Synthesis and Reactivity of Fe(II) Complexes Containing Cis Ammonia Ligands.

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)-NH 3 complexes supported by tetradentate, facially binding ligands with a combination of pyridine and N -heterocyclic carbene donors. Electronic modification of the supporting ligand led to significant shifts in the Fe III/II potential and variations in NH bond acidities. Finally, investigations of ammonia oxidation by cyclic voltammetry, controlled potential bulk electrolysis, and through addition of stoichiometric organic radicals, TEMPO and t Bu3 ArO • are reported. No catalytic oxidation of NH 3 to N 2 was observed, and 15 N 2 was detected only in reactions with t Bu3 ArO • .