Organic ligands containing NPN and PNP structures, methods for their preparation, catalysts and processes for the oligomerization of ethylene

Abstract

This invention provides an organic ligand containing NPN and PNP structures, its preparation method, a catalyst, and an ethylene oligomerization method. The organic ligand containing NPN and PNP structures, as shown in Formula I, exhibits high stability and good temperature resistance. The catalyst comprises an organic ligand containing NPN and PNP junctions as shown in Formula I, which coordinates with a transition metal compound to form a binuclear metal complex. This complex, used in ethylene oligomerization, can highly actively prepare α-olefins with high selectivity for the target product; the combined selectivity for 1-hexene and 1-octene can reach over 95%, with low polymer yield and high economic added value.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis, and in particular to an organic ligand containing NPN and PNP structures, its preparation method, catalyst, and ethylene oligomerization method. Background Technology

[0002] Alpha-olefins are important terminal olefin products with wide applications in polyolefin comonomers, plasticizers, surfactant synthesis intermediates, synthesis of high-grade lubricating oil base oils, and lubricating oil additives. In recent years, the demand for alpha-olefins has grown rapidly, leading to a significant increase in imports. Therefore, the efficient production of alpha-olefins is of paramount importance.

[0003] Currently, the main methods for producing α-olefins include ethylene oligomerization, wax cracking, alkane dehydrogenation, coal chemical extraction, alkane catalytic cracking, extraction separation, fatty alcohol dehydrogenation, olefin dimerization and disproportionation, and internal olefin isomerization. Compared with traditional methods such as wax cracking, coal chemical extraction, and extraction separation, ethylene oligomerization yields products with high linearity and good quality, making it the most important industrial production method. Ethylene oligomerization is further divided into non-selective and selective ethylene oligomerization. Non-selective ethylene oligomerization processes mainly include one-step, two-step, and SHOP processes. This process yields a wide product distribution, but the selectivity for 1-hexene and 1-octene is relatively low, requiring separation and purification according to specific needs in industrial applications. Selective ethylene oligomerization processes mainly include Phillips' selective trimerization and Saosl's selective tetramerization, which provide important pathways for producing α-olefins with specific carbon numbers. In recent years, the increasing demand for 1-hexene and 1-octene has made selective ethylene oligomerization a hot topic in industrial and academic research.

[0004] Based on publicly available journal and patent literature, existing ethylene selective oligomerization catalysts exhibit poor temperature resistance and stability, are prone to decomposition, and thus generate more polymers. Improving catalytic activity while simultaneously reducing polymer production is challenging. The overall selectivity for 1-hexene and 1-octene in the products is not very high. Polymers not only adhere to the reactor walls and agitators, affecting mass and heat transfer, but also encapsulate and / or adsorb the catalyst, promoting byproduct formation, generating more polymers, clogging reactor pipelines, and impacting the continuous long-term operation of the equipment. Therefore, providing a catalyst and a suitable catalytic system that can highly actively prepare α-olefins while reducing the degree of polymerization to decrease polymer production has become a pressing technical problem in this field. Summary of the Invention

[0005] This invention provides an organic ligand containing NPN and PNP structures, the chemical structural formula of which is shown in Formula I below;

[0006]

[0007] Among them, R1, R1', R2, R3, R4, and R4' are independently selected from hydrogen, aryl, substituted aryl, alkyl, alkoxy, mercapto, halide, cycloalkyl, amino, etc.

[0008] For example, R1, R1', R2, R3, R4, and R4' are independently selected from hydrogen, C, and C, respectively. 6-10 Aryl, C 1-6 Alkyl-substituted C 6-14 Aryl and halogen-substituted C 6-14 Aryl, C 1-6 Alkyl, C 1-6 Alkoxy, mercapto, halides, C 3-8 Cycloalkyl, amino, etc., wherein the halogen is selected from fluorine, chlorine, bromine or iodine;

[0009] Preferably, R1 and R1' are independently selected from methyl, ethyl, isopropyl, tert-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, phenyl, and fluoro; more preferably methyl, isopropyl, and tert-butyl.

[0010] Preferably, R2 is independently selected from methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, cyclopropyl, cyclobutyl, cyclopentyl, n-hexyl, cyclohexyl, phenyl, naphthyl, anthracene, biphenyl, 2-fluorophenyl, 4-fluorophenyl, 2-trifluoromethylphenyl, 4-trifluoromethylphenyl, 2-tri-tert-butylsilylphenyl, 4-tri-tert-butylsilylphenyl; preferably phenyl or ethyl.

[0011] Preferably, R3 is independently selected from methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, cyclopropyl, cyclobutyl, cyclopentyl, n-hexyl, cyclohexyl, phenyl, naphthyl, anthracene, biphenyl, 2-substituted phenyl, 4-substituted phenyl; more preferably isopropyl, tert-butyl, cyclopentyl, cyclohexyl, phenyl, 4-methylphenyl;

[0012] Preferably, R4 and R4' are independently selected from ethyl, propyl, isopropyl, tert-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, phenyl, naphthyl, anthracene, biphenyl, halogen-substituted phenyl, alkoxy-substituted phenyl, silyl-substituted phenyl, preferably phenyl, 2-fluorophenyl, naphthyl, or ethyl;

[0013] Preferably, R1 and R1' are selected from the same substituents, and R4 and R4' are selected from the same substituents.

[0014] According to an exemplary embodiment of the present invention, the organic ligand has a structure as shown in any one of Formulas I-1 to I-6:

[0015]

[0016]

[0017] This invention also provides a method for preparing the aforementioned organic ligand, comprising the following steps:

[0018] (1) 2-Bromo-alkylpyridine The reaction of n-butyllithium with the dichloro derivative of phosphine yields compound II;

[0019]

[0020] (2) The compound of formula II is dissolved in a solvent and reacts with the isopropyl magnesium chloride lithium chloride complex to give a solution of formula A.

[0021]

[0022] (3) Dichloro derivatives of phosphine The solution is mixed with the solution one and reacted with compound A to give compound III;

[0023]

[0024] (4) The compound of formula III, n-butyllithium and primary amine (R3-NH2) are reacted to obtain the compound of formula IV;

[0025]

[0026] (5) The monochloro derivatives of the compound of formula IV, n-butyllithium, and phosphine The reaction yields the organic ligand.

[0027] According to an embodiment of the present invention, in step (1), the 2-bromo-alkylpyridine may be selected from 2-bromo-4-methylpyridine, 2-bromo-4-isopropylpyridine or 2-bromo-4-tert-butylpyridine.

