Preparation method and use of cycloheptyl-fused iminopyridineiron complex catalyst

Abstract

A method for preparing a cycloheptyl-fused iminopyridine iron complex catalyst of Formula (I): (I) wherein R1 is H, methyl, ethyl, or isopropyl; R2 is methyl or H. Preferably, the method comprises the

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of olefin catalysts, and particularly relates to a preparation method and use of a cycloheptyl-fused iminopyridine iron complex catalyst. BACKGROUND

[0002] Polyisoprene (PI) is one of the important poly conjugated dienes, and can be prepared by polymerizing an isoprene monomer under suitable polymerization conditions. PI has the same monomer structure as natural rubber, which is why it is called synthetic natural rubber and has a pivotal position in the field of materials. Synthetic natural rubber has excellent raw rubber strength, basic viscosity, aging resistance, and resilience, and can be widely used in materials such as tires, hoses, and medical adhesives. Since the production of natural rubber is limited by environmental and geographical factors, while natural rubber serves as an important strategic material, its current output cannot meet the demands of society. Therefore, further development for the synthesis of PI is of important significance and application prospects.

[0003] The synthesis and application of PI is inseparable from the development of olefin polymerization catalysts. At present, the catalysts used in isoprene polymerization mainly include lithium-based, titanium-based, molybdenum-based, and rare earth-based catalysts. In recent years, transition metal complexes have received extensive attention in PI as olefin polymerization catalysts, and having the advantages such as simplicity, high catalytic activity, desirable stability, and controllable molecular weight and distribution for polymers.

[0004] For example, patent CN111171190A reports an a-imine iron / cobalt complex catalyst that can catalyze the synthesis of PI with a high activity and regulate the molecular weight and molecular weight distribution. Meanwhile, patent CN106632764 reports a pyridine imine iron or cobalt metal complex catalyst that can further regulate the molecular weight and molecular weight distribution of PI by regulating a catalyst structure.

[0005] In general, compared with metallocene catalysts, iron metal complex catalysts have the advantages such as simple synthesis, low cost, and high stability and can further regulate the structure and molecular weight of a product by modifying the ligand structure. In the research of these catalysts, obtaining catalysts with high thermal stability and catalytic activity is the key and an important factor in promoting the industrial applications. SUMMARY

[0006] The present disclosure provides a method for preparing a cycloheptyl-fused iminopyridine iron complex catalyst, the method includes the following steps: heating a compound shown in 5 Formula (II), a compound shown in Formula (III) and a metal halide FeCh in an organic solvent, and conducting reaction to obtain the complex catalyst shown in Formula (I), Formula (I)

[0007] 16 12 24 Formula (II) Formula (111)

[0008]

[0009] wherein in Formula (I), Ri is one selected from the group consisting of H, methyl, ethyl, and isopropyl; and R2 is one selected from the group consisting of methyl and H.

[0010] In some embodiments, the cycloheptyl-fused iminopyridine iron complex catalyst is any one complex selected from the group consisting of:

[0011] Fei: Ri=H; R2=H;

[0012] Fe2: Ri=Me; R2=H; 15

[0013] Fe3:Ri=Et;R2=H;

[0014] Fe4: Ri=i-Pr; R2=H;

[0015] Fe5: Ri=Me; R2=Me; and

[0016] Fe6: Ri=Et; R2=Me;

[0017] wherein Me represents methyl, Et represents ethyl, and i-Pr represents isopropyl. 20

[0018] In some embodiments, a feeding ratio of the compound shown in Formula (II), the compound shown in Formula (III), and the metal halide FeCh is 1:1:0.95, and the feeding ratio refers to a mole ratio; the organic solvent is acetic acid; and the reaction is conducted at a reflux temperature of the acetic acid.

[0019] In some embodiments, before the complex catalyst shown in Formula (I) is obtained, the - 3 -method further comprises cooling a resulting reaction product to room temperature and then precipitating with diethyl ether, and collecting a resulting precipitate by filtration and then washing with the diethyl ether.

[0020] Use of the method for preparing a cycloheptyl-fused iminopyridine iron complex catalyst in 5 preparation of a catalyst for isoprene polymerization.

