A mononuclear cobalt complex based on Salen ligand, preparation method and application thereof

Abstract

The present invention relates to a metal coordination compound, in particular to a mononuclear cobalt complex based on a Salen ligand, a preparation method and an application thereof. The cobalt complex is an N,N-2-bis(2-hydroxy-5-methylphenyl)-4-fluoro-1,2-phenylenediamine cobalt complex, and its molecular formula is C 22 H 17 CoFN2O2 is prepared by dissolving 4-fluoro-1,2-phenylenediamine, 2-hydroxy-4-methylbenzene-1-formaldehyde, and a cobalt salt in a mixed solvent, adjusting the pH of the system to alkaline, reacting under heating conditions of 50°C or higher, cooling the reactants, and collecting the crystals to obtain the target product; wherein the mixed solvent is a composition consisting of DMF, methanol, and acetonitrile in a volume ratio of 1:2:1. The mononuclear cobalt complex of the present invention can be used as a catalyst in photocatalytic carbon dioxide reduction and exhibits high activity and high selectivity in photocatalytic carbon dioxide reduction.

Description

Technical Field

[0001] The present invention relates to a metal coordination compound, in particular to a mononuclear cobalt complex based on a Salen ligand, and a preparation method and application thereof. Background Art

[0002] Photocatalytic carbon dioxide reduction refers to the reduction of carbon dioxide into high-value-added carbon-containing compounds under the drive of light energy, while achieving environmental protection and resource recycling. However, the dissociation energy of the C=O bond in the linear carbon dioxide molecule is as high as 750kJ / mol, and its stability is very high, making it difficult to be activated at room temperature. In order to promote the activation and conversion of carbon dioxide, an effective catalyst must be introduced to promote the reduction of carbon dioxide. Metal complex catalysts have clear catalytic active sites and can be controlled by ligands and metal centers, making them a hot topic of current research. For example, the invention patent with publication number CN113797970A discloses a co-catalyst metal iron complex with photocatalytic carbon dioxide reduction activity, the specific structure of which is as follows:

[0003]

[0004] This complex uses polypyridine as an organic ligand and metallic iron (Fe) ions as a catalytic center. It is often used as a catalyst in photocatalytic carbon dioxide reduction research. However, the oxygen conversion number of this catalyst based on catalyst calculation is only 1176.

[0005] Based on considerations such as the catalytic activity and product selectivity of the catalyst, the applicant hopes to develop a cobalt complex that can be used as a catalyst in photocatalytic carbon dioxide reduction and exhibits high activity and selectivity in this process, so that the developed catalytic system can be well expanded into practical applications. Currently, there are no related studies or reports on the use of N,N-2-bis(2-hydroxy-5-methylphenyl)-4-fluoro-1,2-phenylenediamine cobalt complexes as catalysts in photocatalytic carbon dioxide reduction. Summary of the Invention

[0006] The object of the present invention is to address the above-mentioned problems and provide a mononuclear cobalt complex based on a Salen ligand, a preparation method and an application thereof. The complex can be used as a catalyst in photocatalytic carbon dioxide reduction and exhibits high activity and high selectivity in photocatalytic carbon dioxide reduction.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a mononuclear cobalt complex based on Salen ligand, wherein the cobalt complex is N,N-2-bis(2-hydroxy-5-methylphenyl)-4-fluoro-1,2-phenylenediamine cobalt complex, and its molecular formula is C 22 H 17CoFN2O2, the structural formula is shown below:

[0008]

[0009] The complex belongs to the monoclinic crystal system, P21 / c space group, and its unit cell parameters are: α=90°, β=95.566(4)°, γ=90°; The cobalt ion of the complex is coordinated with two nitrogen atoms and two oxygen atoms of N,N-2-bis(2-hydroxy-5-methylphenyl)-4-fluoro-1,2-phenylenediamine to form a N2O2 planar tetracoordinated mononuclear structure.

[0010] The present invention also provides a method for preparing the above-mentioned mononuclear cobalt complex, which specifically comprises: dissolving 4-fluoro-1,2-phenylenediamine, 2-hydroxy-4-methylbenzene-1-carboxaldehyde and a cobalt salt in a molar ratio of 1:2:1 in a mixed solvent, adjusting the pH value of the system to alkaline, and then heating the reaction at a temperature of ≥50°C. After the reaction is completed, the reactants are cooled to precipitate crystals, and the crystals are collected to obtain the target product; wherein the cobalt salt is CoCl2·6H2O and / or Co(NO3)2·6H2O; and the mixed solvent is a composition composed of DMF, methanol and acetonitrile in a volume ratio of 1:2:1.

