All-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen clusters, their preparation methods and applications

Abstract

This invention discloses a tetranuclear copper(I)-oxygen cluster stabilized by a nitrogen-containing heterocyclic carbene, its preparation method, and its applications, belonging to the field of metal cluster technology. The preparation method includes the following steps: first, 9,10-dichloromethylanthracene or 1,4-dibromomethylnaphthalene is reacted with a 1-substituted imidazole compound in a solvent under heat; then, the product is ion-exchanged with ammonium hexafluorophosphate in a solvent to obtain a bidentate imidazole onium salt of hexafluorophosphate; finally, the obtained product, cuprous salt, and cesium carbonate are mixed and ball-milled to obtain the final product. This invention uses mechanical ball milling to synthesize a tetranuclear copper(I)-oxygen cluster in a one-pot reaction between an imidazole onium salt and a coin-minted copper source. This cluster exhibits high selectivity and high current density for methane in electrocatalytic carbon dioxide reduction, solving the technical problems of cumbersome synthesis steps, low yield, difficulty in structural control, and low product selectivity in deep reduction of ECO2RR electrocatalysts, as well as these issues.

Description

Technical Field

[0001] This invention relates to the field of metal cluster technology, specifically to tetranuclear copper(I) oxygen clusters stabilized by all-nitrogen heterocyclic carbene and their preparation methods and applications. Background Technology

[0002] Electrocatalytic carbon dioxide reduction (ECO2RR) is a crucial method for producing high-value chemicals and fuels, and also an important scientific and technological means to address the energy crisis. Currently, ECO2RR can produce a variety of hydrocarbons and chemicals; however, due to the inert nature of carbon dioxide and the complex multi-electron transfer process, ECO2RR faces challenges such as low current density and low selectivity. Establishing precise catalyst atomic structures to achieve highly selective CO2 reduction has become a key research topic in ECO2RR. Copper, as one of the key metals capable of converting CO2 into deeply reduced products, offers a potential solution to these challenges.

[0003] Copper nanoclusters possess precise atomic and unique electronic structures, making them ideal models for studying the structure-activity relationship of catalytic reactions. In nature, copper clusters often serve as catalytic active sites in biological enzymes, such as laccase and ceruloplasmin, exhibiting natural catalytic activity. Therefore, studying copper clusters is beneficial not only for developing highly efficient catalysts but also for a deeper understanding of reaction mechanisms. Nitrogen heterocyclic carbene (NHC) ligands, as strong σ-electron donors and weak π-acceptors, can form strong CM bonds upon coordination with transition metal elements and have become important organic ligands for stabilizing metal clusters. Coordination with copper can effectively modulate their electronic structure, thereby affecting their electrocatalytic performance in carbon dioxide reduction.

[0004] However, the preparation of copper clusters with precise structures using solution methods is challenging due to the variable valence states and diverse coordination modes of copper, making it difficult to precisely control the synthesis of single clusters. Mechanochemistry, as a green and sustainable synthetic technique, utilizes the mechanical energy provided by automated ball mills to initiate chemical reactions at room temperature, eliminating the need for additional heating. Compared to traditional solution methods, this effectively increases the collision frequency between reactants, significantly shortens reaction time, and improves synthetic efficiency while avoiding the use of solvents. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a tetranuclear copper(I) oxygen cluster stable by all-nitrogen heterocyclic carbene, its preparation method, and its application, thereby solving the technical problems in the prior art such as cumbersome synthesis steps, low yield, difficulty in structural control of copper nanoclusters, and low deep reduction products and product selectivity of ECO2RR electrocatalysts.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, the present invention provides a tetranuclear copper(I) oxygen cluster stable by a fully nitrogen heterocyclic carbene, having the general structural formula shown in Formula I: Formula I: ; In formula I, It has any of the following structures: , and ; It has any of the following structures: and .

[0007] The beneficial effects of this invention are as follows: By combining a bidentate nitrogen-heterocyclic carbene precursor, constructed using a fused ring as a linker and a nitrogen-heterocyclic carbene unit, with coin metal Cu(I), and utilizing the strong basicity of cesium carbonate, a tetranuclear copper(I)-oxygen cluster with a unique structure can be controllably constructed. The resulting tetranuclear copper(I)-oxygen cluster not only benefits from the stable coordination of the nitrogen-heterocyclic carbene but also from the weak Cu···π interaction between the fused ring framework and the cluster nucleus, effectively improving the cluster's stability.

[0008] Furthermore, the structural formula can be selected from any of the following: , , and .

