Synthesis, Structure, and Dynamic Properties of Hybrid Organic−Inorganic Rotaxanes

The synthesis and characterization of a series of hybrid organic−inorganic [2]rotaxanes is described. The ring components are heterometallic octa- ([Cr7MF8(O2CtBu)16]; M = Co, Ni, Fe, Mn, Cu, Zn, and Cd) nuclear cages in which the metal centers are bridged by fluoride and pivalate (tBuCO2−) anions; the thread components feature dialkylammonium units that template the formation of the heterometallic rings about the axle to form the interlocked structures in up to 92% yield in conventional macrocyclization or one-pot ‘stoppering-plus-macrocyclization’ strategies. The presence in the reaction mixture of additives (secondary or tertiary amines or quaternary ammonium salts), and the nature of the stoppering groups (3,5-tBu2C6H3CO2− or tBuCONH−), can have a significant effect on the rotaxane yield. The X-ray crystal structures of 11 different [2]rotaxanes, a pseudorotaxane, and a two-station molecular shuttle show two distinct types of intercomponent hydrogen bond motifs between the ammonium groups of the organic thread and the fluoride groups of the inorganic ring. The different hydrogen bonding motifs account for the very different rates of dynamics observed for the heterometallic ring on the thread (shuttling slow; rotation fast).

本文报道了一系列杂化有机-无机[2]轮烷（[2]rotaxane）的合成与表征工作。该系列轮烷的大环组分为以氟离子与特戊酸根（pivalate，tBuCO2−）为桥联配体的异金属八核笼状结构，其通式为Cr7MF8(O2CtBu)16，其中M分别为Co、Ni、Fe、Mn、Cu、Zn及Cd；轴组分则带有二烷基铵单元，该单元可作为模板诱导异金属大环围绕轴组装形成互锁结构，采用传统大环化反应或一锅法"封端-大环化"策略时，目标产物的产率最高可达92%。反应混合体系中添加剂（仲胺、叔胺或季铵盐）的引入，以及封端基团（3,5-二叔丁基苯甲酸根（3,5-tBu2C6H3CO2−）或特戊酰胺基（tBuCONH−））的种类，均会对轮烷的产率产生显著影响。通过X射线晶体衍射分析，我们解析了11种不同的[2]轮烷、1种准轮烷（pseudorotaxane）以及1种双位点分子梭的晶体结构，发现有机轴的铵基与无机大环的氟基之间存在两种截然不同的组分间氢键基元。这两种不同的氢键作用模式，很好地解释了异金属大环在轴上所表现出的迥异动态行为：环的穿梭过程速率缓慢，而环自身的旋转速率较快。