Organometallic catalyst based on biguanide-based ligand, process for its preparation and use
By coordinating a biguanide-based organomagnesium catalyst with magnesium salts, the problem of tin residue in existing polyester materials was solved, enabling the preparation of low-toxicity catalysts and efficient ring-opening polymerization of cyclic lactones, which is suitable for the preparation of low-toxicity polyester materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SINOCHEM PETROCHEMICAL RESEARCH INSTITUTE (QUANZHOU) CO LTD
- Filing Date
- 2024-08-02
- Publication Date
- 2026-04-14
AI Technical Summary
The residual tin in existing polyester materials causes biotoxicity problems, limiting their application in the food and medical fields. There is a need to develop low-toxicity metal catalysts.
An organomagnesium catalyst based on biguanide ligands is used to catalyze the ring-opening polymerization of cyclic lactones by coordinating with magnesium salts to prepare low-toxicity polyester materials.
A magnesium catalyst with simple preparation method, mild conditions and high catalytic activity is provided, which can catalyze the ring-opening polymerization of cyclic lactones under solvent or solvent-free conditions, thereby reducing the biotoxicity of the material.
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Figure CN118852217B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polymer materials, specifically relating to an organometallic catalyst based on biguanide ligands, its preparation method, and its application. Background Technology
[0002] Polyester materials, represented by polylactic acid, polycaprolactone, and poly1,3-dioxane-2-one, are a typical class of biodegradable polymer materials. They have advantages such as environmental friendliness, good mechanical properties, non-toxicity, non-irritation, and good biocompatibility, and have been successfully applied in agriculture, food, medical and other fields.
[0003] The most common method for preparing polyester materials is the ring-opening polymerization of cyclic lactones, where cyclic lactones undergo ring-opening polymerization under the action of a catalyst to obtain the target polyester material. This type of method typically involves metal catalysts, such as those with aluminum, tin, calcium, zirconium, and zinc as the core metal. Among these, stannous octoate is the most widely used ring-opening polymerization catalyst in industry due to its low cost and high efficiency. However, using stannous octoate as a catalyst in the preparation of polyester materials results in the presence of trace amounts of tin in the material. Since tin has a certain degree of biotoxicity, tin residue in polyester materials limits their application, especially in the food and medical fields. Developing metal catalysts with lower toxicity can effectively solve the problem of tin residue in polyester materials. Therefore, metal catalysts such as aluminum catalysts, zinc catalysts, magnesium catalysts, and zirconium catalysts have been extensively studied. Summary of the Invention
[0004] Based on the above background, the present invention provides an organometallic catalyst based on biguanide ligands, its preparation method and application.
[0005] To achieve the above objectives, the present invention adopts the following technical solution:
[0006] An organometallic catalyst based on a biguanidinium ligand is formed by coordination of a ligand with a biguanidinium structure and a magnesium salt; its chemical structural formula is as follows:
[0007] ,
[0008] Wherein, R1 is selected from straight-chain alkanes with 1-3 carbon atoms; R2 is selected from straight-chain alkanes with 1-3 carbon atoms or -CH2-; R3 is selected from -Cl, -SO3CF3, -Br, -SO3CH3, -SO3PhCH3.
[0009] The preparation method of the organometallic catalyst based on biguanide ligands includes the following steps:
[0010] (1) Dissolve urea compounds in acetonitrile, add phosphorus oxychloride dropwise, and then heat the mixture to prepare Vilsmeier salt;
[0011] (2) Dissolve trans-1,2-cyclohexanediamine and triethylamine in acetonitrile, then add the Vilsmeier salt prepared in step (1) dropwise and heat to carry out the reaction;
[0012] (3) After the reaction is completed, cool to room temperature, add excess sodium hydroxide to the reaction solution for neutralization, then remove the solvent by rotary evaporation, add potassium hydroxide solution to the obtained reaction mixture for redissolution, extract three times with acetonitrile, combine the organic phases, dry with anhydrous sodium sulfate, and then evaporate to dryness to obtain the ligand with biguanide structure.
