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

Abstract

1,3-Dimethoxy-p-tert-butyldihomooxacalix[4]arene-crown-6 (4) was synthesized for the first time. 4 was isolated in a partial cone A conformation in solution at room temperature, as established by NMR measurements (H-1, C-13, COSY and NOESY). Conformational behaviour of 4 and p-tert-butyldihomooxacalix[4]-crown-5 (2) and crown-6 (3) was studied by dynamic H-1 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. 2 and 3 are poor phase transfer agents for all cations, while 4 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+. (C) 2002 Elsevier Science Ltd. All rights reserved.