Hydrazone chiral covalent organic framework material and preparation method and application thereof

Abstract

The application discloses a hydrazone chiral covalent organic framework material and a preparation method thereof. The preparation method comprises the following steps: under an inert atmosphere, a chiral hydrazine precursor with a tert-butyloxycarbonyl protection group is dissolved in an organic solvent together with 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, and then an aqueous acetic acid solution is added, and the mixture is reacted at 90-120 DEG C for 2-5 days; then, insoluble substances are collected, and after washing, drying and deprotection treatment, the hydrazone chiral covalent organic framework material is obtained. The hydrazone chiral covalent organic framework material prepared by the application is used as a heterogeneous catalyst for asymmetric reaction, and exhibits good catalytic effect and chiral selectivity, and also has good chemical stability; after the reaction, the catalyst can be separated and recovered through simple centrifugation or filtration, so that environmental pollution is effectively reduced, the cost is reduced, and the application prospect is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of covalent organic framework materials, and in particular relates to a hydrazone chiral covalent organic framework material and a preparation method and application thereof. Background Art

[0002] Chirality, a ubiquitous property of nature, is essential to most branches of science. Most biomolecules, such as nucleic acids, proteins, and carbohydrates, exist in only one chiral form. In stereochemistry, different enantiomers can often exhibit different physiological activities. For example, R-thalidomide is a significant sedative that relieves nausea, while its mirror-image counterpart, S-thalidomide, is a teratogen that causes congenital disabilities. In the late 1950s, because the different biological activities of R-thalidomide and S-thalidomide were unknown, their racemic mixture (a 1:1 ratio of R- and S-enantiomers) was used to treat morning sickness during pregnancy, resulting in tens of thousands of limb deficiencies in children. Therefore, the design, preparation, and separation of specific enantiomers holds special appeal for chemists, especially in the pharmaceutical industry, where chiral drugs dominate.

[0003] Among the vast majority of methods for generating enantiomerically pure compounds, asymmetric catalysis is considered an ideal approach and is a particularly useful tool for chemists due to its many advantages, such as avoiding expensive or toxic metals and being environmentally friendly. However, homogeneous chiral catalytic systems represented by small organic molecules generally still have some limitations, such as high cost and high catalyst loading, which often limit the potential for industrial and sustainable applications. In addition, due to the difficulty of recycling homogeneous asymmetric organic catalysts, some asymmetric organic catalysts are more serious in terms of pollution emissions and environmental pollution. Therefore, if these groups with chiral catalytic functions can be combined with solid supports to prepare heterogeneous catalysts, then the asymmetric catalysts can be easily recovered using centrifugation, which can not only reduce environmental pollution but also save catalyst costs.

[0004] Since the Yaghi group first reported covalent organic frameworks (COFs) in 2005, these crystalline porous organic polymers have garnered significant interest. COFs are formed by covalently linked organic monomers and possess unique properties, such as large surface area, adjustable pore structure and size, and a highly ordered crystalline porous structure. Compared to traditional inorganic porous materials, COFs can be easily modified with various chiral groups to yield different chiral porous materials due to their expanded pore size range and outstanding structural and compositional tunability. Combined with the unique structure of the material itself, these materials possess enormous potential for applications in enantioselective separation, chiral recognition, and sensing, particularly in heterogeneous asymmetric catalysis. For example, Jiang Donglin's group synthesized a three-component imine-based chiral COF ([(S)-Py]x-TPBDMTP-COFs) via post-modification. The catalytic conversion of cyclohexanone and β-nitrosostyryl compounds was 100%, with ee and dr values ​​of 90–96% and 90 / 10–97 / 3, respectively (Nature Chemistry, 2015, 7, 905). Wang Wei's group synthesized the imine-based LZU-76COF, which catalyzed aldol condensation with an ee value of 87% and could be reused at least three times without loss of enantioselectivity (Journal of the American Chemical Society, 2016, 138, 11489). However, the preparation of chiral COFs remains a major challenge in this field, and the majority of reported chiral COF catalysts are imine-based. However, due to the electrophilicity of the imine bond, water molecules react with the imine chemical bond in an aqueous solution, resulting in poor chemical stability of some imine COFs. Currently, there are no reports on the use of hydrazone chiral COFs as catalysts for heterogeneous asymmetric catalytic reactions. Summary of the Invention

[0005] An object of the present invention is to provide a method for preparing a hydrazone chiral covalent organic framework material in response to the above technical problems. The prepared hydrazone chiral covalent organic framework material has good stability and can be used as a heterogeneous catalyst in an asymmetric aldol condensation reaction.

