](-) . The CAAC-pyridyl radical [3](?) , obtained by reduction of [3](+) with magnesium, has been spectroscopically and crystallographically characterized. In contrast to the lack of ? communication between the CAAC and the pyridine units in cation [3](+) , the unpaired electron of [3](?) is delocalized over an extended ? system involving both heterocycles. PMID:25925367

  9. An overview of N-heterocyclic carbenes

    NASA Astrophysics Data System (ADS)

    Hopkinson, Matthew N.; Richter, Christian; Schedler, Michael; Glorius, Frank

    2014-06-01

    The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. Here we provide a concise overview of N-heterocyclic carbenes in modern chemistry, summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.

  10. Abnormal carbene-silicon halide complexes.

    PubMed

    Wang, Yuzhong; Xie, Yaoming; Wei, Pingrong; Schaefer, Henry F; Robinson, Gregory H

    2016-04-14

    Reaction of the anionic N-heterocyclic dicarbene (NHDC), [:C{[N(2,6-Pr(i)2C6H3)]2CHCLi}]n (1), with SiCl4 gives the trichlorosilyl-substituted (at the C4 carbon) N-heterocyclic carbene complex (7). Abnormal carbene-SiCl4 complex (8) may be conveniently synthesized by combining 7 with HCl·NEt3. In addition, 7 may react with CH2Cl2 in warm hexane, giving the abnormal carbene-complexed SiCl3(+) cation (9). The nature of the bonding in 9 was probed with complementary DFT computations. PMID:26605692

  11. Carbene transfer from triazolylidene gold complexes as a potent strategy for inducing high catalytic activity.

    PubMed

    Canseco-Gonzalez, Daniel; Petronilho, Ana; Mueller-Bunz, Helge; Ohmatsu, Kohsuke; Ooi, Takashi; Albrecht, Martin

    2013-09-01

    A series of gold(I) complexes [AuCl(trz)] were synthesized that contain 1,2,3-triazolylidene (trz) ligands with variable wingtip groups. In the presence of AgBF4, these complexes undergo ligand redistribution to yield cationic complexes [Au(trz)2]BF4 in high yields as a result of efficient carbene transfer. Identical reactivity patterns were detected for carbene gold complexes comprised of Arduengo-type IMes ligands (IMes = N,N'-dimesityl-imidazol-2-ylidene). Reaction of cationic complexes [Au(trz)2](+) with [AuCl(trz')] afforded the heteroleptic complex [Au(trz)(trz')](+) and [AuCl(trz)] (trz, trz' = triazolylidene ligands with different wingtip groups). Carbene transfer occurs spontaneously, yet is markeldy rate-enhanced in the presence of Ag(+). The facile carbene transfer was exploited as a catalyst activation process to form active gold species for the aldol condensation of isocyanides and aldehydes to form oxazolines. The catalytic activity is strongly dependent on the presence of Ag(+) ions to initiate catalyst activation. High turnovers (10(5)) and turnover frequencies (10(4) h(-1)) were accomplished. Structural analysis at early stages of the reaction support the critical role of triazolylidene dissociation to activate the precatalyst and dynamic light scattering revealed the presence of nanoparticles (100 nm diameter) as potential catalytically active species. Furthermore, the triazolylidene scaffold had no impact on the diastereoselectivity of the oxazoline formation, and chiral triazolylidenes did not induce any asymmetry in the product. The facile dissociation of carbenes from [AuCl(carbene)] in the presence of Ag(+) ions suggests a less stable Au-Ccarbene interaction than often assumed, with potential implications for gold-catalyzed reactions that employ a silver salt as (putative) halide scavenger. PMID:23902160

  12. 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

  13. 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

  14. Hammett analysis of a family of carbene-carbene complex equilibria.

    PubMed

    Wang, Lei; Moss, Robert A; Thompson, Jack; Krogh-Jespersen, Karsten

    2011-03-01

    p-X-substituted phenylchlorocarbenes (X = NO(2), CF(3), Cl, H, Me, and MeO) form ?-type complexes with trimethoxybenzene in pentane. The carbenes and complexes are in equilibrium, and logarithms of the measured equilibrium constants are well correlated by Hammett ?(p) constants with ? = 2.48. The carbene complexes are characterized by UV-vis spectroscopy, and computational analysis is afforded by DFT calculations. PMID:21309524

  15. 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.

  16. Carbene based photochemical molecular assemblies for solar driven hydrogen generation.

    PubMed

    Peuntinger, Katrin; Pilz, T David; Staehle, Robert; Schaub, Markus; Kaufhold, Simon; Petermann, Lydia; Wunderlin, Markus; Grls, Helmar; Heinemann, Frank W; Li, Jing; Drewello, Thomas; Vos, Johannes G; Guldi, Dirk M; Rau, Sven

    2014-09-28

    Novel photocatalysts based on ruthenium complexes with NHC (N-heterocyclic carbene)-type bridging ligands have been prepared and structurally and photophysically characterised. The identity of the NHC-unit of the bridging ligand was established unambiguously by means of X-ray structural analysis of a heterodinuclear ruthenium-silver complex. The photophysical data indicate ultrafast intersystem crossing into an emissive and a non-emissive triplet excited state after excitation of the ruthenium centre. Exceptionally high luminescence quantum yields of up to 39% and long lifetimes of up to 2 ?s are some of the triplet excited state characteristics. Preliminary studies into the visible light driven photocatalytic hydrogen formation show no induction phase and constant turnover frequencies that are independent on the concentration of the photocatalyst. In conclusion this supports the notion of a stable assembly under photocatalytic conditions. PMID:25100041

  17. A simple route to phosphamethine cyanines from S,N-heterocyclic carbenes.

    PubMed

    Binder, Justin F; Corrente, Andrea M; Macdonald, Charles L B

    2016-02-01

    Although salts of thiazolium cations are known, many readily prepared iodide salts have eluded spectroscopic and structural characterization; herein, data for a variety of such salts are reported. It has been demonstrated that thiazolium cations can be deprotonated to generate S,N-heterocyclic carbenes and their "electron rich olefin" dimers, but use of the former has been largely overshadowed by that of the more common N-heterocyclic carbenes. We report herein that the deprotonation of thiazolium iodides and their subsequent reaction with a conveniently prepared triphosphenium precursor grants phosphamethine cyanine cations with solid-state geometry and electronic structure unlike those of NHC-stabilized cations. Protection of the phosphorus atom in such ions with elemental sulfur provides an air- and moisture-stable dithiophosphinium salt. PMID:26536127

  18. 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.

  19. 3-Trimethylsilylcycloalkylidenes. ?-Silyl vs ?-Hydrogen Migration to Carbene Centers.

    PubMed

    Creary, Xavier

    2015-11-20

    A series of ?-trimethylsilyl-substituted carbenes have been studied experimentally and by computational methods. In an acyclic system, 1,3-trimethylsilyl migration successfully competes with 1,3-hydrogen migration to the carbene center. The behavior of cyclic 3-trimethylsilyl-substituted carbenes contrasts with that of the acyclic system. Only 1,2-hydrogen migration processes are observed in the five-membered ring due to the high barrier to 1,3-hydrogen migration. In the cyclohexyl system, a small amount of a cyclopropane derived from 1,3-hydrogen migration occurs, as shown by a labeling study. In the cycloheptyl carbene system, a labeling study again showed that 1,3-hydrogen migration to the carbene center leads to the major product. Computational studies suggest that the cyclic carbenes all have lower energy conformations where the trimethylsilyl group is in a pseudo equatorial conformation where it cannot migrate to the carbene center. Computational studies also suggest that cyclohexyl and cycloheptyl carbene systems are slightly stabilized by a rear lobe interaction of the Si-C bond with the carbene center. PMID:26501592

  20. Protonation of Homoenolate Equivalents Generated by N-Heterocyclic Carbenes

    PubMed Central

    Maki, Brooks E.; Chan, Audrey; Scheidt, Karl A.

    2010-01-01

    Homoenolate equivalents are generated by Lewis basic N-heterocyclic carbene catalysts and then protonated to generate efficiently saturated esters from unsaturated aldehydes. This reactivity is extended to the generation of ?-acylvinyl anions from alkynyl aldehydes. The asymmetric protonation of a homoenolate equivalent generated from a ?,?-disubstituted aldehyde can be accomplished with a chiral N-heterocyclic carbene. PMID:22347730

  1. Chemoselective Carbene insertion into the N-H Bond over O-H Bond Using a Well-Defined Single Site (P-P)Cu(I) Catalyst.

    PubMed

    Ramakrishna, Kankanala; Murali, Mani; Sivasankar, Chinnappan

    2015-08-01

    Phosphine-coordinated air-stable Cu(I) catalyst (1) has been synthesized and characterized. Catalyst 1 is found to be active toward highly chemoselective carbene insertion into the N-H bond over the O-H bond and also over the formation of olefins when numerous aminophenols were treated with a variety of ?-aryl diazoesters under normal experimental conditions. PMID:26218454

  2. DFT studies of biarylcarbenes and the carbene-biradical continuum.

    PubMed

    Trindle, Carl

    2003-12-12

    We use electronic structure modeling, mainly density functional methods, to characterize a variety of long-lived bisaryl triplet carbenes. The bisaryl systems have a triplet ground state, favored by a substantial delocalization of the spin into the aromatic rings. One can imagine two extreme cases of the bonding in these species, representable as valence isomers. In the first case, spin delocalization is minor and incidental; the spin is predominantly located on the central carbene carbon. In the second case, spins are separated by large distances and are found primarily on the aromatic rings; the rings are linked by an allenic bridge. The bisphenyl carbenes tend toward the first limit. They can be kinetically stabilized by ortho substituents which shield the reactive center and para substituents which protect that site which has substantial spin density. The bond angle at carbene is opened from about 142 degrees (the B3LYP/6-31G value for the parent bis(phenyl)carbene) to 160 degrees or more by these substituents. Bisanthryl carbenes illustrate the second extreme, favoring a D(2)(d)() structure and possessing a low-lying open shell singlet state. A hypothetical phenyl-9-anthrylcarbine lies between the carbine and diradical extemes. The same principle which guides the design of stabilized diphenylcarbene carbenes and substitution of reactive sites by bulky protective groups serves to stabilize the bis-9-anthrylcarbene biradical. PMID:14656093

  3. 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

  4. Latent rutheniumindenylidene catalysts bearing a N-heterocyclic carbene and a bidentate picolinate ligand

    PubMed Central

    Schmid, Thibault E; Modicom, Florian; Dumas, Adrien; Borr, 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 Brnsted acid. The versatility of the catalyst 4a was subsequently demonstrated in RCM, cross-metathesis (CM) and enyne metathesis reactions. PMID:26425213

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

    PubMed

    Schmid, Thibault E; Modicom, Florian; Dumas, Adrien; Borr, Etienne; Toupet, Loic; Basl, 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 Brnsted acid. The versatility of the catalyst 4a was subsequently demonstrated in RCM, cross-metathesis (CM) and enyne metathesis reactions. PMID:26425213

  6. Au(III)- versus Au(I)-induced cyclization: synthesis of 6-membered mesoionic carbene and acyclic (aryl)(heteroaryl) carbene complexes**

    PubMed Central

    Ung, Gal; Soleilhavoup, Michele

    2013-01-01

    The Golden State: Selective 5-exo- and 6-endo-cyclizations of an alkynyl benzothioamide are achieved. The selectivity is controlled by the oxidation state of the gold precursor (+I or +III) yielding two new types of carbene ligand: an (aryl)(heteroaryl)carbene and a 6-membered mesoionic carbene. PMID:23169762

  7. An ab initio investigation of fluorobromo carbene.

    PubMed

    Sun, Erping; Li, Rui; Sun, Qixiang; Wei, Changli; Xu, Haifeng; Yan, Bing

    2012-10-25

    Fluorobromo carbene, an important halogenated carbene in the stratospheric ozone depletion, has long been received considerable interest. However, the energy, structure, and dynamics of even the lowest excited states have not been well understood. In this paper, we performed a detail ab initio study on CFBr using complete active space second-order perturbation (CASPT2) and multireference configuration interaction (MRCI) method. We investigated the effect of basis set on the CASPT2 results of the ground X(1)A' state and the first excited singlet A(1)A" state. The potential energy surface (PES) of the A(1)A" state along C-Br bond distance was carefully examined at CASPT2/cc-pV5Z level, by optimizing C-F bond and F-C-Br angle at every C-Br bond length in contrast to fix them at the equilibrium values. On the basis of the PES, a reliable barrier height of the A(1)A" state was obtained from CASPT2 and MRCI+Q calculations with different basis sets, considering the scalar relativistic effect, spin-orbit coupling, and core-valence correlation. Finally, we carried out the first theoretical study on higher excited state with energy up to 7 eV. The present calculated results were compared with previous experimental and theoretical results where available. Our results will add some understanding and shed more light on the structure and dynamics of electronic states of CFBr radical. PMID:23004933

  8. Annulated boron substituted N-heterocyclic carbenes: theoretical prediction of highly electrophilic carbenes.

    PubMed

    Bharadwaz, Priyam; Borthakur, Bitupon; Phukan, Ashwini K

    2015-11-14

    Theoretical calculations were carried out to understand the effect of annulation on the electronic and ligand properties of boron substituted N-heterocyclic carbenes (B-NHCs). Annulation results in a decrease in stability as indicated by the calculated values of singlet-triplet separations and stabilization energies as well as HOMO-LUMO gaps. Annulated B-NHCs are found to be weaker σ-donors but better π-acceptors than the parent ones. The decrease in σ-donation ability and the increase in π-accepting ability are further supported by the calculated values of proton affinities, nucleophilicity and electrophilicity indices as well as (31)P NMR chemical shifts of the corresponding NHC-PPh adducts. Most of the annulated B-NHCs are found to have significantly enhanced electrophilicity than the other known carbenes. PMID:26455836

  9. Enantioselective N-heterocyclic carbene-catalyzed synthesis of indenopyrones.

    PubMed

    Chen, Kun-Quan; Zhang, Han-Ming; Wang, Dong-Ling; Sun, De-Qun; Ye, Song

    2015-06-28

    The chiral N-heterocyclic carbene-catalyzed [4 + 2] cyclization of α-chloroaldehydes and arylidene indanediones was developed, giving the corresponding indenopyrones in good yields with high diastereoselectivities and enantioselectivities. PMID:26006112

  10. 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

  11. Light and Temperature Control of the Spin State of Bis(p-methoxyphenyl)carbene: A Magnetically Bistable Carbene.

    PubMed

    Costa, Paolo; Lohmiller, Thomas; Trosien, Iris; Savitsky, Anton; Lubitz, Wolfgang; Fernandez-Oliva, Miguel; Sanchez-Garcia, Elsa; Sander, Wolfram

    2016-02-10

    Bis(p-methoxyphenyl)carbene is the first carbene that at cryogenic temperatures can be isolated in both its lowest energy singlet and triplet states. At 3 K, both states coexist indefinitely under these conditions. The carbene is investigated in argon matrices by IR, UV-vis, and X-band EPR spectroscopy and in MTHF glasses by W-band EPR and Q-band ENDOR spectroscopy. UV (365 nm) irradiation of the system results in formation of predominantly the triplet carbene, whereas visible (450 nm) light shifts the photostationary equilibrium toward the singlet state. Upon annealing at higher temperatures (>10 K), the triplet is converted to the singlet; however, cooling back to 3 K does not restore the triplet. Therefore, depending on matrix temperature and irradiation conditions, matrices containing predominantly the triplet or singlet carbene can be generated. Controlling the magnetic and chemical properties of carbenes by using light of different wavelengths might be of general interest for applications such as information storage and radical-initiated polymerization processes. PMID:26771052

  12. Rhodium-mediated stereoselective polymerization of "carbenes".

    PubMed

    Hetterscheid, Dennis G H; Hendriksen, Coen; Dzik, Wojciech I; Smits, Jan M M; van Eck, Ernst R H; Rowan, Alan E; Busico, Vincenzo; Vacatello, Michele; Van Axel Castelli, Valeria; Segre, Annalaura; Jellema, Erica; Bloemberg, Tom G; de Bruin, Bas

    2006-08-01

    Unprecedented rhodium-catalyzed stereoselective polymerization of "carbenes" from ethyl diazoacetate (EDA) to give high molecular mass poly(ethyl 2-ylidene-acetate) is described. The mononuclear, neutral [(N,O-ligand)M(I)(cod)] (M = Rh, Ir) catalytic precursors for this reaction are characterized by (among others) single-crystal X-ray diffraction. These species mediate formation of a new type of polymers from EDA: carbon-chain polymers functionalized with a polar substituent at each carbon of the polymer backbone. The polymers are obtained as white powders with surprisingly sharp NMR resonances. Solution and solid state NMR data for these new polymers reveal a highly stereoregular polymer, with a high degree of crystallinity. The polymer is likely syndiotactic. Material properties are very different from those of atactic poly(diethyl fumarate) polymer obtained by radical polymerization of diethyl fumarate. Other diazoacetates are also polymerized. Further studies are underway to reveal possible applications of these new materials. PMID:16866530

  13. Cyclic (Amino)(aryl)carbenes (CAArCs) as Strong ?-Donating and ?-Accepting Ligands for Transition Metals.

    PubMed

    Rao, Bin; Tang, Huarong; Zeng, Xiaoming; Liu, Liu; Melaimi, Mohand; Bertrand, Guy

    2015-12-01

    Cyclic (amino)(aryl)carbenes (CAArCs) result from the replacement of the alkyl substituent of cyclic (alkyl)(amino) carbenes (CAACs) by an aryl group. This structural modification leads to enhanced electrophilicity of the carbene center with retention of the high nucleophilicity of CAACs, and therefore CAArCs feature a small singlet-triplet gap. The isoindolium precursors are readily prepared in good yields, and deprotonation at low temperature, in the presence of [RhCl(cod)]2 and [(Me2 S)AuCl] lead to air-stable rhodium and gold CAArC-supported complexes, respectively. The rhodium complexes promote the [3+2] cycloaddition of diphenylcyclopropenone with ethyl phenylpropiolate, and induce the addition of 2-vinylpyridine to alkenes by CH activation. The gold complexes allow for the catalytic three-component preparation of 1,2-dihydroquinolines from aniline and phenyl acetylene. These preliminary results illustrate the potential of CAArC ligands in transition-metal catalysis. PMID:26457345

  14. Two Equilibria of (N-Methyl-3-pyridinium)chlorocarbene, a Cationic Carbene.

    PubMed

    Cang, Hui; Moss, Robert A; Krogh-Jespersen, Karsten

    2016-02-11

    Equilibrium constants and the associated thermodynamic parameters are reported for the equilibria established between the cationic carbene (N-methyl-3-pyridinium)chlorocarbene tetrafluoroborate (MePyr(+)CCl BF4(-), 3) and 1,3,5-trimethoxybenzene (TMB) to form a carbene-TMB complex, as well as between carbene 3 and chloride ion to form the zwitterion, N-methyl-3-pyridinium dichloromethide (10). These equilibrium constants and thermodynamic parameters are contrasted with analogous data for several related carbenes, and the influence of the pyridinium unit in carbene 3 is thereby highlighted. Computational studies augment and elucidate the experimental results. PMID:26830199

  15. Palladium-Catalyzed Intermolecular Carbene Insertion Prior to Intramolecular Heck Cyclization: Synthesis of 2-Arylidene-3-aryl-1-indanones.

    PubMed

    Arunprasath, Dhanarajan; Muthupandi, Pandi; Sekar, Govindasamy

    2015-11-01

    A domino process that converges the migratory insertion of carbene with a Heck reaction has been established as a versatile tool for the synthesis of 2-arylidene-3-aryl-1-indanones from very stable and easily accessible N-tosylhydrazones and 2'-iodochalcones. The reaction selectively proceeds through 5-exo-trig cyclization and delivers the products selectively with the E configuration of the double bond in excellent yields. The one-pot synthesis of 2-arylidene-3-aryl-1-indanones involving in situ synthesis of both 2'-iodochalcones and N-tosylhydrazones has also been demonstrated. PMID:26501560

  16. 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…

  17. 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

  18. 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.

  19. Bis-N-heterocyclic Carbene Aminopincer Ligands Enable High Activity in Ru-Catalyzed Ester Hydrogenation.

    PubMed

    Filonenko, Georgy A; Aguila, Mae Joanne B; Schulpen, Erik N; van Putten, Robbert; Wiecko, Jelena; Mller, Christian; Lefort, Laurent; Hensen, Emiel J M; Pidko, Evgeny A

    2015-06-24

    Bis-N-heterocyclic carbene (NHC) aminopincer ligands were successfully applied for the first time in the catalytic hydrogenation of esters. We have isolated and characterized a well-defined catalyst precursor as a dimeric [Ru2(L)2Cl3]PF6 complex and studied its reactivity and catalytic performance. Remarkable initial activities up to 283,000 h(-1) were achieved in the hydrogenation of ethyl hexanoate at only 12.5 ppm Ru loading. A wide range of aliphatic and aromatic esters can be converted with this catalyst to corresponding alcohols in near quantitative yields. The described synthetic protocol makes use of air-stable reagents available in multigram quantities, rendering the bis-NHC ligands an attractive alternative to the conventional phosphine-based systems. PMID:26052835

  20. Superior Oxygen Stability of N-Heterocyclic Carbene-Coated Au Nanocrystals: Comparison with Dodecanethiol.

    PubMed

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

    2015-12-01

    The stability of Au nanocrystals (NCs) coated with different N-heterocyclic carbenes (NHCs) or dodecanethiol (DDT) to oxygen-based treatments was investigated. A dominant effect of the ligand type was observed with a significantly greater oxygen resistance of NHC-coated Au NCs compared to that of the thiol-based analogues. NHC-coated Au NCs are stable to 10 W oxygen plasma etching for up to 180 s whereas the integrity of DDT-coated Au NCs is strongly affected by the same treatment from 60-80 s. In the latter case, the average size of the NCs (from 2.6 to 6.3 nm) and the method of synthesis have no effect on the stability. NHC-coated Au NCs were found to generate of a smaller quantity of ligand-derived species under molecular oxygen treatment, which could account for the increased stability. PMID:26550843

  1. The First Crystal Structure of a Reactive Dirhodium Carbene Complex and a Versatile Method for the Preparation of Gold Carbenes by Rhodium-to-Gold Transmetalation.

    PubMed

    Werl, Christophe; Goddard, Richard; Frstner, Alois

    2015-12-14

    The dirhodium carbene derived from bis(4-methoxyphenyl)diazomethane and [Rh(tpa)4 ]?CH2 Cl2 (tpa=triphenylacetate) was characterized by UV, IR, and NMR spectroscopy, HRMS, as well as by X-ray diffraction. The isolated complex exhibits prototypical rhodium carbene reactivity in that it cyclopropanates 4-methoxystyrene at low temperature. Experimental structural information on this important type of reactive intermediate is extremely scarce and thus serves as a reference point for mechanistic discussions of rhodium catalysis in general. Moreover, dirhodium carbenes are shown to undergo remarkably facile carbene transfer on treatment with [LAuNTf2 ] (L=phosphine). This formal transmetalation opens a valuable new entry into gold carbene complexes that cannot easily be made otherwise; three fully characterized representatives illustrate this aspect. PMID:26534892

  2. 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 ?,?-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

  3. 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 ??bond and the significant ??back-bonding in the gold carbene moiety. PMID:26189567

  4. Pd(0)-Catalyzed Carbene Insertion into Si-Si and Sn-Sn Bonds.

    PubMed

    Liu, Zhenxing; Tan, Haocheng; Fu, Tianren; Xia, Ying; Qiu, Di; Zhang, Yan; Wang, Jianbo

    2015-10-14

    The first Pd(0)-catalyzed carbene insertion into Si-Si and Sn-Sn bonds has been realized by using N-tosylhydrazones as the carbene precursors. Geminal bis(silane) and geminal bis(stannane) derivatives were obtained in good to excellent yields under mild conditions. Migratory insertion of Pd carbene is supposed to be the key step for the reaction. PMID:26401829

  5. First direct observation of reactive carbenes in the cavities of cation-exchanged Y zeolites.

    PubMed

    Moya-Barrios, Reinaldo; Cozens, Frances L

    2004-03-18

    [reaction: see text] Herein we report the first direct observation of reactive carbenes within the cavities of cation-exchanged Y zeolites. Chloro(phenyl)- and bromo(phenyl)carbenes were generated upon laser photolysis of 3-halo-3-phenyldiazirines incorporated within dry zeolites and the absolute reactivity of the carbenes was investigated as a function of counterbalancing cation and coincorporated quenchers in order to elucidate the behavior of these intermediates within zeolites. Product analysis performed upon thermolysis of the diazirine in Y zeolites yielded products that were identified as those derived from the carbene. PMID:15012055

  6. Generation and reactivity of simple chloro(aryl)carbenes within the cavities of nonacidic zeolites.

    PubMed

    Moya-Barrios, Reinaldo; Cozens, Frances L

    2006-11-22

    A number of para-substituted chloro(aryl)carbenes are generated within the cavities of a series of dry alkali metal cation-exchanged zeolites (LiY, NaY, KY, RbY, and CsY) upon laser flash photolysis of the corresponding diazirine precursor. The absolute reactivity of the chloro(aryl)carbene is found to be strongly dependent on both the nature of the electron-donating and -withdrawing properties of the aryl substituent and the nature of the zeolite charge-balancing cations. The results strongly suggest that two opposing mechanisms for capture of the carbene can occur depending on whether the zeolite framework behaves as a nucleophilic reagent or an electrophilic reagent in its reaction with the carbene center. Hammett relationships for the decay of the carbene as a function of aryl substituent and zeolite counterion versus the sigma+ substituent parameter support a change in mechanism as the carbene center toggles between being electron poor and electron rich. For the electron-poor chloro(4-nitrophenyl)carbene, a framework adduct is proposed upon reaction of the nucleophilic [Si-O-Al]- bridge with the carbene center, and for the electron-rich chloro(4-methoxyphenyl)carbene, an adduct with the tight Li+ cation is proposed. PMID:17105293

  7. 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 Brnsted base-catalyzed conjugate addition allowed for an increase in yields. PMID:26413259

  8. Si-H activation by means of metal ligand cooperation in a methandiide derived carbene complex.

    PubMed

    Weismann, Julia; Gessner, Viktoria H

    2015-10-14

    Si-H bond activation of a number of silanes via metal ligand cooperation in a carbene complex is reported. Thereby, the electronic flexibility of the carbene ligand allows for the activation via a unique mechanism with oxidative addition to an 18e species without a formal change in the number of valence electrons. PMID:26304998

  9. Organometallic rhenium(III) chalcogenide clusters: coordination of N-heterocyclic carbenes.

    PubMed

    Durham, Jessica L; Wilson, Wade B; Huh, Daniel N; McDonald, Robert; Szczepura, Lisa F

    2015-07-01

    The preparation of rhenium based octahedral clusters containing N-heterocyclic carbenes is described. These represent the first examples of [M6(μ3-Q)8](n+) or [M6(μ3-X)8](n+) clusters to contain a carbene ligand of any type (NHC, Fischer or Schrock). Surprisingly, the NHC ligands attenuate their luminescent properties. PMID:26041404

  10. 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

  11. 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…

  12. Enhancement of N-heterocyclic carbenes on rhodium catalyzed olefination of triazoles.

    PubMed

    Zhao, Shixian; Wu, Feifei; Ma, Yuyu; Chen, Wanzhi; Liu, Miaochang; Wu, Huayue

    2016-02-16

    A few rhodium complexes of N-heterocyclic carbenes were prepared through carbene transfer reactions and their structures were characterized by X-ray diffraction analysis. The rhodium complexes of NHCs are found to be efficient catalysts for vinylation of various triazoles via C-H activation. A number of double vinylated triazoles can be obtained in good yields. PMID:26821787

  13. "Decarbonization" of an imino N-heterocyclic carbene via triple benzyl migration from tetrabenzylhafnium

    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...

  14. Synthesis, characterization, and reactivity of a uranium(VI) carbene imido oxo complex.

    PubMed

    Lu, Erli; Cooper, Oliver J; McMaster, Jonathan; Tuna, Floriana; McInnes, Eric J L; Lewis, William; Blake, Alexander J; Liddle, Stephen T

    2014-06-23

    We report the uranium(VI) carbene imido oxo complex [U(BIPM(TMS))(NMes)(O)(DMAP)2] (5, BIPM(TMS) = C(PPh2 NSiMe3)2; Mes = 2,4,6-Me3C6H2; DMAP = 4-(dimethylamino)pyridine) which exhibits the unprecedented arrangement of three formal multiply bonded ligands to one metal center where the coordinated heteroatoms derive from different element groups. This complex was prepared by incorporation of carbene, imido, and then oxo groups at the uranium center by salt elimination, protonolysis, and two-electron oxidation, respectively. The oxo and imido groups adopt axial positions in a T-shaped motif with respect to the carbene, which is consistent with an inverse trans-influence. Complex 5 reacts with tert-butylisocyanate at the imido rather than carbene group to afford the uranyl(VI) carbene complex [U(BIPM(TMS))(O)2(DMAP)2] (6). PMID:24842784

  15. Synthesis, Characterization, and Reactivity of a Uranium(VI) Carbene Imido Oxo Complex**

    PubMed Central

    Lu, Erli; Cooper, Oliver J; McMaster, Jonathan; Tuna, Floriana; McInnes, Eric J L; Lewis, William; Blake, Alexander J; Liddle, Stephen T

    2014-01-01

    We report the uranium(VI) carbene imido oxo complex [U(BIPMTMS)(NMes)(O)(DMAP)2] (5, BIPMTMS=C(PPh2NSiMe3)2; Mes=2,4,6-Me3C6H2; DMAP=4-(dimethylamino)pyridine) which exhibits the unprecedented arrangement of three formal multiply bonded ligands to one metal center where the coordinated heteroatoms derive from different element groups. This complex was prepared by incorporation of carbene, imido, and then oxo groups at the uranium center by salt elimination, protonolysis, and two-electron oxidation, respectively. The oxo and imido groups adopt axial positions in a T-shaped motif with respect to the carbene, which is consistent with an inverse trans-influence. Complex 5 reacts with tert-butylisocyanate at the imido rather than carbene group to afford the uranyl(VI) carbene complex [U(BIPMTMS)(O)2(DMAP)2] (6). PMID:24842784

  16. Stabilization of cyclic and acyclic carbon(0) compounds by differential coordination of heterocyclic carbenes: a theoretical assessment.

    PubMed

    Phukan, Ashwini K; Guha, Ankur Kanti

    2012-08-01

    Recently, donor stabilized divalent carbon(0) compounds have undergone intense experimental and theoretical investigation due to their strong electron rich character. In this Article, some new cyclic and acyclic carbon(0) compounds stabilized by differential coordination modes (such as abnormal, remote and a mixture of both) of N-heterocyclic carbenes are studied theoretically. The cyclic carbon(0) compounds proposed in this study are unusual in the sense that they contain a five membered ring consisting of only carbon atoms with a central carbon atom in the formal oxidation state of zero. All these compounds are found to be very strong nucleophiles which might have wide implications in catalysis. Calculation of first proton affinities of these molecules reveal that they are better ? donors than the carbon(0) compound supported by normal N-heterocyclic carbenes. Quantum chemical calculations indicate that these molecules possess very high donor-acceptor L ? C bond strengths and are thermodynamically stable. Calculation of the bond dissociation energies for the complexation of one and two molecules of AuCl indicates the possible isolation of their gem dimetalated derivatives. PMID:22717622

  17. Polymer-supported N-heterocyclic carbene-palladium complex for heterogeneous Suzuki cross-coupling reaction.

    PubMed

    Kim, Jong-Ho; Kim, Jung-Woo; Shokouhimehr, Mohammadreza; Lee, Yoon-Sik

    2005-08-19

    Poly(1-methylimidazoliummethyl styrene)-surface grafted-poly(styrene) resin was prepared for the first time as a polymer-supported N-heterocyclic carbene (NHC) precursor for palladium complex by suspension polymerization. To prepare this polymer-supported NHC precursor, 1-methyl-3-(4-vinylbenzyl)imidazolium hexafluorophosphate, [MVBIM][PF6-], was synthesized as a monomer and copolymerized with styrene and DVB in water. This polymer-supported NHC precursor with imidazolium as a ligand, which exists solely on the surface of the resin, was well characterized by FE-SEM, CLSM, and IR spectroscopy. The precursor containing imidazolium readily formed a stable complex with Pd(OAc)2, and this polymer-supported N-heterocyclic carbene-palladium complex exhibited excellent catalytic activity for Suzuki cross-coupling reaction in an aqueous medium. The catalyst was recovered quantitatively from the reaction mixture by simple filtration and was able to be reused for a number of recycles with consistent activity in all of the coupling reactions. PMID:16095291

  18. Methanol dehydrogenation by iridium N-heterocyclic carbene complexes.

    PubMed

    Campos, Jesús; Sharninghausen, Liam S; Manas, Michael G; Crabtree, Robert H

    2015-06-01

    A series of homogeneous iridium bis(N-heterocyclic carbene) catalysts are active for three transformations involving dehydrogenative methanol activation: acceptorless dehydrogenation, transfer hydrogenation, and amine monoalkylation. The acceptorless dehydrogenation reaction requires base, yielding formate and carbonate, as well as 2-3 equivalents of H2. Of the few homogeneous systems known for this reaction, our catalysts tolerate air and employ simple ligands. Transfer hydrogenation of ketones and imines from methanol is also possible. Finally, N-monomethylation of anilines occurs through a "borrowing hydrogen" reaction. Notably, this reaction is highly selective for the monomethylated product. PMID:25615426

  19. N-Heterocyclic carbene stabilized Ag-P nanoclusters.

    PubMed

    Khalili Najafabadi, Bahareh; Corrigan, John F

    2015-01-14

    The N-heterocyclic carbene (NHC) 1,3-di-isopropylbenzimidazole-2-ylidene ((i)Pr2-bimy) is found to be an excellent ligand for the stabilization of silver-phosphorus polynuclear complexes. The straightforward preparation and characterization of the clusters [Ag12(PSiMe3)6((i)Pr2-bimy)6] (1) and [Ag26P2(PSiMe3)10((i)Pr2-bimy)8] (2) are described, representing the first examples of such structurally characterized, higher nuclearity complexes obtained using this class of ligands. PMID:25415342

  20. Ruthenium-based complexes containing a benzimidazolium tag covalently connected to N-heterocyclic carbene ligands: environmentally friendly catalysts for olefin metathesis transformations.

    PubMed

    Klu?iar, Marek; Grela, Karol; Mauduit, Marc

    2013-05-28

    Two ruthenium-based pre-catalysts containing an ionic tag covalently connected to a N-heterocyclic carbene (NHC) ligand are reported. These novel complexes, bearing a polar benzimidazolium group, are air-stable and can be easily prepared from commercially available reagents. The quaternary benzimidazolium tag allows the efficient separation of ruthenium waste from the metathesis product after reaction. Application in several olefin metathesis transformations leads to desired products of high purity, which exhibit ruthenium contamination levels as low as 1 ppm after simple filtration through a pad of silica gel. PMID:23360984

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

    PubMed

    Hussong, Matthias W; Rominger, Frank; Krmer, 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

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

    PubMed

    Kelemen, Zsolt; Pter-Szab, Barbara; Szkely, Edit; Hollczki, Oldamur; Firaha, Dzmitry S; Kirchner, Barbara; Nagy, Jzsef; Nyulszi, Lszl

    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

  3. Stable heterocyclopentane-1,3-diyls.

    PubMed

    Hinz, Alexander; Schulz, Axel; Villinger, Alexander

    2015-02-23

    Diphosphadiazanediyl, [(?-NR)P]2 (R=Ter=2,6-dimesitylphenyl), is known to readily activate small molecules with multiple bonds. CO is an especially intriguing species for activation, because either 1,1- or 1,2-bridging mode would lead to a [1.1.1]bicycle or a carbene, respectively. The activation of CO with diphosphadiazanediyl already occurs at ambient temperatures (1?bar, 25?C). However, CO is involved in an unprecedented ring expansion reaction under preservation of the biradical character, which leads to the formation of the first stable cyclopentane-1,3-diyl analogue displaying photochromic molecular switch characteristics. PMID:25604347

  4. A Modular, Air-Stable Nickel Precatalyst

    PubMed Central

    Shields, Jason D.; Gray, Erin E.; Doyle, Abigail G.

    2016-01-01

    The synthesis and catalytic activity of [(TMEDA)Ni(otolyl) Cl], an air-stable, crystalline solid, is described. This complex is an effective precatalyst in a variety of nickel-catalyzed transformations. The lability of TMEDA allows a wide variety of ligands to be used, including mono- and bidentate phosphines, diimines, and N-heterocyclic carbenes. Preliminary mechanistic studies are also reported, which suggest that [(TMEDA)Ni(o-tolyl)Cl] can activate by either a NiB or NiNi transmetalation event, depending on the reaction conditions. PMID:25886092

  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. PMID:25938340

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

    PubMed

    Roy, Sudipta; Dittrich, Birger; Mondal, Totan; Koley, Debasis; Stckl, 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. PMID:25919008

  7. 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

  8. Protein Footprinting by Carbenes on a Fast Photochemical Oxidation of Proteins (FPOP) Platform

    NASA Astrophysics Data System (ADS)

    Zhang, Bojie; Rempel, Don L.; Gross, Michael L.

    2016-03-01

    Protein footprinting combined with mass spectrometry provides a method to study protein structures and interactions. To improve further current protein footprinting methods, we adapted the fast photochemical oxidation of proteins (FPOP) platform to utilize carbenes as the footprinting reagent. A Nd-YAG laser provides 355 nm laser for carbene generation in situ from photoleucine as the carbene precursor in a flow system with calmodulin as the test protein. Reversed-phase liquid chromatography coupled with mass spectrometry is appropriate to analyze the modifications produced in this footprinting. By comparing the modification extent of apo and holo calmodulin on the peptide level, we can resolve different structural domains of the protein. Carbene footprinting in a flow system is promising.

  9. Protein Footprinting by Carbenes on a Fast Photochemical Oxidation of Proteins (FPOP) Platform

    NASA Astrophysics Data System (ADS)

    Zhang, Bojie; Rempel, Don L.; Gross, Michael L.

    2015-12-01

    Protein footprinting combined with mass spectrometry provides a method to study protein structures and interactions. To improve further current protein footprinting methods, we adapted the fast photochemical oxidation of proteins (FPOP) platform to utilize carbenes as the footprinting reagent. A Nd-YAG laser provides 355 nm laser for carbene generation in situ from photoleucine as the carbene precursor in a flow system with calmodulin as the test protein. Reversed-phase liquid chromatography coupled with mass spectrometry is appropriate to analyze the modifications produced in this footprinting. By comparing the modification extent of apo and holo calmodulin on the peptide level, we can resolve different structural domains of the protein. Carbene footprinting in a flow system is promising.

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

    NASA Astrophysics Data System (ADS)

    Jansen van Rensburg, Armand; Landman, Maril; 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 AsPh3carbenecarbene substituents to each other, correlated with the experimental results.

  11. 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

  12. Protein Footprinting by Carbenes on a Fast Photochemical Oxidation of Proteins (FPOP) Platform.

    PubMed

    Zhang, Bojie; Rempel, Don L; Gross, Michael L

    2016-03-01

    Protein footprinting combined with mass spectrometry provides a method to study protein structures and interactions. To improve further current protein footprinting methods, we adapted the fast photochemical oxidation of proteins (FPOP) platform to utilize carbenes as the footprinting reagent. A Nd-YAG laser provides 355 nm laser for carbene generation in situ from photoleucine as the carbene precursor in a flow system with calmodulin as the test protein. Reversed-phase liquid chromatography coupled with mass spectrometry is appropriate to analyze the modifications produced in this footprinting. By comparing the modification extent of apo and holo calmodulin on the peptide level, we can resolve different structural domains of the protein. Carbene footprinting in a flow system is promising. Graphical Abstract ?. PMID:26679355

  13. 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)

  14. Design and Synthesis of C2-Symmetric N-Heterocyclic Carbene Precursors and Metal Carbenoids

    PubMed Central

    Albright, Abigail; Eddings, Daniel; Black, Regina; Welch, Christopher J.; Gerasimchuk, Nikolay N.; Gawley, Robert E.

    2011-01-01

    Chiral, C2-symmetric imidazolium and imidazolinium ions, as well as the corresponding copper or silver bound carbenoids, have been prepared. Structural study of these compounds by X-ray crystallography reveals a chiral pocket that surrounds the putative carbene site or the metal-carbene bond, at carbon 2, in three of the four ligands prepared. Preliminary investigation into the application of these complexes has shown one of them to be highly enantioselective in the hydrosilylation of acetophenone. PMID:21823580

  15. Sydnone anions and abnormal N-heterocyclic carbenes of O-ethylsydnones. Characterizations, calculations and catalyses.

