Three-center chromium metal catalyst and its preparation method and application

Abstract

The present invention belongs to the technical field of polymerization catalysts, and specifically relates to a three-center chromium metal catalyst and a preparation method and application thereof. The three-center chromium metal catalyst is composed of 1,3,5-triaminobenzene, substituted chlorophosphine and CrCl 3 (THF) 3 The preparation method comprises firstly adding 1,3,5-triaminobenzene, substituted chlorophosphine and an acid-binding agent to an anhydrous solvent for reaction to obtain an intermediate ligand; then reacting the intermediate ligand with CrCl 3 (THF) 3 The reaction obtains a three-center chromium metal catalyst. The application is to add the three-center chromium metal catalyst and the co-catalyst to a solvent to catalyze the polymerization reaction of ethylene. The present invention solves the problem that the existing catalysts are insufficient in the selectivity of 1-octene. The three-center chromium metal catalyst is simple to synthesize, the raw materials are easily available, and the use cost is low; at the same time, it has relatively stable selectivity and catalytic activity, and is suitable for industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of polymerization catalysts, and in particular relates to a three-center chromium metal catalyst and a preparation method and application thereof. Background Art

[0002] Linear α-olefins, referred to as LAOs, refer to straight-chain olefins containing α-hydrogen atoms, such as 1-octene. 1-octene is an important raw material for the preparation of fine chemicals such as flavors, dyes, and plasticizers. It is also often used as a comonomer for the preparation of high-performance polyolefins and has high application value in polymer materials and daily chemicals.

[0003] Ethylene oligomerization is the most commonly used method for synthesizing LAO in industry. Among them, the most advanced method for producing 1-octene is ethylene selective tetramerization. This method has the advantages of high atom economy, energy saving, low product separation cost and good quality. The key to ethylene selective tetramerization technology is how to prepare an efficient and highly selective metal catalyst. Among them, SHOP type catalyst (Angew. Chem., Int. Ed. Engl. 1978, 17, 466-467) has the advantages of good solvent applicability and high oxygen tolerance, and is favored by many multinational companies including Shell. Scientific research on catalysts for ethylene catalytic polymerization, for example, in 1998, Brookhart and Gibson et al. simultaneously reported the complex of pyridine diimine Fe(II) and Co(II) (J.Am.Chem.Soc.1998,120,4049-4050;Chem.Commun. 1998,849-850), which can be well utilized to catalyze ethylene polymerization or polymerization by adjusting the substituents on the benzene ring of the complex. Another example is a study report (Chem.Rev. 2011, 111, 2450-2485) that binuclear metal catalysts can simulate the structure of biomimetic enzymes, and the two metal centers can achieve synergistic catalysis through electron transfer and other means, further improving the olefin catalytic performance of metal catalysts.

[0004] Chinese patent CN109096422A discloses a metal catalyst coordinated by an organic ligand and a method for homogeneously catalyzing ethylene polymerization. The general structural formula of the metal catalyst is [R 1 R 2 PLN(R 5 )PR 3 R 4 ]MXn. When used for ethylene catalytic polymerization to prepare polyethylene, L is an organic bridging group of the C2 skeleton, M refers to a transition metal element of the fourth, fifth, or sixth period, and Xn refers to a group chemically bonded to M in addition to the ligand; MXn is a molecular group containing metal chromium. The substituent R of the P atom 1 , R 2 , R3 , R 4 At least one of them is a heteroatom group, and the R 5 represents one of hydrogen, alkyl, alkyl containing heteroatoms, cycloalkyl, heterocycloalkyl, aryl, substituted aryl and derivatives thereof; said R 1 , R 2 , R 3 , R 4 Each independently represents one of a straight-chain alkyl group, a branched-chain alkyl group, a heteroalkyl group, a cycloalkyl group, a heterocycloalkyl group, an aryl group, a substituted aryl group and its derivatives, an amine group, an alkoxy group, an alkylthio group, an oxyaryl group, and a thioaryl group, and R 1 , R 2 , R 3 , R 4 The catalyst is used to catalyze ethylene polymerization, and the catalytic activity is as high as 1.98×10 7 g(PE) / (mol(Cr)•h).

