Nitrogen heterocyclic skeleton imine nickel catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of chemical materials, in particular to an N-heterocyclic skeleton imine nickel catalyst and a preparation method and application thereof. The catalyst comprises a compound as shown in a general formula I, and Ar is selected from one of benzhydryl and dibenzocycloheptyl; r1 is selected from one of chlorine, methoxyl, methyl and tert-butyl; r2 and R3 are respectively and independently CH or N, and at least one of R2 and R3 is N. Nitrogen atoms are introduced into different positions of the catalyst, and when the catalyst and MAO are in concerted catalysis, two different active centers can be obtained, so that polyethylene with bimodal distribution is obtained. Compared with a traditional bimetal catalytic system, the polymerization preparation process is simple, the ligand can realize fine adjustment of molecular weight, branching degree and melting point through electron and space regulation and control, and an efficient and large-scale new way is provided for preparing bimodal distribution polyethylene.

Description

Technical Field

[0001] This application relates to the field of chemical materials technology, specifically to a nitrogen heterocyclic framework imine nickel catalyst, its preparation method, and its application. Background Technology

[0002] Polyolefins prepared from homogeneous single-site catalysts typically exhibit narrow molecular weight distributions. However, a wider molecular weight distribution is often required to improve melt processing properties such as shear thinning and melt strength. In the 1980s, researchers first constructed homogeneous multi-active-site catalytic systems by mixing different metallocene catalysts, enabling the preparation of polyolefins with broad molecular weight distributions in a single reactor without relying on hydrogen as a chain transfer agent. By adjusting the catalyst type and ratio, the molecular weight distribution can be precisely controlled, with each active site maintaining its independent characteristics. For example, the Cp₂HfCl₂ / Et(Ind)₂ZrCl₂ dual-site catalyst produces a bimodal distribution dependent on the Hf / Zr molar ratio. Subsequent studies extended this approach to iron / nickel catalysts and propylene polymerization systems, revealing a significant effect of temperature on the relative site activity. In addition to physical mixing, the design of binuclear and polynuclear metal complexes (such as bridged binuclear metallocenes and confined geometry catalysts) has enabled the systematic tuning of inter-site distances to utilize synergistic effects for customized molecular weight distributions. However, the aforementioned binuclear or multinuclear metal complex systems typically rely on specialized bridging ligands to precisely control the metal spacing and spatial orientation. The synthetic routes for these ligands are complex, costly, and difficult to scale up. For industrial polyolefin production, ligand cost and synthetic reproducibility are decisive factors, making multinuclear systems economically unfeasible. Summary of the Invention

[0003] Based on this, the purpose of this application is to overcome the shortcomings of the prior art and provide a mononuclear nitrogen heterocyclic framework imine nickel catalyst, its preparation method and application, so as to overcome the problems of complex synthesis routes, high cost and difficulty in industrialization of traditional binuclear or polynuclear metal complex system catalysts.

[0004] To achieve the above objectives, this application adopts the following technical solution:

[0005] First, this application provides a nitrogen heterocyclic skeletal imine nickel catalyst, the catalyst comprising a compound having the formula shown in general formula I.

[0006] ,

[0007] Formula I,

[0008] Ar is selected from diphenylmethyl and dibenzocycloheptanyl; R1 is selected from chlorine, methoxy, methyl and tert-butyl; R2 and R3 are each independently CH or N, and at least one of R2 and R3 is N.

[0009] Preferably, the compound has one of the structures shown in formulas I1 to I4:

[0010]

[0011] R1 is derived from one of chlorine, methoxy, methyl, and tert-butyl.

[0012] Preferably, the catalyst comprises one of Ni1 to Ni6:

[0013] ,

[0014] .

[0015] Based on a general inventive concept, this application also provides a method for preparing a nitrogen heterocyclic framework imine nickel catalyst, comprising the following steps:

[0016] S1. Mix 2-acetylpyrazine or 2-acetylpyrimidine with aromatic amine, zinc chloride and acetic acid, and reflux the mixture. After the reflux reaction is complete, cool the reaction solution to room temperature, add the first undesirable solvent to precipitate the mixture, filter the solution, and obtain the first solid material.

[0017] S2. Dissolve the first solid material in dichloromethane, add potassium oxalate aqueous solution and mix and stir, wash with water, and after the solution separates into layers, separate the organic phase, dry the organic phase, then concentrate under reduced pressure, add a second poor solvent to precipitate, filter and vacuum dry to obtain the organic ligand.

[0018] S3. The organic ligand and nickel dibromide (ethylene glycol dimethyl ether) are mixed and dissolved in dichloromethane and stirred at room temperature for 12-16 hours. Part of the solvent is removed by vacuum evaporation. Then, a third undesirable solvent is added to the remaining mixture to precipitate a second solid material. The solid material is filtered and dried under vacuum to obtain the nitrogen heterocyclic framework imine nickel catalyst.

[0019] Preferably, in step S1, the molar ratio of 2-acetylpyrazine or 2-acetylpyrimidine to aromatic amine is 1:(1.5~2).

