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

Abstract

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.

Mononuclear ruthenium polypyridine complexes that catalyze water oxidation

“…The introduction of an amide group in place of one carboxylate group of pdc further lowers the oxidation potential and enhances the catalytic activity of the complex. 60 …”

Effect of Quinoline Substitution on Water Oxidation by [Ru(Ql-tpy)(bpy)(OH2 )](PF6 )2

“…al . reported the advantageous effects of incorporating the carboxylate‐amide ligand in a Ru complex, that significantly reduces redox potentials …”

A ruthenium water oxidation catalyst based on a carboxamide ligand

“…For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6dt00327c driven by the mild single-electron oxidant [Ru(bpy) 3 ] 3+ (bpy = 2,2′-bipyridine). 11 It was also markedly more active than the corresponding dicarboxylate complex. 12 The incorporation of the amide moiety into WOCs thus seemed to create a suitable ligand framework for producing robust catalysts.…”