PNNL

Abstract

Catalysts for the oxidation of NH3 will be critical to utilize NH3 as a large-scale energy carrier. Molecular complexes have not been shown to catalyze the oxidation of NH3 to N2. We report Ru- catalyzed oxidation of ammonia to dinitrogen under ambient conditions using the molecular complex [Cp*Ru(PtBu2NPh2)(15NH3)][BArF4]. Mediating the cleavage of six N-H bonds and the formation of an N···N bond was achieved by coupling H+ and e- transfers as net hydrogen atom abstraction steps using the 2,4,6-tri-tert-butylphenoxyl radical (tBu3ArO•) as the H atom acceptor. Employing an excess of tBu3ArO• under 1 atm of NH3 gas at 23 °C resulted in up to six turnovers. Nitrogen isotopic (15N) labeling studies provide mechanistic insights to confirm the N···N bond forming step in the catalytic cycle.