Bimetal catalyst for synthesizing stereoregularity polyester and application thereof

Abstract

The invention belongs to the technical field of catalysts for synthesizing polyhydroxyalkanoate, and discloses a bimetallic catalyst for synthesizing stereoregularity polyester and application of the bimetallic catalyst. The bimetal catalyst is a bitetradentate Schiff base bimetal complex formed by connecting two metal centers through a benzene skeleton, and can catalyze a cyclic lactone reaction at room temperature under the action of an initiator to efficiently prepare syntactically enriched stereoregular polyhydroxyalkanoate, the conversion frequency of the catalyst is 10 < 2 >-10 < 4 > h <-1 >, the molecular weight of a polymer is adjustable in a range of 10 < 3 >-10 < 5 >, and the molecular weight of the polymer is adjustable in a range of 10 < 3 >-10 < 5 >. The molecular weight distribution is less than 1.5, the syndiotacticity is adjustable between 66% and 94%, and a wide prospect is provided for industrial application.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts for synthesizing polyhydroxyalkanoates, and particularly relates to a bimetallic chiral catalyst for synthesizing syndiotactic polyhydroxyalkanoates by catalyzing a cyclic lactone reaction and an application thereof. Background Art

[0002] Polyhydroxyalkanoates (PHAs) are a large class of biodegradable and biocompatible aliphatic polyesters that are naturally produced in bacteria and other microorganisms. With the increasing concern about resource depletion and plastic pollution, PHAs have become one of the most promising candidates to replace traditional polyolefins in specific markets. Therefore, their commercial applications in packaging, biomedicine, and pharmaceuticals have been widely explored. However, the high cost and limited quantity of bacterial production require efficient chemical synthesis methods. Ring-opening polymerization of cyclic lactones is one of the most effective methods.

[0003] Precise control of polymer microstructures enables unparalleled molecular tunability of material properties, thus promoting applications in different fields. For example, pure isotactic poly (3-hydroxybutyrate) (it-P3HB) has high crystallinity and melting transition temperature (~180°C), and this defect-free nature makes it extremely brittle with an elongation at break of ~5% [Sangroniz A, Zhu JB, Tang X, Etxeberria A, Chen EY-X, Sardon H. Packaging materials with desired mechanical and barrier properties and full chemical recyclability [J], Nat. Commun., 2019, 10, 3559]. However, slightly reducing the isocratic degree to 0.84 successfully shifted the melting transition temperature value to a lower range, thus overcoming the inherent brittleness of [Bruckmoser J, Pongratz S, Stieglitz L, Rieger B. Highly Isoselective Ring-Opening Polymerization of rac-β-Butyrolactone: Access to Synthetic Poly(3-hydroxybutyrate)with Polyolefin-like Material Properties[J], J.Am.Chem.Soc., 2023, 145, 11494–11498.].

[0004] Bimetallic catalysts have shown strong advantages in terms of high rate and selectivity. A series of polymerization reactions, such as lactone or epoxide polymerization, epoxide / CO2, and epoxide / anhydride copolymerization, have witnessed the power of bimetallic catalysis. Therefore, the current research field still has a strong demand for preparing bimetallic system catalysts to catalyze the ring-opening polymerization of cyclic lactones to obtain polyhydroxyalkanoates with high syndiotacticity. Summary of the invention

[0005] The object of the present invention is to provide a chiral bimetallic complex and a synthesis method thereof.

[0006] Another object of the present invention is to provide an application of the above-mentioned bimetallic complex in catalyzing the polymerization reaction of cyclic lactone under the action of an initiator.

[0007] The technical solution of the present invention:

[0008] A bimetallic catalyst for synthesizing stereoregular polyesters, specifically a bimetallic catalyst for synthesizing stereoregular polyhydroxyalkanoates. The bimetallic catalyst is a bi-tetradentate Schiff base bimetallic complex in which two metal centers are connected by a benzene skeleton. The bimetallic catalyst can catalyze a cyclic lactone reaction at room temperature under the action of an initiator to efficiently prepare syndiotactic-enriched stereoregular polyhydroxyalkanoates.