[0006] In order to achieve the above object of the invention, the present invention provides a method for preparing a hydrazone chiral covalent organic framework material, comprising the following steps:

[0007] Under an inert atmosphere, a chiral hydrazide precursor with tert-butyloxycarbonyl protection and 2,4,6-tris(4-formylphenyl)-1,3,5-triazine are dissolved in an organic solvent, and then an acetic acid aqueous solution is added. The reaction is carried out at 90-120° C. for 2-5 days, and then the insoluble matter is collected. After washing, drying and deprotection treatment, a hydrazone chiral covalent organic framework material is obtained. The structural formula of the chiral hydrazide precursor is: In the formula, Boc is tert-butyloxycarbonyl.

[0008] Compared to existing technologies, the hydrazone-based chiral covalent organic framework material produced by the present invention exhibits strong stability and good batch reproducibility. Furthermore, the preparation method is simple to operate, employs mild reaction conditions, is low-cost, and offers high yields, promising promising industrial applications. The hydrazone-based chiral covalent organic framework material produced by this preparation method can be used as a heterogeneous catalyst in asymmetric reactions, exhibiting excellent catalytic efficacy and chiral selectivity. The catalyst can be separated and recovered by simple centrifugation or filtration, effectively reducing environmental pollution and lowering costs.

[0009] Preferably, the molar ratio of the chiral hydrazide precursor to the 2,4,6-tris(4-formaldehydephenyl)-1,3,5-triazine is 3:2.

[0010] Preferably, the molar ratio of the acetic acid to the chiral hydrazide precursor is (1-20):1.

[0011] Preferably, the deprotection treatment uses a 4M hydrochloric acid dioxane solution, and the mass ratio of the volume of the solution to the insoluble matter obtained by the reaction is 1 mL: (20-40) mg.

[0012] Preferably, the deprotection treatment reaction time is 1 to 6 hours.

[0013] Preferably, the organic solvent is any one of a mixed solution of N,N-dimethylacetamide and mesitylene, a mixed solution of 1,4-dioxane and mesitylene, and a mixed solution of o-dichlorobenzene and n-butanol.

[0014] Preferably, the reaction temperature is 110° C. and the reaction time is 3 days.

[0015] The present invention also provides a hydrazone chiral covalent organic framework material prepared by the above preparation method.

[0016] Furthermore, the structural formula of the hydrazone chiral covalent organic framework material is:

[0017]

[0018] The present invention also provides the use of the hydrazone chiral covalent organic framework material in catalyzing heterogeneous asymmetric reactions.

[0019] The raw materials used in the present invention are low in price, the synthesis method is simple, the reaction conditions are mild, and the material is easy to operate. The hydrazone chiral covalent organic framework material prepared by the above-mentioned preparation method has good chemical stability and good batch reproducibility. The prepared hydrazone chiral covalent organic framework material is used as a heterogeneous catalyst in an asymmetric reaction, and it shows good catalytic effect and chiral selectivity, and the catalyst can be separated and recovered by simple centrifugation or filtration, which is green and environmentally friendly and saves costs. At the same time, the hydrazone chiral covalent organic framework material can still maintain the catalytic effect and chiral selectivity after three cycles of recovery, and the material has excellent recycling performance and good chemical stability. In summary, the hydrazone chiral covalent organic framework material provided by the present invention is used as a catalyst in a heterogeneous asymmetric reaction, has good catalytic effect and chiral selectivity, is easy to separate, recycle and reuse, is green and environmentally friendly, saves costs, and is conducive to large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the synthesis process of chiral hydrazide precursor

[0021] Figure 2 The X-ray powder diffraction pattern of the hydrazone chiral covalent organic framework material prepared in Example 1

[0022] Figure 3 This is a Fourier transform infrared spectrum of the hydrazone chiral covalent organic framework material prepared in Example 1.

