Diimine ligands, methods of making and using the same

Abstract

The present application relates to the technical field of nickel-based catalyst, and discloses a diimine ligand, a preparation method and application thereof, wherein the raw materials for preparing the diimine ligand contain acenaphthenequinone, a protective agent, substituted aniline and a catalyst, the protective agent is selected from one or more than two of ortho ester, amine, hydrazine and substituted hydrazine; and the molar ratio of the acenaphthenequinone, the protective agent, the substituted aniline and the catalyst is 1:(0.5-3):(1.6-2.4):(0.1-10). In the present application, a certain amount of protective agent is added to the reaction system, the acenaphthenequinone is reacted with the ortho ester or low-molecular-weight amine to generate ketal or imine, the ketal or imine is separated or not separated, and then reacted with the substituted aniline to generate the target product diimine ligand, no water is generated in the synthesis reaction of the diimine ligand, the balance can be effectively promoted to the forward reaction, and the reaction yield is improved.

Description

Technical Field

[0001] This invention relates to the field of nickel-based catalyst technology, specifically to a diimine ligand, its preparation method, and its application. Background Technology

[0002] With the development of research and application of olefin resin materials, they have gradually become essential materials for people's daily life and industrial and agricultural production, as well as indispensable materials for cutting-edge technology, national defense construction and other fields.

[0003] Currently, polyolefin elastomers are mainly obtained by copolymerizing ethylene and α-olefins using metallocene catalysts. However, metallocene catalysts suffer from drawbacks such as difficult synthesis, low yield, large co-catalyst usage, and high cost. Nickel-based catalysts, especially nickel diimide complex catalysts, can generate highly branched, high-molecular-weight polyethylene from a single ethylene monomer. This work is considered a major milestone in the research of post-transition metal-catalyzed ethylene polymerization. The performance of the prepared polyethylene elastomer products can cover some commercial POE thermoplastic elastomer products. For example, the prepared polyethylene elastomer can replace POE thermoplastic elastomers in the preparation of encapsulation films for photovoltaic modules, demonstrating significant commercial application value.

[0004] The key to nickel-based catalyst preparation lies in the synthesis of diimine ligands. Using weak acids as catalysts is the most classic synthetic method, and early researchers used this method to synthesize N-aryl α-diimine ligands. For structures with low steric hindrance, acid catalysts generally yield good yields. For example, in 2011, researchers used formic acid as a catalyst to synthesize a chlorinated tetrasubstituted N-aryl ring α-diimine ligand with a yield of 88–92%; in 2013, researchers synthesized a highly active o-phenyl-substituted acenaphthene-skeletal α-diimine ligand with a yield of 62–67%; in 2014, researchers used acetic acid as a catalyst to synthesize a class of large conjugated skeleton diimine ligands with a yield of approximately 70%; and in 2019, researchers used formic acid as a catalyst to synthesize para-aryl-substituted α-diimine ligands with a yield of approximately 70%. For ligands with large steric hindrance, the yields are low. For example, in 2011, researchers synthesized a series of asymmetric α-diimine ligands. The yield of the diimine compound in the first step was 26-61%, and the yield of the ligand in the second step was 30-38%. In 2015, researchers synthesized a series of asymmetric α-diimine nickel complexes containing a bis(4-fluorophenyl)methyl-substituted acenaphthene skeleton, with a diimine ligand yield of 35-39%. Also in 2015, researchers synthesized symmetric α-diimine ligands using formic acid as a catalyst, but due to large steric hindrance, the yield was only 7-13%.

[0005] The main reason for the low yield of diimine ligands, especially highly substituted diimines, is that the reaction of ketone and amine condensation to form imine is a reversible reaction. Highly substituted amines have large steric hindrance, which does not favor the forward reaction, resulting in a low yield. Summary of the Invention

[0006] The purpose of this invention is to overcome the problem of low yield in the synthesis of highly substituent diimine ligands in the prior art, and to provide a method for preparing diimine ligands and their applications. This method for preparing diimine ligands involves adding a certain amount of protecting agent to the reaction system, which prevents the generation of water during the reaction and promotes the forward reaction, thereby effectively improving the yield of diimine ligands.

