Ion pair type pyridine bridged bisaminophenoxy alkali metal complex and preparation method and application thereof

Abstract

The application discloses an ion pair type pyridine bridged double aminophenoxyl alkali metal complex (I), a preparation method thereof and application of the ion pair type pyridine bridged double aminophenoxyl alkali metal complex in high-activity and high-selectivity catalysis of lactone ring-opening polymerization. The preparation method comprises the following steps: reacting a neutral ligand with a metal hydride and a quaternary ammonium salt in an organic medium, filtering, concentrating and recrystallizing to obtain the target ion pair type alkali metal complex. The ion pair type pyridine bridged double aminophenoxyl alkali metal complex is a high-efficiency lactone ring-opening polymerization catalyst, and especially, racemic lactide can be obtained to have high stereoregularity polylactide. The ion pair type pyridine bridged double aminophenoxyl alkali metal complex has the following obvious advantages: raw materials are easy to obtain, a synthesis route is simple, the ion pair type pyridine bridged double aminophenoxyl alkali metal complex has high catalytic activity and stereoselectivity for lactone polymerization, and high-regularity and high-molecular-weight polyester materials are obtained.

Description

Technical Field

[0001] This invention relates to a class of ion-pair pyridine-bridged bisaminophenoxy alkali metal complexes, and the application of such complexes in lactone polymerization. Background Technology

[0002] Polyolefin materials are stable in performance, but they are difficult to degrade and easily cause environmental pollution. Furthermore, their raw materials are small-molecule olefins produced from the cracking of non-renewable petroleum resources. Therefore, finding biodegradable polymers to replace polyolefin materials is of great significance. Polylactide (PLA) has advantages such as biocompatibility and biodegradability, and also possesses semi-crystalline properties similar to polyethylene and polypropylene. It has promising applications in fields such as biology, medicine, and food packaging, and has become one of the research hotspots in green materials development in recent years.

[0003] The properties of polylactide (PL) are determined by its microstructure. By utilizing metal complexes to catalyze the ring-opening polymerization of different types of lactide monomers, such as L-LA, D-LA, meso-LA, and racemic-LA, a variety of PLD structures with diverse microstructures can be obtained. Random PLD is amorphous, brittle, lacks stretchability, and degrades rapidly; isotactic PLD is a semi-crystalline material with a high melting point, good thermodynamic properties, and stretchability; while the ring-opening polymerization of racemic PLD yields highly isotactic stereoblock PLD, exhibiting better thermal stability and physicomechanical properties. Furthermore, alkali metals are biocompatible, inexpensive, and readily available. As the metal center of catalysts, they meet the requirements for PLD applications in biomedicine and other fields. Therefore, developing highly active, highly isotactic stereoselective alkali metal complexes for the controlled synthesis of high-performance PLD is of great significance.

[0004] In 2011, Davidson's group synthesized sodium phenoxy groups. The rac-LA ring-opening polymerization was catalyzed in dichloromethane at 20°C with a [LA]0 / [Cat.]0 / [BnOH]0 ratio of 200:1:1. A monomer conversion of 99% was achieved in 5 minutes, but a random polymer with a wide molecular weight distribution (PDI = 1.63) was obtained (Inorg. Chem., 2011, 50(8):3589-3595). In 2013, Mountford's group reported potassium complexes of [OOO]-tridentate bisphenol ligands. At 20°C, with dichloromethane as the solvent, and a [LA]0 / [Cat.]0 / [BnOH]0 ratio of 100:1:4, a monomer conversion of 99% was achieved in 5 minutes, and the polymer molecular weight was close to the theoretical molecular weight, but only a random polymer was obtained (Dalton Trans., 2013, 42(25)). In 2014, Wu's group synthesized phenoxy sodium and potassium complexes with crown ether-assisted coordination. Under conditions of -60℃, tetrahydrofuran, and [LA]0 / [Cat.]0 / [BnOH]0 = 400:1:10, they catalyzed the ring-opening polymerization of rac-LA, achieving a conversion rate of 99% after 5 minutes of reaction, yielding high-isotacticity polylactide (P...). m =0.86)(Macromolecules,2014,47(22):7789-7796). In 2015, the group reported a series of crown ether-assisted coordination, anthracene ring-substituted sodium and potassium phenoxy compounds. Under the conditions of -70℃, toluene, and [LA]0 / [Cat.]0 / [BnOH]0 = 200:1:1, the monomer conversion reached 88% after 16 h of reaction, and the polymerization product had high isotacticity (P m =0.94)(Inorg.Chem.,2015,55(1):136-143). In 2018, Wu's group synthesized a crown ether-assisted coordination of amidine potassium complex, which exhibited high isotactic selectivity (P) under the conditions of -70℃, toluene, and [LA]0 / [Cat.]0 / [BnOH]0 = 1000:1:1. m =0.88), resulting in high molecular weight polylactide (Inorg. Chem., 2018, 57(6):3158-3168.). In 2020, the Mosquera group synthesized potassium crown ether complexes of terpene-derived ligands. In toluene at -70℃, without the addition of alcohol, a 100 equivalent rac-LA ring-opening polymerization reaction was carried out for 180 min, resulting in complete monomer conversion. The obtained polymer had isotacticity P m =0.85; with the addition of benzyl alcohol, the molecular weight distribution narrowed. After adding 10 equivalents of benzyl alcohol, the resulting polymer had a PDI of 1.05. m=0.93 (Organometallics, 2020, 39(12):2278-2286). All the alkali metal complexes reported in the above literature require crown ether-assisted coordination to exhibit good isotactic stereoselectivity for rac-LA polymerization. However, crown ethers are toxic and unsuitable for industrial production. To avoid using crown ethers, in 2019, Wu's group synthesized a series of mononuclear Salen ligand anion-cation pair sodium complexes for the first time, using tetraalkylammonium as the corresponding cation. Under the conditions of -70℃ toluene and [LA]0 / [Cat.]0 / [BnOH]0 = 500:1:5, the conversion rate of the catalytic rac-LA ring-opening polymerization reached 87% after 2220 min, exhibiting moderate isotactic selectivity (P). m =0.82)(Inorg.Chem.2019,58,218–227). Subsequently, Wu's group synthesized tetradentate aminobisphenoloxy sodium complexes, a series of complexes capable of catalyzing 1000 equivalents of rac-LA polymerization with isotactic selectivity reaching P. m =0.82, the polymer molecular weight can reach 50.9 kg / mol, and the molecular weight distribution is narrow (Chem.Asian J.2019,14,662–669).

