H. C. Brown Laboratory, Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA.
Inorg Chem. 2011 Oct 17;50(20):9838-48. doi: 10.1021/ic2002805. Epub 2011 Jul 15.
Uranium compounds supported by redox-active α-diimine ligands, which have methyl groups on the ligand backbone and bulky mesityl substituents on the nitrogen atoms {(Mes)DAB(Me) = [ArN═C(Me)C(Me)═NAr], where Ar = 2,4,6-trimethylphenyl (Mes)}, are reported. The addition of 2 equiv of (Mes)DAB(Me), 3 equiv of KC(8), and 1 equiv of UI(3)(THF)(4) produced the bis(ligand) species ((Mes)DAB(Me))(2)U(THF) (1). The metallocene derivative, Cp(2)U((Mes)DAB(Me)) (2), was generated by the addition of an equimolar ratio of (Mes)DAB(Me) and KC(8) to Cp(3)U. The bond lengths in the molecular structure of both species confirm that the α-diimine ligands have been doubly reduced to form ene-diamide ligands. Characterization by electronic absorption spectroscopy shows weak, sharp transitions in the near-IR region of the spectrum and, in combination with the crystallographic data, is consistent with the formulation that tetravalent uranium ions are present and supported by ene-diamide ligands. This interpretation was verified by U L(III)-edge X-ray absorption near-edge structure (XANES) spectroscopy and by variable-temperature magnetic measurements. The magnetic data are consistent with singlet ground states at low temperature and variable-temperature dependencies that would be expected for uranium(IV) species. However, both complexes exhibit low magnetic moments at room temperature, with values of 1.91 and 1.79 μ(B) for 1 and 2, respectively. Iodomethane was used to test the reactivity of 1 and 2 for multielectron transfer. While 2 showed no reactivity with CH(3)I, the addition of 2 equiv of iodomethane to 1 resulted in the formation of a uranium(IV) monoiodide species, ((Mes)DAB(Me))((Mes)DAB(Me2))UI {3; (Mes)DAB(Me2) = [ArN═C(Me)C(Me(2))NAr]}, which was characterized by single-crystal X-ray diffraction and U M(4)- and M(5)-edge XANES. Confirmation of the structure was also attained by deuterium labeling studies, which showed that a methyl group was added to the ene-diamide ligand carbon backbone.
报道了一种由氧化还原活性的α-二亚胺配体支持的铀化合物，该配体的配体主链上有甲基，氮原子上有大体积的均三甲苯基取代基{(Mes)DAB(Me)=[ArN=C(Me)C(Me)=NAr]，其中 Ar=2,4,6-三甲基苯基 (Mes)}。加入 2 当量的 (Mes)DAB(Me)、3 当量的 KC(8)和 1 当量的 UI(3)(THF)(4)生成双(配体)物种((Mes)DAB(Me))(2)U(THF)(1)。通过向 Cp(3)U 中加入等摩尔比的 (Mes)DAB(Me)和 KC(8)，生成茂基金属衍生物 Cp(2)U((Mes)DAB(Me))(2)。这两种物质的分子结构中的键长证实，α-二亚胺配体已被双重还原形成烯二酰胺配体。电子吸收光谱的表征显示，光谱的近红外区域有弱而尖锐的跃迁，结合晶体学数据，表明存在四价铀离子，并由烯二酰胺配体支撑。这一解释得到了铀 L(III)边近边 X 射线吸收结构(XANES)光谱和变温磁测量的验证。磁数据与低温下的单重态基态和预计为铀(IV)物种的变温依赖性一致。然而，这两种配合物在室温下的磁矩都较低，1 和 2 的磁矩值分别为 1.91 和 1.79μB。碘甲烷被用于测试 1 和 2 的多电子转移反应活性。虽然 2 与 CH(3)I 没有反应活性，但向 1 中加入 2 当量的碘甲烷导致形成铀(IV)单碘化物物种 ((Mes)DAB(Me))((Mes)DAB(Me2))UI{3；(Mes)DAB(Me2)=[ArN=C(Me)C(Me(2))NAr]}，其通过单晶 X 射线衍射和 U M(4)-和 M(5)-边 XANES 进行了表征。氘标记研究也证实了结构的存在，该研究表明一个甲基被添加到烯二酰胺配体的碳主链上。
