A cymene ruthenium complex, a preparation method and application thereof, and a method for preparing a polymer by ring-opening metathesis polymerization of olefins

Abstract

This invention belongs to the field of organometallic catalysis technology, and provides a ruthenium complex of p-cymene, its preparation method and application, and a method for preparing polymers from olefins via ring-opening metathesis polymerization. This invention provides a ruthenium complex of p-cymene having the structure shown in Formula 4. The ruthenium complex of p-cymene provided by this invention contains p-cymene and an asymmetric nitrogen heterocyclic carbene (NHC), exhibits high catalytic activity, and is structurally stable. It can catalyze the ring-opening metathesis polymerization (ROMP) of norbornene under 640 nm red light, 456 nm blue light, and 390 nm ultraviolet light. Its catalytic activity is weak in the absence of light, and no additional photosensitizer is required, making it an excellent photocatalyst. Formula 4

Description

Technical Field

[0001] This invention relates to the field of organometallic catalysis technology, and in particular to a method for preparing and applying ruthenium complexes of cymenes and a method for preparing polymers from olefins via ring-opening metathesis polymerization. Background Technology

[0002] Ring-opening metathesis polymerization (ROMP) is a highly distinctive polymerization method in the preparation of polymer materials. Currently, ruthenium carbene complex catalysts are commonly used for ring-opening metathesis reactions. A recent study (Deep Red to Near-Infrared Light-Controlled Ruthenium-Catalyzed Olefin Metathesis, ACS Catal. 2023, 13, 4384-4390) reported a ruthenium catalyst containing an easily leaving NHC ligand that can catalyze ring-closure metathesis (RCM) and ROMP reactions under red light irradiation in the presence of a triphenanthroline osmium complex as a photosensitizer, thus advancing the development of photocontrolled olefin metathesis reactions. The literature (Combining aligand photogenerator and a Ru precatalyst: a photoinduced approach to cross-linked ROMP polymer films, RSC Adv, 2019, 9, 27789-27799) reports a blue / ultraviolet light-generated photo-controlled olefin metathesis catalyst composed of NHC and p-cymene ruthenium chloride dimer, demonstrating the application of p-cymene ruthenium catalysts in the field of photo-controlled olefin metathesis.

[0003] As can be seen from the literature reports above, the photocatalytic ring-opening polymerization of olefins requires either a photosensitizer or higher-energy blue or ultraviolet light. Therefore, it is imperative to research and develop catalysts that do not require photosensitizers or high-energy light to achieve the ring-opening polymerization of olefins. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a ruthenium complex of p-cymene, its preparation method and application, and a method for preparing polymers from olefins via ring-opening metathesis polymerization. The ruthenium complex of p-cymene provided by this invention does not require a photosensitizer; the ring-opening metathesis polymerization of olefins can be achieved under low-energy infrared light irradiation, simplifying the process of olefin ring-opening metathesis polymerization and reducing costs.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a ruthenium complex of cymene, having the structure shown in Formula 4: Formula 4.

[0006] This invention also provides a method for preparing the ruthenium complex of cymene as described in the above technical solution, comprising the following steps: 1-Methylimidazole and 3,5-dimethylbenzyl bromide were subjected to N-alkylation to give 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide; The 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide was subjected to an in-situ deprotonation metallization reaction with silver oxide to obtain a nitrogen heterocyclic carbene silver complex. The nitrogen-heterocyclic carbene silver complex and the p-cymene ruthenium dichloride dimer were subjected to a transmetallation reaction in the presence of potassium chloride to obtain the p-cymene ruthenium complex.

[0007] Preferably, the molar ratio of 1-methylimidazole to 3,5-dimethylbenzyl bromide is 1:0.8~1.2, the temperature of the N-alkylation reaction is 70~90℃, and the time is 12~18h; the solvent used in the N-alkylation reaction is an aprotic solvent, which includes tetrahydrofuran and / or acetonitrile.