[0021] A catalyst composition for isoprene polymerization, comprising / consisting of the complex catalyst as described in claim 1 or 2 and a cocatalyst;

[0022] wherein the cocatalyst is one or more selected from the group consisting of aluminoxane, aluminum alkyl, and aluminum alkyl chloride; 10

[0023] the aluminoxane is one or two selected from the group consisting of methylaluminoxane and triisobutylaluminum-modified methylaluminoxane;

[0024] the aluminum alkyl is one or more selected from the group consisting of triisobutylaluminum, 15 CXI CXI trimethylaluminum, and triethylaluminum; and

[0025] the aluminum alkyl chloride is one or more selected from the group consisting of dimethylaluminum chloride, ethylaluminum sesquichloride, and methylaluminum sesquichloride.

[0026] In some embodiments, the cocatalyst is the methylaluminoxane, a molar ratio of the cocatalyst methylaluminoxane to iron element in the complex catalyst shown in Formula (I) is in a range of (10-250):1.

[0027] A method for preparing polyisoprene (PI), including: catalyzing polymerization of isoprene under a condition of using the catalyst composition for isoprene polymerization as described in claim 8 as a catalyst to obtain the PI.

[0028] In some embodiments, the polymerization is conducted at a temperature of -40 °C to 100 °C;

[0029] the polymerization is conducted under a normal pressure;

[0030] the polymerization is conducted for 0.2 min to 120 min; 25

[0031] the polymerization is conducted in a solvent, and the solvent is toluene; and

[0032] the polymerization is conducted in an inert atmosphere, and the inert atmosphere is a nitrogen atmosphere. BRIEF DESCRIPTION OF THE DRAWINGS 30

[0033] FIG. 1 shows a reaction flow diagram for preparing the complex catalyst shown in Formula (I) in the preparation method and use of a cycloheptyl-fused iminopyridine iron complex catalyst of the present disclosure.

[0034] FIG. 2 shows a schematic structural diagram of the Fe2 crystal of the complex catalyst in the preparation method and use of a cycloheptyl-fused iminopyridine iron complex catalyst of the present disclosure.

[0035] FIG. 3 shows a schematic structural diagram of the Fe3 crystal of the complex catalyst in the preparation method and use of a cycloheptyl-fused iminopyridine iron complex catalyst of the present disclosure. 5

[0036] FIG. 4 shows a schematic structural diagram of the Fe6 crystal of the complex catalyst in the preparation method and use of a cycloheptyl-fused iminopyridine iron complex catalyst of the present disclosure.

[0037] FIG. 5 to FIG. 14 show the hydrogen nuclear magnetic spectrums and the carbon spectrums of the polymers in the preparation method and use of a cycloheptyl-fused iminopyridine iron complex 10 catalyst of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the drawings in the examples of the present disclosure. 15 Apparently, the described embodiments are merely a part rather than all of the embodiments of the present disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative effort shall fall within the protection scope of the present disclosure. All experimental methods used in the following examples are conventional methods, unless otherwise specified. ^211

[0039] All materials, reagents etc. used in the following examples may be commercially available, unless otherwise specified.

[0040] Unless otherwise specified, the concentrations in the following examples are molar concentrations.

[0041] The molecular weight and molecular weight distribution of the polymers obtained in the 25 following examples of isoprene polymerization are measured by conventional high-temperature gel permeation chromatography (GPC). The polymerization activity of the polymers is calculated according to the following formula: polymerization activity = polymer output / (catalyst dosagexpolymerization time).

[0042] The compounds synthesized below are confirmed by infrared and elemental analysis. 30

[0043] As an embodiment, the synthesis of the complexes in the following examples is conducted according to the method shown in FIG. 1.

[0044] Example 1

[0045] Preparation of (E)-2,6-dihydro-N-(5,6,7,8-tetrahydrocycloheptapyridin-9-ene)aniline [Fei: Ri=H; R2=H; X=C1]:

[0046] 5,6,7,8-tetrahydro-9H-cycloheptapyridin-9-one (1.36 mmol), aniline (1.36 mmol), and a catalytic amount of ferrous chloride were added to an acetic acid solution (20 mL) to obtain a mixture. The mixture was heated and refluxed for 12 h. A refluxed product was cooled to room temperature and precipitated with a large amount of diethyl ether. A resulting precipitate was filtered, and washed 5 with diethyl ether 2 to 3 times, and then dried under vacuum to obtain 0.24 g of a purple solid. A yield of the purple solid was 48%.

