Synthesis method of diolefin coordinated rhodium tetrafluoroborate

Abstract

The invention belongs to the technical field of preparation of noble metal homogeneous catalysts, and particularly relates to a synthesis method of diolefin coordinated rhodium tetrafluoroborate, rhodium trichloride is used as a raw material, [Rh (diene) Cl] 2 is obtained through diolefin ligand coordination, then hydrolysis is performed under alkaline conditions to obtain diolefin coordinated hydroxyl rhodium dimer [Rh (diene) (OH)] 2, and the diolefin coordinated hydroxyl rhodium dimer [Rh (diene) (OH)] 2 reacts with tetrafluoroboric acid to obtain the diolefin coordinated rhodium tetrafluoroborate. And a high-purity [Rh (diene) 2] [BF4] product is obtained with high yield. According to the synthesis method, silver tetrafluoroborate is not used, the production cost is remarkably reduced, the content of impurity ions such as silver is reduced, other impurities are not introduced, the purity and quality of the product are improved, the post-treatment purification process is greatly simplified, and the one-way total yield is 87% or above.

Description

Technical Field

[0001] The invention belongs to the technical field of noble metal homogeneous catalyst preparation, and particularly relates to a method for synthesizing diene coordinated rhodium tetrafluoroborate. Background Art

[0002] Rhodium (I) complexes are an important class of noble metal homogeneous catalysts, which are widely used in the research and development and industrial production of hydroformylation, hydrogenation, cross-coupling and hydrosilylation reactions in the fields of information materials, emerging drugs, polymers and other advanced materials. Especially in the field of asymmetric hydrogenation, Knowle et al. first applied Rh(PPh3)3Cl to the asymmetric hydrogenation of olefins in 1968. Monsanto Company made further improvements and produced L-dopa, a specific drug for the treatment of Parkinson's disease. Other well-known rhodium (I) catalytic system products include pharmaceutical intermediate sacubitril, flavor L-menthol, sweetener asparagus, herbicide glufosinate, etc., all of which reflect the magical charm and infinite vitality of rhodium (I) complex catalytic asymmetric hydrogenation.

[0003] With the continuous progress of basic research and process production in recent years, more and more rhodium (I) ligand catalytic systems have been developed. On the one hand, according to the structure of the reaction substrate, chiral ligands such as DuanPhos, TangPhos, MingPhos, BINAPINE, etc. have been designed and developed by scientists; on the other hand, different forms of rhodium (I) complex precursors have also been continuously developed, such as 1,5-cyclooctadiene (COD), norbornadiene (2,5-NBD) and other olefin ligands can stabilize rhodium (I) while showing strong Lewis acidity, which can further improve the catalytic effect of rhodium; nitrate (NO3), tetrafluoroborate (BF4), hexafluorotellurate (SbF6), trifluoromethanesulfonate (OTf) and other counterions also have a great influence on the catalytic effect. Among them, diene-coordinated rhodium tetrafluoroborate ([Rh(diene)2][BF4]) often has good substrate adaptability, high product yield and enantioselectivity in asymmetric hydrogenation reactions, and is widely used in the synthesis of drugs such as ramipril, sitagliptin, and naproxen.

[0004] The preparation method of diolefin coordinated rhodium tetrafluoroborate was first reported in the literature J.Am.Chem.Soc.1971,93,3089 and Inorg.Synth.1970,15,88. Generally, the synthesis route is two steps. The first step is that rhodium trichloride is coordinated with a diolefin ligand (diene) in an alcohol solution to obtain a diolefin coordinated rhodium chloride dimer ([Rh(diene)Cl]2), and then ion exchange is carried out with an excess of silver tetrafluoroborate to obtain the final product, and the total yield is less than 50%.

[0005] Patents CN105585596A, CN111087274A and CN103214520A improve the preparation process and increase the amount of silver tetrafluoroborate, so that the total yield can reach 85%. However, the use of excessive silver tetrafluoroborate (2.5-3.5eq) has high cost and the introduction of a large amount of silver ions makes the impurity content of the product too high, which ultimately leads to unsatisfactory catalytic activity.