[0013] (4) Dissolve the obtained ligand with biguanide structure and magnesium salt in an organic solvent, then add the ligand solution dropwise to the magnesium salt solution and stir to carry out the reaction;
[0014] (5) After the reaction is completed, the reaction system is cooled to room temperature, filtered and dried to obtain the organometallic catalyst.
[0015] Further, in step (1), the urea compound is any one of tetramethylurea, 1,3-dimethyl-2-imidazolinone, and tetraethylurea; the molar ratio of the urea compound to phosphorus oxychloride is 1:1 to 1:2; the temperature at which phosphorus oxychloride is added is -20 ℃ to 4 ℃; the heating reaction is carried out in an inert gas at a reaction temperature of 40 ℃ to 60 ℃ and a reaction time of 6 h to 12 h.
[0016] Further, in step (2), the molar ratio of trans-1,2-cyclohexanediamine to Vilsmeier salt is 1:2-1:2.5, and the molar ratio of trans-1,2-cyclohexanediamine to triethylamine is 1:2-1:2.5; the temperature at which Vilsmeier salt is added is -20℃ to 4℃, and the reaction is carried out in an inert gas at a temperature of 85℃ to 100℃ for 12 h to 20 h.
[0017] Further, in step (3), the mass concentration of the potassium hydroxide solution is 50%; the chemical structural formula of the resulting ligand with a biguanide structure is:
[0018] ,
[0019] R1 is selected from straight-chain alkanes with 1-3 carbon atoms; R2 is selected from straight-chain alkanes with 1-3 carbon atoms or -CH2-.
[0020] Further, in step (4), the magnesium salt is any one of magnesium chloride, magnesium trifluoromethanesulfonate, magnesium bromide, magnesium methanesulfonate, and magnesium p-toluenesulfonate; the molar ratio of the ligand with the biguanide structure to the magnesium salt is 1:1-1.5:1; the organic solvent used is one or more of benzene, toluene, xylene, trimethylbenzene, tetrahydrofuran, dioxane, pyridine, and acetonitrile; the reaction is carried out in an inert gas at a temperature of 40 ℃~80 ℃ for 0.5 h-2 h.
[0021] The organometallic catalyst based on biguanide ligands can be used to catalyze the ring-opening polymerization of cyclic lactones.
[0022] Furthermore, its application method specifically includes the following steps:
[0023] Step 1: In a glove box, the cyclic lactone and the organometallic catalyst based on the biguanide ligand are thoroughly mixed and heated to react;
[0024] Step 2: After the reaction system cools to room temperature, transfer it outside the glove box, add a good solvent to completely dissolve the reactants, add the resulting solution dropwise to a poor solvent, precipitate the polymer, centrifuge to remove the solvent, and vacuum dry the precipitate to obtain the cyclic lactone polymer.
[0025] Furthermore, the cyclic lactone mentioned in step one is any one or more of L-lactide, D-lactide, D,L-lactide, ε-caprolactone, and 1,3-dioxane-2-one.
[0026] Furthermore, the molar ratio of the cyclic lactone used in step one to the organometallic catalyst based on the biguanidin ligand is 200:1-1000:1.
[0027] Furthermore, the heating reaction in step one is carried out at a temperature of 60 ℃ to 160 ℃ for a time of 0.5 h to 12 h.
[0028] Furthermore, the heating reaction described in step one can be carried out with or without a solvent. The solvent is any one or more of benzene, toluene, xylene, trimethylbenzene, tetrahydrofuran, propylene oxide, and cyclohexene oxide.
[0029] Furthermore, the heating reaction described in step one can be carried out with the participation of an initiator. The initiator is any one of n-butanol, 1,4-butanediol, and lauryl alcohol. The molar ratio of the initiator to the organometallic catalyst based on the biguanide ligand is 1:1 to 20:1.
[0030] Furthermore, the good solvent mentioned in step two is any one or more of benzene, toluene, xylene, trimethylbenzene, tetrahydrofuran, dichloromethane, dichloroethane, trichloromethane, and hexafluoroisopropanol.
