Ethylene selective oligomerization catalytic system and reaction method

Abstract

The application provides an ethylene selective oligomerization catalytic system and a reaction method, and the catalytic system comprises: a ligand a; a transition metal compound b, the transition metal compound b is a metal compound of groups IVB-VIII; and an activator c, the activator c is a compound containing a group IIIA metal; wherein the structural general formula of the ligand a is shown as formula (I): formula (I); R 1 ~R 4 are respectively and independently selected from an alkyl group, hydrogen, an aryl group or a derivative of the aryl group; R 5 are respectively and independently selected from hydrogen or an alkyl group; R 6 and R 7 are respectively and independently selected from an aryl group or a derivative of the aryl group. The obtained catalytic system has higher activity and excellent selectivity. The selectivity of the catalytic system to the target product 1-octene can be up to 80.05 %, which is higher than that of a most representative PNP type catalyst.

Description

Technical Field

[0001] This invention belongs to the field of homogeneous catalysis technology, and particularly relates to a selective oligomerization catalytic system and reaction method for ethylene. Background Technology

[0002] Linear α-olefins (LAOs) are typically long-chain olefins with 6 or more carbon atoms and vinyl functional groups located at the chain ends, primarily referring to 1-hexene and 1-octene. They have a wide range of industrial applications, with global demand exceeding 4 million tons (Pet. Chem. 2010, 50, 283-289; DGMK Tagungsber, 2009, 2, 63-74). These short-chain olefins are mainly consumed globally as comonomers for producing linear low-density polyethylene, and as intermediates for plasticizers and fatty acids (Angew. Chem. Int. Ed. 2013, 52, 12492-12496; Chem. Eur. J. 2014, 20, 7962-7978). The selective oligomerization of ethylene has advantages such as good atom economy and a simple process route, making it the main method for producing higher linear α-olefins such as 1-hexene, 1-octene, 1-decene, and 1-dodecene.

[0003] Over the past 20 years, in-depth research on ethylene oligomerization by academic and industrial communities has led to significant progress in this field (Coord. Chem. Rev. 2011, 255, 861-880; Organometallics. 2004, 23, 6288-6292; Organometallics. 2009, 28, 4852-4867). In 2003, Chevron-Phillips achieved the first industrial-scale production of selective trimerization of ethylene, marking a milestone in the history of ethylene oligomerization (Coor. Chem. Rev. 2011, 255, 1499-1517; Russ. J. Appl. Chem. 2008, 81, 1655-1666). Bollmann et al. of Sasol developed the first truly functional ethylene tetramerization catalytic system (J. Am. Chem. Soc. 2004, 126, 14712-14713), with a selectivity for 1-octene exceeding 70%. SK Energy researchers developed a Cr-PCCP catalyst with a selectivity for 1-octene of 60% (J. Mol. Catal. A: Chem. 2008, 283, 114-119). Currently, the process for ethylene oligomerization to 1-hexene is relatively mature, but catalytic systems for ethylene tetramerization to 1-octene are usually accompanied by a wide distribution of byproducts, and good compatibility between selectivity and activity for 1-octene has not yet been achieved. Summary of the Invention

[0004] This invention proposes an ethylene tetramerization catalyst system with high selectivity and catalytic activity for C8 linear α-olefins (1-octene) by finely adjusting the electronic properties and steric hindrance of the catalyst ligand substituents.

[0005] This invention proposes a catalyst system for the selective oligomerization of ethylene, comprising:

[0006] Ligand a;

[0007] Transition metal compound b, which is a metal compound belonging to groups IVB to VIII;

[0008] Activator C, which is a compound containing a Group IIIA metal;

[0009] The general structural formula of ligand a is shown in formula (I):

[0010]

[0011] R 1 ~R 4 Derivatives, each independently selected from alkyl, hydrogen, aryl, or aryl groups; R 5 Each is independently selected from hydrogen or alkyl groups; R 6 and R 7 Derivatives selected independently from aryl or aryl groups.

[0012] Furthermore, the alkyl group is C1-C. 10 The alkyl group; preferably, the alkyl group is selected from methyl, ethyl, n-propyl, isopropyl, cyclopentyl or cyclohexyl.

