Preparation method and application of bimodal linear polyethylene chromium carbene catalyst

Abstract

The invention discloses a preparation method and application of a bimodal linear polyethylene chromium carbene catalyst, and belongs to the technical field of chemical synthesis. The preparation method comprises the following steps: firstly, preparing 1-nitro-2-aromatic thioether benzene by taking 1-fluoro-2-nitrobenzene, aromatic mercaptan and potassium tert-butoxide as raw materials; then preparing 1-amino-2-aromatic sulfide benzene by taking the 1-nitro-2-aromatic sulfide benzene and hydrazine hydrate as raw materials; then preparing 8-hydroxyimidazole [1, 5-alpha] quinolinium salt by taking 1-amino-2-aromatic thioether benzene, 8-hydroxyquinoline-2-formaldehyde, a formaldehyde solution and a hydrogen hydrochloride-1, 4-dioxane solution as raw materials; and finally, taking 8-hydroxyimidazole [1, 5-alpha] quinolinium salt, silver trifluoromethanesulfonate, bis (trimethylsilyl) sodium amide and chromium trichloride as raw materials to react, thereby obtaining the compound. According to the preparation method, the possibility that the catalyst is poisoned is effectively reduced, the catalytic activity of the catalyst is improved, and the catalyst has good thermal stability.

Description

Technical Field

[0001] The invention relates to the technical field of chemical synthesis, and in particular to a preparation method and application of a bimodal linear polyethylene chromium carbene catalyst. Background Art

[0002] As one of the most important ligands in organometallic chemistry, metal-nitrogen heterocyclic carbene complexes are widely used in catalysis, metal drugs and materials science due to their unique electronic and steric effects on metal centers.

[0003] In 1991, Kevin's group reported the first nitrogen heterocyclic compounds with imidazole [1,5-α] quinoline skeleton (see J.Org Chem 1991, 56, 2400); in 2015, Nozaki's group reported the nitrogen heterocyclic carbene compounds with a rigid skeleton of bidentate imidazole [1,5-α] quinoline (see J.Am.Chem.Soc.2015, 137, 10934-10937). Compared with traditional imidazole nitrogen heterocyclic carbene, imidazole [1,5-α] quinoline has a more rigid skeleton and stronger electron donating ability. A large number of studies have shown that the introduction of sulfur or phosphorus elements in the multidentate ligand can further improve the catalytic activity and regioselectivity of the metal center.

[0004] As one of the earliest metals used in olefin polymerization, metallic chromium has attracted widespread attention from scholars since its introduction. However, nitrogen-heterocyclic chromium carbene compounds, as classic olefin polymerization catalysts, are prone to β-H elimination, leading to catalyst poisoning. How to reduce the possibility of catalyst poisoning is one of the key issues that need to be urgently addressed in the field of nitrogen-heterocyclic chromium carbene compounds. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a preparation method and application of a bimodal linear polyethylene chromium carbene catalyst to solve the problem that the existing nitrogen heterocyclic chromium carbene compounds are prone to β-H elimination, resulting in catalyst poisoning.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] A method for preparing a bimodal linear polyethylene chromium carbene catalyst comprises the following steps:

[0008] (1) stirring 1-fluoro-2-nitrobenzene, aromatic mercaptan and potassium tert-butoxide in a solvent to react to obtain 1-nitro-2-aromatic sulfide benzene;

[0009] (2) mixing the 1-nitro-2-aromatic sulfide benzene obtained in step (1) and hydrazine hydrate in a solvent, adding a catalyst to carry out a reflux reaction, and obtaining 1-amino-2-aromatic sulfide benzene;

[0010] (3) mixing the 1-amino-2-aromatic sulfide benzene obtained in step (2), 8-hydroxyquinoline-2-carboxaldehyde, formaldehyde solution and hydrogen chloride-1,4-dioxane solution, stirring and reacting in a solvent to obtain 8-hydroxyimidazo[1,5-α]quinolinium salt;

[0011] (4) The 8-hydroxyimidazo[1,5-α]quinolinium salt obtained in step (3), silver trifluoromethanesulfonate, sodium bis(trimethylsilyl)amide and chromium trichloride are stirred and reacted in a solvent to obtain the product.

