Method for preparing racemic structural body by isomerization conversion of bridged double metallocene catalyst

Abstract

The invention discloses a method for preparing a racemic structure through isomerization conversion of a bridged double metallocene catalyst. According to the method, a meso-structural body raw material containing the bridged double-metallocene catalyst, an ether solvent and a catalyst are mixed and react to obtain a rac-structural body of the bridged double-metallocene catalyst. According to the method, the high-purity rac-structural body can be obtained, and the byproduct meso-structural body is effectively utilized, so that the yield and yield of the rac-structural body are improved, and the product can be directly used for preparing the bridged double metallocene catalyst.

Description

Technical Field

[0001] The invention belongs to the field of olefin polymerization catalysts and relates to an isomerization conversion method of a bridged dimetallocene catalyst and an application of the catalyst in preparing a racemic structure. Background Art

[0002] The metallocene catalyst system, which is composed of a metallocene compound of a transition metal (such as titanium, zirconium, and hafnium) and a cocatalyst (such as methylaluminoxane), is a homogeneous catalyst with a single catalyst active site. Compared with the traditional Ziegler-Natta (ZN) catalyst system, the polymerization products of the metallocene catalyst system show a narrower molecular weight distribution and a better comonomer insertion rate, and the polymer properties can be changed by changing the conformation of the ligand in the catalyst. This type of catalyst has been widely used in ethylene catalytic polymerization, propylene catalytic polymerization, or copolymerization of ethylene and α-olefins, greatly enriching the category of high-performance polyolefins. Since the 1980s, the category of metallocene catalysts has become increasingly rich, from single metallocene to double metallocene, from non-bridged to bridged structure, and the bridging atom from C bridge to Si bridge. Among them, the bridged double metallocene catalyst has the characteristics of high activity and good structural stability, and its spatial conformation is conducive to the formation of highly isotactic polyolefin products. This type of bridged double metallocene catalyst has been used in the commercial production of polypropylene, polyethylene, or polyolefin copolymers. The bridged bimetallocene catalyst has a chiral structure, with a pair of spatial isomer mixtures, including a racemic structure (rac-structure) and a meso structure (meso-structure). In these two isomers, the rac-structure has a higher application value in the field of polyolefins, and its olefin polymerization activity is high, copolymerization ability is strong, and the polymerized product has high isotacticity, and the meso-structure is less used in the field of olefin polymerization because it has poor olefin polymerization performance. In the process of synthesizing the bridged bimetallocene catalyst reported at present, the product directly obtained by the chemical reaction is a mixture of a rac-structure and a meso-structure, and then a pure rac-structure is obtained by a recrystallization process, and the meso-structure is abandoned as a by-product (Angew.Chem.Int.Ed.2022,61,e202210797;Organometallics 2006,25,1217-1229). Such methods have the disadvantages that the meso-structure is not effectively utilized and the rac-structure yield is low. Summary of the invention

[0003] In order to improve the above technical problems, the present invention provides a method for isomerization conversion of a bridged dimetallocene catalyst, wherein a low-value meso-structure produced during the synthesis of the bridged dimetallocene catalyst is converted into a rac-structure under certain conditions, and a high-purity rac-structure is further obtained by extraction with an organic solvent, and the output and yield of the rac-structure are significantly improved.

[0004] The present invention provides a method for isomerization conversion of a bridged bimetallocene catalyst, the method comprising:

[0005] The raw material containing the meso-structure of the bridged dimetallocene catalyst is mixed with an ether solvent and a catalyst for reaction to obtain the rac-structure of the bridged dimetallocene catalyst;

[0006] The rac-structure has a structure as shown in Formula Ia, and the meso-structure has a structure as shown in Formula Ib:

[0007]

[0008] Wherein, M is titanium, zirconium or hafnium;

[0009] X is C 1～20 Alkyl, halogen substituted C 1～20 Alkyl or halogen;

[0010] R1, R2, R3 are the same or different and are independently selected from hydrogen, C 1～20 Alkyl or halogen substituted C 1～20 alkyl;

[0011] The catalyst is selected from metal halides or quaternary ammonium salts.

[0012] According to an embodiment of the present invention, the M is preferably zirconium or hafnium.

[0013] According to an embodiment of the present invention, X is C 1～10 Alkyl, halogen substituted C 1～10 Alkyl or halogen, preferably C 1～4 Alkyl, halogen substituted C 1～4 Alkyl or halogen, exemplified by methyl, chlorine.

