A catalytic system for selective tetramerization of ethylene containing PNP ligands and its preparation method and application

Abstract

This invention provides a catalytic system for selective tetramerization of ethylene containing PNP ligands, its preparation method, and its application, belonging to the field of ethylene oligomerization technology. The catalytic system comprises a Cr(III)-containing PNP complex and an activator. The Cr(III)-containing PNP complex is obtained by reacting benzenesulfonamide or isopropylammonium sulfate, diphenylphosphine chloride or diisopropylphosphine chloride, with a Cr(III) metal compound. This complex can be premixed with the activator or added separately to the ethylene tetramerization reaction. The catalytic system prepared in this scheme introduces a sulfonyl group with strong electron-withdrawing ability onto the nitrogen atom. The sulfonyl-containing PNP chromium complex can be obtained by rearranging PPN-type compounds under the induction of a chromium source. By introducing the sulfonyl group, the catalytic system exhibits high catalytic activity, up to 4050 kg / g Cr·h, with a total selectivity of up to 96.3% for 1-hexene and 1-octene.

Description

Technical Field

[0001] The invention belongs to the technical field of ethylene oligomerization reaction, and specifically relates to a catalytic system for ethylene selective tetramerization containing a PNP ligand, and a preparation method and application thereof. Background Art

[0002] Linear α-olefins (LAO) are important chemical raw materials that can be used to prepare lubricants, surfactants, detergents, etc., and have extremely high economic application value. Among them, 1-hexene and 1-octene are indispensable comonomers in the synthesis of polyolefin elastomers (POE), high-density polyethylene (HDPE), and linear low-density polyethylene (LLDPE) (the amount of comonomer in POE is greater than 20%, the comonomer content in HDPE is 1-2%, and the comonomer content in LLDPE is generally 8-10%). Ethylene polymerization is an important method for producing linear α-olefins. Compared with traditional methods such as wax cracking process, extraction separation method, fatty alcohol dehydrogenation method, olefin dimerization and disproportionation, and internal olefin isomerization method, the product has a high degree of linearization, a narrow degree of polymerization distribution, and a low separation cost. It has great comprehensive advantages and is now widely used in industrial production.

[0003] Traditional ethylene oligomerization catalysis mainly uses metal titanium, zirconium, iron and other catalytic systems. These catalytic systems mainly follow the Cossee-Arlman mechanism, that is, ethylene molecules are coordinated and inserted into the metal center of the catalyst. With the continuous insertion of ethylene molecules, the linear chain of the metal alkyl chain grows, and the product linear α-olefins are usually normally distributed. In industrial applications, further separation and purification must be performed according to actual needs. The highly selective polymerization of ethylene mainly follows the metal cyclization mechanism. The α-olefins produced in this way are Schulz-Flory distributed, and the product at the peak has a high content. This method provides an important way to produce α-olefins with a specific carbon number. In recent years, the growing demand for 1-hexene and 1-octene has made the selective polymerization of ethylene a hot topic in industry and academia.

[0004] At present, reports on the selective polymerization of ethylene mainly focus on the preparation of 1-butene, 1-hexene and 1-octene by dimerization, trimerization and tetramerization. In these catalytic systems, slight changes in the catalyst structure have a great influence on the product distribution, and the regulation of the catalyst structure depends on the changes in the skeleton and substituents of the ligand. In 2002, British Petroleum reported the use of the Cr / Ar2PN(R)PAr2 (Ar is an aromatic group substituted with ortho-methoxy) system for the selective preparation of 1-hexene (Chemical Communication, 2002, 858). In 2003, Phillips Petroleum used the developed Phillips trimerization chromium catalyst to achieve industrialization of ethylene trimerization (US5523507). Sinopec (Yanshan) and PetroChina (Daqing) also used similar catalytic systems to achieve industrial production of 1-hexene. 1-Octene can be used in the production of high-quality polyethylene (PE), polyolefin elastomers (POE), lubricant base oil (PAO), plasticizers, surfactants and other fields. Compared with 1-hexene, 1-octene has higher economic value. Until 2004, Sasol successfully achieved ethylene tetramerization using the above-mentioned PNP type ligand / chromium catalyst system through modification of substituents, and the 1-octene selectivity can reach up to 67.5% (J. Am. Chem. Soc. 2004, 126, 45, 14712–14713). In 2007, Sasol conducted a detailed study on the substituents on the nitrogen atom of the PNP ligand, including alkyl, aryl, and alkenyl. The introduction of different substituents has a significant effect on the catalytic performance. When the substituent on the nitrogen atom is tert-butyl, the catalytic activity can reach 1558 kg / (g Cr / h) and the 1-octene selectivity is 58.0%. The total selectivity of 1-hexene and 1-octene reaches 88.3%, but the content of C10 and above by-products is high (8.0%). In 2022, Barman et al. found that when an electron-withdrawing substituent (trifluoromethyl, methoxy) was introduced into the meta position of the phenyl group on the nitrogen atom of the PNP ligand, it showed higher catalytic activity (ACS Omega 2022, 7, 16333─16340; ACS Omega 2023,8, 26437─26443). When a methoxy group was introduced into the meta position of the phenyl group, the catalytic activity reached 3342 kg / (g Cr / h), the selectivity for 1-octene reached 67.9%, the total selectivity for 1-hexene and 1-octene reached 88.7%, and the content of C10 and above by-products was only 1.4%. The enhancement of the electron-withdrawing ability of the substituent on the nitrogen atom seems to be beneficial to improving the activity of the catalyst, and can reduce the content of C10 and above by-products, and improve the total selectivity of 1-hexene and 1-octene. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a catalytic system for selective tetramerization of ethylene containing a PNP ligand, and a preparation method and application thereof. A sulfonyl group with strong electron-withdrawing ability is introduced on the nitrogen atom of the PNP ligand, and the PNP chromium complex containing the sulfonyl group can be obtained by rearrangement of a PPN-type compound under the induction of a chromium source. The catalytic system has the characteristics of high catalytic activity and low content of C10 and above by-products.

