A dinuclear metal complex containing np structure, preparation method and application thereof

Abstract

The application provides a double nuclear metal complex containing NP structure, a preparation method and application thereof. The complex is used as a main catalyst in a catalytic system, and is combined with a cocatalyst selected from at least one of alkyl aluminum, halogenated alkyl aluminum, alkyl aluminoxane, modified alkyl aluminoxane, other organic aluminum compounds and boron-containing compounds to perform ethylene polymerization. The catalyst prepared by using the ligand of the application and the corresponding catalytic system are used for ethylene oligomerization, and high catalytic activity and high selectivity of target products can be obtained, the polymer generation amount is reduced, the polymer adhesion amount on the reactor wall and stirring paddle is reduced, the reactor blockage is alleviated, and continuous long-period operation of the device is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology and relates to a catalytic system for ethylene oligomerization, specifically to a binuclear metal complex containing an NP structure, its preparation method, and its application as an ethylene oligomerization catalyst. Background Technology

[0002] Linear α-olefins are an important class of organic chemical raw materials, widely used in the homopolymerization and copolymerization of polyethylene, surfactants, lubricants, and oil additives. Among them, 1-hexene and 1-octene can be used as comonomers to copolymerize with ethylene to produce linear low-density polyethylene. In particular, high-purity 1-hexene and 1-octene can significantly improve the tear resistance, abrasion resistance, and other properties of linear low-density polyethylene.

[0003] With the continuous development of the global economy, the demand for high-performance polyethylene is constantly increasing, leading to a rapid increase in the demand for 1-hexene and 1-octene. Industrially, the main methods for producing 1-hexene and 1-octene include paraffin cracking, ethylene oligomerization, and extraction separation, with ethylene oligomerization being the primary method. Currently, industrially applied ethylene oligomerization processes include Gulf's one-step process, Ethyl's two-step process, and Shell's SHOP process. The carbon number distribution of the products obtained from these processes conforms to the Schulz-Flory distribution, with low contents of 1-hexene and 1-octene, where the 1-octene content is <30%. To obtain high-purity 1-hexene and 1-octene, further separation through distillation is required, which involves complex processes and significant equipment investment. In contrast, selective ethylene oligomerization can selectively produce 1-hexene and / or 1-octene, offering higher atom economy and commercial application value. Sasol's patent WO 04056478 discloses a PNP framework catalyst. In the ethylene tetramerization reaction, the C8 component selectivity is approximately 66%, and the C6 component selectivity is approximately 21%. Specifically, 1-hexene accounts for only 82% of the C6 component, and the total selectivity for 1-hexene and 1-octene is approximately 84%. US20100137669 discloses a "PCCP" type symmetric framework catalyst. In the ethylene tetramerization reaction, this catalyst is more stable than the PNP system, with a total selectivity for 1-hexene and 1-octene of approximately 84%. Gambarotta et al. synthesized a bispyridine ligand, which, after coordination with chromium, was used to catalyze ethylene polymerization. The product mainly consists of a waxy solid phase and a liquid phase, with the liquid phase containing more than 99% 1-octene. It is evident that by adjusting the structure of the ligand, the catalytic activity of ethylene oligomerization and the selectivity of the target product can be modulated. Existing ethylene oligomerization typically suffers from the following drawbacks: low catalyst activity; insufficient overall selectivity for 1-hexene and 1-octene among the main products, resulting in low product purity; high co-catalyst usage, impacting the economic viability of ethylene oligomerization for α-olefin production; formation of filamentous and waxy polymers, with filamentous polymers entangled in the agitator and adhering to the reactor wall, and waxy polymers suspended in the reaction solvent and adhering to the reactor wall, affecting mass and heat transfer; and excessive polymer formation leading to reactor blockage, hindering continuous long-term operation. Therefore, designing a novel ligand for ethylene oligomerization and developing a highly selective catalytic system that achieves high catalytic activity and high overall selectivity for 1-hexene and 1-octene while reducing polymer formation at a lower co-catalyst dosage has become a pressing technical challenge in this field. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, the present invention provides a ligand based on the NP structure, a binuclear metal complex containing the NP structure, a method for preparing both and their application in ethylene oligomerization.

[0005] This invention provides a ligand containing an NP structure, having the structure shown in Formula I:

[0006]

[0007] Among them, R1, R2, R3, R4 and R5 may be the same or different, and are independently selected from hydrogen, aryl, substituted aryl, alkyl, alkoxy, thiophene, halide, cycloalkyl, amino, etc.

[0008] For example, R1, R2, R3, R4, and R5 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, halides, C 3-8 Cycloalkyl, amino, etc., wherein the halogen is selected from fluorine, chlorine, bromine or iodine;

[0009] Preferably, R1 and R2 are independently selected from methyl, ethyl, isopropyl, tert-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and phenyl, respectively; preferably methyl and isopropyl.

