Thermally Stable Uranium Dinitrogen Complex with Siloxide Supporting Ligands

A new dinitrogen adduct of a homoleptic
uranium tris­(siloxide)
complex, [U­{OSi­(Mes)3}3]2(μ-η2:η2-N2), is reported. Synthesis
of the 15N-labeled isotopomer and Raman spectroscopy confirm
the reductive activation of N2 to a (N2)2– dianion. The 15N NMR shift of the 15N2-labeled isotopomer is also reported. Crystallographic
characterization shows a side-on (N2)2– coordinated in either an eclipsed or staggered conformation in different
crystals. The U–N2–U complex is stable to
vacuum and shows high thermal stability, retaining the formally reduced
dinitrogen at 100 °C. The parent three-coordinate uranium­(III)
[U­{OSi­(Mes)3}3] could not be isolated in our
hands, with N2-free syntheses affording only uranium­(IV)
compounds. The rational synthesis and full characterization of two
such U­(IV) byproducts, [U­{OSi­(Mes)3}­{N­(SiMe3)2}3] and [U­{OSi­(Mes)3}4], is also reported.

本文报道了一种均配型三(硅氧基)铀配合物的新型二氮加合物：[U{OSi(Mes)3}3]2(μ-η2:η2-N2)（其中Mes为均三甲苯基）。通过合成15N标记的同位素异构体并结合拉曼光谱分析，证实了N2被还原活化为(N2)2–二阴离子。本文同时报道了该15N2标记同位素异构体的15N核磁共振化学位移。晶体结构表征结果显示，(N2)2–以侧基配位模式结合，在不同晶体中分别呈现重叠式或交叉式构象。该U–N2–U配合物在真空环境下稳定性良好，且具有优异的热稳定性，在100 ℃下仍能保留形式上被还原的二氮单元。本研究中未能分离得到母体三配位三价铀配合物[U{OSi(Mes)3}3]，无氮合成路径仅能得到四价铀化合物。本文还报道了两种四价铀副产物的理性合成与全面表征：[U{OSi(Mes)3}{N(SiMe3)2}3]与[U{OSi(Mes)3}4]，其中SiMe3为三甲基硅基。