A binuclear rare earth complex, a preparation method and application thereof

Abstract

The application relates to the technical field of multifunctional new materials, in particular to a binuclear rare earth complex, a preparation method and application, the binuclear rare earth complex has a chemical molecular formula of RE2L2{[RE2L2(CH3OH)2Cl2]·2CH3OH}, RE is a chlorinated salt of a rare earth element; L is a ligand, and a structural formula is: by preparing a ligand containing multiple coordination sites, introducing a pyridine N atom to increase chelation capacity, making the final complex molecule centrosymmetric, playing an important role in catalytic reactions, and improving the activity, selectivity and stability of a catalyst. In the catalytic process, high CO2 pressure and high reaction temperature are not needed, the reaction condition is mild, the disadvantages caused by harsh reaction conditions are avoided, and the problems of harsh reaction conditions, low efficiency and high cost of a catalyst for catalyzing the cycloaddition reaction of CO2 and an epoxide in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of multifunctional new materials, in particular to a binuclear rare earth complex, a preparation method and applications. Background Art

[0002] In recent years, global warming has caused increasingly severe environmental disasters, including climate anomalies, glacial melting, and sea level rise. Recent research indicates that human activities have pushed atmospheric carbon dioxide levels to their highest level in 23 million years, exceeding nature's capacity for absorption and conversion. Carbon capture, storage, and utilization are key strategies for achieving carbon neutrality. However, their thermodynamic stability significantly limits their applications. The cycloaddition reaction of CO2 and epoxides is a 100% atom-economic reaction, and the resulting products, cyclocarbonates, are used as green solvents, fuel additives, fine chemical raw materials, urethane synthesis, monomers for polycarbonate production, and pharmaceutical and chemical intermediate components.

[0003] The catalysts currently widely used in industrial production still require high CO2 pressure and high reaction temperature. From the perspective of utilizing carbon resources and preventing global warming, it is very necessary to create catalysts that can also play a catalytic role at milder reaction temperatures and pressures. In the past few decades, many homogeneous and heterogeneous catalyst systems have been produced, including metal oxides, alkali metal halides, quaternary ammonium salts or phosphonium salts, imidazolium salts or ionic liquids and metal complexes. However, these catalytic systems still have some defects, such as low catalytic activity, the use of pure carbon dioxide and harsh reaction conditions (high temperature or high pressure). Future research and development should focus on finding more efficient, low-cost and sustainable catalyst systems to promote the conversion and utilization of CO2. This will help reduce dependence on limited fossil fuels, reduce greenhouse gas emissions, promote the sustainable utilization of carbon resources, and contribute to the realization of clean energy and sustainable development goals. Summary of the Invention

[0004] In view of the problems in the prior art of harsh conditions, low efficiency and high cost in the cycloaddition reaction of CO2 and epoxide catalyzed by catalysts, the present invention provides a binuclear rare earth complex, a preparation method and an application.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A binuclear rare earth complex, whose chemical formula is: RE2L2{[RE2L2(CH3OH)2Cl2]·2CH3OH}, and the general molecular structure formula is:

[0007] ,

[0008] Wherein, RE in the chemical formula and molecular structure formula is a chloride salt of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium or lutetium; L in the chemical formula is a ligand used to synthesize the binuclear rare earth complex, and the ligand structure formula is:

[0009] A method for preparing a binuclear rare earth complex comprises:

[0010] Prepare ligand L; the structural formula of the ligand L is:

[0011] A binuclear rare earth complex is prepared using ligand L and rare earth metal chloride; the chemical formula of the binuclear rare earth complex is: RE2L2{[RE2L2(CH3OH)2Cl2]·2CH3OH}, and the general molecular structure formula is:

[0012]

[0013] , wherein RE in the chemical formula and molecular structure formula is a chloride salt of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium or lutetium.

[0014] Preferably, the rare earth metal chloride is a hexahydrate chloride salt of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium or lutetium.

[0015] Furthermore, the method for preparing ligand L is:

[0016] 6-aminopyridine-2-carboxylic acid methyl ester is reacted with water and hydrazine in a methanol solvent by heating, stirring and refluxing to obtain 6-aminopyridine hydrazide;

[0017] 6-aminopyridine hydrazide and o-vanillin were heated, stirred and refluxed in methanol solvent to fully react to obtain ligand L.

