Two-Electron Oxidative Atom and Group Transfer Reactions at a Well-Defined Uranium(II) Center

The multi-electron redox chemistry of uranium(II) compounds remains largely unexplored. Herein, we report a series of two-electron oxidative atom and group transfer reactions at a well-defined uranium(II) center. The reactions of uranium(II) complexes [M][(^AdTPBN₃)U] (M=K(2,2,2-cryptand) and K(18-crown-6)(THF)) with pyridine-N-oxide or nitrosobenzene, elemental sulfur/selenium or triphenylphosphine sulfide/selenide, and ditellurium salt led to the isolation of uranium(IV) terminal oxo and chalcogenido complexes [M][(^AdTPBN₃)UX] (X=O, S, Se, Te). In addition, the reactions of [M][(^AdTPBN₃)U] with aryl azides ArN₃ or diazoalkanes R₂CN₂ quantitatively yielded uranium(IV) terminal imido [M][(^AdTPBN₃)UNAr] or hydrazonido(2-) complexes [M][(^AdTPBN₃)UN₂CR₂], respectively. Notably, the low-temperature reaction between [M][(^AdTPBN₃)U] and mesityl azide allowed the isolation of the first uranium(IV) aryldiazenylimido complex as an intermediate. These uranium(IV)-element multiply bound compounds were fully characterized by X-ray crystallography, ¹H NMR spectroscopy, absorption spectroscopy, solution and solid-state magnetometry, and elemental analysis. The controlled two-electron oxidative reactions at a uranium(II) center not only expand the redox reactivity of uranium(II) but also offer a convenient new route to access uranium-element multiply bound compounds.