[0006] To achieve the above object, the present invention first provides a catalytic system for selective tetramerization of ethylene containing a PNP ligand, wherein the catalytic system for selective tetramerization of ethylene containing a PNP ligand comprises a Cr(III)-containing PNP complex and an activator as shown in the following formula 1:

[0007] ;

[0008] Among them, the group R 1 Selected from C1-C 30 Alkyl, C1-C 30 Alkenyl, C1-C 20 Alkoxy, C4-C 30 One of the aromatic groups;

[0009] R 2 , R 3 , R 4 , R 5 Each independently selected from C1-C 30 Alkyl, C4-C 30 One of the aromatic groups;

[0010] X is selected from chlorine, bromine and iodine; n is 2 or 3.

[0011] Preferably, the alkyl group is selected from any one of methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, sec-pentyl, tert-pentyl, neopentyl, cyclopentyl, n-hexyl, sec-hexyl, tert-hexyl, neohexyl, cyclohexyl, n-heptyl, tert-heptyl, neoheptyl, cycloheptyl, n-octyl, sec-octyl, tert-octyl, neo-octyl, cyclooctyl, n-nonyl, sec-nonyl, tert-nonyl, neo-nonyl, cyclononyl, n-decyl, sec-decyl, tert-decyl, neo-decyl, cyclodecyl, isopropyl, isobutyl, isopentyl, isohexyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, and adamantyl; The alkenyl group is selected from any one of vinyl, 1-propenyl, 2-propenyl, allyl, 1-butenyl, 1-isobutenyl, 3-butenyl, 2-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 2-methyl-1-butenyl, 2-methyl-2-butenyl, 2-methyl-3-butenyl, 1-methyl-2-butenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, 5-hexenyl, 2-cyclohexenyl, 3-cyclohexenyl, 2-methyl-2-cyclohexenyl and 2,6-dimethyl-2-cyclohexenyl.

[0012] Preferably, the alkoxy group is selected from methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, n-pentyloxy, isopentyloxy, tert-pentyloxy, neopentyloxy, cyclopentyloxy, n-hexyloxy, sec-hexyloxy, tert-hexyloxy, neo-hexyloxy, cyclohexyloxy, n-heptyloxy, tert-heptyloxy, neo-heptyloxy, cycloheptyloxy, n-octyloxy, sec-octyloxy, tert-octyloxy, neo-octyloxy, cyclooctyloxy, n-nonyloxy, sec-nonyloxy, tert-nonyloxy, neo-nonyloxy, cyclononyloxy , any one of n-decyloxy, secondary decyloxy, tert-decyloxy, neodecyloxy, and cyclodecyloxy; the aromatic group is selected from phenyl, 3-fluorophenyl, 2-fluorophenyl, 4-fluorophenyl, 3-chlorophenyl, 2-chlorophenyl, 4-chlorophenyl, 3-bromophenyl, 2-bromophenyl, 4-bromophenyl, 2,5-difluorophenyl, 3,4-difluorophenyl, 3,5-difluorophenyl, 2,6-difluorophenyl, 2,4-difluorophenyl, 2,3-difluorophenyl, 2,6-dichlorophenyl, 2,4-dichlorophenyl , 3,5-dichlorophenyl, 3,4-dichlorophenyl, 2,5-dichlorophenyl, 2,3-dichlorophenyl, 2,6-dibromophenyl, 2,4-dibromophenyl, 3,5-dibromophenyl, 3,4-dibromophenyl, 2,5-dibromophenyl, 2,3-dibromophenyl, 2,3,5,6-tetrafluorophenyl, 2,3,4,5,6-pentafluorophenyl, 4-ethylphenyl, 2-ethylphenyl, 3-ethylphenyl, 2,4-dimethylphenyl, 2,4-diisopropylphenyl, 2,4-di-tert-butylphenyl any one of phenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, 3,5-dimethylphenyl, 3,5-di-tert-butylphenyl, 2,4,6-trimethylphenyl, 2-fluoro-4-methylphenyl, 2,6-difluoro-4-methylphenyl, naphthyl, anthracenyl, biphenyl, 7-fluoro-1-naphthyl, 8-fluoro-1-naphthyl, 7-chloro-1-naphthyl, 8-chloro-1-naphthyl, 9-fluoro-1-anthracenyl, 9-chloro-1-anthracenyl, 8-fluoro-1-anthracenyl and 8-chloro-1-anthracenyl.

[0013] Preferably, the activator is selected from one or a mixture of alkyl aluminum compounds, aluminoxane compounds, organic boron compounds, inorganic acids or inorganic salts.

[0014] Preferably, the alkyl aluminum compound is selected from any one of alkyl aluminum halides, alkyl aluminum hydrides or alkyl aluminum sesquichlorides; the aluminoxane compound is selected from any one of methyl aluminoxane, ethyl aluminoxane, isobutyl aluminoxane, modified aluminoxane or methyl aluminoxane with volatile components removed; the organic boron compound is selected from any one of boroxine, triethylborane, triphenylborane and tris(pentafluorophenyl)borane;

[0015] Preferably, the modified aluminoxane includes modified methyl aluminoxane (MMAO-3A).

[0016] Preferably, the alkyl aluminum compound is selected from any one of trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, tri-n-butyl aluminum, tri-n-hexylaluminum or tri-n-octyl aluminum.

[0017] Preferably, the alkylaluminum sesquichloride is selected from diethylaluminum monochloride (AlEt2Cl) or triethylaluminum trichloride (Al2Et3Cl3).

[0018] Preferably, the preparation method of the Cr(III)-containing PNP complex is as follows: dissolving a sulfonamide-containing compound in tetrahydrofuran (THF) and triethylamine and stirring, adding diphenylphosphine chloride or diisopropylphosphine chloride dropwise and stirring at room temperature overnight, then filtering the suspension under a nitrogen atmosphere, removing the solvent from the obtained transparent solution in vacuum to obtain a solid, dissolving the solid in dichloromethane, adding n-pentane to obtain a suspension, filtering to obtain a solid, washing to obtain a PNP ligand primary product, drying it under vacuum, placing it in a reaction tube filled with argon, adding a Cr(III) metal compound and redistilled toluene to react, filtering the reaction in anhydrous and oxygen-free conditions after the reaction is completed, and draining the obtained solid to obtain a powder, which is a Cr(III)-containing PNP complex, wherein the molar ratio of the PNP ligand primary product to the Cr(III) metal compound is 1:1.

