A bimetallic polymer catalyst, its preparation method and application

Abstract

The present invention discloses a bimetallic polymer catalyst, its preparation method and application. After two chiral ligands are complexed with a metal, a random copolymer is synthesized by a radical copolymerization method. This catalyst has a chiral amplification effect, can synergistically combine the advantages of two chiral catalysts, catalyze an asymmetric hydrogenation reaction (ATH) and a decarboxylative Mannich reaction cascade reaction, exhibits high catalytic activity and stereoselectivity, and moreover, this catalyst can be recycled, and its catalytic activity and selectivity have high recycling stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation and application of supported catalysts, and particularly relates to a bimetallic polymer catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] In most cases, the use of bimetallic species shows better activity than monometallic species. Generally, the unique reactivity, selectivity, and modified catalytic activity of the corresponding monometallic species can be seen from the reactions catalyzed by bimetallic nanoparticles. The combined characteristics of the two different metals present in the catalyst are usually referred to as the "synergistic effect", which is caused by the changes occurring on the catalyst surface due to heterogeneous metal-metal interactions. Although there are some reports on dual catalytic strategies, the multi-catalyst systems involved do not fully cooperate. Developing bimetallic catalysts for the synergistic catalysis of multi-step sequence reactions is of great significance. However, the effective catalysis in a single operation due to the interaction between the intrinsically complex microenvironment and chirality of the dual catalysts is a huge challenging task.

[0003] Loading chiral metal catalysts through polymers can, on the one hand, promote the progress of reactions under certain circumstances, and on the other hand, facilitate the recycling of the catalysts. Ding Yunjie et al. reported a phosphine-containing polymer chiral catalyst and its application in asymmetric synthesis reactions. Due to the uniform embedding of chiral ligands into the polymer backbone, relatively high catalytic activity was achieved. They also reported the application of a chiral hypercrosslinked material with a pore structure in asymmetric hydrogenation reactions. However, there are no relevant cases of efficiently and highly selectively applying bimetallic chiral catalysts supported by polymers in asymmetric reactions. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a preparation method of a heterogeneous bimetallic chiral catalyst. This method simultaneously introduces noble metals and non-noble metals into the chiral polymer catalyst and avoids ligand exchange. The coordination induction and assembly of metals play a crucial role in obtaining good yields and selectivities in catalytic reactions. The synergistic effect of the dual chiral metal catalysts is well exerted in the random copolymer, and at the same time, there is a chiral amplification effect, achieving a catalytic effect that cannot be achieved by small molecule blending. The success of this research will make the application of chiral metal catalysts more economical, cheaper, and environmentally friendly.

[0005] The present invention adopts the following technical solution to solve the above technical problem. A preparation method of a bimetallic chiral polymer catalyst. After complexing two chiral ligands with metals, a random copolymer is synthesized by a free radical copolymerization method. The obtained catalyst has a chiral amplification effect, can synergistically combine the advantages of the two chiral catalysts, catalyze the cascade reaction of asymmetric hydrogenation reaction and decarboxylative Mannich reaction, and exhibits high catalytic activity and stereoselectivity.

[0006] Further, the specific steps are as follows: Add chiral ligands A-Ru and B-Cu into a Schlenk flask, add them into a dry solvent, ultrasonically dissolve them, then add AIBN, and react at 60-90 °C for 8-24 h. After the reaction is completed, wash the reaction solution in a mixed solvent of a large amount of n-hexane / ether 1:1 to remove unreacted monomers, and dry it under vacuum for 24 h to obtain a chiral copolymer. The specific synthesis route in the preparation process is as follows:

[0007]

[0008] m = 1000 - 60000, n = 1000 - 80000.

[0009] The present invention provides a bimetallic chiral polymer catalyst prepared by the above method.

[0010] The present invention also provides the use of the catalyst prepared by the above method in an asymmetric hydrogenation reaction and a decarboxylative Mannich reaction cascade reaction. The specific process is as follows: Add β 0.06 mmol of α-keto acid, 0.04 mmol of cyclic aldimine and 5 - 50 mg of the polymer catalyst into a round-bottom flask, dissolve them with 1 - 20 mL of solvent, then add 0.2 mmol of ammonium formate, disperse evenly, first react at -20 °C for 5 - 10 h, then react at 60 °C for 10 - 24 h. After the reaction is completed, add ether to separate the catalyst, then centrifuge to recover the catalyst, extract with ethyl acetate and saturated brine respectively, dry with anhydrous MgSO4, then filter and rotary evaporate to concentrate the organic phase, and then purify the product by column chromatography with PE:EA = 4:1.

[0011] Compared with the prior art, the present invention has the following advantages: This method simultaneously introduces noble metals and non-noble metals into the chiral polymer catalyst and avoids ligand exchange. The coordination induction and assembly of metals play a crucial role in obtaining good yields and selectivities in catalytic reactions. The synergistic effect of the bimetallic chiral catalyst is well exerted in the random copolymer, and at the same time has a chiral amplification effect, achieving a catalytic effect that cannot be achieved by small molecule blending. The success of this research will make the application of chiral metal catalysts more economical, cheaper and environmentally friendly. In addition, the catalyst recovery method is simple and effective, and can be recycled repeatedly without significantly reducing the catalytic activity. Description of the Drawings

[0012] Figure 1 It is a circular dichroism CD test chart of the bimetallic catalyst prepared in Example 1. Detailed Embodiments

[0013] The above content of the present invention will be further described in detail through the following examples. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples. All technologies implemented based on the above content of the present invention belong to the scope of the present invention. Example 1

