Salen ligand and carbene compound and preparation method thereof

Abstract

The invention discloses a Salen ligand, a carbene compound and a preparation method of the Salen ligand and the carbene compound, and belongs to the technical field of chemical synthesis. The chemical structural formula of the Salen ligand is shown as a formula I, and the formula I is # imgabs0 #; in the formula I, M comprises any one of Pd, Ni, Cu and Zn; r comprises any one of methyl, ethyl and n-butyl; r'comprises any one of C1-C5 alkyl, phenyl and biphenyl; and X comprises PF6. Salen and carbene are combined to realize concerted catalysis, stability enhancement and multifunctional integration, the structure adjustability and metal coordination capability of the Salen ligand are retained, high reaction activity and stability of carbene are introduced, a multifunctional composite system is formed, the catalytic activity of the single Salen ligand is remarkably improved, and the Salen ligand has a wide application prospect. The application field of the Salen ligand is widened, and the technical problem that Salen is rarely researched in the carbene field is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical synthesis, and in particular to a Salen ligand and a carbene compound and a preparation method thereof. Background Art

[0002] Salen ligands are prepared from primary diamine compounds and salicylaldehyde compounds. They are a type of chelating ligand commonly used in coordination chemistry and homogeneous catalysis. They can form stable metal-Salen complexes with metal ions and are used as catalysts.

[0003] Salen ligands are easy to synthesize, have strong coordination ability, and can form stable complexes with a variety of metal ions. Metal-Salen complexes have shown good asymmetric induction effects and catalytic activity in asymmetric catalytic oxidative addition of olefins. Its unique molecular magnetism, pharmacological activity and optical properties make Salen ligands widely used in chemical catalysis, materials, sensors and biomedicine.

[0004] Salen ligands offer a high degree of structural designability. By modifying the structures of salicylaldehyde and diamine and introducing different substituents, the electronic properties and steric hindrance of salen can be adjusted, thereby preparing salen complexes with diverse performance to meet the needs of various catalytic reactions. They exhibit excellent chemical and thermal stability and can withstand certain reaction conditions, such as solubility in some organic solvents. They are stable, insensitive to water and air, easy to store and handle, and convenient for recycling and reuse in practical applications.

[0005] Nitrogen heterocyclic carbenes (NHCs), as strong σ-donating ligands, can form relatively stable metal-carbene bonds with most metals. Due to their advantages such as ease of synthesis, structural tunability, and stable bonding, they have been used as carbon donors to construct supramolecular metal complexes. In recent years, nitrogen heterocyclic carbene complexes have been widely used in a variety of fields, including catalysis, biomedicine, and materials science. Compared to traditional ligands, nitrogen heterocyclic carbenes possess stronger electron-donating properties, resulting in more stable metal-carbene complexes. Due to their high s-donating and low p-accepting capacities, NHCs have been found to have the potential to bind to a wide range of metal ions. Their unique electronic properties have led to extensive research in coordination chemistry and transition metal catalysis, where they have demonstrated promising results, such as in various C-C bond formation reactions. Carbene catalysis, particularly nitrogen heterocyclic carbenes (NHCs), has demonstrated significant advantages in organic synthesis and materials science, with key features including high catalytic activity, excellent stability, and versatility.

[0006] The flexible structural adjustability and functionality of Salen ligands have broadened its research field. However, there are few reports on them in the field of carbenes. It is particularly interesting to see whether introducing Salen structural elements into the field of carbenes can bring more possibilities in the field of catalysis. Summary of the Invention

[0007] In order to solve the above technical problems, the purpose of the present invention is to provide a Salen ligand and a carbene compound and a preparation method thereof, so as to solve the problem of the existing lack of catalyst materials with stronger catalytic performance through the combination of Salen and carbene.

[0008] The technical solution of the present invention to solve the above technical problems is as follows:

[0009] The first object of the present invention is to provide a Salen ligand, the chemical structure of which is shown in Formula I:

[0010] Formula I:

[0011] In Formula I, M includes any one of Pd, Ni, Cu and Zn;

[0012] R includes any one of methyl, ethyl and n-butyl;

[0013] R' includes any one of a C1-C5 hydrocarbon group, a phenyl group, and a biphenyl group;

[0014] X includes PF6 or Br;

[0015] Y includes (1S, 2S) or (1R, 2R) Any one of them.

[0016] Furthermore, the chemical structural formula is shown in any one of Formula II to Formula IV:

[0017] Formula II:

[0018] In Formula II, M includes any one of Pd, Ni, Cu and Zn;

[0019] Formula III:

[0020] In formula III, M includes any one of Pd, Ni, Cu and Zn;

[0021] Formula IV:

[0022] In Formula IV, M includes any one of Pd, Ni, Cu and Zn.

[0023] The second object of the present invention is to provide a method for preparing the above-mentioned Salen ligand, wherein the method for preparing the Salen ligand represented by Formula II comprises the following steps:

[0024] (1) mixing salicylaldehyde and formaldehyde to carry out chloromethylation reaction to prepare 5-chloromethyl-2-hydroxybenzaldehyde;

[0025] (2) First, 5-chloromethyl-2-hydroxybenzaldehyde and N-methylimidazole were subjected to a CN coupling reaction, and then the reaction product was subjected to an ion exchange reaction with NH4PF6;

[0026] (3) mixing the final product obtained in step (2) with ethylenediamine to carry out a Schiff base reaction to obtain a Schiff base;

[0027] (4) mixing a Schiff base and a metal salt to carry out a metal coordination reaction to obtain;

[0028] The metal salt includes any one of Pd salt, Ni salt, Cu salt and Zn salt.

