Back-to-back type binuclear ketimine nickel complex as well as preparation method and application thereof

Abstract

The invention discloses a back-to-back type binuclear ketimine nickel complex as well as a preparation method and application thereof, belongs to the technical field of olefin polymerization, and designs and synthesizes a series of back-to-back type binuclear ketimine nickel complexes with different steric hindrances. The synthesized nickel complex can be used for single-component initiation of ethylene homogeneous polymerization and ethylene and polar monomer copolymerization, and the complex shows high thermal stability and catalytic activity in the process of catalyzing ethylene homopolymerization. Meanwhile, the complex also realizes efficient copolymerization of ethylene and various polar monomers, shows relatively strong polar functional group tolerance in ethylene copolymerization, and obtains a copolymer with a relatively high polar monomer insertion rate, so that the nickel-based complex disclosed by the invention has important industrial application value in the field of olefin polymerization.

Description

Technical Field

[0001] The present invention belongs to the technical field of olefin polymerization, and specifically relates to a back-to-back type binuclear ketimine nickel complex, a preparation method thereof, and an application thereof. Background Art

[0002] Polyolefins are the most widely used plastics in the world and play a crucial role in modern society. Polyolefins have excellent mechanical properties, chemical stability, acid and alkali resistance, corrosion resistance, low price, and easy processing, etc., and thus have a wide range of applications in various fields of daily life, such as packaging, electronics, fabrics, etc. Polyethylene plastic is the plastic with the largest global production volume at present, and the global demand for polyethylene exceeded 150 million tons in 2023.

[0003] Since polyethylene is composed of saturated carbon-hydrogen bonds, many properties of the polymer such as printability, surface properties, colorability, and poor compatibility with other polymer materials greatly limit its application in many important fields. Introducing a small amount of polar functional groups (even 0.5 mol%) into polyethylene can effectively improve the defects of most polyethylene (PE), and can greatly improve the surface properties, adhesion, flexibility, solvent resistance, rheology, and co-solubility and co-blending properties with other polymers and polymer material additives of the polymer, etc. The synthesis of high-end polyolefin products by transition metal-catalyzed polymerization has been recognized as one of the most interesting topics in this field. In the past few decades, the design and preparation of high-performance catalysts for olefin polymerization have received great attention. However, in this field, there is still a need to provide catalysts for olefin polymerization, especially catalysts for the production of polyolefins used in high-end scenarios.

[0004] Herein, we innovatively synthesized a back-to-back type binuclear nickel complex, and this type of catalyst exhibits ultra-high thermal stability and relatively high polymerization activity in ethylene homopolymerization. In ethylene copolymerization, the catalyst shows strong tolerance to polar functional groups, and a copolymer with a relatively high polar monomer insertion rate is obtained. Summary of the Invention

[0005] In view of the extensive research on transition metal catalysts in ethylene homopolymerization and ethylene copolymerization with polar monomers, the purpose of the present invention is to provide a novel metal complex, a preparation method thereof, and an application thereof in catalytic olefin coordination polymerization. The present invention uses a bimetallic catalytic center and designs and synthesizes a series of back-to-back type binuclear ketimine ligands and nickel complexes by utilizing the synergistic effect between metals, and applies them to ethylene homopolymerization and ethylene copolymerization with polar monomers. The complexes have relatively high thermal stability, catalytic activity, and tolerance to polar functional groups.

[0006] A back-to-back type binuclear ketimine nickel complex, the structure of the complex is:

[0007]

[0008] In general formula (I), R1 and R2 are selected from one or more of substituted phenyl groups having 1 to 20 carbon atoms, isopropyl groups, and alkyl groups; R3 is selected from one or more of alkyl groups having 1 to 6 carbon atoms, alkoxy groups, hydroxyl groups, fluorine, chlorine, bromine, and iodine; R4 and R5 are each independently selected from hydrogen, fluorine, chlorine, bromine, iodine, hydrocarbon groups having 1 to 20 carbon atoms, aryl groups, oxygen-containing groups, nitrogen-containing groups, sulfur-containing groups, boron-containing groups, aluminum-containing groups, phosphorus-containing groups, silicon-containing groups, or tin-containing groups, and a part of R4 and R5 can form a ring with each other.

