Bridged calixarenes calix arene crown

The crown ether bridge in calix[4]arene 19 freezes the calixarene stmcture in a rigid flattened-cone conformation also pushing the two metal ions apart. The bimetallic complex 19—Zu2 cleaves HPNP eight times less effectively than the flexible 2—Zu2 [17], thus confirming that a certain degree of flexibility is beneficial and is an important requisite in a supramolecular catalyst. 

Abstract. The synthesis of 1,2- and l,3-calix[4]-Z w-crowns, double calix[4]arenes and double calixcrowns have been shown to depend on the reaction conditions (nature of the base, structure of the ditosylates, and the stoichiometry of the reactants). The 1,3-altemate conformation of the 1,3-calix[4]- w-crowns was shown to be favourable to the selective complexation of cesium cation. The observed Na /Cs selectivity was exploited in separation processes using them as carriers in transport through supported liquid membranes (SLMs). The best Na "/Cs selectivity (1/45 000) was observed for the naphthyl derivative 7. Calix(aza)crowns and 1,3-calix[4]-/ w-(aza)-crowns were also produced through the preliminary formation of the Schiff base-calixarenes, which were further hydrogenated. The syntheses consisted of the 1,3-selective alkylation of calixarenes followed by cyclization into a 1,3-bridged calixarene or by the direct 1,3-capping of the calixarene with appropriate ditosylates. Soft metal complexation by these ligands is also presented. 

The two remaining phenolic units are either derived with long alkyl chains to enhance carrier lipophilicity or bridged with a second polyethylene glycol chain to rigidify the calixarene frame leading to bis-crown-calix[4]arene (Figure 2 compounds 4, 5,6,7 and 8). 

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