[0013] Furthermore, the aryl group is C6-C. 20 The aryl group is preferably selected from phenyl or substituted phenyl groups. More preferably, the aryl group is selected from phenyl, 4-methylphenyl or 4-methoxyphenyl, and the substituted phenyl group is selected from 2-fluorophenyl.

[0014] Furthermore, the aryl derivatives are selected from naphthyl, substituted naphthyl, or fluorenyl.

[0015] Furthermore, transition metal compound b is a compound containing chromium, molybdenum, tungsten, cobalt, titanium, tantalum, vanadium, zirconium, iron, nickel, or palladium.

[0016] Furthermore, activator c is one or a mixture of two or more of alkylaluminum compounds and alkylaluminoxane compounds; wherein the alkylaluminoxane compounds include alkylaluminoxane compounds with volatile components removed.

[0017] Furthermore, the molar ratio of ligand a, transition metal compound b, and activator c is 1:0.5–100:0.1–5000.

[0018] This invention proposes a reaction method for selective oligomerization of ethylene, comprising an ethylene oligomerization reaction carried out in the presence of any of the above-mentioned catalyst systems.

[0019] Furthermore, the reaction is carried out in an inert solvent, which is one or more of alkanes, aromatics, alkenes, or ionic liquids; the reaction temperature is 0℃ to 200℃; and the reaction pressure is 0.1MPa to 50MPa.

[0020] This invention has the following advantages:

[0021] This invention designs a catalytic system with both high activity and excellent selectivity by studying the correlation between the selectivity of ethylene oligomerization and ligand steric hindrance and electronic effects. Its selectivity for the target product 1-octene can reach as high as 80.05%, exceeding that of the most representative PNP-type catalysts currently available. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. In the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0023] An embodiment of the present invention provides a catalyst system for the selective oligomerization of ethylene, characterized in that it comprises:

[0024] Ligand a;

[0025] Transition metal compound b, which is a metal compound belonging to groups IVB to VIII;

[0026] Activator C, which is a compound containing a Group IIIA metal;

[0027] The general structural formula of ligand a is shown in formula (I):

[0028]

[0029] R 1 ~R 4 Derivatives, each independently selected from alkyl, hydrogen, aryl, or aryl groups; R 5 Each is independently selected from hydrogen or alkyl groups; R 6 and R 7 Derivatives selected independently from aryl or aryl groups.

[0030] Among them, R 1 ~R 4 They can be the same or different. R 5 and R 1 ~R 4They can be the same or different.

[0031] The catalyst system for selective oligomerization of ethylene proposed in this invention includes ligand a, transition metal compound b, and activator c. Ligand a has the general structural formula shown in formula (I) and contains phosphorus and nitrogen atoms; transition metal compound b is a metal compound belonging to groups IVB to VIII, with a central metal atom; and activator c is a compound containing a group IIIA metal.

[0032] The ligand a proposed in this invention is an asymmetric ligand. PNP ligands possess excellent ethylene tetramerization properties, while similar PCP ligands completely lack this property. The ligand a proposed in this invention can be considered a PCPN ligand. Compared to PCP ligands, the introduction of the N atom allows the catalytic system's product distribution to shift from a broad distribution to ethylene tetramerization and ethylene trimerization. Furthermore, the steric hindrance of the N atom substituent further enhances its selectivity for 1-C8 to as high as 80.05%, surpassing that of classic PNP ligands and achieving unexpected technical effects. This catalytic system also possesses suitable catalytic activity.

[0033] In one embodiment of the present invention, the alkyl group is C1-C. 10 The alkyl group is selected from methyl, ethyl, n-propyl, isopropyl, cyclopentyl, or cyclohexyl. More preferably, the alkyl group is selected from methyl, ethyl, or n-propyl.

[0034] In one embodiment of the present invention, the aryl group is C6-C. 20 The aryl group is preferably selected from phenyl or substituted phenyl groups. More preferably, the aryl group is selected from phenyl, 4-methylphenyl, or 4-methoxyphenyl. The substituted phenyl group is selected from 2-fluorophenyl. The derivative of the aryl group is selected from naphthyl, substituted naphthyl, or fluorenyl.

