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Sample records for aliphatic c-h bonds

  1. Chemoselective hydroxylation of aliphatic sp3 C-H bonds using a ketone catalyst and aqueous H2O2.

    PubMed

    Pierce, Conor J; Hilinski, Michael K

    2014-12-19

    The first ketone-catalyzed method for the oxidation of aliphatic C-H bonds is reported. The reaction conditions employ aryl trifluoromethyl ketones in catalytic amounts and hydrogen peroxide as the terminal oxidant. Hydroxylation is stereospecific and chemoselective for tertiary over secondary C-H bonds. A catalytic cycle invoking a dioxirane as the active oxidant is proposed.

  2. Fine Control over Site and Substrate Selectivity in Hydrogen Atom Transfer-Based Functionalization of Aliphatic C-H Bonds.

    PubMed

    Salamone, Michela; Carboni, Giulia; Bietti, Massimo

    2016-10-07

    The selective functionalization of unactivated aliphatic C-H bonds over intrinsically more reactive ones represents an ongoing challenge of synthetic chemistry. Here we show that in hydrogen atom transfer (HAT) from the aliphatic C-H bonds of alkane, ether, alcohol, amide, and amine substrates to the cumyloxyl radical (CumO(•)) fine control over site and substrate selectivity is achieved by means of acid-base interactions. Protonation of the amines and metal ion binding to amines and amides strongly deactivates the C-H bonds of these substrates toward HAT to CumO(•), providing a powerful method for selective functionalization of unactivated or intrinsically less reactive C-H bonds. With 5-amino-1-pentanol, site-selectivity has been drastically changed through protonation of the strongly activating NH2 group, with HAT that shifts to the C-H bonds that are adjacent to the OH group. In the intermolecular selectivity studies, trifluoroacetic acid, Mg(ClO4)2, and LiClO4 have been employed in a orthogonal fashion for selective functionalization of alkane, ether, alcohol, and amide (or amine) substrates in the presence of an amine (or amide) one. Ca(ClO4)2, that promotes deactivation of amines and amides by Ca(2+) binding, offers, moreover, the opportunity to selectively functionalize the C-H bonds of alkane, ether, and alcohol substrates in the presence of both amines and amides.

  3. Mild Aliphatic and Benzylic Hydrocarbon C-H Bond Chlorination Using Trichloroisocyanuric Acid.

    PubMed

    Combe, Sascha H; Hosseini, Abolfazl; Parra, Alejandro; Schreiner, Peter R

    2017-03-03

    We present the controlled monochlorination of aliphatic and benzylic hydrocarbons with only 1 equiv of substrate at 25-30 °C using N-hydroxyphthalimide (NHPI) as radical initiator and commercially available trichloroisocyanuric acid (TCCA) as the chlorine source. Catalytic amounts of CBr4 reduced the reaction times considerably due to the formation of chain-carrying ·CBr3 radicals. Benzylic C-H chlorination affords moderate to good yields for arenes carrying electron-withdrawing (50-85%) or weakly electron-donating groups (31-73%); cyclic aliphatic substrates provide low yields (24-38%). The products could be synthesized on a gram scale followed by simple purification via distillation. We report the first direct side-chain chlorination of 3-methylbenzoate affording methyl 3-(chloromethyl)benzoate, which is an important building block for the synthesis of vasodilator taprostene.

  4. Transition metal-free intramolecular regioselective couplings of aliphatic and aromatic C-H bonds.

    PubMed

    Tian, Hua; Yang, Haijun; Zhu, Changjin; Fu, Hua

    2016-01-29

    Cross-dehydrogenative couplings of two different C-H bonds have emerged as an attractive goal in organic synthesis. However, achieving regioselective C-H activation is a great challenge because C-H bonds are ubiquitous in organic compounds. Actually, the regioselective couplings promoted by enzymes are a common occurrence in nature. Herein, we have developed simple, efficient and general transition metal-free intramolecular couplings of alphatic and aromatic C-H bonds. The protocol uses readily available aryl triazene as the radical initiator, cheap K2S2O8 as the oxidant, and the couplings were performed well with excellent tolerance of functional groups. Interestingly, α-carbon configuration of some amino acid residues in the substrates was kept after the reactions, and the couplings for substrates with substituted phenylalanine residues exhibited complete β-carbon diastereoselectivity for induction of the chiral α-carbon. Therefore, the present study should provide a novel strategy for regioselective cross-dehydrogenative couplings of two different C-H bonds.

  5. Tuning reactivity and selectivity in hydrogen atom transfer from aliphatic C-H bonds to alkoxyl radicals: role of structural and medium effects.

    PubMed

    Salamone, Michela; Bietti, Massimo

    2015-11-17

    Hydrogen atom transfer (HAT) is a fundamental reaction that takes part in a wide variety of chemical and biological processes, with relevant examples that include the action of antioxidants, damage to biomolecules and polymers, and enzymatic and biomimetic reactions. Moreover, great attention is currently devoted to the selective functionalization of unactivated aliphatic C-H bonds, where HAT based procedures have been shown to play an important role. In this Account, we describe the results of our recent studies on the role of structural and medium effects on HAT from aliphatic C-H bonds to the cumyloxyl radical (CumO(•)). Quantitative information on the reactivity and selectivity patterns observed in these reactions has been obtained by time-resolved kinetic studies, providing a deeper understanding of the factors that govern HAT from carbon and leading to the definition of useful guidelines for the activation or deactivation of aliphatic C-H bonds toward HAT. In keeping with the electrophilic character of alkoxyl radicals, polar effects can play an important role in the reactions of CumO(•). Electron-rich C-H bonds are activated whereas those that are α to electron withdrawing groups are deactivated toward HAT, with these effects being able to override the thermodynamic preference for HAT from the weakest C-H bond. Stereoelectronic effects can also influence the reactivity of the C-H bonds of ethers, amines, and amides. HAT is most rapid when these bonds can be eclipsed with a lone pair on an adjacent heteroatom or with the π-system of an amide functionality, thus allowing for optimal orbital overlap. In HAT from cyclohexane derivatives, tertiary axial C-H bond deactivation and tertiary equatorial C-H bond activation have been observed. These effects have been explained on the basis of an increase in torsional strain or a release in 1,3-diaxial strain in the HAT transition states, with kH(eq)/kH(ax) ratios that have been shown to exceed one order of

  6. An Iminium Salt Organocatalyst for Selective Aliphatic C-H Hydroxylation.

    PubMed

    Wang, Daoyong; Shuler, William G; Pierce, Conor J; Hilinski, Michael K

    2016-08-05

    The first examples of catalysis of aliphatic C-H hydroxylation by an iminium salt are presented. The method allows the selective organocatalytic hydroxylation of unactivated 3° C-H bonds at room temperature using hydrogen peroxide as the terminal oxidant. Hydroxylation of an unactivated 2° C-H bond is also demonstrated. Furthermore, improved functional group compatibility over other catalytic methods is reported in the form of selectivity for aliphatic C-H hydroxylation over alcohol oxidation. On the basis of initial mechanistic studies, an oxaziridinium species is proposed as the active oxidant.

  7. Manganese-catalyzed late-stage aliphatic C-H azidation.

    PubMed

    Huang, Xiongyi; Bergsten, Tova M; Groves, John T

    2015-04-29

    We report a manganese-catalyzed aliphatic C-H azidation reaction that can efficiently convert secondary, tertiary, and benzylic C-H bonds to the corresponding azides. The method utilizes aqueous sodium azide solution as the azide source and can be performed under air. Besides its operational simplicity, the potential of this method for late-stage functionalization has been demonstrated by successful azidation of various bioactive molecules with yields up to 74%, including the important drugs pregabalin, memantine, and the antimalarial artemisinin. Azidation of celestolide with a chiral manganese salen catalyst afforded the azide product in 70% ee, representing a Mn-catalyzed enantioselective aliphatic C-H azidation reaction. Considering the versatile roles of organic azides in modern chemistry and the ubiquity of aliphatic C-H bonds in organic molecules, we envision that this Mn-azidation method will find wide application in organic synthesis, drug discovery, and chemical biology.

  8. Iron-Catalyzed Oxyfunctionalization of Aliphatic Amines at Remote Benzylic C-H Sites.

    PubMed

    Mbofana, Curren T; Chong, Eugene; Lawniczak, James; Sanford, Melanie S

    2016-09-02

    We report the development of an iron-catalyzed method for the selective oxyfunctionalization of benzylic C(sp(3))-H bonds in aliphatic amine substrates. This transformation is selective for benzylic C-H bonds that are remote (i.e., at least three carbons) from the amine functional group. High site selectivity is achieved by in situ protonation of the amine with trifluoroacetic acid, which deactivates more traditionally reactive C-H sites that are α to nitrogen. The scope and synthetic utility of this method are demonstrated via the synthesis and derivatization of a variety of amine-containing, biologically active molecules.

  9. (18)F-Fluorination of Unactivated C-H Bonds in Branched Aliphatic Amino Acids: Direct Synthesis of Oncological Positron Emission Tomography Imaging Agents.

    PubMed

    Nodwell, Matthew B; Yang, Hua; Čolović, Milena; Yuan, Zheliang; Merkens, Helen; Martin, Rainer E; Bénard, François; Schaffer, Paul; Britton, Robert

    2017-03-15

    A mild and selective photocatalytic C-H (18)F-fluorination reaction has been developed that provides direct access to (18)F-fluorinated amino acids. The biodistribution and uptake of three (18)F-labeled leucine analogues via LAT1 mediated transport in several cancer cell lines is reported. Positron emission tomography imaging of mice bearing PC3 (prostate) or U87 (glioma) xenografts using 5-[(18)F]-fluorohomoleucine showed high tumor uptake and excellent tumor visualization, highlighting the utility of this strategy for rapid tracer discovery for oncology.

  10. Metal-free oxidative olefination of primary amines with benzylic C-H bonds through direct deamination and C-H bond activation.

    PubMed

    Gong, Liang; Xing, Li-Juan; Xu, Tong; Zhu, Xue-Ping; Zhou, Wen; Kang, Ning; Wang, Bin

    2014-09-14

    An oxidative olefination reaction between aliphatic primary amines and benzylic sp(3) C-H bonds has been achieved using N-bromosuccinimide as catalyst and tert-butyl hydroperoxide as oxidant. The olefination proceeds under mild metal-free conditions through direct deamination and benzylic C-H bond activation, and provides easy access to biologically active 2-styrylquinolines with (E)-configuration.

  11. Toluene and Ethylbenzene Aliphatic C-H Bond Oxidations Initiated by a Dicopper(II)-μ-1,2-Peroxo Complex

    PubMed Central

    Lucas, Heather R.; Li, Lei; Sarjeant, Amy A. Narducci; Vance, Michael A.; Solomon, Edward I.; Karlin, Kenneth D.

    2009-01-01

    With an anisole containing polypyridylamine potential tetradentate ligand OL, a μ-1,2-peroxo-dicopper(II) complex [{OLCuII}2(O22-)]2+ forms from the reaction of the mononuclear compound [CuI(OL)(MeCN)]B(C6F5)4(OLCuI) with O2 in non-coordinating solvents at -80 °C. Thermal decay of this peroxo complex in the presence of toluene or ethylbenzene leads to rarely seen C-H activation chemistry; benzaldehyde and acetophenone/1-phenylethanol mixtures, respectively, are formed. Experiments with 18O2 confirm that the oxygen source in the products is molecular O2 and deuterium labeling experiments indicate kH/kD = 7.5 ± 1 for the toluene oxygenation. The O2-reaction of [CuI(BzL)(CH3CN)]+ (BzLCuI) leads to a dicopper(III)-bis-μ-oxo species [{BzLCuIII}2(μ-O2-)2]2+ at -80 °C and from such solutions, very similar toluene oxygenation chemistry occurs. Ligand BzL is a tridentate chelate, possessing the same moiety found in OL, but without the anisole O-atom donor. In these contexts, the nature of the oxidant species in or derived from [{OLCuII}2(O22-)]2+ is discussed and likely mechanisms of reaction initiated by toluene H-atom abstraction chemistry are detailed. To confirm the structural formulations of the dioxygen-adducts, UV-vis and resonance Raman spectroscopic studies have been carried out and these results are reported and compared to previously described systems including [{CuII(PYL)}2(O2)]2+ (PYL =TMPA = tris(2-methylpyridyl)amine). Using (L)CuI, CO-binding properties (i.e., νC-O values) along with electrochemical property comparisons, the relative donor abilities of OL, BzL and PYL are assessed. PMID:19216527

  12. Oxidative aliphatic C-H fluorination with fluoride ion catalyzed by a manganese porphyrin.

    PubMed

    Liu, Wei; Huang, Xiongyi; Cheng, Mu-Jeng; Nielsen, Robert J; Goddard, William A; Groves, John T

    2012-09-14

    Despite the growing importance of fluorinated organic compounds in drug development, there are no direct protocols for the fluorination of aliphatic C-H bonds using conveniently handled fluoride salts. We have discovered that a manganese porphyrin complex catalyzes alkyl fluorination by fluoride ion under mild conditions in conjunction with stoichiometric oxidation by iodosylbenzene. Simple alkanes, terpenoids, and even steroids were selectively fluorinated at otherwise inaccessible sites in 50 to 60% yield. Decalin was fluorinated predominantly at the C2 and C3 methylene positions. Bornyl acetate was converted to exo-5-fluoro-bornyl acetate, and 5α-androstan-17-one was fluorinated selectively in the A ring. Mechanistic analysis suggests that the regioselectivity for C-H bond cleavage is directed by an oxomanganese(V) catalytic intermediate followed by F delivery via an unusual manganese(IV) fluoride that has been isolated and structurally characterized.

  13. Site-Selective Aliphatic C-H Chlorination Using N-Chloroamides Enables a Synthesis of Chlorolissoclimide.

    PubMed

    Quinn, Ryan K; Könst, Zef A; Michalak, Sharon E; Schmidt, Yvonne; Szklarski, Anne R; Flores, Alex R; Nam, Sangkil; Horne, David A; Vanderwal, Christopher D; Alexanian, Erik J

    2016-01-20

    Methods for the practical, intermolecular functionalization of aliphatic C-H bonds remain a paramount goal of organic synthesis. Free radical alkane chlorination is an important industrial process for the production of small molecule chloroalkanes from simple hydrocarbons, yet applications to fine chemical synthesis are rare. Herein, we report a site-selective chlorination of aliphatic C-H bonds using readily available N-chloroamides and apply this transformation to a synthesis of chlorolissoclimide, a potently cytotoxic labdane diterpenoid. These reactions deliver alkyl chlorides in useful chemical yields with substrate as the limiting reagent. Notably, this approach tolerates substrate unsaturation that normally poses major challenges in chemoselective, aliphatic C-H functionalization. The sterically and electronically dictated site selectivities of the C-H chlorination are among the most selective alkane functionalizations known, providing a unique tool for chemical synthesis. The short synthesis of chlorolissoclimide features a high yielding, gram-scale radical C-H chlorination of sclareolide and a three-step/two-pot process for the introduction of the β-hydroxysuccinimide that is salient to all the lissoclimides and haterumaimides. Preliminary assays indicate that chlorolissoclimide and analogues are moderately active against aggressive melanoma and prostate cancer cell lines.

  14. Site-selective C-H arylation of primary aliphatic amines enabled by a catalytic transient directing group

    NASA Astrophysics Data System (ADS)

    Liu, Yongbing; Ge, Haibo

    2017-01-01

    Transition-metal-catalysed direct C-H bond functionalization of aliphatic amines is of great importance in organic and medicinal chemistry research. Several methods have been developed for the direct sp3 C-H functionalization of secondary and tertiary aliphatic amines, but site-selective functionalization of primary aliphatic amines in remote positions remains a challenge. Here, we report the direct, highly site-selective γ-arylation of primary alkylamines via a palladium-catalysed C-H bond functionalization process on unactivated sp3 carbons. Using glyoxylic acid as an inexpensive, catalytic and transient directing group, a wide array of γ-arylated primary alkylamines were prepared without any protection or deprotection steps. This approach provides straightforward access to important structural motifs in organic and medicinal chemistry without the need for pre-functionalized substrates or stoichiometric directing groups and is demonstrated here in the synthesis of analogues of the immunomodulatory drug fingolimod directly from commercially available 2-amino-2-propylpropane-1,3-diol.

  15. C-H fluorination: U can fluorinate unactivated bonds

    NASA Astrophysics Data System (ADS)

    Neumann, Constanze N.; Ritter, Tobias

    2016-09-01

    Introducing C-F bonds into organic molecules is a challenging task, particularly through C-H activation methods. Now, a uranium-based photocatalyst turns traditional selectivity rules on their heads and fluorinates unfunctionalized alkane Csp3-H bonds, even in the presence of C-H bonds that are typically more reactive.

  16. Manganese Porphyrins Catalyze Selective C-H Bond Halogenations

    SciTech Connect

    Liu, Wei; Groves, John T.

    2010-08-31

    We report a manganese porphyrin mediated aliphatic C-H bond chlorination using sodium hypochlorite as the chlorine source. In the presence of catalytic amounts of phase transfer catalyst and manganese porphyrin Mn(TPP)Cl 1, reaction of sodium hypochlorite with different unactivated alkanes afforded alkyl chlorides as the major products with only trace amounts of oxygenation products. Substrates with strong C-H bonds, such as neopentane (BDE =~100 kcal/mol) can be also chlorinated with moderate yield. Chlorination of a diagnostic substrate, norcarane, afforded rearranged products indicating a long-lived carbon radical intermediate. Moreover, regioselective chlorination was achieved by using a hindered catalyst, Mn(TMP)Cl, 2. Chlorination of trans-decalin with 2 provided 95% selectivity for methylene-chlorinated products as well as a preference for the C2 position. This novel chlorination system was also applied to complex substrates. With 5α-cholestane as the substrate, we observed chlorination only at the C2 and C3 positions in a net 55% yield, corresponding to the least sterically hindered methylene positions in the A-ring. Similarly, chlorination of sclareolide afforded the equatorial C2 chloride in a 42% isolated yield. Regarding the mechanism, reaction of sodium hypochlorite with the MnIII porphyrin is expected to afford a reactive MnV=O complex that abstracts a hydrogen atom from the substrate, resulting in a free alkyl radical and a MnIV—OH complex. We suggest that this carbon radical then reacts with a MnIV—OCl species, providing the alkyl chloride and regenerating the reactive MnV=O complex. The regioselectivity and the preference for CH2 groups can be attributed to nonbonded interactions between the alkyl groups on the substrates and the aryl groups of the manganese porphyrin. The results are indicative of a bent [Mnv=O---H---C] geometry due to the C—H approach to the Mn

  17. Iron Complex Catalyzed Selective C-H Bond Oxidation with Broad Substrate Scope.

    PubMed

    Jana, Sandipan; Ghosh, Munmun; Ambule, Mayur; Sen Gupta, Sayam

    2017-02-17

    The use of a peroxidase-mimicking Fe complex has been reported on the basis of the biuret-modified TAML macrocyclic ligand framework (Fe-bTAML) as a catalyst to perform selective oxidation of unactivated 3° C-H bonds and activated 2° C-H bonds with low catalyst loading (1 mol %) and high product yield (excellent mass balance) under near-neutral conditions and broad substrate scope (18 substrates which includes arenes, heteroaromatics, and polar functional groups). Aliphatic C-H oxidation of 3° and 2° sites of complex substrates was achieved with predictable selectivity using steric, electronic, and stereoelectronic rules that govern site selectivity, which included oxidation of (+)-artemisinin to (+)-10β-hydroxyartemisinin. Mechanistic studies indicate Fe(V)(O) to be the active oxidant during these reactions.

  18. C-H bond activation by f-block complexes.

    PubMed

    Arnold, Polly L; McMullon, Max W; Rieb, Julia; Kühn, Fritz E

    2015-01-02

    Most homogeneous catalysis relies on the design of metal complexes to trap and convert substrates or small molecules to value-added products. Organometallic lanthanide compounds first gave a tantalizing glimpse of their potential for catalytic C-H bond transformations with the selective cleavage of one C-H bond in methane by bis(permethylcyclopentadienyl)lanthanide methyl [(η(5) -C5 Me5 )2 Ln(CH3 )] complexes some 25 years ago. Since then, numerous metal complexes from across the periodic table have been shown to selectively activate hydrocarbon C-H bonds, but the challenges of closing catalytic cycles still remain; many f-block complexes show great potential in this important area of chemistry.

  19. Metal-catalysed azidation of tertiary C-H bonds suitable for late-stage functionalization.

    PubMed

    Sharma, Ankit; Hartwig, John F

    2015-01-29

    Many enzymes oxidize unactivated aliphatic C-H bonds selectively to form alcohols; however, biological systems do not possess enzymes that catalyse the analogous aminations of C-H bonds. The absence of such enzymes limits the discovery of potential medicinal candidates because nitrogen-containing groups are crucial to the biological activity of therapeutic agents and clinically useful natural products. In one prominent example illustrating the importance of incorporating nitrogen-based functionality, the conversion of the ketone of erythromycin to the -N(Me)CH2- group in azithromycin leads to a compound that can be dosed once daily with a shorter treatment time. For such reasons, synthetic chemists have sought catalysts that directly convert C-H bonds to C-N bonds. Most currently used catalysts for C-H bond amination are ill suited to the intermolecular functionalization of complex molecules because they require excess substrate or directing groups, harsh reaction conditions, weak or acidic C-H bonds, or reagents containing specialized groups on the nitrogen atom. Among C-H bond amination reactions, those forming a C-N bond at a tertiary alkyl group would be particularly valuable, because this linkage is difficult to form from ketones or alcohols that might be created in a biosynthetic pathway by oxidation. Here we report a mild, selective, iron-catalysed azidation of tertiary C-H bonds that occurs without excess of the valuable substrate. The reaction tolerates aqueous environments and is suitable for the functionalization of complex structures in the late stages of a multistep synthesis. Moreover, this azidation makes it possible to install a range of nitrogen-based functional groups, including those from Huisgen 'click' cycloadditions and the Staudinger ligation. We anticipate that these reactions will create opportunities to modify natural products, their precursors and their derivatives to produce analogues that contain different polarity and charge as a

  20. Metal-catalysed azidation of tertiary C-H bonds suitable for late-stage functionalization

    NASA Astrophysics Data System (ADS)

    Sharma, Ankit; Hartwig, John F.

    2015-01-01

    Many enzymes oxidize unactivated aliphatic C-H bonds selectively to form alcohols; however, biological systems do not possess enzymes that catalyse the analogous aminations of C-H bonds. The absence of such enzymes limits the discovery of potential medicinal candidates because nitrogen-containing groups are crucial to the biological activity of therapeutic agents and clinically useful natural products. In one prominent example illustrating the importance of incorporating nitrogen-based functionality, the conversion of the ketone of erythromycin to the -N(Me)CH2- group in azithromycin leads to a compound that can be dosed once daily with a shorter treatment time. For such reasons, synthetic chemists have sought catalysts that directly convert C-H bonds to C-N bonds. Most currently used catalysts for C-H bond amination are ill suited to the intermolecular functionalization of complex molecules because they require excess substrate or directing groups, harsh reaction conditions, weak or acidic C-H bonds, or reagents containing specialized groups on the nitrogen atom. Among C-H bond amination reactions, those forming a C-N bond at a tertiary alkyl group would be particularly valuable, because this linkage is difficult to form from ketones or alcohols that might be created in a biosynthetic pathway by oxidation. Here we report a mild, selective, iron-catalysed azidation of tertiary C-H bonds that occurs without excess of the valuable substrate. The reaction tolerates aqueous environments and is suitable for the functionalization of complex structures in the late stages of a multistep synthesis. Moreover, this azidation makes it possible to install a range of nitrogen-based functional groups, including those from Huisgen `click' cycloadditions and the Staudinger ligation. We anticipate that these reactions will create opportunities to modify natural products, their precursors and their derivatives to produce analogues that contain different polarity and charge as a

  1. Catalytic alkylation of remote C-H bonds enabled by proton-coupled electron transfer

    NASA Astrophysics Data System (ADS)

    Choi, Gilbert J.; Zhu, Qilei; Miller, David C.; Gu, Carol J.; Knowles, Robert R.

    2016-11-01

    Despite advances in hydrogen atom transfer (HAT) catalysis, there are currently no molecular HAT catalysts that are capable of homolysing the strong nitrogen-hydrogen (N-H) bonds of N-alkyl amides. The motivation to develop amide homolysis protocols stems from the utility of the resultant amidyl radicals, which are involved in various synthetically useful transformations, including olefin amination and directed carbon-hydrogen (C-H) bond functionalization. In the latter process—a subset of the classical Hofmann-Löffler-Freytag reaction—amidyl radicals remove hydrogen atoms from unactivated aliphatic C-H bonds. Although powerful, these transformations typically require oxidative N-prefunctionalization of the amide starting materials to achieve efficient amidyl generation. Moreover, because these N-activating groups are often incorporated into the final products, these methods are generally not amenable to the direct construction of carbon-carbon (C-C) bonds. Here we report an approach that overcomes these limitations by homolysing the N-H bonds of N-alkyl amides via proton-coupled electron transfer. In this protocol, an excited-state iridium photocatalyst and a weak phosphate base cooperatively serve to remove both a proton and an electron from an amide substrate in a concerted elementary step. The resultant amidyl radical intermediates are shown to promote subsequent C-H abstraction and radical alkylation steps. This C-H alkylation represents a catalytic variant of the Hofmann-Löffler-Freytag reaction, using simple, unfunctionalized amides to direct the formation of new C-C bonds. Given the prevalence of amides in pharmaceuticals and natural products, we anticipate that this method will simplify the synthesis and structural elaboration of amine-containing targets. Moreover, this study demonstrates that concerted proton-coupled electron transfer can enable homolytic activation of common organic functional groups that are energetically inaccessible using

  2. Catalytic alkylation of remote C-H bonds enabled by proton-coupled electron transfer.

    PubMed

    Choi, Gilbert J; Zhu, Qilei; Miller, David C; Gu, Carol J; Knowles, Robert R

    2016-11-10

    Despite advances in hydrogen atom transfer (HAT) catalysis, there are currently no molecular HAT catalysts that are capable of homolysing the strong nitrogen-hydrogen (N-H) bonds of N-alkyl amides. The motivation to develop amide homolysis protocols stems from the utility of the resultant amidyl radicals, which are involved in various synthetically useful transformations, including olefin amination and directed carbon-hydrogen (C-H) bond functionalization. In the latter process-a subset of the classical Hofmann-Löffler-Freytag reaction-amidyl radicals remove hydrogen atoms from unactivated aliphatic C-H bonds. Although powerful, these transformations typically require oxidative N-prefunctionalization of the amide starting materials to achieve efficient amidyl generation. Moreover, because these N-activating groups are often incorporated into the final products, these methods are generally not amenable to the direct construction of carbon-carbon (C-C) bonds. Here we report an approach that overcomes these limitations by homolysing the N-H bonds of N-alkyl amides via proton-coupled electron transfer. In this protocol, an excited-state iridium photocatalyst and a weak phosphate base cooperatively serve to remove both a proton and an electron from an amide substrate in a concerted elementary step. The resultant amidyl radical intermediates are shown to promote subsequent C-H abstraction and radical alkylation steps. This C-H alkylation represents a catalytic variant of the Hofmann-Löffler-Freytag reaction, using simple, unfunctionalized amides to direct the formation of new C-C bonds. Given the prevalence of amides in pharmaceuticals and natural products, we anticipate that this method will simplify the synthesis and structural elaboration of amine-containing targets. Moreover, this study demonstrates that concerted proton-coupled electron transfer can enable homolytic activation of common organic functional groups that are energetically inaccessible using

  3. Transition-metal-catalyzed additions of C-H bonds to C-X (X = N, O) multiple bonds via C-H bond activation.

    PubMed

    Yan, Guobing; Wu, Xiangmei; Yang, Minghua

    2013-09-14

    Chemical transformations via catalytic C-H bond activation have been established as one of the most powerful tools in organic synthetic chemistry. Transition-metal-catalyzed addition reactions of C-H bonds to polar C-X (X = N, O) multiple bonds, such as aldehydes, ketones, imines, isocyanates, nitriles, isocyanides, carbon monoxide and carbon dioxide, have undergone a rapid development in recent years. In this review, recent advances in this active area have been highlighted and their mechanisms have been discussed.

  4. Aliphatic Halogenase Enables Late-Stage C-H Functionalization: Selective Synthesis of a Brominated Fischerindole Alkaloid with Enhanced Antibacterial Activity.

    PubMed

    Zhu, Qin; Hillwig, Matthew L; Doi, Yohei; Liu, Xinyu

    2016-03-15

    The anion promiscuity of a newly discovered standalone aliphatic halogenase WelO5 was probed and enabled the selective synthesis of 13R-bromo-12-epi-fischerindole U via late-stage enzymatic functionalization of an unactivated sp(3) C-H bond. Pre-saturating the WelO5 active site with a non-native bromide anion was found to be critical to the highly selective in vitro transfer of bromine, instead of chlorine, to the target carbon center and also allowed the relative binding affinity of bromide and chloride towards the WelO5 enzyme to be assessed. This study further revealed the critical importance of halogen substitution on modulating the antibiotic activity of fischerindole alkaloids and highlights the promise of WelO5-type aliphatic halogenases as enzymatic tools to fine-tune the bioactivity of complex natural products.

  5. Catalytic C-H bond silylation of aromatic heterocycles.

    PubMed

    Toutov, Anton A; Liu, Wen-Bo; Betz, Kerry N; Stoltz, Brian M; Grubbs, Robert H

    2015-12-01

    This protocol describes a method for the direct silylation of the carbon-hydrogen (C-H) bond of aromatic heterocycles using inexpensive and abundant potassium tert-butoxide (KOt-Bu) as the catalyst. This catalytic cross-dehydrogenative coupling of simple hydrosilanes and various electron-rich aromatic heterocycles enables the synthesis of valuable silylated heteroarenes. The products thus obtained can be used as versatile intermediates, which facilitate the divergent synthesis of pharmaceutically relevant compound libraries from a single Si-containing building block. Moreover, a variety of complex Si-containing motifs, such as those produced by this protocol, are being actively investigated as next-generation therapeutic agents, because they can have improved pharmacokinetic properties compared with the original all-carbon drug molecules. Current competing methods for C-H bond silylation tend to be incompatible with functionalities, such as Lewis-basic heterocycles, that are often found in pharmaceutical substances; this leaves de novo synthesis as the principal strategy for preparation of the target sila-drug analog. Moreover, competing methods tend to be limited in the scope of hydrosilane that can be used, which restricts the breadth of silicon-containing small molecules that can be accessed. The approach outlined in this protocol enables the chemoselective and regioselective late-stage silylation of small heterocycles, including drugs and drug derivatives, with a broad array of hydrosilanes in the absence of precious metal catalysts, stoichiometric reagents, sacrificial hydrogen acceptors or high temperatures. Moreover, H2 is the only by-product generated. The procedure normally requires 48-75 h to be completed.

  6. Metal-Free Oxidative C-C Bond Formation through C-H Bond Functionalization.

    PubMed

    Narayan, Rishikesh; Matcha, Kiran; Antonchick, Andrey P

    2015-10-12

    The formation of C-C bonds embodies the core of organic chemistry because of its fundamental application in generation of molecular diversity and complexity. C-C bond-forming reactions are well-known challenges. To achieve this goal through direct functionalization of C-H bonds in both of the coupling partners represents the state-of-the-art in organic synthesis. Oxidative C-C bond formation obviates the need for prefunctionalization of both substrates. This Minireview is dedicated to the field of C-C bond-forming reactions through direct C-H bond functionalization under completely metal-free oxidative conditions. Selected important developments in this area have been summarized with representative examples and discussions on their reaction mechanisms.

  7. Oxidative addition of methane and benzene C--H bonds to rhodium center: A DFT study

    NASA Astrophysics Data System (ADS)

    Bi, Siwei; Zhang, Zhenwei; Zhu, Shufen

    2006-11-01

    A density functional theory study on mechanisms of the oxidative addition of methane and benzene C-H bonds to the rhodium center containing Cp and PMe 3 ligands has been performed. Our calculated results confirm that the C-H bond cleavage from a sigma complex to a hydride alkyl complex is the rate-determining step. Compared with the case of methane C-H bond, the oxidative addition of benzene C-H bond is more favorable kinetically and thermodynamically. Stronger backdonation from metal center to the σ ∗ antibonding orbital of benzene C-H bond is responsible for the observations.

  8. Iron-Catalyzed C-H Alkylation of Heterocyclic C-H Bonds.

    PubMed

    Babu, Kaki Raveendra; Zhu, Nengbo; Bao, Hongli

    2017-01-06

    An efficient, iron-catalyzed C-H alkylation of benzothiazoles by using alkyl diacyl peroxides and alkyl tert-butyl peresters which are readily accessible from carboxylic acids to synthesize 2-alkylbenzothiazoles is developed. This reaction is environmentally benign and compatible with a broad range of functional groups. Various primary, secondary, and tertiary alkyl groups can be efficiently incorporated into diverse benzothiazoles. The effectiveness of this method is illustrated by late-stage functionalization of biologically active heterocycles.

  9. Iridium-Catalyzed, Hydrosilyl-Directed Borylation of Unactivated Alkyl C-H Bonds.

    PubMed

    Larsen, Matthew A; Cho, Seung Hwan; Hartwig, John

    2016-01-27

    We report the iridium-catalyzed borylation of primary and secondary alkyl C-H bonds directed by a Si-H group to form alkylboronate esters site selectively. The reactions occur with high selectivity at primary C-H bonds γ to the hydrosilyl group to form primary alkyl bisboronate esters. In the absence of such primary C-H bonds, the borylation occurs selectively at a secondary C-H bond γ to the hydrosilyl group, and these reactions of secondary C-H bonds occur with high diastereoselectivity. The hydrosilyl-containing alkyl boronate esters formed by this method undergo transformations selectively at the carbon-boron or carbon-silicon bonds of these products under distinct conditions to give the products of amination, oxidation, and arylation.

  10. Oxidative aliphatic C-H fluorination with manganese catalysts and fluoride ion

    PubMed Central

    Liu, Wei; Huang, Xiongyi; Groves, John T

    2014-01-01

    Fluorination is a reaction that is useful in improving the chemical stability and changing the binding affinity of biologically active compounds. The protocol described here can be used to replace aliphatic, C(sp3)-H hydrogen in small molecules with fluorine. Notably, isolated methylene groups and unactivated benzylic sites are accessible. The method uses readily available manganese porphyrin and manganese salen catalysts and various fluoride ion reagents, including silver fluoride (AgF), tetrabutylammonium fluoride and triethylamine trihydrofluoride (TREAT·HF), as the source of fluorine. Typically, the reactions afford 50–70% yield of mono-fluorinated products in one step. Two representative examples, the fragrance component celestolide and the nonsteroidal anti-inflammatory drug ibuprofen, are described; they produced useful isolated quantities (250–300 mg, ~50% yield) of fluorinated material over periods of 1–8 h. The procedures are performed in a typical fume hood using ordinary laboratory glassware. No special precautions to rigorously exclude water are required. PMID:24177292

  11. C-H bond activation of benzene by unsaturated η2-cyclopropene and η2-benzyne complexes of niobium.

    PubMed

    Boulho, Cédric; Oulié, Pascal; Vendier, Laure; Etienne, Michel; Pimienta, Véronique; Locati, Abel; Bessac, Fabienne; Maseras, Feliu; Pantazis, Dimitrios A; McGrady, John E

    2010-10-13

    We report the synthesis of a niobium cyclopropyl complex, Tp(Me2)NbMe(c-C(3)H(5))(MeCCMe), and show that thermal loss of methane from this compound generates an intermediate that is capable of activating both aliphatic and aromatic C-H bonds. Isotopic labeling, trapping studies, a detailed kinetic analysis, and density functional theory all suggest that the active intermediate is an η(2)-cyclopropene complex formed via β-hydrogen abstraction rather than an isomeric cyclopropylidene species. C-H activation chemistry of this type represents a rather unusual reactivity pattern for η(2)-alkene complexes but is favored in this case by the strain in the C(3) ring which prevents the decomposition of the key intermediate via loss of cyclopropene.

  12. Aliphatic C-C Bond Cleavage in α-Hydroxy Ketones by a Dioxygen-Derived Nucleophilic Iron-Oxygen Oxidant.

    PubMed

    Bhattacharya, Shrabanti; Rahaman, Rubina; Chatterjee, Sayanti; Paine, Tapan K

    2017-03-17

    A nucleophilic iron-oxygen oxidant, formed in situ in the reaction between an iron(II)-benzilate complex and O2 , oxidatively cleaves the aliphatic C-C bonds of α-hydroxy ketones. In the cleavage reaction, α-hydroxy ketones without any α-C-H bond afford a 1:1 mixture of carboxylic acid and ketone. Isotope labeling studies established that one of the oxygen atoms from dioxygen is incorporated into the carboxylic acid product. Furthermore, the iron(II) complex cleaves an aliphatic C-C bond of 17-α-hydroxyprogesterone affording androstenedione and acetic acid. The O2 -dependent aliphatic C-C bond cleavage of α-hydroxy ketones containing no α-C-H bond bears similarity to the lyase activity of the heme enzyme, cytochrome P450 17A1 (CYP17A1).

  13. Surface-Controlled Mono/Diselective ortho C-H Bond Activation.

    PubMed

    Li, Qing; Yang, Biao; Lin, Haiping; Aghdassi, Nabi; Miao, Kangjian; Zhang, Junjie; Zhang, Haiming; Li, Youyong; Duhm, Steffen; Fan, Jian; Chi, Lifeng

    2016-03-02

    One of the most charming and challenging topics in organic chemistry is the selective C-H bond activation. The difficulty arises not only from the relatively large bond-dissociation enthalpy, but also from the poor reaction selectivity. In this work, Au(111) and Ag(111) surfaces were used to address ortho C-H functionalization and ortho-ortho couplings of phenol derivatives. More importantly, the competition between dehydrogenation and deoxygenation drove the diversity of reaction pathways of phenols on surfaces, that is, diselective ortho C-H bond activation on Au(111) surfaces and monoselective ortho C-H bond activation on Ag(111) surfaces. The mechanism of this unprecedented phenomenon was extensively explored by scanning tunneling microscopy, density function theory, and X-ray photoelectron spectroscopy. Our findings provide new pathways for surface-assisted organic synthesis via the mono/diselective C-H bond activation.

  14. Cobalt(III)-catalyzed synthesis of indazoles and furans by C-H bond functionalization/addition/cyclization cascades.

    PubMed

    Hummel, Joshua R; Ellman, Jonathan A

    2015-01-14

    The development of operationally straightforward and cost-effective routes for the assembly of heterocycles from simple inputs is important for many scientific endeavors, including pharmaceutical, agrochemical, and materials research. In this article we describe the development of a new air-stable cationic Co(III) catalyst for convergent, one-step benchtop syntheses of N-aryl-2H-indazoles and furans by C-H bond additions to aldehydes followed by in situ cyclization and aromatization. Only a substoichiometric amount of AcOH is required as an additive that is both low-cost and convenient to handle. The syntheses of these heterocycles are the first examples of Co(III)-catalyzed additions to aldehydes, and reactions are demonstrated for a variety of aromatic, heteroaromatic, and aliphatic derivatives. The syntheses of both N-aryl-2H-indazoles and furans have been performed on 20 mmol scales and should be readily applicable to larger scales. The reported heterocycle syntheses also demonstrate the use of directing groups that have not previously been applied to Co(III)-catalyzed C-H bond functionalizations. Additionally, the synthesis of furans demonstrates the first example of Co(III)-catalyzed functionalization of alkenyl C-H bonds.

  15. Transition-state metal aryl bond stability determines regioselectivity in palladium acetate mediated C-H bond activation of heteroarenes.

    PubMed

    Petit, Alban; Flygare, Josh; Miller, Alex T; Winkel, Gerrit; Ess, Daniel H

    2012-07-20

    Density functional calculations reveal that the stability of developing metal aryl bonds in Pd(II)-acetate C-H activation transition states determines regioselectivity in arene and heteroarene compounds. This kinetic-thermodynamic connection explains the general preference for activation of the strongest C-H bond and provides the possibility for regioselectivity prediction.

  16. Evolution of C-H Bond Functionalization from Methane to Methodology.

    PubMed

    Hartwig, John F

    2016-01-13

    This Perspective presents the fundamental principles, the elementary reactions, the initial catalytic systems, and the contemporary catalysts that have converted C-H bond functionalization from a curiosity to a reality for synthetic chemists. Many classes of elementary reactions involving transition-metal complexes cleave C-H bonds at typically unreactive positions. These reactions, coupled with a separate or simultaneous functionalization process lead to products containing new C-C, C-N, and C-O bonds. Such reactions were initially studied for the conversion of light alkanes to liquid products, but they have been used (and commercialized in some cases) most often for the synthesis of the more complex structures of natural products, medicinally active compounds, and aromatic materials. Such a change in direction of research in C-H bond functionalization is remarkable because the reactions must occur at an unactivated C-H bond over functional groups that are more reactive than the C-H bond toward classical reagents. The scope of reactions that form C-C bonds or install functionality at an unactivated C-H bond will be presented, and the potential future utility of these reactions will be discussed.

  17. Selective functionalisation of saturated C-H bonds with metalloporphyrin catalysts.

    PubMed

    Che, Chi-Ming; Lo, Vanessa Kar-Yan; Zhou, Cong-Ying; Huang, Jie-Sheng

    2011-04-01

    The recent surge of interest in metal-catalysed C-H bond functionalisation reactions reflects the importance of such reactions in biomimetic studies and organic synthesis. This critical review focuses on metalloporphyrin-catalysed saturated C-H bond functionalisation reported since the year 2000, including C-O, C-N and C-C bond formation via hydroxylation, amination and carbenoid insertion, respectively, together with a brief description of previous achievements in this area. Among the metalloporphyrin-catalysed reactions highlighted herein are the hydroxylation of steroids, cycloalkanes and benzylic hydrocarbons; intermolecular amination of steroids, cycloalkanes and benzylic or allylic hydrocarbons; intramolecular amination of sulfamate esters and organic azides; intermolecular carbenoid insertion into benzylic, allylic or alkane C-H bonds; and intramolecular carbenoid C-H insertion of tosylhydrazones. These metalloporphyrin-catalysed saturated C-H bond functionalisation reactions feature high regio-, diastereo- or enantioselectivity and/or high product turnover numbers. Mechanistic studies suggest the involvement of metal-oxo, -imido (or nitrene), and -carbene porphyrin complexes in the reactions. The reactivity of such metal-ligand multiple bonded species towards saturated C-H bonds, including mechanistic studies through both experimental and theoretical means, is also discussed (244 references).

  18. Characterizing Pressure-Induced Uranium C=H Agostic Bonds**

    PubMed Central

    Arnold, Polly L; Prescimone, Alessandro; Farnaby, Joy H; Mansell, Stephen M; Parsons, Simon; Kaltsoyannis, Nikolas

    2015-01-01

    The diuranium(III) compound [UN′′2]2(μ-η6:η6-C6H6) (N′′=N(SiMe3)2) has been studied using variable, high-pressure single-crystal X-ray crystallography, and density functional theory. In this compound, the low-coordinate metal cations are coupled through π- and δ-symmetric arene overlap and show close metal=CH contacts with the flexible methyl CH groups of the sterically encumbered amido ligands. The metal–metal separation decreases with increasing pressure, but the most significant structural changes are to the close contacts between ligand CH bonds and the U centers. Although the interatomic distances are suggestive of agostic-type interactions between the U and ligand peripheral CH groups, QTAIM (quantum theory of atoms-in-molecules) computational analysis suggests that there is no such interaction at ambient pressure. However, QTAIM and NBO analyses indicate that the interaction becomes agostic at 3.2 GPa. PMID:25882329

  19. Facile P-C/C-H Bond-Cleavage Reactivity of Nickel Bis(diphosphine) Complexes.

    PubMed

    Zhang, Shaoguang; Li, Haixia; Appel, Aaron M; Hall, Michael B; Bullock, R Morris

    2016-07-04

    Unusual cleavage of P-C and C-H bonds of the P2 N2 ligand, in heteroleptic [Ni(P2 N2 )(diphosphine)](2+) complexes under mild conditions, results in the formation of an iminium formyl nickelate featuring a C,P,P-tridentate coordination mode. The structures of both the heteroleptic [Ni(P2 N2 )(diphosphine)](2+) complexes and the resulting iminium formyl nickelate have been characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis. Density functional theory (DFT) calculations were employed to investigate the mechanism of the P-C/C-H bond cleavage, which involves C-H bond cleavage, hydride rotation, Ni-C/P-H bond formation, and P-C bond cleavage.

  20. Transition-metal-catalyzed π-bond-assisted C - H bond functionalization: an emerging trend in organic synthesis.

    PubMed

    Gandeepan, Parthasarathy; Cheng, Chien-Hong

    2015-04-01

    Transition-metal-catalyzed C - H activation is considered to be an important tool in organic synthesis and has been accepted and widely used by chemists because it is straightforward, cost-effective, and environmentally friendly. A variety of functional groups have been used to direct metal complexes and achieve regioselective C - H activation. Most directing is achieved through the σ-bond coordination of functional groups to the metal catalyst, followed by ortho-selective C - H bond cleavage. However, recent work has demonstrated that π-coordinating functional groups can also assist in guiding metal complexes for site-selective C - H bond activation. This emerging approach significantly expands the scope of C - H activation reactions in organic synthesis. Herein, recent developments in this field are summarized.

  1. Oxidative addition of C--H bonds in organic molecules to transition metal centers

    SciTech Connect

    Bergman, R.G.

    1989-04-01

    Alkanes are among the most chemically inert organic molecules. They are reactive toward a limited range of reagents, such as highly energetic free radicals and strongly electrophilic and oxidizing species. This low reactivity is a consequence of the C--H bond energies in most saturated hydrocarbons. These values range from 90 to 98 kcal/mole for primary and secondary C--H bonds; in methane, the main constituent of natural gas, the C--H bond energy is 104 kcal/mole. This makes methane one of the most common but least reactive organic molecules in nature. This report briefly discusses the search for metal complexes capable of undergoing the C--H oxidative addition process allowing alkane chemistry to be more selective than that available using free radical reagents. 14 refs.

  2. Activation of remote meta-C-H bonds assisted by an end-on template.

    PubMed

    Leow, Dasheng; Li, Gang; Mei, Tian-Sheng; Yu, Jin-Quan

    2012-06-27

    Functionalization of unactivated carbon-hydrogen (C-H) single bonds is an efficient strategy for rapid generation of complex molecules from simpler ones. However, it is difficult to achieve selectivity when multiple inequivalent C-H bonds are present in the target molecule. The usual approach is to use σ-chelating directing groups, which lead to ortho-selectivity through the formation of a conformationally rigid six- or seven-membered cyclic pre-transition state. Despite the broad utility of this approach, proximity-driven reactivity prevents the activation of remote C-H bonds. Here we report a class of easily removable nitrile-containing templates that direct the activation of distal meta-C-H bonds (more than ten bonds away) of a tethered arene. We attribute this new mode of C-H activation to a weak 'end-on' interaction between the linear nitrile group and the metal centre. The 'end-on' coordination geometry relieves the strain of the cyclophane-like pre-transition state of the meta-C-H activation event. In addition, this template overrides the intrinsic electronic and steric biases as well as ortho-directing effects with two broadly useful classes of arene substrates (toluene derivatives and hydrocinnamic acids).

  3. Transition-Metal-Catalyzed C-H Bond Addition to Carbonyls, Imines, and Related Polarized π Bonds.

    PubMed

    Hummel, Joshua R; Boerth, Jeffrey A; Ellman, Jonathan A

    2016-12-12

    The transition-metal-catalyzed addition of C-H bonds to carbonyls, imines, and related polarized π bonds has emerged as a particularly efficient and powerful approach for the construction of an incredibly diverse array of heteroatom-substituted products. Readily available and stable inputs are typically employed, and reactions often proceed with very high functional group compatibility and without the production of waste byproducts. Additionally, many transition-metal-catalyzed C-H bond additions to polarized π bonds occur within cascade reaction sequences to provide rapid access to a diverse array of different heterocyclic as well as carbocyclic products. This review highlights the diversity of transformations that have been achieved, catalysts that have been used, and types of products that have been prepared through the transition-metal-catalyzed addition of C-H bonds to carbonyls, imines, and related polarized π bonds.

  4. Amide-directed photoredox-catalysed C-C bond formation at unactivated sp(3) C-H bonds.

    PubMed

    Chu, John C K; Rovis, Tomislav

    2016-11-10

    Carbon-carbon (C-C) bond formation is paramount in the synthesis of biologically relevant molecules, modern synthetic materials and commodity chemicals such as fuels and lubricants. Traditionally, the presence of a functional group is required at the site of C-C bond formation. Strategies that allow C-C bond formation at inert carbon-hydrogen (C-H) bonds enable access to molecules that would otherwise be inaccessible and the development of more efficient syntheses of complex molecules. Here we report a method for the formation of C-C bonds by directed cleavage of traditionally non-reactive C-H bonds and their subsequent coupling with readily available alkenes. Our methodology allows for amide-directed selective C-C bond formation at unactivated sp(3) C-H bonds in molecules that contain many such bonds that are seemingly indistinguishable. Selectivity arises through a relayed photoredox-catalysed oxidation of a nitrogen-hydrogen bond. We anticipate that our findings will serve as a starting point for functionalization at inert C-H bonds through a strategy involving hydrogen-atom transfer.

  5. Amide-directed photoredox-catalysed C-C bond formation at unactivated sp3 C-H bonds

    NASA Astrophysics Data System (ADS)

    Chu, John C. K.; Rovis, Tomislav

    2016-11-01

    Carbon-carbon (C-C) bond formation is paramount in the synthesis of biologically relevant molecules, modern synthetic materials and commodity chemicals such as fuels and lubricants. Traditionally, the presence of a functional group is required at the site of C-C bond formation. Strategies that allow C-C bond formation at inert carbon-hydrogen (C-H) bonds enable access to molecules that would otherwise be inaccessible and the development of more efficient syntheses of complex molecules. Here we report a method for the formation of C-C bonds by directed cleavage of traditionally non-reactive C-H bonds and their subsequent coupling with readily available alkenes. Our methodology allows for amide-directed selective C-C bond formation at unactivated sp3 C-H bonds in molecules that contain many such bonds that are seemingly indistinguishable. Selectivity arises through a relayed photoredox-catalysed oxidation of a nitrogen-hydrogen bond. We anticipate that our findings will serve as a starting point for functionalization at inert C-H bonds through a strategy involving hydrogen-atom transfer.

  6. The direct arylation of allylic sp3 C-H bonds via organic and photoredox catalysis

    NASA Astrophysics Data System (ADS)

    Cuthbertson, James D.; MacMillan, David W. C.

    2015-03-01

    The direct functionalization of unactivated sp3 C-H bonds is still one of the most challenging problems facing synthetic organic chemists. The appeal of such transformations derives from their capacity to facilitate the construction of complex organic molecules via the coupling of simple and otherwise inert building blocks, without introducing extraneous functional groups. Despite notable recent efforts, the establishment of general and mild strategies for the engagement of sp3 C-H bonds in C-C bond forming reactions has proved difficult. Within this context, the discovery of chemical transformations that are able to directly functionalize allylic methyl, methylene and methine carbons in a catalytic manner is a priority. Although protocols for direct oxidation and amination of allylic C-H bonds (that is, C-H bonds where an adjacent carbon is involved in a C = C bond) have become widely established, the engagement of allylic substrates in C-C bond forming reactions has thus far required the use of pre-functionalized coupling partners. In particular, the direct arylation of non-functionalized allylic systems would enable access to a series of known pharmacophores (molecular features responsible for a drug's action), though a general solution to this long-standing challenge remains elusive. Here we report the use of both photoredox and organic catalysis to accomplish a mild, broadly effective direct allylic C-H arylation. This C-C bond forming reaction readily accommodates a broad range of alkene and electron-deficient arene reactants, and has been used in the direct arylation of benzylic C-H bonds.

  7. The direct arylation of allylic sp(3) C-H bonds via organic and photoredox catalysis.

    PubMed

    Cuthbertson, James D; MacMillan, David W C

    2015-03-05

    The direct functionalization of unactivated sp(3) C-H bonds is still one of the most challenging problems facing synthetic organic chemists. The appeal of such transformations derives from their capacity to facilitate the construction of complex organic molecules via the coupling of simple and otherwise inert building blocks, without introducing extraneous functional groups. Despite notable recent efforts, the establishment of general and mild strategies for the engagement of sp(3) C-H bonds in C-C bond forming reactions has proved difficult. Within this context, the discovery of chemical transformations that are able to directly functionalize allylic methyl, methylene and methine carbons in a catalytic manner is a priority. Although protocols for direct oxidation and amination of allylic C-H bonds (that is, C-H bonds where an adjacent carbon is involved in a C = C bond) have become widely established, the engagement of allylic substrates in C-C bond forming reactions has thus far required the use of pre-functionalized coupling partners. In particular, the direct arylation of non-functionalized allylic systems would enable access to a series of known pharmacophores (molecular features responsible for a drug's action), though a general solution to this long-standing challenge remains elusive. Here we report the use of both photoredox and organic catalysis to accomplish a mild, broadly effective direct allylic C-H arylation. This C-C bond forming reaction readily accommodates a broad range of alkene and electron-deficient arene reactants, and has been used in the direct arylation of benzylic C-H bonds.

  8. Carboxylate-assisted ruthenium-catalyzed alkyne annulations by C-H/Het-H bond functionalizations.

    PubMed

    Ackermann, Lutz

    2014-02-18

    To improve the atom- and step-economy of organic syntheses, researchers would like to capitalize upon the chemistry of otherwise inert carbon-hydrogen (C-H) bonds. During the past decade, remarkable progress in organometallic chemistry has set the stage for the development of increasingly viable metal catalysts for C-H bond activation reactions. Among these methods, oxidative C-H bond functionalizations are particularly attractive because they avoid the use of prefunctionalized starting materials. For example, oxidative annulations that involve sequential C-H and heteroatom-H bond cleavages allow for the modular assembly of regioselectively decorated heterocycles. These structures serve as key scaffolds for natural products, functional materials, crop protecting agents, and drugs. While other researchers have devised rhodium or palladium complexes for oxidative alkyne annulations, my laboratory has focused on the application of significantly less expensive, yet highly selective ruthenium complexes. This Account summarizes the evolution of versatile ruthenium(II) complexes for annulations of alkynes via C-H/N-H, C-H/O-H, or C-H/N-O bond cleavages. To achieve selective C-H bond functionalizations, we needed to understand the detailed mechanism of the crucial C-H bond metalation with ruthenium(II) complexes and particularly the importance of carboxylate assistance in this process. As a consequence, our recent efforts have resulted in widely applicable methods for the versatile preparation of differently decorated arenes and heteroarenes, providing access to among others isoquinolones, 2-pyridones, isoquinolines, indoles, pyrroles, or α-pyrones. Most of these reactions used Cu(OAc)2·H2O, which not only acted as the oxidant but also served as the essential source of acetate for the carboxylate-assisted ruthenation manifold. Notably, the ruthenium(II)-catalyzed oxidative annulations also occurred under an ambient atmosphere of air with cocatalytic amounts of Cu(OAc)2

  9. Cross dehydrogenative arylation (CDA) of a benzylic C-H bond with arenes by iron catalysis.

    PubMed

    Li, Yi-Zhou; Li, Bi-Jie; Lu, Xing-Yu; Lin, Song; Shi, Zhang-Jie

    2009-01-01

    Hooking up: FeCl(2) catalyzes the efficient cross dehydrogenative arylation of substrates having benzylic C-H bonds (see scheme). High regioselectivity was observed during the cross-coupling between compounds containing aromatic C(sp(2))-H bonds and benzylic C(sp(3))-H bonds. This process is proposed to proceed by single-electron-transfer oxidation and Friedel-Crafts alkylation.

  10. A study on Zr-Ir multiple bonding active for C-H bond cleavage.

    PubMed

    Oishi, Masataka; Oshima, Masato; Suzuki, Hiroharu

    2014-07-07

    Zr-Ir hydrido complexes with ansa-(cyclopentadienyl)(amide) as the supporting ligand in the zirconium fragment, e.g., (L(1)ZrR)(Cp*Ir)(μ-H)3 [L(1) = Me2Si(η(5)-C5Me4)(N(t)Bu), R = Cl (5), Ph (7), Me (10), alkyl, and aryl] were designed, synthesized, and isolated as tractable early-late heterodinuclear complexes. Despite the presence of the three supporting hydride ligands, Zr-Ir distances in the crystal structures of 5, alkyl, and aryl complexes [2.74-2.76 Å] were slightly longer than the sum of the element radii of Zr and Ir [2.719 Å]. These hydrocarbyl complexes displayed the thermolytic C-H activation of a variety of aromatic compounds and several organometallic compounds. Also, the substrate scope and limitation in the Zr-Ir system were studied. The regiochemical outcomes during the C-H activation of pyridine derivatives and methoxyarenes suggested the in situ generation of a Lewis acidic active intermediate, i.e., (L(1)Zr)(Cp*IrH2) (III). The existence of III and relevant σ-complex intermediates {L(1)Zr(η(2)-R-H)}(Cp*IrH2) (IIR) (R = Me, Ph) in the ligand exchange was demonstrated by the direct isolation of a Et3PO-adduct of III (39b) from 7 and kinetic studies. The structure of the direct Zr-Ir bonds in IIPh, IIMe, III, and 39b were probed using computational studies. The unprecedented strong M-M' interactions in the early-late heterobimetallic (ELHB) complexes have been proposed herein.

  11. Mechanism of a C-H bond activation reaction in room-temperature alkane solution

    SciTech Connect

    Bromberg, S.E.; Yang, H.; Asplund, M.C.

    1997-10-10

    Chemical reactions that break alkane carbon-hydrogen (C-H) bonds are normally carried out under conditions of high temperature and pressure because these bonds are extremely strong ({approx} 100 kilocalories per mole), but certain metal complexes can activate C-H bonds in alkane solution under the mild conditions of room temperature and pressure. Time-resolved infrared experiments probing the initial femtosecond dynamics through the nano- and microsecond kinetics to the final stable products have been used to generate a detailed picture of the C-H activation reaction. Structures of all of the intermediates involved in the reaction of Tp*Rh(CO){sub 2} (Tp* = HB-Pz{sub 3}*, Pz* = 3,5-di-methylpyrazolyl) in alkane solution have been identified and assigned, and energy barriers for each reaction step from solvation to formation of the final alkyl hydride product have been estimated from transient lifetimes. 27 refs., 6 figs.

  12. The mechanism of a C-H Bond Activation reaction in roomtemperature alkane solution

    SciTech Connect

    Bromberg, Steven E.; Yang, Haw; Asplund, Matthew C.; Lian, T.; McNamara, B.K.; Kotz, K.T.; Yeston, J.S.; Wilkens, M.; Frei, H.; Bergman,Robert G.; Harris, C.B.

    1997-07-31

    Chemical reactions that break alkane carbon-hydrogen (C-H) bonds are normally carried out under conditions of high temperature and pressure because these bonds are extremely strong ({approx}100 kilocalories per mole), but certain metal complexes can activate C-H bonds in alkane solution under the mild conditions of room temperature and pressure. Time-resolved infrared experiments probing the initial femtosecond dynamics through the nano- and microsecond kinetics to the final stable products have been used to generate a detailed picture of the C-H activation reaction. Structures of all of the intermediates involved in the reaction of Tp*Rh(CO)2 (Tp* = HB-Pz3*, Pz* = 3,5-dimethylpyrazolyl) in alkane solution have been identified and assigned, and energy barriers for each reaction step from solvation to formation of the final alkylhydride product have been estimated from transient lifetimes.

  13. The C-H Stretching Features at 3.2--3.5 μm of Polycyclic Aromatic Hydrocarbons with Aliphatic Sidegroups

    NASA Astrophysics Data System (ADS)

    Yang, X. J.; Li, Aigen; Glaser, R.; Zhong, J. X.

    2016-07-01

    The so-called “unidentified” infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 μm are ubiquitously seen in a wide variety of astrophysical regions. The UIE features are characteristic of the stretching and bending vibrations of aromatic hydrocarbon materials, e.g., polycyclic aromatic hydrocarbon (PAH) molecules. The 3.3 μm aromatic C-H stretching feature is often accompanied by a weaker feature at 3.4 μm. The latter is generally thought to result from the C-H stretch of aliphatic groups attached to the aromatic systems. The ratio of the observed intensity of the 3.3 μm aromatic C-H feature to that of the 3.4 μm aliphatic C-H feature allows one to estimate the aliphatic fraction of the UIE carriers, provided that the intrinsic oscillator strengths of the 3.3 μm aromatic C-H stretch ({A}3.3) and the 3.4 μm aliphatic C-H stretch ({A}3.4) are known. While previous studies on the aliphatic fraction of the UIE carriers were mostly based on the {A}3.4/{A}3.3 ratios derived from the mono-methyl derivatives of small PAH molecules, in this work we employ density functional theory to compute the infrared vibrational spectra of PAH molecules with a wide range of sidegroups including ethyl, propyl, butyl, and several unsaturated alkyl chains, as well as all the isomers of dimethyl-substituted pyrene. We find that, except for PAHs with unsaturated alkyl chains, the corresponding {A}3.4/{A}3.3 ratios are close to that of mono-methyl PAHs. This confirms the predominantly aromatic nature of the UIE carriers previously inferred from the {A}3.4/{A}3.3 ratio derived from mono-methyl PAHs.

  14. Copper-Catalyzed, Directing Group-Assisted Fluorination of Arene and Heteroarene C-H Bonds

    PubMed Central

    Truong, Thanh; Klimovica, Kristine; Daugulis, Olafs

    2013-01-01

    We have developed a method for direct, copper-catalyzed, auxiliary-assisted fluorination of β-sp2 C-H bonds of benzoic acid derivatives and γ-sp2 C-H bonds of α,α-disubstituted benzylamine derivatives. The reaction employs CuI catalyst, AgF fluoride source, and DMF, pyridine, or DMPU solvent at moderately elevated temperatures. Selective mono- or difluorination can be achieved by simply changing reaction conditions. The method shows excellent functional group tolerance and provides a straightforward way for the preparation of ortho-fluorinated benzoic acids. PMID:23758609

  15. A Chiral Nitrogen Ligand for Enantioselective, Iridium-Catalyzed Silylation of Aromatic C-H Bonds.

    PubMed

    Su, Bo; Zhou, Tai-Gang; Li, Xian-Wei; Shao, Xiao-Ru; Xu, Pei-Lin; Wu, Wen-Lian; Hartwig, John F; Shi, Zhang-Jie

    2017-01-19

    Iridium catalysts containing dative nitrogen ligands are highly active for the borylation and silylation of C-H bonds, but chiral analogs of these catalysts for enantioselective silylation reactions have not been developed. We report a new chiral pyridinyloxazoline ligand for enantioselective, intramolecular silylation of symmetrical diarylmethoxy diethylsilanes. Regioselective and enantioselective silylation of unsymmetrical substrates was also achieved in the presence of this newly developed system. Preliminary mechanistic studies imply that C-H bond cleavage is irreversible, but not the rate-determining step.

  16. Copper-catalyzed oxaziridine-mediated oxidation of C-H bonds.

    PubMed

    Motiwala, Hashim F; Gülgeze, Belgin; Aubé, Jeffrey

    2012-08-17

    The highly regio- and chemoselective oxidation of activated C-H bonds has been observed via copper-catalyzed reactions of oxaziridines. The oxidation proceeded with a variety of substrates, primarily comprising allylic and benzylic examples, as well as one example of an otherwise unactivated tertiary C-H bond. The mechanism of the reaction is proposed to involve single-electron transfer to the oxaziridines to generate a copper-bound radical anion, followed by hydrogen atom abstraction and collapse to products, with regeneration of the catalyst by a final single-electron transfer event. The involvement of allylic radical intermediates was supported by a radical-trapping experiment with TEMPO.

  17. Ligand-based carbon-nitrogen bond forming reactions of metal dinitrosyl complexes with alkenes and their application to C-H bond functionalization.

    PubMed

    Zhao, Chen; Crimmin, Mark R; Toste, F Dean; Bergman, Robert G

    2014-02-18

    Over the past few decades, researchers have made substantial progress in the development of transition metal complexes that activate and functionalize C-H bonds. For the most part, chemists have focused on aliphatic and aromatic C-H bonds and have put less effort into complexes that activate and functionalize vinylic C-H bonds. Our groups have recently developed a novel method to functionalize vinylic C-H bonds that takes advantage of the unique ligand-based reactivity of a rare class of metal dinitrosyl complexes. In this Account, we compare and discuss the chemistry of cobalt and ruthenium dinitrosyl complexes, emphasizing alkene binding, C-H functionalization, and catalysis. Initially discovered in the early 1970s by Brunner and studied more extensively in the 1980s by the Bergman group, the cyclopentadienylcobalt dinitrosyl complex CpCo(NO)2 reacts reversibly with alkenes to give, in many cases, stable and isolable cobalt dinitrosoalkane complexes. More recently, we found that treatment with strong bases, such as lithium hexamethyldisilazide, Verkade's base, and phosphazene bases, deprotonates these complexes and renders them nucleophilic at the carbon α to the nitroso group. This conjugate anion of metal dinitrosoalkanes can participate in conjugate addition to Michael acceptors to form new carbon-carbon bonds. These functionalized cobalt complexes can further react through alkene exchange to furnish the overall vinylic C-H functionalized organic product. This stepwise sequence of alkene binding, functionalization, and retrocycloaddition represents an overall vinylic C-H functionalization reaction of simple alkenes and does not require directing groups. We have also developed an asymmetric variant of this reaction sequence and have used this method to synthesize C1- and C2-symmetric diene ligands with high enantioinduction. Building upon these stepwise reactions, we eventually developed a simple one-pot procedure that uses stoichiometric amounts of a cobalt

  18. C-H and N-H bond dissociation energies of small aromatic hydrocarbons

    SciTech Connect

    Barckholtz, C.; Barckholtz, T.A.; Hadad, C.M.

    1999-01-27

    A survey of computational methods was undertaken to calculate the homolytic bond dissociation energies (BDEs) of the C-H and N-H bonds in monocyclic aromatic molecules that are representative of the functionalities present in coal. These include six-membered rings (benzene, pyridine, pyridazine, pyrimidine, pyrazine) and five-membered rings (furan, thiophene, pyrrole, oxazole). By comparison of the calculated C-H BDEs with the available experimental values for these aromatic molecules, the B3LYP/6-31G(d) level of theory was selected to calculate the BDEs of polycyclic aromatic hydrocarbons (PAHs), including carbonaceous PAHs (naphthalene, anthracene, pyrene, coronene) and heteroatomic PAHs (benzofuran, benzothiophene, indole, benzoxazole, quinoline, isoquinoline, dibenzofuran, carbazole). The cleavage of a C-H or a N-H bond generates a {sigma} radical that is, in general, localized at the site from which the hydrogen atom was removed. However, delocalization of the unpaired electron results in {approximately} 7 kcal {center{underscore}dot} mol{sup {minus}1} stabilization of the radical with respect to the formation of phenyl when the C-H bond is adjacent to a nitrogen atom in the azabenzenes. Radicals from five-membered rings are {approximately} 6 kcal {center{underscore}dot} mol{sup {minus}1} less stable than those formed from six-membered rings due to both localization of the spin density and geometric factors. The location of the heteroatoms in the aromatic ring affects the C-H bond strengths more significantly than does the size of the aromatic network. Therefore, in general, the monocyclic aromatic molecules can be used to predict the C-H BDE of the large PAHs within 1 kcal {center{underscore}dot} mol{sup {minus}1}.

  19. Site-selective and stereoselective functionalization of unactivated C-H bonds

    NASA Astrophysics Data System (ADS)

    Liao, Kuangbiao; Negretti, Solymar; Musaev, Djamaladdin G.; Bacsa, John; Davies, Huw M. L.