[0047] The structure verification data are as follows:

[0048] FT-IR(KBr,cm-1):3068,2945,1607[v(C=N)],1571,1461,1443,1266,1172,801,775.

[0049] Elemental analysis: [C32H32C15Fe2N4+CH2C12]; theoretical value: C, 49.24%; H, 4.69%; N, 10 6.21%; experimental value: C, 49.21%; H, 4.63%; N, 6.13%.

[0050] It can be seen from the above structural verification data that the prepared complex is the target product Fei. 15 CXI CXI 25 30

[0051] Example 2

[0052] Preparation of (E)-2,6-dimethyl-N-(5,6,7,8-tetrahydrocycloheptapyridin-9-ene)aniline ferric chloride [Fe2: Ri=Me; R2=H; X=C1], as shown in FIG. 2:

[0053] A brown-red solid (yield: 58%) was prepared by the same method as in Example 1 (only replacing aniline with 2,6-dimethylaniline), namely the Fe2 compound shown in Formula (I).

[0054] The structure verification data are as follows:

[0055] As shown in FIG. 2, the cationic part of the complex is biphasic, exhibiting a twisted triangular bipyramidal molecular geometry around the metal center. Two nitrogen atoms from the imine group and one chloride atom form a triangular equatorial plane, while nitrogen atoms from the two pyridine rings are located in the axial position of this plane. The angles between the atoms of this triangular plane are slightly distorted from 120°.

[0056] FT-IR(KBr,^):3068,2945,1607[v(C=N)], 1571,1461,1443,1266,1172,801,775.

[0057] Elemental analysis: [C32H32C15Fe2N4+CH2C12]; theoretical value: C, 49.24%; H, 4.69%; N, 6.21%; experimental value: C, 49.21%; H, 4.63%; N, 6.13%.

[0058] It can be seen from the above structural verification data that the prepared complex is the target product Fe2.

[0059] Example 3

[0060] Preparation of (E)-2,6-diethyl-N-(5,6,7,8-tetrahydrocycloheptapyridin-9-ene)aniline ferric chloride [Fe3: Ri=Et; R2=H; X=C1], as shown in FIG. 3:

[0061] A brown-red solid (yield: 54%) was prepared by the same method as in Example 1 (only replacing aniline with 2,6-diethylaniline), namely the Fe3 compound shown in Formula (I).

[0062] The structure verification data are as follows:

[0063] As shown in FIG. 3, the cationic part of the complex Fe3 is biphasic, also exhibiting a twisted triangular bipyramidal molecular geometry around the metal center.

[0064] FT-IR(KBr,cm-1):3071,2935,1604[v(C=N)],1570,1450,1343,1330,1193,802,774.

[0065] Elemental analysis: [C4oH48C15Fe2N4+(C2Hs)20+2CH2C12]; theoretical value: C, 52.33%; H, 5 5.86%; N, 5.42%; experimental value: C, 52.44%; H, 5.20%; N, 5.93%.

[0066] It can be seen from the above structural verification data that the prepared complex is the target product Fe3.

[0067] Example 4

[0068] Preparation of (E)-2,6-diisopropyl-N-(5,6,7,8-tetrahydrocycloheptapyridin-9-ene)aniline 10 ferric chloride [Fe4: Ri=i-Pr; R2=H; X=C1]:

[0069] Abrown solid (yield: 58%) was prepared by the same method as in Example 1 (only replacing aniline with 2,6-diisopropylaniline), namely the Fe4 compound shown in Formula (I).

[0070] The structure verification data are as follows:

[0071] FT-IR(KBr,cm'1):3073,2964,1602[v(C=N)], 1569,1462,1441,1267,1181,870,797.

[0072] Elemental analysis: [C44H56C15Fe2N4+CH2C12]; theoretical values: C, 53.26; H, 5.76; N, 5.52%; experimental values: C, 53.56; H, 5.58; N, 5.62%.

[0073] It can be seen from the above structural verification data that the prepared complex is the target product Fe4.

