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)-catalyze d oxidation of styrene and alpha-methylstyrene by O-2 in benzene-ethan ol containing, NaBH4. The product analysis and the deuterium incorpora tion using NaBD4 suggest that the (sigma-alkyl)Fe-III-Por complex, [C6 H5CH(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 hydr ogen abstraction within the radical pair affords acetophenone and (HO) Fe-III-Por. Acetophenone is readily reduced with NaBH4 to give 1-pheny lethanol. Meanwhile, the reaction of alpha-methylstyrene with BH4- in the presence of Por-(FeCl)-Cl-III may also yield the (sigma-alkyl)Fe-I II-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 direct ly 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 it s O-O bond.