A dinuclear molybdenum compound, a method for preparing the same, a catalyst for the selective oligomerization of ethylene and a method for catalyzing the oligomerization of ethylene

Abstract

This invention provides a binuclear molybdenum compound, its preparation method, a catalyst for selective oligomerization of ethylene, and a method for catalyzing ethylene oligomerization. The binuclear molybdenum compound has the structure shown in Formula I. This invention innovatively applies the binuclear molybdenum compound as the main catalyst in the field of ethylene oligomerization to prepare highly linear α-olefins, providing not only a new direction for the application of molybdenum-based catalysts but also a new approach for the development of catalysts for ethylene oligomerization. Testing showed that using the binuclear molybdenum compound as the main catalyst for selective oligomerization of ethylene yields products mainly concentrated in the C4-C10 range, with a total selectivity of over 95% for C4-C10 and a catalytic activity reaching a maximum of 795.8 kg / g(Mo).h. Furthermore, the solid content of the final polymer is as low as 0.2%.

Description

Technical Field

[0001] This invention belongs to the field of polyolefin catalysts, specifically relating to a binuclear molybdenum compound, its preparation method, a catalyst for selective oligomerization of ethylene, and a method for catalyzing the oligomerization of ethylene. Background Technology

[0002] Linear α-olefins are a class of important chemical raw materials with huge demand, among which C4-C... 24 Linear α-olefins have wide applications in the preparation of low-density polyethylene, high-density polyethylene, high-grade detergents, high-grade lubricants, surfactants, POE, and high-grade linear alcohols.

[0003] Currently, with the continuous development of the global economy, people's requirements for the performance of polyolefin materials, lubricants, base oils, and other materials are gradually increasing. The application of higher linear α-olefins such as 1-hexene, 1-octene, 1-decene, and 1-dodecene in high-performance polyolefins and high-end synthetic lubricants is constantly increasing, and their demand continues to grow. Ethylene oligomerization is one of the main methods for producing high-purity higher linear α-olefins such as 1-hexene, 1-octene, 1-decene, and 1-dodecene, generally including non-selective and selective ethylene oligomerization. Currently, domestic research focuses heavily on selective oligomerization, while research on non-selective oligomerization is relatively limited. In recent years, the mainstream catalytic system for ethylene oligomerization has been the PNP-Cr(III) catalytic system, but this system has reached a bottleneck and is unlikely to achieve significant breakthroughs. Therefore, developing new catalytic systems for ethylene oligomerization is imperative.

[0004] Molybdenum-based catalysts are catalytic systems composed of molybdenum chlorides and additives, primarily used for the production of 1,2-polybutadiene. Studies have reported the synthesis of high molecular weight 1,2-polybutadiene using catalytic systems such as MoO2(OR)2-AlR3 and MoO2(acac)2-AlR3. Additionally, reports indicate the use of MoCl5 as a catalyst for the synthesis of 1,2-polybutadiene, which improves polymerization activity and overcomes the difficulty of controlling the complex reaction system. To better systematically study the synthesis of 1,2-polybutadiene using molybdenum-based catalysts, numerous researchers have investigated the polymerization conditions of various molybdenum-based catalysts and the influence of impurities on the catalytic system. For example, Ni Shaoru's team used MoCl5OPh-R2AlOPh as a catalyst, significantly improving catalytic activity; the system yielded over 7000g of polymer after 7 hours of reaction at 50℃. Furthermore, based on research findings on pentavalent molybdenum, Yang Yuwei et al. conducted research on tetravalent molybdenum catalytic systems, finding similar patterns to the corresponding pentavalent molybdenum systems.

[0005] In summary, research on molybdenum-based catalysts mainly focuses on chlorides or modified chlorides in the IV and V valence states, with 1,2-polybutadiene as the primary target product. There are no reports of applying molybdenum-based catalysts to other fields. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a binuclear molybdenum compound, its preparation method, a catalyst for selective oligomerization of ethylene, and a method for catalyzing the oligomerization of ethylene. The binuclear molybdenum compound can be used as a main catalyst for catalyzing the oligomerization of ethylene to prepare highly linear α-olefins, while providing new ideas and directions for the application of molybdenum-based catalysts and the development of catalysts for ethylene oligomerization.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a binuclear molybdenum compound having the structure shown in Formula I:

[0009]

[0010] Among them, R1, R2, R3, R4, and R5 are each independently selected from substituted or unsubstituted C1 to C2. 10 Alkyl, substituted or unsubstituted C3-C8 cycloalkyl, or substituted or unsubstituted C6-C 18 Aryl groups.

[0011] Preferably, R1, R2, R3, R4, and R5 are each independently selected from methyl, ethyl, isopropyl, isobutyl, cyclopentyl, cyclohexyl, or substituted or unsubstituted C6-C6 groups. 12 Aryl groups.

[0012] Preferably, the binuclear molybdenum compound is selected from any one of formulas C-1 to C-6:

[0013]

[0014] Secondly, the present invention provides a method for preparing the above-mentioned binuclear molybdenum compound, comprising the following steps:

[0015] Under anhydrous and oxygen-free conditions, molybdenum trichloride tris(tetrahydrofuran)trichloride and the ligand compound shown in Formula 1 were reacted at room temperature in the presence of a solvent to obtain the binuclear molybdenum compound shown in Formula I.

[0016]

[0017] Preferably, the solvent is selected from any one or more of toluene, dichloromethane, dichloroethane, cyclohexane, n-heptane, or n-hexane.

[0018] Preferably, the molar ratio of the tri(tetrahydrofuran)trichloride molybdenum chloride and the ligand compound shown in Formula 1 is (1.5 to 2.0):1.

[0019] Thirdly, the present invention provides a catalyst for selective oligomerization of ethylene, comprising a main catalyst and an aluminum-containing co-catalyst;

[0020] The main catalyst is the binuclear molybdenum compound involved in the above technical solution.

