CN114891035A - Difunctional tetranuclear metal lithium complex and preparation method and application thereof - Google Patents

Abstract

The invention discloses a bifunctional tetranuclear metal lithium complex, a preparation method and application, and belongs to the technical field of complex synthesis. The bifunctional metal lithium complex is applied to catalyze the polymerization of lactide and the degradation of polylactide, and the specific method includes: mixing and stirring the lactide and the catalyst according to the proportion, and performing a ring-opening polymerization reaction under anhydrous, oxygen-free and gas protection, Finally, polylactide is obtained; after adding methanol to the system, the degradation product of polylactide can be obtained at room temperature. The method of the invention has simple steps, strong controllability and low cost, can obtain a biodegradable polyester material with better performance, and can degrade the waste polyester material into a green solvent. The degradable plastic obtained by the invention meets the requirements of green development and has broad application prospects. In the polymerization process, the characteristics of "highly controllable", "living" and "multi-functional" are realized, and at the same time, the chemical recovery of polyester materials into high value-added chemicals can be realized to achieve the effect of recycling.

Description

A kind of bifunctional tetranuclear metal lithium complex and preparation method and application

technical field

The invention belongs to the technical field of complex synthesis, in particular to a bifunctional tetranuclear metal lithium complex and a preparation method and application.

Background technique

Since the first commercial production of polyethylene in the 1930s, many high molecular polymers have become an integral part of modern life, and they are widely used in polyesters, polyolefins, silicones and others for engineering and rubber applications. Although these materials are widely used for their excellent mechanical properties and durability, their long-term degradation time due to the handling of these plastic articles has drawn global attention to the increasing environmental pollution. The European Union has decided to ban or restrict the use of certain consumer products that contain persistent, non-degradable and toxic substances. The "China 21st Century Agenda" formulated by the Chinese government pointed out: "Taking the road of sustainable development is China's own needs and inevitable choice in the future and the next century." Therefore, we are all looking for greener alternatives and focusing on research on material degradation.

Furthermore, with the rapid depletion of fossil feedstocks on Earth, the development of alternative biodegradable polymers (preferably from sustainable sources) is a necessity. Currently, polylactide (PLA) has taken the lead in this field due to its excellent biodegradability and biocompatibility, making it an environmentally friendly alternative to traditional petrochemical synthetic polymers. To date, the polymerization of lactide has been studied in a variety of existing catalysts, including main group metal complexes, transition metals, rare earth metals, alkali/alkaline earth metals, and non-metallic organocatalysts. PLA is generally synthesized by metal-catalyzed ring-opening polymerization (ROP). The current problem is how to modify the degradable material catalyst and polyester material to expand the application scope of cyclic ester materials such as biomedicine such as sutures and drug carriers. , commodity packaging materials and gene delivery vectors. At the same time, the way of recycling plastics has also been challenged. At present, most of them still use landfill or other dumping methods. For unreasonable recycling, we need to innovate and develop alternative strategies that can economically transform plastic waste into valuable products and enable efficient recycling to meet the daunting challenges facing modern society.

In order to realize a circular economy, further developing catalysts and realizing multifunctional catalysis is an effective way to obtain PLA, a biodegradable material with better performance, and is also the key to solving the problem of chemical degradation of discarded degradable plastic PLA.

SUMMARY OF THE INVENTION

Aiming at the problems that some polyester catalysts have biological toxicity and poor polymerization controllability, and most of the catalysts cannot realize polylactide depolymerization, the present invention provides a bifunctional tetranuclear metal lithium complex and a preparation method and application.

The purpose of the present invention is to provide a bifunctional tetranuclear metal lithium complex catalyst with few side reactions, high conversion rate, good selectivity and dual functions of catalysis, and a synthesis method and application thereof.

In order to achieve the above object, the present invention has adopted the following technical solutions:

A bifunctional tetranuclear metal lithium complex, the structural formula of the bifunctional tetranuclear metal lithium complex is:

α＝90(13)°，β＝104.358(5)°，γ＝90°。The crystal of the bifunctional tetranuclear metal lithium complex belongs to the monoclinic system, the C 2/c space group, and the unit cell parameters are:

α=90(13)°, β=104.358(5)°, γ=90°.

