A process for the preparation of tris(dimethylamino)cyclopentadienyl hafnium

Abstract

The application provides a preparation method of tris(dimethylamine) cyclopentadienyl hafnium, which comprises the following steps: step S1, preparing a THF solution of cyclopentadienyl magnesium chloride by using methyl magnesium chloride and cyclopentadiene; step S2, preparing cyclopentadienyl hafnium chloride by reacting the THF solution of cyclopentadienyl magnesium chloride prepared in step S1 with a hafnium source; step S3, generating tris(dimethylamine) cyclopentadienyl hafnium crude product by reacting the cyclopentadienyl hafnium chloride prepared in step S2 with an amine ligand; and step S4, purifying the tris(dimethylamine) cyclopentadienyl hafnium crude product.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis, and specifically to a method for preparing tris(dimethylamino)cyclopentadienyl hafnium. Background Technology

[0002] With the continuous development of microelectronics technology, the size of semiconductor devices is constantly shrinking. However, traditional SiO2 materials face many challenges at the microscale, such as increased leakage current and power consumption. To address these issues, high-k materials (High-K materials) have emerged. Among them, hafnium oxide, as a metal-based material, has attracted much attention due to its high dielectric constant. Hafnium oxide materials can effectively reduce gate leakage current, improve device switching performance and reliability, and simultaneously reduce power consumption.

[0003] Tris(dimethylamino)cyclopentadienyl hafnium, as a novel high dielectric constant material precursor, possesses characteristics such as high thermal stability, high vapor pressure, and good reactivity. It can be used in chemical vapor deposition (CVD) or atomic layer deposition (ALD) techniques to prepare hafnium oxide thin films.

[0004] There are two main methods for preparing tris(dimethylamino)cyclopentadienyl hafnium in the existing technology: One method involves reacting dimethylamine with n-butyllithium to obtain dimethylaminolithium, then adding hafnium tetrachloride to react and obtain tetra(dimethylamino)hafnium, and finally introducing cyclopentadiene monomer for reaction. After filtration, the product is purified by atmospheric and vacuum distillation to obtain high-purity tris(dimethylamino)cyclopentadienyl hafnium. This method has a low product yield of only 36%. The second method uses N,N-dimethyltrimethylsilane as a raw material, mixes it with hafnium tetrachloride, and then sequentially adds dimethylamine and cyclopentadiene to finally generate tris(dimethylamino)cyclopentadienyl hafnium. Although this method avoids the traditional route, the raw material cost of N,N-dimethyltrimethylsilane is high, making it uneconomical. Furthermore, the intermediate product has a complex structure and is prone to generating other byproducts, making it difficult to guarantee the yield and product purity.

[0005] In summary, existing preparation methods suffer from a series of problems, such as low yield, high cost, and potential environmental pollution. To address these shortcomings, the present invention aims to provide a method with high yield, reasonable raw material cost, and a simple intermediate product structure that is less prone to generating other byproducts or difficult-to-purify products. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing tris(dimethylamino)cyclopentadienyl hafnium. This method uses low-cost raw materials, has simple synthesis steps, produces few intermediate products, has a high yield, and produces high-purity products.

[0007] The present invention provides a method for preparing tris(dimethylamino)cyclopentadienyl hafnium, characterized in that the preparation method includes the following steps: Step S1: Prepare a THF solution of cyclopentadienyl magnesium chloride using methyl magnesium chloride and cyclopentadiene; Step S2: Prepare cyclopentadienyl hafnium trichloride by reacting the THF solution of cyclopentadienyl magnesium chloride prepared in step S1 with a hafnium source; Step S3: The cyclopentadienyl hafnium trichloride prepared in step S2 is reacted with an amino ligand to generate tris(dimethylamino)cyclopentadienyl hafnium crude product; Step S4: Purification of crude tris(dimethylamino)cyclopentadienyl hafnium product.

[0008] Further, step S1 includes the following steps: Step S1-1: Under reaction conditions of 0~25℃, add methyl magnesium chloride to THF to form a mixture and stir for 10 min; Step S1-2: Maintain a temperature of 0℃~25℃, add cyclopentadiene dropwise to the mixture from step S1-1, and continue mixing and stirring for 3~5 h to obtain a THF solution of cyclopentadienyl magnesium chloride.