    2016-05-01

    The laboratory synthesis of complex organic molecules relies heavily on the introduction and manipulation of functional groups, such as carbon-oxygen or carbon-halogen bonds; carbon-hydrogen bonds are far less reactive and harder to functionalize selectively. The idea of C-H functionalization, in which C-H bonds are modified at will instead of the functional groups, represents a paradigm shift in the standard logic of organic synthesis. For this approach to be generally useful, effective strategies for site-selective C-H functionalization need to be developed. The most practical solutions to the site-selectivity problem rely on either intramolecular reactions or the use of directing groups within the substrate. A challenging, but potentially more flexible approach, would be to use catalyst control to determine which site in a particular substrate would be functionalized. Here we describe the use of dirhodium catalysts to achieve highly site-selective, diastereoselective and enantioselective C-H functionalization of n-alkanes and terminally substituted n-alkyl compounds. The reactions proceed in high yield, and functional groups such as halides, silanes and esters are compatible with this chemistry. These studies demonstrate that high site selectivity is possible in C-H functionalization reactions without the need for a directing or anchoring group present in the molecule.

  20. Selective intermolecular amination of C-H bonds at tertiary carbon centers.

    PubMed

    Roizen, Jennifer L; Zalatan, David N; Du Bois, J

    2013-10-18

    C-H insertion: A method for intermolecular amination of tertiary CH bonds is described that uses limiting amounts of substrate and a convenient phenol-derived nitrogen source. Structure-selectivity and mechanistic studies suggest that steric interaction between the substrate and active oxidant is the principal determinant of product selectivity.

  1. Cobalt(III)-Catalyzed C-H Bond Amidation with Isocyanates.

    PubMed

    Hummel, Joshua R; Ellman, Jonathan A

    2015-05-15

    The first examples of cobalt(III)-catalyzed C-H bond addition to isocyanates are described, providing a convergent strategy for arene and heteroarene amidation. Using a robust air- and moisture-stable catalyst, this transformation demonstrates a broad isocyanate scope and good functional-group compatibility and has been performed on gram scale.

  2. Facile P-C/C-H Bond-Cleavage Reactivity of Nickel Bis(diphosphine) Complexes

    SciTech Connect

    Zhang, Shaoguang; Li, Haixia; Appel, Aaron M.; Hall, Michael B.; Bullock, R. Morris

    2016-06-07

    Unusual cleavage of P-C and C-H bonds of the P2N2 ligand in heteroleptic [Ni(P2N2)(diphosphine)]2+ complexes results in the formation of an iminium formyl nickelate featuring a C,P,P-tridentate coordination mode.

  3. Teaching enantioselectivity to C-H bond functionalizations: initial steps of a rather long shot.

    PubMed

    Cramer, Nicolai

    2012-01-01

    The direct functionalization of non-activated C-H bonds, especially in an enantioselective manner, requires metal catalysts equipped with ligands with specifically designed properties. Examples for asymmetric C(sp(2))-H and C(sp(3))-H functionalizations using palladium- and rhodium catalysts are shown. This work was rewarded by the 2012 Werner Prize of the Swiss Chemical Society.

  4. Rhodium-Catalyzed C-C Bond Formation via Heteroatom-Directed C-H Bond Activation

    SciTech Connect

    Colby, Denise; Bergman, Robert; Ellman, Jonathan

    2010-05-13

    Once considered the 'holy grail' of organometallic chemistry, synthetically useful reactions employing C-H bond activation have increasingly been developed and applied to natural product and drug synthesis over the past decade. The ubiquity and relative low cost of hydrocarbons makes C-H bond functionalization an attractive alternative to classical C-C bond forming reactions such as cross-coupling, which require organohalides and organometallic reagents. In addition to providing an atom economical alternative to standard cross - coupling strategies, C-H bond functionalization also reduces the production of toxic by-products, thereby contributing to the growing field of reactions with decreased environmental impact. In the area of C-C bond forming reactions that proceed via a C-H activation mechanism, rhodium catalysts stand out for their functional group tolerance and wide range of synthetic utility. Over the course of the last decade, many Rh-catalyzed methods for heteroatom-directed C-H bond functionalization have been reported and will be the focus of this review. Material appearing in the literature prior to 2001 has been reviewed previously and will only be introduced as background when necessary. The synthesis of complex molecules from relatively simple precursors has long been a goal for many organic chemists. The ability to selectively functionalize a molecule with minimal pre-activation can streamline syntheses and expand the opportunities to explore the utility of complex molecules in areas ranging from the pharmaceutical industry to materials science. Indeed, the issue of selectivity is paramount in the development of all C-H bond functionalization methods. Several groups have developed elegant approaches towards achieving selectivity in molecules that possess many sterically and electronically similar C-H bonds. Many of these approaches are discussed in detail in the accompanying articles in this special issue of Chemical Reviews. One approach that has

  5. Time resolved infrared studies of C-H bond activation by organometallics

    SciTech Connect

    Asplund, M.C. |

    1998-06-01

    This work describes how step-scan Fourier Transform Infrared spectroscopy and visible and near infrared ultrafast lasers have been applied to the study of the photochemical activation of C-H bonds in organometallic systems, which allow for the selective breaking of C-H bonds in alkanes. The author has established the photochemical mechanism of C-H activation by Tp{sup *}Rh(CO){sub 2}(Tp{sup *} = HB-Pz{sup *}{sub 3}, Pz = 3,5-dimethylpyrazolyl) in alkane solution. The initially formed monocarbonyl forms a weak solvent complex, which undergoes a change in Tp{sup *} ligand connectivity. The final C-H bond breaking step occurs at different time scales depending on the structure of the alkane. In linear solvents, the time scale is <50 ns and cyclic alkanes is {approximately}200 ps. The reactivity of the Tp{sup *}Rh(CO){sub 2} system has also been studied in aromatic solvents. Here the reaction proceeds through two different pathways, with very different time scales. The first proceeds in a manner analogous to alkanes and takes <50 ns. The second proceeds through a Rh-C-C complex, and takes place on a time scale of 1.8 {micro}s.

  6. Rh(III)-Catalyzed C-H Bond Addition/Amine-Mediated Cyclization of Bis-Michael Acceptors.

    PubMed

    Potter, Tyler J; Ellman, Jonathan A

    2016-08-05

    A Rh(III)-catalyzed C-H bond addition/primary amine-promoted cyclization of bis-Michael acceptors is reported. The C-H bond addition step occurs with high chemoselectivity, and the subsequent intramolecular Michael addition, mediated by a primary amine catalyst, sets three contiguous stereocenters with high diastereoselectivity. A broad range of directing groups and both aromatic and alkenyl C-H bonds were shown to be effective in this transformation, affording functionalized piperidines, tetrahydropyrans, and cyclohexanes.

  7. Mechanism of catalytic functionalization of primary C-H bonds using a silylation strategy.

    PubMed

    Parija, Abhishek; Sunoj, Raghavan B

    2013-08-16

    The mechanism of Ir-catalyzed γ-functionalization of a primary sp(3)(C-H) bond in 2-methyl cyclohexanol is examined using the density functional theory (M06). The nature of the active catalyst for the initial silylation of alcohol is identified as the monomer derived from [Ir(cod)OMe]2 while that for γ-sp(3)(C-H) activation leading to oxasilolane is [IrH(nbe)(phen)]. The rate-determining step is found to involve Si-C coupling through reductive elimination.

  8. Catalytic intermolecular amination of C-H bonds: method development and mechanistic insights.

    PubMed

    Fiori, Kristin Williams; Du Bois, J

    2007-01-24

    Reaction methodology for intermolecular C-H amination of benzylic and 3 degrees C-H bonds is described. This process uses the starting alkane as the limiting reagent, gives optically pure tetrasubstituted amines through stereospecific insertion into enantiomeric 3 degrees centers, displays high chemoselectivity for benzylic oxidation, and enables the facile preparation of isotopically enriched 15N-labeled compounds. Access to substituted amines, amino alcohols, and diamines is thereby made possible in a single transformation. Important information relevant to understanding the initial steps in the catalytic cycle, reaction chemoselectivity, the nature of the active oxidant, and pathways for catalyst inactivation has been gained through mechanistic analysis; these studies are also presented.

  9. Aromatic and aliphatic CH hydrogen bonds fight for chloride while competing alongside ion pairing within triazolophanes.

    PubMed

    Hua, Yuran; Ramabhadran, Raghunath O; Uduehi, Esther O; Karty, Jonathan A; Raghavachari, Krishnan; Flood, Amar H

    2011-01-03

    Triazolophanes are used as the venue to compete an aliphatic propylene CH hydrogen-bond donor against an aromatic phenylene one. Longer aliphatic C-H...Cl(-) hydrogen bonds were calculated from the location of the chloride within the propylene-based triazolophane. The gas-phase energetics of chloride binding (ΔG(bind) , ΔH(bind) , ΔS(bind) ) and the configurational entropy (ΔS(config) ) were computed by taking all low-energy conformations into account. Comparison between the phenylene- and propylene-based triazolophanes shows the computed gas-phase free energy of binding decreased from ΔG(bind) =-194 to -182 kJ mol(-1) , respectively, with a modest enthalpy-entropy compensation. These differences were investigated experimentally. An (1) H NMR spectroscopy study on the structure of the propylene triazolophane's 1:1 chloride complex is consistent with a weaker propylene CH hydrogen bond. To quantify the affinity differences between the two triazolophanes in dichloromethane, it was critical to obtain an accurate binding model. Four equilibria were identified. In addition to 1:1 complexation and 2:1 sandwich formation, ion pairing of the tetrabutylammonium chloride salt (TBA(+) ⋅Cl(-) ) and cation pairing of TBA(+) with the 1:1 triazolophane-chloride complex were observed and quantified. Each complex was independently verified by ESI-MS or diffusion NMR spectroscopy. With ion pairing deconvoluted from the chloride-receptor binding, equilibrium constants were determined by using (1) H NMR (500 μM) and UV/Vis (50 μM) spectroscopy titrations. The stabilities of the 1:1 complexes for the phenylene and propylene triazolophanes did not differ within experimental error, ΔG=(-38±2) and (-39±1) kJ mol(-1) , respectively, as verified by an NMR spectroscopy competition experiment. Thus, the aliphatic CH donor only revealed its weaker character when competing with aromatic CH donors within the propylene-based triazolophane.

  10. Synthesis of Planar Chiral Ferrocenes via Transition-Metal-Catalyzed Direct C-H Bond Functionalization.

    PubMed

    Gao, De-Wei; Gu, Qing; Zheng, Chao; You, Shu-Li

    2017-02-21

    Ferrocenes are of great interest in the fields of materials science, organic synthesis, and biomedical research. Of particular significance is the fact that ferrocenes bearing planar chirality have been demonstrated to be highly efficient ligands or catalysts in asymmetric catalysis, some of which have been employed in the industrial synthesis of pharmaceuticals and agrochemicals. So far, the main methods for the synthesis of planar chiral ferrocenes involve diastereoselective directed ortho-metalation (DoM), enantioselective DoM, and chiral resolution. Despite the fact that these approaches are well developed and widely applied, the use of chiral auxiliaries or external stoichiometric chiral bases is required in most cases. Additionally, the practicality of these processes is hampered by the requirement of sensitive organometallic reagents, the poor compatibility with functional groups, and the low atom economy in some cases. Therefore, the development of highly efficient strategies to introduce planar chirality on the backbone of ferrocene that do not possess these limitations is highly desirable. Meanwhile, transition-metal-catalyzed asymmetric C-H bond functionalization reactions have attracted much attention over the past few years owing to their emerging potential for providing a straightforward approach for the preparation of chiral molecules. In addition to the majority of the work focusing on the installation of central chirality, methods for the catalytic asymmetric synthesis of planar chiral compounds via C-H bond functionalization have also been explored. In this Account, we summarize our recent efforts aimed at the development of novel methods to synthesize planar chiral compounds via asymmetric C-H bond functionalization and also highlight related achievements by other groups. First, we briefly introduce the precedent examples of diastereoselective and enantioselective synthesis of planar chiral ferrocenes. Subsequently, asymmetric syntheses of

  11. Enantioselective functionalization of allylic C-H bonds following a strategy of functionalization and diversification.

    PubMed

    Sharma, Ankit; Hartwig, John F

    2013-11-27

    We report the enantioselective functionalization of allylic C-H bonds in terminal alkenes by a strategy involving the installation of a temporary functional group at the terminal carbon atom by C-H bond functionalization, followed by the catalytic diversification of this intermediate with a broad scope of reagents. The method consists of a one-pot sequence of palladium-catalyzed allylic C-H bond oxidation under neutral conditions to form linear allyl benzoates, followed by iridium-catalyzed allylic substitution. This overall transformation forms a variety of chiral products containing a new C-N, C-O, C-S, or C-C bond at the allylic position in good yield with a high branched-to-linear selectivity and excellent enantioselectivity (ee ≤97%). The broad scope of the overall process results from separating the oxidation and functionalization steps; by doing so, the scope of nucleophile encompasses those sensitive to direct oxidative functionalization. The high enantioselectivity of the overall process is achieved by developing an allylic oxidation that occurs without acid to form the linear isomer with high selectivity. These allylic functionalization processes are amenable to an iterative sequence leading to (1,n)-functionalized products with catalyst-controlled diastereo- and enantioselectivity. The utility of the method in the synthesis of biologically active molecules has been demonstrated.

  12. A method to obtain the absorption coefficient spectrum of single grain coal in the aliphatic C-H stretching region using infrared transflection microspectroscopy.

    PubMed

    Tonoue, Ryota; Katsura, Makoto; Hamamoto, Mai; Bessho, Hiroki; Nakashima, Satoru

    2014-01-01

    A method was developed to obtain the absorption coefficient spectrum of a grain of coal (as small as 10(-7)) in the region of aliphatic and aromatic C-H stretching bands (2700-3200 cm(-1)) using infrared transflection microspectroscopy. In this method, the complex refractive index n - ik was determined using an optimization algorithm with the Kramers-Kronig transform so that the calculated transflection spectrum from the Fresnel equation corresponded to the measured one. The obtained absorption coefficients were compared with the bulk values determined from the potassium bromide (KBr) pellet measurement method.

  13. Catalytic C-H bond functionalisation chemistry: the case for quasi-heterogeneous catalysis.

    PubMed

    Reay, Alan J; Fairlamb, Ian J S

    2015-11-25

    This feature article examines the potential of heterogeneous Pd species to mediate catalytic C-H bond functionalisation processes employing suitable substrates (e.g. aromatic/heteroaromatic compounds). A focus is placed on the reactivity of supported and non-supported Pd nanoparticle (PdNPs) catalysts, in addition to the re-appropriation of well-established heterogeneous Pd catalysts such as Pd/C. Where possible, reasonable comparisons are made between PdNPs and traditional 'homogeneous' Pd precatalyst sources (which form PdNPs). The involvement of higher order Pd species in traditional cross-coupling processes, such as Mizoroki-Heck, Sonogashira and Suzuki-Miyaura reactions, allows the exemplification of potential future topics for study in the area of catalytic C-H bond functionalisation processes.

  14. Theoretical study of the C-H bond dissociation energy of C2H

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1990-01-01

    A theoretical study of the convergence of the C-H bond dissociation energy D(0) in C2H with respect to both the one- and n-particle spaces is presented. The calculated C-H bond energies of C2H2 and C2H4, which are in excellent agreement with experiment, are used for calibration. The best estimate for D(0) of 112.4 + or - 2.0 kcal/mol is slightly below the recent experimental value of 116.3 + or - 2.6 kcal/mol, but substantially above a previous theoretical estimate of 102 kcal/mol. The remaining discrepancy with experiment may reflect primarily the uncertainty in the experimental D(0) value of C2 required in the analysis.

  15. Activation of C-H and B-H bonds through agostic bonding: an ELF/QTAIM insight.

    PubMed

    Zins, Emilie-Laure; Silvi, Bernard; Alikhani, M Esmaïl

    2015-04-14

    Agostic bonding is of paramount importance in C-H bond activation processes. The reactivity of the σ C-H bond thus activated will depend on the nature of the metallic center, the nature of the ligand involved in the interaction and co-ligands, as well as on geometric parameters. Because of their importance in organometallic chemistry, a qualitative classification of agostic bonding could be very much helpful. Herein we propose descriptors of the agostic character of bonding based on the electron localization function (ELF) and Quantum Theory of Atoms in Molecules (QTAIM) topological analysis. A set of 31 metallic complexes taken, or derived, from the literature was chosen to illustrate our methodology. First, some criteria should prove that an interaction between a metallic center and a σ X-H bond can indeed be described as "agostic" bonding. Then, the contribution of the metallic center in the protonated agostic basin, in the ELF topological description, may be used to evaluate the agostic character of bonding. A σ X-H bond is in agostic interaction with a metal center when the protonated X-H basin is a trisynaptic basin with a metal contribution strictly larger than the numerical uncertainty, i.e. 0.01 e. In addition, it was shown that the weakening of the electron density at the X-Hagostic bond critical point with respect to that of X-Hfree well correlates with the lengthening of the agostic X-H bond distance as well as with the shift of the vibrational frequency associated with the νX-H stretching mode. Furthermore, the use of a normalized parameter that takes into account the total population of the protonated basin, allows the comparison of the agostic character of bonding involved in different complexes.

  16. Transition-metal-catalyzed group transfer reactions for selective C-H bond functionalization of artemisinin.

    PubMed

    Liu, Yungen; Xiao, Wenbo; Wong, Man-Kin; Che, Chi-Ming

    2007-10-11

    Three types of novel artemisinin derivatives have been synthesized through transition-metal-catalyzed intramolecular carbenoid and nitrenoid C-H bond insertion reactions. With rhodium complexes as catalysts, lactone 11 was synthesized via carbene insertion reaction at the C16 position in 90% yield; oxazolidinone 13 was synthesized via nitrene insertion reaction at the C10 position in 87% yield based on 77% conversion; and sulfamidate 14 was synthesized via nitrene insertion reaction at the C8 position in 87% yield.

  17. Theoretical study of the C-H bond dissociation energy of acetylene

    NASA Technical Reports Server (NTRS)

    Taylor, Peter R.; Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1990-01-01

    The authors present a theoretical study of the convergence of the C-H bond dissociation energy (D sub o) of acetylene with respect to both the one- and n-particle spaces. Their best estimate for D sub o of 130.1 plus or minus 1.0 kcal/mole is slightly below previous theoretical estimates, but substantially above the value determined using Stark anticrossing spectroscopy that is asserted to be an upper bound.

  18. Chelation-assisted palladium-catalyzed direct cyanation of 2-arylpyridine C-H bonds.

    PubMed

    Jia, Xiaofei; Yang, Dongpeng; Zhang, Shouhui; Cheng, Jiang

    2009-10-15

    A chelation-assisted palladium-catalyzed ortho-cyanation of the sp2 C-H bond by CuCN provided aromatic nitriles in moderate to good yields. Notably, the reaction could be conducted on a 10 mmol scale. The key intermediate of the natural product of Menispermum dauricum DC was concisely synthesized by the procedure. This new approach represents an exceedingly practical method for the synthesis of aromatic nitriles and offers an attractive alternative to the traditional Sandmeyer reaction.

  19. Asymmetric Intramolecular Alkylation of Chiral Aromatic Imines via Catalytic C-H Bond Activation

    SciTech Connect

    Watzke, Anja; Wilson, Rebecca; O'Malley, Steven; Bergman, Robert; Ellman, Jonathan

    2007-04-16

    The asymmetric intramolecular alkylation of chiral aromatic aldimines, in which differentially substituted alkenes are tethered meta to the imine, was investigated. High enantioselectivities were obtained for imines prepared from aminoindane derivatives, which function as directing groups for the rhodium-catalyzed C-H bond activation. Initial demonstration of catalytic asymmetric intramolecular alkylation also was achieved by employing a sterically hindered achiral imine substrate and catalytic amounts of a chiral amine.

  20. Visible-Light-Promoted Vinylation of Tetrahydrofuran with Alkynes through Direct C-H Bond Functionalization.

    PubMed

    Li, Jing; Zhang, Jing; Tan, Haibo; Wang, David Zhigang

    2015-05-15

    Mild and direct C-H bond functionalizations and vinylations of tetrahydrofuran with alkynes have been accomplished through visible light photocatalysis, yielding a range of vinyl tetrahydrofurans under the synergistic actions of organic dye-type photocatalyst eosin Y, tert-butyl hydroperoxide (t-BuOOH), and a 45 W household lightbulb. A significant kinetic isotope effect (KIE) was recorded, which helps shed light on the mechanistic course.

  1. Synthesis of new class of alkyl azarene pyridinium zwitterions via iodine mediated sp3 C-H bond activation.

    PubMed

    Kumar, Atul; Gupta, Garima; Srivastava, Suman

    2011-12-16

    An efficient and conceptually different approach toward C-H bond activation by using iodine mediated sp(3) C-H functionalization for the synthesis of alkyl azaarene pyridinium zwitterions is described. This work has the interesting distinction of being the first synthesis of a new class of alkyl azaarene pyridinium zwitterion via transition-metal-free sp(3) C-H bond activation of an alkyl azaarene.

  2. Palladium-Catalyzed Enantioselective C-H Activation of Aliphatic Amines Using Chiral Anionic BINOL-Phosphoric Acid Ligands.

    PubMed

    Smalley, Adam P; Cuthbertson, James D; Gaunt, Matthew J

    2017-02-01

    The design of an enantioselective Pd(II)-catalyzed C-H amination reaction is described. The use of a chiral BINOL phosphoric acid ligand enables the conversion of readily available amines into synthetically valuable aziridines in high enantiomeric ratios. The aziridines can be derivatized to afford a range of chiral amine building blocks incorporating motifs readily encountered in pharmaceutically relevant molecules.

  3. The Breathing Orbital Valence Bond Method in Diffusion Monte Carlo: C-H Bond Dissociation ofAcetylene

    SciTech Connect

    Domin, D.; Braida, Benoit; Lester Jr., William A.

    2008-05-30

    This study explores the use of breathing orbital valence bond (BOVB) trial wave functions for diffusion Monte Carlo (DMC). The approach is applied to the computation of the carbon-hydrogen (C-H) bond dissociation energy (BDE) of acetylene. DMC with BOVB trial wave functions yields a C-H BDE of 132.4 {+-} 0.9 kcal/mol, which is in excellent accord with the recommended experimental value of 132.8 {+-} 0.7 kcal/mol. These values are to be compared with DMC results obtained with single determinant trial wave functions, using Hartree-Fock orbitals (137.5 {+-} 0.5 kcal/mol) and local spin density (LDA) Kohn-Sham orbitals (135.6 {+-} 0.5 kcal/mol).

  4. C-H bonds as ubiquitous functionality: preparation of multiple regioisomers of arylated 1,2,4-triazoles via C-H arylation.

    PubMed

    Joo, Jung Min; Guo, Pengfei; Sames, Dalibor

    2013-01-18

    We describe a general approach for the synthesis of complex aryl 1,2,4-triazoles. The electronic character of the C-H bonds and the triazole ring allows for the regioselective C-H arylation of 1-alkyl- and 4-alkyltriazoles under catalytic conditions. We have also developed the SEM and THP switch as well as trans-N-alkylation, which enable sequential arylation of the triazole ring to prepare 3,5-diaryltriazoles. This new strategy provides rapid access to a variety of arylated 1,2,4-triazoles and well complements existing cyclization methods.

  5. Reactivity of mononuclear alkylperoxo copper(II) complex. O-O bond cleavage and C-H bond activation.

    PubMed

    Kunishita, Atsushi; Ishimaru, Hirohito; Nakashima, Satoru; Ogura, Takashi; Itoh, Shinobu

    2008-04-02

    A detailed reactivity study has been carried out for the first time on a new mononuclear alkylperoxo copper(II) complex, which is generated by the reaction of copper(II) complex supported by the bis(pyridylmethyl)amine tridentate ligand containing a phenyl group at the 6-position of the pyridine donor groups and cumene hydroperoxide (CmOOH) in CH3CN. The cumylperoxo copper(II) complex thus obtained has been found to undergo homolytic cleavage of the O-O bond and induce C-H bond activation of exogenous substrates, providing important insights into the catalytic mechanism of copper monooxygenases.

  6. Palladium-Catalyzed Allylic C-H Bond Functionalization of Olefins

    NASA Astrophysics Data System (ADS)

    Liu, Guosheng; Wu, Yichen

    Transition metal-mediated carbon-hydrogen bond cleavage and functionalization is a mechanistically interesting and synthetically attractive process. One of the important cases is the removal of a allylic hydrogen from an olefin by a PdII salt to yield a π-allylpalladium complex, followed by nucleophilic attack to efficient produce allylic derivatives. In contrast to the well-known allylic acetoxylation of cyclohexene, the reaction of open-chain olefins is fairly poor until recent several years. Some palladium catalytic systems have been reported to achieve allylic C-H functionalization, including acetoxylation, amination and alkylation of terminal alkenes. In the most of cases, ligand is crucial to the success of the transformation. This review surveys the recent development of palladium-catalyzed allylic C-H functionalziation of alkenes. These results promise a significant increase in the scope of olefin transformation.

  7. Trapping a Highly Reactive Nonheme Iron Intermediate That Oxygenates Strong C-H Bonds with Stereoretention.

    PubMed

    Serrano-Plana, Joan; Oloo, Williamson N; Acosta-Rueda, Laura; Meier, Katlyn K; Verdejo, Begoña; García-España, Enrique; Basallote, Manuel G; Münck, Eckard; Que, Lawrence; Company, Anna; Costas, Miquel

    2015-12-23

    An unprecedentedly reactive iron species (2) has been generated by reaction of excess peracetic acid with a mononuclear iron complex [Fe(II)(CF3SO3)2(PyNMe3)] (1) at cryogenic temperatures, and characterized spectroscopically. Compound 2 is kinetically competent for breaking strong C-H bonds of alkanes (BDE ≈ 100 kcal·mol(-1)) through a hydrogen-atom transfer mechanism, and the transformations proceed with stereoretention and regioselectively, responding to bond strength, as well as to steric and polar effects. Bimolecular reaction rates are at least an order of magnitude faster than those of the most reactive synthetic high-valent nonheme oxoiron species described to date. EPR studies in tandem with kinetic analysis show that the 490 nm chromophore of 2 is associated with two S = 1/2 species in rapid equilibrium. The minor component 2a (∼5% iron) has g-values at 2.20, 2.19, and 1.99 characteristic of a low-spin iron(III) center, and it is assigned as [Fe(III)(OOAc)(PyNMe3)](2+), also by comparison with the EPR parameters of the structurally characterized hydroxamate analogue [Fe(III)(tBuCON(H)O)(PyNMe3)](2+) (4). The major component 2b (∼40% iron, g-values = 2.07, 2.01, 1.95) has unusual EPR parameters, and it is proposed to be [Fe(V)(O)(OAc)(PyNMe3)](2+), where the O-O bond in 2a has been broken. Consistent with this assignment, 2b undergoes exchange of its acetate ligand with CD3CO2D and very rapidly reacts with olefins to produce the corresponding cis-1,2-hydroxoacetate product. Therefore, this work constitutes the first example where a synthetic nonheme iron species responsible for stereospecific and site selective C-H hydroxylation is spectroscopically trapped, and its catalytic reactivity against C-H bonds can be directly interrogated by kinetic methods. The accumulated evidence indicates that 2 consists mainly of an extraordinarily reactive [Fe(V)(O)(OAc)(PyNMe3)](2+) (2b) species capable of hydroxylating unactivated alkyl C-H bonds with

  8. Zinc(II)-Mediated Carbene Insertion into C-H Bonds in Alkanes.

    PubMed

    Kulkarni, Naveen V; Dash, Chandrakanta; Jayaratna, Naleen B; Ridlen, Shawn G; Karbalaei Khani, Sarah; Das, Animesh; Kou, Xiaodi; Yousufuddin, Muhammed; Cundari, Thomas R; Dias, H V Rasika

    2015-12-07

    The cationic zinc adduct {[HB(3,5-(CF3)2Pz)3]Zn(NCMe)2}ClO4 catalyzes the functionalization of tertiary, secondary, and primary C-H bonds of alkanes via carbene insertion. Ethyl diazoacetate serves as the :CHCO2Et carbene precursor. The counteranion, supporting ligand, and coordinating solvents affect the catalytic activity. An in situ generated {[HB(3,5-(CF3)2Pz)3]Zn}(+) species containing a bulkier {B[3,5-(CF3)2C6H3]4}(-) anion gives the best results among the zinc catalysts used.

  9. Annulation of Aromatic Imines via Directed C-H BondActivation

    SciTech Connect

    Thalji, Reema K.; Ahrendt, Kateri A.; Bergman, Robert G.; Ellman,Jonathan A.

    2005-04-14

    A directed C-H bond activation approach to the synthesis of indans, tetralins, dihydrofurans, dihydroindoles, and other polycyclic aromatic compounds is presented. Cyclization of aromatic ketimines and aldimines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using (PPh{sub 3}){sub 3}RhCl (Wilkinson's catalyst). The cyclization of a range of aromatic ketimines and aldimines provides bi- and tricyclic ring systems with good regioselectivity. Different ring sizes and substitution patterns can be accessed through the coupling of monosubstituted, 1,1- or 1,2-disubstituted, and trisubstituted alkenes bearing both electron-rich and electron-deficient functionality.

  10. Selective molecular recognition, C-H bond activation, and catalysis in nanoscale reaction vessels

    SciTech Connect

    Fiedler, Dorothea; Leung, Dennis H.; Raymond, Kenneth N.; Bergman, Robert G.

    2004-11-27

    Supramolecular chemistry represents a way to mimic enzyme reactivity by using specially designed container molecules. We have shown that a chiral self-assembled M{sub 4}L{sub 6} supramolecular tetrahedron can encapsulate a variety of cationic guests, with varying degrees of stereoselectivity. Reactive iridium guests can be encapsulated and the C-H bond activation of aldehydes occurs, with the host cavity controlling the ability of substrates to interact with the metal center based upon size and shape. In addition, the host container can act as a catalyst by itself. By restricting reaction space and preorganizing the substrates into reactive conformations, it accelerates the sigmatropic rearrangement of enammonium cations.

  11. Rhodium(III)-catalyzed indazole synthesis by C-H bond functionalization and cyclative capture.

    PubMed

    Lian, Yajing; Bergman, Robert G; Lavis, Luke D; Ellman, Jonathan A

    2013-05-15

    An efficient, one-step, and highly functional group-compatible synthesis of substituted N-aryl-2H-indazoles is reported via the rhodium(III)-catalyzed C-H bond addition of azobenzenes to aldehydes. The regioselective coupling of unsymmetrical azobenzenes was further demonstrated and led to the development of a new removable aryl group that allows for the preparation of indazoles without N-substitution. The 2-aryl-2H-indazole products also represent a new class of readily prepared fluorophores for which initial spectroscopic characterization has been performed.

  12. Electrostatic and Charge-Induced Methane Activation by a Concerted Double C-H Bond Insertion.

    PubMed

    Geng, Caiyun; Li, Jilai; Weiske, Thomas; Schlangen, Maria; Shaik, Sason; Schwarz, Helmut

    2017-02-01

    A mechanistically unique, simultaneous activation of two C-H bonds of methane has been identified during the course of its reaction with the cationic copper carbide, [Cu-C](+). Detailed high-level quantum chemical calculations support the experimental findings obtained in the highly diluted gas phase using FT-ICR mass spectrometry. The behavior of [Cu-C](+)/CH4 contrasts that of [Au-C](+)/CH4, for which a stepwise bond-activation scenario prevails. An explanation for the distinct mechanistic differences of the two coinage metal complexes is given. It is demonstrated that the coupling of [Cu-C](+) with methane to form ethylene and Cu(+) is modeled very well by the reaction of a carbon atom with methane mediated by an oriented external electric field of a positive point charge.

  13. C-H Bond Activation/Arylation Catalyzed by Arene-Ruthenium-Aniline Complexes in Water.

    PubMed

    Binnani, Chinky; Tyagi, Deepika; Rai, Rohit K; Mobin, Shaikh M; Singh, Sanjay K

    2016-11-07

    Water-soluble arene-ruthenium complexes coordinated with readily available aniline-based ligands were successfully employed as highly active catalysts in the C-H bond activation and arylation of 2-phenylpyridine with aryl halides in water. A variety of (hetero)aryl halides were also used for the ortho-C-H bond arylation of 2-phenylpyridine to afford the corresponding ortho- monoarylated products as major products in moderate to good yields. Our investigations, including time-scaled NMR spectroscopy and mass spectrometry studies, evidenced that the coordinating aniline-based ligands, having varying electronic and steric properties, had a significant influence on the catalytic activity of the resulting arene-ruthenium-aniline-based complexes. Moreover, mass spectrometry identification of the cycloruthenated species, {(η(6) -arene)Ru(κ(2) -C,N-phenylpyridine)}(+) , and several ligand-coordinated cycloruthenated species, such as [(η(6) -arene)Ru(4-methylaniline)(κ(2) -C,N-phenylpyridine)](+) , found during the reaction of 2-phenylpyridine with the arene-ruthenium-aniline complexes further authenticated the crucial roles of these species in the observed highly active and tuned catalyst. At last, the structures of a few of the active catalysts were also confirmed by single-crystal X-ray diffraction studies.

  14. An alternative interpretation of the C-H bond strengths of alkanes.

    PubMed

    Gronert, Scott

    2006-02-03

    A new model based on 1,3 repulsive steric interactions (geminal repulsion) is proposed for explaining the variation in the C-H bond strengths of the alkanes. The model builds from the assumption that 1,3 repulsive interactions are the major factor in determining the stability of a C-C or C-H bond in an alkane. From this simple premise, the model successfully reproduces the effect of branching on the stability of alkanes, alkyl radicals, and alkenes. The results suggest that geminal repulsion can provide a simple, unified explanation for these fundamental stability trends. Although previous explanations have been widely accepted, it is shown that the theoretical support for them is relatively shallow and that the current hyperconjugative stabilization model is inconsistent with several experimental and computational results concerning alkyl radicals. In contrast, an explanation based on geminal repulsion provides a general conceptual framework for rationalizing each of these stability trends and is based on a physical effect that is known to play a role in the stability of alkanes and related species.

  15. A theoretical view on CrO2+-mediated C-H bond activation in ethane

    NASA Astrophysics Data System (ADS)

    Tong, YongChun; Zhang, XiaoYong; Wang, QingYun; Xu, XinJian; Wang, YongCheng

    2015-06-01

    The gas-phase reaction of C-H bond activation in ethane by CrO2+ has been investigated using density functional theory (DFT) at the UB3LYP/6-311G(2d,p) level. Our results reveal that the activation process is actually a spin-forbidden reaction. The involved crossing point between the doublet and quartet potential energy surfaces (PES) has been discussed by two well-known methods, i.e., intrinsic reaction coordinate (IRC) approach for crossing point (CP) and Harvey's algorithm for minimum energy crossing point (MECP). The obtained single ( P1ISC = 2.48 × 10-3) and double ( P1ISC = 4.95 × 10-3) passes estimated at MECP show that the intersystem crossing (ISC) occurs with a little probability. The C-H bond activation processes should proceed to be endothermic by 73.16 kJ/mol on the doublet surface without any spin change.

  16. Cu-catalyzed cross-dehydrogenative coupling: A versatile strategy for C-C bond formations via the oxidative activation of sp3 C-H bonds

    NASA Astrophysics Data System (ADS)

    Li, Zhiping; Bohle, D. Scott; Li, Chao-Jun

    2006-06-01

    Cu-catalyzed cross-dehydrogenative coupling (CDC) methodologies were developed based on the oxidative activation of sp3 C-H bonds adjacent to a nitrogen atom. Various sp, sp2, and sp3 C-H bonds of pronucleophiles were used in the Cu-catalyzed CDC reactions. Based on these results, the mechanisms of the CDC reactions also are discussed. C-H activation | catalysis | Baylis-Hillman reaction | Mannich reaction | Friedel-Crafts reaction

  17. Palladium-catalyzed oxidative arylalkylation of activated alkenes: dual C-H bond cleavage of an arene and acetonitrile.

    PubMed

    Wu, Tao; Mu, Xin; Liu, Guosheng

    2011-12-23

    Not one but two: The title reaction proceeds through the dual C-H bond cleavage of both aniline and acetonitrile. The reaction affords a variety of cyano-bearing indolinones in excellent yield. Mechanistic studies demonstrate that this reaction involves a fast arylation of the olefin and a rate-determining C-H activation of the acetonitrile.

  18. Revealing the nature of the active site on the carbon catalyst for C-H bond activation.

    PubMed

    Sun, XiaoYing; Li, Bo; Su, Dangsheng

    2014-09-28

    A reactivity descriptor for the C-H bond activation on the nanostructured carbon catalyst is proposed. Furthermore the calculations reveal that the single ketone group can be an active site in ODH reaction.

  19. The role of group 14 element hydrides in the activation of C-H bonds in cyclic olefins.

    PubMed

    Summerscales, Owen T; Caputo, Christine A; Knapp, Caroline E; Fettinger, James C; Power, Philip P

    2012-09-05

    Formally, triple-bonded dimetallynes ArEEAr [E = Ge (1), Sn (2); Ar = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)] have been previously shown to activate aliphatic, allylic C-H bonds in cyclic olefins, cyclopentadiene (CpH), cyclopentene (c-C(5)H(8)) and 1,4-cyclohexadiene, with intriguing selectivity. In the case of the five-membered carbocycles, cyclopentadienyl species ArECp [E = Ge (3), Sn (4)] are formed. In this study, we examine the mechanisms for activation of CpH and c-C(5)H(8) using experimental methods and describe a new product found from the reaction between 1 and c-C(5)H(8), an asymmetrically substituted digermene ArGe(H)Ge(c-C(5)H(9))Ar (5), crystallized in 46% yield. This compound contains a hydrogenated cyclopentyl moiety and is found to be produced in a 3:2 ratio with 3, explaining the fate of the liberated H atoms following triple C-H activation. We show that when these C-H activation reactions are carried out in the presence of tert-butyl ethylene (excess), compounds {ArE(CH(2)CH(2)tBu)}(2) [E = Ge(8), Sn(9)] are obtained in addition to ArECp; in the case of CpH, the neohexyl complexes replace the production of H(2) gas, and for c-C(5)H(8) they displace cyclopentyl product 5 and account for all the hydrogen removed in the dehydroaromatization reactions. To confirm the source of 8 and 9, it was demonstrated that these molecules are formed cleanly between the reaction of (ArEH)(2) [E = Ge(6), Sn(7)] and tert-butyl ethylene, new examples of noncatalyzed hydro-germylation and -stannylation. Therefore, the presence of transient hydrides of the type 6 and 7 can be surmised to be reactive intermediates in the production of 3 and 4, along with H(2), from 1 and 2 and CpH (respectively), or the formation of 3 and 5 from 1. The reaction of 6 or 7 with CpH gave 3 or 4, respectively, with concomitant H(2) evolution, demonstrating the basic nature of these low-valent group 14 element hydrides and their key role in the 'cascade' of C-H activation steps

  20. Activation of C-H bond in methane by Pd atom from the bonding evolution theory perspective.

    PubMed

    Nizovtsev, Anton S

    2013-08-15

    We report detailed study focused on the electron density redistribution during the simple oxidative addition reaction being the crucial stage of various catalytic processes. The bonding evolution theory based on the electron localization function and Thom's catastrophe theory shows that activation of methane's C-H bond by Pd atom consist of six elementary steps. The important feature revealed is the pronounced reorganization of Pd's outer core maxima corresponding to N-shell electrons of metal. Electronic rearrangements identified in this model reaction are likely to be the case in the more complex reactions of the same type involving transition metal compounds and, in principle, can be observed by modern ultrafast spectroscopy and diffraction techniques.

  1. Are non-linear C-H⋯O contacts hydrogen bonds or Van der Waals interactions?. Establishing the limits between hydrogen bonds and Van der Waals interactions

    NASA Astrophysics Data System (ADS)

    Novoa, Juan J.; Lafuente, Pilar; Mota, Fernando

    1998-07-01

    The hydrogen bond nature of angular C-H⋯O contacts is examined to determine when these contacts are better classified as hydrogen bonds or as Van der Waals bonds. To classify the bond we propose to look at the nature of the intermolecular bond critical point present in the electron density of the complex containing the bond. The physics behind this approach is explained using a qualitative orbital overlap model aimed at describing the main changes in the electronic density of the complex produced by the C-H⋯O bending.

  2. Carbon-Hydrogen (C-H) Bond Activation at PdIV: A Frontier in C–H Functionalization Catalysis

    PubMed Central

    Topczewski, Joseph J.; Sanford, Melanie S.

    2014-01-01

    The direct functionalization of carbon-hydrogen (C-H) bonds has emerged as a versatile strategy for the synthesis and derivatization of organic molecules. Among the methods for C-H bond activation, catalytic processes that utilize a PdII/PdIV redox cycle are increasingly common. The C-H activation step in most of these catalytic cycles is thought to occur at a PdII centre. However, a number of recent reports have suggested the feasibility of C-H cleavage occurring at PdIV complexes. Importantly, these latter processes often result in complementary reactivity and selectivity relative to analogous transformations at PdII. This Mini Review highlights proposed examples of C-H activation at PdIV centres. Applications of this transformation in catalysis as well as mechanistic details obtained from stoichiometric model studies are discussed. Furthermore, challenges and future perspectives for the field are reviewed. PMID:25544882

  3. Directing group-controlled regioselectivity in an enzymatic C-H bond oxygenation.

    PubMed

    Negretti, Solymar; Narayan, Alison R H; Chiou, Karoline C; Kells, Petrea M; Stachowski, Jessica L; Hansen, Douglas A; Podust, Larissa M; Montgomery, John; Sherman, David H

    2014-04-02

    Highly regioselective remote hydroxylation of a natural product scaffold is demonstrated by exploiting the anchoring mechanism of the biosynthetic P450 monooxygenase PikCD50N-RhFRED. Previous studies have revealed structural and biochemical evidence for the role of a salt bridge between the desosamine N,N-dimethylamino functionality of the natural substrate YC-17 and carboxylate residues within the active site of the enzyme, and selectivity in subsequent C-H bond functionalization. In the present study, a substrate-engineering approach was conducted that involves replacing desosamine with varied synthetic N,N-dimethylamino anchoring groups. We then determined their ability to mediate enzymatic total turnover numbers approaching or exceeding that of the natural sugar, while enabling ready introduction and removal of these amino anchoring groups from the substrate. The data establish that the size, stereochemistry, and rigidity of the anchoring group influence the regioselectivity of enzymatic hydroxylation. The natural anchoring group desosamine affords a 1:1 mixture of regioisomers, while synthetic anchors shift YC-17 analogue C-10/C-12 hydroxylation from 20:1 to 1:4. The work demonstrates the utility of substrate engineering as an orthogonal approach to protein engineering for modulation of regioselective C-H functionalization in biocatalysis.

  4. Enzymatic hydroxylation of an unactivated methylene C-H bond guided by molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Narayan, Alison R. H.; Jiménez-Osés, Gonzalo; Liu, Peng; Negretti, Solymar; Zhao, Wanxiang; Gilbert, Michael M.; Ramabhadran, Raghunath O.; Yang, Yun-Fang; Furan, Lawrence R.; Li, Zhe; Podust, Larissa M.; Montgomery, John; Houk, K. N.; Sherman, David H.

    2015-08-01

    The hallmark of enzymes from secondary metabolic pathways is the pairing of powerful reactivity with exquisite site selectivity. The application of these biocatalytic tools in organic synthesis, however, remains under-utilized due to limitations in substrate scope and scalability. Here, we report how the reactivity of a monooxygenase (PikC) from the pikromycin pathway is modified through computationally guided protein and substrate engineering, and applied to the oxidation of unactivated methylene C-H bonds. Molecular dynamics and quantum mechanical calculations were used to develop a predictive model for substrate scope, site selectivity and stereoselectivity of PikC-mediated C-H oxidation. A suite of menthol derivatives was screened computationally and evaluated through in vitro reactions, where each substrate adhered to the predicted models for selectivity and conversion to product. This platform was also expanded beyond menthol-based substrates to the selective hydroxylation of a variety of substrate cores ranging from cyclic to fused bicyclic and bridged bicyclic compounds.

  5. Activation of C-H bonds in nitrones leads to iridium hydrides with antitumor activity.

    PubMed

    Song, Xiaoda; Qian, Yong; Ben, Rong; Lu, Xiang; Zhu, Hai-Liang; Chao, Hui; Zhao, Jing

    2013-08-22

    We report the design and synthesis of a series of new cyclometalated iridium hydrides derived from the C-H bond activation of aromatic nitrones and the biological evaluation of these iridium hydrides as antitumor agents. The nitrone ligands are based on the structure of a popular antioxidant, α-phenyl-N-tert-butylnitrone (PBN). Compared to cisplatin, the iridium hydrides exhibit excellent antitumor activity on HepG2 cells. The metal-coordinated compound with the most potent anticancer activity, 2f, was selected for further analysis because of its ability to induce apoptosis and interact with DNA. During in vitro studies and in vivo efficacy analysis with tumor xenograft models in Institute of Cancer Research (ICR) mice, complex 2f exhibited antitumor activity that was markedly superior to that of cisplatin. Our results suggest, for the first time, that metal hydrides could be a new type of metal-based antitumor agent.

  6. Dimethylphosphinate bridged binuclear Rh(i) catalysts for the alkoxycarbonylation of aromatic C-H bonds.

    PubMed

    Iturmendi, Amaia; Sanz Miguel, Pablo J; Popoola, Saheed A; Al-Saadi, Abdulaziz A; Iglesias, Manuel; Oro, Luis A

    2016-11-14

    A variety of binuclear rhodium(i) complexes featuring two bridging dimethylphosphinate ligands ((CH3)2PO2(-)) have been prepared and tested in the alkoxycarbonylation of aromatic C-H bonds. The complex [Rh(μ-κO,O'-(CH3)2PO2)(cod)]2 has been prepared by a reaction of [Rh(μ-MeO)(cod)]2 with 2 equivalents of dimethylphosphinic acid. Binuclear complexes [Rh(μ-κO,O'-(CH3)2PO2)(CO)L]2 (L = PPh3, P(OMe)Ph2 and P(OPh)3) were obtained by carbonylation of the related mononuclear complexes [Rh(κO-(CH3)2PO2)(cod)(L)], which were prepared in situ by the reaction of [Rh(μ-κO,O'-(CH3)2PO2)(cod)]2 with 2 equivalents of L. Conversely, if L = IPr, the reaction of [Rh(μ-κO,O'-(CH3)2PO2)(CO)L]2 with carbon monoxide affords the mononuclear complex [Rh(κO-(CH3)2PO2)(CO)2IPr]. The subsequent reaction with trimethylamine N-oxide gives the corresponding binuclear complex [Rh(μ-κO,O'-(CH3)2PO2)(CO)(IPr)]2 by abstraction of one of the carbonyl ligands. Complexes [Rh(μ-κO,O'-(CH3)2PO2)(cod)]2 and [Rh(κO-(CH3)2PO2)(cod)(L)] (L = IPr, PPh3, P(OMe)Ph2, P(OPh)3) are active precatalysts in the alkoxycarbonylation of C-H bonds, with the ligand system playing a key role in the catalytic activity. The complexes that feature more labile Rh-L bonds give rise to better catalysts, probably due to the more straightforward substitution of L by a second carbonyl ligand, since a more electrophilic carbonyl carbon atom is more susceptible toward aryl migration. In fact, complexes [Rh(μ-κO,O'-(CH3)2PO2)(CO)2]2 and [Rh(μ-Cl)(CO)2]2, generated in situ from [Rh(μ-κO,O'-(CH3)2PO2)(cod)]2 and [Rh(μ-Cl)(cod)2]2, respectively, are the most active catalysts tested in this work.

  7. Hydrogen-bond-assisted controlled C-H functionalization via adaptive recognition of a purine directing group.

    PubMed

    Kim, Hyun Jin; Ajitha, Manjaly J; Lee, Yongjae; Ryu, Jaeyune; Kim, Jin; Lee, Yunho; Jung, Yousung; Chang, Sukbok

    2014-01-22

    We have developed the Rh-catalyzed selective C-H functionalization of 6-arylpurines, in which the purine moiety directs the C-H bond activation of the aryl pendant. While the first C-H amination proceeds via the N1-chelation assistance, the subsequent second C-H bond activation takes advantage of an intramolecular hydrogen-bonding interaction between the initially formed amino group and one nitrogen atom, either N1 or N7, of the purinyl part. Isolation of a rhodacycle intermediate and the substrate variation studies suggest that N1 is the main active site for the C-H functionalization of both the first and second amination in 6-arylpurines, while N7 plays an essential role in controlling the degree of functionalization serving as an intramolecular hydrogen-bonding site in the second amination process. This pseudo-Curtin-Hammett situation was supported by density functional calculations, which suggest that the intramolecular hydrogen-bonding capability helps second amination by reducing the steric repulsion between the first installed ArNH and the directing group.

  8. Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation

    SciTech Connect

    Lewis, Jared; Bergman, Robert; Ellman, Jonathan

    2008-02-04

    Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct funtionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes their work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. They initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. They then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, they discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. They then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy{sub 3}){sub 2}] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazolein, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy{sub 3}){sub 2} fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, they developed conditions that efficiently and intermolecularly alkylate a variety of

  9. At least 10% shorter C-H bonds in cryogenic protein crystal structures than in current AMBER forcefields.

    PubMed

    Pang, Yuan-Ping

    2015-03-06

    High resolution protein crystal structures resolved with X-ray diffraction data at cryogenic temperature are commonly used as experimental data to refine forcefields and evaluate protein folding simulations. However, it has been unclear hitherto whether the C-H bond lengths in cryogenic protein structures are significantly different from those defined in forcefields to affect protein folding simulations. This article reports the finding that the C-H bonds in high resolution cryogenic protein structures are 10-14% shorter than those defined in current AMBER forcefields, according to 3709 C-H bonds in the cryogenic protein structures with resolutions of 0.62-0.79 Å. Also, 20 all-atom, isothermal-isobaric, 0.5-μs molecular dynamics simulations showed that chignolin folded from a fully-extended backbone formation to the native β-hairpin conformation in the simulations using AMBER forcefield FF12SB at 300 K with an aggregated native state population including standard error of 10 ± 4%. However, the aggregated native state population with standard error reduced to 3 ± 2% in the same simulations except that C-H bonds were shortened by 10-14%. Furthermore, the aggregated native state populations with standard errors increased to 35 ± 3% and 26 ± 3% when using FF12MC, which is based on AMBER forcefield FF99, with and without the shortened C-H bonds, respectively. These results show that the 10-14% bond length differences can significantly affect protein folding simulations and suggest that re-parameterization of C-H bonds according to the cryogenic structures could improve the ability of a forcefield to fold proteins in molecular dynamics simulations.

  10. Consequences of metal-oxide interconversion for C-H bond activation during CH4 reactions on Pd catalysts.

    PubMed

    Chin, Ya-Huei Cathy; Buda, Corneliu; Neurock, Matthew; Iglesia, Enrique

    2013-10-16

    Mechanistic assessments based on kinetic and isotopic methods combined with density functional theory are used to probe the diverse pathways by which C-H bonds in CH4 react on bare Pd clusters, Pd cluster surfaces saturated with chemisorbed oxygen (O*), and PdO clusters. C-H activation routes change from oxidative addition to H-abstraction and then to σ-bond metathesis with increasing O-content, as active sites evolve from metal atom pairs (*-*) to oxygen atom (O*-O*) pairs and ultimately to Pd cation-lattice oxygen pairs (Pd(2+)-O(2-)) in PdO. The charges in the CH3 and H moieties along the reaction coordinate depend on the accessibility and chemical state of the Pd and O centers involved. Homolytic C-H dissociation prevails on bare (*-*) and O*-covered surfaces (O*-O*), while C-H bonds cleave heterolytically on Pd(2+)-O(2-) pairs at PdO surfaces. On bare surfaces, C-H bonds cleave via oxidative addition, involving Pd atom insertion into the C-H bond with electron backdonation from Pd to C-H antibonding states and the formation of tight three-center (H3C···Pd···H)(‡) transition states. On O*-saturated Pd surfaces, C-H bonds cleave homolytically on O*-O* pairs to form radical-like CH3 species and nearly formed O-H bonds at a transition state (O*···CH3(•)···*OH)(‡) that is looser and higher in enthalpy than on bare Pd surfaces. On PdO surfaces, site pairs consisting of exposed Pd(2+) and vicinal O(2-), Pd(ox)-O(ox), cleave C-H bonds heterolytically via σ-bond metathesis, with Pd(2+) adding to the C-H bond, while O(2-) abstracts the H-atom to form a four-center (H3C(δ-)···Pd(ox)···H(δ+)···O(ox))(‡) transition state without detectable Pd(ox) reduction. The latter is much more stable than transition states on *-* and O*-O* pairs and give rise to a large increase in CH4 oxidation turnover rates at oxygen chemical potentials leading to Pd to PdO transitions. These distinct mechanistic pathways for C-H bond activation, inferred from theory

  11. Functionalization of non-activated C-H bonds in the synthesis of vitamin D metabolites and analogs.

    PubMed

    Moman, Edelmiro

    2014-01-01

    The development of non-microbial methods for the selective functionalization of non-activated C-H bonds has constituted a challenge, with important economical and environmental implications, for chemists for over a century. The present review provides a comprehensive and current compendium that illustrates the power of C-H functionalization and, namely, of remote functionalization strategies, to expeditiously access vitamin D analogs with intricate structures.

  12. On blue shifts of C--H stretching modes of dimethyl ether in hydrogen- and halogen-bonded complexes

    NASA Astrophysics Data System (ADS)

    Karpfen, Alfred; Kryachko, Eugene S.

    2006-11-01

    A systematic investigation of a representative series of intermolecular complexes formed between dimethyl ether (DME) and various interacting partners such as H 2O, hydrogen halides, dihalogens, halomethanes, DME, and the ions Li + and H + was performed at the MP2/6-311++G(2d,2p) computational level. Although, except (DME) 2, DME-HCF 3, DME-HCClF 2, and DME-HCCl 2F, the C-H bonds of DME are not involved in the hydrogen bonding of these complexes, their C-H stretching frequencies are all blue-shifted. It is shown that the mechanism of these blue shifts originates from the existence of a negative intramolecular coupling between the C-O and C-H bonds inherent to the DME molecule.

  13. Graphene Oxide Catalyzed C-H Bond Activation: The Importance Oxygen Functional Groups for Biaryl Construction

    SciTech Connect

    Gao, Yongjun; Tang, Pei; Zhou, Hu; Zhang, Wei; Yang, Hanjun; Yan, Ning; Hu, Gang; Mei, Donghai; Wang, Jianguo; Ma, Ding

    2016-02-24

    A heterogeneous, inexpensive and environment-friendly carbon catalytic system was developed for the C-H bond arylation of benzene resulting in the subsequent formation of biaryl compounds. The oxygen-containing groups on these graphene oxide sheets play an essential role in the observed catalytic activity. The catalytic results of model compounds and DFT calculations show that these functional groups promote this reaction by stabilization and activation of K ions at the same time of facilitating the leaving of I. And further mechanisms studies show that it is the charge induced capabilities of oxygen groups connected to specific carbon skeleton together with the giant π-reaction platform provided by the π-domain of graphene that played the vital roles in the observed excellent catalytic activity. D. Mei acknowledges the support from the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle. Computing time was granted by the grand challenge of computational catalysis of the William R. Wiley Environmental Molecular Sciences Laboratory.

  14. Nickel-Catalyzed Insertion of Alkynes and Electron-Deficient Olefins into Unactivated sp(3) C-H Bonds.

    PubMed

    Maity, Soham; Agasti, Soumitra; Earsad, Arif Mahammad; Hazra, Avijit; Maiti, Debabrata

    2015-08-03

    Insertion of unsaturated systems such as alkynes and olefins into unactivated sp(3) C-H bonds remains an unexplored problem. We herein address this issue by successfully incorporating a wide variety of functionalized alkynes and electron-deficient olefins into the unactivated sp(3) C-H bond of pivalic acid derivatives with excellent syn- and linear- selectivity. A strongly chelating 8-aminoquinoline directing group proved beneficial for these insertion reactions, while an air-stable and inexpensive Ni(II) salt has been employed as the active catalyst.

  15. Making Fe(BPBP)-catalyzed C-H and C[double bond, length as m-dash]C oxidations more affordable.

    PubMed

    Yazerski, Vital A; Spannring, Peter; Gatineau, David; Woerde, Charlotte H M; Wieclawska, Sara M; Lutz, Martin; Kleijn, Henk; Gebbink, Robertus J M Klein

    2014-04-07

    The limited availability of catalytic reaction components may represent a major hurdle for the practical application of many catalytic procedures in organic synthesis. In this work, we demonstrate that the mixture of isomeric iron complexes [Fe(OTf)2(mix-BPBP)] (mix-1), composed of Λ-α-[Fe(OTf)2(S,S-BPBP)] (S,S-1), Δ-α-[Fe(OTf)2(R,R-BPBP)] (R,R-1) and Δ/Λ-β-[Fe(OTf)2(R,S-BPBP)] (R,S-1), is a practical catalyst for the preparative oxidation of various aliphatic compounds including model hydrocarbons and optically pure natural products using hydrogen peroxide as an oxidant. Among the species present in mix-1, S,S-1 and R,R-1 are catalytically active, act independently and represent ca. 75% of mix-1. The remaining 25% of mix-1 is represented by mesomeric R,S-1 which nominally plays a spectator role in both C-H and C[double bond, length as m-dash]C bond oxidation reactions. Overall, this mixture of iron complexes displays the same catalytic profile as its enantiopure components that have been previously used separately in sp(3) C-H oxidations. In contrast to them, mix-1 is readily available on a multi-gram scale via two high yielding steps from crude dl/meso-2,2'-bipyrrolidine. Next to its use in C-H oxidation, mix-1 is active in chemospecific epoxidation reactions, which has allowed us to develop a practical catalytic protocol for the synthesis of epoxides.

  16. Acid-catalyzed oxidative addition of a C-H bond to a square planar d⁸ iridium complex.

    PubMed

    Hackenberg, Jason D; Kundu, Sabuj; Emge, Thomas J; Krogh-Jespersen, Karsten; Goldman, Alan S

    2014-06-25

    While the addition of C-H bonds to three-coordinate Ir(I) fragments is a central theme in the field of C-H bond activation, addition to square planar four-coordinate complexes is far less precedented. The dearth of such reactions may be attributed, at least in part, to kinetic factors elucidated in seminal work by Hoffmann. C-H additions to square planar carbonyl complexes in particular are unprecedented, in contrast to the extensive chemistry of oxidative addition of other substrates (e.g., H2, HX) to Vaska's Complex and related species. We report that Bronsted acids will catalyze the addition of the alkynyl C-H bond of phenylacetylene to the pincer complex (PCP)Ir(CO). The reaction occurs to give exclusively the trans-C-H addition product. Our proposed mechanism, based on kinetics and DFT calculations, involves initial protonation of (PCP)Ir(CO) to generate a highly active five-coordinate cationic intermediate, which forms a phenylacetylene adduct that is then deprotonated to give product.

  17. Asymmetric Synthesis of (-)-Incarvillateine Employing an Intramolecular Alkylation via Rh-Catalyzed Olefinic C-H Bond Activation

    SciTech Connect

    Tsai, Andy; Bergman, Robert; Ellman, Jonathan

    2008-02-18

    An asymmetric total synthesis of (-)-incarvillateine, a natural product having potent analgesic properties, has been achieved in 11 steps and 15.4% overall yield. The key step is a rhodium-catalyzed intramolecular alkylation of an olefinic C-H bond to set two stereocenters. Additionally, this transformation produces an exocyclic, tetrasubstituted alkene through which the bicyclic piperidine moiety can readily be accessed.

  18. Efficient photocatalytic selective nitro-reduction and C-H bond oxidation over ultrathin sheet mediated CdS flowers.

    PubMed

    Pahari, Sandip Kumar; Pal, Provas; Srivastava, Divesh N; Ghosh, Subhash Ch; Panda, Asit Baran

    2015-06-28

    We report here a visible light driven selective nitro-reduction and oxidation of saturated sp(3) C-H bonds using ultrathin (0.8 nm) sheet mediated uniform CdS flowers as catalyst under a household 40 W CFL lamp and molecular oxygen as oxidant. The CdS flowers were synthesized using a simple surfactant assisted hydrothermal method.

  19. Activation of Propane C-H and C-C Bonds by Gas-Phase Pt Atom: A Theoretical Study

    PubMed Central

    Li, Fang-Ming; Yang, Hua-Qing; Ju, Ting-Yong; Li, Xiang-Yuan; Hu, Chang-Wei

    2012-01-01

    The reaction mechanism of the gas-phase Pt atom with C3H8 has been systematically investigated on the singlet and triplet potential energy surfaces at CCSD(T)//BPW91/6-311++G(d, p), Lanl2dz level. Pt atom prefers the attack of primary over secondary C-H bonds in propane. For the Pt + C3H8 reaction, the major and minor reaction channels lead to PtC3H6 + H2 and PtCH2 + C2H6, respectively, whereas the possibility to form products PtC2H4 + CH4 is so small that it can be neglected. The minimal energy reaction pathway for the formation of PtC3H6 + H2, involving one spin inversion, prefers to start at the triplet state and afterward proceed along the singlet state. The optimal C-C bond cleavages are assigned to C-H bond activation as the first step, followed by cleavage of a C-C bond. The C-H insertion intermediates are kinetically favored over the C-C insertion intermediates. From C-C to C-H oxidative insertion, the lowering of activation barrier is mainly caused by the more stabilizing transition state interaction ΔE≠int, which is the actual interaction energy between the deformed reactants in the transition state. PMID:22942766

  20. Enantioselective C-H bond addition of pyridines to alkenes catalyzed by chiral half-sandwich rare-earth complexes.

    PubMed

    Song, Guoyong; O, Wylie W N; Hou, Zhaomin

    2014-09-03

    Cationic half-sandwich scandium alkyl complexes bearing monocyclopentadienyl ligands embedded in chiral binaphthyl backbones act as excellent catalysts for the enantioselective C-H bond addition of pyridines to various 1-alkenes, leading to formation of a variety of enantioenriched alkylated pyridine derivatives in high yields and excellent enantioselectivity (up to 98:2 er).

  1. Electrophilic, Ambiphilic, and Nucleophilic C-H bond Activation. Understanding the electronic continuum of C-H bond activation through transition-state and reaction pathway interaction energy decompositions

    SciTech Connect

    Ess, Daniel H.; Goddard, William A.; Periana, Roy A.

    2010-10-29

    The potential energy and interaction energy profiles for metal- and metal-ligand-mediated alkane C-H bond activation were explored using B3LYP density functional theory (DFT) and the absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA). The set of complexes explored range from late transition metal group 10 (Pt and Pd) and group 11 (Au) metal centers to group 7-9 (Ir, Rh, Ru, and W) metal centers as well as a group 3 Sc complex. The coordination geometries, electron metal count (d8, d6, d4, and d0), and ligands (N-heterocycles, O-donor, phosphine, and Cp*) are also diverse. Quantitative analysis using ALMO-EDA of both directions of charge-transfer stabilization (occupied to unoccupied orbital stabilization) energies between the metal-ligand fragment and the coordinated C-H bond in the transition state for cleavage of the C-H bond allows classification of C-H activation reactions as electrophilic, ambiphilic, or nucleophilic on the basis of the net direction of charge-transfer energy stabilization. This bonding pattern transcends any specific mechanistic or bonding paradigm, such as oxidative addition, σ-bond metathesis, or substitution. Late transition metals such as Au(III), Pt(II), Pd(II), and Rh(III) metal centers with N-heterocycle, halide, or O-donor ligands show electrophilically dominated reaction profiles with forward charge-transfer from the C-H bond to the metal, leading to more stabilization than reverse charge transfer from the metal to the C-H bond. Transition states and reaction profiles for d6 Ru(II) and Ir(III) metals with Tp and acac ligands were found to have nearly equal forward and reverse charge-transfer energy stabilization. This ambiphilic region also includes the classically labeled electrophilic cationic species Cp*(PMe3)Ir(Me). Nucleophilic character, where the metal to C-H bond charge-transfer interaction is most stabilizing, was found in

  2. Interference energy in C-H and C-C bonds of saturated hydrocarbons: dependence on the type of chain and relationship to bond dissociation energy.

    PubMed

    Vieira, Francisco Senna; Fantuzzi, Felipe; Cardozo, Thiago Messias; Nascimento, Marco Antonio Chaer

    2013-05-16

    Interference energy for C-H and C-C bonds of a set of saturated hydrocarbons is calculated by the generalized product function energy partitioning (GPF-EP) method in order to investigate its sensitivity to the type of chain and also its contribution to the bond dissociation energy. All GPF groups corresponding to chemical bonds are calculated by use of GVB-PP wave functions to ensure the correct description of bond dissociation. The results show that the interference energies are practically the same for all the C-H bonds, presenting only small variations (0.5 kcal.mol(-1)) due to the structural changes in going from linear to branched and cyclic chains. A similar trend is verified for the C-C bonds, the sole exception being the cyclopropane molecule, for which only the C-C bond exhibits a more significant variation. On the other hand, although the interference energy is quantitatively the most important contribution to the bond dissociation energy (DE), one cannot predict DE only from the bond interference energy. Differences in the dissociation energies of C-C and C-H bonds due to structural changes in the saturated hydrocarbons can be mainly attributed to quasi-classical effects.

  3. Copper/silver-mediated direct ortho-ethynylation of unactivated (hetero)aryl C-H bonds with terminal alkyne.

    PubMed

    Liu, Yue-Jin; Liu, Yan-Hua; Yin, Xue-Song; Gu, Wen-Jia; Shi, Bing-Feng

    2015-01-02

    A copper/silver-mediated oxidative ortho-ethynylation of unactivated aryl C-H bonds with terminal alkyne has been developed. The reaction uses the removable PIP directing group and features broad substrate scope, high functional-group tolerance, and compatibility with a wide range of heterocycles, providing an efficient synthesis of aryl alkynes. This procedure highlights the potential of copper catalysts to promote unique, synthetically enabling C-H functionalization reactions that lie outside of the current scope of precious metal catalysis.

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

    PubMed

    Turner, Zoë R

    2016-08-01

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

  5. C-H bond activation of methane in aqueous solution: a hybrid quantum mechanical/effective fragment potential study.

    PubMed

    Da Silva, Júlio C S; Rocha, Willian R

    2011-12-01

    In this study, we investigated the C-H bond activation of methane catalyzed by the complex [PtCl(4)](2-), using the hybrid quantum mechanical/effective fragment potential (EFP) approach. We analyzed the structures, energetic properties, and reaction mechanism involved in the elementary steps that compose the catalytic cycle of the Shilov reaction. Our B3LYP/SBKJC/cc-pVDZ/EFP results show that the methane activation may proceed through two pathways: (i) electrophilic addition or (ii) direct oxidative addition of the C-H bond of the alkane. The electrophilic addition pathway proceeds in two steps with formation of a σ-methane complex, with a Gibbs free energy barrier of 24.6 kcal mol(-1), followed by the cleavage of the C-H bond, with an energy barrier of 4.3 kcal mol(-1) . The activation Gibbs free energy, calculated for the methane uptake step was 24.6 kcal mol(-1), which is in good agreement with experimental value of 23.1 kcal mol(-1) obtained for a related system. The results shows that the activation of the C-H bond promoted by the [PtCl(4)](2-) catalyst in aqueous solution occurs through a direct oxidative addition of the C-H bond, in a single step, with an activation free energy of 25.2 kcal mol(-1), as the electrophilic addition pathway leads to the formation of a σ-methane intermediate that rapidly undergoes decomposition. The inclusion of long-range solvent effects with polarizable continuum model does not change the activation energies computed at the B3LYP/SBKJC/cc-pVDZ/EFP level of theory significantly, indicating that the large EFP water cluster used, obtained from Monte Carlo simulations and analysis of the center-of-mass radial pair distribution function, captures the most important solvent effects.

  6. O-H hydrogen bonding promotes H-atom transfer from α C-H bonds for C-alkylation of alcohols.

    PubMed

    Jeffrey, Jenna L; Terrett, Jack A; MacMillan, David W C

    2015-09-25

    The efficiency and selectivity of hydrogen atom transfer from organic molecules are often difficult to control in the presence of multiple potential hydrogen atom donors and acceptors. Here, we describe the mechanistic evaluation of a mode of catalytic activation that accomplishes the highly selective photoredox α-alkylation/lactonization of alcohols with methyl acrylate via a hydrogen atom transfer mechanism. Our studies indicate a particular role of tetra-n-butylammonium phosphate in enhancing the selectivity for α C-H bonds in alcohols in the presence of allylic, benzylic, α-C=O, and α-ether C-H bonds.

