Metal nitrogen heterocyclic carbene covalent organic framework catalyst and its preparation method and application

Abstract

The invention discloses a metal nitrogen heterocyclic carbene covalent organic framework catalyst and a preparation method and application thereof. The catalyst contains a nitrogen heterocyclic carbene covalent organic framework structure connected by a carbon-carbon double bond and is anchored with a metal species coordinated with the nitrogen heterocyclic carbene active site. The preparation method comprises: subjecting a triimidazolyl organic compound to a quaternization reaction with bromoacetonitrile to prepare a tricyanomethylimidazolium monomer; dissolving the tricyanomethylimidazolium monomer and a trialdehyde monomer in an organic solvent, and constructing an imidazolium covalent organic framework connected by a carbon-carbon double bond through a Knoevenagel condensation reaction; dissolving the imidazolium covalent organic framework in an organic solvent, deprotonating it under alkaline conditions to release the nitrogen heterocyclic carbene active site, and then reacting with a metal active component to prepare the metal nitrogen heterocyclic carbene covalent organic framework catalyst. The catalyst is used for catalyzing the synthesis of symmetric diselenides from elemental selenium and aryl iodine, and has wide applicability and high efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation and organic synthesis, and relates to a metal nitrogen heterocyclic carbene covalent organic framework catalyst and a preparation method and application thereof. Background Art

[0002] Symmetrical diselenides, as important organic synthesis intermediates and functional materials, have broad applications in medicinal chemistry, materials science, and organic synthesis. Traditional synthetic methods primarily rely on homogeneous catalytic systems, such as transition metal complexes like palladium and nickel, to catalyze the reaction of aryl halides with selenium reagents. However, these methods face challenges such as difficult catalyst separation, high precious metal consumption, demanding reaction conditions (such as high temperature, high pressure, or highly polar solvents), and environmental pollution from sulfur-based byproducts (such as hydrogen sulfide). Furthermore, the poor reusability of homogeneous catalysts limits their large-scale application.

[0003] Covalent organic frameworks (COFs) are an emerging class of porous crystalline materials with the characteristics of structural tunability, large specific surface area, and excellent chemical stability, showing broad application prospects in the field of catalysis. By introducing functional structural units (such as nitrogen-containing heterocyclic ligands) into the COFs skeleton, precise anchoring of metal active sites can be achieved, thereby constructing efficient heterogeneous catalysts. As a type of ligand with strong coordination ability, N-Heterocyclic Carbene (NHC) and its metal complexes have shown excellent catalytic performance in coupling reactions, oxidation reactions, etc. However, traditional NHC metal catalysts are mostly homogeneous systems, and the immobilization of NHC ligands often faces challenges such as poor dispersion of active sites and unstable framework structure.

[0004] Currently, strategies for introducing NHC ligands into COFs primarily include post-modification and in situ synthesis. Post-modification methods suffer from low ligand grafting efficiency and uneven metal coordination. While in situ synthesis can achieve covalent bonding between ligands and the framework, retaining the NHC's coordination active sites and achieving highly dispersed metal ion anchoring during framework construction remain key challenges in this field. Furthermore, existing COF-based catalysts generally suffer from low catalytic efficiency, narrow substrate applicability (especially for aryl halides containing different functional groups), and insufficient cyclic stability in catalyzing selenium-mediated organic reactions, making them difficult to meet the demands of green chemistry and industrial production. Summary of the Invention

[0005] The present invention aims to address the technical problems of low catalytic efficiency, narrow substrate applicability, and insufficient catalyst cycle stability in the existing synthesis of symmetrical diselenides. The present invention provides a metal nitrogen heterocyclic carbene covalent organic framework catalyst and its preparation method and application. The technical solution adopted is:

[0006] In a first aspect, the present invention provides a metal nitrogen heterocyclic carbene covalent organic framework catalyst, which contains a nitrogen heterocyclic carbene covalent organic framework structure connected by a carbon-carbon double bond, and the nitrogen heterocyclic carbene covalent organic framework structure is anchored with a metal species coordinated to the nitrogen heterocyclic carbene active site.

[0007] In one embodiment of the present invention, the structure of the metal nitrogen heterocyclic carbene covalent organic framework catalyst is shown in Formula I:

[0008] ;

[0009] Ⅰ

[0010] In the general formula I, A is N or C, X is Cl, Br or I, and M is Au, Ag or Cu.

[0011] In a second aspect, the present invention provides a method for preparing the above-mentioned metal nitrogen heterocyclic carbene covalent organic framework catalyst, comprising the steps of:

[0012] S1: quaternizing a triimidazolyl organic compound with bromoacetonitrile to obtain a tricyanomethylimidazolium monomer;

[0013] S2: dissolving the tricyanomethylimidazolium monomer and the trialdehyde monomer in an organic solvent, and constructing an imidazolium-based covalent organic framework connected by carbon-carbon double bonds through a Knoevenagel condensation reaction;

[0014] S3: dissolving the imidazolium-based covalent organic framework in an organic solvent, deprotonating it under alkaline conditions to release nitrogen heterocyclic carbene active sites, and then reacting with metal active components to obtain a metal nitrogen heterocyclic carbene covalent organic framework catalyst.

[0015] In one embodiment of the present invention, in step S1, the triimidazolyl organic compound and the bromoacetonitrile are dissolved in an organic solvent, stirred and reacted at 60° C. to 180° C. for 12 h to 48 h, and after the reaction is completed, cooled to room temperature, precipitated, filtered, washed, and vacuum dried to obtain a tricyanomethylimidazolium monomer.

[0016] In one embodiment of the present invention, the molar ratio of the triimidazolyl organic compound to the bromoacetonitrile is 1:3~10; the triimidazolyl organic compound includes one or more of 1,3,5-tris(4-imidazolylphenyl)benzene, 2,4,6-tris-(4-imidazolylphenyl)-1,3,5-triazine, 1,3,5-triimidazolylbenzene, tris-(4-imidazolylphenyl)amine and tris-(4-imidazolylphenyl)methane.

