Catalytic Ammonia Oxidation to Dinitrogen by Hydrogen Atom Abstraction

Papri Bhattacharya; Zachariah M Heiden; Geoffrey M Chambers; Samantha I Johnson; R Morris Bullock; Michael T Mock

doi:10.1002/anie.201903221

Catalytic Ammonia Oxidation to Dinitrogen by Hydrogen Atom Abstraction

Angew Chem Int Ed Engl. 2019 Aug 19;58(34):11618-11624. doi: 10.1002/anie.201903221. Epub 2019 Jun 11.

Authors

Papri Bhattacharya¹, Zachariah M Heiden², Geoffrey M Chambers¹, Samantha I Johnson¹, R Morris Bullock¹, Michael T Mock³

Affiliations

¹ Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA, 99352, USA.
² Washington State University, Pullman, WA, 99164, USA.
³ Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT, 59717, USA.

PMID: 31115120
DOI: 10.1002/anie.201903221

Abstract

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 N₂ are rare. This report describes the use of [Cp*Ru(P^tBu ₂ N^Ph ₂ )(¹⁵ NH₃ )][BAr^F ₄ ], (P^tBu ₂ N^Ph ₂ =1,5-di(phenylaza)-3,7-di(tert-butylphospha)cyclooctane; Ar^F =3,5-(CF₃ )₂ C₆ H₃ ), to catalytically oxidize NH₃ to dinitrogen under ambient conditions. 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 (HAA) steps using the 2,4,6-tri-tert-butylphenoxyl radical (^t Bu₃ ArO^. ) as the H atom acceptor. Employing an excess of ^t Bu₃ ArO^. under 1 atm of NH₃ gas at 23 °C resulted in up to ten turnovers. Nitrogen isotopic (¹⁵ N) labeling studies provide initial mechanistic information suggesting a monometallic pathway during the N⋅⋅⋅N bond-forming step in the catalytic cycle.

Keywords: ammonia oxidation; dinitrogen; homogeneous catalysis; radical reactions; ruthenium.

Abstract

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