[0009] Further, the hafnium source in step S2 is hafnium tetrachloride, and step S2 includes the following steps: Step S2-1: Under conditions of 0℃~25℃, add hafnium tetrachloride to THF and mix thoroughly for 10~15 min to form a hafnium tetrachloride THF suspension; Step S2-2: Maintain the reaction conditions of 0℃~25℃, add cyclopentadienyl magnesium chloride THF solution dropwise to the formed hafnium tetrachloride THF suspension, and after the addition is complete, raise the temperature to 60~70℃ and reflux for 3~6 h. Steps S2-3: After the reaction is complete, cool to room temperature, filter the product, and wash with THF 2-4 times. Step S2-4: Take the filtrate from step S2-3, concentrate the filtrate under reduced pressure to obtain crude cyclopentadienyl hafnium trichloride, then add n-hexane for recrystallization, stir for 1 h, filter to obtain the filter cake, and dry at 60~80℃ for 4~8 h to obtain cyclopentadienyl hafnium trichloride.

[0010] Furthermore, the molar ratio of cyclopentadiene, methyl magnesium chloride, and hafnium tetrachloride used is 1:1:0.9~0.95.

[0011] Further, step S3 includes: Step S3-1: Add cyclopentadienyl hafnium trichloride to THF, stir thoroughly for 1-5 min, then add triethylamine, continue stirring for 3-8 min, and then cool the system to 0℃-25℃. Step S3-2: Maintaining the conditions of 0℃~25℃, add a dimethylaminetetrahydrofuran solution with a concentration of 0.1~0.2g / mL dropwise to the system in step S3-1, and continue mixing and stirring for 3~5 h to obtain the reaction mixture; Step S3-3: Concentrate the reaction mixture obtained in step S3-2 under reduced pressure to obtain crude tris(dimethylamino)cyclopentadienyl hafnium product.

[0012] Furthermore, the molar ratio of cyclopentadienyl hafnium trichloride, dimethylamine tetrahydrofuran solution, and triethylamine is 1:3.05:3.05.

[0013] Further, step S4 includes: Step S4-1: Add n-hexane to the obtained tris(dimethylamino)cyclopentadienyl hafnium crude product to recrystallize the impurities, and stir for 45 min to 1.5 h; Step S4-2: Filter the recrystallized mixture from step S4-1, take the filtrate, and distill the filtrate under reduced pressure at a vacuum of 0.4 MPa and a temperature of 100℃ to finally obtain tris(dimethylamino)cyclopentadienyl hafnium.

[0014] Furthermore, steps 1 to 4 are all carried out under anhydrous and oxygen-free conditions.

[0015] Furthermore, the vacuum concentration conditions in steps S2-4 and S3-3 are a vacuum degree of 0.1 MPa and a temperature of 40°C.

[0016] Furthermore, the filtration in steps S2-3, S2-4, and S4-2 is performed under reduced pressure.

[0017] This invention provides a method for preparing tris(dimethylamino)cyclopentadienyl hafnium. Cyclopentadienyl magnesium chloride is prepared by reacting methyl magnesium chloride with cyclopentadiene. Cyclopentadienyl magnesium chloride is a common Grignard reagent, essentially a strong nucleophile. It then undergoes a nucleophilic substitution reaction with hafnium tetrachloride, introducing a cyclopentadienyl ligand to the metal center (metal hafnium), thereby forming cyclopentadienyl hafnium trichloride. After removing the substituted magnesium chloride from the system, an amino ligand is introduced. Triethylamine, an acid-binding agent, is then added to capture protons. Dimethylamine is subsequently added, and the lone pair electrons of the nitrogen atom on the dimethylamine attack the metal center, thus generating tris(dimethylamino)cyclopentadienyl hafnium.

[0018] Compared with the traditional lithium dimethylaminomethoxide method, the reaction conditions of this invention are mild and safe, eliminating the need for strong base reagents (such as lithium dimethylaminomethoxide) that are extremely sensitive to moisture and air, significantly reducing operational risks and lowering equipment requirements. The raw materials are inexpensive and readily available, significantly reducing reaction costs. Reaction byproducts are easily filtered and separated, eliminating the need for overly complex purification steps. This application does not involve complex alkali buffer solvents, making it environmentally friendly. Furthermore, the method of this invention avoids the residue of alkali metal ions such as lithium and sodium, which is beneficial for obtaining high-purity products. In addition, the method of this invention avoids the use of strong bases in the reaction; therefore, the reaction has good controllability and safety, and the post-processing steps are simple, showing good prospects for large-scale production. Attached Figure Description