[0012] Furthermore, in step (1), the molar ratio of 1-fluoro-2-nitrobenzene, aromatic thiol and potassium tert-butoxide is (0.8-1.2):(1.0-1.5):(1.0-1.5); the solvent is ethanol; the stirring reaction temperature is 20-30° C. and the time is 10-15 hours.

[0013] Preferably, in step (1), the molar ratio of 1-fluoro-2-nitrobenzene, aromatic thiol and potassium tert-butoxide is 1:1.2:1.2; the solvent is ethanol; the stirring reaction temperature is 25° C. and the time is 12 hours.

[0014] Furthermore, the chemical reaction formula of step (1) is:

[0015]

[0016] Furthermore, in step (2), the molar ratio of 1-nitro-2-aromatic sulfide benzene, hydrazine hydrate and catalyst is (0.8-1.2):(3-5):(0.01-0.1); the solvent is ethanol, and the catalyst is palladium carbon; the reflux reaction temperature is 80-90°C, and the time is 10-15h.

[0017] Preferably, in step (2), the molar ratio of 1-nitro-2-aromatic sulfide benzene, hydrazine hydrate and catalyst is 1:4:0.05; the solvent is ethanol, and the catalyst is palladium carbon; the reflux reaction temperature is 85° C., and the time is 12 h.

[0018] Furthermore, the chemical reaction formula of step (2) is:

[0019]

[0020] Furthermore, in step (3), the molar ratio of 1-amino-2-aromatic sulfide benzene to 8-hydroxyquinoline-2-carboxaldehyde is 1:(1-1.3); the solvent is ethanol; the stirring reaction temperature is 20-30° C. and the time is 50-100 hours.

[0021] Preferably, in step (3), the molar ratio of 1-amino-2-aromatic sulfide benzene to 8-hydroxyquinoline-2-carboxaldehyde is 1:1; the solvent is ethanol; the stirring reaction temperature is 25° C. and the time is 72 hours.

[0022] Furthermore, the chemical reaction formula of step (3) is:

[0023]

[0024] Furthermore, in step (4), the molar ratio of 8-hydroxyimidazole [1,5-α] quinolinium salt, silver trifluoromethanesulfonate, sodium bis(trimethylsilyl)amide and chromium trichloride is (0.05-0.2): (0.05-0.2): (0.1-0.3): (0.05-0.2); the solvent is tetrahydrofuran; the reaction temperature is 20-30° C., and the reaction time is 20-60 h.

[0025] Preferably, in step (4), the molar ratio of 8-hydroxyimidazole [1,5-α] quinolinium salt, silver trifluoromethanesulfonate, sodium bis(trimethylsilyl)amide and chromium trichloride is 0.1:0.1:0.2:0.1; the solvent is tetrahydrofuran; the reaction temperature is 25° C. and the reaction time is 48 h.

[0026] Furthermore, the chemical reaction formula of step (4) is:

[0027]

[0028] Furthermore, in the process of synthesizing the chromium carbene catalyst in step (4), 8-hydroxyimidazole [1,5-α] quinolinium salt is firstly treated with sodium bis(trimethylsilyl)amide as a strong base to remove the proton of C-2 on the imidazole group, and then silver trifluoromethanesulfonate is added, and then metal exchange is carried out with chromium trichloride.

[0029] Furthermore, the chemical structure of the bimodal linear polyethylene chromium carbene catalyst is shown in Formula I:

[0030] Formula I:

[0031] In the formula, Ar is a C6-C 10 , C 12 , C 19 and C 32 Any one of the aromatic groups.

[0032] The application of the above-mentioned bimodal linear polyethylene chromium carbene catalyst in catalyzing ethylene polymerization reaction.

