Iron complex, main catalyst containing iron complex, catalyst composition and ethylene oligomerization reaction method

Abstract

The invention provides an iron complex, a main catalyst containing the iron complex, a catalyst composition and an ethylene oligomerization reaction method. The iron complex provided by the invention has a structure as shown in a formula (I) and can be completely dissolved in an organic solvent, the concentration of the main catalyst can be accurately metered in industrial operation, and stable operation of reaction can be ensured. Under the action of the catalyst composition, the concentration of the main catalyst solution is uniform, accurate metering is facilitated, and the ethylene oligomerization reaction is rapid in initiation, stable in operation and good in repeatability. # imgabs0 #

Description

Technical Field

[0001] The invention relates to the technical field of ethylene polymerization, and in particular to an iron complex, a main catalyst, a catalyst composition, a preparation method of the iron complex and the main catalyst, and an ethylene polymerization reaction method. Background Art

[0002] Linear α-olefins are widely used in the fields of ethylene comonomers, surfactant synthesis intermediates, plasticizer alcohols, synthetic lubricants and oil additives. In recent years, with the continuous development of the polyolefin industry, the demand for α-olefins has grown rapidly worldwide. At present, most α-olefins are prepared by ethylene polymerization. The catalysts used in the ethylene polymerization method mainly include nickel, chromium, zirconium and aluminum. In recent years, the Brookhart group (Brookhart, M et al, J. Am. Chem. Soc., 1998, 120, 7143-7144; WO99 / 02472, 1999) and the Gibson group (Gibson, VC et al, Chem. Commun., 1998, 849-850; Chem. Eur. J., 2000, 2221-2231) have respectively discovered that some tridentate pyridine imine complexes of Fe(II) and Co(II) can catalyze ethylene polymerization. Not only are the catalytic activities of the catalysts very high, but the selectivity for α-olefins is also very high.

[0003] Sun Wenhua's research group at the Institute of Chemistry, Chinese Academy of Sciences, reported a catalyst for ethylene oligomerization (Organometallics 2006, 25, 666-677). The catalyst is 2-acetyl-1,10-phenanthroline-2,6-dimethylaniline iron (II) chloride. Under the action of cocatalyst methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), when the molar ratio of the metal aluminum in the cocatalyst to the central metal in the main catalyst is 1000, the oligomerization and polymerization activity at 40°C reaches a maximum of 3.9×10 7 g·mol(Fe) -1 ·h -1 However, in actual industrial operation, since the main catalyst cannot be well dissolved in the solvent, the concentration of the main catalyst solution cannot be accurately measured, and the catalyst feed amount cannot be smoothly controlled, resulting in reaction fluctuations and unstable operation. There are major safety hazards and cause large fluctuations in product quality. Summary of the invention

[0004] In order to solve the technical problems in the prior art that the main catalyst solution cannot be well dissolved in the solvent and its concentration cannot be accurately measured, resulting in large fluctuations in the ethylene polymerization reaction and inability to run smoothly, one of the purposes of the present invention is to provide an iron complex, which can be completely dissolved in an organic solvent as a main catalyst. In industrial operation, the concentration of the main catalyst can be accurately measured to ensure smooth operation of the reaction.

[0005] A second object of the present invention is to provide a main catalyst that can be completely dissolved in an organic solvent, so that the concentration of the main catalyst can be accurately measured during industrial operation to ensure smooth operation of the reaction.

[0006] The third object of the present invention is to provide a method for preparing the above-mentioned main catalyst or iron complex, which has simple steps and good repeatability.

[0007] A fourth object of the present invention is to provide a catalyst composition.

[0008] A fifth object of the present invention is to provide an application of the above-mentioned iron complex or main catalyst.

[0009] A sixth object of the present invention is to provide an ethylene polymerization method.

