A Sn(II) catalyst and its preparation method and application
By preparing Sn(II) catalysts and using the spatial geometric constraint strategy of the ligand to change the valence electron structure of Sn(II), the problems of difficult synthesis and limited application of main-group catalysts were solved, and efficient catalysis of defluorination of polyfluoroaromatics and reduction of nitroaromatics was achieved, replacing precious metal catalysts and realizing the Sn(II)/Sn(IV) catalytic cycle.
Patent Information
- Application Number
- CN202411434632.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-15
- Publication Date
- 2025-09-30
- Estimated Expiration
- 2044-10-15
AI Technical Summary
Existing main-group catalysts are difficult to synthesize, have low efficiency, and have limited applications. Traditional precious metal catalysts are expensive and difficult to recycle. Existing low-priced Group XIV element compound catalysts have slow reaction rates, narrow substrate ranges, and large catalyst dosages, making it difficult to establish a balance between stability, reactivity, and catalytic activity.
Using Sn(II) catalyst, the valence electron structure of the central atom Sn(II) is changed through the spatial geometric constraint strategy of the ligand, making it electrophilic and nucleophilic, thereby realizing the conversion of Sn(II)/Sn(IV) oxidation states for defluorination and hydrogenation of polyfluoroaromatic hydrocarbons and reduction of nitroaromatic hydrocarbons.
The highly efficient catalysis of defluorination hydrogenation of polyfluoroaromatics and reduction of nitroaromatics has been achieved. The catalyst raw materials are easily available and the synthesis is simple. It can replace transition metal catalysts and realize Sn(II)/Sn(IV) catalytic cycle. It has been applied in the field of organic synthesis for the first time.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of organic synthesis, in particular to a Sn(II) catalyst and a preparation method and application thereof. Background Art
[0002] Homogeneous catalysis is a key research area in chemistry, with widespread applications in industrial fields such as organic chemistry, fine chemicals, pharmaceuticals, and polymer production. Traditional homogeneous catalytic synthesis primarily utilizes noble metal complexes such as palladium, ruthenium, and rhodium as catalysts. However, precious metals are limited in crustal reserves, expensive, and difficult to recycle, making them incompatible with the concept of green and sustainable development. From a long-term perspective, the development of inexpensive, readily available, and environmentally friendly main-group element catalysts is a major trend in catalytic synthetic chemistry. In recent years, synthetic chemists have conducted extensive research on low-valent main-group element compounds with transition-metal-like valence electron structures. In addition to exploring new structures, properties, and reactivity of low-valent main-group compounds, chemists have been striving to develop greener, more affordable, and readily available main-group element catalysts to replace low-abundance, expensive, and potentially toxic noble metal catalysts.
[0003] Currently, main-group element compounds can be used as ligands for transition metals in the field of organic catalysis. This utilizes the electronic and steric properties of the main-group compounds themselves to modify the valence electron structure of the central metal, thereby changing the catalytic activity of the transition metal catalyst. However, this strategy still cannot avoid the use of transition metal catalysts. The main-group compounds only serve as ligands and do not participate in the reaction as catalytically active species. In addition, main-group element compounds can be used as organic small molecule catalysts, utilizing their electrophilicity or nucleophilicity to participate in organic small molecule catalytic reactions. However, this type of catalytic system has problems such as slow reaction speed, narrow substrate range, and large catalyst dosage, and its development prospects in industrial application are limited. In the prior art, researchers have successively synthesized low-valent phosphorus compounds and low-valent bismuth compound catalysts and used them in the field of organic synthesis as alternatives to transition metal catalysts. However, for low-valent Group XIV element compounds whose raw materials are cheap and easy to obtain and can mimic the reactivity of transition metals, people have not been able to find corresponding methods to modify them and make them catalytically active. How to establish a balance between the stability, reactivity and catalytic activity of Group XIV element compounds, develop main-group catalysts centered on Group XIV elements, and apply them to the field of organic synthesis has always been a key scientific issue that needs to be solved urgently. Summary of the Invention
[0004] In view of the technical problems of existing main-group catalysts such as difficulty in synthesis, low efficiency and limited application, the present invention provides a Sn(II) catalyst and a preparation method thereof.
[0005] The preparation method of the Sn(II) catalyst provided by the present invention is as follows:
[0006] S1. Add the backbone molecule and solvent A into a reaction vessel, introduce inert gas to exclude air, and place the reaction vessel in an ice bath to lower the solution temperature to 0°C. Then add n-butyl lithium, stir at 0°C for 30 minutes, and then stir at room temperature for 30 minutes to obtain solution A.