[0029] Furthermore, in step (1), the mass volume ratio of salicylaldehyde, concentrated hydrochloric acid and formaldehyde aqueous solution is 5-10 g:40-60 mL:4-6 mL.

[0030] Furthermore, the mass concentration of the formaldehyde aqueous solution in step (1) is 30%-40%.

[0031] Furthermore, the concentration of concentrated hydrochloric acid in step (1) is 30%-40%.

[0032] Furthermore, the reaction temperature in step (1) is room temperature and the reaction time is 20-30 hours.

[0033] Furthermore, in step (2), the molar ratio of 5-chloromethyl-2-hydroxybenzaldehyde to N-methylimidazole is (0.8-1.2): (0.8-1.2); the reaction temperature is room temperature, the reaction time is 1-5 hours, and the reaction solvent is toluene.

[0034] Furthermore, in step (2), the molar ratio of 5-chloromethyl-2-hydroxybenzaldehyde to NH4PF6 is (2-4): (5-7); the reaction temperature with NH4PF6 is room temperature, the reaction time is 10-15h, and the reaction solvent is water.

[0035] Furthermore, in step (3), the molar ratio of the final product obtained in step (2) to ethylenediamine is (0.8-1.2): (0.4-0.6); the reaction temperature is 70-80° C., the reaction time is 4-8 h, and the reaction solvent is methanol.

[0036] Furthermore, in step (4), the molar ratio of the Schiff base to the metal salt is (0.8-1.2): (0.8-1.2); the reaction temperature is room temperature; the reaction time is 1-5 hours; and the reaction solvent is acetonitrile.

[0037] Furthermore, in step (4), the metal salt is an acetate of any one of Pd, Ni, Cu and Zn.

[0038] Furthermore, the preparation method of the Salen ligand represented by formula III comprises the following steps:

[0039] (a) mixing 2,4-dihydroxybenzaldehyde, 1,3-dibromopropane and CsHCO3 to carry out a substitution reaction;

[0040] (b) first subjecting the product obtained in step (a) to a CN coupling reaction with N-methylimidazole, and then subjecting the obtained product to an ion exchange reaction with NH4PF6 to obtain an imidazolium salt;

[0041] (c) mixing the imidazolium salt obtained in step (b) with ethylenediamine to perform a Schiff base reaction;

[0042] (d) mixing the product obtained in step (c) with a metal salt to carry out a metal coordination reaction to obtain;

[0043] The metal salt includes any one of Pd salt, Ni salt, Cu salt and Zn salt.

[0044] Furthermore, in step (a), the molar ratio of 2,4-dihydroxybenzaldehyde, 1,3-dibromopropane and CsHCO3 is (10-20): (10-20): (10-20); the reaction temperature is 70-90°C, the reaction time is 3-5h, and the reaction solvent is acetonitrile.

[0045] Furthermore, in step (b), the molar ratio of the product obtained in step (a) to N-methylimidazole is (0.8-1.2): (0.8-1.2); the reaction temperature is 70-90° C., and the reaction time is 10-15 h.

[0046] Furthermore, in step (b), the molar ratio of the product obtained in step (a) to NH4PF6 is (1-3): (3-6); the reaction conditions with NH4PF6 are first reacting at 60-90°C for 10-15h, and then continuing the reaction at room temperature for 20-30h, and the reaction solvents are methanol and water.

[0047] Furthermore, in step (c), the molar ratio of imidazolium salt to ethylenediamine is (0.3-0.6): (0.2-0.3); the reaction temperature is 70-90° C., the reaction time is 10-15 h, and the reaction solvent is methanol.

[0048] Furthermore, in step (d), the molar ratio of the product obtained in step (c) to the metal salt is (0.15-0.2): (0.1-0.3); the reaction temperature is 70-90° C., the reaction time is 10-15 h, and the reaction solvent is acetonitrile.

[0049] Furthermore, in step (d), the metal salt is an acetate of any one of Pd, Ni, Cu and Zn.

[0050] Furthermore, the preparation method of the Salen ligand represented by Formula IV comprises the following steps:

[0051] (A) 2,4-dihydroxybenzaldehyde, 1,5-dibromopentane, and CsHCO3 are mixed to perform a substitution reaction;

[0052] (B) first subjecting the product obtained in step (A) to a CN coupling reaction with N-methylimidazole, and then subjecting the obtained product to an ion exchange reaction with NH4PF6 to obtain an imidazolium salt;

[0053] (C) mixing the imidazolium salt obtained in step (B) with ethylenediamine to perform a Schiff base reaction;

[0054] (D) mixing the product obtained in step (C) with a metal salt to carry out a metal coordination reaction to obtain;

[0055] The metal salt includes any one of Pd salt, Ni salt, Cu salt and Zn salt.

[0056] Furthermore, in step (A), the molar ratio of 2,4-dihydroxybenzaldehyde, 1,3-dibromopropane and CsHCO3 is (10-20): (10-20): (10-20); the reaction temperature is 70-90°C, the reaction time is 3-5h, and the reaction solvent is acetonitrile.

