Pub No:
Iron Porphines
Chang, C.K., DiNello, R.K., and David Dolphin
Inorganic Syntheses, D.H. Busch, Ed., John Wiley & Sons, New York, Vol. XX,
IRON PORPHINES Iron porphines constitute the active site of hemoproteins and as such are among the most important and most widely studied series of metal complexes. The syntheses of iron protoporphyrin (heme) and its derivatives are important for the reconstitution of hemoproteins (particularly when one wishes to incorporate 57Fe for Mossbauer studies), as well as for model studies. In addition to the naturally occurring porphyrins, iron complexes of both 5,10,15,20-tetraphenyl- 21H,23H-porphine (H2tpp) and octaethyl-21H,23H-porphine (H2oep) are widely used in model studies of the natural systems. The most commonly employed method for the insertion of iron into the porphyrin macrocycle are those using iron(II) sulfate in acetic acid and, more recently, refluxing dimethylformamide (DMF) as solvent. While these two methods are applicable to a wide variety of porphyrins, there are other variations suitable for special applications. In addition, working with the water- soluble, naturally occurring dicarboxylic acid porphyrins presents additional considerations. It is difficult to generalize as to which method of iron incorporation should be used for a porphyrin with specific peripheral substituents: none- theless a general rationale is outlined here. Protoporphyrin and its derivatives, because of their labile vinyl substituents, are susceptible to acid-catalyzed hydration. For this reason aqueous solutions should be avoided in the preparation of protoporphyrin dimethyl ester from protohemin, and subsequent reinsertion of the iron. Thus the direct esterification of protohemin under basic conditions appears to be the method of choice. More stable porphyrins such as H2oep are most conveniently prepared by the direct insertion of iron(III)ion using the iron(III) chloride method; the resultant Fe(III) (oep)Cl can be separated directly from the reaction medium as shining purple crystals. However, this method fails to give successful results with protoporphyrin derivatives. In general, the iron(II) sulfate method is the mildest and should be used for all prophyrins unless one is certain that the more rapid alternatives [boiling DMF with iron (I I) chloride, or preferably the more stable iron(II) perchlorate] will have no ill effect on the peripheral substituents. THE FOLLOWING PROCEEDURES WERE REPORTED:- A. chloroldimethyl protoporphyrinato(2-)] iron(III), Chloroldimethyl 7,12-DiethenyI-3,8,13,17-tetramethyl- 21H,23H-porphine-2,18-dipropionato-(2-)] iron (III) B. Chloro[octaethyl-21H,23H-porphinato(2-)] iron(III) C. Chloro[mesoporphyrinato(2-)] iron(III), (Mesohemin IX), chloro[7,12-diethyl-3,8,13,17- tetrameth yl-21H,3H-porphine-2,18-dipropionato (2) ] - iron(III) D. The insertion of 57Fe into porphyrins

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