A pyrrole-bridged ethylene oligomerization catalyst composition and its application

Abstract

The present invention discloses a pyrrole bridged ethylene polymerization catalyst composition and its application. The ethylene polymerization catalyst composition comprises a catalyst ligand represented by formula (I), a transition metal compound and an aluminum-containing cocatalyst, or comprises a catalyst complex represented by formula (II) and an aluminum-containing cocatalyst. The catalyst composition of the present invention has the characteristics of high catalytic activity, high selectivity, etc., and has good industrial application prospects and economic value.

Description

Technical Field

[0001] The invention relates to the field of ethylene oligomerization, specifically to the field of ethylene trimerization or ethylene tetramerization, and more specifically to a pyrrole bridged ethylene oligomerization catalyst composition and application of the composition in ethylene oligomerization or ethylene trimerization or ethylene tetramerization. Background Art

[0002] α-Olefins are important organic raw materials and chemical intermediates, mainly used in the production of high-quality polyethylene (PE), lubricant base oils, plasticizers, detergents and other fields. Among them, 1-hexene or 1-octene has a wide range of uses. The linear low-density polyethylene (LLDPE) produced by copolymerization of 1-hexene or 1-octene with ethylene can significantly improve the various properties of PE, especially the mechanical properties, optical properties, tear strength and impact strength of polyethylene. The product is very suitable for packaging films and agricultural covering films such as greenhouses and sheds. The polyolefin plastomers and polyolefin elastomers produced by copolymerization of 1-octene and ethylene currently have a large market consumption and demand. With the continuous development of the polyolefin industry, the demand for α-olefins is growing rapidly worldwide.

[0003] Ethylene oligomerization is one of the most important reactions in the olefin polymerization industry. Through oligomerization, cheap small molecule ethylene can be converted into high value-added products, namely α-olefins of different length chains. Since the 1970s, the research on olefin polymerization and oligomerization catalyzed by transition metal complexes has gradually attracted the attention of scientists. People have begun to study new catalysts and improve existing catalysts to improve the activity of catalysts and the selectivity of catalytic products. Among the many explorations, the earliest, fastest-growing and most concentrated one is the nickel-based cationic catalytic system, such as the long-reported US patents US3686351A and US3676523A, and the Shell SHOP process based on the patented technology. The Shell SHOP process involves OP bridging ligands, but the catalyst contains toxic organic phosphorus groups, and the synthesis steps are complicated and the stability is poor. Later, many patents such as OO, PN, PP and NN type coordinated nickel catalysts were developed, such as JP11060627, WO9923096A1, CN1401666A, CN1769270A, etc. However, the catalysts obtained from the above patents generally have the disadvantage that the preparation method is relatively complicated.

[0004] Sasol's patent WO2004056478A1 discloses a PNP skeleton catalyst. In the ethylene tetramerization reaction, the selectivity of the C8 component is about 66wt%, the selectivity of the C6 component is about 21wt%, of which the content of 1-hexene in the C6 component is only 82%, and the total selectivity of 1-hexene and 1-octene is about 84%. The US20100137669A1 patent discloses a PCCP symmetric skeleton catalyst. In the ethylene tetramerization reaction, the catalyst is more stable than the PNP system, and the total selectivity of 1-hexene and 1-octene does not exceed 85%.

[0005] In the above reaction systems, although by-products such as cycloolefins and cyclized products present in the C6 product can be removed by separation and purification, it is disadvantageous to the economic efficiency of the entire process. Summary of the invention

[0006] In view of the above problems existing in the prior art, the present invention provides a new pyrrole-bridged ethylene oligomerization catalyst composition. The catalyst composition of the present invention has the characteristics of high catalytic activity, high selectivity, etc., and has good industrial application prospects and economic value.