[0007] To achieve the above objectives, the present invention provides a diimine ligand, wherein the raw materials for preparing the diimine ligand contain acenaphthoquinone, a protecting agent, a substituted aniline, and a catalyst, wherein the protecting agent is selected from one or more of orthoesters, amines, hydrazines, and substituted hydrazines; and the molar ratio of the amounts of acenaphthoquinone, the protecting agent, the substituted aniline, and the catalyst is 1:(0.5-3):(1.6-2.4):(0.1-10).

[0008] Preferably, the orthoester is selected from one or more of trimethyl orthoformate, triethyl orthoformate, trimethyl orthoacetate, and triethyl orthoacetate.

[0009] Preferably, the amine is selected from one or more of methylamine, ethylamine, propylamine, butylamine, ethylenediamine, 1,3-propanediamine, butyldiamine and hexamethylenediamine.

[0010] Preferably, the substituted hydrazine is selected from one or more of hydrazine hydrate, methylhydrazine, dimethylhydrazine and ethylhydrazine.

[0011] Preferably, the substituted aniline is selected from compounds of formula (I).

[0012]

[0013] Among them, R1, R2, R3, R4, and R5 are each independently selected from H, F, Cl, Br, I, NO2, benzyl, diphenylmethyl, C1-C6 alkyl, and C1-C6 alkoxy.

[0014] Preferably, the catalyst is selected from one or more of protic acids, Lewis acids, and acid salts.

[0015] Preferably, the protic acid is selected from one or more of sulfuric acid, hydrochloric acid, hydrobromic acid, formic acid, acetic acid, trifluoroacetic acid, difluoroacetic acid, oxalic acid, benzenesulfonic acid, and p-toluenesulfonic acid.

[0016] Preferably, the Lewis acid is selected from one or more of ferric chloride, zinc chloride, titanium tetrachloride, aluminum trichloride, and boron trifluoride.

[0017] Preferably, the acid salt is selected from potassium bisulfate and / or sodium bisulfate.

[0018] A second aspect of the present invention provides a method for preparing the above-mentioned diimine ligand, the method comprising mixing acenaphthoquinone, a protecting agent, a substituted aniline and a catalyst, and reacting them.

[0019] Preferably, the reaction is carried out in the presence of a solvent.

[0020] Preferably, the solvent is selected from one or more of alkanes, haloalkanes, alkylbenzenes, ethers, esters, alcohols, and nitriles.

[0021] Preferably, the weight ratio of the acenaphthene to the solvent is 1:(3-60).

[0022] Preferably, the reaction temperature is 20–120°C, and the reaction time is 2–16 h.

[0023] A third aspect of the present invention provides the application of the above-mentioned diimine ligand in the preparation of nickel-based catalysts.

[0024] A fourth aspect of the present invention provides a nickel-based catalyst, wherein the raw materials for preparing the nickel-based catalyst contain the above-mentioned diimine ligand.

[0025] The fifth aspect of the present invention provides a method for preparing the above-mentioned nickel-based catalyst, the method comprising reacting a diimine ligand with a nickel salt to obtain a nickel-based catalyst.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) In this invention, by adding a certain amount of protective agent to the reaction system, acenaphthene reacts with orthoesters or low molecular weight amines and other protective agents to generate ketals or imines. The ketals or imines are separated or not separated and then reacted with substituted aniline to generate the target product diimine ligand. No water is generated in the diimine ligand synthesis reaction, which can effectively promote the equilibrium to the forward reaction and improve the reaction yield. It is especially suitable for the synthesis of sterically hindered non-synthetic diimine ligands.

[0028] (2) In this invention, when two different substituted anilines are used to prepare asymmetric diimine ligands, the exchange reaction rate between the substituted aniline and the imine and between imines with different structures is slowed down due to the low water content in the reaction system. The amount of by-product symmetric diimine ligands generated is reduced, and the yield of the target product asymmetric diimine ligand is increased. This effect is particularly obvious for the synthesis of sterically hindered asymmetric diimine ligands.

[0029] (3) In this invention, when orthoester is used as a protective agent, the synthesis of diimine ligand can be completed in one step, with short process steps and simple operation;

[0030] (4) In this invention, when small molecule amines or hydrazine are used as protective agents, the water generated by the reaction can be removed by desolventizing, and then substituted aniline can be added to directly carry out the reaction. The reaction can be carried out in the same reaction vessel without transfer, thus avoiding material loss.

