Asymmetric alpha-diimine nickel catalysts, methods of making and using the same

Abstract

The application discloses an unsymmetrical (alpha-diimine) nickel olefin catalyst based on a vinylidene acen as a skeleton, and a preparation method and application thereof. The structural formula of the catalyst is shown as formula (I), wherein X is chlorine or bromine. The catalyst has simple preparation process, and shows a result opposite to general rules when catalyzing ethylene polymerization, that is, a larger substituent group leads to a polymerization product with higher crystallinity. In addition, the catalyst also shows good thermal stability and polymerization activity, and has good industrial application prospect.

Description

Technical Field

[0001] This invention relates to asymmetric (α-diimine) nickel olefin catalysts, their preparation methods and applications, and particularly to asymmetric α-diimine nickel catalysts based on vinyleneacenaphthene, their preparation methods and applications, and the application of using the catalyst to catalyze the polymerization of ethylene or propylene to obtain polyethylene or polypropylene. Background Technology

[0002] Polyolefins, as one of the most widely used synthetic polymers, have been extensively applied in all aspects of daily life. In the process of preparing polyolefins, the development and improvement of new catalysts are crucial factors driving the advancement and improvement of polyolefin production efficiency and product performance.

[0003] While pre-transition metal catalysts play a crucial role in olefin polymerization, the polyethylene structures they produce are almost always linear, making it impossible to prepare non-linear (e.g., branched) polymers. Post-transition metal catalysts, on the other hand, possess unique advantages such as lower oxygen affinity and stronger tolerance to polar groups. In 1995, Brookhart et al. pioneered the development of (α-diimine) nickel / palladium catalysts, the specific structural formula of which is shown in formula (Ⅳ). The "chain-walking" mechanism of this type of catalyst makes it possible to synthesize polymers with high activity and high molecular weight and high degree of branching, thus attracting widespread attention to transition metal catalysts in olefin polymerization. Equation (Ⅳ) Typically, much research has focused on modifying the ortho-position groups (R' in the formula) of aryl groups while maintaining the diimine backbone structure. When R' is a sterically hindered group, the crystallinity of the resulting polymer usually decreases. This is primarily because sterically hindered groups (such as ortho-substitution) on aniline severely impede the rotation of aniline units around single bonds. This makes the entire molecular chain more rigid. While moderate rigidity is beneficial for forming rod-like ordered structures, excessive steric hindrance prevents the molecular chain from eliminating packing defects through minor conformational adjustments. The chain segments are "frozen," unable to fit into the lattice, resulting in decreased crystallinity. Furthermore, these sterically hindered groups generate strong steric repulsion, preventing close proximity between molecular chains. Crystal formation requires sufficiently small inter-chain spacing (bound by van der Waals forces). Large steric hindrance increases the distance between molecular chains, making crystallization impossible or resulting in incomplete crystals, thus leading to decreased crystallinity. Long (J. AM.CHEM. SOC., 2013, 135(44): 16316-9), Chen (Chin. J. Chem., 2021, 40(2): 215-22), Dai (Organometallics., 2021, 41(2): 124-32) et al. replaced R' with a sterically hindered substituent, and the crystallinity of the resulting polymers decreased with the increase of the steric hindrance of the substituent.

[0004] While low crystallinity endows polyethylene (such as low-density polyethylene LDPE) with good flexibility and transparency, it also brings a series of significant performance shortcomings. Due to the loose arrangement and loose packing of molecular chains, the material's mechanical strength and rigidity are significantly insufficient, making it difficult to withstand large loads as a structural material. At the same time, the loose amorphous regions provide permeation channels for gas molecules and chemical reagents, resulting in a significant decrease in the material's barrier properties and chemical corrosion resistance. In addition, low crystallinity leads to poor thermal stability and a low melting point, making it prone to softening and deformation at slightly higher temperatures, severely limiting its application range. It is these inherent defects in strength, heat resistance, and barrier properties that highlight the importance of increasing crystallinity. Only by increasing the regularity of molecular chains and constructing a dense crystalline structure can polyethylene achieve superior mechanical properties and service stability while maintaining processability, thereby meeting the stringent requirements of high-end industrial fields such as pipelines and containers.