[0009] A preparation method of a back-to-back type binuclear ketimine nickel complex. The synthesis process of the nickel complex is as follows: Under an argon or nitrogen atmosphere, dissolve the ligand in tetrahydrofuran, add 1.1 equivalents of potassium hydride and react for two hours, then remove the solvent under vacuum to obtain the ligand potassium salt. Then dissolve the metal nickel precursor (such as Ni(COD)2, Py2NiMe2, etc.) in a good solvent (such as toluene, trichlorobenzene, xylene, dichloromethane, etc.) and add it to the ligand potassium salt, react at room temperature for 1 to 12 hours. After the reaction, filter and concentrate the solvent, and add a poor solvent (such as n-hexane, n-heptane, n-pentane, etc.) for recrystallization, and filter and dry to obtain the back-to-back type binuclear ketimine nickel complex (I).

[0010] The structure of the ligand is as follows:

[0011]

[0012] In general formula (II), R1 and R2 are selected from one or more of substituted phenyl groups having 1 to 20 carbon atoms, isopropyl groups, and alkyl groups; R3 is selected from one or more of alkyl groups having 1 to 6 carbon atoms, alkoxy groups, hydroxyl groups, fluorine, chlorine, bromine, and iodine.

[0013] The ligand is, under nitrogen or argon, using tetrahydrofuran as a solvent, aniline is stirred with four equivalents of triethylamine at room temperature for two hours, then the reaction system is transferred to a 0 °C constant temperature low-temperature bath, and 0.5 equivalent of oxalyl chloride is slowly added dropwise to the reaction system. After reacting for 6 to 12 hours, it is filtered through diatomaceous earth and the solvent is concentrated, and n-hexane is added for recrystallization to obtain the ligand (II).

[0014] An application of a back-to-back type binuclear ketimine nickel complex as a catalyst for catalyzing the homopolymerization of olefins or the copolymerization of olefins with polar monomers.

[0015] The olefins include ethylene or α-olefins, etc. The α-olefins refer to terminal olefins having 3 to 18 carbon atoms, such as one or a mixture of several of propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 1-decene, 1-dodecene, and 1-octadecene.

[0016] The polar monomer is an α-olefin derivative having 2 to 20 carbon atoms containing a polar group, or a cycloolefin derivative containing a polar group; the polar group is an organic functional group containing oxygen, nitrogen, sulfur, or selenium, including a hydroxyl group, a carboxyl group, an ester group, an alkoxy group, a ketone group, an amine group, an amide group, a thioether, a silyl ether, or a selenoether.

[0017] The polymerization reaction method includes slurry polymerization, loop polymerization, gas-phase polymerization, or other forms of polymerization processes.

[0018] The polymerization reaction is generally carried out in an organic solvent, such as hydrocarbons, cycloalkanes, or aromatic hydrocarbons. To facilitate the polymerization reaction operation, hydrocarbons having less than 12 carbon atoms can be used as the organic solvent, such as hexane, toluene, chlorobenzene, and their mixtures.

[0019] The polymerization temperature is maintained at 0 to 200 °C. The pressure of the polymerized ethylene can vary within 0.1 to 50 MPa, and the concentration of the comonomer can be controlled within 0.1 to 2 mol / L.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The present invention provides a nickel catalyst having a structure of general formula (I). By synthesizing a back-to-back type binuclear nickel catalyst and utilizing the synergistic effect between metals, the catalyst has high polymerization activity, thermal stability, and tolerance to polar monomers during the catalytic olefin polymerization process. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the application of the nickel complex in the catalytic homopolymerization of olefins or the copolymerization of olefins / polar monomers.

[0023] Figures 2 to 7 They respectively correspond to the DSC test diagrams of the polymers in Items 1 to 6 in Table 1.

