Imidazole-pyridine bidentate ligand, synthesis method thereof, metal catalyst prepared from imidazole-pyridine bidentate ligand and application of metal catalyst

Abstract

The invention 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 designed and developed imidazole-pyridine bidentate ligand synthesis method is simple, ligand synthesis only needs 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 preparation method of the copper-nitrogen heterocyclic carbene complex catalyst, the catalyst prepared from the imidazole-pyridine bidentate ligand connected with the mesitylene substituent and the metal nickel has high catalytic activity and shows better reaction activity in carbon dioxide carboxylation reaction.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of catalysts for synthesizing acrylic acid from carbon dioxide, and in particular to an imidazole-pyridine bidentate ligand, a metal catalyst, and a synthesis method and application thereof. Background Art

[0002] Carbon dioxide is not only a greenhouse gas, but also an important and effective carbon resource. It is abundant, non-toxic, pollution-free, and non-flammable, and can be used to produce organic chemicals, materials, sugars, etc. Since the carbon in the carbon dioxide molecule is in the highest oxidation state and its molecule is thermodynamically and kinetically inert, 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 produce unsaturated carboxylic acids and their derivatives with the assistance of transition metal catalysts has attracted great attention. Among them, the catalytic carboxylation reaction of carbon dioxide and ethylene to prepare acrylic acid and its derivatives has attracted much attention due to its atom economy. Transition metal catalytic reactions based on nickel-based catalytic systems are one of the very important research hotspots for the chemical conversion and high-value utilization of carbon dioxide.

[0003] The carboxylation reaction of carbon dioxide and ethylene is a direct reaction of ethylene and carbon dioxide catalyzed by a metal catalyst. The reaction mechanism is that the metal catalyst activates carbon dioxide and then reacts with ethylene to form a metal lactone ring intermediate. This intermediate can be hydrolyzed or undergo a β-H elimination reaction under heating or the action of acid and alkali. At the same time, the metal catalyst leaves and enters the next catalytic cycle again, and finally acrylic acid or propionic acid compounds are obtained.

[0004] From the reaction mechanism, the metal propionate lactone ring generated by the metal catalyst activating carbon dioxide and reacting with ethylene is the key intermediate of the carbon dioxide carboxylation reaction. Under normal circumstances, the catalytic activity and stability of the metal catalyst are important factors affecting the reaction rate of the metal propionate lactone ring. In 2019, the Japanese research team reported an alkylphosphine-substituted imidazole ligand (Chem. Eur. J. 2019, 25, 13504-13508), which can generate a carbene intermediate under the action of a strong base to form a metal nickel catalyst with a phosphine-carbene bidentate coordination with nickel metal. This carbene-coordinated nickel catalyst has good stability and catalytic activity, and its catalyzed carbon dioxide carboxylation reaction conversion number can reach up to 450, which is the highest conversion number of carbon dioxide carboxylation reaction without the participation of reducing metals. However, this type of ligand also has many problems, such as the ligand synthesis route is cumbersome and the yield is low, 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 applicable to the preparation of copper nitrogen heterocyclic carbene complex catalysts, and are not effective for the preparation of bidentate nickel carbene catalysts. In order to solve the above problems, it is of great significance to develop an imidazole-based ligand that is simple in synthesis, easy to store and use, and suitable for bidentate nickel catalysts. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention provides an imidazole-pyridine bidentate ligand used in the reaction of synthesizing acrylic acid from carbon dioxide, 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 invention is simple, and the ligand synthesis only requires two steps of 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 preparation method of copper-nitrogen heterocyclic carbene complex catalyst, the catalyst prepared by the imidazole-pyridine bidentate ligand connected with mesitylene substituent and metal nickel has high catalytic activity and shows good reaction activity in the carbon dioxide carboxylation reaction.

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

[0007] The second object of the present invention is to provide a method for synthesizing the imidazole-pyridine bidentate ligand.

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

[0009] A fourth object of the present invention is to provide an application of the metal catalyst.

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

[0011] In a first aspect, the present invention provides an imidazole-pyridine bidentate ligand, wherein the imidazole-pyridine bidentate ligand has a structure as shown in the following formula I:

[0012]

[0013] The anion X - Selected from Cl - Br - ,I - .

