Electron-transfer reaction between the semiquinone anion radical and metallo-tetraphenylporphyrins

Abstract

The rates of electron-transfer from 2,5-di-t-butylbenzoquinone anion radical to Co^II-, Fe^II-, and Mg^II-tetraphenylporphyrins in tetrahydrofuran have been determined with a stopped-flow apparatus, and the second-order rate constants obtained were: k(Co^II)=(5 ± 2)× 10⁵, k(Fe^II)=(9 ± 4)× 10⁶, and k(Mg^II) > 10⁷ 1 mol^–1 s^–1 at 25 °C; a mechanism for the reaction of the Fe^II-porphyrin involving initial electron transfer to the metal atom, followed by relocation on the porphyrin ring is suggested.