Chiral imide-based covalent organic framework material and method for preparing the same

Abstract

The present application relates to a kind of chiral imide group covalent organic framework material and its preparation method, belong to covalent organic framework material technical field.The chiral imide group covalent organic framework material of the present application is with imide bond as connecting unit, with higher thermal stability and chemical stability, and the precise construction of framework chirality is realized by chiral induction strategy, to give material clear chiral characteristics, with important application potential in chiral recognition, chiral separation and asymmetric catalysis etc.;Its preparation is with R / S-tetrahydrofuran-2-methyl acid as chiral inducer, isoquinoline as catalyst, imidazole as reaction medium, and imide bond connecting type covalent organic framework material with crystallinity and significant chiral signal can be prepared by solvothermal reaction.

Description

Technical Field

[0001] This invention belongs to the field of covalent organic framework materials technology, and particularly relates to a chiral imide-based covalent organic framework material and its preparation method. Background Technology

[0002] Covalent organic frameworks (COFs) are a class of porous crystalline organic materials formed by organic molecular components linked by covalent bonds. Due to their designable framework structure, adjustable pore size, and high specific surface area, they have attracted widespread attention in many fields such as gas adsorption and separation, catalysis, sensing, and energy storage.

[0003] Common COF (carbon ion exchange) linkages include boroxane bonds, borate ester bonds, and imine bonds. Among these, linkages formed by dynamic reversible covalent reactions can facilitate the smooth crystallization process of the framework and error correction, thereby obtaining a highly ordered crystalline structure. However, they also bring limitations in terms of insufficient chemical stability: early boroxane or borate ester linked COFs are sensitive to moisture and acidic environments, and are prone to hydrolysis leading to structural degradation; even if some imine linked COF systems can maintain structural stability under suitable conditions, their stability still depends on the framework composition, substituent effects, and the medium in which they are located. In strong acids, strong bases, or long-term aqueous environments, problems such as bond exchange, hydrolysis, or structural transformation are likely to occur.

[0004] Chiral covalent organic frameworks (CCOFs), as a class of functional materials with promising applications, possess a designable pore environment and framework structure. Chiral microenvironments can be constructed through the introduction of chiral monomers, post-modification, or chiral induction, thus attracting widespread attention in fields such as chiral separation, asymmetric catalysis, and chiral recognition. Especially in pharmaceuticals and agrochemicals, different enantiomers of many chiral active molecules often exhibit different biological activities, making efficient enantiomer recognition and separation crucial. Introducing a chiral environment into COFs holds promise for endowing the material with the ability to differentially recognize enantiomer molecules, further enabling applications in separation or enantioselective catalysis. Compared to amorphous porous organic materials, the defined crystal structure and tunable pore environment of COFs also facilitate the study of structure-activity relationships in chiral recognition and mass transfer processes. Based on the tunability of their composition and structure, CCOFs can be further developed into membrane separation materials, adsorption separation materials, or heterogeneous asymmetric catalytic materials, demonstrating excellent application potential.

[0005] Currently, the construction of chiral COFs mainly includes direct synthesis, post-synthetic modification, and chiral induction strategies. Direct synthesis involves introducing monomers containing chiral centers to directly construct the chiral framework. While this method can solidify chiral sites at the molecular level, it typically relies on expensive or synthetically complex chiral precursors, and the large size of the chiral groups can affect the crystallinity and pore structure of the framework. Post-synthetic modification involves first constructing an achiral COF framework and then introducing chiral groups through chemical reactions. This method is advantageous for preserving the original framework structure, but it suffers from cumbersome steps, limited modification efficiency, and difficulty in precisely controlling the distribution of chiral sites. In contrast, chiral induction strategies introduce chiral auxiliaries, chiral catalysts, or chiral induction environments during COF synthesis, allowing achiral precursors to form a chiral framework during assembly. This eliminates the need for pre-designing and synthesizing chiral framework monomers, offering significant advantages in simplifying synthetic routes and reducing precursor design complexity. This makes it a highly promising method for constructing chiral COFs.

[0006] However, current research on chiral construction still faces many challenges: on the one hand, for systems constructed from achiral precursors, how to effectively induce and stably maintain the framework chirality remains a problem, especially in systems that rely on dynamic reversible bonding, where enantioselection and chiral locking during crystallization are often difficult to balance; on the other hand, existing reports on the construction of chiral COFs from achiral precursors through chiral induction or transformation strategies mainly focus on reversible linkage systems such as imine bonds, while there are currently no publicly available reports on imine bond linkage systems—especially on the direct construction of chiral imine bond COFs from achiral precursors through chiral induction.