[0009] In a second aspect, the present invention provides a method for preparing the above-described all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound (synthetic reaction formula as follows). Figure 1 (As shown), including the following steps: S1. 9,10-dichloromethylanthracene or 1,4-dibromomethylnaphthalene reacts with a 1-substituted imidazole compound in a solvent by heating to obtain a bidentate imidazole onium salt of a halide ion. S2. The bidentate imidazole onion salt of halide ions obtained in S1 is ion exchanged with ammonium hexafluorophosphate in a solvent to obtain the bidentate imidazole onion salt of hexafluorophosphate. S3. The bidentate imidazole onium salt, cuprous salt and cesium carbonate obtained in S2 were mixed and ball-milled to obtain a tetranuclear copper(I) oxygen cluster stable by all-nitrogen heterocyclic carbene.

[0010] The beneficial effects of this invention are as follows: This invention is the first to synthesize tetranuclear copper(I) oxygen clusters by one-pot synthesis of imidazolium salt and coin metal copper source through mechanical ball milling. This method effectively reduces the use of organic solvents, and has a short reaction time and high yield, solving the technical problems of cumbersome synthesis steps, low yield and difficulty in structural control of copper nanoclusters in the prior art.

[0011] Furthermore, the reaction temperature in S1 is 100-150 ℃, and the reaction time is 24-96 h.

[0012] Furthermore, the 1-substituted imidazole compound in S1 is selected from... , and .

[0013] Furthermore, the solvent in S1 is N,N-dimethylformamide.

[0014] Furthermore, the reaction temperature in S2 is room temperature, and the reaction time is 10-15 h.

[0015] Furthermore, the solvent in S2 is methanol.

[0016] Furthermore, the molar ratio of bidentate imidazole onium salt, cuprous salt and cesium carbonate in S3 is 1:(3-5):(5-7); the cuprous salt includes cuprous chloride.

[0017] Furthermore, in S3, the ball milling speed is 300-600 rpm, and the time is 60-180 min.

[0018] A third aspect of the present invention provides the application of the above-described all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound in electrocatalytic carbon dioxide reduction.

[0019] The beneficial effects of this invention are as follows: The tetranuclear copper(I) oxygen cluster compound with a precise structure obtained by this invention has a stable coordination mode of nitrogen heterocyclic carbene and a unique spatial structure. It has high selectivity and high current density for the 8-electron product methane in the electrocatalytic process, which effectively solves the technical problems of low deep reduction products and low product selectivity of ECO2RR electrocatalyst.

[0020] In a fourth aspect, the present invention provides a precursor for preparing the above-mentioned all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound, having the general structural formula shown in Formula II: Formula II: ; In formula II, It has any of the following structures: , and ; It has any of the following structures: and .

[0021] The beneficial effects of this invention are as follows: This invention combines fused rings (naphthalene and anthracene) as linkers with nitrogen-heterocyclic carbene units to construct a series of bidentate nitrogen-heterocyclic carbene precursors. The introduction of fused rings increases the number of weak intermolecular forces, effectively promoting the formation of tetranuclear copper(I) clusters. The introduction of methylene groups between the fused rings and the carbene units increases the spatial coordination flexibility of the ligands.

[0022] The present invention has the following beneficial effects: 1. This invention designs and synthesizes a series of bidentate nitrogen-heterocyclic carbene precursors by covalently linking a fused-ring aromatic skeleton with a nitrogen-heterocyclic carbene unit. The fused ring possesses a large electron cloud density and steric hindrance; its introduction into the nitrogen-heterocyclic carbene precursor increases intermolecular weak interactions, effectively promoting the formation of tetranuclear copper(I) clusters and providing greater stabilization for subsequently formed clusters. The introduction of the methylene group between the fused ring and the carbene unit increases the spatial coordination flexibility of the ligands. These features effectively avoid the tendency to form simple carbene complexes, providing a new strategy for constructing complex and tunable clusters.

[0023] 2. This invention utilizes a mechanical ball milling method to coordinate the aforementioned ligands with the coin metal Cu(I) and employs cesium carbonate as a base to controllably construct a tetranuclear copper(I) oxygen cluster with a unique structure. The resulting cluster nucleus is not only stably coordinated by a nitrogen heterocyclic carbene but also subjected to weak Cu···π interactions between the cluster nucleus and the fused ring framework, effectively improving the structural stability of the cluster and providing a new approach to cluster structure design.