[0005] Significant breakthroughs have been achieved in the research of isotactic polymerization of racemic lactide, with high isotacticity polylactide obtained through effective design of metal complex catalyst structures. Currently, most alkali metal complexes exhibiting high isotactic selectivity for the ring-opening polymerization of racemic lactide contain crown ethers as auxiliary ligands. However, crown ethers are toxic and unsuitable for industrial production. Alkali metal complexes without crown ethers as auxiliary ligands exhibit only moderate isotactic selectivity for the polymerization of racemic lactide at low temperatures. Therefore, further development of high isotactic selectivity alkali metal complex catalysts without crown ether coordination is needed to promote their industrial application. The anion-cation-p-type pyridine-bridged bisaminophenoloxy alkali metal complex disclosed in this invention, without crown ethers as auxiliary ligands, exhibits high isotactic selectivity and high catalytic activity at low temperatures. Summary of the Invention

[0006] One of the objectives of this invention is to disclose a class of ion-pair pyridine-bridged bisaminophenoloxy alkali metal complexes.

[0007] The second objective of this invention is to disclose a method for preparing a class of ion-pair type pyridine-bridged bisaminophenoloxy alkali metal complexes.

[0008] The third objective of this invention is to disclose the application of a class of ion-pair pyridine-bridged bisaminophenoloxy alkali metal complexes in lactone polymerization.

[0009] The technical concept of this invention: Salan-type bisphenol ligands are characterized by readily available raw materials, simple synthesis, and tunable structure. By changing substituents to adjust electronic and steric effects, the catalytic activity and stereoselectivity of metal complexes can be effectively controlled. However, they only have four coordination sites, which is unfavorable for stabilizing mononuclear metal centers in alkali metal catalysts. This invention proposes to introduce a pyridine group into the bridging site of the Salan ligand, giving it five chelating coordination sites. Based on this, an additional cation is used to stabilize excess ligand anions to obtain mononuclear ion-pair type alkali metal complexes. Furthermore, by changing the substituents in the ligand, the Lewis acidity of the metal center and the steric hindrance around the metal center can be adjusted, aiming to achieve highly active and highly isotactic stereoselective catalytic ring-opening polymerization of racemic lactide using non-crown ether-assisted coordination alkali metal complexes.

[0010] The ion-pair pyridine-bridged bisaminophenoxy alkali metal complex (I) provided by the present invention is characterized by having the following general formula:

[0011]

[0012] In formula (I):

[0013] R 1 ~R 2 Representing C1 to C respectively 20 Alkyl groups with straight, branched, or cyclic structures, C7–C6 30 Mono- or polyaryl substituted alkyl groups, or halogens;

[0014] R 3 Representing C1 to C 20 Alkyl groups with straight, branched, or cyclic structures, C7–C6 30 Mono- or polyaryl substituted alkyl groups, C6-C 18 aryl;

[0015] R 4 Representing C1 to C 10 Alkyl groups with straight, branched, or cyclic structures;

[0016] M represents Na and K.

[0017] More characteristically, in equation (I),

[0018] R 1 ~R 2 Representing C1-C8 straight-chain, branched, or cyclic alkyl groups, C7-C8 respectively. 20 Mono- or polyaryl substituted alkyl groups, or halogens; R 3 It is an alkyl group with a C1-C8 straight chain, branched chain, or cyclic structure, and a C7-C8... 20 Mono- or polyaryl substituted alkyl groups, C6-C12 aryl; R 4 It is an alkyl group with a C1 to C6 straight chain, branched chain, or cyclic structure.

[0019] Preferably, in formula (I), R 1 ~R 2 They are methyl, isopropyl, tert-butyl, cumyl, and triphenylmethyl, respectively; R 3 The compounds are methyl, ethyl, tert-butyl, n-butyl, cyclopentyl, cyclohexyl, benzyl, and phenyl; R 4 The derivatives are methyl, ethyl, isopropyl, and n-butyl.

[0020] The preferred structure of the ion-pair type pyridine-bridged diaminophenoloxy alkali metal complex is as follows:

[0021]

[0022] Preferred ion-pair pyridine-bridged bis(aminophenol) alkali metal complexes typically have the following structures for their pyridine-bridged aminobisphenol ligands:

[0023]

[0024] The preparation method of the ion-pair type pyridine-bridged bisaminophenoloxy alkali metal complex (I) of the present invention includes the following steps:

[0025]

[0026] The 2-bromomethyl-4,6-disubstituted phenol of formula (III) and the 2,6-di(substituted aminomethyl)pyridine of formula (IV) were reacted in an organic medium in the presence of an alkylamine at a temperature of 0–90 °C for a time of 2–72 hours. The pyridine-bridged bisaminophenol ligand compound (II) was then collected from the reaction product.

[0027] Optionally, the pyridine-bridged bisaminophenol ligand compound shown in formula (II) is reacted with a metal hydride in an organic medium at a temperature of 0–100 °C for 2–24 hours; then a quaternary ammonium salt [NR] is added. 4 4]X continued to react at a temperature of 0–100 °C for 2–24 hours, and then the ion-pair pyridine-bridged bisaminophenoloxy alkali metal complex (I) was collected from the reaction product.

[0028] In the above preparation method, the substituent R 1 ~R 3 Consistent with the corresponding groups of the ion-pair pyridine-bridged bisaminophenoloxy alkali metal complex (I) as described in this invention;

[0029] The alkylamine is triethylamine, tributylamine, or triisopropylamine;

[0030] The metal hydride MH is NaH or KH;

[0031] Quaternary ammonium salts [NR] 4 In X, R 4 Consistent with the corresponding group of the ion-pair type pyridine-bridged aminobisphenol oxyalkali metal complex (I) described in this invention; X is Cl, Br, I or OH;

[0032] Pyridine-bridged bisaminophenol ligands (II) with metal hydrides and quaternary ammonium salts [NR] 4 4] The molar ratio of X is 1:2.0~4.0:0.8~1.5, preferably 1:2.2~2.5:0.9~1.2;

[0033] The organic medium is selected from one or two of tetrahydrofuran, diethyl ether, toluene, benzene, petroleum ether, and n-hexane.

