Comparison of the redox chemistry of primary and secondary amides of U(IV): isolation of a U(VI) bis(imido) complex or a homoleptic U(VI) amido complex.

Reaction of UCl4 with 6 equiv of LiNH(t)Bu generates the U(IV) homoleptic amide complex [Li(THF)2Cl]2[Li]2[U(NH(t)Bu)6] (1 · THF) in 57% yield. In the solid-state, 1 · THF exists as a one-dimensional coordination polymer consisting of alternating [Li]2[U(NH(t)Bu)6] and [Li(THF)2Cl]2 building blocks. Recrystallization of 1 · THF from DME/hexanes affords the monomeric DME derivative, [Li(DME)2ClLi]2[U(NH(t)Bu)6] (1 · DME), which was also characterized by X-ray crystallography. The oxidation of 1 · THF with 1 equiv of AgOTF generates the U(VI) bis(imido) complex [Li(THF)]2[U(N(t)Bu)2(NH(t)Bu)4] (2) in low yield. In contrast, oxidation of 1 · THF with 1 equiv of I2, in the presence of excess tert-butylamine, cleanly affords the U(VI) bis(imido) U(N(t)Bu)2(NH(t)Bu)2(NH2(t)Bu)2 (3) in 78% yield. We have also explored the reactivity of UCl4 with the lithium salt of a secondary amide. Thus, reaction of 6 equiv of (LiNC5H10) (HNC5H10 = piperidine) with UCl4 in DME produces the U(IV) amide, [Li(DME)][U(NC5H10)5] (4). Oxidation of this material with 0.5 equiv of I2, followed by addition of Li(NC5H10), produces [Li(DME)3][U(NC5H10)6] (5) in moderate yield. Oxidation of 5 with 0.5 equiv of I2 generates U(NC5H10)6 (6) in good yield. The structures of 4-6 were elucidated by X-ray crystallographic analysis, while the magnetic properties of 4 and 5 were investigated by SQUID magnetometry. Additionally, the solution phase redox properties of 5 were examined by cyclic voltammetry.