Catalytic Water Oxidation by a Molecular Ruthenium Complex: Unexpected Generation of a Single-Site Water Oxidation Catalyst

The increasing energy demand calls for the development of sustainable energy conversion processes. Here, the splitting of H₂O to O₂ and H₂, or related fuels, constitutes an excellent example of solar-to-fuel conversion schemes. The critical component in such schemes has proven to be the catalyst responsible for mediating the four-electron oxidation of H₂O to O₂. Herein, we report on the unexpected formation of a single-site Ru complex from a ligand envisioned to accommodate two metal centers. Surprising N–N bond cleavage of the designed dinuclear ligand during metal complexation resulted in a single-site Ru complex carrying a carboxylate–amide motif. This ligand lowered the redox potential of the Ru complex sufficiently to permit H₂O oxidation to be carried out by the mild one-electron oxidant [Ru­(bpy)₃]³⁺ (bpy = 2,2′-bipyridine). The work thus highlights that strongly electron-donating ligands are important elements in the design of novel, efficient H₂O oxidation catalysts