[0023] Figure 4 The solid-state NMR spectra of the hydrazone chiral covalent organic framework containing Boc protective group prepared in Comparative Example 1 and the hydrazone chiral covalent organic framework material prepared in Example 1 are shown in FIG.

[0024] Figure 5 Thermogravimetric curves of the chiral covalent organic framework containing Boc protective group prepared in Comparative Example 1 and the hydrazone chiral covalent organic framework material prepared in Example 1

[0025] Figure 6 The invention discloses a nuclear magnetic hydrogen spectrum of diastereoisomer products obtained by using the hydrazone chiral covalent organic framework material prepared by the present invention to catalyze the aldol condensation reaction of cyclohexanone and p-nitrobenzaldehyde.

[0026] Figure 7 Liquid chromatography separation diagram of the enantiomeric products obtained by catalyzing the aldol condensation reaction of cyclohexanone and p-nitrobenzaldehyde using the hydrazone chiral covalent organic framework material prepared in the present invention DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to specific embodiments. It should be understood that the present invention is not limited to the following embodiments, and any modifications or variations based on the present invention will fall within the scope of the present invention.

[0028] In the present invention, the equipment and raw materials used can be purchased from the market or commonly used in the art.

[0029] Example 1:

[0030] In this embodiment, a hydrazone chiral covalent organic framework material is prepared according to the following steps:

[0031] A microwave tube was added with the chiral hydrazide precursor (12.2 mg, 0.03 mmol) and 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (7.9 mg, 0.02 mmol). N,N-dimethylacetamide (0.85 mL) and mesitylene (0.15 mL) were then added, followed by 0.1 mL of 12 M aqueous acetic acid. Ultrasonic dispersion was performed for 5 minutes to obtain a suspension. The suspension was frozen in liquid nitrogen, vacuumized, and degassed three times, then sealed and placed in an oven at 110°C for 3 days. After the reaction was completed, the solid was cooled to room temperature, filtered, and washed sequentially with DMF, THF, and methanol, and finally washed once with anhydrous ether and air-dried. The dried powder was transferred to a 10 mL glass vial. 1 mL of 4 M dioxane hydrochloride solution was added per 30 mg of the product, and the mixture was stirred at room temperature for 2 hours to remove the Boc protecting group. After the reaction, the solid was filtered and washed with 6 mL of THF (once), 6 mL of 2% triethylamine in methanol (twice), 6 mL of deionized water (once), and 6 mL of THF (once). Finally, it was washed once with 6 mL of anhydrous ether and dried in a vacuum oven for 6 hours. The desired hydrazone chiral covalent organic framework material was obtained with a yield of 86.4%.

[0032] Among them, the synthesis route of chiral hydrazide precursor is as follows Figure 1 As shown, the specific steps include:

[0033] (1) Synthesis of Compound 1: N-Boc-L-proline (2.468 g, 11.48 mmol), 5-amino-dimethyl isophthalate (2.0 g, 9.56 mmol) and N, N′-dicyclohexylcarbodiimide (DCC, 2.838 g, 13.75 mmol) were added to a single-necked flask, and then 50 mL of dichloromethane solution was added, and the mixture was stirred at room temperature for 24 hours. After the reaction was completed, 100 mL of water was added to the reaction mixture, and the mixture was extracted with dichloromethane. The organic phases were combined and dried over Na2SO4. After the solvent was dried, the crude product was purified by silica gel column chromatography (ethyl acetate: n-hexane = 1:4, V / V) to obtain Compound 1 as a white powder (4.10 g, yield 88%). 1 H NMR(600MHz,DMSO-d6)δ10.44(s,1H),8.54(s,2H),8.17(s,1H),4.22(m,1H),3.90(m ,6H),3.45(m,1H),3.44(m,1H),2.21(m,1H),1.88(m,3H),1.40(s.3H),1.39(s.6H).