[0010] To achieve one of the above purposes, the present invention adopts the following technical solution:

[0011] An iron complex, the structural formula of which is shown in formula (I),

[0012]

[0013] In formula (I), R1-R 13 are the same or different, and are independently selected from any one of hydrogen, C1-C6 alkyl, halogen, C1-C6 alkoxy, nitro and monocyclic aromatic groups; R 14 C1-C 20 Straight chain alkyl or C3-C 20 Branched chain alkyl.

[0014] In some preferred embodiments of the present invention, in formula (I), R1-R 13 are the same or different, and are independently selected from any one of hydrogen, C1-C4 alkyl, halogen, C1-C4 alkoxy, nitro and monocyclic C6-C8 aryl; R 14 C1-C 16 Straight chain alkyl or C3-C 16 Branched chain alkyl.

[0015] In some preferred embodiments of the present invention, in formula (I), R1-R 13are the same or different, and are independently selected from any one of hydrogen, methyl, ethyl, n-propyl, isopropyl, fluorine, chlorine, bromine, methoxy, ethoxy, nitro and monocyclic C6-C7 aryl; R 14 C2-C 16 Straight chain alkyl or C3-C 16 Branched chain alkyl.

[0016] In some preferred embodiments of the present invention, in formula (I), R1-R7 are hydrogen, R8 is methyl, R9 and R 13 All are methyl, R 10 -R 12 All are hydrogen, R 14 It is ethyl, isohexyl, isooctyl or hexadecyl.

[0017] To achieve the second of the above objectives, the present invention adopts the following technical solutions:

[0018] A main catalyst comprises the above iron complex and an organic solvent.

[0019] In some preferred embodiments of the present invention, the mass ratio of the organic solvent to the iron complex is (2000-200):1; more preferably (1000-500):1.

[0020] In some preferred embodiments of the present invention, the organic solvent is selected from C5-C 20 Straight chain alkanes, C3-C 20 Branched alkanes and C3-C 20 The at least one cycloalkane is preferably selected from any one of n-hexane, cyclohexane, n-heptane and methylcyclohexane, and more preferably cyclohexane.

[0021] To achieve the second of the above objectives, the present invention adopts the following technical solutions:

[0022] A method for preparing a main catalyst comprises:

[0023] Allowing the compound represented by formula (II) and the compound represented by formula (III) to react in an organic solvent to generate an iron complex represented by formula (I), preferably, the reaction is carried out under an inert gas atmosphere;

[0024]

[0025]

[0026] Formula (I) - Formula (III), R1-R 13 The definition is the same as that of 13are the same or different, and are each independently selected from any one of hydrogen, C1-C6 alkyl, halogen, C1-C6 alkoxy, nitro and monocyclic aryl; preferably, each independently selected from any one of hydrogen, C1-C4 alkyl, halogen, C1-C4 alkoxy, nitro and monocyclic C6-C8 aryl; more preferably, each independently selected from any one of hydrogen, methyl, ethyl, n-propyl, isopropyl, fluorine, chlorine, bromine, methoxy, ethoxy, nitro and monocyclic C6-C7 aryl;

[0027] R 14 C1-C 20 Straight chain alkyl or C3-C 20 Branched alkyl, preferably C1-C 16 Straight chain alkyl or C3-C 16 More preferably, R 14 C2-C 16 Straight chain alkyl or C3-C 16 Branched chain alkyl.

[0028] In some preferred embodiments of the present invention, R1-R7 are all hydrogen, R8 is methyl, R9 and R 13 All are methyl, R 10 -R 12 All are hydrogen, R 14 It is ethyl, isohexyl, isooctyl or hexadecyl.

[0029] In some preferred embodiments of the present invention, the preparation method comprises the following steps:

[0030] S1. dispersing the compound represented by formula (II) and the compound represented by formula (III) in an organic solvent respectively to obtain a solution A containing the compound represented by formula (II) and a solution B containing the compound represented by formula (III);

[0031] S2. Mix the solution A and the solution B, preferably continue stirring for 1 h to 48 h after mixing, to obtain the main catalyst.

[0032] In some preferred embodiments of the present invention, in step S1, the molar ratio of the compound represented by formula (II) to the compound represented by formula (III) is (1.0-1.9):1, preferably (1.0-1.5):1, and more preferably (1.2-1.5):1.