[0007] Imidine bonds, as a type of intrinsically stable linkage, have attracted widespread attention in recent years. These COFs are typically constructed from aromatic amines and aromatic dianhydrides via imidization reactions. Compared to traditional imine linkages, imine bonds exhibit higher thermal and chemical stability, making them a crucial direction for improving the chemical stability of reversibly linked COF materials. Researchers have explored two main approaches: first, a post-reaction linking transformation strategy, which involves first synthesizing highly crystalline reversibly linked COFs and then stabilizing the link through subsequent chemical transformations (e.g., oxidizing an imine-linked COF to an amide-linked framework). However, this method requires secondary transformation and post-processing, limiting its applicability to the type of the original COF skeleton and reaction compatibility; second, a novel method for directly constructing intrinsically high-stability linkages, i.e., directly preparing imine-linked COFs. However, due to the weak dynamic reversibility of imidization reactions, while beneficial for obtaining stable chemical bonds, directly constructing imine-linked COFs with both high crystallinity and high porosity presents significant challenges.

[0008] In summary, developing a chiral COF preparation method based on imide bonds can not only leverage the advantages of the irreversibility and high stability of imide bonds, but also provide a feasible way to introduce and fix the chiral environment. Solving the core problem of "difficulty in balancing high stability, high crystallinity and chiral controllability" remains an important issue that urgently needs to be addressed in this field. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a chiral imide-based covalent organic framework material and its preparation method. This chiral imide-based covalent organic framework material uses imide bonds as connecting units, exhibits high thermal and chemical stability, and achieves precise chiral construction of the framework through a chiral induction strategy, thereby endowing the material with clear chiral characteristics. It has significant application potential in fields such as chiral recognition, chiral separation, and asymmetric catalysis. The preparation method uses R / S-tetrahydrofuran-2-carboxylic acid as a chiral inducing agent, isoquinoline as a catalyst, and imidazole as a reaction medium. Through a solvothermal reaction, an imide-bonded covalent organic framework material with crystallinity and significant chiral signal can be obtained.

[0010] The first objective of this invention is to provide a chiral imide-based covalent organic framework material, which is formed by an imidization reaction of an amine monomer and an anhydride monomer, and has the following structural formula: ; In this context, "*" represents a repeating unit; “ "Selected from" , or .

[0011] A second objective of this invention is to provide a method for preparing the chiral imide-based covalent organic framework material, comprising the following steps: Amine monomers and anhydride monomers were mixed, and a chiral inducer and catalyst were added. After ultrasonic treatment, imidazole was added, and the mixture was degassed by a cycle of freezing, vacuuming, and thawing in a liquid nitrogen bath. The imidization reaction was carried out under a protective atmosphere. The reaction product was then subjected to filtration, washing, Soxhlet extraction, and vacuum drying to obtain the chiral imide-based covalent organic framework material.

[0012] In one embodiment of the present invention, the amine monomer is selected from one or more of 1,3,5-tris(4-aminophenyl)triazine, 4,4',4''-(pyrimidin-2,4,6-triyl)triphenylamine or 4,4',4''-(pyridine-2,4,6-triyl)triphenylamine.

[0013] In one embodiment of the present invention, the anhydride monomer is perylenetetracarboxylic dianhydride.

[0014] In one embodiment of the present invention, the molar ratio of the amine monomer to the anhydride monomer is (2.8-3.2):2.

[0015] In one embodiment of the present invention, the chiral inducer is R / S-tetrahydrofuran-2-carboxylic acid.

[0016] In one embodiment of the present invention, the catalyst is isoquinoline.

[0017] In one embodiment of the present invention, the molar ratio of the amine monomer, chiral inducer, catalyst and imidazole is 1:(100-110):(0.38-0.42):(480-500).

[0018] In one embodiment of the present invention, the temperature of the liquid nitrogen bath is 75K-80K.

[0019] In one embodiment of the present invention, the imidization reaction is carried out at a temperature of 175°C-185°C for 3-4 days.

[0020] The technical solution of the present invention has the following advantages compared with the prior art: (1) The chiral imide-based covalent organic framework material of the present invention uses imide bonds as connecting units, which has the advantages of designable covalent organic framework structure, adjustable pore size and high specific surface area. It also has significant chiral optical response, and the intrinsic properties of imide bonds can significantly improve the thermal stability and chemical stability of the material.

