PN group coordinated 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 P-N group coordinated chromium metal catalyst and a preparation method and application thereof. The P-N group coordinated chromium metal catalyst comprises an amine compound, substituted chlorophosphine and CrCl 3 (THF) 3 The preparation method is to add an amine compound together with a substituted chlorophosphine and an acid-binding agent to an anhydrous solvent under a nitrogen atmosphere, and stir, and synthesize an intermediate through a hydrochloric acid elimination reaction; then add CrCl 3 (THF) 3 and anhydrous solvent for coordination reaction. The application is to add a P-N group coordinated chromium metal catalyst, a co-catalyst and a polymerization solvent under an ethylene atmosphere to catalyze the polymerization of ethylene to prepare 1-octene. The P-N group coordinated chromium metal catalyst of the present invention can take into account both high catalytic activity and high selectivity for producing 1-octene, and the preparation method is simple to operate, the raw materials are easily available, and the catalyst yield is high; and the catalyst dosage is small, which 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 PN group coordinated chromium metal catalyst and a preparation method and application thereof. Background Art

[0002] Linear α-olefins, referred to as LAOs, refer to straight-chain monoolefins with double bonds at the ends of the molecular chain. Due to their unique molecular structure, linear α-olefins exhibit excellent performance in a variety of chemical reactions such as copolymerization and hydrogenation, and are widely used in the production of polyolefin copolymers, detergents, lubricants and plasticizers. Among them, 1-octene (C8) has a moderate molecular weight and is most suitable as a comonomer for the synthesis of high-performance polyolefins. Its demand is increasing, and its market prospects are very broad.

[0003] The industry often uses the selective oligomerization of ethylene to prepare 1-octene, that is, the selective tetramerization of ethylene is catalyzed by a specific catalyst, such as zirconium-based, alkyl aluminum, chromium-based, etc. This method has the advantages of high selectivity, low energy consumption, and a relatively simple process flow. The key to the selective tetramerization of ethylene is to select a catalyst with high catalytic activity and high selectivity. Therefore, the preparation of a catalyst with high catalytic activity and high selectivity is crucial for the selective tetramerization of ethylene to synthesize 1-octene.

[0004] However, the metal catalysts used in the prior art often have difficulty in achieving both high catalytic activity and high selectivity, especially the selectivity for 1-octene.

[0005] Chinese patent CN107282119A discloses a catalyst composition for ethylene polymerization and a polymerization method, the composition includes a main catalyst chlorinated substituted 2-formyl-1,10-phenanthroline-2,6-diethylaniline iron (II) complex shown in formula (I), an aluminum-containing co-catalyst and tert-butyl hydroperoxide: wherein R1 to R6 are independently selected from hydrogen, C1 to C6 alkyl, halogen, C1 to C6 alkoxy and nitro. The catalytic activity of the catalytic system in this patent is relatively high, but it is insufficient in the selective polymerization preparation of 1-octene. Chinese patent CN114618588A discloses a catalyst system for ethylene polymerization, the catalyst system consists of four components: component A, component B, component C and component D, component A is a chromium-containing compound, component B is a diphosphine ligand, component C is an alkyl aluminum co-catalyst, and component D is a chlorosilane promoter; the chlorosilane promoter is R2 m Cl 3-m Si(CH2) p CH n Cl 3-n, wherein m is 0, 1 or 2, n is 0, 1, 2 or 3, p is 0, 1, 2 or 3, and R2 is methyl or ethyl; the chromium-containing compound is one of CrCl3(THF)3 and Cr(acac)3; the bisphosphine amine ligand is Ph2PN(R1)PPh2, wherein R1 is methyl, isopropyl, cyclohexyl, cyclopentyl or phenyl; the alkyl aluminum co-catalyst is one of methylaluminoxane, ethylaluminoxane and isobutylaluminoxane; the patent has a high selectivity for preparing 1-octene, but a relatively low catalytic activity.

[0006] In response to the reason why existing catalysts find it difficult to achieve both high catalytic activity and high selectivity, there is a theory that the more diverse the adsorption configurations of ethylene molecules and intermediate compounds on the catalyst surface and the more catalyst adsorption sites there are, the easier it is for ethylene and intermediate compounds to adsorb on the catalyst, and the higher the catalytic activity; but the easier it is for multiple ethylene or intermediate compounds to adsorb on the catalyst, the more likely it is that the intermediate compounds will be more likely to compete for chain growth and chain termination on the catalyst surface, resulting in a diversity of product chain lengths, which in turn results in poor reaction selectivity.