[0028] According to an embodiment of the present invention, in step (1), the molar ratio of 2-bromo-alkylpyridine, n-butyllithium, and phosphine dichloride is (2-2.3):(2-2.5):1; preferably (2-2.1):(2.04-2.15):1, for example 2:2.04:1.

[0029] According to an embodiment of the present invention, in step (1), the dichloride of the phosphine is (2-benzylbromo)phosphine dichloride.

[0030] According to an embodiment of the present invention, in step (1), 2-bromo-alkylpyridine is first dissolved in a solvent, n-butyllithium is added to the system to react, and then a dichloro derivative of phosphine is added to the system to react.

[0031] As an example, step (1) includes: dissolving 2-bromo-alkylpyridine in a solvent, adding n-butyllithium at -80 to 0°C, and reacting for 1 to 8 hours; then adding a dichloro derivative of phosphine and reacting for 1 to 24 hours; and filtering, extracting, purifying, and drying the reaction solution to obtain compound II.

[0032]

[0033] According to an embodiment of the present invention, in step (1), the extraction is performed using a mixed solution of water and sulfuric acid, the concentration of the dilute sulfuric acid used is 1 mol / L, and the extraction is performed twice, 20 ml each time.

[0034] According to an embodiment of the present invention, in step (2), the molar ratio of the compound of formula II to the isopropyl magnesium chloride lithium chloride complex is 1:(1 to 1.5); preferably 1:(1.02 to 1.1), for example 1:1, 1:1.01, 1:1.05, 1:1.08.

[0035] According to an embodiment of the present invention, in step (2), the reaction is first carried out at -80 to 0°C for 1 to 8 hours, and then the reaction is continued at room temperature for 1 to 3 hours.

[0036] According to an embodiment of the present invention, step (2) includes: dissolving the compound of formula II in a solvent, adding isopropyl magnesium chloride lithium chloride complex at -80 to 0°C, reacting for 1 to 8 hours, and continuing to react the reaction solution at room temperature for 2 hours to obtain solution one.

[0037] According to an embodiment of the present invention, in step (3), the dichloro derivative of the phosphine is one or two of phenylphosphine dichloride, cyclohexylphosphine dichloride, ethylphosphine dichloride, and propylphosphine dichloride.

[0038] According to an embodiment of the present invention, in step (3), the molar ratio of the compound of formula A and the dichloro derivative of phosphine is 1:(1 to 1.5); preferably 1:(1.02 to 1.1), for example 1:1, 1:1.01, 1:1.05, 1:1.08.

[0039] According to an embodiment of the present invention, step (3) includes: dissolving the dichloro derivative of phosphine in a solvent, adding solution one at -80 to 0°C, reacting with compound A for 1 to 4 hours, and after post-treatment, obtaining compound III;

[0040]

[0041] According to an embodiment of the present invention, in step (4), the molar ratio of the compound of formula III, n-butyllithium, and primary amine is (1-1.3):(1-1.5):(1-1.8); preferably (1-1.1):(1.02-1.15):(1.05-1.2), for example 1:1.02:1.

[0042] According to an embodiment of the present invention, in step (4), the primary amine is selected from one or more of isopropylamine, tert-butylamine, cyclopentylamine and aniline.

[0043] According to an embodiment of the present invention, in step (4), the compound of formula III is first dissolved in a solvent, n-butyllithium is added to the system to react, and then a primary amine is added to the system to react.

[0044] According to an embodiment of the present invention, step (4) includes: dissolving the compound of formula III in a solvent, adding n-butyllithium at -80 to 0°C, reacting for 1 to 8 hours, then adding a primary amine, reacting for 1 to 8 hours, and then post-treating the reaction solution to obtain the compound of formula IV;

[0045]

[0046] According to an embodiment of the present invention, in step (5), the monochloro derivative of the phosphine is selected from one or more of diethylphosphine chloride, diphenylphosphine chloride, diisopropylphosphine chloride, di-tert-butylphosphine chloride, di(4-tolyl)phosphine chloride, di(2-tolyl)phosphine chloride, di(2-methoxyphenyl)phosphine chloride, and di(2-fluorophenyl)phosphine chloride.

[0047] According to an embodiment of the present invention, in step (5), the molar ratio of the compound of formula IV, n-butyllithium, and the monochloro derivative of phosphine is (1-1.3):(1-1.5):(1-1.8); preferably (1-1.1):(1.02-1.15):(1.05-1.2), for example 1:1:1.

[0048] According to an embodiment of the present invention, in step (5), the compound of formula IV is first dissolved in a solvent, n-butyllithium is added to the system to react, and then a monochloro derivative of phosphine is added to the system to react, thereby obtaining the organic ligand.

[0049] According to an embodiment of the present invention, step (5) includes: dissolving the compound of formula IV in a solvent, adding n-butyllithium at -80 to 0°C, reacting for 1 to 8 hours, then adding a monochloro derivative of phosphine, reacting for 1 to 24 hours, and purifying and drying the reaction solution to obtain the organic ligand.

[0050] According to an embodiment of the present invention, all the above-mentioned reactions are carried out under a nitrogen atmosphere.

[0051] According to an embodiment of the present invention, steps (1)-(5) are all carried out in a solvent, which may be the same or different. The solvent is selected from one or more of ethanol, dichloromethane, toluene, xylene, acetonitrile, tetrahydrofuran, n-hexane, cyclohexane, and diethyl ether. For example, the amount of solvent used is 1 to 50 ml of solvent per mmol of raw material dissolved therein, preferably 1 to 10 ml.

[0052] For example, in step (1), the solvent is diethyl ether; in step (2), the solvent is tetrahydrofuran; in step (3), the solvents are tetrahydrofuran and diethyl ether; in step (4), the solvent is diethyl ether; and in step (5), the solvent is diethyl ether.

[0053] According to an embodiment of the present invention, steps (1)-(5) are all carried out under an inert atmosphere, such as nitrogen or argon.

[0054] The present invention also provides a catalyst comprising a transition metal compound and the organic ligand.

[0055] In one embodiment, the catalyst is a complex formed from a transition metal compound and the organic ligand.

