A photoactive nickel complex provides evidence for a general Ni(I)/Ni(III) paradigm in 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 provided evidence that (Csp2)–heteroatom bond formations proceed through NiI/NiIII cycles. Related C(sp2)–C(sp3) cross-couplings were proposed to operate via generation of C-centered radicals and a catalytic cycle that involves Ni0, NiI and NiIII species. However, the exact mechanism of C(sp2)–C(sp3) couplings is still under debate. We demonstrate that light-mediated C(sp2)–C(sp3) bond formations can operate via a NiI/NiIII manifold without C-centered radical intermediates. 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 C(sp2)–C(sp3) cross-couplings between aryl halides and benzyltrifluoroborate salts without involving photoredox reactivity. Mechanistic investigations unveiled an unprecedented direct transmetalation between a NiI intermediate and the organoboron species that serves as the crucial catalytic step. Our study demonstrates that light-mediated C(sp2)–heteroatom and C(sp2)–C(sp3) cross-couplings can both proceed through similar NiI/NiIII cycles. This new paradigm for light-mediated nickel catalysis will be pivotal for the rational design of photoactive ligands and novel cross-coupling methodologies.