[0007] In view of the above-mentioned deficiencies in the prior art, the inventors of the present invention have conducted in-depth research on this type of phosphorus-containing catalyst and discovered a pyrrole-bridged ethylene oligomerization catalyst composition, comprising a catalyst ligand shown in formula (I), a transition metal compound and an aluminum-containing co-catalyst, or a catalyst complex shown in formula (II) and an aluminum-containing co-catalyst. The catalyst ligand or complex is a pyrrole-bridged diphosphine structure, and contains ortho-halogen substituents on the aromatic ring, with a novel structure, simple preparation and low cost. The catalyst composition of the present invention can effectively catalyze ethylene oligomerization reactions, especially ethylene trimerization and tetramerization reactions, with a catalytic activity of more than 0.8×10 8 g·mol(Cr) -1 ·h -1 , up to 3.0×10 8 g·mol(Cr) -1 ·h -1 , under different conditions, the total selectivity of 1-hexene and 1-octene is above 93wt%, and the highest can exceed 97wt%. Compared with the catalyst of the comparative example, the catalyst activity of the catalyst composition provided by the present invention is significantly improved, especially the content of 1-hexene in C6 is greatly increased, and the by-products such as cycloolefins and cyclized products are significantly reduced. Therefore, the catalyst composition of the present invention has the characteristics of high catalytic activity, high selectivity, etc., and has good industrial application prospects and economic value.

[0008] The first aspect of the present invention provides a pyrrole-bridged ethylene oligomerization catalyst composition, comprising a catalyst ligand represented by formula (I), a transition metal compound and an aluminum-containing cocatalyst, or a catalyst complex represented by formula (II) and an aluminum-containing cocatalyst,

[0009]

[0010] In formula (I), R1, R2, R3, and R4 are the same or different and are each independently selected from a hydrogen or fluorine atom;

[0011] In formula (II), R1', R2', R3', and R4' are the same or different and are independently selected from hydrogen or fluorine atoms, M is a transition metal, X is selected from halogen, and n is an integer of 1-3.

[0012] According to some embodiments of the present invention, in formula (II), M is selected from at least one of chromium, molybdenum, iron, titanium, zirconium and nickel.

[0013] According to some embodiments of the present invention, the aluminum-containing cocatalyst is an organic aluminum compound, preferably at least one selected from alkyl aluminum compounds, alkoxy aluminum compounds and alkyl aluminum chloride compounds, more preferably selected from methylaluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, diethylaluminum monochloride, ethylaluminum dichloride, ethylaluminumoxane and modified methylaluminoxane, more preferably selected from at least one of modified methylaluminoxane, methylaluminoxane and triethylaluminum. In the present invention, the modified methylaluminoxane can be an alkyl-modified methylaluminoxane, such as the conventional alkyl-modified methylaluminoxane MMAO in the art.

[0014] According to some embodiments of the present invention, the transition metal compound is selected from at least one of compounds of chromium, molybdenum, iron, titanium, zirconium and nickel; preferably, the transition metal compound is selected from at least one of chromium acetylacetonate, chromium isooctanoate, tri(tetrahydrofuran)chromium trichloride and di(tetrahydrofuran)chromium dichloride.

[0015] According to some embodiments of the present invention, the molar ratio of the transition metal compound, the catalyst ligand represented by formula (I) and the aluminum-containing co-catalyst, calculated as metal element, is 1:0.1-10:1-1000, preferably 1:0.25-2:10-700, and more preferably 1:0.5-2:100-500.

[0016] According to some embodiments of the present invention, the molar ratio of the catalyst complex represented by formula (II) to the aluminum-containing co-catalyst is 1:1-1000, preferably 1:10-700, and more preferably 1:100-500.

[0017] According to some embodiments of the present invention, the organic solvent may be an organic solvent commonly used in polymerization reactions, preferably, at least one selected from methylcyclohexane, heptane, cyclohexane, toluene and xylene.

[0018] According to a specific embodiment of the present invention, a pyrrole-bridged ethylene oligomerization catalyst composition comprises: a catalyst ligand represented by formula (I), a transition metal compound and an aluminum-containing co-catalyst;

[0019]

[0020] In formula (I), R1, R2, R3, and R4 are the same or different and are each independently selected from a hydrogen or fluorine atom.

