Design method of ethylene tetramerization catalyst based on remote steric hindrance effect

Abstract

The invention relates to a method for improving selectivity of 1-octylene in a Cr / PCCP system by reducing steric hindrance of a ligand far-end substituent. Different from traditional trial and error type high-throughput experimental screening, the invention provides a design strategy based on a compound space, fine regulation and control of a molecular skeleton can be realized, and the design method is used for directionally guiding the design of a high-selectivity ethylene tetramerization catalyst. Comprising the following steps: carrying out catalyst molecular configuration optimization and global conformation search by using density functional theory (DFT) and CREST software, and measuring and calculating the buried volume of a specific region of a far-end substituent group on a ligand skeleton by combining an online SambVca 2.0 tool, so as to quantify the remote steric hindrance for oriented design of a new PCCP ligand with high 1-octylene selectivity. Time-consuming high-throughput experiment screening is avoided, the catalyst development cost is greatly reduced, and the economic benefit is improved.

Description

Technical Field

[0001] This invention relates to the field of catalyst design, and in particular to a method for designing ethylene tetramerization catalysts based on the long-range steric hindrance effect. The method utilizes a steric hindrance reduction strategy to design new ligands, thereby improving the selectivity of high-value 1-octene products in the system. Background Technology

[0002] Linear α-olefins are important polyolefin comonomers and crucial intermediates in the production of high-value chemicals such as plasticizers, detergents, surfactants, cosmetics, and lubricants. Polyolefin elastomers (POEs) produced using 1-octene as a comonomer possess excellent mechanical properties and processing characteristics, making them widely in demand in the polyolefin industry.

[0003] In 2002, BP first reported on PNP for ethylene trimerization. OMe The type ligand (Chem. Commun. 2002, 8, 858-859) achieves a 1-hexene selectivity of up to 91.5% by introducing a methoxy group (i.e., an OMe group) with swing-coordination capability onto the phenyl substituent of the phosphorus atom, while generating a certain amount of polyethylene byproducts. In 2004, Sasol of South Africa achieved the first selective ethylene tetramerization reaction by removing the methoxy group on the benzene ring and adjusting the substituents on the nitrogen atom of the PNP backbone (J. Am. Chem. Soc. 2004, 126, 14712–14713), with an activity as high as 591,000 (g / g Cr / h). The resulting 1-octene selectivity reached up to 66%, and the polymer PE mass percentage was about 1.0%, but the 1-hexene selectivity was less than 10%, resulting in a low coselectivity of the system (< 80%). Subsequently, they found that the carbon-bridged bisphosphine PCCP framework also exhibited catalytic activity comparable to the PNP system (J. Mol. Catal. A: Chem. 2008, 283, 114–119), but with poor selectivity, with the highest selectivity for 1-octene being only 56.8%. A series of modifications were then made to the PCCP ligand (ACS Catal. 2013, 3, 2311–2317; Catal. Commun. 2019, 121, 15-18), but the selectivity for 1-octene remained relatively low, still lagging behind the PNP system.

[0004] Zhang Jun et al. from East China University of Science and Technology disclosed a catalyst for the selective tetramerization of ethylene containing PCCP ligands and its preparation method (CN117983306A). By introducing sterically tunable diaminophosphine and cyclodiphosphonazine fragments, the catalytic activity and 1-octene selectivity were improved, but a certain amount of PE byproducts were produced. Jiang Tao et al. from Tianjin University of Science and Technology reported an asymmetric PCCP-type ligand (CN114160211B). By adjusting the steric hindrance and electronic effects of the ligand substituents, the catalyst's spatial configuration was optimized, achieving high-activity catalysis at high temperatures. The total selectivity for 1-hexene and 1-octene reached 85%–92%, significantly reducing the content of byproducts such as methylcyclopentane. China Petroleum & Chemical Corporation invented a phenyl fluorine-modified saturated PCCP ligand (CN111434670B), with a total selectivity for 1-hexene and 1-octene exceeding 92%. Other types of ethylene tetramer PCCP ligands include oxygen-doped PCCP ligands (CN109195703A) reported by IFP of France and fluorine-containing, polyalkyl-substituted unsaturated PCCP ligands (CN113583052B) reported by China Petroleum & Chemical Corporation.

