Spectroelectrochemical one-electron reduction product of (TPP)Zn in nonaqueous media? Not always the expected porphyrin π-anion radical

Zinc tetraphenylporphyrin (TPP)Zn was examined as to its as to its electroreduction properties by cyclic voltammetry and spectroelectrochemistry in six nonaqueous solvents containing tetrabutylammonium perchlorate (TBAP). The porphyrin undergoes an initial one-electron reduction to give a pi-anion radical on the cyclic voltammetry timescale but the radical was not stable on the spectroelectrochemical timescale when utilizting chlorinated alkane solvents containing 0.1 M TBAP (CH2Cl2 , 1-2,dichloroethane (C2H4Cl2)) where chloride, generated from minute amounts of reduced solvent, formed an axially coordinated complex, (TPP)Zn-II(Cl-), prior to reduction of the porphyrin. This spectroelectrochemically characterized product exhibits red-shifted Soret and Q-bands as compared to that of the neutral (TPP)Zn under the same solution conditions and analytical plots obtained from recording the spectrum as a function of potential rule out the possibility of forming the superoxide complex, (TPP)Zn-II(O-2(-)), in chlorinated alkane solvents.