  7. Synthesis of a Benzodiazepine-derived Rhodium NHC Complex by C-H Bond Activation

    SciTech Connect

    Bergman, Roberg G.; Gribble, Jr., Michael W.; Ellman, Jonathan A.

    2008-01-30

    The synthesis and characterization of a Rh(I)-NHC complex generated by C-H activation of 1,4-benzodiazepine heterocycle are reported. This complex constitutes a rare example of a carbene tautomer of a 1,4-benzodiazepine aldimine stabilized by transition metal coordination and demonstrates the ability of the catalytically relevant RhCl(PCy{sub 3}){sub 2} fragment to induce NHC-forming tautomerization of heterocycles possessing a single carbene-stabilizing heteroatom. Implications for the synthesis of benzodiazepines and related pharmacophores via C-H functionalization are discussed.

  8. Oxidation-promoted activation of a ferrocene C-H bond by a rhodium complex.

    PubMed

    Labande, Agnès; Debono, Nathalie; Sournia-Saquet, Alix; Daran, Jean-Claude; Poli, Rinaldo

    2013-05-14

    The oxidation of a rhodium(I) complex containing a ferrocene-based heterodifunctional phosphine N-heterocyclic carbene (NHC) ligand produces a stable, planar chiral rhodium(III) complex with an unexpected C-H activation on ferrocene. The oxidation of rhodium(I) to rhodium(III) may be accomplished by initial oxidation of ferrocene to ferrocenium and subsequent electron transfer from rhodium to ferrocenium. Preliminary catalytic tests showed that the rhodium(III) complex is active for the Grignard-type arylation of 4-nitrobenzaldehyde via C-H activation of 2-phenylpyridine.

  9. Direct approaches to nitriles via highly efficient nitrogenation strategy through C-H or C-C bond cleavage.

    PubMed

    Wang, Teng; Jiao, Ning

    2014-04-15

    Because of the importance of nitrogen-containing compounds in chemistry and biology, organic chemists have long focused on the development of novel methodologies for their synthesis. For example, nitrogen-containing compounds show up within functional materials, as top-selling drugs, and as bioactive molecules. To synthesize these compounds in a green and sustainable way, researchers have focused on the direct functionalization of hydrocarbons via C-H or C-C bond cleavage. Although researchers have made significant progress in the direct functionalization of simple hydrocarbons, direct C-N bond formation via C-H or C-C bond cleavage remains challenging, in part because of the unstable character of some N-nucleophiles under oxidative conditions. The nitriles are versatile building blocks and precursors in organic synthesis. Recently, chemists have achieved the direct C-H cyanation with toxic cyanide salts in the presence of stoichiometric metal oxidants. In this Account, we describe recent progress made by our group in nitrile synthesis. C-H or C-C bond cleavage is a key process in our strategy, and azides or DMF serve as the nitrogen source. In these reactions, we successfully realized direct nitrile synthesis using a variety of hydrocarbon groups as nitrile precursors, including methyl, alkenyl, and alkynyl groups. We could carry out C(sp(3))-H functionalization on benzylic, allylic, and propargylic C-H bonds to produce diverse valuable synthetic nitriles. Mild oxidation of C═C double-bonds and C≡C triple-bonds also produced nitriles. The incorporation of nitrogen within the carbon skeleton typically involved the participation of azide reagents. Although some mechanistic details remain unclear, studies of these nitrogenation reactions implicate the involvement of a cation or radical intermediate, and an oxidative rearrangement of azide intermediate produced the nitrile. We also explored environmentally friendly oxidants, such as molecular oxygen, to make our

  10. C-H bond activation enables the rapid construction and late-stage diversification of functional molecules

    NASA Astrophysics Data System (ADS)

    Wencel-Delord, Joanna; Glorius, Frank

    2013-05-01

    The beginning of the twenty-first century has witnessed significant advances in the field of C-H bond activation, and this transformation is now an established piece in the synthetic chemists' toolbox. This methodology has the potential to be used in many different areas of chemistry, for example it provides a perfect opportunity for the late-stage diversification of various kinds of organic scaffolds, ranging from relatively small molecules like drug candidates, to complex polydisperse organic compounds such as polymers. In this way, C-H activation approaches enable relatively straightforward access to a plethora of analogues or can help to streamline the lead-optimization phase. Furthermore, synthetic pathways for the construction of complex organic materials can now be designed that are more atom- and step-economical than previous methods and, in some cases, can be based on synthetic disconnections that are just not possible without C-H activation. This Perspective highlights the potential of metal-catalysed C-H bond activation reactions, which now extend beyond the field of traditional synthetic organic chemistry.

  11. Palladium-catalyzed regioselective carbonylation of C-H bonds of N-alkyl anilines for synthesis of isatoic anhydrides.

    PubMed

    Guan, Zheng-Hui; Chen, Ming; Ren, Zhi-Hui

    2012-10-24

    A Pd-catalyzed regioselective C-H bond carbonylation of N-alkyl anilines for the synthesis of isatoic anhydrides has been developed. The key Pd-catalyst intermediate has been isolated and characterized. This novel Pd-catalyzed carbonylation reaction tolerates a wide range of functional groups and is a reliable method for the rapid elaboration of readily available N-alkyl anilines into a variety of substituted isatoic anhydrides under mild conditions.

  12. Easy activation of two C-H bonds of an N-heterocyclic carbene N-methyl group.

    PubMed

    Cabeza, Javier A; del Río, Ignacio; Miguel, Daniel; Sánchez-Vega, M Gabriela

    2005-08-21

    The first trinuclear clusters containing NHC ligands are described; the compound [Ru3(Me2Im)(CO)11](Me2Im=1,3-dimethylimidazol-2-ylidene) is easily converted into [Ru3(mu-H)2(mu3-MeImCH)(CO)9] by a process involving the activation of two C-H bonds of a methyl group that is an example of degradation of a metal-coordinated NHC ligand under mild conditions.

  13. I2-Mediated 2H-indazole synthesis via halogen-bond-assisted benzyl C-H functionalization.

    PubMed

    Yi, Xiangli; Jiao, Lei; Xi, Chanjuan

    2016-10-18

    I2-Mediated benzyl C-H functionalization has been developed for the synthesis of 2H-indazoles, which features high efficiency, simple conditions and no need for metals. Mechanistic experiments and DFT calculations have revealed halogen bond assistance and a radical chain process for this reaction. The azo group and the bound iodine cooperate in the hydrogen abstraction step, which circumvents the thermodynamic disfavor of direct hydrogen abstraction by a simple iodine radical.

  14. Vapour-induced solid-state C-H bond activation for the clean synthesis of an organopalladium biothiol sensor.

    PubMed

    Monas, Andrea; Užarević, Krunoslav; Halasz, Ivan; Kulcsár, Marina Juribašić; Ćurić, Manda

    2016-10-27

    Room-temperature accelerated aging in the solid state has been applied for atom- and energy-efficient activation of either one or two C-H bonds of azobenzene and methyl orange by palladium(ii) acetate. Organopalladium complexes are prepared in quantitative reactions without potentially harmful side products. Dicyclopalladated methyl orange is water-soluble and is a selective chromogenic biothiol sensor at physiologically-relevant micromolar concentrations in buffered aqueous media.

  15. Palladium(II)-Catalyzed C-H Bond Activation/C-C and C-O Bond Formation Reaction Cascade: Direct Synthesis of Coumestans.

    PubMed

    Neog, Kashmiri; Borah, Ashwini; Gogoi, Pranjal

    2016-12-02

    A palladium catalyzed cascade reaction of 4-hydroxycoumarins and in situ generated arynes has been developed for the direct synthesis of coumestans. This cascade strategy proceeds via C-H bond activation/C-O and C-C bond formations in a single reaction vessel. This methodology affords moderate to good yields of coumestans and is tolerant of a variety of functional groups including halide. The methodology was applied to the synthesis of natural product flemichapparin C.

  16. Mild Palladium Catalyzed ortho C-H Bond Functionalizations of Aniline Derivatives.

    PubMed

    Tischler, Ms Orsolya; Tóth, Mr Balázs; Novák, Zoltán

    2017-02-01

    This account collects the developments and transformations which avoid the utilization of harsh reaction conditions in the field of palladium catalyzed, ortho-directed C-H activation of aniline derivatives from the first attempts to up-to-date results, including the results of our research laboratory. The discussed functionalizations performed under mild conditions include acylation, olefination, arylation, alkylation, alkoxylation reactions. Beside the optimization studies and the synthetic applications mechanistic investigations are also presented.

  17. Rare-earth-catalyzed C-H bond addition of pyridines to olefins.

    PubMed

    Guan, Bing-Tao; Hou, Zhaomin

    2011-11-16

    An efficient and general protocol for the ortho-alkylation of pyridines via C-H addition to olefins has been developed, using cationic half-sandwich rare-earth catalysts, which provides an atom-economical method for the synthesis of alkylated pyridine derivatives. A wide range of pyridine and olefin substrates including α-olefins, styrenes, and conjugated dienes are compatible with the catalysts.

  18. Origin of superlubricity in a-C:H:Si films: a relation to film bonding structure and environmental molecular characteristic.

    PubMed

    Chen, Xinchun; Kato, Takahisa; Nosaka, Masataka

    2014-08-27

    Superlubricity of Si-containing hydrogenated amorphous carbon (a-C:H:Si) films has been systematically investigated in relation to the film bonding structure and the environmental atmosphere. Structural diversity induced by hydrogen incorporation (i.e., 17.3-36.7 at. % H), namely sp(2)-bonded a-C, diamond-like or polymer-like, and tribointeractions activated by the participation of environmental gaseous molecules mainly determine the frictional behaviors of a-C:H:Si films. A suitable control of hydrogen content in the film (i.e., the inherent hydrogen coverage) is obligate to obtain durable superlubricity in a distinct gaseous atmosphere such as dry N2, reactive H2 or humid air. Rapid buildup of running-in-induced antifriction tribolayers at the contact interface, which is more feasible in self-mated sliding, is crucial for achieving a superlubric state. Superior tribological performances have been observed for the polymer-like a-C:H:Si (31.9 at. % H) film, as this hydrogen-rich sample can exhibit superlow friction in various atmospheres including dry inert N2 (μ ∼ 0.001), Ar (μ ∼ 0.012), reactive H2 (μ ∼ 0.003) and humid air (μ ∼ 0.004), and can maintain ultralow friction in corrosive O2 (μ ∼ 0.084). Hydrogen is highlighted for its decisive role in obtaining superlow friction. The occurrence of superlubricity in a-C:H:Si films is generally attributed to a synergistic effect of phase transformation, surface passivation and shear localization, for instance, the near-frictionless state occurred in dry N2. The contribution of each mechanism to the friction reduction depends on the specific intrafilm and interfilm interactions along with the atmospheric effects. These antifriction a-C:H:Si films are promising for industrial applications as lubricants.

  19. The Mechanism of N-O Bond Cleavage in Rhodium-Catalyzed C-H Bond Functionalization of Quinoline N-oxides with Alkynes: A Computational Study.

    PubMed

    Li, Yingzi; Liu, Song; Qi, Zisong; Qi, Xiaotian; Li, Xingwei; Lan, Yu

    2015-07-06

    Metal-catalyzed C-H activation not only offers important strategies to construct new bonds, it also allows the merge of important research areas. When quinoline N-oxide is used as an arene source in C-H activation studies, the N-O bond can act as a directing group as well as an O-atom donor. The newly reported density functional theory method, M11L, has been used to elucidate the mechanistic details of the coupling between quinoline N-O bond and alkynes, which results in C-H activation and O-atom transfer. The computational results indicated that the most favorable pathway involves an electrophilic deprotonation, an insertion of an acetylene group into a Rh-C bond, a reductive elimination to form an oxazinoquinolinium-coordinated Rh(I) intermediate, an oxidative addition to break the N-O bond, and a protonation reaction to regenerate the active catalyst. The regioselectivity of the reaction has also been studied by using prop-1-yn-1-ylbenzene as a model unsymmetrical substrate. Theoretical calculations suggested that 1-phenyl-2-quinolinylpropanone would be the major product because of better conjugation between the phenyl group and enolate moiety in the corresponding transition state of the regioselectivity-determining step. These calculated data are consistent with the experimental observations.

  20. C-H bond strengths and acidities in aromatic systems: effects of nitrogen incorporation in mono-, di-, and triazines.

    PubMed

    Wren, Scott W; Vogelhuber, Kristen M; Garver, John M; Kato, Shuji; Sheps, Leonid; Bierbaum, Veronica M; Lineberger, W Carl

    2012-04-18

    The negative ion chemistry of five azine molecules has been investigated using the combined experimental techniques of negative ion photoelectron spectroscopy to obtain electron affinities (EA) and tandem flowing afterglow-selected ion tube (FA-SIFT) mass spectrometry to obtain deprotonation enthalpies (Δ(acid)H(298)). The measured Δ(acid)H(298) for the most acidic site of each azine species is combined with the EA of the corresponding radical in a thermochemical cycle to determine the corresponding C-H bond dissociation energy (BDE). The site-specific C-H BDE values of pyridine, 1,2-diazine, 1,3-diazine, 1,4-diazine, and 1,3,5-triazine are 110.4 ± 2.0, 111.3 ± 0.7, 113.4 ± 0.7, 107.5 ± 0.4, and 107.8 ± 0.7 kcal mol(-1), respectively. The application of complementary experimental methods, along with quantum chemical calculations, to a series of nitrogen-substituted azines sheds light on the influence of nitrogen atom substitution on the strength of C-H bonds in six-membered rings.

  1. A versatile tripodal Cu(I) reagent for C-N bond construction via nitrene-transfer chemistry: catalytic perspectives and mechanistic insights on C-H aminations/amidinations and olefin aziridinations.

    PubMed

    Bagchi, Vivek; Paraskevopoulou, Patrina; Das, Purak; Chi, Lingyu; Wang, Qiuwen; Choudhury, Amitava; Mathieson, Jennifer S; Cronin, Leroy; Pardue, Daniel B; Cundari, Thomas R; Mitrikas, George; Sanakis, Yiannis; Stavropoulos, Pericles

    2014-08-13

    A Cu(I) catalyst (1), supported by a framework of strongly basic guanidinato moieties, mediates nitrene-transfer from PhI═NR sources to a wide variety of aliphatic hydrocarbons (C-H amination or amidination in the presence of nitriles) and olefins (aziridination). Product profiles are consistent with a stepwise rather than concerted C-N bond formation. Mechanistic investigations with the aid of Hammett plots, kinetic isotope effects, labeled stereochemical probes, and radical traps and clocks allow us to conclude that carboradical intermediates play a major role and are generated by hydrogen-atom abstraction from substrate C-H bonds or initial nitrene-addition to one of the olefinic carbons. Subsequent processes include solvent-caged radical recombination to afford the major amination and aziridination products but also one-electron oxidation of diffusively free carboradicals to generate amidination products due to carbocation participation. Analyses of metal- and ligand-centered events by variable temperature electrospray mass spectrometry, cyclic voltammetry, and electron paramagnetic resonance spectroscopy, coupled with computational studies, indicate that an active, but still elusive, copper-nitrene (S = 1) intermediate initially abstracts a hydrogen atom from, or adds nitrene to, C-H and C═C bonds, respectively, followed by a spin flip and radical rebound to afford intra- and intermolecular C-N containing products.

  2. Reactivity of oxygen radical anions bound to scandia nanoparticles in the gas phase: C-H bond activation.

    PubMed

    Tian, Li-Hua; Meng, Jing-Heng; Wu, Xiao-Nan; Zhao, Yan-Xia; Ding, Xun-Lei; He, Sheng-Gui; Ma, Tong-Mei

    2014-01-20

    The activation of C-H bonds in alkanes is currently a hot research topic in chemistry. The atomic oxygen radical anion (O(-·)) is an important species in C-H activation. The mechanistic details of C-H activation by O(-·) radicals can be well understood by studying the reactions between O(-·) containing transition metal oxide clusters and alkanes. Here the reactivity of scandium oxide cluster anions toward n-butane was studied by using a high-resolution time-of-flight mass spectrometer coupled with a fast flow reactor. Hydrogen atom abstraction (HAA) from n-butane by (Sc2O3)(N)O(-) (N=1-18) clusters was observed. The reactivity of (Sc2O3)(N)O(-) (N=1-18) clusters is significantly sizedependent and the highest reactivity was observed for N=4 (Sc8O13(-)) and 12 (Sc24O37(-)). Larger (Sc2O3)(N)O(-) clusters generally have higher reactivity than the smaller ones. Density functional theory calculations were performed to interpret the reactivity of (Sc2O3)(N)O(-) (N=1-5) clusters, which were found to contain the O(-·) radicals as the active sites. The local charge environment around the O(-·) radicals was demonstrated to control the experimentally observed size-dependent reactivity. This work is among the first to report HAA reactivity of cluster anions with dimensions up to nanosize toward alkane molecules. The anionic O(-·) containing scandium oxide clusters are found to be more reactive than the corresponding cationic ones in the C-H bond activation.

  3. Computational study on the mechanism and selectivity of C-H bond activation and dehydrogenative functionalization in the synthesis of rhazinilam.

    PubMed

    Ellis, Corey S; Ess, Daniel H

    2011-09-02

    The key platinum mediated C-H bond activation and functionalization steps in the synthesis of (-)-rhazinilam (Johnson, J. A.; Li, N.; Sames, D. J. Am. Chem. Soc. 2002, 124, 6900) were investigated using the M06 and B3LYP density functional approximation methods. This computational study reveals that ethyl group dehydrogenation begins with activation of a primary C-H bond in preference to a secondary C-H bond in an insertion/methane elimination pathway. The C-H activation step is found to be reversible while the methane elimination (reductive elimination) transition state controls rate and diastereoselectivity. The chiral oxazolinyl ligand induces ethyl group selectivity through stabilizing weak interactions between its phenyl group (or cyclohexyl group) and the carboxylate group. After C-H activation and methane elimination steps, Pt-C bond functionalization occurs through β-hydride elimination to give the alkene platinum hydride complex.

  4. Uranium azide photolysis results in C-H bond activation and provides evidence for a terminal uranium nitride

    NASA Astrophysics Data System (ADS)

    Thomson, Robert K.; Cantat, Thibault; Scott, Brian L.; Morris, David E.; Batista, Enrique R.; Kiplinger, Jaqueline L.

    2010-09-01

    Uranium nitride [U≡N]x is an alternative nuclear fuel that has great potential in the expanding future of nuclear power; however, very little is known about the U≡N functionality. We show, for the first time, that a terminal uranium nitride complex can be generated by photolysis of an azide (U-N=N=N) precursor. The transient U≡N fragment is reactive and undergoes insertion into a ligand C-H bond to generate new N-H and N-C bonds. The mechanism of this unprecedented reaction has been evaluated through computational and spectroscopic studies, which reveal that the photochemical azide activation pathway can be shut down through coordination of the terminal azide ligand to the Lewis acid B(C6F5)3. These studies demonstrate that photochemistry can be a powerful tool for inducing redox transformations for organometallic actinide complexes, and that the terminal uranium nitride fragment is reactive, cleaving strong C-H bonds.

  5. Understanding trends in C-H bond activation in heterogeneous catalysis.

    PubMed

    Latimer, Allegra A; Kulkarni, Ambarish R; Aljama, Hassan; Montoya, Joseph H; Yoo, Jong Suk; Tsai, Charlie; Abild-Pedersen, Frank; Studt, Felix; Nørskov, Jens K

    2017-02-01

    While the search for catalysts capable of directly converting methane to higher value commodity chemicals and liquid fuels has been active for over a century, a viable industrial process for selective methane activation has yet to be developed. Electronic structure calculations are playing an increasingly relevant role in this search, but large-scale materials screening efforts are hindered by computationally expensive transition state barrier calculations. The purpose of the present letter is twofold. First, we show that, for the wide range of catalysts that proceed via a radical intermediate, a unifying framework for predicting C-H activation barriers using a single universal descriptor can be established. Second, we combine this scaling approach with a thermodynamic analysis of active site formation to provide a map of methane activation rates. Our model successfully rationalizes the available empirical data and lays the foundation for future catalyst design strategies that transcend different catalyst classes.

  6. Understanding trends in C-H bond activation in heterogeneous catalysis

    NASA Astrophysics Data System (ADS)

    Latimer, Allegra A.; Kulkarni, Ambarish R.; Aljama, Hassan; Montoya, Joseph H.; Yoo, Jong Suk; Tsai, Charlie; Abild-Pedersen, Frank; Studt, Felix; Nørskov, Jens K.

    2016-10-01

    While the search for catalysts capable of directly converting methane to higher value commodity chemicals and liquid fuels has been active for over a century, a viable industrial process for selective methane activation has yet to be developed. Electronic structure calculations are playing an increasingly relevant role in this search, but large-scale materials screening efforts are hindered by computationally expensive transition state barrier calculations. The purpose of the present letter is twofold. First, we show that, for the wide range of catalysts that proceed via a radical intermediate, a unifying framework for predicting C-H activation barriers using a single universal descriptor can be established. Second, we combine this scaling approach with a thermodynamic analysis of active site formation to provide a map of methane activation rates. Our model successfully rationalizes the available empirical data and lays the foundation for future catalyst design strategies that transcend different catalyst classes.

  7. Matching plasmon resonances to the C=C and C-H bonds in estradiol

    NASA Astrophysics Data System (ADS)

    Mbomson, Ifeoma G.; McMeekin, Scott; De La Rue, Richard; Johnson, Nigel P.

    2015-03-01

    We tune nanoantennas to resonate within mid-infrared wavelengths to match the vibrational resonances of C=C and C-H of the hormone estradiol. Modelling and fabrication of the nanoantennas produce plasmon resonances between 2 μm to 7 μm. The hormone estradiol was dissolved in ethanol and evaporated, leaving thickness of a few hundreds of nanometres on top of gold asymmetric split H-like shaped on a fused silica substrate. The reflectance was measured and a red-shift is recorded from the resonators plasmonic peaks. Fourier transform infrared spectroscopy is use to observe enhanced spectra of the stretching modes for the analyte which belongs to alkenyl biochemical group.

  8. Design and development of POCN-pincer palladium catalysts for C-H bond arylation of azoles with aryl iodides.

    PubMed

    Khake, Shrikant M; Soni, Vineeta; Gonnade, Rajesh G; Punji, Benudhar

    2014-11-14

    Well-defined and efficient POCN-ligated palladium complexes have been developed for the direct C-H bond arylation of azoles with aryl iodides. The phosphinite-amine pincer ligands 1-(R2PO)-C6H4-3-(CH2N(i)Pr2) [(R2)POCN(iPr2)-H; R = (i)Pr (), R = (t)Bu ()] and corresponding palladium complexes {2-(R2PO)-C6H3-6-(CH2N(i)Pr2)}PdCl [((R2)POCN(iPr2))PdCl; R = (i)Pr (), R = (t)Bu ()] were synthesized in good yields. Treatment of palladium complex with KI and AgOAc afforded the complexes ((iPr2)POCN(iPr2))PdI () and ((iPr2)POCN(iPr2))Pd(OAc) (), respectively. Similarly, the reaction of with benzothiazolyl-lithium produces the ((iPr2)POCN(iPr2))Pd(benzothiazolyl) () complex in a quantitative yield. The pincer palladium complex efficiently catalyzes the C-H bond arylation of benzothiazole, substituted-benzoxazoles and 5-aryl oxazoles with diverse aryl iodides in the presence of CuI as a co-catalyst under mild reaction conditions. This represents the first example of a pincer palladium complex being applied for the direct C-H bond arylation of any heterocycle with low catalyst loading. A preliminary mechanistic investigation reveals that palladium nanoparticles are presumably not the catalytically active form of and supports the direct involvement of the catalyst , with complex being a probable key intermediate in the catalytic reaction.

  9. Rh-Catalyzed, Regioselective, C-H Bond Functionalization: Access to Quinoline-Branched Amines and Dimers.

    PubMed

    Reddy, M Damoder; Fronczek, Frank R; Watkins, E Blake

    2016-11-04

    Rh-catalyzed, chelation-induced, C-5 regioselective C-H functionalization of 8-amidoquinolines with a range of N-Boc aminals is reported for the first time. The addition of in situ generated imines to C(sp(2))-H bonds afforded branched amines in good to excellent yields. Moreover, this transformation features good functional group compatibility, broad substrate scope, and mild reaction conditions and is suitable for gram-scale synthesis. In addition, an unprecedented, chelation-induced, site-selective, remote dimerization of quinolines led to the formation of dimer frameworks in moderate yields under Rh-catalyzed conditions.

  10. Synthesis of Active Hexafluoroisopropyl Benzoates through a Hydrogen-Bond-Enabled Palladium(II)-Catalyzed C-H Alkoxycarbonylation Reaction.

    PubMed

    Wang, Yang; Gevorgyan, Vladimir

    2017-03-13

    A Pd(II) -catalyzed ortho C-H alkoxycarbonylation reaction of aryl silanes toward active hexafluoroisopropyl (HFIP) benzoate esters has been developed. This efficient reaction features high selectivity and good functional-group tolerance. Notably, given the general nature of the silyl-tethered directing group, this method delivers products bearing two independently modifiable sites. NMR studies reveal the presence of hydrogen bonding between HFIP and a pyrimidine nitrogen atom of the directing group, and it is thought to be crucial for the success of this alkoxycarbonylation reaction.

  11. Mechanochemical Rhodium(III)-Catalyzed C-H Bond Functionalization of Acetanilides under Solventless Conditions in a Ball Mill.

    PubMed

    Hermann, Gary N; Becker, Peter; Bolm, Carsten

    2015-06-15

    In a proof-of-principle study, a planetary ball mill was applied to rhodium(III)-catalyzed C-H bond functionalization. Under solventless conditions and in the presence of a minute amount of Cu(OAc)2, the mechanochemical activation led to the formation of an active rhodium species, thus enabling an oxidative Heck-type cross-coupling reaction with dioxygen as the terminal oxidant. The absence of an organic solvent, the avoidance of a high reaction temperature, the possibility of minimizing the amount of the metallic mediator, and the simplicity of the protocol result in a powerful and environmentally benign alternative to the common solution-based standard protocol.

  12. Lactamization of sp(2) C-H Bonds with CO2 : Transition-Metal-Free and Redox-Neutral.

    PubMed

    Zhang, Zhen; Liao, Li-Li; Yan, Si-Shun; Wang, Lei; He, Yun-Qi; Ye, Jian-Heng; Li, Jing; Zhi, Yong-Gang; Yu, Da-Gang

    2016-06-13

    The first direct use of carbon dioxide in the lactamization of alkenyl and heteroaryl C-H bonds to synthesize important 2-quinolinones and polyheterocycles in moderate to excellent yields is reported. Carbon dioxide, a nontoxic, inexpensive, and readily available greenhouse gas, acts as an ideal carbonyl source. Importantly, this transition-metal-free and redox-neutral process is eco-friendly and desirable for the pharmaceutical industry. Moreover, these reactions feature a broad substrate scope, good functional group tolerance, facile scalability, and easy product derivatization.

  13. Towards ideal synthesis: alkenylation of aryl C-H bonds by a Fujiwara-Moritani reaction.

    PubMed

    Zhou, Lihong; Lu, Wenjun

    2014-01-13

    An overview of recent progress in the Fujiwara-Moritani reaction, which is the palladium-catalyzed oxidative coupling of arenes with olefins to afford alkenyl arenes, is described. It is emphasized that regioselectivity on aryl ortho- or meta-CH activation could be controlled very well in the presence of Pd, Rh, or Ru catalysts with the assistance of various chelation groups on aromatic rings in this coupling reaction. Catalytic alkenylation of aryl CH bonds from simple arenes is also discussed, especially from electron-deficient arenes. These advanced protocols would not only make the Fujiwara-Moritani reaction more useful and applicable in organic synthesis but also light the way for the further development of the functionalization of normal CH bonds.

  14. Preferential activation of primary C-H bonds in the reactions of small alkanes with the diatomic MgO(+*) cation.

    PubMed

    Schröder, Detlef; Roithová, Jana; Alikhani, Esmail; Kwapien, Karolina; Sauer, Joachim

    2010-04-06

    The C-H bond activation of small alkanes by the gaseous MgO(+*) cation is probed by mass spectrometric means. In addition to H-atom abstraction from methane, the MgO(+*) cation reacts with ethane, propane, n- and iso-butane through several pathways, which can all be assigned to the occurrence of initial C-H bond activations. Specifically, the formal C-C bond cleavages observed are assigned to C-H bond activation as the first step, followed by cleavage of a beta-C-C bond concomitant with release of the corresponding alkyl radical. Kinetic modeling of the observed product distributions reveals a high preference of MgO(+*) for the attack of primary C-H bonds. This feature represents a notable distinction of the main-group metal oxide MgO(+*) from various transition-metal oxide cations, which show a clear preference for the attack of secondary C-H bonds. The results of complementary theoretical calculations indicate that the C-H bond activation of larger alkanes by the MgO(+*) cation is subject to pronounced kinetic control.

  15. Polymer- and silica-supported iron BPMEN-inspired catalysts for C-H bond functionalization reactions.

    PubMed

    Feng, Yan; Moschetta, Eric G; Jones, Christopher W

    2014-11-01

    Direct catalytic C-H bond functionalization is a key challenge in synthetic chemistry, with many popular C-H activation methodologies involving precious-metal catalysts. In recent years, iron catalysts have emerged as a possible alternative to the more common precious-metal catalysts, owing to its high abundance, low cost, and low toxicity. However, iron catalysts are plagued by two key factors: the ligand cost and the low turnover numbers (TONs) typically achieved. In this work, two approaches are presented to functionalize the popular N(1),N(2)-dimethyl-N(1),N(2)-bis(pyridin-2-ylmethyl)ethane-1,2-diamine (BPMEN) ligand, so that it can be supported on porous silica or polymer resin supports. Four new catalysts are prepared and evaluated in an array of catalytic C-H functionalization reactions by using cyclohexane, cyclohexene, cyclooctane, adamantane, benzyl alcohol, and cumene with aqueous hydrogen peroxide. Catalyst recovery and recycling is demonstrated by using supported catalysts, which allows for a modest increase in the TON achieved with these catalysts.

  16. Catalytic oxygenation of sp3 "C-H" bonds with Ir(III) complexes of chelating triazoles and mesoionic carbenes.

    PubMed

    Hohloch, Stephan; Kaiser, Selina; Duecker, Fenja Leena; Bolje, Aljoša; Maity, Ramananda; Košmrlj, Janez; Sarkar, Biprajit

    2015-01-14

    Cp*-Ir(III) complexes with additional chelating ligands are known active pre-catalysts for the oxygenation of C-H bonds. We present here eight examples of such complexes where the denticity of the chelating ligands has been varied from the well-known 2,2'-bpy through pyridyl-triazole, bi-triazole to ligands containing pyridyl-triazolylidene, triazolyl-triazolylidene and bi-triazolylidenes. Additionally, we also compare the catalytic results to complexes containing chelating cyclometallated ligands with additional triazole or triazolylidene donors. Single crystal X-ray structural data are presented for all the new complexes that contain one or more triazolylidene donors of the mesoionic carbene type. We present the first example of a metal complex containing a chelating triazole-triazolylidene ligand. The results of the catalytic screening show that complexes containing unsymmetrical donors of the pyridyl-triazole or pyridyl-triazolylidene types are the most potent pre-catalysts for the C-H oxygenation of cyclooctane in the presence of either m-CPBA or NaIO4 as a sacrificial oxidant. These pre-catalysts can also be used to oxygenate C-H bonds in other substrates such as fluorene and ethyl benzene. The most potent pre-catalysts presented here work with a lower catalyst loading and under milder conditions while delivering better product yields in comparison with related literature known Ir(III) pre-catalysts. These results thus point to the potential of ligands with unsymmetrical donors obtained through the click reaction in oxidation catalysis.

  17. Highly Active Gold(I)-Silver(I) Oxo Cluster Activating sp³ C-H Bonds of Methyl Ketones under Mild Conditions.

    PubMed

    Pei, Xiao-Li; Yang, Yang; Lei, Zhen; Chang, Shan-Shan; Guan, Zong-Jie; Wan, Xian-Kai; Wen, Ting-Bin; Wang, Quan-Ming

    2015-04-29

    The activation of C(sp(3))-H bonds is challenging, due to their high bond dissociation energy, low proton acidity, and highly nonpolar character. Herein we report a unique gold(I)-silver(I) oxo cluster protected by hemilabile phosphine ligands [OAu3Ag3(PPhpy2)3](BF4)4 (1), which can activate C(sp(3))-H bonds under mild conditions for a broad scope of methyl ketones (RCOCH3, R = methyl, phenyl, 2-methylphenyl, 2-aminophenyl, 2-hydroxylphenyl, 2-pyridyl, 2-thiazolyl, tert-butyl, ethyl, isopropyl). Activation happens via triple deprotonation of the methyl group, leading to formation of heterometallic Au(I)-Ag(I) clusters with formula RCOCAu4Ag4(PPhpy2)4(BF4)5 (PPhpy2 = bis(2-pyridyl)phenylphosphine). Cluster 1 can be generated in situ via the reaction of [OAu3Ag(PPhpy2)3](BF4)2 with 2 equiv of AgBF4. The oxo ion and the metal centers are found to be essential in the cleavage of sp(3) C-H bonds of methyl ketones. Interestingly, cluster 1 selectively activates the C-H bonds in -CH3 rather than the N-H bonds in -NH2 or the O-H bond in -OH which is traditionally thought to be more reactive than C-H bonds. Control experiments with butanone, 3-methylbutanone, and cyclopentanone as substrates show that the auration of the C-H bond of the terminal methyl group is preferred over secondary or tertiary sp(3) C-H bonds; in other words, the C-H bond activation is influenced by steric effect. This work highlights the powerful reactivity of metal clusters toward C-H activation and sheds new light on gold(I)-mediated catalysis.

  18. A Highly Reactive Mononuclear Non-Heme Manganese(IV)-Oxo Complex That Can Activate the Strong C-H Bonds of Alkanes

    SciTech Connect

    Wu, Xiujuan; Seo, Mi Sook; Davis, Katherine M; Lee, Yong-Min; Chen, Junying; Cho, Kyung-Bin; Pushkar, Yulia N; Nam, Wonwoo

    2012-03-15

    A mononuclear non-heme manganese(IV)-oxo complex has been synthesized and characterized using various spectroscopic methods. The Mn(IV)-oxo complex shows high reactivity in oxidation reactions, such as C-H bond activation, oxidations of olefins, alcohols, sulfides, and aromatic compounds, and N-dealkylation. In C-H bond activation, the Mn(IV)-oxo complex can activate C-H bonds as strong as those in cyclohexane. It is proposed that C-H bond activation by the non-heme Mn(IV)-oxo complex does not occur via an oxygen-rebound mechanism. The electrophilic character of the non-heme Mn(IV)-oxo complex is demonstrated by a large negative ρ value of ~4.4 in the oxidation of para-substituted thioanisoles.

  19. The Stereoselective Formation of Bicyclic Enamines with Bridgehead Unsaturation via Tandem C-H Bond Activation/Alkenylation/Electrocyclization

    SciTech Connect

    Ellman, Jonathan A.; Yotphan, Sirilata; Bergman, Robert

    2007-12-10

    Rhodium-catalyzed intermolecular C-H activation of {alpha}, {beta}-unsaturated imines in the presence of alkynes leads to a tandem process in which coupling to the alkyne occurs at the {beta}-C-H bond of the imine, followed by electrocyclization of the resulting azatriene intermediates to give dihydropyridines (eq 1). Consideration of the intramolecular version of this overall transformation (Scheme 1) raises interesting regiochemical issues. For example in a compound such as 1, where the nitrogen and alkyne are connected by a 4-carbon tether, the presumed first-formed hydrido(vinyl)rhodium function can add to the triple bond in a 1,2-fashion, producing complex 2 with a new endocyclic double bond. Alternatively, addition might occur in a 2,1-fashion, leading to product 4 with an exocyclic double bond. We now wish to report that this intramolecular cyclization occurs smoothly at 100 C, and the exocyclic double bond route is exclusively followed. Remarkably, products such as 4 do not resist further cyclization. Even though both the transition state for this process and the resulting product are presumably strained, the overall transformation leads to good yields of unusual bridgehead doubly-bonded enamines such as 5. The unique chemistry of conjugated enamine 5 is consistent with the increased strain of this molecule as well as with inhibited conjugation between the nitrogen lone pair and the adjacent double bond (vida infra). We began our investigation into the C-H activation/cyclization of alkyne-tethered imine 1 by extensive screening of transition metal catalysts for this process. Rhodium-based catalysts were found to be the most efficient (Table 1), leading exclusively to the bridgehead dienamine; none of the catalysts that were employed in the screening led to quinolizidine 3 or to the product of intramolecular Diels-Alder reaction. The optimized reaction conditions employ the electron-rich monophosphine ligand (p-NMe{sub 2})PhPEt{sub 2} in 1:1 ratio relative

  20. Rh(III)-catalyzed addition of alkenyl C-H bond to isocyanates and intramolecular cyclization: direct synthesis 5-ylidenepyrrol-2(5H)-ones.

    PubMed

    Hou, Wei; Zhou, Bing; Yang, Yaxi; Feng, Huijin; Li, Yuanchao

    2013-04-19

    The rhodium-catalyzed addition of an alkenyl C-H bond to isocyanates via sp(2) C-H bond activation followed by an intramolecular cyclization is described. This atom-economic and catalytic reaction affords a simple and straightforward access to biologically relevant 5-ylidene pyrrol-2(5H)-ones and can be carried out under mild and neutral conditions in the absence of any additives and environmentally hazardous waste production.

  1. Tuning the reactivity of Fe(V)(O) toward C-H bonds at room temperature: effect of water.

    PubMed

    Singh, Kundan K; Tiwari, Mrityunjay k; Ghosh, Munmun; Panda, Chakadola; Weitz, Andrew; Hendrich, Michael P; Dhar, Basab B; Vanka, Kumar; Sen Gupta, Sayam

    2015-02-16

    The presence of an Fe(V)(O) species has been postulated as the active intermediate for the oxidation of both C-H and C═C bonds in the Rieske dioxygenase family of enzymes. Understanding the reactivity of these high valent iron-oxo intermediates, especially in an aqueous medium, would provide a better understanding of these enzymatic reaction mechanisms. The formation of an Fe(V)(O) complex at room temperature in an aqueous CH3CN mixture that contains up to 90% water using NaOCl as the oxidant is reported here. The stability of Fe(V)(O) decreases with increasing water concentration. We show that the reactivity of Fe(V)(O) toward the oxidation of C-H bonds, such as those in toluene, can be tuned by varying the amount of water in the H2O/CH3CN mixture. Rate acceleration of up to 60 times is observed for the oxidation of toluene upon increasing the water concentration. The role of water in accelerating the rate of the reaction has been studied using kinetic measurements, isotope labeling experiments, and density functional theory (DFT) calculations. A kinetic isotope effect of ∼13 was observed for the oxidation of toluene and d8-toluene showing that C-H abstraction was involved in the rate-determining step. Activation parameters determined for toluene oxidation in H2O/CH3CN mixtures on the basis of Eyring plots for the rate constants show a gain in enthalpy with a concomitant loss in entropy. This points to the formation of a more-ordered transition state involving water molecules. To further understand the role of water, we performed a careful DFT study, concentrating mostly on the rate-determining hydrogen abstraction step. The DFT-optimized structure of the starting Fe(V)(O) and the transition state indicates that the rate enhancement is due to the transition state's favored stabilization over the reactant due to enhanced hydrogen bonding with water.

  2. Graphene-hemin hybrid material as effective catalyst for selective oxidation of primary C-H bond in toluene

    NASA Astrophysics Data System (ADS)

    Li, Yongjia; Huang, Xiaoqing; Li, Yujing; Xu, Yuxi; Wang, Yang; Zhu, Enbo; Duan, Xiangfeng; Huang, Yu

    2013-05-01

    An effective hemin catalyst on graphene support for selective oxidation of primary C-H bond in toluene is reported with an over 50% conversion rate achieved at mild conditions. Significantly this hybrid material shows catalytic efficiency in toluene oxidation with selectivity towards benzoic acid. The role of graphene support is discussed here as providing large contact area between the catalyst and the substrate, maintaining hemin in catalytically active monomer form, attracting electron to promote site isolation, as well as protecting hemin from oxidative degradation during the reaction. Moreover, graphene is suggested to largely alter the final product selectivity, due to the different π-π interaction strength between the graphene support and the substrate/oxidized products. With longer reaction time, overall conversion rate tends to maintain relatively unchanged while toluene undergoes a series of oxidation to convert mostly to benzoic acid.

  3. Oxygen activation and intramolecular C-H bond activation by an amidate-bridged diiron(II) complex.

    PubMed

    Jones, Matthew B; Hardcastle, Kenneth I; Hagen, Karl S; MacBeth, Cora E

    2011-07-18

    A diiron(II) complex containing two μ-1,3-(κN:κO)-amidate linkages has been synthesized using the 2,2',2''-tris(isobutyrylamido)triphenylamine (H(3)L(iPr)) ligand. The resulting diiron complex, 1, reacts with dioxygen (or iodosylbenzene) to effect intramolecular C-H bond activation at the methine position of the ligand isopropyl group. The ligand-activated product, 2, has been isolated and characterized by a variety of methods including X-ray crystallography. Electrospray ionization mass spectroscopy of 2 prepared from(18)O(2) was used to confirm that the oxygen atom incorporated into the ligand framework is derived from molecular oxygen.

  4. Graphene-hemin hybrid material as effective catalyst for selective oxidation of primary C-H bond in toluene

    PubMed Central

    Li, Yongjia; Huang, Xiaoqing; Li, Yujing; Xu, Yuxi; Wang, Yang; Zhu, Enbo; Duan, Xiangfeng; Huang, Yu

    2013-01-01

    An effective hemin catalyst on graphene support for selective oxidation of primary C-H bond in toluene is reported with an over 50% conversion rate achieved at mild conditions. Significantly this hybrid material shows catalytic efficiency in toluene oxidation with selectivity towards benzoic acid. The role of graphene support is discussed here as providing large contact area between the catalyst and the substrate, maintaining hemin in catalytically active monomer form, attracting electron to promote site isolation, as well as protecting hemin from oxidative degradation during the reaction. Moreover, graphene is suggested to largely alter the final product selectivity, due to the different π-π interaction strength between the graphene support and the substrate/oxidized products. With longer reaction time, overall conversion rate tends to maintain relatively unchanged while toluene undergoes a series of oxidation to convert mostly to benzoic acid.

  5. Use of chemical auxiliaries to control p450 enzymes for predictable oxidations at unactivated C-h bonds of substrates.

    PubMed

    Auclair, Karine; Polic, Vanja

    2015-01-01

    Cytochrome P450 enzymes (P450s) have the ability to oxidize unactivated C-H bonds of substrates with remarkable regio- and stereoselectivity. Comparable selectivity for chemical oxidizing agents is typically difficult to achieve. Hence, there is an interest in exploiting P450s as potential biocatalysts. Despite their impressive attributes, the current use of P450s as biocatalysts is limited. While bacterial P450 enzymes typically show higher activity, they tend to be highly selective for one or a few substrates. On the other hand, mammalian P450s, especially the drug-metabolizing enzymes, display astonishing substrate promiscuity. However, product prediction continues to be challenging. This review discusses the use of small molecules for controlling P450 substrate specificity and product selectivity. The focus will be on two approaches in the area: (1) the use of decoy molecules, and (2) the application of substrate engineering to control oxidation by the enzyme.

  6. Rh(III)/Cu(II)-cocatalyzed synthesis of 1H-indazoles through C-H amidation and N-N bond formation.

    PubMed

    Yu, Da-Gang; Suri, Mamta; Glorius, Frank

    2013-06-19

    Substituted 1H-indazoles can be formed from readily available arylimidates and organo azides by Rh(III)-catalyzed C-H activation/C-N bond formation and Cu-catalyzed N-N bond formation. For the first time the N-H-imidates are demonstrated to be good directing groups in C-H activation, also capable of undergoing intramolecular N-N bond formation. The process is scalable and green, with O2 as the terminal oxidant and N2 and H2O formed as byproducts. Moreover, the products could be transformed to diverse important derivatives.

  7. Importance of the C-H...N weak hydrogen bonding on the coordination structures of manganese(III) porphyrin complexes.

    PubMed

    Ikezaki, Akira; Nakamura, Mikio

    2003-04-07

    The reactions between Mn(Por)Cl and Bu(4)N(+)CN(-) have been examined in various solvents by UV-vis and (1)H NMR spectroscopy, where Por's are dianions of meso-tetraisopropylporphyrin (T(i)PrP), meso-tetraphenylporphyrin (TPP), meso-tetrakis(p-(trifluoromethyl)phenyl)porphyrin (p-CF(3)-TPP), meso-tetramesitylporphyrin (TMP), and meso-tetrakis(2,6-dichlorophenyl)porphyrin (2,6-Cl(2)-TPP). Population ratios of the reaction products, Mn(Por)(CN) and [Mn(Por)(CN)(2)](-), have been sensitively affected by the solvents used. In the case of Mn(T(i)PrP)Cl, the following results are obtained: (i) The bis-adduct is preferentially formed in dipolar aprotic solvents such as DMSO, DMF, and acetonitrile. (ii) Both the mono- and bis-adduct are formed in the less polar solvents such as CH(2)Cl(2) and benzene though the complete conversion to the bis-adduct is achieved with much smaller amount of the ligand in benzene solution. (iii) Only the mono-adduct is formed in CHCl(3) solution even in the presence of a large excess of cyanide. (iv) Neither the mono- nor the bis-adduct is obtained in methanol solution. The results mentioned above have been explained in terms of the C-H.N and O-H.N hydrogen bonding in chloroform and methanol solutions, respectively, between the solvent molecules and cyanide ligand; hydrogen bonding weakens the coordination ability of cyanide and reduces the population of the bis-adduct. The importance of the C-H.N weak hydrogen bonding is most explicitly shown in the following fact: while the starting complex is completely converted to the bis-adduct in CH(2)Cl(2) solution, the conversion from the mono- to the bis-adduct is not observed even in the presence of 7000 equiv of Bu(4)N(+)CN(-) in CHCl(3) solution. The effective magnetic moments of the bis-adduct has been determined by the Evans method to be 3.2 micro(B) at 25 degrees C, suggesting that the complex adopts the usual (d(xy))(2)(d(xz), d(yz))(2) electron configuration despite the highly ruffled

  8. Heterolytic Activation of C-H Bonds on Cr(III)-O Surface Sites Is a Key Step in Catalytic Polymerization of Ethylene and Dehydrogenation of Propane.

    PubMed

    Conley, Matthew P; Delley, Murielle F; Núñez-Zarur, Francisco; Comas-Vives, Aleix; Copéret, Christophe

    2015-06-01

    We describe the reactivity of well-defined chromium silicates toward ethylene and propane. The initial motivation for this study was to obtain a molecular understanding of the Phillips polymerization catalyst. The Phillips catalyst contains reduced chromium sites on silica and catalyzes the polymerization of ethylene without activators or a preformed Cr-C bond. Cr(II) sites are commonly proposed active sites in this catalyst. We synthesized and characterized well-defined chromium(II) silicates and found that these materials, slightly contaminated with a minor amount of Cr(III) sites, have poor polymerization activity and few active sites. In contrast, chromium(III) silicates have 1 order of magnitude higher activity. The chromium(III) silicates initiate polymerization by the activation of a C-H bond of ethylene. Density functional theory analysis of this process showed that the C-H bond activation step is heterolytic and corresponds to a σ-bond metathesis type process. The same well-defined chromium(III) silicate catalyzes the dehydrogenation of propane at elevated temperatures with activities similar to those of a related industrial chromium-based catalyst. This reaction also involves a key heterolytic C-H bond activation step similar to that described for ethylene but with a significantly higher energy barrier. The higher energy barrier is consistent with the higher pKa of the C-H bond in propane compared to the C-H bond in ethylene. In both cases, the rate-determining step is the heterolytic C-H bond activation.

  9. Merging allylic C-H bond activation and C-C bond cleavage en route to the formation of a quaternary carbon stereocenter in acyclic systems.

    PubMed

    Vasseur, Alexandre; Marek, Ilan

    2017-01-01

    This protocol describes a diastereoselective approach for the synthesis of complex molecular architectures containing two stereogenic centers in a 1,4 relationship, one of which being an all-carbon quaternary stereogenic center. Such molecules could be intermediates in the synthesis of steroids, for example. Conceived as a single-flask synthetic sequence from ω-ene cyclopropanes, the protocol involves a concerted allylic C-H and C-C bond activation promoted by the Negishi reagent (Cp2Zr(η(2)-butene)). This zirconium-promenade-based procedure affords bifunctionalized products in high diastereomeric ratios after reaction of ω-ene cyclopropanes with the Negishi complex, followed by a thermal treatment and sequential addition of two different electrophiles. The method proves to be particularly efficient when carbonyl compounds are used as first electrophiles and hydrogen or elemental halides are used as second electrophiles. In addition, it offers the opportunity to create new C-C bonds via remote functionalization of a (sp(3))-C-H bond, a result of a copper or copper/palladium transmetalation step that extends the scope of the process to alkyl, acyl and aromatic halide compounds as second electrophiles. The typical described protocol allows the synthesis of the highly diastereo-enriched 2-((1R*,2S*)-2-butyl-2 propylcyclopropyl)ethanol and may provide a new entry to access complex molecular segments of natural products such as steroids or C30 botryococcene. It requires a simple reaction setup and takes ∼18.5 h to run the reaction and 2 h for isolation and purification.

  10. A steric tethering approach enables palladium-catalysed C-H activation of primary amino alcohols.

    PubMed

    Calleja, Jonas; Pla, Daniel; Gorman, Timothy W; Domingo, Victoriano; Haffemayer, Benjamin; Gaunt, Matthew J

    2015-12-01

    Aliphatic primary amines are a class of chemical feedstock essential to the synthesis of higher-order nitrogen-containing molecules, commonly found in biologically active compounds and pharmaceutical agents. New methods for the construction of complex amines remain a continuous challenge to synthetic chemists. Here, we outline a general palladium-catalysed strategy for the functionalization of aliphatic C-H bonds within amino alcohols, an important class of small molecule. Central to this strategy is the temporary conversion of catalytically incompatible primary amino alcohols into hindered secondary amines that are capable of undergoing a sterically promoted palladium-catalysed C-H activation. Furthermore, a hydrogen bond between amine and catalyst intensifies interactions around the palladium and orients the aliphatic amine substituents in an ideal geometry for C-H activation. This catalytic method directly transforms simple, easily accessible amines into highly substituted, functionally concentrated and structurally diverse products, and can streamline the synthesis of biologically important amine-containing molecules.

  11. A steric tethering approach enables palladium-catalysed C-H activation of primary amino alcohols

    NASA Astrophysics Data System (ADS)

    Calleja, Jonas; Pla, Daniel; Gorman, Timothy W.; Domingo, Victoriano; Haffemayer, Benjamin; Gaunt, Matthew J.

    2015-12-01

    Aliphatic primary amines are a class of chemical feedstock essential to the synthesis of higher-order nitrogen-containing molecules, commonly found in biologically active compounds and pharmaceutical agents. New methods for the construction of complex amines remain a continuous challenge to synthetic chemists. Here, we outline a general palladium-catalysed strategy for the functionalization of aliphatic C-H bonds within amino alcohols, an important class of small molecule. Central to this strategy is the temporary conversion of catalytically incompatible primary amino alcohols into hindered secondary amines that are capable of undergoing a sterically promoted palladium-catalysed C-H activation. Furthermore, a hydrogen bond between amine and catalyst intensifies interactions around the palladium and orients the aliphatic amine substituents in an ideal geometry for C-H activation. This catalytic method directly transforms simple, easily accessible amines into highly substituted, functionally concentrated and structurally diverse products, and can streamline the synthesis of biologically important amine-containing molecules.

  12. Visible-Light-Driven Oxidation of Primary C-H Bonds over CdS with Dual Co-catalysts Graphene and TiO2

    NASA Astrophysics Data System (ADS)

    Yang, Min-Quan; Zhang, Yanhui; Zhang, Nan; Tang, Zi-Rong; Xu, Yi-Jun

    2013-11-01

    Selective activation of primary C-H bonds for fine chemicals synthesis is of crucial importance for the sustainable exploitation of available feedstocks. Here, we report a viable strategy to synthesize ternary GR-CdS-TiO2 composites with an intimate spatial integration and sheet-like structure, which is afforded by assembling two co-catalysts, graphene and TiO2, into the semiconductor CdS matrix with specific morphology as a visible light harvester. The GR-CdS-TiO2 composites are able to serve as a highly selective visible-light-driven photocatalyst for oxidation of saturated primary C-H bonds using benign oxygen as oxidant under ambient conditions. This work demonstrates a wide, promising scope of adopting co-catalyst strategy to design more efficient semiconductor-based photocatalyst toward selective activation of C-H bonds using solar light and molecular oxygen.

  13. The Unexpected Reactivity of the Carbon Sites on the Nanostructured Carbon Catalysts towards the C-H Bond Activation from the Analysis of the Aromaticity.

    PubMed

    Sun, XiaoYing; Li, Bo; Su, DangSheng

    2016-06-06

    It is believed that the oxygen groups on the carbon catalysts are responsible for the observed reactivity for C-H bond activations. On the other hand, the oxygen groups also reduce the aromaticity of the host. The loss of the aromaticity increases reactivities of the carbon atoms and they become the active sites for the C-H bond activation. The newly identified C-C site exhibits the comparable catalytic performance in the oxidative dehydrogenation (ODH) of propane compared with the conventional oxygen groups like quinone and ketone. A series of calculations indicate that the aromaticity might be a useful descriptor for the carbon catalysts.

  14. Facile fabrication of magnetically recyclable metal-organic framework nanocomposites for highly efficient and selective catalytic oxidation of benzylic C-H bonds.

    PubMed

    Chen, Yifa; Huang, Xianqiang; Feng, Xiao; Li, Jikun; Huang, Yingyu; Zhao, Jingshu; Guo, Yuexin; Dong, Xinmei; Han, Ruodan; Qi, Pengfei; Han, Yuzhen; Li, Haiwei; Hu, Changwen; Wang, Bo

    2014-08-07

    HKUST-1@Fe3O4 chemically bonded core-shell nanoparticles have been prepared by growing HKUST-1 thin layers joined by carboxyl groups onto Fe3O4 nanospheres. These magnetic core-shell MOF nanostructures show exceptional catalytic activity for the oxidation of benzylic C-H bonds and they can be recovered by magnetic separation and reused without losing any activity.

  15. Identification of the Chemical Bonding Prompting Adhesion of a-C:H Thin Films on Ferrous Alloy Intermediated by a SiCx:H Buffer Layer.

    PubMed

    Cemin, F; Bim, L T; Leidens, L M; Morales, M; Baumvol, I J R; Alvarez, F; Figueroa, C A

    2015-07-29

    Amorphous carbon (a-C) and several related materials (DLCs) may have ultralow friction coefficients that can be used for saving-energy applications. However, poor chemical bonding of a-C/DLC films on metallic alloys is expected, due to the stability of carbon-carbon bonds. Silicon-based intermediate layers are employed to enhance the adherence of a-C:H films on ferrous alloys, although the role of such buffer layers is not yet fully understood in chemical terms. The chemical bonding of a-C:H thin films on ferrous alloy intermediated by a nanometric SiCx:H buffer layer was analyzed by X-ray photoelectron spectroscopy (XPS). The chemical profile was inspected by glow discharge optical emission spectroscopy (GDOES), and the chemical structure was evaluated by Raman and Fourier transform infrared spectroscopy techniques. The nature of adhesion is discussed by analyzing the chemical bonding at the interfaces of the a-C:H/SiCx:H/ferrous alloy sandwich structure. The adhesion phenomenon is ascribed to specifically chemical bonding character at the buffer layer. Whereas carbon-carbon (C-C) and carbon-silicon (C-Si) bonds are formed at the outermost interface, the innermost interface is constituted mainly by silicon-iron (Si-Fe) bonds. The oxygen presence degrades the adhesion up to totally delaminate the a-C:H thin films. The SiCx:H deposition temperature determines the type of chemical bonding and the amount of oxygen contained in the buffer layer.

  16. Activation of two C-H bonds of NHC N-methyl groups on triosmium and triruthenium carbonyl clusters.

    PubMed

    Cabeza, Javier A; Del Río, Ignacio; Miguel, Daniel; Pérez-Carreño, Enrique; Sánchez-Vega, M Gabriela

    2008-04-14

    The thermolysis of the NHC triosmium cluster [Os3(Me2Im)(CO)11] (1a; Me2Im = 1,3-dimethylimidazol-2-ylidene) in toluene at reflux temperature sequentially affords the edge-bridged cluster [Os3(micro-H)(micro-kappa2-MeImCH2)(CO)10] () and the face-capped derivative [Os3(micro-H)2(micro3-kappa2-MeImCH)(CO)9] (3a). These products result from the sequential oxidative addition of one (2a) and two (3a) N-methyl C-H bonds of the original NHC ligand. The related face-capped triruthenium cluster [Ru3(micro-H)2(micro3-kappa2-MeImCH)(CO)9] (3b) has been prepared by heating the NHC triruthenium cluster [Ru3(Me2Im)(CO)11] (1b) in THF at reflux temperature. In this case, the pentanuclear derivatives [Ru5(Me2Im)(micro4-kappa2-CO)(CO)14] (4b) and [Ru5(Me2Im)2(micro4-kappa2-CO)(CO)13] (5b) are minor reaction products, but a ruthenium cluster analogous to has not been obtained. The face-capped oxazole-derived NHC triruthenium cluster [Ru3(micro-H)2(micro3-kappa2-OxCH)(CO)9] (3c; MeOx = N-methyloxazol-2-ylidene) is the only isolated product of the thermolysis of [Ru3(MeOx)(CO)11] (1c) in THF at reflux temperature.

  17. Palladium-catalyzed meta-selective C-H bond activation with a nitrile-containing template: computational study on mechanism and origins of selectivity.

    PubMed

    Yang, Yun-Fang; Cheng, Gui-Juan; Liu, Peng; Leow, Dasheng; Sun, Tian-Yu; Chen, Ping; Zhang, Xinhao; Yu, Jin-Quan; Wu, Yun-Dong; Houk, K N

    2014-01-08

    Density functional theory investigations have elucidated the mechanism and origins of meta-regioselectivity of Pd(II)-catalyzed C-H olefinations of toluene derivatives that employ a nitrile-containing template. The reaction proceeds through four major steps: C-H activation, alkene insertion, β-hydride elimination, and reductive elimination. The C-H activation step, which proceeds via a concerted metalation-deprotonation (CMD) pathway, is found to be the rate- and regioselectivity-determining step. For the crucial C-H activation, four possible active catalytic species-monomeric Pd(OAc)2, dimeric Pd2(OAc)4, heterodimeric PdAg(OAc)3, and trimeric Pd3(OAc)6-have been investigated. The computations indicated that the C-H activation with the nitrile-containing template occurs via a Pd-Ag heterodimeric transition state. The nitrile directing group coordinates with Ag while the Pd is placed adjacent to the meta-C-H bond in the transition state, leading to the observed high meta-selectivity. The Pd2(OAc)4 dimeric mechanism also leads to the meta-C-H activation product but with higher activation energies than the Pd-Ag heterodimeric mechanism. The Pd monomeric and trimeric mechanisms require much higher activation free energies and are predicted to give ortho products. Structural and distortion energy analysis of the transition states revealed significant effects of distortions of the template on mechanism and regioselectivity, which provided hints for further developments of new templates.

  18. Hydroxy functionalization of non-activated C-H and C=C bonds: new perspectives for the synthesis of alcohols through biocatalytic processes.

    PubMed

    Gröger, Harald

    2014-03-17

    New perspectives through enzymes: Recent breakthroughs have been achieved in the selective hydroxy functionalization of non-activated C-H and C=C bonds. Enzymes turned out to be suitable catalysts for the ω-hydroxylation of (substituted) alkanes and regioselective hydroxylation of aromatic hydrocarbons with atmospheric oxygen as the oxidant, and the asymmetric addition of water to non-activated alkenes.

  19. The Effect of the Electronic Nature of Spectator Ligands in the C-H Bond Activation of Ethylene by Cr(III) Silicates: An ab initio Study.

    PubMed

    Núñez-Zarur, Francisco; Comas-Vives, Aleix

    2015-01-01

    The Phillips catalyst, chromium oxides supported on silica, is one of the most widely used catalysts for the industrial production of polyethylene (PE). We recently synthesized a well-defined mononuclear Cr(III) silicate as active site model of the Phillips catalyst. The catalytic activity of this well-defined catalyst was similar to the industrial Phillips catalyst. We proposed that C-H bond activation of ethylene over a Cr-O bond initiates polymerization in this Cr(III) catalyst. Our results also showed that the presence of a second ethylene olefin in the coordination sphere of Cr decreases the intrinsic energy barrier of the C-H activation of ethylene. In order to understand the effect of this additional ligand in the C-H activation of ethylene by the Cr(III) catalyst, we evaluated the energetics of this step with different spectator ligands (C2H4, C2F4, N2 and CO) coordinated to the Cr center. The Charge Decomposition Analysis (CDA) of the bonding interactions between the Cr(III) catalyst and the ligands showed that the intrinsic energy barrier for the C-H activation of ethylene decreases with the increasing electron-donor properties of the spectator ligand.

  20. C-H⋯O Hydrogen Bonded Complexes Between Chloroform and Cyclic Ketones: Correlation of Spectral Shifts and Complex Stability with Ring Size

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Anamika; Chakraborty, Tapas

    2010-06-01

    Stable C-H⋯O hydrogen bonded complexes between choloroform and three small cyclic ketones (cyclohexanone, cyclopentanone, cyclobutanone) are identified by use of FTIR spectroscopy in CCl4 solution at room temperature. The C-H stretching fundamental of chloroform (νC-H) in the said three complexes exhibits blue shifting with enhancement in νC-H transition intensity. However, the red shifts of the νC=O bands of the cyclic ketones in the complexes show no apparent correlation with the corresponding blue shifts of νC-H. The spectral analysis reveals that the stability of the complexes decreases with the ring size of the cyclic ketones. Electronic structure calculation at DFT/B3LYP/6-311++G(d,p) and MP2/6-31+G(d) levels predict that the complex binding energies are correlated with the dipole moment, proton affinity, and n(O)→σ∗(C-H) hyperconjugative charge transfer ability of the cyclic ketones.

  1. A Metallacycle Fragmentation Strategy for Vinyl Transfer from Enol Carboxylates to Secondary Alcohol C-H Bonds via Osmium- or Ruthenium-Catalyzed Transfer Hydrogenation.

    PubMed

    Park, Boyoung Y; Luong, Tom; Sato, Hiroki; Krische, Michael J

    2015-06-24

    A strategy for catalytic vinyl transfer from enol carboxylates to activated secondary alcohol C-H bonds is described. Using XPhos-modified ruthenium(0) or osmium(0) complexes, enol carboxylate-carbonyl oxidative coupling forms transient β-acyloxy-oxametallacycles, which eliminate carboxylate to deliver allylic ruthenium(II) or osmium(II) alkoxides. Reduction of the metal(II) salt via hydrogen transfer from the secondary alcohol reactant releases the product of carbinol C-H vinylation and regenerates ketone and zero-valent catalyst.

  2. Thermodynamics of Boroxine Formation from the Aliphatic Boronic Acid Monomers R–B(OH)2 (R = H, H3C, H2N, HO, and F): A Computational Investigation

    PubMed Central

    Bhat, Krishna L.; Markham, George D.; Larkin, Joseph D.; Bock, Charles W.

    2011-01-01

    Boroxines are the 6-membered cyclotrimeric dehydration products of organoboronic acids: 3 R– B(OH)2 → R3B3O3 + 3 H2O, and in recent years have emerged as a useful class of organoboron molecules with applications in organic synthesis both as reagents and catalysts, as structural components in boronic acid derived pharmaceutical agents, as anion acceptors and electrolyte additives for battery materials [AL Korich and PM Iovine, Dalton Trans. 39 (2010) 1423–1431]. Second-order Møller-Plesset perturbation theory, in conjunction with the Dunning-Woon correlation-consistent cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ basis sets, was used to investigate the structures and relative energies of the endo-exo, anti, and syn conformers of the aliphatic boronic acids R–B(OH)2 (R = H, H3C, H2N, HO, and F), as well as the thermodynamics of their boroxine formation; single-point calculations at the MP2/aug-cc-pVQZ, MP2/aug-cc-pV5Z, and CCSD(T)/aug-cc-pVTZ level using the MP2/aug-cc-pVTZ optimized geometries were also performed in selected cases. The endo-exo conformer was generally lowest in energy in vacuo, as well as in PCM and CPCM models of aqueous and carbon tetrachloride media. The values of ΔH2980 for boroxine formation via dehydration from the endo-exo conformers of these aliphatic boronic acids ranged from −2.9 for (H2N)3B3O3 to +12.2 kcal/mol for H3B3O3 at the MP2/aug-cc-pVTZ level in vacuo; for H3B3O3 the corresponding values in PCM:UFF implicit carbon tetrachloride and aqueous media were +11.2 and +9.8 kcal/mol, respectively. Based on our calculations, we recommend that ΔHf(298 K) for boroxine listed in the JANAF compilation needs to be revised from −290.0 kcal/mol to approximately −277.0 kcal/mol. PMID:21650154

  3. FTIR and molecular mechanics studies of H-bonds in aliphatic polyurethane and polyamide-66 model molecules.

    PubMed

    Wang, Guoqing; Zhang, Chunxia; Guo, Xiaohe; Ren, Zhiyong

    2008-02-01

    Model aliphatic polyurethane (APU) hard segment based on 1,6-hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO) were prepared. FTIR and molecular mechanics (MM) simulation were used to conduct the systematic studies on APU and polyamide-66 (PA-66) whose sole difference lies in the alkoxyl oxygen. It was found that the introduction of the alkoxyl not only increases the conformations in APU, makes it a possible H-bond acceptor, but also weakens the H-bond between NH and O=C in APU. There are two conformers stably existed in APU with lowest energy, leading to eight H-bond complexes based on NH as donor and (1) O=C as acceptor, and another two complexes based on (2) alkoxyl O and (3) urethane N as acceptors, whereas there is only one stable conformer in PA-66, leading to one H-bond complex. One predominant H-bond complex has been found in APU with probability of about 95%. The simulated results are consistent with the nuNH and nuC=O band shifting in FTIR.

  4. Synthesis of ferrocene derivatives with planar chirality via palladium-catalyzed enantioselective C-H bond activation.

    PubMed

    Pi, Chao; Cui, Xiuling; Liu, Xiuyan; Guo, Mengxing; Zhang, Hanyu; Wu, Yangjie

    2014-10-03

    The first catalytic and enantioselective C-H direct acylation of ferrocene derivatives has been developed. A series of 2-acyl-1-dimethylaminomethylferrocenes with planar chirality were provided under highly efficient and concise one-pot conditions with up to 85% yield and 98% ee. The products obtained could be easily converted to various chiral ligands via diverse transformations.

  5. Enantioselective synthesis of planar chiral ferrocenes via Pd(0)-catalyzed intramolecular direct C-H bond arylation.

    PubMed

    Gao, De-Wei; Yin, Qin; Gu, Qing; You, Shu-Li

    2014-04-02

    A highly efficient synthesis of planar chiral ferrocenes by enantioselective Pd(0)-catalyzed direct C-H arylation from readily available starting materials under mild reaction conditions was developed (up to 99% yield, 99% ee). The products can be easily transformed to the highly efficient planar ferrocene ligands, which have demonstrated high efficiency in Pd-catalyzed asymmetric allylic alkylation and amination reactions.

  6. Non-innocent additives in a palladium(II)-catalyzed C-H bond activation reaction: insights into multimetallic active catalysts.

