(NHC)Ni(0)-Catalyzed Branched-Selective Alkene Hydrosilylation with Secondary and Tertiary Silanes

Abstract

Hydrosilylation is a valuable approach for the construction of organosilanes, which are precursors to silicone materials that are widely incorporated in our everyday lives. The industry currently relies primarily on Karstedt’s catalyst, Pt2(dvtms)3 (dvtms = 1,3-divinyltetramethyldisiloxane), a precious metal catalyst that exhibits linear selectivity, with regioselectivity favoring the branched product remaining an outstanding challenge. The use of more Earth-abundant, base-metal catalysts has been a recent focus for hydrosilylation reactions, and most reports focus on the development of linear-selective catalysts and are commonly limited to primary and/or secondary silanes. We demonstrate that (NHC)­Ni(0) (NHC = N-heterocyclic carbene) complexes are active in the branched-selective hydrosilylation of alkenes with secondary or tertiary silanes, including industrially relevant alkoxy- and chlorosilanes. The scope of alkenes and silanes has been expanded beyond what is currently known for Ni-catalyzed hydrosilylation reactions, including both steric and electronic profiles. In-depth mechanistic studies were also carried out, including stoichiometric and catalytic experiments investigating kinetic and thermodynamic reaction parameters. Radical trap experiments suggest against a one-electron pathway. The rate law of the reaction has a normal dependence on the Ni catalyst and silane and has an inverse dependence on the alkene. Deuterium-labeling studies reveal that hydrosilylation proceeds through a Chalk–Harrod-type mechanism, with the alkene reversibly inserting into a Ni–H bond. Hammett analyses show that the rate of reaction is faster with electron-rich alkenes and electron-poor silanes. Additional mechanistic evidence points to the resting state of the catalyst being a (NHC)­Ni­(alkene)2 complex, and the rate-determining step being migratory insertion and/or reductive elimination.

Ruthenium(II) Complexes of an Imidazole Carboxamido Ligand for Base-Free Transfer Hydrogenation in Air

“…A good linear fit is obtained, however, by plotting the initial rate against [ 1 ] 1/2 (Figure B), which suggests that the rate of transfer hydrogenation is half-order with respect to catalyst loading. Consistent with previously reported monomeric catalysts, − we propose that the half-order dependence with respect to [ 1 ] arises from a pre-equilibrium chloride dissociation from the catalyst resting state (see the Supporting Information).…”

Nickel-Catalyzed Exhaustive Hydrodefluorination of Perfluoroalkyl Arenes

“…Finally, hydrosilylation catalyzed by Ni/ICy occurs to give alkyl silanes 4 and 5 . A related Ni/NHC catalysis for the hydrosilylation of alkenes, including vinyl arenes, has been developed by Cook and co-workers . According to their mechanistic proposal, the hydrosilylation proceeds via the Chalk–Harrod mechanism: oxidative addition of the Si–H bond to Ni(0), insertion of the alkene, and reductive elimination to give alkyl silanes.…”

N-Heterocyclic carbenes as privileged ligands for nickel-catalysed alkene functionalisation

“…Scheme 48 Ni/NHC-catalysed hydrosilylation of alkenes with 21, 31 and chlorosilanes. 120 Scheme 49 Ni/NHC-catalysed hydroamination of activated alkenes with 21 amines. 125 Preliminary computational calculations to determine the nature of bonding of the (NHC) 2 NiBr 2 complex were performed, which showed that the 1,2,4-triazole based NHC is a strong s-donating ligand like the common imidazole based NHC ligands (Chart 1).…”

“…In 2022, Cook et al reported a Ni 0 /NHC-catalysed branched-selective hydrosilylation reaction of styrenes with 2°, 3° and chlorosilanes 120 (Scheme 48). Industrially relevant silanes, particularly those substituted with chlorine or alkoxy groups, have not been extensively studied in the field of base-metal catalysis.…”

“…Scheme 48 Ni/NHC-catalysed hydrosilylation of alkenes with 21, 31 and chlorosilanes 120. Scheme 49 Ni/NHC-catalysed hydroamination of activated alkenes with 21 amines 125.…”