[0024] 3. This invention applies the aforementioned tetranuclear copper(I) oxygen clusters to the electrocatalytic reduction of carbon dioxide. This series of clusters with precise structures, due to the strong coordination effect of nitrogen heterocyclic carbenes, significantly enhances the activity of copper for electrocatalytic carbon dioxide reduction. Furthermore, the unique spatial arrangement between the aromatic ring and the cluster core provides suitable space for stabilizing reaction intermediates. Ultimately, these clusters exhibit high selectivity and high current density for the 8-electron product methane during electrocatalysis, effectively solving the technical challenges of low product selectivity and limited deep reduction products in ECO2RR electrocatalysts. Attached Figure Description

[0025] Figure 1 The reaction formula for the preparation of a nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound; Figure 2 The cation portion of the crystal structure of the nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster 2a is shown, where gray represents carbon, blue represents nitrogen, brown represents copper, and red represents oxygen. Figure 3The cation portion of the crystal structure of the nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster 2b is shown, where gray represents carbon, blue represents nitrogen, brown represents copper, and red represents oxygen. Figure 4 The cation portion of the crystal structure of the nitrogen heterocyclic carbene-stabilized tetranuclear copper(I)oxy cluster 2c is shown, where gray represents carbon, blue represents nitrogen, brown represents copper, and red represents oxygen. Figure 5 The cation portion of the crystal structure of the nitrogen heterocyclic carbene-stabilized tetranuclear copper(I)oxy cluster 2d is shown, where gray represents carbon, blue represents nitrogen, brown represents copper, and red represents oxygen. Figure 6 LSV curves of nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen clusters 2a-2d in Ar-saturated and CO2-saturated 1.0 mol / L KOH solutions; Figure 7 Bar chart of Faraday efficiency for the tetranuclear copper(I) oxygen cluster 2a stabilized by nitrogen heterocyclic carbene at different potentials; Figure 8 Bar chart of Faraday efficiency for the tetranuclear copper(I) oxygen cluster 2b stabilized by nitrogen heterocyclic carbene at different potentials; Figure 9 Bar chart of Faraday efficiency for the tetranuclear copper(I) oxygen cluster 2c stabilized by nitrogen heterocyclic carbene at different potentials; Figure 10 Bar chart showing the Faraday efficiency of the tetranuclear copper(I) oxygen cluster 2d at different potentials for nitrogen heterocyclic carbene-stabilized products. Detailed Implementation

[0026] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0027] Example 1: A method for preparing a nitrogen-heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster 2a, the synthetic reaction formula of which is shown below: ; Specifically, the following steps are included: Synthesis of S1, bidentate imidazole onium salts of chloride ions: 9,10-Di(chloromethyl)anthracene (0.62 g, 2.25 mmol) and 1-ethylimidazole (0.45 g, 4.73 mmol) were added to a 100 mL Schlenk tube and stirred thoroughly under a nitrogen atmosphere. 5 mL of N,N-dimethylformamide (DMF) was added, and the mixture was reacted in an oil bath at 110 °C for 24 h. After the reaction was complete, the mixture was cooled to room temperature, and the reaction solution changed from a clear yellow solution to a brownish-yellow turbidity with a yellow precipitate. The reacted liquid was transferred to a 50 mL centrifuge tube, and 30 mL of ethyl acetate was added. A large amount of yellow precipitate was observed to precipitate. The precipitate was washed three times with ethyl acetate by centrifugation and dried to obtain a yellow solid, which was the bidentate imidazole onium salt of chloride ions.

[0028] Synthesis of S2, bidentate imidazole onium salts of hexafluorophosphate: The yellow solid obtained in S1 was added to a 50 mL round-bottom flask, and 15 mL of methanol was added dropwise with stirring until completely dissolved, yielding a clear, brownish-yellow solution. Upon addition of ammonium hexafluorophosphate (1.84 g, 11.27 mmol), a large amount of yellow precipitate was observed to form. The mixture was stirred at room temperature for 12 h. After the reaction was complete, the filter cake was collected, washed three times with water and methanol, and dried to obtain yellow powder 1a, which is the bidentate imidazole onium salt of hexafluorophosphate ions. Yield: 89% (1.38 g, 2.01 mmol).

