Assessing the Potential of Zwitterionic NHC·CS₂ Adducts for Probing the Stereoelectronic Parameters of N‐Heterocyclic Carbenes

Abstract

Five imidazol(in)ium-2-dithiocarboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding Nheterocyclic carbenes (NHCs) by reaction with carbon disulfide. They were characterized by IR, UV/Vis, and NMR spectroscopy, and by thermogravimetric analysis. Their molecular structures were determined by X-ray diffraction. For the sake of comparison, tricyclohexylphosphonium dithiocarboxylate was also examined. The data acquired were scrutinized to evaluate their usefulness for assessing the steric and elec-

Betaine Adducts of N‐Heterocyclic Carbenes: Synthesis, Properties, and Reactivity

“…1,3-Dimesitylimidazolium-2-dithiocarboxylate (IMes·CS 2 ) and its saturated heterocycle analogue (SIMes·CS 2 ) precipitated from the reaction medium, whereas betaines bearing 2,6-diisopropylphenyl (IDip·CS 2 and SIDip·CS 2 ) or cyclohexyl substituents (ICy·CS 2 ) on their nitrogen atoms remained soluble in thf. [38] (10) Last but not least, the group of Nakayama has reported the formation of 1,3-dimethylimidazolinium-2-dithiocarboxylate from 1,3-dimethyl-2-methyleneimidazolidine and disulfur dichloride in the presence of triethylamine. [39] The reaction most likely proceeds via two consecutive additionelimination steps (Scheme 3).…”

“…[38] Indeed, a wide range of imidazol(in)ium or benzimidazolium derivatives bearing various alkyl or aryl groups on their nitrogen atoms have been characterized by this technique (Scheme 4). In all the compounds investigated so far, the central heterocycle and the dithiocarboxylate unit are nearly orthogonal, with N1-C2-C6-S7 torsion angles varying between 72°and 115° (Table 1).…”

Activation of carbon dioxide and carbon disulfide by a scandium N-heterocyclic carbene complex

“…In previously reported imidazolium-2-dithiocarboxylates the CS 2 carbon resonance is usually observed in the range 220 -226 ppm, and the C 2 in the unsaturated imidazolium ring around 149 ppm. 30,31 In a separate reaction, we also isolated the CS 2 adduct of the proligand, HL.CS 2 ; full characterisation including a single crystal X-ray structure, is in the SI. * Crystals of 4 were also grown by adding a few drops of thf, then three equivalents of CS2 to a toluene solution of 1 at room temperature.…”

Cyclic(alkyl)(amino)carbenes and the Research Prospect in Olefin Metathesis Reaction

“…最近, 通过测定卡宾与 CO 2 或 CS 2 加合物的羰基伸缩振动频率来评估配体的电 子效应 [21] , 与过渡金属羰基化合物不同的是, 这种加合 物上的羧基或二硫代羧基阴离子不会对卡宾空轨道有 π 反馈作用, 故其反映的是配体纯粹的 σ 给电子作用 [22] .…”