[0021] (2) The preparation method of the present invention uses R / S-tetrahydrofuran-2-carboxylic acid as a chiral inducer, isoquinoline as a catalyst, and imidazole as a reaction medium. It uses non-chiral amine monomers and anhydride monomers as reaction precursors to directly construct chiral imide-based covalent organic framework materials through a one-step solvothermal reaction. Among them, R / S-tetrahydrofuran-2-carboxylic acid can provide a chiral induction environment during the reaction process, avoiding the adverse effects of directly introducing large-volume chiral framework monomers on the ordered construction of the framework. The synergistic effect of isoquinoline and imidazole reaction medium can promote monomer dispersion, imidization reaction and ordered assembly of the framework, so that the obtained material has both excellent crystallinity and significant chiral signal while maintaining high stability of imide bonds.

[0022] (3) The preparation method described in this invention adopts a chiral induction strategy, which does not require the prior synthesis of chiral monomers, nor does it require post-modification or bond type transformation of achiral frameworks. This can effectively simplify the synthesis route, broaden the scope of application, and enable the obtained chiral imide-based covalent organic framework materials to show good application potential in fields such as chiral recognition, chiral separation and asymmetric catalysis. Attached Figure Description

[0023] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein: Figure 1 Fourier transform infrared spectra of R / S-TT-PT, R / S-PM-PT and R / S-PD-PT prepared for embodiments of the present invention; Figure 2 UV-Vis absorption spectra of R / S-TT-PT, R / S-PM-PT and R / S-PD-PT prepared for embodiments of the present invention; Figure 3 Scanning electron microscope images of R / S-TT-PT, R / S-PM-PT and R / S-PD-PT prepared for embodiments of the present invention; Figure 4 Powder X-ray diffraction patterns of R / S-TT-PT, R / S-PM-PT and R / S-PD-PT prepared for embodiments of the present invention; Figure 5 Circular dichroism spectra of R / S-TT-PT, R / S-PM-PT and R / S-PD-PT prepared for embodiments of the present invention; Figure 6 The powder X-ray diffraction pattern and circular dichroism spectrum of R / S-TT-PT' prepared in Comparative Example 1 of this invention are shown. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0025] In this invention, unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] In this invention, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0027] In this invention, unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods, and the materials and reagents used are commercially available unless otherwise specified. Example 1

[0028] The chiral imide-based covalent organic framework material and its preparation method in this embodiment specifically include the following steps: 1,3,5-tris(4-aminophenyl)triazine (79.74 mg, 0.225 mmol) and perylenetetracarboxylic dianhydride (58.84 mg, 0.15 mmol) were weighed and placed in a 25 mL Schlenk tube. 2 mL of R / S-tetrahydrofuran-2-carboxylic acid and 10 μL of isoquinoline were added sequentially. After sonication for 5 min, 7.5 g of imidazole was added. The mixture was degassed three times by freezing in a 77 K liquid nitrogen bath, followed by vacuuming and thawing. Nitrogen gas was introduced and the tube was sealed with a polytetrafluoroethylene valve. The imidization reaction was carried out at 180 °C for 3 days. After the reaction, a reddish-brown solid was obtained. The solid was collected by filtration and washed sequentially with acetone, N,N-dimethylformamide, and tetrahydrofuran. The solid was then extracted with tetrahydrofuran by Soxhlet extraction for 24 h and vacuum dried for 12 h to obtain a chiral imide-based covalent organic framework material, denoted as R / S-TT-PT, with a yield of 82%. Example 2

[0029] The chiral imide-based covalent organic framework material and its preparation method in this embodiment specifically include the following steps: 4,4',4''-(pyrimidine-2,4,6-trimethyl)triphenylamine (79.52 mg, 0.225 mmol) and perylene tetracarboxylic dianhydride (58.84 mg, 0.15 mmol) were weighed and placed in a 25 mL Schlenk tube. 2 mL of R / S-tetrahydrofuran-2-carboxylic acid and 10 μL of isoquinoline were added sequentially. After sonication for 5 min, 7.5 g of imidazole was added. The mixture was degassed three times by freezing in a 77 K liquid nitrogen bath, followed by vacuuming and thawing. Nitrogen gas was introduced and the tube was sealed with a polytetrafluoroethylene valve. The imidization reaction was carried out at 180 °C for 3 days. After the reaction, a reddish-brown solid was obtained. The solid was collected by filtration and washed sequentially with acetone, N,N-dimethylformamide, and tetrahydrofuran. The solid was then extracted with tetrahydrofuran by Soxhlet extraction for 24 h and vacuum dried for 12 h to obtain a chiral imide-based covalent organic framework material, denoted as R / S-PM-PT, with a yield of 85%. Example 3