[0021] Preferably, the aluminum-containing cocatalyst comprises alkylaluminum and / or alkoxyaluminum.

[0022] Preferably, the molar ratio of the main catalyst to the aluminum-containing co-catalyst is 1:(100-800).

[0023] Fourthly, the present invention provides a method for ethylene oligomerization, comprising the following steps:

[0024] In the presence of an organic solvent and a catalyst for selective oligomerization of ethylene, ethylene undergoes an oligomerization reaction to obtain the desired product.

[0025] Preferably, the organic solvent is selected from any one or more of n-hexane, cyclohexane, toluene, methylcyclohexane, or n-heptane.

[0026] Preferably, the oligomerization reaction is carried out at a temperature of 60–75°C.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention provides a binuclear molybdenum compound with the structure shown in Formula I, obtained by reacting trivalent molybdenum with an NPNPN ligand compound shown in Formula I. This invention breaks with the traditional application areas of molybdenum-based catalysts, innovatively applying the binuclear molybdenum compound as a catalyst in the preparation of highly linear α-olefins via ethylene oligomerization. This not only provides a new direction for the application of molybdenum-based catalysts but also offers new ideas for the development of catalysts for ethylene oligomerization. The dual active sites (i.e., binuclear molybdenum) in the binuclear molybdenum compound greatly enhance its catalytic activity as an ethylene oligomerization catalyst, while the tetrahydrofuran in the structure effectively inhibits the formation of high molecular weight polymers. Testing revealed that, compared with existing non-selective ethylene catalytic systems, the binuclear molybdenum compound provided by this invention, as a catalyst for selective ethylene oligomerization, produces products mainly concentrated between C4 and C10, with a total selectivity of over 95% for C4-C10. Specifically, the selectivity for 1-butene is greater than 99%, and the selectivities for 1-hexene, 1-octene, and 1-decene are all greater than 98%, with a maximum catalytic activity of 795.8 kg / g(Mo).h. In addition, the final polymer has a solid content of less than 0.2%, which is conducive to achieving long-term continuous production and improving production efficiency. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] To address the issue that existing molybdenum-based catalysts are mainly used in the production of 1,2-polybutadiene and in ethylene oligomerization catalysis systems where significant breakthroughs are difficult, this invention provides a binuclear molybdenum compound having the structure shown in Formula I:

[0031]

[0032] Among them, R1, R2, R3, R4, and R5 are each independently selected from substituted or unsubstituted C1 to C2. 10 Alkyl, substituted or unsubstituted C3-C8 cycloalkyl, or substituted or unsubstituted C6-C 18 Aryl groups.

[0033] In some embodiments of the present invention, the binuclear molybdenum compound has the structure shown in Formula I, wherein R1, R2, R3, R4, and R5 are each independently preferably derived from methyl, ethyl, isopropyl, isobutyl, cyclopentyl, cyclohexyl, or substituted or unsubstituted C6-C6 groups. 12 Aryl groups.

[0034] In some embodiments of the present invention, the binuclear molybdenum compound has the structure shown in Formula I, wherein R1, R2, R3, R4, and R5 are each independently preferred from methyl, ethyl, isopropyl, isobutyl, cyclopentyl, cyclohexyl, phenyl, or substituted phenyl.

[0035] In some embodiments of the present invention, the binuclear molybdenum compound is selected from any one of formulas C-1 to C-6:

[0036]

[0037] This invention breaks with the traditional application areas of molybdenum-based catalysts, innovatively applying the aforementioned binuclear molybdenum compound as the main catalyst to the preparation of highly linear α-olefins via ethylene oligomerization. This not only provides a new direction for the application of molybdenum-based catalysts but also offers new ideas for the development of catalysts for ethylene oligomerization. In this invention, the aforementioned binuclear molybdenum compound possesses dual active sites (i.e., binuclear molybdenum), which greatly enhances its catalytic activity as a main catalyst for ethylene oligomerization. Furthermore, the tetrahydrofuran present in the structure of the binuclear molybdenum compound effectively inhibits the formation of high molecular weight polymers.

[0038] The present invention also provides a method for preparing the above-mentioned binuclear molybdenum compound, comprising the following steps:

[0039] Under anhydrous and oxygen-free conditions, molybdenum trichloride tris(tetrahydrofuran)trichloride and the ligand compound shown in Formula 1 were reacted at room temperature in the presence of a solvent to obtain the binuclear molybdenum compound shown in Formula I.

[0040]

[0041] In this invention, the tris(tetrahydrofuran)trichloride molybdenum can be purchased commercially or prepared in-house. Preferred preparation method for tris(tetrahydrofuran)trichloride is the following:

[0042] Under anhydrous and oxygen-free conditions, molybdenum trichloride, zinc powder, and tetrahydrofuran are reacted to produce tri(tetrahydrofuran)molybdenum trichloride.

[0043] In this invention, it is preferred that the materials are fed and reacted under anhydrous and oxygen-free conditions, with the molar ratio of molybdenum trichloride, zinc powder and tetrahydrofuran being 1:(0.01-0.1):(10-200), more preferably 1:(0.04-0.07):(50-100).

[0044] In some embodiments of the present invention, preferably under anhydrous and oxygen-free conditions, molybdenum trichloride and zinc powder are wrapped in filter paper and placed in the extraction tube of a Soxhlet extractor in a certain proportion. Then, a certain proportion of dry tetrahydrofuran is placed in a distillation flask, a condenser is installed, and a reflux reaction is carried out to obtain tri(tetrahydrofuran)trichloride. The temperature of the reflux reaction is preferably 80-100°C, more preferably 90°C. The reflux reaction ends when the extract no longer has color, and the time is generally preferably 18-24 hours, more preferably 20 hours.