[0033] In some preferred embodiments of the present invention, in step S1, the organic solvent is selected from C5-C 20 Straight chain alkanes, C3-C 20 Branched chain alkanes or C3-C 20 The cycloalkane is preferably selected from any one of n-hexane, cyclohexane, n-heptane and methylcyclohexane, and more preferably cyclohexane.

[0034] In some preferred embodiments of the present invention, the mass ratio of the compound represented by formula (II) to the organic solvent is (1500-375):1; the mass ratio of the compound represented by formula (III) to the organic solvent is (500-125):1.

[0035] In some preferred embodiments of the present invention, the inert gas is at least one of nitrogen, helium and argon, preferably nitrogen.

[0036] In some preferred embodiments of the present invention, the preparation method is carried out at a temperature of 15°C to 35°C.

[0037] A method for preparing an iron complex, characterized in that, based on the above-mentioned preparation method, it also includes a step of separating the iron complex from the main catalyst.

[0038] In some preferred embodiments of the present invention, the contact reaction is carried out under stirring conditions, the stirring speed is 300-2000 rpm, preferably 700-1000 rpm; the stirring time is 0.5-24 h, preferably 20-24 h.

[0039] According to the present invention, the stirring time can be determined according to the specific situation, and the stirring is carried out until the reactants in the solution are completely dissolved.

[0040] To achieve the fourth objective above, the present invention adopts the following technical solutions:

[0041] A catalyst composition comprising:

[0042] 1) the above-mentioned iron complex or main catalyst or the iron complex or main catalyst obtained by the above-mentioned preparation method;

[0043] 2) Aluminoxane.

[0044] In some preferred embodiments of the present invention, the aluminoxane is a C1-C6 alkyl aluminoxane or a modified C1-C6 alkyl aluminoxane. The modified aluminoxane of the present invention is a conventional commercial product.

[0045] In some preferred embodiments of the present invention, the C1-C6 alkylaluminoxane includes any one of methylaluminoxane, ethylaluminoxane and isobutylaluminoxane.

[0046] In some preferred embodiments of the present invention, the modified C1-C6 alkylaluminoxane includes any one of modified methylaluminoxane, modified ethylaluminoxane and modified isobutylaluminoxane.

[0047] In some preferred embodiments of the present invention, the molar ratio of aluminum in the aluminoxane to Fe in the main catalyst is (30-1000):1.

[0048] In some preferred embodiments of the present invention, the molar ratio of aluminum in the aluminoxane to Fe in the main catalyst is (100-700):1.

[0049] In some preferred embodiments of the present invention, the molar ratio of aluminum in the aluminoxane to Fe in the main catalyst is (300-400):1.

[0050] In some preferred embodiments of the present invention, the content of the main catalyst is 1-500 μmol / L based on the total volume of the catalyst composition.

[0051] In some preferred embodiments of the present invention, the content of the main catalyst is 10-300 μmol / L based on the total volume of the catalyst composition.

[0052] In some preferred embodiments of the present invention, the content of the main catalyst is 5-50 μmol / L based on the total volume of the catalyst composition.

[0053] To achieve the fifth objective above, the present invention adopts the following technical solutions:

[0054] Application of the above iron complex or main catalyst, or the iron complex or main catalyst prepared by the above preparation method, or the above catalyst composition in the field of ethylene polymerization.

[0055] In some preferred embodiments of the present invention, the applied temperature is 10-90°C.

[0056] In some preferred embodiments of the present invention, the applied temperature is 40-85°C.

[0057] In some preferred embodiments of the present invention, the applied temperature is 50-80°C.

[0058] To achieve the sixth objective above, the present invention adopts the following technical solution:

[0059] An ethylene oligomerization reaction method comprises: allowing ethylene to undergo an ethylene oligomerization reaction under the action of the above-mentioned catalyst composition.

