Graves Christopher R, Yang Ping, Kozimor Stosh A, Vaughn Anthony E, Clark David L, Conradson Steven D, Schelter Eric J, Scott Brian L, Thompson J D, Hay P Jeffrey, Morris David E, Kiplinger Jaqueline L
Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
J Am Chem Soc. 2008 Apr 16;130(15):5272-85. doi: 10.1021/ja711010h. Epub 2008 Mar 26.
Reaction of (C5Me5)2U(=N-2,4,6-(t)Bu3-C6H2) or (C5Me5)2U(=N-2,6-(i)Pr2-C6H3)(THF) with 5 equiv of CuX(n) (n = 1, X = Cl, Br, I; n = 2, X = F) affords the corresponding uranium(V)-imido halide complexes, (C5Me5)2U(=N-Ar)(X) (where Ar = 2,4,6-(t)Bu3-C6H2 and X = F (3), Cl (4), Br (5), I (6); Ar = 2,6-(i)Pr2-C6H3 and X = F (7), Cl (8), Br (9), I (10)), in good isolated yields of 75-89%. These compounds have been characterized by a combination of single-crystal X-ray diffraction, (1)H NMR spectroscopy, elemental analysis, mass spectrometry, cyclic voltammetry, UV-visible-NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. The uranium L(III)-edge X-ray absorption spectrum of (C5Me5)2U(=N-2,4,6-(t)Bu3-C6H2)(Cl) (4) was analyzed to obtain structural information, and the U=N imido (1.97(1) A), U-Cl (2.60(2) A), and U-C5Me5 (2.84(1) A) distances were consistent with those observed for compounds 3, 5, 6, 8-10, which were all characterized by single-crystal X-ray diffraction studies. All (C5Me5)2U(=N-Ar)(X) complexes exhibit U(V)/U(IV) and U(VI)/U(V) redox couples by voltammetry, with the potential separation between these metal-based couples remaining essentially constant at approximately 1.50 V. The electronic spectra are comprised of pi-->pi* and pi-->nb(5f) transitions involving electrons in the metal-imido bond, and metal-centered f-f bands illustrative of spin-orbit and crystal-field influences on the 5f(1) valence electron configuration. Two distinct sets of bands are attributed to transitions derived from this 5f(1) configuration, and the intensities in these bands increase dramatically over those found in spectra of classical 5f(1) actinide coordination complexes. Temperature-dependent magnetic susceptibilities are reported for all complexes with mu(eff) values ranging from 2.22 to 2.53 mu(B). The onset of quenching of orbital angular momentum by ligand fields is observed to occur at approximately 40 K in all cases. Density functional theory results for the model complexes (C5Me5)2U(=N-C6H5)(F) (11) and (C5Me5)2U(=N-C6H5)(I) (12) show good agreement with experimental structural and electrochemical data and provide a basis for assignment of spectroscopic bands. The bonding analysis describes multiple bonding between the uranium metal center and imido nitrogen which is comprised of one sigma and two pi interactions with variable participation of 5f and 6d orbitals from the uranium center.
（五甲基环戊二烯基）₂U（=N-2,4,6-三叔丁基苯）或（五甲基环戊二烯基）₂U（=N-2,6-二异丙基苯）（四氢呋喃）与5当量的CuXₙ（n = 1，X = Cl、Br、I；n = 2，X = F）反应，得到相应的铀（V）-亚胺卤化物配合物（五甲基环戊二烯基）₂U（=N-Ar）（X）（其中Ar = 2,4,6-三叔丁基苯且X = F（3）、Cl（4）、Br（5）、I（6）；Ar = 2,6-二异丙基苯且X = F（7）、Cl（8）、Br（9）、I（10）），分离产率良好，为75 - 89%。这些化合物通过单晶X射线衍射、¹H核磁共振光谱、元素分析、质谱、循环伏安法、紫外-可见-近红外吸收光谱以及变温磁化率进行了表征。分析了（五甲基环戊二烯基）₂U（=N-2,4,6-三叔丁基苯）（Cl）（4）的铀L（III）边X射线吸收光谱以获取结构信息，U=N亚胺键（1.97(1) Å）、U-Cl（2.60(2) Å）和U-五甲基环戊二烯基（2.84(1) Å）的键长与通过单晶X射线衍射研究表征的化合物3、5、6、8 - 10所观察到的一致。通过伏安法，所有（五甲基环戊二烯基）₂U（=N-Ar）（X）配合物均表现出U（V）/U（IV）和U（VI）/U（V）氧化还原对，这些基于金属的氧化还原对之间的电位差基本保持恒定，约为1.50 V。电子光谱由涉及金属-亚胺键中电子的π→π*和π→nb（5f）跃迁以及说明自旋轨道和晶体场对5f¹价电子构型影响的以金属为中心的f-f带组成。两组不同的谱带归因于源自该5f¹构型的跃迁，并且这些谱带中的强度比经典5f¹锕系配位配合物光谱中的强度显著增加。报道了所有配合物的变温磁化率，μeff值范围为2.22至2.53 μB。在所有情况下，观察到配体场对轨道角动量的猝灭在约40 K时开始。模型配合物（五甲基环戊二烯基）₂U（=N-苯基）（F）（11）和（五甲基环戊二烯基）₂U（=N-苯基）（I）（12）的密度泛函理论结果与实验结构和电化学数据显示出良好的一致性，并为光谱带的归属提供了依据。键合分析描述了铀金属中心与亚胺氮之间的多重键合，其由一个σ键和两个π键相互作用组成，铀中心的5f和6d轨道有不同程度的参与。