[0010] Preferably, R3 is independently selected from methyl, ethyl, isopropyl, tert-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, phenyl, methylphenyl, ethylphenyl, propylphenyl, naphthyl, anthracene; more preferably isopropyl, tert-butyl, cyclopropyl, cyclopentyl, phenyl;

[0011] Preferably, R4 and R5 are independently selected from phenyl, halogen-substituted phenyl, alkylphenyl, alkoxyphenyl, naphthyl, biphenyl, thiophenyl, and pyridyl; preferably phenyl or 2-fluorophenyl.

[0012] Preferably, R1 and R2 are selected from the same substituents, and R4 and R5 are selected from the same substituents.

[0013] According to an exemplary embodiment of the present invention, the ligand has a structure as shown in any one of Formulas I-1 to I-8:

[0014]

[0015]

[0016]

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

[0018] (a) 2-Bromo-alkylpyridine reacts with phosphine trichloride to give compound a;

[0019]

[0020] The structural formula of the 2-bromo-alkylpyridine is as follows: R is selected from hydrogen, aryl, substituted aryl, alkyl, alkoxy, thiophene, halide, cycloalkyl, amino, etc.;

[0021] For example, R is selected from hydrogen, C 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, halides, C 3-8 Cycloalkyl, amino, etc., wherein the halogen is selected from fluorine, chlorine, bromine or iodine; preferably, R is selected from methyl, ethyl, isopropyl, tert-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, phenyl; preferably methyl or isopropyl;

[0022] As an example, the 2-bromo-alkylpyridine is selected from 2-bromo-4-isopropylpyridine or 2-bromo-4-methylpyridine;

[0023] (b) The compound of formula a and the amine The reaction yields compound b;

[0024]

[0025] (c) The compound of formula b reacts with the monochloro derivative of the phosphine shown in formula d to obtain the ligand;

[0026]

[0027] According to an embodiment of the present invention, in step (a), the reaction is carried out in a solvent.

[0028] According to an embodiment of the present invention, in step (a), the reaction is carried out in the presence of n-butyllithium, preferably, the temperature at which the n-butyllithium is added is -80 to 0°C.

[0029] According to an embodiment of the present invention, in step (a), the molar ratio of 2-bromo-alkylpyridine, n-butyllithium, and phosphine trichloride is (2-2.2):(2.02-2.5):1, for example, 2:2.04:1.

[0030] According to an embodiment of the present invention, in step (a), n-butyllithium is first added and reacted for 1 to 8 hours, and then phosphine trichloride is added and reacted for 1 to 24 hours.

[0031] According to an embodiment of the present invention, in step (a), the trichloride of the phosphine is phosphorus trichloride.

[0032] According to an embodiment of the present invention, step (a) includes the following operations: dissolving 2-bromo-alkylpyridine in a solvent, adding n-butyllithium at -80 to 0°C, reacting for 1 to 8 hours, then adding phosphorus trichloride, reacting for 1 to 24 hours, and filtering, extracting, purifying and drying the reaction solution to obtain compound of formula a.

[0033] According to an embodiment of the present invention, in step (b), the reaction is carried out in a solvent.

[0034] According to an embodiment of the present invention, in step (b), the molar ratio of the amine and the compound of formula a is 1:(1 to 1.5), for example, 1:1, 1:1.1, 1:1.2, 1:1.3, or 1:1.4.

[0035] According to an embodiment of the present invention, in step (b), the amine is added to the solvent at a temperature of -80 to 0°C.

[0036] According to an embodiment of the present invention, in step (b), the amine is one or more of isopropylamine, tert-butylamine, cyclopropylamine, cyclopentylamine, and aniline.

[0037] According to an embodiment of the present invention, in step (b), the reaction time is 1 to 8 hours.

[0038] According to an embodiment of the present invention, in step (b), the reaction system further includes triethylamine.

[0039] According to an embodiment of the present invention, step (b) includes the following operations: dissolving compound a in a solvent, adding an amine at -80 to 0°C, reacting for 1 to 8 hours, and then treating the reaction solution to obtain compound b.

[0040] According to an embodiment of the present invention, in step (c), the reaction is carried out in a solvent.

[0041] According to an embodiment of the present invention, in step (c), the molar ratio of the monochloro derivative of the phosphine to the compound of formula b is 1:(1 to 1.5), for example, 1:1, 1:1.1, 1:1.2, 1:1.3, or 1:1.4.

[0042] According to an embodiment of the present invention, in step (c), the monochloro derivative of the phosphine is diphenylphosphine chloride, di(4-tolyl)phosphine chloride, di(2-tolyl)phosphine chloride, di(2-methoxyphenyl)phosphine chloride, or di(2-fluorophenyl)phosphine chloride.

[0043] According to an embodiment of the present invention, in step (c), the reaction is carried out in the presence of n-butyllithium.

