Electrocatalytic Ammonia Oxidation Mediated by a Polypyridyl Iron Catalyst

Electrocatalytic ammonia oxidation (AO) mediated by iron­(II) tris­(2-pyridylmethyl)­amine (TPA) bis-ammine triflate, [(TPA)­Fe­(NH3)2]­OTf2, is reported. Interest in (electro)­catalytic AO is growing rapidly, and this report adds a first-row transition metal (iron) complex to the known Ru catalysts recently reported. The featured system is well behaved and has been studied in detail by electrochemical methods. Cyclic voltammetry experiments in the presence of ammonia indicate an onset potential corresponding to ammonia oxidation at 0.7 V vs Fc/Fc+. Controlled potential coulometry (CPC) at an applied bias of 1.1 V confirms the generation of 16 equiv of N2 with a Faradaic efficiency for N2 of ∼80%. Employing 15NH3 yields exclusively 30N2, demonstrating the conversion of ammonia to N2. A suite of electrochemical studies is consistent with an initial EC step that generates an FeIII–NH2 intermediate (at 0.4 V) followed by an anodically shifted catalytic wave. The data indicate a rate-determining step that is first order in both [Fe] and [NH3] and point to a fast catalytic rate (kobs) of ∼107 M–1·s–1 as computed by foot of the wave analysis (FOWA).