[0007] The solvent A is selected from at least one of diethyl ether, diisopropyl ether, tetrahydrofuran and tetrahydropyran.
[0008] The structural formula of the skeleton molecule is as follows:
[0009]
[0010] The Chinese name of the backbone molecule is bis(triphenylphosphine)carbene, which is the Chinese translation of carbodiphosphorane.
[0011] S2. Dissolve tin dichloride in solvent B to obtain solution B, add solution B to solution A, stir at room temperature for 6-18 hours, then remove solvent B by distillation under reduced pressure, add solvent C for extraction, extract the target product with solvent C, and then remove solvent C under reduced pressure to obtain Sn(II) catalyst, also known as tin carbene catalyst.
[0012] The solvent B is selected from at least one of tetrahydrofuran, ether, toluene, benzene, xylene or trimethylbenzene.
[0013] The solvent C is selected from at least one of benzene, toluene, chlorobenzene, xylene and trimethylbenzene.
[0014] Preferably, the molar ratio of the backbone molecule, n-butyl lithium, and tin dichloride is 1:(2.0-2.2):1.
[0015] Preferably, in step S1, the prepared solution A is subjected to reduced pressure distillation to remove the solvent A in the solution A, and then the subsequent step S2 is performed. Because the effective shelf life of the solution A is very short when the solution A contains the solvent A, the shelf life can be extended by removing the solvent A from the solution A.
[0016] Preferably, in step S2, solvent B is removed by distillation under reduced pressure. After complete removal of solvent B, solvent C is added, and the amount of solvent C is controlled to completely dissolve the target product without dissolving the by-product lithium chloride. After adding solvent C, ultrasonic dispersion is performed to completely dissolve the target product while the lithium chloride remains undissolved. The mixture is then allowed to stand for several minutes, and then filtered to remove solid lithium chloride. The resulting liquid phase is then subjected to reduced pressure to remove solvent C, thereby obtaining the target product.
[0017] The preparation reaction formula of Sn(II) catalyst is as follows:
[0018]
[0019] The Sn(II) catalyst can be used as a catalyst in the defluorination reaction of polyfluoroaromatics and the reduction reaction of nitroaromatics.
[0020] The solvent used in the defluorination hydrogenation reaction of polyfluoroaromatics and the reduction reaction of nitroaromatics is one of tetrahydrofuran, toluene, benzene, xylene, and trimethylbenzene. The reaction temperature is 20-120° C. and the reaction time is 0.5-48 hours.
[0021] The molar ratio of the Sn(II) catalyst to the polyfluoroaromatic hydrocarbon is (1-10):100.
[0022] The molar ratio of the Sn(II) catalyst to the nitroaromatic hydrocarbon is (1-100):1000.
[0023] Compared with the prior art, the present invention is beneficial in that:
[0024] (1) The present invention utilizes the spatial geometric constraint strategy of the ligand to change the valence electron structure of the central atom Sn(II), so that the compound has both electrophilicity and nucleophilicity, can undergo Sn(II) / Sn(IV) oxidation state conversion, and can be used in the field of organic synthesis as a transition metal-like catalyst.
[0025] (2) The low-valent tin compound can be used as a catalyst to achieve the defluorination hydrogenation of polyfluoroaromatic systems to generate corresponding hydrogenation products; it can also achieve efficient reduction of nitroaromatic systems to generate reduction products such as azobenzene and aniline according to demand. Existing Sn(II) compounds are unable to undergo the Sn(II) / Sn(IV) valence-variable catalytic cycle and therefore cannot be used as catalysts for the defluorination hydrogenation of polyfluoroaromatics and the reduction of nitroaromatics. The catalyst prepared by the present invention has achieved the defluorination hydrogenation of polyfluoroaromatics and the reduction of nitroaromatics for the first time using a heavy group XIV compound.
[0026] (3) Compared with traditional transition metal catalysts, this catalyst has readily available raw materials and is simple to synthesize, making it a viable alternative to transition metal catalysts in organic synthesis reactions. Furthermore, this compound is the first organotin compound capable of a Sn(II) / Sn(IV) catalytic cycle and the first Group XIV organic compound capable of a redox cycle.
[0027] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 The catalyst prepared in Example 1 119Sn NMR test results diagram.
[0029] Figure 2 The catalyst prepared in Example 1 was used before, during and after the hydrogenation of perfluoropyridine. 31 P NMR test results diagram.
[0030] Figure 3 The catalyst prepared in Example 1 was used for hydrogenation of perfluoropyridine 19 F NMR test results.
