Spectral and electrocatalytic studies for unusual oxidation and reduction states of chromium porphyrins in aqueous solutions

Abstract

Abstract Chromium(III) meso -tetrakis(3-sulfonatomesityl)porphyrin (Cr III TSMP) in aqueous solution exhibits two p K a s at 8.5 and 11.6, respectively. The redox reactions depend on the pH in the solution. In acidic solutions, the first oxidation at +0.875 V (versus Ag|AgCl) is a one-electron step corresponding to the porphyrin ring cation radical formation. The first two oxidations are separated in pH 9.0 solution. A possible internal electron transfer between the metal center and the porphyrin ring occurs in the pH 9.4–12.5 region. OCr IV TSMP is not reactive towards alkene oxidation while OCr IV TSMP +⋅ reacts with alkene to give enone at room temperature. The spectroelectrochemical results have been confirmed by chemical methods. The electrochemical reduction occurs at the porphyrin ring first and the second reduction is metal centered.