[0020] Preferably, the aromatic amine is selected from 2,6-diphenylmethyl-4-chloroaniline, 2,6-diphenylmethyl-4-methoxyaniline, 2,6-diphenylmethyl-4-methylaniline, 2,6-diphenylmethyl-4-tert-butylaniline, or 2,6-dibenzocycloheptyl-4-methylaniline.

[0021] Preferably, in step S3, the molar ratio of the organic ligand to nickel dibromide (ethylene glycol dimethyl ether) is 1:1.

[0022] Preferably, in step S1, the temperature of the reflux reaction is 80℃~90℃, and the time of the reflux reaction is 5h~5.5h.

[0023] Preferably, in step S2, the potassium oxalate aqueous solution is added and mixed for 1 to 1.5 hours.

[0024] Preferably, the first undesirable solvent is diethyl ether, the second undesirable solvent is methanol, and the third undesirable solvent is diethyl ether.

[0025] Preferably, in step S2, the organic phase is dried with anhydrous magnesium sulfate.

[0026] Based on a general inventive concept, this application also provides the application of a nitrogen heterocyclic framework imine nickel catalyst in the catalytic polymerization of ethylene to prepare bimodal polyethylene.

[0027] Preferably, the reaction for preparing bimodal polyethylene by ethylene polymerization is carried out under the catalytic conditions of the nitrogen heterocyclic framework imine nickel catalyst and methylaluminoxane.

[0028] Preferably, the molar ratio of the nitrogen heterocyclic skeletal imine nickel catalyst to methylaluminoxane is 1:(1~3).

[0029] Preferably, in the reaction of ethylene polymerization to prepare bimodal polyethylene, the reaction pressure is 6 atm to 10 atm, the reaction temperature is 30°C to 90°C, and the reaction time is 60 min to 120 min.

[0030] Compared with the prior art, this application has the following beneficial effects:

[0031] The nitrogen-containing heterocyclic framework imine nickel catalyst provided in this application introduces a nitrogen-containing heterocycle (such as pyrazine or pyrimidine) as a functionalizing modification group into the imine ligand framework; the non-coordinated nitrogen atom on the nitrogen heterocycle serves as a potential auxiliary coordination site or electronic effect regulating group. This molecular design enables the mononuclear catalyst molecule to generate active centers with differentiated performance.

[0032] In terms of catalytic effect: During the ethylene polymerization process, the catalyst and the co-catalyst methylaluminoxane (MAO) of this application synergistically exhibit excellent and controllable catalytic performance: (1) Achieving a broad / bimodal molecular weight distribution: During the polymerization process, the nitrogen atoms introduced on the ligand skeleton can interact specifically with MAO. This interaction gives the composite catalyst two different active centers. One of these two different activities tends to undergo rapid chain growth and generate high molecular weight polymer chains; the other has different chain transfer / chain growth kinetics and contributes to the low molecular weight part. The coexistence and competition of the two make it possible to directly generate polyethylene with a broad peak or obvious bimodal molecular weight distribution in a single reactor and a single polymerization batch. (2) Finely tunable polymer structure: By systematically adjusting the position of nitrogen atoms on the skeleton (R2, R3) and the electronic effect of aromatic ring substituents (R1), the competitive balance between chain growth and chain transfer can be finely controlled at the molecular level, thereby achieving directional adjustment of key parameters such as polymer molecular weight and branching degree, ensuring the stability of the polymerization process and the stability of the product structure. (3) Maintaining high catalytic activity and product performance: This catalytic system exhibits high catalytic activity (up to 10) even under mild conditions. 6 g·mol -1 ·h -1 The resulting polyethylene has both a suitable high molecular weight and a high melting point, ensuring the material's good mechanical properties.

[0033] Regarding the preparation method, the nitrogen heterocyclic framework imine nickel catalyst provided in this application has a simple preparation process, requiring no synthesis of expensive and complex multidentate bridging ligands. The raw materials are readily available, which is beneficial for achieving high-yield, high-purity large-scale production. As a mononuclear catalyst system, its polymerization behavior is stable and reproducible. This preparation method is compatible with existing solution-based and gas-phase polyolefin production processes, requiring no major modifications or adjustments to existing industrial equipment, thus significantly reducing the technology transfer threshold and industrialization costs. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0035] Figure 1 The proton NMR spectrum of ligand L1 prepared for Preparation Example 1.

[0036] Figure 2 The carbon NMR spectrum of ligand L1 prepared for Preparation Example 1.

[0037] Figure 3The mass spectrum of ligand L1 prepared for Preparation Example 1.

[0038] Figure 4 The mass spectrum of the nitrogen heterocyclic framework imine nickel catalyst Ni1 prepared for Example 1.

[0039] Figure 5 The proton NMR spectrum of ligand L2 prepared for Preparation Example 2.

[0040] Figure 6 The carbon NMR spectrum of ligand L2 prepared for Preparation Example 2.

[0041] Figure 7 The mass spectrum of ligand L2 prepared for Example 2.

[0042] Figure 8 The mass spectrum of the nitrogen heterocyclic framework imine nickel catalyst Ni2 prepared for Preparation Example 2.

