Substituent control of potassium and rubidium uptake by asymmetric calix[4]-thiacalix[4]tubes

Abstract

Herein we report on the synthesis and ionophore properties of the first asymmetric p-tert-butylcalix[4]-p-R-thiacalix[4]tubes 7a–c (R = t-Bu, H, 1-adamantyl). The target compounds were obtained by the condensation of tosyloxyethoxy-p-tert-butylcalix[4]arene with the corresponding p-R-thiacalix[4]arenes in the presence of K₂CO₃ in acetonitrile. The complexation with sodium, potassium and rubidium iodides was studied in CDCl₃–CD₃OD (4 : 1) medium by means of ¹H NMR measurements. It was found that the ionophore properties of calixtubes 7a–c are controlled by the character of the substituents at the upper rim of the thiacalix[4]arene fragment and it was shown that only the molecular tube 7c with an adamantane-containing thiacalixarene unit is capable of quantitatively binding potassium (swiftly) and rubidium (slowly) cations.