[0014] According to an embodiment of the present invention, R1, R2, and R3 are independently selected from hydrogen, C 1～10 Alkyl or halogen substituted C 1～10 Alkyl, preferably hydrogen, C 1～4 Alkyl or halogen substituted C 1～4 Alkyl groups are exemplified by hydrogen, methyl, ethyl, isopropyl, and tert-butyl.

[0015] According to an embodiment of the present invention, the halogen includes F, Cl, Br, and I.

[0016] According to an exemplary embodiment of the present invention, M is zirconium, X is chlorine, R1 is methyl, and / or R2 and R3 are hydrogen.

[0017] When M is zirconium, X is chlorine, R1 is methyl, and R2 and R3 are hydrogen, the bridged dual metallocene catalyst is dimethylsilylbis(2-methyl-4-phenyl-indenyl)zirconium dichloride.

[0018] According to an embodiment of the present invention, the raw material may be a meso-structure of a bridged dual metallocene catalyst or a mixture of a meso-structure and a rac-structure.

[0019] According to an embodiment of the present invention, the ether solvent is selected from monoether solvents and / or diether solvents.

[0020] According to an embodiment of the present invention, the diether solvent has a structure shown in Formula II:

[0021]

[0022] R a , R b The same or different, independently selected from C 1～20 Alkyl, preferably C 1～10 Alkyl, preferably C 1～4 The alkyl group is exemplified by methyl, ethyl, propyl or butyl. In some embodiments, the diether solvent is ethylene glycol dimethyl ether.

[0023] According to an embodiment of the present invention, the monoether reagent has a structure as shown in Formula III:

[0024]

[0025] R c , R d The same or different, independently selected from C 1～20 Alkyl; or, R c , R d Connect to form C 3～20 Cyclic ethers;

[0026] Preferably, R c , R d Independently selected from C 1～10 Alkyl; or, R c , R d Connect to form C 3～10 Cyclic ethers;

[0027] For example, R c , R d Selected from methyl, ethyl, propyl, tert-butyl or connected to form tetrahydrofuran.

[0028] According to an embodiment of the present invention, the ether solvent is an ultra-dry ether solvent.

[0029] According to an embodiment of the present invention, the metal halide is preferably an alkali metal halide LY, where L represents a first main group metal element, preferably lithium, sodium, potassium; and Y represents a halogen, preferably chlorine or bromine. Exemplarily, the metal halide is lithium chloride.

[0030] According to an embodiment of the present invention, the quaternary ammonium salt has a structure as shown in Formula IV:

[0031]

[0032] R1, R2, R3, R4 are the same or different and are independently selected from C 1～20 Alkyl, preferably C 1～10 Alkyl, preferably C 1～4 Alkyl, exemplified by methyl, ethyl, propyl, butyl;

[0033] Y represents halogen, preferably chlorine or bromine.

[0034] In an exemplary embodiment, the quaternary ammonium salt is tetramethylammonium chloride.

[0035] According to an embodiment of the present invention, the mass ratio of the meso-structure of the bridged dimetallocene catalyst to the ether solvent is 1:(2-200), for example 1:(5-150), exemplified by 1:8, 1:9, 1:10, 1:20, 1:50, 1:80, 1:85, 1:90, 1:100.

[0036] According to an embodiment of the present invention, the mass ratio of the meso-structure to the catalyst of the bridged dimetallocene catalyst is (0.1-25):1, for example (0.5-20):1, exemplified by 0.5:1, 1:1, 5:1, 10:1, 11:1, 13:1, 15:1, 17:1.

[0037] According to an embodiment of the present invention, the reaction temperature is 30 to 150° C., preferably 50 to 100° C.; and / or the reaction time is 0.5 to 48 h, preferably 4 to 20 h.

[0038] According to an embodiment of the present invention, the reaction is carried out under an inert atmosphere (e.g., nitrogen atmosphere) that is anhydrous and oxygen-free. The anhydrous and oxygen-free refers to a system in which the mass content of water does not exceed 1%, preferably does not exceed 0.5%, and more preferably does not exceed 0.2%, and the mass content of oxygen does not exceed 5%, further preferably does not exceed 1%, and more preferably does not exceed 0.5%.

