5-Methyl-5-aryldipyrromethanes: synthesis, crystal structure and anion binding studies

Abstract

The eco-friendly and selective syntheses of 5-methyl-5-aryldipyrromethanes (1–4) in which aryl is FC6H4 1, ClC6H5 2, CH3OC6H5 3 and CH3C6H5 4, have been reported in the presence of citric acid (weak organic acid) and characterised by IR, 1H NMR, 13C NMR and mass spectroscopy. The structures of 2–4 have been confirmed by X-ray crystallography. Anion binding studies of 1–4 with different anions (e.g. F− , Cl− , CH3COO− , and ) have been carried out by 1H NMR titrations and binding constants have been evaluated using EQNMR program, revealing that they bind fluoride selectively compared with other anions with 1:1 stoichiometry in CDCl3. The binding affinities of these compounds are influenced by the nature of the substituent on the meso-carbon atom.