[0006] Patent CN112679554A adds acetylacetonato dicarbonyl rhodium to dichloromethane for dissolution, adds tetrafluoroboric acid, and obtains the corresponding product through extraction, liquid separation, rotary evaporation and other steps, avoiding the introduction of silver ions, improving the purity of the product, and significantly reducing the production cost. However, its raw material acetylacetonato carbonyl rhodium is generally obtained by reacting rhodium trichloride and acetylacetone in N, N-dimethylformamide, and nearly 10% of rhodium remains in the high-boiling amide organic solvent, which is difficult to recover, and a large amount of carbon monoxide is released during the reaction process, which does not meet the requirements of modern green chemistry from the perspective of economy and environmental protection. At the same time, due to the extremely high price of rhodium, it is particularly important to improve the total yield and reduce the recovery cost in actual production.

[0007] Based on the above literature, it is urgent to develop an efficient, convenient, green and large-scale production method for the synthesis of high-purity [Rh(diene)2][BF4]. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention provides a method for synthesizing high-purity diolefin-coordinated rhodium tetrafluoroborate. Figure 1 , using rhodium trichloride as a raw material, after obtaining [Rh(diene)Cl]2 through coordination with a diene ligand, it is hydrolyzed under alkaline conditions to obtain a diene coordinated hydroxyl rhodium dimer ([Rh(diene)(OH)]2), which is then reacted with tetrafluoroboric acid to obtain a high-purity [Rh(diene)2][BF4] product with a high yield. The reaction route avoids the use of silver tetrafluoroborate, significantly reduces production costs, reduces the content of impurity ions such as silver, does not introduce other impurities, improves product purity and quality, greatly simplifies the post-processing purification process, and the total yield per pass is more than 87%. At the same time, the rhodium that does not participate in the reaction is easier to recover, which is in line with the concept of modern green synthetic chemistry and is more conducive to industrial production.

[0009] Specifically, the present invention provides the following technical solutions:

[0010] A method for synthesizing rhodium tetrafluoroborate coordinated by diene comprises the following steps:

[0011] 1) under the protection of an inert atmosphere, adding hydrated rhodium trichloride to a solvent, and dissolving the rhodium trichloride to obtain a first solution;

[0012] 2) adding a diene ligand (diene) to the first solution, heating it to reflux temperature, and performing reflux reaction for a period of time, wherein a precipitate is a diene-coordinated rhodium chloride dimer [Rh(diene)Cl]2, and separating the diene-coordinated rhodium chloride dimer [Rh(diene)Cl]2;

[0013] 3) dissolving the separated diolefin coordinated rhodium chloride dimer [Rh(diene)Cl]2 in an organic solvent to obtain a second solution; then dropping the second solution into an inorganic alkaline aqueous solution with a pH>13 to react, and a precipitate is diolefin coordinated rhodium chloride dimer [Rh(diene)(OH)]2, and separating the diolefin coordinated rhodium chloride dimer [Rh(diene)(OH)]2;

[0014] 4) Under the protection of an inert atmosphere, the separated diene-coordinated rhodium chloride dimer [Rh(diene)(OH)]2 is dissolved in an organic solvent to obtain a third solution; tetrafluoroboric acid is then added dropwise to the third solution, and then the diene ligand (diene) is added to the third solution. After a period of reaction, [Rh(diene)2]BF4 is obtained.

[0015] Preferably, in step 1), the solvent is a low-carbon alcohol, or a mixed solvent of a low-carbon alcohol and water, and the low-carbon alcohol is one of methanol, ethanol, n-propanol, and isopropanol. If the low-carbon alcohol is replaced by a high-carbon alcohol, there are disadvantages such as low yield.

[0016] Preferably, in step 1), the concentration of rhodium in the first solution is 10-40 g / L. If the rhodium concentration is lower than the above range, there are disadvantages such as excessive use of solvent and poor economic efficiency. If the rhodium concentration is higher than the above range, there is a disadvantage of generating more impurities such as bridged rhodium clusters.

