Preparation and application of polymaleic anhydride-proline / COF hollow mesoporous catalyst

Abstract

The invention relates to a preparation method of a polymaleic anhydride-proline / COF hollow mesoporous catalyst as well as a product and application thereof, and belongs to the technical field of preparation of functional materials. A self-stabilization precipitation polymerization method is adopted, no stabilizer or surfactant needs to be added, and the prepared microspheres are clean in surface, simple in post-treatment, free of stirring, simple in reaction system, short in reaction time and high in polymerization efficiency. The preparation method comprises the following steps: firstly, synthesizing COF serving as a template from 4, 4-bibenzaldehyde and s-triphenylamine, and performing dehydration polymerization on residual-NH2, divinyl benzene, maleic anhydride and proline to form a special hollow mesoporous catalyst which is relatively good in crystallinity, high in specific surface area, uniform in pore distribution and compact in structure arrangement, namely a polymaleic anhydride-proline / COF hollow mesoporous catalyst. Excellent stereoselectivity and yield are obtained by catalyzing direct nitro-Mannich asymmetric cascade reaction, and the preparation method is simple and high in yield.

Description

Technical Field

[0001] This invention belongs to the field of functional material preparation technology, specifically relating to the preparation method of polymaleic anhydride-proline / COF hollow mesoporous catalyst, its products, and applications. Background Technology

[0002] Traditional methods for preparing hollow polymer microspheres mainly include emulsion polymerization, template polymerization, and self-assembly. These methods all have certain limitations. Self-stabilizing precipitation polymerization is a method for preparing polymer microspheres with advantages such as: no need for any stabilizers or surfactants, clean microsphere surface, simple post-processing, no need for stirring, simple reaction system, short reaction time, and high polymerization efficiency. The polymaleic anhydride-proline / COF hollow mesoporous catalyst of this invention is synthesized using this method. This process is an improvement on self-stabilizing precipitation polymerization, synthesizing core-shell polymer microspheres through stabilizer-free precipitation polymerization. The synthesized hollow polymer microspheres have good morphology, uniform particle size, are lightweight, easy to synthesize, have a large specific surface area, and are low in cost. Using hollow polymer microspheres to load nanomaterials can not only effectively stabilize nanomaterials and inhibit their aggregation, but also achieve a synergistic effect between polymers and nanoparticles. Therefore, it can be applied to fields such as catalysts, enzyme immobilization, and adsorption. Researching methods for loading nanomaterials using hollow polymer microspheres prepared by self-stabilizing polymerization has significant scientific and practical implications. Summary of the Invention

[0003] In view of this, one objective of the present invention is to provide a method for preparing a polymaleic anhydride-proline / COF hollow mesoporous catalyst; a second objective of the present invention is to provide a polymaleic anhydride-proline / COF hollow mesoporous catalyst; and a third objective of the present invention is to provide an application of the polymaleic anhydride-proline / COF hollow mesoporous catalyst in catalyzing the Diehl-Aarsenic reaction.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] 1. A method for preparing a polymaleic anhydride-proline / COF hollow mesoporous catalyst, the preparation method comprising the following steps:

[0006] 1) Preparation of COF template: After dissolving biphenylaldehyde and triphenylamine, acetic acid was added dropwise for catalysis, followed by washing and drying to obtain orange-yellow mesoporous COF powder with a yield of approximately 88%.

[0007] 2) Self-stabilizing precipitation polymerization of polymaleic anhydride-proline / COF hollow mesoporous catalyst: COF powder, maleic anhydride, and proline were placed in a three-necked flask, oxygen was removed, solvent was injected, and the mixture was grown at a constant temperature of 75 °C on a COF template. Then, a crosslinking agent, n-heptane, and an initiator were added, and the mixture was heated in an oil bath at 75 °C for 3 h for rapid polymerization. Impurities were separated and washed to remove impurities. The catalyst was then dried to obtain the polymaleic anhydride-proline / COF hollow mesoporous catalyst.

[0008] 2. Preferably, in step (1), the catalyst is acetic acid or formic acid.

[0009] 3. In step (1), the reaction raw materials are any combination of biphenylaldehyde and triphenylamine, or triphenylaldehyde and tetraphenylamine, or biphenylaldehyde and tetraphenylamine.