[0017] In one embodiment of the present invention, in step S2, the Knoevenagel condensation reaction is carried out in an alkaline environment, the tricyanomethylimidazolium monomer and the trialdehyde monomer are dissolved in an organic solvent, stirred at 60°C~180°C for 12h~72h, and after the reaction is completed, cooled to room temperature, precipitated, filtered, washed, and vacuum dried to obtain an imidazolium-based covalent organic framework connected by a carbon-carbon double bond.

[0018] In one embodiment of the present invention, the molar ratio of the tricyanomethylimidazolium monomer to the trialdehyde monomer is 1:1, and the trialdehyde monomer includes one or more of 1,3,5-tris(4-formylphenyl)benzene, 2,4,6-tris-(4-formylphenyl)-1,3,5-triazine, 1,3,5-trialdehydebenzene, tris-(4-formylphenyl)amine and tris-(4-formylphenyl)methane.

[0019] In one embodiment of the present invention, in step S3, the imidazolium-based covalent organic framework is dissolved in an organic solvent, the pH is adjusted to 8-12, deprotonated, the nitrogen heterocyclic carbene active site is released, and then a metal active component is added, and the reaction is stirred at 25°C-100°C for 12h-24h to obtain a metal nitrogen heterocyclic carbene covalent organic framework catalyst.

[0020] In one embodiment of the present invention, the amount of the metal active component is 1 to 6 times the molar amount of the triimidazolyl organic compound, and the metal active component includes one or more of cuprous chloride, cuprous bromide, cuprous iodide, silver oxide and tetrahydrothiophene gold chloride.

[0021] In the third aspect, the present invention provides an application of the above-mentioned metal nitrogen heterocyclic carbene covalent organic framework catalyst or the metal nitrogen heterocyclic carbene covalent organic framework catalyst prepared by the above-mentioned preparation method, which is used to catalyze the synthesis of symmetric diselenides by elemental selenium and aromatic iodine, wherein the aromatic iodine includes substituted aromatic iodine with electron-withdrawing or electron-donating functional groups at the ortho, meta, and para positions.

[0022] Beneficial effects of the present invention:

[0023] 1. The metal nitrogen heterocyclic carbene covalent organic framework catalyst of the present invention has a covalent organic framework skeleton, which is connected by carbon-carbon double bonds to form a two-dimensional layered structure, has a thermal decomposition temperature of >180°C, and has excellent acid / alkali stability (can tolerate pH 2-11); the active site distribution of the catalyst is: the nitrogen heterocyclic carbene (NHC) is fixed in the framework structure in the form of a covalent bond, and the coordinated metal ion (Cu + 、Ag + 、Au +) are evenly anchored on it, with a metal loading of 5wt%~12wt%, and TEM characterization shows no agglomeration phenomenon; the catalyst has a pore synergistic effect, and the regular pore structure (pore size matches the size of aromatic iodide molecules) promotes substrate diffusion, and the residual charge of the imidazolium group enhances the adsorption and activation of halogenated hydrocarbons; the catalyst solves the separation problem of traditional homogeneous catalysts, and realizes simple centrifugal separation of catalyst and product through heterogeneous catalysis. After five cycles of use, the catalytic activity does not decrease significantly (yield retention rate>90%), and the catalyst has a wide substrate applicability and good compatibility with sensitive functional groups such as ester groups and amide groups, filling the technical gap of low catalytic efficiency of existing COF catalysts for complex substituted aromatic iodine.

[0024] 2. The present invention prepares metal nitrogen heterocyclic carbene covalent organic framework catalysts through a three-step method of quaternization reaction-Kronowingel condensation-coordination anchoring. The quaternization reaction provides reactive sites for subsequent framework construction. The imidazolium-based covalent organic frameworks (ImCOFs) prepared by the Kronowingel condensation reaction have a regular pore structure (pore diameter 3nm~5nm) and a high specific surface area, providing an ordered carrier for metal coordination. The metal active components are anchored by alkaline deprotonation to achieve highly dispersed anchoring of the metal active components, thereby preparing the target catalyst M-NHC-COFs. This preparation method has mild reaction conditions and uses copper, silver, and gold instead of metals such as palladium and platinum, reducing the catalyst cost by more than 60%, making it suitable for large-scale production of hundreds of grams.

[0025] 3. When the metal nitrogen heterocyclic carbene covalent organic framework catalyst of the present invention is used in the synthesis of symmetric diselenides, no additional additives or inert gas protection are required, and it can efficiently catalyze the "one-pot" reaction of elemental selenium and aryl iodide, thereby realizing the green synthesis of symmetric diselenides; the system exhibits excellent catalytic activity for aryl iodide containing ortho-, meta-, and para-position electron-withdrawing groups (such as -NO2, -CN) or electron-donating groups (such as -CH3, -OCH3), the synthesis process is simple, the reaction conditions are mild (80℃~100℃, normal pressure), the yield of the target product reaches 85%~95%, and no odorous gases such as hydrogen sulfide are generated during the reaction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of a method for preparing a metal nitrogen heterocyclic carbene covalent organic framework catalyst provided by an embodiment of the present invention;

[0027] Figure 2 is the tricyanomethylimidazolium monomer 2a in Example 1 of the present invention 1 H NMR (DMSO- d 6, 500 MHz) spectrum;

[0028] Figure 3 is the tricyanomethylimidazolium monomer 2a in Example 1 of the present invention13 C NMR (DMSO- d 6, 125 MHz) spectrum;

[0029] Figure 4 is the structural formula of the imidazolium-based covalent organic framework (ImCOF1-2a) in Example 1 of the present invention;

[0030] Figure 5 is an infrared spectrum of the imidazolium-based covalent organic framework (ImCOF1-2a) and its monomers 1 and 2a in Example 1 of the present invention;