[0019] Figure 1 The 1H NMR spectrum of tris(dimethylamino)cyclopentadienyl hafnium prepared by the method of Example 1 of the present invention; Figure 2 The 1H NMR spectrum of the tris(dimethylamino)cyclopentadienyl hafnium prepared according to the method of Example 1 of the present invention to determine its purity; Figure 3 Nuclear magnetic resonance spectrum of cyclopentadienyl hafnium trichloride, an intermediate product of tris(dimethylamino)cyclopentadienyl hafnium prepared by the method of Example 1 of the present invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The principles and features of the present invention are described below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0021] This invention provides a method for preparing tris(dimethylamino)cyclopentadienyl hafnium, the method comprising the following steps: Step S1: Prepare a THF (tetrahydrofuran) solution of cyclopentadienyl magnesium chloride (CpMgCl) using methyl magnesium chloride (CH3ClMg) and cyclopentadiene (Cp). This step involves the direct reaction of the basic Grignard reagent CpMgCl with cyclopentadiene. The methyl anion rapidly abstracts a hydrogen atom from the -CH2- group of the cyclopentadiene molecule, introducing cyclopentadiene through a simple, efficient, and irreversible acid-base neutralization reaction, thus forming the cyclopentadiene Grignard reagent. The reaction equation is as follows:

[0022] Specifically, in some embodiments, step S1 above includes the following steps: Step S1-1: Under reaction conditions of 0~25℃, preferably 0℃~10℃, add methyl magnesium chloride to THF to form a mixture and stir for 10 min. Step S1-2: Under conditions of 0℃~25℃, preferably 0℃~10℃, add cyclopentadiene dropwise to the mixture from step S1-1, and continue mixing and stirring for 3~5 h to obtain a THF solution of cyclopentadienyl magnesium chloride. It should be noted that during the dropwise addition of cyclopentadiene, it is necessary to maintain a low temperature and add it slowly over a time of 20~40 min, preferably 30 min. The dropping rate can be adjusted according to the total amount of reactants and the dropping time.

[0023] The method of this invention utilizes the strong alkalinity of magnesium methyl chloride to directly deprotonate cyclopentadiene, generating a cyclopentadienyl anion in situ, which then combines with magnesium ions to obtain the product. The entire process requires no additional catalyst, operates under mild reaction conditions, and the byproduct methane is easily separated, ensuring high product purity. Furthermore, due to the requirements of subsequent reactions, the cyclopentadienyl magnesium chloride generated in this step can be directly converted into a THF solution of cyclopentadienyl magnesium chloride without further separation.

[0024] Next, in step S2, the cyclopentadienyl magnesium chloride THF solution prepared in step S1 is reacted with a hafnium source to prepare cyclopentadienyl hafnium trichloride (CpHfCl3). In some embodiments, hafnium tetrachloride (HfCl4) is used as the hafnium source. In this step, cyclopentadienyl magnesium chloride acts as a nucleophile, undergoing halogen-cyclopentadienyl exchange with HfCl4 to ultimately form CpHfCl3, as shown in the following reaction formula:

[0025] Specifically, step S2 above includes: Step S2-1: Under conditions of 0℃~25℃, preferably 0℃~10℃, add hafnium tetrachloride to a THF solution and mix thoroughly for 10~15 min to form a hafnium tetrachloride THF suspension. Step S2-2: Maintaining the reaction conditions of 0℃~25℃, preferably 0℃~10℃, add a cyclopentadienyl magnesium chloride THF solution dropwise to the formed hafnium tetrachloride THF suspension over a time of 40 min~90 min, preferably 60 min. The dropping rate can be adjusted according to the total amount of reactants and the dropping time. After the addition is complete, raise the temperature to 60~70℃ and reflux for 3~6 h. During this process, cyclopentadienyl magnesium chloride acts as a nucleophile, providing cyclopentadienyl anions (Cp). ⁻ When mixed with HfCl4, Cp ⁻It attacks the central hafnium atom, replacing a chloride ion to generate cyclopentadienyl hafnium chloride (CpHfCl3), while also generating magnesium chloride (MgCl2) as a byproduct. Therefore, the product contains not only cyclopentadienyl hafnium trichloride, but also magnesium chloride, a byproduct of the reaction, which needs to be separated.

[0026] Step S2-3: After the reaction is complete, cool to room temperature and filter the product. Since cyclopentadienyl hafnium trichloride can dissolve in THF, while magnesium chloride is insoluble in THF, the filtered cake is magnesium chloride. Wash with THF 2-4 times. At this time, the cyclopentadienyl hafnium trichloride mixed in the magnesium chloride can be fully dissolved and washed into the filtrate.

[0027] Step S2-4: Take the filtrate from step S2-3 and concentrate it under reduced pressure to obtain crude cyclopentadienyl hafnium trichloride. The conditions for reduced pressure concentration are: vacuum degree 0.1 MPa and temperature 40℃. After concentration, a solid crude cyclopentadienyl hafnium trichloride is obtained. Hexane is then added for recrystallization, and the mixture is stirred for 1 h. The filter cake is collected and dried at 60-80℃ for 4-8 h. The product is a white to light yellow powder, which is cyclopentadienyl hafnium trichloride. It should be noted that the THF solution of cyclopentadienyl magnesium chloride in step S2-2 should be added slowly over a time of 40-90 min, preferably 60 min. The dropping rate can be adjusted according to the total amount of reactants and the dropping time. It should also be noted that to increase the yield, the filtration in step S2-3 is carried out under reduced pressure, preferably under vacuum.

