A pyridine imine nickel complex, its preparation method and use

Abstract

The application provides a pyridine imine nickel complex as shown in formula (I), wherein R 1 , R 2 , R 3 , R 4 and X are as defined in the description. The nickel complex has the advantages of high catalytic activity, simple preparation method, low cost, stable performance and the like, the prepared polyethylene has a weight average molecular weight Mw of 2.50-9.59 kg·mol ‑1 -1, a narrow molecular weight distribution of 2.01-3.43, high branching degree, adjustable double bond content and great industrial application value.

Description

Technical Field

[0001] This invention relates to the field of polyolefin catalyst technology, specifically to a pyridineimine nickel complex, its preparation method, and its uses. Background Technology

[0002] With the development of research and application of olefin resin materials, they have gradually become essential materials for people's daily lives and industrial and agricultural production, and also indispensable materials in cutting-edge technology and national defense construction. Among them, polyethylene materials have the characteristics of good chemical resistance, low price, simple preparation, low density, and good mechanical properties. In addition, as the most produced variety of general synthetic resins, the technological level of polyethylene is an important indicator of the development level of a country's petrochemical industry, and the design and development of olefin polymerization catalyst / co-catalyst systems are key to the development of polyethylene products. In 1995, Brookhart et al. originally reported the use of α-diimine nickel / palladium complex (Formula 1) for catalyzing ethylene polymerization and copolymerization, which has moderate catalytic activity and yields polyethylene products with certain branching and higher molecular weight; it can also achieve copolymerization of ethylene with polar monomers to obtain functionalized polyolefins. However, the catalytic performance and preparation methods of the above catalysts still need further improvement.

[0003]

[0004] There is a need in this field to further develop olefin polymerization catalysts with higher catalytic activity, simpler preparation methods, lower costs, and more stable performance. Summary of the Invention

[0005] To address the problems existing in the prior art, one objective of this invention is to provide a pyridineimine nickel complex. This nickel complex has advantages such as high catalytic activity, simple preparation method, low cost, and stable performance, and the resulting polyethylene has a weight-average molecular weight (Mw) of 2.50–9.59 kg·mol⁻¹. -1 The molecular weight distribution is relatively narrow, ranging from 2.01 to 3.43, and the resulting polyethylene has a high degree of branching and the double bond content can be controlled, making it of great industrial application value.

[0006] This invention provides a nickel complex represented by formula (Ⅰ):

[0007]

[0008] Among them, R 1 Selected from H, F, Cl, Br, I, nitro, trifluoromethoxy, trifluoromethyl, C 1-6 Alkyl or C 1-6 Alkoxy;

[0009] R 2 R 3 and R4 Whether the groups are the same or different, they are each independently selected from H, F, Cl, Br, I, nitro, C. 1-6 Alkyl or C 1-6 Alkoxy;

[0010] X may be the same or different, and each is independently selected from F, Cl, Br or I.

[0011] According to the nickel complex of the present invention, wherein R 1 Selected from H, F, Cl, trifluoromethoxy, C 1-6 Alkyl; R 2 R 3 R 4 Whether the two are the same or different, they are each independently selected from H and C. 1-3 Alkyl group; X may be the same or different, each independently selected from Cl or Br.

[0012] According to the nickel complex of the present invention, wherein the nickel complex represented by formula (I) is selected from, but not limited to, the following nickel complexes:

[0013] Nickel complex 1: where R 1 =Me, X=Br, R 2 =Me,R 3 and R 4 For H;

[0014] Nickel complex 2: where R 1 =Et, X=Br, R 2 =Me,R 3 and R 4 For H;

[0015] Nickel complex 3: where R 1 =iPr, X=Br, R 2 =Me,R 3 and R 4 For H;

[0016] Nickel complex 4: where R 1 =F, X=Br, R 2 =Me,R 3 and R 4 For H;

[0017] Nickel complex 5: where R 1 =OCF3, X=Br, R 2 =Me,R 3 and R 4 For H.

[0018] Another object of the present invention is to provide a method for preparing the nickel complex shown in formula (I) above, comprising the following steps:

[0019]

[0020] The compound of formula (II) was subjected to a complexation reaction with a nickel-containing compound to obtain the nickel complex shown in formula (I).

[0021] Among them, X and R 1 R 2 R 3 and R 4 As defined above.

[0022] According to the method for preparing the nickel complex represented by formula (I) of the present invention, the nickel-containing compound is selected from nickel-containing halides, nickel-containing halide hydrates, and nickel-containing halide solvates. For example, the nickel-containing compound is NiBr2·DME or NiCl2·6H2O.

[0023] According to the method for preparing the nickel complex represented by formula (I) of the present invention, the reaction is carried out under the protection of an inert gas such as nitrogen.

[0024] According to the method for preparing the nickel complex represented by formula (I) of the present invention, the molar ratio of the nickel-containing compound to the compound of formula (II) is 1:1 to 2, preferably 1:1 to 1.5, more preferably 1:1 to 1.2, for example 1:1, 1:1.05, 1:1.1, 1:1.15, 1:1.2, and most preferably 1:1.05.

[0025] According to the method for preparing the nickel complex represented by formula (I) of the present invention, the reaction temperature is 10-35°C, preferably 15-30°C, more preferably 20-25°C; the reaction time is 4-24 hours, preferably 8-18 hours, more preferably 8-12 hours.

[0026] According to the method for preparing the nickel complex of formula (I) of the present invention, the complexation reaction is carried out in a solvent selected from one or more of alcohol solvents, dichloromethane, and chloroform, for example selected from ethanol and / or dichloromethane.

[0027] According to the method for preparing the nickel complex represented by formula (I) of the present invention, the molar volume ratio (mmol / mL) of the compound of formula (II) to the solvent is 1:30 to 1:50, preferably 1:35 to 1:45, and more preferably 1:38 to 1:42.

[0028] According to the method for preparing the nickel complex represented by formula (I) of the present invention, after the reaction is completed, the reaction solution is concentrated under reduced pressure to remove the solvent and obtain a residue. The residue is dissolved in a good solvent, and then a poor solvent is added for recrystallization to precipitate a solid. The solid is then filtered, washed, and dried to obtain the final product.

[0029] According to the method for preparing the nickel complex represented by formula (I) of the present invention, the good solvent is dichloromethane.