[0031] Figure 6 is an X-ray powder diffraction (XRD) spectrum of the imidazolium-based covalent organic framework (ImCOF1-2a) in Example 1 of the present invention;

[0032] Figure 7 is an X-ray photoelectron energy (XPS) spectrum of the imidazolium-based covalent organic framework (ImCOF1-2a) in Example 1 of the present invention, wherein, Figure 7 (a) is the full XPS spectrum of ImCOF1-2a, Figure 7 (b) is the high-resolution spectrum of C 1s, Figure 7 (c) is the high-resolution spectrum of N 1s, Figure 7 (d) is the high-resolution spectrum of Br 3d;

[0033] Figure 8 is the structural formula of the metal nitrogen heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a) in Example 1 of the present invention;

[0034] Figure 9 is an X-ray powder diffraction (XRD) spectrum of the metal nitrogen heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a) in Example 1 of the present invention;

[0035] Figure 10 is the X-ray photoelectron energy (XPS) spectrum of the metal nitrogen heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a) in Example 1 of the present invention, wherein, Figure 10 (a) is the full XPS spectrum of Cu-NHC-COF1-2a, Figure 10 (b) is the high-resolution spectrum of C1s. Figure 10 (c) is the high-resolution spectrum of N 1s, Figure 10 (d) is the high-resolution spectrum of Cu 2p;

[0036] Figure 11 This is a thermogravimetric analysis (TGA) spectrum of the metal nitrogen heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a) in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] The present invention provides a metal-nitrogen heterocyclic carbene covalent organic framework catalyst (M-NHC-COFs) with high stability and high catalytic activity. The metal-nitrogen heterocyclic carbene covalent organic framework catalyst contains a nitrogen heterocyclic carbene covalent organic framework structure connected by a carbon-carbon double bond, and the nitrogen heterocyclic carbene covalent organic framework structure is anchored with a metal species coordinated to the nitrogen heterocyclic carbene active site.

[0039] The metal nitrogen heterocyclic carbene covalent organic framework catalyst provided by the present invention, when applied to the synthesis of symmetric diselenides, can solve the technical problems existing in the existing symmetric diselenide synthesis, such as low catalytic efficiency, narrow substrate applicability and insufficient catalyst cyclic stability.

[0040] Specifically, the structure of the metal nitrogen heterocyclic carbene covalent organic framework catalyst is shown in Formula I:

[0041] ;

[0042] Ⅰ

[0043] In the general formula I, A is a N element or a C element, X is a Cl element, a Br element or an I element, and M is an Au element, an Ag element or a Cu element.

[0044] The M-NHC-COFs catalyst has the following core structural features:

[0045] It has a covalent organic framework skeleton: a two-dimensional layered structure is formed by carbon-carbon double bonds, the thermal decomposition temperature is >180°C, and it has excellent acid / alkali stability (can tolerate pH 2~11).

[0046] The active site distribution of the catalyst is as follows: nitrogen heterocyclic carbene (NHC) is fixed in the framework structure in the form of covalent bonds, and the coordinated metal ions (Cu + 、Ag + 、Au + ) are evenly anchored thereon, with a metal loading of 5wt%~12wt%, and TEM characterization shows no agglomeration.

[0047] This catalyst has a pore synergistic effect. The regular pore structure (pore size matches the size of aromatic iodide molecules) promotes substrate diffusion, and the residual charge of the imidazolium group enhances the adsorption and activation of halogenated hydrocarbons. This catalyst solves the separation problem of traditional homogeneous catalysts and realizes simple centrifugal separation of catalyst and product through heterogeneous catalysis. After five cycles of use, there is no significant decrease in catalytic activity (yield retention rate >90%). In addition, this catalyst has a wide substrate applicability and good compatibility with sensitive functional groups such as ester groups and amide groups, filling the technical gap of low catalytic efficiency of existing COF catalysts for complex substituted aromatic iodides.

[0048] The present invention also provides a method for preparing the above-mentioned metal nitrogen heterocyclic carbene covalent organic framework catalyst. Figure 1 The preparation method of the metal nitrogen heterocyclic carbene covalent organic framework catalyst comprises the following steps:

[0049] S1: quaternizing a triimidazolyl organic compound with bromoacetonitrile to obtain a tricyanomethylimidazolium monomer;

[0050] S2: Dissolve tricyanomethylimidazolium monomer and trialdehyde monomer in an organic solvent, and construct an imidazolium-based covalent organic framework connected by carbon-carbon double bonds through Knoevenagel condensation reaction;

[0051] S3: The imidazolium-based covalent organic framework is dissolved in an organic solvent, deprotonated under alkaline conditions to release the nitrogen heterocyclic carbene active site, and then reacted with the metal active component to obtain a metal nitrogen heterocyclic carbene covalent organic framework catalyst.

[0052] The present invention introduces imidazolium-based structural units into the COFs skeleton, releases highly active NHC sites through alkaline deprotonation, achieves uniform anchoring of monovalent metal active species, and constructs a heterogeneous catalytic system with both structural stability and catalytic activity.

[0053] Step S1: Construct an active monomer through a quaternization reaction. A triimidazolyl organic compound and bromoacetonitrile are dissolved in an organic solvent and reacted with stirring at 60°C to 180°C for 12 to 48 hours. After completion of the reaction, the mixture is cooled to room temperature, precipitated, filtered, washed, and vacuum-dried to obtain a tricyanomethylimidazolium monomer as a light brown solid powder. The organic solvent can be selected from N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, dioxane, etc. Ethyl acetate, diethyl ether, n-hexane, petroleum ether, etc. can be added for precipitation.

[0054] The triimidazolyl organic compound includes one or more of 1,3,5-tris(4-imidazolylphenyl)benzene, 2,4,6-tris-(4-imidazolylphenyl)-1,3,5-triazine, 1,3,5-triimidazolylbenzene, tris-(4-imidazolylphenyl)amine and tris-(4-imidazolylphenyl)methane.