[0009] The structure of the bi-tetradentate Schiff base bimetallic complex is:

[0010]

[0011] Where M is Y 3+ Sc 3+ ,La 3 or Yb 3 ;

[0012] R 1 For H, CH3, CH2CH3, CH(CH3)2, C(CH3)3, C(CH3)2C6H5, CCH3(C6H5)2, C(C6H5)3, (adamyl), OCH3, OCH2CH3, F, Cl, Br, I or NO2;

[0013] R 2 It is H, CH3, CH2CH3, CH(CH3)2, C(CH3)3, C(CH3)2C6H5, CCH3(C6H5)2, C(C6H5)3, adamyl, OCH3, OCH2CH3, F, Cl, Br, I or NO2;

[0014]

[0015] X is N(SiHMe2)2, N(SiMe3)2, CH2SiMe3 or THF.

[0016] The chiral ligand in the biquadridentate Schiff base chiral bimetallic complex is prepared by the reaction of salicylaldehyde containing a substituted group, a dialdehyde compound and a diamine compound. Taking the synthesis of a typical bimetallic yttrium complex as an example: under an inert atmosphere, a diamine compound and a salicylaldehyde containing a substituted group react in an organic solvent at a molar ratio of 1:1 at room temperature for 48-96 hours to obtain a half-Schiff base intermediate. The half-Schiff base intermediate reacts with a dialdehyde compound at a molar ratio of 2:1 in an organic solvent at 25°C-70°C for 24-48 hours to obtain a biquadridentate Schiff base ligand. The biquadridentate Schiff base chiral ligand is obtained by column chromatography to separate the racemic ligand to obtain (R,R / S,S)-ligand and (R,S / S,R)-ligand. The biquadridentate Schiff base ligand reacts with Y[N(SiHMe2)2]3(THF)2 at a molar ratio of 1 / 2 in an organic solvent at room temperature for 3-7 days to obtain a bimetallic yttrium complex.

[0017] The dialdehyde compound is 2,4-dihydroxyisophthalaldehyde, 2,5-dihydroxyterephthalaldehyde or 2,3-dihydroxyterephthalaldehyde;

[0018] The diamine compound is 5,5',6,6',7,7',8,8'-octahydro-[1,1'-binaphthyl]-2,2'-diamine or 1,1'-binaphthylamine, 2,2'-diaminobiphenyl.

[0019] The organic solvent is one or a mixture of two or more of toluene, xylene, methanol, n-hexane, dichloromethane, ethyl acetate, ether and tetrahydrofuran.

[0020] The specific synthesis steps of polyhydroxyalkanoate are as follows: under an inert atmosphere, a catalyst, a cyclic lactone, an initiator, and a solvent are added to a reaction bottle in sequence, and the reaction time is 1 to 120 minutes at room temperature; the reaction is stopped, and a white solid is obtained after washing with methanol, which is a polyhydroxyalkanoate polymer.

[0021] The initiator is one of 2,2-diphenylethanol, 1,4-butanediol, terephthalic acid, benzyl alcohol, isopropyl alcohol, and 4-methylbenzyl alcohol. The solvent is one of toluene, benzene, dichloromethane, chlorobenzene, n-hexane, cyclohexane, n-pentane, tetrahydrofuran, ethylene glycol dimethyl ether, chloroform, and 1,4-dioxane, or a mixture of two or more thereof.

[0022] When the bimetallic catalyst provided by the present invention is used, the molar ratio of the bimetallic catalyst, the initiator and the cyclic lactone in the reaction system is 1:2:200 to 1:2:1600, the reaction temperature is 25° C., and the reaction time is 1 to 120 minutes.

[0023] The structural formula of cyclic lactone is:

[0024]

[0025] Beneficial effects of the present invention:

[0026] (1) A new bimetallic chiral rare earth catalyst was synthesized, which can catalyze the homopolymerization of cyclic lactones to achieve efficient preparation of polyhydroxyalkanoate polymer materials;

[0027] (2) The post-treatment process of the obtained polyhydroxyalkanoate polymer is simple, the reaction temperature is mild, the process is simple, and it is suitable for industrial production process;

[0028] (3) The conversion frequency of the obtained bimetallic catalyst for catalytic homopolymerization of cyclic lactones can reach 10 4 h -1 , high catalytic activity, and has the prospect of industrial application;

[0029] (4) The obtained bimetallic catalyst has strong applicability and abundant substrates;

[0030] (5) The syndiotacticity of the obtained polyhydroxyalkanoate polymer material reaches up to 94%, and the molecular weight distribution is relatively narrow. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the H NMR spectrum of the ligand (R,R)-L1 according to Example 1 of the present invention.

