A method for synthesizing a bridged bis-metallocene catalyst racemic structure

Abstract

The application provides a synthesis method of a bridged double metallocene catalyst racemic structure. The synthesis reaction adopts a simple method without separating an intermediate lithium salt, and rac-structure and meso-structure can be obtained in a high yield. Through grading extraction, pure rac-structure, and a mixture of rac-structure and meso-structure can be obtained. Then, the mixture of meso-structure and rac-structure is converted into pure rac structure under certain conditions, the meso-structure is effectively utilized, and product loss caused by a repeated recrystallization purification method is avoided, so that the yield of the rac-structure is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of olefin polymerization catalysts and relates to a method for synthesizing a racemic structure of a bridged dimorphocene catalyst. Background Technology

[0002] Metallocene catalysts are homogeneous catalysts with a single active site. Compared to the traditional Ziegler-Natta (ZN) catalyst system, the polymerization products exhibit a narrower molecular weight distribution and better comonomer insertion rate, and the polymer properties can be altered by changing the conformational changes of the ligands in the catalyst. These catalysts have been widely used in the catalytic polymerization of ethylene, propylene, or the copolymerization of ethylene with α-olefins, greatly enriching the variety of high-performance polyolefins. Since the 1980s, the variety of metallocene catalysts has become increasingly diverse, ranging from monometallocenes to dimetallocenes, from non-bridged to bridged structures, and from C-bridges to Si-bridges. Among them, bridged dimetallocene catalysts are characterized by high activity and good structural stability, and their spatial conformation is conducive to the formation of highly isotactic polyolefin products. These bridged dimetallocene catalysts have been applied to the commercial production of polypropylene, polyethylene, or polyolefin copolymers. The molecules of bridged dimetallocene catalysts have a chiral structure and a pair of spatial isomers, including a racemic structure (rac-structure) and a meso-structure (meso-structure). Of these two isomers, the rac-structure has higher application value in the field of polyolefins, with high olefin polymerization activity, strong copolymerization ability, and high isotacticity of the polymerization products. The meso-structure, on the other hand, is less used in the field of olefin polymerization due to its poor olefin polymerization performance.

[0003] In currently reported synthesis processes of bridged bis(metallocene) catalysts, the direct chemical reaction yields a mixture of rac- and meso-structures, which are then subjected to a cumbersome recrystallization process to obtain the pure rac-structure (Angew. Chem. Int. Ed. 2022, 61, e202210797; Organometallics 2006, 25, 1217-1229). These methods are cumbersome and yield low rac-structure yields, only 10%–30%. Summary of the Invention

[0004] The technical problem this invention aims to solve is to provide a method for synthesizing racemic structures of bridged bis(metallocene) catalysts in high yield. The synthesis reaction does not separate the intermediate dilithium salt, and the reaction can yield both RAC- and meso-structures in high yield. After fractional extraction, pure RAC-structures and mixtures of RAC- and meso-structures can be obtained separately. Then, under certain conditions, the mixture of meso- and RAC-structures is converted into pure RAC-structures, effectively utilizing the meso-structures while avoiding product loss caused by repeated recrystallization purification methods, thereby significantly improving the yield of RAC-structures.