[0008] Preferably, the molar ratio of 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide to silver oxide is 1:0.8~1.2, the temperature of the in-situ deprotonation metallization reaction is 40~100℃, and the time is 4~16h; the solvent used in the in-situ deprotonation metallization reaction is an aprotic solvent, which includes dichloromethane and / or acetonitrile.

[0009] Preferably, the molar ratio of 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide to p-cymene ruthenium dichloride dimer is 1:0.4~0.6, and the molar ratio of 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide to potassium chloride is 1:8~12; the temperature of the metal transfer reaction is 10~30℃, and the time is 14~24h.

[0010] The present invention also provides the application of the p-cymene ruthenium complex described in the above technical solution or the p-cymene ruthenium complex prepared by the above technical solution in the catalytic ring-opening metathesis polymerization (ROMP) of olefins.

[0011] This invention also provides a method for preparing polymers from olefins via ring-opening metathesis polymerization, comprising the following steps: The olefin, catalyst, and solvent are mixed and subjected to ring-opening metathesis polymerization under light irradiation to obtain the polymer. The catalyst is the p-cymene ruthenium complex described in the above technical solution or the p-cymene ruthenium complex prepared by the preparation method described in the above technical solution.

[0012] Preferably, the olefin includes norbornene.

[0013] Preferably, when the olefin is norbornene, the molar ratio of norbornene to catalyst is 1:0.0005~0.02, and the solvent is an aprotic solvent, including one or more of chloroform, dichloromethane and 1,2-dichloroethane.

[0014] Preferably, the light used for illumination includes red light, blue light, or ultraviolet light; the wavelength of the red light is 620~660nm, the wavelength of the blue light is 456nm, and the wavelength of the ultraviolet light is 390nm. The ring-opening metathesis polymerization reaction is carried out at a temperature of 10~30℃ for 1~24h.

[0015] This invention provides a ruthenium complex of cymene.

[0016] The p-cymene ruthenium complex provided by this invention contains p-cymene and asymmetric nitrogen heterocyclic carbene (NHC), exhibiting high catalytic activity and structural stability. It can catalyze the ring-opening metathesis polymerization (ROMP) of norbornene under 640nm red light, 456nm blue light, and 390nm ultraviolet light. Its catalytic activity is weak in the absence of light, and no additional photosensitizer is required, making it an excellent photocatalyst.

[0017] This invention also provides a method for preparing polymers from olefins via ring-opening metathesis polymerization. The method of this invention uses the p-cymene ruthenium complex described in the above technical solution as a catalyst to catalyze the ring-opening metathesis polymerization of olefins. The catalyst dosage is low, red light catalysis can be achieved without the introduction of additional photosensitizers, and the conversion rate is high. Attached Figure Description

[0018] Figure 1 This is a flowchart of the preparation of p-cymene ruthenium complex 4 in Example 1; Figure 2 The 1H NMR spectrum of the cymene ruthenium complex prepared in Example 1; Figure 3 The carbon NMR spectrum of the ruthenium complex of cymene prepared in Example 1; Figure 4 The infrared spectrum of the ruthenium complex of cymene prepared in Example 1; Figure 5 The image shows the UV absorption spectrum of the ruthenium complex prepared in Example 1. Detailed Implementation

[0019] This invention provides a ruthenium complex of cymene, having the structure shown in Formula 4: Formula 4.

[0020] This invention also provides a method for preparing the ruthenium complex of cymene as described in the above technical solution, comprising the following steps: 1-Methylimidazole and 3,5-dimethylbenzyl bromide were subjected to N-alkylation to give 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide; The 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide was subjected to an in-situ deprotonation metallization reaction with silver oxide to obtain a nitrogen heterocyclic carbene silver complex. The nitrogen-heterocyclic carbene silver complex and the p-cymene ruthenium dichloride dimer were subjected to a metal transfer reaction in the presence of potassium chloride to obtain the p-cymene ruthenium complex.

