Synthesis of Nickel and Palladium Complexes Based on Aryloxide Imidazolidin (Imidazolin)-2-Imine Ligands and Their Application in Cyclic Olefin (Co) Polymerizations

Author:Li Ming Yuan

Supervisor:cai zheng guo

Database:Doctor

Degree Year:2019

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Pages:196

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Norbornene-based cyclic olefin copolymers as a class of polyolefin,have outstanding performance,such as high glass transition temperature,good chemical and UV resistance,excellent transparency,which can be easily tailored by changing the microstructure of polymers.The incorporation of very low amount of polar functional groups on the polymer backbone can greatly improve the surface property of these copolymers,so that the application of the norbornene-based materials can be further extended.The late transition-metal catalysts,because of their lower oxophilicity than those of early transition metal catalysts,provide great potential for the direct copolymerization of olefin with polar monomers.A milestone discovery was made in 1995 by Brookhart et al.,who reported the direct copolymerization of ethylene and acrylate monomer withα-diimine nickel and palladium catalysts.Later in the 2000s,neutral salicylaldimine nickel catalysts were reported by Grubbs et al.,which are capable for the copolymerization of ethylene with a few other special polar monomers.Subsequently,late transition metal catalyst has obtained the unprecedented development.Although researchers have paid a great amount of efforts on modifing warious ligand scaffolds and many pioneering achievements have been made in the past few decades,the drawbacks,such as low activity and molecular weight,uncontrollable comonomer content,regional selectivity and stereotactic regularity are still hindering the further research on late transition metal catalysts.Therefore,desigin of novel nickel and palladium olefin polymerization catalysts,by synthesis of novel ligand structures,with high activity,long lifetime,good tolerance toward heteroatoms and excellent copolymerization performance is an effective way to solve the above problems.This paper mainly focuses on this issue.In chapter 2,a series of novel[N,O]bidentate aryloxide imidazolidin-2-imine ligands L1-L3and their neutral nickel complexes Ni1-Ni3 were synthesized and characterized.The coordination ability of the novel imidazolidine-2-imide ligands was confirmed by X-ray diffraction analysis results along with the comparison among salicylaldimine framework,aryloxide N-heterocyclic carbene framework and aryloxide imidazolidin-2-imine framework.The chelating ligand,the type and ratio of cocatalyst,and temperature showed significant influences on the polymerization activities and the properties of PNBs in these catalytic systems.In the presence of various cocatalysts such as MAO,MMAO,Et2AlCl and EtAlCl2,all of the nickel complexes exhibited remarkably high activities toward the addition polymerization of norbornene to give high-molecular-weight PNBs.Under the same conditions,the Ni/MAO catalystic system exhibited the highest activity.The highest activity of complexes Ni1,Ni2 and Ni3 are 1.48×106g·mol-Ni-1·h-1,1.36×106 g·mol-Ni-1·h-11 and 1.34×106 g·mol-Ni-1·h-1,respectively.The highest high molecular weight Mn of resulted PNBs is 7.45×106 g·mol-1 with a narrow PDI(1.21-1.58).The activity of these aryloxide imidazolidin-2-imine nickel catalysts in norbornene homopolymerization is similar to those of the aryloxide NHCs nickel catalysts,but slightly lower than those of the salicylaldimine nickel catalysts.This is the first example,to the best of our knowledge,of neutral nickel complexes bearing aryloxide-functionalized imidazolidin-2-imine ligands in the field of olefin polymerization.In chapter 3,a series of novel palladium complexes Pd1-Pd3 bearing aryloxide imidazolidin-2-imine ligands were synthesized,characterized and applied in the polymerization of norbornene.The the chelating ligand,the type and ratio of cocatalyst,and temperature showed significant influences on the polymerization activities and the properties of PNBs in these catalytic systems.Upon activation with MAO,all of the palladium complexes exhibited high avtivity and good thermal stability.The Pd1/MAO catalystic system exhibited the highest activity of 2.63×107 g·mol-Pd-1·h-1 with an Al/Pd ratio of 9000 at 60 oC.The activity of Pd1/MAO catalystic system is still