New Molybdenum (Ⅵ) Catalysts For The Epoxidation Of Olefins: Synthesis, Reactivity, Crystal Structurres And Catalytic Capability

Epoxides are one of the most important organic intermediates that have been found applications in synthesis of many products such as pesticide, enantioselective drugs, plastic, paints, rubber promoters and polyester. The preparation of epoxides by reaction between alkyl peroxides and olefins catalyzed by high-valent transition metal complexes is one of the most important means of preparation of epoxides. The transition metals, such as Mo, V, Ti, Re, containing catalysts for the epoxidation of cyclohexene have been widely investigated. MoO2X2L2 (X, L = F, OPMePh2 (1); Cl, OPMePh2 (2); Br, OPMePh2 (3); F, OPPh3 (4); Cl, OPPh3 (5); Br, OPPh3 (6)) have been prepared in order to investigate the variation in catalytic activity with changes in electronicand steric properties. MoO2F2(OPMePh2)2 (1) was first prepared and characterized by IR, 1H NMR and element analysis. MoO(O2)2(OPMePh2)2 (7) was also prepared by the reaction of H2O2 and 1. The structures of 1 and 7 have been solved by single crystal X-ray diffraction.When the epoxidation of cyclohexene with TBHP was catalyzed by 1-6, it has been found that the ligand of halides has significant influence on the catalytic activity of the compounds, and OPMePh2 containing species show better activity than those with OPPh3. The results indicate that smaller ligands with lower electronegativity give higher catalytic activity. The species with X=C1 and L= OPMePh2 (2) displays the best activity in 1-6. We have also investigated the epoxidation of cyclohexene catalyzed by 2 systemically. First of all, the mechanism of this reaction was studied by the solution phase IR spectroscopy and 31P NMR. The results confirmed that the actual catalytic species in the epoxidation catalyzed by 2 with TBHP should not be peroxo species but a volatile seven-coordinate peroxomolybdenum complex. We have also studied the kinetics of the cyclohexene epoxidation catalyzed by 2 with TBHP and the apparent reaction order, frequency factor and activation energy are obtained. The influences of the reaction conditions were also investigated. The best parameters, such as solvent, reaction time, and molar ratio of cyclohexene to catalyst or peroxide, are determined.We have demonstrated the epoxidation of allyl chloride can be catalyzed by 1-3 in mild conditions. The results indicates that the reaction conditions, such as species of catalyst and oxidant, solvent, reaction time, and the molar ratio of allyl chloride to catalyst or peroxide, have significant affect on the epoxidation reaction. The catalytic effect of 1 and 2 is more efficient. TBHP is the appropriate oxidant of this reaction. The reaction quickly reaches the high conversion at the beginning of the reaction and does not proceed significantly further. The results show that polychlorinated hydrocarbons are better solvent for this catalytic reaction.The epoxidation of allyl chloride catalyzed by 1-6 with H2O2 was also investigated. The results reveal that only 6 has obvious catalytic effect for the epoxidation. When 6 serves as the catalyst, the influence of reaction conditions, such as reaction time, solvent, and the molar ratio of allyl chloride to catalyst or H2O2, was studied.