[0028] The reactant ratio used in steps S1 to S2 above, i.e., the molar ratio of cyclopentadiene, methylmagnesium chloride, and hafnium tetrachloride, is 1:1:0.9~0.95. It should be noted that in the preceding step, 1 mol of cyclopentadiene reacts with 1 mol of methylmagnesium chloride to generate 1 mol of cyclopentadienylmagnesium chloride, which then reacts with hafnium tetrachloride. When the molar ratio of cyclopentadienylmagnesium chloride to hafnium tetrachloride is 2:1, the reaction tends to generate hafnium dichlorocerocene (Cp2HfCl2). Therefore, to ensure complete reaction of hafnium tetrachloride, the present invention sets the reactant input according to the above molar ratio, allowing HfCl4 to react fully while avoiding the formation of Cp2HfCl2.

[0029] After synthesizing CpHfCl3, in step S3, the cyclopentadienyl hafnium trichloride (CpHfCl3) prepared in step S2 reacts with an amino ligand to generate crude tris(dimethylamino)cyclopentadienyl hafnium. Compared with the traditional synthesis of tris(dimethylamino)cyclopentadienyl hafnium, this invention abandons flammable and air-sensitive alkyllithium or dimethylaminolithium, uses dimethylamine as an amino ligand, and adds triethylamine as an acid-binding agent to strip the active hydrogen on the nitrogen atom of dimethylamine, thereby allowing the amino group of dimethylamine to further replace the chlorine atom on CpHfCl3, thus generating tris(dimethylamino)cyclopentadienyl hafnium.

[0030] Specifically, step S3 includes: step S3-1, adding cyclopentadienyl hafnium trichloride to THF, stirring thoroughly for 1-5 min, then adding triethylamine, continuing stirring for 3-8 min, and then cooling the system to 0℃-25℃; step S3-2, maintaining the conditions of 0℃-25℃, adding a dimethylaminetetrahydrofuran solution with a concentration of 0.1-0.2 g / mL dropwise to the system in step S3-1, continuing to mix and stir for 3-5 h to obtain a reaction mixture; step S3-3, concentrating the reaction mixture obtained in step S3-2 under reduced pressure to obtain crude tri(dimethylamino)cyclopentadienyl hafnium product.

[0031] In the above process, the CpHfCl3 prepared in step S2 is dissolved in THF, followed by the addition of triethylamine as an acid-binding agent, and then a dimethylaminetetrahydrofuran solution. Under the action of triethylamine, the chlorine atoms of CpHfCl3 are replaced, thus forming a mixture of tris(dimethylamino)cyclopentadienylhafnium. It is important to note that the dimethylaminetetrahydrofuran solution should be added slowly, at a rate of 1-2 mL / min, preferably 1.5 mL / min. The adding time varies depending on the specific amount used. To control product formation, the addition is usually completed within 1.5 hours. In industrial production, the adding rate can be adjusted.

[0032] At this point, the mixture contains the target product tris(dimethylamino)cyclopentadienyl hafnium, the byproduct triethylamine dihydrochloride, and unreacted raw materials dimethylamine and triethylamine. The tris(dimethylamino)cyclopentadienyl hafnium mixture is subjected to vacuum filtration (i.e. vacuum concentration) at a vacuum degree of 0.1 MPa and a temperature of 40°C to obtain crude tris(dimethylamino)cyclopentadienyl hafnium product.

[0033] It is important to note that since CpHfCl3 has three chlorine atoms, in order for dimethylamine to fully replace these three chlorine atoms, it is necessary to avoid overly complex purification steps in subsequent purification processes. Therefore, a slight excess of dimethylamine is required, and the amount of triethylamine used as the acid-binding agent should also be consistent with that of dimethylamine. Thus, in the above steps, the molar ratio of cyclopentadienyl hafnium trichloride, dimethylamine tetrahydrofuran solution, and triethylamine is 1:3.05:3.05.

