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

Abstract

The invention provides an imidazole-phosphine bidentate ligand, a synthesis method thereof, a metal catalyst prepared from the imidazole-phosphine bidentate ligand and application of the metal catalyst, and relates to the technical field of catalyst preparation. According to the invention, 2, 3-butanedione, sym-tritoluidine and formaldehyde are used as raw materials to firstly synthesize the sym-trimethylbenzene substituted imidazole derivative, then the sym-trimethylbenzene substituted imidazole derivative and chloromethyl diphenylphosphine are subjected to substitution reaction to synthesize the imidazole-phosphine ligand, the synthesis method is simple, and the total yield can reach 56%. Compared with dicyclohexylphosphine, the diphenylphosphine substituent imidazole-phosphine bidentate ligand disclosed by the invention is not easy to oxidize, good in stability and convenient to store and use, and is a bidentate ligand with a very good industrial application prospect.

Description

Technical Field

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

[0002] There are many types of organic compounds prepared from carbon dioxide as raw materials. As early as the last century, some carbon dioxide-based compounds have achieved large-scale industrial production, such as urea widely used in agriculture, salicylic acid used in medicine, and degradable polyester materials or polymer monomers. Carbon dioxide and methane can react to produce synthesis gas and hydrogen, and can further produce carbon one chemical products such as methanol and ethanol and Fischer-Tropsch synthetic oil. Carbon dioxide can also be made into hydrogenated chemicals such as methane, formic acid, methanol, mixed low-carbon alcohols, carbamates and other chemicals, as well as synthetic dibasic acids and various carboxylic acids such as formic acid and acetic acid. Carbon dioxide can also be coupled with alkanes for dehydrogenation to produce olefins. There is still a lot of room for research in the industrial production of carbon dioxide-based organic chemicals. The research and industrial production of these new directions provide directions for the chemical utilization and emission reduction of greenhouse gases, but also pose huge challenges.

[0003] Acrylic acid is an important fine chemical raw material and polymer monomer. 10% of the world's acrylic acid production capacity adopts the propylene oxidation method. The propylene oxidation method is divided into two steps. First, propylene is oxidized to acrolein under the action of a highly active multiphase catalyst. In the second step, acrolein is deeply oxidized to acrylic acid. The obvious disadvantages of this reaction process are: first, the reaction conditions are harsh and the safety is very strict; second, excessive oxidation produces about 10% of carbon dioxide and carbon monoxide as by-products, producing greenhouse gases.

[0004] Since Hoberg et al. pioneered the synthesis route of acrylic acid from ethylene and carbon dioxide in 1980, the chemical community has paid extensive attention to the research on the carboxylation reaction of unsaturated hydrocarbons to prepare unsaturated carboxylic acid esters. The carboxylation reaction of carbon dioxide and ethylene is a direct reaction of ethylene and carbon dioxide catalyzed by a metal catalyst. Its reaction mechanism is that the metal catalyst activates carbon dioxide and then reacts with ethylene to form a propionic acid metal lactone ring intermediate. This intermediate can be hydrolyzed or undergo a β-H elimination reaction under heating or acid-base action. 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.

[0005] The metal propionic acid lactone ring generated by the reaction of carbon dioxide with ethylene after the metal catalyst activates carbon dioxide 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 propionic acid 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. In order to solve the above problems, it is of great significance to develop imidazole-based ligands with simple synthesis methods and easy storage and use. Summary of the invention

[0006] In view of the deficiencies of the prior art, the present invention provides an imidazole-phosphine bidentate ligand used in the reaction of synthesizing acrylic acid from carbon dioxide, a synthesis method thereof, a metal catalyst coordinated thereto, and a method for preparing acrylic acid by carboxylation reaction of carbon dioxide and ethylene. The synthesis method of the imidazole-phosphine bidentate ligand designed and developed by the present invention is simple, the total yield can reach 56%, and the preparation process only requires two steps of reaction. Compared with dicyclohexylphosphine, the diphenylphosphine-substituted imidazole-phosphine bidentate ligand disclosed in the present invention is not easily oxidized, has good stability, is convenient to store and use, and is a bidentate ligand with great industrial application prospects.

