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.