Synthesis, conformational behaviour, alkali and alkaline-earth metal cation extraction and transport studies of p-tert-butyldihomooxacalix[4]crowns

1,3-Dimethoxy-p-tert-butyldihomooxacalix[4]arene-crown-6 () was synthesized for the first time. was isolated in a partial cone A conformation in solution at room temperature, as established by NMR measurements (1H, 13C, COSY and NOESY). Conformational behaviour of and p-tert-butyldihomooxacalix[4]-crown-5 () and crown-6 () was studied by dynamic 1H NMR and by MD/MM calculations. Two-phase (water/CH2Cl2) picrate extraction studies and transport experiments with the same salts through a CH2Cl2 membrane were performed to evaluate the binding properties of these ligands towards alkali and alkaline earth metal cations. and are poor phase transfer agents for all cations, while is a reasonable extractant for the alkali cations, showing preference for Cs+. However, all three calixcrowns are good carriers for the alkali cations and display a very selective transport for Ba2+.