[0029] The NMR and mass spectrometry results of bidentate imidazole onium salt 1a of hexafluorophosphate are shown below: 1 H NMR (400 MHz, DMSO- d 6): δ = 9.00 (s, 2H), 8.59 (dd, J = 8.0, 4.0 Hz, 4H), 7.79 (t, J = 1.6 Hz, 2H), 7.77 (d, J = 3.2 Hz, 2H), 7.76 (d, J = 3.2 Hz, 2H), 7.59 (t, J = 2.0 Hz, 2H), 6.55 (s, 4H), 4.11 (q, J = 8.0 Hz, 4H), 1.34 (t, J = 6.0 Hz, 6H) ppm. 13 C{ 1 H} NMR (100 MHz, DMSO- d 6): δ= 135.6, 130.7, 127.7,126.9, 124.6, 122.6, 122.2, 44.9, 44.3, 15.2 ppm. HR MS (ESI, positive ions): m / z = 541.1959 (calcd for [H2-1a(PF6)] + 541.1950). Synthesis of S3, tetranuclear copper(I) oxygen cluster 2a: Cs₂CO₃ (256.3 mg, 0.79 mmol), CuCl (51.9 mg, 0.52 mmol), and imidazolium salt 1a (90.0 mg, 0.13 mmol) were added to a prepared 50 mL zirconia ball mill jar (containing 36 grinding balls of the same material with diameters of 5 mm, 4 with diameters of 8 mm, and 4 with diameters of 10 mm). The jar was sealed in an N₂ glove box and placed in a planetary ball mill. The reaction was carried out at 450 rpm for 120 min. After the reaction was completed, a pale yellow solid powder was obtained. The ball mill jar was transferred back to the N₂ glove box, and the product was extracted multiple times with 20 mL of ultra-dry acetonitrile. After centrifugation, a clear yellow solution was obtained. This solution was concentrated to 1 mL and added to 10 mL of ultra-dry diethyl ether, immediately precipitating a large amount of pale yellow solid precipitate. The solid was collected by centrifugation and dried under vacuum to obtain the target product, tetranuclear copper(I) oxygen cluster 2a, with a yield of 89% (78.7 mg, 0.06 mmol).

[0030] The crystal structure of tetranuclear copper(I) oxygen cluster 2a is as follows: Figure 2 As shown; The NMR and mass spectrometry results are shown below: 1 H NMR (400 MHz, DMSO- d 6): δ = 8.22 (dd, J = 7.0, 3.5 Hz, 8H), 7.89 (d, J = 1.6 Hz, 4H), 7.57 (d, J = 4.0 Hz, 4H), 7.55 (d, J = 2.0 Hz, 8H), 6.20 (s,8H), 3.54 (q, J = 10.0 Hz, 8H), 0.88 (t, J = 6.0 Hz, 12H) ppm. 13 C{1 H} NMR (100MHz, DMSO- d 6): δ = 170.1, 130.5, 128.5, 127.3, 124.8, 123.5, 120.9, 46.5,45.8, 16.4 ppm. HR-MS (ESI, positive ions): m / z = 1203.1129 (calcd for [2a-PF6] + 1203.1074). Example 2: A method for preparing a nitrogen-heterocyclic carbene-stabilized tetranuclear copper(I)-oxygen cluster compound 2b, the synthetic reaction formula of which is shown below: ; Specifically, the following steps are included: Synthesis of S1, bidentate imidazole onium salts of bromide ions: 1,4-bis(bromomethyl)naphthalene (0.51 g, 1.62 mmol) and 1-ethylimidazole (0.33 g, 3.41 mmol) were added to a 50 mL Schlenk tube and stirred thoroughly under a nitrogen atmosphere. 5 mL of DMF was added, and the mixture was reacted in an oil bath at 110 °C for 24 h. After the reaction, the mixture was cooled to room temperature, and no significant changes were observed before and after the reaction; both solutions remained colorless and transparent. The resulting liquid was transferred to a 50 mL centrifuge tube, and 30 mL of ethyl acetate was added. A large amount of white precipitate was observed to form. After washing three times with ethyl acetate by centrifugation and drying, a white solid was obtained, which was the bidentate imidazole onium salt of bromide ions.

[0031] Synthesis of S2, bidentate imidazole onion salt of hexafluorophosphate: A white solid was added to a 50 mL pear-shaped flask, and 15 mL of methanol was added dropwise with stirring until completely dissolved, yielding a colorless, clear solution. Upon addition of ammonium hexafluorophosphate (1.32 g, 8.12 mmol), a large amount of white precipitate was observed to form. The mixture was stirred at room temperature for 12 h. After the reaction was complete, the filter cake was collected, washed three times with water and methanol, and dried to obtain a white powder 1b, which is the bidentate imidazole onium salt of hexafluorophosphate. Yield: 85% (0.88 g, 1.38 mmol).

