A kind of α-diimine nickel catalyst and its preparation method and application

Abstract

The present invention relates to the field of olefin catalytic polymerization, and is intended to provide an α-diimine nickel catalyst and its preparation method and application. Including: hydrochloric acid, zinc chloride, aniline compounds and diphenylmethanol are reacted in a solvent-free state at 160°C, aniline is diphenylmethylated, and diphenylmethyl substituted aniline is obtained; using ethanol as solvent and formic acid as catalyst, ethylidene acenaphthenequinone and para-position large sterically hindered substituted aniline are reacted under nitrogen protection and 80°C to obtain α-diimine compounds; using dichloromethane as solvent, (DME) NiBr2 and α-diimine compounds are reacted under nitrogen protection, room temperature and stirring; washing the reaction product with ether to obtain an orange solid powder is an α-diimine nickel catalyst. The catalyst of the present invention can be used for olefin polymerization, and has the characteristics of simple preparation method, low synthesis difficulty, controllable cost and high yield; in terms of catalytic ethylene polymerization, the catalyst has the characteristics of high catalytic activity and good thermal stability relative to existing catalysts, and is easy to industrialize.

Description

Technical Field

[0001] The invention relates to the field of olefin catalytic polymerization, and in particular to an alpha-diimine nickel olefin polymerization catalyst of ethylene acenaphthene combined with para-position large sterically hindered substituted aniline, and a preparation method and application thereof. Background Art

[0002] As the world's largest and most widely used polymer product, polyolefins are irreplaceable in the industry. Due to its excellent performance, wide variety, easy availability of raw materials and low price, polyethylene has a wide range of uses, including food industry, building materials facilities, electronic appliances, medical machinery and defense industry. Therefore, the research and development of new polyolefin materials is of great significance in expanding application areas and improving use value. In 1995, the Brookhart team funded by DuPont reported a class of α-diimine nickel / palladium catalysts that can catalyze ethylene polymerization to obtain high molecular weight polyethylene (J.Am.Chem.Soc., 1995, 117(23): 6414-6415). This type of catalyst has a unique chain walking behavior, and its great application potential has attracted the attention of many people. Among them, compared with expensive palladium, nickel-based catalysts are more valuable for industrial applications due to their cheaper advantages.

[0003] The structure of the classic Brookhart-type α-diimine nickel catalyst is as follows:

[0004]

[0005] However, the defect of poor thermal stability limits the further industrial application of α-diimine nickel catalysts. In order to make this type of α-diimine nickel catalyst truly applied to industrial production, scholars mainly regulate the polymerization behavior of the catalyst and the structure and performance of the product by designing the catalyst structure, such as the modification of the N-aryl group and the modification of the skeleton structure. Among them, Long et al. proposed an α-diimine nickel catalyst with bulky benzhydryl substituted at the 2,6 positions of the N-aryl group (J.Am.Chem.Soc., 2013, 135: 16316-16319; ACS Catal., 2014, 4: 2501-2504). These catalysts showed excellent thermal stability, but because the 2,6 positions of the N-aryl group were all bulky benzhydryl substituted, the branching degree of polyethylene obtained by catalyzing ethylene polymerization by this type of catalyst was significantly reduced. Fu Zhisheng et al. proposed an α-diimine nickel catalyst (CN102827312A) with an ethyleneacenaphthene skeleton. The introduction of the ethyleneacenaphthene skeleton not only improves the thermal stability of the catalyst, but also the degree of branching of the product obtained by catalyzing ethylene polymerization is higher than that of the classic Brookhart catalyst. However, with the increase of polymerization temperature and the extension of polymerization time, the polymerization activity of this type of catalyst decreases significantly, especially for catalysts whose ortho-substituted groups of aniline are methyl or ethyl, which are smaller than isopropyl. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide an α-diimine nickel catalyst and a preparation method and application thereof.

[0007] To solve the technical problem, the solution of the present invention is:

[0008] Provided is an α-diimine nickel catalyst, the molecular structure of the catalyst is shown in formula (I):

[0009]

[0010] In formula (I), R1 and R2 are methyl or ethyl; Ph is phenyl.