[0043] Figure 9 The proton NMR spectrum of ligand L3 prepared for Preparation Example 3.

[0044] Figure 10 The carbon NMR spectrum of ligand L3 prepared for Preparation Example 3.

[0045] Figure 11 The mass spectrum of ligand L3 prepared for Preparation Example 3.

[0046] Figure 12 The mass spectrum of the nitrogen heterocyclic framework imine nickel catalyst Ni3 prepared for Preparation Example 3.

[0047] Figure 13 The proton NMR spectrum of ligand L4 prepared in Preparation Example 4.

[0048] Figure 14 The carbon NMR spectrum of ligand L4 prepared for Preparation Example 4.

[0049] Figure 15 The mass spectrum of ligand L4 prepared for Preparation Example 4.

[0050] Figure 16 The mass spectrum of the nitrogen heterocyclic framework imine nickel catalyst Ni4 prepared for Preparation Example 4.

[0051] Figure 17 The proton NMR spectrum of ligand L5 prepared in Preparation Example 5.

[0052] Figure 18 The carbon NMR spectrum of ligand L5 prepared in Preparation Example 5.

[0053] Figure 19 The mass spectrum of ligand L5 prepared for Preparation Example 5.

[0054] Figure 20 Mass spectrum of the nitrogen heterocyclic framework imine nickel catalyst Ni5 prepared for Preparation Example 5.

[0055] Figure 21 The proton NMR spectrum of ligand L6 prepared in Preparation Example 6.

[0056] Figure 22 The carbon NMR spectrum of ligand L6 prepared in Preparation Example 6.

[0057] Figure 23 The mass spectrum of ligand L6 prepared for Preparation Example 6.

[0058] Figure 24 Mass spectrum of the nitrogen heterocyclic framework imine nickel catalyst Ni6 prepared for Preparation Example 6.

[0059] Figure 25 The image shows the carbon NMR spectrum of the bimodal polyethylene prepared in Example 1.

[0060] Figure 26 The image shows a gel permeation chromatogram of the bimodal polyethylene prepared in Example 1. Detailed Implementation

[0061] The embodiments described in this specification are merely for explaining this application and are not intended to limit this application.

[0062] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0063] Those skilled in the art will understand that the order in which the steps are written in the various embodiments or examples does not imply a strict execution order and does not limit the implementation process in any way. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but sequentially is preferred.

[0064] The following abbreviations may be used in this document: Me is methyl, OMe is methoxy, Bu is butyl, tBu is tert-butyl, PTSA is p-toluenesulfonic acid; Toluene is toluene; DCM is dichloromethane.

[0065] In this application, room temperature refers to a temperature range of 25°C to 30°C.

[0066] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0067] The synthesis steps involved in the preparation examples are all preferred catalyst synthesis steps.

[0068] The compound testing and characterization methods used in each preparation example of this application are as follows:

[0069] NMR analysis was performed using a Bruker AVANCE III HD 400, with tetramethylsilane (TMS) as an internal standard, at 25 °C to test the structure of the compounds.

[0070] The synthetic routes of the nitrogen heterocyclic framework imine nickel catalysts in each preparation example are shown below:

[0071] ;

[0072] Where DP represents DB indicates ; Indicates the connection site.

[0073] Preparation Example 1

[0074] (1) Synthesis of catalyst ligand L1:

[0075] In a 100 mL round-bottom flask, 0.5 g (1.1 mmol) of 2,6-diphenylmethyl-4-chloroaniline and 0.12 g (1 mmol) of 2-acetylpyrazine were added to 5 mL of acetic acid containing anhydrous ZnCl2 (0.2 g, 1.5 mmol) to obtain a mixed solution. The solution was then refluxed and stirred at 90 °C for 5 hours. After the reaction was stopped, part of the acetic acid was evaporated under reduced pressure. Diethyl ether was added to the remaining solution and stirred three times (10 mL × 3). A precipitate formed, which was filtered to obtain a pale yellow zinc complex and dried under vacuum.

[0076] In a 250 mL round-bottom flask, add 40 mL of an aqueous solution of potassium oxalate (0.3 g, 1.6 mmol), the zinc complex, and 40 mL of dichloromethane; stir at room temperature for 1 hour; wash three times with water, each time using 20 mL (i.e., 3 × 20 mL); the solution separates into layers, and the organic phase is collected; add an appropriate amount of anhydrous MgSO4 and let stand for 40 min; filter with diatomaceous earth, and concentrate the resulting solution under reduced pressure to remove part of the solvent. Dilute the remaining solution in ethanol and stir three times (10 mL × 3), filter, and obtain a pale yellow solid. After vacuum drying, the target product ligand L1 (0.39 g, yield 70%) is obtained.