    PubMed

    Wiechmann, Sascha; Freese, Tyll; Drafz, Martin H H; Hbner, Eike G; Namyslo, Jan C; Nieger, Martin; Schmidt, Andreas

    2014-10-14

    Deprotonated sydnones, which can be represented as anionic N-heterocyclic carbenes, were prepared as Li adducts and compared with deprotonated O-ethylsydnones (5-ethoxy-1,2,3-oxadiazol-4-ylidenes) which belong to the class of abnormal NHCs. The Pd complexes of the sydnone anions (X-ray analysis) as well as of the O-ethylsydnone carbenes proved to be efficient catalysts in aryl couplings of thiophenes. PMID:25156208

  16. N-heterocyclic carbene-main-group chemistry: a rapidly evolving field.

    PubMed

    Wang, Yuzhong; Robinson, Gregory H

    2014-11-17

    This Award Article targets the evolving, yet surprisingly fruitful, chemistry of N-heterocyclic carbenes with low-oxidation-state main-group elements. Specifically, the chemistry of carbene-stabilized diatomic allotropes, diborenes, gallium octahedra, beryllium borohydride, and a host of related compounds will be presented. Providing a valuable historical perspective, the foundational work concerning the organometallic chemistry of gallium with sterically demanding m-terphenyl ligands from this laboratory will also be discussed. PMID:25343222

  17. Quantitative description of structural effects on the stability of gold(I) carbenes.

    PubMed

    Ringger, David H; Kobylianskii, Ilia J; Serra, Daniel; Chen, Peter

    2014-10-27

    The gas-phase bond-dissociation energies of a SO2 -imidazolylidene leaving group of three gold(I) benzyl imidazolium sulfone complexes are reported (E0 =46.61.7, 49.61.7, and 48.92.1?kcal?mol(-1) ). Although these energies are similar to each other, they are reproducibly distinguishable. The energy-resolved collision-induced dissociation experiments of the three [L]-gold(I) (L=ligand) carbene precursor complexes were performed by using a modified tandem mass spectrometer. The measurements quantitatively describe the structural and electronic effects a p-methoxy substituent on the benzyl fragment, and trans [NHC] and [P] gold ligands, have towards gold carbene formation. Evidence for the formation of the electrophilic gold carbene in solution was obtained through the stoichiometric and catalytic cyclopropanation of olefins under thermal conditions. The observed cyclopropane yields are dependent on the rate of gold carbene formation, which in turn is influenced by the ligand and substituent. The donation of electron density to the carbene carbon by the p-methoxy benzyl substituent and [NHC] ligand stabilizes the gold carbene intermediate and lowers the dissociation barrier. Through the careful comparison of gas-phase and solution chemistry, the results suggest that even gas-phase leaving-group bond-dissociation energy differences of 2-3?kcal?mol(-1) enormously affect the rate of gold carbene formation in solution, especially when there are competing reactions. The thermal decay of the gold carbene precursor complex was observed to follow first-order kinetics, whereas cyclopropanation was found to follow pseudo-first-order kinetics. Density-functional-theory calculations at the M06-L and BP86-D3 levels of theory were used to confirm the observed gas-phase reactivity and model the measured bond-dissociation energies. PMID:25236486

  18. 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 Brnsted 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

  19. DFT prediction of multitopic N-heterocyclic carbenes using Clar's aromatic sextet theory.

    PubMed

    Suresh, Cherumuttathu H; Ajitha, Manjaly J

    2013-04-19

    Existence of several multitopic N-heterocyclic carbene (NHC) ligands with up to four carbene centers have been predicted on the basis of Clar's aromatic sextet theory. Assessment on stability and reactivity of NHCs was made by quantifying aromaticity, aromatic stabilization energy (E(aroma)), strength of carbene lone pair, proton affinity, and CuCl binding energy. On NICS(0) and HOMA scales of aromaticity, several NHCs showed high aromaticity, while E(aroma) (17.2-19.4 kcal/mol) indicated substantial stability for the N-heterocycle. Homodesmotic reactions suggested that heat of formation of most of the newly designed carbenes is very close to that of the existing bis-NHCs. Designing a multitopic ligand through branching via C(sp3) linkage was very effective as it improved the stability of the carbene. Electrostatic potential minimum (V(min)) at the carbene lone pair suggested that annelation of heterocycle to a benzenoid ring or branching through C(sp3) linkage can only marginally influence the electron donating power of the ligand. Hence, all multitopic NHCs showed proton affinity (252.3-267.4 kcal/mol) and CuCl binding energy (62.9-66.6 kcal/mol) very close to those of 1,3-dimethylimidazolidine-2-ylidene (1). It has also been demonstrated that branched multitopic 3-dimensional NHCs are attractive for designing metal-organic framework with narrow (1-1.5 nm) cage/pore size. PMID:23461408

  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[double bond, length as m-dash]O.

    PubMed

    Garca, 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

  1. Stabilization of fully reduced iron-sulfur clusters by carbene ligation: the [FenSn]0 oxidation levels (n = 4, 8).

    PubMed

    Deng, Liang; Holm, R H

    2008-07-30

    The all-ferrous [Fe4S4](0) state has been demonstrated in the fully reduced Fe protein of the Azotobacter vinelandii nitrogenase complex. We seek synthetic analogues of this state more tractable than the recently prepared but highly unstable cluster [Fe4S4(CN)4](4-) (Scott, Berlinguette, Holm, and Zhou, Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 9741). The N-heterocyclic carbene 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (Pr(i)2NHCMe2) has been found to stabilize the fully reduced clusters [Fe8S8(Pr(i)2NHCMe2)6] (4) and [Fe4S4(Pr(i)2NHCMe2)4] (5), which are prepared by cluster assembly or phosphine substitution of FenSn (n = 8, 16) clusters. Cluster 4 is also obtained by reaction of the carbene with all-ferrous [Fe7S6(PEt3)5Cl2] (3) and cluster 5 by carbene cleavage of 4. Detailed structures of 3 (monocapped prismatic), 4, and 5 are described; the latter two are the first iron-sulfur clusters with Fe-C sigma bonds. Cluster 4 possesses the [Fe8(mu3-S) 6(mu4-S)2] edge-bridged double cubane structure and 5 the cubane-type [Fe4(mu3-S)4] stereochemistry. The all-ferrous formulations of the clusters are confirmed by X-ray structure parameters and (57)Fe isomer shifts. Both clusters are stable under conventional aprotic anaerobic conditions, enabling further study of reactivity. The collective properties of 5 indicate that it is a meaningful synthetic analogue of the core of the fully reduced protein-bound cluster. PMID:18593124

  2. Effect of substituents at the heteroatom on the structure and ligating properties of heterocyclic carbene, silylene, germylene and abnormal carbene: a theoretical study.

    PubMed

    Guha, Ankur Kanti; Sarmah, Satyajit; Phukan, Ashwini K

    2010-08-21

    The effect of substituents at the heteroatom on the electronic structures of different N-heterocyclic carbenes (1, 2 and 3), silylene (4) and germylene (5) are examined using Density Functional Theory. The kinetic and thermodynamic stabilities of these molecules are assessed by examining the HOMO-LUMO gap and hydrogenation energies, respectively. The extent of cyclic electron delocalization present in these five-membered ring systems are quantified with the help of NICS calculations. The ligating properties of 1-5 and the recently synthesized free abnormal carbene 6 (Bertrand et al., Science, 2009, 326, 556-559) are examined by looking at the energies of the sigma symmetric electron-donating orbital of the respective molecules. Among the systems considered, 6 is found to have the strongest sigma-donating ability. A comparative study of the ligating properties between the two isomeric carbenes 1 and 6 is performed by calculating the carbonyl stretching frequencies of some iridium carbonyl complexes of these two tautomeric carbenes. PMID:20607170

  3. Synthesis and reactivity of triethylborane adduct of N-heterocyclic carbene: versatile synthons for synthesis of N-heterocyclic carbene complexes.

    PubMed

    Yamaguchi, Yoshitaka; Kashiwabara, Taigo; Ogata, Kenichi; Miura, Yumiko; Nakamura, Yoshiyuki; Kobayashi, Kimiko; Ito, Takashi

    2004-10-01

    The reaction of an imidazolium salt with LiBEt(3)H afforded triethylborane adduct of imidazol-2-ylidene, which can act as a carbene precursor for the synthesis of a transition metal complex as well as a main group element complex. PMID:15467851

  4. 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; Pthig, Alexander; Francesconi, Lynn C.; Herrmann, Wolfgang A.; Khn, 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

  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 Brnsted 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

  6. Imidazolium carboxylates as versatile and selective N-heterocyclic carbene transfer agents: synthesis, mechanism, and applications.

    PubMed

    Voutchkova, Adelina M; Feliz, Marta; Clot, Eric; Eisenstein, Odile; Crabtree, Robert H

    2007-10-24

    N,N'-Disubstituted imidazolium carboxylates, readily synthetically available, isolable, air- and water-stable reagents, efficiently transfer N-heterocyclic carbene (NHC) groups to Rh, Ir, Ru, Pt, and Pd, to give novel NHC complexes, e.g., [Pd(NHC)3OAc]OAc and [Pt(NHC)3Cl]Cl (NHC = 1,3-dimethyl imidazol-2-ylidene). The NHC esters are also effective. Tuning the reaction conditions for NHC transfer can give either mono- or bis-NHCs, or bis- and tris-NHCs. A net N to C rearrangement of the N-alkyl imidazole complex to the corresponding NHC complex was seen with (MeO)2CO (DMC). DFT calculations identify the steps needed to form the carboxylate from imidazole and DMC: SN2 methyl transfer from DMC to imidazole, followed by proton transfer from the imidazolium CH to the carboxylate counterion, produces the free NHC H-bonded to MeOH with a weakly associated CO2. The nucleophilic NHC attacks CO2 to form NHC-CO2. NHC transfer to the metal with loss of CO2 has been calculated for Rh(cod)Cl. A proposed two-cis-site reactivity model rationalizes the experimental data: two such vacant sites at the metal are needed to allow coordination of the NHC-CO2 carboxylate and subsequent CC cleavage with NHC transfer. Partial cod decoordination or chloride loss is thus required for Rh(cod)Cl. Chloride dissociation, calculated to be easier in polar solvent, is confirmed experimentally from the retarding effect of excess chloride. PMID:17900114

  7. A continuum of progress: applications of N-hetereocyclic carbene catalysis in total synthesis.

    PubMed

    Izquierdo, Javier; Hutson, Gerri E; Cohen, Daniel T; Scheidt, Karl A

    2012-11-19

    N-Heterocyclic carbene (NHC) catalyzed transformations have emerged as powerful tactics for the construction of complex molecules. Since Stetter's report in 1975 of the total synthesis of cis-jasmon and dihydrojasmon by using carbene catalysis, the use of NHCs in total synthesis has grown rapidly, particularly over the last decade. This renaissance is undoubtedly due to the recent developments in NHC-catalyzed reactions, including new benzoin, Stetter, homoenolate, and aroylation processes. These transformations employ typical as well as Umpolung types of bond disconnections and have served as the key step in several new total syntheses. This Minireview highlights these reports and captures the excitement and emerging synthetic utility of carbene catalysis in total synthesis. PMID:23074146

  8. A Non-Diazo Approach to ?-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, ?-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as CH 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 ?-oxo gold carbenes if both nucleophile and electrophile are oxygen. Hence, this approach would enable readily available and safer alkynes to replace hazardous ?-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 ?-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 ?-oxo gold carbene intermediates. The intermolecular approach offers excellent synthetic flexibility because no tethering of the oxidant is required, and its reduced form is not tangled with the product. We were the first research group to develop this strategy, through the use of pyridine/quinolone N-oxides as the external oxidants. In this manner, we can effectively make a CC triple bond a surrogate of an ?-diazo carbonyl moiety in various gold catalyses. With terminal alkynes, we demonstrated that we can efficiently trap exclusively formed terminal carbene centers by internal nucleophiles en route to the formation of cyclic products, including strained oxetan-3-ones and azetidin-3-ones, and by external nucleophiles when a P,N-bidentate ligand is coordinated to gold. With internal alkynes, we generated synthetically useful regioselectivities in the generation of the ?-oxo gold carbene moiety, which enables expedient formation of versatile enone products. Other research groups have also applied this strategy en route to versatile synthetic methods. The ?-oxo gold carbenes appear to be more electrophilic than their Rh counterpart, which many chemists have focused on in a large array of excellent work on metal carbene chemistry. The ease of accessing the reactive gold carbenes opens up a vast area for developing new synthetic methods that would be distinctively different from the known Rh chemistry and promises to generate a new round of gold rush. PMID:24428596

  9. Insertion of Cyclic Alkyl(amino) Carbene into the Si-H Bonds of Hydrochlorosilanes.

    PubMed

    Mohapatra, Chandrajeet; Samuel, Prinson P; Li, Bin; Nieptter, Benedikt; Schrmann, Christian J; Herbst-Irmer, Regine; Stalke, Dietmar; Maity, Bholanath; Koley, Debasis; Roesky, Herbert W

    2016-03-01

    Carbenes are known for their ability to abstract HCl from hydrochlorosilanes to form carbene hydrochloride adducts. In contrast, the Si-H bond insertion products RSiCl2(cAACH) (2, 4, 6, and 8) have been formed in the reaction of RSiHCl2 [R = Ar(SiMe3)N (1), Cp* (3), PhC(NtBu)2 (5), Cl (7); Ar = 2,6-iPr2C6H3] with a cyclic alkyl(amino) carbene (cAAC:) irrespective of the steric demand of the R group. The new products have been characterized by various analytical tools including X-ray crystallography, electron ionization mass spectrometry, and NMR spectroscopy. Theoretical investigations have also been performed to understand why cAAC prefers insertion into the Si-H bond rather than the dehydrohalogenation pathway. PMID:26859316

  10. A Continuum of Progress: Applications of N-Hetereocyclic Carbene Catalysis in Total Synthesis

    PubMed Central

    Izquierdo, Javier; Hutson, Gerri E.; Cohen, Daniel T.; Scheidt, Karl A.

    2013-01-01

    N-Heterocyclic carbene (NHC) catalyzed transformations have emerged as powerful tactics for the construction of complex molecules. Since Stetters report in 1975 of the total synthesis of cis-jasmon and dihydrojasmon by using carbene catalysis, the use of NHCs in total synthesis has grown rapidly, particularly over the last decade. This renaissance is undoubtedly due to the recent developments in NHC-catalyzed reactions, including new benzoin, Stetter, homoenolate, and aroylation processes. These transformations employ typical as well as Umpolung types of bond disconnections and have served as the key step in several new total syntheses. This Minireview highlights these reports and captures the excitement and emerging synthetic utility of carbene catalysis in total synthesis. PMID:23074146

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

    PubMed

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

    2015-12-22

    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. 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.

  13. {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.

  14. Zwitterionic borane adducts of N-heterocyclic carbenes from mesomeric betaines of uracil.

    PubMed

    Zhang, Jiaxi; Pidlypnyi, Nazar; Nieger, Martin; Namyslo, Jan C; Schmidt, Andreas

    2014-05-01

    We prepared a series of imidazolium-substituted uracil-anions which are members of the class of cross-conjugated heterocyclic mesomeric betaines. They are in tautomeric equilibrium with their N-heterocyclic carbenes, uracil-6-yl-imidazol-2-ylidenes. These carbenes can be trapped by reaction with sulfur, selenium, as well as by triethylborane and triphenylborane, respectively. The latter trapping reaction yielded the first representatives of a new heterocyclic zwitterionic ring system, imidazo[2',1':3,4][1,4,2]diazaborolo[1,5-c]pyrimidinium-10-ide. Results of two single crystal X-ray structure analyses are presented. PMID:24658502

  15. Highly selective palladiumbenzothiazole carbene-catalyzed allylation of active methylene compounds under neutral conditions

    PubMed Central

    Cotugno, Pietro; Zambonin, Carlo Giorgio; Ciminale, Francesco

    2015-01-01

    Summary The Pdbenzothiazol-2-ylidene complex I was found to be a chemoselective catalyst for the TsujiTrost allylation of active methylene compounds carried out under neutral conditions and using carbonates as allylating agents. The proposed protocol consists in a simplified procedure adopting an in situ prepared catalyst from Pd2dba3 and 3-methylbenzothiazolium salt V as precursors. A comparison of the performance of benzothiazole carbene with phosphanes and an analogous imidazolium carbene ligand is also proposed. PMID:26199653

  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. 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.

  18. Late-Stage Diversification of Chiral N-Heterocyclic-Carbene Precatalysts for Enantioselective Homoenolate Additions

    PubMed Central

    Zheng, Pinguan; Gondo, Chenaimwoyo A.

    2011-01-01

    A library of chiral triazolium salts has been prepared by late-state diversification of a triazolium amine salt. By utilizing a primary amine as a functional handle, a single triazolium salt can be transformed into a variety of chiral N-heterocyclic carbene precatalysts. This approach makes the preparation of chiral N-heterocyclic carbenes possible by a single-step modification of a triazolium salt, rather than the usual need for multistep organic synthesis and challenging heterocycle formation for each member of a catalyst library. We have screened these catalysts for control of diastereo- and enantioselectivity in a ?-lactam-forming reaction between ?,?-unsaturated aldehydes and cyclic ketimines. PMID:21254434

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

    PubMed

    Gmez, Gabriela Elena; Monti, Jos Luis E; Mundo, Mariana Roco; Delfino, Jos Mara

    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

  20. Carbene insertion into a P-H bond: parent phosphinidene-carbene adducts from PH3 and bis(phosphinidene)mercury complexes.

    PubMed

    Bispinghoff, Mark; Tondreau, Aaron M; Grützmacher, Hansjörg; Faradji, Charly A; Pringle, Paul G

    2016-04-14

    PH3 reacts with the in situ generated N-heterocyclic carbene DippNHC* (DippNHC* = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) to give the phosphanyl-imidazolidine [(Dipp)NHC*-H]-[PH2]. Upon treatment with an ortho-quinone, [(Dipp)NHC*-H]-[PH2] is dehydrogenated to give the parent phosphinidene-carbene adduct (Dipp)NHC*[double bond, length as m-dash]PH. Alternative routes to [(Dipp)NHC*-H]-[PH2] and (Dipp)NHC*[double bond, length as m-dash]PH employ NaPH2 and (TMS)3P7 (TMS = trimethylsilyl), respectively, as phosphorus sources. The adduct (Dipp)NHC*[double bond, length as m-dash]PH and the related adduct (Dipp)NHC[double bond, length as m-dash]PH ((Dipp)NHC = bis(2,6-diisopropylphenyl)imidazol-2-ylidene) possessing an unsaturated NHC backbone both react with HgCl2 to give the bis(carbene-phosphinidenyl) complexes [((Dipp)NHC*[double bond, length as m-dash]P)2Hg] and [((Dipp)NHC[double bond, length as m-dash]P)2Hg]. PMID:26122315

  1. Extremely efficient hydroboration of ketones and aldehydes by copper carbene catalysis.

    PubMed

    Bagherzadeh, Sharareh; Mankad, Neal P

    2016-03-01

    A readily available copper carbene complex, (IPr)CuOtBu, catalyses the hydroboration of ketones and aldehydes even at very low catalyst loadings (0.1 mol%), in some cases with turnover frequencies exceeding 6000 h(-1). Carbonyl reduction occurs selectivitily in the presence of other reducible functional groups including alkenes, nitriles, esters, and alkyl chlorides. PMID:26871503

  2. Divergent Reactivity of Rhodium(I) Carbenes Derived from Indole Annulations.

    PubMed

    Li, Xiaoxun; Li, Hui; Song, Wangze; Tseng, Po-Sen; Liu, Lingyan; Guzei, Ilia A; Tang, Weiping

    2015-10-26

    Rhodium(I) carbenes were generated from propargylic alcohol derivatives as the result of a dehydrative indole annulation. Depending on the choice of the electron-withdrawing group on the aniline nitrogen nucleophile, either a cyclopropanation product or dimerization product was obtained chemoselectively. Intramolecular hydroamidation occurred for the same type of propargylic alcohol derivatives when other transition-metal catalysts were employed. PMID:26480329

  3. Pericyclic rearrangements of N-heterocyclic carbenes of indazole to substituted 9-aminoacridines.

    PubMed

    Guan, Zong; Wiechmann, Sascha; Drafz, Martin; Hbner, Eike; Schmidt, Andreas

    2013-06-01

    On deprotonation, 1-arylindazolium salts form 1-arylindazol-3-ylidenes which rearrange spontaneously via ring cleavage, ring closure and subsequent proton transfer to substituted 9-aminoacridines. By contrast, the N-heterocyclic carbene of 2-phenylindazolium cannot rearrange similarly and was trapped by sulfur. PMID:23613125

  4. N-Heterocyclic carbenes as supporting ligands in transition metal complexes of N2.

    PubMed

    Ohki, Yasuhiro; Seino, Hidetake

    2016-01-01

    Recent developments have substantially expanded the scope of N-heterocyclic carbenes (NHCs) as ancillary ligands in coordination chemistry and homogeneous catalysis. This review provides a short overview of the emerging field of NHC-supported transition metal complexes of N2 and the possibilities to catalytically activate N2 in these complexes. PMID:26646731

  5. Hydrogenations at room temperature and atmospheric pressure with mesoionic carbene-stabilized borenium catalysts.

    PubMed

    Eisenberger, Patrick; Bestvater, Brian P; Keske, Eric C; Crudden, Cathleen M

    2015-02-16

    1,2,3-Triazolylidene-based mesoionic carbene boranes have been synthesized in a convenient one-pot protocol from the corresponding 1,2,3-triazolium salts, base, and borane. Borenium ions are obtained by hydride abstraction and serve as catalysts in mild hydrogenation reactions of imines and unsaturated N-heterocycles at ambient pressure and temperature. PMID:25586407

  6. ?-Fluoroallenoate Synthesis via N-Heterocyclic Carbene-Catalyzed Fluorination Reaction of Alkynals.

    PubMed

    Wang, Xu; Wu, Zijun; Wang, Jian

    2016-02-01

    The first catalytic ?-fluoroallenoate synthesis is described. With a suitable combination of N-heterocyclic carbene precatalyst, base, and fluorine reagent, the reaction proceeded smoothly to yield a wide range of ?-fluoroallenoates with excellent chemoselectivity. These substituted ?-fluorinated allenoates have been synthesized for the first time, and they are versatile synthetic intermediates toward other useful fluorine-containing building blocks. PMID:26771540

  7. Nitrogen heterocyclic carbene containing pentacoordinate iron dicarbonyl as a [Fe]-hydrogenase active site model.

    PubMed

    Jiang, Shuang; Zhang, Tianyong; Zhang, Xia; Zhang, Guanghui; Li, Bin

    2015-10-14

    A novel pentacoordinate mono iron dicarbonyl complex bearing a nitrogen heterocyclic carbene ligand was reported as a model of a [Fe]-hydrogenase active site, which exhibits interesting proton coupled CO binding reactivity, electro-catalytic proton reduction and catalytic transfer hydrogenation reactivity. PMID:26369379

  8. 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

  9. 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

  10. 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. PMID:25476754

  11. Mesoionic Carbene-Gold(I) Catalyzed Bis-Hydrohydrazination of Alkynes with Parent Hydrazine.

    PubMed

    Tolentino, Daniel R; Jin, Liqun; Melaimi, Mohand; Bertrand, Guy

    2015-10-01

    A novel synthetic route gives access to mesoionic carbene and cyclopropenylidene supported gold chloride complexes. The corresponding cationic MIC-gold complex obtained by chloride abstraction allows for the first transition metal-catalyzed functionalization of both nitrogens of parent hydrazine. PMID:25597889

  12. 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 ? 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 ? degeneracy for the oxides. The relevance of the present results for the epoxidation and the olefin metathesis reactions are discussed.

  13. Intramolecular Transannulation of Alkynyl Triazoles via Alkyne-Carbene Metathesis Step: Access to Fused Pyrroles

    PubMed Central

    Shi, Yi; Gevorgyan, Vladimir

    2013-01-01

    An intramolecular Rh-catalyzed transannulation reaction of alkynyl triazoles has been developed. This method allows efficient construction of various 5,5-fused pyrroles, including tetrahydropyrrolo and spiro systems. The method demonstrates excellent functional group compatibility. A rhodium carbene-alkyne metathesis mechanism is proposed for this transformation. PMID:24093728

  14. Intramolecular transannulation of alkynyl triazoles via alkyne-carbene metathesis step: access to fused pyrroles.

    PubMed

    Shi, Yi; Gevorgyan, Vladimir

    2013-10-18

    An intramolecular Rh-catalyzed transannulation reaction of alkynyl triazoles has been developed. This method allows efficient construction of various 5,5-fused pyrroles, including tetrahydropyrrolo and spiro systems. The method demonstrates excellent functional group compatibility. A rhodium carbene-alkyne metathesis mechanism is proposed for this transformation. PMID:24093728

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

    PubMed Central

    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.

    2009-01-01

    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

  16. Carbene-anchored/pendent-imidazolium species as precursors to di-N-heterocyclic carbene-bridged mixed-metal complexes.

    PubMed

    Zamora, Matthew T; Ferguson, Michael J; McDonald, Robert; Cowie, Martin

    2009-09-21

    Reaction of a series of linked diimidazolium dibromide salts with one-half equivalent of [Rh(mu-OAc)(COD)](2) under reflux conditions generates a series of carbene-anchored/pendent-imidazolium complexes, [RhBr(COD)((R)C(H)-eta(1)-C(eth))][Br] ((Me)C(H)-eta(1)-C(eth) = ethylene[(N-methyl)imidazolium][(N-methyl)imidazole-2-ylidene] and (tBu)C(H)-eta(1)-C(eth) = ethylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imidazole-2-ylidene]) via deprotonation of one end of the diimidazolium salt and coordination of the resulting carbene to Rh. Reaction of these complexes with carbon monoxide or the appropriate diphosphine yields either [RhBr(CO)(2)((R)C(H)-eta(1)-C(eth))][Br] (R = Me, (t)Bu) or [RhBr(P( intersection)P)((Me)C(H)-eta(1)-C(eth))][Br] (P( intersection)P = Ph(2)PCH(2)PPh(2), Ph(2)PCH(2)CH(2)PPh(2), Et(2)PCH(2)PEt(2)), respectively. The resulting diphosphine complexes readily decompose in solution. A series of palladium complexes [PdI(3-n)(PR(3))(n)(L)][I](n) (n = 1,2) and [PdI(P( intersection)P)(L)][I](2) (L = (tBu)C(H)-eta(1)-C(meth), (tBu)C(H)-eta(1)-C(eth); (tBu)C(H)-eta(1)-C(meth) = methylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imidazole-2-ylidene]), containing the linked NHC-imidazolium moiety, have also been prepared by reacting the triiodo complexes, [PdI(3)((tBu)C(H)-eta(1)-C(meth))] and [PdI(3)((tBu)C(H)-eta(1)-C(eth))] with several mono- and diphosphines. Attempts to generate mixed Rh/Pd complexes using Pd(OAc)(2) to deprotonate the pendent arm of several of the above carbene-anchored/pendent-imidazolium complexes of Rh have proven unsuccessful. However, a targeted di-NHC-bridged heterobimetallic complex [PdI(2)(PEt(3))(mu-(tBu)CC(meth))RhI(COD)] ((tBu) CC(meth) = 1,1'-methylene-3,3'-di-tert-butyldiimidazol-2,2'-diylidene) can be generated by deprotonation of the imidazolium group in [PdI(2)(PEt(3))((tBu)C(H)-eta(1)-C(meth))][I] using half an equivalent of [Rh(mu-OAc)(COD)](2). The X-ray structure determination of this Pd/Rh complex confirms the dicarbene-bridged formulation and shows a metal-metal separation of approximately 6.2 A. Reaction of this Rh/Pd complex with CO yields the corresponding dicarbonyl product [PdI(2)(PEt(3))(mu-(tBu)CC(meth))RhI(CO)(2)] via replacement of the COD ligand. The related dicarbene-bridged Ir/Rh complex [IrBr(COD)(mu-(tBu)CC(meth))RhBr(COD)] can be generated by reaction of [IrBr(COD)((tBu)C(H)-eta(1)-C(meth) )][Br] with [Rh(mu-OAc)(COD)](2), while the Pd/Ir complexes [PdI(2)(PR(3))(mu-(tBu)CC(meth))IrI(COD)] (PR(3) = PPh(3), PMe(2)Ph) can be generated by reaction of the monometallic [PdI(2)(PR(3))((tBu)C(H)-eta(1)-C(meth))][I] species with K[N(SiMe(3))(2)] in the presence of [Ir(mu-Cl)(COD)](2). The carbonyl analogues, [PdI(2)(PR(3))(mu-(tBu)CC(meth))IrI(CO)(2)], can be generated via a gentle purge of CO gas. These di-NHC-bridged heterobimetallic species represent some of the first examples of this class and are the first involving palladium. PMID:20449172

  17. Rhodium(I) N-Heterocyclic Carbene Bioorganometallics as in Vitro Antiproliferative Agents with Distinct Effects on Cellular Signaling.

    PubMed

    Oehninger, Luciano; Spreckelmeyer, Sarah; Holenya, Pavlo; Meier, Samuel M; Can, Suzan; Alborzinia, Hamed; Schur, Julia; Keppler, Bernhard K; Wlfl, Stefan; Ott, Ingo

    2015-12-24

    Organometallics with N-heterocyclic carbene (NHC) ligands have triggered major interest in inorganic medicinal chemistry. Complexes of the type Rh(I)(NHC)(COD)X (where X is Cl or I, COD is cyclooctadiene, and NHC is a dimethylbenzimidazolylidene) represent a promising type of new metallodrugs that have been explored by advanced biomedical methods only recently. In this work, we have synthesized and characterized several complexes of this type. As observed by mass spectrometry, these complexes remained stable over at least 3 h in aqueous solution, after which hydrolysis of the halido ligands occurred and release of the NHC ligand was evident. Effects against mitochondria and general cell tumor metabolism were noted at higher concentrations, whereas phosphorylation of HSP27, p38, ERK1/2, FAK, and p70S6K was induced substantially already at lower exposure levels. Regarding the antiproliferative activity in tumor cells, a clear preference for iodido over chlorido secondary ligands was noted, as well as effects of the substituents of the NHC ligand. PMID:26595649

  18. Formation of Ruthenium Carbenes by gem-Hydrogen Transfer to Internal Alkynes: Implications for Alkyne trans-Hydrogenation

    PubMed Central

    Leutzsch, Markus; Wolf, Larry M; Gupta, Puneet; Fuchs, Michael; Thiel, Walter; Fars, Christophe; Frstner, Alois

    2015-01-01

    Insights into the mechanism of the unusual trans-hydrogenation of internal alkynes catalyzed by {Cp*Ru} complexes were gained by para-hydrogen (p-H2) induced polarization (PHIP) transfer NMR spectroscopy. It was found that the productive trans-reduction competes with a pathway in which both H atoms of H2 are delivered to a single alkyne C atom of the substrate while the second alkyne C atom is converted into a metal carbene. This geminal hydrogenation mode seems unprecedented; it was independently confirmed by the isolation and structural characterization of a ruthenium carbene complex stabilized by secondary inter-ligand interactions. A detailed DFT study shows that the trans alkene and the carbene complex originate from a common metallacyclopropene intermediate. Furthermore, the computational analysis and the PHIP NMR data concur in that the metal carbene is the major gateway to olefin isomerization and over-reduction, which frequently interfere with regular alkyne trans-hydrogenation. PMID:26332643

  19. Synthesis and catalytic activity of gold chiral nitrogen acyclic carbenes and gold hydrogen bonded heterocyclic carbenes in cyclopropanation of vinyl arenes and in intramolecular hydroalkoxylation of allenes.

    PubMed

    Bartolom, Camino; Garca-Cuadrado, Domingo; Ramiro, Zoraida; Espinet, Pablo

    2010-11-01

    Mononuclear and dinuclear chiral gold(I) carbene complexes with carbene ligands of the type HBHC (hydrogen bonded heterocyclic carbenes) and NAC (nitrogen acyclic carbenes) have been prepared by reaction of isocyanide gold(I) complexes and chiral amines or diamines. The reaction of [AuCl(CNPy-2)] (1) (Py = pyridyl) with the corresponding chiral primary amines afforded the chiral HBHC complexes (R)-[AuCl{C(NH(CHMePh))(NHPy-2)}] ((R)-2), and (S)-[AuCl{C(NH{CHMe(1-naphthyl)})(NHPy-2)}] ((S)-3), while the reaction of 2 equiv of 1 with diamines produced (S)-2,2'-bis[NH{C(AuCl)(NHPy-2)}](2)-binaphthyl ((S)-4), (1R,2R)-1,2-bis[NH{C(AuCl)(NHPy-2)}]-diphenylethane ((1R,2R)-5), and (1R,2R)-1,2-bis[NH{C(AuCl)(NHPy-2)}]-cyclohexane ((1R,2R)-6). On the other hand the addition of alkyl amines to (S)-2,2'-[NCAuCl](2)-binaphthyl ((S)-8) gave the chiral NAC complexes (S)-2,2'-bis[NH{C(AuCl)(NMe(2))}](2)-binaphthyl ((S)-9) and (S)-2,2'-bis[NH{C(AuCl)(N(i)Pr(2))}](2)-binaphthyl ((S)-10), while the addition to (S)-2,2'-[NCAuCl](2)-3,3'-Ph(2)-binaphthyl ((S)-12) yielded (S)-2,2'-bis[NH{C(AuCl)(NMe(2))}](2)-3,3'-Ph(2)-binaphthyl ((S)-13) and (S)-2,2'-bis[NH{C(AuCl)(NEt(2))}](2)-3,3'-Ph(2)-binaphthyl ((S)-14). All the complexes are active catalysts in the cyclopropanation of vinyl arenes and in the intramolecular hydroalkoxylation of allenes, providing good yields and modest or poor enantioselectivity. The results show that all these ligands are compatible with different functions and reaction conditions and are worth considering as alternative systems to NHCs or phosphines in gold catalyzed reactions. PMID:20614913

  20. The Real Role of N-Heterocyclic Carbene in Reductive Functionalization of CO2: An Alternative Understanding from Density Functional Theory Study.

    PubMed

    Zhou, Qinghai; Li, Yuxue

    2015-08-19

    The mechanisms of reductive functionalization of CO2 to formamide catalyzed by N-heterocyclic carbene (NHC) were comprehensively studied with DFT calculations. New activation mode with much lower energy barrier than those proposed before was discovered. In this reaction, NHC acts as neither a CO2 nor a silane activator, but as a precursor of the real catalyst, i.e., the in situ formed ionic liquid [NHCH](+)[Carbamate](-). In this loose contact ion pair, the negatively charged O atom of the carbamate anion becomes the new active site and is free to do nucleophilic attack. When amine is absent, CO2 will be converted into methanol. In this case, the NHC-CO2 adduct is the real catalytic species, the active site shifted from the carbene C atom to the negatively charged O atom. These new activation modes follow a pattern of "S(N)2@Si-Acceptor", in which the Si-H bond is activated via concerted backside S(N)2 nucleophilic attack by the negatively charged O atom, and the leaving hydride is directly accepted by a free CO2 molecule. The advantages of these new activation modes originate from the following points: (1) The ionic liquid [NHCH](+)[Carbamate](-) and NHC-CO2 adduct are thermodynamically more stable than NHC. (2) The active site of the NHC catalyst is extended outside a lot. Consequently, the large steric effect between the NHC arms and the substrates in transition state can be avoided to some extent. (3) The O atom has good silicon affinity. In addition, a free CO2 molecule, whose carbon atom is more electrophilic than those of the CO2 moieties in NHC-CO2 adduct and carbamate, acts as an efficient hydride acceptor. PMID:26220202

  1. Cationic rhenium complexes ligated with N-heterocyclic carbenes - an overview.

    PubMed

    Hille, Claudia; Kühn, Fritz E

    2015-12-14

    This review provides an overview of the currently known cationic rhenium NHC complexes. Synthesis, structures and properties are described. The title compounds are potential candidates for both catalytic and medical applications. Besides the variety of ancillary ligands, which are in some cases easily substituted, functionalization can be carried out in the side chain or at the backbone of the carbene ligand as well as - in the case of biscarbene ligands - at the bridging moiety. Cationic Re NHC complexes are promising precursors for radiopharmaceuticals and diagnostics - not only because of the possibility to radiolabel the metal (steps in this direction have been made and described already) - but rather the opportunity to link the complexes to biomolecules via the different possibilities provided by the ligands. The development of OLEDs based on luminescent Re(i) carbene complexes renders another potential application. PMID:26587970

  2. Covalent Carbene Functionalization of Graphene: Toward Chemical Band-Gap Manipulation.

    PubMed

    Sainsbury, Toby; Passarelli, Melissa; Naftaly, Mira; Gnaniah, Sam; Spencer, Steve J; Pollard, Andrew J

    2016-02-24

    In this work, we employ dibromocarbene (DBC) radicals to covalently functionalize solution exfoliated graphene via the formation of dibromocyclopropyl adducts. This is achieved using a basic aqueous/organic biphasic reaction mixture to decompose the DBC precursor, bromoform, in conjunction with a phase-transfer catalyst to facilitate ylide formation and carbene migration to graphene substrates. DBC-functionalized graphene (DBC-graphene) was characterized using a range of spectroscopic and analytical techniques to confirm the covalent nature of functionalization. Modified optical and electronic properties of DBC-graphene were investigated using UV-vis spectroscopy, analysis of electrical I-V transport properties, and noncontact terahertz time-domain spectroscopy. The implications of carbene functionalization of graphene are considered in the context of scalable radical functionalization methodologies for bulk-scale graphene processing and controlled band-gap manipulation of graphene. PMID:26824127

  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. PMID:25215600

  4. Reversible double C-H bond activation of linear and cyclic ethers to form iridium carbenes.

    PubMed

    Valpuesta, Jose E V; lvarez, Eleuterio; Lpez-Serrano, Joaqun; Maya, Celia; Carmona, Ernesto

    2012-10-01

    The double C-H bond activation of a series of linear and cyclic ethers by the iridium complex [Tp(tol')Ir(C(6)H(5))(N(2))] (2?N(2)), which features a cyclometalated hydrotris(3-p-tolylpyrazol-1-yl)borate ligand (Tp(tol')) coordinated in a ?(4)-N,N',N'',C manner, has been studied. Two methyl ethers, namely, Me(2)O and MeOtBu, along with diethyl ether and the cyclic ethers tetrahydrofuran, tetrahydropyran (THP), and 1,4-dioxane have been investigated with formation in every case of the corresponding hydride carbene complexes 3-8, which are stabilized by ?(4)-coordination of the ancillary Tp(tol') ligand. Five of the compounds have been structurally authenticated by X-ray crystallography. A remarkable feature of these rearrangements is the reversibility of the double C-H bond activation of Me(2)O, MeOtBu, Et(2)O, and THP. This has permitted catalytic deuterium incorporation into the methyl groups of the two methyl ethers, although in a rather inefficient manner (for synthetic purposes). Although possible in all cases, C-C coupling by migratory insertion of the carbene into the Ir-C ? bond of the metalated linkage has only been observed for complex 8 that contains a cyclic carbene that results from ?,?-C-H activation of 1,4-dioxane. Computational studies on the formation of iridium carbenes are also reported, which show a role for metalated Tp ligands in the double C-H activation and account for the reversibility of the reaction in terms of the relative stability of the reagents and the products of the reaction. PMID:22962021

  5. An N-Heterocyclic Carbene/Lewis Acid Strategy for the Stereoselective Synthesis of Spirooxindole Lactones

    PubMed Central

    Dugal-Tessier, Julien; OBryan, Elizabeth A.; Schroeder, Thomas B. H.; Cohen, Daniel T.

