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 orgummysemi-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 NaBH 4 over neutral Al 2 O 3 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, 1 H-NMR, 13 C-NMR,HRMSand SC-XRDtechniques. These compounds show visible solvatochromism, whenUV-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. KEYWORDS Ferrocenyl-N-(pyridinylmethylene)anilines, ferrocenyl-N-(pyridinylmethyl)anilines, mechanochemistry technique, solventfree synthesis, antimicrobial activity.
Highlights
Ferrocene is a treasured compound discovered serendipitously[1,2] and its structure was determined[3,4,5] in the early 1950s
Progresses of reactions for the formation of Schiff bases were monitored by FT-IR
The desired amine products were obtained in excellent yields and in very short time
Summary
Ferrocene (dicyclopentadienyl iron) is a treasured compound discovered serendipitously[1,2] and its structure was determined[3,4,5] in the early 1950s This discovery has impacted greatly on the rapid growth of inorganic and bio-organometallic chemistry.[6,7] The unrelenting study on ferrocene and its utilization in many diverse applications are attributed to; (i) the stability of the ferrocene scaffold to moisture, air and temperature; (ii) the ease of functionalizing the cyclopentadienyl rings in ferrocene skeleton via electrophilic substitution to give monosubstituted, 1,1’-disubstituted or 1,2-disubstituted moieties rendering it a pertinent building block; (iii) sufficient rigidity of the sandwich structure providing an appropriate chiral environment; (iv) its readily accessible reversible redox couple; (v) stability of the ferrocenyl group in aqueous aerobic media and (vi) its high electron density and aromaticity.[7,8] The ferrocenyl unit is known to modify the shapes of molecules as well as the physical properties such as colour, polarizability and magnetism.[9] Generally, studies on ferrocene revolve around generation of compounds that are used in materials science,[10] electrochemistry[11,12] catalysis,[13,14,15] medicinal applications[16,17,18,19,20,21,22,23,24] and nonlinear optics[25,26] amongst others. Liquid crystalline ferrocenyl Schiff bases known as ferrocenomesogens, show interesting magnetic traits such as paramagnetism and control of the molecular orientation in magnetic fields.[38,39] there is high interest in transition metal complexes with electronically communicating metal centres spanned by conjugated systems that make ferrocenyl metalloligands appealing.[31,40,41]
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