SC-XRD investigation, DFT/TD-DFT, XRD/HSA-interaction, imine↔enol tautomerization and catecholase potential of new Zwitterionic pyran-2-one Schiff base ligand

Abstract

A novel chelate pyran-2-one derivative zwitterion Schiff base (ZSB) was synthesized with a significant yield. The ZSB ligand was synthesized by a combination in ethanol of 3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-one and 5-amino-2-methoxyphenol at reflux. A comprehensive analysis of the ZSB ligand was performed using a range of physicochemical techniques, including (¹H & ¹³C)-NMR, UV–vis, FT-IR and SC-XRD. The zwitterionic isomer in the solid-state was proved via SC-XRD analysis, which demonstrated the existence of H-bond intramolecular [O⁻ … H–N⁺] interactions units together with E-conformation as kinetic favored isomer structure. Moreover, the electrostatic and interaction behavior in the desired ZSB ligand were further clarified by utilizing Hirschfield surface analysis (HSA) and completing the HOMO/LUMO/DOS studies. In addition, DFT and TD-DFT calculations were utilized to optimize the ZSB and get insights into its practical UV–vis behavior and optical properties. The imine↔enol tautomerization process was assessed via SC-XRD/¹H NMR and estimated via DFT calculation. The work aimed to replicate the function of catecholase oxidation catalysis of 1,2-diol-benzene by examining its efficiency as an in situ ZSB/Cu(II) catalyst complex.