Structure, spectra and biological significance of high-valent iron(IV,V) porphyrins

Oxoferryl(IV) porphyrins such as O=Fe (TPP) were prepared for the first time by laser photolysis (406.7 nm) of the corresponding dioxygen adducts in O-2 matrices at 15 K. Their resonance Raman spectra show the nu (Fe=O) vibrations at 852 cm*u$1 - 1$1 and the porphyrin core vibrations which indicate the Fe atoms to be in the low-spin and + IV state. The pi-cation radical O=Fe (TPP - d(8)(+)) exhibits the nu(Fe=O) band at 815 cm(-1). The structure of an intermediate formed during the epoxidation reaction of ethylene by O=Fe (TPP) was elucidated based on the nu(Fe=O) (804 cm(-1)) band of O=Fe (TPP) - C2H4 in O-2/C2H4 matrices. Oxoferryl-porphyrin, O=Fe (TMP), can be produced via the cleavage of the O - O bond of its peroxo dimer in toluene solution at low temperatures. The nu(Fe=O) vibrations of six-coordinate complexes, O=Fe (por) L, are in the range from 820 to 750 cm(-1) depending on the nature of the axial ligand (L). Complexes containing Fe(V) are rare. However, intridoiron(V) porphyrin, N=Fe (OEP), can be prepared via laser photolysis of the corresponding azido complex (thin him, 30 K). Resonance Raman spectra show the nu(Fe=N) vibration at 876 cm(-1) and the oxidation state marker band at 1384 cm(-1) which is higher than those of Fe(IV) complexes. It is expected to be high spin because N=Fe (OEP) is isoelectronic with the well-known high-spin complex O=Mn (per). The nu(Fe=N) band disappears and a set of new bands emerges when N=Fe (OEP) is irradiated by the 413.1 nm line. These bands are attributed to the nitrido dimer (OEP) Fe - N - Fe (OEP), which shows the symmetric nu(Fe - N - Fe) Vibration at 438 cm(-1). The biological significance of these high-valant iron (IV,V) porphyrins is discussed in relation to cytochome P-450, horseradish peroxidase and cytochrome P-450-LM3,4. (C) 1997 Elsevier Science B.V.