    2012-01-01

    A cooperative catalysis approach for the enantioselective formal [3+2] addition of ?,?-unsaturated aldehydes to isatins has been developed. The N-heterocyclic carbene (NHC)-catalyzed homoenolate annulations of ?-aryl enals require the addition of lithium chloride for high levels of enantioselectivity. This NHC-catalyzed annulation provides efficient access to the 3-hydroxy indole skeleton and has been applied to the first eantioselective total synthesis of maremycin B. PMID:22489096

  6. Unveiling the peculiar hydrogen bonding behavior of solvated N-heterocyclic carbenes.

    PubMed

    Hollczki, Oldamur

    2016-01-01

    To investigate the hydrogen bonding and its dynamics of N-heterocyclic carbenes (NHCs) in solution, a molecular mechanical force field was fitted for the homologous series of 1,3-dialkylimidazol-2-ylidenes. During the exploration of the potential energy surface of the water/1,3-dimethylimidazol-2-ylidene system, it was observed for the first time that the carbene is prone to interaction with hydrogen bond donor molecules also from the rather unusual "on top" orientation, where the direction of the interplay is perpendicular to the plane of the NHC's ring. The fitting of the force field parameters for imidazol-2-ylidenes was found to be the best in the case of a two-site model, which reproduces not only the strength, but also the direction dependency of hydrogen bonding. With the aid of this tool, curious, hitherto unknown types of hydrogen bonding could be unveiled for NHCs. In the case of non-hydrogen bonding solvents, carbenes tend to form short lived, but structurally influental hydrogen bonds between each other via ring hydrogen atoms and the divalent carbon atoms. The chemically highly important hydrogen bond dynamics of NHCs was found to be facilitated by three center hydrogen bonding, where two alcohol molecules bind to a carbene, which is allowed only by the aforementioned relatively strong interaction between the NHC and the hydrogen bond donor in the "on top" orientation. The latter finding has significant effects on processes that involve this kind of replacement, such as the selective transesterification reactions, and the mechanism of proton exchange on azolium rings. PMID:26592182

  7. 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.

  8. Alkyne-Azide Cycloaddition Catalyzed by Silver Chloride and Abnormal Silver N-Heterocyclic Carbene Complex

    PubMed Central

    Ortega-Arizmendi, Aldo I.; Aldeco-Prez, Eugenia; Cuevas-Yaez, 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

  9. NHC?SiCl4 : an ambivalent carbene-transfer reagent.

    PubMed

    Bttcher, Tobias; Steinhauer, Simon; Lewis-Alleyne, Lesley C; Neumann, Beate; Stammler, Hans-Georg; Bassil, Bassem S; Rschenthaler, Gerd-Volker; Hoge, Berthold

    2015-01-01

    The addition of BCl3 to the carbene-transfer reagent NHC?SiCl4 (NHC=1,3-dimethylimidazolidin-2-ylidene) gave the tetra- and pentacoordinate trichlorosilicon(IV) cations [(NHC)SiCl3 ](+) and [(NHC)2 SiCl3 ](+) with tetrachloroborate as counterion. This is in contrast to previous reactions, in which NHC?SiCl4 served as a transfer reagent for the NHC ligand. The addition of BF3 ?OEt2 , on the other hand, gave NHC?BF3 as the product of NHC transfer. In addition, the highly Lewis acidic bis(pentafluoroethyl)silane (C2 F5 )2 SiCl2 was treated with NHC?SiCl4 . In acetonitrile, the cationic silicon(IV) complexes [(NHC)SiCl3 ](+) and [(NHC)2 SiCl3 ](+) were detected with [(C2 F5 )SiCl3 ](-) as counterion. A similar result was already reported for the reaction of NHC?SiCl4 with (C2 F5 )2 SiH2 , which gave [(NHC)2 SiCl2 H][(C2 F5 )SiCl3 ]. If the reaction medium was changed to dichloromethane, the products of carbene transfer, NHC?Si(C2 F5 )2 Cl2 and NHC?Si(C2 F5 )2 ClH, respectively, were obtained instead. The formation of the latter species is a result of chloride/hydride metathesis. These compounds may serve as valuable precursors for electron-poor silylenes. Furthermore, the reactivity of NHC?SiCl4 towards phosphines is discussed. The carbene complex NHC?PCl3 shows similar reactivity to NHC?SiCl4 , and may even serve as a carbene-transfer reagent as well. PMID:25363673

  10. C5N- anion and new carbenic isomers of cyanodiacetylene: A matrix isolation IR study

    NASA Astrophysics Data System (ADS)

    Coupeaud, Anne; Turowski, Micha?; Gronowski, Marcin; Pitri, Nathalie; Couturier-Tamburelli, Isabelle; Ko?os, Robert; Aycard, Jean-Pierre

    2008-04-01

    Products of the vacuum-UV photolysis of cyanodiacetylene (HC5N) in solid argonthe anion C5N-, imine HNC5, and the branched carbene C4(H )CNhave been identified by IR absorption spectroscopy, in addition to the already discovered isonitrile HC4NC. Spectral assignments were assisted by deuterium substitution experiments, by BD(T) calculations, and by the results of a recent density functional theory study.

  11. Theoretical study of the mechanism of the N-heterocyclic carbene-catalyzed cyclotetramerization of acrylates.

    PubMed

    Chang, Dehui; Yang, Qiaoqiao; Li, Meng; Fang, Ran

    2016-01-01

    A theoretical study of the N-heterocyclic carbene (NHC)-catalyzed cyclotetramerization of acrylates forming trisubstituted cyclopentenones indicates a mechanism through a key deoxy-Breslow intermediate generated from one molecule of NHC and two molecules of methyl acrylate (MA). Pathways involving different proton-transfer (? or ?) and the role of a tert-butoxide ( (t) BuO(-)) group were investigated. Graphical abstract TOC. PMID:26696541

  12. Thiazolium carbene catalysts for the fixation of CO2 onto amines.

    PubMed

    Das, Shoubhik; Bobbink, Felix D; Bulut, Safak; Soudani, Mylne; Dyson, Paul J

    2016-02-11

    The catalytic N-formylation and N-methylation of amines using CO2 as the carbon source represents a facile and sustainable approach for the synthesis of pharmaceuticals and natural products. Herein, we describe highly effective and inexpensive thiazolium carbene-based catalysts derived from vitamin B1 for the N-formylation and N-methylation of amines, using polymethylhydrosiloxane (PMHS) as a reducing agent, which operate under ambient conditions. PMID:26739571

  13. Synthesis, characterization and catalytic activity of saturated and unsaturated N-heterocyclic carbene iridium(i) complexes.

    PubMed

    Chang, Yung-Hung; Fu, Ching-Feng; Liu, Yi-Hong; Peng, Shei-Ming; Chen, Jwu-Ting; Liu, Shiuh-Tzung

    2009-02-01

    Both saturated and unsaturated N-benzyl substituted heterocyclic carbene (NHC) iridum(i) complexes were synthesized. The unsaturated carbene complex [(un-NHC-Bn)Ir(CO)(2)Cl] in the cis form was prepared via the carbene transfer from the corresponding silver complex to [Ir(COD)(2)Cl](2) followed by ligand substitution with CO, whereas the saturated complex was obtained via the transfer from (sat-NHC-Bn)W(CO)(5). The treatment of phosphines with (NHC)Ir(CO)(2)Cl complexes yielded the products with the phosphine ligand trans to the carbene moiety via substitution. X-Ray structural determination shows that distances of Ir-C((carbene)) in both (un-NHC-Bn)Ir(CO)(PR(3))Cl and (un-NHC-Bn)Ir(CO)(PR(3))Cl are essentially the same. Analyses of spectroscopic and crystal structural data of iridium complexes [(NHC)Ir(CO)(PR(3))Cl] and Vaska's complex show similar corresponding data in both types of complexes, suggesting that the studied NHC ligands and phosphines have similar bonding with Ir(i) metal center. All iridium complexes studied in this work illustrated their catalytically activity on N-alkylation of amine with alcohol via hydrogen transfer reduction. It appears no dramatic difference on the catalytic activity among these iridium carbene complexes; but the saturated carbene complex (sat-NHC-Bn)Ir(CO)(PR(3))Cl appears to be slightly more active. For example, the reaction of benzyl alcohol with aniline in the presence of catalyst (1 mol%) under basic conditions at 100 degrees C provided the secondary amine (N-benzylaniline) in 96% yield. PMID:19156280

  14. 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. PMID:26938956

  15. Role of quantum mechanical tunneling on the ?-effect of silicon on carbenes in 3-trimethylsilylcyclobutylidene.

    PubMed

    Karmakar, Sharmistha; Datta, Ayan

    2014-03-01

    Quantum mechanical tunneling (QMT) is increasingly being realized as an important phenomenon that can enhance the rate of reactions even at room temperature. Recently, the ability of a trimethylsilane (TMS) group to activate 1,3-H shift to a carbene from a ?-position has been demonstrated. Direct dynamical calculations (using canonical varitational transition state theory) inclusive of small curvature tunneling (CVT-SCT) show that QMT plays a decisive role in such 1,3-hydrogen migration in both the presence and absence of TMS. The presence of a TMS group reduces the activation energy of 1,3-H shift reaction via 1,3-equatorial interaction of the TMS group with the carbene. Tunneling across the smaller barrier enhances the overall forward rate of the reaction. The Arrhenius plot for the reaction shows substantial curvature in comparison to the CVT mechanism at room temperature. Arrhenius plots for the kinetic isotope effects (KIEs) for the ?-deuterated and per deuterated 3-trimethylsilylcyclobutylidene also show strong deviations from the classical over the barrier mechanism. The magnitude of the KIE is suggestive of QMT from the vibrational excited states of the carbenes. PMID:24467461

  16. 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 0.590 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

  17. Chiral N-heterocyclic carbene/Lewis acid cooperative catalysis of the reaction of 2-aroylvinylcinnamaldehydes: a switch of the reaction pathway by Lewis acid activation.

    PubMed

    Wang, Zhan-Yong; Ding, Ya-Li; Wang, Gang; Cheng, Ying

    2015-12-24

    The chiral N-heterocyclic carbene/Lewis acid co-catalyzed reaction of 2-aroylvinylcinnamaldehydes produced good yields of indeno[1,2-c]furan-1-one derivatives with excellent enantioselectivity and diastereoselectivity. A switch of intramolecular cyclization to intermolecular dimerization was achieved by the cooperative catalysis of chiral triazole carbene and Ti(OPr-i)4 catalysts. PMID:26567629

  18. 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

  19. Regarding the mechanism of olefin metathesis with sol-gel-supported Ru-based complexes bearing a bidentate carbene ligand. Spectroscopic evidence for return of the propagating Ru carbene.

    PubMed

    Kingsbury, Jason S; Hoveyda, Amir H

    2005-03-30

    Two isotopically and structurally labeled Ru-based carbenes (2-d4 and 13) have been prepared and attached to the surface of monolithic sol-gel glass. The resulting glass-supported complexes (18-dn and 19) exhibit significant catalytic activity in promoting olefin metathesis reactions and provide products of high purity. Through analysis of the derivatized glass pellets used in a sequence of catalytic ring-closing metathesis reactions mediated by various supported Ru carbenes, it is demonstrated that free Ru carbene intermediates in solution can be scavenged by support-bound styrene ether ligands prior to the onset of competing transition metal decomposition. The observations detailed herein provide rigorous evidence that the initially proposed release/return mechanism is, at least partially, operative. The present investigations shed light on a critical aspect of the mechanism of an important class of Ru-based metathesis complexes (those bearing a bidentate styrene ether ligand). PMID:15783234

  20. Synthesis and biological assays on cancer cells of dinuclear gold complexes with novel functionalised di(N-heterocyclic carbene) ligands.

    PubMed

    Baron, Marco; Bellemin-Laponnaz, Stphane; Tubaro, Cristina; Basato, Marino; Bogialli, Sara; Dolmella, Alessandro

    2014-12-01

    New dinuclear di(N-heterocyclic carbene) silver(I), gold(I) and gold(III) complexes have been synthesised and their antiproliferative effects towards various cancer cell lines have been screened. The di(N-heterocyclic carbene) ligands have a propylene linker between the carbene moieties and the imidazole backbone has been functionalised with a 1-benzyl- or 1-PEG-1,2,3-triazole ring (PEG=poly(ethylene glycol)) via a CuAAC (copper azido alkyne cycloaddition) reaction. The resulting gold(I) and gold(III) complexes display an antiproliferative activity superior to that of the unfunctionalised pristine complexes together with a higher selectivity towards cancerous cells with respect to healthy cells. PMID:25226437

  1. 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 intermolecular approach offers excellent synthetic flexibility because no tethering of the oxidant is required, and its reduced form is not tangled with the product. We were the first research group to develop this strategy, through the use of pyridine/quinolone N-oxides as the external oxidants. In this manner, we can effectively make a C-C triple bond a surrogate of an α-diazo carbonyl moiety in various gold catalyses. With terminal alkynes, we demonstrated that we can efficiently trap exclusively formed terminal carbene centers by internal nucleophiles en route to the formation of cyclic products, including strained oxetan-3-ones and azetidin-3-ones, and by external nucleophiles when a P,N-bidentate ligand is coordinated to gold. With internal alkynes, we generated synthetically useful regioselectivities in the generation of the α-oxo gold carbene moiety, which enables expedient formation of versatile enone products. Other research groups have also applied this strategy en route to versatile synthetic methods. The α-oxo gold carbenes appear to be more electrophilic than their Rh counterpart, which many chemists have focused on in a large array of excellent work on metal carbene chemistry. The ease of accessing the reactive gold carbenes opens up a vast area for developing new synthetic methods that would be distinctively different from the known Rh chemistry and promises to generate a new round of "gold rush". PMID:24428596

  2. 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. PMID:26365530

  3. 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

  4. Cyclic Alkyl(amino) Carbene Stabilized Complexes with Low Coordinate Metals of Enduring Nature.

    PubMed

    Roy, Sudipta; Mondal, Kartik Chandra; Roesky, Herbert W

    2016-03-15

    N-Heterocyclic carbenes (NHCs) are known to stabilize some metal atoms in different oxidation states mostly by their strong σ-donation. After the successful syntheses of cyclic alkyl(amino) carbenes (cAACs), they have been proven to be much more effective in stabilizing electron rich species. In cAAC, one of the σ-withdrawing and π-donating nitrogen atoms of NHC is replaced by a σ-donating quaternary carbon atom leading to a lower lying LUMO. This makes the acceptance of π-back-donation from the element bound to the carbene carbon atom of cAAC energetically more advantageous. Further evidence suggests that the carbene carbon of cAAC can use the lone pair of electrons present on the adjacent nitrogen in a more controlled way depending on the accumulation of electron density on the bound metal. It has been found that cAAC can be utilized as excellent ligand for the stabilization of a complex with three coordinate metal center [(cAAC)2M(I)-Cl; M = Fe, Co, Cr]. Complex (cAAC)2M(II)Cl2 [M = Fe, Co, Cr] was prepared by reacting anhydrous M(II)Cl2 with two equiv of cAAC followed by treatment with one equiv of KC8 (reducing agent) to obtain (cAAC)2M(I)-Cl. The corresponding cation (cAAC)2M(+) was isolated when (cAAC)2M(I)-Cl was reacted with sodium-tetraarylborate (lithium) in toluene or fluorobenzene. The CV of cation (cAAC)2M(+) [M = Co, Fe] suggests that it can reversibly undergo one electron reduction. The cations of Co and Fe were reduced with Na(Hg) or KC8, respectively. (cAAC)2Co(I)Cl can be directly reduced to (cAAC)2Co(0) when reacted with one equiv of KC8. Analogous (cAAC·)2Zn(II) and (cAAC)2Mn complexes are prepared by reduction of (cAAC)MCl2 [M = Zn, Mn] with two equiv of KC8 in the presence of one equiv of cAAC. The square planar (cAAC)2NiCl2 complex was directly reduced by two equiv of LiN(iPr2) (KC8) to (cAAC)2Ni(0). The (cAAC)2Pd(0) and (cAAC)2Pt(0) complexes are prepared by substituting all four triphenylphosphines of (Ph3P)4M(0) [M = Pd, Pt] by two cAACs. Cation (cAAC)2M(+) [M = Cu, Au] was reduced with sodium/potassium to obtain the neutral analogue [(cAAC)2Cu, (cAAC)2Au]. Two coordinate Zn/Mn/Cu/Au are stabilized by two neutral carbene ligands possessing radical electrons on the carbene carbon atoms, while analogous complexes of Co/Fe/Ni/Pd/Pt contain metals in the zero oxidation state. The ground electronic structure of (cAAC)2M was thoroughly studied by theoretical calculations. In this Account, we summarize our developments in stabilizing metal complexes with low coordinate metal atoms in two, one, and most significantly in their zero oxidation states by utilizing cAACs as ligands. PMID:26925983

  5. 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

  6. N-Heterocyclic Carbene Complexes of Rh: Reaction With Dioxygen Without Oxidation

    SciTech Connect

    Praetorius, J.M.; Allen, D.P.; Wang, R.; Webb, J.D.; Grein, F.; Kennepohl, P.; Crudden, C.M.

    2009-05-21

    The reaction of oxygen with rhodium complexes containing N-heterocyclic carbenes was found to give dioxygen complexes with rare square planar geometries and unusually short O-O bond lengths. Analysis of the bonding in these complexes by Rh L-edge X-ray absorption spectroscopy (XAS), Raman spectroscopy, and DFT calculations provides evidence for a bonding model in which singlet oxygen is bound to a Rh(I) d{sup 8} metal complex, rather than the more common Rh(III) d{sup 6} peroxo species with octahedral geometry and O-O bond lengths in the 1.4-1.5 {angstrom} range.

  7. Reductions of Challenging Organic Substrates by a Nickel Complex of a Noninnocent Crown Carbene Ligand

    PubMed Central

    2010-01-01

    The first crown-tetracarbene complex of Ni(II) has been prepared, and its crystal structure determined. The complex can be reduced by Na/Hg, with an uptake of two electrons. The reduced complex reductively cleaves arenesulfonamides, including those derived from secondary aliphatic amines, and effects Birch reduction of anthracenes as well as reductive cleavage of stilbene oxides. Computational studies show that the orbital that receives electrons upon reduction of the complex 2 is predominantly based on the crown carbene ligand and also that the HOMO of the parent complex 2 is based on the ligand. PMID:20961105

  8. Activation of alkyl halides via a silver-catalyzed carbene insertion process.

    PubMed

    Dias, H V Rasika; Browning, R Greg; Polach, Sharon A; Diyabalanage, Himashinie V K; Lovely, Carl J

    2003-08-01

    The silver complex [HB(3,5-(CF3)2Pz)3]Ag(THF) featuring a highly fluorinated tris(pyrazolyl)borate ligand catalyzes the formation of aliphatic carbon-halogen bond activation products under remarkably mild conditions. For example, the reaction between CHCl3 and ethyl diazoacetate (EDA) at room temperature in the presence of the silver catalyst afforded HClC(CO2Et)CCl2H in 60% yield. The presence of beta-hydrogens on the alkyl halide leads to net hydrogen halide addition to the carbene and an alkene. PMID:12889937

  9. The first N-heterocyclic carbene-based nickel catalyst for C-S coupling.

    PubMed

    Zhang, Yugen; Ngeow, Kao Chin; Ying, Jackie Y

    2007-08-30

    We have developed the first N-heterocyclic carbene (NHC)-based transition metal catalysts for C-S coupling reactions. Ni-NHC catalysts showed good to excellent activities toward various aryl halides in C-S coupling reactions. The catalytic activities were greatly affected by the electronic and steric properties of the NHC ligands. The new catalysts were inexpensive, easy to synthesize, and environmentally friendly. They could be excellent candidates to replace Pd-organophosphanes for C-S coupling catalysis. PMID:17676857

  10. Ru-Ag and Ru-Au dicarbene complexes from an abnormal carbene ruthenium system.

    PubMed

    Bitzer, Mario J; Pthig, Alexander; Jandl, Christian; Khn, Fritz E; Baratta, Walter

    2015-07-14

    Reaction of [Ru(OAc)2(PPh3)2] with a P-functionalized imidazolium bromide easily affords a cationic abnormal carbene Ru system. Metalation with Ag2O yields a Ru-Ag complex containing an anionic dicarbene ligand, while subsequent transmetalation with Au(tht)Cl leads to the corresponding Ru-Au system. The bimetallic complexes were characterized by single crystal X-ray diffraction and are the first examples of complexes bearing anionic dicarbene ligands connecting two different d-block elements. PMID:26053614

  11. N-Heterocyclic Carbene-Mediated Microfluidic Oxidative Electrosynthesis of Amides from Aldehydes.

    PubMed

    Green, Robert A; Pletcher, Derek; Leach, Stuart G; Brown, Richard C D

    2016-03-01

    A flow process for N-Heterocyclic Carbene (NHC)-mediated anodic oxidative amidation of aldehydes is described, employing an undivided microfluidic electrolysis cell to oxidize Breslow intermediates. After electrochemical oxidation, the reaction of the intermediate N-acylated thiazolium cation with primary amines is completed by passage through a heating cell to achieve high conversion in a single pass. The flow mixing regimen circumvented the issue of competing imine formation between the aldehyde and amine substrates, which otherwise prevented formation of the desired product. High yields (71-99%), productivities (up to 2.6 g h(-1)), and current efficiencies (65-91%) were realized for 19 amides. PMID:26886178

  12. A two-color fluorogenic carbene complex for tagging olefins via metathesis reaction

    NASA Astrophysics Data System (ADS)

    Wirtz, Marcel; Grter, Andreas; Heib, Florian; Huch, Volker; Zapp, Josef; Herten, Dirk-Peter; Schmitt, Michael; Jung, Gregor

    2015-12-01

    We describe a fluorogenic ruthenium (II) carbene complex in which the chromophore is directly connected to the metal center. The compound introduces a boron dipyrromethene (BODIPY) moiety into target double bonds by metathesis. Tagging of terminal double bonds is demonstrated on immobilized styrene units on a glass surface. We also show that two compounds with distinguishable fluorescence properties are formed in the model reaction with styrene. The outcome of the metathesis reaction is characterized by 19F-NMR, optical spectroscopy, and, finally, single-molecule trajectories. This labeling scheme, in our perception, is of particular interest in the fields of interfacial science and biorthogonal ligation in combination with super-resolution imaging.

  13. Stable compactifications

    SciTech Connect

    Accetta, F.S.; Gleiser, M.; Holman, R.; Kolb, E.W.

    1986-03-01

    We show that compactifications of theories with extra dimensions are unstable if due to monopole configurations of an antisymmetric tensor field balanced against one-loop Casimir corrections. In the case of ten dimensional supergravity, it is possible, at least for a portion of the phase space, to achieve a stable compactification without fine-tuning by including the contribution of fermionic condensates to the monopole configurations. 23 refs., 2 figs.

  14. Synthesis, structure and DFT study of cymantrenyl Fischer carbene complexes of group VI and VII transition metals

    NASA Astrophysics Data System (ADS)

    Fraser, Roan; van Rooyen, Petrus H.; Landman, Marilé

    2016-02-01

    Bi- and trimetallic carbene complexes of group VI and VII transition metals (Cr, Mo, W, Mn and Re), with CpMn(CO)3 as the initial synthon, have been synthesised according to the classical Fischer methodology. Crystal structures of the novel carbene complexes with general formula [Mx(CO)y-1{C(OEt)(MnCp(CO)3)}], where x = 1 then y = 3 or 6; x = 2 then y = 10, of the complexes are reported. A density functional theory (DFT) study was undertaken to determine natural bonding orbitals (NBOs) and conformational as well as isomeric aspects of the polymetallic complexes. Application of the second-order perturbation theory (SOPT) of the natural bond orbital (NBO) method revealed stabilizing interactions between the methylene C-H bonds and the carbonyl ligands of the carbene metal moiety. These stabilization interactions show a linear decrease for the group VI metal carbene complexes down the group.

  15. Regiospecific Synthesis of Benzoxepines through Pd-Catalyzed Carbene Migratory Insertion and C-C Bond Cleavage.

    PubMed

    Xie, Yang; Zhang, Ping; Zhou, Lei

    2016-03-01

    A new method for the synthesis of benzoxepines via migratory insertion into a Pd carbene followed by C-C bond cleavage was developed. Various benzoxepines were constructed by the regioselective ring expansion concomitant with the introduction of an aryl group at their 5-position. PMID:26841938

  16. Cyclopentadiene Construction via Rh-Catalyzed Carbene/Alkyne Metathesis Terminated with Intramolecular Formal [3 + 2] Cycloaddition.

    PubMed

    Zheng, Yang; Mao, Jincheng; Weng, Yuecheng; Zhang, Xiaolu; Xu, Xinfang

    2015-11-20

    A new type of intramolecular carbene cascade reaction of alkynyl-tethered styryl diazoesters is presented, which is terminated with a formal [3 + 2] cycloaddition to give the bicyclic cyclopentadiene derivatives in high yields and selectivity. Additionally, it was found that the ?-H shift is the dominating process in the case of alkyl alkyne-tethered substrates. PMID:26550688

  17. 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...

  18. Formation of ruthenium carbenes by gem-hydrogen transfer to internal alkynes: implications for alkyne trans-hydrogenation.

    PubMed

    Leutzsch, Markus; Wolf, Larry M; Gupta, Puneet; Fuchs, Michael; Thiel, Walter; Fars, Christophe; Frstner, Alois

    2015-10-12

    Insights into the mechanism of the unusual trans-hydrogenation of internal alkynes catalyzed by {Cp*Ru} complexes were gained by para-hydrogen (p-H2 ) induced polarization (PHIP) transfer NMR spectroscopy. It was found that the productive trans-reduction competes with a pathway in which both H?atoms of H2 are delivered to a single alkyne C?atom of the substrate while the second alkyne C?atom is converted into a metal carbene. This "geminal hydrogenation" mode seems unprecedented; it was independently confirmed by the isolation and structural characterization of a ruthenium carbene complex stabilized by secondary inter-ligand interactions. A detailed DFT study shows that the trans alkene and the carbene complex originate from a common metallacyclopropene intermediate. Furthermore, the computational analysis and the PHIP NMR data concur in that the metal carbene is the major gateway to olefin isomerization and over-reduction, which frequently interfere with regular alkyne trans-hydrogenation. PMID:26332643

  19. 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…

  20. Triply cyclometalated trinuclear iridium(iii) and trinuclear palladium(ii) complexes with a tri-mesoionic carbene ligand.

    PubMed

    Maity, Ramananda; Mekic, Amel; van der Meer, Margarethe; Verma, Amit; Sarkar, Biprajit

    2015-10-21

    The first example of a triply cyclometalated homopolynuclear tri-Ir(III) complex with additional carbene donors is presented. Cooperative catalysis and the interplay between homogenous and heterogeneous catalyses are discussed for the tri-Ir(III) complex and a related non-cyclometalated tri-Pd(II) complex. PMID:26264746

  1. 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

  2. Synthesis of Naphthalenes through Three-Component Coupling of Alkynes, Fischer Carbene Complexes, and Benzaldehyde Hydrazones via Isoindole Intermediates

    PubMed Central

    Duan, Shaofeng; Sinha-Mahapatra, Dilip K.; Herndon, James W.

    2008-01-01

    The synthesis of naphthalene derivatives through three-component coupling of 2-alkynylbenzaldehyde hydrazones with carbene complexes and electron-deficient alkynes has been examined. The reaction involves formation of an isoindole derivative, followed by intramolecular DielsAlder reaction, followed by nitrene extrusion. The reaction was highly regioselective using unsymmetrical alkynes. PMID:18351767

  3. Synthesis of naphthalenes through three-component coupling of alkynes, Fischer carbene complexes, and benzaldehyde hydrazones via isoindole intermediates.

    PubMed

    Duan, Shaofeng; Sinha-Mahapatra, Dilip K; Herndon, James W

    2008-04-17

    The synthesis of naphthalene derivatives through three-component coupling of 2-alkynylbenzaldehyde hydrazones with carbene complexes and electron-deficient alkynes has been examined. The reaction involves formation of an isoindole derivative, followed by intramolecular Diels-Alder reaction, followed by nitrene extrusion. The reaction was highly regioselective using unsymmetrical alkynes. PMID:18351767

  4. 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

  5. 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

  6. 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

  7. Syntheses, crystal structures, reactivity, and photochemistry of gold(III) bromides bearing N-heterocyclic carbenes.

    PubMed

    Hirtenlehner, Christa; Krims, Charlotte; Hlbling, Johanna; List, Manuela; Zabel, Manfred; Fleck, Michel; Berger, Raphael J F; Schoefberger, Wolfgang; Monkowius, Uwe

    2011-10-14

    Gold(I) complexes bearing N-heterocyclic carbenes (NHC) of the type (NHC)AuBr (3a/3b) [NHC = 1-methyl-3-benzylimidazol-2-ylidene (= MeBnIm), and 1,3-dibenzylimidazol-2-ylidene (= Bn(2)Im)] are prepared by transmetallation reactions of (tht)AuBr (tht = tetrahydrothiophene) and (NHC)AgBr (2a/2b). The homoleptic, ionic complexes [(NHC)(2)Au]Br (6a/6b) are synthesized by the reaction with free carbene. Successive oxidation of 3a/3b and 6a/6b with bromine gave the respective (NHC)AuBr(3) (4a/4b) and [(NHC)(2)AuBr(2)]Br (7a/7b) in good overall yields as yellow powders. All complexes were characterized by NMR spectroscopy, mass spectrometry, elemental analysis and single crystal X-ray diffraction. Reactions of the Au(III) complexes towards anionic ligands like carboxylates, phenolates and thiophenolates were investigated and result in a complete or partial reduction to a Au(I) complex. Irradiation of the Au(III) complexes with UV light yield the Au(I) congeners in a clean photo-reaction. PMID:21879094

  8. 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

  9. 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

  10. Insights into the strength and nature of carbenehalogen bond interactions: a theoretical perspective.

    PubMed

    Esrafili, Mehdi D; Mohammadirad, Nafiseh

    2013-06-01

    Halogen-bonding, a noncovalent interaction between a halogen atom X in one molecule and a negative site in another, plays critical roles in fields as diverse as molecular biology, drug design and material engineering. In this work, we have examined the strength and origin of halogen bonds between carbene CH? and XCCY molecules, where X?=?Cl, Br, I, and Y?=?H, F, COF, COOH, CF?, NO?, CN, NH?, CH?, OH. These calculations have been carried out using M06-2X, MP2 and CCSD(T) methods, through analyses of surface electrostatic potentials V S(r) and intermolecular interaction energies. Not surprisingly, the strength of the halogen bonds in the CH?XCCY complexes depend on the polarizability of the halogen X and the electron-withdrawing power of the Y group. It is revealed that for a given carbeneX interaction, the electrostatic term is slightly larger (i.e., more negative) than the dispersion term. Comparing the data for the chlorine, bromine and iodine substituted CH?XCCY systems, it can be seen that both the polarization and dispersion components of the interaction energy increase with increasing halogen size. One can see that increasing the size and positive nature of a halogen's ?-hole markedly enhances the electrostatic contribution of the halogen-bonding interaction. PMID:23455928

  11. Asymmetric intramolecular ?-cyclopropanation of aldehydes using a donor/acceptor carbene mimetic.

    PubMed

    Luo, Chaosheng; Wang, Zhen; Huang, Yong

    2015-01-01

    Enantioselective ?-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 ?-cyclopropanation reaction of olefinic aldehydes to form chiral cyclopropane aldehydes. We demonstrate that an ?-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 ?-iodo iminium as a donor/acceptor carbene surrogate will find wide applications in chemical reaction development. PMID:26644194

  12. 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

  13. Stepwise and one-pot syntheses of Ir(III) complexes with imidazolium-based carbene ligands.

    PubMed

    Chien, Chih-Hsien; Fujita, Singo; Yamoto, Suguru; Hara, Takeshi; Yamagata, Tsuneaki; Watanabe, Masami; Mashima, Kazushi

    2008-02-21

    We report the preparation, crystal structure, electrochemistry, and emission properties of Ir(Cinsertion markC:)3, where Cinsertion markC: is an N-heterocyclic carbene ligand. Two synthetic approaches are introduced for generating Ir(III) complexes bearing imidazolium-based carbene ligands whose precursors are [pypiH2][Cl] (1a) (pyridyl[1,2-a]{2-phenylimidazol}-3-ylidene chloride) and [pympiH2][Cl] (1b) (pyridyl[1,2-a-{2-(p-methoxy)phenylimidazol}-3-ylidene chloride). The first method is a stepwise reaction: treatment of [Ir(mu-Cl)(COD)]2, where COD is 1,5-cyclooctadiene, with 4 equiv. of the corresponding carbene (Cinsertion markC:) ligands in the presence of an excess amount of sodium methoxide affords Ir(III) dimers [Ir(mu-Cl)(Cinsertion markC:)2]2 (2a, Cinsertion markC: = pypi(-); 2b, Cinsertion markC: = pympi(-)). These chloro-bridged dimers 2a and 2b react with the corresponding carbene (Cinsertion markC:) ligands to form the desired homoleptic compounds Ir(Cinsertion markC:)3 (3a, Cinsertion markC: = pypi(-); 3b, Cinsertion markC: = pympi(-)). The second method, using a one-pot reaction of [Ir(mu-Cl)(COD)]2 with 6 equiv. of the corresponding carbene (Cinsertion markC:) ligands 1a and 1b in the presence of excess amounts of Ag2O, affords Ir(Cinsertion markC:)3. The two methods are convenient and reproducible procedures for the synthesis of Ir(Cinsertion markC:)3. Complexes 3a and 3b are obtained as mixtures of meridional and facial isomers, which can be separated by recrystallization or flash column chromatography. PMID:18259625

  14. N-heterocyclic carbene catalyzed reaction of phthalaldehydes: controllable stereoselective synthesis of polyhydroxylated spiro- and fused indenones dictated by the structure of NHC catalysts.

    PubMed

    Cheng, Ying; Peng, Jiang-Hua; Li, Yong-Jia; Shi, Xun-Yu; Tang, Ming-Sheng; Tan, Tian-Yu

    2011-03-18

    The N-heterocyclic carbene catalyzed stereoselective dimerization reactions of phthalaldehydes produced polyhydroxylated spiro- or fused indenones. The reaction pathways were dictated by the structures of NHC catalysts. Under the catalysis of a imidazole carbene, phthalaldehydes produced dihydroxylspiro[indene-2,1'-isobenzofuran]-3-ones in good to excellent yields, whereas a triazole carbene catalyzed reaction of phthalaldehydes afforded fully cis-trihydroxylindeno[2,1-a]inden-5-ones in high yields. This work not only provides a highly efficient method for the construction of valuable polyhydroxyl substituted indene derivatives that are not easily assembled by other synthetic means but also reflects the versatility of organocatalysis using N-heterocyclic carbenes. PMID:21341805

  15. Efficient Room-Temperature, Au(+) -Mediated Coupling of a Carbene Ligand with Methane To Generate C2 Hx (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

  16. Mechanistic Investigation of Aromatic C(sp(2))-H and Alkyl C(sp(3))-H Bond Insertion by Gold Carbenes.

    PubMed

    Liu, Yuan; Yu, Zhunzhun; Luo, Zhoujie; Zhang, John Zenghui; Liu, Lu; Xia, Fei

    2016-03-24

    It was recently reported that the gold-carbenes have an unprecedented catalysis toward the functionalization of C(sp(2))-H bonds of aromatic compounds. However, the associated mechanisms of C(sp(2))-H bonds inserted by gold-carbenes have not been comprehensively understood. We carried out a detailed mechanistic investigation of gold-carbene insertion into the C(sp(2))-H bond of anisole by means of theoretical calculations and control experiments. It significantly reveals that the aromatic C(sp(2))-H bond activation starts with the electrophilic addition of aromatic carbon toward the carbene carbon and subsequently followed the [1,3]-proton shift to form an enol intermediate. The rearrangement of enol proceeds through the mechanisms of proton transfer assisted by water molecules or enol intermediates, which are supported by our control experiments. It was also found that the C(sp(3))-H insertions of alkanes by gold-carbenes proceed through a concerted process via a three-centered transition state. The further comparison of different mechanisms provides a clear theoretical scheme to account for the difference in aromatic C(sp(2))-H and alkyl C(sp(3))-H bond activation, which is instructive for the further experimental functionalization of C-H bonds by gold-carbenes. PMID:26929977

  17. Borenium Ion Catalyzed Hydroboration of Alkenes with N-Heterocyclic Carbene Boranes

    PubMed Central

    Prokofjevs, Aleksandrs; Boussonnire, Anne; Li, Linfeng; Bonin, Hlne; Lacte, Emmanuel; Curran, Dennis P.; Vedejs, Edwin

    2012-01-01

    Treatment of alkenes such as 3-hexene, 3-octene, and 1-cyclohexyl-1-butene with the N-heterocyclic carbene-derived borane 2 and catalytic HNTf2 effects hydroboration at room temperature. With 3-hexene, surprisingly facile migration of the boron atom from C3 of the hexyl group to C2 was observed over a time scale of minutes to hours. Oxidative workup gave a mixture of alcohols containing 2-hexanol as the major product. A similar preference for the C(2) alcohol was observed after oxidative workup of the 3-octene, and 1-cyclohexyl-1-butene hydroborations. NHC-borenium cations (or functional equivalents) are postulated as the species that accomplish the hydroborations, and the C(2) selective migrations are attributed to the 4-center inter-conversion of borenium cations with cationic NHC-borane olefin ?-complexes. PMID:22713106

  18. Borenium ion catalyzed hydroboration of alkenes with N-heterocyclic carbene-boranes.

    PubMed

    Prokofjevs, Aleksandrs; Boussonnire, Anne; Li, Linfeng; Bonin, Hlne; Lacte, Emmanuel; Curran, Dennis P; Vedejs, Edwin

    2012-07-25

    Treatment of alkenes such as 3-hexene, 3-octene, and 1-cyclohexyl-1-butene with the N-heterocyclic carbene (NHC)-derived borane 2 and catalytic HNTf(2) (Tf = trifluoromethanesulfonyl (CF(3)SO(2))) effects hydroboration at room temperature. With 3-hexene, surprisingly facile migration of the boron atom from C(3) of the hexyl group to C(2) was observed over a time scale of minutes to hours. Oxidative workup gave a mixture of alcohols containing 2-hexanol as the major product. A similar preference for the C(2) alcohol was observed after oxidative workup of the 3-octene and 1-cyclohexyl-1-butene hydroborations. NHC-borenium cations (or functional equivalents) are postulated as the species that accomplish the hydroborations, and the C(2) selective migrations are attributed to the four-center interconversion of borenium cations with cationic NHC-borane-olefin ?-complexes. PMID:22713106

  19. Metal-N-heterocyclic carbene complexes as anti-tumor agents.

    PubMed

    Hu, Chunqi; Li, Xin; Wang, Wei; Zhang, Ruoyu; Deng, Liping

    2014-04-01

    It has been a long story of the development of anticancer metallopharmaceuticals since the identification of cisplatin. Advances in metallodrugs discovery during the past 40 years have made it an ever-growing area of research in medicinal inorganic chemistry. Meanwhile, the emerging of N-heterocyclic carbene (NHC) chemistry has stimulated the newly burgeoning interests in the biomedical applications of metal-NHC complexes. This review will detail what have been achieved hitherto in the research of metal-NHC complexes as potential anti-tumor agents coupled with gold, silver, copper, platinum and palladium. Their mechanism of action will also be discussed. All the results obtained indicate that this promising approach is worthy of more focuses and further studies. PMID:24350852

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

    PubMed

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

    2014-01-01

    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

  1. N-heterocyclic carbene formation induced fluorescent and colorimetric sensing of fluoride using perimidinium derivatives.

