Dinitrogen cleavage and hydrogenation to ammonia with a uranium complex

Abstract

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 served as effective catalysts for production of NH3 from N2. Although some molecular uranium complexes are known to be capable of combining with N2, further hydrogenation with H2 forming NH3 has not been reported to date. Here, we describe 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 trimethylsilyl chloride (TMSCl). The isolation of this trinuclear imido-nitrido product implies that a multimetallic uranium assembly plays an important role in the activation of N2.

Recent advances in heterometallic clusters with f-block metal–metal bonds: synthesis, reactivity and applications

“…Particularly, due to the synergistic effects from different metal centers, the clusters with M-M bonds have great potential in the activation and conversion of N 2 to N-containing organic compounds. [72][73][74][75] In conclusion, we have highlighted recent advances in the construction of d-f heterometallic molecular clusters with M-M bonds. We hope that this review will attract more chemists to this burgeoning but challenging field and stimulate the steady developments and breakthroughs in future.…”

Progress in the chemistry of molecular actinide-nitride compounds

“…More recently, Xin, Zhu and co-workers also reported that the reduction of a U(IV) azide complex, supported by the (NNP 2 ) 2− ligand ( 5a ), with excess KC 8 under N 2 generates the trinuclear imido–nitride complex, [K 2 ((U(NNP 2 ) 2 (μ-NH) 3 (μ-N))] ( 5 ) (bottom, Scheme 3). 69 The molecular structure of 5 consists of three uranium centers that are bridged by three imido (NH) ligands, and one nitride (N 3− ) ligand with U–N nitride bond lengths which range from 2.204 to 2.218 Å. These distances are comparable to those reported for the U( iv )/U( vi ) tetranitride cluster 1 , and slightly longer than those found in the nitride bridged cluster, [(U IV Cp*(μ-I) 2 ) 3 (μ-N)], reported by Evans and co-workers (2.138(3)–2.157(3) Å).…”

Photolysis, Thermolysis, and Reduction of a Uranium Azide Complex Supported by a Double-Layer N–P Ligand

“…We have developed a phosphorus-substituted Tren ligand (a double layer N–P ligand), which contains three rigid N–P units. The P atoms in this ligand play important roles not only in the construction of heterometallic clusters with M–M bonds but also in the activation of small molecules. − Here, we report the photolysis, thermolysis, and reduction of the uranium azide complex supported by this double layer N–P ligand.…”