A preparation method of a bifunctional tetranuclear metal lithium complex, the synthetic route is as follows:

It includes the following steps: dissolving the silicon-bridged aminoquinaldine in ether, and under the condition of anhydrous and oxygen-free at 0 °C, while stirring, dropwise add n-butyllithium in an equimolar amount with the silicon-bridged aminoquinaldine , then returned to room temperature, stirred continuously for 3 to 8 hours, after the reaction was completed, left standing, filtered to remove the filtrate, washed with n-hexane for several times and purified, the filtrate was concentrated and crystallized to obtain a bifunctional tetranuclear metal lithium complex.

Further, the specific method of the crystallization is to dissolve the obtained solid product in tetrahydrofuran and concentrate, and it must be placed at a low temperature of -30°C under nitrogen protection to precipitate crystals.

Further, the concentration of the n-butyllithium is 2.5mol/L.

Application of a bifunctional tetranuclear metal lithium complex for lactide polymerization and polylactide degradation.

Further, under the condition of no cocatalyst or co-catalyzed with the cocatalyst benzyl alcohol, the lactide polymerization product is obtained in dichloromethane solvent.

Further, the lactide is polymerized under an inert atmosphere at room temperature of 20 to 30°C.

Further, the molar ratio of the lactide to the bifunctional tetranuclear metal lithium complex is 100:1 to 400:1.

Further, under the condition of co-catalysis with methanol, the degradation product of polylactide is obtained in dichloromethane solvent.

Further, under the condition of co-catalysis with methanol, the specific method for obtaining the degradation product of polylactide in a dichloromethane solvent is: preparing an oil bath whose temperature is stable at 20-30 °C; under an inert atmosphere, accurately weigh Amount of complex, add in the A bottle with stirring bar, then add dichloromethane to dissolve completely; Under the same conditions, prepare B bottle, and be 100 by the molar ratio of lactide and bifunctional tetranuclear metal lithium complex: 1 Add bottle B and dissolve in dichloromethane; add the mixed monomer in bottle B to bottle A with constant rotation speed, and monitor in real time to ensure complete polymerization; then at 600 rpm, mix polylactide and methanol with a molar ratio of 10 : 1 was added; every 10 min was sampled to measure ¹ HNMR, the depolymerization reaction was monitored in real time, and the polylactide was completely degraded into methyl lactate after waiting for 1 h.

Compared with the prior art, the present invention has the following advantages:

The bifunctional tetranuclear metal lithium complex of the invention has the characteristics of non-toxicity, high efficiency and controllability as a catalyst, the monomer conversion rate in the polymerization process is all higher than 90%, and polypropylene with controllable molecular weight and narrow molecular weight distribution can be obtained. Lactide. At the same time, the biodegradable plastics can be degraded and recycled, and the multifunctional catalytic degradation can be obtained into a green solution to achieve an economical green cycle.

Description of drawings

FIG. 1 is a single crystal X-ray structure diagram of the bifunctional tetranuclear metal lithium complex of the present invention.

Detailed ways

All reactions were carried out under the protection of high purity nitrogen or argon dried over a potassium column using standard reaction techniques.

Example 1: Synthesis of a bifunctional tetranuclear metal lithium complex

Under anhydrous and anaerobic conditions, to a solution of silicon-bridged aminoquinaldine (1.19 g, 3.20 mmol) in ether (20 mL), at 0 °C, while stirring, was added dropwise ⁿ BuLi (3.00 mL, 2.5 M of n-hexane solution, 6.40 mmol). The solution immediately became cloudy. Return to room temperature, continue stirring for 3 hours, and then purify by washing with n-hexane for several times to obtain 1.18 g of a yellow solid with a yield of 81%.

Example 2: Synthesis of a Bifunctional Tetranuclear Metal Lithium Complex

Under anhydrous and anoxic conditions, to a solution of silicon-bridged aminoquinaldine (1.19 g, 3.20 mmol) in ether (30 mL), at 0°C, while stirring, was added dropwise ⁿ BuLi (3.00 mL, 2.5 M of n-hexane solution, 6.40 mmol). The solution immediately became cloudy. Return to room temperature, continue stirring for 8 hours, and then purify by washing with n-hexane for several times to obtain 1.18 g of a yellow solid with a yield of 81%.

