A butterfly-shaped ternary schiff base rare earth metal catalyst, a preparation method and application thereof

Abstract

This invention relates to the field of multifunctional new materials technology, particularly to a butterfly-shaped trinuclear Schiff base rare earth metal catalyst, its preparation method, and its application. The molecular structure of this catalyst is as follows: where M1 to M3 are rare earth metal ions. These rare earth metal ions possess high Lewis acidity and oxyphilicity, promoting the activation of epoxides and achieving acid-base synergistic catalysis to advance the reaction. The ligand not only readily coordinates with rare earth metal ions, but the -C=N- group in the ligand also exhibits Lewis basicity, facilitating the fixation of carbon dioxide in the target substrate. The addition of hydroxyl groups, in synergy with the -C=N- group, enriches the coordination sites, thereby constructing a unique energy level structure that maintains structural stability even at high temperatures. During catalysis, the reaction is unaffected by additional moisture and air, resulting in low catalytic cost, high catalytic efficiency, and high conversion rate. This invention solves the problems of harsh catalytic conditions, low catalytic efficiency, and low conversion rate associated with existing tetradentate pyridyl Schiff base metal complexes as catalysts.

Description

Technical Field

[0001] This invention relates to the field of multifunctional new materials technology, specifically to a butterfly-shaped trinuclear Schiff base rare earth metal catalyst, its preparation method, and its application. Background Technology

[0002] Carbon dioxide is the most widely distributed and abundant carbon resource on Earth. It is not only non-toxic, harmless, widely available, and inexpensive, but also a sustainable carbon source. Therefore, converting carbon dioxide into high-value-added chemicals is one of the most effective ways to utilize this resource. CO2 can react with various organic compounds to produce high-value-added chemicals, such as polycarbonates, carboxylic acids, esters, cyclic carbonates, formamides, methylamines, carbamates, and oxazolidinone derivatives. Among these, the method of combining carbon dioxide with epoxides to form cyclic carbonates is an atom-economic reaction with 100% atom utilization, attracting increasing attention from scholars. However, due to the high stability of both carbon dioxide and epoxides, they are not easily activated during the reaction, resulting in a low conversion rate, often requiring the addition of catalysts.

[0003] To improve the reactivity of the cycloaddition reaction between carbon dioxide and epoxides, current technologies focus on developing catalysts with high catalytic activity. These include disclosed heterogeneous catalysts such as metal oxides, modified molecular sieves, clays, and polymers. While heterogeneous catalysts are easier to remove from the products, they suffer from low catalytic activity, low selectivity, long reaction times, and harsh reaction conditions. To achieve the cycloaddition reaction of carbon dioxide and epoxides under milder conditions, homogeneous catalysts, such as metal complexes, especially tetradentate Schiff base metal complexes with cobalt or chromium as active centers, have been developed. These complexes exhibit high catalytic activity under milder reaction conditions, but they suffer from low selectivity and the formation of byproducts such as polycarbonate in the cycloaddition reaction products.

[0004] Chinese invention patent CN103447091 B discloses a tetradentate pyridyl Schiff base metal complex, its preparation method, and a method for preparing cyclic carbonates. The method involves preparing a tetradentate pyridyl Schiff base metal complex comprising zinc, magnesium, manganese, or iron metal elements as the active center and a special structure outside the active center. During catalytic reactions, the tetradentate pyridyl Schiff base metal complex acts as the main catalyst, with a quaternary ammonium salt as a co-catalyst, achieving the cycloaddition reaction of carbon dioxide with epoxides. It exhibits good selectivity. However, due to the rigid framework structure of this catalyst, the catalytic carbon dioxide cycloaddition reaction requires high purity of carbon dioxide, harsh reaction conditions, and a long catalytic synthesis time, and also suffers from low conversion rates. Summary of the Invention

[0005] To address the problems of harsh catalytic conditions, low catalytic efficiency, and low conversion rate of tetradentate pyridyl Schiff base metal complexes as catalysts in existing technologies, this invention provides a butterfly-shaped trinuclear Schiff base rare earth metal catalyst, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] This invention provides a butterfly-shaped trinuclear Schiff base rare earth metal catalyst, the molecular structure of which is as follows: Among them, M1 to M3 are rare earth metal ions.

[0008] Furthermore, the rare earth metal ion is Sc 3+ Y 3+ Ce 3+ 、Nd 3+ 、Sm 3+ Gd 3+ Eu 3+ 、Tb 3+ Dy 3+ Er 3+ Ho 3+ Tm 3+ or Yb 3+ .

[0009] This invention provides a method for preparing a butterfly-shaped trinuclear Schiff base rare earth metal catalyst, comprising:

[0010] Preparation of Schiff base ligands;

[0011] A butterfly-shaped trinuclear Schiff base rare earth metal catalyst was prepared using Schiff base ligands and rare earth metal chlorides. The molecular structure of the butterfly-shaped trinuclear Schiff base rare earth metal catalyst is as follows: Among them, M1 to M3 are rare earth metal ions.

[0012] Furthermore, the molecular structural formula of the Schiff base ligand is as follows:

[0013] Further, the rare earth metal chloride salt is ScCl3·6H2O, YCl3·6H2O, CeCl3·6H2O, NdCl3·6H2O, SmCl3·6H2O, GdCl3·6H2O, EuCl3·6H2O, TbCl3·6H2O, DyCl3·6H2O, ErCl3·6H2O, HoCl3·6H2O, TmCl3·6H2O, or YbCl3·6H2O.