[0055] The molar ratio of the triimidazolyl organic compound to bromoacetonitrile is 1:3~10. Excess bromoacetonitrile ensures complete quaternization of the N site of the imidazole ring, providing a reactive site for subsequent framework construction.

[0056] Step S2 constructs a covalent organic framework via Knoevenagel condensation. The Knoevenagel condensation reaction is conducted in an alkaline environment. A tricyanomethylimidazolium monomer and a trialdehyde monomer are dissolved in an organic solvent and reacted with stirring at 60°C to 180°C for 12 to 72 hours. After completion of the reaction, the mixture is cooled to room temperature, precipitated, filtered, washed, and vacuum-dried to obtain a carbon-carbon double-bonded imidazolium covalent organic framework as a brown powder.

[0057] Among them, the molar ratio of the tricyanomethylimidazolium monomer to the trialdehyde monomer is 1:1, and the trialdehyde monomer of this embodiment includes one or more of 1,3,5-tris(4-formylphenyl)benzene, 2,4,6-tris-(4-formylphenyl)-1,3,5-triazine, 1,3,5-trialdehydebenzene, tris-(4-formylphenyl)amine and tris-(4-formylphenyl)methane.

[0058] In step S2, the base is preferably at least one of potassium carbonate, sodium carbonate, sodium hydroxide, potassium hydroxide and potassium tert-butoxide, and the amount of the base is 1 to 6 times the molar amount of the triimidazolyl organic compound. The pH is adjusted to 8 to 12. The higher the pH, the faster the reaction.

[0059] The organic solvent in step S2 can be one or more of n-butanol, 1,2-dichlorobenzene, 1,3,5-trimethylbenzene, methanol and dimethyl sulfoxide.

[0060] In step S2, an imidazolium-based covalent organic framework (ImCOFs) connected by a carbon-carbon double bond is formed through a condensation reaction between an aldehyde group and a cyano group. The framework has a regular pore structure (pore diameter 3nm~5nm) and a high specific surface area, providing an ordered carrier for metal coordination.

[0061] Step S3 is to anchor the copper active component by alkaline deprotonation. The metal active component includes one or more of cuprous chloride, cuprous bromide, cuprous iodide, silver oxide, and tetrahydrothiophene gold chloride, and the amount of the metal active component is 1 to 6 times the molar amount of the triimidazolyl organic compound.

[0062] The organic solvent in step S3 can be one or more of acetone, acetonitrile, and tetrahydrofuran. The pH is adjusted to 8-12 by adding an alkaline substance such as potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, potassium tert-butoxide, or sodium ethoxide. The reaction is stirred at 25°C-100°C for 12-24 hours to achieve highly dispersed anchoring of the metal active components, thereby obtaining a crude product. The target catalyst M-NHC-COFs is then obtained by further centrifugation, washing, and drying.

[0063] The present invention adopts a three-step method of "quaternization reaction-Knoevenagel condensation-coordination anchoring", avoiding the low ligand grafting rate problem of the post-modification method. By generating NHC sites in situ, strong coordination anchoring of metal ions is achieved, and the metal dispersion is improved by more than three times compared with traditional methods. In addition, the preparation method of the M-NHC-COFs catalyst has mild reaction conditions. In addition, the present invention replaces palladium, platinum and other precious metals with relatively inexpensive copper, silver and gold, reducing the catalyst cost by more than 60%, making it suitable for large-scale production of 100 grams (single batch output ≥100g, purity >95%).

[0064] The present invention also provides the use of a metal nitrogen heterocyclic carbene covalent organic framework catalyst in catalyzing the synthesis of symmetrical diselenides with elemental selenium and aryl iodides, wherein the aryl iodides include substituted aryl iodides with electron-withdrawing or electron-donating functional groups at the ortho, meta, or para positions.

[0065] When the M-NHC-COFs catalyst is used in the synthesis of symmetric diselenides, the specific reaction conditions are:

[0066] Using elemental selenium (Se) and aryl iodide as substrates, the M-NHC-COFs catalyst dosage is 1-5% of the total molar amount of the substrates, and the reaction is carried out in N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile or 1,4-dioxane at 80°C-120°C for 2h-24h without the need for additional additives or inert gas protection.

[0067] This system exhibits excellent catalytic activity for aromatic iodides containing ortho-, meta-, and para-position electron-withdrawing groups (such as -NO2 and -CN) or electron-donating groups (such as -CH3 and -OCH3). The yield of the target product reaches 85% to 95%. No odorous gases such as hydrogen sulfide are generated during the reaction process, and the system can be recycled. This solves the problems of high pollution, high cost, and difficulty in scalability in traditional methods, and provides a new technical path for the green synthesis of symmetrical diselenides.

[0068] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0069] Example 1

[0070] Preparation of catalyst Cu-NHC-COF1-2a:

[0071] S1. Synthesis of tricyanomethylimidazolium monomer 2a via quaternization. 1,3,5-Tris(4-imidazolylphenyl)benzene (1.0 mmol, 0.505 g) and bromoacetonitrile (6.0 mmol, 0.720 g) were added to a 100-mL round-bottom flask, dissolved in 20 mL of DMF, and stirred in an oil bath at 120°C for 48 h. After the reaction, the mixture was cooled to room temperature and 100 mL of ethyl acetate was added to completely precipitate. The precipitate was filtered, washed with ethyl acetate, and dried in vacuo (60°C, 12 h) to obtain a light brown solid powder (0.837 g, 97% yield).

[0072] The product tricyanomethylimidazolium monomer 2a was characterized by nuclear magnetic resonance 1 H NMR (DMSO- d 6,500 MHz) and 13 CNMR (DMSO-d6, 125 MHz) was used for characterization. 1 H NMR (DMSO d 6, 500 MHz) spectrum reference Figure 2 . 1 H NMR (500 MHz, DMSO- d 6): δ = 10.11 (s, 3H), 8.52 (s, 3H), 8.31 (d, J = 8.6 Hz, 6H), 8.24 (s, 3H), 8.20 (s, 3H), 7.97 (d, J = 8.6 Hz, 6H), 5.74 (s, 6H).