    PubMed

    Zhang, Dawei; Yang, Haiqiang; Martinez, Alexandre; Jamieson, Kelsey; Dutasta, Jean-Pierre; Gao, Guohua

    2014-12-15

    In this study, two perimidinium derivatives (1 and 2) were designed, synthesized, and developed as efficient fluorescent and colorimetric chemodosisensors for F(-) in DMSO or more competitive media (DMSO containing 10?% water). In the presence of F(-) , the yellow and non-fluorescent solution of 1/2 became colourless and exhibited strong blue fluorescence. This unique spectroscopic behaviour of 1/2 towards F(-) was attributed to the formation of N-heterocyclic carbene deprotonated by F(-) , which immediately reacted with water to give a colourless and fluorescent carbinol. Interestingly, it was found that this carbinol intermediate was unstable and further underwent a redox disproportionation to generate two other optically changed compounds. All the proposed mechanisms for the sensing process have been carefully confirmed by experiments. PMID:25346203

  2. Alkylfluorenyl substituted N-heterocyclic carbenes in copper(I) catalysed hydrosilylation of aldehydes and ketones.

    PubMed

    Teci, Matthieu; Lentz, Nicolas; Brenner, Eric; Matt, Dominique; Toupet, Loïc

    2015-08-21

    Copper(i) complexes featuring N-heterocyclic carbenes (NHCs) in which the nitrogen atoms are substituted by a 9-ethyl-9-fluorenyl group (EF) have been synthesised and tested in the hydrosylilation of functionalized and/or sterically demanding ketones and aldehydes. These reactions, carried out with triethylsilane as hydride source, were best achieved with the imidazolylidene copper complex in which the EF substituents can freely rotate about the corresponding N-CEF bonds. The remarkable stability of the active species, which surpasses that of previously reported Cu-NHC catalysts is likely to rely on the ability of the NHC side arms to protect the copper centre during the catalytic cycle by forming sandwich-like intermediates, but also on its steric flexibility facilitating approach of encumbered substrates. TONs up to 1000 were reached. PMID:26162019

  3. Polyannulated Bis(N-heterocyclic carbene)palladium Pincer Complexes for Electrocatalytic CO2 Reduction.

    PubMed

    Therrien, Jeffrey A; Wolf, Michael O; Patrick, Brian O

    2015-12-21

    Phenanthro- and pyreno-annulated N-heterocyclic carbenes (NHCs) have been incorporated into lutidine-linked bis-NHC Pd pincer complexes to investigate the effect of these polyannulated NHCs on the ability of the complexes to electrochemically reduce CO2 to CO in the presence of 2,2,2-trifluoroacetic acid and 2,2,2-trifluoroethanol as proton sources. These complexes are screened for their ability to reduce CO2 and modeled using density functional theory calculations, where the annulated phenanthrene and pyrene moieties are shown to be additional sites for redox activity in the pincer ligand, enabling increased electron donation. Electrochemical and computational studies are used to gain an understanding of the chemical significance of redox events for complexes of this type, highlighting the importance of anion binding and dissociation. PMID:26624491

  4. Tip-induced gating of molecular levels in carbene-based junctions

    NASA Astrophysics Data System (ADS)

    Foti, Giuseppe; Vázquez, Héctor

    2016-03-01

    We study the conductance of N-heterocyclic carbene-based (NHC) molecules on gold by means of first-principles calculations based on density-functional theory and non-equilibrium Green’s functions. We consider several tip structures and find a strong dependence of the position of the NHC molecular levels with the atomistic structure of the tip. The position of the lowest unoccupied molecular orbital (LUMO) can change by almost 0.8 eV with tip shape. Through an analysis of the net charge transfer, electron redistribution and work function for each tip structure, we rationalize the LUMO shifts in terms of the sum of the work function and the maximum electrostatic potential arising from charge rearrangement. These differences in the LUMO position, effectively gating the molecular levels, result in large conductance variations. These findings open the way to modulating the conductance of NHC-based molecular circuits through the controlled design of the tip atomistic structure.

  5. Highly stereoselective synthesis of cyclopentanes bearing four stereocentres by a rhodium carbene-initiated domino sequence.

    PubMed

    Parr, Brendan T; Davies, Huw M L

    2014-01-01

    Stereoselective synthesis of a cyclopentane nucleus by convergent annulation constitutes a significant challenge for synthetic chemists. Although a number of biologically relevant cyclopentane natural products are known, more often than not, the cyclopentane core is assembled in a stepwise manner because of the lack of efficient annulation strategies. Here we report the rhodium-catalysed reactions of vinyldiazoacetates with (E)-1,3-disubstituted 2-butenols generate cyclopentanes, containing four new stereogenic centres with very high levels of stereoselectivity (99% ee, >97: 3 dr). The reaction proceeds by a carbene-initiated domino sequence consisting of five distinct steps: rhodium-bound oxonium ylide formation, [2,3]-sigmatropic rearrangement, oxy-Cope rearrangement, enol-keto tautomerization and finally an intramolecular carbonyl ene reaction. A systematic study is presented detailing how to control chirality transfer in each of the four stereo-defining steps of the cascade, consummating in the development of a highly stereoselective process. PMID:25082301

  6. Cooperative Catalysis by Carbenes and Lewis Acids in a Highly Stereoselective Route to ?-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 ?-lactams in moderate to good yields and high levels of diastereo- and enantioselectivity. PMID:20729898

  7. 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 46 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 46 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

  8. Cyclic alkyl amino carbene (CAAC) ruthenium complexes as remarkably active catalysts for ethenolysis.

    PubMed

    Marx, Vanessa M; Sullivan, Alexandra H; Melaimi, Mohand; Virgil, Scott C; Keitz, Benjamin K; Weinberger, David S; Bertrand, Guy; Grubbs, Robert H

    2015-02-01

    An expanded family of ruthenium-based metathesis catalysts bearing cyclic alkyl amino carbene (CAAC) ligands was prepared. These catalysts exhibited exceptional activity in the ethenolysis of the seed-oil derivative methyl oleate. In many cases, catalyst turnover numbers (TONs) of more than 100,000 were achieved, at a catalyst loading of only 3?ppm. Remarkably, the most active catalyst system was able to achieve a TON of 340,000, at a catalyst loading of only 1?ppm. This is the first time a series of metathesis catalysts has exhibited such high performance in cross-metathesis reactions employing ethylene gas, with activities sufficient to render ethenolysis applicable to the industrial-scale production of linear ?-olefins (LAOs) and other terminal-olefin products. PMID:25522160

  9. Exploiting Acyl and Enol Azolium Intermediates via NHeterocyclic Carbene Catalyzed Reactions of Alpha-Reducible Aldehydes

    PubMed Central

    Vora, Harit U.; Wheeler, Philip

    2013-01-01

    N-heterocyclic carbenes are well known for their role in catalyzing benzoin and Stetter reactions: the generation of acyl anion equivalents from simple aldehydes to react with a variety of electrophiles. However, when an aldehyde bearing a leaving group or unsaturation adjacent to the acyl anion equivalent is subjected to an NHC, a new avenue of reactivity is unlocked, leading to a number of novel transformations which can generate highly complex products from simple starting materials, many of which are assembled through unconventional bond disconnections. The field of these new reactions - those utilizing ?-reducible aldehydes to access previously unexplored catalytic intermediates has expanded rapidly in the past eight years. This review aims to provide the reader with a historical perspective on the underlying discoveries that led to the current state of the art, a mechanistic description of these reactions, and a summary of the recent advances in this area. PMID:23538785

  10. 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 indazoleindole 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 indazoleindole 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

  11. Ruthenium indenylidene complexes bearing N-alkyl/N-mesityl-substituted N-heterocyclic carbene ligands.

    PubMed

    Yu, Baoyi; Hamad, Fatma B; Sels, Bert; Van Hecke, Kristof; Verpoort, Francis

    2015-07-14

    We report on the synthesis and characterization of second generation ruthenium indenylidene catalysts bearing unsymmetrical N-heterocyclic carbene (NHC) ligands denoted as RuCl2(3-phenyl-1-indenylidene)(1-mesityl-3-R-4,5-dihydroimidazol-2-ylidene)(PCy3), in which R is methyl 8a, octyl 8b or cyclohexyl 8c. The characterization of 8a-c was performed by NMR spectroscopy, elemental analysis, IR, HRMS and single-crystal X-ray diffraction analysis. In addition, the catalytic activity of the obtained initiators was evaluated in various representative metathesis reactions. The results reveal that the complexes 8a-c, bearing an N-alkyl side on the NHC, show a faster catalytic initiation than the reference complex 2. Complex 8a, which performs the best among the investigated indenylidene complexes, exhibits slower initiation but better overall efficiency than its benzylidene analogue 1c, especially in a low catalyst loading. PMID:26052999

  12. 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) , ? = 93.910(4), V = 1639(4) 3, Z = 4, D x = 1.771 g/cm3, F (000) = 864, (Mo K ?) = 1.278 mm-1. The final R 1 = 0.0711 and wR 2 = 0.1903 for reflections with I > 2?( I). In addition, the preliminary biological test showed that the title compound had anti-fungus yeast activity.

  13. Tip-induced gating of molecular levels in carbene-based junctions.

    PubMed

    Foti, Giuseppe; Vázquez, Héctor

    2016-03-29

    We study the conductance of N-heterocyclic carbene-based (NHC) molecules on gold by means of first-principles calculations based on density-functional theory and non-equilibrium Green's functions. We consider several tip structures and find a strong dependence of the position of the NHC molecular levels with the atomistic structure of the tip. The position of the lowest unoccupied molecular orbital (LUMO) can change by almost 0.8 eV with tip shape. Through an analysis of the net charge transfer, electron redistribution and work function for each tip structure, we rationalize the LUMO shifts in terms of the sum of the work function and the maximum electrostatic potential arising from charge rearrangement. These differences in the LUMO position, effectively gating the molecular levels, result in large conductance variations. These findings open the way to modulating the conductance of NHC-based molecular circuits through the controlled design of the tip atomistic structure. PMID:26891059

  14. 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; Grtzel, 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 (? ? 1.3 ?s), 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. PMID:25741900

  15. Role of gold(I) ?-oxo carbenes in the oxidation reactions of alkynes catalyzed by gold(I) complexes.

    PubMed

    Schulz, Ji?; Jakov, Lucie; Skrba, Anton; Roithov, Jana

    2014-08-13

    The gas phase structures of gold(I) complexes formed by intermolecular oxidation of selected terminal (phenylacetylene) and internal alkynes (2-butyne, 1-phenylpropyne, diphenylacetylene) were investigated using tandem mass spectrometry and ion spectroscopy in conjunction with quantum-chemical calculations. The experiments demonstrated that the primarily formed ?-gold(I) vinyloxypyridinium complexes readily undergo rearrangement, dependent on their substituents, to either gold(I) ?-oxo carbenenoids (a synthetic surrogate of the ?-oxo carbenes) or pyridine adducts of gold(I) enone complexes in the condensed phase and that the existence of naked ?-oxo carbenes is highly improbable. Isotopic labeling experiments performed with the reaction mixtures clearly linked the species that exist in solution to the ions transferred to the gas phase. The ions were then fully characterized by CID experiments and IRMPD spectroscopy. The conclusions based on the experimental observations perfectly correspond with the results from quantum-chemical calculations. PMID:25068382

  16. 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. PMID:26740157

  17. 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.

  18. Expedient Mechanosynthesis of N,N-Dialkyl Imidazoliums and Silver(I)-Carbene Complexes in a Ball-Mill.

    PubMed

    Beillard, Audrey; Golliard, Ethan; Gillet, Valentin; Bantreil, Xavier; Mtro, Thomas-Xavier; Martinez, Jean; Lamaty, Frdric

    2015-12-01

    The absence of solvent, associated with intensive mechanical agitation, allowed the first mechanosynthesis of high-value silver(I)-carbene complexes and the corresponding N,N-dialkylimidazolium precursors. This procedure gave outstanding results in terms of yield and reaction time, when compared to solution-based conditions previously described in literature, and was generalized to unprecedented compounds. Silver(I)-carbene complexes could either be obtained from N,N-dialkylimidazolium salts or directly from imidazole and alkyl halides in a one-pot two-step procedure without isolating the imidazolium intermediate. Additionally, an efficient one-pot three-step sequence, including imidazole alkylation, silver metalation, and transmetalation is reported. PMID:26489706

  19. 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…

  20. A spectroscopic study of the reaction of the carbene, tetrabromocyclopentadienylidene, with O 2 in low temperature matrices

    NASA Astrophysics Data System (ADS)

    Dunkin, Ian R.; McCluskey, Adam

    1994-01-01

    The photolysis of tetrabromodiazocyclopentadiene ( 2) in low temperature Ar and N 2 matrices generates the carbene, tetrabromocyclopentadienylidene ( 3). In O 2-doped matrices, ( 3) reacts with oxygen yielding first tetrabromocyclopentadienone O-oxide ( 4), identification of which was aided by experiments with isotopically labelled oxygen, and then tetrabromocyclopentadienone ( 5) and tetrabromo-α-pyrone ( 6). The matrix uv-visible and infrared absorption spectra of tetrabromocyclopentadienone O-oxide ( 4) are reported.

  1. A betaine adduct of N-heterocyclic carbene and carbodiimide, an efficient ligand to produce ultra-small ruthenium nanoparticles.

    PubMed

    Martnez-Prieto, L M; Urbaneja, C; Palma, P; Cmpora, J; Philippot, K; Chaudret, B

    2015-03-18

    The betaine adduct of N-heterocyclic carbene and carbodiimide (ICy((p-tol))NCN) was found to be a very efficient ligand to prepare very small (1-1.3 nm) ruthenium nanoparticles (RuNPs). The coordination of the ligand on the metal surface takes place through the carbodiimide moiety. The resulting RuNPs led to decarbonylation of THF and showed size selectivity for styrene hydrogenation. PMID:25690829

  2. Metal-ligand bifunctional reactivity and catalysis of protic N-heterocyclic carbene and pyrazole complexes featuring ?-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 ? to the metal are surveyed. Protic 2-pyridylidenes as related cooperating non-innocent ligands are also described. PMID:25074357

  3. 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

  4. Iron(ii) triflate/N-heterocyclic carbene-catalysed cross-coupling of arylmagnesiums with aryl chlorides and tosylates.

    PubMed

    Chua, Yi-Yuan; Duong, Hung A

    2016-01-14

    In comparison to iron(ii) halides, iron(ii) triflate exhibits a greater resistance towards reduction by p-tolylmagnesium bromide. This knowledge has led to the development of an iron(ii) triflate/N-heterocyclic carbene-catalysed cross-coupling system of aryl Grignard reagents with aryl chlorides and tosylates with high efficiency, even surpassing that of previously reported catalyst systems employing strongly coordinating counterions in some cases. PMID:26649616

  5. A theobromine derived silver N-heterocyclic carbene: synthesis, characterization, and antimicrobial efficacy studies on cystic fibrosis relevant pathogens

    PubMed Central

    Panzner, Matthew J.; Hindi, Khadijah M.; Wright, Brian D.; Taylor, Jane B.; Han, Daniel S.

    2009-01-01

    The increasing incidence of multidrug-resistant (MDR) pulmonary infections in the cystic fibrosis (CF) population has prompted the investigation of innovative silver based therapeutics. The functionalization of the naturally occurring xanthine theobromine at the N1 nitrogen atom with an ethanol substituent followed by the methylation of the N9 nitrogen atom gives the N-heterocyclic carbene precursor 1-(2-hydroxyethyl)-3,7,9-trimethylxanthinium iodide. The reaction of this xanthinium salt with silver acetate produces the highly hydrophilic silver carbene complex SCC8. The in vitro antimicrobial efficacy of this newly synthesized complex was evaluated with excellent results on a variety of virulent and MDR pathogens isolated from CF patients. A comparative in vivo study between the known caffeine derived silver carbene SCC1 and SCC8 demonstrated the ability of both complexes to improve the survival rates of mice in a pneumonia model utilizing the clinically isolated infectious strain of Pseudomonas aeruginosa PA M57-15. PMID:20449175

  6. Density functional computations of the cyclopropanation of ethene catalyzed by iron (II) carbene complexes Cp(CO)(L)Fe=CHR, L D CO, PMe3, R D Me, OMe, ph, CO2Me

    NASA Astrophysics Data System (ADS)

    Wang, Fen; Meng, Qingxi; Li, Ming

    Density functional theory has been used to study the Fe-catalyzed cyclopropanation of Fe-carbene complexes with ethene. All the intermediates and transition states were optimized completely at the B3LYP/6-31+G(d,p) level. Calculation results confirm that the cyclopropanation of Fe-carbene complexes with ethene involves the two reaction paths I and II. In the reaction path I, the double bond of ethene attacks directly on the carbene carbon of Fe-carbene complexes to generate the cyclopropane. In the reaction path II, ethene substitution for PMe3 or CO in the Fe-carbene complexes leads to the complexes M2; and the attack of one carbon of ethene on the carbene carbon results in the complexes M3 with a Fe bond C bond C bond C four-membered ring, and then generates the cyclopropane via the elimination reaction. For Fe-carbene complexes A, C, D, E, and H, the main reaction mode is the reaction path I; for Fe-carbene complexes B, F, and G, the main reaction mode is the reaction path II.0

  7. Characteristics and nature of the intermolecular interactions in boron-bonded complexes with carbene as electron donor: an ab initio, SAPT and QTAIM study.

    PubMed

    Esrafili, Mehdi D

    2012-05-01

    We report geometries, stabilization energies, symmetry adapted perturbation theory (SAPT) and quantum theory of atoms in molecules (QTAIM) analyses of a series of carbene-BX(3) complexes, where X = H, OH, NH(2), CH(3), CN, NC, F, Cl, and Br. The stabilization energies were calculated at HF, B3LYP, MP2, MP4 and CCSD(T)/aug-cc-pVDZ levels of theory using optimized geometries of all the complexes obtained from B3LYP/aug-cc-pVTZ. Quantitatively, all the complexes indicate the presence of B-C(carbene) interaction due to the short B-C(carbene) distances. Inspection of stabilization energies reveals that the interaction energies increase in the order NH(2) > OH > CH(3) > F > H > Cl > Br > NC > CN, which is the opposite trend shown in the binding distances. Considering the SAPT results, it is found that electrostatic effects account for about 50% of the overall attraction of the studied complexes. By comparison, the induction components of these interactions represent about 40% of the total attractive forces. Despite falling in a region of charge depletion with nabla(2)?(BCP) >0, the B-C(carbene) bond critical points (BCPs) are characterized by a reasonably large value of the electron density (?(BCP)) and H(BCP) <0, indicating that the potential energy overcomes the kinetic energy density at BCP and the B-C(carbene) bond is a polar covalent bond. PMID:21877151

  8. Gold(I) and Gold(III) Complexes of Cyclic (Alkyl)(amino)carbenes

    PubMed Central

    2016-01-01

    The chemistry of Au(I) complexes with two types of cyclic (alkyl)(amino)carbene (CAAC) ligands has been explored, using the sterically less demanding dimethyl derivative Me2CAAC and the 2-adamantyl ligand AdCAAC. The conversion of (AdCAAC)AuCl into (AdCAAC)AuOH by treatment with KOH is significantly accelerated by the addition of tBuOH. (AdCAAC)AuOH is a convenient starting material for the high-yield syntheses of (AdCAAC)AuX complexes by acid/base and CH activation reactions (X = OAryl, CF3CO2, N(Tf)2, C2Ph, C6F5, C6HF4, C6H2F3, CH2C(O)C6H4OMe, CH(Ph)C(O)Ph, CH2SO2Ph), while the cationic complexes [(AdCAAC)AuL]+ (L = CO, CNtBu) and (AdCAAC)AuCN were obtained by chloride substitution from (AdCAAC)AuCl. The reactivity toward variously substituted fluoroarenes suggests that (AdCAAC)AuOH is able to react with CH bonds with pKa values lower than about 31.5. This, together with the spectroscopic data, confirm the somewhat stronger electron-donor properties of CAAC ligands in comparison to imidazolylidene-type N-heterocyclic carbenes (NHCs). In spite of this, the oxidation of Me2CAAC and AdCAAC gold compounds is much less facile. Oxidations proceed with CAu cleavage by halogens unless light is strictly excluded. The oxidation of (AdCAAC)AuCl with PhICl2 in the dark gives near-quantitative yields of (AdCAAC)AuCl3, while [Au(Me2CAAC)2]Cl leads to trans-[AuCl2(Me2CAAC)2]Cl. In contrast to the chemistry of imidazolylidene-type gold NHC complexes, oxidation products containing AuBr or AuI bonds could not be obtained; whereas the reaction with CsBr3 cleaves the AuC bond to give mixtures of [AdCAAC-Br]+[AuBr2]? and [(AdCAAC-Br)]+ [AuBr4]?, the oxidation of (AdCAAC)AuI with I2 leads to the adduct (AdCAAC)AuII2. Irrespective of the steric demands of the CAAC ligands, their gold complexes proved more resistant to oxidation and more prone to halogen cleavage of the AuC bonds than gold(I) complexes of imidazole-based NHC ligands. PMID:26146436

  9. Spherical core-shell magnetic particles constructed by main-chain palladium N-heterocyclic carbenes

    NASA Astrophysics Data System (ADS)

    Zhao, Huaixia; Li, Liuyi; Wang, Jinyun; Wang, Ruihu

    2015-02-01

    The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in Fe3O4@PNP2, and Pd(0) and Pd(ii) coexist in Fe3O4@PNP1 under the same conditions; moreover, the morphologies of these spherical core-shell particles show no significant variation after six consecutive catalytic runs.The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in Fe3O4@PNP2, and Pd(0) and Pd(ii) coexist in Fe3O4@PNP1 under the same conditions; moreover, the morphologies of these spherical core-shell particles show no significant variation after six consecutive catalytic runs. Electronic supplementary information (ESI) available: The additional SEM images, IR spectra, TG-MS curves, Solid state 13C NMR spectra, XPS spectra and XRD spectra of palladium NHC particles. See DOI: 10.1039/c4nr07330d

  10. Gold (I) N-heterocyclic carbene complex inhibits mouse melanoma growth by p53 upregulation

    PubMed Central

    2014-01-01

    Background Cancer treatment using gold (I) complexes is becoming popular. In this study, a gold (I) N-heterocyclic complex designated as complex 3 was synthesized, its cytotoxicity was examined, and its anti-melanoma activity was evaluated in vitro and in vivo. Methods Viability of cancer cells was determined by MTT assay upon treatment with various concentrations of a gold (I) N-heterocyclic carbene complex (complex 3) in a dose and time dependent manner. Mouse melanoma cells B16F10 were selected for further apoptotic studies, including flowcytometric analysis of annexin binding, cell cycle arrest, intracellular ROS generation and loss in the mitochondrial membrane potential. ELISA based assays were done for caspase activities and western blots for determining the expression of various survival and apoptotic proteins. Immunocytology was performed to visualize the translocation of p53 to the nucleus. B16F10 cells were inoculated into mice and post tumor formation, complex 3 was administered. Immunohistology was performed to determine the expressions of p53, p21, NF-?B (p65 and p50), MMP-9 and VEGF. Students t test was used for determining statistical significance. The survival rate data were analyzed by Kaplan-Meier plots. Results Complex 3 markedly inhibited the growth of HCT 116, HepG2, and A549, and induced apoptosis in B16F10 cells with nuclear condensation, DNA fragmentation, externalization of phosphatidylserine, activation of caspase 3 and caspase 9, PARP cleavage, downregulation of Bcl-2, upregulation of Bax, cytosolic cytochrome c elevation, ROS generation, and mitochondrial membrane potential loss indicating the involvement of an intrinsic mitochondrial death pathway. Further, upregulation of p53, p-p53 (ser 15) and p21 indicated the role of p53 in complex 3 mediated apoptosis. The complex reduced tumor size, and caused upregulation of p53 and p21 along with downregulation of NF-?B (p65 and p50), VEGF and MMP-9. These results suggest that it induced anti-melanoma effect in vitro and in vivo by modulating p53 and other apoptotic factors. Conclusions The gold (I) N-heterocyclic carbene complex (C22H26N6AuO2PF6) designated as complex 3 induced ROS and p53 dependent apoptosis in B16F10 cells involving the mitochondrial death pathway along with suppression of melanoma tumor growth by regulating the levels of pro and anti apoptotic factors (p53, p21, NF-?B, VEGF and MMP-9). PMID:24625085

  11. 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}2 Hg] 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)6 Cu10 S8 Hg3 ] 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

  12. Understanding the Mechanism of the Divergent Reactivity of Non-Heteroatom-Stabilized Chromium Carbene Complexes with Furfural Imines: Formation of Benzofurans and Azetines.

    PubMed

    Funes-Ardoiz, Ignacio; González, Jairo; Santamaría, Javier; Sampedro, Diego

    2016-02-19

    The mechanisms of the reaction between non-heteroatom-stabilized alkynyl chromium carbene complexes prepared in situ and furfural imines to yield benzofurans and/or azetines have been explored by means of density functional theory method calculations. The reaction proceeds through a complex cascade of steps triggered by a nucleophilic addition of the imine nitrogen atom. The formation of two benzofuran regioisomers has been explained in terms of competitive nucleophilic attacks to different positions of the carbene complex. Each of these regioisomers can be obtained as the major product depending on the starting materials. The overall sequence could be controlled to yield benzofurans or azetines by adjusting the substituents present in the initial carbene complex. This mechanistic information allowed for the preparation of new benzofurans and azetinylcarbenes in good yields. PMID:26799934

  13. "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

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

    NASA Astrophysics Data System (ADS)

    Landman, Maril; 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.

  15. 4-Alkylated Silver–N-Heterocyclic Carbene (NHC) Complexes with Cytotoxic Effects in Leukemia Cells

    PubMed Central

    Sandtorv, Alexander H; Leitch, Calum; Bedringaas, Siv Lise; Gjertsen, Bjørn Tore; Bjørsvik, Hans-René

    2015-01-01

    Computational chemistry has shown that backbone-alkylated imidazoles ought to be efficient ligands for transition metal catalysts with improved carbene-to-metal donation. In this work, such alkylated imidazoles were synthesized and complexed with silver(I) by means of an eight/nine-step synthetic pathway we devised to access a new class of biologically active silver complexes. The synthesis involves selective iodination of the imidazole backbone, followed by Sonogashira coupling to replace the backbone iodine. The installed alkyne moiety is then subjected to reductive hydrogenation with Pearlman’s catalyst. The imidazole N1 atom is arylated by the palladium-catalyzed Buchwald N-arylation method. The imidazole N3 position was then methylated with methyl iodine, whereupon the synthesis was terminated by complexation of the imidazolium salt with silver(I) oxide. The synthetic pathway provided an overall yield of ≈20 %. The resulting complexes were tested in vitro against HL60 and MOLM-13 leukemic cells, two human-derived cell lines that model acute myeloid leukemia. The most active compounds exhibiting low IC50 values of 14 and 27 μM, against HL60 and MOLM-13 cells, respectively. The imidazole side chain was found to be essential for high cytotoxicity, as the imidazole complex bearing a C7 side chain at the 4-position was four- to sixfold more potent than the corresponding imidazole elaborated with a methyl group. PMID:26250720

  16. Theoretical Insights on the Interaction of N-Heterocyclic Carbenes with Tetravalent Silicon Reagents.

    PubMed

    Pathak, Dipanjali; Deuri, Sanjib; Phukan, Prodeep

    2016-01-14

    Lewis acid-base type interaction between N-heterocyclic carbene (NHC) and tetravalent silicon reagent (SiR) has been investigated computationally. This NHC-Si interaction is of fundamental importance to the understanding of variety of NHC catalyzed organic transformations involving silicon compounds such as cyanosilylation, trifluoromethylsilylation, etc. Geometries of 24 NHCs, 10 silicon reagents, and their 61 Lewis acid-base complexes have been optimized using the B3LYP/6-31+G(d,p) and M05-2X/6-31+G(d,p) level of theory. The strength of NHC-Si interaction has been assessed in terms of binding energy of the complexes, charge transfer (CT) and the length of Si-CNHC bond. Energy decomposition analysis (EDA) and natural bond orbital (NBO) analysis at M052X/6-31+G(d,p) level of theory has been carried out to get a deeper understanding of the nature of bonding and charge delocalization. Proton affinity of the NHCs and fluoride affinity of the SiRs have been calculated and correlated with the binding energy of the resulting complexes. PMID:26654756

  17. Nanofiber composites containing N-heterocyclic carbene complexes with antimicrobial activity

    PubMed Central

    Elzatahry, Ahmed A; Al-Enizi, Abdullah M; Elsayed, Elsayed Ahmed; Butorac, Rachel R; Al-Deyab, Salem S; Wadaan, Mohammad AM; Cowley, Alan H

    2012-01-01

    This report concerns nanofiber composites that incorporate N-heterocyclic carbenes and the use of such composites for testing antimicrobial and antifungal activities. The nanofiber composites were produced by electrospinning mixtures of the gold chloride or gold acetate complexes of a bis(imino)acenaphthene (BIAN)-supported NHC with aqueous solutions of polyvinyl alcohol (PVA). The products were characterized by scanning-electron microscopy, which revealed that nanofibers in the range of 250300 nm had been produced. The biological activities of the nanofiber composites were tested against two Gram-positive bacteria, six Gram-negative bacteria, and two fungal strains. No activity was evident against the fungal strains. However, the gold chloride complex was found to be active against all the Gram-positive pathogens and one of the Gram-negative pathogens. It was also found that the activity of the produced nanofibers was localized and that no release of the bioactive compound from the nanofibers was evident. The demonstrated antimicrobial activities of these novel nanofiber composites render them potentially useful as wound dressings. PMID:22745545

  18. N-Heterocyclic carbenes: versatile second cyclometalated ligands for neutral iridium(III) heteroleptic complexes.

    PubMed

    Li, Tian-Yi; Liang, Xiao; Zhou, Liang; Wu, Chen; Zhang, Song; Liu, Xuan; Lu, Guang-Zhao; Xue, Li-Sha; Zheng, You-Xuan; Zuo, Jing-Lin

    2015-01-01

    With 2-(2,4-difluorophenyl)pyridine (dfppy) as the first cyclometalated ligand and different monoanionic N-heterocyclic carbenes (NHCs) as the second cyclometalated ligands, 16 blue or greenish-blue neutral iridium(III) phosphorescent complexes, (dfppy)2Ir(NHC), were synthesized efficiently. The obtained Ir(III) complexes display typical phosphorescence of 455-485 nm with quantum yields up to 0.73. By modifying the phenyl moiety in the NHCs with electron-withdrawing substituents (e.g., -F or -CF3) or replacing it with N-heteroaromatic rings (pyridine or pyrimidine), the HOMO-LUMO gaps are broadened, and the emissions shift to the more blue region accordingly. Furthermore, to extend the application scope of NHCs as the second cyclometalated ligands, five other Ir(III) complexes from blue to red were synthesized with different first cyclometalated ligands. Finally, the organic light-emitting diodes using one blue emitter exhibit a maximum current efficiency of 37.83 cd A(-1), an external quantum efficiency of 10.3%, and a maximum luminance of 8709 cd m(-2). Our results demonstrate that NHCs as the second cyclometalated ligands are good candidates for the achievement of efficient phosphorescent Ir(III) complexes and corresponding devices. PMID:25495711

  19. Theoretical study on the mechanism of extraction reaction between silylene carbene and its derivatives and thiirane

    NASA Astrophysics Data System (ADS)

    Lu, X. H.; Che, X.; Shi, L.; Han, J. F.; Lian, Z. X.; Li, Y. Q.

    2010-12-01

    The mechanism of the sulfur extraction reaction between singlet silylene carbine and its derivatives and thiirane has been investigated with density functional theory (DFT), including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by B3LYP/6-311G( d, p) method. From the potential energy profile, it can be predicted that the reaction pathway of this kind consists in two steps: (1) the two reactants firstly form an intermediate through a barrier-free exothermic reaction; (2) the intermediate then isomerizes to a product via a transition state. This kind of reactions has similar mechanism: when the silylene carbene and its derivatives [X2Si=C: (X = H, F, Cl, CH3)] and thiirane approach each other, the shift of 3 p lone electron pair of S in thiirane to the 2 p unoccupied orbital of C in X2Si=C: gives a p ? p donor-acceptor bond, thereby leading to the formation of intermediate (INT). As the p ? p donor-acceptor bond continues to strengthen (that is the C-S bond continues to shorten), the intermediate (INT) generates product (P + C2H4) via transition state (TS). It is the substituent electronegativity that mainly affect the extraction reactions. When the substituent electronegativity is greater, the energy barrier is lower, and the reaction rate is greater.

  20. 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. Klingelhfer, 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).

  1. Relativistic effects in the cationic platinum carbene PtCH + 2

    NASA Astrophysics Data System (ADS)

    Heinemann, Christoph; Schwarz, Helmut; Koch, Wolfram; Dyall, Kenneth G.

    1996-03-01

    Fully relativistic four-component Dirac-Fock Coulomb calculations in conjunction with a second-order perturbational estimate for the correlation energy have been performed in benchmark calculations on geometric and electronic structures as well as the binding energy of the cationic platinum carbene complex PtCH+2. The relativistic stabilization of this species amounts to as much as 50 kcal/mol and the combination of relativistic and correlation effects shorten the Pt-C bond length by nearly 1 bohr, changing the bond order from one to two. The relative importance of spin-free and spin-dependent relativistic effects on the geometry, the electronic structure, and the binding energy is evaluated by comparison to the Douglas-Kroll method. Relativistic effective core potentials are shown to describe the spin-free effects reliably. The best theoretical estimate for the bond dissociation energy underestimates the experimental value by 13% due to truncation errors in the one- and n-particle space treatments. The mixed Hartree-Fock/density-functional method Becke3-Lee-Yang-Parr performs surprisingly well with respect to the structure and binding energy of the target molecule.

  2. Correlations and Contrasts in Homo- and Heteroleptic Cyclic (Alkyl)(amino)carbene-Containing Pt(0) Complexes.

    PubMed

    Arnold, Nicole; Braunschweig, Holger; Brenner, Peter B; Celik, Mehmet Ali; Dewhurst, Rian D; Haehnel, Martin; Kramer, Thomas; Krummenacher, Ivo; Marder, Todd B

    2015-08-24

    An improved synthetic route to homoleptic complex [Pt(CAAC(Me))2] (CAAC = cyclic (alkyl)(amino)carbenes) and convenient routes to new heteroleptic complexes of the form [Pt(CAAC(Me))(PR3)] are presented. Although the homoleptic complex was found to be inert to many reagents, oxidative addition and metal-only Lewis pair (MOLP) formation was observed from one of the heteroleptic complexes. The spectroscopic, structural, and electrochemical properties of the zero-valent complexes were explored in concert with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. The homoleptic [Pt(CAAC)2] and heteroleptic [Pt(CAAC)(PR3)] complexes were found to be similar in their spectroscopic and structural properties, but their electrochemical behavior and reactivity differ greatly. The unusually strong color of the CAAC-containing Pt(0) complexes was investigated by TD-DFT calculations and attributed to excitations into the LUMOs of the complexes, which are predominantly composed of bonding ? interactions between Pt and the CAAC carbon atoms. PMID:26241579

  3. Ethylene/propylene copolymerization catalyzed by vanadium complexes containing N-heterocyclic carbenes.

    PubMed

    Zhang, Shu; Zhang, Wen-Chao; Shang, Dan-Dan; Zhang, Zhi-Qian; Wu, Yi-Xian

    2015-09-14

    Various vanadium complexes containing N-heterocyclic carbenes, VOCl3[1,3-R2(NCH=)2C:] (V1, R = 2,6-Me2C6H3; V2, R = 2,6-Et2C6H3; V3, R = 2,6-(i)Pr2C6H3; V4, R = 2,4,6-Me3C6H2), have been synthesized and employed as catalyst precursors for ethylene/propylene copolymerization after activation by Et3Al2Cl3. Complex V4 showed higher catalytic activity of ca. 38 kg copolymer per (mol of V) per h and an ethylene/propylene copolymer with random monomer distribution could be prepared. Complex V3 consumed more cocatalyst than its analogues to reach higher catalytic activity. The obtained copolymers exhibit relatively narrow polydispersity and contain more randomly distributed monomer units than that the copolymers prepared by using the traditional vanadium catalytic system. PMID:25992712

  4. 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 1012 h. One hundred percent mortality was observed at concentrations ?50 M. At sub-lethal concentrations (1030 M), 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

  5. 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.

  6. Probing protein surface with a solvent mimetic carbene coupled to detection by mass spectrometry.

    PubMed

    Gmez, Gabriela E; Mundo, Mariana R; Craig, Patricio O; Delfino, Jos 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 (:CH(2)). 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. PMID:22006407

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

    PubMed

    Farooq, Muhammad; Taha, Nael Abu; 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

  8. Spherical core-shell magnetic particles constructed by main-chain palladium N-heterocyclic carbenes.

    PubMed

    Zhao, Huaixia; Li, Liuyi; Wang, Jinyun; Wang, Ruihu

    2015-02-28

    The encapsulation of the functional species on magnetic core is a facile approach for the synthesis of core-shell magnetic materials, and surface encapsulating matrices play crucial roles in regulating their properties and applications. In this study, two core-shell palladium N-heterocyclic carbene (NHC) particles (Fe3O4@PNP1 and Fe3O4@PNP2) were prepared by a one-pot reaction of semi-rigid tripodal imidazolium salts and palladium acetate in the presence of magnetite nanoparticles. The magnetite nanoparticles are encapsulated inside the main-chain palladium, which act as cores. The conjugated effects of triphenyltriazine and triphenylbenzene in the imidazolium salts have important influence on their physical properties and catalytic performances. Fe3O4@PNP2 shows better recyclability than Fe3O4@PNP1. Unexpectedly, Pd(ii) is well maintained after six consecutive catalytic runs in Fe3O4@PNP2, and Pd(0) and Pd(ii) coexist in Fe3O4@PNP1 under the same conditions; moreover, the morphologies of these spherical core-shell particles show no significant variation after six consecutive catalytic runs. PMID:25631238

  9. Application of silver N-heterocyclic carbene complexes in O-glycosidation reactions

    PubMed Central

    Talisman, Ian J.; Kumar, Vineet; Deschamps, Jeffrey R.; Frisch, Mark

    2011-01-01

    We report the efficient O-glycosidation of glycosyl bromides with therapeutically relevant acceptors facilitated by silver N-heterocyclic carbene (Ag-NHC) complexes. A set of four Ag-NHC complexes was synthesized and evaluated as promoters for glycosidation reactions. Two new bis-Ag-NHC complexes derived from ionic liquids 1-benzyl-3-methyl-1H-imidazolium chloride and 1-(2-methoxyethyl)-3-methyl-1H-imidazolium chloride were found to efficiently promote glycosidation, whereas known mono-Ag complexes of 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride and 1,3-bis(2,6-di-isopropylphenyl)imidazolium chloride failed to facilitate the reaction. The structures of the promoters were established by X-ray crystallography, and these complexes were employed in the glycosidation of different glycosyl bromide donors with biologically valuable acceptors, such as estrone, estradiol, and various flavones. The products were obtained in yields considered good to excellent, and all reactions were highly selective for the ? isomer regardless of neighboring group effects. PMID:21911215

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

    NASA Astrophysics Data System (ADS)

    Gmez, Gabriela E.; Mundo, Mariana R.; Craig, Patricio O.; Delfino, Jos 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.

  11. Iron Porphyrin Carbene Catalytic Intermediates: Structures, Mssbauer and NMR Spectroscopic Properties, and Bonding**

    PubMed Central

    Khade, Rahul L.; Fan, Wenchao; Ling, Yan; Yang, Liu; Oldfield, Eric

    2014-01-01

    Iron porphyrin carbenes (IPCs) are thought to be intermediates involved in the metabolism of various xenobiotics by cytochrome P450, as well as in chemical reactions catalyzed by metalloporphyrins and engineered P450s. While early work proposed IPCs to contain FeII, more recent work invokes a double bond description of the iron carbon bond, similar to that found in FeIV porphyrin oxenes. Here, we report the first quantum chemical investigation of IPC Mssbauer and NMR spectroscopic properties, as well as their electronic structures, together with comparisons to ferrous heme proteins and an FeIV oxene model. The results provide the first accurate predictions of the experimental spectroscopic observables as well as the first theoretical explanation of their electrophilic nature, as deduced from experiment. The preferred resonance structure is FeII?{:C(X)Y}0 and not FeIV={C(X)Y}2-, a result that will facilitate research on IPC reactivities in various chemical and biochemical systems. PMID:24910004

  12. Synthesis of Fischer carbene complexes of iridium by C-H bond activation of methyl and cyclic ethers: Evidence for reversible {alpha}-hydrogen migration

    SciTech Connect

    Luecke, H.F.; Arndtsen, B.A.; Burger, P.; Bergman, R.G.

    1996-03-13

    We report here a mild and versatile route to Fischer carbene complexes of iridium via the activation of C-H bonds of methyl and cyclic ethers, along with our preliminary studies of this rare family of carbene complexes. Theoretical studies suggest that {alpha}-hydrogen migrations can be kinetically favorable if a coordinatively unsaturated species can be accessed. Thus, the lability of the triflate ligand presumably facilitates this process. Further evidence for the rapidity, as well as reversibility, of this rearrangement was obtained by NMR analysis. 20 refs.

  13. Mesomeric betaine--N-heterocyclic carbene interconversions of 1,2,4-triazolium-phenolates. Sulfur, selenium, and borane adduct formation.

    PubMed

    Liu, Ming; Nieger, Martin; Schmidt, Andreas

    2015-01-11

    The conjugated mesomeric betaines 2-(1-phenyl-4H-1,2,4-triazolium-4-yl)phenolates are masked N-heterocyclic carbenes of 1,2,4-triazole which can be trapped as thiones and selenones. Reaction with triethylborane and triphenylborane resulted in the formation of first representatives of a new zwitterionic heterocyclic ring system, benzo[e]1,2,4-triazolo[3,4-c][1,4,2]oxazaborinium-4-ide, as a formal trapping product of an anionic N-heterocyclic carbene. PMID:25358558

  14. Silver-Catalyzed Amidiniumation of Alkynes: Isolation of a Silver Intermediate, Synthesis of Enamine Amido Carbene Precursors, and an Unprecedented Umpolung of Propiolamide.

