An imidazole-pyridine bidentate ligand, a synthesis method thereof, a metal catalyst prepared by the same, and application thereof

Abstract

The application provides an imidazole-pyridine bidentate ligand, a synthesis method thereof, a metal catalyst prepared from the imidazole-pyridine bidentate ligand and application of the metal catalyst, and relates to the technical field of catalyst preparation.The synthesis method of the imidazole-pyridine bidentate ligand developed by the application is simple, the synthesis of the ligand only needs two reaction steps, and the total yield can reach 58%; the synthesized imidazole-pyridine bidentate ligand has good stability and can be stored for a long time in an air environment; compared with the existing preparation method of a copper-nitrogen heterocyclic carbene complex catalyst, the imidazole-pyridine bidentate ligand connected with a mesitylene substituent is prepared into a catalyst with metal nickel, and the catalyst has high catalytic activity and good reaction activity in a carbon dioxide carboxylation reaction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalyst preparation for synthesizing acrylic acid from carbon dioxide, and particularly relates to an imidazole-pyridine bidentate ligand, a metal catalyst, a synthesis method and application thereof. BACKGROUND

[0002] Carbon dioxide is not only a greenhouse gas, but also an important and effective carbon resource. It is abundant, non-toxic, non-polluting and non-flammable, and can be used to produce organic chemicals, materials, sugars and the like. Because the carbon in the carbon dioxide molecule is in the highest oxidation state, and the molecule has thermodynamic and kinetic inertness, people are constantly exploring new reaction pathways and new catalytic systems to effectively utilize carbon dioxide as a resource. In recent years, the use of various unsaturated hydrocarbons to catalyze carbon dioxide and olefins to generate unsaturated carboxylic acids and their derivatives under the assistance of transition metal catalysts has attracted great attention. Among them, the carboxylation reaction of carbon dioxide and ethylene to prepare acrylic acid and its derivatives is particularly noteworthy due to its atomic economy. The transition metal catalytic reaction of the nickel-based catalytic system is one of the very important research hotspots for carbon dioxide chemical conversion and high-value utilization.

[0003] The carboxylation reaction of carbon dioxide and ethylene is a metal catalyst catalyzed reaction of ethylene and carbon dioxide. The reaction mechanism is that the metal catalyst activates carbon dioxide and then reacts with ethylene to generate a propionic acid metal lactone ring intermediate. This intermediate can be hydrolyzed or undergo β-H elimination under the action of heat or acid and base, while the metal catalyst leaves and enters the next catalytic cycle, and finally propenoic acid or propionic acid compounds are obtained.

[0004] From the reaction mechanism, the metal catalyst activates carbon dioxide and reacts with ethylene to form a propionic acid metal lactone ring, which is a key intermediate in the carbon dioxide carboxylation reaction. Generally, the catalytic activity and stability of the metal catalyst are important factors affecting the reaction rate of the propionic acid metal lactone ring. In 2019, a Japanese research team reported an alkyl phosphine-substituted imidazole-based ligand (Chem. Eur. J. 2019, 25, 13504-13508). This ligand can generate a carbene intermediate under the action of strong base to form a phosphine-carbene bidentate coordinated metal nickel catalyst. This carbene coordinated nickel catalyst has good stability and catalytic activity, and the highest conversion number of the carbon dioxide carboxylation reaction catalyzed by it can reach 450, which is the highest conversion number of the carbon dioxide carboxylation reaction without the participation of a reducing metal. However, this type of ligand also has many problems, such as a complex synthesis route and a low yield, and the total synthesis yield is only 39.3%. In addition, the dicyclohexyl phosphine in the ligand is easily oxidized, and the storage and use conditions of the ligand are harsh. Moreover, some existing technologies are only suitable for the preparation of copper nitrogen heterocyclic carbene complex catalysts, and the preparation effect of bidentate nickel carbene catalysts is not good. In order to solve the above problems, it is of great significance to develop an imidazole-based ligand which has a simple synthesis method, is easy to store and use, and is suitable for bidentate nickel catalysts. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides an imidazole-pyridine bidentate ligand, a synthesis method thereof, a metal catalyst coordinated therewith, and a method for preparing acrylic acid by carboxylation reaction of carbon dioxide and ethylene. The synthesis method of the imidazole-pyridine bidentate ligand designed and developed by the present application is simple, and the synthesis of the ligand only requires two-step reaction, and the total yield can reach 58%. The synthesized imidazole-pyridine bidentate ligand has good stability and can be stored for a long time in an air environment. Compared with the existing copper nitrogen heterocyclic carbene complex catalyst preparation method, the imidazole-pyridine bidentate ligand connected with mesitylene substituent has high catalytic activity when prepared into a catalyst with nickel, and exhibits good reaction activity in the carbon dioxide carboxylation reaction.