[0021] According to another specific embodiment of the present invention, a pyrrole-bridged ethylene oligomerization catalyst composition comprises: a catalyst complex represented by formula (II) and an aluminum-containing co-catalyst,

[0022]

[0023] In formula (II), R1', R2', R3', R4' are the same or different, and are independently selected from hydrogen or fluorine atoms, M is a transition metal, X is selected from halogen, n is an integer of 1 to 3, and preferably, M is selected from at least one of chromium, molybdenum, iron, titanium, zirconium and nickel.

[0024] The second aspect of the present invention provides a method for ethylene oligomerization, comprising: carrying out ethylene oligomerization reaction in an organic solvent in the presence of the above-mentioned catalyst composition.

[0025] According to some embodiments of the present invention, the concentration of the catalyst composition is 0.1-10 μmol / L in terms of metal, based on the volume of the organic solvent. For example, when the transition metal is Cr, the concentration of the catalyst composition is 0.1-10 μmol / L in terms of Cr.

[0026] According to some embodiments of the present invention, the reaction conditions may be the reaction conditions commonly used in the art. Preferably, the reaction temperature of the ethylene oligomerization reaction is 0-200°C, preferably 0-100°C, more preferably 30-100°C.

[0027] According to some embodiments of the present invention, the reaction conditions may be the reaction conditions commonly used in the art. Preferably, the ethylene pressure of the ethylene oligomerization reaction is 0.1-20.0 MPa, preferably 0.5-5.0 MPa, more preferably 2.0-5.0 MPa.

[0028] According to some embodiments of the present invention, in the above-mentioned ethylene polymerization process, any two of the catalyst ligand, transition metal compound and aluminum-containing co-catalyst in the catalyst composition can be pre-mixed and then added to the reaction system together with the other one; or the three components of the catalyst ligand, transition metal compound and aluminum-containing co-catalyst can be directly added to the reaction system for in-situ synthesis; or the catalyst ligand, transition metal compound and aluminum-containing co-catalyst can be pre-mixed and then directly added to the reaction system in the form of a mixture.

[0029] According to some embodiments of the present invention, in the above-mentioned ethylene polymerization process, the catalyst complex and the aluminum-containing co-catalyst in the catalyst composition can be pre-mixed and then added to the reaction system together, or the catalyst complex and the aluminum-containing co-catalyst can be directly added to the reaction system.

[0030] The third aspect of the present invention provides a method for ethylene trimerization or ethylene tetramerization, comprising: carrying out ethylene trimerization or ethylene tetramerization reaction in an organic solvent in the presence of the above-mentioned catalyst composition.

[0031] According to some embodiments of the present invention, the concentration of the catalyst composition is 0.1-10 μmol / L in terms of metal, based on the volume of the organic solvent. For example, when the transition metal is Cr, the concentration of the catalyst composition is 0.1-10 μmol / L in terms of Cr.

[0032] According to some embodiments of the present invention, the reaction conditions may be the reaction conditions commonly used in the art. Preferably, the reaction temperature of the ethylene oligomerization reaction is 0-200°C, preferably 0-100°C, more preferably 30-100°C.

[0033] According to some embodiments of the present invention, the reaction conditions may be the reaction conditions commonly used in the art. Preferably, the ethylene pressure of the ethylene oligomerization reaction is 0.1-20.0 MPa, preferably 0.5-5.0 MPa, more preferably 2.0-5.0 MPa.

[0034] According to some embodiments of the present invention, in the above-mentioned ethylene polymerization process, any two of the catalyst ligand, transition metal compound and aluminum-containing co-catalyst in the catalyst composition can be pre-mixed and then added to the reaction system together with the other one; or the three components of the catalyst ligand, transition metal compound and aluminum-containing co-catalyst can be directly added to the reaction system for in-situ synthesis; or the catalyst ligand, transition metal compound and aluminum-containing co-catalyst can be pre-mixed and then directly added to the reaction system in the form of a mixture.