[0033] The present invention has the following beneficial effects:

[0034] The present invention provides a method for preparing a bimodal linear polyethylene chromium carbene catalyst, which effectively reduces the possibility of catalyst poisoning by combining a bidentate imidazole [1,5-α] quinoline nitrogen heterocyclic ligand with regulated steric hindrance and electronic properties with chromium, and effectively improves the catalytic activity of the catalyst in catalyzing ethylene polymerization reactions, has good thermal stability, and can efficiently produce bimodal linear polyethylene. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The H NMR spectrum of 1-naphthylphenylsulfide imidazo[1,5-α]quinolinium salt 1a obtained in Example 1;

[0036] Figure 2 The NMR carbon spectrum of 1-naphthylphenylsulfide imidazo[1,5-α]quinolinium salt 1a obtained in Example 1;

[0037] Figure 3 The H NMR spectrum of 1-(2,4,6-triisopropylphenyl)phenyl sulfide imidazo[1,5-α]quinolinium salt 1b obtained in Example 2;

[0038] Figure 4 The NMR carbon spectrum of 1-(2,4,6-triisopropylphenyl)phenyl sulfide imidazo[1,5-α]quinolinium salt 1b obtained in Example 2;

[0039] Figure 5 The H NMR spectrum of the imidazo[1,5-α]quinolinium salt ligand L1 obtained in Example 3;

[0040] Figure 6 The NMR carbon spectrum of the imidazo[1,5-α]quinolinium salt ligand L1 obtained in Example 3;

[0041] Figure 7 The H NMR spectrum of the imidazo[1,5-α]quinolinium salt ligand L4 obtained in Example 3;

[0042] Figure 8 The NMR carbon spectrum of the imidazo[1,5-α]quinolinium salt ligand L4 obtained in Example 3;

[0043] Fig. 9 This is the hydrogen spectrum of polyethylene produced by chromium carbene catalyst in the test example;

[0044] Fig.10 This is the carbon spectrum of polyethylene produced by chromium carbene catalyst in the test example;

[0045] Fig.11 This is the GPC curve of polyethylene produced by chromium carbene catalyst in the test example. DETAILED DESCRIPTION

[0046] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0047] Embodiment 1:

[0048] A method for preparing a bimodal linear polyethylene chromium carbene catalyst comprises the following steps:

[0049] (1) Preparation of 1-naphthalene-2-nitrophenyl sulfide

[0050] Under anhydrous and oxygen-free conditions, 1.0 mmol 1-naphthol, 1.2 mmol o-fluoronitrobenzene, and 1.2 mmol potassium tert-butoxide were mixed, 15 mL ethanol was added, and the mixture was stirred at room temperature for 12 h. After the reaction, the solution was spin-dried and washed three times with ice ethanol to obtain a yellow powder, namely 1-naphthalene-2-nitrophenyl sulfide, with a yield of 85%. 1 H NMR (400MHz, CDCl3): δ = 8.25 (dd, J = 8.2, 1.6Hz, 1H), 8.18 (s, 1H), 7.95 -7.86(m,3H),7.63-7.51(m,3H),7.32-7.27(m,1H),7.24-7.18(m,1H),6.89(d,J=8.2Hz,1H).

[0051] (2) Preparation of 1-naphthalene-2-aminophenyl sulfide

[0052] Under anhydrous and oxygen-free operating conditions, 1.0 mmol 1-naphthalene-2-nitrobenzenesulfane, 4 mmol hydrazine hydrate, and 0.05 mmol palladium on carbon were mixed, 15 mL ethanol was added, and the mixture was refluxed at 85° C. for 12 h. After the reaction was completed, the mixture was cooled to room temperature and filtered, 15 mL water was added, and dichloromethane was added for extraction three times. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was spin-dried, washed with n-hexane, and dried to obtain a white powder, namely 1-naphthalene-2-nitrobenzenesulfane, with a yield of 88%. 1 H NMR (400MHz, CDCl3) δ = 7.78 (d, J = 7.2Hz, 1H), 7.73 (d, J = 8.7Hz, 1H), 7.67 (d, J = 7.8Hz, 1H), 7 .57-7.50(m,2H),7.47-7.39(m,2H),7.33-7.26(m,2H),6.83(d,J=7.7Hz,2H),4.32(s,2H).

