Chitosan-based coupling reaction catalyst as well as preparation method and application thereof

Abstract

The invention discloses a chitosan-based coupling reaction catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: sequentially modifying chitosan by using an aromatic aldehyde compound and halogenated carboxylic acid to prepare modified chitosan with multiple complexing sites of imino, carboxyl and hydroxyl, taking the modified chitosan as a carrier, and complexing the capturing sites with palladium salt to prepare a catalyst of a functional chitosan-loaded Pd complex. Through a multi-site synergistic complexing effect, the catalyst shows excellent catalytic efficiency and stability in a coupling reaction. Depending on multi-site complexing metal Pd, after the catalyst is recycled for multiple times, the metal falling amount is lower than 0.1%, and the defect that metal of a traditional heterogeneous catalysis system is prone to loss is overcome. In the preparation process, the environment-friendly chitosan with relatively high biocompatibility is used as an initial raw material, so that the preparation method has the advantages of low production energy consumption, environment-friendly and efficient catalytic process, good cycle performance and the like, and has a wide industrial application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of heterogeneous catalysis, and particularly relates to a chitosan-based coupling reaction catalyst and a preparation method and application thereof. Background Art

[0002] In organic catalysis, C-C bond formation is a crucial component of organic synthesis research. The Suzuki coupling reaction is a highly efficient synthetic method for C-C bond formation, accounting for approximately 70% of practical production applications. Since its discovery in the 1970s, it has gained widespread application in fields such as medicine, agriculture, cosmetics, and advanced materials. Due to its mild reaction conditions, commercially available products, and high tolerance to functional groups, this reaction is crucial in the synthesis of complex organic molecules. Pd catalysts play a crucial role in this process. While homogeneous Pd catalysts suffer from the difficulties of separation and precious metal contamination, heterogeneous Pd catalysts effectively overcome these issues. However, heterogeneous Pd catalysts still suffer from poor stability, metal leaching, and the use of toxic solvents during the catalytic process. During the synthesis of heterogeneous catalysts, the choice of support material and ligand directly influences the metal loading and stability, thereby impacting the catalytic and cycling performance of the catalyst. Therefore, developing heterogeneous Pd catalysts with both green, non-toxic, and easily modifiable support materials and ligands with multiple chelating sites is key to achieving efficient catalytic performance. Summary of the Invention

[0003] To solve the above problems, the present invention provides a chitosan-based coupling reaction catalyst, a preparation method and application thereof, which solves the problems of easy metal loss and poor stability of existing catalysts. At the same time, the prepared catalyst can be used at a lower reaction temperature and a green solvent (an aqueous solution of ethanol). The catalytic process is more low-carbon and environmentally friendly, meeting the essence of green chemistry.

[0004] Chitosan has the advantages of biodegradability and biocompatibility, easy availability, and non-toxicity, making it suitable as a carrier material. In addition, the surface of chitosan has rich functional groups and can be easily modified and functionalized to make it easier to complex metal particles. Schiff base ligands have low toxicity, high stability, and are easy to complex metals, and can be used to prepare catalysts with high activity and stability. Based on this, the natural polymer chitosan carrier modified with Schiff base and carboxyl prepared by the present invention has multifunctional binding sites that can be effectively complexed with Pd. The catalyst has the advantages of low cost, easy separation, strong metal binding ability, and high stability, and the catalytic process has the characteristics of suitable reaction temperature and the use of green solvents, which is in line with the principles of green chemistry and sustainable development.

[0005] To achieve the above objectives, this application adopts the following technical solutions:

[0006] A method for preparing a chitosan-based coupling reaction catalyst comprises the following steps:

[0007] (1) Add an appropriate amount of chitosan to an aqueous solution of glacial acetic acid and heat and stir until the chitosan is fully dissolved. Then slowly add an aromatic aldehyde compound to the system and react under an inert atmosphere. After the reaction is completed, add a halogenated carboxylic acid to the reaction system for reaction. After the reaction is completed, cool to room temperature, centrifuge and separate the precipitate, wash and vacuum dry to obtain Schiff base modified carboxymethyl chitosan.