[0005] Despite two decades of development, the Cr / PCCP ethylene tetramerization catalytic system still exhibits lower 1-octene selectivity compared to the classic Cr / PNP system, requiring further improvement. With the rapid advancements in artificial intelligence and data science, methods for optimizing catalyst selectivity based on machine learning models and computer molecular simulations have become a research hotspot. By selecting descriptors and using theoretical calculations to predict the percentage content of the main product, the selectivity of high-value 1-octene products can be effectively controlled. This holds promise for the targeted design and screening of highly selective PCCP ligands with industrial application potential, enabling rapid prediction and optimization of ethylene tetramerization catalyst performance and significantly improving R&D efficiency. Summary of the Invention

[0006] This invention provides a method to improve the selectivity of 1-octene in the Cr / PCCP system. The aim is to guide the design of the catalyst by regulating the steric hindrance effect at the far end, thereby promoting the insertion rate of the fourth ethylene molecule and increasing the percentage of high-value 1-octene products in the liquid phase product.

[0007] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention is a design method for an ethylene tetramerization catalyst based on the long-range steric hindrance effect, comprising the following steps: (1) Constructing an ethylene oligomerization catalyst database: The database includes ligand structures, catalyst system parameters and the corresponding percentage content of 1-octene products.

[0008] (2) Catalyst molecular conformation optimization and descriptor extraction: Density functional theory (DFT) and CREST software were used to optimize the catalyst molecular structure and search for conformations, and descriptors such as electronic, geometric structure information and steric hindrance information were extracted.

[0009] (3) Further, the spatial steric hindrance information descriptor includes the burial volume, Tolman cone angle, and sterimol parameter. The geometric information descriptor includes parameters such as bond length, bond angle, and dihedral angle.

[0010] (4) Further, the steric hindrance information includes the burial volume of a specific region on the PCCP carbon atom substituent.

[0011] (5) Further, the specific new ligand design process is as follows:

[0012] L1 is the prototype PCCP ligand first reported by Sasol (J. Mol. Catal. A: Chem. 2008, 283, 114–119), and has undergone numerous modifications, primarily focusing on the type of substituents on the carbon bridge. Two improved PCCP ligands reported in previous literature (ACS Catal. 2013, 3, 2311–2317; Catal. Commun. 2019, 121, 15-18) were selected, and their burial volumes in specific regions were calculated. For the tert-butyl PCCP ligand L2, the value was 48.1, corresponding to a 1-octene selectivity of 33.1%. For the isopropyl PCCP ligand, the value was 38.4, corresponding to a 1-octene selectivity of 61.1%. Based on these two types of benchmark ligands, a new cyclopropyl PCCP ligand was designed by reducing the distal steric hindrance effect. The burial volume of a specific region was further reduced to 35.4, and the 1-octene selectivity was further improved compared with the existing system.

[0013] (6) Further, the structural formula of the cyclopropyl PCCP ligand can also be:

