A method for the controllable oxidative dehydrogenative coupling of aniline catalyzed by low-cost tungsten

Abstract

A method for the controllable oxidative dehydrogenative coupling of aniline catalyzed by low-valent tungsten. An aniline derivative, an oxidant and a low-valent tungsten compound are added to an organic solvent, and the reaction is heated. After the reaction is completed, the oxidation product is obtained by column chromatography. The invention uses the simply synthesizable low-valent tungsten W-1 or W-2 as a catalyst, and cooperates with the green oxidant hydrogen peroxide to directly generate the product of oxidative dehydrogenative coupling of aniline. It provides a method with simple operation, high yield, economy and high efficiency, and has important application value.

Description

Technical Field

[0001] The present invention belongs to the field of organic synthesis, and particularly relates to an intramolecular oxidative dehydrogenative coupling reaction. Background Art

[0002] Using H2O2 or O2 as oxidants, several notable catalytic systems for the oxidative coupling of anilines have been developed. Most of these catalytic systems are heterogeneous systems, and the main product is only azoarene. Therefore, a homogeneous catalytic system with controllable selectivity is highly worthy of research and can be used for the synthesis of C-N coupling isomers. Previously, Howard used an excessive amount of palladium compound to catalyze the reaction of benzonitrile with o-iodonitrobenzene to form the target coupling product, but the reaction time was too long. The Ramana group and the Xuesen Fan group et al. proposed the redox transformation of o-nitroalkynes with indoles catalyzed by Au(I) to generate 2,3-bisindole derivatives. Although several synthetic strategies have been developed in this field, there are still many challenges, including the commercially available large-scale use of metal catalysts, expanding the substrate scope, using greener conditions, etc. Based on the above, we developed stable low-valent tungsten W-1 and W-2 as catalysts, used the green oxidant H2O2, and reported a well-defined homogeneous W(0)-H2O2 system for the controllable oxidative dehydrogenative coupling of anilines, achieving intramolecular oxidation to obtain C-N coupling isomers. This method has three advantages: (1) using rarely concerned low-valent tungsten as a catalyst; (2) the substrate is easily available o-alkenylaniline; (3) using the oxidant H2O2 as a green oxidant. Summary of the Invention

[0003] Solving Technical Problems: The present invention provides a method for the controllable oxidative dehydrogenative coupling of anilines catalyzed by low-valent tungsten. This method uses low-valent tungsten as a catalyst and hydrogen peroxide as an oxidant, which meets the requirements of green and sustainable development. On the other hand, the reaction conditions used in the present invention are mild and have good industrial production prospects.

[0004] Technical Solution: The application of a low-valent tungsten compound as a catalyst in the controllable oxidative dehydrogenative coupling of anilines, and the structural formulas of the low-valent tungsten compounds are as shown in W-1 and W-2,

[0005]

[0006] Adding an aniline derivative, an oxidant and a low-valent tungsten compound to an organic solvent, heating for reaction, and obtaining a reduction product by column chromatography after the reaction ends. The structural formula of the aniline derivative is: The structural formula of the oxidative dehydrogenative coupling product is:

[0007] Wherein R1 and R2 are: -H, -Me, -Cl or -F.

[0008] The molar ratio of the above aniline derivative, low-valent tungsten compound, and oxidizing agent is 1:(0.02 - 0.15):(2 - 4.0).

[0009] The above oxidizing agent is hydrogen peroxide.

[0010] The above organic solvent is dioxane.

[0011] The above reaction time is 12 hours.

[0012] The preparation method of the above W-1 is as follows: In a nitrogen atmosphere, add 0.2 mmol of tungsten hexacarbonyl, 0.22 mmol of 6,6-dimethyl-2,2-bipyridine, and 6 mL of tetrahydrofuran to a 10 mL reaction flask, then introduce nitrogen in a double-tube, irradiate with 365 nm ultraviolet light at room temperature, stir magnetically for 12 hours, dry the system with a rotary evaporator, add 5 mL of dichloromethane and 2 mL of n-hexane for recrystallization, precipitate a red-brown solid, suck out the supernatant and dry the red-brown solid by rotation to obtain a pure product.

