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 CO2 reduction system that functions in water and without any noble metal nor rare materials. Using the cobalt complex [Co(qpy)(OH2)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 CO2- saturated CH3CN solution with visible light. Upon the addition of a weak Bro''nsted 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.