[0034] (2) Synthesis of chiral hydrazide precursor: Hydrazine hydrate (1.2 mL, 23 mmol), compound 1 (930 mg, 2.3 mmol) and 20 mL of anhydrous ethanol were added to a single-necked flask, and the mixed solution was heated under reflux for 24 h. After the reaction was completed, the mixture was cooled to room temperature and refrigerated overnight to precipitate a large amount of white crystals. The formed white crystals were collected by filtration, washed with cold anhydrous ethanol, and dried in vacuo to obtain the chiral hydrazide precursor (730 mg, yield 78.5%). 1 H NMR(600MHz,DMSO-d6)δ10.23(s,1H),9.69(d,2H),8.15(d,2H),7.86(s,1H),4.56(s,4H), 4.23(m,1H),3.43(m,2H),2.20(m,1H),1.90(m,2H),1.88(m,1H),1.4(s,3H),1.27(s,6H). 13 C NMR(150MHz,DMSO-d6)δ171.75,165.47,153.01,139.18,134.11,120.60,119.63,78.6 3,78.46,60.35,59.97,46.65,46.44,30.88,30.07,28.05,27.86,23.85,23.26.MS:m / z calcd for C 13 H 18 N6O3[MH] -:406.44,found:405.19.

[0035] The synthesis methods of the chiral hydrazide precursors in the following examples and comparative examples are the same as those in this example, and thus are not described again.

[0036] Example 2:

[0037] In this embodiment, a hydrazone chiral covalent organic framework material is prepared according to the following steps:

[0038] A microwave tube was added with the chiral hydrazide precursor (18.3 mg, 0.045 mmol) and 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (11.8 mg, 0.03 mmol). 0.5 mL of o-dichlorobenzene and 0.5 mL of n-butanol were then added, followed by 0.1 mL of 6 M aqueous acetic acid. Ultrasonic dispersion was performed for 5 minutes to obtain a suspension. The suspension was frozen in liquid nitrogen, vacuumized, and degassed three times, then sealed and placed in an oven at 110°C for 3 days. After the reaction was completed, the solid was cooled to room temperature, filtered, and washed sequentially with DMF, THF, and methanol, and finally washed once with anhydrous ether and air-dried. The dried powder was transferred to a 10 mL glass vial. 1 mL of 4 M dioxane hydrochloride solution was added per 30 mg of the product, and the Boc protecting group was removed by stirring at room temperature for 2 hours. After the reaction, the solid was filtered and washed with 6 mL of THF once, 6 mL of 2% triethylamine methanol solution twice, 6 mL of deionized water once, 6 mL of THF once, and finally 6 mL of anhydrous ether once. The solid was dried in a vacuum oven for 6 hours to obtain the desired hydrazone chiral covalent organic framework material.

[0039] Example 3:

[0040] In this embodiment, a hydrazone chiral covalent organic framework material is prepared according to the following steps:

[0041] In a microwave tube, add the chiral hydrazide precursor (12.2 mg, 0.03 mmol) and 2,4,6-tris(4-formylphenyl)-1,3,5-triazine (7.9 mg, 0.02 mmol). Then, add 0.3 mL of dioxane and 0.7 mL of mesitylene. Finally, add 0.1 mL of 6 M aqueous acetic acid. Ultrasonic dispersion is performed for 5 minutes to obtain a suspension. The suspension is frozen in liquid nitrogen, vacuumized, and degassed three times. After sealing, it is placed in an oven at 120°C for 3 days. After the reaction is completed, it is cooled to room temperature. The resulting solid is filtered and washed sequentially with DMF, THF, and methanol, and finally washed once with anhydrous ether and air-dried. The dried powder is finally transferred to a 10 mL glass vial. 1 mL of 4 M hydrochloric acid in dioxane is added per 30 mg of the weight of the product. Stir at room temperature for 2 hours to remove the Boc protecting group. After the reaction, the solid was filtered and washed with 6 mL of THF once, 6 mL of 2% triethylamine methanol solution twice, 6 mL of deionized water once, 6 mL of THF once, and finally 6 mL of anhydrous ether once. The solid was dried in a vacuum oven for 6 hours to obtain the desired hydrazone chiral covalent organic framework material.