[0014] Wherein, the R1 group is independently selected from hydrogen groups or C1-C30 organic groups, including but not limited to methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, sec-pentyl, isopentyl, cyclopentyl, n-hexyl, sec-hexyl, isohexyl, cyclohexyl, n-heptyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, cycloheptyl, adamantyl, methoxy, ethoxy, isopropoxy, tert-butyloxy, benzyl, p-methylbenzyl, o-methylbenzyl, m-methylbenzyl, p-tert-butylbenzyl, m-tert-butylbenzyl One or more of the following: o-tert-butylbenzyl, p-isopropylbenzyl, m-isopropylbenzyl, o-isopropylbenzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylphenyl, 2,4-dimethylphenyl, 2,4-diisopropylphenyl, 2,4-di-tert-butylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, 3,5-dimethylphenyl, 3,5-di-tert-butylphenyl, 2,4,6-trimethylphenyl, naphthyl, anthracene, biphenyl, 2-thienyl, and 3-thienyl; The R2 group is independently selected from hydrogen groups or C1-C30 organogroups, including but not limited to methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, sec-pentyl, isopentyl, cyclopentyl, n-hexyl, sec-hexyl, isohexyl, cyclohexyl, n-heptyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, cycloheptyl, adamantyl, methoxy, ethoxy, isopropoxy, tert-butyloxy, benzyl, p-methylbenzyl, o-methylbenzyl, m-methylbenzyl, p-tert-butylbenzyl, m-tert-butylbenzyl, etc. One or more of the following: o-tert-butylbenzyl, p-isopropylbenzyl, m-isopropylbenzyl, o-isopropylbenzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylphenyl, 2,4-dimethylphenyl, 2,4-diisopropylphenyl, 2,4-di-tert-butylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, 3,5-dimethylphenyl, 3,5-di-tert-butylphenyl, 2,4,6-trimethylphenyl, naphthyl, anthracene, biphenyl, 2-thienyl, and 3-thienyl; The R3 group is independently selected from hydrogen groups or C1-C30 organogroups, including but not limited to methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, sec-pentyl, isopentyl, cyclopentyl, n-hexyl, sec-hexyl, isohexyl, cyclohexyl, n-heptyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, cycloheptyl, adamantyl, methoxy, ethoxy, isopropoxy, tert-butyloxy, benzyl, p-methylbenzyl, o-methylbenzyl, m-methylbenzyl, p-tert-butylbenzyl, m-tert-butylbenzyl. One or more of the following: o-tert-butylbenzyl, p-isopropylbenzyl, m-isopropylbenzyl, o-isopropylbenzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylphenyl, 2,4-dimethylphenyl, 2,4-diisopropylphenyl, 2,4-di-tert-butylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, 3,5-dimethylphenyl, 3,5-di-tert-butylphenyl, 2,4,6-trimethylphenyl, naphthyl, anthracene, biphenyl, 2-thienyl, and 3-thienyl; The R4 group is independently selected from hydrogen groups or C1-C30 organogroups, including but not limited to methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, sec-pentyl, isopentyl, cyclopentyl, n-hexyl, sec-hexyl, isohexyl, cyclohexyl, n-heptyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, cycloheptyl, adamantyl, methoxy, ethoxy, isopropoxy, tert-butyloxy, benzyl, p-methylbenzyl, o-methylbenzyl, m-methylbenzyl, p-tert-butylbenzyl, m-tert-butylbenzyl, etc. One or more of the following: o-tert-butylbenzyl, p-isopropylbenzyl, m-isopropylbenzyl, o-isopropylbenzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylphenyl, 2,4-dimethylphenyl, 2,4-diisopropylphenyl, 2,4-di-tert-butylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, 3,5-dimethylphenyl, 3,5-di-tert-butylphenyl, 2,4,6-trimethylphenyl, naphthyl, anthracene, biphenyl, 2-thiophene, and 3-thiophene.

[0015] The catalyst system may include an activator and an additive, and the method may include the step of mixing heteroatom ligands with transition metal compounds and activators and additives in any order.

[0016] The method may include the step of generating heteroatom coordination compounds in situ from transition metal compounds and heteroatom ligands. The method may include the step of adding a pre-prepared coordination compound, made from heteroatom ligands and a transition metal compound, to a reaction mixture, or the step of adding heteroatom ligands and a transition metal compound separately to a reactor to generate heteroatom coordination compounds of the transition metal in situ. In-situ generation of heteroatom coordination compounds means the generation of a complex in a catalytic medium. Typically, heteroatom coordination compounds are generated in situ. The transition metal compound and heteroatom ligand are typically mixed (in situ and out situ) such that the metal / ligand ratio is about 0.01:100 to 10000:1, preferably 0.1:1 to 10:1.

