Paired Electrocatalysis Unlocks Cross-Dehydrogenative Coupling of C(sp3)-H Bonds Using A Pentacoordinated Cobalt-Salen Catalyst

Abstract

Abstract Cross-dehydrogenative coupling (CDC) of C(sp3)-H bonds is an ideal approach for C(sp3)-C(sp3) bonds construction. However, conventional approaches mainly rely on the single activation mode by either stoichiometric oxidants or electrochemical oxidation, which would lead to inferior selectivity in the reaction between similar C(sp3)-H bonds. We herein developed a paired electrocatalysis strategy to access an unconventional selectivity in the CDC of alcoholic α C(sp3)-H with allylic (or benzylic) C-H bonds, which combines hydrogen evolution reaction (HER) catalysis with hydride transfer (H-T) catalysis. To maximize the synergistic effect of the catalyst combinations, a novel HER catalyst pentacoordinated Co-salen was disclosed, and it displayed a large redox-potential gap (1.98 V) and suitable redox potential. With the optimized catalyst combination, an electrochemical CDC protocol features an unconventional chemoselectivity (C-C vs. C-O coupling), excellent functional group tolerance (83 examples), useful byproduct (hydrogen), high regio- and site-selectivity. A plausible reaction mechanism was also proposed to rationalize the experimental observations.