[0045] In some preferred embodiments of the present invention, after the heating and reflux reaction is completed, the reaction system is preferably cooled to room temperature, and then the mixed solution in the distillation flask is filtered and vacuum dried. The vacuum drying temperature is preferably 50-70°C, more preferably 55°C, and the time is preferably 1-5 hours, more preferably 2 hours, finally yielding dried molybdenum tri(tetrahydrofuran)trichloride (appearing as a light yellow solid compound).

[0046] After obtaining molybdenum trichloride (TMT), according to the present invention, TTM and the ligand compound shown in Formula 1 are reacted at room temperature in the presence of a solvent under anhydrous and oxygen-free conditions to obtain the binuclear molybdenum compound shown in Formula 1. In the present invention, the solvent is selected from any one or more of toluene, dichloromethane, dichloroethane, cyclohexane, n-heptane, or n-hexane, preferably toluene. In the present invention, it is preferred that the molar ratio of TTM and the ligand compound shown in Formula 1 is (1.5–2.0):1, more preferably (1.7–1.8):1, and the two are reacted at room temperature in the presence of the above-mentioned solvent. The reaction is preferably carried out under stirring, and the reaction is terminated when the color of the reaction solution no longer changes, preferably for 4–8 hours, more preferably 5–6 hours. In some embodiments of the present invention, it is preferred that an appropriate amount of TTM and the ligand compound shown in Formula 1 are mixed under anhydrous and oxygen-free conditions, and then an appropriate amount of the above-mentioned solvent is added, followed by stirring at room temperature. Once the color of the reaction solution no longer changes, the reaction is complete. Filter and vacuum dry. The vacuum drying temperature is preferably 50–100°C, more preferably 55–80°C, and the time is preferably 1–5 hours, more preferably 2–3 hours, to obtain the binuclear molybdenum compound shown in Formula I (appearing as a blue-green solid).

[0047] In this invention, the room temperature refers to a temperature of "20-30°C", preferably 25°C.

[0048] The preparation method of the above-mentioned binuclear molybdenum compound provided by the present invention is simple and convenient, requires no expensive instruments and equipment, is easy to implement, and is conducive to large-scale industrial production.

[0049] It should be noted that, in this invention, the ligand compound represented by Formula 1 is a self-made product, and its synthetic route is shown below, but is not limited to the following synthetic route:

[0050]

[0051] The specific preparation steps are as follows:

[0052] S1: Under anhydrous and oxygen-free conditions, R1R2NH, the first acid-binding agent, the first solvent, and the compound shown in Formula A are mixed and subjected to a first reaction to obtain the compound shown in Formula B-1; under anhydrous and oxygen-free conditions, R4R5NH, the second acid-binding agent, the second solvent, and the compound shown in Formula A are mixed and subjected to a second reaction to obtain the compound shown in Formula B-2.

[0053] S2: Under anhydrous and oxygen-free conditions, R3NH2, the third acid-binding agent, the third solvent, and the compound shown in formula B-1 are mixed and subjected to the third reaction to obtain the compound shown in formula C;

[0054] S3: Under anhydrous and oxygen-free conditions, a solution of the compound shown in formula C is mixed with alkyl lithium and subjected to a fourth reaction to obtain the compound shown in formula D;

[0055] S4: Under anhydrous and oxygen-free conditions, a solution of the compound shown in formula D is mixed with a solution of the compound shown in formula B-2 and a fifth reaction is carried out to obtain the ligand compound shown in formula 1.

[0056]

[0057] In this invention, the first acid-binding agent, the second acid-binding agent, and the third acid-binding agent are each independently selected from any one or more of triethylamine, trimethylamine, or tributylamine, preferably triethylamine; the first solvent, the second solvent, and the third solvent are each independently selected from any one or more of tetrahydrofuran, dioxane, toluene, dichloromethane, dichloroethane, diethyl ether, or butyl ether, preferably tetrahydrofuran, diethyl ether, or toluene; the solvent in the solution of the compound represented by formula C is selected from any one or more of tetrahydrofuran, diethyl ether, isopropyl ether, n-hexane, cyclohexane, or n-heptane, preferably n-hexane, n-heptane, or diethyl ether; the solvent in the solution of the compound represented by formula D and the solvent in the solution of the compound represented by formula B-2 are each independently selected from any one or more of tetrahydrofuran, diethyl ether, isopropyl ether, n-hexane, cyclohexane, or n-heptane, preferably n-hexane, n-heptane, or diethyl ether.

[0058] In this invention, in step S1, the molar ratio of the compound represented by formula A, R1R2NH and the first catalyst is 1:1:(1-5), more preferably 1:1:(2-3); in step S1, the molar ratio of the compound represented by formula A, R4R5NH and the second catalyst is 1:1:(1-5), more preferably 1:1:(2-3); in step S2, the molar ratio of the compound represented by formula B-1, R3NH2 and the third catalyst is 1:(1-2):(1-5), more preferably 1:(1.5-2):(2-4); in step S3, the molar ratio of the compound represented by formula C and alkyllithium is 1:(1-2), more preferably 1:1.5; in step S4, the molar ratio of the compound represented by formula D and the compound represented by formula B-2 is (1-1.5):1, more preferably (1.2-1.3):1.

[0059] In this invention, the temperatures of the first, second, fourth, and fifth reactions are each independently -15 to -40°C, preferably -20 to -30°C; the temperature of the third reaction is room temperature. Room temperature refers to a temperature of "20 to 30°C", preferably 25°C.

[0060] In some embodiments of the present invention, R1R2NH, a first acid-binding agent, and a first solvent are preferably mixed under anhydrous and oxygen-free conditions. This mixing is preferably carried out at low temperature with vigorous stirring. Then, compound A is slowly added dropwise to the system while maintaining the low temperature reaction. After the reaction is complete, the mixture is filtered, and the filtrate is rotary evaporated to obtain the compound shown in formula B-1. Similarly, the compound shown in formula B-2 is prepared, except that the starting material R4R5NH is replaced with R1R2NH. It should be noted that the compound shown in formula B-1 and the compound shown in formula B-2 may be the same or different.

