Hindered Lewis acid-base pair as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a hindered Lewis acid-base pair as well as a preparation method and application thereof. According to the invention, borane and C2-carbene are utilized to construct the hindered Lewis acid-base pair, and C2-carbene has strong nucleophilicity, so that the hindered Lewis acid-base pair has high catalytic efficiency and catalytic activity, the molecular weight of the obtained polycarbonate is high, and results of embodiments show that the relative molecular weight of the polycarbonate is up to 783 kg / mol. The invention further provides application of the hindered Lewis acid-base pair obtained by the scheme or the hindered Lewis acid-base pair obtained by the preparation method in catalysis of copolymerization of CO2 and an epoxy compound. Carboxycarbene is creatively used for catalyzing polymerization of CO2 and an epoxy compound, the conversion number (TON) is high, the activity is high, and the polycarbonate selectivity is gt; 99%.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a frustrated Lewis pair and its preparation method and application. Background Art

[0002] As a thermoplastic polymer, polycarbonate has good biodegradability and biocompatibility and is widely used in many fields. At present, polycarbonate is mainly prepared by the copolymerization reaction of CO 2 and epoxides. For this reaction route, various different catalytic systems have been developed to achieve the alternating copolymerization of CO 2 and epoxides, including metal catalysts, organic catalytic systems, and intramolecular bifunctional catalytic systems, etc.

[0003] Among them, metal catalysts have relatively high catalytic activity; compared with metal catalysts, an organic catalytic system formed by using triethylboron as a Lewis acid and an organic catalyst has high activity and high selectivity; in addition, there is also an intramolecular bifunctional catalytic system, which utilizes intramolecular synergistic effects to prepare polycarbonate with high activity and high molecular weight.

[0004] Although the above-mentioned catalyst systems have achieved certain catalytic effects, their overall efficiency and activity are still relatively low. Summary of the Invention

[0005] The purpose of the present invention is to provide a frustrated Lewis pair and its preparation method and application, and the catalytic efficiency and catalytic activity of the frustrated Lewis pair provided by the present invention are high.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a frustrated Lewis pair, including a Lewis acid and a Lewis base; the Lewis acid is an organoborane; the Lewis base is a carbene.

[0008] Preferably, the organoborane includes one or more of triethylborane, tributylborane, tricyclohexylborane, and triphenylborane.

[0009] Preferably, the structure of the carbene is as shown in Formula B:

[0010]

[0011] In Formula B, R 1 , R 2 , R 3 and R 4 are independently methyl or propyl.

[0012] Preferably, the carbene includes one of CDC-1 carbene, CDC-2 carbene, CDC-3 carbene, CDC-4 carbene, CDC-5 carbene, CDC-6 carbene, CDC-7 carbene, CDC-8 carbene, CDC-9 carbene, CDC-10 carbene, CDC-11 carbene, CDC-12 carbene, CDC-13 carbene, CDC-14 carbene, CDC-15 carbene, CDC-16 carbene, CDC-17 carbene, CDC-18 carbene, CDC-19 carbene, CDC-20 carbene and CDC-21 carbene.

[0013] Preferably, the molar ratio of the Lewis acid to the Lewis base is not less than 2:1.

[0014] The present invention also provides a method for preparing the sterically hindered Lewis acid-base pair described in the above solution, comprising the following steps:

[0015] Mix the Lewis acid and the Lewis base to obtain the sterically hindered Lewis acid-base pair.

[0016] The present invention also provides the application of the sterically hindered Lewis acid-base pair described in the above solution or the sterically hindered Lewis acid-base pair obtained by the preparation method described in the above solution in the copolymerization of CO 2 and epoxide.

[0017] Preferably, the application comprises the following steps: Mix the epoxide and the sterically hindered Lewis acid-base pair and then introduce CO 2 to carry out bulk polymerization reaction to obtain polycarbonate.

[0018] Preferably, the epoxide includes one or several of the following structures:

[0019]

[0020] Preferably, the molar ratio of the Lewis base to the epoxide in the sterically hindered Lewis acid-base pair is not greater than 1:100.

[0021] The present invention provides a sterically hindered Lewis acid-base pair. The present invention uses borane and carbene to construct a sterically hindered Lewis acid-base pair. The carbene has strong nucleophilicity, so that the catalytic efficiency and catalytic activity of the sterically hindered Lewis acid-base pair of the present invention are high, and the molecular weight of the obtained polycarbonate is high. The results of the examples show that the relative molecular weight of the polycarbonate reaches up to 783 kg / mol at most.

[0022] The present invention also provides a method for preparing the sterically hindered Lewis acid-base pair described in the above solution. The preparation method provided by the present invention has simple steps, convenient operation and high feasibility.

