A UV-visible light-controllable isomerization and catalytically active NHCs-Pd complex and its preparation method

Abstract

The present invention provides an ultraviolet-visible light-controllable isomerization and catalytically active nitrogen heterocyclic carbene-palladium complex and a preparation method thereof. The method comprises the synthesis of a pyridine-modified spiropyran compound and the synthesis of a spiropyran-modified nitrogen heterocyclic carbene-palladium complex.

Description

Technical Field

[0001] The present invention relates to a synthesis technology that can be used for photosensitive catalysts and photosensitizing substances, and further to a synthesis technology that can be applied to various catalytic reactions and light-controlled organic materials. Specifically, it relates to a nitrogen heterocyclic carbene-palladium complex with ultraviolet-visible light-controllable isomerization and catalytic activity and a preparation method thereof. Background Art

[0002] NHCs (N-Heterocyclic Carbenes) act as electron-donating ligands and can form complexes with a wide variety of transition metals to form a wide variety of complexes for different applications. Compared to traditional metal catalysts, N-metal complex catalysts are generally more stable to chemical environments such as pH, air, temperature, and humidity, and can exhibit higher catalytic activity and chemical selectivity. However, due to the uncontrollable nature of their catalytic activity, researchers also hope to selectively promote or inhibit the catalytic activity of the complex by modifying its structure and applying a "switch." Compared to magnetic fields, pH, temperature, gas atmospheres, etc., changing the light source is low-cost, clean, mild, reversible, and easy to initiate, making it a standout among many "switches."

[0003] In 2021, Hong et al. reported that the azobenzene structure was modified into CAAC-type NHCs, and then coordinated with the transition metal ruthenium to generate the target photosensitive catalysis. The authors controlled the reaction activity of the catalyst by changing the light source and adjusting the configuration of azobenzene in the catalyst molecular structure. When in dark conditions or under white light irradiation, its configuration is the E configuration on the left. Catalysts with such a configuration have very high catalytic activity for the metathesis reaction of olefins; however, under ultraviolet light irradiation, the azobenzene structure is transformed into the Z configuration, which will severely increase the steric hindrance near the active center of the catalyst, affecting the contact between the substrate molecule and the metal active center, thereby greatly inhibiting the reaction activity. In this work, the authors used the different steric hindrances near the active center of the catalyst under different light sources to achieve the catalytic activity of the photocontrolled catalyst. See the following formula:

[0004]

[0005] That same year, Sasai et al. synthesized an azobenzene-modified binaphthylcrown ether for alkylation of ortho-carbon imines. Unlike the previous work, under white light, the E-configuration of the azobenzene causes the flexible crown ether to become taut, preventing substrate molecules from entering the ether to participate in the reaction. However, under ultraviolet light, the Z-configuration of the azobenzene significantly reduces the rotational inhibition, increasing the chances of substrate molecules entering the crown ether molecule. This achieves photo-controlled catalytic activity. See the formula below:

[0006]

[0007] The cases discussed in the previous two articles involved modifying azobenzene into the catalyst structure itself, leveraging the isomerization of azobenzene under different light sources to influence the catalytic activity through changes in steric hindrance and spatial configuration. This approach has the primary advantage of highly efficient light-induced changes in catalytic activity, but its disadvantage is that it only utilizes steric hindrance to alter the catalyst's activity. We would like to employ more diverse approaches to control catalytic activity, such as directly influencing the electron distribution and aromaticity of the catalyst structure by varying the light source, thereby altering catalytic activity. Among the many light-controllable molecular groups, the incorporation of spiropyran compounds into catalysts has received relatively little attention. In addition to ring opening and closing in the spatial structure, the photoisomerization of spiropyrans also generates nitrogen cations and oxygen anions. Summary of the Invention

[0008] The technical problem to be solved by this invention is to provide a nitrogen heterocyclic carbene-palladium complex with controllable catalytic activity, thereby overcoming the drawback of current metal complex catalysts, which suffer from uncontrollable reactivity. The goal is to synthesize a series of previously unreported ultraviolet-visible light-controllable spiropyran-modified nitrogen heterocyclic carbene-palladium complexes. The goal is to selectively alter their catalytic activity by isomerizing their structures simply by changing the light source.