[0018] Furthermore, in the process of heating, stirring and refluxing 6-aminopyridine-2-carboxylic acid methyl ester with water and hydrazine in a methanol solvent to fully react to obtain 6-aminopyridine hydrazide, the temperature of heating, stirring and refluxing is 50° C. to 70° C., the reaction time is 1 to 3 hours, and the molar ratio of 6-aminopyridine-2-carboxylic acid methyl ester to water and hydrazine is 1:(1 to 1.2).

[0019] Furthermore, in the process of heating, stirring and refluxing 6-aminopicolinohydrazide and o-vanillin in a methanol solvent to fully react to obtain ligand L, the heating, stirring and reflux temperature is 50°C to 70°C, the reaction time is 5 to 12 hours, and the molar ratio of 6-aminopicolinohydrazide to o-vanillin is 1:(0.95 to 1.05).

[0020] Furthermore, the method for preparing a binuclear rare earth complex using ligand L and rare earth metal chloride is as follows:

[0021] A reaction solvent, triethylamine and rare earth metal chloride are added to the ligand L to react to obtain a binuclear rare earth complex.

[0022] Preferably, the reaction solvent is one or more of methanol, ethanol and acetonitrile.

[0023] Furthermore, the molar ratio of the ligand L to the rare earth metal chloride is 1:(1-4), the reaction temperature for obtaining the binuclear rare earth complex is 25° C.-40° C., and the reaction time is 12-72 h.

[0024] The present invention provides an application of the above binuclear rare earth complex in catalyzing the synthesis of cyclic carbonates from carbon dioxide.

[0025] The ligand used to synthesize the binuclear rare earth complex has the following structural formula: This complex has a simple structure, and the ligand used contains multiple coordination sites. The pyridinium nitrogen atom introduced into the molecule enhances chelating ability. It can react with a variety of rare earth metal chlorides at room temperature to form a binuclear rare earth complex. The complex molecules are centrosymmetric. Through their molecular order and predictability, they can play a significant role in catalytic reactions, influencing the activity, selectivity, and stability of the catalyst. During the catalytic process, high CO2 pressure and high reaction temperature are not required, and the reaction conditions are mild, avoiding the drawbacks of harsh reaction conditions. Furthermore, the complex achieves a catalytic conversion rate of 90% or higher for epoxides and a selectivity for cyclic carbonates greater than 99%.

[0026] The present invention provides a method for preparing a binuclear rare earth complex. A Schiff base ligand is synthesized through a two-step reaction. The ligand has a simple structure and contains multiple coordination sites. A pyridine N atom is introduced into the molecule to increase the chelating ability. The ligand can react with a variety of rare earth metal chlorides at room temperature to generate a binuclear rare earth complex with a high yield, which can meet the requirements of mass production.

[0027] The present invention provides a method for using a binuclear rare earth complex as a catalyst to synthesize cyclic carbonates from carbon dioxide. This method does not require harsh reaction conditions and exhibits high activity, good selectivity, and low cost, contributing to the achievement of clean energy and sustainable development goals. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The figure is a schematic diagram of the crystal structure of a binuclear rare earth complex of the present invention.

[0029] Figure 2 The present invention is a flow chart of a method for preparing a binuclear rare earth complex.

[0030] Figure 3 The present invention provides a synthetic route for a binuclear rare earth complex.

[0031] Figure 4 This is the infrared spectrum of the ligand L synthesized in the present invention.

[0032] Figure 5 For the synthesis of ligand L of the present invention 1 H NMR spectrum.

[0033] Figure 6 For the synthesis of ligand L of the present invention 13 C NMR spectrum.

[0034] Figure 7 This is the infrared spectrum of the binuclear rare earth complex prepared in Example 5-7 of the present invention.

[0035] Figure 8 This is a thermal stability analysis chart of the binuclear rare earth complexes prepared in Examples 5-7 of the present invention.

[0036] Figure 9 This is the NMR image of the cyclic carbonate synthesized in Example 9 of the present invention.

[0037] Figure 10 This is the NMR image of the cyclic carbonate synthesized in Example 10 of the present invention.

[0038] Figure 11 This is the NMR image of the cyclic carbonate synthesized in Example 11 of the present invention.

[0039] Figure 12 This is the NMR image of the cyclic carbonate synthesized in Example 12 of the present invention.

[0040] Figure 13 This is the NMR image of the cyclic carbonate synthesized in Example 13 of the present invention.

