title: Cobalt triarylcorroles containing one, two or three nitro groups. Effect of NO₂ substitution on electrochemical properties and catalytic activity for reduction of molecular oxygen in acid media.
abstract: Cobalt(III) triarylcorroles containing 0-3 nitro groups on the para-position of the three meso-phenyl rings of the macrocycle were synthesized and characterized by electrochemistry, mass spectrometry, (UV-vis) and (1)H 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) π-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 O2 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.
authors: School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China.
authors: Bihong
authors: B
authors: Li
authors: School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China. Electronic address: zpou2003@yahoo.com.
authors: Zhongping
authors: Z
authors: Ou
authors: School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China.
authors: Deying
authors: D
authors: Meng
authors: School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China.
authors: Jijun
authors: J
authors: Tang
authors: Department of Chemistry, University of Houston, Houston, TX 77204-5003, USA.
authors: Yuanyuan
authors: Y
authors: Fang
authors: School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China.
authors: Rui
authors: R
authors: Liu
authors: Department of Chemistry, University of Houston, Houston, TX 77204-5003, USA. Electronic address: kkadish@uh.edu.
authors: Karl M
authors: KM
authors: Kadish
mesh_terms: D002384:Catalysis; D056831:Coordination Complexes / Q000737:chemistry*; D055664:Electrochemical Techniques; D004563:Electrochemistry; D009585:Nitrogen Dioxide / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D011166:Porphyrins; D009585:Nitrogen Dioxide; D010100:Oxygen
keywords: Cobalt corroles; Dioxygen reduction; Electrochemistry; Nitro-substitution; Synthesis