[0057] Furthermore, in step (B), the molar ratio of the product obtained in step (A) to N-methylimidazole is (0.8-1.2): (0.8-1.2); the reaction temperature is 70-90° C., and the reaction time is 10-15 h.

[0058] Furthermore, in step (B), the molar ratio of the product obtained in step (A) to NH4PF6 is (1-2): (5-7); the reaction conditions with NH4PF6 are first reacting at 60-90°C for 10-15h, and then continuing the reaction at room temperature for 20-30h, and the reaction solvents are methanol and water.

[0059] Furthermore, in step (C), the molar ratio of imidazolium salt to ethylenediamine is (0.4-0.8): (0.2-0.4); the reaction temperature is 70-90° C., the reaction time is 10-15 h, and the reaction solvent is methanol.

[0060] Furthermore, in step (D), the molar ratio of the product obtained in step (C) to the metal salt is (0.8-1.2): (0.8-1.2); the reaction temperature is 70-90° C., the reaction time is 10-15 h, and the reaction solvent is acetonitrile.

[0061] Furthermore, in step (D), the metal salt is an acetate of any one of Pd, Ni, Cu and Zn.

[0062] The fourth object of the present invention is to provide a method for preparing a silver carbene compound based on the above-mentioned Salen ligand, comprising the following steps:

[0063] Salen ligand, silver oxide and potassium carbonate are mixed and ball-milled to prepare a silver carbene compound.

[0064] Furthermore, the molar ratio of the Salen ligand, silver oxide and potassium carbonate is (2-5): (5-10): (10-20); the ball milling speed is 300-600 rpm, and the time is 60-120 min.

[0065] A fifth object of the present invention is to provide a Salen silver carbene compound obtained by the above-mentioned preparation method.

[0066] A sixth object of the present invention is to provide a method for preparing a gold carbene compound based on a silver carbene compound, comprising the following steps:

[0067] The silver carbene compound and Au(THT)Cl are mixed and reacted to prepare a gold carbene compound.

[0068] Furthermore, the molar ratio of the silver carbene compound to Au(THT)Cl is (0.5-2):(1-4); and the reaction solvent is acetonitrile.

[0069] Furthermore, the silver carbene compound and Au(THT)Cl are mixed and dissolved in acetonitrile, and stirred overnight for 20-30 hours to obtain the obtained product.

[0070] A seventh object of the present invention is to provide a Salen gold carbene compound obtained by the above-mentioned preparation method.

[0071] The eighth object of the present invention is to provide the use of the above-mentioned Salen ligand, Salen silver carbene compound, or Salen gold carbene compound in the field of catalysis.

[0072] The present invention has the following beneficial effects:

[0073] The present invention prepares a series of Salen ligands and carbene compounds thereof, and realizes synergistic catalysis, stability enhancement and multifunctional integration by combining Salen and carbene, providing new ideas for asymmetric catalysis, green chemistry and biomedicine. It not only retains the structural adjustability and metal coordination ability of Salen ligands, but also introduces the high reactivity and stability of carbene, forming a multifunctional composite system, achieving a significant improvement in the catalytic activity of a single Salen ligand, and broadening the application field of Salen ligands. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 The synthetic route and structural diagram of the Ni-Salen silver carbene compound M in Example 2 are shown;

[0075] Figure 2 The synthetic route and structural diagram of the Ni-Salen silver carbene compound S in Example 3 are shown;

[0076] Figure 3 are the chemical structural formulas of the Schiff base d, Ni-Salen ligand, and silver carbene compound in the test example, wherein (a) is the Schiff base d, (b) is the Ni-Salen ligand, and (c) is the silver carbene compound;

[0077] Figure 4 Schematic diagram of the single crystal structure of the silver carbene compound in the experimental example, where (a) is the front view and (b) is the side view;

[0078] Figure 5 is the Schiff base d, Ni-Salen ligand and silver carbene compound in the test example 1 H NMR spectra, where (a) is Schiff base d, (b) is Ni-Salen ligand, and (c) is silver carbene compound;

[0079] Figure 6 HR-ESI mass spectra of Schiff base d, Ni-Salen ligand and silver carbene compound in the test example;

[0080] Figure 7 The electrocatalytic performance characterization results of the test example are shown, where (a) is the correlation curve between current density and potential, (b) is the equivalent circuit diagram, and (c) is the measured overpotential value at a certain current. DETAILED DESCRIPTION

[0081] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not intended to limit the scope of the invention. In the embodiments, if specific conditions are not specified, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0082] Example 1:

[0083] A method for preparing a Salen ligand comprises the following steps:

[0084] (1) Synthesis of compound b

[0085] The chemical reaction formula for the synthesis of compound b is as follows:

[0086]

[0087] To a 200 mL Schlenk tube were added salicylaldehyde a (8.595 g, 141.39 mmol, prepared according to the literature Can. J. Chem. 2012, 90, 60-70) and formaldehyde (5.4 mL, 37 wt%). To this mixture was added concentrated hydrochloric acid (50 mL, 36%) under a nitrogen atmosphere, and the resulting mixture was stirred at room temperature for 24 hours. The solid was separated, filtered, washed with water, dissolved in CH2Cl2, dried over anhydrous magnesium sulfate, allowed to stand for a period of time, filtered again, and spin-dried. After recrystallization from n-hexane, a light pink solid b was obtained, which was collected by filtration, washed with n-hexane, and dried in vacuo. Yield: 5.94 g (34.82 mmol, 49.8% yield).