[0011] In the above preparation method, the pH of the system is adjusted to 8.5-10.

[0012] In the above preparation method, the pH value of the system is adjusted to alkaline by adding alkaline substances.

[0013] Preferably, the alkaline substance is triethylamine.

[0014] In the above preparation method, the reaction is carried out at 80-90° C. and the reaction time is 24-36 hours.

[0015] The mononuclear cobalt complex of the present invention can be used as a catalyst in a photocatalytic carbon dioxide reduction reaction.

[0016] In summary, due to the adoption of the above-mentioned technical scheme, the present invention has the following beneficial effects: traditional homogeneous catalysts generally use precious metal complexes with higher costs, which are not conducive to large-scale production and application. The applicant has conducted research on cobalt-based metal complex catalysts based on the earth's abundant reserves of cobalt-based metals. The present invention synthesizes a cobalt complex with a novel structure in situ, and provides a mononuclear cobalt complex based on Salen ligand, its preparation method and application. The test results show that when the mononuclear cobalt complex is used as a catalyst at a concentration of 0.1 μM, it catalyzes the reduction of carbon dioxide to produce 1.69 μmol of carbon monoxide, the catalytic turnover number TON value is as high as 3380, and the selectivity for carbon monoxide is as high as 86%. This shows that in an aqueous system and under visible light conditions, the complex provided by the present invention exhibits excellent performance of high activity and high selectivity in carbon dioxide reduction, and the catalytic effect is significantly higher than most reported catalytic systems, and has a significant catalytic effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the infrared spectrum of the final product obtained by the present invention.

[0018] Figure 2 It is a crystal structure diagram of the final product obtained by the present invention. DETAILED DESCRIPTION

[0019] In order to help those skilled in the art better understand the present invention, the following clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0020] The present application provides a mononuclear cobalt complex based on Salen ligand, wherein the cobalt complex is N,N-2-bis(2-hydroxy-5-methylphenyl)-4-fluoro-1,2-phenylenediamine cobalt complex, and its molecular formula is C 22 H 17 CoFN2O2, the structural formula is shown below:

[0021]

[0022] The complex belongs to the monoclinic crystal system, P21 / c space group, and its unit cell parameters are: α=90°, β=95.566(4)°, γ=90°; The cobalt ion of the complex is coordinated with two nitrogen atoms and two oxygen atoms of N,N-2-bis(2-hydroxy-5-methylphenyl)-4-fluoro-1,2-phenylenediamine to form a N2O2 planar tetracoordinated mononuclear structure.

[0023] Example 1: This example prepares a mononuclear cobalt complex based on Salen ligand, comprising the following steps:

[0024] 4-Fluoro-1,2-phenylenediamine (0.0209 g, 0.05 mmol), 2-hydroxy-4-methylbenzene-1-carboxaldehyde (10 μL, 0.1 mmol) and Co(NO3)2·6H2O (0.0118 g, 0.05 mmol) were placed in a semi-closed glass tube with a length of 20 cm, and then 2 mL of a mixed solvent consisting of DMF, methanol and acetonitrile (the volume ratio of DMF, methanol and acetonitrile was 1:2:1) was added. Ultrasonic dissolution was performed, and the pH value of the system was adjusted to 9.5 with triethylamine. After that, the glass tube was sealed at high temperature in a vacuum, and the sealed glass tube was placed in an oven at 80°C for 24 h. After stopping the reaction, the temperature was slowly cooled to room temperature. Black-gold needle-shaped crystals were observed to precipitate at the bottom of the glass tube. The crystals were collected and dried to obtain the product.

[0025] The product obtained in this example was characterized:

[0026] (1) The structure was characterized by infrared spectroscopy, and the results are as follows: Figure 1 shown.

[0027] IR(KBr,cm -1 ): 3436w, 2914w, 1622m, 1577s, 1523vs, 1464m, 1356m, 1322w, 1272w, 1223w, 1179w, 981w, 818s, 503m.

[0028] (2) Analyze the crystal structure using single crystal diffraction.