[0031] (5) In this invention, when preparing asymmetric diimine ligands, the two-step reaction of substituted aniline with different structures and acenaphthoquinone can be carried out in the same reaction vessel, and the asymmetric diimine ligands can be purified by recrystallization. The process is short and the post-processing is simple. Attached Figure Description

[0032] Figure 1 This is the NMR spectrum of the symmetrical diimine ligand prepared in Example 1;

[0033] Figure 2 This is the NMR spectrum of the asymmetric diimine ligand prepared in Example 2;

[0034] Figure 3 This is the NMR spectrum of the nickel diimine bromide catalyst prepared in Example 2. Detailed Implementation

[0035] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0036] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0037] The first aspect of the present invention provides a diimine ligand, wherein the raw materials for preparing the diimine ligand contain acenaphthoquinone, a protective agent, a substituted aniline, and a catalyst.

[0038] In this invention, in order to prevent the generation of no water in the reaction, effectively drive the equilibrium to the forward reaction, and improve the reaction yield, a certain amount of protective agent needs to be added to the reaction system. The protective agent is selected from one or more of orthoesters, amines, hydrazines, and substituted hydrazines.

[0039] In this invention, the orthoester is selected from one or more of trimethyl orthoformate, triethyl orthoformate, trimethyl orthoacetate, and triethyl orthoacetate. Preferably, the orthoester is trimethyl orthoacetate and / or triethyl orthoacetate.

[0040] In this invention, the amine is selected from one or more of methylamine, ethylamine, propylamine, butylamine, ethylenediamine, 1,3-propanediamine, butyldiamine and hexamethylenediamine.

[0041] In this invention, the substituted hydrazine is selected from one or more of hydrazine hydrate, methylhydrazine, dimethylhydrazine and ethylhydrazine.

[0042] In this invention, the substituted aniline is selected from compounds of formula (I).

[0043]

[0044] Among them, R1, R2, R3, R4, and R5 are each independently selected from H, F, Cl, Br, I, NO2, benzyl, diphenylmethyl, C1-C6 alkyl, and C1-C6 alkoxy.

[0045] In this invention, the benzyl group is selected from compounds represented by formula (II).

[0046]

[0047] In a preferred embodiment of the present invention, R6, R7, R8, R9, R 10 Each is independently selected from H, F, Cl, Br, I, NO2, C1-C6 alkyl and C1-C6 alkoxy.

[0048] In this invention, the diphenylmethyl group is selected from compounds represented by formula (III).

[0049]

[0050] In a preferred embodiment of the present invention, R 11 R 12 R 13 R 14 R 15 R 16 R 17 R 18 R 19 R 20 Each is independently selected from H, F, Cl, Br, I, NO2, C1-C6 alkyl and C1-C6 alkoxy.

[0051] In this invention, the C1-C6 alkyl group is selected from one or more of methyl, ethyl, propyl, isopropyl, butyl, pentyl, n-hexyl and cyclohexyl.

[0052] In this invention, the C1-C6 alkoxy group is selected from one or more of methoxy, ethoxy, propoxy, isopropoxy, butoxy, pentoxy, n-hexoxy, and cyclohexoxy.

[0053] In this invention, in order to accelerate the reaction rate, a catalyst needs to be added to the reaction system. The catalyst is selected from one or more of protic acids, Lewis acids and acid salts.

[0054] In this invention, the protic acid is selected from one or more of sulfuric acid, hydrochloric acid, hydrobromic acid, formic acid, acetic acid, trifluoroacetic acid, difluoroacetic acid, oxalic acid, benzenesulfonic acid, and p-toluenesulfonic acid.

[0055] In this invention, when the catalyst is a weak acid such as acetic acid or oxalic acid, the amount of the catalyst can be appropriately increased.

[0056] In this invention, when the catalyst is a strong acid such as hydrochloric acid or hydrobromic acid, saturated sodium bicarbonate needs to be added to the reaction system. The saturated sodium bicarbonate is used to neutralize the remaining strong acid.

[0057] In this invention, the Lewis acid is selected from one or more of ferric chloride, zinc chloride, titanium tetrachloride, aluminum trichloride, and boron trifluoride.

[0058] In this invention, the acid salt is selected from potassium bisulfate and / or sodium bisulfate.