[0011] The present invention also provides an α-diimine compound for preparing the aforementioned α-diimine nickel catalyst, and the molecular structure of the α-diimine compound is shown in formula (II):

[0012]

[0013] In formula (II), R1 and R2 are methyl or ethyl; Ph is phenyl.

[0014] The present invention further provides a method for preparing the aforementioned α-diimine nickel catalyst, comprising the following steps:

[0015] (1) weighing hydrochloric acid, zinc chloride, an aniline compound and diphenylmethanol in a molar ratio of 1:0.5:1:1; reacting at 160° C. for 1 h in the absence of a solvent to perform diphenylmethylation on the aniline to obtain diphenylmethyl-substituted aniline; the aniline compound is 2,6-dimethylaniline or 2,6-diethylaniline;

[0016] (2) weighing ethylidene acenaphthenequinone and para-position sterically hindered substituted aniline in a molar ratio of 1:2.2; using ethanol as a solvent and formic acid as a catalyst, reacting at 80° C. for 48 hours under nitrogen protection to obtain an α-diimine compound used as a ligand;

[0017] (3) Weigh (DME) NiBr2 and α-diimine compound in a molar ratio of 1:1.1; use dichloromethane as solvent, react for 24 hours under nitrogen protection, room temperature and stirring conditions; wash the reaction product with ether several times to obtain an orange solid powder, which is the α-diimine nickel catalyst.

[0018] The reaction process of this method can be described by the reaction equation as follows:

[0019]

[0020] The present invention also provides the use of the aforementioned α-diimine nickel catalyst in catalyzing olefin polymerization to prepare polyethylene.

[0021] Description of the invention principle:

[0022] 1. The early research and development results of the research team of the applicant of the present invention are specifically recorded in the application document of the Chinese invention patent application "Ethyleneacenaphthene (α-diimine) nickel olefin catalyst and its preparation method and application" (CN20121027633.9). The typical catalyst structure (III) proposed in the document is as follows:

[0023]

[0024] Wherein, R is methyl or isopropyl.

[0025] According to the literature, the catalyst with R being isopropyl has shown good thermal stability. However, the catalyst with R being methyl or ethyl, which is smaller than isopropyl (Comparative Examples 3 and 4), although the thermal stability is improved compared with the catalyst with acenaphthenequinone as the skeleton (Brookhart-type catalyst), the improvement is not enough and the high temperature activity is still low, which limits the further application of the catalyst.

[0026] 2. Based on the above research results, the inventor team proposed an innovative technical solution based on further research, that is, on the basis of the catalyst product described in formula (III), a diphenylmethyl group was introduced at the para position of the N-aryl group.

[0027] It is generally believed by those skilled in the art that the introduction of a large-sized substituent group (such as diphenylmethyl) at the ortho position of the N-aryl group can improve the thermal stability of the catalyst by hindering the rotation of the N-aryl group around the C-N bond. For typical public literature recording such views, reference can be made to the research content of Brookhart, Long, etc. (J.Am.Chem.Soc.2000,122,6686-6700; J.Am.Chem.Soc.2013,135,16316-16319; ACS Catal.2014,4,2501-2504). However, while this method improves the thermal stability of the catalyst, it also greatly reduces the branching degree of the obtained polyethylene and greatly increases the molecular weight of the obtained polyethylene. That is, it has a great impact on the molecular structure of the polymer product.

[0028] However, the applicant's R&D team discovered during a systematic study that when the substituent group at the ortho position of the N-aryl group is relatively small (such as methyl or ethyl), the introduction of a diphenylmethyl group at the para position of the N-aryl group will also hinder the rotation of the N-aryl group around the C-N bond. That is, the catalyst thus obtained has significantly improved thermal stability when used to catalyze ethylene polymerization under the same conditions as the catalyst in the prior art (Comparative Examples 3 and 4). The molecular weight of the polyethylene obtained by catalyzing ethylene polymerization does not change significantly, and the degree of branching of the polyethylene does not decrease significantly. This is an unexpected technical effect for those skilled in the art.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. Compared with the prior art, the catalyst provided by the present invention is used for olefin polymerization and has the characteristics of simple preparation method, low synthesis difficulty, controllable cost and high yield;

