Calix[4]arenes bridged with two different crown ether loops: Influence of crown size on metal ion recognition

A series of calix[4]arene-bis-crown ethers were synthesized in a fixed 1,3-alternate conformation with good yields by the reaction of a monocyclic calixcrown ether with multi-ethyleneglycol di-p-toluenesulfonate in the presence of cesium carbonate. In the preparation of the monocyclic calixcrown ethers (1 and 2), the use of potassium carbonate as a base provided the best yield regardless of the template concept. In two phase extraction and competitive transport experiments for ligand-metal complexation, calix[4]arene biscrown (5) provided the best selectivity for potassium ion. When a calixbiscrown ether (4) bearing different sized crown ether loops coordinates to K+ and Cs+, respectively, the changes of peak splitting patterns and chemical shift on H-1 NMR spectra are dependent on the complexed metal ion species.