The test results of the products of above-mentioned embodiment 1 and embodiment 2 gained are identical, specifically see the following:

¹ H NMR (600 MHz, C ₆ D ₆ ): δ 7.52 (d, J=8.7 Hz, 5H, ArH), 7.41 (s, 2H, ArH), 7.38 (t, J=7.7 Hz, 2H, ArH) ,7.07(t,J=8.1Hz,1H,ArH),6.94(d,J=8.1Hz,4H,ArH),6.80(s,2H,ArH),6.77(d,J=8.4Hz,2H,ArH) ), 6.40(m, 2H, ArH), 3.33(m, 8H, THF), 2.51(s, 3H, CH ₃ ), 1.89(s, 4H, CH ₃ ), 1.28(m, 8H, THF), 0.88 (s, 5H, CH ₃ ), 0.45 (s, 6H, SiMe ₂ ), 0.30 (s, 6H, SiMe ₂ ). ¹³ C NMR (151 MHz, C ₆ D ₆ ) δ 158.75, 155.41, 155.32, 146.56, 139.10, _{137.71,136.08,121.66,121.21,117.48,115.58,110.87,109.42,67.36,45.63,25.23,24.68,23.88,4.29,2.07,1.02} , _{-1.87.Anal.calcd} for C O ₅₂ H ₆₀ Li ₄ N ₂ : C; 68.41; H; 6.62; N; 12.27. Found: C; 68.35; H, 6.74; N, 12.25.

Example 3 Structure determination of bifunctional tetranuclear metal lithium complexes

作为辐射光源。使用SMART软件确定晶胞参数，通过SADABS程序进行吸收校正。晶体结构使用SHELXS-2014程序采用直接法解出，并采用全矩阵最小二乘法基于F²进行精修，理论加氢确定所有H原子位置。晶体结构见图1，晶体学测定数据见表1。Select crystals of suitable size and collect crystal data at room temperature using Bruker Apex II CCD diffractometer, graphite monochromator Mo-Kα

as a radiation source. The unit cell parameters were determined using SMART software, and absorption correction was performed by the SADABS program. The crystal structure was solved by the direct method using the SHELXS-2014 program, and refined based on F2 by the full ^- matrix least squares method, and all H atom positions were determined by theoretical hydrogenation. The crystal structure is shown in Figure 1, and the crystallographic measurement data is shown in Table 1.

Table 1 Crystallographic data of bifunctional tetranuclear metal lithium complexes

Li(1)-O(1),2.028(7)；Li(1)-N(1),2.118(4)；Li(1)-N(2),2.118(4)；Li(1)-N(5),2.391(2)；Li(1)-N(8),2.391(2)；Li(2)-N(1),2.076(5)；Li(2)-N(4)`,2.097(5)；Li(2)-N(7),2.003(5)；Li(2)-N(8),2.164(5)；Li(3)-O(1),1.932(7)；Li(3)-N(3),2.039(4)；Li(3)-N(4),2.039(4)；Li(4)-N(2),2.076(5)；Li(4)-N(6),2.097(5)；Li(4)-N(4),2.003(5)；Li(4)-N(5),2.164(5)；Partial bond length

Li(1)-O(1), 2.028(7); Li(1)-N(1), 2.118(4); Li(1)-N(2), 2.118(4); Li(1)- N(5), 2.391(2); Li(1)-N(8), 2.391(2); Li(2)-N(1), 2.076(5); Li(2)-N(4)` , 2.097(5); Li(2)-N(7), 2.003(5); Li(2)-N(8), 2.164(5); Li(3)-O(1), 1.932(7) ; Li(3)-N(3), 2.039(4); Li(3)-N(4), 2.039(4); Li(4)-N(2), 2.076(5); Li(4) -N(6), 2.097(5); Li(4)-N(4), 2.003(5); Li(4)-N(5), 2.164(5);

Partial bond angle (°): N(1)-Li(1)-O(1): 81.7(5); N(2)-Li(1)-N(1): 114.3(2); N(1) )-Li(1)-N(2): 113.98(12); Li(1)-N(1)-Li(2): 51.08(11); Li(2)-N(4)-Li(3 ): 89.4(2); N(3)-Li(3)-N(4): 122.8(3); Li(3)-N(3)-Li(4): 44.06(14).

Example 4: Application of a bifunctional tetranuclear metal lithium complex catalyst

Under nitrogen protection, the compound of Example 1 above (0.05mmol) was added to the reaction flask, and then 5mL of dichloromethane solution was added, and then 5mmol of lactide monomer solution was accurately added to keep the monomer: catalyst: co-agent Catalyst=100:1:0, and the temperature was controlled at 30°C under stirring. After 4 hours of reaction, 0.1 mL of the reaction solution was taken and analyzed by 600 M NMR. At the same time, 3 drops of glacial acetic acid was added to terminate the reaction, then 200 mL of methanol was added to precipitate the product to obtain a white polymer, the supernatant was filtered, and an appropriate amount of methanol was added to fully wash the precipitate. The calculated conversion was 99%, and the molecular weight distribution was PDI=1.60. The PDIs were all detected by GPC.

