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.
ASJC Scopus subject areas