[0061] In some embodiments of the present invention, preferably under anhydrous and oxygen-free conditions, R3NH2, triethylamine, and a solvent are first mixed, preferably under low temperature and stirring conditions; then, the compound of formula B-1 is slowly added dropwise to the system, preferably in solution form, and the solvent used is selected from one or more of tetrahydrofuran, dioxane, toluene, dichloromethane, dichloroethane, diethyl ether, or butyl ether, preferably one or more of tetrahydrofuran, diethyl ether, or toluene. After the addition is complete, the reaction system is heated to room temperature to continue the reaction. After the reaction is complete, the mixture is filtered and the filtrate is rotary evaporated to obtain the compound shown in formula C.

[0062] In some embodiments of the present invention, under anhydrous and oxygen-free conditions, the compound represented by formula C is dissolved in a suitable solvent and stirred vigorously at low temperature. Then, a certain proportion of alkyllithium is slowly added dropwise to the reaction system, and the reaction is carried out overnight at a low temperature. After the reaction is complete, the mixture is filtered, and the filter cake is preferably washed with any one of n-hexane, cyclohexane, n-heptane, methylcyclohexane, cyclopentane, diethyl ether, or petroleum ether, preferably with n-hexane. Then, it is dried under vacuum to obtain the compound represented by formula D (as a white solid).

[0063] In some embodiments of the present invention, preferably under anhydrous and oxygen-free conditions, the compound represented by formula D is dissolved in a corresponding solvent and stirred vigorously at low temperature. Then, a certain proportion of the compound represented by formula B-2 is dissolved in a corresponding solvent and slowly added dropwise to the reaction system. After the addition is complete, the reaction is carried out at low temperature overnight. After the reaction is complete, the mixture is filtered, and the filtrate is rotary evaporated to obtain an oily crude product. The present invention preferably uses an ether-n-hexane solvent (the volume ratio of ether to n-hexane is preferably 3:1) to recrystallize the obtained oily crude product, finally obtaining the ligand compound represented by formula 1.

[0064] In this invention, the temperature of the low-temperature reaction mentioned above is independently -15 to -40°C, preferably -20 to -30°C; the room temperature is "20 to 30°C", preferably 25°C.

[0065] This invention also provides a catalyst for selective oligomerization of ethylene, comprising a main catalyst and an aluminum-containing co-catalyst. The main catalyst is a binuclear molybdenum compound of Formula I as described in the above technical solution. The aluminum-containing co-catalyst comprises alkylaluminum and / or alkoxyaluminum, specifically selected from any one or more of methylaluminoxane (MAO), modified methylaluminoxane (MMAO), methylaluminum, ethylaluminum, propylaluminum, isopropylaluminum, n-butylaluminum, sec-butylaluminum, tert-butylaluminum, pentylaluminum, hexylaluminum, cyclohexylaluminum, tert-octylaluminum, or triethylaluminum, preferably a mixture of MMAO and triethylaluminum. In this invention, the molar ratio of the main catalyst to the aluminum-containing co-catalyst is 1:(100-800), preferably 1:(200-500).

[0066] The present invention also provides a method for ethylene oligomerization, comprising the following steps:

[0067] In the presence of an organic solvent and a catalyst for selective oligomerization of ethylene, ethylene undergoes an oligomerization reaction to obtain the desired product.

[0068] In this invention, the organic solvent is selected from any one or more of n-hexane, cyclohexane, toluene, methylcyclohexane, or n-heptane. The oligomerization reaction is carried out at a temperature of 60–75°C, preferably 70°C.

[0069] In some specific embodiments of the present invention, the method for ethylene oligomerization includes the following steps:

[0070] In a sealed autoclave, nitrogen is used to purge the reactor three times. An organic solvent is then introduced under negative pressure, with the volume of the organic solvent being 0.3–0.6 times, preferably 0.4 times, of the reactor volume. Hydrogen is then introduced, and the reactor is heated to a certain temperature. Under slight positive pressure, a certain proportion of co-catalyst and main catalyst solutions are sequentially injected into the reactor using a syringe. Hydrogen is then pressurized to a certain pressure, preferably 0.01–0.1 MPa, more preferably 0.05–0.08 MPa. Finally, ethylene is introduced to a certain pressure, preferably 4.0–5.5 MPa, more preferably 4.5–5.0 MPa. The reaction is then carried out at 60–75°C, preferably 70°C, under maintained temperature and pressure. In this invention, the solvent in the main catalyst solution is selected from toluene, xylene, or n-heptane, preferably toluene; the concentration of molybdenum in the main catalyst solution is 1.5–4 μmol / mL, preferably 2 μmol / mL.

[0071] To verify the reactivity of the binuclear molybdenum compound provided by this invention as a catalyst, this invention preferably involves cooling and releasing the gas after the ethylene oligomerization reaction is completed, weighing the resulting reaction solution, and calculating the reactivity of the ligand based on the weight gain.

[0072] The reactivity can be calculated using the following formula:

[0073] Reactivity (kg / g(Cr).h) = (mass of solution after reaction - mass of solution before reaction) / [52 × molar amount of main catalyst × residence time (h)].

[0074] Tests have shown that the binuclear molybdenum compound of Formula I provided by this invention, when used as the main catalyst in combination with an aluminum-containing co-catalyst for ethylene oligomerization, exhibits certain catalytic activity, reaching up to 795.8 kg / g(Cr).h.

[0075] The present invention also analyzed the selectivity of the target products by gas chromatography and found that when a binuclear molybdenum compound is used as the main catalyst and combined with an aluminum-containing co-catalyst for ethylene oligomerization, the range of products prepared is mainly concentrated between C4 and C10, and the total selectivity of C4 to C10 can reach more than 95%. Among them, the selectivity of 1-butene is greater than 99%, and the selectivity of 1-hexene, 1-octene and 1-decene are all greater than 98%.

