Catalytic Ammonia Oxidation to Dinitrogen by Hydrogen Atom Abstraction

Catalysts for the oxidation of NH3 are critical for the utilization of NH3 as a large-scale energy carrier. Molecular catalysts capable of oxidizing NH3 to N-2 are rare. This report describes the use of [Cp*Ru((P2N2Ph)-N-tBu)((NH3)-N-15)][BAr4F], ((P2N2Ph)-N-tBu=1,5-di(phenylaza)-3,7-di(tert-butylphospha)cyclooctane; Ar-F=3,5-(CF3)(2)C6H3), to catalytically oxidize NH3 to dinitrogen under ambient conditions. The cleavage of six N-H bonds and the formation of an N equivalent to N bond was achieved by coupling H+ and e(-) transfers as net hydrogen atom abstraction (HAA) steps using the 2,4,6-tri-tert-butylphenoxyl radical ((Bu3ArO.)-Bu-t) as the H atom acceptor. Employing an excess of (Bu3ArO.)-Bu-t under 1 atm of NH3 gas at 23 degrees C resulted in up to ten turnovers. Nitrogen isotopic (N-15) labeling studies provide initial mechanistic information suggesting a monometallic pathway during the N...N bond-forming step in the catalytic cycle.