[0007] One of the objects of the present invention is to provide an imidazole-phosphine bidentate ligand.

[0008] The second object of the present invention is to provide a method for synthesizing the imidazole-phosphine bidentate ligand.

[0009] The third object of the present invention is to provide a metal catalyst made from the imidazole-phosphine bidentate ligand.

[0010] A fourth object of the present invention is to provide an application of the metal catalyst.

[0011] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0012] In a first aspect, the present invention provides an imidazole-phosphine bidentate ligand, wherein the imidazole-phosphine bidentate ligand has a structure as shown in the following formula I:

[0013]

[0014] The anion X - Selected from Cl - Br - ,I - .

[0015] In a second aspect, the present invention provides a method for synthesizing the above-mentioned imidazole-phosphine bidentate ligand, comprising the following steps:

[0016]

[0017] 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;

[0018] S2: The mesitylene-substituted imidazole derivative obtained in S1 undergoes a substitution reaction with a halomethyldiphenylphosphine to obtain an imidazole-phosphine bidentate ligand.

[0019] 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.

[0020] In some embodiments, in step S1, the molar ratio of mesitylidine to ammonium acetate is 1:1 to 1:1.5.

[0021] In some embodiments, in step S1, the molar ratio of mesitylidine to acetic acid is 1:3 to 1:8.

[0022] In some embodiments, in step S1, the reaction temperature is 130-160° C., and the reaction time is 10-15 hours.

[0023] In some embodiments, the purification in step S1 comprises the following steps:

[0024] 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.

[0025] In some embodiments, step S2 comprises:

[0026] 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, a tetrahydrofuran solution of halogenated methyl diphenyl phosphine is dropped into the reaction system, stirred at room temperature overnight, and the precipitate is filtered out to obtain an imidazole-phosphine bidentate ligand.

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

[0028] 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.

[0029] Specifically, the synthesis method of the imidazole-phosphine bidentate ligand comprises the following steps:

[0030] (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;

[0031] (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;

[0032] (3) The mesitylene-substituted imidazole derivative obtained in step (2) is dissolved in anhydrous tetrahydrofuran to obtain a dichloromethane solution (concentration of 0.2 mol / L) of the mesitylene-substituted imidazole derivative, and then sodium hydride is slowly added in batches. After reacting for half an hour, a tetrahydrofuran solution (concentration of 0.5 mol / L) of halomethyl diphenylphosphine 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-phosphine bidentate ligand.

[0033] In a third aspect, the present invention provides a metal catalyst prepared from the above-mentioned imidazole-phosphine bidentate ligand by the following method:

[0034] In a glove box, 0.1 mmol of the above-mentioned imidazole-phosphine 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.

[0035] In some embodiments, the anhydrous solvent is anhydrous tetrahydrofuran or anhydrous toluene.

[0036] In some embodiments, the metal compound is bis-(1,5-cyclooctadiene)nickel or (1,5-cyclooctadiene)palladium(II) dichloride.

[0037] 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.

[0038] 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.

[0039] The reaction is a heterogeneous reaction carried out in a tank reactor.

[0040] Preferably, the β-H elimination promoter is one of sodium tert-butoxide, sodium phenolate and sodium acetate, preferably sodium tert-butoxide.

[0041] Preferably, the molar ratio of the metal catalyst to the β-H elimination promoter is 1:100-1:500, preferably 1:200-1:300.

[0042] Preferably, the solvent is one of tetrahydrofuran, anisole, toluene, dimethyl sulfoxide, and N-methylpyrrolidone, preferably N-methylpyrrolidone.

[0043] Preferably, the mass purity of carbon dioxide is 90%-100%; the mass purity of ethylene is 90%-100%.

[0044] Preferably, the reaction temperature is 80-160°C, preferably 120-140°C; the reaction time is 12-24h, preferably 15-18h.

[0045] Technical effects:

[0046] 1. The synthesis method of the imidazole-phosphine bidentate ligand designed and developed by the present invention is simple, the total yield can reach 56%, and the preparation process only requires two steps of reaction to obtain the imidazole-phosphine bidentate ligand.