[0076] In addition, when the above-mentioned binuclear molybdenum compound is used as the main catalyst and combined with an aluminum-containing co-catalyst for ethylene oligomerization, the solid content of the final polymer is as low as 0.2%, which is conducive to achieving long-term continuous production and improving production efficiency.

[0077] In summary, this invention breaks through the traditional application areas of molybdenum-based catalysts, innovatively applying binuclear molybdenum compounds as catalysts to the preparation of highly linear α-olefins via ethylene oligomerization. This not only provides a new direction for the application of molybdenum-based catalysts, but also offers new ideas for the development of catalysts for ethylene oligomerization.

[0078] To further illustrate the present invention, the following embodiments provide a detailed description. The experimental materials used in the following embodiments of the present invention are all commercially available products.

[0079] The selection of functional groups of catalyst ligands involved in the following preparation examples or embodiments of the present invention and the ligands themselves are shown in Table 1 below:

[0080] Table 1

[0081]

[0082] Preparation Example 1

[0083] This preparation example provides tris(tetrahydrofuran)trichloride molybdenum trichloride, which is prepared by the following method:

[0084] Under anhydrous and oxygen-free conditions, 10.11 g of molybdenum trichloride and 0.33 g of zinc powder were weighed out, wrapped in filter paper, and placed in the extraction tube of a Soxhlet extractor. 200 mL of dry tetrahydrofuran was weighed out and placed in a distillation flask, which was then fitted with a condenser and heated to 90 °C under reflux for 12 h. Once the extract was colorless, the reaction was complete. The mixture was cooled to room temperature, filtered, and dried under vacuum at 55 °C for 2 h, finally yielding 17.11 g of a pale yellow solid compound. The preparation was then complete.

[0085] The elemental analysis of the product is as follows: theoretical value (actual value): C: 34.43 (34.27); H: 5.78 (5.92); O: 11.47 (11.67).

[0086] Atomic absorption spectrometry determined the actual mass percentage of Mo to be 23.08%, while the theoretical value is 22.92%.

[0087] Preparation Example 2

[0088] This preparation example provides a ligand compound represented by formula C(i)-1, and the synthetic route is as follows:

[0089]

[0090] The specific preparation method is as follows (all operations are carried out under anhydrous and oxygen-free conditions):

[0091] (1) Weigh 100 mL of 2 mol / L dimethylamine THF solution, 30.4 g of triethylamine, and 100 mL of THF and add them to the reaction flask. Stir vigorously at -20℃ and slowly add 35.8 g of compound A. Keep the reaction at low temperature for 2 h. After the reaction is complete, filter and rotary evaporate the filtrate to obtain 36.6 g of compound B-1-1.

[0092] (2) Weigh 8.5 g of cyclopentylamine, 15.2 g of triethylamine, and 80 mL of THF and add them to a reaction flask. Stir vigorously at low temperature. Weigh 18.7 g of B-1-1 and slowly add it dropwise to the reaction system using a constant dropping method. After the addition is complete, heat the reaction system to room temperature and continue the reaction for 5 h. After the reaction is complete, filter and rotary evaporate the filtrate to obtain 20.3 g of compound C-1.

[0093] (3) Weigh 11.8g of compound C-1 and dissolve it in n-hexane, and stir vigorously at -35℃. Then, measure 32mL of 1.6mol / L n-butyllithium hexane solution and slowly add it dropwise to the reaction system. Keep the reaction at low temperature overnight. After the reaction is complete, filter the mixture, wash the filter cake with n-hexane, and then dry it under vacuum to obtain 10.2g of white solid compound D-1.

[0094] (4) Dissolve 10.2 g of compound D-1 in n-hexane and stir vigorously at -35 °C. Then dissolve 7.9 g of compound B-1-1 in n-hexane and slowly add it dropwise to the reaction system. After the addition is complete, keep the reaction at low temperature overnight. After the reaction is complete, filter and rotary evaporate the filtrate to obtain crude oil product L-1. Then recrystallize the crude product using a solution of diethyl ether (30 mL) and n-hexane (10 mL) to finally obtain 7.2 g of white or pale yellow solid compound C(i)-1.

[0095] The NMR data for compound C(i)-1 are as follows:

[0096] 1 H-NMR (δ, ppm): 7.34~7.43 (6H, m, benzene-H); 7.12~7.20 (4H, m, benzene-H); 2.80~2.86 (1H, m, N-cyclopentyl-H); 2.40~2.48 (12H, s, NCH); 1.50~1.86 (8H, m, cyclopentyl-H).

[0097] Preparation Example 3

[0098] This preparation example provides a ligand compound represented by formula C(i)-2, and the synthetic route is as follows:

[0099]

[0100] The specific preparation method is as follows (all operations are carried out under anhydrous and oxygen-free conditions):

[0101] (1) First, weigh 14.6g of diethylamine, 30.4g of triethylamine and 100mL of THF and add them to the reaction flask. Stir vigorously at -20℃ and slowly add 35.8g of compound A. Keep the reaction at low temperature for 2h. After the reaction is complete, filter and rotary evaporate the filtrate to obtain 37.2g of compound B-1-2.

[0102] (2) Add 8.5g of cyclopentylamine, 15.2g of triethylamine, and 80mL of THF to a reaction flask and stir vigorously at low temperature. Weigh 21.5g of B-1-2 and slowly add it dropwise to the reaction system using a constant dropping method. After the addition is complete, heat the reaction system to room temperature and continue the reaction for 5 hours. After the reaction is complete, filter and rotary evaporate the filtrate to obtain 21.6g of compound C-2.