[0005] This invention provides a method for synthesizing racemic structures of bridged dicyclopentadienyl metal catalysts, the method comprising the following steps: (1-1) Under an inert atmosphere, the bridged bis-crenocyanate ligand shown in Formula I and alkyl lithium were reacted in ultra-dry toluene to obtain a dispersion of the bridged bis-crenocyanate ligand dilithium salt. (1-2) Add ultra-dry tetrahydrofuran to the dispersion until a homogeneous solution is formed, add the homogeneous solution to a toluene dispersion of a transition metal salt or its complex, and react to obtain the reaction system; The transition metal in the transition metal salt or its complex is selected from titanium, zirconium, or hafnium; (2-1) Remove the low-boiling-point solvent in the reaction system described in step (1-2) by depressurization, filter, and obtain filtrate A and filter cake B; (2-2) Dissolve the filter cake B with an ultra-dry organic solvent, filter, remove the solvent from the filtrate under reduced pressure, and obtain the rac-structure shown in Formula II; The filtrate A was concentrated and mixed with n-hexane, filtered, and the solid was collected, which was a mixture of rac-structure and meso-structure. (3-1) Under an inert atmosphere, the mixture of rac-structure and meso-structure described in step (2-2) and metal halide and / or metal quaternary ammonium salt are reacted in an ultra-dry ether reagent, and the reaction product is filtered to obtain filter cake C; (3-2) The filter cake C is dissolved in an ultra-dry organic solvent, filtered, and the filtrate D is collected; after the solvent is removed by vacuum, the filtrate D is used to obtain the rac-structure shown in Formula II; Formula I Formula II Among them, R1, R2, R 3、 R 4、 R 5、 R6 may be the same or different, and are independently selected from hydrogen or C1~C10 alkyl groups; M is titanium, zirconium, or hafnium, with zirconium or hafnium being preferred; X is a C1-C10 alkyl group or a halogen, preferably methyl or chlorine.

[0006] According to an embodiment of the present invention, the alkyllithium is selected from C 1~6 Alkyl lithium, such as C 1~4 Alkyl lithium, exemplified by methyl lithium, tert-butyl lithium, or n-butyl lithium.

[0007] According to an embodiment of the present invention, in formula I or formula II, R1, R2, R 3、 R 4、 R 5、 R6 is independently selected from hydrogen or C1-C4 alkyl groups, such as H, methyl, ethyl, isopropyl, or tert-butyl.

[0008] According to an embodiment of the present invention, step (1-1) includes: under an inert atmosphere, the bridged biscrone ligand represented by Formula I is first dissolved in ultra-dry toluene, and an alkyl lithium (e.g., n-BuLi) solution is added to the system at a low temperature (e.g., -20ºC to 10ºC, 0 to 10ºC), and the mixture is stirred at room temperature for 8 to 15 hours (e.g., 12 hours).

[0009] According to an embodiment of the present invention, the transition metal salt is selected from one or more of titanium tetrachloride, zirconium tetrachloride, and hafnium tetrachloride.

[0010] According to embodiments of the present invention, the transition metal salt complex is selected from complexes of transition metal salts and tetrahydrofuran (e.g., ZrCl4(THF)2, HfCl4(THF)2) or complexes of transition metal salts and amines (e.g., ZrCl4). 2NH2(CH2)3CH3, HfCl4 2NH2(CH2)3CH3).

[0011] According to an embodiment of the present invention, the molar ratio of the bridging bisoprotaxy ligand represented by Formula I to the transition metal salt or its complex is 1:(0.9~1.1), preferably 1:1.

[0012] According to an embodiment of the present invention, step (1-2) includes: adding ultra-dry tetrahydrofuran to the dispersion to form a homogeneous solution, adding the homogeneous solution to an ultra-dry toluene solution of a transition metal salt or its complex at a low temperature (e.g. -20ºC to 0ºC), and reacting at a higher temperature (e.g., reacting at 20 to 70°C for 2 to 20 hours, preferably at 40 to 60°C for 10 to 20 hours) to obtain the reacted system.

[0013] According to an embodiment of the present invention, the low-boiling-point solvent in step (2-1) is tetrahydrofuran.

[0014] According to an embodiment of the present invention, the ultra-dry organic solvent in steps (2-2) and (3-2) is toluene, dichloromethane, or a mixture of both.

[0015] According to an embodiment of the present invention, the metal halide in step (3-1) has the following general formula: LY, where L is a first group metal element, preferably lithium, sodium, or potassium; Y is a halogen, preferably chlorine or bromine; for example, the metal halide is lithium chloride, sodium chloride, potassium chloride, lithium bromide, sodium bromide, or potassium bromide.