[0031] Furthermore, the unsuitable solvent mentioned in step two is any one or more of methanol, ethanol, diethyl ether, petroleum ether, n-hexane, and cyclohexane.
[0032] The beneficial effects of this invention are:
[0033] (1) This invention provides an organomagnesium catalyst with a biguanide structure, which is simple to prepare under mild conditions;
[0034] (2) The magnesium catalyst provided by the present invention has low toxicity and high catalytic activity, and can be used to catalyze the ring-opening polymerization reaction of cyclic lactones under solvent or solvent-free conditions (it can be used for both bulk melt polymerization and solution polymerization). Attached Figure Description
[0035] Figure 1 The image shows the 1H NMR spectrum of the biguanide ligand prepared in Example 1.
[0036] Figure 2 The image shows the 1H NMR spectrum of the organometallic catalyst with a biguanide structure prepared in Example 1.
[0037] Figure 3 The image shows a gel permeation chromatogram of the poly-L-lactide prepared in Application Example 4.
[0038] Figure 4 The image shows a gel permeation chromatogram of the L-lactide-1,3-dioxane-2-one copolymer prepared in Example 7.
[0039] Figure 5 The image shows a gel permeation chromatogram of the polycaprolactone prepared in Example 8.
[0040] Figure 6 The image shows a gel permeation chromatogram of poly(1,3-dioxane-2-one) prepared in Application Example 10. Detailed Implementation
[0041] An organometallic catalyst based on a biguanide ligand is prepared by the following steps:
[0042] (1) In an inert gas, urea compounds are dissolved in acetonitrile, and phosphorus oxychloride is added dropwise at a molar ratio of 1:1 to 1:2 at -20 ℃ to 4 ℃. Then the reaction is carried out at 40 ℃ to 60 ℃ for 6 h to 12 h to obtain Vilsmeier salt.
[0043] (2) In an inert gas atmosphere, trans-1,2-cyclohexanediamine and triethylamine are weighed in a molar ratio of 1:2-1:2.5, and acetonitrile is added to dissolve them. Then, at -20 ℃ to 4 ℃, the Vilsmeier salt prepared in step (1) is added dropwise in a molar ratio of trans-1,2-cyclohexanediamine to Vilsmeier salt of 1:2-1:2.5, and the reaction is carried out at 85 ℃ to 100 ℃ for 12 h to 20 h.
[0044] (3) After the reaction is completed, cool to room temperature, add excess sodium hydroxide to the reaction solution to neutralize the acidic substances produced by the reaction, then remove the solvent by rotary evaporation, then add a 50 wt% potassium hydroxide solution to the obtained reaction mixture to redissolve, extract three times with acetonitrile, combine the organic phases, dry with anhydrous sodium sulfate, and then evaporate to dryness to obtain a ligand with a biguanide structure.
[0045] (4) In an inert gas, the obtained ligand with biguanide structure and magnesium salt were dissolved in an organic solvent at a molar ratio of 1:1-1.5:1. Then, the ligand solution was added dropwise to the magnesium salt solution at 40 ℃~80 ℃ and reacted at the same temperature for 0.5 h-2 h.
[0046] (5) After the reaction is complete, the reaction system is cooled to room temperature, filtered, and dried to obtain the organometallic catalyst, whose chemical structural formula is:
[0047] ,
[0048] Wherein, R1 is selected from straight-chain alkanes with 1-3 carbon atoms; R2 is selected from straight-chain alkanes with 1-3 carbon atoms or -CH2-; R3 is selected from -Cl, -SO3CF3, -Br, -SO3CH3, -SO3PhCH3.
[0049] The urea compound mentioned in step (1) is any one of tetramethylurea, 1,3-dimethyl-2-imidazolinone, and tetraethylurea.
[0050] In step (4), the magnesium salt is any one of magnesium chloride, magnesium trifluoromethanesulfonate, magnesium bromide, magnesium methanesulfonate, and magnesium p-toluenesulfonate; the organic solvent used is one or more of benzene, toluene, xylene, trimethylbenzene, tetrahydrofuran, dioxane, pyridine, and acetonitrile.