[0103] (3) Weigh 13.2g of compound C-2 and dissolve it in n-hexane, and stir vigorously at -35℃. Then, measure 32mL of 1.6mol / L n-butyllithium hexane solution and slowly add it dropwise to the reaction system. Keep the reaction at low temperature overnight. After the reaction is complete, filter the mixture, wash the filter cake with n-hexane, and then dry it under vacuum to obtain 12.9g of white solid compound D-2.

[0104] (4) Dissolve 12.9 g of compound D-2 in n-hexane and stir vigorously at -35 °C. Then dissolve 9.3 g of compound B-1-2 in n-hexane and slowly add it dropwise to the reaction system. After the addition is complete, keep the reaction at low temperature overnight. After the reaction is complete, filter and rotary evaporate the filtrate to obtain crude oil product L-2. Then recrystallize the crude product using a solution of diethyl ether (30 mL) and n-hexane (10 mL) to finally obtain 8.5 g of white or pale yellow solid compound C(i)-2.

[0105] The NMR data for compound C(i)-2 are as follows:

[0106] 1 H-NMR (δ, ppm): 7.36 ~ 7.45 (6H, m, benzene-H); 7.14 ~ 7.21 (4H, m, benzene-H); 2.92 ~ 3.0 (8H, m, NPCH) ; 2.62~2.66 (1H, m, N-cyclopentyl-H); 1.51~1.87 (8H, m, cyclopentyl-H); 0.97~1.06 (12H, t, NCCH).

[0107] Preparation Example 4

[0108] This preparation example provides a ligand compound represented by formula C(i)-3, and the synthetic route is as follows:

[0109]

[0110] The specific preparation method is as follows (all operations are carried out under anhydrous and oxygen-free conditions):

[0111] (1) Weigh 20.2g of diisopropylamine, 30.4g of triethylamine and 120mL of THF and add them to the reaction flask. Stir vigorously at -20℃ and slowly add 35.8g of compound A. Keep the reaction at low temperature for 2h. After the reaction is complete, filter and rotary evaporate the filtrate to obtain 40.5g of compound B-1-3.

[0112] (2) Weigh 8.5 g of cyclopentylamine, 15.2 g of triethylamine, and 80 mL of THF and add them together to a reaction flask. Stir vigorously at low temperature. Weigh 24.4 g of B-1-3 and slowly add it dropwise to the reaction system using a constant dropping method. After the addition is complete, heat the reaction system to room temperature and continue the reaction for 5 h. After the reaction is complete, filter and rotary evaporate the filtrate to obtain 24.1 g of compound C-3.

[0113] (3) Weigh 14.6 g of compound C-3 and dissolve it in n-hexane, and stir vigorously at -35 °C. Then, measure 32 mL of 1.6 mol / L n-butyllithium hexane solution and slowly add it dropwise to the reaction system. Keep the reaction at low temperature overnight. After the reaction is complete, filter the mixture, wash the filter cake with n-hexane, and then dry it under vacuum to obtain 14.4 g of white solid compound D-3.

[0114] (4) Dissolve 14.4 g of compound D-3 in n-hexane and stir vigorously at -35 °C. Then dissolve 12.2 g of compound B-1-3 in n-hexane and slowly add it dropwise to the reaction system. After the addition is complete, keep the reaction at low temperature overnight. After the reaction is complete, filter and rotary evaporate the filtrate to obtain crude oil product L-3. Then recrystallize the crude product using a solution of diethyl ether (30 mL) and n-hexane (10 mL) to finally obtain 9.6 g of white or pale yellow solid compound C(i)-3.

[0115] The NMR data for compound C(i)-3 are as follows:

[0116] 1 H-NMR (δ, ppm): 7.36~7.45 (6H,m, benzene-H); 7.14~7.21 (4H,m, benzene-H); 2.81~2.85 (4H,m, PNCH) ; 2.62~2.66 (1H, m, N-cyclopentyl-H); 1.71~1.82 (8H, m, cyclopentyl-H); 0.97~1.06 (24H, t, NCCH).

[0117] Preparation Example 5

[0118] This preparation example provides a ligand compound represented by formula C(i)-4, and the synthetic route is as follows:

[0119]

[0120] For specific preparation methods, please refer to Preparation Examples 2-4;

[0121] The NMR data for compound C(i)-4 are as follows:

[0122] 1H-NMR (δ, ppm): 7.36~7.45 (6H,m, benzene-H); 7.14~7.21 (4H, m, benzene-H); 2.94~3.01 (4H, m, PNCH ); 2.62~2.66 (1H, m, N-cyclopentyl-H); 1.71~1.82 (8H, m, cyclopentyl-H); 0.97~1.06 (18H, m, NCCH).

[0123] Preparation Example 6

[0124] This preparation example provides a ligand compound represented by formula C(i)-5, and the synthetic route is as follows:

[0125]

[0126] For specific preparation methods, please refer to Preparation Examples 2-4;

[0127] The NMR data for compound C(i)-5 are as follows:

[0128] 1 H-NMR (δ, ppm): 7.36~7.45 (6H, m, benzene-H); 7.14~7.21 (4H, m, benzene-H); 2.81~2.85 (2H, m, PNCH); 2.62~2.66 (1H, m, N-cyclopentyl-H); 2.40~2.46 (6H, d, PNCH); 1.71~1.82 (8H, m, cyclopentyl-H); 0.97~1.06 (12H, m, NCCH).

[0129] Preparation Example 7

[0130] This preparation example provides a ligand compound represented by formula C(i)-6, and the synthetic route is as follows:

[0131]

[0132] For specific preparation methods, please refer to Preparation Examples 2-4;

[0133] 13.5 g of compound D-2 was dissolved in n-hexane and stirred vigorously at -35°C. Then, 9.4 g of compound B-1 was dissolved in n-hexane and slowly added dropwise to the reaction system. After the addition was complete, the mixture was kept at low temperature and reacted overnight. After the reaction was complete, the mixture was filtered, and the filtrate was rotary evaporated to obtain an oily crude product L-6. The crude product was then recrystallized using a solution of diethyl ether (30 mL) and n-hexane (10 mL) to finally obtain 6.6 g of white or pale yellow solid compound L-6.