[0016] According to an embodiment of the present invention, the metal quaternary ammonium salt in step (3-1) has the following general formula: R1 ’ R2 ’ R3 ’ R4 ’ Independently, it is a C1-C18 alkyl group, preferably a C1-C10 alkyl group, and even more preferably a C1-C4 alkyl group, such as methyl, ethyl, propyl, butyl; Y is a halogen, preferably chlorine or bromine. For example, the metal quaternary ammonium salt is tetrabutylammonium chloride.

[0017] According to an embodiment of the present invention, the reaction temperature in step (3-1) is 30~150℃, preferably 50~100℃; the reaction time is 0.5~48h, preferably 4~12h.

[0018] According to an embodiment of the present invention, the ether reagent in step (3-1) is selected from monoether reagents and / or diether reagents.

[0019] According to an embodiment of the present invention, the diether reagent in step (3-1) has a structure of formula III: Formula III Among them, R a R b The alkyl groups, whether the same or different, are independently C1 to C10 alkyl groups, preferably C1 to C4 alkyl groups, such as methyl, ethyl, propyl, and butyl; for example, the diether reagent is selected from ethylene glycol dimethyl ether and / or ethylene glycol diethyl ether.

[0020] According to an embodiment of the present invention, the monoether reagent in step (3-1) has a structure of formula IV: Formula IV Among them, R c R d Whether identical or different, they are independently C1 to C10 alkyl groups, preferably C1 to C4 alkyl groups, such as methyl, ethyl, propyl, tert-butyl; or, R c R dThey can also be linked into a ring to form a cyclic ether, and the preferred monoether reagent is tetrahydrofuran.

[0021] According to an embodiment of the present invention, the method includes the following steps: (1) A simple method without separating the intermediate dilithium salt is used to carry out the coordination reaction. The steps are as follows: (1-1): In an anhydrous and oxygen-free inert gas atmosphere, the bridged bis-penetrone ligand shown in Formula I is dissolved in ultra-dry toluene, and n-BuLi solution is added at low temperature (preferably -20~10℃), and the temperature is raised to room temperature until the reaction is completed to obtain a dispersion of the bridged bis-penetrone ligand dilithium salt. (1-2): Add an appropriate amount of tetrahydrofuran to form a homogeneous solution from the dispersion in step (1-1). Add this homogeneous solution to the toluene dispersion of the transition metal salt or its complex at a low temperature (preferably -20~0℃). Then raise the temperature to a certain level (preferably 20~70℃) and react for a certain time (preferably 2~15h) to obtain the reaction system. (2) The product is fractionated and extracted, and the steps are as follows: (2-1): Remove some of the low-boiling-point solvent from the system after the reaction described in step (1-2) under reduced pressure, and then filter to obtain filtrate A and filter cake B; (2-2): Transfer filter cake B to a flask, add ultra-dry organic solvent, stir to dissolve, filter, remove solvent from filtrate under reduced pressure to obtain yellow powder, which is the rac-structure. This is the first batch of rac-structures. Concentrate filtrate A, add n-hexane, stir, filter and collect the powder, which is a mixture of rac-structure and meso-structure; (3) The isomerization transformation of the meso-structure is carried out in the following steps: (3-1): Under an anhydrous and oxygen-free inert gas atmosphere, the mixture of meso-structure and rac-structure obtained in step (2-2) above is dispersed in an ultra-dry ether reagent, and metal halide and / or metal quaternary ammonium salt are added. The mixture is reacted at 30~150℃ for 0.5~48h. After the reaction is completed, the mixture is filtered to obtain filter cake C. (3-2) Add ultra-dry organic solvent to dissolve filter cake C, filter, collect filtrate D, remove solvent from filtrate D under reduced pressure, and obtain yellow powder, which is the second batch of rac-structures.

