Center of Novel Functional Molecules, Department of Chemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong SAR, PR China.
Org Biomol Chem. 2010 Jan 7;8(1):83-9. doi: 10.1039/b915864b. Epub 2009 Nov 20.
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 -CH(2)NH(2)(+)CH(2)-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(+)-HO] hydrogen bonds and weaker, yet not insignificant, [C-HO] 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 -CH(2)NH(2)(+)CH(2)-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.
大量的水（>100 摩尔当量）需要通过水解作用将哑铃型分子的两个动态[2]轮烷的环部分从哑铃型分子上拆离下来。这两个动态[2]轮烷由[24]冠-8 环组成，每个环都包含两个亚胺键，环绕着一个哑铃型分子，哑铃型分子由二苄基铵离子组成，每个苄基取代基在其 3-和 5-位上带有两个甲氧基。提出了一种部分拆离两个动态[2]轮烷的机制，涉及到通过水分子裂解动力学不稳定的亚胺键。需要注意的是，最重要的实验观察结果是，与模板化-CH(2)NH(2)(+)CH(2)-中心相关的大环二亚胺的水解，在强大的[N(+)-HO]氢键和较弱但并非不重要的[C-HO]相互作用提供的分子识别面前，是一项艰巨的任务。亚胺键形成和水解的动态性质使得在亚胺键水解过程中产生的无环成分可以再次被诱导向-CH(2)NH(2)(+)CH(2)-模板环化，从而形成[2]轮烷。在存在多个亚胺键的化合物中进行动态化学时，大量存在的亚胺键的不情愿性是非常重要的。
