Catalyst for selective tetramerization of ethylene, preparation method and application thereof

Abstract

The present invention relates to a catalyst for selective tetramerization of ethylene, a preparation method thereof, and an application thereof. The catalyst comprises a ligand, a transition metal compound, and an activator, wherein the chemical structure of the ligand is as shown in the following formula (I): #imgabs0# wherein the groups R1 to R2 are each independently a halogen, a hydrocarbon group, a substituted heterohydrocarbon group, hydrogen, an aryl group, a heteroatom aromatic hydrocarbon, or a heterohydrocarbon group; and the groups R3 to R6 are each independently an aliphatic hydrocarbon group, a cycloalkyl group, a heterohydrocarbon group, a substituted hydrocarbon group, a substituted heterohydrocarbon group, a substituted cycloalkyl group, an aryl group, a heteroatom aromatic hydrocarbon group, a substituted aromatic hydrocarbon group, or a substituted heteroatom aromatic hydrocarbon group, and at least one of R3 to R6 is an aliphatic hydrocarbon group, a cycloalkyl group, a heterohydrocarbon group, a substituted hydrocarbon group, a substituted heterohydrocarbon group, or a substituted cycloalkyl group. Compared with the prior art, the present invention can further improve the reaction selectivity in an anhydrous system through component adjustment and process optimization.

Description

Technical Field

[0001] The present invention relates to the technical field of ethylene oligomerization reaction, and in particular to a catalyst for selective ethylene tetramerization, a preparation method and application thereof. Background Art

[0002] Linear α-olefins (LAOs) are important chemical raw materials used in the production of lubricants, surfactants, and other materials. 1-Hexene and 1-octene are essential comonomers in the synthesis of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE). (The comonomer content in LLDPE is generally 8-10%, and in HDPE, 1-2%). Ethylene oligomerization, a key method for producing linear α-olefins, significantly improves product quality compared to traditional methods such as wax cracking, coal extraction, and extraction separation, and is now widely used in industrial production.

[0003] Traditional ethylene oligomerization catalysis primarily utilizes titanium, zirconium, and iron-based catalysts. These catalytic systems primarily follow the Cossee-Arlman mechanism, whereby ethylene molecules insert into the catalyst metal center for linear chain growth. The resulting linear α-olefins typically exhibit a normal distribution and require separation and purification based on demand for industrial applications. Highly selective ethylene oligomerization, on the other hand, primarily follows a metallocyclization mechanism. The α-olefins produced exhibit a Schulz-Flory distribution, with a high peak product content. This method provides an important pathway for producing α-olefins with specific carbon numbers. In recent years, the growing demand for 1-hexene and 1-octene has made selective ethylene oligomerization a hot topic in both industrial and academic research.

[0004] Currently, reports on highly selective ethylene oligomerization primarily focus on dimerization, trimerization, and tetramerization to produce 1-butene, 1-hexene, and 1-octene. In these catalytic systems, catalyst structural control plays a key role in product distribution, and this control depends on variations in the ligand backbone and substituents. In recent years, research in this field has focused on the catalytic mechanism and ligand design of ethylene selective oligomerization, achieving some significant results. In 2002, British Petroleum reported the use of a Cr / PNP catalytic system for the selective production of 1-hexene (Chem. Commun. 2002, 858). In 2003, Phillips Petroleum achieved industrialized ethylene trimerization using its developed Phillips chromium trimerization catalyst (US Pat. No. 5,523,507). Sinopec (Yanshan) and PetroChina (Daqing) have also subsequently achieved industrialized production of 1-hexene using similar catalytic systems. The selective production of 1-octene via ethylene tetramerization is currently not commercially viable. 1-Octene can be used to produce high-quality polyethylene (PE), polyolefin elastomers (POE), lubricant base oils (PAO), plasticizers, surfactants, and other materials. Compared to 1-hexene, 1-octene has higher economic value. In 2008, Sasol synthesized a series of more stable carbon-bridged bisphosphine ligands for catalyzing the selective tetramerization of ethylene (J. Mol. Catal. A: Chem. 2008, 283, 114). In 2010, SK Energy of South Korea developed a series of dimethyl-substituted DPPE-type ligands with chiral backbones for catalyzing the selective tetramerization of ethylene (Organometallics 2010, 29, 5805). However, the activity was relatively low, reaching a maximum of only 238 kg / (g Cr / h). In 2013, Zhang et al. designed and synthesized a series of vinyl-bridged bisphosphine ligands containing a bisphenylphosphine group (-PPh2), Ph2P(R)C=C(H)PPh2, which catalyzed the selective trimerization and tetramerization of ethylene, exhibiting good catalytic activity (ACS Catal., 2013, 3, 2311). However, due to the high production of 1-hexene, the 1-octene content was only approximately 50%. Moreover, when the polymer content exceeded 1%, polymer adhesion to the wall and entanglement with the agitator blades were likely to occur, hindering the continuous operation of the industrial unit. The polymer formation was due to the poor stability of the catalyst, and the degradation products of the catalyst caused the high polymerization of ethylene. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a catalyst for selective tetramerization of ethylene and its preparation method and application.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] To further improve the selectivity for 1-octene and the activity of the catalyst system, the present invention creatively introduces one or more alkyl groups to the phosphorus atom of a vinyl-bridged bisphosphine ligand (Ph2P(R)C=C(H)PPh2) in place of the phenyl group. By introducing an alkyl group with less steric hindrance, the present invention successfully increases the 1-octene selectivity of the catalyst system to 81%. Furthermore, because the alkyl group has a stronger electron-donating capacity than the phenyl group, the introduction of the alkyl group into the ligand increases the electron cloud density of the phosphorus atom, significantly increasing the stability of the chromium metal active center, extending the catalyst life, and effectively improving the activity of the catalyst system. The increased catalyst life also reduces catalyst degradation, thereby reducing the polymer content in the reaction to 0.05-0.1%. The specific scheme is as follows:

[0008] A catalyst for selective tetramerization of ethylene, comprising a ligand, a transition metal compound, and an activator, wherein the chemical structure of the ligand is shown in the following formula (I):

[0009]

[0010] wherein the groups R1 to R2 are each independently halogen, hydrocarbon, substituted heterohydrocarbon, hydrogen, aryl, heteroaromatic or heterohydrocarbon;

[0011] The groups R3 to R6 are each independently an aliphatic hydrocarbon group, a cycloalkyl group, a heteroalkyl group, a substituted hydrocarbon group, a substituted heteroalkyl group, a substituted cycloalkyl group, an aryl group, a heteroatom aryl group, a substituted aryl group or a substituted heteroatom aryl group, and at least one of R3 to R6 is an aliphatic hydrocarbon group, a cycloalkyl group, a heteroalkyl group, a substituted hydrocarbon group, a substituted heteroalkyl group or a substituted cycloalkyl group; preferably an aliphatic hydrocarbon group.

[0012] Furthermore, the groups R1 and R2 are independently hydrogen, fluorine, chlorine, bromine, iodine, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, 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-butyl 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, anthracenyl, biphenyl, 2-thienyl, 3-thienyl.

[0013] The radicals R3 to R6 are each independently methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, sec-pentyl, isopentyl, cyclopentyl, n-hexyl, sec-hexyl, isohexyl, cyclohexyl, n-heptyl, cycloheptyl, n-octyl, n-decyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, adamantyl, methoxy, ethoxy, isopropyloxy, tert-butyloxy, benzyl, p-methylbenzyl, o-methylbenzyl, m-methylbenzyl, p-tert-butylbenzyl, m-tert-butylbenzyl, o-tert-butylbenzyl, p-isopropylbenzyl, m-isopropylbenzyl, o-isopropylbenzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylbenzyl R3 to R6 are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, sec-pentyl, isopentyl, cyclopentyl, n-hexyl, sec-hexyl, isohexyl, cyclohexyl, n-heptyl, cycloheptyl, n-octyl, n-decyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, adamantyl, methoxy, ethoxy, isopropyloxy, and tert-butyloxy.

[0014] Preferably, the radicals R1 and R2 are each independently selected from hydrogen, fluorine, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, n-heptyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, cycloheptyl, adamantyl, methoxy, ethoxy, isopropyloxy, tert-butyloxy, benzyl, p-methylbenzyl, o-methylbenzyl, m-methylbenzyl, p-isopropylbenzyl, m-isopropylbenzyl, o-isopropylbenzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, naphthyl, anthracenyl, biphenyl, 2-thienyl, and 3-thienyl.

[0015] Preferably, the radicals R3 to R6 are independently ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, n-heptyl, cycloheptyl, n-octyl, n-decyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, adamantyl, isopropoxy, tert-butyloxy, benzyl, p-methylbenzyl, o-methylbenzyl, m-methylbenzyl, p-tert-butylbenzyl, m-tert-butylbenzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylbenzene, 1,2-dimethyl ... R3 to R6 are ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, n-heptyl, cycloheptyl, n-octyl, n-decyl, 2-methylcyclopentyl, 2,6-dimethylcyclohexyl, adamantyl, isopropyloxy, and tert-butyloxy.

[0016] More preferably, R1 and R2 are independently selected from hydrogen, fluorine, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, n-heptyl, 2-methylcyclopentyl, cycloheptyl, isopropoxy, tert-butyloxy, benzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, naphthyl, anthracenyl, 2-thienyl, and 3-thienyl.