[0088] The NMR results are as follows:

[0089] 1 H NMR (400MHz, CDCl3): δ = 11.07 (s, 1H), 9.90 (s, 1H), 7.59 (d, 1H, J = 4Hz, Ar-H), 7.55 (dd, 1H, J = 4, 8Hz, Ar-H), 6.99 (d, 1H, J = 12Hz, Ar-H), 4.59 (s, 2H).

[0090] (2) Synthesis of compound c

[0091] The chemical reaction formula for the synthesis of compound C is as follows:

[0092]

[0093] 5-Chloromethyl-2-hydroxybenzaldehyde b (500 mg, 2.931 mmol) obtained in step (1) was added to a 25 mL Schlenk tube. After dissolving it with toluene (10 mL), N-methylimidazole (240.64 mg, 2.931 mmol) was added dropwise with a syringe and stirred at room temperature for 3 h under a nitrogen atmosphere. After precipitation of a yellow solid, it was filtered, washed with ether, and then dried in a vacuum. The obtained solid was transferred to a flask and dissolved in 40 mL of water. NH4PF6 (1 g, 6.135 mmol) was then dissolved in H2O (10 mL), and this solution was added to the former, immediately forming a white precipitate, which was further stirred at room temperature for 12 h. The precipitate was collected by filtration, washed with CH3OH, and dried in a vacuum to obtain imidazolium salt c. Yield: 765 mg (2.112 mmol, yield 72.06%).

[0094] The NMR and mass spectrometry results are shown below:

[0095] 1 H NMR (400MHz, DMSO-d6): δ=11.00(s,H),10.28(s,H),9.13(s,H),7.76(d,J=4Hz,2H),7.67(s,H),7.58(dd,1H,J=4,8Hz),7.03(d,J=8Hz H),5.34(s,2H),3.83(s,3H).

[0096] ESI-MS(positive ions):m / z=217.0976(calcd for{[c](PF6)} + 217.0972).

[0097] (3) Synthesis of Schiff base d

[0098] The chemical reaction formula for the synthesis of Schiff base d is as follows:

[0099]

[0100] Add a magnet to a 50 mL Schlenk tube. Take a 10 mL sample tube and add substance c (500 mg, 1.38 mmol) obtained in step (2), pierce it, and seal it with sealing film. Put it into a glove box and add about 10 mL of methanol, then take it out. Add ethylenediamine (41.48 mg, 0.69 mmol) under N2 atmosphere. Stir at 80 ° C for 6 h. After the reaction is completed, the solution is cooled to room temperature and diethyl ether (10 mL) is added. A dark yellow solid precipitates. The insoluble material, i.e., Schiff base d, is collected by filtration, washed with diethyl ether, and dried in vacuo. Yield: 330 mg (0.441 mmol, yield 63.88%).

[0101] The NMR and mass spectrometry results are shown below:

[0102] 1 H NMR (400MHz, DMSO-d6): δ=13.57(s,H),9.12(s,H),8.58(s,H),7.74(d,J=20Hz,2H),7.52(s,H),7.39(dd,J=2,4Hz H), 6.92 (d, J = 8Hz, H), 5.32 (s, H), 3.95 (s, 2H), 3.83 (s, 3H).

[0103] ESI-MS(positive ions):m / z=229.1194(calcd for{[d](PF6)} 2+ 229.1210).

[0104] (4) Synthesis of Ni-Salen ligand e

[0105] The chemical reaction formula for the synthesis of Ni-Salen ligand e is shown below:

[0106]

[0107] Add a magnet to a 50 mL Schlenk tube. Take a 10 mL sample tube and add the substance d obtained in step (3) (200 mg, 0.2673 mmol) and nickel acetate (47.26 mg, 0.2673 mmol), pierce the tube, and seal it with sealing film. Place it in a glove box, add about 15 mL of acetonitrile, and take it out. Stir at 80°C for 3 hours. After the reaction is completed, the solution is cooled to room temperature and methanol (10 mL) is added. A brown-yellow solid precipitates. The insoluble matter, i.e., Ni-salen ligand, is collected by filtration, washed with ether, and dried in vacuo. Yield: 198 mg (0.246 mmol, yield 92.11%).

[0108] The NMR results are as follows:

[0109] 1 H NMR (400MHz, DMSO-d6): δ=9.11(s,H),8.19(s,H),7.73(dd,J=2,4Hz,2H),7.49(d,J=4Hz,H),7.38(dd,J=4,12Hz,H),6.89(d,J=12Hz H),5.27(s,2H),3.87(s,2H),3.83(s,3H).

[0110] A method for preparing a Ni-Salen silver carbene compound comprises the following steps:

[0111] The chemical reaction formula for the synthesis of Ni-Salen silver carbene compound is as follows:

[0112]

[0113] Prepared Ni-Salen ligand e (30 mg, 0.0373 mmol), Ag2O (16.3 mg, 0.0703 mmol), and K2CO3 (29.2 mg, 0.2113 mmol) were weighed in sequence and placed in a ball mill. Milled at 450 rpm for 90 min. The sample was scraped from the mill and extracted with 15 mL of acetonitrile. The mixture was filtered, rotary evaporated, concentrated, and added dropwise to diethyl ether. The precipitate was collected by centrifugation and dried under vacuum to obtain a light green solid. Yield: 26.5 mg (0.0173 mmol, 92.72%).