[0014] Furthermore, the method for preparing the Schiff base ligand is as follows:

[0015] The intermediate was obtained by reacting 1,3-propanediamine and 3-amino-2-hydroxyacetophenone.

[0016] The intermediate was reacted with o-vanillin to give the Schiff base ligand.

[0017] Furthermore, the method for preparing butterfly-shaped trinuclear Schiff base rare earth metal catalysts using Schiff base ligands and rare earth metal chlorides is as follows:

[0018] Schiff base ligands and rare earth metal chlorides were dissolved in a solvent, and triethylamine was added. The reaction was carried out at room temperature to obtain a butterfly-shaped trinuclear Schiff base rare earth metal catalyst.

[0019] A butterfly-shaped trinuclear Schiff base rare earth metal catalyst was prepared using the method described above.

[0020] Such as the application of the butterfly-shaped trinuclear Schiff base rare earth metal catalyst in the preparation of cyclic carbonates.

[0021] Furthermore, a cycloaddition reaction is carried out using a butterfly-shaped trinuclear Schiff base rare earth metal catalyst as the catalyst, tetrabutylammonium bromide as the co-catalyst, and epoxide and carbon dioxide as the reaction substrate to obtain cyclic carbonates; wherein the epoxide is epichlorohydrin, allyl glycidyl ether, styrene oxide, butyl glycidyl ether, or phenyl glycidyl ether; the cycloaddition reaction time is 1-3 h, the reaction temperature is 60℃-120℃, the conversion rate reaches 99%, and the molar ratio of epoxide, catalyst, and co-catalyst is 1000:(0.4-1):(2-8).

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention relates to a butterfly-shaped trinuclear Schiff base rare earth metal catalyst. Its molecular structural formula is as follows: In this catalyst, M1 to M3 are rare earth metal ions. The catalyst uses rare earth metal ions as the active center and butterfly-shaped ligands as a flexible framework. The rare earth metal ions possess high Lewis acidity and oxyphilicity, which can promote the activation of epoxides, thus achieving acid-base synergistic catalysis to advance the reaction. The butterfly-shaped ligands, as a flexible framework, not only coordinate more easily with rare earth metal ions, but also exhibit Lewis basicity in the -C=N- groups, facilitating the fixation of carbon dioxide in the target substrate. The addition of hydroxyl groups, synergistically with the -C=N- groups, enriches the coordination sites of the butterfly-shaped ligands, thereby constructing a novel Schiff base complex with a unique energy level structure for the catalytic conversion of carbon dioxide. This allows the catalyst to maintain structural stability even at high temperatures. During catalysis, the reaction is unaffected by additional moisture and air, resulting in mild reaction conditions, low catalytic cost, high catalytic efficiency, and high conversion rate.

[0024] This invention provides a method for preparing a butterfly-shaped trinuclear Schiff base rare earth metal catalyst. The method involves preparing a Schiff base ligand and then using the Schiff base ligand and a rare earth metal chloride to prepare the butterfly-shaped trinuclear Schiff base rare earth metal catalyst. This method uses Schiff base ligands and rare earth metal chlorides as raw materials, employs mild reaction conditions, requires no harsh reaction environment or equipment, utilizes widely available and low-cost raw materials, and features short reaction time, high yield, and suitability for industrialization. It effectively controls production input costs while improving production efficiency and yield. Furthermore, the produced rare earth metal catalyst exhibits better stability and higher catalytic efficiency.

[0025] A butterfly-shaped trinuclear Schiff base rare earth metal catalyst was prepared using the method described above. The smallest structural unit of this catalyst comprises one Schiff base ligand and three rare earth metal ions. The complex has a symmetrical structure, belongs to the monoclinic crystal system, and has a C2 / c space group. In the complex, M1 and M2 have the same coordination environment, both forming an octet structure with the two phenolic hydroxyl groups (O), the imine group (N), the methanol molecule (O), the two H2O molecules (O), and the two hydroxide ions (O). M3 forms an octet structure with the two phenolic hydroxyl groups (O), the two methoxy groups (O), the two hydroxide ions (O), and the two water molecules (O) on the Schiff base ligand. This catalyst exhibits good catalytic stability, high catalytic efficiency and conversion rate, and low catalytic cost.

[0026] The above-mentioned butterfly-shaped trinuclear Schiff base rare earth metal catalyst is used in the preparation of cyclic carbonates. Using the butterfly-shaped trinuclear Schiff base rare earth metal catalyst as the catalyst, tetrabutylammonium bromide as the co-catalyst, and epoxides and carbon dioxide as the reaction substrates for cycloaddition reactions, cyclic carbonates can be synthesized rapidly and stably. The cycloaddition reaction is short, highly efficient, and the conversion rate can reach up to 99%. Furthermore, the catalyst is recyclable and low-cost, improving the economics of synthesizing cyclic carbonates and demonstrating significant application and promotion value. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the crystal structure of a butterfly-shaped trinuclear Schiff base rare earth metal catalyst according to the present invention.

[0028] Figure 2 This is a schematic diagram of the catalytic mechanism of a butterfly-shaped trinuclear Schiff base rare earth metal catalyst according to the present invention.

[0029] Figure 3 This is a flowchart illustrating the preparation method of a butterfly-shaped trinuclear Schiff base rare earth metal catalyst according to the present invention.