[0017] As a preference, in step 2) and step 4), the diene ligands are independently selected from at least one of butadiene, dicyclopentadiene (DCPD), 1,5-cyclooctadiene (COD), 2,5-norbornene (2,5-NBD), and 1,5-hexadiene (HEX). Such diene ligands form a feedback π* bond with Rh(I) of d8 electronic structure, stabilize the rhodium center, and show strong Lewis acidity.

[0018] Preferably, in step 2), the amount of the diene ligand added is 2 to 5 times the amount of the rhodium element in the first solution.

[0019] Preferably, in step 2), the reflux temperature is 65-85° C., and the reflux reaction time is 12-24 h.

[0020] Preferably, in step 2), after the reflux reaction, a solid filter cake is obtained by filtration, and then the solid filter cake is washed (with ethanol and water in sequence) and dried to separate the diene coordinated rhodium chloride dimer [Rh(diene)Cl]2.

[0021] Preferably, in step 3), the organic solvent is selected from at least one of ethanol, acetone and tetrahydrofuran.

[0022] Preferably, in step 3), the inorganic alkaline aqueous solution is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution.

[0023] Preferably, in step 3), the second solution is added dropwise into the inorganic alkaline aqueous solution via a constant pressure dropping funnel.

[0024] As a preference, in step 3), the reaction temperature is 20-50°C and the reaction time is 3-5h (excluding the dropwise addition time).

[0025] Preferably, in step 3), a solid filter cake is obtained by filtration, and then the solid filter cake is washed (preferably with water and 0.1-2 wt% nitric acid, alternately washed 3-5 times), thereby isolating the diene-coordinated rhodium chloride dimer [Rh(diene)(OH)]2.

[0026] More preferably, step 3) further comprises the following steps: concentrating the filtrate obtained by the filtration to 1 / 4 to 1 / 3 of the original volume, cooling to obtain a precipitate, filtering it a second time, combining the solid filter cakes and then washing it.

[0027] Preferably, in step 4), the organic solvent is selected from at least one of dichloromethane, chloroform and 1,2-dichloroethane.

[0028] Preferably, in step 4), the amount of tetrafluoroboric acid added is 2.5 to 3.5 times the amount of rhodium element in the first solution.

[0029] Preferably, in step 4), the tetrafluoroboric acid is added dropwise to the third solution in the form of a tetrafluoroboric acid aqueous solution; the concentration of the tetrafluoroboric acid in the tetrafluoroboric acid aqueous solution is 0.5-1.5M.

[0030] Preferably, in step 4), the tetrafluoroboric acid is added dropwise to the third solution via a constant pressure dropping funnel.

[0031] Preferably, in step 4), the amount of the diene ligand added is 2.5 to 5 times the amount of the rhodium element in the first solution.

[0032] Preferably, in step 4), the diene ligand is added to the third solution in batches. Since the addition of the diene ligand generates heat, adding it all at once will cause local overheating, so batch addition is adopted.

[0033] Preferably, in step 4), the reaction temperature is 15 to 40° C. and the reaction time is 2 to 3 hours.

[0034] As a preference, step 4) also includes the step of purifying the [Rh(diene)2]BF4 obtained by the reaction:

[0035] The reaction solution after the reaction is cooled to room temperature, and then extracted (the solvent used for extraction is dichloromethane or chloroform or 1,2-dichloroethane, etc.), separated (the lower organic phase is taken), dried (dried with anhydrous sodium sulfate and / or anhydrous magnesium sulfate), the solvent is removed by rotary evaporation, and vacuum dried to obtain the [Rh(diene)2]BF4 product.

[0036] The high-purity diolefin coordinated rhodium tetrafluoroborate prepared by the synthesis method of the present invention has a simple and clear reaction process route, mild conditions, cheap and easy-to-obtain raw materials, avoids the use of silver tetrafluoroborate, has a low production cost, the content of metal impurity ions such as silver, calcium, magnesium, and iron in the product is less than 20ppm, the content of other counter anions is less than 30ppm, the total product yield is ≥87%, and the unconverted rhodium coordination form is simple and easy to recover, and the route is suitable for industrial production. The obtained diolefin coordinated rhodium tetrafluoroborate product has low chlorine content and metal impurity content, good batch stability, and is suitable as an asymmetric hydrogenation catalyst for structural substrates such as enamides, enol esters and acrylic acid.

