Synthesis, Characterization Of Lanthanide Complexes Supported By Salen Ligands And Their Catalytic Behavior For The Ring-opening Polymerization Of Rac-lactide

A series of lanthanide complexes supported by different salen-type ligands(L1-L11)were synthesized and characterized, and their catalytic performances for the polymerization of rac-lactide(rac-LA) were also studied.The salen ligands used in this thesis are:(CH3)2C[CH2N=CH(C6H2-2-OH)]2, marked as L1H2;(CH3)2C[CH2N=CH(C6H2-2-OH-3, 5-Cl2)]2, marked as L2H2;(CH3)2C[CH2N=CH(C6H2-2-OH-3, 5- But 2)]2, marked as L3H2;(CH3)2C[CH2N=CH(C6H2-2-OH-3, 5-(CMe2Ph) 2)]2, marked as L4H2;CH2[CH2N=CH(C6H2-2-OH-3, 5-Cl2)]2, marked as L5H2;CH2[CH2N=CH(C6H2-2-OH)]2, marked as L6H2;[CH2N=CH(C6H2-2-OH)]2, marked as L7H2;[CH(Ph) N=CH(C6H2-2-OH)]2, marked as L8H2;[CH(Ph) N=CH(C6H2-2-OH-3, 5-Cl2)]2, marked as L9H2;[CH(Ph) N=CH(C6H2-2-OH-3, 5-But 2)]2, marked as L10H2;[CH(Ph) N=CH(C6H2-2-OH-3, 5-(CMe2Ph) 2)]2, marked as L11H2;The main contents were listed below.1. Synthesis of lanthanide complexes: reactions of Ln(OAr)3 with salen ligands L1H2-L5H2, L7H2, L10H2 and L11H2 gave the neutral lanthanide aryloxides L1Ln(OAr)(THF)2 [Ln = Y(1); Ln = Yb(2)], L2Ln(OAr)(THF)n [Ln = Y(3), n=2; Ln = Yb(4), n=1], L3Y(OAr)(5), L4Y(OAr)(THF)(6), L5Yb(OAr)(THF)(7), L7Y(OAr)(THF)2(8),L10Y(OAr)(9), L11Y(OAr)(10)(OAr=2,6-But2-4-Me C6H2O). Reacion of complex 6 with HMPA afforded complex L4Y(OAr)(HMPA)(11). Reactions of Ln[N(Si Me3)2]3 with salen ligands L3H2, L6H2, L8H2 and L9H2, and then with phenol or alcohols(Ar OH, Ph CH2 OH or Pri OH) gave the lanthanide Salen aryloxo or alkoxo complexes [L3Y(?-OR)]2[R= CH2Ph(12), Pri(13)], L8Y(OAr)(THF)(14), L9Y(OAr)(THF)2(15), [( ?-L6)Ln(OAr)(HMPA)]3[Ln=Y(16), Yb(17), Sm(18)], L6Nd(OAr)(HMPA)2(19). Among these complexes 12, 13 are dinuclear structure, complexes 16, 17, 18 are trinuclear structure. All of these complexes were characterized by elemental analysis, IR analysis, 1H and 13 C NMR analysis for the yttrium complexes only. All of these complexes were characterized by X-ray single crystal diffraction except complexes 6, 10, 11, 13.2. The polymerization behavior of complexes 1-16 was investigated and the influence of the ligand substituents, coordinating solvents and central metals on the catalytic activity and stereoselectivity was also discussed.(1) The substituents on the Salen ligands have a greatly effect on the catalytic activity and stereoselectivity of rac-LA polymerization.Using yttrium complexes that contain a 2, 2-dimethylpropylene bridge between the two Schiff base groups as initiators for the ROP of rac-LA, the decreasing activity order for the substituent groups is But > Cl > H ≈ CMe2 Ph, whereas the decreasing order in heteroselectivity is H(Pr = 0.80) ≈ Cl(Pr = 0.81) > CMe2Ph(Pr = 0.75) > But(Pr = 0.63).However, using yttrium complexes that contain a 1, 2-diphenylethylene bridge in the ligand as initiators for the ROP of rac-LA, the decreasing activity order for the substituent groups is Cl > But > CMe2 Ph > H, and the decreasing order in heteroselectivity is H > Cl >CMe2Ph > But.(2) The bridge groups in the salen ligand have an obvious influence on the catalytic behavior for rac-LA polymerization. The complexes that contain a1,2-diphenylethylene bridge display a higher activity for rac-LA polymerization than those that contain a 2,2-dimethylpropylene or ethylene bridge and the complexes that contain a1,2-diphenylethylene or ethylene bridge show a higher steroselectivity for rac-LA polymerization than those that contain a 2,2-dimethylpropylene bridge.(3) In comparison with complex 6 with a THF coordination, complex 11 with a HMPA coordination exhibitbetter activity and stereoselectivity for rac-LA polymerization.(4) The initiating groups can affect the catalytic activity, but have no obvious effect on the stereoselectivity for rac-LA polymerization.3. The catalytic behavior of complexes 16-19 for the ROP of rac-LA was examined. It was found that the solvent greatly influenced the stereoselectivity for the ROP of rac-LA.The decreasing order in heteroselectivity for different solvent was tetrahydrofuran ≈dimethoxyethane > diethylether > chloroform > hexamethylphosphoramide when complex17 was used as initiator for the ROP of rac-LA. However, the increasing activity activity,17 < 16 < 18, and the decreasing order in heteroselectivity, 17 > 16 > 18, are observed for rac-LA polymerization in THF. The catalytic activity increased with the increase of ionic radius of central metal, while the stereoselectivity decreased.