[0034] In the preparation method of the dimethylenepyridine-bridged bisaminophenol ligand (I) of the present invention, the synthesis of 2-bromomethyl-4,6-disubstituted phenol as shown in formula (III) can be obtained by reacting 2,4-substituted phenol with paraformaldehyde in a 33% hydrogen bromide acetic acid solution according to the following route (Inorg. Chem., 2002, 41, 3656; J. Org. Chem., 1994, 59, 1939):

[0035]

[0036] In the preparation method of the dimethylenepyridine-bridged bisaminophenol ligand (II) of the present invention, the synthesis of 2,6-bis(substituted aminomethyl)pyridine as shown in formula (IV) can be carried out according to the following route (Chem.-Eur.J., 2005, 11(8), 2385-2394), that is, 2,6-pyridinedimethylethanol is oxidized to obtain 2,6-pyridinedicarboxaldehyde, and then reacted with primary amine R 3 The reaction of NH2 followed by reduction with a reducing agent yields:

[0037]

[0038] The synthesis of 2,6-bis(substituted aminomethyl)pyridine as shown in formula (IV) can also be carried out via the following route, referring to the method in the literature (Nat. Commun., 2021, 12, 1572): reacting 2,6-pyridinediethanol with hydrogen bromide to give 2,6-dibromomethylpyridine, followed by reaction with a primary amine R. 3 The reaction of NH2 followed by reduction with a reducing agent yields:

[0039]

[0040] In the above preparation method, the reducing agent is a common reducing agent in organic reactions, such as sodium borohydride or lithium aluminum hydride.

[0041] The ion-pair type pyridine aminobisphenol alkali metal complex of the present invention is a highly efficient lactone polymerization catalyst that can be used for the polymerization of L-lactide, D-lactide, rac-lactide, and meso-lactide, and the polymerization methods are solution polymerization and melt polymerization.

[0042] Using the ion-pair pyridine-bridged bisaminophenol alkali metal complex of the present invention as a catalyst, lactide is polymerized. The molar ratio of catalyst to monomer during polymerization is 1:1 to 10000, preferably 1:20 to 5000, and most preferably 1:100 to 3000.

[0043] Using the cationic-anionic pyridine-bridged bisaminophenoxy alkali metal complex of the present invention as a catalyst, a certain amount of alcohol can be added as a chain transfer agent to control the molecular weight of the resulting polymer during the polymerization of lactide. The molar ratio of catalyst to alcohol and lactide monomer during polymerization is 1:1 to 50:1 to 10000, preferably 1:1 to 20:20 to 5000, and most preferably 1:1 to 10:100 to 3000; the alcohol is C1 to C2. 10 Alkyl alcohols with straight-chain, branched, or cyclic structures, C7–C6 20 Mono- or polyaryl substituted alkyl alcohols, preferably isopropanol or benzyl alcohol.

[0044] Using the ion-pair pyridine-bridged bisaminophenoloxy alkali metal complex of the present invention as a catalyst, when catalyzing the polymerization of lactide, the lactide is polymerized at -70 to 140°C in the presence of alcohol, preferably -70 to 100°C, and most preferably -70 to 50°C.

[0045] Using the ion-pair pyridine-bridged diaminophenol alkali metal complex of the present invention as a catalyst, a solvent may also be included in the catalytic polymerization of lactones. The solvent is preferably one or more of toluene, tetrahydrofuran, dichloromethane, n-hexane, petroleum ether, m-xylene, o-xylene, mesitylene, and trichlorobenzene. Specifically, it may be one, two, three, four, or five kinds of solvents.

[0046] The catalyst provided by this invention is easy to prepare and has stable properties. Furthermore, the catalyst exhibits high catalytic activity and stereoselectivity in the ring-opening polymerization of lactide, and highly isotactic selective polymerization can be achieved by controlling the ligand structure and polymerization conditions. The invention is further illustrated below with specific embodiments, but is not limited thereto. Detailed Implementation

[0047] Example 1

[0048] ligand L 1 Synthesis of H2

[0049] (1) Synthesis of 2,6-pyridinedicarboxaldehyde

[0050]

[0051] Under argon protection, 2,6-pyridinediethanol (5.40 g, 38.8 mmol), 40 mL of 1,4-dioxane, and selenium dioxide (4.44 g, 43.5 mmol) were added sequentially to a flask, and the mixture was heated to 110 °C for 5 h. The reaction mixture was filtered to obtain a yellow solution, which was concentrated until slightly turbid, and 15 mL of petroleum ether was slowly added. The mixture was then placed in a refrigerator for crystallization. The obtained solid was dried under vacuum to remove the solvent, yielding a light brown solid of 2,6-pyridinedicarboxaldehyde (4.83 g, 90%).

[0052] 1 H NMR (400MHz, CDCl3): δ10.15(s,2H,-CHO),8.17(d, 3 J = 7.6 Hz, 2H, PyH), 8.08 (t, 3 J = 7.6 Hz, 1H, PyH.

[0053] (2) Synthesis of 2,6-bis(benzylaminomethyl)pyridine

[0054]

[0055] 2,6-pyridinedicarboxaldehyde (1.35 g, 10.0 mmol) and 30 mL of methanol were added to a 100 mL round-bottom flask, followed by benzylamine (2.2 mL, 20 mmol). The mixture was heated under reflux for 12 hours. After cooling, NaBH4 (1.51 g, 40.0 mmol) was slowly added. The mixture was heated to 70 °C and reacted for 12 hours. Methanol was removed under vacuum, and the reaction was quenched with a saturated potassium carbonate solution. The mixture was poured into a separatory funnel, extracted with dichloromethane, dried over anhydrous sodium sulfate, filtered, and the solvent was removed from the filtrate to obtain 2,6-bis(benzylaminomethyl)pyridine (3.11 g, 98%).