[0034] Further, step S4 involves the purification of the crude tris(dimethylamino)cyclopentadienyl hafnium product. This purification step removes byproducts and excess reactants from the reaction mixture, thereby obtaining a pure tris(dimethylamino)cyclopentadienyl hafnium product. Specifically, step S4 includes: Step S4-1: Add n-hexane to the obtained crude tris(dimethylamino)cyclopentadienylhafnium product to recrystallize the impurities, and stir for 45 min to 1.5 h. It should be noted that in this step, n-hexane is added to recrystallize the byproduct triethylamine dihydrochloride, unreacted dimethylamine, and triethylamine (impurities), not to recrystallize the crude tris(dimethylamino)cyclopentadienylhafnium product itself. In other words, the impurities referred to here are the byproduct triethylamine dihydrochloride and the unreacted dimethylamine and triethylamine. Therefore, in the subsequent filtration process, after filtering out the solids, the filtrate is collected for post-processing to obtain the target product.

[0035] Step S4-2: Filter the product from step S4-1, take the filtrate, and concentrate the filtrate under reduced pressure at a vacuum of 0.4 MPa and a temperature of 100℃ to finally obtain tris(dimethylamino)cyclopentadienyl hafnium.

[0036] It should be noted that steps S1 to S4 of the present invention are all carried out under anhydrous and oxygen-free conditions, for example, by introducing an inert gas into the reaction apparatus for protection. Furthermore, to improve the yield, the filtration in steps S2-3, S2-4, and S4-2 is carried out under reduced pressure, with a vacuum degree of 0.4 MPa.

[0037] Compared to traditional methods using lithium dimethylamino or n-butyllithium, the reaction conditions of this invention are milder and safer: traditional routes rely on strongly basic alkyl lithium reagents that spontaneously combust in air and react violently with water, posing high operational risks; while this invention utilizes triethylamine to capture the hydrogen chloride generated in the reaction, driving a stable reaction and completely avoiding the use of hazardous reagents. The raw materials, triethylamine and dimethylamine, are inexpensive and readily available, resulting in lower costs. Secondly, product purification is significantly simplified: lithium salt byproducts produced by traditional routes have some solubility in organic solvents, making separation difficult; while the byproduct triethylamine dihydrochloride of this invention precipitates directly, requiring only simple filtration to obtain a high-purity product. This invention achieves a transformation from a dangerous and cumbersome traditional process to a mild, efficient, and clean process, combining practicality and innovation.

[0038] The preparation method of the present invention will be specifically illustrated below through examples.

[0039] Example 1 A method for preparing tris(dimethylamino)cyclopentadienyl hafnium involves adding methyl magnesium chloride (37.4 g, 0.5 mol) to THF (500 mL) at a reaction temperature of 10°C to form a mixture and stirring for 10 min. While maintaining the temperature at 10°C, cyclopentadiene (33.1 g, 0.5 mol, added dropwise over 30 min) is then added to obtain a THF solution of cyclopentadienyl magnesium chloride. Subsequently, hafnium tetrachloride (144.1 g, 0.45 mol) is added to THF (300 mL) at 10°C and mixed thoroughly for 10 min to form a THF suspension of hafnium tetrachloride. While maintaining the reaction temperature at 10°C, the aforementioned THF solution of cyclopentadienyl magnesium chloride is added dropwise to the formed THF suspension of hafnium tetrachloride (dropwise over 1 h). After the addition is complete, the temperature is raised to 60°C and the reaction is refluxed for 5 h. After the reaction was complete, the mixture was cooled to room temperature. The product was filtered under reduced pressure and washed three times with 100 mL of THF each time. The filtrate was then subjected to reduced pressure distillation at 0.1 MPa and 40 °C. Cold n-hexane was added for recrystallization, and the mixture was stirred for 1 h. The filter cake was then dried at 70 °C for 8 h to obtain cyclopentadienyl hafnium trichloride (NMR spectrum as shown). Figure 3(As shown); Cyclopentadienyl hafnium trichloride (52.5 g, 0.15 mol) was added to THF and stirred thoroughly for 2 min. Then, triethylamine (46.2 g, 0.457 mol) was added, and stirring was continued for 5 min. The system was then cooled to 10 °C. While maintaining the 10 °C condition, dimethylamine tetrahydrofuran solution (206 mL, adding over 1.5 h) was slowly added dropwise to obtain a tri(dimethylamino)cyclopentadienyl hafnium mixture. The obtained tri(dimethylamino)cyclopentadienyl hafnium mixture was concentrated under reduced pressure at a vacuum of 0.1 MPa and a temperature of 40 °C to obtain a crude tri(dimethylamino)cyclopentadienyl hafnium product. Cold n-hexane (100 mL) was added to the obtained crude tri(dimethylamino)cyclopentadienyl hafnium product for recrystallization, and the mixture was stirred for 1 minute. h, the product was filtered under reduced pressure, and the filtrate was collected and distilled under reduced pressure at a vacuum of 0.4 MPa and a temperature of 100 °C to finally obtain tris(dimethylamino)cyclopentadienylhafnium. The calculated yield was 92%, and the purity was ≥99% (the purity detection graph of NMR is shown in the figure). Figure 2 (As shown). Subsequent 1H NMR identification (400 MHz, C6D6) was performed: δ 2.940 (d, J = 7.5 Hz, 4H), δ 6.075 (s, 18H). The NMR spectrum is shown below. Figure 1 As shown.