[0051] To make the content of this invention easier to understand, the technical solution of this invention will be further described below in conjunction with specific embodiments, but this invention is not limited thereto.
[0052] Unless otherwise stated, the terms used in this invention generally have the meanings commonly understood by those skilled in the art.
[0053] In the following embodiments, various processes and methods not described in detail are conventional methods known in the art.
[0054] Example 1
[0055]
[0056] In a nitrogen atmosphere, tetramethylurea (3.6 mL, 30 mmol) was dissolved in 30 mL of acetonitrile, and phosphorus oxychloride (2.8 mL, 30 mmol) was added dropwise at 0 °C. The reaction system was heated to 40 °C and reacted for 6 h to prepare Vilsmeier salt. At 0 °C, the prepared Vilsmeier salt was added dropwise to a 30 mL acetonitrile solution containing trans-1,2-cyclohexanediamine (1.8 mL, 15 mmol) and triethylamine (4.2 mL, 30 mmol). The reaction system was heated to 88 °C and reacted for 15 h. After the reaction was completed, the mixture was cooled to room temperature, and sodium hydroxide (1.2 g, 30 mmol) was added to the reaction solution. After stirring and mixing, the solvent was removed by rotary evaporation. The resulting reaction mixture was reconstituted with 15 mL of 50 wt% potassium hydroxide solution, and then extracted three times with acetonitrile (40-60 mL each time). The organic phases were combined. After drying the organic phase with anhydrous sodium sulfate, it was evaporated to dryness to obtain 2.9 g of biguanide ligand, with a yield of 61.7%.
[0057] In a nitrogen atmosphere, the obtained biguanidin ligand (100.8 mg, 0.3 mmol) and magnesium chloride (28.0 mg, 0.3 mmol) were dissolved in 4 mL of tetrahydrofuran, respectively. Then, the ligand solution was added dropwise to the magnesium chloride solution at 60 °C, and the reaction was carried out at the same temperature for 0.5 h. After the reaction was completed, the reaction system was cooled to room temperature, filtered, and dried to obtain 64.6 mg of organometallic catalyst with biguanidin structure, with a yield of 54.1%.
[0058] Example 2
[0059]
[0060] The synthesis of the ligands was the same as in Example 1.
[0061] Under nitrogen protection, 101.4 mg (0.3 mmol) of biguanide ligand and 94.4 mg (0.3 mmol) of magnesium trifluoromethanesulfonate were weighed out. The biguanide ligand was dissolved in 4 mL of dioxane, and the magnesium trifluoromethanesulfonate was dissolved in 4 mL of tetrahydrofuran. The ligand solution was then added dropwise to the magnesium trifluoromethanesulfonate solution at 60 °C, and the reaction was carried out at the same temperature for 0.5 h. After the reaction was completed, the reaction system was cooled to room temperature, filtered, and dried to obtain 95.1 mg of organometallic catalyst with a biguanide structure, with a yield of 51.3%.
[0062] Example 3
[0063]
[0064] Under a nitrogen atmosphere, 1,3-dimethyl-2-imidazolinone (3.3 mL, 30 mmol) was dissolved in 30 mL of acetonitrile, and phosphorus oxychloride (2.8 mL, 30 mmol) was added dropwise at 0 °C. The reaction system was heated to 40 °C and reacted for 6 h to prepare Vilsmeier salt. At 0 °C, the prepared Vilsmeier salt was added dropwise to a 30 mL acetonitrile solution containing trans-1,2-cyclohexanediamine (1.8 mL, 15 mmol) and triethylamine (4.2 mL, 30 mmol). The reaction system was heated to 90 °C and reacted for 15 h. After the reaction was completed, the mixture was cooled to room temperature, and sodium hydroxide (1.2 g, 30 mmol) was added to the reaction solution. After stirring and mixing, the solvent was removed by rotary evaporation. The resulting reaction mixture was reconstituted with 15 mL of 50 wt% potassium hydroxide solution, and then extracted three times with acetonitrile (40-60 mL each time). The organic phases were combined. After drying the organic phase with anhydrous sodium sulfate, it was evaporated to dryness to obtain 3.6 g of biguanide ligand, with a yield of 78.3%.
