Gold-Catalyzed Formal C-C Bond Insertion Reaction of 2-Aryl-2-diazoesters with 1,3-Diketones.

Science.gov (United States)

Ren, Yuan-Yuan; Chen, Mo; Li, Ke; Zhu, Shou-Fei

2018-06-29

The transition-metal-catalyzed formal C-C bond insertion reaction of diazo compounds with monocarbonyl compounds is well established, but the related reaction of 1,3-diketones instead gives C-H bond insertion products. Herein, we report a protocol for a gold-catalyzed formal C-C bond insertion reaction of 2-aryl-2-diazoesters with 1,3-diketones, which provides efficient access to polycarbonyl compounds with an all-carbon quaternary center. The aryl ester moiety plays a crucial role in the unusual chemoselectivity, and the addition of a Brønsted acid to the reaction mixture improves the yield of the C-C bond insertion product. A reaction mechanism involving cyclopropanation of a gold carbenoid with an enolate and ring-opening of the resulting donor-acceptor-type cyclopropane intermediate is proposed. This mechanism differs from that of the traditional Lewis-acid-catalyzed C-C bond insertion reaction of diazo compounds with monocarbonyl compounds, which involves a rearrangement of a zwitterion intermediate as a key step. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rh(I)-Catalyzed Arylation of Heterocycles via C-H Bond Activation: Expanded Scope Through Mechanistic Insight

Energy Technology Data Exchange (ETDEWEB)

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.

Rh(III)-Catalyzed C-H Activation of Benzoylacetonitriles and Tandem Cyclization with Diazo Compounds to Substituted Benzo[ de]chromenes.

Science.gov (United States)

Fang, Feifei; Zhang, Chunmei; Zhou, Chaofan; Li, Yazhou; Zhou, Yu; Liu, Hong

2018-04-06

Rh (III)-catalyzed C-H activation of benzoylacetonitriles in coupling with diazo compounds was developed to synthesize diversified substituted benzo[ de]chromenes via a formal (4 + 2) cycloaddition with a diazo compound and subsequent tandem (4 + 2) cycloaddition with another diazo compound. Intriguingly, synthesis of substituted benzo[ de]chromenes and their decarboxylation products could be realized by controlling the reaction conditions. These reactions have a broad range of substrates, moderate to good yields, and high regioselectivity.

Palladium-catalyzed aryl C-H olefination with unactivated, aliphatic alkenes.

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Deb, Arghya; Bag, Sukdev; Kancherla, Rajesh; Maiti, Debabrata

2014-10-01

Palladium-catalyzed coupling between aryl halides and alkenes (Mizoroki-Heck reaction) is one of the most popular reactions for synthesizing complex organic molecules. The limited availability, problematic synthesis, and higher cost of aryl halide precursors (or their equivalents) have encouraged exploration of direct olefination of aryl carbon-hydrogen (C-H) bonds (Fujiwara-Moritani reaction). Despite significant progress, the restricted substrate scope, in particular noncompliance of unactivated aliphatic olefins, has discouraged the use of this greener alternative. Overcoming this serious limitation, we report here a palladium-catalyzed chelation-assisted ortho C-H bond olefination of phenylacetic acid derivatives with unactivated, aliphatic alkenes in good to excellent yields with high regio- and stereoselectivities. The versatility of this operationally simple method has been demonstrated through drug diversification and sequential C-H olefination for synthesizing divinylbenzene derivatives.

Regioselective C2 Oxidative Olefination of Indoles and Pyrroles through Cationic Rhodium(III)-Catalyzed C-H Bond Activation.

Science.gov (United States)

Li, Bin; Ma, Jianfeng; Xie, Weijia; Song, Haibin; Xu, Shansheng; Wang, Baiquan

2013-09-02

Be economic with your atoms! An efficient Rh-catalyzed oxidative olefination of indoles and pyrroles with broad substrate scope and tolerance is reported. The catalytic reaction proceeds with excellent regio- and stereoselectivity. The directing group N,N-dimethylcarbamoyl was crucial for the reaction and could be removed easily. Copyright © 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-Catalyzed ortho-Olefination of Phenyl Acetic and Phenyl Propylacetic Esters via C-H Bond Activation.

Science.gov (United States)

Hu, Jundie; Guan, Mingyu; Han, Jian; Huang, Zhi-Bin; Shi, Da-Qing; Zhao, Yingsheng

2015-08-21

A highly regioselective palladium-catalyzed ester-directed ortho-olefination of phenyl acetic and propionic esters with olefins via C-H bond activation has been developed. A wide variety of phenyl acetic and propionic esters were tolerated in this transformation, affording the corresponding olefinated aromatic compounds. The ortho-olefination of heterocyclic acetic and propionic esters also took place smoothly giving the products in good yields, thus proving the potential utility of this protocol in synthetic chemistry.

Rhodium(III)- and iridium(III)-catalyzed C7 alkylation of indolines with diazo compounds.

Science.gov (United States)

Ai, Wen; Yang, Xueyan; Wu, Yunxiang; Wang, Xuan; Li, Yuanchao; Yang, Yaxi; Zhou, Bing

2014-12-22

A Rh(III)-catalyzed procedure for the C7-selective C-H alkylation of various indolines with α-diazo compounds at room temperature is reported. The advantages of this process are: 1) simple, mild, and pH-neutral reaction conditions, 2) broad substrate scope, 3) complete regioselectivity, 4) no need for an external oxidant, and 5) N2 as the sole byproduct. Furthermore, alkylation and bis-alkylation of carbazoles at the C1 and C8 positions have also been developed. More significantly, for the first time, a successful Ir(III)-catalyzed intermolecular insertion of arene C-H bonds into α-diazo compounds is reported. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pd-Catalyzed Acetoxylation of γ-C(sp3)-H Bonds of Amines Directed by a Removable Bts-Protecting Group.

Science.gov (United States)

Zheng, Yong; Song, Weibin; Zhu, Yefu; Wei, Bole; Xuan, Lijiang

2018-02-16

Pd-catalyzed acetoxylation of γ-C(sp 3 )-H bonds directed by Bts-protected amines using inexpensive PhI(OAc) 2 as oxidant is reported. The Bts-protecting group is easily introduced and removed under mild conditions. This protocol provides an important strategy for the construction of γ-hydroxyl amine derivatives.

Reactions at the Metal Vertex of a Monometal Metallocarborane Cluster. The Chemistry of (closo-3,3-(PPh3)2-3-(HSO4)-3,1,2-RhC2B9H11) and (closo-3-(PPh3)-3,3-(NO3)-3,1,2RhC2B9H11).

Science.gov (United States)

1982-03-09

4) produced by dissociation of PPh 3 from (2) or through an ionic species such as [closo-3,3- (PPh 3)2 -3,1,2-RhC 289 H ] [HSO4 (4a). Secondly, the...acetylene molecule and subsequent insertion into a metal-carbon bond has been observed in the linear oligomerization of acetylere catalyzed by [Ni(CO...monoxide were obtained from Liquid Carbonic and used without further treatment. Phenylacetylene (Aldrich) was distilled under vacuum before use and n

Tandem Rh-Catalyzed Oxidative C-H Olefination and Cyclization of Enantiomerically Enriched Benzo-1,3-Sulfamidates: Stereoselective Synthesis of trans-1,3-Disubstituted Isoindolines.

Science.gov (United States)

Achary, Raghavendra; Jung, In-A; Lee, Hyeon-Kyu

2018-04-06

A tandem process, involving Rh(III)-catalyzed oxidative C-H olefination of enantiomerically enriched 4-aryl-benzo-1,3-sulfamidates and subsequent intramolecular aza-Michael cyclization has been developed. The reaction produces trans-benzosulfamidate-fused-1,3-disubstituted isoindolines as major products, in which the configurational integrity of the stereogenic center in the starting material is preserved. Further transformations of the benzosulfamidate-fused-1,3-disubstituted isoindolines are described.

Synthesis of propargylic and allenic carbamates via the C-H amination of alkynes.

Science.gov (United States)

Grigg, R David; Rigoli, Jared W; Pearce, Simon D; Schomaker, Jennifer M

2012-01-06

Propargylic amines are important intermediates for the synthesis of nitrogen-containing heterocycles. The insertion of a nitrene into a propargylic C-H bond has not been explored, despite the attention directed toward the Rh-catalyzed amination of other types of C-H bonds. In this communication, the conversion of a series of homopropargylic carbamates to propargylic carbamates and aminated allenes is described. © 2011 American Chemical Society

Modification of Purine and Pyrimidine Nucleosides by Direct C-H Bond Activation

Directory of Open Access Journals (Sweden)

Yong Liang

2015-03-01

Full Text Available Transition metal-catalyzed modifications of the activated heterocyclic bases of nucleosides as well as DNA or RNA fragments employing traditional cross-coupling methods have been well-established in nucleic acid chemistry. This review covers advances in the area of cross-coupling reactions in which nucleosides are functionalized via direct activation of the C8-H bond in purine and the C5-H or C6-H bond in uracil bases. The review focuses on Pd/Cu-catalyzed couplings between unactivated nucleoside bases with aryl halides. It also discusses cross-dehydrogenative arylations and alkenylations as well as other reactions used for modification of nucleoside bases that avoid the use of organometallic precursors and involve direct C-H bond activation in at least one substrate. The scope and efficiency of these coupling reactions along with some mechanistic considerations are discussed.

Copper-catalyzed aerobic oxidative C-H functionalization of substituted pyridines: synthesis of imidazopyridine derivatives.

Science.gov (United States)

Yu, Jipan; Jin, Yunhe; Zhang, Hao; Yang, Xiaobo; Fu, Hua

2013-12-02

A novel, efficient, and practical method for the synthesis of imidazopyridine derivatives has been developed through the copper-catalyzed aerobic oxidative C-H functionalization of substituted pyridines with N-(alkylidene)-4H-1,2,4-triazol-4-amines. The procedure occurs by cleavage of the N-N bond in the N-(alkylidene)-4H-1,2,4-triazol-4-amines and activation of an aryl C-H bond in the substituted pyridines. This is the first example of the preparation of imidazopyridine derivatives by using pyridines as the substrates by transition-metal-catalyzed C-H functionalization. This method should provide a novel and efficient strategy for the synthesis of other nitrogen heterocycles. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Studies on the experimental variables effects on rhodium catalyzed hydroformylation of unsaturated fatty esters and comparison of [RhH(CO)(PPh3)3] and [RhCl3.3H2O] as starting catalytic precursors

International Nuclear Information System (INIS)

Mendes, Ana N.F.; Gregorio, Jose R.; Rosa, Ricardo G. da

2005-01-01

Hydroformylation experiments were performed with technical-grade methyl oleate (MO) and soybean oil (SO) using [RhH(CO)(PPh 3 ) 3 ] and [RhCl 3 .3H 2 O] (double bond/Rh = 745) as catalyst precursors modified or not by triphenylphosphine. [RhH(CO)(PPh 3 ) 3 ] shows 100% conversion and 80-91% selectivity to aldehydes in only 4h for both substrates under mild conditions (100 deg C, 40 bar, CO/H 2 = 2:1, ligand/Rh = 10:1). Despite the rapid isomerization of the soybean oil, producing trans isomers and conjugated dienes, no effects were observed on its further conversion to aldehydes. The reaction of soybean oil conducted with pure [RhCl 3 .3H 2 O] produced only conjugated dienes, and when this precursor was modified with triphenylphosphine (ligand/Rh = 10:1) no reaction was observed at all. Curiously, yellow crystals corresponding to the complex [Rh(Cl)(CO)(PPh 3 ) 2 ] were quantitatively isolated at the end of the reaction. (author)

Rh-catalyzed linear hydroformylation of styrene

NARCIS (Netherlands)

Boymans, E.H.; Janssen, M.C.C.; Mueller, C.; Lutz, M.; Vogt, D.

2012-01-01

Usually the Rh-catalyzed hydroformylation of styrene predominantly yields the branched, chiral aldehyde. An inversion of regioselectivity can be achieved using strong p-acceptor ligands. Binaphthol-based diphosphite and bis(dipyrrolyl-phosphorodiamidite) ligands were applied in the Rh-catalyzed

Controlled Rh-Catalyzed Mono- and Double-decarbonylation of Alkynyl α-Diones To Form Conjugated Ynones and Disubstituted Alkynes.

Science.gov (United States)

Whittaker, Rachel E; Dong, Guangbin

2015-11-06

A Rh-catalyzed controlled decarbonylation of alkynyl α-diones is described. By using different ligand and solvent combinations, mono- and double-decarbonylation can be selectively achieved to give conjugated ynones and disubstituted alkynes, respectively. A fundamental study on catalytic activation of unstrained C-C bonds under nonoxidative conditions is presented.

Rh(III)-catalyzed olefination of N-sulfonyl imines: synthesis of ortho-olefinated benzaldehydes.

Science.gov (United States)

Zhang, Tao; Wu, Lamei; Li, Xingwei

2013-12-20

Rh(III)-catalyzed olefination of N-sulfonyl imines using acrylates and styrenes has been achieved for the synthesis of ortho-olefinated benaldehydes. This reaction proceeds via a chelation assisted C-H olefination/in situ hydrolysis process.

Cu-catalyzed esterification reaction via aerobic oxygenation and C-C bond cleavage: an approach to α-ketoesters.

Science.gov (United States)

Zhang, Chun; Feng, Peng; Jiao, Ning

2013-10-09

The Cu-catalyzed novel aerobic oxidative esterification reaction of 1,3-diones for the synthesis of α-ketoesters has been developed. This method combines C-C σ-bond cleavage, dioxygen activation and oxidative C-H bond functionalization, as well as provides a practical, neutral, and mild synthetic approach to α-ketoesters which are important units in many biologically active compounds and useful precursors in a variety of functional group transformations. A plausible radical process is proposed on the basis of mechanistic studies.

Metal-organic cooperative catalysis in C-H and C-C bond activation and its concurrent recovery.

Science.gov (United States)

Park, Young Jun; Park, Jung-Woo; Jun, Chul-Ho

2008-02-01

The development of an efficient catalytic activation (cleavage) system for C-H and C-C bonds is an important challenge in organic synthesis, because these bonds comprise a variety of organic molecules such as natural products, petroleum oils, and polymers on the earth. Among many elegant approaches utilizing transition metals to activate C-H and C-C bonds facilely, chelation-assisted protocols based on the coordinating ability of an organic moiety have attracted great attention, though they have often suffered from the need for an intact coordinating group in a substrate. In this Account, we describe our entire efforts to activate C-H or C-C bonds adjacent to carbonyl groups by employing a new concept of metal-organic cooperative catalysis (MOCC), which enables the temporal installation of a 2-aminopyridyl group into common aldehydes or ketones in a catalytic way. Consequently, a series of new catalytic reactions such as alcohol hydroacylation, oxo-ester synthesis, C-C triple bond cleavage, hydrative dimerization of alkynes, and skeletal rearrangements of cyclic ketones was realized through MOCC. In particular, in the quest for an optimized MOCC system composed of a Wilkinson's catalyst (Ph 3P) 3RhCl and an organic catalyst (2-amino-3-picoline), surprising efficiency enhancements could be achieved when benzoic acid and aniline were introduced as promoters for the aldimine formation process. Furthermore, a notable accomplishment of C-C bond activation has been made using 2-amino-3-picoline as a temporary chelating auxiliary in the reactions of unstrained ketones with various terminal olefins and Wilkinson's catalyst. In the case of seven-membered cyclic ketones, an interesting ring contraction to five- or six-membered ones takes place through skeletal rearrangements initiated by the C-C bond activation of MOCC. On the other hand, the fundamental advances of these catalytic systems into recyclable processes could be achieved by immobilizing both metal and organic

Computational Study of Pincer Iridium Catalytic Systems: C-H, N-H, and C-C Bond Activation and C-C Coupling Reactions

Science.gov (United States)

Zhou, Tian

Computational chemistry has achieved vast progress in the last decades in the field, which was considered to be only experimental before. DFT (density functional theory) calculations have been proven to be able to be applied to large systems, while maintaining high accuracy. One of the most important achievements of DFT calculations is in exploring the mechanism of bond activation reactions catalyzed by organometallic complexes. In this dissertation, we discuss DFT studies of several catalytic systems explored in the lab of Professor Alan S. Goldman. Headlines in the work are: (1) (R4PCP)Ir alkane dehydrogenation catalysts are highly selective and different from ( R4POCOP)Ir catalysts, predicting different rate-/selectivity-determining steps; (2) The study of the mechanism for double C-H addition/cyclometalation of phenanthrene or biphenyl by (tBu4PCP)Ir(I) and ( iPr4PCP)Ir illustrates that neutral Ir(III) C-H addition products can undergo a very facile second C-H addition, particularly in the case of sterically less-crowded Ir(I) complexes; (3) (iPr4PCP)Ir pure solid phase catalyst is highly effective in producing high yields of alpha-olefin products, since the activation enthalpy for dehydrogenation is higher than that for isomerization via an allyl pathway; higher temperatures favor the dehydrogenation/isomerization ratio; (4) (PCP)Ir(H)2(N2H4) complex follows a hydrogen transfer mechanism to undergo both dehydrogenation to form N 2 and H2, as well as hydrogen transfer followed by N-N bond cleavage to form NH3, N2, and H2; (5) The key for the catalytic effect of solvent molecule in CO insertion reaction for RMn(CO)5 is hydrogen bond assisted interaction. The basicity of the solvent determines the strength of the hydrogen bond interaction during the catalytic path and determines the catalytic power of the solvent; and (6) Dehydrogenative coupling of unactivated C-H bonds (intermolecular vinyl-vinyl, intramolecular vinyl-benzyl) is catalyzed by precursors of the

Palladium-Catalyzed ortho C-H Arylation of Benzaldehydes Using ortho-Sulfinyl Aniline Transient Auxiliary.

Science.gov (United States)

Mu, Delong; He, Gang; Chen, Gong

2018-05-03

A PdII-catalyzed ortho-(Csp2)-H arylation reaction of benzaldehydes using catalytic amount of 2-methylsulfinyl-aniline as transient auxiliary was developed. This reaction is compatible with a broad range of benzaldehyde and aryl iodide substrates. Compared with other related reaction systems, an excellent regioselectivity for ortho-C(sp2)-H bonds over benzylic C(sp3)-H bonds was obtained for ortho-alkyl-benzaldehyde substrates. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mo-Mo Quintuple Bond is Highly Reactive in H-H, C-H, and O-H σ-Bond Cleavages Because of the Polarized Electronic Structure in Transition State.

Science.gov (United States)

Chen, Yue; Sakaki, Shigeyoshi

2017-04-03

The recently reported high reactivity of the Mo-Mo quintuple bond of Mo 2 (N ∧ N) 2 (1) {N ∧ N = μ-κ 2 -CH[N(2,6-iPr 2 C 6 H 3 )] 2 } in the H-H σ-bond cleavage was investigated. DFT calculations disclosed that the H-H σ-bond cleavage by 1 occurs with nearly no barrier to afford the cis-dihydride species followed by cis-trans isomerization to form the trans-dihydride product, which is consistent with the experimental result. The O-H and C-H bond cleavages by 1 were computationally predicted to occur with moderate (ΔG° ⧧ = 9.0 kcal/mol) and acceptable activation energies (ΔG° ⧧ = 22.5 kcal/mol), respectively, suggesting that the Mo-Mo quintuple bond can be applied to various σ-bond cleavages. In these σ-bond cleavage reactions, the charge-transfer (CT Mo→XH ) from the Mo-Mo quintuple bond to the X-H (X = H, C, or O) bond and that (CT XH→Mo ) from the X-H bond to the Mo-Mo bond play crucial roles. Though the HOMO (dδ-MO) of 1 is at lower energy and the LUMO + 2 (dδ*-MO) of 1 is at higher energy than those of RhCl(PMe 3 ) 2 (LUMO and LUMO + 1 of 1 are not frontier MO), the H-H σ-bond cleavage by 1 more easily occurs than that by the Rh complex. Hence, the frontier MO energies are not the reason for the high reactivity of 1. The high reactivity of 1 arises from the polarization of dδ-type MOs of the Mo-Mo quintuple bond in the transition state. Such a polarized electronic structure enhances the bonding overlap between the dδ-MO of the Mo-Mo bond and the σ*-antibonding MO of the X-H bond to facilitate the CT Mo→XH and reduce the exchange repulsion between the Mo-Mo bond and the X-H bond. This polarized electronic structure of the transition state is similar to that of a frustrated Lewis pair. The easy polarization of the dδ-type MOs is one of the advantages of the metal-metal multiple bond, because such polarization is impossible in the mononuclear metal complex.

Redox-neutral rhodium-catalyzed C-H functionalization of arylamine N-oxides with diazo compounds: primary C(sp(3))-H/C(sp(2))-H activation and oxygen-atom transfer.

Science.gov (United States)

Zhou, Bing; Chen, Zhaoqiang; Yang, Yaxi; Ai, Wen; Tang, Huanyu; Wu, Yunxiang; Zhu, Weiliang; Li, Yuanchao

2015-10-05

An unprecedented rhodium(III)-catalyzed regioselective redox-neutral annulation reaction of 1-naphthylamine N-oxides with diazo compounds was developed to afford various biologically important 1H-benzo[g]indolines. This coupling reaction proceeds under mild reaction conditions and does not require external oxidants. The only by-products are dinitrogen and water. More significantly, this reaction represents the first example of dual functiaonalization of unactivated a primary C(sp(3) )H bond and C(sp(2) )H bond with diazocarbonyl compounds. DFT calculations revealed that an intermediate iminium is most likely involved in the catalytic cycle. Moreover, a rhodium(III)-catalyzed coupling of readily available tertiary aniline N-oxides with α-diazomalonates was also developed under external oxidant-free conditions to access various aminomandelic acid derivatives by an O-atom-transfer reaction. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-Catalyzed Reductive Insertion of Alcohols into Aryl Ether Bonds

Energy Technology Data Exchange (ETDEWEB)

Wang, Meng [Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999 Richland WA 99352 USA; Gutiérrez, Oliver Y. [Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999 Richland WA 99352 USA; Camaioni, Donald M. [Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999 Richland WA 99352 USA; Lercher, Johannes A. [Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999 Richland WA 99352 USA; Department of Chemistry and Catalysis Research Institute, TU München, Lichtenbergstrasse 4 85748 Garching Germany

2018-03-06

Pd/C catalyzes C-O bond cleavage of aryl ethers (diphenyl ether and cyclohexyl phenyl ether) by methanol in H2. The aromatic C-O bond is cleaved by reductive methanolysis, which is initiated by Pd-catalyzed partial hydrogenation of one phenyl ring to form an enol ether. The enol ether reacts rapidly with methanol to form a ketal, which generates methoxycyclohexene by eliminating phenol or an alkanol. Subsequent hydrogenation leads to methoxycyclohexane.

Highly enantioselective rhodium(I)-catalyzed carbonyl carboacylations initiated by C-C bond activation.

Science.gov (United States)

Souillart, Laetitia; Cramer, Nicolai

2014-09-01

The lactone motif is ubiquitous in natural products and pharmaceuticals. The Tishchenko disproportionation of two aldehydes, a carbonyl hydroacylation, is an efficient and atom-economic access to lactones. However, these reaction types are limited to the transfer of a hydride to the accepting carbonyl group. The transfer of alkyl groups enabling the formation of CC bonds during the ester formation would be of significant interest. Reported herein is such asymmetric carbonyl carboacylation of aldehydes and ketones, thus affording complex bicyclic lactones in excellent enantioselectivities. The rhodium(I)-catalyzed transformation is induced by an enantiotopic CC bond activation of a cyclobutanone and the formed rhodacyclic intermediate reacts with aldehyde or ketone groups to give highly functionalized lactones. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Selectivity control in pd-catalyzed c-h functionalization reactions

OpenAIRE

Flores Gaspar, Areli

2013-01-01

Benzocyclobutenones are an intriguing four-membered ring ketone. In the present thesis, we have developed a new protocol for selectively preparing benzocyclobutenones through intramolecular acylation of aryl bromides via palladium catalyzed C-H bond functionalization reactions based on rac-BINAP ligand. We also found that a subtle modification on the ligand backbone lead to a new catalytic manifold for preparing configurationally-pure styrene derivatives, when using dcpp (bis-dicyclohexylphos...

Palladium(II)-catalyzed ortho-C-H arylation/alkylation of N-benzoyl α-amino ester derivatives.

Science.gov (United States)

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%. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rh-Catalyzed Annulations of N-Methoxybenzamides and Ketenimines: Sterically and Electronically Controlled Synthesis of Isoquinolinones and Isoindolinones.

Science.gov (United States)

Zhou, Xiaorong; Zhang, Zhiyin; Zhao, Hongyang; Lu, Ping; Wang, Yanguang

2017-04-07

Rhodium-catalyzed C-H activation/annulation reactions of ketenimines with N-methoxybenzamides are reported. The outcome of reactions is dependent on the structure of ketenimines. The β-alkyl-substituted ketenimines furnish 3-iminoisoquinolin-1(2H)-ones in a formal [4 + 2] annulation manner, while the β-ester substituted ketenimines afford 3-aminoisoindolin-1-ones in a formal [4 + 1] annulation manner. The synthesized [4 + 2] products undergo an intramolecular Cu-catalyzed C-N coupling to be converted to benzo[4,5]imidazo[1,2-b]isoquinolin-11-ones, which can be directly prepared from ketenimines and N-methoxybenzamides by a one-pot Rh-catalyzed annulation/Cu-catalyzed C-N coupling sequence.

Isolation and X-ray structures of four Rh(PCP) complexes including a Rh(I) dioxygen complex with a short O-O bond

KAUST Repository

Hayashi, Yukiko

2013-07-01

The reaction of RhCl3·H2O with tBu2P(CH2)5PtBu 2 afforded several complexes including [RhIII(H)Cl{ tBu2- P(CH2)2CH(CH2) 2PtBu2}] (1), [RhIIIHCl 2{tBu2P(CH2)5P tBu2}]2 (2), [RhICl{ tBu2P(CH2)2CH=CHCH2P tBu2}] (3) and [RhICl{tBu 2PCH2C(O)CH=CHCH2PtBu2}] (4). X-ray crystal structures of 3 and 4 showed that the C=C bond on the C 5 unit of tBu2P(CH2) 5PtBu2 is bound to Rh(I) in a η2 configuration. In 4, the Rh atom has a trigonal pyramidal coordination geometry. The X-ray crystal structure of 2 consists of two rhodium( III) centers bridged by two tBu2P(CH2)5P tBu2 ligands with two phosphorus atoms, one from each ligand, trans to one another. The crystal structure of the rhodium oxygen adduct with 1,3-bis(di-t-butylphosphinomethyl) benzene [RhO2{ tBu2PCH2(C6H3)CH 2PtBu2}] (5) was also investigated. In this species the O2 is η2 coordinated to the Rh(I) center with asymmetric Rh-O bond lengths (2.087(7) and 1.998(8) Å). The O-O bond distance is short (1.337(11) Å) with νO-O of 990.5 cm -1. DFT calculations on complex 5 yielded two η2- O2 structures that differed in energy by only 0.76 kcal/mol. The lower energy one (5a) had near C2 symmetry, and had nearly equal Rh-O bond lengths, while the higher energy structure (5b) had near Cs symmetry and generally good agreement with the experimental structure. The calculated UV-Vis and IR spectra of complex 5 are in excellent agreement with experiment. © 2012 Elsevier Ltd. All rights reserved.

Isolation and X-ray structures of four Rh(PCP) complexes including a Rh(I) dioxygen complex with a short O-O bond

KAUST Repository

Hayashi, Yukiko; Szalda, David J.; Grills, David C.; Hanson, Jonathan C.; Huang, Kuo-Wei; Muckerman, James T.; Fujita, Etsuko

2013-01-01

The reaction of RhCl3·H2O with tBu2P(CH2)5PtBu 2 afforded several complexes including [RhIII(H)Cl{ tBu2- P(CH2)2CH(CH2) 2PtBu2}] (1), [RhIIIHCl 2{tBu2P(CH2)5P tBu2}]2 (2), [RhICl{ tBu2P(CH2)2CH=CHCH2P tBu2}] (3) and [RhICl{tBu 2PCH2C(O)CH=CHCH2PtBu2}] (4). X-ray crystal structures of 3 and 4 showed that the C=C bond on the C 5 unit of tBu2P(CH2) 5PtBu2 is bound to Rh(I) in a η2 configuration. In 4, the Rh atom has a trigonal pyramidal coordination geometry. The X-ray crystal structure of 2 consists of two rhodium( III) centers bridged by two tBu2P(CH2)5P tBu2 ligands with two phosphorus atoms, one from each ligand, trans to one another. The crystal structure of the rhodium oxygen adduct with 1,3-bis(di-t-butylphosphinomethyl) benzene [RhO2{ tBu2PCH2(C6H3)CH 2PtBu2}] (5) was also investigated. In this species the O2 is η2 coordinated to the Rh(I) center with asymmetric Rh-O bond lengths (2.087(7) and 1.998(8) Å). The O-O bond distance is short (1.337(11) Å) with νO-O of 990.5 cm -1. DFT calculations on complex 5 yielded two η2- O2 structures that differed in energy by only 0.76 kcal/mol. The lower energy one (5a) had near C2 symmetry, and had nearly equal Rh-O bond lengths, while the higher energy structure (5b) had near Cs symmetry and generally good agreement with the experimental structure. The calculated UV-Vis and IR spectra of complex 5 are in excellent agreement with experiment. © 2012 Elsevier Ltd. All rights reserved.

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

Science.gov (United States)

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. © 2017 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis of heterocyclic compounds through palladium-catalyzed C-H cyclization processes.

Science.gov (United States)

Inamoto, Kiyofumi

2013-01-01

Herein, we describe our development of synthetic methods for heterocyclic compounds based on the palladium-catalyzed carbon-hydrogen bond (C-H) functionalization/intramolecular carbon-heteroatom (nitrogen or sulfur) bond formation process. By this C-H cyclization method, we efficiently prepared various N-heterocycles, including indazoles, indoles, and 2-quinolinones, as well as S-heterocycles such as benzothiazoles and benzo[b]thiophenes. Yields are typically good to high and good functional-group tolerance is observed for each process, thereby indicating that the method provides a novel, highly applicable synthetic route to the abovementioned biologically important heterocyclic frameworks. As an application of this approach, an auto-tandem-type, one-pot process involving the oxidative Heck reaction and subsequent C-H cyclization using cinnamamides and arylboronic acids as starting materials in the presence of a palladium catalyst was also developed for the rapid construction of the 2-quinolinone nucleus.

Copper-Catalyzed Oxidative Reaction of β-Keto Sulfones with Alcohols via C-S Bond Cleavage: Reaction Development and Mechanism Study.

Science.gov (United States)

Du, Bingnan; Wang, Wenmin; Wang, Yang; Qi, Zhenghang; Tian, Jiaqi; Zhou, Jie; Wang, Xiaochen; Han, Jianlin; Ma, Jing; Pan, Yi

2018-02-16

A Cu-catalyzed cascade oxidative radical process of β-keto sulfones with alcohols has been achieved by using oxygen as an oxidant. In this reaction, β-keto sulfones were converted into sulfinate esters under the oxidative conditions via cleavage of C-S bond. Experimental and computational studies demonstrate that a new pathway is involved in this reaction, which proceeds through the formation of the key four-coordinated Cu II intermediate, O-O bond homolysis induced C-S bond cleavage and Cu-catalyzed esterification to form the final products. This reaction provides a new strategy to sulfonate esters and enriches the research content of C-S bond cleavage and transformations. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Deceptively Simple Thermolysis of Trivalent Permethyltitanocene Derivatives (η5-C5Me5)2TiR. Formation of a Tetramethylfulvene Titanium Compound (η6-C5Me4CH2)(η5-C5Me5)Ti and RH, Catalyzed by Permethyltitanocene Hydride, (η5-C5Me5)2TiH

NARCIS (Netherlands)

Luinstra, Gerrit A.; Teuben, Jan H.

1992-01-01

The complexes Cp*2TiR (Cp* = η5-C5Me5; R = Me, Et, n-Pr, C2H3, CH2CMe3, Ph) undergo thermolysis to yield the fulvene complex Cp*FvTi (Fv = η6-C5Me4CH2) and RH. Kinetic measurements and deuterium labeling studies show that the decomposition is catalyzed by Cp*2TiH, which is formed either by

Initial Stages in the Rhodium(III)-Catalyzed C-H Bond Activation of Primary Alcohols in Aqueous Solution

DEFF Research Database (Denmark)

Eriksen, J.; Monsted, L.; Monsted, O.

2010-01-01

The mechanism of the catalytic HID exchange in primary alcohol substrates derived from aldopentoses, promoted by a macrocyclic rhodium(III) complex, has been shown to occur by a reversible redox reaction that gives aldehyde and a rhodium hydride complex. Hydride exchange in the latter complex...... promotes the introduction of solvent hydrogen in the primary alcohol formed by the reverse reaction. The hydride complex has been crystallographically characterized as a trifluoromethanesulfonate salt that contains the trans-[Rh(cycb)(H)(OH2)](2+) (cycb = rac-5,5,7,12,12,14-hexamethyl-1......,4,8,11-tetraazacyclotetradecane) cation. The hydride complex is stable for extended periods of time in acidic solution in the absence of oxidants. In basic solutions a series of base-catalyzed reactions take place to yield ultimately the same mixture of [Rh(cycb)(OH)(2)](+) isomers as produced by base hydrolysis of the trans...

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

Science.gov (United States)

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.

Complementary Strategies for Directed C(sp3 )-H Functionalization: A Comparison of Transition-Metal-Catalyzed Activation, Hydrogen Atom Transfer, and Carbene/Nitrene Transfer.

Science.gov (United States)

Chu, John C K; Rovis, Tomislav

2018-01-02

The functionalization of C(sp 3 )-H bonds streamlines chemical synthesis by allowing the use of simple molecules and providing novel synthetic disconnections. Intensive recent efforts in the development of new reactions based on C-H functionalization have led to its wider adoption across a range of research areas. This Review discusses the strengths and weaknesses of three main approaches: transition-metal-catalyzed C-H activation, 1,n-hydrogen atom transfer, and transition-metal-catalyzed carbene/nitrene transfer, for the directed functionalization of unactivated C(sp 3 )-H bonds. For each strategy, the scope, the reactivity of different C-H bonds, the position of the reacting C-H bonds relative to the directing group, and stereochemical outcomes are illustrated with examples in the literature. The aim of this Review is to provide guidance for the use of C-H functionalization reactions and inspire future research in this area. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium-catalyzed C-H bond activation for the synthesis of quinonoid compounds: Significant Anti-Trypanosoma cruzi activities and electrochemical studies of functionalized quinones.

Science.gov (United States)

Jardim, Guilherme A M; Silva, Thaissa L; Goulart, Marilia O F; de Simone, Carlos A; Barbosa, Juliana M C; Salomão, Kelly; de Castro, Solange L; Bower, John F; da Silva Júnior, Eufrânio N

2017-08-18

Thirty four halogen and selenium-containing quinones, synthesized by rhodium-catalyzed C-H bond activation and palladium-catalyzed cross-coupling reactions, were evaluated against bloodstream trypomastigotes of T. cruzi. We have identified fifteen compounds with IC 50 /24 h values of less than 2 μM. Electrochemical studies on A-ring functionalized naphthoquinones were also performed aiming to correlate redox properties with trypanocidal activity. For instance, (E)-5-styryl-1,4-naphthoquinone 59 and 5,8-diiodo-1,4-naphthoquinone 3, which are around fifty fold more active than the standard drug benznidazole, are potential derivatives for further investigation. These compounds represent powerful new agents useful in Chagas disease therapy. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

Copper-catalyzed transformation of ketones to amides via C(CO)-C(alkyl) bond cleavage directed by picolinamide.

Science.gov (United States)

Ma, Haojie; Zhou, Xiaoqiang; Zhan, Zhenzhen; Wei, Daidong; Shi, Chong; Liu, Xingxing; Huang, Guosheng

2017-09-13

Copper catalyzed chemoselective cleavage of the C(CO)-C(alkyl) bond leading to C-N bond formation with chelation assistance of N-containing directing groups is described. Inexpensive Cu(ii)-acetate serves as a convenient catalyst for this transformation. This method highlights the emerging strategy to transform unactivated alkyl ketones into amides in organic synthesis and provides a new strategy for C-C bond cleavage.

Scope and Limitations of Auxiliary-Assisted, Palladium-Catalyzed Arylation and Alkylation of sp2 and sp3 C-H Bonds

Science.gov (United States)

Nadres, Enrico T.; Santos, Gerson Ivan Franco; Shabashov, Dmitry; Daugulis, Olafs

2013-01-01

The scope of palladium-catalyzed, auxiliary-assisted direct arylation and alkylation of sp2 and sp3 C-H bonds of amine and carboxylic acid derivatives has been investigated. The method employs a palladium acetate catalyst, substrate, aryl, alkyl, benzyl, or allyl halide, and inorganic base in t-amyl alcohol or water solvent at 100-140 °C. Aryl and alkyl iodides as well as benzyl and allyl bromides are competent reagents in this transformation. Picolinic acid auxiliary is used for amine γ-functionalization and 8-aminoquinoline auxiliary is used for carboxylic acid β-functionalization. Some optimization of base, additives, and solvent is required for achieving best results. PMID:24090404

Construction of axial chirality by rhodium-catalyzed asymmetric dehydrogenative Heck coupling of biaryl compounds with alkenes.

Science.gov (United States)

Zheng, Jun; You, Shu-Li

2014-11-24

Enantioselective construction of axially chiral biaryls by direct C-H bond functionalization reactions has been realized. Novel axially chiral biaryls were synthesized by the direct C-H bond olefination of biaryl compounds, using a chiral [Cp*Rh(III)] catalyst, in good to excellent yields and enantioselectivities. The obtained axially chiral biaryls were found as suitable ligands for rhodium-catalyzed asymmetric conjugate additions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ruthenium(II)-Catalyzed C-H Activation of Imidamides and Divergent Couplings with Diazo Compounds: Substrate-Controlled Synthesis of Indoles and 3H-Indoles.

Science.gov (United States)

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. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanistic Insight into Ketone α-Alkylation with Unactivated Olefins via C-H Activation Promoted by Metal-Organic Cooperative Catalysis (MOCC): Enriching the MOCC Chemistry.

Science.gov (United States)

Dang, Yanfeng; Qu, Shuanglin; Tao, Yuan; Deng, Xi; Wang, Zhi-Xiang

2015-05-20

Metal-organic cooperative catalysis (MOCC) has been successfully applied for hydroacylation of olefins with aldehydes via directed C(sp(2))-H functionalization. Most recently, it was reported that an elaborated MOCC system, containing Rh(I) catalyst and 7-azaindoline (L1) cocatalyst, could even catalyze ketone α-alkylation with unactivated olefins via C(sp(3))-H activation. Herein we present a density functional theory study to understand the mechanism of the challenging ketone α-alkylation. The transformation uses IMesRh(I)Cl(L1)(CH2═CH2) as an active catalyst and proceeds via sequential seven steps, including ketone condensation with L1, giving enamine 1b; 1b coordination to Rh(I) active catalyst, generating Rh(I)-1b intermediate; C(sp(2))-H oxidative addition, leading to a Rh(III)-H hydride; olefin migratory insertion into Rh(III)-H bond; reductive elimination, generating Rh(I)-1c(alkylated 1b) intermediate; decoordination of 1c, liberating 1c and regenerating Rh(I) active catalyst; and hydrolysis of 1c, furnishing the final α-alkylation product 1d and regenerating L1. Among the seven steps, reductive elimination is the rate-determining step. The C-H bond preactivation via agostic interaction is crucial for the bond activation. The mechanism rationalizes the experimental puzzles: why only L1 among several candidates performed perfectly, whereas others failed, and why Wilkinson's catalyst commonly used in MOCC systems performed poorly. Based on the established mechanism and stimulated by other relevant experimental reactions, we attempted to enrich MOCC chemistry computationally, exemplifying how to develop new organic catalysts and proposing L7 to be an alternative for L1 and demonstrating the great potential of expanding the hitherto exclusive use of Rh(I)/Rh(III) manifold to Co(0)/Co(II) redox cycling in developing MOCC systems.

C-H Bond Functionalization via Hydride Transfer: Direct Coupling of Unactivated Alkynes and sp3 C-H Bonds Catalyzed by Platinum Tetraiodide

Science.gov (United States)

Vadola, Paul A.; Sames, Dalibor

2010-01-01

We report a catalytic intramolecular coupling between terminal unactivated alkynes and sp3 C-H bonds via the through-space hydride transfer (HT-cyclization of alkynes). This method enables one-step preparation of complex heterocyclic compounds by α-alkenylation of readily available cyclic ethers and amines. We show that PtI4 is an effective Lewis acid catalyst for the activation of terminal alkynes for the hydride attack and subsequent C-C bond formation. In addition, we have shown that the activity of neutral platinum salts (PtXn) can be modulated by the halide ligands. This modulation in turn allows for fine-tuning of the platinum center reactivity to match the reactivity and stability of selected substrates and products. PMID:19852462

Electronic structure and bonding in the RhC molecule by all-electron ab initio HF–Cl calculations and mass spectrometric measurements

DEFF Research Database (Denmark)

Shim, Irene; Gingerich, K. A.

1984-01-01

In the present study we present all-electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of the 2Sigma+ ground state as well as of 16 excited states of the RhC molecule. The calculated spectroscopic constants of the lowest lying states are in good agreement...... with the experimental data. The chemical bond in the electronic ground state is mainly due to interaction of the 4d orbitals of Rh with the 2s and 2p orbitals of C. The bond is a triple bond composed of two pi bonds and one sigma bond. The 5s electron of Rh hardly participates in the bond formation. It is located...

Rh(iii)-catalyzed C-H olefination of N-pentafluoroaryl benzamides using air as the sole oxidant.

Science.gov (United States)

Lu, Yi; Wang, Huai-Wei; Spangler, Jillian E; Chen, Kai; Cui, Pei-Pei; Zhao, Yue; Sun, Wei-Yin; Yu, Jin-Quan

2015-03-01

The oxidative olefination of a broad array of arenes and heteroarenes with a variety of activated and unactivated olefins has be achieved via a rhodium(iii)-catalyzed C-H activation reaction. The use of an N -pentafluorophenyl benzamide directing group is crucial for achieving catalytic turnovers in the presence of air as the sole oxidant without using a co-oxidant.

Toward Efficient Palladium-Catalyzed Allylic C-H Alkylation

DEFF Research Database (Denmark)

Jensen, Thomas; Fristrup, Peter

2009-01-01

Recent breakthroughs have proved that direct palladium (II)-catalyzed allylic C-H alkylation can be achieved. This new procedure shows that the inherent requirement for a leaving group in the Tsuji-Trost palladium-catalyzed allylic alkylation can be lifted. These initial reports hold great promise...... for the development of allylic C-H alkylation into a widely applicable methodology, thus providing a means to enhance synthetic efficiency in these reactions....

Utilisation of an eta(3)-allyl hydride complex, formed by UV irradiation, as a controlled source of 16-electron (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe).

Science.gov (United States)

Sexton, Catherine J; López-Serrano, Joaquín; Lledós, Agustí; Duckett, Simon B

2008-10-21

Low temperature UV irradiation of solutions of (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe)(2) yields (eta(5)-C(5)Me(5))Rh(eta(3)-CH(2)CHCH(2))(H), which provides controlled access to the 16-electron fragment (eta(5)-C(5)Me(5))Rh(CH(2)[double bond, length as m-dash]CHMe).