[0017] More preferably, the radicals R3 to R6 are independently selected from ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, n-heptyl, cycloheptyl, isopropoxy, tert-butyloxy, benzyl, phenyl, p-fluorophenyl, o-fluorophenyl, m-fluorophenyl, p-ethylphenyl, o-ethylphenyl, m-ethylphenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, naphthyl, anthracenyl, and at least one of R3 to R6 is selected from ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, n-heptyl, cycloheptyl, isopropoxy, tert-butyloxy.

[0018] In some embodiments, the ligand compound is one of the following substances, but it should be understood that the scope of the present invention is not limited to these examples:

[0019]

[0020]

[0021]

[0022] The transition metal in the catalyst system of the present invention can be a transition metal compound commonly used in the art. The metal atom in the transition metal compound is a metal active center and plays an important role in the catalytic process.

[0023] Furthermore, 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. Preferably, the transition metal in the transition metal compound is selected from one of chromium, cobalt, titanium, iron, nickel or palladium. More preferably, the transition metal in the transition metal compound is selected from chromium. Specifically, the corresponding transition metal compound is any chromium compound that can cause oligomerization. The selectable chromium compounds include the general formula CrR n The compound shown in the formula, wherein R n is an organic anion or a neutral molecule, R n It generally contains 1 to 15 carbon atoms, n is an integer from 0 to 6, and the valence of Cr is from 0 to 6. n The group is an organic compound or other group containing a carboxyl group, a β-diketonate group, and a hydrocarbon group. From the perspective of easy solubility and ease of operation, more suitable chromium compounds include chromium trichloride-tris(tetrahydrofuran) complex, (benzene) tricarbonyl chromium, chromium (III) octoate, hexacarbonyl chromium, chromium (III) acetylacetonate, chromium (III) naphthenate, chromium (III) 2-ethylhexanoate, chromium (III) acetate, 2,2,6,6-tetramethylheptanedione chromium (III) and chromium (III) chloride. Preferably, the chromium compound is selected from chromium trichloride-tris(tetrahydrofuran) complex, chromium (III) acetylacetonate, and chromium (III) 2-ethylhexanoate.

[0024] The activator in the catalyst system of the present invention plays an activating role in the catalyst system. The activator useful in the present invention can be any compound that forms an active catalyst when mixed with the ligand and the transition metal compound. The activator can be used alone or in combination.

[0025] Furthermore, the activator includes one or a mixture of alkyl aluminum compounds, aluminoxane compounds, organic boron compounds, inorganic acids or inorganic salts.

[0026] Specifically, the activator can be an alkylaluminum compound, which can be various trialkylaluminums, such as trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum or tri-n-octylaluminum; the alkylaluminum compound can also be an alkylaluminum halide, alkylaluminum hydride or alkylaluminum sesquichloride, such as diethylaluminum monochloride (AlEt2Cl) and triethylaluminum trichloride (Al2Et3Cl3).

[0027] Specifically, the activator can be an aluminoxane compound, which can be prepared by mixing water with an alkyl aluminum compound (e.g., trimethylaluminum). The prepared aluminoxane oligomeric compound can be a linear compound, a cyclic compound, a cage compound, or a mixture thereof. Suitable aluminoxane compounds can be selected from methylaluminoxane (MAO), ethylaluminoxane, isobutylaluminoxane, modified aluminoxane, and the methylaluminoxane DMAO of the removal of volatile components.

[0028] Specifically, suitable boron compounds may include boroxine, triethylborane, triphenylborane, tris(pentafluorophenyl)borane, etc. The organic boron compound may be used in a mixed form with an organic aluminum compound.

[0029] Preferably, the activator may be selected from methylaluminoxane (MAO), ethylaluminoxane, isobutylaluminoxane and modified methylaluminoxane (MMAO).

[0030] Furthermore, the aluminoxane compound specifically includes modified methylaluminoxane MMAO-3A.

[0031] Furthermore, the molar ratio of the ligand to the transition metal element in the transition metal compound is (0.01-100):1, preferably (0.1-10):1, more preferably (0.5-2):1;

[0032] The molar ratio of the activator to the transition metal element in the transition metal compound is (1-10000):1, preferably (1-2000):1, and more preferably (600-1000):1.

[0033] A method for preparing the catalyst for selective tetramerization of ethylene as described above comprises the following steps: pre-mixing or directly adding a ligand, a transition metal compound and an activator into a reaction system for in-situ synthesis, thereby obtaining the catalyst for selective tetramerization of ethylene.

[0034] The preparation method of the catalyst system of the present invention is further described below:

[0035] In some embodiments, the ligand represented by formula (I), the transition metal compound, and the activator may be mixed simultaneously or in any order, in the presence or absence of a solvent, to provide an active catalyst. The mixing of the catalyst components may be performed at a temperature of -20 to 250°C, and the presence of an olefin during the mixing of the catalyst components generally exhibits a protective effect, thereby providing improved catalytic performance. Further, the mixing of the catalyst components may be performed at a temperature in the range of about 20 to 100°C.