[0019] Preferably, the sulfonamide-containing compound is selected from benzenesulfonamide or isopropylammonium sulfide, and the Cr(III) metal compound is

[0020] Including any one of CrCl3(THF)3, Cr(acac)3, Cr(CH3COO)3 and CrCl3.

[0021] Based on a general inventive concept, the present scheme also provides an application of a catalytic system for selective tetramerization of ethylene containing a PNP ligand for highly selectively catalyzing ethylene tetramerization to prepare 1-hexene and 1-octene, characterized in that the application method is: in an inert solvent or solvent-free condition, a Cr(III) PNP complex and an activator are premixed or separately added to a polymerization reactor containing a reaction medium, ethylene gas is introduced to a reaction pressure of 10-5000 psig, and the polymerization reaction is carried out at a temperature of 0-200°C.

[0022] Preferably, the concentration of the Cr(III)-containing PNP complex in the inert solvent is 0.01-10000 μmol / L, and the molar ratio of the activator to the Cr(III)-containing PNP complex is (1-10000):1.

[0023] Preferably, the inert solvent is selected from one or more of alkanes, aromatic hydrocarbons, olefins or ionic liquids.

[0024] The catalytic mechanism of the catalytic system of this scheme is as follows:

[0025] A sulfonyl group with strong electron-withdrawing ability was introduced on the nitrogen atom. The PNP chromium complex containing the sulfonyl group can be obtained by rearrangement of the PPN-type compound under the induction of a chromium source. By introducing the sulfonyl group, the 1-octene selectivity of the catalytic system can be increased to a maximum of 74.9%, and the catalytic activity can reach a maximum of 4050 kg / g Cr·h.

[0026] The selective tetramerization of ethylene is often accompanied by the co-trimerization or co-tetramerization of 1-hexene / 1-octene with ethylene to produce C 10 The byproducts above 100% are due to the strong electron-withdrawing ability of the sulfonyl group, which leads to a decrease in the electron cloud density on the chromium metal center. The coordination ability of 1-hexene and 1-octene generated during the reaction with the chromium metal center is weakened. 10 The content of by-products above 1-hexene was greatly reduced, and the total selectivity of 1-hexene and 1-octene reached 96.3%.

[0027] Furthermore, during the mixing process of the catalyst components (including the Cr(III)PNP complex and the activator), the presence of olefins can exhibit a protective effect, further improving the catalytic performance.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) A new method for synthesizing PNP complexes was provided, and a chromium complex of a PNP ligand containing a strong electron-withdrawing group on the nitrogen atom was obtained. A sulfonyl group with strong electron-withdrawing ability was creatively introduced on the nitrogen atom. By introducing the sulfonyl group, the catalyst had a high catalytic activity, which could reach up to 4050 kg / g Cr·h.

[0030] (2) The use of the catalyst in this scheme increases the selectivity of 1-octene to 76.7%, and the total selectivity of 1-hexene and 1-octene can reach up to 96.3%, which can effectively reduce C 10 and above by-product content, the content of the generated polymer is significantly reduced;

[0031] (3) During the mixing process of the Cr(III)PNP complex and the activator, the presence of olefins can exhibit a protective effect and further improve the catalytic performance. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, specific embodiments are described in detail below.

[0033] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention are within the scope of the present invention.

[0034] Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art; unless otherwise specified, the reagents used in the examples are commercially available.

[0035] Example 1 Synthesis of Cr(III)-containing PNP complex 1.

[0036] S1. Preparation of PNP ligand initial product 1a: Dissolve benzenesulfonamide (0.50 g, 3.18 mmol) in 15 mL THF and triethylamine (1.69 g, 16.8 mmol), stir to form a homogeneous transparent clear liquid, and then add diphenylphosphine chloride (1.40 g, 6.36 mmol) dropwise. The suspension was stirred at room temperature for 5 minutes, then filtered under a nitrogen atmosphere, and the filtrate was concentrated to obtain a solid. The solid was dissolved in 1 mL of dichloromethane, 20 mL of n-pentane was added to form a precipitate, the precipitate was filtered, and washed with pentane (2×10 mL). Finally, the product was dried under vacuum to obtain the PNP ligand initial product 1a (1.14 g, 68%), the structural formula is shown below, and the NMR data is: 1 H NMR (CDCl3) δ 7.12-7.17 (m, 4H), 7.22-7.44 (m, 16H), 7.64-7.82 (m, 5H).

[0037] ;

[0038] S2. In a dry Schlenk reaction tube filled with argon, add 1a (0.55 g, 0.85 mmol) and CrCl3(THF)3 (0.37 g, 0.85 mmol), add 10 mL of redistilled toluene, and react at 80 °C for 8 h. After the reaction, filter the anhydrous and oxygen-free solution, wash the solid with n-hexane (5 mL×3), and dry it to obtain a powder containing Cr(III) PNP complex 1 (0.36 g, 62.0%), with the following structural formula:

[0039] .

[0040] Example 2 Synthesis of Cr(III)-containing PNP complex 2.

[0041] S1. Preparation of PNP ligand initial product 2a: Benzenesulfonamide (0.50 g, 3.18 mmol) (9.38 mmol, 1 equivalent) was dissolved in 15 mL THF and triethylamine (1.69 g, 16.8 mmol), stirred to form a transparent colorless solution, and diphenylphosphine chloride (0.70 g, 3.18 mmol) was added dropwise and stirred at room temperature overnight, and then the suspension was filtered under a nitrogen atmosphere. The obtained transparent solution was vacuum-dried to remove the solvent to obtain a solid. It was dissolved in 15 mL THF and triethylamine (0.64 g, 6.36 mmol), stirred to form a transparent clear liquid, and diisopropylphosphine chloride (0.48 g, 3.18 mmol) was added dropwise. The suspension was stirred at room temperature for 5 minutes, then filtered under a nitrogen atmosphere, and the filtrate was concentrated to obtain a solid. The solid was dissolved in 1 mL of dichloromethane, and 20 mL of n-pentane was added to obtain a suspension, which was filtered to obtain a solid and washed with pentane (2×10 mL). Finally, the product was dried under vacuum to obtain the PNP ligand primary product 2a (1.05 g, 72.1 %), the structural formula of which is shown below, and the NMR data are as follows: 1 H NMR (CDCl3) δ0.90-0.95 (d, 12H), 1.55-1.62 (m, 2H), 7.22-7.34 (m, 10H), 7.66-7.82 (m, 5H).

