Self-Assembling Calix[4]arene [2]Catenanes. Preorganization, Conformation, Selectivity, and Efficiency.

A novel class of preorganized U-shape calix[4]arene clefts, dicationic salts 3a,c,e.2Cl, 3b.2PF(6)(), and 3f.2Br, consisting of one cone calix[4]arene and two bipyridine residues being linked by an aliphatic chain, have been designed and synthesized as precursors for self-assembly of calix[4]arene [2]catenanes by utilizing pi-stacking interactions between the hydroquinone and bipyridinium units. Conformationally flexible 6.2PF(6)() and cone 10.2Cl, whose conformation is fixed by two propyloxy groups on the lower rim, were also prepared in order to explore the effects of conformation and hydrogen bonding of the calix[4]arene moiety on self-assembly. For all reactions, bis-p-phenylene-34-crown ether-10 (11) was employed as the donor component. Alternate cone [2]catenane 13.4Cl is obtained in 8% yield from reaction of ethylene-incorporating 3a.2Cl and 1,4-bis(bromomethyl)benzene (12a). Three cone and one conformationally flexible [2]catenanes were obtained in moderate to good yields from reactions of propylene-incorporating 3b.PF(6)() and 3c.2Cl with 12a, 1,3-bis(bromomethyl)benzene (12b) or 4,4'-(bromomethyl)biphenyl (12c). Both cone and partial cone [2]catenanes were generated in moderate yields from butylene-incorporating 3c.2Cl with four tert-butyl groups on the calix[4]arene moiety and with 12a. In contrast, only cone [2]catenane was obtained from similar tert-butyl-free cleft 3d.2Cl. Cone and conformationally flexible [2]catenanes were obtained in moderate yields, respectively, from the reactions of 3d.2Cl and 3e.2Cl with 12c. No catenanes were isolated from reaction of phenylene-incorporating 3f.2Br or 6.2Cl, whereas reaction of 10.2Cl afforded cone [2]catenane in low yield. It was demonstrated that hydrogen bonding, which may be destroyed after catenation, within the calix[4]arene moiety is crucial for efficient self-assembly of the [2]catenanes. The dynamic (1)H NMR and absorption spectra and luminescent properties of the [2]catenanes were investigated, which reveal that incorporation of calix[4]arene into the tetracationic cyclophane reduces pi-stacking interactions between the donor and acceptor units and catenation has substantial influence on conformational distributions of the calix[4]arene moiety. The results demonstrate the versatility of calix[4]arene derivatives as building blocks in the construction of supramolecular structures.