[0035] According to some embodiments of the present invention, in the above-mentioned ethylene polymerization process, the catalyst complex and the aluminum-containing co-catalyst in the catalyst composition can be pre-mixed and then added to the reaction system together, or the catalyst complex and the aluminum-containing co-catalyst can be directly added to the reaction system.

[0036] Beneficial effects of the present invention:

[0037] (1) The catalyst ligand or complex in the pyrrole-bridged ethylene oligomerization catalyst composition of the present invention is a pyrrole-bridged diphosphine structure, which is simple to prepare and has low cost.

[0038] (2) The pyrrole-bridged ethylene oligomerization catalyst composition of the present invention can effectively catalyze ethylene oligomerization reactions, especially ethylene trimerization and tetramerization reactions, with high catalyst activity and good product selectivity; and by-products such as cycloolefins and cyclized products in the C6 product are significantly reduced.

[0039] (3) The catalyst composition described in the present invention has the characteristics of high catalytic activity and high selectivity, and has good industrial application prospects and economic value. DETAILED DESCRIPTION

[0040] In order to make the present invention more easily understood, the present invention will be described in detail below in conjunction with embodiments. These embodiments are only for illustration and are not intended to limit the application scope of the present invention.

[0041] The test method of the present invention and the equipment used in the test are as follows:

[0042] (1) In the embodiments of the present invention, nuclear magnetic resonance is detected using a Bruker AV400 nuclear magnetic resonance instrument, wherein the detection conditions of the nuclear magnetic resonance are: deuterated chloroform is used as the solvent.

[0043] (2) Room temperature test The gas chromatography was tested using an Agilent 7890 chromatograph, wherein the detection conditions of the gas chromatography were: chromatographic column SE-54, high-purity nitrogen carrier gas, FID detector; and the column temperature was raised using a two-step program.

[0044] [Preparation Example 1]

[0045] Preparation of catalyst ligand I 1 (R1=R2=R3=R4=F)

[0046] Under nitrogen protection, N-Boc-2,5-dibromopyrrole (15mmol) and tetrahydrofuran (200mL) were added to a three-necked flask, cooled to -78°C, n-butyl lithium (30mmol) was added dropwise, stirred for 1 hour, di-(2-fluorophenyl)phosphine chloride (30mmol) was added dropwise, and after the addition was completed, the mixture was transferred to room temperature for reaction for 18 hours. After the reaction was complete, the solvent was removed under reduced pressure. The residue was dissolved in toluene (50mL) under nitrogen protection, heated to 155°C for reaction for 18 hours, and the solvent was removed under vacuum after the reaction was complete to obtain a yellow solid, which was recrystallized from toluene to obtain a white solid product, namely catalyst ligand I. 1 .

[0047] 1 H-NMR (δ, ppm, CDCl3, TMS): 6.9~7.2 (m, 16H, Ar-H), 5.9 (s, 2H, CH), 4.9 (s, 1H, NH).

[0048] [Preparation Example 2]

[0049] Preparation of catalyst ligand I 2 (R1=R2=H,R3=R4=F)

[0050] Under nitrogen protection, add N-Boc-2,5-dibromopyrrole (15mmol) and tetrahydrofuran (200mL) to a three-necked flask, cool to -78°C, add n-butyl lithium (30mmol) dropwise, stir for 1 hour, first add di-(2-fluorophenyl)phosphine chloride (15mmol), then add diphenylphosphine chloride (15mmol) half an hour later, and after adding, transfer to room temperature for 18 hours. After the reaction is complete, remove the solvent under reduced pressure. The residue is separated by column chromatography, dissolved in toluene (50mL) under nitrogen protection, heated to 155°C for 18 hours, and the solvent is removed in vacuo after the reaction is complete. The residue is recrystallized from toluene to obtain a white solid product, namely catalyst ligand I. 2 .

