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.