Substrate and co-catalyst effects on the local coordination environment of a Fe–porphyrin catalyst

The effect of imidazole and pentachlorophenol (PCP) on coordination and redox properties of a Fe–porphyrin catalyst were studied by EPR and UV–Vis spectroscopy. In the EPR spectra three different Fe–porphyrin species were resolved, corresponding to (a) FeR4P–Cl (S = 5/2, gx = 6.13, gy = 5.77, gz = 1.99), (b) FeR4P-[Imidazole]1 (S = 5/2, gx = 6.80, gy = 5.20, gz = 1.99), and (c) FeR4P-[Imidazole]2 (S = 1/2, g1 = 2.85, g2 = 2.30, g3 = 1.56). The stability constants logK for FeR4P-[Imidazole]1 and FeR4P-[Imidazole]2 have been estimated. PCP affects the redox potential of the Fe–porphyrin species. The system FeR4P/Imid/NaIO4/PCP behaves as an integral entity with redox potential appropriate for efficient redox cycling of the iron.