[0030] Figure 4 This is a synthetic route diagram of a butterfly-shaped trinuclear Schiff base rare earth metal catalyst according to the present invention.

[0031] Figure 5This is a synthetic route diagram of the Schiff base ligand H4L in the synthetic pathway of a butterfly-shaped trinuclear Schiff base rare earth metal catalyst of the present invention.

[0032] Figure 6 The image shows the infrared curve of the Schiff base ligand H4L in the synthesis pathway of the butterfly-shaped trinuclear Schiff base rare earth metal catalyst of the present invention.

[0033] Figure 7 This invention relates to a butterfly-shaped trinuclear Schiff base rare earth metal catalyst synthesis pathway for Schiff base ligands. 13 CNMR spectrum.

[0034] Figure 8 This invention relates to a butterfly-shaped trinuclear Schiff base rare earth metal catalyst synthesis pathway for Schiff base ligands. 1 HNMR spectrum.

[0035] Figure 9 This is an infrared comparison image of a butterfly-shaped trinuclear Schiff base rare earth metal catalyst of the present invention and the Schiff base ligand H4L in the synthesis route.

[0036] Figure 10 Thermogravimetric analysis of different butterfly-shaped trinuclear Schiff base rare earth metal catalysts of the present invention.

[0037] Figure 11 This invention relates to a butterfly-shaped trinuclear Schiff base rare earth metal catalyst for the catalytic oxidation of styrene to crude product. 1 HNMR spectrum.

[0038] Figure 12 This invention relates to a butterfly-shaped trinuclear Schiff base rare earth metal catalyst for the catalytic conversion of n-butyl glycidyl ether into crude product. 1 HNMR spectrum.

[0039] Figure 13 This invention relates to a butterfly-shaped trinuclear Schiff base rare earth metal catalyst for the catalytic conversion of glycidyl phenyl ether into crude product. 1 HNMR spectrum.

[0040] Figure 14 This invention relates to a butterfly-shaped trinuclear Schiff base rare earth metal catalyst for the catalytic conversion of allyl glycidyl ether into crude product. 1 HNMR spectrum. Detailed Implementation

[0041] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0042] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0043] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0044] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0045] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0046] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0047] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0048] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0049] This invention discloses a butterfly-shaped trinuclear Schiff base rare earth metal catalyst, the molecular structure of which is as follows: Wherein, M1 to M3 are rare earth metal ions. Preferably, the rare earth metal ions are Sc. 3+ Y 3+ Ce 3+ 、Nd 3+ 、Sm 3+ Gd 3+ Eu 3+ 、Tb 3+ Dy 3+ Er 3+ Ho 3+ Tm 3+ or Yb 3+ .

[0050] See Figure 1 Taking rare earth element Er as an example, it should be noted that the coordinating anions and solvent molecules are omitted in this structure. The crystal structure is analyzed as follows: the smallest structural unit of the catalyst includes one Schiff base ligand H4L and three rare earth metal ions. The complex has a symmetrical structure, belongs to the monoclinic crystal system, and has a space group of C2 / c. In the complex, the coordination environments of rare earth metal ions Er1 and Er2 are the same, both forming an eight-coordinate structure with the two phenolic hydroxyl groups O and the imine group N on ligand H4L, the O of methanol molecules, the O of two H2O molecules, and the O of two hydroxide ions. Er3 forms an eight-coordinate structure with the two phenolic hydroxyl groups O, the two methoxy groups O, the two hydroxide ions O, and the O of two water molecules on ligand H4L. Among them, the Er-O bond length is 2.235(3)-2.479(4). Within the range, Er 3+ The bond angles formed with N and O are in the range of 67.63(13)-153.19(11). In subsequent catalytic experiments, the uncoordinated N atoms in the ligand can act as active sites to promote acid-base synergistic catalysis, thereby improving conversion efficiency. The main crystal structure data are shown in Table 1 below:

[0051] Table 1 Crystal structure data of the catalyst

[0052]

[0053]

[0054] See Figure 2The catalytic principle of this butterfly-shaped trinuclear Schiff base rare earth metal catalyst is as follows: the complex formed by the Schiff base ligand H4L and rare earth metal ions through coordination self-assembly contains a large coordination cavity, which can adsorb carbon dioxide and thus improve the reaction conversion rate.

[0055] See Figures 3 to 5 The present invention also provides a method for preparing a butterfly-shaped trinuclear Schiff base rare earth metal catalyst, comprising:

[0056] S1: Preparation of Schiff base ligands, the specific method is as follows:

[0057] 1,3-Propanediamine and 3-amino-2-hydroxyacetophenone were uniformly dispersed in methanol or acetonitrile at a molar ratio of 1:2. The reaction was carried out at 50℃~60℃ for 4~6 hours. After filtration, washing, and drying, an intermediate was obtained, denoted as M. The structural formula of the intermediate is as follows:

[0058]

[0059] Intermediate M and o-vanillin were uniformly dispersed in methanol or acetonitrile at a molar ratio of 1:2. The reaction was carried out at 55℃~65℃ for 4~6 hours. After filtration, washing, and drying, the Schiff base ligand was obtained, denoted as H4L. The structural formula of the Schiff base ligand is as follows:

[0060] The intermediate was reacted with o-vanillin to give the Schiff base ligand.