[0029] A black needle-shaped crystal of appropriate size was selected and placed on a Bruker SMART CCD diffractometer. The initial crystal structures of the products obtained in this example were solved by the SHELXS-97 direct method, and the geometric hydrogenation, non-hydrogen atomic coordinates and anisotropic thermal parameters were refined by the full matrix least squares method using SHELXL-97. The obtained crystallographic and structural refinement data are shown in Table 1, and some bond length and bond angle data are shown in Table 2 and Table 3 respectively. The chemical structure of the obtained black needle-shaped crystals is shown in Figure 2 As shown, the obtained black needle-shaped crystals were determined to be the target product of the present invention.

[0030] Example 2: This example prepares a mononuclear cobalt complex based on Salen ligand, comprising the following steps:

[0031] 4-Fluoro-1,2-phenylenediamine (0.0418 g, 0.1 mmol), 2-hydroxy-4-methylbenzene-1-carboxaldehyde (20 μL, 0.2 mmol) and Co(NO3)2·6H2O (0.0236 g, 0.1 mmol) were placed in a semi-closed 20 cm long glass tube, and then 4 mL of a mixed solvent consisting of DMF, methanol and acetonitrile (the volume ratio of DMF, methanol and acetonitrile was 1:2:1) was added. Ultrasonic dissolution was performed, and the pH value of the system was adjusted to 8.5 with triethylamine. After that, the glass tube was vacuum-sealed at high temperature and placed in an oven at 50°C for 36 h. After stopping the reaction, the temperature was slowly lowered to room temperature. Black-gold needle-shaped crystals were observed to precipitate at the bottom of the glass tube. The crystals were collected and dried to obtain the product.

[0032] The product obtained in this example was characterized:

[0033] (1) The structure was characterized by infrared spectroscopy, and the results are as follows: Figure 1 shown.

[0034] IR(KBr,cm -1 ): 3436w, 2914w, 1622m, 1577s, 1523vs, 1464m, 1356m, 1322w, 1272w, 1223w, 1179w, 981w, 818s, 503m.

[0035] (2) Analyze the crystal structure using single crystal diffraction.

[0036] A black needle-shaped crystal of appropriate size was selected and placed on a Bruker SMART CCD diffractometer using graphite monochromatized Mo-K α The initial crystal structures of the products obtained in this example were solved by the SHELXS-97 direct method, and the geometric hydrogenation, non-hydrogen atomic coordinates and anisotropic thermal parameters were refined by the full matrix least squares method using SHELXL-97. The obtained crystallographic and structural refinement data are shown in Table 1, and some bond length and bond angle data are shown in Table 2 and Table 3 respectively. The chemical structure of the obtained black needle-shaped crystals is shown in Figure 2 As shown, the obtained black needle-shaped crystals were determined to be the target product of the present invention.

[0037] Example 3: This example prepares a mononuclear cobalt complex based on Salen ligand, comprising the following steps:

[0038] 4-Fluoro-1,2-phenylenediamine (0.0618 g, 0.15 mmol), 2-hydroxy-4-methylbenzene-1-carboxaldehyde (30 μL, 0.3 mmol) and CoCl2·6H2O (0.0354 g, 0.15 mmol) were placed in a semi-closed 20 cm long glass tube, and then 6 mL of a mixed solvent consisting of DMF, methanol and acetonitrile (the volume ratio of DMF, methanol and acetonitrile was 1:2:1) was added. Ultrasonic dissolution was performed, and the pH value of the system was adjusted to 10 with triethylamine. After that, the glass tube was vacuum-sealed at high temperature and placed in a 90°C oven for 48 h. After stopping the reaction, the temperature was slowly cooled to room temperature. Black-gold needle-shaped crystals were observed to precipitate at the bottom of the glass tube. The crystals were collected and dried to obtain the product.

[0039] The product obtained in this example was characterized:

[0040] (1) The structure was characterized by infrared spectroscopy, and the results are as follows: Figure 1 shown.

[0041] IR(KBr,cm -1 ): 3436w, 2914w, 1622m, 1577s, 1523vs, 1464m, 1356m, 1322w, 1272w, 1223w, 1179w, 981w, 818s, 503m.

[0042] (2) Analyze the crystal structure using single crystal diffraction.