[0059] In this invention, if the molar ratio of the protecting agent to the acenaphthoquinone is too small, the reaction will be incomplete, resulting in a low yield of the diimine ligand. If the molar ratio of the protecting agent to the acenaphthoquinone is too large, the reaction will be more complete, but this will increase the amount of catalyst required, making the reaction uneconomical. If the molar ratio of the substituted aniline to the acenaphthoquinone is too small, the acenaphthoquinone will react incompletely, resulting in a low yield of the diimine ligand. If the molar ratio of the substituted aniline to the acenaphthoquinone is too large, some of the substituted aniline will not participate in the reaction, making the reaction process uneconomical. Therefore, the molar ratio of the acenaphthoquinone, protecting agent, substituted aniline, and catalyst needs to be controlled within a reasonable range.

[0060] In this invention, the molar ratio of the acenaphthoquinone, the protective agent, the substituted aniline, and the catalyst is 1:(0.5-3):(1.6-2.4):(0.1-10). Specifically, the molar ratio of the acenaphthoquinone, the protective agent, the substituted aniline, and the catalyst can be 1:2:2.4:0.3, 1:1.5:2.05:1.1, 1:1.2:2.4:4.2, or 1:3:2:1.5.

[0061] In this invention, the substituted aniline is selected from one or more of 2-bis(p-chlorophenyl)methyl-4,6-dimethylaniline, 3,4,5-trimethylaniline and 2,5-di-tert-butylaniline.

[0062] In a preferred embodiment of the present invention, the substituted aniline is a mixture of substituted aniline A and substituted aniline B, wherein substituted aniline A is 2-bis(p-chlorophenyl)methyl-4,6-dimethylaniline, and substituted aniline B is 3,4,5-trimethylaniline and / or 2,5-di-tert-butylaniline.

[0063] In this invention, when the substituted aniline is a mixture of substituted aniline A and substituted aniline B, due to the different structures of the two different substituted anilines, an asymmetric diimine ligand will be prepared. If the molar ratio of one of the substituted anilines is too large, the yield of the byproduct symmetric diimine ligand will increase, while the yield of the target product asymmetric diimine ligand will decrease. Therefore, the amount of different substituted anilines must be appropriate, and the molar ratio of the substituted aniline A to the substituted aniline B is 1:(0.8~1.2). Specifically, the molar ratio of the substituted aniline A to the substituted aniline B can be 1:0.8, 1:0.9, 1:1, 1:1.1, or 1:1.2.

[0064] In one specific embodiment of the present invention, the molar ratio of the substituted aniline A to the substituted aniline B is 1:1.

[0065] A second aspect of the present invention provides a method for preparing the above-mentioned diimine ligand, the method comprising mixing acenaphthoquinone, a protecting agent, a substituted aniline and a catalyst, and reacting them.

[0066] In the method described in this invention, the reaction is carried out in the presence of a solvent, which is an organic compound containing 5-10 carbon atoms.

[0067] In the method described in this invention, the solvent is selected from one or more of alkanes, haloalkanes, alkylbenzenes, ethers, esters, alcohols, and nitriles.

[0068] In a preferred embodiment of the present invention, the solvent is selected from one or more of the following: pentane, hexane, cyclohexane, heptane, octane, dichloromethane, chloroform, dichloroethane, trichloroethane, benzene, toluene, xylene, diethyl ether, methyl tert-butyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, methanol, ethanol, propanol, butanol, cyclohexanol, ethyl acetate, butyl acetate, acetonitrile, propionitrile, and benzonitrile.

[0069] In the method described in this invention, if the amount of solvent used is large, the raw material dissolution performance is good and the reaction rate is fast; however, if the amount of solvent used is too large, it is uneconomical. Therefore, it is necessary to control the solvent within a reasonable range.

[0070] In the method described in this invention, the weight ratio of acenaphthoquinone to the solvent is 1:(3-60); preferably, the weight ratio is 1:(3-40); and even more preferably, the weight ratio is 1:(3-30). Specifically, the weight ratio of acenaphthoquinone to the solvent can be 1:3, 1:10, 1:20, or 1:30.

[0071] In the method described in this invention, the reaction rate is fast when the reaction temperature is high, but excessively high reaction temperature will lead to an increase in side reactions and a decrease in reaction selectivity; in addition, aniline with a lower molecular weight requires a lower reaction temperature.

[0072] In the method described in this invention, the reaction temperature is 20 to 120°C. Specifically, the reaction temperature can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, or 120°C.

[0073] In the method described in this invention, the reaction time is 2 to 16 hours, specifically, the reaction time can be 2 hours, 6 hours, 10 hours, 14 hours or 16 hours.

