Beltrán Tomás F, Zaragoza Guillermo, Delaude Lionel
Laboratory of Organometallic Chemistry and Homogeneous Catalysis, Institut de Chimie (B6a), Allée du six Août 13, Quartier Agora, Université de Liège, 4000 Liège, Belgium.
Dalton Trans. 2017 Jul 18;46(28):9036-9048. doi: 10.1039/c7dt01889d.
The superbulky N-heterocyclic carbenes (NHCs) 2,6-bis(diphenylmethyl)-4-methylimidazol-2-ylidene (IDipMe) and its 4-methoxy analogue (IDipOMe) reacted instantaneously with carbon disulfide to afford the corresponding imidazolium-2-dithiocarboxylate zwitterions in high yields. These new dithiolate ligands were fully characterized and their coordination chemistry toward common Re(i) and Ru(ii) metal sources was thoroughly investigated. Neutral [ReBr(CO)(SC·NHC)] chelates featured three facially-arranged carbonyl groups on a distorted octahedron, whereas cationic [RuCl(p-cymene)(SC·NHC)]PF complexes displayed a piano-stool geometry. The molecular structures of the six new compounds revealed that the NHC·CS inner salts were highly flexible. Indeed, the torsion angle between their anionic and cationic moieties varied between ca. 63° in the free ligands and 3° in the ruthenium complexes. Concomitantly, the S-C-S bite angle underwent a contraction from 131° to 110-113° upon chelation. Computation of the %V parameter showed that the dithiocarboxylate unit of the NHC·CS betaines chiefly determined the steric requirements of the imidazolium moieties, irrespective of the metal center involved in the complexation. The replacement of the p-methyl substituents of IDipMe with p-methoxy groups in IDipOMe did not significantly affect the ligand bulkiness. The more electron-donating methoxy group led, however, to small changes in various IR wavenumbers used to probe the electron donor properties of the carbene moiety.
超大位阻的氮杂环卡宾（NHCs）2,6-双（二苯基甲基）-4-甲基咪唑-2-亚基（IDipMe）及其4-甲氧基类似物（IDipOMe）与二硫化碳瞬间反应，以高产率得到相应的咪唑-2-二硫代羧酸盐两性离子。对这些新型二硫醇盐配体进行了全面表征，并深入研究了它们与常见铼（I）和钌（II）金属源的配位化学。中性[ReBr(CO)(SC·NHC)]螯合物在扭曲的八面体上具有三个面式排列的羰基，而阳离子[RuCl(p-异丙基苯)(SC·NHC)]PF配合物呈现出钢琴凳几何构型。六种新化合物的分子结构表明，NHC·CS内盐具有高度的灵活性。实际上，它们阴离子和阳离子部分之间的扭转角在游离配体中约为63°，在钌配合物中为3°。同时，螯合时S-C-S咬角从131°收缩至110 - 113°。%V参数的计算表明，NHC·CS甜菜碱的二硫代羧酸盐单元主要决定了咪唑鎓部分的空间需求，而与参与络合的金属中心无关。在IDipOMe中用对甲氧基取代IDipMe的对甲基取代基并没有显著影响配体的位阻。然而，给电子性更强的甲氧基导致用于探测卡宾部分给电子性质的各种红外波数发生了微小变化。