[0008] (2) Disperse the Schiff base modified carboxymethyl chitosan in a solvent, add palladium salt under the protection of an inert atmosphere, and react. After the reaction is completed, cool to room temperature, centrifuge and separate the precipitate, continue washing with solvent for multiple times until the filtrate is colorless, and vacuum dry to obtain a chitosan-based coupling reaction catalyst.

[0009] The inert gas in (1) is nitrogen or argon.

[0010] The aromatic aldehyde compound in (1) is selected from one of 2,9-diformyl-1,10-phenanthroline, 2,2'-bipyridine-6,6'-dicarboxaldehyde, 2-quinolinecarboxaldehyde, 8-quinolinecarboxaldehyde, 2-pyridinecarboxaldehyde, and 2-pyridineacetaldehyde, and its structural formula is as follows:

[0011]

[0012] The halogenated carboxylic acid in (1) includes at least one of 1-chloroacetic acid and 2-chloropropionic acid.

[0013] In the above (1), the reaction time after adding the aromatic aldehyde compound is 12 to 20 hours, and the reaction time after adding the halogenated carboxylic acid is 2 to 4 days.

[0014] The solvent in (2) is at least one of water, ethanol, acetonitrile, and N,N-dimethylformamide (DMF).

[0015] The reaction temperature of step (2) is 50°C to 80°C, and the reaction time of step (2) is 12 to 24 hours.

[0016] The palladium salt in (2) is at least one of sodium chloropalladate, palladium acetate, palladium dichloride, and palladium nitrate.

[0017] The mass ratio of the palladium salt in (2) to the Schiff base modified carboxymethyl chitosan is 1:2 to 1:10.

[0018] The present invention also provides the use of the chitosan-based coupling reaction catalyst in a Suzuki coupling reaction. As a heterogeneous catalyst, the material can efficiently catalyze the Suzuki coupling reaction under mild conditions, such as in a green solvent and at a relatively low reaction temperature. After five cycles, the Pd content in the catalyst barely decreased, and the catalyst still exhibited excellent catalytic performance after the final recycling.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The carrier chitosan used in the present invention is a natural polymer that is biodegradable, biocompatible, non-toxic, and readily available. Furthermore, chitosan contains a large number of hydroxyl and amino groups, making it easy to modify and readily complex various metal ions.

[0021] (2) Chitosan modified with Schiff base and carboxyl groups has multifunctional binding sites, which enhances the complexation with Pd and further strengthens its binding effect, effectively preventing metal shedding, enhancing its stability, increasing the metal loading rate, and reducing the loss of Pd during the reaction. It can be reused multiple times by simple centrifugal separation and still maintains high catalytic efficiency.

[0022] (3) When chitosan-based coupling reaction catalysts are used in Suzuki reaction, the solvent used is an aqueous solution of ethanol, which is a greener solvent.

[0023] (4) When chitosan-based coupling reaction catalysts are used in Suzuki reaction, the reaction temperature is low, the reaction conditions are suitable, and the yield of the obtained product is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the synthesis route of catalyst OCMCS-SB-Pd-a of Example 1;

[0025] Figure 2 TEM image of catalyst OCMCS-SB-Pd-b of Example 2;

[0026] Figure 3 SEM images of the catalyst OCMCS-SB-Pd-a (a) and OCMCS-SB-Pd-a after five cycles of use (b) in Example 1;

[0027] Figure 4 This is a comparison chart of the catalytic activity and Pd content of the catalyst OCMCS-SB-Pd-a of Example 1, the catalyst OCMCS-SB-Pd-a after five cycles of use in Example 1, and the catalyst CS-Pd of Comparative Example 1 under the same reaction conditions. DETAILED DESCRIPTION

[0028] The following examples further illustrate the present invention in detail. It should be understood that the specific embodiments described herein are only used to illustrate the present invention and are not intended to limit the present invention. All technologies implemented based on the above content of the present invention belong to the scope of the present invention.

