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 MoIVCl3 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 MoIV(N) fragments featuring a filled dπ orbital. Effective π‐backbonding from such a MoIV(N) fragment leads to the isolation of PMe3, CO, and CNtBu substituted analogues. Further, reactivity of the Mo‐nitride species with π‐acidic CO and isocyanide leads to the formation of MoII‐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.