Ferrocene derivatives as electron carriers for selective oxidation and reduction reactions through a liquid membrane

1-Hexadecanoyl- and 1-hexadecyl-ferrocene, which undergo one-electron oxidation to the corresponding ferrocenium cations at distinctly different potentials (0.25 and –0.05 V vs. ferrocenium–ferrocene, respectively, in dichloromethane solution, 0.1 mol dm–3 in NBu4ClO4), have been used as carriers for the cross-transport of electrons and perchlorate ions across a bulk dichloromethane membrane. The liquid membrane interfaces an aqueous layer containing [FeII(CN)6]4–(the electron source phase, e.s.p) and an aqueous layer containing CeIV(the electron receiving phase, e.r.p.). The occurrence of the transport is accounted for on the basis of an empirical juxtaposition of the electrochemical scales (i) in water and (ii) in CH2Cl2, which gives the sequence: E°(CeIV/III) > E°[Fe(C5H5)(C5H4COC15H31)+/0] > E°[Fe(C5H5)(C5H4C16H33)+/0] > E°[FeIII/II(CN)63–/4–]. The special position of the potential of the aqueous FeIII–FeII couple, which is intermediate between those of the two ferrocene derivatives, makes it possible to carry out selective electron-transport experiments: if the e.r.p. contains a mixture of CeIV and FeIII, when [Fe(C5H5)(C5H4C16H33)] is used as a carrier, both the oxidizing cations are reduced; when [Fe(C5H5)(C5H4COC15H31)] is used, CeIV is reduced, but FeIII is left intact. These examples clearly illustrate the novel principle of the selective oxidation and reduction reactions performed under three-phase conditions.