[0005] The patent does not conduct an in-depth study on the types of substituents, the selection of substituents is relatively general, and the selectivity of the prepared metal catalyst for catalyzing the polymerization of ethylene to prepare 1-octene is not discussed. 1 , R 2 , R 3 , R 4 and R 5 Can represent a variety of different groups, and R 1 , R 2 , R 3 , R 4 They can be the same or different. Different combinations of substituents can easily lead to significant changes in the electron density and charge distribution of the central transition metal. At the same time, different combinations of substituents can also produce different steric effects and spatial conformational changes. These factors will affect the selectivity of the catalyst.

[0006] Therefore, the existing metal catalysts for catalyzing the oligomerization or polymerization of ethylene in industry still have many deficiencies in terms of the selectivity of 1-octene, and thus there is an urgent need to obtain a new catalyst that is simple to synthesize, has readily available raw materials, and has a low cost of use; and at the same time has relatively stable selectivity and catalytic activity to adapt to industrial production. Summary of the invention

[0007] The purpose of the present invention is to provide a three-center chromium metal catalyst to solve the shortcomings of existing catalysts in 1-octene selectivity; the present invention also provides a preparation method and application.

[0008] In order to solve the problems existing in the prior art, the technical solution provided by the present invention is:

[0009] The three-center chromium metal catalyst has the following structural formula:

[0010]

[0011] R is one of phenyl, methyl, ethyl or isopropyl.

[0012] in:

[0013] When R is a methyl group, the structural formula is as follows, abbreviated as Cr1, and when R is a phenyl group, the structural formula is as follows, abbreviated as Cr2.

[0014]

[0015] The preparation method of the three-center chromium metal catalyst is as follows: firstly, 1,3,5-triaminobenzene, substituted chlorophosphine and an acid-binding agent are added to an anhydrous solvent for reaction to obtain an intermediate ligand; then, the intermediate ligand is reacted with CrCl3(THF)3 to obtain a three-center chromium metal catalyst.

[0016] in:

[0017] The acid-binding agent is triethylamine; the anhydrous solvent is tetrahydrofuran or dichloromethane; and the substituted chlorophosphine is dimethylchlorophosphine or diphenylchlorophosphine.

[0018] The molar ratio of 1,3,5-triaminobenzene to substituted chlorophosphine is 1:(6.05-6.15); the molar ratio of 1,3,5-triaminobenzene to CrCl3(THF)3 is 1:(3.05-3.15).

[0019] The application of the three-center chromium metal catalyst in catalyzing the polymerization of ethylene is as follows: the three-center chromium metal catalyst and the co-catalyst are added to a solvent to catalyze the polymerization reaction of ethylene.

[0020] in:

[0021] The molar ratio of the co-catalyst to the three-center chromium metal catalyst is (200-500):1.

[0022] The solvent is one or more of n-hexane, n-heptane, dichloromethane or toluene.

[0023] The temperature of the polymerization reaction is 20-120° C., and the pressure of the polymerization reaction is 5-30 atm.

[0024] The co-catalyst is one or more of tris(pentafluorophenyl)borane, trityltetrakis(pentafluorophenyl)borate, aluminoxane, triethylaluminum or diethylaluminum chloride.

[0025] The aluminoxane is methylaluminoxane or modified methylaluminoxane.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) Through the design of microscopic molecular structure, an organic phosphine ligand is coordinated at the 1, 3, and 5 positions of the benzene ring respectively. The three organic phosphine ligands are rotationally symmetric along the center of the benzene ring; and each organic phosphine ligand itself has a certain axial symmetry.

