Cation-Complexing Properties of Synthetic Macrocyclic Polyether-Diester Ligands Containing the Furan, Benzene, Tetrahydrofuran, and Thiophene Subcyclic Units

Article abstract of DOI:10.1021/ja00397a041

Thirteen new macrocyclic polyether-diester ligands containing the furan, 3,4-dimethoxyfuran, tetrahydrofuran, and thiophene subcyclic units have been prepared by reacting a diacid dichloride with the appropriate glycol.The tetrahydrofurano ligands were also prepared by reducing the furan ring of the furano ligands.Certain of these ligands and corresponding macrocyclic polyether-diester ligands containing a benzene subcyclic unit have been shown to form complexes with alkylammonium and metal cations.Complexation with alkylammonium cations was accompanied by significant chemical-shift changes on the 1H NMR spectra.Free energies of activation (ΔG<*>) for the dissociation of the alkylammonium complexes were determined from their temperature-dependent 1H NMR spectra.The relative kinetic stability (as measured by the ΔG<*> 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 ΔH and TΔS values were determined in methanol by a calorimetric titration technique for the reaction of Na⁺, K⁺, Cs⁺, and Sr²⁺ with the tetrahydrofurano ligands.The complexes formed between the 18-membered ring containing a tetrahydrofuran subcyclic unit and the alkali-metal cations were about as stable as those formed from 2,6-diketo-18-crown-6 (2) but were less stable than those formed from the corresponding pyridine analogue (1).The 21- and 24-membered ring compounds containing a furan subcyclic unit were found to be effective carriers of Cs⁺ across a CHCl3 liquid membrane separating aqueous phases.