[0041] Figure 14 The diagram shows the mechanism of the synthesis of cyclic carbonates from epoxides catalyzed by the binuclear rare earth complex of the present invention. DETAILED DESCRIPTION

[0042] To facilitate understanding of the features and effects of the present invention by those skilled in the art, the following provides a general description and definition of the terms and expressions used in the specification and claims. Unless otherwise indicated, all technical and scientific terms used herein have the ordinary meanings as understood by those skilled in the art regarding the present invention. In the event of conflict, the definitions in this specification shall prevail.

[0043] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0044] Herein, all features such as values, amounts, amounts, and concentrations defined in numerical ranges or percentage ranges are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to include and specifically disclose all possible subranges and individual values ​​within the range (including integers and fractions).

[0045] In this document, unless otherwise specified, “include,” “including,” “contains,” “has” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0046] In this document, for the sake of brevity, not all possible combinations of the various technical features in each embodiment or example are described. Therefore, as long as there are no contradictions in the combination of these technical features, the various technical features in each embodiment or example can be combined in any way, and all possible combinations should be considered to be within the scope of this specification.

[0047] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0048] The following examples were prepared using conventional instruments and equipment in the art. Experimental methods in the following examples, where specific conditions are not specified, were generally performed under conventional conditions or according to the conditions recommended by the manufacturer. The various raw materials used in the following examples, unless otherwise specified, were conventional commercially available products, with specifications conventional in the art. In the present specification and the following examples, unless otherwise specified, "%" indicates percentage by weight, "part" indicates parts by weight, and "ratio" indicates weight ratio.

[0049] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0050] The present invention discloses a binuclear rare earth complex, referring to Figure 1 , its chemical formula is RE2L2{[RE2L2(CH3OH)2Cl2]·2CH3OH}, and its molecular structure formula is:

[0051]

[0052] Wherein, RE is a chloride salt of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium or lutetium, the chloride ion participates in the coordination, L is a ligand used to synthesize the binuclear rare earth complex, and its molecular structure is: The crystal structure of this binuclear rare earth complex reveals that the complex molecule is composed of two rare earth metal ions and two ligands. The two rare earth metal ions share a heptad coordination pattern, forming a seven-coordination pattern with four oxygen atoms, two nitrogen atoms, and one chloride atom. The coordinating atoms come from an imine nitrogen atom, a pyridine nitrogen atom, a phenolic hydroxyl oxygen atom, two carbonyl oxygen atoms, a methanol molecule, and a chloride atom in the ligand. The resulting coordinated molecule is centrosymmetric. Its molecular-level order and predictability can play a crucial role in catalytic reactions, influencing the activity, selectivity, and stability of the catalyst, thereby optimizing and controlling complex chemical transformations.

[0053] See also Figure 2 and Figure 3 The present invention provides a method for preparing a binuclear rare earth complex, comprising:

[0054] S1: Prepare ligand L; the structural formula of the ligand L is: The specific operations are:

[0055] Mix methyl 6-aminopyridine-2-carboxylate with water and hydrazine at a molar ratio of 1: (1 to 1.2), heat with stirring and reflux in methanol solvent at 50°C to 70°C for 1 to 3 hours to fully react and obtain 6-aminopyridine hydrazide. The specific reaction formula is as follows:

[0056]

[0057] 6-Aminopicolinohydrazide and o-vanillin are heated at a molar ratio of 1:(0.95-1.05) in methanol solvent at 50°C-70°C under reflux for 5-12 hours to obtain ligand L. The specific reaction formula is as follows:

[0058]

[0059] S2: Using ligand L and rare earth metal chloride, a binuclear rare earth complex is prepared; the chemical formula of the binuclear rare earth complex is: RE2L2{[RE2L2(CH3OH)2Cl2]·2CH3OH}, and the general molecular structure formula is:

[0060]

[0061] , wherein RE in the chemical formula and molecular structure general formula is a chloride salt of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium or lutetium. The rare earth metal chloride is a hexahydrate chloride salt of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium or lutetium; the specific operation is:

[0062] Add a reaction solvent, triethylamine and a rare earth metal chloride to the ligand L, stir until clear, filter the solution, and allow it to react at 25°C to 40°C for 12 to 72 hours. Crystals precipitate from the solution, which are filtered and dried to obtain a binuclear rare earth complex; wherein the reaction solvent is one or more of methanol, ethanol and acetonitrile.

