Electron transfer properties of mono- and diferrocenyl based Cu complexes attached as self-assembled monolayers on gold electrodes by “self-induced” electroclick

Two new Cu complexes bearing a 6-ethynyl bis-(methyl-pyridyl) amine (6eBMPA) moiety, as an electroclickable function linked to a ferrocenyl-based triazolyl arm (ligands 3 and 4) have been synthetized and characterized by UV–Visible, EPR spectroscopies and cyclic voltammetry in acetonitrile. Two different spacer groups between the terminal ferrocene and the triazolyl group were inserted: an hexyl chain in the case of the complex Cu-3, an ethenyl-bridged diferrocenyl system for the complex Cu-4. The monoelectronic oxidation of the diferrocenyl species yields a stable mixed-valence complex. NIR–Visible spectroscopic studies show a moderate interaction between ferrocenyl units (class II according to the Robin–Day classification). The immobilization of these systems as SAMs on an azidoundecanethiol modified gold electrode has been successfully operated by using the “self-induced electroclick” procedure. The voltammetric characterization of the surface-tagged Cu complexes indicates that good surface coverage was achieved, with moderately fast electron-transfer reaction between the electrode and the redox active immobilized systems (k0(Cu) = 2–4 s−1, k0(Fc) = 20–90 s−1). Remarkably, the rate of charge transport is significantly controlled by the nature of the spacer on the ferrocenyl triazole arm.