[0030] According to the method for preparing the nickel complex represented by formula (I) of the present invention, the undesirable solvent is diethyl ether or n-hexane, preferably anhydrous diethyl ether.

[0031] Another object of the present invention is to provide a catalyst composition comprising a main catalyst and an optional co-catalyst, wherein the main catalyst is a nickel complex as shown in formula (I) above.

[0032] According to the catalyst composition of the present invention, the co-catalyst is selected from one or more of aluminoxane, alkylaluminum and alkylaluminum chloride.

[0033] According to the catalyst composition of the present invention, the aluminoxane is methylaluminoxane (MAO) and / or triisobutylaluminum-modified methylaluminoxane (MMAO), the alkylaluminum is trimethylaluminum (AlMe3), and the alkylaluminum chloride is one or more of sesquiethylaluminum chloride (EASC), dichloroethylaluminum (EtAlCl2), and diethylaluminum chloride (Et2AlCl).

[0034] According to the catalyst composition of the present invention, when the catalyst composition includes a co-catalyst, the molar ratio of metal Al in the co-catalyst to the central metal Ni of the nickel complex shown in formula (I) is (30-8000):1, preferably (100-5000):1, more preferably (200-4000):1, and most preferably (300-3500):1, for example, 300:1, 400:1, 450:1, 500:1, 550:1, 800:1, 1000:1, 1400:1, 1800:1, 2000:1, 2500:1, 3000:1, and 3500:1.

[0035] According to the catalyst composition of the present invention, when the co-catalyst is triisobutylaluminum-modified methylaluminoxane (MMAO), the molar ratio of metal Al in triisobutylaluminum-modified methylaluminoxane (MMAO) to the central metal Ni of the nickel complex shown in formula (I) is (1500-3500):1, preferably (1800-3500):1, for example, 1800:1, 2000:1, 2500:1, 2800:1, 3000:1, 3500:1, more preferably 2000:1.

[0036] According to the catalyst composition of the present invention, when the co-catalyst is dichloroethylaluminum, the molar ratio of metallic Al in dichloroethylaluminum to the central metallic Ni of the nickel complex shown in formula (I) is (200-700):1, preferably (300-600):1, for example, 300:1, 350:1, 400:1, 450:1, 500:1, 550:1, 600:1, and more preferably 500:1.

[0037] Another object of the present invention is to provide a method for preparing polyethylene, comprising: carrying out an ethylene polymerization reaction under the action of the catalyst composition described above to obtain polyethylene.

[0038] According to the method for preparing polyethylene of the present invention, the polymerization reaction temperature is 20-50°C, for example 20°C, 30°C, 40°C, 50°C; the polymerization reaction time is 5-60 min, for example 5 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min; and the polymerization reaction pressure is 1-10 atm, for example 1 atm, 3 atm, 5 atm, 8 atm, 10 atm.

[0039] According to the method for preparing polyethylene of the present invention, the solvent used in the polymerization reaction is selected from one or more of toluene, o-xylene, n-hexane, cyclohexane, n-heptane, cycloheptane, dichloromethane, ethanol, and tetrahydrofuran, preferably toluene.

[0040] Another object of the present invention is to provide the use of the nickel complex shown in formula (I) above in the preparation of polyolefins, wherein the polyolefin is preferably polyethylene.

[0041] Another object of the present invention is to provide a ligand compound of formula (II) having the following structural formula:

[0042]

[0043] Among them, R 1 Selected from H, F, Cl, Br, I, nitro, trifluoromethoxy, trifluoromethyl, C 1-6 Alkyl or C 1-6 Alkoxy;

[0044] R 2 R 3 and R 4 Whether the groups are the same or different, they are each independently selected from H, F, Cl, Br, I, nitro, C. 1-6 Alkyl or C 1-6 Alkyl group.

[0045] The ligand compound represented by formula (II) according to the present invention is selected from, but not limited to, the following compounds:

[0046] Compound of formula (II-1): where R 1 =Me,R 2 =Me,R 3 and R 4 For H;

[0047] Compound of formula (II-2): where R 1 =Et,R 2 =Me,R 3 and R 4 For H;

[0048] Compound of formula (II-3): where R 1 =iPr,R 2 =Me,R 3 and R 4 For H;

[0049] Compound of formula (II-4): where R 1 =F,R 2 =Me,R 3 and R 4 For H;

[0050] Compound of formula (II-5): where R 1 =OCF3,R 2 =Me,R 3 and R 4 For H.

[0051] Another object of the present invention is to provide a method for preparing the ligand compound represented by formula (II) above, comprising the following steps:

[0052]

[0053] 1) Compounds of formula (III) and (IV) were reacted with zinc chloride using a template method to obtain zinc complexes;

[0054] 2) Dissolve the zinc complex described in step 1) in a good solvent, add a saturated aqueous solution of potassium carbonate or potassium oxalate, stir and separate the liquids, recrystallize the organic phase to obtain the ligand compound shown in formula (II).

[0055] According to the method for preparing the ligand compound represented by formula (II) of the present invention, in step 1), the template reaction is carried out under acid catalysis, such as formic acid and / or acetic acid.

[0056] According to the method for preparing the ligand compound represented by formula (II) of the present invention, in step 1), the template reaction is carried out under heating and reflux conditions for 1 to 10 hours, more preferably 3 to 8 hours, for example, 3, 4, 5, 6, 7, or 8 hours.

[0057] According to the method for preparing the ligand compound represented by formula (II) of the present invention, in step 1), the molar ratio of the compound of formula (III), the compound of formula (IV) to zinc chloride is 0.5-2:1:0.5-2, preferably 0.8-1.5:1:0.8-1.5, more preferably 0.8-1.2:1:1-1.5, for example, 1:1:1.2.

[0058] According to the method for preparing the ligand compound represented by formula (II) of the present invention, in step 2), the good solvent is dichloromethane or acetone.

[0059] According to the method for preparing the ligand compound represented by formula (II) of the present invention, in step 2), the stirring process is carried out at room temperature for a stirring time of 0.5-5h, for example, 0.5h, 1h, 2h, 3h, 4h, 5h.

[0060] According to the method for preparing the ligand compound of formula (II) of the present invention, in step 2), the recrystallization is performed using dichloromethane and methanol to obtain the purified ligand compound of formula (II), wherein the volume ratio of dichloromethane to methanol is 1:10 to 1:30, preferably 1:15 to 1:25, for example, 1:15, 1:20, 1:25.

