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Kinetic and Density Functional Studies on Alkyl-Carbene Elimination from PdII Heterocyclic Carbene Complexes: A New Type of Reductive Elimination with Clear Implications for Catalysis
journal contributionposted on 2023-05-16, 13:05 authored by McGuinness, DS, Saendig, NS, Brian YatesBrian Yates, Cavell, KJ
A number of new methyl-Pd II complexes of heterocyclic carbenes of the form [PdMe(tmiy)L 2]BF 4 have been prepared, and their reaction behavior has been studied (tmiy = 1,3,4,5-tetramethylimidazolin-2-ylidene, L = cyclooctadiene (8), methyldiphenylphosphine (9), triphenyl phosphite (10), triphenylphosphine (11)). In common with other hydrocarbyl-M carbene complexes (M = Pd, Ni) the complexes are predisposed to a facile decomposition process. A detailed mechanism for the process and of the decomposition pathway followed is presented herein. All complexes decompose with first-order kinetics to yield 1,2,3,4,5-pentamethylimidazolium tetrafluoroborate and Pd 0 species. The kinetic investigations combined with density functional studies show that the complexes decompose via a mechanism of concerted reductive elimination of the methyl group and carbene. The reaction represents a new type of reductive elimination from transition metals and also represents a low-energy pathway to catalyst deactivation for catalysts based on heterocyclic carbenes. The theoretical studies indicate extensive involvement of the p(Ï€) orbital on the carbene carbon in the transition structure. Methods of stabilizing catalysts based on heterocyclic carbene complexes are suggested, and the possibility of involvement of carbene species during catalysis in ionic liquids is discussed.
Publication titleJournal of the American Chemical Society
Department/SchoolSchool of Natural Sciences
PublisherAmerican Chemical Society
Place of publicationWashington DC