Selective 4e–/4H+ O2 Reduction by an Iron(tetraferrocenyl)Porphyrin Complex: From Proton Transfer Followed by Electron Transfer in Organic Solvent to Proton Coupled Electron Transfer in Aqueous Medium

An iron porphyrin catalyst bearing four ferrocenes and a hydrogen bonding distal pocket is found to catalyze 4e–/4H+ oxygen reduction reaction (ORR) in organic solvent under homogeneous conditions in the presence of 2–3 equiv of Trifluoromethanesulphonic acid. Absorption spectroscopy, electron param...

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Bibliographic Details
Published in:Inorganic chemistry 2013-12, Vol.52 (24), p.14317-14325
Main Authors: Mittra, Kaustuv, Chatterjee, Sudipta, Samanta, Subhra, Dey, Abhishek
Format: Article
Language:English
Subjects:
Coordination Complexes - chemistry
Electrons
Hydrogen Bonding
Iron - chemistry
Metalloporphyrins - chemistry
Models, Molecular
Organic Chemicals - chemistry
Oxidation-Reduction
Oxygen - chemistry
Solvents
Water - chemistry
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Summary:An iron porphyrin catalyst bearing four ferrocenes and a hydrogen bonding distal pocket is found to catalyze 4e–/4H+ oxygen reduction reaction (ORR) in organic solvent under homogeneous conditions in the presence of 2–3 equiv of Trifluoromethanesulphonic acid. Absorption spectroscopy, electron paramagnetic resonance (EPR), and resonance Raman data along with H2O2 assay indicate that one out of the four electrons necessary to reduce O2 to H2O is donated by the ferrous porphyrin while three are donated by the distal ferrocene residues. The same catalyst shows 4e–/4H+ reduction of O2 in an aqueous medium, under heterogeneous conditions, over a wide range of pH. Both the selectivity and the rate of ORR are found to be pH independent in an aqueous medium. The ORR proceeds via a proton transfer followed by electron transfer (PET) step in an organic medium and while a 2e–/1H+ proton coupled electron transfer (PCET) step determines the electrochemical potential of ORR in an aqueous medium.
ISSN:0020-1669
1520-510X
DOI:10.1021/ic402297f