Mononuclear bis-N-alkoxy-beta-ketimine magnesium complex as well as synthesis method and application of mononuclear bis-N-alkoxy-beta-ketimine magnesium complex

Abstract

The invention belongs to the field of preparation and application of metal complex catalysts, and discloses a mononuclear double N-alkoxy-beta-ketimine magnesium complex as well as a synthesis method and application thereof. The mononuclear double N-alkoxy-beta-ketimine magnesium complex is applied to catalysis of ring-opening polymerization of caprolactone, the mononuclear double N-alkoxy-beta-ketimine magnesium complex is used as a catalyst, caprolactone is used as a raw material, bulk polymerization is performed at 110 DEG C under the protection of anhydrous and anaerobic inert gas, and the mononuclear double N-alkoxy-beta-ketimine magnesium complex is obtained. And the ring opening polymerization of caprolactone can be catalyzed to prepare polycaprolactone without the participation of a solvent and a cocatalyst. The catalyst is low in toxicity, simple in preparation method, novel in structure and high in catalytic activity, the dosage of the catalyst is low in the catalysis process, and high-molecular-weight polycaprolactone can be obtained.

Description

Technical Field

[0001] The present invention belongs to the field of preparation and application of metal complex catalysts, and particularly relates to a mononuclear bis-N-alkoxy-β-ketoimine magnesium complex, a preparation method thereof, and an application thereof in the ring-opening polymerization reaction of ε-caprolactone. Background Art

[0002] Polycaprolactone (PCL) has broad application prospects in the biomedical and pharmaceutical fields due to its good solubility, biocompatibility, and excellent blend compatibility. PCL has good mechanical properties, a controllable degradation rate, and can be decomposed into carbon dioxide and water in the body, making it an ideal biomedical material that can be applied to drug delivery, surgical suture materials, bone tissue implant materials, etc. Therefore, the research significance is great. There are two existing methods for synthesizing PCL. The first method is the direct polycondensation of 6-hydroxyhexanoic acid. In this process, water molecules are generated as by-products, and it is necessary to remove water molecules to drive the reaction equilibrium towards the formation of the polymer. In addition, during the direct polycondensation process, the reaction process of the polymer cannot be controlled, resulting in the formation of polymers with low molecular weights and poor mechanical properties, limiting the application range. The second method is the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) to prepare PCL. In this process, no water molecules are generated, and the synthesized polymer has the advantages of high molecular weight and controllable molecular weight. Therefore, ROP is considered a better PCL synthesis process with a wide application range. Metal compounds are commonly used as catalysts to initiate the polymerization of monomers during the ring-opening polymerization reaction of ε-caprolactone.

[0003] Currently, industrial production of PCL is mainly carried out by the ring-opening polymerization of ε-caprolactone catalyzed by stannous octoate and stannous chloride. It has been found that the polymers obtained by the metal catalysts catalyzing ε-caprolactone contain some metal residues. Tin itself is toxic and harmful to the human body, which will limit the application of PCL in the food and pharmaceutical fields. Therefore, developing environmentally friendly metal catalysts, synthesizing polycaprolactone with controllable molecular weight (Mn) and narrow molecular weight distribution and realizing the green and environmental protection process for producing polycaprolactone is of great significance. Summary of the Invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a mononuclear bis-N-alkoxy-β-ketoimine magnesium complex, a synthesis method and an application thereof. Using the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex as a catalyst and ε-caprolactone as a raw material, under anhydrous and anaerobic conditions and protected by an inert gas, bulk polymerization is carried out at 110 °C, and the ring-opening polymerization of ε-caprolactone can be catalyzed to prepare polycaprolactone without the participation of a solvent and a cocatalyst.

[0005] The above object of the present invention is achieved by the following technical solutions:

[0006] A mononuclear bis-N-alkoxy-β-ketoimine magnesium complex, the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex having a structure as shown in General Formula I:

[0007]

[0008] wherein R is one of -CH2CH2- and -CH2CH2CH2-.

[0009] Another object of the present invention is to protect a preparation method of the above mononuclear bis-N-alkoxy-β-ketoimine magnesium complex, the steps including:

[0010] Under the protection of an inert gas, at a temperature of -20 to 0 °C, (n-Bu)2Mg is slowly added dropwise to a β-ketoimine ligand solution having a structure as shown in General Formula II, and the reaction can be completed by naturally rising to room temperature. The structure of General Formula II is as follows:

[0011]

[0012] wherein R is one of -CH2CH2- and -CH2CH2CH2-.

