A Pseudotetrahedral Uranium(V) Complex
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Abstract
A series of uranium
amides were synthesized from <i>N</i>,<i>N</i>,<i>N</i>-cyclohexyl(trimethylsilyl)lithium amide [Li][N(TMS)Cy]
and uranium tetrachloride to give U(NCySiMe<sub>3</sub>)<sub><i>x</i></sub>(Cl)<sub>4–<i>x</i></sub>, where <i>x</i> = 2, 3, or 4. The diamide was isolated as a bimetallic,
bridging lithium chloride adduct ((UCl<sub>2</sub>(NCyTMS)<sub>2</sub>)<sub>2</sub>-LiCl(THF)<sub>2</sub>), and the tris(amide) was isolated
as the lithium chloride adduct of the monometallic species (UCl(NCyTMS)<sub>3</sub>-LiCl(THF)<sub>2</sub>). 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<sup>V</sup> 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<sup>IV</sup> and U<sup>V</sup> tetraamide complexes. Spectroscopic
investigations consisting of UV–vis, NIR, MCD, EPR, and U L<sub>3</sub>-edge XANES, along with density functional and wave function
calculations, of the four-coordinate U<sup>IV</sup> and U<sup>V</sup> complexes have been used to understand the electronic structure
of these pseudotetrahedral complexes
