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

This essay for EurJIC's special issue on "Redox Catalysis for Artificial Photosynthesis" introduces the reader to the field of water oxidation using molecular catalysts. The most essential challenge our society must address during the 21st century is perhaps the realization of a system for producing sustainable energy on the global scale. Currently, there exists an urgent need to develop effective and economical carbon‐neutral or carbon‐free energy technologies. The production of solar fuels through water splitting constitutes a key enabling element. The construction of robust and efficient catalysts for oxidation of water is therefore essential. In this essay the progress and mechanistic considerations pertaining to molecular water oxidation catalysts are described and discussed from a personal perspective. [ABSTRACT FROM AUTHOR]

The production of clean and sustainable energy is considered as one of the most urgent issues for our society. Mastering the oxidation of water to dioxygen is essential for the production of solar fuels. A study of the influence of the substituents on the catalytic activity of a series of mononuclear Ru complexes ( 2 a- e) based on a tetradentate ligand framework is presented. At neutral pH, using [Ru(bpy)3](PF6)3 (bpy=2,2'-bipyridine) as the terminal oxidant, a good correlation between the turnover frequency (TOF) and the Hammett σmeta parameters was obtained. Additionally, a general pathway for the deactivation of Ru-based catalysts 2 a- e during the catalytic oxidation of water through poisoning by carbon monoxide was demonstrated. These results highlight the importance of ligand design for fine-tuning the catalytic activity of water oxidation catalysts. [ABSTRACT FROM AUTHOR]