[0013] The preparation method of the above W-2 is as follows: In a nitrogen atmosphere, add 0.2 mmol of tungsten hexacarbonyl, 0.22 mmol of 2,6-dimethyl-N-(2'-pyridylmethylene)aniline, and 6 mL of tetrahydrofuran to a 10 mL reaction flask, then introduce nitrogen in a double-tube, irradiate with 365 nm ultraviolet light at room temperature, stir magnetically for 12 hours, dry the system with a rotary evaporator, add 5 mL of dichloromethane and 2 mL of n-hexane for recrystallization, precipitate a red-brown solid, suck out the supernatant and dry the red-brown solid by rotation to obtain a pure product.

[0014] Beneficial effects: The present invention uses the simply synthesizable low-valent tungsten W-1 or W-2 as a catalyst, and cooperates with the green oxidizing agent hydrogen peroxide to directly generate the product of aniline oxidative dehydrogenation coupling. Compared with the existing process, it has the following advantages: (1) The metal tungsten catalyst is inexpensive and simple to prepare, can efficiently catalyze this reaction, and the reaction process is mild and has low energy consumption, which can greatly reduce the process cost; (2) Hydrogen peroxide is used as the oxidizing agent, without toxic by-product emissions, is economical and green, and the process operation is simple. (3) The substrate scope of the present invention is wide, especially suitable for the oxidative dehydrogenation coupling of bulk raw materials such as o-alkenylaniline that are easily obtained at home and abroad and have been mass-produced industrially, greatly expanding the application scope of the aniline derivative coupling method. In summary, the present invention provides a simple, mild, easy-to-control, low-energy-consumption, high-yield, economical, green and efficient aniline dehydrogenation coupling method, which has important application value. Description of the Drawings

[0015] Figure 1 . 1H NMR spectrum of compound 2a

[0016] Figure 213C NMR of compound 2a;

[0017] Figure 3 1H NMR of compound 2b;

[0018] Figure 4 13C NMR of compound 2b;

[0019] Figure 5 19F NMR of compound 2b;

[0020] Figure 6 1H NMR of compound 2c;

[0021] Figure 7 13C NMR of compound 2c;

[0022] Figure 8 1H NMR of compound 2d;

[0023] Figure 9 13C NMR of compound 2d;

[0024] Figure 10 1H NMR of compound 2e;

[0025] Figure 11 13C NMR of compound 2e;

[0026] Figure 12 19F NMR of compound 2e;

[0027] Figure 13 1H NMR of compound 2f;

[0028] Figure 14 13C NMR of compound 2f;

[0029] Figure 15 19F NMR of compound 2f;

[0030] Figure 16 1H NMR of compound 2g;

[0031] Figure 17 13C NMR of compound 2g;

[0032] Figure 18 19F NMR of compound 2g;

[0033] Figure 19 1H NMR of compound 2h;

[0034] Figure 20 13C NMR of compound 2h;

[0035] Figure 21 . 19F NMR spectrum of compound 2h;

[0036] Figure 22 . 1H NMR spectrum of compound 2i;

[0037] Figure 23 . 13C NMR spectrum of compound 2i;

[0038] Figure 24 . 19F NMR spectrum of compound 2i;

[0039] Figure 25 . 1H NMR spectrum of compound 2j;

[0040] Figure 26 . 13C NMR spectrum of compound 2j;

[0041] Figure 27 . 19F NMR spectrum of compound 2j;

[0042] Figure 28 . 1H NMR spectrum of compound 2k;

[0043] Figure 29 . 13C NMR spectrum of compound 2k;

[0044] Figure 30 . 1H NMR spectrum of compound 2l;

[0045] Figure 31 . 13C NMR spectrum of compound 2l;

[0046] Figure 32 . 1H NMR spectrum of compound 2m;

[0047] Figure 33 . 13C NMR spectrum of compound 2m;

[0048] Figure 34 . 1H NMR spectrum of compound 2n;

[0049] Figure 35 . 13C NMR spectrum of compound 2n;

[0050] Figure 36 . 1H NMR spectrum of catalyst W-1;

[0051] Figure 37 . 13C NMR spectrum of catalyst W-1;

[0052] Figure 38 . 1H NMR spectrum of catalyst W-2;

[0053] Figure 39 . 13C NMR spectrum of catalyst W-2. Detailed Embodiments

[0054] To deepen the understanding of the present invention, the following will further describe the present invention in detail in combination with embodiments. These embodiments are only used to explain the present invention and do not limit the scope of protection.