[0021] Unless otherwise specified, the raw materials used in this invention are preferably commercially available products.

[0022] This invention involves the N-alkylation reaction of 1-methylimidazole and 3,5-dimethylbenzyl bromide to obtain 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide. In this invention, the molar ratio of 1-methylimidazole to 3,5-dimethylbenzyl bromide is preferably 1:0.8~1.2, more preferably 1:1. In this invention, the solvent used for the N-alkylation reaction is preferably an aprotic solvent, which preferably includes tetrahydrofuran and / or acetonitrile, more preferably tetrahydrofuran (THF). In this invention, the temperature of the N-alkylation reaction is preferably 70~90℃, specifically preferably 70℃, 75℃, 80℃, 85℃ or 90℃; the time is preferably 12~18h, specifically preferably 12h, 13h, 14h, 15h, 16h, 17h or 18h. In this invention, the N-alkylation reaction is preferably carried out under reflux and an argon atmosphere. After the N-alkylation reaction is completed, the present invention preferably further includes: evaporating the solvent in the N-alkylation reaction solution under reduced pressure to obtain the 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide.

[0023] After obtaining 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide, the present invention involves an in-situ deprotonation metallization reaction of the 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide and silver oxide (Ag₂O) to obtain a nitrogen-containing heterocyclic carbene silver complex. In this invention, the molar ratio of the 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide to silver oxide is preferably 1:0.8~1.2, more preferably 1:1. In this invention, the solvent used in the deprotonation-metal complexation reaction is preferably an aprotic solvent, which preferably includes dichloromethane and / or acetonitrile, more preferably acetonitrile (MeCN). In this invention, the preferred temperature for the in-situ deprotonation metallization reaction is 40-100℃, specifically 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, or 100℃; the preferred time is 4-16 hours, specifically 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, or 16 hours. In this invention, the in-situ deprotonation metallization reaction is preferably carried out under light-protected conditions, reflux heating, and an argon atmosphere. After the in-situ deprotonation metallization reaction is completed, the resulting in-situ deprotonation metallization reaction solution is preferably cooled to room temperature to obtain a system containing the nitrogen-containing heterocyclic carbene silver complex. In this invention, the nitrogen-containing heterocyclic carbene silver complex is preferably dispersed in an aprotic solvent.

[0024] After obtaining the nitrogen-heterocyclic carbene silver complex, the present invention involves subjecting the nitrogen-heterocyclic carbene silver complex and p-cymene ruthenium dichloride dimer to a metal transfer reaction in the presence of potassium chloride to obtain the p-cymene ruthenium complex. In this invention, the molar ratio of 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide to p-cymene ruthenium dichloride dimer is preferably 1:0.4~0.6, specifically preferably 1:0.49 or 1:0.5. In this invention, the molar ratio of 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide to potassium chloride is preferably 1:8~12, specifically preferably 1:10. In this invention, the temperature of the metal transfer reaction is preferably 10~30℃, more preferably 20℃; the time is preferably 14~24h, specifically preferably 14h, 16h, 18h, 20h, 22h or 24h. In this invention, the metal transfer reaction is preferably carried out under stirring and an argon atmosphere. After the metal transfer reaction is completed, the present invention preferably includes: filtering the obtained metal transfer reaction solution with diatomaceous earth to obtain a filtrate; subjecting the filtrate to a first vacuum evaporation to obtain a crude product; subjecting the crude product to column chromatography purification, and after the orange fraction is completely eluted, subjecting the collected column buffer to a second vacuum evaporation to obtain the p-cymene ruthenium complex. In this invention, the eluent used for the column chromatography purification is preferably a mixed solution of dichloromethane and acetone in a volume ratio of 10:1.

[0025] The present invention also provides the application of the p-cymene ruthenium complex described in the above technical solution or the p-cymene ruthenium complex prepared by the above technical solution in the catalytic ring-opening metathesis polymerization (ROMP) of olefins.