[0030] The chiral imide-based covalent organic framework material and its preparation method in this embodiment specifically include the following steps: 4,4',4''-(pyridine-2,4,6-triyl)triphenylamine (79.30 mg, 0.225 mmol) and perylene tetracarboxylic dianhydride (58.84 mg, 0.15 mmol) were weighed and placed in a 25 mL Schlenk tube. 2 mL of R / S-tetrahydrofuran-2-carboxylic acid and 10 μL of isoquinoline were added sequentially. After sonication for 5 min, 7.5 g of imidazole was added. The mixture was degassed three times by freezing in a 77 K liquid nitrogen bath, followed by vacuuming and thawing. Nitrogen gas was introduced and the tube was sealed with a polytetrafluoroethylene valve. The imidization reaction was carried out at 180 °C for 3 days. After the reaction, a reddish-brown solid was obtained. The solid was collected by filtration and washed sequentially with acetone, N,N-dimethylformamide, and tetrahydrofuran. The solid was then extracted with tetrahydrofuran by Soxhlet extraction for 24 h and vacuum dried for 12 h to obtain a chiral imide-based covalent organic framework material, denoted as R / S-PD-PT, with a yield of 79%. Comparative Example 1

[0031] The procedure is basically the same as in Example 1, except that: 7.5g of imidazole is added first, followed by 2mL of R / S-tetrahydrofuran-2-carboxylic acid and 10μL of isoquinoline, denoted as R / S-TT-PT'. Comparative Example 2

[0032] The chiral imide-based covalent organic framework material and its preparation method described in this comparative example specifically include the following steps: S1. Weigh 35.44 mg (0.1 mmol) of 1,3,5-tris(4-aminophenyl)triazine and 58.84 mg (0.15 mmol) of perylene tetracarboxylic dianhydride into a 25 mL Schlenk tube. Add 2 mL of N-methyl-2-pyrrolidone, 0.5 mL of mesitylene, and 10 μL of isoquinoline in sequence. After sonication for 5 min, add 5 g of imidazole. Degas the mixture three times by freezing, vacuuming, and thawing in a 77 K liquid nitrogen bath. Purge with nitrogen and seal with a polytetrafluoroethylene valve. Indinate the mixture at 180 °C for 3 days. After the reaction, a reddish-brown solid is obtained. Collect the solid by filtration and wash it in sequence with N-methyl-2-pyrrolidone, ethanol, and tetrahydrofuran. Then extract with tetrahydrofuran by Soxhlet extraction for 24 h and vacuum dry for 12 h to obtain an imide-based covalent organic framework material with a yield of 72%. S2. The imide-based covalent organic framework material was immersed in pure R / S-tetrahydrofuran-2-carboxylic acid for 2 days to obtain the supported imide-based covalent organic framework material.

[0033] Circular dichroism spectroscopy analysis showed that after subsequent soaking and loading with R / S-tetrahydrofuran-2-carboxylic acid, the resulting material did not exhibit any new chiral signal corresponding to that in the examples. This indicates that post-loading alone is insufficient to impart the same chiral optical response to the imide-linked covalent organic framework material as in the examples. It suggests that the chirality of the material in the examples originates from the chiral-induced construction during the synthesis process, rather than from the simple adsorption or loading of the chiral inducing agent. Test Example 1

[0034] The covalent organic framework materials prepared in the examples and comparative examples were characterized and analyzed, and the results are as follows: Figures 1-6 As shown.

[0035] from Figure 1 It can be seen that the characteristic -C=O absorption peak (1770 cm⁻¹) of the anhydride group in the raw material perylenetetracarboxylic dianhydride is present. -1 ) and the characteristic absorption peak of the amino group in amine monomers (3325 cm⁻¹) -1 It was not detected in any of the three materials: R / S-TT-PT, R / S-PM-PT, and R / S-PD-PT. All three materials showed a value of 1706 cm⁻¹. -1 The characteristic symmetrical vibration peak of the imide bond appears at 1349 cm⁻¹. -1 The presence of the characteristic stretching vibration peak of -CNC in the six-membered imide ring, together with the disappearance of the characteristic peak of the raw material, confirms that the amine monomer and the anhydride monomer have successfully formed an imide bond through the imidization reaction.

[0036] from Figure 2 It can be seen that the three materials R / S-TT-PT, R / S-PM-PT and R / S-PD-PT all exhibit similar UV-Vis absorption characteristics, showing obvious broad absorption bands in the visible region with similar absorption edge positions, indicating that this series of materials has similar conjugated framework structures and electronic transition characteristics. Their absorption bands correspond to the characteristic bands of circular dichroism spectroscopy, indicating that the chiral optical response of the materials is related to the electronic structure of the framework itself. Combined with the results of Comparative Example 2, it can be further confirmed that the chiral response does not come from the simple loading or physical adsorption of chiral inducers.

