The synthesis, structure, and reactivity with CO₂ and CS₂ of new U(IV) complexes with a redox-active Schiff base are reported. The reaction of UI₃ with the heptadentate Schiff base ligand 2,2′,2″-tris(salicylideneimino)triethylamine (trensal) did not lead to the formation of a U(III) complex but to the reductive coupling and C–C bond formation between two imino groups of the Schiff base, yielding the U(IV) complex [U₂(bis-trensal)], 1. Further reduction of 1 led to the dinuclear macrocyclic complex [{K(THF)₃}₂U₂(cyclo-trensal)], 3-THF, through a second C–C bond formation reaction between two additional imino groups. Complexes 1 and 3 are oxidized by AgOTf resulting in the cleavage of the C–C bonds and leading to the formation of the U(IV) complex [U(trensal)]OTf, 2. Complex 1 does not reduce CO₂ or CS₂ but undergoes insertion of CO₂ into one of the U–N bonds. In contrast, the reaction of 3 with 2 equiv of CO₂ leads to the reductive disproportionation of CO₂ to afford carbonate in 80% yield. In the presence of a large excess of CO₂ multiple reactions take place, as supported by the isolation of the crystals of [{K(THF)₃}U₂(μ-O)(CO₂–CO-cyclo-trensal)(U(trensal))], 4. The higher reductive activity toward CO₂ of complex 3 compared to previously reported U(IV) complexes of reduced Schiff bases is interpreted in terms of its redox properties.

中文翻译：

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氧化还原活性席夫碱配体支持的多金属铀（IV）配合物还原二氧化碳

报道了具有氧化还原活性席夫碱的新型U（IV）配合物的合成，结构和与CO ₂和CS ₂的反应性。UI ₃与七齿Schiff碱配体2,2'，2''-三（水杨亚胺基）三乙胺（trensal）的反应不会导致U（III）配合物的形成，但会导致还原偶联和C–C键在席夫碱的两个亚氨基之间形成U（IV）络合物[U ₂（bis-trensal）]，1。1的进一步还原导致双核大环复合物[{K（THF）₃ } ₂ U ₂（环-trensal）]，3-THF通过另外两个亚氨基之间的第二次CC键形成反应。复合物1和3被AgOTf氧化，导致C-C键断裂，并导致形成U（IV）复合物[U（trensal）] OTf，2。复杂1不减少CO ₂或CS ₂，但CO的经历插入₂到U-N键中的一个。相比之下，反应3与2当量的CO ₂导致CO的还原歧化₂，得到收率80％的碳酸盐。在大量过量的CO ₂存在下分离[[K（THF）₃ } U ₂（μ-O）（CO ₂ -CO-环-trensal）（U（trensal））]，4的晶体有助于发生多个反应。与以前报道的还原的席夫碱的U（IV）配合物相比，配合物3对CO ₂的还原活性更高，这是因为其氧化还原特性。