[0031] 2. In terms of catalytic ethylene polymerization, this catalyst has the characteristics of high catalytic activity and good thermal stability compared with existing catalysts, and is easy to industrialize. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the contents of specific embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0033] The α-diimine nickel catalyst specifically involved in each embodiment of the present invention is shown in the structural formula (I), and the intermediate product α-diimine compound ligand is shown in the structural formula (II). In the α-diimine compound ligand structural formula, the options of R1 and R2 are shown in the following table:

[0034]

[0035] 1. Preparation of ligands L1 and L2

[0036] Example 1, preparation of L1: First, add 2,6-dimethylaniline (6.0 g, 50 mmol) and diphenylmethanol (9.2 g, 50 mmol) to a 150 mL thick-walled pressure bottle with a magnetic stirrer. Dissolve anhydrous ZnCl2 (3.4 g, 25 mmol) in concentrated hydrochloric acid (37% H2O, about 4.2 mL, 50 mmol), add the solution to the reaction flask, and raise the temperature to 160°C. After heating at 160°C for 1 h, cool the reaction mixture and dissolve it in 200 mL CH2Cl2. Add 5% NaHCO3 aqueous solution to the solution, adjust the pH to neutral, and separate the dichloromethane solution. Wash the CH2Cl2 layer with water (3 times, 100 mL), dry it with anhydrous magnesium sulfate (more than 2 hours), and concentrate the solution by distillation. Precipitate the product with a large amount of methanol and wash it with methanol (3 times, 100 mL). 2,6-Dimethyl-4-benzhydrylaniline was obtained as a white crystalline solid and dried in vacuo to constant weight in a yield of 69%. 1 H NMR (500MHz, CDCl3) δ7.30(t,J=7.5Hz,4H),7.22(t,J=7.4Hz,2H),7.15(d,J =7.2Hz,4H),6.73(s,2H),5.44(s,1H),3.64(d,J=87.5Hz,2H),2.15(s,6H). 13 C NMR (126MHz, CDCl3) δ144.67,140.84,133.37,129.38,129.22,128.13,125.96,121.66,56.16,17.75.

[0037] Then, 200 mL of anhydrous ethanol, 2.1 g of ethylacenaphthenequinone (2.1 g, 10 mmol) and 2,6-dimethyl-4-benzhydrylaniline (6.3 g, 22 mmol) were added to a 500 mL reaction bottle with a magnetic stirrer under nitrogen protection, and several drops of formic acid were added. The reaction was refluxed at 80 ° C for 48 h. After the reaction was completed, the crude product was filtered to obtain a crude product, which was purified by recrystallization with dichloromethane / methanol, and filtered to obtain a yellow solid, which was ligand L1. It was vacuum dried to constant weight, with a yield of 71%. 1 H NMR(500MHz, CDCl3)δ7.35(t,J=7.5Hz,8H),7.26–7.22(m,12H),7.15(d,J=7.1Hz ,2H),6.90(s,4H),6.61(d,J=7.2Hz,2H),5.59(s,2H),3.46(s,4H),2.05(s,12H). 13CNMR (126MHz, CDCl3) δ162.20,148.34,148.08,144.45,139.45,138.89,137.59,129.52,129.23, 128.26,126.18,125.69,125.27,124.43,121.26,56.47,32.20,17.89.ESI-MS(m / z):747.37[M+H] + .