[0010] 4. Preferably, in step (1), the reaction raw materials are biphenylaldehyde and triphenylamine, or triphenylaldehyde and tetraphenylamine, or biphenylaldehyde and tetraphenylamine.

[0011] When the reaction raw materials are biphenylaldehyde and triphenylamine, the ratio of the raw materials is: 128 mg 4,4-biphenyldialdehyde and 192.6 mg triphenylamine;

[0012] When the reaction raw materials are triphenylaldehyde and tetraphenylamine, the ratio of the raw materials is: 192 mg of triphenylaldehyde and 256.8 mg of tetraphenylamine;

[0013] When the reaction raw materials are biphenylaldehyde and methyltetraphenylamine, the ratio of the raw materials is: 128 mg 4,4-biphenyldialdehyde and 256.8 mg methyltetraphenylamine;

[0014] 4. Preferably, in step (2), the gas that removes oxygen can be either nitrogen or argon.

[0015] 5. Preferably, in step (2), the self-stabilizing precipitation polymerization conditions are: heating at 55-75 ℃ for 0.8-1.5 h.

[0016] 6. Preferably, in step (2), the mass ratio of the self-stabilizing precipitation polymerization raw materials is: COF powder: maleic anhydride: proline = 90-100 mg: 48.1-96.2 mg: 6.3-12.6 mg.

[0017] 7. Preferably, in step (2), the mass ratio of the self-stabilized precipitation polymerization fast polymerization crosslinking agent, solvent, and initiator is: divinylbenzene / ethylene glycol dimethacrylate: n-heptane: AIBN = 2.15-4.3 mL / 1.1-2.2 mL: 6.25-12.5 mL: 2.6-5.2 mg.

[0018] 8. Preferably, in step (2), after centrifugation, the supernatant is discarded, and the liquid is washed twice with chloroform, dichloromethane or ethyl acetate, and then washed once with petroleum ether.

[0019] 9. The polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared according to the above preparation method.

[0020] 10. Based on the above, the application of polymaleic anhydride-proline / COF hollow mesoporous catalyst in catalyzing direct nitro-Mannich asymmetric tandem reaction.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. This invention discloses a method for preparing a polymaleic anhydride-proline / COF hollow mesoporous catalyst. This method first employs a self-stabilizing precipitation polymerization method, requiring no stabilizers or surfactants. The prepared microspheres have clean surfaces, simple post-treatment, require no stirring, have a simple reaction system, short reaction time, and high polymerization efficiency. First, COF is synthesized as a template, and then dehydrated and polymerized with divinylbenzene, maleic anhydride, and proline using the -NH2 sites to form a unique hollow mesoporous catalyst with good crystallinity, which is the polymaleic anhydride-proline / COF hollow mesoporous catalyst. This preparation method is simple and yields high output.

[0023] 2. This invention also discloses a polymaleic anhydride-proline / COF hollow mesoporous catalyst. This material has a high specific surface area, uniform pore distribution, and a compact structure. In catalyzing direct nitro-Mannich asymmetric tandem reactions, the ee value reaches 96%, and the Dr ratio reaches 98:2. Furthermore, it exhibits high reusability (the ee value still reaches 90% after 10 reuses). Kinetic studies indicate that the spatial network structure is the main factor driving concentration gradient diffusion catalysis. Therefore, the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in this invention has promising application prospects in catalyzing direct nitro-Mannich asymmetric tandem reactions.

[0024] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein:

[0026] Figure 1 This is a flowchart illustrating the preparation of the polymaleic anhydride-proline / COF hollow mesoporous catalyst of the present invention.

[0027] Figure 2 SEM image of the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1;

[0028] Figure 3 TEM image of a polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1;

[0029] Figure 4 The XRD patterns of the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1, the COF prepared in Comparative Example 1, and the AlP@CNPC prepared in Comparative Example 2 are shown.

[0030] Figure 5 The pore size distribution diagrams are shown for the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1 and the AlP@CNPC prepared in Comparative Example 2.

[0031] Figure 6 The infrared spectrum of the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1;

[0032] Figure 7 The HPLC chromatogram shows the asymmetric direct nitro-Mannich reaction of N-Boc imine with nitro compounds catalyzed by the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1.