[0040] Example 2 A method for preparing tris(dimethylamino)cyclopentadienyl hafnium involves adding methyl magnesium chloride (37.4 g, 0.5 mol) to THF (500 mL) at a reaction temperature of 10°C to form a mixture and stirring for 10 min. While maintaining the temperature at 10°C, cyclopentadiene (33.1 g, 0.5 mol, added dropwise over 30 min) is then added to obtain a THF solution of cyclopentadienyl magnesium chloride. Subsequently, hafnium tetrachloride (152.1 g, 0.475 mol) is added to THF (300 mL) at 10°C and thoroughly mixed for 10 min to form a THF suspension of hafnium tetrachloride. While maintaining the reaction temperature at 10°C, the aforementioned THF solution of cyclopentadienyl magnesium chloride is added dropwise to the formed THF suspension of hafnium tetrachloride (dropping time 1 h). After the addition is complete, the temperature is raised to 70°C and the reaction is refluxed for 3 hours. After the reaction was complete, the mixture was cooled to room temperature. The product was filtered under reduced pressure and washed three times with 100 mL of THF each time. The filtrate was collected and distilled under reduced pressure at 0.1 MPa and 40°C. Cold n-hexane was then added for recrystallization. The mixture was stirred for 1 h, filtered, and the filter cake was dried at 70°C for 8 h to obtain cyclopentadienyl hafnium trichloride. 52.5 g (0.15 mol) of cyclopentadienyl hafnium trichloride was added to THF and stirred thoroughly for 2 min. Then, 46.2 g (0.457 mol) of triethylamine was added, and stirring was continued for 5 min. The system was then cooled to 10°C and maintained at 10°C. 206 mL of dimethylaminetetrahydrofuran solution was slowly added dropwise over 1.5 h to obtain a tri(dimethylamino)cyclopentadienyl hafnium mixture. The obtained tri(dimethylamino)cyclopentadienyl hafnium mixture was then distilled under reduced pressure at 0.1 MPa and 40°C. Cold n-hexane was then added for recrystallization. The reaction mixture was stirred for 1 h, and the product was dried over 10 h. The product was concentrated under reduced pressure at 40°C and 1 MPa to obtain crude tris(dimethylamino)cyclopentadienylhafnium. Cold n-hexane (100 mL) was added to the crude product for recrystallization, and the mixture was stirred for 1 h. The product was then filtered under reduced pressure, and the filtrate was collected and distilled under reduced pressure at 100°C and 0.4 MPa to finally obtain tris(dimethylamino)cyclopentadienylhafnium. The calculated yield was 72%, and the purity was ≥99%. Subsequent 1H NMR spectroscopy (400 MHz, C6D6) identification showed: δ2.940 (d, J = 7.5 Hz, 4H), δ6.075 (s, 18H).

[0041] Example 3 A method for preparing tris(dimethylamino)cyclopentadienyl hafnium involves adding methyl magnesium chloride (37.4 g, 0.5 mol) to THF (500 mL) at a reaction temperature of 10°C to form a mixture and stirring for 10 min. While maintaining the temperature at 10°C, cyclopentadiene (33.1 g, 0.5 mol, added dropwise over 30 min) is then added to obtain a THF solution of cyclopentadienyl magnesium chloride. Subsequently, hafnium tetrachloride (152.1 g, 0.475 mol) is added to THF (300 mL) at 10°C and thoroughly mixed for 10 min to form a THF suspension of hafnium tetrachloride. While maintaining the reaction temperature at 10°C, the aforementioned THF solution of cyclopentadienyl magnesium chloride is added dropwise to the formed THF suspension of hafnium tetrachloride (dropping time 1 h). After the addition is complete, the temperature is raised to 70°C and the reaction is refluxed for 3 hours. After the reaction was complete, the mixture was cooled to room temperature. The product was filtered under reduced pressure and washed three times with 100 mL of THF each time. The filtrate was collected and distilled under reduced pressure at 0.1 MPa and 40°C. Cold n-hexane was then added for recrystallization. The mixture was stirred for 1 h, filtered, and the filter cake was dried at 70°C for 8 h to obtain cyclopentadienyl hafnium trichloride. 52.5 g (0.15 mol) of cyclopentadienyl hafnium trichloride was added to THF and stirred thoroughly for 2 min. Then, 46.2 g (0.457 mol) of triethylamine was added, and stirring was continued for 5 min. The system was then cooled to 10°C and maintained at 10°C. 206 mL of dimethylaminetetrahydrofuran solution was slowly added dropwise over 1.5 h to obtain a tri(dimethylamino)cyclopentadienyl hafnium mixture. The obtained tri(dimethylamino)cyclopentadienyl hafnium mixture was then distilled under reduced pressure at 0.1 MPa and 40°C. Cold n-hexane was then added for recrystallization. The reaction mixture was stirred for 1 h, and the product was dried over 10 h. The product was concentrated under reduced pressure at 40°C and 1 MPa to obtain crude tris(dimethylamino)cyclopentadienylhafnium. Cold n-hexane (100 mL) was added to the crude product for recrystallization, and the mixture was stirred for 1 h. The product was then filtered under reduced pressure, and the filtrate was collected and distilled under reduced pressure at 100°C and 0.4 MPa to finally obtain tris(dimethylamino)cyclopentadienylhafnium, with a calculated yield of 70% and a purity ≥99%. Subsequent 1H NMR (400 MHz, C6D6) analysis revealed δ 2.940 (d, J = 7.5 Hz, 4H) and δ 6.075 (s, 18H).