Remote C−H Activation of Quinolines through Copper-Catalyzed Radical Cross-Coupling

KAUST Repository

Xu, Jun

2016-01-12

Achieving site selectivity in carbon-hydrogen (C-H) functionalization reactions is a formidable challenge in organic chemistry. Herein, we report a novel approach to activating remote C-H bonds at the C5 position of 8-aminoquinoline through copper-catalyzed sulfonylation under mild conditions. Our strategy shows high conversion efficiency, a broad substrate scope, and good toleration with different functional groups. Furthermore, our mechanistic investigations suggest that a single-electron-transfer process plays a vital role in generating sulfonyl radicals and subsequently initiating C-S cross-coupling. Importantly, our copper-catalyzed remote functionalization protocol can be expanded for the construction of a variety of chemical bonds, including C-O, C-Br, C-N, C-C, and C-I. These findings provide a fundamental insight into the activation of remote C-H bonds, while offering new possibilities for rational design of drug molecules and optoelectronic materials requiring specific modification of functional groups. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A potential role of substrate as a base for deprotonation pathway in Rh-catalysed C-H amination of heteroArenes: DFT insights

KAUST Repository

Ajitha, Manjaly John; Huang, Kuo-Wei; Kwak, Jaesung; Kim, Hyun Jin; Chang, Sukbok; Jung, Yousung

2016-01-01

The possibility of direct introduction of a new functionality through C–H bond activation is an attractive strategy in covalent synthesis. Here, we investigated the mechanism of Rh-catalysed C-H amination of the hetero-aryl substrate (2

Palladium Catalyzed Allylic C-H Alkylation

DEFF Research Database (Denmark)

Engelin, Casper Junker; Fristrup, Peter

2011-01-01

are highlighted with emphasis on those leading to C-C bond formation, but where it was deemed necessary for the general understanding of the process closely related C-H oxidations and aminations are also included. It is found that C-H cleavage is most likely achieved by ligand participation which could involve......-H alkylation reaction which is the topic of the current review. Particular emphasis is put on current mechanistic proposals for the three reaction types comprising the overall transformation: C-H activation, nucleophillic addition, and re-oxidation of the active catalyst. Recent advances in C-H bond activation...... an acetate ion coordinated to Pd. Several of the reported systems rely on benzoquinone for re-oxidation of the active catalyst. The scope for nucleophilic addition in allylic C-H alkylation is currently limited, due to demands on pKa of the nucleophile. This limitation could be due to the pH dependence...

Twisted Amides: From Obscurity to Broadly Useful Transition-Metal-Catalyzed Reactions by N-C Amide Bond Activation.

Science.gov (United States)

Liu, Chengwei; Szostak, Michal

2017-05-29

The concept of using amide bond distortion to modulate amidic resonance has been known for more than 75 years. Two classic twisted amides (bridged lactams) ingeniously designed and synthesized by Kirby and Stoltz to feature fully perpendicular amide bonds, and as a consequence emanate amino-ketone-like reactivity, are now routinely recognized in all organic chemistry textbooks. However, only recently the use of amide bond twist (distortion) has advanced to the general organic chemistry mainstream enabling a host of highly attractive N-C amide bond cross-coupling reactions of broad synthetic relevance. In this Minireview, we discuss recent progress in this area and present a detailed overview of the prominent role of amide bond destabilization as a driving force in the development of transition-metal-catalyzed cross-coupling reactions by N-C bond activation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Manganese Catalyzed C–H Halogenation

Energy Technology Data Exchange (ETDEWEB)

Liu, Wei; Groves, John T.

2015-06-16

formation. Indeed, this idea led to the discovery of the first Mn-catalyzed direct aliphatic C–H fluorination reactions utilizing simple, nucleophilic fluoride salts. Mechanistic studies and DFT calculations have revealed a trans-difluoromanganese(IV) species as the key fluorine transfer intermediate. In addition to catalyzing normal 19F-fluorination reactions, manganese salen complexes were found to enable the incorporation of radioactive 18F fluorine via C–H activation. This advance represented the first direct C_sp3–H bond ¹⁸F labeling with no-carrier-added [¹⁸F]fluoride and facilitated the late-stage labeling of drug molecules for PET imaging. Given the high reactivity and enzymatic-like selectively of metalloporphyrins, we envision that this new Heteroatom-Rebound Catalysis (HRC) strategy will find widespread application in the C–H functionalization arena and serve as an effective tool for forming new carbon–heteroatom bonds at otherwise inaccessible sites in target molecules.

Cu(II)-catalyzed esterification reaction via aerobic oxidative cleavage of C(CO)-C(alkyl) bonds.

Science.gov (United States)

Ma, Ran; He, Liang-Nian; Liu, An-Hua; Song, Qing-Wen

2016-02-04

A novel Cu(II)-catalyzed aerobic oxidative esterification of simple ketones for the synthesis of esters has been developed with wide functional group tolerance. This process is assumed to go through a tandem sequence consisting of α-oxygenation/esterification/nucleophilic addition/C-C bond cleavage and carbon dioxide is released as the only byproduct.

Ruthenium(II)-catalyzed direct addition of indole/pyrrole C2-H bonds to alkynes.

Science.gov (United States)

Liang, Libo; Fu, Shaomin; Lin, Dongen; Zhang, Xiao-Qi; Deng, Yuanfu; Jiang, Huanfeng; Zeng, Wei

2014-10-17

A ruthenium-catalyzed C2-hydroindolation of alkynes has been achieved. This protocol provides a rapid and concise access to kinds of 2-alkenyl-substituted N-(2-pyridyl)indoles in which the pyridyl moiety can be easily removed to afford free (N-H) indoles under mild conditions. Various arenes and alkynes, including electron-deficient and electron-rich internal alkynes and terminal alkynes, allow for this transformation.

Platinum-Catalyzed, Terminal-Selective C(sp(3))-H Oxidation of Aliphatic Amines.

Science.gov (United States)

Lee, Melissa; Sanford, Melanie S

2015-10-14

This Communication describes the terminal-selective, Pt-catalyzed C(sp(3))-H oxidation of aliphatic amines without the requirement for directing groups. CuCl2 is employed as a stoichiometric oxidant, and the reactions proceed in high yield at Pt loadings as low as 1 mol%. These transformations are conducted in the presence of sulfuric acid, which reacts with the amine substrates in situ to form ammonium salts. We propose that protonation of the amine serves at least three important roles: (i) it renders the substrates soluble in the aqueous reaction medium; (ii) it limits binding of the amine nitrogen to Pt or Cu; and (iii) it electronically deactivates the C-H bonds proximal to the nitrogen center. We demonstrate that this strategy is effective for the terminal-selective C(sp(3))-H oxidation of a variety of primary, secondary, and tertiary amines.

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

Science.gov (United States)

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.

Rhodium(III)-catalyzed [3+2] annulation of 5-aryl-2,3-dihydro-1H-pyrroles with internal alkynes through C(sp²)-H/alkene functionalization.

Science.gov (United States)

Zhou, Ming-Bo; Pi, Rui; Hu, Ming; Yang, Yuan; Song, Ren-Jie; Xia, Yuanzhi; Li, Jin-Heng

2014-10-13

This study describes a new rhodium(III)-catalyzed [3+2] annulation of 5-aryl-2,3-dihydro-1H-pyrroles with internal alkynes using a Cu(OAc)2 oxidant for building a spirocyclic ring system, which includes the functionalization of an aryl C(sp(2))-H bond and addition/protonolysis of an alkene C=C bond. This method is applicable to a wide range of 5-aryl-2,3-dihydro-1H-pyrroles and internal alkynes, and results in the assembly of the spiro[indene-1,2'-pyrrolidine] architectures in good yields with excellent regioselectivities. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium-catalyzed enantioselective intramolecular C-H silylation for the syntheses of planar-chiral metallocene siloles.

Science.gov (United States)

Zhang, Qing-Wei; An, Kun; Liu, Li-Chuan; Yue, Yuan; He, Wei

2015-06-01

Reported herein is the rhodium-catalyzed enantioselective C-H bond silylation of the cyclopentadiene rings in Fe and Ru metallocenes. Thus, in the presence of (S)-TMS-Segphos, the reactions took place under very mild conditions to afford metallocene-fused siloles in good to excellent yields and with ee values of up to 97%. During this study it was observed that the steric hindrance of chiral ligands had a profound influence on the reactivity and enantioselectivity of the reaction, and might hold the key to accomplishing conventionally challenging asymmetric C-H silylations. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

THE DECEPTIVELY SIMPLE THERMOLYSIS OF TRIVALENT PERMETHYLTITANOCENE DERIVATIVES (ETA-5-C5ME5)2TIR - FORMATION OF A TETRAMETHYLFULVENE TITANIUM COMPOUND (ETA-6-C5ME4CH2)(ETA-5-C5ME5)TI AND RH, CATALYZED BY PERMETHYLTITANOCENE HYDRIDE, (ETA-5-C5ME5)2TIH

NARCIS (Netherlands)

LUINSTRA, GA; TEUBEN, JH

1992-01-01

The complexes Cp*2TiR (Cp* = eta-5-C5Me5; R = Me, Et, n-Pr, C2H3, CH2CMe3, Ph) undergo thermolysis to yield the fulvene complex Cp*FvTi (Fv = eta-6-C5Me4CH2) and RH. Kinetic measurements and deuterium labeling studies show that the decomposition is catalyzed by Cp*2TiH, which is formed either by

Rh(III-Catalyzed, Highly Selectively Direct C–H Alkylation of Indoles with Diazo Compounds

Directory of Open Access Journals (Sweden)

Kang Wan

2016-06-01

Full Text Available Rh(III-catalyzed regioselective alkylation of indoles with diazo compounds as a highly efficient and atom-economic protocol for the synthesis of alkyl substituted indoles has been developed. The reaction could proceed under mild conditions and afford a series of desired products in good to excellent yields.

Rh-Catalyzed (5+2) Cycloadditions of 3-Acyloxy-1,4-enynes and Alkynes: Computational Study of Mechanism, Reactivity, and Regioselectivity

Science.gov (United States)

Xu, Xiufang; Liu, Peng; Shu, Xing-zhong; Tang, Weiping; Houk, K. N.

2013-01-01

The mechanism of Rh-catalyzed (5+2) cycloadditions of 3-acyloxy-1,4-enyne (ACE) and alkynes is investigated using density functional theory calculations. The catalytic cycle involves 1,2-acyloxy migration, alkyne insertion, and reductive elimination to form the cycloheptatriene product. In contrast to the (5+2) cycloadditions with vinylcyclopropanes (VCP), in which alkyne inserts into a rhodium-allyl bond, alkyne insertion into a Rh–C(sp2) bond is preferred. The 1,2-acyloxy migration is found to be the rate-determining step of the catalytic cycle. The electron-rich p-dimethylaminobenzoate substrate promotes 1,2-acyloxy migration and significantly increases the reactivity. In the regioselectivity-determining alkyne insertion step, the alkyne substituent prefers to be distal to the forming C–C bond and thus distal to the OAc group in the product. PMID:23725341

Cp*Co(III) Catalyzed Site-Selective C-H Activation of Unsymmetrical O-Acyl Oximes: Synthesis of Multisubstituted Isoquinolines from Terminal and Internal Alkynes.

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Sun, Bo; Yoshino, Tatsuhiko; Kanai, Motomu; Matsunaga, Shigeki

2015-10-26

The synthesis of isoquinolines by site-selective C-H activation of O-acyl oximes with a Cp*Co(III) catalyst is described. In the presence of this catalyst, the C-H activation of various unsymmetrically substituted O-acyl oximes selectively occurred at the sterically less hindered site, and reactions with terminal as well as internal alkynes afforded the corresponding products in up to 98 % yield. Whereas the reactions catalyzed by the Cp*Co(III) system proceeded with high site selectivity (15:1 to 20:1), use of the corresponding Cp*Rh(III) catalysts led to low selectivities and/or yields when unsymmetrical O-acyl oximes and terminal alkynes were used. Deuterium labeling studies indicate a clear difference in the site selectivity of the C-H activation step under Cp*Co(III) and Cp*Rh(III) catalysis. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nickel-Catalyzed C sp2 –C sp3 Cross-Coupling via C–O Bond Activation

KAUST Repository

Guo, Lin

2016-06-13

A new and efficient nickel-catalyzed alkylation of CAr-O electrophiles with B-alkyl-9-BBNs is described. The transformation is characterized by its functional group tolerance and provides a practical and versatile access to various Csp2-Csp3 bonds through Csp2-O substitution, without the restriction of β-hydride elimination. Moreover, the advantage of the newly developed method was demonstrated in a selective and sequential C-O bond activation process. © 2016 American Chemical Society.

A potential role of substrate as a base for deprotonation pathway in Rh-catalysed C-H amination of heteroArenes: DFT insights

KAUST Repository

Ajitha, Manjaly John

2016-03-29

The possibility of direct introduction of a new functionality through C–H bond activation is an attractive strategy in covalent synthesis. Here, we investigated the mechanism of Rh-catalysed C-H amination of the hetero-aryl substrate (2-phenylpyridine) using phenyl azide as nitrogen source by density functional theory (DFT). For the deprotocyclometallation and protodecyclometallation processes of the title reaction, we propose a stepwise base-assisted mechanism (pathway I) instead of previously reported concerted mechanism (pathway II). In the new mechanism proposed here, 2-phenylpyridine acts as a base in the initial deprotonation step (C-H bond cleavage) and transports the proton towards the final protonation step. In fact, the N-H bond of the strong conjugate acid (formed during initial C-H bond cleavage) considered in pathway I (via TS4) is more acidic than the C-H bond of the neutral substrate considered in pathway II (via TS5). The higher activation barrier of TS5 mainly originates from the ring strain of the four membered cyclic transition state. The vital role of base, as disclosed here, can potentially have broader mechanistic implications for the development of reaction conditions of transition metal catalysed reactions.

Rhodium-catalyzed C-H functionalization with N-acylsaccharins.

Science.gov (United States)

Wu, Hongxiang; Liu, Tingting; Cui, Ming; Li, Yue; Jian, Junsheng; Wang, Hui; Zeng, Zhuo

2017-01-18

A rhodium-catalyzed C-H functionalization with activated amides by decarbonylation has been developed. Notably, this is the first C-H arylation employing N-acylsaccharins as coupling partners to give biaryls in good to excellent yields. The highlight of the work is the high tolerance of functional groups such as formyl, ester, and vinyl and the use of a removable directing group.

Cleavage of sp3 C-O bonds via oxidative addition of C-H bonds.

Science.gov (United States)

Choi, Jongwook; Choliy, Yuriy; Zhang, Xiawei; Emge, Thomas J; Krogh-Jespersen, Karsten; Goldman, Alan S

2009-11-04

(PCP)Ir (PCP = kappa(3)-C(6)H(3)-2,6-[CH(2)P(t-Bu)(2)](2)) is found to undergo oxidative addition of the methyl-oxygen bond of electron-poor methyl aryl ethers, including methoxy-3,5-bis(trifluoromethyl)benzene and methoxypentafluorobenzene, to give the corresponding aryloxide complexes (PCP)Ir(CH(3))(OAr). Although the net reaction is insertion of the Ir center into the C-O bond, density functional theory (DFT) calculations and a significant kinetic isotope effect [k(CH(3))(OAr)/k(CD(3))(OAr) = 4.3(3)] strongly argue against a simple insertion mechanism and in favor of a pathway involving C-H addition and alpha-migration of the OAr group to give a methylene complex followed by hydride-to-methylene migration to give the observed product. Ethoxy aryl ethers, including ethoxybenzene, also undergo C-O bond cleavage by (PCP)Ir, but the net reaction in this case is 1,2-elimination of ArO-H to give (PCP)Ir(H)(OAr) and ethylene. DFT calculations point to a low-barrier pathway for this reaction that proceeds through C-H addition of the ethoxy methyl group followed by beta-aryl oxide elimination and loss of ethylene. Thus, both of these distinct C-O cleavage reactions proceed via initial addition of a C(sp(3))-H bond, despite the fact that such bonds are typically considered inert and are much stronger than C-O bonds.

Recent advances in the ruthenium(ii)-catalyzed chelation-assisted C-H olefination of substituted aromatics, alkenes and heteroaromatics with alkenes via the deprotonation pathway.

Science.gov (United States)

Manikandan, Rajendran; Jeganmohan, Masilamani

2017-08-08

The transition-metal-catalyzed chelation-assisted alkenylation at the inert C-H bond of aromatics with alkenes is one of the efficient methods to synthesize substituted vinylarenes in a highly regio- and stereoselective manner. Palladium, rhodium and ruthenium complexes are frequently used as catalysts for this type of transformation. The present review describes the recent advances in the ruthenium-catalyzed chelation-assisted alkenylation at the C-H bond of aromatics, alkenes and heteroaromatics with alkenes via the deprotonation pathway. Several directing groups including 2-pyridyl, carbonyl, amidine, amide, amine, imidate, sulphonic acid, triazole, cyano, oxazolidinone and hydontoin are widely used in the reaction. The scope, limitation and mechanistic investigation of the alkenylation reactions are discussed elaborately. This feature article includes all the reported ruthenium-catalyzed alkenylation reactions via the deprotonation pathway until the end of March 2017.

Borane-catalyzed cracking of C-C bonds in coal; Boran-katalysierte C-C-Bindungungsspaltung in Steinkohle

Energy Technology Data Exchange (ETDEWEB)

Narangerel, J; Haenel, M W [Max-Planck-Institut fuer Kohlenforschung, Muelheim an der Ruhr (Germany)

1998-09-01

Coal, especially coking coal, was reacted with hydrogen at comparatively mild reaction conditions (150-280 degrees centigrade, 20 MPa hydrogen pressure) in the presence of catalysts consisting of borange reagents and certain transition metal halides to obtaine more than 80 percent of pyridine-soluble products. The influence of the degree of coalification, catalyst and temperature on the borane-catalyzed hydrogenolysis of C-C bonds in coal was investigated. (orig.) [Deutsch] Steinkohlen, insbesondere im Inkohlungsbereich der Fettkohlen (Kokskohlen), werden in Gegenwart von Katalysatoren aus Boran-Reagentien und bestimmten Uebergangsmetallhalogeniden mit Wasserstoff bei vergleichsweise milden Reaktionsbedingungen (250-280 C, 20 MPa Wasserstoffdruck) in zu ueber 80% pyridinloesliche Produkte umgewandelt. Der Einfluss von Inkohlungsgrad, Katalysator und Temperatur auf die Boran-katalysierte C-C-Bindungshydrogenolyse in Kohle wurde untersucht. (orig.)

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

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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

A General Catalyst for Site-Selective C(sp(3))-H Bond Amination of Activated Secondary over Tertiary Alkyl C(sp(3))-H Bonds.

Science.gov (United States)

Scamp, Ryan J; Jirak, James G; Dolan, Nicholas S; Guzei, Ilia A; Schomaker, Jennifer M

2016-06-17

The discovery of transition metal complexes capable of promoting general, catalyst-controlled and selective carbon-hydrogen (C-H) bond amination of activated secondary C-H bonds over tertiary alkyl C(sp(3))-H bonds is challenging, as substrate control often dominates when reactive nitrene intermediates are involved. In this letter, we report the design of a new silver complex, [(Py5Me2)AgOTf]2, that displays general and good-to-excellent selectivity for nitrene insertion into propargylic, benzylic, and allylic C-H bonds over tertiary alkyl C(sp(3))-H bonds.

Platinum-Catalyzed Terminal-Selective C(sp3)–H Oxidation of Aliphatic Amines

Science.gov (United States)

Lee, Melissa; Sanford, Melanie S.

2016-01-01

This paper describes the terminal-selective Pt-catalyzed C(sp3)–H oxidation of aliphatic amines without the requirement for directing groups. CuCl2 is employed as a stoichiometric oxidant, and the reactions proceed in high yield at Pt loadings as low as 1 mol %. These transformations are conducted in the presence of sulfuric acid, which reacts with the amine substrates in situ to form ammonium salts. We propose that protonation of the amine serves at least three important roles: (i) it renders the substrates soluble in the aqueous reaction medium; (ii) it limits binding of the amine nitrogen to Pt or Cu; and (ii) it electronically deactivates the C–H bonds proximal to the nitrogen center. We demonstrate that this strategy is effective for the terminal-selective C(sp3)–H oxidation of a variety of primary, secondary and tertiary amines. PMID:26439251

Rhenium-catalyzed dehydrogenative olefination of C(sp(3))-H bonds with hypervalent iodine(III) reagents.

Science.gov (United States)

Gu, Haidong; Wang, Congyang

2015-06-07

A dehydrogenative olefination of C(sp(3))-H bonds is disclosed here, by merging rhenium catalysis with an alanine-derived hypervalent iodine(III) reagent. Thus, cyclic and acyclic ethers, toluene derivatives, cycloalkanes, and nitriles are all successfully alkenylated in a regio- and stereoselective manner.

Preparation of PtSn/C, PtRu/C, PtRh/C, PtRuRh/C and PtSnRh/C electrocatalysts using an alcohol-reduction process for methanol and ethanol oxidation

International Nuclear Information System (INIS)

Dias, Ricardo Rodrigues

2009-01-01

In this work, Pt/C, PtRh (90:10), PtRh/C (50:50), PtSn/C (50:50), PtRu (50:50)/C, PtRuRh/C (50:40:10) and PtSnRh/C (50:40:10) were prepared by an alcohol-reduction process with metal loading of 20 wt.% using H 2 PtCl 6 .6H 2 O (Aldrich), SnCl 2 .2H 2 O (Aldrich),and RhCl 2 .XH 2 O (Aldrich) as metals sources and Vulcan XC72 as support. The electrocatalysts were characterized by EDX, XRD and cyclic voltammetry (CV). The electro-oxidation of ethanol was studied by CV, chronoamperomety at room temperature in acid medium and tests at 100 deg C on a single cell of a direct methanol or ethanol fuel cell. The EDX analysis showed that the metal atomic ratios of the obtained electrocatalysts were similar to the nominal atomic ratios used in the preparation. The diffractograms of electrocatalysts prepared showed four peaks at approximately 2θ = 40 0 , 47 0 , 67 0 and 82 0 , which are associated with the (111), (200), (220) and (311) planes, respectively, of a face cubic-centered (fcc) structure characteristic of platinum and platinum alloys. The average crystallite sizes using the Scherrer equation and the calculated values were in the range of 2–3 nm. For PtSn/C and PtSnRh/C two additional peaks were observed at 2θ = 34 0 and 52 0 that were identified as a SnO 2 phase. PtSn/C (50:50) and PtSnRh/C (50:40:10) electrocatalyst showed the best performance for ethanol oxidation at room temperature. For methanol oxidation at room temperature PtRu/C, PtSn/C and PtRuRh/C electrocatalysts showed the best performance. Tests at 100 deg C on a single cell of a direct ethanol fuel cell PtSnRh/C showed the best performance, for methanol oxidation PtRuRh/C showed the best performance. (author)

Palladium-catalyzed Suzuki-Miyaura coupling of amides by carbon-nitrogen cleavage: general strategy for amide N-C bond activation.

Science.gov (United States)

Meng, Guangrong; Szostak, Michal

2016-06-15

The first palladium-catalyzed Suzuki-Miyaura cross-coupling of amides with boronic acids for the synthesis of ketones by sterically-controlled N-C bond activation is reported. The transformation is characterized by operational simplicity using bench-stable, commercial reagents and catalysts, and a broad substrate scope, including substrates with electron-donating and withdrawing groups on both coupling partners, steric-hindrance, heterocycles, halides, esters and ketones. The scope and limitations are presented in the synthesis of >60 functionalized ketones. Mechanistic studies provide insight into the catalytic cycle of the cross-coupling, including the first experimental evidence for Pd insertion into the amide N-C bond. The synthetic utility is showcased by a gram-scale cross-coupling and cross-coupling at room temperature. Most importantly, this process provides a blueprint for the development of a plethora of metal catalyzed reactions of typically inert amide bonds via acyl-metal intermediates. A unified strategy for amide bond activation to enable metal insertion into N-C amide bond is outlined ().

Ligand-Controlled Chemoselective C(acyl)–O Bond vs C(aryl)–C Bond Activation of Aromatic Esters in Nickel Catalyzed C(sp2)–C(sp3) Cross-Couplings

KAUST Repository

Chatupheeraphat, Adisak

2018-02-20

A ligand-controlled and site-selective nickel catalyzed Suzuki-Miyaura cross-coupling reaction with aromatic esters and alkyl organoboron reagents as coupling partners was developed. This methodology provides a facile route for C(sp2)-C(sp3) bond formation in a straightforward fashion by successful suppression of the undesired β-hydride elimination process. By simply switching the phosphorus ligand, the ester substrates are converted into the alkylated arenes and ketone products, respectively. The utility of this newly developed protocol was demonstrated by its wide substrate scope, broad functional group tolerance and application in the synthesis of key intermediates for the synthesis of bioactive compounds. DFT studies on the oxidative addition step helped rationalizing this intriguing reaction chemoselectivity: whereas nickel complexes with bidentate ligands favor the C(aryl)-C bond cleavage in the oxidative addition step leading to the alkylated product via a decarbonylative process, nickel complexes with monodentate phosphorus ligands favor activation of the C(acyl)-O bond, which later generates the ketone product.

Rhodium (II) carbene C-H insertion in water and catalyst reuse; Insercao C-H de carbenoides de rodio em agua e reutilizacao do catalisador

Energy Technology Data Exchange (ETDEWEB)

Candeias, Nuno R.; Gois, Pedro M.P.; Afonso, Carlos A.M. [Instituto Superior Tecnico, Lisboa (Portugal)]. E-mail: carlosafonso@ist.utl.pt

2007-07-01

A five-session laboratory experiment is described for the synthesis of a beta-lactam via Rh(II) catalysed intramolecular C-H insertion of a alpha-diazo-alpha-ethoxycarbonyl acetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst Rh{sub 2}(OAc){sub 4}. The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutilization. (author)

Pd(II)-Catalyzed Enantioselective C-H Olefination of Diphenylacetic Acids

Science.gov (United States)

Shi, Bing-Feng; Zhang, Yang-Hui; Lam, Jonathan K.; Wang, Dong-Hui; Yu, Jin-Quan

2009-01-01

Pd(II)-catalyzed enantioselective C-H olefination of diphenylacetic acid substrates has been achieved through the use of mono-protected chiral amino acid ligands. The absolute configuration of the resulting olefinated products is consistent with that of a proposed C-H insertion intermediate. PMID:20017549

Oxidative C-H/C-H Cross-Coupling Reactions between N-Acylanilines and Benzamides Enabled by a Cp*-Free RhCl3/TFA Catalytic System.

Science.gov (United States)

You, Jingsong; Shi, Yang; Zhang, Luoqiang; Lan, Jingbo; Zhang, Min; Zhou, Fulin; Wei, Wenlong

2018-06-03

Using the dual chelation-assisted strategy, a completely regiocontrolled oxidative C-H/C-H cross-coupling reaction between an N-acylaniline and a benzamide has been accomplished for the first time, which enables a step-economical and highly efficient pathway to 2-amino-2'-carboxybiaryl scaffolds from readily available substrates. A Cp*-free RhCl3/TFA catalytic system has been developed to replace the generally used [Cp*RhCl2]2/AgSbF6 (Cp* = pentamethyl cyclopentadienyl) in oxidative C-H/C-H cross-coupling reactions between two (hetero)arenes. The RhCl3/TFA system avoids the use of expensive Cp* ligand and AgSbF6. As an illustrative example, the protocol developed herein greatly streamlines access to naturally occurring benzo[c]phenanthridine alkaloid oxynitidine in an excellent overall yield. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thiocarbamate-Directed Tandem Olefination-Intramolecular Sulfuration of Two Ortho C-H Bonds: Application to Synthesis of a COX-2 Inhibitor.

Science.gov (United States)

Li, Wendong; Zhao, Yingwei; Mai, Shaoyu; Song, Qiuling

2018-02-16

A palladium-catalyzed dual ortho C-H bond activation of aryl thiocarbamates is developed. This tandem reaction initiates by thiocarbamate-directed ortho C-H palladation, which leads to favorable olefin insertion rather than reductive elimination. The oxidative Heck reaction followed by another C-H activation and sulfuration affords the dual-functionalized products. This reaction provides a concise route to the S,O,C multisubstituted benzene skeleton which could be successfully applied for the synthesis of a COX-2 inhibitor.

Stacking reactions of the borole complex Cp*Rh(η5-C4H4BPh) with the dicationic fragments [Cp*M]2+ (M = Rh or Ir)

International Nuclear Information System (INIS)

Loginov, D.A.; Muratov, D.V.; Starikova, Z.A.; Petrovskij, P.V.; Kudinov, A.R.

2006-01-01

The reaction of the (borole)rhodium iodide complex [(η-C 4 H 4 BPh)RhI] 4 with Cp*Li afforded the sandwich compound Cp*Rh(η-C 4 H 4 BPh) (1). The reactions of compound 1 with the solvated complexes [Cp*M(MeNO 2 ) 3 ] 2+ (BF 4 - ) 2 gave triple-decker cationic complexes with the central borole ligand [Cp*Rh(μ-η 5 :η 5 -C 4 H 4 BPh)MCp*] 2+ (BF 4 - ) 2 (M = Rh or Ir). The structure of complex 1 was established by X-ray diffraction [ru

Selective C(sp2)-C(sp) bond cleavage: the nitrogenation of alkynes to amides.

Science.gov (United States)

Qin, Chong; Feng, Peng; Ou, Yang; Shen, Tao; Wang, Teng; Jiao, Ning

2013-07-22

Breakthrough: A novel catalyzed direct highly selective C(sp2)-C(sp) bond functionalization of alkynes to amides has been developed. Nitrogenation is achieved by the highly selective C(sp2)-C(sp) bond cleavage of aryl-substituted alkynes. The oxidant-free and mild conditions and wide substrate scope make this method very practical. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Iron-Catalyzed C-O Bond Activation: Opportunity for Sustainable Catalysis.

Science.gov (United States)

Bisz, Elwira; Szostak, Michal

2017-10-23

Oxygen-based electrophiles have emerged as some of the most valuable cross-coupling partners in organic synthesis due to several major strategic and environmental benefits, such as abundance and potential to avoid toxic halide waste. In this context, iron-catalyzed C-O activation/cross-coupling holds particular promise to achieve sustainable catalytic protocols due to its natural abundance, inherent low toxicity, and excellent economic and ecological profile. Recently, tremendous progress has been achieved in the development of new methods for functional-group-tolerant iron-catalyzed cross-coupling reactions by selective C-O cleavage. These methods establish highly attractive alternatives to traditional cross-coupling reactions by using halides as electrophilic partners. In particular, new easily accessible oxygen-based electrophiles have emerged as substrates in iron-catalyzed cross-coupling reactions, which significantly broaden the scope of this catalysis platform. New mechanistic manifolds involving iron catalysis have been established; thus opening up vistas for the development of a wide range of unprecedented reactions. The synthetic potential of this sustainable mode of reactivity has been highlighted by the development of new strategies in the construction of complex motifs, including in target synthesis. The most recent advances in sustainable iron-catalyzed cross-coupling of C-O-based electrophiles are reviewed, with a focus on both mechanistic aspects and synthetic utility. It should be noted that this catalytic manifold provides access to motifs that are often not easily available by other methods, such as the assembly of stereodefined dienes or C(sp 2 )-C(sp 3 ) cross-couplings, thus emphasizing the synthetic importance of this mode of reactivity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium(I)-catalyzed cyclization of allenynes with a carbonyl group through unusual insertion of a C-O bond into a rhodacycle intermediate.

Science.gov (United States)

Oonishi, Yoshihiro; Yokoe, Takayuki; Hosotani, Akihito; Sato, Yoshihiro

2014-01-20

Rhodium(I)-catalyzed cyclization of allenynes with a tethered carbonyl group was investigated. An unusual insertion of a CO bond into the C(sp(2) )-rhodium bond of a rhodacycle intermediate occurs via a highly strained transition state. Direct reductive elimination from the obtained rhodacyle intermediate proceeds to give a tricyclic product containing an 8-oxabicyclo[3.2.1]octane skeleton, while β-hydride elimination from the same intermediate gives products that contain fused five- and seven-membered rings in high yields. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium (II) carbene C-H insertion in water and catalyst reuse

International Nuclear Information System (INIS)

Candeias, Nuno R.; Gois, Pedro M.P.; Afonso, Carlos A.M.

2007-01-01

A five-session laboratory experiment is described for the synthesis of a beta-lactam via Rh(II) catalysed intramolecular C-H insertion of a alpha-diazo-alpha-ethoxycarbonyl acetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst Rh 2 (OAc) 4 . The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutilization. (author)

The Mechanism of Rh-Catalyzed Transformation of Fatty Acids to Linear Alpha olefins

Directory of Open Access Journals (Sweden)

Sondre H. Hopen Eliasson

2017-12-01

Full Text Available Linear alpha olefins (LAOs are key commodity chemicals and petrochemical intermediates that are currently produced from fossil resources. Fatty acids are the obvious renewable starting material for LAOs, which can be obtained via transition-metal-catalyzed decarbonylative dehydration. However, even the best catalysts that have been obtained to date, which are based on palladium, are not active and stable enough for industrial use. To provide insight for design of better catalysts, we here present the first computationally derived mechanism for another attractive transition-metal for this reaction, rhodium. By comparing the calculated mechanisms and free energy profiles for the two metals, Pd and Rh, we single out important factors for a facile, low-barrier reaction and for a stable catalyst. While the olefin formation is rate limiting for both of the metals, the rate-determining intermediate for Rh is, in contrast to Pd, the starting complex, (PPh32Rh(COCl. This complex largely draws its stability from the strength of the Rh(I–CO bond. CO is a much less suitable ligand for the high-oxidation state Rh(III. However, for steric reasons, rhodium dissociates a bulkier triphenylphosphine and keeps the carbonyl during the oxidative addition, which is less favorable than for Pd. When compared to Pd, which dissociates two phosphine ligands at the start of the reaction, the catalytic activity of Rh also appears to be hampered by its preference for high coordination numbers. The remaining ancillary ligands leave less space for the metal to mediate the reaction.

Directed C-H Bond Oxidation of (+)-Pleuromutilin.

Science.gov (United States)

Ma, Xiaoshen; Kucera, Roman; Goethe, Olivia F; Murphy, Stephen K; Herzon, Seth B

2018-05-01

Antibiotics derived from the diterpene fungal metabolite (+)-pleuromutilin (1) are useful agents for the treatment Gram-positive infections in humans and farm animals. Pleuromutilins elicit slow rates of resistance development and minimal cross-resistance with existing antibiotics. Despite efforts aimed at producing new derivatives by semisynthesis, modification of the tricyclic core is underexplored, in part due to a limited number of functional group handles. Herein, we report methods to selectively functionalize the methyl groups of (+)-pleuromutilin (1) by hydroxyl-directed iridium-catalyzed C-H silylation, followed by Tamao-Fleming oxidation. These reactions provided access to C16, C17, and C18 monooxidized products, as well as C15/C16 and C17/C18 dioxidized products. Four new functionalized derivatives were prepared from the protected C17 oxidation product. C6 carboxylic acid, aldehyde, and normethyl derivatives were prepared from the C16 oxidation product. Many of these sequences were executed on gram scales. The efficiency and practicality of these routes provides an easy method to rapidly interrogate structure-activity relationships that were previously beyond reach. This study will inform the design of fully synthetic approaches to novel pleuromutilins and underscores the power of the hydroxyl-directed iridium-catalyzed C-H silylation reaction.

Stereoselective synthesis of 1,3-disubstituted isoindolines via Rh(III)-catalyzed tandem oxidative olefination-cyclization of 4-aryl cyclic sulfamidates.

Science.gov (United States)

Son, Se-Mi; Seo, Yeon Ji; Lee, Hyeon-Kyu

2016-03-21

Rh(III)-catalyzed tandem ortho C-H olefination of cyclic 4-aryl sulfamidates (1) and subsequent intramolecular cyclization are described. This reaction serves as a method for the direct and stereoselective synthesis of 1,3-disubstituted isoindolines (3) starting with enantiomerically enriched 4-aryl cyclic sulfamidates. In this process, the configurational integrity of the stereogenic center in the starting cyclic sulfamidate is completely retained. In addition, the process generates trans-1,3-disubstituted isoindolines exclusively.

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

Science.gov (United States)

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.

Ligand-controlled, tunable silver-catalyzed C-H amination.

Science.gov (United States)

Alderson, Juliet M; Phelps, Alicia M; Scamp, Ryan J; Dolan, Nicholas S; Schomaker, Jennifer M

2014-12-03

The development of readily tunable and regioselective C-H functionalization reactions that operate solely through catalyst control remains a challenge in modern organic synthesis. Herein, we report that simple silver catalysts supported by common nitrogenated ligands can be used to tune a nitrene transfer reaction between two different types of C-H bonds. The results reported herein represent the first example of ligand-controlled and site-selective silver-promoted C-H amination.

N-oxide as a traceless oxidizing directing group: mild rhodium(III)-catalyzed C-H olefination for the synthesis of ortho-alkenylated tertiary anilines.

Science.gov (United States)

Huang, Xiaolei; Huang, Jingsheng; Du, Chenglong; Zhang, Xingyi; Song, Feijie; You, Jingsong

2013-12-02

Double role: A traceless directing group also acts as an internal oxidant in a novel Rh(III) -catalyzed protocol developed for the synthesis of ortho-alkenylated tertiary anilines. A five-membered cyclometalated Rh(III) complex is proposed as a plausible intermediate and confirmed by X-ray crystallographic analysis. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A bonding study of c-C5H8 adsorption on Pt(111)

International Nuclear Information System (INIS)

Simonetti, S.; Jasen, P.; Gonzalez, E.; Juan, A.; Brizuela, G.

2006-01-01

The chemisorption of cyclopentane (c-C 5 H 8 ) on Pt(111) has been studied using a qualitative band-structure calculations in the framework of tight-binding implementation with the YAeHMOP package. We modeled the metal surface by a two-dimensional slab of finite thickness with an overlayer of c-C 5 H 8 , in a (3x3) di-σ geometry. The c-C 5 H 8 molecule is attached to the surface with its C?C atoms bonded mainly with two Pt atoms while the opposite CH 2 bends towards the surface. The Pt?Pt bonds in the underlying surface and the C?C bonds of c-C 5 H 8 are weakened upon the chemisorption. A noticeable Pt-H and Pt-C interactions has been observed. We found that of Pt 5d z 2 band plays an important role in the bonding between c-C 5 H 8 and the surface, as do the Pt 6s and 6p z bands. The HOMO-LUMO bands of c-C 5 H 8 are very dispersed, indicative of a strong interaction with the metal surface

Iridium/Bipyridine-Catalyzed ortho-Selective C-H Borylation of Phenol and Aniline Derivatives.

Science.gov (United States)

Li, Hong-Liang; Kanai, Motomu; Kuninobu, Yoichiro

2017-11-03

An iridium-catalyzed ortho-selective C-H borylation of phenol and aniline derivatives has been successfully developed. Iridium/bipyridine-catalyzed C-H borylation generally occurred at the meta- and para-positions of aromatic substrates. Introduction of an electron-withdrawing substituent on the bipyridine-type ligand and a methylthiomethyl group on the hydroxy and amino groups of the phenol and aniline substrates, however, dramatically altered the regioselectivity, affording exclusively ortho-borylated products. The reaction proceeded in good to excellent yields with good functional group tolerance. C-H borylation was applied to the synthesis of a calcium receptor modulator.

Palladium catalyzed selective distal C-H olefination of biaryl systems.

Science.gov (United States)

Maity, Soham; Hoque, Ehtasimul; Dhawa, Uttam; Maiti, Debabrata

2016-11-29

Palladium catalyzed selective distal C-H activation with nitrile based templates has been of significant research interest in recent times. In this report, we disclose the distal C-H olefination of biphenyl systems with high regio- and stereo-selectivity and useful synthetic yields. The utility of this method has been demonstrated through its wide olefin scope, its operation at the gram scale and the easy removal/recovery of the directing group.

Mechanistic Studies of Cobalt-Catalyzed C(sp2)-H Borylation of Five-Membered Heteroarenes with Pinacolborane.

Science.gov (United States)

Obligacion, Jennifer V; Chirik, Paul J

2017-07-07

Studies into the mechanism of cobalt-catalyzed C(sp 2 )-H borylation of five-membered heteroarenes with pinacolborane (HBPin) as the boron source established the catalyst resting state as the trans -cobalt(III) dihydride boryl, ( iPr PNP)Co(H) 2 (BPin) ( iPr PNP = 2,6-( i Pr 2 PCH 2 ) 2 (C 5 H 3 N)), at both low and high substrate conversions. The overall first-order rate law and observation of a normal deuterium kinetic isotope effect on the borylation of benzofuran versus benzofuran-2- d 1 support H 2 reductive elimination from the cobalt(III) dihydride boryl as the turnover-limiting step. These findings stand in contrast to that established previously for the borylation of 2,6-lutidine with the same cobalt precatalyst, where borylation of the 4-position of the pincer occurred faster than the substrate turnover and arene C-H activation by a cobalt(I) boryl is turnover-limiting. Evaluation of the catalytic activity of different cobalt precursors in the C-H borylation of benzofuran with HBPin established that the ligand design principles for C- H borylation depend on the identities of both the arene and the boron reagent used: electron-donating groups improve catalytic activity of the borylation of pyridines and arenes with B 2 Pin 2 , whereas electron-withdrawing groups improve catalytic activity of the borylation of five-membered heteroarenes with HBPin. Catalyst deactivation by P-C bond cleavage from a cobalt(I) hydride was observed in the C-H borylation of arene substrates with C-H bonds that are less acidic than those of five-membered heteroarenes using HBPin and explains the requirement of B 2 Pin 2 to achieve synthetically useful yields with these arene substrates.

Magnetic behavior in heterometallic one-dimensional chains or octanuclear complex regularly aligned with metal-metal bonds as -Rh-Rh-Pt-Cu-Pt

Science.gov (United States)

Uemura, Kazuhiro

2018-06-01

Heterometallic one-dimensional chains, [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}]n(PF6)2n (1 and 2, piam = pivalamidate) and [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}2](CF3CO2)2(ClO4)2·2H2O (3), are paramagnetic one-dimensional chains or octanuclear complexes that are either aligned as -Rh-Rh-Pt-Cu-Pt- (1 and 2) or as Pt-Cu-Pt-Rh-Rh-Pt-Cu-Pt (3) with metal-metal bonds. Compounds 1-3 have rare structures, from the standpoint of that the paramagnetic species of Cu atoms are linked by direct metal-metal bonds. Magnetic susceptibility measurements for 1-3 performed at temperatures of 2 K-300 K indicated that the unpaired electrons localize in the Cu 3dx2-y2 orbitals, where S = 1/2 Cu(II) atoms are weakly antiferromagnetically coupled with J = -0.35 cm-1 (1), -0.47 cm-1 (2), and -0.45 cm-1 (3).

Aerobic Asymmetric Dehydrogenative Cross-Coupling between Two C(sp3)-H Groups Catalyzed by a Chiral-at-Metal Rhodium Complex.

Science.gov (United States)

Tan, Yuqi; Yuan, Wei; Gong, Lei; Meggers, Eric

2015-10-26

A sustainable C-C bond formation is merged with the catalytic asymmetric generation of one or two stereocenters. The introduced catalytic asymmetric cross-coupling of two C(sp3)-H groups with molecular oxygen as the oxidant profits from the oxidative robustness of a chiral-at-metal rhodium(III) catalyst and exploits an autoxidation mechanism or visible-light photosensitized oxidation. In the latter case, the catalyst serves a dual function, namely as a chiral Lewis acid for catalyzing enantioselective enolate chemistry and at the same time as a visible-light-driven photoredox catalyst. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Preparation of PtSn/C, PtRu/C, PtRh/C, PtRuRh/C and PtSnRh/C electrocatalysts using an alcohol-reduction process for methanol and ethanol oxidation; Preparacao e caracterizacao de eletrocatalisadores PtRu, PtSn, PtRh, PtRuRh e PtSnRh para oxidacao direta de alcoois em celulas a combustivel tipo PEM utilizando a metodologia da reducao por alcool

Energy Technology Data Exchange (ETDEWEB)

Dias, Ricardo Rodrigues

2009-07-01

In this work, Pt/C, PtRh (90:10), PtRh/C (50:50), PtSn/C (50:50), PtRu (50:50)/C, PtRuRh/C (50:40:10) and PtSnRh/C (50:40:10) were prepared by an alcohol-reduction process with metal loading of 20 wt.% using H{sub 2}PtCl{sub 6}.6H{sub 2}O (Aldrich), SnCl{sub 2}.2H{sub 2}O (Aldrich),and RhCl{sub 2}.XH{sub 2}O (Aldrich) as metals sources and Vulcan XC72 as support. The electrocatalysts were characterized by EDX, XRD and cyclic voltammetry (CV). The electro-oxidation of ethanol was studied by CV, chronoamperomety at room temperature in acid medium and tests at 100 deg C on a single cell of a direct methanol or ethanol fuel cell. The EDX analysis showed that the metal atomic ratios of the obtained electrocatalysts were similar to the nominal atomic ratios used in the preparation. The diffractograms of electrocatalysts prepared showed four peaks at approximately 2{theta} =40 deg, 47 deg, 67 deg and 82 deg, which are associated with the (111), (200), (220) and (311) planes, respectively, of a face cubic-centered (fcc) structure characteristic of platinum and platinum alloys. The average crystallite sizes using the Scherrer equation and the calculated values were in the range of 2-3 nm. For Pt Sn/C and PtSnRh/C two additional peaks were observed at 2 = 34 deg and 52 deg that were identified as a SnO{sub 2} phase. Pt Sn/C (50:50) and PtSnRh/C (50:40:10) electro catalyst showed the best performance for ethanol oxidation at room temperature. For methanol oxidation at room temperature Pt Ru/C, Pt Sn/C and PtRuRh/C electrocatalysts showed the best performance. Tests at 100 deg C on a single cell of a direct ethanol fuel cell PtSnRh/C showed the best performance, for methanol oxidation PtRuRh/C showed the best performance. (author)

Rh-Catalyzed rearrangement of vinylcyclopropane to 1,3-diene units attached to N-heterocycles

Directory of Open Access Journals (Sweden)

Alberto Brandi

2011-03-01

Full Text Available Dienes embedded in quinolizidine and indolizidine structures can be prepared in four steps from cyclic nitrones and bicyclopropylidene. The key intermediates α-spirocyclopropanated N-heterocyclic ketones, generated via a domino 1,3-dipolar cycloaddition/thermal rearrangement sequence, were converted by Wittig methylenation to the corresponding vinylcyclopropanes (VCPs, which underwent rearrangement to 1,3-dienes in the presence of the Wilkinson Rh(I complex under microwave heating. The previously unexplored Rh(I-catalyzed opening of the VCP moiety embedded in an azapolycyclic system occurs at high temperature (110–130 °C to afford the corresponding 1,3-dienes in moderate yield (34–53%.

