Synthesis And Characterization Of Rare-Earth Metal Complexes Stabilized By Ethylene Diamino-Bridged Bis (phenolate) Ligands And T Heir Performance In The Ring-Oping Poly Merization Of Cyclic Esters

A series of new salan-ligated rare-earth metal amide complexes were prepared.All of scandium,yttrium and lanthanum complexes were characterized by 1H and 13C NMR spectroscopy.The structures of some complexes were confirmed by single-crystal X-ray diffraction analysis.These rare-earth metal amides are active for the ring-opening polymerization(ROP)of rfac-?-butyrolactone(rac-BBL)and the copolymerization of L-lactide and ?-caprolactone.The ligands used in this thesis are:[CH2N(Ph)CH2-(2-OH-C6H2-tBu2-3,5)]2,abbreviated as L1H2;[CH2N(Cy)CH2-(2-OH-C6H2-tBu2-3,5)]2,abbreviated as L2H2;[CH2N(tBu)CH2-(2-OH-C6H2-tBu-3,5)]2,abbreviated as L3H2;[CH2N(Me)CH2-(2-OH-C6H2-tBu2-3,5)]2,abbreviated as L4H2;[CH2N(Cy)CH2-(2-OH-C6H2-Me-3,5)]2,abbreviated as L5H2;[CH2N(tBu)CH2-(2-OH-C6H2-Me-3,5)]2,abbreviated as L6H2.1.Synthesis and characterization of lanthanide complexes stabilized by ethylene diamine-bridged bis(phenolate)ligandsTreatment of the ethylene diamine-bridged bis(phenol)s L1H2-L4H2 with one equivalent of Ln[N(SiMe3)2]3(?-Cl)Li(THF)3 in toluene at 95 0C,after workup,afforded the rare-earth metal amide complexes L1LnN(SiMe3)2[Ln=Sc(1)],L2LnN(SiMe3)2[Ln=Sc(7),Sm(10),Nd(11),La(12)],L3LnN(SiMe3)2[Ln=Sm(15),Nd(16)],and L4YbN(SiMe3)2(17).However,the reaction of L5H2 and L6H2 with Ln[N(SiMe3)2]3(?-Cl)Li(THF)3 under the same conditions produced a series of unexpected heterometallic rare earth metal-lithium complexes L5LnLi[N(SiMe3)2]2[Ln=Y(18),Nd(19)],(L5)2YLiCl(20),L6LnLi[N(SiMe3)2]2[Ln=Y(21),Yb(22)Nd(23)],(L6)2LnLiCl[Ln=Y(24),Nd(25)],and(L6)3Yb2(u-Cl)Li3(26)by recrystallization from the mixture of toluene and hexane.2.Ring-opening polymerization of rac-?-butyrolactone catalyzed by rare-earth metal amide complexesTo assess the catalytic behaviour of the complexes 2-5 and 7-12,these complexes were employed as initiators for the ROP of rac-?-butyrolactone(rac-BBL)in a constant feeding ratio of[rac-BBL]:[Ln]=200:1.The effects of the structures of the ancillanry ligands and the ionic radii of the rare earth metal ions on the catalytic performance of the metal complexes were explored.It was found that the substituents on the bridging amino groups had significant influence on the polymerization stereoselectivity.Complexes 2 and 3,which featured phenyl groups on the bridging N atoms,gave isotactic-rich PHB(Pm>0.66);whereas the complexes 8,9,and 17,which featured alkyl groups on the bridging N atoms,gave syndiotactic-rich PHB(Pr>0.72).Furthermore,the stereoselectivity decreases with the increase of the bulkiness of the substituents on the N atoms(Me>Cy>tBu).On the other hand,the properties of substituents on the N atoms have also effect on the catalytic activity of the corresponding rare earth metal complexes for rac-BBL polymerization.For the ytterbium complexes,the sequence of the activities of these complexes with different substituents is Me>Ph>Cy>>tBu.In addition,the polymerization activity depends on the ionic radii of the rare earth metals.The lanthanum complex with the largest ionic radius showed the highest catalytic activity.The polymerization of rac-BBL catalyzed by these rare earth metal amides was confirmed via the coordination insertion mechanism by NMR and MALDI-TOF characterization of the oligomers.3.The copolymerization of ?-caprolactone and L-lactide catalyzed by rare-earth metal amido complexesThe copolymerization of ?-caprolactone and L-lactide catalyzed by complexes 4,10-12,15-16 were explored.It was found that the substituents on the bridged amino groups and polymerization temperature have profound influence on the catalytic performance of these complexes.Complexes 10-12 with the cyclohexyl(Cy)substituents on the bridged amino groups showed higher activity in comparison with those complexes bearing phenyl and tert-butyl groups.Among them,complex 11 can catalyze the copolymerization of L-LA and ?-CL at 90? to produce random copolymers.The block copolymer of L-LA and ?-CL can be obtained when the polymerization was conducted at 0?.Furthermore,the structure of the copolmer can be tuned from block copolymer to random copolymer by increasing polymerization temperature from 0? to 90?.NMR detection of the copolymerization process showed that L-LA was consumed very fast in the initial stage of copolymerization,and then?-CL began to participate in the copolymerization.Further study revealed that transesterification plays a crucial role on the formation of L-LA and?-CL random copolymer.4.Study on degradation of poly(lactide-co-caprolactone)The degradation behavior of the copolymers of L-LA and ?-CL was investigated.It was found that the chain structure of the copolymer and the degradation environment had a significant effect on its degradation behavior.The polymer with CL-LA link and CL-CL link ratio of 35:65 showed the fastest degradation rate in PBS solution at 37 ?.The degradation rate of the random copolymer at 80? is 63 times fast than that at 37?.The degradation rate of the random copolymers is greater under alkaline solution than those under acidic and neutral solution.