    PubMed

    Anand, Megha; Sunoj, Raghavan B; Schaefer, Henry F

    2014-04-16

    The role of a widely employed additive (AgOAc) in a palladium acetate-catalyzed ortho-C-H bond activation reaction has been examined using the M06 density functional theory. A new hetero-bimetallic Pd-(μ-OAc)3-Ag is identified as the most likely active species. This finding could have far-reaching implications with respect to the notion of the active species in palladium catalysis in the presence of other metal salt additives.

  7. Metal-free sp3 C-H bond dual-(het)arylation: I2-promoted domino process to construct 2,2-bisindolyl-1-arylethanones.

    PubMed

    Zhu, Yan-ping; Liu, Mei-cai; Jia, Feng-cheng; Yuan, Jing-jing; Gao, Qing-he; Lian, Mi; Wu, An-xin

    2012-07-06

    A molecular I(2)-promoted sp(3) C-H bond dual-(het)arylation protocol was developed for the synthesis of 2,2-bisindolyl-1-arylethanones. Through a logical design, three mechanism-different reactions (iodination, Kornblum oxidation, and Friedel-Crafts reaction) were assembled in a single reactor. A variety of 2,2-bisindolyl-1-aryl ethanones were synthesized from simple and readily available aryl methyl ketones and indoles. In the reaction, metal, base, and ligand were all avoidable.

  8. Iodine-catalyzed [Formula: see text] C-H bond activation by selenium dioxide: synthesis of diindolylmethanes and di(3-indolyl)selanides.

    PubMed

    Naidu, P Seetham; Majumder, Swarup; Bhuyan, Pulak J

    2015-11-01

    An efficient reaction protocol was developed for the synthesis of several diindolylmethane derivatives via the [Formula: see text] C-H bond activation of aryl methyl ketones by [Formula: see text] and indoles in the presence of catalytic amounts of [Formula: see text] at 80 [Formula: see text] using dioxane as solvent. Unexpectedly, an interesting class of di(3-indolyl)selenide compounds was isolated when the reaction was carried out at room temperature.

  9. A Palladium-Catalyzed Method for the Synthesis of Carbazoles via Tandem C-H Functionalization and C-N Bond Formation

    PubMed Central

    Tsang, W. C. Peter; Munday, Rachel H.; Brasche, Gordon; Zheng, Nan; Buchwald, Stephen L.

    2009-01-01

    The development of a new method for the assembly of unsymmetrical carbazoles is reported. The strategy involves the selective intramolecular functionalization of an arene C-H bond and the formation of a new arene C-N bond. The substitution pattern of the carbazole product can be controlled by the design of the biaryl amide substrate, and the method is compatible with a variety of functional groups. The utility of the new protocol was demonstrated by the concise synthesis of three natural products from commercially available materials. PMID:18761437

  10. Promotional effects of chemisorbed oxygen and hydroxide in the activation of C-H and O-H bonds over transition metal surfaces

    NASA Astrophysics Data System (ADS)

    Hibbitts, David; Neurock, Matthew

    2016-08-01

    Electronegative coadsorbates such as atomic oxygen (O*) and hydroxide (OH*) can act as Brønsted bases when bound to Group 11 as well as particular Group 8-10 metal surfaces and aid in the activation of X-H bonds. First-principle density functional theory calculations were carried out to systematically explore the reactivity of the C-H bonds of methane and surface methyl intermediates as well as the O-H bond of methanol directly and with the assistance of coadsorbed O* and OH* intermediates over Group 11 (Cu, Ag, and Au) and Group 8-10 transition metal (Ru, Rh, Pd, Os, Ir, and Pt) surfaces. C-H as well as O-H bond activation over the metal proceeds via a classic oxidative addition type mechanism involving the insertion of the metal center into the C-H or O-H bond. O* and OH* assist C-H and O-H activation over particular Group 11 and Group 8-10 metal surfaces via a σ-bond metathesis type mechanism involving the oxidative addition of the C-H or O-H bond to the metal along with a reductive deprotonation of the acidic C-H and O-H bond over the M-O* or M-OH* site pair. The O*- and OH*-assisted C-H activation paths are energetically preferred over the direct metal catalyzed C-H scission for all Group 11 metals (Cu, Ag, and Au) with barriers that are 0.4-1.5 eV lower than those for the unassisted routes. The barriers for O*- and OH*-assisted C-H activation of CH4 on the Group 8-10 transition metals, however, are higher than those over the bare transition metal surfaces by as much as 1.4 eV. The C-H activation of adsorbed methyl species show very similar trends to those for CH4 despite the differences in structure between the weakly bound methane and the covalently adsorbed methyl intermediates. The activation of the O-H bond of methanol is significantly promoted by O* as well as OH* intermediates over both the Group 11 metals (Cu, Ag, and Au) as well as on all Group 8-10 metals studied (Ru, Rh, Pd, Os, Ir, and Pt). The O*- and OH*-assisted CH3O-H barriers are 0.6 to 2

  11. Direct Synthesis of Protoberberine Alkaloids by Rh-Catalyzed C-H Bond Activation as the Key Step.

    PubMed

    Jayakumar, Jayachandran; Cheng, Chien-Hong

    2016-01-26

    A one-pot reaction of substituted benzaldehydes with alkyne-amines by a Rh-catalyzed C-H activation and annulation to afford various natural and unnatural protoberberine alkaloids is reported. This reaction provides a convenient route for the generation of a compound library of protoberberine salts, which recently have attracted great attention because of their diverse biological activities. In addition, pyridinium salt derivatives can also be formed in good yields from α,β-unsaturated aldehydes and amino-alkynes. This reaction proceeds with excellent regioselectivity and good functional group compatibility under mild reaction conditions by using O2 as the oxidant.

  12. Cleavage of ether, ester, and tosylate C(sp3)-O bonds by an iridium complex, initiated by oxidative addition of C-H bonds. Experimental and computational studies.

    PubMed

    Kundu, Sabuj; Choi, Jongwook; Wang, David Y; Choliy, Yuriy; Emge, Thomas J; Krogh-Jespersen, Karsten; Goldman, Alan S

    2013-04-03

    A pincer-ligated iridium complex, (PCP)Ir (PCP = κ(3)-C6H3-2,6-[CH2P(t-Bu)2]2), is found to undergo oxidative addition of C(sp(3))-O bonds of methyl esters (CH3-O2CR'), methyl tosylate (CH3-OTs), and certain electron-poor methyl aryl ethers (CH3-OAr). DFT calculations and mechanistic studies indicate that the reactions proceed via oxidative addition of C-H bonds followed by oxygenate migration, rather than by direct C-O addition. Thus, methyl aryl ethers react via addition of the methoxy C-H bond, followed by α-aryloxide migration to give cis-(PCP)Ir(H)(CH2)(OAr), followed by iridium-to-methylidene hydride migration to give (PCP)Ir(CH3)(OAr). Methyl acetate undergoes C-H bond addition at the carbomethoxy group to give (PCP)Ir(H)[κ(2)-CH2OC(O)Me] which then affords (PCP-CH2)Ir(H)(κ(2)-O2CMe) (6-Me) in which the methoxy C-O bond has been cleaved, and the methylene derived from the methoxy group has migrated into the PCP Cipso-Ir bond. Thermolysis of 6-Me ultimately gives (PCP)Ir(CH3)(κ(2)-O2CR), the net product of methoxy group C-O oxidative addition. Reaction of (PCP)Ir with species of the type ROAr, RO2CMe or ROTs, where R possesses β-C-H bonds (e.g., R = ethyl or isopropyl), results in formation of (PCP)Ir(H)(OAr), (PCP)Ir(H)(O2CMe), or (PCP)Ir(H)(OTs), respectively, along with the corresponding olefin or (PCP)Ir(olefin) complex. Like the C-O bond oxidative additions, these reactions also proceed via initial activation of a C-H bond; in this case, C-H addition at the β-position is followed by β-migration of the aryloxide, carboxylate, or tosylate group. Calculations indicate that the β-migration of the carboxylate group proceeds via an unusual six-membered cyclic transition state in which the alkoxy C-O bond is cleaved with no direct participation by the iridium center.

  13. Directed Evolution of RebH for Catalyst-Controlled Halogenation of Indole C-H Bonds.

    PubMed

    Andorfer, Mary C; Park, Hyun June; Vergara-Coll, Jaylie; Lewis, Jared C

    2016-06-01

    RebH variants capable of chlorinating substituted indoles ortho-, meta-, and para- to the indole nitrogen were evolved by directly screening for altered selectivity on deuterium-substituted probe substrates using mass spectrometry. This systematic approach allowed for rapid accumulation of beneficial mutations using simple adaptive walks and should prove generally useful for altering and optimizing the selectivity of C-H functionalization catalysts. Analysis of the beneficial mutations showed that structure-guided selection of active site residues for targeted mutagenesis can be complicated either by activity/selectivity tradeoffs that reduce the possibility of detecting such mutations or by epistatic effects that actually eliminate the benefits of a mutation in certain contexts. As a corollary to this finding, the precise manner in which the beneficial mutations identified led to the observed changes in RebH selectivity is not clear. Docking simulations suggest that tryptamine binds to these variants as tryptophan does to native halogenases, but structural studies will be required to confirm these models and shed light on how particular mutations impact tryptamine binding. Similar directed evolution efforts on other enzymes or artificial metalloenzymes could enable a wide range of C-H functionalization reactions.

  14. Enthalpy of formation of the cyclohexadienyl radical and the C-H bond enthalpy of 1,4-cyclohexadiene: an experimental and computational re-evaluation.

    PubMed

    Gao, Yide; DeYonker, Nathan J; Garrett, E Chauncey; Wilson, Angela K; Cundari, Thomas R; Marshall, Paul

    2009-06-25

    A quantitative understanding of the thermochemistry of cyclohexadienyl radical and 1,4-cyclohexadiene is beneficial for diverse areas of chemistry. Given the interest in these two species, it is surprising that more detailed thermodynamic data concerning the homolytic C-H bond enthalpies of such entities have not been forthcoming. We thus undertook an experimental and computational evaluation of (a) the enthalpy of formation of cyclohexadienyl radical (C(6)H(7)), (b) the homolytic C-H bond enthalpy of 1,4-cyclohexadiene (C(6)H(8)), and (c) the enthalpy of the addition of a hydrogen atom to benzene. Using laser photolysis experiments coupled with highly accurate ab initio quantum mechanical techniques, a newly recommended enthalpy of formation for C(6)H(7) is determined to be 208.0 +/- 3.9 kJ mol(-1), leading to a homolytic bond dissociation enthalpy of 321.7 +/- 2.9 kJ mol(-1), almost 9 kJ mol(-1) higher than previously determined enthalpies that used less certain experimental values for the C(6)H(7) enthalpy of formation.

  15. A General Nickel-Catalyzed Method for C-H Bond Alkynylation of Heteroarenes Through Chelation Assistance.

    PubMed

    Khake, Shrikant M; Soni, Vineeta; Gonnade, Rajesh G; Punji, Benudhar

    2017-02-24

    A general nickel-catalyzed method for the alkynylation of heteroarenes through monodentate chelation assistance is described. Many heterocycles, including indoles, pyrroles, imidazoles, and pyrazole, efficiently coupled with (triisopropylsilyl)alkynyl bromide, and synthetically important functional groups, such as halides, ether, nitrile, and nitro, are tolerated. Synthetic applicability of this Ni-catalyzed method is demonstrated by the removal of the triisopropylsilyl group and further functionalization to triazolyl, benzofuranyl, and alkynyl arene derivatives. Preliminary mechanistic investigations of the alkynylation of indole suggest that the reaction proceeds through kinetically relevant C-H activation and follows a two-electron redox pathway. A catalytically relevant Ni species, namely, [(Phen)3 Ni]NiBr4 (PheN=1,10-phenanthroline), was isolated and structurally characterized.

  16. Nickel-catalyzed thiolation of unactivated aryl C-H bonds: efficient access to diverse aryl sulfides.

    PubMed

    Yan, Sheng-Yi; Liu, Yue-Jin; Liu, Bin; Liu, Yan-Hua; Shi, Bing-Feng

    2015-03-07

    A nickel-catalyzed thiolation of unactivated C(sp(2))-H bonds with disulfides employing the PIP directing group was described. This process uses a catalytic nickel catalyst and no metallic oxidants or cocatalysts are required. The reaction tolerates various important functional groups and heteroarenes, providing an efficient synthetic pathway to access diverse diaryl sulfides.

  17. An iron(III)-monoamidate complex catalyst for selective hydroxylation of alkane C-H bonds with hydrogen peroxide.

    PubMed

    Hitomi, Yutaka; Arakawa, Kengo; Funabiki, Takuzo; Kodera, Masahito

    2012-04-02

    Selective oxidation: the success of the title reaction is caused by the strong electron donation from the amidate moiety of the dpaq ligand to the iron center (dpaq=2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate). This process facilitates the O-O bond heterolysis of the intermediate Fe(III)OOH species to generate a selective oxidant without forming highly reactive hydroxyl radicals.

  18. Trimethylsilylmethyl complexes of the rare-earth metals with sterically hindered N-heterocyclic carbene ligands: adduct formation and C-H bond activation.

    PubMed

    Fegler, Waldemar; Spaniol, Thomas P; Okuda, Jun

    2010-08-07

    Tris(trimethylsilylmethyl) complexes of yttrium and lutetium [LnR(3)(THF)(2)] (R = CH(2)SiMe(3)) were treated with sterically bulky N-heterocyclic carbenes (NHC) 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes). IPr gave labile mono-adducts [LnR(3)(NHC)], isolated as thermally robust crystals and fully characterized by NMR spectroscopy and X-ray diffraction. IMes gave a similar lutetium mono-adduct [LuR(3)(IMes)] with the lutetium alkyl [LuR(3)(THF)(2)], whereas the yttrium alkyl [YR(3)(THF)(2)] resulted in the formation of an ortho-metalated product. This compound, isolated as a crystalline bis(THF) adduct, contains a strained six-membered chelate ring that has been formed by the C-H bond activation of one of the ortho-methyl groups of the mesityl group. In contrast [LuR(3)(IMes)] only slowly underwent a similar C-H bond activation.

  19. Cooperation and competition between halogen bonding and van der Waals forces in supramolecular engineering at the aliphatic hydrocarbon/graphite interface: position and number of bromine group effects.

    PubMed

    Zha, Bao; Dong, Meiqiu; Miao, Xinrui; Peng, Shan; Wu, Yican; Miao, Kai; Hu, Yi; Deng, Wenli

    2017-01-07

    Herein, the photophysical properties of two π-conjugated thienophenanthrene derivatives (6,9- and 5,10-DBTD) are reported. Their self-assembled monolayers in aliphatic hydrocarbon solvents under different concentrations were investigated by scanning tunneling microscopy on a graphite surface. The STM results revealed that the self-assembled structures of the two geometrical isomers exhibited absolutely different behaviors. At the aliphatic solvent/graphite interface, 6,9-DBTD produced almost a single stable coassembled linear structure, except for that with n-tridecane as the solvent. However, the self-assembly of 5,10-DBTD showed structural diversity, and it presented a gradient variety through increasing the chain length of the aliphatic solvents as well as the solution concentration. All ordered self-assembled adlayers critically depend on not only the interchain van der Waals (vdW) interactions, but also on multiple intermolecular interactions, including BrO[double bond, length as m-dash]C and BrS hetero-halogen bonds, homo-BrBr interactions, and HBr and HO hydrogen bonds. We proposed that the cooperation and competition of the intermolecular interactions involving a Br atom and interchain vdW forces induce this structural variety. Density functional theory calculations support to unravel the different elementary structural units based on halogen bonds and hydrogen bonds and were useful tools to dissect and explain the formation mechanism.

  20. Hard three-dimensional sp 2 carbon-bonded phase formed by ion beam irradiation of fullerene, a-C and polymeric a-C:H films

    NASA Astrophysics Data System (ADS)

    Baptista, D. L.; Foerster, C. E.; Lepienski, C. M.; Zawislak, F. C.

    2004-06-01

    The formation of new carbon amorphous phase through the ion irradiation of fullerene, a-C and polymeric a-C:H films is presented. The carbon films were subjected to N irradiation at 400 keV in the fluence range from 10 13 to 3 × 10 16 N cm -2. Modifications in the carbon structure, as function of the irradiation fluence, were investigated using the Rutherford backscattering spectrometry, nuclear reaction analysis, Fourier transform infrared, Raman spectroscopy, UV-VIS-NearIR spectrophotometry and nanoindentation techniques. After high fluence, the three carbon samples were transformed into very similar hard (≈14 GPa) and non-hydrogenated amorphous carbon layers with very low optical gaps (≈0.2 eV) and an unusual sp 2 rich-bonded atomic network. The mechanical properties of the irradiated films correlated with the bonding topologies of this new sp 2 carbon phase are analyzed in terms of the constraint-counting model. The results show that the unusual rigidity was achieved by the distortion of the sp 2 carbon bond angles, giving origin to a constrained three-dimensional sp 2 carbon bonded network.

  1. Thermochemistry of C7H16 to C10H22 alkane isomers: primary, secondary, and tertiary C-H bond dissociation energies and effects of branching.

    PubMed

    Hudzik, Jason M; Bozzelli, Joseph W; Simmie, John M

    2014-10-09

    Standard enthalpies of formation (ΔH°f 298) of methyl, ethyl, primary and secondary propyl, and n-butyl radicals are evaluated and used in work reactions to determine internal consistency. They are then used to calculate the enthalpy of formation for the tert-butyl radical. Other thermochemical properties including standard entropies (S°(T)), heat capacities (Cp(T)), and carbon-hydrogen bond dissociation energies (C-H BDEs) are reported for n-pentane, n-heptane, 2-methylhexane, 2,3-dimethylpentane, and several branched higher carbon number alkanes and their radicals. ΔH°f 298 and C-H BDEs are calculated using isodesmic work reactions at the B3LYP (6-31G(d,p) and 6-311G(2d,2p) basis sets), CBS-QB3, CBS-APNO, and G3MP2B3 levels of theory. Structures, moments of inertia, vibrational frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level for contributions to entropy and heat capacities. Enthalpy calculations for these hydrocarbon radical species are shown to have consistency with the CBS-QB3 and CBS-APNO methods using all work reactions. Our recommended ideal gas phase ΔH°f 298 values are from the average of all CBS-QB3, CBS-APNO, and for G3MP2B3, only where the reference and target radical are identical types, and are compared with literature values. Calculated values show agreement between the composite calculation methods and the different work reactions. Secondary and tertiary C-H bonds in the more highly branched alkanes are shown to have bond energies that are several kcal mol(-1) lower than the BDEs in corresponding smaller molecules often used as reference species. Entropies and heat capacities are calculated and compared to literature values (when available) when all internal rotors are considered.

  2. A Tale of Copper Coordination Frameworks: Controlled Single-Crystal-to-Single-Crystal Transformations and Their Catalytic C-H Bond Activation Properties.

    PubMed

    Chen, Yifa; Feng, Xiao; Huang, Xianqiang; Lin, Zhengguo; Pei, Xiaokun; Li, Siqing; Li, Jikun; Wang, Shan; Li, Rui; Wang, Bo

    2015-09-28

    Metal-organic frameworks (MOFs), as a class of microporous materials with well-defined channels and rich functionalities, hold great promise for various applications. Yet the formation and crystallization processes of various MOFs with distinct topology, connectivity, and properties remain largely unclear, and the control of such processes is rather challenging. Starting from a 0D Cu coordination polyhedron, MOP-1, we successfully unfolded it to give a new 1D-MOF by a single-crystal-to-single-crystal (SCSC) transformation process at room temperature as confirmed by SXRD. We also monitored the continuous transformation states by FTIR and PXRD. Cu MOFs with 2D and 3D networks were also obtained from this 1D-MOF by SCSC transformations. Furthermore, Cu MOFs with 0D, 1D, and 3D networks, MOP-1, 1D-MOF, and HKUST-1, show unique performances in the kinetics of the C-H bond catalytic oxidation reaction.

  3. The ansa effect in permethylmolybdenocene chemistry: A [Me{sub 2}Si] ansa bridge promotes intermolecular C-H and C-C bond activation

    SciTech Connect

    Churchill, D.; Shin, J.H.; Hascall, T.; Hahn, J.M.; Bridgewater, B.M.; Parkin, G.

    1999-06-21

    Access to the [Me{sub 2}Si] ansa-bridged permethylmolybdenocene system is provided by the synthesis of [Me{sub 2}Si(C{sub 5}Me{sub 4}){sub 2}]MoCl{sub 2} from the reaction of MoCl{sub 5} with a mixture of [Me{sub 2}Si(C{sub 5}Me{sub 4}){sub 2}]Li{sub 2} and NaBH{sub 4}, followed by treatment with CHCl{sub 3}. Comparison with the chemistry of the non-ansa Cp{sup *}{sub 2}MoX{sub 2} system indicates that incorporation of the [Me{sub 2}Si] ansa bridge promotes intermolecular C-H and C-C bond activation reactions.

  4. Ligand versus Complex: C-F and C-H Bond Activation of Polyfluoroaromatics at a Cyclic (Alkyl)(Amino)Carbene.

    PubMed

    Paul, Ursula S D; Radius, Udo

    2017-03-17

    C-F and C-H bond activation reactions of polyfluoroaromatics at the cyclic (alkyl)(amino)carbene (cAAC) cAAC(methyl) (1) are reported. Studies on the C-F bond activation using the cAAC-stabilized nickel(0) complex [Ni(cAAC(methyl) )2 ] (2) have shown that 2 does not react with fluorinated arenes. However, these investigations led to the observation of C-F bond cleavage of perfluorinated arenes by the carbene ligand cAAC(methyl) (1) itself. The reaction of 1 with C6 F6 , C6 F5 -C6 F5 , C6 F5 -CF3 , and C5 F5 N afforded the insertion products of cAAC into one of the C-F bonds of the substrate, that is, the C-F bond activation products (cAAC(methyl) )F(Ar(f) ) (Ar(f) =C6 F5 4 a, C6 F4 -C6 F5 4 b, C6 F4 -CF3 4 c, C5 F4 N 4 d). These products decompose readily upon heating to 80 °C within a few hours in solution with formation of ionic iminium salts [(cAAC(methyl) )(Ar(f) )][X] 6 a-d or neutral alkenyl perfluoroaryl imine compounds 7 a-d. The compounds (cAAC(methyl) )F(Ar(f) ) 4 a-d readily transfer fluoride, which has been exemplified by the fluoride transfer of all compounds using BF3 etherate as fluoride acceptor. Fluoride transfer has also been achieved starting from (cAAC(methyl) )F(C6 F4 -CF3 ) (4 c) or (cAAC(methyl) )F(C5 F4 N) (4 d) to other selected substrates such as trimethylchlorosilane, benzoyl chloride and tosyl chloride. Instead of C-F bond activation, insertion of the cAAC into the C-H bond was observed if 1 was treated with the partially fluorinated arenes C6 F5 H, 1,2,4,5-C6 F4 H2 , 1,3,5-C6 F3 H3 , and 1,3-C6 F2 H4 . The compounds (cAAC(methyl) )H(Ar(f) ) (Ar(f) =C6 F5 12 e, 2,3,5,6-C6 F4 H 12 f, 2,4,6-C6 F3 H2 12 g and 2,6-C6 F2 H3 12 h) have been isolated in good yields and have been characterized including X-ray analysis. Fluorobenzene C6 FH5 (pKa ≈37), the least C-H acidic fluoroarene used in this study, does not react. In order to investigate the scope and limitations of this type of cAAC C-H bond activation

  5. Unexpected intermediates and products in the C-F bond activation of tetrafluorobenzenes with a bis(triethylphosphine)nickel synthon: direct evidence of a rapid and reversible C-H bond activation by Ni(0).

    PubMed

    Johnson, Samuel A; Huff, Carla W; Mustafa, Ferheen; Saliba, Mark

    2008-12-24

    The reaction of (PEt(3))(2)Ni(eta(2)-C(14)H(10)), a source of the reactive Ni(PEt(3))(2) moiety, with 1,2,4,5-F(4)C(6)H(2) yields a mixture of three C-F bond activation products that include the unexpected products (PEt(3))(2)NiF-2,3,5,6-F(4)C(6)H and (PEt(3))(2)NiF-2,3,5-F(3)C(6)H(2). Monitoring the reaction mixture via (19)F and (1)H NMR also reveals the presence of the C-H bond activation product, (PEt(3))(2)NiH-2,3,5,6-F(4)C(6)H which is produced in a rapid equilibrium reaction. This observation provides insight into the steps necessary to modify nickel complexes for selective C-F bond activation in a variety of polyfluorinated aromatic substrates, but also expands the potential of simple nickel compounds for C-H bond activation and functionalization reactions.

  6. C-H bond activation of the methyl group of the supporting ligand in an osmium(III) complex upon reaction with H2O2: formation of an organometallic osmium(IV) complex.

    PubMed

    Sugimoto, Hideki; Ashikari, Kenji; Itoh, Shinobu

    2013-01-18

    Oxidation of the hydroxoosmium(III) complex resulted in C-H bond activation of the methyl group of the supporting ligand (N,N'-dimethyl-2,11-diaza[3.3](2,6)pyridinophane). The product was an osmium(IV) complex exhibiting a seven-coordinate structure with an additional Os-CH(2) bond.

  7. A kinetico-mechanistic study on the C-H bond activation of primary benzylamines; cooperative and solid-state cyclopalladation on dimeric complexes.

    PubMed

    Font, Helena; Font-Bardia, Mercè; Gómez, Kerman; González, Gabriel; Granell, Jaume; Macho, Israel; Martínez, Manuel

    2014-09-28

    The cyclometallation reactions of dinuclear μ-acetato complexes of the type [Pd(AcO)(μ-AcO)L]2 (L = 4-RC6H4CH2NH2, R = H, Cl, F, CF3), a process found to occur readily even in the solid state, have been studied from a kinetico-mechanistic perspective. Data indicate that the dinuclear acetato bridged derivatives are excellent starting materials to activate carbon-hydrogen bonds in a facile way. In all cases the established concerted ambiphilic proton abstraction by a coordinated acetato ligand has been proved. The metallation has also been found to occur in a cooperative manner, with the metallation of the first palladium unit of the dimeric complex being rate determining; no intermediate mono-metallated compounds are observed in any of the processes. The kinetically favoured bis-cyclopalladated compound obtained after complete C-H bond activation does not correspond to the final isolated XRD-characterized complexes. This species, bearing the classical open-book dimeric form, has a much more complex structure than the final isolated compound, with different types of acetato ligands.

  8. Predicting C-H/pi interactions with nonlocal density functional theory.

    PubMed

    Hooper, Joe; Cooper, Valentino R; Thonhauser, Timo; Romero, Nichols A; Zerilli, Frank; Langreth, David C

    2008-04-21

    We examine the performance of a recently developed nonlocal density functional in predicting a model noncovalent interaction, namely the weak bond between an aromatic pi system and an aliphatic C--H group. The new functional is a significant improvement over traditional density functionals, providing results which compare favorably to high-level quantum-chemistry techniques, but at considerably lower computational cost. Interaction energies in several model C--H/pi systems are in good general agreement with coupled-cluster calculations, though equilibrium distances are consistently overpredicted when using the revPBE functional for exchange. The new functional predicts changes in energy upon addition of halogen substituents correctly.

  9. Oxidative addition of Pd to C-H, C-C and C-Cl bonds: Importance of relativistic effects in DFT calculations

    NASA Astrophysics Data System (ADS)

    Diefenbach, Axel; Bickelhaupt, F. Matthias

    2001-09-01

    To assess the importance of relativistic effects for the quantum chemical description of oxidative addition reactions of palladium to C-H, C-C and C-Cl bonds, we have carried out a systematic study of the corresponding reactions of CH4, C2H6 and CH3Cl with Pd-d10 using nonrelativistic (NR), quasirelativistic (QR), and zeroth-order regularly approximated (ZORA) relativistic density functional theory (DFT) at the BP86/TZ(2)P level. Relativistic effects are important according to both QR and ZORA, the former yielding similar but somewhat more pronounced effects than the latter, more reliable method: activation barriers are reduced by 6-14 kcal/mol and reaction enthalpies become 15-20 kcal/mol more exothermic if one goes from NR to ZORA. This yields, for example, 298 K activation enthalpies ΔH298≠ of -5.0 (C-H), 9.6 (C-C) and -6.0 kcal/mol (C-Cl) relative to the separate reactants at ZORA-BP86/TZ(2)P. In accordance with gas-phase experiments on reactions of Pd with alkanes, we find reaction profiles with pronounced potential wells for reactant complexes (collisionally stabilized and observed in experiments for alkanes larger than CH4) at -11.4 (CH4), -11.6 (C2H6) and -15.6 kcal/mol (CH3Cl) relative to separated reactants [ZORA-BP86/TZ(2)P]. Furthermore, we analyze the height of and the relativistic effects on the activation energies ΔE≠ in terms of the activation strain ΔEstrain≠ of and the transition-state interaction ΔEint≠ between the reactants in the activated complex, with ΔE≠=ΔEstrain≠+ΔEint≠.

  10. Reactivity and selectivity patterns in hydrogen atom transfer from amino acid C-H bonds to the cumyloxyl radical: polar effects as a rationale for the preferential reaction at proline residues.

    PubMed

    Salamone, Michela; Basili, Federica; Bietti, Massimo

    2015-04-03

    Absolute rate constants for hydrogen atom transfer (HAT) from the C-H bonds of N-Boc-protected amino acids to the cumyloxyl radical (CumO(•)) were measured by laser flash photolysis. With glycine, alanine, valine, norvaline, and tert-leucine, HAT occurs from the α-C-H bonds, and the stability of the α-carbon radical product plays a negligible role. With leucine, HAT from the α- and γ-C-H bonds was observed. The higher kH value measured for proline was explained in terms of polar effects, with HAT that predominantly occurs from the δ-C-H bonds, providing a rationale for the previous observation that proline residues represent favored HAT sites in the reactions of peptides and proteins with (•)OH. Preferential HAT from proline was also observed in the reactions of CumO(•) with the dipeptides N-BocProGlyOH and N-BocGlyGlyOH. The rate constants measured for CumO(•) were compared with the relative rates obtained previously for the corresponding reactions of different hydrogen-abstracting species. The behavior of CumO(•) falls between those observed for the highly reactive radicals Cl(•) and (•)OH and the significantly more stable Br(•). Taken together, these results provide a general framework for the description of the factors that govern reactivity and selectivity patterns in HAT reactions from amino acid C-H bonds.

  11. Rare-earth-metal alkylaluminates supported by N-donor-functionalized cyclopentadienyl ligands: C-H bond activation and performance in isoprene polymerization.

    PubMed

    Jende, Lars N; Maichle-Mössmer, Cäcilia; Anwander, Reiner

    2013-11-25

    Homoleptic tetramethylaluminate complexes [Ln(AlMe4)3] (Ln=La, Nd, Y) reacted with HCp(NMe2) (Cp(NMe2) =1-[2-(N,N-dimethylamino)-ethyl]-2,3,4,5-tetramethyl-cyclopentadienyl) in pentane at -35 °C to yield half-sandwich rare-earth-metal complexes, [{C5 Me4CH2CH2NMe2 (AlMe3)}Ln(AlMe4)2]. Removal of the N-donor-coordinated trimethylaluminum group through donor displacement by using an equimolar amount of Et2O at ambient temperature only generated the methylene-bridged complexes [{C5Me4CH2CH2NMe(μ-CH2)AlMe3}Ln(AlMe4)] with the larger rare-earth-metal ions lanthanum and neodymium. X-ray diffraction analysis revealed the formation of isostructural complexes and the C-H bond activation of one aminomethyl group. The formation of Ln(μ-CH2)Al moieties was further corroborated by (13)C and (1)H-(13)C HSQC NMR spectroscopy. In the case of the largest metal center, lanthanum, this C-H bond activation could be suppressed at -35 °C, thereby leading to the isolation of [(Cp(NMe2))La(AlMe4)2], which contains an intramolecularly coordinated amino group. The protonolysis reaction of [Ln(AlMe4)3] (Ln=La, Nd) with the anilinyl-substituted cyclopentadiene HCp(AMe2) (Cp(AMe2) =1-[1-(N,N-dimethylanilinyl)]-2,3,4,5-tetramethylcyclopentadienyl) at -35 °C generated the half-sandwich complexes [(Cp(AMe2))Ln(AlMe4)2]. Heating these complexes at 75 °C resulted in the C-H bond activation of one of the anilinium methyl groups and the formation of [{C5Me4C6H4NMe(μ-CH2)AlMe3}Ln(AlMe4)] through the elimination of methane. In contrast, the smaller yttrium metal center already gave the aminomethyl-activated complex at -35 °C, which is isostructural to those of lanthanum and neodymium. The performance of complexes [{C5Me4CH2CH2NMe(μ-CH2 )AlMe3}-Ln(AlMe4)], [(Cp(AMe2))Ln(AlMe4)2], and [{C5Me4C6H4NMe(μ-CH2)AlMe3}Ln(AlMe4)] in the polymerization of isoprene was investigated upon activation with [Ph3C][B(C6F5)4], [PhNMe2 H][B(C6F5)4], and B(C6F5)3. The highest stereoselectivities were observed

  12. Distinctive activation and functionalization of hydrocarbon C-H bonds initiated by Cp*W(NO)(η(3)-allyl)(CH2CMe3) complexes.

    PubMed

    Baillie, Rhett A; Legzdins, Peter

    2014-02-18

    Converting hydrocarbon feedstocks into value-added chemicals continues to offer challenges to contemporary preparative chemists. A particularly important remaining challenge is the selective activation and functionalization of the C(sp(3))-H linkages of alkanes, which are relatively abundant but chemically inert. This Account outlines the discovery and development of C-H bond functionalization mediated by a family of tungsten organometallic nitrosyl complexes. Specifically, it describes how gentle thermolyses of any of four 18-electron Cp*W(NO)(η(3)-allyl)(CH2CMe3) complexes (Cp* = η(5)-C5Me5; η(3)-allyl = η(3)-H2CCHCHMe, η(3)-H2CCHCHSiMe3, η(3)-H2CCHCHPh, or η(3)-H2CCHCMe2) results in the loss of neopentane and the transient formation of a 16-electron intermediate species, Cp*W(NO)(η(2)-allene) and/or Cp*W(NO)(η(2)-diene). We have never detected any of these species spectroscopically, but we infer their existence based on trapping experiments with trimethylphosphine (PMe3) and labeling experiments using deuterated hydrocarbon substrates. This Account first summarizes the syntheses and properties of the four chiral Cp*W(NO)(η(3)-allyl)(CH2CMe3) complexes. It then outlines the various types of C-H activations we have effected with each of the 16-electron (η(2)-allene) or (η(2)-diene) intermediate nitrosyl complexes, and presents the results of mechanistic investigations of some of these processes. It next describes the characteristic chemical properties of the Cp*W(NO)(η(3)-allyl)(η(1)-hydrocarbyl) compounds formed by the single activations of C(sp(3))-H bonds, with particular emphasis on those reactions that result in the selective functionalization of the original hydrocarbon substrate. We are continuing development of methods to release the acyl ligands from the metal centers while keeping the Cp*W(NO)(η(3)-allyl) fragments intact, with the ultimate aim of achieving these distinctive conversions of alkanes into functionalized organics in a

  13. The Molybdenum Active Site of Formate Dehydrogenase Is Capable of Catalyzing C-H Bond Cleavage and Oxygen Atom Transfer Reactions.

    PubMed

    Hartmann, Tobias; Schrapers, Peer; Utesch, Tillmann; Nimtz, Manfred; Rippers, Yvonne; Dau, Holger; Mroginski, Maria Andrea; Haumann, Michael; Leimkühler, Silke

    2016-04-26

    Formate dehydrogenases (FDHs) are capable of performing the reversible oxidation of formate and are enzymes of great interest for fuel cell applications and for the production of reduced carbon compounds as energy sources from CO2. Metal-containing FDHs in general contain a highly conserved active site, comprising a molybdenum (or tungsten) center coordinated by two molybdopterin guanine dinucleotide molecules, a sulfido and a (seleno-)cysteine ligand, in addition to a histidine and arginine residue in the second coordination sphere. So far, the role of these amino acids in catalysis has not been studied in detail, because of the lack of suitable expression systems and the lability or oxygen sensitivity of the enzymes. Here, the roles of these active site residues is revealed using the Mo-containing FDH from Rhodobacter capsulatus. Our results show that the cysteine ligand at the Mo ion is displaced by the formate substrate during the reaction, the arginine has a direct role in substrate binding and stabilization, and the histidine elevates the pKa of the active site cysteine. We further found that in addition to reversible formate oxidation, the enzyme is further capable of reducing nitrate to nitrite. We propose a mechanistic scheme that combines both functionalities and provides important insights into the distinct mechanisms of C-H bond cleavage and oxygen atom transfer catalyzed by formate dehydrogenase.

  14. Reactions of organoaluminum compounds with acetylene as a method for the synthesis of aliphatic derivatives with a z-disubstituted double bond

    SciTech Connect

    Andreeva, N.I.; Kuchin, A.V.; Tolstikov, G.A.

    1985-11-01

    This paper develops a method for the synthesis of aliphatic compounds with a Z-disubstituted double bond, which are important synthons for the preparation of such natural products as insect pheromones, aromatic principles, etc. In the carbalumination reaction of acetylene Z-alkenyldialkylaluminums are formed selectively. A-Alkenyldialkylaluminums are highly reactive and can readily be converted into Z-allyl alcohols and their ethers, and into Z-iodovinyl derivatives. By the reactions of vinyl organoaluminum compounds with the complex CH/sub 3/COClhaAlCl/sub 3/ E-conjugated ketones were obtained.

  15. Transition-metal-free Chemoselective Oxidative C-C Coupling of the sp(3) C-H Bond of Oxindoles with Arenes and Addition to Alkene: Synthesis of 3-Aryl Oxindoles, and Benzofuro- and Indoloindoles.

    PubMed

    Sattar, Moh; Rathore, Vandana; Prasad, Ch Durga; Kumar, Sangit

    2017-04-04

    A transition-metal (TM)-free and halogen-free NaOtBu-mediated oxidative cross-coupling between the sp(3) C-H bond of oxindoles and sp(2) C-H bond of nitroarenes has been developed to access 3-aryl substituted and 3,3-aryldisubstituted oxindoles in DMSO at room temperature in a short time. Interestingly, the sp(3) C-H bond of oxindoles could also react with styrene under TM-free conditions for the practical synthesis of quaternary 3,3-disubstituted oxindoles. The synthesized 3-oxindoles have also been further transformed into advanced heterocycles, that is, benzofuroindoles, indoloindoles, and substituted indoles. Mechanistic experiments of the reaction suggests the formation of an anion intermediate from the sp(3) C-H bond of oxindole by tert-butoxide base in DMSO. The addition of nitrobenzene to the in-situ generated carbanion leads to the 3-(nitrophenyl)oxindolyl carbanion in DMSO which is subsequently oxidized to 3-(nitro-aryl) oxindole by DMSO.

  16. The selective activation of a C-F bond with an auxiliary strong Lewis acid: a method to change the activation preference of C-F and C-H bonds.

    PubMed

    Wang, Lin; Sun, Hongjian; Li, Xiaoyan; Fuhr, Olaf; Fenske, Dieter

    2016-11-15

    The selective activation of the C-F bonds in substituted (2,6-difluorophenyl)phenylimines (2,6-F2H3C6-(C[double bond, length as m-dash]NH)-n'-R-C6H4 (n' = 2, R = H (1); n' = 2, R = Me (2); n' = 4, R = tBu (3))) by Fe(PMe3)4 with an auxiliary strong Lewis acid (LiBr, LiI, or ZnCl2) was explored. As a result, iron(ii) halides ((H5C6-(C[double bond, length as m-dash]NH)-2-FH3C6)FeX(PMe3)3 (X = Br (8); Cl (9)) and (n-RH4C6-(C[double bond, length as m-dash]NH)-2'-FH3C6)FeX(PMe3)3 (n = 2, R = Me, X = Br (11); n = 4, R = tBu, X = I (12))) were obtained. Under similar reaction conditions, using LiBF4 instead of LiBr or ZnCl2, the reaction of (2,6-difluorophenyl)phenylimine with Fe(PMe3)4 afforded an ionic complex [(2,6-F2H3C6-(C[double bond, length as m-dash]NH)-H4C6)Fe(PMe3)4](BF4) (10) via the activation of a C-H bond. The method of C-F bond activation with an auxiliary strong Lewis acid is appropriate for monofluoroarylmethanimines. Without the Lewis acid, iron(ii) hydrides ((2-RH4C6-(C[double bond, length as m-dash]NH)-2'-FH3C6)FeH(PMe3)3 (R = H (13); Me (14))) were generated from the reactions of Fe(PMe3)4 with the monofluoroarylmethanimines (2-FH4C6-(C[double bond, length as m-dash]NH)-2'-RC6H4 (R = H (4); Me (5))); however, in the presence of ZnCl2 or LiBr, iron(ii) halides ((2-RH4C6-(C[double bond, length as m-dash]NH)-H4C6)FeX(PMe3)3 (R = H, X = Cl (15); R = Me, X = Br (16))) could be obtained through the activation of a C-F bond. Furthermore, a C-F bond activation with good regioselectivity in (pentafluorophenyl)arylmethanimines (F5C6-(C[double bond, length as m-dash]NH)-2,6-Y2C6H3 (Y = F (6); H (7))) could be realized in the presence of ZnCl2 to produce iron(ii) chlorides ((2,6-Y2H3C6-(C[double bond, length as m-dash]NH)-F4C6)FeCl(PMe3)3 (Y = F (17); H (18))). This series of iron(ii) halides could be used to catalyze the hydrosilylation reaction of aldehydes. Due to the stability of iron(ii) halides to high temperature, the reaction mixture was allowed to be

  17. Cocrystals of 1,4-diethynylbenzene with 1,3-diacetylbenzene and benzene-1,4-dicarbaldehyde exhibiting strong nonconventional alkyne-carbonyl C-H...O hydrogen bonds between the components.

    PubMed

    Bosch, Eric

    2016-10-01

    Weak interactions between organic molecules are important in solid-state structures where the sum of the weaker interactions support the overall three-dimensional crystal structure. The sp-C-H...N hydrogen-bonding interaction is strong enough to promote the deliberate cocrystallization of a series of diynes with a series of dipyridines. It is also possible that a similar series of cocrystals could be formed between molecules containing a terminal alkyne and molecules which contain carbonyl O atoms as the potential hydrogen-bond acceptor. I now report the crystal structure of two cocrystals that support this hypothesis. The 1:1 cocrystal of 1,4-diethynylbenzene with 1,3-diacetylbenzene, C10H6·C10H10O2, (1), and the 1:1 cocrystal of 1,4-diethynylbenzene with benzene-1,4-dicarbaldehyde, C10H6·C8H6O2, (2), are presented. In both cocrystals, a strong nonconventional ethynyl-carbonyl sp-C-H...O hydrogen bond is observed between the components. In cocrystal (1), the C-H...O hydrogen-bond angle is 171.8 (16)° and the H...O and C...O hydrogen-bond distances are 2.200 (19) and 3.139 (2) Å, respectively. In cocrystal (2), the C-H...O hydrogen-bond angle is 172.5 (16)° and the H...O and C...O hydrogen-bond distances are 2.25 (2) and 3.203 (2) Å, respectively.

  18. Binding to Redox-Inactive Alkali and Alkaline Earth Metal Ions Strongly Deactivates the C-H Bonds of Tertiary Amides toward Hydrogen Atom Transfer to Reactive Oxygen Centered Radicals.

    PubMed

    Salamone, Michela; Carboni, Giulia; Mangiacapra, Livia; Bietti, Massimo

    2015-09-18

    The effect of alkali and alkaline earth metal ions on the reactions of the cumyloxyl radical (CumO(•)) with N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) was studied by laser flash photolysis. In acetonitrile, a >2 order of magnitude decrease in the rate constant for hydrogen atom transfer (HAT) from the C-H bonds of these substrates (kH) was measured after addition of Li(+). This behavior was explained in terms of a strong interaction between Li(+) and the oxygen atom of both DMF and DMA that increases the extent of positive charge on the amide, leading to C-H bond deactivation toward HAT to the electrophilic radical CumO(•). Similar effects were observed after addition of Ca(2+), which was shown to strongly bind up to four equivalents of the amide substrates. With Mg(2+), weak C-H deactivation was observed for the first two substrate equivalents followed by stronger deactivation for two additional equivalents. No C-H deactivation was observed in DMSO after addition of Li(+) and Mg(2+). These results point toward the important role played by metal ion Lewis acidity and solvent Lewis basicity, indicating that C-H deactivation can be modulated by varying the nature of the metal cation and solvent and allowing for careful control over the HAT reactivity of amide substrates.

  19. The amide C-N bond of isatins as the directing group and the internal oxidant in Ru-catalyzed C-H activation and annulation reactions: access to 8-amido isocoumarins.

    PubMed

    Kaishap, Partha Pratim; Sarma, Bipul; Gogoi, Sanjib

    2016-07-28

    The N-O, N-N and O-O bonds are the frequently used internally oxidative directing groups used in various redox-neutral coupling reactions. The sole use of the C-N bond as the oxidizing directing group was reported recently by Li X. and co-workers for the Rh(iii)-catalyzed C-H activation of phenacyl ammonium salts. Herein, we report the use of the amide C-N bond of isatins as the oxidizing directing group for the Ru(ii)-catalyzed redox-neutral C-H activation and annulation reactions with alkynes which afford 8-amido isocoumarins. The reaction also features excellent regioselectivity with alkyl aryl substituted alkynes.

  20. Ruthenium-catalyzed alkylation of indoles with tertiary amines by oxidation of a sp3 C-H bond and Lewis acid catalysis.

    PubMed

    Wang, Ming-Zhong; Zhou, Cong-Ying; Wong, Man-Kin; Che, Chi-Ming

    2010-05-17

    Ruthenium porphyrins (particularly [Ru(2,6-Cl(2)tpp)CO]; tpp=tetraphenylporphinato) and RuCl(3) can act as oxidation and/or Lewis acid catalysts for direct C-3 alkylation of indoles, giving the desired products in high yields (up to 82% based on 60-95% substrate conversions). These ruthenium compounds catalyze oxidative coupling reactions of a wide variety of anilines and indoles bearing electron-withdrawing or electron-donating substituents with high regioselectivity when using tBuOOH as an oxidant, resulting in the alkylation of N-arylindoles to 3-{[(N-aryl-N-alkyl)amino]methyl}indoles (yield: up to 82%, conversion: up to 95%) and the alkylation of N-alkyl or N-H indoles to 3-[p-(dialkylamino)benzyl]indoles (yield: up to 73%, conversion: up to 92%). A tentative reaction mechanism involving two pathways is proposed: an iminium ion intermediate may be generated by oxidation of an sp(3) C-H bond of the alkylated aniline by an oxoruthenium species; this iminium ion could then either be trapped by an N-arylindole (pathway A) or converted to formaldehyde, allowing a subsequent three-component coupling reaction of the in situ generated formaldehyde with an N-alkylindole and an aniline in the presence of a Lewis acid catalyst (pathway B). The results of deuterium-labeling experiments are consistent with the alkylation of N-alkylindoles via pathway B. The relative reaction rates of [Ru(2,6-Cl(2)tpp)CO]-catalyzed oxidative coupling reactions of 4-X-substituted N,N-dimethylanilines with N-phenylindole (using tBuOOH as oxidant), determined through competition experiments, correlate linearly with the substituent constants sigma (R(2)=0.989), giving a rho value of -1.09. This rho value and the magnitudes of the intra- and intermolecular deuterium isotope effects (k(H)/k(D)) suggest that electron transfer most likely occurs during the initial stage of the oxidation of 4-X-substituted N,N-dimethylanilines. Ruthenium-catalyzed three-component reaction of N-alkyl/N-H indoles

  1. N-tosyloxycarbamates as a source of metal nitrenes: rhodium-catalyzed C-H insertion and aziridination reactions.

    PubMed

    Lebel, Hélène; Huard, Kim; Lectard, Sylvain

    2005-10-19

    The rhodium-catalyzed decomposition of N-tosyloxycarbamates to generate metal nitrenes which undergo intramolecular C-H insertion or aziridination reaction is described. Aliphatic N-tosyloxycarbamates produce oxazolidinones with high yields and stereospecificity through insertion in benzylic, tertiary, and secondary C-H bonds. Intramolecular aziridination occurs with allylic N-tosyloxycarbamates to produce aziridines as single diastereomers. The reaction proceeds at room temperature using a rhodium catalyst and an excess of potassium carbonate and does not require the use of strong oxidant, such as hypervalent iodine reagents. A rhodium nitrene species is presumably involved, as both reactions are stereospecific.

  2. P450-catalyzed intramolecular sp(3) C-H amination with arylsulfonyl azide substrates.

    PubMed

    Singh, Ritesh; Bordeaux, Melanie; Fasan, Rudi

    2014-01-06

    The direct amination of aliphatic C-H bonds represents a most valuable transformation in organic chemistry. While a number of transition metal-based catalysts have been developed and investigated for this purpose, the possibility to execute this transformation with biological catalysts has remained largely unexplored. Here, we report that cytochrome P450 enzymes can serve as efficient catalysts for mediating intramolecular benzylic C-H amination reactions in a variety of arylsulfonyl azide compouds. Under optimized conditions, the P450 catalysts were found to support up to 390 total turnovers leading to the formation of the desired sultam products with excellent regioselectivity. In addition, the chiral environment provided by the enzyme active site allowed for the reaction to proceed in a stereo- and enantioselective manner. The C-H amination activity, substrate profile, and enantio/stereoselectivity of these catalysts could be modulated by utilizing enzyme variants with engineered active sites.

  3. Intramolecular iron-mediated C-H bond heterolysis with an assist of pendant base in a [FeFe]-hydrogenase model.

    PubMed

    Zheng, Dehua; Wang, Ning; Wang, Mei; Ding, Shengda; Ma, Chengbing; Darensbourg, Marcetta Y; Hall, Michael B; Sun, Licheng

    2014-12-03

    Although many metalloenzymes containing iron play a prominent role in biological C-H activation processes, to date iron-mediated C(sp(3))-H heterolysis has not been reported for synthetic models of Fe/S-metalloenzymes. In contrast, ample precedent has established that nature's design for reversible hydrogen activation by the diiron hydrogenase ([FeFe]-H2ase) active site involves multiple irons, sulfur bridges, a redox switch, and a pendant amine base, in an intricate arrangement to perform H-H heterolytic cleavage. In response to whether this strategy might be extended to C-H activation, we report that a [FeFe]-H2ase model demonstrates iron-mediated intramolecular C-H heterolytic cleavage via an agostic C-H interaction, with proton removal by a nearby pendant amine, affording Fe(II)-[Fe'(II)-CH-S] three-membered-ring products, which can be reduced back to 1 by Cp2Co in the presence of HBF4. The function of the pendant base as a proton shuttle was confirmed by the crystal structures of the N-protonated intermediate and the final deprotonated product in comparison with that of a similar but pendant-amine-free complex that does not show evidence of C-H activation. The mechanism of the process was backed up by DFT calculations.

  4. Dehydrofluorination of Hydrofluorocarbons by Titanium Alkylidynes via Sequential C-H/C-F Bond Activation Reactions. A Synthetic, Structural, and Mechanistic Study of 1,2-CH Bond Addition and [beta]-Fluoride Elimination

    SciTech Connect

    Fout, A.R.; Scott, J.; Miller, D.L.; Bailey, B.C.; Pink, M.; Mindiola, D.J.

    2009-01-07

    The neopentylidene-neopentyl complex (PNP)Ti=CH{sup t}Bu(CH{sub 2}{sup t}Bu) (1); (PNP{sup -} = N[2-P(CHMe{sub 2}){sub 2}-4-methylphenyl]{sub 2}) extrudes neopentane in neat fluorobenzene under mild conditions (25 C) to generate the transient titanium alkylidyne (PNP)Ti-C{sup t}Bu (A), which subsequently undergoes regioselective 1,2-CH bond addition of a fluorobenzene across the Ti-C linkage to generate (PNP)Ti=CH{sup t}Bu(o-FC{sub 6}H{sub 4}) (2). Kinetic and mechanistic studies suggest that the C-H activation process is pseudo-first-order in titanium, with the {alpha}-hydrogen abstraction being the rate-determining step and the post-rate-determining step being the C-H bond activation of fluorobenzene. At 100 C complex 2 does not equilibrate back to A and the preference for C-H activation in benzene versus fluorobenzene is 2:3, respectively. Compound 1 also reacts readily, and in most cases cleanly, with a series of hydrofluoroarenes (HAr{sub F}), to form a family of alkylidene-arylfluoride derivatives of the type (PNP)Ti=CH{sup t}Bu(Ar{sub F}). Thermolysis of the latter compounds generates the titanium alkylidene-fluoride (PNP)Ti=CH{sup t}Bu(F) (14) by a {beta}-fluoride elimination, concurrent with formation of o-benzyne. {beta}-Fluoride elimination to yield 14 occurs from 2 under elevated temperatures with k{sub average} = 4.96(16) x 10{sup -5} s{sup -1} and with activation parameters {Delta}H{sub {-+}} = 29(1) kcal/mol and {Delta}S{sub {-+}} = -3(4) cal/mol {center_dot}K. It was found that {beta}-fluoride elimination is accelerated when electron-rich groups are adjacent to the fluoride group, thus implying that a positive charge buildup at the arylfluoride ring occurs in the activated complex of 2. The alkylidene derivative (PNP)Ti=CHSiMe{sub 3}(CH{sub 2}SiMe{sub 3}) (15) also undergoes {alpha}-hydrogen abstraction to form the putative (PNP)Ti'-CSiMe{sub 3} (B) at higher temperatures (>70 C) and dehydrofluorinates the same series of HArF when the reaction

  5. Birge-Sponer Estimation of the C-H Bond Dissociation Energy in Chloroform Using Infrared, Near-Infrared, and Visible Absorption Spectroscopy: An Experiment in Physical Chemistry

    ERIC Educational Resources Information Center

    Myrick, M. L.; Greer, A. E.; Nieuwland, A. A.; Priore, R. J.; Scaffidi, J.; Andreatta, Danielle; Colavita, Paula

    2008-01-01

    The fundamental and overtone vibrational absorption spectroscopy of the C-H unit in CHCl[subscript 3] is measured for transitions from the v = 0 energy level to v = 1 through v = 5 energy levels. The energies of the transitions exhibit a linearly-decreasing spacing between adjacent vibrational levels as the vibrational quantum number increases.…

  6. Rare-earth metal complexes having an unusual indolyl-1,2-dianion through C-H activation with a novel η1:(μ2-η1:η1) bonding with metals.

    PubMed

    Zhu, Xiancui; Zhou, Shuangliu; Wang, Shaowu; Wei, Yun; Zhang, Lijun; Wang, Fenhua; Wang, Shaoyin; Feng, Zhijun

    2012-12-21

    Studies on the reactions of 3-(tert-butyliminomethine)indole or 3-(tert-butylaminomethylene)indole with rare-earth metal amides [(Me(3)Si)(2)N](3)RE(III)(μ-Cl)Li(THF)(3) (RE = Y, Yb) led to the discovery of different reactivity patterns with isolation of novel rare-earth metal complexes having a unique indolyl-1,2-dianion in a novel η(1):(μ(2)-η(1):η(1)) bonding mode through C-H activation.

  7. 1,2-Diphosphonium dication: a strong P-based Lewis acid in frustrated lewis pair (FLP)-activations of B-H, Si-H, C-H, and H-H bonds.

    PubMed

    Holthausen, Michael H; Bayne, Julia M; Mallov, Ian; Dobrovetsky, Roman; Stephan, Douglas W

    2015-06-17

    A highly Lewis acidic diphosphonium dication [(C10H6)(Ph2P)2](2+) (1), in combination with a Lewis basic phosphine, acts as a purely phosphorus-based frustrated Lewis pair (FLP) and abstracts hydride from [HB(C6F5)3](-) and Et3SiH demonstrating the remarkable hydridophilicity of 1. The P-based FLP is also shown to activate H2 and C-H bonds.

  8. Does a higher metal oxidation state necessarily imply higher reactivity toward H-atom transfer? A computational study of C-H bond oxidation by high-valent iron-oxo and -nitrido complexes.

    PubMed

    Geng, Caiyun; Ye, Shengfa; Neese, Frank

    2014-04-28

    In this work, the reactions of C-H bond activation by two series of iron-oxo ( (Fe(IV)), (Fe(V)), (Fe(VI))) and -nitrido model complexes ( (Fe(IV)), (Fe(V)), (Fe(VI))) with a nearly identical coordination geometry but varying iron oxidation states ranging from iv to vi were comprehensively investigated using density functional theory. We found that in a distorted octahedral coordination environment, the iron-oxo species and their isoelectronic nitrido analogues feature totally different intrinsic reactivities toward C-H bond cleavage. In the case of the iron-oxo complexes, the reaction barrier monotonically decreases as the iron oxidation state increases, consistent with the gradually enhanced electrophilicity across the series. The iron-nitrido complex is less reactive than its isoelectronic iron-oxo species, and more interestingly, a counterintuitive reactivity pattern was observed, i.e. the activation barriers essentially remain constant independent of the iron oxidation states. The detailed analysis using the Polanyi principle demonstrates that the different reactivities between these two series originate from the distinct thermodynamic driving forces, more specifically, the bond dissociation energies (BDEE-Hs, E = O, N) of the nascent E-H bonds in the FeE-H products. Further decomposition of the BDEE-Hs into the electron and proton affinity components shed light on how the oxidation states modulate the BDEE-Hs of the two series.

  9. Highly Enantioselective Oxidation of Nonactivated Aliphatic C–H Bonds with Hydrogen Peroxide Catalyzed by Manganese Complexes

    PubMed Central

    2017-01-01

    Monosubstituted cycloalkanes undergo regio- and enantioselective aliphatic C–H oxidation with H2O2 catalyzed by biologically inspired manganese catalysts. The reaction furnishes the corresponding ketones resulting from oxidation at C3 and C4 methylenic sites (K3 and K4, respectively) leading to a chiral desymmetrization that proceeds with remarkable enantioselectivity (64% ee) but modest regioselectivity at C3 (K3/K4 ≈ 2) for tert-butylcyclohexane, and with up to 96% ee and exquisite regioselectity toward C3 (up to K3/K4 > 99) when N-cyclohexylalkanamides are employed as substrates. Efficient H2O2 activation, high yield, and highly enantioselective C–H oxidation rely on the synergistic cooperation of a sterically bulky manganese catalyst and an oxidatively robust alkanoic acid. This represents the first example of nonenzymatic highly enantioselective oxidation of nonactivated methylenic sites. Furthermore, the principles of catalyst design disclosed in this work constitute a unique platform for further development of stereoselective C–H oxidation reactions. PMID:28386597

  10. 1,1'-Diethyl-4,4'-bipyridine-1,1'-diium bis(1,1,3,3-tetracyano-2-ethoxypropenide): multiple C-H...N hydrogen bonds form a complex sheet structure.

    PubMed

    Setifi, Zouaoui; Lehchili, Fouzia; Setifi, Fatima; Beghidja, Adel; Ng, Seik Weng; Glidewell, Christopher

    2014-03-01

    In the title salt, C14H18N2(2+) · 2C9H5N4O(-), the 1,1'-diethyl-4,4'-bipyridine-1,1'-diium dication lies across a centre of inversion in the space group P21/c. In the 1,1,3,3-tetracyano-2-ethoxypropenide anion, the two independent -C(CN)2 units are rotated, in conrotatory fashion, out of the plane of the central propenide unit, making dihedral angles with the central unit of 16.0(2) and 23.0(2)°. The ionic components are linked by C-H...N hydrogen bonds to form a complex sheet structure, within which each cation acts as a sixfold donor of hydrogen bonds and each anion acts as a threefold acceptor of hydrogen bonds.

  11. Intermolecular interactions involving C-H bonds, 3, Structure and energetics of the interaction between CH{sub 4} and CN{sup {minus}}

    SciTech Connect

    Novoa, J.J.; Whangbo, Myung-Hwan; Williams, J.M.

    1991-12-31

    On the basis of SCF and single reference MP2 calculations, the full potential energy surface of the interaction between CH{sub 4} and CN{sup {minus}} was studied using extended basis sets of up to near Hartree-Fock limit quality. Colinear arrangements C-N{sup {minus}}{hor_ellipsis}H-CH{sub 3} and N-C{sup {minus}}{hor_ellipsis}H-CH{sub 3} are found to be the only two energy minima. The binding energies of these two structures are calculated to be 2.5 and 2.1 kcal/mol, respectively, at the MP2 level. The full vibrational analyses of two structures show a red shift of about 30 cm{sup {minus}1} for the v{sub s} C-H stretching.

  12. Synthesis and catalytic applications of 1,2,3-triazolylidene gold(i) complexes in silver-free oxazoline syntheses and C-H bond activation.

    PubMed

    Pretorius, René; Fructos, Manuel R; Müller-Bunz, Helge; Gossage, Robert A; Pérez, Pedro J; Albrecht, Martin

    2016-10-07

    A series of novel 1,2,3-triazolylidene gold(i) chloride complexes have been synthesised and fully characterised. Silver-free methodologies for chloride ion abstraction of these complexes were evaluated for their potential as Au-based catalyst precursors. Using simple potassium salts or MeOTf as chloride scavengers produced metal complexes that catalyse both the regioselective synthesis of oxazolines and the C-H activation of benzene or styrene for carbene transfer from ethyl diazoacetate. These results indicate that Ag-free activation of 1,2,3-triazolylidene gold(i) chloride complexes is feasible for the generation of catalytically active Au triazolylidene species. However, silver-mediated activation imparts substantially higher catalytic activity in oxazoline synthesis.

  13. Rhodium(III)-catalyzed allylic C-H bond amination. Synthesis of cyclic amines from ω-unsaturated N-sulfonylamines.

    PubMed

    Cochet, Thomas; Bellosta, Véronique; Roche, Didier; Ortholand, Jean-Yves; Greiner, Alfred; Cossy, Janine

    2012-11-11

    For the first time, intramolecular allylic amination was conducted using rhodium(III) according to an "inner-sphere" type mechanism with amines activated by only one electron-withdrawing group. The activation of C(sp(3))-H bonds was chemoselective and allows the access to a variety of substituted cyclic amines such as pyrrolidines and piperidines.

  14. Formation of a ruthenium(IV)-oxo complex by electron-transfer oxidation of a coordinatively saturated ruthenium(II) complex and detection of oxygen-rebound intermediates in C-H bond oxygenation.

    PubMed

    Kojima, Takahiko; Nakayama, Kazuya; Ikemura, Kenichiro; Ogura, Takashi; Fukuzumi, Shunichi

    2011-08-03

    A coordinatively saturated ruthenium(II) complex having tetradentate tris(2-pyridylmethyl)amine (TPA) and bidentate 2,2'-bipyridine (bpy), [Ru(TPA)(bpy)](2+) (1), was oxidized by a Ce(IV) ion in H(2)O to afford a Ru(IV)-oxo complex, [Ru(O)(H(+)TPA)(bpy)](3+) (2). The crystal structure of the Ru(IV)-oxo complex 2 was determined by X-ray crystallography. In 2, the TPA ligand partially dissociates to be in a facial tridentate fashion and the uncoordinated pyridine moiety is protonated. The spin state of 2, which showed paramagnetically shifted NMR signals in the range of 60 to -20 ppm, was determined to be an intermediate spin (S = 1) by the Evans' method with (1)H NMR spectroscopy in acetone-d(6). The reaction of 2 with various oraganic substrates in acetonitrile at room temperature afforded oxidized and oxygenated products and a solvent-bound complex, [Ru(H(+)TPA)(bpy)(CH(3)CN)], which is intact in the presence of alcohols. The oxygenation reaction of saturated C-H bonds with 2 proceeds by two-step processes: the hydrogen abstraction with 2, followed by the dissociation of the alcohol products from the oxygen-rebound complexes, Ru(III)-alkoxo complexes, which were successfully detected by ESI-MS spectrometry. The kinetic isotope effects in the first step for the reaction of dihydroanthrathene (DHA) and cumene with 2 were determined to be 49 and 12, respectively. The second-order rate constants of C-H oxygenation in the first step exhibited a linear correlation with bond dissociation energies of the C-H bond cleavage.

  15. Model-free estimation of the effective correlation time for C-H bond reorientation in amphiphilic bilayers: 1H-13C solid-state NMR and MD simulations

    NASA Astrophysics Data System (ADS)

    Ferreira, Tiago Mendes; Ollila, O. H. Samuli; Pigliapochi, Roberta; Dabkowska, Aleksandra P.; Topgaard, Daniel

    2015-01-01

    Molecular dynamics (MD) simulations give atomically detailed information on structure and dynamics in amphiphilic bilayer systems on timescales up to about 1 μs. The reorientational dynamics of the C-H bonds is conventionally verified by measurements of 13C or 2H nuclear magnetic resonance (NMR) longitudinal relaxation rates R1, which are more sensitive to motional processes with correlation times close to the inverse Larmor frequency, typically around 1-10 ns on standard NMR instrumentation, and are thus less sensitive to the 10-1000 ns timescale motion that can be observed in the MD simulations. We propose an experimental procedure for atomically resolved model-free estimation of the C-H bond effective reorientational correlation time τe, which includes contributions from the entire range of all-atom MD timescales and that can be calculated directly from the MD trajectories. The approach is based on measurements of 13C R1 and R1ρ relaxation rates, as well as 1H-13C dipolar couplings, and is applicable to anisotropic liquid crystalline lipid or surfactant systems using a conventional solid-state NMR spectrometer and samples with natural isotopic composition. The procedure is demonstrated on a fully hydrated lamellar phase of 1-palmitoyl-2-oleoyl-phosphatidylcholine, yielding values of τe from 0.1 ns for the methyl groups in the choline moiety and at the end of the acyl chains to 3 ns for the g1 methylene group of the glycerol backbone. MD simulations performed with a widely used united-atom force-field reproduce the τe-profile of the major part of the acyl chains but underestimate the dynamics of the glycerol backbone and adjacent molecular segments. The measurement of experimental τe-profiles can be used to study subtle effects on C-H bond reorientational motions in anisotropic liquid crystals, as well as to validate the C-H bond reorientation dynamics predicted in MD simulations of amphiphilic bilayers such as lipid membranes.

  16. Intermolecular C-H bond activation of benzene and pyridines by a vanadium(III) alkylidene including a stepwise conversion of benzene to a vanadium-benzyne complex

    SciTech Connect

    Andino, José G; Kilgore, Uriah J; Pink, Maren; Ozarowski, Andrew; Krzystek, J; Telser, Joshua; Baik, Mu-Hyun; Mindiola, Daniel J

    2012-01-20

    Breaking of the carbon-hydrogen bond of benzene and pyridine is observed with (PNP)V(CH2tBu)2 (1), and in the case of benzene, the formation of an intermediate benzyne complex (C) is proposed, and indirect proof of its intermediacy is provided by identification of (PNP)V=O(η2-C6H4) in combination with DFT calculations.

  17. Yttrium-Assisted C-H and C-C Bond Activation of Ethylene Probed by Mass-Analyzed Threshold Ionization Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kim, Jong Hyun; Yang, Dong-Sheng

    2016-06-01

    The reaction between Y atom and ethylene (CH2=CH2) was performed in a laser-ablation supersonic molecular beam source. Y(C2H2), Y(C2H4), and Y(C4H6) were observed by time-of-flight mass spectrometry and investigated with mass-analyzed threshold ionization (MATI) spectroscopy and theoretical calculations. Y(C2H2) is formed by hydrogen elimination, Y(C2H4) by simple association, and La(C4H6) by C-C bond coupling and dehydrogenation. Both Y(C2H2) and Y(C2H4) have a C2v triangular structure with a C=C double bond in Y(C2H2) and a C-C single bond in Y(C2H4). Y(C4H6) has a five-membered metallacyclic structure (Cs) with Y binding to the two terminal carbon atoms of butene, which is the exactly same as that of Y(C4H6) formed in the Y + 1-butene reaction. For all three complexes, ionization has a small effect on the metal-carbon bond lengths because the rejected electron has basically a Y 5s character. The adiabatic ionization energies are measured to be 45679(5) wn for Y(C2H2), 45603(5) wn for Y(C2H4) and 43475(5) wn for Y(C4H6). The metal-ligand stretching frequencies of the three complexes are also measured from the MATI spectra.