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

Science.gov (United States)

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.

Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-). Theoretical evidence for a competitive charge transfer mechanism.

Science.gov (United States)

Hu, Zhenming; Boyd, Russell J; Nakatsuji, Hiroshi

2002-03-20

Molecular structures and excited states of CpM(CO)(2) (Cp = eta(5)-C(5)H(5); M = Rh, Ir) and [Cl(2)Rh(CO)(2)](-) complexes have been investigated using the B3LYP and the symmetry-adapted cluster (SAC)/SAC-configuration interaction (SAC-CI) theoretical methods. All the dicarbonyl complexes have singlet ground electronic states with large singlet-triplet separations. Thermal dissociations of CO from the parent dicarbonyls are energetically unfavorable. CO thermal dissociation is an activation process for [Cl(2)Rh(CO)(2)](-) while it is a repulsive potential for CpM(CO)(2). The natures of the main excited states of CpM(CO)(2) and [Cl(2)Rh(CO)(2)](-) are found to be quite different. For [Cl(2)Rh(CO)(2)](-), all the strong transitions are identified to be metal to ligand CO charge transfer (MLCT) excitations. A significant feature of the excited states of CpM(CO)(2) is that both MLCT excitation and a ligand Cp to metal and CO charge transfer excitation are strongly mixed in the higher energy states with the latter having the largest oscillator strength. A competitive charge transfer excited state has therefore been identified theoretically for CpRh(CO)(2) and CpIr(CO)(2). The wavelength dependence of the quantum efficiencies for the photoreactions of CpM(CO)(2) reported by Lees et al. can be explained by the existence of two different types of excited states. The origin of the low quantum efficiencies for the C-H/S-H bond activations of CpM(CO)(2) can be attributed to the smaller proportion of the MLCT excitation in the higher energy states.

Preparation of PtSn/C, PtRu/C, PtRh/C, PtRuRh/C and PtSnRh/C electrocatalysts using an alcohol-reduction process for methanol and ethanol oxidation; Preparacao e caracterizacao de eletrocatalisadores PtRu, PtSn, PtRh, PtRuRh e PtSnRh para oxidacao direta de alcoois em celulas a combustivel tipo PEM utilizando a metodologia da reducao por alcool

Energy Technology Data Exchange (ETDEWEB)

Dias, Ricardo Rodrigues

2009-07-01

In this work, Pt/C, PtRh (90:10), PtRh/C (50:50), PtSn/C (50:50), PtRu (50:50)/C, PtRuRh/C (50:40:10) and PtSnRh/C (50:40:10) were prepared by an alcohol-reduction process with metal loading of 20 wt.% using H{sub 2}PtCl{sub 6}.6H{sub 2}O (Aldrich), SnCl{sub 2}.2H{sub 2}O (Aldrich),and RhCl{sub 2}.XH{sub 2}O (Aldrich) as metals sources and Vulcan XC72 as support. The electrocatalysts were characterized by EDX, XRD and cyclic voltammetry (CV). The electro-oxidation of ethanol was studied by CV, chronoamperomety at room temperature in acid medium and tests at 100 deg C on a single cell of a direct methanol or ethanol fuel cell. The EDX analysis showed that the metal atomic ratios of the obtained electrocatalysts were similar to the nominal atomic ratios used in the preparation. The diffractograms of electrocatalysts prepared showed four peaks at approximately 2θ = 40{sup 0}, 47{sup 0}, 67{sup 0} and 82{sup 0}, which are associated with the (111), (200), (220) and (311) planes, respectively, of a face cubic-centered (fcc) structure characteristic of platinum and platinum alloys. The average crystallite sizes using the Scherrer equation and the calculated values were in the range of 2–3 nm. For PtSn/C and PtSnRh/C two additional peaks were observed at 2θ = 34{sup 0} and 52{sup 0} that were identified as a SnO{sub 2} phase. PtSn/C (50:50) and PtSnRh/C (50:40:10) electrocatalyst showed the best performance for ethanol oxidation at room temperature. For methanol oxidation at room temperature PtRu/C, PtSn/C and PtRuRh/C electrocatalysts showed the best performance. Tests at 100 deg C on a single cell of a direct ethanol fuel cell PtSnRh/C showed the best performance, for methanol oxidation PtRuRh/C showed the best performance. (author)

Alkane Activation at Ambient Temperatures: Unusual Selectivities, C-C, C-H Bond Scission versus C-C Bond Coupling

NARCIS (Netherlands)

Trionfetti, C.; Agiral, A.; Gardeniers, Johannes G.E.; Lefferts, Leonardus; Seshan, Kulathuiyer

2008-01-01

Activating bonds: A cold plasma generated by dielectric barrier discharge in a microreactor converts alkanes (C1–C3) at atmospheric pressure. Large amounts of products with higher molecular weight than the starting hydrocarbons are observed showing that C-H activation at lower T favourably leads to

Laccase-catalyzed C-S and C-C coupling for a one-pot synthesis of 1,4-naphthoquinone sulfides and 1,4-naphthoquinone sulfide dimers

CSIR Research Space (South Africa)

Wellington, Kevin W

2013-06-01

Full Text Available Oxidative C-S and C-C bond formation with aryl and alkyl thiols was catalyzed under mild conditions in a reaction vessel open to air at pH 4.5 in the presence of a commercial laccase (Novozym 51003 or Suberase) and a cosolvent (DMF) to afford 1...

Directing-Group-mediated C-H-Alkynylations.

Science.gov (United States)

Caspers, Lucien D; Nachtsheim, Boris J

2018-05-18

C-C triple bonds are amongst the most versatile functional groups in synthetic chemistry. Complementary to the Sonogashira coupling the direct metal-catalyzed alkynylation of C-H bonds has emerged as a highly promising approach in recent years. To guarantee a high regioselectivity suitable directing groups (DGs) are necessary to guide the transition metal (TM) into the right place. In this Focus Review we present the current developments in DG-mediated C(sp 2 )-H and C(sp 3 )-H modifications with terminal alkynes under oxidative conditions and with electrophilic alkynylation reagents. We will discuss further modifications of the alkyne, in particular subsequent cyclizations to carbo- and heterocycles and modifications of the DG in the presence of the alkyne. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium(III)-catalyzed vinylic sp2 C-H bond functionalization: efficient synthesis of pyrido[1,2-α]benzimidazoles and imidazo[1,2-α]pyridines.

Science.gov (United States)

Dong, Lin; Huang, Ji-Rong; Qu, Chuan-Hua; Zhang, Qian-Ru; Zhang, Wei; Han, Bo; Peng, Cheng

2013-09-28

A simple approach for synthesis of novel aza-fused scaffolds such as pyrido[1,2-α]benzimidazoles and imidazo[1,2-α]pyridines was developed by Rh(III)-catalyzed direct oxidative coupling between alkenes and unactivated alkynes without an extra directing group. The method would allow a broad substrate scope, providing fused heterocycles with potential biological properties.

Inserção C-H de carbenóides de ródio em água e reutilização do catalisador Rhodium (II carbene C-H insertion in water and catalyst reuse

Directory of Open Access Journals (Sweden)

Nuno R. Candeias

2007-01-01

Full Text Available A five-session laboratory experiment is described for the synthesis of a beta-lactam via Rh(II catalysed intramolecular C-H insertion of a alpha-diazo-alpha-ethoxycarbonylacetamide. The metallo-carbene, responsible for the C-H bond activation, was generated from the diazo substrate and the catalyst Rh2(OAc4. The high stability and solubility of the catalyst and the exclusive C-H insertion of the Rh-carbene allows the synthesis of this important heterocycle in water and the catalyst reutilization.

Multiple C-H Bond Activations and Ring-Opening C-S Bond Cleavage of Thiophene by Dirhenium Carbonyl Complexes.

Science.gov (United States)

Adams, Richard D; Dhull, Poonam; Tedder, Jonathan D

2018-06-14

The reaction of Re 2 (CO) 8 (μ-C 6 H 5 )(μ-H) (1) with thiophene in CH 2 Cl 2 at 40 °C yielded the new compound Re 2 (CO) 8 (μ-η 2 -SC 4 H 3 )(μ-H) (2), which contains a bridging σ-π-coordinated thienyl ligand formed by the activation of the C-H bond at the 2 position of the thiophene. Compound 2 exhibits dynamical activity on the NMR time scale involving rearrangements of the bridging thienyl ligand. The reaction of compound 2 with a second 1 equiv of 1 at 45 °C yielded the doubly metalated product [Re 2 (CO) 8 (μ-H)] 2 (μ-η 2 -2,3-μ-η 2 -4,5-C 4 H 2 S) (3), formed by the activation of the C-H bond at the 5 position of the thienyl ligand in 2. Heating 3 in a hexane solvent to reflux transformed it into the ring-opened compound Re(CO) 4 [μ-η 5 -η 2 -SCC(H)C(H)C(H)][Re(CO) 3 ][Re 2 (CO) 8 (μ-H)] (4) by the loss of one CO ligand. Compound 4 contains a doubly metalated 1-thiapentadienyl ligand formed by the cleavage of one of the C-S bonds. When heated to reflux (125 °C) in an octane solvent in the presence of H 2 O, the new compound Re(CO) 4 [η 5 -μ-η 2 -SC(H)C(H)C(H)C(H)]Re(CO) 3 (5) was obtained by cleavage of the Re 2 (CO) 8 (μ-H) group from 4 with formation of the known coproduct [Re(CO) 3 (μ 3 -OH)] 4 . All new products were characterized by single-crystal X-ray diffraction analyses.

S,O-Ligand-Promoted Palladium-Catalyzed C-H Functionalization Reactions of Nondirected Arenes

NARCIS (Netherlands)

Naksomboon, K.; Valderas, C.; Gomez-Martinez, M.; Alvarez-Casao, Y.; Fernández Ibáñez, M.A.

Pd(II)-catalyzed C-H functionalization of non directed arenes has been realized using an inexpensive and easily accessible type of bidentate S,O-ligand. The catalytic system shows high efficiency in the C-H olefination reaction of electron-rich and electron-poor arenes. This methodology is

Synthesis of heterocycles via transition-metal-catalyzed hydroarylation of alkynes.

Science.gov (United States)

Yamamoto, Yoshihiko

2014-03-07

Transition-metal (TM)-catalyzed hydroarylation reactions of alkynes have received much attention, because they enable the net insertion of alkyne C-C triple bonds into C-H bonds of aromatic precursors, resulting in regio- and stereo-selective formation of synthetically useful arylalkenes. Taking advantage of this feature, TM-catalyzed alkyne hydroarylations have been successfully used for the synthesis of heterocycles. TM-catalyzed alkyne hydroarylations can be classified into three major categories depending on the type of reaction and precursors involved: (1) palladium-catalyzed reductive Heck reactions of alkynes with aryl halides, (2) TM-catalyzed conjugate arylation reactions of activated alkynes with arylboronic acids, and (3) TM-catalyzed aromatic C-H alkenylations with alkynes. This review surveys heterocycle synthesis via TM-catalyzed hydroarylation of alkynes according to the above classification, with an emphasis on the scope and limitations, as well as the underlying mechanisms.

Influence of the Crystal Structure of Titanium Oxide on the Catalytic Activity of Rh/TiO2 in Steam Reforming of Propane at Low Temperature.

Science.gov (United States)

Yu, Lin; Sato, Katsutoshi; Toriyama, Takaaki; Yamamoto, Tomokazu; Matsumura, Syo; Nagaoka, Katsutoshi

2018-05-01

Solid oxide fuel cells (SOFCs) using liquefied petroleum gas(LPG) reduce CO2 emissions due to their high energy-conversion efficiency. Although SOFCs can convert LPG directly, coking occurs easily by decomposition of hydrocarbons, including C-C bonds on the electrode of fuel cell stacks. It is therefore necessary to develop an active steam pre-reforming catalyst that eliminates the hydrocarbons at low temperature, where waste heat of SOFCs is used. Here we show that the crystal structure of the TiO2 that anchors Rh particles is crucial for catalytic activity of Rh/TiO2 catalysts for propane pre-reforming. Our experimental results revealed that strong metal support interaction (SMSI) induced during H2 pre-reduction were optimized over Rh/TiO2 with a rutile structure; this catalyst catalyzed the reaction much more effectively than conventional Rh/γ-Al2O3. In contrast, the SMSI was too strong for Rh/TiO2 with an anatase structure, and the surface of the Rh particles was therefore covered mostly with partially reduced TiO2. The result was very low activity. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Palladium-Catalyzed Enantioselective C-H Olefination of Diaryl Sulfoxides through Parallel Kinetic Resolution and Desymmetrization.

Science.gov (United States)

Zhu, Yu-Chao; Li, Yan; Zhang, Bo-Chao; Zhang, Feng-Xu; Yang, Yi-Nuo; Wang, Xi-Sheng

2018-03-07

The first example of Pd II -catalyzed enantioselective C-H olefination with non-chiral or racemic sulfoxides as directing groups was developed. A variety of chiral diaryl sulfoxides were synthesized with high enantioselectivity (up to 99 %) through both desymmetrization and parallel kinetic resolution (PKR). This is the first report of Pd II -catalyzed enantioselective C(sp 2 )-H functionalization through PKR, and it represents a novel strategy to construct sulfur chiral centers. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mechanistic Study of the Oxidative Coupling of Styrene with 2-Phenylpyridine Derivatives Catalyzed by Cationic Rhodium( III) via C–H Activation

Science.gov (United States)

Brasse, Mikaël; Cámpora, Juan; Ellman, Jonathan A.; Bergman, Robert G.

2013-01-01

The Rh(III) catalyzed oxidative coupling of alkenes with arenes provides a greener alternative to the classical Heck reaction for the synthesis of arene-functionalized alkenes. The present mechanistic study gives insights for the rational development of this key transformation. The catalyst resting states and the rate law of the reaction have been identified. The reaction rate is solely dependent on catalyst and alkene concentrations and the rate determining step is the migratory insertion of alkene into a Rh–C(aryl) bond. PMID:23590843

The Effect of Surface Site Ensembles on the Activity and Selectivity of Ethanol Electrooxidation by Octahedral PtNiRh Nanoparticles.

Science.gov (United States)

Erini, Nina; Beermann, Vera; Gocyla, Martin; Gliech, Manuel; Heggen, Marc; Dunin-Borkowski, Rafal E; Strasser, Peter

2017-06-01

Direct ethanol fuel cells are attractive power sources based on a biorenewable, high energy-density fuel. Their efficiency is limited by the lack of active anode materials which catalyze the breaking of the C-C bond coupled to the 12-electron oxidation to CO 2 . We report shape-controlled PtNiRh octahedral ethanol oxidation electrocatalysts with excellent activity and previously unachieved low onset potentials as low as 0.1 V vs. RHE, while being highly selective to complete oxidation to CO 2 . Our comprehensive characterization and in situ electrochemical ATR studies suggest that the formation of a ternary surface site ensemble around the octahedral Pt 3 Ni 1 Rh x nanoparticles plays a crucial mechanistic role for this behavior. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Energy Technology Data Exchange (ETDEWEB)

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.

Rhodium-catalyzed C-H alkynylation of arenes at room temperature.

Science.gov (United States)

Feng, Chao; Loh, Teck-Peng

2014-03-03

The rhodium(III)-catalyzed ortho C-H alkynylation of non-electronically activated arenes is disclosed. This process features a straightforward and highly effective protocol for the synthesis of functionalized alkynes and represents the first example of merging a hypervalent iodine reagent with rhodium(III) catalysis. Notably, this reaction proceeds at room temperature, tolerates a variety of functional groups, and more importantly, exhibits high selectivity for monoalkynylation. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Science.gov (United States)

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

Cobalt-catalyzed C-H olefination of aromatics with unactivated alkenes.

Science.gov (United States)

Manoharan, Ramasamy; Sivakumar, Ganesan; Jeganmohan, Masilamani

2016-08-18

A cobalt-catalyzed C-H olefination of aromatic and heteroaromatic amides with unactivated alkenes, allyl acetates and allyl alcohols is described. This method offers an efficient route for the synthesis of vinyl and allyl benzamides in a highly stereoselective manner. It is observed that the ortho substituent on the benzamide moiety is crucial for the observation of allylated products in unactivated alkenes.

Synthesis of binuclear rhodacarboranes from dianions 1,4- and 1,3-C6H4(CH2-9-C2H2B9H9-7,8-nido)22- and (Ph3P)3RhCl

International Nuclear Information System (INIS)

Zakharkin, L.I.; Zhigareva, G.G.

1996-01-01

Dianions 1,4 and 1,3-C 6 H 4 (CH 2 -9-C 2 H 2 B 9 H 9 -7,8-nido) 2 2- obtained from nido 7,8-dicarbollide-ion and 1,4-bis(bromomethyl) and 1,3-bis(bromomethyl)benzenes react with (Ph 3 P) 3 RhCl to give binuclear rhodacarboranes, 1,4- and 1,3-[3,3-(Ph 3 P) 2 -3-H-3,1,2-RhC 2 B 9 H 10 -4-CH 2 ] 2 C 6 H 6 with chemical reaction yield 85% and 87% respectively. 7 refs., 1 fig., 1 tab

A new face of phenalenyl-based radicals in the transition metal-free C-H arylation of heteroarenes at room temperature: trapping the radical initiator via C-C σ-bond formation.

Science.gov (United States)

Ahmed, Jasimuddin; P, Sreejyothi; Vijaykumar, Gonela; Jose, Anex; Raj, Manthan; Mandal, Swadhin K

2017-11-01

The radical-mediated transition metal-free approach for the direct C-H bond functionalization of arenes is considered as a cost effective alternative to transition metal-based catalysis. An organic ligand-based radical plays a key role by generating an aryl radical which undergoes a subsequent functionalization process. The design principle of the present study takes advantage of a relatively stable odd alternant hydrocarbon-based phenalenyl (PLY) radical. In this study, the first transition metal-free catalyzed direct C-H arylation of a variety of heteroarenes such as azoles, furan, thiophene and pyridine at room temperature has been reported using a phenalenyl-based radical without employing any photoactivation step. This protocol has been successfully applied to the gram scale synthesis of core moieties of bioactive molecules. The phenalenyl-based radical initiator has been characterized crystallographically by trapping it via the formation of a C-C σ-bond between the phenalenyl radical and solvent-based radical species.

Thermal Methane Conversion to Syngas Mediated by Rh1-Doped Aluminum Oxide Cluster Cations RhAl3O4.

Science.gov (United States)

Li, Ya-Ke; Yuan, Zhen; Zhao, Yan-Xia; Zhao, Chongyang; Liu, Qing-Yu; Chen, Hui; He, Sheng-Gui

2016-10-05

Laser ablation generated RhAl 3 O 4 + heteronuclear metal oxide cluster cations have been mass-selected using a quadrupole mass filter and reacted with CH 4 or CD 4 in a linear ion trap reactor under thermal collision conditions. The reactions have been characterized by state-of-the-art mass spectrometry and quantum chemistry calculations. The RhAl 3 O 4 + cluster can activate four C-H bonds of a methane molecule and convert methane to syngas, an important intermediate product in methane conversion to value-added chemicals. The Rh atom is the active site for activation of the C-H bonds of methane. The high electron-withdrawing capability of Rh atom is the driving force to promote the conversion of methane to syngas. The polarity of Rh oxidation state is changed from positive to negative after the reaction. This study has provided the first example of methane conversion to syngas by heteronuclear metal oxide clusters under thermal collision conditions. Furthermore, the molecular level origin has been revealed for the condensed-phase experimental observation that trace amounts of Rh can promote the participation of lattice oxygen of chemically very inert support (Al 2 O 3 ) to oxidize methane to carbon monoxide.

Ternary electrocatalysts for oxidizing ethanol to carbon dioxide: making ir capable of splitting C-C bond.

Science.gov (United States)

Li, Meng; Cullen, David A; Sasaki, Kotaro; Marinkovic, Nebojsa S; More, Karren; Adzic, Radoslav R

2013-01-09

Splitting the C-C bond is the main obstacle to electrooxidation of ethanol (EOR) to CO(2). We recently demonstrated that the ternary PtRhSnO(2) electrocatalyst can accomplish that reaction at room temperature with Rh having a unique capability to split the C-C bond. In this article, we report the finding that Ir can be induced to split the C-C bond as a component of the ternary catalyst. We characterized and compared the properties of several carbon-supported nanoparticle (NP) electrocatalysts comprising a SnO(2) NP core decorated with multimetallic nanoislands (MM' = PtIr, PtRh, IrRh, PtIrRh) prepared using a seeded growth approach. An array of characterization techniques were employed to establish the composition and architecture of the synthesized MM'/SnO(2) NPs, while electrochemical and in situ infrared reflection absorption spectroscopy studies elucidated trends in activity and the nature of the reaction intermediates and products. Both EOR reactivity and selectivity toward CO(2) formation of several of these MM'/SnO(2)/C electrocatalysts are significantly higher compared to conventional Pt/C and Pt/SnO(2)/C catalysts. We demonstrate that the PtIr/SnO(2)/C catalyst with high Ir content shows outstanding catalytic properties with the most negative EOR onset potential and reasonably good selectivity toward ethanol complete oxidation to CO(2).

Pd(II)-Catalyzed Olefination of sp3 C–H Bonds

Science.gov (United States)

Wasa, Masayuki; Engle, Keary M.; Yu, Jin-Quan

2010-01-01

The first Pd(II)-catalyzed sp3 C–H olefination reaction has been developed using N-arylamide directing groups. Following olefination, the resulting intermediates were found to undergo rapid 1,4-addition to give the corresponding γ lactams. Notably, this method was effective with substrates containing α-hydrogen atoms and could be applied to effect methylene C–H olefination of cyclopropane substrates. PMID:20187642

Recent Advances in Ring-Opening Functionalization of Cycloalkanols by C-C σ-Bond Cleavage.

Science.gov (United States)

Wu, Xinxin; Zhu, Chen

2018-06-01

Cycloalkanols prove to be privileged precursors for the synthesis of distally substituted alkyl ketones and polycyclic aromatic hydrocarbons (PAHs) by virtue of cleavage of their cyclic C-C bonds. Direct functionalization of cyclobutanols to build up other chemical bonds (e. g., C-F, C-Cl, C-Br, C-N, C-S, C-Se, C-C, etc.) has been achieved by using the ring-opening strategy. Mechanistically, the C-C cleavage of cyclobutanols can be involved in two pathways: (a) transition-metal catalyzed β-carbon elimination; (b) radical-mediated 'radical clock'-type ring opening. The recent advances of our group for the ring-opening functionalization of tertiary cycloalkanols are described in this account. © 2018 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Reactive carbon-chain molecules: synthesis of 1-diazo-2,4-pentadiyne and spectroscopic characterization of triplet pentadiynylidene (H-C[triple bond]C-:C-C[triple bond]C-H).

Science.gov (United States)

Bowling, Nathan P; Halter, Robert J; Hodges, Jonathan A; Seburg, Randal A; Thomas, Phillip S; Simmons, Christopher S; Stanton, John F; McMahon, Robert J

2006-03-15

1-Diazo-2,4-pentadiyne (6a), along with both monodeuterio isotopomers 6b and 6c, has been synthesized via a route that proceeds through diacetylene, 2,4-pentadiynal, and 2,4-pentadiynal tosylhydrazone. Photolysis of diazo compounds 6a-c (lambda > 444 nm; Ar or N2, 10 K) generates triplet carbenes HC5H (1) and HC5D (1-d), which have been characterized by IR, EPR, and UV/vis spectroscopy. Although many resonance structures contribute to the resonance hybrid for this highly unsaturated carbon-chain molecule, experiment and theory reveal that the structure is best depicted in terms of the dominant resonance contributor of penta-1,4-diyn-3-ylidene (diethynylcarbene, H-C[triple bond]C-:C-C[triple bond]C-H). Theory predicts an axially symmetric (D(infinity h)) structure and a triplet electronic ground state for 1 (CCSD(T)/ANO). Experimental IR frequencies and isotope shifts are in good agreement with computed values. The triplet EPR spectrum of 1 (absolute value(D/hc) = 0.6157 cm(-1), absolute value(E/hc) = 0.0006 cm(-1)) is consistent with an axially symmetric structure, and the Curie law behavior confirms that the triplet state is the ground state. The electronic absorption spectrum of 1 exhibits a weak transition near 400 nm with extensive vibronic coupling. Chemical trapping of triplet HC5H (1) in an O2-doped matrix affords the carbonyl oxide 16 derived exclusively from attack at the central carbon.

New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles

Energy Technology Data Exchange (ETDEWEB)

Huang, Qinhua [Iowa State Univ., Ames, IA (United States)

2004-12-19

The tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridinecarbaldehydes have been cyclized under very mild reaction conditions in the presence of I₂, ICl, PhSeCl, PhSCl and p-O₂NC₆H₄SCl to give the corresponding halogen-, selenium- and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively. Monosubstituted isoquinolines and naphthyridines have been synthesized by the metal-catalyzed ring closure of these same iminoalkynes. This methodology accommodates a variety of iminoalkynes and affords the anticipated heterocycles in moderate to excellent yields. The Pd(II)-catalyzed cyclization of 2-(1-alkynyl)arylaldimines in the presence of various alkenes provides an efficient way to synthesize a variety of 4-(1-alkenyl)-3-arylisoquinolines in moderate to excellent yields. The introduction of an ortho-methoxy group on the arylaldimine promotes the Pd-catalyzed cyclization and stabilizes the resulting Pd(II) intermediate, improving the yields of the isoquinoline products. Highly substituted naphthalenes have been synthesized by the palladium-catalyzed annulation of a variety of internal alkynes, in which two new carbon-carbon bonds are formed in a single step under relatively mild reaction conditions. This method has also been used to synthesize carbazoles, although a higher reaction temperature is necessary. The process involves arylpalladation of the alkyne, followed by intramolecular Heck olefination and double bond isomerization. This method accommodates a variety of functional groups and affords the anticipated highly substituted naphthalenes and carbazoles in good to excellent yields. Novel palladium migratiodarylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement

Mechanistic Insights on C-O and C-C Bond Activation and Hydrogen Insertion during Acetic Acid Hydrogenation Catalyzed by Ruthenium Clusters in Aqueous Medium

Energy Technology Data Exchange (ETDEWEB)

Shangguan, Junnan; Olarte, Mariefel V.; Chin, Ya-Huei [Cathy

2016-06-07

Catalytic pathways for acetic acid (CH3COOH) and hydrogen (H2) reactions on dispersed Ru clusters in the aqueous medium and the associated kinetic requirements for C-O and C-C bond cleavages and hydrogen insertion are established from rate and isotopic assessments. CH3COOH reacts with H2 in steps that either retain its carbon backbone and lead to ethanol, ethyl acetate, and ethane (47-95 %, 1-23 %, and 2-17 % carbon selectivities, respectively) or break its C-C bond and form methane (1-43 % carbon selectivities) at moderate temperatures (413-523 K) and H2 pressures (10-60 bar, 298 K). Initial CH3COOH activation is the kinetically relevant step, during which CH3C(O)-OH bond cleaves on a metal site pair at Ru cluster surfaces nearly saturated with adsorbed hydroxyl (OH*) and acetate (CH3COO*) intermediates, forming an adsorbed acetyl (CH3CO*) and hydroxyl (OH*) species. Acetic acid turnover rates increase proportionally with both H2 (10-60 bar) and CH3COOH concentrations at low CH3COOH concentrations (<0.83 M), but decrease from first to zero order as the CH3COOH concentration and the CH3COO* coverages increase and the vacant Ru sites concomitantly decrease. Beyond the initial CH3C(O)-OH bond activation, sequential H-insertions on the surface acetyl species (CH3CO*) lead to C2 products and their derivative (ethanol, ethane, and ethyl acetate) and the competitive C-C bond cleavage of CH3CO* causes the eventual methane formation. The instantaneous carbon selectivities towards C2 species (ethanol, ethane, and ethyl acetate) increase linearly with the concentration of proton-type Hδ+ (derived from carboxylic acid dissociation) and chemisorbed H*. The selectivities towards C2 products decrease with increasing temperature, because of higher observed barriers for C-C bond cleavage than H-insertion. This study offers an interpretation of mechanism and energetics and provides kinetic evidence of carboxylic acid assisted proton-type hydrogen (Hδ+) shuffling during H

Pyrroloindolone synthesis via a Cp*Co(III)-catalyzed redox-neutral directed C-H alkenylation/annulation sequence.

Science.gov (United States)

Ikemoto, Hideya; Yoshino, Tatsuhiko; Sakata, Ken; Matsunaga, Shigeki; Kanai, Motomu

2014-04-09

A unique synthetic utility of a Cp*Co(III) catalyst in comparison with related Cp*Rh(III) catalysts is described. A C2-selective indole alkenylation/annulation sequence proceeded smoothly with catalytic amount of a [Cp*Co(III)(C6H6)](PF6)2 complex and KOAc. Intramolecular addition of an alkenyl-Cp*Co species to a carbamoyl moiety gave pyrroloindolones in 58-89% yield in one pot. Clear difference was observed between the catalytic activity of the Cp*Co(III) complex and those of Cp*Rh(III) complexes, highlighting the unique nucleophilic activity of the organocobalt species. The Cp*Co(III) catalysis was also suitable for simple alkenylation process of N-carbamoyl indoles, and broad range of alkynes, including terminal alkynes, were applicable to give C2-alkenylated indoles in 50-99% yield. Mechanistic studies on C-H activation step under Cp*Co(III) catalysis with the aid of an acetate unit as well as evaluation of the difference between organo-Co(III) species and organo-Rh(III) species are also described.

Ruthenium(II)-catalyzed synthesis of pyrrole- and indole-fused isocoumarins by C-H bond activation in DMF and water

Digital Repository Service at National Institute of Oceanography (India)

Singh, K.S.; Sawant, S.G.; Dixneuf, P.H.

stream_size 26907 stream_content_type text/plain stream_name ChemCatChem_8_1046a.pdf.txt stream_source_info ChemCatChem_8_1046a.pdf.txt Content-Encoding UTF-8 Content-Type text/plain; charset=UTF-8 Author version...: ChemCatChem, vol.8(6); 2016; 1046-1050 Ruthenium(II) catalysed synthesis of pyrrole and indole fused isocoumarins via C-H bond activation in DMF and water† Keisham S. Singh*,a Sneha G. Sawanta, Pierre H. Dixneuf*,b Abstract: Pyrrole and indole...

Can laccases catalyze bond cleavage in lignin?

DEFF Research Database (Denmark)

Munk, Line; Sitarz, Anna Katarzyna; Kalyani, Dayanand

2015-01-01

illustrations of the putative laccase catalyzed reactions, including the possible reactions of the reactive radical intermediates taking place after the initial oxidation of the phenol-hydroxyl groups, we show that i) Laccase activity is able to catalyze bond cleavage in low molecular weight phenolic lignin......-substituted phenols, benzenethiols, polyphenols, and polyamines, which may be oxidized. In addition, the currently available analytical methods that can be used to detect enzyme catalyzed changes in lignin are summarized, and an improved nomenclature for unequivocal interpretation of the action of laccases on lignin...

A comparative DFT study on the dehydrogenation of methanol on Rh(100) and Rh(110)

Science.gov (United States)

Zhang, Minhua; Wu, Xingyu; Yu, Yingzhe

2018-04-01

Numerous density functional theory calculations have been performed to investigate the complete mechanisms of methanol dehydrogenation on Rh(100) and Rh(110) surfaces. The adsorption properties of relevant species were discussed in details. In addition, a comprehensive reaction network including four reaction pathways was built and analyzed. It is found that the initial Osbnd H bond scission of CH3OH seems to be more favorable than Csbnd H bond cleavage on both Rh(100) and Rh(110) surfaces from the perspective of activation barriers. It is also concluded that path1 (CH3OH → CH3O → CH2O → CHO → CO) is the predominant pathway on both Rh(100) and Rh (110) surfaces. On the whole, in most of the dehydrogenation reactions investigated, the energy barriers on Rh(100) are lower than those on Rh (110). Remarkable differences in the activity and predominant reaction pathway on Rh(100), Rh(110) and Rh(111) indicate that the dehydrogenation of methanol might be structure-sensitive.

A computational mechanistic study of Pd(ii)-catalyzed γ-C(sp3)-H olefination/cyclization of amines: the roles of bicarbonate and ligand effect.

Science.gov (United States)

Liu, Jian-Biao; Tian, Ying-Ying; Zhang, Xin; Wang, Lu-Lin; Chen, De-Zhan

2018-04-03

The detailed mechanism of palladium-catalyzed γ-C(sp3)-H olefination/cyclization of triflyl-protected amines was investigated by density functional theory (DFT) calculations. The olefinated intermediate was initially formed in the first catalytic cycle involving ligand exchange, bicarbonate-assisted C(sp3)-H bond cleavage, alkene insertion and 'reductive β-hydride elimination'. The following syn-addition and reductive elimination furnish the aza-Wacker product. The first step of reductive elimination is the rate-determining step. The mechanism unveils the important roles of bicarbonate: aiding the C-H activation and abstracting the β-proton in the second step of reductive elimination. The parallel bridging mode in the metal-olefin intermediate facilitates the syn-addition, explaining the experimentally observed stereoselectivity. The effect of the monodentate pyridine-based ligands is also discussed.

Ligand-enabled ortho-C-H olefination of phenylacetic amides with unactivated alkenes.

Science.gov (United States)

Lu, Ming-Zhu; Chen, Xing-Rong; Xu, Hui; Dai, Hui-Xiong; Yu, Jin-Quan

2018-02-07

Although chelation-assisted C-H olefination has been intensely investigated, Pd(ii)-catalyzed C-H olefination reactions are largely restricted to acrylates and styrenes. Here we report a quinoline-derived ligand that enables the Pd(ii)-catalyzed olefination of the C(sp 2 )-H bond with simple aliphatic alkenes using a weakly coordinating monodentate amide auxiliary. Oxygen is used as the terminal oxidant with catalytic copper as the co-oxidant. A variety of functional groups in the aliphatic alkenes are tolerated. Upon hydrogenation, the ortho -alkylated product can be accessed. The utility of this reaction is also demonstrated by the late-stage diversification of drug molecules.

Pd-Catalyzed C-H activation/oxidative cyclization of acetanilide with norbornene: concise access to functionalized indolines.

Science.gov (United States)

Gao, Yang; Huang, Yubing; Wu, Wanqing; Huang, Kefan; Jiang, Huanfeng

2014-08-07

An efficient Pd-catalyzed oxidative cyclization reaction for the synthesis of functionalized indolines by direct C-H activation of acetanilide has been developed. The norbornylpalladium species formed via direct ortho C-H activation of acetanilides is supposed to be a key intermediate in this transformation.

C2-Selective Branched Alkylation of Benzimidazoles by Rhodium(I)-Catalyzed C-H Activation.

Science.gov (United States)

Tran, Gaël; Confair, Danielle; Hesp, Kevin D; Mascitti, Vincent; Ellman, Jonathan A

2017-09-01

Herein, we report a Rh(I)/bisphosphine/K 3 PO 4 catalytic system allowing for the first time the selective branched C-H alkylation of benzimidazoles with Michael acceptors. Branched alkylation with N,N-dimethyl acrylamide was successfully applied to the alkylation of a broad range of benzimidazoles incorporating a variety of N-substituents and with both electron-rich and -poor functionality displayed at different sites of the arene. Moreover, the introduction of a quaternary carbon was achieved by alkylation with ethyl methacrylate. The method was also shown to be applicable to the C2-selective branched alkylation of azabenzimidazoles.

How easy is CO2 fixation by M-C bond containing complexes (M = Cu, Ni, Co, Rh, Ir)?

KAUST Repository

Nolan, Steve; Cavallo, Luigi; Poater, Albert; Vummaleti, Sai V. C.; Talarico, Giovanni

2015-01-01

A comparison between different M–C bonds (M = Cu(I), Ni(II), Co(I), Rh(I) and Ir(I)) has been reported by using density functional theory (DFT) calculations to explore the role of the metal in the fixation or incorporation of CO2 into such complexes. The systems investigated are various metal based congeners of the Ir-complex 8 [(cod)(IiPr)Ir-CCPh], with a ligand scaffold based on cod and IiPr ligands (cod = 1,5-cyclooctadiene; IiPr = 1,3-bis(isopropyl)imidazol-2-ylidene). The results of this study show that the calculated CO2 insertion barriers follow the trend: Cu(I) (20.8 kcal mol−1) < Rh(I) (30.0 kcal mol−1) < Co(I) (31.3 kcal mol−1) < Ir(I) (37.5 kcal mol−1) < Ni(II) (45.4 kcal mol−1), indicating that the Cu(I) based analogue is the best CO2 fixer, while Ni(II) is the worst in the studied series.

How easy is CO2 fixation by M-C bond containing complexes (M = Cu, Ni, Co, Rh, Ir)?

KAUST Repository

Nolan, Steve

2015-11-27

A comparison between different M–C bonds (M = Cu(I), Ni(II), Co(I), Rh(I) and Ir(I)) has been reported by using density functional theory (DFT) calculations to explore the role of the metal in the fixation or incorporation of CO2 into such complexes. The systems investigated are various metal based congeners of the Ir-complex 8 [(cod)(IiPr)Ir-CCPh], with a ligand scaffold based on cod and IiPr ligands (cod = 1,5-cyclooctadiene; IiPr = 1,3-bis(isopropyl)imidazol-2-ylidene). The results of this study show that the calculated CO2 insertion barriers follow the trend: Cu(I) (20.8 kcal mol−1) < Rh(I) (30.0 kcal mol−1) < Co(I) (31.3 kcal mol−1) < Ir(I) (37.5 kcal mol−1) < Ni(II) (45.4 kcal mol−1), indicating that the Cu(I) based analogue is the best CO2 fixer, while Ni(II) is the worst in the studied series.

Mechanism of Intramolecular Rhodium- and Palladium-Catalyzed Alkene Alkoxyfunctionalizations

KAUST Repository

Vummaleti, Sai V. C.

2015-11-13

Density functional theory calculations have been used to investigate the reaction mechanism for the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-bis(diphenylphosphino)propane) and [Pd]/BPh3 dual catalytic system assisted intramolecular alkoxycyanation ([Pd] = Pd-Xantphos) using acylated and cyanated 2-allylphenol derivatives as substrates, respectively. Our results substantially confirm the proposed mechanism for both [Rh]- and [Pd]/ BPh3-mediated alkoxyfunctionalizations, offering a detailed geometrical and energetical understanding of all the elementary steps. Furthermore, for the [Rh]-mediated alkoxyacylation, our observations support the hypothesis that the quinoline group of the substrate is crucial to stabilize the acyl metal complex and prevent further decarbonylation. For [Pd]/BPh3-catalyzed alkoxycyanation, our findings clarify how the Lewis acid BPh3 cocatalyst accelerates the only slow step of the reaction, corresponding to the oxidative addition of the cyanate O-CN bond to the Pd center. © 2015 American Chemical Society.

Mechanism of Intramolecular Rhodium- and Palladium-Catalyzed Alkene Alkoxyfunctionalizations

KAUST Repository

Vummaleti, Sai V. C.; Alghamdi, Miasser; Poater, Albert; Falivene, Laura; Scaranto, Jessica; Beetstra, Dirk J.; Morton, Jason G.; Cavallo, Luigi

2015-01-01

Density functional theory calculations have been used to investigate the reaction mechanism for the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-bis(diphenylphosphino)propane) and [Pd]/BPh3 dual catalytic system assisted intramolecular alkoxycyanation ([Pd] = Pd-Xantphos) using acylated and cyanated 2-allylphenol derivatives as substrates, respectively. Our results substantially confirm the proposed mechanism for both [Rh]- and [Pd]/ BPh3-mediated alkoxyfunctionalizations, offering a detailed geometrical and energetical understanding of all the elementary steps. Furthermore, for the [Rh]-mediated alkoxyacylation, our observations support the hypothesis that the quinoline group of the substrate is crucial to stabilize the acyl metal complex and prevent further decarbonylation. For [Pd]/BPh3-catalyzed alkoxycyanation, our findings clarify how the Lewis acid BPh3 cocatalyst accelerates the only slow step of the reaction, corresponding to the oxidative addition of the cyanate O-CN bond to the Pd center. © 2015 American Chemical Society.

Studies on the selectivity of the reaction of (CO){sub 5}W=C(aryl)H with enynes: transfer of the carbene ligand to the C=C Bond versus insertion of the C triple bond C into the W=C Bond

Energy Technology Data Exchange (ETDEWEB)

Fischer, H.; Volkland, H.P.; Stumpf, R.

1996-10-01

The strongly electrophilic monophenylcarbene complex [(CO){sub 5}W=C(Ph)H] (2a) reacts with the enynes H-C triple bond C-R(R=-C(Me)=CH{sub 2})(3), -C{sub 6}H{sub 4}-CH=CH{sub 2}-p (5) and subsequently with PMe{sub 3} to form the C{sub a}lpha-PMe{sub 3} adducts of the vinylidene complexes [(CO){sub 5}W-{l_brace}C(PMe{sub 3})=CH-C{sub 3}H{sub 3}(Me)Ph{r_brace}] (4) and [(CO){sub 5}W {l_brace}C(PMe{sub 3})=CH-C{sub 6}H{sub 4}-C{sub 3}H{sub 4}Ph{r_brace}] (6). The reaction very likely proceeds by transfer of the carbene ligand to the C=C bond of the enyne to form a cyclopropyl-substituted alkyne complex which is in equilibrium with its vinylidene isomer.

Rhodium Catalyzed Annulation of N-Benzoylsulfonamide with Isocyanide via C-H Activation

Science.gov (United States)

Zhu, Chen; Xie, Weiqing; Falck, John R.

2012-01-01

Isocyanide insertion: the first rhodium-catalyzed annulation of N-benzoylsulfonamide incorporating with isocyanide via C-H activation is described. The transformation is broadly compatible with N-benzoylsulfonamides bearing various electron-properties as well as isocyanides. From practical point of view, this methodology provides the most straightforward approach to a series of 3-(imino)isoindolinones. PMID:21972033

Iodine-catalyzed sp³ C-H bond activation by selenium dioxide: synthesis of diindolylmethanes and di(3-indolyl)selanides.

Science.gov (United States)

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.

Synthesis of Bioactive 2-(Arylaminothiazolo[5,4-f]-quinazolin-9-ones via the Hügershoff Reaction or Cu- Catalyzed Intramolecular C-S Bond Formation

Directory of Open Access Journals (Sweden)

Damien Hédou

2016-06-01

Full Text Available A library of thirty eight novel thiazolo[5,4-f]quinazolin-9(8H-one derivatives (series 8, 10, 14 and 17 was prepared via the Hügershoff reaction and a Cu catalyzed intramolecular C-S bond formation, helped by microwave-assisted technology when required. The efficient multistep synthesis of the key 6-amino-3-cyclopropylquinazolin-4(3H-one (3 has been reinvestigated and performed on a multigram scale from the starting 5-nitroanthranilic acid. The inhibitory potency of the final products was evaluated against five kinases involved in Alzheimer’s disease and showed that some molecules of the 17 series described in this paper are particularly promising for the development of novel multi-target inhibitors of kinases.

