Solvent and substituent effect on electrochemistry of ferrocenylcarboxylic acids

Abstract

The redox properties of six ferrocenyl carboxylic acids (1–6) in dichloromethane and acetonitrile are compared. The formal reduction potential of Fe of the ferrocenyl group in these carboxylic acids occur ca. 0.1 V more positive in DCM than in CH3CN. The carboxylic group is directly connected to ferrocenyl, or by an ethene group, or by an alkyl chain of varying length. The length of the alkyl chain separating the two groups affected the formal reduction potential of Fe of the ferrocenyl group. The formal reduction potential was also affected by the electron-withdrawing carbonyl group. The extent of the effect depended on whether the carbonyl group was directly bound to a ferrocenyl moiety or, isolated by an sp3 hybridized carbon atom backbone (-CH2-CH2-) or a non-isolated sp2 hybridized carbon atom backbone (-CH=CH-). The results obtained were further validated by density functional theory (DFT) calculations on ferrocenyl carboxylic acids (1–6) as well as selected substituted ferrocenyl compounds from literature. A linear relationship between the formal reduction potential of substituted ferrocenes and DFT calculated HOMO energies were obtained.