[0061] Beneficial effects

[0062] 1. This invention provides a pyridine imine nickel complex with a sterically hindered substituent, fluorodiphenylmethyl, which improves the thermal stability of the complex. The molecular weight and molecular weight distribution of the polymer are effectively controlled by altering the para-position structure of the imine aryl group and the polymerization conditions. This nickel complex has advantages such as high catalytic activity, simple preparation method, low cost, and stable performance.

[0063] 2. This invention also provides a method for preparing the nickel complex, which has the advantages of simple operation, mild reaction conditions, high yield, and short preparation cycle. Furthermore, the method for preparing the ligand compound represented by intermediate formula (II) provided by this invention also has the advantages of simple operation, mild reaction conditions, high yield, and short preparation cycle.

[0064] 3. This invention also provides the use of this nickel complex. First, the ligand compound represented by intermediate formula (II) is prepared into a nickel complex via a complexation reaction, and then it is used in ethylene polymerization, exhibiting high reactivity (up to 10.8 × 10⁻⁶). 6 g·mol -1 (Ni)·h -1 Furthermore, the ethylene polymerization reaction conditions are mild, resulting in highly branched polyethylene materials with low molecular weight (Mw = 2.50–9.59 kg·mol⁻¹). -1 Narrow distribution (M) w / M n Features include a pH value of 2.01-3.43 and high branching (up to 151 / 1000C).

[0065] 4. The nickel complex designed and synthesized in this invention can catalyze the self-polymerization of ethylene to obtain highly branched polyethylene containing terminal double bonds or internal double bonds. Furthermore, the content and position of the double bonds can be precisely controlled by adjusting the structure of the nickel complex and the catalytic conditions, demonstrating the catalyst's extremely strong ability to regulate polyethylene molecules. Therefore, the nickel complex of this invention has extremely high industrial application potential and market prospects, and will undoubtedly bring significant economic benefits. Attached Figure Description

[0066] Figure 1 This is a crystal structure diagram of the nickel complex 4 prepared in Example 9 of this application.

[0067] Figure 2 This is a crystal structure diagram of nickel complex 5 prepared in Example 10 of this application.

[0068] Figure 3 The temperature-raised 1H NMR spectrum of the polymer prepared in Example 11a) of this application is shown.

[0069] Figure 4 The temperature-raised carbon NMR spectrum of the polymer prepared in Example 11a) of this application is shown.

[0070] Figure 5 The temperature-raised hydrogen NMR spectrum of the polymer prepared in Example 11h of this application is shown.

[0071] Figure 6 The temperature-raised carbon NMR spectrum of the polymer prepared in Example 11h of this application. Detailed Implementation

[0072] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the description of this invention, those skilled in the art can make improvements or modifications to the invention, and these equivalent forms also fall within the scope defined by this invention.

[0073] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0074] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0075] Unless otherwise specified, all concentrations in the following examples are molar concentrations.

[0076] The molecular weight and molecular weight distribution of the polymers obtained in the following ethylene polymerization examples were determined by conventional high-temperature GPC method, the melting point was determined by conventional DSC method, and the polymerization activity of the polymers was calculated by the following formula: Polymer activity = Polymer yield / (Catalyst dosage · Polymerization time).

[0077] All the synthesized complexes described below were confirmed by infrared, nuclear magnetic resonance and elemental analysis.

[0078] Example 1: Preparation of compound (II-1)

[0079]

[0080] In a 100 mL round-bottom flask, 2,6-bis(bis(4-fluorophenyl)methyl)-4-methylaniline (1.05 g, 2.07 mmol), 2-acetylpyridine (0.25 g, 2.07 mmol), zinc chloride (0.34 g, 2.5 mmol), and acetic acid (3 mL) were added. The mixture was heated to reflux and reacted for 4 h. The solution was cooled to room temperature, filtered, and washed with 30 mL of diethyl ether to remove residual acetic acid, yielding an orange-red solid. The solid was dried and dissolved in 15 mL of dichloromethane. A saturated potassium carbonate solution (3 mL) was added, and the mixture was stirred at room temperature for 1 h. The mixture was then separated, and the organic phase was dried over anhydrous magnesium sulfate and filtered. After removing the solvent from the filtrate, the solution was recrystallized from dichloromethane and methanol (the volume ratio of dichloromethane to methanol was approximately 1:20). After filtration and drying, an orange solid was obtained. Yield: 65%.

[0081] The structural evidence is as follows:

[0082] FT-IR (cm) -1 ):2919(w),1858(w),1644(m),1600(m),1505(s),1465(w),1361(w),1301(w),1 217(s),1157(s),1099(W),1038(w),1016(w),869(w),835(s),783(m),726(w).

[0083] 1H NMR (400MHz, CDCl3, TMS): δ8.60(d,J:6.40Hz,1H),7.93(d,J:8.00Hz,1H),7.72(t,J:8.00Hz,1H) ,7.34(t,J:6.40Hz,1H),6.86-6.96(m,16H),6.61(s,2H),5.20(s,2H),2.18(s,3H),1.20(s,3H).

[0084] 13 C NMR (100MHz, CDCl3, TMS):169.4,162.6,162.5,160.2,155.7,148.6,145.7,139.1,138.2,138.1,136.1 ,132.0,131.9,131.0,130.7,130.6,128.5,124.8,121.1,115.3,115.1,114.9,114.7,50.5,21.2,17.0.

[0085] 19 F NMR (470MHz, CDCl3): δ-116.29,-117.05.

[0086] Elemental analysis: C 40 H 30 F4N2(614.69):C,88.16;H,6.92;N,4.56.Found:C,87.76;H,6.83;N,4.59.

[0087] Example 2 Preparation of compound (II-2)

[0088]

[0089] The method is basically the same as in Example 1, except that the aniline compound (compound of formula (IV)) involved in the reaction is 2,6-bis(bis(4-fluorophenyl)methyl)-4-ethylaniline, and the yield is 73%.

[0090] The structural evidence is as follows:

[0091] FT-IR (cm) -1 ):2962(w),2285(w),2082(w),1640(m),1600(m),1505(m),1460(w),1367(w),1 301(w),1258(s),1215(m),1155(w),1013(m),873(w),788(s),731(w),667(w).

