Synthesis And Characterization Of Lanthanide Complexes Supported By Amino Bridged Bis(Phenolatc)and Their Application In Preparation Of Polylactide And Random Poly(Lactide-co-caprolactone)

Using three types of amino bridged bis(phenolate)as ligands,26 lanthanide complexes were synthesized.All of these complexes were characterized by elemental analysis,and X-ray single crystal structure determination,as well as 1H and 13C NMRfor yttrium and lanthanum complexes.The catalytic properties of these lanthanide complexes on the polymerization of lactides and L-lacOCA,and the copolymerization of L-lactide(L-LA)and ?-caprolactone(?-CL)were investigated.The effect of the ligands and lanthanide metals on the catalytic properties of lanthanide derivatives was elucidated.The amino bridged bis(phenol)s used in this thesis are:Me2NCH2CH2N[CH2-(2-OH-C6H2-R2-3,5)]2,[R=tBu,abbreviated as L1H2;R=Me,abbreviated as L2H2;R=CPhMe2,abbreviated as L3H2;R=Cl,abbreviated as L4H2];O(CH2CH2)2N-CH2CH2N[CH2-(2-OH-C6H2-R2-3,5)]2,[R=tBu,abbreviated as L5H2;R=Me,abbreviated as L6H2;R=Cl,abbreviated as L7H2];1-C2H5-NC4H9-2-CH2N[CH2-(2-OH-C6H2-tBu2-3,5)]2,abbreviated as L8H2;C5H10N-CH2CH2N[CH2-(2-OH-C6H2-tBu2-3,5)]2,abbreviated as L9H2;PhN[CH2-(2-OH-C6H2-tBu2-3,5)]2,abbreviated as L10H2;2-CH3O-C6H2-N[CH2-(2-OH-C6H2-tBu2-3,5)]2,abbreviated as L11H2;CH2-(2-OH-C6H2-tBu2-3,5)2,abbreviated as L11*H2;F5C6N[CH2-(2-OH-C6H2-tBu2-3,5)]2,abbreviated as L12H2;N,N'-(CH2Ph)2-N,N'-[CH2-(2-OH-C6H2-Me2-3,5)]2,abbreviated as L13H2.The main contents are listed below.1.The reactions of(C5H5)3Ln(THF)(Ln=La,Yb)with amino bridged bis(phenol)s L1H2-L3H2,and then with p-cresol gave the neutral lanthanide complexes L1Yb(OC6H4-4-CH3)(THF)(1),L1La(OC6H4-4-CH3)(THF)2(2),[L2La(OC6H4-4-CH3)(THF)]2(3)and L3La(OC6H4-4-CH3)(THF)2(4).For chlorine-substituted amino bridged bis(phenol)L4H2,the reaction of L4H2 with(C5H5)3Yb(THF),and then with p-cresol,gave homoleptic lanthanide complex L4Yb(L4H)(5).The reaction of ligand L4H2 with Yb(OAr)3(OAr=OC6H3-2,6-'Bu2-4-CH3)gave the neutral lanthanide aryloxide L4Yb(OC6H3-2,6'Bu2-4-CH3)(THF)(6).2.The reaction of(C5H5)3Y(THF)with amino bridged bis(phenol)s L5H2 gave the intermediate species L4YCp(THF)(7),which is proved by the 'H NMR spectrum and structure determination.Further reaction of complex 7 with benzyl alcohol gave the expected lanthanide alkoxide L5Y(OCH2Ph)(THF)(8).Then reactions of(C5H5)3Ln(THF)(Ln=Y,Yb)with amino bridged bis(phenol)s L5H2,L7H2and L9H2,and then with benzyl alcohol gave the desired neutral lanthanide complexes L5Y(OCH2Ph)(THF)(8),L5Yb(OCH2Ph)(THF)(9),L8Y(OCH2Ph)(THF)(10),L8Yb(OCH2Ph)(THF)(11),L9Y(OCH2Ph)(THF)(12)and L9Yb(OCH2Ph)(THF)(13).The steric hindrance of substituent groups of the benzene ring in amino bridged bis(phenol)s has a significant effect on the synthesis of the corresponding lanthanide complexes.Similar reactions of L6H2-L7H2 with(C5H5)3Ln(THF)(Ln=Y,Yb)gave the unexpected homoleptic lanthanide complexes L6Y(L6H)(14),L6Yb(L6H)(15),L7Yb(L7H)(16).3.The reactions of(C5H5)3Ln(THF)(Ln=Y,Yb)with amino bridged bis(phenol)s L10H2-L12H2,and then with benzyl alcohol or p-cresol can not generate the desired lanthanide complexes.The reactions of Ln[N(SiMe3)2]3(?-Cl)Li(THF)3(Ln=Y,Yb)with L10H2 gave the neutral benzylamino-bridged bis(phenolate)lanthanide complexes L10YN(SiMe3)2(THF)(17)and L10YbN(SiMe3)2(THF)(18).The reaction of anhydrous LaCl3 with L10Na2 gave lanthanum-alkali heterobimetallic complex L102LaNa(THF)2(19),instead of desired L10LaCl(THF)x.The reactions of Ln[N(SiMe3)2]3(THF)3(Ln=Yb,La,Nd)with L11H2-L12H2 also gave the unexpected lanthanide complexes[(L11H)Yb(L11*)](20),(L12)2La3(21)and(L12)2Nd3(22).4.The reactions of(C5H5)3Ln(THF)(Ln=Y,Sm,Nd,La)with N,N'-dibenzyl-ethylenediamino bridged bis(phenol)s L13H2,and then with p-cresol gave four neutral lanthanide aryloxides[L13Y(OC6H4-4-CH3)]2(23),[L13Sm(OC6H4-4-CH3)]2(24),[L13Nd(OC6H4-4-CH3)]2(25)and[L13La(OC6H4-4-CH3)(THF)]2(26).X-Ray diffraction showed that complexes 23-26 have dinuclear structures in the solid state,bridging atoms are the oxygen atoms from