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

[0015]

[0016] S1: in the presence of ammonium acetate and acetic acid, mesitylene, 2,3-butanedione and paraformaldehyde are heated to react, and after the reaction, the pH value of the system is adjusted to 9, and after purification, a mesitylene-substituted imidazole derivative is obtained;

[0017] S2: The mesitylene-substituted imidazole derivative obtained in S1 undergoes a substitution reaction with 2-halogenated methylpyridine to obtain an imidazole-pyridine bidentate ligand.

[0018] In some embodiments, in step S1, the molar ratio of mesitylidine, 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 mesitylidine to ammonium acetate is 1:1 to 1:1.5.

[0020] In some embodiments, in step S1, the molar ratio of mesitylidine to 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 in step S1 comprises the following steps:

[0023] The reaction mixture was extracted three times with ethyl acetate, the obtained organic phases were mixed, washed with saturated brine and then dried over anhydrous sodium sulfate, filtered, and the clarified organic phase was distilled under reduced pressure to remove the solvent, and the obtained brown viscous oil was purified by column chromatography to obtain a mesitylene-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-halomethylpyridine is dropped into the reaction system, stirred at room temperature overnight, and the precipitate is filtered out to obtain an imidazole-pyridine bidentate ligand.

[0026] In some embodiments, in step S2, the molar ratio of the mesitylene-substituted imidazole derivative to 2-halogenated methylpyridine 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) adding mesitylidine, 2,3-butanedione, paraformaldehyde, ammonium acetate and acetic acid into a round-bottom flask and heating for reaction, then cooling the temperature to room temperature and adjusting the pH value of the reaction system to 9 with 1N potassium carbonate solution;

[0030] (2) extracting the mixture obtained in step (1) with ethyl acetate three times (100 mL×3), mixing the obtained organic phases, washing with saturated brine and then drying with anhydrous sodium sulfate, filtering and distilling the clarified ethyl acetate solution under reduced pressure to remove the solvent, and purifying the obtained brown viscous oil by column chromatography to obtain a mesitylene-substituted imidazole derivative;

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

[0032] In a third aspect, the present invention 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 was put into a 20 mL Shrek tube, and then 2 mL of anhydrous solvent was added and stirred thoroughly to make it evenly dispersed. Then 0.11 mmol of potassium tert-butoxide was slowly added. After stirring for 30 minutes, the reaction system turned into a yellow solution. Finally, 0.1 mmol of a metal compound was added and stirred for 2 hours to obtain a 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 a fourth aspect, the present invention provides a use of the above metal catalyst in the preparation of acrylic acid by carboxylation reaction of carbon dioxide and ethylene.

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

[0038] The reaction is a heterogeneous reaction carried out in a tank reactor.

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

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

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

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

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

[0044] Technical effects:

[0045] 1. The imidazole-pyridine bidentate ligand designed and developed by the present invention has a simple synthesis method, and the ligand synthesis only requires two steps of 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 catalyst prepared by the imidazole-pyridine bidentate ligand with mesitylene substituents and metallic nickel showed good reaction activity in the carbon dioxide carboxylation reaction.

[0048] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples. DETAILED DESCRIPTION

[0049] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[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): indicates the number of catalytic reactions or the number of target products generated per unit active site under certain conditions. It measures the catalytic efficiency and capacity of the catalyst.

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

[0053] Example 1

[0054] In a 100 ml round-bottom flask, add mesitylene (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (15 mmol), ammonium acetate (10 mmol) and acetic acid (2.0 mL), then raise the reaction temperature to 130 ° C for 10 hours; after the reaction, lower the temperature to room temperature and adjust the pH value of the reaction system to 9 with 1N potassium carbonate solution, extract with ethyl acetate three times (100 mL × 3), mix the obtained organic phases, wash with saturated brine and then dry with anhydrous sodium sulfate, filter and distill the clarified ethyl acetate solution under reduced pressure to remove the solvent, and the obtained brown viscous oil is purified by column chromatography to obtain mesitylene-substituted imidazole derivatives with a yield of 57%. The prepared mesitylene substituted imidazole derivative (5.7 mmol) was dissolved in anhydrous tetrahydrofuran, and then sodium hydride (6.3 mmol) was slowly added in batches. After half an hour of reaction, 2-chloromethylpyridine (5.7 mmol) was dissolved in 20 mL of tetrahydrofuran and then dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-pyridine ligand was obtained, and the total yield was 41%.

