Oxidation-Induced Ambiphilicity Triggers N-N Bond Formation and Dinitrogen Release in Octahedral Terminal Molybdenum (V) Nitrido Complexes

Coupling of octahedral, terminal d1 molybdenum (V) nitrido complexes supported by a dianionic pentadentate ligand via N-N bond formation to give mu-dinitrogen complexes was found to be thermodynamically feasible but faces significant kinetic barriers. However, upon oxidation, a kinetically favored nucleophilic/electrophilic N-N bond forming mechanism was enabled to give monocationic mu-dinitrogen dimers. Computational and experimental evidence for this “oxidation induced ambiphilic nitrido coupling” mechanism is presented. The factors influencing release of dinitrogen from the resulting mu-dinitrogen dimers was also probed and it was found that further oxidation to a dicationic species is required to induce (very rapid) loss of dinitrogen. The mechanistic path discovered for N-N bond formation and dinitrogen release follows an ECECC sequence (E = “electrochemical step”; C = “chemical step”). Experimental evidence for the intermediacy of a highly electrophilic, cationic d0 molybdenum (VI) nitrido in the N-N bond forming mechanism via trapping with an isonitrile reagent is also discussed. Together these results are relevant to the development of molecular catalysts capable of mediating ammonia oxidation to dihydrogen and dinitrogen.