[0007] Therefore, designing a catalyst that has both high catalytic activity and high selectivity for the preparation of 1-octene by ethylene polymerization is one of the current research topics for practitioners in the petrochemical field. Summary of the invention

[0008] The purpose of the present invention is to provide a PN group coordinated chromium metal catalyst to solve the problem that the existing catalysts are difficult to achieve both high catalytic activity and high selectivity, especially the selectivity of 1-octene; the present invention also provides a preparation method and application.

[0009] In view of the deficiencies of the prior art, the technical solution provided by the present invention is:

[0010] The chemical structure of the PN group coordinated chromium metal catalyst is as follows:

[0011] ;

[0012] Among them, R 1 is one of methyl, ethyl or isopropyl; R 2 is one of methyl, ethyl or isopropyl; R 3 It is one of methyl, ethyl or isopropyl.

[0013] in:

[0014] The PN group coordinated chromium metal catalyst is any one of PN1, PN2 or PN3.

[0015]

[0016] The preparation method of the PN group coordinated chromium metal catalyst is as follows: under a nitrogen atmosphere, an amine compound together with a substituted chlorophosphine and an acid binding agent are added to an anhydrous solvent and stirred, and an intermediate is synthesized through a hydrochloric acid elimination reaction; CrCl3(THF)3 and an anhydrous solvent are then added to the intermediate for a coordination reaction to obtain a PN group coordinated chromium metal catalyst.

[0017] in:

[0018] The amine compound comprises isopropylamine or methylamine hydrochloride; the substituted chlorophosphine is a disubstituted compound of phosphorus trichloride; the molar ratio of the amine compound to the substituted chlorophosphine is 1:2.1-2.3, and the hydrochloric acid elimination reaction is carried out at room temperature.

[0019] The disubstituted compound of phosphorus trichloride is bis(dimethylammonia)chlorophosphine or bis(diethylammonia)chlorophosphine; the acid binding agent is triethylamine, and the molar ratio of the amine compound to the acid binding agent is 1:2-3; and the anhydrous solvent is one or more of dichloromethane, ether, xylene, n-hexane or tetrahydrofuran.

[0020] The molar ratio of the intermediate to CrCl3(THF)3 is 1.1-1.2:1, and the coordination reaction takes 6-8 hours at room temperature.

[0021] The application of the PN group coordinated chromium metal catalyst in catalyzing ethylene polymerization is as follows: in an ethylene atmosphere, the PN group coordinated chromium metal catalyst, a co-catalyst and a polymerization solvent are added to catalyze ethylene polymerization to prepare 1-octene.

[0022] The molar ratio of the co-catalyst to the PN group coordinated chromium metal catalyst is 200-800:1.

[0023] The ethylene polymerization temperature is 0-180°C, and the ethylene polymerization pressure is 10-50atm.

[0024] The co-catalyst is one or more of aluminoxane or alkyl aluminum; the polymerization solvent is one or more of toluene, n-hexane, n-heptane, ether or dichloromethane.

[0025] The aluminoxane is one or more of methylaluminoxane, ethylaluminoxane or isobutylaluminoxane; the alkylaluminum is one or more of sesquiethylaluminum chloride, triisobutylaluminum, diethylaluminum chloride or ethylaluminum dichloride.

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

[0027] (1) The PN group coordinated chromium metal catalyst in the present invention is designed to have both high catalytic activity and high selectivity: First, R 1 , R2 and R 3 The type of substituent makes the PN group coordinated chromium metal catalyst have a suitable molecular configuration, which will produce a unique steric hindrance to the Cr atom. On the one hand, this steric hindrance effect can accurately regulate the angle and shape of the ethylene molecule or its intermediate state when it is adsorbed on the Cr atom, so that the subsequent ethylene molecule or its intermediate state is more inclined to undergo polymerization reaction in a specific configuration, thereby improving the selectivity of the production of 1-octene; on the other hand, it limits the combination of other non-target molecular chains with Cr atoms and reduces the occurrence of side reactions.

