Viologen-calix[6]arene pseudorotaxanes. ion-pair recognition and threading/dethreading molecular motions
Viologen-calix[6]arene pseudorotaxanes. ion-pair recognition and threading/dethreading molecular motions
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DOI：
10.1021/jo0494127
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发表时间：
2004-09-03
影响因子：
3.6
通讯作者：
Secchi, A
中科院分区：
文献类型：
--
作者：
Credi, A;Dumas, S;Secchi, A
杯[6]芳烃轮的空腔被N-苯基脲基在其上边缘上扩展和硬化，在CH 2Cl 2溶液中形成具有包含紫精（4，4 '-联吡啶）单元的分子轴的准轮烷物种。在这些条件下，自组装过程非常有效，相关的DeltaGdegree值约为-8 kcalmol（-1）。基于联吡啶的线的抗衡阴离子在络合物的形成中确实起着重要作用。客体的甲苯磺酸盐或六氟磷酸盐的使用影响络合物的稳定性和穿线过程的速率。这样的效果已被解释在离子对识别方面，这表明通过杯芳烃轮的脲基基团的紫精螺纹的抗衡阴离子的协调是至关重要的紧密的离子对的线程之前的断裂。通过循环伏安法获得了与轴紫精单元的氧化还原过程耦合的穿线/脱线反应的速率常数。准轮烷物种经历快速脱线程（亚微秒时间尺度）的电化学还原的客人。包封到杯芳烃腔中后，用于还原紫精单元的非均相电子转移动力学减慢。
A calix[6]arene wheel, whose cavity has been extended and rigidified by N-phenylureido groups on the upper rim, forms pseudorotaxane species with molecular axles containing the viologen (4,4'-bipyridinium) unit in CH2Cl2 solution. In these conditions, the self-assembly process is very efficient, with associated DeltaGdegrees values of around -8 kcal mol(-1). The counteranions of the bipyridinium-based threads play indeed an important role in the formation of the complex. The use of either tosylate or hexafluorophosphate salts of the guests affects both the stability of the complexes and the rate of the threading process. Such effects have been interpreted in terms of ion-pair recognition, suggesting that coordination of the counteranions of the viologen thread by the ureido groups of the calixarene wheel is crucial for the breaking of tight ion pairs prior to threading. The rate constants of the threading/dethreading reactions coupled with the redox processes of the viologen unit of the axle have been obtained by means of cyclic voltammetry. The pseudorotaxane species undergo fast dethreading (submicrosecond time scale) on electrochemical reduction of the guest. The heterogeneous electron-transfer kinetics for the reduction of the viologen unit is slowed upon encapsulation into the calixarene cavity.