[0043] A black needle-shaped crystal of appropriate size was selected and placed on a Bruker SMART CCD diffractometer using graphite monochromatized Mo-K α The initial crystal structures of the products obtained in this example were solved by the SHELXS-97 direct method, and the geometric hydrogenation, non-hydrogen atomic coordinates and anisotropic thermal parameters were refined by the full matrix least squares method using SHELXL-97. The obtained crystallographic and structural refinement data are shown in Table 1, and some bond length and bond angle data are shown in Table 2 and Table 3 respectively. The chemical structure of the obtained black needle-shaped crystals is shown in Figure 2 As shown, the obtained black needle-shaped crystals were determined to be the target product of the present invention.

[0044] Table 1 Crystallographic data of cobalt complexes of the present invention

[0045]

[0046] Table 2 Bond length data of some cobalt complexes of the present invention

[0047]

[0048] Table 3 Partial bond angle data of cobalt complexes of the present invention (°)

[0049]

[0050] Through the above characterization, it can be determined that the obtained black-gold needle-shaped crystals are the complex described in the present invention, namely, N,N-2-bis(2-hydroxy-5-methylphenyl)-4-fluoro-1,2-phenylenediamine cobalt complex.

[0051] It is worth noting that in the above preparation method, the molar ratio of 4-fluoro-1,2-phenylenediamine, 2-hydroxy-4-methylbenzene-1-carboxaldehyde, and cobalt salt is a stoichiometric ratio. In actual operation, the amounts of 4-fluoro-1,2-phenylenediamine and cobalt salt can be relatively excessive. The amount of solvent used can be determined as needed, generally to the extent that it can dissolve the raw materials involved in the reaction. Specifically, based on 1 mmol of 4-fluoro-1,2-phenylenediamine, the total amount of mixed solvent used for all raw materials is generally 2-10 mL.

[0052] In addition, in the above preparation method, an alkaline substance is used to adjust the pH value of the system to alkaline. The alkaline substance can be a conventional choice in the prior art, preferably triethylamine, and further preferably the pH of the system is adjusted to ≥8.5, and more preferably the pH of the system is adjusted to 8.5-10. Usually, the mixed solution obtained after adjusting the pH value is placed in a container, evacuated, sealed, and then placed under heating conditions for reaction. The reaction is preferably carried out at ≥50°C, and more preferably at 80-90°C. When the reaction is carried out at 80-90°C, the reaction time is generally controlled to be 24-36h. The reaction usually uses a thick-walled hard glass tube with one end closed to contain the mixed solution obtained after adjusting the pH value.

[0053] The present invention also includes the use of the cobalt complex in the preparation of a catalyst, specifically as a catalyst in photocatalytic carbon dioxide reduction. In a specific application, the photocatalytic system includes a photosensitizer, a catalyst, a sacrificial agent, and a solvent, wherein the catalyst is the cobalt complex of the present invention, and the selection of the photosensitizer, sacrificial agent, and solvent is the same as in the prior art. Specifically, the photosensitizer is preferably [Ru(phen)3](PF6)2, [Ru(phen)3]Cl2, or [Ru(bpy)3]Cl2, more preferably [Ru(phen)3](PF6)2; the sacrificial agent is preferably triethanolamine (TEOA) and / or triethylamine (TEA), and the solvent is preferably a mixed solution comprising water and acetonitrile (wherein the volume ratio of water to acetonitrile is 1:4). In the photocatalytic system, the concentration of the photosensitizer is preferably 400-500 μmol / L, the concentration of the catalyst is preferably 0.05-1 μmol / L, and the concentration of the sacrificial agent is preferably 0.30-0.35 mol / L.

[0054] Example 4: Determination of the catalytic activity and selectivity of the complex.

[0055] (1) Materials used

[0056] Photosensitizer: [Ru(phen)3](PF6)2, catalyst: cobalt complex prepared according to the steps described in Example 1 of the present invention (hereinafter referred to as complex 1), sacrificial agent: TEOA, LED light source (wavelength 450nm, light intensity 100mW·cm -2 , the irradiation area is 0.8cm 2 ), a 15-20 mL quartz reactor, carbon dioxide gas, rubber tubing, analytical balance, stirrer and gas chromatograph.