[0060] In some preferred embodiments of the present invention, the reaction conditions include: reaction pressure of 0.1-30 MPa; reaction temperature of -20-150° C.; reaction time of 30-100 min.

[0061] In some preferred embodiments of the present invention, the reaction temperature is 40-60°C.

[0062] According to the present invention, too low a temperature will result in the inability to initiate the reaction, and too high a temperature will result in poor polymerization reaction. Therefore, the present invention preferably uses a reaction temperature of -20-150°C, and more preferably a reaction temperature of 40-60°C.

[0063] The above catalyst composition can be applied to the polymerization reaction of ethylene. Ethylene undergoes polymerization reaction under the action of the above catalyst composition. A specific embodiment may include the following steps: (1) replacing the reaction system by high-temperature drying, vacuum replacement and other operations to ensure that there is no water and oxygen in the reaction system; (2) using ethylene to replace the reaction system so that the reaction system is in an ethylene environment; (3) adding the catalyst composition to the reaction system and stirring it thoroughly; (4) introducing ethylene to start the polymerization reaction, maintaining the reaction pressure at 0.1-30MPa and the reaction temperature at -20-150°C for 30-100min; (5) stopping the reaction and taking the reaction product for gas chromatography (GC) analysis.

[0064] In the polymerization process, the main catalyst and aluminoxane (co-catalyst) are mixed under an ethylene atmosphere, and the polymerization activity increases with the increase of ethylene pressure.

[0065] The catalyst composition of the present invention is used to carry out ethylene polymerization, and the obtained ethylene polymerization products include C4, C6, C8, C 10 , C 12 , C 14 , C 16 , C 18 , C 20 , C 22 The selectivity of α-olefins can reach more than 96%. After the ethylene polymerization reaction is completed, GC analysis is performed, and the results show that the polymerization activity can reach 3.2×10 7 g·mol(Fe) -1 ·h -1 , and the data reproducibility is good. In addition, the remaining reaction mixture was neutralized with 5% ethanol solution acidified with dilute hydrochloric acid, and no polymer was obtained.

[0066] Compared with the prior art, the present invention has at least the following advantages or beneficial effects:

[0067] 1. The main catalyst provided by the present invention can be accurately measured in industrial operation to ensure smooth operation of the reaction, reduce potential safety hazards and energy consumption in the operation of the device, and ensure product quality.

[0068] 2. The present invention provides a method for preparing a main catalyst. The main catalyst prepared by the preparation method can be completely dissolved in an organic solvent. Therefore, the concentration of the main catalyst can be accurately measured in industrial operation to ensure smooth operation of the reaction. The preparation method has simple synthesis steps and good repeatability.

[0069] 3. The present invention provides a catalyst composition comprising the above-mentioned main catalyst. Under the action of the catalyst composition, the concentration of the main catalyst solution is uniform, which is conducive to accurate metering. The ethylene polymerization reaction is initiated quickly, runs smoothly and has good repeatability. DETAILED DESCRIPTION

[0070] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0071] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail with reference to specific embodiments below. The preparation of the main catalyst in all embodiments of the present invention is carried out at room temperature, that is, within the aforementioned specified temperature range, which has no effect on the experimental results.

[0072] In the following embodiments, unless otherwise specified, normal temperature refers to 20°C to 25°C.

[0073] Example 1

[0074] (I) Preparation of main catalyst

[0075] 1) Under nitrogen protection, 2-acetyl-1,10-phenanthroline-2,6-dimethylaniline is dissolved in cyclohexane at room temperature, wherein the molar concentration of 2-acetyl-1,10-phenanthroline-2,6-dimethylaniline is 1-4 mol / L, to obtain solution A;

[0076] 2) Under nitrogen protection, dissolving ferrous isooctanoate in cyclohexane at room temperature, wherein the molar concentration of ferrous isooctanoate is 1-4 mol / L, to obtain solution B;

[0077] 3) Under nitrogen protection, solution A and solution B were mixed and stirred for 30 min (rotation speed was 800 rpm), wherein the molar ratio of 2-acetyl-1,10-phenanthroline-2,6-dimethylaniline to ferrous isooctanoate was 1.9:1, and a transparent iron complex solution was obtained. Then, stirring was continued for 24 h without changing the rotation speed to obtain a soluble iron complex solution, wherein the concentration of elemental iron was 1 μmol / L.