[0037] The beneficial effects of the present invention are at least:

[0038] 1) The method for synthesizing the diolefin-coordinated rhodium tetrafluoroborate provided by the present invention, wherein the counter ion tetrafluoroborate in the product is obtained from a tetrafluoroboric acid solution, thereby avoiding the use of silver tetrafluoroborate, fundamentally reducing the impurities such as chloride ions and silver ions which are difficult to remove in the washing stage and have a greater impact on the catalytic effect, simplifying the washing process, and the product having a higher catalytic activity;

[0039] 2) The method for synthesizing diolefin coordinated rhodium tetrafluoroborate provided by the present invention uses common hydrated rhodium trichloride as a synthetic raw material, and obtains high-purity diolefin coordinated rhodium tetrafluoroborate through coordination, hydrolysis, acidification and other processes. The reaction process route is simple and clear, the conditions are mild, the raw materials are cheap and easy to obtain, and the use of expensive chemical reagents such as silver tetrafluoroborate is avoided. The production cost is low, and the route is suitable for industrial production;

[0040] 3) The method for synthesizing the diolefin coordinated rhodium tetrafluoroborate provided by the present invention has the characteristics of low metal and counter ion impurity content. The content of metal impurity ions such as silver, calcium, magnesium, and iron is less than 35ppm, and the content of other counter anions is less than 30ppm, which meets the use requirements of fine chemical rhodium catalysts such as medicine, pesticides, flavors and fragrances, and is suitable as an asymmetric hydrogenation catalyst for structural substrates such as enamides, enol esters and acrylic acid;

[0041] 4) The method for synthesizing the diolefin-coordinated rhodium tetrafluoroborate provided by the present invention can produce high-purity diolefin-coordinated rhodium tetrafluoroborate, with a total product yield of ≥87% per pass in terms of rhodium, and the coordination form of the unconverted rhodium is simple, mainly diene, Cl and hydroxyl, and the rhodium waste liquid can be easily recovered. This route is suitable for industrial production;

[0042] 5) In the method for synthesizing the diene-coordinated rhodium tetrafluoroborate provided by the present invention, the concentration of the rhodium element in the first solution in step 1) is preferably 10-40 g / L. Studies have shown that when the rhodium concentration is higher than the above range, there is a disadvantage of generating more impurities such as bridged rhodium clusters;

[0043] 6) In the method for synthesizing the diene-coordinated rhodium tetrafluoroborate provided by the present invention, the diene ligand in step 4) is preferably added to the third solution in batches. Since the addition of the diene ligand generates heat, adding it all at once will cause local overheating, so batch addition is adopted. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The figure is a comparison between the synthetic route of the present invention and the synthetic route of the existing synthetic method (wherein the upper synthetic route is the present invention, and the lower synthetic route is the existing synthetic method). DETAILED DESCRIPTION

[0045] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. If no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in the field or the product manual shall be followed.

[0046] Example 1

[0047] (1) Under nitrogen protection, 400.0 g of hydrated rhodium trichloride (1.52 mol, rhodium content 38.5%, containing 154 g of rhodium) was added to a mixed solvent containing 10.0 L of water and 2.0 L of ethanol, and stirred continuously for 2 h to completely dissolve it. The rhodium concentration of the solution was 12.8 g / L.

[0048] (2) Add 0.4 L of 1,5-cyclooctadiene (density 0.882 g / ml, molecular weight 108.18, 2.14 eq) into the reactor at once and heat under reflux at 95°C. The color of the solution gradually becomes lighter and clear, and a large amount of orange-yellow solid precipitates. The reaction is stopped after 18 hours. After the solution is cooled, it is filtered, and the filter cake is washed with ethanol and distilled water in turn. The filtrate is retained and can be used in the next production. Vacuum drying is performed to obtain 361.7 g of an orange-yellow powder [(COD)RhCl]2 product, and the Rh content is 41.72% as measured by ICP-OES (inductively coupled plasma emission spectrometer). The yield is calculated to be 98.0%.