    PubMed

    Lv, Shichang; Wang, Jiwei; Zhang, Caiyun; Xu, Sheng; Shi, Min; Zhang, Jun

    2015-12-01

    A silver-catalyzed amidiniumation of N-propiolic formamidines for the synthesis of novel enamine amido carbene precursors is reported. Isolation of a first silver intermediate in silver-catalyzed amidiniumation of alkynes and other organogold intermediates supports our proposed mechanisms. Several control experiments reveal the unexpected effects of both HOTf and substrate substituents on the choice of either a ? or ?,??silver activation mode and the cyclization fashion. Bis(hydroxyimidazol)ium salts were obtained through an unprecedented umpolung of propiolamides. The byproduct Ag2 O as either an oxidant or silver source promotes the syntheses of N-heterocyclic carbene (NHC) precursors or Ag/NHC complexes. PMID:26473976

  15. Optimizing P,N-Bidentate Ligands for Oxidative Gold Catalysis: Highly Efficient Intermolecular Trapping of ?-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 ?-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

  16. An Alkylidene Carbene C-H Activation Approach toward the Enantioselective Syntheses of Spirolactams: Application to the Synthesis of (-)-Adalinine.

    PubMed

    Annadi, Krishna; Wee, Andrew G H

    2016-02-01

    A method based on in situ alkylidene carbene generation-C-H insertion reaction of 5-(3-oxobutyl)pyrrolidin-2-ones and 6-(3-oxobutyl)piperidin-2-ones is developed for the enantioselective synthesis of 1-azaspiro[4,4]non-6-ene-2-ones and 6-azaspiro[4,5]dec-1-ene-7-ones. The required 5-(3-oxobutyl)pyrrolidin-2-ones and 6-(3-oxobutyl)piperidin-2-ones are prepared from the Wacker oxidation of internal alkenes typified by 5-(but-2-enyl)pyrrolidin-2-ones and 6-(but-2-enyl)piperidin-2-ones, respectively. Excellent regioselectivity (?92:8) is realized for the Wacker oxidation, and high yields (78-89%) of the desired lactam ketones are obtained. The results from further investigations into the Wacker oxidation suggested that the high regioselectivity of the oxidation in these lactam alkenes might be due to the participation of the lactam nitrogen via intramolecular coordination to Pd(II) during the reaction. Studies on alkylidene carbene generation-C-H insertion reaction of the lactam ketones revealed that the reaction efficiency is sensitive to the reaction temperature and the amount of lithio(trimethylsilyl)diazomethane employed, which led to the development of optimal reaction conditions for effecting alkylidene carbene generation-C-H insertion. Using the optimal reaction conditions, good to high yields (53-76%) of both ?- and ?-lactam spirocycles were obtained. The synthetic utility of the spirolactams was demonstrated by the synthesis of (-)-adalinine. PMID:26730565

  17. Stereoelectronic effects in C-H bond oxidation reactions of Ni(I) N-heterocyclic carbene complexes.

    PubMed

    Poulten, Rebecca C; Lpez, Isidoro; Llobet, Antoni; Mahon, Mary F; Whittlesey, Michael K

    2014-07-21

    Activation of O2 by the three-coordinate Ni(I) ring-expanded N-heterocyclic carbene complexes Ni(RE-NHC)(PPh3)Br (RE-NHC = 6-Mes, 1; 7-Mes, 2) produced the structurally characterized dimeric Ni(II) complexes Ni(6-Mes)(Br)(?-OH)(?-O-6-Mes')NiBr (3) and Ni(7-Mes)(Br)(?-OH)(?-O-7-Mes')NiBr (4) containing oxidized ortho-mesityl groups from one of the carbene ligands. NMR and mass spectrometry provided evidence for further oxidation in solution to afford bis-?-aryloxy compounds; the 6-Mes derivative was isolated, and its structure was verified. Low-temperature UV-visible spectroscopy showed that the reaction between 1 and O2 was too fast even at ca. -80 C to yield any observable intermediates and also supported the formation of more than one oxidation product. Addition of O2 to Ni(I) precursors containing a less electron-donating diamidocarbene (6-MesDAC, 7) or less bulky 6- or 7-membered ring diaminocarbene ligands (6- or 7-o-Tol; 8 and 9) proceeded quite differently, affording phosphine and carbene oxidation products (Ni(O?PPh3)2Br2 and (6-MesDAC)?O) and the mononuclear Ni(II) dibromide complexes (Ni(6-o-Tol)(PPh3)Br2 (10) and (Ni(7-o-Tol)(PPh3)Br2 (11)) respectively. Electrochemical measurements on the five Ni(I) precursors show significantly higher redox potentials for 1 and 2, the complexes that undergo oxygen atom transfer from O2. PMID:24972307

  18. 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 sigma donates, and subsequent back-bonding occurs into a pi* antibonding orbital. This is a different type of interaction not seen in the three existing classes of metal-carbene complexes, namely Fischer, Schrock, and Grubbs. Finally, the virtual engineering of enhanced chemical warfare agent (CWA) detection systems is discussed. As part of a U.S. Department of Defense supported research project, in silico chemical modifications to a previously synthesized zinc-porphyrin, ZnCS1, were made to attempt to achieve preferential binding of the nerve agent sarin versus its simulant, DIMP (diisopropyl methylphosphonate). Upon modification, a combination of steric effects and induced hydrogen bonding allowed for the selective binding of sarin. The success of this work demonstrates the role that high performance computing can play in national security research, without the associated costs and high security required for experimentation.

  19. Asymmetric Synthesis of Functionalized Cyclopentanones via a Multicatalytic Secondary Amine/N-Heterocyclic Carbene Catalyzed Cascade Sequence

    PubMed Central

    Lathrop, Stephen P.; Rovis, Tomislav

    2009-01-01

    A one-pot, asymmetric multicatalytic formal [3+2] reaction between 1,3-dicarbonyls and α,β-unsaturated aldehydes is described. The multicatalytic process involves a secondary amine catalyzed Michael addition followed by a N-heterocyclic carbene catalyzed intramolecular crossed benzoin reaction to afford densely functionalized cyclopentanones with high enantioselectivities. The reaction proceeds with a variety of alkyl and aryl enals as well as a range of 1,3-dicarbonyls (diketones and β-ketoesters). The functionalized products are obtained from cheap, readily available starting materials in a rapid and efficient manner in a one-pot, one-step operation. PMID:19731910

  20. 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

  1. Highly selective carboxylative cyclization of allenylmethylamines with carbon dioxide using N-heterocyclic carbene-silver(I) catalysts.

    PubMed

    Yamashita, Kyohei; Hase, Shun; Kayaki, Yoshihito; Ikariya, Takao

    2015-05-15

    Silver(I) carboxylate complexes promote the carboxylative cyclization of allenylmethylamines to afford 5-alkenyl-1,3-oxazolidin-2-ones in 2-propanol. The use of an N-heterocyclic carbene ligand (IPr) under pressurized CO2 is effective in suppressing the intramolecular hydroamination that leads to 2,5-dihydropyrroles. The mechanism involving a nucleophilic attack of the carbamate of the allene moiety and a subsequent protonation was realized on the basis of experimental and theoretical results involving a model intermediate, the alkenylgold(I) complex, which was synthesized from Au(OH)(IPr) and 1-methylamino-2,3-butadiene. PMID:25918943

  2. Structurally Characterized Cationic Silver(I) and Ruthenium(II)carbene complexes of 1,2,3-Triazol-5-ylidenes

    PubMed Central

    Cai, Jiajia; Yang, Xiaoping; Arumugam, Kuppuswamy

    2011-01-01

    A novel 1,3,4-substituted 1,2,3-triazolium salt was found to function as an effective precursor for the synthesis of the first structurally characterized cationic silver(I) and ruthenium(II)carbene complexes of overall 1:2 ligand-to-metal stoichiometry. The Ag(I) complex crystallized in the form of an eight silver atom-containing cluster, whereas the Ru(II) complex proved to be a discrete species and was found to be capable of initiating the ring-opening metathesis polymerization of norbornene upon activation with (trimethylsilyl)diazomethane. PMID:22140293

  3. N-Heterocyclic Carbene Ligand-Enabled C(sp(3) )-H Arylation of Piperidine and Tetrahydropyran Derivatives.

    PubMed

    Ye, Shengqing; Yang, Weibo; Coon, Timothy; Fanning, Dewey; Neubert, Tim; Stamos, Dean; Yu, Jin-Quan

    2016-03-24

    Pd(II) -catalyzed C(sp(3) )-H arylation of saturated heterocycles with a wide range of aryl iodides is enabled by an N-heterocyclic carbene (NHC) ligand. A C(sp(3) )-H insertion step by the Pd(II) /NHC complex in the absence of ArI is demonstrated experimentally for the first time. Experimental data suggests that the previously established NHC-mediated Pd(0) /Pd(II) catalytic manifold does not operate in this reaction. This transformation provides a new approach for diversifying pharmaceutically relevant piperidine and tetrahydropyran ring systems. PMID:26841330

  4. Stable Fly Research

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Adult stable flies feed on the blood of humans, pets and livestock, inflicting painful bites. Stable flies need one and sometimes two bloodmeals each day to develop their eggs. Unlike mosquitoes where only the females bloodfeed, both male and female stable flies require blood to reproduce. Stable fl...

  5. 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-generated [MCH2] species with an inert molecule such as CH4, CO2, or NH3 constitutes a route to activate and functionalize methane under ambient conditions. Clearly, while these gas-phase studies cannot be translated directly to formally related processes in solution or those that occur at a surface, they nevertheless provide a conceptual mechanistic understanding and permit researchers to probe directly the remarkable intrinsic features of these elusive molecules and, in a broader context, help to identify the active site of a catalyst, the so-called "aristocratic atoms". PMID:26870872

  6. Design and synthesis of iridium bis(carbene) complexes for efficient blue electrophosphorescence.

    PubMed

    Hsieh, Cheng-Han; Wu, Fang-Iy; Fan, Chun-Hsiang; Huang, Min-Jie; Lu, Kun-Yi; Chou, Pei-Yu; Yang, Yu-Han Ou; Wu, Shih-Hsiang; Chen, I-Chia; Chou, Shu-Hua; Wong, Ken-Tsung; Cheng, Chien-Hong

    2011-08-01

    Five iridium bis(carbene) complexes, [Ir(pmi)(2)(pypz)] (1), [Ir(mpmi)(2)(pypz)] (2), [Ir(fpmi)(2)(pypz)] (3), [Ir(fpmi)(2)(pyim)] (4), and [Ir(fpmi)(2)(tfpypz)] (5) (pmi=1-phenyl-3-methylimdazolin-2-ylidene-C,C(2'); fpmi=1-(4-fluorophenyl)-3-methylimdazolin-2-ylidene-C,C(2'); mpmi=1-(4-methyl-phenyl)-3-methylimdazolin-2-ylidene-C,C(2'); pypz=2-(1H-pyrazol-5-yl)pyridinato; pyim=2-(1H-imidazol-2-yl)pyridinato; and tfpypz=2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridinato), were synthesized and their structures were characterized by NMR spectroscopy, mass spectroscopy and X-ray diffraction. These complexes showed phosphorescent emission with the emission maxima between 453 and 490 nm. Various spectrophotometric measurements, cyclic voltammetric studies, and density functional theory (DFT) calculations show that, unlike most of the phosphorescent cyclometalated iridium complexes, the lowest unoccupied molecular orbital (LUMO) energy and the emissive state of these iridium complexes are mainly controlled by the N,N'-heteroaromatic (N^N) ligand. Despite the fact that the LUMO levels of these complexes are mainly on the N^N ligands, the efficiencies of the electroluminescent (EL) devices are very high. For example, the EL devices using [Ir(mpmi)(2)(pypz)], [Ir(fpmi)(2)(pypz)], and [Ir(fpmi)(2)(tfpypz)] as the dopant emitters exhibited light- to deep-blue electrophosphorescence with external quantum efficiencies of 15.2, 14.1, and 7.6% and Commission Internationale d'nclairage (x,y) coordinates (CIE(x,y)) of (0.14, 0.27), (0.14, 0.18) and (0.14, 0.10), respectively. PMID:21732435

  7. Lipophilicity-dependent ruthenium N-heterocyclic carbene complexes as potential anticancer agents.

    PubMed

    Lv, Gaochao; Guo, Liubin; Qiu, Ling; Yang, Hui; Wang, Tengfei; Liu, Hong; Lin, Jianguo

    2015-04-28

    Five Ru(II)-N-heterocyclic carbenes (NHC) (1-5) were synthesized by reacting the appropriately substituted imidazolium chlorides with Ag2O, forming the NHC-silver chloride in situ followed by transmetalation with dimeric p-cymene ruthenium(II) dichloride. All the complexes were characterized by NMR and ESI-MS, and complex 1 was also characterized by single-crystal X-ray diffraction. The IC50 values of these five complexes were determined by the MTT-based assay on four human cancer cell lines, SKOV-3 (ovarian), PC-3 (prostate), MDA-MB-231 (breast) and EC109 (esophagus). The cytotoxicities of these complexes changed from a moderate effect to a fine one, corresponding to the increasing lipophilicity order of the complex of 2 < 1 < 3 < 4 < 5 (0.91, 0.88, 1.36, 1.85 and 2.62 for 15 respectively). Complex 5 showed the most cytotoxicity with the IC50 values 10.3 0.3 ?M for SKOV-3, 2.9 0.1 ?M for PC-3, 8.2 0.6 ?M for MDA-MB-231, 6.4 0.2 ?M for EC109 cell lines. Due to the superior cytotoxicity of complex 5 against the PC-3 cell lines, further biological evaluations were carried out to elucidate its action mechanism. The morphologic changes and cell cycle analysis showed that complex 5 can inhibit PC-3 cell lines by inducing cell cycle arrest at the G2/M phase. The DNA binding experiments further demonstrate that complex 5 has a better binding ability for DNA (Kb = 2.2 10(6) M(-1)) than complexes 1-4 (3.8 10(5), 7.0 10(5), 5.7 10(5), and 1.9 10(5) respectively). PMID:25797411

  8. 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

  9. 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. PMID:26477971

  10. 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(?N)] (?N 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. PMID:25280253

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

    PubMed

    Hans, Morgan; Lorkowski, Jan; Demonceau, Albert; Delaude, Lionel

    2015-01-01

    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 (ICyHBF4). 1,3-Dibenzylimidazolium tetrafluoroborate (IBnHBF4) 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 C(2) 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 (IMesHCl), 1,3-dimesitylimidazolium tetrafluoroborate (IMesHBF4), 1,3-dimesitylimidazolinium chloride (SIMesHCl), 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride (IDipHCl or IPrHCl), 1,3-bis(2,6-diisopropylphenyl)imidazolinium chloride (SIDipHCl or SIPrHCl), and 1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazolium chloride (IDip*HCl or IPr*HCl). PMID:26734080

  12. 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

  13. Structural and theoretical investigation of 2-iminoimidazolines--carbene analogues of iminophosphoranes.

    PubMed

    Tamm, Matthias; Petrovic, Dejan; Randoll, Sren; Beer, Stephan; Bannenberg, Thomas; Jones, Peter G; Grunenberg, Jrg

    2007-02-01

    The preparation of 2-iminoimidazolines - has been accomplished by the Staudinger reaction of the carbenes 1,3-di-tert-butylimidazolin-2-ylidene (), 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene (), 1,3-diisopropylimidazolin-2-ylidene (), 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (), 1,3-bis(2,6-diisopropylphenylimidazolin-2-ylidene () and 1,3,4,5-tetramethylimidazolin-2-ylidene () with trimethylsilyl azide (Me3SiN3) followed by desilylation of the resulting 2-trimethylsilyliminoimidazolines -. The X-ray crystal structures of and have been established, revealing C1-N1-Si1 angles that are more obtuse than the corresponding P-N-Si angles observed in related trimethylsilyl iminophosphoranes. Together with , the disilylated side product 1,3-diisopropyl-2-(trimethylsilylimino)-4-trimethylsilylimidazoline () has been isolated and structurally characterized. Cleavage of the N-Si bonds in and formation of is easily achieved by stirring in methanol. The molecular structures of the 2-iminoimidazolines are reported, indicating that the structural parameters are best described by non-ylidic resonance structures and that electron delocalization within the imidazole heterocycle does not play a crucial role in these imine systems. Compound forms a head-to-head dimer in the solid state via weak intermolecular N-H...N contacts, which have additionally been characterized by means of compliance constants. To further analyze the electronic structure of these imines in comparison to related guanidine ligands, the proton affinities (PAs) of the model compounds 2-imino-1,3-dimethylimidazoline (), 2-imino-1,3-dimethylimidazolidine () and tetramethylguanidine () have been calculated by means of density functional theory. Finally, the charge distribution in - and the relative contribution of relevant resonance structures have been determined using natural bond orbitals (NBO) and natural resonance theory (NRT). PMID:17252136

  14. N-Heterocyclic carbenes and charge separation in heterometallic s-block silylamides.

    PubMed

    Hill, Michael S; Kociok-Khn, Gabriele; MacDougall, Dugald J

    2011-06-01

    Addition of the N-heterocyclic carbene (NHC), 1,3-bis(2,6-di-isopropylphenyl)imidazol-2-ylidene (IPr), to equimolar quantities of group 1 and group 2 bis(trimethylsilyl)amides results in the isolation of charge separated species, [M(IPr)(2)](+)[M'{N(SiMe(3))(2)}(3)](-) (M = Li, Na, K; M' = Mg, Ca, Sr, Ba). Although these systems were found to be prone to the separation of oily, most likely liquid clathrate, materials, either slow cooling or careful diffusion of the less polar solvent hexane into toluene solutions yielded nine crystalline heterobimetallic complexes in which the coordination sphere of the cationic group 1 center was found by X-ray diffraction analysis to be provided by two IPr ligands. These derivatives are the first examples of any compounds in which coordination at the central alkali metal cation is provided exclusively by NHC ligands and, for the cases where M = Na, are the first instances of any type in which an NHC ligand is bound to sodium. The anionic group 2-containing component of each compound was found to comprise three bis(trimethylsilyl)amido ligands coordinated in an approximately trigonal array about the divalent metal center. The bonding within the unusual cationic components of the compounds has been investigated by density functional theoretical (DFT) methods. Natural Bond Orbital (NBO) analyses have revealed that the coordination is provided by donation of the sp-hydridized IPr lone pair into the valence s-orbital of the alkali metal cation and are consistent with weaker binding, and consequently more labile solution behavior, as group 1 is descended. PMID:21517018

  15. Electrochemiluminescent ruthenium(II) N-heterocyclic carbene complexes: a combined experimental and theoretical study.

    PubMed

    Barbante, Gregory J; Francis, Paul S; Hogan, Conor F; Kheradmand, Peyman R; Wilson, David J D; Barnard, Peter J

    2013-07-01

    A series of four Ru(II) complexes of the form [Ru(bpy)2(C(^)N)](2+) (where C(^)N is a bidentate pyridine-functionalized imidazolylidene- or benzimidazolylidene-based N-heterocyclic carbene (NHC) ligand and bpy is 2,2'-bipyridine) have been synthesized using a Ag(I) transmetalation protocol from the Ru(II) precursor compound, Ru(bpy)2Cl2. The synthesized azolium salts and Ru(II) complexes were characterized by elemental analysis, (1)H and (13)C NMR spectroscopy, cyclic voltammetry, and electronic absorption and emission spectroscopy. The molecular structures for two benzimidazolium salts and three Ru(II) complexes were determined by single crystal X-ray diffraction. The complexes display photoluminescence within the range 611-629 nm, with the emission wavelength of the benzimidazolylidene containing structures, slightly blue-shifted relative to the imidazolylidene containing complexes. All complexes exhibited a reversible, one-electron oxidation, which is assigned to the Ru(2+/3+) redox couple. When compared to [Ru(bpy)3](2+), complexes of imidazolylidene containing ligands were oxidized at more negative potentials, while those of the benzimidazolylidene containing ligands were oxidized at more positive potentials. All four complexes exhibited moderately intense electrochemiluminescence (ECL) with the obtained ECL spectra closely resembling the photoluminescence spectra. The ability to predictably fine-tune the highest occupied molecular orbital (HOMO) level of the Ru(II) complexes via the flexible synthetic strategy offered by NHCs is valuable for the design of ECL-based multiplexed detection strategies. PMID:23772555

  16. Nearly degenerate isomers of C(BH)2: cumulene, carbene, or carbone?

    PubMed

    Barua, Shiblee R; Allen, Wesley D; Kraka, Elfi; Jerabek, Paul; Sure, Rebecca; Frenking, Gernot

    2013-11-18

    The ground electronic state of C(BH)2 exhibits both a linear minimum and a peculiar angle-deformation isomer with a central B-C-B angle near 90. Definitive computations on these species and the intervening transition state have been executed by means of coupled-cluster theory including single and double excitations (CCSD), perturbative triples (CCSD(T)), and full triples with perturbative quadruples (CCSDT(Q)), in concert with series of correlation-consistent basis sets (cc-pVXZ, X=D, T, Q, 5, 6; cc-pCVXZ, X=T, Q). Final energies were pinpointed by focal-point analyses (FPA) targeting the complete basis-set limit of CCSDT(Q) theory with auxiliary core correlation, relativistic, and non-Born-Oppenheimer corrections. Isomerization of the linear species to the bent form has a minuscule FPA reaction energy of 0.02 kcal mol(-1) and a corresponding barrier of only 1.89 kcal mol(-1). Quantum tunneling computations reveal interconversion of the two isomers on a timescale much less than 1 s even at 0 K. Highly accurate CCSD(T)/cc-pVTZ and composite c~CCSDT(Q)/cc-pCVQZ anharmonic vibrational frequencies confirm matrix-isolation infrared bands previously assigned to linear C(BH)2 and provide excellent predictions for the heretofore unobserved bent isomer. Chemical bonding in the C(BH)2 species was exhaustively investigated by the atoms-in-molecules (AIM) approach, molecular orbital plots, various population analyses, local mode vibrations and force constants, unified reaction valley analysis (URVA), and other methods. Linear C(BH)2 is a cumulene, whereas bent C(BH)2 is best characterized as a carbene with little carbone character. Weak B-B attraction is clearly present in the unusual bent isomer, but its strength is insufficient to form a CB2 ring with a genuine boron-boron bond and attendant AIM bond path. PMID:24123325

  17. "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…

  18. "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 IMesHCl and NaOH to catalyze the formation of 1,3,4-triphenylcyclopentene from cinnamaldehyde and chalcone in water. Deprotonation of IMesHCl with NaOH forms the "N"-heterocyclic carbene IMes that reacts with cinnamaldehyde to form a homoenolate equivalent

  19. 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). PMID:23883399

  20. Rhodium-catalyzed NH insertion of pyridyl carbenes derived from pyridotriazoles: a general and efficient approach to 2-picolylamines and imidazo[1,5-a]pyridines.

    PubMed

    Shi, Yi; Gulevich, Anton V; Gevorgyan, Vladimir

    2014-12-15

    A general and efficient NH insertion reaction of rhodium pyridyl carbenes derived from pyridotriazoles was developed. Various NH-containing compounds, including amides, anilines, enamines, and aliphatic amines, smoothly underwent the NH insertion reaction to afford 2-picolylamine derivatives. The developed transformation was further utilized in a facile one-pot synthesis of imidazo[1,5-a]pyridines. PMID:25332116

  1. 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...

  2. A new palladium(II) complex of a functionalized N-heterocyclic carbene: Synthesis, characterization and application in Suzuki Miyaura cross-coupling reactions

    NASA Astrophysics Data System (ADS)

    Linninger, Claudia S.; Herdtweck, Eberhardt; Hoffmann, Stephan D.; Herrmann, Wolfgang A.; Kühn, Fritz E.

    2008-11-01

    trans-[PdBr 2(NHC)Im] was prepared by reacting the corresponding imidazolium (Im) salt with palladium(II) acetate in dimethylsulfoxide in an in-situ reaction without generating a free carbene. Both the salt and the complex were characterized spectroscopically and by X-ray structure analysis. The complex was tested in homogeneous Suzuki-Miyaura cross-coupling reactions.

  3. N-Heterocyclic carbene ligands bearing poly(ethylene glycol) chains: effect of the chain length on palladium-catalyzed coupling reactions employing aryl chlorides.

    PubMed

    Fujihara, Tetsuaki; Yoshikawa, Takahiro; Satou, Motoi; Ohta, Hidetoshi; Terao, Jun; Tsuji, Yasushi

    2015-12-21

    N-Heterocyclic carbenes bearing poly(ethylene glycol) chains of different lengths have been designed and employed as ligands in palladium-catalyzed coupling reactions. The catalyst system having longer chains was found to be highly efficient for Suzuki-Miyaura coupling and borylation reactions employing aryl chlorides under mild reaction conditions. PMID:26465096

  4. Suzuki-Miyaura cross-coupling of bulky anthracenyl carboxylates by using pincer nickel N-heterocyclic carbene complexes: an efficient protocol to access fluorescent anthracene derivatives.

    PubMed

    Xu, Mizhi; Li, Xingbao; Sun, Zheming; Tu, Tao

    2013-12-21

    A series of fluorescent (hetero)-aryl substituted anthracene derivatives were readily accessible from the corresponding bulky anthracen-9-yl carboxylates via Suzuki-Miyaura cross-coupling reactions by using pincer nickel N-heterocyclic carbene complex even at the catalyst loading as low as 0.1 mol% in the presence of catalytic amounts of PCy3. PMID:24177710

  5. Transition metal-induced activation of alkynes leading to metal carbene species: synthetic application to new ?-conjugated molecules

    NASA Astrophysics Data System (ADS)

    Abo, T.; Ohe, K.

    2008-03-01

    The in situ generation of furylcarbene complexes by means of transition metals was applied to catalytic carbene reactions, such as Wittig-type olefination and cycloisomerization reactions. In the presence of [Rh(OAc)2]2 as a catalyst and triphenylphosphine as a carbene accepter, carbonyl-ene-ynes 1a reacted with benzaldehyde to give a 2-styrylfuran derivative 3a. The reaction involving phosphine-ylide formation followed by Wittig-type olefination with aldehydes was applied to synthesis of furfurylidene-containing p-extended conjugated molecules. A Ruthenium catalyst underwent cycloisomerization of 1,2-bis(carbonylenyl)acetylene 10a,b to afford 2,2'-bifuran structures. The crystal structure of 5,5'-diphenyl-2,2'-bifuran 11b was determined by X-ray crystallography. The ORTEP drawings of 11b exhibited transoid and highly planar structure. The emission bands of the bisfuran 11b were observed at 414 and 440 nm, its quantum yield (84%) was higher than that of a similar 5,5'-diphenyl-2,2'-bithiophene.

  6. Relative rates of the reaction of (ethoxycarbonyl)carbene with several aromatic and heteroaromatic compounds. Selectivity and mechanism

    SciTech Connect

    Pomerantz, M.; Rooney, P.

    1988-09-02

    The relative rates of reaction of (ethoxycarbonyl)carbene (1), formed by the thermal decomposition of ethyl diazoacetate (2), with toluene, anisole, phenanthrene, pyridine, quinoline, acridine, furan, benzofuran, dibenzofuran, thiophene, benzothiophene, dibenzothiophene, pyrrole, indole, carbazole, fluorene, 1,2-dimethoxybenzene, 1,4-dimethoxybenzene, 1,2,4-trimethoxybenzene, 1-methoxynaphthalene, 2-methoxynaphthalene, 2,6-dimethoxynaphthalene, and 2,7-dimethoxynaphthalene versus naphthalene at 150/degrees/C were measured. The relative rate data for the four series toluene, naphthalene, and phenanthrene, the furans, the thiophenes, and the pyrroles are consistent with direct addition of 1 to the aromatic ring systems. Significantly, the more nucleophilic ring systems show a selectivity of up to a factor of about 100 relative to the simple benzene derivative toluene. The pyridine, quinoline, acridine series appears to react with 1 by an ylide mechanism, and in these cases, the selectivities are even larger, up to about 150 relative to toluene. Thus, unlike the reaction of 1 with a series of substituted benzenes, where the selectivity is fairly modest, the heteroaromatic systems studied here show selectivities that are quite large. Methoxy substitution on benzene and naphthalene gives rise to only limited increases in selectivity with one or two groups on the ring system; however, 1,2,4-trimethoxybenzene shows a significantly increased selectivity. Kinetic measurements were consistent with carbene formation being the rate-determining step in these reactions. 29 references, 3 tables.

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

    PubMed

    Campos, Jess; Ortega-Moreno, Laura; Conejero, Salvador; Peloso, Riccardo; Lpez-Serrano, Joaqun; 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 ?-agostic structure 4?a, whereas ?-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 ?-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

  8. Gold(I) complexes bearing mixed-donor ligands derived from N-heterocyclic carbenes.

    PubMed

    Chia, Eugene Y; Naeem, Saira; Delaude, Lionel; White, Andrew J P; Wilton-Ely, James D E T

    2011-07-01

    The new 2-phenylthiocarbamoyl-1,3-dimesitylimidazolium inner salt (IMesCSNPh) reacts with [AuCl(L)] in the presence of NH(4)PF(6) to yield [(L)Au(SCNPhIMes)](+) (L = PMe(3), PPh(3), PCy(3), CNBu(t)). The carbene-containing precursor [(IDip)AuCl] reacts with IMesCSNPh under the same conditions to afford the complex [(IDip)Au(SCNPhIMes)](+) (IDip = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). Treatment of the diphosphine complex [(dppm)(AuCl)(2)] with one equivalent of IMesCSNPh yields the digold metallacycle, [(dppm)Au(2)(SCNPhIMes)](2+), while reaction of [L(2)(AuCl)(2)] with two equivalents of IMesCSNPh results in [(L(2)){Au(SCNPhIMes)}(2)](2+) (L(2) = dppb, dppf, or dppa; dppb = 1,4-bis(diphenylphosphino)butane, dppf = 1,1'-bis(diphenylphosphino)ferrocene, dppa = 1,4-bis(diphenylphosphino)acetylene). The homoleptic complex [Au(SCNPhIMes)(2)](+) is formed on reaction of [AuCl(tht)] (tht = tetrahydrothiophene) with two equivalents of the imidazolium-2-phenylthiocarbamoyl ligand. This product reacts with AgOTf to yield the mixed metal compound [AuAg(SCNPhIMes)(2)](2+). Over time, the unusual trimetallic complex [Au(AgOTf)(2)(SCNPhIMes)(2)](+) is formed. The sulfur-oxygen mixed-donor ligands IMesCOS and SIMesCOS (SIMes = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) were used to prepare [(L)Au(SOCIMes)](+) and [(L)Au(SOCSIMes)](+) from [(L)AuCl] (L = PPh(3), CN(t)Bu). The bimetallic examples [(dppf){Au(SOCIMes)}(2)](2+) and [(dppf){Au(SOCSIMes)}(2)](2+) were synthesized from the reaction of [(dppf)(AuCl)(2)] with the appropriate ligand. Reaction of [(tht)AuCl] with one equivalent of IMesCOS or SIMesCOS yields [Au(SOCIMes)(2)](+) and [Au(SOCSIMes)(2)](+), respectively. The compounds [(Ph(3)P)Au(SCNPhIMes)]PF(6), [(Cy(3)P)Au(SCNPhIMes)]PF(6) and [Au(AgOTf)(2)(SCNPhIMes)(2)]OTf were characterized crystallographically. PMID:21369614

  9. 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){?(3)-P,C,P'-C(NCH2PCy2)2C10H6}] (2), while the latter reaction provides the asymmetric PNP-coordinated complex [RuCl2(PPh3){?(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){?(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){?(3)-P,C,P'-C(NCH2PR2)2C10H6}] (R = Cy 7a, R = Ph 7b, respectively), each as two isomers. The reactions of 1b with [Ru2(?-Cl)2Cl2(?-C6H3Me3)2] or [AuCl(THT)] (THT = tetrahydrothiophene) provide the bimetallic complexes [Ru2{?-H2C(NCH2PPh2)2C10H6}Cl4(?-C6H3Me3)2] (8) and [Au2{?-H2C(NCH2PPh2)2C10H6}Cl2] (9) without C-H activation occurring. PMID:26492361

  10. GrubbsHoveyda 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)(=CH2-(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

  11. 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

  12. H(C)Ag: a triple resonance NMR experiment for (109) Ag detection in labile silver-carbene complexes.

    PubMed

    Weske, Sebastian; Li, Yingjia; Wiegmann, Sara; John, Michael

    2015-04-01

    In silver complexes, indirect detection of (109) Ag resonances via (1) H,(109) Ag-HMQC frequently suffers from small or absent JHAg couplings or rapid ligand dissociation. In these cases, it would be favourable to employ H(X)Ag triple resonance spectroscopy that uses the large one-bond JXAg coupling (where the donor atom of the ligand X is the relay nucleus). We have applied an HMQC-based version of the H(C)Ag experiment to a labile silver-NHC complex (NHC=N-heterocyclic carbene) at natural (13) C isotopic abundance and variable temperature. In agreement with simulations, H(C)Ag detection became superior to (1) H,(109) Ag-HMQC detection above -20?C. PMID:25641122

  13. Fluorescent silver(I) and gold(I)-N-heterocyclic carbene complexes with cytotoxic properties: mechanistic insights.

    PubMed

    Citta, Anna; Schuh, Esther; Mohr, Fabian; Folda, Alessandra; Massimino, Maria Lina; Bindoli, Alberto; Casini, Angela; Rigobello, Maria Pia

    2013-08-01

    Silver(I) and gold(I)-N-heterocyclic carbene (NHC) complexes bearing a fluorescent anthracenyl ligand were examined for cytotoxicity in normal and tumor cells. The silver(I) complex exhibits greater cytotoxicity in tumor cells compared with normal cells. Notably, in cell extracts, this complex determines a more pronounced inhibition of thioredoxin reductase (TrxR), but it is ineffective towards glutathione reductase (GR). Both gold and silver complexes lead to oxidation of the thioredoxin system, the silver(I) derivative being particularly effective. In addition, the dimerization of peroxiredoxin 3 (Prx3) was also observed, demonstrating the ability of these compounds to reach the mitochondrial target. The fluorescence microscopy visualization of the subcellular distribution of the complexes shows a larger diffusion of these molecules in tumor cells with respect to normal cells. PMID:23661165

  14. 25 years of N-heterocyclic carbenes: activation of both main-group element-element bonds and NHCs themselves.

    PubMed

    Würtemberger-Pietsch, Sabrina; Radius, Udo; Marder, Todd B

    2016-04-14

    N-Heterocyclic carbenes (NHCs) are widely used ligands and reagents in modern inorganic synthesis as well as in homogeneous catalysis and organocatalysis. However, NHCs are not always innocent bystanders. In the last few years, more and more examples were reported of reactions of NHCs with main-group elements which resulted in modification of the NHC. Many of these reactions lead to ring expansion and the formation of six-membered heterocyclic rings involving insertion of the heteroatom into the C-N bond and migration of hydrides, phenyl groups or boron-containing fragments. Furthermore, a few related NHC rearrangements were observed some decades ago. In this Perspective, we summarise the history of NHC ring expansion reactions from the 1960s till the present. PMID:26675582

  15. An efficient N-heterocyclic carbene-ruthenium complex: application towards the synthesis of polyesters and polyamides.

    PubMed

    Malineni, Jagadeesh; Keul, Helmut; Möller, Martin

    2015-03-01

    The ruthenium benzimidazolylidene-based N-heterocyclic carbene (NHC) complex 4 catalyzes the direct dehydrogenative condensation of primary alcohols into esters and primary alcohols in the presence of amines to the corresponding amides in high yields. This efficient new catalytic system shows a high selectivity towards the conversion of diols to polyesters and of a mixture of diols and diamines to polyamides. The only side product formed in this reaction is molecular hydrogen. Remarkable is the conversion of hydroxytelechelic polytetrahydrofuran (Mn = 1000 g mol(-1))--a polydispers starting material--into a hydrolytically degradable polyether with ester linkages (Mn = 32 600 g mol(-1)) and, in the presence of aliphatic diamines, into a polyether with amide linkages in the back bone (Mn = 16 000 g mol(-1) ). PMID:25653190

  16. Possible formation of crystalline sodium carbene carbonate Na[subscript 2](CO)CO[subscript 3] at high pressure

    SciTech Connect

    Tschauner, O.; Kiefer, B.; McClure, J.; Sinogeikin, S.

    2010-05-24

    Combined experimental and ab-initio computational studies suggest that at pressures above 20 GPa and temperatures above 1500 K sodium formate deprotonizes under formation of Na{sub 2}{sup +} [C=O| CO{sub 3}{sup 2-}]. This new compound involves mesomeric C-O bonds with carbonate plus carbene units as limiting states and CO{sub 2} chains as intermediate. Sodium is six-fold coordinated by O-atoms. The formation of this new compound implies nucleophilic addition as reaction mechanism which is consistent with previously observed reduced stability of the H-O bond at these high pressures. The findings suggest further that the sextet state of carbon is energetically less unfavourable at high pressure than at ambient pressure.

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

    PubMed

    Bernardi, Thierry; Badel, Stphanie; Mayer, Pascal; Groelly, Jrome; de Frmont, Pierre; Jacques, Batrice; 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

  18. Synthesis and coordination compounds of a bis(imino)acenaphthene (BIAN)-supported N-heterocyclic carbene.

    PubMed

    Vasudevan, Kalyan V; Butorac, Rachel R; Abernethy, Colin D; Cowley, Alan H

    2010-08-21

    The bis(imino)acenaphthene-supported N-heterocyclic carbene IPr(BIAN) has been prepared by deprotonation of the precursor imidazolium chloride. Treatment of IPr(BIAN) imidazolium chloride with Ag(2)O afforded the silver complex [IPr(BIAN)]AgCl which can be converted into the corresponding gold complex [IPr(BIAN)]AuCl by reaction with (tht)AuCl (tht = tetrahydrothiophene). The iridium complex [IPr(BIAN)]Ir(COD)Cl was prepared by reaction of the imidazolium chloride with KO(t)Bu and [Ir(COD)Cl](2) and subsequently converted to the carbonyl complex [IPr(BIAN)]Ir(CO)(2)Cl by exposure to an atmosphere of CO. All new compounds were characterized by single-crystal X-ray diffraction, multinuclear NMR, MS and HRMS data. PMID:20625611

  19. Imidazolium Ionic Liquids, Imidazolylidene Heterocyclic Carbenes, and Zeolitic Imidazolate Frameworks for CO2 Capture and Photochemical Reduction.

    PubMed

    Wang, Sibo; Wang, Xinchen

    2016-02-01

    Imidazolium ionic liquids (ILs), imidazolylidene N-heterocyclic carbenes (NHCs), and zeolitic imidazolate frameworks (ZIFs) are imidazolate motifs which have been extensively investigated for CO2 adsorption and conversion applications. Summarized in this minireview is the recent progress in the capture, activation, and photochemical reduction of CO2 with these three imidazolate building blocks, from homogeneous molecular entities (ILs and NHCs) to heterogeneous crystalline scaffolds (ZIFs). The developments and existing shortcomings of the imidazolate motifs for their use in CO2 utilizations is assessed, with more of focus on CO2 photoredox catalysis. The opportunities and challenges of imidazolate scaffolds for future advancement of CO2 photochemical conversion for artificial photosynthesis are discussed. PMID:26683833

  20. INVERSE STABLE SUBORDINATORS

    PubMed Central

    MEERSCHAERT, MARK M.; STRAKA, PETER

    2013-01-01

    The inverse stable subordinator provides a probability model for time-fractional differential equations, and leads to explicit solution formulae. This paper reviews properties of the inverse stable subordinator, and applications to a variety of problems in mathematics and physics. Several different governing equations for the inverse stable subordinator have been proposed in the literature. This paper also shows how these equations can be reconciled. PMID:25045216

  1. Synthesis and characterization of divalent manganese, iron, and cobalt complexes in tripodal phenolate/N-heterocyclic carbene ligand environments.

