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 N-2 with a Faradaic efficiency for N-2 of similar to 80%. Employing (NH3)-N-15 yields exclusively N-30(2), demonstrating the conversion of ammonia to N-2. A suite of electrochemical studies is consistent with an initial EC step that generates an Fe-III-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 (k(obs)) of similar to 10(7) M-1.s(-1) as computed by foot of the wave analysis (FOWA).