Synthesis, Characterization, and Multielectron Reduction Chemistry of Uranium Supported by Redox-Active α-Diimine Ligands

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 {MesDABMe = [ArNC(Me)C(Me)NAr], where Ar = 2,4,6-trimethylphenyl (Mes)}, are reported. The addition of 2 equiv of MesDABMe, 3 equiv of KC8, and 1 equiv of UI3(THF)4 produced the bis(ligand) species (MesDABMe)2U(THF) (1). The metallocene derivative, Cp2U(MesDABMe) (2), was generated by the addition of an equimolar ratio of MesDABMe and KC8 to Cp3U. 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 LIII-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 μB 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 CH3I, the addition of 2 equiv of iodomethane to 1 resulted in the formation of a uranium(IV) monoiodide species, (MesDABMe)(MesDABMe2)UI {3; MesDABMe2 = [ArNC(Me)C(Me2)NAr]}, which was characterized by single-crystal X-ray diffraction and U M4- and M5-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.

本文报道了由具有配体骨架上甲基基团和氮原子上的体积庞大的甲苯基取代基的氧化还原活性α-二胺配体支撑的铀化合物（MesDABMe = [ArNC(Me)C(Me)NAr]，其中Ar = 2,4,6-三甲基苯基（Mes））。加入2当量的MesDABMe、3当量的KC8和1当量的UI3(THF)4，产生了双配体物种（MesDABMe）2U(THF)（1）。通过向Cp3U中添加等摩尔比的MesDABMe和KC8，生成了环戊二烯衍生物Cp2U(MesDABMe)（2）。这两种物种的分子结构中的键长证实了α-二胺配体已双还原形成烯丙二胺配体。电子吸收光谱的表征显示在近红外光谱区域存在微弱而尖锐的跃迁，与晶体结构数据相结合，与存在并受烯丙二胺配体支撑的四价铀离子的构型一致。此解释经U LIII边缘X射线吸收近边缘结构（XANES）光谱学和变温磁性测量得到验证。磁性数据与低温下的单重态基态以及预期为铀(IV)物种的变温依赖性一致。然而，这两种配合物在室温下均表现出较低的磁矩，分别为1和2的1.91和1.79 μB。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CH3I无反应，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（MesDABMe）（MesDABMe2）UI（3；MesDABMe2 = [ArNC(Me)C(Me2)NAr]），该物种经单晶X射线衍射和U M4-和M5边缘XANES表征。结构确认还通过氘标记研究完成，该研究表明甲基基团被添加到烯丙二胺配体碳骨架上。