[0056] According to embodiments of the present invention, the transition metal compound is selected from one or more compounds of chromium, molybdenum, tungsten, cobalt, rhodium, titanium, vanadium, zirconium, iron, nickel, or palladium, preferably compounds of chromium, zirconium, nickel, and titanium; for example, the transition metal compound includes inorganic salts, organic salts, coordination compounds, or organometallic complexes of transition metals, preferably one or more of chromium acetylacetonate, chromium chloride, chromium tetrahydrofuran trichloride, chromium isooctanoate, chromium octanoate, chromium hexacarbonyl, chromium (benzene)tricarbonyl, chromium naphthenate, chromium acetate, and chromium 2,2,6,6-tetramethylheptadecanoate.

[0057] According to an embodiment of the present invention, the molar ratio of the transition metal compound to the organic ligand is (1-5):1, preferably (2-3):1.

[0058] The present invention also provides a method for preparing the catalyst, comprising the following steps: mixing the organic ligand and the transition metal compound in a solvent that has undergone dehydration and deoxygenation treatment, and then obtaining the catalyst through post-treatment;

[0059] According to an embodiment of the present invention, the solvent is dichloromethane;

[0060] According to an embodiment of the present invention, the mixing temperature is room temperature and the time is 10-30 hours;

[0061] According to an embodiment of the present invention, the post-processing includes filtering to separate the solid, washing the solid, and drying.

[0062] The present invention provides a catalytic system comprising the above-described catalyst.

[0063] According to an embodiment of the present invention, the catalytic system further includes a catalyst and / or an auxiliary agent.

[0064] According to an embodiment of the present invention, the cocatalyst is one or more of alkylaluminoxane, modified alkylaluminoxane, other organoaluminum compounds, and boron-containing compounds, preferably methylaluminoxane and / or modified methylaluminoxane.

[0065] According to an embodiment of the present invention, the auxiliary agent is one or more of hydrogen, chloroalkanes, alkylaluminum, chloroalkylaluminum, alkylzinc, and chloroalkylzinc.

[0066] According to an embodiment of the present invention, the molar ratio of the co-catalyst to the transition metal compound in the catalyst is (100-2000):1, preferably (200-1000):1, for example 400:1, 420:1, 450:1, 460:1, 500:1, 600:1, 650:1, based on the molar ratio of aluminum to the transition metal element.

[0067] The present invention also provides the application of the above-mentioned catalyst or catalytic system in ethylene oligomerization.

[0068] This invention provides a method for ethylene oligomerization, comprising the following steps:

[0069] Ethylene is polymerized in an inert solvent after dehydration and deoxygenation under the catalytic system conditions described above to obtain α-olefins.

[0070] According to an embodiment of the present invention, the temperature of the polymerization reaction is 30–120°C, preferably 40–100°C; the pressure of the polymerization reaction is 1–10 MPa, preferably 2–8 MPa; and the time of the polymerization reaction is 5–240 min, preferably 10–120 min.

[0071] According to an embodiment of the present invention, the inert solvent is selected from one or more of the following: n-butane, isobutane, n-pentane, isopentane, cyclopentane, n-hexane, cyclohexane, cyclohexene, methylcyclopentane, methylcyclohexane, ethylcyclohexane, n-heptane, n-octane, isooctane, n-nonane, benzene, chlorobenzene, toluene, xylene, and trimethylbenzene. For example, the amount of the inert solvent used is 30 to 500 ml of inert solvent per μmol of transition metal element, preferably 50 to 300 ml of inert solvent per μmol of transition metal element.

[0072] According to an embodiment of the present invention, the α-olefin includes 1-hexene and 1-octene.

[0073] The beneficial effects of this invention are:

[0074] This invention designs an organic ligand containing NPN and PNP structures, exhibiting high stability and good temperature resistance. Using the ligand, catalyst, and corresponding catalytic system of this invention, ethylene oligomerization can be carried out at higher temperatures, enabling the highly active preparation of α-olefins. Specifically, the combined selectivity for 1-hexene and 1-octene can reach over 95%, with a significantly reduced polymer yield and high economic added value. Detailed Implementation

[0075] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0076] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0077] The synthetic routes for organic ligands containing NPN and PNP structures are shown below:

[0078]

[0079] Example 1

[0080] 1) Preparation of ligand 1:

[0081] (1) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, 8.5 ml of n-butyllithium (2.4 M n-hexane solution) was added. Then, 35 ml of ether solution containing 0.1 g / ml of 2-bromo-4-methylpyridine (20 mmol, 3.5 g) was added dropwise, keeping the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, 27.2 ml of ether solution containing 0.1 g / ml of (2-benzylbromo)dichloride (10 mmol, 2.72 g) was added dropwise to the above reaction solution, keeping the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 4 h, and then the reaction system was slowly heated to 30°C and reacted for 2 h. The reaction system was extracted twice with 40 ml of 1M dilute sulfuric acid. The aqueous phases were combined and adjusted to neutral with saturated sodium hydroxide aqueous solution. A yellow solid precipitated out. The solid was filtered and dried to obtain product 1 with a yield of 60%.

[0082] (2) The reaction flask was purged with nitrogen three times. Under the conditions of -80℃, N2 protection and stirring, a tetrahydrofuran solution (10 mmol) of product one was added. Then, a tetrahydrofuran solution of isopropyl magnesium chloride lithium chloride complex (concentration 1.3M, 7.7 ml, equivalent to 10 mmol of isopropyl magnesium chloride lithium chloride complex) was added dropwise. The reaction was carried out for 1 h, and then at 30℃ for another 2 h to obtain solution one.

[0083] (3) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80℃, a tetrahydrofuran (60 mL) solution of phenylphosphine dichloride (10 mmol, 1.8 g) was first added, followed by the dropwise addition of solution one. The reaction was allowed to proceed for 1 h. The solvent was then removed under vacuum, and 100 mL of diethyl ether was added to the residue to obtain a precipitate. The precipitate was filtered, and the supernatant was desolventized under vacuum and dried to obtain product two, with a yield of 60%.

[0084] (4) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, product two (8 mmol) was dissolved in diethyl ether, and 3.4 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70°C during the addition. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, isopropylamine (8 mmol) was added dropwise, and the reaction was carried out for 6 h. After post-treatment, the reaction solution was dried to obtain product three, with a yield of 84%.