[0061] S2: A butterfly-shaped trinuclear Schiff base rare earth metal catalyst was prepared using Schiff base ligands and rare earth metal chlorides. The Schiff base ligands were dissolved in methanol or acetonitrile, and triethylamine was added until the solution turned orange-red. Rare earth metal chlorides were then added, and the solution changed from orange-red to orange-yellow. The solution was volatilized at room temperature, sealed, and allowed to stand until yellow crystals precipitated. The solution was then filtered and dried to obtain the rare earth metal catalyst. The molar ratio of Schiff base ligands to rare earth metal chlorides was 1:4. The amount of triethylamine added was determined by the color change of the solution, and its main function was deprotonation. The rare earth chloride salt is ScCl3·6H2O, YCl3·6H2O, CeCl3·6H2O, NdCl3·6H2O, SmCl3·6H2O, GdCl3·6H2O, EuCl3·6H2O, TbCl3·6H2O, DyCl3·6H2O, ErCl3·6H2O, HoCl3·6H2O, TmCl3·6H2O, or YbCl3·6H2O. The molecular structure of the butterfly-shaped trinuclear Schiff base rare earth metal catalyst is: Among them, M1 to M3 are rare earth metal ions.

[0062] Example 1

[0063] 3.023 g (0.02 mol) of 3-amino-2-hydroxyacetophenone was added to a round-bottom flask, followed by 80 mL of methanol solution. Then, 0.743 g (0.01 mol) of 1,3-propanediamine was added and mixed thoroughly. The mixture was heated under reflux in an oil bath at 55 °C for 5 h, during which the solution changed from black to yellow. After cooling, the solution was filtered to obtain a yellow solid, i.e., the intermediate, with a calculated yield of 85%.

[0064] 1.7 g (0.005 mol) of the intermediate was added to a round-bottom flask, along with 1.521 g (0.01 mol) of o-vanillin and an appropriate amount of methanol solution. The mixture was thoroughly mixed and heated under reflux at 60 °C for 6 h. A red solution was obtained, which was cooled and filtered to obtain a red solid, i.e., the Schiff base ligand, denoted as H4L. The yield was calculated to be 90%.

[0065] 0.03 g (0.05 mmol) of Schiff base ligand was placed in a 10 mL sample vial, followed by 2 mL of methanol solution and 2 mL of acetonitrile solution. Then, 0.076 g (0.2 mmol) of ErCl3·6H2O was added, along with 40 μL of triethylamine solution. The mixture was thoroughly mixed. The vial was sealed with plastic wrap, punctured, and allowed to evaporate at room temperature for one week. Pale yellow crystalline particles precipitated in the vial. The precipitate was filtered, washed, and dried to obtain the complex crystals. The calculated yield was approximately 86%. EA (%) C 37 H 52 N4O 18 Er3. Calc: C, 29.93; H, 3.50; N, 3.77; Found: C, 30.18; H, 3.58; N, 3.69. IR (KBr, ν, cm -1 ), 1599(s), 1553(m), 1455(m), 1391(w), 1298(s), 741(s).

[0066] Example 2

[0067] 3.023 g (0.02 mol) of 3-amino-2-hydroxyacetophenone was added to a round-bottom flask, followed by 80 mL of methanol solution. Then, 0.743 g (0.01 mol) of 1,3-propanediamine was added and mixed thoroughly. The mixture was heated under reflux in an oil bath at 55 °C for 5 h, during which the solution changed from black to yellow. After cooling, the solution was filtered to obtain a yellow solid, i.e., the intermediate, with a calculated yield of 85%.

[0068] 1.7 g (0.005 mol) of the intermediate was added to a round-bottom flask, along with 1.521 g (0.01 mol) of o-vanillin and an appropriate amount of methanol solution. The mixture was thoroughly mixed and heated under reflux at 60 °C for 6 h. A red solution was obtained, which was cooled and filtered to obtain a red solid, i.e., the Schiff base ligand, denoted as H4L. The yield was calculated to be 90%.

[0069] 0.03 g (0.05 mmol) of Schiff base ligand H4L was placed in a 10 mL sample vial, followed by 2 mL of methanol solution and 2 mL of acetonitrile solution. Then, 0.078 g (0.2 mmol) of YbCl3·6H2O was added, along with 40 μL of triethylamine solution. The mixture was thoroughly mixed. The vial was sealed with plastic wrap, punctured, and allowed to evaporate at room temperature for one week. Pale yellow crystalline particles precipitated in the vial. The precipitate was filtered, washed, and dried to obtain the complex crystals. The yield was calculated to be approximately 90%. EA (%) C 37 H 58 N4O 19 Yb3. Calc: C, 29.15; H, 3.81; N, 3.67; Found: C, 29.30; H, 3.68; N, 3.76. IR (KBr, ν, cm -1 ), 1599(s), 1553(m), 1455(m), 1391(w), 1298(s), 741(s).

[0070] Example 3

[0071] 3.023 g (0.02 mol) of 3-amino-2-hydroxyacetophenone was added to a round-bottom flask, followed by 80 mL of methanol solution. Then, 0.743 g (0.01 mol) of 1,3-propanediamine was added and mixed thoroughly. The mixture was heated under reflux in an oil bath at 55 °C for 5 h, during which the solution changed from black to yellow. After cooling, the solution was filtered to obtain a yellow solid, intermediate M, with a calculated yield of 85%.

[0072] 1.7 g (0.005 mol) of the intermediate was added to a round-bottom flask, along with 1.521 g (0.01 mol) of o-vanillin and an appropriate amount of methanol solution. The mixture was thoroughly mixed and heated under reflux at 60 °C for 6 h. A red solution was obtained, which was cooled and filtered to obtain a red solid, namely the Schiff base ligand H4L, with a calculated yield of 90%.

