Metal N-heterocyclic carbene covalent organic framework catalyst as well as preparation method and application thereof

Abstract

The invention discloses a metal N-heterocyclic carbene covalent organic framework catalyst and a preparation method and application thereof, the catalyst contains an N-heterocyclic carbene covalent organic framework structure connected through carbon-carbon double bonds, and metal species coordinated with N-heterocyclic carbene active sites are anchored; the preparation method comprises the following steps: carrying out quaternization reaction on a triimidazolyl organic compound and bromoacetonitrile to prepare a tricyanomethylimidazolium monomer; the preparation method comprises the following steps: dissolving a tricyanomethylimidazolium monomer and a trialdehyde monomer in an organic solvent, and constructing a carbon-carbon double bond connected midazolium covalent organic framework through a Knoevenagel condensation reaction; the preparation method comprises the following steps: dissolving an imidazolium covalent organic framework in an organic solvent, deprotonating under an alkaline condition to release N-heterocyclic carbene active sites, and reacting with a metal active component to prepare the metal N-heterocyclic carbene covalent organic framework catalyst. The catalyst is used for catalyzing elemental selenium and aryl iodide to synthesize symmetric diselenide, and is wide in applicability and efficient.

Description

Technical Field

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

[0002] Symmetric diselenides, as important organic synthesis intermediates and functional materials, have extensive applications in the fields of medicinal chemistry, materials science, and organic synthesis. Traditional synthesis methods mainly rely on homogeneous catalytic systems, such as the reaction of aryl halides with selenium reagents catalyzed by transition metal complexes such as palladium and nickel. However, there are problems such as difficult catalyst separation, large consumption of precious metals, harsh reaction conditions (such as high temperature, high pressure, or strongly polar solvents), and environmental pollution by chalcogenide by-products (such as hydrogen sulfide). In addition, the reusable performance of homogeneous catalysts is not good, which limits their large-scale application.

[0003] Covalent Organic Frameworks (COFs) are a class of emerging porous crystalline materials, which have characteristics such as adjustable structure, large specific surface area, and excellent chemical stability, and show broad application prospects in the field of catalysis. By introducing functional structural units (such as nitrogen-containing heterocyclic ligands) into the COF framework, precise anchoring of metal active sites can be achieved, thereby constructing highly efficient heterogeneous catalysts. As a class of ligands with strong coordination ability, N-Heterocyclic Carbene (NHC) metal complexes show 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] At present, the strategies for introducing NHC ligands into COF materials mainly include post-modification methods and in-situ synthesis methods. The post-modification method has problems such as low ligand grafting rate and uneven metal coordination; although the in-situ synthesis method can achieve covalent bonding of the ligand and the framework, how to retain the coordination active sites of NHC and achieve high-dispersion anchoring of metal ions during the framework construction process is still a research difficulty in this field. In addition, existing COF-based catalysts generally have problems such as low catalytic efficiency, narrow substrate applicability (especially for aryl halides containing different functional groups), and insufficient catalyst cycle stability in the organic reactions involving selenium, and it is difficult to meet the requirements of green chemistry and industrial production. Summary of the Invention

[0005] The present invention aims to solve the technical problems existing in the synthesis of existing symmetric diselenides, such as low catalytic efficiency, narrow substrate applicability, and insufficient catalyst cycle stability. The present invention provides a metal N-heterocyclic carbene covalent organic framework catalyst, a preparation method thereof, and an application thereof. The technical solution adopted is: In a first aspect, the present invention provides a metal N-heterocyclic carbene covalent organic framework catalyst, wherein the metal N-heterocyclic carbene covalent organic framework catalyst contains an N-heterocyclic carbene covalent organic framework structure connected by a carbon-carbon double bond, and the N-heterocyclic carbene covalent organic framework structure is anchored with a metal species coordinated with the N-heterocyclic carbene active site.

[0006] In one embodiment of the present invention, the structure of the metal N-heterocyclic carbene covalent organic framework catalyst is shown in General Formula I: ; Ⅰ In the General Formula I, A is an 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.

[0007] In a second aspect, the present invention provides a preparation method of the above-mentioned metal N-heterocyclic carbene covalent organic framework catalyst, including the steps of: S1: Performing a quaternization reaction on a triimidazolyl organic compound and bromoacetonitrile to obtain a tricyanomethylimidazolium monomer; S2: Dissolving the tricyanomethylimidazolium monomer and a trialdehyde monomer in an organic solvent, and constructing an imidazolium-based covalent organic framework connected by a carbon-carbon double bond through a Knoevenagel condensation reaction; S3: Dissolving the imidazolium-based covalent organic framework in an organic solvent, deprotonating it under alkaline conditions to release the N-heterocyclic carbene active site, and then reacting it with a metal active component to obtain a metal N-heterocyclic carbene covalent organic framework catalyst.

[0008] In one embodiment of the present invention, in the step S1, the triimidazolyl organic compound and the bromoacetonitrile are dissolved in an organic solvent, and stirred and reacted at 60°C to 180°C for 12 h to 48 h. After the reaction is completed, it is cooled to room temperature, and the tricyanomethylimidazolium monomer is obtained through precipitation, filtration, washing, and vacuum drying.