[0031] Figure 4 The catalyst prepared in Example 1 was used before, during and after the reduction reaction of nitrobenzene. 31 P NMR test results diagram. DETAILED DESCRIPTION
[0032] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.
[0033] Example 1
[0034] A method for preparing a Sn(II) catalyst, comprising the following steps:
[0035] (1) 0.1 mmol of bis(triphenylphosphine) carbene and 20 mL of ether were added to a reaction vessel; the reaction vessel was then purged three times under argon protection, and the reaction vessel was placed in an ice bath to reduce the solution temperature to 0°C. 0.22 mmol of n-butyl lithium (a commercially available n-butyl lithium solution with a concentration of 1.6 or 2.5 M in n-hexane) was then added, and the mixture was stirred at 0°C for 30 min, and then stirred at room temperature for 30 min to obtain solution A; solution A was subjected to reduced pressure distillation to remove the solvent ether.
[0036] (2) 0.1 mmol of tin dichloride was dissolved in 20 mL of tetrahydrofuran to obtain solution B; solution B was added to the material after the solvent was removed by vacuum distillation in step S1, and the mixture was stirred at room temperature for 12 h. The solvent tetrahydrofuran was removed by vacuum distillation to obtain a solid; then 30 mL of toluene was added, and ultrasonic dispersion was performed for 10 min to dissolve the target catalyst in the toluene, while the by-product lithium chloride did not dissolve. After standing for 10 min, the lithium chloride was filtered out by suction, and the filter cake was washed three times with toluene. The liquid phases were combined and vacuum distilled to dryness to obtain the target Sn(II) catalyst with a yield of 85%.
[0037] The chemical reaction formula is as follows:
[0038]
[0039] In another embodiment, the solution A obtained in step (1) may be used directly in the subsequent steps without being evaporated under reduced pressure to remove the ether solvent.
[0040] The catalyst prepared in Example 1 was subjected to structural characterization, and the results were as follows: 31 P NMR (162MHz, benzene-d6): δ = 24.1 (s). like Figure 1 As shown, 119 Sn NMR (149MHz, benzene-d6): δ = 135.9 (s). HRMS(ESI):m / zcalculated for C 37 H 28 P2Sn[M+MeO] + :685.0876, found:685.0875.UV-vis(THF solution)[nm]:λ=320.
[0041] Application Example 1
[0042] The catalyst prepared in Example 1 was used for the defluorination and hydrogenation reaction of polyfluoroaromatics. The reaction equation is as follows:
[0043]
[0044] The specific method is as follows: 30 μL of pentafluoropyridine, 30 mg of catalyst, 30 μL of phenylsilane and 1.5 mL of tetrahydrofuran were mixed and added to a reaction tube. The atmosphere was replaced with argon three times and the reaction was carried out at 60°C for 2 hours. After the reaction, the reaction was cooled to room temperature and the conversion rate of pentafluoropyridine, the yield of the product and the state of the catalyst were detected by nuclear magnetic resonance. The results are shown in FIG. Figure 2 and Figure 3 , the substrate conversion rate and the target product yield were both 99%, and there was no catalyst loss.
[0045] Application Example 2
[0046] The catalyst prepared in Example 1 was used for the reduction reaction of nitroaromatics, and the reaction equation is as follows:
[0047]
[0048] Specific method: 50 μL nitrobenzene, 30 mg catalyst, 60 μL phenylsilane and 1.5 mL tetrahydrofuran were mixed and added to the reaction tube. The atmosphere was replaced with argon three times and stirred at room temperature for 30 minutes. After the reaction, the mixture was cooled to room temperature and the conversion rate of nitrobenzene, the yield of aniline and the state of the catalyst were detected by gas chromatography-mass spectrometry. The results are shown in Figure 2. Figure 4 , the substrate conversion rate and the target product yield were both 99%, and there was no catalyst loss.
[0049] Comparative Example 1
[0050] To illustrate the advantages of the catalyst prepared by the present invention, this comparative example provides an application of an existing reported tin catalyst 1 in defluorination hydrogenation. The molecular structure of catalyst 1 is as follows:
[0051]
[0052] The catalytic reaction equation is as follows:
[0053]
[0054] The specific reaction conditions were the same as those for the Sn(II) catalyst in Application Example 1: 30 μL of pentafluoropyridine, 30 mg of Catalyst 1, 30 μL of phenylsilane, and 1.5 mL of tetrahydrofuran were mixed and added to a reaction tube. The atmosphere was replaced with argon three times, and the reaction was carried out at 60°C for 2 h. After the reaction, the reaction was cooled to room temperature. The conversion of pentafluoropyridine and the yield of the product were measured by nuclear magnetic resonance spectroscopy. The substrate conversion and the yield of the target product were both less than 1%.