[0022] Beneficial effects This invention provides a method for synthesizing racemic structures of bridging dicerocene catalysts. The synthesis reaction employs a simple method that does not separate the intermediate dilithium salt, thereby improving the overall yield of the RAC- and Meso- structures. The reaction products are fractionally extracted to obtain pure RAC- structures and mixtures of RAC- and Meso- structures, respectively. The mixture of Meso- and RAC- structures is then converted into pure RAC structures, effectively utilizing the Meso-structure while avoiding product loss caused by repeated recrystallization purification methods. This significantly improves the yield of the RAC-structure, achieving an overall yield of over 44%, far exceeding the yield levels (10%–30%) reported in existing literature.

[0023] Terminology Definitions and Explanations Unless otherwise stated, the definitions of terms recorded in this application specification and claims, including definitions as examples, exemplary definitions, preferred definitions, and definitions of specific compounds in the embodiments, can be arbitrarily combined and combined with each other. Such combinations and combinations shall fall within the scope of this application specification.

[0024] Unless otherwise stated, the numerical ranges described in this specification and claims are equivalent to describing at least each specific integer value therein. For example, the numerical range "1-10" is equivalent to describing each integer value in the numerical range "1-10", namely 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0025] Term "C" 1-10 "alkyl" should be understood to refer to straight-chain and branched alkyl groups having 1 to 10 carbon atoms, "C 1-4 "Alkyl" means a straight-chain or branched alkyl group having 1, 2, 3, or 4 carbon atoms. The alkyl group is, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, 2-methylbutyl, 1-methylbutyl, 1-ethylpropyl, 1,2-dimethylpropyl, neopentyl, 1,1-dimethylpropyl, 4-methylpentyl, 3-methylpentyl, 2-methylpentyl, 1-methylpentyl, 2-ethylbutyl, 1-ethylbutyl, 3,3-dimethylbutyl, 2,2-dimethylbutyl, 1,1-dimethylbutyl, 2,3-dimethylbutyl, 1,3-dimethylbutyl, or 1,2-dimethylbutyl, or their isomers.

[0026] "Super dry solvent" refers to a solvent with a water content of ≤50ppm. Detailed Implementation

[0027] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0028] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0029] Example 1 In an inert atmosphere, 4.69 g (10 mmol) of bis(2-methyl-4-phenyl-indene)dimethylsilane was dissolved in ultra-dry toluene. The solution was cooled to 0–10 °C, and 8.4 mL of 2.5 M n-BuLi hexane solution was added. The mixture was stirred overnight at room temperature to obtain a yellow slurry of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt. Ultra-dry tetrahydrofuran was added and stirred to dissolve the slurry, yielding a homogeneous solution of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt. 3.77 g (10 mmol) of ZrCl4(THF)2 was dispersed in ultra-dry toluene, and the solution was cooled to -20 °C. The homogeneous solution of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt obtained in the previous step was slowly added, the solution was slowly restored to room temperature, and then heated to 50 °C for 18 h.

[0030] Tetrahydrofuran was removed from the system under reduced pressure, followed by filtration to obtain filtrate A and filter cake B. Filter cake B was transferred to a flask, dichloromethane was added, and the mixture was heated to dissolve the filter cake. After filtration, the solvent in the filtrate was removed under reduced pressure to obtain a yellow powder, which is the rac-structure, with a mass of 1.05 g. Filtrate A was concentrated, n-hexane was added, and the mixture was stirred. After filtration, an orange powder was obtained, which is a mixture of rac-structure and meso-structure (in a 1 / 2.2 ratio), with a mass of 2.69 g.

[0031] In an inert atmosphere, 2.69 g of the mixture of the above-mentioned rac-structure and meso-structure were mixed with 0.13 g of LiCl, and 11.0 g of ultra-dry ethylene glycol dimethyl ether was added. The mixture was reacted at 70 °C for 6 h. After cooling to room temperature, the mixture was filtered, and the filter cake was added to ultra-dry dichloromethane. The mixture was heated and filtered while hot. The filtrate was evaporated under reduced pressure to remove the solvent, yielding a yellow powder, which was the rac-structure, with a mass of 1.77 g.