[0042] Comparative Example 1:

[0043] The preparation method of the chiral covalent organic framework material with Boc group protection in this comparative example is different from that in Example 1 in that it does not include the step of removing the Boc protecting group.

[0044] Test result analysis:

[0045] The hydrazone chiral covalent organic framework material obtained in Example 1 was characterized, and the test results are as follows:

[0046] See also Figure 2 , which is the X-ray powder diffraction pattern of the hydrazone chiral covalent organic framework material obtained in Example 1. It can be seen from the figure that the obtained hydrazone chiral covalent organic framework material has obvious X-ray diffraction peaks, indicating that the obtained material has a crystalline structure.

[0047] See also Figure 3Fourier infrared spectrum of , wherein curve a is 2,4,6-tris (4-formylphenyl) -1,3,5-triazine, curve b is chiral hydrazide monomer, curve c is hydrazone chiral covalent organic framework containing Boc protecting group obtained in Comparative Example 1, and curve d is hydrazone chiral covalent organic framework material obtained in Example 1. As can be seen from the figure, the characteristic peak of 2,4,6-tris (4-formylphenyl) -1,3,5-triazine monomer belonging to the aldehyde group disappears in the chiral framework material, indicating that the aldehyde group reacts with the amino group during the synthesis of the chiral framework material. In addition, after removing the Boc protecting group, the infrared absorption peak of the material remains basically unchanged, indicating that the framework structure of the hydrazone chiral covalent organic framework material can still be maintained after removing the Boc protecting group.

[0048] See also Figure 4 , which are solid-state NMR spectra of the hydrazone chiral covalent organic framework containing a Boc protecting group (a) prepared in Comparative Example 1 and the hydrazone chiral covalent organic framework (b) prepared in Example 1. As can be seen from the figure, the characteristic peaks at 28,80 ppm disappear, indicating that the Boc group has been removed, while the tetrahydropyrrolidine group remains in the material framework.

[0049] See also Figure 5 , which is a thermogravimetric curve of the chiral covalent organic framework containing Boc protecting group (a) prepared in Comparative Example 1 and the hydrazone chiral covalent organic framework material (b) prepared in Example 1. As can be seen from the figure, the chiral covalent framework with Boc group loses weight before 280°C, which is attributed to the decomposition of the Boc group. However, the hydrazone chiral covalent organic framework material with the Boc protecting group removed does not lose weight significantly before 280°C. A weight loss platform appears at around 334°C, indicating that the structural framework of the hydrazone chiral covalent organic framework material begins to decompose, which is consistent with the chiral framework material with Boc group.

[0050] The performance of the hydrazone chiral covalent organic framework materials prepared in Examples 2 and 3 is not significantly different from that of the hydrazone chiral covalent organic framework material prepared in Example 1. They both have good catalytic effects and chiral selectivity in catalyzing the asymmetric aldol condensation reaction of cyclohexanone and p-nitrobenzaldehyde. Therefore, the performance is not characterized one by one. The following application examples all use the hydrazone chiral covalent organic framework material prepared in Example 1.

[0051] The following application examples take the asymmetric aldol condensation reaction of cyclohexanone and nitrobenzaldehyde as an example to verify the catalytic activity and chiral selectivity of the chiral covalent organic framework material prepared by the present invention for the asymmetric aldol condensation reaction of aldehydes and ketones.

[0052]

[0053] Application Example 1

[0054] 20.5 mg of the hydrazone chiral covalent organic framework material prepared in Example 1, 15.1 mg of p-nitrobenzaldehyde, 0.3 mL of cyclohexanone, 0.3 mL of water, and 1 mL of DMF were added to a reaction tube, followed by the addition of 2.3 μL of trifluoroacetic acid. The reaction was stirred at room temperature for 7 days. After the reaction was completed, the liquid was collected by centrifugation or filtration and washing. After concentration under reduced pressure, the residue was purified by column chromatography (ethyl acetate:n-hexane = 1:4, V / V) to obtain the target product with a yield of 96.0% and an ee value of 83.2% (measured by high performance liquid chromatography, as shown in FIG. 2 ). Figure 7 As shown), the dr value is 1:8.5 (measured by nuclear magnetic hydrogen spectrum, as Figure 6 shown).

