As shown by combined use of cyclic voltammetry, thin-layer spectroelectrochemistry, UV-vis, and Raman spectroscopy of electrolyzed solutions, the presence of carbon monoxide as an axial ligand triggers the formation of the phlorin anion complexes upon reduction of iron(I) porphyrins at the expense of the corresponding iron("0") porphyrins. The presence of electron-withdrawing substituents on the phenyl groups of TPP, such as fluorine atoms, considerably slows down the protonation of the meso-carbon that yields the phlorin anion complex. The electrochemical properties of the phlorin anion complexes, investigated in the case where the metal is zinc, are also dependent upon the axial ligand, particularly CO. In the latter case, clear evidence of the stepwise character of the -(2e- + H+) oxidation of the phlorin anion complex back to the parent porphyrin was obtained.