[0028] Better symmetry first reduces intramolecular stress and makes bonding more stable, making it difficult for ligands in the catalyst molecule to migrate or dissociate even at higher temperatures; in addition, better symmetry also makes the electron cloud distribution more uniform, reduces collisions and scattering of electrons during the transfer process, lowers the electron transfer energy barrier, and makes it easier for the Cr active center to overlap with the electron cloud of the reactant molecule, thereby improving the catalytic activity; further, since Cr and the central benzene ring are basically located in the same plane, the Cr active center in the three organophosphorus ligands and the π electron cloud of the central benzene ring can easily achieve synergistic effects through electron transfer, and electrons can more easily find the path with the lowest energy during the transfer process. The existence of side reactions is usually due to the existence of multiple different electron transfer paths or transfer steps, thereby reducing the probability of side reactions.

[0029] (2) The three-center chromium metal catalyst prepared by the present invention can be used to catalyze the polymerization of ethylene. Practical application has proved that it has achieved high catalytic activity (polymerization activity ≥5.85×10 7 g·mol -1 (Cr)·h -1 ) and 1-octene selectivity (selectivity ≥ 80%). In addition, the amount of co-catalyst used is small, the cost of use is low, it is suitable for industrial production, and effectively promotes the development of ethylene selective polymerization to prepare linear α-olefins.

[0030] (3) The three-center chromium metal catalyst in the present invention is not easily deactivated by oxidation when stored for a long time in an environment of 35°C; it also has excellent high temperature resistance and is not easily quenched in a high temperature environment. The polymerization temperature can reach up to 120°C, which meets the production temperature requirements of most polymerization production lines and has a wider range of applications.

[0031] (4) The preparation method of the present invention is simple to operate, does not require complex reaction equipment and harsh preparation conditions, the raw materials are easily available, and the yield of the three-center chromium metal catalyst is high (the catalyst yield is ≥92%). BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the nuclear magnetic phosphorus spectrum of the intermediate ligand 1 in Example 1;

[0033] Figure 2 is the nuclear magnetic phosphorus spectrum of the intermediate ligand 2 in Example 2;

[0034] Figure 3 This is the gas chromatogram of the polymerization product in Example 6. DETAILED DESCRIPTION

[0035] The present invention is further described below with reference to the embodiments.

[0036] Example 1

[0037] Preparation of intermediate ligand 1 (1,3,5-tris(methyl substituted PNP)):

[0038] In a nitrogen atmosphere, 1,3,5-triaminobenzene (1.23 g, 10.00 mmol), dimethylphosphine chloride (5.84 g, 60.50 mmol) and triethylamine (6.07 g, 60.00 mmol) were added to 100 mL of dichloromethane, stirred overnight at 25 °C, filtered under reduced pressure, and then 50 mL of toluene was added for rinsing, then filtered under reduced pressure and dried to obtain 4.59 g of light yellow powder, which was labeled and named intermediate ligand 1. The yield was calculated to be 95%. The NMR phosphorus spectrum is shown in Figure 1 .

[0039] The yield calculation method is: yield = actual molar number of product / molar number of 1,3,5-triaminobenzene × 100%.

[0040] 1 H NMR (400 MHz, CDCl3): δ 5.32 (s, 3 H), 0.98 (d, J = 4.1 Hz, 36 H)ppm. 13 C NMR (100 MHz, CDCl3): δ 112.35, 26.76 ppm. 31 P NMR (162 MHz, CDCl3): δ67.90 ppm. Anal. Calcd for C 18 H 39 N3P6: C, 44.73; H, 8.13; N, 8.69. Found: C, 44.57; H, 8.03; N, 8.49.

[0041] Example 2

[0042] Preparation of intermediate ligand 2 (1,3,5-tris(phenyl substituted PNP)):

[0043] In a nitrogen atmosphere, 1,3,5-triaminobenzene (1.23 g, 10.00 mmol), diphenylphosphine chloride (13.57 g, 61.50 mmol) and triethylamine (6.07 g, 60.00 mmol) were added to 100 mL of tetrahydrofuran, stirred overnight at 25°C, filtered under reduced pressure, and then 50 mL of toluene was added for rinsing, then filtered under reduced pressure and dried to obtain 11.17 g of light yellow powder, which was labeled and named intermediate ligand 2. According to the algorithm of Example 1, the yield was calculated to be 91%. The nuclear magnetic phosphorus spectrum is shown in Figure 2 .

