Facile and Reversible Electrogeneration of Porphyrin Trianions and Tetraanions in Nonaqueous Media.

The first examples for the facile, reversible, and stepwise electrogeneration of triply ring-reduced porphyrin macrocycles are presented. The investigated compounds are represented as MTPP(NO2 )(PE)6 , MTTP(PE)8 , NiTPP(NO2 )(Ph)4 , and MTPP(CN)4 , where TTP and TPP are the dianions of tetratolylporphyrin and tetraphenylporphyrin, respectively, NO2 , phenylethynyl (PE), and CN are substituents at the β-pyrrole positions of the macrocycle, and M = CuII , NiII , ZnII , CoII , or 2H. Each porphyrin undergoes three or four reductions within the negative potential limit of the electrochemical solvent. The UV-visible spectra of the first three reduction products were characterized by means of thin-layer UV-vis spectroelectrochemistry, and the generation of multianionic porphyrins is interpreted in terms of extensive stabilization of the LUMOs due to the electron-withdrawing and/or extended π-conjugation of the β-substituents.