[0038] Example 2, preparation of L2: First, add 2,6-diethylaniline (7.5 g, 50 mmol) and diphenylmethanol (9.2 g, 50 mmol) to a 150 mL thick-walled pressure bottle with a magnetic stirrer. Dissolve anhydrous ZnCl2 (3.4 g, 25 mmol) in concentrated hydrochloric acid (37% H2O, about 4.2 mL, 50 mmol), add the solution to the reaction flask, and raise the temperature to 160°C. After heating at 160°C for 1 h, cool the reaction mixture and dissolve it in 200 mL CH2Cl2. Add 5% NaHCO3 aqueous solution to the solution, adjust the pH to neutral, and separate the dichloromethane solution. Wash the CH2Cl2 layer with water (3 times, 100 mL), dry with anhydrous magnesium sulfate (more than 2 hours), and concentrate the solution by distillation. Precipitate the product with a large amount of methanol and wash with methanol (3 times, 100 mL). 2,6-Diethyl-4-benzhydrylaniline was obtained as a white crystalline solid and dried in vacuo to constant weight in a yield of 75%. 1 H NMR (500MHz, CDCl3) δ7.27(d,J=21.3Hz,4H),7.20(d,J=16.2Hz,2H),7.14(d,J=8.4Hz,4 H), 6.72 (s, 2H), 5.46 (s, 1H), 3.66 (s, 2H), 2.49 (q, J = 7.5Hz, 4H), 1.19 (t, J = 7.5Hz, 6H). 13 CNMR (126MHz, CDCl3) δ144.94,139.84,133.62,129.52,128.21,127.74,127.31,126.04,56.53,24.52,13.23.

[0039] Then, 200 mL of anhydrous ethanol, 2.1 g of ethylacenaphthenequinone (2.1 g, 10 mmol) and 2,6-diethyl-4-benzhydrylaniline (6.9 g, 22 mmol) were added to a 500 mL reaction bottle with a magnetic stirrer under nitrogen protection, and several drops of formic acid were added. The reaction was refluxed at 80 ° C for 48 h. After the reaction was completed, the crude product was filtered to obtain a crude product, which was purified by recrystallization with dichloromethane / methanol, and filtered to obtain a yellow solid, which was ligand L2. It was vacuum dried to constant weight, with a yield of 76%. 1 H NMR (500MHz, CDCl3) δ7.34(t,J=7.5Hz,8H),7.24(t,J=5.9Hz,12H),7.13(d,J=7.2Hz,2H),6.93(s,4H),6.57(d,J=7.2 Hz,2H),5.62(s,2H),3.45(s,4H),2.50(dq,J=15.0,7.5Hz,4H),2.39(dt,J=14.6,7.4Hz,4H),1.01(t,J=7.5Hz,12H). 13 C NMR (126MHz, CDCl3) δ162.13,148.19,147.49,144.64,139.50,139.11,137.62,131.28,129.56,128. 26,127.68,126.17,125.83,124.82,121.14,56.70,32.20,24.90,14.08.ESI-MS(m / z):803.44[M+H] + .

[0040] 2. Preparation of α-diimine nickel catalyst

[0041] Example 3, Preparation of C1:

[0042] Under nitrogen protection, L1 (0.822 g, 1.1 mmol) and (DME) NiBr2 (0.308 g, 1.0 mmol) were added to 50 mL of dichloromethane and stirred at room temperature for 24 hours. After the reaction was completed, the dichloromethane was vacuum-dried and the remaining red-brown solid was washed with n-hexane three times until the color of the supernatant did not change. The amount of n-hexane used each time was 30 mL. The n-hexane was then drained to obtain orange solid C1 with a yield of 98%. Anal. Calcd for C 30 H 26 Br2N2Ni: C, 56.92; H, 4.14; N, 4.43. Found: C, 55.93; H, 4.18; N, 4.12.

[0043] Example 4, Preparation of C2:

[0044] Under nitrogen protection, L2 (0.884 g, 1.1 mmol) and (DME) NiBr2 (0.308 g, 1.0 mmol) were dissolved in 50 mL of dichloromethane and stirred at room temperature for 24 hours. After the reaction was completed, the dichloromethane was vacuum-dried. The remaining red-brown solid was washed with n-hexane three times until the color of the supernatant did not change. The amount of n-hexane used each time was 30 mL. The n-hexane was then drained to obtain orange solid C2 with a yield of 95%. Anal. Calcd for C 60 H 54 Br2N2Ni: C, 70.54; H, 5.33; N, 2.74. Found: C, 66.07; H, 5.36; N, 2.36.