[0056] 1 H NMR (400MHz, CDCl3): δ 7.61 (t, 3 J=7.6Hz,1H,Py-H),7.40–7.30(m,8H,Ar-Hand Ph-H),7.25(tt, 3 J = 7.0 Hz 4 J = 1.5 Hz, 2H, Ar-H), 7.19 (d, 3J=7.6Hz,2H,Py-H),3.93(s,4H,Py-CH2-),3.86(s,4H,Ph-CH2-),2.39(br s,2H,-NH-).

[0057] (3) Ligand L 1 Synthesis of H2

[0058]

[0059] Add 3.11 g (approximately 9.82 mmol) of 2,6-bis(benzylaminomethyl)pyridine and 60 mL of dichloromethane to a 100 mL round-bottom flask, followed by 11 mL of triethylamine. Then add 6.00 g (20.0 mmol) of 2-bromomethyl-4,6-di-tert-butylphenol, resulting in a yellow reaction solution. After the reaction is complete, pour the solution into 50 mL of water, shake to separate the layers, extract with dichloromethane, combine the organic phases, wash with water, dry with anhydrous sodium sulfate, filter, and dry under vacuum to obtain a yellow oily substance. Recrystallize from dichloromethane / methanol to give 5.89 g of a pale yellow solid, with a yield of 78%.

[0060] 1 H NMR(400MHz, CDCl3): δ10.77(br s,2H,ArOH),7.60(t, 3 J = 7.7 Hz, 1H, Py-H), 7.35 (d, 3 J = 7.3 Hz, 4H, Ph-H), 7.29 (t, 3 J = 7.3 Hz, 4H, Ph-H), 7.23 (t, 3 J = 7.3 Hz, 2H, Ph-H), 7.21 (d, 4 J = 2.3 Hz, 2H, Ar-H), 7.18 (d, 3 J = 7.7 Hz, 2H, Py-H), 6.87 (d, 4 J=2.3Hz,2H,Ar-H),3.84(s,4H,Py-CH2-),3.79(s,4H,Ar-CH2-),3.72(s,4H,Ph-CH2-),1.48(s,18H,-C(CH3)3),1.28(s,18H,-C(CH3)3). 13 C{ 1H}NMR (100MHz, CDCl3, 298K): δ157.62,153.99,140.61,137.53,137.30,137.08,135.63,129.96,12 9.66,128.68,128.36,127.63,127.28,124.43,124.19,123.24,122.94,122.24,121.94,121.67(All Ar-C),58.92(Py-CH2),58.51(Ar-CH2),58.10(Ph-CH2),35.09(C(CH3)3),34.26(C(CH3)3),31.89,31.77,29.80(all C(CH3)3).ESI-HRMS calcd.for C 51 H 67 N3O2+H + [M+H]:754.5307; found:754.5309.

[0061] Example 2

[0062] ligand L 2 Synthesis of H2

[0063] (1) Synthesis of 2,6-bis(cyclohexylaminomethyl)pyridine

[0064]

[0065] Except for the use of cyclohexylamine (4.00 g, 40.3 mmol), 2,6-pyridinedicarboxaldehyde (2.70 g, 20.0 mmol), and NaBH4 (3.20 g, 80.0 mmol) as raw materials, the process was the same as that used in the synthesis of 2,6-bis(benzylaminomethyl)pyridine, yielding 2,6-bis(cyclohexylaminomethyl)pyridine (4.49 g, 75%).

[0066] 1 H NMR (400MHz, CDCl3): δ 7.53 (t, 3 J = 7.7 Hz, 1H, Py-H), 7.10 (d, 3 J=7.7Hz,2H,Py-H),3.87(s,4H,-CH2-),2.45(tt, 3 J=10.1,3.8Hz,2H,CH of cyclohexyl),2.32(br s,2H,-NH-),1.90(br d, 3J=11.5Hz,4H,CH2 of cyclohexyl),1.74–1.65(m,4H,CH2 ofcyclohexyl),1.62–1.53(m,2H,CH2 of cyclohexyl),1.28-1.04(m,10H,CH2 ofcyclohexyl).

[0067] (2) Ligand L 2 Synthesis of H2

[0068]

[0069] Except for the use of 2,6-bis(cyclohexylaminomethyl)pyridine (3.01 g, 10.0 mmol) and 2-bromomethyl-4,6-di-tert-butylphenol (6.00 g, 20.0 mmol) as raw materials, the reaction procedure was the same as that of L. 1 With the same H2, a yellow solid (4.52 g, 61%) was finally obtained.

[0070] 1 H NMR (400MHz, CDCl3): δ11.17(br s,2H,Ar-OH),7.56(t, 3 J=7.7Hz,1H,Py-H),7.21-7.16(m,4H,Ar-H&Py-H),6.84(d, 4 J=2.4Hz,2H,Ar-H),3.85(s,4H,Py-CH2),3.81(s,4H,Ar-CH2),2.63(tt, 3 J=11.5,3.0Hz,2H,CH2 of cyclohexyl),1.94(br d, 3 J=11.5Hz,4H,CH2of cyclohexyl),1.77(br d, 3 J=12.0Hz,4H,CH2 of cyclohexyl),1.59(br d, 3 J=10.6Hz,2H,CH of cyclohexyl),1.42(s,18H,Ar-C(CH3)3)1.46-1.38(m,2H,CH2 ofcyclohexyl),1.27(s,Ar-C(CH3)3),1.31-1.22(m,2H,CH2 of cyclohexyl),1.19-1.01(m,6H,CH2 of cyclohexyl). 13 C{ 1H}NMR (100MHz, CDCl3, 298K): δ158.47,154.47,140.39,137.27,136.99,136.47,124.05,123.81,122.90,122.60,121.89,121.70,121.40 (all Ar-C),58.88,58.68(Py-CH2N-),55.72(-NCH2Ar),54.48(-NCH-),34.97,34.24(C(CH3)3),31.91,31.77,29.75,29.69(all C(CH3)3),28.22,28.11,26.05(all-CH2-of cyclohexyl).ESI-HRMS calcd.for C 49 H 75 N3O2+H + [M+H]:738.5933; found:738.5940.