[0073] Figure 2In the case of tricyanomethylimidazolium monomer 2a, the hydrogen signal (N-CH-N) on C2 appears as a singlet at 10.11 ppm. This is due to the strong electron-withdrawing effect of the quaternary ammonium unit formed by the nitrogen atom of the imidazolium salt. The N-CH-N group is in a strongly deshielded region, and the chemical shift appears relatively highfield, confirming that the synthesized product is an imidazolium salt. The two hydrogen groups on the outer benzene ring appear as doublets at 7.97 ppm and 8.31 ppm, respectively, with an integrated area ratio of 1:1 and a coupling constant of 8.6 Hz. The hydrogen signal on the methylene group (-CH2-) directly connecting the imidazole ring to the benzene ring appears as a singlet at 5.74 ppm. This is due to the enhanced acidity of the methylene group (-CH2-) in the imidazolium ring due to the electron-withdrawing effect. The integrated area ratio of hydrogen on the organic monomer is 1:1:2:1:1:2:2, which is completely consistent with the structure of tricyanomethylimidazolium monomer 2a.

[0074] Nuclear magnetic resonance imaging 13 C NMR (DMSO- d 6, 125 MHz) spectrum reference Figure 3 .

[0075] Figure 3 middle, δ The peaks at 141.2, 140.1, 137.0, 134.2, 129.0, 125.5, 123.4, 122.5, 122.0, and 114.5 ppm are attributed to the carbon atoms on the aromatic ring of tricyanomethylimidazolium monomer 2a, respectively. The peak at 37.2 ppm is the characteristic carbon atom of the cyanomethyl group in tricyanomethylimidazolium monomer 2a, which is located relatively downfield due to the strong electron-withdrawing effect of the cyano group. This further confirms the correctness of the structure and composition of tricyanomethylimidazolium monomer 2a. Furthermore, the purity of tricyanomethylimidazolium monomer 2a is >99.5%, as confirmed by NMR spectroscopy.

[0076] S2. Construct an imidazolium-based covalent organic framework (ImCOF1-2a) by Knoevenagel condensation. The structural formula of ImCOF1-2a is shown in Figure 2. Figure 4 .

[0077] Tricyanomethylimidazolium monomer 2a (0.3 mmol, 259 mg) obtained in S1 and 1,3,5-(4-formyl)benzene (0.3 mmol, 0.117 g) were dissolved in a mixture of n-butanol (15 mL) and 1,2-dichlorobenzene (5 mL). Potassium hydroxide (0.9 mmol, 0.051 g) was added, and the mixture was refluxed at 120°C for 48 h. After cooling, the precipitate was filtered, washed with ethanol, and dried in vacuo (80°C, 24 h) to obtain 0.336 g of a brown powder (80.3% yield).

[0078] The product and its monomer were characterized by infrared spectroscopy. Figure 5 .

[0079] Figure 5 After the Knoevenagel condensation reaction, the trialdehyde monomer -1 The typical C=O stretching vibration peak at 2981 cm-1 and the tricyanomethylimidazolium monomer 2a at 2981 cm-1 -1 The stretching vibration peak of -CH2- at 1601cm disappears, which proves that the reaction is complete. -1 The appearance of C=C groups at 3434 cm of ImCOF1-2a proves the formation of vinyl groups. -1 The peak of H2O appears at , which is consistent with the characteristic of imidazolium group absorbing water easily.

[0080] X-ray powder diffraction (XRD) spectrum of imidazolium-based covalent organic framework (ImCOF1-2a) Figure 6 .

[0081] Figure 6 Medium, 2 θ There are strong diffraction peak signals at = 10.5°, 21°, 21.9°, 23.5°, 24.6°, 27.2°, 38.8°, 45.7°, 47.9°, 55.8°, 61.4°, 63.1°, 69.9°, 74.8°, 82.8°, 87.5°, and 89.1°, indicating that the ImCOF1-2a molecules are arranged regularly and are a crystalline compound.

[0082] Reference Figure 7 The correctness of the composition and structure of ImCOF1-2a was further verified by X-ray photoelectron spectroscopy (XPS).

[0083] Through the XPS full spectrum of ImCOF1-2a ( Figure 7Characteristic peaks such as C 1s, O 1s, N 1s, and Br 3d are seen in (a), indicating that the sample contains carbon (C), oxygen (O), nitrogen (N), and bromine (Br) elements (the oxygen element comes from the water molecules adsorbed by ImCOF1-2a). The appearance of these peaks provides basic information for determining the elemental composition of the sample.

[0084] By peak fitting, the high-resolution spectrum of C 1s ( Figure 7 (b) Carbon peaks under different chemical environments can be seen: the peak with a binding energy of 284.8 eV is attributed to C-C and C-H bonds, which are characteristic binding energy positions of carbon-carbon and carbon-hydrogen bonds commonly found in organic compounds. The peak with a binding energy of 286.1 eV corresponds to the C-N bond, indicating the presence of carbon-nitrogen chemical bonds in the sample. The peak with a binding energy of 289.1 eV is attributed to the C=N + bond, indicating the presence of positively charged carbon-nitrogen double bond structure in the sample.

[0085] The high-resolution spectrum of N 1s ( Figure 7 (c) After peak fitting, two main peaks are seen: the peak with a binding energy of 399.4 eV corresponds to the CN bond, indicating that the nitrogen atom and the carbon atom are connected in the form of a single bond; the peak with a binding energy of 401.7 eV corresponds to the C=N + bond, indicating the presence of a positively charged carbon-nitrogen double bond structure, which is consistent with the C = N + The results of the keys confirm each other.