  18. Versatile reactivity of Pd-catalysts: mechanistic features of the mono-N-protected amino acid ligand and cesium-halide base in Pd-catalyzed C-H bond functionalization.

    PubMed

    Musaev, Djamaladdin G; Figg, Travis M; Kaledin, Alexey L

    2014-07-21

    The widely used C-H functionalization strategies and some complexities in the Pd-catalyzed chemical transformations were analyzed. It was emphasized that in the course of catalysis various Pd-intermediates (including nano-scale Pd-clusters) could act as active catalysts. However, both identification of these catalytically active species and determination of factors controlling the overall catalytic process require more comprehensive and multi-disciplinary approaches. Recent joint computational and experimental approaches were instrumental in: (1) demonstrating that the addition of Pd(OAc)2 as a catalyst precursor to RSeH and RSH reagents forms the [Pd(SeR)2]n and [Pd(SR)2]n clusters, respectively, which show an unprecedented ability for selective synthesis of Markovnikov-type products starting with a mixture of reagents RSH/RSeH and acetylenic hydrocarbons; (2) predicting a valid mechanism of the amino acid ligand-assisted Pd(II)-catalyzed C-H activation that is shown to proceed via the formation of the catalytically active Pd(II) intermediate with a bidentately coordinated dianionic amino acid ligand; (3) demonstrating that the amino acid ligand plays crucial roles in the ligand-assisted Pd(II)-catalyzed C-H activation by acting as: (a) a weakly coordinating ligand to stabilize the desirable Pd(II)-precatalyst, (b) a soft proton donor and a bidentately coordinated dianionic ligand in the catalytically active Pd(II) intermediate, and (c) a proton acceptor accelerating the C-H deprotonation via the CMD mechanism; and (4) revealing the roles of the CsF base (and "cesium effect") in the Pd(0)/PCy3-catalyzed intermolecular arylation of the terminal β-C(sp(3))-H bond of aryl amide and predicting the unprecedented "Cs2-I-F cluster" assisted mechanism for this reaction.

  19. Elementary steps of iron catalysis: exploring the links between iron alkyl and iron olefin complexes for their relevance in C-H activation and C-C bond formation.

    PubMed

    Casitas, Alicia; Krause, Helga; Goddard, Richard; Fürstner, Alois

    2015-01-26

    The alkylation of complexes 2 and 7 with Grignard reagents containing β-hydrogen atoms is a process of considerable relevance for the understanding of C-H activation as well as C-C bond formation mediated by low-valent iron species. Specifically, reaction of 2 with EtMgBr under an ethylene atmosphere affords the bis-ethylene complex 1 which is an active precatalyst for prototype [2+2+2] cycloaddition reactions and a valuable probe for mechanistic studies. This aspect is illustrated by its conversion into the bis-alkyne complex 6 as an unprecedented representation of a cycloaddition catalyst loaded with two substrates molecules. On the other hand, alkylation of 2 with 1 equivalent of cyclohexylmagnesium bromide furnished the unique iron alkyl species 11 with a 14-electron count, which has no less than four β-H atoms but is nevertheless stable at low temperature against β-hydride elimination. In contrast, the exhaustive alkylation of 1 with cyclohexylmagnesium bromide triggers two consecutive C-H activation reactions mediated by a single iron center. The resulting complex has a diene dihydride character in solution (15), whereas its structure in the solid state is more consistent with an η(3) -allyl iron hydride rendition featuring an additional agostic interaction (14). Finally, the preparation of the cyclopentadienyl iron complex 25 illustrates how an iron-mediated C-H activation cascade can be coaxed to induce a stereoselective CC bond formation. The structures of all relevant new iron complexes in the solid state are presented.

  20. Interaction between anions and cationic metal complexes containing tridentate ligands with exo-C-H groups: complex stability and hydrogen bonding.

    PubMed

    Martínez-García, Héctor; Morales, Dolores; Pérez, Julio; Puerto, Marcos; del Río, Ignacio

    2014-05-05

    [Re(CO)3 ([9]aneS3 )][BAr'4 ] (1), prepared by reaction of ReBr(CO)5 , 1,4,7-trithiacyclononane ([9]aneS3 ) and NaBAr'4 , forms stable, soluble supramolecular adducts with chloride (2), bromide, methanosulfonate (3) and fluoride (4) anions. These new species were characterized by IR, NMR spectroscopy and, for 2 and 3, also by X-ray diffraction. The results of the solid state structure determinations indicate the formation of CH⋅⋅⋅X hydrogen bonds between the anion (X) and the exo-CH groups of the [9]aneS3 ligand, in accord with the relatively large shifts found by (1) H NMR spectroscopy in dichloromethane solution for those hydrogens. The stability of the chloride adduct contrasts with the lability of the [9]aneS3 ligand in allyldicarbonyl molybdenum complexes recently studied by us. With fluoride, in dichloromethane solution, a second, minor neutral dimeric species 5 is formed in addition to 4. In 4, the deprotonation of a CH group of the [9]aneS3 ligand, accompanied by CS bond cleavage and dimerization, afforded 5, featuring bridging thiolates. Compounds [Mo(η(3) -methallyl)(CO)2 (TpyN)][BAr'4 ] (6) and [Mo(η(3) -methallyl)(CO)2 (TpyCH)][BAr'4 ] (7) were synthesized by the reactions of [MoCl(η(3) -methallyl)(CO)2 (NCMe)2 ], NaBAr'4 and tris(2-pyridyl)amine (TpyN) or tris(2-pyridyl)methane (TpyCH) respectively, and characterized by IR and (1) H and (13) C NMR spectroscopy in solution, and by X-ray diffraction in the solid state. Compound 6 undergoes facile substitution of one of the 2-pyridyl groups by chloride, bromide, and methanosulfonate anions. Stable supramolecular adducts were formed between 7 and chloride, bromide, iodide, nitrate, and perrhenate anions. The solid state structures of these adducts (12-16) were determined by X-ray diffraction. Binding constants in dichloromethane were calculated from (1) H NMR titration data for all the new supramolecular adducts. The signal of the bridgehead CH group is the one that undergoes a

  1. Water as a green solvent for efficient synthesis of isocoumarins through microwave-accelerated and Rh/Cu-catalyzed C-H/O-H bond functionalization

    SciTech Connect

    Li, Qiu; Yan, Yunnan; Wang, Xiaowei; Gong, Binwei; Tang, Xiaobo; Shi, JingJing; Xu, H. Eric; Yi, Wei

    2014-08-14

    Green chemistry that uses water as a solvent has recently received great attention in organic synthesis. Here we report an efficient synthesis of biologically important isocoumarins through direct cleavage of C–H/O–H bonds by microwave-accelerated and Rh/Cu-catalyzed oxidative annulation of various substituted benzoic acids, where water is used as the only solvent in the reactions. The remarkable features of this “green” methodology include high product yields, wide tolerance of various functional groups as substrates, and excellent region-/site-specificities, thus rendering this methodology a highly versatile and eco-friendly alternative to the existing methods for synthesizing isocoumarins and other biologically important derivatives such as isoquinolones.

  2. Selective activation of C-F and C-H bonds with iron complexes, the relevant mechanism study by DFT calculations and study on the chemical properties of hydrido iron complex.

    PubMed

    Xu, Xiaofeng; Jia, Jiong; Sun, Hongjian; Liu, Yuxia; Xu, Wengang; Shi, Yujie; Zhang, Dongju; Li, Xiaoyan

    2013-03-14

    The reactions of (2,6-difluorophenyl)phenylmethanone (2,6-F(2)C(6)H(3)-C(=O)-C(6)H(5)) (1) and (2,6-difluorophenyl)phenylmethanimine (2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(5)) (3) with Fe(PMe(3))(4) afforded different selective C-F/C-H bond activation products. The reaction of 1 with Fe(PMe(3))(4) gave rise to bis-chelate iron(II) complex [C(6)H(5)-C(=O)-3-FC(6)H(3))Fe(PMe(3))](2) (2) via C-F bond activation. The reaction of 3 with Fe(PMe(3))(4) delivered chelate hydrido iron(II) complex 2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(4))Fe(H)(PMe(3))(3) (4) through C-H bond activation. The DFT calculations show the detailed elementary steps of the mechanism of formation of hydrido complex 4 and indicate 4 is the kinetically preferred product. Complex 4 reacted with HCl, CH(3)Br and CH(3)I delivered the chelate iron halides (2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(4))Fe(PMe(3))(3)X (X = Cl (5); Br (6); I (7)). A ligand (PMe(3)) replacement by CO of 4 was observed giving (2,6-F(2)C(6)H(3)-C(=NH)-C(6)H(4))Fe(H)(CO)(PMe(3))(2) (8). The chelate ligand exchange occurred through the reaction of 4 with salicylaldehydes. The reaction of 4 with Me(3)SiC[triple bond, length as m-dash]CH afforded (2,6-F(2)C(6)H(3)-C([double bond, length as m-dash]N)-C(6)H(5))Fe(C≡C-SiMe(3))(PMe(3))(3) (11). A reaction mechanism from 4 to 11 was discussed with the support of IR monitoring. The molecular structures of complexes 2, 4, 6, 7, 10 and 11 were determined by X-ray diffraction.

  3. Synthesis, X-ray structure, magnetic resonance, and DFT analysis of a soluble copper(II) phthalocyanine lacking C-H bonds.

    PubMed

    Moons, Hans; Łapok, Łukasz; Loas, Andrei; Van Doorslaer, Sabine; Gorun, Sergiu M

    2010-10-04

    The synthesis, crystal structure, and electronic properties of perfluoro-isopropyl-substituted perfluorophthalocyanine bearing a copper atom in the central cavity (F(64)PcCu) are reported. While most halogenated phthalocyanines do not exhibit long-term order sufficient to form large single crystals, this is not the case for F(64)PcCu. Its crystal structure was determined by X-ray analysis and linked to the electronic properties determined by electron paramagnetic resonance (EPR). The findings are corroborated by density functional theory (DFT) computations, which agree well with the experiment. X-band continuous-wave EPR spectra of undiluted F(64)PcCu powder, indicate the existence of isolated metal centers. The electron-withdrawing effect of the perfluoroalkyl (R(f)) groups significantly enhances the complexes solubility in organic solvents like alcohols, including via their axial coordination. This coordination is confirmed by X-band (1)H HYSCORE experiments and is also seen in the solid state via the X-ray structure. Detailed X-band CW-EPR, X-band Davies and Mims ENDOR, and W-band electron spin-echo-detected EPR studies of F(64)PcCu in ethanol allow the determination of the principal g values and the hyperfine couplings of the metal, nitrogen, and fluorine nuclei. Comparison of the g and metal hyperfine values of F(64)PcCu and other PcCu complexes in different matrices reveals a dominant effect of the matrix on these EPR parameters, while variations in the ring substituents have only a secondary effect. The relatively strong axial coordination occurs despite the diminished covalency of the C-N bonds and potentially weakening Jahn-Teller effects. Surprisingly, natural abundance (13)C HYSCORE signals could be observed for a frozen ethanol solution of F(64)PcCu. The (13)C nuclei contributing to the HYSCORE spectra could be identified as the pyrrole carbons by means of DFT. Finally, (19)F ENDOR and easily observable paramagnetic NMR were found to relate well to the

  4. Ethane C-H bond activation on the Fe(iv)-oxo species in a Zn-based cluster of metal-organic frameworks: a density functional theory study.

    PubMed

    Impeng, Sarawoot; Siwaipram, Siwarut; Bureekaew, Sareeya; Probst, Michael

    2017-02-01

    We first investigate the feasibility of designing a Fe-oxo complex for the activation of alkane C-H bonds by (a) incorporating an Fe ion into a Zn-based cluster derived from a metal-organic framework (MOF) and (b) creating the Fe-oxo complex via decomposition of N2O over a Fe(2+)-substituted Zn-based cluster (Fe-Zn3O(pyrazole)6). From the energy profile, it turns out that both steps should be feasible and that the resulting Fe-oxo complex is stable. In the main step, we then investigate the reactivity of this Fe-oxo cluster for the C-H bond cleavage of ethane by calculating the reaction energy profile and analyzing the electronic structure along the relevant steps. Two mechanisms, namely the σ and π pathways on the triplet and quintet potential energy surfaces, were unraveled for this study of catalytic activity. It is shown that the σ pathway on the quintet surface is kinetically and thermodynamically favorable with an energy barrier of 22.5 kcal mol(-1). The π pathway on the quintet and triplet surfaces has activation energies of 26.9 kcal mol(-1) and 24.9 kcal mol(-1), respectively. An alternative unusual pathway called the δ mechanism on the triplet surface is also observed with an energy barrier of 12.6 kcal mol(-1). It is, however, thermodynamically at a disadvantage compared to the σ pathway on the quintet surface. Favorable d-d interaction on the Fe center and less steric hindrance from the equatorial ligands at the transition state are the key factors that cause the σ pathway on the quintet surface to have the lowest activation energy. All our calculations are of the cluster type and have been performed at the B3LYP-D3/def2-TZVP level of theory.

  5. Reactivity of Tp(Me2) -supported yttrium alkyl complexes toward aromatic N-heterocycles: ring-opening or C-C bond formation directed by C-H activation.

    PubMed

    Yi, Weiyin; Zhang, Jie; Huang, Shujian; Weng, Linhong; Zhou, Xigeng

    2014-01-13

    Unusual chemical transformations such as three-component combination and ring-opening of N-heterocycles or formation of a carbon-carbon double bond through multiple C-H activation were observed in the reactions of Tp(Me2) -supported yttrium alkyl complexes with aromatic N-heterocycles. The scorpionate-anchored yttrium dialkyl complex [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with 1-methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24-membered rare-earth metallomacrocyclic compound [Tp(Me2) Y(μ-N,C-Im)(η(2) -N,C-Im)]6 (1; Im=1-methylimidazolyl) through two kinds of C-H activations at the C2- and C5-positions of the imidazole ring. However, [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with two equivalents of 1-methylbenzimidazole to afford a C-C coupling/ring-opening/C-C coupling product [Tp(Me2) Y{η(3) -(N,N,N)-N(CH3 )C6 H4 NHCHC(Ph)CN(CH3 )C6 H4 NH}] (2). Further investigations indicated that [Tp(Me2) Y(CH2 Ph)2 (THF)] reacted with benzothiazole in 1:1 or 1:2 molar ratio to produce a C-C coupling/ring-opening product {(Tp(Me2) )Y[μ-η(2) :η(1) -SC6 H4 N(CHCHPh)](THF)}2 (3). Moreover, the mixed Tp(Me2) /Cp yttrium monoalkyl complex [(Tp(Me2) )CpYCH2 Ph(THF)] reacted with two equivalents of 1-methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [Tp(Me2) CpY(μ-N,C-Im)]3 (5), whereas when the above reaction was carried out at 55 °C for two days, two structurally characterized metal complexes [Tp(Me2) Y(Im-Tp(Me2) )] (7; Im-Tp(Me2) =1-methyl-imidazolyl-Tp(Me2) ) and [Cp3 Y(HIm)] (8; HIm=1-methylimidazole) were obtained in 26 and 17 % isolated yields, respectively, accompanied by some unidentified materials. The formation of 7 reveals an uncommon example of construction of a CC bond through multiple C-H activations.

  6. Formation and High Reactivity of the anti-Dioxo Form of High-Spin μ-Oxodioxodiiron(IV) as the Active Species That Cleaves Strong C-H Bonds.

    PubMed

    Kodera, Masahito; Ishiga, Shin; Tsuji, Tomokazu; Sakurai, Katsutoshi; Hitomi, Yutaka; Shiota, Yoshihito; Sajith, P K; Yoshizawa, Kazunari; Mieda, Kaoru; Ogura, Takashi

    2016-04-18

    Recently, it was shown that μ-oxo-μ-peroxodiiron(III) is converted to high-spin μ-oxodioxodiiron(IV) through O-O bond scission. Herein, the formation and high reactivity of the anti-dioxo form of high-spin μ-oxodioxodiiron(IV) as the active oxidant are demonstrated on the basis of resonance Raman and electronic-absorption spectral changes, detailed kinetic studies, DFT calculations, activation parameters, kinetic isotope effects (KIE), and catalytic oxidation of alkanes. Decay of μ-oxodioxodiiron(IV) was greatly accelerated on addition of substrate. The reactivity order of substrates is tolueneC-H bond cleavage of ethylbenzene than the most reactive diiron system reported so far. The KIE for the reaction with toluene/[D8 ]toluene is 95 at -30 °C, which the largest in diiron systems reported so far. The present diiron complex efficiently catalyzes the oxidation of various alkanes with H2 O2 .

  7. Solubility of aliphatic hydrocarbons in piperidinium ionic liquids: measurements and modeling in terms of perturbed-chain statistical associating fluid theory and nonrandom hydrogen-bonding theory.

    PubMed

    Paduszyński, Kamil; Domańska, Urszula

    2011-11-03

    Ionic liquids (ILs) reveal many unique properties which make them very interesting for applications in modern "green" technologies. For that reason, detailed knowledge about correlations between the ions' structure, their combinations, and the bulk properties is of great importance. That knowledge can be accessed by reliable measurements and modeling of systems with ILs in terms of various theoretical approaches. In this paper we report new experimental results on liquid-liquid equilibrium (LLE) measurements of 10 binary systems composed of piperidinium ILs [namely, 1-propyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide and 1-butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide] and aliphatic hydrocarbons (n-hexane, n-heptane, n-octane, cyclohexane, and cycloheptane). Moreover, new results on liquid density of pure 1-butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide are presented. Upper critical solution temperature type of phase behavior for all studied systems was observed. Decrease of solubility of n-alkane with an increase of its alkyl chain length and increase of solubility when changing linear into cyclic structure of hydrocarbon were detected. LLE modeling of investigated systems was performed in terms of two modern theories, namely, perturbed-chain statistical associating fluid theory (PC-SAFT) and nonrandom hydrogen-bonding theory (NRHB). Pure fluid parameters of the models were obtained from fitting of experimental liquid density and solubility parameter data at ambient pressure and tested against high pressure densities. Then literature values of activity coefficients of n-alkanes and cycloalkanes at infinitely diluted mixtures with ILs were used to optimize binary interaction parameters of the models. Finally, the LLE phase diagrams were calculated with average absolute relative deviations of 4.1% and 3.4% of the IL mole fraction for PC-SAFT and NRHB, respectively. The PC-SAFT and NRHB models were both able to capture phase

  8. Seven organic salts assembled from hydrogen-bonds of N-H⋯O, O-H⋯O, and C-H⋯O between acidic compounds and bis(benzimidazole)

    NASA Astrophysics Data System (ADS)

    Jin, Shouwen; Liu, Hui; Gao, Xin Jun; Lin, Zhanghui; Chen, Guqing; Wang, Daqi

    2014-10-01

    Seven crystalline organic acid-base adducts derived from 1,4-bis(benzimidazol-2-yl)butane/1,2-bis(2-benzimidazolyl)-1,2-ethanediol and acidic components (picric acid, 2-hydroxy-5-(phenyldiazenyl)benzoic acid, 5-sulfosalicylic acid, oxalic acid, and 1,5-naphthalenedisulfonic acid) were prepared and characterized by the single crystal X-ray diffraction analysis, IR, mp, and elemental analysis. All of the seven compounds are organic salts involving proton transfer from the acidic components to the bis(benzimidazole). For the salt 3, although a competing carboxyl group is present, it has been observed that only the proton at the -SO3H group is deprotonized rather than the H at the COOH. While in the salt 7, both COOH and SO3H were ionized to exhibit a valence number of -2. For 4, the oxalic acid existed as unionized molecule, monoanion, and dianion simultaneously in one compound. All supramolecular architectures of the organic salts 1-7 involve extensive intermolecular N-H⋯O, O-H⋯O, and C-H⋯O hydrogen bonds as well as other noncovalent interactions. Since the potentially hydrogen bonding phenol group is present in the ortho position to the carboxyl group in 2, 3, and 7, it forms the more facile intramolecular O-H⋯O hydrogen bonding. The role of weak and strong noncovalent interactions in the crystal packing is ascertained. These weak interactions combined, all the complexes displayed 3D framework structure.

  9. Alkyne insertion into the M-P and M-H bonds (M=Pd, Ni, Pt, and Rh): a theoretical mechanistic study of the C-P and C-H bond-formation steps.

    PubMed

    Ananikov, Valentine P; Beletskaya, Irina P

    2011-06-06

    In hydrogen-metal-phosphorus (H-M-P) transition metal complexes (proposed as intermediates of H-P bond addition to alkynes in the catalytic hydrophosphorylation, hydrophosphinylation, and hydrophospination reactions), alkyne insertion into the metal-hydrogen bond was found much more facile compared to alkyne insertion into the metal-phosphorus bond. The conclusion was verified for different metals (Pd, Ni, Pt, and Rh), ligands, and phosphorus groups at various theory levels (B3LYP, B3PW91, BLYP, MP2, and ONIOM). The relative reactivity of the metal complexes in the reaction with alkynes was estimated and decreased in the order of Ni>Pd>Rh>Pt. A trend in relative reactivity was established for various types of phosphorus groups: PR(2)>P(O)R(2)>P(O)(OR)(2), which showed a decrease in rate upon increasing the number of the oxygen atoms attached to the phosphorus center.

  10. Metal-Catalyzed Decarboxylative C-H Functionalization.

    PubMed

    Wei, Ye; Hu, Peng; Zhang, Min; Su, Weiping

    2017-03-07

    C-H bond activation and decarboxylation are two significant processes in organic synthesis. The combination of these processes provides a novel synthetic strategy, that is, decarboxylative C-H bond functionalization. Considerable attention has been focused on such an active research field. This review offers an overview of the utility of decarboxylative C-H bond functionalization in the synthesis of various organic compounds, such as styrenes, chalcones, biaryls, and heterocycles, covering most of the recent advances of the decarboxylative functionalization of Csp-H, Csp(2)-H, and Csp(3)-H bonds, as well as their scopes, limitations, practical applications, and synthetic potentials.

  11. General allylic C-H alkylation with tertiary nucleophiles.

    PubMed

    Howell, Jennifer M; Liu, Wei; Young, Andrew J; White, M Christina

    2014-04-16

    A general method for intermolecular allylic C-H alkylation of terminal olefins with tertiary nucleophiles has been accomplished employing palladium(II)/bis(sulfoxide) catalysis. Allylic C-H alkylation furnishes products in good yields (avg. 64%) with excellent regio- and stereoselectivity (>20:1 linear:branched, >20:1 E:Z). For the first time, the olefin scope encompasses unactivated aliphatic olefins as well as activated aromatic/heteroaromatic olefins and 1,4-dienes. The ease of appending allyl moieties onto complex scaffolds is leveraged to enable this mild and selective allylic C-H alkylation to rapidly diversify phenolic natural products. The tertiary nucleophile scope is broad and includes latent functionality for further elaboration (e.g., aliphatic alcohols, α,β-unsaturated esters). The opportunities to effect synthetic streamlining with such general C-H reactivity are illustrated in an allylic C-H alkylation/Diels-Alder reaction cascade: a reactive diene is generated via intermolecular allylic C-H alkylation and approximated to a dienophile contained within the tertiary nucleophile to furnish a common tricyclic core found in the class I galbulimima alkaloids.

  12. Thermochemical properties of methyl-substituted cyclic alkyl ethers and radicals for oxiranes, oxetanes, and oxolanes: C-H bond dissociation enthalpy trends with ring size and ether site.

    PubMed

    Auzmendi-Murua, Itsaso; Charaya, Sumit; Bozzelli, Joseph W

    2013-01-17

    Cyclic ethers are an important product from the gas-phase reactions of hydrocarbon radicals with molecular oxygen in the atmospheric chemistry of diolefins and in low to moderate temperature combustion and oxidation reaction systems. They are also important in organic synthesis. Structures, and fundamental thermochemical parameters-enthalpy (ΔH°(f,298)), entropy (S°(298)), and heat capacity (C(p)(T))-have been calculated for a series of cyclic alkyl ethers and their carbon centered radicals. Enthalpies of formation (ΔH°(f,298)) are determined at the B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p), and CBS-QB3 levels using several work reactions for each species. Entropy (S) and heat capacity (C(p)(T)) values from vibration, translational, and external rotational contributions are calculated using the rigid-rotor-harmonic-oscillator approximation based on the vibration frequencies and structures obtained from the density functional studies. Contributions from the internal methyl rotors are substituted for torsion frequencies. Calculated enthalpies of formation for a series of 12 cyclic ethers and methyl substituted cyclic ethers are in good agreement with available literature values. C-H bond dissociation enthalpies are reported for 28 carbon sites of 3 to 5 member ring cyclic ethers for use in understanding effects of the ring and the ether oxygen on kinetics and stability. Trends in carbon-hydrogen bond energies for the ring and methyl substituents relative to ring size and to distance from the ether group are described.

  13. Weak coordination as a powerful means for developing broadly useful C-H functionalization reactions.

    PubMed

    Engle, Keary M; Mei, Tian-Sheng; Wasa, Masayuki; Yu, Jin-Quan

    2012-06-19

    Reactions that convert carbon-hydrogen (C-H) bonds into carbon-carbon (C-C) or carbon-heteroatom (C-Y) bonds are attractive tools for organic chemists, potentially expediting the synthesis of target molecules through new disconnections in retrosynthetic analysis. Despite extensive inorganic and organometallic study of the insertion of homogeneous metal species into unactivated C-H bonds, practical applications of this technology in organic chemistry are still rare. Only in the past decade have metal-catalyzed C-H functionalization reactions become more widely utilized in organic synthesis. Research in the area of homogeneous transition metal-catalyzed C-H functionalization can be broadly grouped into two subfields. They reflect different approaches and goals and thus have different challenges and opportunities. One approach involves reactions of completely unfunctionalized aromatic and aliphatic hydrocarbons, which we refer to as "first functionalization". Here the substrates are nonpolar and hydrophobic and thus interact very weakly with polar metal species. To overcome this weak affinity and drive metal-mediated C-H cleavage, chemists often use hydrocarbon substrates in large excess (for example, as solvent). Because highly reactive metal species are needed in first functionalization, controlling the chemoselectivity to avoid overfunctionalization is often difficult. Additionally, because both substrates and products are comparatively low-value chemicals, developing cost-effective catalysts with exceptionally high turnover numbers that are competitive with alternatives (including heterogeneous catalysts) is challenging. Although an exciting field, first functionalization is beyond the scope of this Account. The second subfield of C-H functionalization involves substrates containing one or more pre-existing functional groups, termed "further functionalization". One advantage of this approach is that the existing functional group (or groups) can be used to chelate

  14. Oxidative C-H/C-H Coupling Reactions between Two (Hetero)arenes.

    PubMed

    Yang, Yudong; Lan, Jingbo; You, Jingsong

    2017-01-13

    Transition metal-mediated C-H bond activation and functionalization represent one of the most straightforward and powerful tools in modern organic synthetic chemistry. Bi(hetero)aryls are privileged π-conjugated structural cores in biologically active molecules, organic functional materials, ligands, and organic synthetic intermediates. The oxidative C-H/C-H coupling reactions between two (hetero)arenes through 2-fold C-H activation offer a valuable opportunity for rapid assembly of diverse bi(hetero)aryls and further exploitation of their applications in pharmaceutical and material sciences. This review provides a comprehensive overview of the fundamentals and applications of transition metal-mediated/catalyzed oxidative C-H/C-H coupling reactions between two (hetero)arenes. The substrate scope, limitation, reaction mechanism, regioselectivity, and chemoselectivity, as well as related control strategies of these reactions are discussed. Additionally, the applications of these established methods in the synthesis of natural products and exploitation of new organic functional materials are exemplified. In the last section, a short introduction on oxidant- or Lewis acid-mediated oxidative Ar-H/Ar-H coupling reactions is presented, considering that it is a very powerful method for the construction of biaryl units and polycylic arenes.

  15. Enhanced Reactivity in Hydrogen Atom Transfer from Tertiary Sites of Cyclohexanes and Decalins via Strain Release: Equatorial C-H Activation vs Axial C-H Deactivation.

    PubMed

    Salamone, Michela; Ortega, Vanesa B; Bietti, Massimo

    2015-05-01

    Absolute rate constants for hydrogen atom transfer (HAT) from cycloalkanes and decalins to the cumyloxyl radical (CumO(•)) were measured by laser flash photolysis. Very similar reactivities were observed for the C-H bonds of cyclopentane and cyclohexane, while the tertiary C-H bond of methylcyclopentane was found to be 6 times more reactive than the tertiary axial C-H bond of methylcyclohexane, pointing toward a certain extent of tertiary axial C-H bond deactivation. Comparison between the cis and trans isomers of 1,2-dimethylcyclohexane, 1,4-dimethylcyclohexane and decalin provides a quantitative evaluation of the role played by strain release in these reactions. kH values for HAT from tertiary equatorial C-H bonds were found to be at least 1 order of magnitude higher than those for HAT from the corresponding tertiary axial C-H bonds (kH(eq)/kH(ax) = 10-14). The higher reactivity of tertiary equatorial C-H bonds was explained in terms of 1,3-diaxial strain release in the HAT transition state. Increase in torsional strain in the HAT transition state accounts instead for tertiary axial C-H bond deactivation. The results are compared with those obtained for the corresponding C-H functionalization reactions by dioxiranes and nonheme metal-oxo species indicating that CumO(•) can represent a convenient model for the reactivity patterns of these oxidants.

  16. Enzyme-controlled nitrogen-atom transfer enables regiodivergent C-H amination.

    PubMed

    Hyster, Todd K; Farwell, Christopher C; Buller, Andrew R; McIntosh, John A; Arnold, Frances H

    2014-11-05

    We recently demonstrated that variants of cytochrome P450BM3 (CYP102A1) catalyze the insertion of nitrogen species into benzylic C-H bonds to form new C-N bonds. An outstanding challenge in the field of C-H amination is catalyst-controlled regioselectivity. Here, we report two engineered variants of P450BM3 that provide divergent regioselectivity for C-H amination-one favoring amination of benzylic C-H bonds and the other favoring homo-benzylic C-H bonds. The two variants provide nearly identical kinetic isotope effect values (2.8-3.0), suggesting that C-H abstraction is rate-limiting. The 2.66-Å crystal structure of the most active enzyme suggests that the engineered active site can preorganize the substrate for reactivity. We hypothesize that the enzyme controls regioselectivity through localization of a single C-H bond close to the iron nitrenoid.

  17. 7-Amino-5-methyl-2-phenyl-6-(phenyldiazenyl)pyrazolo[1,5-a]pyrimidine crystallizes with Z' = 2: pseudosymmetry and the formation of complex sheets built from N-H...N and C-H...pi(arene) hydrogen bonds.

    PubMed

    Portilla, Jaime; Estupiñan, Diego; Cobo, Justo; Glidewell, Christopher

    2010-03-01

    The title compound, C(19)H(16)N(6), crystallizes with Z' = 2 in the space group P2(1)/n. The two molecules in the selected asymmetric unit are approximate mirror images of one another; most corresponding pairs of atoms are related by an approximate half-cell translation along [100]. Each molecule contains an intramolecular N-H...N hydrogen bond and the molecules are linked into complex sheets by a combination of two intermolecular N-H...N and four C-H...pi(arene) hydrogen bonds. Comparisons are made with some other 7-aminopyrazolo[1,5-a]pyrimidines.

  18. Benzylic C-H trifluoromethylation of phenol derivatives.

    PubMed

    Egami, Hiromichi; Ide, Takafumi; Kawato, Yuji; Hamashima, Yoshitaka

    2015-12-04

    Phenol derivatives were trifluoromethylated using copper/Togni reagent. In dimethylformamide, the benzylic C-H bond at the para position of the hydroxyl group was selectively substituted with a CF3 group. In contrast, aromatic C-H trifluoromethylation occurred in alcoholic solvents. Practical utility of the reactions was demonstrated by application to the synthesis of a potent enoyl-acyl carrier protein reductase (FabI) inhibitor.

  19. Low-dimensional hydrogen-bonded structures in the 1:1 and 1:2 proton-transfer compounds of 4,5-dichlorophthalic acid with the aliphatic Lewis bases triethylamine, diethylamine, n-butylamine and piperidine.

    PubMed

    Smith, Graham; Wermuth, Urs D

    2010-07-01

    The structures of the proton-transfer compounds of 4,5-dichlorophthalic acid (DCPA) with the aliphatic Lewis bases triethylamine, diethylamine, n-butylamine and piperidine, namely triethylaminium 2-carboxy-4,5-dichlorobenzoate, C(6)H(16)N(+) x C(8)H(3)Cl(2)O(4)(-), (I), diethylaminium 2-carboxy-4,5-dichlorobenzoate, C(4)H(12)N(+) x C(8)H(3)Cl(2)O(4)(-), (II), bis(butanaminium) 4,5-dichlorobenzene-1,2-dicarboxylate monohydrate, 2C(4)H(12)N(+) x C(8)H(2)Cl(2)O(4)(2-) x H(2)O, (III), and bis(piperidinium) 4,5-dichlorobenzene-1,2-dicarboxylate monohydrate, 2C(5)H(12)N(+) x C(8)H(2)Cl(2)O(4)(2-) x H(2)O, (IV), have been determined at 200 K. All compounds have hydrogen-bonding associations, giving discrete cation-anion units in (I) and linear chains in (II), while (III) and (IV) both have two-dimensional structures. In (I), a discrete cation-anion unit is formed through an asymmetric R(1)(2)(4) N(+)-H...O(2) hydrogen-bonding association, whereas in (II), chains are formed through linear N-H...O associations involving both aminium H-atom donors. In compounds (III) and (IV), the primary N-H...O-linked cation-anion units are extended into a two-dimensional sheet structure via amide-carboxyl N-H...O and amide-carbonyl N-H...O interactions. In the 1:1 salts (I) and (II), the hydrogen 4,5-dichlorophthalate anions are essentially planar with short intramolecular carboxyl-carboxyl O-H...O hydrogen bonds [O...O = 2.4223 (14) and 2.388 (2) A, respectively]. This work provides a further example of the uncommon zero-dimensional hydrogen-bonded DCPA-Lewis base salt and the one-dimensional chain structure type, while even with the hydrate structures of the 1:2 salts with the primary and secondary amines, the low dimensionality generally associated with 1:1 DCPA salts is also found.

  20. The C-H Dissociation Energy of C2H6

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R. (Technical Monitor)

    1994-01-01

    The C-H bond energy in C2H6 is computed to be 99.76 +/- 0.35 kcal/mol, which is in excellent agreement with the most recent experimental values. The calculation of the C-H bond energy by direct dissociation and by an isodesmic reaction is discussed.

  1. Enzyme catalysis: C-H activation is a Reiske business

    NASA Astrophysics Data System (ADS)

    Bruner, Steven D.

    2011-05-01

    Enzymes that selectively oxidize unactivated C-H bonds are capable of constructing complex molecules with high efficiency. A new member of this enzyme family is RedG, a Reiske-type oxygenase that catalyses chemically challenging cyclizations in the biosynthesis of prodiginine natural products.

  2. Differential steric effects in Cl reactions with aligned CHD3(v1 = 1) by the R(0) and Q(1) transitions. I. Attacking the excited C-H bond

    NASA Astrophysics Data System (ADS)

    Wang, Fengyan; Liu, Kopin

    2016-10-01

    When a CHD3 molecule is pumped to the C-H stretching-excited state by absorbing a linearly polarized infrared (IR) photon via the R(0) branch of the v1 = 1←0 transition, the rotational angular momentum j of the prepared state |" separators=" jK > = |" separators=" 10 > preferentially lies in a plane perpendicular to the IR polarization axis ɛIR. By way of contrast, when the Q(1) branch is used, the state of |" separators=" jK > = |" separators=" 1 ± 1 > is prepared with j aligned along the direction of ɛIR. Reported here is a detailed study of the title reaction by actively controlling the collision geometries under these two IR-excitation schemes at collision energy Ec = 8.6 kcal mol-1, using a crossed molecular beam, product imaging approach. We found that under the R(0) excitation, the polarization-dependent differential cross sections for the HCl(v = 0) + CD3(00) channel can largely be understood by invoking dual reaction mechanisms. The forward-scattered products are most likely mediated by a time-delayed resonance mechanism—as the formation of the HCl(v = 1) + CD3(00) channel, whereas the backward/sideways scattered products are governed by a direct abstraction mechanism. Compared to the previous results at lower Ec of 3.8 kcal mol-1, the sighting of opening-up the attack angle at the transition state of the direct pathway is proposed. Results under the Q(1) excitation are, however, perplexing and bear no obvious correlation to the corresponding ones for the R(0) excitation, defying simple intuitive interpretation. Possible reasons are put forward, which call for theoretical investigations for deeper insights. The results on the alternative isotope channel, DCl + CHD2, will be reported in the following paper.

  3. Main group multiple C-H/N-H bond activation of a diamine and isolation of a molecular dilithium zincate hydride: experimental and DFT evidence for alkali metal-zinc synergistic effects.

    PubMed

    Campbell, Ross; Cannon, Daniel; García-Álvarez, Pablo; Kennedy, Alan R; Mulvey, Robert E; Robertson, Stuart D; Sassmannshausen, Jörg; Tuttle, Tell

    2011-08-31

    The surprising transformation of the saturated diamine (iPr)NHCH(2)CH(2)NH(iPr) to the unsaturated diazaethene [(iPr)NCH═CHN(iPr)](2-) via the synergic mixture nBuM, (tBu)(2)Zn and TMEDA (where M = Li, Na; TMEDA = N,N,N',N'-tetramethylethylenediamine) has been investigated by multinuclear NMR spectroscopic studies and DFT calculations. Several pertinent intermediary and related compounds (TMEDA)Li[(iPr)NCH(2)CH(2)NH(iPr)]Zn(tBu)(2) (3), (TMEDA)Li[(iPr)NCH(2)CH(2)CH(2)N(iPr)]Zn(tBu) (5), {(THF)Li[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu)}(2) (6), and {(TMEDA)Na[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu)}(2) (11), characterized by single-crystal X-ray diffraction, are discussed in relation to their role in the formation of (TMEDA)M[(iPr)NCH═CHN(iPr)]Zn(tBu) (M = Li, 1; Na, 10). In addition, the dilithio zincate molecular hydride [(TMEDA)Li](2)[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu)H 7 has been synthesized from the reaction of (TMEDA)Li[(iPr)NCH(2)CH(2)NH(iPr)]Zn(tBu)(2)3 with nBuLi(TMEDA) and also characterized by both X-ray crystallographic and NMR spectroscopic studies. The retention of the Li-H bond of 7 in solution was confirmed by (7)Li-(1)H HSQC experiments. Also, the (7)Li NMR spectrum of 7 in C(6)D(6) solution allowed for the rare observation of a scalar (1)J(Li-H) coupling constant of 13.3 Hz. Possible mechanisms for the transformation from diamine to diazaethene, a process involving the formal breakage of four bonds, have been determined computationally using density functional theory. The dominant mechanism, starting from (TMEDA)Li[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu) (4), involves the formation of a hydride intermediate and leads directly to the observed diazaethene product. In addition the existence of 7 in equilibrium with 4 through the dynamic association and dissociation of a (TMEDA)LiH ligand, also provides a secondary mechanism for the formation of the diazaethene. The two reaction pathways (i.e., starting from 4 or 7) are quite distinct and provide excellent examples in which the

  4. Pd-catalyzed direct C-H bond functionalization of spirocyclic σ1 ligands: generation of a pharmacophore model and analysis of the reverse binding mode by docking into a 3D homology model of the σ1 receptor.

    PubMed

    Meyer, Christina; Schepmann, Dirk; Yanagisawa, Shuichi; Yamaguchi, Junichiro; Dal Col, Valentina; Laurini, Erik; Itami, Kenichiro; Pricl, Sabrina; Wünsch, Bernhard

    2012-09-27

    To explore the hydrophobic binding region of the σ(1) receptor protein, regioisomeric spirocyclic thiophenes 9-11 were developed as versatile building blocks. Regioselective α- and β-arylation using the catalyst systems PdCl(2)/bipy/Ag(2)CO(3) and PdCl(2)/P[OCH(CF(3))(2)](3)/Ag(2)CO(3) allowed the introduction of various aryl moieties at different positions in the last step of the synthesis. The increasing σ(1) affinity in the order 4 < 5/6 < 7/8 indicates that the positions of the additional aryl moiety and the S atom in the spirocyclic thiophene systems control the σ(1) affinity. The main features of the pharmacophore model developed for this class of σ(1) ligands are a positive ionizable group, a H-bond acceptor group, two hydrophobic moieties, and one hydrophobic aromatic group. Docking of the ligands into a σ(1) 3D homology model via molecular mechanics/Poisson-Boltzmann surface area calculations led to a very good correlation between the experimentally determined and estimated free energy of receptor binding. These calculations support the hypothesis of a reverse binding mode of ligands bearing the aryl moiety at the "top" (compounds 2, 3, 7, and 8) and "left" (compounds 4, 5, and 6) positions, respectively.

  5. Scalable and sustainable electrochemical allylic C-H oxidation

    NASA Astrophysics Data System (ADS)

    Horn, Evan J.; Rosen, Brandon R.; Chen, Yong; Tang, Jiaze; Chen, Ke; Eastgate, Martin D.; Baran, Phil S.

    2016-05-01

    New methods and strategies for the direct functionalization of C-H bonds are beginning to reshape the field of retrosynthetic analysis, affecting the synthesis of natural products, medicines and materials. The oxidation of allylic systems has played a prominent role in this context as possibly the most widely applied C-H functionalization, owing to the utility of enones and allylic alcohols as versatile intermediates, and their prevalence in natural and unnatural materials. Allylic oxidations have featured in hundreds of syntheses, including some natural product syntheses regarded as “classics”. Despite many attempts to improve the efficiency and practicality of this transformation, the majority of conditions still use highly toxic reagents (based around toxic elements such as chromium or selenium) or expensive catalysts (such as palladium or rhodium). These requirements are problematic in industrial settings; currently, no scalable and sustainable solution to allylic oxidation exists. This oxidation strategy is therefore rarely used for large-scale synthetic applications, limiting the adoption of this retrosynthetic strategy by industrial scientists. Here we describe an electrochemical C-H oxidation strategy that exhibits broad substrate scope, operational simplicity and high chemoselectivity. It uses inexpensive and readily available materials, and represents a scalable allylic C-H oxidation (demonstrated on 100 grams), enabling the adoption of this C-H oxidation strategy in large-scale industrial settings without substantial environmental impact.

  6. A General Strategy for the Nickel-Catalyzed C-H Alkylation of Anilines.

    PubMed

    Ruan, Zhixiong; Lackner, Sebastian; Ackermann, Lutz

    2016-02-24

    The C-H alkylation of aniline derivatives with both primary and secondary alkyl halides was achieved with a versatile nickel catalyst of a vicinal diamine ligand. Step-economic access to functionalized 2-pyrimidyl anilines, key structural motifs in anticancer drugs, is thus provided. The C-H functionalization proceeded through facile C-H activation and SET-type C-X bond cleavage with the assistance of a monodentate directing group, which could be removed in a traceless fashion.

  7. Pressure-dependent studies on hydration of the C-H group in formic acid

    NASA Astrophysics Data System (ADS)

    Chang, Hai-Chou; Jiang, Jyh-Chiang; Chao, Ming-Chi; Lin, Ming-Shan; Lin, Sheng Hsien; Chen, Hsin-Yen; Hsueh, Hung-Chung

    2001-11-01

    The infrared spectroscopic profiles of HCOOD/D2O mixtures were measured as a function of pressure and concentration. The C-H bond of HCOOD shortens as the pressure is elevated, while the increase in C-H bond length upon diluting HCOOD with D2O was observed. Based on the experimental results, the shift in frequency of C-H stretching band is concluded to relate to the mechanism of the hydration of the C-H group and the water structure in the vicinity of the C-H group. The pressure-dependent results can be attributed to the strengthening of C-H---O electrostatic/dispersion interaction upon increasing pressure. The observations are in accord with ab initio calculation forecasting a blueshift of the C-H stretching mode via C-H---O interaction in HCOOD-water/(HCOOD)2-(D2O) complexes relative to the noninteracting monomer/dimer. Hydrogen-bonding nonadditivity and the size of water clusters are suggested to be responsible to cause the redshift in C-H stretching mode upon dilution HCOOD with D2O.

  8. On the Importance of C-H/π and C-H⋅⋅⋅H-C Interactions in the Solid State Structure of 15-Lipoxygenase Inhibitors Based on Eugenol Derivatives.

    PubMed

    Mirzaei, Masoud; Nikpour, Mohsen; Bauzá, Antonio; Frontera, Antonio

    2015-07-20

    In this manuscript the X-ray structures of two potent and known inhibitors of 15-lipoxygenase, that is, 4-allyl-2-methoxyphenyl-1-admantanecarboxylate (1) and allyl-2-methoxyphenyl-1-cyclohexanecarboxylate (2), are reported. Their solid-state architectures show that they have a strong ability to establish C-H/π and C-H⋅⋅⋅H-C interactions. For the former interaction, the adamantane or cyclohexane moieties are the C-H donors and the electron-rich methoxyphenyl ring is the π system. For the latter, the C-H bonds belong to the aliphatic rings of the inhibitors. Interestingly, the active site of lipoxygenase enzyme family is rich in isoleucine and leucine amino acids that participate in the binding of the unsaturated fatty acid substrate by means of multiple hydrophobic C-H⋅⋅⋅H-C interactions. By means of theoretical calculations, we analyze the ability of compounds 1 and 2 to establish C-H/π and C-H⋅⋅⋅H-C interactions in the solid state.

  9. Pd(II)-catalyzed ortho- or meta-C-H olefination of phenol derivatives.

    PubMed

    Dai, Hui-Xiong; Li, Gang; Zhang, Xing-Guo; Stepan, Antonia F; Yu, Jin-Quan

    2013-05-22

    A combination of weakly coordinating auxiliaries and ligand acceleration allows for the development of both ortho- and meta-selective C-H olefination of phenol derivatives. These reactions demonstrate the feasibility of directing C-H functionalizations when functional groups are distal to target C-H bonds. The meta-C-H functionalization of electron-rich phenol derivatives is unprecedented and orthogonal to previous electrophilic substitution of phenols in terms of regioselectivity. These methods are also applied to functionalize α-phenoxyacetic acids, a fibrate class of drug scaffolds.

  10. Arene-metal π-complexation as a traceless reactivity enhancer for C-H arylation.

    PubMed

    Ricci, Paolo; Krämer, Katrina; Cambeiro, Xacobe C; Larrosa, Igor

    2013-09-11

    Current approaches to facilitate C-H arylation of arenes involve the use of either strongly electron-withdrawing substituents or directing groups. Both approaches require structural modification of the arene, limiting their generality. We present a new approach where C-H arylation is made possible without altering the connectivity of the arene via π-complexation of a Cr(CO)3 unit, greatly enhancing the reactivity of the aromatic C-H bonds. We apply this approach to monofluorobenzenes, highly unreactive arenes, which upon complexation become nearly as reactive as pentafluorobenzene itself in their couplings with iodoarenes. DFT calculations indicate that C-H activation via a concerted metalation-deprotonation transition state is facilitated by the predisposition of C-H bonds in (Ar-H)Cr(CO)3 to bend out of the aromatic plane.

  11. Pushing the limits of catalytic C-H amination in polyoxygenated cyclobutanes.

    PubMed

    Nocquet, Pierre-Antoine; Hensienne, Raphaël; Wencel-Delord, Joanna; Laigre, Eugénie; Sidelarbi, Khadidja; Becq, Frédéric; Norez, Caroline; Hazelard, Damien; Compain, Philippe

    2016-03-07

    A synthetic route to a new class of conformationally constrained iminosugars based on a 5-azaspiro[3.4]octane skeleton has been developed by way of Rh(ii)-catalyzed C(sp(3))-H amination. The pivotal stereocontrolled formation of the quaternary C-N bond by insertion into the C-H bonds of the cyclobutane ring was explored with a series of polyoxygenated substrates. In addition to anticipated regioselective issues induced by the high density of activated α-ethereal C-H bonds, this systematic study showed that cyclobutane C-H bonds were, in general, poorly reactive towards catalytic C-H amination. This was demonstrated inter alia by the unexpected formation of a oxathiazonane derivative, which constitutes a very rare example of the formation of a 9-membered ring by way of catalyzed C(sp(3))-H amination. A complete stereocontrol could be however achieved by activating the key insertion position as an allylic C-H bond in combination with reducing the electron density at the undesired C-H insertion sites by using electron-withdrawing protecting groups. Preliminary biological evaluations of the synthesized spiro-iminosugars were performed, which led to the identification of a new class of correctors of the defective F508del-CFTR gating involved in cystic fibrosis.

  12. Ligand Lone-Pair Influence on Hydrocarbon C-H Activation. A Computational Perspective

    SciTech Connect

    Ess, Daniel H.; Gunnoe, T. Brent; Cundari, Thomas R.; Goddard, William A.; Periana, Roy A.

    2010-12-03

    Mid to late transition metal complexes that break hydrocarbon C-H bonds by transferring the hydrogen to a heteroatom ligand while forming a metal-alkyl bond offer a promising strategy for C-H activation. Here we report a density functional (B3LYP, M06, and X3LYP) analysis of cis-(acac)2MX and TpM(L)X (M = Ir, Ru, Os, and Rh; acac = acetylacetonate, Tp = tris(pyrazolyl)borate; X = CH3, OH, OMe, NH2, and NMe2) systems for methane C-H bond activation reaction kinetics and thermodynamics. We address the importance of whether a ligand lone pair provides an intrinsic kinetic advantage through possible electronic dπ-pπ repulsions for M-OR and M-NR2 systems versus M-CH3 systems. This involves understanding the energetic impact of the X ligand group on ligand loss, C-H bond coordination, and C-H bond cleavage steps as well as understanding how the nucleophilicity of the ligand X group, the electrophilicity of the transition metal center, and cis-ligand stabilization effect influence each of these steps. We also explore how spectator ligands and second- versus third-row transition metal centers impact the energetics of each of these C-H activation steps.

  13. THE CARRIERS OF THE INTERSTELLAR UNIDENTIFIED INFRARED EMISSION FEATURES: AROMATIC OR ALIPHATIC?

    SciTech Connect

    Li Aigen; Draine, B. T. E-mail: draine@astro.princeton.edu

    2012-12-01

    The unidentified infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 {mu}m, commonly attributed to polycyclic aromatic hydrocarbon (PAH) molecules, have been recently ascribed to coal- or kerogen-like organic nanoparticles with a mixed aromatic-aliphatic structure. However, we show in this Letter that this hypothesis is inconsistent with observations. We estimate the aliphatic fraction of the UIE carriers based on the observed intensities of the 3.4 {mu}m and 6.85 {mu}m emission features by attributing them exclusively to aliphatic C-H stretch and aliphatic C-H deformation vibrational modes, respectively. We derive the fraction of carbon atoms in aliphatic form to be <15%. We conclude that the UIE emitters are predominantly aromatic, with aliphatic material at most a minor part of the UIE carriers. The PAH model is consistent with astronomical observations and PAHs dominate the strong UIE bands.

  14. Enantioselective synthesis of planar-chiral benzosiloloferrocenes by Rh-catalyzed intramolecular C-H silylation.

    PubMed

    Shibata, Takanori; Shizuno, Tsubasa; Sasaki, Tomoya

    2015-05-07

    The first synthesis of planar-chiral benzosiloloferrocenes was achieved by the intramolecular reaction of 2-(dimethylhydrosilyl)arylferrocenes. The enantioselective cross dehydrogenative coupling of an sp(2) C-H bond of ferrocene with a Si-H bond proceeded efficiently with the use of a Rh-chiral diene catalyst.

  15. Metal-Catalyzed Azidation of Tertiary C–H Bonds Suitable for Late-Stage Functionalization

    PubMed Central

    Sharma, Ankit

    2014-01-01

    Some enzymes are able to selectively oxidize unactivated aliphatic C-H bonds to form alcohols; however biological systems do not possess enzymes that are able to catalyze the analogous amination of a C-H bond.1,2 The absence of such chemistry is limiting because nitrogen-containing groups are found in therapeutic agents and clinically useful natural products. In one prominent example, the conversion of the ketone of erythromycin to the –N(Me)CH2– group in azithromycin leads to a compound that can be dosed once daily with a shorter length of treatment.3,4 For such reasons, synthetic chemists are very interested in identifying catalysts that can directly convert C-H bonds to C-N bonds. Most currently used catalysts for C-H bond amination are ill suited for the functionalization of complex molecules, because they require excess substrate or directing groups, harsh reaction conditions, weak or acidic C-H bonds, or reagents containing specialized groups on the nitrogen atom.5-14 Among C-H bond amination reactions, those forming a carbon-nitrogen bond at a tertiary alkyl group would be particularly valuable, because this linkage is difficult to generate enzymatically from ketone or alcohol precursors.15 In this manuscript, we report a mild, selective, iron-catalyzed azidation of tertiary C-H bonds with substrate as limiting reagent. The reaction tolerates aqueous environments and is suitable for “late-stage” functionalization of complex structures. Moreover, this azidation creates the ability to install a range of nitrogen functional groups, including those from bio-orthogonal Huisgen “click” cycloadditions and the Staudinger ligation.16-19 For these reasons, we anticipate this methodology will create opportunities to easily modify natural products, their precursors, and their derivatives to analogs that contain distinct polarity and charge from nitrogen-containing groups. It could also be used to help identify targets of biologically active molecules by

  16. C. H. Patterson: The Counselor's Counselor.

    ERIC Educational Resources Information Center

    Goodyear, Rodney K.; Watkins, C. Edward, Jr.

    1983-01-01

    Interviewed C. H. Patterson, spokesperson for client-centered therapy and for counseling itself. Discusses some of the books and articles he has written and their impact on the profession. The interview reviews Patterson's career and focuses on him as a person and as a professional. (JAC)

  17. Trends in applying C-H oxidation to the total synthesis of natural products.

    PubMed

    Qiu, Yuanyou; Gao, Shuanhu

    2016-04-01

    Covering: 2006 to 2015C-H functionalization remains one of the frontier challenges in organic chemistry and drives quite an active area of research. It has recently been applied in various novel strategies for the synthesis of natural products. It can dramatically increase synthetic efficiency when incorporated into retrosynthetic analyses of complex natural products, making it an essential part of current trends in organic synthesis. In this Review, we focus on selected case studies of recent applications of C-H oxidation methodologies in which the C-H bond has been exploited effectively to construct C-O and C-N bonds in natural product syntheses. Examples of syntheses representing different types of C-H oxidation are discussed to illustrate the potential of this approach and inspire future applications.

  18. Enhanced Reactivity in Dioxirane C-H Oxidations via Strain Release: A Computational and Experimental Study

    PubMed Central

    Zou, Lufeng; Paton, Robert S.; Eschenmoser, Albert; Newhouse, Timothy R.; Baran, Phil S.; Houk, K. N.

    2013-01-01

    The site- and stereo-selectivities of C-H oxidations of substituted cyclohexanes and trans-decalins by dimethyldioxirane (DMDO) were investigated computationally with quantum mechanical density functional theory (DFT). The multi-configuration CASPT2 method was employed on model systems to establish the preferred mechanism and transition state geometry. The reaction pathway involving a rebound step is established to account for the retention of stereochemistry. The oxidation of sclareolide with dioxirane reagents is reported, including the oxidation by the in situ generated tBu-TFDO, a new dioxirane that better discriminates between C-H bonds based on steric effects. The release of 1,3-diaxial strain in the transition state contributes to the site selectivity and enhanced axial reactivity for tertiary C-H bonds, a result of the lowering of distortion energy. In addition to this strain release factor, steric and inductive effects contribute to the rates of C-H oxidation by dioxiranes. PMID:23461537

  19. Characterization of nanocomposite a-C:H/Ag thin films synthesized by a hybrid deposition process

    NASA Astrophysics Data System (ADS)

    Venkatesh, M.; Taktak, S.; Meletis, E. I.

    2015-08-01

    Silver containing amorphous carbon films were deposited on Si wafer using a hybrid deposition process combining d.c. magnetron sputtering and PECVD. The concentration of Ag in the films was varied from 1.3 to 8.3 at % by changing d.c. magnetron current of Ag target. The influence of incorporated Ag in the a-C:H on the atomic bond structure of the films were investigated by XPS, FTIR, Raman, and HRTEM methods of analysis. The XPS, FTIR, and Raman studies demonstrated that as the silver concentration increased in the a-C:H, sp2 bonding content increased and a-C:H films changed to more graphitic structure. The high resolution TEM cross sectional studies revealed that crystalline Ag particles formed with a size in the range of 2-4 nm throughout an amorphous a-C:H matrix.

  20. Metal-free oxidation of aromatic carbon-hydrogen bonds through a reverse-rebound mechanism.

    PubMed

    Yuan, Changxia; Liang, Yong; Hernandez, Taylor; Berriochoa, Adrian; Houk, Kendall N; Siegel, Dionicio

    2013-07-11

    Methods for carbon-hydrogen (C-H) bond oxidation have a fundamental role in synthetic organic chemistry, providing functionality that is required in the final target molecule or facilitating subsequent chemical transformations. Several approaches to oxidizing aliphatic C-H bonds have been described, drastically simplifying the synthesis of complex molecules. However, the selective oxidation of aromatic C-H bonds under mild conditions, especially in the context of substituted arenes with diverse functional groups, remains a challenge. The direct hydroxylation of arenes was initially achieved through the use of strong Brønsted or Lewis acids to mediate electrophilic aromatic substitution reactions with super-stoichiometric equivalents of oxidants, significantly limiting the scope of the reaction. Because the products of these reactions are more reactive than the starting materials, over-oxidation is frequently a competitive process. Transition-metal-catalysed C-H oxidation of arenes with or without directing groups has been developed, improving on the acid-mediated process; however, precious metals are required. Here we demonstrate that phthaloyl peroxide functions as a selective oxidant for the transformation of arenes to phenols under mild conditions. Although the reaction proceeds through a radical mechanism, aromatic C-H bonds are selectively oxidized in preference to activated Csp3-H bonds. Notably, a wide array of functional groups are compatible with this reaction, and this method is therefore well suited for late-stage transformations of advanced synthetic intermediates. Quantum mechanical calculations indicate that this transformation proceeds through a novel addition-abstraction mechanism, a kind of 'reverse-rebound' mechanism as distinct from the common oxygen-rebound mechanism observed for metal-oxo oxidants. These calculations also identify the origins of the experimentally observed aryl selectivity.

  1. Cobalt-catalyzed intramolecular C-H amination with arylsulfonyl azides.

    PubMed

    Ruppel, Joshua V; Kamble, Rajesh M; Zhang, X Peter

    2007-11-08

    Cobalt complexes of porphyrins are effective catalysts for intramolecular C-H amination with arylsulfonyl azides. The cobalt-catalyzed process can proceed efficiently under mild and neutral conditions in low catalyst loading without the need of other reagents or additives, generating nitrogen gas as the only byproduct. The catalytic system can be applied to primary, secondary, and tertiary C-H bonds and is suitable for a broad range of arylsulfonyl azides, leading to high-yielding syntheses of various benzosultams.

  2. Binuclear biologically active Co(II) complexes with octazamacrocycle and aliphatic dicarboxylates

    NASA Astrophysics Data System (ADS)

    Tanasković, S. B.; Vučković, G.; Antonijević-Nikolić, M.; Stanojković, T.; Gojgić-Cvijović, G.

    2012-12-01

    Four new cationic Co(II) complexes with N,N',N'',N'''-tetrakis (2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) and dianion of one the aliphatic dicarboxylic acids: butanedioic acid (succinic) acid = succH2, pentanedioic (glutaric) acid = gluH2, hexanedioic acid (adipic) acid = adipH2 or decanedioic acid (sebacic) acid = sebH2 of general formula [Co2(L)(tpmc)](ClO4)2ṡxY, L2- = succ, x = 1, Y = H2O; L = glu, x = 1, Y = H2O; L = adip, x = 1.5, Y = H2O; L = seb, x = 1, Y = CH3CN were isolated. The composition and charge are proposed based on elemental analyses (C, H, N) and electrical conductivity measurements. UV-Vis and FTIR spectral data and magnetic moments were in accordance with high-spin Co(II) state. It is proposed that in all complexes Co(II) is hexa-coordinated out of cyclam ring and that both carboxylic groups from dicarboxylate bridge participate in coordination. Oxygens from one group are most likely bonded to the same Co(II) ion thus forming a four-membered ring. The in vitro antibacterial/antiproliferative activities of the complexes were in some cases enhanced compared with the simple Co(II) salt and free ligands, tested as controls.

  3. Cobalt-catalyzed C-H borylation.

    PubMed

    Obligacion, Jennifer V; Semproni, Scott P; Chirik, Paul J

    2014-03-19

    A family of pincer-ligated cobalt complexes has been synthesized and are active for the catalytic C-H borylation of heterocycles and arenes. The cobalt catalysts operate with high activity and under mild conditions and do not require excess borane reagents. Up to 5000 turnovers for methyl furan-2-carboxylate have been observed at ambient temperature with 0.02 mol % catalyst loadings. A catalytic cycle that relies on a cobalt(I)-(III) redox couple is proposed.

  4. C-H activation reactions as useful tools for medicinal chemists.

    PubMed

    Caro-Diaz, Eduardo J E; Urbano, Mariangela; Buzard, Daniel J; Jones, Robert M

    2016-11-15

    In recent years, there has been an exponential rise in the number of reports describing synthetic methods that utilize catalytic sp(3) and sp(2) C-H bond activation. Many have emerged as powerful synthetic tools for accessing biologically active motifs. Indeed, application to C-C and C-heteroatom bond formation, provides new directives for the construction of new pharmaceutical entities. Herein, we highlight some recent novel C-H activation processes that exemplify the utility of these transformations in medicinal chemistry.

  5. A convenient synthesis of anthranilic acids by Pd-catalyzed direct intermolecular ortho-C-H amidation of benzoic acids.

    PubMed

    Ng, Ka-Ho; Ng, Fo-Ning; Yu, Wing-Yiu

    2012-12-11

    An efficient method for synthesis of anthranilic acids by Pd-catalyzed ortho-C-H amidation of benzoic acids is disclosed. The amidation is proposed to proceed by carboxylate-assisted ortho-C-H palladation to form an arylpalladium(II) complex, followed by nitrene insertion to the Pd-C bond.

  6. alpha-Diimine Ligand Coordination and C H Bond Activation in the Reaction of Os3(CO)10(MeCN)2 with 6-R-2,2'-Bipyridine (where R = Et, Ph): X-ray Diffraction Structures of the Ortho-Metalated

    SciTech Connect

    Carrano, Carl J.; Wang, Xiaoping; Poola, Bhaskar; Powell, Cynthia B.; Richmond, Michael G.

    2009-01-01

    The reactivity of the labile cluster Os3(CO)10(MeCN)2 (1) with the monofunctionalized heterocyclic ligands 6-R-2,2 -bipyridine (where R = Et, Ph) has been investigated. The alkyl-substituted heterocycle 6-Et-2,2 -bipyridine reacts with 1 in refluxing CH2Cl2 to give an isomeric mixture of HOs3(CO)9(N2C12H11) due to cyclometalation of the side-chain ethyl group (2) and ortho metalation of the unsubstituted bipyridine ring (3). The solid-state structure of the latter cluster, HOs3(CO)9(N2C10H6-6-Et) (3), has unequivocally established the site of the C-H bond activation in the product. Treatment of 1 with the aryl-substituted ligand 6-Ph-2,2 -bipyridine proceeds similarly with ortho metalation at the ancillary phenyl group and the C-6 ortho site of the unsubstituted bipyridine ring, as verified by 1H NMR spectroscopy. The X-ray diffraction structure of the thermodynamically more stable bipyridine-metalated cluster HOs3(CO)9(N2C10H6-6-Ph) (5) has been determined. The course of these reactions is discussed with respect to our recent study involving the reaction of cluster 1 with the ligand 6-Me-2,2 -bipyridine. Graphical Abstract The reaction between the labile cluster Os3(CO)10(MeCN)2 (1) and the monofunctionalized heterocyclic ligand 6-Et-2,2 -bipyridine proceeds readily at room temperature to furnish an isomeric mixture of the cyclometalated and ortho-metalated hydride-bridged clusters HOs3(CO)9(N2C12H11) (2 and 3). Treatment of 1 with 6-Ph-2,2 -bipyridine also yields two distinct hydride-containing clusters that result from independent ortho-metalation paths involving the 6-phenyl substituent and unsubstituted bipyridine group. The bipyridine-derived ortho metalation attendant in the new clusters HOs3(CO)9(N2C10H6-6-Et) (3) and HOs3(CO)9(N2C10H6-6-Ph) (5) has been established by X-ray crystallography.

  7. Palladium-catalysed transannular C-H functionalization of alicyclic amines

    NASA Astrophysics Data System (ADS)

    Topczewski, Joseph J.; Cabrera, Pablo J.; Saper, Noam I.; Sanford, Melanie S.

    2016-03-01

    Discovering pharmaceutical candidates is a resource-intensive enterprise that frequently requires the parallel synthesis of hundreds or even thousands of molecules. C-H bonds are present in almost all pharmaceutical agents. Consequently, the development of selective, rapid and efficient methods for converting these bonds into new chemical entities has the potential to streamline pharmaceutical development. Saturated nitrogen-containing heterocycles (alicyclic amines) feature prominently in pharmaceuticals, such as treatments for depression (paroxetine, amitifadine), diabetes (gliclazide), leukaemia (alvocidib), schizophrenia (risperidone, belaperidone), malaria (mefloquine) and nicotine addiction (cytisine, varenicline). However, existing methods for the C-H functionalization of saturated nitrogen heterocycles, particularly at sites remote to nitrogen, remain extremely limited. Here we report a transannular approach to selectively manipulate the C-H bonds of alicyclic amines at sites remote to nitrogen. Our reaction uses the boat conformation of the substrates to achieve palladium-catalysed amine-directed conversion of C-H bonds to C-C bonds on various alicyclic amine scaffolds. We demonstrate this approach by synthesizing new derivatives of several bioactive molecules, including varenicline.

  8. Guided desaturation of unactivated aliphatics

    NASA Astrophysics Data System (ADS)

    Voica, Ana-Florina; Mendoza, Abraham; Gutekunst, Will R.; Fraga, Jorge Otero; Baran, Phil S.

    2012-08-01

    The excision of hydrogen from an aliphatic carbon chain to produce an isolated olefin (desaturation) without overoxidation is one of the most impressive and powerful biosynthetic transformations for which there are no simple and mild laboratory substitutes. The versatility of olefins and the range of reactions they undergo are unsurpassed in functional group space. Thus, the conversion of a relatively inert aliphatic system into its unsaturated counterpart could open new possibilities in retrosynthesis. In this article, the invention of a directing group to achieve such a transformation under mild, operationally simple, metal-free conditions is outlined. This ‘portable desaturase’ (TzoCl) is a bench-stable, commercial entity (Aldrich, catalogue number L510092) that is facile to install on alcohol and amine functionalities to ultimately effect remote desaturation, while leaving behind a synthetically useful tosyl group.

  9. Aliphatic hydrocarbons of the fungi.

    NASA Technical Reports Server (NTRS)

    Weete, J. D.

    1972-01-01

    Review of studies of aliphatic hydrocarbons which have been recently detected in the spores of phytopathogenic fungi, and are found to be structurally very similar to the alkanes of higher plants. It appears that the hydrocarbon components of the few mycelial and yeast forms reported resemble the distribution found in bacteria. The occurence and distribution of these compounds in the fungi is discussed. Suggested functional roles of fungal spore alkanes are presented.

  10. Dirhodium Catalyzed C-H Arene Amination using Hydroxylamines

    PubMed Central

    Paudyal, Mahesh P.; Adebesin, Adeniyi Michael; Burt, Scott R.; Ess, Daniel H.; Ma, Zhiwei; Kürti, László; Falck, John R.

