PNNL

Abstract

The development of earth-abundant transition metal complexes for electrocatalytic ammonia oxidation is needed to facilitate a renewable energy economy. Important to this goal is a fundamental understanding of how ammonia binds to complexes as a function of ligand geometry and electronic effects. We report the synthesis and characterization of a series of Fe(II)–NH3 com-plexes supported by tetradentate, facially-binding ligands with a combination of pyridine and N-heterocyclic carbene donors. Elec-tronic modification of the supporting ligand led to significant shifts in the FeIII/II potential and variations in NH bond acidities. Finally, investigations of ammonia oxidation by cyclic voltammetry, controlled potential bulk electrolysis, and through addition of stoichio-metric organic radicals TEMPO and tBu3ArO• are reported. No catalysis of oxidation of NH3 to N2 was observed, and 15N2 was detected only in reactions with tBu3ArO•.