Synthesis, Characterization And Catalytic Behavior Of Anthanide Complexes Supported By Amine Bridged Bis(Phenolate)

Using amine bridged bis（phenolate） as ancillary ligands,31lanthanide complexes weresynthesized. All of these complexes were characterized by elemental analysis, IR, andX-ray single crystal diffraction, as well as1H and13C NMR for the yttrium complexes. Theinfluence of the ligands and lanthanide metals on the synthesis, stability and reactivity ofthe bis（phenolate） lanthanide derivatives were elucidated. Furthermore, the catalyticbehavior of some of these lanthanide complexes for the polymerization of rac-lactide（rac-LA） and rac-β-butyrolactone （rac-BBL） were studied.The amine bridged bis（phenol）s ligands used in this thesis are:Me₂NCH₂CH₂N[CH₂-（2-OH-C₆H₂-Bu^t₂-3,5）]₂, abbreviated as L1H₂;Me₂NCH₂CH₂N[CH₂-（2-OH-C₆H₂-Me2-3,5）]₂, abbreviated as L²H₂;Me₂NCH₂CH₂N（2-OH-C₆H₂-Me2-3,5）（2-OH-C₆H₂-Bu^t₂-3,5）, abbreviated as L³H₂;Me₂NCH₂CH₂N（2-OH-C₆H₂-Cl2-3,5）（2-OH-C₆H₂-Bu^t₂-3,5）, abbreviated as L⁴H₂;MeOCH₂CH₂N[CH₂-（2-OH-C₆H₂-Bu^t₂-3,5）]₂, abbreviated as L5H₂;（CH₂）₃OCHCH₂N[CH₂-（2-OH-C₆H₂-Bu^t₂-3,5）]₂, abbreviated as L6H₂;BunN[CH₂-（2-OH-C₆H₂-Bu^t₂-3,5）]₂, abbreviated as L⁷H₂;[CH₂N（Me）CH₂-（2-OH-C₆H₂-Bu^t₂-3,5）]₂, abbreviated as L⁸H₂;（2-OH-C₆H₂-Bu^t₂-3,5）CH=NCH₂CH₂N（Me）CH₂（2-OH-C₆H₂-Bu^t₂-3,5）,abbreviated as L⁹H₂;（2-OH-C₆H₂-Bu^t₂-3,5）CH=NCH₂CH₂N（Me）CH₂[2-OH-C₆H₂-（CPhMe₂）2-3,5],abbreviated as L¹0H₂;（2-OH-C₆H₄）CH=NCH₂CH₂N（Ph）CH₂（2-OH-C₆H₂-Bu^t₂-3,5）, abbreviated as L¹¹H₂;（2-OH-C₆H₂-Bu^t₂-3,5）CH=NCH₂CH₂N（Ph）CH₂（2-OH-C₆H₂-Bu^t₂-3,5）, abbreviated as L¹²H₂.The main contents were listed below.1. Reactions of （C₅H₅）₃Ln（THF） with amine bridged bis（phenol）s^L2H₂-L⁴H₂, whichhave different substituents on the ligands framework, and then with p-cresol gave theneutral lanthanide aryloxides [L²Y（OC₆H₄-4-CH₃）]₂（1）,[L2Yb（OC₆H₄-4-C₃）]₂（2）,[L³Y（OC₆H₄-4-CH₃）]₂（3）,[L⁴Y（OC₆H₄-4-CH₃）]₂（4）. X-ray diffraction confirmed thatthese complexes have dinuclear structures, and bridging atoms are the oxygen atoms fromamine bridged bis（phenolate） groups. It was found that these complexes are efficientinitiators for rac-LA polymerization, producing PLAs with heterotactic bias. Theintroduction of sterically demanding substituents on the phenyl ring prompts thepolymerization stereoselectivity. Central metals have crucial influence on thepolymerization stereoselectivity, the ytterbium aryloxide complex2（Pr=0.91） showedbetter stereoselectivity than the yttrium complex1（Pr=0.73）.2. Reactions of （C₅H₅）₃Y（THF） with amine bridged bis（phenol）s L⁵H₂-L⁸H₂, whichhave different amine bridge on the ligands framework, and then with p-cresol gave thelanthanide aryloxides [L⁵Y（OC₆H₄-4-C₃）]₂（5）,[L⁶Y（OC₆H₄-4-C₃）]₂,[HL⁷Y（OC₆H₄-4-C₃）2（THF）2]（7）,[L⁸Y（OC₆H₄-4-C₃）]₂（8）. X-ray diffraction showedthat complexes5,6and8have dinuclear structures, and bridging atoms are p-cresolaryloxide oxygen atoms. When the amine bridged bis（phenol） without a pendant donorgroup on the bridge L7H₂was used, a zwitterionic complex7was isolated. Reactions of（C₅H₅）₃Ln（THF）（Ln=Y, Yb） with amine bridged bis（phenol）s L⁵H₂and L⁸H₂, and thenwith2,6-diisopropylphenol gave the mononuclear lanthanide aryloxides[L⁵Y（OC₆H₃-2,6-Pri₂）（THF）]（9）,[L⁵Yb（OC₆H₃-2,6-Pri₂）（THF）]（10）,[L⁸Y（OC₆H₃-2,6-Pri₂）（THF）]（11）. The catalytic behavior of these complexes towardsrac-LA polymerization