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

Abstract

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 (15 min.) at 25 8C with 1.40 equivalents 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 1.25 equivalents 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 deter-) 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. Epoxidation is a key reaction to give various epoxy resins, which are widely used as high-demand fine chemicals in applications such as surface protection, binders, and casts in electronic devices. [1] In recent

Biologically Inspired C−H and C=C Oxidations with Hydrogen Peroxide Catalyzed by Iron Coordination Complexes

“…More recently, an in situ assembled hexadentate iron complex has been demonstrated to catalyze efficiently metal‐based aliphatic C−H oxidation ([Fe(L4) 2 ](OTf) 2 ) . The combination of iron salts with picolinic acid and 6‐methyl‐picolinic acid (L6 and L7, respectively) or a thymine‐derived ligand (L5) results in catalytic systems capable of olefin epoxidation or C−H oxidation, respectively (Figure ).…”

“…First, catalysts bringing enhanced or novel selectivities are necessary. Structurally simple catalysts or simplified formulations of existing catalysts will also be convenient for synthetic applications. Furthermore, as a general issue, the substrate scope needs to be substantially expanded.…”

Mixed Picolinate and Quinaldinate Iron(III) Complexes for the Catalytic Oxidation of Alcohols with Hydrogen Peroxide

“…The molecular structures of complexes 3 d , 4 c , 4 d , and 6 are depicted in Figure . In the mixed‐ligand complexes 3 d , 4 c , and 4 d , the pyridine moiety of the two sterically hindered ligands coordinate to the Fe center in a trans manner, and three N and O atoms are arranged in a meridional form, which are the same structural features as in 3 a . The Fe−N bond lengths of the Fe III –picolinate complexes are listed in Table .…”

“…The ORTEP‐3 program was used to draw the molecule . [Fe(6‐Mepic) 2 (pic)]( 3 a ), [Fe(pic) 3 ]( 8 ), and [Fe(6‐Mepic) 3 ]( 9 ) were prepared according to literature procedures. 35 % H 2 O 2 in CH 3 CN was prepared by dilution of 87 % aq.…”

Metal-catalyzed Hydrogen Peroxide Oxidation for Synthesis of Value-added Chemicals

“…We have demonstrated high yield, high rate syntheses of styrene oxides using an iron complex coordinated by two types of picolinates in the presence of H2O2 11) . The developed iron catalyst was effective for the oxidation of various styrenes to give the corresponding epoxides in over 90 % yields at 25 under chloride-free conditions.…”