| In this thesis, a series of bimetallic lanthanide amido complexes stabilized byphenylene bridged bis（β–diketiminate） ligands was synthesized. All of them were wellcharacterized. The influence of reaction conditions and steric effect on the synthesis ofbimetallic amido complexes stabilized by meta-phenylene bridged bis（β–diketiminate）ligands was studied. Furthermore, the catalytic properties of some of these bimetalliccomplexes for the polymerization of lactide, and the polymerization of isopreneincorprated with AlR3and borate were investigated. In addition, the steric effect ofligands and amido groups on the the insertion reaction of these bimetallic lanthanideamido complexes with carbodiimides was explored. The main contents were listedbelow.1. Using para/meta-phenylene bridged bis（β–diketiminate） ligands as ancillaryligands, a series of bimetallic lanthanide amido complexes stabilized by phenylenebridged bis（β–diketiminate） ligands was synthesized. All of them werewell-characterized by elemental analysis, FT-IR and X-ray single crystal diffraction.Structure analyses displayed that all of these bimetallic lanthanide amido complexeshave C2-symmetric bimetallic structure.2. Complexes PARA-{Ln[N（SiMe3）2]2}2（Ln=Nd （1）, Sm （2）, Y （3））,PARACH3-{Ln[N（SiMe3）2]2}2（Ln=Sm （5）, Y （6））, PARA-{Y[NPh2]2（THF）}2（14）,PARA-[Nd（NiPr2）2]2（18）, META-{Nd[N（SiMe3）2]2}2（26） were screened for thering-opening polymerization （ROP） of lactides. It was found that all of these complexescan initiate the ROP of L-lactide in toluene with extremely high activity. The ancillaryligands, amido groups and central metals have profound influence on the catalytic activity. Furthermore, the bimetallic complex18, which bearing smallest amido groups,showed the highest catalytic activity; Compared with complexes2and3, complexes5and6, which bearing less steric hindrance, showed higher catalytic activity. The activityof complexes1and26is similar. In addition, Complexes1and26were also screenedfor the ROP of rac-lactide. It was found that these complexes also can initiate the ROPof rac-lactide in THF at room temperature with high activity, and afforded the resultingpolymers with high molecular weight, but relatively broad PDI. However,microstructural analysis of the resulting polymers revealed that these complexes exerteda moderate level of heterotacticity （Pr=0.65–0.73）. Additionally, the activity ofcomplex26is higher than that of complex1, which revealed that the structure of theligand has an effect on the catalytic activity.3. In the presence of excess AlR3and on activation with1equiv of [Ph3C][B（C6F5）4],complexes PARA-{Y[N（SiMe3）2]2}2（3）, PARACH3-{Ln[N（SiMe3）2]2}2（Ln=Sm （5）, Y（6））, PARA-{Ln[N（HSiMe2）2]2}2（Ln=Sm （9）, Y （10））, METACH3-{Y[N（SiMe3）2]2}2（33） can initiate the cis-1,4-polymerization of isoprene at room temperature with highactivity and selectivity （cis-1,4-seletivity up to93.4%）, respectively. The influences ofpolymerization conditions, cocatalysts, structures of the ligands, amido groups and thecentral metals had been thoroughly investigated. In addition, the polymerization ofisoprene initiated by these ternary catalytic systems was well controlled.4. To elucidate the cooperative effect, the corresponding monometallic complexesL2,6-iPrPh-Y[N（SiMe3）2]2（21） and L2,6-iPrPh-Y[N（HSiMe2）2]2（22） were synthesized. Thepolymerization behavior of the ternary system of complexes3,21,10and22withAliBu3/[Ph3C][B（C6F5）4] for the polymerization of isoprene were studied, respectively.It was found that there is no cooperative effect in the bimetallic system of complexes3and10, which can be attributed to the fact that the distance between two metals in thesetwo complexes is too far.5. By means of X-ray diffraction and1H NMR spectroscopy analyses, theintermediates