[0055] Referring to the specific structures of the intramolecular coupling isomer products obtained from the conversion of aniline as described above, the corresponding products are selected for the embodiments.

[0056] Example 1

[0057] Preparation of the intramolecular reaction product of aniline to form the coupling isomer product (2a): In a nitrogen atmosphere, 0.2 mmol of 2-styrylaniline, 0.01 mmol of W-1, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube under magnetic stirring and heated to 90 °C in an oil bath for 12 hours. After removing the oil bath, 1 mL of water was added to the reaction solution to terminate the reaction. The reaction solution was extracted three times with 2 mL of ethyl acetate, and the combined organic phases were dried with anhydrous MgSO4 for 30 minutes and then filtered. The filtrate was concentrated using a rotary evaporator. After concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent, and a pure product was obtained after column chromatography with a yield of 55%. The mass spectrometry analysis data of this product are as follows: theoretical value, 224.0712; experimental value, 224.0764. ( Figure 1-2 )

[0058] Example 2

[0059] Preparation of the intramolecular reaction product of aniline to form the coupling isomer product (2b): In a nitrogen atmosphere, 0.2 mmol of 2-(4-fluorostyryl)aniline, 0.01 mmol of W-2, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube under magnetic stirring and heated to 90 °C in an oil bath for 12 hours. After removing the oil bath, 1 mL of water was added to the reaction solution to terminate the reaction. The reaction solution was extracted three times with 2 mL of ethyl acetate, and the combined organic phases were dried with anhydrous MgSO4 for 30 minutes and then filtered. The filtrate was concentrated using a rotary evaporator. After concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent, and a pure product was obtained after column chromatography with a yield of 62%. The mass spectrometry analysis data of this product are as follows: theoretical value, 242.0617; experimental value, 242.0636.

[0060] ( Figure 3-5 )

[0061] Example 3

[0062] Preparation of the coupling isomer product (2c) formed by the intramolecular reaction of aniline: Under a nitrogen atmosphere, 0.2 mmol of 2-(4-chlorostyryl)aniline, 0.01 mmol of W-1, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube under magnetic stirring, and the mixture was heated to 90 °C in an oil bath and reacted for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried with anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated using a rotary evaporator. After concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent, and the pure product was obtained by column chromatography with a yield of 62%. The mass spectrometry analysis data of this product are as follows: theoretical value, 258.0322; experimental value, 258.0353.

[0063] ( Figure 6-7 )。

[0064] Example 4

[0065] Preparation of the coupling isomer product (2d) formed by the intramolecular reaction of aniline: Under a nitrogen atmosphere, 0.2 mmol of 2-(4-methylstyryl)aniline, 0.01 mmol of W-2, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube under magnetic stirring, and the mixture was heated to 90 °C in an oil bath and reacted for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried with anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated using a rotary evaporator. After concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent, and the pure product was obtained by column chromatography with a yield of 63%. The mass spectrometry analysis data of this product are as follows: theoretical value, 238.0868; experimental value, 238.0835.

[0066] ( Figure 8-9 )。

[0067] Example 5

[0068] Preparation of the product (2e) of the intramolecular reaction of aniline to form a coupling isomer: Under a nitrogen atmosphere, 0.2 mmol of 2-(4-chlorostyryl)-5-fluoroaniline, 0.01 mmol of W-1, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube under magnetic stirring, and the mixture was heated to 90 °C in an oil bath and reacted for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried with anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated using a rotary evaporator. After concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent, and a pure product was obtained after column chromatography with a yield of 58%. The mass spectrometry analysis data of this product are as follows: theoretical value, 276.0228; experimental value, 276.0286.( Figure 10-12 )。

[0069] Example 6

[0070] Preparation of the product (2f) of the intramolecular reaction of aniline to form a coupling isomer: Under a nitrogen atmosphere, 0.2 mmol of 2-(3-methylstyryl)aniline, 0.01 mmol of W-2, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube under magnetic stirring, and the mixture was heated to 90 °C in an oil bath and reacted for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried with anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated using a rotary evaporator. After concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent, and a pure product was obtained after column chromatography with a yield of 74%. The mass spectrometry analysis data of this product are as follows: theoretical value, 242.0617; experimental value, 242.0636.