[0032] Figure 2 It is the H NMR spectrum of the ligand (R,S / S,R)-L1 according to Example 2 of the present invention.

[0033] Figure 3 This is the H NMR spectrum of the ligand (R,R / R,S / S,R / S,S)-L8 according to Example 3 of the present invention.

[0034] Figure 4 This is the H NMR spectrum of the ligand (R,R / R,S / S,R / S,S)-L9 according to Example 4 of the present invention.

[0035] Figure 5 This is the NMR carbon spectrum of the chiral polyester obtained according to row 3 of Table 1 of Example 5 of the present invention.

[0036] Figure 6 This is the NMR carbon spectrum of the chiral polyester obtained according to row 2 of Table 2 of Example 6 of the present invention. DETAILED DESCRIPTION

[0037] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0038] Embodiment 1:

[0039] The synthesis of ligand (R,R)-L1 has the following structural formula:

[0040]

[0041] The reaction formula is as follows:

[0042]

[0043] Under N2 protection, (R)-1,1'-bi-2,2'-naphthylamine (2.84g, 10mmol), 3,5-di-tert-butyl salicylaldehyde (2.34g, 10mmol) and magnesium sulfate (6.02g) were added to a 250mL three-necked reaction bottle, dissolved in a mixed solution of 40mL toluene / 40mL methanol / 40mL dichloromethane, and reacted at room temperature for 72 hours. After the reaction, the product (1.5g, yield 30%) was concentrated and purified by flash column chromatography and dissolved in 20mL methanol with 2,4-dihydroxyisophthalaldehyde (0.24g, 1.5mmol) and reacted at 70 degrees for 24 hours. After the reaction, the product (R,R)-L1 (0.7g, yield 62%) was concentrated and purified by flash column chromatography.

[0044] Embodiment 2:

[0045] The synthesis of ligand (R,S / S,R)-L1 has the following structural formula:

[0046]

[0047] The reaction formula is as follows:

[0048]

[0049] Under N2 protection, racemic 1,1'-bi-2,2'-naphthylamine (2.84g, 10mmol), 3,5-di-tert-butyl salicylaldehyde (2.34g, 10mmol) and magnesium sulfate (6.02g) were added to a 250mL three-necked reaction bottle, dissolved in a mixed solution of 40mL toluene / 40mL methanol / 40mL dichloromethane, and reacted at room temperature for 72 hours. After the reaction, the product (1.5g, yield 30%) obtained by concentration and purification by flash column chromatography was dissolved in 20mL methanol with 2,4-dihydroxyisophthalaldehyde (0.24g, 1.5mmol) and reacted at 70 degrees for 24 hours. After the reaction, the enantiomeric mixed product (R,R / S,S / R,S / S,R)-L1 (0.7g, yield 62%) was obtained by concentration and purification by flash column chromatography. The product was separated by silica gel column chromatography using petroleum ether / ethyl acetate (4 / 1) as the mobile phase. The eluent of the product with less polarity was collected in a test tube and the solvent was removed in vacuo to obtain the target product as an orange solid (R,S / S,R)-L1 (0.35 g, yield 50%).

[0050] Embodiment three:

[0051] The synthesis of ligand (R,R / R,S / S,R / S,S)-L8 has the following structural formula:

[0052]

[0053] The reaction formula is as follows:

[0054]

[0055] Under N2 protection, racemic 1,1'-bi-2,2'-naphthylamine (2.84g, 10mmol), 3,5-di-tert-butyl salicylaldehyde (2.34g, 10mmol) and magnesium sulfate (6.02g) were added to a 250mL three-necked reaction bottle, dissolved in a mixed solution of 40mL toluene / 40mL methanol / 40mL dichloromethane, and reacted at room temperature for 72 hours. After the reaction, the product (1.5g, yield 30%) obtained by concentration and purification by flash column chromatography was dissolved in 20mL methanol with 2,5-dihydroxyisophthalaldehyde (0.24g, 1.5mmol) and reacted at 70 degrees for 48 hours. After the reaction, the enantiomeric mixed product (R,R / S,S / R,S / S,R)-L8 (0.9g, yield 80%) was obtained by concentration and purification by flash column chromatography.