[0077] NMR analysis: Figure 1 and Figure 2 The figures show the 1H and 1C NMR spectra of ligand L1 prepared in Preparation Example 1, respectively, where the horizontal axis f1 represents the first dimension of the frequency dimension, with units of ppm; the specific data are as follows: 1 H NMR (400MHz, CDCl3) δ9.17 (s, 1H, aryl-H), 8.63 (s, 1H, aryl-H), 8.54 (s, 1H, aryl-H) , 7.26–6.93 (m, 20H, aryl-H), 6.87 (s, 2H, aryl-H), 5.23 (s, 2H, CH), 0.94 (s, 3H, CH3). 13 C NMR (101MHz, CDCl3) δ169.11 (N=C), 150.29, 146.19, 145.38, 143.49, 143.19, 142.48, 141.50, 13 4.33, 129.70, 129.31, 128.59, 128.54, 128.35, 128.09, 126.67, 126.56, 52.21(CH), 16.78(CH3).

[0078] Figure 3 Mass spectrum of ligand L1, mass spectrometry analysis: ESI-MS (m / z): theoretical value C 38 H 31 ClN3 + :564.2201, test value 564.2194, [M+H] + .

[0079] (2) Synthesis of catalyst Ni1:

[0080] Under a nitrogen atmosphere, ligand L1 (0.1 mmol), 20 mL of dichloromethane (DCM), and (DME)NiBr2 (DME = ethylene glycol dimethyl ether, 0.1 mmol) were added to a 25 mL round-bottom flask, and the mixture was stirred at room temperature for 12 h. After the reaction was stopped, part of the solvent was concentrated under vacuum, and 5 mL of diethyl ether was added to the remaining solution for dilution (5 mL × 3). The precipitated solid was filtered and dried under vacuum to obtain the target product catalyst Ni1 (yield 88%).

[0081] Figure 4 The mass spectrum of catalyst Ni1 is shown. Mass spectrometry analysis: MALDI-TOF-MS (m / z): theoretical value C. 38 H 30 BrClN3Ni + :700.0660, test value 700.0686, [M-Br] + .

[0082] Preparation Example 2

[0083] (1) Synthesis of ligand L2:

[0084] The preparation method for ligand L2 in this preparation example is basically the same as the method for synthesizing ligand L1 in preparation 1. The only difference is the specific type of aromatic amine. Specifically, the aromatic amine used in this preparation example is 2,6-diphenylmethyl-4-methoxyaniline. The rest of the operation is the same as in Example 1, and the yield is 85%.

[0085] Figure 5 and Figure 6 The images show the proton and carbon NMR spectra of ligand L2, respectively; NMR analysis: 1 H NMR (400MHz, CDCl3) δ9.24–9.15 (s, 1H, aryl-H), 8.62 (s, 1H, aryl-H), 8.53 (s, 1H, aryl-H), 7.26- 6.97 (m, 20H, aryl-H), 6.46 (s, 2H, aryl-H), 5.26 (s, 2H, CH), 3.57 (s, 3H, OCH3), 0.98 (s, 3H, CH3). 13 C NMR (101MHz, CDCl3) δ170.28 (N=C), 155.48, 150.54, 145.29, 143.61, 143.11, 143.07, 142.14, 142.07, 1 33.73, 129.75, 129.38, 128.43, 128.19, 126.44, 126.31, 113.85, 55.18(OCH3), 52.35(CH), 16.64(CH3).

[0086] Figure 7 Mass spectrum of ligand L2; Mass spectrometry analysis: ESI-MS (m / z): theoretical value C 39 H 34 N3O + : 560.2696, test value 560.2698, [M+H] + .

[0087] (2) Synthesis of catalyst Ni2:

[0088] The steps for synthesizing Ni2 in this preparation example are basically the same as those for synthesizing catalyst Ni1 in preparation 1. The only difference is that the ligand used in this preparation example is ligand L2. The rest of the operations are the same as in preparation example 1, and the yield is 91%.

[0089] Figure 8 Mass spectrum of catalyst Ni2; Mass spectrometry analysis: MALDI-TOF-MS (m / z): Theoretical value C 39 H 33 BrN3NiO + : 696.1155, test value 696.1183, [M-Br] + .

[0090] Preparation Example 3

[0091] (1) Synthesis of ligand L3:

[0092] The preparation method for ligand L3 in this preparation example is basically the same as the method for synthesizing ligand L1 in preparation 1. The only difference is the specific type of aromatic amine. Specifically, the aromatic amine used in this preparation example is 2,6-diphenylmethyl-4-methylaniline. The rest of the operation is the same as in Example 1, and the yield is 77%.

[0093] Figure 9 and Figure 10 The images show the 1H and 1C NMR spectra of ligand L3, respectively; NMR analysis: 1 H NMR (400MHz, CDCl3) δ9.33-9.13 (m, 1H, aryl-H), 8.73–8.62 (m, 1H, aryl-H), 8.54 (m, 1H, aryl-H), 7. 26-6.96 (m, 20H, aryl-H), 6.79 (s, 2H, aryl-H), 5.27 (s, 2H, CH), 2.19 (s, 3H, CH3), 0.96 (s, 3H, CH3). 13C NMR (101MHz, CDCl3) δ168.52 (N=C), 150.68, 145.34, 145.20, 143.60, 143.48, 143.07, 142.42, 132.11, 1 32.09, 129.81, 129.42, 128.73, 128.38, 128.12, 126.31, 126.16, 52.19(CH), 21.37(CH3), 16.62(CH3).