Unified mechanism of alkali and alkaline earth catalyzed gasification reactions of carbon by CO2 and H2O

Science.gov (United States)

Chen, S.G.; Yang, R.T.

1997-01-01

From molecular orbital calculations, a unified mechanism is proposed for the gasification reactions of graphite by CO2 and H2O, both uncatalyzed and catalyzed by alkali and alkaline earth catalysts. In this mechanism, there are two types of oxygen intermediates that are bonded to the active edge carbon atoms: an in-plane semiquinone type, Cf(O), and an off-plane oxygen bonded to two saturated carbon atoms that are adjacent to the semiquinone species, C(O)Cf(O). The rate-limiting step is the decomposition of these intermediates by breaking the C-C bonds that are connected to Cf(O). A new rate equation is derived for the uncatalyzed reactions, and that for the catalyzed reactions is readily available from the proposed mechanism. The proposed mechanism can account for several unresolved experimental observations: TPD and TK (transient kinetics) desorption results of the catalyzed systems, the similar activation energies for the uncatalyzed and catalyzed reactions, and the relative activities of the alkali and alkaline earth elements. The net charge of the edge carbon active site is substantially changed by gaining electron density from the alkali or alkaline earth element (by forming C-O-M, where M stands for metal). The relative catalytic activities of these elements can be correlated with their abilities of donating electrons and changing the net charge of the edge carbon atom. As shown previously (Chen, S. G.; Yang, R. T. J. Catal. 1993, 141, 102), only clusters of the alkali compounds are active. This derives from the ability of the clusters to dissociate CO2 and H2O to form O atoms and the mobility of the dissociated O atoms facilitated by the clusters.

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

Science.gov (United States)

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

Nickel-Catalyzed C-S Bond Formation via Decarbonylative Thioetherification of Esters, Amides and Intramolecular Recombination Fragment Coupling of Thioesters

KAUST Repository

Lee, Shao-Chi

2018-01-15

A nickel catalyzed cross-coupling protocol for the straightforward C-S bond formation has been developed. Various mercaptans and a wide range of ester and amide substrates bearing various substituents were tolerated in this process which afforded products in good to excellent yields. Furthermore, an intramolecular protocol for the synthesis of thioethers starting from thioesters has been developed. The utility of this protocol has been demonstrated in the synthesis of benzothiophene on the bench top.

Nickel-Catalyzed C-S Bond Formation via Decarbonylative Thioetherification of Esters, Amides and Intramolecular Recombination Fragment Coupling of Thioesters

KAUST Repository

Lee, Shao-Chi; Liao, Hsuan-Hung; Chatupheeraphat, Adisak; Rueping, Magnus

2018-01-01

A nickel catalyzed cross-coupling protocol for the straightforward C-S bond formation has been developed. Various mercaptans and a wide range of ester and amide substrates bearing various substituents were tolerated in this process which afforded products in good to excellent yields. Furthermore, an intramolecular protocol for the synthesis of thioethers starting from thioesters has been developed. The utility of this protocol has been demonstrated in the synthesis of benzothiophene on the bench top.

Phenylacetylene and H bond

Indian Academy of Sciences (India)

... all resembling H bonds. Non-linear H bonds due to secondary interactions. C-H stretching frequency shows blue shift. Heavy atom distances are longer than the sum of van der Waals radii. Formed a task group through IUPAC to come up with a modern definition of H bond. 15 international experts including Desiraju.

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

International Nuclear Information System (INIS)

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

Catalyst-Dependent Chemoselective Formal Insertion of Diazo Compounds into C-C or C-H Bonds of 1,3-Dicarbonyl Compounds.

Science.gov (United States)

Liu, Zhaohong; Sivaguru, Paramasivam; Zanoni, Giuseppe; Anderson, Edward A; Bi, Xihe

2018-05-08

A catalyst-dependent chemoselective one-carbon insertion of diazo compounds into the C-C or C-H bonds of 1,3-dicarbonyl species is reported. In the presence of silver(I) triflate, diazo insertion into the C(=O)-C bond of the 1,3-dicarbonyl substrate leads to a 1,4-dicarbonyl product containing an all-carbon α-quaternary center. This reaction constitutes the first example of an insertion of diazo-derived carbenoids into acyclic C-C bonds. When instead scandium(III) triflate was applied as the catalyst, the reaction pathway switched to formal C-H insertion, affording 2-alkylated 1,3-dicarbonyl products. Different reaction pathways are proposed to account for this powerful catalyst-dependent chemoselectivity. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cat-CVD-prepared oxygen-rich μc-Si:H for wide-bandgap material

International Nuclear Information System (INIS)

Matsumoto, Yasuhiro; Ortega, Mauricio; Peza, Juan-Manuel; Reyes, Mario-Alfredo; Escobosa, Arturo

2005-01-01

Microcrystalline phase-involved oxygen-rich a-Si:H (hydrogenated amorphous silicon) films have been obtained using catalytic chemical vapor deposition (Cat-CVD) process. Pure SiH 4 (silane), H 2 (hydrogen), and O 2 (oxygen) gases were introduced in the chamber by maintaining a pressure of 0.1 Torr. A tungsten catalyzer was fixed at temperatures of 1750 and 1950 deg. C for film deposition on glass and crystalline silicon substrates at 200 deg. C. As revealed from X-ray diffraction spectra, the microcrystalline phase appears for oxygen-rich a-Si:H samples deposited at a catalyzer temperature of 1950 deg. C. However, this microcrystalline phase tends to disappear for further oxygen incorporation. The oxygen content in the deposited films was corroborated by FTIR analysis revealing Si-O-Si bonds and typical Si-H bonding structures. The optical bandgap of the sample increases from 2.0 to 2.7 eV with oxygen gas flow and oxygen incorporation to the deposited films. In the present thin film deposition conditions, no strong tungsten filament degradation was observed after a number of sample preparations

Bioorthogonal Diversification of Peptides through Selective Ruthenium(II)-Catalyzed C-H Activation.

Science.gov (United States)

Schischko, Alexandra; Ren, Hongjun; Kaplaneris, Nikolaos; Ackermann, Lutz

2017-02-01

Methods for the chemoselective modification of amino acids and peptides are powerful techniques in biomolecular chemistry. Among other applications, they enable the total synthesis of artificial peptides. In recent years, significant momentum has been gained by exploiting palladium-catalyzed cross-coupling for peptide modification. Despite major advances, the prefunctionalization elements on the coupling partners translate into undesired byproduct formation and lengthy synthetic operations. In sharp contrast, we herein illustrate the unprecedented use of versatile ruthenium(II)carboxylate catalysis for the step-economical late-stage diversification of α- and β-amino acids, as well as peptides, through chemo-selective C-H arylation under racemization-free reaction conditions. The ligand-accelerated C-H activation strategy proved water-tolerant and set the stage for direct fluorescence labelling as well as various modes of peptide ligation with excellent levels of positional selectivity in a bioorthogonal fashion. The synthetic utility of our approach is further demonstrated by twofold C-H arylations for the complexity-increasing assembly of artificial peptides within a multicatalytic C-H activation manifold. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

From ketones to esters by a Cu-catalyzed highly selective C(CO)-C(alkyl) bond cleavage: aerobic oxidation and oxygenation with air.

Science.gov (United States)

Huang, Xiaoqiang; Li, Xinyao; Zou, Miancheng; Song, Song; Tang, Conghui; Yuan, Yizhi; Jiao, Ning

2014-10-22

The Cu-catalyzed aerobic oxidative esterification of simple ketones via C-C bond cleavage has been developed. Varieties of common ketones, even inactive aryl long-chain alkyl ketones, are selectively converted into esters. The reaction tolerates a wide range of alcohols, including primary and secondary alcohols, chiral alcohols with retention of the configuration, electron-deficient phenols, as well as various natural alcohols. The usage of inexpensive copper catalyst, broad substrate scope, and neutral and open air conditions make this protocol very practical. (18)O labeling experiments reveal that oxygenation occurs during this transformation. Preliminary mechanism studies indicate that two novel pathways are mainly involved in this process.

Cobalt-Catalyzed C(sp(2))-H Borylation: Mechanistic Insights Inspire Catalyst Design.

Science.gov (United States)

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

2016-08-24

A comprehensive study into the mechanism of bis(phosphino)pyridine (PNP) cobalt-catalyzed C-H borylation of 2,6-lutidine using B2Pin2 (Pin = pinacolate) has been conducted. The experimentally observed rate law, deuterium kinetic isotope effects, and identification of the catalyst resting state support turnover limiting C-H activation from a fully characterized cobalt(I) boryl intermediate. Monitoring the catalytic reaction as a function of time revealed that borylation of the 4-position of the pincer in the cobalt catalyst was faster than arene borylation. Cyclic voltammetry established the electron withdrawing influence of 4-BPin, which slows the rate of C-H oxidative addition and hence overall catalytic turnover. This mechanistic insight inspired the next generation of 4-substituted PNP cobalt catalysts with electron donating and sterically blocking methyl and pyrrolidinyl substituents that exhibited increased activity for the C-H borylation of unactivated arenes. The rationally designed catalysts promote effective turnover with stoichiometric quantities of arene substrate and B2Pin2. Kinetic studies on the improved catalyst, 4-(H)2BPin, established a change in turnover limiting step from C-H oxidative addition to C-B reductive elimination. The iridium congener of the optimized cobalt catalyst, 6-(H)2BPin, was prepared and crystallographically characterized and proved inactive for C-H borylation, a result of the high kinetic barrier for reductive elimination from octahedral Ir(III) complexes.

Temperature-dependent transitions between normal and inverse isotope effects pertaining to the interaction of H-H and C-H bonds with transition metal centers.

Science.gov (United States)

Parkin, Gerard

2009-02-17

Deuterium kinetic isotope effects (KIEs) serve as versatile tools to infer details about reaction mechanisms and the nature of transition states, while equilibrium isotope effects (EIEs) associated with the site preferences of hydrogen and deuterium enable researchers to study aspects of molecular structure. Researchers typically interpret primary deuterium isotope effects based on two simple guidelines: (i) the KIE for an elementary reaction is normal (k(H)/k(D) > 1) and (ii) the EIE is dictated by deuterium preferring to be located in the site corresponding to the highest frequency oscillator. In this Account, we evaluate the applicability of these rules to the interactions of H-H and C-H bonds with a transition metal center. Significantly, experimental and computational studies question the predictability of primary EIEs in these systems based on the notion that deuterium prefers to occupy the highest frequency oscillator. In particular, the EIEs for (i) formation of sigma-complexes by coordination of H-H and C-H bonds and (ii) oxidative addition of dihydrogen exhibit unusual temperature dependencies, such that the same system may demonstrate both normal (i.e., K(H)/K(D) > 1) and inverse (i.e., K(H)/K(D) ZPE (where SYM is the symmetry factor, MMI is the mass-moment of inertia term, EXC is the excitation term, and ZPE is the zero-point energy term), and the distinctive temperature profile results from the inverse ZPE (enthalpy) and normal [SYM x MMI x EXC] (entropy) components opposing each other and having different temperature dependencies. At low temperatures, the ZPE component dominates and the EIE is inverse, while at high temperatures, the [SYM x MMI x EXC] component dominates and the EIE is normal. The inverse nature of the ZPE term is a consequence of the rotational and translational degrees of freedom of RH (R = H, CH(3)) becoming low-energy isotopically sensitive vibrations in the product, while the normal nature of the [SYM x MMI x EXC] component

Noble metal catalyzed hydrogen generation from formic acid in nitrite-containing simulated nuclear waste media

International Nuclear Information System (INIS)

King, R.B.; Bhattacharyya, N.K.; Wiemers, K.D.

1994-08-01

Simulants for the Hanford Waste Vitrification Plant (HWVP) feed containing the major non-radioactive components Al, Cd, Fe, Mn, Nd, Ni, Si, Zr, Na, CO 3 2- , NO 3 -, and NO 2 - were used as media to evaluate the stability of formic acid towards hydrogen evolution by the reaction HCO 2 H → H 2 + CO 2 catalyzed by the noble metals Ru, Rh, and/or Pd found in significant quantities in uranium fission products. Small scale experiments using 40-50 mL of feed simulant in closed glass reactors (250-550 mL total volume) at 80-100 degree C were used to study the effect of nitrite and nitrate ion on the catalytic activities of the noble metals for formic acid decomposition. Reactions were monitored using gas chromatography to analyze the CO 2 , H 2 , NO, and N 2 O in the gas phase as a function of time. Rhodium, which was introduced as soluble RhCl 3 ·3H 2 O, was found to be the most active catalyst for hydrogen generation from formic acid above ∼80 degree C in the presence of nitrite ion in accord with earlier observations. The inherent homogeneous nature of the nitrite-promoted Rh-catalyzed formic acid decomposition is suggested by the approximate pseudo first-order dependence of the hydrogen production rate on Rh concentration. Titration of the typical feed simulants containing carbonate and nitrite with formic acid in the presence of rhodium at the reaction temperature (∼90 degree C) indicates that the nitrite-promoted Rh-catalyzed decomposition of formic acid occurs only after formic acid has reacted with all of the carbonate and nitrite present to form CO 2 and NO/N 2 O, respectively. The catalytic activities of Ru and Pd towards hydrogen generation from formic acid are quite different than those of Rh in that they are inhibited rather than promoted by the presence of nitrite ion

C-H and H-H Bond Activation via Ligand Dearomatization/Rearomatization of a PN3P-Rhodium(I) Complex

KAUST Repository

Huang, Kuo-Wei

2015-04-13

A neutral complex PN3P-Rh(I)Cl (2) was prepared from a reaction of the PN3P pincer ligand (1) with [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene). Upon treatment with a suitable base, H–H and Csp2–H activation reactions can be achieved through the deprotonation/reprotonation of one of the N–H arms and dearomatization/rearomatization of the central pyridine ring with the oxidation state of Rh remaining I.

Solution and solid-phase halogen and C-H hydrogen bonding to perrhenate.

Science.gov (United States)

Massena, Casey J; Riel, Asia Marie S; Neuhaus, George F; Decato, Daniel A; Berryman, Orion B

2015-01-28

(1)H NMR spectroscopic and X-ray crystallographic investigations of a 1,3-bis(4-ethynyl-3-iodopyridinium)benzene scaffold with perrhenate reveal strong halogen bonding in solution, and bidentate association in the solid state. A nearly isostructural host molecule demonstrates significant C-H hydrogen bonding to perrhenate in the same phases.

Stereoselective Synthesis of Functionalized 1,3-Disubstituted Isoindolines via Rh(III)-Catalyzed Tandem Oxidative Olefination-Cyclization of 4-Aryl-cyclic Sulfamidate-5-Carboxylates.

Science.gov (United States)

Achary, Raghavendra; Jung, In-A; Son, Se-Mi; Lee, Hyeon-Kyu

2017-07-21

A new method for the direct, stereoselective synthesis of highly functionalized 1,3-disubstituted isoindolines 6 from enantiomerically enriched cyclic 4-aryl-sulfamidate-5-carboxylates (5) is described. The process involves sulfamidate directed, Rh(III)-catalyzed tandem ortho C-H olefination of the 4-aryl-sulfamidate-5-carboxylates and subsequent cyclization by aza-Michael addition. In the reaction, which generates trans-1,3-disubstituted isoindolines exclusively, the configurational integrity of the stereogenic center in the starting cyclic sulfamidate is completely retained in the product. Examples are provided which show that the cyclic sulfamidate moiety not only serves as a chiral directing group but also as a versatile handle for further functionalization of the generated isoindoline ring system.

Palladium-catalyzed C-H olefination of uracils and caffeines using molecular oxygen as the sole oxidant.

Science.gov (United States)

Zhang, Xinyu; Su, Lv; Qiu, Lin; Fan, Zhenwei; Zhang, Xiaofeng; Lin, Shen; Huang, Qiufeng

2017-04-18

The palladium-catalyzed oxidative C-H olefination of uracils or caffeines with alkenes using an atmospheric pressure of molecular oxygen as the sole oxidant has been disclosed. This novel strategy offers an efficient and environmentally friendly method to biologically important C5-alkene uracil derivatives or C8-alkene caffeine derivatives.

Transition Metal Catalyzed Hydroarylation of Multiple Bonds: Exploration of Second Generation Ruthenium Catalysts and Extension to Copper Systems

Energy Technology Data Exchange (ETDEWEB)

T. Brent Gunnoe

2011-02-17

Catalysts provide foundational technology for the development of new materials and can enhance the efficiency of routes to known materials. New catalyst technologies offer the possibility of reducing energy and raw material consumption as well as enabling chemical processes with a lower environmental impact. The rising demand and expense of fossil resources has strained national and global economies and has increased the importance of accessing more efficient catalytic processes for the conversion of hydrocarbons to useful products. The goals of the research are to develop and understand single-site homogeneous catalysts for the conversion of readily available hydrocarbons into useful materials. A detailed understanding of these catalytic reactions could lead to the development of catalysts with improved activity, longevity and selectivity. Such transformations could reduce the environmental impact of hydrocarbon functionalization, conserve energy and valuable fossil resources and provide new technologies for the production of liquid fuels. This project is a collaborative effort that incorporates both experimental and computational studies to understand the details of transition metal catalyzed C-H activation and C-C bond forming reactions with olefins. Accomplishments of the current funding period include: (1) We have completed and published studies of C-H activation and catalytic olefin hydroarylation by TpRu{l_brace}P(pyr){sub 3}{r_brace}(NCMe)R (pyr = N-pyrrolyl) complexes. While these systems efficiently initiate stoichiometric benzene C-H activation, catalytic olefin hydroarylation is hindered by inhibition of olefin coordination, which is a result of the steric bulk of the P(pyr){sub 3} ligand. (2) We have extended our studies of catalytic olefin hydroarylation by TpRu(L)(NCMe)Ph systems to L = P(OCH{sub 2}){sub 3}CEt. Thus, we have now completed detailed mechanistic studies of four systems with L = CO, PMe{sub 3}, P(pyr){sub 3} and P(OCH{sub 2}){sub 3}CEt

Acetic Acid Can Catalyze Succinimide Formation from Aspartic Acid Residues by a Concerted Bond Reorganization Mechanism: A Computational Study

Directory of Open Access Journals (Sweden)

Ohgi Takahashi

2015-01-01

Full Text Available Succinimide formation from aspartic acid (Asp residues is a concern in the formulation of protein drugs. Based on density functional theory calculations using Ace-Asp-Nme (Ace = acetyl, Nme = NHMe as a model compound, we propose the possibility that acetic acid (AA, which is often used in protein drug formulation for mildly acidic buffer solutions, catalyzes the succinimide formation from Asp residues by acting as a proton-transfer mediator. The proposed mechanism comprises two steps: cyclization (intramolecular addition to form a gem-diol tetrahedral intermediate and dehydration of the intermediate. Both steps are catalyzed by an AA molecule, and the first step was predicted to be rate-determining. The cyclization results from a bond formation between the amide nitrogen on the C-terminal side and the side-chain carboxyl carbon, which is part of an extensive bond reorganization (formation and breaking of single bonds and the interchange of single and double bonds occurring concertedly in a cyclic structure formed by the amide NH bond, the AA molecule and the side-chain C=O group and involving a double proton transfer. The second step also involves an AA-mediated bond reorganization. Carboxylic acids other than AA are also expected to catalyze the succinimide formation by a similar mechanism.

Acetic acid can catalyze succinimide formation from aspartic acid residues by a concerted bond reorganization mechanism: a computational study.

Science.gov (United States)

Takahashi, Ohgi; Kirikoshi, Ryota; Manabe, Noriyoshi

2015-01-12

Succinimide formation from aspartic acid (Asp) residues is a concern in the formulation of protein drugs. Based on density functional theory calculations using Ace-Asp-Nme (Ace = acetyl, Nme = NHMe) as a model compound, we propose the possibility that acetic acid (AA), which is often used in protein drug formulation for mildly acidic buffer solutions, catalyzes the succinimide formation from Asp residues by acting as a proton-transfer mediator. The proposed mechanism comprises two steps: cyclization (intramolecular addition) to form a gem-diol tetrahedral intermediate and dehydration of the intermediate. Both steps are catalyzed by an AA molecule, and the first step was predicted to be rate-determining. The cyclization results from a bond formation between the amide nitrogen on the C-terminal side and the side-chain carboxyl carbon, which is part of an extensive bond reorganization (formation and breaking of single bonds and the interchange of single and double bonds) occurring concertedly in a cyclic structure formed by the amide NH bond, the AA molecule and the side-chain C=O group and involving a double proton transfer. The second step also involves an AA-mediated bond reorganization. Carboxylic acids other than AA are also expected to catalyze the succinimide formation by a similar mechanism.

Bulk gold catalyzed oxidation reactions of amines and isocyanides and iron porphyrin catalyzed N-H and O-H bond insertion/cyclization reactions of diamines and aminoalcohols

Energy Technology Data Exchange (ETDEWEB)

Klobukowski, Erik [Iowa State Univ., Ames, IA (United States)

2011-01-01

conditions, it was found that the oxidative dehydrogenation of dibenzylamine to Nbenzylidenebenzylamine, with N-methylmorpholine N-oxide (NMMO), was nearly quantitative (96%) within 24 h. However, the reaction with oxygen was much slower, with only a 52% yield of imine product over the same time period. Moreover, the rate of reaction was found to be influenced by the nature of the amine N-oxide. For example, the use of the weakly basic pyridine N-oxide (PyNO) led to an imine yield of only 6% after 24 h. A comparison of amine N-oxide and O2 was also examined in the oxidation of PhCH{sub 2}OH to PhCHO catalyzed by bulk gold. In this reaction, a 52% yield of the aldehyde was achieved when NMMO was used, while only a 7% product yield was afforded when O{sub 2} was the oxidant after 48 h. The bulk gold-catalyzed oxidative dehydrogenation of cyclic amines generates amidines, which upon treatment with Aerosil and water were found to undergo hydrolysis to produce lactams. Moreover, 5-, 6-, and 7-membered lactams could be prepared through a one-pot reaction of cyclic amines by treatment with oxygen, water, bulk gold, and Aerosil. This method is much more atom economical than industrial processes, does not require corrosive acids, and does not generate undesired byproducts. Additionally, the gold and Aerosil catalysts can be readily separated from the reaction mixture. The second project involved studying iron(III) tetraphenylporphyrin chloride, Fe(TPP)Cl, as a homogeneous catalyst for the generation of carbenes from diazo reagents and their reaction with heteroatom compounds. Fe(TPP)Cl, efficiently catalyzed the insertion of carbenes derived from methyl 2-phenyldiazoacetates into O-H bonds of aliphatic and aromatic alcohols. Fe(TPP)Cl was also found to be an effective catalyst for tandem N-H and O-H insertion/cyclization reactions when 1,2-diamines and 1,2-alcoholamines were treated with diazo reagents. This approach provides a one-pot process for synthesizing piperazinones and

Development of melamine modified urea formaldehyde resins based o nstrong acidic pH catalyzed urea formaldehyde polymer

Science.gov (United States)

Chung-Yun Hse

2009-01-01

To upgrade the performance of urea-formaldehyde (UF) resin bonded particleboards, melamine modified urea-formaldehyde (MUF) resins based on strong acidic pH catalyzed UF polymers were investigated. The study was conducted in a series of two experiments: 1) formulation of MUF resins based on a UF polymer catalyzed with strong acidic pH and 2) determination of the...

Palladium-Catalyzed Tandem Oxidative Arylation/Olefination of Aromatic Tethered Alkenes/Alkynes.

Science.gov (United States)

Gao, Yang; Gao, Yinglan; Wu, Wanqing; Jiang, Huanfeng; Yang, Xiaobo; Liu, Wenbo; Li, Chao-Jun

2017-01-18

We describe herein a palladium-catalyzed tandem oxidative arylation/olefination reaction of aromatic tethered alkenes/alkynes for the synthesis of dihydrobenzofurans and 2 H-chromene derivatives. This reaction features a 1,2-difunctionalization of C-C π-bond with two C-H bonds using O 2 as terminal oxidant at room temperature. The products obtained are valuable synthons and important scaffolds in biological agents and natural products. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

c-C5H5 on a Ni(1 1 1) surface: Theoretical study of the adsorption, electronic structure and bonding

International Nuclear Information System (INIS)

German, E.; Simonetti, S.; Pronsato, E.; Juan, A.; Brizuela, G.

2008-01-01

In the present work the ASED-MO method is applied to study the adsorption of cyclopentadienyl anion on a Ni(1 1 1) surface. The adsorption with the centre of the aromatic ring placed above the hollow position has been identified to be energetically the most favourable. The aromatic ring remains almost flat, the H atoms are tilted 17 deg. away from the metal surface. We modelled the metal surface by a two-dimensional slab of finite thickness, with an overlayer of c-C 5 H 5 - , one c-C 5 H 5 - per nine surface Ni atoms. The c-C 5 H 5 - molecule is attached to the surface with its five C atoms bonding mainly with three Ni atoms. The Ni-Ni bond in the underlying surface and the C-C bonds of c-C 5 H 5 - are weakened upon adsorption. We found that the band of Ni 5d z 2 orbitals plays an important role in the bonding between c-C 5 H 5 - and the surface, as do the Ni 6s and 6p z bands

Bite angle effects of diphosphines in C-C and C-X bond forming cross coupling reactions

NARCIS (Netherlands)

Birkholz, M.N.; Freixa, Z.; van Leeuwen, P.W.N.M.

2009-01-01

Catalytic reactions of C-C and C-X bond formation are discussed in this critical review with particular emphasis on cross coupling reactions catalyzed by palladium and wide bite angle bidentate diphosphine ligands. Especially those studies have been collected that allow comparison of the ligand bite

Automated Quantum Mechanical Predictions of Enantioselectivity in a Rhodium-Catalyzed Asymmetric Hydrogenation.

Science.gov (United States)

Guan, Yanfei; Wheeler, Steven E

2017-07-24

A computational toolkit (AARON: An automated reaction optimizer for new catalysts) is described that automates the density functional theory (DFT) based screening of chiral ligands for transition-metal-catalyzed reactions with well-defined reaction mechanisms but multiple stereocontrolling transition states. This is demonstrated for the Rh-catalyzed asymmetric hydrogenation of (E)-β-aryl-N-acetyl enamides, for which a new C 2 -symmetric phosphorus ligand is designed. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photoelectron Diffraction Imaging for C2H2 and C2H4 Chemisorbed on Si(100) Reveals a New Bonding Configuration

International Nuclear Information System (INIS)

Xu, S. H.; Keeffe, M.; Yang, Y.; Chen, C.; Yu, M.; Lapeyre, G. J.; Rotenberg, E.; Denlinger, J.; Yates, J. T. Jr.

2000-01-01

A new adsorption site for adsorbed acetylene on Si(100) is observed by photoelectron imaging based on the holographic principle. The diffraction effects in the carbon 1s angle-resolved photoemission are inverted (including the small-cone method) to obtain an image of the atom's neighboring carbon. The chemisorbed acetylene molecule is bonded to four silicon surface atoms. In contrast to the C 2 H 2 case, the image for adsorbed C 2 H 4 shows it bonded to two Si surface atoms. (c) 2000 The American Physical Society

Amidines for versatile ruthenium(II)-catalyzed oxidative C-H activations with internal alkynes and acrylates.

Science.gov (United States)

Li, Jie; John, Michael; Ackermann, Lutz

2014-04-25

Cationic ruthenium complexes derived from KPF6 or AgOAc enabled efficient oxidative CH functionalizations on aryl and heteroaryl amidines. Thus, oxidative annulations of diversely decorated internal alkynes provided expedient access to 1-aminoisoquinolines, while catalyzed C-H activations with substituted acrylates gave rise to structurally novel 1-iminoisoindolines. The powerful ruthenium(II) catalysts displayed a remarkably high site-, regio- and, chemoselectivity. Therefore, the catalytic system proved tolerant of a variety of important electrophilic functional groups. Detailed mechanistic studies provided strong support for the cationic ruthenium(II) catalysts to operate by a facile, reversible C-H activation. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Aerobic Pd-Catalyzed sp3 C–H Olefination: A Route to Both N-Heterocyclic Scaffolds and Alkenes

Science.gov (United States)

Stowers, Kara J.; Fortner, Kevin C.

2011-01-01

This communication describes a new method for the Pd/polyoxometalate-catalyzed aerobic olefination of unactivated sp3 C–H bonds. Nitrogen heterocycles serve as directing groups, and air is used as the terminal oxidant. The products undergo reversible intramolecular Michael addition, which protects the mono-alkenylated product from over-functionalization. Hydrogenation of the Michael adducts provides access to bicyclic nitrogen-containing scaffolds that are prevalent in alkaloid natural products. Additionally, the cationic Michael adducts undergo facile elimination to release α,β-unsaturated olefins, which can be elaborated in numerous C–C and C–heteroatom bond-forming reactions. PMID:21476513

Metal-free, visible-light-mediated direct C-H arylation of heteroarenes with aryl diazonium salts.

Science.gov (United States)

Hari, Durga Prasad; Schroll, Peter; König, Burkhard

2012-02-15

Visible light along with 1 mol % eosin Y catalyzes the direct C-H bond arylation of heteroarenes with aryl diazonium salts by a photoredox process. We have investigated the scope of the reaction for several aryl diazonium salts and heteroarenes. The general and easy procedure provides a transition-metal-free alternative for the formation of aryl-heteroaryl bonds.

CO and ethanol electro-oxidation on Pt-Rh/C

OpenAIRE

Calderón-Cárdenas, Alfredo; Ortiz-Restrepo, John E.; Mancilla-Valencia, Nelson D.; Torres-Rodriguez, Gerardo A.; Lima, Fabio H. B.; Bolaños-Rivera, Alberto; Gonzalez, Ernesto R.; Lizcano-Valbuena, William H.

2014-01-01

In this work we studied the effect of the composition and thermal treatment in H2 of Pt-Rh/C materials with atomic ratios close to Pt:Rh 3:1, 1:1 and 1:3 and metal loading of 40 wt. %, for the COads and ethanol oxidation. Catalysts were prepared by chemical reduction with formic acid and physically characterized by energy dispersive X-rays spectroscopy (EDX), electron backscattering (EBS) and transmission electron microscopy (TEM), showing Pt:Rh ratios close to the nominals values, similar av...

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

Science.gov (United States)

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.

C-H and H-H Bond Activation via Ligand Dearomatization/Rearomatization of a PN3P-Rhodium(I) Complex

KAUST Repository

Huang, Kuo-Wei; Wang, Yuan; Zheng, Bin; Pan, Yupeng; Pan, Chengling; He, Lipeng

2015-01-01

A neutral complex PN3P-Rh(I)Cl (2) was prepared from a reaction of the PN3P pincer ligand (1) with [Rh(COD)Cl]2 (COD = 1,5-cyclooctadiene). Upon treatment with a suitable base, H–H and Csp2–H activation reactions can be achieved through

Mechanistic investigation of the gold-catalyzed aerobic oxidation of aldehydes: added insight from Hammett studies and isotopic labelling experiments

DEFF Research Database (Denmark)

Fristrup, Peter; Johansen, Louise Bahn; Christensen, Claus Hviid

2008-01-01

The gold-catalyzed aerobic oxidation of aldehydes proceeds through development of a partial negative charge and has a significant kinetic isotope effect (k(H)/k(D) = 2.8-2.9), which illustrates that activation of the C-H bond takes place in the rate-determining step.......The gold-catalyzed aerobic oxidation of aldehydes proceeds through development of a partial negative charge and has a significant kinetic isotope effect (k(H)/k(D) = 2.8-2.9), which illustrates that activation of the C-H bond takes place in the rate-determining step....

Applications of Palladium-Catalyzed C-N Cross-Coupling Reactions.

Science.gov (United States)

Ruiz-Castillo, Paula; Buchwald, Stephen L

2016-10-12

Pd-catalyzed cross-coupling reactions that form C-N bonds have become useful methods to synthesize anilines and aniline derivatives, an important class of compounds throughout chemical research. A key factor in the widespread adoption of these methods has been the continued development of reliable and versatile catalysts that function under operationally simple, user-friendly conditions. This review provides an overview of Pd-catalyzed N-arylation reactions found in both basic and applied chemical research from 2008 to the present. Selected examples of C-N cross-coupling reactions between nine classes of nitrogen-based coupling partners and (pseudo)aryl halides are described for the synthesis of heterocycles, medicinally relevant compounds, natural products, organic materials, and catalysts.

Mechanism and Regioselectivity of Rh(III)-Catalyzed Intermolecular Annulation of Aryl-Substituted Diazenecarboxylates and Alkenes: DFT Insights

KAUST Repository

Ajitha, Manjaly John

2016-02-05

The mechanism of Rh-catalyzed intermolecular annulation of aryl-substituted diazenecarboxylates and alkenes was investigated using density functional theory (DFT) (PCM-M062X/6-311+G(d,p)//M062X/6-31G(d)). The acetate ligand (OAc)-assisted C-H activation via the formation of a five-membered rhodacycle (I-TS1; ΔG‡ = 19.4 kcal/mol) is more favorable compared to that via a four-membered intermediate (II-TS1; ΔG‡ = 27.8 kcal/mol). Our results also revealed that the seven-membered intermediate (I-3, ΔGrel = -6.8 kcal/mol) formed after the alkene insertion could undergo a coordination switch with the adjacent nitrogen atom (via TScs; ΔG‡ = 16.5 kcal/mol) to produce a thermodynamically stable six-membered intermediate (II-3, ΔGrel = -10.4 kcal/mol), eventually leading to a cyclization process followed by a barrierless ligand-assisted protonation to yield the final product. The β-hydride elimination product was found to be kinetically and thermodynamically undesirable. The rate-determining step is identified as the initial C-H activation, consistent with the previous kinetic studies. Notably, DFT studies offered important insights on the ability of the substrate (diazene carboxylate) to promote the switchable coordination site selectivity during the reaction to achieve a lower energy pathway. © 2016 American Chemical Society.

Synthesis of phenanthridines via palladium-catalyzed picolinamide-directed sequential C–H functionalization

Directory of Open Access Journals (Sweden)

Ryan Pearson

2013-05-01

Full Text Available We report a new synthesis of phenanthridines based on palladium-catalyzed picolinamide-directed sequential C–H functionalization reactions starting from readily available benzylamine and aryl iodide precursors. Under the catalysis of Pd(OAc2, the ortho-C–H bond of benzylpicolinamides is first arylated with an aryl iodide. The resulting biaryl compound is then subjected to palladium-catalyzed picolinamide-directed intramolecular dehydrogenative C–H amination with PhI(OAc2 oxidant to form the corresponding cyclized dihydrophenanthridines. The benzylic position of these dihydrophenanthridines could be further oxidized with Cu(OAc2, removing the picolinamide group and providing phenathridine products. The cyclization and oxidation could be carried out in a single step and afford phenathridines in moderate to good yields.

Recent advances in C(sp3–H bond functionalization via metal–carbene insertions

Directory of Open Access Journals (Sweden)

Bo Wang

2016-04-01

Full Text Available The recent development of intermolecular C–H insertion in the application of C(sp3–H bond functionalizations, especially for light alkanes, is reviewed. The challenging problem of regioselectivity in C–H bond insertions has been tackled by the use of sterically bulky metal catalysts, such as metal porphyrins and silver(I complexes. In some cases, high regioselectivity and enantioselectivity have been achieved in the C–H bond insertion of small alkanes. This review highlights the most recent accomplishments in this field.

Metal-metal bonded compounds. V. Compounds with Ir (Rh)-Hg bonds containing a bridging and a chelating triazenido group which interconvert intramolecularly

NARCIS (Netherlands)

Koten, G. van; Vliet, P.I. van; Kokkes, M.; Vrieze, K.

1980-01-01

The compounds [(Diene)(RN{3}R'){2}MHgCl]{2} (M = Ir; Diene = COD; R = CH{3}, C{2}H{5}; R' = p-CH{3}C{6}H{4} and M = Rh; Diene = COD, NOR; R = CH{3}, C{2}H{5}, p-CH{3}-C{6}H{4}; R' = p-CH{3}C{6}H{4} have been prepared by reaction of [(Diene)MCl]{2} with [Hg(RN{3}R'){2}] and by reaction of

Electron pairing analysis of the Fischer-type chromium-carbene complexes (CO){sub 5}Cr=C(X)R (X=H, OH, OCH{sub 3}, NH{sub 2}, NHCH{sub 3} and R=H, CH{sub 3}, CH=CH{sub 2}, Ph, C-CH )

Energy Technology Data Exchange (ETDEWEB)

Poater, Jordi; Cases, Montserrat; Fradera, Xavier; Duran, Miquel; Sola, Miquel

2003-10-15

The electron-pair density distributions of a series of 25 Fischer carbene complexes of the type (CO){sub 5}Cr=C(X)R (X=H, OH, OCH{sub 3}, NH{sub 2}, NHCH{sub 3} and R=H, CH{sub 3}, CH=CH{sub 2}, Ph, C-CH) are analyzed using the Atoms in Molecules theory. Localization and delocalization indices are used to characterize the electron pairing taking place in the Cr=C---X moiety in these complexes. Electron delocalization between the Cr and C atoms and between the C atom and the X group are related to the {pi}-donor strength of the X group and the degree of back-donation between the chromium pentacarbonyl and the carbene fragments. The results obtained with the Atoms in Molecules theory complement those obtained in a previous study by means of energy and charge decomposition analyses. Electron delocalization between the Cr atom and the X group is consistent with the hypothesis of a weak 3-center 4-electron bonding interaction in the Cr=C-X group of atoms. Except for X=H, {delta}(Cr,X) increases with the decrease of the {pi}-donor character of the X group.

Theoretical Study on the Aza-Diels-Alder Reaction Catalyzed by PHCl2 Lewis Acid via Pnicogen Bonding.

Science.gov (United States)

Yaghoobi, Fereshteh; Sohrabi Mahboub, Mahdi

2018-03-15

The reaction mechanism of the Aza-Diels-Alder (A-D-A) cycloaddition reaction between X 2 C═NNH 2 , where X = H, F, Cl, Br, and 1,3-butadiene catalyzed by a PHCl 2 Lewis acid was characterized using density functional theory calculations. The influences of various substituents of X on the studied reaction were analyzed using the activation strain model (ASM), which is also termed as the distortion-interaction model. Calculations showed that the smallest and largest values of the activation energies belong to the substituents of F and Br, respectively. The activation energy of the studied reactions was decreased within 8.6 kcal·mol -1 in the presence of PHCl 2 catalyst. Investigations showed that the pnicogen bonding is adequately capable of activating the A-D-A reaction. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis were implemented to understand the nature of C 4,Cbut ···C XIm and C 1,Cbut ···N XIm bonds at the TS structures. Additionally, the energy decomposition analysis (EDA) based on the ETS-NOCV scheme was used to characterize the nature of C 4,Cbut ···C XIm and C 1,Cbut ···N XIm bond. The results of the study mirror the fact that the PHCl 2 Lewis acid may be suggested as a simple suitable catalyst for experimental studies on the A-D-A reactions.

Iridium complexes containing mesoionic C donors: selective C(sp3)-H versus C(sp2)-H bond activation, reactivity towards acids and bases, and catalytic oxidation of silanes and water.

Science.gov (United States)

Petronilho, Ana; Woods, James A; Mueller-Bunz, Helge; Bernhard, Stefan; Albrecht, Martin

2014-11-24

Metalation of a C2-methylated pyridylimidazolium salt with [IrCp*Cl2]2 affords either an ylidic complex, resulting from C(sp(3))-H bond activation of the C2-bound CH3 group if the metalation is performed in the presence of a base, such as AgO2 or Na2CO3, or a mesoionic complex via cyclometalation and thermally induced heterocyclic C(sp(2))-H bond activation, if the reaction is performed in the absence of a base. Similar cyclometalation and complex formation via C(sp(2))-H bond activation is observed when the heterocyclic ligand precursor consists of the analogous pyridyltriazolium salt, that is, when the metal bonding at the C2 position is blocked by a nitrogen rather than a methyl substituent. Despite the strongly mesoionic character of both the imidazolylidene and the triazolylidene, the former reacts rapidly with D(+) and undergoes isotope exchange at the heterocyclic C5 position, whereas the triazolylidene ligand is stable and only undergoes H/D exchange under basic conditions, where the imidazolylidene is essentially unreactive. The high stability of the Ir-C bond in aqueous solution over a broad pH range was exploited in catalytic water oxidation and silane oxidation. The catalytic hydrosilylation of ketones proceeds with turnover frequencies as high as 6,000 h(-1) with both the imidazolylidene and the triazolylidene system, whereas water oxidation is enhanced by the stronger donor properties of the imidazol-4-ylidene ligands and is more than three times faster than with the triazolylidene analogue. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

(cGnRH-II) on plasma steroid hormone, maturation and ovulation

African Journals Online (AJOL)

PRECIOUS

2009-12-01

Dec 1, 2009 ... (LHRHa) and salmon gonadotropin-releasing hormone analogue (sGnRHa) in ..... Four out of six fish reached GVBD at 12 h after injection. Egg quality .... of the sbGnRH and cGnRH-II genes from the striped bass, Morone.

Dual C-H functionalization of N-aryl amines: synthesis of polycyclic amines via an oxidative Povarov approach.

Science.gov (United States)

Min, Chang; Sanchawala, Abbas; Seidel, Daniel

2014-05-16

Iminium ions generated in situ via copper(I) bromide catalyzed oxidation of N-aryl amines readily undergo [4 + 2] cycloadditions with a range of dienophiles. This method involves the functionalization of both a C(sp(3))-H and a C(sp(2))-H bond and enables the rapid construction of polycyclic amines under relatively mild conditions.

Nickel-Catalyzed Synthesis of Primary Aryl and Heteroaryl Amines via C–O Bond Cleavage

KAUST Repository

Yue, Huifeng

2017-03-13

A nickel-catalyzed protocol for the conversion of aryl and heteroaryl alcohol derivatives to primary and secondary aromatic amines via C(sp2)-O bond cleavage is described. The new amination protocol can be applied to a range of substrates bearing diverse functional groups and uses readily available benzophenone imines as an effective nitrogen source.

Nickel-Catalyzed Synthesis of Primary Aryl and Heteroaryl Amines via C–O Bond Cleavage

KAUST Repository

Yue, Huifeng; Guo, Lin; Liu, Xiangqian; Rueping, Magnus

2017-01-01

A nickel-catalyzed protocol for the conversion of aryl and heteroaryl alcohol derivatives to primary and secondary aromatic amines via C(sp2)-O bond cleavage is described. The new amination protocol can be applied to a range of substrates bearing diverse functional groups and uses readily available benzophenone imines as an effective nitrogen source.

ESI-MS study on non-covalent bond complex of rhFKBP12 and new neurogrowth promoter

Institute of Scientific and Technical Information of China (English)

WANG; Hongxia; (王红霞); ZHANG; Xuemin; (张学敏); YANG; Songcheng; (杨松成); XIAO; Junhai; (肖军海); NIE; Aihua; (聂爱华); ZHAO; Liqin; (赵丽琴); LI; Song; (李松)

2003-01-01

An ESI-MS method for studying the non-covalent bond complex of rhFKBP12 with its nonimmunosuppressive ligands was developed. The method was used to screen out three compounds capable of binding to rhFKBP12 non-covalently from 52 compounds. By competing binding experiment, the binding site and the relative binding strength of these three compounds 000107, 000308 and A2B12 with rhFKBP12 were measured. All of them have the same binding site as FK506 does. X-ray crystalline diffraction experiment of non-covalent bond complex of 000107, 000308 with rhFKBP12 by Tsinghua University showed the same results. Among them 000308 has good effect on stimulating neurite to grow in chicken sensory neuronal cultures.

Synthesis of oxindole from acetanilide via Ir(iii)-catalyzed C-H carbenoid functionalization.

Science.gov (United States)

Patel, Pitambar; Borah, Gongutri

2016-12-22

Herein we disclose the first report on the synthesis of oxindole derivatives from acetanilide via Ir(iii)-catalyzed intermolecular C-H functionalization with diazotized Meldrum's acid. A broad range of substituted anilides were found to react smoothly under the Ir(iii)-catalytic system to afford the corresponding N-protected oxindoles. The N-protecting groups, such as Ac, Bz or Piv, can be easily removed to furnish the oxindole. Various synthetic applications of the synthesized oxindole were also demonstrated.