[0051] 1 H-NMR (δ, ppm, CDCl3, TMS): 7.0~7.3 (m, 18H, Ar-H), 6.0 (s, 2H, CH), 5.1 (s, 1H, NH).

[0052] [Preparation Example 3]

[0053] Preparation of catalyst complex II 1 (R1=R2=H, R3=R4=F, M is Cr, X is Cl, n is 2)

[0054] Under nitrogen protection, 5 mmol of catalyst ligand I 2and 5mmol CrCl3(THF)3 were transferred to a Schlenk tube, 50mL toluene solution was added, and then the temperature was raised to 80°C and stirred for 8 hours. The reaction solution was cooled to room temperature and filtered, and the obtained solid was washed with toluene and n-hexane respectively, and vacuum dried to obtain the corresponding bisphosphine chromium complex, i.e., catalyst complex II 1 .

[0055] 1 H-NMR (δ, ppm, CDCl3, TMS): 7.0~7.3 (m, 18H, Ar-H), 6.0 (s, 2H, CH), 5.1 (s, 1H, NH). Elemental analysis test C 28 H 21 Cl2CrF2NP2(calcd): C, 56.50 (56.59); H, 3.88 (3.56); N, 2.29 (2.36).

[0056] [Example 1]

[0057] A 300 mL stainless steel polymerization autoclave was used. The autoclave was heated to 80°C, evacuated and replaced with nitrogen several times, then filled with ethylene for replacement, and then cooled to the set temperature. Methylcyclohexane was then added at 40°C, and 0.5 μmol of chromium acetylacetonate and catalyst ligand I were added at the same time. 1 (obtained in Preparation Example 1) and co-catalyst modified methylaluminoxane (MMAO), the total volume of the mixed solution is 100 mL, wherein the molar ratio of chromium acetylacetonate (in terms of chromium), ligand and co-catalyst is 1:2:500, that is, ligand I 1 The added amount was 1.0 μmol / L in terms of Cr, and the added amount of MMAO was 250 μmol. The reaction pressure was controlled at 3 MPa and the temperature was 40° C. Ethylene was introduced to carry out ethylene polymerization reaction.

[0058] After half an hour, the reaction was completed, the system was cooled to room temperature, the gas phase product was collected in a gas metering tank, the liquid phase product was collected in a conical flask, and 1 mL of ethanol was added as a terminator to terminate the reaction. The gas and liquid phase products were measured and analyzed by gas chromatography (the chromatograph was HP 5890). The data results are shown in Table 1.

[0059] [Example 2]

[0060] Same as Example 1, except that the catalyst ligand I 1 Replaced with catalyst ligand I 2 The data results are shown in Table 1.

[0061] [Example 3]

[0062] A 300 mL stainless steel polymerization autoclave was used. The autoclave was heated to 80°C, evacuated and replaced with nitrogen several times, then filled with ethylene for replacement, and then cooled to the set temperature. Methylcyclohexane was then added at 40°C, followed by 0.5 μmol of catalyst complex II. 1 (R1=R2=H, R3=R4=F, M=Cr,X n =Cl2), and finally 100 μmol of co-catalyst modified methylaluminoxane (MMAO) was added, and the total volume of the mixed solution was 100 mL, wherein the molar ratio of the catalyst complex to the co-catalyst was 1: 500. The reaction pressure was controlled at 3 MPa and the temperature was 40°C, and ethylene was introduced to carry out ethylene polymerization.

[0063] After half an hour, the reaction was completed, the system was cooled to room temperature, the gas phase product was collected in a gas metering tank, the liquid phase product was collected in a conical flask, and 1 mL of ethanol was added as a terminator to terminate the reaction. The gas and liquid phase products were measured and analyzed by gas chromatography (the chromatograph was HP 5890). The data results are shown in Table 1.

[0064] [Example 4]

[0065] Same as Example 1, except that the modified methylaluminoxane is replaced by triethylaluminum. The data results are shown in Table 1.

[0066] [Example 5]

[0067] Same as Example 1, except that the reaction temperature was changed from 40° C. to 30° C. The data results are shown in Table 1.