[0092] 1 H NMR (400MHz, CDCl3, TMS): δ8.59(d,J:4.80Hz,1H),7.96(d,J:7.80Hz,1H),7.72(t,J:7.50Hz,1H),7.35( t,J:5.40Hz,1H),6.85-6.96(m,16H),6.63(s,2H),5.21(s,2H),2.46(q,2H),1.19(s,3H),1.05(s,3H).).

[0093] 13 C NMR (100MHz, CDCl3, TMS):168.3,162.0,158.7,154.6,147.6,144.9,138.2,138.1,137.4,137.1,135.1,13 0.9,130.0,129.9,129.7,129.6,126.3,123.8,120.1,114.3,114.0,113.9,113.6,49.5,27.4,16.0,14.7.

[0094] 19 F NMR (470MHz, CDCl3): δ-116.32,-117.14.

[0095] Elemental analysis: C 41 H 32 F4N2(628.71):C,78.33;H,5.13;N,4.46.Found:C,78.73;H,5.15;N,4.48.

[0096] Example 3 Preparation of compound (II-3)

[0097]

[0098] The method is basically the same as in Example 1, except that the aniline compound involved in the reaction is 2,6-bis(bis(4-fluorophenyl)methyl)-4-isopropylaniline, and the yield is 68%.

[0099] The structural evidence is as follows:

[0100] FT-IR (cm) -1 ):2959(w),2932(w),1973(w),1637(C=N,m),1599(m),1503(s),1464(w),1366(w) ,1301(w),1218(s),1155(m),1097(m),1015(w),832(s),782(m),729(m),664(w).

[0101] 1 H NMR (400MHz, CDCl3, TMS): δ8.59(d,1H),7.97(d,J:8.00Hz,1H),7.72(t,J:7.60Hz,1H),7.35(t,J: 5.20Hz,1H),6.66-6.99(m,16H),6.47(s,2H),5.21(s,2H),2.71(m,1H),1.21(s,3H),1.07(d,6H).

[0102] 13 C NMR (100MHz, CDCl3, TMS): δ162.5,160.2,160.1,155.7,148.6,145.9,143.0,139.2,139.2,138.2,138.2,136.1,131 .7,131.0,130.9,130.7,130.6,125.9,124.8,121.1,115.3,115.1,114.9,114.6,58.4,50.6,33.5,24.0,18.2,17.1.

[0103] 19 F NMR (470MHz, CDCl3): δ-116.35,-117.13.

[0104] Elemental analysis: C 42 H 34 F4N2(642.74):C,78.49;H,5.33;N,4.36.Found:C,78.03;H,5.29;N,4.32.

[0105] Example 4 Preparation of compound (II-4)

[0106]

[0107] The method is basically the same as in Example 1, except that the aniline compound involved in the reaction is 2,6-bis(bis(4-fluorophenyl)methyl)-4-fluoroaniline, and the yield is 75%.

[0108] The structural evidence is as follows:

[0109] FT-IR (cm) -1):3070(w),2962(w),2282(w),2110(w),1642(C=N,m),1599(m),1505(s),1466(w),1441(m),1363(w ),1302(m),1259(m),1219(s),1155(m),1095(m),1016(m),873(w),760(s),748(w),722(w),681(w).

[0110] 1 H NMR (400MHz, CDCl3, TMS): δ8.61(d,J:4.40Hz,1H),7.94(d,J:7.60Hz,1H),7.73(t,J:1.60Hz,1H ),7.37(t,J:1.60Hz,1H),6.88-6.94(m,16H),6.55(d,J:9.60Hz,2H),5.21(s,2H),1.20(s,3H).

[0111] 13 C NMR (100MHz, CDCl3, TMS): δ170.2,162.8,162.7,160.3,157.7,155.4,148.7,144.1,138.2,137.4,137.3,13 6.2,134.2,134.1,131.0,130.9,130.6,130.5,125.0,121.1,115.5,115.3,115.2,114.9,114.7,50.5,17.0.

[0112] 19 F NMR (470MHz, CDCl3): δ-115.67,-116.41,-119.70.

[0113] Elemental analysis: C 39 H 27 F5N2(618.65):C,75.72;H,4.40;N,4.53.Found:C,75.42;H,4.42;N,4.55.

[0114] Example 5 Preparation of compound (II-5)

[0115]

[0116] The method is basically the same as in Example 1, except that the aniline compound involved in the reaction is 2,6-bis(bis(4-fluorophenyl)methyl)-4-trifluoromethoxyaniline, and the yield is 80%.

[0117] The structural evidence is as follows:

[0118] FT-IR (cm) -1 ):3044(w),2914(w),1892(w),1643(C=N,m),1602(m),1583(w),1567(w),1505(s),1465(w),1442(m),1366(m),1303(w),1254(m),1 224(w),1209(w),1195(w),1172(w),1154(w),1098(m),1043(w),1014(m),993(w),875(w),833(s),794(w),783(w),740(m),656(m).

[0119] 1 H NMR (400MHz, CDCl3, TMS): δ8.59(d,J:4.00Hz,1H),7.93(d,J:7.60Hz,1H),7.72(t,J :7.60Hz,1H),7.35(t,J:6.40Hz,1H),6.88-6.94(m,16H),6.67(s,2H),5.19(s,2H).

[0120] 13 C NMR (100MHz, CDCl3, TMS): δ160.3,148.7,146.7,138.0,137.1,136.2,134.0,130.9 ,130.8,130.6,130.5,125.1,121.1,120.8,115.6,115.4,115.2,115.0,50.5,17.2.

[0121] 19 F NMR (470MHz, CDCl3): δ-58.22,-115.53,-116.29.

[0122] Elemental analysis: C 40 H 27 F7N2O(684.66):C,70.17;H,3.98;N,4.09.Found:C,69.78;H,4.01;N,4.08.

[0123] Example 6 Preparation of Nickel Complex 1

[0124]

[0125] In a 25 mL Shrek flask, the ligand compound (formula (II-1)) prepared in Example 1 (0.3 g, 0.52 mmol), (DME)NiBr2 (0.08 g, 0.26 mmol), dichloromethane (10 mL), and ethanol (10 mL) were added. The solution was stirred at room temperature under N2 for 12 h. The solvent was removed under reduced pressure, and the product was dissolved in a small amount of dichloromethane. Then, diethyl ether was added, and a solid precipitated. The solid was filtered, washed with diethyl ether, and dried to obtain an orange solid. Yield: 58%.