[0063] Example 1

[0064] Take 3.043 g of methyl 6-aminopyridine-2-carboxylate, water, and 1.001 g of hydrazine, add 50 mL of methanol solution, stir until completely dissolved, heat under reflux at 70 ° C and stir for 2 h to obtain a white solution, filter and vacuum dry to obtain 2.842 g of 6-aminopyridine hydrazide, a white powder, with a calculated yield of 93.38%.

[0065] 1.20 g of 6-aminopicolinohydrazide and 1.20 g of o-vanillin were added to 50 mL of methanol solution, and the mixture was heated under reflux at 70°C with stirring for 6 h to obtain a yellow solution, which was filtered and dried in vacuo to obtain 2.054 g of yellow powder, namely ligand L, with a calculated yield of 91.00%.

[0066] 0.05 mmol of ligand L and 0.1 mmol of EuCl3·6H2O were placed in a beaker. 2 mL of methanol and 2 mL of acetonitrile were added. 30 μL of triethylamine was added and stirred to obtain a yellow, clear solution. Filter the solution into a 10 mL sample vial, seal it with plastic wrap, pierce a small hole, and let it stand at room temperature for 48 hours to obtain the binuclear rare earth complex. Yield: 72.4%.

[0067] Example 2

[0068] Take 1.522 g of methyl 6-aminopyridine-2-carboxylate, water, and 0.501 g of hydrazine, add 50 mL of methanol solution, stir until completely dissolved, heat under reflux at 70 ° C and stir for 2 h to obtain a white solution, filter and vacuum dry to obtain a white powder, namely 1.379 g of 6-aminopyridine hydrazide, with a calculated yield of 90.64%.

[0069] 1.379 g of 6-aminopyridine hydrazide and 1.379 g of o-vanillin were added to 50 mL of methanol solution, and the mixture was heated under reflux at 70°C with stirring for 6 h to obtain a yellow solution, which was filtered and dried in vacuo to obtain 2.395 g of yellow powder, namely ligand L, with a calculated yield of 92.33%.

[0070] Place 0.05 mmol of ligand L and 0.1 mmol of ScCl3·6H2O in a beaker, add 2 mL of methanol solution and 2 mL of acetonitrile solution, and stir with 30 μL of triethylamine to obtain a clear yellow solution. Filter the solution into a 10 mL sample vial, seal with plastic wrap, pierce a small hole, and let stand at room temperature for 48 hours to obtain a binuclear rare earth complex. Yield: 72.3%.

[0071] Example 3

[0072] Take 1.529 g of methyl 6-aminopyridine-2-carboxylate, water, and 0.503 g of hydrazine, add 50 mL of methanol solution, stir until completely dissolved, heat under reflux at 70 ° C and stir for 2 h to obtain a white solution, filter and vacuum dry to obtain a white powder, namely 1.393 g of 6-aminopyridine hydrazide, with a calculated yield of 91.10%.

[0073] 1.393 g of 6-aminopyridine hydrazide and 1.393 g of o-vanillin were added to 50 mL of methanol solution, and the mixture was heated under reflux at 70°C with stirring for 6 h to obtain a yellow solution, which was filtered and dried in vacuo to obtain 2.440 g of yellow powder, namely ligand L, with a calculated yield of 93.13%.

[0074] 0.05 mmol of ligand L and 0.1 mmol of TbCl3·6H2O were placed in a beaker, followed by 2 mL of methanol and 2 mL of acetonitrile. 30 μL of triethylamine was added and stirred to yield a clear yellow solution. Filter the solution into a 10 mL sample vial, seal with plastic wrap, pierce the vial, and allow to stand at room temperature for 48 hours to yield the binuclear rare earth complex. Yield: 73.1%.

[0075] Example 4

[0076] Take 3.043 g of methyl 6-aminopyridine-2-carboxylate, water, and 1.001 g of hydrazine, add 50 mL of methanol solution, stir until completely dissolved, heat under reflux at 70 ° C and stir for 2 h to obtain a white solution, filter and vacuum dry to obtain 2.728 g of 6-aminopyridine hydrazide, a white powder, with a calculated yield of 89.63%.

[0077] 2.728 g of 6-aminopicolinohydrazide and 2.728 g of o-vanillin were added to 50 mL of methanol solution, and the mixture was heated under reflux at 70°C with stirring for 6 h to obtain a yellow solution, which was filtered and dried in vacuo to obtain 4.655 g of yellow powder, namely ligand L, with a calculated yield of 90.71%.