[0009] The technical problem to be solved can be implemented through the following technical solutions.

[0010] A UV-visible light-controlled isomerization and catalytically active nitrogen heterocyclic carbene-palladium complex, the structural formula of which is as follows:

[0011]

[0012] Among them, R 1 and R 2 One of the following seven substituents is used:

[0013] a、R 1 =F, R 2 =Me;

[0014] b. R 1 =F, R 2 =Et;

[0015] c. R 1 =Cl, R 2 =Me;

[0016] d, R 1 =Br, R 2 =Me;

[0017] e、R1 =CH3, R 2 =Me;

[0018] f、R 1 =H, R 2 =Et;

[0019] g、R 1 =OBn,R 2 =Me.

[0020] Furthermore, the complex is prepared by the following route:

[0021]

[0022] Another technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned ultraviolet-visible light-controllable isomerization and catalytically active nitrogen heterocyclic carbene-palladium complex, which adopts the following preparation route:

[0023]

[0024] Among them, R 1 and R 2 One of the following seven substituents is used:

[0025] a、R 1 =F, R 2 =Me;

[0026] b. R 1 =F, R 2 =Et;

[0027] c. R 1 =Cl, R 2 =Me;

[0028] d, R 1 =Br, R 2 =Me;

[0029] e、R 1 =CH3, R 2 =Me;

[0030] f、R 1 =H, R 2 =Et;

[0031] g、R 1 =OBn,R 2 =Me.

[0032] Furthermore, the method includes the synthesis of a pyridine-modified spiropyran compound and the synthesis of a spiropyran-modified nitrogen heterocyclic carbene-palladium complex.

[0033] The synthesis of pyridine-modified spiropyran compounds is carried out by the following steps:

[0034] (1) Take a three-necked flask and add indole iodide and 3-hydroxypyridine-4-aldehyde in sequence;

[0035] (2) After placing the condensation reflux pipe, evacuate the double-row pipe and pass argon gas;

[0036] (3) Add anhydrous methanol and anhydrous triethylamine under vacuum and argon gas;

[0037] (4) Reflux and stir at 65-80°C overnight;

[0038] (5) Monitor the reaction results by TLC and concentrate under vacuum after the reaction is completed;

[0039] (6) Purify the target pyridine-modified spiropyran compound using column chromatography separation.

[0040] Furthermore, the molar ratio of the indole iodide to 3-hydroxypyridine-4-aldehyde is 1:1; and the added amounts of the anhydrous methanol and anhydrous triethylamine are 40-60 mL of anhydrous methanol and 0.1-0.2 mL of anhydrous triethylamine for every 1.98 mmol of indole iodide.

[0041] Preferably, the synthesis of the pyridine-modified spiropyran compound adopts the following steps:

[0042] (1) Take a three-necked flask and add 1.98 mmol of indole iodide and 1.98 mmol of 3-hydroxypyridine-4-aldehyde in sequence;

[0043] (2) After placing the condensation reflux pipe, evacuate the double-row pipe and pass argon gas;

[0044] (3) Add 50 mL of anhydrous methanol and 0.1 mL of anhydrous triethylamine under vacuum and argon atmosphere;

[0045] (4) Reflux and stir at 70°C overnight;

[0046] (5) Monitor the reaction results by TLC and concentrate under vacuum after the reaction is completed;

[0047] (6) Purify the target pyridine-modified spiropyran compound using column chromatography separation.

[0048] The synthesis of the spiropyran-modified nitrogen heterocyclic carbene-palladium complex is carried out by the following steps:

[0049] (1) Take a Shrek tube and add spiropyran compound, PdCl2, 1,3-bis(2,6-diisopropylphenyl)imidazole chloride and K2CO3 in sequence;

[0050] (2) Use double-row pipes for vacuuming and argon flow;

[0051] (3) Adding the reaction solvent under vacuum;

[0052] (4) Stir at 60-80°C overnight;

[0053] (5) Monitor the reaction completion by TLC; extract the reaction solution with deionized water and DCM; wash the collected organic phase with saturated NaCl solution; dry the organic phase with anhydrous sodium sulfate and concentrate it under vacuum;

[0054] (6) Purify the target SPP-NHC-Pd (Spiropyran-containing NHC-Pd) complex by column chromatography separation.