[0068] [Example 6]

[0069] Same as Example 1, except that the reaction temperature was changed from 40° C. to 60° C. The data results are shown in Table 1.

[0070] [Example 7]

[0071] Same as Example 1, except that the reaction temperature was changed from 40° C. to 100° C. The data results are shown in Table 1.

[0072] [Example 8]

[0073] Same as Example 3, except that the reaction pressure was changed from 3 MPa to 5 MPa. The data results are shown in Table 1.

[0074] [Example 9]

[0075] The same as Example 1, except that the molar ratio of chromium acetylacetonate (calculated as chromium), ligand and co-catalyst is 1:2:500 instead of 1:0.5:100. The data results are shown in Table 1.

[0076] [Example 10]

[0077] The same as Example 1, except that the molar ratio of chromium acetylacetonate (calculated as chromium), ligand and co-catalyst is 1:2:500 instead of 1:2:700. The data results are shown in Table 1.

[0078] [Example 11]

[0079] The same as Example 1, except that the molar ratio of chromium acetylacetonate (calculated as chromium), ligand and co-catalyst is 1:2:500 instead of 1:10:1000. The data results are shown in Table 1.

[0080] [Example 12]

[0081] Same as Example 3, except that the molar ratio of the catalyst complex to the co-catalyst is 1:500 instead of 1:100. The data results are shown in Table 1.

[0082] [Example 13]

[0083] Same as Example 3, except that the molar ratio of the catalyst complex to the co-catalyst is 1:500 instead of 1:700. The data results are shown in Table 1.

[0084] [Example 14]

[0085] Same as Example 3, except that the molar ratio of the catalyst complex to the co-catalyst is 1:500 instead of 1:1000. The data results are shown in Table 1.

[0086] [Comparative Example 1]

[0087] The compound bis[(S,S)-(phenyl)2PCH(Me)CH(Me)P(phenyl)2dichloro(μ-chloro)chromium] was used to carry out the polymerization of ethylene.

[0088] The implementation method is as described in Comparative Example 2 in CN104169003A. The data results are shown in Table 1.

[0089] [Comparative Example 2]

[0090] The compound bis[(S,S)-(o-fluoro-phenyl)2PCH(Me)CH(Me)P(o-fluoro-phenyl)2dichloro(μ-chloro)chromium] was used to carry out the polymerization of ethylene.

[0091] The implementation method is as described in Example 4 of CN104169003A. The data results are shown in Table 1.

[0092] Table 1

[0093]

[0094] From the data in Table 1, it can be seen that the catalytic activity of the pyrrole-bridged bisphosphine catalyst provided by the present invention exceeds 0.8×10 8 g·mol(Cr) -1 ·h -1 , up to 3.0×10 8 g·mol(Cr) -1 ·h -1 , under different conditions, the total selectivity of 1-hexene and 1-octene is above 93wt%, and the highest can exceed 97wt%. Compared with the catalyst of comparative example 1, the catalyst activity of the catalyst composition provided by the present invention is significantly improved, especially the content of 1-hexene in C6 is greatly increased, and the by-products such as cycloolefins and cyclized products are significantly reduced; compared with the catalyst of the comparative example, the catalyst activity of the catalyst composition provided by the present invention is significantly improved, indicating that the catalyst performance described in the present invention is better. The change of the catalyst ligand or complex structure affects the coordination ability and electronic effect of the ligand or complex, and thus has a very obvious effect on the catalytic performance.

[0095] The catalyst composition of the present invention can effectively catalyze ethylene trimerization and tetramerization reactions, has rapid initiation, stable operation, good repeatability, strong practicability, and broad industrial prospects.

[0096] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, under the technical enlightenment provided by the present invention, as common knowledge in the field, other equivalent variations and improvements can also be made, which should also be regarded as the protection scope of the present invention.