[0006] One of the purposes of the present application is to provide an imidazole-pyridine bidentate ligand.

[0007] The second purpose of the present application is to provide a synthesis method of the imidazole-pyridine bidentate ligand.

[0008] The third purpose of the present application is to provide a metal catalyst made of the imidazole-pyridine bidentate ligand.

[0009] The fourth purpose of the present application is to provide an application of the metal catalyst.

[0010] In order to achieve the above-mentioned purposes of the present application, the following technical solutions are adopted:

[0011] In a first aspect, the present application provides an imidazole-pyridine bidentate ligand having the following formula I:

[0012]

[0013] wherein anion X - is selected from Cl - , Br - , I - .

[0014] In a second aspect, the present application provides a method for synthesizing the above imidazole-pyridine bidentate ligand, comprising the following steps:

[0015]

[0016] S1: heating reaction of mesitylamine, 2,3-butanedione and paraformaldehyde in the presence of ammonium acetate and acetic acid, adjusting the pH value of the system to 9 after the reaction, and obtaining a mesityl-substituted imidazole derivative after purification;

[0017] S2: substitution reaction of the mesityl-substituted imidazole derivative obtained in S1 with 2-halogenomethylpyridine to obtain the imidazole-pyridine bidentate ligand.

[0018] In some embodiments, in step S1, the molar ratio of mesitylamine, 2,3-butanedione and paraformaldehyde is 1:1:1.5 to 1:1:2.5.

[0019] In some embodiments, in step S1, the molar ratio of mesitylamine and ammonium acetate is 1:1 to 1:1.5.

[0020] In some embodiments, in step S1, the molar ratio of mesitylamine and acetic acid is 1:3 to 1:8.

[0021] In some embodiments, in step S1, the reaction temperature is 130-160°C, and the reaction time is 10-15 hours.

[0022] In some embodiments, the purification of step S1 comprises the following steps:

[0023] The mixture after the reaction is extracted with ethyl acetate three times, the obtained organic phase is mixed, washed with saturated brine and dried with anhydrous sodium sulfate, the clarified organic phase is filtered under reduced pressure after filtration to remove the solvent, and the obtained brown viscous oil is purified by column chromatography to obtain the mesityl-substituted imidazole derivative.

[0024] In some embodiments, step S2 comprises:

[0025] The mesitylene-substituted imidazole derivative prepared in S1 is dissolved in anhydrous tetrahydrofuran to obtain a tetrahydrofuran solution of the mesitylene-substituted imidazole derivative, and then sodium hydride is slowly added in batches. After the reaction, the tetrahydrofuran solution of 2-halogenomethylpyridine is dropped into the reaction system, and stirred at room temperature overnight. The precipitate is filtered out to obtain the imidazole-pyridine bidentate ligand.

[0026] In some embodiments, in step S2, the molar ratio of the mesitylene-substituted imidazole derivative to 2-halogenomethylpyridine is 1:1 to 1:1.2.

[0027] In some embodiments, in step S2, the molar ratio of the mesitylene-substituted imidazole derivative to sodium hydride is 1:1.1 to 1:1.5.

