Light-Promoted C(sp³)-C(sp³) Reductive Elimination from Dialkyl Ni^II Complexes

Ni-catalyzed cross-coupling is a powerful strategy to forge C(sp³)-C(sp³) bonds. Typically, to do so requires overcoming a challenging C-C bond-forming reductive elimination, often enabled by the intermediacy of highly oxidized Ni species or outer-sphere processes. While direct C(sp³)-C(sp³) reductive elimination from the Ni^II base oxidation state is normally thermally inaccessible, light-activation provides an avenue to affect such transformations. Here, we investigate the mechanism of light-induced C(sp³)-C(sp³) bond formation from dialkyl bipyridine Ni^II complexes through a variety of organometallic, spectroscopic, and computational studies. Wavelength-dependent quantum yields, ligand electronics-reactivity relationships, excited-state lifetimes, computed barriers, and product distributions from crossover studies support a photolysis/radical rebound mechanism. This reactivity paradigm complements existing strategies in the literature to promote reductive elimination from Ni^II, such as the use of destabilizing, sterically hindered ligands and reduction of electron density at Ni through the binding of electron-deficient olefins. Hence, we envision that light-induced reductive elimination may enable the development of challenging C(sp³)-C(sp³) couplings.