[0028] In addition, the P and N atoms in the PN ligand have different electronegativity. The N atom has a higher electronegativity and is electron-accepting; the P atom has a lower electronegativity and is electron-donating. They can simultaneously form stable coordination bonds with the Cr active center. This dual coordination allows the PN ligand to use its π electron cloud as a bridge for electron transfer, promoting the transfer and rearrangement of electrons within the catalyst. This dual coordination electronic effect helps to reduce the activation barrier of the reaction and improve its selectivity and catalytic activity. On the other hand, the PN group and the ethylene molecule, through coordination, hydrogen bonding, etc., guide the ethylene molecule to bind to the Cr active site at a specific angle and configuration, undergoing a polymerization reaction to generate the target product 1-octene, thereby improving selectivity.

[0029] (2) In addition to the microscopic molecular design, the present invention also proves through experimental verification and chromatographic analysis that the PN group coordinated chromium metal catalyst prepared by the present invention can have both high catalytic activity and high selectivity, and its catalytic activity for ethylene polymerization is ≥2.95×10 7 g·mol -1 (Cr)·h -1 , the selectivity of 1-octene is ≥82%.

[0030] (3) The method for preparing the PN group coordinated chromium metal catalyst of the present invention is simple, easy to operate, and the raw materials are readily available; the catalyst product yield is high, basically above 88%; and the amount of catalyst used is small, which is suitable for industrial production.

[0031] (4) The PN group coordinated chromium metal catalyst prepared by the present invention has excellent high temperature resistance. The polymerization reaction can be carried out at a maximum temperature of 180°C, which can cope with the operation conditions of most chemical production lines and is conducive to the industrial application of the PN group coordinated chromium metal catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the nuclear magnetic phosphorus spectrum of the [(Me2N)2P]-NMe intermediate in Example 1;

[0033] Figure 2 [(Me2N)2P]-N in Example 2 iNMR phosphorus spectrum of Pr intermediate;

[0034] Figure 3 [(Et2N)2P]-N in Example 3 i NMR phosphorus spectrum of Pr intermediate;

[0035] Figure 4 is the gas chromatogram of the oligomerization product in Example 7;

[0036] Figure 5 This is the gas chromatogram of the polymerization product in Example 25. DETAILED DESCRIPTION

[0037] The present invention is further described below with reference to the embodiments.

[0038] Example 1

[0039] Preparation of [(Me2N)2P]-NMe intermediate: The chemical reaction formula is shown below,

[0040] .

[0041] Add bis(dimethylamino)chlorophosphine (3.2462 g, 21 mmol), methylamine hydrochloride (0.6752 g, 10 mmol) and triethylamine (3.0357 g, 30 mmol) to 100 mL of tetrahydrofuran, stir overnight at 25 °C in a nitrogen atmosphere, filter under reduced pressure, add 50 mL of n-hexane for rinsing, and then dry under reduced pressure to obtain 2.4606 g of a light yellow oily intermediate, named [(Me2N)2P]-NMe intermediate, with a yield of 92%. See the attached NMR phosphorus spectrum. Figure 1 .

[0042] Among them, yield = mole number of intermediate / mole number of amine compound × 100%.

[0043] 1 H NMR (CDCl3): δ 2.47 (t, d, J =10.5Hz,3H), 2.42 (d, d, J =12.0 Hz,24H)ppm. 13 C NMR (CDCl3) δ 38.54, 32.42 ppm. 31 P NMR (CDCl3): δ 65.40 (s) ppm.Anal.Calcd for C9H 27 N5P2: C, 40.44; H, 10.18; N, 26.20. Found: C, 40.13; H, 10.01; N, 26.23.

[0044] Example 2

[0045] [(Me2N)2P]-N i Preparation of Pr intermediate: The chemical reaction formula is shown below,

[0046] .

[0047] Bis(dimethylamino)chlorophosphine (3.5554 g, 23 mmol), isopropylamine (0.5911 g, 10 mmol) and triethylamine (2.0238 g, 20 mmol) were added to 100 mL of dichloromethane, stirred overnight at 25 °C in a nitrogen atmosphere, filtered under reduced pressure, and then rinsed with 50 mL of n-hexane, and then dried under reduced pressure to obtain 2.8025 g of a light yellow oily intermediate, named [(Me2N)2P]-N i The yield of Pr intermediate was calculated in the same way as in Example 1, and the yield was 95%. Figure 2 .

