Mark M. Morrison

Substituent effects on the redox reactions of tetraphenylporphyrins.

The effect of substituents on pi radical reactions of para-substituted tetraphenylporphyrins was investigated by cyclic voltammetry in methylene chloride. In all cases electron donating substituents produced a more difficult reduction and an easier oxidation. Plots of E1/2 vs. a yielded Hammett linear free energy relationships for cation radical and dication formation and anion radical and dianion formation. An average reaction constant of p=0.07+/-0.01 V was obtained. This was true for tetraphenylporphyrins containing the central metals VO, Mn, Fe, Co, Ni, Cu, and Zn, as well as the free base H2 (p-X)TPP. The value of p appears not to be directly affected by the central metal oxidation state or the overall charge on the complex.

Investigation of substituent effects on the redox properties and oxygen binding of several metalloporphyrins

Abstract Studies of substituent effects on the redox reactions of synthetic metalloporphyrin complexes, such as those described in this paper, are an essential first step in understanding function-property-structure relationships in the biologically important cobalt and iron metalloporphyrins. Furthermore, since HAMMETT linear free energy relationships have been shown to be sensitive to the solvent media, care must be taken in directly comparing physical measurements obtained under different experimental conditions in different solvents.