[0114] The NMR and mass spectrometry results are shown below:

[0115] 1 H NMR (400MHz, DMSO-d6): δ = 7.47 (d, J = 8Hz, 2H), 7.41 (s, H), 7.04 (d, J = 8Hz, H), 6.81 ( s,H),6.67(d,J=12Hz,H),5.18(s,2H),3.90(s,3H),3.63(s,2H).ESI-MS(positive ions):m / z=621.0572(calcd for{[f(PF6)} 2+ 621.0494.

[0116] A method for preparing a Ni-Salen gold carbene compound comprises the following steps:

[0117] The chemical reaction formula for the synthesis of Ni-Salen gold carbene compound is as follows:

[0118]

[0119] The prepared Ni-Salen silver carbene compound f (19 mg, 0.0124 mmol) and Au(THT)Cl (8.345 mg, 0.0260 mmol) were weighed and dissolved in 15 mL of acetonitrile. After stirring overnight for 24 h, the mixture was filtered, rotary evaporated, concentrated, and added dropwise to diethyl ether. The mixture was centrifuged, and the precipitate was collected and dried in vacuo to obtain a yellow solid. Yield: 17 mg (0.0099 mmol, 80.15%).

[0120] The NMR and mass spectrometry results are shown below:

[0121] 1H NMR (400MHz, DMSO-d6): δ = 7.56 (d, J = 16Hz, 2H), 7.08 (s, H), 6.90 (dd, J = 4, 8H z,H),6.74(s,H),6.61(d,J=8Hz,H),5.26(s,2H),3.91(s,3H),3.34(s,2H).

[0122] ESI-MS(positive ions):m / z=709.1212(calcd for{[f(PF6)} 2+ 709.1131.

[0123] Example 2:

[0124] A method for preparing a Salen ligand comprises the following steps:

[0125] (1) Synthesis of Compound I

[0126] The chemical reaction formula for the synthesis of compound I is shown below:

[0127]

[0128] Add a magnetic rod to a 100mL Schlenk tube. Add substance g (2,4-dihydroxybenzaldehyde) (2071.8mg, 15mmol) and substance h (2908.8mg, 15mmol) to a 10mL sample tube, pierce the tube, and seal it with parafilm. Place the tube in a glove box, add approximately 30mL of acetonitrile, and remove it. Add 1,3-dibromopropane (3088.917mg, 15.3mmol) under an N2 atmosphere. Stir at 80°C for 4h. After the reaction is complete, cool the solution to room temperature, filter to remove the solids, and concentrate using a rotary evaporator. The crude material is purified by column chromatography (EtOAc / PE) to obtain the product as a white solid, which, after recrystallization, is compound I. Yield: 1.2g (4.631mmol, 30.88%).

[0129] The NMR results are as follows:

[0130] 1 H NMR (400MHz, CDCl3): δ=11.47(s,H),9.72(s,H),7.45(d,J=8Hz,H),6.56(dd,J=4,12Hz,H),6.44(d,J=4Hz,H),4.17(t,2H),3.59(t,2H),2.36(m,2H).

[0131] (2) Synthesis of Compound J

[0132] The chemical reaction formula for the synthesis of compound J is shown below:

[0133]

[0134] Compound I (388 mg, 1.497 mmol) obtained in step (1) was added to a 25 mL Schlenk tube. After dissolving it with toluene (10 mL), N-methylimidazole (122.94 mg, 1.497 mmol) was added dropwise with a syringe and stirred at 80 ° C for 12 h under a nitrogen atmosphere. After the white solid was precipitated, it was filtered, washed with ether, and then dried in a vacuum. The obtained solid was transferred to a flask and dissolved in 10 mL of methanol. NH4PF6 (776.60 mg, 4.764 mmol) was added, heated at 80 ° C for 12 h, cooled, and distilled water was added and stirred at room temperature for another 24 h. The precipitate was collected by filtration, washed with water, and dried in a vacuum to obtain a purple solid imidazolium salt J. Yield: 310 mg (0.763 mmol, 50.74%).

[0135] The NMR results are as follows:

[0136] 1 H NMR (400MHz, DMSO-d6): δ = 11.02 (s, H), 10.01 (s, H), 9.13 (s, H), 7.80 (t, J = 4Hz, H), 7.70 (t, J = 4Hz, H), 7.64 (d, J = 8 Hz,H),6.52(dd,J=4,8Hz,H),6.44(d,J=4Hz,H),4.34(t,J=8Hz,2H),4.09(t,J=8Hz,2H),3.84(s,3H),2.28(m,2H).

[0137] (3) Synthesis of Compound K

[0138] The chemical reaction formula for the synthesis of compound K is shown below:

[0139]

[0140] To a 100 mL Schlenk tube, add imidazolium salt J (200 mg, 0.493 mmol) prepared in step (2). Dissolve it in methanol (CH3OH, 10 mL), then add ethylenediamine (15.10 mg, 0.246 mmol) dropwise using a pipette. Stir at 80°C under a nitrogen atmosphere for 12 h. After cooling, add a small amount of diethyl ether, and filter to obtain a pale yellow solid, K. Yield: 130 mg (0.1554 mmol, 63.17%).