[0042] ;

[0043] S2. In a dry Schlenk reaction tube filled with argon, add 2a (0.39 g, 0.85 mmol) and CrCl3(THF)3 (0.37 g, 0.85 mmol), add 10 mL of redistilled toluene, and react at 80 °C for 8 h. After the reaction, filter the anhydrous and oxygen-free solution, wash the solid with n-hexane (5 mL×3), and drain to obtain a powder of Cr(III)PNP complex 2 (0.36 g, 70.0 %), with the following structural formula:

[0044] .

[0045] Example 3 Synthesis of Cr(III)PNP complex 3.

[0046] S1. Preparation of PNP ligand primary product 3a: Dissolve benzenesulfonamide (0.50 g, 3.18 mmol) in 15 mL THF and triethylamine (1.69 g, 16.8 mmol), stir to form a uniform transparent clear liquid, and then add diisopropylphosphine chloride (0.97 g, 6.36 mmol) dropwise. The suspension was stirred at room temperature for 5 minutes, then filtered under a nitrogen atmosphere, and the filtrate was concentrated to obtain a solid. The solid was dissolved in 1 mL of dichloromethane, and 20 mL of n-pentane was added to form a precipitate. The precipitate was filtered and washed with pentane (2×10 mL). Finally, the product was dried under vacuum to obtain a powdered PNP ligand primary product 3a ( (0.90 g, 73.0 %), the structural formula is shown below, and the NMR data is: 1 H NMR (CDCl3) δ 0.67-0.71 (d, 12H), 0.88-0.94 (d, 12H), 1.58-1.62 (m, 2H), 3.61-3.72 (m, 2H), 7.64-7.84 (m, 5H).

[0047] ;

[0048] S2. Add 3a (0.33 g, 0.85 mmol) and CrCl3(THF)3 (0.37 g, 0.85 mmol) to a dry Schlenk reaction tube filled with argon, add 10 mL of redistilled toluene, and react at 80 °C for 8 h. After the reaction, filter the anhydrous and oxygen-free solution, wash the solid with n-hexane (5 mL×3), and dry it to obtain a powder containing Cr(III) PNP complex 3 (0.29 g, 63.4 %), with the following structural formula:

[0049] .

[0050] Example 4 Synthesis of Cr(III)-containing PNP complex 4.

[0051] S1. Preparation of PNP ligand initial product 4a: Benzenesulfonamide (0.50 g, 3.18 mmol) (9.38 mmol, 1 equivalent) was dissolved in 15 mL THF and triethylamine (1.69 g, 16.8 mmol), stirred to form a transparent colorless solution, and diphenylphosphine chloride (0.70 g, 3.18 mmol) was added dropwise and stirred at room temperature overnight, and then the suspension was filtered under a nitrogen atmosphere. The obtained transparent solution was vacuum-dried to remove the solvent to obtain a solid. It was dissolved in 15 mL THF and triethylamine (0.64 g, 6.36 mmol), stirred to form a transparent clear liquid, and dicyclohexylphosphine chloride (0.74 g, 3.18 mmol) was added dropwise. The suspension was stirred at room temperature for 5 minutes, then filtered under a nitrogen atmosphere, and the filtrate was concentrated to obtain a solid. The solid was dissolved in 1 mL of dichloromethane, and 20 mL of n-pentane was added to obtain a suspension, which was filtered to obtain a solid and washed with pentane (2×10 mL). Finally, the product was dried under vacuum to obtain the PNP ligand primary product 4a (1.18 g, 69 %), the structural formula of which is shown below, and the NMR data are as follows: 1 H NMR (CDCl3) δ1.28-1.31 (m, 4H), 1.39-1.42 (m, 2H), 1.4-1.55 (m, 13H), 1.59-1.63 (m, 2H), 7.22-7.33 (m, 10H), 7.66-7.82 (m, 5H).

[0052] ;

[0053] S2. Add 4a (0.46 g, 0.85 mmol) and CrCl3(THF)3 (0.37 g, 0.85 mmol) to a dry Schlenk reaction tube filled with argon, add 10 mL of redistilled toluene, and react at 80 °C for 8 h. After the reaction, filter the anhydrous and oxygen-free solution, wash the solid with n-hexane (5 mL×3), and drain to obtain a powder containing Cr(III) PNP complex 4 (0.39 g, 65.7 %), with the following structural formula:

[0054] .

[0055] Example 5 Synthesis of Cr(III)-containing PNP complex 5.

[0056] S1. Preparation of PNP ligand primary product 5a: Referring to the preparation method of compound 1a, dicyclohexylphosphine chloride (1.45 g, 6.36 mmol) was used instead of diphenylphosphine chloride to obtain powdered PNP ligand primary product 5a (1.23 g, 72.0%).1 H NMR (CDCl3) δ 1.27-1.32 (m, 8H), 1.39-1.55 (m, 28H), 1.59-1.64 (m, 8H), 7.65-7.69 (m, 2H), 7.74-7.82 (m, 3H).

[0057] ;

[0058] S2. Add 5a (0.47 g, 0.85 mmol) and CrCl3(THF)3 (0.37 g, 0.85 mmol) to a dry Schlenk reaction tube filled with argon, add 10 mL of redistilled toluene, and react at 80 °C for 8 h. After the reaction, filter the anhydrous and oxygen-free solution, wash the solid with n-hexane (5 mL×3), and dry it to obtain a powder containing Cr(III) PNP complex 5 (0.38 g, 63.5 %), with the following structural formula:

[0059] .

[0060] Example 6 Synthesis of Cr(III)-containing PNP complex 6.

[0061] S1. Preparation of PNP ligand initial product 6a: Dissolve isopropylammonium sulfide (0.39 g, 3.18 mmol) in 15 mL THF and triethylamine (1.69 g, 16.8 mmol), stir to form a homogeneous transparent clear liquid, and then add diphenylphosphine chloride (1.40 g, 6.36 mmol) dropwise. The suspension was stirred at room temperature for 5 minutes, then filtered under a nitrogen atmosphere, and the filtrate was concentrated to obtain a solid. The solid was dissolved in 1 mL of dichloromethane, 20 mL of n-pentane was added to form a precipitate, the precipitate was filtered, and washed with pentane (2×10 mL). Finally, the product was dried under vacuum to obtain a powdered PNP ligand initial product 6a (1.34 g, 86.0 %), the structural formula is shown below, and the NMR data is: 1 H NMR (CDCl3) δ 1.30-1.36 (d, 6H), 3.17-3.22 (m, 1H), 7.12-7.16 (m, 4H), 7.23-7.33 (m, 10H), 7.38-7.44 (m, 6H).

