Preparation Of Chiral Salen Mn(Ⅲ) Complexes And Their Catalytic Performance For Olefin Asymmetric Epoxidation

A novel chiral Salen ligand was synthesized by the reaction of 5-benzyloxy-3-tert-butyl salicylaldehyde with (lR,2R)-diaminocyclohexane. From this ligand, several Salen metal (Mn³⁺,Fe³⁺,Co²⁺,Ni²⁺)complexes were prepared. Their structures were characterized by FT-IR, UV-Vis, ¹H NMR and elementary analysis. The enantioselective epoxidation of non-functional olefins catalyzed by Salen Mn(III) complex was studied. The effects of molar ratio of catalyst, pH of buffered NaClO, axial base, the choice of solvent and reaction temperature were obtained. It was found that the conversion of 1,2-dihydronaphthalene and cis-β-methylstyrene can go up to 94.7% and 99.0%, respectively, and the ee of epoxides reached 64.8% and 81.7%, when the reaction was run at 0°C with the molar ratio of 0.2% of catalyst using NaClO (pH 11.30, PyNO) as oxidant and CH₂Cl₂ as solvent. And it was found that the ee increased in the order of styrene, a-methylstyrene, 1,2-dihydronaphthalene, cis-β-methylstyrene.MCM-41 supported heterogenized Salen Mn(III) complex was prepared by anchoring method, the catalyst was characterized by FT-IR, UV-Vis,¹H NMR and ICP. It was applied as catalyst in olefin enantioselective epoxidation. It was found that the activity decreased sharply after the chiral complex was immobilized on MCM-41. But by prolonging reaction time in epoxidation of 1,2-dihydronaphthalene, 60.5% conversion and 52.4%ee were also obtained.A novel chiral oligomeric cyclic Salen ligand was synthesized by the reaction of a novel dialdehyde with (lR,2R)-l,2-diaminocyclohexane. From this ligand, the chiral oligomeric cyclic Salen Mn(III) complex was prepared. The new ligand and the complex were characterized by ¹HNMR, 13C NMR, FT-IR, UV-Vis, GPC and elementary analysis. The complex was used as a catalyst for enantioeslective epoxidation of olefins with NaClO and m-CPBA as oxidants. It was found that conversion of c/s-/?-methylstyrene and ee of epoxide reached 98.5% and 78.1% when m-CPBA was used as oxidant. The recyclability of the catalyst in m-CPBA system was also studied with c/s-/?-methylstyrene as substrate, the catalyst can be run for 3 times without much loss of activity, the conversion of substrate and ee of epoxide can go up to 81.5% and 70.4%, respectively, when the reaction was run for the third time.