A simple route to FeCpCp'

A new method for the synthesis of the mixed-ligand compound FeCpCp' (where Cp' denotes the pentamethyl cyclopentadienyl group) is described from the reaction of a solution of NaCp' and LiCp with FeCl2 in THF. The mixture of products includes FeCp(2), FeCpCp' and FeCp(2)' in approximately a 1 : 3 : 1 mole ratio. Partial oxidation of the mixture leads to preferential precipitation of the ferricinium salts of the derivatives with the most negative reduction potentials. Subsequent treatment with a reducing agent regenerates the ferrocenes. Implementation of a couple of redox cycles allows the isolation of pure samples of each product, including FeCpCp'. Extension of the method to the preparation of other unsymmetrical ferrocenes is straightforward so long as there is a modest spread in the reduction potentials of the components. The development of new synthetic methods is worthwhile because substituted ferrocenes are useful reagents in studies of electron-transfer processes. The method described herein is attractive because it is quite simple and adaptable to large-scale preparations.