[0009] In one embodiment of the present invention, 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.

[0010] In one embodiment of the present invention, in the 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, and stirred at 60 °C to 180 °C for 12 h to 72 h. After the reaction is completed, it is cooled to room temperature, and then precipitated, filtered, washed, and vacuum dried to obtain an imidazolium-based covalent organic framework connected by carbon-carbon double bonds.

[0011] In one embodiment of the present invention, the molar ratio of the tricyanomethylimidazolium monomer to the trialdehyde monomer is 1:1. 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-triformylbenzene, tris(4-formylphenyl)amine, and tris(4-formylphenyl)methane.

[0012] In one embodiment of the present invention, in the step S3, the imidazolium-based covalent organic framework is dissolved in an organic solvent, the pH is adjusted to 8 to 12 for deprotonation to release the N-heterocyclic carbene active sites, and then a metal active component is added, and stirred at 25 °C to 100 °C for 12 h to 24 h to obtain a metal N-heterocyclic carbene covalent organic framework catalyst.

[0013] In one embodiment of the present invention, the dosage of the metal active component is 1 to 6 times the molar amount of the triimidazolyl organic compound. The metal active component includes one or several of cuprous chloride, cuprous bromide, cuprous iodide, silver oxide, and tetrahydrothiophene gold chloride.

[0014] In the third aspect, the present invention provides an application of the above metal N-heterocyclic carbene covalent organic framework catalyst or the metal N-heterocyclic carbene covalent organic framework catalyst prepared by the above preparation method, which is used for catalyzing the synthesis of symmetric diselenides from elemental selenium and aryl iodides. The aryl iodides include substituted aryl iodides with electron-withdrawing or electron-donating functional groups at the ortho, meta, and para positions.

[0015] Advantages of the present invention: 1. The metal N-heterocyclic carbene covalent organic framework catalyst of the present invention has a covalent organic framework skeleton, forms a two-dimensional layered structure through carbon-carbon double bonds, has a thermal decomposition temperature > 180 °C, and excellent acid / base stability (can withstand pH 2 to 11); the active site distribution of the catalyst: the N-heterocyclic carbene (NHC) is fixed in the framework structure by covalent bonds, and the coordinated metal ions (Cu + 、Ag + 、Au +)It is evenly anchored thereon, with a metal loading of 5wt% - 12wt%, and TEM characterization shows no agglomeration phenomenon; this catalyst has a pore synergy effect, and the regular pore structure (pore diameter matching the size of aryl 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 problem of separation of traditional homogeneous catalysts, and realizes simple centrifugal separation of the catalyst and the product through heterogeneous catalysis. After being recycled five times, the catalytic activity does not decrease significantly (yield retention rate > 90%), and 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 the low catalytic efficiency of existing COF catalysts for aryl iodides with complex substituents.

[0016] 2. The metal N-heterocyclic carbene covalent organic framework catalyst of the present invention is prepared by a three-step method of quaternization reaction - Knoevenagel condensation - coordination anchoring. The quaternization reaction provides reactive sites for subsequent framework construction; the imidazolium-based covalent organic framework (ImCOFs) prepared by the Knoevenagel condensation reaction has a regular pore structure (pore diameter 3nm - 5nm) and a high specific surface area, providing an ordered carrier for metal coordination; the metal active component is highly dispersed and anchored through alkaline deprotonation anchoring to obtain the target catalyst M-NHC-COFs. This preparation method has mild reaction conditions, uses copper, silver, and gold instead of metals such as palladium and platinum, and the catalyst cost is reduced by more than 60%, which is suitable for production on a scale of hundreds of grams.

[0017] 3. When the metal N-heterocyclic carbene covalent organic framework catalyst of the present invention is applied to the synthesis of symmetric diselenides, no additional additives or inert gas protection is required, and it can efficiently catalyze the "one-pot" reaction of elemental selenium and aryl iodide to achieve the green synthesis of symmetric diselenides; this system shows excellent catalytic activity for aryl iodides containing ortho, meta, and para 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°C - 100°C, atmospheric pressure), the yield of the target product reaches 85% - 95%, and no odor gas such as hydrogen sulfide is generated during the reaction process. Brief Description of the Drawings

[0018] Figure 1 is a flow chart of the preparation method of the metal N-heterocyclic carbene covalent organic framework catalyst provided by the embodiment of the present invention; Figure 2 is the 1 1H NMR (DMSO- d 6, 500 MHz) spectrum of the tricyanomethylimidazolium monomer 2a in Example 1 of the present invention; Figure 3 is the 13 13C NMR (DMSO-d 6, 125 MHz) spectrum; Figure 4 is the structural formula of imidazolium-based covalent organic framework (ImCOF1-2a) in Example 1 of the present invention; Figure 5 is the infrared spectrum of imidazolium-based covalent organic framework (ImCOF1-2a) and its monomers 1 and 2a in Example 1 of the present invention; Figure 6 is the X-ray powder diffraction (XRD) spectrum of imidazolium-based covalent organic framework (ImCOF1-2a) in Example 1 of the present invention; Figure 7 is the X-ray photoelectron spectroscopy (XPS) spectrum of imidazolium-based covalent organic framework (ImCOF1-2a) in Example 1 of the present invention, where 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; Figure 8 is the structural formula of metal N-heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a) in Example 1 of the present invention; Figure 9 is the X-ray powder diffraction (XRD) spectrum of metal N-heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a) in Example 1 of the present invention; Figure 10 is the X-ray photoelectron spectroscopy (XPS) spectrum of metal N-heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a) in Example 1 of the present invention, where 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; Figure 11 is the thermogravimetric analysis (TGA) spectrum of metal N-heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a) in Example 1 of the present invention. Detailed implementation mode

[0019] The present invention will be described in detail below with reference to the accompanying drawings and specific implementation modes.