[0036] In some embodiments, a separable metal-ligand complex can be prepared in situ from a transition metal compound and a ligand of formula (I). The metal-ligand complex is then added to a reaction medium. Alternatively, the chromium compound and the ligand can be added separately to a reactor to prepare the chromium-ligand complex in situ. In situ complex preparation refers to preparing the complex in the medium where the catalytic reaction occurs, and finally, adding an activator.

[0037] An application of the above-mentioned catalyst for selective tetramerization of ethylene, wherein the catalyst is used for the selective tetramerization of ethylene to produce 1-octene.

[0038] Furthermore, the reaction is carried out in an inert solvent, the reaction temperature is 0-200°C, preferably 10-120°C, more preferably 20-100°C, and further preferably 35-60°C, the reaction pressure is 0.1-50 MPa, preferably 1.0-10 MPa, preferably 4-10 MPa, and the concentration of the transition metal in the transition metal compound in the inert solvent is 0.01-10000 μmol / L, preferably 1-500 μmol / L.

[0039] Furthermore, the inert solvent comprises one or a mixture of alkanes, aromatic hydrocarbons, alkenes or ionic liquids. Typical solvents include, but are not limited to, benzene, toluene, xylene, cumene, chlorobenzene, dichlorobenzene, fluorobenzene, n-heptane, n-hexane, methylcyclohexane, cyclohexane, 1-hexene, 1-octene, etc., preferably toluene and methylcyclohexane.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] (1) The present invention creatively introduces one or more alkyl groups to replace phenyl groups on the phosphorus atom of the vinyl-bridged bisphosphine ligand, resulting in a significant improvement in the selectivity of 1-octene;

[0042] (2) The present invention uses a specially modified methylaluminoxane as an activator, so that the catalyst system can achieve high reaction activity without the need for adding water;

[0043] (3) The present invention can further improve the selectivity of 1-octene by optimizing process parameters. DETAILED DESCRIPTION

[0044] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0045] Example 1

[0046] (1) Preparation of ligand L1

[0047] In a 50 mL Schlenk flask filled with argon, ethynylbenzene (1.0 g, 10.0 mmol) and tetrahydrofuran (10 mL) were added, stirred, and cooled to 0°C. n-Butyllithium (4.0 mL, 2.5 M solution in hexane, 10.0 mmol) was added dropwise to the solution, and stirred at this temperature for 30 minutes. Cy(Et)PCl (1.8 g, 10.0 mmol) was then added dropwise. After the addition was complete, the mixture was warmed to room temperature and stirred for 1 hour. After the reaction was complete, the volatiles were removed in vacuo, and the mixture was extracted with petroleum ether (30 mL). The resulting mixture was then filtered to remove insoluble salts, and the filtrate was dried in vacuo and purified on a silica gel column to yield the product as a white solid (2.4 g, 98.0%).

[0048] In a Schlenk tube filled with argon, the above 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 dry and degassed DMF (15 mL) were added and stirred. 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 layer was dried over sodium sulfate and concentrated under reduced pressure. Purification was performed on a silica gel column to obtain a white solid product L1 (0.8 g, 54.9%).

[0049] 1 H NMR(400MHz, CDCl3)δ=7.45-7.40(m,6H),7.37–7.29(m,5H),7.18–7.15(m,4H) ,6.66–6.60(m,1H),1.50-1.46(m,2H),1.46–1.30(m,11H),1.00-0.96(m,3H); 31 P NMR (162MHz, CDCl3) δ = -5.70 (d, J = 145.6Hz), -17.72 (d, J = 144.6Hz).

[0050]

[0051] (2) Preparation of Complex 1

[0052] Ligand L1 (215.1 mg, 0.5 mmol) and CrCl₃(THF)₃ (187.3 mg, 0.5 mmol) were added to a dry, argon-filled Schlenk reaction tube. Redistilled dichloromethane (10 mL) was added and stirred at room temperature for 2 hours. After the reaction, the mixture was filtered and the filtrate was drained. The resulting solid was washed with n-hexane (5 mL x 3) and drained to obtain 300.0 mg (0.46 mmol, 91%) of a blue powder.

[0053] Example 2

[0054] (1) Preparation of ligand L2

[0055] In a 50 mL Schlenk flask filled with argon, ethynylbenzene (1.0 g, 10.0 mmol) and redistilled tetrahydrofuran (10 mL) were added, stirred, and cooled to 0°C. n-Butyllithium (4.0 mL, 2.5 M in hexane, 10.0 mmol) was slowly added to the solution, and stirred at this temperature for 30 minutes. Et2PCl (1.2 g, 10.0 mmol) was then added dropwise, and the mixture was warmed to ambient temperature and stirred for 1 hour. After removing the volatiles in vacuo, the mixture was extracted with petroleum ether (30 mL). The resulting mixture was then filtered to remove insoluble salts, and the filtrate was dried in vacuo and purified on a silica gel column to obtain the product as a white solid (1.86 g, 98.0%).