[0094] Figure 11 Mass spectrum of ligand L3; Mass spectrometry analysis: ESI-MS (m / z): theoretical value C 39 H 34 N3 + 544.2747, Test value, 544.2751, [M+H] + .

[0095] (2) Synthesis of catalyst Ni3:

[0096] The steps for synthesizing Ni3 in this preparation example are basically the same as those for synthesizing catalyst Ni1 in preparation 1. The only difference is that the ligand used in this preparation example is ligand L3. The rest of the operations are the same as in preparation example 1, and the yield is 87%.

[0097] Figure 12 Mass spectrum of catalyst Ni3; Mass spectrometry analysis: MALDI-TOF-MS (m / z): Theoretical value C 39 H 33 BrN3Ni + 680.1206, test value; 680.1219, [M-Br] + .

[0098] Preparation Example 4

[0099] (1) Synthesis of ligand L4:

[0100] The preparation method for ligand L4 in this preparation example is basically the same as the method for synthesizing ligand L1 in preparation 1. The only difference is the specific type of aromatic amine. Specifically, the aromatic amine used in this preparation example is 2,6-diphenylmethyl-4-tert-butylaniline. The rest of the operation is the same as in Example 1, and the yield is 81%.

[0101] Figure 13 and Figure 14 The NMR spectra of ligand L4 are shown in both proton and carbon formats; NMR analysis: 1H NMR (400MHz, CDCl3) δ9.18 (s, 1H, aryl-H), 8.61 (d, J=2.5Hz, 1H, aryl-H), 8.52 (s, 1H, aryl-H), 7.24 -6.98(m, 20H, aryl-H), 6.88(s, 2H, aryl-H), 5.25(s, 2H, CH), 1.10(s, 9H, C(CH3)3, 0.98(s, 3H, CH3). 13 C NMR (101MHz, CDCl3) δ168.30 (N=C), 150.69, 145.30, 145.14, 143.62, 143.58, 143.01, 142.64, 131.39, 129.77, 129.38, 128.32 , 128.02, 126.26, 126.11, 125.12, 77.37, 77.25, 77.05, 76.73, 52.47(CH), 34.33(CH(CH3)3), 31.34, (CH(CH3)3), 16.70(CH3).

[0102] Figure 15 Mass spectrum of ligand L4; Mass spectrometry analysis: ESI-MS (m / z): theoretical value C 42 H 40 N3 + 586.3217, Test value; 586.3218, [M+H] + .

[0103] (2) Synthesis of catalyst Ni4:

[0104] The steps for synthesizing Ni4 in this preparation example are basically the same as those for synthesizing catalyst Ni1 in Preparation 1. The only difference is that the ligand used in this preparation example is ligand L4; the rest of the operations are the same as in Example 1, with a yield of 76%.

[0105] Figure 16 Mass spectrum of catalyst Ni4; Mass spectrometry analysis: MALDI-TOF-MS (m / z): Theoretical value C 42 H 39 BrN3Ni + : 722.1675, test value 722.1640, [M-Br] + .

[0106] Preparation Example 5

[0107] (1) Synthesis of ligand L5:

[0108] The preparation method for ligand L5 in this preparation example is basically the same as the method for synthesizing ligand L1 in preparation 1. The only difference is that the specific type of aromatic amine is different. Specifically, the aromatic amine used in this preparation example is 2,6-dibenzocycloheptayl-4-methylaniline.

[0109] Figure 17 and Figure 18 The NMR spectra of ligand L5 are shown in both proton and carbon formats; NMR analysis: 1 H NMR (400MHz, CDCl3) δ9.31–9.26 (m, 1H, aryl-H), 8.68 (d, J=2.5Hz, 1H, aryl-H), 8.61 (s, 1H, aryl-H), 7.15–6.67 (m, 20H, aryl-H) -H), 6.56 (m, 2H, aryl-H), 4.90 (s, 2H, CH), 3.57–3.27 (m, 4H, CH2), 2.84–2.58 (m, 4H, CH2), 2.13 (s, 3H, CH3), 1.07 (s, 3H, CH3). 13 C NMR (101MHz, CDCl3) δ169.33 (N=C), 150.24, 144.98, 144.38, 142.89, 141.09, 139.91, 139.40, 139.29, 131.61, 131.34, 130.8 1, 130.67, 129.96, 129.71, 126.90, 126.83, 125.80, 125.67, 56.27(CH), 32.21(CH2), 31.20(CH2), 21.62(CH3), 16.09(CH3).

[0110] Figure 19 Mass spectrum of ligand L5; Mass spectrometry analysis: ESI-MS (m / z): theoretical value C 43 H 38 N3 + : 596.3060, test value 596.3059, [M+H] + .

[0111] (2) Synthesis of catalyst Ni5:

[0112] The steps for synthesizing Ni5 in this preparation example are basically the same as those for synthesizing catalyst Ni1 in Preparation 1. The only difference is that the ligand used in this preparation example is ligand L5; the rest of the operations are the same as in Example 1, with a yield of 79%.