Room-temperature Pd-catalyzed C-H chlorination by weak coordination: one-pot synthesis of 2-chlorophenols with excellent regioselectivity.

Science.gov (United States)

Sun, Xiuyun; Sun, Yonghui; Zhang, Chao; Rao, Yu

2014-02-07

A room-temperature Pd(II)-catalyzed regioselective chlorination reaction has been developed for a facile one-pot synthesis of a broad range of 2-chlorophenols. The reaction demonstrates an excellent regioselectivity and reactivity for C-H chlorination. This reaction represents one of the rare examples of mild C-H functionalization at ambient temperature.

Nickel-Catalyzed Alkoxy-Alkyl Interconversion with Alkylborane Reagents through C−O Bond Activation of Aryl and Enol Ethers

KAUST Repository

Guo, Lin

2016-11-07

A nickel-catalyzed alkylation of polycyclic aromatic methyl ethers as well as methyl enol ethers with B-alkyl 9-BBN and trialkylborane reagents that involves the cleavage of stable C(sp2)−OMe bonds is described. The transformation has a wide substrate scope and good chemoselectivity profile while proceeding under mild reaction conditions; it provides a versatile way to form C(sp2)−C(sp3) bonds that does not suffer from β-hydride elimination. Furthermore, a selective and sequential alkylation process by cleavage of inert C−O bonds is presented to demonstrate the advantage of this method.

Ligand-Enabled γ-C(sp(3))-H Olefination of Amines: En Route to Pyrrolidines.

Science.gov (United States)

Jiang, Heng; He, Jian; Liu, Tao; Yu, Jin-Quan

2016-02-17

Pd(II)-catalyzed olefination of γ-C(sp(3))-H bonds of triflyl (Tf) and 4-nitrobenzenesulfonyl (Ns) protected amines is achieved. Subsequent aza-Wacker oxidative cyclization or conjugate addition of the olefinated intermediates provides a variety of C-2 alkylated pyrrolidines. Three pyridine- and quinoline-based ligands are developed to match different classes of amine substrates, demonstrating a rare example of ligand-enabled C(sp(3))-H olefination reactions. The use of Ns protecting group to direct C(sp(3))-H activation of alkyl amines is also a significant step toward practical C-H functionalizations of alkyl amines.

Gas-phase reactivity of lanthanide cations with fluorocarbons: C-F versus C-H and C-C bond activation

International Nuclear Information System (INIS)

Cornehl, H.H.; Hornung, G.; Schwarz, H.

1996-01-01

The gas-phase reactivity of the fluorinated hydrocarbons CF 4 , CHF 3 , CH 3 F, C 2 F 6 , 1,1-C 2 H 4 F 2 , and C 6 F 6 with the lanthanide cations Ce + , Pr + , Sm + , Ho + , Tm + , and Yb + and the reactivity of C 6 H 5 F with all lanthanide cations Ln + (Ln = La-Lu, with the exception of Pm + ) have been examined by Fourier-transform ion cyclotron resonance mass spectrometry. The perfluorinated compounds tetrafluoromethane and hexafluoroethane as well as trifluoromethane do not react with any lanthanide cation. Selective activation of the strong C-F bonds in fluoromethane, 1,1-difluoroethane, hexafluorobenzene, and fluorobenzene appears as a general reaction scheme along the 4f row. Experimental evidence is given for a 'harpoon'-like mechanism for the F atom abstraction process which operates via an initial electron transfer from the lanthanide cation to the fluorinated substrate in the encounter complex Ln + RF. The most reactive lanthanides La + , Ce + , Gd + , and Tb + and also the formal closed-shell species Lu + exhibit additional C-H and C-C bond activation pathways in the reaction with fluorobenzene, namely dehydrohalogenation as well as loss of a neutral acetylene molecule. In the case of Tm + and Yb + the formation of neutral LnF 3 is observed in a multistep process via C-C coupling and charge transfer. 17 refs., 2 figs., 2 tabs

Supramolecular Recognition Allows Remote, Site-Selective C-H Oxidation of Methylenic Sites in Linear Amines.

Science.gov (United States)

Olivo, Giorgio; Farinelli, Giulio; Barbieri, Alessia; Lanzalunga, Osvaldo; Di Stefano, Stefano; Costas, Miquel

2017-12-18

Site-selective C-H functionalization of aliphatic alkyl chains is a longstanding challenge in oxidation catalysis, given the comparable relative reactivity of the different methylenes. A supramolecular, bioinspired approach is described to address this challenge. A Mn complex able to catalyze C(sp 3 )-H hydroxylation with H 2 O 2 is equipped with 18-benzocrown-6 ether receptors that bind ammonium substrates via hydrogen bonding. Reversible pre-association of protonated primary aliphatic amines with the crown ether selectively exposes remote positions (C8 and C9) to the oxidizing unit, resulting in a site-selective oxidation. Remarkably, such control of selectivity retains its efficiency for a whole series of linear amines, overriding the intrinsic reactivity of C-H bonds, no matter the chain length. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis, crystal structures, and characterization of double complex salts [Au(en)2][Rh(NO2)6]·2H2O and [Au(en)2][Rh(NO2)6

Science.gov (United States)

Plyusnin, Pavel E.; Makotchenko, Evgenia V.; Shubin, Yury V.; Baidina, Iraida A.; Korolkov, Ilya V.; Sheludyakova, Liliya A.; Korenev, Sergey V.

2015-11-01

Double complex salts of rhodium(III) and gold(III) of the composition [Au(en)2][Rh(NO2)6]·2H2O (1) and [Au(en)2][Rh(NO2)6] (2) have been prepared. Crystal structures of the compounds have been determined by single crystal X-ray diffraction. The compounds have been characterized by PXRD, IR, far-IR, CHN and DTA. The complexes have a layered structures. The presence of water in 1 makes the structure of the hydrated DCS less dense as compared to the anhydrous one. The environment of the cation and the anion in the two structures is the same, oxygen atoms of the nitro groups are involved in hydrogen bonds N-H⋯O, N⋯O distances being approximately the same. The structures of 1 and 2 are notable in having shortened contacts between the gold atoms and the oxygen atoms of the nitro groups of the neighboring complex anions. The thermal behavior of the complexes in a hydrogen atmosphere was investigated. The final product of thermolysis prepared at the temperature 600°C is a two-phase mixture of pure metallic gold and the solid solution Rh0.93Au0.07.

Competition between weak OH···π and CH··O hydrogen bonds: THz spectroscopy of the C2H2—H2O and C2H4—H2O complexes

DEFF Research Database (Denmark)

Andersen, Jonas; Heimdal, Jimmy; Nelander, B.

2017-01-01

an intermolecular CH⋯O hydrogen-bonded configuration of C2v symmetry with the H2O subunit acting as the hydrogen bond acceptor. The observation and assignment of two large-amplitude donor OH librational modes of the C2H4—H2O complex at 255.0 and 187.5 cm−1, respectively, confirms an intermolecular OH⋯π hydrogen...

New Concept of C–H and C–C Bond Activation via Surface Organometallic Chemistry

KAUST Repository

Samantaray, Manoja

2015-08-18

In this chapter we describe the recent applications of well-defined oxidesupported metal alkyls/alkylidenes/alkylidynes and hydrides of group IV, V, and VI transition metals in the field of C–H and C–C bond activation. The activation of ubiquitous C–H and C–C bonds of paraffin is a long-standing challenge because of intrinsic low reactivity. There are many concepts derived from surface organometallic chemistry (SOMC): surface organometallic fragments are always intermediates in heterogeneous catalysis. The study of their synthesis and reactivity is a way to rationalize mechanism of heterogeneous catalysis and to achieve structure activity relationship. By surface organometallic chemistry one can enter any catalytic center by a reaction intermediate leading in fine to single site catalysts. With surface organometallic chemistry one can coordinate to the metal which can play a role in different elementary steps leading for example to C–H activation and Olefin metathesis. Because of the development of SOMC there is a lot of space for the improvement of homogeneous catalysis. After the 1997 discovery of alkane metathesis using silica-supported tantalum hydride by Basset et al. at low temperature (150ºC) the focus in this area was shifted to the discovery of more and more challenging surface complexes active in the application of C–H and C–C bond activation. Here we describe the evolution of well-defined metathesis catalyst with time as well as the effect of support on catalysis. We also describe here which metal–ligand combinations are responsible for a variety of C–H and C–C bond activation.

Formation of C-C and C-O bonds and oxygen removal in reactions of alkanediols, alkanols, and alkanals on copper catalysts.

Science.gov (United States)

Sad, María E; Neurock, Matthew; Iglesia, Enrique

2011-12-21

This study reports evidence for catalytic deoxygenation of alkanols, alkanals, and alkanediols on dispersed Cu clusters with minimal use of external H(2) and with the concurrent formation of new C-C and C-O bonds. These catalysts selectively remove O-atoms from these oxygenates as CO or CO(2) through decarbonylation or decarboxylation routes, respectively, that use C-atoms present within reactants or as H(2)O using H(2) added or formed in situ from CO/H(2)O mixtures via water-gas shift. Cu catalysts fully convert 1,3-propanediol to equilibrated propanol-propanal intermediates that subsequently form larger oxygenates via aldol-type condensation and esterification routes without detectable involvement of the oxide supports. Propanal-propanol-H(2) equilibration is mediated by their chemisorption and interconversion at surfaces via C-H and O-H activation and propoxide intermediates. The kinetic effects of H(2), propanal, and propanol pressures on turnover rates, taken together with measured selectivities and the established chemical events for base-catalyzed condensation and esterification reactions, indicate that both reactions involve kinetically relevant bimolecular steps in which propoxide species, acting as the base, abstract the α-hydrogen in adsorbed propanal (condensation) or attack the electrophilic C-atom at its carbonyl group (esterification). These weakly held basic alkoxides render Cu surfaces able to mediate C-C and C-O formation reactions typically catalyzed by basic sites inherent in the catalyst, instead of provided by coadsorbed organic moieties. Turnover rates for condensation and esterification reactions decrease with increasing Cu dispersion, because low-coordination corner and edge atoms prevalent on small clusters stabilize adsorbed intermediates and increase the activation barriers for the bimolecular kinetically relevant steps required for both reactions. © 2011 American Chemical Society

Origin of the Ability of α-Fe2 O3 Mesopores to Activate C-H Bonds in Methane.

Science.gov (United States)

Dong, Bing; Han, Zhen; Zhang, Yongbo; Yu, Youyi; Kong, Aiguo; Shan, Yongkui

2016-02-01

Methane is a most abundant and inexpensive hydrocarbon feedstock for the production of chemicals and fuels. However, it is extremely difficult to directly convert methane to higher hydrocarbons because the C-H bonds in methane are the most stable C-H bonds of all hydrocarbons. The activation of the C-H bonds in methane by using an efficient and mild route remains a daunting challenge. Here, we show that the inner surface structures of the pore walls in mesoporous α-Fe 2 O 3 possess excellent catalytic performance for methane activation and convert C-H bonds into the C-O bonds in an O 2 atmosphere at 140 °C. We found that such unusual structures are mainly comprised of turbostratic ribbons and K crystal faces and have higher catalytic activity than the (110) plane. These results are without precedent in the history of catalysis chemistry and will provide a new pathway for designing and preparing highly efficient catalytic materials. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The mechanism of transition-metal (Cu or Pd)-catalyzed synthesis of benzimidazoles from amidines: theoretical investigation.

Science.gov (United States)

Li, Juan; Gu, Honghong; Wu, Caihong; Du, Lijuan

2014-11-28

In this study, the Cu(OAc)2- and [PdCl2(PhCN)2]-catalyzed syntheses of benzimidazoles from amidines were theoretically investigated using density functional theory calculations. For the Cu-catalyzed system, our calculations supported a four-step-pathway involving C-H activation of an arene with Cu(II) via concerted metalation-deprotonation (CMD), followed by oxidation of the Cu(II) intermediate and deprotonation of the imino group by Cu(III), and finally reductive elimination from Cu(III). In our calculations, the barriers for the CMD step and the oxidation step are the same. The results are different from the ones reported by Fu et al. in which the whole reaction mechanism includes three steps and the CMD step is rate determining. On the basis of the calculation results for the [PdCl2(PhCN)2]-catalyzed system, C-H bond breaking by CMD occurs first, followed by the rate-determining C-N bond formation and N-H deprotonation. Pd(III) species is not involved in the [PdCl2(PhCN)2]-catalyzed syntheses of benzimidazoles from amidines.

Rhodium-Biphephos-Catalyzed Tandem Isomerization–Hydroformylation of Oleonitrile

Directory of Open Access Journals (Sweden)

Lucas Le Goanvic

2018-01-01

Full Text Available Tandem isomerization–hydroformylation of oleonitrile (an 18-carbon nitrile with a remote internal (9-C=C bond has been studied using Rh-bisphosphite catalyst systems, targeting formation of the linear aldehyde. The best compromise between regioselectivity (l/b = 58:42 and chemoselectivity (60% was obtained at 120 °C and 10 bar CO/H2 (1:1 with a catalyst based on Biphephos at a 0.5 mol % catalyst load and a low ligand excess (2 equiv. versus Rh. These values stand among the better reported ones for the tandem isomerization–hydroformylation of long chain olefins with a single-component catalyst system.

Hydrogenation of graphene nanoflakes and C-H bond dissociation of hydrogenated graphene nanoflakes: a density functional theory study

Institute of Scientific and Technical Information of China (English)

Sheng Tao; Hui-Ting Liu; Liu-Ming Yan; Bao-Hua Yue; Ai-Jun Li

2017-01-01

The Gibbs free energy change for the hydrogenation of graphene nanoflakes Cn (n =24,28,30 and 32) and the C-H bond dissociation energy of hydrogenated graphene nanoflakes CnHm (n =24,28,30 and 32;and m =1,2 and 3) are evaluated using density functional theory calculations.It is concluded that the graphene nanoflakes and hydrogenated graphene nanoflakes accept the ortharyne structure with peripheral carbon atoms bonded via the most triple bonds and leaving the least unpaired dangling electrons.Five-membered rings are formed at the deep bay sites attributing to the stabilization effect from the pairing of dangling electrons.The hydrogenation reactions which eliminate one unpaired dangling electron and thus decrease the overall multiplicity of the graphene nanoflakes or hydrogenated graphene nanoflakes are spontaneous with negative or near zero Gibbs free energy change.And the resulting C-H bonds are stable with bond dissociation energy in the same range as those of aromatic compounds.The other C-H bonds are not as stable attributing to the excessive unpaired dangling electrons being filled into the C-H anti-bond orbital.

Metal-metal bonding and aromaticity in [M2(NHCHNH)3]2 (μ-E)2 (E = O, S; M = Nb, Mo, Tc, Ru, Rh).

Science.gov (United States)

Yan, Xiuli; Meng, Lingpeng; Sun, Zheng; Li, Xiaoyan

2016-02-01

The nature of M-M bonding and aromaticity of [M2(NHCHNH)3]2(μ-E)2 (E = O, S; M = Nb, Mo, Tc, Ru, Rh) was investigated using atoms in molecules (AIM) theory, electron localization function (ELF), natural bond orbital (NBO) and molecular orbital analysis. These analyses led to the following main conclusions: in [M2(NHCHNH)3]2(μ-E)2 (E = O, S; M = Nb, Mo, Tc, Ru, Rh), the Nb-Nb, Ru-Ru, and Rh-Rh bonds belong to "metallic" bonds, whereas Mo-Mo and Tc-Tc drifted toward the "dative" side; all these bonds are partially covalent in character. The Nb-Nb, Mo-Mo, and Tc-Tc bonds are stronger than Ru-Ru and Rh-Rh bonds. The M-M bonds in [M2(NHCHNH)3]2(μ-S)2 are stronger than those in [M2(NHCHNH)3]2(μ-O)2 for M = Nb, Mo, Tc, and Ru. The NICS(1)ZZ values show that all of the studied molecules, except [Ru2(NHCHNH)3]2(μ-O)2, are aromaticity molecules. O-bridged compounds have more aromaticity than S-bridged compounds. Graphical Abstract Left Molecular graph, and right electron localization function (ELF) isosurface of [M2(NHCHNH)3]2(μ-E)2(E = O, S; M = Nb, Mo, Tc, Ru, Rh).

Activity of PtSnRh/C nanoparticles for the electrooxidation of C1 and C2 alcohols

International Nuclear Information System (INIS)

Teran, Freddy E.; Santos, Deise M.; Ribeiro, Josimar; Kokoh, Kouakou B.

2012-01-01

A systematic investigation of alcohol adsorption and oxidation on binary and ternary electrocatalysts in acid medium was performed. Binary (PtRh) and ternary (PtRhSn) were prepared by the Pechini modified method on carbon Vulcan XC-72, and different nominal compositions were characterized by energy dispersive X-ray and X-ray diffraction (XRD) techniques. The XRD results showed that the Pt 80 Rh 20 /C and Pt 70 Sn 10 Rh 20 /C electrocatalysts consisted of the Pt displaced phase, suggesting the formation of a solid solution between the metals Pt/Rh and Pt/Sn. Electrochemical investigations on these different electrode materials were carried out as a function of the electrocatalyst composition, in acid medium (0.5 mol dm −3 H 2 SO 4 ), and in the absence and presence of different alcohols (methanol, ethanol and ethylene glycol). The electrochemical results obtained at room temperature have shown that the Pt 70 Sn 10 Rh 20 /C catalyst display better catalytic activity for alcohol oxidation compared with the binary catalyst. In situ reflectance infrared spectroscopy measurements have shown that the oxidation of alcohols mentioned produced CO 2 at low potentials indicating that the materials synthesized could be used as efficient anodes in the fuel cell applications. - Highlights: ► Pt-based catalysts were synthesized by thermal decomposition polymeric precursors. ► Pt 70 Sn 10 Rh 20 /C displays better catalytic activity for the oxidation of alcohols. ► The co-catalysts tin and rhodium promote the removal of CO to CO 2 at low potentials. ► Ethylene glycol is oxidizing strongly to CO 2 at low potentials. ► Pt 70 Sn 10 Rh 20 /C catalyst is an efficient anode material for a direct alcohol fuel cell.

Noble metal-catalyzed homogeneous and heterogeneous processes in treating simulated nuclear waste media with formic acid

International Nuclear Information System (INIS)

King, R.B.; Bhattacharyya, N.K.; Smith, H.D.

1995-09-01

Simulants for the Hanford Waste Vitrification Plant feed containing the major non-radioactive components Al, Cd, Fe, Mn, Nd, Ni, Si, Zr, Na, CO 3 2 -, NO 3 -, and NO 2 - were used to study reactions of formic acid at 90 degrees C catalyzed by the noble metals Ru, Rh, and/or Pd found in significant quantities in uranium fission products. Such reactions were monitored using gas chromatography to analyze the CO 2 , H 2 , NO, and N 2 O in the gas phase and a microammonia electrode to analyze the NH 4 +/NH 3 in the liquid phase as a function of time. The following reactions have been studied in these systems since they are undesirable side reactions in nuclear waste processing: (1) Decomposition of formic acid to CO 2 + H 2 is undesirable because of the potential fire and explosion hazard of H 2 . Rhodium, which was introduced as soluble RhCl 3 -3H 2 O, was found to be the most active catalyst for H 2 generation from formic acid above ∼ 80 degrees C in the presence of nitrite ion. The H 2 production rate has an approximate pseudo first-order dependence on the Rh concentration, (2) Generation of NH 3 from the formic acid reduction of nitrate and/or nitrite is undesirable because of a possible explosion hazard from NH 4 NO 3 accumulation in a waste processing plant off-gas system. The Rh-catalyzed reduction of nitrogen-oxygen compounds to ammonia by formic acid was found to exhibit the following features: (a) Nitrate rather than nitrite is the principal source of NH 3 . (b) Ammonia production occurs at the expense of hydrogen production. (c) Supported rhodium metal catalysts are more active than rhodium in any other form, suggesting that ammonia production involves heterogeneous rather than homogeneous catalysis

Palladium-Catalyzed C-H Functionalization Using Guanidine as a Directing Group: Ortho Arylation and Olefination of Arylguanidines

Science.gov (United States)

Shao, Jiaan; Chen, Wenteng; Giulianotti, Marc A.; Houghten, Richard A.; Yu, Yongping

2012-01-01

Palladium-catalyzed C-H functionalization using guanidine as the directing group was achieved under mild reaction conditions. Various guanidine derivatives were produced in moderate to good yields by using simple unactivated arenes or ethyl acrylate as the source of arylation or olefination respectively. PMID:23095022

Hydrodeoxygenation of Phenol to Benzene and Cyclohexane on Rh(111) and Rh(211) Surfaces: Insights from Density Functional Theory

DEFF Research Database (Denmark)

Garcia-Pintos, Delfina; Voss, Johannes; Jensen, Anker Degn

2016-01-01

Herein we describe the C-O cleavage of phenol and cyclohexanol over Rh (111) and Rh (211) surfaces using density functional theory calculations. Our analysis is complemented by a microkinetic model of the reactions, which indicates that the C-O bond cleavage of cyclohexanol is easier than that of...

Manganese-Catalyzed C−H Functionalizations: Hydroarylations and Alkenylations Involving an Unexpected Heteroaryl Shift

KAUST Repository

Wang, Chengming

2017-06-24

A manganese-catalyzed regio- and stereoselective hydroarylation of allenes is reported. The C−H functionalization method provides access to various alkenylated indoles in excellent yields. Moreover, a hydroarylation/cyclization cascade involving an unexpected C−N bond cleavage and aryl shift has been developed, which provides a new synthetic approach to substituted pyrroloindolones.

Manganese-Catalyzed C−H Functionalizations: Hydroarylations and Alkenylations Involving an Unexpected Heteroaryl Shift

KAUST Repository

Wang, Chengming; Wang, Ai; Rueping, Magnus

2017-01-01

A manganese-catalyzed regio- and stereoselective hydroarylation of allenes is reported. The C−H functionalization method provides access to various alkenylated indoles in excellent yields. Moreover, a hydroarylation/cyclization cascade involving an unexpected C−N bond cleavage and aryl shift has been developed, which provides a new synthetic approach to substituted pyrroloindolones.

Enantioselective carbenoid insertion into C(sp3–H bonds

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J. V. Santiago

2016-05-01

Full Text Available The enantioselective carbenoid insertion into C(sp3–H bonds is an important tool for the synthesis of complex molecules due to the high control of enantioselectivity in the formation of stereogenic centers. This paper presents a brief review of the early issues, related mechanistic studies and recent applications on this chemistry area.

Rhenium and Manganese-Catalyzed Selective Alkenylation of Indoles

KAUST Repository

Wang, Chengming

2018-04-06

An efficient rhenium‐catalyzed regioselective C‐H bond alkenylation of indoles is reported. The protocol operates well for internal as well as terminal alkynes, affording products in good to excellent yields. Furthermore, a manganese catalyzed, acid free, regioselective C2‐alkenylation of indoles with internal alkynes is described. The directing groups can be easily removed after the reaction and the resulting products can be used as valuable building blocks for the synthesis of diverse heterocyclic compounds.

Rhenium and Manganese-Catalyzed Selective Alkenylation of Indoles

KAUST Repository

Wang, Chengming; Rueping, Magnus

2018-01-01

An efficient rhenium‐catalyzed regioselective C‐H bond alkenylation of indoles is reported. The protocol operates well for internal as well as terminal alkynes, affording products in good to excellent yields. Furthermore, a manganese catalyzed, acid free, regioselective C2‐alkenylation of indoles with internal alkynes is described. The directing groups can be easily removed after the reaction and the resulting products can be used as valuable building blocks for the synthesis of diverse heterocyclic compounds.

Ag1 Pd1 Nanoparticles-Reduced Graphene Oxide as a Highly Efficient and Recyclable Catalyst for Direct Aryl C-H Olefination.

Science.gov (United States)

Hu, Qiyan; Liu, Xiaowang; Wang, Guoliang; Wang, Feifan; Li, Qian; Zhang, Wu

2017-12-14

The efficient and selective palladium-catalyzed activation of C-H bonds is of great importance for the construction of diverse bioactive molecules. Despite significant progress, the inability to recycle palladium catalysts and the need for additives impedes the practical applications of these reactions. Ag 1 Pd 1 nanoparticles-reduced graphene oxide (Ag 1 Pd 1 -rGO) was used as highly efficient and recyclable catalyst for the chelation-assisted ortho C-H bond olefination of amides with acrylates in good yields with a broad substrate scope. The catalyst can be recovered and reused at least 5 times without losing activity. A synergistic effect between the Ag and Pd atoms on the catalytic activity was found, and a plausible mechanism for the AgPd-rGO catalyzed C-H olefination is proposed. These findings suggest that the search for such Pd-based bimetallic alloy nanoparticles is a new method towards the development of superior recyclable catalysts for direct aryl C-H functionalization under mild conditions. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ti-Catalyzed Selective Isomerization of Terminal Mono-substituted Olefins

International Nuclear Information System (INIS)

Lee, Hyung Soo; Lee, Gab Yong

2005-01-01

The isomerization of olefins occurs either by a metal hydride addition-elimination or by a π-allyl metal hydride intermediate. HCo(CO) 4 , [(C 2 H 4 ) 2 RhCl] 2 , Ni[P(OEt) 3 ] 4 , and PtCl 2 (PPh 3 ) 2 -SnCl 2 are effective catalysts for isomerization of olefins via a metal hydride addition-elimination mechanism, 3,4 and Fe 3 (CO) 12 catalyzed isomerization of 3-ethyl-1-pentene and isomerization of 1-heptene catalyzed by (PhCN) 2 PdCl 2 occur via a π-allyl metal hydride mechanism. The cis/trans ratio of 2-butene obtained from isomerization of 1-butene by RhH(CO)(PPh 3 ) 3 has also been investigated. The skeletal isomerization of olefins catalyzed by (R 3 P) 2 NiCl 2 is developed such as conversion of cis-1,4-hexadiene to trans-2-methyl-1,3-pentadiene. Titanium complexes serve as an effective catalysts for a variety of reactions such as hydroalumination, hydroboration, and hydrogenation of unsaturated hydrocarbons. We have been interested in the selective reactions of unsaturated hydrocarbons by using titanium and zirconium compounds. The reagent system composed of LiAlH 4 /Cp 2 TiCl 2 ≤ 2 in the molar ratio promotes the isomerization of 1-octene, but the detailed reaction for isomerization of olefins has not been reported. We report here a selective isomerization of olefins with low valent titanium complex generated from Cp 2 TiCl 2 (Cp=cyclopentadienyl) and LiAlH 4

Rh-Ni and Rh-Co Catalysts for Autothermal Reforming of Gasoline

Energy Technology Data Exchange (ETDEWEB)

Jung, Yeongyu; Lee, Daehyung; Kim, Yongmin; Lee, Jinhee; Nam, Sukwoo; Choi, Daeki; Yoon, Chang Won [Korea Institute of Science and Technology, Seoul (Korea, Republic of)

2014-01-15

Rh doped Ni and Co catalysts, Rh-M/CeO{sub 2}(20 wt %)-Al{sub 2}O{sub 3} (0.2 wt % of Rh; M = Ni or Co, 20 wt %) were synthesized to produce hydrogen via autothermal reforming (ATR) of commercial gasoline at 700 .deg. C under the conditions of a S/C ratio of 2.0, an O/C ratio of 0.84, and a gas hourly space velocity (GHSV) of 20,000 h{sup -1}. The Rh-Ni/CeO{sub 2}(20 wt %)-Al{sub 2}O{sub 3} catalyst (1) exhibited excellent activities, with H{sub 2} and (H{sub 2}+CO) yields of 2.04 and 2.58 mol/mol C, respectively. In addition, this catalyst proved to be highly stable over 100 h without catalyst deactivation, as evidenced by energy dispersive spectroscopy (EDX) and elemental analyses. Compared to 1, Rh-Co/CeO{sub 2}(20 wt %)-Al{sub 2}O{sub 3} catalyst (2) exhibited relatively low stability, and its activity decreased after 57 h. In line with this observation, elemental analyses confirmed that nearly no carbon species were formed at 1 while carbon deposits (10 wt %) were found at 2 following the reaction, which suggests that carbon coking is the main process for catalyst deactivation.

Borylnitrenes: electrophilic reactive intermediates with high reactivity towards C-H bonds.

Science.gov (United States)

Bettinger, Holger F; Filthaus, Matthias

2010-12-21

Borylnitrenes (catBN 3a and pinBN 3b; cat = catecholato, pin = pinacolato) are reactive intermediates that show high tendency towards insertion into the C-H bonds of unactivated hydrocarbons. The present article summarizes the matrix isolation investigations that were aimed at identifying, characterizing and investigating the chemical behaviour of 3a by spectroscopic means, and of the experiments in solution and in the gas phase that were performed with 3b. Comparison with the reactivity reported for difluorovinylidene 1a in solid argon indicates that 3a shows by and large similar reactivity, but only after photochemical excitation. The derivative 3b inserts into the C-H bonds of hydrocarbon solvents in high yields and thus allows the formation of primary amines, secondary amines, or amides from "unreactive" hydrocarbons. It can also be used for generation of methylamine or methylamide from methane in the gas phase at room temperature. Remaining challenges in the chemistry of borylnitrenes are briefly summarized.

Enantioselective copper-catalyzed carboetherification of unactivated alkenes.

Science.gov (United States)

Bovino, Michael T; Liwosz, Timothy W; Kendel, Nicole E; Miller, Yan; Tyminska, Nina; Zurek, Eva; Chemler, Sherry R

2014-06-16

Chiral saturated oxygen heterocycles are important components of bioactive compounds. Cyclization of alcohols onto pendant alkenes is a direct route to their synthesis, but few catalytic enantioselective methods enabling cyclization onto unactivated alkenes exist. Herein reported is a highly efficient copper-catalyzed cyclization of γ-unsaturated pentenols which terminates in C-C bond formation, a net alkene carboetherification. Both intra- and intermolecular C-C bond formations are demonstrated, thus yielding functionalized chiral tetrahydrofurans as well as fused-ring and bridged-ring oxabicyclic products. Transition-state calculations support a cis-oxycupration stereochemistry-determining step. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Part I: A Comparative Thermal Aging Study on the Regenerability of Rh/Al2O3 and Rh/CexOy-ZrO2 as Model Catalysts for Automotive Three Way Catalysts

Directory of Open Access Journals (Sweden)

Qinghe Zheng

2015-10-01

Full Text Available The rhodium (Rh component in automotive three way catalysts (TWC experiences severe thermal deactivation during fuel shutoff, an engine mode (e.g., at downhill coasting used for enhancing fuel economy. In a subsequent switch to a slightly fuel rich condition, in situ catalyst regeneration is accomplished by reduction with H2 generated through steam reforming catalyzed by Rh0 sites. The present work reports the effects of the two processes on the activity and properties of 0.5% Rh/Al2O3 and 0.5% Rh/CexOy-ZrO2 (CZO as model catalysts for Rh-TWC. A very brief introduction of three way catalysts and system considerations is also given. During simulated fuel shutoff, catalyst deactivation is accelerated with increasing aging temperature from 800 °C to 1050 °C. Rh on a CZO support experiences less deactivation and faster regeneration than Rh on Al2O3. Catalyst characterization techniques including BET surface area, CO chemisorption, TPR, and XPS measurements were applied to examine the roles of metal-support interactions in each catalyst system. For Rh/Al2O3, strong metal-support interactions with the formation of stable rhodium aluminate (Rh(AlO2y complex dominates in fuel shutoff, leading to more difficult catalyst regeneration. For Rh/CZO, Rh sites were partially oxidized to Rh2O3 and were relatively easy to be reduced to active Rh0 during regeneration.

(3-Methylbenzonitrile-1κN-cis-tetrakis(μ-N-phenylacetamidato-1:2κ4N:O;1:2κ4O:N-dirhodium(II(Rh—Rh

Directory of Open Access Journals (Sweden)

Cassandra T. Eagle

2014-08-01

Full Text Available The complex molecule of the title compound, [Rh2{N(C6H5COCH3}4(NCC7H7], has crystallographically-imposed mirror symmetry. The four acetamide ligands bridging the dirhodium core are arranged in a 2,2-cis manner with two N atoms and two O atoms coordinating to the unique RhII atom cis to one another. The Neq—Rh—Rh—Oeq torsion angles on the acetamide bridge are 0.75 (7 and 1.99 (9°. The axial nitrile ligand completes the distorted octahedral coordination sphere of one RhII atom and shows a nonlinear coordination, with an Rh—N—C bond angle of 162.8 (5°; the N—C bond length is 1.154 (7 Å.

Rhodium-catalyzed redox-neutral coupling of phenidones with alkynes.

Science.gov (United States)

Fan, Zhoulong; Lu, Heng; Li, Wei; Geng, Kaijun; Zhang, Ao

2017-07-21

A switchable synthesis of N-substituted indole derivatives from phenidones via rhodium-catalyzed redox-neutral C-H activation has been achieved. In this protocol, we firstly disclosed that the reactivity of Rh(iii) catalysis could be enhanced through employing palladium acetate as an additive. Some representative features include external oxidant-free, applicable to terminal alkynes, short reaction time and operational simplicity. The utility of this method is further showcased by the economical synthesis of potent anticancer PARP-1 inhibitors.

Eosin Y as a Direct Hydrogen Atom Transfer Photocatalyst for the Functionalization of C-H Bonds.

Science.gov (United States)

Fan, Xuan-Zi; Rong, Jia-Wei; Wu, Hao-Lin; Zhou, Quan; Deng, Hong-Ping; Tan, Jin Da; Xue, Cheng-Wen; Wu, Li-Zhu; Tao, Hai-Rong; Wu, Jie

2018-05-02

Eosin Y, a well-known economical alternative to metal catalysts in visible-light-driven single-electron transfer-based organic transformations, can behave as an effective direct hydrogen atom transfer catalyst for C-H activation. Using the alkylation of C-H bonds with electron-deficient alkenes as a model study revealed an extremely broad substrate scope, enabling easy access to a variety of important synthons. This eosin Y-based photocatalytic hydrogen atom transfer strategy is promising for diverse functionalization of a wide range of native C-H bonds in a green and sustainable manner. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct α-C-H bond functionalization of unprotected cyclic amines

Science.gov (United States)

Chen, Weijie; Ma, Longle; Paul, Anirudra; Seidel, Daniel

2018-02-01

Cyclic amines are ubiquitous core structures of bioactive natural products and pharmaceutical drugs. Although the site-selective abstraction of C-H bonds is an attractive strategy for preparing valuable functionalized amines from their readily available parent heterocycles, this approach has largely been limited to substrates that require protection of the amine nitrogen atom. In addition, most methods rely on transition metals and are incompatible with the presence of amine N-H bonds. Here we introduce a protecting-group-free approach for the α-functionalization of cyclic secondary amines. An operationally simple one-pot procedure generates products via a process that involves intermolecular hydride transfer to generate an imine intermediate that is subsequently captured by a nucleophile, such as an alkyl or aryl lithium compound. Reactions are regioselective and stereospecific and enable the rapid preparation of bioactive amines, as exemplified by the facile synthesis of anabasine and (-)-solenopsin A.

Identification and H(D)-bond energies of C-H(D)Cl interactions in chloride-haloalkane clusters: a combined X-ray crystallographic, spectroscopic, and theoretical study.

Science.gov (United States)

Serebryanskaya, Tatiyana V; Novikov, Alexander S; Gushchin, Pavel V; Haukka, Matti; Asfin, Ruslan E; Tolstoy, Peter M; Kukushkin, Vadim Yu

2016-05-18

The cationic (1,3,5-triazapentadiene)Pt(II) complex [Pt{NH[double bond, length as m-dash]C(N(CH2)5)N(Ph)C(NH2)[double bond, length as m-dash]NPh}2]Cl2 ([]Cl2) was crystallized from four haloalkane solvents giving [][Cl2(CDCl3)4], [][Cl2(CHBr3)4], [][Cl2(CH2Cl2)2], and [][Cl2(C2H4Cl2)2] solvates that were studied by X-ray diffraction. In the crystal structures of [][Cl2(CDCl3)4] and [][Cl2(CHBr3)4], the Cl(-) ion interacts with two haloform molecules via C-DCl(-) and C-HCl(-) contacts, thus forming the negatively charged isostructural clusters [Cl(CDCl3)2](-) and [Cl(CHBr3)2](-). In the structures of [][Cl2(CH2Cl2)2] and [][Cl2(C2H4Cl2)2], cations [](2+) are linked to a 3D-network by a system of H-bondings including one formed by each Cl(-) ion with CH2Cl2 or C2H4Cl2 molecules. The lengths and energies of these H-bonds in the chloride-haloalkane clusters were analyzed by DFT calculations (M06 functional) including AIM analysis. The crystal packing noticeably affected the geometry of the clusters, and energy of C-HCl(-) hydrogen bonds ranged from 1 to 6 kcal mol(-1). An exponential correlation (R(2) > 0.98) between the calculated Cl(-)H distances and the energies of the corresponding contacts was found and used to calculate hydrogen bond energies from the experimental Cl(-)H distances. Predicted energy values (3.3-3.9 kcal mol(-1) for the [Cl(CHCl3)2](-) cluster) are in a reasonable agreement with the energy of the Cl3C-HCl(-) bond estimated using ATRFTIR spectroscopy (2.7 kcal mol(-1)).

Activity of PtSnRh/C nanoparticles for the electrooxidation of C1 and C2 alcohols

Energy Technology Data Exchange (ETDEWEB)

Teran, Freddy E. [Universite de Poitiers, IC2MP UMR CNRS 7285, ' Equipe E-lyse' , 4 rue Michel Brunet-B27, BP 633, 86022 Poitiers cedex (France); Santos, Deise M. [Departamento de Quimica, CCE-UFES, Av. Fernando Ferrari, 514, Goiabeiras-Vitoria, ES (Brazil); Ribeiro, Josimar, E-mail: josimar.ribeiro@ufes.br [Universite de Poitiers, IC2MP UMR CNRS 7285, ' Equipe E-lyse' , 4 rue Michel Brunet-B27, BP 633, 86022 Poitiers cedex (France); Departamento de Quimica, CCE-UFES, Av. Fernando Ferrari, 514, Goiabeiras-Vitoria, ES (Brazil); Kokoh, Kouakou B. [Universite de Poitiers, IC2MP UMR CNRS 7285, ' Equipe E-lyse' , 4 rue Michel Brunet-B27, BP 633, 86022 Poitiers cedex (France)

2012-07-01

A systematic investigation of alcohol adsorption and oxidation on binary and ternary electrocatalysts in acid medium was performed. Binary (PtRh) and ternary (PtRhSn) were prepared by the Pechini modified method on carbon Vulcan XC-72, and different nominal compositions were characterized by energy dispersive X-ray and X-ray diffraction (XRD) techniques. The XRD results showed that the Pt{sub 80}Rh{sub 20}/C and Pt{sub 70}Sn{sub 10}Rh{sub 20}/C electrocatalysts consisted of the Pt displaced phase, suggesting the formation of a solid solution between the metals Pt/Rh and Pt/Sn. Electrochemical investigations on these different electrode materials were carried out as a function of the electrocatalyst composition, in acid medium (0.5 mol dm{sup -3} H{sub 2}SO{sub 4}), and in the absence and presence of different alcohols (methanol, ethanol and ethylene glycol). The electrochemical results obtained at room temperature have shown that the Pt{sub 70}Sn{sub 10}Rh{sub 20}/C catalyst display better catalytic activity for alcohol oxidation compared with the binary catalyst. In situ reflectance infrared spectroscopy measurements have shown that the oxidation of alcohols mentioned produced CO{sub 2} at low potentials indicating that the materials synthesized could be used as efficient anodes in the fuel cell applications. - Highlights: Black-Right-Pointing-Pointer Pt-based catalysts were synthesized by thermal decomposition polymeric precursors. Black-Right-Pointing-Pointer Pt{sub 70}Sn{sub 10}Rh{sub 20}/C displays better catalytic activity for the oxidation of alcohols. Black-Right-Pointing-Pointer The co-catalysts tin and rhodium promote the removal of CO to CO{sub 2} at low potentials. Black-Right-Pointing-Pointer Ethylene glycol is oxidizing strongly to CO{sub 2} at low potentials. Black-Right-Pointing-Pointer Pt{sub 70}Sn{sub 10}Rh{sub 20}/C catalyst is an efficient anode material for a direct alcohol fuel cell.

Synthesis of 1,2,4-Triazoles via Oxidative Heterocyclization: Selective C-N Bond Over C-S Bond Formation.

Science.gov (United States)

Gogoi, Anupal; Guin, Srimanta; Rajamanickam, Suresh; Rout, Saroj Kumar; Patel, Bhisma K

2015-09-18

The higher propensity of C-N over C-S bond forming ability was demonstrated, through formal C-H functionalization during the construction of 4,5-disubstituted 1,2,4-triazole-3-thiones from arylidenearylthiosemicarbazides catalyzed by Cu(II). However, steric factors imparted by the o-disubstituted substrates tend to change the reaction path giving thiodiazole as the major or an exclusive product. Upon prolonging the reaction time, the in situ generated thiones are transformed to 4,5-disubstituted 1,2,4-triazoles via a desulfurization process. Two classes of heterocycles viz. 4,5-disubstituted 1,2,4-triazole-3-thiones and 4,5-disubstituted 1,2,4-triazoles can be synthesized from arylidenearylthiosemicarbazides by simply adjusting the reaction time. Desulfurization of 1,2,4-triazole-3-thiones is assisted by thiophilic Cu to provide 1,2,4-triazoles with concomitant formation of CuS and polynuclear sulfur anions as confirmed from scanning electron microscope and energy dispersive X-ray spectroscopy measurements. A one-pot synthesis of an antimicrobial compound has been successfully achieved following this strategy.

Oxidative C-H Activation Approach to Pyridone and Isoquinolone through an Iron-Catalyzed Coupling of Amides with Alkynes.

Science.gov (United States)

Matsubara, Tatsuaki; Ilies, Laurean; Nakamura, Eiichi

2016-02-04

An iron catalyst combined with a mild organic oxidant promotes both C-H bond cleavage and C-N bond formation, and forms 2-pyridones and isoquinolones from an alkene- or arylamide and an internal alkyne, respectively. An unsymmetrical alkyne gives the pyridone derivative with high regioselectivity, this could be due to the sensitivity of the reaction to steric effects because of the compact size of iron. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ligand-Enabled γ-C(sp3)–H Olefination of Amines: En Route to Pyrrolidines

Science.gov (United States)

Jiang, Heng; He, Jian; Liu, Tao

2016-01-01

Pd(II)-catalyzed olefination of γ-C(sp3)–H bonds of triflyl (Tf) and 4-nitrobenzenesulfonyl (Ns) protected amines is achieved. Subsequent aza-Wacker oxidative cyclization or conjugate addition of the olefinated intermediates provides a variety of C-2 alkylated pyrrolidines. Three pyridine- and quinoline-based ligands are developed to match different classes of amine substrates, demonstrating a rare example of ligand-enabled C(sp3)–H olefination reaction. The use of Ns protecting group to direct C(sp3)–H activation of alkyl amine is also a significant step towards practical C–H functionalizations of alkyl amines. PMID:26796676

Late metal carbene complexes generated by multiple C-H activations: examining the continuum of M=C bond reactivity.

Science.gov (United States)

Whited, Matthew T; Grubbs, Robert H

2009-10-20

Unactivated C(sp(3))-H bonds are ubiquitous in organic chemicals and hydrocarbon feedstocks. However, these resources remain largely untapped, and the development of efficient homogeneous methods for hydrocarbon functionalization by C-H activation is an attractive and unresolved challenge for synthetic chemists. Transition-metal catalysis offers an attractive possible means for achieving selective, catalytic C-H functionalization given the thermodynamically favorable nature of many desirable partial oxidation schemes and the propensity of transition-metal complexes to cleave C-H bonds. Selective C-H activation, typically by a single cleavage event to produce M-C(sp(3)) products, is possible through myriad reported transition-metal species. In contrast, several recent reports have shown that late transition metals may react with certain substrates to perform multiple C-H activations, generating M=C(sp(2)) complexes for further elaboration. In light of the rich reactivity of metal-bound carbenes, such a route could open a new manifold of reactivity for catalytic C-H functionalization, and we have targeted this strategy in our studies. In this Account, we highlight several early examples of late transition-metal complexes that have been shown to generate metal-bound carbenes by multiple C-H activations and briefly examine factors leading to the selective generation of metal carbenes through this route. Using these reports as a backdrop, we focus on the double C-H activation of ethers and amines at iridium complexes supported by Ozerov's amidophosphine PNP ligand (PNP = [N(2-P(i)Pr(2)-4-Me-C(6)H(3))(2)](-)), allowing isolation of unusual square-planar iridium(I) carbenes. These species exhibit reactivity that is distinct from the archetypal Fischer and Schrock designations. We present experimental and theoretical studies showing that, like the classical square-planar iridium(I) organometallics, these complexes are best described as nucleophilic at iridium. We discuss

Renewable Formate from C-H Bond Formation with CO2: Using Iron Carbonyl Clusters as Electrocatalysts.