[0055] Preferably, the synthesis of the spiropyran-modified nitrogen heterocyclic carbene-palladium complex adopts the following steps:

[0056] (1) Take a Shrek tube and add 0.5-1.0 mmol of spiropyran compound, 0.5 mmol of PdCl2, 0.55 mmol of 1,3-bis(2,6-diisopropylphenyl)imidazole chloride and 2.5 mmol of K2CO3 in sequence;

[0057] (2) Use double-row pipes for vacuuming and argon flow;

[0058] (3) Add 2 mL of reaction solvent under vacuum and argon gas;

[0059] (4) Stir at 60-80°C overnight;

[0060] (5) Monitor the reaction completion by TLC; extract the reaction solution with deionized water and DCM; wash the collected organic phase with saturated NaCl solution; dry the organic phase with anhydrous sodium sulfate and concentrate it under vacuum;

[0061] (6) Purify the target SPP-NHC-Pd (Spiropyran-containing NHC-Pd) complex by column chromatography separation.

[0062] The UV-visible light-controlled isomerization and catalytically active nitrogen heterocyclic carbene-palladium complex and its preparation method employ the aforementioned technical solution. A highly simplified synthesis method involves first incorporating a photocontrollable spiropyran group into the pyridine molecule. This is then followed by the traditional synthesis of Pd-PEPPSI complexes, where the photocontrollable spiropyran group is incorporated into the nitrogen heterocyclic carbene-palladium complex. Subsequently, the catalyst's structure and catalytic activity are reversibly altered by UV / visible light conversion. The resulting photocontrollable catalyst exhibits excellent photochromic properties, similar to the spiropyran. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 The hydrogen spectrum characterization of the synthesized target catalyst 4a;

[0064] Figure 2 Carbon spectrum characterization of the synthesized target catalyst 4a;

[0065] Figure 3 Fluorine spectrum characterization of the synthesized target catalyst 4a;

[0066] Figure 4 The hydrogen spectrum characterization of the synthesized target catalyst 4b;

[0067] Figure 5 Carbon spectrum characterization of the synthesized target catalyst 4b;

[0068] Figure 6 Fluorine spectrum characterization of the synthesized target catalyst 4b;

[0069] Figure 7 The hydrogen spectrum characterization of the synthesized target catalyst 4c;

[0070] Figure 8 Carbon spectrum characterization of the synthesized target catalyst 4c;

[0071] Figure 9 The hydrogen spectrum characterization of the synthesized target catalyst 4d;

[0072] Figure 10 Carbon spectrum characterization of the synthesized target catalyst 4d;

[0073] Figure 11 The hydrogen spectrum characterization of the synthesized target catalyst 4e;

[0074] Figure 12 Carbon spectrum characterization of the synthesized target catalyst 4e;

[0075] Figure 13 The hydrogen spectrum characterization of the synthesized target catalyst 4f;

[0076] Figure 14Carbon spectrum characterization of the synthesized target catalyst 4f;

[0077] Figure 15 The hydrogen spectrum characterization of the synthesized target catalyst 4g;

[0078] Figure 16 This is the carbon spectrum characterization of the synthesized target catalyst 4g. DETAILED DESCRIPTION

[0079] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0080] The present invention provides a nitrogen heterocyclic carbene-palladium complex with ultraviolet-visible light-controllable isomerization and catalytic activity and a preparation method thereof, which mainly includes a synthesis method of a pyridine-modified spiropyran compound and a synthesis method of a spiropyran-modified nitrogen heterocyclic carbene-palladium complex.