[0035] In one embodiment of the present invention, the transition metal compound b is a compound containing chromium, molybdenum, tungsten, cobalt, titanium, tantalum, vanadium, zirconium, iron, nickel, or palladium. For example, the transition metal compound b can be one of CrCl3(THF)3, CrCl2(THF)2, CoCl3, and NiBr2. More preferably, the transition metal compound b is a chromium-containing transition metal compound. Selectable chromium compounds include those with the general formula CrR. n The compound shown has R in its formula. n R is an organic anion or neutral molecule. n It typically contains 1 to 10 carbon atoms, where n is an integer from 0 to 6, and chromium has a valence state of 0 to 6. Specifically, R... nThe functional group is an organic compound or its functional group containing a carboxyl group, a β-diketone group, or a hydrocarbon group. From the perspective of ease of solubility and handling, more suitable chromium compounds include one of chromium acetate, chromium isooctanoate, chromium n-octanoate, chromium acetylacetone, chromium diisoprene, chromium diphenyl, CrCl3(THF)3, CrCl2(THF)2, (phenyl)tricarbonyl chromium, and chromium hexacarbonyl.

[0036] In one embodiment of the present invention, the activator c is one or a mixture of two or more of alkylaluminum compounds and alkylaluminoxane compounds; wherein the alkylaluminoxane compounds include alkylaluminoxane compounds with volatile components removed.

[0037] Specifically, activator c can be a compound containing a Group IIIA metal, such as alkylaluminum compounds or alkylaluminoxane compounds. The alkylaluminum compound can be various trialkylaluminum compounds, such as triethylaluminum (TEA), triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, or tri-n-octylaluminum; the alkylaluminum compound can also be an alkylaluminum halide, an alkylaluminum hydride, or an alkylaluminum sesquichloride, such as diethylaluminum chloride (AlEt2Cl) and triethylaluminum chloride (Al2Et3Cl3); the alkylaluminoxane compound can be selected from methylaluminoxane (MAO), ethylaluminoxane, isobutylaluminoxane, modified aluminum oxane, and methylaluminoxane (DMAO) with volatile components removed. Preferably, activator c can be a mixture of an alkylaluminum compound and an alkylaluminoxane with volatile components removed, wherein the alkylaluminum compound is TEA and the alkylaluminoxane compound is DMAO. Preferably, the molar ratio of TEA to DMAO is 0.01 to 100, more preferably 0.1 to 10.

[0038] In this invention, TEA has a relatively weak alkylation ability, making it more suitable for the catalyst system proposed in this invention; at the same time, DMAO can shield the influence of volatile components such as toluene on the catalyst complexation process, thereby improving the activity of the catalyst system. The combination of the two can further reduce the amount of activator used.

[0039] Furthermore, the molar ratio of ligand a, transition metal compound b, and activator c is 1:0.5–100:0.1–5000.

[0040] Furthermore, the molar ratio of ligand a, transition metal compound b, and activator c is 1:0.5–100:0.1–200.

[0041] Furthermore, the molar ratio of transition metal compound b to activator c is 1:1 to 500.

[0042] Furthermore, the molar ratio of transition metal compound b to activator c is 1:1 to 200.

[0043] The preparation method of the catalyst system of the present invention will be further described below.

[0044] In one embodiment of the present invention, the preparation method of ligand a may include the following steps:

[0045] (1) Preparation of Ph2PCH2Li(TMEDA)

[0046] Take diphenylmethylphosphine, add a small amount of n-hexane, and cool in a refrigerator for 10-20 minutes. Take n-BuLi, add a small amount of n-hexane, and cool in a refrigerator for 10-20 minutes. Then, take out both reagents and slowly add n-BuLi dropwise to the prepared solution. Stir the reaction for about 30 minutes, then add N,N,N',N'-tetramethylethylenediamine (TMEDA) and continue stirring for 10 hours. After the reaction is complete, filter the solution through a sintered glass funnel to collect the yellow solid, and dry it under vacuum to obtain the product Ph2PCH2Li (TMEDA). The molar ratio of diphenylmethylphosphine:n-BuLi:TMEDA can be 1:1~2:1~2; preferably, the molar ratio of diphenylmethylphosphine:n-BuLi:TMEDA can be 1:1.05:1.

