Synthesis And Structure Of Rare Metal Complexes Derived From Chiral Sulfonamide Ligands And Their Use As Catalysts For The Polymerization Of Rac-Lactide

Polylactide as a new type of environmentally-friendly and biodegradable material has been attaching extensive interest these years,and it has been exploited for a wide scope of applications such as slow release drug delivery,biodegradable sutures,packaging materials and tissue engineering.However,the physical and mechanical properties of polylactides,as well as the rate of degradation,are intimately related to the chain stereochemistry.In past years,a variety of chiral rare-earth metal complexes have been prepared,and employed as catalysts for ring-opening polymerization（ROP）of rac-lactide.But only a few of them have been proven to be excellent initiators with high stereoselectivity and highly catalytic activity.Therefore,exploration of novel chiral are-earth metal complexes for ROP of rac-lactide is still a desirable and challenging goal.In this thesis,a series of novel chiral rare-earth metal complexes 1-13 have been prepared by reaction of Ln[N（SiMe₃）₂]₃（Ln=Y,Yb,Sm,Nd）with the corresponding chiral sulfonamides（1-3H,1-4H,2-3H,2-4H,2-5H,2-6H）derived from（S）-Phenylacetamine and（S）-1,2,3,4-tetrahydro-hydromine.Meanwhile,we found that the ionic radius of rare-earth metals and reaction temperature plays important roles in the complex formation and its structure.For example,the single ligand complexes（2-4H）-Sm[N（Si Me₃）₂]₂（7）、（2-4H）-Nd[N（SiMe₃）₂]₂（8）can be readily obtained by reaction of the corresponding ligand precursors（2-3H,2-4H）at 80°C,while the bis-ligand complexes（2-3H）-SmN（SiMe₃）₂（11）、（2-3H）-NdN（SiMe₃）₂（12）、（2-4H）-NdN（SiMe3）2（13）are generated at 85°C.Ln[N（SiMe3）2]3（Ln=Y,Yb）containing smaller rare-earth metal ions react with 2-3H or 2-4H only to give single ligand complexes（2-3H）-Y[N（Si Me₃）₂]₂（6）,（2-4H）-Y[N（SiMe₃）₂]₂（9）and（2-4H）-Yb[N（SiMe3）2]2（10）.The compounds were characterized by various spectroscopic methods,and the solid-state structures of complexes 1-13 were further confirmed by single-crystal X-ray diffraction analyses.Complexes 1-13 are active catalysts for the ring-opening polymerization（ROP）of rac-lactide,leading to heterotactic-medium polylactides under mild conditions.Meanwhile,most of these complexes can effectively produce polylactides with narrow polydispersities,desirable molecular weights,and moderate to high heteroselectivities.