XAS and EPR in Situ Observation of Ru(V) Oxo Intermediate in a Ru Water Oxidation Complex**

In this study, we combine in situ spectroelectrochemistry coupled with electron paramagnetic resonance (EPR) and X-ray absorption spectroscopies (XAS) to investigate a molecular Ru-based water oxidation catalyst bearing a polypyridinic backbone [Ru-II(OH2)(Py(2)Metacn)](2+). Although high valent key intermediate species arising in catalytic cycles of this family of compounds have remain elusive due to the lack of additional anionic ligands that could potentially stabilize them, mechanistic studies performed on this system proposed a water nucleophilic attack (WNA) mechanism for the O-O bond formation. Employing in situ experimental conditions and complementary spectroscopic techniques allowed to observe intermediates that provide support for a WNA mechanism, including for the first time a Ru(V) oxo intermediate based on the Py(2)Metacn ligand, in agreement with the previously proposed mechanism.

Automated summary

In this study, a molecular Ru-based water oxidation catalyst bearing a polypyridinic backbone was investigated using in situ spectroelectrochemistry coupled with EPR and XAS techniques. The study proposed a water nucleophilic attack mechanism for O-O bond formation, and observed intermediates supporting this mechanism, including a Ru(V) oxo intermediate based on the Py(2)Metacn ligand for the first time.