[0044] According to an embodiment of the present invention, in step (c), the monochloro derivative of the phosphine is added to the solvent at a temperature of -80 to 0°C.

[0045] According to an embodiment of the present invention, in step (c), the reaction time is 1 to 8 hours.

[0046] According to an embodiment of the present invention, step (c) includes the following operations: dissolving product b in a solvent, adding n-butyllithium first at -80 to 0°C, then adding a monochloro derivative of phosphine, reacting for 1 to 8 hours, and obtaining the ligand by purifying and drying the reaction solution.

[0047] According to an embodiment of the present invention, the solvents in steps (a), (b), and (c) are selected from one or more of acetonitrile, dichloromethane, toluene, diethyl ether, and tetrahydrofuran, preferably all of which are diethyl ether.

[0048] The present invention also provides a complex, wherein the complex is formed by the ligand and metal Cr, and the molar ratio of the ligand to metal Cr is 1:(2-2.5);

[0049] Preferably, the source of the metallic Cr is one or more of the following: chromium trichloride tetrahydrofuran, chromium dichloride tetrahydrofuran, chromium acetylacetone, chromium isooctanoate, chromium octanoate, chromium chloride hexahydrate, chromium naphthenate, and chromium sulfate.

[0050] Preferably, the complex has a structure as shown in Formula II:

[0051]

[0052] R1, R2, R3, R4, and R5 have the limitations shown above.

[0053] The present invention also provides a method for preparing the above-mentioned complex, comprising the following steps: adding the ligand solution dropwise to a Cr metal solution, heating and refluxing under an inert atmosphere, recrystallizing to obtain the complex; wherein the molar ratio of the ligand to Cr metal is 1:(2-2.5), for example 1:2;

[0054] According to an embodiment of the present invention, the inert atmosphere is nitrogen or argon;

[0055] According to an embodiment of the present invention, the temperature of the heating and reflux is 110-150°C, and the time is 2-24 hours;

[0056] According to an embodiment of the present invention, the solvent used for recrystallization is solvent C, selected from n-hexane or cyclohexane, preferably n-hexane or cyclohexane after dehydration and deoxygenation;

[0057] In one embodiment, the preparation method includes the following steps: under high-purity N2 protection, at 30-60°C and with stirring, the ligand solution is added dropwise to a metal Cr solution, then the temperature is raised to 110-150°C, refluxed under N2 atmosphere for 2-24 hours, then the solvent is removed by vacuum distillation, and the dehydrated and deoxygenated n-hexane or cyclohexane is added for recrystallization to obtain a solid powder, which is the complex.

[0058] According to an embodiment of the present invention, the method for preparing the ligand solution is as follows: under an inert atmosphere (e.g., high-purity N2 / Ar) protection, the ligand is dissolved in solvent A to obtain the ligand solution;

[0059] For example, the molar ratio of the ligand to solvent A is 1:(80-200), preferably 1:(90-100);

[0060] For example, solvent A is toluene or dichloromethane.

[0061] In some preferred embodiments of the present invention, under high-purity N2 protection, the ligand is first transferred to a container, and purified toluene or dichloromethane is added. The molar ratio of the ligand to solvent A is 1:(90-100). The temperature is adjusted to 30-60°C, and the mixture is stirred continuously at a constant temperature to obtain the ligand solution.

[0062] According to an embodiment of the present invention, the method for preparing the metallic Cr solution is as follows: under an inert atmosphere (e.g., high-purity N2 / Ar) protection, the metallic chromium raw material is dissolved in solvent B to obtain the metallic Cr solution;

[0063] For example, the molar ratio of the metallic chromium component to the solvent is 1:(80-200), preferably 1:(90-100);

[0064] For example, the metallic chromium raw material is selected from one or more of tetrahydrofuran trichlorochromium, tetrahydrofuran dichlorochromium, acetylacetone chromium, isooctanoate chromium, octanoate chromium, chromium chloride hexahydrate, chromium naphthenate, and chromium sulfate, preferably tetrahydrofuran trichlorochromium;

[0065] For example, solvent B is toluene or dichloromethane.

[0066] In some preferred embodiments of the present invention, under the protection of high-purity N2, the metallic chromium raw material is first transferred to a container, and refined toluene or dichloromethane is added. The molar ratio of the metallic chromium raw material to solvent B is 1:(90-100). The temperature is adjusted to 30-60°C, and the mixture is stirred continuously at a constant temperature to obtain the metallic Cr solution.

[0067] The present invention also provides the application of the above-mentioned complex in the ethylene oligomerization reaction; preferably, the complex is used in combination as a main catalyst and a co-catalyst to catalyze the ethylene oligomerization reaction.

[0068] The present invention also provides a catalyst system containing the above-mentioned complex.

