Synthetic, structural and electrochemical studies on some doubly bridged trichalcogen [3.3] ferrocenophanes

The novel doubly bridged trichalcogen compounds 1,2,3,9,11-pentathia-10- selena[3.3](1,1′)(2,2′)-ferrocenophane 1 and its 1,3,9,11-tetrathia-2,10-diselena analogue have been prepared by disruption of the trisulfur bridges in 1,2,3,9,10,11-hexathia[3.3](1,1′)(2,2′) ferrocenophane with lithium aluminium hydride followed by reformation of the bridges using selenium dichloride. The crystal structure of 1 has been determined and indicates a chair-chair conformation of the trichalcogenide linkages, which is the most populous conformeric form in solution. Electrochemistry of various trichalcogen-bridged metallocenophanes indicates chemical reversibility of their redox changes. One-electron removal of the ferrocene systems is shown to be more difficult on introduction of first, one and then two, trichalcogen bridging groups and redox potentials decrease upon substitution of electron-withdrawing sulfur atoms for less withdrawing selenium atoms.