[0056] Embodiment 4:

[0057] The synthesis of ligand (R,R / R,S / S,R / S,S)-L9 has the following structural formula:

[0058]

[0059] The reaction formula is as follows:

[0060]

[0061] Under N2 protection, racemic 1,1'-bi-2,2'-naphthylamine (2.84g, 10mmol), 3,5-di-tert-butyl salicylaldehyde (2.34g, 10mmol) and magnesium sulfate (6.02g) were added to a 250mL three-necked reaction bottle, dissolved in a mixed solution of 40mL toluene / 40mL methanol / 40mL dichloromethane, and reacted at room temperature for 72 hours. After the reaction, the product (1.5g, yield 30%) was concentrated and purified by flash column chromatography and dissolved in 20mL methanol with 2,3-dihydroxyisophthalaldehyde (0.24g, 1.5mmol) and reacted at 70 degrees for 48 hours. After the reaction, the enantiomeric mixed product (R,R / S,S / R,S / S,R)-L9 (0.66g, yield 60%) was obtained by concentration and purification by flash column chromatography.

[0062] Embodiment five:

[0063] In a 10 mL flask, add a certain amount of the main catalyst (any metal complex described in the first claim), β-butyrolactone and a toluene solution of the initiator in the following order at ambient temperature. Keep the flask at an appropriate temperature and after a regular reaction time, stop stirring and add a 1% wt. benzoic acid / chloroform solution to quench the reaction. Take 20 microliters of the reaction solution and use Varian INOVA-400MHz to measure its 1 HNMR, calculate the polymerization conversion rate; the polymerization product was washed three times with dichloromethane / methanol precipitation, dried to constant weight under vacuum, and the polymer molecular weight and distribution were determined by gel permeation chromatography; the 500MHz NMR was used to determine its 13 CNMR, calculate the stereoregularity of polyhydroxyalkanoates.

[0064] Table 1. Polymerization of racemic β-butyrolactone catalyzed by metal complexes

[0065]

[0066] Note 1: Polymerization conditions: reaction temperature 25°C, reaction solvent toluene, monomer = 1 mol, catalyst = 5 μmol, ratio of monomer to catalyst and initiator alcohol is 200:1:2;

[0067] Note 2: All products are single syndiotactic polyesters, and the monomer conversion rate and stereoregularity are calculated from the nuclear magnetic resonance spectrum;

[0068] Note 3: Molecular weight and molecular weight distribution were determined by gel permeation chromatography using chloroform as eluent.

[0069] Embodiment six:

[0070] In a 10 mL flask, add a certain amount of the main catalyst (any metal complex described in the first claim), β-lactone and toluene solution of the initiator in the following order at ambient temperature. Keep the flask at an appropriate temperature and after a regular reaction time, stop stirring and add 1% wt. benzoic acid / chloroform solution to quench the reaction. Take 20 microliters of the reaction solution and use Varian INOVA-400MHz to measure its 1 HNMR, calculate the polymerization conversion rate; the polymerization product was washed three times with dichloromethane / methanol precipitation, dried to constant weight under vacuum, and the polymer molecular weight and distribution were determined by gel permeation chromatography; the 500MHz NMR was used to determine its 13 CNMR, calculate the stereoregularity of polyhydroxyalkanoates.

[0071] Table 2. Polymerization of several racemic four-membered ring lactones catalyzed by (R,S / S,R)-Y1

[0072]

[0073] Note 1: Polymerization conditions: reaction temperature 25°C, reaction solvent toluene, monomer = 1 mol, co-catalyst = 5 μmol, ratio of monomer to catalyst and initiator alcohol is 200:1:2;

[0074] Note 2: All products are single syndiotactic polyesters, and the monomer conversion rate and stereoregularity are calculated from the nuclear magnetic resonance spectrum;

[0075] Note 3: Molecular weight and molecular weight distribution were determined by gel permeation chromatography using chloroform as eluent.

