Concerted metalation-deprotonation (CMD) is a mechanistic pathway through which transition-metal catalyzed C–H activation reactions can take place. In a CMD pathway, the C–H bond of the substrate is cleaved and the new C–Metal bond forms through a single transition state.[1] This process does not go through a metal species that is bound to the cleaved hydrogen atom. Instead, a carboxylate or carbonate base deprotonates the substrate.[2] The first proposal of a concerted metalation deprotonation pathway was by S. Winstein and T. G. Traylor in 1955 for the acetolysis of diphenylmercury.[3] It was found to be the lowest energy transition state in a number of computational studies,[4] was experimentally confirmed through NMR experiments,[5][6] and has been hypothesized to occur in mechanistic studies.[7]
While there are a number of different possible mechanisms for C–H activation, a CMD pathway is common for high valent, late transition metals like PdII,[8] RhIII, IrIII, and RuII.[9] The C–H bonds that have been found to undergo C–H activation through CMD include those that are aryl,[1] alkyl,[10][11] and alkenyl.[2] Investigations into CMD paved the way for the development of many new C–H functionalization reactions, especially in the areas of direct arylation and alkylation by palladium and ruthenium.[2]
^ abLapointe, David; Fagnou, Keith (2010-09-18). "Overview of the Mechanistic Work on the Concerted Metallation–Deprotonation Pathway". Chemistry Letters. 39 (11): 1118–1126. doi:10.1246/cl.2010.1118. ISSN 0366-7022.
^ abcAckermann, Lutz (2011-03-09). "Carboxylate-Assisted Transition-Metal-Catalyzed C−H Bond Functionalizations: Mechanism and Scope". Chemical Reviews. 111 (3): 1315–1345. doi:10.1021/cr100412j. ISSN 0009-2665. PMID 21391562.
^Winstein, S.; Traylor, T. G. (1955-07-01). "Mechanisms of Reaction of Organomercurials. II. Electrophilic Substitution on Saturated Carbon. Acetolysis of Dialkylmercury Compounds". Journal of the American Chemical Society. 77 (14): 3747–3752. doi:10.1021/ja01619a021. ISSN 0002-7863.
^Davies, David L.; Macgregor, Stuart A.; McMullin, Claire L. (2017-07-12). "Computational Studies of Carboxylate-Assisted C–H Activation and Functionalization at Group 8–10 Transition Metal Centers". Chemical Reviews. 117 (13): 8649–8709. doi:10.1021/acs.chemrev.6b00839. hdl:2381/40233. ISSN 0009-2665. PMID 28530807.
^Kapdi, Anant R. (2014-01-29). "Organometallic aspects of transition-metal catalysed regioselective C–H bond functionalisation of arenes and heteroarenes". Dalton Transactions. 43 (8): 3021–3034. doi:10.1039/C3DT52737A. ISSN 1477-9234. PMID 24419051.
^Olah, George A.; Yu, Simon H.; Parker, David G. (1976-05-01). "Organometallic chemistry. XII. Proton and carbon-13 nuclear magnetic resonance study of arenemercurinium ions, the intermediate complexes of aromatic mercuration". The Journal of Organic Chemistry. 41 (11): 1983–1986. doi:10.1021/jo00873a020. ISSN 0022-3263.
^Fung, Chung W.; Khorramdel-Vahed, Mehdi; Ranson, Richard J.; Roberts, Roger M. G. (1980-01-01). "Kinetics and mechanism of mercuriation of aromatic compounds by mercury trifluoroacetate in trifluoroacetic acid". Journal of the Chemical Society, Perkin Transactions 2 (2): 267–272. doi:10.1039/P29800000267. ISSN 1364-5471.
^Gorelsky, Serge I.; Lapointe, David; Fagnou, Keith (2008-07-29). "Analysis of the Concerted Metalation-Deprotonation Mechanism in Palladium-Catalyzed Direct Arylation Across a Broad Range of Aromatic Substrates". Journal of the American Chemical Society. 130 (33): 10848–10849. doi:10.1021/ja802533u. ISSN 0002-7863. PMID 18661978.
^Gensch, T.; Hopkinson, M. N.; Glorius, F.; Wencel-Delord, J. (2016-05-17). "Mild metal-catalyzed C–H activation: examples and concepts". Chemical Society Reviews. 45 (10): 2900–2936. doi:10.1039/C6CS00075D. ISSN 1460-4744. PMID 27072661.
^Hartwig, John F. (2016-01-13). "Evolution of C–H Bond Functionalization from Methane to Methodology". Journal of the American Chemical Society. 138 (1): 2–24. doi:10.1021/jacs.5b08707. ISSN 0002-7863. PMC 4809212. PMID 26566092.
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