[0032] The NMR and mass spectrometry results of the bidentate imidazole onium salt 1b of hexafluorophosphate are shown below: 1 H NMR (400 MHz, DMSO- d 6): δ= 9.29 (s, 2H), 8.25 (dd, J = 6.4, 3.2 Hz, 2H), 7.84 (t, J = 1.6 Hz, 2H), 7.77 (t, J = 1.6 Hz, 2H), 7.73 (dd, J = 8.0, 4.0Hz, 2H), 7.52 (s, 2H), 4.20 (q, J = 8.0 Hz, 4H), 1.41 (t, J = 8.0 Hz, 6H) ppm. 13 C{ 1 H} NMR (100 MHz, DMSO- d 6): δ = 136.2, 131.8, 130.8, 127.7, 127.2, 124.0,122.9, 122.5, 49.8, 44.5, 15.1 ppm. HR-MS (ESI, positive ions): m / z = 491.1843(calcd for [H2-1b(PF6)] + 491.1794). Synthesis of S3, tetranuclear copper(I) oxygen cluster 2b: Cs₂CO₃ (276.5 mg, 0.85 mmol), CuCl (56.0 mg, 0.57 mmol), and imidazolium salt 1b (90.0 mg, 0.14 mmol) were added to a prepared 50 mL zirconia ball mill jar (containing 36 grinding balls of the same material with diameters of 5 mm, 4 with diameters of 8 mm, and 4 with diameters of 10 mm). The jar was sealed in an N₂ glove box and placed in a planetary ball mill. The reaction was carried out at 450 rpm for 120 min. After the reaction was completed, a pale yellow solid powder was obtained. The ball mill jar was transferred back to the N₂ glove box, and the product was extracted multiple times with 20 mL of ultra-dry acetonitrile. After centrifugation, a colorless and clear solution was obtained. This solution was concentrated to 1 mL and added to 10 mL of ultra-dry diethyl ether, immediately precipitating a large amount of pale yellow solid precipitate. The solid was collected by centrifugation and dried under vacuum to obtain the target product, tetranuclear copper(I) oxygen cluster 2b, with a yield of 67% (59.2 mg, 0.05 mmol).

[0033] The crystal structure of tetranuclear copper(I) oxygen cluster 2b is as follows: Figure 3 As shown; The NMR and mass spectrometry results are shown below: 1 H NMR (400 MHz, DMSO- d 6): δ = 7.82 (d, J = 1.6 Hz, 4H), 7.81 (s, 4H), 7.64 (dd, J = 6.4, 3.2 Hz, 4H), 7.56 (d, J = 1.6 Hz, 4H), 7.50 (dd, J = 8.0, 4.0Hz, 4H), 5.98 (d, J = 14.4 Hz, 2H), 5.36 (d, J = 14.4 Hz, 2H), 3.87 (br, 8H), 1.11 (t, J = 6.0 Hz, 12H) ppm. 13 C{ 1 H} NMR (100 MHz, DMSO- d 6): δ = 171.0, 133.4,131.8, 130.2, 127.2, 124.5, 123.2, 120.1, 52.0, 46.5, 16.6 ppm. HR-MS (ESI, positive ions): m / z = 1103.0889 (calcd for [2b-PF6] + 1103.0759). Example 3: A method for preparing a nitrogen-heterocyclic carbene-stabilized tetranuclear copper(I)-oxygen cluster compound 2c, the synthetic reaction formula of which is shown below: ; Specifically, the following steps are included: Synthesis of S1, bidentate imidazole salts of chloride ions: 9,10-Di(chloromethyl)anthracene (0.62 g, 2.25 mmol) and N-benzylimidazole (0.75 g, 4.73 mmol) were added to a 50 mL Schlenk tube and stirred thoroughly under a nitrogen atmosphere. 5 mL of DMF was added, and the mixture was reacted in an oil bath at 120 °C for 24 h. After the reaction was complete, the mixture was cooled to room temperature, and the reaction solution changed from a clear yellow solution to a brownish-yellow turbidity with a yellow precipitate. The reacted liquid was transferred to a 50 mL centrifuge tube, and 30 mL of ethyl acetate was added. A large amount of yellow precipitate was observed to precipitate. The precipitate was washed three times with ethyl acetate by centrifugation and dried to obtain a yellow solid, which was the bidentate imidazole onium salt of chloride ions.

[0034] Synthesis of S2, bidentate imidazole onion salt of hexafluorophosphate: The yellow solid was added to a 50 mL round-bottom flask, and 15 mL of methanol was added dropwise with stirring until completely dissolved, yielding a clear, brownish-yellow solution. Upon addition of ammonium hexafluorophosphate (1.84 g, 11.27 mmol), a large amount of yellow precipitate was observed to form. The mixture was stirred at room temperature for 12 h. After the reaction was complete, the filter cake was collected, washed three times with water and methanol, and dried to obtain a yellow powder, 1c, which is the bidentate imidazole onium salt of hexafluorophosphate. Yield: 91% (1.66 g, 2.05 mmol).

