Evidence for a unifying Ni(I)/Ni(III) mechanism in light-mediated cross-coupling catalysis

Advances in nickel catalysis have significantly broadened the synthetic chemists’ toolbox, particularly through methodologies leveraging paramagnetic nickel species via photoredox catalysis or electrochemistry. Key to these reactions are oxidation state modulations of nickel via single electron transfer events. Recent mechanistic studies indicate that C(sp²)–heteroatom bond formations proceed through Ni^I/Ni^III cycles. Related C(sp²)–C(sp³) cross-couplings operate via the photocatalytic generation of C-centered radicals and a catalytic cycle that involves Ni⁰, Ni^I and Ni^III species. Here, we show that light-mediated nickel-catalyzed C(sp²)–C(sp³) bond formations can be carried out without using an exogenous photoredox catalysts but with a photoactive ligand. In a pursuit to expand the scope of C(sp²)–heteroatom couplings using donor-acceptor ligands, we identified a photoactive nickel complex capable of catalyzing cross-couplings between aryl halides and benzyl trifluoroborate salts.  Mechanistic investigations provide evidence that transmetalation between a photochemically generated Ni^I species and the organoboron species is the key catalytic step in a Ni^I/Ni^III catalytic cycle under these conditions.