[0053] (3) Preparation of 1-naphthylphenylsulfide imidazo[1,5-α]quinolinium salt 1a

[0054] The structural formula is:

[0055] Add 1mmol of 1-naphthalene-2-aminophenyl sulfide dissolved in 5mL of ethanol to an ice-cooled flask, and add 1mmol of hydrochloric acid-dioxane solution. Stir the reactants at this temperature for 2 minutes, then add 5mmol of formalin (40% formaldehyde aqueous solution by mass) and additional ethanol (10mL), warm the reaction to room temperature and stir the reaction under air for 1h. After adding a portion of 1.0mmol of 8-hydroxyquinoline-2-carboxaldehyde, seal the flask with a rubber septum and stir at room temperature for 3 days. After the reaction is completed, the resulting mixture is spin-dried, dissolved in dichloromethane, and ethyl acetate is added to obtain a large amount of precipitate, which is collected by filtration and washed three times with ethyl acetate. The yellow precipitate, i.e., 1-naphthylphenyl sulfide imidazole [1,5-α] quinolinium salt 1a, is obtained with a yield of 80%.

[0056] The results of NMR experiments are as follows Figure 1-Figure 2 shown. 1 H NMR (400MHz, DMSO-d6): δ = 10.14 (s, 1H), 8.51 (d, J = 8.4Hz, 1H), 7.96 (d, J = 8.0 Hz,1H),7.62(t,J=7.9Hz,1H),7.51(d,J=8.1Hz,1H),7.40-7.09(m,13H)ppm. 13 C{ 1 H}NMR(100MHz,DMSO-d6)δ=149.26,135.98,133.86,133.32,133.05,132.65,132.45,130.91,129.86,129.76,129.60,129.17,12 9.02,128.78,127.99,127.70,127.50,127.38,127.31,127.02,119.87,118.21,117.04,116.81,115.38ppm.HRMS(ESI,positive ions):m / z=419.1213(calcd for[1a-Cl] + 419.1188).

[0057] (4) Preparation of chromium carbene compound 2a

[0058] The structural formula is:

[0059] In a nitrogen glove box, 0.1 mmol of ligand 1-(2,4,6-triisopropylphenyl)phenyl sulfide imidazole [1,5-α] quinolinium salt was dissolved in 10 mL of ultra-dry tetrahydrofuran, and then 0.2 mmol of sodium bis(trimethylsilyl)amide was added to the solution, and the reaction was stirred at room temperature for 12 hours. After the reaction was completed, the solid was separated by filtration, and 0.1 mmol of silver trifluoromethanesulfonate was added to the filtrate, and the mixture was stirred at room temperature in the dark for 12 hours. After the reaction was completed, the solid was separated by filtration, and 0.1 mmol of chromium trichloride was added to the filtrate, and the mixture was stirred in the dark for 24 hours. After the reaction was completed, the solid was separated by filtration, concentrated, and a large amount of ether was added to precipitate a white solid. The solid was collected by filtration, washed with ether, and dried to obtain chromium carbene compound 2a with a yield of 53%. Elemental analysis: C 56.3%, H 2.9%, N 4.8%, S 5.5%.

[0060] Embodiment 2:

[0061] A method for preparing a bimodal linear polyethylene chromium carbene catalyst comprises the following steps:

[0062] (1) Preparation of 1-(2,4,6-triisopropylphenyl)-2-nitrophenyl sulfide

[0063] Under anhydrous and oxygen-free operating conditions, 1.0 mmol 1-thiophenol-2,4,6-triisopropylbenzene, 1.2 mmol o-fluoronitrobenzene, and 1.2 mmol potassium tert-butoxide were mixed, 15 mL ethanol was added, and the mixture was stirred at room temperature for 12 h. After the reaction was completed, the solution was spin-dried and washed three times with ice ethanol to obtain a yellow powder, namely 1-(2,4,6-triisopropylphenyl)-2-nitrophenyl sulfide, with a yield of 95%. 1 H NMR (400MHz, CDCl3): δ8.28(d,J=7.6Hz,1H),7.36-7.28(m,1H),7.22-7.14(m,3H),6.67(d,J=8 .5Hz,1H),3.61-3.47(m,2H),3.05-2.91(m,1H),1.32(d,J=6.9Hz,6H),1.14(d,J=6.9Hz,12H).

