Synthesis and binding properties of calix[4]arenes with [2 + 2′] mixed ligating functional groups

Abstract

A series of mixed [2 + 2′] p-tert-butylcalix[4]arene have been synthesised by selective 1,3-dialkylation of phenolic groups using various alkylating agents such as benzyl bromide, methyl iodide, ethyl bromoacetate, and 2-methoxyethyl tosylate. The extraction and complexation properties of the synthesized calixarenes towards alkali and alkaline earth metal cations have been investigated in acetonitrile by means of UV spectrophotometry and ¹H NMR spectroscopy. The results show the formation of ML and/or ML₂ species depending on the ligand and the cation. The enthalpies and entropies of complexation of alkali metal cations by a tetraglycol, diglycol–dibenzyl and diglycol–diester derivatives have been obtained from calorimetric measurements. The results revealed that the formation of ML species is controlled by enthalpy while the formation of ML₂ from ML is entropy driven.