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 <i>k</i>_obs (TOF_max) 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 of ¹⁵NH₃ using ¹H and ¹⁵N 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.