Diversion of Catalytic C–N Bond Formation to Catalytic Oxidation of NH3 through Modification of the Hydrogen Atom Abstractor

We report that (TMP ) Ru(NH 3 ) 2 (TMP = tetramesitylporphryin) is a molecular catalyst for oxidation of ammonia to dinitrogen. An aryloxy radical, tri- er -butylphenoxyl ( ArO ·), abstracts H atoms from a bound ammonia ligand of (TMP)Ru(NH 3 ) 2 , leading to the discovery of a new catalytic C-N coupling to the para position of ArO · to form 4-amino-2,4,6-tri- er -butylcyclohexa-2,5-dien-1-one. Modification of the aryloxy radical to 2,6-di- er -butyl-4-tritylphenoxyl radical, which contains a trityl group at the para position, prevents C-N coupling and diverts the reaction to catalytic oxidation of NH 3 o give N 2 . We achieved 125 ± 5 turnovers at 22 °C for oxidation of NH 3 , the highest turnover number (TON) reported to date for a molecular catalyst.