Iron porphyrin dioxygen adduct

Proniewicz LM, Paeng IR, Nakamoto K. 1991. Resonance raman spectra of two isomeric dioxygen adducts of iron(II) porphyrins and rr-cation radical and nonradical oxoferryl porphyrins produced in dioxygen matrixes Simultaneous observation of more than seven oxygen isotope sensitive bands J Am Chem Soc 113 3294. 

The reaction of iron(II) porphyrins is an area of extreme interest and importance and will be discussed separately. The second row analogues of FeI porphyrins, Ru" porphyrins, have been found to bind dioxygen reversibly153 but only UV data are available on these dioxygen adducts. 

There are three different approaches which can be employed to prevent irreversible oxidation of iron(II) porphyrins and promote dioxygen adduct formation (1) low temperatures to reduce the rate of dimerization (2) steric hindrance to prevent dimerization and (3) immobilization of the heme to prevent dimerization. 

Steric hindrance. An obvious way of preventing p-oxo dimer formation, i.e. irreversible oxidation of iron(II) porphyrins, is to introduce bulky substituents at the porphyrin such that the resultant dioxygen adducts are unable to approach each other closely enough for dimer formation to occur. 

Iron(II) meso-tetrakis(2,4,6-trimethoxyphenyl)porphyrin and the triethoxy analogue have been synthesized by Vaska. These are different to the capped and picket fence porphyrins in that both sides of the porphyrin are sterically hindered. Dioxygen uptake by these iron(II) porphyrins at 25 °C in solution was found to be partially reversible. La Mar and co-workers166 have shown that the porphyrins Fe[T(2,4,6-OMe)3PP], Fe[T(2,4,6-OEt)3PP] and Fe[TpivPP] take up oxygen at low temperatures, in the absence of a base such as Melm or pyridine, to give dioxygen adducts of the... 

Matsu-Ura, M., Tani, F., Nakayama, S., Nakamura, N., and Naruta, Y. (2000) Hydrogen-bonded dioxygen adduct of an iron porphyrin with an alkanethiolate ligand an elaborate model of cytochrome P450, Angewan. Chem., Internal. Ed. 39, 1989-1991. 

N. Nakamura, and Y. Naruta (2001). Synthesis and characterization of alkanethiolate-coordinated iron porphyrins and their dioxygen adducts as models for the active center of cytochrome P450 Direct evidence for hydrogen bonding to bound dioxygen. J. Am. Chem. Soc. 123, 1133-1142. 

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