[0126] The structural evidence is as follows:

[0127] FT-IR (cm) -1 ):3353(w),3063(w),2921(w),1630(w),1598(C=N,m),1571(w),1505(s),1450(w),1372(w),131 8(w),1253(w),1221(s),1158(s),1097(w),1061(w),1021(w),982(w),837(s),783(m),727(w).

[0128] 19 F NMR (470MHz, CDCl3): δ-116.13,-117.52.

[0129] Elemental analysis: C 40 H 30 Br2F4N2Ni(833.19):C,57.66;H,3.63;N,3.36.Found:C,57.63;H,3.56;N,3.57.

[0130] Example 7 Preparation of Nickel Complex 2

[0131]

[0132] The method is basically the same as in Example 6, except that the ligand compound involved in the reaction is the compound of formula (II-2) prepared in Example 2, with a yield of 63%.

[0133] The structural evidence is as follows:

[0134] FT-IR (cm) -1):3061(w),2970(w),2894(w),1627(w),1597(m),1571(w),1505(s),1455(w),1425(w),1373( w),1318(w),1220(s),1158(m),1095(w),1051(w),1020(w),878(w),836(s),783(m),726(w).

[0135] 19 F NMR (470MHz, CDCl3): δ-115.44,-116.82.

[0136] Elemental analysis: C 41 H 32 Br2F4N2Ni(847.22):C,58.13;H,3.81;N,3.31.Found:C,58.02;H,3.84;N,3.34.

[0137] Example 8 Preparation of nickel complex 3

[0138]

[0139] The method is basically the same as in Example 6, except that the ligand compound involved in the reaction is the compound of formula (II-3) prepared in Example 3, with a yield of 60%.

[0140] The structural evidence is as follows:

[0141] FT-IR (cm) -1 ):3063(w),2962(w),1598(m),1574(w),1505(s),1449(w),1372(w),1317(w),1256(w), 1223(s),1158(m),1134(w),1097(w),1020(w),877(w),837(s),783(m),750(w),726(w).

[0142] 19 F NMR (470MHz, CDCl3): δ-115.45,-116.82.

[0143] Elemental analysis C 42 H 34 Br2F4N2Ni(861.24):C,58.57;H,3.98;N,3.25.Found:C,58.53;H,4.03;N,3.42.

[0144] Example 9: Preparation of Nickel Complex 4

[0145]

[0146] The method is basically the same as in Example 6, except that the ligand compound involved in the reaction is the compound of formula (II-4) prepared in Example 4, with a yield of 77%. The molecular structure of nickel complex 4 is as follows. Figure 1 As shown.

[0147] The structural evidence is as follows:

[0148] FT-IR (cm) -1 ):3358(w),3070(W),1912(W),1630(W),1597(C=N,m),1574(w),1505(s),1448(m),1373(w),1320(w),1263( w),1224(s),1157(w),1100(w),1055(w),1007(w),942(w),869(w),839(s),781(w),725(w),684(w),651(w).

[0149] 19 F NMR (470MHz, CDCl3): δ-115.66,-116.41,-119.6.

[0150] Elemental analysis C 39 H 27 Br2F5N2Ni(837.15):C,55.96;H,3.25;N,3.35.Found:C,55.85;H,3.18;N,3.28.

[0151] Example 10 Preparation of nickel complex 5

[0152]

[0153] The method is basically the same as in Example 6, except that the ligand compound involved in the reaction is the compound of formula (II-5) prepared in Example 5, with a yield of 84%. The molecular structure of nickel complex 5 is as follows: Figure 2 As shown.

[0154] The structural evidence is as follows:

[0155] FT-IR (cm) -1):3761(w),3062(w),2161(w),2028(w),1971(w),1624(w),1598(m),1574(w),1505(s),1449(w),1373(w), 1317(w),1263(m),1221(s),1190(w),1156(m),1098(w),1017(w),982(w),879(w),834(s),784(m),730(w).

[0156] 19 F NMR (470MHz, CDCl3): δ-57.84,-114.76,-115.72.

[0157] Elemental analysis C 40 H 27 Br2F7N2NiO(903.16):C,53.20;H,3.01;N,3.10.Found:C,53.06;H,3.03;N,2.89.

[0158] Example 11: Ethylene polymerization catalyzed by nickel complex 1 / EtAlCl2 system

[0159] a) Under an ethylene atmosphere, 25 ml of toluene, 50 ml of a toluene solution of nickel complex 1 (2 μmol), 2 ml of co-catalyst EtAlCl2 (0.5 mol / L hexane solution), and 25 ml of toluene were sequentially added to a 250 ml high-pressure reactor. At this point, the Al / Ni ratio was 500:1. The stirring speed was maintained at 400 rpm. When the system temperature reached 30°C, the ethylene pressure in the reactor was increased to 10 atm. During the reaction, the system temperature and the ethylene pressure remained constant at 10 atm. After reacting for 30 min, stirring was stopped, and the reaction solution was neutralized with a 10% hydrochloric acid ethanol solution to obtain a polymer precipitate. After washing several times with ethanol, the precipitate was dried under vacuum to constant weight, yielding 3.20 g of polymer. The polymerization activity was 3.20 × 10⁻⁶. 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 5.39 kg·mol -1 PDI = 2.65 (polymer weight-average molecular weight M) w The molecular weight distribution (PDI) was obtained by high-temperature GPC testing, and the polymer T... m =67.8℃ (polymer melting temperature T) m (Originally obtained from DSC testing).

[0160] Take 30 mg of the obtained polymer, dissolve it in 1 ml of deuterated tetrachloroethane, and test it at 100 °C. 1 H NMR and 13 C NMR data. 1 In HNMR, signal peaks were found at 4.8–5.8 ppm, which proved to be shift peaks of terminal double bonds and intrachain double bonds. 13 In the C10 NMR, part of the obtained signal peaks were between 10 and 40 ppm, indicating shifts in methyl, methylene, and methine groups; another part was between 110 and 140 ppm, indicating shifts in terminal double bonds and intramolecular double bonds. The obtained polymer was a highly branched (91 / 1000C) polyethylene containing terminal and intramolecular double bonds. See the detailed spectrum below. Figure 3 and Figure 4 .

