Probing and Evaluating the Anion Binding Effects in One‐Walled meso‐Phenylboronic Acid Appended Calix[4]pyrrole (C4P) Based Supramolecular Receptors

Abstract

Herein, binding affinities of one‐walled meso‐phenylboronic acid functionalized calix[4]pyrroles (C4Ps, 3 a & 3 b) with diverse anions including spherical, linear, trigonal, and tetrahedral through UV‐Vis spectroscopy have successfully been revealed in acetonitrile solvent. The C4P derivative 3 b was newly synthesized from an easily accessible 3‐acetylphenylboronic acid via both conventional as well as green protocols. Structure of the final compound 3 b and the dipyrromethane (DPM) 2 b, were unambiguously established by means of 1H‐NMR, 13C‐NMR, and HRMS spectral data. From the outcomes of the UV‐Vis titrations of 3 a/3 b with different anions (e. g., F−, Cl−, Br−, I−, NO3−, HSO4−, H2PO4−, CH3COO−, & SCN−), used as their tetrabutylammonium (TBA) salts in CH3CN, 1 : 1 stoichiometric binding mode were observed from the BindFit v0.5 and Job plots. Overall, the binding affinity of receptor (3 b) with different anions were found higher in comparison to the receptor (3 a), presumably due to more cooperative NH and/or OH hydrogen bonding interactions. On the basis of varied size of halide ions, typical trend of anion binding affinity i. e., F−>Cl−>Br−>I−, was detected with increase in size of halide ions from F− to I−. Hopefully, these anion binding investigations with C4P‐based meso‐functionalized architectures will open new possibilities to the researchers to generate even more interesting artificial anion receptors based on vital boronic acid functionality, as biological and chemical importance of the anions is continuously motivating the synthetic chemists worldwide.