[0032] In this example, a total of 2.82 g of the rac-structure of dimethylsilyl bis(2-methyl-4-phenyl-indenyl)zirconia was obtained, with a yield of 45%.

[0033] 1¹H NMR (CDCl₃, 500 MHz), rac-structure, δ (ppm): 7.63–7.70 (m, 6H), 7.35–7.46 (m, 8H), 7.11–7.15 (m, 2H), 6.97 (s, 2H), 2.27 (s, 6H), 1.36 (s, 6H). Example 2 In an inert atmosphere, 4.69 g (10 mmol) of bis(2-methyl-4-phenyl-indene)dimethylsilane was dissolved in ultra-dry toluene. The solution was cooled to 0–10 °C, and 8.4 mL of 2.5 M n-BuLi hexane solution was added. The mixture was stirred overnight at room temperature to obtain a yellow slurry of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt. Ultra-dry tetrahydrofuran was added and stirred to dissolve the slurry, yielding a homogeneous solution of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt. 3.77 g (10 mmol) of ZrCl4(THF)2 was dispersed in ultra-dry toluene. The solution was cooled to -20 °C, and the homogeneous solution of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt obtained in the previous step was slowly added. The mixture was slowly restored to room temperature and then heated to 80 °C for 10 h.

[0034] Tetrahydrofuran was removed from the system under reduced pressure, followed by filtration to obtain filtrate A and filter cake B. Filter cake B was transferred to a flask, toluene was added, and the filter cake was heated to dissolve. After filtration, the solvent in the filtrate was removed under reduced pressure to obtain a yellow powder, which is the rac-structure, with a mass of 1.10 g. Filtrate A was concentrated, hexane was added, and the mixture was stirred. The resulting orange powder, which is a mixture of rac-structure and meso-structure (in a ratio of 1 / 1.9), had a mass of 2.77 g.

[0035] In an inert atmosphere, 2.77 g of the mixture of the above-mentioned rac-structure and meso-structure were mixed with 0.15 g of tetrabutylammonium chloride, and 12.0 g of ultra-dry ethylene glycol dimethyl ether was added. The mixture was reacted at 60 °C for 8 h. After cooling to room temperature, the mixture was filtered, and the filter cake was dissolved in dichloromethane by heating. After filtration, the filtrate was evaporated under reduced pressure to remove the solvent, yielding a yellow powder, which is the rac-structure, with a mass of 1.79 g.

[0036] In this example, a total of 2.89 g of the rac-structure of dimethylsilyl bis(2-methyl-4-phenyl-indenyl)zirconia was obtained, with a yield of 46%.

[0037] 1¹H NMR (CDCl₃, 500 MHz), rac-structure, δ (ppm): 7.63–7.70 (m, 6H), 7.35–7.46 (m, 8H), 7.11–7.15 (m, 2H), 6.97 (s, 2H), 2.27 (s, 6H), 1.36 (s, 6H). Example 3 In an inert atmosphere, 7.03 g (15 mmol) of bis(2-methyl-4-phenyl-indene)dimethylsilane was dissolved in ultra-dry toluene. The solution was cooled to 0–10 °C, and 12.6 mL of 2.5 M n-BuLi hexane solution was added. The mixture was stirred overnight at room temperature to obtain a yellow slurry of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt. Ultra-dry tetrahydrofuran was added and stirred to dissolve, yielding a homogeneous solution of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt. 5.66 g (15 mmol) of ZrCl4(THF)2 was dispersed in ultra-dry toluene. The solution was cooled to -20 °C, and the homogeneous solution of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt obtained in the previous step was slowly added. The mixture was slowly restored to room temperature and then heated to 60 °C for 12 h.

