Ru(II)-Re(I) binuclear photocatalysts connected by -CH2XCH2- (X = O, S, CH2) for CO2 reduction

We developed Ru(II)-Re(I) supramolecular photocatalysts in which each metal complex unit is connected by a -CH2XCH2- (X = O, S, CH2) chain. The photocatalyst with X = O exhibited the best photocatalytic efficiency for CO2 reduction in the reported systems using a NAD(P)H model compound as an electron donor because the introduced oxygen atom strengthened the oxidation power of the Ru photosensitizer unit in the excited state and accelerated electron transfer from the one-electron-reduced Ru photosensitizer unit to the Re catalyst unit. In contrast, the catalytic ability of the photocatalyst with X = S rapidly decreased during irradiation because the supramolecular structure split into mononuclear complexes. A detailed mechanism for the efficient photocatalytic reaction involving these supramolecular photocatalysts was investigated for the first time.