[0033] Figure 8 This is a diagram showing the asymmetric direct nitro-Mannich reaction of N-Boc imine with nitro compounds cyclically catalyzed by the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1. Detailed Implementation

[0034] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0035] Example 1

[0036] A polymaleic anhydride-proline / COF hollow mesoporous catalyst is prepared by the following method:

[0037] 1) Preparation of COF template: 128 mg of 4,4-bibenzaldehyde and 192.6 mg of triphenylamine were dissolved in 15 mL of 1,4-dioxane. After complete dissolution, 5 mL of 6 mol / L acetic acid was slowly added dropwise under ultrasonic conditions. The resulting mixture was left at room temperature for 60 hours and then washed alternately with DMF and 1,4-dioxane to remove unreacted raw materials and impurities. The cleaned mesoporous COF was vacuum dried at 65 °C for 8 hours to finally obtain orange-yellow mesoporous COF powder with a yield of approximately 88%.

[0038] 2) Self-stabilizing precipitation polymerization of polymaleic anhydride-proline / COF hollow mesoporous catalyst: Weigh 100 mg of prepared COF powder, 96.2 mg of maleic anhydride (MAH), and 12.6 mg of proline, and place them in a 250 mL three-necked flask. Purge with nitrogen for 30 min to remove oxygen, then inject 25 mL of dehydrated dichloromethane. Heat in a 75 °C thermostatic oil bath for 1.5 h without stirring to allow the catalyst to grow on the COF template. Next, add 4.3 mL of divinylbenzene, 12.5 mL of n-heptane, and 5.2 mg of AIBN. Continue heating in the oil bath at 75 °C for 3 h at a speed of 100-180 rpm / min. After heating, allow to cool naturally to room temperature, then centrifuge at 9000-12000 rpm / min for 4-6 min. After centrifugation, the supernatant was discarded, and the sample was washed twice with chloroform, followed by a final wash with petroleum ether. The purpose of centrifugation was to remove impurities from the core and pores. The centrifuged sample was then air-dried in a fume hood for 12 hours, and finally thoroughly dried in a vacuum oven at 45°C for 12 hours to obtain the polymaleic anhydride-proline / COF hollow mesoporous catalyst.

[0039] Example 2

[0040] A polymaleic anhydride-proline / COF hollow mesoporous catalyst is prepared by the following method:

[0041] 1) Preparation of COF template: 192 mg of triphenylmethane and 256.8 mg of tetraphenylamine were dissolved in 15 mL of 1,4-dioxane. After complete dissolution, 5 mL of 6 mol / L acetic acid was slowly added dropwise under ultrasonic conditions. After the resulting mixture was left at room temperature for 60 hours, it was washed alternately with DMF and 1,4-dioxane to remove unreacted raw materials and impurities. The cleaned mesoporous COF was vacuum dried at 65 °C for 8 hours to finally obtain orange-yellow mesoporous COF powder with a yield of about 79%.

[0042] 2) Self-stabilizing precipitation polymerization of polymaleic anhydride-proline / COF hollow mesoporous catalyst: Weigh 100 mg of prepared COF powder, 96.2 mg of maleic anhydride (MAH), and 12.6 mg of proline, and place them in a 250 mL three-necked flask. Purge with nitrogen for 30 min to remove oxygen, then inject 25 mL of dehydrated dichloromethane. Heat in a 75 °C thermostatic oil bath for 1.5 h without stirring to allow the catalyst to grow on the COF template. Next, add 4.3 mL of divinylbenzene, 12.5 mL of n-heptane, and 5.2 mg of AIBN. Continue heating in the oil bath at 75 °C for 3 h at a speed of 100-180 rpm / min. After heating, allow to cool naturally to room temperature, then centrifuge at 9000-12000 rpm / min for 4-6 min. After centrifugation, the supernatant was discarded, and the sample was washed twice with chloroform, followed by a final wash with petroleum ether. The purpose of centrifugation was to remove impurities from the core and pores. The centrifuged sample was then air-dried in a fume hood for 12 hours, and finally thoroughly dried in a vacuum oven at 45°C for 12 hours to obtain the polymaleic anhydride-proline / COF hollow mesoporous catalyst.