[0078] (II) Ethylene polymerization reaction

[0079] (1) The reactor is replaced by high-temperature drying, vacuum replacement and other operations to ensure that there is no water and oxygen in the reactor;

[0080] (2) replacing the reactor with ethylene to place the reactor in an ethylene environment;

[0081] (3) Add 97 mL of cyclohexane and 2 mL of the iron complex solution (primary catalyst) prepared in step (i) into the reaction kettle, and then add 1 mL of methylaluminoxane solution (the solubility of aluminoxane is 2 mol / L) to make the total amount of the catalyst composition 100 mL, wherein the molar ratio of aluminum in aluminoxane to Fe in the primary catalyst is 350:1. After sufficient stirring, ethylene is introduced to start the oligomerization reaction;

[0082] (4) maintaining the ethylene pressure at 1 MPa and the reaction temperature at 50° C. for 30 min;

[0083] (5) The reaction was stopped, a small amount of the reaction product was taken out for gas chromatography (GC) analysis, and the remaining mixture was neutralized with 5% hydrochloric acid-acidified ethanol solution, and no polymer was obtained. The analysis results are shown in Table 1.

[0084] Example 2

[0085] This embodiment is substantially the same as embodiment 1, except that in step (i), the molar ratio of 2-acetyl-1,10-phenanthroline-2,6-dimethylaniline to ferrous isooctanoate is 1.5:1.

[0086] Example 3

[0087] This embodiment is substantially the same as embodiment 1, except that in step (i), the molar ratio of 2-acetyl-1,10-phenanthroline-2,6-dimethylaniline to ferrous isooctanoate is 1.2:1.

[0088] Example 4

[0089] This embodiment is substantially the same as embodiment 3, except that the ferrous isooctanoate in step (i) is replaced with ferrous dodecanoate.

[0090] Example 5

[0091] This embodiment is substantially the same as embodiment 3, except that the ferrous isooctanoate in step (i) is replaced by ferrous hexadecanoate.

[0092] Example 6

[0093] This embodiment is substantially the same as embodiment 3, except that the ferrous isooctanoate in step (a) is replaced with ferrous acetate.

[0094] Example 7

[0095] This embodiment is basically the same as embodiment 3, except that the methylaluminoxane solution in step (ii) is replaced by an ethylaluminoxane solution, and the solubility of the ethylaluminoxane solution is 2 mol / L.

[0096] Example 8

[0097] This embodiment is basically the same as embodiment 3, except that the methylaluminoxane solution in step (ii) is replaced by an isobutylaluminoxane solution, and the solubility of the isobutylaluminoxane solution is 2 mol / L.

[0098] Example 9

[0099] This example is basically the same as Example 3, except that the methylaluminoxane solution in step (ii) is replaced with an n-butyl-modified methylaluminoxane solution (obtained from commercial sources), and the solubility of the modified methylaluminoxane solution is 2 mol / L.

[0100] Example 10

[0101] This embodiment is basically the same as embodiment 3, except that the molar ratio of aluminum in aluminoxane to Fe in the main catalyst is 1000:1.

[0102] Embodiment 11

[0103] This embodiment is basically the same as embodiment 3, except that the molar ratio of aluminum in aluminoxane to Fe in the main catalyst is 500:1.

[0104] Example 12

[0105] This embodiment is basically the same as embodiment 3, except that the molar ratio of aluminum in aluminoxane to Fe in the main catalyst is 100:1.

[0106] Embodiment 13

[0107] This embodiment is substantially the same as embodiment 3, except that the temperature of the ethylene polymerization reaction is 60°C.

[0108] Embodiment 14

[0109] This embodiment is basically the same as embodiment 3, except that the temperature of the ethylene polymerization reaction is 80°C.