[0024] Figures 8 to 13 They respectively correspond to the GPC test diagrams of the polymers in Items 1 to 6 in Table 1.

[0025] Figures 14 to 22 They respectively correspond to the DSC test diagrams of the polymers in Items 1 to 9 in Table 2.

[0026] Figures 23 to 31 They respectively correspond to the high-temperature 1H NMR spectra of the polymers in Items 1 to 9 in Table 2.

[0027] Figures 32 to 40 They respectively correspond to the high-temperature GPC test diagrams of the polymers in Items 1 to 9 in Table 2. DETAILED DESCRIPTION OF THE INVENTION

[0028] To make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0029] A back-to-back type binuclear ketimine nickel complex, the structure of the complex is:

[0030]

[0031] In the general formula (I), R1 and R2 are selected from one or more of substituted phenyl groups, isopropyl groups, and alkyl groups having 1 to 20 carbon atoms. R3 is selected from one or more of alkyl groups, alkoxy groups, hydroxyl groups, fluorine, chlorine, bromine, and iodine having 1 to 6 carbon atoms. R4 and R5 are each independently selected from hydrogen, fluorine, chlorine, bromine, iodine, hydrocarbon groups, aryl groups, oxygen-containing groups, nitrogen-containing groups, sulfur-containing groups, boron-containing groups, aluminum-containing groups, phosphorus-containing groups, silicon-containing groups, or tin-containing groups, and a part of R4 and R5 can form a ring with each other.

[0032] Specifically, the metal nickel complex having the structure of the general formula (I) has the structures of formula (I1), formula (I2), and formula (I3):

[0033]

[0034]

[0035] According to an embodiment of the present application, a preparation method of a back-to-back type binuclear ketimine nickel complex is further provided. The synthesis process of the nickel complex is as follows: Under an argon or nitrogen atmosphere, a ligand having the structure of the general formula (II) is dissolved in tetrahydrofuran, 1.1 equivalents of potassium hydride is added and reacted for two hours, and then the solvent is removed under vacuum to obtain a ligand potassium salt. Then, the metal nickel precursor NiClPh(PPh3)2 is dissolved in toluene and added to the ligand potassium salt, and the reaction is carried out at room temperature for 6 to 12 hours. After the reaction is completed, the solvent is filtered and concentrated, and n-hexane is added for recrystallization, and then filtered and dried to obtain the back-to-back type binuclear ketimine nickel complex (I).

[0036] The structure of the ligand is:

[0037]

[0038] In the general formula (II), R1 and R2 are selected from one or more of substituted phenyl groups, isopropyl groups, and alkyl groups having 1 to 20 carbon atoms. R3 is selected from one or more of alkyl groups, alkoxy groups, hydroxyl groups, fluorine, chlorine, bromine, and iodine having 1 to 6 carbon atoms.

[0039] The ligand is aniline using tetrahydrofuran as a solvent under nitrogen or argon Stir with four equivalents of triethylamine at room temperature for two hours, then transfer the reaction system to a constant temperature low-temperature bath at 0 °C, and add 0.5 equivalent of oxalyl chloride dropwise slowly into the reaction system. After reacting for 6 hours, filter with diatomaceous earth and concentrate the solvent, and add n-hexane for recrystallization to obtain ligand (II).

[0040] Specifically, the ligand with the general formula (II) structure has the structures of formula (II 1), formula (II 2), and formula (II 3):

[0041]

[0042] According to the embodiments of the present application, there is also provided an application of a back-to-back type binuclear ketimine nickel complex, including being used for catalyzing olefin homopolymerization or olefin / polar monomer copolymerization. Olefins include ethylene, α-olefins, etc. α-olefins refer to terminal olefins with C3 to C18, such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 1-decene, 1-dodecene, 1-octadecene, and their mixtures, etc.; the polar monomer is a C2 to C20 1-olefin derivative containing a polar group and a cycloolefin derivative containing a polar group, and the polar group is an organic functional group containing oxygen, nitrogen, sulfur, or selenium, including hydroxyl group, carboxyl group, ester group, alkoxy group, amine group, ketone group, amine group, amide group, thioether, silyl ether, or selenoether.