[0043] Example 3

[0044] A polymaleic anhydride-proline / COF hollow mesoporous catalyst is prepared by the following method:

[0045] 1) Preparation of COF template: 128 mg of 4,4-biphenyldicarboxaldehyde and 256.8 mg of mesityleneamine were dissolved in 15 mL of 1,4-dioxane. After complete dissolution, 5 mL of 6 mol / L acetic acid was slowly added dropwise under ultrasonic conditions. After the resulting mixture was left at room temperature for 60 hours, it was washed alternately with DMF and 1,4-dioxane to remove unreacted raw materials and impurities. The cleaned mesoporous COF was vacuum dried at 65 °C for 8 hours to finally obtain orange-yellow mesoporous COF powder with a yield of about 85%.

[0046] 2) Self-stabilizing precipitation polymerization of polymaleic anhydride-proline / COF hollow mesoporous catalyst: Weigh 100 mg of prepared COF powder, 96.2 mg of maleic anhydride (MAH), and 12.6 mg of proline, and place them in a 250 mL three-necked flask. Purge with nitrogen for 30 min to remove oxygen, then inject 25 mL of dehydrated dichloromethane. Heat in a 75 °C thermostatic oil bath for 1.5 h without stirring to allow the catalyst to grow on the COF template. Next, add 4.3 mL of divinylbenzene, 12.5 mL of n-heptane, and 5.2 mg of AIBN. Continue heating in the oil bath at 75 °C for 3 h at a speed of 100-180 rpm / min. After heating, allow to cool naturally to room temperature, then centrifuge at 9000-12000 rpm / min for 4-6 min. After centrifugation, the supernatant was discarded, and the sample was washed twice with chloroform, followed by a final wash with petroleum ether. The purpose of centrifugation was to remove impurities from the core and pores. The centrifuged sample was then air-dried in a fume hood for 12 hours, and finally thoroughly dried in a vacuum oven at 45°C for 12 hours to obtain the polymaleic anhydride-proline / COF hollow mesoporous catalyst.

[0047] Examples 4-6

[0048] Examples 4, 5, and 6 were conducted using the same methods and synthesis conditions as Example 1, except that the self-stabilizing precipitation polymerization conditions in step 2) of Example 1 were changed to 55, 60, and 65 °C, respectively, to prepare different polymaleic anhydride-proline / COF hollow mesoporous catalysts.

[0049] Examples 7-9

[0050] 2. The implementation methods and synthesis conditions of Examples 7, 8 and 9 are the same as those of Example 1. The difference is that in Step (2) of Example 1, the mass ratios of the self-stabilizing precipitation polymerization raw materials are as follows: COF powder: maleic anhydride: proline = 90: 48.1 mg: 6.3 mg; COF powder: maleic anhydride: proline = 95: 72.1 mg: 9.4 mg; COF powder: maleic anhydride: proline = 98: 86.2 mg: 9.8 mg; different polymaleic anhydride-proline / COF hollow mesoporous catalysts are prepared.

[0051] Examples 10-11

[0052] The implementation method and synthesis conditions are the same as in Example 1. The difference is that the mass ratio of the self-stabilized precipitation polymerization crosslinking agent, solvent and initiator in step (2) of Example 1 is: divinylbenzene / ethylene glycol dimethacrylate: n-heptane: AIBN = 2.15 mL / 1.1 mL: 6.25 mL: 2.6 mg, to prepare polymaleic anhydride-proline / COF hollow mesoporous catalyst.

[0053] Performance testing

[0054] 1. Physical property testing of various products in the examples

[0055] Figure 1 This is a flowchart illustrating the preparation of the polymaleic anhydride-proline / COF hollow mesoporous catalyst of the present invention.

[0056] Figure 2 The image shows a SEM image of the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1. As can be seen from the image, the size of the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1 is 388±21 nm, and the surface of the catalyst is relatively smooth.

[0057] Figure 3 This is a TEM image of a polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1. From... Figure 3 As can be seen, the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1 is a hollow sphere.

[0058] Figure 4 The polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1 shows two distinct diffraction peaks near 3.6° and 26.94° in XRD, corresponding to the COF (100) plane and (001) plane, respectively. This is consistent with the reported results, indicating that the structure remains unchanged during the catalyst preparation process.

