Diphenylpyrrole‐Strapped Calix[4]pyrrole Extractant for the Fluoride and Chloride Anions

The anion binding features of diphenylpyrrole‐strapped calix[4]pyrrole 1 have been investigated by means of 1H NMR spectroscopy and ITC (isothermal titration calorimetry), as well as single crystal X‐ray diffraction analyses. Receptor 1 bearing an auxiliary pyrrolic NH donor and solubilizing phenyl groups on the strap was found to bind F–, Cl–, and Br–as their tetrabutylammonium salts with high affinity in DMSO‐d6. In addition, receptor 1 was found to extract the fluoride anion (as both its tetraethylammonium (TEA+) and tetrabutylammonium (TBA+) salts), as well as the chloride anion into chloroform‐d from an aqueous source phase. Cation metathesis using TBAI or the use of a dual host approach involving crown ethers enabled receptor 1 to extract simple alkali metal fluoride or chloride salts from water. Quantitative binding of NaF by receptor 1 was observed in 20% D2O‐DMSO‐d6 allowing for the direct determination of the NaF concentration in an unknown sample.