A cyano-modified tetrapyridine cobalt complex and its preparation method and application

Abstract

The invention discloses a cobalt complex with cyano-modified tetrapyridine as a ligand, a synthesis method and application thereof. The synthesis method of the cobalt complex with cyano-modified tetrapyridine as a ligand is to dissolve the ligand 4′,4″-dicyano tetrapyridine in a mixed solvent of methanol and dichloromethane, then add a cobalt salt, stir the obtained mixture at room temperature for 24 hours, filter and remove insoluble matter after the reaction, remove the organic solvent by rotary evaporation, and wash the obtained solid with water, ethanol and dichloromethane respectively to prepare the cobalt complex with 4′,4″-dicyano tetrapyridine as a ligand. The synthesis method of the invention has the advantages of simple process, high yield, mild reaction conditions, simple product purification treatment method, etc. The cobalt complex with 4′,4″-dicyano tetrapyridine as a ligand synthesized by the invention has good catalytic activity for the photocatalytic selective reduction of carbon dioxide to formic acid under normal temperature and pressure conditions, and the TON (turnover number) can reach 1048, and has good potential application prospects.

Description

Technical Field

[0001] The invention belongs to the field of metal complexes, and in particular relates to a cobalt complex using 4',4"-dicyano tetrapyridine as a ligand, a synthesis method and application thereof. Background Art

[0002] With the rapid growth of population and industrialization, global energy consumption is also increasing sharply; at the same time, the carbon dioxide content in the atmosphere has also risen from 280ppm before the industrial revolution to 416ppm in 2020 (Lin Huiwen, Zhang Huabin, Ye Jinhua et.al., Toward solar-driven carbon recycling [J]. Joule, 2022, 6, 1-21.). The greenhouse effect caused by excessive carbon dioxide emissions will lead to a series of environmental problems such as global warming, glacier melting and loss of biodiversity. Therefore, the conversion and utilization of carbon dioxide is imminent (Gong Eunhee, Ali Shahzad, In Su-Il*et.al., Solar fuels: research and development strategies to accelerate photocatalytic CO 2 conversion into hydrocarbon fuels[J]. Energy Environmental Science, 2022. DOI: 10.1039 / d1ee0271).

[0003] So far, the methods reported to convert carbon dioxide into hydrocarbons or high-value-added chemicals mainly include thermal catalysis, biocatalysis, electrocatalysis and photocatalytic reduction. Among them, the photocatalytic reduction process is the use of solar energy and photocatalysts to convert CO 2 and H 2 O is catalytically converted to produce high value-added chemicals (e.g. methanol, ethanol, hydrocarbons, etc.) Matej, PhotocatalyticCO 2 reduction: a review of Ab initio mechanism, kinetics, and multiscale modeling simulations [J]. ACS Catalysis, 10, 14984-15007.). Therefore, photocatalytic carbon dioxide reduction is also considered to be one of the most promising solutions to solve global energy and environmental problems.

[0004] In recent years, photocatalytic CO 2 There is an increasing number of studies on the reduction of CO; this is because compared with other catalytic methods, photocatalytic CO 2 The process is actually artificially simulating natural photosynthesis and has the following incomparable advantages: first, the external energy supply for the reaction is only solar energy, which is inexhaustible; second, the reaction is based on H 2 O and CO 2 The raw materials are easy to obtain; third, the reaction conditions are mild, generally at room temperature and pressure; fourth, there is no secondary pollution in the reaction (Albero Josep, Peng Yong, García Hermenegildo, et.al., Photocatalytic CO 2 reduction to C2+products[J].ACSCatalysis,2020,10,5734-5749.). Therefore, it is of great significance to study and develop catalysts that can directly use visible light to reduce carbon dioxide. 2 The catalysts for the reaction are still in their infancy. Existing catalysts still have a series of problems such as limited light absorption capacity, poor activation of carbon dioxide, complex synthesis process and low stability. In addition, the products of the photocatalytic carbon dioxide reduction reaction reported so far are relatively simple and mostly dominated by carbon monoxide. Therefore, it is very promising to design and synthesize photocatalysts that can reduce carbon dioxide to more complex basic chemical raw materials (such as formic acid). Summary of the invention

