Synthesis of metal ion-specific bindings of new functionalized aza-crown ethers

Abstract

The high-pressure S_NAr reaction was first applied to the synthesis of new functionalized diaza-crown ethers, which are directly connected to various heteroaromatic substituents as cation binding sites. The yields of the reaction were moderate to excellent (51% to quantitative). In a CH₂Cl₂ liquid membrane cation-transport experiment, diaza-crown ethers having 2′-thiazoyl-, 2′-benzoxazoyl-, 2′-pyrazinyl-, and 6′-pyridazinyl groups exhibited almost perfect Ag + ion selectivity. Cation extraction and ¹³C-NMR titration experiments revealed that attachment of heteroaromatics to the diaza-crown ring, if in the proper position, provides excellent Ag+ ion specificity. Since the binding and transport selectivity of these crown ethers were higher than those of the known crowns, the high-pressure technique proved a useful method for synthesis odf a new type of specific crown ethers. Single crystals of the complexes of diaza-crown ethers with silver trifluoromethanesulfonate (AgO₃SCF₃): AgTf and the corresponding metal-free diaza-crown compounds were successfully prepared. The short Ag+…Ag+ distances (2.790 and 2.969 Å) in the Ag complexes were confirmed for these Ag complexes by X-ray crystallography.