[0062] ;

[0063] S2. Add 6a (0.42 g, 0.85 mmol) and CrCl3(THF)3 (0.37 g, 0.85 mmol) to a dry Schlenk reaction tube filled with argon, add 10 mL of redistilled toluene, and react at 80 °C for 8 h. After the reaction, filter the anhydrous and oxygen-free solution, wash the solid with n-hexane (5 mL×3), and dry it to obtain a powder containing Cr(III) PNP complex 6 (0.44 g, 81.2 %), with the following structural formula:

[0064] .

[0065] Example 7 Synthesis of Cr(III)-containing PNP complex 7.

[0066] S1. Preparation of the initial product of PNP ligand 7a: Dissolve isopropylammonium sulfide (0.39 g, 3.18 mmol) in 15 mL THF and triethylamine (1.69 g, 16.8 mmol), stir to form a transparent colorless solution, add diphenylphosphine chloride (0.70 g, 3.18 mmol) dropwise, stir overnight at room temperature, and then filter the suspension under a nitrogen atmosphere. The obtained transparent solution is vacuum-dried to remove the solvent to obtain a solid. Dissolve it in 15 mL THF and triethylamine (0.64 g, 6.36 mmol), stir to form a transparent clear liquid, and then add diisopropylphosphine chloride (0.48 g, 3.18 mmol) dropwise. The suspension is stirred at room temperature for 5 minutes, then filtered under a nitrogen atmosphere, and the filtrate is concentrated to obtain a solid. Dissolve the solid in 1 mL dichloromethane, add 20 mL n-pentane to obtain a suspension, filter to obtain a solid, and wash with pentane (2×10 mL). Finally, the product was dried under vacuum to obtain the PNP ligand primary product 7a (1.15 g, 85.3 %), the structural formula is shown below, and the NMR data are: 1 H NMR (CDCl3) δ 0.88-0.95 (d,12H), 1.30-1.35 (d, 6H), 1.58-1.63 (m, 2H), 3.18-3.23 (m, 1H), 7.22-7.35 (m,10H).

[0067] ;

[0068] S2. In a dry Schlenk reaction tube filled with argon, add 7a (0.36 g, 0.85 mmol) and CrCl3(THF)3 (0.37 g, 0.85 mmol), add 10 mL of redistilled toluene, and react at 80 °C for 8 h. After the reaction, filter the anhydrous and oxygen-free solution, wash the solid with n-hexane (5 mL×3), and dry it to obtain a powder containing Cr(III) PNP complex 7 (0.41 g, 84.9 %), with the following structural formula:

[0069] .

[0070] Example 8 Synthesis of Cr(III)-containing PNP complex 8.

[0071] S1. Preparation of the initial product of PNP ligand 8a: Dissolve isopropylammonium sulfide (0.39 g, 3.18 mmol) in 15 mL THF and triethylamine (1.69 g, 16.8 mmol), stir to form a homogeneous transparent clear liquid, and then add diisopropylphosphine chloride (0.97 g, 6.36 mmol) dropwise. The suspension was stirred at room temperature for 5 minutes, then filtered under a nitrogen atmosphere, and the filtrate was concentrated to obtain a solid. The solid was dissolved in 1 mL of dichloromethane, and 20 mL of n-pentane was added to form a precipitate, which was filtered and washed with pentane (2×10 mL). Finally, the product was dried under vacuum to obtain a powdered PNP ligand primary product 8a (0.90 g, 79.6 %) with the structural formula shown below and NMR data as follows: 1H NMR (CDCl3) δ 0.67-0.72 (d, 12H), 0.90-0.95 (d, 12H), 1.30-1.36 (d, 6H), 1.57-1.63 (m, 2H), 3.17-3.23 (m, 1H), 3.65-3.72 (m, 2H).

[0072] ;

[0073] S2. Add 8a (0.30 g, 0.85 mmol) and CrCl3(THF)3 (0.37 g, 0.85 mmol) to a dry Schlenk reaction tube filled with argon, add 10 mL of redistilled toluene, and react at 80 °C for 8 h. After the reaction, filter the anhydrous and oxygen-free solution, wash the solid with n-hexane (5 mL×3), and dry it to obtain a powder containing Cr(III) PNP complex 8 (0.38 g, 89.0 %), with the following structural formula:

[0074] .

[0075] Example 9 Synthesis of Cr(III)-containing PNP complex 9.

[0076] S1. Preparation of PNP ligand initial product 9a: Dissolve isopropylammonium sulfide (0.39 g, 3.18 mmol) in 15 mL THF and triethylamine (1.69 g, 16.8 mmol), stir to form a homogeneous transparent clear liquid, and then add diphenylphosphine chloride (1.40 g, 6.36 mmol) dropwise. The suspension was stirred at room temperature for 5 minutes, then filtered under a nitrogen atmosphere, and the filtrate was concentrated to obtain a solid. The solid was dissolved in 1 mL of dichloromethane, 20 mL of n-pentane was added to form a precipitate, the precipitate was filtered, and washed with pentane (2×10 mL). Finally, the product was dried under vacuum to obtain a powdered PNP ligand initial product 9a (1.30 g, 81.2%), the structural formula is shown below, and the NMR data is: 1 H NMR (CDCl3) δ 1.28-1.34 (m, 12H), 1.38-1.62 (m, 16H), 3.18-3.22 (m, 1H), 7.22-7.36 (m, 10H).

[0077] ;

[0078] S2. Add 9a (0.43 g, 0.85 mmol) and CrCl3(THF)3 (0.37 g, 0.85 mmol) to a dry Schlenk reaction tube filled with argon, add 10 mL of redistilled toluene, and react at 80 °C for 8 h. After the reaction, filter the anhydrous and oxygen-free solution, wash the solid with n-hexane (5 mL×3), and dry it to obtain a powder containing Cr(III) PNP complex 9 (0.47 g, 85.5 %), with the following structural formula:

[0079] .

[0080] Example 10 Synthesis of Cr(III)-containing PNP complex.