[0035] The NMR and mass spectrometry results of bidentate imidazole onium salts of hexafluorophosphate 1c are shown below: 1 H NMR (400 MHz, DMSO- d 6): δ = 9.20 (s, 2H), 8.60 (dd, J = 8.0, 4.0 Hz,4H), 7.73-7.81 (m, 6H), 7.56 (br, 2H), 7.35-7.42 (m, 6H), 7.27-7.34 (m, 4H),6.58 (s, 2H), 5.34 (s, 4H) ppm. 13 C{ 1 H} NMR (100 MHz, DMSO- d 6): δ = 136.1,134.8, 130.7, 129.0, 128.8, 128.1, 127.7, 127.0, 124.6, 122.9, 122.7, 52.0,45.1 ppm. HR-MS (ESI, positive ions): m / z= 665.2246 (calcd for [H2-1c(PF6)] + 665.2263). Synthesis of S3, tetranuclear copper(I) oxygen cluster 2c: Cs₂CO₃ (217.0 mg, 0.67 mmol), CuCl (44.0 mg, 0.44 mmol), and imidazolium salt 1c (90.0 mg, 0.11 mmol) were added to a prepared 50 mL zirconia ball mill jar (containing 36 grinding balls of the same material with diameters of 5 mm, 4 with diameters of 8 mm, and 4 with diameters of 10 mm). The jar was sealed in an N₂ glove box and placed in a planetary ball mill. The reaction was carried out at 450 rpm for 120 min. After the reaction was completed, a pale yellow solid powder was obtained. The ball mill jar was transferred back to the N₂ glove box, and the product was extracted multiple times with 20 mL of ultra-dry acetonitrile. After centrifugation, a clear yellow solution was obtained. This solution was concentrated to 1 mL and added to 10 mL of ultra-dry diethyl ether, immediately precipitating a large amount of pale yellow solid precipitate. The solid was collected by centrifugation and dried under vacuum to obtain the target product, tetranuclear copper(I) oxygen cluster 2c, with a yield of 91% (80.7 mg, 0.05 mmol).

[0036] The crystal structure of tetranuclear copper(I) oxygen cluster 2c is as follows: Figure 4 As shown; The NMR and mass spectrometry results are shown below: 1 H NMR (400 MHz, DMSO- d 6): δ = 8.01 (br, 4H), 7.95 (dd, J = 7.2, 2.6 Hz,8H), 7.53 (br, 2H), 7.50 (dd, J = 6.4, 3.2 Hz, 8H), 7.10 ppm (t, J = 8.0 Hz, 4H), 6.93 (t, J = 8.0 Hz, 8H), 6.56 (d, J = 8.0 Hz, 8H), 6.02 (s, 8H), 4.42 (s, 8H) ppm. 13 C{ 1 H} NMR (100 MHz, DMSO- d 6): δ= 171.9, 136.4, 130.2, 128.5, 128.4,127.6, 127.3, 126.4, 124.5, 124.0, 121.8, 54.3, 45.7 ppm. HR-MS (ESI, positive ions): m / z = 1451.1632 (calcd for [2c-PF6] + 1451.1705). Example 4: A method for preparing a nitrogen-heterocyclic carbene-stabilized tetranuclear copper(I)-oxygen cluster compound 2d, the synthetic reaction formula of which is shown below: ; Specifically, the following steps are included: Synthesis of S1, bidentate imidazole salts of chloride ions: 9,10-Di(chloromethyl)anthracene (0.75 g, 2.73 mmol) and N-benzylbenzimidazole (1.19 g, 5.72 mmol) were added to a 50 mL Schlenk tube and stirred thoroughly under a nitrogen atmosphere. 5 mL of DMF was added, and the mixture was reacted in an oil bath at 120 °C for 24 h. After the reaction was complete, the mixture was cooled to room temperature, and the reaction solution changed from a yellow turbidity to a brownish-yellow turbidity. The reacted liquid was transferred to a 50 mL centrifuge tube, and 30 mL of ethyl acetate was added. A large amount of dark yellow precipitate was observed to precipitate. The precipitate was washed three times with ethyl acetate by centrifugation and dried to obtain a dark yellow solid, which was the bidentate imidazole onium salt of chloride ions.

[0037] Synthesis of S2, bidentate imidazole onion salt of hexafluorophosphate: A deep yellow solid was added to a 50 mL round-bottom flask, and 15 mL of methanol was added dropwise with stirring until completely dissolved, yielding a clear, brownish-yellow solution. Upon addition of ammonium hexafluorophosphate (2.22 g, 13.63 mmol), a large amount of yellow precipitate was observed to form. The mixture was stirred at room temperature for 12 h. After the reaction was complete, the filter cake was collected, washed three times with water and methanol, and dried to obtain a deep yellow powder, which was the bidentate imidazole onium salt of hexafluorophosphate. Yield: 81% (2.01 g, 2.21 mmol).