[0049] (3) In a 50L reactor, 84g potassium hydroxide was added and dissolved in 4.5L water. 361.7g orange-yellow powder obtained in step (1) was dissolved in 20L acetone and added to the above-mentioned alkali solution through a constant pressure dripping staircase. The mixture was stirred at room temperature for 5h to obtain a yellow precipitate, which was filtered to obtain a filter cake. The filtrate was concentrated to 5L, and a yellow precipitate was precipitated. The filter cake was filtered again to obtain a filter cake. The above-mentioned filter cakes were combined and washed alternately with water and 0.4wt% nitric acid for 3 times to obtain 308.0g yellow powder [(COD)Rh(OH)]2. The Rh content was 45.08% as measured by ICP-OES. The reaction yield was calculated to be 92.0%.

[0050] (4) Under nitrogen protection, add 308.0g of yellow powder obtained in (3) into a 20L reactor, add 8L of dichloromethane to dissolve it, and then add 1L of 5.0M tetrafluoroboric acid to the reactor. Then, add 0.5L of COD to the reaction bottle in batches. After the feeding is completed, slowly heat the temperature to 25°C, stir at constant temperature for 2-3h, and stop the reaction. At room temperature, extract, separate, collect the organic phase solution containing the product, dry it with anhydrous sodium sulfate, remove the solvent by rotary evaporation, and dry it in vacuum to obtain 538.9g of orange-red product [Rh(COD)2]BF4. The Rh content was 25.30% detected by ICP-OES, and the calculated yield was 98.2%. According to ICP-OES and ion chromatography (IC), the impurity contents of Ag, Au, Al, Fe, Ni, Si, Ca, etc. were all less than 35ppm, and the Cl ion content was less than 20ppm. The calculated product purity was 99.6%.

[0051] Example 2

[0052] (1) Under nitrogen protection, 320.0 g of hydrated rhodium trichloride (1.216 mol, rhodium content 38.5%, containing 123.2 g of rhodium) was added to a reaction kettle containing 6 L of methanol and stirred continuously for 1 h. The rhodium concentration of the solution was 20.5 g / L.

[0053] (2) Add 0.6L of 2,5-norbornadiene (density 0.906g / ml, molecular weight 92.14, 4.85eq) to the reactor at one time and heat to react at 65°C. The color of the solution gradually becomes lighter and clear, and a large amount of orange-yellow solid precipitates. The reaction is stopped after 15 hours of reaction. After the solution is cooled, it is filtered and the filter cake is washed with ethanol and distilled water in turn. The filtrate can be used in the next production. Vacuum drying is performed to obtain 262.3g of orange-yellow powder [(NBD)RhCl]2 product. The Rh content is 44.62% as measured by ICP. The yield is calculated to be 95.0%. The filtrate is used again.

[0054] (3) In a 50L reactor, add 50g of sodium hydroxide and dissolve it in 3.5L of water. Dissolve 262.3g of the orange-yellow obtained in step (1) in 15L of tetrahydrofuran and add it to the above-mentioned alkali solution through a constant pressure dripping staircase. Stir at room temperature for 5h to obtain a yellow precipitate. Filter to obtain a filter cake. Concentrate the filtrate to 3L, and a yellow precipitate is precipitated. Filter twice to obtain a filter cake. Combine the above filter cakes and wash them alternately with water and 0.5wt% nitric acid for 3 times to obtain 223.5g of orange-yellow powder [(NBD)Rh(OH)]2. The Rh content is 48.50% as measured by ICP. The yield is 92.6%.

[0055] (4) Under nitrogen protection, add 223.5g of orange-yellow (2,5-norbornadiene) hydroxyrhodium dimer obtained in (3) into a 20L reactor, add 6L of chloroform to dissolve it, and then add 0.75L of 5.0M tetrafluoroboric acid dropwise into the reactor. Then, add 0.32L of NBD into the reaction bottle in batches. After the feeding is completed, slowly heat the temperature to 25°C, stir at a constant temperature for 2 to 3 hours, and stop the reaction. At room temperature, extract, separate, collect the organic phase solution containing the product, dry it with anhydrous sodium sulfate, remove the solvent by rotary evaporation, and vacuum dry it to obtain 388.4g of orange-red product [Rh(NBD)2]BF4. The rhodium content was 27.49% as determined by ICP-OES, and the yield was 98.5%. According to ICP-OES and ion chromatography (IC), the impurity contents of Ag, Au, Al, Fe, Ni, Si, Ca, etc. are all less than 40ppm, the Cl ion content is less than 20ppm, and the product purity is measured to be 99.5%.