[0023] The present invention also provides the use of the frustrated Lewis pair described in the above solution or the frustrated Lewis pair obtained by the preparation method described in the above solution in the copolymerization of CO 2 and epoxides. The present invention creatively uses carbodicarbenes to catalyze the polymerization of CO 2 and epoxides. Due to the steric hindrance of the Lewis acid and the Lewis base, the two can coexist in the system and synergistically catalyze the polymerization, with a high turnover number (TON) and high activity, a polycarbonate selectivity > 99%, and a high molecular weight polycarbonate is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 GPC curve of the polycarbonate prepared in Example 1;

[0026] Figure 2 Time-of-flight mass spectrum of the polycarbonate prepared in Example 1;

[0027] Figure 3 Mechanism diagram of the catalytic synthesis of polycarbonate by the frustrated Lewis pair of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The present invention provides a frustrated Lewis pair, including a Lewis acid and a Lewis base.

[0029] In the present invention, the Lewis acid is preferably an organoborane; the organoborane preferably includes triethylborane (the structure is as shown in formula BEt 3 ), tributylborane (the structure is as shown in formula B n Bu 3 ), tricyclohexylborane (the structure is as shown in formula BCy 3 ), and triphenylborane (the structure is as shown in formula BPh 3 ), or one or more of them.

[0030]

[0031] In the present invention, the Lewis base is preferably a carbodicarbene, and the structure of the carbodicarbene is preferably as shown in formula B:

[0032]

[0033] In formula B, R 1 、R2 , R 3 and R 4 are independently methyl or propyl.

[0034] In the present invention, the propyl group is preferably n-propyl or isopropyl.

[0035] In the present invention, the carbene preferably includes one of CDC-1 carbene, CDC-2 carbene, CDC-3 carbene, CDC-4 carbene, CDC-5 carbene, CDC-6 carbene, CDC-7 carbene, CDC-8 carbene, CDC-9 carbene, CDC-10 carbene, CDC-11 carbene, CDC-12 carbene, CDC-13 carbene, CDC-14 carbene, CDC-15 carbene, CDC-16 carbene, CDC-17 carbene, CDC-18 carbene, CDC-19 carbene, CDC-20 carbene and CDC-21 carbene, and the structure is as follows:

[0036]

[0037] In the present invention, the molar ratio of the Lewis acid to the Lewis base is preferably not less than 2:1, and specifically can be 2:1, 4:1, 8:1, 16:1, 32:1, 64:1 or 128:1. For the frustrated Lewis pair provided by the present invention, the Lewis acid is cheap and easily available, and the loading amount of the Lewis base carbene is low, indicating that the carbene in the present invention has high activity and still has high catalytic activity even at a very low loading amount, greatly reducing the catalyst cost.

[0038] The present invention also provides a preparation method of the frustrated Lewis pair described in the above solution, including the following steps:

[0039] Mix the Lewis acid and the Lewis base to obtain the frustrated Lewis pair.

[0040] In the present invention, the mixing is preferably stirring mixing. By mixing in the present invention, the Lewis acid and the Lewis base are distributed in the same space, but the two do not undergo a chemical reaction.

[0041] The present invention also provides the application of the frustrated Lewis pair described in the above solution or the frustrated Lewis pair obtained by the preparation method described in the above solution in the copolymerization of CO 2 and epoxide.

[0042] In the present invention, the application preferably includes the following steps: Mix the epoxide and the frustrated Lewis pair and then introduce CO 2 for bulk polymerization reaction to obtain polycarbonate.

[0043] In the present invention, the epoxide preferably includes one or more of the following structures:

[0044]

[0045] In the present invention, the epoxide is preferably purified before use; the purification is preferably: drying the epoxide and then distilling it; the number of times of drying is preferably more than 2 times; the drying reagent is preferably calcium hydride.

[0046] In the present invention, the molar ratio of the Lewis base to the epoxide in the hindered Lewis acid-base pair is preferably not greater than 1:100, and specifically can be 1:100, 1:300, 1:500, 1:800, 1:1000, 1:5000, 1:10000, 1:20000, 1:40000, 1:80000, 1:160000 or 1:320000.

[0047] In the present invention, the temperature of the bulk polymerization reaction is preferably -30 to 180 °C, and specifically can be -30 °C, 0 °C, 30 °C, 60 °C, 70 °C, 80 °C, 100 °C, 120 °C, 150 °C or 180 °C, and the holding reaction time is preferably 0.5 to 120 h, and specifically can be 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 10 h, 16 h, 21 h, 30 h, 45 h, 62 h or 120 h.

[0048] In the present invention, the equipment for the bulk polymerization reaction is preferably an oil bath and a high-pressure reactor placed in the oil bath.

[0049] The mechanism of the synthesis of polycarbonate catalyzed by the hindered Lewis acid-base pair of the present invention is as Figure 3 shown: During the bulk polymerization reaction, the Lewis base LB first attacks CO 2 , and then attacks CHO activated by the Lewis acid LA, inserts in turn, and finally obtains polycarbonate.

[0050] To further illustrate the present invention, the solutions of the present invention will be described in detail below with reference to the drawings and examples, but they should not be construed as limiting the protection scope of the present invention.