[0055] Application Example 2

[0056] 20.5 mg of the hydrazone chiral covalent organic framework material prepared in Example 1, 15.1 mg of p-nitrobenzaldehyde, 0.3 mL of cyclohexanone, 0.3 mL of water, and 1 mL of DMF were added to a reaction tube. 1.8 μL of acetic acid was then added and the reaction was stirred at room temperature for 4 days. After completion of the reaction, the liquid was collected by centrifugation or filtration and washing. After concentration under reduced pressure, the residue was purified by column chromatography (ethyl acetate:n-hexane = 1:4, v / v) to obtain the desired product with a yield of 98.0%, an ee value of 51.1% (determined by HPLC), and a dr value of 1:6.1 (determined by H-NMR spectroscopy).

[0057] Application Example 3

[0058] 20.4 mg of the hydrazone chiral covalent organic framework material prepared in Example 1, 15.1 mg of p-nitrobenzaldehyde, 0.3 mL of cyclohexanone, 0.3 mL of water, and 1 mL of DMF were added to a reaction tube. 3.7 mg of benzoic acid was then added and the reaction was stirred at room temperature for 4 days. After completion of the reaction, the liquid was collected by centrifugation or filtration and washing. After concentration under reduced pressure, the residue was purified by column chromatography (ethyl acetate:n-hexane = 1:4, v / v) to obtain the desired product with a yield of 96.7%, an ee value of 61.4% (determined by HPLC), and a dr value of 1:4.8 (determined by H-NMR spectroscopy).

[0059] Application Example 4

[0060] 20.4 mg of the hydrazone chiral covalent organic framework material prepared in Example 1, 15.1 mg of m-nitrobenzaldehyde, 0.3 mL of cyclohexanone, 0.3 mL of water, and 1 mL of DMF were added to a reaction tube. Then, 2.3 μL of trifluoroacetic acid was added and the reaction was stirred at room temperature for 7 days. After completion of the reaction, the liquid was collected by centrifugation or filtration and washing. After concentration under reduced pressure, the residue was purified by column chromatography (ethyl acetate:n-hexane = 1:4, v / v) to obtain the desired product with a yield of 81.9%, an ee value of 80.1% (determined by HPLC), and a dr value of 1:6.7 (determined by H-NMR spectroscopy).

[0061] Comparative Application Example 1

[0062] 23.5 mg of the Boc-protected chiral covalent organic framework material prepared in Comparative Example 1, 15.1 mg of p-nitrobenzaldehyde, 0.3 mL of cyclohexanone, 0.3 mL of water, and 1 mL of DMF were added to a reaction tube, followed by the addition of 2.3 μL of trifluoroacetic acid. The mixture was stirred at room temperature for 7 days. After completion of the reaction, the liquid was collected by centrifugation or filtration and washing, and the residue was concentrated under reduced pressure. The residue was purified by column chromatography (ethyl acetate:n-hexane = 1:4, V / V) to obtain the desired product with a yield of 20.9%, an ee value of 9.2% (determined by HPLC), and a dr value of 1:1 (determined by H-NMR spectroscopy).

[0063] From the data, it can be seen that the catalytic effect and chiral selectivity of the chiral covalent organic framework material with Boc group protection prepared in Comparative Example 1 in the asymmetric aldol condensation reaction are significantly reduced. This is because when the Boc group is not removed, the catalytic active site is protected by the tert-butyloxycarbonyl group.

[0064] Comparison of catalytic effect and chiral selectivity:

[0065] The catalytic effect and chiral selectivity of the hydrazone chiral covalent organic framework material prepared in this application and other chiral solid-phase catalyst materials for the asymmetric aldol condensation reaction of cyclohexanone and p-nitrobenzaldehyde are compared, as shown in Table 1:

[0066] Table 1 Comparison of catalytic effects and chiral selectivity of asymmetric aldol condensation catalysts

[0067]

[0068] As can be seen from Table 1, the hydrazone chiral covalent organic framework material of the present invention has very good catalytic effect and chiral selectivity in catalyzing the asymmetric aldol condensation reaction of cyclohexanone and p-nitrobenzaldehyde.