[0028] Specifically, the synthesis method of the imidazole-pyridine bidentate ligand comprises the following steps:

[0029] (1) Mesitylene amine, 2,3-butanedione, paraformaldehyde, ammonium acetate and acetic acid are added to a round-bottom flask for heating reaction, and then the temperature is reduced to room temperature, and the pH value of the reaction system is adjusted to 9 with 1N potassium carbonate solution;

[0030] (2) The mixture prepared in step (1) is extracted with ethyl acetate three times (100 mL x 3), and the obtained organic phase is mixed, washed with saturated brine, and then dried with anhydrous sodium sulfate. After suction filtration, the clear ethyl acetate solution is distilled under reduced pressure to remove the solvent, and the obtained brown viscous oil is purified by column chromatography to obtain the mesitylene-substituted imidazole derivative;

[0031] (3) The mesitylene-substituted imidazole derivative prepared in step (2) is dissolved in anhydrous tetrahydrofuran to obtain a tetrahydrofuran solution of the mesitylene-substituted imidazole derivative (concentration of 0.2 mol / L), and then sodium hydride is slowly added in batches. After half an hour of reaction, the tetrahydrofuran solution (concentration of 0.5 mol / L) of 2-halogenomethylpyridine is dropped into the reaction system, and finally stirred at room temperature overnight. The precipitate is filtered out to obtain the imidazole-pyridine bidentate ligand.

[0032] In a third aspect, the present application provides a metal catalyst prepared from the above-mentioned imidazole-pyridine bidentate ligand by the following method:

[0033] In a glove box, 0.1 mmol of the above-mentioned imidazole-pyridine bidentate ligand is placed in a 20 mL Schlenk tube, then 2 mL of anhydrous solvent is added, and it is fully stirred to make it uniformly dispersed, then 0.11 mmol of potassium tert-butoxide is slowly added, and after stirring for 30 minutes, the reaction system becomes a yellow solution. Finally, 0.1 mmol of a metal compound is added and stirred for 2 hours to obtain the metal catalyst.

[0034] In some embodiments, the anhydrous solvent is anhydrous tetrahydrofuran or anhydrous toluene.

[0035] In some embodiments, the metal compound is bis-(1,5-cyclooctadiene)nickel or (1,5-cyclooctadiene)palladium(II) dichloride.

[0036] In the fourth aspect, the application provides a use of the above-mentioned metal catalyst in the carboxylation reaction of carbon dioxide and ethylene to prepare acrylic acid.

[0037] In some embodiments, the use comprises the following steps: adding the β-H elimination promoter, the metal catalyst and the solvent into a reaction kettle, sealing, filling carbon dioxide to a pressure of 1.0-2.0 MPa in the reaction kettle, and then filling the reaction kettle with ethylene to a specified pressure of 4.0-5.0 MPa for reaction.

[0038] The reaction is a heterogeneous reaction in a kettle reactor.

[0039] Preferably, the β-H elimination promoter is one of sodium tert-butoxide, sodium phenoxide and sodium acetate, and preferably sodium tert-butoxide.

[0040] Preferably, the molar ratio of the metal catalyst to the β-H elimination promoter is 1:100-1:500, and preferably 1:200-1:300.

[0041] Preferably, the solvent is one of tetrahydrofuran, anisole, toluene, dimethyl sulfoxide and N-methyl pyrrolidone, and preferably tetrahydrofuran.

[0042] Preferably, the mass purity of carbon dioxide is 90%-100%, and the mass purity of ethylene is 90%-100%.

[0043] Preferably, the reaction temperature is 80-160℃, and preferably 130-140℃; and the reaction time is 12-24h, and preferably 15-18h.

[0044] Technical effects:

[0045] 1. The imidazole-pyridine bidentate ligand designed and developed by the application has a simple synthesis method, and the synthesis of the ligand only needs two-step reaction, and the total yield can reach 58%.

[0046] 2. The synthesized imidazole-pyridine bidentate ligand has good stability and can be stored for a long time in an air environment.

[0047] 3. The imidazole-pyridine bidentate ligand connected with mesitylene substituent group and the metal nickel prepared into a catalyst show good reactivity in the carboxylation reaction of carbon dioxide.

[0048] The application has been described in detail above, but the above embodiments are merely illustrative in nature and are not intended to limit the application. Furthermore, the present application is not limited by any theory of prior art or the following examples or the following examples described in the following examples. DETAILED DESCRIPTION

[0049] The application will be further described in conjunction with the following examples. It should be noted that the following examples are provided for illustration purposes only and do not constitute a limitation on the scope of the application.

