The only operating mechanism in the oxidation of water to dioxygen catalyzed by the mononuclear cis-[RuII(bpy)2(H2O)2]2+ complex when treated with excess CeIV was unambiguously established. Theoretical calculations together with 18O-labeling experiments (see plot) revealed that it is the nucleophilic attack of water on a RuO group.
![The cis-[RuII(bpy)2(H2O)2]2+ water-oxidation catalyst revisited](https://www.iciq.org/wp-content/uploads/2014/03/The-cis-RuIIbpy2H2O22_7745.gif)