[0074] In one specific embodiment, after the reaction of the acenaphthoquinone, the protective agent, the substituted aniline and the catalyst is completed, the reaction product is cooled to room temperature, filtered, desolventized, and then a poor solvent is added for recrystallization, filtered, and the filter cake is dried to obtain the diimine ligand.

[0075] In the method described in this invention, the undesirable solvent is selected from one or more of alcohols, ethers, alkanes, and haloalkanes. Specifically, the alcohol is methanol, ethanol, or propanol; the ether is diethyl ether, diisopropyl ether, methyl tert-butyl ether, tetrahydrofuran, or 2-methyltetrahydrofuran; the alkane is n-pentane, n-hexane, cyclohexane, petroleum ether, or n-heptane; and the haloalkanes are dichloromethane, chloroform, dichloroethane, etc.

[0076] In the method described in this invention, the drying conditions are: a temperature of 60–120°C and a time of 2–6 hours. Specifically, the drying temperature can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, or 120°C, and the drying time can be 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0077] In the method described in this invention, there are no special requirements for the equipment used in the drying operation; it can be any equipment commonly used in the art, such as an oven.

[0078] In another specific embodiment, after the reaction of the acenaphthoquinone, the protective agent, the substituted aniline and the catalyst is completed, the reaction product is cooled to room temperature, filtered, the filtrate is concentrated, cooled, and then a poor solvent is added for recrystallization to obtain the diimine ligand.

[0079] In the method described in this invention, the purification of the diimine ligand can be carried out by recrystallization or column chromatography.

[0080] A third aspect of the present invention provides the application of the above-mentioned diimine ligand in the preparation of nickel-based catalysts.

[0081] A fourth aspect of the present invention provides a nickel-based catalyst, wherein the raw materials for preparing the nickel-based catalyst contain the above-mentioned diimine ligand.

[0082] The fifth aspect of the present invention provides a method for preparing a nickel-based catalyst, the method comprising reacting a diimine ligand with a nickel salt to obtain a nickel-based catalyst.

[0083] In this invention, the reaction conditions between the nickel salt and the diimine ligand during the preparation of the nickel-based catalyst are: temperature 10–30°C and time 8–30 h. Specifically, the reaction temperature can be 10°C, 20°C, or 30°C, and the reaction time can be 8 h, 12 h, 16 h, 20 h, 24 h, 28 h, or 30 h.

[0084] In this invention, when preparing the nickel-based catalyst, the molar ratio of the diimine ligand to the nickel salt is 1:(0.9 to 1.1). Specifically, the molar ratio of the diimine ligand to the nickel salt can be 1:0.9, 1:1, or 1:1.1.

[0085] In this invention, when preparing the nickel-based catalyst, the nickel salt is selected from one or more of nickel bromide, nickel chloride, or their alcohol or ether complexes. Specifically, the nickel salt is selected from one or more of ethylene glycol dimethyl ether nickel bromide, diethanol dimethyl ether nickel chloride, diethylene glycol dimethyl ether nickel bromide, diethylene glycol dimethyl ether nickel chloride, and diethylene glycol nickel bromide.

[0086] In this invention, the preparation of the nickel-based catalyst is carried out in the presence of a solvent, which is an organic compound containing 5-10 carbon atoms. Specifically, the solvent is selected from one or more of alkanes, haloalkanes, alkylbenzenes, ethers, esters, alcohols, and nitriles. Preferably, the solvent is selected from one or more of pentane, hexane, cyclohexane, heptane, octane, dichloromethane, chloroform, dichloroethane, trichloroethane, benzene, toluene, xylene, diethyl ether, methyl tert-butyl ether, tetrahydrofuran, methyltetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, methanol, ethanol, propanol, butanol, cyclohexanol, ethyl acetate, butyl acetate, acetonitrile, propionitrile, and benzonitrile.

[0087] In this invention, when preparing the nickel-based catalyst, the weight ratio of the diimine ligand to the solvent is 1:(5-40). Specifically, the weight ratio of the diimine ligand to the solvent can be 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35 or 1:40.

[0088] In this invention, the nickel-based catalyst can be purified by recrystallization.

[0089] The present invention will be described in detail below through embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following embodiments.

[0090] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available. The room temperature mentioned in the following embodiments refers to 25°C.