[0013] Further, in the preparation method, the molar ratio of the β-ketoimine ligand having a structure as shown in General Formula II to (n-Bu)2Mg is 1:1 to 1.6.

[0014] Further, in the preparation method, the solvent in the β-ketoimine ligand solution having a structure as shown in General Formula II is one or more of acetonitrile, toluene, and tetrahydrofuran.

[0015] Further, in the preparation method, the solvent in the (n-Bu)2Mg solution is one or more of n-hexane, n-heptane, and tetrahydrofuran.

[0016] Another object of the present invention is to protect the application of the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex.

[0017] Further, the application of the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex is specifically the application of the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex in the ring-opening polymerization of ε-caprolactone.

[0018] The beneficial effects of the present invention compared with the prior art are as follows: The present invention develops a novel preparation method and application of a mononuclear bis-N-alkoxy-β-ketoimine magnesium complex. Using the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex as a catalyst and ε-caprolactone as a raw material, under anhydrous, anaerobic and inert gas argon protection, bulk polymerization is carried out at 110 °C. The ring-opening polymerization of ε-caprolactone can be catalyzed to prepare polycaprolactone without the participation of solvents and cocatalysts. The catalyst is of low toxicity, the preparation method is simple, the structure is novel, the catalytic activity is high, and the amount of catalyst used is low during the catalytic process. The polymer obtained by the reaction has a high molecular weight (68619 - 266896 g / mol). Brief Description of the Drawings

[0019] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0020] Figure 1 It is a schematic diagram of the crystal structure of the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex 2a. Specific Embodiments

[0021] The present invention will be described in detail below in conjunction with the embodiments. However, the following embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention. The experimental methods adopted by the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained from commercial channels. The ligands 1a and 1b were synthesized according to the reference [Organometallics, 2010, 29, 13, 2951 - 2959.].

[0022] The reaction formula of the following embodiments is:[[]]

[0023]

[0024] Example 1

[0025] Synthesis of [CH3C(O)CHC(CH3)NCH2CH2OCH2]2Mg (2a): Under the protection of argon gas environment, 1a (0.25 g, 0.8 mmol) was dissolved in dehydrated tetrahydrofuran. The reaction tube was placed in a dry ice-ethanol bath at -20 - 0 °C, and dibutylmagnesium (0.8 mL, 1 M in n-hexane, 0.8 mmol) was added dropwise. The reaction naturally rose to room temperature to obtain a turbid solution. After standing, it was divided into two phases. The upper layer was a colorless clear solution, and the lower layer was a pale yellow precipitate. After filtering off the precipitate, a colorless solution was obtained. After drying the solvent, it was washed and purified with n-hexane to obtain a white powder. Yield: 0.16 g (62%). 11H NMR (400 MHz, CDCl3): δ 4.83 (s, 2H, γ-CH), 4.43 - 4.36 (m, 2H, OCH2), 3.78 - 3.71 (m, 4H, OCH2), 3.67 - 3.58 (m, 4H, NCH2CH2O), 3.54 - 3.47 (m, 2H, NCH2CH2O), 3.38 - 3.29 (m, 2H, NCH2CH2O), 1.88 (s, 6H, CH3C(O)), 1.87 (s, 6H, C(CH3)). 13 13C NMR (101 MHz, CDCl3) δ 180.19, 171.97, 97.10, 66.58, 63.49, 44.72, 27.83, 21.98. Anal. Calcd for C 16 H 26 MgN2O4: C, 57.42; H, 7.83; N, 8.37. Found: C, 57.46; H, 7.61; N, 8.73.

