Synthesis And Catalysis Of Polydentate Ketoimines And Their Homonuclear/heteronuclear Iron Complexes

Polylactide?PLA?has good biocompatibility and excellent physical and chemical properties,which has been used in many aspects of production and life.The ring opening polymerization of lactide is an effective way to prepare polylactide,and the metal complex is the best catalyst to initiate the ring opening polymerization.The research show that the structure and metal species of metal complexes affect the catalytic activity and stereoselectivity of the complexes in ring opening polymerization of lactones.As one of the essential trace elements in human body,iron is non-toxic,cheap and biocompatible.Polylactide catalyzed by iron complex can be safely used in the field of medicine and food.?-ketoimines?NacacH?are a kind of ligands which are easy to be prepared and have large modulation space.In this paper,polydentate?-ketoimines were prepared by introducing O and N heteroatoms into the branched chain of?-ketoimines,and then reacted with simple metal salts to prepare polydentate ketoiminate iron complexes.Ten polydentate?-ketoimines containing heteroatoms were synthesized and characterized by NMR.Heteronuclear iron lithium complexes(Nacac^CH2CH2CH2O)₂[N?SiMe₃?₂]₄O₂Fe₄Li₄?2b?,₃^{[NacacCH2CH2N?CH3?2]}OCl₃Fe₃Li?3j?and homonuclear iron complexes[Nacac^{CH2CH2N?CH3?2}FeCl]₂O?4j?were synthesized by the reaction of polydentate?-ketoimines with n-BuLi,FeCl₂?THF?_1.5 and LiN?SiMe₃?₂.The structures were characterized by HRMS,IR and XRD.Complex 2b is the first heteronuclear metal complex with a hexagonal prism core,3j is a tetranuclear iron lithium complex,and complex 4j is a dinuclear iron complex with bridging oxygen atom.The above mentioned 3 kinds of iron complexes can initiate rac-LA ring opening polymerization?ROP?of rac-LA under melt condition,and the obtained polylactide can be characterized by ¹H NMR and gel permeation chromatography?GPC?.Complex 2b has the best catalytic activity among these 3 iron complexes,and can reach a TOF value of 38480h^-1within 3 minutes,and the number average molecular weight of the polymer reaches 52,000g/mol.The stereoselectivity of complexes 3j and 4j are good.Under the optimum catalytic conditions,the Pm values of the polymer were 0.35 and 0.34,respectively.