[0069] According to an embodiment of the present invention, the catalyst system includes a main catalyst and a co-catalyst, wherein the main catalyst is the complex, and the co-catalyst is selected from one or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, bis(diisobutylaluminum)oxide, methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, polymethylaluminoxane, modified methylaluminoxane MMAO-3A, ​​modified methylaluminoxane MMAO-7, modified methylaluminoxane MMAO-12, [Ph3C][Al{OC(CF3)3}4], triphenylmethyltetra(pentafluorophenyl)borate, N,N-dimethylphenylammonium tetra(pentafluorophenyl)borate, and tri(pentafluorophenyl)borane, preferably MMAO-3A.

[0070] According to an embodiment of the present invention, the molar ratio of Al in the co-catalyst to Cr in the complex is (1-1500):1, for example (100-1000):1, preferably 400:1, 500:1, 600:1, or 700:1.

[0071] The present invention also provides the application of the above-described catalyst system in the ethylene oligomerization reaction.

[0072] According to an embodiment of the present invention, the main products of the ethylene oligomerization reaction are 1-octene and 1-hexene.

[0073] According to an embodiment of the present invention, hydrogen may be added as needed during the ethylene oligomerization reaction, and the hydrogen pressure is 0-1 MPa, preferably 0.1 MPa.

[0074] The present invention also provides a method for preparing 1-octene and 1-hexene by ethylene oligomerization reaction, comprising the following steps: adding solvent D, the co-catalyst and the complex (i.e. the main catalyst) to a reaction vessel in an ethylene environment, reacting, and after the reaction is completed, stopping the ethylene flow, rapidly cooling, depressurizing, separating, and obtaining 1-octene and 1-hexene.

[0075] According to an embodiment of the present invention, the molar ratio of Al in the co-catalyst to Cr in the complex is as defined above.

[0076] According to an embodiment of the present invention, before the reaction, the reactor is heated to 100-150°C, evacuated for 1-4 hours, and then replaced with high-purity nitrogen and ethylene three times respectively, while maintaining an ethylene environment.

[0077] According to an embodiment of the present invention, solvent D and the co-catalyst are first stirred and mixed, and then the complex is added.

[0078] According to an embodiment of the present invention, the reaction conditions include: ethylene oligomerization reaction at 35-70°C and 2MPa-8MPa, and stopping the ethylene flow after 5-240 minutes of reaction.

[0079] According to an embodiment of the present invention, the solvent D is preferably one or more of the following: dehydrated and deoxygenated n-hexane, cyclohexane, benzene, cyclohexene, heptane, octane, methylcyclohexane, toluene, o-xylene, m-xylene, p-xylene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, chlorobenzene, 2-methylpentane, 2,2-dimethylpentane, 2,4-dimethylpentane, 2,2,4-trimethylpentane, 1-decene, n-dodecene, n-tetradecene, and n-hexadecene.

[0080] The beneficial effects of this invention are:

[0081] The catalytic system of the present invention, which uses a binuclear metal complex based on an NP structure and uses it as the main catalyst, is used for ethylene oligomerization. Under the preferred catalytic system conditions, it can not only achieve high catalytic activity and high selectivity of the target products (the total selectivity of the target products 1-hexene and 1-octene can reach up to 95%), but also reduce the amount of polymer generated (the polymer content is less than 0.5%). It also reduces the amount of polymer adhering to the reactor wall and the agitator, alleviates reactor clogging, and is conducive to continuous long-term operation of the equipment. Attached Figure Description

[0082] Figure 1 The image shows the adhesion of polymer to the agitator and cooling coil assembly after 10 hours of operation of the ethylene oligomerization reactor using the main catalyst prepared in Example 7. Detailed Implementation

[0083] 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.

[0084] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products with analytical or chemical purity specifications; or they can be prepared by known methods.

[0085] The preparation route of the ligand is as follows:

[0086]

[0087]

[0088] Example 1

[0089] 1) Preparation method of ligand 1:

[0090] The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, 8.5 mL of n-butyllithium solution (2.4 M n-hexane solution) was added. Then, a solution of 2-bromo-4-isopropylpyridine (20 mmol, 4.0 g) in diethyl ether was added dropwise, maintaining the temperature below -70°C during the addition. After the addition was complete, the reaction mixture was reacted at -80°C for 2 h. Next, a solution of phosphine trichloride (10 mmol, 1.4 g) in diethyl ether was added dropwise, maintaining the temperature below -70°C during the addition. After the addition was complete, the reaction mixture was reacted at -80°C for 4 h, and then the reaction mixture was slowly heated to 30°C and reacted for 2 h. The reaction mixture was extracted twice with 40 mL of 1 M dilute sulfuric acid. The aqueous phases were combined, adjusted to neutral with saturated sodium hydroxide solution, and a yellow solid precipitated. This solid was filtered, dried, and the product yielded compound a (60%).

