Synthesis, crystal structures and electrochemical properties of ferrocenyl imidazole derivatives

Six ferrocenyl imidazole derivatives substituted with -Cl, -NO2 and -CH3 on the 2-position of the 1H-imidazole ring have been synthesized. Of the six compounds, the di-substituted ferrocenes, i.e. compounds 4 (1,1'-ferrocenylmethyl(2-chloroimidazole)), 5 (1,1'-ferrocenyl(2-nitroimidazole)), and 6 (1,1'-ferrocenylmethyl(2-methylimidazole)) are reported for the first time. The structure-property relationships of compounds 4, 5 and 6 were investigated by means of UV-visible, FTIR, H-1-NMR, C-13-NMR spectroscopy and electrochemical studies. UV-visible analysis in acetonitrile showed that the pi -pi* band of compounds 2 (1-ferrocenylmethyl(2-nitroimidazole)) and 5 appeared at longer wavelength compared to 1 (1-ferrocenylmethyl(2-chloroimidazole)), 3 (1ferrocenylmethyl(2-methylimidazole)), 4 and 6. This phenomenon is due to the different electronics around the imidazole moieties. In cyclic voltammetry analysis, all compounds exhibited a quasi-reversible redox wave for the ferrocenyl and imidazole moieties. Density functional theoretical (DFT) calculations with the B3LYP/6-311+G(d) basis set were performed on compounds 1-6, and the calculated HUMO-LUMO band gap energies correlated with those obtained from electrochemical and spectroscopic data. The X-ray crystallographic analysis highlighted the effect of electron-withdrawing and electron-donating substituents on the conformation of the cyclopentadienyl rings attached to the ferrocenyl moiety.