Design And Synthesis Of Chiral Bifunctional (Pyrrolidine Salen)M(III) Complexes

The chiral Salen ligand,one of most important ligands for asymmetric catalytic reaction, has been widely applied in hydrolytic kinetic resolution of racemic epoxides,asymmetric ring-opening of epoxides,asymmetric cyclopropanation reaction,Diels-Alder reaction, asymmetric oxidation of sulfides,asymmetric epoxidation of unfunctionalized alkenes,as well as cycloaddition or copolymerization of CO₂ and epoxides.In this thesis,chiral metal-salen complexes with an anchored functionl group on its pyrrolidine ring were synthesized and applied to the asymmetric cycloaddition of CO₂ and epoxides and epoxidation of unfunctionalized alkenes.1.Synthesis of chiral(pyrrolidine salen)Cr(â…¢) complexes containing an electrophilic and nucleophilic center in one molecule and their catalytic properties for asymmetric cycloaddition of CO₂ and epoxides.The binary catalyst system,consisting of the chiral SalenM(â…¢) complex as the electrophlie and quaternary ammonium salt or sterically hindered strong base as the nucleophile,can effectively catalyze the cycloaddition of CO₂ and epoxides at mild conditions. However,the reaction rate was dependent on the catalyst concentration,and nearly complete loss in activity was observed at a high[epoxide]/[catalyst]ratio.As a result,a catalyst containing an electrophilic center[(pyrrolidine salen)Cr(â…¢)]and a sterically hindered base or quaternary ammonium salt in one molecule,which was linked with 1,10-dibromodecane,was synthesized and applied to the cycloaddition of CO₂ and epoxides. With the intramolecular two-centers cooperation catalysis,the catalyst concentration had negligible influence on the reaction rate.At a condition of[PO]/[catalyst]ratio of 50000,25℃and 0.5 MPa pressure,the functional catalyst could effectively catalyze the cycloaddition of CO₂ and epoxides in the absence of any cocatalyst.2.Synthesis of bifunctional chiral(pyrrolidine salen)Mn(â…¢) complexes and their catalytic performance for asymmetric epoxidation of unfunctionalized alkenes enantioselectivity of epoxidationIt's well known that chiral SalenMn(â…¢) complexes are effective catalysts for the asymmetric epoxidation of unfunctionalized alkenes.Although high product was observed in the epoxidation of non-functionalised cis or cyclic alkenes using NaOCl as oxidant under biphasic systems,a prolong reaction time is seem to be prerequisite for obtaining high yield even in the presence of the expensive pyridine N-oxide as cocatalyst.In this thesis,a catalytic system based on the chiral pyrrolidine SalenMn(â…¢) complexes Mn-1～Mn-3 with an anchored functional group,linked by a 1,10-dibromodecane bridge,was synthesized and used for the asymmetric epoxidation of substituted chromenes with NaClO/PPNO as oxidant system in the aqueous/organic biphasic medium.The SalenMn(â…¢) complex 1,bearing an imidazole group at the N_aza-substituent in the pyrrolidine backbone,showed high activity and enantioselectivity in the absence of any cocatalyst,while SalenMn(â…¢) complexes 2 and 3 with an anchored internal quaternary ammonium salts could increase the epoxidation reaction rate and displayed significantly high activity owing to the phase transfer capability of the intramolecular quaternary ammonium salt unit of the SalenMn(â…¢) catalyst.