Inter-ring η⇌η haptotropic rearrangements of 18ē and 19ē (η-pentamethylcyclopentadienyl)(η-9-methylfluorenyl)iron complexes.

New cationic complexes [(η-CH)Fe(η-Cp)]PF and [(η-9-CH-CH)Fe(η-Cp)]PF were obtained by the reaction of CpFe(CO)Br with fluorene and 9-methylfluorene, respectively. Deprotonation of these complexes by t-BuOK in THF affords zwitter-ionic compounds (η-CH)Fe(η-Cp) and (η-9-CH-CH)Fe(η-Cp) ( A). When A is heated in nonane at 150 °C it undergoes η⇌η inter-ring rearrangement with the formation of hexamethyldibenzoferrocene ( B). The electrochemical behavior of A and B was studied by cyclic voltammetry. One-electron reduction of A and B to the corresponding radical anions induces inter-ring haptotropic rearrangement A⇌η B. The equilibrium in the 19ē state is shifted to the η-isomeric radical anion A, while in the 18ē precursors, it shifts to the η-isomer B. [ABSTRACT FROM AUTHOR]