[0020] The present invention provides a metal - N - heterocyclic carbene covalent organic framework catalyst (M - NHC - COFs) with high stability and high catalytic activity. The metal - N - heterocyclic carbene covalent organic framework catalyst contains a N - heterocyclic carbene covalent organic framework structure connected by carbon - carbon double bonds, and the N - heterocyclic carbene covalent organic framework structure is anchored with metal species coordinated with N - heterocyclic carbene active sites.

[0021] When the metal - N - heterocyclic carbene covalent organic framework catalyst provided by the present invention is applied to the synthesis of symmetrical diselenides, it can solve the technical problems existing in the existing synthesis of symmetrical diselenides, such as low catalytic efficiency, narrow substrate applicability, and insufficient catalyst cycle stability.

[0022] Specifically, the structure of the metal - N - heterocyclic carbene covalent organic framework catalyst is shown in General Formula Ⅰ: ; Ⅰ In General Formula Ⅰ, A is N element or C element, X is Cl element, Br element or I element, and M is Au element, Ag element or Cu element.

[0023] The M - NHC - COFs catalyst has the following core structural features: It has a covalent organic framework skeleton: formed into a two - dimensional layered structure by connecting through carbon - carbon double bonds, with a thermal decomposition temperature > 180 °C and excellent acid / base stability (tolerable pH 2 - 11).

[0024] The active site distribution of the catalyst: N - heterocyclic carbene (NHC) is fixed in the framework structure in the form of covalent bonds, and the coordinated metal ions (Cu + 、Ag + 、Au + ) are uniformly anchored thereon, with a metal loading of 5wt% - 12wt%, and TEM characterization shows no agglomeration phenomenon.

[0025] The catalyst has a pore synergy effect. The regular pore structure (pore size matching the size of aryl 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 problem of separation of traditional homogeneous catalysts, realizes simple centrifugal separation of the catalyst and the product through heterogeneous catalysis, and the catalytic activity does not decrease significantly after being recycled five times (yield retention rate > 90%). Moreover, 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 aryl iodides with complex substituents.

[0026] The present invention also provides a preparation method of the above - mentioned metal - N - heterocyclic carbene covalent organic framework catalyst. Referring to Figure 1 , the preparation method of the metal - N - heterocyclic carbene covalent organic framework catalyst includes the following steps: S1: Quaternize a triimidazolyl organic compound with bromoacetonitrile to obtain a tricyanomethylimidazolium monomer; S2: Dissolve the tricyanomethylimidazolium monomer and a trialdehyde monomer in an organic solvent, and construct an imidazolium-based covalent organic framework connected by carbon-carbon double bonds through a Knoevenagel condensation reaction; S3: Dissolve the imidazolium-based covalent organic framework in an organic solvent, deprotonate it under alkaline conditions to release the N-heterocyclic carbene active site, and then react with a metal active component to obtain a metal N-heterocyclic carbene covalent organic framework catalyst.

[0027] In the present invention, by introducing an imidazolium-based structural unit into the COFs framework, highly active NHC sites are released through alkaline deprotonation, realizing the uniform anchoring of monovalent metal active species, and constructing a heterogeneous catalytic system with both structural stability and catalytic activity.

[0028] Step S1 constructs an active monomer through a quaternization reaction. Dissolve the triimidazolyl organic compound and bromoacetonitrile in an organic solvent, stir and react at 60 °C to 180 °C for 12 h to 48 h. After the reaction is completed, cool to room temperature, precipitate, filter, wash, and vacuum dry to obtain the tricyanomethylimidazolium monomer, which is a light brown solid powder. The organic solvent can be selected from N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, dioxane, etc., and ethyl acetate, diethyl ether, n-hexane, petroleum ether, etc. can be added for precipitation.

[0029] Among them, 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.

[0030] The molar ratio of the triimidazolyl organic compound to bromoacetonitrile is 1:3 to 10. By using an excessive amount of bromoacetonitrile, the complete quaternization of the N site of the imidazole ring is ensured, providing reactive sites for subsequent framework construction.

[0031] Step S2 constructs a covalent organic framework through a Knoevenagel condensation. The Knoevenagel condensation reaction is carried out in an alkaline environment. Dissolve the tricyanomethylimidazolium monomer and the trialdehyde monomer in an organic solvent, stir and react at 60 °C to 180 °C for 12 h to 72 h. After the reaction is completed, cool to room temperature, precipitate, filter, wash, and vacuum dry to obtain the imidazolium-based covalent organic framework connected by carbon-carbon double bonds, which is a brown powder.