[0043] The polymerization reaction method adopts slurry polymerization, loop polymerization, gas-phase polymerization or other forms of polymerization processes.

[0044] The polymerization reaction is generally carried out in an organic solvent, such as hydrocarbons, cycloalkanes or aromatic hydrocarbons. For the convenience of polymerization reaction operation, the organic solvent can use hydrocarbons with less than 12 carbons, such as one or several of hexane, toluene, and chlorobenzene.

[0045] Among them, the polymerization temperature of the polymerization reaction is 0 to 160 °C, for example, it can be selected as 25 °C; the polymerization pressure of the olefin is 0.1 to 50 MPa. The concentration of the comonomer can be selected as 0.1 to 2 mol / L.

[0046] In order to further understand the present invention, the metal nickel complex provided by the present invention will be described in detail below in conjunction with embodiments, and the protection scope of the present invention is not limited by the following embodiments.

[0047] The following examples illustrate the specific content of the present invention. The data given include the synthesis of ligands, the synthesis of nickel metal complexes, and the methods for homopolymerization of ethylene or copolymerization of ethylene with polar monomers. Among them, the synthesis of the catalyst and the polymerization process are carried out under anhydrous and anaerobic conditions. All sensitive substances are stored in a glove box. All solvents are strictly dried to remove water. Ethylene gas is purified through a column for removing water and oxygen, and methyl acrylate is purified by vacuum distillation for removing water and oxygen. Unless otherwise specified, all raw materials are purchased from the market.

[0048] The silica gel column uses silica gel with a mesh size of 200 - 300. NMR is measured using a Bruker 400 MHz NMR instrument; elemental analysis is determined by the Physical and Chemical Center of the University of Science and Technology of China; molecular weight and molecular weight distribution are measured by GPC (polystyrene columns, HR2 and HR4, oven temperature is 160 °C, using Water 1515 and Water 2414 pumps; the mobile phase is 1,2,4-trichlorobenzene, the flow rate is 1.0 mL per minute, and polydisperse polystyrene is used as the standard).

[0049] Example 1:

[0050] Preparation of ligand II1:

[0051]

[0052] Using tetrahydrofuran as the solvent, is stirred with four equivalents of triethylamine at room temperature for two hours, and then the reaction system is transferred to a constant temperature low-temperature bath at 0 °C. 0.5 equivalent of oxalyl chloride is slowly added dropwise to the reaction system. After reacting for 6 hours, it is filtered through diatomaceous earth and the solvent is concentrated. Recrystallization with n-hexane gives the white solid ligand II1.

[0053] The NMR data of II1 are as follows:

[0054] 1H NMR(400MHz,CDCl3):δ8.79(s,2H,N-H),6.94(s,4H,Ph-H),2.30(s,6H,Ph-CH3),2.23(s,12H,Ph-CH3).13C NMR(101MHz,CDCl3):δ158.30,137.64,134.71,129.70,129.12,20.96,18.34.

[0055] Elemental Analysis: Elemental Analysis C20H24N2O2: C, 74.03; H, 7.47; N, 8.64. Found: C, 73.98; H, 7.52; N, 8.61.

[0056] Example 2:

[0057] Preparation of Ligand II2:

[0058]

[0059] Except for using different anilines, the same method as that for II1 was adopted.

[0060] 1H NMR data of II2 are as follows:

[0061] 1H NMR (400 MHz, CDCl3): δ 8.85 (s, 2H, N-H), 7.39–7.33 (m, 2H, Ph-H), 7.24 (d, J = 7.7 Hz, 4H, Ph-H), 3.07 (hept, J = 6.9 Hz, 4H, HC(CH3)2), 1.24 (d, J = 6.9 Hz, 24H, HC(CH3)2). 13C NMR (101 MHz, CDCl3): δ 159.57, 145.78, 129.73, 128.93, 123.78, 32.42, 29.09, 23.58.

