A Pseudotetrahedral Uranium(V) Complex

A series of uranium amides were synthesized from N, N, N-cyclohexyl(trimethylsilyl)lithium amide [Li][N(TMS)Cy] and uranium tetrachloride to give U(NCySiMe₃) _x(Cl)_{4- x}, where x = 2, 3, or 4. The diamide was isolated as a bimetallic, bridging lithium chloride adduct ((UCl₂(NCyTMS)₂)₂-LiCl(THF)₂), and the tris(amide) was isolated as the lithium chloride adduct of the monometallic species (UCl(NCyTMS)₃-LiCl(THF)₂). The tetraamide complex was isolated as the four-coordinate pseudotetrahedron. Cyclic voltammetry revealed an easily accessible reversible oxidation wave, and upon chemical oxidation, the U^V amido cation was isolated in near-quantitative yields. The synthesis of this family of compounds allows a direct comparison of the electronic structure and properties of isostructural U^IV and U^V tetraamide complexes. Spectroscopic investigations consisting of UV-vis, NIR, MCD, EPR, and U L₃-edge XANES, along with density functional and wave function calculations, of the four-coordinate U^IV and U^V complexes have been used to understand the electronic structure of these pseudotetrahedral complexes.