[0055] Example 2

[0056] In a 100 ml round-bottom flask, add mesitylene (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (2.0 mL), then raise the reaction temperature to 130 ° C for 10 hours; after the reaction, lower the temperature to room temperature and adjust the pH value of the reaction system to 9 with 1N potassium carbonate solution, extract with ethyl acetate three times (100 mL × 3), mix the obtained organic phases, wash with saturated brine and then dry with anhydrous sodium sulfate, filter and distill the clarified ethyl acetate solution under reduced pressure to remove the solvent, and the obtained brown viscous oil is purified by column chromatography to obtain mesitylene-substituted imidazole derivatives with a yield of 60%. The prepared mesitylene 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 then dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-pyridine ligand was obtained with a yield of 45%.

[0057] Example 3

[0058] In a 100 ml round-bottom flask, add mesitylene (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (2.0 mL), then raise the reaction temperature to 160 ° C for 15 hours; after the reaction, lower the temperature to room temperature and adjust the pH value of the reaction system to 9 with 1N potassium carbonate solution, extract with ethyl acetate three times (100 mL × 3), mix the obtained organic phases, wash with saturated brine and then dry with anhydrous sodium sulfate, filter and distill the clarified ethyl acetate solution under reduced pressure to remove the solvent, and the obtained brown viscous oil is purified by column chromatography to obtain mesitylene-substituted imidazole derivatives with a yield of 68%. The prepared mesitylene 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 then dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-pyridine ligand was obtained, and the total yield was 51%.

[0059] Example 4

[0060] In a 100 ml round-bottom flask, add mesitylene (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (5.0 mL), then raise the reaction temperature to 160 ° C for 15 hours; after the reaction, lower the temperature to room temperature and adjust the pH value of the reaction system to 9 with 1N potassium carbonate solution, extract with ethyl acetate three times (100 mL × 3), mix the obtained organic phases, wash with saturated brine and then dry with anhydrous sodium sulfate, filter and distill the clarified ethyl acetate solution under reduced pressure to remove the solvent, and the obtained brown viscous oil is purified by column chromatography to obtain mesitylene-substituted imidazole derivatives with a yield of 65%. The prepared mesitylene substituted imidazole derivative (6.5 mmol) was dissolved in anhydrous tetrahydrofuran, and then sodium hydride (7.2 mmol) was slowly added in batches. After half an hour of reaction, 2-chloromethylpyridine (6.5 mmol) was dissolved in 20 mL of tetrahydrofuran and then dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-pyridine ligand was obtained, and the total yield was 48%.

[0061] Example 5

[0062] In a 100 ml round-bottom flask, add mesitylene (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (2.0 mL), then raise the reaction temperature to 160 ° C for 15 hours; after the reaction, lower the temperature to room temperature and adjust the pH value of the reaction system to 9 with 1N potassium carbonate solution, extract with ethyl acetate three times (100 mL × 3), mix the obtained organic phases, wash with saturated brine and then dry with anhydrous sodium sulfate, filter and distill the clarified ethyl acetate solution under reduced pressure to remove the solvent, and the obtained brown viscous oil is purified by column chromatography to obtain mesitylene-substituted imidazole derivatives with a yield of 68%. The prepared mesitylene 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 (8.2 mmol) was dissolved in 20 mL tetrahydrofuran and then dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-pyridine ligand was obtained, and the total yield was 53%.

[0063] Example 6

[0064] In a 100 ml round-bottom flask, add mesitylene (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (5.0 mL), then raise the reaction temperature to 160 ° C for 15 hours; after the reaction, lower the temperature to room temperature and adjust the pH value of the reaction system to 9 with 1N potassium carbonate solution, extract with ethyl acetate three times (100 mL × 3), mix the obtained organic phases, wash with saturated brine and then dry with anhydrous sodium sulfate, filter and distill the clarified ethyl acetate solution under reduced pressure to remove the solvent, and the obtained brown viscous oil is purified by column chromatography to obtain mesitylene-substituted imidazole derivatives with a yield of 68%. The prepared mesitylene 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 of reaction, 2-chloromethylpyridine (8.2 mmol) was dissolved in 20 mL tetrahydrofuran and then dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-pyridine ligand was obtained, and the total yield was 58%.

