Self-assembly of novel [2]catenanes and [2]pseudorotaxanes incorporating thiacrown ethers or their acyclic analogues

A series of π electron rich macrocyclic polythioethers and their acyclic analogues have been synthesized in good yields. The association constants for the complexation of the π electron deficient bis(hexafluorophosphate) bipyridinium-based salt, paraquat, by these macrocycles, as well as those for the complexation of corresponding acyclic compounds by the bipyridinium-based tetracationic cyclophane, cyclobis(paraquat -p-phenylene), are significantly lower than those observed in the case of the 'all-oxygen' analogues. Nonetheless, yields as high as 86% were recorded in the template-directed syntheses of [2]catenanes composed of cyclobis(paraquat-p-phenylene) and the macrocyclic polythioethers. Single-crystal X-ray crystallographic analyses of the [2]catenanes incorporating constitutionally unsymmetrical π electron rich macrocyclic polythioethers revealed that, in all cases, the dioxyaromatic units are located inside the cavity of the tetracationic cyclophane component in preference to the dithiaaromatic units. A similar selectivity was observed in solution by variable-temperature ¹H NMR spectroscopy. However, inversion of the ratio between the two translational isomers of the two [2]catenanes bearing 1,5-dithianaphthalene, as one of their π electron rich ring systems, and either 1,4-dioxybenzene or 1,5-dioxynaphthalene, as the other, occurs upon increasing the temperature from -30 to +30 C. These [2]catenanes can be viewed as temperature-responsive molecular switches.