[0086] From the high-resolution spectrum of Br 3d ( Figure 7 Two characteristic peaks are observed in (d): the Br 3d5 / 2 peak with a binding energy of 68.3 eV and the Br 3d3 / 2 peak with a binding energy of 70.0 eV. These two peaks are typical features of bromine in an XPS spectrum and are used to confirm the presence of bromide anions in the sample and their chemical environment.

[0087] S3. Anchoring Cu by alkaline deprotonation + ImCOF1-2a (0.5 mmol, 0.209 g) was dispersed in 25 mL of acetone, and potassium carbonate (1.0 mmol, 0.138 g) was added. The mixture was stirred at 60°C for 2 h to deprotonate the imidazolium group. Copper iodide (0.75 mmol, 0.123 g) was added, and stirring was continued for 22 h. The solid was isolated by centrifugation, washed with deionized water and ethanol, and dried in vacuo (60°C for 12 h) to obtain 0.234 g (91.4% yield) of the metal nitrogen heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a).

[0088] Cu-NHC-COF1-2a structural formula reference Figure 8 .

[0089] The X-ray powder diffraction spectrum (XRD) of the metal nitrogen heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a) prepared in this example is as follows: Figure 9 . Figure 9 Middle 2 θ = 36.8°, 42.5°, 61.6° and 73.7° correspond to the diffraction peaks of the monovalent copper active component 111, 200, 220 and 311 crystal planes, respectively. θ The signals at = 25.8°, 29.8°, and 50.2° are the diffraction spectra of the nitrogen heterocyclic carbene covalent organic framework, indicating that the monovalent copper active component is successfully loaded on the nitrogen heterocyclic carbene covalent organic framework.

[0090] The correctness of the composition and structure of Cu-NHC-COF1-2a was further verified by X-ray photoelectron spectroscopy (XPS). Figure 10 .

[0091] The XPS spectrum of Cu-NHC-COF1-2a ( Figure 10 Characteristic peaks such as Cu 2p, C 1s, N 1s and I 3d can be seen in (a), indicating that the sample contains copper (Cu), carbon (C), nitrogen (N) and iodine (I) elements, indicating that the copper active component is successfully loaded in the catalyst structure.

[0092] By peak fitting, the high-resolution spectrum of C 1s ( Figure 10 (b) Carbon peaks under different chemical environments can be seen: the peak with a binding energy of 284.8 eV is attributed to the C-C and C-H bonds, which are the characteristic binding energy positions of common carbon-carbon and carbon-hydrogen bonds; the peak with a binding energy of 286.2 eV corresponds to the C=N bond in the nitrogen heterocyclic carbene; the peak with a binding energy of 289.0 eV is attributed to the C-Cu bond formed by the coordination of the nitrogen heterocyclic carbene and the monovalent copper ion.

[0093] The high-resolution spectrum of N 1s ( Figure 10 (c) After peak fitting, there is only one peak. The original peak with a binding energy of 401.7 eV corresponds to C=N + The bond signal peak completely disappeared, and was replaced by a new peak with a binding energy of 400.1 eV, corresponding to the CN bond in the copper nitrogen heterocyclic carbene. This indicates that the monovalent copper ion is successfully coordinated with the nitrogen heterocyclic carbene unit in the covalent organic framework through the C-Cu bond and is immobilized in the framework.

[0094] From the Cu 2p high-resolution spectrum ( Figure 10 Two characteristic peaks are observed in (d): the Cu 2p1 / 2 peak with a binding energy of 953.6 eV and the Cu 2p3 / 2 peak with a binding energy of 933.5 eV. These two peaks are typical of monovalent copper in the XPS spectrum, indicating that the copper atoms retain their +1 valence state after being immobilized.

[0095] Thermogravimetric analysis of Cu-NHC-COF1-2a was performed, and the thermogravimetric analysis spectrum (TGA) was referenced Figure 11 , Figure 11 It shows that this type of catalyst has good stability within 180℃.

[0096] The metal nitrogen heterocyclic carbene covalent organic framework catalyst prepared in Example 1 was used to test the reactivity of aryl iodides with different substituents under the same reaction conditions (90°C, 12 h, 2% catalyst dosage), i.e., substrate universality testing. The results are shown in Table 1. The data in Table 1 show that the catalyst of the present invention exhibits good catalytic activity for substituents at different positions and with different electronic effects, as well as for heterocyclic substrates, and its substrate applicability is significantly superior to that of existing COF-based catalysts (literature reports that similar catalysts have a yield of only 75% for substrates substituted with meta-cyano groups).

[0097] Table 1

[0098]

[0099] Example 2

[0100] Preparation of catalyst Ag-NHC-COF1-2a:

[0101] ImCOF1-2a (0.5 mmol, 0.209 g) prepared by the method of Example 1 was dispersed in 25 mL of dichloromethane, and silver oxide (0.75 mmol, 0.174 g) was added. Silver oxide is a basic oxide that acts as both a base and a metal active component in the reaction. The mixture was stirred at 25°C for 24 h. The solid was separated by centrifugation, washed with ethanol and then with dichloromethane, and dried in vacuo to obtain 0.236 g of Ag-NHC-COF1-2a catalyst (yield 93%).

[0102] Example 3

[0103] Preparation of catalyst Au-NHC-COF1-2a:

[0104] Ag-NHC-COF1-2a (0.3 mmol, 0.152 g) was dispersed in 25 mL of acetonitrile, and tetrahydrothiophene gold chloride (0.3 mmol, 0.096 g) was added. The mixture was stirred at 25°C for 24 h. The solid was isolated by centrifugation, washed with acetonitrile, and dried under vacuum to obtain 0.171 g of Au-NHC-COF1-2a catalyst (95.5% yield). This process allows the direct preparation of Au-NHC-COF1-2a from Ag-NHC-COF1-2a via a metal exchange reaction, omitting the use of a base.