[0038] Tetrahydrofuran was removed from the system under reduced pressure, followed by filtration to obtain filtrate A and filter cake B. Filter cake B was transferred to a flask, toluene was added, and the filter cake was heated to dissolve. After filtration, the solvent in the filtrate was removed under reduced pressure to obtain a yellow powder, which is the rac-structure, with a mass of 1.57 g. Filtrate A was concentrated, hexane was added, and the mixture was stirred. After filtration, an orange powder was obtained, which is a mixture of rac-structure and meso-structure (in a 1 / 2.1 ratio), with a mass of 3.98 g.

[0039] In an inert atmosphere, 3.98 g of the mixture of the above-mentioned rac-structure and meso-structure were mixed with 0.15 g of tetrabutylammonium chloride and 0.1 g of lithium chloride, and 20.0 g of ultra-dry ethylene glycol dimethyl ether was added. The mixture was reacted at 60 °C for 5 h. After cooling to room temperature, the mixture was filtered, and the filter cake was dissolved in dichloromethane by heating. The mixture was then filtered again, and the filtrate was evaporated under reduced pressure to remove the solvent, yielding a yellow powder, which was the rac-structure, with a mass of 2.60 g.

[0040] In this example, a total of 4.17 g of the rac-structure of dimethylsilyl bis(2-methyl-4-phenyl-indenyl)zirconia was obtained, with a yield of 44%.

[0041] 1¹H NMR (CDCl₃, 500 MHz), rac-structure, δ (ppm): 7.63–7.70 (m, 6H), 7.35–7.46 (m, 8H), 7.11–7.15 (m, 2H), 6.97 (s, 2H), 2.27 (s, 6H), 1.36 (s, 6H). Example 4 In an inert atmosphere, 5.81 g (10 mmol) of bis[2-methyl-4-(4-tert-butyl-phenyl)-indenyl]dimethylsilane was dissolved in ultra-dry toluene. The solution was cooled to 0–10 °C, and 8.4 mL of 2.5 M n-BuLi hexane solution was added. The mixture was stirred overnight at room temperature to obtain a yellow slurry of bis[2-methyl-4-(4-tert-butyl-phenyl)-indenyl]dimethylsilane dilithium salt. Ultra-dry tetrahydrofuran was added, and the solution was stirred to dissolve, yielding a homogeneous solution of bis[2-methyl-4-(4-tert-butyl-phenyl)-indenyl]dimethylsilane dilithium salt. 4.65 g (10 mmol) of HfCl4(THF)2 was dispersed in ultra-dry toluene and cooled to -20 °C. A homogeneous solution of bis[2-methyl-4-(4-tert-butyl-phenyl)-indenyl]dimethylsilane dilithium salt obtained in the previous step was slowly added. The mixture was slowly restored to room temperature and then heated to 60 °C for 15 h.

[0042] Tetrahydrofuran was removed from the system under reduced pressure, followed by filtration to obtain filtrate A and filter cake B. Filter cake B was transferred to a flask, dichloromethane was added, and the mixture was heated to dissolve the filter cake. After filtration, the solvent in the filtrate was removed under reduced pressure to obtain a yellow powder, which is the rac-structure, with a mass of 1.47 g. Filtrate A was concentrated to a certain concentration, hexane was added, and the mixture was stirred. The resulting orange powder, which is a mixture of rac-structure and meso-structure (in a 1 / 1.5 ratio), had a mass of 3.45 g.

[0043] In an inert atmosphere, 3.45 g of the mixture of the above-mentioned rac-structure and meso-structure were mixed with 0.10 g of lithium chloride, and 20.0 g of ultra-dry ethylene glycol dimethyl ether was added. The mixture was reacted at 60 °C for 7 h. After cooling to room temperature, the mixture was filtered, and the filter cake was dissolved in dichloromethane by heating. The mixture was then filtered while hot, and the solvent was removed by evaporation under reduced pressure to obtain a yellow powder, which is the rac-structure, with a mass of 2.25 g.

[0044] In this embodiment, a total of 3.72 g of the rac-structure of dimethylsilyl bis[2-methyl-4-(4-tert-butyl-phenyl)-indenyl] hafnium dichloride was obtained, with a yield of 45%.

