Metal complexes that transport electrons across liquid membranes: the iron [FeII,IIIL3]2+,3+ redox system (L = 4,4'-di-tert-butyl-2,2'-bipyridine)

Lipophilic [FeL3][ClO4]2 (L = 4,4'-di-tert-butyl-2,2'-bipyridine) was prepd. to be used as a carrier for the transport of electrons from an aq. oxidizing phase to an aq. reducing phase, sepd. by a CH2Cl2 bulk liq. membrane. Two-phase redox expts. indicated that CH2Cl2-dissolved [FeL3][ClO4]2 is oxidized by aq. CeIv to give [FeL3][ClO4]3. [FeL3][ClO4]3 was reduced, under 2-phase conditions, by a series of aq. reducing agents according to the rate sequence: NO2- > [Fe(CN)64- > FeII > SO32-. Three-phase expts. were carried out in which electrons are transported by [FeL3][ClO4]2 from the aq. reducing phase to the aq. phase contg. CeIV, across the bulk liq. membrane, and ClO4- ions are transported by [FeL3][ClO4]3 in the opposite direction. The rate of the electron transport is controlled by the rate of the slowest of the 2 redox processes at the 2 sides of the membrane. By varying the concns. of the aq. reactants, it is possible to det. the 2-phase rate-detg. step of the overall 3-phase process and to perform selective oxidn. by CeIV of the investigated reducing agents.