    PubMed

    K, Martina; Hohenberger, Johannes; Adelhardt, Mario; Zolnhofer, Eva M; Mossin, Susanne; Heinemann, Frank W; Sutter, Jrg; Meyer, Karsten

    2014-03-01

    Two novel tripodal ligands, (BIMPN(Mes,Ad,Me))(-) and (MIMPN(Mes,Ad,Me))(2-), combining two types of donor atoms, namely, NHC and phenolate donors, were synthesized to complete the series of N-anchored ligands, ranging from chelating species with tris(carbene) to tris(phenolate) chelating arms. The complete ligand series offers a convenient way of tuning the electronic and steric environment around the metal center, thus, allowing for control of the complex's reactivity. This series of divalent complexes of Mn, Fe, and Co was synthesized and characterized by (1)H NMR, IR, and UV/vis spectroscopy as well as by single-crystal X-ray diffraction studies. Variable-temperature SQUID magnetization measurements in the range from 2 to 300 K confirmed high-spin ground states for all divalent complexes and revealed a trend of increasing zero-field splitting |D| from Mn(II), to Fe(II), to Co(II) complexes. Zero-field (57)Fe Mssbauer spectroscopy of the Fe(II) complexes 3, 4, 8, and 11 shows isomer shifts ? that increase gradually as carbenes are substituted for phenolates in the series of ligands. From the single-crystal structure determinations of the complexes, the different steric demand of the ligands is evident. Particularly, the molecular structure of 1-in which a pyridine molecule is situated next to the Mn-Cl bond-and those of azide complexes 2, 4, and 6 demonstrate the flexibility of these mixed-ligand derivatives, which, in contrast to the corresponding symmetrical TIMEN(R) ligands, allow for side access of, e.g., organic substrates, to the reactive metal center. PMID:24299260

  2. Random stable matchings

    NASA Astrophysics Data System (ADS)

    Mertens, Stephan

    2005-10-01

    The stable matching problem is a prototype model in economics and social sciences where agents act selfishly to optimize their own satisfaction, subject to mutually conflicting constraints. A stable matching is a pairing of adjacent vertices in a graph such that no unpaired vertices prefer each other to their partners under the matching. The problem of finding stable matchings is known as the stable marriage problem (on bipartite graphs) or as the stable room-mates problem (on the complete graph). It is well known that not all instances on non-bipartite graphs admit a stable matching. Here we present numerical results for the probability that a graph with n vertices and random preference relations admits a stable matching. In particular we find that this probability decays algebraically on graphs with connectivity ?(n) and exponentially on regular grids. On finite connectivity Erds-Rnyi graphs the probability converges to a value larger than zero. On the basis of the numerical results and some heuristic reasoning we formulate five conjectures on the asymptotic properties of random stable matchings.

  3. 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

  4. 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 (0.1500??M), and can be used for the luminescent imaging of endocytosis of the complex in these cells. PMID:25765974

  5. 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.

  6. Enantioselective N-Heterocyclic Carbene-Catalyzed ?-Hydroxylation of Enals Using Nitroarenes: An Atom Transfer Reaction That Proceeds via Single Electron Transfer

    PubMed Central

    2015-01-01

    A novel oxidative N-heterocyclic carbene-catalyzed reaction pathway has been discovered. Alkyl and aryl enals undergo ?-hydroxylation via oxygen atom transfer from electron-deficient nitrobenzenes, followed by trapping of the resultant acyl azolium by the solvent. The proposed mechanism involves a single electron transfer event to initiate the reaction followed by radical recombination. This represents a profound mechanistic departure from the established two-electron disconnects in NHC catalysis. PMID:25302860

  7. A Bis(Diphosphanyl N-Heterocyclic Carbene) Gold Complex: A Synthon for Luminescent Rigid AuAg2 Arrays and Au5 and Cu6 Double Arrays.

    PubMed

    Ai, Pengfei; Mauro, Matteo; De Cola, Luisa; Danopoulos, Andreas A; Braunstein, Pierre

    2016-03-01

    A mononuclear bis(NHC)/Au(I) (NHC=N-heterocyclic carbene) cationic complex with a rigid bis(phosphane)-functionalized NHC ligand (PCNHC P) was used to construct linear Au3 and Ag2 Au arrays, a Au5 cluster with two intersecting crosslike Au3 arrays, and an unprecedented Cu6 complex with two parallel Cu3 arrays. The impact of metallophilic interactions on photoluminescence was studied experimentally. PMID:26823329

  8. Synthesis of novel polysubstituted N-benzyl-1H-pyrroles via a cascade reaction of alkynyl Fischer carbenes with α-imino glycine methyl esters.

    PubMed

    de la Cruz, Fabiola N; López, Julio; Jiménez-Halla, J Óscar C; Flores-Álamo, Marcos; Tamaríz, Joaquín; Delgado, Francisco; Vázquez, Miguel A

    2015-12-28

    An efficient and simple synthesis of novel and densely substituted N-benzyl-1H-pyrroles 6a-r is described by a 1,4-addition/isomerization/ring closure/demetalation cascade process of alkynyl Fischer carbene complexes 1a-f and 2a and α-imino glycine methyl esters 3a, b, d, g, h, and k promoted with LDA. PMID:26488365

  9. 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.

  10. Nickel(0)/N-Heterocyclic Carbene-Catalyzed Asymmetric [2 + 2 + 2] Cycloaddition of Two Enones and an Alkyne: Access to Cyclohexenes with Four Contiguous Stereogenic Centers.

    PubMed

    Kumar, Ravindra; Tokura, Hiromu; Nishimura, Akira; Mori, Tadashi; Hoshimoto, Yoichi; Ohashi, Masato; Ogoshi, Sensuke

    2015-12-18

    A nickel(0)/chiral N-heterocyclic carbene (NHC)-catalyzed fully intermolecular, enantioselective [2 + 2 + 2] cycloaddition of two enones and an alkyne has been developed to access enantioenriched cyclohexenes. A single diastereomer was obtained with a successive generation of four contiguous stereogenic centers. The absolute configuration of cyclohexene derivative 3aa was determined by X-ray diffraction and circular dichroism (CD) spectral studies. PMID:26618525

  11. C-H activation in Ir(III) and N-demethylation in Pt(II) complexes with mesoionic carbene ligands: examples of monometallic, homobimetallic and heterobimetallic complexes.

    PubMed

    Maity, Ramananda; Tichter, Tim; van der Meer, Margarethe; Sarkar, Biprajit

    2015-11-14

    Mononuclear Pt(II) and the first dinuclear Pt(II) complexes along with a cyclometalated heterobimetallic Ir(III)/Pd(II) complex bearing mesoionic carbene donor ligands are presented starting from the same bis-triazolium salt. The mononuclear Pt(II) complex possesses a free triazole moiety which is generated from the corresponding triazolium salt through an N-demethylation reaction, whereas the mononuclear Ir(III) complex features an unreacted triazolium unit. PMID:26443200

  12. [3,3]-Sigmatropic Rearrangement vs. Carbene Formation in Gold-Catalyzed Transformations of Alkynyl Aryl Sulfoxides: Mechanistic Studies and Expanded Reaction Scope

    PubMed Central

    Lu, Biao; Li, Yuxue; Wang, Youliang; Aue, Donald H.; Luo, Yingdong; Zhang, Liming

    2013-01-01

    Gold-catalyzed intramolecular oxidation of terminal alkynes with an arenesulfinyl group as the tethered oxidant is a reaction in gold chemistry of high impact, as it introduced to the field the highly-valued concept of gold carbene generation via alkyne oxidation. The proposed intermediacy of ?-oxo gold carbenes in these reactions, however, has never been substantiated. Detailed experimental studies suggest that the involvement of such reactive intermediates in the formation of dihydrobenzothiepinones is highly unlikely. Instead, a [3,3]-sigmatropic rearrangement of the initial cyclization intermediate offers a reaction path that can readily explain the high reaction efficiency and the lack of sulfonium formation. With internal alkyne substrates, however, the generation of a gold carbene species becomes competitive with the [3,3]-sigmatropic rearrangement. This reactive intermediate, nevertheless, does not proceed to afford the Friedel-Crafts type cyclization product. Extensive Density Functional Theory studies support the mechanistic conclusion that the cyclized product is formed via an intramolecular [3,3]-sigmatropic rearrangement instead of the previously proposed Friedel-Crafts type cyclization. With the new mechanistic insight, the product scope of this versatile formation of mid-sized sulfur-containing cycloalkenones has been expanded readily to various dihydrobenzothiocinones, a tetrahydrobenzocyclononenone, and even those without the entanglement of a fused benzene ring. Besides gold, Hg(OTf)2 can be an effective catalyst, thereby offering a cheap alternative for this intramolecular redox reaction. PMID:23731178

  13. Coinage-metal mediated ring opening of cis-1,2-dimethoxycyclopropane: trends from the gold, copper, and silver Fischer carbene bond strength.

    PubMed

    Batiste, Laurent; Chen, Peter

    2014-07-01

    N-heterocyclic carbene (NHC) supported coinage metal cations proved to react in the gas phase with the electron-rich cis-1,2-dimethoxycyclopropane. Upon Collision Induced Dissociation (CID), several spectrometric fragment-ion signals were observed, one corresponding to the recovery of the bare cation IMes-M(+) (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) and the second to the methoxymethylidene metal complex IMes-M-[HCOCH3](+). The gold and copper complexes appear to stabilize the carbene sufficiently enough to promote the latter channel. On the contrary, the silver complex binds weakly to the methoxymethylidene moiety as observed by the predominance of the bare cation IMes-M(+) channel. Density Functional Theory (DFT) investigations of the Potential Energy Surface and Bond Energy Decomposition Analyses provided results that correlate well with the experimental data. In the case of the bare cation channel, two distinct reaction pathways were found: a straightforward decoordination of the cyclopropane and a cationic rearrangement of the three-membered ring into a dimethoxypropylene isomer before dissociation. However, for the abstraction of the methoxymethylidene moiety by the metal cation, only one pathway was found. In analogy to earlier studies by other groups, we found the trend Au > Cu > Ag for the metal-carbene bond strength. PMID:24911627

  14. A Stable Urban Ecosystem

    ERIC Educational Resources Information Center

    Meier, Richard L.

    1976-01-01

    Describes a model for the future evolution of a stable ecosystem in a densely-populated society. Discusses designs for limiting population growth, resource-conserving settlements, and ways to feed growing cities. (MLH)

  15. Synthesis and Suzuki Reactions of N-Heterocyclic Carbene Difluoro(aryl)-boranes.

    PubMed

    Nerkar, Swapnil; Curran, Dennis P

    2015-07-17

    Readily available NHC-arylboranes (NHC-BH2Ar) are converted in high yield to stable NHC-difluoro(aryl)boranes (NHC-BF2Ar) by treatment with 2 equiv of 1-chloromethyl-4-fluoro-1,4-diazonia-bicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor). In turn, the NHC-difluoro(aryl)boranes participate directly in Suzuki reactions under conditions previously used for anionic trifluoroborate salts. Accordingly, NHC-difluoroboranes are a new class of stable precursors for Suzuki reactions. PMID:26147155

  16. Air-Stable (CAAC)CuCl and (CAAC)CuBH4 Complexes as Catalysts for the Hydrolytic Dehydrogenation of BH3NH3.

    PubMed

    Hu, Xingbang; Soleilhavoup, Michèle; Melaimi, Mohand; Chu, Jiaxiang; Bertrand, Guy

    2015-05-11

    The first stable copper borohydride complex [(CAAC)CuBH4] [CAAC = cyclic(alkyl)(amino)carbene] bearing a single monodentate ligand was prepared by addition of NaBH4 or BH3NH3 to the corresponding [(CAAC)CuCl] complex. Both complexes are air-stable and promote the catalytic hydrolytic dehydrogenation of ammonia borane. The amount of hydrogen released reaches 2.8 H2/BH3 NH3 with a turnover frequency of 8400 mol H2 molcat(-1) h(-1) at 25 °C. In a fifteen-cycle experiment, the catalyst was reused without any loss of efficiency. PMID:25802096

  17. 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 progressively saturated with fractures as time passed from its initial consolidation. The comparison of time-constrained paleostress data derived from three different locations of the shield shows a remarkably similar stress evolution through time, despite the different geological frameworks of the investigated areas. This suggests that the southern SS has behaved as a coherent rigid crustal block since the Late Mesoproterozoic. By that time, the SS had already reached structural maturity with respect to the saturation of brittle structural features. Therefore, structural reactivation rather than generation of new faults and fractures is the key mechanism that has controlled the mechanical evolution of the shield and that will steer its future evolution within the brittle regime. Comparable brittle structural histories within parts of the shield that are far apart also imply that far-field stresses can propagate over large distances and can lead to similar deformational histories, with the local geological conditions only playing a second-order role on the final brittle strain pattern recorded by the rock.

  18. 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

  19. N-heterocyclic carbene gold(I) and silver(I) complexes bearing functional groups for bio-conjugation

    PubMed Central

    Garner, Mary E.; Niu, Weijia; Chen, Xigao; Ghiviriga, Ion; Tan, Weihong; Veige, Adam S.

    2015-01-01

    This work describes several synthetic approaches to append organic functional groups to gold and silver N-heterocyclic carbene (NHC) complexes suitable for applications in biomolecule conjugation. Carboxylate appended NHC ligands (3) lead to unstable AuI complexes that convert into bis-NHC species (4). A benzyl protected carboxylate NHC-AuI complex 2 was synthesized but deprotection to produce the carboxylic acid functionality could not be achieved. A small library of new alkyne functionalized NHC proligands were synthesized and used for subsequent silver and gold metalation reactions. The alkyne appended NHC gold complex 13 readily react with benzyl azide in a copper catalyzed azide-alkyne cycloaddition reaction to form the triazole appended NHC gold complex 14. Cell cytotoxicity studies were performed on DLD-1 (colorectal adenocarcinoma), Hep-G2 (hepatocellular carcinoma), MCF-7 (breast adenocarcinoma), CCRF-CEM (human T-Cell leukemia), and HEK (human embryonic kidney). Complete spectroscopic characterization of the ligands and complexes was achieved using 1H and 13C NMR, gHMBC, ESI-MS, and combustion analysis. PMID:25490699

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

    PubMed

    Pazio, A; Wo?niak, 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

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

    PubMed

    Franz, Daniel; Szilvsi, 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 (L(Dip)N)AlTe(L(Et))2 (L(Dip)=1,3-(2,6-diisopropylphenyl)-imidazolin-2-imine, L(Et)=1,3-diethyl-4,5-dimethyl-imidazolin-2-ylidene). Unique features of (L(Dip)N)AlTe(L(Et))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 (L(Dip)N)AlTe(L(Et))2 equilibrates with dimeric {(L(Dip)N)AlTe(L(Et))}2 in which the chalcogen atoms assume their common role as bridges between the metal centres. These findings demonstrate that (L(Dip)N)AlTe(L(Et))2 comprises the elusive Al=Te double bond in the form of an N-heterocyclic carbene-stabilized species. PMID:26612781

  2. Experimental and computational studies on the mechanism of zwitterionic ring-opening polymerization of ?-valerolactone with N-heterocyclic carbenes.

    PubMed

    Acharya, Ashwin K; Chang, Young A; Jones, Gavin O; Rice, Julia E; Hedrick, James L; Horn, Hans W; Waymouth, Robert M

    2014-06-19

    Experimental and computational investigations of the zwitterionic ring-opening polymerization (ZROP) of ?-valerolactone (VL) catalyzed by the N-heterocyclic carbenes (NHC) 1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene (1) and 1,3,4,5-tetramethyl-imidazol-2-ylidene (2) were carried out. The ZROP of ?-valerolactone generates cyclic poly(valerolactone)s whose molecular weights are higher than predicted from [VL]0/[NHC]0. Kinetic studies reveal the rate of polymerization is first order in [VL] and first order in [NHC]. Density functional theory (DFT) calculations were carried out to elucidate the key steps involved in the ring-opening of ?-valerolactone and its subsequent oligomerization. These studies have established that the initial steps of the mechanism involve nucleophilic attack of the NHC on ?-valerolactone to form a zwitterionic tetrahedral intermediate. DFT calculations indicate that the highest activation barrier of the entire mechanism is associated with the ring-opening of the tetrahedral intermediate formed from the NHC and ?-valerolactone, a result consistent with inefficient initiation to generate reactive zwitterions. The large barrier in this step is due to the fact that ring-opening requires a partial positive charge to develop next to the directly attached NHC moiety which already bears a delocalized positive charge. PMID:24702523

  3. 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…

  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. Stable Coulomb Bubbles?

    SciTech Connect

    Moretto, L.; Tso, K.; Wozniak, G.

    1997-02-01

    Coulomb bubbles, though stable against monopole displacement, are unstable at least with respect to quadrupole and octupole distortions. We show that there exists a temperature at which the pressure of the vapor filling the bubble stabilizes all the radial modes. In extremely thin bubbles, the crispation modes become unstable due to the surface-surface interaction. {copyright} {ital 1997} {ital The American Physical Society}

  6. Calix[4]arenes with one and two N-linked imidazolium units as precursors of N-heterocyclic carbene complexes. Coordination chemistry and use in Suzuki-Miyaura cross-coupling.

    PubMed

    Brenner, Eric; Matt, Dominique; Henrion, Mickaël; Teci, Matthieu; Toupet, Loïc

    2011-10-14

    The calix[4]arene-imidazolium salts 5-(3-butyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxy-calix[4]arene bromide (cone) (2), and 5,11-bis(3-alkyl-1-imidazolylium)-25,26,27,28-tetrabenzyloxycalix[4]arene diiodide (cone) (R = methyl, 3a; R = n-butyl, 3b) have been synthesised. Reaction of 2 in dioxane with PdCl(2) in the presence of CsCO(3) and KBr (80 °C, 24 h) gives the carbene complex trans-[PdBr(2)(calix-monocarbene)(2)] (14), containing two N-heterocyclic carbene ligands derived from 2 (yield: 63%). Repeating the reaction in pyridine instead of dioxane gives the mixed pyridine-carbene complex trans-[PdBr(2)(calix-carbene)(pyridine)] (15) in 75% yield. Treatment of the bis-imidazolium salt 3a with [Pd(OAc)(2)] affords a chelate complex, trans-[PdI(2){calix-bis(carbene)}] (16), in which a metallo-(bis-carbene) fragment caps the upper rim of the calixarene basket. Complex 16, as well as its analogue 17, obtained from 3b, display apparent C(s)-symmetry in solution. This is not the case in the solid state, a single X-ray diffraction study carried out for 16 revealing a pinced cone structure for the calixarene skeleton, which reduces the symmetry to C(1). The chelate complex 17 shows poor activity in Suzuki-Miyaura cross-coupling of phenyl boronic acid and p-tolyl halides, an observation that suggests the presence of a strained metallocyclic unit preventing easy stereochemical rearrangement to an active species. Unlike 17, complexes 14 and 15 show good activities in cross-coupling. A comparative study using the carbene precursor 1-butyl-3-(2,6-diisopropylphenyl)imidazolium bromide (18), which is devoid of the receptor fragment, strongly suggests that the carbene ligands of 14 and 15 operate typically as bulky NHC-ligands. PMID:21879086

  7. Carbene-induced synthesis of the first borironium cations using the [(?(5)-C5Me5)Fe(CO)2](-) anion as an unlikely leaving group.

    PubMed

    Braunschweig, Holger; Dewhurst, Rian D; Ferkinghoff, Katharina

    2015-12-15

    Reaction of N-heterocyclic carbenes with ferroborirene complex [{(?(5)-C5Me5)Fe(CO)2}{BC2(SiMe3)2}] results in heterolytic Fe-B bond cleavage, yielding borironium ions, a new class of boron-containing heterocycles. The reaction rests on the surprising ability of the reactive [(?(5)-C5Me5)Fe(CO)2](-) anion to act as a leaving group. The properties of these species were investigated by multinuclear NMR spectroscopy, as well as single-crystal X-ray diffraction. PMID:26511336

  8. Confocal and fluorescence lifetime imaging sheds light on the fate of a pyrene-tagged carbon monoxide-releasing Fischer carbene chromium complex.

    PubMed

    Arrowsmith, Rory L; Atkin, Anthony J; Botchway, Stanley W; Fairlamb, Ian J S; Lynam, Jason M; Moir, James W B; Pascu, Sofia I; Ward, Jonathan S; Zhang, Wei-Qiang

    2015-03-21

    The synthesis of a new pyrene-containing Fischer carbene complex is described. The complex has a broad absorbance spectrum between 300 and 400 nm and, on excitation at 345 nm in CH2Cl2 solution, emission is observed at 395 and 415 nm. Emission is also observed in PBS buffer, but in this case the resulting spectra are much broader. Confocal and fluorescence lifetime imaging indicate that emission occurs on treating HeLa cells with the complex and co-localisation studies demonstrate that this is from the mitochondria and lipid-rich regions of the cell. PMID:25553721

  9. Evaluation of the carbene hydride mechanism in the carbon-carbon bond formation process of alkane metathesis through a DFT study.

    PubMed

    Schinzel, Sandra; Chermette, Henry; Copéret, Christophe; Basset, Jean-Marie

    2008-06-25

    Olefin metathesis on a silica supported tantalumhydridocarbene complex, the key carbon-carbon making process in alkane metathesis, requires a large number of elementary steps in contrast to the known olefin metathesis pathway, which corresponds to successive [2 + 2]-cycloaddition and cycloreversion steps. The direct pathway is forbidden because it requires the formation of a high energy reaction intermediates, an olefin adduct of trigonal bipyramid (TBP) geometry, where the carbene is trans to an hydride ligand. Extra low-energy steps are therefore necessary to connect the reactants to products, the key being a turnstile interconversion at the metallacyclobutane intermediates. PMID:18510314

  10. Highly Unsaturated Platinum and Palladium Carbenes PtC3 and PdC3 Isolated and Characterized in the Gas Phase.

    PubMed

    Bittner, Dror M; Zaleski, Daniel P; Tew, David P; Walker, Nicholas R; Legon, Anthony C

    2016-03-01

    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

  11. Versatile synthesis of cationic N-heterocyclic carbene-gold(i) complexes containing a second ancillary ligand. Design of heterobimetallic ruthenium-gold anticancer agents.

    PubMed

    Fernández-Gallardo, Jacob; Elie, Benelita T; Sanaú, Mercedes; Contel, María

    2016-02-11

    We describe a versatile and quick route to cationic gold(i) complexes containing N-heterocyclic carbenes and a second ancillary ligand (such as phosphanes, phosphites, arsines and amines) of interest for the synthesis of compounds with potential catalytic and medicinal applications. The general synthetic strategy has been applied in the preparation of novel cationic heterobimetallic ruthenium(ii)-gold(i) complexes that are highly cytotoxic to renal cancer Caki-1 and colon cancer HCT 116 cell lines while showing a synergistic effect and being more selective than their monometallic counterparts. PMID:26804743

  12. 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

  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. Synthesis of novel synthetic intermediates from the reaction of benzimidazole and triazole carbenes with ketenimines and their application in the construction of spiro-pyrroles.

    PubMed

    Mo, Jun-Ming; Ma, Yang-Guang; Cheng, Ying

    2009-12-01

    2-(2-Alkoxycarbonyl-1-arylamino-1-propenyl)benzimidazolium and 5-(2-alkoxycarbonyl-1-arylamino-1-propenyl)triazolium salts were synthesized in good yields from the reaction of benzimidazole and triazole carbenes with ketenimines. Upon treatment with a base, both salts were converted into novel 1,3-dipoles which underwent [3+2] cycloaddition reactions with electron-deficient alkynes and allenes to produce benzimidazole-spiro-pyrroles or triazole-spiro-pyrroles. This work provides novel synthons for the construction of multifunctional spiro-pyrrole derivatives that are not easy accessible by other synthetic methods and are potentially amenable to further transformations. PMID:19907793

  15. Synthesis, electronic structure, and magnetism of [Ni(6-Mes)2]+: a two-coordinate nickel(I) complex stabilized by bulky N-heterocyclic carbenes.

    PubMed

    Poulten, Rebecca C; Page, Michael J; Algarra, Andrs G; Le Roy, Jennifer J; Lpez, Isidoro; Carter, Emma; Llobet, Antoni; Macgregor, Stuart A; Mahon, Mary F; Murphy, Damien M; Murugesu, Muralee; Whittlesey, Michael K

    2013-09-18

    The two-coordinate cationic Ni(I) bis-N-heterocyclic carbene complex [Ni(6-Mes)2]Br (1) [6-Mes =1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene] has been structurally characterized and displays a highly linear geometry with a C-Ni-C angle of 179.27(13). Density functional theory calculations revealed that the five occupied metal-based orbitals are split in an approximate 2:1:2 pattern. Significant magnetic anisotropy results from this orbital degeneracy, leading to single-ion magnet (SIM) behavior. PMID:23971827

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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, carbenebis(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(?4-C8H12) (3), {PhB(OxMe2)2ImMes}Rh(?4-C8H12) (4), {PhB(OxMe2)2ImMes}Rh(CO)2 (5), {PhB(OxMe2)2ImMes}Ir(?4-C8H12) (6), and {PhB(OxMe2)2ImMes}Ir(CO)2 (7) are synthesized along with ToMM(?4-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(?-Cl)(?2-C8H14)2]2 (M = Rh, Ir) provide {?4-PhB(OxMe2)2ImMes?CH2}Rh(?-H)(?-Cl)Rh(?2-C8H14)2 (10) and {PhB(OxMe2)2ImMes}IrH(?3-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 CH bond oxidative addition providing the compounds {?4-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-[Ir](H)(Ph) complex. Alternatively, the rhodium carbonyl 5 or iridium isocyanide {PhB(OxMe2)2ImMes}Ir(CO)CNtBu (15) reacts with PhSiH3 in the dark to form the silyl compound {PhB(OxMe2)2ImMes}RhH(SiH2Ph)CO (14) or {PhB(OxMe2)2ImMes}IrH(SiH2Ph)CNtBu (17). These examples demonstrate the enhanced thermal reactivity of {PhB(OxMe2)2ImMes}-supported iridium and rhodium carbonyl compounds in comparison to tris(oxazolinyl)borate, tris(pyrazolyl)borate, and cyclopentadienyl-supported compounds.

  3. Carbon monoxide induced reductive elimination of disulfide in an N-heterocyclic carbene (NHC)/thiolate dinitrosyl iron complex (DNIC).

    PubMed

    Pulukkody, Randara; Kyran, Samuel J; Bethel, Ryan D; Hsieh, Chung-Hung; Hall, Michael B; Darensbourg, Donald J; Darensbourg, Marcetta Y

    2013-06-01

    Dinitrosyliron complexes (DNICs) are organometallic-like compounds of biological significance in that they appear in vivo as products of NO degradation of iron-sulfur clusters; synthetic analogues have potential as NO storage and releasing agents. Their reactivity is expected to depend on ancillary ligands and the redox level of the distinctive Fe(NO)2 unit: paramagnetic {Fe(NO)2}(9), diamagnetic dimerized forms of {Fe(NO)2}(9) and diamagnetic {Fe(NO)2}(10) DNICs (Enemark-Feltham notation). The typical biological ligands cysteine and glutathione themselves are subject to thiolate-disulfide redox processes, which when coupled to DNICs may lead to intricate redox processes involving iron, NO, and RS(-)/RS. Making use of an N-heterocyclic carbene-stabilized DNIC, (NHC)(RS)Fe(NO)2, we have explored the DNIC-promoted RS(-)/RS oxidation in the presence of added CO wherein oxidized {Fe(NO)2}(9) is reduced to {Fe(NO)2}(10) through carbon monoxide (CO)/RS ligand substitution. Kinetic studies indicate a bimolecular process, rate = k [Fe(NO)2](1)[CO](1), and activation parameters derived from kobs dependence on temperature similarly indicate an associative mechanism. This mechanism is further defined by density functional theory computations. Computational results indicate a unique role for the delocalized frontier molecular orbitals of the Fe(NO)2 unit, permitting ligand exchange of RS and CO through an initial side-on approach of CO to the electron-rich N-Fe-N site, ultimately resulting in a 5-coordinate, 19-electron intermediate with elongated Fe-SR bond and with the NO ligands accommodating the excess charge. PMID:23668326

  4. 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

  5. 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…

  6. gem-Difluoroolefination of Diazo Compounds with TMSCF3 or TMSCF2Br: Transition-Metal-Free Cross-Coupling of Two Carbene Precursors.

    PubMed

    Hu, Mingyou; Ni, Chuanfa; Li, Lingchun; Han, Yongxin; Hu, Jinbo

    2015-11-18

    A new olefination protocol for transition-metal-free cross-coupling of two carbene fragments arising from two different sources, namely, a nonfluorinated carbene fragment resulting from a diazo compound and a difluorocarbene fragment derived from Ruppert-Prakash reagent (TMSCF3) or TMSCF2Br, has been developed. This gem-difluoroolefination proceeds through the direct nucleophilic addition of diazo compounds to difluorocarbene followed by elimination of N2. Compared to previously reported Cu-catalyzed gem-difluoroolefination of diazo compounds with TMSCF3, which possesses a narrow substrate scope due to a demanding requirement on the reactivity of diazo compounds and in-situ-generated CuCF3, this transition-metal-free protocol affords a general and efficient approach to various disubstituted 1,1-difluoroalkenes, including difluoroacrylates, diaryldifluoroolefins, as well as arylalkyldifluoroolefins. In view of the ready availability of diazo compounds and difluorocarbene reagents and versatile transformations of 1,1-difluoroalkenes, this new gem-difluoroolefination method is expected to find wide applications in organic synthesis. PMID:26501359

  7. Marginally Stable Nuclear Burning

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; Altamirano, D.

    2012-01-01

    Thermonuclear X-ray bursts result from unstable nuclear burning of the material accreted on neutron stars in some low mass X-ray binaries (LMXBs). Theory predicts that close to the boundary of stability oscillatory burning can occur. This marginally stable regime has so far been identified in only a small number of sources. We present Rossi X-ray Timing Explorer (RXTE) observations of the bursting, high- inclination LMXB 4U 1323-619 that reveal for the first time in this source the signature of marginally stable burning. The source was observed during two successive RXTE orbits for approximately 5 ksec beginning at 10:14:01 UTC on March 28, 2011. Significant mHz quasi- periodic oscillations (QPO) at a frequency of 8.1 mHz are detected for approximately 1600 s from the beginning of the observation until the occurrence of a thermonuclear X-ray burst at 10:42:22 UTC. The mHz oscillations are not detected following the X-ray burst. The average fractional rms amplitude of the mHz QPOs is 6.4% (3 - 20 keV), and the amplitude increases to about 8% below 10 keV.This phenomenology is strikingly similar to that seen in the LMXB 4U 1636-53. Indeed, the frequency of the mHz QPOs in 4U 1323-619 prior to the X-ray burst is very similar to the transition frequency between mHz QPO and bursts found in 4U 1636-53 by Altamirano et al. (2008). These results strongly suggest that the observed QPOs in 4U 1323-619 are, like those in 4U 1636-53, due to marginally stable nuclear burning. We also explore the dependence of the energy spectrum on the oscillation phase, and we place the present observations within the context of the spectral evolution of the accretion-powered flux from the source.

  8. 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.

  9. Bi-stable optical actuator

    DOEpatents

    Holdener, Fred R. (Tracy, CA); Boyd, Robert D. (Livermore, CA)

    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.

  10. Stable superstring relics

    SciTech Connect

    Chang, S.; Coriano, C.; Faraggi, A.E. |

    1996-05-15

    The authors investigate the cosmological constraints on exotic stable matter states which arise in realistic free fermionic superstring models. These states appear in the superstring models due to a ``Wilson-line`` breaking of the unifying non-Abelian gauge symmetry. In the models that they consider the unifying SO(10) gauge symmetry is broken at the string level to SO(6) x SO(4), SU(5) x U(1) or SU(3) x SU(2) x U(1). The exotic matter states are classified according to the patterns of the SO(10) symmetry breaking. In SO(6) x XO(4) and SU(5) x U(1) type models one obtains fractionally charged states with Q{sub e.m.} = {+-}1/2. In SU(3) x SU(2) x U(1) type models one also obtains states with the regular charges under the Standard Model gauge group but with ``fractional`` charges under the U(1){sub z{prime}} symmetry. These states include down-like color triplets and electroweak doublets, as well as states which are Standard Model singlets. By analyzing the renormalizable and nonrenormalizable terms of the superpotential in a specific superstring model, the authors show that these exotic states can be stable. They investigate the cosmological constraints on the masses and relic density of the exotic states. They propose that, while the abundance and the masses of the fractionally charged states are highly constrained, the Standard Model-like states, and in particular the Standard Model singlet, are good dark matter candidates.

  11. 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. PMID:21543623

  12. 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

  13. Stable Anisotropic Materials.

    PubMed

    Li, Yijing; Barbic, Jernej

    2015-10-01

    The Finite Element Method (FEM) is commonly used to simulate isotropic deformable objects in computer graphics. Several applications (wood, plants, muscles) require modeling the directional dependence of the material elastic properties in three orthogonal directions. We investigate linear orthotropic materials, a special class of linear anisotropic materials where the shear stresses are decoupled from normal stresses, as well as general linear (non-orthotropic) anisotropic materials. Orthotropic materials generalize transversely isotropic materials, by exhibiting different stiffness in three orthogonal directions. Orthotropic materials are, however, parameterized by nine values that are difficult to tune in practice, as poorly adjusted settings easily lead to simulation instabilities. We present a user-friendly approach to setting these parameters that is guaranteed to be stable. Our approach is intuitive as it extends the familiar intuition known from isotropic materials. Similarly to linear orthotropic materials, we also derive a stability condition for a subset of general linear anisotropic materials, and give intuitive approaches to tuning them. In order to simulate large deformations, we augment linear corotational FEM simulations with our orthotropic and general anisotropic materials. PMID:26340037

  14. Stable isotope laser spectroscopy

    NASA Astrophysics Data System (ADS)

    Becker, J. F.; Yaldaei, Ramil; McKay, Christopher P.

    1989-03-01

    Recent advances in semiconductor laser technology have produced a reliable lightweight device ideally suited for a spacecraft high resolution molecular spectrometer. Lead-salt tunable diode lasers (TDL) emit in several spectral modes, each with a very narrow linewidth of -0.0003/cm. This spectral resolution is much narrower than typical Doppler broadened molecular linewidths in the mid-IR range. Thus it is possible to detect individual rotational lines within the vibrational band and measure their intensity, which can be used to determine gas concentration. The narrow spectral lines of any impurity gas tend to lie between the narrow lines of the gas of interest. This represents a major advantage over the accepted gas chromatograph mass spectrometer (GCMS) technique for measuring gas concentrations and isotope ratios. The careful and extensive gas purification procedures required to remove impurities for reliable GCMS measurements will not be required for an IR laser gas analysis. The infrared laser gas analysis technique is being developed to measure stable isotopic ratios of gases such as CO2, CH4, N2O, and NH3. This will eventually lead to development of instruments capable of in situ istopic measurements on planets such as Mars. The carbon (C-12, C-13) isotope ratio is indicative of the type of carbon fixation mechanisms (e.g., photosynthesis, respiration) in operation on a planet, while the nitrogen (N-14, N-15) isotope ratio can probably be used to date nitrogen-bearing Martian samples. The absorbance ratio of two adjacent lines of CO2 in the 2300/cm (4.3 micron) region of the spectrum was measured. The precision of the measurement is presently better than 1 percent and significant improvement is anticipated as rapid sweep-integration techniques and computer controlled data acquistion capabilities are incorporated.

  15. Stable isotope laser spectroscopy

    NASA Technical Reports Server (NTRS)

    Becker, J. F.; Yaldaei, Ramil; Mckay, Christopher P.

    1989-01-01

    Recent advances in semiconductor laser technology have produced a reliable lightweight device ideally suited for a spacecraft high resolution molecular spectrometer. Lead-salt tunable diode lasers (TDL) emit in several spectral modes, each with a very narrow linewidth of -0.0003/cm. This spectral resolution is much narrower than typical Doppler broadened molecular linewidths in the mid-IR range. Thus it is possible to detect individual rotational lines within the vibrational band and measure their intensity, which can be used to determine gas concentration. The narrow spectral lines of any impurity gas tend to lie between the narrow lines of the gas of interest. This represents a major advantage over the accepted gas chromatograph mass spectrometer (GCMS) technique for measuring gas concentrations and isotope ratios. The careful and extensive gas purification procedures required to remove impurities for reliable GCMS measurements will not be required for an IR laser gas analysis. The infrared laser gas analysis technique is being developed to measure stable isotopic ratios of gases such as CO2, CH4, N2O, and NH3. This will eventually lead to development of instruments capable of in situ istopic measurements on planets such as Mars. The carbon (C-12, C-13) isotope ratio is indicative of the type of carbon fixation mechanisms (e.g., photosynthesis, respiration) in operation on a planet, while the nitrogen (N-14, N-15) isotope ratio can probably be used to date nitrogen-bearing Martian samples. The absorbance ratio of two adjacent lines of CO2 in the 2300/cm (4.3 micron) region of the spectrum was measured. The precision of the measurement is presently better than 1 percent and significant improvement is anticipated as rapid sweep-integration techniques and computer controlled data acquistion capabilities are incorporated.

  16. 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.

  17. The antimicrobial efficacy of sustained release silvercarbene 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 silvercarbene 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

  18. Selective Double Carbomagnesiation of Internal Alkynes Catalyzed by Iron-N-Heterocyclic Carbene Complexes: A Convenient Method to Highly Substituted 1,3-Dienyl Magnesium Reagents.

    PubMed

    Liu, Yuesheng; Wang, Lijun; Deng, Liang

    2016-01-13

    Controlled multicarbometalation of alkynes has been envisaged as an efficient synthetic method for dienyl and polyenyl metal reagents, but an effective catalyst enabling the transformation has remained elusive. Herein, we report that an iron(II)-N-heterocyclic carbene (NHC) complex (IEt2Me2)2FeCl2 (IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) can serve as a precatalyst for the double carbometalation of internal unsymmetrical alkynes with alkyl Grignard reagents, producing highly substituted 1,3-dienyl magnesium reagents with high regio- and stereoselectivity. Mechanistic studies suggest the involvement of low-coordinate organoiron(II)-NHC species as the in-cycle intermediates. The strong ?-donating nature of IEt2Me2 and its appropriate steric property are thought the key factors endowing the iron-NHC catalyst fine performance. PMID:26713433

  19. Bond Energies and Thermochemical Properties of Ring-Opened Diradicals and Carbenes of exo-Tricyclo[5.2.1.0(2,6)]decane.

    PubMed

    Hudzik, Jason M; Castillo, lvaro; Bozzelli, Joseph W

    2015-09-24

    Exo-tricyclo[5.2.1.0(2,6)]decane (TCD) or exo-tetrahydrodicyclopentadiene is an interesting strained ring compound and the single-component high-energy density hydrocarbon fuel known as JP-10. Important initial reactions of TCD at high temperatures could cleave a strained carbon-carbon (C-C) bond in the ring system creating diradicals also constrained by the remaining ring system. This study determines the thermochemical properties of these diradicals (TCD-H2 mJ-nJ where m and n correspond to the cleaved carbons sites) including the carbon-carbon bond dissociation energy (C-C BDE) corresponding to the cleaved TCD site. Thermochemical properties including enthalpies (?Hf298), entropies (S(T)), heat capacities (Cp(T)), and C-H and C-C BDEs for the parent (TCD-H2 m-n), radical (TCD-H2 mJ-n and m-nJ), diradical (TCD-H2 mJ-nJ), and carbene (TCD-H2 mJJ-n and m-nJJ) species are determined. Structures, vibrational frequencies, moments of inertia, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level of theory. Standard enthalpies of formation in the gas phase for the TCD-H2 m-n parent and radical species are determined using the B3LYP density functional theory and the higher level G3MP2B3 and CBS-QB3 composite methods. For singlet and triplet TCD diradicals and carbenes, M06-2X, ?B97X-D, and CCSD(T) methods are included in the analysis to determine ?Hf298 values. The C-C BDEs are further calculated using CASMP2(2,2)/aug-cc-pvtz//CASSCF(2,2)/cc-pvtz and with the CASMP2 energies extrapolated to the complete basis set limit. The bond energies calculated with these methods are shown to be comparable to the other calculation methods. Isodesmic work reactions are used for enthalpy analysis of these compounds for effective cancelation of systematic errors arising from ring strain. C-C BDEs range from 77.4 to 84.6 kcal mol(-1) for TCD diradical singlet species. C-H BDEs for the parent TCD-H2 m-n carbon sites range from 93 to 101 kcal mol(-1) with a similar range seen for loss of the second hydrogen to generate the diradical singlet species. A wider range for C-C BDEs is seen for the carbenes from about 77 to 100 kcal mol(-1) as compared to the diradicals. Results from the DFT methods for the parents, radicals, diradicals, and carbenes are in good agreement with results from the composite methods using our sets of work reactions. PMID:26295335

  20. 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

  1. How does the addition of steric hindrance to a typical N-heterocyclic carbene ligand affect catalytic activity in olefin metathesis?

