Intramolecular proton transfer of 2-((2,4- dimethylphenyl)iminomethyl)-3,5-dimethoxyphenol Schiff-base ligand: A density functional theory (DFT) study

Abstract

The title Schiff-base ligand could exist as two enol-imino (E) and keto-enamine (K) tautomers. Here, employing density functional theory, and handling the solvent effects with the polarizable continuum model (PCM), the structural parameters, energetic behavior, natural bond orbital analysis, as well as tautomerization mechanism of the E and K tautomers are investigated. The percentage of tautomers and activation energy of the tautomerization reaction have been computed in the gas and solution phases. In the gas phase, the E form is dominant, whereas considering the solvent effect prefers the K tautomer in the polar solvents. The tautomerization reaction includes an intramolecular-proton transfer, which affects considerably the structural parameters as well as atomic charges of the ligand. The presented model leads to results which have good consistency with the experimental and theoretical evidence. Key words: Density functional theory, polarizable continuum model (PCM), enol-keto tautomerism, intramolecular proton transfer, Schiff base.