[0055] Comparative Example 2
[0056] This comparative example provides a reported use of tin catalyst 2 and catalyst 3 in the reduction of nitroaromatics.
[0057] The molecular structures of catalyst 2 and catalyst 3 are as follows:
[0058]
[0059] The reaction equation is as follows:
[0060]
[0061] The specific reaction conditions were the same as those for the Sn(II) catalyst in Application Example 2: 50 μL of nitrobenzene, 12 mg of Catalyst 2 or 30 mg of Catalyst 3, 60 μL of phenylsilane, and 1.5 mL of tetrahydrofuran were mixed and added to a reaction tube. The atmosphere was replaced with argon three times and stirred at room temperature for 30 minutes. After the reaction, the reaction was cooled to room temperature. The conversion of nitrobenzene and the yield of aniline were measured by gas chromatography-mass spectrometry. Both the substrate conversion and the target product yield were less than 1%.
[0062] The experimental comparison of the two application examples and the comparative example above demonstrates that the Sn(II) catalyst prepared by the present invention can catalyze both the defluorination and hydrofluorination of polyfluoroaromatic hydrocarbons and the reduction of nitroaromatic hydrocarbons. Existing Sn(II) catalysts, however, lack catalytic activity in these reactions due to their inability to undergo Sn(II) / Sn(IV) valence changes. Compared to traditional transition metal catalysts, this catalyst, with readily available raw materials and simple synthesis, can replace transition metal catalysts in organic synthesis reactions.
[0063] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.
Claims
1. A Sn(II) catalyst, characterized in that The molecular structure is as follows:
2. A method for preparing the Sn(II) catalyst according to claim 1, characterized in that: Here are the steps: S1. Add the backbone molecule and solvent A to a reaction vessel, introduce inert gas to exclude air, and place the reaction vessel in an ice bath to reduce the solution temperature to 0°C. Then, add n-butyl lithium, stir at 0°C for 30 minutes, and then stir at room temperature for 30 minutes to obtain solution A; the solvent A is selected from at least one of diethyl ether, diisopropyl ether, tetrahydrofuran, and tetrahydropyran; The structural formula of the skeleton molecule is as follows: S2. Dissolve tin dichloride in solvent B to obtain solution B, add solution B to solution A, stir at room temperature for 6-18 hours, then remove solvent B by distillation under reduced pressure, add solvent C, extract the target product with solvent C, and then remove solvent C by distillation under reduced pressure to obtain Sn(II) catalyst; The solvent B is selected from at least one of tetrahydrofuran, ether, toluene, benzene, xylene or trimethylbenzene; The solvent C is selected from at least one of benzene, toluene, chlorobenzene, xylene and trimethylbenzene.
3. The method for preparing the Sn(II) catalyst according to claim 2, wherein: The molar ratio of the skeleton molecule, n-butyl lithium and tin dichloride is 1:(2.0-2.2):
1.
4. The method for preparing the Sn(II) catalyst according to claim 2, wherein: In step S1, the prepared solution A is then distilled under reduced pressure to remove the solvent A in the solution A, and then the subsequent step S2 is performed.
5. The method for preparing the Sn(II) catalyst according to claim 2, wherein: In step S2, solvent B is removed by distillation under reduced pressure. After solvent B is completely removed, solvent C is added, and the amount of solvent C is controlled so that the target product is completely dissolved without dissolving by-products.
6. The method for preparing the Sn(II) catalyst according to claim 5, wherein: In step S2, after adding solvent C, ultrasonic dispersion is performed to completely dissolve the target product, and then the mixture is allowed to stand for several minutes and then filtered. The obtained liquid phase is subjected to reduced pressure distillation to remove solvent C, thereby obtaining the target product.
7. Use of the Sn(II) catalyst as claimed in claim 1, characterized in that: Catalyst for the defluorination of polyfluoroaromatics or the reduction of nitroaromatics.
8. The use of the Sn(II) catalyst according to claim 7, characterized in that: The molar ratio of the Sn(II) catalyst to the polyfluoroaromatic hydrocarbon is (1-10):
100.
9. The use of the Sn(II) catalyst according to claim 7, characterized in that: The molar ratio of the Sn(II) catalyst to the nitroaromatic hydrocarbon is (1-100):1000.