Voltage-Driven Molecular Catalysis: A Promising Approach to Electrosynthesis

The combination of electrocatalysis and molecular catalysis is an increasingly popular approach to designing catalysts for electrosynthetic processes. We recently found that the electrostatic potential drop across the double layer contributes to the driving force for electron transfer between a dissolved reactant and a molecular catalyst immobilized directly on the electrode surface. The applied electrode potential can increase the oxidizing (or reducing) ability of a surface-bound molecular catalyst, thus making it suitable for charge-transfer processes, which it normally would not be able to catalyze. In this article, we report the initial application of voltage-driven molecular catalysis to electroorganic synthesis. The metal-free, purely organic molecular catalyst (TEMPO) attached to a carbon electrode showed potential-dependent activity for the oxidation of toluene, which does not occur if TEMPO is used as a homogeneous catalyst. Surface-attached TEMPO also shows significant catalytic activity toward benzyl alcohol oxidation even at pH 7. The products of toluene and benzyl alcohol oxidations were identified by nuclear magnetic resonance, Fourier transform infrared, and ultraviolet-visible spectroscopy to evaluate the reaction yield and selectivity. The effect of the applied electrode potential on these catalytic processes was elucidated by density functional theory calculations.