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(NO)(PE), MTTP(PE), NiTPP(NO)(Ph), and MTPP(CN), where TTP and TPP are the dianions of tetratolylporphyrin and tetraphenylporphyrin, respectively, NO, phenylethynyl (PE), and CN are substituents at the β-pyrrole positions of the macrocycle, and M = Cu, Ni, Zn, Co, 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.