[0091] Example 1

[0092] 15.5 g (48 mmol) of 2-bis(p-fluorophenyl)methyl-4,6-dimethylaniline, acenaphthoquinone (3.6 g, 20 mmol), p-toluenesulfonic acid (1.08 g, 6 mmol), trimethyl orthoacetate (4.8 g, 40 mmol), and 150 g of dichloroethane were added to a 500 mL four-necked flask equipped with a condenser. The mixture was stirred at 60 °C for 12 h, then cooled to room temperature, filtered, and dissolved to obtain crude symmetrical diimine ligands. 200g of diethyl ether was added to the crude symmetrical diimine ligand for recrystallization. The mixture was filtered, and the filter cake was dried in an oven at 80°C for 4 hours to obtain 11.9g of symmetrical diimine ligand, with a yield of 75% (wherein, the protecting agent was trimethyl orthoacetate, the substituted aniline was 2-di(p-fluorophenyl)methyl-4,6-dimethylaniline, the catalyst was p-toluenesulfonic acid, and the molar ratio of the acenaphthoquinone, protecting agent, substituted aniline, and catalyst was 1:2:2.4:0.3).

[0093] In a 500 mL four-necked flask, the synthesized symmetrical diimine ligand (8.5 g, 10 mmol), dichloromethane (150 g), and diethylene glycol dimethyl ether nickel bromide (3.1 g, 10 mmol) were added. The mixture was stirred at 10 °C for 30 h to carry out the reaction. The mixture was concentrated under reduced pressure, and 150 g of diethyl ether was added. The mixture was stirred and recrystallized. The mixture was filtered, and the filter cake was washed with diethyl ether to obtain 10.1 g of nickel bromide diimine catalyst, with a yield of 94%.

[0094] Example 2

[0095] Add acenaphthoquinone (3.6 g, 20 mmol), ethylenediamine (1.8 g, 30 mmol), acetic acid (6 g, 100 mmol), and ethylene glycol dimethyl ether (100 g) to a 500 mL four-necked flask equipped with a condenser. Stir and reflux for 4 h, then evaporate to dryness under reduced pressure. Add ethylene glycol dimethyl ether (100 g), 2-di(p-chlorophenyl)methyl-4,6-dimethylaniline (6.5 g, 20 mmol), and p-toluenesulfonic acid (3.8 g, 22 mmol) to the residue. Stir at 40 °C for 12 h, then add 2,4,6-trimethylaniline (2.8 g, 21 mmol). After stirring at 80℃ for 6 hours, the mixture was cooled to room temperature, filtered, concentrated, and cooled to room temperature to obtain crude asymmetric diimine ligand. Then, 120 g of methyl tert-butyl ether was added to the crude asymmetric diimine ligand for recrystallization to obtain 7.4 g of asymmetric diimine ligand, with a yield of 61% (wherein the protecting agent is ethylenediamine, the substituted aniline is 2-di(p-chlorophenyl)methyl-4,6-dimethylaniline and 2,4,6-trimethylaniline, the catalyst is p-toluenesulfonic acid, and the molar ratio of acenaphthoquinone, protecting agent, substituted aniline and catalyst is 1:1.5:2.05:1.1).

[0096] In a 500 mL four-necked flask, the synthesized asymmetric diimine ligand (6.04 g, 10 mmol), dichloromethane (180 g), methanol (30 g), and diethylene glycol dimethyl ether nickel bromide (3.1 g, 10 mmol) were added. The mixture was stirred at 20 °C for 16 h, concentrated under reduced pressure, and 150 g of diethyl ether was added. The mixture was stirred and recrystallized, filtered, and the filter cake was washed with diethyl ether to obtain 7.4 g of nickel bromide diimine catalyst, with a yield of 90%.