above 107 g·mol-Pd-1·h-1 at 80 oC.The activities of this aryloxide imidazolidin-2-imine palladium/MAO catalystic system in norbornene homopolymerization are similar to those of the aryloxide NHCs palladium/MAO catalystic system and the salicylaldimine palladium/MAO catalystic system.However,all the PNBs otbtained by Pd/MAO catalystic system shoewed very poor solubility,the molecular weight and distribution information can not be obtained by GPC mothed.Moreover,soluble PNBs can be obtained by the Pd/EtAlCl2 system.The Pd1/EtAlCl2 catalystic system exhibited the highest activity of 1.21×107 g·mol-Pd-1·h-1 at 40oC.The activity of Pd1/EtAlCl2 catalystic system is still above 107 g·mol-Pd-1·h-1 at 80 oC.The highest high molecular weight Mn of resulted polynorbornene is 3.27×105 g·mol-1 with a narrow DPI(1.58-2.00).The activity of complexes Pd2 and Pd3,under the same conditions,are 1.21×107 g·mol-Pd-1·h-1 and 1.16×107 g·mol-Pd-1·h-1,respectively.The activity of this aryloxide imidazolidin-2-imine palladium/EtAlCl2 catalystic system in norbornene homopolymerization is similar to that of the aryloxide NHCs palladium/Et2AlCl catalystic system.However,the molecular weight Mn significantly higher than the latter,suggesting the excellent catalystic ability of these palladium catalysts.In chapter 4,a series of novel aryloxide imidazolin-2-imine bidentate ligands L4-L6 and their neutral nickel complexes Ni4-Ni6 with bulkier substituents on the imidazolin-2-imine ligand were synthesized and characterized.In the presence of B(C6F5)3,these nickel complexes exhibited remarkably high activity and particularly good thermal stability toward the addition polymerization of norbornene.The highest activities of Ni4(2.69×107 g·mol-Ni-1·h-1),Ni5(2.11×107 g·mol-Ni-1·h-1),and Ni6(1.81×107 g·mol-Ni-1·h-1)were obtained at 40°C and 60°C,respectively.Morever,all of the nickel complexes still maintained high activity(107 g·mol-Ni-1·h-1)even at 80°C.Ni4 bearing a 2,4,6-trimethylphenyl substituent showed higher activity and higher molecular weight in comparison to complexes Ni5 and Ni6 at the same polymerization temperature range from 25 to 80°C,and the activity and Mn is both in the following order:Ni4>Ni5>Ni6.Most importantly,these catalysts were able to promote the direct copolymerization of norbornene with various polar monomers,such as allyl acetate,allyl ethyl ether,allyl benzene,and some OH/COOMe/Br/Cl-containing long-chain monomers,with high activity(3.7-16.9×104g·mo-Ni-1·h-1),reasonable comonomer incorporation(0.14-3.08 mol%),and high copolymer molecular weight(Mn=5.31-19.76×104 g·mol-1).The glass ring transition temperature Tg of some copolymers ranged from 324.8 to 328.2°C,which is lower that of the norbornene homopolymer.According to the TGA data,all of the copolymers exhibited similar thermal stabilities and decomposition temperatures(Td)up to 421.5°C,suggesting the good thermal stability of the copolymers prepared in this catalytic system.In chapter 5,a series of novel palladium complexes Pd4-Pd6 bearing aryloxide imidazolin-2-imine ligands were synthesized,characterized and applied in the polymerization of norbornene.In the presence of very low EtAlCl2 loadings(100 equiv.),these palladium complexes exhibited high activity(106 g·mol-Pd-1·h-1)and good thermal stability toward the addition polymerization of norbornene to gave polynorbornene with high molecular weight and good solubility at room temperature.The polymerization temperature significantly influenced the activity,where the highest activities of Pd4(1.36×106 g·mol-Pd-1·h-1),Pd5(1.34×106g·mol-Pd-1·h-1),and Pd6(1.54×106 g·mol-Pd-1·h-1)were obtained at 40°C,60°C and 80°C,respectively.Morever,both complexes Pd5 and Pd6 still maintained high activity(106g·mol-Pd-1·h-1)even at 100°C.Most importantly,these Palladium catalysts were able to promote the copolymerization of norbornene with 1-dodecene and 1-octadecene with high activity(105g·mol-Pd-1·h-1)to yield moderate-molecular-weight(Mn≈104 g·mol-1)copolymers.The 1-alkene incorporation of resulting copolymers was modulated in a wide range(5.1–15.3 mol%)by changing comonomer feed ratio,accompanied by the control of the glass transition temperature(Tg=231.6-309.6 oC),which is also lower that of the norbornene homopolymer(Tg>400oC).This is the first example,to the best of our knowledge,of palladium complexes bearing aryloxide imidazolin-2-imine ligands in the copolymerization of norbornene and higherα-olefins.