[0065] In a nitrogen atmosphere, the obtained biguanidin ligand (100.2 mg, 0.3 mmol) and magnesium chloride (28.0 mg, 0.3 mmol) were dissolved in 4 mL of tetrahydrofuran, respectively. Then, the ligand solution was added dropwise to the magnesium chloride solution at 60 °C, and the reaction was carried out at the same temperature for 0.5 h. After the reaction was completed, the reaction system was cooled to room temperature, filtered, and dried to obtain 77.3 mg of organometallic catalyst with biguanidin structure, with a yield of 64.3%.
[0066] Application Example 1
[0067] Under anhydrous and oxygen-free conditions, 6.1 mg of the organometallic catalyst with a biguanide structure obtained in Example 1 and 1068.2 mg of L-lactide were weighed, thoroughly mixed, and heated to 150 °C for 7 h. After the reaction was complete, the reaction system was allowed to return to room temperature, and dichloromethane was added. The resulting solution was then added dropwise to anhydrous ethanol, precipitating a white solid. The solvent was removed by centrifugation, and the resulting solid was dried under vacuum to obtain poly(L-lactide). The molecular weight of the obtained poly(L-lactide) was 11.5 kg / mol, and the molecular weight distribution was 1.70.
[0068] Application Example 2
[0069] The specific operation of this application embodiment is the same as that of application embodiment 1, except that 1.35 mg of 1,4-butanediol was added as an initiator to the reaction system. The molecular weight of the poly-L-lactide obtained from the reaction is 10.6 kg / mol, and the molecular weight distribution is 1.57.
[0070] Application Example 3
[0071] The specific operation of this application embodiment is the same as that of application embodiment 2, except that 1 mL of toluene was added as a reaction solvent in the reaction system, and the reaction time was 10 h. The molecular weight of the poly-L-lactide obtained from the reaction was 10.2 kg / mol, and the molecular weight distribution was 1.33.
[0072] Application Example 4
[0073] The specific operation of this application embodiment is the same as that of application embodiment 1, except that 1 mL of propylene oxide is added to the reaction system as a reaction solvent, the reaction temperature is 60 °C, and the reaction time is 3 h. The molecular weight of the poly-L-lactide obtained from the reaction is 29.3 kg / mol, and the molecular weight distribution is 1.17.
[0074] Application Example 5
[0075] Under anhydrous and oxygen-free conditions, 6.2 mg of the organometallic catalyst with a biguanide structure obtained in Example 1 and 1066.5 mg of D,L-lactide were weighed, thoroughly mixed, and heated to 150 °C for 7 h. After the reaction was complete, the reaction system was allowed to return to room temperature, and dichloromethane was added. The resulting solution was then added dropwise to anhydrous ethanol, precipitating a white solid. The solvent was removed by centrifugation, and the resulting solid was dried under vacuum to obtain poly(D,L-lactide). The obtained poly(D,L-lactide) had a molecular weight of 12.4 kg / mol and a molecular weight distribution of 1.71.
[0076] Application Example 6
[0077] Under anhydrous and oxygen-free conditions, 6.0 mg of the organometallic catalyst with a biguanide structure obtained in Example 3 and 1067.5 mg of D-lactide were weighed, thoroughly mixed, and heated to 150 °C for 7 h. After the reaction was complete, the reaction system was allowed to return to room temperature, and dichloromethane was added. The resulting solution was then added dropwise to anhydrous ethanol, precipitating a white solid. The solvent was removed by centrifugation, and the resulting solid was dried under vacuum to obtain poly(D-lactide). The obtained poly(D-lactide) had a molecular weight of 10.6 kg / mol and a molecular weight distribution of 1.67.