[0032] Among them, the molar ratio of the tricyanomethylimidazolium monomer to the trialdehyde monomer is 1:1. The trialdehyde monomer in this example 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-triformylbenzene, tris(4-formylphenyl)amine, and tris(4-formylphenyl)methane.

[0033] 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, and the higher the pH, the faster the reaction.

[0034] In step S2, the organic solvent can be one or several of n-butanol, 1,2-dichlorobenzene, 1,3,5-trimethylbenzene, methanol, and dimethyl sulfoxide.

[0035] In step S2, a covalent organic framework (ImCOFs) with carbon-carbon double bond-linked imidazolium groups is formed through the condensation reaction of aldehyde groups and cyano groups. This framework has a regular pore structure (pore diameter 3 nm to 5 nm) and a high specific surface area, providing an ordered carrier for metal coordination.

[0036] In step S3, copper active components are anchored through alkaline deprotonation. Among them, the metal active components include one or several of cuprous chloride, cuprous bromide, cuprous iodide, silver oxide, and tetrahydrothiophene gold chloride, and the amount of the metal active components is 1 to 6 times the molar amount of the triimidazolyl organic compound.

[0037] In step S3, the organic solvent can be one or several of acetone, acetonitrile, and tetrahydrofuran. By adding alkaline substances such as potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, potassium tert-butoxide, and sodium ethoxide, the pH is adjusted to 8 to 12, and the reaction is stirred at 25 °C to 100 °C for 12 h to 24 h to achieve highly dispersed anchoring of the metal active components, obtaining a crude product, and further centrifuging, washing, and drying to obtain the target catalyst M-NHC-COFs.

[0038] The present invention adopts a three-step method of "quaternization reaction - Knoevenagel condensation - coordination anchoring" to avoid the problem of low ligand grafting rate in the post-modification method. Through the in-situ generation of NHC sites, strong coordination anchoring of metal ions is achieved, and the metal dispersion is increased by more than 3 times compared with the traditional method; moreover, the preparation method of this M-NHC-COFs catalyst has mild reaction conditions, and the present invention uses relatively inexpensive copper, silver, and gold to replace precious metals such as palladium and platinum, reducing the catalyst cost by more than 60%, and is suitable for production on a scale of 100 grams (single batch output ≥ 100 g, purity > 95%).

[0039] The present invention also provides an application of a metal N-heterocyclic carbene covalent organic framework catalyst in the synthesis of symmetrical diselenides by catalyzing elemental selenium and aryl iodides, and the aryl iodides include substituted aryl iodides with electron-withdrawing or electron-donating functional groups at the ortho, meta, and para positions.

[0040] When the M-NHC-COFs catalyst is applied to the synthesis of symmetrical diselenides, the specific reaction conditions are as follows: Using elemental selenium (Se) and aryl iodide as substrates, the dosage of the M-NHC-COFs catalyst 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 2 h - 24 h without additional additives or inert gas protection.

[0041] This system shows excellent catalytic activity for aryl iodides containing electron-withdrawing groups (such as -NO2, -CN) or electron-donating groups (such as -CH3, -OCH3) at the ortho, meta, and para positions. The yield of the target product reaches 85% - 95%. No odor gases such as hydrogen sulfide are generated during the reaction process, and it can be recycled, solving the problems of large pollution, high cost, and difficulty in scaling up in traditional methods, and providing a new technical route for the green synthesis of symmetrical diselenides.

[0042] 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 specific examples.

[0043] Example 1 Preparation of the catalyst Cu-NHC-COF1-2a: S1. Synthesize the tricyanomethylimidazolium monomer 2a through a quaternization reaction. Add 1,3,5-tris(4-imidazolylphenyl)benzene (1.0 mmol, 0.505 g) and bromoacetonitrile (6.0 mmol, 0.720 g) to a 100 mL round-bottom flask, dissolve them in 20 mL of DMF, and stir and react in an oil bath at 120 °C for 48 h. After the reaction is completed, cool to room temperature, add 100 mL of ethyl acetate to it to completely precipitate the precipitate, filter, wash with ethyl acetate, and dry in vacuo (60 °C, 12 h) to obtain a light brown solid powder, 0.837 g (yield 97%).

[0044] Characterize the product tricyanomethylimidazolium monomer 2a by nuclear magnetic resonance 1 H NMR (DMSO- d 6, 500 MHz) and 13 CNMR (DMSO-d6, 125 MHz). The spectrum of the nuclear magnetic resonance 1 H NMR (DMSO d 6, 500 MHz) is referred toFigure 2 . 1 1H NMR (500 MHz, DMSO- d 6): δ δ = 10.11 (s, 3H), 8.52 (s, 3H), 8.31 (d, J J = 8.6 Hz, 6H), 8.24 (s, 3H), 8.20 (s, 3H), 7.97 (d, J J = 8.6 Hz, 6H), 5.74 (s, 6H).