[0045] 1H NMR ( CDCl3, 500 MHz ), rac-structure, δ ( ppm ): 7.67-7.69 (d, 2H), 7.56-7.58 (d, 4H), 7.44-7.45(d, 4H), 7.34-7.36 (d, 2H), 7.05-7.10 (m, 2H), 6.91 (s, 2H), 2.344 (s, 6H), 1.334 (s, 18H), 1.330 (s, 6H). Comparative Example 1 In an inert atmosphere, 4.69 g (10 mmol) of bis(2-methyl-4-phenyl-indene)dimethylsilane was dissolved in ultra-dry toluene, cooled to 0–10 °C, and 8.4 mL of 2.5 M n-BuLi hexane solution was added. The mixture was stirred overnight at room temperature to obtain a yellow slurry of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt. The slurry was filtered to obtain dilithium salt powder. Ultra-dry tetrahydrofuran was added and stirred to dissolve the powder, yielding a homogeneous solution of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt. 3.77 g (10 mmol) of ZrCl4(THF)2 was dispersed in ultra-dry toluene, cooled to -20 °C, and the homogeneous solution of bis(2-methyl-4-phenyl-indene)dimethylsilane dilithium salt obtained in the previous step was slowly added. The mixture was slowly restored to room temperature, heated to 50 °C, and reacted for 18 h.

[0046] The solution was cooled to room temperature and filtered. The filter cake was dissolved in dichloromethane and then filtered again. The filtrate was concentrated until the catalyst precipitated, yielding a mixture of rac- and meso-structures. The mixture of rac- and meso-structures was recrystallized in dichloromethane to give 1.07 g of rac-structure, with a yield of 17%.

[0047] 1 ¹H NMR (CDCl₃, 500 MHz), rac-structure, δ (ppm): 7.63–7.70 (m, 6H), 7.35–7.46 (m, 8H), 7.11–7.15 (m, 2H), 6.97 (s, 2H), 2.27 (s, 6H), 1.36 (s, 6H). Comparative Example 2 In an inert atmosphere, 4.69 g (10 mmol) of bis(2-methyl-4-phenyl-indenyl)dimethylsilane was dissolved in ultra-dry toluene. The solution was cooled to 0–10 °C, and 8.4 mL of 2.5 M n-BuLi hexane solution was added. The mixture was refluxed for 3 h to obtain a yellow slurry of bis(2-methyl-4-phenyl-indenyl)dimethylsilane dilithium salt. The solution was then cooled to -25 °C, and 2.33 g (10 mmol) of ZrCl4 was added. The mixture was slowly restored to room temperature, and the reaction was allowed to proceed overnight.

[0048] The filter cake was dissolved in toluene after filtration, and the filtrates were combined. Toluene was removed to obtain a mixture of rac- and meso-structures. The mixture of rac- and meso-structures was recrystallized in dichloromethane to give 0.94 g of rac-structure, with a yield of 14.9%.