[0065] Example 7

[0066] In a 100 ml round-bottom flask, add mesitylene (10 mmol), 2,3-butanedione (10 mmol), paraformaldehyde (25 mmol), ammonium acetate (15 mmol) and acetic acid (5.0 mL), then raise the reaction temperature to 160 ° C for 15 hours; after the reaction, lower the temperature to room temperature and adjust the pH value of the reaction system to 9 with 1N potassium carbonate solution, extract with ethyl acetate three times (100 mL × 3), mix the obtained organic phases, wash with saturated brine and then dry with anhydrous sodium sulfate, filter and distill the clarified ethyl acetate solution under reduced pressure to remove the solvent, and the obtained brown viscous oil is purified by column chromatography to obtain mesitylene-substituted imidazole derivatives with a yield of 68%. The prepared mesitylene 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 of reaction, 2-chloromethylpyridine (7.5 mmol) was dissolved in 20 mL tetrahydrofuran and then dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-pyridine ligand was obtained, and the total yield was 55%.

[0067] Each example was prepared according to the following method:

[0068] In a glove box, 0.1 mmol of imidazole-pyridine bidentate ligand was placed in a 20 mL Shrek tube, and then 2 mL of anhydrous tetrahydrofuran was added and stirred thoroughly to make it evenly dispersed. Then 0.11 mmol of potassium tert-butoxide was slowly added. After stirring for 30 minutes, the reaction system turned into a yellow solution. Finally, 0.1 mmol of bis-(1,5-cyclooctadiene) nickel was added and stirred for 2 hours to obtain the imidazole-pyridine-nickel catalyst.

[0069] Examples 8-12 (Solvent types see Table 1)

[0070] In a 150ml autoclave, under nitrogen protection, the imidazole-pyridine-nickel catalyst (0.1mmol) prepared in Example 6, β-H elimination promoter (10mmol), solvent (35ml) were added in sequence, the autoclave was sealed, the gas in the autoclave was replaced 3 times with carbon dioxide, carbon dioxide was added until the pressure of the autoclave was 1MPa, and then ethylene was added until the pressure of the autoclave was 5MPa. The temperature was slowly raised to 80°C by a temperature controller, the reaction was carried out for 12h, cooled to room temperature, the autoclave was unloaded, the solvent was removed by vacuum distillation, the obtained light yellow solid was added with 10mL of deuterated water internal standard solution, and the reaction TON was calculated after sufficient shaking and dissolution by nuclear magnetic resonance hydrogen spectrum analysis.

[0071] Table 1

[0072]

[0073] Examples 13-20 (see Table 2 for the amount of sodium tert-butoxide added, reaction temperature and reaction time)

[0074] In a 150ml autoclave, under nitrogen protection, the imidazole-pyridine-nickel catalyst (0.1mmol) prepared in Example 6, sodium tert-butoxide, and tetrahydrofuran (35ml) were added in sequence, and the autoclave was sealed. The gas in the autoclave was replaced with carbon dioxide three times, and then carbon dioxide was added to the autoclave until the pressure of the autoclave was 1MPa, and then ethylene was added to the autoclave until the pressure of the autoclave was 5MPa. The temperature was slowly raised to the specified temperature by a temperature controller and reacted for a predetermined time, cooled to room temperature, unloaded, and the solvent was removed by vacuum distillation. The obtained light yellow solid was added with 10mL of deuterated water internal standard solution and fully shaken to dissolve, and then the reaction TON was calculated by nuclear magnetic resonance hydrogen spectrum analysis.