[0047] (2) Preparation of Ph2PCH2P(NR) 1 R 2 (NR) 3 R 4 )

[0048] Take ClP(NR) diluted with n-hexane 1 R 2 (NR) 3 R 4 Cool the solution in a refrigerator for 10-20 minutes. Then, add Ph₂PCH₂Li(TMEDA) to the solution in small amounts several times while stirring vigorously for 12 hours. After the reaction is complete, filter the solution using a sintered glass funnel. Remove volatile components from the filtrate by vacuum distillation to obtain a brown oily substance or solid as the product Ph₂PCH₂P(NR). 1 R 2 (NR) 3 R 4 ); where ClP(NR) 1 R 2 (NR) 3 R 4 The molar ratio of Ph₂PCH₂Li(TMEDA) can be 1:1 to 2; preferably, ClP(NR) 1 R 2 (NR) 3 R 4 The molar ratio of Ph2PCH2Li(TMEDA) can be 1:1.05.

[0049] In one embodiment of the present invention, the preparation method of the catalyst system may include the following steps:

[0050] Components a, b, and c can be premixed or directly added to the reaction system for in-situ synthesis. In other words, the catalyst can be prepared by premixing ligand a, transition metal compound b, and activator c; alternatively, ligand a, transition metal compound b, and activator c can be directly added to the reaction system for in-situ synthesis.

[0051] The reaction involving ligand a (of formula (I)), transition metal compound b, and activator c can occur via liquid-phase reaction, such as in the presence of a solvent (e.g., toluene, benzene, and their derivatives); solid-phase reaction; or in-situ reaction to generate a catalyst during oligomerization. The reaction can involve one, two, or three of the aforementioned ligands, transition metal compounds, and organometallic activators. This reaction process also constitutes the aging (pre-complexation) of the catalyst.

[0052] The method for the catalyst system of the present invention in the ethylene oligomerization reaction is further described below.

[0053] The present invention also provides a method for ethylene oligomerization, comprising an ethylene oligomerization reaction carried out in the presence of the above-described catalyst system.

[0054] In embodiments of the present invention, the reaction is carried out in an inert solvent, which is one or more of alkanes, aromatics, alkenes, or ionic liquids. Typical solvents include, but are not limited to, benzene, toluene, xylene, cumene, n-heptane, n-hexane, methylcyclohexane, cyclohexane, 1-hexene, 1-octene, ionic liquids, etc., with methylcyclohexane being preferred.

[0055] In embodiments of the present invention, the reaction temperature is 0°C to 200°C, preferably 45°C to 100°C.

[0056] In embodiments of the present invention, the pressure of the ethylene oligomerization reaction can be carried out at a pressure of 0.1 MPa to 50 MPa, preferably 1.0 MPa to 10 MPa.

[0057] In embodiments of the present invention, the concentration of the catalyst in the reaction system can range from 0.01 μmol metal / L to 1000 μmol metal / L, preferably from 0.1 μmol metal / L to 10 μmol metal / L. It should be noted that the metal here refers to the transition metal in transition metal compound b.

[0058] The following specific examples further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0059] Example 1 Preparation and application of a catalyst system for selective oligomerization of ethylene

[0060] 1. Ligand synthesis

[0061] Preparation of (diphenylphosphinomethyl)-N,N,N',N'-tetraethylphosphinediamine (L1)

[0062] The L1 structure is as follows:

[0063]

[0064] Among them, R 1 -R 4 For ethyl, R 5 For hydrogen, R 6 and R 7 It is a phenyl group.