[0029] Example 1

[0030] Example 1 provides a chitosan-based coupling reaction catalyst, referring to Figure 1 , and its preparation method is:

[0031] (1) 0.3 g of chitosan was mixed with 25 mL of 2% glacial acetic acid solution (2% by volume) and stirred at 70 °C for 2 h to fully dissolve the chitosan. Then, a DMF solution containing 0.82 g of 2,9-diformyl-1,10-phenanthroline was added dropwise to the system and reacted under a nitrogen atmosphere for 15 h. Subsequently, a DMF solution containing 1.5 g of 1-chloroacetic acid was added dropwise and reacted at 60 °C under a nitrogen atmosphere for 4 d. After the reaction was completed, the mixture was cooled to room temperature and centrifuged to obtain a purple solid, which was washed several times with DMF and ethanol until the filtrate became colorless. The solid was dried in a vacuum at 60 °C overnight to obtain a powdery solid, which was designated as OCMCS-SB-a.

[0032] (2) 0.4 g of the obtained OCMCS-SB-a was dispersed in 15 mL of distilled water and stirred under nitrogen for 1 h. Subsequently, 15 mL of an aqueous solution containing 0.2 g of Na2PdCl4 was added and the mixture was reacted at 70°C for 24 h. After the reaction, the mixture was cooled to room temperature and centrifuged to obtain a solid. The solid was washed several times with distilled water until the filtrate was colorless and finally dried under vacuum at 60°C for 24 h to obtain a chitosan-based coupling reaction catalyst, which was designated as OCMCS-SB-Pd-a.

[0033] Example 2

[0034] Example 2 provides a chitosan-based coupling reaction catalyst, the preparation method of which is as follows:

[0035] (1) 0.3 g of chitosan was mixed with 25 mL of 2% glacial acetic acid solution (2% by volume) and stirred at 70 °C for 2 h to fully dissolve the chitosan. Then, a DMF solution containing 0.74 g of 2,2'-bipyridine-6,6'-dicarboxaldehyde was added dropwise to the system and reacted under a nitrogen atmosphere for 12 h. Subsequently, a DMF solution containing 1.5 g of 1-chloroacetic acid was added dropwise and the reaction was continued at 60 °C for 2 d. After the reaction was completed, the mixture was cooled to room temperature and centrifuged to obtain a solid. The solid was washed several times with DMF and ethanol until the filtrate became colorless. The solid was dried in a vacuum at 60 °C overnight to obtain a powdery solid, which was designated as OCMCS-SB-b.

[0036] (2) 0.4 g of the obtained OCMCS-SB-b was dispersed in 15 mL of acetonitrile and stirred under nitrogen for 1 h. Subsequently, 15 mL of acetonitrile solution containing 0.1 g of Pd(OAc)2 was added and the mixture was reacted at 60°C for 20 h. After the reaction, the mixture was cooled to room temperature, centrifuged, and washed with acetonitrile several times until the filtrate was colorless. Finally, the mixture was dried in vacuum at 60°C for 24 h to obtain a chitosan-based coupling reaction catalyst, which was designated as OCMCS-SB-Pd-b.

[0037] Figure 2 The transmission electron microscope image of the catalyst OCMCS-SB-Pd-b in Example 2 is shown in FIG. Figure 2 As shown in the figure, Pd is evenly distributed on the surface of modified chitosan with a particle size of 6-16 nm, ensuring the high catalytic activity and stability of the catalyst.

[0038] Example 3

[0039] Example 3 provides a chitosan-based coupling reaction catalyst, the preparation method of which is as follows:

[0040] (1) 0.3 g of chitosan was mixed with 25 mL of 2% glacial acetic acid solution (2% by volume) and stirred at 70 °C for 2 h to fully dissolve the chitosan. Then, a DMF solution containing 10.62 g of 2-quinolinecarboxaldehyde was added dropwise to the system and reacted under an argon atmosphere for 18 h. Subsequently, a DMF solution containing 1.5 g of 2-chloropropionic acid was added dropwise and stirred at 60 °C under an argon atmosphere for 3 d. After the reaction was completed, the solid was cooled to room temperature and centrifuged to obtain a solid. The solid was washed several times with DMF and ethanol until the filtrate became colorless. The solid was dried in a vacuum at 60 °C overnight to obtain a powdery solid, which was designated as OCMCS-SB-c.

