Water Oxidation by In Situ Generated [Ru II (OH 2 )(NC NHC O)(pic) 2 ] +

A dinuclear ruthenium complex [Ru II (NC NHC O)(pic) 2 ] 2 2+ ( 2 ) was firstly prepared and characterized spectroscopically and electrochemically. Instead of the conventional ligand exchange, complex  2 dissociates in situ to afford two single‐site Ru aqua complexes, [Ru II (OH 2 )(NC NHC O)(pic) 2 ] + , which mediates water oxidation through proton‐coupled electron transfer events. In electrokinetic studies, complex  2 demonstrated a TOF of 150.3 s −1 comparable to those state‐of‐the‐art catalysts at neutral conditions. TONs of 2173 and 217 were attained in chemical and photochemical water oxidation when 2 was used as a catalyst, exhibiting good stability. Notably, a TOF of 1.3 s −1 was achieved at CAN‐driven water oxidation, which outperformed most of the reported single‐site Ru complexes, indicating that complex  2 is one of most active water oxidation catalysts (WOCs) to date. The unique coordination configuration and outstanding catalytic performance of complex  2 might shed light on the design of novel molecular WOCs.