[0059] Figure 5 The N2 adsorption-desorption diagram and pore size distribution diagram are shown for the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1. Figure 5 The mid-spectrum shows that the polymaleic anhydride-proline / COF hollow mesoporous catalyst exhibits typical type I isothermal curves, characteristic of mesoporous materials. Nitrogen adsorption-desorption measurements at 77 K show that the BET specific surface area and porosity of polymaleic anhydride-proline / COF are 961.54 m². 2 g -1 and 0.9817 cm 3 g -1Notably, the specific surface area and pore volume of polymaleic anhydride-proline / COF were reduced by 138.2 m² compared to reported COF. 2 g -1 and 0.1128 cm 3 g -1 The significant decrease in specific surface area and the simultaneous reduction in pore volume may be due to two reasons. On the one hand, the pores of COF are occupied by the polymer, leading to a decrease in specific surface area; on the other hand, the higher proportion of polymer significantly increases the overall mass, further reducing the specific surface area.

[0060] Figure 6 The image shows the infrared spectrum of the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1. It can be observed from the image that O=CH at 2889 cm⁻¹ −1 The disappearance of the characteristic absorption peak of the aldehyde group during stretching provides direct evidence for the completion of the co-condensation reaction. (3185-3309 cm⁻¹) −1 The NH stretch and C=O at 1643 cm −1 Characteristic absorption peak, -COOH stretches at 1594 cm⁻¹ −1 The rise of a strong peak indicates that the maleic anhydride-proline COF hollow mesoporous catalyst was successfully prepared.

[0061] Similarly, the polymaleic anhydride-proline / COF hollow mesoporous catalysts prepared in other embodiments were subjected to the various performance tests described above. The results were similar to those of the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1 above, indicating that the preparation method of the present invention can indeed prepare polymaleic anhydride-proline / COF hollow mesoporous catalysts with good crystallinity, high specific surface area, low density, tight structural arrangement and unique hollow shell structure.

[0062] 2. Catalytic asymmetric direct nitro-Mannich asymmetric tandem reaction

[0063] 14.2 mg of N-Boc-benzaldehyde imine and 11.8 mg of the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1 were added to a dry catalytic tube. 21.8 mg of α-nitrotoluene and 2.0 mL of dehydrated toluene were added at 25 °C. The reaction was stopped after 18 h (TLC monitoring of the reaction). Column chromatography yielded a white solid (29.4 mg, 77% yield, ee%=96%, Dr=98:2). Figure 7 This is an HPLC chromatogram of the directnitro-Mannich asymmetric tandem reaction catalyzed by the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1. Figure 7As shown in the spectral data, the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1 exhibits an ee% of 96% for the direct nitro-Mannich asymmetric tandem reaction, indicating that the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1 demonstrates excellent enantioselectivity and diastereoselectivity in the direct nitro-Mannich asymmetric tandem reaction of N-Boc imines and nitro compounds.

[0064] The reaction formula obtained in the above catalytic reaction is:

[0065] ,

[0066] In the above direct nitro-Mannich asymmetric tandem reaction, the solvent was toluene (5 mL), the reaction temperature was 25 °C, and the amount of heterogeneous catalyst polymaleic anhydride-proline / COF was 11.8 mg.

[0067] Similarly, the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared in Example 1 was used to catalyze the above direct nitro-Mannich asymmetric tandem reaction, with continuous catalysis, such as... Figure 8 The results can be repeated 10 times, with ee% all above 90% and Dr above 85.15.

