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A coupling reaction in organic chemistry is a general term for a variety of reactions where two hydrocarbon fragments are coupled with the aid of a metal catalyst. In one important reaction type a main group organometallic compound of the type RM (R = organic fragment, M = main group centre) reacts with an organic halide of the type R'X with formation of a new carbon-carbon bond in the product R-R' 〔''Organic Synthesis using Transition Metals'' Rod Bates ISBN 978-1-84127-107-1〕〔''New Trends in Cross-Coupling: Theory and Applications'' Thomas Colacot (Editor) 2014 ISBN 978-1-84973-896-5〕 Contributions to coupling reactions by Ei-ichi Negishi and Akira Suzuki were recognized with the 2010 Nobel Prize in Chemistry, which was shared with Richard F. Heck.〔''Palladium-Catalyzed Cross-Coupling: A Historical Contextual Perspective to the 2010 Nobel Prize'' Dr. Carin C. C. Johansson Seechurn, Dr. Matthew O. Kitching, Dr. Thomas J. Colacot, Prof. Victor Snieckus Angew. Chem. Int. Ed. 2012, 51, 5062-5085. 〕 Broadly speaking, two types of coupling reactions are recognized: *cross couplings involve reactions between two different partners, for example bromobenzene (PhBr) and vinyl chloride to give styrene (PhCH=CH2). *homocouplings couple two identical partners, for example, the conversion of iodobenzene (PhI) to biphenyl (Ph-Ph). ==Mechanism== The reaction mechanism usually begins with oxidative addition of one organic halide to the catalyst. Subsequently, the second partner undergoes transmetallation, which places both coupling partners on the same metal centre. The final step is reductive elimination of the two coupling fragments to regenerate the catalyst and give the organic product. Unsaturated organic groups couple more easily in part because they add readily. The intermediates are also less prone to beta-hydride elimination.〔Hartwig, J. F. Organotransition Metal Chemistry, from Bonding to Catalysis; University Science Books: New York, 2010. ISBN 1-891389-53-X〕 In one computational study, unsaturated organic groups were shown to undergo much easier coupling reaction on the metal center.〔V. P. Ananikov, D. G. Musaev, K. Morokuma, “Theoretical Insight into the C-C Coupling Reactions of the Vinyl, Phenyl, Ethynyl, and Methyl Complexes of Palladium and Platinum” Organometallics 2005, 24, 715. 〕 The rates for reductive elimination followed the following order: vinyl-vinyl > phenyl-phenyl > alkynyl-alkynyl > alkyl-alkyl. The activation barriers and the reaction energies for unsymmetrical R-R′ couplings were found to be close to the averages of the corresponding values of the symmetrical R-R and R′-R′ coupling reactions; for example: vinyl-vinyl > vinyl-alkyl > alkyl-alkyl. Another mechanistic approach proposes that specifically in aqueous solutions, coupling actually occurs via a radical mechanism rather than a metal-assisted one. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Coupling reaction」の詳細全文を読む スポンサード リンク
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