[0044] 1 H NMR (400 MHz, CDCl3) δ 7.51-7.24 (m, 60 H), 5.33 (s, 3 H) ppm. 13 CNMR (100 MHz, CDCl3): δ 133.45, 129.12, 128.17, 109.07 ppm. 31 P NMR (162 MHz, CDCl3): δ 69.21 ppm. Anal. Calcd for C 78 H 63 N3P6: C, 76.28; H, 5.17; N, 3.42. Found: C, 76.05; H, 5.01; N, 3.44.

[0045] Example 3

[0046] Preparation of catalyst Cr1:

[0047] The intermediate ligand 1 (0.48 g, 1.00 mmol) and CrCl3(THF)3 (1.14 g, 3.05 mmol) were added to 20 mL of dichloromethane and stirred at room temperature for 6 h to obtain a blue suspension. After reduced pressure concentration, 20 mL of ether was added for precipitation. After filtration and drying, 0.88 g of a blue solid powder product was obtained, which was a three-center chromium metal catalyst. A label was attached and recorded as Cr1. According to the algorithm of Example 1, the yield was 92%. Anal. Calcd for C 18 H 39 Cl9Cr3N3P6: C, 22.56; H, 4.10; N, 4.38. Found: C, 22.43; H, 4.15; N, 4.32.

[0048] Example 4

[0049] Preparation of catalyst Cr2:

[0050] The intermediate ligand 2 (1.23 g, 1.00 mmol) and CrCl3(THF)3 (1.18 g, 3.15 mmol) were added to 20 mL of dichloromethane and stirred at room temperature for 6 h to obtain a blue suspension. After reduced pressure concentration, 20 mL of ether was added for precipitation. After filtration and drying, 1.58 g of a blue solid powder product was obtained, which was a three-center chromium metal catalyst. A label was attached and recorded as Cr2. According to the algorithm in Example 1, the yield was 93%. Anal. Calcd for C 78 H 63 Cl9Cr3N3P6: C, 55.00; H, 3.73; N, 2.47. Found: C, 49.77; H, 3.67; N, 2.28.

[0051] Example 5

[0052] Cr1 catalyzes ethylene polymerization:

[0053] In the glove box, 1mmol Cr1 was placed in a 350ml polymerization bottle, then taken out of the glove box and connected to the polymerization line, vacuumed and replaced with ethylene gas three times. 50ml of solvent and co-catalyst solution were injected with a syringe; the solvent was toluene, the co-catalyst was methylaluminoxane MAO, and the molar ratio of the co-catalyst to Cr1 was 300:1. The reaction was stirred for 30 minutes at a polymerization temperature of 100℃ and a polymerization pressure of 30 atm. The polymerization activity of the three-center chromium metal catalyst Cr1 was obtained: 8.06×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 82%.

[0054] Cr1 after long-term storage is used to catalyze ethylene polymerization:

[0055] The prepared Cr1 was stored in a dark and dry place at 35°C for 12 months. The catalytic ethylene polymerization experiment was repeated according to the above steps, and the upper organic phase was taken for gas chromatography analysis. The polymerization activity of the three-center chromium metal catalyst Cr1 was obtained: 6.05×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 80%.

