A fundamental bonding model in coordination and organometallic chemistry is the synergic, donor–acceptor interaction between a metal and a neutral π-acceptor ligand, in which the ligand σ donates to the metal, which π back-bonds to the ligand. This interaction typically involves a metal with an electron-rich, mid-, low- or even negative oxidation state and a ligand with a π* orbital. Here, we report that treatment of a uranium–carbene complex with an organoazide produces a uranium(v)–bis(imido)–dinitrogen complex, stabilized by a lithium counterion. This complex, which was isolated in a crystalline form, involves an electron-poor, high-oxidation-state uranium(v) 5f¹ ion that is π back-bonded to the poor π-acceptor ligand dinitrogen. We propose that this is made possible by a combination of cooperative heterobimetallic uranium–lithium effects and the presence of suitable ancillary ligands that render the uranium ion unusually electron rich. This electron-poor back-bonding could have implications for the field of dinitrogen activation.

配位和有机金属化学中的基本键合模型是金属与中性π-受体配体之间的协同施主-受体相互作用，其中配体σ贡献给金属，而π反向键合到配体上。这种相互作用通常涉及具有富电子，中，低或什至负氧化态的金属和具有π *轨道的配体。在这里，我们报道用有机叠氮化物处理铀-卡宾络合物会产生铀（v）-双（亚氨基）-二氮络合物，并由锂抗衡离子稳定。以晶体形式分离出的该络合物涉及电子贫乏的高氧化态铀（v）5 fπ背键键合至不良π受体配体二氮的^1个离子。我们认为，这是通过协同异双金属铀-锂效应以及合适的辅助配体（使铀离子异常富电子）的结合而实现的。这种电子贫乏的背键可能对二氮活化领域有影响。