    2016-01-01

    Primary and N-alkyl arylamine motifs are key functional groups in pharmaceuticals, agrochemicals and functional materials as well as in bioactive natural products. However, there is a dearth of generally applicable methods for the direct replacement of aryl hydrogens with –NH2/-NH-alkyl moieties. Here, we present a mild dirhodium-catalyzed C-H amination for conversion of structurally diverse monocyclic and fused aromatics to the corresponding primary and N-alkyl arylamines using either NH2/NHalkyl-O-(sulfonyl)hydroxylamines as aminating agents; the relatively weak RSO2O-N bond functions as an internal oxidant. The methodology is operationally simple, scalable, and fast at or below ambient temperature, furnishing arylamines in moderate-to-good yields and with good regioselectivity. It can be readily extended to the synthesis of fused N-heterocycles. PMID:27609890

  11. C-H and C-N Activation at Redox-Active Pyridine Complexes of Iron.

    PubMed

    MacLeod, K Cory; Lewis, Richard A; DeRosha, Daniel E; Mercado, Brandon Q; Holland, Patrick L

    2017-01-19

    Pyridine activation by inexpensive iron catalysts has great utility, but the steps through which iron species can break the strong (105-111 kcal mol(-1) ) C-H bonds of pyridine substrates are unknown. In this work, we report the rapid room-temperature cleavage of C-H bonds in pyridine, 4-tert-butylpyridine, and 2-phenylpyridine by an iron(I) species, to give well-characterized iron(II) products. In addition, 4-dimethylaminopyridine (DMAP) undergoes room-temperature C-N bond cleavage, which forms a dimethylamidoiron(II) complex and a pyridyl-bridged tetrairon(II) square. These facile bond-cleaving reactions are proposed to occur through intermediates having a two-electron reduced pyridine that bridges two iron centers. Thus, the redox non-innocence of the pyridine can play a key role in enabling high regioselectivity for difficult reactions.

  12. Transition-Metal-Free Deacylative Cleavage of Unstrained C(sp(3))-C(sp(2)) Bonds: Cyanide-Free Access to Aryl and Aliphatic Nitriles from Ketones and Aldehydes.

    PubMed

    Ge, Jing-Jie; Yao, Chuan-Zhi; Wang, Mei-Mei; Zheng, Hong-Xing; Kang, Yan-Biao; Li, Yadong

    2016-01-15

    A transition-metal-free deacylative C(sp(3))-C(sp(2)) bond cleavage for the synthetically practical oxidative amination of ketones and aldehydes to nitriles is first described, using cheap and commercially abundant NaNO2 as the oxidant and the nitrogen source. Various nitriles bearing aryl, heteroaryl, alkyl, and alkenyl groups could be smoothly obtained from ketones and aldehydes in high yields, avoiding highly toxic cyanides or transition metals.

  13. Charge-transfer-directed radical substitution enables para-selective C-H functionalization

    NASA Astrophysics Data System (ADS)

    Boursalian, Gregory B.; Ham, Won Seok; Mazzotti, Anthony R.; Ritter, Tobias

    2016-08-01

    Efficient C-H functionalization requires selectivity for specific C-H bonds. Progress has been made for directed aromatic substitution reactions to achieve ortho and meta selectivity, but a general strategy for para-selective C-H functionalization has remained elusive. Herein we introduce a previously unappreciated concept that enables nearly complete para selectivity. We propose that radicals with high electron affinity elicit arene-to-radical charge transfer in the transition state of radical addition, which is the factor primarily responsible for high positional selectivity. We demonstrate with a simple theoretical tool that the selectivity is predictable and show the utility of the concept through a direct synthesis of aryl piperazines. Our results contradict the notion, widely held by organic chemists, that radical aromatic substitution reactions are inherently unselective. The concept of radical substitution directed by charge transfer could serve as the basis for the development of new, highly selective C-H functionalization reactions.

  14. Analyzing site selectivity in Rh2(esp)2-catalyzed intermolecular C-H amination reactions.

    PubMed

    Bess, Elizabeth N; DeLuca, Ryan J; Tindall, Daniel J; Oderinde, Martins S; Roizen, Jennifer L; Du Bois, J; Sigman, Matthew S

    2014-04-16

    Predicting site selectivity in C-H bond oxidation reactions involving heteroatom transfer is challenged by the small energetic differences between disparate bond types and the subtle interplay of steric and electronic effects that influence reactivity. Herein, the factors governing selective Rh2(esp)2-catalyzed C-H amination of isoamylbenzene derivatives are investigated, where modification to both the nitrogen source, a sulfamate ester, and substrate are shown to impact isomeric product ratios. Linear regression mathematical modeling is used to define a relationship that equates both IR stretching parameters and Hammett σ(+) values to the differential free energy of benzylic versus tertiary C-H amination. This model has informed the development of a novel sulfamate ester, which affords the highest benzylic-to-tertiary site selectivity (9.5:1) observed for this system.

  15. On the aliphatic versus aromatic content of the carriers of the `unidentified' infrared emission features

    NASA Astrophysics Data System (ADS)

    Yang, X. J.; Glaser, R.; Li, Aigen; Zhong, J. X.

    2016-10-01

    Although it is generally accepted that the unidentified infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 μm are characteristic of the stretching and bending vibrations of aromatic hydrocarbon materials, the exact nature of their carriers remains unknown: whether they are free-flying, predominantly aromatic gas-phase molecules, or amorphous solids with a mixed aromatic/aliphatic composition are being debated. Recently, the 3.3 and 3.4 μm features which are commonly respectively attributed to aromatic and aliphatic C-H stretches have been used to place an upper limit of ˜2 per cent on the aliphatic fraction of the UIE carriers (i.e. the number of C atoms in aliphatic chains to that in aromatic rings). Here we further explore the aliphatic versus aromatic content of the UIE carriers by examining the ratio of the observed intensity of the 6.2 μm aromatic C-C feature (I6.2) to that of the 6.85 μm aliphatic C-H deformation feature (I6.85). To derive the intrinsic oscillator strengths of the 6.2 μm stretch (A6.2) and the 6.85 μm deformation (A6.85), we employ density functional theory to compute the vibrational spectra of seven methylated polycyclic aromatic hydrocarbon molecules and their cations. By comparing I6.85/I6.2 with A6.85/A6.2, we derive the fraction of C atoms in methyl(ene) aliphatic form to be at most ˜10 per cent, confirming the earlier finding that the UIE emitters are predominantly aromatic. We have also computed the intrinsic strength of the 7.25 μm feature (A7.25), another aliphatic C-H deformation band. We find that A6.85 appreciably exceeds A7.25. This explains why the 6.85 μm feature is more frequently detected in space than the 7.25 μm feature.

  16. Direct C-H alkylation and indole formation of anilines with diazo compounds under rhodium catalysis.

    PubMed

    Mishra, Neeraj Kumar; Choi, Miji; Jo, Hyeim; Oh, Yongguk; Sharma, Satyasheel; Han, Sang Hoon; Jeong, Taejoo; Han, Sangil; Lee, Seok-Yong; Kim, In Su

    2015-12-18

    The rhodium(III)-catalyzed direct functionalization of aniline C-H bonds with α-diazo compounds is described. These transformations provide a facile construction of ortho-alkylated anilines with diazo malonates or highly substituted indoles with diazo acetoacetates.

  17. Approximate thermochemical tables for some C-H and C-H-O species

    NASA Technical Reports Server (NTRS)

    Bahn, G. S.

    1973-01-01

    Approximate thermochemical tables are presented for some C-H and C-H-O species and for some ionized species, supplementing the JANAF Thermochemical Tables for application to finite-chemical-kinetics calculations. The approximate tables were prepared by interpolation and extrapolation of limited available data, especially by interpolations over chemical families of species. Original estimations have been smoothed by use of a modification for the CDC-6600 computer of the Lewis Research Center PACl Program which was originally prepared for the IBM-7094 computer Summary graphs for various families show reasonably consistent curvefit values, anchored by properties of existing species in the JANAF tables.

  18. Addition, cycloaddition, and metathesis reactions of the cationic carbyne complexes [Cp(CO)[sub 2]Mn[triple bond]CCH[sub 2]R][sup +] and neutral vinylidene complexes Cp(CO)[sub 2]M=C=C(H)R (M = Mn, Re)

    SciTech Connect

    Terry, M.R.; Mercando, L.A.; Kelley, C.; Geoffroy, G.L. ); Nombel, P.; Lugan, N.; Mathieu, R. ); Ostrander, R.L.; Owens-Waltermire, B.E.; Rheingold, A.L. )

    1994-03-01

    The cationic alkylidyne complexes [Cp(CO)[sub 2]M=VCCH[sub 2]R][sup +] (M = Re, R = H; M = Mn, R = H, Me, Ph) undergo facile deprotonation to give the corresponding neutral vinylidene complexes Cp(CO)[sub 2]M=C=C(H)R. For [Cp(CO)[sub 2]Re=VCCH[sub 3

  19. Synthesis of antiviral tetrahydrocarbazole derivatives by photochemical and acid-catalyzed C-H functionalization via intermediate peroxides (CHIPS).

    PubMed

    Gulzar, Naeem; Klussmann, Martin

    2014-06-20

    The direct functionalization of C-H bonds is an important and long standing goal in organic chemistry. Such transformations can be very powerful in order to streamline synthesis by saving steps, time and material compared to conventional methods that require the introduction and removal of activating or directing groups. Therefore, the functionalization of C-H bonds is also attractive for green chemistry. Under oxidative conditions, two C-H bonds or one C-H and one heteroatom-H bond can be transformed to C-C and C-heteroatom bonds, respectively. Often these oxidative coupling reactions require synthetic oxidants, expensive catalysts or high temperatures. Here, we describe a two-step procedure to functionalize indole derivatives, more specifically tetrahydrocarbazoles, by C-H amination using only elemental oxygen as oxidant. The reaction uses the principle of C-H functionalization via Intermediate PeroxideS (CHIPS). In the first step, a hydroperoxide is generated oxidatively using visible light, a photosensitizer and elemental oxygen. In the second step, the N-nucleophile, an aniline, is introduced by Brønsted-acid catalyzed activation of the hydroperoxide leaving group. The products of the first and second step often precipitate and can be conveniently filtered off. The synthesis of a biologically active compound is shown.

  20. Allylic C-H amination for the preparation of syn-1,3-amino alcohol motifs.

    PubMed

    Rice, Grant T; White, M Christina

    2009-08-26

    A highly selective and general Pd/sulfoxide-catalyzed allylic C-H amination reaction en route to syn-1,3-amino alcohol motifs is reported. Key to achieving this reactivity under mild conditions is the use of electron-deficient N-nosyl carbamate nucleophiles that are thought to promote functionalization by furnishing higher concentrations of anionic species in situ. The reaction is shown to be orthogonal to classical C-C bond-forming/-reduction sequences as well as nitrene-based C-H amination methods.

  1. Mechanistic Insight into the Rh(III)-Catalyzed C-H Activation of 2-Acetyl-1-Arythydrazines in Water.

    PubMed

    Wu, Weirong; Liu, Tao; Huang, Caiyun; Zhang, Jing; Man, Xiaoping

    2017-03-02

    A mechanistic study of the Cp*Rh(III)-catalyzed C-H functionalization of 2-acetyl-1-arythydrazines with diazo compounds in water was carried out by using density functional theory calculations. The results reveal that the acetyl-bonded N-H deprotonation is prior to the phenyl C-H activation. The mechanisms from protonation by acetic acid disagree with the proposal by the Wang group. Different from the Rh(III)-catalyzed C-H activation reported by experimental literature, the rate-determining step of the whole catalytic cycle with an overall barrier of 31.7 kcal mol(-1) (IV → TS12-P') is the protonation process of hydroxy O rather than the C-H bond cleavage step. The present theoretical study rationalizes the experimental observation at the molecular level.

  2. Elaboration of copper-oxygen mediated C-H activation chemistry in consideration of future fuel and feedstock generation.

    PubMed

    Lee, Jung Yoon; Karlin, Kenneth D

    2015-04-01

    To contribute solutions to current energy concerns, improvements in the efficiency of dioxygen mediated C-H bond cleavage chemistry, for example, selective oxidation of methane to methanol, could minimize losses in natural gas usage or produce feedstocks for fuels. Oxidative C-H activation is also a component of polysaccharide degradation, potentially affording alternative biofuels from abundant biomass. Thus, an understanding of active-site chemistry in copper monooxygenases, those activating strong C-H bonds is briefly reviewed. Then, recent advances in the synthesis-generation and study of various copper-oxygen intermediates are highlighted. Of special interest are cupric-superoxide, Cu-hydroperoxo and Cu-oxy complexes. Such investigations can contribute to an enhanced future application of C-H oxidation or oxygenation processes using air, as concerning societal energy goals.

  3. Diverse sp3 C-H functionalization through alcohol β-sulfonyloxylation

    NASA Astrophysics Data System (ADS)

    Xu, Yan; Yan, Guobing; Ren, Zhi; Dong, Guangbin

    2015-10-01

    Site-selective C-H functionalization has emerged as an attractive tool for derivatizing complex synthetic intermediates, but its use for late-stage diversification is limited by the functional groups that can be introduced, especially at unactivated sp3-hybridized positions. To overcome this, we introduce a strategy that directly installs a sulfonyloxy group at a β-C-H bond of a masked alcohol and subsequently employs nucleophilic substitution reactions to prepare various derivatives. Hydroxyl groups are widely found in bioactive molecules and are thus readily available as synthetic handles. A directing group is easily added (and subsequently removed) from the alcohols such that a formal site-selective β-C-H sulfonyloxylation of these alcohols is achieved. Substitution reactions with carbon, nitrogen, oxygen and other nucleophiles then lead to diverse functionalizations that may help to streamline the synthesis of complex analogues for drug discovery.

  4. Cp*Rh(III)-Catalyzed Low Temperature C-H Allylation of N-Aryl-trichloro Acetimidamide.

    PubMed

    Debbarma, Suvankar; Bera, Sourav Sekhar; Maji, Modhu Sudan

    2016-12-02

    The readily synthesized trichloro acetimidamide was found to be an excellent directing group for the directed C-H-allylation reactions. Depending on the allylating agent used, selectively either mono- or diallylated products were readily synthesized. Moreover, the trichloro acetimidamide directing group was found to be highly efficient even at lower temperature for the C-H-allylation reaction. Due to mildness of the reaction conditions, double bond isomerization or cyclization to indole side product was not observed.

  5. Mixed aliphatic and aromatic composition of evaporating very small grains in NGC 7023 revealed by the 3.4/3.3 μm ratio

    NASA Astrophysics Data System (ADS)

    Pilleri, P.; Joblin, C.; Boulanger, F.; Onaka, T.

    2015-05-01

    Context. A chemical scenario was proposed for photon-dominated regions (PDRs) according to which UV photons from nearby stars lead to the evaporation of very small grains (VSGs) and the production of gas-phase polycyclic aromatic hydrocarbons (PAHs). Aims: Our goal is to achieve better insight into the composition and evolution of evaporating very small grains (eVSGs) and PAHs through analyzing the infrared (IR) aliphatic and aromatic emission bands. Methods: We combined spectro-imagery in the near- and mid-IR to study the spatial evolution of the emission bands in the prototypical PDR NGC 7023. We used near-IR spectra obtained with the IRC instrument onboard AKARI to trace the evolution of the 3.3 μm and 3.4 μm bands, which are associated with aromatic and aliphatic C-H bonds on PAHs. The spectral fitting involved an additional broad feature centered at 3.45 μm that is often referred to as the plateau. Mid-IR observations obtained with the IRS instrument onboard the Spitzer Space Telescope were used to distinguish the signatures of eVSGs and neutral and cationic PAHs. We correlated the spatial evolution of all these bands with the intensity of the UV field given in units of the Habing field G0 to explore how their carriers are processed. Results: The intensity of the 3.45 μm plateau shows an excellent correlation with that of the 3.3 μm aromatic band (correlation coefficient R = 0.95) and a relatively poor correlation with the aliphatic 3.4 μm band (R = 0.77). This indicates that the 3.45 μm feature is dominated by the emission from aromatic bonds. We show that the ratio of the 3.4 μm and 3.3 μm band intensity (I3.4/I3.3) decreases by a factor of 4 at the PDR interface from the more UV-shielded layers (G0 ~ 150,I3.4/I3.3 = 0.13) to the more exposed layers (G0> 1 × 104,I3.4/I3.3 = 0.03). The intensity of the 3.3 μm band relative to the total neutral PAH intensity shows an overall increase with G0, associated with an increase of both the hardness of the

  6. Folding and self-assembly of aromatic and aliphatic urea oligomers: towards connecting structure and function.

    PubMed

    Fischer, Lucile; Guichard, Gilles

    2010-07-21

    Folding and self-assembly of biomacromolecules has inspired the development of discrete, non-natural oligomers that fold and/or self-assemble in a controlled manner. Though aromatic and aliphatic oligoamides remain unmatched for structural diversity and synthetic versatility, oligomers based on amide bond surrogates, such as urea backbones, also demonstrated a propensity for folding and self-assembly. In this Perspective, we review the advances in the design of oligomeric aromatic and aliphatic urea sequences (essentially N,N'-linked) that fold and/or self-assemble. Whenever applicable, the relationship between structure and function will be highlighted.

  7. Conversion of 1-alkenes into 1,4-diols through an auxiliary-mediated formal homoallylic C-H oxidation.

    PubMed

    Ghavtadze, Nugzar; Melkonyan, Ferdinand S; Gulevich, Anton V; Huang, Chunhui; Gevorgyan, Vladimir

    2014-02-01

    The ubiquitous nature of C-H bonds in organic molecules makes them attractive as a target for rapid complexity generation, but brings with it the problem of achieving selective reactions. In developing new methodologies for C-H functionalization, alkenes are an attractive starting material because of their abundance and low cost. Here we describe the conversion of 1-alkenes into 1,4-diols. The method involves the installation of a new Si,N-type chelating auxiliary group on the alkene followed by iridium-catalysed C-H silylation of an unactivated δ-C(sp(3))-H bond to produce a silolane intermediate. Oxidation of the C-Si bonds affords a 1,4-diol. The method is demonstrated to have broad scope and good functional group compatibility by application to the selective 1,4-oxygenation of several natural products and derivatives.

  8. Late-Stage Diversification of Biologically Active Molecules via Chemoenzymatic C-H Functionalization.

    PubMed

    Durak, Landon J; Payne, James T; Lewis, Jared C

    2016-03-04

    Engineered variants of rebeccamycin halogenase were used to selectively halogenate a number of biologically active aromatic compounds. Subsequent Pd-catalyzed cross-coupling reactions on the crude extracts of these reactions were used to install aryl, amine, and ether substituents at the halogenation site. This simple, chemoenzymatic method enables non-directed functionalization of C-H bonds on a range of substrates to provide access to derivatives that would be challenging or inefficient to prepare by other means.

  9. Ruthenium(II)-catalyzed C-H activation with isocyanates: a versatile route to phthalimides.

    PubMed

    De Sarkar, Suman; Ackermann, Lutz

    2014-10-20

    A cationic ruthenium(II)-complex was utilized in the efficient synthesis of phthalimide derivatives by C-H activation with synthetically useful amides. The reaction proceeded through a mechanistically unique insertion of a cycloruthenated species into a C-Het multiple bond of isocyanate. The novel method also proved applicable for the synthesis of heteroaromatic unsymmetric diamides as well as a potent COX-2 enzyme inhibitor.

  10. Carbon dioxide utilization via carbonate-promoted C-H carboxylation.

    PubMed

    Banerjee, Aanindeeta; Dick, Graham R; Yoshino, Tatsuhiko; Kanan, Matthew W

    2016-03-10

    Using carbon dioxide (CO2) as a feedstock for commodity synthesis is an attractive means of reducing greenhouse gas emissions and a possible stepping-stone towards renewable synthetic fuels. A major impediment to synthesizing compounds from CO2 is the difficulty of forming carbon-carbon (C-C) bonds efficiently: although CO2 reacts readily with carbon-centred nucleophiles, generating these intermediates requires high-energy reagents (such as highly reducing metals or strong organic bases), carbon-heteroatom bonds or relatively acidic carbon-hydrogen (C-H) bonds. These requirements negate the environmental benefit of using CO2 as a substrate and limit the chemistry to low-volume targets. Here we show that intermediate-temperature (200 to 350 degrees Celsius) molten salts containing caesium or potassium cations enable carbonate ions (CO3(2-)) to deprotonate very weakly acidic C-H bonds (pKa > 40), generating carbon-centred nucleophiles that react with CO2 to form carboxylates. To illustrate a potential application, we use C-H carboxylation followed by protonation to convert 2-furoic acid into furan-2,5-dicarboxylic acid (FDCA)--a highly desirable bio-based feedstock with numerous applications, including the synthesis of polyethylene furandicarboxylate (PEF), which is a potential large-scale substitute for petroleum-derived polyethylene terephthalate (PET). Since 2-furoic acid can readily be made from lignocellulose, CO3(2-)-promoted C-H carboxylation thus reveals a way to transform inedible biomass and CO2 into a valuable feedstock chemical. Our results provide a new strategy for using CO2 in the synthesis of multi-carbon compounds.

  11. Carbon dioxide utilization via carbonate-promoted C-H carboxylation

    NASA Astrophysics Data System (ADS)

    Banerjee, Aanindeeta; Dick, Graham R.; Yoshino, Tatsuhiko; Kanan, Matthew W.

    2016-03-01

    Using carbon dioxide (CO2) as a feedstock for commodity synthesis is an attractive means of reducing greenhouse gas emissions and a possible stepping-stone towards renewable synthetic fuels. A major impediment to synthesizing compounds from CO2 is the difficulty of forming carbon-carbon (C-C) bonds efficiently: although CO2 reacts readily with carbon-centred nucleophiles, generating these intermediates requires high-energy reagents (such as highly reducing metals or strong organic bases), carbon-heteroatom bonds or relatively acidic carbon-hydrogen (C-H) bonds. These requirements negate the environmental benefit of using CO2 as a substrate and limit the chemistry to low-volume targets. Here we show that intermediate-temperature (200 to 350 degrees Celsius) molten salts containing caesium or potassium cations enable carbonate ions (CO32-) to deprotonate very weakly acidic C-H bonds (pKa > 40), generating carbon-centred nucleophiles that react with CO2 to form carboxylates. To illustrate a potential application, we use C-H carboxylation followed by protonation to convert 2-furoic acid into furan-2,5-dicarboxylic acid (FDCA)—a highly desirable bio-based feedstock with numerous applications, including the synthesis of polyethylene furandicarboxylate (PEF), which is a potential large-scale substitute for petroleum-derived polyethylene terephthalate (PET). Since 2-furoic acid can readily be made from lignocellulose, CO32--promoted C-H carboxylation thus reveals a way to transform inedible biomass and CO2 into a valuable feedstock chemical. Our results provide a new strategy for using CO2 in the synthesis of multi-carbon compounds.

  12. Anaerobic digestion of aliphatic polyesters.

    PubMed

    Šmejkalová, Pavla; Kužníková, Veronika; Merna, Jan; Hermanová, Soňa

    2016-01-01

    Anaerobic processes for the treatment of plastic materials waste represent versatile and effective approach in environmental protection and solid waste management. In this work, anaerobic biodegradability of model aliphatic polyesters, poly(L-lactic acid) (PLA), and poly(ɛ-caprolactone) (PCL), in the form of powder and melt-pressed films with varying molar mass, was studied. Biogas production was explored in batch laboratory trials at 55 ± 1°C under a nitrogen atmosphere. The inoculum used was thermophilic digested sludge (total solids concentration of 2.9%) from operating digesters at the Central Waste Water Treatment Plant in Prague, Czech Republic. Methanogenic biodegradation of PCLs typically yielded from 54 to 60% of the theoretical biogas yield. The biodegradability of PLAs achieved from 56 to 84% of the theoretical value. High biogas yield (up to 677 mL/g TS) with high methane content (more than 60%), comparable with conventionally processed materials, confirmed the potential of polyester samples for anaerobic treatment in the case of their exploitation in agriculture or as a packaging material in the food industry.

  13. Enantiotopos-selective C-H oxygenation catalyzed by a supramolecular ruthenium complex.

    PubMed

    Frost, James R; Huber, Stefan M; Breitenlechner, Stefan; Bannwarth, Christoph; Bach, Thorsten

    2015-01-07

    Spirocyclic oxindoles undergo an enantioselective oxygenation reaction (nine examples; e.r. up to 97:3) upon catalysis by a chiral ruthenium porphyrin complex (1 mol %). The catalyst exhibits a lactam ring, which is responsible for substrate association through hydrogen bonds, and an active ruthenium center, which is in a defined spatial relationship to the oxygenation substrate. DFT calculations illustrate the perfect alignment of the active site with the reactive C-H bond and suggest--in line with the kinetic isotope effect--an oxygen rebound mechanism for the reaction.

  14. C-H Hot Bands in the Near-IR Emission Spectra of Leonids

    NASA Technical Reports Server (NTRS)

    Freund, F. T.; Scoville, J.; Holm, R.; Seelemann, R.; Freund, M. M.

    2002-01-01

    The reported infrared (IR) emission spectra from 1999 Leonid fireballs show a 3.4 micron C-H emission band and unidentified bands at longer wavelengths. Upon atmospheric entry, the Leonid meteorites were flash-heated to temperatures around 2400K, which would destroy any organics on the surface of the meteorite grains. We propose that the nu(sub )CH emission band in the Leonid emission spectra arises from matrix-embedded C(sub n)-H-O entities that are protected from instant pyrolysis. Our model is based on IR absorption nu(sub )CH bands, which we observed in laboratory-grown MgO and natural olivine single crystals, where they arise from C(sub n)-H-O units imbedded in the mineral matrix, indicative of aliphatic -CH2- and -CH3 organics. Instead of being pyrolyzed, the C(sub n)-H-O entities in the Leonid trails become vibrationally excited to higher levels n = 1, 2, 3 etc. During de-excitation they emit at 3.4 microns, due to the (0 => 1) transition, and at longer wavelengths, due to hot bands. As a first step toward verifying this hypothesis we measured the C-H vibrational manifold of hexane (C6H14). The calculated positions of the (2 => l ) , (3 => 2), and possibly (4 => 3) hot bands agree with the Leonid emission bands at 3.5, 3.8 and 4.l microns.

  15. RIR MAPLE procedure for deposition of carbon rich Si/C/H films

    NASA Astrophysics Data System (ADS)

    Dřínek, Vladislav; Strašák, Tomáš; Novotný, Filip; Fajgar, Radek; Bastl, Zdeněk

    2014-02-01

    We applied the resonant infrared matrix assisted pulsed laser evaporation (RIR MAPLE) technique to demonstrate a new approach to a controlled deposition of carbon rich amorphous Si/C/H film. In absence of radicals and accelerated species commonly generated in PECVD and sputtering setups, the RIR MAPLE method does not decompose precursor molecules. Moreover, unlike the standard MAPLE procedure, in which solvent molecules absorb laser energy from excimer or near infrared lasers, we applied the pulsed TEA CO2 laser to excite the dendrimer precursor molecules in a frozen target. In this manner we achieved just cross-linking of the starting precursor on substrates and the deposition of carbon rich Si/C/H film. The film was analyzed by Fourier Transformed Infrared (FTIR), UV/VIS, Raman and X-ray Photoelectron (XPS) spectroscopy and Atomic Force Microscopy (AFM) technique. According to analyses the film retained the precursor elemental composition free of graphitic (sp2) clusters. In course of reaction only the peripheral allyl groups containing C=C bonds were opened to achieve cross-linking. Whereas annealing to 300 °C was necessary for the elimination of =C-H1, 2 bonds in the films prepared at 200 °C, those bonds vanished completely for the films prepared at substrate temperature 255 °C. The film posseses a smooth surface with root mean square (RMS) parameter up to 10 nm within scanned distance 2.5 μm.

  16. Ruthenium-Catalyzed Ortho C-H Arylation of Aromatic Nitriles with Arylboronates and Observation of Partial Para Arylation.

    PubMed

    Koseki, Yuta; Kitazawa, Kentaroh; Miyake, Masashi; Kochi, Takuya; Kakiuchi, Fumitoshi

    2016-12-29

    Ruthenium-catalyzed C-H arylation of aromatic nitriles with arylboronates is described. The use of RuH2(CO){P(4-MeC6H4)3}3 as a catalyst provided higher yields of the ortho arylation products than the conventional RuH2(CO)(PPh3)3 catalyst. The arylation takes place mostly at the ortho positions, but unprecedented para arylation was also partially observed to give ortho,para diarylation products. In addition to C-H bond cleavage, the cyano group was also found to function as a directing group for cleavage of C-O bonds in aryl ethers.

  17. Palladium(II)-catalyzed ortho-C-H arylation/alkylation of N-benzoyl α-amino ester derivatives.

    PubMed

    Misal Castro, Luis C; Chatani, Naoto

    2014-04-14

    The palladium-catalyzed arylation/alkylation of ortho-C-H bonds in N-benzoyl α-amino ester derivatives is described. In such a system both the NH-amido and the CO2R groups in the α-amino ester moieties play a role in successful C-H activation/C-C bond formation using iodoaryl coupling partners. A wide variety of functional groups and electron-rich/deficient iodoarenes are tolerated. The yields obtained range from 20 to 95%.

  18. Aliphatic amine responsive organogel system based on a simple naphthalimide derivative.

    PubMed

    Cao, Xinhua; Zhang, Tingting; Gao, Aiping; Li, Keli; Cheng, Qiuli; Song, Lijuan; Zhang, Min

    2014-09-07

    A new gelator 1 based on a simple naphthalimide derivative was synthesized and fully characterized. It was found that the organogel 1 was formed only in a mixed solvent of methanol and H2O (1/1, v/v). The organogel was thoroughly characterized by using various microscopic techniques including field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and UV-vis, fluorescence and Fourier transform infrared (FTIR) spectroscopy. Hydrogen bonds were the main driving force for the organogel formation. Interestingly, the organogel 1 exhibited the ability to distinguish aliphatic amines from aromatic amines. The gel state and fluorescence emission intensity were both changed after two minutes after the addition of aliphatic amines. This organogel system could be applied in the detection of aliphatic amine pollutants.

  19. Role of Lewis acid additives in a palladium catalyzed directed C-H functionalization reaction of benzohydroxamic acid to isoxazolone.

    PubMed

    Athira, C; Sunoj, Raghavan B

    2016-12-20

    Metallic salts as well as protic additives are widely employed in transition metal catalyzed C-H bond functionalization reactions to improve the efficiency of catalytic protocols. In one such example, ZnCl2 and pivalic acid are used as additives in a palladium catalyzed synthesis of isoxazolone from a readily available benzohydroxamic acid under one pot conditions. In this article, we present some important mechanistic insights into the role of ZnCl2 and pivalic acid, gained by using density functional theory (M06) computations. Two interesting modes of action of ZnCl2 are identified in various catalytic steps involved in the formation of isoxazolone. The conventional Lewis acid coordination wherein zinc chloride (ZnCl2·(DMA)) binds to the carbonyl group is found to be more favored in the C-H activation step. However, the participation of a hetero-bimetallic Pd-Zn species is preferred in reductive elimination leading to Caryl-N bond formation. Pivalic acid helps in relay proton transfer in C-H bond activation through a cyclometallation deprotonation (CMD) process. The explicit inclusion of ZnCl2 and solvent N,N-dimethyl acetamide (DMA) stabilizes the transition state and also helps reduce the activation barrier for the C-H bond activation step. The electronic communication between the two metal species is playing a crucial role in stabilizing the Caryl-N bond formation transition state through a Pd-Zn hetero-bimetallic interaction.

  20. Protonated alcohols are examples of complete charge-shift bonds.

    PubMed

    Anderson, Peter; Petit, Alban; Ho, Junming; Mitoraj, Mariusz Pawel; Coote, Michelle L; Danovich, David; Shaik, Sason; Braïda, Benoît; Ess, Daniel H

    2014-11-07

    Accurate gas-phase and solution-phase valence bond calculations reveal that protonation of the hydroxyl group of aliphatic alcohols transforms the C-O bond from a principally covalent bond to a complete charge-shift bond with principally "no-bond" character. All bonding in this charge-shift bond is due to resonance between covalent and ionic structures, which is a different bonding mechanism from that of traditional covalent bonds. Until now, charge-shift bonds have been previously identified in inorganic compounds or in exotic organic compounds. This work showcases that charge-shift bonds can occur in common organic species.

  1. Probing C-H⋯N interaction in acetylene-benzonitrile complex using matrix isolation infrared spectroscopy and DFT computations

    NASA Astrophysics Data System (ADS)

    Gopi, R.; Ramanathan, N.; Sundararajan, K.

    2017-04-01

    Hydrogen-bonded complexes of acetylene (C2H2) and the benzonitrile (C6H5CN) have been investigated using matrix isolation infrared spectroscopy and DFT computations. The structure of the complexes and the energies were computed at B3LYP and B3LYP+D3 levels of theory using 6-311++G (d, p) and aug-cc-pVDZ basis sets. DFT computations indicated two minima corresponding to the C-H⋯N (global) and C-H⋯π interactions (local) of 1:1 C2H2-C6H5CN complexes, where C2H2 is the proton donor in both complexes. Experimentally, the 1:1 C-H⋯N complex identified from the shifts in the C-H and Ctbnd N stretching modes corresponding to the C2H2 and C6H5CN sub-molecules in N2 and Ar matrices. Atoms in Molecules and Natural Bond Orbital analyses were performed to understand the nature of interaction and to unravel the reasons for red-shifting of the C-H stretching frequency in these complexes. Energy decomposition analysis was carried out to discern the various stabilizing and destabilizing components as a result of hydrogen bonding in the C2H2-C6H5CN complexes.

  2. Iodine-mediated [Formula: see text] C-H functionalization of methyl ketones: a one-pot synthesis of functionalized indolizines via the 1,3-dipolar cycloaddition reaction between pyridinium ylides and ynones.

    PubMed

    Yavari, Issa; Sheykhahmadi, Jamil; Naeimabadi, Maryam; Halvagar, Mohammad Reza

    2017-02-01

    An efficient transition-metal-free approach toward C-H bond activation by using molecular [Formula: see text]-mediated [Formula: see text] C-H bond functionalization for the synthesis of indolizine derivatives via 1,3-dipolar cycloaddition reaction of nitrogen ylides with ynones is described.

  3. para-C-H Borylation of Benzene Derivatives by a Bulky Iridium Catalyst.

    PubMed

    Saito, Yutaro; Segawa, Yasutomo; Itami, Kenichiro

    2015-04-22

    A highly para-selective aromatic C-H borylation has been accomplished. By a new iridium catalyst bearing a bulky diphosphine ligand, Xyl-MeO-BIPHEP, the C-H borylation of monosubstituted benzenes can be affected with para-selectivity up to 91%. This catalytic system is quite different from the usual iridium catalysts that cannot distinguish meta- and para-C-H bonds of monosubstituted benzene derivatives, resulting in the preferred formation of meta-products. The para-selectivity increases with increasing bulkiness of the substituent on the arene, indicating that the regioselectivity of the present reaction is primarily controlled by steric repulsion between substrate and catalyst. Caramiphen, an anticholinergic drug used in the treatment of Parkinson's disease, was converted into five derivatives via our para-selective borylation. The present [Ir(cod)OH]2/Xyl-MeO-BIPHEP catalyst represents a unique, sterically controlled, para-selective, aromatic C-H borylation system that should find use in streamlined, predictable chemical synthesis and in the rapid discovery and optimization of pharmaceuticals and materials.

  4. The galactic distribution of aliphatic hydrocarbons in the diffuse interstellar medium

    NASA Technical Reports Server (NTRS)

    Sandford, Scott A.; Pendleton, Yvonne J.; Allamandola, Louis J.

    1995-01-01

    The infrared absorption feature near 2950(exp -1) (3.4 micron), characteristic of dust in the diffuse interstellar medium (ISM), is attributed to C-H stretching vibrations of aliphatic hydrocarbons. We show here that the strength of the band does not scale linearly with visual extinction everywhere, but instead increases more rapidly for objects near the center of the Galaxy, a behavior that parallels that of the Si-O stretching band due to silicate materials in the diffuse ISM. This implies that the grains responsible for the diffuse medium aliphatic C-H and silicate Si-O stretching bands are different from those responsible for much of the observed visual extinction. It also suggests that the distribution of the carbonaceous component of the diffuse ISM is not uniform throughout the Galaxy, but instead may increase in density toward the center of the Galaxy. The similar behavior of the C-H and Si-O stretching bands suggests that these two components may be coupled, perhaps in the form of silicate-core, organic-mantle grains. Several possible models of the distribution of this material are presented and it is demonstrated that the inner parts of the Galaxy has a carrier density that is 5 to 35 times higher than in the local ISM. Depending on the model used, the density of aliphatic material in the local ISM is found to be about 1 to 2 -CH3 groups m(exp -3) and about 2 to 5 -CH2- groups m(exp -3). These densities are consistent with the strengths of the 2955 and 2925 cm(exp -1) (3.4 micron) band being described by the relations A(sub nu)/tau(sub 2955 cm(exp -1)) = 270 +/- 40 and A(sub nu)/tau(sub 2925 cm(exp -1)) = 250 +/- 40 in the local diffuse ISM.

  5. Complementation of biotransformations with chemical C-H oxidation: copper-catalyzed oxidation of tertiary amines in complex pharmaceuticals.

    PubMed

    Genovino, Julien; Lütz, Stephan; Sames, Dalibor; Touré, B Barry

    2013-08-21

    The isolation, quantitation, and characterization of drug metabolites in biological fluids remain challenging. Rapid access to oxidized drugs could facilitate metabolite identification and enable early pharmacology and toxicity studies. Herein, we compared biotransformations to classical and new chemical C-H oxidation methods using oxcarbazepine, naproxen, and an early compound hit (phthalazine 1). These studies illustrated the low preparative efficacy of biotransformations and the inability of chemical methods to oxidize complex pharmaceuticals. We also disclose an aerobic catalytic protocole (CuI/air) to oxidize tertiary amines and benzylic CH's in drugs. The reaction tolerates a broad range of functionalities and displays a high level of chemoselectivity, which is not generally explained by the strength of the C-H bonds but by the individual structural chemotype. This study represents a first step toward establishing a chemical toolkit (chemotransformations) that can selectively oxidize C-H bonds in complex pharmaceuticals and rapidly deliver drug metabolites.

  6. Enantioselective amine α-functionalization via palladium-catalysed C-H arylation of thioamides

    NASA Astrophysics Data System (ADS)

    Jain, Pankaj; Verma, Pritha; Xia, Guoqin; Yu, Jin-Quan

    2016-10-01

    Saturated aza-heterocycles are highly privileged building blocks that are commonly encountered in bioactive compounds and approved therapeutic agents. These N-heterocycles are also incorporated as chiral auxiliaries and ligands in asymmetric synthesis. As such, the development of methods to functionalize the α-methylene C-H bonds of these systems enantioselectively is of great importance, especially in drug discovery. Currently, enantioselective lithiation with (-)-sparteine followed by Pd(0) catalysed cross-coupling to prepare α-arylated amines is largely limited to pyrrolidines. Here we report a Pd(II)-catalysed enantioselective α-C-H coupling of a wide range of amines, which include ethyl amines, azetidines, pyrrolidines, piperidines, azepanes, indolines and tetrahydroisoquinolines. Chiral phosphoric acids are demonstrated as effective anionic ligands for the enantioselective coupling of methylene C-H bonds with aryl boronic acids. This catalytic reaction not only affords high enantioselectivities, but also provides exclusive regioselectivity in the presence of two methylene groups in different steric environments.

  7. Aliphatic amines in the Murchison meteorite

    NASA Technical Reports Server (NTRS)

    Jungclaus, G.; Cronin, J. R.; Moore, C. B.; Yuen, G. U.

    1976-01-01

    The paper reports on the determination of aliphatic amines in water extracts of the Murchison meteorite. The amines were analyzed by gas chromatography both as the free amines and as 2,4-dinitrophenyl (DNP) derivatives. The results give evidence for the presence of all of the possible primary aliphatic monoamines (eight) with fewer than five carbon atoms. Two of the seven possible secondary or tertiary aliphatic monoamines were identified. The identified primary amines total 80 nmol per g meteorite, and seem to be chemically or physically trapped in the meteorite. Similarities between the water-extractable amines and amino acids suggest that (1) a simple carbon compound, methane, for example, is the precursor of meteorite amines and amino acids, and (2) both amines and amino acids are extracted from the meteorite both as such and in the form of acid-hydrolyzable derivative or precursor species.

  8. Microbial degradation of aliphatic and aliphatic-aromatic co-polyesters.

    PubMed

    Shah, Aamer Ali; Kato, Satoshi; Shintani, Noboru; Kamini, Numbi Ramudu; Nakajima-Kambe, Toshiaki

    2014-04-01

    Biodegradable plastics (BPs) have attracted much attention since more than a decade because they can easily be degraded by microorganisms in the environment. The development of aliphatic-aromatic co-polyesters has combined excellent mechanical properties with biodegradability and an ideal replacement for the conventional nondegradable thermoplastics. The microorganisms degrading these polyesters are widely distributed in various environments. Although various aliphatic, aromatic, and aliphatic-aromatic co-polyester-degrading microorganisms and their enzymes have been studied and characterized, there are still many groups of microorganisms and enzymes with varying properties awaiting various applications. In this review, we have reported some new microorganisms and their enzymes which could degrade various aliphatic, aromatic, as well as aliphatic-aromatic co-polyesters like poly(butylene succinate) (PBS), poly(butylene succinate)-co-(butylene adipate) (PBSA), poly(ε-caprolactone) (PCL), poly(ethylene succinate) (PES), poly(L-lactic acid) (PLA), poly(3-hydroxybutyrate) and poly(3-hydoxybutyrate-co-3-hydroxyvalterate) (PHB/PHBV), poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(butylene adipate-co-terephthalate (PBAT), poly(butylene succinate-co-terephthalate) (PBST), and poly(butylene succinate/terephthalate/isophthalate)-co-(lactate) (PBSTIL). The mechanism of degradation of aliphatic as well as aliphatic-aromatic co-polyesters has also been discussed. The degradation ability of microorganisms against various polyesters might be useful for the treatment and recycling of biodegradable wastes or bioremediation of the polyester-contaminated environments.

  9. C-H activation: Complex peptides made simple

    NASA Astrophysics Data System (ADS)

    Bartlett, Sean; Spring, David R.

    2017-01-01

    Nature oxidizes biosynthetic intermediates into structurally and functionally diverse peptides. An iron-catalysed C-H oxidation mimics this approach in the lab, enabling chemists to synthesize structural analogues with ease.

  10. Oxidative esterification via photocatalytic C-H activation

    EPA Science Inventory

    Direct oxidative esterification of alcohol via photocatalytic C-H activation has been developed using VO@g-C3N4 catalyst; an expeditious esterification of alcohols occurs under neutral conditions using visible light as the source of energy.

  11. Gold(I)-mediated C-H activation of arenes.

    PubMed

    Lu, Pengfei; Boorman, Tanya C; Slawin, Alexandra M Z; Larrosa, Igor

    2010-04-28

    We demonstrate the first Au(I)-mediated C-H activation of arenes. Au(I) salts undergo C-H activation with electron-poor arenes, in stark contrast to Au(III) salts, which activate electron-rich arenes. This operationally simple and highly regioselective process occurs under very mild conditions and gives access to a variety of Au(I)-arene complexes in excellent yields.

  12. Iridium-catalyzed C-H borylation of heteroarenes: scope, regioselectivity, application to late-stage functionalization, and mechanism.

    PubMed

    Larsen, Matthew A; Hartwig, John F

    2014-03-19

    A study on the iridium-catalyzed C-H borylation of heteroarenes is reported. Several heteroarenes containing multiple heteroatoms were found to be amenable to C-H borylation catalyzed by the combination of an iridium(I) precursor and tetramethylphenanthroline. The investigations of the scope of the reaction led to the development of powerful rules for predicting the regioselectivity of borylation, foremost of which is that borylation occurs distal to nitrogen atoms. One-pot functionalizations are reported of the heteroaryl boronate esters formed in situ, demonstrating the usefulness of the reported methodology for the synthesis of complex heteroaryl structures. Application of this methodology to the synthesis and late-stage functionalization of biologically active compounds is also demonstrated. Mechanistic studies show that basic heteroarenes can bind to the catalyst and alter the resting state from the olefin-bound complex observed during arene borylation to a species containing a bound heteroarene, leading to catalyst deactivation. Studies on the origins of the observed regioselectivity show that borylation occurs distal to N-H bonds due to rapid N-H borylation, creating an unfavorable steric environment for borylation adjacent to these bonds. Computational studies and mechanistic studies show that the lack of observable borylation of C-H bonds adjacent to basic nitrogen is not the result of coordination to a bulky Lewis acid prior to C-H activation, but the combination of a higher-energy pathway for the borylation of these bonds relative to other C-H bonds and the instability of the products formed from borylation adjacent to basic nitrogen.

  13. CCN activity of aliphatic amine secondary aerosol

    NASA Astrophysics Data System (ADS)

    Tang, X.; Price, D.; Praske, E.; Vu, D.; Purvis-Roberts, K.; Silva, P. J.; Cocker, D. R., III; Asa-Awuku, A.

    2014-01-01

    Aliphatic amines can form secondary aerosol via oxidation with atmospheric radicals (e.g. hydroxyl radical and nitrate radical). The particle composition can contain both secondary organic aerosol (SOA) and inorganic salts. The fraction of organic to inorganic materials in the particulate phase influences aerosol hygroscopicity and cloud condensation nuclei (CCN) activity. SOA formed from trimethylamine (TMA) and butylamine (BA) reactions with hydroxyl radical (OH) is composed of organic material of low hygroscopicity (single hygroscopicity parameter, κ ≤ 0.25). Secondary aerosol formed from the tertiary aliphatic amine (TMA) with N2O5 (source of nitrate radical, NO3), contains less volatile compounds than the primary aliphatic amine (BA) aerosol. TMA + N2O5 form semi-volatile organics in low RH conditions that have κ ~ 0.20, indicative of slightly soluble organic material. As RH increases, several inorganic amine salts are formed as a result of acid-base reactions. The CCN activity of the humid TMA-N2O5 aerosol obeys Zdanovskii, Stokes, and Robinson (ZSR) ideal mixing rules. Higher CCN activity (κ > 0.3) was also observed for humid BA+N2O5 aerosols compared with dry aerosol (κ ~ 0.2), as a result of the formation of inorganic salts such as NH4NO3 and butylamine nitrate (C4H11N · HNO3). Compared with TMA, BA+N2O5 reactions produce more volatile aerosols. The BA+N2O5 aerosol products under humid experiments were found to be very sensitive to the temperature within the stream-wise continuous flow thermal gradient CCN counter. The CCN counter, when set above a 21 °C temperature difference, evaporates BA+N2O5 aerosol formed at RH ≥ 30%; κ ranges from 0.4 to 0.7 and is dependent on the instrument supersaturation (ss) settings. The aerosol behaves non-ideally, hence simple ZSR rules cannot be applied to the CCN results from the primary aliphatic amine system. Overall, aliphatic amine aerosol systems κ ranges from 0.2 < κ < 0.7. This work indicates that

  14. Aerobic synthesis of substituted quinoline from aldehyde and aniline: copper-catalyzed intermolecular C-H active and C-C formative cyclization.

    PubMed

    Yan, Rulong; Liu, Xingxing; Pan, Congming; Zhou, Xiaoqiang; Li, Xiaoni; Kang, Xing; Huang, Guosheng

    2013-09-20

    An efficient method for the direct synthesis of substituted quinolines from anilines and aldehydes through C-H functionalization, C-C/C-N bond formation, and C-C bond cleavage has been developed. The method is simple and practical and employs air as an oxidant.

  15. 40 CFR 721.6140 - Dialkyldithiophosphoric acid, aliphatic amine salt.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ..., aliphatic amine salt. 721.6140 Section 721.6140 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.6140 Dialkyldithiophosphoric acid, aliphatic amine salt. (a) Chemical... as a dialkyldithiophosphoric acid, aliphatic amine salt (P-90-1839) is subject to reporting...

  16. 40 CFR 721.6140 - Dialkyldithiophosphoric acid, aliphatic amine salt.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ..., aliphatic amine salt. 721.6140 Section 721.6140 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.6140 Dialkyldithiophosphoric acid, aliphatic amine salt. (a) Chemical... as a dialkyldithiophosphoric acid, aliphatic amine salt (P-90-1839) is subject to reporting...

  17. 40 CFR 721.6140 - Dialkyldithiophosphoric acid, aliphatic amine salt.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ..., aliphatic amine salt. 721.6140 Section 721.6140 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.6140 Dialkyldithiophosphoric acid, aliphatic amine salt. (a) Chemical... as a dialkyldithiophosphoric acid, aliphatic amine salt (P-90-1839) is subject to reporting...

  18. 40 CFR 721.6140 - Dialkyldithiophosphoric acid, aliphatic amine salt.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ..., aliphatic amine salt. 721.6140 Section 721.6140 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.6140 Dialkyldithiophosphoric acid, aliphatic amine salt. (a) Chemical... as a dialkyldithiophosphoric acid, aliphatic amine salt (P-90-1839) is subject to reporting...

  19. 40 CFR 721.6140 - Dialkyldithiophosphoric acid, aliphatic amine salt.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ..., aliphatic amine salt. 721.6140 Section 721.6140 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.6140 Dialkyldithiophosphoric acid, aliphatic amine salt. (a) Chemical... as a dialkyldithiophosphoric acid, aliphatic amine salt (P-90-1839) is subject to reporting...

  20. 40 CFR 721.10534 - Brominated aliphatic alcohol (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Brominated aliphatic alcohol (generic... Specific Chemical Substances § 721.10534 Brominated aliphatic alcohol (generic). (a) Chemical substance and... aliphatic alcohol (PMN P-12-260) is subject to reporting under this section for the significant new...

  1. 40 CFR 721.10534 - Brominated aliphatic alcohol (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Brominated aliphatic alcohol (generic... Specific Chemical Substances § 721.10534 Brominated aliphatic alcohol (generic). (a) Chemical substance and... aliphatic alcohol (PMN P-12-260) is subject to reporting under this section for the significant new...

  2. 40 CFR 721.10199 - Substituted aliphatic amine (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Substituted aliphatic amine (generic... Specific Chemical Substances § 721.10199 Substituted aliphatic amine (generic). (a) Chemical substance and... aliphatic amine (PMN P-06-702) is subject to reporting under this section for the significant new...

  3. 40 CFR 721.2270 - Aliphatic dicarboxylic acid salt.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Aliphatic dicarboxylic acid salt. 721... Substances § 721.2270 Aliphatic dicarboxylic acid salt. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as aliphatic dicarboxylic...

  4. 40 CFR 721.2270 - Aliphatic dicarboxylic acid salt.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Aliphatic dicarboxylic acid salt. 721... Substances § 721.2270 Aliphatic dicarboxylic acid salt. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as aliphatic dicarboxylic...

  5. 40 CFR 721.2270 - Aliphatic dicarboxylic acid salt.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Aliphatic dicarboxylic acid salt. 721... Substances § 721.2270 Aliphatic dicarboxylic acid salt. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as aliphatic dicarboxylic...

  6. 40 CFR 721.2270 - Aliphatic dicarboxylic acid salt.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Aliphatic dicarboxylic acid salt. 721... Substances § 721.2270 Aliphatic dicarboxylic acid salt. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as aliphatic dicarboxylic...

  7. Palladium-catalyzed direct ortho C-H arylation of 2-arylpyridine derivatives with aryltrimethoxysilane.

    PubMed

    Li, Wu; Yin, Zhangwei; Jiang, Xiaoqing; Sun, Peipei

    2011-10-21

    A Pd(OAc)(2)-catalyzed cross-coupling reaction between 2-arylpyridine and aryltrimethoxysilane in the presence of AgF and BQ in 1,4-dioxane was studied. After various reaction parameters (catalyst, oxidant, additive, solvent and reaction temperature) were examined, the optimal conditions for the reaction were identified. The synthesis is compatible to aryltrimethoxysilane with both electron-withdrawing and electron-donating groups on the aryl moiety with moderate yields. The kinetic isotope effect (k(H)/k(D)) for the C-H bond activation was provided.

  8. Study of L-ascorbic acid (vitamin C)/H 2O mixture across glass transition

    NASA Astrophysics Data System (ADS)

    Migliardo, F.; Branca, C.; Faraone, A.; Magazù, S.; Migliardo, P.

    2001-07-01

    In this paper, we report quasi elastic neutron scattering (QENS) spectra of vitamin C aqueous solutions, obtained using MIBEMOL spectrometer (LLB). The main purpose of this work is to characterize the relaxational and vibrational properties of the Vitamin C/H 2O system below and above the glass transition temperature by analysing the low-frequency neutron scattering spectra. The determination of the relative weight of vibrational over relaxational contributions allows to get information on the fragility degree of this peculiar hydrogen-bond system.

  9. Local network structure of a-SiC:H and its correlation with dielectric function

    SciTech Connect

    Kageyama, Shota; Matsuki, Nobuyuki; Fujiwara, Hiroyuki

    2013-12-21

    The microscopic disordered structures of hydrogenated amorphous silicon carbide (a-Si{sub 1−x}C{sub x}:H) layers with different carbon contents have been determined based on the correlations between the dielectric function in the ultraviolet/visible region and the local bonding states studied by high-sensitivity infrared attenuated total reflection spectroscopy. We find that the microscopic structure of the a-Si{sub 1−x}C{sub x}:H layers fabricated by plasma-enhanced chemical vapor deposition shows a sharp structural transition at a boundary of x = 6.3 at. %. In the regime of x ≤ 6.3 at. %, (i) the amplitude of the a-SiC:H dielectric function reduces and (ii) the SiH{sub 2} content increases drastically with x, even though most of the C atoms are introduced into the tetrahedral sites without bonding with H. In the regime of x > 6.3 at. %, on the other hand, (i) the amplitude of the dielectric function reduces further and (ii) the concentration of the sp{sup 3} CH{sub n} (n = 2,3) groups increases. Moreover, we obtained the direct evidence that the sp{sup 2} C bonding state in the a-SiC matrix exists in the configuration of C = CH{sub 2} and the generation of the graphite-like C = CH{sub 2} unit suppresses the band gap widening significantly. At high C contents of x > 6.3 at. %, the a-SiC:H layers show quite porous structures due to the formation of microvoids terminated with the SiH{sub 2}/CH{sub n} groups. By taking the SiH{sub 2}/CH{sub n} microvoid generation in the network and the high-energy shift of the dielectric function by the local bonding states into account, the a-SiC:H dielectric function model has been established. From the analysis using this model, we have confirmed that the a-SiC:H optical properties in the ultraviolet/visible region are determined almost completely by the local network structures.

  10. Mechanistic insights into C-H amination via dicopper nitrenes.

    PubMed

    Aguila, Mae Joanne B; Badiei, Yosra M; Warren, Timothy H

    2013-06-26

    We examine important reactivity pathways relevant to stoichiometric and catalytic C-H amination via isolable β-diketiminato dicopper alkylnitrene intermediates {[Cl2NN]Cu}2(μ-NR). Kinetic studies involving the stoichiometric amination of ethylbenzene by {[Cl2NN]Cu}2(μ-N(t)Bu) (3) demonstrate that the terminal nitrene [Cl2NN]Cu═N(t)Bu is the active intermediate in C-H amination. Initial rates exhibit saturation behavior at high ethylbenzene loadings and an inverse dependence on the copper species [Cl2NN]Cu, both consistent with dissociation of a [Cl2NN]Cu fragment from 3 prior to C-H amination. C-H amination experiments employing 1,4-dimethylcyclohexane and benzylic radical clock substrate support a stepwise H-atom abstraction/radical rebound pathway. Dicopper nitrenes [Cu]2(μ-NCHRR') derived from 1° and 2° alkylazides are unstable toward tautomerization to copper(I) imine complexes [Cu](HN═CRR'), rendering 1° and 2° alkylnitrene complexes unsuitable for C-H amination.

  11. Growth mechanism and composition of ultrasmooth a-C:H:Si films grown from energetic ions for superlubricity

    SciTech Connect

    Chen, Xinchun Kato, Takahisa

    2014-01-28

    Growth mechanism and ion energy dependence of composition of ultrasmooth a-C:H:Si films grown from ionization of tetramethylsilane (TMS) and toluene mixture at a fixed gas ratio have been investigated by varying the applied bias voltage. The dynamic scaling theory is employed to evaluate the roughness evolution of a-C:H:Si films, and to extract roughness and growth exponents of α ∼ 0.51 and β ∼ 0, respectively. The atomically smooth surface of a-C:H:Si films with Ra ∼ 0.1 nm is thermally activated by the energetic ion-impact induced subsurface “polishing” process for ion dominated deposition. The ion energy (bias voltage) plays a paramount role in determining the hydrogen incorporation, bonding structure and final stoichiometry of a-C:H:Si films. The hydrogen content in the films measured by ERDA gradually decreases from 36.7 to 17.3 at. % with increasing the bias voltage from 0.25 to 3.5 kV, while the carbon content in the films increases correspondingly from 52.5 to 70.1 at. %. The Si content is kept almost constant at ∼9–10 at. %. Depending on the ion-surface interactions, the bonding structure of a-C:H:Si films grown in different ion energy regions evolves from chain-developed polymer-like to cross-linked diamond-like to sp{sup 2}-bonded a–C as revealed by XPS, Raman, and FTIR analysis. Such a structural evolution is reflected in their measured nanomechanical properties such as hardness, modulus, and compressive stress. An enhanced viscoplastic behavior (i.e., viscoplastic exponent of ∼0.06) is observed for polymeric a-C:H:Si films. A hydrogen content threshold (H > 20 at. %) exists for the as-grown a-C:H:Si films to exhibit superlow friction in dry N{sub 2} atmosphere. An extremely low friction coefficient of ∼0.001 can be obtained for polymer-like a-C:H:Si film. These near-frictionless a-C:H:Si films are strongly promising for applications in industrial lubricating systems.

  12. Growth mechanism and composition of ultrasmooth a-C:H:Si films grown from energetic ions for superlubricity

    NASA Astrophysics Data System (ADS)

    Chen, Xinchun; Kato, Takahisa

    2014-01-01

    Growth mechanism and ion energy dependence of composition of ultrasmooth a-C:H:Si films grown from ionization of tetramethylsilane (TMS) and toluene mixture at a fixed gas ratio have been investigated by varying the applied bias voltage. The dynamic scaling theory is employed to evaluate the roughness evolution of a-C:H:Si films, and to extract roughness and growth exponents of α ˜ 0.51 and β ˜ 0, respectively. The atomically smooth surface of a-C:H:Si films with Ra ˜ 0.1 nm is thermally activated by the energetic ion-impact induced subsurface "polishing" process for ion dominated deposition. The ion energy (bias voltage) plays a paramount role in determining the hydrogen incorporation, bonding structure and final stoichiometry of a-C:H:Si films. The hydrogen content in the films measured by ERDA gradually decreases from 36.7 to 17.3 at. % with increasing the bias voltage from 0.25 to 3.5 kV, while the carbon content in the films increases correspondingly from 52.5 to 70.1 at. %. The Si content is kept almost constant at ˜9-10 at. %. Depending on the ion-surface interactions, the bonding structure of a-C:H:Si films grown in different ion energy regions evolves from chain-developed polymer-like to cross-linked diamond-like to sp2-bonded a-C as revealed by XPS, Raman, and FTIR analysis. Such a structural evolution is reflected in their measured nanomechanical properties such as hardness, modulus, and compressive stress. An enhanced viscoplastic behavior (i.e., viscoplastic exponent of ˜0.06) is observed for polymeric a-C:H:Si films. A hydrogen content threshold (H > 20 at. %) exists for the as-grown a-C:H:Si films to exhibit superlow friction in dry N2 atmosphere. An extremely low friction coefficient of ˜0.001 can be obtained for polymer-like a-C:H:Si film. These near-frictionless a-C:H:Si films are strongly promising for applications in industrial lubricating systems.

  13. C-H functionalization directed by transformable nitrogen heterocycles: synthesis of ortho-oxygenated arylnaphthalenes from arylphthalazines.

    PubMed

    Rastogi, Shiva K; Medellin, Derek C; Kornienko, Alexander

    2014-01-21

    Two protocols for oxygenation of aromatic C-H bonds ortho-positioned to the phthalazine ring were developed. The transannulation of the phthalazine ring to a naphthalene moiety by an Inverse Electron Demand Diels-Alder (IEDDA) reaction led to the synthesis of naphtho[2,1-c]chromenes, 1-(ortho-hydroxyaryl)naphthalenes and 6,7-dihydrobenzo[b]naphtho[1,2-d]oxepine. This new strategy based on the utilization of transformable nitrogen heterocycles in C-H functionalization chemistry can be potentially applicable to the synthesis of a broad range of biaryl compounds.

  14. A study of aliphatic amino acids using simulated vibrational circular dichroism and Raman optical activity spectra*

    NASA Astrophysics Data System (ADS)

    Ganesan, Aravindhan; Brunger, Michael J.; Wang, Feng

    2013-11-01

    Vibrational optical activity (VOA) spectra, such as vibrational circular dichroism (VCD) and Raman optical activity (ROA) spectra, of aliphatic amino acids are simulated using density functional theory (DFT) methods in both gas phase (neutral form) and solution (zwitterionic form), together with their respective infrared (IR) and Raman spectra of the amino acids. The DFT models, which are validated by excellent agreements with the available experimental Raman and ROA spectra of alanine in solution, are employed to study other aliphatic amino acids. The inferred (IR) intensive region (below 2000 cm-1) reveals the signature of alkyl side chains, whereas the Raman intensive region (above 3000 cm-1) contains the information of the functional groups in the amino acids. Furthermore, the chiral carbons of the amino acids (except for glycine) dominate the VCD and ROA spectra in the gas phase, but the methyl group vibrations produce stronger VCD and ROA signals in solution. The C-H related asymmetric vibrations dominate the VOA spectra (i.e., VCD and ROA) > 3000 cm-1 reflecting the side chain structures of the amino acids. Finally the carboxyl and the C(2)H modes of aliphatic amino acids, together with the side chain vibrations, are very active in the VCD/IR and ROA/Raman spectra, which makes such the vibrational spectroscopic methods a very attractive means to study biomolecules.

  15. Renaissance of Aliphatic Polycarbonates: New Techniques and Biomedical Applications

    PubMed Central

    Xu, Jianwen; Feng, Ellva; Song, Jie

    2014-01-01

    Aliphatic polycarbonates were discovered a long time ago, with their conventional applications mostly limited to low molecular weight oligomeric intermediates for copolymerization with other polymers. Recent developments in polymerization techniques have overcome the difficulty in preparing high molecular weight aliphatic polycarbonates. These in turn, along with new functional monomers, have enabled the preparation of a wide range of aliphatic polycarbonates with diverse chemical compositions and structures. This review summarizes the latest polymerization techniques for preparing well-defined functional aliphatic polycarbonates, as well as the new applications of those aliphatic polycarbonates, esecially in the biomedical field. PMID:24994939

  16. Oxidative esterification via photocatalytic C-H activation

    EPA Pesticide Factsheets

    Direct oxidative esterification of alcohol via photocatalytic C??H activation has been developed using VO@g-C3N4 catalyst; an expeditious esterification of alcohols occurs under neutral conditions using visible light as the source of energy.This dataset is associated with the following publication:Varma , R., S. Verma, R.B.N. Baig, C. Han, and M. Nadagouda. Oxidative esterification via photocatalytic C-H activation. GREEN CHEMISTRY. Royal Society of Chemistry, Cambridge, UK, 18: 251-254, (2015).

  17. Electron cyclotron resonance deposition of a-Si:H and a-C:H films

    NASA Technical Reports Server (NTRS)

    Shing, Y. H.; Yang, C. L.; Allevato, C. E.; Pool, F. S.

    1989-01-01

    Amorphous silicon (a-Si:H) and amorphous carbon (a-C:H) films have been deposited by electron cyclotron resonance (ECR) microwave plasma enhanced CVD. A high deposition rate of 25 A/sec and a light-to-dark conductivity ratio of 500,000 for a-Si:H films have been achieved by the ECR process using a pure silane plasma. ECR microwave plasmas have been analyzed by in situ optical emission spectroscopy (OES) and have shown a strong H-asterisk emission at 434 nm indicating higher chemical reactivity than RF plasmas. The linear correlation between the film deposition rate and the SiH-asterisk emission intensity of ECR silane plasma suggests that SiH-asterisk species are related to the neutral radicals which are responsible for the a-Si:H film deposition. Hard and soft a-C:H films have been deposited by ECR with and without RF bias power, respectively. The RF bias to the substrate is found to play a critical role in determining the film structure and the carbon bonding configuration of ECR deposited a-C:H films. Raman spectra of these films indicate that ECR deposition conditions can be optimized to produce diamond films.

  18. Pd-catalyzed C-H fluorination with nucleophilic fluoride.

    PubMed

    McMurtrey, Kate B; Racowski, Joy M; Sanford, Melanie S

    2012-08-17

    The palladium-catalyzed C-H fluorination of 8-methylquinoline derivatives with nucleophilic fluoride is reported. This transformation involves the use of AgF as the fluoride source in combination with a hypervalent iodine oxidant. Both the scope and mechanism of the reaction are discussed.

  19. Project T.E.A.C.H.: An Evaluative Study.

    ERIC Educational Resources Information Center

    Howarth, Les

    A survey of 17 graduates of Project T.E.A.C.H. (Teacher Effectiveness and Classroom Handling), an inservice education program offered through the Ontario (Canada) Public School Men Teacher's Association in conjunction with Lesley College, used closed- and open-ended questions to obtain evaluations of the project's effectiveness. Five project areas…

  20. Measurement of 2J(H,C)- and 3J(H,C)-coupling constants by alpha/beta selective HC(C)H-TOCSY.

    PubMed

    Duchardt, E; Richter, C; Reif, B; Glaser, S J; Engels, J W; Griesinger, C; Schwalbe, H

    2001-10-01

    A new heteronuclear NMR pulse sequence for the measurement of nJ(C,H) coupling constants, the alpha/beta selective HC(C)H-TOCSY, is described. It is shown that the S3E element (Meissner et al., 1997a,b) can be used to obtain spin state selective coherence transfer in molecules, in which adjacent CH moieties are labeled with 13C. Application of the alpha/beta selective HC(C)H-TOCSY to a 10 nt RNA tetraloop 5'-CGCUUUUGCG-3', in which the four uridine residues are 13C labeled in the sugar moiety, allowed measurement of two bond and three bond J(C,H) coupling constants, which provide additional restraints to characterize the sugar ring conformation of RNA in cases of conformational averaging.

  1. The Effect of Nano Confinement on the C-H Activation and its Corresponding Structure-Activity Relationship

    NASA Astrophysics Data System (ADS)

    Shao, Jing; Yuan, Linghua; Hu, Xingbang; Wu, Youting; Zhang, Zhibing

    2014-11-01

    The C-H activation of methane, ethane, and t-butane on inner and outer surfaces of nitrogen-doped carbon nanotube (NCNTs) are investigated using density functional theory. It includes NCNTs with different diameters, different N and O concentrations, and different types (armchair and zigzag). A universal structure-reactivity relationship is proposed to characterize the C-H activation occurring both on the inner and outer surfaces of the nano channel. The C-O bond distance, spin density and charge carried by active oxygen are found to be highly related to the C-H activation barriers. Based on these theoretical results, some useful strategies are suggested to guide the rational design of more effective catalysts by nano channel confinement.

  2. The effect of nano confinement on the C-h activation and its corresponding structure-activity relationship.

    PubMed

    Shao, Jing; Yuan, Linghua; Hu, Xingbang; Wu, Youting; Zhang, Zhibing

    2014-11-27

    The C-H activation of methane, ethane, and t-butane on inner and outer surfaces of nitrogen-doped carbon nanotube (NCNTs) are investigated using density functional theory. It includes NCNTs with different diameters, different N and O concentrations, and different types (armchair and zigzag). A universal structure-reactivity relationship is proposed to characterize the C-H activation occurring both on the inner and outer surfaces of the nano channel. The C-O bond distance, spin density and charge carried by active oxygen are found to be highly related to the C-H activation barriers. Based on these theoretical results, some useful strategies are suggested to guide the rational design of more effective catalysts by nano channel confinement.

