Spontaneous Ammonia Oxidation Through Coordination Induced Bond Weakening in Molybdenum Complexes of a Dianionic Pentadentate Ligand Platform

Ammonia oxidation catalyzed by molecular compounds is of current interest as a carbon free source of dihydrogen. Activation of N-H bonds through coordination to transition metal centers is a key reaction in this process. We report the substantial activation of ammonia through via reaction with low valent Mo complexes of a diborate pentadentate ligand system. Spontaneous loss of hydrogen atoms from (B2Pz4Py)Mo(II)-NH3 at room temperature to produce H2 and the dinuclear -nitrido compound (B2Pz4Py)Mo-N-Mo(B2Pz4Py) is observed due to substantial N-H bond weakening upon coordination to Mo. Mechanistic details are supported through the experimental observation characterization of terminal amido, imido and nitrido complexes and density functional theory computations. The generally under-appreciated role of bridging nitrido intermediates is revealed and discussed, providing guidance for further catalyst development for this process.