[0056] In a Schlenk tube filled with argon, the above white solid product (0.7 g, 3.50 mmol), cuprous iodide (34 mg, 0.18 mmol), cesium carbonate (114 mg, 0.35 mmol) and dry and degassed DMF (15 mL) were added and stirred. Diphenylphosphine (0.73 g, 3.90 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 layer was dried over sodium sulfate and concentrated under reduced pressure to remove the solvent. The product was separated and purified by silica gel column to obtain a white solid product L2 (0.73 g, 55.3%).

[0057] 1 H NMR (400MHz, CDCl3) δ=7.44-7.37(m,6H),7.35-7.28(m,5H),7.17-7.13(m,4H),6.56(d,J=34.5Hz,1H),1.58-1.50(m,4H),1.00-0.93(m,6H); 31 P NMR (162MHz, CDCl3) δ = -5.51 (d, J = 163.6Hz), -20.49 (d, J = 164.0Hz);

[0058]

[0059] (2) Preparation of Complex 2

[0060] Ligand L2 (188.1 mg, 0.5 mmol) and CrCl₃(THF)₃ (187.3 mg, 0.5 mmol) were added to a dry, argon-filled Schlenk reaction tube. Redistilled dichloromethane (10 mL) was added and stirred at room temperature for 2 h. After the reaction, the mixture was filtered and the filtrate was drained. The resulting solid was washed with n-hexane (5 mL x 3) and drained to yield 242.0 mg (0.40 mmol, 80%) of a blue powder.

[0061] Example 3

[0062] (1) Preparation of ligand L3

[0063] In a 50 mL Schlenk flask filled with argon, cyclohexyl acetylene (1.1 g, 10.0 mmol) and 10 mL of redistilled tetrahydrofuran were added, stirred, and cooled to 0°C. n-Butyl lithium (4.00 mL, 2.5 M hexane solution, 10.0 mmol) was slowly added to the solution and stirred at this temperature for 30 minutes. Et2PCl (1.2 g, 10.0 mmol) was then added dropwise, and the mixture was warmed to ambient temperature and stirred for 1 hour. After removing the volatiles in vacuo, the mixture was extracted with petroleum ether (30 mL). The resulting mixture was then filtered to remove insoluble salts, and the filtrate was dried in vacuo and purified by silica gel column separation to obtain the product as a white solid (1.92 g, 98.0%).

[0064] In a Schlenk tube filled with argon, the above white solid product (686.5 mg, 3.5 mmol), cuprous iodide (34.0 mg, 0.2 mmol), cesium carbonate (114.0 mg, 0.4 mmol) and dry and degassed DMF (15 mL) were added and 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 layer was dried over magnesium sulfate and concentrated under reduced pressure to remove the solvent. The resulting residue was separated and purified on a silica gel column to obtain a white solid product L3 (0.43 g, 32.0%).

[0065] 1H NMR (400MHz, CDCl3) δ = 7.45-7.40 (m, 6H), 7.20-7.15 (m, 4H), 6.00 (d, J = 29.4Hz, 1H), 1.58-1.50 (m, 4H), 1.50-1.36 (m, 11H), 0.93-0.90 (m, 6H); 31 P NMR (162MHz, CDCl3) δ = -4.62 (d, J = 110.7Hz), -20.44 (d, J = 108.6Hz);

[0066]

[0067] (2) Preparation of Complex 3

[0068] Ligand L3 (191.1 mg, 0.5 mmol) and CrCl3(THF)3 (187.3 mg, 0.5 mmol) were added to a dry, argon-filled Schlenk reaction tube. Redistilled dichloromethane (10 mL) was added and stirred at room temperature for 2 h. After the reaction, the mixture was filtered and the filtrate was drained. The resulting solid was washed with n-hexane (5 mL x 3) and dried to give 268.9 mg (0.44 mmol, 87%) of a blue powder.

[0069] Example 4

[0070] (1) Preparation of ligand L4

[0071] In a 50 mL Schlenk flask filled with argon, cyclohexyl acetylene (1.1 g, 10.0 mmol) and 10 mL of redistilled tetrahydrofuran were added, stirred, and cooled to 0°C. n-Butyl lithium (4.00 mL, 2.5 M hexane solution, 10.0 mmol) was slowly added to the solution and stirred at this temperature for 30 minutes. Et2PCl (1.2 g, 10.0 mmol) was then added dropwise, and the mixture was warmed to ambient temperature and stirred for 1 hour. After removing the volatiles in vacuo, the mixture was extracted with petroleum ether (30 mL). The resulting mixture was then filtered to remove insoluble salts, and the filtrate was dried in vacuo and purified by silica gel column separation to obtain the product as a white solid (1.92 g, 98.0%).

