Reductive N₂ Cleavage and Nitride Insertion Reactivity at Molybdenum Complexes Supported by a Rigid PNP Pincer

Metal-nitride species represent key reactive intermediates in reductive N₂ cleavage and functionalization. Toward a better understanding of nitride transfer reactivity, we present a series of Mo-nitride complexes supported by a rigid diphosphino-acridane pincer ligand. Notably, the stepwise reduction of a Mo^IVCl₃ complex under N₂ allows the isolation of a bridging diazenido intermediate as well as a dinuclear Mo-nitride species (4) accommodating a bridging N₂ moiety. This is the first example of a Mo(IV) nitride-N₂ species, and extensive ¹⁵N-labeling studies were performed to characterize the bridging dinitrogen, diazenido, and nitride moieties. The structure of 4 adopts two orthogonal π-backbonding interactions between N₂ and two structurally rigidified Mo^IV(N) fragments featuring a filled d_π orbital. Effective π-backbonding from such a Mo^IV(N) fragment leads to the isolation of PMe₃, CO, and CN^tBu substituted analogues. Further, reactivity of the Mo-nitride species with π-acidic CO and isocyanide leads to the formation of Mo^II-isocyanate and -carbodiimide species, respectively. Computational studies suggest that nitride carbonylation proceeds via an associative nitride insertion pathway, encouraging further studies in direct N₂ fixation to value-added products via nitride functionalization.