[0110] Test example

[0111] The ethylene polymerization products in Examples 1-14 were subjected to gas chromatography analysis. The analysis results are shown in Table 1.

[0112] Table 1

[0113]

[0114]

[0115] From the data in Table 1 above, it can be seen that, in the first aspect, the catalyst composition provided by the present invention has a very high oligomerization activity. When ethylene is subjected to an ethylene oligomerization reaction in the presence of the catalyst composition provided by the present invention, the oligomerization reaction can be initiated rapidly. In the second aspect, the catalytic activity of the ethylene oligomerization reaction using the catalyst composition is as high as 3.21×10 7 g·mol(Fe) -1 ·h -1 , indicating that the reaction system initiated by the catalyst composition provided by the present invention runs smoothly and has good repeatability, and has industrial application value; thirdly, from the results of Examples 13 and 14, it can be seen that with the increase of the reaction temperature, the catalyst composition provided by the present invention still maintains a very high activity, but the product is lighter.

[0116] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. An iron complex having a structural formula as shown in formula (I), In formula (I), R1-R 13 are the same or different, and are independently selected from any one of hydrogen, C1-C6 alkyl, halogen, C1-C6 alkoxy, nitro and monocyclic aromatic groups; R 14 C1-C 20 Straight chain alkyl or C3-C 20 Branched chain alkyl.

2. The iron complex according to claim 1, characterized in that In formula (I), R1-R 13 are the same or different, and are independently selected from any one of hydrogen, C1-C4 alkyl, halogen, C1-C4 alkoxy, nitro and monocyclic C6-C8 aryl; R 14 C1-C 16 Straight chain alkyl or C3-C 16 Branched alkyl; preferably, R1-R 13 are the same or different, and are independently selected from any one of hydrogen, methyl, ethyl, n-propyl, isopropyl, fluorine, chlorine, bromine, methoxy, ethoxy, nitro and monocyclic C6-C7 aryl; R 14 C2-C 16 Straight chain alkyl or C3-C 16 More preferably, R1-R7 are hydrogen, R8 is methyl, R9 and R 13 All are methyl, R 10 -R 12 All are hydrogen, R 14 It is ethyl, isohexyl, isooctyl or hexadecyl.

3. A main catalyst, comprising the iron complex according to claim 1 or 2 and an organic solvent; preferably, the mass ratio of the organic solvent to the iron complex is (2000-200):1; more preferably (1000-500):1, and the organic solvent is selected from C5-C 20 Straight chain alkanes, C3-C 20 Branched alkanes and C3-C 20 The at least one cycloalkane is preferably selected from any one of n-hexane, cyclohexane, n-heptane and methylcyclohexane, and more preferably cyclohexane.

4. A method for preparing a main catalyst, comprising: Allowing the compound represented by formula (II) and the compound represented by formula (III) to react in an organic solvent to generate an iron complex represented by formula (I), preferably, the reaction is carried out under an inert gas atmosphere; Formula (I) - Formula (III), R1-R 13 The definition is the same as that of 13 are the same or different, and are each independently selected from any one of hydrogen, C1-C6 alkyl, halogen, C1-C6 alkoxy, nitro and monocyclic aryl; preferably, each independently selected from any one of hydrogen, C1-C4 alkyl, halogen, C1-C4 alkoxy, nitro and monocyclic C6-C8 aryl; more preferably, each independently selected from any one of hydrogen, methyl, ethyl, n-propyl, isopropyl, fluorine, chlorine, bromine, methoxy, ethoxy, nitro and monocyclic C6-C7 aryl; R 14 C1-C 20 Straight chain alkyl or C3-C 20 Branched alkyl, preferably C1-C 16 Straight chain alkyl or C3-C 16 More preferably, R 14 C2-C 16 Straight chain alkyl or C3-C 16 Branched chain alkyl; More preferably, R1-R7 are all hydrogen, R8 is methyl, R9 and R 13 All are methyl, R 10 -R 12 All are hydrogen, R 14 It is ethyl, isohexyl, isooctyl or hexadecyl.