[0072] In a Schlenk tube filled with argon, the above white solid product (686.5 mg, 3.5 mmol), cuprous iodide (34.0 mg, 0.2 mmol), cesium carbonate (114.0 mg, 0.4 mmol) and dry and degassed DMF (15 mL) were added and stirred, and finally ethylphenylphosphine (0.54 g, 3.90 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 layer was dried over sodium sulfate and concentrated under reduced pressure to remove the solvent. The product was separated and purified by silica gel column to obtain a white solid product L4 (0.48 g, 40.6%).

[0073] 1 H NMR (400MHz, CDCl3) δ = 7.48-7.45 (m, 3H), 7.17–7.10 (m, 2H), 5.90 (d, J = 35.0Hz, 1H), 1.58- 1.54(m,4H),1.53-1.50(m,2H),1.50-1.36(m,11H),0.93-0.90(m,6H),0.87-0.83(m,3H); 31 P NMR (162MHz, CDCl3) δ = -6.59 (d, J = 103.1Hz), -26.7 (d, J = 110.1Hz).

[0074]

[0075] (2) Preparation of Complex 4

[0076] Ligand L4 (167.1 mg, 0.5 mmol) and CrCl₃(THF)₃ (187.3 mg, 0.5 mmol) were added to a dry, argon-filled Schlenk reaction tube. Redistilled dichloromethane (10 mL) was added and stirred at room temperature for 2 h. After the reaction, the mixture was filtered and the filtrate was drained. The resulting solid was washed with n-hexane (5 mL x 3) and drained to yield 239.3 mg (0.43 mmol, 85%) of a blue powder.

[0077] Example 5

[0078] (1) Preparation of ligand L5

[0079] Referring to the procedure described in J.Am.Chem.Soc., 2007, 129, 4099., cyclohexyl acetylene (1.1 g, 10.0 mmol) and 10 mL of redistilled tetrahydrofuran were added to a 50 mL Schlenk flask filled with argon, stirred and cooled to 0°C, and n-butyl lithium (4.00 mL, 2.5 M hexane solution, 10.0 mmol) was slowly added to the solution and stirred at this temperature for 30 minutes. Ph2PCl (2.21 g, 10.0 mmol) was then added dropwise, and the mixture was warmed to ambient temperature and stirred for 1 hour. After removing volatiles in vacuo, the mixture was extracted with petroleum ether (30 mL). The resulting mixture was then filtered to remove insoluble salts, and the filtrate was dried in vacuo to obtain the product as a white solid (2.72 g, 98.0%).

[0080] In a Schlenk tube filled with argon, the above 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 dry and degassed DMF (15 mL) were added and stirred. 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 layer was dried over sodium sulfate and concentrated under reduced pressure to remove the solvent. The product was separated and purified by silica gel column to obtain a white solid product L5 (1.1 g, 66.2%).

[0081] 1 H NMR (400MHz, CDCl3) δ = 7.23-7.37 (m, 20H), 7.03 (d, J = 36.0Hz, 1H), 2.08-2.02 (m, 1H),1.49-1.52(m,4H),1.35-1.38(m,2H),1.23-1.31(m,2H),1.13-1.19(m,2H); 31 P NMR (162MHz, CDCl3) δ = -4.08 (d, J = 166.4Hz), -25.83 (d, J = 166.4Hz).

[0082]

[0083] (2) Preparation of Complex 5

[0084] Ligand L5 (226.1 mg, 0.5 mmol) and CrCl₃(THF)₃ (187.3 mg, 0.5 mmol) were added to a dry, argon-filled Schlenk reaction tube. Redistilled dichloromethane (10 mL) was added and stirred at room temperature for 2 h. After the reaction, the mixture was filtered and the filtrate was drained. The resulting solid was washed with n-hexane (5 mL x 3) and dried to yield 303.1 mg (0.44 mmol, 89%) of a blue powder.

[0085] Example 6

[0086] (1) Preparation of ligand L6

[0087] In a 50 mL Schlenk flask filled with argon, ethynylbenzene (1.0 g, 10.0 mmol) and 10 mL of redistilled tetrahydrofuran were added, stirred and cooled to 0°C. n-Butyl lithium (4.00 mL, 2.5 M hexane solution, 10.0 mmol) was slowly added to the solution and stirred at this temperature for 30 minutes. Ph2PCl (2.20 g, 10.0 mmol) was then added dropwise, and the mixture was warmed to ambient temperature and stirred for 1 hour. After removing the volatiles in vacuo, the mixture was extracted with petroleum ether (30 mL). The resulting mixture was then filtered to remove insoluble salts, and the filtrate was dried in vacuo to obtain the product as a white solid (2.80 g, 98.0%).