[0041] (2) 0.4 g of the obtained OCMCS-SB-c was dispersed in 15 mL of distilled water and stirred under argon for 1 h. Subsequently, 15 mL of an aqueous solution containing 0.067 g of Pd(NO3)2 was added and the mixture was reacted at 80°C for 15 h. After the reaction, the mixture was cooled to room temperature, centrifuged, and washed with distilled water several times until the filtrate was colorless. Finally, the mixture was dried in vacuum at 60°C for 24 h to obtain a chitosan-based coupling reaction catalyst, which was designated as OCMCS-SB-Pd-c.

[0042] Example 4

[0043] Example 4 provides a chitosan-based coupling reaction catalyst, the preparation method of which is as follows:

[0044] (1) 0.3 g of chitosan was mixed with 25 mL of 2% glacial acetic acid solution (2% by volume) and stirred at 70 °C for 2 h to fully dissolve the chitosan. Then, a DMF solution containing 10.62 g of 8-quinolinecarboxaldehyde was added dropwise to the system and reacted under an argon atmosphere for 20 h. Subsequently, a DMF solution containing 1.5 g of 1-chloroacetic acid was added dropwise and reacted at 60 °C for 4 days under argon protection. After the reaction was completed, the mixture was cooled to room temperature and centrifuged to obtain a solid. The solid was washed several times with DMF and ethanol until the filtrate became colorless. The solid powder was dried at 60 °C in a vacuum overnight to obtain a solid powder, which was designated as OCMCS-SB-d.

[0045] (2) 0.4 g of the obtained OCMCS-SB-d was dispersed in 15 mL of ethanol and stirred under argon for 1 h. Subsequently, 15 mL of ethanol solution containing 0.05 g of PdCl2 was added and the mixture was reacted at 60°C for 12 h. After the reaction, the mixture was cooled to room temperature, centrifuged, and washed with ethanol several times until the filtrate was colorless. Finally, the mixture was vacuum dried at 60°C for 24 h to obtain a chitosan-based coupling reaction catalyst, which was recorded as OCMCS-SB-Pd-d.

[0046] Example 5

[0047] Example 5 provides a chitosan-based coupling reaction catalyst, the preparation method of which is as follows:

[0048] (1) 0.3 g of chitosan was mixed with 25 mL of 2% glacial acetic acid solution (2% by volume) and stirred at 70 °C for 2 h to fully dissolve the chitosan. Then, a DMF solution containing 0.75 g of 2-pyridinecarboxaldehyde was added dropwise to the system and reacted under a nitrogen atmosphere for 16 h. Subsequently, a DMF solution containing 1.5 g of 1-chloroacetic acid was added dropwise and reacted at 60 °C under a nitrogen atmosphere for 4 d. After the reaction was completed, the solid was cooled to room temperature and centrifuged to obtain a solid, which was washed several times with DMF and ethanol until the filtrate became colorless. The powdered solid was obtained by vacuum drying at 60 °C overnight and was designated as OCMCS-SB-e.

[0049] (2) 0.4 g of the obtained OCMCS-SB-e was dispersed in 15 mL of DMF at room temperature and stirred under nitrogen for 1 h. An aqueous solution containing 0.04 g of Na2PdCl4 was then added and the mixture was reacted at 50°C for 20 h. After the reaction, the mixture was cooled to room temperature, centrifuged, and washed with distilled water several times until the filtrate was colorless. Finally, the mixture was dried in vacuum at 60°C for 24 h to obtain a chitosan-based coupling reaction catalyst, which was designated as OCMCS-SB-Pd-e.