[0075] Table 2

[0076]

[0077] Comparative Examples 1-3 (Comparison of ligand types see Table 3)

[0078] In a 150ml autoclave, under nitrogen protection, bis-(1,5-cyclooctadiene) nickel (0.1mmol), bisphosphine ligand (0.11mmol), sodium tert-butoxide (20mmol), THF (35ml) were added in sequence, the autoclave was sealed, the gas in the autoclave was replaced with carbon dioxide three times, carbon dioxide was added to the autoclave until the pressure was 1MPa, and then ethylene was added to the autoclave until the pressure was 5MPa. The temperature was slowly raised to 140°C by a temperature controller, the reaction was continued for 18h, cooled to room temperature, the autoclave was unloaded, the solvent was removed by vacuum distillation, the obtained light yellow solid was added with 10mL of deuterated water internal standard solution, fully shaken and dissolved, and then the reaction TON was calculated by nuclear magnetic resonance hydrogen spectrum analysis.

[0079] Table 3

[0080]

[0081] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and essence of the claims of the present invention; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. An imidazole-pyridine bidentate ligand, characterized in that: The imidazole-pyridine bidentate ligand has a structure as shown in the following formula I: The anion X - Selected from Cl - Br - ,I - .

2. A method for synthesizing the imidazole-pyridine bidentate ligand according to claim 1, characterized in that: The following steps are involved: S1: in the presence of ammonium acetate and acetic acid, mesitylene, 2,3-butanedione and paraformaldehyde are heated to react, and after the reaction, the pH value of the system is adjusted to 8-9, and after purification, a mesitylene-substituted imidazole derivative is obtained; S2: The mesitylene-substituted imidazole derivative obtained in S1 undergoes a substitution reaction with 2-halogenated methylpyridine to obtain an imidazole-pyridine bidentate ligand.

3. The synthesis method according to claim 2, characterized in that In step S1, the molar ratio of mesitylidine, 2,3-butanedione and paraformaldehyde is 1:1:1.5 to 1:1:2.5; Preferably, in step S1, the molar ratio of mesitylidine to ammonium acetate is 1:1 to 1:1.5; Preferably, in step S1, the molar ratio of mesitylidine to acetic acid is 1:3 to 1:8; Preferably, in step S1, the reaction temperature is 130-160° C., and the reaction time is 10-15 hours.

4. The synthesis method according to claim 2, characterized in that Step S2 includes: The mesitylene-substituted imidazole derivative prepared in S1 is dissolved in anhydrous tetrahydrofuran, and then sodium hydride is slowly added in batches. After the reaction, a tetrahydrofuran solution of 2-halogenated methylpyridine is dripped into the reaction system, and the mixture is stirred at room temperature overnight. The precipitate is filtered out to obtain an imidazole-pyridine bidentate ligand; Preferably, in step S2, the molar ratio of the mesitylene-substituted imidazole derivative to 2-halogenated methylpyridine is 1:1 to 1:1.2; Preferably, in step S2, the molar ratio of the mesitylene-substituted imidazole derivative to sodium hydride is 1:1.1 to 1:1.

5.

5. A metal catalyst, characterized in that The imidazole-pyridine bidentate ligand according to claim 1 is prepared by the following method: Anhydrous solvent is added to the imidazole-pyridine bidentate ligand, and the mixture is stirred thoroughly to make it dispersed evenly. Then potassium tert-butoxide is slowly added, and the reaction system turns into a yellow solution after stirring. Finally, a metal compound is added and stirred to obtain a metal catalyst.

6. The metal catalyst according to claim 5, characterized in that The anhydrous solvent is anhydrous tetrahydrofuran or anhydrous toluene.

7. The metal catalyst according to claim 5, characterized in that The metal compound is bis-(1,5-cyclooctadiene) nickel or (1,5-cyclooctadiene) palladium (II) dichloride.

8. Use of the metal catalyst according to any one of claims 5 to 7 in the preparation of acrylic acid by carboxylation reaction of carbon dioxide and ethylene.

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

10. The use according to claim 9, characterized in that: The β-H elimination promoter is one of sodium tert-butoxide, sodium phenolate and sodium acetate, preferably sodium tert-butoxide; Preferably, the molar ratio of the metal catalyst to the β-H elimination promoter is 1:100-1:500, preferably 1:200-1:300; Preferably, the solvent is one of tetrahydrofuran, anisole, toluene, dimethyl sulfoxide, and N-methylpyrrolidone, preferably tetrahydrofuran; Preferably, the reaction temperature is 80-160°C, preferably 130-140°C; the reaction time is 12-24h, preferably 15-18h.

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