[0081] S1. Preparation of PNP ligand primary product 10a: Dissolve isopropylammonium sulfide (0.39 g, 3.18 mmol) in 15 mL THF and triethylamine (1.69 g, 16.8 mmol), stir to form a homogeneous transparent clear liquid, and then add dicyclohexylphosphine chloride (1.45 g, 6.36 mmol) dropwise. The suspension was stirred at room temperature for 5 minutes, then filtered under a nitrogen atmosphere, and the filtrate was concentrated to obtain a solid. The solid was dissolved in 1 mL of dichloromethane, 20 mL of n-pentane was added to form a precipitate, the precipitate was filtered, and washed with pentane (2×10 mL). Finally, the product was dried under vacuum to obtain a powdered PNP ligand primary product 10a (1.29 g, 79.9 %), the structural formula is shown below, and the NMR data is: 1 H NMR (CDCl3) δ 1.28-1.35 (m, 14H), 1.38-1.55 (m, 28H), 1.59-1.63 (m, 8H), 3.17-3.22 (m, 1H).

[0082] ;

[0083] S2. In a dry Schlenk reaction tube filled with argon, add 10a (0.44 g, 0.85 mmol) and CrCl3(THF)3 (0.37 g, 0.85 mmol), add 10 mL of redistilled toluene, and react at 80 °C for 8 h. After the reaction, filter the anhydrous and oxygen-free solution, wash the solid with n-hexane (5 mL×3), and dry it to obtain a powder containing Cr(III) PNP complex 10 (0.48 g, 84.6 %), with the following structural formula:

[0084] .

[0085] Experimental Example 1 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 1 was investigated.

[0086] S1. Catalyst preactivation: In a dry Schlenk reaction tube filled with argon, add Cr(III)PNP complex 1 (0.62 mg, 0.96 μmol) and dehydrated methylcyclohexane (10 ml), stir for 5 minutes, then add modified methylaluminoxane (MMAO-3A) (0.4 mmol, 1.12 mol / L), react at room temperature for 5 minutes and set aside;

[0087] S1, ethylene polymerization reaction: A 350 mL stainless steel high-pressure gas reactor was evacuated on an oil bath at 120°C for 3 hours to ensure an anhydrous and oxygen-free environment in the reactor, then cooled to the reaction temperature, and the reactor was replaced with ethylene gas three times. First, 100 mL of dehydrated methylcyclohexane was added to the reactor, and then the above-prepared catalyst solution was immediately drawn into the high-pressure reactor with a dry glass syringe, the reactor was sealed, stirring was turned on, and ethylene gas was introduced, the pressure was adjusted to 400 psig, and the reaction was stirred at 60°C for 30 minutes. After the reaction was completed, the ethylene gas supply valve was closed, cooled to 0°C, the pressure was released, the reactor was opened, the quantitative internal standard nonane was added and stirred evenly. The reaction was then quenched with about 30 mL of 10wt% HCl aqueous solution, and a small amount of organic phase was filtered and analyzed by GC. The remaining mixture in the reactor was filtered and the solid was taken, and the solid was added to a 10wt% HCl aqueous solution and stirred for 2 hours, filtered, and weighed after drying to constant weight. The data are shown in Table 1 below.

[0088] Experimental Example 2 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 2 was investigated.

[0089] The Cr(III)-containing PNP complex 1 was replaced by the Cr(III)-containing PNP complex 2 (0.55 mg, 0.96 μmol), and the remaining steps were the same as those in Experimental Example 1. The data are shown in Table 1 below.

[0090] Experimental Example 3 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 3 was investigated.

[0091] The Cr(III)-containing PNP complex 1 was replaced by the Cr(III)-containing PNP complex 3 (0.49 mg, 0.96 μmol), and the remaining steps were the same as those in Experimental Example 1. The data are shown in Table 1 below.

[0092] Experimental Example 4 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 4 was investigated.

[0093] The Cr(III)-containing PNP complex 1 was replaced by the Cr(III)-containing PNP complex 4 (0.63 mg, 0.96 μmol), and the remaining steps were the same as those in Experimental Example 1. The data are shown in Table 1 below.

[0094] Experimental Example 5 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 5 was investigated.

[0095] The Cr(III)-containing PNP complex 1 was replaced by the Cr(III)-containing PNP complex 5 (0.65 mg, 0.96 μmol), and the remaining steps were the same as those in Experimental Example 1. The data are shown in Table 1 below.

[0096] Experimental Example 6 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 6 was investigated.

[0097] The Cr(III)-containing PNP complex 1 was replaced by the Cr(III)-containing PNP complex 6 (0.59 mg, 0.96 μmol), and the remaining steps were the same as those in Experimental Example 1. The data are shown in Table 1 below.

[0098] Experimental Example 7 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 7 was investigated.

[0099] The Cr(III)-containing PNP complex 1 was replaced by the Cr(III)-containing PNP complex 7 (0.52 mg, 0.96 μmol), and the remaining steps were the same as those in Experimental Example 1. The data are shown in Table 1 below.

[0100] Experimental Example 8 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 8 was investigated.

[0101] The Cr(III)-containing PNP complex 1 was replaced by the Cr(III)-containing PNP complex 8 (0.48 mg, 0.96 μmol), and the remaining steps were the same as those in Experimental Example 1. The data are shown in Table 1 below.

[0102] Experimental Example 9 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 9 was investigated.

[0103] The Cr(III)-containing PNP complex 1 was replaced by the Cr(III)-containing PNP complex 9 (0.60 mg, 0.96 μmol), and the remaining steps were the same as those in Experimental Example 1. The data are shown in Table 1 below.

[0104] Experimental Example 10 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 10 was investigated.

[0105] The Cr(III)-containing PNP complex 1 was replaced by the Cr(III)-containing PNP complex 10 (0.61 mg, 0.96 μmol), and the remaining steps were the same as those in Experimental Example 1. The data are shown in Table 1 below.

[0106] Experimental Example 11 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 6 was investigated.

[0107] The ethylene polymerization reaction was carried out at 40°C, and the remaining steps were the same as those in Experimental Example 6. The data are shown in Table 1 below.

[0108] Experimental Example 12 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 6 was investigated.

[0109] The ethylene polymerization reaction was carried out at 80°C, and the remaining steps were the same as those in Experimental Example 6. The data are shown in Table 1 below.