[0050] Example 6

[0051] Example 6 provides a chitosan-based coupling reaction catalyst, the preparation method of which is as follows:

[0052] (1) 0.3 g of chitosan was mixed with 25 mL of 2% glacial acetic acid solution (2% by volume) and stirred at 70 °C for 2 h to fully dissolve the chitosan. Then, a DMF solution containing 0.85 g of 2-pyridineacetaldehyde was added dropwise to the system and reacted under a nitrogen atmosphere for 20 h. Subsequently, a DMF solution containing 1.5 g of 1-chloroacetic acid was added dropwise and reacted at 60 °C for 3 d under a nitrogen atmosphere. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, and washed several times with DMF and ethanol until the filtrate became colorless. The mixture was vacuum dried at 60 °C overnight to obtain a powdery solid, which was designated as OCMCS-SB-f.

[0053] (2) 0.4 g of the obtained OCMCS-SB-f was dispersed in 15 mL of distilled water at room temperature and stirred under nitrogen for 1 h. An aqueous solution containing 0.05 g of Na2PdCl4 was then added and the mixture was reacted at 50°C for 24 h. After the reaction, the mixture was cooled to room temperature, centrifuged, and washed with distilled water several times until the filtrate was colorless. Finally, the mixture was dried in vacuum at 60°C for 24 h to obtain a chitosan-based coupling reaction catalyst, which was designated as OCMCS-SB-Pd-f.

[0054] Comparative Example 1

[0055] (1) Disperse 0.4 g of chitosan in 15 mL of distilled water and stir under nitrogen for 1 h. Then add 15 mL of an aqueous solution containing 0.2 g of Na2PdCl4 and react at 70°C for 24 h. After the reaction is completed, cool to room temperature and centrifuge to obtain a solid. Wash the solid several times with distilled water until the filtrate is colorless. Finally, vacuum dry at 60°C for 24 h to obtain a chitosan-based direct palladium coupling reaction catalyst, which is designated as CS-Pd.

[0056] The catalysts finally prepared from Examples 1-6 and Comparative Example 1 were used to catalyze a Suzuki coupling reaction to evaluate their catalytic performance. The steps of the Suzuki coupling reaction are as follows:

[0057] Aryl halide (0.25 mmol), aromatic boronic acid (0.375 mmol), K2CO3 (1.0 mmol), and the catalyst prepared in the Examples or Comparative Examples were weighed and placed in a round-bottom flask. 5 mL of an ethanol solution (EtOH:H2O = 3:2) was added as the solvent. The reaction system was stirred at 50°C under air. After completion of the reaction, the catalyst was filtered, and the reaction solution was extracted with ethyl acetate. The organic phase was then washed with deionized water and saturated brine using a separatory funnel and dried overnight over MgSO4. The MgSO4 was filtered, and the mixture was concentrated under reduced pressure on a rotary evaporator. The crude product was further purified by TLC (PE / DCM, 20:1) to obtain the desired product.

[0058] Catalyst Separation and Recovery: After the reaction is complete, the catalyst is separated from the reaction mixture by centrifugation. The catalyst is then washed with ethanol and water to remove unreacted organic substrate and inorganic salt residues. Finally, the catalyst is reused in subsequent cycles.

[0059] The catalytic performance of the catalyst of Example 1 is shown in Table 1.

[0060] As shown in Table 1, the catalyst of Example 1 achieved a yield of over 94% for most biphenyl products in the coupling reaction of iodobenzene with phenylboronic acids of various substituents. Even after five cycles of use, the catalyst of Example 1 maintained a catalytic efficiency of 85%, demonstrating excellent recyclability.

[0061] Table 1. Example 1 Catalyst OCMCS-SB-a catalyzes the Suzuki coupling reaction of aryl halides and aryl boronic acids

[0062]

[0063] Note: 1-9 are fresh catalysts from Example 1, and the catalyst used in 10 is the catalyst from Example 1 that was recycled for the fifth time.

[0064] The catalytic performance of the catalyst of Example 2 is shown in Table 2.

[0065] As can be seen from Table 2, the catalyst of Example 2 achieved a yield of over 92% for most biphenyl products in the coupling reaction of iodobenzene with phenylboronic acids of various substituents. Even after five cycles of use, the catalyst of Example 2 maintained a catalytic efficiency of 84%, demonstrating excellent recyclability.

