作者:Ken Cham-Fai Leung、Wing-Yan Wong、Fabio Aricó、Philip C. Haussmann、J. Fraser Stoddart
DOI:10.1039/b915864b
日期:——
Large amounts (>100 mol equivalents) of water are required to effect by hydrolysis the partial disassembly of the rings from the dumbbell components of two dynamic [2]rotaxanes. The two dynamic [2]rotaxanes are comprised of [24]crown-8 rings—each of which incorporate two imine bonds—encircling a dumbbell component composed of a dibenzylammonium ion in which each of the two benzyl substituents carries two methoxyl groups attached to their 3- and 5-positions. A mechanism for the partial disassembly of the two dynamic [2]rotaxanes, involving the cleavage of the kinetically labile imine bonds by water molecules, is proposed. The most important experimental observation to be noted is the fact that the hydrolysis of the macrocyclic diimines, associated with the templating –CH2NH2+CH2–centres in the middle of their dumbbells, turns out to be an uphill task to perform in the face of the molecular recognition provided by strong [N+–H⋯O] hydrogen bonds and weaker, yet not insignificant, [C–H⋯O] interactions. The dynamic nature of the imine bond formation and hydrolysis is such that the acyclic components produced during hydrolysis of the imine bonds can be enticed to cyclise once again around the –CH2NH2+CH2–template, affording the [2]rotaxanes. The reluctance of imine bonds, present in substantial numbers in larger molecular and extended structures, is significant when it comes to exercising dynamic chemistry in compounds where multiple imine bonds are present.
两种动态[2]轮烷的哑铃状成分需要大量(大于 100 摩尔当量)的水才能通过水解作用部分分解环。这两种动态[2]轮烷由[24]冠-8 环组成,其中每个环都包含两个亚胺键,环绕着一个由二苄铵离子组成的哑铃状成分,哑铃状成分中的两个苄基取代基都带有两个甲氧基,分别连接在它们的 3 位和 5 位上。研究人员提出了两种动态 [2]rotaxanes 的部分分解机制,其中涉及水分子裂解动力学上易失效的亚胺键。最重要的实验观察结果是,与哑铃中间的模板化 -CH2NH2+CH2 中心有关的大环二亚胺的水解,在强大的[N+-H⋯O]氢键和较弱但并非不重要的[C-H⋯O]相互作用提供的分子识别面前,是一项艰巨的任务。亚胺键的形成和水解具有动态性质,因此在亚胺键水解过程中产生的非环成分会被引诱再次围绕-CH2NH2+CH2-模板循环,从而产生 [2] rotaxanes。在较大的分子结构和扩展结构中存在大量的亚胺键,当需要在存在多个亚胺键的化合物中进行动态化学反应时,亚胺键的惰性就显得尤为重要。