Photoreduction of CO2 using [Ru(bpy)2(CO)L] n+ catalysts in biphasic solution/supercritical CO2 systems

Article abstract of DOI:10.1021/ic401031j

The reduction of CO₂ in a biphasic liquid-condensed gas system was investigated as a function of the CO₂ pressure. Using 1-benzyl-1,4-dihydronicotinamide (BNAH) as sacrificial electron donor dissolved in a dimethylformamide-water mixture and [Ru(bpy)₂(CO)L]ⁿ⁺ as a catalyst and [Ru(bpy)₃]²⁺ as a photosensitizer, the reaction was found to produce a mixture of CO and formate, in total about 250 μmol after just 2 h. As CO₂ pressure increases, CO formation is greatly favored, being four times greater than that of formate in aqueous systems. In contrast, formate production was independent of CO₂ pressure, present at about 50 μmol. Using TEOA as a solvent instead of water created a single-phase supercritical system and greatly favored formate synthesis, but similarly increasing CO₂ concentration favored the CO catalytic cycle. Under optimum conditions, a turnover number (TON) of 125 was obtained. Further investigations of the component limits led to an unprecedented TON of over 1000, and an initial turnover frequency (TOF) of 1600 h ^-1.