Aerobic alcohol oxidation and oxygen atom transfer reactions catalyzed by a nonheme iron(ii)–α-keto acid complex

Abstract

α-Ketoglutarate-dependent enzymes catalyze many important biological oxidation/oxygenation reactions. Iron(IV)–oxo intermediates have been established as key oxidants in these oxidation reactions. While most reported model iron(II)–α-keto acid complexes exhibit stoichiometric reactivity, selective oxidation of substrates with dioxygen catalyzed by biomimetic iron(II)–α-keto acid complexes remains unexplored. In this direction, we have investigated the ability of an iron(II) complex [(Tp^Ph,Me)Fe^II(BF)] (1) (Tp^Ph,Me = hydrotris(3-phenyl-5-methylpyrazolyl)borate and BF = monoanionic benzoylformate) to catalyze the aerobic oxidation of organic substrates. An iron–oxo oxidant, intercepted in the reaction of 1 with O₂, selectively oxidizes sulfides to sulfoxides, alkenes to epoxides, and alcohols to the corresponding carbonyl compounds. The oxidant from 1 is able to hydroxylate the benzylic carbon of phenylacetic acid to afford mandelic acid with the incorporation of one oxygen atom from O₂ into the product. The iron(II)–benzoylformate complex oxidatively converts phenoxyacetic acids to the corresponding phenols, thereby mimicking the function of iron(II)–α-ketoglutarate-dependent 2,4-dichlorophenoxyacetate dioxygenase (TfdA). Furthermore, complex 1 exhibits catalytic aerobic oxidation of alcohols and oxygen atom transfer reactions with multiple turnovers.