[0078] Application Example 7
[0079] Under anhydrous and oxygen-free conditions, 6.1 mg of the biguanide-based organometallic catalyst obtained in Example 1, 532.6 mg of L-lactide, and 378.8 mg of 1,3-dioxane-2-one were weighed and thoroughly mixed. The mixture was then heated to 150 °C and reacted for 12 h. After the reaction was complete, the reaction system was allowed to return to room temperature, and dichloromethane was added. The resulting solution was then added dropwise to anhydrous ethanol, precipitating a white solid. The solvent was removed by centrifugation, and the resulting solid was dried under vacuum to obtain an L-lactide-1,3-dioxane-2-one copolymer. The molecular weight of the obtained copolymer was 10.1 kg / mol, and the molecular weight distribution was 1.44.
[0080] Application Example 8
[0081] Under anhydrous and oxygen-free conditions, 6.1 mg of the biguanide-based organometallic catalyst obtained in Example 1 and 846.7 mg of ε-caprolactone were weighed and thoroughly mixed. Then, 1 mL of propylene oxide was added to the reaction system as a solvent, and the mixture was heated to 60 °C and reacted for 7 h. After the reaction was complete, the reaction system was allowed to return to room temperature, and dichloromethane was added. The resulting solution was then added dropwise to anhydrous ethanol, precipitating a white solid. The solvent was removed by centrifugation, and the resulting solid was dried under vacuum to obtain polycaprolactone. The obtained polycaprolactone had a molecular weight of 43.3 kg / mol and a molecular weight distribution of 1.25.
[0082] Application Example 9
[0083] Under anhydrous and oxygen-free conditions, 6.0 mg of the organometallic catalyst with a biguanide structure obtained in Example 1 and 844.3 mg of ε-caprolactone were weighed and thoroughly mixed. The reaction system was then heated to 150 °C and reacted for 7 h. After the reaction was completed, the reaction system was allowed to return to room temperature, and dichloromethane was added. The resulting solution was then added dropwise to anhydrous ethanol, precipitating a white solid. The solvent was removed by centrifugation, and the obtained solid was dried under vacuum to obtain polycaprolactone. The obtained polycaprolactone had a molecular weight of 13.3 kg / mol and a molecular weight distribution of 1.20.
[0084] Application Example 10
[0085] Under anhydrous and oxygen-free conditions, 3.3 mg of the organometallic catalyst with a biguanide structure obtained in Example 1 and 754.9 mg of 1,3-dioxane-2-one were weighed and thoroughly mixed. Then, 1 mL of propylene oxide was added to the reaction system as a solvent, and the mixture was heated to 60 °C and reacted for 7 h. After the reaction was complete, the reaction system was allowed to return to room temperature, and dichloromethane was added. The resulting solution was then added dropwise to anhydrous ethanol, precipitating a white solid. The solvent was removed by centrifugation, and the resulting solid was dried under vacuum to obtain poly(1,3-dioxane-2-one). The molecular weight of the obtained poly(1,3-dioxane-2-one) was 32.5 kg / mol, and the molecular weight distribution was 1.56.
[0086] Application Example 11
[0087] Under anhydrous and oxygen-free conditions, 5.2 mg of the organometallic catalyst with a biguanide structure obtained in Example 2 and 403.4 mg of 1,3-dioxane-2-one were weighed and thoroughly mixed. The mixture was heated to 150 °C and reacted for 7 h. After the reaction was completed, the reaction system was allowed to return to room temperature, and dichloromethane was added. The resulting solution was then added dropwise to anhydrous ethanol, precipitating a white solid. The solvent was removed by centrifugation, and the obtained solid was dried under vacuum to obtain poly(1,3-dioxane-2-one). The obtained poly(1,3-dioxane-2-one) had a molecular weight of 46.7 kg / mol and a molecular weight distribution of 1.89.
[0088] Comparative Example
[0089] By replacing the magnesium chloride used in Example 1 with an equimolar amount of zinc chloride, an organozinc catalyst Zn-1 with a biguanidin group structure was prepared, the chemical structural formula of which is: .