[0017] The transition metal may be selected from chromium, molybdenum, tungsten, titanium, tantalum, vanadium, or zirconium, with chromium being preferred.

[0018] The transition metal compound that catalyzes the tetramerization of ethylene in this invention when mixed with heteroatom ligands, activators, and additives can be a simple inorganic or organic salt, coordination compound, or organometallic complex, selected from tri-tetrahydrofuran trichloride chromium complex, (benzene)tricarbonyl chromium, chromium(III) octanoate, chromium hexacarbonyl, chromium(III) acetylacetone, and chromium(III) 2-ethylhexanoate. Preferred transition metal compounds include chromium(III) acetylacetone and chromium(III) 2-ethylhexanoate.

[0019] The activator used in the method of this invention can, in principle, be any compound that produces an active catalyst when mixed with the heteroatom ligand and transition metal compound. Mixtures of activators can also be used. Suitable compounds include organoaluminum compounds, organoboron compounds, organic salts such as lithium methyl bromide and methyl magnesium bromide, and inorganic acids such as salts such as etherified tetrafluoroboric acid, silver tetrafluoroborate, and sodium hexafluoroantimonate.

[0020] Suitable organoaluminum compounds include those of formula A1R x Compounds in which each R is independently an alkyl group, an oxygen-containing group, or a halide ion, and compounds with structures such as LiAlH. Examples include trimethylaluminum (TMA), triethylaluminum (TBA), triisobutylaluminum (TIBA), tri-n-octylaluminum dichloromethylaluminum, ethylaluminum dichlorochloride, dimethylaluminum chloride, diethylaluminum chloride, aluminum isopropoxide, ethylaluminum sesquichloride, methylaluminum sesquichloride, and aluminum oxanes. Alumina oxanes are organoaluminides widely used in the art, typically oligomers, and can be prepared by controlled addition of water to an alkylaluminum compound such as trimethylaluminum. Such compounds can be linear, cyclic, cage-like, or mixtures thereof, and mixtures of different aluminum oxanes can also be used in the method. Suitable examples of organoboron compounds are cycloboroxanes, sodium borohydride, triethylborane, tris(pentafluorophenyl)borane, and tributyl borate, etc.

[0021] The activator may also be or contain compounds that act as reducing or oxidizing agents, such as sodium or zinc metal, or oxygen, etc. The activator may be selected from alkylaluminoxanes such as methylaluminoxane (MAO) and ethylaluminoxane (BAO), as well as modified alkylaluminoxanes such as modified methylaluminoxane (MMAO). Modified methylaluminoxane contains modifying groups other than methyl, such as isobutyl or n-octyl.

[0022] The transition metal and aluminoxane can be mixed in the following proportions to make the aluminum / metal ratio about 1:1 to 10000:1, preferably about 1:1 to 1000:1, more preferably 1:1 to 300:1.

[0023] It should be noted that aluminoxanes generally also contain a considerable amount of the corresponding trialkylaluminum compounds used in their preparation. The presence of these trialkylaluminum compounds in aluminoxanes is attributable to their incomplete hydrolysis with water. Any amount of trialkylaluminum compounds mentioned herein refers to those other than the alkylaluminum compounds contained within the aluminoxane.

[0024] The method can be carried out at temperatures ranging from -20 to 250°C. Temperatures in the range of 15-150°C are preferred. Particularly preferred temperatures are in the range of 30-130°C.

[0025] The method can be carried out at pressures ranging from atmospheric pressure to 50,000 kPa. Ethylene pressures in the range of 1,000-7,000 kPa are preferred. Particularly preferred pressures are in the range of 3,000-5,000 kPa. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This application specification and embodiments are merely exemplary.

[0030] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0031] Unless otherwise specified, the term "parts" in this invention refers to parts by weight.

[0032] Example 1: The present invention is described below with reference to the following embodiments, which do not limit the scope of the invention in any way. Components in the embodiments may be omitted or substituted, and although this may not be ideal, the invention can still be accomplished. These components are not essential to the invention.

