Highly efficient supramolecular photocatalysts for CO2 reduction using visible light.

We report the most efficient homogeneous photocatalyst yet for CO(2) reduction using a wide range of visible-light wavelength. We synthesized new Ru(II)-Re(I) binuclear complexes with 1,3-bis(4'-methyl-[2,2']bipyridinyl-4-yl)-propan-2-ol (bpyC3bpy) as a bridge ligand, specifically Ru-ReP(OEt)(3) and Ru-Repy where a P(OEt)(3) or pyridine ligand coordinates on the Re site. Their photocatalytic activities were compared with Ru-ReCl, which has a Cl(-) ligand on the Re site and has recently been reported as a much better photocatalyst (Phi = 0.12, TN(CO) = 160) than a 1:1 mixed system of the corresponding Ru(II) and Re(I) mononuclear complexes. The best photocatalyst was Ru-ReP(OEt)(3), for which Phi = 0.21 and TN(CO) = 232. A mechanistic study clearly showed that Ru-ReP(OEt)(3) is rapidly converted into the solvento complex Ru-ReSol, (Sol = DMF or TEOA) which is the actual photocatalyst. Although similar rapid ligand substitution occurs with other supramolecules, the pyridine and Cl(-) anions accelerate the decomposition of the supramolecular photocatalysts.