Two series of novel dicationic threading molecules [Quin(CH2)10R]2+ and [3,5-Lut(CH2)10R]2+, where Quin+ = quinuclidinium, 3,5-Lut+ = 3,5-lutidinium, and R+ = N(CH3)3+ and N(CH3)2CH2CH3+, form [2]semi-rotaxanes with α-cyclodextrin (α-CD) in aqueous solution. The quinuclidinium and 3,5-lutidinium are sufficiently bulky to prevent threading while the R+ groups allow for slow threading by α-CD at 25 °C. The resulting [2]semi-rotaxanes exist in two orientational isomers owing to the asymmetry of both the α-CD cavity and the threading molecules. Two-dimensional 1H NMR spectroscopy and kinetics experiments reveal that the isomer in which the narrower rim (primary OHs) is positioned near the R+ group is the kinetically preferred isomer, while the other isomer is the thermodynamically preferred product. The kinetics and mechanism of the formation, dissociation, and interconversion of the two isomers have been determined at 25 °C.
两个系列的新型二阳离子穿线分子[Quin(
CH2)10R]2+和[3,5-Lut( )10R]2+(其中Quin+ =
喹啉鎓,3,5-Lut+ = 3,5-镏
金鎓,R+ = N(
CH3)3+和N( )2 +)在
水溶液中与δ-
环糊精(δ-CD)形成[2]半十字烷。其中的quinuclidinium和3,5-lutidinium具有足够大的体积,可以防止穿线,而R+基团则可以让δ-CD在25°C时缓慢穿线。由于δ-CD空腔和穿线分子都不对称,因此生成的[2]半罗他烷存在两种取向异构体。二维 1H NMR 光谱和动力学实验表明,较窄边缘(初级羟基)位于 R+ 基团附近的异构体是动力学优选异构体,而另一种异构体则是热力学优选产物。这两种异构体在 25 ℃ 下形成、解离和相互转化的动力学和机理已经确定。