Dinitrogen Cleavage and Hydrogenation to Ammonia with a Uranium Complex

The Haber–Bosch process produces ammonia (NH3) from dinitrogen (N2) and dihydrogen (H2), but requires high temperature and pressure. Before iron-based catalysts were exploited in the current industrial Haber–Bosch process, uranium-based materials were used as effective catalysts for production of NH3 from N2. Although some molecular uranium complexes are capable of combining and even reducing N2, however, further hydrogenation with H2 to NH3 has not yet been reported. Here, we report the first example of N2 cleavage and hydrogenation with H2 to NH3 with a molecular uranium complex. The N2 cleavage product contains three uranium centers that are bridged by three imido μ2-NH ligands and one nitrido μ3-N ligand. Labeling experiments with 15N demonstrate that the nitrido ligand in the product originates from N2. Reaction of the N2-cleaved complex with H2 or H+ forms NH3 under mild conditions. A synthetic cycle has been established by the reaction of the N2-cleaved complex with TMSCl. The isolation of this trinuclear imido-nitrido product implies that a multimetallic uranium assembly plays an important role in the activation of N2.