[0056] Example 6

[0057] Cr2 catalyzes ethylene polymerization:

[0058] In the glove box, 1mmol Cr2 was placed in a 350ml polymerization bottle, which was then taken out of the glove box and connected to the polymerization line. The bottle was evacuated and replaced with ethylene gas three times. A 50ml mixture of solvent and co-catalyst was injected with a syringe; the solvent was toluene, the co-catalyst was trityl tetrakis(pentafluorophenyl)borate, and the molar ratio of the co-catalyst to Cr1 was 300:1. The reaction was stirred for 30 min at a polymerization temperature of 20°C and a polymerization pressure of 5 atm. After the reaction was completed, a small amount of the reaction solution was taken, neutralized with 5wt% hydrochloric acid, and the upper organic phase was taken for gas chromatography analysis. The polymerization activity of the three-center chromium metal catalyst Cr2 was obtained: 8.1×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 81%. The gas chromatogram of the oligomerization product is shown in Figure 3 .

[0059] Cr2 after long-term storage is used to catalyze ethylene polymerization:

[0060] The prepared Cr2 was stored in a dark and dry place at 35°C for 12 months. The catalytic ethylene polymerization experiment was repeated according to the above steps, and the upper organic phase was taken for gas chromatography analysis. The polymerization activity of the three-center chromium metal catalyst Cr2 was obtained: 5.85×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 80%.

[0061] Example 7

[0062] Cr2 catalyzes ethylene polymerization:

[0063] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the solvent used is n-hexane and the co-catalyst is tris(pentafluorophenyl)borane. Gas chromatography analysis shows that the catalytic activity of the three-center chromium metal catalyst Cr2 is: 8.28×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 83%.

[0064] Example 8

[0065] Cr2 catalyzes ethylene polymerization:

[0066] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the solvent used is n-hexane and the co-catalyst is modified methylaluminoxane MMAO. Gas chromatography analysis showed that the catalytic activity of the three-center chromium metal catalyst Cr2 was: 7.7×10 7 g·mol-1 (Cr)·h -1 ; 1-octene selectivity 85%.

[0067] Example 9

[0068] Cr2 catalyzes ethylene polymerization:

[0069] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the solvent used is n-heptane and the co-catalyst is diethylaluminum chloride Et2AlCl. Catalytic activity of the three-center chromium metal catalyst Cr2: 6.8×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 81%.

[0070] Example 10

[0071] Cr2 catalyzes ethylene polymerization:

[0072] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the solvent used is dichloromethane and the co-catalyst is triethylaluminum Et3Al. The catalytic activity of the three-center chromium metal catalyst Cr2 is 8.15×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 86%.

[0073] Embodiment 11

[0074] Cr2 catalyzes ethylene polymerization:

[0075] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the polymerization temperature used is 40°C. Catalytic activity of the three-center chromium metal catalyst Cr2: 8.0×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 81%.

[0076] Example 12

[0077] Cr2 catalyzes ethylene polymerization:

[0078] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the polymerization temperature used is 60°C. Catalytic activity of the three-center chromium metal catalyst Cr2: 7.9×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 84%.

[0079] Example 13

[0080] Cr2 catalyzes ethylene polymerization:

[0081] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the polymerization temperature used is 80°C. Catalytic activity of the three-center chromium metal catalyst Cr2: 8.8×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 80%.

[0082] Embodiment 14

[0083] Cr2 catalyzes ethylene polymerization:

[0084] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the polymerization temperature used is 100°C. Catalytic activity of the three-center chromium metal catalyst Cr2: 7.82×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 82%.

[0085] Embodiment 15

[0086] Cr2 catalyzes ethylene polymerization:

[0087] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the polymerization temperature used is 120°C. Catalytic activity of the three-center chromium metal catalyst Cr2: 9.15×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 82%.

[0088] Example 16

[0089] Cr2 catalyzes ethylene polymerization:

[0090] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the co-catalyst used satisfies the molar ratio of the co-catalyst to the three-center chromium metal catalyst of 200:1. The catalytic activity of the three-center chromium metal catalyst Cr2 is: 8.9×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 83%.

[0091] Embodiment 17

[0092] Cr2 catalyzes ethylene polymerization:

[0093] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the co-catalyst used satisfies the molar ratio of the co-catalyst to the three-center chromium metal catalyst of 500:1. The catalytic activity of the three-center chromium metal catalyst Cr2: 7.86×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 85%.

