Tuning of the Anion Affinity and Selectivity of Tripyrromethane-Based Receptors by Simple Structural Modification

Abstract

Tripyrromethane-based tripodal compounds 1–3 were synthesized as anion receptors. It was revealed by 1H NMR spectroscopic analyses carried out in CDCl3 that tripyrromethane 1 with an ester group was capable of recognizing F−, Cl−, Br−, and H2PO4− with relatively high selectivity for F−. By contrast, receptor 2 having an additional hydrogen bond donor of an amide group binds F− and H2PO4− with much improved affinity relative to receptor 1. On the other hand, receptor 3 bearing formyl groups on its two pyrrole subunits showed markedly enhanced selectivity for F− presumably due to the increased acidity of the pyrrolic NHs and the resulting strengthened intermolecular hydrogen bonds. In addition, tripodal receptors 1–3 were found to bind H2PO4−, a tetrahedral oxyanion, more efficiently than 2-dimensional macrocyclic calix[4]pyrrole 4. © 2023 Wiley-VCH GmbH.