[0042] Comparative Example 1 A method for preparing tris(dimethylamino)cyclopentadienyl hafnium, using a conventional synthetic route: Preparation of dimethylaminolithium: 22.4 g (0.35 mol) of n-butyllithium was added to n-hexane, the temperature was lowered to 0℃, and 672 ml of dimethylamine tetrahydrofuran solution (the molar ratio of n-butyllithium to dimethylamine was 1:3) was slowly added dropwise to dissolve it in n-hexane. The mixture was stirred at 25℃ for 3 hours to obtain a dimethylaminolithium solution. Preparation of tetra(dimethylamino)hafnium: 25.3 g (0.079 mol) of hafnium tetrachloride was added to the dimethylaminolithium solution obtained above at 0 °C (the molar ratio of hafnium tetrachloride to dimethylaminolithium was 1:4), and the mixture was stirred at 0 °C for 2 hours to obtain a tetra(dimethylamino)hafnium solution. Preparation of tris(dimethylamino)cyclopentadienyl hafnium: 20.5 g (0.31 mol) of cyclopentadiene monomer and the tetra(dimethylamino)hafnium solution obtained in the above steps (the molar ratio of tetra(dimethylamino)hafnium to cyclopentadiene is 1:1.5) were added to n-hexane and reacted at 0 °C for 10 hours under nitrogen protection to obtain tris(dimethylamino)cyclopentadienyl hafnium; Purification of tris(dimethylamino)cyclopentadienylhafnium: The reaction solution was subjected to vacuum distillation to obtain tris(dimethylamino)cyclopentadienylhafnium product with a yield of 36% and a purity ≥95%. The product was identified by 1H NMR (400MHz, C6D6): δ2.940 (d, J = 7.5 Hz, 4H), δ6.075 (s, 18H), δ6.141 (s, 2H), δ6.208 (s, 1H).

[0043] Comparative Example 2 A method for preparing tris(dimethylamino)cyclopentadienyl hafnium, using a conventional synthetic route: 58.6 g (0.5 mol) of N,N-dimethyltrimethylsilylamine and 320.3 g (1 mol) of hafnium tetrachloride were mixed and added to 586 mL of anhydrous diethyl ether. Under nitrogen protection, the reaction system was stirred at 25 °C for 3 hours. 30 mL of dimethylamine and 15 g of cyclopentadiene were mixed and added dropwise to the above reaction system under nitrogen protection. The reaction was carried out at 25 °C for 1.5 h. The resulting mixture was poured into 500 mL of deionized water and filtered under reduced pressure to obtain a crude product. The crude product was dried at 70 °C for 6 h and then pulverized to 300 mesh. The pulverized product was then calcined at 200 °C for 3 h under nitrogen protection to obtain tri(dimethylamino)cyclopentadienyl hafnium product with a yield of 41% and a purity ≥92%. The product was identified by 1H NMR (400MHz, C6D6): δ2.940 (d, J = 7.5 Hz, 4H), δ6.075 (s, 18H).

