The Synthesis Of Metal Complexes Based On Ketiminate Ligands And Their Application As Catalysts For Rop Of Lactide

Polylactide(PLA), as an important biodegradable, biocompatible and permeable polymer, has been utilized in many therapeutic and pharmaceutical fields. The ring-opening polymerization(ROP) initiated/catalyzed by metal complexes is the most effective method for synthesizing polylactide in terms of its advantages of the well-controlled molecular weight, low polydispersity(PDI) and mild reaction conditions. A series of Ca/Mg/Zn complexes based on ketiminate ligands with pyrazole substituents of different electronic properties have been synthesized, and their catalytic activity and selectivity of L-LA and rac-LA polymerization have been studied.Ⅰ. The reaction of N, N-Dimethyl-1, 2-ethanediamine and 1-phenyl-3-methyl-4-acyl-5-pyrazolone in methanol yielded three NNO ketiminate ligands with different substituents. Treat the NNO tridentate ketiminate ligands with MgnBu2 / ZnEt2 in t in the presence of benzyl alcohol respectively, and got six dinuclear metal complexes [LM(μ-OBn)]2. X-ray crystal structural studies of [L1Mg(μ-OBn)]2, [L3Mg(μ-OBn)]2, [L1Zn(μ-OBn)]2 revealed that they were dinuclear species whereas the geometry around the metal center was penta-coordinated bridging through the benzylalkoxy oxygen atoms in the solid structure.Ⅱ. The activity and selectivity of these above six complexes towards the ROP of L-LA and rac-LA are investigated. Polymerization of L-LA initiated by these six metal benzyloxides proceeded rapidly, yielding PLA with well-controlled molecular weight and a very narrow PDI. Besides, these unsymmetric metal alkoxides have shown great activity and selectivity toward the ROP of rac-LA with the Pr value up to 82%.Ⅲ. [L2M] type of homoleptic complexes has been synathsized with the reaction between the ligands and MgnBu2, ZnEt2, Ca[N(SiMe3)2]2(THF)2, in a molar ratio of 2:1 in toluene. The solid state structure of these complexes has a mononuclear feature with a hexa-coordinated metal center bonding to four N and two O atoms of two NNO-tridentate ketiminate ligands.Ⅳ. The activities of these complexes were investigated towards the ROP of L-LA. With the benzyl alcohol addition, they could effectively catalyze ROP of L-LA. The produced PLA has controlled molecular weight and narrow molecular weight distribution.