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 (LiNHBu)-Bu-t generates the U(IV) homoleptic amide complex [Li(THF)(2)Cl](2)[Li](2)[U((NHBu)-Bu-t)(6)] (1 center dot THF) in 57% yield. In the solid-state, 1 center dot THF exists as a one-dimensional coordination polymer consisting of alternating [Li](2)[U((NHBu)-Bu-t)(6)] and [Li(THF)(2)Cl](2) building blocks. Recrystallization of 1 center dot THF from DME/hexanes affords the monomeric DME derivative, [Li(DME)(2)ClLi](2)[U((NHBu)-Bu-t)(6)] (1 center dot DME), which was also characterized by X-ray crystallography. The oxidation of 1 center dot THF with 1 equiv of AgOTF generates the U(VI) bis(imido) complex [Li(THF)](2)[U((NBu)-Bu-t)(2)((NHBu)-Bu-t)(4)] (2) in low yield. In contrast, oxidation of 1 center dot THF with 1 equiv of 12, in the presence of excess tert-butylamine, cleanly affords the U(VI) bis(imido) U((NBu)-Bu-t)(2)((NHBu)-Bu-t)(2)((NH2Bu)-Bu-t)(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 I-2, 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 I-2 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.