F430 model chemistry. Evidence for alkyl- and hydrido-nickel intermediates in the reactions of the nickel(I) octaethylisobacteriochlorin anion

Abstract

The reactions of Ni^I(OEiBC)- with alkyl (isomeric propyl, butyl, and hexyl) and aryl halides were investigated in acetonitrile, dimethylformamide, and tetrahydrofuran solutions. The principal products result from reduction or dehydrohalogenation of the alkyl or aryl halide. Alkene formation is favored by more polar solvents and by secondary vs primary substitution of the alkyl halide. Isomerization of alkenes occurs during the reaction, which strongly implies the intermediacy of hydrido-nickel intermediates. Coupling processes, which produce significant quantities of ethane from methyl iodide, become insignificant as the length or steric bulk of the alkyl group increases. No coupling products are observed for aryl or benzyl halides. The current observations provide strong support for the nonradical nickel-based mechanism previously proposed and suggest that the dehydrohalogenation processess in this system involve β -hydride elimination.