[0161] b) is basically the same as method a) in this embodiment, except that: 1.2 ml of co-catalyst EtAlCl2 (0.5 mol / L hexane solution) is used to make Al / Ni = 300:1. Polymerization activity: 1.37 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 5.22 kg·mol -1 PDI = 2.68, polymer T m =67.4℃.

[0162] c) is basically the same as method a) in this embodiment, except that 1.6 ml of co-catalyst EtAlCl2 (0.5 mol / L hexane solution) is used to make Al / Ni = 400:1. Polymerization activity: 2.86 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 4.76 kg·mol -1 PDI = 2.56, polymer T m =68.8℃.

[0163] d) is basically the same as method a) in this embodiment, except that: 1.8 ml of co-catalyst EtAlCl2 (0.5 mol / L hexane solution) is used to make Al / Ni = 450:1. Polymerization activity: 3.10 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 4.84 kg·mol -1 PDI = 2.88, polymer T m =69.8℃.

[0164] e) Basically the same as method a) in this embodiment, except that: 2.2 ml of co-catalyst EtAlCl2 (0.5 mol / L hexane solution) is used to make Al / Ni = 550:1. Polymerization activity: 2.65 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 4.53 kg·mol -1 PDI = 2.64, polymer T m =66.1℃.

[0165] f) is basically the same as method a) in this embodiment, except that the polymerization temperature is 20℃. Polymerization activity: 2.76×10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 9.59 kg·mol -1 PDI = 3.02, polymer T m =102.1℃.

[0166] g) is basically the same as method a) in this embodiment, except that the polymerization temperature is 40℃. Polymerization activity: 2.23×10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 3.46 kg·mol -1 PDI = 2.57, polymer T m =58.2℃.

[0167] h) is basically the same as method a) in this embodiment, except that the polymerization temperature is 50℃. Polymerization activity: 0.50×10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 2.63 kg·mol -1 PDI = 2.21, polymer T m =57.4℃.

[0168] Take 30 mg of the obtained polymer, dissolve it in 1 ml of deuterated tetrachloroethane, and test it at 100 °C. 1 H NMR and 13 C NMR data. 1 In H NMR, signal peaks were found at 4.8–5.8 ppm, which proved to be shift peaks of terminal double bonds and intrachain double bonds. 13In the C10 NMR, part of the obtained signal peaks were between 10 and 40 ppm, indicating shifts in methyl, methylene, and methine groups; another part was between 110 and 140 ppm, indicating shifts in terminal double bonds and intramolecular double bonds. The obtained polymer was a highly branched (135 / 1000C) polyethylene containing terminal and intramolecular double bonds. See the detailed spectrum below. Figure 5 and Figure 6 .

[0169] i) Basically the same as method a) in this embodiment, except that the polymerization time is 5 min. Polymerization activity: 2.81 × 10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 4.27 kg·mol -1 PDI = 2.18, polymer T m =63.9℃.

[0170] j) is basically the same as method a) in this embodiment, except that the polymerization time is 15 min. Polymerization activity: 10.2 × 10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 4.97 kg·mol -1 PDI = 2.69, polymer T m =72.1℃.

[0171] k) is basically the same as method a) in this embodiment, except that the polymerization time is 45 min. Polymerization activity: 6.2 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 5.74 kg·mol -1 PDI = 3.42, polymer T m =68.4℃.

[0172] l) is basically the same as method a) in this embodiment, except that the polymerization time is 60 min. Polymerization activity: 2.74 × 10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 6.18 kg·mol -1 PDI = 3.43, polymer T m =68.9℃.

[0173] m) is basically the same as method a) in this embodiment, except that the ethylene pressure is 5 atm. Polymerization activity: 1.14 × 10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 3.98 kg·mol -1 PDI = 2.25, polymer T m =58.0℃.

[0174] Example 12: Ethylene polymerization catalyzed by the nickel complex 2 / EtAlCl2 system

[0175] Basically the same as Example 11a), except that the main catalyst is nickel complex 2. Polymerization activity: 2.88 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 4.61 kg·mol -1 PDI = 2.89, polymer T m =68.3℃.

[0176] Example 13: Ethylene polymerization catalyzed by the nickel complex 3 / EtAlCl2 system

[0177] Basically the same as Example 11a), except that the main catalyst is nickel complex 3. Polymerization activity: 3.53 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 4.75 kg·mol -1 PDI = 2.53, polymer T m =70.1℃.

[0178] Example 14: Ethylene polymerization catalyzed by the nickel complex 4 / EtAlCl2 system

[0179] Basically the same as Example 11a), except that the main catalyst is nickel complex 4. Polymerization activity: 9.27 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 5.83 kg·mol -1 PDI = 2.90, polymer T m =68.1℃.

[0180] Example 15: Ethylene polymerization catalyzed by the nickel complex 5 / EtAlCl2 system.

[0181] a) Basically the same as Example 11a), except that the main catalyst is nickel complex 5. Polymerization activity: 10.8 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 7.94 kg·mol -1 PDI = 2.58, polymer T m =52.9℃. Take 30mg of the obtained polymer, dissolve it in 1ml of deuterated tetrachloroethane, and test at 100℃. 1 H NMR and 13 According to C NMR data, 1 In H NMR, signal peaks were found at 4.8–5.8 ppm, which proved to be shift peaks of terminal double bonds and intrachain double bonds. 13 In C NMR, part of the obtained signal peaks were between 10 and 40 ppm, indicating that they were shift peaks of methyl, methylene and methine, while another part was between 110 and 140 ppm, indicating that they were shift peaks of terminal double bonds and intramolecular double bonds. The obtained polymer was highly branched (151 / 1000C) polyethylene.

[0182] Example 16: Ethylene polymerization catalyzed by a nickel complex 1 / MMAO system

[0183] a) Under an ethylene atmosphere, 25 ml of toluene, 50 ml of a toluene solution of nickel complex 1 (2 μmol), 2.1 ml of MMAO co-catalyst (1.93 mol / L toluene solution), and 25 ml of toluene were sequentially added to a 250 ml high-pressure reactor. At this point, the Al / Ni ratio was 2000:1. The stirring speed was maintained at 400 rpm. When the system temperature reached 30°C, the ethylene pressure in the reactor was increased to 10 atm. During the reaction, the system temperature and the ethylene pressure remained constant at 10 atm. After reacting for 30 min, stirring was stopped, and the reaction solution was neutralized with a 10% hydrochloric acid ethanol solution to obtain a polymer precipitate. After washing several times with ethanol, the precipitate was dried under vacuum to constant weight, yielding 2.51 g of polymer. The polymerization activity was 2.51 × 10⁻⁶. 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 3.68 kg·mol -1 PDI = 2.25 (polymer weight-average molecular weight M) w The molecular weight distribution (PDI) was obtained by high-temperature GPC testing, and the polymer T... m =73.4℃ (polymer melting temperature T) m (Originally obtained from DSC testing).