[0064] (2) Preparation of 1-(2,4,6-triisopropylphenyl)-2-aminophenyl sulfide

[0065] Under anhydrous and oxygen-free operating conditions, 1.0mmol 1-(2,4,6-triisopropylphenyl)-2-nitrophenylene sulfide, 4mmol hydrazine hydrate, and 0.05mmol palladium on carbon were mixed, 15mL ethanol was added, and the mixture was refluxed at 85°C for 12h. After the reaction was completed, the mixture was cooled to room temperature and filtered, 15mL water was added, and dichloromethane was added for extraction three times. The mixture was dried over anhydrous sodium sulfate and filtered. The filtrate was spin-dried, washed with n-hexane, and dried to obtain a white powder, namely 1-naphthalene-2-nitrobenzenesulfane, with a yield of 90%. 1 H NMR (400MHz, CDCl3): δ = 7.13 (s, 2H), 6.93 (t, J = 7.5Hz, 1H), 6.69 (d, J = 7.9Hz, 1H), 6.59 (t, J = 7.6Hz, 1H), 6.47 (d, J = 7.9Hz, 1H), 4.03 (s, 2H), 3.70 (p, J = 6.8Hz, 2H), 2.96 (p, J = 6.9Hz, 1H), 1.32 (d, J = 7.0Hz, 6H), 1.17 (d, J = 6.9Hz, 12H).

[0066] (3) The preparation structural formula of 1-(2,4,6-triisopropylphenyl)phenyl sulfide imidazo[1,5-α]quinolinium salt 1b is:

[0067] Add 1 mmol of 1-naphthalene-2-aminophenyl sulfide dissolved in 5 mL of ethanol to an ice-cooled flask, and add 1 mmol of hydrochloric acid-dioxane solution. Stir the reactants at this temperature for 2 minutes, then add 5 mmol of formalin (40% formaldehyde aqueous solution by mass) and additional ethanol (10 mL). Warm the reaction to ambient temperature and stir under air for 1 hour. After adding a portion of 1.0 mmol of 8-hydroxyquinoline-2-carboxaldehyde, seal the flask with a rubber septum and stir at room temperature for 3 days. After the reaction is completed, the resulting mixture is spin-dried, dissolved in dichloromethane, and ethyl acetate is added to obtain a large amount of precipitate, which is collected by filtration and washed three times with ethyl acetate. The yellow precipitate, i.e., 1-(2,4,6-triisopropylphenyl)phenyl sulfide imidazole [1,5-α] quinolinium salt 1b, is obtained with a yield of 85%.

[0068] The results of NMR experiments are as follows Figure 3-Figure 4 As shown:

[0069] 1H NMR (400MHz, CDCl3): δ = 10.65 (s, 1H), 8.07 (d, J = 9.2Hz, 1H), 7.94 (s, 1H), 7 .54-7.49(m,2H),7.48-7.43(m,2H),7.42-7.37(m,1H),7.33-7.28(m,1H),7 .22(d,J=6.6Hz,1H),7.14(s,2H),6.66(d,J=8.0Hz,1H),3.44(p,J=6.8Hz,2 H), 2.93 (p, J = 6.9Hz, 1H), 1.28 (d, J = 6.9Hz, 6H), 1.14 (d, J = 6.9Hz, 12H) ppm. 13 C{ 1 H}NMR (100MHz, CDCl3): δ=154.02,152.41,137.05,132.38,131.03,130.71,129.88,129.80,129.33,127.68,126.08, 125.98,122.52,120.91,119.50,118.92,118.07,114.27,113.41,34.46,32.45,24.31,23.91ppm.HRMS(ESI,positive ions):m / z=495.2465(calcd for[1b-Cl] + 495.2279).

[0070] (4) Preparation of chromium carbene compound 2b

[0071] The structural formula is:

[0072] In a nitrogen glove box, 0.1mmol of ligand 1-naphthylphenylsulfide imidazole [1,5-α] quinolinium salt was dissolved in 10mL of ultra-dry tetrahydrofuran, and then 0.2mmol of sodium bis(trimethylsilyl)amide was added to the solution, and the reaction was stirred at room temperature for 12h. After the reaction was completed, the solid was separated by filtration, and 0.1mmol of silver trifluoromethanesulfonate was added to the filtrate, and the mixture was stirred at room temperature in the dark for 12h. After the reaction was completed, the solid was separated by filtration, and 0.1mmol of chromium trichloride was added to the filtrate, and the mixture was stirred in the dark for 24h. After the reaction was completed, the solid was separated by filtration, concentrated, and a large amount of ether was added to precipitate a white solid. The solid was collected by filtration, washed with ether, and dried to obtain chromium carbene compound 2a with a yield of 50%. Elemental analysis: C 58.9%, H 5.1%, N 4.3%, S 4.9%.