[0141] The NMR results are as follows:

[0142] 1 H NMR (400MHz, DMSO-d6): δ=13.79(s,H),9.12(s,H),8.43(s,H),7.79(d,J=4Hz,H),7.70(d,J=4Hz,H),7.28(dd,J=4,8 Hz,H),6.34(d,J=8Hz,H),6.29(s,H),4.31(t,J=8Hz,2H),4.02(t,J=8Hz,2H),3.83(s,3H),3.82(s,2H),2.25(m,2H).

[0143] (4) Synthesis of Ni-Salen Ligand K

[0144] The chemical reaction formula for the synthesis of Ni-Salen ligand K is shown below:

[0145]

[0146] Compound J (200 mg, 0.493 mmol) obtained in step (3) was added to a 100 mL Schlenk tube. Dissolved in methanol (CH3OH, 10 mL), ethylenediamine (15.10 mg, 0.246 mmol) was added dropwise using a pipette. The mixture was stirred at 80°C under a nitrogen atmosphere for 12 h. After cooling, a small amount of diethyl ether was added and the mixture was filtered to obtain a pale yellow solid, K. Yield: 130 mg (0.1554 mmol, 63.17%).

[0147] The NMR results are as follows:

[0148] 1 H NMR (400MHz, DMSO-d6): δ=13.79(s,H),9.12(s,H),8.43(s,H),7.79(d,J=4Hz,H),7.70(d,J=4Hz,H),7.28(dd,J=4,8 Hz,H),6.34(d,J=8Hz,H),6.29(s,H),4.31(t,J=8Hz,2H),4.02(t,J=8Hz,2H),3.83(s,3H),3.82(s,2H),2.25(m,2H).

[0149] A method for synthesizing a Ni-Salen silver carbene compound comprises the following steps:

[0150] The synthetic route and structural diagram of Ni-Salen silver carbene compound M are shown in the figure below. Figure 1 shown.

[0151] e (30 mg, 0.0336 mmol), Ag2O (15.57 mg, 0.0672 mmol), and K2CO3 (27.85 mg, 0.2015 mmol) were weighed, placed in a ball mill, and milled at 450 rpm for 90 min. The sample was scraped from the mill and extracted with 15 mL of acetonitrile. The mixture was filtered, rotary evaporated, concentrated, and added dropwise to diethyl ether. The precipitate was collected by centrifugation and dried under vacuum to obtain an orange-red solid. Yield: 27 mg (0.0158 mmol, 94.12%).

[0152] The NMR and mass spectrometry results are shown below:

[0153] 1 H NMR (400MHz, DMSO-d6): δ = 7.60 (d, J = 12Hz, 2H), 7.43 (s, H), 6.99 (d, J = 8Hz, H), 6.08 (s, H), 6.02 (d ,J=8Hz,H),4.27(t,J=8Hz,2H),3.96(t,J=8Hz,2H),3.76(s,3H),3.37(t,J=8Hz,2H),2.26(m,2H).

[0154] ESI-MS(positive ions):m / z=709.1049(calcd for{[M(PF6)} 2+ 709.1018.

[0155] Example 3:

[0156] A method for preparing a Salen ligand comprises the following steps:

[0157] (1) Synthesis of Compound O

[0158] The chemical reaction formula for the synthesis of compound O is as follows:

[0159]

[0160] Add a magnetic rod to a 100mL Schlenk tube. Take a 10mL sample tube and add substance N (2071.8mg, 15mmol) and substance H (2908.8mg, 15.3mmol), pierce the tube, and seal it with sealing film. Place it in a glove box, add about 30mL of acetonitrile, and take it out. Add 1,5-dibromopentane (3590.05mg, 15mmol) under N2 atmosphere. Stir at 80℃ for 4h. After the reaction is completed, the solution is cooled to room temperature, filtered to remove the solid, and concentrated using a rotary evaporator. The crude material is purified by column chromatography (EtOAc / PE) to obtain the product as a white solid. After recrystallization, it is compound O. Yield: 1.3g (4.527mmol, 30.18%).

[0161] The NMR results are as follows:

[0162] 1 H NMR (400MHz, CDCl3): δ = 11.48 (s, H), 9.72 (s, H), 7.41 (d, J = 8Hz, H), 6.53 (dd, J = 4, 8Hz, H), 6.4 1(d,J=4Hz,H), 4.02(t,J=8Hz,2H), 3.44(t,J=8Hz,2H), 1.94(m,2H), 1.84(m,2H), 1.63(m,2H).

[0163] (2) Synthesis of Compound P

[0164] The chemical reaction formula for the synthesis of compound P is as follows:

[0165]

[0166] Compound O (400 mg, 1.393 mmol) obtained in step (1) was added to a 25 mL Schlenk tube. After dissolving it with toluene (10 mL), N-methylimidazole (116.699 mg, 1.393 mmol) was added dropwise with a syringe and stirred at 80 ° C for 12 h under a nitrogen atmosphere. After the white solid precipitated, it was filtered, washed with ether, and then dried in a vacuum. The obtained solid was transferred to a flask and dissolved in 10 mL of methanol. NH4PF6 (1 g, 6.135 mmol) was added, heated at 80 ° C for 12 h, cooled, and distilled water was added and stirred at room temperature for another 24 h. The precipitate was collected by filtration, washed with water, and dried in a vacuum to obtain a purple solid imidazolium salt P. Yield: 153 mg (0.3267 mmol, 23.45%).