[0088] In a Schlenk tube filled with argon, the above white solid product (1.0 g, 3.5 mmol), cuprous iodide (34.0 mg, 0.2 mmol), cesium carbonate (114.0 mg, 0.4 mmol) and dry and degassed DMF (15 mL) were added and stirred. 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 layer was dried over sodium sulfate and concentrated under reduced pressure to remove the solvent. The product was separated and purified by silica gel column to obtain a white solid product L6 (1.0 g, 60.7%).

[0089] 11 H NMR (400MHz, CDCl3) δ=6.86–6.90(m,2H),6.96–7.05(m,3H),7.10–7.20(m,6H),7.21-7.30(m,11H),7.35–7.41(m,4H); 31 P NMR (162MHz, CDCl3) δ = –27.19 (d, J = 144.8Hz), – 6.24 (d, J = 144.8Hz).

[0090]

[0091] (2) Preparation of Complex 6

[0092] Ligand L6 (236.1 mg, 0.5 mmol) and CrCl₃(THF)₃ (187.3 mg, 0.5 mmol) were added to a dry, argon-filled Schlenk reaction tube. Redistilled dichloromethane (10 mL) was added and stirred at room temperature for 2 h. After the reaction, the mixture was filtered and the filtrate was drained. The resulting solid was washed with n-hexane (5 mL x 3) and drained to yield 203.0 mg (0.42 mmol, 83%) of a blue powder.

[0093] Example 7

[0094] (1) Preparation of ligand L7

[0095] In a 50 mL Schlenk flask filled with argon, tert-butylacetylene (0.8 g, 10.0 mmol) and 10 mL of redistilled tetrahydrofuran were added, stirred and cooled to 0°C. n-Butyl lithium (4.00 mL, 2.5 M hexane solution, 10.0 mmol) was slowly added to the solution and stirred at this temperature for 30 minutes. Ph2PCl (2.20 g, 10.0 mmol) was then added dropwise, and the mixture was warmed to ambient temperature and stirred for 1 hour. After removing the volatiles in vacuo, the mixture was extracted with petroleum ether (30 mL). The resulting mixture was then filtered to remove insoluble salts, and the filtrate was dried in vacuo to obtain the product as a white solid (2.60 g, 95.8%).

[0096] In a Schlenk tube filled with argon, the above white solid product (931.4 mg, 3.5 mmol), cuprous iodide (34.0 mg, 0.2 mmol), cesium carbonate (114.0 mg, 0.4 mmol) and dry and degassed DMF (15 mL) were added and stirred. 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 layer was dried over sodium sulfate and concentrated under reduced pressure to remove the solvent. The product was separated and purified by silica gel column to obtain a white solid product L7 (1.1 g, 67.2%).

[0097] 1 H NMR (400MHz, CDCl3) δ = 1.26 (s, 9H), 6.94–7.07 (m, 12H), 7.20–7.27 (m, 4H), 7.31 (dd, J = 16.0, 3.5Hz, 1H), 7.62–7.68 (m, 4H); 31P NMR (162MHz, CDCl3) δ = –30.26 (d, J = 29.3Hz), – 11.35 (d, J = 29.3Hz).

[0098]

[0099] (2) Preparation of Complex 7

[0100] Ligand L7 (226.1 mg, 0.5 mmol) and CrCl₃(THF)₃ (187.3 mg, 0.5 mmol) were added to a dry, argon-filled Schlenk reaction tube. Redistilled dichloromethane (10 mL) was added and stirred at room temperature for 2 h. After the reaction, the mixture was filtered and the filtrate was drained. The resulting solid was washed with n-hexane (5 mL x 3) and drained to yield 306.5 mg (0.45 mmol, 90.0%) of a blue powder.

[0101] Example 8

[0102] (1) Preparation of catalyst

[0103] In a dry Schlenk reaction tube filled with argon, complex 1 (0.33 mg, 0.50 μmol) and redistilled methylcyclohexane (30 ml) were added. After stirring for 5 minutes, modified methylaluminoxane MMAO-3A (0.4 mmol, 1.12 mol / L) was added and reacted at room temperature for 5 minutes before use.

[0104] (2) Ethylene polymerization

[0105] A 200mL stainless steel high-pressure gas reactor was evacuated on a 120°C oil bath for 3 hours to ensure an anhydrous and oxygen-free environment in the reactor, then cooled to the reaction temperature and replaced with ethylene gas three times in the reactor. Immediately, a dry glass syringe was used to draw the above-mentioned catalyst solution and inject it into the autoclave. The reactor was sealed, stirred, and ethylene gas was introduced. The pressure was adjusted to 4.0MPa and the reaction was stirred at 60°C for 60 minutes. After the reaction was completed, the ethylene gas supply valve was closed, cooled to 0°C, the pressure was released, the reactor was opened, and quantitative internal standard nonane was added and stirred. The reaction was subsequently quenched with approximately 30mL of a 10wt% HCl aqueous solution, and a small amount of organic phase was filtered and then subjected to GC analysis. The remaining mixture in the reactor was filtered and the solid was taken. The solid was added to a 10wt% HCl aqueous solution and stirred for 2 hours, filtered, and weighed after drying to constant weight. The data are shown in Table 1.