[0073] 0.03 g (0.05 mmol) of ligand H4L was placed in a 10 mL sample vial, followed by 2 mL of methanol solution and 2 mL of acetonitrile solution. Then, 0.061 g (0.2 mmol) of YCl3·6H2O was added, and 40 μL of triethylamine solution was added. The mixture was thoroughly mixed. The vial was sealed with plastic wrap, punctured, and allowed to evaporate at room temperature for one week. Pale yellow crystalline particles precipitated in the vial. The precipitate was filtered, washed, and dried to obtain the complex crystals. The calculated yield was approximately 82%. EA (%) C 37 H 58 N4O 18 Y3. Calc: C, 35.39; H, 4.62; N, 4.46; Found: C, 35.46; H, 4.43; N, 4.57. IR (KBr, ν, cm -1), 1599(s), 1553(m), 1455(m), 1391(w), 1298(s), 741(s).

[0074] Example 4

[0075] 3.023 g (0.02 mol) of 3-amino-2-hydroxyacetophenone was added to a round-bottom flask, followed by 80 mL of methanol solution. Then, 0.743 g (0.01 mol) of 1,3-propanediamine was added and mixed thoroughly. The mixture was heated under reflux in an oil bath at 55 °C for 5 h, during which the solution changed from black to yellow. After cooling, the solution was filtered to obtain a yellow solid, intermediate M, with a calculated yield of 85%.

[0076] 1.7 g (0.005 mol) of the intermediate was added to a round-bottom flask, along with 1.521 g (0.01 mol) of o-vanillin and an appropriate amount of methanol solution. The mixture was thoroughly mixed and heated under reflux at 60 °C for 6 h. A red solution was obtained, which was cooled and filtered to obtain a red solid, namely the Schiff base ligand H4L, with a calculated yield of 90%.

[0077] 0.03 g (0.05 mmol) of Schiff base ligand H4L was placed in a 10 mL sample vial, followed by 2 mL of methanol solution and 2 mL of acetonitrile solution. Then, 0.074 g (0.2 mmol) of GdCl3·6H2O was added, along with 40 μL of triethylamine solution. The mixture was thoroughly mixed. The vial was sealed with plastic wrap, punctured, and allowed to evaporate at room temperature for one week. Pale yellow crystalline particles precipitated inside the vial. The precipitate was filtered, washed, and dried to obtain the rare earth metal catalyst.

[0078] Example 5

[0079] 3.023 g (0.02 mol) of 3-amino-2-hydroxyacetophenone was added to a round-bottom flask, followed by 80 mL of methanol solution. Then, 0.743 g (0.01 mol) of 1,3-propanediamine was added and mixed thoroughly. The mixture was heated under reflux in an oil bath at 55 °C for 5 h, during which the solution changed from black to yellow. After cooling, the solution was filtered to obtain a yellow solid, intermediate M, with a calculated yield of 85%.

[0080] 1.7 g (0.005 mol) of the yellow solid obtained from the intermediate was added to a round-bottom flask, along with 1.521 g (0.01 mol) of o-vanillin and an appropriate amount of methanol solution. The mixture was thoroughly mixed and heated under reflux at 60 °C for 6 h. A red solution was obtained, which was cooled and filtered to obtain a red solid, namely the Schiff base ligand H4L, with a calculated yield of 90%.

[0081] 0.03 g (0.05 mmol) of Schiff base ligand H4L was placed in a 10 mL sample vial, followed by 2 mL of methanol solution and 2 mL of acetonitrile solution. Then, 0.075 g (0.2 mmol) of DyCl3·6H2O was added, along with 40 μL of triethylamine solution. The mixture was thoroughly mixed. The vial was sealed with plastic wrap, punctured, and allowed to evaporate at room temperature for one week. Pale yellow crystalline particles precipitated in the vial. The precipitate was filtered, washed, and dried to obtain the rare earth metal catalyst.

[0082] Example 6

[0083] 3.023 g (0.02 mol) of 3-amino-2-hydroxyacetophenone was added to a round-bottom flask, followed by 80 mL of methanol solution. Then, 0.743 g (0.01 mol) of 1,3-propanediamine was added and mixed thoroughly. The mixture was heated under reflux in an oil bath at 55 °C for 5 h, during which the solution changed from black to yellow. After cooling, the solution was filtered to obtain a yellow solid, intermediate M, with a calculated yield of 85%.

[0084] 1.7 g (0.005 mol) of the intermediate was added to a round-bottom flask, along with 1.521 g (0.01 mol) of o-vanillin and an appropriate amount of methanol solution. The mixture was thoroughly mixed and heated under reflux at 60 °C for 6 h. A red solution was obtained, which was cooled and filtered to obtain a red solid, namely the Schiff base ligand H4L, with a calculated yield of 90%.

[0085] 0.03 g (0.05 mmol) of Schiff base ligand H4L was placed in a 10 mL sample vial, followed by 2 mL of methanol solution and 2 mL of acetonitrile solution. Then, 0.074 g (0.2 mmol) of TbCl3·6H2O was added, along with 40 μL of triethylamine solution. The mixture was thoroughly mixed. The vial was sealed with plastic wrap, punctured, and allowed to evaporate at room temperature for one week. Pale yellow crystalline particles precipitated in the vial. The precipitate was filtered, washed, and dried to obtain the rare earth metal catalyst.