[0167] The NMR results are as follows:

[0168] 1H NMR (400MHz, DMSO-d6): δ = 11.02 (s, H), 10.00 (s, H), 9.10 (s, H), 7.77 (dd, J = 2Hz, H), 7.70 (dd, J = 2Hz, H), 7.63 (d, J = 8Hz, H), 6.55 (dd,J=4,8Hz,H),6.45(d,J=4Hz,H),4.18(t,J=8Hz,2H),4.03(t,J=6Hz,2H),3.84(s,3H),1.84(m,2H),1.75(m,2H),1.38(m,2H).

[0169] (3) Synthesis of Compound Q

[0170] The chemical reaction formula for the synthesis of compound Q is as follows:

[0171]

[0172] Compound P (270 mg, 0.622 mmol) prepared in step (2) was added to a 100 mL Schlenk tube. Dissolved in methanol (CH3OH, 10 mL), ethylenediamine (19.062 mg, 0.311 mmol) was added dropwise using a pipette. The mixture was stirred at 80°C under a nitrogen atmosphere for 12 h. After cooling, a small amount of diethyl ether was added and the mixture was filtered to obtain a pale yellow solid, Q. Yield: 93 mg (0.1042 mmol, 33.50%).

[0173] The NMR results are as follows:

[0174] 1 H NMR (400MHz, DMSO-d6): δ=13.77(s,H),9.10(s,H),8.43(s,H),7.77(dd,J=1.6Hz,H),7.70(dd,J=1.6Hz,H),7.26(d,J=8Hz,H),6.37(dd, J=4,8Hz,H),6.30(d,J=4Hz,H),4.18(t,J=8Hz,2H),3.96(t,J=8Hz,2H),3.84(s,3H),1.99(m,2H),1.84(m,2H),1.73(m,2H),1.37(m,2H).

[0175] (4) Synthesis of Ni-Salen ligand compound R

[0176] The chemical reaction formula for the synthesis of compound R is shown below:

[0177]

[0178] Add a magnet to a 50 mL Schlenk tube. Take a 10 mL sample tube and add compound Q (90 mg, 0.101 mmol) prepared in step (3) and nickel acetate (17.822 mg, 0.101 mmol), pierce the tube, and seal it with sealing film. Put it into a glove box, add about 12 mL of acetonitrile, and take it out. ○ After stirring at 400 °C for 12 h, the solution was concentrated and ether (10 mL) was added to precipitate an orange-yellow solid. The insoluble material, i.e., the Ni-salen ligand, was collected by filtration. Yield: 80 mg (0.084 mmol, 83.59%).

[0179] A method for synthesizing a Ni-Salen silver carbene compound comprises the following steps:

[0180] The synthetic route and structural diagram of Ni-Salen silver carbene compound S are shown in the figure below. Figure 2 shown.

[0181] R (30 mg, 0.0316 mmol), Ag2O (14.65 mg, 0.0632 mmol), and K2CO3 (26.204 mg, 0.1896 mmol) were weighed in sequence and placed in a ball mill. Milled at 450 r / min for 90 min. The sample was scraped from the mill and extracted with 15 mL of acetonitrile. The mixture was filtered, rotary evaporated, concentrated, and added dropwise to diethyl ether. The mixture was centrifuged, and the precipitate was collected and dried in vacuo to obtain a yellow solid. Yield: 27 mg (0.0148 mmol, 93.87%).

[0182] The NMR results are as follows:

[0183] 1 H NMR (400MHz, DMSO-d6): δ = 7.68 (s, H), 7.51 (s, H), 7.45 (d, J = 4Hz, H), 7.12 (d, J = 8Hz, H), 6.09 (d, J=4Hz,2H),4.16(t,J=4Hz,2H),3.84(s,5H),3.31(s,2H),1.84(m,2H),1.71(m,2H),1.38(m,2H).

[0184] Test example:

[0185] (1) The Schiff base d, Ni-Salen ligand and silver carbene compound prepared in Example 1 were 1 H NMR spectroscopy and HR-ESI mass spectrometry analysis showed that the chemical structures of the samples were as follows: Figure 3 As shown, the single crystal structure diagram of the silver carbene compound is as follows Figure 4 The experimental results are shown in Figure 5and Figure 6 shown.

[0186] From the ligand without metal to the ligand with metal, and then to the silver carbene, the 1 H NMR spectroscopy reveals that the proton signals attributable to the imine bond shift upfield after metallization. Similarly, the proton signals attributable to the imine bond also continue to shift upfield due to the difference in the chemical environment inside and outside the framework.

[0187] In addition, the HR-ESI mass spectral data (positive ion mode) of silver carbene are in perfect agreement with the calculated isotopic distribution. For example, the peak of the isotopic distribution observed at m / z = 621.0572 corresponds perfectly to its theoretical isotopic distribution ([Ni2-L-Ag2] 2+ The calculated value is 621.0494).