[0097] Example 3

[0098] Add acenaphthoquinone (3.6 g, 20 mmol), 40% hydrazine hydrate (1.9 g, 24 mmol), 31% hydrochloric acid (10 g), and toluene (70 g) to a 250 mL four-necked flask equipped with a condenser. Stir and heat to 80 °C. After 8 h, cool to room temperature and separate the layers. Wash the organic layer with 30 g of saturated sodium bicarbonate and evaporate to dryness under reduced pressure. Add 2-methyltetrahydrofuran (150 g), 3,4,5-trimethylaniline (6.5 g, 48 mmol), and potassium bisulfate (4.1 g, 30 g) to the residue. The mixture was stirred at 80°C for 6 hours, then cooled to room temperature, filtered, concentrated, and cooled to room temperature to obtain crude symmetrical diimine ligand. 100 g of diethyl ether was added to the crude symmetrical diimine ligand for recrystallization to obtain 7.0 g of symmetrical diimine ligand, with a yield of 85% (wherein, the protecting agent was hydrazine hydrate, the substituted aniline was 3,4,5-trimethylaniline, the catalyst was hydrochloric acid, and the molar ratio of acenaphthoquinone, protecting agent, substituted aniline, and catalyst was 1:1.2:2.4:4.2).

[0099] In a 500 mL four-necked flask, the synthesized symmetrical diimine ligand (6.8 g, 8 mmol), dichloromethane (150 g), and diethylene glycol dimethyl ether nickel bromide (2.5 g, 8 mmol) were added. The mixture was stirred at 10 °C for 30 h to carry out the reaction. The mixture was concentrated under reduced pressure, and 150 g of diethyl ether was added. The mixture was stirred and recrystallized. The mixture was filtered, and the filter cake was washed with diethyl ether to obtain 8.1 g of nickel bromide diimine catalyst, with a yield of 95%.

[0100] Example 4

[0101] Add acenaphthoquinone (3.6 g, 20 mmol), ethanol (120 g), and acetic acid (1.8 g, 30 mmol) to a 250 mL four-necked flask equipped with a condenser. Then, introduce methylamine (1.86 g, 60 mmol). After stirring at room temperature for 24 h, reflux to remove excess methylamine. Next, add 2-bis(p-fluorophenyl)methyl-4,6-dimethylaniline (6.5 g, 20 mmol) to the residue. After stirring at 30 °C for 24 h, add 2,5-di-tert-butylaniline (4.1 g, 20 mmol) and zinc chloride (0.3 g). After stirring at 70 °C for 16 h, cool to room temperature. The mixture was filtered, concentrated, and cooled to room temperature to obtain crude asymmetric diimine ligand. Then, 200 g of a mixed solvent of cyclohexane and dichloroethane (weight ratio of cyclohexane to dichloroethane 20:1) was added to the crude asymmetric diimine ligand for recrystallization to obtain 10.2 g of asymmetric diimine ligand, with a yield of 72% (wherein, the protecting agent is methylamine, the substituted aniline is 2-di(p-fluorophenyl)methyl-4,6-dimethylaniline and 2,5-di-tert-butylaniline, the catalyst is acetic acid, and the molar ratio of acenaphthoquinone, protecting agent, substituted aniline, and catalyst is 1:3:2:1.5).

[0102] In a 500 mL four-necked flask, the synthesized asymmetric diimine ligand (7.1 g, 10 mmol), dichloromethane (180 g), methanol (30 g), and diethylene glycol dimethyl ether nickel bromide (3.1 g, 10 mmol) were added. The mixture was stirred at 20 °C for 16 h, concentrated under reduced pressure, and 150 g of diethyl ether was added. The mixture was stirred and recrystallized, filtered, and the filter cake was washed with diethyl ether to obtain 8.4 g of nickel bromide diimine catalyst, with a yield of 91%.

[0103] Comparative Example 1

[0104] Following the method of Example 2, except that Comparative Example 1 did not add the protective agent ethylenediamine, and finally obtained 3.4 g of symmetrical diimine ligand, with a yield of 27%.

[0105] Comparative Example 2

[0106] Following the method of Example 4, except that Comparative Example 2 did not add the protective agent methylamine, and finally obtained 5.7 g of asymmetric diimine ligand, with a yield of 40%.

[0107] Comparative Example 3

[0108] The method of Example 1 was followed, except that the amount of the protective agent trimethyl orthoacetate added was 0.96 g (8 mmol), and the molar ratio of the amounts of acenaphthoquinone, the protective agent, the substituted aniline and the catalyst was 1:0.4:2.4:0.3, finally yielding 8 g of symmetrical diimine ligand with a yield of 51%.

[0109] Test Example 1

[0110] The NMR spectra of the symmetric diimine ligand obtained in Example 1, the asymmetric diimine ligand obtained in Example 2, and the nickel bromide diimine catalyst were measured using a Bruker 500 MHz AVNCE NEO NMR spectrometer (parameter parameters: spectral width 20–50 ppm, relaxation time 15–20 s, 16 scans, deuterated chloroform solvent). The results are as follows: Figure 1-3 As shown.

