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Hydrazine Formation via NiIII-NH2 Radical Coupling in Ni-Mediated Ammonia Oxidation

preprint
submitted on 25.08.2020 and posted on 25.08.2020 by Nina Gu, Paul H. Oyala, Jonas Peters

Given the diverse mechanistic possibilities for the overall 6e-/6H+ transformation of ammonia to dinitrogen, identification of M(NHx) intermediates involved in N–N bond formation is a central mechanistic challenge. In analogy to water oxidation mechanisms, which widely invoke metal oxo intermediates, metal imide and nitride intermediates have commonly been proposed for ammonia oxidation, and stoichiometric demonstration of N–N bond formation from these metal-ligand multiply bonded species is well-precedented. In contrast, while the homocoupling of M–NH2 species to form hydrazine has been hypothesized as the key N–N bond forming step in certain molecular ammonia oxidation systems, well-defined examples of this transformation from M–NH2 complexes are essentially without precedent. This work reports the first example of net ammonia oxidation mediated by a molecular Ni species, a transformation carried out via formal NiII/NiIII oxidation states. The available data are consistent with a NiIII–NH2 intermediate featuring substantial spin at N undergoing N–N bond formation to generate a NiII2(N2H4) complex. Additional and structurally unusual Nix(NyHz) species – including a Ni2(trans-N2H2) complex – are characterized and studied as intermediates in the Ni-mediated ammonia oxidation cycle described herein.

Funding

GM070757, NSF-GRFP, Dow Next Generation Educator Fund, Dow Next Generation Instrumentation Grant

History

Email Address of Submitting Author

jpeters@caltech.edu

Institution

California Institute of Technology

Country

United States

ORCID For Submitting Author

0000-0002-6610-4414

Declaration of Conflict of Interest

No conflict of interest

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