[0057] (2) Specific experimental steps:

[0058] 2 mg of the photosensitizer [Ru(phen)3](PF6)2 was weighed in sequence, 200 μL of the sacrificial agent TEOA and 0.1 μM of the complex 1 were transferred to a quartz glass tube, 4 mL of ultra-dry acetonitrile and 1 ml of water were added, and the tube was sealed tightly with a rubber tube. Carbon dioxide gas was then introduced. After 10 to 20 minutes, the tube was irradiated with the LED light source for 10 hours at a constant temperature of 25°C while stirring. After completing the above operations, a gas sample was taken and injected into a gas chromatograph for detection of carbon monoxide, a product of carbon dioxide reduction. The test results are shown in Table 4 below.

[0059] Comparative Example 1:

[0060] 2 mg of the photosensitizer [Ru(phen)3](PF6)2 was weighed and 200 μL of the sacrificial agent TEOA was pipetted into a quartz glass tube. 4 mL of ultra-dry acetonitrile and 1 mL of water were added, and the tube was tightly sealed with a rubber tube. Carbon dioxide gas was introduced. After 10 to 20 minutes, the tube was irradiated with the LED light source for 10 hours at a constant temperature of 25°C while stirring. After the above operation, a gas sample was taken and injected into a gas chromatograph for detection of carbon monoxide, a product of carbon dioxide reduction. The test results are shown in Table 4 below. (This comparative example differs from Example 4 in that complex 1 was not added in the specific experimental steps.)

[0061] Comparative Example 2:

[0062] 2 mg of the photosensitizer [Ru(phen)3](PF6)2 was weighed, 200 μL of the sacrificial agent TEOA and 0.1 μM Co(NO3)2·6H2O were pipetted into a quartz glass tube, 4 mL of ultra-dry acetonitrile and 1 mL of water were added, and the tube was sealed tightly with a rubber tube. Carbon dioxide gas was introduced. After 10 to 20 minutes, the tube was irradiated with the LED light source for 10 hours at a constant temperature of 25°C, while stirring. After the above operations were completed, a gas sample was taken and injected into a gas chromatograph for detection of carbon monoxide, a product of carbon dioxide reduction. The test results are shown in Table 4 below. (This comparative example differs from Example 4 in that Co(NO3)2·6H2O was used instead of complex 1 in the specific experimental steps.)

[0063] Table 4 Experimental data of photocatalytic carbon dioxide reduction using the cobalt complex of the present invention as a catalyst

[0064]

[0065] As shown in Table 4, in the photocatalytic system constructed according to the present invention, when complex 1 was used as a catalyst at a concentration of 0.1 μM, the catalytic reduction of carbon dioxide produced 1.69 μmol of carbon monoxide, with a catalytic turnover number (TON) of 3380 and a selectivity for carbon monoxide of 86%. However, when complex 1 was absent from the system (Comparative Examples 1 and 2), no carbon monoxide was produced in the reaction system, indicating that the carbon monoxide produced in this reaction was indeed derived from the photocatalytic reduction of carbon dioxide by complex 1. This indicates that the complex described in the present invention, as a homogeneous catalyst, exhibits good photocatalytic carbon dioxide reduction performance in aqueous systems.

[0066] The above description is a detailed description of the preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A mononuclear cobalt complex based on a Salen ligand, characterized in that: The molecular formula of the cobalt complex is C 22 H 17 CoFN2O2, the structural formula is shown below:

2. The method for preparing a mononuclear cobalt complex based on a Salen ligand according to claim 1, characterized in that: 4-Fluoro-1,2-phenylenediamine, 2-hydroxy-5-methylbenzene-1-carboxaldehyde and a cobalt salt are dissolved in a mixed solvent in a molar ratio of 1:2:1, the pH value of the system is adjusted to alkaline, and then the reaction is heated at ≥50°C. After the reaction is completed, the reactants are cooled, crystals are precipitated, and the crystals are collected to obtain the target product; wherein the cobalt salt is CoCl2·6H2O and / or Co(NO3)2·6H2O; and the mixed solvent is a composition composed of DMF, methanol and acetonitrile in a volume ratio of 1:2:

1.

3. The preparation method according to claim 2, wherein: Adjust the pH of the system to 8.5-10.

4. The preparation method according to claim 2, wherein: The pH value of the system is adjusted to alkaline by adding alkaline substances.

5. The preparation method according to claim 4, characterized in that: The alkaline substance is triethylamine.

6. The preparation method according to claim 2, wherein: The reaction is carried out at 80-90°C and the reaction time is 24-36 hours.

7. Use of the mononuclear cobalt complex based on Salen ligand according to claim 1 as a catalyst in photocatalytic carbon dioxide reduction.

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