[0134] The NMR data for compound C(i)-6 are as follows:

[0135] 1 H-NMR (δ, ppm): 7.36~7.45 (6H, m, benzene-H); 7.14~7.21 (4H, m, benzene-H); 2.94~2.99 (4H, m, PNCH); 2.62~2.66 (1H, m, N-cyclopentyl-H); 2.40~2.46 (6H, d, PNCH); 1.71~1.82 (8H, m, cyclopentyl-H); 0.97~1.03 (6H, m, NCCH).

[0136] Example 1

[0137] This embodiment provides a main catalyst C-1, the preparation method of which is as follows:

[0138]

[0139] The operation was carried out under anhydrous and oxygen-free conditions. 0.42 g of molybdenum tris(tetrahydrofuran)trichloride and 0.20 g of ligand (C(i)-1) were weighed into a reaction flask, and 50 mL of toluene was added. The mixture was stirred at room temperature for 6 hours. The reaction was considered complete when the color of the reaction solution no longer changed. The mixture was filtered and dried under vacuum at 55 °C for 2 hours to obtain 0.34 g of a pure blue-green solid.

[0140] The elemental analysis of the product is as follows: theoretical value (actual value): C: 34.75 (34.49); H: 4.55 (4.69); O: 1.85 (2.03).

[0141] Atomic absorption spectrometry determined the actual mass percentage of Mo to be 22.46%, while the theoretical value is 22.21%.

[0142] Example 2

[0143] This embodiment provides a main catalyst C-2, the preparation method of which is as follows:

[0144]

[0145] The operation was carried out under anhydrous and oxygen-free conditions. 0.42 g of molybdenum tris(tetrahydrofuran)trichloride and 0.23 g of ligand (C(i)-2) were weighed into a reaction flask, and 70 mL of toluene was added. The mixture was stirred at room temperature for 6 hours. The reaction was considered complete when the color of the reaction solution no longer changed. The mixture was filtered and dried under vacuum at 55 °C for 2 hours to obtain 0.30 g of a pure blue-green solid.

[0146] The elemental analysis of the product is as follows: theoretical value (actual value): C: 37.85 (37.61); H: 5.15 (5.30); O: 1.74 (1.83).

[0147] Atomic absorption spectrometry determined the actual mass percentage of Mo to be 21.02%, while the theoretical value is 20.85%.

[0148] Example 3

[0149] This embodiment provides a main catalyst C-3, the preparation method of which is as follows:

[0150]

[0151] The operation was carried out under anhydrous and oxygen-free conditions. 0.42 g of molybdenum tris(tetrahydrofuran)trichloride and 0.26 g of ligand (C(i)-3) were weighed into a reaction flask, and 60 mL of toluene was added. The mixture was stirred at room temperature for 8 hours. The reaction was considered complete when the color of the reaction solution no longer changed. The mixture was filtered and dried under vacuum at 55 °C for 2 hours to obtain 0.25 g of a pure blue-green solid.

[0152] The elemental analysis of the product is as follows: theoretical value (actual value): C: 40.60 (40.41); H: 5.68 (5.81); O: 1.64 (1.81).

[0153] Atomic absorption spectrometry determined the actual mass percentage of Mo to be 19.88%, while the theoretical value is 19.65%.

[0154] Example 4

[0155] This embodiment provides a main catalyst C-4, the preparation method of which is as follows:

[0156]

[0157] The operation was carried out under anhydrous and oxygen-free conditions. 0.42 g of molybdenum tris(tetrahydrofuran)trichloride and 0.25 g of ligand (C(i)-4) were weighed into a reaction flask, and 50 mL of xylene was added. The mixture was stirred at room temperature for 7 hours. The reaction was considered complete when the color of the reaction solution no longer changed. The mixture was filtered and dried under vacuum at 80 °C for 3 hours to obtain 0.28 g of a pure blue-green solid.

[0158] The elemental analysis of the product is as follows: theoretical value (actual value): C: 39.26 (39.02); H: 5.42 (5.70); O: 1.69 (1.85).

[0159] Atomic absorption spectrometry determined the actual mass percentage of Mo to be 20.35%, while the theoretical value is 20.24%.

[0160] Example 5

[0161] This embodiment provides a main catalyst C-5, the preparation method of which is as follows:

[0162]

[0163] The operation was carried out under anhydrous and oxygen-free conditions. 0.42 g of molybdenum tris(tetrahydrofuran)trichloride and 0.23 g of ligand (C(i)-5) were weighed into a reaction flask, and 60 mL of xylene was added. The mixture was stirred at room temperature for 7 hours. The reaction was considered complete when the color of the reaction solution no longer changed. The mixture was filtered and dried under vacuum at 80 °C for 3 hours to obtain 0.32 g of a pure blue-green solid.

[0164] The elemental analysis of the product is as follows: theoretical value (actual value): C: 37.85 (37.55); H: 5.15 (5.34); O: 1.74 (1.84).

[0165] Atomic absorption spectrometry determined the actual mass percentage of Mo to be 21.09%, while the theoretical value is 20.85%.

[0166] Example 6

[0167] This embodiment provides a main catalyst C-6, the preparation method of which is as follows:

[0168]

[0169] The operation was carried out under anhydrous and oxygen-free conditions. 0.42 g of molybdenum tris(tetrahydrofuran)trichloride and 0.22 g of ligand (C(i)-6) were weighed into a reaction flask, and 60 mL of n-heptane was added. The mixture was stirred at room temperature for 8 hours. The reaction was considered complete when the color of the reaction solution no longer changed. The mixture was filtered and dried under vacuum at 55 °C for 2 hours to obtain 0.31 g of a pure blue-green solid.