[0005] Therefore, there is an urgent need to develop a (α-diimine) nickel olefin polymerization catalyst that can improve the crystallinity of the polymerization product. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an asymmetric α-diimine nickel catalyst based on vinylene acenaphthene and its preparation method.

[0007] In a first aspect, the present invention provides an vinylene acenaphthene asymmetric (α-diimine) nickel olefin catalyst, the chemical structure of which is shown in formula (I): Equation (I) Where X is chlorine or bromine.

[0008] In a second aspect, the present invention provides a ligand compound for the catalyst shown in formula (I), the structural formula of which is shown in formula (II): Formula (II) In a third aspect, the present invention also provides a method for preparing the above-mentioned ligand compound, comprising the following steps: 1) Vinylidene reacts with aniline containing a sterically hindered substituent via a ketamine condensation reaction to yield the compound shown in formula (III):

[0009] 2) The compound shown in formula (III) reacts with 2,6-bis(3-pentyl)aniline via a ketamine condensation reaction to yield the ligand shown in formula (II):

[0010] In some embodiments, the solvent used in step 1) above is selected from at least one of toluene, acetonitrile, acetic acid and anhydrous ethanol, preferably at least one of toluene and acetonitrile.

[0011] In some embodiments, the catalyst used in step 1) above is selected from at least one of p-toluenesulfonic acid and acetic acid.

[0012] In some embodiments, in step 1) above, the ratio of the catalyst, vinylene acenaphthene, aniline with a large sterically hindered substituent, and solvent is 0.1-0.15 mmol: 1-1.1 mmol: 1-1.4 mmol: 5-10 mL.

[0013] In some embodiments, the reaction time of step 1) above is 2-8 hours, preferably 3-6 hours.

[0014] In some embodiments, step 1) above further includes the following step: using a mixed solvent of dichloromethane and petroleum ether or a mixed solvent of petroleum ether and ethyl acetate as eluent, the product is subjected to column chromatography in a silica gel column to obtain the product shown in formula (III).

[0015] In some embodiments, the solvent used in step 2) above is selected from at least one of toluene, acetonitrile, acetic acid and anhydrous ethanol, preferably at least one of toluene and acetonitrile.

[0016] In some embodiments, the catalyst used in step 2) above is selected from at least one of p-toluenesulfonic acid and acetic acid.

[0017] In some embodiments, in step 2) above, the ratio of the catalyst, vinylene acenaphthene, aniline with a large sterically hindered substituent, and solvent is 0.2-0.5 mmol: 1-1.1 mmol: 1-1.4 mmol: 30-70 mL.

[0018] In some embodiments, the reaction time for step 2) above is 6-16 hours, preferably 8-12 hours.

[0019] In some embodiments, step 2) above further includes the following step: eluenting the product in a silica gel column using a mixed solvent of dichloromethane and petroleum ether or a mixed solvent of petroleum ether and ethyl acetate to obtain the product as shown in formula (II).

[0020] In a fourth aspect, the present invention also provides a method for preparing the catalyst shown in formula (I), comprising the following steps: under an inert gas atmosphere, complexing the compound shown in formula (II) with one of ethylene glycol dimethyl ether nickel dibromide, ethylene glycol dimethyl ether nickel dichloride, or nickel dichloride hexahydrate to obtain the catalyst of the present invention. In the structural formula of the catalyst of the present invention, X is chlorine or bromine. In one embodiment of the present invention, X is selected as bromine. In one embodiment of the present invention, X is selected as chlorine.