[0091] The reaction flask was purged with nitrogen three times. Under N2 protection and stirring, compound a (7 mmol) was dissolved in dichloromethane (40 ml), triethylamine (7 ml) was added, and then cyclopentylamine (7 mmol, 0.6 g) was added dropwise at -80 °C. The reaction was carried out for 0.5 h, and then slowly raised to 30 °C and continued for 18 h. The solution was filtered to remove the formed triethylamine hydrochloride. After recrystallization from ethanol, the compound was separated and dried to obtain compound b with a yield of 72%.

[0092] The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, compound b (5 mmol) was dissolved in diethyl ether, and 2.1 mL of n-butyllithium (2.4 M n-hexane solution) was added dropwise, maintaining 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 84%.

[0093] The obtained white solid was characterized by nuclear magnetic resonance:

[0094] 1 ¹H-NMR (400MHz, CDCl₃): δ 8.5–8.7 (s, 2H), 7.35–7.42 (m, 14H), 3.12 (s, 2H), 2.64 (s, 1H), 1.73 (m, 4H), 1.51 (m, 4H), 1.29 (m, 12H). This confirms that the obtained solid is ligand 1.

[0095]

[0096] 2) Preparation method of the corresponding complex of ligand 1:

[0097] The reaction flask was purged with nitrogen three times. Under high-purity N2 protection and stirring conditions, CrCl3(THF)3 (10 mmol, 3.8 g) was dissolved in 100 mL of toluene. Under high-purity N2 protection, at 30–60 °C and with stirring conditions, ligand 1 (5 mmol) was dissolved in 50 mL of toluene and slowly added dropwise to the above CrCl3(THF)3 solution. The temperature was then raised to 110–130 °C and refluxed under N2 atmosphere for 2–24 h. The solvent was then removed by vacuum distillation, and the solution was recrystallized with purified n-hexane or cyclohexane. After drying, a blue-green solid was obtained with a yield of 73%.

[0098] The chemical formula of the blue-green solid was determined to be C using elemental analysis. 41 H 55 Cl6Cr2N3O2P2: C, 50.47; H, 5.16; N, 4.38%. Theoretical C, 49.2; H, 5.5; N, 4.2%.

[0099] Example 2

[0100] 1) Preparation method of ligand 2:

[0101] The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, 8.5 mL of n-butyllithium solution (2.4 M n-hexane solution) was added. Then, a solution of 2-bromo-4-isopropylpyridine (20 mmol, 4.0 g) in diethyl ether was added dropwise, maintaining the temperature below -70°C during the addition. After the addition was complete, the reaction mixture was reacted at -80°C for 2 h. Next, a solution of phosphine trichloride (10 mmol, 1.4 g) in diethyl ether was added dropwise, maintaining the temperature below -70°C during the addition. After the addition was complete, the reaction mixture was reacted at -80°C for 4 h, and then the reaction mixture was slowly heated to 30°C and reacted for 2 h. The reaction mixture was extracted twice with 40 mL of 1 M dilute sulfuric acid. The aqueous phases were combined and adjusted to neutral with a saturated sodium hydroxide solution. A yellow solid precipitated, which was filtered and dried to obtain compound a, in 58% yield.

[0102] The reaction flask was purged with nitrogen three times. Under N2 protection and stirring, compound a (7 mmol) was dissolved in dichloromethane (40 ml), triethylamine (7 ml) was added, and then cyclopentylamine (7 mmol, 0.6 g) was added dropwise at -78 °C. The reaction was carried out for 0.5 h, and then slowly raised to 30 °C and continued for 18 h. The solution was filtered to remove the formed triethylamine hydrochloride. After recrystallization from ethanol, the compound was separated and dried to obtain compound b with a yield of 74%.

[0103] The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80℃, 1.3M (15mmol, 11.5ml) of tetrahydrofuran solution of magnesium chloride and lithium chloride complex was added. Then, 2-bromofluorobenzene (15mmol, 2.6g) was added dropwise. The reaction was carried out for 1 hour, followed by another 4 hours at 30℃ to obtain solution c.

[0104] The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, a tetrahydrofuran solution (60 mL) containing 7.5 mmol (1.1 g) of phosphorus trichloride was added first, followed by dropwise addition of solution c. 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 compound d, with a yield of 60%.

[0105] The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80°C, compound b (5 mmol) was dissolved in diethyl ether, and 2.1 mL of n-butyllithium solution (2.4 M n-hexane solution) was added dropwise, maintaining 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, compound d (5 mmol) was added, 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 80%.

[0106] The obtained white solid was characterized by nuclear magnetic resonance:

[0107] 1 ¹H-NMR (400MHz, CDCl₃): δ 8.5–8.7 (s, 2H), 7–7.42 (m, 12H), 3.12 (s, 2H), 2.64 (s, 1H), 1.73 (m, 4H), 1.51 (m, 4H), 1.29 (m, 12H). This confirms that the obtained solid is ligand 2.