[0047] 2. Compared with dicyclohexylphosphine, the diphenylphosphine-substituted imidazole-phosphine bidentate ligand disclosed in the present invention is not easily oxidized, has good stability, and is convenient to store and use.

[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, chloromethyldiphenylphosphine (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-phosphine ligand was obtained, and the total yield was 34%.

[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 63%. The prepared mesitylene substituted imidazole derivative (6.3 mmol) was dissolved in anhydrous tetrahydrofuran, and then sodium hydride (6.9 mmol) was slowly added in batches. After half an hour of reaction, chloromethyldiphenylphosphine (6.3 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-phosphine ligand was obtained with a yield of 46%.

[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, chloromethyldiphenylphosphine (10.2 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-phosphine ligand was obtained, and the total yield was 56%.

[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 62%. The prepared mesitylene substituted imidazole derivative (6.2 mmol) was dissolved in anhydrous tetrahydrofuran, and then sodium hydride (6.8 mmol) was slowly added in batches. After half an hour of reaction, chloromethyldiphenylphosphine (6.2 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-phosphine 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, chloromethyldiphenylphosphine (10.2 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-phosphine ligand was obtained, and the total yield was 51%.

[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, chloromethyldiphenylphosphine (10.2 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-phosphine ligand was obtained, and the total yield was 50%.

[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, chloromethyldiphenylphosphine (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-phosphine ligand was obtained, and the total yield was 54%.

[0067] Each example prepares the imidazole-phosphine-nickel catalyst according to the following method:

[0068] Take 0.1mmol imidazole-phosphine bidentate ligand and put it into a 20mL Shrek tube, then add 2mL anhydrous tetrahydrofuran, stir well to make it evenly dispersed, then slowly add 0.11mmol potassium tert-butoxide, after stirring for 30 minutes, the reaction system turns into a yellow solution, finally add 0.1mmol bis-(1,5-cyclooctadiene) nickel and stir for 2 hours to obtain imidazole-phosphine-nickel catalyst.

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

[0070] In a 150ml autoclave, under nitrogen protection, the imidazole-phosphine-nickel catalyst (0.1mmol) prepared in Example 3, 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, and then 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 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, and the obtained light yellow solid was added to 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.

[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-phosphine-nickel catalyst (0.1mmol) prepared in Example 3, sodium tert-butoxide, and N-methylpyrrolidone (35ml) were added in sequence, and the autoclave was sealed. The gas in the autoclave was replaced 3 times with carbon dioxide, and then 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 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, add bis-(1,5-cyclooctadiene) nickel (0.1mmol), bisphosphine ligand (0.11mmol), sodium tert-butoxide (20mmol), THF (35ml) in sequence, seal the autoclave, replace the gas in the autoclave with carbon dioxide three times, then fill it with carbon dioxide until the pressure of the autoclave is 1MPa, and then fill it with ethylene until the pressure of the autoclave is 5MPa. The temperature is slowly raised to 140℃ by a temperature controller, react for 15h, cool to room temperature, unload the autoclave, remove the solvent by vacuum distillation, add 10mL of deuterated water internal standard solution to the obtained light yellow solid, shake it thoroughly to dissolve it, and then perform nuclear magnetic resonance hydrogen spectrum analysis to calculate the reaction TON.

[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-phosphine bidentate ligand, characterized in that: The imidazole-phosphine 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-phosphine 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 a halomethyldiphenylphosphine to obtain an imidazole-phosphine 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 halomethyl diphenylphosphine is dripped into the reaction system, and the mixture is stirred at room temperature overnight. The precipitate is filtered out to obtain an imidazole-phosphine bidentate ligand; Preferably, in step S2, the molar ratio of the mesitylene-substituted imidazole derivative to the halomethyl diphenylphosphine is 1:1 to 1:1.5; 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-phosphine bidentate ligand according to claim 1 is prepared by the following method: Anhydrous solvent is added to the imidazole-phosphine 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 N-methylpyrrolidone; Preferably, the reaction temperature is 80-160°C, preferably 120-140°C; the reaction time is 12-24h, preferably 15-18h.

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