Light-Driven Reduction of CO₂ to CO in Water with a Cobalt Molecular Catalyst and an Organic Sensitizer

We report an efficient visible light-driven CO 2 reduction system that functions in water and without any noble metal nor rare materials. Using the cobalt complex [Co(qpy)(OH 2 ) 2 ] 2+ ( 1, qpy = 2,2′:6′,2″:6″,2‴-quaterpyridine) as a catalyst, an organic triazatriangulenium ( TATA + ) salt as the photosensitizer (PS), BIH + TEOA (BIH = 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[ d ]imidazole and TEOA = triethanolamine) as the sacrificial reductant (SD), CO and formate were first produced with a total TON >3700 upon irradiation in CO 2 -saturated CH 3 CN solution with visible light. Upon the addition of a weak Brönsted acid (water), catalysis was enhanced and directed toward CO production (19,000 TON, 93% selectivity). The photocatalytic system was further shown to function in pure water as a solvent. High metrics with a TON for CO of 2600 and 94% selectivity were obtained using TEA (triethylamine) as the SD.