[0105] Example 4

[0106] Application of Metal-Nitrogen Heterocyclic Carbene Covalent Organic Framework Catalyst in the Synthesis of 3,3'-Dimethyldiphenyl Diselenide:

[0107] Elemental selenium (0.200 mmol, 0.016 g), 3-iodotoluene (0.100 mmol, 0.022 g), and the catalyst Cu-NHC-COF1-2a (0.002 g) prepared in Example 1 were added to a 50 mL reaction flask. 2 mL of DMF was injected and the reaction was stirred at 120°C for 2 h. After cooling, the reaction solution was centrifuged to separate the catalyst. The filtrate was purified by silica gel column chromatography (eluent: petroleum ether) to obtain 3,3'-dimethyldiphenyl diselenide as a yellow oily liquid (yield: 93%). f = 0.88 (PE=30:1); NMR results of 3,3'-dimethyldiphenyl diselenide: 1 H NMR (400 MHz, CDCl3) δ 7.45-7.37(m, 4H), 7.15(t, J=7.6Hz, 2H), 7.08-7.02(m, 2H), 2.31(d, J=2.4Jz, 6H); 13 C NMR (101 MHz, CDCl3) δ 139.0, 132.2, 129.0, 128.9, 128.7, 128.6, 21.3, 21.2; ESI + :calculated for C14H14Se2 (M):341.9426; Found: 341.9421.

[0108] The catalyst after the reaction in Example 4 was washed with methanol, vacuum-dried, and then reused. The results showed that the first yield was 93%, the third yield was 91%, and the fifth yield was 90%, demonstrating that the catalyst of the present invention has excellent cyclic stability.

[0109] Example 5

[0110] Effect of tricyanomethylimidazolium monomer type on the performance of metal nitrogen heterocyclic carbene covalent organic framework catalysts:

[0111] The selectivity and conversion of catalysts constructed with different tricyanomethylimidazolium monomers in the catalytic synthesis of 3,3'-dimethyldiphenyl diselenide are shown in Table 2.

[0112] By replacing 1,3,5-(4-imidazolylphenyl)benzene in step S1 of Example 1 with 2,4,6-tris-(4-imidazolylphenyl)-1,3,5-triazine, 1,3,5-triimidazolylbenzene, tris-(4-imidazolylphenyl)amine, and tris-(4-imidazolylphenyl)methane, while keeping all other conditions unchanged, catalysts Cu-NHC-COF1-2b, Cu-NHC-COF1-2c, Cu-NHC-COF1-2d, and Cu-NHC-COF1-2e were prepared, respectively. When these catalysts were used in the selenization reaction of 3-iodotoluene (0.1 mmol), the selectivity and yield of the target product varied to some extent, indicating that the choice of organic monomer has a significant impact on the regulation of catalyst performance. Among them, Cu-NHC-COF1-2b exhibited the best conversion and selectivity in the catalytic synthesis of 3,3'-dimethyldiphenyl diselenide.

[0113] Table 2

[0114]

[0115] Example 6

[0116] Effect of trialdehyde monomer type on the performance of metal nitrogen heterocyclic carbene covalent organic framework catalysts:

[0117] The selectivity and conversion rate of catalysts constructed with different trialdehyde monomers in the catalytic synthesis of 3,3'-dimethyldiphenyl diselenide are shown in Table 3.

[0118] The 1,3,5-tris(4-formylphenyl)benzene in step S1 of Example 1 was replaced with 2,4,6-tris-(4-formylphenyl)-1,3,5-triazine, 1,3,5-trialdehydebenzene, tris-(4-formylphenyl)amine and tris-(4-formylphenyl)methane, and the other conditions remained unchanged to prepare catalysts Cu-NHC-COF2-2a, Cu-NHC-COF3-2a, Cu-NHC-COF4-2a, and Cu-NHC-COF5-2a, respectively.

[0119] When these catalysts were used for the selenization reaction of 3-iodotoluene (0.1 mmol), there were certain differences in the selectivity and yield of the target product, indicating that the choice of trialdehyde monomer has an important influence on the regulation of catalyst performance.

[0120] Among them, Cu-NHC-COF3-2a has the best conversion rate and selectivity in the catalytic synthesis of 3,3'-dimethyldiphenyl diselenide.

[0121] Table 3

[0122]

[0123] Example 7

[0124] Effect of halogen type on catalytic performance:

[0125] The selectivity and conversion of catalysts with different halogen types in the catalytic synthesis of 3,3'-dimethyldiphenyl diselenide are shown in Table 4.

[0126] Table 4

[0127]

[0128] By replacing the cuprous iodide in step S3 of Example 1 with cuprous chloride and cuprous bromide, while maintaining all other conditions, catalysts CuCl-NHC-COF1-2a and CuBr-NHC-COF1-2 were prepared, respectively. The catalysts showed significant differences in yield and selectivity in the synthesis of 3,3'-dimethyldiphenyl diselenide from 3-iodotoluene (0.1 mmol) (Table 3). Taking all factors into consideration, cuprous iodide is a preferred catalyst for the synthesis of copper-nitrogen heterocyclic carbene covalent organic frameworks.

[0129] Example 8

[0130] Effect of metal types on catalytic performance:

[0131] The selectivity and conversion of catalysts with different metal types in the catalytic synthesis of 3,3'-dimethyldiphenyl diselenide are shown in Table 5.

[0132] The Cu-NHC-COF1-2a in Example 4 was replaced with Ag-NHC-COF1-2a and Au-NHC-COF1-2a, with all other conditions remaining unchanged. Au-NHC-COF1-2a exhibited the best yield and selectivity in the synthesis of 3,3'-dimethyldiphenyl diselenide from 3-iodotoluene (0.1 mmol) (Table 4). However, Au-NHC-COF1-2a is relatively expensive, making Cu-NHC-COF1-2a a preferred catalyst for the synthesis of symmetric diselenides from elemental selenium and aryl iodides.