[0085] (5) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, product tri(5 mmol) was dissolved in diethyl ether, and 2.1 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70°C during the addition. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, bis(2-fluorophenyl)phosphine chloride (5 mmol, 1.3 g) was added dropwise, and the reaction was carried out for 6 h. The reaction solution was purified by column chromatography using a mixed solvent of n-hexane and ethyl acetate (volume ratio 1:1) as the eluent. After drying, a white solid was obtained with a yield of 70%. 1 ¹H-NMR (400MHz, CDCl₃): δ 7–8.6 (m, 23H), 2.8–3 (m, 1H), 2–2.7 (m, 8H), 1–1.2 (m, 6H). This confirms that the obtained solid is ligand 1.

[0086]

[0087] 2) Catalyst preparation:

[0088] The reaction flask was purged with nitrogen three times. Under N2 protection, ligand 1 (50 mmol) and the metal compound tetrahydrofuran chromium trichloride (100 mmol, 37.5 g) were added, followed by 50 mL of dehydrated and deoxygenated dichloromethane. The mixture was stirred at room temperature for 24 h. After filtration, the solid was washed with n-hexane (5 mL × 3 times) and dried to obtain a blue powder (90% yield). 20 μmol of the blue powder was mixed with 20 mL of methylcyclohexane and stirred until homogeneous.

[0089] 3) Ethylene oligomerization:

[0090] Ethylene oligomerization was carried out in a 500 mL high-pressure reactor. The reactor was heated to 120 °C and evacuated for 2 h. The reactor was then purged three times with high-purity nitrogen and ethylene, maintaining an ethylene environment. After cooling, 200 mL of dehydrated and deoxygenated methylcyclohexane and co-catalyst MMAO-3A (Al / Cr = 500) were added. The mixture was stirred for 2 min, followed by the addition of the aforementioned catalyst containing ligand 1 (2 μmol Cr). H₂ at 0.1 MPa was then added, and the pressure was brought up to 5 MPa with ethylene. The ethylene oligomerization reaction was carried out under specific conditions (see Table 1) for 30 min. The reaction was terminated with 10 wt% acidified ethanol. After cooling and depressurization, the liquid and solid products were separated by filtration. A small amount of organic phase was taken from the liquid product, filtered, and analyzed by gas chromatography. The solid product was washed with acidified ethanol, dried under vacuum at 60 °C for 8 h, and weighed. The results are shown in Table 1.

[0091] Example 2

[0092] 1) Preparation of ligand 2:

[0093] (1) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, 8.5 ml of n-butyllithium (2.4 M n-hexane solution) was added, followed by dropwise addition of 35 ml of 0.1 g / ml diethyl ether solution (2-bromo-4-methylpyridine, 20 mmol), maintaining the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, 27.2 ml of 0.1 g / ml diethyl ether solution (10 mmol of (2-benzylbromo)phosphine dichloride) was added dropwise to the above reaction solution, maintaining the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 4 h, and then the reaction system was slowly heated to 30°C and reacted for 2 h. The reaction system was extracted twice with 40 ml of 1 M dilute sulfuric acid. The aqueous phases were combined, and the solution was adjusted to neutral with saturated sodium hydroxide aqueous solution. A yellow solid precipitated out. The solid was filtered, dried, and the product was obtained with a yield of 62%.

[0094] (2) The reaction flask was purged with nitrogen three times. Under the conditions of -80℃, N2 protection and stirring, 10 mmol of tetrahydrofuran dispersion of product one was added. Then, a tetrahydrofuran solution of isopropyl magnesium chloride lithium chloride complex (concentration 1.3M, added amount 7.7ml, equivalent to 10 mmol of isopropyl magnesium chloride lithium chloride complex) was added dropwise. The reaction was carried out for 1 h, and then the reaction was carried out at 30℃ for another 2 h to obtain solution one.

[0095] (3) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80℃, a tetrahydrofuran (60 mL) solution of phenylphosphine dichloride (10 mmol, 1.8 g) was first added, followed by the dropwise addition of solution one. The reaction was allowed to proceed for 1 h. The solvent was then removed under vacuum, and 100 mL of diethyl ether was added to the residue to obtain a precipitate. The precipitate was filtered, and the supernatant was removed under vacuum and dried to obtain product two, with a yield of 58%.

[0096] (4) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, product two (8 mmol) was dissolved in diethyl ether, and 3.4 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70°C during the addition. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, cyclopentylamine (8 mmol, 0.68 g) was added dropwise, and the reaction was carried out for 6 h. After post-treatment, the reaction solution was dried to obtain product three, with a yield of 80%.

[0097] (5) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80℃, product tri(5 mmol) was dissolved in diethyl ether, and 2.1 ml of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70℃ during the addition. After the addition was complete, the reaction was carried out at -80℃ for 2 h. Then, diethylphosphine chloride (5 mmol, 0.63 g) was added dropwise, and the reaction was carried out for 6 h. The reaction solution was purified by column chromatography using a mixed solvent of n-hexane and ethyl acetate (volume ratio 1:1) as the eluent. After drying, a white solid was obtained with a yield of 72%. 1 ¹H-NMR (400MHz, CDCl₃): δ 7–8.6 (m, 15H), 2–3 (m, 9H), 1–1.8 (m, 18H). This confirms that the obtained solid is ligand 2.

[0098]

[0099] 2) Catalyst preparation:

[0100] The reaction flask was purged with nitrogen three times. Under N2 protection, ligand 2 (50 mmol) and the metal compound chromium acetylacetone (100 mmol, 34.9 g) were added, followed by 50 mL of dehydrated and deoxygenated dichloromethane. The mixture was stirred at room temperature for 24 h. After filtration, the solid was washed with n-hexane (5 mL × 3 times) and dried to obtain a blue powder (yield 85%). 10 μmol of the blue powder was mixed with 10 mL of cyclohexane and stirred until homogeneous.

[0101] 3) Ethylene oligomerization:

[0102] Ethylene oligomerization was carried out in a 500 mL high-pressure reactor. The reactor was heated to 120 °C and evacuated for 2 h. The reactor was then purged three times with high-purity nitrogen and ethylene, maintaining an ethylene environment. After cooling, 210 mL of dehydrated and deoxygenated cyclohexane and co-catalyst MMAO-3A (Al / Cr = 600) were added. The mixture was stirred for 3 min, followed by the addition of the aforementioned catalyst containing ligand 2 (2 μmol Cr). H₂ at 0.3 MPa was then added, and the pressure was brought up to 5 MPa with ethylene. The ethylene oligomerization reaction was carried out under specific conditions (see Table 1) for 40 min. The reaction was terminated with 10 wt% acidified ethanol. After cooling and depressurization, the liquid and solid products were separated by filtration. A small amount of organic phase was taken from the liquid product, filtered, and analyzed by gas chromatography. The solid product was washed with acidified ethanol, dried under vacuum at 60 °C for 8 h, and weighed. The results are shown in Table 1.

