Spontaneous Ammonia Activation 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 via reaction with low-valent molybdenum complexes of a diborate pentadentate ligand system. Spontaneous loss of dihydrogen from (B(2)Pz(4)Py)Mo-II-NH3 at room temperature to produce the dinuclear mu-nitrido compound (B(2)Pz(4)Py)Mo-N-Mo(B(2)Pz(4)Py) 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.

Automated summary

This study reports the activation of ammonia through coordination to molybdenum centers. Experimental results show that (B(2)Pz(4)Py)Mo-II-NH3 loses dihydrogen at room temperature, resulting in the formation of the dinuclear compound (B(2)Pz(4)Py)Mo-N-Mo(B(2)Pz(4)Py). Mechanistic details were supported through experimental observations and density functional theory calculations, revealing the under-appreciated role of bridging nitrido intermediates in the process.