[0081] Synthesis of pyridine-modified spiropyran compounds: 1-methyl-5-fluoro-2,3,3-trimethyl-3H-indole iodide (636 mg, 1.98 mmol) and 3-hydroxypyridine-4-aldehyde (243.7 mg, 1.98 mmol) were added to a 125 mL three-necked flask in sequence. A condenser reflux tube was placed on the double-row tube, and argon was introduced. 50 mL of anhydrous methanol and 0.1 mL of triethylamine were added using a syringe. The mixture was stirred under reflux at 70°C overnight. The reaction was monitored by TLC. After completion of the reaction, the mixture was concentrated under vacuum. The target pyridine-modified spiropyran compound was then purified by column chromatography. The following is its synthesis route:

[0082]

[0083] Reaction solvent screening for spiropyran-modified NHC-Pd complex 4a (see Table 1 below): To a 10 mL Shrek tube, add the spiropyran compound (298.7 mg, 1.0 mmol), PdCl2 (88.5 mg, 0.5 mmol), 1,3-bis(2,6-diisopropylphenyl)imidazole chloride (243.7 mg, 0.55 mmol), and K2CO3 (345 mg, 2.5 mmol) in sequence. Evacuate and purge with argon using a double-chamber tube. Add 2 mL of solvent via syringe, and stir overnight at 60°C. Completion of the reaction was monitored by TLC. The reaction solution was extracted with deionized water (10 mL) and DCM (10 mL x 3). The collected organic phase was washed with saturated NaCl solution, dried over anhydrous sodium sulfate, and concentrated under vacuum. The target SPP-NHC-Pd complex, a golden powder, was purified by column chromatography. The following is its synthetic route:

[0084]

[0085] Evaluation: In the toluene system, the reaction is accompanied by a large number of side reactions, resulting in a low final separation yield. In 1,4-dioxane and methanol, the reaction is difficult to proceed smoothly, and only a very small amount of target product can be obtained. However, the reaction yield is higher in acetone solution. Therefore, we know that acetone is the best solvent for this reaction.

[0086] Table 1: Solvent screening for the synthesis of SPP-NHC-Pd compounds

[0087]

[0088] Temperature screening of spiropyran-modified NHC-Pd complex 4a (see Table 2 below): To a 10 mL Shrek tube, add the spiropyran compound (298.7 mg, 1.0 mmol), PdCl2 (88.5 mg, 0.5 mmol), 1,3-bis(2,6-diisopropylphenyl)imidazole chloride (425.0 mg, 1.0 mmol), and K2CO3 (345 mg, 2.5 mmol) in sequence. Evacuate and purge with argon using a double-chamber tube. Add 2 mL of acetone as the solvent via a syringe and stir overnight under varying conditions. The reaction was monitored by TLC. The reaction solution was extracted with deionized water (10 mL) and DCM (10 mL x 3). The collected organic phase was washed with saturated NaCl solution, dried over anhydrous sodium sulfate, and concentrated under vacuum. The target golden powder SPP-NHC-Pd complex was purified by column chromatography. The following is its synthetic route:

[0089]

[0090] Evaluation: When the reaction temperature was 50°C, TLC monitoring showed that there was still IPr HCl in the system that had not completely participated in the reaction. When the system temperature was increased to 70°C and 80°C, the side reaction products in the system gradually increased, thereby causing the isolation yield of the target product to decrease. Therefore, we determined that the optimal reaction temperature was 60°C.

[0091] Table 2: Temperature screening of the synthesis methods of SPP-NHC-Pd compounds

[0092]

[0093] Screening of substrate equivalent ratios for spiropyran-modified NHC-Pd complex 4a (see Table 3 below): A 10 mL Shrek tube was charged with a spiropyran compound (149.4-298.7 mg, 0.5-1.0 mmol), PdCl₂ (88.5 mg, 0.5 mmol), 1,3-bis(2,6-diisopropylphenyl)imidazole chloride (425.0 mg, 1.0 mmol), and K₂CO₃ (345 mg, 2.5 mmol). The mixture was evacuated and purged with argon using a double-chamber tube. 2 mL of acetone was added via syringe as the solvent, and the mixture was stirred overnight at various temperatures. The reaction was monitored by TLC. The reaction mixture was extracted with deionized water (10 mL) and DCM (10 mL x 3). The collected organic phase was washed with saturated NaCl solution, dried over anhydrous sodium sulfate, and concentrated under vacuum. The target SPP-NHC-Pd complex, a golden powder, was purified by column chromatography. The following is its synthesis route:

[0094]

[0095] Evaluation: When the spiropyran compound input amount was 0.5 mmol, TLC monitoring showed that there was still a large amount of IPr HCl in the system, which had a significant impact on the reaction conversion rate and thus reduced the isolation yield. However, when the spiropyran compound input amount was gradually increased to 1.0 mmol, we found that the isolation yield of the target product gradually increased. Therefore, we determined that the optimal input amount of the spiropyran compound was 1.0 mmol.

[0096] Table 3: Screening of substrate equivalent ratios for the synthesis of SPP-NHC-Pd compounds

[0097]

[0098] Synthesis of spiropyran-modified NHC-Pd complex 4a: To a 10 mL Shrek tube, add the spiropyran compound (298.7 mg, 1.0 mmol), PdCl2 (88.5 mg, 0.5 mmol), 1,3-bis(2,6-diisopropylphenyl)imidazole chloride (243.7 mg, 0.55 mmol), and K2CO3 (345 mg, 2.5 mmol). Evacuate and purge with argon using a double-row tube. Add 2 mL of acetone as the solvent via a syringe and stir at 70°C overnight. The reaction was monitored by TLC. The reaction solution was extracted with deionized water (10 mL) and DCM (10 mL x 3). The collected organic phase was washed with saturated NaCl solution, dried over anhydrous sodium sulfate, and concentrated under vacuum. Column chromatography was used to purify the target SPP-NHC-Pd complex, yielding 371.2 mg (81%) of a golden powder. NMR characterization of the compound is shown in the attached figure. Figure 1, Attachment Figure 2 and attached Figure 3 The following formula is its synthesis path:

[0099]

[0100] Synthesis of spiropyran-modified NHC-Pd complex 4b: To a 10 mL Shrek tube, add the spiropyran compound (310.4 mg, 1.0 mmol), PdCl2 (88.5 mg, 0.5 mmol), 1,3-bis(2,6-diisopropylphenyl)imidazole chloride (243.7 mg, 0.55 mmol), and K2CO3 (345 mg, 2.5 mmol). Evacuate and purge with argon using a double-row tube. Add 2 mL of acetone as the solvent using a syringe, and stir at 70°C overnight. The reaction was monitored by TLC. The reaction solution was extracted with deionized water (10 mL) and DCM (10 mL x 3). The collected organic phase was washed with saturated NaCl solution, dried over anhydrous sodium sulfate, and concentrated under vacuum. Column chromatography was used to purify the target SPP-NHC-Pd complex, yielding 377.2 mg (86%) of a golden powder. NMR characterization of the compound is shown in the attached figure. Figure 4 , Attachment Figure 5 and attached Figure 6 The following formula is its synthesis path:

[0101]

[0102] Synthesis of spiropyran-modified NHC-Pd complex 4c: To a 10 mL Shrek tube, add the spiropyran compound (312.8 mg, 1.0 mmol), PdCl2 (88.5 mg, 0.5 mmol), 1,3-bis(2,6-diisopropylphenyl)imidazole chloride (243.7 mg, 0.55 mmol), and K2CO3 (345 mg, 2.5 mmol). Evacuate and purge with argon using a double-row tube. Add 2 mL of acetone as the solvent via a syringe and stir at 70°C overnight. The reaction was monitored by TLC. The reaction solution was extracted with deionized water (10 mL) and DCM (10 mL x 3). The collected organic phase was washed with saturated NaCl solution, dried over anhydrous sodium sulfate, and concentrated under vacuum. The target SPP-NHC-Pd complex (344.1 mg, 77%) was purified by column chromatography to yield a golden powder. NMR characterization of the compound is shown in the attached figure. Figure 7 and attached Figure 8 The following formula is its synthesis path:

