Electron transfer within C4 unsaturated spacers between terminal ferrocenyl moieties

The electrochemical and near-IR properties of a series of (bis)ferrocenyl complexes, in which the ferrocenyl moieties are spanned by enyne (E)-(–CHCH–CC–), diyne (–CC–)2, or diene (E)-(–CHCH–)2 C4 unsaturated spacers, were investigated. The experiments performed on 1,4-diferrocenyl-(E)-1-buten-3-yne revealed behaviors indicative of through-bridge/metal–metal electron transfer. The enyne bridged (bis)ferrocenyl cation displays charge transfer properties intermediate between the dienyl and diynyl systems and can be assigned to weakly coupled Class II mixed valence species. The analysis of the collected data according to the classical two-state Hush theory revealed that the efficiency of the electron transfer increases from wholly sp-C to wholly sp2-C bridged complexes. Therefore, the degree of communication is modulated according to the structure of the bridging ligand.