Nonaqueous Electrocatalytic Oxidation of the Alkylaromatic Ethylbenzene by a Surface Bound RuV(O) Catalyst

Abstract

The catalyst [Ru(Mebimpy)(4,4′-((HO)2OPCH2)2bpy(OH2)]2+, where Mebimpy is 2,6-bis(1-methylbenzimidazol-2-yl)pyridine and 4,4′-((HO)2OPCH2)2bpy is 4,4′-bis-methlylenephosphonato-2,2′-bipyridine, attached to nanocrystalline Sn(IV)-doped In2O3 (nanoITO) electrodes (nanoITO|RuII–OH22+) has been utilized for the electrocatalytic oxidation of the alkylaromatics ethylbenzene, toluene, and cumene in propylene carbonate/water mixtures. Oxidative activation of the surface site to nanoITO|RuV(O)3+ is followed by hydrocarbon oxidation at the surface with a rate constant of 2.5 ± 0.2 M–1 s–1 (I = 0.1 M LiClO4, T = 23 ± 2 °C) for the oxidation of ethylbenzene. Electrocatalytic oxidation of ethylbenzene to acetophenone occurs with a faradic efficiency of 95%. H/D kinetic isotope effects determined for oxidation of ethylbenzene point to a mechanism involving oxygen atom insertion into a C–H bond of ethylbenzene followed by further 2e–/2H+ oxidation to acetophenone.