[0048] 1 H NMR (CDCl3): δ 2.86-2.80 (m,1H), 2.45 (d, J =11.5 Hz,24H), 1.67 (d, J =7.0 Hz,6H) ppm. 13 C NMR (CDCl3): δ 46.36, 38.54, 22.86 ppm. 31 P NMR (CDCl3):δ 71.20 (s) ppm. Anal. Calcd for C 11 H 31 N5P2: C, 44.73; H, 10.58; N, 23.71. Found: C, 44.67; H, 10.22; N, 23.56.

[0049] Example 3

[0050] [(Et2N)2P]-N i Preparation of Pr intermediate: The chemical reaction formula is shown below,

[0051] .

[0052] Bis(diethylamino)chlorophosphine (4.635 g, 22 mmol), isopropylamine (0.5911 g, 10 mmol) and triethylamine (2.0238 g, 20 mmol) were added to 100 mL of xylene, stirred overnight at 25 °C in a nitrogen atmosphere, filtered under reduced pressure, and then rinsed with 50 mL of n-hexane, and then dried under reduced pressure to obtain 3.8618 g of a light yellow oily intermediate, named [(Et2N)2P]-N i The yield of Pr intermediate was calculated in the same way as in Example 1, and the yield was 95%. Figure 3 .

[0053] 1 H NMR (CDCl3): δ 3.15-3.09 (m,16H), 2.86-2.80 (m,1 H), 1.66 (d, J =7.0Hz,6H), 1.45-1.30 (m, 24H) ppm. 13 C NMR (CDCl3): δ 46.36, 38.46, 22.86, 15.17ppm. 31 P NMR (CDCl3): δ 70.85 (s) ppm. Anal. Calcd for C 19 H 47 N5P2: C,55.99;H,11.62;N,17.18. Found:C,55.92;H,11.43;N,17.01.

[0054] Example 4

[0055] Preparation of catalyst PN1:

[0056] [(Me2N)2P]-NMe (0.3208 g, 1.2 mmol) and CrCl3(THF)3 (0.3747 g, 1 mmol) were added to 20 mL of dichloromethane and stirred at room temperature for 6 h to obtain a suspension. After concentration under reduced pressure, 20 mL of ether was added for washing. After precipitation, filtration and drying, 0.3750 g of solid powder was obtained, recorded as PN1, and the yield of PN1 was 88.1%.

[0057] Wherein, yield = number of moles of catalyst / number of moles of CrCl3(THF)3 × 100%.

[0058] Anal. Calcd for C9H 27Cl3CrN5P2: C, 25.40; H, 6.39; N, 16.45. Found: C, 25.22; H, 6.03; N, 16.31.

[0059] Example 5

[0060] Preparation of catalyst PN2:

[0061] [(Me2N)2P]-N i Pr (0.3397 g, 1.15 mmol) and CrCl3(THF)3 (0.3747 g, 1 mmol) were added to 20 mL of dichloromethane and stirred at room temperature for 6.5 h to obtain a suspension. After concentration under reduced pressure, 20 mL of ether was added for washing. After precipitation, filtration and drying, 0.4110 g of solid powder was obtained, recorded as PN2, and the yield of PN2 was 90.6%.

[0062] Anal. Calcd for C 11 H 31 Cl3CrN5P2:C,29.12;H,6.89;N,15.44.Found:C,29.01;H,6.66;N,15.29.

[0063] Example 6

[0064] Preparation of catalyst PN3:

[0065] [(Et2N)2P]-N i Pr (0.4484 g, 1.1 mmol) and CrCl3(THF)3 (0.3747 g, 1 mmol) were added to 28 mL of dichloromethane and stirred at room temperature for 8 h to obtain a suspension. After concentration under reduced pressure, 20 mL of ether was added for washing. After precipitation, filtration and drying, 0.5228 g of solid powder was obtained, recorded as PN3, and the yield of PN3 was 92.4%.

[0066] Anal. Calcd for C 19 H 47 Cl3CrN5P2:C,40.33;H,8.37;N,12.38. Found:C,40.16;H,8.21;N,12.35.

[0067] Example 7

[0068] PN1 catalyzes ethylene polymerization:

[0069] In the glove box, 1mmol PN1 was placed in a 350ml polymerization bottle. The polymerization bottle was then taken out of the glove box and connected to the polymerization line. Vacuum was evacuated and replaced with ethylene gas three times. Methylaluminoxane solution and 50ml of toluene were injected with a syringe to make the molar ratio of methylaluminoxane to PN1 meet the ratio of 500:1. The reaction was stirred for 30 min at a temperature of 120°C and a pressure of 50 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 gas chromatogram is attached. Figure 4 The catalytic activity of PN1 is 4.11×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 83%.

