Covalent modification of carbon surfaces with ferrocene groups through a self-mediated oxidation of tetrabutylammonium salts of ferrocene-carboxylic acids

In this work, a one-step and efficient electrochemical method to covalently modify carbon surfaces with ferrocene moieties is reported. The method is based on the electrochemical oxidation of ferrocenecarboxylate, ferroceneacetate and ferroceneheptanoate ions in acetonitrile on glassy carbon and HOPG electrodes. It is shown that the covalent surface modification is possible because of the intervention of radicals, which are generated in a self-mediated electron transfer process. The activation step of the mediated mechanism allows to generate a transient ferrocenium-carboxylate zwitterion that, depending on the concentration and the length of the aliphatic chain separating the ferrocene moiety from the carboxylate functional group, is consumed by either an intramolecular or an intermolecular electron transfer reaction to afford a ferrocenyl or a ferrocenylalkyl radical, which then reacts with the carbon surface. An important feature of the process is the fact that the ferrocene layer does not inhibit the electrode surface but rather acts as a surface redox catalyst for further oxidation and decarboxylation processes.

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► Direct method to attach covalently ferrocene groups on carbon electrodes.
► Mediated oxidation of carboxylates and covalent grafting of carbon surfaces.
► Functionalization of carbon surfaces with ferrocene groups.
► Self-mediated oxidation of tetrabutylammonium ferrocene-carboxylate ions.
► Adsorbed ferrocene groups as surface redox catalysts.