Highly efficient supramolecular photocatalysts for CO2 reduction using visible light

We report the most efficient homogeneous photocatalyst yet for CO2 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)](3+) and [Ru-Repy](3+) where a P(OEt)(3) or pyridine ligand coordinates on the Re site. Their photocatalytic activities were compared with [Ru-ReCl](2+), which has a Cl- ligand on the Re site and has recently been reported as a much better photocatalyst (Phi = 0.12, TNCO = 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)](3+), for which Phi = 0.21 and TNCO = 232. A mechanistic study clearly showed that [Ru-ReP(OEt)(3)](3+) is rapidly converted into the solvento complex [Ru-ReSol](3+), (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.