Example 5: Application of a bifunctional tetranuclear metal lithium complex catalyst

Under nitrogen protection, the compound described in Example 1 (0.05 mmol) was added to the reaction flask, 5 mL of dichloromethane solution was added, and then 50 μmol of cocatalyst benzyl alcohol was added, and the reaction was stirred for 30 min for pre-reaction. Subsequently, 5 mmol of lactide monomer solution was accurately added to keep monomer:catalyst:cocatalyst=100:1:1, and the temperature was controlled at 20°C under stirring. After 4 hours of reaction, 0.1 mL of the reaction solution was taken and analyzed by 600 M NMR. At the same time, 3 drops of glacial acetic acid was added to terminate the reaction, then 200 mL of methanol was added to precipitate the product to obtain a white polymer, the supernatant was filtered, and an appropriate amount of methanol was added to fully wash the precipitate. The calculated conversion was 98%, and the molecular weight distribution PDI=1.18. The PDIs were all detected by GPC.

Example 6: Application of a bifunctional tetranuclear metal lithium complex catalyst

Under nitrogen protection, the compound described in Example 1 (0.05 mmol) was added to the reaction flask, 5 mL of dichloromethane solution was added, and then 50 μmol of cocatalyst benzyl alcohol was added, and the reaction was stirred for 30 min for pre-reaction. Subsequently, 5mmol of lactide monomer solution was accurately added, keeping monomer:catalyst:cocatalyst=100:1:1, and the temperature was controlled at 30°C under stirring. After 4 hours of reaction, 0.1 mL of the reaction solution was taken and analyzed by 600 M NMR. At the same time, 3 drops of glacial acetic acid were added to terminate the reaction, then 200 mL of methanol was added to precipitate the product to obtain a white polymer, the supernatant was filtered, and an appropriate amount of methanol was added to fully wash the precipitate. The calculated conversion was 98%, and the molecular weight distribution PDI=1.19. The PDIs were all detected by GPC.

Example 7: Application of a bifunctional tetranuclear metal lithium complex catalyst

Under nitrogen protection, the compound described in Example 1 (0.05 mmol) was added to the reaction flask, 5 mL of dichloromethane solution was added, and then 50 μmol of cocatalyst benzyl alcohol was added, and the reaction was stirred for 30 min for pre-reaction. Subsequently, 10 mmol of lactide monomer solution was accurately added, keeping monomer:catalyst:cocatalyst=200:1:1, and the temperature was controlled at 30°C under stirring. After 4 hours of reaction, 0.1 mL of the reaction solution was taken and analyzed by 600 M NMR. At the same time, 3 drops of glacial acetic acid was added to terminate the reaction, then 200 mL of methanol was added to precipitate the product to obtain a white polymer, the supernatant was filtered, and an appropriate amount of methanol was added to fully wash the precipitate. The calculated conversion was 99%, and the molecular weight distribution was PDI=1.21. The PDIs were all detected by GPC.

Example 8: Application of a bifunctional tetranuclear metal lithium complex catalyst

Under nitrogen protection, the compound described in Example 1 (0.05 mmol) was added to the reaction flask, 5 mL of dichloromethane solution was added, and then 50 μmol of cocatalyst benzyl alcohol was added, and the reaction was stirred for 30 min for pre-reaction. Subsequently, 20 mmol of lactide monomer solution was accurately added, keeping monomer:catalyst:cocatalyst=400:1:1, and the temperature was controlled at 30°C under stirring. After 4 hours of reaction, 0.1 mL of the reaction solution was taken and analyzed by 600 M NMR. At the same time, 3 drops of glacial acetic acid were added to terminate the reaction, then 200 mL of methanol was added to precipitate the product to obtain a white polymer, the supernatant was filtered, and an appropriate amount of methanol was added to fully wash the precipitate. The calculated conversion was 98%, and the molecular weight distribution was PDI=1.30. The PDIs were all detected by GPC.

Example 9: Application of a bifunctional tetranuclear metal lithium complex catalyst

An oil bath with a stable temperature of 20° C. was prepared in advance. Under nitrogen protection, the compound described in Example 1 (0.05 mmol) was added to a Schlenk bottle equipped with a stirrer, and 5 mL of dichloromethane was added to dissolve it completely. Subsequently, the lactide monomer was added in the ratio of [LA]:[Cat]=100:1, and ¹ HNMR was measured every 1 h, and the polymerization reaction was monitored in real time. After waiting for 4 h, the conversion rate exceeded 99%. Subsequently, 2.0 mL of MeOH (n _PLA : n _MeOH = 10:1) was added, and the depolymerization reaction was monitored in real time. After waiting for 1 hour, the conversion rate exceeded 99%, and the polylactide was completely degraded to methyl lactate (Me-La).