    PubMed

    Poater, Albert; Falivene, Laura; Urbina-Blanco, Csar A; Manzini, Simone; Nolan, Steven P; Cavallo, Luigi

    2013-05-28

    Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in mind that there is a significant structural difference between both ligands in different olefin metathesis reactions, here by means of DFT we characterize where the NHC ligand plays a more active role and where it is a simple spectator, or at least its modification does not significantly change its catalytic role/performance. PMID:23455458

  2. Palladium-N-heterocyclic carbene (NHC)-catalyzed asymmetric synthesis of indolines through regiodivergent C(sp3)-H activation: scope and DFT study.

    PubMed

    Katayev, Dmitry; Larionov, Evgeny; Nakanishi, Masafumi; Besnard, Cline; Kndig, E Peter

    2014-11-10

    Two bulky, chiral, monodentate N-heterocyclic carbene ligands were applied to palladium-catalyzed asymmetric C-H arylation to incorporate C(sp(3))-H bond activation. Racemic mixtures of the carbamate starting materials underwent regiodivergent reactions to afford different trans-2,3-substituted indolines. Although this CAr-Calkyl coupling requires high temperatures (140-160?C), chiral induction is high. This regiodivergent reaction, when carried out with enantiopure starting materials, can lead to single structurally different enantiopure products, depending on the catalyst chirality. The C-H activation at a tertiary center was realized only in the case of a cyclopropyl group. No C-H activation takes place alpha to a tertiary center. A detailed DFT study is included and analyses of methyl versus methylene versus methine C-H activation is used to rationalize experimentally observed regio- and enantioselectivities. PMID:25262613

  3. 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

  4. NHC carbene supported half-sandwich hydridosilyl complexes of ruthenium: the impact of supporting ligands on SiH interligand interactions.

    PubMed

    Mai, Van Hung; Kuzmina, Lyudmila G; Churakov, Andrei V; Korobkov, Ilia; Howard, Judith A K; Nikonov, Georgii I

    2015-12-14

    Reaction of complex [CpRu(pyr)3][PF6] () with the NHC carbene IPr (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) results in the NHC complex [Cp(IPr)Ru(pyr)2][PF6] (), which was studied by NMR specroscopy and X-ray diffraction analysis. Reaction of [Cp(IPr)Ru(pyr)2][PF6] () with LiAlH4 leads to the trihydride Cp(IPr)RuH3 () characterised by spectroscopic methods. Heating compound with hydrosilanes gives the dihydrido silyl derivatives Cp(IPr)RuH2(SiR3) (). Systematic X-ray diffraction studies suggest that complexes have stronger interligand SiH interactions than the isolobal phosphine complexes Cp(Pr3P)RuH2(SiR3). PMID:26599264

  5. Synthesis of N-heterocyclic carbene-PdCl2-(iso)quinoline complexes and their application in arylamination at low catalyst loadings.

    PubMed

    Liu, Feng; Zhu, Yi-Ran; Song, Lu-Gan; Lu, Jian-Mei

    2016-02-16

    A new type of N-heterocyclic carbene-PdCl2-(iso)quinoline complexes were successfully achieved in acceptable to good yields from easily available starting materials under mild conditions, and their structures were unambiguously confirmed using X-ray single crystal diffraction. Furthermore, their catalytic activity toward Buchwald-Hartwig arylamination of aryl chlorides with primary and secondary amines was fully tested. Under the optimal reaction conditions, the expected arylated amines can be obtained in high to excellent yields at low catalyst loadings (0.005-0.05 mol%). It may be worth noting here that comparison of these complexes with other well-defined and easily available NHC-Pd(ii) complexes bearing different N-containing ancillary ligands was also carried out, showing their superior catalytic activity over all others. PMID:26880100

  6. Do stable atmospheric layers exist?

    NASA Astrophysics Data System (ADS)

    Lovejoy, S.; Tuck, A. F.; Hovde, S. J.; Schertzer, D.

    2008-01-01

    The notion of stable atmospheric layers is a classical idealization used for understanding atmospheric dynamics and thermodynamics. Using state of the art drop sonde data and using conditional, dynamical and convective stability criteria we show that apparently stable layers are typically composed of a hierarchy of unstable layers themselves with embedded stable sublayers, and unstable sub-sub layers etc. i.e. in a Russian Matryoshka doll-like fractal hierarchy. We therefore argue that the notion of stable atmospheric layers is untenable and must be replaced by modern scaling notions.

  7. Proton-Transfer Polymerization by N-Heterocyclic Carbenes: Monomer and Catalyst Scopes and Mechanism for Converting Dimethacrylates into Unsaturated Polyesters.

    PubMed

    Hong, Miao; Tang, Xiaoyan; Falivene, Laura; Caporaso, Lucia; Cavallo, Luigi; Chen, Eugene Y-X

    2016-02-17

    This contribution presents a full account of experimental and theoretical/computational investigations into the N-heterocyclic carbene (NHC)-catalyzed proton-transfer polymerization (HTP) that converts common dimethacrylates (DMAs) containing no protic groups into unsaturated polyesters. This new HTP proceeds through the step-growth propagation cycles via enamine intermediates, consisting of the proposed conjugate addition-proton transfer-NHC release fundamental steps. This study examines the monomer and catalyst scopes as well as the fundamental steps involved in the overall HTP mechanism. DMAs having six different types of linkages connecting the two methacrylates have been polymerized into the corresponding unsaturated polyesters. The most intriguing unsaturated polyester of the series is that based on the biomass-derived furfuryl dimethacrylate, which showed a unique self-curing ability. Four MeO- and Cl-substituted TPT (1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene) derivatives as methanol insertion products, (Rx)TPT(MeO/H) (R = MeO, Cl; x = 2, 3), and two free carbenes (catalysts), (OMe2)TPT and (OMe3)TPT, have been synthesized, while (OMe2)TPT(MeO/H) and (OMe2)TPT have also been structurally characterized. The structure/reactivity relationship study revealed that (OMe2)TPT, being both a strong nucleophile and a good leaving group, exhibits the highest HTP activity and also produced the polyester with the highest Mn, while the Cl-substituted TPT derivatives are least active and efficient. Computational studies have provided mechanistic insights into the tail-to-tail dimerization coupling step as a suitable model for the propagation cycle of the HTP. The extensive energy profile was mapped out, and the experimentally observed unicity of the TPT-based catalysts was satisfactorily explained with the thermodynamic formation of key spirocyclic species. PMID:26779897

  8. 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.

  9. 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. PMID:24033186

  10. 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

  11. 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

    Muoz, 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 ?(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 ?(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

  12. N-heterocyclic carbene gold(I) and copper(I) complexes in C-H bond activation.

    PubMed

    Gaillard, Sylvain; Cazin, Catherine S J; Nolan, Steven P

    2012-06-19

    Environmental concerns have and will continue to have a significant role in determining how chemistry is carried out. Chemists will be challenged to develop new, efficient synthetic processes that have the fewest possible steps leading to a target molecule, the goal being to decrease the amount of waste generated and reduce energy use. Along this path, chemists will need to develop highly selective reactions with atom-economical pathways producing nontoxic byproduct. In this context, C-H bond activation and functionalization is an extremely attractive method. Indeed, for most organic transformations, the presence of a reactive functionality is required. In Total Synthesis, the "protection and deprotection" approach with such reactive groups limits the overall yield of the synthesis, involves the generation of significant chemical waste, costs energy, and in the end is not as green as one would hope. In turn, if a C-H bond functionalization were possible, instead of the use of a prefunctionalized version of the said C-H bond, the number of steps in a synthesis would obviously be reduced. In this case, the C-H bond can be viewed as a dormant functional group that can be activated when necessary during the synthetic strategy. One issue increasing the challenge of such a desired reaction is selectivity. The cleavage of a C-H bond (bond dissociation requires between 85 and 105 kcal/mol) necessitates a high-energy species, which could quickly become a drawback for the control of chemo-, regio-, and stereoselectivity. Transition metal catalysts are useful reagents for surmounting this problem; they can decrease the kinetic barrier of the reaction yet retain control over selectivity. Transition metal complexes also offer important versatility in having distinct pathways that can lead to activation of the C-H bond. An oxidative addition of the metal in the C-H bond, and a base-assisted metal-carbon bond formation in which the base can be coordinated (or not) to the metal complexes are possible. These different C-H bond activation modes provide chemists with several synthetic options. In this Account, we discuss recent discoveries involving the versatile NHC-gold(I) and NHC-copper(I) hydroxide complexes (where NHC is N-heterocyclic carbene) showing interesting Brønsted basic properties for C-H bond activation or C-H bond functionalization purposes. The simple and easy synthesis of these two complexes involves their halide-bearing relatives reacting with simple alkali metal hydroxides. These complexes can react cleanly with organic compounds bearing protons with compatible pK(a) values, producing only water as byproduct. It is a very simple protocol indeed and may be sold as a C-H bond activation, although the less flashy "metalation reaction" also accurately describes the process. The synthesis of these complexes has led us to develop new organometallic chemistry and catalysis involving C-H bond activation (metalation) and subsequent C-H bond functionalization. We further highlight applications with these reactions, in areas such as photoluminescence and biological activities of NHC-gold(I) and NHC-copper(I) complexes. PMID:22166092

  13. Tempered stable Lvy motion driven by stable subordinator

    NASA Astrophysics Data System (ADS)

    Gajda, Janusz; Wy?oma?ska, 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.

  14. Rhodium-Catalyzed NH Insertion of Pyridyl Carbenes Derived from Pyridotriazoles: A General and Efficient Approach to 2-Picolylamines and Imidazo[1,2-a]pyridines

    PubMed Central

    Shi, Yi; Gulevich, Anton V.; Gevorgyan, Vladimir

    2014-01-01

    A general and efficient NH insertion reaction of rhodium pyridyl carbenes derived from pyridotriazoles was developed. Various NH containing compounds, including amides, anilines, enamine and aliphatic amines, smoothly underwent the NH insertion reaction to afford 2-picolylamine derivatives. The developed transformation was further utilized in a facile one-pot synthesis of imidazo[1,2-a]pyridines. PMID:25332116

  15. Stable Spheromaks with Profile Control

    SciTech Connect

    Fowler, T K; Jayakumar, R

    2008-01-29

    A spheromak equilibrium with zero edge current is shown to be stable to both ideal MHD and tearing modes that normally produce Taylor relaxation in gun-injected spheromaks. This stable equilibrium differs from the stable Taylor state in that the current density j falls to zero at the wall. Estimates indicate that this current profile could be sustained by non-inductive current drive at acceptable power levels. Stability is determined using the NIMROD code for linear stability analysis. Non-linear NIMROD calculations with non-inductive current drive could point the way to improved fusion reactors.

  16. 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.

  17. 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)

  18. 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.

  19. Synthesis of a stable adduct of dialane(4) (Al2H4) via hydrogenation of a magnesium(I) dimer.

    PubMed

    Bonyhady, Simon J; Collis, David; Frenking, Gernot; Holzmann, Nicole; Jones, Cameron; Stasch, Andreas

    2010-10-01

    The desorption of dihydrogen from magnesium(II) hydride, MgH2 (containing 7.6 wt% H), is reversible. MgH2 therefore holds promise as a hydrogen storage material in devices powered by fuel cells. We believed that dimeric magnesium(I) dimers (LMgMgL, L=?-diketiminate) could find use as soluble models to aid the study of the mechanisms and/or kinetics of the hydrogenation of magnesium and its alloys. Here, we show that LMgMgL can be readily hydrogenated to yield LMg(-H)2MgL by treatment with aluminium(III) hydride complexes. In one case, hydrogenation was reversed by treating LMg(-H)2MgL with potassium metal. The hydrogenation by-products are the first thermally stable, neutral aluminium(II) hydride complexes to be produced, one of which, [{(IPr)(H)2Al}2] (IPr=:C[{(C6H3-i-Pr(2)-2,6)NCH}2]), is an N-heterocyclic carbene adduct of the elusive parent dialane4 (Al2H4). A computational analysis of this compound is presented. PMID:20861903

  20. 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.

  1. 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.

  2. 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, Stphanie; 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(?(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 ?M and in some cases <1 ?M, whilst still retaining a high degree of selectivity towards cancer cells over healthy cells (1.85 ?M in A2780 ovarian cancer cells versus 435 ?M in human embryonic kidney cells in one case). PMID:24201979

  3. From the parent phosphinidene-carbene adduct NHC[double bond, length as m-dash]PH to cationic P4-rings and P2-cycloaddition products.

    PubMed

    Beil, Andreas; Gilliard, Robert J; Grützmacher, Hansjörg

    2016-02-01

    Reactions of the parent phosphinidene-carbene adduct (Dipp)NHC[double bond, length as m-dash]PH with chlorophosphanes are reported herein. The obtained (Dipp)NHC-substituted chlorodiphosphanes, (Dipp)NHC[double bond, length as m-dash]P-PClR, and the formation of their cationic derivatives, [(Dipp)NHC-P[double bond, length as m-dash]PR](+), were also explored. Depending on the steric demand of their substituents, these cations were found to be monomeric [(Dipp)NHC-PP-N(i)Pr2][GaCl4] or to dimerise to cyclotetraphosphanes [(Dipp)NHC-PP-R]2[GaCl4]2 (R = Ph, NMe2). For R = NMe2, this dication is the first isolated example of a tetrasubstituted all-σ(3) cyclotetraphosphane. Finally, the hetero-Diels-Alder reactivity of these cations was studied with 2,3-dimethylbuta-1,3-diene and cyclopentadiene, resulting in the isolation of a number of cationic 1,2-diphosphinanes. PMID:26400646

  4. Formation of Highly Strained N-Heterocycles via Decomposition of Iron N-Heterocyclic Carbene Complexes: The Value of Labile Fe?C Bonds.

    PubMed

    Haslinger, Stefan; Kck, Jens W; Anneser, Markus R; Cokoja, Mirza; Pthig, Alexander; Khn, Fritz E

    2015-12-01

    An unusual, highly-strained annulated 2,2'-biimdazole was isolated as decomposition product of the outer-sphere one-electron oxidation of an iron(II) N-heterocyclic carbene (NHC) complex bearing a tetradentate bis(NHC)-bis- (pyridine) ligand (NCCN). Reductive elimination leading to the 2,2'-biimdazole is a consequence of the lability of the Fe?C bonds in the transient species and also extends to complexes with modified ligands but the same coordination geometry. Closely related by a two-electron redox step to a family of less-strained tetraazafulvalenes, the obtained 2,2'-biimidazolium salts were studied electrochemically. Introduction of methyl substituents at the methylene tether significantly increased the reversibility of the electrochemical reduction. Furthermore, the reactivity of the 2,2'-biimidazolium salt was examined by oxidative addition of [Ni(cod)2 ] to the central C?C bond, providing a previously unknown way for the formation of NHC transition metal complexes. PMID:26486319

  5. Stepwise strategy to cyclometallated Pt(II) complexes with N-heterocyclic carbene ligands: a luminescence study on new ?-diketonate complexes.

    PubMed

    Fuertes, Sara; Garca, Hector; Perlvarez, 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(?-Cl)(?(3)-2-Me-C3H4)}2] (?(3)-2-Me-C3H4 = ?(3)-2-methylallyl) to give the intermediate N-heterocyclic carbene complex [PtCl(?(3)-2-Me-C3H4)(HCC*-?C*)] (3) (HCC*-?C* = 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(?-Cl)(CC*)}2] (4). Chlorine abstraction from 4 with ?-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 ?-? interactions in the solid-state structure. The influence of the R-substituents of the ?-diketonate ligand on the photophysical properties and the use of the most efficient emitter, 5, as phosphor converter has also been studied. PMID:25412763

  6. 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-?) independent intrinsic pathway and significantly inhibited in vitro synthesis of cytokines, interleukin-1 (IL-1) and TNF-? 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

  7. Human colon cancer targeted pro-apoptotic, anti-metastatic and cytostatic effects of binuclear Silver(I)-N-Heterocyclic carbene (NHC) complexes.

    PubMed

    Asif, Muhammad; Iqbal, Muhammad Adnan; Hussein, Mouayed A; Oon, Chern Ein; Haque, Rosenani A; Khadeer Ahamed, Mohamed B; Abdul Majid, Aman Shah; Abdul Majid, Amin Malik Shah

    2016-01-27

    The current mechanistic study was conducted to explore the effects of increased lipophilicity of binuclear silver(I)-NHC complexes on cytotoxicity. Two new silver(I)-N-Heterocyclic Carbene (NHC) complexes (3 and 4), having lypophilic terminal alkyl chains (Octyl and Decyl), were derived from meta-xylyl linked bis-benzimidazolium salts (1 and 2). Each of the synthesized compounds was characterized by microanalysis and spectroscopic techniques. The complexes were tested for their cytotoxicity against a panel of human cancer c as well normal cell lines using MTT assay. Based on MTT assay results, complex 4 was found to be selectively toxic towards human colorectal carcinoma cell line (HCT 116). Complex 4 was further studied in detail to explore the mechanism of cell death and findings of the study revealed that complex 4 has promising pro-apoptotic and anti-metastatic activities against HCT 116 cells. Furthermore, it showed pronounced cytostatic effects in HCT 116 multicellular spheroid model. Hence, binuclear silver(I)-NHC complexes with longer terminal aliphatic chains have worth to be further studied against human colon cancer for the purpose of drug development. PMID:26649905

  8. Alkali-Metal-Mediated Magnesiations of an N-Heterocyclic Carbene: Normal, Abnormal, and "Paranormal" Reactivity in a Single Tritopic Molecule.

    PubMed

    Martínez-Martínez, Antonio J; Fuentes, M Ángeles; Hernán-Gómez, Alberto; Hevia, Eva; Kennedy, Alan R; Mulvey, Robert E; O'Hara, Charles T

    2015-11-16

    Herein the sodium alkylmagnesium amide [Na4 Mg2 (TMP)6 (nBu)2 ] (TMP=2,2,6,6-tetramethylpiperidide), a template base as its deprotonating action is dictated primarily by its 12 atom ring structure, is studied with the common N-heterocyclic carbene (NHC) IPr [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]. Remarkably, magnesiation of IPr occurs at the para-position of an aryl substituent, sodiation occurs at the abnormal C4 position, and a dative bond occurs between normal C2 and sodium, all within a 20 atom ring structure accommodating two IPr(2-) . Studies with different K/Mg and Na/Mg bimetallic bases led to two other magnesiated NHC structures containing two or three IPr(-) monoanions bound to Mg through abnormal C4 sites. Synergistic in that magnesiation can only work through alkali-metal mediation, these reactions add magnesium to the small cartel of metals capable of directly metalating a NHC. PMID:26417985

  9. Total Syntheses of the Histone Deacetylase Inhibitors Largazole and 2-epi-Largazole: Application of N-Heterocyclic Carbene Mediated Acylations in Complex Molecule Synthesis

    PubMed Central

    Wang, Bo; Huang, Po-Hsien; Chen, Ching-Shih

    2014-01-01

    Details of the evolution of strategies toward convergent assembly of the histone deacetylase inhibiting natural product largazole exploiting ?,?-unsaturated-?,?-epoxy-aldehydes and a thiazole-thiazoline containing ?-amino-acid are described. The initial N-heterocyclic carbene mediated redox amidation exploying these two types of building blocks representing largazoles structural domains of distinct biosynthetic origin directly afforded the seco-acid of largazole. This was accomplished without any protecting groups resident upon either thioester bearing epoxy-aldehyde or the tetrapeptide. However, the ineffective production of largazole via the final macrolactonization led to an alternative intramolecular esterification/macrolactamization strategy employing the established two building blocks. This provided largazole along with its C2-epimer via an unexpected inversion of the ?-stereocenter at the valine residue. The biological evaluation demonstrated that both largazole and 2-epi-largazole led to dose-dependent increases of acetylation of histone H3, indicating their potencies as class I histone deacetylase selective inhibitiors. Enhanced p21 expression was also induced by largazole and its C2 epimer. In addition, 2-epi-largazole displayed more potent activity than largazole in cell viability assays against PC-3 and LNCaP prostate cancer cell lines. PMID:21244075

  10. Carbene- and carbyne-like behavior of the Mo-P multiple bond in a dimolybdenum complex inducing trigonal-pyramidal coordination of a phosphinidene ligand.

    PubMed

    Alvarez, M Angeles; Amor, Inmaculada; Garca, M Esther; Garca-Viv, Daniel; Ruiz, Miguel A

    2007-08-01

    The phosphinidene complex [Mo2Cp(micro-kappa1:kappa1,eta5-PC5H4)(CO)2(eta6-R*H)] (2; Cp = eta5-C5H5; R* = 2,4,6-C6H2tBu3) has substantially different Mo-P bonds and displays a high reactivity located at the short Mo-P bond. Sideways cycloaddition or addition processes are observed toward RCCR, HCl, and [Fe2(CO)9], to give respectively metallacyclobutene and arylphosphide-bridged and heterometallic phosphinidene-bridged derivatives, a behavior reminiscent of the nucleophilic mononuclear phosphinidene complexes (carbene-like behavior), which is in good agreement with the ground-state electronic structure of 2 derived from density functional theory calculations. However, the reaction of 2 with [Co2(CO)8] implies the addition of two cobalt fragments to its short Mo-P bond and thus reveals a carbyne-like behavior of compound 2. In most of the new products, the P atom displays an unprecedented trigonal-pyramidal-like environment, instead of the expected tetrahedral distribution of bonds. PMID:17608475

  11. N-Heterocyclic Carbene-Catalyzed Ring Opening Polymerization of ?-Caprolactone with and without Alcohol Initiators: Insights from Theory and Experiment.

    PubMed

    Jones, Gavin O; Chang, Young A; Horn, Hans W; Acharya, Ashwin K; Rice, Julia E; Hedrick, James L; Waymouth, Robert M

    2015-04-30

    Computational investigations with density functional theory (DFT) have been performed on the N-heterocyclic carbene (NHC) catalyzed ring-opening polymerization of ?-caprolactone in the presence and in the absence of a methanol initiator. Much like the zwitterionic ring opening (ZROP) of ?-valerolactone which was previously reported, calculations predict that the mechanism of the ZROP of caprolactone that occurs without an alcohol present involves a high-barrier step involving ring opening of the zwitterionic tetrahedral intermediate formed after the initial nucleophilic attack of NHC on caprolactone. However, the operative mechanism by which caprolactone is polymerized in the presence of an alcohol initiator does not involve the analogous mechanism involving initial nucleophilic attack by the organocatalytic NHC. Instead, the NHC activates the alcohol through hydrogen bonding and promotes nucleophilic attack and the subsequent ring-opening steps that occur during polymerization. The largest free energy barrier for the hydrogen-bonding mechanism in alcohol involves nucleophilic attack, while that for both ZROP processes involves ring opening of the initially formed zwitterionic tetrahedral intermediate. The DFT calculations predict that the rate of polymerization in the presence of alcohol is faster than the reaction performed without an alcohol initiator; this prediction has been validated by experimental kinetic studies. PMID:25848823

  12. Highly stable microwave delay line

    NASA Technical Reports Server (NTRS)

    Higa, W. H.

    1967-01-01

    TWM /Traveling Wave Master/ comb structure serves as a highly stable microwave delay line for determining the short-term stability of the hydrogen maser frequency standards used in the deep space network. Cryogenic cooling is used to minimize signal attenuation and thermal noise.

  13. 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.

  14. 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...

  15. Stable interactions via proper deformations

    NASA Astrophysics Data System (ADS)

    Kaparulin, D. S.; Lyakhovich, S. L.; Sharapov, A. A.

    2016-04-01

    A new method is proposed for switching on interactions that are compatible with global symmetries and conservation laws of the original free theory. The method is applied to the control of stability in Lagrangian and non-Lagrangian theories with higher derivatives. By way of illustration, a wide class of stable interactions is constructed for the Pais–Uhlenbeck oscillator.

  16. 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.

  17. Highly convenient amine-free sonogashira coupling in air in a polar mixed aqueous medium by trans- and cis-[(NHC)2PdX2] (X=Cl, Br) complexes of N/O-functionalized N-heterocyclic carbenes.

    PubMed

    Ray, Lipika; Barman, Samir; Shaikh, Mobin M; Ghosh, Prasenjit

    2008-01-01

    Two new trans- and cis-[(NHC)(2)PdX(2)] (X=Cl, Br) complexes of N/O-functionalized N-heterocyclic carbenes employed in a highly convenient amine-free Sonogashira cross-coupling reaction in air in a polar mixed aqueous medium are reported. Specifically, the trans-[{1-benzyl-3-(3,3-dimethyl-2-oxobutyl)imidazol-2-ylidene}(2)PdBr(2)] (3) and cis-[{1-benzyl-3-(N-tert-butylacetamido)imidazol-2-ylidene}(2)PdCl(2)] (4) complexes effectively catalyzed the Sonogashira cross-coupling reaction of aryl iodides with substituted acetylenes in air in a mixed solvent (DMF/H(2)O, 3:1 v/v) under amine-free conditions. Interestingly, these trans- and cis-[(NHC)(2)PdX(2)] (X=Cl, Br) complexes, with two N-heterocyclic carbene ligands, exhibited superior activity compared with the now popular PEPPSI (pyridine enhanced precatalyst preparation, stabilization and initiation)-themed analogues, trans-[(NHC)Pd(pyridine)X(2)] (X=Cl, Br), 3 a and 4 a, with one N-heterocyclic carbene ligand and a "throw away" pyridine ligand in a trans disposition to each other. The higher activities of 3 and 4 compared with PEPPSI analogues 3 a and 4 a are attributed to more-electron-rich metal centers, as revealed by DFT studies, in the former complexes and is in concurrence with a more electron-rich metal center being effective in facilitating the oxidative addition of aryl halide, often a rate-determining step in palladium-mediated cross-coupling reactions. Complexes 3 and 4 were prepared from the corresponding silver analogues by transmetalation with [(cod)PdCl(2)], whereas the corresponding PEPPSI analogues 3 a and 4 a were obtained directly from the imidazolium halide salts by reaction with PdCl(2) in pyridine in the presence of K(2)CO(3) as base. PMID:18563770

  18. Phase stable RF transport system

    DOEpatents

    Curtin, Michael T. (Los Alamos, NM); Natter, Eckard F. (San Francisco, CA); Denney, Peter M. (Los Alamos, NM)

    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.

  19. 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.

  20. Thermally stable emulsion explosive composition

    SciTech Connect

    Sudweeks, W.B.; Lawrence, L.D.

    1982-03-30

    A thermally stable, cap-sensitive, water-in-oil emulsion explosive composition is described which has a discontinuous aqueous oxidizer salt solution phase containing calcium nitrate, a continuous oil or water-immiscible liquid or organic phase, an emulsifier, and a density reducing agent. The salt solution contains calcium nitrate in an amount of at least 20% by weight based on the total composition. 9 claims.

  1. 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.

  2. Dispersal polymorphism in stable habitats.

    PubMed

    Kisdi, Eva

    2016-03-01

    In fragmented but temporally stable landscapes, kin competition selects for dispersal when habitat patches are small, whereas the loss of dispersal is favoured when dispersal is costly and local populations are large enough for kin interactions to be negligible. In heterogeneous landscapes with both small and large patches, contrasting levels of kin competition facilitate the coexistence of low-dispersal and high-dispersal strategies. In this paper, I use both adaptive dynamics and inclusive fitness to analyse the evolution of dispersal in a simple model assuming that each patch supports either a single individual or a large population. With this assumption, many results can be obtained analytically. If the fraction of individuals living in small patches is below a threshold, then evolutionary branching yields two coexisting dispersal strategies. An attracting and evolutionarily stable dimorphism always exists (also when the monomorphic population does not have a branching point), and contains a strategy with zero dispersal and a strategy with dispersal probability between one half and the ESS of the classic Hamilton-May model. The present model features surprisingly rich population dynamics with multiple equilibria and unprotected dimorphisms, but the evolutionarily stable dimorphism is always protected. PMID:26739375

  3. Synthesis and structure of [U{C(PPh2NMes)2}2] (Mes = 2,4,6-Me3C6H2): A homoleptic uranium bis(carbene) complex with two formal U=C double bonds.

    PubMed

    Cooper, Oliver J; McMaster, Jonathan; Lewis, William; Blake, Alexander J; Liddle, Stephen T

    2010-06-01

    Treatment of H2C(PPh2NMes)2 (1, Mes = 2,4,6-Me3C6H2) with two equivalents of ButLi afforded the methandiide complex [Li2{C(PPh2NMes)2}2]2 (2); reaction of 2 with [UI3(THF)4] gave [U{C(PPh2NMes)2}2] (3), which is the first homoleptic uranium bis(carbene) complex with two formal U=C double bonds. PMID:20401420

  4. 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 IrCNHC distances are 2.043(5)2.056(5) . 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 (??=?340530?nm (????103?dm3 mol?1 cm?1)) originate from a d?(IrIII)????*(N^N) metal-to-ligand charge transfer transition, where the d?(IrIII) level contain significant contribution from the C^C^C ligands. All these complexes are emissive in the yellow-spectral region (553604?nm in CH3CN and CH2Cl2) upon photo-excitation with quantum yields of 10?310?1.

  5. 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

  6. Luminescent Iridium(III) Complexes Supported by N-Heterocyclic Carbene-based C^C^C-Pincer Ligands and Aromatic Diimines.

    PubMed

    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 (C(1)^C^C(1)) or 1,3-bis(3-butylbenzimidazolin-2-ylidene)phenyl anion (C(2)^C^C(2)) 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) . The hydride chemical shifts for complexes bearing C(1)^C^C(1) (-20.6 to -20.3?ppm) are more upfield than those with C(2)^C^C(2) (-19.5 and -19.2?ppm), revealing that C(1)^C^C(1) is a better electron donor than C(2)^C^C(2). Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (??=?340-530?nm (????10(3)?dm(3) mol(-1) cm(-1))) originate from a d?(Ir(III))????*(N^N) metal-to-ligand charge transfer transition, where the d?(Ir(III)) 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

  7. Accessing a Biologically Relevant Benzofuran Skeleton by a One-Pot Tandem Heck Alkynylation/Cyclization Reaction Using Well-Defined Palladium N-Heterocyclic Carbene Complexes.

    PubMed

    Kumar, Anuj; Gangwar, Manoj Kumar; Prakasham, A P; Mhatre, Darshan; Kalita, Alok Ch; Ghosh, Prasenjit

    2016-03-21

    Well-defined palladium N-heterocyclic carbene (NHC) complexes were employed in the one-pot tandem Heck alkynylation/cyclization sequence for preparing biologically relevant benzofuran compounds under copper-free conditions in a time-efficient step-reduced fashion. In particular, a series of binuclear palladium complexes, 1b-1e and 2b-2e, of the alkyl-bridged NHC ligands, namely, {1,1'-di-R1-4,4'-R2-di-1,2,4-triazoline-5,5'-diylid-2-ene] (R1 = i-Pr; R2 = -(CH2)2-, -(CH2)3-), and their mononuclear analogues, trans-(NHC)PdBr2(pyridine) (3b) and cis-(NHC)PdBr2(PPh3) (3c), successfully catalyzed the one-pot tandem Heck alkynylation/cyclization reaction of 2-iodophenol with a variety of terminal alkyne substrates, yielding 2-substituted benzofuran derivatives. The mononuclear complexes 3b and 3c were nearly half as active as the representative dinuclear analogue 1c under analogous reaction conditions, thereby implying that, at the same mole percent of the palladium loading, the monometallic 3b and 3c and the bimetallic 1c complexes were equally effective as catalysts. The two sites of the bimetallic complex 1c performed as two separate independent catalytic sites, displaying no cooperativity effect in the catalysis. Finally, the practical utility of the aforementioned catalysts was demonstrated for a representative catalyst 1c through the convenient synthesis of a key intermediate, 3-[2-(benzo[d][1,3]dioxol-5-yl)-7-methoxybenzofuran-5-yl]propan-1-ol, in a total-synthesis protocol of the natural product Egonol. PMID:26928799

  8. 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 kgmol?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 7279C (Tm,1) and 166177C (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

  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. Stable Hemiaminals: 2-Aminopyrimidine Derivatives.

    PubMed

    Kwiecie?, 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

  11. Mammalian stable expression of biotherapeutics.

    PubMed

    Jostock, Thomas; Knopf, Hans-Peter

    2012-01-01

    Many therapeutically relevant proteins, like IgG antibodies, are highly complex, multimeric glycoproteins that are difficult to express in microbial systems and thus usually produced in mammalian host cells. During the past two decades, stable mammalian expression technologies have made huge progress resulting in highly increased speed of cell line development and yield of manufacturing processes. Here, we give an overview of technologies that are applied at different stages of state-of-the-art cell line development processes for biomanufacturing. PMID:22735957

  12. Stable transfection of Acanthamoeba castellanii.

    PubMed

    Peng, Zhihua; Omaruddin, Romaica; Bateman, Erik

    2005-03-22

    A simple method for stable transfection of Acanthamoeba castellanii using plasmids which confer resistance to neomycin G418 is described. Expression of neomycin phosphotransferase is driven by the Acanthamoeba TBP gene promoter, and can be monitored by cell growth in the presence of neomycin G418 or by Western blot analysis. Transfected cells can be passaged in the same manner as control cells and can be induced to differentiate into cysts, in which form they maintain resistance to neomycin G418 for at least several weeks, although expression of neomycin phosphotransferase is repressed during encystment. Expression of EGFP or an HA-tagged EGFP-TBP fusion can be driven from the same plasmid, using an additional copy of the Acanthamoeba TBP gene promoter or a deletion mutant. The TBP-EGFP fusion is localized to the nucleus, except in a small proportion of presumptive pre-mitotic cells. EGFP expression can also be driven by the cyst-specific CSP21 gene promoter, which is completely repressed in growing cells but strongly induced in differentiating cells. Transfected cells maintain their phenotype for several weeks, even in the absence of neomycin G418, suggesting that transfected genes are stably integrated within the genome. These results demonstrate the utility of the neomycin resistance based plasmids for stable transfection of Acanthamoeba, and may assist a number of investigations. PMID:15777844

  13. 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.

  14. 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 Cte 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.

  15. 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. PMID:20023883

  16. Scaling Behavior in the Stable Marriage Problem

    NASA Astrophysics Data System (ADS)

    Oméro, Marie-José; Dzierzawa, Michael; Marsili, Matteo; Zhang, Yi-Cheng

    1997-12-01

    We study the optimization of the stable marriage problem. All individuals attempt to optimize their own satisfaction, subject to mutually conflicting constraints. We find that the stable solutions are generally not the globally best solution, but reasonably close to it. All the stable solutions form a special sub-set of the meta-stable states, obeying interesting scaling laws. Both numerical and analytical tools are used to derive our results.

  17. Stable massive particles at colliders

    SciTech Connect

    Fairbairn, M.; Kraan, A.C.; Milstead, D.A.; Sjostrand, T.; Skands, P.; Sloan, T.; ,

    2006-11-01

    We review the theoretical motivations and experimental status of searches for stable massive particles (SMPs) which could be sufficiently long-lived as to be directly detected at collider experiments. The discovery of such particles would address a number of important questions in modern physics including the origin and composition of dark matter in the universe and the unification of the fundamental forces. This review describes the techniques used in SMP-searches at collider experiments and the limits so far obtained on the production of SMPs which possess various colour, electric and magnetic charge quantum numbers. We also describe theoretical scenarios which predict SMPs, the phenomenology needed to model their production at colliders and interactions with matter. In addition, the interplay between collider searches and open questions in cosmology such as dark matter composition are addressed.

  18. Stable States of Biological Organisms

    NASA Astrophysics Data System (ADS)

    Yukalov, V. I.; Sornette, D.; Yukalova, E. P.; Henry, J.-Y.; Cobb, J. P.

    2009-04-01

    A novel model of biological organisms is advanced, treating an organism as a self-consistent system subject to a pathogen flux. The principal novelty of the model is that it describes not some parts, but a biological organism as a whole. The organism is modeled by a five-dimensional dynamical system. The organism homeostasis is described by the evolution equations for five interacting components: healthy cells, ill cells, innate immune cells, specific immune cells, and pathogens. The stability analysis demonstrates that, in a wide domain of the parameter space, the system exhibits robust structural stability. There always exist four stable stationary solutions characterizing four qualitatively differing states of the organism: alive state, boundary state, critical state, and dead state.

  19. 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.

  20. Dimensionally stable metallic hydride composition

    DOEpatents

    Heung, Leung K. (Aiken, SC)

    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.

  1. Xenon Suboxides Stable under Pressure.

    PubMed

    Hermann, Andreas; Schwerdtfeger, Peter

    2014-12-18

    We present results from first-principles calculations on solid xenon-oxygen compounds under pressure. We find that the xenon suboxide Xe3O2 is the first compound to become more stable than the elements, at around P = 75 GPa. Other, even more xenon-rich compounds follow at higher pressures, while no region of enthalpic stability is found for the monoxide XeO. We establish the spectroscopic fingerprints of a variety of structural candidates for a recently synthesized xenon-oxygen compound at atmospheric pressure and, on the basis of the proposed stoichiometry XeO2, suggest an orthorhombic structure that comprises extended sheets of square-planar-coordinated xenon atoms connected through bent Xe-O-Xe linkages. PMID:26273984

  2. 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...

  3. 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.

  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. Resolution of P-stereogenic P-heterocycles via the formation of diastereomeric molecular and coordination complexes (a review).

    PubMed

    Bagi, Pter; Ujj, Viktria; Czugler, Mtys; Fogassy, Elemr; Keglevich, Gyrgy

    2016-02-01

    TADDOL derivatives and the Ca(2+)-salts of tartaric acid derivatives were found to be versatile and generally applicable resolving agents for the preparation of the enantiomers of P-stereogenic heterocyclic phosphine oxides and phosphinates via the formation of the corresponding diastereomeric molecular and coordination complexes. A few of the diastereomeric intermediates were characterized by single crystal X-ray crystallography to gain insights into the binding mode of the corresponding heterocyclic phosphine oxide ("guest") and the resolving agent ("host") and to study the underlying phenomenon of enantiomeric recognition. PMID:26564410

  6. 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 ?,?-diynes. In the RCM of ?,?-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

  7. 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 enamine formation/dimerization through proton transfer vs polymerization through conjugate addition, and mapped out extensive energy profiles for chain initiation, propagation, and termination steps, thereby satisfactorily explaining the experimental observations. PMID:24245532

  8. Low-spin hexacoordinate Mn(III): synthesis and spectroscopic investigation of homoleptic tris(pyrazolyl)borate and tris(carbene)borate complexes.

    PubMed

    Forshaw, Adam P; Smith, Jeremy M; Ozarowski, Andrew; Krzystek, J; Smirnov, Dmitry; Zvyagin, S A; Harris, T David; Karunadasa, Hemamala I; Zadrozny, Joseph M; Schnegg, Alexander; Holldack, Karsten; Jackson, Timothy A; Alamiri, Ahmad; Barnes, Diane M; Telser, Joshua

    2013-01-01

    Three complexes of Mn(III) with "scorpionate" type ligands have been investigated by a variety of physical techniques. The complexes are [Tp(2)Mn]SbF(6) (1), [Tp(2)*Mn]SbF(6) (2), and [{PhB(MeIm)(3)}(2)Mn](CF(3)SO(3)) (3a), where Tp(-) = hydrotris(pyrazolyl)borate anion, Tp*(-) = hydrotris(3,5-dimethylpyrazolyl)borate anion, and PhB(MeIm)(3)(-) = phenyltris(3-methylimidazol-2-yl)borate anion. The crystal structure of 3a is reported; the structures of 1 and 2 have been previously reported, but were reconfirmed in this work. The synthesis and characterization of [{PhB(MeIm)(3)}(2)Mn]Cl (3b) are also described. These complexes are of interest in that, in contrast to many hexacoordinate (pseudo-octahedral) complexes of Mn(III), they exhibit a low-spin (triplet) ground state, rather than the high-spin (quintet) ground state. Solid-state electronic absorption spectroscopy, SQUID magnetometry, and high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy were applied. HFEPR, in particular, was useful in characterizing the S = 1 spin Hamiltonian parameters for complex 1, D = +19.97(1), E = 0.42(2) cm(-1), and for 2, D = +15.89(2), E = 0.04(1) cm(-1). In addition, frequency domain Fourier-transform THz-EPR spectroscopy, using coherent synchrotron radiation, was applied to 1 only and gave results in good agreement with HFEPR. Variable-temperature dc magnetic susceptibility measurements of 1 and 2 were also in good agreement with the HFEPR results. This magnitude of zero-field splitting (zfs) is over 4 times larger than that in comparable hexacoordinate Mn(III) systems with S = 2 ground states. Complexes 3a and 3b (i.e., regardless of counteranion) have a yet much larger magnitude zfs, which may be the result of unquenched orbital angular momentum so that the spin Hamiltonian model is not appropriate. The triplet ground state is rationalized in each complex by ligand-field theory (LFT) and by quantum chemistry theory, both density functional theory and unrestricted Hartree-Fock methods. This analysis also shows that spin-crossover behavior is not thermally accessible for these complexes as solids. The donor properties of the three different scorpionate ligands were further characterized using the LFT model that suggests that the tris(carbene)borate is a strong ?-donor with little or no ?-bonding. PMID:23259486

  9. Silver(I) complexes of mono- and bidentate N-heterocyclic carbene ligands: synthesis, crystal structures, and in vitro antibacterial and anticancer studies.