[0074] Example 5

[0075] Preparation of (E)-2,4,6-trimethyl-N-(5,6,7,8-tetrahydrocycloheptapyridin-9-ene)aniline ferric chloride [Fe5: Ri=Me; R2=Me; X=C1]:

[0076] Abrown solid (yield: 58%) was prepared by the same method as in Example 1 (only replacing aniline with 2,4,6-trimethylaniline), namely the Fe5 compound shown in Formula (I).

[0077] The structure verification data are as follows: 25

[0078] FT-IR(KBr,cm'1):3069,2944,1611 [v(C=N)], 1572,1460,1450,1266,1212,863,807.

[0079] Elemental analysis: [C38H44C15Fe2N4+CH2C12]; theoretical value: C, 50.33%; H, 4.98%; N, 6.02%; experimental value: 50.73%; H, 4.90%; N, 5.93%.

[0080] It can be seen from the above structural verification data that the prepared complex is the target product Fe5. 30

[0081] Example 6

[0082] Preparation of (E)-2,6-diethyl-4-methyl-N-(5,6,7,8-tetrahydrocycloheptapyridin-9-ene)aniline ferric chloride [Fe6: Ri=Et; R2=Me; X=C1], as shown in FIG. 4:

[0083] Abrown solid (yield: 58%) was prepared by the same method as in Example 1 (only replacing aniline with 2,6-diethyl-4-methylaniline), namely the Fe6 compound shown in Formula (I).

[0084] The structure verification data are as follows:

[0085] As shown in FIG. 4, the cationic part of the complex Fe6 is also biphasic, also exhibiting a twisted triangular bipyramidal molecular geometry around the metal center.

[0086] FT-IR(KBr,cm-1):3072,2964,1607[v(C=N)],1572,1457,1380,1266,1248,864,803. 5

[0087] Elemental analysis: [C42H52C15Fe2N4+2CH3COOH+CH2C12]; theoretical value: C, 51.00%; H, 5.65%; N, 5.06%; experimental value: C, 50.64%; H, 5.32%; N, 5.31%.

[0088] It can be seen from the above structural verification data that the prepared complex is the target product Fe6. 10 15 CXI CXI 25

[0089] Example 7

[0090] Polymerization of isoprene under the co-catalyzation of the complex Fe2 and methylaluminoxane (MAO), as shown in FIG. 5:

[0091] Under a nitrogen atmosphere, the catalyst Fe2 (5 pmol), toluene (5 mL), and the cocatalyst MAO (1.67 mol / L toluene solution) were added into a Schlenk tube in sequence, at this time, Al / Fe = 100:1. A resulting mixture was stirred at 500 rpm for 1 min to 2 min to ensure proper mixing. Then an isoprene monomer (2 mL) was introduced into the stirred mixture to initiate polymerization. The polymerization was maintained at room temperature for 120 min. Then a dilute ethanol HC1 solution (10% HC1) was added thereto to terminate the polymerization, and then a resulting polymerized product was washed with ethanol 3 to 4 times to remove any impurities. The polymerized product was dried at room temperature for 24 h so that it reached a constant weight, and no further changes were observed. 1.36 g of a polymer was obtained. The polymer has a polymerization activity of 1.4 x 105 g^olofcat.)’1^1, a polymer molecular weight Mn of 42.4 kg / mol, and a polymer dispersity index (PDI) of 1.8 (Mn was a number-average molecular weight of the polymer, obtained from high-temperature GPC). The polymer prepared in Example 7 was taken and dissolved with 1,1,2,2,-tetrachloroethane, and filtered to obtain a solution. The solution was added to deuterated chloroform (CDCh) to determine 1H and 13C data of the polymer. According to the integrated values of signal peak shifts at 5.12 (ppm) and 4.70 (ppm) in the 1HNMR spectrum and the integrated values of signal peak shifts at 23.7 (ppm) and 16.2 (ppm) in the 13CNMR spectrum, it was calculated that a ratio of a cis-1,4 structure, a trans-1,4 structure, and a 3,4 structure in the PI structure obtained in Example 7 was 61%: 3%: 36%. 30

[0092] Example 8

[0093] As shown in FIG. 6, the steps were basically the same as in Example 7, except that Al / Fe=250 and the resulting polymer has a mass of 1.36 g, a polymerization activity of 1.4 x io5 g(molofcat.)’ a polymer molecular weight Mn of 35.2 kg / mol, and a polymer dispersity index (PDI) of 1.9. A ratio of a cis-1,4 structure, a trans-1,4 structure, and a 3,4 structure was 62%: 3%: 35%.

