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Water oxidation is a fundamental step in artificial photosynthesis for solar fuels production. In this study, we report a single‐site Ru‐based water oxidation catalyst, housing a dicarboxylate‐benzimidazole ligand, that mediates both chemical and light‐driven oxidation of water efficiently under neutral conditions. The importance of the incorporation of the negatively charged ligand framework is manifested in the low redox potentials of the developed complex, which allows water oxidation to be driven by the mild one‐electron oxidant [Ru(bpy)3]3+ (bpy=2,2’‐bipyridine). Furthermore, combined experimental and DFT studies provide insight into the mechanistic details of the catalytic cycle.

Herein is described a highly active ruthenium-based water oxidation catalyst [RuX(mcbp)(OHn)(py)2] (5, mcbp2− = 2,6-bis(1- methyl-4-(carboxylate)benzimidazol-2-yl)pyridine; n = 2, 1, and 0 for X = II, III, and IV, respectively), which can be generated in a mixture of RuIII/RuIV states from either [RuII(mcbp)(py)2] (4II) or [RuIII(Hmcbp)(py)2]2+ (4III). Complexes 4II and 4III were isolated and characterized by single crystal X-ray analysis, NMR, UV-vis, FT-IR, ESI-HRMS, EPR, and elemental analysis, and their redox properties were studied in detail by electrochemical and spectroscopic methods. Unlike for the parent catalyst [Ru(tda)(py)2] (1, tda2− = [2,2′:6′,2′′- terpyridine]-6,6′′-dicarboxylate), for which full transformation to the catalytically active species [RuIV(tda)(O)(py)2] (2) could not be carried out — stoichiometric generation of the catalytically active Ru-aqua complex 5 from 4II was achieved under mild conditions (pH 7.0) and short reaction times. The redox properties of the catalys were studied and its activity for electrocatalytic water oxidation was evaluated, reaching TOFmax ≈ 40 000 s−1 at pH 9.0 (from the foot-of- the-wave analysis, FOWA), which is comparable to the activity of the state-of-the-art catalyst 2.

A shift in energy dependence from fossil fuels to sustainable and carbon-neutral alternatives is a daunting challenge that faces the human society. Light harvesting for the production of solar fuels has been extensively investigated as an attractive approach to clean and abundant energy. An essential component in solar energy conversion schemes is a catalyst for water oxidation. Ruthenium-based catalysts have received significant attention due to their ability to efficiently mediate the oxidation of water. In this context, the design of robust catalysts capable of driving water oxidation at low overpotential is a key challenge for realizing efficient visible light-driven water splitting. Herein, recent progress in the development within this field is presented with a focus on homogeneous ruthenium-based systems and surface-immobilized ruthenium assemblies for photo-induced oxidation of water.