[0021] In one embodiment of the present invention, under a nitrogen atmosphere, the compound represented by formula (II) is used as a ligand, and the nickel-containing compound complexed with the ligand is selected as nickel dimethyl ether dibromide (DME)NiBr2, wherein the molar ratio of the ligand to (DME)NiBr2 is 1:1-1.2, preferably 1:1.1; the solvent used is dichloromethane, the reaction temperature is 15-35 °C, preferably 25 °C, and the reaction time is 8-30 hours, preferably 16-24 hours.

[0022] In a fifth aspect, the present invention also provides a catalyst composition for catalyzing olefin polymerization, the composition comprising a main catalyst and a co-catalyst, the main catalyst being selected from the catalyst shown in formula (I), the co-catalyst being selected from at least one of alkylaluminum chloride, alkylaluminum and aluminoxane, and the olefin being ethylene or propylene.

[0023] In one embodiment of the present invention, the composition comprises a main catalyst and a co-catalyst, wherein the main catalyst is selected from the catalyst shown in formula (I), the co-catalyst is selected from at least one of alkylaluminum chloride, alkylaluminum and aluminoxane, and the olefin is ethylene or propylene.

[0024] Optionally, in the above catalyst composition, the aluminum oxane is methylaluminoxane (MAO), modified methylaluminoxane (MMAO), ethylaluminoxane, or isobutylaluminoxane.

[0025] Optionally, in the above catalyst composition, the alkylaluminum is trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, or tri-n-octylaluminum.

[0026] Optionally, in the above catalyst composition, the alkylaluminum chloride is diethylaluminum chloride, sesqui-diethylaluminum chloride, or ethylaluminum dichloride.

[0027] Considering the effectiveness and cost of the co-catalyst, in a preferred embodiment, the co-catalyst in the above-mentioned catalyst composition is alkyl aluminum chloride.

[0028] In a preferred embodiment, when alkylaluminum chloride is used as a co-catalyst, the molar ratio of metallic aluminum in alkylaluminum chloride to metallic nickel in the catalyst is referred to as the aluminum-nickel ratio, which ranges from 50 to 2000:1.

[0029] In a sixth aspect, the present invention also discloses the application of the catalyst shown in formula (I) in catalyzing the polymerization of ethylene and propylene to prepare polyethylene and polypropylene.

[0030] The beneficial effects of this invention are as follows: 1. The catalyst modified with sterically hindered groups disclosed herein unexpectedly improves the crystallinity of the polymerization product despite the increased steric hindrance of aniline, providing a (α-diimine) nickel olefin polymerization catalyst with good crystallinity and polymerization activity.

[0031] 2. The catalysts modified with sterically hindered groups provided in this disclosure can exhibit unconventional properties, not only yielding polymer products with higher crystallinity, but also improving the processability of the polymer products (higher molecular weight, higher polydispersity index, and lower branching degree), thus giving them superior mechanical properties.

[0032] 3. In addition, this type of catalyst has a low synthesis threshold, simple ligand synthesis, low amount of co-catalyst required, and significant overall production cost advantages. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0034] Example 1, Preparation of intermediate of formula (III): p-Toluenesulfonic acid (0.1 g, 0.6 mmol) was added to an anhydrous ethanol (80 mL) solution of 2,6-bis(diphenylmethyl)-4-methylaniline (8.8 g, 20 mmol) and vinylacenaphthene (4.1 g, 20 mmol), and the mixture was refluxed for 24 h. The solvent was removed, and the residue was subjected to silica gel column chromatography with a 2:1 volume ratio of dichloromethane and petroleum ether to obtain intermediate of formula (III) with a mass of 11.7 g, yield: 93%.

[0035] Example 2, Preparation of ligand (II): Zinc chloride (0.2 g, 1.5 mmol) was added to a solution of 2,6-bis(3-pentyl)aniline (0.35 g, 1.5 mmol) and intermediate of formula (III) (0.627 g, 1 mmol) in acetic acid (5 mL), and the mixture was refluxed for 30 min. The solvent was removed, and the residue was subjected to silica gel column chromatography with a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 30:1 to obtain ligand (II) with a mass of 0.5 g, yield: 59.3%.