[0045] Figure 2 In the 1H NMR spectrum, the hydrogen signal of C2 of the tricyanomethylimidazolium monomer 2a (N-CH-N) appears as a singlet at 10.11 ppm. This is due to the strong electron-withdrawing effect of the quaternary ammonium salt unit formed by the nitrogen atom of the imidazolium salt. N-CH-N is in a strongly deshielded region, and the chemical shift appears at a relatively high field position, which proves that the synthesized product is an imidazolium salt. The two sets of hydrogens on the outer benzene ring appear as doublets at 7.97 ppm and 8.31 ppm respectively, with an integral area ratio of 1:1 and a coupling constant of 8.6 Hz. The hydrogen signal of the methylene group (-CH2-) directly connected to the imidazole ring and the benzene ring appears as a singlet at 5.74 ppm. This is because the introduction of the cyano group and the imidazole group enhances the acidity of the methylene group (-CH2-) between them. Under the influence of the electron-withdrawing effect, the chemical shift of the hydrogen signal will appear in a relatively low field region. The integral area ratio of the hydrogens on this organic monomer is 1:1:2:1:1:2:2, which is completely consistent with the structure of the tricyanomethylimidazolium monomer 2a.

[0046] Nuclear magnetic resonance 13 13C NMR (DMSO- d 6, 125 MHz) spectrum is referred to Figure 3 .

[0047] Figure 3 In the 13C NMR spectrum, δ the signal peaks at δ = 141.2, 140.1, 137.0, 134.2, 129.0, 125.5, 123.4, 122.5, 122.0, 114.5 ppm are respectively attributed to the carbon signals on the aromatic ring of the tricyanomethylimidazolium monomer 2a. The signal peak at 37.2 ppm is the characteristic carbon signal of the cyanomethyl group in the tricyanomethylimidazolium monomer 2a, which is in a relatively low field position due to the strong electron-withdrawing effect of the cyano group. This further confirms the correctness of the structure and composition of the tricyanomethylimidazolium monomer 2a. In addition, through the nuclear magnetic resonance spectrum, it can be proved that the purity of the tricyanomethylimidazolium monomer 2a > 99.5%.

[0048] S2. Construct the imidazolium-based covalent organic framework (ImCOF1-2a) through Knoevenagel condensation. The structural formula of ImCOF1-2a is referred to Figure 4 .

[0049] Dissolve the tricyanomethylimidazolium monomer 2a (0.3 mmol, 259 mg) obtained in S1 and 1,3,5-(4-formyl)benzene (0.3 mmol, 0.117 g) in a mixed solution of n-butanol (15 mL) and 1,2-dichlorobenzene (5 mL), add potassium hydroxide (0.9 mmol, 0.051 g), and reflux at 120 °C for 48 h. After the reaction solution is cooled, filter out the precipitate, wash it with ethanol, and dry it under vacuum (80 °C, 24 h) to obtain 0.336 g of brown powder (yield 80.3%).

[0050] Characterize the product and its monomer by infrared spectroscopy, referring to Figure 5 .

[0051] Figure 5 In, after the Knoevenagel condensation reaction, the typical C=O stretching vibration peak of the trialdehyde monomer at 1687 cm -1 and the stretching vibration peak of -CH2- of the tricyanomethylimidazolium monomer 2a at 2981 cm -1 disappear, which proves that the reaction is complete. The appearance of the C=C group at 1601 cm -1 proves the formation of vinyl in ImCOF1-2a. At the same time, the peak of H2O appears at 3434 cm -1 in ImCOF1-2a, which also conforms to the characteristic of the imidazolium group being easy to absorb water.

[0052] The X-ray powder diffraction spectrum (XRD) of the imidazolium-based covalent organic framework (ImCOF1-2a) is referred to Figure 6 .

[0053] Figure 6 In, strong diffraction peak signals exist at 2 θ = 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°, 89.1°, indicating that the molecular arrangement of ImCOF1-2a is regular and it belongs to a crystalline compound.

[0054] Refer to Figure 7 , and the composition and structure of ImCOF1-2a are further verified to be correct by X-ray photoelectron spectroscopy (XPS).

[0055] Through the XPS full spectrum of ImCOF1-2a (Figure 7 Characteristic peaks such as C 1s, O 1s, N 1s, and Br 3d can be seen in (a), indicating that the sample contains elements carbon (C), oxygen (O), nitrogen (N), and bromine (Br). (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.

[0056] Through peak deconvolution fitting, from the high-resolution spectrum of C 1s ( Figure 7 b), carbon peaks in 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 common carbon-carbon and carbon-hydrogen bonds in organic compounds. The peak with a binding energy of 286.1 eV corresponds to the C-N bond, indicating the presence of a carbon-nitrogen chemical bond in the sample. The peak with a binding energy of 289.1 eV is attributed to the C=N + bond, indicating the presence of a positively charged carbon-nitrogen double bond structure in the sample.

[0057] For the high-resolution spectrum of N 1s ( Figure 7 c), two main peaks can be seen after peak deconvolution fitting: the peak with a binding energy of 399.4 eV corresponds to the C-N bond, indicating that the nitrogen atom is connected to the carbon atom in a single bond form; 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 result of the C = N + bond in the C 1s spectrum.

[0058] From the high-resolution spectrum of Br 3d ( Figure 7 d), two characteristic peaks can be seen: the binding energy of the Br 3d5 / 2 peak is 68.3 eV, and the binding energy of the Br3d3 / 2 peak is 70.0 eV. These two peaks are typical features of bromine element in the XPS spectrum and are used to determine the presence of bromide ions in the sample and their chemical environment.

