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 rr-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 . PF6 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 H-1 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.