Self-Photosensitizing Cobalt Complexes for Photocatalytic CO₂ Reduction Coupled with CH₃OH Oxidation

The use of metal complexes as homogeneous molecular catalysts has attracted considerable attention regarding photocatalytic CO₂ reduction. Enhancing these complexes with photosensitivity and photooxidation capabilities, aiming to create multifunctional molecular devices, presents significant challenges. In response to these challenges, we successfully designed and synthesized three innovative metal complexes. The complexes demonstrate a remarkable ability to perform CO₂ photoreduction in tandem with methanol photooxidation, allowing for the simultaneous production of formic acid without requiring additional photosensitizers and electron sacrificial reductants. An optimal turnover number (TON) value of 855 was obtained under simulated sunlight. Even under natural sunlight, the TON can reach 207, much higher than the value of the physical mixture of the photocatalytic reductive and oxidative moieties. Spectroscopic studies and density functional theory (DFT) calculations revealed that integrating reduction and oxidation sites in one molecular catalyst can promote charge transfer kinetics and enhance activity for CO₂ reduction and methanol oxidation. This is the first report that non-noble metal homogeneous catalysts can simultaneously possess photosensitivity, photoreduction, and photo-oxidation functions, offering new insights into designing homogeneous catalysts for artificial photosynthesis.