[0078] 0.05 mmol of ligand L and 0.1 mmol of GdCl3·6H2O were placed in a beaker. 2 mL of methanol and 2 mL of acetonitrile were added. 30 μL of triethylamine was added and stirred to obtain a yellow, clear solution. Filter the solution into a 10 mL sample vial, seal it with plastic wrap, pierce a small hole, and let it stand at room temperature for 48 hours to obtain the binuclear rare earth complex. Yield: 72.6%.

[0079] Example 5

[0080] Take 3.043 g of methyl 6-aminopyridine-2-carboxylate, water, and 1.001 g of hydrazine, add 50 mL of methanol solution, stir until completely dissolved, heat under reflux at 70 ° C and stir for 2 h to obtain a white solution, filter and vacuum dry to obtain 2.842 g of 6-aminopyridine hydrazide, a white powder, with a calculated yield of 93.38%.

[0081] 1.20 g of 6-aminopicolinohydrazide and 1.20 g of o-vanillin were added to 50 mL of methanol solution, and the mixture was heated under reflux at 70°C with stirring for 6 h to obtain a yellow solution, which was filtered and dried in vacuo to obtain 2.054 g of yellow powder, namely ligand L, with a calculated yield of 91.00%.

[0082] 0.05 mmol of ligand L and 0.1 mmol of DyCl3·6H2O were placed in a beaker, 2 mL of methanol solution and 2 mL of acetonitrile solution were added, and 30 μL of triethylamine was added and stirred to obtain a yellow clear solution. Filter the solution into a 10 mL sample vial, seal it with plastic wrap, pierce a small hole, and let it stand at room temperature for 48 hours to obtain yellow rectangular crystals of Dy2L2. Yield: 72.4%; Infrared spectrum, IR (KBr, cm -1 ): 1634cm -1 (m, C=N), 1599cm -1 (s), 1457cm -1 (s), 1296cm -1 (s), 1221cm -1 (m), 1077cm -1 (m), 942cm -1 (m), 855cm -1 (m), 735cm -1 (s), 574cm -1 (w, Dy-O), 530cm -1 (w, Dy-N). EA(%)C32 H 40 Cl2N8O 10 Dy2: calc. C, 35.14; H, 3.66; N, 10.25. Found: C, 35.12; H, 3.68; N, 10.23. The crystal size is basically 0.15mm×0.14mm×0.12mm.

[0083] Example 6

[0084] Take 3.043 g of methyl 6-aminopyridine-2-carboxylate, water, and 1.001 g of hydrazine, add 50 mL of methanol solution, stir until completely dissolved, heat under reflux at 70 ° C and stir for 2 h to obtain a white solution, filter and vacuum dry to obtain 2.842 g of 6-aminopyridine hydrazide, a white powder, with a calculated yield of 93.38%.

[0085] 1.20 g of 6-aminopicolinohydrazide and 1.20 g of o-vanillin were added to 50 mL of methanol solution, and the mixture was heated under reflux at 70°C with stirring for 6 h to obtain a yellow solution, which was filtered and dried in vacuo to obtain 2.054 g of yellow powder, namely ligand L, with a calculated yield of 91.00%.

[0086] 0.05 mmol of ligand L and 0.1 mmol of ErCl3·6H2O were placed in a beaker, 2 mL of methanol solution and 2 mL of acetonitrile solution were added, and 30 μL of triethylamine was added and stirred to obtain a yellow clear solution. Filter the solution into a 10 mL sample vial, seal it with plastic wrap, pierce a small hole, and let it stand at room temperature for 48 hours to obtain yellow rectangular crystals of Er2L2. Yield: 78.6%; Infrared spectrum, IR (KBr, cm -1 ): 1636cm -1 (w, C=N), 1597cm -1 (s), 1562cm -1 (m), 1462cm -1 (s), 1300cm -1 (s), 1215cm -1 (m), 1082cm -1 (m), 1001cm -1 (s), 947cm -1 (m), 851cm -1 (m), 726cm -1 (s), 571cm -1 (w, Er-O), 530cm -1 (w, Er-N); EA(%)C 32 H 40 Cl2N8O 10Er2: calc. C, 34.84; H, 3.62; N, 10.16. Found: C, 34.82; H, 3.65; N, 10.13. The crystal size is basically 0.14mm×0.12mm×0.1mm.

