Oxygen Reduction to Water Mediated by a Dirhodium Hydrido-Chloride Complex

The two-electron mixed-valence dirhodium complex Rh20,II(tfepma)2(CNtBu)2Cl2 (tfepma = CH3N[P(OCH2CF3)2]2) reacts with HCl to furnish two isomeric dirhodium hydrido-chloride complexes, Rh2II,II(tfepma)2(CNtBu)2Cl3H. In the presence of HCl, the hydride complex effects the reduction of 0.5 equiv of O2 to 1 equiv of H2O, generating Rh2II,II(tfepma)2(CNtBu)2Cl4, which can be prepared independently by chlorine oxidation of the Rh20,II precursor. The starting Rh20,II complex is regenerated photochemically to close an oxygen-to-water reduction photocycle.