amino bridge bis(phenolate)ligands.5.Complexes 1-4,8-13,17,18,23-26 were used as catalyst to catalyze the ROP of rac-lactide,and the influence of ligands,central metals and polymerization temperature on the polymerization were explored.It was found that lanthanide complexes supported by amino bridged bis(phenolate)ligands containing N-heterocyclic ring as side arm,show the highest catalytic activity and exhibit the best stereoselectivity.The activity decreasing order of La>Nd>Sm>Y is consistent with the order of their ionic radii,whereas the order reversed in the stereoselectivity.The catalytic behavior of these complexes for L-lactide polymerization was also investigated.It was found that lanthanide aryloxides stabilized by N,N-dimethyl amino bridge bis(phenolate)ligand showed the highest activity,and good controllability with increasing order of the ionic radii of the central metals.6.Ring-opening polymerization of L-lacOCA catalyzed by rare-earth metal aryloxo complexes 2-4,Y-1[L1Y(OC6H4-4-CH3)(THF)]and Y-2{Y[THFONOO-tBu](OC6H4-4-CH3)}2 {THFONOO-tBu=(CH2)3OCHCH2N[CH2-(2-O-C6H2-3,5-tBu2)]2} was investigated.The catalytic activity decreased as the increase of the bulkiness of the substituents(from methyl to cumyl groups).The ionic radii of lanthanide metals also affected the polymerization activity.The yttrium complex showed higher catalytic activity than the lanthanum complex bearing the same ancillary ligand.Kinetics study indicated that the polymerization follows first-order kinetics for both the monomer concentration and the catalyst concentration.1H NMR end group analysis and MALDI-TOF analysis of the oligomer revealed that L-lacOCA polymerization initiated by these organolanthanide complexes proceeded via a coordination-insertion mechanism.7.The catalytic behavior of complexes 1,2,23-26 towards the copolymerization of L-lactide/?-caprolactone was investigated.It was found that these lanthanide complexes can catalyze the "one-pot" copolymerization of these two monomers,and polymerization temperature has significant influence on the structure of the copolymer.The gradient copolymer was obtained when the copolymerization was conducted at 30? whereas the randomness index of the resultant copolymer increased as the increase of polymerization temperature.Random copolymer was obtained using the lanthanum complex 2 as the catalyst when polymerization temperature increased to 90?.The structure of the ancillary ligand has somewhat influence on the preparation of random copolymer.Amino-amino bridged bis(phenolate)lanthanum complex 2 can catalyze the "one pot" random copolymerization of L-lactide and ?-caprolactone at 90?,whereas the dinuclear Salan lanthanum aryloxide 26 can catalyze the "one pot" copolymerization of these two monomers at 130?.1H NMR monitoring reaction revealed that L-LA was consumed rapidly within the first 4 min,meanwhile,?-CL reacted rather sluggishly.As the reaction time was prolonged,the percentage of ?-CL units,as well as the CL-LA heterodiads in the copolymer,gradually increased.This result is consistent with the results of NMR characterization of the resultant copolymers.These findings suggest that transesterification may play a predominate role in random copolymer formation.8.According to the copolymerization mechanism mentioned above,the copolymerization of PLA and ?-caprolactone should be occurred under suitable conditions.To test this hypothesis,depolymerization of PLLA was tested using complex 2 as the catalyst.It was found that the depolymerization indeed occurred.Thus,PLLA was treated with s-CL,which indeed led to copolymer formation.1H NMR analysis revealed CL-LA heterodiads,and suggested that they are random copolymers.Starting from different ?-CL and PLA ratios(ranging from 1:4 to 4:1),random copolymers of various compositions were obtained.To the best of our knowledge,this is the first example of random copolymerization of PLA with CL catalyzed by metal-based catalyst.This new strategy is useful not only for preparation of random LA/CL copolymers,but also for direct modification of PLA.