[0087] Example 7

[0088] Take 3.043 g of methyl 6-aminopyridine-2-carboxylate, water, and 1.001 g of hydrazine, add 50 mL of methanol solution, stir until completely dissolved, heat under reflux at 70 ° C and stir for 2 h to obtain a white solution, filter and vacuum dry to obtain 2.842 g of 6-aminopyridine hydrazide, a white powder, with a calculated yield of 93.38%.

[0089] 1.20 g of 6-aminopicolinohydrazide and 1.20 g of o-vanillin were added to 50 mL of methanol solution, and the mixture was heated under reflux at 70°C with stirring for 6 h to obtain a yellow solution, which was filtered and dried in vacuo to obtain 2.054 g of yellow powder, namely ligand L, with a calculated yield of 91.00%.

[0090] 0.05 mmol of ligand L and 0.1 mmol of YbCl3·6H2O were placed in a beaker, 2 mL of methanol solution and 2 mL of acetonitrile solution were added, and 30 μL of triethylamine was added and stirred to obtain a yellow clear solution. Filter the solution into a 10 mL sample vial, seal it with plastic wrap, pierce a small hole, and let it stand at room temperature for 48 hours to obtain yellow rectangular crystals of Yb2L2. Yield: 65.4%; Infrared spectrum, IR (KBr, cm -1 ): 1634cm -1 (m, C=N), 1599cm -1 (s), 1457cm -1 (s), 1296cm -1 (s), 1221cm -1 (m), 1077cm -1 (m), 942cm -1 (m), 855cm -1 (m), 735cm -1 (s), 570cm -1 (w, Tb-O), 529cm -1 (w, Yb-N); EA(%)C 32 H 40 Cl2N8O 10 Yb2: calc. C, 34.47; H, 3.59; N, 10.05. Found: C, 34.45; H, 3.61; N, 10.03. The crystal size is basically 0.18mm×0.13mm×0.12mm.

[0091] See also Figure 4, infrared spectrum analysis was performed on the ligand L prepared in Example 1. It was found that at 1534 cm -1 The position can be attributed to the stretching vibration of the aromatic ring skeleton in ligand L. 1453cm -1 The 1296 cm-1 peak can be attributed to the stretching vibration between the carbon atom and the nitrogen atom on the pyridine ring in methyl 6-aminopyridine-2-carboxylate. -1 The C-O-C stretching vibration of the ether group in o-vanillin can be attributed to 1245 cm -1 The peaks in this range are attributed to the C=O stretching vibration of the ester group in methyl 6-aminopyridine-2-carboxylate. -1 The peak near 820 cm is attributed to the CH vibration of the benzene ring. -1 The peak near 765 cm is usually attributed to the bending vibration of the benzene ring. -1 The peaks near 1604 cm are attributed to the out-of-plane bending vibration of CH in the trisubstituted benzene ring of ligand L. -1 The increased peak indicates that the synthetic intermediate reacted with o-vanillin to form a characteristic mechanism reaction of Schiff base synthesis, forming C=N. It can be seen that the ligand was successfully synthesized.

[0092] See also Figure 5 and Figure 6 The ligand L prepared in Example 1 was subjected to hydrogen and carbon nuclear magnetic resonance spectrum analysis, indicating that the ligand was successfully synthesized. 1 HNMR (400MHz, dmso) δ (ppm): 11.82 (s, 1H, Ar-OH), 11.03 (s, H, -NH-), 8.69 (s, H, =CH-), 7.56-6.68 (m, 3H, Ar-H), 6.10 (s, 2H, -NH2), 3.78 (s, 3H, -CH3). 13 CNMR (100 MHz, DMSO) δ (ppm): 161.19, 159.11, 149.35, 148.40, 147.82, 147.71, 138.69, 121.47, 119.45, 119.33, 114.37, 112.45, 111.46, 56.30. The remaining unexplained peaks are solvent peaks and impurity peaks.

[0093] See also Figure 7 The infrared spectra of the binuclear rare earth complexes prepared in Examples 5-7 were measured and compared with the ligands. The infrared spectra of the three complexes have the same peak values, indicating that their coordination modes are the same. Compared with the ligands, the complexes have a peak value of 1600 cm -1 The characteristic peak of the imine C=N group nearby is red-shifted to 765cm -1 The characteristic peak of CH in the nearby trisubstituted benzene ring is blue-shifted, indicating that the N atom in the ligand and the O atom in the benzene ring substituent are coordinated with the metal ion.