[0026] Example 2

[0027] Synthesis of [CH3C(O)CHC(CH3)NCH2CH2CH2OCH2]2Mg (2b): Under the protection of argon, 1b (0.25 g, 0.7 mmol) was dissolved in anhydrous tetrahydrofuran. The reaction tube was placed in a dry ice - ethanol bath at -20 - 0 °C, and dibutylmagnesium (0.7 mL, 1 M in n - hexane, 0.7 mmol) was added dropwise. The reaction naturally rose to room temperature, resulting in a turbid solution. After standing, it was divided into two phases. The upper layer was a colorless clear solution, and the lower layer was a pale yellow precipitate. After filtering off the precipitate, a colorless solution was obtained. After drying the solvent, it was washed and purified with n - hexane to obtain a white powder. Yield: 0.13 g (47%). 1 1H NMR (400 MHz, CDCl3): δ 4.70 (s, 2H, γ-CH), 4.41 - 4.47 (m, 2H, OCH2), 3.88 - 3.81 (m, 2H, OCH2), 3.70 - 3.62 (m, 4H, NCH2CH2CH2O), 3.58 - 3.53 (m, 4H, NCH2CH2CH2O), 1.89 (s, 6H, CH3C(O)), 1.80 (s, 6H, C(CH3)), 1.78 - 1.72 (m, 4H, NCH2CH2CH2O). 13 13C NMR (101 MHz, CDCl3) δ 177.90, 168.47, 97.91, 74.42, 69.26, 48.46, 31.13, 27.39, 20.64. Anal. Calcd for C 16 H 26MgN2O4: C, 59.60; H, 8.34; N, 7.72. Found: C, 59.56; H, 8.13; N, 8.19.

[0028] Example 3

[0029] A method for the ring-opening polymerization of ε-caprolactone catalyzed by a mononuclear bis-N-alkoxy-β-ketoimine magnesium complex at 110 °C with a monomer-to-catalyst molar ratio of 200:1, the method comprising the following steps:

[0030] Under argon protection, 0.5 mL (3.61 mmol) of ε-caprolactone was drawn with a syringe and added to a Schlenk flask, which was preheated in an IKA at 110 °C for about 10 min. 2a (0.018 mmol) was added to the ε-caprolactone, and the mixture was stirred well. Samples were taken at regular intervals. A small amount of the sample was taken out with a syringe under argon protection and detected by 1 1H NMR (400 MHz, CDCl3) for the conversion of ε-caprolactone. After the reaction was completed, the bottle stopper was directly opened and exposed to air, and the temperature was lowered with an ice-water bath. The reaction was quenched by adding about 1 mL of a 5% acetic acid methanol solution. It was detected that 95% monomer conversion could be achieved at 6 minutes of catalysis. A small amount (1 - 2 mL) of CH2Cl2 was added to dissolve the mixture completely, and then a large amount of cold methanol solution (-18 °C) was added while stirring vigorously to precipitate the polymer completely. The crude polymer obtained was washed repeatedly with cold methanol solution using a suction filtration device, and the residual solvent was dried under vacuum with an oil pump at high temperature to obtain the pure polymer. The molecular weight of the polymer Mn = 68619 g / mol and the molecular weight distribution were detected by GPC

[0031] Example 4

[0032] A method for the ring-opening polymerization of ε-caprolactone catalyzed by the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex 2a under the condition of a monomer-to-catalyst molar ratio of 300:1, the method being the same as that in Example 3. The difference from Example 3 was that the catalytic reaction time t = 35 min, the monomer conversion conv. = 88%, the molecular weight of the polymer Mn = 80619 g / mol, and the molecular weight distribution of the polymer D = 1.94.

[0033] Example 5

[0034] A method for the ring-opening polymerization of ε-caprolactone catalyzed by the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex 2b under the condition of a monomer-to-catalyst molar ratio of 300:1, the method being the same as that in Example 3. The difference from Example 3 was that the catalytic reaction time t = 1 min, the monomer conversion conv. = 92%, the molecular weight of the polymer Mn = 86593 g / mol, and the molecular weight distribution of the polymer D = 1.79.

[0035] Example 6

[0036] A method for the ring-opening polymerization of ε-caprolactone catalyzed by the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex 2b under the condition that the molar ratio of the monomer to the catalyst is 500:1. This method is the same as that in Example 3. The difference from Example 3 is that the catalytic reaction time t = 3 min, the monomer conversion conv. = 93%, the polymer molecular weight Mn = 104924 g / mol, and the polymer molecular weight distribution

[0037] Example 7

[0038] A method for the ring-opening polymerization of ε-caprolactone catalyzed by the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex 2b under the condition that the molar ratio of the monomer to the catalyst is 1000:1. This method is the same as that in Example 3. The difference from Example 3 is that the catalytic reaction time t = 6 min, the monomer conversion conv. = 95%, the polymer molecular weight Mn = 266898 g / mol, and the polymer molecular weight distribution

[0039] The detection data of the preparation of polycaprolactone by the ring-opening polymerization of ε-caprolactone catalyzed by the mononuclear bis-N-alkoxy-β-ketoimine magnesium complexes 2a and 2b in the above examples are shown in Table 1

[0040] Table 1 Data table of the preparation of polycaprolactone by the ring-opening polymerization of ε-caprolactone catalyzed by the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex at 110 °C

[0041]

[0042] Note: 1 The monomer conversion was determined by 1 1H NMR spectrum.

