Olefin-oxoiron complex

TT-cation radical complexes.In the reactions, oxoiron(IV) porphyrin rr-cation radicals of electron-rich porphyrins reacted fast with ROOH (i.e., catalase and peroxidase type of chemistry one-electron oxidation of ROOH) (Scheme 2, pathway A). On the other hand, oxoiron(IV) porphyrin rr-cation radicals of electron-deficient porphyrins reacted fast with olefins to yield epoxide products (i.e., cytochrome P450 type of chemistry oxygen atom transfer) (Scheme 2, pathway B). These results demonstrated that electron-deficient iron porphyrin complexes are better catalysts in hydrocarbon oxygenations by hydroperoxides, since these complexes can avoid the facile decomposition of oxoiron intermediates by ROOH (Scheme 2, pathway A). Indeed, highly electron-deficient iron(III) porphyrin complexes efficiently catalyze alkane hydroxylations by H2O2 in aprotic solvents. 

It has been considered that the oxoiron(IV) porphyrins are such poor oxidants that they can only oxygenate triphenylphosphine to triphenylphosphine oxide. " However, an olefin epoxidation by an oxoiron(IV) porphyrin complex was demonstrated by Groves and co-workers, in which (TMP)Fe =0, prepared by ligand metathesis of (TMP)" Fe (C104)2 over basic alumina. 

The above scheme includes the formation of the oxoiron(IV) porphyrin cation radical via 0-atom transfer from PhIO within an intermediate complex. The double bond approaches from the side and parallel to the porphyrin ring. This geometry is clearly favorable for the cis-olefins. The epoxidation step consists in oxygen atom transfer directly from the oxoiron(IV) to the olefin within an intermediate that has been detected with mCPBA as oxidant [46]. According to... 

The different mechanistic proposals for epoxidation reflect a complex oxidation pattern dependent on a variety of factors. At this time it does not seem either possible or necessary to accommodate all the observed features of metalloporphyrin catalyzed epoxidation within a single mechanism. The crucial importance of oxoiron(IV) porphyrin cation radicals has been established beyond doubt but the net 0-atom transfer to the olefin may perhaps occur via more than one kind of intermediate. 

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