Unravelling the Super-Reductive State of Iridium Photoredox Catalysts

Harnessing the excited state of reduced species has long posed a challenge in the field of photocatalysis. This study presents the isolation and characterization of 1-electron reduced iridium complexes commonly employed in photoredox catalysis. Stochiometric reactions unveiled an unprecedented super-reductant ability for the isolated complexes under light irradiation, reaching potentials below 3 V vs SCE. Notably, the reduced iridium complex can also be electrochemically generated in situ with analogous super-reductant ability, enabling electro(photo)catalysis. Experimental and computational studies reveal that photoreactivity rises from intrinsic excitation of the reduced (bpy●‒)* ligand within the iridium complex, while the metal center acts as a spectator. Corroborating this finding, the organic salt Li+bpy●‒ exhibited equivalent super-reducing reactivity under photochemical conditions. Our findings shed light on the access to the super-reductant states of iridium photoredox catalysts and other metalated bipyridines, opening new opportunities for electro(photo) synthetic methodologies.