[0188] The single crystal structure is a binuclear macrocyclic structure of Ni-Salen carbene type formed by potassium ion complexation. The distance between Ni-Ni bonds is (11), the distance between Ag-Ag bonds is (6), the distance between the OK keys is (47), the distance between the two ligand planes is

[0189] (2) The electrocatalytic performance of the Ni-Salen ligand, silver carbene compound and gold carbene compound prepared in Example 1 was characterized. The experimental results are as follows: Figure 7 shown.

[0190] In the figure, AC represents Ni-Salen ligand, silver carbene compound and gold carbene compound respectively. Figure 7 From the correlation curve of current density and potential in Figure (a), we can see that the faster the current decreases from A to C, the stronger the current response and the better the catalytic effect. Figure 7 From the equivalent circuit diagram in Figure (b), we can see that the impedance decreases from A to C, indicating that the conductivity increases. Figure 7 As shown in Figure (c), the measured overpotentials at a constant current decrease from A to C, indicating that the catalytic performance increases. In summary, the present invention produces a class of electrocatalytically active Salen ligands. By combining these ligands with carbenes, silver and gold carbene compounds are prepared, further enhancing the catalytic performance of the compounds.

[0191] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A Salen ligand, characterized in that The chemical structural formula is shown in Formula I: Formula I: ; In Formula I, M includes any one of Pd, Ni, Cu and Zn; R includes any one of methyl, ethyl and n-butyl; R' includes any one of a C1-C5 hydrocarbon group, a phenyl group, and a biphenyl group; X includes PF6 or Br; Y includes 、 、(1 S , 2 S ) or (1 R , 2 R ) 、 、 、 Any one of them.

2. The Salen ligand according to claim 1, characterized in that The chemical structural formula is shown in any one of Formula II to Formula IV: Formula II: ; In Formula II, M includes any one of Pd, Ni, Cu and Zn; Formula III: ; In formula III, M includes any one of Pd, Ni, Cu and Zn; Formula IV: ; In Formula IV, M includes any one of Pd, Ni, Cu and Zn.

3. The method for preparing the Salen ligand according to claim 1 or 2, characterized in that: The preparation method of the Salen ligand shown in Formula II comprises the following steps: (1) Salicylaldehyde and formaldehyde are mixed and subjected to chloromethylation reaction to prepare 5-chloromethyl-2-hydroxybenzaldehyde; (2) First, 5-chloromethyl-2-hydroxybenzaldehyde and N-methylimidazole were subjected to a CN coupling reaction, and then the reaction product was subjected to an ion exchange reaction with NH4PF6; (3) mixing the final product obtained in step (2) with ethylenediamine to carry out a Schiff base reaction to obtain a Schiff base; (4) Mixing a Schiff base and a metal salt to carry out a metal coordination reaction to obtain a catalytic converter; The metal salt includes any one of Pd salt, Ni salt, Cu salt and Zn salt.

4. The method for preparing the Salen ligand according to claim 3, wherein The preparation method of the Salen ligand shown in formula III comprises the following steps: (a) mixing 2,4-dihydroxybenzaldehyde, 1,3-dibromopropane and CsHCO3 to carry out a substitution reaction; (b) first subjecting the product obtained in step (a) to a CN coupling reaction with N-methylimidazole, and then subjecting the obtained product to an ion exchange reaction with NH4PF6 to obtain an imidazolium salt; (c) mixing the imidazolium salt obtained in step (b) with ethylenediamine to carry out a Schiff base reaction; (d) mixing the product obtained in step (c) with a metal salt to carry out a metal coordination reaction to obtain; The metal salt includes any one of Pd salt, Ni salt, Cu salt and Zn salt.

5. The method for preparing the Salen ligand according to claim 3, wherein The preparation method of the Salen ligand shown in Formula IV comprises the following steps: (A) 2,4-dihydroxybenzaldehyde, 1,5-dibromopentane and CsHCO3 are mixed to carry out a substitution reaction; (B) first subjecting the product obtained in step (A) to a CN coupling reaction with N-methylimidazole, and then subjecting the obtained product to an ion exchange reaction with NH4PF6 to obtain an imidazolium salt; (C) mixing the imidazolium salt obtained in step (B) with ethylenediamine to carry out a Schiff base reaction; (D) mixing the product obtained in step (C) with a metal salt to carry out a metal coordination reaction to obtain; The metal salt includes any one of Pd salt, Ni salt, Cu salt and Zn salt.

6. A method for preparing a silver carbene compound based on the Salen ligand according to claim 1 or 2, characterized in that: The following steps are involved: Salen ligand, silver oxide and potassium carbonate are mixed and ball-milled to prepare a silver carbene compound.

7. A Salen silver carbene compound, characterized in that It is prepared by the preparation method according to claim 6.

8. A method for preparing a gold carbene compound based on the silver carbene compound according to claim 7, characterized in that: The following steps are included; The silver carbene compound and Au(THT)Cl are mixed and reacted to prepare a gold carbene compound.

9. A Salen gold carbene compound, characterized in that It is prepared by the preparation method according to claim 8.

10. Use of the Salen ligand according to claim 1 or 2, the Salen silver carbene compound according to claim 7, or the Salen gold carbene compound according to claim 9 in the field of catalysis.

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