[0094] Embodiment 18

[0095] Cr2 catalyzes ethylene polymerization:

[0096] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the polymerization pressure is 10 atm. The catalytic activity of the three-center chromium metal catalyst Cr2 is 8.3×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 80%.

[0097] Embodiment 19

[0098] Cr2 catalyzes ethylene polymerization:

[0099] The polymerization process and reaction conditions are the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the polymerization pressure is 20 atm. The catalytic activity of the three-center chromium metal catalyst Cr2 is: 9.2×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 82%.

[0100] Embodiment 20

[0101] Cr2 catalyzes ethylene polymerization:

[0102] The polymerization process and reaction conditions were the same as those of the Cr2-catalyzed ethylene polymerization process in Example 6, except that the polymerization pressure was 30 atm. The catalytic activity of the three-center chromium metal catalyst Cr2: 8.5×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 87%.

[0103] Comparative Example 1

[0104] Catalyst Cr3 preparation:

[0105]

[0106] The Cr3 ligand, bis(diphenylphosphine)(isopropyl)amine, was produced by Shanghai MacLean Biochemical Technology Co., Ltd.

[0107] Add Cr3 ligand (0.43 g, 1.00 mmol) and CrCl3(THF)3 (0.37 g, 1.00 mmol) to 20 mL of dichloromethane and stir at room temperature for 6 hours to obtain a blue suspension. After vacuum concentration, add 20 mL of ether to precipitate and filter to obtain 0.53 g of a blue solid powder product, which is a single-center chromium metal catalyst, denoted as Cr3, with a yield of 90.5%. Anal. Calcd for C 27 H 27 Cl3P2NCr: C, 55.36; H, 4.65; N, 2.93. Found: C, 53.23; H, 4.15; N, 2.78.

[0108] Comparative Example 2

[0109] Cr3 catalyzes ethylene polymerization:

[0110] The polymerization process and reaction conditions were the same as those in Example 6, except that the catalyst used was Cr3. The catalytic activity of the single-site chromium metal catalyst Cr3 was: 5.33×10 5 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 52%.

[0111] Comparative Example 3

[0112] Cr2 catalyzes ethylene polymerization:

[0113] The polymerization process and reaction conditions were the same as those in Example 6, except that the polymerization pressure was 0.1 atm and the catalytic activity of the single-site chromium metal catalyst Cr2 was 9.3×10 5 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 62%.

[0114] Comparative Example 4

[0115] Cr2 catalyzes ethylene polymerization:

[0116] The polymerization process and reaction conditions were the same as those in Example 6, except that the polymerization pressure was 55 atm and the catalytic activity of Cr2 was 1.22×10 6 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 60%.

[0117] Comparative Example 5

[0118] Cr2 catalyzes ethylene polymerization:

[0119] The polymerization process and reaction conditions were the same as those in Example 6, except that the polymerization temperature was 3°C and the catalytic activity of Cr2 was 1.41×10 6 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 58%.

[0120] Comparative Example 6

[0121] Cr2 catalyzes ethylene polymerization:

[0122] The polymerization process and reaction conditions were the same as those in Example 6, except that the polymerization temperature was 155°C and the catalytic activity of Cr2 was 1.33×10 6 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 65%.

[0123] Comparative Example 7

[0124] Cr2 catalyzes ethylene polymerization:

[0125] The polymerization process and reaction conditions were the same as those in Example 6, except that 3.6 g of 1,3,5-triaminobenzene was added to prepare Cr2. The catalytic activity of Cr2 was 5.6×10 5 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 45%.

[0126] Comparative Example 8

[0127] Cr2 catalyzes ethylene polymerization:

[0128] The polymerization process and reaction conditions were the same as those in Example 6, except that 3.0 g, 2.99 mmol CrCl3(THF)3 was added to prepare Cr2. The catalytic activity of Cr2 was 8.1×10 5 g·mol -1 (Cr)·h -1 ; 1-octene selectivity 49%.