[0066] Table 2. Suzuki coupling reaction of aryl halides and arylboronic acids catalyzed by catalyst OCMCS-SB-b in Example 2

[0067]

[0068] Note: 1-9 are fresh catalysts from Example 2, and the catalyst used in 10 is the catalyst from Example 2 that was recycled for the fifth time.

[0069] The catalytic performance of the catalyst of Example 3 is shown in Table 3.

[0070] As shown in Table 3, the catalyst of Example 3 achieved a yield of over 90% for most biphenyl products in the Suzuki coupling reaction between iodobenzene and phenylboronic acids of various substituents. Even after five cycles of use, the catalyst of Example 3 still achieved a yield of 84%, demonstrating excellent recyclability.

[0071] Table 3. Suzuki coupling reaction of aryl halides and arylboronic acids catalyzed by catalyst OCMCS-SB-c in Example 3

[0072]

[0073] Note: 1-9 are fresh catalysts from Example 3, and the catalyst used in 10 is the catalyst from Example 3 that was recycled for the fifth time.

[0074] The catalytic performance of the catalyst of Example 4 is shown in Table 4.

[0075] As can be seen from Table 4, the catalyst of Example 4 achieved a biphenyl product yield exceeding 92% for the Suzuki coupling reaction between iodobenzene and phenylboronic acids of various substituents. Even after five cycles of use, the catalyst of Example 4 still achieved a yield of 82%, demonstrating excellent recyclability.

[0076] Table 4. Suzuki coupling reaction of aryl halides and arylboronic acids catalyzed by catalyst OCMCS-SB-d in Example 4

[0077]

[0078] Note: 1-9 are fresh catalysts from Example 4, and the catalyst used in 10 is the catalyst from Example 4 that was recycled for the fifth time.

[0079] The catalytic performance of the catalyst of Example 5 is shown in Table 5.

[0080] As can be seen from Table 5, the catalyst of Example 5 achieved a biphenyl product yield exceeding 91% for the Suzuki coupling reaction between iodobenzene and phenylboronic acids of various substituents. Even after five cycles of use, the catalyst of Example 5 still achieved a yield of 85%, demonstrating excellent recyclability.

[0081] Table 5. Suzuki coupling reaction of aryl halides and aryl boronic acids catalyzed by catalyst OCMCS-SB-e in Example 5

[0082]

[0083] Note: 1-9 are fresh catalysts from Example 5, and the catalyst used in 10 is the catalyst from Example 5 that was recycled for the fifth time.

[0084] The catalytic performance of the catalyst of Example 6 is shown in Table 6.

[0085] As can be seen from Table 6, the catalyst of Example 6 achieved a biphenyl product yield exceeding 90% for the Suzuki coupling reaction between iodobenzene and phenylboronic acids of various substituents. Even after five cycles of use, the catalyst of Example 6 still achieved a yield of 81%, demonstrating excellent recyclability.

[0086] Table 6. Suzuki coupling reaction of aryl halides and aryl boronic acids catalyzed by catalyst OCMCS-SB-f in Example 6

[0087]

[0088] Note: 1-9 are fresh catalysts from Example 6, and the catalyst used in 10 is the catalyst from Example 6 that was recycled for the fifth time.

[0089] Figure 3 (a) is a scanning electron microscope image of fresh OCMCS-SB-Pd-a in Example 1. Figure 3 (b) is a scanning electron microscope image of the catalyst after the catalyst in Example 1 was recycled 5 times. Figure 3 It can be observed that the catalyst of Example 1 presents a rough, irregular, block-like morphology, and the morphology of the catalyst of Example 1 hardly changes after recycling.