[0045] 3. Catalytic Ethylene Pressure Polymerization

[0046] Example 5, ethylene pressure polymerization is carried out under anhydrous and oxygen-free conditions. The ethylene pressure is 0.8MPa, the polymerization temperature is 60°C, 100mL of n-heptane is added to a 300mL stainless steel reactor, and then 0.3mL of a 2.0mol / L n-hexane solution of diethylaluminum chloride as a co-catalyst is injected therein. 1μmol of the main catalyst C1 is dissolved in 2mL of dichloromethane and injected, and the ethylene is pressurized to 0.8MPa and stirred. After reacting for half an hour, the polymer solution is poured into an ethanol solution acidified with hydrochloric acid for sedimentation, the polymer is filtered, and then washed with ethanol several times. After vacuum drying to constant weight, 7.5g of polymer is weighed. The catalytic activity is 15.1×10 6 g PE ·mol Ni -1 ·h -1 The weight average molecular weight of the polymerization product is 45 kDa, the polydispersity coefficient is 1.52, and the branching degree is 54 / 1000C.

[0047] Example 6: The polymerization temperature in Example 5 was raised to 80°C, and other conditions remained unchanged. The catalytic activity was 4.8×10 6 g PE ·mol Ni -1 ·h -1 The weight average molecular weight of the polymerization product is 23 kDa, the polydispersity coefficient is 1.59, and the branching degree is 77 / 1000C.

[0048] Example 7, the polymerization temperature in Example 5 was lowered to 40°C, and other conditions remained unchanged. The catalytic activity was 20.3×10 6 g PE ·mol Ni -1 ·h -1, branching degree 33 / 1000C. Combined with Example 5, the polymerization temperature was increased from 40°C to 80°C, and the activity reduction rate was 76%.

[0049] Example 8: The catalyst C1 in Example 5 was replaced by C2, and other conditions remained unchanged. The catalytic activity was 12.2×10 6 g PE ·mol Ni -1 ·h -1 The weight average molecular weight of the polymerization product is 105 kDa, the polydispersity coefficient is 1.65, and the branching degree is 67 / 1000C.

[0050] Example 9: The polymerization temperature in Example 8 was raised to 80°C, and other conditions remained unchanged. The catalytic activity was 5.6×10 6 g PE ·mol Ni -1 ·h -1 The weight average molecular weight of the polymerization product is 64 kDa, the polydispersity coefficient is 1.46, and the branching degree is 89 / 1000C.

[0051] Example 10: The polymerization temperature in Example 8 was lowered to 40°C, and other conditions remained unchanged. The catalytic activity was 15.7×10 6 g PE ·mol Ni -1 ·h -1 , branching degree 47 / 1000C. Combined with Example 9, the polymerization temperature was increased from 40°C to 80°C, and the activity reduction rate was 64%.

[0052] Comparative Example:

[0053] Formula (III) is a catalyst proposed in a patent publication (CN20121027633.9), and formula (IV) is a ligand compound used to prepare the catalyst.

[0054]

[0055]

[0056] Comparative Example 1, preparation of L3, in a 500mL reaction bottle with a magnetic stirrer under nitrogen protection, add 200mL of anhydrous ethanol, ethylidene acenaphthenequinone (2.1g, 10mmol) and 2,6-dimethylaniline (2.7g, 22mmol) and then add several drops of formic acid. The reaction was refluxed at 80°C for 48h. After the reaction was completed, the crude product was filtered to obtain a crude product, which was purified by recrystallization with dichloromethane / methanol, and filtered to obtain a yellow solid. It was vacuum dried to constant weight, with a yield of 73%.

[0057] Comparative Example 2, L4 was prepared by using 2,6-diethylaniline instead of 2,6-dimethylaniline. Other operations were the same as those in Comparative Example 1, and the yield was 67%.

[0058] Comparative Example 3, C3 was prepared by replacing the ligand in Example 3 with the ligand synthesized in Comparative Example 1. Other operations were the same as in Example 3, with a yield of 98%.

[0059] Comparative Example 4, preparation of C4, using the ligand synthesized in Comparative Example 2 to replace the ligand in Example 3, other operations are the same as Example 3, the yield is 94%.

[0060] Comparative Example 5: The catalyst in Example 6 was replaced by the diimine nickel bromide complex synthesized by C3. Other operations were the same as those in Example 6. The catalytic activity was 3.6×10 6 g PE ·mol Ni -1 ·h -1 The weight average molecular weight of the polymer product is 22 kDa and the degree of branching is 92 / 1000C.