[0170] The elemental analysis of the product is as follows: theoretical value (actual value): C: 36.35 (36.11); H: 4.82 (5.01); O: 1.79 (1.89).

[0171] Atomic absorption spectrometry determined the actual mass percentage of Mo to be 21.77%, while the theoretical value is 21.51%.

[0172] Catalytic activity verification test

[0173] The main catalysts C-1 to C-6 obtained in Examples 1-6 were weighed and prepared into toluene solutions with a Mo content of 2 μmol / mL. Nitrogen was used to purge the solution three times. 200 mL of dry cyclohexane was then introduced under negative pressure, followed by the introduction of hydrogen gas. Under slightly positive pressure, 0.4 mL of 7% MMAO and 0.5 mL of the main catalyst solution were injected sequentially. The pressure was then increased to 0.1-0.5 MPa with hydrogen, and finally ethylene was introduced to 5.0 MPa. The reaction temperature was controlled at 60-75°C, and the reaction was maintained at this temperature and pressure for 1 hour. After the reaction was completed, the reaction solution was weighed, and the reaction activity was calculated based on the weight gain.

[0174] The corresponding feedstock and final activity test results for the main catalysts C-1 to C-6 obtained in Examples 1 to 6 are shown in Table 2 below:

[0175] Table 2

[0176]

[0177] As shown in Table 2, the main catalysts C-1 to C-6 provided by this invention, when used in combination with aluminum-containing co-catalysts for the selective oligomerization reaction of ethylene, exhibit certain catalytic activity, with a maximum of 795.8 kg / g(Ti).h.

[0178] Selective testing

[0179] Gas chromatography analysis was performed on the main catalysts C-1 to C-6 obtained in Examples 1 to 6 to calculate their selectivity and the solid content of the obtained products.

[0180] The specific parameters of the colorimetric chromatogram are as follows:

[0181] Chromatographic column: HP-5 (30m × 0.32mm × 0.25μm)

[0182] Inlet temperature: 300℃;

[0183] Detector: FID, Temperature: 320℃

[0184] Column temperature: Initial temperature 50℃, hold for 5 min, then increase to 300℃ at 20℃ / min and hold for 15 min; Column flow rate: 1.0 mL / min;

[0185] Split ratio: Split injection, split ratio 20:1;

[0186] Injection volume: 0.25 μL.

[0187] The test method for solid content is as follows:

[0188] After the reaction is complete, a reaction weight gain is obtained. The reaction solution is then filtered to obtain a solid, which is dried under vacuum at 60°C for 2 hours and then weighed. The solid content is obtained by dividing the mass obtained by the reaction weight gain.

[0189] The test results are shown in Table 3 below:

[0190] Table 3

[0191]

[0192] As shown in Table 3, the main catalysts C-1 to C-6 provided by this invention, when used in combination with aluminum-containing co-catalysts for the selective oligomerization reaction of ethylene, produce products mainly concentrated between C4 and C10. The total selectivity of C4 to C10 can reach more than 95%, with the selectivity of 1-butene greater than 99%, and the selectivity of 1-hexene, 1-octene, and 1-decene all greater than 98%. Moreover, the solid content of the polymer is as low as 0.2%.

[0193] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A binuclear molybdenum compound, characterized in that, It has the structure shown in Equation I: Formula I; R1, R2, R4, and R5 are each independently selected from methyl, ethyl, or isopropyl. R3 is selected from cyclopentyl.

2. The binuclear molybdenum compound according to claim 1, characterized in that, The binuclear molybdenum compound is selected from any one of formulas C-1 to C-6: 。 3. A method for preparing a binuclear molybdenum compound as described in claim 1 or 2, characterized in that, Includes the following steps: Under anhydrous and oxygen-free conditions, molybdenum tris(tetrahydrofuran)trichloride and the ligand compound shown in Formula 1 react at room temperature in the presence of a solvent to obtain the binuclear molybdenum compound shown in Formula I; wherein R1, R2, R4, and R5 in Formula 1 are each independently selected from methyl, ethyl, or isopropyl; and R3 is selected from cyclopentyl. Formula 1; Formula I.

4. The preparation method according to claim 3, characterized in that, The solvent is selected from any one or more of toluene, dichloromethane, dichloroethane, cyclohexane, n-heptane, or n-hexane; The molar ratio of the tri(tetrahydrofuran)trichloride molybdenum chloride and the ligand compound shown in Formula 1 is (1.5~2.0):

1.

5. A catalyst for selective oligomerization of ethylene, characterized in that, Includes the main catalyst and aluminum-containing co-catalyst; The main catalyst is the binuclear molybdenum compound according to claim 1 or 2, or the binuclear molybdenum compound prepared by the preparation method according to claim 3 or 4.

6. The catalyst for selective oligomerization of ethylene according to claim 5, characterized in that, The aluminum-containing cocatalyst includes alkylaluminum and / or alkoxyaluminum.

7. The catalyst for selective oligomerization of ethylene according to claim 5, characterized in that, The molar ratio of the main catalyst to the aluminum-containing co-catalyst is 1:(100~800).

8. A method for ethylene oligomerization, characterized in that, Includes the following steps: In the presence of an organic solvent and a catalyst for selective oligomerization of ethylene, ethylene undergoes an oligomerization reaction to obtain the desired product. The catalyst for selective oligomerization of ethylene is any one of the catalysts for selective oligomerization of ethylene according to claims 5 to 7.

9. The method according to claim 8, characterized in that, The organic solvent is selected from any one or more of n-hexane, cyclohexane, toluene, methylcyclohexane, or n-heptane.

10. The method according to claim 8, characterized in that, The oligomerization reaction occurs at a temperature of 60-75°C.

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