[0071] Example 3

[0072] ligand L 3 Synthesis of H2

[0073] (1) Synthesis of 2,6-di(bromomethyl)pyridine

[0074]

[0075] Add 6.4 mL of 33 wt% acetic acid solution of hydrogen bromide and 26 mL of glacial acetic acid to a 100 mL round-bottom flask. While stirring, add 1.82 g (13.1 mmol) of 2,6-pyridinediethanol and heat under reflux for 8 h. After the reaction is complete, cool. Under ice-water bath cooling, slowly add sodium hydroxide solution to adjust the pH to 9. A grayish-white solid precipitates out; filter to obtain 2,6-bis(bromomethyl)pyridine as a white solid (2.20 g, 63%).

[0076] 1 H NMR (400MHz, CDCl3): δ 7.71 (t, 3 J = 7.8 Hz, 1H, Py-H), 7.38 (d, 3 J=7.8Hz,2H,Py-H),4.54(s,4H,Py-CH2-).

[0077] (2) Synthesis of 2,6-bis(tert-butylaminomethyl)pyridine

[0078]

[0079] Add 12.7 mL of tert-butylamine (120 mmol) and 3.317 g of potassium carbonate (240 mmol) to a 100 mL round-bottom flask and set aside. Dissolve 2,6-di(bromomethyl)pyridine (2.65 g, 10.0 mmol) in 20 mL of DMF and slowly add it dropwise to the aforementioned round-bottom flask, reacting for 8 h. Quench the reaction with 50 mL of water, extract with 100 mL of DCM, and dry with anhydrous sodium sulfate. After filtering to remove the desiccant, remove the solvent from the filtrate under vacuum to obtain a pale yellow transparent liquid (2.02 g, 80%).

[0080] 1 H NMR (400MHz, CDCl3): δ 7.51 (t, 3 J = 2.7 Hz, 1H, Py-H), 7.12 (d, 3 J=2.7Hz,2H,Py-H),5.25(s,2H,-NH-),3.81(s,4H,Py-CH2-),1.14(s,18H,-C(CH3)3).

[0081] (3) Ligand L 3 Synthesis of H2

[0082]

[0083] Except for the use of 2,6-bis(tert-butylaminomethyl)pyridine (2.02 g, 8.10 mmol) and 2-bromomethyl-4,6-di-tert-butylphenol (4.85 g, 16.2 mmol) as raw materials, the other procedures were the same as those for ligand L. 1 The synthesis of H2 was the same. Recrystallization from dichloromethane / petroleum ether gave a white solid (3.84 g, yield 56%).

[0084] 1 H NMR (400MHz, CDCl3): δ10.91(br s,2H,Ar-OH),7.31(t, 3 J = 7.7 Hz, 1H, Py-H), 7.12 (d, 4 J = 2.4 Hz, 2H, Ar-H), 7.09 (d, 3 J = 7.7 Hz, 2H, Py-H), 6.81 (d, 4 J=2.4Hz,2H,Ar-H),3.91(s,4H,Py-CH2-),3.81(s,4H,Ar-CH2-),1.38(s,18H,Ar-C(CH3)3),1.25(s,18H,Ar-C(CH3)3),1.19(s,18H,NC(CH3)3). 13 C{ 1H}NMR (100MHz, CDCl3, 298K): δδ159.69,154.18,140.61,136.52,136.20,135.57,123.67,123.45,123.01,122.80,122.52,121.37,121.03(all Ar-C),56.99(Py-CH2N-),56.24(-NCH2Ar),54.77(NC(CH3)3),34.87,34.22(C(CH3)3),31.90,31.76,29.73,29.65(all C(CH3)3),27.12,26.96(NC(CH3)3).ESI-HRMS calcd.forC 45 H 71 N3O2+H + [M+H]:686.5620; found:686.5626.

[0085] Example 4

[0086] Synthesis of complex Na1:

[0087]

[0088] Weigh L 1 H2 (377 mg, 0.500 mmol) was placed in a 50 mL Schlenk flask and dried in a 60 °C oven for 8 h. Then, it was placed in an argon-atmosphere glove box. 20 mL of tetrahydrofuran was added to dissolve the H2, followed by the addition of NaH (36 mg, 1.5 mmol), and the mixture was stirred for 8 h. Tetrabutylammonium chloride (139 mg, 0.5 mmol) was weighed and added to the reaction flask. The flask walls were rinsed with a small amount of tetrahydrofuran, and the mixture was stirred for 12 h. After the reaction was complete, the mixture was filtered in a glove box to remove residual NaH, the generated sodium chloride, and other solid impurities. The filtrate was concentrated under vacuum until the solution became slightly viscous. Hexane was slowly added dropwise until the solution became slightly turbid. The mixture was allowed to stand overnight at room temperature, resulting in the precipitation of a solid. The mother liquor was discarded, and the solid was washed with a small amount of hexane, removed from the glove box, and dried under vacuum to obtain a white solid (672 mg, 66%).

[0089] 1 H NMR (400MHz, C6D6): δ 7.53 (d, 4 J = 2.8 Hz, 2H, Ar-H), 7.24 (d, 3 J = 7.0 Hz, 4H, Ph-H), 7.14 (d, 4 J = 2.8 Hz, 2H, Ar-H), 7.08 (t, 3 J = 7.0 Hz, 4H, Ph-H), 7.03(t,3 J = 7.0 Hz, 2H, Ph-H), 6.70 (t, 3 J = 7.6 Hz, 1H, Py-H), 6.20 (d, 3 J=7.6Hz,2H,Py-H),4.50-3.90(br s,4H,NCH2Py),4.11(s,4H,NCH2Ar),4.00–3.59(br s,4H,NCH2Py),3.04-2.89(m,8H,N(CH2CH2CH2CH3)4),1.82(s,18H,Ar-C(CH3) 3),1.51(s,18H,Ar-C(CH3)3),1.35–1.18(m,16H,N(CH2CH2CH2CH3)4),0.81(t, 3 J=7.0Hz,12H,N(CH2CH2CH2CH3)4). 13 C{ 1 H}NMR (100MHz, C6D6): δ170.09,160.17,136.24,136.00,135.75,131.51,128.33,127.98,127.78,127.14,124.11,123.48,119.93(All Ar-C),61.35(N-CH2-Py),59.34(N-CH2-Ar),58.62(N-CH2-Ph),54.04(NCH2CH2CH2CH3),36.07(C(CH3)3),34.00(C(CH3)3),32.79( C(CH3)3),30.95(C(CH3)3),25.82(THF),24.38(NCH2CH2CH2CH3),20.11(NCH2CH2CH2CH3),13.81(NCH2CH2CH2CH3).Anal.Calcd.for C 67 H 101 N4NaO2: C, 79.08; H, 10.01; N, 5.51%. Found: C, 78.90; H, 10.05; N, 5.33%.

