Practical Iron-Catalyzed Hydrogen Peroxide Epoxidation of Aromatic Olefins using a Combination of Two Kinds of Simple Picolinate Ligands under Halide-Free Reaction Conditions

High-yield syntheses of epoxides using an iron complex having two types of picolinates in the presence of hydrogen peroxide under halide-free reaction conditions were achieved. The reaction is very simple. The complex, prepared with iron(II) acetate, 2-picolinic acid (picH) and 6-methyl-2-picolinic acid (Me-picH) in acetonitrile, quickly catalyzed an epoxidation of styrene (15min.) at 25 degrees C with 1.40equivalents of 35% aqueous hydrogen peroxide solution to afford styrene oxide in 95% yield with 96% selectivity. We also carried out a 100-g scale epoxidation of styrene using 1.25equivalents of 35% aqueous hydrogen peroxide solution with the iron catalyst to give styrene oxide in 80% isolated yield. The developed iron catalyst was efficiently applicable to the epoxidation of various aromatic olefins to give the corresponding epoxides in high yields. To obtain more information about this catalytic system, the pre-catalyst of this reaction was isolated and the structure was determined to be [Fe(pic)(Me-pic)(2)] by single-crystal X-ray analysis. The [Fe(pic)(Me-pic)(2)] catalyst effectively epoxidized styrene to styrene oxide in 93% yields. The system should be suitable for large-scale preparations of aromatic olefins due to the employment of simple ligands with halide- and amine-free reaction conditions.