[0111] exist Figure 1 middle, 1 H NMR (CDCl3, 500MHz, TMS): δ = 7.70 (d, J = 8.5Hz, 1H), 7.14 (t, J = 7.5Hz, 1H), 7.04 (s, 1H), 7.01-6.90 (m, 4H), 6.79 -6.76(m,2H),6.61(s,1H),6.31(d,J=7.2Hz,1H),6.00(t,J=8.5Hz,2H),5.64(s,1H),2.33(s,3H),2.25(s,3H);

[0112] exist Figure 2 middle, 1 H NMR (CDCl3, 500MHz, TMS): δ = 7.83-7.77 (m, 2H), 7.34 (t, J = 7.4Hz, 1H), 7.20 (t, J = 7.4Hz, 1H), 7.06-7.01 (m, 4H), 6.96-6.89 (m, 5H), 6.67- 6.64(m,2H),6.40(d,J=7.2Hz,1H),6.17(t,J=8.7Hz,2H),5.70(s,1H),2.38(s,3H),2.33(s,3H),2.22(s,3H),2.09(s,3H),2.04(s,3H);

[0113] exist Figure 3 middle,1 H NMR (500MHz, CDCl3, TMS): δ = 33.14 (s, 3H), 32.43 (s, 3H), 28.51 (s, 3H), 26.89 (s, 3H), 26.04 (s, 1H), 25.55 (s, 3H), 25.04 (s, 1H), 24.29 (s, 1 H),23.81(s,1H),21.13(s,1H),20.53(s,1H),17.23(s,1H),16.41(s, 1H),8.40(s,2H),7.17(s,2H),5.99(s,1H),5.65(s,3H),3.09(s,2H).

[0114] As can be seen from the results of the examples and comparative examples, by adding a certain amount of protecting agent to the reaction system, the present invention effectively promotes the equilibrium towards the forward reaction and improves the yield of the diimine ligand by preventing the formation of anhydrous diimine ligands during the synthesis reaction. Furthermore, considering the need to reduce costs and avoid raw material waste, the amount of protecting agent added should be controlled within the range specified in this invention.

[0115] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a diimine ligand, characterized in that, The method involves mixing acenaphthoquinone, a protecting agent, a substituted aniline, and a catalyst, and then reacting them. The protective agent is selected from one or more of orthoesters, amines, hydrazines, and substituted hydrazides; the orthoester is selected from one or more of trimethyl orthoformate, triethyl orthoformate, trimethyl orthoacetate, and triethyl orthoacetate; the amine is selected from one or more of methylamine, ethylamine, propylamine, butylamine, ethylenediamine, 1,3-propanediamine, butyldiamine, and hexamethylenediamine; the substituted hydrazine is selected from one or more of hydrazine hydrate, methylhydrazine, dimethylhydrazine, and ethylhydrazine. The molar ratio of the acenaphthoquinone, the protective agent, the substituted aniline, and the catalyst is 1:(0.5~3):(1.6~2.4):(0.1~10). The catalyst is a protic acid, which is selected from one or more of sulfuric acid, hydrochloric acid, hydrobromic acid, formic acid, acetic acid, trifluoroacetic acid, difluoroacetic acid, oxalic acid, benzenesulfonic acid and p-toluenesulfonic acid. The substituted aniline is selected from compounds of formula (I). Formula (I) Among them, R1, R2, R3, R4, and R5 are each independently selected from H, diphenylmethyl, and C1-C6 alkyl; The diphenylmethyl group is selected from the compounds shown in formula (III). Equation (III) Among them, R 11 R 12 R 13 R 14 R 15 R 16 R 17 R 18 R 19 R 20 Each is independently selected from H, F, Cl, Br, and I.

2. The method according to claim 1, characterized in that, The reaction is carried out in the presence of a solvent.

3. The method according to claim 2, characterized in that, The solvent is selected from one or more of alkanes, haloalkanes, alkylbenzenes, ethers, esters, alcohols, and nitriles.

4. The method according to claim 2, characterized in that, The weight ratio of the acenaphthene to the solvent is 1:(3~60).

5. The method according to any one of claims 1-4, characterized in that, The reaction temperature is 20~120℃, and the reaction time is 2~16h.

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