[0184] b) Basically the same as method a) in this embodiment, except that the polymerization temperature is 20℃. Polymerization activity: 2.07×10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 7.32 kg·mol -1 PDI = 2.63, polymer T m =102.8℃.

[0185] c) is basically the same as method a) in this embodiment, except that the polymerization temperature is 40℃. Polymerization activity: 1.18×10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 2.62 kg·mol -1 PDI = 2.26, polymer T m =63.1℃.

[0186] d) Basically the same as method a) in this embodiment, except that the polymerization temperature is 50℃. Polymerization activity: 0.30×10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 2.50 kg·mol -1 PDI = 2.03, polymer T m =58.4℃.

[0187] e) Basically the same as method a) in this embodiment, except that the reaction time is 5 min. Polymerization activity: 1.87 × 10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 3.30 kg·mol -1 PDI = 2.02, polymer T m =69.1℃.

[0188] f) is basically the same as method a) in this embodiment, except that the reaction time is 15 min. Polymerization activity: 2.40 × 10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 3.55 kg·mol -1 PDI = 2.27, polymer T m =71.3℃.

[0189] g) is basically the same as method a) in this embodiment, except that the reaction time is 45 min. Polymerization activity: 1.76 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 3.72 kg·mol -1 PDI = 2.19, polymer T m =76.6℃.

[0190] h) is basically the same as method a) in this embodiment, except that the reaction time is 60 min. Polymerization activity: 1.52 × 10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 3.75 kg·mol -1 PDI = 2.40, polymer T m =73.5℃.

[0191] i) Basically the same as method a) in this embodiment, except that the ethylene pressure is 5 atm. Polymerization activity: 1.01 × 10 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 2.92 kg·mol -1 PDI = 2.01, polymer T m =58.5℃.

[0192] j) is basically the same as method a) in this embodiment, except that: 3.6 ml of co-catalyst MMAO (1.93 mol / L toluene solution) is used, and the Al / Ni ratio is 3500:1. Polymerization activity: 1.86 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 The polymer's weight-average molecular weight Mw = 3.72 kg·mol⁻¹ -1 PDI = 2.25, polymer T m =74.9℃.

[0193] Example 17: Ethylene polymerization catalyzed by nickel complex 2 / MMAO system

[0194] Basically the same as Example 16a), except that the main catalyst is nickel complex 2. Polymerization activity: 2.05 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w= 3.69 kg·mol -1 PDI = 2.28, polymer T m =74.5℃.

[0195] Example 18: Ethylene polymerization catalyzed by nickel complex 3 / MMAO system

[0196] Basically the same as Example 16a), except that the main catalyst is nickel complex 3. Polymerization activity: 2.62 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 3.49 kg·mol -1 PDI = 2.36, polymer T m =74.4℃.

[0197] Example 19: Ethylene polymerization catalyzed by nickel complex 4 / MMAO system

[0198] Basically the same as Example 16a), except that the main catalyst is nickel complex 4. Polymerization activity: 7.84 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 3.98 kg·mol -1 PDI = 2.38, polymer T m =72.5℃.

[0199] Example 20: Ethylene polymerization catalyzed by nickel complex 5 / MMAO system

[0200] a) Basically the same as Example 16a), except that the main catalyst is nickel complex 5. Polymerization activity: 10.1 × 10⁻⁶ 6 g·mol -1 (Ni)·h -1 Polymer weight-average molecular weight M w = 3.83 kg·mol -1 PDI = 2.38, polymer T m =77.4℃. Take 30mg of the obtained polymer, dissolve it in 1ml of deuterated tetrachloroethane, and test at 100℃. 1 H NMR and 13 According to C NMR data, 1 In H NMR, signal peaks were found at 4.8–5.8 ppm, which proved to be shift peaks of terminal double bonds and intrachain double bonds. 13In C NMR, part of the obtained signal peaks were between 10 and 40 ppm, indicating that they were shift peaks of methyl, methylene and methine, while another part was between 110 and 140 ppm, indicating that they were shift peaks of terminal double bonds and intramolecular double bonds. The obtained polymer was highly branched (142 / 1000C) polyethylene.

[0201] 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 nickel complex of formula (Ⅰ): Equation (Ⅰ) in, R 1 Selected from F or trifluoromethoxy; R 2 R 3 R 4 Whether the two are the same or different, each is independently selected from H or C. 1-3 Alkyl group; X may be the same or different, each independently selected from Cl or Br.

2. The nickel complex of formula (Ⅰ) according to claim 1, wherein, The nickel complex represented by formula (Ⅰ) is selected from the following nickel complexes: Nickel complex 4: where R 1 = F, X = Br, R 2 = Me, R 3 and R 4 For H; Nickel complex 5: where R 1 = OCF3, X = Br, R 2 = Me, R 3 and R 4 For H.

3. A method for preparing the nickel complex of formula (I) as described in claim 1 or 2, comprising the following steps: The compound of formula (II) was subjected to a complexation reaction with a nickel-containing compound to obtain the nickel complex shown in formula (I). in, X, R 1 R 2 R 3 and R 4 As defined in claim 1.

4. The preparation method according to claim 3, wherein, The nickel-containing compound is selected from nickel-containing halides, nickel-containing halide hydrates, and nickel-containing halide solvates; The reaction is carried out under the protection of an inert gas; The complexation reaction is carried out in a solvent selected from one or more of alcohol solvents, dichloromethane, and chloroform, wherein the molar volume ratio of the compound of formula (II) to the solvent is 1:30 to 1:

50.

5. The preparation method according to claim 4, wherein, The nickel-containing compound is NiBr2·DME or NiCl2·6H2O; The solvent is selected from ethanol and / or dichloromethane.