[0069] Recycling and repeated application test:

[0070] The hydrazone chiral covalent organic framework (CHF) obtained by centrifugation or filtration in the above application example was washed with dichloromethane and a 2% methanolic triethylamine solution, dried, and reused to catalyze the reaction of cyclohexanone and p-nitrobenzaldehyde. The catalytic performance and chiral selectivity of this repeated application are shown in Table 2.

[0071] Table 2 Catalytic effects and chiral selectivity of hydrazone chiral covalent organic framework materials in recycling and repeated application catalytic experiments

[0072]

[0073] As can be seen from Table 2, the hydrazone chiral covalent organic framework material of the present invention can still maintain good catalytic effect and chiral selectivity after three recycling cycles. It also shows that the obtained hydrazone chiral covalent organic framework material has good chemical stability. However, due to the electrophilicity of the imine bond, water molecules and the imine chemical bond produce an electrophilic addition reaction in an aqueous environment, resulting in poor chemical stability of some imine COFs. In the hydrazone bond, due to the resonance of the lone pair of electrons of the nitrogen atom connected to the imine (─C ─ ─N=N + ─), the carbon atom carries a partial negative charge, which weakens the electrophilicity and makes the hydrazone bond more stable.

[0074] The present invention is not limited to the applications listed in the specification and implementation methods, and can be fully applied to various fields suitable for the present invention. Without departing from the spirit and essence of the present invention, it is easy for those familiar with the art to implement additional modifications and variations, but these corresponding modifications and variations should all fall within the scope of protection required by the present invention.

[0075] The above descriptions are only some embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. Those skilled in the art should be aware that any solutions obtained by equivalent substitutions and obvious changes made using the contents of the present invention specification should be included in the protection scope of the present invention.

Claims

1. A method for preparing a hydrazone chiral covalent organic framework material, characterized in that: The following steps are involved: Under an inert atmosphere, a chiral hydrazide precursor with tert-butyloxycarbonyl protection and 2,4,6-tris(4-formylphenyl)-1,3,5-triazine are dissolved in an organic solvent, and then an acetic acid aqueous solution is added. The reaction is carried out at 90-120°C for 2-5 days. The insoluble matter is then collected and washed, dried, and deprotected to obtain a hydrazone chiral covalent organic framework material. The structural formula of the chiral hydrazide precursor is: In the formula, Boc is tert-butyloxycarbonyl.

2. The preparation method according to claim 1, wherein: The molar ratio of the chiral hydrazide precursor to the 2,4,6-tris(4-formaldehydephenyl)-1,3,5-triazine is 3:

2.

3. The preparation method according to claim 1, wherein: The molar ratio of the acetic acid to the chiral hydrazide precursor is (1-20):

1.

4. The preparation method according to claim 1, wherein: The deprotection treatment uses a 4M hydrochloric acid dioxane solution, and the mass ratio of the volume of the dioxane solution to the insoluble matter obtained by the reaction is 1 mL: (20-40) mg.

5. The preparation method according to claim 4, characterized in that: The deprotection treatment reaction time is 1 to 6 hours.

6. The preparation method according to claim 1, wherein: The organic solvent is any one of a mixed solution of N,N-dimethylacetamide and mesitylene, a mixed solution of 1,4-dioxane and mesitylene, and a mixed solution of o-dichlorobenzene and n-butanol.

7. The preparation method according to claim 1, wherein: The reaction temperature was 110°C and the reaction time was 3 days.

8. A hydrazone chiral covalent organic framework material prepared by the preparation method according to any one of claims 1 to 7.

9. The hydrazone chiral covalent organic framework material according to claim 8, characterized in that: Its structural formula is:

10. Use of the hydrazone chiral covalent organic framework material according to claim 8 or 9 in catalyzing heterogeneous asymmetric reactions.

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