[0094] Example 9

[0095] As shown in FIG. 7, the steps were basically the same as in Example 7, except that Al / Fe=50 and the resulting polymer has a mass of 1.22 g, a polymerization activity of 1.2 x io5 g(molofcat.)’ a polymer molecular weight Mn of 52.2 kg / mol, and a polymer dispersity index (PDI) of 1.6. A 5 ratio of a cis-1,4 structure, a trans-1,4 structure, and a 3,4 structure was 61%: 2%: 37%.

[0096] Example 10

[0097] As shown in FIG. 8, the steps were basically the same as in Example 7, except that Al / Fe=10 and the resulting polymer has a mass of 0.14 g, a polymerization activity of 0.1 x io5 g(molofcat.)’ a polymer molecular weight Mn of 67.3 kg / mol, and a polymer dispersity index (PDI) of 1.6. A 10 ratio of a cis-1,4 structure, a trans-1,4 structure, and a 3,4 structure was 61%: 1%: 38%.

[0098] Example 11

[0099] As shown in FIG. 9, the steps were basically the same as in Example 7, except that the polymerization was conducted at 50°C and the resulting polymer has a mass of 1.36 g, a polymerization activity of 1.4 x 105 g^olofcat.)’1^1, a polymer molecular weight Mn of 30.5 kg / mol, and a polymer dispersity index (PDI) of 1.6. A ratio of a cis-1,4 structure, a trans-1,4 structure, and a 3,4 structure was 53%: 12%: 35%.

[0100] Example 12

[0101] As shown in FIG. 10, the steps were basically the same as in Example 7, except that the iron complex was Fei, the polymerization was conducted at -25°C for 10 min, and the resulting polymer has a mass of 1.33 g, a polymerization activity of 16.0 x io5 g^olofcat.)’1^1, a polymer molecular weight Mn of 151.2 kg / mol, and a polymer dispersity index (PDI) of 1.8. A ratio of a cis-1,4 structure, a trans-1,4 structure, and a 3,4 structure was 51%: 1%: 48%.

[0102] Example 13

[0103] As shown in FIG. 11, the steps were basically the same as in Example 7, except that the iron 25 complex was Fei, the polymerization was conducted at 0°C for 10 min, and the resulting polymer has a mass of 1.36 g, a polymerization activity of 16.3 x io5 g^olofcat.)’1^1, a polymer molecular weight Mn of 192.9 kg / mol, and a polymer dispersity index (PDI) of 1.9. A ratio of a cis-1,4 structure, a trans-1,4 structure, and a 3,4 structure was 50%: 4%: 46%.

[0104] Example 14 30

[0105] As shown in FIG. 12, the steps were basically the same as in Example 7, except that the iron complex was Fei, the polymerization was conducted at 50°C for 10 min, and the resulting polymer has a mass of 1.31 g, a polymerization activity of 15.9 x io5 g^olofcat.)’1^1, a polymer molecular weight Mn of 120.9 kg / mol, and a polymer dispersity index (PDI) of 2.1. A ratio of a cis-1,4 structure, a trans-1,4 structure, and a 3,4 structure was 46%: 11%: 43%.

[0106] Example 15

[0107] As shown in FIG. 13, the steps were basically the same as in Example 7, except that the iron complex was Fei, the polymerization was conducted at 75°C for 10 min, and the resulting polymer has a mass of 1.24 g, a polymerization activity of 14.9 x io5 g^olofcat.)’1^1, a polymer molecular 5 weight Mn of 111.1 kg / mol, and a polymer dispersity index (PDI) of 2.8. A ratio of a cis-1,4 structure, a trans-1,4 structure, and a 3,4 structure was 45%: 13%: 42%.