[0113] Figure 20 Mass spectrum of catalyst Ni5; Mass spectrometry analysis: MALDI-TOF-MS (m / z): Theoretical value C 43 H37 BrN3Ni + : 732.1519, test value 732.1501, [M-Br] + .

[0114] Preparation Example 6

[0115] (1) Synthesis of ligand L6:

[0116] The preparation method for ligand L6 in this preparation example is basically the same as the method for synthesizing ligand L1 in preparation 1. The only difference is that 2-acetylpyrazine in Example 1 is replaced with 2-acetylpyrimidine. The rest of the operation is the same as in Example 1, and the yield is 77%.

[0117] Figure 21 and Figure 22 The images show the proton and carbon NMR spectra of ligand L6, respectively; NMR analysis: 1 H NMR (400MHz, CDCl3) δ8.87 (d, J=4.8Hz, 2H, aryl-H), 7.35 (t, J=4.8Hz, 1H, aryl-H), 7.25-7.0 2 (m, 20H, aryl-H), 6.69 (s, 2H, aryl-H), 5.41 (s, 2H, CH), 2.17 (s, 3H, CH3), 0.59 (s, 3H, CH3). 13 C NMR(101 MHz, CDCl3) δ162.49 (N=C), 157.20, 143.87, 142.29, 132.39, 132.10, 129.95, 129.55, 128. 72, 128.49, 128.31, 128.02, 126.19, 125.98, 121.26, 51.85(CH), 21.36(CH3), 17.73(CH3).

[0118] Figure 23 Mass spectrum of ligand L6; Mass spectrometry analysis: ESI-MS (m / z): theoretical value C 39 H 34 N3 + : 544.2747, test value 547.2744, [M+H] + .

[0119] (2) Synthesis of catalyst Ni6:

[0120] The steps for synthesizing Ni6 in this preparation example are basically the same as those for synthesizing catalyst Ni1 in Preparation 1. The only difference is that the ligand used in this preparation example is ligand L6; the rest of the operations are the same as in Example 1, with a yield of 89%.

[0121] Figure 24 Mass spectrum of catalyst Ni6; Mass spectrometry analysis: MALDI-TOF-MS (m / z): Theoretical value C 39 H 33 BrN3Ni + : 680.1206, test value 680.1198, [M-Br] + .

[0122] Comparative Preparation Example 1

[0123] (1) Synthesis of ligand L7:

[0124] In a 100 mL round-bottom flask, anhydrous toluene (15 mL), 2,6-diphenylmethylaniline (0.47 g, 1.1 mmol), 2-acetylpyridine (0.12 g, 1 mmol), and p-toluenesulfonic acid monohydrate (20 mg) were added. The mixture was refluxed and stirred at 100 °C for 24 h. After the reaction was stopped, part of the solvent was evaporated under reduced pressure, and the remaining solution was diluted with methanol (5 mL × 3) and stirred. The solution was filtered to obtain a pale yellow solid, which was dried under vacuum to obtain the target product (0.32 g, yield 61%).

[0125] NMR analysis: 1 H NMR (400MHz, CDCl3) δ8.87 (d, J=4.8Hz, 2H, aryl-H), 7.35 (t, J=4.8Hz, 2H, aryl-H), 7.25–7.02 (m, 20H, aryl-H), 6.69 (s, 2H, aryl-H), 5.41 (s, 3H, CH), 2.17 (s, 3H, CH3). 13 C NMR (101MHz, CDCl3) δ162.49(N=C), 157.20, 143.87, 142.29, 132.39, 132.10, 129.95, 129.55, 128. 72, 128.49, 128.31, 128.02, 126.19, 125.98, 121.26, 51.85(CH), 21.36(CH3).

[0126] Mass spectrometry analysis: ESI-MS (m / z): Theoretical value C 39 H 33 N2 + : 529.2638, test value 529.2639, [M+H] + .

[0127] (2) Synthesis of catalyst Ni7:

[0128] The steps for synthesizing Ni7 in this preparation example are basically the same as those for synthesizing catalyst Ni1 in Preparation Example 1. The only difference is that the ligand used in this preparation example is ligand L7. The rest of the operations are the same as in Preparation Example 1, and the yield is 91%.

[0129] Mass spectrometry analysis: MALDI-TOF-MS (m / z): Theoretical value C 39 H 32 BrN2Ni + : 665.1097, test value 665.1099, [M-Br] + .

[0130] The specific structures of the catalysts Ni1~Ni7 prepared in each preparation example are shown below:

[0131] ,

[0132] .

[0133] The following are examples of the application of catalysts Ni1 to Ni7 prepared in the above preparation examples and comparative preparation examples in the catalytic polymerization of ethylene to prepare polyethylene with a bimodal distribution.