[0103] Example 3

[0104] 1) Preparation of ligand 3:

[0105] (1) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, 8.5 ml of n-butyllithium (2.4 M n-hexane solution) was added. Then, 40 ml (20 mmol) of diethyl ether solution with a mass concentration of 0.1 g / ml of 2-bromo-4-isopropylpyridine was added dropwise, keeping the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, 27.2 ml of diethyl ether solution with a mass concentration of 0.1 g / ml of (2-benzyl bromide)phosphine dichloride (10 mmol, 2.72 g) was added dropwise to the above reaction solution, keeping the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 4 h, and then the reaction system was slowly heated to 30°C and reacted for 2 h. The reaction system was extracted twice with 40 ml of 1M dilute sulfuric acid. The aqueous phases were combined and adjusted to neutral with saturated sodium hydroxide aqueous solution. A yellow solid precipitated out. The solid was filtered and dried to obtain product 1 with a yield of 58%.

[0106] (2) The reaction flask was purged with nitrogen three times. Under the conditions of -80℃, N2 protection and stirring, 10 mmol of tetrahydrofuran dispersion of product one was added. Then, a tetrahydrofuran solution of isopropyl magnesium chloride lithium chloride complex (concentration 1.3M, added amount 7.7 ml, equivalent to 10 mmol of isopropyl magnesium chloride lithium chloride complex) was added dropwise. The reaction was carried out for 1 h, and then the reaction was carried out at 30℃ for another 2 h to obtain solution one.

[0107] (3) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80℃, a tetrahydrofuran (60 mL) solution of ethylphosphine dichloride (10 mmol, 1.31 g) was first added, followed by the dropwise addition of solution one. The reaction was allowed to proceed for 1 h. The solvent was then removed under vacuum, and 100 mL of diethyl ether was added to the residue to obtain a precipitate. The precipitate was filtered, and the supernatant was removed under vacuum and dried to obtain product two, with a yield of 59%.

[0108] (4) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, product two (8 mmol) was dissolved in diethyl ether, and 3.4 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70°C during the addition. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, aniline (8 mmol, 0.75 g) was added dropwise, and the reaction was carried out for 6 h. After post-treatment, the reaction solution was dried to obtain product three, with a yield of 82%.

[0109] (5) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, product tri(5 mmol) was dissolved in diethyl ether, and 2.1 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70°C during the addition. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, diphenylphosphine chloride (5 mmol, 1.1 g) was added dropwise, and the reaction was carried out for 6 h. The reaction solution was purified by column chromatography using a mixed solvent of n-hexane and ethyl acetate (volume ratio 1:1) as the eluent. After drying, a white solid was obtained with a yield of 71%. 1 ¹H-NMR (400MHz, CDCl₃): δ 7–8.6 (m, 22H), 6–6.8 (m, 3H), 2–3.5 (m, 4H), 1–1.8 (m, 17H). This confirms that the obtained solid is ligand 3.

[0110]

[0111] 2) Catalyst preparation:

[0112] The reaction flask was purged with nitrogen three times. Under N2 protection, ligand 3 (50 mmol) and the metal compound tetrahydrofuran chromium trichloride (100 mmol, 37.5 g) were added, followed by 50 mL of dehydrated and deoxygenated dichloromethane. The mixture was stirred at room temperature for 24 h. After filtration, the solid was washed with n-hexane (5 mL × 3 times) and dried to obtain a blue powder (yield 87%). 10 μmol of the blue powder was mixed with 10 mL of cyclohexene and stirred until homogeneous.

[0113] 3) Ethylene oligomerization:

[0114] Ethylene oligomerization was carried out in a 500 mL high-pressure reactor. The reactor was heated to 120 °C and evacuated for 2 h. The reactor was then purged three times with high-purity nitrogen and ethylene, maintaining an ethylene environment. After cooling, 220 mL of dehydrated and deoxygenated cyclohexene and co-catalyst MMAO-3A (Al / Cr = 420) were added. The mixture was stirred for 3 min, followed by the addition of the aforementioned catalyst containing ligand 3 at a concentration of 1 μmol Cr. H₂ at 0.2 MPa was then added, and the pressure was increased to 4.9 MPa with ethylene. The ethylene oligomerization reaction was carried out under specific conditions (see Table 1) for 45 min. The reaction was terminated with 10 wt% acidified ethanol. After cooling and depressurization, the liquid and solid products were separated by filtration. A small amount of organic phase was taken from the liquid product, filtered, and analyzed by gas chromatography. The solid product was washed with acidified ethanol, dried under vacuum at 60 °C for 8 h, and weighed. The results are shown in Table 1.

[0115] Example 4

[0116] 1) Preparation of ligand 4:

[0117] (1) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, 8.5 ml of n-butyllithium (2.4 M n-hexane solution) was added. Then, 40 ml of ether solution containing 0.1 g / ml of 2-bromo-4-isopropylpyridine (20 mmol, 4.0 g) was added dropwise, keeping the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, 272 ml of ether solution containing 0.1 g / ml of (2-benzylbromo)dichloride (10 mmol, 2.72 g) was added dropwise to the above reaction solution, keeping the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 4 h, and then the reaction system was slowly heated to 30°C and reacted for 2 h. The reaction system was extracted twice with 40 ml of 1M dilute sulfuric acid. The aqueous phases were combined and adjusted to neutral with saturated sodium hydroxide aqueous solution. A yellow solid precipitated out. The solid was filtered and dried to obtain product 1 with a yield of 63%.

[0118] (2) The reaction flask was purged with nitrogen three times. Under the conditions of -80℃, N2 protection and stirring, 10 mmol of tetrahydrofuran dispersion of product one was added. Then, a tetrahydrofuran solution of isopropyl magnesium chloride lithium chloride complex (concentration 1.3M, added amount 7.7 ml, equivalent to 10 mmol of isopropyl magnesium chloride lithium chloride complex) was added dropwise. The reaction was carried out for 1 h, and then the reaction was carried out at 30℃ for another 2 h to obtain solution one.

[0119] (3) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80℃, a tetrahydrofuran (60 mL) solution of phenylphosphine dichloride (10 mmol, 1.79 g) was first added, followed by the dropwise addition of solution one. The reaction was allowed to proceed for 1 h. The solvent was then removed under vacuum, and 100 mL of diethyl ether was added to the residue to obtain a precipitate. The precipitate was filtered, and the supernatant was desolventized under vacuum and dried to obtain product two, with a yield of 61%.

