Service de Chimie Inorganique et Biologique (SCIB), Institut Nanosciences et Cryogénie (INAC), CEA , F-38054 Grenoble, France.
J Am Chem Soc. 2014 May 7;136(18):6716-23. doi: 10.1021/ja5017624. Epub 2014 Apr 23.
The metal-mediated redox transformation of CO2 in mild conditions is an area of great current interest. The role of cooperativity between a reduced metal center and a Lewis acid center in small-molecule activation is increasingly recognized, but has not so far been investigated for f-elements. Here we show that the presence of potassium at a U, K site supported by sterically demanding tris(tert-butoxy)siloxide ligands induces a large cooperative effect in the reduction of CO2. Specifically, the ion pair complex [K(18c6)][U(OSi(O(t)Bu)3)4], 1, promotes the selective reductive disproportionation of CO2 to yield CO and the mononuclear uranium(IV) carbonate complex [U(OSi(O(t)Bu)3)4(μ-κ(2):κ(1)-CO3)K2(18c6)], 4. In contrast, the heterobimetallic complex [U(OSi(O(t)Bu)3)4K], 2, promotes the potassium-assisted two-electron reductive cleavage of CO2, yielding CO and the U(V) terminal oxo complex [UO(OSi(O(t)Bu)3)4K], 3, thus providing a remarkable example of two-electron transfer in U(III) chemistry. DFT studies support the presence of a cooperative effect of the two metal centers in the transformation of CO2.
在温和条件下，金属介导的 CO2 氧化还原转化是当前研究的热点领域。在小分子活化中，还原金属中心和路易斯酸中心之间的协同作用的作用越来越受到重视，但迄今为止尚未针对 f 族元素进行研究。在这里，我们表明，在受空间位阻的三（叔丁氧基）硅氧烷配体支持的 U、K 位上存在钾，可以在 CO2 的还原中诱导出很大的协同效应。具体来说，离子对配合物[K(18c6)][U(OSi(O(t)Bu)3)4]，1，促进 CO2 的选择性还原歧化，生成 CO 和单核铀(IV)碳酸盐配合物[U(OSi(O(t)Bu)3)4(μ-κ(2):κ(1)-CO3)K2(18c6)]，4。相比之下，杂双金属配合物[U(OSi(O(t)Bu)3)4K]，2，促进 CO2 的钾辅助两电子还原裂解，生成 CO 和 U(V)末端氧配合物[UO(OSi(O(t)Bu)3)4K]，3，从而为 U(III)化学中的两电子转移提供了一个显著的例子。DFT 研究支持在 CO2 的转化中两个金属中心之间存在协同效应。