[0050] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0051] TON (Turnover Number): represents the number of catalytic reactions or the number of target product generated per unit active site under certain conditions. It measures the catalytic efficiency and capacity of the catalyst.

[0052] The calculation method of the carbon dioxide carboxylation reaction TON is: the number of moles of sodium acrylate generated / the number of moles of catalyst added.

[0053] Example 1

[0054] In a 100ml round-bottom flask, mesitylamine (10mmol), 2,3-butanedione (10mmol), paraformaldehyde (15mmol), ammonium acetate (10mmol) and acetic acid (2.0mL) were added, and then the reaction temperature was raised to 130°C for 10 hours; after the reaction was completed, the temperature was lowered to room temperature, the pH value of the reaction system was adjusted to 9 with 1N potassium carbonate solution, and the organic phase was extracted with ethyl acetate three times (100mL x 3), then the obtained organic phase was mixed, washed with saturated brine and dried with anhydrous sodium sulfate, filtered and the clear ethyl acetate solution was distilled under reduced pressure to remove the solvent, and the brown viscous oil obtained was purified by column chromatography to obtain a mesityl-substituted imidazole derivative with a yield of 57%. The prepared mesityl-substituted imidazole derivative (5.7mmol) was dissolved in anhydrous tetrahydrofuran, and then sodium hydride (6.3mmol) was added slowly in batches, after half an hour of reaction, 2-chloromethylpyridine (5.7mmol) was dissolved in 20mL of tetrahydrofuran and added dropwise into the reaction system, and finally stirred overnight at room temperature, the precipitate was filtered out to obtain an imidazole-pyridine ligand with a total yield of 41%.

[0055] Example 2

[0056] In a 100 ml round bottom flask, mesitylamine (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (2.0 mL) were added, and then the reaction temperature was raised to 130 °C for 10 hours; after the reaction was completed, the temperature was lowered to room temperature, the pH of the reaction system was adjusted to 9 with 1 N potassium carbonate solution, and the organic phase was extracted three times with ethyl acetate (100 mL x 3). The obtained organic phase was mixed, washed with saturated brine, and dried with anhydrous sodium sulfate. After filtration, the clear ethyl acetate solution was distilled under reduced pressure to remove the solvent, and the brown viscous oil obtained was purified by column chromatography to obtain a mesityl-substituted imidazole derivative with a yield of 60%. The prepared mesityl-substituted imidazole derivative (6.0 mmol) was dissolved in anhydrous tetrahydrofuran, and then sodium hydride (6.6 mmol) was slowly added in batches. After half an hour of reaction, 2-chloromethylpyridine (6.0 mmol) was dissolved in 20 mL of tetrahydrofuran and added dropwise into the reaction system. Finally, the mixture was stirred at room temperature overnight, and the precipitate was filtered to obtain an imidazole-pyridine ligand with a yield of 45%.

[0057] Example 3

[0058] In a 100 ml round bottom flask, mesitylamine (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (2.0 mL) were added, and then the reaction temperature was raised to 160 °C for 15 hours; after the reaction was completed, the temperature was lowered to room temperature, the pH of the reaction system was adjusted to 9 with 1 N potassium carbonate solution, and the organic phase was extracted three times with ethyl acetate (100 mL x 3). The obtained organic phase was mixed, washed with saturated brine, and dried with anhydrous sodium sulfate. After filtration, the clear ethyl acetate solution was distilled under reduced pressure to remove the solvent, and the brown viscous oil obtained was purified by column chromatography to obtain a mesityl-substituted imidazole derivative with a yield of 68%. The prepared mesityl-substituted imidazole derivative (6.8 mmol) was dissolved in anhydrous tetrahydrofuran, and then sodium hydride (7.5 mmol) was slowly added in batches. After half an hour of reaction, 2-chloromethylpyridine (6.8 mmol) was dissolved in 20 mL of tetrahydrofuran and added dropwise into the reaction system. Finally, the mixture was stirred at room temperature overnight, and the precipitate was filtered to obtain an imidazole-pyridine ligand with a total yield of 51%.

