Synthesis Of Novel Chiral Salen Mn(Ⅲ) Complexes With Sugar Moieties And Their Application In The Asymmetric Epoxidation Of Alkenes

In this thesis, two synthetic routes for the incorporation of sugar moiety into C5(5') or C3(3') of salicylaldehyde part of Salen Mn(â…¢) complex were designed and several corresponding compounds were prepared, as carbohydrate derivatives are widely used in asymmetric catalytic reactions. Four new salicylaldehyde derivatives with a glucose or mannose moiety were synthesized with 2-tert-butylphenol or 4-tert-butylphenol as the starting material, followed by the formylation, chloromethylation, nucleophilic substitution reaction with the desired carbohydrate. The salicylaldehyde derivatives condensed with ethylenediamine to give the Schiff bases, which coordinated with Mn(â…¢) to afford four novel sugar-based Salen Mn(â…¢) complexes. In addition, a few ligands were developed by the reactions of 1, 2∶5, 6-Di-O-isopropylidene-3-O-methylene-[5-(3-tert-butyl-2-hydroxybenzaldehyde)]-α-D-gluc ofuranose with (1R, 2R)-cyclohexanediamine, (1S, 2S)-diphenylethylenediamine and racemic cyclohexanediamine, and the other Mn(â…¢), Fe(â…¢), Co(â…¡), Cu(â…¡)complexes were synthesized. The compounds were characterized by NMR, FT-IR, UV-Vis, TG-DTA, FABMS and elementary analysis. The crystal structures of two sugar-based salicylaldehyde derivatives were determined.These complexes were then used as catalysts in the asymmetric epoxidation of styrene, 1, 2-dihydronaphthalene,α-methyl-styrene and cis-β-methyl-styrene with NaClO and m-CPBA as oxidants. Two Salen Mn(â…¢) complexes with chiral diimine bridges showed good catalytic performance. The complex derived from (1S, 2S)-diphenylethylenediamine performanced well in the epoxidation of terminal alkene styrene. Under the optimized reaction conditions, which were styrene 0.5 mmol, m-CPBA 1.0 mmol, NMO 2.5 mmol, catalyst 0.01 mmol, CH₂Cl₂ 2.5 ml, running at -78℃in five minutes, 100% of conversion and selectivity and 74.0% of enantiomeric excess were obtained. It was revealed that the absolute configuration of main epoxides was decided by chiral diimine bridge's configutation. Salen Mn(â…¢) complexes derived from (R, R) and (S, S) diamines derivatives gave reversed epoxide configuration.Complexes without chiral diimine bridge but with sugar moieties at C5(5') or C3(3') also had an asymmetric inducing effect in the epoxidation reaction, which was strengthened when the sugar ring was closer to metal Mn. Complexes with glucose moieties were found to be in agreement with (R, R)-catalysts, whereas those with mannose moieties were identical with (S, S)-catalysts in affecting the absolute configuration of main epoxides.The recycle runs of the catalyst were performed in hydrophobic ionic liquid [bmim][PF₆] with m-CPBA as the oxidant. The enantiomeric excess was 50.8% in the fourth recycle run for the epoxidantion of styrene catalyzed by the complex derived from (1S, 2S)-diphenylethylenediamine, with only 13.3% of loss compared with that in the first run.