Voelkel Martin H H, Wonner Patrick, Huber Stefan Matthias
Fakultät für Chemie und Biochemie Ruhr-Universität Bochum Universitätsstraße 150 44801 Bochum Germany.
ChemistryOpen. 2020 Feb 11;9(2):214-224. doi: 10.1002/open.201900355. eCollection 2020 Feb.
Preorganization is a powerful tool in supramolecular chemistry which has been utilized successfully in intra- and intermolecular halogen bonding. In previous work, we had developed a bidentate bis(iodobenzimidazolium)-based halogen bond donor which featured a central trifluoromethyl substituent. This compound showed a markedly increased catalytic activity compared to unsubstituted bis(iodoimidazolium)-based Lewis acids, which could be explained either by electronic effects (the electron withdrawal by the fluorinated substituent) or by preorganization (the hindered rotation of the halogen bonding moieties). Herein, we systematically investigate the origin of this increased Lewis acidity via a comparison of the two types of compounds and their respective derivatives with or without the central trifluoromethyl group. Calorimetric measurements of halide complexations indicated that preorganization is the main reason for the higher halogen bonding strength. The performance of the catalysts in a series of benchmark reactions corroborates this finding.
预组织是超分子化学中的一种强大工具，已成功应用于分子内和分子间的卤素键合。在先前的工作中，我们开发了一种基于双齿双（碘苯并咪唑鎓）的卤素键供体，其具有中心三氟甲基取代基。与未取代的基于双（碘咪唑鎓）的路易斯酸相比，该化合物显示出显著提高的催化活性，这可以通过电子效应（氟化取代基的吸电子作用）或预组织（卤素键合部分的受阻旋转）来解释。在此，我们通过比较两种类型的化合物及其带有或不带有中心三氟甲基基团的各自衍生物，系统地研究了这种路易斯酸性增加的起源。卤化物络合的量热测量表明，预组织是卤素键强度较高的主要原因。催化剂在一系列基准反应中的性能证实了这一发现。
