Pentaalkyl ester derivatives of p-benzylcalix[5]arene and p-tert-octylcalix[5]arene: synthesis, crystal structure and metal ion complexation

We report the synthesis of two pentamethyl ester derivatives of the p-benzyl- (1) and p-tert-octylcalix[5]arenes (2) in the cone conformation. The detailed structure of the already known pentaethyl ester derivative of 1, established by X-ray crystallography, shows the 1,2-alternate conformation of this compound. The binding properties of the three pentaalkyl esters have been assessed by liquid–liquid extraction and complexation of alkali and silver metal ions in methanol and acetonitrile. These ligands display high selectivities within the alkali series, which depend on different factors such as the conformation, the substituents on the para-positions and the functional groups, and the solvent.