[0071] ( Figure 13-15 )。

[0072] Example 7

[0073] Preparation of the coupling isomer product (2g) formed by the intramolecular reaction of aniline: Under a nitrogen atmosphere, 0.2 mmol of 5-methyl-2-(4-methylstyryl)aniline, 0.01 mmol of W-1, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube and the mixture was heated to 90 °C with magnetic stirring using an oil bath for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried over anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated using a rotary evaporator, and after concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent. After column chromatography, the pure product was obtained with a yield of 47%. The mass spectrometry analysis data of this product are as follows: theoretical value, 256.0774; experimental value, 256.0758.( Figure 16-18 )。

[0074] Example 8

[0075] Preparation of the coupling isomer product (2h) formed by the intramolecular reaction of aniline: Under a nitrogen atmosphere, 0.2 mmol of 2-fluoro-6-(4-methylstyryl)aniline, 0.01 mmol of W-2, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube and the mixture was heated to 90 °C with magnetic stirring using an oil bath for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried over anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated using a rotary evaporator, and after concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent. After column chromatography, the pure product was obtained with a yield of 70%. The mass spectrometry analysis data of this product are as follows: theoretical value, 256.0774; experimental value, 256.0736.( Figure 19-21 )。

[0076] Example 9

[0077] Preparation of the coupling isomer product (2i) formed by the intramolecular reaction of aniline: Under a nitrogen atmosphere, 0.2 mmol of 2-(4-chlorostyryl)-6-fluoroaniline, 0.01 mmol of W-2, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube and the mixture was heated to 90 °C with magnetic stirring using an oil bath for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried over anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated using a rotary evaporator, and after concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent. After column chromatography, the pure product was obtained with a yield of 40%. The mass spectrometry analysis data of this product are as follows: theoretical value, 276.0228; experimental value, 276.0285.(Figure 22-24 )。

[0078] Example 10

[0079] Preparation of the coupling isomer product (2j) by intramolecular reaction of aniline: Under a nitrogen atmosphere, 0.2 mmol of 2-fluoro-6-(4-fluorovinyl)aniline, 0.01 mmol of W-1, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube, and the mixture was heated to 90 °C with magnetic stirring in an oil bath and reacted for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried with anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated by a rotary evaporator. After concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent, and pure product was obtained after column chromatography with a yield of 45%. The mass spectrometry analysis data of this product are as follows: theoretical value, 260.0523; experimental value, 260.0547.

[0080] ( Figure 25-27 )。

[0081] Example 11

[0082] Preparation of the coupling isomer product (2k) by intramolecular reaction of aniline: Under a nitrogen atmosphere, 0.2 mmol of 2-(4-chlorostyryl)-6-methylaniline, 0.02 mmol of W-1, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube, and the mixture was heated to 90 °C with magnetic stirring in an oil bath and reacted for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried with anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated by a rotary evaporator. After concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent, and pure product was obtained after column chromatography with a yield of 66%. The mass spectrometry analysis data of this product are as follows: theoretical value, 272.0478; experimental value, 272.0449.( Figure 28-29 )。

[0083] Example 12

[0084] Preparation of the product (2l) of the intramolecular reaction of aniline to form a coupling isomer: Under a nitrogen atmosphere, 0.2 mmol of 2-(4-chlorostyryl)-4-methylaniline, 0.01 mmol of W-1, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube under magnetic stirring, and the mixture was heated to 90 °C in an oil bath and reacted for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried with anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated using a rotary evaporator. After concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent, and pure product was obtained after column chromatography with a yield of 71%. The mass spectrometry analysis data of this product are as follows: theoretical value, 272.0478; experimental value, 272.0491.( Figure 30-31 )。

[0085] Example 13

[0086] Preparation of the product (2m) of the intramolecular reaction of aniline to form a coupling isomer: Under a nitrogen atmosphere, 0.2 mmol of 4-methyl-2-styrylaniline, 0.01 mmol of W-1, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube under magnetic stirring, and the mixture was heated to 90 °C in an oil bath and reacted for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried with anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated using a rotary evaporator. After concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent, and pure product was obtained after column chromatography with a yield of 67%. The mass spectrometry analysis data of this product are as follows: theoretical value, 238.0868; experimental value, 238.0810.