[0073] Embodiment 3:

[0074] The chromium carbene compounds were prepared using pyrazolyl imidazo[1,5-α]pyridinium salts with different N-substituents, as shown in Table 1:

[0075] Table 1 Examples of reactions for preparing chromium carbene compounds from imidazo[1,5-α]quinolinium salts with different S-substituents

[0076]

[0077]

[0078]

[0079]

[0080] Among them, imidazo[1,5-α]quinolinium salt ligand L1: The results of NMR experiments are as follows Figure 5-Figure 6 shown. 1 H NMR (400MHz, CDCl3): δ = 12.79 (s, 1H), 10.49 (d, J = 1.7Hz, 1H), 8.03 (d, J = 8.2Hz, 1H), 7.83 (d, J = 1.8Hz, 1H), 7.64 (t, J = 7.8Hz, 1 H),7.51–7.47(m,1H),7.45(t,J=2.6Hz,2H),7.44(d,J=1.6Hz,1H),7.42-7.40(m,1H),7.19(d,J=7.7Hz,1H),2.48(s,3H)ppm. 13 C{ 1 H} NMR (100MHz, CDCl3): δ = 149.98, 136.13, 132.24, 131.01, 129.72, 128.94, 127.30, 127.13, 126. 46,126.10,119.26,119.09,114.69,113.70,77.47,77.16,76.84,15.67ppm.HRMS(ESI,positive ions):m / z=307.0900(calcd for[L1-Cl] + 307.0987).

[0081] Imidazolium [1,5-α]quinolinium salt ligand L4: The results of NMR experiments are as follows Figure 7-Figure 8 shown. 1H NMR (400MHz, CDCl3): δ = 10.37 (s, 1H), 8.53 (d, J = 1.7Hz, 1H), 7.87-7.84 (m, 1H), 7.80-7.74 (m, 3H), 7.7 2-7.67(m,3H),7.59-7.55(m,3H),7.50(d,J=7.9Hz,1H),7.43-7.29(m,5H),7.24(d,J=8.1Hz,1H)ppm. 13 C{ 1 H}NMR (100MHz, CDCl3): δ=134.09,133.85,132.54,132.33,131.96,131.07,130.44,129.73,129.49,12 9.44,128.89,128.77,128.44,127.71,126.26,119.20,118.20,115.32,114.25ppm.HRMS(ESI,positive ions):m / z=369.1056(calcd for[L4-Cl] + 369.1148).

[0082] Test example:

[0083] The chromium carbene compound 2b prepared in Example 2 was used as a catalyst for ethylene polymerization, and the polymerization process was as follows:

[0084] In the glove box, add ultra-dry toluene (25 mL) and co-catalyst to a dry 50 mL high-pressure polymerization reaction steel kettle, add chromium carbene compound 2b dissolved in 0.5 mL dichloromethane, stir evenly, seal and remove from the glove box, and transfer to the high-pressure polymerization pipeline. After introducing 5 atm ethylene gas to replace the nitrogen in the kettle three times, adjust the ethylene pressure at the same time. Adjust the stirring rate and temperature, and start the timing after the temperature rises to the set value. After the reaction is completed, wait for the kettle to cool down, release the pressure of the reactor, add a large amount of ethanol to quench the co-catalyst, filter, repeatedly wash the polymer with ethanol, and vacuum dry at 60°C. Weigh the dried ethylene homopolymer, calculate the catalyst activity and characterize the polymerization product.

[0085] The effects of reaction conditions on the ethylene polymerization reaction of chromium carbene compound 2b are shown in Table 2.

[0086] Table 2 Results of screening conditions for ethylene polymerization of chromium carbene compound 2b

[0087]

[0088] In the table, the polymerization conditions are: 2 μmol chromium carbene compound 2b, 20 mL toluene, 0.5 mL dichloromethane; Al b =AlClMe2; Activity c :10 3 g(PE)·mol -1 (Cr)·h -1 ; 16 d The catalyst used is 1-(2,4,6-triisopropylphenyl)phenyl sulfide imidazo[1,5-α]quinolinium salt 1b, 17 d The catalyst used is CrCl3, 18 d Only AlMe2Cl was used as catalyst.