[0033] Example 1-1 (Structure optimization and conformation search of cyclopropyl PCCP ligand L4)

[0034] The molecular structure of the cyclopropyl-substituted PCCP ligand was constructed, and DFT calculations were performed. After structural convergence, conformational search was conducted using CREST software to identify the lowest energy conformation. Then, the equatorial steric hindrance of the substituent was calculated using online SambVca 2.0 software to quantify long-range steric hindrance. The measured value was 35.4. Comparison with the established PCCP database indicated low long-range steric hindrance, placing it within the high 1-octene selectivity range. Based on Example 1-1, further organic synthesis was performed on the cyclopropyl PCCP ligand classified as having high 1-octene selectivity, as shown in Example 1-2. Examples 1-2 (Synthesis of cyclopropyl PCCP ligand L4) In a nitrogen-filled 50.0 mL Shrek flask, cyclopropylacetylene (0.7 g, 10.0 mmol) and 10 mL of redistilled tetrahydrofuran were added, stirred, and cooled to 0 °C. Butyllithium (4.0 mL, 2.5 M hexane solution, 10.0 mmol) was slowly added to the solution, and the mixture was stirred at this temperature for 30 minutes. Then, diphenylphosphine chloride (2.21 g, 10.0 mmol) was added dropwise, and the mixture was heated to room temperature and stirred for 1 hour. After removing volatiles under vacuum, the mixture was extracted with petroleum ether (30 mL). The resulting mixture was then filtered to remove insoluble salts, and the filtrate was dried under vacuum to give a white solid product (2.5 g, 98%).

[0035] In a nitrogen-filled Shrek flask, the above-mentioned white solid product (0.9 g, 3.5 mmol), cuprous iodide (34.0 mg, 0.2 mmol), cesium carbonate (114.0 mg, 0.4 mmol), and dried and degassed DMF (15 mL) were added. The mixture was stirred, and finally diphenylphosphine (0.7 g, 3.9 mmol) was added. The resulting mixture was stirred at 90 °C for 6 hours. After cooling to room temperature, water (20 mL) was added, and the product was extracted with ethyl acetate (15 mL × 3). The combined organic layers were dried over sodium sulfate and concentrated under reduced pressure to remove the solvent. Silica gel column chromatography was used for purification to give white solid product L4 (0.92 g, 60%).

[0036] Examples 1-3 (Ethylene tetramerization experiment of cyclopropyl PCCP ligand L4) The ethylene tetramerization reaction was carried out in a 300 mL autoclave. Before the oligomerization began, the autoclave was purged with nitrogen three times and ethylene twice. Then, methylcyclohexane was added to the autoclave, and the mixture was stirred under an ethylene atmosphere and heated to the set temperature. Pre-determined amounts of methylaluminoxane, ligand L4, and chromium precursor were added to the autoclave, and the mixture was stirred for 5 min. Ethylene was introduced into the autoclave, and the pressure was adjusted to the set value to initiate the reaction. After 30 min of reaction, the ethylene gas was shut off, and the reaction system was rapidly cooled to 20 °C. The molar ratio of methylaluminoxane, ligand L4, and chromium precursor was 600:1.2:1, and the reaction conditions were 50 °C, 4.5 MPa, and the reaction volume was 2.5 μmol of chromium per reaction. The experimental products were analyzed using a deionized water phase followed by organic phase analysis. The final oligomerization results included: 21.9% 1-hexene, 62.7% 1-octene, and 0.6% PE, confirming the system as a high 1-octene selectivity system, consistent with the prediction.

[0037] The advantage of this invention lies in that, by controlling the distal steric hindrance effect, rational PCCP ligand design can be achieved to optimize its 1-octene selectivity, avoiding time-consuming high-throughput screening, significantly shortening the catalyst development cycle, and improving the economic efficiency of production. The embodiments described above are merely preferred embodiments of the invention and are not intended to limit the scope of the invention. Various modifications and improvements made to the technical solutions of this invention by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims.

