Synthesis And Structure Of New Zinc Complexes Derived From Chiral Azetidine Ligands And Their Use As Catalysts For The Polymerization Of Rac-lactide

In past decades,azetidine derivatives have received considerable attentions due to their potential use in medicine.Furthermore,these compounds are excellent ligands in organometallic chemistry because of their advantages in rigidity of skeleton structures,facile modulation of the steric properties,and strong coordination ability of tertiary nitrogen atom and so on.However,azetidino complexes have been reported rarely to date,and this research work is at the beginning.Moreover,to the best of our knowledge,only one example of azetidino zinc complex has been reported.Therefore,in thesis our study efforts focused on the synthesis of chiral organozinc complexes with azetidine ligands and exploration of their application in polymerization of rac-lactide.The observations are:A series of sulfonylamidoazetidines(1a-1f)and iminoazetidines(Schiff bases 2a-2d)have been designed and successfully prepared from chiral 3-aminoazetidine.These azetidine derivatives can readily react with the equivalent of diethyl zinc to afford the corresponding chiral organozinc complexes(1a-1f,2a-2d)under mild conditions.The structures of the zinc complexes depends strongly on the steric hindrance of the ligands,for example: treatment of sulfonylamidoazetidines(1aH,1cH,1eH,1fH)with diethylzinc affords a range of dimer organozinc complexes{(1a)ZnEt}2(1)?{(1c)ZnEt}2(3)?{(1e)ZnEt}2(5)?{(1f)ZnEt}2(6).In contrast,under the similar reaction conditions the sulfonylamidoazetidines 1bH and 1dH react with diethylzinc to give the multinulear complexes(2 and 4)without active ethyl group.In addition,the different coordination pattern was also observed by reaction of iminoazetidines(2a-2d)with diethylzinc yielding bis-ligated compounds((2a)2Zn(7)?{(2b)ZnEt}2(8)?(2b)2Zn(9)?(2c)2Zn(10)?{(2d)ZnEt}(11))without active ethyl group.Also,the central ion of these complexes does not coordinate to the tertiary nitrogen atom.All of the ligands and chiral zinc complexes were confirmed by various spectra,elemental analysis and nuclear magnetic resonance,and some of them were characterized by X-ray diffraction.The complexes(1a)2ZnEt(1)?(1c)2ZnEt(3)?(1e)2ZnEt(5)?(1f)2ZnEt(6)?(2a)2Zn(7)?(2b)2Zn2Et2(8)?(2d)2Zn2Et2(11)can be employed as catalysts for ring-opening polymerization of rac-lactide exhibiting high activity and selectivity.