Characterization of (Tetrabenzoporphinato)iron

(Tetrabenzoporphinato)iron chloride (ClFeTBP) was characterized by cyclic voltammetry, by EPR, optical absorption, and magnetic circular dichroism (MCD) spectroscopy, and by conductance measurements. ClFeTBP is a pentacoordinated iron(III) high-spin-state complex. However, the extent of dissociation of the Fe-Cl bond is larger than that in (meso-tetraphenyl-porphinato)iron(III) chloride (ClFeIIITPP). As with other iron(III) porphyrins, electrochemical or chemical reduction of ClFeIIITBP seems to produce stepwise iron(II) and iron(I) complexes and chemical oxidation gives the FeIIITBP π cation radical. Unlike most porphyrins, optically pure and stable mono- and bis(imidazole) complexes are obtained; they are both iron(III) low-spin-state complexes. EPR data suggest ClFeTBP in pyridine exists as a mixture of iron(III) high- and intermediate-spin complexes. The results are examined in comparison with those for iron porphyrins and hemes previously studied and are of interest since tetra-benzoporphyrins are structurally intermediary between general porphyrins and phthalocyanines.