School of Chemistry, The University of Manchester, Manchester, UK.
Nat Chem. 2019 Sep;11(9):806-811. doi: 10.1038/s41557-019-0306-x. Epub 2019 Aug 19.
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) 5f 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.
在配位和金属有机化学中，一个基本的成键模型是金属和中性π受体配体之间的协同、供体-受体相互作用，其中配体σ给电子给金属，而金属π反馈给配体。这种相互作用通常涉及具有富电子、中、低甚至负氧化态的金属和具有π*轨道的配体。在这里，我们报告说，用有机叠氮化物处理一种铀卡宾配合物会产生一种铀（V）-双（亚氨基）-二氮复合物，由锂离子稳定。这种以晶体形式分离出来的配合物涉及一个缺电子、高氧化态铀（V）5f 离子，它与贫π受体配体二氮之间发生π反馈。我们提出，这是通过协同的杂双金属铀-锂效应的组合以及存在合适的辅助配体来实现的，这些配体使铀离子异常富电子。这种缺电子的反馈键合可能对氮气活化领域有影响。