[0094] See also Figure 8 The binuclear rare earth complexes prepared in Examples 5-7 were subjected to thermogravimetric analysis. The experiments were performed using a TGA / NETZSCH STA449C thermogravimetric analyzer under nitrogen protection, with temperatures ranging from room temperature to 800°C. The experimental results showed that the binuclear rare earth complexes prepared in Examples 5-7 exhibited good stability below 200°C. Within this temperature range, the mass of the complexes showed little noticeable change, indicating that the complexes can maintain their structural and property stability at relatively high temperatures. This provides a certain degree of assurance for their application in catalytic reactions.

[0095] The present invention provides a use of the above-mentioned binuclear rare earth complex in catalyzing the synthesis of cyclic carbonates from carbon dioxide. The binuclear rare earth complex exhibits good catalytic performance in catalyzing the cycloaddition reaction of carbon dioxide and epoxide.

[0096] Example 8

[0097] In order to explore the influence of catalysts and external factors on the reaction, the optimal co-catalyst, reaction time, reaction temperature and reaction pressure were screened. 0.1 mol% of the complex prepared in Examples 5-7 was taken, 10 mmol of styrene oxide was taken as a substrate and placed in a 30 mL high-pressure reactor, 0.8 mol% of the co-catalyst tetrabutylammonium bromide (TBAB), tetrabutylammonium iodide (TBAI) and tetrabutylammonium chloride (TBAC) were added respectively, and the reaction was carried out at temperatures of 100°C, 80°C and 60°C, and pressures of 1 MPaCO2, 1.5 MPa CO2 and 2 MPa CO2 for 1 to 4 hours. The optimal reaction conditions were finally screened out as follows: 0.1 mol% complex, 0.8 mol% co-catalyst TBAB, 100°C, 1 MPa CO2 and 4 hours. The specific reaction formula is as follows:

[0098]

[0099] Example 9

[0100] 10 mmol of styrene oxide as a substrate was placed in a 30 mL autoclave, 0.1 mol% of the complex Dy2L2 prepared in Example 5 and 0.8 mol% of the co-catalyst TBAB were added, and the reaction was carried out at 100°C and 1 MPa CO2 for 4 h. Figure 9 ,pass 1 HNMR analysis showed that the conversion rate was 98% and the selectivity of cyclic carbonate was greater than 99%.

[0101] Example 10

[0102] 10 mmol of allyl glycidyl ether as a substrate was placed in a 30 ml autoclave, 0.1 mol% of the complex Dy2L2 prepared in Example 5 and 0.8 mol% of the co-catalyst TBAB were added, and the reaction was carried out at 100°C and 1 MPa CO2 for 4 h. Figure 10 ,pass 1 HNMR analysis showed that the conversion rate was 98% and the selectivity of cyclic carbonate was greater than 99%.

[0103] Example 11

[0104] 10 mmol of phenyl glycidyl ether as a substrate was placed in a 30 ml autoclave, 0.1 mol% of the complex Dy2L2 prepared in Example 5 and 0.8 mol% of the co-catalyst TBAB were added, and the reaction was carried out at 100°C and 1 MPa CO2 for 4 h. Figure 11 ,pass 1 HNMR analysis showed that the conversion rate was 99% and the selectivity of cyclic carbonate was greater than 99%.

[0105] Example 12

[0106] 10 mmol of n-butyl glycidyl ether was placed in a 30 ml autoclave as a substrate, 0.1 mol% of the complex Dy2L2 prepared in Example 5 and 0.8 mol% of the co-catalyst TBAB were added, and the reaction was carried out at 100°C and 1 MPa CO2 for 4 h. Figure 12 ,pass 1 HNMR analysis showed that the conversion rate was 99% and the selectivity of cyclic carbonate was greater than 99%.

[0107] Example 13

[0108] 10 mmol of propylene oxide was placed in a 30 ml autoclave as a substrate, and 0.1 mol% of the complex Dy2L2 prepared in Example 5 and 0.8 mol% of the co-catalyst TBAB were added. Since propylene oxide has a low boiling point, the reaction was carried out at 50°C and 1 MPaCO2 for 6 h. Figure 13 ,pass 1 HNMR analysis showed that the conversion rate was 90% and the selectivity of cyclic carbonate was greater than 99%.

