Journal
JOURNAL OF INORGANIC BIOCHEMISTRY
Volume 136, Issue -, Pages 130-139Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.jinorgbio.2013.12.014
Keywords
Cobalt corroles; Nitro-substitution; Synthesis; Electrochemistry; Dioxygen reduction
Funding
- Natural Science Foundation of China [21071067]
- Robert A. Welch Foundation [E-680]
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Cobalt(III) triarylcorroles containing 0-3 nitro groups on the para-position of the three meso-phenyl rings of the macrocycle were synthesiied and characterized by electrochemistry, mass spectrometry, (UV-vis) and H-1 NMR spectroscopy. The examined compounds are represented as (NO2Ph)(n)Ph(3 - n)CorCo(PPh3), where n varies from 0 to 3 and Cor represents the core of the corrole. Each compound can undergo two metal-centered one-electron reductions leading to formation of Co(II) and Co(I) derivatives in CH2Cl2 or pyridine containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). A stepwise two electron reduction of each NO2Ph group of the compound is also observed. The first is reversible and occurs in a single overlapping step at the same potential which involves an overall one-, two- or three-electron transfer process for compounds 2-4, respectively. This indicates the lack of an interaction between these redox active sites on the corroles. The second reduction of the NO2Ph groups is irreversible and located at a potential which overlaps the Co(II)/Co(I) process of the compounds. Thin-layer UV-visible spectroelectrochemical measurements in CH2Cl2, 0.1 M TBAP demonstrate the occurrence of an equilibrium between a Co(III) it-anion radical and a Co(II) derivative with an uncharged macrocycle after the first controlled potential reduction of the nitro-substituted corroles. All four cobalt corroles were also examined as catalysts for the electroreduction of O-2 when coated on an edge-plane pyrrolytic graphite electrode in 1.0 M HClO4. This study indicates that the larger the number of nitro-substituents on the cobalt corrole, the better the compound acts as a catalyst. (C) 2014 Elsevier Inc All rights reserved.
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