[0005] The object of the present invention is to provide a cobalt complex with 4',4"-dicyanoquaterpyridine as a ligand, a synthesis method thereof and an application thereof in photocatalytic carbon dioxide reduction.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A cobalt complex with cyano-modified tetrapyridine as a ligand, wherein the molecular formula of the complex is [Co II ( CN qpy)(H 2 O) 2 ] n [X] n ;in, CN tby represents 4′,4″-dicyano tetrapyridine ligand, X is ClO 4 - , Cl - , NO 3 - ,Br - or SO 42- One of the following, n=1 or 2.

[0008] Preferably, when X is ClO 4 - When n=2, the crystal of the complex belongs to the triclinic system, the space group is P-1, and the unit cell parameters are

[0009] The method for synthesizing a cobalt complex with cyano-modified tetrapyridine as a ligand specifically comprises the following steps: dissolving the ligand 4′,4″-dicyano tetrapyridine in a mixed solvent, then adding a cobalt salt, stirring the obtained mixture for reaction, filtering to remove insoluble matter after the reaction, then removing the organic solvent, washing the obtained solid with water, ethanol and dichloromethane in sequence, and drying the obtained solid to prepare the cobalt complex with 4′,4″-dicyano tetrapyridine as a ligand.

[0010] Preferably, the molar ratio of the ligand 4′,4″-dicyanotetrapyridine to the cobalt salt is 1:2.

[0011] Preferably, the mixed solvent consists of methanol and dichloromethane.

[0012] Preferably, the cobalt salt is selected from one of cobalt perchlorate, cobalt chloride, cobalt bromide, cobalt nitrate or cobalt sulfate.

[0013] Preferably, the stirring reaction conditions are: the reaction temperature is room temperature, and the reaction time is 24 hours.

[0014] The cobalt complex using 4',4"-dicyano tetrapyridine as a ligand is used in photocatalytic carbon dioxide reduction.

[0015] Compared with the existing methods, the principles of the present invention are as follows:

[0016] The present invention uses 4′,4″-dicyano tetrapyridine as a ligand to prepare a cobalt complex; the tetrapyridine ligand and its derivatives used are an important class of multifunctional ligands, which have strong coordination ability and can form a wide variety of metal complexes with transition metals such as iron, cobalt, nickel, copper, ruthenium, etc. The metal complexes formed by tetrapyridine and its derivatives can be widely used in catalytic materials, luminescent materials, anti-tumor and other fields, such as tetrapyridine cobalt complexes can be used for photocatalytic water oxidation and hydrogen production. However, the products of the tetrapyridine cobalt complexes reported in the literature in the photocatalytic reduction of carbon dioxide are mostly carbon monoxide. The cobalt complex with 4′,4″-dicyano tetrapyridine as a ligand provided by the present invention can photocatalytically selectively reduce carbon dioxide to formic acid under normal temperature and pressure conditions, wherein the central metal of the cobalt complex is a high active site under photocatalytic reaction conditions, which can promote CO 2Activate and regulate the binding of HCOO* intermediates to improve the efficiency of formic acid production.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1) The synthesis method of the cobalt complex with 4′,4″-dicyanoquaterpyridine as a ligand provided by the present invention is simple and efficient, requiring only a one-step reaction, and the purification method is also simple, requiring only washing the product with ethanol to obtain a high-purity final product, and the yield of the cobalt complex can reach 52% (calculated based on the content of 4′,4″-dicyanoquaterpyridine).

[0019] 2) The method for synthesizing the cobalt complex with 4′,4″-dicyanoquaterpyridine as a ligand provided by the present invention also has the advantages of mild reaction conditions, no need for high temperature and high pressure, no need for special equipment, and is suitable for large-scale industrial production.