[0059] Example 4

[0060] In a 100 ml round bottom flask, mesitylamine (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (5.0 mL) were added, and then the reaction temperature was raised to 160 °C for 15 hours; after the reaction was completed, the temperature was lowered to room temperature, and the pH of the reaction system was adjusted to 9 with a 1 N potassium carbonate solution, and then extracted three times with ethyl acetate (100 mL x 3), the organic phase was mixed, washed with saturated brine, and then dried over anhydrous sodium sulfate, filtered, and then the clear ethyl acetate solution was distilled under reduced pressure to remove the solvent, and the brown viscous oil obtained was purified by column chromatography to obtain a mesityl-substituted imidazole derivative, with a yield of 65%. The prepared mesityl-substituted imidazole derivative (6.5 mmol) was dissolved in anhydrous tetrahydrofuran, and then sodium hydride (7.2 mmol) was slowly added in batches, and after half an hour of reaction, 2-chloromethylpyridine (6.5 mmol) was dissolved in 20 mL of tetrahydrofuran and added dropwise into the reaction system, and finally stirred overnight at room temperature, and then the precipitate was filtered to obtain an imidazole-pyridine ligand, with a total yield of 48%.

[0061] Example 5

[0062] In a 100 ml round bottom flask, mesitylamine (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (2.0 mL) were added, and then the reaction temperature was raised to 160 °C for 15 hours; after the reaction was completed, the temperature was lowered to room temperature, and the pH of the reaction system was adjusted to 9 with a 1 N potassium carbonate solution, and then extracted three times with ethyl acetate (100 mL x 3), the organic phase was mixed, washed with saturated brine, and then dried over anhydrous sodium sulfate, filtered, and then the clear ethyl acetate solution was distilled under reduced pressure to remove the solvent, and the brown viscous oil obtained was purified by column chromatography to obtain a mesityl-substituted imidazole derivative, with a yield of 68%. The prepared mesityl-substituted imidazole derivative (6.8 mmol) was dissolved in anhydrous tetrahydrofuran, and then sodium hydride (7.5 mmol) was slowly added in batches, and after half an hour of reaction, 2-chloromethylpyridine (8.2 mmol) was dissolved in 20 mL of tetrahydrofuran and added dropwise into the reaction system, and finally stirred overnight at room temperature, and then the precipitate was filtered to obtain an imidazole-pyridine ligand, with a total yield of 53%.

[0063] Example 6

[0064] In a 100 ml round bottom flask, mesitylamine (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (5.0 mL) were added, and then the reaction temperature was raised to 160°C for 15 hours. After the reaction was completed, the temperature was lowered to room temperature, and the pH of the reaction system was adjusted to 9 with 1 N potassium carbonate solution. The organic phase was extracted three times with ethyl acetate (100 mL x 3), and then the obtained organic phase was mixed, washed with saturated brine, and dried with anhydrous sodium sulfate. After the filtration, the clear ethyl acetate solution was distilled under reduced pressure to remove the solvent, and the obtained brown viscous oil was purified by column chromatography to obtain a mesityl-substituted imidazole derivative with a yield of 68%. The obtained mesityl-substituted imidazole derivative (6.8 mmol) was dissolved in anhydrous tetrahydrofuran, and then sodium hydride (10.2 mmol) was slowly added in batches. After half an hour, 2-chloromethylpyridine (8.2 mmol) was dissolved in 20 mL of tetrahydrofuran and then added dropwise into the reaction system. Finally, the mixture was stirred at room temperature overnight, and the precipitate was filtered to obtain an imidazole-pyridine ligand with a total yield of 58%.