6. The preparation method according to any one of claims 3-5, wherein, The molar ratio of the nickel-containing compound to the compound of formula (II) is 1:1~2; The reaction temperature is 10~35℃; the reaction time is 4~24 hours.

7. The preparation method according to claim 6, wherein, The molar ratio of the nickel-containing compound to the compound of formula (II) is 1:1 to 1.5; The reaction temperature is 15~30℃; the reaction time is 8~18 hours.

8. The preparation method according to claim 7, wherein, The molar ratio of the nickel-containing compound to the compound of formula (II) is 1:1 to 1.2; The reaction temperature is 20~25℃; the reaction time is 8~12 hours.

9. The preparation method according to any one of claims 3-5, wherein, After the reaction is complete, the reaction solution is concentrated under reduced pressure to remove the solvent and obtain the residue. The residue is dissolved in a good solvent, and then a poor solvent is added for recrystallization to precipitate the solid. The solid is then filtered, washed, and dried to obtain the final product.

10. The preparation method according to claim 9, wherein, The good solvent is dichloromethane; the bad solvent is diethyl ether or n-hexane.

11. The preparation method according to claim 10, wherein, The unsuitable solvent is anhydrous diethyl ether.

12. A catalyst composition comprising a main catalyst and optionally a co-catalyst, wherein, The main catalyst is the nickel complex of formula (Ⅰ) as described in claim 1 or 2.

13. The catalyst composition according to claim 12, wherein, The cocatalyst is selected from one or more of aluminoxane, alkylaluminum, and alkylaluminum chloride.

14. The catalyst composition according to claim 13, wherein, The aluminum oxane is methylaluminoxane and / or triisobutylaluminum-modified methylaluminoxane, the alkylaluminum is trimethylaluminum, and the alkylaluminum chloride is one or more of sesquiethylaluminum chloride, dichloroethylaluminum, and diethylaluminum chloride.

15. The catalyst composition according to any one of claims 12-14, wherein, When the catalyst composition includes a co-catalyst, the molar ratio of metallic Al in the co-catalyst to the central metallic Ni of the nickel complex shown in formula (I) is (30-8000):

1.

16. The catalyst composition according to claim 15, wherein, When the catalyst composition includes a co-catalyst, the molar ratio of metallic Al in the co-catalyst to the central metallic Ni of the nickel complex shown in formula (I) is (100-5000):

1.

17. The catalyst composition according to claim 16, wherein, When the catalyst composition includes a co-catalyst, the molar ratio of metallic Al in the co-catalyst to the central metallic Ni of the nickel complex shown in formula (I) is (200-4000):

1.

18. The catalyst composition according to any one of claims 12-14, wherein, When the cocatalyst is triisobutylaluminum-modified methylaluminoxane, the molar ratio of metal Al in the triisobutylaluminum-modified methylaluminoxane to the central metal Ni of the nickel complex shown in formula (Ⅰ) is (1500-3500):

1.

19. The catalyst composition according to any one of claims 12-14, wherein, When the cocatalyst is dichloroethylaluminum, the molar ratio of metallic Al in dichloroethylaluminum to the central metallic Ni of the nickel complex shown in formula (Ⅰ) is (200-700):

1.

20. The catalyst composition according to any one of claims 12-14, wherein, When the cocatalyst is triisobutylaluminum-modified methylaluminoxane, the molar ratio of metal Al in the triisobutylaluminum-modified methylaluminoxane to the central metal Ni of the nickel complex shown in formula (Ⅰ) is (1800-3500):

1. When the cocatalyst is dichloroethylaluminum, the molar ratio of metallic Al in dichloroethylaluminum to the central metallic Ni of the nickel complex shown in formula (Ⅰ) is (300-600):

1.

21. A method for preparing polyethylene, comprising: Under the action of the catalyst composition as described in any one of claims 12-20, ethylene polymerization is carried out to obtain polyethylene.

22. The preparation method according to claim 21, wherein, The polymerization temperature is 20~50℃; the polymerization time is 5~60min; and the polymerization pressure is 1~10atm.

23. The preparation method according to claim 21 or 22, wherein, The solvent used in the polymerization reaction is selected from one or more of toluene, o-xylene, n-hexane, cyclohexane, n-heptane, cycloheptane, dichloromethane, ethanol, and tetrahydrofuran.

24. Use of the nickel complex of formula (I) as described in claim 1 or 2 in the preparation of polyolefins.

25. The use as described in claim 24, wherein the polyolefin is polyethylene.

26. A ligand compound represented by formula (II), having the following structural formula: in, R 1 Selected from F or trifluoromethoxy; R 2 R 3 R 4 Whether the two are the same or different, each is independently selected from H or C. 1-3 alkyl.

27. The ligand compound of formula (II) according to claim 26, selected from the following compounds: Compound of formula (II-4): where R 1 = F, R 2 = Me, R 3 and R 4 For H; Compound of formula (II-5): where R 1 = OCF3, R 2 = Me, R 3 and R 4 For H.

28. A method for preparing a ligand compound of formula (II) as described in claim 26 or 27, comprising the following steps: 1) Compounds of formula (III) and (IV) were reacted with zinc chloride using a template method to obtain zinc complexes; 2) Dissolve the zinc complex described in step 1) in a good solvent, add a saturated aqueous solution of potassium carbonate or potassium oxalate, stir and separate the liquids, recrystallize the organic phase to obtain the ligand compound shown in formula (II).

29. The preparation method according to claim 28, wherein, In step 1), the template reaction is carried out under acid catalysis.

30. The preparation method according to claim 29, wherein, In step 1), the acid is formic acid and / or acetic acid.

31. The preparation method according to any one of claims 28-30, wherein, In step 1), the template reaction is carried out under reflux conditions for 1 to 10 hours; The molar ratio of the compound of formula (III), the compound of formula (IV) to zinc chloride is 0.5~2:1:0.5~2.

32. The preparation method according to claim 31, wherein, In step 1), the template reaction is carried out under reflux conditions for 3 to 8 hours; The molar ratio of the compound of formula (III), the compound of formula (IV) to zinc chloride is 0.8~1.5:1:0.8~1.

5.

33. The preparation method according to any one of claims 28-30, wherein, In step 2), the good solvent is dichloromethane or acetone; The stirring process is carried out at room temperature for 0.5-5 hours. The recrystallization was performed using dichloromethane and methanol to obtain the purified ligand compound represented by formula (II).

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