    PubMed

    Haque, Rosenani A; Choo, Sze Yii; Budagumpi, Srinivasa; Iqbal, Muhammad Adnan; Al-Ashraf Abdullah, Amirul

    2015-01-27

    A series of benzimidazole-based N-heterocyclic carbene (NHC) proligands {1-benzyl-3-(2-methylbenzyl)-benzimidazolium bromide/hexafluorophosphate (1/4), 1,3-bis(2-methylbenzyl)-benzimidazolium bromide/hexafluorophosphate (2/5) and 1,3-bis(3-(2-methylbenzyl)-benzimidazolium-1-ylmethylbenzene dibromide/dihexafluorophosphate (3/6)} has been synthesized by the successive N-alkylation method. Ag complexes {1-benzyl-3-(2-methylbenzyl)-benzimidazol-2-ylidenesilver(I) hexafluorophosphate (7), 1,3-bis(2-methylbenzyl)-benzimidazol-2-ylidenesilver(I) hexafluorophosphate (8) and 1,3-bis(3-(2-methylbenzyl)-benzimidazol-2-ylidene)-1-ylmethylbenzene disilver(I) dihexafluorophosphate (9)} of NHC ligands have been synthesized by the treatment of benzimidazolium salts with Ag2O at mild reaction conditions. Both, NHC proligands and Ag-NHC complexes have been characterized by (1)H and (13)C{(1)H} NMR and FTIR spectroscopy and elemental analysis technique. Additionally, the structure of the NHC proligand 5 and the mononuclear Ag complexes 7 and 8 has been elucidated by the single crystal X-ray diffraction analysis. Both the complexes exhibit the same general structural motif with linear coordination geometry around the Ag centre having two NHC ligands. Preliminary in vitro antibacterial potentials of reported compounds against a Gram negative (Escherichia coli) and a Gram positive (Bacillus subtilis) bacteria evidenced the higher activity of mononuclear silver(I) complexes. The anticancer studies against the human derived colorectal cancer (HCT 116) and colorectal adenocarcinoma (HT29) cell lines using the MTT assay method, revealed the higher activity of Ag-NHC complexes. The benzimidazolium salts 4-6 and Ag-NHC complexes 7-9 displayed the following IC50 values against the HCT 116 and HT29 cell lines, respectively, 31.8 1.9, 15.2 1.5, 4.8 0.6, 10.5 1.0, 18.7 1.6, 1.20 0.3 and 245.0 4.6, 8.7 0.8, 146.1 3.1, 7.6 0.7, 5.5 0.8, 103.0 2.3 ?M. PMID:25461313

  10. Spin-spin contributions to the zero-field splitting tensor in organic triplets, carbenes and biradicals-a density functional and ab initio study.

    PubMed

    Sinnecker, Sebastian; Neese, Frank

    2006-11-01

    An evaluation study for the direct dipolar electron spin-spin (SS) contribution to the zero-field splitting (ZFS) tensor in electron paramagnetic resonance (EPR) spectroscopy is presented. Calculations were performed on a wide variety of organic systems where the SS contribution to the ZFS dominates over the second-order spin-orbit coupling (SOC) contribution. Calculations were performed using (hybrid) density functional theory (DFT), as well as complete active space self-consistent field (CASSCF) wave functions. In the former case, our implementation is an approximation, because we use the two-particle reduced spin-density matrix of the noninteracting reference system. In the latter case, the SS contribution is approximated by a mean-field method which, nevertheless, gives accurate results, compared to the approximation free computation of the SS part in a CASSCF framework. For the case of the triplet dioxygen molecule, it was shown that restricted open-shell density functional theory (RODFT), as well as CASSCF, can provide accurate spin-spin couplings while spin-unrestricted DFT leads to much larger errors. Furthermore, 15 organic radicals, including several 1,3 and 1,5 diradicals, dinitroxide biradicals, and even a chlorophyll a model system, were examined as test cases to demonstrate the accuracy and efficiency of our approach within a DFT framework. Accurate D values with root-mean-square deviations of 0.0035 cm(-1) were obtained. Furthermore, all trends, including those due to substituent effects, were correctly reproduced. In a different set of calculations, the polyacenes benzene, naphthalene, anthracene, and tetracene were studied. Applying DFT, the absolute D values were noticeably underestimated, but it was possible to correctly reproduce the trend to smaller D values with larger size of the systems. Finally, it was demonstrated that our approach is also well-suited for the study of carbenes. The smaller organic radicals of this work were also studied, through the use of CASSCF wave functions. This was a special advantage in the case of the triplet polyacenes, where the CASSCF approach gave better results than the DFT method. In comparing spin-restricted and spin-unrestricted results, it was shown through a natural orbital analysis and comparison to high-level ab initio calculations that even small amounts of spin polarization introduced by the unrestricted calculations lead to large deviations between the unrestricted Kohn-Sham (UKS) and restricted open-shell Kohn-Sham (ROKS) approaches. It is challenging to understand why the ROKS results show much better correlation with the experimental data. PMID:17078624

  11. Complexes of an anionic gallium(I) N-heterocyclic carbene analogue with group 14 element(II) fragments: synthetic, structural and theoretical studies.

    PubMed

    Green, Shaun P; Jones, Cameron; Lippert, Kai-Alexander; Mills, David P; Stasch, Andreas

    2006-09-01

    The reactions of the anionic gallium(I) N-heterocyclic carbene (NHC) analogue, [K(tmeda)][:Ga{[N(Ar)C(H)]2}], Ar = C6H3Pri2-2,6, with the heavier group 14 alkene analogues, R2E=ER2, E = Ge or Sn, R = -CH(SiMe3)2, have been carried out. In 2:1 stoichiometries, these lead to the ionic [K(tmeda)][R2EGa{[N(Ar)C(H)]2}] complexes which exhibit long E-Ga bonds. The nature of these bonds has been probed by DFT calculations, and the complexes have been compared to neutral NHC adducts of group 14 dialkyls. The 4:1 reaction of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with R2Sn=SnR2 leads to the digallyl stannate complex, [K(tmeda)][RSn[Ga{[N(Ar)C(H)]2}]2], presumably via elimination of KR. In contrast, the reaction of the gallium heterocycle with PbR2 affords the digallane4, [Ga{[N(Ar)C(H)]2}]2, via an oxidative coupling reaction. For sake of comparison, the reactions of [K(tmeda)][:Ga{[N(Ar)C(H)]2}] with Ar'2E=EAr'2, E = Ge, Sn or Pb, Ar' = C6H2Pri3-2,4,6, were carried out and led to either no reaction (E = Ge), the formation of [K(tmeda)][Ar'2SnGa{[N(Ar)C(H)]2}] (E = Sn), or the gallium(III) heterocycle, [Ar'Ga{[N(Ar)C(H)]2}] (E = Pb). Salt elimination reactions between [K(tmeda)][:Ga{[N(Ar)C(H)]2}] and the guanidinato group 14 complexes [(Giso)ECl], E = Ge or Sn, Giso = [Pri2NC{N(Ar)}2]-, gave the neutral [(Giso)EGa{[N(Ar)C(H)]2}] complexes. All complexes have been characterized by NMR spectroscopy and X-ray crystallographic studies. PMID:16933925

  12. 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 (Sections 1 through 5).

  13. Formation of stable clusters in colloidal suspensions.

    PubMed

    Kovalchuk, Nina; Starov, Victor; Langston, Paul; Hilal, Nidal

    2009-01-01

    The experimental evidence and theoretical explanations of stable cluster formation in colloidal suspensions are reviewed. The clusters form in the intermediate range between a stable suspension built up by singlets and the irreversible coagulation or gelation of the suspension. The stable clusters develop as a result of a balance between competing short range attraction and long range repulsion between colloidal particles or due to reversible flocculation in the shallow secondary potential well. Heteroaggregation in binary colloids can also result in formation of stable clusters. PMID:19073333

  14. Even the normal is abnormal: N-heterocyclic carbene C(2) binding to a phosphaalkene without breaking the P[double bond, length as m-dash]C ?-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

    2016-01-01

    The reaction of MesP[double bond, length as m-dash]CPh2 with the least sterically demanding N-heterocyclic carbene (NHC = IMe) results in formation of the 'abnormal' (C(4)-substituted) 4-phosphino-NHC (). In contrast, reaction with Me2IMe gives the unprecedented 'normal' C(2) adduct, Me2IMe ? P(Mes)[double bond, length as m-dash]CPh2 (). Particularly striking is the asymmetric and weak bonding of the NHC to the P[double bond, length as m-dash]C moiety in . DFT calculations indicate that the P[double bond, length as m-dash]C natural bond order in (1.54) still reflects significant ?-character to the bond (cf. MesP[double bond, length as m-dash]CPh2: NBO = 1.98). Further computational analysis suggests that ?-delocalization into the remote C-phenyl substituents is key to stabilizing the NHC adduct. PMID:26592925

  15. 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

  16. Water-soluble IrIII N-heterocyclic carbene based catalysts for the reduction of CO2 to formate by transfer hydrogenation and the deuteration of aryl amines in water.

    PubMed

    Azua, Arturo; Sanz, Sergio; Peris, Eduardo

    2011-03-28

    Two new water-soluble [IrI(2)(AcO)(bis-NHC)] complexes (NHC=N-heterocyclic carbene) incorporating a sulfonate functionality have been synthesized. The two complexes have been tested in the reduction of CO(2) with H(2) and iPrOH, and their activity has been compared with similar species without the sulfonate moiety. In both reactions, the complex with the two abnormally bound NHCs shows the best catalytic efficiencies, due to the higher ?-electron-donor character of the ligand. Remarkably, the activities obtained for the reduction of CO(2) under the transfer hydrogenation conditions are the best reported to date in terms of TON value (max. TON=2700). The two new complexes have also shown very good activity in the selective deuteration of arylamines, a process that is known to proceed through a chelate assisted N-directed process. PMID:21365699

  17. Theoretical study of the mechanism for the sequential N-O and N-N bond cleavage within N2O adducts of N-heterocyclic carbenes by a vanadium(iii) complex.

    PubMed

    Robinson, Robert; Shaw, Miranda F; Stranger, Robert; Yates, Brian F

    2016-01-01

    A theoretical study into the reactions of the N2O adducts of N-heterocyclic carbenes (NHCs) and a V((III)) complex was carried out using DFT calculations. Unlike most transition metal reactions with N2O that simply release N2 following O-atom transfer onto the metal centre, this NHC-based system traps the entire N2O molecule and then cleaves both the N-O and N-N bond in two consecutive reactions. The NHC presence increases the reactivity of N2O by altering the distribution of electron density away from the O-atom towards the two N-atoms. This electronic redistribution enables V-N binding interactions to form a reactive N,O-donor intermediate species. Our results show that bond breaking with concomitant ligand migration occurs via a concerted process for both the N-O and N-N cleavage reactions. PMID:26649949

  18. 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.

  19. Hydrogen-bonding pincer complexes with two protic N-heterocyclic carbenes from direct metalation of a 1,8-bis(imidazol-1-yl)carbazole by platinum, palladium, and nickel.

    PubMed

    Marelius, David C; Darrow, Evan H; Moore, Curtis E; Golen, James A; Rheingold, Arnold L; Grotjahn, Douglas B

    2015-07-27

    Pincer protic N-heterocyclic carbene (PNHC) complexes were synthesized by direct metalation, the formation of a metal carbon bond from an unfunctionalized C?H bond in a single synthetic step. Significantly, direct metalation succeeded even for a first-row metal, nickel. The chloride complexes were isolated and then converted to the acetate, triflate, or in the platinum case, a hydride analogue. Crystal structures and (1) H, (13) C, and (15) N?NMR data, as well as IR spectra, document the effects of intramolecular hydrogen bonding and the planar but flexible pincer framework. Anti-Markovnikov addition of O?H bonds to alkynes, including catalyzed alkyne hydration, were demonstrated on the Pt triflate analog. PMID:26134355

  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, ?(q), due to the spin quantum tunneling magnetization, which became larger with increasing S(total) of the complex. PMID:22898723

  1. 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...

  2. 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 L.; Camaioni, Donald M.; Walter, Eric D.; Bullock, R. Morris

    2012-03-05

    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 ? 104 M?1 s?1, khomolysis ~ 0.5 s?1 (i.e., Kdim ~ 5 ? 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, Biosciences and Geosciences. Pacific Northwest National Laboratory is a multiprogram national laboratory operated for DOE by Battelle. The EPR studies were performed at EMSL, a national scientific user facility sponsored by the Department of Energys Office of Biological and Environmental Research located at Pacific Northwest National Laboratory.

  3. Bi-stable optical element actuator device

    DOEpatents

    Holdener, Fred R. (Tracy, CA); Boyd, Robert D. (Livermore, CA)

    2002-01-01

    The present invention is a bistable optical element actuator device utilizing a powered means to move an actuation arm, to which an optical element is attached, between two stable positions. A non-powered means holds the actuation arm in either of the two stable positions. The optical element may be a electromagnetic (EM) radiation or particle source, an instrument, or EM radiation or particle transmissive reflective or absorptive elements. A bearing is used to transfer motion and smoothly transition the actuation arm between the two stable positions.

  4. Development of stable isotope manufacturing in Russia

    NASA Astrophysics Data System (ADS)

    Pokidychev, A.; Pokidycheva, M.

    1999-12-01

    For the past 25 years, Russia has relied heavily on the electromagnetic separation process for the production of middle and heavy mass stable isotopes. The separation of most light isotopes had been centered in Georgia which, after the collapse of the USSR, left Russia without this capability. In the mid-1970s, development of centrifuge technology for the separation of stable isotopes was begun. Alternative techniques such as laser separation, physical-chemical methods, and ion cyclotron resonance have also been investigated. Economic considerations have played a major role in the development and current status of the stable isotope enrichment capabilities of Russia.

  5. A stable diazo photoaffinity label with high absorptivity and effective photoactivation beyond 300 nm.

    PubMed

    Hahn, K M; Southwick, P L

    1991-08-01

    The sulfosuccinimidyl active ester of 3-(3-carbethoxy-4-diazo-5-oxo-2-pyrrolin-1-yl)propanoic acid (DIAZOPY-SE) has been synthesized for use as a photoaffinity labeling reagent. This compound was obtained from commercial chemicals by a four-step synthesis requiring no complex procedures or special apparatus. The active ester efficiently derivatizes protein amino groups with the chromophore 3-carbethoxy-4-diazo-5-oxo-2-pyrroline (DIAZOPY, epsilon 8800 M-1 cm-1 at lambda max 330 nm), which on irradiation yielded products expected from formation of a reactive carbene intermediate. Brief irradiation of DIAZOPY in 2-propanol using wavelengths greater than 300 nm for photolysis yielded mainly an isopropyl ether resulting from insertion of the carbene into the O-H bond of the alcohol. Formed concurrently and to a somewhat lesser extent was an isopropyl ester, resulting from a ring-contracting Wolff rearrangement of the carbene and subsequent reaction with isopropanol. Analogous products were produced by photolysis in 2-propanol of DIAZOPY-PA (for DIAZOPY propanoic acid), the carboxylic acid precursor of DIAZOPY-SE. Facile protein derivatization by DIAZOPY-SE was demonstrated using actin and sheep IgG. Actin labeled with DIAZOPY-SE and irradiated while in the F-actin (reversibly polymerized) form was crosslinked to yield a covalently-linked dimer, illustrating the potential of the reagent in photoaffinity applications. Advantages of DIAZOPY-SE as a photoaffinity labeling reagent include ease of synthesis, chemical and photostability, efficient photolysis at wavelengths greater than 300 nm, and a capacity for crosslinking by carbene insertion processes. PMID:1776676

  6. Applications of stable isotopes in clinical pharmacology

    PubMed Central

    Schellekens, Reinout C A; Stellaard, Frans; Woerdenbag, Herman J; Frijlink, Henderik W; Kosterink, Jos G W

    2011-01-01

    This review aims to present an overview of the application of stable isotope technology in clinical pharmacology. Three main categories of stable isotope technology can be distinguished in clinical pharmacology. Firstly, it is applied in the assessment of drug pharmacology to determine the pharmacokinetic profile or mode of action of a drug substance. Secondly, stable isotopes may be used for the assessment of drug products or drug delivery systems by determination of parameters such as the bioavailability or the release profile. Thirdly, patients may be assessed in relation to patient-specific drug treatment; this concept is often called personalized medicine. In this article, the application of stable isotope technology in the aforementioned three areas is reviewed, with emphasis on developments over the past 25 years. The applications are illustrated with examples from clinical studies in humans. PMID:21801197

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Nonlinear plants, factorizations and stable feedback systems

    NASA Technical Reports Server (NTRS)

    Desoer, Charles A.; Kabuli, M. Guntekin

    1987-01-01

    For nonlinear plants represented by causal maps defined over extended spaces, right factorization and normalized right-coprime factorization concepts are discussed in terms of well-posed stable feedback systems. This setup covers continuous-time, discrete-time, time-invariant or time-varying input-output maps. The nonlinear maps are factored in terms of causal bounded-input bounded-output stable maps. In factored form, all instabilities of the original map are represented by the inverse of a causal stable `denominator' map. The existence of maps with right factorizations and normalized right-coprime factorizations is shown using a well-posed stable unity-feedback system. In the case where one of the subsystems has a normalized right-coprime factorization, the stability of the feedback system is equivalent to the stability of the pseudostate map.

  13. 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.

  14. Stable vector bundles and string theory

    SciTech Connect

    Gomez, Tomas L.; Sols, Ignacio; Lukic, Sergio

    2009-05-06

    In [4], Braun, He, Ovrut and Pantev proposed a model of string theory (based on the Calabi-Yau 3-fold X) whose low energy limit predicts certain properties of the Standard Model of particle Physics. This model depends on two vector bundles that have to be stable. We calculate the ample cone of X, and prove that one of them is stable, and the other one is not.

  15. A (pentafluoroethyl)(trifluoromethyl)carbene complex of iridium and reductive activation of its sp(3)?, ?, and ? carbon-fluorine bonds to give perfluoro-2-butyne, perfluoro-1,2,3-butatriene and perfluoro-1-irida-2-methyl-2-cyclobutene) complexes.

    PubMed

    Yuan, Jian; Hughes, Russell P; Rheingold, Arnold L

    2015-12-01

    The (pentafluoroethyl)(trifluoromethyl)carbene complex Cp*Ir(CO)[[double bond, length as m-dash]C(CF3)(C2F5)] was synthesized by the reductive activation of the ?-C-F bond in the perfluoro-sec-butyl-iridium complex Cp*Ir(CO)[CF(CF3)(C2F5)](I) with Na/Pb alloy. This compound exists as two geometric isomers in solution; the structure of one isomer has been determined by a single crystal X-ray diffraction study and contains two independent molecules in the asymmetric unit. Further reduction of this carbene complex with Na/Pb alloy afforded the perfluoro-2-butyne iridium complex Cp*Ir(CO)(?(2)-CF3C[triple bond, length as m-dash]CCF3) by an overall 2-electron reduction and elimination of two ?-fluorides. When magnesium graphite was utilized as the reducing agent for the further reduction, Cp*Ir(CO)(?(2)-CF3C[triple bond, length as m-dash]CCF3) was produced as a minor product and the major product was the perfluoroiridacyclobutene complex Cp*Ir(CO)(?(2,4)-CF3CCFCF2) resulting from a ?-C-F bond activation. Direct reduction of the precursor Cp*Ir(CO)[CF(CF3)(C2F5)](i) with magnesium graphite generated the tetrafluorobutatriene iridium complex Cp*Ir(CO)(?(2,3)-CF2[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]CF2) along with the perfluoro-2-butyne complex and perfluoroiridacyclobutene complexes in a ratio of 1?:?2?:?6. These reductive inner-sphere pathways to unsaturated fluorocarbon ligands illustrate that carbon-fluorine bond activation can take place at ?-, ?- and ?-carbons but that selectivity in these heterogeneous reductions is difficult to control, with a variety of fluoride eliminations possible for complex perfluoroalkyl ligands. Density Functional Theory (DFT/B3LYP-D3/LACV3P**++) is used to explore the relative energetics of products and intermediates in these reactions. PMID:26158776

  16. 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.

  17. Low work function, stable thin films

    DOEpatents

    Dinh, Long N. (Concord, CA); McLean, II, William (Oakland, CA); Balooch, Mehdi (Berkeley, CA); Fehring, Jr., Edward J. (Dublin, CA); Schildbach, Marcus A. (Livermore, CA)

    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.

  18. 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.

  19. 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.

  20. 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.

  1. Stable high-temperature (500 C) thermistors

    NASA Astrophysics Data System (ADS)

    Carlson, R. O.

    1984-12-01

    Thermistors which are stable in their resistance-temperature characteristic after extended high-temperature exposure have been formed by attaching platinum wires or Fernico (Kovar) ribbons with Birox thick film paste to thermistor spinel material (from two vendors) with a resistivity of 2000 ? cm. Other resistivity compositions were not stable at elevated temperatures. Shifts in the original calibration curve were less than 2 C at room temperature after 10 000 h at 240 C, even with periodic jumps to 500 C. Held and measured at 500 C, resistance shifts were less than 2 C for periods up to 750 h. These thermistor structures should provide low-cost, stable, reliable, and interchangeable temperature sensors for oven and furnace measurement and control.

  2. The Seismicity of Stable Continental Regions

    NASA Astrophysics Data System (ADS)

    van Lanen, X.; Mooney, W. D.

    2004-12-01

    The large impact on humans of large magnitude earthquakes in stable continental regions provides a strong motivation to study the systematic nature of their occurrence, to improve the assessment of seismic hazards. Unfortunately, limited historical information of these events complicates studies to better understand these events. The existing main hypotheses to explain their occurrence are (1) reactivation of zones of weakness; (2) localization of stress by physical stress concentrators; (3) crustal weakening by fluids; (4) anomalous high temperatures; and (5) stress changes due to deglaciation or sediment loading. In this study stable continental seismicity patterns were compared with potential field data (Bouguer gravity and aeromagnetic anomaly maps are made). The study cannot disprove any of the existing hypotheses for the occurrence of these events, but it is possible to evaluate some of them. A significant portion of stable continental seismicity follows long linear geophysical trends (500-2000 km) that are correlated with major tectonic features, such as rifted margins and suture zones. The correlation of seismicity with localized stress concentrators is not consistent with this observation, which rather supports the zone of weakness hypothesis. However, in several cases of seismicity not observed in linear trends, the localized stress concentrator hypothesis is instead favorable. Rifted margins commonly have both sedimentary loads and high-density mafic lower crust, both of which provide a stress perturbation. The observed correlation with rifted margins is strong in Australia but less pronounced for eastern North America and is therefore not uniform. The correlation of seismicity with geophysical anomaly maps is an effective means of testing the multiple hypotheses that have been advanced for the genesis of earthquakes in Stable Continental Regions. We favor the view that multiple hypotheses are valid for stable continental earthquakes. Additional studies will help better our assessment of seismic hazards in Stable Continental Regions.

  3. 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 calcium. ImagesFIG. 1FIG. 3FIG. 4FIG. 5 PMID:6120036

  4. Transversely stable soliton trains in photonic lattices

    SciTech Connect

    Yang Jianke

    2011-09-15

    We report the existence of transversely stable soliton trains in optics. These stable soliton trains are found in two-dimensional square photonic lattices when they bifurcate from X-symmetry points with saddle-shaped diffraction inside the first Bloch band and their amplitudes are above a certain threshold. We also show that soliton trains with low amplitudes or bifurcated from edges of the first Bloch band ({Gamma} and M points) still suffer transverse instability. These results are obtained in the continuous lattice model and are further corroborated by the discrete model.

  5. Stable Tricyclic Antitubercular Ozonides Derived from Artemisinin.

    PubMed

    Chaudhary, Sandeep; Sharma, Vashundhra; Jaiswal, Pradeep K; Gaikwad, Anil N; Sinha, Sudhir K; Puri, Sunil K; Sharon, Ashoke; Maulik, Prakas R; Chaturvedi, Vinita

    2015-10-16

    New, highly stable tricyclic antitubercular ozonides 9 and 10 derived from artemisinin are reported in 39 and 9% yields, respectively. The ozonide groups of 9 and 10 were found to be stable under strong basic and acidic conditions. The absolute configuration of ozonides 9 was confirmed by X-ray crystallography. Ozonide 10 shows promising antitubercular activity against M. tuberculosis H37Ra and M. tuberculosis H37Rv with MIC values of 0.39 and 3.12 μg/mL, respectively. PMID:26430796

  6. Contribution of stable sources to ICRF improvements

    NASA Astrophysics Data System (ADS)

    Gontier, A.-M.; Feissel-Vernier, Martine

    2005-01-01

    A set of stable compact radio sources is proposed for the future maintenance of the ICRF axes using VLBI-derived time series of coordinates of extragalactic radio sources. The proposed selection scheme makes a combined use of statistical and deterministic tests. It identifies 199 stable sources to be compared to the current 212 defining sources. Their consideration for the maintenance of the frame axes is expected to improve the frame stability by a factor of five reaching the level of less than 10 microarcseconds in the medium term. The time behaviour of the radio source directions and their type of noise will be presented.

  7. Development of thermally stable polymer concrete

    SciTech Connect

    Megahed, T.N.E.D., Kukacka, L.E.; Fontana, J.J.

    1989-10-01

    This work pertains to the development of a polymer concrete type that is thermally stable under working temperatures of 200{degree} to 300{degree}F. This material is highly durable and thermally stable with high flexural strength and ductility. Its consistency, while fresh, is suitable for both casting in place or precasting techniques. Several optimization stages were applied ranging from mixing ratios and type of aggregate to resin formulation itself. An optimized range of mixing ratios is developed along with optimized mix ingredients, relating mechanical performance to elevated temperature at various degrees of workability.

  8. 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.

  9. Linear arrays of stable atmospheric pressure microplasmas

    SciTech Connect

    Zhang Zhibo; Hopwood, Jeffrey

    2009-10-19

    Microdischarges produce cold atmospheric plasma when the discharge current is limited by the quenching of a microwave resonator. A quarter-wavelength microstripline resonator is shown to support stable atmospheric microplasma in pure argon. Electrical characterization of the microplasma shows that its impedance is resistive and capacitive (Z{sub p}=500-j900 {omega}). An array of these linear resonators generates a stable, line-shaped microplasma operating from a single power source due to close-coupling among adjacent resonators. Both simulations and experiments confirm that coupled-mode theory describes the collective behavior of linear microplasma arrays.

  10. 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 Schutkowski. "Diet and social status during the La Tène period in Bohemia: carbon and nitrogen stable isotope analysis of bone collagen from Kutná Hora-Karlov and Radovesice." Journal of Anthropological Archaeology 24.2 (2005): 135-147. Schutkowski, Holger, et al. "Diet, status and decomposition at Weingarten: trace element and isotope analyses on early mediaeval skeletal material." Journal of Archaeological Science 26.6 (1999): 675-685. Zernitskaya, Valentina, et al. "Vegetation pattern and sedimentation changes in the context of the Lateglacial climatic events: Case study of Staroje Lake (Eastern Belarus)." Quaternary International (2014).

  11. HUNT STABLE COMPLEX LOOKING SOUTHWEST THROUGH EASTERNMOST SET OF PIERS ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    HUNT STABLE COMPLEX LOOKING SOUTHWEST THROUGH EASTERNMOST SET OF PIERS TOWARD STABLE - Overhills, Fort Bragg Military Reservation, Approximately 15 miles NW of Fayetteville, Overhills, Harnett County, NC

  12. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Lancet, M.S.; Winschel, R.A.; Burke, F.P.

    1991-01-01

    The purpose of obtaining stable carbon isotope analyses of coprocessing products is to determine the amount of coal (or petroleum) carbon that is present in any reaction product. This carbon-sourcing of distillate fractions, soluble resid, and insoluble organic matter, etc. is useful in modeling reactions, and evaluating synergistic effects if they exist.

  13. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Lancet, M.S.; Winschel, R.A.; Burke, F.P.

    1991-12-31

    The purpose of obtaining stable carbon isotope analyses of coprocessing products is to determine the amount of coal (or petroleum) carbon that is present in any reaction product. This carbon-sourcing of distillate fractions, soluble resid, and insoluble organic matter, etc. is useful in modeling reactions, and evaluating synergistic effects if they exist.

  14. Dynamically stable magnetic suspension/bearing system

    DOEpatents

    Post, Richard F. (Walnut Creek, CA)

    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.

  15. Nuclear Structure: From Stable to Unstable Nuclei

    NASA Astrophysics Data System (ADS)

    Voronov, V. V.

    2015-11-01

    A finite rank separable approximation for Skyrme interactions is applied to study the collective nuclear modes in stable and unstable nuclei. The coupling between one- and two-phonon terms in the wave functions are taken into account. Some possibilities for experimental investigations of the manifestations of the pseudospin symmetry in the spectra of odd nuclei with Z ? 100 are indicated.

  16. 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.

  17. Ultra-stable superconducting cavity maser oscillator

    NASA Technical Reports Server (NTRS)

    Strayer, Donald M. (Inventor); Dick: G. John (Inventor)

    1989-01-01

    An ultra-stable superconducting triple cavity ruby maser oscillator (10) is obtained by providing the oscillator with a superconducting quantum interference device (SQUID) (50), which measures the magnetic field at the ruby (14) and compensates for changes by adjusting the RF pump signal amplitude (42), thereby attaining stabilities of about four orders of magnitude greater than presently attainable.

  18. Stable Fly Project in Campo Grande, Brazil

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Andrew Li, Jerry Hogsette, and Beto Perez de Leon, all USDA, and Lane Foil, LSU, are collaborating as consultants on an Embrapa-funded research project for the control of large stable fly populations associated with sugar cane production in Brazil. Our Brazilian counterpart, Dr. Paulo Cançado, is t...

  19. 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...

  20. 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.

  1. Stable Fly Project in Campo Grande, Brazil

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Andrew Li, Jerry Hogsette, and Adalberto Prez de Len, all USDA-ARS, and Lane Foil, LSU, are collaborating as consultants on an Embrapa-funded research project for the control of large stable fly populations associated with sugar cane production in Brazil. Our Brazilian counterpart, Dr. Paulo Cana...

  2. A new look at stable isotope thermometry

    NASA Astrophysics Data System (ADS)

    Eiler, John M.; Valley, John W.; Baumgartner, Lukas P.

    1993-06-01

    Interdiffusion between coexisting minerals affects all rocks and causes resetting and discordance of stable isotope geothermometers that is commonly observed in slowly cooled igneous and metamorphic rocks. The Fast Grain Boundary (FGB) model describes the stable isotope fractionations and intracrystalline zonation which result from closed system interdiffusion ( EILER et al., 1991, 1992). This model assumes that grain boundary diffusion is much faster than volume diffusion, and it accounts for exchange among all minerals in a rock. Previous models of closure temperature violate mass balance restrictions and will be inaccurate in most rocks. Modeling results are described for amphibolites and hornblende granites and gneisses; biotite granites, schists, and gneisses; pelitic and semi-pelitic rocks; garnet peridotites; anorthosites, gabbros, pyroxenites, and related rocks; and calc-silicate rocks. Examples of mineral pairs and specific rock types that allow accurate stable isotope thermometry include plagioclase-pyroxene in pyroxene bearing anorthosites and garnet-quartz in garnetiferous quartzites. In contrast, the same mineral pairs in related rocks such as pyroxenites and pelitic schists will exhibit reset apparent temperatures. Closed-system processes are capable of producing a variety of patterns of stable isotope resetting, discordance, mineral zonation, and fractionation reversals. Examples include large reversals of quartz-feldspar fractionations in micaceous rocks, and oscillatory zonation in feldspar from some quartz-rich rocks. These results permit reinterpretation of many studies of stable isotope thermometry, speedometry, and retrograde alteration history. FGB modeling of mineral zonation provides an important new guide to applying recently developed micro-analytical tools to slowly cooled rocks. Application of the FGB model to quartzo-feldspathic gneisses from the Adirondack Mountains, New York, demonstrates the usefulness of diffusion modeling in discriminating closed-system, diffusion controlled retrogression from open-system retrogression, and illustrates the possible importance of incorporating the effect of water activity on mineral diffusivity.

  3. Development of a Safety Management Web Tool for Horse Stables.

    PubMed

    Leppl, Jarkko; Kolstrup, Christina Lunner; Pinzke, Stefan; Rautiainen, Risto; Saastamoinen, Markku; Srkijrvi, 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

  4. Air-stable droplet interface bilayers

    NASA Astrophysics Data System (ADS)

    Collier, Charles; ORNL Team

    2015-03-01

    Droplet interface bilayers are versatile model membranes useful for synthetic biology and biosensing; however, to date they have been for the most part confined to fluid reservoirs. Here, we demonstrate that when two or more water droplets meet on an oil-infused substrate, they exhibit noncoalescence due to the formation of a thin oil film that gets squeezed between the droplets from the bottom up. We show that when phospholipids are included in the water droplets, a stable droplet interface bilayer forms between the noncoalescing water droplets. As with traditional oil-submerged droplet interface bilayers, we were able to characterize ion channel transport by incorporating peptides into each droplet. We demonstrate the ability of these air-stable droplet interface bilayers (airDIBs) to incorporate ligand-gated ion channels via fusion of microsomes, which enables the biosensing of airborne matter.

  5. Comparison of stable isotope reference samples

    NASA Astrophysics Data System (ADS)

    Coplen, Tyler B.; Kendall, Carol; Hopple, Jessica

    1983-03-01

    Use of light stable isotope ratio measurements has proliferated in the past decade. The need for procuring additional stable isotope reference materials was recognized at an International Atomic Energy Agency (IAEA) consultants' meeting convened in 19761. This group recommended acquisition of two carbonates, two carbon dioxide samples, a biotite, a sulphate, and other reference materials. We report here on the mass-spectrometric analysis of these and other reference samples in a single laboratory to minimize interlaboratory calibration errors. A result of this work is an improved equation for relating the PDB isotope scale (belemnite from the Peedee Formation of South Carolina adopted in the 1950s as a reference in palaeotemperature studies2) to the V-SMOW (Vienna-Standard Mean Ocean Water) scale1.

  6. 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.}

  7. Stable, selectable, integrative DNA transformation in Physarum.

    PubMed

    Burland, T G; Bailey, J; Pallotta, D; Dove, W F

    1993-10-15

    The Physarum polycephalum actin promoter, PardC, can drive transient expression of heterologous genes in Physarum amoebae. The hph gene, encoding hygromycin (Hy) phosphotransferase, can confer resistance to Hy on a broad spectrum of organisms. When PardC is translationally fused to hph and transformed into yeasts on high-copy-number vectors, the yeasts become Hy resistant (HyR), showing that PardC-hph is a functional, selectable genetic element. To establish a stable transformation system for Physarum, we electroporated plasmids bearing PardC-hph into Physarum amoebae and then selected for HyR transformants. We show that HyR amoebae arise upon the stable integration of PardC-hph into the nuclear genome in single copy. These results establish a transformation system that can be used to add plasmid-borne genetic information to Physarum. PMID:8224865

  8. 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.

  9. Targeting Stable Rotors to Treat Atrial Fibrillation

    PubMed Central

    Narayan, Sanjiv M; Krummen, David E

    2012-01-01

    Therapy for atrial fibrillation (AF) remains suboptimal, in large part because its mechanisms are unclear. While pulmonary vein ectopy may trigger AF, it remains uncertain how AF, once triggered, is actually sustained. Recent discoveries show that human AF is maintained by a small number of rotors or focal sources. AF sources are widely distributed in patient-specific locations, often remote from pulmonary veins and in the right atrium and stable for prolonged periods of time. In a multicentre experience, brief targeted ablation at sources (focal impulse and rotor modulation [FIRM]) terminated AF predominantly to sinus rhythm prior to pulmonary vein isolation and eliminated AF on rigorous followup. This review summarises the evidence for stable rotors and focal sources of human AF and their clinical role as ablation targets to eliminate paroxysmal, persistent and long-standing persistent AF.

  10. Stable Lithium Argon compounds under high pressure

    NASA Astrophysics Data System (ADS)

    Li, Xiaofeng; Hermann, Andreas; Peng, Feng; Lv, Jian; Wang, Yanchao; Wang, Hui; Ma, Yanming

    2015-11-01

    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.

  11. 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.

  12. Complex symmetric matrices with strongly stable iterates

    NASA Technical Reports Server (NTRS)

    Tadmor, E.

    1985-01-01

    Complex-valued symmetric matrices are studied. A simple expression for the spectral norm of such matrices is obtained, by utilizing a unitarily congruent invariant form. A sharp criterion is provided for identifying those symmetric matrices whose spectral norm is not exceeding one: such strongly stable matrices are usually sought in connection with convergent difference approximations to partial differential equations. As an example, the derived criterion is applied to conclude the strong stability of a Lax-Wendroff scheme.

  13. 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 (?15N and ?18O) 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 mixing fractions.

  14. 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.

  15. 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.

  16. Stable numerical boundary conditions for Stokes equations

    SciTech Connect

    Meth, K.Z. . Matam-Advanced Technology Center)

    1994-10-01

    The author works with the vorticity-stream function formulation of the Stokes equations. Two boundary conditions are given for the stream function while no boundary conditions are given for the vorticity. A derived boundary condition for the vorticity is considered and it is proven that the resulting fully discrete numerical method is stable. The results are then extended to the three-dimensional Stokes equations using a staggered grid.

  17. Stable Spheromaks Sustained by Neutral Beam Injection

    SciTech Connect

    Fowler, T K; Jayakumar, R; McLean, H S

    2008-05-14

    It is shown that spheromak equilibria, stable at zero-beta but departing from the Taylor state, could be sustained by non-inductive current drive at acceptable power levels. Stability to both ideal MHD and tearing modes is verified using the NIMROD code for linear stability analysis. Non-linear NIMROD calculations with non-inductive current drive and pressure effects could point the way to improved fusion reactors.

  18. Mechanisms for stable single bubble sonoluminescence

    SciTech Connect

    Brenner, M.P.; Lohse, D.; Oxtoby, D.; Dupont, T.F.

    1996-02-01

    A gas bubble trapped in water by an oscillating acoustic field is expected to either shrink or grow on a diffusive time scale, depending on the forcing strength and the bubble size. At high ambient gas concentration this has long been observed. However, recent sonoluminescence experiments show that when the ambient gas concentration is low the bubble can be stable for days. This paper discusses mechanisms leading to stability. {copyright} {ital 1996 The American Physical Society.}

  19. 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.

  20. Stable carbon isotope analysis of coprocessing materials

    SciTech Connect

    Lancet, M.S.; Winschel, R.A.; Burke, F.P.

    1991-01-01

    Consol R D is developing and demonstrating stable carbon isotope analysis as a method to quantitatively distinguish coal-derived and petroleum-derived carbon in products from coal/petroleum coprocessing. The approach taken is to develop the method, then demonstrate its application an authentic continuous-unit products. The experimental details used for stable carbon isotope analyses by the organization that performs most of those analyses under this contract are described. A method was developed previously under this contract to correct the carbon sourcing calculations performed from stable carbon isotope analyses for selective isotopic fractionation. The method relies on three assumptions. This quarter, a study was completed to define the sensitivity of the carbon sourcing results to errors in the assumptions. Carbon contents and carbon isotope ratios were determined for the available feeds and product fractions from HRI bench-scale coprocessing Run 238-10 (Texas lignite/Hondo vacuum still bottoms (VSB), Texas lignite/Cold Lake VSB and Westerholt coal/Cold Lake VSB). These data were used for carbon sourcing calculations and individual feedstock conversion calculations. A previously devised means for correcting for selective isotope fractionation was applied. 6 refs., 30 figs., 16 tabs.