[0059] S3. Anchoring Cu through base deprotonation + . Disperse ImCOF1-2a (0.5 mmol, 0.209 g) in 25 mL of acetone, add potassium carbonate (1.0 mmol, 0.138 g), and stir at 60 °C for 2 h to deprotonate the imidazolium group. Add copper(I) iodide (0.75 mmol, 0.123 g), continue stirring for 22 h, centrifuge to separate the solid, wash with deionized water and ethanol, and dry in vacuo (60 °C, 12 h) to obtain 0.234 g of the metal N-heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a) (yield 91.4%).

[0060] The structural formula of Cu-NHC-COF1-2a refers to Figure 8 .

[0061] The X-ray powder diffraction spectrum (XRD) of the metal N-heterocyclic carbene covalent organic framework catalyst (Cu-NHC-COF1-2a) prepared in this example was referred to Figure 9 . Figure 9 In [2], θ the signals at 2θ = 36.8°, 42.5°, 61.6° and 73.7° corresponded to the diffraction peaks of the (111), (200), (220) and (311) crystal planes of the monovalent copper active component respectively. θ The signals at 2θ = 25.8°, 29.8° and 50.2° were the diffraction spectra of the N-heterocyclic carbene covalent organic framework, indicating that the monovalent copper active component was successfully loaded on the N-heterocyclic carbene covalent organic framework.

[0062] The composition and structure of Cu-NHC-COF1-2a were further verified by X-ray photoelectron spectroscopy (XPS), referring to Figure 10 .

[0063] From the survey spectrum of Cu-NHC-COF1-2a ( Figure 10 a), characteristic peaks of Cu 2p, C 1s, N 1s and I 3d could be seen, indicating that the sample contained elements such as copper (Cu), carbon (C), nitrogen (N) and iodine (I), suggesting that the copper active component was successfully loaded into the catalyst structure.

[0064] By peak fitting, from the high-resolution spectrum of C 1s ( Figure 10 b), carbon peaks in different chemical environments could be seen: the peak with a binding energy of 284.8 eV was attributed to C-C and C-H bonds, which were the characteristic binding energy positions of common C-C and C-H bonds; the peak with a binding energy of 286.2 eV corresponded to the C=N bond in the N-heterocyclic carbene; the peak with a binding energy of 289.0 eV was attributed to the C-Cu bond formed by the coordination of the N-heterocyclic carbene with the monovalent copper ion. For the high-resolution spectrum of N 1s ( Figure 10 c), there was only one peak after peak fitting. The original peak with a binding energy of 401.7 eV corresponding to the C=N + bond signal peak completely disappeared, replaced by a new peak with a binding energy of 400.1 eV, corresponding to the C-N bond in the copper N-heterocyclic carbene, indicating that the monovalent copper ion was successfully coordinated with the N-heterocyclic carbene unit in the covalent organic framework through the C-Cu bond and was immobilized in the framework.

[0065] From the high-resolution spectrum of Cu 2p ( Figure 10 d), two characteristic peaks were seen: the binding energy of the Cu 2p1 / 2 peak was 953.6 eV, and the binding energy of the Cu2p3 / 2 peak was 933.5 eV. These two peaks were typical characteristics of monovalent copper in the XPS spectrum, indicating that the copper atom maintained its +1 valence state after being immobilized.

[0066] The Cu-NHC-COF1-2a was detected by thermogravimetric analysis, and the thermogravimetric analysis spectrum (TGA) was referred to Figure 11 , Figure 11 indicating that such catalysts have good stability within 180 °C.

[0067] The metal N-heterocyclic carbene covalent organic framework catalyst prepared in Example 1 was used to test the reaction performance of aryl iodides with different substituents under the same reaction conditions (90 °C, 12 h, catalyst dosage 2%), that is, the substrate generality test. The results are shown in Table 1. The data in Table 1 indicate that the catalyst of the present invention exhibits good catalytic activity for substrates with different positions, different electronic effect substituents and heterocyclic substrates, and the substrate applicability is significantly better than that of existing COF-based catalysts (the reported yield of the same type of catalyst for meta-cyano-substituted substrates is only 75%).

[0068] Table 1

[0069] Example 2 Preparation of catalyst Ag-NHC-COF1-2a: 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 and acts as both a base and a metal active component in the reaction. It was stirred at 25 °C for 24 h, the solid was separated by centrifugation, washed with ethanol, then washed with dichloromethane, and dried in vacuo to obtain 0.236 g of Ag-NHC-COF1-2a catalyst (yield 93%). Example 3 Preparation of catalyst Au-NHC-COF1-2a: Ag-NHC-COF1-2a (0.3 mmol, 0.152 g) was dispersed in 25 mL of acetonitrile, and thiothene gold chloride (0.3 mmol, 0.096 g) was added. It was stirred at 25 °C for 24 h, the solid was separated by centrifugation, washed with acetonitrile, and dried in vacuo to obtain 0.171 g of Au-NHC-COF1-2a catalyst (yield 95.5%). In this process, Au-NHC-COF1-2a was directly prepared from Ag-NHC-COF1-2a through a metal exchange reaction, and the use of a base could be omitted.

