Dinickel-Catalyzed Vinylidene–Alkene Cyclization Reactions

A dinickel catalyst promotes reductive cyclization reactions of 1,1-dichloroalkenes containing pendant olefins. The reactions can be conducted with a Zn reductant or electrocatalytically using a carbon working electrode. Mechanistic studies are consistent with the intermediacy of a Ni2(vinylidene) species, which adds to the alkene and generates a metallacyclic intermediate. β-Hydride elimination followed by C–H reductive elimination forms the cyclization product. The proposed dinickel metallacycle is structurally characterized and its stoichiometric conversion into product is demonstrated. Spin-polarized, unrestricted DFT calculations are used to further examine the cyclization mechanism. These calculations reveal that both nickel centers function cooperatively to mediate the key oxidative addition, migratory insertion, β-hydride elimination, and reductive elimination steps.