[0051] Example

[0052] In the example of the present invention, CDC-2 carbene is combined with triethylboron to form a hindered Lewis acid-base pair, and catalyzes the polymerization of CO 2 and cyclohexene oxide. The specific steps are as follows: Add 2 mL of cyclohexene oxide (M) to the high-pressure reactor, then add CDC-2 carbene (LB) and triethylboron (LA) to the high-pressure reactor, and then introduce CO 2Bulk polymerization was carried out. The specific parameters and test results of Examples 1 to 12 are shown in Table 1, where the molecular weight and molecular weight distribution were measured using a gel permeation chromatograph detector, and the molecular weight is relative to that of polystyrene.

[0053] Table 1 Parameters and test results of the polymerization of CO 2 and cyclohexene oxide catalyzed in Examples 1 - 12

[0054]

[0055] It can be seen from Table 1 that the monomer ratio can be as high as 320,000 equivalents, the amount of the Lewis base is as low as 3.1 ppm, the highest TON of the bulk polymerization reaction in the examples reaches 227,200, and the highest TOF reaches 4,200 h -1 , the highest relative molecular weight reaches 783 kg / mol, and the selectivity of the reaction is above 99%, indicating that the sterically hindered Lewis acid-base pair provided by the present invention has high catalytic efficiency and activity.

[0056] Test Example

[0057] GPC analysis was performed on the polycarbonate prepared in Example 1, and the results are as Figure 1 shown. It can be seen from Figure 1 that the polymer shows a bimodal distribution, which is due to the presence of trace amounts of water or alcohol as a chain transfer agent in the system. This is common in the field of copolymerization of epoxy and carbon dioxide. Through multiple drying of the epoxide and in combination with the sterically hindered Lewis acid-base pair of the present invention, a polymer with a molecular weight as high as 783 kg / mol was prepared.

[0058] Time-of-flight mass spectrometry was performed on the polycarbonate prepared in Example 1, and the results are as Figure 2 shown. It can be seen from Figure 2 that through MALDI TOF testing, the end group structure of the polycarbonate can be determined. 142 in 142n represents the molecular weight of the repeating unit, that is, CO 2 and the epoxide CHO alternate copolymerize, and then 333 represents the end group structure of the polycarbonate, that is, the molecular weight of LB plus the molecular weight of an H.

[0059] From the above examples, it can be seen that the sterically hindered Lewis acid-base pair provided by the present invention has high catalytic efficiency and activity, and the polycarbonate obtained has a high molecular weight.

[0060] Although the above examples have described the present invention in detail, they are only a part of the embodiments of the present invention, not all embodiments. Other embodiments can be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A hindered Lewis acid-base pair, characterized in that: Includes Lewis acids and Lewis bases; The Lewis acid is an organoborane; The Lewis base is a carbon dicarbene.

2. The hindered Lewis acid-base pair according to claim 1, characterized in that The organic borane includes one or more of triethylborane, tributylborane, tricyclohexylborane and triphenylborane.

3. The hindered Lewis acid-base pair according to claim 1 or 2, characterized in that: The structure of the carbon dicarbene is shown in Formula B: In formula B, R1, R2, R3 and R4 are independently methyl or propyl.

4. The hindered Lewis acid-base pair according to claim 3, characterized in that: The carbon dicarbene includes one of CDC-1 carbon dicarbene, CDC-2 carbon dicarbene, CDC-3 carbon dicarbene, CDC-4 carbon dicarbene, CDC-5 carbon dicarbene, CDC-6 carbon dicarbene, CDC-7 carbon dicarbene, CDC-8 carbon dicarbene, CDC-9 carbon dicarbene, CDC-10 carbon dicarbene, CDC-11 carbon dicarbene, CDC-12 carbon dicarbene, CDC-13 carbon dicarbene, CDC-14 carbon dicarbene, CDC-15 carbon dicarbene, CDC-16 carbon dicarbene, CDC-17 carbon dicarbene, CDC-18 carbon dicarbene, CDC-19 carbon dicarbene, CDC-20 carbon dicarbene and CDC-21 carbon dicarbene, and the structure is shown below:

5. The hindered Lewis acid-base pair according to claim 1 or 2, characterized in that: The molar ratio of the Lewis acid to the Lewis base is not less than 2:

1.

6. The method for preparing the hindered Lewis acid-base pair according to any one of claims 1 to 5, characterized in that: The following steps are involved: A Lewis acid and a Lewis base are mixed to obtain the hindered Lewis acid-base pair.

7. Use of the hindered Lewis acid-base pair according to any one of claims 1 to 5 or the hindered Lewis acid-base pair obtained by the preparation method according to claim 6 in catalyzing the copolymerization of CO2 and epoxy compounds.

8. The use according to claim 7, characterized in that: The following steps are involved: The epoxy compound and the hindered Lewis acid-base pair are mixed and then CO2 is introduced to carry out bulk polymerization reaction to obtain polycarbonate.

9. The use according to claim 8, characterized in that: The epoxy compound includes one or more of the following structures:

10. The use according to claim 8, characterized in that: The molar ratio of the Lewis base to the epoxy compound in the hindered Lewis acid-base pair is not greater than 1:100.

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