[0038] The NMR and mass spectrometry results of the bidentate imidazole onium salts of hexafluorophosphate for 1 day are shown below: 1 H NMR (400 MHz, DMSO- d 6): δ = 8.91 (s, 2H), 8.17 (dd, J= 8.0, 4.0 Hz, 2H), 7.89 (d, J = 8.0 Hz, 2H), 7.52 (d, J = 8.0 Hz, 2H), 7.77-7.82 (m, 6H),7.28 (t, J = 8.0 Hz, 2H), 7.31-7.37 (m, 4H), 6.87-6.91 (m, 6H), 6.81-6.84 (m,4H), 6.45 (s, 4H), 5.16 (s, 2H) ppm. 13 C{ 1 H} NMR (100 MHz, DMSO- d 6): δ = 141.7,134.2, 132.0, 131.1, 128.9, 127.9, 127.7, 127.2, 127.0, 126.1, 124.8, 114.6,114.1, 49.8, 43.8 ppm. HR-MS (ESI, positive ions): m / z = 765.2522 (calcd for[H2-1d(PF6)] + 765.2576). Synthesis of S3, tetranuclear copper(I) oxygen cluster 2d: Cs₂CO₃ (227.8 mg, 0.70 mmol), CuCl (39.1 mg, 0.40 mmol), and imidazolium salt 1d (90.0 mg, 0.10 mmol) were added to a prepared 50 mL zirconia ball mill jar (containing 36 grinding balls of the same material with diameters of 5 mm, 4 with diameters of 8 mm, and 4 with diameters of 10 mm). The jar was sealed in an N₂ glove box and placed in a planetary ball mill. The reaction was carried out at 450 rpm for 120 min. After the reaction was completed, a pale yellow solid powder was obtained. The ball mill jar was transferred back to the N₂ glove box, and the product was extracted multiple times with 20 mL of ultra-dry acetonitrile. After centrifugation, a clear yellow solution was obtained. This solution was concentrated to 1 mL and added to 10 mL of ultra-dry diethyl ether, immediately precipitating a large amount of pale yellow solid precipitate. The solid was collected by centrifugation and dried under vacuum to obtain the target product, tetranuclear copper(I) oxygen cluster 2d, with a yield of 96% (85.3 mg, 0.05 mmol).

[0039] The crystal structure of tetranuclear copper(I)oxy cluster 2d is as follows: Figure 5 As shown; The NMR and mass spectrometry results are shown below: 1 H NMR (400 MHz, DMSO- d 6): δ = 8.15 (d, J = 8.0 Hz, 4H), 7.94 (dd, J =8.0, 4.0 Hz, 8H), 7.57-7.61 (m, 4H), 7.45-7.50 (m, 16H), 6.83-6.92 (m, 12H), 6.79 (d, J = 8.0 Hz, 8H), 6.23 (s, 8H), 4.87 (s, 8H) ppm. 13 C{ 1 H} NMR (100 MHz, DMSO- d 6): δ = 179.8, 134.0, 134.5, 132.7, 130.6, 128.1, 127.7, 127.6, 126.5,124.8, 124.6, 124.3, 112.3, 52.5, 43.5 ppm. HR-MS (ESI, positive ions): m / z =1651.2335 (calcd for [2d-PF6] + 1651.2336). Experimental Example 1: Performance Test of Electrocatalytic Carbon Dioxide Reduction I. Sample preparation and experimental equipment setup: (1) Preparation of test samples: The preparation steps of the working electrode are as follows: 10 mg of tetranuclear copper(I) oxygen cluster compound was placed in a mortar, and 1 mL of isopropanol was gradually added while grinding. After thorough grinding, the suspension was extracted, and 200 µL of distilled water and 40 μL of Nafion were added. After sonication for 1 h, a uniformly dispersed sample was obtained. 100 µL of the sample was spread in batches on a 1×1 cm plate. 2 Apply the gas diffusion carbon paper (YLS-30 T) and dry it in air until ready for use.

[0040] (2) Flow cell: Electrochemical measurements at high current densities were performed in a flow cell consisting of a gas diffusion electrode (using a CHI1140E electrochemical workstation), an anion exchange membrane, and a carbon paper gas diffusion layer anode. A Hg / HgO electrode (1.0 mol / L KOH solution) was used as the reference electrode, and platinum foil as the counter electrode. A 1.0 mol / L KOH aqueous solution was used as the electrolyte and circulated on the anode side by a peristaltic pump. High-purity CO2 (99.9999%) gas was introduced at a flow rate of 30 mL / min. -1 A constant flow rate is supplied to the cathode side via a flow controller.