[0103]

[0104] Synthesis of spiropyran-modified NHC-Pd complex 4d: To a 10 mL Shrek tube, add the spiropyran compound (357.3 mg, 1.0 mmol), PdCl2 (88.5 mg, 0.5 mmol), 1,3-bis(2,6-diisopropylphenyl)imidazole chloride (243.7 mg, 0.55 mmol), and K2CO3 (345 mg, 2.5 mmol). Evacuate and purge with argon using a double-row tube. Add 2 mL of acetone as the solvent using a syringe, and stir at 70°C overnight. Completion of the reaction was monitored by TLC. The reaction solution was extracted with deionized water (10 mL) and DCM (10 mL x 3). The collected organic phase was washed with saturated NaCl solution, dried over anhydrous sodium sulfate, and concentrated under vacuum. Column chromatography was used to purify the target SPP-NHC-Pd complex, yielding 365.2 mg (79%) of a golden powder. NMR characterization of the compound is shown in the attached figure. Figure 9 and attached Figure 10 The following formula is its synthesis path:

[0105]

[0106] Synthesis of spiropyran-modified NHC-Pd complex 4e: To a 10 mL Shrek tube, spiropyran compound 3e (292.3 mg, 1.0 mmol), PdCl2 (88.5 mg, 0.5 mmol), 1,3-bis(2,6-diisopropylphenyl)imidazole chloride (243.7 mg, 0.55 mmol), and K2CO3 (345 mg, 2.5 mmol) were added in sequence; vacuum and argon were applied using a double-row tube; 2 mL of acetone was added as solvent using a syringe, and the mixture was stirred at 70°C overnight. The reaction was monitored by TLC, and the reaction solution was extracted with deionized water (10 mL) and DCM (10 mL × 3). The collected organic phase was washed with saturated NaCl solution and dried over anhydrous sodium sulfate, and then concentrated under vacuum. The target golden powder SPP-NHC-Pd complex 352.3 mg (82%) was purified by column chromatography. The NMR characterization of the compound is shown in the attached Figure 11 and attached Figure 12 The following formula is its synthesis path:

[0107]

[0108] Synthesis of spiropyran-modified NHC-Pd complex 4f: To a 10 mL Shrek tube, add spiropyran compound 3f (292.3 mg, 1.0 mmol), PdCl2 (88.5 mg, 0.5 mmol), 1,3-bis(2,6-diisopropylphenyl)imidazole chloride (243.7 mg, 0.55 mmol), and K2CO3 (345 mg, 2.5 mmol) in sequence; use a double-row tube for vacuum and argon flow; add 2 mL of acetone as solvent using a syringe, and stir at 70°C overnight. The reaction was monitored by TLC, and the reaction solution was extracted with deionized water (10 mL) and DCM (10 mL × 3). The collected organic phase was washed with saturated NaCl solution and dried over anhydrous sodium sulfate, and then concentrated under vacuum. The target golden powder SPP-NHC-Pd complex 316.6 mg (73%) was purified by column chromatography. The NMR characterization of the compound is shown in the attached Figure 13 and attached Figure 14 The following formula is its synthesis path:

[0109]

[0110] Synthesis method of 4g of spiropyran-modified NHC-Pd complex: Take a 10mL Shrek tube and add 3g of spiropyran compound (384.5mg, 1.0mmol), PdCl2 (88.5mg, 0.5mmol), 1,3-bis(2,6-diisopropylphenyl)imidazole chloride (243.7mg, 0.55mmol), and K2CO3 (345mg, 2.5mmol) in sequence; use a double-row tube to evacuate and pass argon; use a syringe to add 2mL of acetone as solvent and stir at 70°C overnight. The reaction was monitored by TLC, and the reaction solution was extracted with deionized water (10 mL) and DCM (10 mL × 3). The collected organic phase was washed with saturated NaCl solution and dried over anhydrous sodium sulfate, and then concentrated under vacuum. Column chromatography was used to purify the target golden powder SPP-NHC-Pd complex 309.2 mg (65%). The NMR characterization of the compound is shown in the attached Figure 15 and attached Figure 16 The following formula is its synthesis path:

[0111]

[0112] The synthesized photocatalysts exhibit excellent photochromic properties, similar to those of spiropyrans. Experimental results indicate that spiropyrans possess unique photochromic properties, typically undergoing ring-opening isomerization under UV or blue light, which manifests as a macroscopic color change. Specifically, the seven synthesized SPP-NHC-Pd compounds 4a-4g appear as golden powders under white light, but rapidly transform to green after 30 seconds of UV irradiation. This photochromic phenomenon is highly recyclable, persisting even after dozens of cycles.

[0113]

[0114] The above is one of the substituent structures of the NHCs-Pd complex of the present invention.

[0115] Following the experimental steps described above, we successfully synthesized seven photocontrollable NHCs-Pd complexes with different substituents, as shown below:

[0116]

[0117] We further tested the effectiveness of the synthesized photocontrollable molecule in the coupling reaction of amides with phenylboronic acid compounds in aqueous solution under different light sources. The experimental procedure was as follows: N,N-di-tert-butyloxycarbonylbenzamide (0.2 mmol, 1 equiv), phenylboronic acid (0.4 mmol, 2 equiv), cesium carbonate (0.6 mmol, 3 equiv), and SPP-NHC-Pd (0.01 mmol, 0.05 equiv) were added sequentially to two 25 mL Shrek tubes. The mixture was evacuated and then refilled with argon three times. 1 mL of water and 20 μL of tetrahydrofuran were added via syringe. The Shrek tubes were then exposed to 365 nm UV light and white light for 2 h, respectively. After completion of the reaction, the reaction was monitored by TLC. The reaction mixture was extracted with water and DCM. The collected organic phase was concentrated and dried, and the desired product was purified by column chromatography.

[0118] The following formula is the general formula for the coupling reaction of N,N-boc2-benzamide and 4-methylphenylboronic acid in aqueous phase under different light sources using SPP-NHC-Pd as catalyzer.

[0119]

[0120] Table 4 below shows the catalytic reaction results of the above reactions catalyzed by 4a-4g respectively, as well as the catalytic reaction results of 4a for the above reactions under the action of different bases.

[0121] The table shows that compounds 4a-4g can all catalyze the cross-coupling reaction of amide compounds with phenylboronic acid compounds relatively smoothly under UV light, while the reaction rate is very slow under white light. Furthermore, 4a is the catalyst with the best catalytic activity. Through optimization of the catalyst and base, we ultimately determined that the optimal reaction conditions are 4a as the catalyst and cesium carbonate as the base.

[0122] Table 4:

[0123]

[0124] The following formula is: The general formula of substrate expansion of amide compounds and phenylboronic acid compounds in aqueous phase under different light sources using 4a as catalyst

[0125]

[0126] Table 5 below shows the substrate expansion range of amide compounds and phenylboronic acid compounds in the aqueous phase catalyzed by 4a under different light sources.

[0127] According to the table, the reaction has very good tolerance for substrates. Whether it is an amide containing electron-withdrawing substituents, electron-donating substituents, aromatic heterocycles, or phenylboronic acid compounds, the coupling reaction can be very smoothly carried out under ultraviolet light and converted into the target product with high to very high yields. In general, the reaction is very strongly inhibited under white light.

[0128] Table 5:

[0129] .

Claims

1. A nitrogen heterocyclic carbene-palladium complex with ultraviolet-visible light-controlled isomerization and catalytic activity, characterized in that: The structural formula is as follows: Among them, R 1 and R 2 One of the following seven substituents is used: a、R 1 =F,R 2 =Me; b、R 1 =F, R 2 =And; c、R 1 =Cl,R 2 =Me; d、R 1 =Br,R 2 =Me; and、R 1 =CH3,R 2 =Me; f、R 1 =H, R 2 =And; g、R 1 =OBn,R 2 =Me。 2. A method for preparing a nitrogen heterocyclic carbene-palladium complex with ultraviolet-visible light-controlled isomerization and catalytic activity, characterized in that: The following preparation route was adopted: Among them, R 1 and R 2 One of the following seven substituents is used: a、R 1 =F,R 2 =Me; b、R 1 =F, R 2 =And; c、R 1 =Cl,R 2 =Me; d、R 1 =Br,R 2 =Me; and、R 1 =CH3,R 2 =Me; f、R 1 =H, R 2 =And; g、R 1 =OBn,R 2 =Me。 3. The preparation method according to claim 2, characterized in that The method comprises the synthesis of a pyridine-modified spiropyran compound and the synthesis of a spiropyran-modified nitrogen heterocyclic carbene-palladium complex.