Example 10: Application of a bifunctional tetranuclear metal lithium complex catalyst

An oil bath with a stable temperature of 30° C. was prepared in advance. Under nitrogen protection, the compound described in Example 1 (0.05 mmol) was added to a Schlenk bottle equipped with a stirrer, and 5 mL of dichloromethane was added to dissolve it completely. Subsequently, the lactide monomer was added in the ratio of [LA]:[Cat]=100:1, and ¹ HNMR was measured every 1 h, and the polymerization reaction was monitored in real time. After waiting for 4 h, the conversion rate exceeded 99%. Subsequently, 2.0 mL of MeOH (n _PLA : n _MeOH = 10:1) was added, and the depolymerization reaction was monitored in real time. After waiting for 1 hour, the conversion rate exceeded 99%, and the polylactide was completely degraded to methyl lactate (Me-La).

Contents that are not described in detail in the specification of the present invention belong to the prior art known to those skilled in the art. Although the illustrative specific embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, As long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the inventive concept are included in the protection list.

Claims (10)

1. A bifunctional tetranuclear lithium metal complex characterized by: the structural formula of the bifunctional tetranuclear metal lithium complex is as follows:

the crystal of the difunctional tetranuclear metal lithium complex belongs to a monoclinic system, a C2/C space group, and the unit cell parameters are as follows:

α＝90(13)°，β＝104.358(5)°，γ＝90°。

2. the method of claim 1, wherein the method comprises the steps of: the method comprises the following steps: dissolving silicon-bridged aminoquinaldine in diethyl ether, dropwise adding n-butyllithium with the same molar weight as the silicon-bridged aminoquinaldine while stirring at 0 ℃ under anhydrous and oxygen-free conditions, then recovering to room temperature, continuously stirring for 3-8 h, standing after the reaction is finished, filtering to remove filtrate, washing and purifying with n-hexane for multiple times, concentrating the filtrate, and crystallizing to obtain the bifunctional tetranuclear lithium metal complex.

3. The method for preparing a bifunctional tetranuclear lithium metal complex according to claim 2, characterized in that: the specific method of the crystallization is to dissolve the obtained solid product in tetrahydrofuran, concentrate the solid product and separate out crystals by placing the solid product at a low temperature of-30 ℃ under the protection of nitrogen.

4. The method of claim 2, wherein the method comprises the steps of: the concentration of the n-butyllithium is 2.5 mol/L.

5. The use of a bifunctional tetranuclear lithium metal complex according to claim 2, characterized in that: the method is applied to lactide polymerization and polylactide degradation.

6. Use according to claim 5, characterized in that: under the condition of no need of cocatalyst or under the condition of cocatalyst and benzyl alcohol co-catalysis, the lactide polymerization product is obtained in dichloromethane solvent.

7. Use according to claim 6, characterized in that: and polymerizing the lactide at room temperature under the inert atmosphere at the temperature of 20-30 ℃.

8. Use according to claim 7, characterized in that: the molar ratio of the lactide to the bifunctional tetranuclear metal lithium complex is 100: 1-400: 1.

9. Use according to claim 5, characterized in that: obtaining degradation products of the polylactide in methylene chloride solvent under the condition of co-catalysis with methanol.

10. Use according to claim 9, characterized in that: the specific method for obtaining the degradation product of the polylactide in the dichloromethane solvent under the co-catalysis condition of the degradation product and the methanol is as follows: preparing an oil bath with the temperature stable at 20-30 ℃; accurately weighing the complex under an inert atmosphere, adding the complex into a bottle A with a stirrer, and adding dichloromethane until the dichloromethane is completely dissolved; preparing a bottle B under the same condition, adding the bottle B according to the molar ratio of lactide to the difunctional tetranuclear metal lithium complex of 100:1, and dissolving the bottle B in dichloromethane; adding the mixed monomer in the bottle B into the bottle A with constant rotating speed, and simultaneously monitoring in real time to ensure complete polymerization; then polylactide and methanol were added at a molar ratio of 10:1 at 600 rpm; sampling every 10min ¹ Monitoring depolymerization reaction in real time once by HNMR, and waiting for 1h to completely degrade polylactide intoIs methyl lactate.

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