[0056] Example 3

[0057] (1) Under nitrogen protection, 500.0 g of hydrated rhodium trichloride (1.90 mol, rhodium content 38.5%, containing 192.5 g of rhodium) was added to a reactor containing 3.6 L of isopropanol and 1.3 L of water as a mixed solvent, and stirred continuously for 0.5 h. The rhodium concentration of the solution was 39.3 g / L.

[0058] (2) Add 0.92L of 1,5-hexadiene (density 0.697g / ml, molecular weight 82.146, 4.11eq) into the reactor at one time and heat to react at 45°C. The color of the solution gradually becomes lighter and clear, and a large amount of orange-yellow solid precipitates. The reaction is stopped after 26 hours. After the solution is cooled, it is filtered and the filter cake is washed with ethanol and distilled water in turn. The filtrate can be used in the next production. Vacuum drying can obtain 391.0g of orange-yellow solid powder (1,5-hexadiene) rhodium chloride dimer. The Rh content is 46.62% as measured by ICP. The yield is calculated to be 94.7%, 1 H NMR test structure and standard spectrum Figure 1 To.

[0059] (3) In a 50L reactor, 90g potassium hydroxide was added and dissolved in 5L water, 391.0g orange-yellow obtained in step (1) was dissolved in 20L n-hexane, added to the above-mentioned alkali solution through a constant pressure dripping staircase, stirred at room temperature for 6h, a yellow precipitate was obtained, filtered to obtain a filter cake, the filtrate was concentrated to 4L, a yellow precipitate was precipitated, and a filter cake was obtained by secondary filtration. The above-mentioned filter cakes were combined and washed alternately with water and 1wt% nitric acid for 3 times to obtain 333.9g orange-yellow (1,5-hexadiene) hydroxyl rhodium dimer, and the Rh content was 50.88% measured by ICP. The yield was 93.2%.

[0060] (4) Under nitrogen protection, add 333.9g of orange-yellow (1,5-hexadiene) hydroxyrhodium dimer obtained in (3) into a 20L reactor, add 8L of 1,2-dichloroethane to dissolve it, and then drop 1.0L of 5.5M tetrafluoroboric acid into the reactor. Then, add 0.55L of HEX into the reaction bottle in batches. After the feeding is completed, slowly heat the temperature to 25°C, stir at constant temperature for 2 to 3 hours, and stop the reaction. At room temperature, extract, separate, collect the organic phase solution containing the product, dry it with anhydrous sodium sulfate, remove the solvent by rotary evaporation, and vacuum dry it to obtain 456.7g of orange-red product [Rh(HEX)2]BF4. The rhodium content was 36.38% as determined by ICP, and the yield was 97.8%. According to ICP-OES and ion chromatography (IC), the impurity contents of Ag, Au, Al, Fe, Ni, Si, Ca, etc. are all less than 40ppm, the Cl ion content is less than 20ppm, and the product purity is measured to be 99.6%.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for synthesizing rhodium tetrafluoroborate coordinated by diene, characterized in that: The following steps are involved: 1) under the protection of an inert atmosphere, adding hydrated rhodium trichloride to a solvent, and dissolving the rhodium trichloride to obtain a first solution; 2) adding a diene ligand to the first solution, heating it to the reflux temperature, and performing a reflux reaction for a period of time, wherein a precipitate is a diene-coordinated rhodium chloride dimer [Rh(diene)Cl]2, and separating the diene-coordinated rhodium chloride dimer [Rh(diene)Cl]2; 3) dissolving the separated diolefin coordinated rhodium chloride dimer [Rh(diene)Cl]2 in an organic solvent to obtain a second solution; then dropping the second solution into an inorganic alkaline aqueous solution with a pH>13 to react, and a precipitate is diolefin coordinated rhodium chloride dimer [Rh(diene)(OH)]2, and separating the diolefin coordinated rhodium chloride dimer [Rh(diene)(OH)]2; 4) Under the protection of an inert atmosphere, the separated diene-coordinated rhodium chloride dimer [Rh(diene)(OH)]2 is dissolved in an organic solvent to obtain a third solution; tetrafluoroboric acid is then added dropwise to the third solution, and then the diene ligand (diene) is added to the third solution. After a period of reaction, [Rh(diene)2]BF4 is obtained.

