Aryl (ferrocenyl)-capped ethenylazaferrocenes: synthesis, structure and electrochemistry

Abstract

The Horner–Wadsworth–Emmons reaction of 2,5-dimethylazaferrocene-1′-carbaldehyde with diethyl benzylphosphonate, diethyl p-methoxybenzylphosphonate and diethyl (ferrocenylmethyl)phosphonate afforded (E)-1-(2,5-dimethylazaferrocen-1′-yl)-2-phenylethene (2a), (E)-1-(2,5-dimethylazaferrocen-1′-yl)-2-(p-methoxyphenyl)ethene (2b) and (E)-1-(2,5-dimethylazaferrocen-1′-yl)-2-ferrocenylethene (2c), respectively. Cyclic voltammetry showed significant difference in the electrochemical behaviour of these compounds in comparison to their ferrocenyl counterparts. The styryl group, which is an electron-withdrawing group in the ferrocenyl compound, displays a reverse effect in the azaferrocenyl complex 2a. Introduction of the p-methoxystyryl group to 2,5-dimethylazaferrocene brings about a cathodic shift of the redox potential of 370 mV, whereas for the ferrocenyl analog the shift is only 60 mV. Compound 2c shows two redox waves due to two non-equivalent metallocenyl moieties, but there is only weak electronic coupling between redox centres. The W(CO)₅-complex of 2c (4) was synthesised and its structure determined by X-ray diffraction.