[0070] Example 4 Application of metal N-heterocyclic carbene covalent organic framework catalyst in the synthesis of 3,3'-dimethyldiphenyl diselenide: 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 magnetically at 120 °C for 2 h. After the reaction solution was cooled, the catalyst was separated by centrifugation, and the filtrate was purified by silica gel column chromatography (the eluent was petroleum ether) to obtain a yellow oily liquid 3,3'-dimethyldiphenyldiselenide (yield 93%). R f = 0.88 (PE=30:1); NMR results of 3,3'-dimethyldiphenyldiselenide: 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.

[0071] The catalyst after the reaction in Example 4 was washed with methanol and dried under vacuum and then reused. The results showed that the yield was 93% for the first time, 91% for the third time, and 90% for the fifth time, proving that the catalyst of the present invention has excellent cycle stability.

[0072] Example 5 Effect of tricyanomethylimidazolium monomer type on the performance of metal N-heterocyclic carbene covalent organic framework catalysts: The selectivities and conversions of catalysts constructed with different tricyanomethylimidazolium monomers in the reaction for the catalytic synthesis of 3,3'-dimethyldiphenyldiselenide are shown in Table 2.

[0073] Replace 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-trimidazolylbenzene, tris(4-imidazolylphenyl)amine, and tris(4-imidazolylphenyl)methane. Under other unchanged conditions, catalysts Cu-NHC-COF1-2b, Cu-NHC-COF1-2c, Cu-NHC-COF1-2d, and Cu-NHC-COF1-2e are respectively prepared. When these catalysts are used in the selenization reaction of 3-iodotoluene (0.1 mmol), there are certain differences in both selectivity and the yield of the target product, indicating that the selection of organic monomers has an important influence on the regulation of catalyst performance. Among them, Cu-NHC-COF1-2b has the best conversion rate and selectivity in the catalytic synthesis of 3,3'-dimethyldiphenyl diselenide.

[0074] Table 2

[0075] Example 6 Effect of the type of trialdehyde monomer on the performance of metal N-heterocyclic carbene covalent organic framework catalysts: 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.

[0076] Replace 1,3,5-tris(4-formylphenyl)benzene in step S1 of Example 1 with 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 1,3,5-triformylbenzene, tris(4-formylphenyl)amine, and tris(4-formylphenyl)methane. Under other unchanged conditions, catalysts Cu-NHC-COF2-2a, Cu-NHC-COF3-2a, Cu-NHC-COF4-2a, and Cu-NHC-COF5-2a are respectively prepared.

[0077] When these catalysts are used in the selenization reaction of 3-iodotoluene (0.1 mmol), there are certain differences in both selectivity and the yield of the target product, indicating that the selection of trialdehyde monomers has an important influence on the regulation of catalyst performance.

[0078] Among them, Cu-NHC-COF3-2a has the best conversion rate and selectivity in the catalytic synthesis of 3,3'-dimethyldiphenyl diselenide.

[0079] Table 3

[0080] Example 7 Effect of the type of halogen on catalytic performance: The selectivity and conversion rate of catalysts with different halogen types in the catalytic synthesis of 3,3'-dimethyl diphenyl diselenide are shown in Table 4.

[0081] Table 4

[0082] Replace cuprous iodide in step S3 of Example 1 with cuprous chloride and cuprous bromide, and keep the other conditions unchanged to prepare catalysts CuCl-NHC-COF1-2a and CuBr-NHC-COF1-2 respectively. There are obvious differences in the yield and selectivity of the catalysts in the reaction of synthesizing 3,3'-dimethyl diphenyl diselenide from 3-iodotoluene (0.1 mmol) (Table 3). Considering comprehensively, cuprous iodide is preferred when synthesizing copper-nitrogen heterocyclic carbene covalent organic framework catalysts.

[0083] Example 8 Effect of metal type on catalytic performance: The selectivity and conversion rate of catalysts with different metal types in the catalytic synthesis of 3,3'-dimethyl diphenyl diselenide are shown in Table 5.

[0084] Replace Cu-NHC-COF1-2a in Example 4 with Ag-NHC-COF1-2a and Au-NHC-COF1-2a, and keep the other conditions unchanged. The yield and selectivity of Au-NHC-COF1-2a are the best in the reaction of synthesizing 3,3'-dimethyl diphenyl diselenide from 3-iodotoluene (0.1 mmol) (Table 4). However, the cost of Au-NHC-COF1-2a is relatively high. When catalyzing the synthesis of symmetrical diselenides from elemental selenium and aryl iodides, Cu-NHC-COF1-2a is preferred.

[0085] Table 5

[0086] Comparative example Comparison with the catalyst without introducing NHC sites: Omit the basic deprotonation process in step S3 of Example 1, and directly mix ImCOF1-2a with cuprous iodide and stir to prepare the comparative catalyst Cu@ImCOF1-2a. When this catalyst is used in the reaction of p-iodonitrobenzene (0.1 mmol), the yield is only 65%, and the yield drops to 42% after being recycled twice. Obviously, the catalyst without introducing NHC sites has a worse effect than the Cu-NHC-COF1-2a catalyst in Example 1.