[0014] Preparation of Polymer Bimetallic Chiral Catalyst

[0015] Add 2 mmol of chiral ligand A-Ru and 1 mmol of B-Cu into a Schlenk flask, add them to 1 mL of DMF, ultrasonically dissolve them, then add 1% of AIBN based on the total amount of monomers, and react at 70 °C for 24 h. After the reaction, wash the reaction solution in a mixed solvent of a large amount of n-hexane / ether 1:1 to remove unreacted monomers, and vacuum dry for 24 h to obtain a chiral copolymer. Example 2

[0016] Add β -keto acid (0.06 mmol), cyclic aldehyde imine (0.04 mmol) and 5 mg of the chiral copolymer catalyst prepared in Example 1 into a 10 mL round-bottom flask, dissolve it in 1.2 mL of THF / H2O 1:1 solvent, then add ammonium formate (0.2 mmol). After dispersing evenly, react at -20 °C for 5 h first, and then at 60 °C for 18 h. After the reaction, add 3 mL of ether to separate the catalyst, then centrifuge to recover the catalyst, extract with ethyl acetate and saturated brine respectively, dry with anhydrous MgSO4, then filter and rotary evaporate to concentrate the organic phase, and then purify the product by column chromatography (PE:EA = 4:1). Yield: 60%, ee value: 99%, Dr: 96:1. Example 3

[0017] Add β -keto acid (0.06 mmol), cyclic aldehyde imine (0.04 mmol) and 5 mg of the chiral copolymer catalyst prepared in Example 1 into a 10 mL round-bottom flask, dissolve it in 1.2 mL of THF / H2O 4:1 solvent, then add ammonium formate (0.2 mmol). After dispersing evenly, react at -20 °C for 5 h first, and then at 60 °C for 18 h. After the reaction, add 3 mL of ether to separate the catalyst, then centrifuge to recover the catalyst, extract with ethyl acetate and saturated brine respectively, dry with anhydrous MgSO4, then filter and rotary evaporate to concentrate the organic phase, and then purify the product by column chromatography (PE:EA = 4:1). Yield: 80%, ee value: 98%, Dr: 99:1. Example 4

[0018] Add β-keto acid (0.06 mmol), cyclic aldimine (0.04 mmol) and 5 mg of the copolymer catalyzed by Example 3 were added to a 10 mL round-bottom flask, dissolved in 1.2 mL of THF / H2O 4:1 solvent, then ammonium formate (0.2 mmol) was added. After being dispersed evenly, the reaction was carried out at -20 °C for 5 h first, and then at 60 °C for 18 h. After the reaction was completed, 3 mL of diethyl ether was added to separate the catalyst, and then the catalyst was recovered by centrifugation. It was extracted with ethyl acetate and saturated brine respectively, dried over anhydrous MgSO4, then filtered and the organic phase was concentrated by rotary evaporation. Then the product was purified by column chromatography (PE:EA = 4:1). Yield: 79%, ee value: 98%, Dr: 98:1. Example 5

[0019] Add β -keto acid (0.06 mmol), cyclic aldimine (0.04 mmol) and 5 mg of the copolymer catalyzed by Example 4 were added to a 10 mL round-bottom flask, dissolved in 1.2 mL of THF / H2O 4:1 solvent, then ammonium formate (0.2 mmol) was added. After being dispersed evenly, the reaction was carried out at -20 °C for 5 h first, and then at 60 °C for 18 h. After the reaction was completed, 3 mL of diethyl ether was added to separate the catalyst, and then the catalyst was recovered by centrifugation. It was extracted with ethyl acetate and saturated brine respectively, dried over anhydrous MgSO4, then filtered and the organic phase was concentrated by rotary evaporation. Then the product was purified by column chromatography (PE:EA = 4:1). Yield: 77%, ee value: 98%, Dr: 99:1.

[0020] As Figure 1 shown, the CD test results show that the copolymerization of the bimetallic catalyst has a chiral amplification effect.

Claims

1. A method for preparing a bimetallic polymer catalyst, characterized in that, After complexing two chiral ligands with a metal, an amorphous copolymer is synthesized by radical copolymerization. The obtained catalyst has a chiral amplification effect and can synergistically combine the advantages of the two chiral catalysts to catalyze the cascade reaction of asymmetric hydrogenation and decarboxylative Mannich reaction, showing high catalytic activity and stereoselectivity. The specific steps are as follows: Add chiral ligand A-Ru and B-Cu into a Schlenk flask, add them into a dry solvent, ultrasonically dissolve them, then add AIBN, and react at 60-90 °C for 8-24 h. After the reaction is completed, wash the reaction solution with a large amount of a mixed solvent of n-hexane / ethyl ether 1:1 to remove unreacted monomers, and dry in vacuo for 24 h to obtain a chiral copolymer. The specific synthetic route during the preparation process is as follows: ； m = 1000 - 60000, n = 1000 - 80000.

2. A bimetallic polymer catalyst, characterized in that, Obtained by the method according to claim 1.

3. A bimetallic polymer catalyst according to claim 2 is used in an asymmetric hydrogenation reaction and a decarboxylative Mannich reaction cascade reaction, characterized in that, The specific process is as follows: β 0.06 mmol of keto acid, 0.04 mmol of cyclic aldimine and 5 - 50 mg of polymer catalyst are added to a round-bottom flask, and 1 - 20 mL of solvent is added to dissolve them. Then, 0.2 mmol of ammonium formate is added. After being dispersed evenly, the reaction is carried out at -20 °C for 5 - 10 h first, and then at 60 °C for 10 - 24 h. After the reaction is completed, ether is added to separate the catalyst, and then the catalyst is recovered by centrifugation. The product is extracted with ethyl acetate and saturated brine respectively, dried over anhydrous MgSO4, and then filtered and rotary evaporated to concentrate the organic phase. Then, the product is purified by column chromatography with PE:EA = 4:1.

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