Lower rim tetra-substituted and upper rim ferrocene amide calix[4]arenes: synthesis, conformation and anion-binding properties

Calix[4]arenes containing ferrocene amide at the upper rim and methoxy or ethoxycarbonylmethoxy (ethyl ester) groups at the lower rim (5a, 5b and 5c) have been synthesized. It was found that tetramethoxy 5a and dimethoxy diethyl ester 5c were conformationally labile and existed in both cone and partial cone conformation in solution. Anion-binding studies by 1H NMR titration in CDCl3 showed that 5b bound Cl− selectively with high stability. Compound 5c formed complexes with Cl− and H2PO4− where the former was more stable. The ratio of cone to partial cone conformation in compound 5a was found to decrease upon binding Cl− and H2PO4− and in a polar solvent.