[0110] Experimental Example 13 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 6 was investigated.

[0111] The amount of MMAO-3A was replaced with 0.32 mmol, and the remaining steps were the same as those in Experimental Example 6. The data are shown in Table 1 below.

[0112] Experimental Example 14 Investigation of the catalytic polymerization of ethylene by Cr(III)-containing PNP complex 6

[0113] The amount of MMAO-3A was replaced with 0.56 mmol, and the remaining steps were the same as those in Experimental Example 6. The data are shown in Table 1 below.

[0114] Experimental Example 15 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 6 was investigated.

[0115] The reaction pressure was changed to 300 psig, and the remaining steps were the same as those in Experimental Example 6. The data are shown in Table 1 below.

[0116] Experimental Example 16 The ethylene polymerization reaction catalyzed by the Cr(III)-containing PNP complex 6 was investigated.

[0117] The reaction pressure was changed to 200 psig, and the remaining steps were the same as those in Experimental Example 6. The data are shown in Table 1 below.

[0118] Comparative Example 1 The polymerization reaction of ethylene catalyzed by bis(diphenylphosphine)(isopropyl)amine was investigated.

[0119] S1. Catalyst preactivation: In a dry Schlenk reaction tube filled with argon, add bis(diphenylphosphine)(isopropyl)amine (0.36 mg, 0.96 μmol), chromium acetylacetonate (0.28 mg, 0.80 μmol) and dehydrated methylcyclohexane (10 ml), stir for 5 minutes, then add modified methylaluminoxane (MMAO-3A) (0.4 mmol, 1.12 mol / L), react at room temperature for 5 minutes and set aside;

[0120] S1, ethylene polymerization reaction: A 350 mL stainless steel high-pressure gas reactor was evacuated on an oil bath at 120°C for 3 hours to ensure an anhydrous and oxygen-free environment in the reactor, then cooled to the reaction temperature, and the reactor was replaced with ethylene gas three times. First, 100 mL of dehydrated methylcyclohexane was added to the reactor, and then the above-prepared catalyst solution was immediately drawn into the high-pressure reactor with a dry glass syringe, the reactor was sealed, stirring was turned on, and ethylene gas was introduced, the pressure was adjusted to 400psig, and the reaction was stirred at 60°C for 30 minutes. After the reaction was completed, the ethylene gas supply valve was closed, cooled to 0°C, the pressure was released, the reactor was opened, the quantitative internal standard nonane was added and stirred evenly. The reaction was then quenched with about 30 mL of 10wt% HCl aqueous solution, and a small amount of organic phase was filtered and analyzed by GC. The remaining mixture in the reactor was filtered and the solid was taken, and the solid was added to a 10wt% HCl aqueous solution and stirred for 2 hours, filtered, and weighed after drying to constant weight. The data are shown in Table 1 below:

[0121]

[0122] It can be seen from Table 1 that the catalyst provided by the present invention has a high catalytic activity, which can reach up to 4050 kg / g Cr·h, and the selectivity of 1-octene can reach up to 76.7%, and the total selectivity of 1-hexene and 1-octene can reach up to 96.3%. By comparing Example 1, Experimental Example 6 and Comparative Example 1, it can be seen that the introduction of sulfonyl groups can effectively reduce C 10 and above by-products, thereby improving the overall selectivity of 1-hexene and 1-octene, while the catalytic activity is also effectively improved, and the content of the generated polymer is significantly reduced.

