Synthesis Of N-alkyl-?-ketiminate Iron Complexes And Their Catalytic Properties For Ring-opening Polymerization Of Rac-Lactide

Polylactide (PLA) was synthesized by the polymerization of lactic acid. PLA has rich raw material sources, excellent crimpness, high strength, high modulus and biocompatibility, so it was be used in clothing, thin film, fiber and preparation of drugs slow-release system, bone repair and tissue engineering scaffold material. Aluminum complexes, tin complexes, and rare earth elements complexes can be used to initiate the ring-opening polymerization (ROP) of lactide and get large number-average molecular weight and a narrow molecular weight distribution. Although plenty of active metal catalysts have been discussed, the residue of metal in polymers takes a toxic risk for creature, which limits the application of polylactide in biomedical and pharmaceutical fields. Therefore, exploring non-toxic metal catalysts, which can initiate the ROP of lactide in control to yield environmentally benign polylactide, has great significance.In this thesis, we report six new N-alky1-?-ketiminate iron complexes 3a-4a, which were prepared by the treatments of FeCl2(THF)1.5 with corresponding ?-ketiminate ligands. These complexes have been characterized by IR, EI-HRMS and X-ray structure determination, which show that these iron complexes are mononuclear iron complexes bearing two N-alky1-?-ketiminate ligands. [NacacH6Fe4Li2Si4H18O4N2]?exane (5a), a multimetallic iron complex, was synthesized by FeCl2(THF)1.5, LiN(SiMe3)2 and corresponding N-alky1-?-ketiminate ligands. The complex has been characterized by IR and X-ray structure determination.The above reported seven N-alky1-?-ketiminate complexes can initiate the ROP of rac-LA and the polymers have been examined by 1H NMR and GPC. Among the examined catalysts, complex 3a,3b and 3e can achieve approximate 100% conversion within one hour at 70?. Complex 3b shows better catalytic activity and stereoselectivity with complete conversion in 1 h and number-average molecular weight over 16000 g/mol, a narrow molecular distribution (PDI=1.73) and good isotacticity (Pm=0.79) of the resulting polymer. Besides, under the same condition complexes 3c and 4a also obtained moderate isotacticity (Pm=0.77 and 0.75).