Oxygen Reduction Catalyzed by a Fluorinated Tetraphenylporphyrin Free Base at Liquid/Liquid Interfaces

Abstract

The diprotonated form of a fluorinated free base porphyrin, namely 5-(p-aminophenyl)-10,15,20-tris(pentafluorophenyl)porphyrin (H(2)FAP), 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 H(4)FAP(2+) is observed by UV-vis spectroscopy and ion-transfer voltammetry, due to the double protonation of H(2)FAP at the imino nitrogen atoms in the tetrapyrrole ring. H(4)FAP(2+) 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 H(4)FAP(2+) 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 H(4)FAP(2+) on oxygen.

Ionic partition diagram of tetraphenylporphyrin at the water|1,2-dichloroethane interface

“…Free-base porphyrins have been recently shown to act as catalysts for oxygen reduction [29,36], and the present methodology is useful to determine the ionic partition diagrams of these molecules to better understand their catalytic role upon their protonation.…”

Structural, spectroscopic and electrochemical investigations on fluorinated meso-tetraaryl porphyrins

“…Pyrrole (0.5 mL, 7.2 mmol) and 3,5-difluorobenzaldehyde (0.8 mL, 7.2 mmol) were taken in a 500 mL two necked RB flask containing 300 mL of CH 2 Cl 2 and purged with N 2 gas for 15 min followed by the addition of BF 3 . OEt 2 (0.1 mL, 2.5 M).…”

“…These porphyrin analogs find a variety of enhanced material applications such as efficient catalysts for various chemical transformations, dyes for solar cells, optical sensors, etc. [1][2][3][4][5]. They have numerous biological applications especially in medicinal chemistry as photosensitizers in photodynamic therapy to kill cancer cells [6,7].…”

Room temperature ionic liquids based on cationic porphyrin derivatives and tetrakis(pentafluorophenyl)borate anion

“…In addition, porphyrins have also aroused remarkable and extensive interest for many years due to their wideranging applications in photophysics [28], coordination chemistry [29], liquid crystals [30], solar cells [31,32], catalysis [33,34], photovoltaic devices [35], photodynamic therapy (PDT) [36] and artificial light-harvesting antennas [37]. The porphyrin derivatives based on tetrakis(perfluorophenyl)-borate salts and cationic porphyrins.…”