[0062] Elemental Analysis: Elemental Analysis C26H36N2O2: C, 76.38; H, 9.03; N, 6.91. Found: C, 76.41; H, 9.05; N, 6.89.

[0063] Example 3:

[0064] Preparation of Ligand II3:

[0065]

[0066] Except for using different anilines, the same method as that for II1 was adopted.

[0067] 1H NMR data of II3 are as follows:

[0068] 1H NMR (400 MHz, CDCl3): δ 8.15 (s, 2H, N-H), 7.19 (dq, J = 12.8, 7.1 Hz, 25H, Ph-H), 7.03–6.97 (m, 16H, Ph-H), 6.64 (s, 4H, Ph-H), 5.47 (s, 4H, HCPh2), 2.14 (s, 6H, Ph-CH3). 13C NMR (101 MHz, CDCl3): δ 158.13, 142.60, 141.81, 137.59, 129.78, 129.37, 128.42, 126.54, 53.42, 52.32, 21.62.

[0069] Elemental Analysis C68H56N2O2: C, 87.49; H, 6.07; N, 3.01. Found: C, 87.51; H, 6.09; N, 3.03.

[0070] Example 4:

[0071] Preparation of metal nickel complex (I1):

[0072]

[0073] Under an argon or nitrogen atmosphere, dissolve ligand (II1) in tetrahydrofuran, add 1.1 equivalents of potassium hydride and react for two hours. Then remove the solvent under vacuum to obtain the potassium salt of the ligand. Then dissolve the metal nickel precursor NiClPh(PPh3)2 in toluene and add it to the potassium salt of the ligand. React at room temperature for 6 hours. After the reaction, filter and concentrate the solvent, add n-hexane for recrystallization, filter and dry to obtain the back-to-back type binuclear ketimine nickel complex (I1).

[0074] Example 5:

[0075] Preparation of metal nickel complex (I2):

[0076]

[0077] Under an argon or nitrogen atmosphere, dissolve ligand (II2) in tetrahydrofuran, add 1.1 equivalents of potassium hydride and react for two hours. Then remove the solvent under vacuum to obtain the potassium salt of the ligand. Then dissolve the metal nickel precursor NiClPh(PPh3)2 in toluene and add it to the potassium salt of the ligand. React at room temperature for 10 hours. After the reaction, filter and concentrate the solvent, add n-hexane for recrystallization, filter and dry to obtain the back-to-back type binuclear ketimine nickel complex (I2).

[0078] Example 6:

[0079] Preparation of metal nickel complex (I3):

[0080]

[0081] Under an argon or nitrogen atmosphere, dissolve ligand (II3) in tetrahydrofuran, add 1.1 equivalents of potassium hydride and react for two hours. Then remove the solvent under vacuum to obtain the potassium salt of the ligand. Then dissolve the metal nickel precursor NiClPh(PPh3)2 in toluene and add it to the potassium salt of the ligand. React at room temperature for 10 hours. After the reaction, filter and concentrate the solvent, add n-hexane for recrystallization, filter and dry to obtain the back-to-back type binuclear ketimine nickel complex (I3).

[0082] Application Example 1:

[0083] The catalysts prepared in Examples 4 to 6 were respectively used for ethylene polymerization reaction, and the specific polymerization method was as follows:

[0084] In a Vigor glove box under a nitrogen atmosphere, a certain amount of solvent toluene and cocatalyst B(C6F5)3 were added to a pressure-resistant polymerization flask equipped with a magnetic stirrer. A certain amount of metal nickel complex was dissolved in a small amount of dichloromethane and equally aspirated into a medical syringe. The pressure-resistant flask and the metal nickel complex were taken out of the glove box. The polymerization flask was installed on a high-vacuum ethylene polymerization line, and the flask was purged three times with low-pressure ethylene to make the inside of the flask a complete ethylene environment. The reaction system in the polymerization flask was brought to the polymerization temperature by an oil bath or an ice-water bath. Under low pressure, the metal nickel complex in the syringe was injected into the pressure-resistant flask, and then the specified ethylene pressure was maintained in the polymerization flask and for a certain reaction time. After venting the ethylene, ethanol acidified with 5% hydrochloric acid was added to the polymerization flask. The polymer was filtered, washed three times with ethanol, and then dried in a constant-temperature vacuum drying oven, weighed, and the activity was calculated.

