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(NCySiMe) (Cl), where x = 2, 3, or 4. The diamide was isolated as a bimetallic, bridging lithium chloride adduct ((UCl(NCyTMS))-LiCl(THF)), and the tris(amide) was isolated as the lithium chloride adduct of the monometallic species (UCl(NCyTMS)-LiCl(THF)). 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 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 and U tetraamide complexes. Spectroscopic investigations consisting of UV-vis, NIR, MCD, EPR, and U L-edge XANES, along with density functional and wave function calculations, of the four-coordinate U and U complexes have been used to understand the electronic structure of these pseudotetrahedral complexes.