[0089] According to Table 2, the activity of chromium carbene compound 2b at 70°C is 965×10 3 g(PE)mol -1 (Cr)h -1 , and a polymer insoluble in toluene was obtained, which indicates that the imidazole [1,5-α] quinoline containing sulfur side arm group has good thermal stability. The chromium carbene compound 2b prepared by the present invention significantly improves the catalytic activity for ethylene polymerization compared with other commonly used catalysts. After the obtained polymer was analyzed by nuclear magnetic resonance spectroscopy and gel chromatography, it was found that the polymerization products were all bimodal linear polyethylene. The results are as follows Figure 9-11 shown.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a bimodal linear polyethylene chromium carbene catalyst, characterized in that: The following steps are involved: (1) stirring 1-fluoro-2-nitrobenzene, aromatic mercaptan and potassium tert-butoxide in a solvent to react to obtain 1-nitro-2-aromatic sulfide benzene; (2) mixing the 1-nitro-2-aromatic sulfide benzene obtained in step (1) and hydrazine hydrate in a solvent, adding a catalyst to carry out a reflux reaction, and obtaining 1-amino-2-aromatic sulfide benzene; (3) mixing the 1-amino-2-aromatic sulfide benzene obtained in step (2), 8-hydroxyquinoline-2-carboxaldehyde, formaldehyde solution and hydrogen chloride-1,4-dioxane solution, stirring and reacting in a solvent to obtain 8-hydroxyimidazo[1,5-α]quinolinium salt; (4) The 8-hydroxyimidazo[1,5-α]quinolinium salt obtained in step (3), silver trifluoromethanesulfonate, sodium bis(trimethylsilyl)amide and chromium trichloride are stirred and reacted in a solvent to obtain a product.

2. The method for preparing a bimodal linear polyethylene chromium carbene catalyst according to claim 1, characterized in that: In the step (1), the molar ratio of 1-fluoro-2-nitrobenzene, aromatic mercaptan and potassium tert-butoxide is (0.8-1.2):(1.0-1.5):(1.0-1.5); the solvent is ethanol; the stirring reaction temperature is 20-30° C. and the reaction time is 10-15 hours.

3. The method for preparing a bimodal linear polyethylene chromium carbene catalyst according to claim 1, characterized in that: In the step (2), the molar ratio of 1-nitro-2-aromatic sulfide benzene, hydrazine hydrate and catalyst is (0.8-1.2):(3-5):(0.01-0.1); the solvent is ethanol, and the catalyst is palladium carbon; the reflux reaction temperature is 80-90° C., and the reaction time is 10-15 hours.

4. The method for preparing a bimodal linear polyethylene chromium carbene catalyst according to claim 1, characterized in that: In the step (3), the molar ratio of 1-amino-2-aromatic sulfide benzene to 8-hydroxyquinoline-2-carboxaldehyde is 1:(1-1.3); the solvent is ethanol; the stirring reaction temperature is 20-30° C. and the time is 50-100 hours.

5. The method for preparing a bimodal linear polyethylene chromium carbene catalyst according to claim 1, characterized in that: In the step (4), the molar ratio of 8-hydroxyimidazole [1,5-α] quinolinium salt, silver trifluoromethanesulfonate, sodium bis(trimethylsilyl)amide and chromium trichloride is (0.05-0.2): (0.05-0.2): (0.1-0.3): (0.05-0.2); the solvent is tetrahydrofuran; the reaction temperature is 20-30° C., and the reaction time is 20-60 hours.

6. The method for preparing a bimodal linear polyethylene chromium carbene catalyst according to claim 1, characterized in that: The chemical structure of the obtained bimodal linear polyethylene chromium carbene catalyst is shown in Formula I: Formula I: In the formula, Ar is a C6-C 10 , C 12 , C 19 and C 32 Any one of the aromatic groups.

7. Use of the bimodal linear polyethylene chromium carbene catalyst according to any one of claims 1 to 6 in catalyzing ethylene polymerization.

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