The Preparation Of Manganganese (Ⅲ) Salen Catalysis For Enantioselective Epoxidation Of Alkenes

A new schiff base ligand was synthesized by the condensation of methyl 3-formyl-4-hydroxylbenzoate with 1,2-diaminocyclohexane. Three complexes of Mn(Ⅲ), Fe(Ⅲ) and Ni(Ⅱ) were also prepared from the ligand. The new ligand and complexes were characterized by elementary analysis, FT-IR, ~1H NMR, UV-Vis and TG-DTA.Two new salicylaldehyde derivatives, 5-(1,1-dimethylethyl)-3-fcrmyl-4-hydroxybenzoic acid and methyl ester, were synthesized, and a novel chiral ligand was obtained by reaction of the ester with (1R,2R)-1,2-diaminocyclohexane. Then four chiral complexes of Mn(Ⅲ), Fe(Ⅲ), Ni(Ⅱ) and Cu(Ⅱ) were prepared from the chiral ligand. The chiral ligand and complexes were characterized by elementary analysis, ~1H NMR, FT-IR and UV-Vis. From experiments, it was found that the homogenous catalyst exhibited relatively high catalytic activity and enantioselectivity in asymmetric epoxidation of different alkenes under various conditions. For example, the e.e. were 90.3% and 83.9% respectively with 1,2-dihydronaphthalene and cis-P-methylstyrene as substrates in certain conditions.A C2-unsymmetric Manganese(Ⅲ) Salen complex was anchored onto the surface of MCM-41 by a multi-step grafting method. The resulting material was characterized by FT-IR, XRD, DR UV-Vis, nitrogen adsorption and ICR It was found that the conversion of cyclohexene can reach 100%) with 90.7% selectivity under the optimum conditions, which are cyclohexene 20 mmol, isobutraldehyde 50 mmol and the heterogenized catalyst 0.02 mmol in acetonitrile 50 mL at 35 ℃ for 8 h. This catalyst can be reused by simple filtration up to 6 times without much loss of activity though Mn leaching took place in some degree. Furthermore, it also showed relativelyhigh activity and epoxide selectivity in the aerobic epoxidation of norbornylene, 1,2-dihydronaphthalene, styrene and a-methylstyrene.Two chiral heterogenized catalysts were designed and synthesized. One was prepared by the combination method of anchoring and sol-gel technique, the other was prepared by immobilizing the Salen-Mn(III) complex on the channels of MCM-41 molecular sieves modified with aminopropyl groups. The resulting catalysts were characterized by FT-IR, DR UV-Vis, XRD, TG-DTA, nitrogen adsorption and ICP. Their activities were investigated with the catalytic enantioselective epoxidation reactions. Experimental results showed that the catalytic properties of the latter were superior to that of the former. Under certain conditions, 45.9% yield and 84.3% e.e. were obtained with 1,2-dihydronaphthalene as substrate.