This research is led by Prof. Congqing Zhu (State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing, China) and Prof. Laurent Maron (LPCNO, CNRS & INSA, Université Paul Sabatier, Toulouse, France). The Haber–Bosch process produces ammonia (NH 3 ) from dinitrogen (N 2 ) and dihydrogen (H 2 ), but requires high temperature and pressure. Although uranium-based materials have been reported as effective catalysts in Haber–Bosch process, the direct hydrogenation with H 2 forming NH 3 activated by a uranium complex has not been accomplished. “The study of N2 activation and hydrogenation by uranium molecular complex could help us to further understand the detail mechanism for Haber–Bosch process at the molecular level and also may help us to design more effective catalysts for ammonia formation.” Zhu says.
The research team initially synthesized a uranium azide complex 2 from uranium precursor 1 and NaN 3 . Then 2 was reduced with an excess of KC 8 affording a N 2 -cleaved product 3 , which contains three uranium centers that are bridged by three imido μ 2 -NH ligands and one nitrido μ 3 -N ligand. The 15 N-labeling experiments 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. “The isolation of this trinuclear imido-nitrido product suggests that multimetallic uranium assembly plays an important role in the activation of N 2 in the cleavage of the N≡N triple bond in N 2 and that multiple uranium can cooperate is a promising strategy for activation and conversion of small molecules.” Zhu says. A synthetic cycle has been established by the reaction of the N 2 -cleaved complex with trimethylsilyl chloride (TMSCl) to generate N(SiMe 3 ) 3 , HN(SiMe 3 ) 2 and 1 . The detailed mechanism of N 2 activation by multimetallic synergy was revealed by DFT calculations.
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See the article:
Dinitrogen cleavage and hydrogenation to ammonia with a uranium complex
https://doi.org/10.1093/nsr/nwac144
National Science Review