Ammonia oxidation catalyzed by molecular compounds is of current interest as a potentially carbon free source of dihydrogen. Activation of N-H bonds through coordination to transition metal centers is a key reaction in this process. In this talk, we report the substantial activation of ammonia via reaction with low valent Mo complexes of a diborate pentadentate ligand system. Spontaneous loss of hydrogen atoms from (B2Pz4Py)Mo(II)-NH3 (1) at room temperature to produce H2 and the dinuclear μ-nitrido compound (B2Pz4Py)Mo-N-Mo(B2Pz4Py) (2) is observed due to substantial N-H bond weakening upon coordination to Mo. Mechanistic details are supported through the experimental observation and characterization of terminal amido, imido and nitrido complexes. Density functional theory computations provide support for a proposed mechanism for the stoichiometric conversion of one equivalent of NH3 to H2 and 2. The generally under-appreciated role of bridging nitrido intermediates is revealed and discussed, providing guidance for further catalyst development for this process.

Molybdenum complexes for ammonia oxidation

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