Claims

1. A method for improving the selectivity of the main product 1-octene in the Cr / PCCP ethylene tetramerization reaction, characterized in that... The structure-selectivity correlation of catalysts was used to guide the design of new ligands, with a focus on the effect of long-range steric hindrance on the selectivity of 1-octene. This included constructing an ethylene oligomerization catalyst database, optimizing the molecular conformation of catalysts, extracting descriptors, and designing molecules. The descriptors included electronic, geometric, and steric hindrance information of the catalysts. Finally, a novel Cr / PCCP ethylene tetramerization catalytic system was obtained through high-pressure ethylene oligomerization experiments, achieving a 1-octene selectivity of over 62%.

2. The structure-selective association according to claim 1, characterized in that, The electronic structure information includes HOMO orbital energies, LUMO orbital energies, and atomic charge distributions; the geometric information includes bond lengths, bond angles, and dihedral angles; the steric hindrance information includes the percentage of buried volume. V bur The parameters include the Tolman cone angle and Sterimol parameters; the ligands are carbon-bridged PCCP type ligands; the diversity of the ligands lies in the different substituents on the C and P atoms of the ligand backbone; the molecular design strategy is used to increase the mass percentage of the main product 1-octene; the descriptor extraction includes the following steps: first, the manually constructed catalyst molecular structure is optimized using the DFT method, then the automated conformation acquisition software CREST is used to perform conformation search to lock the lowest energy conformation, and this operation is repeated for each catalytic system to obtain a molecular structure database, the molecular xyz format is converted using an automated script, and then the online tool SambVca 2.0 is used to extract the descriptors.

3. The structure-selectivity association according to claim 1, characterized in that, Includes the following steps: 1) Construct a molecular model based on the catalyst structure; 2) Perform conformational search on the catalyst and extract descriptors; 3) List the mass percentages of 1-hexene and 1-octene reported in the literature; 4) Establish the structure-activity relationship; 5) Design new ligands.

