Mechanisms for (porphyrinato)iron(III)-catalyzed oxygenation of styrenes by O-2 in presence of BH4-

Mechanisms have been proposed for the (porphyrinato)iron(III)-catalyzed oxidation of styrene and alpha-methylstyrene by O-2 in benzene-ethanol containing, NaBH4. The product analysis and the deuterium incorporation using NaBD4 suggest that the (sigma-alkyl)Fe-III-Por complex, [C6H5CH(CH3)]Fe-III-Por, is formed as an intermediate in the reaction of styrene. Insertion of O-2 to the (sigma-alkyl)Fem-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 alpha-methylstyrene with BH4- in the presence of Por-(FeCl)-Cl-III may also yield the (sigma-alkyl)Fe-III-Por complex, which takes up O-2 to form a (peroxy)iron(III) complex, (C6H5C(CH3)(2)OO)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.