Capturing the Elusive [RuV═O]⁺ Intermediate in Water Oxidation

Although several Run+ (n = 2 or 3) complexes have been reported to be excellent biomimetics for the water oxidation process of photosystem II, investigation and spectroscopic characterization of the reactive intermediates such as [RuIV/V═O]n+ involved in the catalytic process are not only scarce but also a daunting task. Here, we report a catalyst [RuIII(L)(PPh3)(H2O)]+ (2) found to show electrochemical water oxidation efficiency with a considerably low overpotential of 195 mV compared to other Run+ water oxidation catalysts reported in the nonaqueous media. Besides, the Schiff base ligand (L) employed in this study facilitates the stabilization of a [LRuV═O]+ species. By the use of multispectroscopic techniques (spectroelectrochemistry, electron paramagnetic resonance, and resonance Raman), we have shed light on the electronic structure of the elusive [LRuV═O]+ species. Based on the experimental results, a plausible intermolecular radical coupling (I2M) mechanism is proposed, which is corroborated by theoretical calculations.