π-Cation Radicals and Dications of Metalloporphyrins
Fajer, J., Borg, D.C., Forman, A., David Dolphin, and Felton, R.H.
J. Am. Chem. Soc.
Zn tetraphenylporphyrin (I) and Mg octaethylporphyrin (II) undergo reversible one- and two-electron oxidations. Removal of the first electron by controlled potential electrolysis or by oxidation with XeF2 or Br2 results in cation radicals whose ESR spectra clearly indicate electron abstraction from the porphyrin ring. The observed hyperfine structure is assigned, with the help of deuterium labeling, to interaction of the unpaired electron with the meso protons of II+ and with the protons on the Ph groups of I+. Electronic absorption spectra of the radicals, dications, and of a dimer of II+ which exists at low temperatures are presented. The results of an SCF-MO study are compared with the experimental ESR and optical data. The calculations suggest that a radical may occupy either of two close-lying ground states. The ground-state symmetries of I+ and II+ are 2A2u and 2A1u of the D4h point group.