  3. Asymmetric Lewis acid organocatalysis of the Diels-Alder reaction by a silylated C-H acid.

    PubMed

    Gatzenmeier, Tim; van Gemmeren, Manuel; Xie, Youwei; Höfler, Denis; Leutzsch, Markus; List, Benjamin

    2016-02-26

    Silylium ion equivalents have shown promise as Lewis acid catalysts for a range of important C-C bond-forming reactions. Here we describe chiral C-H acids that upon in situ silylation, generate silylium-carbanion pairs, which are extremely active Lewis acid catalysts for enantioselective Diels-Alder reactions of cinnamates with cyclopentadiene. Enantiomeric ratios of up to 97:3 and diastereomeric ratios of more than 20:1 are observed across a diverse set of substitution patterns with 1 mole percent (mol %) of C-H acid catalyst and 10 mol % of a silylating reagent. The results show promise for broad applications of such C-H acid-derived silylium ion equivalents in asymmetric Lewis acid catalysis.

  4. Computational study on C-H...π interactions of acetylene with benzene, 1,3,5-trifluorobenzene and coronene.

    PubMed

    Dinadayalane, Tandabany C; Paytakov, Guvanchmyrat; Leszczynski, Jerzy

    2013-07-01

    Meta-hybrid density functional theory calculations using M06-2X/6-31+G(d,p) and M06-2X/6-311+G(d,p) levels of theory have been performed to understand the strength of C-H(…)π interactions of two possible types for benzene-acetylene, 1,3,5-trifluorobenzene-acetylene and coronene-acetylene complexes. Our study reveals that the C-H(...)π interaction complex where acetylene located above to the center of benzene ring (classical T-shaped) is the lowest energy structure. This structure is twice more stable than the configuration characterized by H atom of benzene interacting with the π-cloud of acetylene. The binding energy of 2.91 kcal/mol calculated at the M06-2X/6-311+G(d,p) level for the lowest energy configuration (1A) is in very good agreement with the experimental binding energy of 2.7 ± 0.2 kcal/mol for benzene-acetylene complex. Interestingly, the C-H(...)π interaction of acetylene above to the center of the aromatic ring is not the lowest energy configuration for 1,3,5-trifluorobenzene-acetylene and coronene-acetylene complexes. The lowest energy configuration (2A) for the former complex possesses both C-H(...)π interaction and C-H(...)F hydrogen bond, while the lowest energy structure for the coronene-acetylene complex involves both π-π and C-H(...)π interactions. C-H stretching vibrational frequencies and the frequency shifts are reported and analyzed for all of the configurations. We observed red-shift of the vibrational frequency for the stretching mode of the C-H bond that interacts with the π-cloud. Acetylene in the lowest-energy structures of the complexes exhibits significant red-shift of the C-H stretching frequency and change in intensity of the corresponding vibrational frequency, compared to bare acetylene. We have examined the molecular electrostatic potential on the surfaces of benzene, 1,3,5-trifluorobenzene, coronene and acetylene to explain the binding strengths of various complexes studied here.

  5. Enantioselective Intramolecular Hydroarylation of Alkenes via Directed C-H Bond Activation

    SciTech Connect

    Harada, Hitoshi; Thalji, Reema; Bergman, Robert; Ellman, Jonathan

    2008-05-22

    Highly enantioselective catalytic intramolecular ortho-alkylation of aromatic imines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using [RhCl(coe){sub 2}]{sub 2} and chiral phosphoramidite ligands. Cyclization of substrates containing 1,1- and 1,2-disubstituted as well as trisubstituted alkenes were achieved with enantioselectivities >90% ee for each substrate class. Cyclization of substrates with Z-alkene isomers proceeded much more efficiently than substrates with E-alkene isomers. This further enabled the highly stereoselective intramolecular alkylation of certain substrates containing Z/E-alkene mixtures via a Rh-catalyzed alkene isomerization with preferential cyclization of the Z-isomer.

  6. C...H...N Hydrogen Bond Formation in Trimethylamine Dimer upon One-Photon Ionization

    NASA Astrophysics Data System (ADS)

    Nakayama, Yuichiro; Matsuda, Yoshiyuki; Fujii, Asuka

    2011-06-01

    Structures of trimethylamine dimer cluster cations which are generated by the vacuum-ultraviolet photoionization are investigated by a combination of infrared spectroscopic methods and theoretical reaction-pass calculations. In the trimethylamine dimer cluster cation, a proton of a methyl group is shared with the N atom of the other trimethylamine moiety. This is evidence that the methyl group acts as a proton donor in the cation state.

  7. Palladium-catalyzed allylic C-H fluorination.

    PubMed

    Braun, Marie-Gabrielle; Doyle, Abigail G

    2013-09-04

    The first catalytic allylic C-H fluorination reaction using a nucleophilic fluoride source is reported. Under the influence of a Pd/Cr cocatalyst system, simple olefin substrates undergo fluorination with Et3N·3HF in good yields with high branched:linear regioselectivity. The mild conditions and broad scope make this reaction a powerful alternative to established methods for the preparation of allylic fluorides from prefunctionalized substrates.

  8. Rh(III)-Catalyzed Diastereoselective Annulation of Amides with Quinone Monoacetals: Access to Bridged Nine-Membered Heterocycles via C-H Activation.

    PubMed

    Yang, Wei; Dong, Jinhuan; Wang, Jingyi; Xu, Xianxiu

    2017-02-03

    An unprecedented Rh(III)-catalyzed annulation of various benzamides and acrylamides with quinone monoacetals was developed for the facile and efficient one-pot synthesis of bridged nine-membered benzo[c]azonine-1,5(2H)-diones and 2-azabicyclo[4.3.1]dec-4-ene-3,8-diones. It is the first example of synthesis of nine-membered heterocycles through Rh(III)-catalyzed C-H bond functionalization, and both aryl and vinyl C-H bonds are tolerant in this reaction. A plausible mechanism is proposed on the basis of control experiments.

  9. Interplay of Tunneling, Two-State Reactivity, and Bell-Evans-Polanyi Effects in C-H Activation by Nonheme Fe(IV)O Oxidants.

    PubMed

    Mandal, Debasish; Shaik, Sason

    2016-02-24

    The study of C-H bond activation reactions by nonheme Fe(IV)O species with nine hydrocarbons shows that the kinetic isotope effect (KIE) involves strong tunneling and is a signature of the reactive spin states. Theory reproduces the observed spike-like appearance of plots of KIE(exp) against the C-H bond dissociation energy, and its origins are discussed. The experimentally observed Bell-Evans-Polanyi correlations, in the presence of strong tunneling, are reproduced, and the pattern is rationalized.

  10. Spreading coefficients of aliphatic hydrocarbons on water

    SciTech Connect

    Takii, Taichi; Mori, Y.H. . Dept. of Mechanical Engineering)

    1993-11-01

    Experiments have been performed to determine the equilibrium spreading coefficients of some aliphatic hydrocarbons (C[sub 6]C[sub 10]) on water. The thickness of a discrete lens of each hydrocarbon sample floating on a stagnant water pool was measured interferometrically and used to calculate the spreading coefficient of the hydrocarbon with the aid of Langmuir's capillarity theory. The dependences of the spreading coefficient, thus observed, on temperature (0--50 C) and on the number of carbon atoms in the hydrocarbon molecule are in qualitative agreement with the predictions based on the Lifshitz theory of van der Waals forces.

  11. Aliphatic hydrocarbons of the Murchison meteorite

    NASA Technical Reports Server (NTRS)

    Cronin, John R.; Pizzarello, Sandra

    1990-01-01

    Hydrocarbon fractions from the Murchison meteorite were prepared using benzene-methanol as the extraction solvent, fractionated on silica gel columns, and analyzed using gas chromatography combined with mass spectrometry and IR and NMR techniques. Results indicate that the most abundant aliphatic hydrocarbon components of the Murchison meteorite are C15 to C30 branched-alkyl-substituted mono-, di-, and tricyclic alkanes. It is shown that the n-alkanes, methyl alkanes, and isoprenoid alkanes that are sometimes found in extracts of the Murchison meteorite are terrestrial contaminants.

  12. The combined C-H functionalization/Cope rearrangement: discovery and applications in organic synthesis.

    PubMed

    Davies, Huw M L; Lian, Yajing

    2012-06-19

    The development of methods for the stereoselective functionalization of sp(3) C-H bonds is a challenging undertaking. This Account describes the scope of the combined C-H functionalization/Cope rearrangement (CHCR), a reaction that occurs between rhodium-stabilized vinylcarbenoids and substrates containing allylic C-H bonds. Computational studies have shown that the CHCR reaction is initiated by a hydride transfer to the carbenoid from an allyl site on the substrate, which is then rapidly followed by C-C bond formation between the developing rhodium-bound allyl anion and the allyl cation. In principle, the reaction can proceed through four distinct orientations of the vinylcarbenoid and the approaching substrate. The early examples of the CHCR reaction were all highly diastereoselective, consistent with a reaction proceeding via a chair transition state with the vinylcarbenoid adopting an s-cis conformation. Recent computational studies have revealed that other transition state orientations are energetically accessible, and these results have guided the development of highly stereoselective CHCR reactions that proceed through a boat transition state with the vinylcarbenoid in an s-cis configuration. The CHCR reaction has broad applications in organic synthesis. In some new protocols, the CHCR reaction acts as a surrogate to some of the classic synthetic strategies in organic chemistry. The CHCR reaction has served as a synthetic equivalent of the Michael reaction, the vinylogous Mukaiyama aldol reaction, the tandem Claisen rearrangement/Cope rearrangement, and the tandem aldol reaction/siloxy-Cope rearrangement. In all of these cases, the products are generated with very high diastereocontrol. With a chiral dirhodium tetracarboxylate catalyst such as Rh(2)(S-DOSP)(4) or Rh(2)(S-PTAD)(4), researchers can achieve very high levels of asymmetric induction. Applications of the CHCR reaction include the effective enantiodifferentiation of racemic dihydronaphthalenes and

  13. The interstellar C-H stretching band near 3.4 microns - Constraints on the composition of organic material in the diffuse interstellar medium

    NASA Technical Reports Server (NTRS)

    Sandford, S. A.; Allamandola, L. J.; Tielens, A. G. G. M.; Pendleton, Y.; Sellgren, K.

    1991-01-01

    The composition and history of dust in the diffuse ISM was studied using 3600-2700/cm absorption spectra of objects which have widely varying amounts of visual extinctions along different lines of sight. The 3300/cm and 2950/cm features are attributed to O-H and C-H stretching vibrations, respectively. The O-H feature in OH 32.8-0.3 is suggestive of circumstellar water ice and is probably not due to material in the diffuse ISM. The features in the 3100-2700/cm region are attributed either to C-H vibrations or to M stars. The spectra of the latter show a series of narrow features in this region that are identified with photospheric OH. Objects in which these bands are seen include OH 01-477, T629-5, and the Galactic center source IRS 7. The C-H stretch feature of diffuse ISM dust has subpeaks which fall within 5/cm of C-H stretching vibrations in the -CH2- and -CH3 groups of saturated aliphatic hydrocarbons.

  14. Biofiltration of gasoline and diesel aliphatic hydrocarbons.

    PubMed

    Halecky, Martin; Rousova, Jana; Paca, Jan; Kozliak, Evguenii; Seames, Wayne; Jones, Kim

    2015-02-01

    The ability of a biofilm to switch between the mixtures of mostly aromatic and aliphatic hydrocarbons was investigated to assess biofiltration efficiency and potential substrate interactions. A switch from gasoline, which consisted of both aliphatic and aromatic hydrocarbons, to a mixture of volatile diesel n-alkanes resulted in a significant increase in biofiltration efficiency, despite the lack of readily biodegradable aromatic hydrocarbons in the diesel mixture. This improved biofilter performance was shown to be the result of the presence of larger size (C₉-C(12)) linear alkanes in diesel, which turned out to be more degradable than their shorter-chain (C₆-C₈) homologues in gasoline. The evidence obtained from both biofiltration-based and independent microbiological tests indicated that the rate was limited by biochemical reactions, with the inhibition of shorter chain alkane biodegradation by their larger size homologues as corroborated by a significant substrate specialization along the biofilter bed. These observations were explained by the lack of specific enzymes designed for the oxidation of short-chain alkanes as opposed to their longer carbon chain homologues.

  15. OLFACTORY RESPONSES OF BLOWFLIES TO ALIPHATIC ALDEHYDES

    PubMed Central

    Dethier, V. G.

    1954-01-01

    The response of the blowfly Phormia regina to stimulation by aldehydes in the vapor phase has been studied by means of a specially designed olfactometer. The median rejection threshold and the maximum acceptance threshold were selected as criteria of response. For both acceptance and rejection the distribution of thresholds in the population is normal with respect to the logarithm of concentration. When thresholds are expressed as molar concentrations, the values decrease progressively as chain length is increased. There is no attraction beyond decanal and no rejection beyond dodecanal. When thresholds are expressed as activities, most members of the aldehyde series are approximately equally stimulating at rejection and equally stimulating at acceptance. The relationship is most exact over the middle range of chain lengths. There is a tendency for the terminal members to stimulate at higher activities. These relationships are in close agreement with those which were found earlier to apply to the normal aliphatic alcohols. The similarity between the relative actions of the members of the two series suggests that the relation of equal olfactory stimulation at equal thermodynamic activities by homologous aliphatic compounds at least for homologues of intermediate chain length may be of rather general application in olfaction. PMID:13174780

  16. Scalable C-H Oxidation with Copper: Synthesis of Polyoxypregnanes.

    PubMed

    See, Yi Yang; Herrmann, Aaron T; Aihara, Yoshinori; Baran, Phil S

    2015-11-04

    Steroids bearing C12 oxidations are widespread in nature, yet only one preparative chemical method addresses this challenge in a low-yielding and not fully understood fashion: Schönecker's Cu-mediated oxidation. This work shines new light onto this powerful C-H oxidation method through mechanistic investigation, optimization, and wider application. Culminating in a scalable, rapid, high-yielding, and operationally simple protocol, this procedure is applied to the first synthesis of several parent polyoxypregnane natural products, representing a gateway to over 100 family members.

  17. Seeing the B-A-C-H motif

    NASA Astrophysics Data System (ADS)

    Catravas, Palmyra

    2005-09-01

    Musical compositions can be thought of as complex, multidimensional data sets. Compositions based on the B-A-C-H motif (a four-note motif of the pitches of the last name of Johann Sebastian Bach) span several centuries of evolving compositional styles and provide an intriguing set for analysis since they contain a common feature, the motif, buried in dissimilar contexts. We will present analyses which highlight the content of this unusual set of pieces, with emphasis on visual display of information.

  18. C-H Activation on Co,O Sites: Isolated Surface Sites versus Molecular Analogs.

    PubMed

    Estes, Deven P; Siddiqi, Georges; Allouche, Florian; Kovtunov, Kirill V; Safonova, Olga V; Trigub, Alexander L; Koptyug, Igor V; Copéret, Christophe

    2016-11-16

    The activation and conversion of hydrocarbons is one of the most important challenges in chemistry. Transition-metal ions (V, Cr, Fe, Co, etc.) isolated on silica surfaces are known to catalyze such processes. The mechanisms of these processes are currently unknown but are thought to involve C-H activation as the rate-determining step. Here, we synthesize well-defined Co(II) ions on a silica surface using a metal siloxide precursor followed by thermal treatment under vacuum at 500 °C. We show that these isolated Co(II) sites are catalysts for a number of hydrocarbon conversion reactions, such as the dehydrogenation of propane, the hydrogenation of propene, and the trimerization of terminal alkynes. We then investigate the mechanisms of these processes using kinetics, kinetic isotope effects, isotopic labeling experiments, parahydrogen induced polarization (PHIP) NMR, and comparison with a molecular analog. The data are consistent with all of these reactions occurring by a common mechanism, involving heterolytic C-H or H-H activation via a 1,2 addition across a Co-O bond.

  19. Halides with Fifteen Aliphatic C–H···Anion Interaction Sites

    NASA Astrophysics Data System (ADS)

    Shi, Genggongwo; Aliakbar Tehrani, Zahra; Kim, Dongwook; Cho, Woo Jong; Youn, Il-Seung; Lee, Han Myoung; Yousuf, Muhammad; Ahmed, Nisar; Shirinfar, Bahareh; Teator, Aaron J.; Lastovickova, Dominika N.; Rasheed, Lubna; Lah, Myoung Soo; Bielawski, Christopher W.; Kim, Kwang S.

    2016-07-01

    Since the aliphatic C–H···anion interaction is relatively weak, anion binding using hydrophobic aliphatic C–H (Cali–H) groups has generally been considered not possible without the presence of additional binding sites that contain stronger interactions to the anion. Herein, we report X-ray structures of organic crystals that feature a chloride anion bound exclusively by hydrophobic Cali–H groups. An X-ray structure of imidazolium-based scaffolds using Cali–H···A‑ interactions (A‑ = anion) shows that a halide anion is directly interacting with fifteen Cali–H groups (involving eleven hydrogen bonds, two bidentate hydrogen-bond-type binding interactions and two weakly hydrogen-bonding-like binding interactions). Additional supporting interactions and/or other binding sites are not observed. We note that such types of complexes may not be rare since such high numbers of binding sites for an anion are also found in analogous tetraalkylammonium complexes. The Cali–H···A‑ interactions are driven by the formation of a near-spherical dipole layer shell structure around the anion. The alternating layers of electrostatic charge around the anion arise because the repulsions between weakly positively charged H atoms are reduced by the presence of the weakly negatively charged C atoms connected to H atoms.

  20. Halides with Fifteen Aliphatic C–H···Anion Interaction Sites

    PubMed Central

    Shi, Genggongwo; Aliakbar Tehrani, Zahra; Kim, Dongwook; Cho, Woo Jong; Youn, Il-Seung; Lee, Han Myoung; Yousuf, Muhammad; Ahmed, Nisar; Shirinfar, Bahareh; Teator, Aaron J.; Lastovickova, Dominika N.; Rasheed, Lubna; Lah, Myoung Soo; Bielawski, Christopher W.; Kim, Kwang S.

    2016-01-01

    Since the aliphatic C–H···anion interaction is relatively weak, anion binding using hydrophobic aliphatic C–H (Cali–H) groups has generally been considered not possible without the presence of additional binding sites that contain stronger interactions to the anion. Herein, we report X-ray structures of organic crystals that feature a chloride anion bound exclusively by hydrophobic Cali–H groups. An X-ray structure of imidazolium-based scaffolds using Cali–H···A− interactions (A− = anion) shows that a halide anion is directly interacting with fifteen Cali–H groups (involving eleven hydrogen bonds, two bidentate hydrogen-bond-type binding interactions and two weakly hydrogen-bonding-like binding interactions). Additional supporting interactions and/or other binding sites are not observed. We note that such types of complexes may not be rare since such high numbers of binding sites for an anion are also found in analogous tetraalkylammonium complexes. The Cali–H···A− interactions are driven by the formation of a near-spherical dipole layer shell structure around the anion. The alternating layers of electrostatic charge around the anion arise because the repulsions between weakly positively charged H atoms are reduced by the presence of the weakly negatively charged C atoms connected to H atoms. PMID:27444513

  1. 40 CFR 721.2270 - Aliphatic dicarboxylic acid salt.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Aliphatic dicarboxylic acid salt. 721... Substances § 721.2270 Aliphatic dicarboxylic acid salt. (a) Chemical substance and significant new uses... salt (PMN P-92-1352) is subject to reporting under this section for the significant new uses...

  2. SPITZER'S VIEW ON AROMATIC AND ALIPHATIC HYDROCARBON EMISSION IN HERBIG Ae STARS

    SciTech Connect

    Acke, B.; Waters, L. B. F. M.; Bouwman, J.; Juhasz, A.; Henning, Th.; Van den Ancker, M. E.; Meeus, G.; Tielens, A. G. G. M.

    2010-07-20

    The chemistry of astronomical hydrocarbons, responsible for the well-known infrared emission features detected in a wide variety of targets, remains enigmatic. Here we focus on the group of young intermediate-mass Herbig Ae stars. We have analyzed the aliphatic and polycyclic aromatic hydrocarbon (PAH) emission features in the infrared spectra of a sample of 53 Herbig Ae stars, obtained with the Infrared Spectrograph aboard the Spitzer Space Telescope. We confirm that the PAH-to-stellar luminosity ratio is higher in targets with a flared dust disk. However, a few sources with a flattened dust disk still show relatively strong PAH emission. Since PAH molecules trace the gas disk, this indicates that gas disks may still be flared, while the dust disk has settled due to grain growth. There are indications that the strength of the 11.3 {mu}m feature also depends on dust disk structure, with flattened disks being less bright in this feature. We confirm that the CC bond features at 6.2 and 7.8 {mu}m shift to redder wavelengths with decreasing stellar effective temperature. Moreover, we show that this redshift is accompanied by a relative increase of aliphatic CH emission and a decrease of the aromatic 8.6 {mu}m CH feature strength. Cool stars in our sample are surrounded by hydrocarbons with a high aliphatic/aromatic CH ratio and a low aromatic CH/CC ratio, and vice versa for the hot stars. We conclude that, while the overall hydrocarbon emission strength depends on the dust disk's geometry, the relative differences seen in the IR emission features in disks around Herbig Ae stars are mainly due to chemical differences of the hydrocarbon molecules induced by the stellar UV field. Strong UV flux reduces the aliphatic component and emphasizes the spectral signature of the aromatic molecules in the IR spectra.

  3. Validation of Alternatives to Aliphatic Isocyanate Polyurethanes

    NASA Technical Reports Server (NTRS)

    Curran, Jerome

    2007-01-01

    The National Aeronautics and Space Administration (NASA) Headquarters chartered the Acquisition Pollution Prevention (AP2) Office to coordinate agency activities affecting pollution prevention issues identified during system and component acquisition and sustainment processes. The primary objective of this effort is to demonstrate and validate alternatives to aliphatic isocyanate polyurethane coatings. Successful completion of this project will result in one or more isocyanate-free coating systems qualified for use at Air Force Space Command (AFSPC) and NASA centers participating in this study. The objective of this project is to qualify the candidates under the specifications for the standard system. This project will compare coating performance of the proposed alternatives to existing coating systems or standards.

  4. Mn-salen catalysed benzylic C-H activation for the synthesis of aryl [(18)F]CF3-containing PET probes.

    PubMed

    Carroll, L; Evans, H L; Spivey, A C; Aboagye, E O

    2015-05-18

    The development of a Mn-salen complex catalysed oxidative benzylic fluorination of non-activated C-H bonds using [(18)F]fluoride is described for installation of [(18)F]CHRF, [(18)F]CR2F and particularly [(18)F]CF3 containing groups in the presence of other functional groups.

  5. Synthesis of 1H-indazoles and 1H-pyrazoles via FeBr3/O2 mediated intramolecular C-H amination.

    PubMed

    Zhang, Tianshui; Bao, Weiliang

    2013-02-01

    A new synthesis of substituted 1H-indazoles and 1H-pyrazoles from arylhydrazones via FeBr(3)/O(2) mediated C-H activation/C-N bond formation reactions is reported. The corresponding 1,3-diaryl-substituted indazoles and trisubstituted pyrazoles were obtained in moderate to excellent yields under mild conditions.

  6. Haemocompatibility of hydrogenated amorphous carbon (a-C:H) films synthesized by plasma immersion ion implantation-deposition

    NASA Astrophysics Data System (ADS)

    Yang, P.; Kwok, S. C. H.; Chu, P. K.; Leng, Y. X.; Chen, J. Y.; Wang, J.; Huang, N.

    2003-05-01

    Diamond-like-carbon has attracted much attention recently as a potential biomaterial in blood contacting biomedical devices. However, previous reports in this area have not adequately addressed the biocompatibility and acceptability of the materials in blood contacting applications. In this study, hydrogenated amorphous carbon (a-C:H) films were fabricated on silicon wafers (1 0 0) using plasma immersion ion implantation-deposition. A series of a-C:H films with different structures and chemical bonds were fabricated under different substrate voltages. The results indicate that film graphitization is promoted at higher substrate bias. The film deposited at a lower substrate bias of -75 V possesses better blood compatibility than the films at higher bias and stainless steel. Our results suggest two possible paths to improve the blood compatibility, suppression of the endogenic clotting system and reduction of platelet activation.

  7. Ortho-Functionalized Aryltetrazines by Direct Palladium-Catalyzed C-H Halogenation: Application to Fast Electrophilic Fluorination Reactions.

    PubMed

    Testa, Christelle; Gigot, Élodie; Genc, Semra; Decréau, Richard; Roger, Julien; Hierso, Jean-Cyrille

    2016-04-25

    A general catalyzed direct C-H functionalization of s-tetrazines is reported. Under mild reaction conditions, N-directed ortho-C-H activation of tetrazines allows the introduction of various functional groups, thus forming carbon-heteroatom bonds: C-X (X=I, Br, Cl) and C-O. Based on this methodology, we developed electrophilic mono- and poly-ortho-fluorination of tetrazines. Microwave irradiation was optimized to afford fluorinated s-aryltetrazines, with satisfactory selectivity, within only ten minutes. This work provides an efficient and practical entry for further accessing highly substituted tetrazine derivatives (iodo, bromo, chloro, fluoro, and acetate precursors). It gives access to ortho-functionalized aryltetrazines which are difficult to obtain by classical Pinner-like syntheses.

  8. Catalytic Friedel-Crafts C-H Borylation of Electron-Rich Arenes: Dramatic Rate Acceleration by Added Alkenes.

    PubMed

    Yin, Qin; Klare, Hendrik F T; Oestreich, Martin

    2017-03-20

    In the electrophilic C-H borylation of electron-rich aromatic compounds with catecholborane, the catalytic generation of the boron electrophile is initiated by heterolysis of the B-H bond by various Lewis and Brønsted acids, with a boronium ion formed exclusively. After ligand dissociation, the corresponding borenium ion undergoes regioselective electrophilic aromatic substitution on aniline derivatives as well as nitrogen-containing heterocycles. The catalysis is optimized using B(C6 F5 )3 as the initiator and proceeds without the addition of an external base or dihydrogen acceptor. Temperatures above 80 °C are generally required to secure efficient turnover in these Friedel-Crafts-type reactions. Mechanistic experiments reveal that regeneration of the boronium/borenium ion with dihydrogen release is rate-determining. This finding finally led to the discovery that, with added alkenes, catalytic C-H borylations can, for the first time, be carried out at room temperature.

  9. Density functional study of hydrogen bond formation between methanol and organic molecules containing Cl, F, NH2, OH, and COOH functional groups.

    PubMed

    Kolev, Stefan K; St Petkov, Petko; Rangelov, Miroslav A; Vayssilov, Georgi N

    2011-12-08

    Various hydrogen-bonded complexes of methanol with different proton accepting and proton donating molecules containing Cl, F, NH(2), OH, OR, and COOH functional groups have been modeled using DFT with hybrid B3LYP and M05-2X functionals. The latter functional was found to provide more accurate estimates of the structural and thermodynamic parameters of the complexes of halides, amines, and alcohols. The characteristics of these complexes are influenced not only by the principle hydrogen bond of the methanol OH with the proton acceptor heteroatom, but also by additional hydrogen bonds of a C-H moiety with methanol oxygen as a proton acceptor. The contribution of the former hydrogen bond in the total binding enthalpy increases in the order chlorides < fluorides < alcohols < amines, while the contribution of the second type of hydrogen bond increases in the reverse order. A general correlation was found between the binding enthalpy of the complex and the electrostatic potential at the hydrogen center participating in the formation of the hydrogen bond. The calculated binding enthalpies of different complexes were used to clarify which functional groups can potentially form a hydrogen bond to the 2'-OH hydroxyl group in ribose, which is strong enough to block it from participation in the intramolecular catalytic activation of the peptide bond synthesis. Such blocking could result in inhibition of the protein biosynthesis in the living cell if the corresponding group is delivered as a part of a drug molecule in the vicinity of the active site in the ribosome. According to our results, such activity can be accomplished by secondary or tertiary amines, alkoxy groups, deprotonated carboxyl groups, and aliphatic fluorides, but not by the other modeled functional groups.

  10. Two-State Reactivity in Low-Valent Iron-Mediated C-H Activation and the Implications for Other First-Row Transition Metals.

    PubMed

    Sun, Yihua; Tang, Hao; Chen, Kejuan; Hu, Lianrui; Yao, Jiannian; Shaik, Sason; Chen, Hui

    2016-03-23

    C-H bond activation/functionalization promoted by low-valent iron complexes has recently emerged as a promising approach for the utilization of earth-abundant first-row transition metals to carry out this difficult transformation. Herein we use extensive density functional theory and high-level ab initio coupled cluster calculations to shed light on the mechanism of these intriguing reactions. Our key mechanistic discovery for C-H arylation reactions reveals a two-state reactivity (TSR) scenario in which the low-spin Fe(II) singlet state, which is initially an excited state, crosses over the high-spin ground state and promotes C-H bond cleavage. Subsequently, aryl transmetalation occurs, followed by oxidation of Fe(II) to Fe(III) in a single-electron transfer (SET) step in which dichloroalkane serves as an oxidant, thus promoting the final C-C coupling and finalizing the C-H functionalization. Regeneration of the Fe(II) catalyst for the next round of C-H activation involves SET oxidation of the Fe(I) species generated after the C-C bond coupling. The ligand sphere of iron is found to play a crucial role in the TSR mechanism by stabilization of the reactive low-spin state that mediates the C-H activation. This is the first time that the successful TSR concept conceived for high-valent iron chemistry is shown to successfully rationalize the reactivity for a reaction promoted by low-valent iron complexes. A comparative study involving other divalent middle and late first-row transition metals implicates iron as the optimum metal in this TSR mechanism for C-H activation. It is predicted that stabilization of low-spin Mn(II) using an appropriate ligand sphere should produce another promising candidate for efficient C-H bond activation. This new TSR scenario therefore emerges as a new strategy for using low-valent first-row transition metals for C-H activation reactions.

  11. Adsorption of halogenated aliphatic contaminants by graphene nanomaterials.

    PubMed

    Zhou, Yang; Apul, Onur Guven; Karanfil, Tanju

    2015-08-01

    In this study, adsorption of ten environmentally halogenated aliphatic synthetic organic compounds (SOCs) by a pristine graphene nanosheet (GNS) and a reduced graphene oxide (rGO) was examined, and their adsorption behaviors were compared with those of a single-walled carbon nanotube (SWCNT) and a granular activated carbon (GAC). In addition, the impacts of background water components (i.e., natural organic matter (NOM), ionic strength (IS) and pH) on the SOC adsorption behavior were investigated. The results indicated HD3000 and SWCNT with higher microporous volumes exhibited higher adsorption capacities for the selected aliphatic SOCs than graphenes, demonstrating microporosity of carbonaceous adsorbents played an important role in the adsorption. Analysis of adsorption isotherms demonstrated that hydrophobic interactions were the dominant contributor to the adsorption of aliphatic SOCs by graphenes. However, π-π electron donor-acceptor and van der Waals interactions are likely the additional mechanisms contributing to the adsorption of aliphatic SOCs on graphenes. Among the three background solution components examined, NOM showed the most influential effect on adsorption of the selected aliphatic SOCs, while pH and ionic strength had a negligible effects. The NOM competition on aliphatic adsorption was less pronounced on graphenes than SWCNT. Overall, in terms of adsorption capacities, graphenes tested in this study did not exhibit a major advantage over SWCNT and GAC for the adsorption of aliphatic SOCs.

  12. Influence of Non-fundamental Modes on Mid-infrared Spectra: Anharmonic DFT Study of Aliphatic Ethers.

    PubMed

    Beć, Krzysztof B; Grabska, Justyna; Ozaki, Yukihiro; Hawranek, Jerzy P; Huck, Christian W

    2017-02-23

    Fundamental and non-fundamental vibrational modes, first overtones, and binary combination modes of selected aliphatic ethers (di-n-propylether, di-iso-propylether, n-butylmethyl ether, n-butylethyl ether, di-n-butyl ether, tert-buytlmethyl ether, and tert-amylmethyl ether) were modeled in a fully anharmonic generalized second-order vibrational perturbation theory (GVPT2) approach on the DFT-B2PLYP/SNST level. The modeling procedure of theoretical line shapes took into account conformational isomers of studied molecules. The calculated spectra of the above ethers were compared to the corresponding experimental spectra in the infrared (IR) region (4000-560 cm(-1)) of the absorption index k(ν) derived from the neat liquid thin-film transmission data. It was found that IR spectra of aliphatic ethers are heavily influenced by the bands originating from non-fundamental modes, particularly from the combination modes in the C-H stretching region (3200-2800 cm(-1)). Because of the effects of vibrational resonances, the intensities of overtones and combination bands originating from methyl and methylene deformation modes increase sufficiently to influence the experimental line shape in this region. Less significant contributions from non-fundamental vibrational modes were noticed in the lower IR region (1600-560 cm(-1)), particularly in the vicinity of the C-O stretching band. The 2700-1600 cm(-1) region, which is rich in weak bands due to non-fundamental vibrations, was reproduced accurately as well. It was concluded that a fully anharmonic approach allows significantly more accurate reproduction of the complex IR line shapes, particularly in the C-H stretching region of aliphatic ethers. On the basis of the achieved agreement between the experimental and calculated spectra, it may be concluded that the anharmonic GVPT2 method can adequately reproduce the anharmonic effects and vibrational resonances in particular, influencing the IR spectra of aliphatic ethers. The

  13. The HCClF_2-HCCH Complex: Microwave Spectrum, Structure and C-H\\cdotsπ Interactions

    NASA Astrophysics Data System (ADS)

    Peebles, Rebecca A.; Sexton, John M.; Elliott, Ashley A.; Steber, Amanda L.; Peebles, Sean A.; Neill, Justin L.; Muckle, Matt T.; Pate, Brooks H.

    2010-06-01

    The HCF_3-HCCH complex was recently found to have a weak C-H\\cdotsπ interaction between the fluoroform and acetylene, as well as having a secondary interaction between the fluorine atoms and one of the acetylene hydrogen atoms; however, extensive splittings due to large amplitude motions within the complex have complicated our efforts at making a full assignment of the HCF_3-HCCH spectrum. In an attempt to remove some of the ambiguity in the HCF_3-HCCH study, we have substituted a chlorine atom for one fluorine atom and undertaken an investigation of the HCClF_2-HCCH complex. This eliminates the possibility of internal rotation of the methane subunit, while still maintaining a C-H\\cdotsπ interaction. Using the chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometer at the University of Virginia and the Balle-Flygare FTMW spectrometer at Eastern Illinois University, the spectra of four isotopologues of HCClF_2-HCCH have been assigned, with no indication of internal motions within the complex. The structure has been determined from the experimental moments of inertia, confirming that this dimer has the expected weak C-H\\cdotsπ interaction. In addition, the off-diagonal χab quadrupole coupling constant has been used to determine the angle between the C-Cl bond and the a-axis of the complex. This, and Kraitchman coordinates for the chlorine atom, help confirm the structural details from the inertial fit. The structural results will be compared with other complexes showing C-H\\cdotsπ and C-H\\cdotsO interactions. S. A. Peebles, M. M. Serafin, R. A. Peebles, 61st International Symposium on Molecular Spectroscopy, Talk MH13, June 19, 2006.

  14. Composites of vinyl polystyrylpyridine/bismaleimide-aliphatic ether copolymers

    NASA Technical Reports Server (NTRS)

    Heimbuch, Alvin H.; Rosser, Robert W.; Hsu, Ming-Ta S.

    1989-01-01

    An aliphatic ether bismaleimide was prepared and coreacted with a polyvinylstyrylpyridine (VPSP) oligomer. Studies showed that a controlled ratio of aliphatic to aromatic units in the polymer backbone improved both processibility and interlaminar shear properties for the carbon-fiber composite system. This modified resin was readily soluble in tetrahydrofuran, allowing for better fiber impregnation and thus enhancing adhesive properties and reproducibility. DSC studies have shown a lower cure temperature for the copolymer than for the neat aliphatic bismaleimide, and a glass transition temperature of 260 C, which is more than adequate for most applications. Limited measurements indicated an improvement in toughness (impact resistance).

  15. Encapsulation of testosterone and its aliphatic and aromatic dimers by milk beta-lactoglobulin.

    PubMed

    Chanphai, P; Vesper, A R; Bekale, L; Bérubé, G; Tajmir-Riahi, H A

    2015-05-01

    The encapsulation of testosterone and it aliphatic dimer (alip) and aromatic dimer (arom) with milk β-lactoglobulin (β-LG) was studied in aqueous solution at pH 7.4. Multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling were used to characterize testosterone-β-LG binding and protein aggregation process. Spectroscopic analysis showed that steroids bind β-LG via hydrophobic and H-bonding interactions with overall binding constants K test-β-LG = 5.6 (± 0.6) × 10(4)M(-1), K test-dimeralip-β-LG = 4.8 (± 0.5) × 10(3)M(-1) and K test-dimer-arom-β-LG = 2.9 (± 0.4) × 10(4)M(-1). The binding affinity was testosterone > testosterone dimer-aromatic > testosterone dimer-aliphatic. Transmission electron microscopy showed major changes in protein morphology as testosterone-protein complexation occurred with increase in the diameter of the protein aggregate indicating encapsulation of steroids by β-LG. Modeling showed the presence of H-bonding stabilized testosterone-β-LG complexes with the free binding energy of -9.82 Kcal/mol indicating that the interaction process is spontaneous at room temperature.

  16. Palladium-Catalyzed Construction of Heteroatom-Containing π-Conjugated Systems by Intramolecular Oxidative C-H/C-H Coupling Reaction.

    PubMed

    Saito, Kenta; Chikkade, Prasanna Kumara; Kanai, Motomu; Kuninobu, Yoichiro

    2015-06-01

    Synthesis of heteroatom-containing ladder-type π-conjugated molecules was successfully achieved via a palladium-catalyzed intramolecular oxidative C-H/C-H cross-coupling reaction. This reaction provides a variety of π-conjugated molecules bearing heteroatoms, such as nitrogen, oxygen, phosphorus, and sulfur atoms, and a carbonyl group. The π-conjugated molecules were synthesized efficiently, even in gram scale, and larger π-conjugated molecules were also obtained by a double C-H/C-H cross-coupling reaction and successive oxidative cycloaromatization.

  17. Biotic and abiotic carbon to sulfur bond cleavage

    SciTech Connect

    Frost, J.W.

    1991-01-01

    Cleavage of aliphatic organosulfonate carbon to sulfur (C-S) bonds, a critical link in the global biogeochemical sulfur cycle, has been identified in Escherichia coli K-12. Enormous quantities of inorganic sulfate are continuously converted (Scheme I) into methanesulfonic acid 1 and acylated 3-(6-sulfo-{alpha}-D-quinovopyranosyl)-L-glycerol 2. Biocatalytic desulfurization (Scheme I) of 1 and 2, which share the structural feature of an aliphatic carbon bonded to a sulfonic acid sulfur, completes the cycle, Discovery of this desulfurization in E. coli provides an invaluable paradigm for study of a biotic process which, via the biogeochemical cycle, significantly influences the atmospheric concentration of sulfur-containing molecules.

  18. Molecular Recognition in Mn-Catalyzed C-H Oxidation. Reaction Mechanism and Origin of Selectivity from a DFT Perspective

    PubMed Central

    Balcells, David; Moles, Pamela; Blakemore, James; Raynaud, Christophe; Brudvig, Gary W.; Crabtree, Robert H.

    2010-01-01

    Experimental studies have shown that the C-H oxidation of ibuprofen and methylcyclohexane acetic acid can be carried out with high selectivies using [(terpy’)Mn(OH2)(μ-O)2Mn(OH2)(terpy’)]3+ as catalyst, where terpy’ is a terpyridine ligand functionalized with a phenylene linker and a Kemp’s triacid serving to recognize the reactant via H-bonding. Experiments, described here, suggest that the sulfate counter anion, present in stochiometric amounts, coordinates to manganese in place of water. DFT calculations have been carried out using [(terpy’)Mn(O)(μ-O)2Mn(SO4)(terpy’)]+ as model catalyst, to analyze the origin of selectivity and its relation to molecular recognition, as well as the mechanism of catalyst inhibition by tert-butyl benzoic acid. The calculations show that a number of spin states, all having radical oxygen character, are energetically accessible. All these spin states promote C-H oxidation via a rebound mechanism. The catalyst recognizes the substrate by a double H bond. This interaction orients the substrate inducing highly selective C-H oxidation. The double hydrogen bond stabilizes the reactant, the transition state and the product to the same extent. Consequently, the reaction occurs at lower energy than without molecular recognition. The association of the catalyst with tert-butyl benzoic acid is shown to shield the access of unbound substrate to the reactive oxo site, hence preventing non-selective hydroxylation. It is shown that the two recognition sites of the catalyst can be used in a cooperative manner to control the access to the reactive centre. PMID:19623399

  19. Iron Mineral Catalyzed C-H Activation As a Potential Pathway for Halogenation Processes

    NASA Astrophysics Data System (ADS)

    Tubbesing, C.; Schoeler, H. F.; Benzing, K.; Krause, T.; Lippe, S.; Rudloff, M.

    2014-12-01

    Due to increasing drinking water demand of mankind and an expected climate change the impact of salt lakes and salt deserts will increase within the next decades. Furthermore, a rising sea level influences coastal areas like salt marshes and abets processes which will lead to elevated organohalogen formation. An additional increase of the global warming potential, of particle formation and stratospheric ozone depletion is expected. Understanding these multifaceted processes is essential for mankind to be prepared for these alterations of the atmosphere. For example, Keppler et al. (2000) described the production of volatile halogenated organic compounds via oxidation of organic matter driven by ferric iron. However, the formation of long-chained alkyl halides in salt lakes is yet undisclosed. Despite the relative "inertness" of alkanes a direct halogenation of these compounds might be envisaged. In 2005 Vaillancourt et al. discovered a nonheme iron enzyme which is able to halogenate organic compounds via generating the high valent ferryl cation as reaction center. Based on various publications about C-H activation (Bergman, 2007) we postulate a halogenation process in which an iron containing minerals catalyse the C-H bond cleavage of organic compounds in soils. The generated organic radicals are highly reactive towards halides connected to the iron complex. We suggest that next to diagenetically altered iron containing enzymes, minerals such as oxides, hydroxides and sulfides are involved in abiotic halogenation processes. We applied the amino acid methionine as organic model compound and soluble iron species as reactants. All samples were incubated in aqueous phases containing various NaCl concentrations. As a result various halogenated ethanes and ethenes were identified as reaction products. References Bergman, R. G. (2007) Nature, 446(7134) 391-393 Keppler, F., et al. (2000) Nature, 403(6767) 298-301 Vaillancourt, F. H., et al. (2005) Nature, 436(7054) 1191-1194

  20. Visible-Light Photoredox-Catalyzed C-H Difluoroalkylation of Hydrazones through an Aminyl Radical/Polar Mechanism.

    PubMed

    Xu, Pan; Wang, Guoqiang; Zhu, Yuchen; Li, Weipeng; Cheng, Yixiang; Li, Shuhua; Zhu, Chengjian

    2016-02-18

    An unprecedented visible-light-induced direct C-H bond difluoroalkylation of aldehyde-derived hydrazones was developed. This reaction represents a new way to synthesize substituted hydrazones. The salient features of this reaction include difluorinated hydrazone synthesis rather than classical amine synthesis, extremely mild reaction conditions, high efficiency, wide substrate scope, ease in further transformations of the products, and one-pot syntheses. Mechanistic analyses and theoretical calculations indicate that this reaction is enabled by a novel aminyl radical/polar crossover mechanism, with the aminyl radical being oxidized into the corresponding aminyl cation through a single electron transfer (SET) process.

  1. ANAEROBIC AND AEROBIC TREATMENT OF CHLORINATED ALIPHATIC COMPOUNDS

    EPA Science Inventory

    Biological degradation of 12 chlorinated aliphatic compounds (CACs) was assessed in bench-top reactors and in serum bottle tests. Three continuously mixed daily batch-fed reactor systems were evaluated: anaerobic, aerobic, and sequential-anaerobic-aerobic (sequential). Glucose,...

  2. Silver-Catalyzed Decarboxylative Bromination of Aliphatic Carboxylic Acids.

    PubMed

    Tan, Xinqiang; Song, Tao; Wang, Zhentao; Chen, He; Cui, Lei; Li, Chaozhong

    2017-03-13

    The silver-catalyzed Hunsdiecker bromination of aliphatic carboxylic acids is described. With Ag(Phen)2OTf as the catalyst and dibromoisocyanuric acid as the brominating agent, various aliphatic carboxylic acids underwent decarboxylative bromination to provide the corresponding alkyl bromides under mild conditions. This method not only is efficient and general but also enjoys wide functional group compatibility. An oxidative radical mechanism involving Ag(II) intermediates is proposed.

  3. Process for producing peracids from aliphatic hydroxy carboxylic acids

    DOEpatents

    Chum, H.L.; Palasz, P.D.; Ratcliff, M.A.

    1984-12-20

    A process is described for producing peracids from lactic acid-containing solutions derived from biomass processing systems. It consists of adjusting the pH of the solution to about 8 to 9 and removing alkaline residue fractions therefrom to form a solution comprised substantially of lower aliphatic hydroxy acids. The solution is oxidized to produce volatile lower aliphatic aldehydes. The aldehydes are removed as they are generated and converted to peracids.

  4. Process for producing peracids from aliphatic hydroxy carboxylic acids

    DOEpatents

    Chum, Helena L.; Ratcliff, Matthew A.; Palasz, Peter D.

    1986-01-01

    A process for producing peracids from lactic acid-containing solutions derived from biomass processing systems comprising: adjusting the pH of the solution to about 8-9 and removing alkaline residue fractions therefrom to form a solution comprised substantially of lower aliphatic hydroxy acids; oxidizing the solution to produce volatile lower aliphatic aldehydes; removing said aldehydes as they are generated; and converting said aldehydes to peracids.

  5. Importance of C-H-donor and C-H-anion contact interactions for the crystal packing, the lattice softness and the superconducting transition temperatures of organic conducting salts

    SciTech Connect

    Whangbo, M.-H.; Novoa, J.J.; Jung, D. . Dept. of Chemistry); Williams, J.M.; Kinj, A.M.; Wang, H.H.; Geiser, U.; Beno, M.A.; Carlson, K.D. )

    1990-01-01

    The organic donor molecule BEDT-TTF and its analogs 2--4 have yielded a number of ambient-pressure superconducting salts. What structural and electronic factors govern the magnitudes of their superconducting transition temperature {Tc} has been a topic of intense studies. Examination of the band electronic structures of closely related superconducting salts shows, that the magnitudes of their {Tc}'s are primarily determined by the softness of their crystal lattices. The crystal packing and the lattice softness of organic donor salts are strongly influenced by the donor{hor ellipsis}donor and donor{hor ellipsis}anion contact interactions involving the donor-molecule C-H bonds. In the present work, we briefly review the electronic structures of some representative organic salt superconductors and discuss the softness of their crytsal lattices on the basis of the interaction energies calculated for the C-H{hor ellipsis}donor and C-H{hor ellipsis}anion contact interactions. 34 refs., 14 figs., 8 tabs.

  6. Bent Bonds and Multiple Bonds.

    ERIC Educational Resources Information Center

    Robinson, Edward A.; Gillespie, Ronald J.

    1980-01-01

    Considers carbon-carbon multiple bonds in terms of Pauling's bent bond model, which allows direct calculation of double and triple bonds from the length of a CC single bond. Lengths of these multiple bonds are estimated from direct measurements on "bent-bond" models constructed of plastic tubing and standard kits. (CS)

  7. Theoretical study of the bond dissociation energies of methanol

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Walch, Stephen P.

    1992-01-01

    A theoretical study of the bond dissociation energies for H2O and CH3OH is presented. The C-H and O-H bond energies are computed accurately with the modified coupled-pair functional method using a large basis set. For these bonds, an accuracy of +/- 2 kcal/mol is achieved, which is consistent with the C-H and C-C single bond energies of other molecules. The C-O bond is much more difficult to compute accurately because it requires higher levels of correlation treatment and more extensive one-particle basis sets.

  8. Room-temperature C-H arylation: merger of Pd-catalyzed C-H functionalization and visible-light photocatalysis.

    PubMed

    Kalyani, Dipannita; McMurtrey, Kate B; Neufeldt, Sharon R; Sanford, Melanie S

    2011-11-23

    This communication describes the development of a room-temperature ligand-directed C-H arylation reaction using aryldiazonium salts. This was achieved by the successful merger of palladium-catalyzed C-H functionalization and visible-light photoredox catalysis. The new method is general for a variety of directing groups and tolerates many common functional groups.

  9. Structure and spectroscopic properties of neutral and cationic tetratomic [C,H,N,Zn] isomers: A theoretical study

    SciTech Connect

    Redondo, Pilar; Largo, Antonio; Vega-Vega, Álvaro; Barrientos, Carmen

    2015-05-14

    The structure and spectroscopic parameters of the most relevant [C,H,N,Zn] isomers have been studied employing high-level quantum chemical methods. For each isomer, we provide predictions for their molecular structure, thermodynamic stabilities as well as vibrational and rotational spectroscopic parameters which could eventually help in their experimental detection. In addition, we have carried out a detailed study of the bonding situations by means of a topological analysis of the electron density in the framework of the Bader’s quantum theory of atoms in molecules. The analysis of the relative stabilities and spectroscopic parameters suggests two linear isomers of the neutral [C,H,N,Zn] composition, namely, cyanidehydridezinc HZnCN ({sup 1}Σ) and hydrideisocyanidezinc HZnNC ({sup 1}Σ), as possible candidates for experimental detections. For the cationic [C,H,N,Zn]{sup +} composition, the most stable isomers are the ion-molecule complexes arising from the direct interaction of the zinc cation with either the nitrogen or carbon atom of either hydrogen cyanide or hydrogen isocyanide, namely, HCNZn{sup +} ({sup 2}Σ) and HCNZn{sup +} ({sup 2}Σ)

  10. Mechanistic Details of Pd(II)-Catalyzed C-H Iodination with Molecular I2: Oxidative Addition vs Electrophilic Cleavage.

    PubMed

    Haines, Brandon E; Xu, Huiying; Verma, Pritha; Wang, Xiao-Chen; Yu, Jin-Quan; Musaev, Djamaladdin G

    2015-07-22

    Transition metal-catalyzed C-H bond halogenation is an important alternative to the highly utilized directed-lithiation methods and increases the accessibility of the synthetically valuable aryl halide compounds. However, this approach often requires impractical reagents, such as IOAc, or strong co-oxidants. Therefore, the development of methodology utilizing inexpensive oxidants and catalyst containing earth-abundant transition metals under mild experimental conditions would represent a significant advance in the field. Success in this endeavor requires a full understanding of the mechanisms and reactivity governing principles of this process. Here, we report intimate mechanistic details of the Pd(II)-catalyzed C-H iodination with molecular I2 as the sole oxidant. Namely, we elucidate the impact of the: (a) Pd-directing group (DG) interaction, (b) nature of oxidant, and (c) nature of the functionalized C-H bond [C(sp(2))-H vs C(sp(3))-H] on the Pd(II)/Pd(IV) redox and Pd(II)/Pd(II) redox-neutral mechanisms of this reaction. We find that both monomeric and dimeric Pd(II) species may act as an active catalyst during the reaction, which preferentially proceeds via the Pd(II)/Pd(II) redox-neutral electrophilic cleavage (EC) pathway for all studied substrates with a functionalized C(sp(2))-H bond. In general, a strong Pd-DG interaction increases the EC iodination barrier and reduces the I-I oxidative addition (OA) barrier. However, the increase in Pd-DG interaction alone is not enough to make the mechanistic switch from EC to OA: This occurs only upon changing to substrates with a functionalized C(sp(3))-H bond. We also investigated the impact of the nature of the electrophile on the C(sp(2))-H bond halogenation. We predicted molecular bromine (Br2) to be more effective electrophile for the C(sp(2))-H halogenation than I2. Subsequent experiments on the stoichiometric C(sp(2))-H bromination by Pd(OAc)2 and Br2 confirmed this prediction.The findings of this study advance

  11. Copper-catalyzed oxidative carbon-heteroatom bond formation: a recent update.

    PubMed

    Zhu, Xu; Chiba, Shunsuke

    2016-08-08

    This review updates recent advances in Cu-catalyzed (anaerobic) oxidative carbon-heteroatom bond formation on sp(3)- and sp(2)-C-H bonds as well as alkenes, classified according to the types of stoichiometric oxidants.

  12. Hydrogen atom transfer from 1,n-alkanediamines to the cumyloxyl radical. Modulating C-H deactivation through acid-base interactions and solvent effects.

    PubMed

    Milan, Michela; Salamone, Michela; Bietti, Massimo

    2014-06-20

    A time-resolved kinetic study on the effect of trifluoroacetic acid (TFA) on the hydrogen atom transfer (HAT) reactions from 1,n-alkanediamines (R2N(CH2)nNR2, R = H, CH3; n = 1-4), piperazine, and 1,4-dimethylpiperazine to the cumyloxyl radical (CumO(•)), has been carried out in MeCN and DMSO. Very strong deactivation of the α-C-H bonds has been observed following nitrogen protonation and the results obtained have been explained in terms of substrate basicity, of the distance between the two basic centers and of the solvent hydrogen bond acceptor ability. At [substrate] ≤ 1/2 [TFA] the substrates exist in the doubly protonated form HR2N(+)(CH2)nN(+)R2H, and no reaction with CumO(•) is observed. At 1/2 [TFA] < [substrate] ≤ [TFA], HAT occurs from the C-H bonds that are α to the nonprotonated nitrogen in R2N(CH2)nN(+)R2H. At [substrate] > [TFA], HAT occurs from the α-C-H bonds of R2N(CH2)nNR2, and the mesured kH values are very close to those obtained in the absence of TFA. Comparison between MeCN and DMSO clearly shows that in the monoprotonated diamines R2N(CH2)nN(+)R2H remote C-H deactivation can be modulated through solvent hydrogen bonding.

  13. Cloud condensation nuclei (CCN) activity of aliphatic amine secondary aerosol

    NASA Astrophysics Data System (ADS)

    Tang, X.; Price, D.; Praske, E.; Vu, D. N.; Purvis-Roberts, K.; Silva, P. J.; Cocker, D. R., III; Asa-Awuku, A.

    2014-06-01

    Aliphatic amines can form secondary aerosol via oxidation with atmospheric radicals (e.g., hydroxyl radical and nitrate radical). The particle can contain both secondary organic aerosol (SOA) and inorganic salts. The ratio of organic to inorganic materials in the particulate phase influences aerosol hygroscopicity and cloud condensation nuclei (CCN) activity. SOA formed from trimethylamine (TMA) and butylamine (BA) reactions with hydroxyl radical (OH) is composed of organic material of low hygroscopicity (single hygroscopicity parameter, κ, ≤ 0.25). Secondary aerosol formed from the tertiary aliphatic amine (TMA) with N2O5 (source of nitrate radical, NO3) contains less volatile compounds than the primary aliphatic amine (BA) aerosol. As relative humidity (RH) increases, inorganic amine salts are formed as a result of acid-base reactions. The CCN activity of the humid TMA-N2O5 aerosol obeys Zdanovskii, Stokes, and Robinson (ZSR) ideal mixing rules. The humid BA + N2O5 aerosol products were found to be very sensitive to the temperature at which the measurements were made within the streamwise continuous-flow thermal gradient CCN counter; κ ranges from 0.4 to 0.7 dependent on the instrument supersaturation (ss) settings. The variance of the measured aerosol κ values indicates that simple ZSR rules cannot be applied to the CCN results from the primary aliphatic amine system. Overall, aliphatic amine aerosol systems' κ ranges within 0.2 < κ < 0.7. This work indicates that aerosols formed via nighttime reactions with amines are likely to produce hygroscopic and volatile aerosol, whereas photochemical reactions with OH produce secondary organic aerosol of lower CCN activity. The contributions of semivolatile secondary organic and inorganic material from aliphatic amines must be considered for accurate hygroscopicity and CCN predictions from aliphatic amine systems.

  14. A Catalytic Role for C-H/π Interactions in Base Excision Repair by Bacillus cereus DNA Glycosylase AlkD.

    PubMed

    Parsons, Zachary D; Bland, Joshua M; Mullins, Elwood A; Eichman, Brandt F

    2016-09-14

    DNA glycosylases protect genomic integrity by locating and excising aberrant nucleobases. Substrate recognition and excision usually take place in an extrahelical conformation, which is often stabilized by π-stacking interactions between the lesion nucleobase and aromatic side chains in the glycosylase active site. Bacillus cereus AlkD is the only DNA glycosylase known to catalyze base excision without extruding the damaged nucleotide from the DNA helix. Instead of contacting the nucleobase itself, the AlkD active site interacts with the lesion deoxyribose through a series of C-H/π interactions. These interactions are ubiquitous in protein structures, but evidence for their catalytic significance in enzymology is lacking. Here, we show that the C-H/π interactions between AlkD and the lesion deoxyribose participate in catalysis of glycosidic bond cleavage. This is the first demonstration of a catalytic role for C-H/π interactions as intermolecular forces important to DNA repair.

  15. Intramolecular cyclopropanation and C-H insertion reactions with metal carbenoids generated from cyclopropenes.

    PubMed

    Archambeau, Alexis; Miege, Frédéric; Meyer, Christophe; Cossy, Janine

    2015-04-21

    Activation of unsaturated carbon-carbon bonds by means of transition metal catalysts is an exceptionally active research field in organic synthesis. In this context, due to their high ring strain, cyclopropenes constitute an interesting class of substrates that displays a versatile reactivity in the presence of transition metal catalysts. Metal complexes of vinyl carbenes are involved as key intermediates in a wide variety of transition metal-catalyzed ring-opening reactions of cyclopropenes. Most of the reported transformations rely on intermolecular or intramolecular addition of nucleophiles to these latter reactive species. This Account focuses specifically on the reactivity of carbenoids resulting from the ring-opening of cyclopropenes in cyclopropanation and C-H insertion reactions, which are arguably two of the most representative transformations of metal complexes of carbenes. Compared with the more conventional α-diazo carbonyl compounds, the use of cyclopropenes as precursors of metal carbenoids in intramolecular cyclopropanation or C-H insertion reactions has been largely underexploited. One of the challenges is to devise appropriately substituted and readily available cyclopropenes that would not only undergo regioselective ring-opening under mild conditions but also trigger the subsequent desired transformations with a high level of chemoselectivity and stereoselectivity. These goals were met by considering several substrates derived from the readily available 3,3-dimethylcyclopropenylcarbinols or 3,3-dimethylcyclopropenylcarbinyl amines. In the case of 1,6-cyclopropene-enes, highly efficient and diastereoselective gold(I)-catalyzed ring-opening/intramolecular cyclopropanations were developed as a route to diversely substituted heterocycles and carbocycles possessing a bicyclo[4.1.0]heptane framework. The use of rhodium(II) catalysts enabled us to widen the scope of this transformation for the synthesis of medium-sized heterocyclic scaffolds

  16. Chiral Cyclopentadienyls: Enabling Ligands for Asymmetric Rh(III)-Catalyzed C-H Functionalizations.

    PubMed

    Ye, Baihua; Cramer, Nicolai

    2015-05-19

    Transition-metal catalyzed C-H functionalizations became a complementary and efficient bond-forming strategy over the past decade. In this respect, Cp*Rh(III) complexes have emerged as powerful catalysts for a broad spectrum of reactions giving access to synthetically versatile building blocks. Despite their high potential, the corresponding catalytic enantioselective transformations largely lag behind. The targeted transformations require all the remaining three coordination sites of the central rhodium atom of the catalyst. In consequence, the chiral information on a competent catalyst can only by stored in the cyclopentadienyl unit. The lack of suitable enabling chiral cyclopentadienyl (Cp(x)) ligands is the key hurdle preventing the development of such asymmetric versions. In this respect, an efficient set of chiral Cp(x) ligands useable with a broad variety of different transition-metals can unlock substantial application potential. This Account provides a description of our developments of two complementary classes of C2-symmetric Cp(x) derivatives. We have introduced a side- and back-wall concept to enforce chirality transfer onto the central metal atom. The first generation consists of a fused cyclohexane unit having pseudo axial methyl groups as chiral selectors and a rigidifying acetal moiety. The second ligand generation derives from an atrop-chiral biaryl-backbone and which possesses adjustable substituents at its 3,3'-positions. Both ligand families can be modulated in their respective steric bulk to adjust for the specific needs of the targeted application. The cyclopentadienes can be metalated under standard conditions. The corresponding chiral rhodium(I) ethylene complexes are relatively air and moisture and represent storable stable precatalysts for the targeted asymmetric Rh(III)-catalyzed C-H functionalizations. These complexes are then conveniently oxidized in situ by dibenzoyl peroxide to give the reactive Cp(x)Rh(III)(OBz)2 species. For

  17. Radical-Mediated C-H Functionalization: A Strategy for Access to Modified Cyclodextrins.

    PubMed

    Alvarez-Dorta, Dimitri; León, Elisa I; Kennedy, Alan R; Martín, Angeles; Pérez-Martín, Inés; Suárez, Ernesto

    2016-12-02

    A simple and efficient radical C-H functionalization to access modified cyclodextrins (CDs) has been developed. The well-defined conformation of glycosidic and aglyconic bonds in α-, β-, and γ-CDs favors the intramolecular 1,8-hydrogen atom transfer (HAT) promoted by the 6(I)-O-yl radical, which abstracts regioselectively the hydrogen at C5(II) of the contiguous pyranose. The C5(II)-radical evolves by a polar crossover mechanism to a stable 1,3,5-trioxocane ring between two adjacent glucoses or alternatively triggers the inversion of one α-d-glucose into a 5-C-acetoxy-β-l-idose unit possessing a (1)C4 conformation. The 6(I,IV)- and 6(I,III)-diols of α- and β-CDs behave similarly to the monoalcohols, forming mostly compounds originating from two 1,8-HAT consecutive processes. In the case of 6(I,II)-diols the proximity of the two 6-O-yl radicals in adjacent sugar units allows the formation of unique lactone rings within the CD framework via a 1,8-HAT-β-scission tandem mechanism. X-ray diffraction carried out on the crystalline 1,4-bis(trioxocane)-α-CD derivative shows a severe distortion toward a narrower elliptical shape for the primary face.

  18. Properties of a-C:H:Si thin films deposited by middle-frequency magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Jiang, Jinlong; Wang, Yubao; Du, Jinfang; Yang, Hua; Hao, Junying

    2016-08-01

    The silicon doped hydrogenated amorphous carbon (a-C:H:Si) films were prepared on silicon substrates by middle-frequency magnetron sputtering silicon target in an argon and methane gas mixture atmosphere. The deposition rate, chemical composition, structure, surface properties, stress, hardness and tribological properties in the ambient air of the films were systemically investigated using X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), atomic force microscopy (AFM), nanoindentation and tribological tester. The results show that doped silicon content in the films is controlled in the wide range from 39.7 at.% to 0.2 at.% by various methane gas flow rate, and methane flow rate affects not only the silicon content but also its chemical bonding structure in the films due to the transformation of sputtering modes. Meanwhile, the sp3 carbon component in the films linearly increases with increasing of methane flow rate. The film deposited at moderate methane flow rate of 40-60 sccm exhibits the very smooth surface (RMS roughness 0.4 nm), low stress (0.42 GPa), high hardness (21.1 GPa), as well as low friction coefficient (0.038) and wear rate (1.6 × 10-7 mm3/Nm). The superior tribological performance of the films could be attributed to the formation and integral covering of the transfer materials on the sliding surface and their high hardness.

  19. Palladium mediated intramolecular multiple C-X/C-H cross coupling and C-H activation: synthesis of carbazole alkaloids calothrixin B and murrayaquinone A.

    PubMed

    Kaliyaperumal, Srinivasan A; Banerjee, Shyamapada; U K, Syam Kumar

    2014-08-28

    Straightforward palladium mediated syntheses of calothrixin B and murrayaquinone A are described. Regioselective palladium mediated intramolecular multiple C-X/C-H cross coupling reaction on N-(4-((2-bromophenyl)amino)-2,5-dimethoxybenzyl)-N-(2-iodophenyl)acetamide followed by CAN oxidation afforded calothrixin B in excellent yield in two steps. A linear synthesis has also been developed for calothrixin B. Utilizing C-H functionalization as well as palladium mediated intramolecular C-X/C-H cross coupling reaction, murrayaquinone A synthesis was achieved. Overall, these synthetic methodologies provide an expedient entry to these biologically active alkaloids in a short reaction sequence.

  20. Alcohols as alkylating agents in heteroarene C-H functionalization

    NASA Astrophysics Data System (ADS)

    Jin, Jian; MacMillan, David W. C.

    2015-09-01

    Redox processes and radical intermediates are found in many biochemical processes, including deoxyribonucleotide synthesis and oxidative DNA damage. One of the core principles underlying DNA biosynthesis is the radical-mediated elimination of H2O to deoxygenate ribonucleotides, an example of `spin-centre shift', during which an alcohol C-O bond is cleaved, resulting in a carbon-centred radical intermediate. Although spin-centre shift is a well-understood biochemical process, it is underused by the synthetic organic chemistry community. We wondered whether it would be possible to take advantage of this naturally occurring process to accomplish mild, non-traditional alkylation reactions using alcohols as radical precursors. Because conventional radical-based alkylation methods require the use of stoichiometric oxidants, increased temperatures or peroxides, a mild protocol using simple and abundant alkylating agents would have considerable use in the synthesis of diversely functionalized pharmacophores. Here we describe the development of a dual catalytic alkylation of heteroarenes, using alcohols as mild alkylating reagents. This method represents the first, to our knowledge, broadly applicable use of unactivated alcohols as latent alkylating reagents, achieved via the successful merger of photoredox and hydrogen atom transfer catalysis. The value of this multi-catalytic protocol has been demonstrated through the late-stage functionalization of the medicinal agents, fasudil and milrinone.

  1. Photo-induced oxidant-free oxidative C-H/N-H cross-coupling between arenes and azoles

    NASA Astrophysics Data System (ADS)

    Niu, Linbin; Yi, Hong; Wang, Shengchun; Liu, Tianyi; Liu, Jiamei; Lei, Aiwen

    2017-02-01

    Direct cross-coupling between simple arenes and heterocyclic amines under mild conditions is undoubtedly important for C-N bonds construction. Selective C(sp2)-H amination is more valuable. Herein we show a selective C(sp2)-H amination of arenes (alkyl-substituted benzenes, biphenyl and anisole derivatives) accompanied by hydrogen evolution by using heterocyclic azoles as nitrogen sources. The reaction is selective for C(sp2)-H bonds, providing a mild route to N-arylazoles. The KIE (kinetic isotope effect) experiment reveals the cleavage of C-H bond is not involved in the rate-determining step. Kinetic studies indicate the first-order behaviour with respect to the arene component. It is interesting that this system works without the need for any sacrificial oxidant and is highly selective for C(sp2)-H activation, whereas C(sp3)-H bonds are unaffected. This study may have significant implications for the functionalization of methylarenes which are sensitive to oxidative conditions.

  2. Aliphatic alcohols in spirits inhibit phagocytosis by human monocytes.

    PubMed

    Pál, László; Árnyas, Ervin M; Bujdosó, Orsolya; Baranyi, Gergő; Rácz, Gábor; Ádány, Róza; McKee, Martin; Szűcs, Sándor

    2015-04-01

    A large volume of alcoholic beverages containing aliphatic alcohols is consumed worldwide. Previous studies have confirmed the presence of ethanol-induced immunosuppression in heavy drinkers, thereby increasing susceptibility to infectious diseases. However, the aliphatic alcohols contained in alcoholic beverages might also impair immune cell function, thereby contributing to a further decrease in microbicidal activity. Previous research has shown that aliphatic alcohols inhibit phagocytosis by granulocytes but their effect on human monocytes has not been studied. This is important as they play a crucial role in engulfment and killing of pathogenic microorganisms and a decrease in their phagocytic activity could lead to impaired antimicrobial defence in heavy drinkers. The aim of this study was to measure monocyte phagocytosis following their treatment with those aliphatic alcohols detected in alcoholic beverages. Monocytes were separated from human peripheral blood and phagocytosis of opsonized zymosan particles by monocytes treated with ethanol and aliphatic alcohols individually and in combination was determined. It was shown that these alcohols could suppress the phagocytic activity of monocytes in a concentration-dependent manner and when combined with ethanol, they caused a further decrease in phagocytosis. Due to their additive effects, it is possible that they may inhibit phagocytosis in a clinically meaningful way in alcoholics and episodic heavy drinkers thereby contribute to their increased susceptibility to infectious diseases. However, further research is needed to address this question.

