Deuterium exchange of pyrrolic NH protons accelerated by fluoride and bicarbonate in CDCl3, CD3CN, and DMSO-d6

Abstract

The anion binding features of pyrrole- and benzene-strapped calix[4]pyrroles 1 and 2, in particular, for F⁻ and HCO₃⁻ have been examined by means of NMR spectroscopy in DMSO-d₆, CDCl₃, and CD₃CN, respectively. Receptors 1 and 2 were found to bind F⁻ and HCO₃⁻ tightly via slow binding/release equilibria in these solvents. A combination of ¹H and ¹⁹F NMR spectroscopic analyses with mass spectrometry revealed that contacting calix[4]pyrroles 1 and 2 with F⁻ and HCO₃⁻ salts prompts deuterium exchange of the NH protons in the three nominally aprotic deuterated solvents considered in this study.