[0108]

[0109] 2) Preparation method of the corresponding complex of ligand 2:

[0110] The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions, CrCl3(THF)3 (1.00 mmol, 0.4 g) was dissolved in 10 mL of toluene. Under high-purity N2 protection, at 30–60 °C and with stirring conditions, ligand 2 (1.10 mmol) was dissolved in 10 mL of toluene and slowly added dropwise to the above CrCl3(THF)3 solution. The temperature was then raised to 110–130 °C and refluxed under N2 atmosphere for 2–24 h. The solvent was then removed by vacuum distillation, and the solution was recrystallized with purified n-hexane or cyclohexane. After drying, a blue-green solid was obtained with a yield of 78%.

[0111] The chemical formula of the blue-green solid was determined to be C using elemental analysis. 41 H 53 F₂Cl₆Cr₂N₃O₂P₂: C, 49.47; H, 4.96; N, 4.36%. Theoretical: C, 47.49; H, 5.12; N, 4.05%.

[0112] Example 3

[0113] The difference between the preparation method of ligand 3 and that in Example 1 is:

[0114] The ether solution of 2-bromo-4-isopropyl-pyridine in Example 1 was replaced with an ether solution of 2-bromo-4-methyl-pyridine (20 mmol, 3.5 g). After drying, a white solid was obtained in 75% yield. The obtained white solid was characterized by NMR.

[0115] 1 ¹H-NMR (400MHz, CDCl₃): δ 8.5–8.7 (s, 2H), 7.35–7.42 (m, 14H), 2.64 (s, 1H), 2.37 (m, 6H), 1.73 (m, 4H), 1.51 (m, 4H), 1.29 (m, 12H). This confirms that the obtained solid is ligand 3.

[0116]

[0117] The preparation method of the corresponding complex of ligand 3 is the same as that in Example 1(2), with a yield of 81%.

[0118] The chemical formula of the complex was determined to be C using elemental analysis. 37 H 47 Cl6Cr2N3O2P2:C, 49.17;H, 4.76;N, 4.66. Theoretical C, 47.03;H, 4.98;N, 4.45.

[0119] Example 4

[0120] The difference between the preparation method of ligand 4 and that in Example 2 is:

[0121] The ether solution of 2-bromo-4-isopropyl-pyridine in Example 2 was replaced with an ether solution of 2-bromo-4-methyl-pyridine (20 mmol, 3.5 g). After drying, a white solid was obtained in 70% yield. The obtained white solid was characterized by NMR.

[0122] 1¹H-NMR (400MHz, CDCl₃): δ 8.5–8.7 (s, 2H), 7–7.42 (m, 12H), 2.64 (s, 1H), 2.37 (m, 6H), 1.73 (m, 4H), 1.51 (m, 4H). This confirms that the obtained solid is ligand 4.

[0123]

[0124] The preparation method of the corresponding complex of ligand 4 is the same as that in Example 2(2), with a yield of 75%.

[0125] The chemical formula of the complex was determined to be C using elemental analysis. 37 H 45 F2Cl6Cr2N3O2P2:C,47.21;H,4.36;N,4.46. Theoretical C,45.31;H,4.59;N,4.29.

[0126] Example 5

[0127] The difference between the preparation method of ligand 5 and that in Example 2 is:

[0128] The ether solution of 2-bromo-4-isopropyl-pyridine and cyclopentylamine in Example 2 were replaced with an ether solution of 2-bromo-4-methyl-pyridine (20 mmol, 3.5 g) and isopropylamine (7 mmol, 0.42 g), respectively. After drying, a white solid was obtained with a yield of 82%. The obtained white solid was characterized by NMR.

[0129] 1 ¹H-NMR (400MHz, CDCl₃): δ 8.5–8.7 (s, 2H), 7–7.42 (m, 12H), 2.97 (s, 1H), 2.37 (m, 6H), 1.05 (m, 6H). This confirms that the obtained solid is ligand 5.

[0130]

[0131] The preparation method of the corresponding complex of ligand 5 is the same as that in Example 2(2), with a yield of 77%.

[0132] C was determined using elemental analysis. 35 H 43 F2Cl6Cr2N3O2P2:C,46.15;H,4.19;N,4.56. Theoretical C,44.03;H,4.51;N,4.4.

[0133] Example 6

[0134] The difference between the preparation method of ligand 6 and that in Example 1 is:

[0135] The ether solution of 2-bromo-4-isopropyl-pyridine and cyclopentylamine in Example 1 were replaced with an ether solution of 2-bromo-4-methyl-pyridine (20 mmol, 3.5 g) and isopropylamine (7 mmol, 0.4 g), respectively. After drying, a white solid was obtained with a yield of 77%. The obtained white solid was characterized by NMR:

[0136] 1 ¹H-NMR (400MHz, CDCl₃): δ 8.5–8.7 (s, 2H), 7.35–7.42 (m, 14H), 2.97 (s, 1H), 2.37 (m, 6H), 1.05 (m, 6H). This confirms that the obtained solid is ligand 6.