5. The preparation method according to claim 4, characterized in that: The preparation method comprises the following steps: S1. dispersing the compound represented by formula (II) and the compound represented by formula (III) in an organic solvent respectively to obtain a solution A containing the compound represented by formula (II) and a solution B containing the compound represented by formula (III); S2. mixing the solution A and the solution B, preferably continuing to stir for 1h-48h after mixing, to obtain the main catalyst; Preferably, in step S1, the molar ratio of the compound represented by formula (II) to the compound represented by formula (III) is (1.0-1.9):1, preferably (1.0-1.5):1, and more preferably (1.2-1.5):

1.

6. The preparation method according to claim 4 or 5, characterized in that: In step S1, the organic solvent is selected from C5-C 20 Straight chain alkanes, C3-C 20 Branched chain alkanes or C3-C 20 Cycloalkane, preferably any one selected from n-hexane, cyclohexane, n-heptane and methylcyclohexane, more preferably cyclohexane; and / or The mass ratio of the compound represented by formula (II) to the organic solvent is (1500-375):1; and / or The mass ratio of the compound represented by formula (III) to the organic solvent is (500-125):1; and / or The inert gas is at least one of nitrogen, helium and argon, preferably nitrogen; and / or The preparation method is carried out at a temperature of 15°C to 35°C.

7. A method for preparing the iron complex according to claim 1 or 2, characterized in that: Based on the preparation method described in any one of claims 4 to 6, it also includes a step of separating the iron complex from the main catalyst.

8. A catalyst composition comprising: 1) The iron complex according to claim 1 or 2, or the main catalyst according to claim 3, or the main catalyst prepared by the preparation method according to any one of claims 4 to 6, or the iron complex prepared by the preparation method according to claim 7; 2) Aluminoxane; preferably an alkylaluminoxane; more preferably a C1-C6 alkylaluminoxane or a modified C1-C6 alkylaluminoxane; further preferably, the C1-C6 alkylaluminoxane includes any one of methylaluminoxane, ethylaluminoxane and isobutylaluminoxane, preferably isobutylaluminoxane; and / or, the modified C1-C6 alkylaluminoxane includes any one of modified methylaluminoxane, modified ethylaluminoxane and modified isobutylaluminoxane, preferably modified methylaluminoxane.

9. The catalyst composition according to claim 8, characterized in that The molar ratio of the aluminum in the aluminoxane to the Fe in the iron complex or the main catalyst is (30-1000):1, preferably (100-700):1, and more preferably (300-400):

1.

10. The catalyst composition according to claim 8 or 9, characterized in that Based on the total volume of the catalyst composition, the content of the main catalyst is 1-500 μmol / L, preferably 10-300 μmol / L, and more preferably 5-50 μmol / L.

11. Use of the iron complex according to claim 1 or 2, or the main catalyst according to claim 3, or the main catalyst prepared by the preparation method according to any one of claims 4 to 6, or the iron complex prepared by the preparation method according to claim 7, or the catalyst composition according to any one of claims 8 to 10 in the field of olefin polymerization, preferably in the field of C1 to C6 olefin polymerization, more preferably in the field of C1 to C4 olefin polymerization, more preferably, the polymerization is oligomerization, and further preferably, the olefin is ethylene; Preferably, the applied temperature is 10°C to 90°C, preferably 40°C to 85°C, more preferably 50°C to 80°C.

12. An ethylene oligomerization method comprising: Allow ethylene to undergo oligomerization reaction under the action of the iron complex according to claim 1 or 2, the main catalyst according to claim 3, the main catalyst prepared by the preparation method according to any one of claims 4 to 6, the iron complex prepared by the preparation method according to claim 7, or the catalyst composition according to any one of claims 8 to 10; Preferably, the reaction conditions include: reaction pressure of 0.1 MPa to 30 MPa; reaction temperature of -20°C to 150°C, preferably 40°C to 60°C; reaction time of 30 min to 100 min.

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