[0086] Example 7

[0087] 3.023 g (0.02 mol) of 3-amino-2-hydroxyacetophenone was added to a round-bottom flask, followed by 80 mL of methanol solution. Then, 0.743 g (0.01 mol) of 1,3-propanediamine was added and mixed thoroughly. The mixture was heated under reflux in an oil bath at 55 °C for 5 h, during which the solution changed from black to yellow. After cooling, the solution was filtered to obtain a yellow solid, intermediate M, with a calculated yield of 85%.

[0088] 1.7 g (0.005 mol) of the intermediate was added to a round-bottom flask, along with 1.521 g (0.01 mol) of o-vanillin and an appropriate amount of methanol solution. The mixture was thoroughly mixed and heated under reflux at 60 °C for 6 h. A red solution was obtained, which was cooled and filtered to obtain a red solid, namely the Schiff base ligand H4L, with a calculated yield of 90%.

[0089] 0.03 g (0.05 mmol) of Schiff base ligand H4L was placed in a 10 mL sample vial, followed by 2 mL of methanol solution and 2 mL of acetonitrile solution. Then, 0.073 g (0.2 mmol) of EuCl3·6H2O was added, and 40 μL of triethylamine solution was added. The mixture was thoroughly mixed. The vial was sealed with plastic wrap, punctured, and allowed to evaporate at room temperature for one week. Pale yellow crystalline particles precipitated in the vial. The precipitate was filtered, washed, and dried to obtain the rare earth metal catalyst.

[0090] See Figure 6 The Schiff base ligand H4L prepared in Example 1 was subjected to infrared spectroscopy at 3000 cm⁻¹. -1 The peaks on the left and right are absorption peaks of the CH stretching vibration on the benzene ring, at 1604 cm⁻¹. -1 This is the stretching vibration of the characteristic C=N group of a Schiff base, 1520 cm⁻¹. -1 and 1453cm -1 The peak at 1349 cm⁻¹ represents the vibrational peak of the C=C skeleton on the benzene ring. -1 The characteristic peak of CN is at 1245 cm⁻¹. -1 The peak at 1071 cm⁻¹ represents the Ar-O stretching vibration of aromatic ethers. -1 This is the OC stretching vibration peak on aromatic ethers, 838 cm⁻¹ -1 The peak at 730 cm⁻¹ represents the out-of-plane bending vibration of the CH group on the benzene ring. -1 The absorption peak is due to the out-of-plane bending vibration of the phenolic hydroxyl group, indicating that the Schiff base ligand has been successfully synthesized.

[0091] See Figure 7 and Figure 8 The Schiff base ligand prepared in Example 1 was subjected to H-spectrum, C-spectrum, and NMR analysis. The proton NMR spectrum can be interpreted as follows: 1 ¹H NMR (400MHz, DMSO-d6) δ (ppm): 10.22 (s, 1H, Ar-OH), 9.11 (s, 1H, CN=CH), 6.62–7.56 (m, 6H, Ar-CH), 3.73–3.80 (m, 3H, -CH3), 2.47 (m, 3H, O=C-CH3); The carbon NMR spectrum can be resolved as follows: 13CNMR (100MHz, DMSO) δ175.17, 174.39, 163.28, 161.17, 154.31, 152.80, 14 8.98, 138.85, 136.25, 128.53, 124.28, 124.16, 123.64, 119.55, 119.32, 11 8.82, 118.60, 117.69, 117.01, 116.48, 116.05, 115.42, 114.55, 69.54, 69. 13, 62.65, 56.27, 51.65, 40.65, 40.35, 40.14, 39.72, 39.51, 39.30, 15.24. Furthermore, the successful synthesis of Schiff base ligand H4L was confirmed.

[0092] See Figure 9 Infrared spectroscopy measurements were performed on different rare earth metal catalysts and Schiff base ligands in Examples 1 to 3. In the figures: H4L represents the Schiff base ligand; 1 represents the rare earth metal catalyst prepared with ErCl3·6H2O as the rare earth metal chloride; 2 represents the rare earth metal catalyst prepared with YbCl3·6H2O as the rare earth metal chloride; and 3 represents the rare earth metal catalyst prepared with YCl3·6H2O as the rare earth metal chloride. The results showed that their infrared spectra were essentially identical, indicating that their coordination structures were the same. Compared with the infrared spectrum of the catalyst and the Schiff base ligand H4L, the infrared spectrum at a wavelength of 1599 cm⁻¹... -1 The peak at 1298 cm⁻¹ is likely due to the blue shift caused by the coordination of the C=N group on the Schiff base ligand H₄L with the metal ion. -1 The peak at 741 cm⁻¹ represents the Ar-O stretching vibration peak of aromatic ethers. -1 The peak at 1553 cm⁻¹ represents the bending vibration of the phenolic hydroxyl group. Compared to the peak position of H₄L, it has undergone a red shift, indicating that the O on the phenolic hydroxyl group of H₄L has coordinated with the metal ion. -1 and 1455cm -1 The peak at 1391 cm⁻¹ is the vibrational peak of the C=C skeleton on the benzene ring. -1 The peak at that location is a characteristic peak of CN.

