Water Oxidation Intermediates Applied to Catalysis: Benzyl Alcohol Oxidation

Abstract
Four distinct intermediates, RuIV═O2+, RuIV(OH)3+, RuV═O3+, and RuV(OO)3+, formed by oxidation of the catalyst [Ru(Mebimpy)(4,4′-((HO)2OPCH2)2bpy)(OH2)]2+ [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl) and 4,4′-((HO)2OPCH2)2bpy = 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 RuV(OO)3+ (∼3000) and RuIV(OH)3+ (∼2000) compared to RuIV═O2+. The appearance of an intermediate for RuIV═O2+ as the oxidant supports an O-atom insertion mechanism, and H/D kinetic isotope effects support net hydride-transfer oxidations for RuIV(OH)3+ and RuV(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.