  3. Drude polarizable force field for aliphatic ketones and aldehydes, and their associated acyclic carbohydrates

    NASA Astrophysics Data System (ADS)

    Small, Meagan C.; Aytenfisu, Asaminew H.; Lin, Fang-Yu; He, Xibing; MacKerell, Alexander D.

    2017-02-01

    The majority of computer simulations exploring biomolecular function employ Class I additive force fields (FF), which do not treat polarization explicitly. Accordingly, much effort has been made into developing models that go beyond the additive approximation. Development and optimization of the Drude polarizable FF has yielded parameters for selected lipids, proteins, DNA and a limited number of carbohydrates. The work presented here details parametrization of aliphatic aldehydes and ketones (viz. acetaldehyde, propionaldehyde, butaryaldehyde, isobutaryaldehyde, acetone, and butanone) as well as their associated acyclic sugars (uc(d)-allose and uc(d)-psicose). LJ parameters are optimized targeting experimental heats of vaporization and molecular volumes, while the electrostatic parameters are optimized targeting QM water interactions, dipole moments, and molecular polarizabilities. Bonded parameters are targeted to both QM and crystal survey values, with the models for ketones and aldehydes shown to be in good agreement with QM and experimental target data. The reported heats of vaporization and molecular volumes represent a compromise between the studied model compounds. Simulations of the model compounds show an increase in the magnitude and the fluctuations of the dipole moments in moving from gas phase to condensed phases, which is a phenomenon that the additive FF is intrinsically unable to reproduce. The result is a polarizable model for aliphatic ketones and aldehydes including the acyclic sugars uc(d)-allose and uc(d)-psicose, thereby extending the available biomolecules in the Drude polarizable FF.

  4. Computational rationalization of the selective C-H and C-F activations of fluoroaromatic imines and ketones by cobalt complexes.

    PubMed

    Li, Jingjing; Zhang, Dongju; Sun, Hongjian; Li, Xiaoyan

    2014-03-28

    While selective C-H and C-F activations of fluoroaromatic imines and ketones with transition metal complexes supported by PMe3 have been successfully achieved in recent publications, insight into the molecular mechanism and energetics of those reactions is still lacking. Focusing on three typical substrates, 2,6-difluorobenzophenone imine (A) and 2,6-difluorobenzophenone (B), and 2,4'-difluorobenzophenone (C), the present work theoretically studied their C-H and C-F cyclometalation reactions promoted by the activator Co(PMe3)4 or CoMe(PMe3)4. It is found that reaction A + Co(PMe3)4 favors the C-F activation, reaction A + CoMe(PMe3)4 prefers the C-H activation, whereas both the C-H and C-F activation pathways may be viable for reactions B + CoMe(PMe3)4 and C + CoMe(PMe3)4. The experimentally observed C-H and C-F cyclometalation products have been rationalized by analyzing the thermodynamic and kinetic properties of two activation pathways. From calculated results combined with the experimental observations, we believe that three factors, i.e. the oxidation state of the metal center in the activators, the anchoring group of substrates, and substituted fluoroatom counts of the aromatic ring in substrates, affect the selectivity of C-H and C-F activations of fluoroaromatic ketones and imines. Calculated results are enlightening about the rational design of activators and substrates of fluoroaromatic imines and ketones to obtain the exclusive C-H or C-F bond activation product.

  5. Template-directed C-H insertion: synthesis of the dioxabicyclo[3.2.1]octane core of the zaragozic acids.

    PubMed

    Wardrop, D J; Velter, A I; Forslund, R E

    2001-07-26

    [reaction: see text] The preparation of (+/-)-24, a model for the core of the zaragozic acids, is reported. The pivotal reaction in this endeavor is the dirhodium(II)-catalyzed intramolecular C-H bond insertion of 2-diazoacetyl-1,3-dioxane 4, a transformation which generates four of the six stereocenters present in the core structure. A novel method for the diastereoselective synthesis of pyruvic acid acetals was also developed and employed in the preparation of 4 from xylitol derivative 7.

  6. Aerobic oxidative cyclization of benzamides via meta-selective C-H tert-alkylation: rapid entry to 7-alkylated isoquinolinediones.

    PubMed

    Tang, Shi; Deng, You-Lin; Li, Jie; Wang, Wen-Xin; Wang, Ying-Chun; Li, Zeng-Zeng; Yuan, Li; Chen, Shi-Lu; Sheng, Rui-Long

    2016-03-25

    A novel copper-catalyzed aerobic oxidative cyclization of benzamides via meta-selective C-H tert-alkylation using AIBN and analogues as radical precursors was described. This strategy provides an elusive and rapid means to 7-tert-alkylated isoquinolinediones, as well as the construction of tertiary alkyl-aryl C(sp(3))-C(sp(2)) bonds with positional selectivity.

  7. Synthesis of 2,3-dihydro-1H-indazoles by Rh(III)-catalyzed C-H cleavage of arylhydrazines.

    PubMed

    Yao, Jinzhong; Feng, Ruokun; Lin, Cong; Liu, Zhanxiang; Zhang, Yuhong

    2014-08-07

    A rhodium-catalyzed efficient method for the synthesis of 2,3-dihydro-1H-indazoles is described. The reaction of arylhydrazines with olefins results in the corresponding 2,3-dihydro 1H-indazoles with exclusive regioselectivity via C-H bond activation. The utility of the methodology is illustrated by a rapid synthesis of 1H-indazoles under mild reaction conditions in half an hour.

  8. Nickel-Catalyzed Stereoselective Alkenylation of C(sp(3))-H Bonds with Terminal Alkynes.

    PubMed

    Lin, Cong; Chen, Zhengkai; Liu, Zhanxiang; Zhang, Yuhong

    2017-02-17

    A nickel-catalyzed stereoselective alkenylation of an unactivated β-C(sp(3))-H bond in aliphatic amide with terminal alkynes using 8-aminoquinoline auxiliary is reported for the first time. This reaction displays excellent functional group tolerance with respect to both aliphatic amides and terminal alkynes and features a cheap nickel catalytic system. The 8-aminoquinolyl directing group could be smoothly removed, and the resultant β-styrylcarboxylic acid derivatives could serve as versatile building blocks for further transformation.

  9. Ruthenium(II)-Catalyzed C-H Activation of Imidamides and Divergent Couplings with Diazo Compounds: Substrate-Controlled Synthesis of Indoles and 3H-Indoles.

    PubMed

    Li, Yunyun; Qi, Zisong; Wang, He; Yang, Xifa; Li, Xingwei

    2016-09-19

    Indoles are an important structural motif that is commonly found in biologically active molecules. In this work, conditions for divergent couplings between imidamides and acceptor-acceptor diazo compounds were developed that afforded NH indoles and 3H-indoles under ruthenium catalysis. The coupling of α-diazoketoesters afforded NH indoles by cleavage of the C(N2 )-C(acyl) bond whereas α-diazomalonates gave 3H-indoles by C-N bond cleavage. This reaction constitutes the first intermolecular coupling of diazo substrates with arenes by ruthenium-catalyzed C-H activation.

  10. Catalytic Asymmetric Hydroamination of Unactivated Internal Olefins to Aliphatic Amines

    PubMed Central

    Yang, Yang; Shi, Shi-Liang; Niu, Dawen; Liu, Peng; Buchwald, Stephen L.

    2015-01-01

    Catalytic assembly of enantiopure aliphatic amines from abundant and readily available precursors has long been recognized as a paramount challenge in synthetic chemistry. Herein, we describe a mild and general copper-catalyzed hydroamination that effectively converts unactivated internal olefins, an important yet unexploited class of abundant feedstock chemicals, into highly enantioenriched α-branched amines (≥ 96% enantiomeric excess) featuring two minimally differentiated aliphatic substituents. This method provides a powerful means to access a broad range of advanced, highly functionalized enantioenriched amines of interest in pharmaceutical research and other areas. PMID:26138973

  11. Rh(III)-Catalyzed meta-C-H Olefination Directed by a Nitrile Template.

    PubMed

    Xu, Hua-Jin; Lu, Yi; Farmer, Marcus E; Wang, Huai-Wei; Zhao, Dan; Kang, Yan-Shang; Sun, Wei-Yin; Yu, Jin-Quan

    2017-02-15

    A range of Rh(III)-catalyzed ortho-C-H functionalizations have been developed; however, extension of this reactivity to remote C-H functionalizations through large-ring rhodacyclic intermediates has yet to be demonstrated. Herein we report the first example of the use of a U-shaped nitrile template to direct Rh(III)-catalyzed remote meta-C-H activation via a postulated 12-membered macrocyclic intermediate. Because the ligands used for Rh(III) catalysts are significantly different from those of Pd(II) catalysts, this offers new opportunities for future development of ligand-promoted meta-C-H activation reactions.

  12. Neutron Scattering of Aromatic and Aliphatic Liquids

    PubMed Central

    Falkowska, Marta; Bowron, Daniel T.; Manyar, Haresh G.

    2016-01-01

    Abstract Organic solvents, such as cyclohexane, cyclohexene, methylcyclohexane, benzene and toluene, are widely used as both reagents and solvents in industrial processes. Despite the ubiquity of these liquids, the local structures that govern the chemical properties have not been studied extensively. Herein, we report neutron diffraction measurements on liquid cyclohexane, cyclohexene, methylcyclohexane, benzene and toluene at 298 K to obtain a detailed description of the local structure in these compounds. The radial distribution functions of the centres of the molecules, as well as the partial distribution functions for the double bond for cyclohexene and methyl group for methylcyclohexane and toluene have been calculated. Additionally, probability density functions and angular radial distribution functions were extracted to provide a full description of the local structure within the chosen liquids. Structural motifs are discussed and compared for all liquids, referring specifically to the functional group and aromaticity present in the different liquids. PMID:26990367

  13. Applicability of the theory of thermodynamic similarity to predict the enthalpies of vaporization of aliphatic aldehydes

    NASA Astrophysics Data System (ADS)

    Esina, Z. N.; Korchuganova, M. R.

    2015-06-01

    The theory of thermodynamic similarity is used to predict the enthalpies of vaporization of aliphatic aldehydes. The predicted data allow us to calculate the phase diagrams of liquid-vapor equilibrium in a binary water-aliphatic aldehyde system.

  14. 40 CFR 721.10199 - Substituted aliphatic amine (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... aliphatic amine (PMN P-06-702) is subject to reporting under this section for the significant new uses...-specific cartridge) and should include a particulate filter (N100 if oil aerosols are absent, R100, or P100... (HEPA) filters; supplied-air respirator operated in pressure demand or continuous flow mode and...

  15. 40 CFR 721.10199 - Substituted aliphatic amine (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... aliphatic amine (PMN P-06-702) is subject to reporting under this section for the significant new uses...-specific cartridge) and should include a particulate filter (N100 if oil aerosols are absent, R100, or P100... (HEPA) filters; supplied-air respirator operated in pressure demand or continuous flow mode and...

  16. 40 CFR 721.10199 - Substituted aliphatic amine (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... aliphatic amine (PMN P-06-702) is subject to reporting under this section for the significant new uses...-specific cartridge) and should include a particulate filter (N100 if oil aerosols are absent, R100, or P100... (HEPA) filters; supplied-air respirator operated in pressure demand or continuous flow mode and...

  17. Degradation Characterization of Aliphatic POLYESTERS—IN Vitro Study

    NASA Astrophysics Data System (ADS)

    Vieira, A. C.; Vieira, J. C.; Guedes, R. M.; Marques, A. T.

    2008-08-01

    The most popular and important biodegradable polymers are aliphatic polyesters, such as polylactic acid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL), polyhydoxyalkanoates (PHA's) and polyethylene oxide (PEO). However, each of these has some shortcomings which restrict its applications. Blending techniques are an extremely promising approach which can improve or tune the original properties of the polymers[1]. Aliphatic polyesters are a central class of biodegradable polymers, because hydrolytic and/or enzymatic chain cleavage of these materials leads to α-hydroxyacids, which in most cases are ultimately metabolized in human body. This is particularly useful for controlled release devices and for other biomedical applications like suture fibers and ligaments. For aliphatic polyesters, hydrolysis rates are affected by the temperature, molecular structure, and ester group density as well as by the species of enzyme used. The degree of crystallinity may be a crucial factor, since enzymes attack mainly the amorphous domains of a polymer. Four different aliphatic polyesters were characterized in terms of degradation. Sutures fibers of PGA-PCL, PGA, PLA-PCL and PDO were used in this study. Weight loss, pH, molecular weight, crystallinity and strength were measured after six stages of incubation in distilled water, physiological saline and phosphate buffer solution (PBS). Degradation rate was determined, using a first order kinetic equation for all materials in the three incubation media. A relatively wide range of mechanical properties and degradation rates were observed among the materials studied. PBS was the most aggressive environment for the majority of cases.

  18. Introducing Aliphatic Substitution with a Discovery Experiment Using Competing Electrophiles

    ERIC Educational Resources Information Center

    Curran, Timothy P.; Mostovoy, Amelia J.; Curran, Margaret E.; Berger, Clara

    2016-01-01

    A facile, discovery-based experiment is described that introduces aliphatic substitution in an introductory undergraduate organic chemistry curriculum. Unlike other discovery-based experiments that examine substitution using two competing nucleophiles with a single electrophile, this experiment compares two isomeric, competing electrophiles…

  19. Suppression of the Ethanol Withdrawal Syndrome by Aliphatic Diols

    DTIC Science & Technology

    1979-06-07

    Two halogenated hydrocarbons , alcohols exert their intoxicating properties through an interac- which are amphiphiles like alcohols and diols, were both...induce a virtually identical spectrum of phatic hydrocarbons could not. The data suggest that short- intoxication signs. Because of their pharmacological...their ability to induce to determine if partitioning into membrasps is an important intoxication since 1) alcohols and aliphatic hydrocarbons with

  20. Cloud condensation nuclei activity of aliphatic amine secondary aerosol

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aliphatic amines can form secondary aerosol via oxidation with atmospheric radicals (e.g. hydroxyl radical and nitrate radical). The resulting particle composition can contain both secondary organic aerosol (SOA) and inorganic salts. The fraction of organic to inorganic materials in the particulate ...

  1. Ruthenium-catalyzed direct C-H amidation of arenes including weakly coordinating aromatic ketones.

    PubMed

    Kim, Jiyu; Kim, Jinwoo; Chang, Sukbok

    2013-06-03

    C-H activation: The ruthenium-catalyzed direct sp(2) C-H amidation of arenes by using sulfonyl azides as the amino source is presented (see scheme). A wide range of substrates were readily amidated including arenes bearing weakly coordinating groups. Synthetic utility of the thus obtained products was demonstrated in the preparation of biologically active heterocycles.

  2. 40 CFR 721.7250 - Polyaziridinyl ester of an aliphatic alcohol (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Polyaziridinyl ester of an aliphatic... Specific Chemical Substances § 721.7250 Polyaziridinyl ester of an aliphatic alcohol (generic). (a... generically as a polyaziridinyl ester of an aliphatic alcohol (PMN P-01-97) is subject to reporting under...

  3. 40 CFR 721.7250 - Polyaziridinyl ester of an aliphatic alcohol (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Polyaziridinyl ester of an aliphatic... Specific Chemical Substances § 721.7250 Polyaziridinyl ester of an aliphatic alcohol (generic). (a... generically as a polyaziridinyl ester of an aliphatic alcohol (PMN P-01-97) is subject to reporting under...

  4. 40 CFR 721.10289 - Hexanedioic acid polymer with aliphatic polyol dihydrogen phosphate aromatic ester (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... aliphatic polyol dihydrogen phosphate aromatic ester (generic). 721.10289 Section 721.10289 Protection of... polymer with aliphatic polyol dihydrogen phosphate aromatic ester (generic). (a) Chemical substance and... acid polymer with aliphatic polyol dihydrogen phosphate aromatic ester (PMN P-11-333) is subject...

  5. 40 CFR 721.10289 - Hexanedioic acid polymer with aliphatic polyol dihydrogen phosphate aromatic ester (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... aliphatic polyol dihydrogen phosphate aromatic ester (generic). 721.10289 Section 721.10289 Protection of... polymer with aliphatic polyol dihydrogen phosphate aromatic ester (generic). (a) Chemical substance and... acid polymer with aliphatic polyol dihydrogen phosphate aromatic ester (PMN P-11-333) is subject...

  6. 40 CFR 721.10608 - Aliphatic diisocyanate polymer with alkanediol and alkylglycol (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Aliphatic diisocyanate polymer with... Significant New Uses for Specific Chemical Substances § 721.10608 Aliphatic diisocyanate polymer with.... (1) The chemical substance identified generically as aliphatic diisocyanate polymer with...

  7. 40 CFR 721.10608 - Aliphatic diisocyanate polymer with alkanediol and alkylglycol (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Aliphatic diisocyanate polymer with... Significant New Uses for Specific Chemical Substances § 721.10608 Aliphatic diisocyanate polymer with.... (1) The chemical substance identified generically as aliphatic diisocyanate polymer with...

  8. 40 CFR 721.2098 - Aliphatic polycarboxylic acid metal salt (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Aliphatic polycarboxylic acid metal... Specific Chemical Substances § 721.2098 Aliphatic polycarboxylic acid metal salt (generic). (a) Chemical... as an aliphatic polycarboxylic acid metal salt (PMN P-01-7) is subject to reporting under...

  9. 40 CFR 721.2098 - Aliphatic polycarboxylic acid metal salt (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Aliphatic polycarboxylic acid metal... Specific Chemical Substances § 721.2098 Aliphatic polycarboxylic acid metal salt (generic). (a) Chemical... as an aliphatic polycarboxylic acid metal salt (PMN P-01-7) is subject to reporting under...

  10. 40 CFR 721.2098 - Aliphatic polycarboxylic acid metal salt (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Aliphatic polycarboxylic acid metal... Specific Chemical Substances § 721.2098 Aliphatic polycarboxylic acid metal salt (generic). (a) Chemical... as an aliphatic polycarboxylic acid metal salt (PMN P-01-7) is subject to reporting under...

  11. 40 CFR 721.2098 - Aliphatic polycarboxylic acid metal salt (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Aliphatic polycarboxylic acid metal... Specific Chemical Substances § 721.2098 Aliphatic polycarboxylic acid metal salt (generic). (a) Chemical... as an aliphatic polycarboxylic acid metal salt (PMN P-01-7) is subject to reporting under...

  12. 40 CFR 721.2098 - Aliphatic polycarboxylic acid metal salt (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Aliphatic polycarboxylic acid metal... Specific Chemical Substances § 721.2098 Aliphatic polycarboxylic acid metal salt (generic). (a) Chemical... as an aliphatic polycarboxylic acid metal salt (PMN P-01-7) is subject to reporting under...

  13. Double C-H functionalization in sequential order: direct synthesis of polycyclic compounds by a palladium-catalyzed C-H alkenylation-arylation cascade.

    PubMed

    Ohno, Hiroaki; Iuchi, Mutsumi; Kojima, Naoto; Yoshimitsu, Takehiko; Fujii, Nobutaka; Tanaka, Tetsuaki

    2012-04-23

    Palladium-catalyzed cascade C-H alkenylation and arylation provides convenient access to polycyclic aromatic compounds. Treatment of 3-bromoaniline derivatives bearing a bromocinnamyl group on the nitrogen atom with a catalytic amount of [Pd(OAc)(2)] and PCy(3)·HBF(4) in the presence of Cs(2)CO(3) in dioxane affords naphthalene-fused indole derivatives in good yields. This double cyclization reaction is also applicable to heterocyclic substrates, giving fused indoles containing a heteroaromatic ring such as dibenzofuran, dibenzothiophene, carbazole, indole, or benzofuran through heterocyclic C-H arylation. When using a 2,6-unsubstituted aniline derivative, the first C-H arylation preferentially proceeds at the more hindered position of the aniline ring.

  14. a-C:H/a-C:H(N) thin film deposition using 2.45 GHz expanding surface wave sustained plasmas

    NASA Astrophysics Data System (ADS)

    Hong, Suk-Ho; Douai, David; Berndt, Johannes; Winter, Jörg

    2005-08-01

    Thin film properties such as homogeneity (radial profiles), optical constants, carbon density in the film, and the surface structures are strongly dependent on deposition conditions. We have investigated a-C:H/a-C:H(N) thin film deposition by expanding Ar-CH4 and Ar/N2-CH4 surface wave sustained plasmas at a frequency of 2.45 GHz. The influence of the plasma parameters such as pressure, input power, gas mixture rate, and an external bias voltage on the change of the film properties is systematically studied. An external bias applied to the substrate leads to more dense and harder a-C:H films, i.e. change from soft polymer-like to hard diamond-like. Rutherford backscattering and atomic force microscope surface topology confirm the densification of the films.

  15. Manganese(I)-Catalyzed Dispersion-Enabled C-H/C-C Activation.

    PubMed

    Meyer, Tjark H; Liu, Weiping; Feldt, Milica; Wuttke, Axel; Mata, Ricardo A; Ackermann, Lutz

    2017-03-20

    C-H/C-C Functionalizations were achieved with the aid of a versatile manganese(I) catalyst. Thus, an organometallic manganese-catalyzed C-H activation set the stage for silver-free C-H/C-C transformations with ample substrate scope and excellent levels of chemo-, site-, and diastereo-selectivities. The robust nature of the manganese(I) catalysis regime was reflected by the first C-H/C-C functionalization on amino acids under racemization-free reaction conditions. Detailed experimental and computational mechanistic studies provided strong evidence for a facile C-H activation and a rate-determining C-C cleavage, with considerable contribution from London dispersion interactions.

  16. Diamond-like a-C:H coatings deposited in a non-self-sustained discharge with plasma cathode

    NASA Astrophysics Data System (ADS)

    Gavrilov, N. V.; Mamaev, A. S.; Kaĭigorodov, A. S.

    2009-01-01

    Hydrogenated amorphous carbon (a-C:H) coatings have been obtained by means of acetylene decomposition in a non-self-sustained periodic pulse discharge (2A, 50 kHz, 10 μs) with hollow cathode. The discharge operation was maintained by plasma cathode emission with grid stabilization based on dc glow discharge. Using the proposed method, it is possible to control the deposition conditions (total pressure of the Ar + C2H2 mixture, partial pressure of C2H2, ion current density, carbon ion energy) within broad limits, to apply a-C:H coatings onto large-area articles, and to perform deposition in one technological cycle with ion etching and ion implantation treatments aimed at improving the adhesion of coatings to substrates (Ti, Al, stainless steel, VK8 hard alloy) at temperatures below 150°C. Results of determining the deposition rate (1-8 μm), the nanohardness of coatings (up to 70 GPa), and the fraction of sp 3 bonds (25-70%) in the diamond-like coating material are presented.

  17. Understanding the differential performance of Rh2(esp)2 as a catalyst for C-H amination.

    PubMed

    Zalatan, David N; Du Bois, J

    2009-06-10

    Catalytic amination of saturated C-H bonds is performed efficiently with the use of Rh(2)(esp)(2). Efforts to identify pathways for catalyst degradation and/or arrest have revealed a single-electron oxidation event that gives rise to a red-colored, mixed-valence dimer, [Rh(2)(esp)(2)](+). This species is fortuitously reduced by carboxylic acid, a byproduct generated in the reaction cycle with each turnover of the diacyloxyiodine oxidant. These findings have led to the conclusion that the high performance of Rh(2)(esp)(2) is due in part to the superior kinetic stability of its one-electron oxidized form relative to other dimeric Rh complexes.

  18. Sticker Bonding.

    ERIC Educational Resources Information Center

    Frazier, Laura Corbin

    2000-01-01

    Introduces a science activity on the bonding of chemical compounds. Assigns students the role of either a cation or anion and asks them to write the ions they may bond with. Assesses students' understanding of charge, bonding, and other concepts. (YDS)

  19. A Quantitative Structure-Property Relationship (QSPR) Study of aliphatic alcohols by the method of dividing the molecular structure into substructure.

    PubMed

    Liu, Fengping; Cao, Chenzhong; Cheng, Bin

    2011-01-01

    A quantitative structure-property relationship (QSPR) analysis of aliphatic alcohols is presented. Four physicochemical properties were studied: boiling point (BP), n-octanol-water partition coefficient (lg P(OW)), water solubility (lg W) and the chromatographic retention indices (RI) on different polar stationary phases. In order to investigate the quantitative structure-property relationship of aliphatic alcohols, the molecular structure ROH is divided into two parts, R and OH to generate structural parameter. It was proposed that the property is affected by three main factors for aliphatic alcohols, alkyl group R, substituted group OH, and interaction between R and OH. On the basis of the polarizability effect index (PEI), previously developed by Cao, the novel molecular polarizability effect index (MPEI) combined with odd-even index (OEI), the sum eigenvalues of bond-connecting matrix (SX(1CH)) previously developed in our team, were used to predict the property of aliphatic alcohols. The sets of molecular descriptors were derived directly from the structure of the compounds based on graph theory. QSPR models were generated using only calculated descriptors and multiple linear regression techniques. These QSPR models showed high values of multiple correlation coefficient (R > 0.99) and Fisher-ratio statistics. The leave-one-out cross-validation demonstrated the final models to be statistically significant and reliable.

  20. Cross-dehydrogenative coupling (CDC): exploring C-C bond formations beyond functional group transformations.

    PubMed

    Li, Chao-Jun

    2009-02-17

    Synthetic chemists aspire both to develop novel chemical reactions and to improve reaction conditions to maximize resource efficiency, energy efficiency, product selectivity, operational simplicity, and environmental health and safety. Carbon-carbon bond formation is a central part of many chemical syntheses, and innovations in these types of reactions will profoundly improve overall synthetic efficiency. This Account describes our work over the past several years to form carbon-carbon bonds directly from two different C-H bonds under oxidative conditions, cross-dehydrogenative coupling (CDC). We have focused most of our efforts on carbon-carbon bonds formed via the functionalization of sp(3) C-H bonds with other C-H bonds. In the presence of simple and cheap catalysts such as copper and iron salts and oxidants such as hydrogen peroxide, dioxygen, tert-butylhydroperoxide, and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ), we can directly functionalize various sp(3) C-H bonds by other C-H bonds without requiring preactivation. We demonstrate (1) reaction of alpha-C-H bonds of nitrogen in amines, (2) reaction of alpha-C-H bonds of oxygen in ethers, (3) reaction of allylic and benzylic C-H bonds, and (4) reaction of alkane C-H bonds. These CDC reactions can tolerate a variety of functional groups, and some can occur under aqueous conditions. Depending on the specific transformation, we propose the in situ generation of different intermediates. These methods provide an alternative to the separate steps of prefunctionalization and defunctionalization that have traditionally been part of synthetic design. As a result, these methods will increase synthetic efficiencies at the most fundamental level. On an intellectual level, the development of C-C bond formations based on the reaction of only C-H bonds (possibly in water) challenges us to rethink some of the most fundamental concepts and theories regarding chemical reactivities. A successful reaction requires the

  1. Rh(III)-Catalyzed Cascade Annulation/C-H Activation of o-Ethynylanilines with Diazo Compounds: One-Pot Synthesis of Benzo[a]carbazoles via 1,4-Rhodium Migration.

    PubMed

    Guo, Songjin; Yuan, Kai; Gu, Meng; Lin, Aijun; Yao, Hequan

    2016-10-05

    A Rh(III)-catalyzed cascade annulation/C-H activation of o-ethynylanilines with diazo compounds has been developed. This concise method allows for the rapid formation of a number of benzo[a]carbazoles in high yields, exhibiting good functional group tolerance and scalability. The key to the success of this approach involves one C-N bond and two C-C bond formation, and an aryl-to-aryl 1,4-rhodium migration.

  2. Ni nanoparticle catalyzed growth of MWCNTs on Cu NPs @ a-C:H substrate

    NASA Astrophysics Data System (ADS)

    Ghodselahi, T.; Solaymani, S.; Akbarzadeh Pasha, M.; Vesaghi, M. A.

    2012-11-01

    NiCu NPs @ a-C:H thin films with different Cu content were prepared by co-deposition by RF-sputtering and RF-plasma enhanced chemical vapor deposition (RF-PECVD) from acetylene gas and Cu and Ni targets. The prepared samples were used as catalysts for growing multi-wall carbon nanotubes (MWCNTs) from liquid petroleum gas (LPG) at 825 °C by thermal chemical vapor deposition (TCVD). By addition of Cu NPs @ a-C:H thin layer as substrate for Ni NPs catalyst, the density of the grown CNTs is greatly enhanced in comparison to bare Si substrate. Furthermore the average diameter of the grown CNTs decreases by decreasing of Cu content of Cu NPs @ a-C:H thin layer. However Cu NPs @ a-C:H by itself has no catalytic property in MWCNTs growth. Morphology and electrical and optical properties of Cu NPs @ a-C:H thin layer is affected by Cu content and each of them is effective parameter on growth of MWCNTs based on Ni NPs catalyst. Moreover, adding of a low amount of Ni NPs doesn't vary optical, electrical and morphology properties of Cu NPs @ a-C:H thin layer but it has a profound effect on its catalytic activity. Finally the density and diameter of MWCNTs can be optimized by selection of the Cu NPs @ a-C:H thin layer as substrate of Ni NPs.

  3. N-Acyl Amino Acid Ligands for Ruthenium(II)-Catalyzed meta-C-H tert-Alkylation with Removable Auxiliaries.

    PubMed

    Li, Jie; Warratz, Svenja; Zell, Daniel; De Sarkar, Suman; Ishikawa, Eloisa Eriko; Ackermann, Lutz

    2015-11-04

    Acylated amino acid ligands enabled ruthenium(II)-catalyzed C-H functionalizations with excellent levels of meta-selectivity. The outstanding catalytic activity of the ruthenium(II) complexes derived from monoprotected amino acids (MPAA) set the stage for the first ruthenium-catalyzed meta-functionalizations with removable directing groups. Thereby, meta-alkylated anilines could be accessed, which are difficult to prepare by other means of direct aniline functionalizations. The robust nature of the versatile ruthenium(II)-MPAA was reflected by challenging remote C-H transformations with tertiary alkyl halides on aniline derivatives as well as on pyridyl-, pyrimidyl-, and pyrazolyl-substituted arenes. Detailed mechanistic studies provided strong support for an initial reversible C-H ruthenation, followed by a SET-type C-Hal activation through homolytic bond cleavage. Kinetic analyses confirmed this hypothesis through an unusual second-order dependence of the reaction rate on the ruthenium catalyst concentration. Overall, this report highlights the exceptional catalytic activity of ruthenium complexes derived from acylated amino acids, which should prove instrumental for C-H activation chemistry beyond remote functionalization.

  4. Use of the Wilkinson catalyst for the ortho-C-H heteroarylation of aromatic amines: facile access to highly extended π-conjugated heteroacenes for organic semiconductors.

    PubMed

    Huang, Yumin; Wu, Di; Huang, Jingsheng; Guo, Qiang; Li, Juan; You, Jingsong

    2014-11-03

    An unprecedented catalytic system composed of the Wilkinson catalyst [Rh(PPh3)3Cl] and CF3COOH enabled the highly regioselective cross-coupling of aromatic amines with a variety of heteroarenes through dual C-H bond cleavage. This protocol provided a facile and rapid route from readily available substrates to (2-aminophenyl)heteroaryl compounds, which may be conveniently transformed into highly extended π-conjugated heteroacenes. The experimental studies and calculations showed that thianaphtheno[3,2-b]indoles have large HOMO-LUMO energy gaps and low-lying HOMO levels, and could therefore potentially be high-performance organic semiconductors. Herein we report the first use of a rhodium(I) catalyst for oxidative C-H/C-H coupling reactions. The current innovative catalyst system is much less expensive than [RhCp*Cl2]2/AgSbF6 and could open the door for the application of this approach to other types of C-H activation processes.

  5. Blue-shift of the C-H stretching vibration in CHF3-H2O complex: Matrix isolation infrared spectroscopy and ab initio computations

    NASA Astrophysics Data System (ADS)

    Gopi, R.; Ramanathan, N.; Sundararajan, K.

    2016-09-01

    As a result of hydrogen bonding in CHF3-H2O complex, ab initio computations exhibited a blue shift in the C-H stretching region of CHF3 sub-molecule. In this work, we have investigated whether the blue-shifting in CHF3-H2O complex can be experimentally discerned using matrix isolation infrared spectroscopy. The 1:1 CHF3-H2O complex was therefore trapped and studied in argon and neon matrices. Experimentally a blue shift of 20.3 and 32.3 cm-1 in the C-H stretching region of CHF3 sub-molecule for the CHF3-H2O complex was observed in argon and neon matrices. The structure of the complex and the energies were computed at MP2 level of theory using a 6-311++G(d,p) and aug-cc-pVDZ basis sets. Computations indicated only one minimum corresponded to a C-H⋯O interaction between the hydrogen of fluoroform and oxygen of water. AIM and NBO analyses were performed to understand the reasons for blue-shifting of the C-H stretching wavenumber in the complex.

  6. meta-C-H Bromination on Purine Bases by Heterogeneous Ruthenium Catalysis.

    PubMed

    Warratz, Svenja; Burns, David J; Zhu, Cuiju; Korvorapun, Korkit; Rogge, Torben; Scholz, Julius; Jooss, Christian; Gelman, Dmitri; Ackermann, Lutz

    2017-02-01

    Methods for positionally selective remote C-H functionalizations are in high demand. Herein, we disclose the first heterogeneous ruthenium catalyst for meta-selective C-H functionalizations, which enabled remote halogenations with excellent site selectivity and ample scope. The versatile heterogeneous Ru@SiO2 catalyst was broadly applicable and could be easily recovered and reused, which set the stage for the direct fluorescent labeling of purines. In contrast to palladium, rhodium, iridium, or cobalt complexes, solely the ruthenium catalysis manifold provided access to meta-halogenated purine derivatives, illustrating the unique power of ruthenium C-H activation catalysis.

  7. Red-Shifting versus Blue-Shifting Hydrogen Bonds: Perspective from Ab Initio Valence Bond Theory.

    PubMed

    Chang, Xin; Zhang, Yang; Weng, Xinzhen; Su, Peifeng; Wu, Wei; Mo, Yirong

    2016-05-05

    Both proper, red-shifting and improper, blue-shifting hydrogen bonds have been well-recognized with enormous experimental and computational studies. The current consensus is that there is no difference in nature between these two kinds of hydrogen bonds, where the electrostatic interaction dominates. Since most if not all the computational studies are based on molecular orbital theory, it would be interesting to gain insight into the hydrogen bonds with modern valence bond (VB) theory. In this work, we performed ab initio VBSCF computations on a series of hydrogen-bonding systems, where the sole hydrogen bond donor CF3H interacts with ten hydrogen bond acceptors Y (═NH2CH3, NH3, NH2Cl, OH(-), H2O, CH3OH, (CH3)2O, F(-), HF, or CH3F). This series includes four red-shifting and six blue-shifting hydrogen bonds. Consistent with existing findings in literature, VB-based energy decomposition analyses show that electrostatic interaction plays the dominating role and polarization plays the secondary role in all these hydrogen-bonding systems, and the charge transfer interaction, which denotes the hyperconjugation effect, contributes only slightly to the total interaction energy. As VB theory describes any real chemical bond in terms of pure covalent and ionic structures, our fragment interaction analysis reveals that with the approaching of a hydrogen bond acceptor Y, the covalent state of the F3C-H bond tends to blue-shift, due to the strong repulsion between the hydrogen atom and Y. In contrast, the ionic state F3C(-) H(+) leads to the red-shifting of the C-H vibrational frequency, owing to the attraction between the proton and Y. Thus, the relative weights of the covalent and ionic structures essentially determine the direction of frequency change. Indeed, we find the correlation between the structural weights and vibrational frequency changes.

  8. Rapid synthesis of fused N-heterocycles by transition-metal-free electrophilic amination of arene C-H bonds.

    PubMed

    Gao, Hongyin; Xu, Qing-Long; Yousufuddin, Muhammed; Ess, Daniel H; Kürti, László

    2014-03-03

    We disclose an efficient and operationally simple protocol for the preparation of fused N-heterocycles starting from readily available 2-nitrobiaryls and PhMgBr under mild conditions. More than two dozen N-heterocycles, including two bioactive natural products, have been synthesized using this method. A stepwise electrophilic aromatic cyclization mechanism was proposed by DFT calculations.

  9. Rh(I)-Catalyzed Arylation of Heterocycles via C-H Bond Activation: Expanded Scope Through Mechanistic Insight

    SciTech Connect

    Lewis, Jared; Berman, Ashley; Bergman, Robert; Ellman, Jonathan

    2007-07-18

    A practical, functional group tolerant method for the Rh-catalyzed direct arylation of a variety of pharmaceutically important azoles with aryl bromides is described. Many of the successful azole and aryl bromide coupling partners are not compatible with methods for the direct arylation of heterocycles using Pd(0) or Cu(I) catalysts. The readily prepared, low molecular weight ligand, Z-1-tert-butyl-2,3,6,7-tetrahydrophosphepine, which coordinates to Rh in a bidentate P-olefin fashion to provide a highly active yet thermally stable arylation catalyst, is essential to the success of this method. By using the tetrafluoroborate salt of the corresponding phosphonium, the reactions can be assembled outside of a glove box without purification of reagents or solvent. The reactions are also conducted in THF or dioxane, which greatly simplifies product isolation relative to most other methods for direct arylation of azoles employing high-boiling amide solvents. The reactions are performed with heating in a microwave reactor to obtain excellent product yields in two hours.

  10. Copper-dioxygen complex mediated C-H bond oxygenation: relevance for particulate methane monooxygenase (pMMO).

    PubMed

    Himes, Richard A; Karlin, Kenneth D

    2009-02-01

    Particulate methane monooxygenase (pMMO), an integral membrane protein found in methanotrophic bacteria, catalyzes the oxidation of methane to methanol. Expression and greater activity of the enzyme in the presence of copper ion suggest that pMMO is a cuprous metalloenzyme. Recent advances - especially the first crystal structures of pMMO - have energized the field, but the nature of the active site(s) and the mechanism of methane oxidation remain poorly understood-yet hotly contested. Herein the authors briefly review the current understanding of the pMMO metal sites and discuss advances in small molecule Cu-O(2) chemistry that may contribute to an understanding of copper-ion mediated hydrocarbon oxidation chemistry.

  11. Activation of C-H bonds of arenes: selectivity and reactivity in bis(pyridyl) platinum(II) complexes.

    PubMed

    Zhang, Fenbao; Kirby, Christopher W; Hairsine, Douglas W; Jennings, Michael C; Puddephatt, Richard J

    2005-10-19

    The reaction of [PtMe2(NN)] and B(C6F5)3/H2O in CF3CH2OH with arenes Ar-H gives [PtAr{HOB(C6F5)3}(LL)] if the bis(pyridyl) ligand NN forms a six-membered, but not five-membered, chelate ring; methyl-substituted arenes give selectivity for metalation of meta > para > ortho, but methoxy-substituted arenes give ortho > meta, para.

  12. Lanthanum-mediated C-H bond activation of propyne and identification of La(C₃H₂) isomers.

    PubMed

    Hewage, Dilrukshi; Roudjane, Mourad; Silva, W Ruchira; Kumari, Sudesh; Yang, Dong-Sheng

    2015-03-26

    η(2)-Propadienylidenelanthanum [La(η(2)-CCCH2)] and deprotiolanthanacyclobutadiene [La(HCCCH)] of La(C3H2) are identified from the reaction mixture of neutral La atom activation of propyne in the gas phase. The two isomers are characterized with mass-analyzed threshold ionization spectroscopy combined with electronic structure calculations and spectral simulations. La(η(2)-CCCH2) and La(HCCCH) are formed by concerted 1,3- and 3,3-dehydrogenation, respectively. Both isomers prefer a doublet ground state with a La 6s-based unpaired electron, and La(η(2)-CCCH2) is slightly more stable than La(HCCCH). Ionization of the neutral doublet state of either isomer produces a singlet ion state by removing the La-based electron. The geometry change upon ionization results in the excitation of a symmetric metal-hydrocarbon stretching mode in the ionic state, whereas thermal excitation leads to the observation of the same stretching mode in the neutral state. Although the La atom is in a formal oxidation state of +2, the ionization energies of these metal-hydrocarbon radicals are lower than that of the neutral La atom. Deuteration has a very small effect on the ionization energies of the two isomers and the metal-hydrocarbon stretching mode of La(η(2)-CCCH2), but it reduces considerably the metal-ligand stretching frequencies of La(HCCCH).

  13. Biotic and abiotic carbon to sulfur bond cleavage. Technical report, July 1, 1991--September 30, 1991

    SciTech Connect

    Frost, J.W.

    1991-12-31

    Cleavage of aliphatic organosulfonate carbon to sulfur (C-S) bonds, a critical link in the global biogeochemical sulfur cycle, has been identified in Escherichia coli K-12. Enormous quantities of inorganic sulfate are continuously converted (Scheme I) into methanesulfonic acid 1 and acylated 3-(6-sulfo-{alpha}-D-quinovopyranosyl)-L-glycerol 2. Biocatalytic desulfurization (Scheme I) of 1 and 2, which share the structural feature of an aliphatic carbon bonded to a sulfonic acid sulfur, completes the cycle, Discovery of this desulfurization in E. coli provides an invaluable paradigm for study of a biotic process which, via the biogeochemical cycle, significantly influences the atmospheric concentration of sulfur-containing molecules.

  14. Biodegradation of Trihalomethanes and Other Halogenated Aliphatic Compounds

    NASA Technical Reports Server (NTRS)

    Smith, G. B.

    1996-01-01

    The biological dehalogenation of common water pollutants such as trichloromethane (chloroform) and other halogenated aliphatic compounds was the subject of this project. Samples from diverse water environments such as from groundwater contaminated with halogenated compounds and wastewaters from regional treatment plants were studied to identify conditions that favor certain dehalogenation reactions over others. Gene probe analyses of DNA extracted from the dichlormethane-degrading wastewater indicated the presence of the gene coding for dichloromethane dehalogenase, indicating the genetic basis for the dechlorination activity observed. These studies indicate that methanogenic bacteria are the organisms responsible for the chloroform dechlorination. Dechlorination of a common chlorofluorocarbon (CFC-11) was identified in samples taken from a regional aquifer contaminated with halogenated aliphatic compounds.

  15. Lipstick dermatitis due to C18 aliphatic compounds.

    PubMed

    Hayakawa, R; Matsunaga, K; Suzuki, M; Arima, Y; Ohkido, Y

    1987-04-01

    An 18-year-old girl developed cheilitis. She had a past history of lip cream dermatitis, but the cause was not found. Patch tests with 2 lipsticks were strongly positive. Tests with the ingredients were positive to 2 aliphatic compounds, glyceryl diisostearate and diisostearyl malate. Impurities in the materials were suspected as the cause. Analysis by gas chromatography detected 3 chemicals in glyceryl diisostearate and 1 in diisostearyl malate as impurities. Patch testing with the impurities and glyceryl monoisostearate 0.01% pet in glyceryl diisostearate and isostearyl alcohol 0.25% pet in diisostearyl malate were strongly positive. The characteristics common to the 2 chemicals were liquidity at room temperature, branched C18 aliphatic compound and primary alcohol. Chemicals lacking any of the above 3 features did not react.

  16. IMPROVED BONDING METHOD

    DOEpatents

    Padgett, E.V. Jr.; Warf, D.H.

    1964-04-28

    An improved process of bonding aluminum to aluminum without fusion by ultrasonic vibrations plus pressure is described. The surfaces to be bonded are coated with an aqueous solution of alkali metal stearate prior to assembling for bonding. (AEC) O H19504 Present information is reviewed on steady state proliferation, differentiation, and maturation of blood cells in mammals. Data are cited from metabolic tracer studies, autoradiographic studies, cytologic studies, studies of hematopoietic response to radiation injuries, and computer analyses of blood cell production. A 3-step model for erythropoiesis and a model for granulocyte kinetics are presented. New approaches to the study of lymphocytopoiesis described include extracorporeal blood irradiation to deplete lymphocytic tissue without direct injury to the formative tissues as a means to study the stressed system, function control, and rates of proliferation. It is pointed out that present knowledge indicates that lymphocytes comprise a mixed family, with diverse life spans, functions, and migration patterns with apparent aimless recycling from modes to lymph to blood to nodes that has not yet been quantitated. Areas of future research are postulated. (70 references.) (C.H.)

  17. Aerobic microorganism for the degradation of chlorinated aliphatic hydrocarbons

    DOEpatents

    Fliermans, Carl B.

    1989-01-01

    A chlorinated aliphatic hydrocarbon-degrading microorganism, having American Type Culture Collection accession numbers ATCC 53570 and 53571, in a biologically pure culture aseptically collected from a deep subsurface habitat and enhanced, mineralizes trichloroethylene and tetrachloroethylene to HCl, H.sub.2 O and Co.sub.2 under aerobic conditions stimulated by methane, acetate, methanol, tryptone-yeast extract, propane and propane-methane.

  18. Manganese-Mediated Coupling Reaction of Vinylarenes and Aliphatic Alcohols

    PubMed Central

    Zhang, Wei; Wang, Nai-Xing; Bai, Cui-Bing; Wang, Yan-Jing; Lan, Xing-Wang; Xing, Yalan; Li, Yi-He; Wen, Jia-Long

    2015-01-01

    Alcohols and alkenes are the most abundant and commonly used organic building blocks in the large-scale chemical synthesis. Herein, this is the first time to report a novel and operationally simple coupling reaction of vinylarenes and aliphatic alcohols catalyzed by manganese in the presence of TBHP (tert-butyl hydroperoxide). This coupling reaction provides the oxyalkylated products of vinylarenes with good regioselectivity and accomplishes with the principles of step-economies. A possible reaction mechanism has also been proposed. PMID:26470633

  19. Synthesis of Dihydropyridines and Pyridines from Imines and Alkynes via C-H Activation

    SciTech Connect

    Ellman, Jonathan A.; Colby, Denise; Bergman, Robert

    2007-11-20

    A convenient one-pot C-H alkenylation/electrocyclization/aromatization sequence has been developed for the synthesis of highly substituted pyridine derivatives from alkynes and {alpha},{beta}-unsaturated N-benzyl aldimines and ketimines that proceeds through dihydropyridine intermediates. A new class of ligands for C-H activation was developed, providing broader scope for the alkenylation step than could be achieved with previously reported ligands. Substantial information was obtained about the mechanism of the reaction. This included the isolation of a C-H activated complex and its structure determination by X-ray analysis; in addition, kinetic simulations using the Copasi software were employed to determine rate constants for this transformation, implicating facile C-H oxidative addition and slow reductive elimination steps.

  20. Synthesis of dihydropyridines and pyridines from imines and alkynes via C-H activation.

    PubMed

    Colby, Denise A; Bergman, Robert G; Ellman, Jonathan A

    2008-03-19

    A convenient one-pot C-H alkenylation/electrocyclization/aromatization sequence has been developed for the synthesis of highly substituted pyridine derivatives from alkynes and alpha,beta-unsaturated N-benzyl aldimines and ketimines that proceeds through dihydropyridine intermediates. A new class of ligands for C-H activation was developed, providing broader scope for the alkenylation step than could be achieved with previously reported ligands. Substantial information was obtained about the mechanism of the reaction. This included the isolation of a C-H activated complex and its structure determination by X-ray analysis; in addition, kinetic simulations using the Copasi software were employed to determine rate constants for this transformation, implicating facile C-H oxidative addition and slow reductive elimination steps.

  1. H-H, C-H, and C-C NMR spin-spin coupling constants calculated by the FP-INDO method for aromatic hydrocarbons

    NASA Technical Reports Server (NTRS)

    Long, S. A. T.; Memory, J. D.

    1978-01-01

    The FP-INDO (finite perturbation-intermediate neglect of differential overlap) method is used to calculate the H-H, C-H, and C-C coupling constants in hertz for molecules of six different benzenoid hydrocarbons: benzene, naphthalene, biphenyl, anthracene, phenanthrene, and pyrene. The calculations are based on both the actual and the average molecular geometries. It is found that only the actual molecular geometries can always yield the correct relative order of values for the H-H coupling constants. For the calculated C-C coupling constants, as for the calculated C-H coupling constants, the signs are positive (negative) for an odd (even) number of bonds connecting the two nuclei. Agreements between the calculated and experimental values of the coupling constants for all six molecules are comparable to those reported previously for other molecules.

  2. Regioselective Synthesis of Quinazolinone-/Phenanthridine-Fused Heteropolycycles by Pd-Catalyzed Direct Intramolecular Aerobic Oxidative C-H Amination from Aromatic Strained Amides.

    PubMed

    Banerji, Biswadip; Bera, Suvankar; Chatterjee, Satadru; Killi, Sunil Kumar; Adhikary, Saswati

    2016-03-01

    A new route for the expedient synthesis of specific regioisomer of quinazolinone- and phenanthridine-fused heterocycles through a palladium-catalyzed regioselective intramolecular oxidative C-H amination from cyclic strained amides of aromatic amido-amidine systems (quinazolinones) has been developed. The amine functionalization of an aromatic C-H bond from a strained amide nitrogen involved in aromaticity has been a challenging work so far. The fusion of two heterocyclic cores, quinazolinone and phenanthridine, can occur in two different ways (linear and angular), but under the conditions reported here, only linear type isomer is exclusively produced. This approach provides a variety of substituted quinazolinone- and phenanthridine-fused derivatives in moderate to excellent yields. Moreover, such fused molecules show excellent fluorescent properties and have great potential to be a new type of fluorophores for the use in medicinal and material science.

  3. Biodegradation of aliphatic vs. aromatic hydrocarbons in fertilized arctic soils

    USGS Publications Warehouse

    Braddock, J.F.

    1999-01-01

    A study was carried out to test a simple bioremediation treatment strategy in the Arctic and analyze the influence of fertilization the degradation of aliphatic and aromatic hydrocarbons, e.g., pristine, n-tetradecane, n-pentadecane, 2-methylnaphthalene, naphthalene, and acenaphthalene. The site was a coarse sand pad that once supported fuel storage tanks. Diesel-range organics concentrations were 250-860 mg/kg soil at the beginning of the study. Replicate field plots treated with fertilizer yielded final concentrations of 0, 50, 100, or 200 mg N/kg soil. Soil pH and soil-water potentials decreased due to fertilizer application. The addition of fertilizer considerably increased soil respiration potentials, but not the populations of microorganisms measured. Fertilizer addition also led to ??? 50% loss of measured aliphatic and aromatic hydrocarbons in surface and subsurface soils. For fertilized plots, hydrocarbon loss was not associated with the quantity of fertilizer added. Losses of aliphatic hydrocarbons were ascribed to biotic processes, while losses of aromatic hydrocarbons were due to biotic and abiotic processes.

  4. Asymmetric Allylic C-H Oxidation for the Synthesis of Chromans.

    PubMed

    Wang, Pu-Sheng; Liu, Peng; Zhai, Yu-Jia; Lin, Hua-Chen; Han, Zhi-Yong; Gong, Liu-Zhu

    2015-10-14

    An enantioselective intramolecular allylic C-H oxidation to generate optically active chromans has been accomplished under the cooperative catalysis of a palladium complex of chiral phosphoramidite ligand and 2-fluorobenzoic acid. Mechanistic studies suggest that this reaction commences with a Pd-catalyzed allylic C-H activation event and then undergoes asymmetric allylic alkoxylation. The synthetic significance of the method has been embodied by concisely building up a key chiral intermediate to access (+)-diversonol.

  5. Multidirectional Synthesis of Substituted Indazoles via Iridium-Catalyzed C-H Borylation.

    PubMed

    Sadler, Scott A; Hones, Andrew C; Roberts, Bryan; Blakemore, David; Marder, Todd B; Steel, Patrick G

    2015-05-15

    In the absence of a steric directing group, iridium-catalyzed C-H borylation of N-protected indazoles occurs rapidly and selectively at C-3 and the resulting boronate esters can be utilized in a range of downstream conversions. The functional group tolerance of the iridium-catalyzed C-H borylation reaction enables simple and efficient multidirectional syntheses of substituted indazoles to be realized.

  6. A chiral rhodium carboxamidate catalyst for enantioselective C-H amination.

    PubMed

    Zalatan, David N; Du Bois, J

    2008-07-23

    Rh2(S-nap)4, a chiral dirhodium tetracarboxamidate complex, has been developed and shown to be an effective catalyst for the asymmetric, intramolecular C-H amination of sulfamate esters. Enantiomeric excesses range from 60-99% for a collection of disparately substituted 3-arylpropylsulfamates. In addition, Rh2(S-nap)4 is found to promote chemoselective allylic C-H oxidation of unsaturated sulfamates, a property not observed with other dirhodium complexes tested to date.

  7. Structure of an isolated unglycosylated antibody C(H)2 domain.

    PubMed

    Prabakaran, Ponraj; Vu, Bang K; Gan, Jianhua; Feng, Yang; Dimitrov, Dimiter S; Ji, Xinhua

    2008-10-01

    The C(H)2 (C(H)3 for IgM and IgE) domain of an antibody plays an important role in mediating effector functions and preserving antibody stability. It is the only domain in human immunoglobulins (Igs) which is involved in weak interchain protein-protein interactions with another C(H)2 domain solely through sugar moieties. The N-linked glycosylation at Asn297 is conserved in mammalian IgGs as well as in homologous regions of other antibody isotypes. To examine the structural details of the C(H)2 domain in the absence of glycosylation and other antibody domains, the crystal structure of an isolated unglycosylated antibody gamma1 C(H)2 domain was determined at 1.7 A resolution and compared with corresponding C(H)2 structures from intact Fc, IgG and Fc receptor complexes. Furthermore, the oligomeric state of the protein in solution was studied using size-exclusion chromatography. The results suggested that the unglycosylated human antibody C(H)2 domain is a monomer and that its structure is similar to that found in the intact Fc, IgG and Fc receptor complex structures. However, certain structural variations were observed in the Fc receptor-binding sites. Owing to its small size, stability and non-immunogenic Ig template, the C(H)2-domain structure could be useful for the development by protein design of antibody domains exerting effector functions and/or antigen specificity and as a robust scaffold in protein-engineering applications.

  8. A convenient and validated enantiomer separation of chiral aliphatic amines as nitrobenzoxadiazole derivatives on polysaccharide-derived chiral stationary phases under simultaneous ultraviolet and fluorescence detection.

    PubMed

    Adhikari, Suraj; Kang, Jong Seong; Lee, Wonjae

    2016-12-01

    A convenient method using a fluorogenic agent, 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD-Cl), was developed for enantiomer separation of chiral aliphatic amines including amino alcohols by normal high-performance liquid chromatography. The enantiomer separation of chiral aliphatic amines as NBD derivatives was performed on six covalently bonded and four coated-type polysaccharide-derived chiral stationary phases (CSPs) under simultaneous ultraviolet (UV) and fluorescence detection (FLD). Among the covalently bonded CSPs, Chiralpak IE showed the best enantiomer separation for most analytes. The other CSPs also showed good enantioselectivity except for Chiralpak IB. On the other hand, Chiralpak AD-H and Amylose-1 generally exhibited better enantiomer separation of NBD derivatized chiral amines among the coated CSPs. The developed analytical technique was also applied to determine the optical purity of commercially available (R)- and (S)-leucinol; the impurity was found to be 0.06%. The developed method was validated and proved to be an accurate, precise, sensitive, and selective method suitable for separation of chiral aliphatic amines as NBD derivatives under simultaneous UV and FLD.

  9. Observation of a C-H\\cdotsAROMATIC Interaction in the FLUOROBENZENE\\cdotsHCCH Weakly Bound Complex

    NASA Astrophysics Data System (ADS)

    Ulrich, Nathan W.; Peebles, Sean A.; Peebles, Rebecca A.; Dhahir, Yasser J.; Seifert, Nathan A.; Perez, Cristobal; Pate, Brooks H.

    2013-06-01

    Chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy has been used to determine the structure of the C_6H_5F\\cdotsHCCH weakly bound complex. Assignment of spectra for the parent and all six unique ^{13}C isotopologues in natural abundance has allowed a full structure determination, using both Kraitchman substitution and least-squares methods. The acetylene lies nearly perpendicular to the fluorobenzene ring, approximately above the ring center, and in the dimer ab symmetry plane. There is a slight tilt of the hydrogen atom nearest the fluorobenzene away from the carbon atom bonded to the fluorine. The distance between the centers of mass of the two monomers is approximately 4.18(1)Å, with C-H\\cdotsC distances of between 2.81(1)Å and 2.92(1)Å. The experimentally determined structure is in reasonable agreement with the minimum energy configuration from an MP2/6-311++G(2d,2p) ab initio calculation. Comparison will also be made with similar complexes of aromatic compounds with potential hydrogen bond donors.

  10. DFT Mechanistic Study of Rh(III)-Catalyzed [3 + 2]/[5 + 2] Annulation of 4-Aryl-1,2,3-triazoles and Alkynes Unveils the Dual C-H Activation Strategy.

    PubMed

    Zhang, Zhongchao; Yang, Shengwen; Li, Juan; Liao, Xiaojian

    2016-10-21

    Li and co-workers recently developed a dual C-H bond activation strategy, using a Rh(III) catalyst, for [3 + 2]/[5 + 2] annulation of primary 4-aryl-1,2,3-triazoles and alkynes. The Rh(III)-catalyzed dual annulation of 4-aryl-1,2,3-triazoles and alkynes is challenging because only single annulation is achieved using Rh(II) and Ni(0) catalysts. Intrigued by the novel strategy, we performed a density functional theory study to unravel this challenging dual C-H bond activation. A Friedel-Crafts type mechanism proved be more favorable than a concerted metalation-deprotonation (CMD) mechanism for the first C-H bond activation. The second C-H bond activation proceeded via a CMD mechanism. More importantly, the calculation explained why only AgSbF6, among several candidates, performed perfectly, whereas others failed, and why the dual annulation of 4-aryl-1,2,3-triazoles with alkynes was achieved with a Rh(III) catalyst but not with Rh(II) and Ni(0) catalysts. Due to the active catalyst being [Cp*Rh(OAc)](+), AgSbF6, in which SbF6(-) is a stable anion, among several candidates performed perfectly. The success of the Rh(III)-catalyzed dual C-H bond activation has two origins: (i) the active catalyst [Cp*Rh(OAc)](+) is more stable than Cp*Rh(OAc)2 when the Ag salt is AgSbF6, and this facilitates the first alkyne insertion; and (ii) a rhodium-carbene is easily formed.

  11. Cost-Benefit Analysis for Alternatives to Aliphatic Isocyanate Polyurethanes

    NASA Technical Reports Server (NTRS)

    Lewis, Pattie

    2007-01-01

    NASA and Air Force Space Command (AFSPC) have similar missions and therefore similar facilities and structures in similar environments. The standard practice for protecting metallic substrates in atmospheric environments is the application of an applied coating system. The most common topcoats used in coating systems are polyurethanes that contain isocyanates. Isocyanates are classified as potential human carcinogens and are known to cause cancer in animals. The primary objective of this effort was to demonstrate and validate alternatives to aliphatic isocyanate polyurethanes resulting in one or more isocyanate-free coatings qualified for use at AFSPC and NASA installations participating in this project. This Cost-Benefit Analysis (CBA) quantifies the estimated capital and process costs of coating alternatives and cost savings relative to the current coatings. The estimates in this CBA are to be used for assessing the relative merits of the selected alternatives. The actual economic effects at any specific facility will depend on the alternative material or technology implemented, the number of actual applications converted, future workloads, and other factors . The participants initially considered eighteen (18) alternative coatings as described in the Potential Alternatives Report entitled Potential Alternatives Report for Validation of Alternatives to Aliphatic Isocyanate Polyurethanes, prepared by ITB. Of those, 8 alternatives were selected for testing in accordance with the Joint Test Protocol entitled Joint Test Protocol for Validation of Alternatives to Aliphatic Isocyanate Polyurethanes, and the Field Test Plan entitled Field Evaluations Test Plan for Validation of Alternatives 10 Aliphatic Isocyanate Polyurethanes, both of which were prepared by ITB. A joint Test Report entitled Joint Test Report for Validation of Alternatives to Aliphatic Isocyanate Polyurethanes, prepared by ITB, documents the results of the laboratory and field testing, as well as any

  12. On the activation of σ-bonds by electric fields: A Valence Bond perspective

    NASA Astrophysics Data System (ADS)

    Rincón, Luis; Mora, Jose R.; Torres, F. Javier; Almeida, Rafael

    2016-09-01

    The activation of non-polar σ -bonds induced by an electric field is studied from the perspective of the Valence Bond theory. As representative examples we study the dissociation of the H-H and C-H bonds of molecular hydrogen and methane, respectively, under the experience of an homogeneous as well as an heterogeneous field oriented along the bond axis. For all cases, the increase in the electric field have similar effects: (i) the stabilization of the potential energy, (ii) an increment of the equilibrium bond length and (iii) the transition from an homolytic dissociation mechanism to an heterolytic one when the bond is subjected under a strong enough field. These general observations are thoroughly explained using a simple Valence Bond model that involve the increment of the resonance energy between the covalent and the ionic structures, and the curve crossing between the two structures after some field strength.

  13. Low-energy reaction rate constants for the Ni+-assisted decomposition of acetaldehyde: observation of C-H and C-C activation.

    PubMed

    Dee, S Jason; Castleberry, Vanessa A; Villarroel, Otsmar J; Laboren, Ivanna E; Bellert, Darrin J

    2010-02-04

    Rate constants for the low-energy Ni(+)-assisted dissociative reaction of acetaldehyde have been measured under jet-cooled conditions in the gas phase. The rate constants are acquired through monitoring the time dependence of fragment Ni(+)CO formation. The decomposition of the precursor Ni(+)-acetaldehyde cluster ion proceeds via consecutive, parallel reaction coordinates that originate with the Ni(+)-assisted cleavage of either a C-C or an aldehyde C-H bond. The energies used to initiate these reactions are well below that required to cleave sigma-bonds in the isolated acetaldehyde molecule. Direct measurement of the reaction kinetics over a range of energies indicates that the rate-limiting step in the dissociative mechanism changes at cluster ion internal energies = 17,200 +/- 400 cm(-1). Arguments are presented that this energy marks the closure of the dissociative coordinate that initiates with C-H sigma-bond activation and thus provides a measure of the activation energy of this dissociative pathway.

  14. Hydrogen-bonded sheets in benzylmethylammonium hydrogen maleate.

    PubMed

    Santacruz, Lynay; Abonia, Rodrigo; Cobo, Justo; Low, John N; Glidewell, Christopher

    2007-10-01

    In the title compound, C(8)H(12)N(+).C(4)H(3)O(4)(-), there is a short and almost linear but asymmetric O-H...O hydrogen bond in the anion. The ions are linked into C(2)(2)(6) chains by two short and nearly linear N-H...O hydrogen bonds and the chains are further weakly linked into sheets by a single C-H...O hydrogen bond.

  15. Rh(III)-Catalyzed Carbocyclization of 3-(Indolin-1-yl)-3-oxopropanenitriles with Alkynes and Alkenes through C-H Activation.

    PubMed

    Zhou, Tao; Wang, Yanwei; Li, Bin; Wang, Baiquan

    2016-10-07

    Rh(III)-catalyzed carbocyclization reactions of 3-(indolin-1-yl)-3-oxopropanenitriles with alkynes and alkenes have been developed to form 1,7-fused indolines through C-H activation. These reactions have a broad range of substrates and high yields. Unsymmetrical aryl-alkyl substituted alkynes proceeded smoothly with high regioselectivity. Electron-rich alkynes could undergo further oxidative coupling reaction to form polycyclic compounds. For alkenes, 1,2-dihydro-4H-pyrrolo[3,2,1-ij]quinolin-4-ones were formed via C(sp(2))-H bond alkenylation and C(sp(2))-H, C(sp(3))-H oxidative coupling reactions.

  16. 5,11-Diisopropyl-2,8-dimethyl-1H,7H-diimidazo[c,h][1,6]diazecine dihydrate

    PubMed Central

    Mendoza-Díaz, Guillermo; de Lourdes Betancourt-Mendiola, María; Bernès, Sylvain

    2010-01-01

    Crystals of the title compound, C18H30N6·2H2O, are composed of units of diimidazo[c,h][1,6]diazecine and two water mol­ecules. The asymmetric unit contains one half-molecule of diazecine and one uncoordinated water molecule in a general position. The complete ten-membered heterocycle is generated by an inversion center.The organic residue and water mol­ecules form a two-dimensional hydrogen-bonded network. The 1,6-diazecine ring shows a chair conformation, with angles and distances in normal ranges. PMID:21588282

  17. N-Doped Cationic PAHs by Rh(III)-Catalyzed Double C-H Activation and Annulation of 2-Arylbenzimidazoles with Alkynes.

    PubMed

    Villar, José M; Suárez, Jaime; Varela, Jesús A; Saá, Carlos

    2017-04-07

    A novel class of N-doped cationic PAHs (polycyclic aromatic hydrocarbons) bearing the benzo[c,d]fluoranthene scaffold has been synthesized by the Rh(III)-catalyzed double-oxidative annulation of 2-arylbenzimidazoles with alkynes. The overall process involves a double C-N bond formation through a double C-H/N-H functionalization.The solid-state structures and electronic properties of the new N-doped PAHs were analyzed. These cationic azapolycycles were readily reduced in the presence of LiAlH4 or by the addition of PhLi to give interesting phenyl and diphenylmethanediamine derivatives.

  18. Theoretical study of the bond dissociation energies of propyne (C3H4)

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1992-01-01

    The C-C and C-H bond dissociation energies (BDEs) of propyne have been computed using the modified coupled-pair functional method. Due to hyperconjugation, the C-C and methyl C-H single bonds are stronger and weaker, respectively than those in ethane. The acetylenic C-H and C triple bond C BDEs are larger and smaller, respectively, than in acetylene, also as a result of the hyperconjugation. Our best estimate of 92.5 +/- 2 kcal/mol for the methyl C-H BDE in propyne is slightly larger than the experimental value. For the acetylenic C-H BDE in propyne we predict 135.9 +/- 2 kcal/mol.

  19. Optical properties of a-C:H thin films modified by Ti and Ag

    NASA Astrophysics Data System (ADS)

    Prikhodko, Oleg Yu.; Mikhailova, Svetlana L.; Mukhametkarimov, Ershan C.; Maksimova, Suyumbika Ya.; Manabaev, Nurlan K.; Dauthan, Kuanysh

    2016-09-01

    Structure and optical properties of amorphous diamond-like carbon (a-C: H) thin films modified with Ag, Ti and Ag + Ti metal impurities are studied. The films were prepared by ion-plasma magnetron sputtering of combined polycrystalline graphite and metal target in the mixture of Ar and CH4 gases. AFM, SEM and TEM methods show that a-C:H films are heterogeneous, nanostructured and characterized by the presence of silver nanoclusters on the surface sized 60 nm and both Ti and Ag nanoclusters with a mean size (2 ÷ 3) nm in the bulk of films. It was found that in a- C:H films as well as in a-C:H films plasma resonance absorption due to excitation of surface plasmons in silver nanoclusters in the visible region of spectrum takes place. Intensity of the resonance absorption in the a- C:H films increases with increase in concentration of silver. The results are important for produce of nanomaterials with nonlinear optical properties based on the amorphous diamond-like carbon films containing metal nanoclusters.

  20. Structural studies of aliphatic substituted phthalocyanine-lipid multilayers.

    PubMed

    Zarbakhsh, Ali; Campana, Mario; Mills, David; Webster, John R P

    2010-10-05

    A Langmuir-Blodgett film of aliphatic substituted phthalocyanines on a C18 silane supporting layer coupled onto a silicon substrate has been investigated using neutron reflectometry. This multilayer structure is seen as a possible candidate for phthalocyanine-lipid biosensor devices. The results show the suitability of the C18 ligands as an anchoring layer for the phthalocyanines. The scattering length density profiles demonstrate the effectiveness of a lipid monolayer in partitioning the composition of phthalocyanine layers from that of the bulk liquid. The effectiveness of this barrier is a critical factor in the efficiency of such devices.