4. The catalyst molecule design method based on structure-selectivity correlation according to claim 1, characterized in that, The novel PCCP ligand framework structure with a 1-octene selectivity of over 62% is as follows: ， Wherein, the ligand structural formula is: The R1 group is independently selected from hydrogen groups or C1-C30 organogroups, including but not limited to methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, sec-pentyl, isopentyl, cyclopentyl, n-hexyl, sec-hexyl, isohexyl, cyclohexyl, n-heptyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, cycloheptyl, adamantyl, methoxy, ethoxy, isopropoxy, tert-butyloxy, benzyl, p-methylbenzyl, o-methylbenzyl, m-methylbenzyl, p-tert-butylbenzyl, m-tert-butylbenzyl, etc. One or more of the following: o-tert-butylbenzyl, p-isopropylbenzyl, m-isopropylbenzyl, o-isopropylbenzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylphenyl, 2,4-dimethylphenyl, 2,4-diisopropylphenyl, 2,4-di-tert-butylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, 3,5-dimethylphenyl, 3,5-di-tert-butylphenyl, 2,4,6-trimethylphenyl, naphthyl, anthracene, biphenyl, 2-thienyl, and 3-thienyl; The R2 group is independently selected from hydrogen groups or C1-C30 organogroups, including but not limited to methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, sec-pentyl, isopentyl, cyclopentyl, n-hexyl, sec-hexyl, isohexyl, cyclohexyl, n-heptyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, cycloheptyl, adamantyl, methoxy, ethoxy, isopropoxy, tert-butyloxy, benzyl, p-methylbenzyl, o-methylbenzyl, m-methylbenzyl, p-tert-butylbenzyl, m-tert-butylbenzyl, etc. One or more of the following: o-tert-butylbenzyl, p-isopropylbenzyl, m-isopropylbenzyl, o-isopropylbenzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylphenyl, 2,4-dimethylphenyl, 2,4-diisopropylphenyl, 2,4-di-tert-butylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, 3,5-dimethylphenyl, 3,5-di-tert-butylphenyl, 2,4,6-trimethylphenyl, naphthyl, anthracene, biphenyl, 2-thienyl, and 3-thienyl; The R3 group is independently selected from hydrogen groups or C1-C30 organogroups, including but not limited to methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, sec-pentyl, isopentyl, cyclopentyl, n-hexyl, sec-hexyl, isohexyl, cyclohexyl, n-heptyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, cycloheptyl, adamantyl, methoxy, ethoxy, isopropoxy, tert-butyloxy, benzyl, p-methylbenzyl, o-methylbenzyl, m-methylbenzyl, p-tert-butylbenzyl, m-tert-butylbenzyl. One or more of the following: o-tert-butylbenzyl, p-isopropylbenzyl, m-isopropylbenzyl, o-isopropylbenzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylphenyl, 2,4-dimethylphenyl, 2,4-diisopropylphenyl, 2,4-di-tert-butylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, 3,5-dimethylphenyl, 3,5-di-tert-butylphenyl, 2,4,6-trimethylphenyl, naphthyl, anthracene, biphenyl, 2-thienyl, and 3-thienyl; The R4 group is independently selected from hydrogen groups or C1-C30 organogroups, including but not limited to methyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, tert-butyl, cyclobutyl, n-pentyl, sec-pentyl, isopentyl, cyclopentyl, n-hexyl, sec-hexyl, isohexyl, cyclohexyl, n-heptyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, cycloheptyl, adamantyl, methoxy, ethoxy, isopropoxy, tert-butyloxy, benzyl, p-methylbenzyl, o-methylbenzyl, m-methylbenzyl, p-tert-butylbenzyl, m-tert-butylbenzyl, etc. One or more of the following: o-tert-butylbenzyl, p-isopropylbenzyl, m-isopropylbenzyl, o-isopropylbenzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylphenyl, 2,4-dimethylphenyl, 2,4-diisopropylphenyl, 2,4-di-tert-butylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, 3,5-dimethylphenyl, 3,5-di-tert-butylphenyl, 2,4,6-trimethylphenyl, naphthyl, anthracene, biphenyl, 2-thiophene, and 3-thiophene.

5. The method according to claim 1, characterized in that, The catalyst structure optimization was performed using the DFT method and CREST conformation search software; the descriptor specifically refers to the burial volume descriptor; further, the burial volume is the burial volume of the substituent equatorial region, which is measured using the online web tool SambVca 2.

0.

6. The experimental method for ethylene oligomerization according to claim 1, characterized in that... The olefin feedstock is brought into contact with the catalyst system. The transition metal in the transition metal compound is selected from one of iron, cobalt, nickel, copper, titanium, vanadium, chromium, manganese, molybdenum, tungsten, nickel, or palladium. The activator includes one or a mixture of several of alkylaluminum compounds, aluminoxane compounds, and organoboron compounds. The aluminoxane compound specifically includes modified methylaluminoxane MMAO-3A. ​​The molar ratio of the ligand to the transition metal element in the transition metal compound is (0.01~100):1; the molar ratio of the activator to the transition metal element in the transition metal compound is (1~10000):

1. The specific experimental method is as follows: the ligand, transition metal compound, and activator are pre-mixed or directly added to the reaction system for in-situ synthesis, thus obtaining the catalyst for selective tetramerization of ethylene.

7. The catalyst for selective tetramerization of ethylene according to claim 1, characterized in that, This catalyst is used for the selective tetramerization of ethylene to produce 1-octene.

8. The catalyst for selective tetramerization of ethylene according to claim 1, characterized in that, The reaction is carried out in an inert solvent at a temperature of 0–200 °C and a pressure of 0.1–50 MPa. The concentration of the transition metal in the transition metal compound in the inert solvent is 0.01–10000 μmol / L.

9. The application of the catalyst for selective tetramerization of ethylene according to claim 1, characterized in that, The inert solvent includes one or a mixture of several of alkanes, aromatics, alkenes, or ionic liquids.

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