[0109] See also Figure 14, which is the catalytic mechanism of the complex-catalyzed synthesis of cyclic carbonates from carbon dioxide. The lanthanide metal site (Ln) can activate the epoxide. The first step is the coordination activation of the epoxide with the Lewis acid site of the rare earth metal site, and then the nucleophilic attack of the bromide ion completes the ring opening. The epoxy ring opens to form a negative ion. Subsequently, CO2 inserts into the Ln-O epoxide bond to form a carbonate intermediate. This is a rapid process, and the ring closure occurs, releasing the cyclic carbonate and the complex as well as the bromide for the next catalytic cycle.

[0110] In summary, the present invention provides a binuclear rare earth complex, a preparation method, and an application thereof. A Schiff base ligand is synthesized by a two-step reaction. The ligand has a simple structure, contains multiple coordination sites, and a pyridine N atom is introduced into the molecule to increase the chelating ability. The ligand can react with a variety of rare earth metal chlorides at room temperature to form a binuclear rare earth complex with a high yield. The ligand used contains multiple coordination sites, and a pyridine N atom is introduced into the molecule to increase the chelating ability. The ligand can react with a variety of rare earth metal chlorides at room temperature to form a binuclear rare earth complex. The complex molecule is centrosymmetric. Through its orderliness and predictability at the molecular level, it can play an important role in the catalytic reaction and affect the activity, selectivity, and stability of the catalyst. During the catalytic process, high CO2 pressure and high reaction temperature are not required, the reaction conditions are mild, and the disadvantages brought by harsh reaction conditions are avoided. The catalytic conversion rate is high and the selectivity is good.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to impose any limitation on the technical solution of the present invention. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can also be subjected to several simple modifications and replacements, and these modifications and replacements are also within the scope of protection covered by the claims.

Claims

1. A binuclear rare earth complex, characterized in that: Its molecular structure formula is: ， Among them, RE in the molecular structure formula is scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium or lutetium.

2. A method for preparing a binuclear rare earth complex, characterized in that: include: Prepare ligand L; wherein the ligand L has the structural formula: ; A binuclear rare earth complex is prepared using ligand L and rare earth metal chloride; the molecular structure of the binuclear rare earth complex is as follows: , Among them, RE in the molecular structure formula is scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium or lutetium.

3. The method for preparing a binuclear rare earth complex according to claim 2, characterized in that: The rare earth metal chloride is a hexahydrate chloride of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium or lutetium.

4. The method for preparing a binuclear rare earth complex according to claim 2, wherein: The method for preparing ligand L is: 6-aminopyridine-2-carboxylic acid methyl ester is reacted with water and hydrazine in a methanol solvent by heating, stirring and refluxing to obtain 6-aminopyridine hydrazide; 6-aminopyridine hydrazide and o-vanillin were heated, stirred and refluxed in methanol solvent to fully react to obtain ligand L.

5. The method for preparing a binuclear rare earth complex according to claim 4, wherein: In the process of heating, stirring and refluxing 6-aminopyridine-2-carboxylic acid methyl ester with water and hydrazine in a methanol solvent to fully react to obtain 6-aminopyridine hydrazide, the heating, stirring and refluxing temperature is 50°C to 70°C, the reaction time is 1 to 3 hours, and the molar ratio of 6-aminopyridine-2-carboxylic acid methyl ester to water and hydrazine is 1:(1 to 1.2).

6. The method for preparing a binuclear rare earth complex according to claim 4, wherein: In the process of heating, stirring and refluxing 6-aminopicolinohydrazide and o-vanillin in a methanol solvent to fully react to obtain ligand L, the heating, stirring and refluxing temperature is 50°C to 70°C, the reaction time is 5 to 12 h, and the molar ratio of 6-aminopicolinohydrazide to o-vanillin is 1:(0.95 to 1.05).

7. The method for preparing a binuclear rare earth complex according to claim 2, characterized in that: The method for preparing a binuclear rare earth complex using ligand L and rare earth metal chloride is as follows: A reaction solvent, triethylamine and rare earth metal chloride are added to the ligand L to react to obtain a binuclear rare earth complex.

8. The method for preparing a binuclear rare earth complex according to claim 7, characterized in that: The reaction solvent is one or more of methanol, ethanol and acetonitrile.

9. The method for preparing a binuclear rare earth complex according to claim 7, wherein: The molar ratio of the ligand L to the rare earth metal chloride is 1:(1-4), the reaction temperature for obtaining the binuclear rare earth complex is 25°C-40°C, and the reaction time is 12-72 h.

10. Use of the binuclear rare earth complex according to claim 1 in catalyzing the synthesis of cyclic carbonates from carbon dioxide.

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