[0061] Comparative Example 6: The catalyst in Example 7 was replaced by the diimine nickel bromide complex synthesized by C3. Other operations were the same as those in Example 7. The catalytic activity was 22.4×10 6 g PE ·mol Ni -1 ·h -1 , branching degree 41 / 1000C. Combined with Comparative Example 5, the activity reduction rate is 84%. Compared with Example 6 and Example 7, the activity reduction degree is higher and the thermal stability is reduced.

[0062] Comparative Example 7: The catalyst in Example 9 was replaced by the diimine nickel bromide complex synthesized by C4. Other operations were the same as those in Example 9. The catalytic activity was 4.9×10 6 g PE ·mol Ni -1 ·h -1 The weight average molecular weight of the polymer product is 61 kDa and the branching degree is 94 / 1000C.

[0063] Comparative Example 8: The catalyst in Example 10 was replaced by the diimine nickel bromide complex synthesized by C4. Other operations were the same as those in Example 10. The catalytic activity was 16.5×10 6 g PE ·mol Ni -1 ·h -1, branching degree 41 / 1000C. Combined with Comparative Example 5, the activity decrease rate is 70%. Compared with Example 9 and Example 10, the activity decrease degree is higher and the thermal stability is worse. The comparative example proves that the introduction of diphenylmethyl in the para-position of aniline can improve the heat resistance of the catalyst.

[0064] The polymerization results of all embodiments and comparative examples are summarized in Table 1.

[0065] Table 1 Summary of aggregation results

[0066]

[0067] It can be more intuitively learned from Table 1 that: on the basis of C3 and C4, the activity of C1 and C2 obtained after the introduction of diphenylmethyl at the para position of aniline at a high temperature of 80°C in catalytic ethylene polymerization is much lower than the polymerization activity at 40°C; and the molecular weight of the prepared polyethylene does not change significantly due to the introduction of diphenylmethyl at the para position of aniline, and the degree of branching of the polyethylene does not decrease significantly due to the introduction of diphenylmethyl at the para position of aniline. This is an effect that cannot be achieved by introducing diphenylmethyl at the ortho position of aniline. For related literature, please refer to (J. Catal., 2022, 413: 311-320). After the introduction of diphenylmethyl at the ortho position of the catalyst, the degree of branching of the product obtained by catalyzing ethylene polymerization at 80°C is reduced from 91 branches / 1000 carbons to 60 branches / 1000 carbons, and the weight-average molecular weight is increased from 78kDa to 228KDa, which is very obvious.

Claims

1. An α-diimine nickel catalyst, characterized in that The molecular structure of the catalyst is shown in formula (I): In formula (I), R1 and R2 are methyl or ethyl; Ph is phenyl; The α-diimine nickel catalyst is prepared by the following steps: (1) weighing hydrochloric acid, zinc chloride, an aniline compound and diphenylmethanol in a molar ratio of 1:0.5:1:1, wherein the aniline compound is 2,6-dimethylaniline or 2,6-diethylaniline; reacting the aniline compound at 160°C for 1 hour without a solvent to obtain a diphenylmethyl substituted aniline having a diphenylmethyl group at the para position; (2) Weighing ethylidene acenaphthene quinone and diphenylmethyl substituted aniline in a molar ratio of 1:2.2; using ethanol as solvent and formic acid as catalyst, reacting at 80 °C for 48 h under nitrogen protection to obtain an α-diimine compound used as a ligand; The molecular structure of the α-diimine compound is shown in formula (II): In formula (II), R1 and R2 are methyl or ethyl; Ph is phenyl; (3) Weigh (DME)NiBr2 and α-diimine compound in a molar ratio of 1:1.1; use dichloromethane as solvent, react for 24 hours under nitrogen protection, room temperature and stirring conditions; wash the reaction product with ether several times to obtain an orange solid powder, which is the α-diimine nickel catalyst.

2. Use of the α-diimine nickel catalyst according to claim 1 in catalyzing olefin polymerization to prepare polyethylene.

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