Synthesis, physical and antimicrobial studies of ferrocenyl-N-(pyridinylmethylene)anilines and ferrocenyl-N-(pyridinylmethyl)anilines

Abstract

Ferrocenyl-N-(pyridinylmethylene)anilines Schiff bases were synthesized by reaction of 3- or 4-ferrocenylaniline with either 2-, 3-, or 4-pyridinecarboxaldehyde under solvent-free conditions via mechanochemistry technique. Products were obtained in excellent yields within 10 min of grinding. The reactions afforded a melt or gummy semi-solid that solidified to the desired Schiff bases within a short time. These Schiff bases were reduced to their corresponding amines, ferrocenyl-N-(pyridinylmethyl)anilines, with NaBH4 over neutral Al2 O3 solid support via grinding. Amines were obtained in excellent yields after intermittent grinding for approximately 1 h. Herein, five novel ferrocenyl-N-(pyridinylmethylene)anilines (compounds 3, 4, 6-8) and six ferrocenyl-N-(pyridinylmethyl)anilines (compounds 9-14) are reported. Compounds were characterized through FT-IR,1H-NMR, 13 C-NMR, HRMS and SC-XRD techniques. These compounds show visible solvatochromism, when UV-Vis absorption was measured in polar and nonpolar solvents. In changing solvent from polar to non-polar, the Schiff bases exhibited a blue shift while the amines portrayed a red shift. Electrochemical studies on these compounds reveal that redox behaviour of the iron centre is influenced by the position imine or amine groups. Antimicrobial properties of these compounds were studied for Escherichia coli, Staphylococcus aureus, Salmonella typhimirium and Candida albicans. Highest activity was recorded against Gram-positive bacteria and fungi.