[0039] According to an embodiment of the present invention, the method further comprises: removing the ether solvent in the reaction product under reduced pressure, adding a first organic solvent to the residue, filtering, collecting the filtrate, and concentrating the filtrate; adding a second organic solvent to the concentrated filtrate, stirring, and filtering to obtain a solid, which is a rac-structure;

[0040] Preferably, the first organic solvent is selected from one or both of toluene and dichloromethane;

[0041] Preferably, the second organic solvent is C 5～12 Alkanes, preferably one or both of n-hexane and n-heptane;

[0042] Preferably, the first organic solvent and / or the second organic solvent is an ultra-dry organic solvent;

[0043] Preferably, after adding the first organic solvent, the mixture is heated to 70-90° C. and filtered while hot.

[0044] According to a preferred embodiment of the present invention, the method comprises the following steps:

[0045] (1) in an inert atmosphere without water or oxygen, dispersing a meso-structure or a mixture of a meso-structure and a rac-structure of a bridged dimetallocene catalyst in an ultra-dry ether solvent, adding the metal halide or quaternary ammonium salt, and heating to 50-100° C.;

[0046] (2) After the reaction in step (1) is completed, the solvent in the reaction product is removed under reduced pressure, and the first organic solvent is added to the residue, filtered, the filtrate is collected, and the filtrate is concentrated; then the second organic solvent is added to the concentrated filtrate, stirred, filtered to obtain a solid, and dried to obtain a yellow powder, which is the rac-structure.

[0047] The present invention also provides application of the above method in preparing the rac-structure of the bridged dimetallocene catalyst.

[0048] Beneficial Effects

[0049] During the synthesis of the bridged dimetallocene catalyst, a meso-structure is produced along with a rac-structure. The method of the present invention can be used to convert an undesirable meso-structure into a desired rac-structure, and then a high-purity rac-structure can be obtained through organic solvent extraction, washing and purification, so that the content of the meso-structure is less than 5%, or even less than 2%, and the by-product meso-structure is effectively utilized, thereby increasing the output and yield of the rac-structure, and the product can be directly used to prepare the bridged dimetallocene catalyst. DETAILED DESCRIPTION

[0050] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations 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 included in the scope that the present invention is intended to protect.

[0051] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0052] Example 1

[0053] In an inert atmosphere, 1.0 g of dimethylsilylbis(2-methyl-4-phenyl-indenyl)zirconium dichloride (the ratio of rac-structure to meso-structure is 1 / 1.42, containing 0.41 g of rac-structure) is mixed with 5.0 g of ultra-dry ethylene glycol dimethyl ether and 0.05 g of LiCl, and reacted at 65° C. for 8 h; ethylene glycol dimethyl ether is removed under reduced pressure, 150 ml of ultra-dry toluene is added to the residue, heated to 80° C., filtered while hot, toluene is concentrated to 15 ml under reduced pressure, 15 ml of ultra-dry n-hexane is added, stirred overnight, and filtered to obtain 0.85 g of yellow powder. After testing, the mass ratio of rac-structure to meso-structure in the yellow powder is 1 / 0.01. The content of rac-structure increases from 0.41 g before conversion to 0.84 g after conversion, and the mass proportion of meso-structure is less than 2%, which meets the requirements of rac-structure as an olefin polymerization catalyst.

[0054] 1 H 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).

[0055] Example 2

[0056] In an inert atmosphere, 40g of dimethylsilylbis(2-methyl-4-phenyl-indenyl)zirconium dichloride (the ratio of rac-structure to meso-structure is 1 / 2.75, containing 10.67g of rac-structure) is mixed with 300g of ultra-dry ethylene glycol dimethyl ether and 2.6g of LiCl, and reacted at 70°C for 7h; ethylene glycol dimethyl ether is removed under reduced pressure, 5L of ultra-dry toluene is added to the residue, heated to 80°C, filtered while hot, the filtrate is concentrated to 500ml, 500ml of ultra-dry n-hexane is added, stirred overnight, filtered, and dried to obtain 31g of yellow powder. After testing, the mass ratio of rac-structure to meso-structure in the yellow powder is 1 / 0.01. The content of rac-structure increases from 10.67g before conversion to 30.70g after conversion. After nuclear magnetic resonance detection, the mass proportion of meso-structure in the product is less than 2%, which meets the requirements of rac-structure as an olefin polymerization catalyst.

[0057] 1 H 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).