[0065] Example 7

[0066] In a 100 ml round bottom flask, mesitylamine (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (5.0 mL) were added, and then the reaction temperature was raised to 160°C for 15 hours. After the reaction was completed, the temperature was lowered to room temperature, and the pH of the reaction system was adjusted to 9 with 1 N potassium carbonate solution. The organic phase was extracted three times with ethyl acetate (100 mL x 3), and then the obtained organic phase was mixed, washed with saturated brine, and dried with anhydrous sodium sulfate. After the filtration, the clear ethyl acetate solution was distilled under reduced pressure to remove the solvent, and the obtained brown viscous oil was purified by column chromatography to obtain a mesityl-substituted imidazole derivative with a yield of 68%. The obtained mesityl-substituted imidazole derivative (6.8 mmol) was dissolved in anhydrous tetrahydrofuran, and then sodium hydride (10.2 mmol) was slowly added in batches. After half an hour, 2-chloromethylpyridine (7.5 mmol) was dissolved in 20 mL of tetrahydrofuran and then added dropwise into the reaction system. Finally, the mixture was stirred at room temperature overnight, and the precipitate was filtered to obtain an imidazole-pyridine ligand with a total yield of 55%.

[0067] Each example was prepared according to the following method to prepare an imidazole-pyridine-nickel catalyst:

[0068] In a glove box, 0.1 mmol of imidazole-pyridine bidentate ligand was taken into a 20 mL Schlenk tube, then 2 mL of anhydrous tetrahydrofuran was added, and it was stirred to disperse uniformly, then 0.11 mmol of potassium tert-butoxide was slowly added, and after stirring for 30 minutes, the reaction system became a yellow solution, and finally 0.1 mmol of bis-(1,5-cyclooctadiene) nickel was added and stirred for 2 hours to prepare an imidazole-pyridine-nickel catalyst.

[0069] Examples 8-12 (solvent types are shown in Table 1)

[0070] In a 150 ml high-pressure reaction kettle, under nitrogen protection, imidazole-pyridine-nickel catalyst (0.1 mmol) prepared in Example 6, β-H elimination promoter (10 mmol), solvent (35 ml) were sequentially added, the reaction kettle was sealed, the gas in the reaction kettle was replaced with carbon dioxide for 3 times, then carbon dioxide was filled into the reaction kettle to make the pressure of the reaction kettle 1 MPa, then ethylene was filled into the reaction kettle to make the pressure of the reaction kettle 5 MPa. The temperature was slowly raised to 80°C controlled by a temperature controller, and the reaction was carried out for 12 h, then the reaction kettle was cooled to room temperature, the reaction kettle was unloaded, and the solvent was removed by distillation under reduced pressure. The prepared light yellow solid was added into 10 mL of deuterium water internal standard solution, shaken and dissolved, and then subjected to nuclear magnetic resonance hydrogen spectrum analysis to calculate the TON of the reaction.

[0071] Table 1

[0072]

[0073] Examples 13-20 (amount of sodium tert-butoxide added, reaction temperature, and reaction time are shown in Table 2)

[0074] In a 150 ml high-pressure reaction kettle, under nitrogen protection, imidazole-pyridine-nickel catalyst (0.1 mmol) prepared in Example 6, sodium tert-butoxide, tetrahydrofuran (35 ml) were sequentially added, the reaction kettle was sealed, the gas in the reaction kettle was replaced with carbon dioxide for 3 times, then carbon dioxide was filled into the reaction kettle to make the pressure of the reaction kettle 1 MPa, then ethylene was filled into the reaction kettle to make the pressure of the reaction kettle 5 MPa. The temperature was slowly raised to the specified temperature controlled by a temperature controller, and the reaction was carried out for the predetermined time, then the reaction kettle was cooled to room temperature, the reaction kettle was unloaded, and the solvent was removed by distillation under reduced pressure. The prepared light yellow solid was added into 10 mL of deuterium water internal standard solution, shaken and dissolved, and then subjected to nuclear magnetic resonance hydrogen spectrum analysis to calculate the TON of the reaction.

[0075] Table 2

[0076]

[0077] Comparative Examples 1-3 (ligand types are shown in Table 3)

[0078] In a 150ml high-pressure reactor, under nitrogen protection, add double-(1,5-cyclooctadiene) nickel (0.1mmol), bisphosphine ligand (0.11mmol), sodium tert-butoxide (20mmol), THF (35ml) in sequence, seal the reactor, replace the gas in the reactor with carbon dioxide for 3 times, then fill carbon dioxide into the reactor to 1MPa, then fill ethylene into the reactor to 5MPa. Slowly increase the temperature to 140℃ by temperature controller, react for 18h, cool to room temperature, discharge the reactor, remove the solvent by reduced pressure distillation, add the prepared light yellow solid into 10mL deuterium water internal standard solution, shake well to dissolve, then perform nuclear magnetic resonance hydrogen spectrum analysis to calculate the TON of the reaction.

