Synthesis, Characterization And Catalysis Of A Series Of Chiral ?-Diketiminate-Magnesium Complexes And Their Use As Catalysts For The Polymerization Of Rac-Lactide

Polylactide has been attaching extensive interest these years due to its biocompatibility and biodegradability,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 degradation,are intimately related to the chain stereochemistry.Thus,the directing polymerization of rac-lactide via stereoselective catalysts remains a challenge and opportunity for chemists.Chiral magnesium complexes have been proven to be attractive initiators with high stereoselectivity,excellent biocompatibility,non-toxicity and highly catalytic activity,Therefore,exploration of chiral magnesium complexes forfor ring-opening polymerization of rac-lactide of rac-lactide is of great interest and importance.Nine C₁-symmetric chiral ?-diketiminate ligands CF₃C[NHCH?CH₃?Naph]CHC[N?2,6-Et₂C₆H₃?]CH₃?HL₁?, CF₃C[NHCH?CH₃?Naph]CHC[N?2,6-ⁱPr₂C₆H₃?]CH₃?HL₂?, CF₃C[NHCH?CH₂OCH₂Ph?ⁱPr)]CHC[N?2,6-Me₂C₆H₃?]CH₃?HL₃?, CF₃C[NHCH?CH₂OCH₃?ⁱPr]CHC[N?2,6-ⁱPr₂C₆H₃?]CH₃?HL₄?, CF₃C[NHCH?CH₂OCH₂Ph?ⁱPr]CHC[N?2,4,6-Me₃C₆H₂?]CH₃?HL₅?, CF₃C[NHCH?CH₂OCH₂Ph?ⁱBu]CHC[N?2,6-Me₂C₆H₃?]CH₃?HL₆?, CF₃C[NHCH?CH₂OCH₃?Ph]CHC[N?2,6-ⁱPr₂C₆H₃?]CH₃?HL₇?, CF₃C[NHCH?CH₂OCH₂Ph?ⁱPr)]CHC[N?2,6-ⁱPr₂C₆H₃?]CH₃?HL₈? and CF₃C[NHCH?CH₂OCH₂Ph?ⁱBu)]CHC[N?2,6-ⁱPr₂C₆H₃?]CH₃?HL9? have been designed andsuccessfully prepared from chiral amines and chiral amino alcohols.A series of chiral magnesium complexes {CF₃C[NCH?CH₃?Naph]CHC[N?2,6-Et₂C₆H₃?]CH₃}Mg?nBu??THF??1?, {CF₃C[NCH?CH₃?Naph]CHC[N?2,6-ⁱPr₂C₆H₃?]CH₃}Mg?nBu??THF??2?, {CF₃C[NCH?CH₂OCH₂Ph?ⁱPr)]CHC[N?2,6-Me₂C₆H₃?]CH₃}Mg?nBu??3?, {CF₃C[NCH?CH₂OCH₃?ⁱPr]CHC[N?2,6-ⁱPr₂C₆H₃?]CH₃}Mg?nBu??4?, {CF₃C[NCH?CH₂OCH₂Ph?ⁱPr]CHC[N?2,4,6-Me₃C₆H₂?]CH₃}Mg?nBu??5?, {CF₃C[NCH?CH₂OCH₂Ph?ⁱBu]CHC[N?2,6-Me₂C₆H₃?]CH₃}Mg?nBu??6?, {CF₃C[NCH?CH₂OCH₃?Ph]CHC[N?2,6-ⁱPr₂C₆H₃?]CH₃}Mg?nBu??THF??7?, {CF₃C[NCH?CH₂OCH₂C₆H₄?ⁱPr)]CHC[N?2,6-ⁱPr₂C₆H₃?]CH₃}Mg?THF??8? and {CF₃C[NCH?CH₂OCH₂C₆H₄?ⁱBu)]CHC[N?2,6-ⁱPr₂C₆H₃?]CH₃}Mg?THF??9? have been prepared from the reaction between these ligands and MgⁿBu₂,respectively.All the ligandsand complexes have been characterized by nuclear magnetic resonance,IR spectroscopy,and the complexes have been further confirmed by X-ray diffraction analyses.The chiral magnesium complexes are active catalysts for the ring-opening polymerization?ROP?of rac-lactide,leading to heterotactic-rich polylactides.These complexes show medium to high heteroselectivity?P_r=0.60-0.92?.