[0085] The results of the metal nickel complexes prepared in Examples 4 to 6 for catalyzing ethylene polymerization are shown in Table 1 below:

[0086] Table 1. Catalytic ethylene polymerization by metal nickel complexes a

[0087] Item Catalyst Temperature / °C Yield / g <![CDATA[Active b > <![CDATA[Melting point c / ℃]]> <![CDATA[Number-average molecular weight d > <![CDATA[Molecular weight distribution d > 1 Example 4 (I1) 50 1.32 1.00 122.5 19.7 2.6 2 Example 4 (I 1) 90 1.23 0.93 112.3 4.0 3.3 3 Example 5 (I 2) 50 1.67 1.27 122.1 70.7 2.0 4 Example 5 (I 2) 90 1.66 1.26 104.1 18.1 2.3 5 Example 6 (I 3) 50 2.56 1.94 124.5 274.3 1.6 6 Example 6 (I3) 90 3.12 2.36 111.3 98.6 1.8

[0088] Among them, a polymerization conditions: metal nickel complex 2 umol, toluene = 28 mL, dichloromethane = 2 mL, ethylene = 8 atmospheres, time = 20 minutes, b activity = 106 g·mol-1·h-1; c melting point was measured by a differential scanning calorimeter (DSC); d number-average molecular weight = 104 g mol-1, and the molecular weight was measured by high-temperature GPC at 150 °C using polystyrene as the standard and trichlorobenzene as the solvent.

[0089] Application Example 2:

[0090] The catalysts prepared in Examples 4 to 6 were respectively used for copolymerization of ethylene and polar monomers, and the specific polymerization method was as follows:

[0091] In a Vigor glove box under a nitrogen atmosphere, a certain amount of solvent toluene, cocatalyst B(C6F5)3, and copolymerizable polar monomer were added to a pressure-resistant polymerization bottle equipped with a magnetic stir bar. A certain amount of metal nickel complex was dissolved in a small amount of dichloromethane and sucked into a medical syringe. The pressure-resistant bottle and the syringe were taken out of the glove box. The pressure-resistant bottle was installed on a high-vacuum ethylene polymerization line, and the bottle was purged with ethylene three times to make the inside of the bottle a complete ethylene environment. The reaction system in the polymerization bottle was brought to the polymerization temperature by means of an oil bath or an ice-water bath. Under low pressure, the metal nickel complex in the syringe was injected into the pressure-resistant bottle. After that, the specified ethylene pressure was maintained in the polymerization bottle and for a certain reaction time. After venting the ethylene, ethanol acidified with 5% hydrochloric acid was added to the polymerization bottle. The polymer was filtered, washed three times with ethanol, and then dried in a constant-temperature vacuum drying oven, weighed, and the activity was calculated.

[0092] The results of the polymerization of ethylene and polar monomer catalyzed by the metal nickel complexes prepared in Examples 4-6 are shown in Table 2 below:

[0093] Table 2. Copolymerization of ethylene and polar monomer catalyzed by metal nickel complexes a

[0094]

[0095] Among them, a polymerization conditions: 10 μmol of metal nickel complex, toluene = 28 mL, dichloromethane = 2 mL, ethylene = 8 atmospheres, concentration of copolymerizable monomer = 1 mol / L, time = 30 minutes, polymerization temperature = 50 °C; b activity = 104 g·mol-1·h-1; c melting point was measured by a differential scanning calorimeter; d insertion ratio of polar monomer was measured by 1H NMR. e number-average molecular weight = 104 gmol-1, molecular weight determination was carried out by GPC using polystyrene as the standard and trichlorobenzene as the solvent at 150 °C.