[0037] from Figure 3 It can be seen that the three materials R / S-TT-PT, R / S-PM-PT and R / S-PD-PT all exhibit relatively regular rod-shaped or large block-shaped morphologies, indicating that the obtained materials have good morphological uniformity and a certain degree of ordered growth characteristics.

[0038] from Figures 4-6It can be seen that R / S-TT-PT, R / S-PM-PT, and R / S-PD-PT all exhibit obvious diffraction peaks, indicating that the obtained materials have good crystallinity and long-range ordered structure. Among them, R / S-TT-PT shows obvious characteristic diffraction peaks at 2θ = 2.67°, which belong to the (100) crystal plane in the AA stacking mode of the two-dimensional framework. The peaks are sharp and have high intensity, indicating that they all have excellent crystallinity and a high degree of ordered assembly of the framework. R / S-tetrahydrofuran-2-carboxylic acid and the three target materials all exhibit a symmetrical Cotton effect. The CD signals of R-COF and S-COF are mirror-symmetrically distributed, and the characteristic CD peak positions of the target materials are significantly shifted compared with R / S-tetrahydrofuran-2-carboxylic acid, confirming that the chiral information has been successfully transferred from the chiral inducer to the COF framework structure, rather than a simple matter. The adsorption or residue of the material resulted in the successful construction of the chiral imide-based covalent organic framework. The intensity of the (100) crystal plane diffraction peak of the R / S-TT-PT' material was much weaker than that of the (110) crystal plane, and the overall crystallinity was significantly lower than that of the sample in Example 1. Furthermore, the intensity of the chiral signal in the CD spectrum was significantly weakened, further demonstrating that the order of feeding has a key influence on the crystallinity and chiral induction effect of the material. The feeding method of adding R / S-tetrahydrofuran-2-carboxylic acid first and then imidazole can more efficiently promote the imidization reaction and the orderly assembly of the framework, resulting in a product with higher crystallinity and a more significant chiral signal. This optimized feeding order was adopted in subsequent synthesis.

[0039] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A chiral imide-based covalent organic framework material, characterized in that, The chiral imide-based covalent organic framework material is formed by imidization of amine monomers and anhydride monomers, and its structural formula is as follows: ； In this context, "*" represents a repeating unit; " "Selected from" , or .

2. A method for preparing a chiral imide-based covalent organic framework material as described in claim 1, characterized in that, Includes the following steps: Amine monomers and anhydride monomers were mixed, and a chiral inducer and catalyst were added. After ultrasonic treatment, imidazole was added, and the mixture was degassed by a cycle of freezing, vacuuming, and thawing in a liquid nitrogen bath. The imidization reaction was carried out under a protective atmosphere. The reaction product was then subjected to filtration, washing, Soxhlet extraction, and vacuum drying to obtain the chiral imide-based covalent organic framework material.

3. The method for preparing the chiral imide-based covalent organic framework material according to claim 2, characterized in that, The amine monomer is selected from one or more of 1,3,5-tris(4-aminophenyl)triazine, 4,4',4''-(pyrimidin-2,4,6-triyl)triphenylamine or 4,4',4''-(pyridine-2,4,6-triyl)triphenylamine.

4. The method for preparing the chiral imide-based covalent organic framework material according to claim 2, characterized in that, The anhydride monomer is perylenetetracarboxylic dianhydride.

5. The method for preparing the chiral imide-based covalent organic framework material according to claim 2, characterized in that, The molar ratio of the amine monomer to the anhydride monomer is (2.8-3.2):

2.

6. The method for preparing the chiral imide-based covalent organic framework material according to claim 2, characterized in that, The chiral inducer is R / S-tetrahydrofuran-2-carboxylic acid.

7. The method for preparing the chiral imide-based covalent organic framework material according to claim 2, characterized in that, The catalyst is isoquinoline.

8. The method for preparing the chiral imide-based covalent organic framework material according to claim 2, characterized in that, The molar ratio of the amine monomer, chiral inducer, catalyst and imidazole is 1:(100-110):(0.38-0.42):(480-500).

9. The method for preparing the chiral imide-based covalent organic framework material according to claim 2, characterized in that, The temperature of the liquid nitrogen bath is 75K-80K.

10. The method for preparing the chiral imide-based covalent organic framework material according to claim 2, characterized in that, The imidization reaction is carried out at a temperature of 175℃-185℃ for 3-4 days.

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