Synthesis and electrochemical properties of calix[4]arene-triester-monoquinones

Abstract

Calix[4]arene-based monoquinones having three efficient ligating groups of alkoxycarbomethyl ethers were prepared and their ionophoric properties were investigated by electrochemical technique. Calix[4]-triester-monoquinones 3a and 3b were prepared from calix[4]arene and p-tert-butylcalix[4]arene by the selective trialkylation followed by oxidation with Tl(NO3)(3) and Tl(CF3CO2)(3), respectively. X-ray crystal structural analysis revealed that the ligand 3a adopted a partial cone conformation with an anti quinone moiety. MM+ calculations suggested that the energy difference between the two conformations is relatively small (<3.5 kcal mole(-1)). Electrochemical studies also showed that the monoquinones 3a and 3b form strong complexes with Na+ ion, and the positive shifts in the reduction potential exceeded those of the closely related diquiones 5a and 5b.