2. The method for synthesizing the diolefin-coordinated rhodium tetrafluoroborate according to claim 1, characterized in that: In step 1), the solvent is a low-carbon alcohol, or a mixed solvent of a low-carbon alcohol and water, and the low-carbon alcohol is one of methanol, ethanol, n-propanol, and isopropanol.

3. The method for synthesizing the diolefin-coordinated rhodium tetrafluoroborate according to claim 1 or 2, characterized in that: In step 1), the concentration of rhodium in the first solution is 10-40 g / L.

4. The method for synthesizing the diolefin-coordinated rhodium tetrafluoroborate according to claim 1 or 2, characterized in that: In step 2) and step 4), the diene ligands are each independently selected from at least one of butadiene, dicyclopentadiene, 1,5-cyclooctadiene, 2,5-norbornene and 1,5-hexadiene.

5. The method for synthesizing the diolefin-coordinated rhodium tetrafluoroborate according to claim 1 or 2, characterized in that: In step 2), the amount of the diene ligand added is 2 to 5 times the amount of the rhodium element in the first solution.

6. The method for synthesizing the diolefin-coordinated rhodium tetrafluoroborate according to claim 1 or 2, characterized in that: In step 2), the reflux temperature is 65-85°C, and the reflux reaction time is 12-24h; And / or, in step 2), after the reflux reaction, a solid filter cake is obtained by filtration, and then the solid filter cake is washed and dried to separate the diene coordinated rhodium chloride dimer [Rh(diene)Cl]2.

7. The method for synthesizing the diolefin-coordinated rhodium tetrafluoroborate according to claim 1 or 2, characterized in that: In step 3), the organic solvent is selected from at least one of ethanol, acetone and tetrahydrofuran; And / or, in step 3), the inorganic alkaline aqueous solution is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution; And / or, in step 3), the second solution is added dropwise into the inorganic alkaline aqueous solution through a constant pressure dropping funnel.

8. The method for synthesizing the diolefin-coordinated rhodium tetrafluoroborate according to claim 1 or 2, characterized in that: In step 3), the reaction temperature is 20-50°C and the reaction time is 3-5h; And / or, in step 3), a solid filter cake is obtained by filtration, and then the solid filter cake is washed to separate the diene coordinated rhodium chloride dimer [Rh(diene)(OH)]2.

9. The method for synthesizing the diolefin-coordinated rhodium tetrafluoroborate according to claim 1 or 2, characterized in that: In step 4), the organic solvent is selected from at least one of dichloromethane, chloroform, and 1,2-dichloroethane; And / or, in step 4), the amount of tetrafluoroboric acid added is 2.5 to 3.5 times the amount of rhodium in the first solution; And / or, in step 4), the tetrafluoroboric acid is added dropwise to the third solution in the form of a tetrafluoroboric acid aqueous solution; the concentration of the tetrafluoroboric acid in the tetrafluoroboric acid aqueous solution is 0.5 to 1.5 M; and / or, in step 4), the tetrafluoroboric acid is added dropwise to the third solution through a constant pressure dropping funnel; And / or, in step 4), the amount of the diene ligand added is 2.5 to 5 times the amount of the rhodium element in the first solution.

10. The method for synthesizing the diene coordinated rhodium tetrafluoroborate according to claim 1 or 2, characterized in that: In step 4), the reaction temperature is 15-40°C and the reaction time is 2-3h; And / or, step 4) further comprises the step of purifying the [Rh(diene)2]BF4 obtained by the reaction: The reaction solution after the reaction was cooled to room temperature, and then extracted, separated, and dried in sequence, the solvent was removed by rotary evaporation, and vacuum dried to obtain the [Rh(diene)2]BF4 product.

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