Science.gov (United States)

Loewen, Natalia D; Neelakantan, Taruna V; Berben, Louise A

2017-09-19

As a society, we are heavily dependent on nonrenewable petroleum-derived fuels and chemical feedstocks. Rapid depletion of these resources and the increasingly evident negative effects of excess atmospheric CO 2 drive our efforts to discover ways of converting excess CO 2 into energy dense chemical fuels through selective C-H bond formation and using renewable energy sources to supply electrons. In this way, a carbon-neutral fuel economy might be realized. To develop a molecular or heterogeneous catalyst for C-H bond formation with CO 2 requires a fundamental understanding of how to generate metal hydrides that selectively donate H - to CO 2 , rather than recombining with H + to liberate H 2 . Our work with a unique series of water-soluble and -stable, low-valent iron electrocatalysts offers mechanistic and thermochemical insights into formate production from CO 2 . Of particular interest are the nitride- and carbide-containing clusters: [Fe 4 N(CO) 12 ] - and its derivatives and [Fe 4 C(CO) 12 ] 2- . In both aqueous and mixed solvent conditions, [Fe 4 N(CO) 12 ] - forms a reduced hydride intermediate, [H-Fe 4 N(CO) 12 ] - , through stepwise electron and proton transfers. This hydride selectively reacts with CO 2 and generates formate with >95% efficiency. The mechanism for this transformation is supported by crystallographic, cyclic voltammetry, and spectroelectrochemical (SEC) evidence. Furthermore, installation of a proton shuttle onto [Fe 4 N(CO) 12 ] - facilitates proton transfer to the active site, successfully intercepting the hydride intermediate before it reacts with CO 2 ; only H 2 is observed in this case. In contrast, isoelectronic [Fe 4 C(CO) 12 ] 2- features a concerted proton-electron transfer mechanism to form [H-Fe 4 C(CO) 12 ] 2- , which is selective for H 2 production even in the presence of CO 2 , in both aqueous and mixed solvent systems. Higher nuclearity clusters were also studied, and all are proton reduction electrocatalysts, but none

(3-Methylbenzonitrile-κNtetrakis(μ-N-phenylacetamidato-κ4N:O;κ4O:N-dirhodium(II(Rh—Rh

Directory of Open Access Journals (Sweden)

Jennie Tan

2013-12-01

Full Text Available In the title compound, [Rh2(C8H8NO4(C8H7N], the four acetamidate ligands bridging the dirhodium core are arranged in a 2,2-trans manner. One RhII atom is five-coordinate, in a distorted pyramidal geometry, while the other is six-coordinate, with a disorted octahedral geometry. For the six-coordinate RhII atom, the axial nitrile ligand shows a non-linear Rh–nitrile coordination with an Rh—N—C bond angle of 166.4 (4° and a nitrile N—C bond length of 1.138 (6 Å. Each unique RhII atom is coordinated by a trans pair of N atoms and a trans pair of O atoms from the four acetamide ligands. The Neq—Rh—Rh—Oeq torsion angles on the acetamide bridge varies between 12.55 (11 and 14.04 (8°. In the crystal, the 3-methylbenzonitrile ring shows a π–π interaction with an inversion-related equivalent [interplanar spacing = 3.360 (6 Å]. A phenyl ring on one of the acetamide ligands also has a face-to-face π–π interaction with an inversion-related equivalent [interplanar spacing = 3.416 (5 Å].

Effective oxidation of benzylic and alkane C-H bonds catalyzed by sodium o-iodobenzenesulfonate with Oxone as a terminal oxidant under phase-transfer conditions.

Science.gov (United States)

Cui, Li-Qian; Liu, Kai; Zhang, Chi

2011-04-07

Catalytic oxidation of benzylic C-H bonds could be efficiently realized using IBS as a catalyst which was generated in situ from the oxidation of sodium 2-iodobenzenesulfonate (1b) by Oxone in the presence of a phase-transfer catalyst, tetra-n-butylammonium hydrogen sulfate, in anhydrous acetonitrile at 60 °C. Various alkylbenzenes, including toluenes and ethylbenzenes, several oxygen-containing functionalities substituted alkylbenzenes, and a cyclic benzyl ether could be efficiently oxidized. And, the same reagent system of cat. 1b/Oxone/cat. n-Bu(4)NHSO(4) could be applied to the effective oxidation of alkanes as well.

Detection and function of an intramolecular disulfide bond in the pH-responsive CadC of Escherichia coli

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Dönhöfer Alexandra

2011-04-01

Full Text Available Abstract Background In an acidic and lysine-rich environment Escherichia coli induces expression of the cadBA operon which encodes CadA, the lysine decarboxylase, and CadB, the lysine/cadaverine antiporter. cadBA expression is dependent on CadC, a membrane-integrated transcriptional activator which belongs to the ToxR-like protein family. Activation of CadC requires two stimuli, lysine and low pH. Whereas lysine is detected by an interplay between CadC and the lysine-specific transporter LysP, pH alterations are sensed by CadC directly. Crystal structural analyses revealed a close proximity between two periplasmic cysteines, Cys208 and Cys272. Results Substitution of Cys208 and/or Cys272 by alanine resulted in CadC derivatives that were active in response to only one stimulus, either lysine or pH 5.8. Differential in vivo thiol trapping revealed a disulfide bond between these two residues at pH 7.6, but not at pH 5.8. When Cys208 and Cys272 were replaced by aspartate and lysine, respectively, virtually wild-type behavior was restored indicating that the disulfide bond could be mimicked by a salt bridge. Conclusion A disulfide bond was found in the periplasmic domain of CadC that supports an inactive state of CadC at pH 7.6. At pH 5.8 disulfide bond formation is prevented which transforms CadC into a semi-active state. These results provide new insights into the function of a pH sensor.

Synthesis and Characterization of Rh-Co Butterfly Clusters Capped by Functionally Substituted 1-Alkynes

Institute of Scientific and Technical Information of China (English)

朱保华; 胡斌; 张伟强; 边治国; 赵全义; 殷元骐; 孙杰

2003-01-01

By the reactions of [Rh2Co2(CO)12] 1 with functionally substituted alkyne ligands HC≡CR 2 (R = FeCp2) and 3 (R = 2-OH-C6H4COOCH2), respectively in n-hexane at room temperature, two new cluster derivatives [Rh2Co2(CO)6(μ-CO)4(μ4, η2-HC≡CR)] 4 (R = FeCp2) and 5 (R = 2-OH-C6H4COOCH2) were obtained respectively. The alkyne was inserted into the Co-Co bond of cluster 1 to give two butterfly clusters. Cluster 4 has been determined by single-crystal X-ray diffraction. Crystallographic data: C22H10Co2FeO10Rh2, Mr = 813.83, orthorhombic, space group P212121, a = 11.5318(7), b = 12.6572(7), c = 17.018(1) A。, V = 2483.9(3) A。3, Z = 4, Dc = 2.176 g/cm3, F(000) = 1568, μ = 3.233 mm-1, the final R = 0.0366 and wR = 0.0899 for 5367 observed reflections with I > 2σ(I). The two clusters have also been characterized by elemental analysis, IR and 1H-NMR spectroscopy.

Synthesis, structure and electronic configuration of [Rh{sub 6}Te{sub 8}(PPh{sub 3}){sub 6}].4C{sub 6}H{sub 6}

Energy Technology Data Exchange (ETDEWEB)

Thiele, Guenther; Balmer, Markus [Marburg Univ. (Germany). Fachbereich Chemie; Dehnen, Stefanie [Marburg Univ. (Germany). Fachbereich Chemie and Wissenschaftliches Zentrum fuer Materialwissenschaften

2016-08-01

[Rh{sub 6}Te{sub 8}(PPh{sub 3}){sub 6}].4C{sub 6}H{sub 6}, the first compound with a molecular Chevrel-type [Rh{sub 6}Te{sub 8}] cluster core has been synthesized and structurally characterized. By means of quantum chemical calculation, the close relationship of its electronic configuration to that of the lighter homologue has been demonstrated. The different crystal solvent content prevents an isostructural crystallization.

Hydrogen Production by Steam Reforming of Ethanol on Rh-Pt Catalysts: Influence of CeO2, ZrO2, and La2O3 as Supports

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Bernay Cifuentes

2015-11-01

Full Text Available CeO2-, ZrO2-, and La2O3-supported Rh-Pt catalysts were tested to assess their ability to catalyze the steam reforming of ethanol (SRE for H2 production. SRE activity tests were performed using EtOH:H2O:N2 (molar ratio 1:3:51 at a gaseous space velocity of 70,600 h−1 between 400 and 700 °C at atmospheric pressure. The SRE stability of the catalysts was tested at 700 °C for 27 h time on stream under the same conditions. RhPt/CeO2, which showed the best performance in the stability test, also produced the highest H2 yield above 600 °C, followed by RhPt/La2O3 and RhPt/ZrO2. The fresh and aged catalysts were characterized by TEM, XPS, and TGA. The higher H2 selectivity of RhPt/CeO2 was ascribed to the formation of small (~5 nm and stable particles probably consistent of Rh-Pt alloys with a Pt surface enrichment. Both metals were oxidized and acted as an almost constant active phase during the stability test owing to strong metal-support interactions, as well as the superior oxygen mobility of the support. The TGA results confirmed the absence of carbonaceous residues in all the aged catalysts.

Manganese Catalyzed Regioselective C–H Alkylation: Experiment and Computation

KAUST Repository

Wang, Chengming

2018-05-08

A new efficient manganese-catalyzed selective C2-alkylation of indoles via carbenoid insertion has been achieved. The newly developed C-H functionalization protocol provides access to diverse products and shows good functional group tolerance. Mechanistic and computational studies support the formation of a Mn(CO)3 acetate complex as the catalytically active species.

Manganese Catalyzed Regioselective C–H Alkylation: Experiment and Computation

KAUST Repository

Wang, Chengming; Maity, Bholanath; Cavallo, Luigi; Rueping, Magnus

2018-01-01

A new efficient manganese-catalyzed selective C2-alkylation of indoles via carbenoid insertion has been achieved. The newly developed C-H functionalization protocol provides access to diverse products and shows good functional group tolerance. Mechanistic and computational studies support the formation of a Mn(CO)3 acetate complex as the catalytically active species.

New Concept of C–H and C–C Bond Activation via Surface Organometallic Chemistry

KAUST Repository

Samantaray, Manoja; Dey, Raju; Kavitake, Santosh Giridhar; Basset, Jean-Marie

2015-01-01

In this chapter we describe the recent applications of well-defined oxidesupported metal alkyls/alkylidenes/alkylidynes and hydrides of group IV, V, and VI transition metals in the field of C–H and C–C bond activation. The activation of ubiquitous C

Complementation of biotransformations with chemical C-H oxidation: copper-catalyzed oxidation of tertiary amines in complex pharmaceuticals.

Science.gov (United States)

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.

Fullerene-catalyzed reduction of azo derivatives in water under UV irradiation

KAUST Repository

Guo, Yong; Li, Wengang; Yan, Jingjing; Moosa, Basem; Amad, Maan H.; Werth, Charles; Khashab, Niveen M.

2012-01-01

Metal-free fullerene (C60) was found to be an effective catalyst for the reduction of azo groups in basic aqueous solution under UV irradiation in the presence of NaBH4. Use of NaBH4 by itself is not sufficient to reduce the azo dyes without the assistance of a metal catalyst such as Pd and Ag. Experimental and theoretical results suggest that C 60 catalyzes this reaction by using its vacant orbital to accept the electron in the bonding orbital of azo dyes, which leads to the activation of the N=N bond. UV irradiation increases the ability of C60 to interact with electron-donor moieties in azo dyes. Filling a vacancy: Experimental and theoretical methods have been combined to show that C60-catalyzed reductions of azo compounds form aromatic amines under UV irradiation (see scheme). The obtained results show that C60 acts as an electron acceptor to catalyze the reduction of azo compounds, and the role of UV irradiation is to increase the ability of C60 to interact with electron-donor moieties in azo compounds. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fullerene-catalyzed reduction of azo derivatives in water under UV irradiation

KAUST Repository

Guo, Yong

2012-09-27

Metal-free fullerene (C60) was found to be an effective catalyst for the reduction of azo groups in basic aqueous solution under UV irradiation in the presence of NaBH4. Use of NaBH4 by itself is not sufficient to reduce the azo dyes without the assistance of a metal catalyst such as Pd and Ag. Experimental and theoretical results suggest that C 60 catalyzes this reaction by using its vacant orbital to accept the electron in the bonding orbital of azo dyes, which leads to the activation of the N=N bond. UV irradiation increases the ability of C60 to interact with electron-donor moieties in azo dyes. Filling a vacancy: Experimental and theoretical methods have been combined to show that C60-catalyzed reductions of azo compounds form aromatic amines under UV irradiation (see scheme). The obtained results show that C60 acts as an electron acceptor to catalyze the reduction of azo compounds, and the role of UV irradiation is to increase the ability of C60 to interact with electron-donor moieties in azo compounds. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Study of the adsorption, electronic structure and bonding of C2H4 on the FeNi(1 1 1) surface

International Nuclear Information System (INIS)

Simonetti, S.; Brizuela, G.; Juan, A.

2010-01-01

The adsorption of C 2 H 4 on the FeNi(1 1 1) alloy surface has been studied by ASED-MO tight binding calculations. The C 2 H 4 molecule presents its most stable geometry with the C=C bond axis parallel to the surface along the [1, -1, 0] direction, bonded on top Fe atom and bonded along a Fe-Fe bridge site. As a consequence, the strength of the local Fe-Fe bond decreases between 37 and 62% of its original bulk value. This bond weakening is mainly due to the new C-Fe interactions however no Fe 3 C carbide formation is evidenced on surface. The Fe-Ni and Ni-Ni superficial bonds are only slightly modified.

N-Boc amines to oxazolidinones via Pd(II)/bis-sulfoxide/Brønsted acid co-catalyzed allylic C-H oxidation.

Science.gov (United States)

Osberger, Thomas J; White, M Christina

2014-08-06

A Pd(II)/bis-sulfoxide/Brønsted acid catalyzed allylic C-H oxidation reaction for the synthesis of oxazolidinones from simple N-Boc amines is reported. A range of oxazolidinones are furnished in good yields (avg 63%) and excellent diastereoselectivities (avg 15:1) to furnish products regioisomeric from those previously obtained using allylic C-H amination reactions. Mechanistic studies suggest the role of the phosphoric acid is to furnish a Pd(II)bis-sulfoxide phosphate catalyst that promotes allylic C-H cleavage and π-allylPd functionalization with a weak, aprotic oxygen nucleophile and to assist in catalyst regeneration.

A thermodynamic description of the system Pd-Rh-H-D-T

Energy Technology Data Exchange (ETDEWEB)

Joubert, J.-M., E-mail: jean-marc.joubert@icmpe.cnrs.fr [Chimie Metallurgique des Terres Rares, Institut de Chimie et des Materiaux Paris-Est, CNRS, Universite Paris-Est, UMR 7182, 2-8 Rue Henri Dunant, F-94320 Thiais (France); Thiebaut, S. [CEA/DAM/Valduc, F-21120 Is sur Tille (France)

2011-02-15

The quinary system D-H-Pd-Rh-T has been described thermodynamically by the CALPHAD approach. Previous descriptions of the binary subsystems have been used. To model the high pressure data an equation of state for the gases D{sub 2} and T{sub 2} compatible with the CALPHAD approach has been obtained similar to that previously used for H{sub 2}. A complete literature search has been undertaken for the three ternary systems H-Pd-Rh, D-Pd-Rh and Pd-Rh-T and the most significant experimental data have been selected for a thermodynamic assessment of these systems. In order to complement the available data, pressure-composition curves have been measured at different temperatures for the two last systems in the present work. Calculations and optimization of the system under para-equilibrium conditions, i.e. in pseudo-binary systems (Pd,Rh)-H, (Pd,Rh)-D or (Pd,Rh)-T, have been achieved using a pseudo-atom describing the Pd-Rh solid solution. This special method allows the presence of a miscibility gap in the binary metallic system to be dealt with. We show that a simple combination of the binary systems alone is unable to properly describe these ternary systems and that ternary interaction parameters have to be introduced. The binary and ternary systems may then be combined to perform calculations in the quinary D-H-Pd-Rh-T system. It is believed that extrapolation in systems containing different isotopes are fairly accurate provided that the so-called Toop model is used.

Forging C-C Bonds Through Decarbonylation of Aryl Ketones.

Science.gov (United States)

Somerville, Rosie J; Martin, Ruben

2017-06-06

The ability of nickel to cleave strong σ-bonds is again in the spotlight after a recent report that demonstrates the feasibility of using nickel complexes to promote decarbonylation of diaryl ketones. This transformation involves the cleavage of two strong C-C(O) bonds and avoids the use of noble metals, hence reinforcing the potential of decarbonylation as a technique for forging C-C bonds. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Science.gov (United States)

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. Copyright © 2013 Wiley Periodicals, Inc.

Manganese-Catalyzed Aminomethylation of Aromatic Compounds with Methanol as a Sustainable C1 Building Block.

Science.gov (United States)

Mastalir, Matthias; Pittenauer, Ernst; Allmaier, Günter; Kirchner, Karl

2017-07-05

This study represents the first example of a manganese-catalyzed environmentally benign, practical three-component aminomethylation of activated aromatic compounds including naphtols, phenols, pyridines, indoles, carbazoles, and thiophenes in combination with amines and MeOH as a C1 source. These reactions proceed with high atom efficiency via a sequence of dehydrogenation and condensation steps which give rise to selective C-C and C-N bond formations, thereby releasing hydrogen and water. A well-defined hydride Mn(I) PNP pincer complex, recently developed in our laboratory, catalyzes this process in a very efficient way, and a total of 28 different aminomethylated products were synthesized and isolated yields of up to 91%. In a preliminary study, a related Fe(II) PNP pincer complex was shown to catalyze the methylation of 2-naphtol rather than its aminomethylation displaying again the divergent behavior of isoelectronic Mn(I) and Fe(II) PNP pincer systems.

Synthesis of Polycyclic Ring Systems Using Transition Metal Catalyzed Cyclizations of Diazo Alkynyl Ketones

Directory of Open Access Journals (Sweden)

Albert Padwa

2000-12-01

Full Text Available The rhodium(II-catalyzed reaction of α-diazo ketones bearing tethered alkyne units represents a new and useful method for the construction of a variety of substituted cyclopentenones. The process proceeds by addition of the rhodium-stabilized carbenoid onto the acetylenic π-bond to give a vinyl carbenoid intermediate. The resulting rhodium complex undergoes a wide assortment of reactions including cyclopropanation, 1,2-hydrogen migration, CH-insertion, addition to tethered alkynes and ylide formation. When 2-alkynyl-2-diazo-3-oxobutanoates were treated with a Rh(II-catalyst, furo[3,4-c]furans were formed in excellent yield.

Direct Vinylation of Alcohols or Aldehydes Employing Alkynes as Vinyl Donors: A Ruthenium Catalyzed C-C Bond Forming Transfer Hydrogenation

Science.gov (United States)

Patman, Ryan L.; Chaulagain, Mani Raj; Williams, Vanessa M.; Krische, Michael J.

2011-01-01

Under the conditions of ruthenium catalyzed transfer hydrogenation, 2-butyne couples to benzylic and aliphatic alcohols 1a–1i to furnish allylic alcohols 2a–2i, constituting a direct C-H vinylation of alcohols employing alkynes as vinyl donors. Under related transfer hydrogenation conditions employing formic acid as terminal reductant, 2-butyne couples to aldehydes 4a, 4b, and 4e to furnish identical products of carbonyl vinylation 2a, 2b, and 2e. Thus, carbonyl vinylation is achieved from the alcohol or the aldehyde oxidation level in the absence of any stoichiometric metallic reagents. Nonsymmetric alkynes 6a–6c couple efficiently to aldehyde 4b to provide allylic alcohols 2m–2o as single regioisomers. Acetylenic aldehyde 7a engages in efficient intramolecular coupling to deliver cyclic allylic alcohol 8a. PMID:19173651

Palladium(II)-Catalyzed meta-C-H Olefination: Constructing Multisubstituted Arenes through Homo-Diolefination and Sequential Hetero-Diolefination.

Science.gov (United States)

Bera, Milan; Maji, Arun; Sahoo, Santosh K; Maiti, Debabrata

2015-07-13

Divinylbenzene derivatives represent an important class of molecular building blocks in organic chemistry and materials science. Reported herein is the palladium-catalyzed synthesis of divinylbenzenes by meta-C-H olefination of sulfone-based arenes. Successful sequential olefinations in a position-selective manner provided a novel route for the synthesis of hetero-dialkenylated products, which are difficult to access using conventional methods. Additionally, 1,3,5-trialkenylated compounds can be generated upon successful removal of the directing group. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ir-catalyzed C-H silylations of phenyldeazapurines

Czech Academy of Sciences Publication Activity Database

Sabat, Nazarii; Poštová Slavětínská, Lenka; Hocek, Michal

2015-01-01

Roč. 56, č. 49 (2015), s. 6860-6862 ISSN 0040-4039 Institutional support: RVO:61388963 Keywords : C-H silylation * deazapurines * iridium catalysis * C-H activations Subject RIV: CC - Organic Chemistry Impact factor: 2.347, year: 2015

Pyridine synthesis by reactions of allyl amines and alkynes proceeding through a Cu(OAc)2 oxidation and Rh(III)-catalyzed N-annulation sequence.

Science.gov (United States)

Kim, Dong-Su; Park, Jung-Woo; Jun, Chul-Ho

2012-11-28

A new methodology has been developed for the synthesis of pyridines from allyl amines and alkynes, which involves sequential Cu(II)-promoted dehydrogenation of the allylamine and Rh(III)-catalyzed N-annulation of the resulting α,β-unsaturated imine and alkyne.

Copper(II)-catalyzed electrophilic amination of quinoline N-oxides with O-benzoyl hydroxylamines.

Science.gov (United States)

Li, Gang; Jia, Chunqi; Sun, Kai; Lv, Yunhe; Zhao, Feng; Zhou, Kexiao; Wu, Hankui

2015-03-21

Copper acetate-catalyzed C-H bond functionalization amination of quinoline N-oxides was achieved using O-benzoyl hydroxylamine as an electrophilic amination reagent, thereby affording the desired products in moderate to excellent yields. Electrophilic amination can also be performed in good yield on a gram scale.

Recent advances in the chemistry of Rh carbenoids: multicomponent reactions of diazocarbonyl compounds

International Nuclear Information System (INIS)

Medvedev, J J; Nikolaev, V A

2015-01-01

Multicomponent reactions of diazo compounds catalyzed by Rh II complexes become a powerful tool for organic synthesis. They enable three- or four-step processes to be carried out as one-pot procedures (actually as one step) with high stereoselectivity to give complex organic molecules, including biologically active compounds. This review addresses recent results in the chemistry of Rh-catalyzed multicomponent reactions of diazocarbonyl compounds with the intermediate formation of N-, O- and C=O–ylides. The diastereo- and enantioselectivity of these reactions and the possibility of using various co-catalysts to increase the efficiency of the processes under consideration are discussed. The bibliography includes 120 references

Synthesis and growth mechanism of Fe-catalyzed carbon nanotubes by plasma-enhanced chemical vapor deposition

International Nuclear Information System (INIS)

Jiang Jun; Feng Tao; Cheng Xinhong; Dai Lijuan; Cao Gongbai; Jiang Bingyao; Wang Xi; Liu Xianghuai; Zou Shichang

2006-01-01

Plasma-enhanced chemical vapor deposition (PECVD) was used to grow Fe-catalyzed carbon nanotubes (CNTs). The nanotubes had a uniform diameter in the range of about 10-20 nm. A base growth mode was responsible for the CNTs growth using a mixture of H 2 (60 sccm) and C 2 H 2 (15 sccm). For a mixture of H 2 (100 sccm) and C 2 H 2 (25 sccm), a complicated growth mechanism took place involving both the base growth and the tip growth. X-ray photoelectron spectroscopy measurements revealed that the grown CNTs contained C-H covalent bonds and Fe-C bonds located at the interface between them and the substrates. The factors determining the growth mechanism of CNTs are discussed and their growth mechanisms with the different gas ratios are suggested

Tunable, Chemo- and Site-Selective Nitrene Transfer Reactions through the Rational Design of Silver(I) Catalysts.

Science.gov (United States)

Alderson, Juliet M; Corbin, Joshua R; Schomaker, Jennifer M

2017-09-19

Carbon-nitrogen (C-N) bonds are ubiquitous in pharmaceuticals, agrochemicals, diverse bioactive natural products, and ligands for transition metal catalysts. An effective strategy for introducing a new C-N bond into a molecule is through transition metal-catalyzed nitrene transfer chemistry. In these reactions, a metal-supported nitrene can either add across a C═C bond to form an aziridine or insert into a C-H bond to furnish the corresponding amine. Typical catalysts for nitrene transfer include Rh 2 L n and Ru 2 L n complexes supported by bridging carboxylate and related ligands, as well as complexes based on Cu, Co, Ir, Fe, and Mn supported by porphyrins and related ligands. A limitation of metal-catalyzed nitrene transfer is the ability to predictably select which specific site will undergo amination in the presence of multiple reactive groups; thus, many reactions rely primarily on substrate control. Achieving true catalyst-control over nitrene transfer would open up exciting possibilities for flexible installation of new C-N bonds into hydrocarbons, natural product-inspired scaffolds, existing pharmaceuticals or biorenewable building blocks. Silver-catalyzed nitrene transfer enables flexible control over the position at which a new C-N bond is introduced. Ag(I) supported by simple N-donor ligands accommodates a diverse range of coordination geometries, from linear to tetrahedral to seesaw, enabling the electronic and steric parameters of the catalyst to be tuned independently. In addition, the ligand, Ag salt counteranion, Ag/ligand ratio and the solvent all influence the fluxional and dynamic behavior of Ag(I) complexes in solution. Understanding the interplay of these parameters to manipulate the behavior of Ag-nitrenes in a predictable manner is a key design feature of our work. In this Account, we describe successful applications of a variety of design principles to tunable, Ag-catalyzed aminations, including (1) changing Ag/ligand ratios to influence

13C NMR spectra and bonding situation of the B-C bond in alkynylboranes

International Nuclear Information System (INIS)

Yamamoto, Yoshinori; Moritani, Ichiro

1975-01-01

13 C NMR spectra of boron substituted alkynes reveal that the β-carbon is deshielded by ca. 21 ppm by a B(O-n-C 4 H 9 ) 2 group. This clearly indicates the presence of a B-C π-bonding in alkynylboranes. (auth.)

Oxidative Olefination of Anilides with Unactivated Alkenes Catalyzed by an (Electron-Deficient η(5) -Cyclopentadienyl)Rhodium(III) Complex Under Ambient Conditions.

Science.gov (United States)

Takahama, Yuji; Shibata, Yu; Tanaka, Ken

2015-06-15

The oxidative olefination of sp(2) C-H bonds of anilides with both activated and unactivated alkenes using an (electron-deficient η(5) -cyclopentadienyl)rhodium(III) complex is reported. In contrast to reactions using this electron-deficient rhodium(III) catalyst, [Cp*RhCl2 ]2 showed no activity against olefination with unactivated alkenes. In addition, the deuterium kinetic isotope effect (DKIE) study revealed that the C-H bond cleavage step is thought to be the turnover-limiting step. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

UV-light promoted C-H bond activation of benzene and fluorobenzenes by an iridium(i) pincer complex.

Science.gov (United States)

Hauser, Simone A; Emerson-King, Jack; Habershon, Scott; Chaplin, Adrian B

2017-03-28

Iridium(i) carbonyl complex [Ir(2,6-(P t Bu 2 CH 2 ) 2 C 6 H 3 )(CO)] undergoes reversible C-H bond activation of benzene and a series of fluorobenzenes on UV irradiation. Exclusive ortho-selectivity is observed in reactions of fluorobenzene and 1,2-difluorobenzene.

Rhodium(III)-Catalyzed ortho-Alkylation of Phenoxy Substrates with Diazo Compounds via C-H Activation: A Case of Decarboxylative Pyrimidine/Pyridine Migratory Cyclization Rather than Removal of Pyrimidine/Pyridine Directing Group.

Science.gov (United States)

Ravi, Manjula; Allu, Srinivasarao; Swamy, K C Kumara

2017-03-03

An efficient Rh(III)-catalyzed ortho-alkylation of phenoxy substrates with diazo compounds has been achieved for the first time using pyrimidine or pyridine as the directing group. Furthermore, bis-alkylation has also been achieved using para-substituted phenoxypyrimidine and 3 mol equiv of the diazo ester. The ortho-alkylated derivatives of phenoxy products possessing the ester functionality undergo decarboxylative pyrimidine/pyridine migratory cyclization (rather than deprotection of pyrimidine/pyridine group) using 20% NaOEt in EtOH affording a novel class of 3-(pyrimidin-2(1H)-ylidene)benzofuran-2(3H)-ones and 6-methyl-3-(pyridin-2(1H)-ylidene)benzofuran-2(3H)-one. The ortho-alkylated phenoxypyridine possessing ester functionality also undergoes decarboxylative pyridine migratory cyclization using MeOTf/NaOMe in toluene providing 6-methyl-3-(1-methylpyridin-2(1H)-ylidene)benzofuran-2(3H)-one.

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.

Science.gov (United States)

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. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

UV photolysis of 4-iodo-, 4-bromo-, and 4-chlorophenol: competition between C-Y (Y = halogen) and O-H bond fission.

Science.gov (United States)

Sage, Alan G; Oliver, Thomas A A; King, Graeme A; Murdock, Daniel; Harvey, Jeremy N; Ashfold, Michael N R

2013-04-28

The wavelength dependences of C-Y and O-H bond fission following ultraviolet photoexcitation of 4-halophenols (4-YPhOH) have been investigated using a combination of velocity map imaging, H Rydberg atom photofragment translational spectroscopy, and high level spin-orbit resolved electronic structure calculations, revealing a systematic evolution in fragmentation behaviour across the series Y = I, Br, Cl (and F). All undergo O-H bond fission following excitation at wavelengths λ ≲ 240 nm, on repulsive ((n∕π)σ∗) potential energy surfaces (PESs), yielding fast H atoms with mean kinetic energies ∼11,000 cm(-1). For Y = I and Br, this process occurs in competition with prompt C-I and C-Br bond cleavage on another (n∕π)σ∗ PES, but no Cl∕Cl∗ products unambiguously attributable to one photon induced C-Cl bond fission are observed from 4-ClPhOH. Differences in fragmentation behaviour at longer excitation wavelengths are more marked. Prompt C-I bond fission is observed following excitation of 4-IPhOH at all λ ≤ 330 nm; the wavelength dependent trends in I∕I∗ product branching ratio, kinetic energy release, and recoil anisotropy suggest that (with regard to C-I bond fission) 4-IPhOH behaves like a mildly perturbed iodobenzene. Br atoms are observed when exciting 4-BrPhOH at long wavelengths also, but their velocity distributions suggest that dissociation occurs after internal conversion to the ground state. O-H bond fission, by tunnelling (as in phenol), is observed only in the cases of 4-FPhOH and, more weakly, 4-ClPhOH. These observed differences in behaviour can be understood given due recognition of (i) the differences in the vertical excitation energies of the C-Y centred (n∕π)σ∗ potentials across the series Y = I bond strength, cf. that of the rival O-H bond, and (ii) the much increased spin-orbit coupling in, particularly, 4-IPhOH. The present results provide (another) reminder of the risks inherent in extrapolating photochemical

Experimental investigation of air relative humidity (RH) cycling tests on MEA/cell aging in PEMFC. Pt. II. Study of low RH cycling test with air RH at 62%/0%

Energy Technology Data Exchange (ETDEWEB)

Huang, B.T.; Chatillon, Y.; Bonnet, C.; Lapicque, F. [Laboratoire Reactions et Genie des Procedes, CNRS-Nancy University, Nancy (France); Leclerc, S. [Laboratoire d' Energetique et de Mecanique Theorique et Appliquee, CNRS-Nancy University, Vandoeuvre-les-Nancy (France); Hinaje, M.; Rael, S. [Groupe de Recherche en Electrotechnique et Electronique de Nancy, Nancy University, Vandoeuvre-les-Nancy (France)

2012-06-15

The effect of low relative humidity (RH) cycling (RH{sub C} 62%/0%) on the degradation mechanisms of a single proton exchange membrane fuel cell (5 x 5 cm{sup 2}) was investigated and compared to a cell operated at constant humidification (RH{sub C} = 62%). The overall cell performance loss was near 33 {mu}V h{sup -1}, which is greater than the voltage decay under constant RH condition near 3 {mu}V h{sup -1}. The electroactive surface was reduced but to an acceptable level. Impedance spectroscopy revealed that the ohmic and charge transfer resistances were reduced by the likely improved hydration of the ionomeric layer at the catalyst due to hydrogen crossover. This was so important that H{sub 2} starvation was finally responsible for the collapse of the cell after 650 h. Transmission electron microscopy showed occurrence of various phenomena, e.g., bubbles and pinholes formation in the membrane due to local overheat from hydrogen combustion at the cathode, and thickness reduction of catalytic layers. The water up take obtained by {sup 1}H NMR within the membrane electrode assembly (MEA) after low RH cycling reduced by 24% compared to a fresh MEA. Observations are also compared to those obtained at high RH cycling (RH{sub C} 62%/100%) presented in Part I of this study [1]. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Competition between weak OH···π and CH··O hydrogen bonds: THz spectroscopy of the C₂H₂—H₂O and C₂H₄—H₂O complexes

DEFF Research Database (Denmark)

Andersen, Jonas; Heimdal, Jimmy; Nelander, B.

2017-01-01

-bonded configuration with the H2O subunit acting as the hydrogen bond donor to the π-cloud of C2H4. A (semi)-empirical value for the change of vibrational zero-point energy of 4.0–4.1 kJ mol−1 is proposed and the combination with quantum chemical calculations at the CCSD(T)-F12b/aug-cc-pVQZ level provides a reliable....... The present findings demonstrate that the relative stability of the weak hydrogen bond motifs is not entirely rooted in differences of electronic energy but also to a large extent by differences in the vibrational zero-point energy contributions arising from the class of large-amplitude intermolecular modes....... estimate of 7.1 ± 0.3 kJ mol−1 for the dissociation energy D0 of the C2H4—H2O complex. In addition, tentative assignments for the two strongly infrared active OH librational modes of the ternary C2H4—HOH—C2H4 complex having H2O as a doubly OH⋯π hydrogen bond donor are proposed at 213.6 and 222.3 cm−1...

In situ generation of nitrilium from nitrile ylide and the subsequent Mumm rearrangement: copper-catalyzed synthesis of unsymmetrical diacylglycine esters.

Science.gov (United States)

Chen, Jijun; Shao, Ying; Ma, Liang; Ma, Meihua; Wan, Xiaobing

2016-12-07

A novel in situ generation of nitrilium from a nitrile ylide and the subsequent Mumm rearrangement of carboxylic acid, nitrile, and diazo compounds gave various unsymmetrical diacylglycine esters in moderate to high yields. This copper-catalyzed cascade reaction enables one-pot generation of two C-N bonds, one C[double bond, length as m-dash]O bond, and one C-H bond, with nitrogen as the only byproduct. The reaction has a broad functional-group tolerance, is rapid, easily scales up to the 100 mmol scale, and is insensitive to air and moisture.

Highly Enantioselective Construction of Tertiary Thioethers and Alcohols via Phosphine-Catalyzed Asymmetric γ-Addition reactions of 5H-Thiazol-4-ones and 5H-Oxazol-4-ones: Scope and Mechanistic Understandings

KAUST Repository

Wang, Tianli

2015-06-02

Phosphine-catalyzed highly enantioselective γ-additions of 5H-thiazol-4-ones and 5H-oxazol-4-ones to allenoates have been developed for the first time. With the employment of amino-acid derived bifunctional phosphines, a wide range of substituted 5H-thiazol-4-one and 5H-oxazol-4-one derivatives bearing heteroarom (S or O)-containing tertiary chiral centers were constructed in high yields and excellent enantioselectivities. The reported method provides a facile access to enantioenriched tertiary thioether/alcohols. The mechanism of γ-addition reaction was investigated by performing DFT calculations, and the hydrogen bonding interactions between the Brønsted acid moiety of the phosphine catalysts and the “C=O” unit of donor molecules were shown to be crucial in asymmetric induction.

Highly Enantioselective Construction of Tertiary Thioethers and Alcohols via Phosphine-Catalyzed Asymmetric γ-Addition reactions of 5H-Thiazol-4-ones and 5H-Oxazol-4-ones: Scope and Mechanistic Understandings

KAUST Repository

Wang, Tianli; Yu, Zhaoyuan; Hoon, Ding Long; Huang, Kuo-Wei; Lan, Yu; Lu, Yixin

2015-01-01

Phosphine-catalyzed highly enantioselective γ-additions of 5H-thiazol-4-ones and 5H-oxazol-4-ones to allenoates have been developed for the first time. With the employment of amino-acid derived bifunctional phosphines, a wide range of substituted 5H-thiazol-4-one and 5H-oxazol-4-one derivatives bearing heteroarom (S or O)-containing tertiary chiral centers were constructed in high yields and excellent enantioselectivities. The reported method provides a facile access to enantioenriched tertiary thioether/alcohols. The mechanism of γ-addition reaction was investigated by performing DFT calculations, and the hydrogen bonding interactions between the Brønsted acid moiety of the phosphine catalysts and the “C=O” unit of donor molecules were shown to be crucial in asymmetric induction.

1,4-Iron Migration for Expedient Allene Annulations through Iron-Catalyzed C-H/N-H/C-O/C-H Functionalizations.

Science.gov (United States)

Mo, Jiayu; Müller, Thomas; Oliveira, João C A; Ackermann, Lutz

2018-06-25

C-H activation bears great potential for enabling sustainable molecular syntheses in a step- and atom-economical manner, with major advances having been realized with precious 4d and 5d transition metals. In contrast, we employed earth abundant, nontoxic iron catalysts for versatile allene annulations through a unique C-H/N-H/C-O/C-H functionalization sequence. The powerful iron catalysis occurred under external-oxidant-free conditions even at room temperature, while detailed mechanistic studies revealed an unprecedented 1,4-iron migration regime for facile C-H activations. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrooxidative Rhodium-Catalyzed C-H/C-H Activation: Electricity as Oxidant for Cross-Dehydrogenative Alkenylation.

Science.gov (United States)

Qiu, Youai; Kong, Wei-Jun; Struwe, Julia; Sauermann, Nicolas; Rogge, Torben; Scheremetjew, Alexej; Ackermann, Lutz

2018-04-06

Rhodium(III) catalysis has enabled a plethora of oxidative C-H functionalizations, which predominantly employ stoichiometric amounts of toxic and/or expensive metal oxidants. In contrast, we describe the first electrochemical C-H activation by rhodium catalysis that avoids hazardous chemical oxidants. Thus, environmentally-benign twofold C-H/C-H functionalizations were accomplished with weakly-coordinating benzoic acids and benzamides, employing electricity as the terminal oxidant with H2 as the sole byproduct. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nonperfect synchronization of bond-forming and bond-rupturing processes in the reaction H + H2 → H2 + H

International Nuclear Information System (INIS)

Chandra, A.K.; Rao, V.S.

1996-01-01

The simplest prototypical hydrogen transfer reaction, i.e., H + H 2 → H 2 + H, is studied by the quantum-mechanical ab initio methods. Results reveal that during this reaction free valence which almost equals the square of the spin density develops on the migrating hydrogen atom. Bond orders are calculated using Mayer's formalism. Both the variations of bond orders and bond lengths along the reaction path are examined. This analysis reveals that the bond formation and bond cleavage processes in this reaction are not perfectly synchronous. The bond clevage process is slightly more advanced on the reaction path. 38 refs., 6 figs., 2 tabs

Um estudo teórico de propriedades moleculares em complexos de hidrogênio trimoleculares C2H4···2HF, C2H2···2HF e C3h6···2HF A theoretical study of molecular properties of C2H4···2HF, C2H2···2HF AND C3H6···2HF trimolecular hydrogen-bonded complexes

Directory of Open Access Journals (Sweden)

Boaz G. Oliveira

2008-01-01

Full Text Available We present a theoretical study of molecular properties in C2H4···2HF, C2H2···2HF and C3H6···2HF trimolecular hydrogen-bonded complexes. From B3LYP/6-311++G(d,p calculations, the most important structural deformations are related to the C=C (C2H4, C≡C (C2H2, C-C (C3H6 and HF bond lengths. According to the Bader's atoms in molecules and CHELPG calculations, it was identified a tertiary interaction between the fluorine atom of the second hydrofluoric acid molecule and hydrogen atoms of the ethylene and acetylene within the C2H4···2HF and C2H2···2HF complexes, respectively. Additionally, the evaluation of the infrared spectrum characterized the new vibrational modes and bathochromic effect of the HF molecules.

Preparation of Benzo[c]carbazol-6-amines via Manganese-Catalyzed Enaminylation of 1-(Pyrimidin-2-yl)-1H-indoles with Ketenimines and Subsequent Oxidative Cyclization.

Science.gov (United States)

Zhou, Xiaorong; Li, Zhenmin; Zhang, Zhiyin; Lu, Ping; Wang, Yanguang

2018-03-02

Manganese-catalyzed C 2 -H enaminylation of 1-(pyrimidin-2-yl)-1H-indoles with ketenimines is reported. The reaction provided 2-enaminylated indole derivatives in moderate to excellent yields with a broad substrate scope. A migration of the directing group pyrimidinyl occurred during this process. The synthesized 2-enaminyl indoles could be conveniently converted into 5-aryl-7H-benzo[c]carbazol-6-amines.

High activity of cubic PtRh alloys supported on graphene towards ethanol electrooxidation.

Science.gov (United States)

Rao, Lu; Jiang, Yan-Xia; Zhang, Bin-Wei; Cai, Yuan-Rong; Sun, Shi-Gang

2014-07-21

Cubic PtRh alloys supported on graphene (PtxRhy/GN) with different atomic ratio of Pt and Rh were directly synthesized for the first time using the modified polyol method with Br(-) for the shape-directing agents. The process didn't use surface-capping agents such as PVP that easily occupy the active sites of electrocatalysts and are difficult to remove. Graphene is the key factor for cubic shape besides Br(-) and keeping catalysts high-dispersed. The X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to characterize the structure and morphology of these electrocatalysts. The results showed that they were composed of homogeneous cubic PtRh alloys. Traditional electrochemical methods, such as cyclic voltammetry and chronoamperometry, were used to investigate the electrocatalytic properties of PtxRhy/GN towards ethanol electrooxidation. It can be seen that PtxRhy/GN with all atomic ratios exhibited high catalytic activity, and the most active one has a composition with Pt : Rh = 9 : 1 atomic ratio. Electrochemical in situ FTIR spectroscopy was used to evaluate the cleavage of C-C bond in ethanol at room temperature in acidic solutions, the results illustrated that Rh in an alloy can promote the split of C-C bond in ethanol, and the alloy catalyst with atomic ratio Pt : Rh = 1 : 1 showed obviously better performance for the C-C bond breaking in ethanol and higher selectivity for the enhanced activity of ethanol complete oxidation to CO2 than alloys with other ratios of Pt and Rh. The investigation indicates that high activity of PtxRhy/GN electrocatalyst towards ethanol oxidation is due to the specific shape of alloys and the synergistic effect of two metal elements as well as graphene support.