arising from the stoichiometric reactions, and the probable active specieswere elucidated. It was found that the reaction of complex22with AlMe3can afford L2,6-iPr2MeY[（μ-Me）2AlMe2]2（23）.1H NMR monitoring reaction of complex23with[Ph3C][B（C6F5）4] revealed that [LPh2,6-iPr]Y[（μ-Me）2AlMe2][B（C6F5）4] should be theintermediate of this polymerization system.6. The influences of reaction conditions, structures of ligands and central metals hadbeen thoroughly investigated for the synthesis of bimetallic latnanide amido complexesstabilized by meta-phenylene bridged bis（β–diketiminate） ligands. It was found that thereaction of META-H2with Ln[N（SiMe3）2]3（μ-Cl）Li（THF）3in a1:2mole ratio in THF at60°C can afford the heterobimetallic complexes [Li（THF）]META{Ln[N（SiMe3）2]2}（Ln=Nd （28）, Sm （29）, Yb （30）） in moderate yields. However, for the lanthanidemetals with large ionic radii, the same reactions performed in toluene at90°C affordedMETA-{Ln[N（SiMe3）2]2}2（Ln=Nd （26）, Sm （27））. But the reaction for Yb onlyafforded complex30. Further investigation revealed that the reaction of less sterichindrance ligand METACH3-H2with Ln[N（SiMe3）2]3（μ-Cl）Li（THF）3in a1:2mole ratioin toluene at90°C afforded the desired bimetallic lanthanide amido complexesMETACH3-{Ln[N（SiMe3）2]2}2（Ln=Nd （31）, Sm （32）, Yb （33）） as the only product.These results confirmed that the steric bulkiness of the preligand has a profound effecton the synthesis of bimetallic latnanide amido complexes stabilized by meta-phenylenebridged bis（β–diketiminate） ligands.7. The reaction of META-H2with NaH in a1:2mole ratio in THF at60°C can affordMETA-[Na（THF）2]2（24） in high yield. The influences of reaction conditions, and thecentral metals had been thoroughly investigated for the reaction of complex24with{Ln（μ-Cl）[N（SiMe3）2]2（THF）}2. It was found that, for La and Nd, the reaction couldafford lanthanide bis（amido） complexes META-{Ln[N（SiMe2）2]2}2（Ln=La （25）, Nd（26））, whereas, for Y and Yb, the reaction produced{Ln[N（SiMe3）2]2}META{Ln[N（SiMe3）2]Cl（THF）}（Ln=Y （35）, Yb （36））. Theseresults revealed that the ionic radii of lanthanide metals have a profound effect on theformation of bimetallic bis（amido） complexes stabilized by meta-phenylene bridgedbis（β–diketiminate） ligands. Presumably, the steric effect plays a dominated role on theformation of the above complexes. 8. Attempts to synthesize the complex META-{Ln[N（SiMe3）2]2}2by the reaction ofMETA-H2with Ln[N（SiMe3）2]3in a1:2mole ratio in toluene at110°C wereunsuccessful, and the unexpected complexes {Ln[N（SiMe3）2]}2（META’）（μ-Cl）（Ln=Y（37）, Yb （38）, Nd （39）, Sm （40）） were isolated in moderate yields via C-H bondactivation of the arene ring, which should be attributed to the presence of impurity in thestarting material Ln[N（SiMe3）2]3. Further1H NMR monitoring reaction confirmed thatcomplexes35and36can be converted to complexes37and38under suitableconditions. Thus, complexes35and36should be the intermediates for the formation ofcomplexes37and38.9. The reactive behavior of the bimetallic bis（amido） complexes with carbodiimideshad been thoroughly investigated. By means of1H NMR monitoring technology, it wasfound that the complexes PARACH3/PARA-{Y[N（SiMe3）2]2}2have no activity towardsthe carbodiimides. However, for PARA-{Ln（NPh2）2（THF）}2, which bearing smalleramido groups, can react with carbodiimides to give the diinsertion productsPARA-{Ln（NPh2）[RNC（NPh2）NR]}2. Furthermore, for PARACH3-{Y（NPh2）2（THF）}2,which bearing less steric hindrance ligand, can react with carbodiimides to givetetrainsertion products PARACH3-{Ln[RNC（NPh2）NR]2}2. These results revealed thatthe steric effect play a dominated role on the reaction of these bimetallic amidocomplexes with carbodiimides. |
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