Claims

1. A pyrrole-bridged ethylene oligomerization catalyst composition, comprising a catalyst ligand represented by formula (I), a transition metal compound and an aluminum-containing cocatalyst, or a catalyst complex represented by formula (II) and an aluminum-containing cocatalyst, In formula (I), R1=R2=R3=R4=F, or, R1=R2=H, R3=R4=F; In formula (II), R1'=R2'=R3'=R4'=F, or, R1'=R2'=H, R3'=R4'=F, M is selected from at least one of chromium, molybdenum, iron, titanium, zirconium and nickel, X is selected from halogen, and n is an integer of 1 to 3; The transition metal compound is selected from at least one of compounds of chromium, molybdenum, iron, titanium, zirconium and nickel; The molar ratio of the transition metal compound, the catalyst ligand represented by formula (I) and the aluminum-containing co-catalyst is 1:0.1-10:1-1000, calculated as the metal element; The molar ratio of the catalyst complex represented by formula (II) to the aluminum-containing co-catalyst is 1:1-1000.

2. The composition according to claim 1, characterized in that The aluminum-containing co-catalyst is an organic aluminum compound.

3. The composition according to claim 2, characterized in that The organic aluminum compound is at least one selected from an alkyl aluminum compound, an alkoxy aluminum compound, and an alkyl aluminum chloride compound.

4. The composition according to claim 3, characterized in that The organoaluminum compound is at least one selected from methylaluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, diethylaluminum monochloride, ethylaluminum dichloride, ethylaluminumoxane and alkyl-modified methylaluminumoxane.

5. The composition according to claim 4, characterized in that The organic aluminum compound is at least one selected from the group consisting of alkyl-modified methylaluminoxane, methylaluminoxane and triethylaluminum.

6. The composition according to claim 1, characterized in that The transition metal compound is at least one selected from chromium acetylacetonate, chromium isooctanoate, tri(tetrahydrofuran)chromium trichloride and di(tetrahydrofuran)chromium dichloride.

7. The composition according to any one of claims 1 to 6, characterized in that The molar ratio of the transition metal compound, the catalyst ligand represented by formula (I) and the aluminum-containing co-catalyst is 1:0.25-2:10-700 calculated as metal element.

8. The composition according to claim 7, characterized in that The molar ratio of the transition metal compound, the catalyst ligand represented by formula (I) and the aluminum-containing co-catalyst is 1:0.5-2:100-500, calculated as metal element.

9. The composition according to any one of claims 1 to 6, characterized in that The molar ratio of the catalyst complex represented by formula (II) to the aluminum-containing co-catalyst is 1:10-700.

10. The composition according to claim 9, characterized in that The molar ratio of the catalyst complex represented by formula (II) to the aluminum-containing co-catalyst is 1:100-500.

11. A method for the polymerization of ethylene, comprising: An ethylene oligomerization reaction is carried out in an organic solvent in the presence of the pyrrole-bridged ethylene oligomerization catalyst composition according to any one of claims 1 to 10.

12. The method according to claim 11, characterized in that Based on the volume of the organic solvent, the concentration of the catalyst composition is 0.1-10 μmol / L in terms of metal.

13. The method according to claim 11 or 12, characterized in that: The reaction temperature of the ethylene oligomerization reaction is 0-200°C; and / or, The ethylene pressure of the ethylene polymerization reaction is 0.1-20.0 MPa.

14. The method according to claim 13, characterized in that The reaction temperature of the ethylene oligomerization reaction is 0-100°C; and / or, The ethylene pressure of the ethylene polymerization reaction is 0.5-5.0 MPa.

15. The method according to claim 14, characterized in that The reaction temperature of the ethylene oligomerization reaction is 30-100°C; and / or, The ethylene pressure of the ethylene polymerization reaction is 2.0-5.0 MPa.

16. A method for ethylene trimerization or ethylene tetramerization, comprising: In the presence of the pyrrole-bridged ethylene oligomerization catalyst composition according to any one of claims 1 to 10, an ethylene trimerization or ethylene tetramerization reaction is carried out in an organic solvent.

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