[0096] Therefore, the above-disclosed embodiments are illustrative in all respects and not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

Claims

1. A back-to-back type binuclear ketimine nickel complex, characterized in that, The structure of the complex is as follows: In general formula (I), R1 and R2 are selected from one or more of substituted phenyl groups, isopropyl groups, and alkyl groups having 1 to 20 carbon atoms; R3 is selected from one or more of alkyl groups, alkoxy groups, hydroxyl groups, fluorine, chlorine, bromine, and iodine having 1 to 6 carbon atoms; R4 and R5 are each independently selected from hydrogen, fluorine, chlorine, bromine, iodine, hydrocarbon groups, aryl groups, oxygen-containing groups, nitrogen-containing groups, sulfur-containing groups, boron-containing groups, aluminum-containing groups, phosphorus-containing groups, silicon-containing groups, or tin-containing groups, wherein R4 and R5 are partially bonded to each other to form a ring.

2. A preparation method of the back-to-back type binuclear ketimine nickel complex as described in claim 1, characterized in that, The synthesis process of the nickel complex is as follows: Under an argon or nitrogen atmosphere, the ligand is dissolved in tetrahydrofuran, 1.1 equivalents of potassium hydride are added and reacted for two hours, and then the solvent is removed under vacuum to obtain the ligand potassium salt. Then, the metal nickel precursor is dissolved in a good solvent and added to the ligand potassium salt, and the reaction is carried out at room temperature for 1 to 12 hours. After the reaction is completed, the solvent is filtered and concentrated, and a poor solvent is added for recrystallization. After filtration and drying, the back-to-back type binuclear ketimine nickel complex (I) is obtained.

3. The preparation method of a back-to-back type binuclear ketimine nickel complex according to claim 2, characterized in that, The metal nickel precursor is Ni(COD)2 or Py2NiMe2.

4. The preparation method of a back-to-back type binuclear ketimine nickel complex according to claim 2, characterized in that, The good solvent is toluene, trichlorobenzene, xylene, or dichloromethane.

5. The preparation method of a back-to-back type binuclear ketimine nickel complex according to claim 2, characterized in that, The poor solvent is n-hexane, n-heptane, or n-pentane.

6. An application of the back-to-back type binuclear ketimine nickel complex described in claim 1, characterized in that: The nickel complex is used for single-component initiation of homogeneous polymerization of ethylene and copolymerization of ethylene with polar monomers. The nickel complex utilizes the mutual synergistic effect of bimetallic nickel to endow the catalyst with thermal stability and catalytic activity.

7. Use of a back-to-back type binuclear ketimine nickel complex according to claim 6, characterized in that, In the homopolymerization of ethylene, the catalyst dosage is 1 to 20 μmol / L, the polymerization pressure is 0.1 to 50 MPa, the reaction temperature is controlled at 0 to 200 °C, and the reaction time is 0.05 to 5.00 hours.

8. Use of a back-to-back type binuclear ketimine nickel complex according to claim 6, characterized in that, In the copolymerization of ethylene with polar monomers, the catalyst dosage is 1 to 20 μmol / L, the polymerization pressure is 0.1 to 50 MPa, the concentration of the polar monomer is controlled at 0.1 to 1 mol / L, the reaction temperature is controlled at 0 to 200 °C, and the reaction time is 0.05 to 5.00 hours.

9. Use of a back-to-back type binuclear ketimine nickel complex according to claim 6, characterized in that, Both the homopolymerization of ethylene and the copolymerization of ethylene with various polar monomers are carried out in an organic solvent, and the organic solvent includes hydrocarbons, cycloalkanes, or aromatic hydrocarbons.

10. Use of a back-to-back type binuclear ketimine nickel complex according to claim 9, characterized in that, The organic solvent uses hydrocarbons having less than 12 carbon atoms, including hexane, toluene, chlorobenzene, and their mixtures.

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