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

Abstract

The invention provides an imidazole-oxazolyl bidentate ligand, a synthesis method thereof, a metal catalyst prepared from the imidazole-oxazolyl bidentate ligand and application of the metal catalyst, and relates to the technical field of catalyst preparation. Compared with the imidazolyl ligand used in the current carbon dioxide carboxylation coupling reaction, the imidazole-oxazolyl bidentate ligand designed and developed by the invention only needs two-step reaction to synthesize, the total yield can reach 54%, the synthesis route is greatly simplified, and meanwhile, the imidazole-oxazolyl bidentate ligand has good stability, is easy to store and has low requirements on storage environment and use conditions; after the imidazole derivative connected with mesitylene is substituted with benzoxazole, the catalytic activity of the nickel catalyst is improved, and the reaction activity of the nickel catalyst in a carbon dioxide carboxylation coupling reaction is improved.

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-oxazolyl bidentate ligand, a metal catalyst, and a synthesis method and application thereof. Background Art

[0002] The entire carbon dioxide molecule is in the lowest energy state, with thermodynamic stability and kinetic inertness. Therefore, the chemical conversion of carbon dioxide generally requires relatively harsh reaction conditions, and the scope of carbon dioxide resource utilization is also greatly limited. Therefore, the development of new and efficient carbon dioxide conversion and utilization technologies has high social and economic value and ecological significance. High-value conversion of carbon dioxide is an effective way to utilize carbon under the background of the "dual carbon" goal.

[0003] Acrylic acid (ester) is an important organic synthetic raw material in industry. It can be self-polymerized or copolymerized with other monomers such as acrylonitrile, butadiene, vinyl chloride, maleic anhydride, etc. to produce synthetic resins, synthetic fibers, synthetic rubbers, coatings, etc., which are widely used in the fields of construction, textiles, plastic processing, packaging materials, etc., and thus the development and optimization of its synthesis method is of great significance. Using carbon dioxide as a carboxyl source to undergo carboxylation coupling reaction with unsaturated hydrocarbons is a new, green, and potential synthetic method for acrylic acid and its derivatives, and is also a new way to utilize carbon dioxide at a high value, and a new route for synthesizing acrylic acid and its derivatives.

[0004] According to the mechanism of carbon dioxide carboxylation coupling reaction, propionic acid metal lactone ring is the key intermediate of carbon dioxide carboxylation coupling reaction, which is generated by the reaction of carbon dioxide with ethylene after activation by a metal catalyst. Under normal circumstances, 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 ligand (Chem. Eur. J. 2019, 25, 13504-13508). This ligand can generate a carbene intermediate under the action of a strong base and react with nickel metal to form a phosphine-carbene bidentate coordinated metal nickel catalyst. This carbene-coordinated nickel catalyst has good stability and catalytic activity. The conversion number of the carbon dioxide carboxylation coupling reaction catalyzed by it can reach up to 450, which is the highest conversion number of the carbon dioxide carboxylation coupling reaction without the participation of reducing metals. However, this type of ligand also has many problems. For example, the ligand synthesis route is complicated and the yield is low. The total synthesis yield is only 39.3%. In addition, the dicyclohexylphosphine in the ligand is easily oxidized, and the storage and use conditions of the ligand are harsh. Summary of the invention

[0005] In view of the deficiencies of the prior art, the present invention provides an imidazole-oxazolyl 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 coupling reaction of carbon dioxide and ethylene. Compared with the imidazole-based ligand used in the current carbon dioxide carboxylation coupling reaction, the synthesis of the imidazole-oxazolyl bidentate ligand designed and developed by the present invention only requires two steps of reaction, and the total yield can reach 54%, which greatly simplifies the synthesis route, and at the same time has good stability, is easy to store, and has low requirements for storage environment and use conditions; after the imidazole derivative connected with mesitylene is replaced with benzoxazole, the catalytic activity of the nickel catalyst is improved, and its reaction activity in the carbon dioxide carboxylation coupling reaction is improved.

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

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

[0008] The third object of the present invention is to provide a metal catalyst made from the imidazole-oxazolyl 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-oxazolyl bidentate ligand, wherein the imidazole-oxazolyl 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-oxazolyl 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 prepared in S1 undergoes a substitution reaction with 2-halogenated benzoxazole to obtain an imidazole-oxazole 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 was dissolved in anhydrous dichloromethane, and then sodium hydride was slowly added in batches. After the reaction, 2-halogenated benzoxazole was dropped into the reaction system, stirred at room temperature overnight, and the precipitate was filtered out to obtain an imidazole-oxazolyl bidentate ligand.

[0026] In some embodiments, in step S2, the molar ratio of the mesitylene-substituted imidazole derivative to the 2-halogenated benzoxazole is 1:1 to 1:1.3.

[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-oxazolyl 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 dichloromethane to obtain a dichloromethane solution of the mesitylene-substituted imidazole derivative (concentration is 0.2 mol / L), and then sodium hydride is slowly added in batches. After reacting for half an hour, 2-halogenated benzoxazole is dropped into the reaction system. Finally, the mixture is stirred at room temperature overnight. After filtering out the precipitate, an imidazole-oxazolyl bidentate ligand is obtained.