[0090] Under anhydrous and oxygen-free conditions, 7.0 mg of an organozinc catalyst Zn-1 with a biguanidin group structure and 894.1 mg of ε-caprolactone were weighed and thoroughly mixed. The reaction system was then heated to 150 °C and reacted for 7 h. After the reaction was completed, the reaction system was allowed to return to room temperature, and dichloromethane was added. The resulting solution was then added dropwise to anhydrous ethanol, and no precipitate formed. This demonstrates that the organomagnesium catalyst of this invention exhibits good catalytic activity for the ring-opening polymerization of cyclic lactones.
[0091] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.
Claims
1. The application of an organometallic catalyst based on a biguanide ligand in the catalytic ring-opening polymerization of cyclic lactones, characterized in that, The catalyst is formed by coordination of a ligand with a biguanide structure and a magnesium salt, and its chemical structural formula is as follows: ， Among them, R1 and R2 are independently selected from straight-chain alkanes with 1-3 carbon atoms; R3 is selected from -Cl, -SO3CF3, -Br, -SO3CH3, and -SO3PhCH3. The cyclic lactone is any one or more of L-lactide, D-lactide, D,L-lactide, ε-caprolactone, and 1,3-dioxane-2-one.
2. The application according to claim 1, characterized in that, Includes the following steps: (1) Dissolve urea compounds in acetonitrile, add phosphorus oxychloride dropwise, and then heat the mixture to prepare Vilsmeier salt; (2) Dissolve trans-1,2-cyclohexanediamine and triethylamine in acetonitrile, then add the Vilsmeier salt prepared in step (1) dropwise and heat to carry out the reaction; (3) After the reaction is completed, cool to room temperature, add excess sodium hydroxide to the reaction solution and stir to mix well, then remove the solvent by rotary evaporation, add potassium hydroxide solution to the obtained reaction mixture to redissolve, extract three times with acetonitrile, combine the organic phases, dry with anhydrous sodium sulfate, and then evaporate to dryness to obtain the ligand with biguanide structure. (4) Dissolve the obtained ligand with biguanide structure and magnesium salt in an organic solvent, then add the ligand solution dropwise to the magnesium salt solution and stir to carry out the reaction; (5) After the reaction is completed, the reaction system is cooled to room temperature, filtered and dried to obtain the organometallic catalyst.
3. The application according to claim 2, characterized in that, In step (1), the urea compound is either tetramethylurea or tetraethylurea; the molar ratio of the urea compound to phosphorus oxychloride is 1:1 to 1:2; the temperature at which phosphorus oxychloride is added is -20 ℃ to 4 ℃; the heating reaction is carried out in an inert gas at a temperature of 40 ℃ to 60 ℃ and a reaction time of 6 h to 12 h.
4. The application according to claim 2, characterized in that, In step (2), the molar ratio of trans-1,2-cyclohexanediamine to Vilsmeier salt is 1:2-1:2.5, and the molar ratio of trans-1,2-cyclohexanediamine to triethylamine is 1:2-1:2.5; the temperature at which Vilsmeier salt is added is -20 ℃ to 4 ℃, and the reaction is carried out in an inert gas at a temperature of 85 ℃ to 100 ℃ for 12 h to 20 h.
5. The application according to claim 2, characterized in that, In step (3), the mass concentration of the potassium hydroxide solution is 50%.
6. The application according to claim 2, characterized in that, In step (4), the magnesium salt is any one of magnesium chloride, magnesium trifluoromethanesulfonate, magnesium bromide, magnesium methanesulfonate, and magnesium p-toluenesulfonate; the molar ratio of the ligand with the biguanide structure to the magnesium salt is 1:1-1.5:1; the organic solvent used is one or more of benzene, toluene, xylene, trimethylbenzene, tetrahydrofuran, dioxane, pyridine, and acetonitrile; the reaction is carried out in an inert gas at a temperature of 40 ℃~80 ℃ for 0.5 h-2 h.
7. The application according to claim 1, characterized in that, The molar ratio of the cyclic lactone used to the organometallic catalyst based on the biguanidin ligand is 200:1-1000:1.