Oxygen reduction catalyzed by a fluorinated tetraphenylporphyrin free base at Liquid/Liquid interfaces

The diprotonated form of a fluorinated free base porphyrin, namely 5-(p-aminophenyl)-10,15,20-tris(pentafluorophenyl)porphyrin (H2FAP), can catalyze the reduction of oxygen by a weak electron donor, namely ferrocene (Fc). At a water/1,2-dichloroethane interface, the interfacial formation of H4FAP2+ is observed by UV-vis spectroscopy and ion-transfer voltammetry, due to the double protonation of H2FAP at the imino nitrogen atoms in the tetrapyrrole ring. H4FAP2+ is shown to bind oxygen, and the complex in the organic phase can easily be reduced by Fc to produce hydrogen peroxide as studied by two-phase reactions with the Galvani potential difference between the two phases being controlled by the partition of a common ion. Spectrophotometric measurements performed in 1,2-dichloroethane solutions clearly evidence that reduction of oxygen by Fc catalyzed by H4FAP2+ only occurs in the presence of the tetrakis(pentafluorophenyl)borate (TB-) counteranion in the organic phase. Finally, ab initio computations support the catalytic activation of H4FAP2+ on oxygen. © 2010 American Chemical Society.