4. The preparation method according to claim 3, characterized in that The synthesis of pyridine-modified spiropyran compounds is carried out as follows: (1) Take a three-necked flask and add indole iodide and 3-hydroxypyridine-4-aldehyde in sequence; (2) After placing the condensation reflux pipe, evacuate the double-row pipe and pass argon gas; (3) Add anhydrous methanol and anhydrous triethylamine under vacuum and argon gas; (4) Reflux and stir at 65-80°C overnight; (5) Monitor the reaction results by TLC and concentrate under vacuum after the reaction is completed; (6) Purify the target pyridine-modified spiropyran compound using column chromatography separation.

5. The preparation method according to claim 4, characterized in that The molar ratio of the indole iodide to 3-hydroxypyridine-4-aldehyde is 1:1; the amount of anhydrous methanol and anhydrous triethylamine added is 40-60 mL of anhydrous methanol and 0.1-0.2 mL of anhydrous triethylamine for every 1.98 mmol of indole iodide.

6. The preparation method according to claim 4, characterized in that The synthesis of pyridine-modified spiropyran compounds is carried out as follows: (1) Take a three-necked flask and add 1.98 mmol of indole iodide and 1.98 mmol of 3-hydroxypyridine-4-aldehyde in sequence; (2) After placing the condensation reflux pipe, evacuate the double-row pipe and pass argon gas; (3) Add 50 mL of anhydrous methanol and 0.1 mL of anhydrous triethylamine under vacuum and argon atmosphere; (4) Reflux and stir at 70°C overnight; (5) Monitor the reaction results by TLC and concentrate under vacuum after the reaction is completed; (6) Purify the target pyridine-modified spiropyran compound using column chromatography separation.

7. The preparation method according to claim 3, characterized in that The synthesis of spiropyran-modified nitrogen heterocyclic carbene-palladium complexes was carried out using the following steps: (1) Take a Shrek tube and add spiropyran compound, PdCl2, 1,3-bis(2,6-diisopropylphenyl)imidazole chloride and K2CO3 in sequence; (2) Use double-row pipes for vacuuming and argon flow; (3) Adding the reaction solvent acetone under vacuum; (4) Stir at 60°C overnight; (5) Monitor the reaction completion by TLC; extract the reaction solution with deionized water and DCM; wash the collected organic phase with saturated NaCl solution; dry the organic phase with anhydrous sodium sulfate and concentrate it under vacuum; (6) Purify the target nitrogen heterocyclic carbene-palladium complex by column chromatography separation.

8. The preparation method according to claim 7, characterized in that The synthesis of spiropyran-modified nitrogen heterocyclic carbene-palladium complexes was carried out using the following steps: (1) Take a Shrek tube and add 0.5-1.0 mmol of spiropyran compound, 0.5 mmol of PdCl2, 0.55 mmol of 1,3-bis(2,6-diisopropylphenyl)imidazole chloride and 2.5 mmol of K2CO3 in sequence; (2) Use double-row pipes for vacuuming and argon flow; (3) Add 2 mL of reaction solvent acetone under vacuum and argon gas; (4) Stir at 60°C overnight; (5) Monitor the reaction completion by TLC; extract the reaction solution with deionized water and DCM; wash the collected organic phase with saturated NaCl solution; dry the organic phase with anhydrous sodium sulfate and concentrate it under vacuum; (6) Purify the target nitrogen heterocyclic carbene-palladium complex by column chromatography separation.

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