[0026] When the ruthenium complex of p-cymene is used to catalyze the ring-opening metathesis polymerization of olefins, the dosage is low, red light catalysis can be achieved without the introduction of additional photosensitizers, and the conversion rate is high.

[0027] This invention also provides a method for preparing polymers from olefins via ring-opening metathesis polymerization, comprising the following steps: The olefin, catalyst, and solvent are mixed and subjected to ring-opening metathesis polymerization under light irradiation to obtain the polymer. The catalyst is the p-cymene ruthenium complex described in the above technical solution or the p-cymene ruthenium complex prepared by the preparation method described in the above technical solution.

[0028] In this invention, the olefin preferably includes norbornene.

[0029] In this invention, when the olefin is norbornene, the molar ratio of norbornene to the catalyst is preferably 1:0.0005~0.02, specifically preferably 1:0.0005, 1:0.001, 1:0.005, 1:0.01, 1:0.015, or 1:0.02. In this invention, the solvent is preferably an aprotic solvent, which preferably includes one or more of chloroform, dichloromethane, and 1,2-dichloroethane, and more preferably dichloromethane.

[0030] In this invention, the light used for illumination preferably includes red light, blue light, or ultraviolet light; the wavelength of the red light is preferably 620~660nm, more preferably 640nm; the wavelength of the blue light is preferably 456nm; and the wavelength of the ultraviolet light is preferably 390nm.

[0031] In this invention, the temperature of the ring-opening metathesis polymerization reaction is preferably 10~30℃, more preferably 20℃; the time is preferably 1~24h, specifically 3h or 7h. In this invention, the ring-opening metathesis polymerization reaction is preferably carried out under stirring and a protective atmosphere, preferably argon.

[0032] After the ring-opening metathesis polymerization reaction is completed, the present invention preferably further includes post-treatment. When the olefin is norbornene, the post-treatment preferably includes the following steps: adding ethyl vinyl ether to the obtained ring-opening metathesis polymerization reaction solution and stirring to quench the ring-opening metathesis polymerization reaction; adding methanol to the quenched reaction solution and stirring to precipitate white polynorbornene; filtering to obtain crude polynorbornene; and subjecting the crude polynorbornene to dichloromethane dissolution-methanol backwashing sequentially to remove residual catalyst to obtain the polynorbornene. In the present invention, the stirring time is preferably 10 min. In the present invention, the number of times the dichloromethane dissolution-methanol backwashing is performed sequentially is preferably 3 times.

[0033] The method for preparing polymers from olefins via ring-opening metathesis polymerization provided by this invention has the advantages of low catalyst dosage, no need to introduce additional photosensitizers, simple operation, high yield, and low cost.

[0034] In this invention, using norbornene (5) as an olefin, polynorbornene (6) is prepared by ring-opening metathesis polymerization under the action of cymene ruthenium complex (4), as follows: .

[0035] The following examples illustrate in detail the ruthenium complexes of cymene provided by the present invention, their preparation methods and applications, and the method for preparing polymers from olefins via ring-opening metathesis polymerization. However, these examples should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1 Example 1 according to Figure 1 The preparation flowchart shown illustrates the preparation of p-cymene ruthenium complex 4. The specific process is as follows: Under argon protection, 1-methylimidazole (1.42 g, 17.3 mmol), 3,5-dimethylbenzyl bromide (3.42 g, 17.2 mmol), and 40 mL of tetrahydrofuran (THF) were added to a 100 mL round-bottom flask. The mixture was heated to reflux at 75 °C for 16 h, and the solvent was evaporated under reduced pressure to obtain 14.82 g of a white solid, 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide, with a yield of 99.6%.