[0087] Hundred-gram preparation example: The process of Example 1 was scaled up by 100 times, and the quaternization reaction was carried out in a 5 L reactor. 84.5 g of tricyanomethylimidazolium monomer was prepared in a single batch (yield: 97.8%); in the Knoevenagel condensation stage, a continuous reaction device was used, and 109.6 g of ImCOF1-2a was prepared in a single batch; by coordinating and anchoring copper active components, 123 g of Cu-NHC-COF1 catalyst was finally prepared, proving that the process of the present invention is suitable for large-scale production.

[0088] The above examples verified the feasibility of each technical feature in the claims through specific parameter combinations, including molar ratio, reaction temperature, solvent selection and catalyst application conditions; the comparative examples highlighted the key role of NHC active sites in copper ion anchoring and catalytic performance; the substrate generality data and cyclic performance tests directly supported the technical effects of high stability and wide applicability in the advantages of the invention; the preparation examples at the 100-g scale proved the feasibility of process scaling up and met the requirements of industrial production.

[0089] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any modification, equivalent replacement and improvement made within the spirit and principle of the present invention by those skilled in the art within the technical scope disclosed by the present invention shall be covered by the protection scope of the present invention.

Claims

1. A metal N-heterocyclic carbene covalent organic framework catalyst, characterized in that, The metal N-heterocyclic carbene covalent organic framework catalyst contains an N-heterocyclic carbene covalent organic framework structure connected by carbon-carbon double bonds, and the N-heterocyclic carbene covalent organic framework structure is anchored with metal species coordinated with N-heterocyclic carbene active sites.

2. The metal N-heterocyclic carbene covalent organic framework catalyst according to claim 1, wherein The structure is as shown in General Formula I: Ⅰ In the General Formula I, A is an 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.

3. A method for preparing the metal N-heterocyclic carbene covalent organic framework catalyst according to claim 1, characterized in that, It includes the steps: S1: Quaternize a triimidazole-based organic compound with bromoacetonitrile to obtain a tricyanomethylimidazolium monomer. S2: Dissolve the tricyanomethylimidazolium monomer and a trialdehyde monomer in an organic solvent, and construct an imidazolium-based covalent organic framework connected by carbon-carbon double bonds through a Knoevenagel condensation reaction. S3: Dissolve the imidazolium-based covalent organic framework in an organic solvent, deprotonate it under alkaline conditions to release N-heterocyclic carbene active sites, and then react with a metal active component to obtain a metal N-heterocyclic carbene covalent organic framework catalyst.

4. The preparation method of the metal N-heterocyclic carbene covalent organic framework catalyst according to claim 3, characterized in that, In the step S1, dissolve the triimidazole-based organic compound and the bromoacetonitrile in an organic solvent, stir and react at 60 °C to 180 °C for 12 h to 48 h. After the reaction is completed, cool to room temperature, precipitate, filter, wash, and vacuum dry to obtain a tricyanomethylimidazolium monomer.

5. The preparation method of the metal N-heterocyclic carbene covalent organic framework catalyst according to claim 4, wherein, The molar ratio of the triimidazole-based organic compound to the bromoacetonitrile is 1: 3 to 10; the triimidazole-based 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-trimidazolylbenzene, tris(4-imidazolylphenyl)amine, and tris(4-imidazolylphenyl)methane.

6. The preparation method of the metal N-heterocyclic carbene covalent organic framework catalyst according to claim 3, wherein In the step S2, the Knoevenagel condensation reaction is carried out in an alkaline environment. Dissolve the tricyanomethylimidazolium monomer and the trialdehyde monomer in an organic solvent, stir and react at 60 °C to 180 °C for 12 h to 72 h. After the reaction is completed, cool to room temperature, precipitate, filter, wash, and vacuum dry to obtain an imidazolium-based covalent organic framework connected by carbon-carbon double bonds.

7. The preparation method of the metal N-heterocyclic carbene covalent organic framework catalyst according to claim 6, 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-triformylbenzene, tris(4-formylphenyl)amine, and tris(4-formylphenyl)methane.

8. The preparation method of the metal N-heterocyclic carbene covalent organic framework catalyst according to claim 3, characterized in that, In the step S3, dissolve the imidazolium-based covalent organic framework in an organic solvent, adjust the pH to 8 to 12, deprotonate it to release N-heterocyclic carbene active sites, then add a metal active component, and stir and react at 25 °C to 100 °C for 12 h to 24 h to obtain a metal N-heterocyclic carbene covalent organic framework catalyst.

9. The preparation method of the metal N-heterocyclic carbene covalent organic framework catalyst according to claim 8, characterized in that, The dosage of the metal active component is 1 to 6 times the molar amount of the triimidazole-based organic compound, and the metal active component includes one or several of cuprous chloride, cuprous bromide, cuprous iodide, silver oxide, and tetrahydrothiophene gold chloride.

10. Use of any one of the metal N-heterocyclic carbene covalent organic framework catalysts described in claims 1 to 2 or the metal N-heterocyclic carbene covalent organic framework catalyst prepared by any one of the preparation methods described in claims 3 to 9, characterized in that, For catalyzing the synthesis of symmetric diselenides from elemental selenium and aryl iodides, where the aryl iodides include substituted aryl iodides with electron-withdrawing or electron-donating functional groups at the ortho, meta, and para positions.

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