[0120] (4) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, product two (8 mmol) was dissolved in diethyl ether, and 3.4 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70°C during the addition. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, isopropylamine (8 mmol, 0.48 g) was added dropwise, and the reaction was carried out for 6 h. After post-treatment, the reaction solution was dried to obtain product three, with a yield of 81%.

[0121] (5) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, product tri(5 mmol) was dissolved in diethyl ether, and 2.1 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70°C during the addition. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, diethylphosphine chloride (5 mmol, 0.63 g) was added dropwise, and the reaction was carried out for 6 h. The reaction solution was purified by column chromatography using a mixed solvent of n-hexane and ethyl acetate (volume ratio 1:1) as the eluent. After drying, a white solid was obtained with a yield of 73%. 1 ¹H-NMR (400MHz, CDCl₃): δ 7–8.6 (m, 15H), 2–3 (m, 5H), 1–1.8 (m, 28H). This confirms that the obtained solid is ligand 4.

[0122]

[0123] 2) Catalyst preparation:

[0124] The reaction flask was purged with nitrogen three times. Under N2 protection, ligand 4 (50 mmol) and the metal compound chromium octanoate (100 mmol, 48.2 g) were added, followed by 50 mL of dehydrated and deoxygenated dichloromethane. The mixture was stirred at room temperature for 24 h. After filtration, the solid was washed with n-hexane (5 mL × 3 times) and dried to obtain a blue powder (yield 83%). 20 μmol of the blue powder was mixed with 20 mL of chlorobenzene and stirred until homogeneous.

[0125] 3) Ethylene oligomerization:

[0126] Ethylene oligomerization was carried out in a 500 mL high-pressure reactor. The reactor was heated to 120 °C and evacuated for 2 h. The reactor was then purged three times with high-purity nitrogen and ethylene, maintaining an ethylene environment. After cooling, 220 mL of dehydrated and deoxygenated chlorobenzene and co-catalyst MMAO-3A (Al / Cr = 450) were added. The mixture was stirred for 2 min, followed by the addition of the aforementioned catalyst containing ligand 4 at a concentration of 1 μmol Cr. H₂ at 0.1 MPa was then added, and the pressure was brought up to 4.8 MPa with ethylene. The ethylene oligomerization reaction was carried out under specific conditions (see Table 1) for 35 min. The reaction was terminated with 10 wt% acidified ethanol. After cooling and depressurization, the liquid and solid products were separated by filtration. A small amount of organic phase was taken from the liquid product, filtered, and analyzed by gas chromatography. The solid product was washed with acidified ethanol, dried under vacuum at 60 °C for 8 h, and weighed. The results are shown in Table 1.

[0127] Example 5

[0128] 1) Preparation of ligand 5:

[0129] (1) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, 8.5 ml of n-butyllithium (2.4 M n-hexane solution) was added. Then, 42.8 ml of ether solution containing 0.1 g / ml of 2-bromo-4-tert-butylpyridine (20 mmol, 4.28 g) was added dropwise, keeping the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, 27.2 ml of ether solution containing 0.1 g / ml of (2-benzylbromo)dichloride (10 mmol, 2.72 g) was added dropwise to the above reaction solution, keeping the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 4 h, and then the reaction system was slowly heated to 30°C and reacted for 2 h. The reaction system was extracted twice with 40 ml of 1M dilute sulfuric acid. The aqueous phases were combined and adjusted to neutral with saturated sodium hydroxide aqueous solution. A yellow solid precipitated out. The solid was filtered and dried to obtain product 1 with a yield of 61%.

[0130] (2) The reaction flask was purged with nitrogen three times. Under the conditions of -80℃, N2 protection and stirring, 10 mmol of tetrahydrofuran dispersion of product one was added. Then, a tetrahydrofuran solution of isopropyl magnesium chloride lithium chloride complex (concentration 1.3M, added amount 7.7 ml, equivalent to 10 mmol of isopropyl magnesium chloride lithium chloride complex) was added dropwise. The reaction was carried out for 1 h, and then the reaction was carried out at 30℃ for another 2 h to obtain solution one.

[0131] (3) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80℃, a tetrahydrofuran (60 mL) solution of ethylphosphine dichloride (10 mmol, 1.31 g) was first added, followed by the dropwise addition of solution one. The reaction was allowed to proceed for 1 h. The solvent was then removed under vacuum, and 100 mL of diethyl ether was added to the residue to obtain a precipitate. The precipitate was filtered, and the supernatant was desolventized under vacuum and dried to obtain product two, with a yield of 62%.

[0132] (4) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, product two (8 mmol) was dissolved in diethyl ether, and 3.4 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70°C during the addition. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, cyclopentylamine (8 mmol, 0.68 g) was added dropwise, and the reaction was carried out for 6 h. After post-treatment, the reaction solution was dried to obtain product three, with a yield of 79%.

[0133] (5) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80℃, product tri(5 mmol) was dissolved in diethyl ether, and 2.1 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70℃ during the addition. After the addition was complete, the reaction was carried out at -80℃ for 2 h. Then, diphenylphosphine chloride (5 mmol, 1.1 g) was added dropwise, and the reaction was carried out for 6 h. The reaction solution was purified by column chromatography using a mixed solvent of n-hexane and ethyl acetate (volume ratio 1:1) as the eluent. After drying, a white solid was obtained with a yield of 75%. 1 ¹H-NMR (400MHz, CDCl₃): δ 7–8.6 (m, 20H), 2–3 (m, 3H), 1–1.8 (m, 31H). This confirms that the obtained solid is ligand 5.

[0134]

[0135] 2) Catalyst preparation:

[0136] The reaction flask was purged with nitrogen three times. Under N2 protection, ligand 5 (50 mmol) and the metal compound tetrahydrofuran chromium trichloride (100 mmol, 37.5 g) were added, followed by 50 mL of dehydrated and deoxygenated dichloromethane. The mixture was stirred at room temperature for 24 h. After filtration, the solid was washed with n-hexane (5 mL × 3 times) and dried to obtain a blue powder (yield 84%). 20 μmol of the blue powder was mixed with 20 mL of methylcyclohexane and stirred until homogeneous.

