Figure 2. Proposed mechanism for the metallaphotoredox-mediated cross-coupling of carboxylic acids to generate sp³–sp³ bonds.

The photoredox catalytic cycle commences with excitation of Ir^III 1 to give the excited state 2. Single electron oxidation of the carboxylate anion derived from acid 3 produces the alkyl radical 4 after CO₂-extrusion along with Ir^II 5. Ni⁰ catalyst 6 captures the alkyl radical 4 to form the Ni^I species 7. Ensuing oxidative addition with alkyl halide 8 leads to nickel(III) intermediate 9. Reductive elimination would then liberate the desired product 10 and Ni^I 11. Both catalytic cycles converge to complete a single turnover via a SET event that regenerates the photoredox and nickel catalysts