Alkali and alkaline-earth metal cation complexation and transport properties by tetraphenyl ketone of p-tert-butyldihomooxacalix[4]arene

The tetraphenyl ketone of p-tert-butyldihomooxacalix[4]arene (2) was synthe sized for the first time. This derivative possesses the cone conformation i n solution at room temperature, which was confirmed by NMR measurements (H- 1, C-13 and NOE 1D), Extraction studies with metal picrates from neutral aq ueous solution into dichloromethane. transport experiments with metal picra tes through a dichloromethane membrane and stability constant measurements by UV absorption spectroscopy in methanol and acetonitrile were performed t o evaluate the binding ability of ketone 2 towards alkali and alkaline eart h metal cations. The tetraphenylketone of p-tert-butylcalix[4]arene (3) was also studied, and the results for the two derivatives were compared. Compo und 2 shows a preference for K+ and Ba2+ cations, being selective only in t he alkaline earth metal cation series. Compound 3 is a stronger binder than 2, but is a weaker extractant. Both show transport rates that are not prop ortional to complex stability or to extraction efficiency. Ketone 2 can be characterized as a selective receptor. Copyright (C) 1999 John Wiley & Sons , Ltd.