Synthesis And Catalysis Of Tridentate Ketimines And Their Iron Complexes

Polylactide（PLA）is widely used in various industries especially in the pharmaceutical industry.due to its good biocompatibility,easy degradation and no pollution.It is used as a surgical suture material and a drug slow-release carrier,etc.At present,ring-opening polymerization of lactide in the presence of metal complexes is the most efficient way to synthesize polylactide.The conditions are mild and the resulting polymer has good performance.The molecular weight and stereoselectivity of the obtained polymer can be adjusted purposely by adjusting the structure of the metal complex.Iron is one of the trace elements necessary for the human body.It is relatively cheap,little toxic,and is harmless to the environment.It has long been used in the ring-opening polymerization of caprolactone and lactide.β-ketoimine is a kind of proligand that is easy to prepare and easy to control.We synthesize ligands with different steric hindrance and electronic effect to coordinate with iron metal under different conditions to obtain iron metal complexes with different structure and catalysis.Eight tridentate ketiminate ligands with different substituents and heteroatoms on the side chains were synthesized,CH₃C（O）CHCNH（CH₂CH₂CH₂N（CH₃）₂）CH₃（1a）、CH₃C（O）CHC NH（CH₂CH₂N（CH₃）₂）CH₃（1b）、CH₃C（O）CHCNH（CH₂CH₂N（CH₂CH₃）₂）CH₃（1c）、（CH₃）₃C（O）CHCNH（CH₂CH₂N（CH₃）₂）（CH₃）₃（1d）、CH₃C（O）CHCNH（CH₂CH₂OCH₃）CH₃（1e）、CH₃C（O）CHCNH（CH₂CH₂CH₂OCH₃）CH3（1f）、CH₃C（O）CHCNH（CH₂CH₂CH₂OH）CH₃（1g）、CH₃C（O）CHCNH（CH₂CH₂CH₂CH₂OH）CH₃（1h）.Complexes[L₂^1aFe](L^1a=CH₃C（O）CHCN（CH₂CH₂CH₂N（CH₃）₂）CH₃)（2a）and[L₂^1bFeLi FeL₂^1b][Fe（N（Si Me₃）₂）₃](L^1b=CH₃C（O）CHCN（CH₂CH₂N（CH₃）₂）CH₃)（2b）were obtained by the reaction of 1a and 1b with FeCl₂（THF）_1.5、Li Bu and Li N（Si Me₃）₂,respectively.2a is a neutral mononuclear iron complex bearing two tridentate ketiminate ligands,and 2b is a Fe-Li-Feheteronuclear ionic complex.The activity of complexes 2a and 2b in catalyzing the ring-opening polymerization of racemic lactide was studied.The results show that both iron complexes can catalyze the ring-opening polymerization of racemic lactide under melt condition.In contrast,the catalytic activity of complex 2b is better.With the molar ratio of monomer to catalyst being 500:1,within 3 min,the monomer conversion reaches 79%,and the stereoselectivity is better（Pm=0.3）.