[0020] 3) The cobalt complex with 4′,4″-dicyano-tetrapyridine as ligand provided by the present invention has good catalytic activity for photocatalytic carbon dioxide reduction under normal temperature and pressure in air atmosphere, and the TON (turnover number) can reach 1048, which can realize the recycling of carbon dioxide and the rational utilization of energy, and provides an ideal artificial photosynthesis simulation system for reference, and has good potential application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 For [Co II ( CN tby)(H 2 O) 2 ][ClO 4 ] 2 The structural formula of .

[0022] Figure 2 It is the structural formula of 4′,4″-dicyano tetrapyridine ligand.

[0023] Figure 3 For [Co II ( CN qpy)(H 2 O) 2 ][ClO 4 ] 2 Crystal structure diagram. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below with reference to the accompanying drawings and examples. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. The specific mass, reaction time, temperature, process parameters, etc. in the examples are only examples within the appropriate range. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention.

[0025] The specific synthesis steps of the ligand 4′,4″-dicyanoquaterpyridine used in the examples of the present invention are as follows:

[0026] 6'-bromo-4-cyano-2,2"-bipyridine (1.2mmol, 312mg), hexamethyltin (0.6mmol, 197mg) and catalyst tetraphenylphosphine palladium (0.06mmol, 69mg) were added to 3mL DMF, heated and stirred under the condition of blowing argon gas, and the temperature was maintained at 120℃ for 72h. After the temperature was cooled to room temperature, it was filtered, washed with water and isopropanol, dissolved in chloroform and passed through a diatomaceous earth column, and the organic solvent was removed by rotary evaporation to prepare 4',4"-dicyano-tetrapyridine 150mg with a yield of 82%. Its chemical structure is as follows: Figure 2 As shown. The ligand 4′,4″-dicyano tetrapyridine was characterized by NMR, and the results are as follows: 1 H NMR (400 MHz, CDCl 3 , ppm): δ, ppm: 8.84 (4H, d); 8.75 (2H, d); 8.63 (2H, d); 7.99-7.95 (2H, m); 7.47-7.44 (2H, m).

[0027] Embodiment 1:

[0028] The specific synthesis steps of the cobalt complex with 4',4"-dicyano-tetrapyridine as a ligand of the present invention are as follows:

[0029] Under nitrogen atmosphere, the ligand 4′,4″-dicyano tetrapyridine (0.1 mmol, 36.0 mg) was dissolved in 15 mL methanol / dichloromethane (v / v, 1:2), cobalt perchlorate (0.2 mmol, 73 mg) was added, and the resulting mixture was stirred at room temperature for 24 h, the insoluble matter was filtered out, and the solvent was removed by rotary evaporation. The solid was washed with water, ethanol, and dichloromethane, respectively, and dried to obtain the complex [Co II ( CN qpy)(H 2 O) 2 ][ClO 4 ] 2, yield 34 mg, yield 52% (calculated based on the content of 4′,4″-dicyano tetrapyridine ligand), its structural formula is as follows Figure 1 As shown. II ( CN qpy)(H 2 O) 2 ][ClO 4 ] 2 Elemental analysis characterization results are as follows: experimental values: C, 40.56; H, 2.48; N, 13.41, theoretical values ​​C, 40.39, H, 2.47, N, 12.85. The theoretical values ​​of elemental analysis are consistent with the experimental values, indicating that the synthesized complex has high purity and the synthesis and purification methods used are feasible.

[0030] [Co II ( CN qpy)(H 2 O) 2 ][ClO 4 ] 2 The steps for preparing the crystals are as follows: slowly diffuse ether into [Co II ( CN qpy)(H 2 O) 2 ][ClO 4 ] 2 In acetonitrile solution, [Co II ( CN qpy)(H 2 O) 2 ][ClO 4 ] 2 of single crystal.