[0036] Example 3, Preparation of catalyst of formula (I): Under a nitrogen atmosphere, ligand of formula (II) (0.158 g, 0.2 mmol) and (DME)NiBr2 (0.062 g, 0.2 mmol) were dissolved in 20 mL of dichloromethane and stirred at room temperature for 24 hours. The dichloromethane was dried under vacuum and washed three times with 20 mL of diethyl ether each time. The diethyl ether was then dried under vacuum to obtain 0.2 g of catalyst of formula (I), with a yield of 94.2%.

[0037] The following examples illustrate catalytic ethylene polymerization: Example 4: Ethylene pressure polymerization was carried out under anhydrous and oxygen-free conditions. The ethylene pressure was 1 MPa, and the polymerization temperature was 60 °C. 1 L of heptane was poured into a 2000 mL stainless steel reactor, followed by the injection of 1.5 mL of a 2.0 mol / L diethylaluminum chloride toluene solution as a co-catalyst. 2 μmol of catalyst (I) was dissolved in 10 mL of toluene solution and injected. The ethylene pressure was increased to 1.0 MPa, and the mixture was stirred. After reacting for half an hour, the polymer solution was poured into an acidified ethanol solution for sedimentation. The polymer was filtered, washed several times with acidified ethanol, and vacuum dried at 60 °C to constant weight. 6.0 g of polymer was then weighed. The catalytic activity was 6.0 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 201 × 10⁻⁶. 4 g / mol, polydispersity index of 2.92, degree of branching of 62, and crystallinity of 18.3%.

[0038] Example 5: The polymerization pressure in Example 4 was adjusted to 1.5 MPa, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 9.7 g of polymer was obtained. The catalytic activity was 9.7 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 277 × 10⁻⁶. 4 g / mol, polydispersity index of 2.88, branching degree of 61, and crystallinity of 19.1%.

[0039] Example 6: The polymerization pressure in Example 4 was adjusted to 1.9 MPa, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 10.6 g of polymer was obtained. The catalytic activity was 10.6 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 291 × 10⁻⁶. 4 g / mol, polydispersity index of 2.75, degree of branching of 58, and crystallinity of 21.3%.

[0040] Example 7: The polymerization pressure in Example 4 was adjusted to 0.7 MPa, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 4.9 g of polymer was obtained. The catalytic activity was 4.9 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 183 × 10⁻⁶. 4 g / mol, polydispersity index of 3.11, degree of branching of 66, and crystallinity of 15.7%.

[0041] Example 8: The polymerization temperature in Example 7 was adjusted to 40 °C, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 3.6 g of polymer was obtained. The catalytic activity was 3.6 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 145 × 10⁻⁶. 4 g / mol, polydispersity index of 2.12, degree of branching of 63, and crystallinity of 21.1%.

[0042] Example 9: The polymerization temperature in Example 7 was adjusted to 80 °C, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 3.1 g of polymer was obtained. The catalytic activity was 3.1 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 159 × 10⁻⁶. 4g / mol, polydispersity index of 4.01, degree of branching of 70, and crystallinity of 13.2%.

[0043] Example 10: The polymerization temperature in Example 7 was adjusted to 100 °C, while other conditions remained unchanged. The polymerization product was vacuum dried at 60 °C to constant weight, and 0.7 g of polymer was obtained. The catalytic activity was 0.7 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 56.0 × 10⁻⁶. 4 g / mol, polydispersity index of 3.95, degree of branching of 77, and crystallinity of 12.3%.

[0044] Example 11: The amount of co-catalyst in Example 4 was adjusted to 1.5 mL with a concentration of 2.0 mol / L, and the amount of catalyst (I) was adjusted to 10 μmol. Other conditions remained unchanged. The polymerization product was vacuum dried at 60°C to constant weight, and 18.0 g of polymer was obtained. The catalytic activity was 3.6 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 68.8 × 10⁻⁶. 4 kg / mol, polydispersity index 3.35, branching degree 75, crystallinity 12.8%.