[0090] Example 5

[0091] Synthesis of Na2 complex

[0092]

[0093] Except for raw materials using L 2Except for H2 (369 mg, 0.5 mmol), NaH (36 mg, 1.5 mmol), and tetrabutylammonium chloride (139 mg, 0.5 mmol), the procedure was the same as for Na1. A white solid (495 mg, 49% yield) was finally obtained.

[0094] 1H NMR (400MHz, C6D6): δ7.42(br s,2H,Ar-H),7.15(br s,2H,Ar-H),6.92(t, 3 J = 7.6 Hz, 1H, Py-H), 6.48 (d, 3 J=7.7Hz,2H,Py-H),4.12-3.68(m,8H,NCH2Ar and NCH2Py),2.87(s,2H,CH of cyclohexyl),2.73-2.63(m,8H,N(CH2CH2CH2CH3)4),2.27(s,4H,CH2 ofcyclohexyl),1.83(s,22H,CH2 of cyclohexyl and Ar-C(CH3)3),1.57(s,22H,CH2 ofcyclohexyl and Ar-C(CH3)3),1.38–1.19(m,8H,CH2 of cyclohexyl),1.13(m,8H,N(CH2CH2CH2CH3)4),1.09–0.99(m,8H,N(CH2CH2CH2CH3)4),0.79(t, 3 J=7.1Hz,12H,N(CH2CH2CH2CH3)4).Anal.Calcd.for C 65 H 109 N4NaO2: C, 77.85; H, 10.97; N, 5.59%. Found: C, 77.61; H, 10.93; N, 5.58%.

[0095] Example 6

[0096] Synthesis of Na3 complex

[0097]

[0098] Weigh 343 mg (0.5 mmol) L 3H2 was placed in a 50 mL Schlenk flask and dried in an oven for 8 hours. After drying, the mixture was placed in a glove box under argon protection for reaction. 20 mL of tetrahydrofuran was added and stirred to dissolve the H2, followed by the addition of NaH (36 mg, 1.5 mmol), and the reaction was allowed to proceed for 8 hours. 139 mg (0.5 mmol) of tetrabutylammonium chloride was weighed and added to the reaction flask, and the flask walls were rinsed with 2 mL of tetrahydrofuran. The reaction was allowed to proceed for 12 hours. After the reaction was complete, the mixture was filtered in a glove box to remove unreacted NaH, the generated sodium chloride, and other solid impurities. The filtrate was concentrated under vacuum until the solution became viscous. Hexane was slowly added dropwise until the solution became turbid. After standing, the solution separated into two layers: a yellow supernatant on top and a dark brown oily substance on the bottom. The lower oily layer was collected separately. Add a small amount of 2 mL of n-hexane and stir for 5 hours. The oily substance gradually becomes solid. After stirring, filter and wash the obtained solid three times with a small amount of n-hexane. Remove the solvent under vacuum to obtain a pale yellow solid (756 mg, 80%).

[0099] 1 H NMR (400MHz, C6D6): δ7.36(br s,2H,Ar-H),7.20(s,2H,Ar-H),6.87(t, 3 J = 7.6 Hz, 1H, Py-H), 6.34 (d, 3 J=7.6Hz,2H,Py-H),4.64-3.60(br d, 4 J=2.5Hz,4H,NCH2Py),3.83(s,8H,NCH2Ar),3.58-3.55(m,2H,0.5THF),2.77 –2.68(m,8H,N(CH2CH2CH2CH3)4),1.79(s,18H,Ar-C(CH3)3),1.57(s,18H,A r-C(CH3)3),1.42-1.39(m,2H,0.5THF),1.31(s,18H,NC(CH3)3),1.20-1.14(m,8H,N(CH2CH2CH2CH3)4),1.08-0.95(m,8H,N(CH2CH2CH2CH3)4),0.76(t, 3 J=7.3Hz,12H,N(CH2CH2CH2CH3)4).Anal.Calcd.for C 61 H 105 N4NaO2·0.5C4H8O: C, 76.78; H, 11.15; N, 5.68%. Found: C, 76.31; H, 11.01; N, 6.07%.

[0100] Example 7

[0101] Synthesis of complex K1:

[0102]

[0103] Weigh L 1 H2 (377 mg, 0.500 mmol) was placed in a 50 mL Schlenk flask and dried in a 60 °C oven for 8 h. Then, it was placed in an argon-atmosphere glove box. 20 mL of tetrahydrofuran was added to dissolve the H2, followed by the addition of KH (36 mg, 1.5 mmol), and the mixture was stirred for 8 h. Tetrabutylammonium chloride (139 mg, 0.5 mmol) was weighed and added to the reaction flask. The flask walls were rinsed with a small amount of tetrahydrofuran, and the mixture was stirred for 12 h. After the reaction was complete, the mixture was filtered in a glove box to remove residual KH, the generated sodium chloride, and other solid impurities. The filtrate was concentrated under vacuum until the solution became slightly viscous. Hexane was slowly added dropwise until the solution became slightly turbid. The mixture was allowed to stand overnight at room temperature, resulting in the precipitation of a solid. The mother liquor was discarded, and the solid was washed with a small amount of hexane, removed from the glove box, and dried under vacuum to obtain a white solid (672 mg, 66%).

[0104] 1 H NMR (400MHz, C6D6): δ 7.47 (d, 4 J = 2.8 Hz, 2H, Ar-H), 7.18 (d, 4 J = 2.8 Hz, 2H, Ar-H), 6.83 (t, 3 J = 7.7 Hz, 1H, Py-H), 6.43 (d, 3 J=7.7Hz,1H,Py-H),4.30-3.70(m,8H,NCH2Pyand NCH2Ar),2.74(m,8H,N(CH2CH2CH2CH3)4),1.87(s,18H,Ar-C(CH3)3),1.51(s,18H,Ar-C(CH3)3),1.23–1.19(m,16H,N(CH2CH2CH2CH3)4and N(CH2CH2CH2CH3)4),1.08(s,18H,NC(CH3)3),0.84(t,12H,N(CH2CH2CH2CH3)4).