[0049] 1 ¹H NMR (CDCl₃, 500 MHz), rac-structure, δ (ppm): 7.63–7.70 (m, 6H), 7.35–7.46 (m, 8H), 7.11–7.15 (m, 2H), 6.97 (s, 2H), 2.27 (s, 6H), 1.36 (s, 6H). The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing racemic structures of bridged dicycloceramic catalysts, characterized in that, The method includes the following steps: (1-1) Under an inert atmosphere, the bridged bis-crenocyanate ligand shown in Formula I and alkyl lithium were reacted in ultra-dry toluene to obtain a dispersion of the bridged bis-crenocyanate ligand dilithium salt. (1-2) Add ultra-dry tetrahydrofuran to the dispersion until a homogeneous solution is formed, add the homogeneous solution to a toluene dispersion of a transition metal salt or its complex, and react to obtain the reaction system; The transition metal in the transition metal salt or its complex is selected from titanium, zirconium, or hafnium; (2-1) Remove the low-boiling-point solvent in the reaction system described in step (1-2) by depressurization, filter, and obtain filtrate A and filter cake B; (2-2) Dissolve the filter cake B with an ultra-dry organic solvent, filter, remove the solvent from the filtrate under reduced pressure, and obtain the rac-structure shown in Formula II; The filtrate A was concentrated and mixed with n-hexane, filtered, and the solid was collected, which was a mixture of rac-structure and meso-structure. (3-1) Under an inert atmosphere, the mixture of rac-structure and meso-structure described in step (2-2) and metal halide and / or metal quaternary ammonium salt are reacted in an ultra-dry ether reagent, and the reaction product is filtered to obtain filter cake C; (3-2) The filter cake C is dissolved in an ultra-dry organic solvent, filtered, and the filtrate D is collected; after the solvent is removed by vacuum, the filtrate D is used to obtain the rac-structure shown in Formula II; Formula I Formula II Among them, R1, R2, R 3、 R 4、 R 5、 R6 may be the same or different, and are independently selected from hydrogen or C1~C10 alkyl groups; M is titanium, zirconium, or hafnium, with zirconium or hafnium being preferred; X is a C1 to C10 alkyl group or halogen, preferably methyl or chlorine.

2. The method according to claim 1, characterized in that, The alkyl lithium is selected from C 1~6 Alkyl lithium.

3. The method according to claim 1, characterized in that, Step (1-1) includes: under an inert atmosphere, the bridged biscrone ligand shown in Formula I is first dissolved in ultra-dry toluene, and the alkyl lithium solution is added to the system at a low temperature of -20ºC to 10ºC, and the reaction is stirred at room temperature for 8 to 15 hours.

4. The method according to claim 1, characterized in that, The transition metal salt is selected from one or more of titanium tetrachloride, zirconium tetrachloride, and hafnium tetrachloride; The transition metal salt complex is selected from the complex of transition metal salt and tetrahydrofuran or the complex of transition metal salt and amine.

5. The method according to claim 1, characterized in that, Steps (1-2) include: adding ultra-dry tetrahydrofuran to the dispersion until a homogeneous solution is formed; adding the homogeneous solution to an ultra-dry toluene solution of a transition metal salt or its complex at a low temperature of -20ºC to 0ºC; reacting at 20 to 70°C for 2 to 20 hours to obtain the reaction system.

6. The method according to claim 1, characterized in that, The low-boiling-point solvent mentioned in step (2-1) is tetrahydrofuran; And / or, the ultra-dry organic solvent described in steps (2-2) and (3-2) is toluene, dichloromethane, or a mixture of both.

7. The method according to claim 1, characterized in that, The metal halide described in step (3-1) has the following general formula: LY, where L is a group I metal element, preferably lithium, sodium, or potassium; and Y is a halogen, preferably chlorine or bromine. And / or, the metal quaternary ammonium salt described in step (3-1) has the following general formula: R1 ’ R2 ’ R3 ’ R4 ’ The independent alkyl group is C1-C18, preferably C1-C10, and even more preferably C1-C4; Y is a halogen, preferably chlorine or bromine; And / or, in step (3-1), the reaction temperature is 30~150℃ and the reaction time is 0.5~48h.

8. The method according to claim 1, characterized in that, The ether reagents mentioned in step (3-1) are selected from monoether reagents and / or diether reagents.

9. The method according to claim 8, characterized in that, In step (3-1), the diether reagent has the structure of formula III: Formula III Among them, R a R b They may be the same or different, and are independently C1 to C10 alkyl groups, preferably C1 to C4 alkyl groups.

10. The method according to claim 8, characterized in that, In step (3-1), the monoether reagent has a structure of formula IV: Formula IV Among them, R c R d They may be the same or different, and are independently C1 to C10 alkyl groups, preferably C1 to C4 alkyl groups; Or, R c R d The reagents are linked together to form a cyclic ether, preferably tetrahydrofuran.

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