Chloride Selective Macrocyclic Bisurea Derivatives with 2,2′-Binaphthalene Moieties as Spacers

Abstract

A cyclic bisurea derivative 2a has been successfully prepared from the corresponding diamine and diisocyanate in the presence of tetrabutylammonium chloride as a template. A more soluble cyclic bisurea 2b has also been prepared by introduction of sterically bulky tert-butyl groups. X-ray crystal analyses of [2a·Cl]^- and [2b·Cl]^- revealed that overall structure was saddle like and the chloride anion was located in the center of the cavity. The bound chloride anion was hydrogen bonded by four N-H of urea groups and weakly hydrogen bonded by four 1-C-H of naphthyl groups, respectively. After removal of the bound chloride anions of [2b·Cl]^- with silver nitrate, two different X-ray crystals of free 2b were obtained; one was intermolecular hydrogen bonded shrunken structure and the other was extended structure. Receptor 2b showed large binding ability for Cl^-, however, the selectivity for Cl^- against basic anions, such as AcO^- and F^-, has been insufficient. In aqueous MeCN, the association constant of 2b for Cl^- was reduced but still large, and the selectivity for hydrophobic Cl^- was greatly improved. In this solvent, 2b also selectively recognized alkaline metal chloride salts. Therefore, cyclic bisurea 2b is highly selective and effective Cl^- selective receptor.