[0129] Discussion of experimental results:

[0130] From the results of Comparative Example 2, it can be seen that compared with the three-center chromium catalysts Cr1 and Cr2, the catalytic activity and 1-octene selectivity of the single-center chromium catalyst Cr3 are lower. The reason is that the spatial configuration stability of the single-center chromium catalyst is worse and it is more susceptible to thermal vibration or solvation effects; in addition, the electron cloud distribution is also more unstable, which affects the catalytic activity and selectivity.

[0131] It can be seen from the results of Comparative Examples 3-6 that when the polymerization temperature range and the polymerization pressure range are far away from the polymerization temperature range and the polymerization pressure range of the present invention, the use effect of the three-center chromium catalyst Cr2 of the present invention will be affected.

[0132] From the results of Comparative Example 7, it can be seen that the catalytic activity of Cr2 prepared in Comparative Example 7 is much lower than that of Example 6. The reason is that the amount of 1,3,5-triaminobenzene added far exceeds the molar ratio of 1,3,5-triaminobenzene to substituted chlorophosphine, which is 1: (6.05-6.15), and the excess 1,3,5-triaminobenzene undergoes self-condensation reaction, and the self-condensation product competes with CrCl3(THF)3 for active sites, resulting in a reduction in the number of active centers of the catalyst or abnormal structure. From the results of Comparative Example 8, it can be seen that the catalytic activity of Cr2 prepared in Comparative Example 8 is much lower than that of Example 6.

Claims

1. A three-center chromium metal catalyst, characterized in that: Its structural formula is as follows: ； Wherein, R is one of phenyl, methyl, ethyl or isopropyl.

2. A method for preparing the three-center chromium metal catalyst according to claim 1, characterized in that: First, 1,3,5-triaminobenzene, substituted chlorophosphine and an acid-binding agent are added to an anhydrous solvent to react to obtain an intermediate ligand; then the intermediate ligand is reacted with CrCl3(THF)3 to obtain a three-center chromium metal catalyst; Among them, the molar ratio of 1,3,5-triaminobenzene to substituted chlorophosphine is 1:(6.05-6.15); the molar ratio of 1,3,5-triaminobenzene to CrCl3(THF)3 is 1:(3.05-3.15).

3. The method for preparing a three-center chromium metal catalyst according to claim 2, characterized in that: The acid-binding agent is triethylamine; the anhydrous solvent is tetrahydrofuran or dichloromethane; and the substituted chlorophosphine is dimethylchlorophosphine or diphenylchlorophosphine.

4. Use of the three-center chromium metal catalyst according to claim 1 in catalyzing ethylene oligomerization, characterized in that: The three-center chromium metal catalyst and the co-catalyst are added to the solvent to catalyze the polymerization reaction of ethylene.

5. Use of the three-center chromium metal catalyst according to claim 4 in catalyzing ethylene oligomerization, characterized in that: The molar ratio of the co-catalyst to the three-center chromium metal catalyst is (200-500):

1.

6. Use of the three-center chromium metal catalyst according to claim 4 in catalyzing ethylene oligomerization, characterized in that: The solvent is one or more of n-hexane, n-heptane, dichloromethane or toluene.

7. Use of the three-center chromium metal catalyst according to claim 4 in catalyzing ethylene oligomerization, characterized in that: The temperature of the polymerization reaction is 20-120° C., and the pressure of the polymerization reaction is 5-30 atm.

8. Use of the three-center chromium metal catalyst according to claim 4 in catalyzing ethylene oligomerization, characterized in that: The co-catalyst is one or more of tris(pentafluorophenyl)borane, trityltetrakis(pentafluorophenyl)borate, aluminoxane, triethylaluminum or diethylaluminum chloride.

9. Use of the three-center chromium metal catalyst according to claim 8 in catalyzing ethylene oligomerization, characterized in that: The aluminoxane is methylaluminoxane or modified methylaluminoxane.

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