[0108] Example 16

[0109] As shown in FIG. 14, the steps were basically the same as in Example 7, except that the iron complex was Fei, the polymerization was conducted at 100°C for 10 min, and the resulting polymer 10 has a mass of 1.22 g, a polymerization activity of 14.6 x io5 g^olofcat.)’1^1, a polymer molecular weight Mn of 100.3 kg / mol, and a polymer dispersity index (PDI) of 3.5. Aratio of a cis-1,4 structure, a trans-1,4 structure, and a 3,4 structure was of 43%: 16%: 41%. The above are merely the preferred embodiments of the present disclosure and are not intended to limit the scope of the present disclosure. Any minor changes, equivalent variations and modifications made to the above embodiments based on the technical essence of the present CXI CXI disclosure should fall within the scope defined by the technical solutions of the present disclosure.

Claims

1. A method for preparing a cycloheptyl-fused iminopyridine iron complex catalyst, comprising the following steps: heating a compound shown in Formula (II), a5 compound shown in Formula (III) and a metal halide FeCh in an organic solvent, and conducting reaction to obtain the cycloheptyl-fused iminopyridine iron complex catalyst shown in Formula (I),Formula (I)10NH,C\J / -,. AAV' 'cm           LA / M1 Q RjCQ Formula (II) Formula (III)wherein in Formula (I), Ri is one selected from the group consisting of H, methyl, ethyl, and isopropyl; and R2 is one selected from the group consisting of methyl and H.15 2. The method of claim 1, wherein the cycloheptyl-fused iminopyridine ironcomplex catalyst is any one complex selected from the group consisting of:Fei: Ri=H; R2=H;Fe2: Rl=Me; R2=H;Fe3: Rl=Et; R2=H;20 Fe4: Ri=i-Pr; R2=H;Fe5: Ri=Me; R2=Me; andFe6: Ri=Et; R2=Me;wherein Me represents methyl, Et represents ethyl, and i-Pr represents isopropyl.25 3. The method of claim 1, wherein a feeding ratio of the compound shown inFormula (II), the compound shown in Formula (III), and the metal halide FeCh is 1:1:0.95;the organic solvent is acetic acid; andthe reaction is conducted at a reflux temperature of the acetic acid.

54. The method of claim 1, wherein before the cycloheptyl-fused iminopyridine iron complex catalyst shown in Formula (I) is obtained, the method further comprises cooling a resulting reaction product to room temperature and then precipitating with diethyl ether, and collecting a resulting precipitate by filtration and then washing with 10 the diethyl ether.

5. Use of the method for preparing a cycloheptyl-fused iminopyridine iron complex catalyst of claim 1 in preparation of a catalyst for isoprene polymerization.15 6. A catalyst composition for isoprene polymerization, comprising the cycloheptyl-fused iminopyridine iron complex catalyst as described in claim 1 or 2 and a cocatalyst; wherein the cocatalyst is one or more selected from the group consisting of aluminoxane, aluminum alkyl, and aluminum alkyl chloride;the aluminoxane is one or two selected from the group consisting of 20 methylaluminoxane and triisobutylaluminum-modified methylaluminoxane;the aluminum alkyl is one or more selected from the group consisting of triisobutylaluminum, trimethylaluminum, and triethylaluminum; andthe aluminum alkyl chloride is one or more selected from the group consisting of dimethylaluminum chloride, ethylaluminum sesquichloride, and methylaluminum 25 sesquichloride.

7. The catalyst composition for isoprene polymerization of claim 6, wherein the cocatalyst is the methylaluminoxane, and a molar ratio of the methylaluminoxane to iron element in the cycloheptyl-fused iminopyridine iron complex catalyst shown in 30 Formula (I) is in a range of (10-250):1.

8. A method for preparing polyisoprene (PI), comprising: catalyzing polymerization of isoprene under a condition of using the catalyst composition for isoprene polymerization of claim 7 as a catalyst to obtain the PI.

9. The method of claim 8, wherein the polymerization is conducted at a temperature of-40 °C to 100 °C;the polymerization is conducted under a normal pressure;5 the polymerization is conducted for 0.2 min to 120 min;the polymerization is conducted in a solvent, and the solvent is toluene; andthe polymerization is conducted in an inert atmosphere, and the inert atmosphere is a nitrogen atmosphere.

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