[0137]

[0138] The preparation method of the corresponding complex of ligand 6 is the same as that in Example 1(2), with a yield of 80%.

[0139] The chemical formula of the complex was determined to be C using elemental analysis. 35 H 45 Cl6Cr2N3O2P2: C, 47.55%; H, 4.59%; N, 4.76%. Theoretical C, 45.75%; H, 4.9%; N, 4.58%.

[0140] Example 7

[0141] The difference between the preparation method of ligand 7 and that in Example 1 is:

[0142] The cyclopentylamine in Example 1 was replaced with isopropylamine (7 mmol, 0.4 g). After drying, a white solid was obtained, with a yield of 78%. The obtained white solid was characterized by NMR.

[0143] 1 ¹H-NMR (400MHz, CDCl₃): δ 8.5–8.7 (s, 2H), 7.35–7.42 (m, 14H), 3.12 (s, 2H), 2.97 (s, 1H), 1.29 (m, 12H), 1.05 (m, 6H). This confirms that the obtained solid is ligand 7.

[0144]

[0145] The preparation method of the corresponding complex of ligand 7 is the same as that in Example 1(2), with a yield of 79%.

[0146] The chemical formula of the complex was determined to be C using elemental analysis. 39 H 53 Cl6Cr2N3O2P2: C, 50.1%; H, 5.19%; N, 4.53%. Theoretical C, 48.05%; H, 5.44%; N, 4.31%.

[0147] Example 8

[0148] The difference between the preparation method of ligand 8 and that in Example 2 is:

[0149] In Example 2, cyclopentylamine was replaced with isopropylamine (7 mmol, 0.4 g). After drying, a white solid was obtained, with a yield of 81%. The obtained white solid was characterized by NMR.

[0150] 1 ¹H-NMR (400MHz, CDCl₃): δ 8.5–8.7 (s, 2H), 7–7.42 (m, 12H), 3.12 (s, 2H), 2.97 (s, 1H), 1.29 (m, 12H), 1.05 (m, 6H). This confirms that the obtained solid is ligand 8.

[0151]

[0152] The preparation method of the corresponding complex of ligand 8 is the same as that in Example 2(2), with a yield of 83%.

[0153] The chemical formula of the complex was determined to be C using elemental analysis. 39 H 51 F2C l6 Cr2N3O2P2: C, 48.12; H, 4.76; N, 4.35%. Theoretical C, 46.34; H, 5.05; N, 4.16%.

[0154] Comparative Example 1

[0155] Preparation method of ligand 9:

[0156] The reaction flask was purged with nitrogen three times. Under N2 protection and stirring conditions at -80℃, 40 mL of dichloromethane was added first, followed by 7 mL of triethylamine and isopropylamine (7 mmol, 0.4 g) sequentially. After the temperature stabilized, diphenylphosphine chloride (15 mmol, 3.3 g) was added dropwise. The reaction was allowed to proceed for 1 h, then the temperature was raised to 30℃ and the reaction was allowed to continue for 18 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%. The obtained white solid was characterized by NMR. 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 9.

[0157]

[0158] The preparation method of the corresponding complex of ligand 9 is the same as that in Example 1(2), with a yield of 78%.

[0159] C was determined using elemental analysis. 31 H 35 Cl3CrNOP2: C, 58.42; H, 4.96; N, 2.38%. Theoretical C, 56.58; H, 5.32; N, 2.13%.

[0160] Application Examples

[0161] The complexes prepared in the above examples and comparative examples were subjected to ethylene oligomerization under the following conditions:

[0162] 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 were added. The mixture was stirred for 5 min, and then 1 μmol of the complex prepared in Examples 1-8 or Comparative Example 1 was added as the main catalyst. The molar ratio of Al in the co-catalyst to Cr in the complex was 500:1. The ethylene oligomerization reaction was carried out under certain conditions (see Table 1).

[0163] The complexes prepared in Examples 1-8 and Comparative Example 1 were subjected to ethylene oligomerization reaction according to the above method. The results of the oligomerization product detection and analysis are shown in Table 1.

[0164] Table 1. Distribution of oligomerization products and catalyst activity in Examples 1-8 and Comparative Example 1

[0165]

[0166]

[0167] As can be seen from Table 1, the ligands, catalysts and their corresponding catalytic systems prepared by the method of the present invention can achieve a total selectivity of up to about 95% for the target products 1-hexene and 1-octene in the ethylene oligomerization reaction. The catalysts have high activity and the polymer content is less than 0.5%, showing potential for industrial application.