[0134] Example 1

[0135] After vacuum drying the high-pressure polymerization flask at 100°C for at least 1 hour, it was placed in a glove box, and a certain amount of solvent and 2 μmol of MAO co-catalyst were added. The high-pressure polymerization flask was then taken out and connected to an ethylene pipeline and placed on a reactor with a pre-set polymerization temperature of 30°C. The ethylene pressure was adjusted to 2 atm, and the pipeline gas was purged. Subsequently, 2 μmol of Ni1 catalyst was dissolved in 1 mL of CH2Cl2 and injected into the reactor through a long needle under an ethylene atmosphere. The ethylene flow rate was adjusted to achieve a reactor pressure of 6 atm, and the timer was started for 30 minutes after the gas flow stabilized. After the polymerization reaction was completed, the gas in the reactor was vented, cooled to room temperature, and 100 mL of acidic ethanol solution was poured in. After filtration, the polymer was vacuum dried for 24 hours and weighed.

[0136] Examples 2-6

[0137] The preparation methods of Examples 2-6 are basically the same as those of Example 1. The main difference is that the Ni catalysts used are different. The catalysts used in Examples 2-6 are Ni2, Ni3, Ni4, Ni5 and Ni6, respectively. See Table 1 for details.

[0138] Example 7

[0139] The preparation methods of Example 7 and Example 1 are basically the same, the main difference being that the polymerization temperature conditions used are different, the polymerization temperature of this example is 50℃.

[0140] Examples 8-12

[0141] The preparation methods of Examples 8-12 are basically the same as those of Example 7. The main difference is that the Ni catalysts used are different. The catalysts used in Examples 8-12 are Ni2, Ni3, Ni4, Ni5 and Ni6, respectively. See Table 1 for details.

[0142] Comparative Example 1

[0143] The preparation method of Comparative Example 1 is basically the same as that of Example 1. The main difference is that the Ni catalyst used is different. Specifically, the catalyst used in this comparative example is Ni7.

[0144] Comparative Example 2

[0145] The preparation method of this comparative example is basically the same as that of Example 7. The main difference is that the Ni catalyst used is different. Specifically, the catalyst used in this comparative example is Ni7.

[0146] Performance testing:

[0147] Catalytic activity: Measured by the mass of polymer produced per mole of catalyst per hour of polymerization reaction, expressed in units of 10-1. 6 g·mol -1 ·h -1 .

[0148] Polymer molecular weight and molecular weight distribution: determined by high-temperature GPC at 150℃; the unit of polymer molecular weight is kg / mol.

[0149] Branching degree: refers to the number of branches per 1000 carbon atoms, determined by... 1 HNMR nuclear magnetic resonance integral determination.

[0150] Melting point: Measured using a DSC Q25 instrument under a stable nitrogen atmosphere at a heating / cooling rate of 10℃ / min, within the range of 0~180℃. The second heating data was used.

[0151] Table 1 below shows the experimental conditions for ethylene polymerization using the catalyst provided in this application, including data on the polymerization results such as catalyst, temperature (T), yield (Yield), catalytic activity (Act.), polymer weight-average molecular weight (Mw), molecular weight distribution (Mw / Mn), degree of branching (brs), and melting point (Tm).

[0152] Table 1. Statistical table of aggregation results for each embodiment and comparative example.

[0153]

[0154] In the table, yield refers to the mass of the polymer, in grams; wax indicates that the obtained polyethylene wax has a low viscosity and no obvious melting point.

[0155] As can be seen from the data in Table 1, under polymerization pressure of 6 atm and temperatures of 30℃ and 50℃, the Ni1~Ni6 catalysts exhibit high catalytic activity in the polymerization of ethylene (10... 6 g·mol -1 ·h -1 This process yields bimodal polyethylene with a medium molecular weight and a high melting point (96℃~125℃). Among these, Figure 25 The image shows the carbon spectrum of the bimodal polyethylene prepared in Example 1. In the graph, B represents the branching point, and the subscripts 1, 2, and n represent the branch lengths. Starting from the position next to the branching point, the subscripts are numbered αBn, βBn, and γBn. 1Bn, 2Bn, 3Bn, and 4Bn represent the first, second, third, and fourth main chain carbon atoms located on either side of the branching point B, from near to far along the main chain direction. S1, S2, and S3 are the side chain carbons numbered sequentially from the terminal methyl group towards the main chain direction; for example, S1 represents the terminal methyl group, and S2 represents the subterminal carbon. As can be seen from the graph, the obtained polyethylene is predominantly methyl-branched, accompanied by long-chain branching and terminal groups. Figure 26 The image shows a gel permeation chromatogram (GPC) of the bimodal polyethylene prepared in Example 1. Here, dw / dlogM represents the logarithmic molecular weight distribution, a mass distribution curve expressed as the logarithm of molecular weight (curve 1); %Ht represents the high-molecular-weight tail fraction (High-MW tail fraction), which is the percentage of the high-molecular-weight tail in the total mass, as shown in curve 2. The graph shows that the obtained polyethylene is predominantly low in molecular weight, but contains significant long polymer chains, resulting in a significantly broadened molecular weight distribution.

