Mechanisms for (porphyrinato) iron(III)-catalyzed oxygenation of styrenes by O₂ in presence of BH₄/^-

Mechanisms have been proposed for the (porphyrinato)iron(III)-catalyzed oxidation of styrene and α-methylstyrene by O₂ in benzene-ethanol containing NaBH₄. The product analysis and the deuterium incorporation using NaBD₄ suggest that the (σ-alkyl)Fe(III)-Por complex, [C₆H₅CH(CH₃)]Fe(III)-Por, is formed as an intermediate in the reaction of styrene. Insertion of O₂ to the (σ-alkyl)Fe(III)-Por complex having a radical character yields a (peroxy)iron(III) complex, [C₆H₅CH(CH₃)OO]Fe(III)-Por. The homolytic fission of the O-O bond followed by the hydrogen abstraction within the radical pair affords acetophenone and (HO)Fe(III)-Por. Acetophenone is readily reduced with NaBH₄ to give 1- phenylethanol. Meanwhile, the reaction of α-methylstyrene with BH₄ in the presence of Por-Fe(III)Cl may also yield the (σ-alkyl)Fe(III)-Por complex, which takes up O₂ to form a (peroxy)iron(III) complex, (C₆H₅C(CH₃)₂OO)Fe(III)-Por. The (peroxy)iron(III) complex is directly reduced by BH₄/^- to give 2 phenyl-2-propanol and (HO)Fe(III)-Por. In the reaction of styrene, such direct reduction of the (peroxy)iron(III) complex as a minor pathway competes with the homolytic fission of its O-O bond.