[0105] Example 8

[0106] Under argon protection, racemic lactide (0.144 g, 1.0 mmol) was added to a polymerization flask and dissolved in 0.4 mL of toluene, followed by 0.1 mL of benzyl alcohol in toluene solution. 0.5 mL of catalyst Na1 in toluene solution was added to the polymerization flask. [rac-LA]0 = 1.0 M, [Na]0 = 0.002 M, [BnOH]0 = 0.002 M, [rac-LA]0:[Na]0:[BnOH]0 = 500:1:1. The reaction temperature was controlled at 25 ± 1 °C, and the reaction was carried out for 102 seconds. Petroleum ether was added to terminate the reaction. The solvent was removed, and the residue was dissolved in dichloromethane. Methanol was added to precipitate the polymer. The mixture was vacuum dried for 24 h. The conversion rate was 76%, M n =2.82×10 4 g / mol, molecular weight distribution PDI = 1.62, isotacticity P m =0.52.

[0107] Example 9

[0108] Under argon protection, racemic lactide (0.144 g, 1.0 mmol) was added to a polymerization flask and dissolved in 0.3 mL of toluene, followed by 0.2 mL of a benzyl alcohol toluene solution. 0.5 mL of a Na1 catalyst toluene solution was added to the polymerization flask. The concentrations were: [rac-LA]0 = 1.0 M, [Na]0 = 0.002 M, [BnOH]0 = 0.004 M, and [rac-LA]0:[Na]0:[BnOH]0 = 500:1:2. The reaction temperature was controlled at 25 ± 1 °C, and the reaction was carried out for 84 seconds. Petroleum ether was added to terminate the reaction. The solvent was removed, and the residue was dissolved in dichloromethane. Methanol was added to precipitate the polymer. The mixture was then vacuum dried for 24 h. The conversion rate was 92%. n =3.79×10 4 g / mol, molecular weight distribution PDI = 1.44, isotacticity P m =0.53.

[0109] Example 10

[0110] Except for the temperature being changed to -50±1℃, the other operations were the same as in Example 9. After reacting for 31 minutes, the conversion rate was 56%, M n =2.40×10 4 g / mol, molecular weight distribution PDI = 1.48, isotacticity P m =0.72.

[0111] Example 11

[0112] Under argon protection, racemic lactide (0.144 g, 1.0 mmol) was added to a polymerization flask and dissolved in 0.1 mL of toluene, followed by 0.4 mL of a benzyl alcohol toluene solution. 0.5 mL of a Na1 catalyst toluene solution was added to the polymerization flask. [rac-LA]0 = 1.0 M, [rac-LA]0:[Na]0:[BnOH]0 = 500:1:4. The reaction temperature was controlled at 25 ± 1 °C, and the reaction was carried out for 72 seconds. Petroleum ether was added to terminate the reaction. The solvent was removed, and the residue was dissolved in dichloromethane. Methanol was added to precipitate the polymer. The mixture was vacuum dried for 24 h. The conversion rate was 97%, M n =2.95×10 4 g / mol, molecular weight distribution PDI = 1.55, isotacticity P m =0.53.

[0113] Example 12

[0114] Except for replacing the catalyst with Na2, the other operations were the same as in Example 8. After 2 minutes of reaction, the conversion rate was 75%, M n =2.91×10 4 g / mol, molecular weight distribution PDI = 1.30, isotacticity P m =0.53.

[0115] Example 13

[0116] Except for replacing the catalyst with Na2, the other operations were the same as in Example 9. After reacting for 102 seconds, the conversion rate was 94%, M n =2.42×10 4 g / mol, molecular weight distribution PDI = 1.47, isotacticity P m =0.54.

[0117] Example 14

[0118] Except for replacing the catalyst with Na2 and changing the temperature to -50±1℃, the other operations were the same as in Example 10. After reacting for 82 minutes, the conversion rate was 95%, M n =3.88×10 4 g / mol, molecular weight distribution PDI = 1.78, isotacticity P m =0.76.

[0119] Example 15

[0120] Except for replacing the catalyst with Na3, the other operations were the same as in Example 8. After 2 minutes of reaction, the conversion rate was 86%, M n =4.47×10 4 g / mol, molecular weight distribution PDI = 1.49, isotacticity P m =0.52.

[0121] Example 16

[0122] Except for replacing the catalyst with Na3, the other operations were the same as in Example 9. After reacting for 90 seconds, the conversion rate was 90%, M n =4.14×10 4 g / mol, molecular weight distribution PDI = 1.32, isotacticity P m =0.53.

[0123] Example 17

[0124] Except for replacing the catalyst with Na3 and changing the temperature to -50±1℃, the other operations were the same as in Example 10. After reacting for 32 minutes, the conversion rate was 63%, M n =3.59×10 4 g / mol, molecular weight distribution PDI = 1.38, isotacticity P m =0.88.

[0125] Example 18

[0126] Under argon protection, racemic lactide (0.144 g, 1.0 mmol) was added to a polymerization flask and dissolved in 0.2 mL of toluene, followed by 0.3 mL of a benzyl alcohol toluene solution. 0.5 mL of a Na3 catalyst toluene solution was added to the polymerization flask. The concentrations were: [rac-LA]0 = 1.0 M, [Na]0 = 0.002 M, [BnOH]0 = 0.006 M, and [rac-LA]0:[Na]0:[BnOH]0 = 500:1:3. The reaction temperature was controlled at -50 ± 1 °C, and the reaction was carried out for 22 minutes. Petroleum ether was added to terminate the reaction. The solvent was removed, and the residue was dissolved in dichloromethane. Methanol was added to precipitate the polymer. The mixture was then vacuum dried for 24 h. The conversion rate was 74%. n =2.65×10 4 g / mol, molecular weight distribution PDI = 1.30, isotacticity P m =0.80.

