Dinitrogen cleavage and hydrogenation to ammonia with a uranium complex

The Haber–Bosch process produces ammonia (NH(3)) from dinitrogen (N(2)) and dihydrogen (H(2)), 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(3) from N(2). Although some molecular uranium complexes are known to be capable of combining with N(2), further hydrogenation with H(2) forming NH(3) has not been reported to date. Here, we describe the first example of N(2) cleavage and hydrogenation with H(2) to NH(3) with a molecular uranium complex. The N(2) cleavage product contains three uranium centers that are bridged by three imido μ(2)-NH ligands and one nitrido μ(3)-N ligand. Labeling experiments with (15)N demonstrate that the nitrido ligand in the product originates from N(2). Reaction of the N(2)-cleaved complex with H(2) or H(+) forms NH(3) under mild conditions. A synthetic cycle has been established by the reaction of the N(2)-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(2).