Synthesis And Characterization Of Rare-earth Metal Complexes Supported By Schiff-base Ligands And Their Performance In The Stereospecific Ring-opening Polymerizatioin Of Rac-lactide

In this paper, using bridged Schiff-base ligand(salen type ligand) O[C6H4-N=CH(2-OH-3,5-But2C6H2)]2 and ?-ketoiminato ligands(C6H5)COCH=C(CH3)NH-4-OCH3-C6H4、(C6H5)COCH=C(CH3)NH-2-OCH3-C6H4 as ancillary ligands, 22 rare-earth metal complexes were synthesized and all of them were characterized by X-ray single crystal diffraction,elemental analysis and FT-IR, as well as 1H and 13 C NMR for the scandium and yttrium complexes. Furthermore, the catalytic behavior of some of these rare-earth metal complexes for the ring-opening polymerization of rac- lactide was also studied. The main results are summarized as follows:1. Reactions of L1Na2(L1H2 = O[C6H4-N=CH(2-OH-3,5-But2C6H2)]2) and Ln Cl3(Ln = Sc, Yb, Y, Sm, Nd) afforded salen rare-earth metal complexes L1 Ln Cl(THF)n [Ln = Sc(1), n=0; Yb(2), n=0; Y(3), n=1; Sm(4), n=1; Nd(5), n=1].2. The amine elimination reactions of bridged Schiff-base ligand O[C6H4-N=CH(2-OH-3,5-But2C6H2)]2(L1H2) with Ln[N(Si Me3)2]3 were investigated, and two salen rare-earth metal amido complexes L1 Ln N(Si Me3)2(Ln = Yb(6), Y(7)) were synthesized.3. Proton exchange reactions of bridged Schiff-base ligand O[C6H4-N=CH(2-OH-3,5-But2C6H2)]2(L1H2) with Ln(OAr)3(THF)(Ar O = 2,6-But-4-Me C6H2O) afforded salen rare-earth metal complexes L1 Ln OAr(THF)n [Ln = Sc(8), n=0; Yb(9), n=0; Y(10), n=1; Sm(11), n=1; Nd(12), n=1] which can also be synthesized by metathesis reactions of salen rare-earth metal complexes 1-5 with Na OAr.4. The amine elimination reactions of L1H2 with Ln[N(Si Me3)2]3 and then with p-methyl phenol and HOCH2CH2OCH3, respectively, produced the salen rare-earth metal aryloxide complex L1Yb(OC6H4-4-Me)(13) and the salen rare-earth metal alkoxo complex [L1Y(OCH2CH2OCH3)]2(14) in high isolated yield.5. Treatments of β-ketoiminate ligand(C6H5)COCH=C(CH3)NH-4-OCH3-C6H4(HL2) with Ln[N(Si Me3)2]3(Ln = Yb 、 Y 、 Sm 、 Nd) afforded three amido complexes L22 Ln N(Si Me3)2(Ln = Y(15) 、Sm(16) 、Nd(17)) and a homoleptic complex Ln L23(18).6. Treatments of the ?-ketoiminate ligand(C6H5)COCH2C=(CH3)NH-4-OCH3-C6H4(HL2) with 0.5 equiv. of(Ar O)3Ln(THF) afforded two rare-earth metal aryloxides bearing two ?-ketoiminato ligands [Ln L22(OAr)(Ln = Y(19)、Nd(20))].7. Similarly, treatments of the ?-ketoiminate ligand(C6H5)COCH2C=(CH3)NH-2-OCH3-C6H4(HL3) with 0.5 equiv. of(Ar O)3Ln(THF) afforded two rare-earth metal complexes bearing two different ?-ketoiminato ligands [ Ln L32(OAr)(Ln = Y(21)、Nd(22))].8. The schiff base rare-earth metal complexes 6-17, 19-22 could initiate the polymerization of rac- lactide under mild conditions. The decreasing order of observed activity is in agreement with the decreasing order of the ionic radii of the central metals, whereas the increasing order in stereoselectivity follows the decreasing order of the ionic radii. The ytterbium salen rare-earth metal complexes 6、13 show relatively poor catalytic activity, but displayed the better stereoselectivity(Pr up to 0.90).