Water Oxidation Intermediates Applied to Catalysis: Benzyl Alcohol Oxidation

Four distinct intermediates, Ru-IV=O2+, Ru-IV(OH)(3+), Ru-V=O3+, and Ru-V(OO)(3+), formed by oxidation of the catalyst [Ru(Mebimpy)(4,4'-((HO)(2)OPCH2)(2)bpy)(OH2)](2+) [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl) and 4,4'-((HO)(2)OPCH2)(2)bpy = 4,4'-bismethylenephosphonato-2,2'-bipyridine] on nanoITO (1-PO3H2) have been identified and utilized for electrocatalytic benzyl alcohol oxidation. Significant catalytic rate enhancements are observed for Ru-V(OO)(3+) (similar to 3000) and Ru-IV(OH)(3+) (similar to 2000) compared to Ru-IV=O2+. The appearance of an intermediate for Ru-IV=O2+ as the oxidant supports an O-atom insertion mechanism, and H/D kinetic isotope effects support net hydride-transfer oxidations for Ru-IV(OH)(3+) and Ru-V(OO)(3+). These results illustrate the importance of multiple reactive intermediates under catalytic water oxidation conditions and possible control of electrocatalytic reactivity on modified electrode surfaces.