[0137] 3) Ethylene oligomerization:

[0138] Ethylene oligomerization was carried out in a 500 mL high-pressure reactor. The reactor was heated to 120 °C and evacuated for 2 h. The reactor was then purged three times with high-purity nitrogen and ethylene, maintaining an ethylene environment. After cooling, 210 mL of dehydrated and deoxygenated methylcyclohexane and co-catalyst MMAO-3A (Al / Cr = 480) were added. The mixture was stirred for 5 min, followed by the addition of the aforementioned catalyst containing ligand 5 at a concentration of 2 μmol Cr. H₂ was then added at 0.1 MPa, and the pressure was further increased to 5 MPa with ethylene. The ethylene oligomerization reaction was carried out under specific conditions (see Table 1) for 25 min. The reaction was terminated with 10 wt% acidified ethanol. After cooling and depressurization, the liquid and solid products were separated by filtration. A small amount of organic phase was taken from the liquid product, filtered, and analyzed by gas chromatography. The solid product was washed with acidified ethanol, dried under vacuum at 60 °C for 8 h, and weighed. The results are shown in Table 1.

[0139] Example 6

[0140] 1) Preparation of ligand 6:

[0141] (1) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, 8.5 ml of n-butyllithium (2.4 M n-hexane solution) was added. Then, 42.8 ml of ether solution containing 0.1 g / ml of 2-bromo-4-tert-butylpyridine (20 mmol, 4.28 g) was added dropwise, keeping the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, 27.2 ml of ether solution containing 0.1 g / ml of (2-benzylbromo)dichloride (10 mmol, 2.72 g) was added dropwise to the above reaction solution, keeping the temperature below -70°C during the addition process. After the addition was complete, the reaction was carried out at -80°C for 4 h, and then the reaction system was slowly heated to 30°C and reacted for 2 h. The reaction system was extracted twice with 40 ml of 1M dilute sulfuric acid. The aqueous phases were combined and adjusted to neutral with saturated sodium hydroxide aqueous solution. A yellow solid precipitated out. The solid was filtered and dried to obtain product 1 with a yield of 65%.

[0142] (2) The reaction flask was purged with nitrogen three times. Under the conditions of -80℃, N2 protection and stirring, 10 mmol of tetrahydrofuran dispersion of product one was added. Then, a tetrahydrofuran solution of isopropyl magnesium chloride lithium chloride complex (concentration 1.3M, added amount 7.7ml, equivalent to 10 mmol of isopropyl magnesium chloride lithium chloride complex) was added dropwise. The reaction was carried out for 1 h, and then the reaction was carried out at 30℃ for another 2 h to obtain solution one.

[0143] (3) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80℃, a tetrahydrofuran (60 mL) solution of phenylphosphine dichloride (10 mmol) was first added, followed by the dropwise addition of solution one. The reaction was allowed to proceed for 1 hour. The solvent was then removed under vacuum, and 100 mL of diethyl ether was added to the residue to obtain a precipitate. The precipitate was filtered, and the supernatant was desolventized under vacuum and dried to obtain product two, with a yield of 64%.

[0144] (4) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, product two (8 mmol) was dissolved in diethyl ether, and 3.4 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70°C during the addition. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, cyclopentylamine (8 mmol, 0.68 g) was added dropwise, and the reaction was carried out for 6 h. After post-treatment, the reaction solution was dried to obtain product three, with a yield of 85%.

[0145] (5) The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, product tri(5 mmol) was dissolved in diethyl ether, and 2.1 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, keeping the temperature below -70°C during the addition. After the addition was complete, the reaction was carried out at -80°C for 2 h. Then, diethylphosphine chloride (5 mmol, 0.63 g) was added dropwise, and the reaction was carried out for 6 h. The reaction solution was purified by column chromatography using a mixed solvent of n-hexane and ethyl acetate (volume ratio 1:1) as the eluent. After drying, a white solid was obtained with a yield of 74%. 1 ¹H-NMR (400MHz, CDCl₃): δ 7–8.6 (m, 15H), 2–3 (m, 3H), 1–1.9 (m, 36H). This confirms that the obtained solid is ligand 6.

[0146]

[0147] 2) Catalyst preparation:

[0148] The reaction flask was purged with nitrogen three times. Under N2 protection, ligand 6 (50 mmol) and the metal compound tetrahydrofuran chromium trichloride (100 mmol, 37.5 g) were added, followed by 50 mL of dehydrated and deoxygenated dichloromethane. The mixture was stirred at room temperature for 24 h. After filtration, the solid was washed with n-hexane (5 mL × 3 times) and dried to obtain a blue powder (yield 88%). 20 μmol of the blue powder was mixed with 20 mL of methylcyclohexane and stirred until homogeneous.

[0149] 3) Ethylene oligomerization:

[0150] Ethylene oligomerization was carried out in a 500 mL high-pressure reactor. The reactor was heated to 120 °C and evacuated for 2 h. The reactor was then purged three times with high-purity nitrogen and ethylene, maintaining an ethylene environment. After cooling, 220 mL of dehydrated and deoxygenated methylcyclohexane and co-catalyst MMAO-3A (Al / Cr = 460) were added. The mixture was stirred for 1 min, followed by the addition of the aforementioned catalyst containing ligand 6 at a concentration of 1 μmol Cr. H₂ was then added at 0.5 MPa, and the pressure was further increased to 5 MPa with ethylene. The ethylene oligomerization reaction was carried out under specific conditions (see Table 1) for 50 min. The reaction was terminated with 10 wt% acidified ethanol. After cooling and depressurization, the liquid and solid products were separated by filtration. A small amount of organic phase was taken from the liquid product, filtered, and analyzed by gas chromatography. The solid product was washed with acidified ethanol, dried under vacuum at 60 °C for 8 h, and weighed. The results are shown in Table 1.

[0151] Comparative Example 1

[0152] 1) Preparation method of ligand 7:

[0153] The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, 30 ml of dichloromethane was added first, followed by 7 ml of triethylamine and 7 mmol of isopropylamine. After the temperature stabilized, 15 mmol of diphenylphosphine chloride was added dropwise. The reaction was carried out for 1 h, and then the temperature was raised to 30°C and the reaction was carried out for 24 h. The mixture was filtered, the solvent was removed, and the mixture was recrystallized from ethanol. After drying, a white solid was obtained with a yield of 85%. 1 ¹H-NMR (400MHz, CDCl₃): δ 7.20–7.44 (m, 20H), 3.10–3.25 (m, 1H), 0.65 (d, 6H). This confirms that the obtained solid is ligand 7.