[0041] II. Testing of electrocatalytic carbon dioxide reduction performance: (1) Linear scanning voltammetry test: Samples 2a-2d were subjected to linear sweep voltammetry (LSV) tests in a flow cell apparatus under saturated argon and carbon dioxide atmospheres, respectively, at a scan rate of 100 mV / s. -1 .

[0042] Experimental results are as follows Figure 6 As shown.

[0043] The results showed that the current response of 2a-2d under a carbon dioxide atmosphere was significantly better than that under an argon atmosphere, indicating that 2a-2d all have good CO2 responsiveness and preferential activity for CO2 reduction. Among them, 2a and 2c showed the most significant response under a CO2 atmosphere. Furthermore, no characteristic Cu was found within the range of the LSV's applied potential. + The electroreduction signal indicates that copper in the catalyst possesses a certain degree of stability in its structure.

[0044] (2) Faraday efficiency test of electrocatalytic products: A bar chart showing the Faraday efficiency and corresponding potential of each product of electrocatalytic carbon dioxide reduction, calculated using gas chromatography and hydrogen nuclear magnetic resonance spectroscopy.

[0045] Experimental results are as follows Figures 7-10 As shown in the figure and Table 1.

[0046] Figures 7-10 The results show that the main products of clusters 2a-2d are all methane, and they exhibit a "volcano" pattern of first increasing and then decreasing with increasing potential, while hydrogen, the product of the competing hydrogen evolution reaction, shows a trend of first decreasing and then increasing.

[0047] Table 1. Performance test results of electrocatalytic carbon dioxide reduction of tetranuclear copper(I) oxygen clusters 2a-2d

[0048] As can be seen from Table 1, the tetranuclear copper(I) oxygen cluster compound prepared by this invention can be successfully applied to the battery for electrocatalytic carbon dioxide reduction, exhibiting high methane selectivity and current density. This solves the problem of low selectivity of existing copper-based catalysts and has potential application value in the industrial electrocatalytic preparation of methane fuel.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A tetranuclear copper(I) oxygen cluster compound stabilized by an all-nitrogen heterocyclic carbene, characterized in that, The general structural formula is shown in Formula I: Formula I: ; In formula I, It has any of the following structures: , and ; It has any of the following structures: and .

2. The all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound according to claim 1, characterized in that, The structural formula can be selected from any of the following: , , and .

3. The method for preparing the all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound according to claim 1 or 2, characterized in that, Includes the following steps: S1. 9,10-dichloromethylanthracene or 1,4-dibromomethylnaphthalene reacts with a 1-substituted imidazole compound in a solvent by heating to obtain a bidentate imidazole onium salt of a halide ion. S2. The bidentate imidazole onion salt of halide ions obtained in S1 is ion exchanged with ammonium hexafluorophosphate in a solvent to obtain the bidentate imidazole onion salt of hexafluorophosphate. S3. The bidentate imidazole onium salt, cuprous salt and cesium carbonate obtained in S2 were mixed and ball-milled to obtain a tetranuclear copper(I) oxygen cluster stable by all-nitrogen heterocyclic carbene.

4. The method for preparing the all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound according to claim 3, characterized in that, The reaction temperature in S1 is 100-150 ℃, and the reaction time is 24-96 h.

5. The method for preparing the all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound according to claim 3, characterized in that, The 1-substituted imidazole compound in S1 is selected from... , and .

6. The method for preparing the all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound according to claim 3, characterized in that, The reaction in S2 is carried out at room temperature for 10-15 hours.

7. The method for preparing the all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound according to claim 3, characterized in that, The molar ratio of bidentate imidazole onium salt, cuprous salt and cesium carbonate in S3 is 1:(3-5):(5-7); the cuprous salt includes cuprous chloride.

8. The method for preparing the all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound according to claim 3, characterized in that, In S3, the ball milling speed is 300-600 rpm and the time is 60-180 min.

9. The application of the all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound as described in claim 1 or 2 in electrocatalytic carbon dioxide reduction.

10. A precursor for preparing the all-nitrogen heterocyclic carbene-stabilized tetranuclear copper(I) oxygen cluster compound as described in claim 1 or 2, characterized in that, The general structural formula is shown in Formula II: Formula II: ; In formula II, It has any of the following structures: , and ; It has any of the following structures: and .

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