Physikalische Organische Chemie, Technische Universität Dresden, 101062 Dresden, Germany.
Chem Asian J. 2011 Mar 1;6(3):863-7. doi: 10.1002/asia.201000744. Epub 2011 Jan 19.
Owing to numerous new applications, the interest in "task-specific" ionic liquids increased significantly over the last decade. But, unfortunately, the imidazolium-based ionic liquids (by far the most frequently used cations) have serious limitations when it comes to modifications of their properties. The new generation of ionic liquids, called tunable aryl-alkyl ionic liquids (TAAILs), replaces one of the two alkyl chains on the imidazolium ring with an aryl ring which allows a large degree of functionalization. Inductive, mesomeric, and steric effects as well as potentially also π-π and π-π(+) interactions provide a wide range of possibilities to tune this new class of ILs. We investigated the influence of electron-withdrawing and -donating substituents at the para-position of the aryl ring (NO(2), Cl, Br, EtO(CO), H, Me, OEt, OMe) by studying the changes in the melting points of the corresponding bromide and bis(trifluoromethanesulfonyl)imide, (N(Tf)(2)(-)), salts. In addition, we calculated (B3LYP/6-311++G(d,p)) the different charge distributions of substituted 1-aryl-3-propyl-imidazolium cations to understand the experimentally observed effects. The results indicated that the presence of electron-donating and -withdrawing groups leads to strong polarization effects in the cations.
由于众多新的应用，“任务特定”离子液体的兴趣在过去十年中显著增加。但是，不幸的是，基于咪唑鎓的离子液体（迄今为止最常用的阳离子）在其性质的改性方面存在严重的局限性。新一代的离子液体，称为可调芳烃-烷基离子液体（TAAILs），用芳环取代咪唑鎓环上的两个烷基链之一，这允许进行很大程度的官能化。诱导、中介和空间效应，以及潜在的π-π和π-π(+)相互作用，为调整这种新型 ILs 提供了广泛的可能性。我们通过研究相应的溴化物和双（三氟甲烷磺酰基）亚胺（N(Tf)(2)(-))盐的熔点变化，研究了芳环对位的吸电子和给电子取代基（NO(2)、Cl、Br、EtO(CO)、H、Me、OEt、OMe）对其的影响。此外，我们还计算了取代的 1-芳基-3-丙基-咪唑鎓阳离子的不同电荷分布（B3LYP/6-311++G(d,p)），以理解实验观察到的效应。结果表明，供电子和吸电子基团的存在会导致阳离子的强烈极化效应。