[0154]

[0155] 2) Catalyst preparation:

[0156] The preparation method of the catalyst corresponding to ligand 7 is the same as that in Example 5(2), except that the ligand is replaced with ligand 7, with a yield of 78%.

[0157] 3) Ethylene oligomerization:

[0158] The ethylene oligomerization reaction method is the same as 3) in Example 5, except that the catalyst containing ligand 5 is replaced with a catalyst containing ligand 7. The results are shown in Table 1.

[0159] Table 1 Catalyst activity and product selectivity for ethylene oligomerization

[0160]

[0161] From the catalyst activity and product selectivity test data of Examples 1-6 and Comparative Example 1 in Table 1, it can be seen that the ligands, catalysts and their corresponding catalytic systems prepared by the method of the present invention can be used for ethylene oligomerization reaction to prepare α-olefins with high activity, high selectivity of target products, and the sum of the selectivity of 1-hexene and 1-octene can reach more than 95%, with polymer content less than 0.3 wt%, high economic added value and potential industrial application prospects.

[0162] Example 7

[0163] The ethylene oligomerization method was the same as in Example 5, except that the ethylene oligomerization reaction was carried out at high temperatures of 70°C and 90°C. The catalyst activity and product selectivity of Example 5 and Comparative Example 1 were tested, and the results are shown in Table 2. Table 2 shows that the catalyst of Example 5 has high stability and good temperature resistance.

[0164] Table 2. High-temperature activity and product selectivity of catalysts for ethylene oligomerization.

[0165]

[0166] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An organic ligand containing NPN and PNP structures, wherein the chemical structural formula of the organic ligand is shown in Formula I below; Formula I in, R1, R1 ’ Same or different, selected independently from C 1-6 alkyl; R2 is selected from C 1-6 Alkyl, C 6-10 Aryl; R3 is selected from C 1-6 Alkyl, C 3-8 cycloalkyl, C 6-10 Aryl; R4, R4 ’ Same, selected from C 1-6 Alkyl, C 6-10 Aryl, fluorinated C 6-14 Aryl.

2. The organic ligand according to claim 1, characterized in that, R1, R1 ’ Same, selected from methyl, ethyl, isopropyl, tert-butyl; R2 is selected from methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, and phenyl. R3 is selected from methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, cyclopropyl, cyclobutyl, cyclopentyl, n-hexyl, cyclohexyl, and phenyl. R4, R4 ’ Same, selected from ethyl, propyl, isopropyl, tert-butyl, phenyl, 2-fluorophenyl.

3. The organic ligand according to claim 2, characterized in that, R1, R1 ’ Selected from methyl and tert-butyl; R2 is selected from ethyl or phenyl; R3 is selected from isopropyl, cyclopentyl, and phenyl; R4, R4 ’ Selected from ethyl, phenyl, and 2-fluorophenyl.

4. The organic ligand according to any one of claims 1 to 3, characterized in that, The organic ligand has a structure as shown in any one of Formulas I-1 to I-6: Formula I-1 Formula I-2 Formula I-3 Formula I-4 Formula I-5 Formula I-6.

5. The method for preparing the organic ligand according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: (1) The dichloro derivative of 2-bromo-alkylpyridine, n-butyllithium, and phosphine is reacted to yield compound II; the structural formula of the 2-bromo-alkylpyridine is: ; Formula I (2) The compound of formula II is dissolved in a solvent and reacts with the isopropyl magnesium chloride-lithium chloride complex to give a solution of formula A. Formula A (3) A solution of the dichlorophosphine is mixed with the solution and reacted with compound A to give compound III; the structural formula of the dichlorophosphine is: ; Formula I II (4) The compound of formula III, n-butyllithium and a primary amine are reacted to obtain the compound of formula IV; the primary amine has the structural formula R3-NH2; Formula IV (5) The monochloro derivatives of the compound of formula IV, n-butyllithium, and phosphine ( The reaction yields the organic ligand; the structural formula of the monochloro derivative is as follows: .

6. A catalyst, characterized in that, The catalyst comprises a transition metal compound and the organic ligand as described in any one of claims 1-4.

7. The catalyst according to claim 6, characterized in that, The catalyst is a complex formed from a transition metal compound and the organic ligand; The transition metal compound is selected from one or more compounds of chromium, molybdenum, tungsten, cobalt, rhodium, titanium, vanadium, zirconium, iron, nickel, or palladium.

8. The catalyst according to claim 7, characterized in that, The transition metal compound is selected from compounds of chromium, zirconium, nickel, and titanium.

9. The catalyst according to claim 7, characterized in that, The transition metal compound is selected from one or more of chromium acetylacetone, chromium chloride, chromium tetrahydrofuran trichloride, chromium isooctanoate, chromium octanoate, chromium hexacarbonyl, chromium (benzene)tricarbonyl, chromium naphthenate, chromium acetate, and chromium 2,2,6,6-tetramethylheptanedionate.

10. The catalyst according to claim 7, characterized in that, The molar ratio of the transition metal compound to the organic ligand is (1~5):

1.

11. A method for preparing the catalyst according to any one of claims 6-10, characterized in that, The preparation method includes the following steps: the organic ligand and the transition metal compound are mixed in a solvent that has undergone dehydration and deoxygenation treatment, and the catalyst is obtained after post-treatment.

12. A catalytic system, characterized in that, The catalytic system includes the catalyst according to any one of claims 6-10, and the catalytic system further includes a co-catalyst and / or an auxiliary agent.

13. The catalytic system according to claim 12, characterized in that, The cocatalyst is one or more of alkylaluminoxane, modified alkylaluminoxane, and boron-containing compounds; The additive is one or more of hydrogen, chloroalkanes, alkylaluminum, chloroalkylaluminum, alkylzinc, and chloroalkylzinc.

14. The catalytic system according to claim 12, characterized in that, The molar ratio of the co-catalyst to the transition metal compound in the catalyst is (100~2000):1, expressed as the molar ratio of aluminum to transition metal.

15. The use of the catalyst according to any one of claims 6-10 in ethylene oligomerization.

16. The application of the catalytic system according to any one of claims 12-14 in ethylene oligomerization.

17. A method for ethylene oligomerization, characterized in that, The method includes the following steps: Ethylene is polymerized in an inert solvent after dehydration and deoxygenation under the catalytic system conditions described in any one of claims 12-14 to obtain an α-olefin; wherein the α-olefin is selected from 1-hexene and 1-octene.

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