[0087] ( Figure 32-33 )。

[0088] Example 14

[0089] Preparation of the coupling isomer product (2n) formed by the intramolecular reaction of aniline: Under a nitrogen atmosphere, 0.2 mmol of 3-chloro-2-styrylaniline, 0.01 mmol of W-1, 0.6 mmol of hydrogen peroxide, and 2 mL of dioxane were added to a 10 mL reaction flask. Then, nitrogen was introduced into the double-tube under magnetic stirring, and the mixture was heated to 90 °C in an oil bath and reacted for 12 hours. The oil bath was removed, 1 mL of water was added to the reaction solution to terminate the reaction, and the mixture was extracted three times with 2 mL of ethyl acetate. The organic phases were combined and dried over anhydrous MgSO4 for 30 minutes, and then filtered. The filtrate was concentrated using a rotary evaporator. After concentration, ethyl acetate and petroleum ether (1:80, v:v) were used as the eluent, and the pure product was obtained after column chromatography with a yield of 53%. The mass spectrometry analysis data of this product are as follows: theoretical value, 258.0322; experimental value, 258.0392.

[0090] ( Figure 34-35 )。

Claims

1. Application of low-valent tungsten compounds as catalysts in the controllable oxidative dehydrogenative coupling of aniline derivatives, characterized in that, The structural formula of the low-valent tungsten compound is as shown in W-1 or W-2 below. An aniline derivative, an oxidizing agent, and a low-valent tungsten compound are added to an organic solvent, and the mixture is heated for reaction. The oxidizing agent is hydrogen peroxide. After the reaction is completed, an oxidative dehydrogenation coupling product is obtained through column chromatography. The structural formula of the aniline derivative is: The oxidative dehydrogenation coupling product is any one of the following structural formulas: Among them, R1 and R2 are determined according to the structural formula of the above oxidative dehydrogenation coupling product.

2. The application according to claim 1, characterized in that The molar ratio of the aniline derivative, low-valent tungsten compound, and oxidant is 1:(0.02 - 0.15):(2 - 4.0).

3. The application according to claim 1, characterized in that, The organic solvent is dioxane.

4. The application according to claim 1, characterized in that, The reaction time is 12 hours.

5. The application according to claim 1, wherein The preparation method of the low-valent tungsten compound W-1 is as follows: In a nitrogen atmosphere, add 0.2 mmol of tungsten hexacarbonyl, 0.22 mmol of 6,6-dimethyl-2,2-bipyridine, and 6 mL of tetrahydrofuran to a 10 mL reaction flask. Then, introduce nitrogen in a double-tube system, irradiate with 365 nm ultraviolet light at room temperature, stir magnetically for 12 hours, dry the system with a rotary evaporator, add 5 mL of dichloromethane and 2 mL of n-hexane for recrystallization, precipitate a red-brown solid, suck out the supernatant, and dry the red-brown solid by evaporation to obtain W-1.

6. The application according to claim 1, characterized in that, The preparation method of the low-valent tungsten compound W-2 is as follows: In a nitrogen atmosphere, add 0.2 mmol of tungsten hexacarbonyl, 0.22 mmol of 2,6-dimethyl-N-(2'-pyridylmethylene)aniline, and 6 mL of tetrahydrofuran to a 10 mL reaction flask. Then, introduce nitrogen in a double-tube system, irradiate with 365 nm ultraviolet light at room temperature, stir magnetically for 12 hours, dry the system with a rotary evaporator, add 5 mL of dichloromethane and 2 mL of n-hexane for recrystallization, precipitate a red-brown solid, suck out the supernatant, and dry the red-brown solid by evaporation to obtain W-2.

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