[0168] from Figure 1 As shown, when the complex prepared in Example 7 is used as the main catalyst to catalyze the oligomerization reaction of ethylene, after the reaction device has been running for 10 hours, the generated polymer is less attached to the reactor wall and the agitator, which alleviates reactor blockage and is conducive to continuous long-term operation of the device.

[0169] 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. A ligand containing an NP structure, having a structure as shown in Formula I: Formula I in, Whether R1 and R2 are the same or different, they are independently selected from C. 1-6 alkyl; R3 is selected from C 1-6 Alkyl, C 3-8 cycloalkyl; R4 and R5 are the same, selected from phenyl or halogen-substituted phenyl.

2. The ligand according to claim 1, characterized in that, The halogen is selected from fluorine, chlorine, bromine or iodine.

3. The ligand according to claim 1, characterized in that, R1 and R2 are the same, so C is selected. 1-6 alkyl.

4. The ligand according to claim 1 or 3, characterized in that, R1 and R2 are selected from methyl, ethyl, isopropyl, and tert-butyl.

5. The ligand according to claim 1, characterized in that, R3 is selected from methyl, ethyl, isopropyl, tert-butyl, cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.

6. The ligand according to claim 1, characterized in that, R1 and R2 are the same and are selected from methyl, ethyl, isopropyl, and tert-butyl. R3 is selected from methyl, ethyl, isopropyl, tert-butyl, cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.

7. The ligand according to claim 1, characterized in that, R1 and R2 are the same and are selected from methyl and isopropyl groups; R3 is selected from isopropyl or cyclopentyl; R4 and R5 are selected from phenyl and 2-fluorophenyl.

8. The ligand according to claim 1, characterized in that, The ligand has a structure as shown in any one of Formulas I-1 to I-8: Formula I-1 Formula I-2 Formula I-3 Formula I-4 Formula I-5 Formula I-6 Formula I-7 Formula I-8.

9. A method for preparing the ligand according to any one of claims 1-8, characterized in that, The preparation method includes the following steps: (a) 2-Bromo-alkylpyridine reacts with phosphine trichloride to give compound a; a The structural formula of the 2-bromo-alkylpyridine is as follows: R is selected from C 1-6 alkyl; (b) The compound of formula a and the amine The reaction yields compound b; b (c) The compound of formula b reacts with the monochloro derivative of the phosphine shown in formula d to obtain the ligand; d。 10. A complex, characterized in that, The complex is formed by the ligand as described in any one of claims 1-8 and metallic Cr, wherein the molar ratio of the ligand to metallic Cr is 1:(2~2.5).

11. The complex according to claim 10, characterized in that, The source of the metallic Cr is one or more of the following: chromium trichloride in tetrahydrofuran, chromium dichloride in tetrahydrofuran, chromium acetylacetone, chromium isooctanoate, chromium octanoate, chromium chloride hexahydrate, chromium naphthenate, and chromium sulfate.

12. The complex according to claim 10, characterized in that, The complex has a structure as shown in Formula II: Formula II.

13. The method for preparing the complex according to any one of claims 10-12, characterized in that, The preparation method includes the following steps: adding the ligand solution dropwise to a Cr metal solution, heating and refluxing under an inert atmosphere, recrystallizing to obtain the complex; the molar ratio of the ligand to Cr metal is 1:(2~2.5).

14. The use of the complex according to any one of claims 10-12 in the oligomerization reaction of ethylene.

15. The application according to claim 14, characterized in that, The complex is used as a main catalyst in combination with a co-catalyst to catalyze the oligomerization reaction of ethylene.

16. A catalyst system for ethylene oligomerization, characterized in that, Contains the complex according to any one of claims 10-12.

17. The catalyst system according to claim 16, characterized in that, The catalyst system includes a main catalyst and a co-catalyst. The main catalyst is the complex, and the co-catalyst is selected from one or more of the following: trimethylaluminum, triethylaluminum, triisobutylaluminum, bis(diisobutylaluminum)oxide, methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, polymethylaluminoxane, modified methylaluminoxane MMAO-3A, ​​modified methylaluminoxane MMAO-7, modified methylaluminoxane MMAO-12, [Ph3C][Al{OC(CF3)3}4], triphenylmethyltetra(pentafluorophenyl)borate, N,N-dimethylphenylammonium tetra(pentafluorophenyl)borate, and tri(pentafluorophenyl)borane.

18. A method for preparing 1-octene and 1-hexene by ethylene oligomerization, characterized in that, The method includes the following steps: adding solvent D, co-catalyst and the complex according to any one of claims 10-12 to a reaction vessel in an ethylene environment, reacting, stopping the ethylene flow after the reaction is completed, rapidly cooling, depressurizing, separating, and obtaining 1-octene and 1-hexene.

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