[0106] Example 9

[0107] The difference from Example 8 is that complex 1 is replaced by complex 2 (0.30 mg, 0.5 μmol). The data are shown in Table 1.

[0108] Example 10

[0109] The difference from Example 8 is that the complex 1 used is replaced by complex 3 (0.31 mg, 0.5 μmol). The data are shown in Table 1.

[0110] Example 11

[0111] The difference from Example 8 is that the complex 1 used is replaced by complex 4 (0.28 mg, 0.5 μmol). The data are shown in Table 1.

[0112] Example 12

[0113] The difference from Example 11 is that the ethylene oligomerization reaction is carried out at 35°C. The data are shown in Table 1.

[0114] Example 13

[0115] The difference from Example 11 is that the ethylene oligomerization reaction is carried out at 80°C. The data are shown in Table 1.

[0116] Example 14

[0117] The difference from Example 11 is that the amount of MMAO-3A used is 0.3 mmol. The data are shown in Table 1.

[0118] Example 15

[0119] The difference from Example 11 is that the amount of MMAO-3A used is 0.5 mmol. The data are shown in Table 1.

[0120] Example 16

[0121] The difference from Example 11 is that the reaction pressure of ethylene oligomerization is 2.0 MPa. The data are shown in Table 1.

[0122] Example 17

[0123] The difference from Example 11 is that the reaction pressure of ethylene oligomerization is 1.0 MPa. The data are shown in Table 1.

[0124] Comparative Example 1

[0125] The difference from Example 11 is that complex 4 is replaced by complex 5 (0.35 mg, 0.5 μmol). The data are shown in Table 1.

[0126] Comparative Example 2

[0127] The difference from Example 11 is that complex 4 is replaced by complex 6 (0.35 mg, 0.5 μmol). The data are shown in Table 1.

[0128] Comparative Example 3

[0129] The difference from Example 11 is that complex 4 is replaced by complex 7 (0.34 mg, 0.5 μmol). The data are shown in Table 1.

[0130] Table 1

[0131]

[0132] As shown in Table 1, the catalyst provided by the present invention has high catalytic activity, reaching a maximum of 3146 kg / g Cr / h, and 1-octene selectivity of 75.7%, with a maximum of 81.0%. Compared with Comparative Examples 1 to 3, the catalytic activity and 1-octene selectivity of the catalyst provided by the present invention are significantly improved, which supports the concept of the present invention.

[0133] In the present invention, the ligands L1 to L4 and the three comparative ligands L5 to L7 containing four phenyl groups, the catalytic activity and 1-octene selectivity of L1 to L4 are all higher than those of L5 to L7. Moreover, the catalysts containing L1 to L4 produce very little polymer in the reaction (0.05% to 0.1%), which is significantly less than that of L5 to L7 (1.1 to 1.3%), which mutually confirms the concept of the present invention.

[0134] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. A catalyst for selective tetramerization of ethylene, characterized in that: The catalyst comprises a ligand, a transition metal compound and an activator, wherein the chemical structure of the ligand is shown in the following formula (I): ， wherein R1 is phenyl, cyclohexyl, cyclopentyl or cycloheptyl, and R2 is hydrogen; R5 is phenyl, R6 is phenyl, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl; R3 and R4 are each independently methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclohexyl, cyclopentyl or cycloheptyl; The transition metal is Cr; The activator comprises one or a mixture of alkyl aluminum compounds, aluminoxane compounds, and organic boron compounds; The aluminoxane compound specifically includes modified methyl aluminoxane 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.

2. A method for preparing the catalyst for selective tetramerization of ethylene as claimed in claim 1, characterized in that: The method comprises the following steps: pre-mixing a ligand, a transition metal compound and an activator or directly adding them into a reaction system for in-situ synthesis, thereby obtaining a catalyst for selective tetramerization of ethylene.

3. Use of the catalyst for selective tetramerization of ethylene as claimed in claim 1, characterized in that: The catalyst is used for the selective tetramerization of ethylene to produce 1-octene.

4. Use of the catalyst for selective tetramerization of ethylene according to claim 3, 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.

5. Use of the catalyst for selective tetramerization of ethylene according to claim 4, characterized in that: The inert solvent includes one or a mixture of alkanes, aromatic hydrocarbons, alkenes or ionic liquids.

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