Zapf Ludwig, Peters Sven, Bertermann Rüdiger, Radius Udo, Finze Maik
Institute for Sustainable Chemistry & Catalysis with Boron (ICB) Institute of Inorganic Chemistry, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
Chemistry. 2022 Jul 11;28(39):e202200275. doi: 10.1002/chem.202200275. Epub 2022 Jun 1.
The 1-methyl-3-(tricyanoborane)imidazolin-2-ylidenate anion (2) was obtained in high yield by deprotonation of the B(CN) -methylimidazole adduct 1. Regarding charge and stereo-electronic properties, anion 2 closes the gap between well-known neutral NHCs and the ditopic dianionic NHC, the 1,3-bis(tricyanoborane)imidazolin-2-ylidenate dianion (IIb). The influence of the number of N-bonded tricyanoborane moieties on the σ-donating and π-accepting properties of NHCs was assessed by quantum chemical calculations and verified by experimental data on 2, IIb, and 1,3-dimethylimidazolin-2-ylidene (IMe, IIa). Therefore NHC 2, which acts as a ditopic ligand via the carbene center and the cyano groups, was reacted with alkyl iodides, selenium, and [Ni(CO) ] yielding alkylated imidazoles 3 and 4, the anionic selenium adduct 5, and the anionic nickel tricarbonyl complex 8, respectively. The results of this study prove that charge, number of coordination sites, buried volume (%V ) and σ-donor and π-acceptor abilities of NHCs can be effectively fine-tuned via the number of tricyanoborane substituents.
通过对B(CN) -甲基咪唑加合物1进行去质子化反应，以高产率得到了1-甲基-3-(三氰基硼烷)咪唑啉-2-亚基阴离子(2)。就电荷和立体电子性质而言，阴离子2填补了众所周知的中性NHC与双齿二价阴离子NHC即1,3-双(三氰基硼烷)咪唑啉-2-亚基二阴离子(IIb)之间的差距。通过量子化学计算评估了与氮键合的三氰基硼烷部分的数量对NHC的σ供电子和π吸电子性质的影响，并通过对2、IIb和1,3-二甲基咪唑啉-2-亚基(IMe, IIa)的实验数据进行了验证。因此，通过卡宾中心和氰基作为双齿配体的NHC 2分别与烷基碘、硒和[Ni(CO)₄]反应，生成了烷基化咪唑3和4、阴离子硒加合物5以及阴离子三羰基镍配合物8。本研究结果证明，通过三氰基硼烷取代基的数量，可以有效地微调NHC的电荷、配位点数量、掩埋体积(%V)以及σ供体和π受体能力。
