Electrocatalytic Ammonia Oxidation with Coordinatively Saturated Ruthenium Catalyst

Abstract

This communication describes the investigation of a coordinatively saturated complex [Ru(tpy)(dmabpy)Cl]+ ([Ru(Cl)]+) as an ammonia oxidation catalyst. Cyclic voltammetry measurements show an ideal S-shaped wave, indicating total catalysis conditions with a kobs (TOFmax) of 9360 h-1. The reaction was found to be first-order in [Ru(Cl)]+ and third-order in [NH3]. Stoichiometric reactions of the one-electron oxidized species, [Ru(Cl)]2+, were monitored following the addition of15NH3 using1H and15N NMR spectroscopy. These experiments showed that the chloride-coordinated complex rapidly converts NH3 to N2. NMR spectroscopy and electrochemistry results definitively show that NH3 does not substitute the Cl- ligand to form the previously reported [Ru(NH3)]2+ catalyst which operates by a different mechanistic pathway. Taken together these results indicate outersphere electron transfer mediated ammonia oxidation reaction.