A water-soluble Wilkinson's complex as homogeneous catalyst for the photochemical reduction of water

A water-soluble Wilkinson's complex, chlorotris(diphenylphosphinobenzene-m-sulphonate)rhodium(I) (Rh^ICl(dpm)₃³⁻), was examined as a homogeneous catalyst for the reduction of water coupled with the photoreaction of Ru(bpy)₃²⁺ using ascorbic acid as a sacrificial electron donor. A high quantum yield of H₂ (440 nm), i.e. 0.30, was obtained at pH 5. This value was found to be limited by the photochemical generation of Ru(bpy)₃⁺, indicating that the catalytic process maintained by the rhodium complex is almost quantitative. Studies by cyclic voltammetry, laser flash photolysis and pulse radiolysis revealed the catalysis mechanism which involves a Rh(II)-hydride species.