[0045] Comparative Example 1: A solution of 2,6-dimethylaniline (0.18 g, 1.5 mmol) and intermediate of formula (III) (0.627 g, 1 mmol) in toluene (50 mL) was reacted with p-toluenesulfonic acid (0.086 g, 0.5 mmol) and refluxed for 12 h. The solvent was removed, and the residue was subjected to silica gel column chromatography with a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 30:1 to obtain 0.33 g of 2,6-dimethylaniline ligand, yield: 45%.

[0046] Comparative Example 2: The ligand of formula (II) in Example 3 was replaced with the 2,6-dimethylaniline ligand synthesized in Comparative Example 1. Other operations were the same as in Example 3, and 0.167 g of 2,6-dimethylaniline diimine nickel bromide complex was obtained with a yield of 88%.

[0047] Comparative Example 3: The catalyst in Example 4 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 2. All other operations were the same as in Example 4. The polymerization product was vacuum dried at 60 °C to constant weight, and 16.2 g of polymer was obtained. The catalytic activity was 16.2 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 134 × 10⁻⁶. 4g / mol, polydispersity index of 1.85, degree of branching of 82, and crystallinity of 7.7%.

[0048] Comparative Example 4: The catalyst in Example 5 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 2. All other operations were the same as in Example 5. The polymerization product was vacuum dried at 60 °C to constant weight, and 18.8 g of polymer was obtained. The catalytic activity was 18.8 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 129 × 10⁻⁶. 4 g / mol, polydispersity index of 2.04, degree of branching of 76, and crystallinity of 8.8%.

[0049] Comparative Example 5: The catalyst in Example 6 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 2. All other operations were the same as in Example 6. The polymerization product was vacuum dried at 60 °C to constant weight, and 19.8 g of polymer was obtained. The catalytic activity was 19.8 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 117 × 10⁻⁶. 4 g / mol, polydispersity index of 2.07, degree of branching of 72, and crystallinity of 12.0%.

[0050] Comparative Example 6: The catalyst in Example 7 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 2. All other operations were the same as in Example 7. The polymerization product was vacuum dried at 60 °C to constant weight, and 9.4 g of polymer was obtained. The catalytic activity was 9.4 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 114 × 10⁻⁶. 4 g / mol, polydispersity index of 2.01, degree of branching of 83, and crystallinity of 7.5%.

[0051] Comparative Example 7: The catalyst in Example 8 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 2. All other operations were the same as in Example 8. The polymerization product was vacuum dried at 60 °C to constant weight, and 10.8 g of polymer was obtained. The catalytic activity was 10.8 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 183 × 10⁻⁶. 4 g / mol, polydispersity index of 2.42, degree of branching of 71, and crystallinity of 10.8%.

[0052] Comparative Example 8: The catalyst in Example 9 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 2. All other operations were the same as in Example 9. The polymerization product was vacuum dried at 60 °C to constant weight, and 6.9 g of polymer was obtained. The catalytic activity was 6.9 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 58.5 × 10⁻⁶. 4 g / mol, polydispersity index of 1.92, degree of branching of 92, and crystallinity of 4.7%.

[0053] Comparative Example 9: The catalyst in Example 10 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 2. All other operations were the same as in Example 10. The polymerization product was vacuum dried at 60 °C to constant weight, and 2.2 g of polymer was obtained. The catalytic activity was 2.2 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 34.1 × 10⁻⁶. 4 g / mol, polydispersity index of 1.96, branching degree of 98, and crystallinity of 1.4%.

