Anodic oxidation of organometallic sandwich complexes using [Al(OC(CF3)3)4]− or [AsF6]− as the supporting electrolyte anion

Anodic voltammetry and electrolysis of the metallocenes ferrocene, ruthenocene, and nickelocene have been studied in dichloromethane containing two different fluorine-containing anions in the supporting electrolyte. The perfluoroalkoxyaluminate anion [Al(OC(CF3)3)4]− has very low nucleophilicity, as shown by its inertness towards the strong electrophile [RuCp2]+ and by computation of its electrostatic potential in comparison to other frequently used electrolyte anions. The low ion-pairing ability of this anion was shown by the large spread in E1/2 potentials (ΔE1/2 = 769 mV) for the two one-electron oxidations of bis(fulvalene)dinickel. The hexafluoroarsenate anion [AsF6]−, on the other hand, reacts rapidly with the ruthenocenium ion and is much more strongly ion-pairing towards oxidized bis(fulvalene)dinickel (ΔE1/2 = 492 mV). In terms of applications of these two anions to the anodic oxidation of organometallic sandwich complexes, the behavior of [Al(OC(CF3)3)4]− is similar to that of other weakly-coordinating anions such as [B(C6F5)4]−, whereas that of [AsF6]− is similar to the more traditional electrolyte anions such as [PF6]− and [BF4]−. Additionally, the synthesis and crystal structure of [Cp2Fe][Al(OC(CF3)3)4] are reported.