[0043] 2 The molecular weight was measured by gel permeation chromatography (GPC) using polystyrene as the standard substance and tetrahydrofuran as the eluent.

[0044] 3 Calculation formula for the turnover frequency TOF: TOF = conversion × ([CL]:[Mg]) / time.

[0045] As can be seen from Table 1, the monomer conversion rate of the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex prepared by the present invention in the polymerization of ε-caprolactone to prepare polycaprolactone at 110 °C is 88% - 95%, and the number-average molecular weight is 68,619 - 266,896 g / mol, which shows a significant improvement in both monomer conversion rate and number-average molecular weight compared with the existing methods for polymerizing ε-caprolactone to prepare polycaprolactone. Moreover, the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex prepared by the present invention can catalyze the polymerization of ε-caprolactone to prepare polycaprolactone without the participation of a cocatalyst. The catalyst preparation method is simple and the structure is novel. Under the condition of 110 °C, high-molecular-weight polymers can be catalyzed to obtain.

[0046] Among these two complexes, the catalytic effect of complex 2b is better. When the molar ratio of monomer to catalyst is 300:1, 92% monomer conversion can be achieved after catalyzing for 1 min, and the turnover frequency TOF = 16560 h -1 , the molecular weight of the polymer Mn = 86,593 g / mol, and the molecular weight distribution of the polymer D = 1.79. Under the same conditions, it shows a faster catalytic rate, a higher molecular weight and a narrower molecular weight distribution than 2a. Therefore, 2b was continued to be selected as the catalyst, and the catalyst dosage was reduced. When the molar ratio of monomer to catalyst was adjusted to 1000:1, the molecular weight of the polymer Mn could be increased to 266,896 g / mol.

[0047] The above-described embodiments are only the preferred embodiments of the present invention, and not all the feasible embodiments of the present invention. For those of ordinary skill in the art, any obvious changes made without departing from the principles and spirit of the present invention should be considered to be included within the protection scope of the claims of the present invention.

Claims

1. A mononuclear bis-N-alkoxy-β-ketoimine magnesium complex, characterized in that, The mononuclear bis-N-alkoxy-β-ketoimine magnesium complex has a structure as shown in General Formula I: wherein R is one of -CH2CH2- and -CH2CH2CH2-.

2. The preparation method of the mononuclear bis(N-alkoxy-β-ketoimine) magnesium complex according to claim 1, characterized in that the step It includes: Under the protection of an inert gas, at a temperature of -20 to 0 °C, (n-Bu)2Mg is slowly added dropwise to a β-ketoimine ligand solution having a structure as shown in General Formula II, and the reaction can be completed by naturally raising the temperature to room temperature; the structure of General Formula II is as follows: wherein R is one of -CH2CH2- and -CH2CH2CH2-.

3. The preparation method of the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex according to claim 2, characterized in that, The molar ratio of the β-ketoimine ligand having a structure as shown in General Formula II to (n-Bu)2Mg is 1:1 to 1.

6.

4. The preparation method of the mononuclear bis(N-alkoxy-β-ketoimine) magnesium complex according to claim 2, characterized in that, The solvent in the β-ketoimine ligand solution having a structure as shown in General Formula II is one or more of acetonitrile, tetrahydrofuran, and toluene.

5. The preparation method of the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex according to claim 2, characterized in that, The solvent in the (n-Bu)2Mg solution is one or more of n-hexane, n-heptane, and tetrahydrofuran.

6. Application of the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex according to Claim 1.

7. The application of the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex according to Claim 6, specifically the application of the mononuclear bis-N-alkoxy-β-ketoimine magnesium complex in the ring-opening polymerization of ε-caprolactone.

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