[0079] Table 3

[0080]

[0081] The above examples are only used to illustrate the technical solutions of the present application, but not to limit it. Although the present application has been described in detail with reference to the foregoing examples, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing examples can be modified, or some or all of the technical features can be replaced by equivalents, without departing from the spirit and essence defined in the claims of the present application.

Claims

1. An imidazole-pyridine bidentate ligand, characterized in that, The imidazole-pyridine bidentate ligand has the following formula I structure: Formula I wherein the anion X - is selected from Cl - or I - .

2. A method of synthesizing the imidazole-pyridine bidentate ligand of claim 1, characterized in that, The method comprises the following steps: S1: heating reaction of mesitylamine, 2,3-butanedione and paraformaldehyde in the presence of ammonium acetate and acetic acid, adjusting the pH value of the system to 8-9 after reaction, and obtaining the mesityl-substituted imidazole derivative after purification; S2: substitution reaction of the mesityl-substituted imidazole derivative prepared in S1 with 2-halogenomethylpyridine to obtain the imidazole-pyridine bidentate ligand.

3. The method of synthesis of claim 2, wherein, In step S1, the molar ratio of mesitylamine, 2,3-butanedione and paraformaldehyde is 1:1:1.5 to 1:1:2.5; In step S1, the molar ratio of mesitylamine and ammonium acetate is 1:1 to 1:1.5; In step S1, the molar ratio of mesitylamine and acetic acid is 1:3 to 1:8; In step S1, the reaction temperature is 130-160℃, and the reaction time is 10-15 hours.

4. The method of synthesis of claim 2, wherein, Step S2 comprises: The mesityl-substituted imidazole derivative prepared in S1 is dissolved in anhydrous tetrahydrofuran, then sodium hydride is slowly added in batches, a tetrahydrofuran solution of 2-halogenomethylpyridine is dropped into the reaction system after reaction, and the precipitate is filtered out after stirring overnight at room temperature to obtain the imidazole-pyridine bidentate ligand.

5. The method of synthesis of claim 4, wherein, In step S2, the molar ratio of the mesityl-substituted imidazole derivative and 2-halogenomethylpyridine is 1:1 to 1:1.2; In step S2, the molar ratio of the mesityl-substituted imidazole derivative and sodium hydride is 1:1.1 to 1:1.

5.

6. A metal catalyst characterized in that, The imidazole-pyridine bidentate ligand of claim 1 is prepared by the following method: Anhydrous solvent is added to the imidazole-pyridine bidentate ligand, and fully stirred to make it uniformly dispersed, then potassium tert-butoxide is slowly added, the reaction system becomes a yellow solution after stirring, and finally a metal compound is added and stirred to obtain a metal catalyst; The anhydrous solvent is anhydrous tetrahydrofuran or anhydrous toluene; The metal compound is bis-(1,5-cyclooctadiene) nickel.

7. Use of the metal catalyst of claim 6 in the carboxylation reaction of carbon dioxide and ethylene to prepare acrylic acid.

8. Use according to claim 7, characterized in that, The use comprises the following steps: adding a β-H elimination promoter, a metal catalyst and a solvent into a reaction kettle, sealing, charging carbon dioxide to a pressure of 1.0-2.0 MPa in the reaction kettle, then charging ethylene to a specified pressure of 4.0-5.0 MPa in the reaction kettle to react.

9. Use according to claim 8, characterized in that, The β-H elimination promoter is one of sodium tert-butoxide, sodium phenoxide and sodium acetate; The molar ratio of the metal catalyst and the β-H elimination promoter is 1:100-1:500; The solvent is one of tetrahydrofuran, anisole, toluene, dimethyl sulfoxide and N-methyl pyrrolidone; The reaction temperature is 80-160℃, and the reaction time is 12-24h.

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