[0058] Example 3

[0059] In an inert atmosphere, 0.5 g of dimethylsilylbis(2-methyl-4-phenyl-indenyl)zirconium dichloride (the ratio of rac-structure to meso-structure is 1 / 1.42, containing 0.21 g of rac-structure) is mixed with 2.5 mL of ultra-dry tetrahydrofuran and 0.52 g of tetramethylammonium chloride, and reacted at 80° C. for 14 h; tetrahydrofuran is removed under reduced pressure, 70 ml of ultra-dry toluene is added to the residue, heated to 80° C., filtered while hot, toluene is concentrated to 7 ml under reduced pressure, 7 ml of ultra-dry n-hexane is added, stirred overnight, and filtered to obtain 0.35 g of yellow powder. After testing, the mass ratio of rac-structure to meso-structure in the yellow powder is 1 / 0.02. The content of rac-structure increases from 0.21 g before conversion to 0.34 g after conversion. After nuclear magnetic resonance testing, the mass content of meso-structure in the product is less than 2%, which meets the requirements of rac-structure as an olefin polymerization catalyst.

[0060] 1 H 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).

[0061] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for isomerization conversion of a bridged dual metallocene catalyst, characterized in that: The method comprises: The raw material containing the meso-structure of the bridged dimetallocene catalyst is mixed with an ether solvent and a catalyst for reaction to obtain the rac-structure of the bridged dimetallocene catalyst; The rac-structure has a structure as shown in Formula Ia, and the meso-structure has a structure as shown in Formula Ib: Wherein, M is titanium, zirconium or hafnium; X is C 1～20 Alkyl, halogen substituted C 1～20 Alkyl or halogen; R1, R2, R3 are the same or different and are independently selected from hydrogen, C 1～20 Alkyl or halogen substituted C 1～20 alkyl; The catalyst is selected from metal halides or quaternary ammonium salts.

2. The method according to claim 1, characterized in that The M is zirconium or hafnium; And / or, X is C 1～10 Alkyl, halogen substituted C 1～10 Alkyl or halogen, preferably C 1～4 Alkyl, halogen substituted C 1～4 Alkyl or halogen; And / or, said R1, R2, R3 are independently selected from hydrogen, C 1～10 Alkyl or halogen substituted C 1～10 Alkyl, preferably hydrogen, C 1～4 Alkyl or halogen substituted C 1～4 alkyl.

3. The method according to claim 1, characterized in that M is zirconium, X is chlorine, R1 is methyl, and / or R2 and R3 are hydrogen.

4. The method according to claim 1, characterized in that The raw material is a meso-structure of a bridged dual metallocene catalyst or a mixture of a meso-structure and a rac-structure.

5. The method according to claim 1, characterized in that: The ether solvent is selected from monoether solvents and / or diether solvents; Preferably, the diether solvent has a structure shown in Formula II: R a , R b The same or different, independently selected from C 1～20 Alkyl, preferably C 1～10 alkyl; Preferably, the monoether reagent has a structure as shown in Formula III: R c , R d The same or different, independently selected from C 1～20 Alkyl; or, R c , R d Connect to form C 3～20 Cyclic ethers; Preferably, R c , R d Independently selected from C 1～10 Alkyl; or, R c , R d Connect to form C 3～10 Cyclic ethers; Preferably, the ether solvent is an ultra-dry ether solvent.

6. The method according to claim 1, characterized in that The metal halide is an alkali metal halide LY, where L represents a first main group metal element; and Y represents a halogen; And / or, the quaternary ammonium salt has a structure as shown in Formula IV: R1, R2, R3, R4 are the same or different and are independently selected from C 1～20 Alkyl, preferably C 1～10 alkyl; Y represents halogen.

7. The method according to claim 1, characterized in that The mass ratio of the meso-structure of the bridged dimetallocene catalyst to the ether solvent is 1:(2-200); And / or, the mass ratio of the meso-structure of the bridged dimetallocene catalyst to the catalyst is (0.1-25):

1.

8. The method according to claim 1, characterized in that The reaction temperature is 30 to 150° C., and / or the reaction time is 0.5 to 48 hours; And / or, the reaction is carried out under an inert atmosphere free of water and oxygen.

9. The method according to claim 1, characterized in that: The method further comprises: removing the ether solvent in the reaction product under reduced pressure, adding a first organic solvent to the residue, filtering, collecting the filtrate, and concentrating the filtrate; adding a second organic solvent to the concentrated filtrate, stirring, and filtering to obtain a solid, which is a rac-structure; Preferably, the first organic solvent is selected from one or both of toluene and dichloromethane; Preferably, the second organic solvent is C 5～12 Alkanes; Preferably, the first organic solvent and / or the second organic solvent is an ultra-dry organic solvent; Preferably, after adding the first organic solvent, the mixture is heated to 70-90° C. and filtered while hot.

10. Use of the method according to any one of claims 1 to 9 in preparing a rac-structure of a bridged dimetallocene catalyst.

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