Preparation Of MCM-41 Supported Chiral Salen Mn(Ⅲ) Complex Catalysts And Their Catalytic Performance In The Asymmetric Epoxidation Of Olefins

A novel chiral ligand and its Salen Mn(â…¢) complex with a carboxyl group with strong electron withdrawing effect was synthesized by the reaction of 3-tert-butyl-5-formyl-4-hydroxybenzoic acid with (1S, 2S)-1, 2-diphenylethylenediamine. The structures of intermediates and complex were characterized by elementary analysis, ¹H NMR and FT-IR. The enantioselective epoxidation of styrene catalyzed by Salen Mn(â…¢) complex was studied. The effects of molar ratio of catalyst to substrate, solvent and reaction temperature on the epoxidation of styrene were investigated. The catalyst showed good catalytic performance in the asymmetric epoxidation of unfuctionalized alkenes including 1, 2-dihydronaphthalene,α-methylstyrene, cis-β-methylstyrene, styrene with NaClO and m-CPBA as oxidants respectively. It was found that the conversion of cis-β-methylstyrene can go up to 99.4% with 84.0% enantiomeric excess, when the reaction was run at -78℃with m-CPBA as oxidant.The chiral Salen-Mn(â…¢) complex was anchored onto the a secondary amino modified mesoporous molecular sieves MCM-41 by a novel multi-step grafting method through the formation of amide and two heterogenized catalysts E₁, E₂ with different Mn contents were obtained and characterized by XRD, N₂ adsorption, ICP, FT-IR and DR UV-Vis. The effects of axial base, solvent, reaction temperature and molar ratios of oxidants to substrate on the asymmetric epoxidation ofα-methylstyrene were obtained. The catalytic activity of E₁ or E₂ for enantioselective epoxidation of non-functional olefins and the recyclability of catalyst E₁ was studied. Compared to those of homogeneous catalysts, both the catalytic activity and the enantiomeric excess of the heterogenized catalysts were obviously decreased. Catalyst E₁ can be run for 4 times in the m-CPBA system but no recyclability was received when using NaClO as oxidant.Chiral Salen Mn(â…¢) complex was supported onto MCM-41 through the formation of tertiary amine and two heterogenized catalysts E₃ and E₄ with the same structure but different Mn contents were obtained. The heterogenized catalysts were characterized by XRD, FTIR, UV-Vis, ICP and nitrogen sorption. The catalysis and recyclability in the asymmetric epoxidation of unfuctionalized alkenes were studied with NaClO and m-CPBA as oxidants respectively. It was found too much high complex supported on MCM-41 has no help on the performance of the catalyst to the asymmetric epoxidation of alkenes and recyclability of the catalyst.