was investigated. Complex7showed very poor activity, whereasthe other complexes showed similar activity. When the pendant donor group isN,N-dimethyl, the corresponding complex gave the best stereoselectivity.3. Reactions of （C₅H₅）₃Ln（THF）（Ln=Y, Yb, Er, Sm） with L¹H₂, and then with different alcohols gave the lanthanide alkoxides L¹Ln（OCH₂CF₃）（THF）[Ln=Y（12）, Yb（13）, Er （14）, Sm （15）], L1Y（OCH₂Ph）（THF）（16）, L¹Y（OPri）（THF）（17）. NMR tubemonitoring reaction showed that both the acidity of the alcohols and the ionic radii of thelanthanide metals have significantly influence on the proton exchange reaction. Thesecomplexes represented very few examples of crystallographically characterized lanthanidealkoxide complexes bearing amine bridged bis（phenolate） in the literature. Theselanthanide alkoxides are sensitive to moisture, and the yttrium complex[（L¹Y）₂（μ-OPri）（μ-OH）]（18） was also isolated as a byproduct during the synthesis ofcomplex17. It was found that complexes12-17can initiate efficiently the ring-openingpolymerization of rac-LA and rac-BBL in a controlled manner. For rac-LA, thepolymerization gave the PLA with very narrow molecular weight distributions （PDI≤1.12）, and very high heterotacticity （Prup to0.99）. The observed activity increasing orderis in agreement with the order of the ionic radii, whereas the order for stereoselectivity is inreverse order. For rac-BBL polymerization, the resultant PHB have narrow moleculardistributions （PDI≤1.26）, and high syndiotacticity （Prup to0.83）. It is worthy to note thatthe activity decreasing order, Yb> Er> Y>> Sm, is observed for rac-BBL polymerization,which is opposite to the order of ionic radii, and to the order of activity for rac-LApolymerization.4. Reactions of （C₅H₅）₃Ln（THF）（Ln=Y, Yb, Sm） with L¹H₂, and then with benzoicacid gave the lanthanide carboxylates L¹Ln（OCOPh）（THF）[Ln=Y （19）, Yb （20）, Sm（21）]. The ligands redistribution reaction was not observed, although the acidity of benzoicacid is strong. Complexes19-21were inert toward the ROP of rac-LA and rac-BBL.5. Salalen-type ligand was introduced in organolanthanide chemistry for the firsttime. The amine elimination reactions of Ln[N（SiMe₃）₂]₃（μ-Cl）Li（THF）3with Salalen-typeligands L⁹H₂were investigated, and a series of neutral lanthanide amido complexesL⁹LnN（SiMe3_）2（THF）（Ln=Y （22）, Sm （23）, Nd （24）） were synthesized. Reactions of thelanthanide amides with benzyl alcohol produced the dimeric lanthanide alkoxo complexes（L⁹LnOCH₂Ph）₂[Ln=Y （25）, Sm （26）] in high isolated yield, which can also be synthesized using （C₅H₅）3Ln（THF） as the precursors. The proton exchange reactions ofL⁹H₂-L¹²H₂with （C₅H₅）₃Ln（THF）（Ln=Y, Sm, Yb）, and then with alcohol or phenol gavethe desired lanthanide alkoxides or aryloxides [L⁹Sm（OCH₂CF₃）]₂（27）,[L⁹Yb（OCH₂Ph）]₂（28）,[L¹⁰Y（OCH₂Ph）]₂（29）,[L¹⁰Sm（OC₆H₄-4-C₃）]₂（30）,[L¹¹Y（OCH₂Ph）]₂（31）. It wasfound that these complexes showed very poor activity toward the ROP of rac-BBL, butdisplayed good activity and stereoselectivity for the ROP of rac-LA, giving PLAs withmoderate to good heterotacticity. The neodymium amide24showed the highest catalyticactivity, whereas the yttrium complex22showed the best stereoselectivity. Introduction ofsterically demanding substituents on the phenol ring has no obvious effect on thestereocontrollability for rac-LA polymerization.