[0044] Based on the data from the above embodiments and comparative examples, the present invention uses mild methyl magnesium chloride to prepare cyclopentadienyl magnesium chloride, which is then reacted with hafnium tetrachloride to generate cyclopentadienyl hafnium trichloride. This avoids the use of n-butyllithium, which has a higher risk factor, thus increasing safety. The addition of triethylamine as an acid trapping agent captures protons. Subsequently, dimethylamine is added, and the lone pair electrons of nitrogen on the dimethylamine attack the metal center, thereby generating tris(dimethylamino)cyclopentadienyl hafnium. This avoids the introduction of unnecessary impurities and improves the purity of the reaction product, making the product of the present invention suitable for electronic-grade applications.

[0045] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. The specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A method for preparing tris(dimethylamino)cyclopentadienyl hafnium, characterized in that, The preparation method includes the following steps: Step S1: Prepare a THF solution of cyclopentadienyl magnesium chloride using methyl magnesium chloride and cyclopentadiene; Step S2: Prepare cyclopentadienyl hafnium trichloride by reacting the THF solution of cyclopentadienyl magnesium chloride prepared in step S1 with a hafnium source; Step S3: The cyclopentadienyl hafnium trichloride prepared in step S2 is reacted with an amino ligand to generate tris(dimethylamino)cyclopentadienyl hafnium crude product; Step S4: Purification of crude tris(dimethylamino)cyclopentadienyl hafnium product.

2. The preparation method according to claim 1, characterized in that, Step S1 includes the following steps: Step S1-1: Under reaction conditions of 0~25℃, add methyl magnesium chloride to THF to form a mixture and stir for 10 min; Step S1-2: Maintain a temperature of 0℃~25℃, add cyclopentadiene dropwise to the mixture from step S1-1, and continue mixing and stirring for 3~5 h to obtain a THF solution of cyclopentadienyl magnesium chloride.

3. The preparation method according to claim 2, characterized in that, The hafnium source in step S2 is hafnium tetrachloride, and step S2 includes the following steps: Step S2-1: Under conditions of 0℃~25℃, add hafnium tetrachloride to THF and mix thoroughly for 10~15 min to form a hafnium tetrachloride THF suspension; Step S2-2: Maintain the reaction conditions of 0℃~25℃, add cyclopentadienyl magnesium chloride THF solution dropwise to the formed hafnium tetrachloride THF suspension, and after the addition is complete, raise the temperature to 60~70℃ and reflux for 3~6 h. Steps S2-3: After the reaction is complete, cool to room temperature, filter the product, and wash with THF 2-4 times. Step S2-4: Take the filtrate from step S2-3, concentrate the filtrate under reduced pressure to obtain crude cyclopentadienyl hafnium trichloride, then add n-hexane for recrystallization, stir for 1 h, filter to obtain the filter cake, and dry at 60~80℃ for 4~8 h to obtain cyclopentadienyl hafnium trichloride.

4. The preparation method according to claim 3, characterized in that, The molar ratio of cyclopentadiene, methyl magnesium chloride and hafnium tetrachloride used is 1:1:0.9~0.

95.

5. The preparation method according to claim 4, characterized in that, Step S3 includes: Step S3-1: Add cyclopentadienyl hafnium trichloride to THF, stir thoroughly for 1-5 min, then add triethylamine, continue stirring for 3-8 min, and then cool the system to 0℃-25℃. Step S3-2: Maintaining the conditions of 0℃~25℃, add a dimethylaminetetrahydrofuran solution with a concentration of 0.1~0.2 g / mL dropwise to the system in step S3-1, and continue mixing and stirring for 3~5 h to obtain the reaction mixture; Step S3-3: Concentrate the reaction mixture obtained in step S3-2 under reduced pressure to obtain crude tris(dimethylamino)cyclopentadienyl hafnium product.

6. The preparation method according to claim 5, characterized in that, The molar ratio of cyclopentadienyl hafnium trichloride, dimethylamine tetrahydrofuran solution, and triethylamine is 1:3.05:3.

05.

7. The preparation method according to claim 6, characterized in that, Step S4 includes: Step S4-1: Add n-hexane to the obtained tris(dimethylamino)cyclopentadienyl hafnium crude product to recrystallize the impurities, and stir for 45 min to 1.5 h; Step S4-2: Filter the recrystallized mixture from step S4-1, take the filtrate, and distill the filtrate under reduced pressure at a vacuum of 0.4 MPa and a temperature of 100°C to finally obtain tris(dimethylamino)cyclopentadienyl hafnium.

8. The preparation method according to claims 1 to 7, characterized in that, Steps 1 to 4 are all carried out under anhydrous and oxygen-free conditions.

9. The preparation method according to claim 7, characterized in that, The vacuum concentration conditions in steps S2-4 and S3-3 are a vacuum degree of 0.1 MPa and a temperature of 40°C.

10. The preparation method according to claim 7, characterized in that, The filtration in steps S2-3, S2-4 and S4-2 is performed under reduced pressure.

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