Synthesis Of Phosphinobenzenamine Nickel And Palladium Complexes And Their Application In Olefin (Co) Polymerizations

Polyolefin materials have become a kind of the largest and most widely used synthetic polymer material due to their low cost,excellent comprehensive performance,and easy processing.The introduction of a small amount of polar functional groups to the polyolefin backbone can improve the polyolefin properties such as excellent adhesion,compatibility,and printability to expand their further application range.the preparation of functional polyolefins by the direct copolymerization of olefins and polar monomers is the simplest and most effective way.In recent years,a large number of studies have shown that the interaction between the central metal and the polar heteroatoms through the change of the catalyst skeleton structure and the precise regulation of the steric hindrance effect and electron effect of the ligand substituent group is the key to the development of efficient post-transition metal catalysts.Among them,most post-transition metal catalysts mainly adopt the method of introducing a large steric hindrance substituent to the ligand to achieve effective shielding of the axial position of the central metal,but this method has the disadvantages of complex synthesis and high cost.Therefore,metal-organic complexes that design a new ligand skeleton structure based on the electron effect and supplemented by steric hindrance effect have become another option for the development of efficient post-transition metal catalysts.In this study,thirteen nickel and palladium metal complexes of phosphinobenzenamine ligands with strong feeding capacity were synthesized and applied to catalyze the copolymerization of olefins and polar monomers,the influence of ligand structure and various polymerization parameters on catalytic performance was systematically studied,focusing on revealing the influence mechanism of the electron effect of ligands on the copolymerization of olefins and polar monomers,which provided a good theoretical basis for the development of efficient post-transition metal catalysts,the research content is mainly divided into the following points:In chapter 2,starting from the traditional skeleton structure of phosphino-phenolate catalyst,replacing the original oxygen atom with a nitrogen atom with lower electronegativity to enhance the electron donating of the ligand,by introducing different aryl substituents on the phosphine atoms,the axial shielding effect of the metal center is increased.five new N^P phosphinobenzenamine ligands L1-L5 and their palladium complexes Pd1-Pd5 were synthesized and characterized.The single crystal test results of complexes Pd1,Pd2 and Pd4 showed that palladium atoms adopted a coordination method close to the plane,while ligands containing different substituents had a buried volume percentage(V_bur)of 46.9%-51.7%for palladium atoms.With the activation of Na BAr F,Pd4 with methoxy-substituted showed the highest catalytic activity among all palladium complexes(1.38×10⁵ g mol^-1 h^-1),and obtained a high molecular weight(1.32×10⁶g mol^-1)norbornene homopolymer.However,Pd4/Na BAr F system cannot catalyze the copolymerization of norbornene and methyl acrylate.This class of palladium catalysts showed excellent thermal stability in the homopolymerization of ethylene,and Pd2 achieved the highest activity at 100°C,reaching 4.92×10⁵ g mol^-1 h^-1.This palladium catalyst can prepare semi-crystalline polyethylene containing unsaturated double bonds,with a molecular weight range of 2.35×10³ g mol^-1-7.67×10³ g mol^-1.In addition,these palladium catalysts also exhibit excellent polar monomer tolerance,Pd2 can catalyze the effective copolymerization of ethylene and methyl acrylate to obtain a copolymer with the polar monomer insertion rate of 0.1 mol%,Pd5 can catalyze the copolymerization of ethylene and 5-hexenyl acetate to obtain a copolymer with an insertion rate of 1.85 mol%,and maintain high catalytic activity(1.14×10⁴ g mol^-1 h^-1)and molecular weight(5.48×10³ g mol^-1).These palladium catalysts are significantly higher than the N^P palladium catalyst reported in the literature in terms of ethylene homopolymerization activity and molecular weight,and the effective copolymerization of ethylene and polar monomer catalyzed by N^P palladium catalyst is realized for the first time,which proves the rationality of the design of the new phosphinobenzenamine ligand.However,this kind of palladium catalyst still has some gaps compared with the classical catalyst structure in terms of polymerization activity,polymer molecular weight and polar monomer insertion rate,which may be caused by weakening the coordination ability of palladium atoms and ethylene monomers by the highly electronic phosphinobenzenamine ligand.As a result,this phosphinobenzenamine ligand is expected to play its role in nickel-metal catalytic systems with more aerophilic.In chapter 3,based on the above results,the corresponding nickel complexes Ni1-Ni5 were successfully synthesized using the ligands obtained in Chapter 2.The single crystal test results of Ni1-Ni5 showed that Ni atoms coordinated with ligands in a twisted tetrahedral manner,and the V_bur of palladium atoms by ligands containing different substituents was 44.7%-57.1%.In the presence of MAO,the nickel complex showed good thermal stability for the homopolymerization of norbornene,and the highest activity reached 3.88×10⁶ g mol^-1 h^-1at 80°C.This nickel catalyst can also catalyze the effective copolymerization of norbornene and methyl acrylate,Ni1 achieved the highest