[0070] Example 8

[0071] The polymerization process and reaction conditions were the same as those in Example 7, except that the cocatalyst used was ethylaluminoxane and the polymerization solvent was n-hexane. The catalytic activity of PN1 was 3.63×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 85%.

[0072] Example 9

[0073] The polymerization process and reaction conditions were the same as those in Example 7, except that the cocatalyst used was isobutylaluminoxane and the polymerization solvent was ether. The catalytic activity of PN1 was 3.45×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 82%.

[0074] Example 10

[0075] The polymerization process and reaction conditions were the same as in Example 7, except that the cocatalyst used was diethylaluminum chloride and the polymerization solvent was dichloromethane. The catalytic activity of PN1 was 2.95×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 86%.

[0076] Embodiment 11

[0077] The polymerization process and reaction conditions were the same as in Example 7, except that the cocatalyst used was ethylaluminum dichloride and the polymerization solvent was n-heptane. The catalytic activity of PN1 was 3.25×10 7 g·mol -1 (Cr)·h -1; 1-octene selectivity is 84%.

[0078] Example 12

[0079] The polymerization process and reaction conditions were the same as those in Example 7, except that the cocatalyst used was sesquiethylaluminum chloride and the polymerization solvent was dichloromethane. The catalytic activity of PN1 was 3.20×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 86%.

[0080] Example 13

[0081] The polymerization process and reaction conditions were the same as those in Example 7, except that the cocatalyst used was triisobutylaluminum and the polymerization solvent was dichloromethane. The catalytic activity of PN1 was 3.88×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 85%.

[0082] Embodiment 14

[0083] The polymerization process and reaction conditions were the same as in Example 7, except that the reaction temperature for ethylene oligomerization was 180°C. Catalytic activity of Cr1: 4.02×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 83%.

[0084] Embodiment 15

[0085] The polymerization process and reaction conditions were the same as in Example 7, except that the reaction temperature for ethylene oligomerization was 100°C. The catalytic activity of PN1 was 4.24×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 82%.

[0086] Example 16

[0087] The polymerization process and reaction conditions were the same as in Example 7, except that the reaction temperature for ethylene oligomerization was 60°C. The catalytic activity of PN1 was 4.28×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 83%.

[0088] Embodiment 17

[0089] The polymerization process and reaction conditions were the same as in Example 7, except that the reaction temperature for ethylene oligomerization was 20°C. The catalytic activity of PN1 was 3.85×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 88%.

[0090] Embodiment 18

[0091] The polymerization process and reaction conditions were the same as in Example 7, except that the reaction temperature for ethylene oligomerization was 0°C. The catalytic activity of PN1 was 4.18×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 82%.

[0092] Embodiment 19

[0093] The polymerization process and reaction conditions were the same as in Example 7, except that the molar ratio of the co-catalyst to PN1 was 800:1. The catalytic activity of PN1 was 3.42×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 87%.

[0094] Embodiment 20

[0095] The polymerization process and reaction conditions were the same as in Example 7, except that the molar ratio of the co-catalyst to PN1 was 200:1. The catalytic activity of PN1 was 3.77×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 84%.

[0096] Embodiment 21

[0097] The polymerization process and reaction conditions were the same as in Example 7, except that the reaction pressure was 10 atm. The catalytic activity of PN1 was 3.08×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 83%.

[0098] Embodiment 22

[0099] The polymerization process and reaction conditions were the same as in Example 7, except that the molar ratio of the co-catalyst to PN1 was 200:1. The catalytic activity of PN1 was 3.77×10 7 g·mol -1 (Cr)·h -1; 1-octene selectivity is 84%.

[0100] Embodiment 23

[0101] The polymerization process and reaction conditions were the same as in Example 7, except that the reaction pressure was 30 atm. The catalytic activity of PN1 was 4.30×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 82%.

[0102] Embodiment 24

[0103] PN2 catalyzes ethylene polymerization:

[0104] The polymerization process and reaction conditions were the same as those in Example 7, except that the PN group-coordinated chromium metal catalyst used was PN2. The catalytic activity of PN2 was 4.82×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 86%.

