Catalytic Ammonia Oxidation to Dinitrogen by a Nickel Complex

We report a nickel complex for catalytic oxidation of ammonia to dinitrogen under ambient conditions. Using the aryloxyl radical 2,4,6‐tri‐tert‐butylphenoxyl (tBu3ArO⋅) as a H atom acceptor to cleave the N−H bond of a coordinated NH3 ligand up to 56 equiv of N2 per Ni center can be generated. Employing the N‐oxyl radical 2,2,6,6‐(tetramethylpiperidin‐1‐yl)oxyl (TEMPO⋅) as the H‐atom acceptor, up to 15 equiv of N2 per Ni center are formed. A bridging Ni‐hydrazine product identified by isotopic nitrogen (15N) studies and supported by computational models indicates the N−N bond forming step occurs by bimetallic homocoupling of two paramagnetic [Ni]−NH2 fragments. Ni‐mediated hydrazine disproportionation to N2 and NH3 completes the catalytic cycle. A nickel complex for catalytic oxidation of NH3 to N2 is demonstrated using the radicals 2,4,6‐tri‐tert‐butylphenoxyl (tBu3ArO⋅) or 2,2,6,6‐(tetramethylpiperidine‐1‐yl)oxyl (TEMPO) as the H‐atom acceptor to cleave the N−H bond of a NH3 ligand. Two Ni−NH2 fragments form an N−N bond in a bridging Ni‐hydrazine product. Ni‐mediated hydrazine disproportionation affords N2 and NH3 in the proposed catalytic cycle. (BDFE=Bond Dissociation Free Energy)