Self-complementary [2]catenanes and their related [3]catenanes

Three [3]catenanes with cavities large enough to accommodate aromatic guest s have been designed and synthesized (yields = 5-20 %) by means of kinetica lly controlled self-assembly processes The X-ray structural analysis of one of three [3]catenanes confirmed the presence of a rectangular cavity (dime nsions = 7 x 11 Angstrom) lined by pi-electron-rich recognition sites and h ydrogen-bond acceptor groups. Ln spite of their apparently ideal recognitio n features, none of these [3]catenanes bind guests incorporating a pi-elect ron-deficient bipyridinium unit. However, the template-directed syntheses o f the [3]catenanes also produce, in yields of 2-23%, [2]catenanes incorpora ting a 1,5-dioxynaphtho[38]crown-10 interlocked with a bipyridinium-based t etracationic cyclophane. The X-ray structural analyses of two of these [2]c atenanes revealed that a combination of [pi ... pi] and [C-H ... pi] intera ctions is responsible for the formation of supramolecular homodimers in the solid state. H-1 NMR spectroscopic investigations of the four [2]catenanes demonstrated that supramolecular homodimers are also formed (K-a-17-31 M-1 , T = 185 K) in (CD3)(2)CO solutions. Dynamic H-1 NMR spectroscopy revealed that the 1,5-dioxynaphtho[38]crown-10 and tetracationic cyclophane compone nts in the four [2]catenanes and in the three [3]catenanes circumrotate: (D elta G(c)* = 9-14 kcal mol(-1)) through each other's cavity in (CD3)(2)CO. Similarly, the 1,5-dioxynaphthalene and the bipyridinium ring systems rotat e (Delta G(c)* = 10-14 kcal mol(-1)) about their [O ... O] and [N ... N] ax es, respectively, in solution.