Arylamide-Ligated Rare-Earth Metal Complexes:Synthesis,Structure,and Catalytic Properties In The Polymerization Of Vinyl Monomers

In this thesis,a series of arylamide-ligated rare-earth metal complexes were synthesized and characterized by using pyrrole-modified or phenyl-bridged arylamides as auxiliary ligands.The polymerization behaviors of the rare-earth metal complexes bearing pyrrole-modified arylamide ligands for styrene and 2-vinylpyridine were studied.The polymerization performance and cooperative effect of the bimetallic arylamide-ligated rare-earth metal complexes for the stereoselective polymerization of 2-vinylpyridine were investigated.The specific works are as followings:1.Acid-base reaction of the pyrrole-modified arylamide ligands 2,5-Me₂C₄H₂NSiMe₂NHC₆H₄R（R=H,Cl-p,MeO-p）with 1 equiv.of Ln（CH₂C₆H₄NMe₂-o）₃ in toluene gave（2,5-Me₂C₄H₂NSiMe₂NC₆H₅）Ln（CH₂C₆H₄NMe₂-o）₂（Ln=Sc（1）,Y（2）,Lu（3））,（2,5-Me₂C₄H₂NSiMe₂NC₆H₄Cl-p）Y（CH₂C₆H₄NMe₂-o）₂（4）,and（2,5-Me₂C₄H₂NSiMe₂NC₆H₄OMe-p）Y（CH₂C₆H₄NMe₂-o）₂（5）.These complexes were well-characterized by elemental analysis and NMR spectroscopy.1,2 and 4 were structurally determined by single-crystal X-ray diffraction.It was found that there was no interaction between the pyrrole ring and central metals in complexes 1-5.The catalyst systems of 1-5/AlⁱBu₃/[Ph₃C][B（C₆F₅）₄]were able to promote styrene polymerization to afford pure and highly syndiotactic polystyrene（rrrr>99%）.Among them,complex 4 with the cheap central metal yttrium promoted the polymerization in a controlled fashion,and showed much higher activity than the expensive scandium analogue 1.In addition,complex 1-5 had good activity for 2-vinylpyridine polymerization,and the polymerization activity of complex 4 could reach up to11520 h^-1（TOF）.2.Acid-base reaction of 1,4-（C₆H₅NH）₂C₆H₄ with 2 equiv.of Ln（CH₂SiMe₃）₃（THF）₂ or Ln（CH₂C₆H₄NMe₂-o）₃ in THF gave the bimetallic arylamide-ligated rare-earth metal alkyl complexes[1,4-（C₆H₅N）₂C₆H₄][Ln（CH₂SiMe₃）₂（THF）₂]₂（Ln=Sc（6）,Lu（7）,Y（8））,and aminobenzyl complexes[1,4-（C₆H₅N）₂C₆H₄][Ln（CH₂C₆H₄NMe₂-o）₂（THF）_x]₂（Ln=Sc（9）,x=0;Lu（10）,Y（11）,x=1）.To reveal the polymerization differences between the bimetallic and monometallic rare-earth metal complexes,the mono-arylamide-ligated scandium complex[（C₆H₅）₂N]Sc（CH₂C₆H₄NMe₂-o）₂（12）was prepared by the reaction of Sc（CH₂C₆H₄NMe₂-o）₃with one equivalent amount of diphenylamine（C₆H₅）₂NH.All these rare-earth metal complexes were characterized by elemental analysis and NMR spectroscopy.The molecular structures of complexes 9 and 11 were authenticated by single-crystal X-ray diffraction.When the center metals are Lu³⁺and Y³⁺or the active group is-CH₂SiMe₃,the two rare-earth ions are on the opposite side of the ligand skeleton;when the center metal is Sc³⁺and the active group is aminobenzyl,the two rare-earth ions are on the same side of the ligand skeleton.Complexes 7,8,10 and 11 alone were highly active for iso-specific polymerization of 2VP,and the iso-selectivity mm could be improved up to 96%on activated with two equivalents of[Ph NMe₂H][B（C₆F₅）₄].In comparison,the bimetallic scandium complexes 6 and 9 showed relatively poor activity toward 2-vinylpyridine polymerization.The stereo-selectivity was ready to switch from iso-specific to syndio-specific on addition of organic borate.The polymerization proceeded through the group transfer mechanism experimentally verified by MALDI-TOF of the oligomer.Preliminary results indicated that the binuclear rare-earth complexes exhibit higher polymerization activity than the mononuclear analogues,which might mainly stem from the cooperative effect.