[0156] A comparison of Examples 1-6 with Examples 7-12 shows that the molecular weight of polyethylene obtained after ethylene polymerization increases to varying degrees with increasing temperature, accompanied by an extremely high polydispersity index. In contrast, the polymer obtained with the control catalyst Ni7 exhibits a narrow distribution and has no obvious melting point. This phenomenon is due to the interaction between the non-coordinated nitrogen atoms on the ligand backbone and the co-catalyst MAO during polymerization. The nitrogen-nickel centers coordinated to MAO may become more electron-deficient, accelerating chain growth and producing a higher molecular weight polymer, while also contributing to the formation of polyethylene with a bimodal distribution. Increased temperature promotes stronger coordination interactions, thereby increasing the proportion of high molecular weight components. This ultimately leads to an overall increase in molecular weight, although high temperatures typically reduce the molecular weight of both high and low molecular weight catalytic species due to increased chain transfer relative to chain growth.

[0157] Meanwhile, the electronic effects of para-aryl substituents significantly influence the ethylene polymerization catalyzed by nickel complexes. Generally, electron-withdrawing substituents tend to increase the molecular weight of the resulting polyethylene. Notably, although the methoxy group is an electron-donating substituent, it may coordinate with MAO after activation, transforming into an electron-withdrawing moiety. This coordination increases the electrophilicity of the metal center, accelerates chain growth, and also makes the catalyst more susceptible to deactivation. This explains why methoxy-substituted catalysts on Ni2 exhibit lower activity but produce polyethylene with higher molecular weight and wider distribution. Furthermore, electron-donating substituents such as methyl or tert-butyl groups also show excellent catalytic activity at lower temperatures.

[0158] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A nitrogen-heterocyclic skeletal imine nickel catalyst, characterized in that, The catalyst comprises compounds having the general formula I. ， Formula I, Ar is selected from diphenylmethyl and dibenzocycloheptanyl; R1 is selected from chlorine, methoxy, methyl and tert-butyl; R2 and R3 are each independently CH or N, and at least one of R2 and R3 is N.

2. The catalyst according to claim 1, characterized in that, The catalyst includes one of Ni1 to Ni6: ， 。 3. The method for preparing the nitrogen heterocyclic framework imine nickel catalyst according to any one of claims 1 to 2, characterized in that, Includes the following steps: S1. Mix 2-acetylpyrazine or 2-acetylpyrimidine with aromatic amine, anhydrous zinc chloride and acetic acid, and reflux the mixture. After the reflux reaction is complete, cool the reaction solution to room temperature, add the first undesirable solvent to precipitate the mixture, filter the solution, and obtain the first solid material. S2. Dissolve the first solid material in dichloromethane, add potassium oxalate aqueous solution and mix and stir, wash with water, and after the solution separates into layers, separate the organic phase, dry the organic phase, then concentrate under reduced pressure, add a second poor solvent to precipitate, filter and vacuum dry to obtain the organic ligand. S3. The organic ligand and nickel dibromide (ethylene glycol dimethyl ether) are mixed and dissolved in dichloromethane and stirred at room temperature for 12-16 hours. Part of the solvent is removed by vacuum evaporation, and then a third undesirable solvent is added to the remaining mixture to precipitate a second solid material. The mixture is filtered and vacuum dried to obtain the nitrogen heterocyclic framework imine nickel catalyst.

4. The preparation method according to claim 3, characterized in that, The preparation method satisfies at least one of the following conditions: (1) In step S1, the molar ratio of 2-acetylpyrazine or 2-acetylpyrimidine to aromatic amine is 1:(1.5~2); (2) The aromatic amine is selected from 2,6-diphenylmethyl-4-chloroaniline, 2,6-diphenylmethyl-4-methoxyaniline, 2,6-diphenylmethyl-4-methylaniline, 2,6-diphenylmethyl-4-tert-butylaniline or 2,6-dibenzocycloheptyl-4-methylaniline.

5. The preparation method according to claim 3, characterized in that, In step S3, the molar ratio of the organic ligand to nickel dibromide (ethylene glycol dimethyl ether) is 1:

1.

6. The preparation method according to claim 3, characterized in that, The preparation method satisfies at least one of the following conditions: (1) In step S1, the temperature of the reflux reaction is 80℃~90℃; the time of the reflux reaction is 5h~5.5h; (2) In step S2, the time for mixing and stirring the potassium oxalate aqueous solution is 1h~1.5h; (3) The first undesirable solvent is diethyl ether, the second undesirable solvent is methanol, and the third undesirable solvent is diethyl ether.

7. The application of the nitrogen heterocyclic framework imine nickel catalyst according to any one of claims 1 to 2 or the nitrogen heterocyclic framework imine nickel catalyst obtained by the method according to any one of claims 3 to 6 in the catalytic polymerization of ethylene to prepare bimodal polyethylene.

8. The application according to claim 7, characterized in that: The reaction of ethylene polymerization to prepare bimodal polyethylene was carried out under the catalytic conditions of the nitrogen heterocyclic skeleton imine nickel catalyst and methylaluminoxane.

9. The application according to claim 8, characterized in that: The molar ratio of the nitrogen heterocyclic framework imine nickel catalyst to methylaluminoxane is 1:(1~3).

10. The application according to claim 8, characterized in that, In the reaction of ethylene polymerization to prepare bimodal polyethylene, the reaction pressure is 6 atm to 10 atm, the reaction temperature is 30°C to 90°C, and the reaction time is 60 min to 120 min.

Images