Novel Rare-Earth Metal Complexes:Synthesis And Catalysis On Highly Stereoselective Polymerization Of Polar Functionalized Olefins

The introduction of polar groups into polyolefin can improve the hydrophilicity,printability and compatibility with other polar materials,and realize the high performance of polyolefin.Coordination copolymerization of polar and non-polar olefin not only reflects mild conditions,but also can control the composition and steric regularity of the copolymer,which is the most direct method to prepare functional polyolefin.However,in the process of coordination polymerization,oxygen,nitrogen,sulfur and other heteroatoms of polar olefin will preferentially coordinate with the central metal of the catalyst and form stable complexes,which will lead to the poisoning and deactivation of the catalyst.In the previous work,it was found that under certain conditions polar olefin can be activated rather than toxic polymerization reaction.The rare earth alkyl complexes with different ligand structures were synthesized and their catalytic polymerization behaviors for various polar ilefins were studied.The specific work content is as follows:（1）Base on theβ-diketiminato ligand,a series ofβ-diketiminato rare-earth metal bisalkyl complexes 1-5 L^1-5Ln（CH2SiMe3）2（THF）n（n=1:Y（1a）,Ln=Gd（1b）,Tb（1c）,Dy（1d）,Ho（1e）,Er（1f）,Tm（1g）,Lu（1h）;n=0:Ln=Sc（1i））were successfully synthesized.In combination with AlⁱBu₃ and[Ph₃C][B（C₆F₅）₄],complexes 1c（Tb）-1g（Tm）exhibited high activities and excellent iso-selectivities for the polymerization of ortho-methoxystyrene（oMOS）,in which,the polar methoxy group of oMOS didn’t poison but activated the polymerization throughσ-πchelation to the active species together with the vinyl group.Moreover,the large Gd-attached precursor 1b showed a higher activity albeit with a slightly decreased isoselectivity.Whereas,the small Sc-attached precursor 1i was completely inert.Meanwhile,the spacial sterics and the coordination mode ofβ-diketiminato ligand could obviously affect and even block oMOS polymerization.This work sheds a new light on the coordination polymerization of polar monomers.（2）Under the activation of AlⁱBu₃ and[Ph₃C][C（C₆F₅）₄],pyridylmethylene fluorenyl yttrium complex（Flu-CH2-Py）Y（CH2SiMe3）2（THF）（6）can catalyze polymerization of ortho-alkoxy-substituted styrenes in high activity.The afforded polymers have a perfect syndiotacticity（rrrr>99%）.Increasing the steric effect of ortho-oxygen substituents of monomers could reduce the activity of the polymerization but do not affect the stereoselectivity.Moreover,the syndioselective copolymerizations of a polar o-alkoxystyrene monomer with styrene have also successfully achieved by using this catalytic system.Changing the steric effect of the ortho-oxygen substituents could adjust the insertion rate of polar styrene and styrene,then control the sequence structure of the obtained copolymer,affording functionalized syndiotactic polystyrene with tapered,gradient and random sequence.These results provide new ideas for the regulation of the composition and sequence structure of copolymers.（3）A series of thiophene-fused cyclopentadienyl scandium complexes 7-9 were successfully synthesized.Combination with alkylaluminium and organoborate,these complexes showed extremely low activity and no selectivity for 1-hexene polymerization.Surprisingly,highly stereo-selective coordination polymerization of unprotected polar 4-methylthio-1-butene has been achieved in high activity for the first time under the same polymerization conditions.High-molecular-weight（M_n=110×10³）and perfectly syndiotactic（rrrr>99%）poly（4-methylthio-1-butene）（P（MTB））was afforded.Thus the methylthio-group-assisted mechanism that the unmasked methylthio group promoted the polymerization throughσ-πchelation to the active scandium center together with the vinyl group was proposed.Moreover,the methylsulfonyl functionalized syndiotactic poly（1-butene）was also easily prepared by the oxidation of P（MTB）.These results provided a new route for the synthesis of functionalized stereo-regular polyolefins.