Dinitrogen cleavage and hydrogenation to ammonia with a uranium complex.

The Haber-Bosch process produces ammonia (NH) from dinitrogen (N) and dihydrogen (H), but requires high temperature and pressure. Before iron-based catalysts were exploited in the current industrial Haber-Bosch process, uranium-based materials served as effective catalysts for production of NH from N. Although some molecular uranium complexes are known to be capable of combining with N, further hydrogenation with H forming NH has not been reported to date. Here, we describe the first example of N cleavage and hydrogenation with H to NH with a molecular uranium complex. The N cleavage product contains three uranium centers that are bridged by three imido -NH ligands and one nitrido -N ligand. Labeling experiments with N demonstrate that the nitrido ligand in the product originates from N. Reaction of the N-cleaved complex with H or H forms NH under mild conditions. A synthetic cycle has been established by the reaction of the N-cleaved complex with trimethylsilyl chloride. The isolation of this trinuclear imido-nitrido product implies that a multi-metallic uranium assembly plays an important role in the activation of N.