Anodic oxidation of organometallic sandwich complexes using [Al(OC(CF 3) 3) 4] − or [AsF 6] − as the supporting electrolyte anion

Abstract

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(CF 3) 3) 4] − has very low nucleophilicity, as shown by its inertness towards the strong electrophile [RuCp 2] + 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 E 1/2 potentials (Δ E 1/2 = 769 mV) for the two one-electron oxidations of bis(fulvalene)dinickel. The hexafluoroarsenate anion [AsF 6] −, on the other hand, reacts rapidly with the ruthenocenium ion and is much more strongly ion-pairing towards oxidized bis(fulvalene)dinickel (Δ E 1/2 = 492 mV). In terms of applications of these two anions to the anodic oxidation of organometallic sandwich complexes, the behavior of [Al(OC(CF 3) 3) 4] − is similar to that of other weakly-coordinating anions such as [B(C 6F 5) 4] −, whereas that of [AsF 6] − is similar to the more traditional electrolyte anions such as [PF 6] − and [BF 4] −. Additionally, the synthesis and crystal structure of [Cp 2Fe][Al(OC(CF 3) 3) 4] are reported.