[0037] Under argon protection, 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide 1 (1.18 g, 4.2 mmol), silver oxide (0.97 g, 4.2 mmol), and 150 mL of acetonitrile (MeCN) obtained in the previous step were added to a 500 mL round-bottom flask. The flask was wrapped with aluminum foil and heated to reflux at 85 °C for 5 h in the dark. After the solution cooled to room temperature, ruthenium dichloride dimer of p-cymene was added (1.25 g, 2.04 mmol) and potassium chloride (3.13 g, 42 mmol). The reaction was continued at room temperature (20 °C) with stirring for 15 h. The solution was then filtered through diatomaceous earth, and the filtrate was evaporated to dryness under reduced pressure. The solution was purified by column chromatography using a mixture of dichloromethane and acetone (volume ratio 10:1) as the eluent. After the orange fraction was completely eluted, the column chromatography solution was evaporated to dryness under reduced pressure to obtain 1.46 g of orange-red solid, with a yield of 70.5%.

[0038] The purity of the orange-red solid was determined by relative quantitative proton NMR spectroscopy, and the result was >99%.

[0039] Figure 2 The image shows the 1H NMR spectrum of an orange-red solid. Detailed information is as follows: 1H NMR spectrum ( 1 ¹H NMR (500 MHz, CDCl₃): 1.25 ppm (6H), 2.05 ppm (3H), 2.29 ppm (6H), 2.92 ppm (1H), 4.04 ppm (3H), 5.00 ppm (2H), 5.32 ppm (2H), 5.59 ppm (2H), 6.85 ppm (2H), 6.93 ppm (1H), 6.97 ppm (2H). The peak at 1.64 ppm is for water, and the peak at 7.26 ppm is for chloroform solvent.

[0040] Figure 3 The image shows the carbon NMR spectrum of an orange-red solid. Detailed information is as follows: Carbon spectrum ( 13 C10 NMR (500 MHz, CDCl3): 18.65 ppm, 21.31 ppm, 30.78 ppm, 39.78 ppm, 54.77 ppm, 99.24 ppm, 108.34 ppm, 123.11 ppm, 123.70 ppm, 125.36 ppm, 129.48 ppm, 137.57 ppm, 138.45 ppm. The peaks at 76.80 ppm, 77.06 ppm, and 77.31 ppm are for chloroform solvent.

[0041] Figure 4 The infrared spectrum of the orange-red solid is shown below. Detailed information includes: Infrared spectrum (IR, cm⁻¹) -1, KBr): 2963, 2921, 2870, 1608, 1577, 1539, 1453, 1295, 851, 798.

[0042] The resulting orange-red solid was dissolved in dichloromethane to obtain a solution with a concentration of 10. -5 A solution of mol / L was prepared and subjected to ultraviolet absorption. The results are as follows: Figure 5 As shown, from Figure 5 It can be seen that the maximum absorption peak is located at 406 nm.

[0043] The above characterization results show that the obtained orange-red solid sample is consistent with the structure of the p-cymene ruthenium complex catalyst described in this invention.

[0044] In summary, the preparation method provided by this invention is stable and feasible, with high yield and high purity.

[0045] Application Example 1 Preparation of polynorbornene Under argon protection, (0.4708 g, 5 mmol) norbornene and p-cymene ruthenium complex 4 (0.0253 g, 0.05 mmol) and 5 mL of dichloromethane were added to a 10 mL Schlenk tube. The mixture was irradiated with 640 nm red light at room temperature (20 °C) and stirred for 3 h. The reaction system turned into a dark orange-red gel. Two drops of ethyl vinyl ether were added to the system and stirred for 10 min to quench the reaction. Then, a large amount of methanol was added to the reaction solution and stirred to wash. White polynorbornene precipitated out. After filtration, it was dissolved in dichloromethane and back-eluted with methanol three times to remove residual catalyst in the polynorbornene. After drying, polynorbornene was obtained with a yield of 57.45%.

[0046] Comparative Application Example 1 The difference from Application Example 1 is that the illumination condition was changed to blue light with a wavelength of 456nm, and the yield was 60.94%.

[0047] Comparative Application Example 2 The difference from Application Example 1 is that the illumination conditions were changed to ultraviolet light with a wavelength of 390nm, and the yield was 76.57%.

