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

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posted on 07.02.2020, 20:38 by Peter L. Dunn, Samantha I. Johnson, Werner Kaminsky, R. Morris Bullock
We report that (TMP)Ru­(NH3)2 (TMP = tetramesitylporphryin) is a molecular catalyst for oxidation of ammonia to dinitrogen. An aryloxy radical, tri-tert-butylphenoxyl (ArO·), abstracts H atoms from a bound ammonia ligand of (TMP)­Ru­(NH3)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-tert-butylcyclohexa-2,5-dien-1-one. Modification of the aryloxy radical to 2,6-di-tert-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 NH3 to give N2. We achieved 125 ± 5 turnovers at 22 °C for oxidation of NH3, the highest turnover number (TON) reported to date for a molecular catalyst.