Self-complementary

Abstract

Three [3]catenanes with cavities large enough to accommodate aromatic guests have been designed and synthesized (yields = 5-20 %) by means of kinetically controlled self-assembly processes. The X-ray structural analysis of one of three [3]catenanes confirmed the presence of a rectangular cavity (dimensions = 7 x 11 A) lined by pi-electron-rich recognition sites and hydrogen-bond acceptor groups. In spite of their apparently ideal recognition features, none of these [3]catenanes bind guests incorporating a pi-electron-deficient bipyridinium unit. However, the template-directed syntheses of the [3]catenanes also produce, in yields of 2-23%, [2]catenanes incorporating a 1,5-dioxynaphtho[38]crown-10 interlocked with a bipyridinium-based tetracationic cyclophane. The X-ray structural analyses of two of these [2]catenanes revealed that a combination of [pi...pi] and [C-H...pi] interactions is responsible for the formation of supramolecular homodimers in the solid state. 1H NMR spectroscopic investigations of the four [2]catenanes demonstrated that supramolecular homodimers are also formed (Ka= 17-31M(-1), T= 185 K) in (CD3)2CO solutions. Dynamic 1H NMR spectroscopy revealed that the 1,5-dioxynaphtho[38]crown-10 and tetracationic cyclophane components in the four [2]catenanes and in the three [3]catenanes circumrotate (deltaGc(not equal to) = 9-14 kcal mol(-1)) through each other's cavity in (CD3)2CO. Similarly, the 1,5-dioxynaphthalene and the bipyridinium ring systems rotate (deltaGc(not equal to) =10-14 kcal mol(-1)) about their [O...O] and [N...N] axes, respectively, in solution.