[0090] Figure 4 This is a comparison chart of the catalytic activity and Pd content of the fresh catalyst OCMCS-SB-Pd-a of Example 1, the catalyst OCMCS-SB-Pd-a of Example 1 after five cycles of use, and the catalyst CS-Pd of Comparative Example 1 under the same reaction conditions. Figure 4The reaction in refers to the coupling reaction between iodobenzene and phenylboronic acid. The catalytic activity of the catalyst CS-Pd of Comparative Example 1 directly loaded with chitosan is 75%. Compared with the catalyst of Comparative Example 1, the catalyst of Example 1 modified with Schiff base at multiple sites shows more excellent catalytic performance. The catalytic activity of Example 1 can be as high as 97%. After the catalyst of Example 1 is recycled 5 times, the catalyst activity is slightly reduced, but its catalytic activity is still higher than that of the catalyst of Comparative Example 1. Moreover, the Pd metal content in the fresh catalyst of Example 1 is 7.66%, and the metal content of the catalyst of Example 1 after recycling is 7.59%, while the metal content of the catalyst of Comparative Example 1 is 5.54%. The above data show that the catalyst of Example 1 has excellent catalytic activity and high stability and can be recycled. The catalyst of Example 1 has a high metal loading, indicating that the chelation of imino, pyridyl and carboxyl groups to palladium metal ions is beneficial to improving catalytic activity and metal loading.

[0091] In summary, the Schiff base-modified multi-site catalyst OCMCS-SB-Pd synthesized in the present invention exhibits good catalytic activity and recycling performance. In the Suzuki coupling reaction, relying on the synergistic complexation between the imine group, pyridine group and carboxyl group and Pd, this multifunctional complex catalyst exhibits excellent catalytic performance and can effectively prevent metal loss (metal shedding amount <0.1%).

[0092] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for illustrating the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements should all be included in the scope of protection of the present invention.

Claims

1. A method for preparing a chitosan-based coupling reaction catalyst, characterized in that: The following steps are involved: (1) Chitosan is added to a glacial acetic acid solution and heated and stirred until the chitosan is fully dissolved, and then an aromatic aldehyde compound is added to the system. Under the protection of an inert gas, after the reaction is completed, a halogenated carboxylic acid is added to the reaction system to react to obtain Schiff base modified carboxymethyl chitosan; (2) Dispersing the Schiff base modified carboxymethyl chitosan in a solvent, adding palladium salt under the protection of an inert atmosphere, and reacting to finally obtain the chitosan-based supported palladium catalyst.

2. The method for preparing a chitosan-based coupling reaction catalyst according to claim 1, wherein: The inert gas includes nitrogen or argon.

3. The method for preparing a chitosan-based coupling reaction catalyst according to claim 1, wherein: The aromatic aldehyde compound includes at least one of 2,9-diformyl-1,10-phenanthroline, 2,2'-bipyridine-6,6'-dicarbaldehyde, 2-quinolinecarboxaldehyde, 8-quinolinecarboxaldehyde, 2-pyridinecarboxaldehyde, and 2-pyridineacetaldehyde.

4. The method for preparing a chitosan-based coupling reaction catalyst according to claim 1, wherein: The halogenated carboxylic acid includes at least one of 1-chloroacetic acid and 2-chloropropionic acid.

5. The method for preparing a chitosan-based coupling reaction catalyst according to claim 1, wherein Under heating conditions at 70° C., the reaction time after adding the aromatic aldehyde compound is 12 to 20 hours; and then the reaction time after adding the substituted carboxylic acid at 60° C. is 2 to 4 days.

6. The method for preparing a chitosan-based coupling reaction catalyst according to claim 1, wherein: The palladium salt is at least one of sodium chloropalladate, palladium acetate, palladium dichloride, and palladium nitrate.

7. The method for preparing a chitosan-based coupling reaction catalyst according to claim 1, wherein: The solvent is at least one of water, ethanol, acetonitrile and N,N-dimethylformamide.

8. The method for preparing a chitosan-based coupling reaction catalyst according to claim 1, wherein: The mass ratio of the palladium salt to the Schiff base modified carboxymethyl chitosan is 1:2-1:10; The reaction temperature in step (2) is 50°C to 80°C; The reaction time of step (2) is 12 to 24 hours.

9. A chitosan-based coupling reaction catalyst, characterized in that The chitosan-based coupling reaction catalyst is prepared by the preparation method of the chitosan-based coupling reaction catalyst according to any one of claims 1 to 8.

10. Use of the chitosan-based coupling reaction catalyst according to claim 9 in a Suzuki coupling reaction.

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