Measurement of 2J(H,C)- and 3J(H,C)-coupling constants by α/β selective HC(C)H-TOCSY

International Nuclear Information System (INIS)

Duchardt, Elke; Richter, Christian; Reif, Bernd; Glaser, Steffen J.; Engels, Joachim W.; Griesinger, Christian; Schwalbe, Harald

2001-01-01

A new heteronuclear NMR pulse sequence for the measurement of n J(C,H) coupling constants, the α/βselective HC(C)H-TOCSY, is described. It is shown that the S 3 E 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 13 C. Application of the α/β selective HC(C)H-TOCSY to a 10nt RNA tetraloop 5'-CGCUUUUGCG-3', in which the four uridine residues are 13 C 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

Ligand-Controlled Chemoselective C(acyl)–O Bond vs C(aryl)–C Bond Activation of Aromatic Esters in Nickel Catalyzed C(sp2)–C(sp3) Cross-Couplings

KAUST Repository

Chatupheeraphat, Adisak; Liao, Hsuan-Hung; Srimontree, Watchara; Guo, Lin; Minenkov, Yury; Poater, Albert; Cavallo, Luigi; Rueping, Magnus

2018-01-01

step helped rationalizing this intriguing reaction chemoselectivity: whereas nickel complexes with bidentate ligands favor the C(aryl)-C bond cleavage in the oxidative addition step leading to the alkylated product via a decarbonylative process, nickel

Molecularly Tuning the Radicaloid N-H···O═C Hydrogen Bond.

Science.gov (United States)

Lu, Norman; Chung, Wei-Cheng; Ley, Rebecca M; Lin, Kwan-Yu; Francisco, Joseph S; Negishi, Ei-Ichi

2016-03-03

Substituent effects on the open shell N-H···O═C hydrogen-bond has never been reported. This study examines how 12 functional groups composed of electron donating groups (EDG), halogen atoms and electron withdrawing groups (EWG) affect the N-H···O═C hydrogen-bond properties in a six-membered cyclic model system of O═C(Y)-CH═C(X)N-H. It is found that group effects on this open shell H-bonding system are significant and have predictive trends when X = H and Y is varied. When Y is an EDG, the N-H···O═C hydrogen-bond is strengthened; and when Y is an EWG, the bond is weakened; whereas the variation in electronic properties of X group do not exhibit a significant impact upon the hydrogen bond strength. The structural impact of the stronger N-H···O═C hydrogen-bond are (1) shorter H and O distance, r(H···O) and (2) a longer N-H bond length, r(NH). The stronger N-H···O═C hydrogen-bond also acts to pull the H and O in toward one another which has an effect on the bond angles. Our findings show that there is a linear relationship between hydrogen-bond angle and N-H···O═C hydrogen-bond energy in this unusual H-bonding system. In addition, there is a linear correlation of the r(H···O) and the hydrogen bond energy. A short r(H···O) distance corresponds to a large hydrogen bond energy when Y is varied. The observed trends and findings have been validated using three different methods (UB3LYP, M06-2X, and UMP2) with two different basis sets.

C-H Bond Functionalization via Hydride Transfer: Formation of α-Arylated Piperidines and 1,2,3,4-Tetrahydroisoquinolines via Stereoselective Intramolecular Amination of Benzylic C-H Bonds

OpenAIRE

Vadola, Paul A.; Carrera, Ignacio; Sames, Dalibor

2012-01-01

We here report a study of the intramolecular amination of sp3 C-H bonds via the hydride transfer cyclization of N-tosylimines (HT-amination). In this transformation, 5-aryl-aldehydes are subjected to N-toluenesulfonamide in the presence of BF3•OEt2 to effect imine formation and HT-cyclization, leading to 2-aryl-piperidines and 3-aryl-1,2,3,4-tetrahydroisoquinolines in a one-pot procedure. We examined the reactivity of a range of aldehyde substrates as a function of their conformational flexib...

Experimental investigation of air relative humidity (RH) cycling tests on MEA/cell aging in PEMFC. Pt. I. Study of high RH cycling test with air RH at 62%/100%

Energy Technology Data Exchange (ETDEWEB)

Huang, B.T.; Chatillon, Y.; Bonnet, C.; Lapicque, F. [Laboratoire Reactions et Genie des Procedes, CNRS-Nancy University, Nancy (France); Leclerc, S. [Laboratoire d' Energetique et de Mecanique Theorique et Appliquee, CNRS-Nancy University, Vandoeuvre-les-Nancy (France); Hinaje, M.; Rael, S. [Groupe de Recherche en Electrotechnique et Electronique de Nancy, CNRS-Nancy University, Vandoeuvre-les-Nancy (France)

2012-06-15

The effect of high air relative humidity (RH) cycling (RH{sub C} 62%/100%) on the degradation mechanisms of a single (5 x 5 cm{sup 2}) proton exchange membrane fuel cells was investigated. The cell performance was compared to a cell operated at constant humidification (RH{sub C} = 62%). Runs were conducted over approximately 1,500 h at 0.3 A cm{sup -2}. The overall loss in cell performance for the high RH cycling test was 12 {mu}V h{sup -1} whereas it was at 3 {mu}V h{sup -1} under constant humidification. Impedance spectroscopy reveals that the ohmic and charge transfer resistances were little modified in both runs. H{sub 2} crossover measurement indicated that both high RH cycling and constant RH test did not promote serious effect on gas permeability. The electroactive surface loss for anode and cathode during high air RH cycling was more significant than at constant RH operation. The water uptake determined by {sup 1}H nuclear magnetic resonance within the membrane electrode assembly (MEA) after high RH cycling was reduced by 12% in comparison with a fresh MEA. Transmission electron microscopy showed bubbles and pinholes formation in the membrane, catalyst particles agglomeration (also observed by X-ray diffraction), catalyst particles migration in the membrane and thickness reduction of the catalytic layers. Scanning electron microscopy was conducted to observe the changes in morphology of gas diffusion layers after the runs. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Metal-catalyzed living radical polymerization and radical polyaddition for precision polymer synthesis

Energy Technology Data Exchange (ETDEWEB)

Mizutani, M; Satoh, K [Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Kamigaito, M, E-mail: kamigait@apchem.nagoya-u.ac.j

2009-08-01

The metal-catalyzed radical addition reaction can be evolved into two different polymerization mechanisms, i.e.; chain- and step-growth polymerizations, while both the polymerizations are based on the same metal-catalyzed radical formation reaction. The former is a widely employed metal-catalyzed living radical polymerization or atom transfer radical polymerization of common vinyl monomers, and the latter is a novel metal-catalyzed radical polyaddition of designed monomer with an unconjugated C=C double bond and a reactive C-Cl bond in one molecule. The simultaneous ruthenium-catalyzed living radical polymerization of methyl acrylate and radical polyaddition of 3-butenyl 2-chloropropionate was achieved with Ru(Cp*)Cl(PPh{sub 3}){sub 2} to afford the controlled polymers, in which the homopolymer segments with the controlled chain length were connected by the ester linkage.

Mechanistic insight into benzenethiol catalyzed amide bond formations from thioesters and primary amines

DEFF Research Database (Denmark)

Stuhr-Hansen, Nicolai; Bork, Nicolai; Strømgaard, Kristian

2014-01-01

The influence of arylthiols on cysteine-free ligation, i.e. the reaction between an alkyl thioester and a primary amine forming an amide bond, was studied in a polar aprotic solvent. We reacted the ethylthioester of hippuric acid with cyclohexylamine in the absence or presence of various quantities...... of thiophenol (PhSH) in a slurry of disodium hydrogen phosphate in dry DMF. Quantitative conversions into the resulting amide were observed within a few hours in the presence of equimolar amounts of thiophenol. Ab initio calculations showed that the reaction mechanism in DMF is similar to the well-known aqueous...... reaction mechanism. The energy barrier of the catalyzed amidation reaction is approximately 40 kJ mol(-1) lower than the non-catalyzed amidation reaction. At least partially this can be explained by a hydrogen bond from the amine to the π-electrons of the thiophenol, stabilizing the transition state...

A two-state computational investigation of methane C--H and ethane C--C oxidative addition to [CpM(PH3)]n+ (M = Co, Rh, Ir; n = 0, 1).

Science.gov (United States)

Petit, Alban; Richard, Philippe; Cacelli, Ivo; Poli, Rinaldo

2006-01-11

Reductive elimination of methane from methyl hydride half-sandwich phosphane complexes of the Group 9 metals has been investigated by DFT calculations on the model system [CpM(PH(3))(CH(3))(H)] (M = Co, Rh, Ir). For each metal, the unsaturated product has a triplet ground state; thus, spin crossover occurs during the reaction. All relevant stationary points on the two potential energy surfaces (PES) and the minimum energy crossing point (MECP) were optimized. Spin crossover occurs very near the sigma-CH(4) complex local minimum for the Co system, whereas the heavier Rh and Ir systems remain in the singlet state until the CH(4) molecule is almost completely expelled from the metal coordination sphere. No local sigma-CH(4) minimum was found for the Ir system. The energetic profiles agree with the nonexistence of the Co(III) methyl hydride complex and with the greater thermal stability of the Ir complex relative to the Rh complex. Reductive elimination of methane from the related oxidized complexes [CpM(PH(3))(CH(3))(H)](+) (M = Rh, Ir) proceeds entirely on the spin doublet PES, because the 15-electron [CpM(PH(3))](+) products have a doublet ground state. This process is thermodynamically favored by about 25 kcal mol(-1) relative to the corresponding neutral system. It is essentially barrierless for the Rh system and has a relatively small barrier (ca. 7.5 kcal mol(-1)) for the Ir system. In both cases, the reaction involves a sigma-CH(4) intermediate. Reductive elimination of ethane from [CpM(PH(3))(CH(3))(2)](+) (M = Rh, Ir) shows a similar thermodynamic profile, but is kinetically quite different from methane elimination from [CpM(PH(3))(CH(3))(H)](+): the reductive elimination barrier is much greater and does not involve a sigma-complex intermediate. The large difference in the calculated activation barriers (ca. 12.0 and ca. 30.5 kcal mol(-1) for the Rh and Ir systems, respectively) agrees with the experimental observation, for related systems, of oxidatively

UV photolysis of 4-iodo-, 4-bromo-, and 4-chlorophenol: Competition between C-Y (Y = halogen) and O-H bond fission

Science.gov (United States)

Sage, Alan G.; Oliver, Thomas A. A.; King, Graeme A.; Murdock, Daniel; Harvey, Jeremy N.; Ashfold, Michael N. R.

2013-04-01

The wavelength dependences of C-Y and O-H bond fission following ultraviolet photoexcitation of 4-halophenols (4-YPhOH) have been investigated using a combination of velocity map imaging, H Rydberg atom photofragment translational spectroscopy, and high level spin-orbit resolved electronic structure calculations, revealing a systematic evolution in fragmentation behaviour across the series Y = I, Br, Cl (and F). All undergo O-H bond fission following excitation at wavelengths λ ≲ 240 nm, on repulsive ((n/π)σ*) potential energy surfaces (PESs), yielding fast H atoms with mean kinetic energies ˜11 000 cm-1. For Y = I and Br, this process occurs in competition with prompt C-I and C-Br bond cleavage on another (n/π)σ* PES, but no Cl/Cl* products unambiguously attributable to one photon induced C-Cl bond fission are observed from 4-ClPhOH. Differences in fragmentation behaviour at longer excitation wavelengths are more marked. Prompt C-I bond fission is observed following excitation of 4-IPhOH at all λ ≤ 330 nm; the wavelength dependent trends in I/I* product branching ratio, kinetic energy release, and recoil anisotropy suggest that (with regard to C-I bond fission) 4-IPhOH behaves like a mildly perturbed iodobenzene. Br atoms are observed when exciting 4-BrPhOH at long wavelengths also, but their velocity distributions suggest that dissociation occurs after internal conversion to the ground state. O-H bond fission, by tunnelling (as in phenol), is observed only in the cases of 4-FPhOH and, more weakly, 4-ClPhOH. These observed differences in behaviour can be understood given due recognition of (i) the differences in the vertical excitation energies of the C-Y centred (n/π)σ* potentials across the series Y = I increased spin-orbit coupling in, particularly, 4-IPhOH. The present results provide (another) reminder of the risks inherent in extrapolating photochemical behaviour measured for one molecule at one wavelength to other (related) molecules and to

Conformation-induced remote meta-C-H activation of amines

Science.gov (United States)

Tang, Ri-Yuan; Li, Gang; Yu, Jin-Quan

2014-03-01

Achieving site selectivity in carbon-hydrogen (C-H) functionalization reactions is a long-standing challenge in organic chemistry. The small differences in intrinsic reactivity of C-H bonds in any given organic molecule can lead to the activation of undesired C-H bonds by a non-selective catalyst. One solution to this problem is to distinguish C-H bonds on the basis of their location in the molecule relative to a specific functional group. In this context, the activation of C-H bonds five or six bonds away from a functional group by cyclometallation has been extensively studied. However, the directed activation of C-H bonds that are distal to (more than six bonds away) functional groups has remained challenging, especially when the target C-H bond is geometrically inaccessible to directed metallation owing to the ring strain encountered in cyclometallation. Here we report a recyclable template that directs the olefination and acetoxylation of distal meta-C-H bonds--as far as 11 bonds away--of anilines and benzylic amines. This template is able to direct the meta-selective C-H functionalization of bicyclic heterocycles via a highly strained, tricyclic-cyclophane-like palladated intermediate. X-ray and nuclear magnetic resonance studies reveal that the conformational biases induced by a single fluorine substitution in the template can be enhanced by using a ligand to switch from ortho- to meta-selectivity.

Interplay of Electronic Cooperativity and Exchange Coupling in Regulating the Reactivity of Diiron(IV)-oxo Complexes towards C-H and O-H Bond Activation.

Science.gov (United States)

Ansari, Azaj; Ansari, Mursaleem; Singha, Asmita; Rajaraman, Gopalan

2017-07-26

Activation of inert C-H bonds such as those of methane are extremely challenging for chemists but in nature, the soluble methane monooxygenase (sMMO) enzyme readily oxidizes methane to methanol by using a diiron(IV) species. This has prompted chemists to look for similar model systems. Recently, a (μ-oxo)bis(μ-carboxamido)diiron(IV) ([Fe IV 2 O(L) 2 ] 2+ L=N,N-bis-(3',5'-dimethyl-4'-methoxypyridyl-2'-methyl)-N'-acetyl-1,2-diaminoethane) complex has been generated by bulk electrolysis and this species activates inert C-H bonds almost 1000 times faster than mononuclear Fe IV =O species and at the same time selectively activates O-H bonds of alcohols. The very high reactivity and selectivity of this species is puzzling and herein we use extensive DFT calculations to shed light on this aspect. We have studied the electronic and spectral features of diiron {Fe III -μ(O)-Fe III } +2 (complex I), {Fe III -μ(O)-Fe IV } +3 (II), and {Fe IV -μ(O)-Fe IV } +4 (III) complexes. Strong antiferromagnetic coupling between the Fe centers leads to spin-coupled S=0, S=3/2, and S=0 ground state for species I-III respectively. The mechanistic study of the C-H and O-H bond activation reveals a multistate reactivity scenario where C-H bond activation is found to occur through the S=4 spin-coupled state corresponding to the high-spin state of individual Fe IV centers. The O-H bond activation on the other hand, occurs through the S=2 spin-coupled state corresponding to an intermediate state of individual Fe IV centers. Molecular orbital analysis reveals σ-π/π-π channels for the reactivity. The nature of the magnetic exchange interaction is found to be switched during the course of the reaction and this offers lower energy pathways. Significant electronic cooperativity between two metal centers during the course of the reaction has been witnessed and this uncovers the reason behind the efficiency and selectivity observed. The catalyst is found to prudently choose the desired spin

Hypovalency--a kinetic-energy density description of a 4c-2e bond.

Science.gov (United States)

Jacobsen, Heiko

2009-06-07

A bond descriptor based on the kinetic energy density, the localized-orbital locator (LOL), is used to characterize the nature of the chemical bond in electron deficient multi-center bonds. The boranes B(2)H(6), B(4)H(4), B(4)H(10), [B(6)H(6)](2-), and [B(6)H(7)](-) serve as prototypical examples of hypovalent 3c-2e and 4c-2e bonding. The kinetic energy density is derived from a set of Kohn-Sham orbitals obtained from pure density functional calculations (PBE/TZVP), and the topology of LOL is analyzed in terms of (3,-3) attractors (Gamma). The B-B-B and B-H-B 3c-2e, and the B-B-H-B 4c-2e bonding situations are defined by their own characteristic LOL profiles. The presence of one attractor in relation to the three or four atoms that are engaged in electron deficient bonding provides sufficient indication of the type of 3c-2e or 4c-2e bond present. For the 4c-2e bond in [B(6)H(7)](-) the LOL analysis is compared to results from an experimental QTAIM study.

Reactivity of the parent amido complexes of iridium with olefins: C-NH2 bond formation versus C-H activation.

Science.gov (United States)

Mena, Inmaculada; García-Orduña, Pilar; Polo, Víctor; Lahoz, Fernando J; Casado, Miguel A; Oro, Luis A

2017-08-29

Herein we report on the different chemical reactivity displayed by two mononuclear terminal amido compounds depending on the nature of the coordinated diene. Hence, treatment of amido-bridged iridium complexes [{Ir(μ-NH 2 )(tfbb)} 3 ] (1; tfbb = tetrafluorobenzobarrelene) with dppp (dppp = bis(diphenylphosphane)propane) leads to the rupture of the amido bridges forming the mononuclear terminal amido compound [Ir(NH 2 )(dppp)(tfbb)] (3) in the first stage. On changing the reaction conditions, the formation of a C-NH 2 bond between the amido moiety and the coordinated diene is observed and a new dinuclear complex [{Ir(1,2-η 2 -4-κ-C 12 H 8 F 4 N)(dppp)} 2 (μ-dppp)] (4) has been isolated. On the contrary, the diiridium amido-bridged complex [{Ir(μ-NH 2 )(cod)} 2 ] (2; cod = 1,5-cyclooctadiene) in the presence of dppb (dppb = bis(diphenylphosphane)butane) allows the isolation of a mononuclear complex [Ir(1,2,3-η 3 -6-κ-C 8 H 10 )H(dppb)] (5), as a consequence of the extrusion of ammonia. The monitoring of the reaction of 2 with dppb (and dppp) allowed us to detect terminal amido complexes [Ir(NH 2 )(P-P)(cod)] (P-P = dppb (6), dppp (7)) in solution, as confirmed by an X-ray analysis of 7. Complex 7 was observed to evolve into hydrido species 5 at room temperature. DFT studies showed that C-H bond activation occurs through the deprotonation of one methylene fragment of the cod ligand by the highly basic terminal amido moiety instead of C-H oxidative addition to the Ir(i) center.

Mechanism of C-C and C-H bond cleavage in ethanol oxidation reaction on Cu2O(111): a DFT-D and DFT+U study.

Science.gov (United States)

Xu, Han; Miao, Bei; Zhang, Minhua; Chen, Yifei; Wang, Lichang

2017-10-04

The performance of transition metal catalysts for ethanol oxidation reaction (EOR) in direct ethanol fuel cells (DEFCs) may be greatly affected by their oxidation. However, the specific effect and catalytic mechanism for EOR of transition metal oxides are still unclear and deserve in-depth exploitation. Copper as a potential anode catalyst can be easily oxidized in air. Thus, in this study, we investigated C-C and C-H bond cleavage reactions of CH x CO (x = 1, 2, 3) species in EOR on Cu 2 O(111) using PBE+U calculations, as well as the specific effect of +U correction on the process of adsorption and reaction on Cu 2 O(111). It was revealed that the catalytic performance of Cu 2 O(111) for EOR was restrained compared with that of Cu(100). Except for the C-H cleavage of CH 2 CO, all the reaction barriers for C-C and C-H cleavage were higher than those on Cu(100). The most probable pathway for CH 3 CO to CHCO on Cu 2 O(111) was the continuous dehydrogenation reaction. Besides, the barrier for C-C bond cleavage increased due to the loss of H atoms in the intermediate. Moreover, by the comparison of the traditional GGA/PBE method and the PBE+U method, it could be concluded that C-C cleavage barriers would be underestimated without +U correction, while C-H cleavage barriers would be overestimated. +U correction was proved to be necessary, and the reaction barriers and the values of the Hubbard U parameter had a proper linear relationship.

Electrooxidative Ruthenium-Catalyzed C-H/O-H Annulation by Weak O-Coordination.

Science.gov (United States)

Qiu, Youai; Tian, Cong; Massignan, Leonardo; Rogge, Torben; Ackermann, Lutz

2018-05-14

Electrocatalysis has been identified as a powerful strategy for organometallic catalysis, and yet electrocatalytic C-H activation is restricted to strongly N-coordinating directing groups. The first example of electrocatalytic C-H activation by weak O-coordination is presented, in which a versatile ruthenium(II) carboxylate catalyst enables electrooxidative C-H/O-H functionalization for alkyne annulations in the absence of metal oxidants; thereby exploiting sustainable electricity as the sole oxidant. Mechanistic insights provide strong support for a facile organometallic C-H ruthenation and an effective electrochemical reoxidation of the key ruthenium(0) intermediate. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nickel-Catalyzed C sp2 –C sp3 Cross-Coupling via C–O Bond Activation

KAUST Repository

Guo, Lin; Hsiao, Chien-Chi; Yue, Huifeng; Liu, Xiangqian; Rueping, Magnus

2016-01-01

through Csp2-O substitution, without the restriction of β-hydride elimination. Moreover, the advantage of the newly developed method was demonstrated in a selective and sequential C-O bond activation process. © 2016 American Chemical Society.

Modeling evolution of hydrogen bonding and stabilization of transition states in the process of cocaine hydrolysis catalyzed by human butyrylcholinesterase.

Science.gov (United States)

Gao, Daquan; Zhan, Chang-Guo

2006-01-01

Molecular dynamics (MD) simulations and quantum mechanical/molecular mechanical (QM/MM) calculations were performed on the prereactive enzyme-substrate complex, transition states, intermediates, and product involved in the process of human butyrylcholinesterase (BChE)-catalyzed hydrolysis of (-)-cocaine. The computational results consistently reveal a unique role of the oxyanion hole (consisting of G116, G117, and A199) in BChE-catalyzed hydrolysis of cocaine, compared to acetylcholinesterase (AChE)-catalyzed hydrolysis of acetylcholine. During BChE-catalyzed hydrolysis of cocaine, only G117 has a hydrogen bond with the carbonyl oxygen (O31) of the cocaine benzoyl ester in the prereactive BChE-cocaine complex, and the NH groups of G117 and A199 are hydrogen-bonded with O31 of cocaine in all of the transition states and intermediates. Surprisingly, the NH hydrogen of G116 forms an unexpected hydrogen bond with the carboxyl group of E197 side chain and, therefore, is not available to form a hydrogen bond with O31 of cocaine in the acylation. The NH hydrogen of G116 is only partially available to form a weak hydrogen bond with O31 of cocaine in some structures involved in the deacylation. The change of the estimated hydrogen-bonding energy between the oxyanion hole and O31 of cocaine during the reaction process demonstrates how the protein environment can affect the energy barrier for each step of the BChE-catalyzed hydrolysis of cocaine. These insights concerning the effects of the oxyanion hole on the energy barriers provide valuable clues on how to rationally design BChE mutants with a higher catalytic activity for the hydrolysis of (-)-cocaine. 2005 Wiley-Liss, Inc.

Unusual reactions of diazocarbonyl compounds with α,β-unsaturated δ-amino esters: Rh(II-catalyzed Wolff rearrangement and oxidative cleavage of N–H-insertion products

Directory of Open Access Journals (Sweden)

Valerij A. Nikolaev

2016-08-01

Full Text Available Rh(II-сatalyzed reactions of aroyldiazomethanes, diazoketoesters and diazodiketones with α,β-unsaturated δ-aminoesters, in contrast to reactions of diazomalonates and other diazoesters, give rise to the Wolff rearrangement and/or oxidative cleavage of the initially formed N–H-insertion products. These oxidation processes are mediated by Rh(II catalysts possessing perfluorinated ligands. The formation of pyrrolidine structures, characteristic for catalytic reactions of diazoesters, was not observed in these processes at all.

Efficient C-O and C-N bond forming cross-coupling reactions catalyzed by core-shell structured Cu/Cu2O nanowires

KAUST Repository

Elshewy, Ahmed M.

2013-12-01

Oxygen and Nitrogen containing compounds are of utmost importance due to their interesting and diverse biological activities. The construction of the C-O and C–N bonds is of significance as it opens avenues for the introduction of ether and amine linkages in organic molecules. Despite significant advancements in this field, the construction of C-O and C–N bonds is still a major challenge for organic chemists, due to the involvement of harsh reaction conditions or the use of expensive catalysts or ligands in many cases. Thus, it is a challenge to develop alternative, milder, cheaper and more reproducible methodologies for the construction of these types of bonds. Herein, we introduce a new efficient ligand free catalytic system for C-O and C-N bond formation reactions.

CoFeRh alloys

International Nuclear Information System (INIS)

Tabakovic, Ibro; Qiu Jiaoming; Riemer, Steve; Sun Ming; Vas'ko, Vlad; Kief, Mark

2008-01-01

The electrochemical behavior of Rh(III) species in CoFe solution containing RhCl 3 , NH 4 Cl, H 3 BO 3 , CoSO 4 , FeSO 4 , saccharin, and NaLS (Na lauryl sulfate) has been investigated. The electrochemistry of Rh(III) species is influenced by each of the compounds present in CoFe plating solution, but especially by addition of saccharin and H 3 BO 3 to the RhCl 3 -NH 4 Cl solution. The nucleation and growth of Rh on GC (glassy carbon), Ru, and Cu electrodes from NH 4 Cl solution was studied using the potentiostatic current-transient methods. The results support a predominantly progressive nucleation of Rh on all three-electrode surfaces. The nucleation kinetic parameters ANo (steady state nucleation rate) and Ns (saturation nuclear number density) were found to vary with potential and are electrode-dependent in order: GC > Ru∼Cu. The electrodeposited Rh films obtained from NH 4 Cl solution and nonmagnetic CoFeRh film obtained from CoFe solution were characterized in terms of the following properties: morphology, surface roughness, crystal structure and chemical composition. The origin of light elements found in Rh and CoFeRh films (O, Cl, S, C, N) was discussed

Secondary deuterium isotope effects for acid-catalyzed hydrolysis of inosine and adenosine

International Nuclear Information System (INIS)

Romero, R.; Stein, R.; Bull, H.G.; Cordes, E.H.

1978-01-01

Kinetic α deuterium isotope effects have been measured for acid-catalyzed hydrolysis of inosine and adenosine. For inosine hydrolysis, values of k/sub H/k/sub D/ follow: in 1.0 M HCl, 1.21 and 1.20 at 25 and 50 0 C, respectively; in 0.1 M HCl, 1.19 and 1.18 at 25 and 50 0 C, respectively. For adenosine hydrolysis, k/sub H/k/sub D/ is 1.23 in 0.1 M HCl at 25 0 C. The values require that the transition states for hydrolysis of both the monocation and dication of inosine and the dication of adenosine have marked oxocarbonium ion character. Detailed mechanisms which accord with this and other experimental observations include (1) a classical Al mechanism in which the C--N bond is largely cleaved in the transition state; (2) a mechanism involving some form of nucleophilic participation by solvent in which bond cleavage is advanced relative to bond formation in the transition state; or (3) complete C--N bond cleavage with rate-determining diffusion apart of oxocarbonium ion and purine base. 53 references, 1 figure, 2 tables

Redox-Neutral Rhodium-Catalyzed [4+1] Annulation through Formal Dehydrogenative Vinylidene Insertion.

Science.gov (United States)

Liu, Huan; Song, Shengjin; Wang, Cheng-Qiang; Feng, Chao; Loh, Teck-Peng

2017-01-10

A synthetic protocol for the expedient construction of 5-methylene-1H-pyrrol-2(5H)-one derivatives through rhodium-catalyzed [4+1] annulation with gem-difluoroacrylate as the C 1 component was reported. By taking advantage of the twofold C-F bond cleavage occurring during the annulation, this reaction not only allows the synthesis of these heterocyclic compounds under overall oxidant-free conditions but also renders the transformation stereospecific. The very mild reaction conditions employed ensure compatibility with a wide variety of synthetically useful functional groups. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pressure-induced structural transition and thermodynamic properties of RhN2 and the effect of metallic bonding on its hardness

International Nuclear Information System (INIS)

Liu Jun; Kuang Xiao-Yu; Wang Zhen-Hua; Huang Xiao-Fen

2012-01-01

The elastic constant, structural phase transition, and effect of metallic bonding on the hardness of RhN 2 under high pressure are investigated through the first-principles calculation by means of the pseudopotential plane-wave method. Three structures are chosen to investigate for RhN 2 , namely, simple hexagonal P6/mmm (denoted as SH), orthorhombic Pnnm (marcasite), and simple tetragonal P4/mbm (denoted as ST). Our calculations show that the SH phase is energetically more stable than the other two phases at zero pressure. On the basis of the third-order Birch—Murnaghan equation of states, we find that the phase transition pressures from an SH to a marcasite structure and from a marcasite to an ST structure are 1.09 GPa and 354.57 GPa, respectively. Elastic constants, formation enthalpies, shear modulus, Young's modulus, and Debye temperature of RhN 2 are derived. The calculated values are, generally speaking, in good agreement with the previous theoretical results. Meanwhile, it is found that the pressure has an important influence on physical properties. Moreover, the effect of metallic bonding on the hardness of RhN 2 is investigated. This is a quantitative investigation on the structural properties of RhN 2 , and it still awaits experimental confirmation. (condensed matter: structural, mechanical, and thermal properties)

Atroposelective Synthesis of Axially Chiral Biaryls by Palladium-Catalyzed Asymmetric C-H Olefination Enabled by a Transient Chiral Auxiliary.

Science.gov (United States)

Yao, Qi-Jun; Zhang, Shuo; Zhan, Bei-Bei; Shi, Bing-Feng

2017-06-01

Atroposelective synthesis of axially chiral biaryls by palladium-catalyzed C-H olefination, using tert-leucine as an inexpensive, catalytic, and transient chiral auxiliary, has been realized. This strategy provides a highly efficient and straightforward access to a broad range of enantioenriched biaryls in good yields (up to 98 %) with excellent enantioselectivities (95 to >99 % ee). Kinetic resolution of trisubstituted biaryls bearing sterically more demanding substituents is also operative, thus furnishing the optically active olefinated products with excellent selectivity (95 to >99 % ee, s-factor up to 600). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dynamic GnRH and hCG testing

DEFF Research Database (Denmark)

Bang, A. Kirstine; Nordkap, Loa; Almstrup, Kristian

2017-01-01

OBJECTIVE: Gonadotropin-releasing hormone (GnRH) and human chorionic gonadotropin (hCG) stimulation tests may be used to evaluate the pituitary and testicular capacity. Our aim was to evaluate changes in follicular-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone after Gn...... influence of the tests was illustrated by results from 45 patients suspected of disordered hypothalamic-pituitary-gonadal axis. METHODS: Baseline, stimulated, relative and absolute changes in serum FSH and LH were determined by ultrasensitive TRIFMA, and testosterone was determined by LC-MS/MS. RESULTS......: For the reference group, LH and FSH increased almost 400% and 40% during GnRH testing, stimulated levels varied from 4.4 to 58.8 U/L and 0.2 to 11.8 U/L and FSH decreased in nine men. Testosterone increased approximately 110% (range: 18.7-67.6 nmol/L) during hCG testing. None of the polymorphisms had any major...

Mechanism of H2O2 dismutation catalyzed by a new catalase mimic (a non-heme dibenzotetraaza[14]annulene-Fe(III) complex): a density functional theory investigation.

Science.gov (United States)

Wang, Xin; Li, Shuhua; Jiang, Yuansheng

2004-10-04

The mechanism of H(2)O(2) dismutation catalyzed by the dibenzotetraaza[14]annulene-Fe(III) complex ([Fe(C(24)H(22)N(4)O(4))](+)) which was recently reported (Paschke, J.; Kirsch, M.; Korth, H. G.; de Groot, H.; Sustmann, R. J. Am. Chem. Soc. 2001, 123, 11099) has been investigated by density functional theory using the B3LYP hybrid functional. The quartet potential energy profile of the catalytic reaction has been explored. In the whole catalytic cycle, the rate-determining step is found to be the O-O bond homolytic cleavage, without the assistance of solvent molecules in the second coordination shell. The calculated free energy barrier for this step is 10.8 kcal/mol, which is in reasonable agreement with the experimental facts. The calculations also show that the hydroxyl and hydroperoxyl radicals may be generated in the reaction processes, but they can be efficiently quenched in strongly exothermic steps. This study provides a satisfactory explanation to the observed efficiency of the H(2)O(2) dismutation catalyzed by this complex.

The hydrogen bond between N-H or O-H and organic fluorine: favourable yes, competitive no.

Science.gov (United States)

Taylor, Robin

2017-06-01

A study was made of X-H...F-C interactions (X = N or O) in small-molecule crystal structures. It was primarily based on 6728 structures containing X-H and C-F and no atom heavier than chlorine. Of the 28 451 C-F moieties in these structures, 1051 interact with X-H groups. However, over three-quarters of these interactions are either the weaker components of bifurcated hydrogen bonds (so likely to be incidental contacts) or occur in structures where there is a clear insufficiency of good hydrogen-bond acceptors such as oxygen, nitrogen or halide. In structures where good acceptors are entirely absent, there is about a 2 in 3 chance that a given X-H group will donate to fluorine. Viable alternatives are X-H...π hydrogen bonds (especially to electron-rich aromatics) and dihydrogen bonds. The average H...F distances of X-H...F-C interactions are significantly shorter for CR 3 F (R = C or H) and Csp 2 -F acceptors than for CRF 3 . The X-H...F angle distribution is consistent with a weak energetic preference for linearity, but that of H...F-C suggests a flat energy profile in the range 100-180°. X-H...F-C interactions are more likely when the acceptor is Csp 2 -F or CR 3 F, and when the donor is C-NH 2 . They also occur significantly more often in structures containing tertiary alcohols or solvent molecules, or with Z' > 1, i.e. when there may be unusual packing problems. It is extremely rare to find X-H...F-C interactions in structures where there are several unused good acceptors. When it does happen, there is often a clear reason, e.g. awkwardly shaped molecules whose packing isolates a donor group from the good acceptors.

Remote C−H Activation of Quinolines through Copper-Catalyzed Radical Cross-Coupling

KAUST Repository

Xu, Jun; Shen, Chao; Zhu, Xiaolei; Zhang, Pengfei; Ajitha, Manjaly John; Huang, Kuo-Wei; An, Zhongfu; Liu, Xiaogang

2016-01-01

Achieving site selectivity in carbon-hydrogen (C-H) functionalization reactions is a formidable challenge in organic chemistry. Herein, we report a novel approach to activating remote C-H bonds at the C5 position of 8-aminoquinoline through copper

Quantification of the selective activation of C--H bonds in short chain alkanes: The reactivity of ethane, propane, isobutane, n-butane, and neopentane on Ir(111)

International Nuclear Information System (INIS)

Johnson, D.F.; Weinberg, W.H.

1995-01-01

The initial probabilities of precursor-mediated, dissociative chemisorption of the saturated hydrocarbons 13 C-labeled ethane, propane, isobutane, n-butane, and neopentane on the close-packed Ir(111) surface have been measured. The selective activation of primary (1 degree), secondary (2 degree), and tertiary (3 degree) C--H bonds has been quantified by examining the reactivities of the selectively deuterated isotopomers of propane, C 3 H 8 , CH 3 CD 2 CH 3 , and C 3 D 8 , and of isobutane, (CH 3 ) 3 CH, (CH 3 ) 3 CD, and (CD 3 ) 3 CH. With respect to the bottom of the physically adsorbed well for each hydrocarbon, the apparent C--H bond activation energies have been found to be 10.4±0.3 kcal/mol (ethane), 11.4±0.3 kcal/mol (propane), 11.5±0.3 kcal/mol (n-butane), 11.3±0.3 kcal/mol (i-butane), and 11.3±0.3 kcal/mol (neopentane). For all the alkanes examined, the ratios of the preexponential factors of the rate coefficients of reaction and desorption are 1x10 -2 . The C--D bond activation energies are higher than the corresponding C--H bond activation energies by 480 cal/mol (ethane), 630 cal/mol (propane), and 660 cal/mol (i-butane). By analyzing the primary kinetic isotope effects for the selectively deuterated isotopomers of propane and isobutane, the 2 degree C--H bond activation energy is found to be 310±160 cal/mol less than the 1 degree C--H bond activation energy on this surface, and similarly, 3 degree C--H bond cleavage is less by 80±70 cal/mol. The quantification of the branching ratios within the C--H bond activation channel for propane and isobutane on this surface shows that the formation of 1 degree-alkyl intermediates is, in general, favored over the formation of either 2 degree- or 3 degree-alkyl intermediates. (Abstract Truncated)

Si/C and H coadsorption at 4H-SiC{0001} surfaces

Energy Technology Data Exchange (ETDEWEB)

Wachowicz, E., E-mail: elwira@ifd.uni.wroc.pl [Institute of Experimental Physics, University of Wrocław, Plac M. Borna 9, PL-50-204 Wrocław (Poland); Interdisciplinary Centre for Mathematical and Computational Modelling, University of Warsaw, Pawińskiego 5a, PL-02-106 Warsaw (Poland)

2016-06-15

Highlights: • Si on C-terminated and C on Si-terminated surface adsorb in the H{sub 3} hollow site. • The preferred adsorption site is in contrary to the stacking order of bulk crystal. • The presence of hydrogen increases the adsorption energy of Si/C. • Hydrogen weakens the bonds between the adsorbed Si or C and the surface. • Carbon adsorbs on top of the surface carbon on the C-terminated surface. • With both C and H on Si-terminated surface the surface state vanishes. - Abstract: Density functional theory (DFT) study of adsorption of 0.25 monolayer of either Si or C on 4H-SiC{0001} surfaces is presented. The adsorption in high-symmetry sites on both Si- and C-terminated surfaces was examined and the influence of the preadsorbed 0.25 ML of hydrogen on the Si/C adsorption was considered. It was found out that for Si on C-terminated surface and C on Si-terminated the most favourable is threefolded adsorption site on both clean and H-precovered surface. This is contrary to the bulk crystal stacking order which would require adsorption on top of the topmost surface atom. In those cases, the presence of hydrogen weakens the bonding of the adsorbate. Carbon on the C-terminated surface, only binds on-top of the surface atom. The C−C bond-length is almost the same for the clean surface and for one with H and equals to ∼1.33 Å which is shorter by ∼0.2 than in diamond. The analysis of the electronic structure changes under adsorption is also presented.

Material and orientation dependent activity for heterogeneously catalyzed carbon-bromine bond homolysis

Energy Technology Data Exchange (ETDEWEB)

Walch, Hermann; Gutzler, Rico; Sirtl, Thomas; Eder, Georg; Lackinger, Markus [LMU Munich, Section Crystallography (Germany)

2010-07-01

Adsorption of the organic molecule 1,3,5-tris(4-bromophenyl)benzene on different metallic substrates, namely Cu(111), Ag(111) and Ag(110) has been studied by variable temperature Scanning Tunneling Microscopy (STM). Depending on substrate temperature, material and orientation, we observe a surface-catalyzed dehalogenation reaction. Deposition onto the catalytically active substrates Cu(111) and Ag(110) held at room temperature leads to cleavage of the carbon-bromine bonds and subsequent formation of protopolymers, i.e radical metal coordination complexes. However upon deposition on Ag(111) no such reaction has been observed. Instead, various self-assembled ordered structures based on intact molecules could be identified. Also sublimation onto either substrate held at 80 K did not result in any dehalogenation, thereby exemplifying that the dehalogenation reaction is thermally activated. We explain the differences in catalytic activity by charge transfer into unoccupied molecular orbitals and subsequent destabilization of the C-Br bond, whereby enhanced molecule-substrate interaction leads to an increasing magnitude of charge transfer. The interaction strength follows the general reactivity order Cu>Ag>Au for (111) faces and is generally enhanced on higher corrugated surfaces as the (110) facet in case of fcc substrates.

Boron-Based Catalysts for C-C Bond-Formation Reactions.

Science.gov (United States)

Rao, Bin; Kinjo, Rei

2018-05-02

Because the construction of the C-C bond is one of the most significant reactions in organic chemistry, the development of an efficient strategy has attracted much attention throughout the synthetic community. Among various protocols to form C-C bonds, organoboron compounds are not just limited to stoichiometric reagents, but have also made great achievements as catalysts because of the easy modification of the electronic and steric impacts on the boron center. This review presents recent developments of boron-based catalysts applied in the field of C-C bond-formation reactions, which are classified into four kinds on the basis of the type of boron catalyst: 1) highly Lewis acidic borane, B(C 6 F 5 ) 3 ; 2) organoboron acids, RB(OH) 2 , and their ester derivatives; 3) borenium ions, (R 2 BL)X; and 4) other miscellaneous kinds. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rhodium(III)-catalyzed three-component reaction of imines, alkynes, and aldehydes through C-H activation.

Science.gov (United States)

Huang, Ji-Rong; Song, Qiang; Zhu, Yu-Qin; Qin, Liu; Qian, Zhi-Yong; Dong, Lin

2014-12-15

An efficient rhodium(III)-catalyzed tandem three-component reaction of imines, alkynes and aldehydes through CH activation has been developed. High stereo- and regioselectivity, as well as good yields were obtained in most cases. The simple and atom-economical approach offers a broad scope of substrates, providing polycyclic skeletons with potential biological properties. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

CoFeRh alloys

Energy Technology Data Exchange (ETDEWEB)

Tabakovic, Ibro [Seagate Technology, Research and Development, Bloomington, MN 55435 (United States)], E-mail: ibro.m.tabakovic@seagate.com; Qiu Jiaoming; Riemer, Steve; Sun Ming; Vas' ko, Vlad; Kief, Mark [Seagate Technology, Research and Development, Bloomington, MN 55435 (United States)

2008-01-01

The electrochemical behavior of Rh(III) species in CoFe solution containing RhCl{sub 3}, NH{sub 4}Cl, H{sub 3}BO{sub 3}, CoSO{sub 4}, FeSO{sub 4}, saccharin, and NaLS (Na lauryl sulfate) has been investigated. The electrochemistry of Rh(III) species is influenced by each of the compounds present in CoFe plating solution, but especially by addition of saccharin and H{sub 3}BO{sub 3} to the RhCl{sub 3}-NH{sub 4}Cl solution. The nucleation and growth of Rh on GC (glassy carbon), Ru, and Cu electrodes from NH{sub 4}Cl solution was studied using the potentiostatic current-transient methods. The results support a predominantly progressive nucleation of Rh on all three-electrode surfaces. The nucleation kinetic parameters ANo (steady state nucleation rate) and Ns (saturation nuclear number density) were found to vary with potential and are electrode-dependent in order: GC > Ru{approx}Cu. The electrodeposited Rh films obtained from NH{sub 4}Cl solution and nonmagnetic CoFeRh film obtained from CoFe solution were characterized in terms of the following properties: morphology, surface roughness, crystal structure and chemical composition. The origin of light elements found in Rh and CoFeRh films (O, Cl, S, C, N) was discussed.

Palladium-Catalyzed Cross-Coupling Reactions of Perfluoro Organic Compounds

Directory of Open Access Journals (Sweden)

Masato Ohashi

2014-09-01

Full Text Available In this review, we summarize our recent development of palladium(0-catalyzed cross-coupling reactions of perfluoro organic compounds with organometallic reagents. The oxidative addition of a C–F bond of tetrafluoroethylene (TFE to palladium(0 was promoted by the addition of lithium iodide, affording a trifluorovinyl palladium(II iodide. Based on this finding, the first palladium-catalyzed cross-coupling reaction of TFE with diarylzinc was developed in the presence of lithium iodide, affording α,β,β-trifluorostyrene derivatives in excellent yield. This coupling reaction was expanded to the novel Pd(0/PR3-catalyzed cross-coupling reaction of TFE with arylboronates. In this reaction, the trifluorovinyl palladium(II fluoride was a key reaction intermediate that required neither an extraneous base to enhance the reactivity of organoboronates nor a Lewis acid additive to promote the oxidative addition of a C–F bond. In addition, our strategy utilizing the synergetic effect of Pd(0 and lithium iodide could be applied to the C–F bond cleavage of unreactive hexafluorobenzene (C6F6, leading to the first Pd(0-catalyzed cross-coupling reaction of C6F6 with diarylzinc compounds.

Molecular and crystal structure of nido-9-C5H5N-11-I-7,8-C2B9H10: supramolecular architecture via hydrogen bonding X-H...I (X = B, C)

International Nuclear Information System (INIS)

Polyanskaya, T.M.