[0093] See Figure 10Thermogravimetric analysis (TGA) was performed on different rare earth metal catalysts in Examples 1 to 3 to evaluate their thermal stability. In the figures: 1 represents the rare earth metal catalyst prepared with ErCl3·6H2O as the rare earth metal chloride, 2 represents the rare earth metal catalyst prepared with YbCl3·6H2O as the rare earth metal chloride, and 3 represents the rare earth metal catalyst prepared with YCl3·6H2O as the rare earth metal chloride. It can be seen that in the TGA curves within the range of 30℃ to 800℃, the mass of the complex decreased by 5.79% between 60℃ and 100℃, which is attributed to the vaporization of free methanol molecules in the crystals due to the increased temperature. The mass decreased again when the temperature increased to 180℃, which is attributed to the loss of free water molecules in the complex. When the temperature increased from 480℃ to 700℃, the mass decreased by 12%, which may be due to the decomposition of coordinated methanol and water molecules in the complex. Finally, the remaining mass should be ligands and metal ions. It can be inferred that the structure of the complex did not change before being heated to 200℃, indicating that this type of catalyst has high thermal stability and great potential as a catalyst.

[0094] A butterfly-shaped trinuclear Schiff base rare earth metal catalyst was prepared using the method described above. The smallest structural unit of this catalyst comprises one Schiff base ligand and three rare earth metal ions. The complex has a symmetrical structure, belongs to the monoclinic crystal system, and has a C2 / c space group. In the complex, M1 and M2 have the same coordination environment, both forming an octet structure with the two phenolic hydroxyl groups (O), the imine group (N), the methanol molecule (O), the two H2O molecules (O), and the two hydroxide ions (O). M3 forms an octet structure with the two phenolic hydroxyl groups (O), the two methoxy groups (O), the two hydroxide ions (O), and the two water molecules (O) on the Schiff base ligand. This catalyst exhibits good catalytic stability, high catalytic efficiency and conversion rate, and low catalytic cost.

[0095] The application of the butterfly-shaped trinuclear Schiff base in the catalytic synthesis of cyclic carbonates, as described above. A cycloaddition reaction is carried out using a butterfly-shaped trinuclear Schiff base rare earth metal catalyst as the catalyst, tetrabutylammonium bromide as the co-catalyst, and epoxides and carbon dioxide as the reaction substrates to obtain cyclic carbonates. The epoxide is epichlorohydrin, allyl glycidyl ether, styrene oxide, butyl glycidyl ether, or phenyl glycidyl ether. The cycloaddition reaction time is 1–3 h, the reaction temperature is 60℃–120℃, the conversion rate reaches 99%, and the molar ratio of epoxide, catalyst, and co-catalyst is 1000:(0.4–1):(2–8).

[0096] Example 8

[0097] The effects of different metal ions on catalytic efficiency were investigated. Taking the cycloaddition reaction of styrene oxide with carbon dioxide as an example, 10 mmol of styrene oxide, 0.1 mol% of rare earth metal catalyst and 0.8 mol% of tetrabutylammonium bromide (TBAB) co-catalyst were added to a high-pressure reactor. The gas in the reactor was circulated and purged three times to eliminate interference from other gases. Then the reaction was carried out at 120 °C and 1.0 MPa CO2 for 2 h.

[0098] The catalytic effects are shown in the table below:

[0099] Catalytic efficiency of the catalyst in the reaction of CO2 and styrene oxide

[0100]

[0101] This shows that the catalytic conversion rates of the catalyst were 89%, 88%, and 89%, with TOF values ​​of 445 h⁻¹. -1 440h -1 445h -1 The catalytic activities are not significantly different. Therefore, the catalytic efficiencies of different rare earth metal complexes for the cycloaddition reactions of carbon dioxide and styrene oxide are similar. In the table, 1 represents a rare earth metal catalyst prepared with ErCl3·6H2O as the rare earth metal chloride, 2 represents a rare earth metal catalyst prepared with YbCl3·6H2O as the rare earth metal chloride, and 3 represents a rare earth metal catalyst prepared with YCl3·6H2O as the rare earth metal chloride.

[0102] Example 9 investigates the effects of temperature, pressure, reaction time, catalyst dosage, co-catalyst dosage, water, and air on the catalytic effect in the reaction. The following experiments were conducted.

[0103] Catalytic performance of rare earth metal catalyst 1 in the cycloaddition of carbon dioxide and styrene oxide

[0104]

[0105]

[0106] The experimental data in the table show that when 10 mmol of styrene oxide and 1 MPa of CO2 react at 80℃ for 4 hours, the conversion rate is almost 0 when only a catalyst is added, and 19% when only a co-catalyst is added. The conversion rate increases to 99% when both catalyst and co-catalyst are present, indicating that synergistic catalysis by both catalyst and co-catalyst is necessary to effectively promote the reaction. With other conditions unchanged, the conversion rate is 94% when reacting at 120℃ for 2 hours. As the temperature decreases from 100℃ to 80℃, the conversion rate decreases from 89% to 85%. At 60℃, the conversion rate decreases significantly to 70%. Therefore, the optimal reaction temperature is 80℃. When the pressure decreases from 1 MPa to 0.4 MPa, the conversion rate also decreases from 85% to 52%, indicating that pressure has a significant impact on the catalytic effect of the reaction. When the reaction time was increased from 1 h to 4 h in 1 h increments, the conversion rate increased from 68% to 99%. The conversion rates at 3 h and 4 h were not significantly different, at 98% and 99% respectively; therefore, 3 h was selected as the optimal reaction time. The highest conversion rate (98%) was achieved at a catalyst dosage of 0.01 mmol. The conversion rates of the co-catalyst TBAB at low loadings (0.04 mmol and 0.02 mmol) were 60% and 42%, respectively. Furthermore, adding additional water to the reaction system or not removing air from the system had no significant effect on the conversion rate, indicating that the catalytic system prepared in this invention has good tolerance.

