Highly efficient supramolecular photocatalysts for CO2 reduction using visible light

Abstract

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 (Φ = 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]³⁺, for which Φ = 0.21 and TN_CO = 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.