[0065] Take 10 g of diphenylmethylphosphine (50 mmol, PPh₂CH₃) and add an appropriate amount of n-hexane to the solution and store it in a refrigerator. Take 22 mL of n-BuLi (2.4 M) and cool it in a refrigerator for 10-20 min. Then take out the two reagents and slowly add n-BuLi dropwise to the solution. Stir the reaction for about 30 min. Take 5.58 g of N,N,N',N'-tetramethylethylenediamine (5.58 g, 52 mmol) and slowly add it dropwise to the solution. Stir for 10 h, filter, and remove volatile components from the obtained solid by vacuum distillation to obtain the product PPh₂CH₂Li (TMEDA) as a yellow solid.

[0066] Dissolve 0.84 g (4 mmol) of di(diethylamino)phosphorus chloride in an appropriate amount of n-hexane and cool in a refrigerator for 30 min. While stirring vigorously, add small amounts of PPh₂CH₂Li(TMEDA) (1.3 g, 4.05 mmol) to the above solution in several batches, stirring overnight. Filter and remove volatile components by vacuum distillation to obtain product L1, a brown oily substance.

[0067] The structures of all the products obtained in the experiment were verified to be correct by NMR spectroscopy. 1 H NMR (400MHz, CDCl3) δ = 7.48 (m, 4H), δ = 7.30-7.29 (m, 6H), δ = 3.02-2.99 (m, 8H), δ = 2.46, 2.45 (d, 8H, J = 4Hz), δ = 1.02-0.99 (12, 6H). 31 P NMR (162MHz, CDCl3) δ = 80.85, 79.90 (d, J = 153.9Hz), δ = -22.11, -23.06 (d, J = 153.9Hz). 13C NMR (100MHz, CDCl3) δ = 140.37, 140.29, 140.22, 140.14, 133.03, 133.01, 132.83, 132. 82,128.33,128.26,42.67,42.51,28.76,28.60,28.55,28.40,14.92,14.89.HRMS (EIS + ):m / z=375.42([M+H] + ).

[0068] 2. Catalyst Preparation

[0069] Add 20 mL of undehydrated methylcyclohexane, (diphenylphosphinomethyl)-N,N,N',N'-tetraethylphosphinediamine (L1) (1.2 mg, 3.15 μmol), and CrCl3·(THF)3 (1.12 mg, 3 μmol) to a stirred 100 mL reactor that has been fully purged with N2. React at room temperature for 5 min and then set aside.

[0070] 3. Ethylene oligomerization reaction

[0071] A 100 mL low-pressure reactor was evacuated for 20 min, purged with nitrogen several times, and then purged with ethylene. The reactor was heated to a predetermined temperature, and 20 mL of dehydrated methylcyclohexane, 0.87 mL of MAO (1.5 mmol), and the aforementioned ligand L1 were added. The oligomerization reaction was carried out at 30 °C and 1 MPa. After reacting for 30 min, the reactor was cooled in an ice bath and depressurized. The reaction was terminated with 10% (w / w) acidified ethanol.

[0072] Example 2

[0073] Same as Example 1. The difference is that, in the ligand, R 1 R 2 Methyl, R 3 R 4 The product is methyl. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0074] Example 3

[0075] Same as Example 1. The difference is that, in the ligand, R 1 R 2 Isopropyl, R 3 R 4 It is isopropyl. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0076] Example 4

[0077] Same as Example 1. The difference is that, in the ligand, R 1 R 2 Cyclopentyl, R 3 R 4 It is cyclopentyl. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0078] Example 5

[0079] Same as Example 1. The difference is that, in the ligand, R 1 R 2 It is 2-fluorophenyl, R 3 R 4 It is 2-fluorophenyl. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0080] Example 6

[0081] Same as Example 1. The difference is that the reaction temperature is 30°C. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0082] Example 7

[0083] Same as Example 1. The difference is that the reaction temperature is 70°C. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0084] Example 8

[0085] Same as Example 1. The difference is that the reaction temperature is 90℃. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0086] Example 9

[0087] Same as Example 1. The difference is R 5 It is cyclopentyl. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0088] Example 10

[0089] Same as Example 1. The difference is that the reaction pressure is 2.0 MPa. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0090] Example 11

[0091] Same as Example 1. The difference is that the reaction pressure is 3.0 MPa. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0092] Example 12

[0093] Same as Example 1. The difference is that the reaction pressure is 4.0 MPa. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0094] Example 13

[0095] Same as Example 1. The difference is that the reaction pressure is 5.0 MPa. The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0096] Comparative Example 1

[0097] Same as Example 1. The difference lies in the structure of the ligand, as shown in the following formula:

[0098]

[0099] The distribution of oligomers is shown in Table 1, and the experimental conditions and catalytic activity are shown in Table 2.