[0127] Example 19

[0128] Under argon protection, racemic lactide (0.144 g, 1.0 mmol) was added to a polymerization flask and dissolved in 0.2 mL of toluene, followed by 0.3 mL of a benzyl alcohol toluene solution. 0.5 mL of a Na3 catalyst toluene solution was added to the polymerization flask. [rac-LA]0 = 1.0 M, [rac-LA]0:[Na]0:[BnOH]0 = 2000:1:2. The reaction temperature was controlled at -50 ± 1 °C, and the reaction was carried out for 56 minutes. Petroleum ether was added to terminate the reaction. The solvent was removed, and the residue was dissolved in dichloromethane. Methanol was added to precipitate the polymer. The mixture was then vacuum dried for 24 h. The conversion rate was 80%, M n =1.31×105 g / mol, molecular weight distribution PDI = 1.90, isotacticity P m =0.73.

[0129] Example 20

[0130] Except for replacing the catalyst with Na3, the monomer was replaced with L-lactide (0.144 g, 1.0 mmol). Other procedures were the same as in Example 9. The reaction was carried out for 48 seconds, and petroleum ether was added to terminate the reaction. The solvent was removed, the residue was dissolved in dichloromethane, and methanol was added to precipitate the polymer. The mixture was then vacuum dried for 24 h. The conversion rate was 84%, M n =5.00×10 4 g / mol, molecular weight distribution PDI = 1.54, isotacticity P m =0.85.

[0131] Example 21

[0132] Except for replacing the catalyst with Na3, the monomer was replaced with L-lactide (0.144 g, 1.0 mmol). Other procedures were the same as in Example 10. The reaction was carried out for 25 minutes, and petroleum ether was added to terminate the reaction. The solvent was removed, and the residue was dissolved in dichloromethane. Methanol was added to precipitate the polymer. The mixture was then vacuum dried for 24 hours. The conversion rate was 85%, M n =4.13×10 4 g / mol, molecular weight distribution PDI = 1.04, isotacticity P m =1.

[0133] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An ion-pair type pyridine-bridged bisaminophenoxy alkali metal complex (I), characterized in that, It has the following general formula: In formula (I): R 1 -R 2 These represent alkyl, cumyl, or triphenylmethyl groups with C1-C8 straight-chain or branched structures, respectively. R 3 Alkyl, cyclopentyl, cyclohexyl, or C7-C6 straight-chain or branched structures. 20 Mono- or polyaryl substituted alkyl groups; R 4 Alkyl groups representing C1-C6 straight-chain or branched structures; M represents Na or K.

2. The ion-pair pyridine-bridged bisaminophenoxy alkali metal complex (I) according to claim 1, characterized in that, R 1 -R 2 It is methyl, isopropyl, tert-butyl, cumyl, or triphenylmethyl; R 3 It is methyl, ethyl, tert-butyl, n-butyl, cyclopentyl, cyclohexyl, or benzyl; R 4 It can be methyl, ethyl, isopropyl, or n-butyl.

3. The method for preparing the ion-pair type pyridine-bridged bisaminophenoloxy alkali metal complex (I) according to any one of claims 1-2, comprising the following steps: The 2-bromomethyl-4,6-disubstituted phenol of formula (III) and the 2,6-bis(substituted aminomethyl)pyridine of formula (IV) were reacted in an organic medium in the presence of an alkylamine at a temperature of 0-90 ºC for 2-72 hours. The pyridine-bridged bisaminophenol ligand compound (II) was then collected from the reaction product. The pyridine-bridged diaminophenol ligand compound shown in formula (II) was reacted with metal hydride MH in an organic medium at a temperature of 0-100 ºC for 2-24 hours; then a quaternary ammonium salt [NR] was added. 4 4]X continued to react at a temperature of 0-100 ºC for 2-24 hours, and then the ion-pair pyridine-bridged bisaminophenoloxy alkali metal complex (I) was collected from the reaction product. In the above preparation method, the substituent R 1 -R 3 Consistent with the corresponding groups of the ion-pair pyridine-bridged bisaminophenoloxy alkali metal complex (I) according to any one of claims 1-2; The alkylamine is triethylamine, tributylamine, or triisopropylamine; The metal hydride MH is either NaH or KH; Quaternary ammonium salts [NR] 4 In X, R 4 The corresponding group is consistent with the corresponding group of the ion-pair pyridine-bridged aminobisphenol oxyalkali metal complex (I) according to any one of claims 1-2; X is Cl, Br, I or OH.

4. The method according to claim 3, characterized in that, Pyridine-bridged bisaminophenol ligands (II) with metal hydrides and quaternary ammonium salts [NR] 4 4] The molar ratio of X is 1: 2.0-4.0: 0.8-1.5; The organic medium is selected from one or two of tetrahydrofuran, diethyl ether, toluene, benzene, petroleum ether, and n-hexane.

5. The application of the ion-pair pyridine-bridged bisaminophenoxy alkali metal complex (I) according to any one of claims 1-2, characterized in that, Used for the ring-opening polymerization of L-lactide, D-lactide, rac-lactide, and meso-lactide.

6. The application according to claim 5, characterized in that, Using the ion-pair pyridine-bridged bisaminophenol alkali metal complex (I) as a catalyst, lactide is polymerized, wherein the molar ratio of catalyst to monomer during polymerization is 1:1-10000.

7. The application according to claim 5, characterized in that, Using the ion-pair pyridine-bridged bisaminophenoxy alkali metal complex (I) according to any one of claims 1-2 as a catalyst, lactide is polymerized in the presence of an alcohol, wherein the molar ratio of catalyst to alcohol and lactide during polymerization is 1:1-50:1-10000; wherein the alcohol is C1-C 10 Alkyl alcohols with straight or branched structures, cyclopentanol, cyclohexanol, or C7-C 20 Mono- or polyaryl-substituted alkyl alcohols.

8. The application according to claim 5, characterized in that, Using the ion-pair pyridine-bridged bisaminophenoxy alkali metal complex (I) according to any one of claims 1-2 as a catalyst, lactide is polymerized at -70 to -140 °C in the presence of an alcohol, wherein the molar ratio of catalyst to alcohol and lactide during polymerization is 1:1-50:1-10000; wherein the alcohol is C1-C 10 Alkyl alcohols with straight or branched structures, cyclopentanol, cyclohexanol, or C7-C 20 Mono- or polyaryl-substituted alkyl alcohols.

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