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

[0033] In a glove box, 0.1 mmol of the above-mentioned imidazole-oxazolyl 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-mentioned metal catalyst in the preparation of acrylic acid by carboxylation coupling 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 N-methylpyrrolidone.

[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 120-140°C; the reaction time is 12-24h, preferably 15-18h.

[0044] Technical effect:

[0045] 1. The synthesis of the imidazole-oxazolyl bidentate ligand designed and developed by the present invention requires only two steps of reaction, and the total yield can reach 54%, which greatly simplifies the synthesis route.

[0046] 2. Imidazole-oxazole ligands have good stability, are easy to store, and have low requirements for storage environment and usage conditions.

[0047] 3. The catalytic activity of the nickel catalyst was improved by replacing the imidazole derivatives connected with mesitylene with benzoxazole, and its reaction activity in the carbon dioxide carboxylation coupling reaction was improved.

[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 coupling 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 dichloromethane, and then sodium hydride (6.3 mmol) was slowly added in batches. After half an hour of reaction, 2-chlorobenzoxazole (5.7 mmol) was dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-oxazolyl bidentate ligand was obtained, and the total yield was 38%.

[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 dichloromethane, and then sodium hydride (6.6 mmol) was slowly added in batches. After half an hour of reaction, 2-chlorobenzoxazole (6.0 mmol) was dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-oxazolyl bidentate ligand was obtained with a yield of 40%.

[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 dichloromethane, and then sodium hydride (7.5 mmol) was slowly added in batches. After half an hour of reaction, 2-chlorobenzoxazole (6.8 mmol) was dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-oxazolyl bidentate ligand was obtained, and the total yield was 46%.

[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 dichloromethane, and then sodium hydride (7.2 mmol) was slowly added in batches. After half an hour of reaction, 2-chlorobenzoxazole (6.5 mmol) was dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-oxazolyl bidentate ligand was obtained, and the total yield was 44%.

[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 dichloromethane, and then sodium hydride (10.2 mmol) was slowly added in batches. After half an hour of reaction, 2-chlorobenzoxazole (8.8 mmol) was dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-oxazolyl bidentate ligand was obtained, and the total yield was 54%.

[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 dichloromethane, and then sodium hydride (7.5 mmol) was slowly added in batches. After half an hour of reaction, 2-chlorobenzoxazole (8.8 mmol) was dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-oxazolyl bidentate ligand was obtained, and the total yield was 51%.

[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 dichloromethane, and then sodium hydride (8.8 mmol) was slowly added in batches. After half an hour of reaction, 2-chlorobenzoxazole (7.5 mmol) was dropped into the reaction system. Finally, the mixture was stirred at room temperature overnight. After filtering out the precipitate, the imidazole-oxazolyl bidentate ligand was obtained, and the total yield was 52%.

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

[0068] In a glove box, 0.1 mmol of imidazole-oxazole bidentate ligand was put into 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-oxazole-nickel catalyst.

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

[0070] In a 150ml autoclave, under nitrogen protection, the imidazole-oxazole-nickel catalyst (0.1mmol) prepared in Example 5, β-H elimination promoter (10mmol), and solvent (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 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, and the reaction was carried out for 12h, cooled to room temperature, and 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]

[0074] Examples 13-20 (see Table 2 for the amount of sodium tert-butoxide added, reaction temperature and reaction time)

[0075] In a 150ml autoclave, under nitrogen protection, the imidazole-oxazole-nickel catalyst (0.1mmol) prepared in Example 5, sodium tert-butoxide, and N-methylpyrrolidone (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.

[0076] Table 2

[0077]

[0078] Comparative Examples 1-3 (Comparison of ligand types see Table 3)

[0079] 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.

[0080] Table 3

[0081]

[0082] 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-oxazolyl bidentate ligand, characterized in that: The imidazole-oxazolyl 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-oxazolyl 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 prepared in S1 undergoes a substitution reaction with 2-halogenated benzoxazole to obtain an imidazole-oxazole 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 dichloromethane, and then sodium hydride is slowly added in batches. After the reaction, 2-halogenated benzoxazole is dropped into the reaction system, stirred at room temperature overnight, and the precipitate is filtered out to obtain an imidazole-oxazolyl bidentate ligand; Preferably, in step S2, the molar ratio of the mesitylene-substituted imidazole derivative to the 2-halogenated benzoxazole is 1:1 to 1:1.3; 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-oxazolyl bidentate ligand according to claim 1 is prepared by the following method: Anhydrous solvent is added to the imidazole-oxazolyl bidentate ligand, and the mixture is stirred thoroughly to make it dispersed evenly. Then potassium tert-butoxide is slowly added. After stirring, the reaction system turns into a yellow solution. Finally, a metal compound is added and stirred to prepare 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 coupling 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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