[0133] Table 5

[0134]

[0135] Comparative Example

[0136] Compared with the catalyst without NHC site introduction:

[0137] By omitting the alkaline deprotonation step in step S3 of Example 1, ImCOF1-2a was directly mixed and stirred with cuprous iodide to produce the comparative catalyst Cu@ImCOF1-2a. This catalyst, when used in the reaction of p-iodonitrobenzene (0.1 mmol), yielded only 65%, and after two cycles, the yield dropped to 42%. Clearly, the catalyst without NHC sites was inferior to the Cu-NHC-COF1-2a catalyst of Example 1.

[0138] Hundred gram level preparation example:

[0139] The process of Example 1 was scaled up 100-fold, and the quaternization reaction was carried out in a 5-L reactor to prepare 84.5 g of tricyanomethylimidazolium monomer (yield 97.8%) in a single batch. A continuous reaction apparatus was used in the Knoevenagel condensation stage to prepare 109.6 g of ImCOF1-2a in a single batch. By coordinating and anchoring the copper active component, 123 g of Cu-NHC-COF1 catalyst was finally prepared, demonstrating that the process of the present invention is suitable for large-scale production.

[0140] The above examples verify the feasibility of the various technical features in the claims through specific parameter combinations, including molar ratio, reaction temperature, solvent selection and catalyst application conditions; the comparative examples highlight the key role of NHC active sites in copper ion anchoring and catalytic performance; substrate universality data and cycle performance tests directly support the technical effects of high stability and wide applicability among the advantages of the invention; the 100-gram preparation example proves the feasibility of process scale-up and meets the needs of industrial production.

[0141] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A metal nitrogen heterocyclic carbene covalent organic framework catalyst, characterized in that The metal nitrogen heterocyclic carbene covalent organic framework catalyst contains a nitrogen heterocyclic carbene covalent organic framework structure connected by a carbon-carbon double bond, and the nitrogen heterocyclic carbene covalent organic framework structure is anchored with a metal species coordinated with the nitrogen heterocyclic carbene active site; the structure of the metal nitrogen heterocyclic carbene covalent organic framework catalyst is shown in general formula I: Ⅰ In the general formula I, A is N or C, X is Cl, Br or I, and M is Au, Ag or Cu.

2. A method for preparing the metal nitrogen heterocyclic carbene covalent organic framework catalyst according to claim 1, characterized in that: Including steps: S1: quaternizing a triimidazolyl organic compound with bromoacetonitrile to obtain a tricyanomethylimidazolium monomer; in step S1, the triimidazolyl organic compound and the bromoacetonitrile are dissolved in an organic solvent, stirred at 60° C. to 180° C. for 12 h to 48 h, and cooled to room temperature after the reaction is completed. The mixture is precipitated, filtered, washed, and vacuum-dried to obtain the tricyanomethylimidazolium monomer; S2: dissolving the tricyanomethylimidazolium monomer and the trialdehyde monomer in an organic solvent, and constructing an imidazolium covalent organic framework connected by a carbon-carbon double bond through a Knoevenagel condensation reaction; in the step S2, the Knoevenagel condensation reaction is carried out in an alkaline environment, dissolving the tricyanomethylimidazolium monomer and the trialdehyde monomer in an organic solvent, stirring and reacting at 60° C. to 180° C. for 12 h to 72 h, cooling to room temperature after the reaction is completed, precipitating, filtering, washing, and vacuum drying to obtain an imidazolium covalent organic framework connected by a carbon-carbon double bond; S3: dissolving the imidazolium-based covalent organic framework in an organic solvent, deprotonating it under alkaline conditions to release nitrogen heterocyclic carbene active sites, and then reacting with metal active components to obtain a metal nitrogen heterocyclic carbene covalent organic framework catalyst.

3. The method for preparing the metal nitrogen heterocyclic carbene covalent organic framework catalyst according to claim 2, characterized in that The molar ratio of the triimidazolyl organic compound to the bromoacetonitrile is 1: 3 to 10; the triimidazolyl organic compound includes one or more of 1,3,5-tris(4-imidazolylphenyl)benzene, 2,4,6-tris-(4-imidazolylphenyl)-1,3,5-triazine, 1,3,5-triimidazolylbenzene, tris-(4-imidazolylphenyl)amine and tris-(4-imidazolylphenyl)methane.

4. The method for preparing the metal nitrogen heterocyclic carbene covalent organic framework catalyst according to claim 3, characterized in that The molar ratio of the tricyanomethylimidazolium monomer to the trialdehyde monomer is 1:1, and the trialdehyde monomer includes one or more of 1,3,5-tris(4-formylphenyl)benzene, 2,4,6-tris-(4-formylphenyl)-1,3,5-triazine, 1,3,5-trialdehydebenzene, tris-(4-formylphenyl)amine and tris-(4-formylphenyl)methane.

5. The method for preparing the metal nitrogen heterocyclic carbene covalent organic framework catalyst according to claim 2, wherein In step S3, the imidazolium-based covalent organic framework is dissolved in an organic solvent, the pH is adjusted to 8-12, deprotonated to release the nitrogen heterocyclic carbene active site, and then a metal active component is added. The reaction is stirred at 25° C.-100° C. for 12 h-24 h to obtain a metal nitrogen heterocyclic carbene covalent organic framework catalyst.

6. The method for preparing the metal nitrogen heterocyclic carbene covalent organic framework catalyst according to claim 5, characterized in that: The amount of the metal active component is 1 to 6 times the molar amount of the triimidazolyl organic compound, and the metal active component includes one or more of cuprous chloride, cuprous bromide, cuprous iodide, silver oxide and tetrahydrothiophene gold chloride.

7. Use of any one of the metal nitrogen heterocyclic carbene covalent organic framework catalysts according to claim 1 or the metal nitrogen heterocyclic carbene covalent organic framework catalysts prepared by any one of the preparation methods of claims 2 to 6, characterized in that: It is used to catalyze the synthesis of symmetrical diselenides by reacting elemental selenium with aryl iodide, wherein the aryl iodide includes substituted aryl iodide with electron-withdrawing or electron-donating functional groups at the ortho, meta, or para positions.

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