Iron(III, II)-induced activation of dioxygen for the oxygenation of cyclohexene and related unsaturated hydrocarbons

Labile iron complexes [e.g., [Fe-III(bpy)(2)](aq)(3+), [Fe-II(bpy)(2)](aq)(2+), [Fe-III(H2O)(6)](aq)(3+) and [Fe-II(H2O)(6)](aq)(2+) in base-free acetoo, nitrile activate dioxygen for the direct oxygenation of cyclohexene [to ketone, alcohol, and epoxide; c-C6H10 -->c-C6H8(O), c-C6H9OH, c-C6H10-epoxide] and related unsaturated hydrocarbons with allylic carbon centers. For example, the combination of 1 mM [Fe-III(bpy)(2)](aq)(3+)/O-2 (1 atm)/1 M c-C6H10 yields 51 mM c-C6H8(O), 42 mM c-C6H9OH, and 3 mM c-C6H10-epoxide within 24 h (about 100 catalyst turnovers-product molecules per catalyst molecule). With 1 mM [(FeH2O)-H-II)(6)](2+) in place of [Fe-III(bpy)(2)](aq)(3+), the product yield is 35 mM c-C6H8(O), 16 mM c-C6H9OH, and 0.1 mM epoxide. Under anhydrous conditions, the combination of 1 mM [Fe-II(bpy)(2)](2+) (MeCN)/O-2 (1 atm)/2M c-C(6)H(10)n a 1-h reaction yields 48 mM c-C6H8(O), 43 M c-C6H9OH, and 3 mM c-C6H10-epoxide. Excess ligand or added H2O inhibits the reaction rate, and 0.1 M H3O+, 0.3 mM alpha-tocopherol (vitamin E), or 1 mM 2,6-di-tert-butyl-4-methylphenol (BHT) completely suppresses product formation. (C) 2000 Elsevier Science B.V. All rights reserved.