Cation-complexing properties of synthetic macrocyclic polyether-diester ligands containing the furan, benzene, tetrahydrofuran, and thiophene subcyclic units

Abstract

The synthesis of 13 new macrocyclic polyether-diester ligands containing the furan, 3,4-dimethoxyfuran, tetrahydrofuran, and thiophene subcyclic by the reaction of a diacid dichloride with the appropriate glycol is described. The complexation properties of these ligands with alkylammonium and metal cations were determined and compared with the crown ethers. The free energies of activation (..delta..G*) for the dissociation of the alkylammonium complexes were determined from their temperature-dependent /sup 1/H NMR spectra. The relative kinetic stability (as measured by the ..delta..G* values) for the complexes between benzylammonium perchlorate and ligands containing an aromatic subcyclic unit increased with increasing ring size in the order 18-<21-<24-membered ring. Formation constants as well as ..delta..H and T..delta..S values were determined in methanol by a calorimetric titration technique for the reaction of Na/sup +/, K/sup +/, Cs/sup +/ and Sr/sup 2 +/ with the tetrahydrofurano ligands. The 21- and 24-membered ring compounds containing a furan subcyclic unit were found to be effective carriers of Cs/sup +/ across a CHC1/sub 3/ ligand membrane separating aqueous phases.