Sun, Bin Ou, Zhongping Meng, Deying Fang, Yuanyuan Song, Yang Zhu, Weihua Solntsev, Pavlo V. Nemykin, Victor N. Kadish, Karl M. Electrochemistry and Catalytic Properties for Dioxygen Reduction Using Ferrocene-Substituted Cobalt Porphyrins Cobalt porphyrins having 0–4 <i>meso</i>-substituted ferrocenyl groups were synthesized and examined as to their electrochemical properties in <i>N</i>,<i>N</i>′-dimethylformamide (DMF) containing 0.1 M tetra-<i>n</i>-butylammonium perchlorate as a supporting electrolyte. The examined compounds are represented as (Fc)<sub><i>n</i></sub>(CH<sub>3</sub>Ph)<sub>4–<i>n</i></sub>PorCo, where Por is a dianion of the substituted porphyrin, Fc and CH<sub>3</sub>Ph represent ferrocenyl and/or <i>p-</i>CH<sub>3</sub>C<sub>6</sub>H<sub>4</sub> groups linked at the four <i>meso</i>-positions of the macrocycle, and <i>n</i> varies from 0 to 4. Each porphyrin undergoes two reversible one-electron reductions and two to six one-electron oxidations in DMF, with the exact number depending upon the number of Fc groups on the compound. The first electron addition is metal-centered to generate a Co­(I) porphyrin. The second is porphyrin ring-centered and leads to formation of a Co­(I) π-anion radical. The first oxidation of each Co­(II) porphyrin is metal-centered to generate a Co­(III) derivative under the given solution conditions. Each ferrocenyl substituent can also be oxidized by one electron, and this occurs at more positive potentials. Each compound was investigated as a catalyst for the electoreduction of dioxygen when adsorbed on a graphite electrode in 1.0 M HClO<sub>4</sub>. The number of electrons transferred (<i>n</i>) during the catalytic reduction was 2.0 for the three ferrocenyl substituted compounds, consistent with only H<sub>2</sub>O<sub>2</sub> being produced as a product of the reaction. Most monomeric cobalt porphyrins exhibit <i>n</i> values between 2.6 and 3.1 under the same solution conditions, giving a mixture of H<sub>2</sub>O and H<sub>2</sub>O<sub>2</sub> as a reduction product, although some monomeric porphyrins can give an <i>n</i> value of 4.0. Our results in the current study indicate that appending ferrocene groups directly to the <i>meso</i> positions of a porphyrin macrocycle will increase the selectivity of the oxygen reduction, resulting in formation of only H<sub>2</sub>O<sub>2</sub> as a reaction product. This selectivity of the electrocatalytic oxygen reduction reaction is explained on the basis of steric hindrance by the ferrocene substituents which prevent dimerization. compound;appending ferrocene groups;DMF;1.0 M HClO 4.;electrocatalytic oxygen reduction reaction;ferrocenyl;3C;monomeric cobalt porphyrins exhibit n values;CH;H 2O;Co;solution conditions 2014-08-18
    https://acs.figshare.com/articles/journal_contribution/Electrochemistry_and_Catalytic_Properties_for_Dioxygen_Reduction_Using_Ferrocene_Substituted_Cobalt_Porphyrins/2263435
10.1021/ic501210t.s001