[0054] Comparative Example 10: The catalyst in Example 11 was replaced with the 2,6-dimethylaniline diimine nickel bromide complex synthesized in Comparative Example 2. All other operations were the same as in Example 11. The polymerization product was vacuum dried at 60 °C to constant weight, and 31.5 g of polymer was obtained. The catalytic activity was 6.3 × 10⁻⁶. 6 gPE[mol(Ni)h] -1 The weight-average molecular weight of the polymer product is 42.2 × 10⁻⁶. 4 g / mol, polydispersity index of 2.15, degree of branching of 96, and crystallinity of 2.1%.

[0055] By comparing Examples 4-11 with Comparative Examples 3-10, it was found that compared to the 2,6-dimethylaniline-diimine nickel bromide complex with two methyl groups on aniline, the method of introducing a larger benzene ring in the catalyst shown in Formula (I) resulted in a different crystallization behavior than usual. Generally, a moderate increase in steric hindrance hinders the orderly stacking of molecular chains, leading to a decrease in crystallinity; however, the present invention found that the resulting polymer has higher crystallinity. We speculate that this is because, compared to the small-sized methyl groups, the introduction of the 3-pentyl group in the catalyst shown in Formula (I), although increasing the embedding volume, effectively inhibits chain coiling and branching reactions during polymerization, promoting more linear growth of the polymer chain. During crystallization, the regularity of the polymer chain is a key factor determining crystallization ability. When the substituent is too large, although crystallinity is usually reduced due to hindering stacking, the inventors of this disclosure unexpectedly discovered that the introduction of the 3-pentyl group can, by regulating the chain growth path, endow the molecular chain with higher structural regularity, enabling the chain segments to overcome steric hindrance and arrange themselves in an orderly manner upon cooling. Therefore, the catalyst of formula (I), with its greater steric hindrance, produces polymers with higher crystallinity than the 2,6-dimethylaniline diimine nickel bromide complex, which has less steric hindrance, leading to unconventional properties. For example, it simultaneously increases the polymer's crystallinity and molecular weight, resulting in better thermal stability, and reduces the polymer's branching degree, leading to superior dimensional stability. Furthermore, comparing Examples 4-11 with Comparative Examples 3-10, the catalyst of formula (I) shows a significantly higher synthesis yield and a significant cost advantage. Therefore, the unusual catalytic properties of the 3-pentyl-modified ethylenamate biasymmetric α-diimine nickel catalyst make it a promising candidate for applications in the field of polyolefin thermoplastic materials.

Claims

1. The vinylene acenaphthene asymmetric (α-diimine) nickel olefin catalyst shown in formula (Ⅰ): Equation (I) in, X is chlorine or bromine.

2. The asymmetric (α-diimine) nickel olefin catalyst according to claim 1, characterized in that: The aniline structures on both sides of the main vinylacenaphthene framework are different.

3. The compound represented by formula (II): Formula (II).

4. A method for preparing the compound according to claim 3, comprising the following steps: 1) Vinylidene reacts with aniline containing a sterically hindered substituent via a ketamine condensation reaction to yield the compound shown in formula (III): ； 2) The compound shown in formula (III) reacts with 2,6-bis(3-pentyl)aniline via a ketamine condensation reaction to yield the compound shown in formula (II): 。 5. A method for preparing the catalyst according to claim 1 or 2, comprising the following steps: under an inert gas protection environment, complexing the compound according to claim 3 with one of ethylene glycol dimethyl ether nickel dibromide, ethylene glycol dimethyl ether nickel dichloride, or nickel dichloride hexahydrate to obtain the catalyst according to claim 1 or 2.

6. A catalyst composition for catalyzing olefin polymerization, characterized in that, It comprises a main catalyst and a co-catalyst, wherein the main catalyst is selected from the catalyst according to claim 1 or 2, wherein the co-catalyst is selected from at least one of alkylaluminum chloride, alkylaluminum or aluminoxane, and the olefin is ethylene or propylene.

7. The application of the (α-diimine) nickel olefin catalyst according to claim 1 in the catalytic polymerization of ethylene to prepare polyethylene.

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