copolymerization activity(3.76×10⁵ g mol^-1 h^-1),and Ni3 obtained the highest molecular weight(6.2×10⁴ g mol^-1),the highest insertion rate of methyl acrylate in the copolymer product was 6.47 mol%.This class of highly powered phosphinobenzenamine ligands also gives nickel catalysts excellent ethylene polymerization capabilities.The highest activity of ethylene homopolymerization catalyzed by the Ni/MAO system reached 2.64×10⁵ g mol^-1 h^-1,and the introduction of steric hindrance substituents on the ligand could effectively prevent the chain transfer reaction,which significantly increased the molecular weight of polyethylene products,up to 5.61×10⁵ g mol^-1.Polyethylene obtained from different nickel catalysts also has differences in chain structure,and products dominated by long branched chains or ethyl branched chains can be obtained.More importantly,the catalysts Ni2 and Ni3 can also be used to catalyze the copolymerization of ethylene and methyl acrylate,obtaining polar functionalized polyethylene with high molecular weight(～10⁴ g mol^-1)and high polar monomer insertion rate（up to 15.5 mol%）,and the polar functional group units in the molecular chain can be selectively distributed in the polymer chain and at the end of the molecular chain according to the regulation of ethylene polymerization pressure.Compared with the palladium catalyst in Chapter 2,increasing the electrophilicity of the metal center is conducive to the coordination of the olefin double bond with the metal center,so the nickel catalyst exhibits higher ethylene polymerization activity than the palladium catalyst.In terms of the insertion rate of polar monomers,the interaction between the methyl acrylate double bond with the metal center is stronger,so the nickel catalytic system can obtain a copolymer with a higher insertion rate.At the same time,the nickel catalytic system also has a significant improvement in the molecular weight of homopolymer and copolymer compared with the palladium catalytic system.However,the results of density functional theory（DFT）calculations showed that the weak electrophilicity in the nickel center metal also affected the coordination ability of the double bonds and center mental,resulting in the copolymerization activity of ethylene and methyl acrylate was lower than that of the reported nickel phosphino-phenolate catalyst(10⁴ g mol^-1 h^-1 vs.10⁵ g mol^-1h^-1),but there was a great improvement in MA insertion rate（15.5 mol%vs.7.6 mol%）.The above results prove that the rational regulation of the central metal electron effect and the ligand electron and steric hindrance effect can achieve a significant improvement in catalytic performance.Combined with the results of the above two chapters,in the chapter 4,we further regulate the substituents on the ligand nitrogen atoms,introduce a benzene ring with conjugation effect to the ligand nitrogen atom to buffer the electronization of the ligand skeleton,synthesize novel ligands L6 and L7 and nickel complexes Ni6,Ni6’and Ni7,respectively,and carry out structural characterization.The single crystal test results showed that the nickel atoms in Ni6 and Ni7 were almost combined with the ligand in a planar coordination mode,and the V_bur of the ligand was 47.2%and 51.2%,respectively.In the neutral nickel complex Ni6’,the central metal nickel formed a form of biligand combination and presented a planar coordination mode,and the V_bur is 47.0%.Under the activation of MAO,nickel catalysts Ni6 and Ni7 can catalyze the vinyl polymerization of norbornene with high activity(3.60×10⁶ g mol^-1 h^-1)to obtain polynorbornene products with high molecular weight(2.74×10⁶ g mol^-1).The neutral catalyst Ni6’,on the other hand,formed an overly stable metal center due to the coordination of the two ligands,which significantly reduced the catalytic activity(0.09×10⁶ g mol^-1 h^-1).At the same time,these nickel catalysts also show good resistance to polar groups,and can catalyze the copolymerization of norbornene and methyl acrylate with moderate activity(5.80×10⁴ g mol^-1 h^-1),so that the copolymer has a high molecular weight(6.20×10⁴ g mol^-1)and insertion rate（up to 5.90 mol%）.The introduction of benzene substituents on nitrogen atoms in Ni6 can significantly increase the molecular weight of homopolymers and copolymers compared to Ni1 with methyl substitution in Chapter 3.the benzene ring substituent conjugation effect on the nitrogen atom of the complex Ni7 increases the oxygen philicity of the metal center,making coordination insertion of olefins more likely to occur.Therefore,although the two exhibit similar catalytic activity in the homopolymerization of norbornene,Ni7 can catalyze the copolymerization of NB and MA and obtain a high molecular weight copolymer.In addition,Ni6and Ni7 can also be used to catalyze ethylene oligomerization,among which the molecular weight of ethylene oligomer obtained by Ni7/MMAO system is up to 309.8 g mol-1,and the selectivity for1-olefin reaches 94.8%.In summary,based on the phosphino-phenolate catalyst framework,this paper designs and synthesizes a new strongly powered phosphinobenzenamine ligand,which realizes the regulation of electrophility of metal center by changing the central metal and the auxiliary adjustment of the substitution steric hindrance and electron effect on the phosphorus and nitrogen atoms of the ligand,and finally makes the catalytic system significantly improve the activity,polar monomer tolerance,molecular weight and polar monomer insertion rate,which is of great significance for the development of efficient post-transition metal catalytic systems.