[0100] Table 1 Comparison of carbon number distribution of oligomerization products

[0101] <![CDATA[C4]]> <![CDATA[1-C6 ＝ ]]> Methylcyclopentane Methylenecyclopentane <![CDATA[1-C8 ＝ ]]> <![CDATA[≥C 10 ]]> Example 1 14.47 14.29 2.70 4.81 55.47 8.26 Example 2 18.74 28.73 1.59 1.68 45.64 3.62 Example 3 11.99 27.34 2.83 4.67 50.45 2.72 Example 4 14.05 30.87 2.63 4.69 40.72 7.04 Example 5 14.10 34.59 3.45 4.01 40.86 2.99 Example 6 15.51 11.58 2.10 3.05 63.02 4.74 Example 7 14.06 22.55 2.54 3.96 51.03 5.86 Example 8 11.08 30.10 1.98 2.77 48.93 5.14 Example 9 11.87 33.69 2.30 3.26 45.91 2.97 Example 10 10.21 14.25 1.87 2.26 60.05 11.36 Example 11 3.14 10.19 1.12 1.27 71.51 12.77 Example 12 3.02 5.02 1.10 1.26 79.00 10.60 Example 13 1.20 4.61 0.96 0.99 80.05 12.19 Comparative Example 1 16.55 26.12 2.56 2.99 17.13 34.65

[0102] Table 2 Experimental conditions and catalyst activities of the examples and comparative examples

[0103]

[0104] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. 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 catalyst system for the selective oligomerization of ethylene, characterized in that, include: Ligand a; Transition metal compound b, which is a metal compound belonging to groups IVB to VIII; Activator C, which is a compound containing a Group IIIA metal; The general structural formula of ligand a is shown in formula (I): ； R 1 ~R 4 Derivatives, each independently selected from alkyl, hydrogen, aryl, or aryl groups; R 5 Independently selected from hydrogen; R 6 and R 7 Derivatives selected independently from aryl or aryl groups; The alkyl group is C1-C. 10 Alkyl groups; The aryl group is C6-C. 20 Aryl groups.

2. The catalyst system according to claim 1, characterized in that, The alkyl group is selected from methyl, ethyl, n-propyl, isopropyl, cyclopentyl, or cyclohexyl.

3. The catalyst system according to claim 1, characterized in that, The aryl group is selected from phenyl or substituted phenyl groups.

4. The catalyst system according to claim 3, characterized in that, The substituted phenyl group is selected from 2-fluorophenyl, 4-methylphenyl, or 4-methoxyphenyl.

5. The catalyst system according to claim 1, characterized in that, The aryl derivatives are selected from naphthyl, substituted naphthyl, or fluorenyl.

6. The catalyst system according to claim 1, characterized in that, The transition metal compound b is a compound containing chromium, molybdenum, tungsten, cobalt, titanium, tantalum, vanadium, zirconium, iron, nickel, or palladium.

7. The catalyst system according to claim 1, characterized in that, The activator c is one or a mixture of two or more of alkylaluminum compounds and alkylaluminoxane compounds; wherein the alkylaluminoxane compounds include alkylaluminoxane compounds with volatile components removed.

8. The catalyst system according to claim 1, characterized in that, The molar ratio of ligand a, transition metal compound b, and activator c is 1:0.5~100:0.1~5000.

9. A reaction method for selective oligomerization of ethylene, comprising an ethylene oligomerization reaction carried out in the presence of any one of the catalyst systems described in claims 1 to 8.

10. The reaction method according to claim 9, characterized in that, The reaction is carried out in an inert solvent, which is one or more of alkanes, aromatics, alkenes or ionic liquids; the reaction temperature is 0 ℃ to 200 ℃; and the reaction pressure is 0.1 MPa to 50 MPa.

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