2006-01-01

A monocrystal X-ray diffraction study of a new iodine-containing cluster compound 9-(pyridine)-11-iodo-decahydro-7,8-dicarba-nido-undecaborane [9-C 5 H 5 N-11-I-7,8-C 2 B 9 H 10 ] has been performed. Crystal data: C 7 H 15 B 9 NI, M = 337.39, monoclinic, space group P2 1 /c, unit cell parameters: a=9.348(1) A, b=11.159(1) A, c=13.442(2) A, β=98.13(1) deg, V=1388.1(5) A 3 , Z=4, d calc = 1.614 g/cm 3 , T = 295 K, F(000)=648, μ=2.276 mm -1 . The structure was solved by a direct method and refined in the full-matrix anisotropic approximation (isotropic for hydrogen atoms) to final agreement factors R 1 = 0.0254, wR 2 = 0.0454 for 2437 I hkl >2σ I from 3590 measured I hkl (an Enraf-Nonius CAD-4 diffractometer, λMoK α , graphite monochromator, θ/2θ-scanning). The molecules are joined into a supramolecular assembly by hydrogen bonds X-H...I (X = B, C) [ru

A general approach to intermolecular carbonylation of arene C-H bonds to ketones through catalytic aroyl triflate formation

Science.gov (United States)

Garrison Kinney, R.; Tjutrins, Jevgenijs; Torres, Gerardo M.; Liu, Nina Jiabao; Kulkarni, Omkar; Arndtsen, Bruce A.

2018-02-01

The development of metal-catalysed methods to functionalize inert C-H bonds has become a dominant research theme in the past decade as an approach to efficient synthesis. However, the incorporation of carbon monoxide into such reactions to form valuable ketones has to date proved a challenge, despite its potential as a straightforward and green alternative to Friedel-Crafts reactions. Here we describe a new approach to palladium-catalysed C-H bond functionalization in which carbon monoxide is used to drive the generation of high-energy electrophiles. This offers a method to couple the useful features of metal-catalysed C-H functionalization (stable and available reagents) and electrophilic acylations (broad scope and selectivity), and synthesize ketones simply from aryl iodides, CO and arenes. Notably, the reaction proceeds in an intermolecular fashion, without directing groups and at very low palladium-catalyst loadings. Mechanistic studies show that the reaction proceeds through the catalytic build-up of potent aroyl triflate electrophiles.

Diazo compounds and N-tosylhydrazones: novel cross-coupling partners in transition-metal-catalyzed reactions.

Science.gov (United States)

Xiao, Qing; Zhang, Yan; Wang, Jianbo

2013-02-19

Transition-metal-catalyzed carbene transformations and cross-couplings represent two major reaction types in organometallic chemistry and organic synthesis. However, for a long period of time, these two important areas have evolved separately, with essentially no overlap or integration. Thus, an intriguing question has emerged: can cross-coupling and metal carbene transformations be merged into a single reaction cycle? Such a combination could facilitate the development of novel carbon-carbon bond-forming methodologies. Although this concept was first explored about 10 years ago, rapid developments inthis area have been achieved recently. Palladium catalysts can be used to couple diazo compounds with a wide variety of organic halides. Under oxidative coupling conditions, diazo compounds can also react with arylboronic acids and terminal alkynes. Both of these coupling reactions form carbon-carbon double bonds. As the key step in these catalytic processes, Pd carbene migratory insertion plays a vital role in merging the elementary steps of Pd intermediates, leading to novel carbon-carbon bond formations. Because the diazo substrates can be generated in situ from N-tosylhydrazones in the presence of base, the N-tosylhydrazones can be used as reaction partners, making this type of cross-coupling reaction practical in organic synthesis. N-Tosylhydrazones are easily derived from the corresponding aldehydes or ketones. The Pd-catalyzed cross-coupling of N-tosylhydrazones is considered a complementary reaction to the classic Shapiro reaction for converting carbonyl functionalities into carbon-carbon double bonds. It can also serve as an alternative approach for the Pd-catalyzed cross-coupling of carbonyl compounds, which is usually achieved via triflates. The combination of carbene formation and cross-coupling in a single catalytic cycle is not limited to Pd-catalyzed reactions. Recent studies of Cu-, Rh-, Ni-, and Co-catalyzed cross-coupling reactions with diazo

Synthesis of Donor/Acceptor-Substituted Diazo Compounds in Flow and Their Application in Enantioselective Dirhodium-Catalyzed Cyclopropanation and C-H Functionalization.

Science.gov (United States)

Rackl, Daniel; Yoo, Chun-Jae; Jones, Christopher W; Davies, Huw M L

2017-06-16

A tandem reaction system has been developed for the preparation of donor/acceptor-substituted diazo compounds in continuous flow coupled to dirhodium-catalyzed C-H functionalization or cyclopropanation. Hydrazones were oxidized in flow by solid-supported N-iodo-p-toluenesulfonamide potassium salt (PS-SO 2 NIK) to generate the diazo compounds, which were then purified by passing through a column of molecular sieves/sodium thiosulfate.

Ethanol electro-oxidation in alkaline medium using Pd/c and PdRh/C electrocatalysts prepared by electron beam irradiation

International Nuclear Information System (INIS)

Silva, Dionisio Furtunato da; Geraldes, Adriana Napoleao; Pino, Eddy Segura; Spinace, Estevam Vitorio; Oliveira Neto, Almir; Linardi, Marcelo

2013-01-01

In this study, carbon-supported Pd (Pd/C) and bimetallic PdRh (Pd:Rh 90:10 atomic ratio) (PdRh/C) electrocatalysts were prepared using electron beam irradiation. The morphology and composition of the obtained materials were characterized by Cyclic voltammetry (VC), Chronoamperometry (CA), Energy dispersive X-ray (EDX), X-ray Diffraction (XRD) and Thermo-gravimetric analysis (TGA). The catalytic activities of the electrocatalysts toward the ethanol electro-oxidation were evaluated in alkaline medium in a single alkaline direct ethanol fuel cell (ADEFC), in a range temperature of 50 to 85 deg C. The best performances were obtained at 85 deg C (25 mW.cm -2 ) and 75 deg C (38 mW.cm -2 ) for Pd/C and PdRh/C electrocatalysts, respectively. The XRD of the PdRh/C electrocatalyst showed the presence of Pd-rich (fcc) phase. CV and CA experiments showed that PdRh/C electrocatalyst demonstrated superior activity toward ethanol electro-oxidation at room temperature, compared to Pd/C electrocatalyst. (author)

Mechanistic aspects of hydrosilylation catalyzed by (ArN=)Mo(H)(Cl)(PMe3)3.

Science.gov (United States)

Khalimon, Andrey Y; Shirobokov, Oleg G; Peterson, Erik; Simionescu, Razvan; Kuzmina, Lyudmila G; Howard, Judith A K; Nikonov, Georgii I

2012-04-02

The reaction of (ArN=)MoCl(2)(PMe(3))(3) (Ar = 2,6-diisopropylphenyl) with L-Selectride gives the hydrido-chloride complex (ArN=)Mo(H)(Cl)(PMe(3))(3) (2). Complex 2 was found to catalyze the hydrosilylation of carbonyls and nitriles as well as the dehydrogenative silylation of alcohols and water. Compound 2 does not show any productive reaction with PhSiH(3); however, a slow H/D exchange and formation of (ArN=)Mo(D)(Cl)(PMe(3))(3) (2(D)) was observed upon addition of PhSiD(3). Reactivity of 2 toward organic substrates was studied. Stoichiometric reactions of 2 with benzaldehyde and cyclohexanone start with dissociation of the trans-to-hydride PMe(3) ligand followed by coordination and insertion of carbonyls into the Mo-H bond to form alkoxy derivatives (ArN=)Mo(Cl)(OR)(PMe(2))L(2) (3: R = OCH(2)Ph, L(2) = 2 PMe(3); 5: R = OCH(2)Ph, L(2) = η(2)-PhC(O)H; 6: R = OCy, L(2) = 2 PMe(3)). The latter species reacts with PhSiH(3) to furnish the corresponding silyl ethers and to recover the hydride 2. An analogous mechanism was suggested for the dehydrogenative ethanolysis with PhSiH(3), with the key intermediate being the ethoxy complex (ArN=)Mo(Cl)(OEt)(PMe(3))(3) (7). In the case of hydrosilylation of acetophenone, a D-labeling experiment, i.e., a reaction of 2 with acetophenone and PhSiD(3) in the 1:1:1 ratio, suggests an alternative mechanism that does not involve the intermediacy of an alkoxy complex. In this particular case, the reaction presumably proceeds via Lewis acid catalysis. Similar to the case of benzaldehyde, treatment of 2 with styrene gives trans-(ArN=)Mo(H)(η(2)-CH(2)═CHPh)(PMe(3))(2) (8). Complex 8 slowly decomposes via the release of ethylbenzene, indicating only a slow insertion of styrene ligand into the Mo-H bond of 8.

Crystal structures of bis[2-(pyridin-2-ylphenyl-κ2N,C1]rhodium(III complexes containing an acetonitrile or monodentate thyminate(1− ligand

Directory of Open Access Journals (Sweden)

Mika Sakate

2016-04-01

Full Text Available The crystal structures of bis[2-(pyridin-2-ylphenyl]rhodium(III complexes with the metal in an octahedral coordination containing chloride and acetonitrile ligands, namely (OC-6-42-acetonitrilechloridobis[2-(pyridin-2-ylphenyl-κ2N,C1]rhodium(III, [RhCl(C11H8N2(CH3CN] (1, thyminate(1− and methanol, namely (OC-6-42-methanol(5-methyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-ido-κN1bis[2-(pyridin-2-ylphenyl-κ2N,C1]rhodium(III, [Rh(C11H8N2(C5H5N2O2(CH3OH]·CH3OH·0.5H2O (2, and thyminate(1− and ethanol, namely (OC-6-42-ethanol(5-methyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-ido-κN1bis[2-(pyridin-2-ylphenyl-κ2N,C1]rhodium(III, [Rh(C11H8N2(C5H5N2O2(C2H5OH]·C2H5OH (3, are reported. The acetonitrile complex, 1, is isostructural with the IrIII analog. In complexes 2 and 3, the monodeprotonated thyminate (Hthym− ligand coordinates to the RhIII atom through the N atom, and the resulting Rh—N(Hthym bond lengths are relatively long [2.261 (2 and 2.252 (2 Å for 2 and 3, respectively] as compared to the Rh—N bonds in the related thyminate complexes. In each of the crystals of 2 and 3, the complexes are linked via a pair of intermolecular N—H...O hydrogen bonds between neighbouring Hthym− ligands, forming an inversion dimer. A strong intramolecular O—H...O hydrogen bond between the thyminate(1− and alcohol ligands in mutually cis positions to each other is also observed.

Synergistic Manganese(I) C-H Activation Catalysis in Continuous Flow: Chemoselective Hydroarylation.

Science.gov (United States)

Wang, Hui; Pesciaioli, Fabio; Oliveira, João C A; Warratz, Svenja; Ackermann, Lutz

2017-11-20

Chemoselective hydroarylations were accomplished by a novel synergistic Brønsted acid/manganese(I)-catalyzed C-H activation manifold. Thus, alkynes bearing O-leaving groups could, for the first time, be employed for C-H alkenylations without concurrent β-O elimination, thereby setting the stage for versatile late-stage diversifications. Also described is the first manganese-catalyzed C-H activation in continuous flow, thus enabling efficient hydroarylations within only 20 minutes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Pd-Catalyzed Consecutive C-H Arylation Triggered Cyclotrimerization: Synthesis of Star-shaped Benzotristhiazoles and Benzotrisoxazoles.

Science.gov (United States)

Xu, Zhanqiang; Oniwa, Kazuaki; Kikuchi, Hiromasa; Bao, Ming; Yamamoto, Yoshinori; Jin, Tienan; Terada, Masahiro

2018-05-18

Star-shaped π-extended molecules comprising discotic aromatic cores and peripheral π-conjugated arms have attracted significant attention as diverse optoelectronic materials in terms of their large π-surface, tunable self-assembly, enhanced charge transport and fluorescence, and liquid crystallinity. Although many efforts have been made in construction of various aromatic discotic cores, a new class of C3-symmetric star-shaped discotic π-molecules consisting of electron-deficient benzotristhiazole and benzotrisoxazole cores remains unexplored owing to the unachievable synthetic approaches, which are expected to exhibit distinct optoelectronic properties. Herein, we report a novel and highly efficient Pd-catalyzed cyclotrimerization of the functionalized thiazoles or oxazoles for the construction of a new class of discotic molecules of benzotristhiazole and benzotrisoxazole central cores with star-shaped π-conjugated arms. The combination of Pd2(dba)3/XPhos catalyst systems with the 4-bromo-substituted thiazole enables the formation of a sufficiently stable thiazole-Pd species that participates in the subsequent C-H arylations consecutively to form the corresponding cyclic trimer products. This new class of star-shaped discotic π-extended products showed tunable energy levels and high fluorescence quantum yields that make them promising candidates in optoelectronic application. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rh-Catalyzed annulations of N-methoxybenzamides with ketenimines: synthesis of 3-aminoisoindolinones and 3-diarylmethyleneisoindolinones with strong aggregation induced emission properties.

Science.gov (United States)

Zhou, Xiaorong; Peng, Zhixing; Zhao, Hongyang; Zhang, Zhiyin; Lu, Ping; Wang, Yanguang

2016-08-23

Rhodium-catalyzed C-H activation/annulation reactions of ketenimines with N-methoxybenzamides furnished 3-aminoisoindolin-1-ones and 3-(diarylmethylene)isoindolin-1-ones. The synthesized 3-(diarylmethylene)isoindolin-1-ones exhibited aggregation induced emissions in aqueous tetrahydrofuran solution and strong green-yellow emissions in solids.

Mechanism of intermolecular hydroacylation of vinylsilanes catalyzed by a rhodium(I) olefin complex: a DFT study.

Science.gov (United States)

Meng, Qingxi; Shen, Wei; Li, Ming

2012-03-01

Density functional theory (DFT) was used to investigate the Rh(I)-catalyzed intermolecular hydroacylation of vinylsilane with benzaldehyde. All intermediates and transition states were optimized completely at the B3LYP/6-31G(d,p) level (LANL2DZ(f) for Rh). Calculations indicated that Rh(I)-catalyzed intermolecular hydroacylation is exergonic, and the total free energy released is -110 kJ mol(-1). Rh(I)-catalyzed intermolecular hydroacylation mainly involves the active catalyst CA2, rhodium-alkene-benzaldehyde complex M1, rhodium-alkene-hydrogen-acyl complex M2, rhodium-alkyl-acyl complex M3, rhodium-alkyl-carbonyl-phenyl complex M4, rhodium-acyl-phenyl complex M5, and rhodium-ketone complex M6. The reaction pathway CA2 + R2 → M1b → T1b → M2b → T2b1 → M3b1 → T4b → M4b → T5b → M5b → T6b → M6b → P2 is the most favorable among all reaction channels of Rh(I)-catalyzed intermolecular hydroacylation. The reductive elimination reaction is the rate-determining step for this pathway, and the dominant product predicted theoretically is the linear ketone, which is consistent with Brookhart's experiments. Solvation has a significant effect, and it greatly decreases the free energies of all species. The use of the ligand Cp' (Cp' = C(5)Me(4)CF(3)) decreased the free energies in general, and in this case the rate-determining step was again the reductive elimination reaction.

Rhodium-Catalyzed Regioselective C7-Olefination of Indazoles Using an N-Amide Directing Group.

Science.gov (United States)

Guo, Lei; Chen, Yanyu; Zhang, Rong; Peng, Qiujun; Xu, Lanting; Pan, Xianhua

2017-02-01

A rhodium-catalyzed regioselective C-H olefination of indazole is described. This protocol relies on the use of an efficient and removable N,N-diisopropylcarbamoyl directing group, which offers facile access to C7-olefinated indazoles with high regioselectivity, ample substrate scope and broad functional group tolerance. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ethanol electro-oxidation in alkaline medium using Pd/c and PdRh/C electrocatalysts prepared by electron beam irradiation

Energy Technology Data Exchange (ETDEWEB)

Silva, Dionisio Furtunato da; Geraldes, Adriana Napoleao; Pino, Eddy Segura; Spinace, Estevam Vitorio; Oliveira Neto, Almir; Linardi, Marcelo, E-mail: dfsilva@ipen.br, E-mail: drinager@ig.com.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

2013-07-01

In this study, carbon-supported Pd (Pd/C) and bimetallic PdRh (Pd:Rh 90:10 atomic ratio) (PdRh/C) electrocatalysts were prepared using electron beam irradiation. The morphology and composition of the obtained materials were characterized by Cyclic voltammetry (VC), Chronoamperometry (CA), Energy dispersive X-ray (EDX), X-ray Diffraction (XRD) and Thermo-gravimetric analysis (TGA). The catalytic activities of the electrocatalysts toward the ethanol electro-oxidation were evaluated in alkaline medium in a single alkaline direct ethanol fuel cell (ADEFC), in a range temperature of 50 to 85 deg C. The best performances were obtained at 85 deg C (25 mW.cm{sup -2}) and 75 deg C (38 mW.cm{sup -2}) for Pd/C and PdRh/C electrocatalysts, respectively. The XRD of the PdRh/C electrocatalyst showed the presence of Pd-rich (fcc) phase. CV and CA experiments showed that PdRh/C electrocatalyst demonstrated superior activity toward ethanol electro-oxidation at room temperature, compared to Pd/C electrocatalyst. (author)

Early-transition-metal ketenimine complexes. Synthesis, reactivity, and structural characterization of complexes with. eta. sup 2 (C,N)-ketenimine groups bound to the halogenobis((trimethylsilyl)cyclopentadienyl)niobium unit. X-ray structure of Nb(. eta. sup 5 -C sub 5 H sub 4 SiMe sub 3 ) sub 2 Cl(. eta. sup 2 (C,N)-PhN double bond C double bond CPh sub 2 )

Energy Technology Data Exchange (ETDEWEB)

Antinolo, A.; Fajardo, M.; Lopez Mardomingo, C.; Otero, A. (Univ. de Alcala de Henares (Spain)); Mourad, Y.; Mugnier, Y. (Centre National de la Recherche Scientifique, Dijon (France)); Sanz-Aparicio, J.; Fonseca, I.; Florencio, F. (CSIC, Madrid (Spain))

1990-11-01

The reaction of Nb({eta}{sup 5}-C{sub 5}H{sub 4}SiMe{sub 3}){sub 2}X (X = Cl, Br) with 1 equiv of various ketenimines, R{sup 1}N{double bond}C{double bond}CR{sup 2}R{sup 3}, leads to the niobium derivatives Nb({eta}{sup 5}-C{sub 5}H{sub 4}SiMe{sub 3}){sub 2}X({eta}{sup 2}(C,N)-R{sup 1}N{double bond}C{double bond}CR{sup 2}R{sup 3}) (1, X = Cl, R{sup 1} = R{sup 2} = R{sup 3} = C{sub 6}H{sub 5}; 2, X = Cl, R{sup 1} = p-CH{sub 3}-C{sub 6}H{sub 4}, R{sup 2} = R{sup 3} = C{sub 6}H{sub 5}; 3, X = Br, R{sup 1} = R{sup 2} = R{sup 3} = C{sub 6}H{sub 5}; 4, X = Br, R{sup 1} = p-CH{sub 3}-C{sub 6}H{sub 4}, R{sup 2} = R{sup 3} = C{sub 6}H{sub 5}; 5, X = Cl, R{sup 1} = R{sup 2} = C{sub 6}H{sub 5}, R{sup 3} = CH{sub 3}; 6, X = Br, R{sup 1} = R{sup 2} = C{sub 6}H{sub 5}, R{sup 3} = CH{sub 3}) with the expected ketenimine C{double bond}N bonding mode. Reduction of 1 with 1 equiv of Na/Hg gives the complex Nb({eta}{sup 5}-C{sub 5}H{sub 4}SiMe{sub 3}){sub 2}({eta}{sup 2}(C,N)-PhN{double bond}C{double bond}CPh{sub 2}) (9) as a paramagnetic compound. The reduction of 9 with 1 equiv of Na/Hg and the subsequent addition of a proton source (ethanol) leads to the iminoacyl compound Nb({eta}{sup 5}-C{sub 5}H{sub 4}SiMe{sub 3}){sub 2}(CRNR{sup 1}) (10, R = CH(Ph{sub 2}), R{sup 1} = Ph). The one- and two-electron reductions of 1 have been studied by cyclic voltammetry experiments. The structure of 1 was determined by single-crystal X-ray diffractometry: a = 24.4904 (14) {angstrom}, b = 11.0435 (04) {angstrom}, c = 26.6130 (15) {angstrom}, {beta} = 109.890 (5){degree}, monoclinic, space group C2/c, Z = 8, V = 6,768.4 (5) {angstrom}{sup 3}, {rho}{sub calcd} = 1.3194 g/mL, R = 0.048, R{sub w} = 0.060 based on 4,806 observed reflections. The structure contains a niobium atom bonded to two cyclopentadienyl rings in a {eta}{sup 5} fashion; the coordination of the metal is completed by a Cl atom and a {eta}{sup 2}(C,N)-bonded ketenimine ligand.

Transition Metal Free C-N Bond Forming Dearomatizations and Aryl C-H Aminations by in Situ Release of a Hydroxylamine-Based Aminating Agent.

Science.gov (United States)

Farndon, Joshua J; Ma, Xiaofeng; Bower, John F

2017-10-11

We outline a simple protocol that accesses directly unprotected secondary amines by intramolecular C-N bond forming dearomatization or aryl C-H amination. The method is dependent on the generation of a potent electrophilic aminating agent released by in situ deprotection of O-Ts activated N-Boc hydroxylamines.

Pd(II)-Catalyzed Alkylation of Tertiary Carbon via Directing-Group-Mediated C(sp(3))-H Activation: Synthesis of Chiral 1,1,2-Trialkyl Substituted Cyclopropanes.

Science.gov (United States)

Hoshiya, Naoyuki; Takenaka, Kei; Shuto, Satoshi; Uenishi, Jun'ichi

2016-01-04

A Pd(OAc)2-catalyzed alkylation reaction of the tertiary carbon of chiral cyclopropane substrates with alkyl iodides and bromides via C(sp(3))-H activation has been developed. This is an elusive example of a C-H activation-mediated alkylation of tertiary carbon to effectively construct a quaternary carbon center. The alkylation proceeded with various alkyl halides, including those of functional groups, to provide a variety of chiral cis- and trans-1,1,2,-trialkyl substituted cyclopropanes of medicinal chemical importance.

1H-1H correlations across N-H···N hydrogen bonds in nucleic acids

International Nuclear Information System (INIS)

Majumdar, Ananya; Gosser, Yuying; Patel, Dinshaw J.

2001-01-01

In 2H J NN -COSY experiments, which correlate protons with donor/acceptor nitrogens across N d ···HN a bonds, the receptor nitrogen needs to be assigned in order to unambiguously identify the hydrogen bond. For many situations this is a non-trivial task which is further complicated by poor dispersion of (N a ,N d ) resonances. To address these problems, we present pulse sequences to obtain direct, internucleotide correlations between protons in uniformly 13 C/ 15 N labeled nucleic acids containing N d ···HN a hydrogen bonds. Specifically, the pulse sequence H2(N1N3)H3 correlates H2(A,ω 1 ):H3(U,ω 2 ) protons across Watson-Crick A-U and mismatched G·A base pairs, the sequences H5(N3N1)H1/H6(N3N1)H1 correlate H5(C,ω 1 )/H6(C,ω 1 ):H1(G,ω 2 ) protons across Watson-Crick G-C base pairs, and the H 2 (N2N7)H8 sequence correlates NH 2 (G,A,C;ω 1 ):H8(G,A;ω 2 ) protons across G·G, A·A, sheared G·A and other mismatch pairs. These 1 H- 1 H connectivities circumvent the need for independent assignment of the donor/acceptor nitrogen and related degeneracy issues associated with poorly dispersed nitrogen resonances. The methodology is demonstrated on uniformly 13 C/ 15 N labeled samples of (a) an RNA regulatory element involving the HIV-1 TAR RNA fragment, (b) a multi-stranded DNA architecture involving a G·(C-A) triad-containing G-quadruplex and (c) a peptide-RNA complex involving an evolved peptide bound to the HIV-1 Rev response element (RRE) RNA fragment

Hydrogen bonded C-H···Y (Y = O, S, Hal) molecular complexes: A natural bond orbital analysis

Science.gov (United States)

Isaev, A. N.

2016-03-01

Hydrogen bonded C-H···Y complexes formed by H2O, H2S molecules, hydrogen halides, and halogen-ions with methane, halogen substituted methane as well as with the C2H2 and NCH molecules were studied at the MP2/aug-cc-pVDZ level. The structure of NBOs corresponding to lone pair of acceptor Y, n Y, and vacant anti-σ-bond C-H of proton donor was analyzed and estimates of second order perturbation energy E(2) characterizing donor-acceptor n Y → σ C-H * charge-transfer interaction were obtained. Computational results for complexes of methane and its halogen substituted derivatives show that for each set of analogous structures, the EnY→σ*C-H (2) energy tends to grow with an increase in the s-component percentage in the lone pair NBO of acceptor Y. Calculations for different C···Y distances show that the equilibrium geometries of complexes lie in the region where the E(2) energy is highest and it changes symbatically with the length of the covalent E-H bond when the R(C···Y) distance is varied. The performed analysis allows us to divide the hydrogen bonded complexes into two groups, depending on the pattern of overlapping for NBOs of the hydrogen bridge.

Iron-catalyzed intermolecular cycloaddition of diazo surrogates with hexahydro-1,3,5-triazines.

Science.gov (United States)

Liu, Pei; Zhu, Chenghao; Xu, Guangyang; Sun, Jiangtao

2017-09-26

We report here an unprecedented iron-catalyzed cycloaddition reaction of diazo surrogates with hexahydro-1,3,5-triazines, providing five-membered heterocycles in moderate to high yields under mild reaction conditions. This cycloaddition features C-N and C-C bond formation using a cheap iron catalyst. Importantly, different to our former report on a gold-catalyzed system, both donor/donor and donor/acceptor diazo substrates are tolerated in this iron-catalyzed protocol.

Unraveling the role of support surface hydroxyls and its effect on the selectivity of C{sub 2} species over Rh/γ-Al{sub 2}O{sub 3} catalyst in syngas conversion: A theoretical study

Energy Technology Data Exchange (ETDEWEB)

Zhang, Riguang; Duan, Tian; Wang, Baojun, E-mail: wangbaojun@tyut.edu.cn; Ling, Lixia

2016-08-30

Highlights: • The selectivity toward CH{sub x} (x = 1–3) depends on γ-Al{sub 2}O{sub 3} support and its surface properties. • Rh/γ-Al{sub 2}O{sub 3} catalyst exhibits the higher selectivity toward CH{sub x} (x = 1,2) formation from syngas. • C{sub 2} species (C{sub 2}H{sub 2},CHCO,CH{sub 2}CHO) are the main products on Rh/γ-Al{sub 2}O{sub 3} catalyst. • γ-Al{sub 2}O{sub 3} surface hydroxyls affect the selectivity of C{sub 2} species over Rh/γ-Al{sub 2}O{sub 3} catalyst. - Abstract: The supported Rh-based catalysts exhibit the excellent catalytic performances for syngas conversion to C{sub 2} species. In this study, all possible elementary steps leading to C{sub 2} species from syngas have been explored to identify the role of support and its surface hydroxyls over Rh/γ-Al{sub 2}O{sub 3} catalyst; Here, the results are obtained using density functional theory (DFT) method. Two models: Rh4 cluster supported on the dry γ-Al{sub 2}O{sub 3}(110) surface, D(Rh4), and on the hydroxylated γ-Al{sub 2}O{sub 3}(110) surface, H(Rh4), have been used to model Rh/γ-Al{sub 2}O{sub 3} catalyst. Our results show that CO prefers to be hydrogenated to CHO, subsequently, starting from CHO species, CH and CH{sub 2} species are the dominate monomers among CH{sub x}(x = 1–3) species rather than CH{sub 3} and CH{sub 3}OH on D(Rh4) and H(Rh4) surfaces, suggesting that γ-Al{sub 2}O{sub 3}-supported Rh catalyst exhibits the high selectivity towards CH{sub x} formation compared to the pure Rh catalyst. On the other hand, D(Rh4) is more favorable for C{sub 2} hydrocarbon (C{sub 2}H{sub 2}) formation, whereas H(Rh4) surface easily produces C{sub 2} hydrocarbon (C{sub 2}H{sub 2}) and C{sub 2} oxygenates (CHCO,CH{sub 2}CHO), indicating that the surface hydroxyls of support can affect the selectivity of C{sub 2} species over Rh/γ-Al{sub 2}O{sub 3} catalyst in syngas conversion. Moreover, compared to the pure Rh(111) surface, Rh/γ-Al{sub 2}O{sub 3} catalyst can achieve the

Rhodium mediated bond activation: from synthesis to catalysis

Energy Technology Data Exchange (ETDEWEB)

Ho, Hung-An [Iowa State Univ., Ames, IA (United States)

2012-01-01

Recently, our lab has developed monoanionic tridentate ligand, To^R, showing the corresponding coordination chemistry and catalyst reactivity of magnesium, zirconium, zinc and iridium complexes. This thesis details synthetic chemistry, structural study and catalytic reactivity of the To^R-supported rhodium compounds. Tl[To^R] has been proved to be a superior ligand transfer agent for synthesizing rhodium complexes. The salt metathesis route of Tl[To^M] with [Rh(μ-Cl)(CO)]₂ and [Rh(μ- Cl)(COE)]₂ gives To^MRh(CO)₂ (2.2) and To^MRhH(β³-C₈H₁₃) (3.1) respectively while Tl[To^M] with [Rh(μ-Cl)(CO)]₂ affords To^PRh(CO)₂ (2.3). 2.2 reacts with both strong and weak electrophiles, resulting in the oxazoline N-attacked and the metal center-attacked compounds correspondingly. Using one of the metal center-attacked electrophiles, 2.3 was demonstrated to give high diastereoselectivity. Parallel to COE allylic C-H activation complex 3.1, the propene and allylbenzene allylic C-H activation products have also been synthesized. The subsequent functionalization attempts have been examined by treating with Brønsted acids, Lewis acids, electrophiles, nucleophiles, 1,3-dipolar reagents and reagents containing multiple bonds able to be inserted. Various related complexes have been obtained under these conditions, in which one of the azide insertion compounds reductively eliminates to give an allylic functionalization product stoichiometrically. 3.1 reacts with various primary alcohols to give the decarbonylation dihydride complex To^MRh(H)₂CO (4.1). 4.1 shows catalytic reactivity for primary alcohol decarbonylation under a photolytic condition. Meanwhile, 2.2 has been found to be more reactive than 4.1 for catalytic alcohol decarbonylation under the same condition. Various complexes and primary

Detailed Mechanistic Studies on Palladium-Catalyzed Selective C-H Olefination with Aliphatic Alkenes: A Significant Influence of Proton Shuttling.

Science.gov (United States)

Deb, Arghya; Hazra, Avijit; Peng, Qian; Paton, Robert S; Maiti, Debabrata

2017-01-18

Directing group-assisted regioselective C-H olefination with electronically biased olefins is well studied. However, the incorporation of unactivated olefins has remained largely unsuccessful. A proper mechanistic understanding of olefination involving unactivated alkenes is therefore essential for enhancing their usage in future. In this Article, detailed experimental and computational mechanistic studies on palladium catalyzed C-H olefination with unactivated, aliphatic alkenes are described. The isolation of Pd(II) intermediates is shown to be effective for elucidating the elementary steps involved in catalytic olefination. Reaction rate and order determination, control experiments, isotopic labeling studies, and Hammett analysis have been used to understand the reaction mechanism. The results from these experimental studies implicate β-hydride elimination as the rate-determining step and that a mechanistic switch occurs between cationic and neutral pathway. Computational studies support this interpretation of the experimental evidence and are used to uncover the origins of selectivity.

Solution Phase Measurement of Both Weak Sigma and C-H---X- Hydrogen Bonding Interactions in Synthetic Anion Receptors

Energy Technology Data Exchange (ETDEWEB)

Berryman, Mr. Orion B. [University of Oregon; Sather, Mr. Aaron C [University of Oregon; Hay, Benjamin [ORNL; Meisner, Mr. Jeffrey S. [University of Oregon; Johnson, Prof. Darren W. [University of Oregon

2008-01-01

A series of tripodal receptors preorganize electron-deficient aromatic rings to bind halides in organic solvents using weak sigma anion-to-arene interactions or C-H---X- hydrogen bonds. 1H NMR spectroscopy proves to be a powerful technique for quantifying binding in solution, and determining the interaction motifs, even in cases of weak binding.

Synthesis of all eight L-glycopyranosyl donors using C-H activation

DEFF Research Database (Denmark)

Frihed, Tobias; Pedersen, Christian Marcus; Bols, Mikael

2014-01-01

by an intramolecular C-H activation of the methyl group in g-position; both steps were catalyzed by iridium. The following Fleming-Tamao oxidation and acetylation gave the suitably protected L-hexoses. This is the first general method for the preparation of all eight L-hexoses as their thioglycosyl donors ready...... for glycosylation and the first example of an iridium-catalyzed C(sp3)-H activation on sulfide-containing compounds....

Loss of retrovirus production in JB/RH melanoma cells transfected with H-2Kb and TAP-1 genes.

Science.gov (United States)

Li, M; Xu, F; Muller, J; Huang, X; Hearing, V J; Gorelik, E

1999-01-20

JB/RH1 melanoma cells, as well as other melanomas of C57BL/6 mice (B16 and JB/MS), express a common melanoma-associated antigen (MAA) encoded by an ecotropic melanoma-associated retrovirus (MelARV). JB/RH1 cells do not express the H-2Kb molecules due to down-regulation of the H-2Kb and TAP-1 genes. When JB/RH1 cells were transfected with the H-2Kb and cotransfected with the TAP-1 gene, it resulted in the appearance of H-2Kb molecules and an increase in their immunogenicity, albeit they lost expression of retrovirus-encoded MAA recognized by MM2-9B6 mAb. Loss of MAA was found to result from a complete and stable elimination of ecotropic MelARV production in the H-2Kb/TAP-1-transfected JB/RH1 cells. Northern blot analysis showed no differences in ecotropic retroviral messages in MelARV-producing and -nonproducing melanoma cells, suggesting that loss of MelARV production was not due to down-regulation of MelARV transcription. Southern blot analysis revealed several rearrangements in the proviral DNA of H-2Kb-positive JB/RH1 melanoma cells. Sequence analysis of the ecotropic proviral DNA from these cells showed numerous nucleotide substitutions, some of which resulted in the appearance of a novel intraviral PstI restriction site and the loss of a HindIII restriction site in the pol region. PCR amplification of the proviral DNAs indicates that an ecotropic provirus found in the H-2Kb-positive cells is novel and does not preexist in the parental H-2Kb-negative melanoma cells. Conversely, the ecotropic provirus of the parental JB/RH1 cells was not amplifable from the H-2Kb-positive cells. Our data indicate that stable loss of retroviral production in the H-2Kb/TAP-1-transfected melanoma cells is probably due to the induction of recombination between a productive ecotropic MelARV and a defective nonecotropic provirus leading to the generation of a defective ecotropic provirus and the loss of MelARV production and expression of the retrovirus-encoded MAA. Copyright 1999

Enantioselective Copper-Catalyzed Carboetherification of Unactivated Alkenes**

Science.gov (United States)

Bovino, Michael T.; Liwosz, Timothy W.; Kendel, Nicole E.; Miller, Yan; Tyminska, Nina

2014-01-01

Chiral saturated oxygen heterocycles are important components of bioactive compounds. Cyclization of alcohols onto pendant alkenes is a direct route to their synthesis, but few catalytic enantioselective methods enabling cyclization onto unactivated alkenes exist. Herein is reported a highly efficient copper-catalyzed cyclization of γ-unsaturated pentenols that terminates in C-C bond formation, a net alkene carboetherification. Both intra- and intermolecular C-C bond formations are demonstrated, yielding functionalized chiral tetrahydrofurans as well as fused-ring and bridged-ring oxabicyclic products. Transition state calculations support a cis-oxycupration stereochemistry-determining step. PMID:24798697

Significance of β-dehydrogenation in ethanol electro-oxidation on platinum doped with Ru, Rh, Pd, Os and Ir.

Science.gov (United States)

Sheng, Tian; Lin, Wen-Feng; Hardacre, Christopher; Hu, P

2014-07-14

In the exploration of highly efficient direct ethanol fuel cells (DEFCs), how to promote the CO2 selectivity is a key issue which remains to be solved. Some advances have been made, for example, using bimetallic electrocatalysts, Rh has been found to be an efficient additive to platinum to obtain high CO2 selectivity experimentally. In this work, the mechanism of ethanol electrooxidation is investigated using the first principles method. It is found that CH3CHOH* is the key intermediate during ethanol electrooxidation and the activity of β-dehydrogenation is the rate determining factor that affects the completeness of ethanol oxidation. In addition, a series of transition metals (Ru, Rh, Pd, Os and Ir) are alloyed on the top layer of Pt(111) in order to analyze their effects. The elementary steps, α-, β-C-H bond and C-C bond dissociations, are calculated on these bimetallic M/Pt(111) surfaces and the formation potential of OH* from water dissociation is also calculated. We find that the active metals increase the activity of β-dehydrogenation but lower the OH* formation potential resulting in the active site being blocked. By considering both β-dehydrogenation and OH* formation, Ru, Os and Ir are identified to be unsuitable for the promotion of CO2 selectivity and only Rh is able to increase the selectivity of CO2 in DEFCs.

A General Cp*CoIII -Catalyzed Intramolecular C-H Activation Approach for the Efficient Total Syntheses of Aromathecin, Protoberberine, and Tylophora Alkaloids.

Science.gov (United States)

Lerchen, Andreas; Knecht, Tobias; Koy, Maximilian; Daniliuc, Constantin G; Glorius, Frank

2017-09-07

Herein, we report a Cp*Co III -catalyzed C-H activation approach as the key step to create highly valuable isoquinolones and pyridones as building blocks that can readily be applied in the total syntheses of a variety of aromathecin, protoberberine, and tylophora alkaloids. This particular C-H activation/annulation reaction was achieved with several terminal as well as internal alkyne coupling partners delivering a broad scope with excellent functional group tolerance. The synthetic applicability of this protocol reported herein was demonstrated in the total syntheses of two Topo-I-Inhibitors and two 8-oxyprotoberberine cores that can be further elaborated into the tetrahydroprotoberberine and the protoberberine alkaloid core. Moreover these building blocks were also transformed to six different tylophora alkaloids in expedient fashion. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metal induced B-Y activation in semisandwich Cp*Rh-, Cp*Ir-, (p-cumene)Ru-, and (p-cumene)Os complexes containing 1,2-dicarba-closo-dodecaborane(12)-1,2-dichalcogenide ligand

International Nuclear Information System (INIS)

Bernd Vrakmejer; Khong Yan; Vol'fgang Milius; Maks Kherberkhol'd

2001-01-01

Reactivity of 16e-semisandwich Cp*M[E 2 C 2 (B 10 H 10 )] and (p-cumene) M' [S 2 C 2 (B 10 H 10 )] complexes (Cp = cyclopentadienyl-ion; M = Rh, Ir; M' Ru, Os; E = S, Se) towards various alkynes was studied using data of NMR and X-ray diffraction analyses of intermediate and final products of the reactions. It is shown that the reactions initiate from introduction of alkyne molecule in one of metal-E bonds, then intramolecular metal-induced B-H activation occurs along with metal-B bond formation, followed by simultaneous hydrogen atom transfer from boron atom through metal atom to alkyne [ru

On the r>h Shift in Kiên Giang Khmer

Directory of Open Access Journals (Sweden)

James Kirby

2017-12-01

Full Text Available This paper presents an acoustic and perceptual study of the r>h shift in the variety of Khmer spoken in Giồng Riềng district, Kiên Giang province, Vietnam. In Phnom Penh Khmer, /r/ is realized as [h] in syllable onsets and onset clusters, and accompanied by lowered pitch, breathiness, and in some cases a change in the quality of the following vowel. In Kiên Giang Khmer, the r>h shift is accompanied by pitch lowering, but without changes in aspiration or vowel quality, and spectral measures did not indicate substantial differences in voice quality. Consistent with their productions, users of this dialect appear to rely solely on differences pitch to identify these lexical items. We discuss the implications of our findings for Khmer dialectology, mechanisms of sound change, and variation in the realization of rhotics more generally.

Beyond 3 Au from the Sun: the Hypervolatiles CH4, C2H6, and CO in the Distant Comet C2006 W3 (Christensen)

Science.gov (United States)

Bonev, Boncho P.; Villanueva, Geronimo L.; Disanti, Michael A.; Boehnhardt, Hermann; Lippi, Manuela; Gibb, Erika L.; Paganini, Lucas; Mumma, Michael J.

2017-01-01

Comet C/2006 W3 (Christensen) remained outside a heliocentric distance (Rh) of 3.1 au throughout its apparition, but it presented an exceptional opportunity to directly sense a suite of molecules released from its nucleus. The Cryogenic Infrared Echelle Spectrograph at ESO-VLT detected infrared emissions from the three hypervolatiles (CO, CH4, and C2H6) that have the lowest sublimation temperatures among species that are commonly studied in comets by remote sensing. Even at Rh 3.25 au, the production rate of each molecule exceeded those measured for the same species in a number of other comets, although these comets were observed much closer to the Sun. Detections of CO at Rh = 3.25, 4.03, and 4.73 au constrained its post-perihelion decrease in production rate, which most likely dominated the outgassing. At 3.25 au, our measured abundances scaled as CO/CH4/C2H6 approx. = 100/4.4/2.1. The C2H6/CH4 ratio falls within the range of previously studied comets at Rh the nucleus of 67P/Churyumov-Gerasimenko conducted at a very similar Rh (3.15 au). The independent detections of H2O (Herschel Space Observatory) and CO (this work) imply a coma abundance H2O/CO approx. = 20% in C/2006 W3 near Rh = 5 au. All these measurements are of high value for constraining models of nucleus sublimation (plausibly CO-driven) beyond Rh = 3au, where molecular detections in comets are still especially sparse.

Rhodium(III)-Catalyzed [3+2]/[5+2] Annulation of 4-Aryl 1,2,3-Triazoles with Internal Alkynes through Dual C(sp2)-H Functionalization.

Science.gov (United States)

Yang, Yuan; Zhou, Ming-Bo; Ouyang, Xuan-Hui; Pi, Rui; Song, Ren-Jie; Li, Jin-Heng

2015-05-26

A rhodium(III)-catalyzed [3+2]/[5+2] annulation of 4-aryl 1-tosyl-1,2,3-triazoles with internal alkynes is presented. This transformation provides straightforward access to indeno[1,7-cd]azepine architectures through a sequence involving the formation of a rhodium(III) azavinyl carbene, dual C(sp(2))-H functionalization, and [3+2]/[5+2] annulation. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Preparation of Rh/Ag bimetallic nanoparticles as effective catalyst for hydrogen generation from hydrolysis of KBH4

Science.gov (United States)

Huang, Liang; Jiao, Chengpeng; Wang, Liqiong; Huang, Zili; Liang, Feng; Liu, Simin; Wang, Yuhua; Zhang, Haijun; Zhang, Shaowei

2018-01-01

ISOBAM-104 protected Rh/Ag bimetallic nanoparticles (NPs) with average diameter less than 3.0 nm were synthesized by a co-reduction method. Ultraviolet-visible spectroscopy, transmission electron microscopy (TEM), high-resolution TEM and x-ray photoelectron spectroscopy (XPS) were employed to characterize the structure, particle size, and electronic structure of the prepared bimetallic NPs. The catalytic activities of prepared bimetallic NPs for hydrogen generation from hydrolysis of a basic KBH4 solution were evaluated in detail. The results indicated that as-prepared Rh/Ag bimetallic NPs showed a higher catalytic activity than corresponding monometallic NPs. Among all the monometallic NPs and bimetallic NPs, Rh80Ag20 bimetallic NPs exhibited the highest catalytic activity with a value of 6010 mol-H2·h-1·mol-catalyst-1 at pH = 12 and 303 K. The high catalytic activities of Rh/Ag bimetallic NPs could be attributed to presence of negatively charged Rh atoms and positively charged Ag atoms, which is supported by the results of XPS and density functional theory calculation. Based on the kinetic study, the apparent activation energy for the hydrolysis reaction of the basic KBH4 solution catalyzed by Rh80Ag20 bimetallic NPs was about 47.0 ± 3.9 kJ mol-1.