[0123] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and changes obtained without departing from the technical concept of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A catalytic system for selective tetramerization of ethylene containing a PNP ligand, characterized in that: The catalytic system for selective tetramerization of ethylene containing a PNP ligand comprises a Cr(III)-containing PNP complex and an activator as shown in the following formula 1: ； Among them, the group R 1 is selected from the group consisting of methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, sec-pentyl, tert-pentyl, neopentyl, cyclopentyl, n-hexyl, sec-hexyl, tert-hexyl, neohexyl, cyclohexyl, n-heptyl, tert-heptyl, neoheptyl, cycloheptyl, n-octyl, sec-octyl, tert-octyl, neooctyl, cyclooctyl, n-nonyl, sec-nonyl, tert-nonyl, neononyl, cyclononyl, n-decyl, sec-decyl, tert-decyl, neodecyl, cyclodecyl, isopropyl, isobutyl, isopentyl, isohexyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, adamantyl, vinyl, 1-propenyl, 2-propenyl, allyl, 1-butenyl, 1-isobutenyl, 3-butenyl, 2-butenyl, 1-pentyl 4-pentenyl, 2-methyl-1-butenyl, 2-methyl-2-butenyl, 2-methyl-3-butenyl, 1-methyl-2-butenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, 5-hexenyl, 2-cyclohexenyl, 3-cyclohexenyl, 2-methyl-2-cyclohexenyl, 2,6-dimethyl-2-cyclohexenyl, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, n-pentyloxy, isopentyloxy, tert-pentyloxy, neopentyloxy, cyclopentyloxy, n-hexyloxy, sec-hexyloxy, tert-hexyloxy, neohexyloxy, cyclohexyloxy, n-heptyloxy, tert-heptyloxy phenyl, 3-fluorophenyl, 2-fluorophenyl, 4-fluorophenyl, 3-chlorophenyl, 2-chlorophenyl, 4-chlorophenyl, 3-bromophenyl, 2-bromophenyl, 4-bromophenyl, 2,5-difluorophenyl, 3,4-difluorophenyl, 3,5-difluorophenyl, 2,6-difluorophenyl, 2,4-difluorophenyl, 2,3-difluorophenyl, 2,6-dichlorophenyl, 2,4-dichlorophenyl, 3,5-dichlorophenyl, 3,4-dichlorophenyl, 2,5-dichlorophenyl, 2,3-dichlorophenyl, 2,6-dibromophenyl, 2,4-dibromophenyl, 3,5-dibromophenyl, 3,4-dibromophenyl, 2,5-dibromophenyl, 2,3-dibromophenyl, 2,3,5,6-tetrafluorophenyl, 2,3,4,5,6-pentafluorophenyl, 4-ethylphenyl, 2-ethylphenyl, 3-ethylphenyl, 2,4-dimethylphenyl, 2,4-diisopropylphenyl, 2,4-di-tert-butylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, 3,5-dimethylphenyl, 3,5-di-tert-butylphenyl, 2,4,6-trimethylphenyl, 2-fluoro-4-methylphenyl, 2,One of 6-difluoro-4-methylphenyl, naphthyl, anthracenyl, biphenyl, 7-fluoro-1-naphthyl, 8-fluoro-1-naphthyl, 7-chloro-1-naphthyl, 8-chloro-1-naphthyl, 9-fluoro-1-anthracenyl, 9-chloro-1-anthracenyl, 8-fluoro-1-anthracenyl or 8-chloro-1-anthracenyl; R 2 , R 3 , R 4 , R 5 each independently selected from methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, sec-pentyl, tert-pentyl, neopentyl, cyclopentyl, n-hexyl, sec-hexyl, tert-hexyl, neohexyl, cyclohexyl, n-heptyl, tert-heptyl, neoheptyl, cycloheptyl, n-octyl, sec-octyl, tert-octyl, neo-octyl, cyclooctyl, n-nonyl, sec-nonyl, tert-nonyl, neo-nonyl, cyclononyl, n-decyl, sec-decyl, tert-decyl, neo-decyl, cyclodecyl, isopropyl, isobutyl, isopentyl, isohexyl, 2- -methylcyclopentyl, 2,6-dimethylcyclohexyl, adamantyl, phenyl, 3-fluorophenyl, 2-fluorophenyl, 4-fluorophenyl, 3-chlorophenyl, 2-chlorophenyl, 4-chlorophenyl, 3-bromophenyl, 2-bromophenyl, 4-bromophenyl, 2,5-difluorophenyl, 3,4-difluorophenyl, 3,5-difluorophenyl, 2,6-difluorophenyl, 2,4-difluorophenyl, 2,3-difluorophenyl, 2,6-dichlorophenyl, 2,4-dichlorophenyl, 3,5-dichlorophenyl, 3, 4-dichlorophenyl, 2,5-dichlorophenyl, 2,3-dichlorophenyl, 2,6-dibromophenyl, 2,4-dibromophenyl, 3,5-dibromophenyl, 3,4-dibromophenyl, 2,5-dibromophenyl, 2,3-dibromophenyl, 2,3,5,6-tetrafluorophenyl, 2,3,4,5,6-pentafluorophenyl, 4-ethylphenyl, 2-ethylphenyl, 3-ethylphenyl, 2,4-dimethylphenyl, 2,4-diisopropylphenyl, 2,4-di-tert-butylphenyl, 2, One of 6-dimethylphenyl, 2,6-diisopropylphenyl, 3,5-dimethylphenyl, 3,5-di-tert-butylphenyl, 2,4,6-trimethylphenyl, 2-fluoro-4-methylphenyl, 2,6-difluoro-4-methylphenyl, naphthyl, anthracenyl, biphenyl, 7-fluoro-1-naphthyl, 8-fluoro-1-naphthyl, 7-chloro-1-naphthyl, 8-chloro-1-naphthyl, 9-fluoro-1-anthracenyl, 9-chloro-1-anthracenyl, 8-fluoro-1-anthracenyl or 8-chloro-1-anthracenyl; X is selected from chlorine, bromine and iodine; n is 2 or 3.

2. The catalytic system for selective tetramerization of ethylene containing PNP ligands according to claim 1, characterized in that: The activator is selected from one or a mixture of alkyl aluminum compounds, aluminoxane compounds, organic boron compounds, inorganic acids or inorganic salts.

3. The catalytic system for selective tetramerization of ethylene containing PNP ligands according to claim 2, characterized in that: The alkyl aluminum compound is selected from any one of alkyl aluminum halides, alkyl aluminum hydrides or alkyl aluminum sesquichlorides; the aluminoxane compound is selected from any one of methyl aluminoxane, ethyl aluminoxane, isobutyl aluminoxane, modified aluminoxane or methyl aluminoxane with volatile components removed; the organic boron compound is selected from any one of cycloboroxine, triethylborane, triphenylborane and tris(pentafluorophenyl)borane.

4. The catalytic system for selective tetramerization of ethylene containing PNP ligands according to claim 1, characterized in that: The preparation method of the Cr(III)-containing PNP complex comprises the following steps: dissolving a sulfonamide-containing compound in tetrahydrofuran and triethylamine and stirring, dropping diphenylphosphine chloride or diisopropylphosphine chloride and stirring overnight at room temperature, then filtering the suspension under a nitrogen atmosphere, removing the solvent from the obtained transparent solution in vacuum to obtain a solid, dissolving the solid in dichloromethane, adding n-pentane to obtain a suspension, filtering to obtain a solid, washing to obtain a PNP ligand primary product, drying it under vacuum, placing it in a reaction tube filled with argon, adding a Cr(III) metal compound and redistilled toluene to react, filtering the solid in anhydrous and oxygen-free conditions after the reaction is completed, and draining the solid to obtain a powder, which is the Cr(III)-containing PNP complex. The molar ratio of the PNP ligand primary product to the Cr(III) metal compound is 1:

1.

5. The catalytic system for selective tetramerization of ethylene containing PNP ligands according to claim 4, characterized in that: The sulfonamide-containing compound is selected from benzenesulfonamide or isopropylammonium sulfate, and the Cr(III) metal compound includes any one of CrCl3(THF)3, Cr(acac)3, Cr(CH3COO)3 and CrCl3.

6. Use of the catalytic system for selective tetramerization of ethylene containing a PNP ligand as claimed in any one of claims 1 to 5 for highly selectively catalyzing tetramerization of ethylene to prepare 1-hexene and 1-octene, characterized in that: The application method is: premixing or separately adding the Cr(III) PNP complex and the activator into a polymerization reactor containing a reaction medium under an inert solvent or solvent-free condition, introducing ethylene gas to a reaction pressure of 10-5000 psig, and performing the polymerization reaction at a temperature of 0-200°C.

7. The use according to claim 6, characterized in that: The concentration of the Cr(III)-containing PNP complex in the inert solvent is 0.01-10000 μmol / L, and the molar ratio of the activator to the Cr(III)-containing PNP complex is (1-10000):

1.

8. The use according to claim 7, characterized in that: The inert solvent is selected from one or more of alkanes, aromatic hydrocarbons, olefins or ionic liquids.

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