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 LiNHtBu generates the U(IV) homoleptic amide complex [Li(THF)2Cl]2[Li]2[U(NHtBu)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(NHtBu)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(NHtBu)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(NtBu)2(NHtBu)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(NtBu)2(NHtBu)2(NH2tBu)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.

将四氯化铀（UCl₄）与6当量的叔丁基氨基锂（LiNHtBu）反应，以57%的产率得到四价铀（U(IV)）的均配酰胺配合物[Li(THF)₂Cl]₂[Li]₂[U(NHtBu)₆]（1·THF，其中THF为四氢呋喃（THF)）。在固态下，1·THF呈一维配位聚合物结构，由交替排布的[Li]₂[U(NHtBu)₆]与[Li(THF)₂Cl]₂结构单元构成。将1·THF于二甲氧基乙烷（DME）/己烷混合溶剂中进行重结晶，可得到单体形式的二甲氧基乙烷衍生物[Li(DME)₂ClLi]₂[U(NHtBu)₆]（1·DME），该配合物同样通过X射线晶体衍射分析（X-ray crystallography）进行了结构表征。以1当量的三氟甲磺酸银（AgOTF）氧化1·THF，以较低产率得到六价铀（U(VI)）的双亚胺基配合物[Li(THF)]₂[U(NtBu)₂(NHtBu)₄]（2）。与之相反，在过量叔丁胺（tert-butylamine）存在下，以1当量的碘（I₂）氧化1·THF，可干净地得到六价铀（U(VI)）的双亚胺基配合物U(NtBu)₂(NHtBu)₂(NH₂tBu)₂（3），产率为78%。我们还探究了四氯化铀（UCl₄）与仲酰胺锂盐的反应活性：将6当量的(LiNC₅H₁₀)（其中HNC₅H₁₀为哌啶（piperidine））与四氯化铀（UCl₄）在二甲氧基乙烷（DME）中反应，得到四价铀（U(IV)）的酰胺配合物[Li(DME)][U(NC₅H₁₀)₅]（4）。以0.5当量的碘（I₂）氧化该配合物，随后加入Li(NC₅H₁₀)，以中等产率得到[Li(DME)₃][U(NC₅H₁₀)₆]（5）。以0.5当量的碘（I₂）氧化5，以较高产率得到U(NC₅H₁₀)₆（6）。配合物4~6的结构均通过X射线晶体衍射分析得以阐明，而4和5的磁学性质则通过超导量子干涉仪磁强法（SQUID magnetometry）进行了表征。此外，我们还通过循环伏安法（cyclic voltammetry）表征了5在溶液相中的氧化还原性质。