IrIII/NiII-Metallaphotoredox catalysis: the oxidation state modulation mechanism versus the radical mechanism.

A novel oxidation state modulation mechanism, merging oxidative quenching (IrIII–*IrIII–IrIV–IrIII) and nickel catalytic (NiII–NiI–NiIII–NiI–NiII) cycles, has been illuminated unambiguously for photoredox-mediated iridium(iii)/nickel(ii) dual catalyzed C–O cross-coupling of aryl bromide and alcohol. Quinuclidine participates in a crucial proton-coupled electron transfer process to accelerate the reaction and regulate C–O coupling selectivity. [ABSTRACT FROM AUTHOR]