[0068] In summary, this invention discloses a method for preparing a polymaleic anhydride-proline / COF hollow mesoporous catalyst. This method first employs a self-stabilizing precipitation polymerization method, which does not require the addition of any stabilizers or surfactants. The prepared microspheres have clean surfaces, simple post-treatment, require no stirring, have a simple reaction system, short reaction time, and high polymerization efficiency. First, COF was synthesized from 4,4-bibenzaldehyde and triphenylamine as a template. The remaining -NH2 was then used to dehydrate and polymerize with divinylbenzene, maleic anhydride, and proline, forming a unique hollow mesoporous catalyst with good crystallinity, high specific surface area, uniform pore distribution, and tight structural arrangement. This polymaleic anhydride-proline / COF hollow mesoporous catalyst exhibits excellent stereoselectivity and yield in catalyzing the direct nitro-Mannich asymmetric tandem reaction. The preparation method is simple and yields high output. In the direct nitro-Mannich asymmetric tandem reaction, the ee value reaches 96%, Dr=98:2, and the reusability is high (the ee value still reaches 90% after 10 reuses), indicating that the polymaleic anhydride-proline / COF hollow mesoporous catalyst has excellent catalytic effect. The reaction kinetics study shows that the spatial network structure is the main factor driving the concentration gradient diffusion catalysis. Therefore, the polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared by the self-stabilizing precipitation polymerization method of this invention has good application prospects in catalyzing direct nitro-Mannich asymmetric tandem reactions.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a polymaleic anhydride-proline / COF hollow mesoporous catalyst, characterized in that, The preparation method includes the following steps: 1) Preparation of COF template: After dissolving biphenylaldehyde and triphenylamine, acetic acid was added dropwise for catalysis, followed by washing and drying to obtain orange-yellow mesoporous COF powder; 2) Self-stabilizing precipitation polymerization of polymaleic anhydride-proline / COF hollow mesoporous catalyst: COF powder, maleic anhydride, and proline were placed in a three-necked flask, oxygen was removed, solvent was injected, and the mixture was grown at a constant temperature of 75 °C on a COF template. Then, a crosslinking agent, n-heptane, and an initiator were added, and the mixture was heated in an oil bath at 75 °C for 3 h for rapid polymerization. Impurities were separated and washed to remove impurities. The catalyst was then dried to obtain the polymaleic anhydride-proline / COF hollow mesoporous catalyst.

2. The preparation method according to claim 1, characterized in that, In step (1), the catalyst is acetic acid.

3. The preparation method according to claim 1, characterized in that, In step (1), the reaction raw materials are any combination of biphenylaldehyde and triphenylamine, triphenylaldehyde and tetraphenylamine, or biphenylaldehyde and tetraphenylamine.

4. The preparation method according to claim 3, characterized in that, In step (1), the reaction raw materials are biphenylaldehyde and triphenylamine, or triphenylaldehyde and tetraphenylamine, or biphenylaldehyde and tetraphenylamine: When the reaction raw materials are biphenylaldehyde and triphenylamine, the ratio of the raw materials is: 128 mg 4,4-biphenyldialdehyde and 192.6 mg triphenylamine; When the reaction raw materials are triphenylaldehyde and tetraphenylamine, the ratio of the raw materials is: 192 mg of triphenylaldehyde and 256.8 mg of tetraphenylamine; When the reaction raw materials are biphenylaldehyde and tetraphenylamine, the ratio of the raw materials is: 128 mg 4,4-biphenyldialdehyde and 256.8 mg tetraphenylamine.

5. The preparation method according to claim 1, characterized in that, In step (2), the gas used to remove oxygen can be either nitrogen or argon.

6. The preparation method according to claim 1, characterized in that, In step (2), the self-stabilizing precipitation polymerization conditions are: heating at 55-75 ℃ for 0.8-1.5 h.

7. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the self-stabilizing precipitation polymerization raw materials is: COF powder: maleic anhydride: proline = 90-100 mg: 48.1-96.2 mg: 6.3-12.6 mg.

8. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the self-stabilized precipitation polymerization followed by rapid polymerization crosslinking agent, solvent, and initiator is: divinylbenzene / ethylene glycol dimethacrylate: n-heptane: AIBN = 2.15-4.3 mL / 1.1-2.2 mL: 6.25-12.5 mL: 2.6-5.2 mg.

9. The preparation method according to claim 1, characterized in that, In step (2), after centrifugation, the supernatant is discarded, and the liquid is washed twice with chloroform, dichloromethane, or ethyl acetate, and then washed once with petroleum ether.

10. The polymaleic anhydride-proline / COF hollow mesoporous catalyst prepared by the preparation method according to any one of claims 1 to 8.

11. The application of the polymaleic anhydride-proline / COF hollow mesoporous catalyst according to claim 9 in catalyzing directnitro-Mannich asymmetric tandem reactions.

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