A pyrrole-based triazolium-phane with NH and cationic CH donor groups as a receptor for tetrahedral oxyanions that functions in polar media

Abstract

The pyrrole-based triazolium-phane 14+·4BF4− has been prepared via the tetraalkylation of a macrocycle originally prepared via click chemistry. It displays a high selectivity for tetrahedral oxyanions relative to various test monoanions and trigonal planar anions in mixed polar organic–aqueous media. This selectivity is solvent dependent and is less pronounced in acetonitrile. Theoretical calculations were carried out in with the chloride anion in an effort to understand the influence of solvent on the intrinsic hydrogen bonding ability of the donor groups (pyrrole N–H, benzene C–H and triazolium C–H). The host–guest interactions between receptor 14+·4BF4− and representative tetrahedral oxyanions were further analysed by 1H NMR spectroscopy, and the findings proved consistent with the differences in the intrinsic strength of the various H-bond donor groups inferred from the electronic structure calculations carried out in methanol, namely that (CH)+–anion interactions are less important in an energetic sense than neutral CH–anion interactions in polar media. Single crystal X-ray diffraction analyses of the mixed salts 14+·HP2O73−·BF4− and 314+·4H2PO4−·8BF4−confirmed that receptor 14+ can bind the pyrophosphate and phosphate anions in the solid state.