Claims

1. A bimetallic catalyst for synthesizing stereoregular polyester, characterized in that: The bimetallic catalyst is a bi-tetradentate Schiff base bimetallic complex in which two metal centers are connected by a benzene skeleton. Under the action of an initiator, the bimetallic catalyst catalyzes a cyclic lactone reaction at room temperature to efficiently prepare a stereoregular polyhydroxyalkanoate with syndiotactic enrichment.

2. The bimetallic catalyst for synthesizing stereoregular polyester according to claim 1, characterized in that: The structure of the bi-tetradentate Schiff base bimetallic complex is: Where M is Y 3+ Sc 3+ ,La 3 or Yb 3 ; R 1 is H, CH3, CH2CH3, CH(CH3)2, C(CH3)3, C(CH3)2C6H5, CCH3(C6H5)2, C(C6H5)3, OCH3, OCH2CH3, F, Cl, Br, I or NO2; R 2 is H, CH3, CH2CH3, CH(CH3)2, C(CH3)3, C(CH3)2C6H5, CCH3(C6H5)2, C(C6H5)3, adamyl, OCH3, OCH2CH3, F, Cl, Br, I or NO2; X is N(SiHMe2)2, N(SiMe3)2, CH2SiMe3 or THF.

3. The bimetallic catalyst for synthesizing stereoregular polyester according to claim 1, characterized in that: The chiral ligand in the biquadrantate Schiff base chiral bimetallic complex is prepared by reacting salicylaldehyde containing a substituted group, a dialdehyde compound and a diamine compound.

4. The bimetallic catalyst for synthesizing stereoregular polyester according to claim 1, characterized in that: The biquadrantate Schiff base chiral bimetallic complex is a bimetallic yttrium complex, and its synthesis steps are as follows: under an inert atmosphere, a diamine compound and a salicylaldehyde containing a substituted group are reacted in an organic solvent at a molar ratio of 1:1 at room temperature for 48-96 hours to obtain a half-Schiff base intermediate; the half-Schiff base intermediate and a dialdehyde compound are reacted in an organic solvent at a molar ratio of 2:1 at 25°C-70°C for 24-48 hours to obtain a biquadrantate Schiff base ligand; the biquadrantate Schiff base ligand and Y[N(SiHMe2)2]3(THF)2 are reacted in an organic solvent at a molar ratio of 1:2 at room temperature for 3-7 days to obtain a bimetallic yttrium complex.

5. The bimetallic catalyst for synthesizing stereoregular polyester according to claim 3 or 4, characterized in that: The dialdehyde compound is 2,4-dihydroxyisophthalaldehyde, 2,5-dihydroxyterephthalaldehyde or 2,3-dihydroxyterephthalaldehyde; The diamine compound is 5,5',6,6',7,7',8,8'-octahydro-[1,1'-binaphthyl]-2,2'-diamine or 1,1'-binaphthylamine, 2,2'-diaminobiphenyl.

6. The bimetallic catalyst for synthesizing stereoregular polyester according to claim 4, characterized in that: The organic solvent is one or a mixture of two or more of toluene, xylene, methanol, n-hexane, dichloromethane, ethyl acetate, ether and tetrahydrofuran.

7. The use of the bimetallic catalyst for synthesizing stereoregular polyester according to claim 1, characterized in that: The specific synthesis steps of polyhydroxyalkanoate are as follows: under an inert atmosphere, a bimetallic catalyst, a cyclic lactone, an initiator, and a solvent are mixed in sequence, and the reaction time is 1 to 120 minutes at room temperature; the reaction is stopped, and a white solid is obtained after washing with methanol, which is a polyhydroxyalkanoate polymer.

8. Use according to claim 7, characterized in that The initiator is one of 2,2-diphenylethanol, 1,4-butanediol, terephthalic acid, benzyl alcohol, isopropanol, and 4-methylbenzyl alcohol; the solvent is one of toluene, benzene, dichloromethane, chlorobenzene, n-hexane, cyclohexane, n-pentane, tetrahydrofuran, ethylene glycol dimethyl ether, chloroform, and 1,4-dioxane, or a mixture of two or more thereof.

9. The use according to claim 7, characterized in that The molar ratio of the bimetallic catalyst, the initiator and the cyclic lactone in the reaction system is 1:2:200 to 1:2:1600.

10. The use according to claim 7, characterized in that The structural formula of cyclic lactone is:

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