[0048] Comparative Application Example 3 The difference from Application Example 1 is that the reaction was carried out in the dark, heated in a water bath at 35°C, and the yield was 1.95%.

[0049] Comparative Application Example 4 The difference from Application Example 1 is that the catalyst is replaced with the catalyst shown in the following formula (0.0306 g, 0.05 mmol): .

[0050] The yield was 1.00%.

[0051] Comparative Application Example 5 The difference from Application Example 1 is that the reaction time was extended to 7 hours, and the yield was 72.56%.

[0052] Comparative Application Example 6 The difference from Application Example 1 is that the solvent was replaced with chloroform, and the yield was 9.73%.

[0053] Comparative Application Example 7 The difference from Application Example 1 is that the solvent was replaced with chloroform, the reaction time was extended to 7 hours, and the yield was 29.25%.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A ruthenium complex for p-cymene, characterized in that, It has the structure shown in Equation 4: Formula 4.

2. The method for preparing the ruthenium complex of p-cymene as described in claim 1, characterized in that, Includes the following steps: 1-Methylimidazolium and 3,5-dimethylbenzyl bromide were subjected to N-alkylation to give 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide; The 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide was subjected to an in-situ deprotonation metallization reaction with silver oxide to obtain a nitrogen heterocyclic carbene silver complex. The nitrogen-heterocyclic carbene silver complex and the p-cymene ruthenium dichloride dimer were subjected to a transmetallation reaction in the presence of potassium chloride to obtain the p-cymene ruthenium complex.

3. The preparation method according to claim 2, characterized in that, The molar ratio of 1-methylimidazole to 3,5-dimethylbenzyl bromide is 1:0.8~1.2; the N-alkylation reaction is carried out at a temperature of 70~90℃ for 12~18h; the solvent used in the N-alkylation reaction is an aprotic solvent, which includes tetrahydrofuran and / or acetonitrile.

4. The preparation method according to claim 2, characterized in that, The molar ratio of 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide to silver oxide is 1:0.8~1.2; the temperature of the in-situ deprotonation metallization reaction is 40~100℃ and the time is 4~16h; the solvent used in the in-situ deprotonation metallization reaction is an aprotic solvent, which includes dichloromethane and / or acetonitrile.

5. The preparation method according to claim 2 or 4, characterized in that, The molar ratio of 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide to p-cymene ruthenium dichloride dimer is 1:0.4~0.6, and the molar ratio of 1-methyl-3-(3,5-dimethylbenzyl)imidazolium bromide to potassium chloride is 1:8~12; the temperature of the metallization reaction is 10~30℃, and the time is 14~24h.

6. The application of the p-cymene ruthenium complex according to claim 1 or the p-cymene ruthenium complex prepared by any one of claims 2 to 5 in the catalytic ring-opening metathesis polymerization of olefins.

7. A method for preparing polymers from olefins via ring-opening metathesis polymerization, characterized in that, Includes the following steps: The olefin, catalyst, and solvent are mixed and subjected to ring-opening metathesis polymerization under light irradiation to obtain the polymer. The catalyst is the p-cymene ruthenium complex according to claim 1 or the p-cymene ruthenium complex prepared by any one of claims 2 to 5.

8. The method according to claim 7, characterized in that, The olefins include norbornene.

9. The method according to claim 8, characterized in that, When the olefin is norbornene, the molar ratio of norbornene to the catalyst is 1:0.0005~0.02, and the solvent is an aprotic solvent, including one or more of chloroform, dichloromethane and 1,2-dichloroethane.

10. The method according to claim 9, characterized in that, The light used for illumination includes red light, blue light, and ultraviolet light; the wavelength of the red light is 620~660nm, the wavelength of the blue light is 456nm, and the wavelength of the ultraviolet light is 390nm. The ring-opening metathesis polymerization reaction is carried out at a temperature of 10~30℃ for 1~24h.

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