[0105] Embodiment 25

[0106] PN3 catalyzes ethylene polymerization:

[0107] The polymerization process and reaction conditions were the same as those in Example 7, except that the PN group coordinated chromium metal catalyst used was PN3. After the reaction was completed, a small amount of the reaction solution was taken and neutralized with 5wt% hydrochloric acid, and the upper organic phase was taken for gas chromatography analysis. The gas chromatogram is attached. Figure 5 PN3 catalytic activity: 4.76×10 7 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 83%.

[0108] Comparative Example 1

[0109] The polymerization process and reaction conditions were the same as in Example 7, except that the PN1 catalyst used was replaced by tetrahydrofuran chromium chloride, with a catalytic activity of 7.9×10 6 g·mol -1 (Cr)·h -1 ; 1-octene selectivity is 53%.

[0110] Comparative Example 2

[0111] The polymerization process and reaction conditions were the same as in Example 7, except that the PN1 catalyst was replaced by tetraethyl titanate, with a catalytic activity of 9.92×10 6 g·mol -1 (Cr)·h -1; 1-octene selectivity is 62%.

[0112] Although the present invention is described in detail by way of the accompanying drawings and in combination with the embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall all be within the scope of the present invention.

Claims

1. A PN group coordinated chromium metal catalyst, characterized in that: The chemical structure of the PN group coordinated chromium metal catalyst is as follows: ； Among them, R 1 is one of methyl, ethyl or isopropyl; R 2 is one of methyl, ethyl or isopropyl; R 3 It is one of methyl, ethyl or isopropyl.

2. A method for preparing the PN group coordinated chromium metal catalyst according to claim 1, characterized in that: Under a nitrogen atmosphere, an amine compound, a substituted chlorophosphine and an acid-binding agent are added to an anhydrous solvent and stirred, and an intermediate is synthesized through a hydrochloric acid elimination reaction; CrCl3(THF)3 and an anhydrous solvent are then added to the intermediate for a coordination reaction to obtain a PN group-coordinated chromium metal catalyst.

3. The method for preparing the PN group coordinated chromium metal catalyst according to claim 2, characterized in that: The amine compound includes isopropylamine or methylamine hydrochloride; the substituted chlorophosphine is a disubstituted compound of phosphorus trichloride; the molar ratio of the amine compound to the substituted chlorophosphine is 1:2.1-2.3, and the hydrochloric acid elimination reaction is carried out at room temperature.

4. The method for preparing the PN group coordinated chromium metal catalyst according to claim 3, characterized in that: The disubstituted compound of phosphorus trichloride is bis(dimethylammonia)chlorophosphine or bis(diethylammonia)chlorophosphine; the acid binding agent is triethylamine, and the molar ratio of the amine compound to the acid binding agent is 1:2-3; and the anhydrous solvent is one or more of dichloromethane, ether, xylene, n-hexane or tetrahydrofuran.

5. The method for preparing the PN group coordinated chromium metal catalyst according to claim 2, characterized in that: The molar ratio of the intermediate to CrCl3(THF)3 is 1.1-1.2:1, and the coordination reaction takes 6-8 hours at room temperature.

6. Use of the PN group coordinated chromium metal catalyst according to claim 1 in catalyzing ethylene polymerization, characterized in that: In an ethylene atmosphere, a PN group coordinated chromium metal catalyst, a co-catalyst and a polymerization solvent are added to catalyze the polymerization of ethylene to prepare 1-octene.

7. Use of the PN group coordinated chromium metal catalyst according to claim 6 in catalyzing ethylene oligomerization, characterized in that: The molar ratio of the co-catalyst to the PN group coordinated chromium metal catalyst is 200-800:

1.

8. Use of the PN group coordinated chromium metal catalyst according to claim 6 in catalyzing ethylene oligomerization, characterized in that: The reaction temperature of the ethylene polymerization is 0-180°C, and the reaction pressure of the ethylene polymerization is 10-50atm.

9. Use of the PN group coordinated chromium metal catalyst according to claim 6 in catalyzing ethylene oligomerization, characterized in that: The co-catalyst is one or more of aluminoxane or alkyl aluminum; the polymerization solvent is one or more of toluene, n-hexane, n-heptane, ether or dichloromethane.

10. Use of the PN group coordinated chromium metal catalyst according to claim 9 in catalyzing ethylene oligomerization, characterized in that: The aluminoxane is one or more of methylaluminoxane, ethylaluminoxane or isobutylaluminoxane; the alkylaluminum is one or more of sesquiethylaluminum chloride, triisobutylaluminum, diethylaluminum chloride or ethylaluminum dichloride.

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