Catalytic Ammonia Oxidation to Dinitrogen by a Nickel Complex

Abstract

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.