Supramolecular Photocatalyst with a Rh(III)-Complex Catalyst Unit for CO2 Reduction

The development of supramolecular photocatalysts has been an important target in the field of artificial photosynthesis because of their efficient reduction of CO2 and water oxidation and reduction, especially for solid materials, such as semiconductor particles, photoelectrodes, and mesoporous light-harvesting materials. We successfully developed the first supramolecular photocatalyst with a Rh complex as a catalyst unit for CO2 reduction. This new photocatalyst consisting of [Rh(BL)(Cp*)Cl]+ as the catalyst and [Ru(dmb)2(BL)]2+ as the photosensitizer (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl, BL = 1,2-bis(4′-methyl[2,2′-bipyridin]-4-yl)ethane, dmb = 4,4′-dimethyl-2,2′-bipyridine) mainly produced formic acid, even though a mixed system of the corresponding mononuclear complexes photocatalytically produced H2 as the main product. The photocatalytic reaction mechanism was investigated based on in situ UV–vis absorption studies and electrochemical measurements.