[0031] The crystals obtained above were characterized:

[0032] Table 1

[0033]

[0034] Structural characterization:

[0035] A single crystal with regular shape and appropriate size was selected and placed in a Rigaku OxfordDiffraction Supernova Dual Source single crystal diffractometer at 199.99(10)K using graphite monochromatized Cu-Kα radiation. As the incident light source, within a certain range of θ Diffraction points were collected in a scanning mode for structure analysis and correction. Non-hydrogen atoms were solved by direct method, and their coordinates and anisotropic thermal parameters were corrected by full matrix least squares method. For mixed hydrogenation, isotropic thermal parameters were used for hydrogen atoms and anisotropic thermal parameters were used for non-hydrogen atoms. The crystal structure analysis and structure correction were completed by SHELXT (Sheldrick, 2015) and SHELXL-2015 (Sheldrick, 2015) program packages, respectively. Detailed crystallographic and structural correction data are shown in Table 1. The structure is shown in Figure 3 shown.

[0036] From the above single crystal structure analysis, it can be seen that [Co II ( CN qpy)(H 2 O) 2 ][ClO 4 ] 2 The crystal belongs to the triclinic system, the space group is P-1, and the unit cell parameters are

[0037] Embodiment 2:

[0038] Cobalt complexes [Co II ( CN qpy)(H 2 O) 2 ][ClO 4 ] 2 The experimental steps of photocatalytic carbon dioxide reduction are as follows: [Co II ( CN qpy)(H 2 O) 2 ][ClO 4 ] 2 (0.01mM), tri(2,6-bipyridine)ruthenium dichloride (0.2mM), 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole (0.025M) and carbon dioxide (10ml, 1atm) were added to 2mL of 15% triethylamine N-methylpyrrolidone solution, the resulting mixture was stirred evenly and irradiated under natural light for 4 hours, and then the final reactant was taken for ion chromatography analysis, the results showed that the final product was formic acid, and the TON (turnover number) could reach 1048.

Claims

1. A cobalt complex with cyano-modified tetrapyridine as a ligand, characterized in that: The molecular formula of the complex is [Co II ( CN qpy)(H2O)2] n [X] n ; in, CN qpy represents 4′,4′′-dicyano tetrapyridine ligand, X is ClO4 - , n=2; the crystal of the complex belongs to the triclinic system, the space group is P-1, the unit cell parameters are a =10.6546Å, b =10.9991Å, c =11.2898Å, V =1307.78 Å3.

2. The method for synthesizing a cobalt complex with cyano-modified tetrapyridine as a ligand according to claim 1, characterized in that: The method comprises the following steps: dissolving the ligand 4′,4′′-dicyano tetrapyridine in a mixed solvent, then adding a cobalt salt, stirring the obtained mixture for reaction, filtering to remove insoluble matter after the reaction, then removing the organic solvent, washing the obtained solid with water, ethanol and dichloromethane in sequence, and drying the obtained solid to prepare the cobalt complex with 4′,4′′-dicyano tetrapyridine as a ligand; wherein, The mixed solvent consists of methanol and dichloromethane; and the cobalt salt is selected from cobalt perchlorate.

3. The method for synthesizing a cobalt complex with cyano-modified tetrapyridine as a ligand according to claim 2, characterized in that: The molar ratio of the ligand 4′,4″-dicyano-tetrapyridine to the cobalt salt is 1:

2.

4. The method for synthesizing a cobalt complex with cyano-modified tetrapyridine as a ligand according to claim 2, characterized in that: The stirring reaction conditions are: the reaction temperature is room temperature, and the reaction time is 24 hours.

5. Use of the cobalt complex with 4′,4′′-dicyanoquaterpyridine as a ligand according to claim 1 or the cobalt complex prepared by the preparation method according to claims 2-4 in photocatalytic carbon dioxide reduction, the experimental steps are as follows: [Co II ( CN qpy)(H2O)2] [ClO4]2 0.01 mM, tri(2,6-bipyridine)ruthenium dichloride 0.2 mM, 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole 0.025 M and carbon dioxide 10 ml, 1atm were added to 2 mL of 15% triethylamine N-methylpyrrolidone solution. The resulting mixture was stirred evenly and irradiated under natural light for 4 hours. The final product was formic acid.

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