[0107] Based on the above experimental results and in line with the concept of high efficiency and energy saving, the following conditions were selected: temperature 80℃, pressure 1MPa, time 3h, catalyst dosage 0.01mmol, and co-catalyst dosage 0.08mmol, to investigate the effect of the catalyst on the catalytic efficiency of the cycloaddition reaction of carbon dioxide and epoxide.

[0108] Example 10

[0109] To investigate the universality of the catalytic system for the cycloaddition reactions of different epoxides and carbon dioxide. Four epoxides with different substituents were selected as substrates, and catalytic experiments were conducted under the following conditions: temperature 80℃, pressure 1 MPa, reaction time 3 h, and catalyst and co-catalyst dosages of 0.01 mmol and 0.08 mmol, respectively. See [link to relevant documentation]. Figures 11 to 14 The product was analyzed by proton nuclear magnetic resonance spectroscopy, which showed that the rare earth metal catalyst had good catalytic effect and improved the product synthesis efficiency.

[0110] In summary, this invention provides a butterfly-shaped trinuclear Schiff base rare earth metal catalyst, its preparation method, and its application. This method uses Schiff base ligands and rare earth metal chlorides as raw materials, reacting at room temperature, followed by the addition of triethylamine to obtain the butterfly-shaped trinuclear Schiff base rare earth metal catalyst. The reaction conditions are mild, requiring no harsh reaction environment or equipment. The raw materials are widely available and low-cost, with a short reaction time and high yield, making it suitable for industrialization. It effectively controls production input costs while improving production efficiency and yield. Furthermore, the produced rare earth metal catalyst exhibits better stability, higher catalytic efficiency, and is unaffected by additional moisture and air, demonstrating good tolerance and significantly reducing the conditions required for the catalytic reaction, thereby lowering catalytic costs.

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

Claims

1. A butterfly-shaped trinuclear Schiff base rare earth metal catalyst, characterized in that, Its cationic molecular structure is: Among them, M1 to M3 are rare earth metal ions.

2. The butterfly-shaped trinuclear Schiff base rare earth metal catalyst according to claim 1, characterized in that, The rare earth metal ion is Sc. 3+ Y 3+ Ce 3+ 、Nd 3+ 、Sm 3+ Gd 3+ Eu 3+ 、Tb 3+ Dy 3+ Er 3+ Ho 3+ Tm 3+ or Yb 3+ .

3. A method for preparing a butterfly-shaped trinuclear Schiff base rare earth metal catalyst, characterized in that, include: Preparation of Schiff base ligands; A butterfly-shaped trinuclear Schiff base rare earth metal catalyst was prepared using Schiff base ligands and rare earth metal chlorides. The cationic molecular formula of the butterfly-shaped trinuclear Schiff base rare earth metal catalyst is as follows: Among them, M1 to M3 are rare earth metal ions; The molecular structural formula of the Schiff base ligand is: The preparation method is as follows: The intermediate was obtained by reacting 1,3-propanediamine and 3-amino-2-hydroxyacetophenone. The intermediate was reacted with o-vanillin to give the Schiff base ligand.

4. The method for preparing the butterfly-shaped trinuclear Schiff base rare earth metal catalyst according to claim 3, characterized in that, The rare earth metal chloride salts are ScCl3·6H2O, YCl3·6H2O, CeCl3·6H2O, NdCl3·6H2O, SmCl3·6H2O, GdCl3·6H2O, EuCl3·6H2O, TbCl3·6H2O, DyCl3·6H2O, ErCl3·6H2O, HoCl3·6H2O, TmCl3·6H2O, or YbCl3·6H2O.

5. The method for preparing the butterfly-shaped trinuclear Schiff base rare earth metal catalyst according to claim 3, characterized in that, The method for preparing butterfly-shaped trinuclear Schiff base rare earth metal catalysts using Schiff base ligands and rare earth metal chlorides is as follows: Schiff base ligands and rare earth metal chlorides were dissolved in a solvent, and triethylamine was added. The reaction was carried out at room temperature to obtain a butterfly-shaped trinuclear Schiff base rare earth metal catalyst.

6. A butterfly-shaped trinuclear Schiff base rare earth metal catalyst, characterized in that, Prepared using the method described in any one of claims 3-5.

7. The application of the butterfly-shaped trinuclear Schiff base rare earth metal catalyst as described in claim 6 in the preparation of cyclic carbonates.

8. The application of the butterfly-shaped trinuclear Schiff base rare earth metal catalyst according to claim 7 in the preparation of cyclic carbonates, characterized in that, A cycloaddition reaction was carried out using a butterfly-shaped trinuclear Schiff base rare earth metal catalyst as the catalyst, tetrabutylammonium bromide as the co-catalyst, and epoxide and carbon dioxide as the reaction substrates to obtain cyclic carbonates. The epoxide was epichlorohydrin, allyl glycidyl ether, styrene oxide, butyl glycidyl ether, or phenyl glycidyl ether. The cycloaddition reaction time was 1-3 h, the reaction temperature was 60℃-120℃, the conversion rate reached 99%, and the molar ratio of epoxide, catalyst, and co-catalyst was 1000:(0.4-1):(2-8).

Images