Chiral oxazoline-pyridine-imine cobalt compounds, methods of synthesis and use thereof

Abstract

This invention discloses a chiral oxazoline-pyridine-imine cobalt compound, its synthesis method, and its applications. The synthesis method involves the condensation reaction of 2-cyano-6-acetylpyridine and an aniline derivative with p-toluenesulfonic acid to generate a pyridine-imine compound. This compound is then cyclized with different chiral amino alcohols in the presence of zinc trifluoromethanesulfonate to generate chiral oxazoline-pyridine-imine ligands. The reaction of these ligands with anhydrous cobalt chloride successfully prepared four chiral oxazoline-pyridine-imine cobalt compounds. The cobalt catalyst synthesized in this invention possesses different chiral groups, electronic effects, and steric hindrance, and can catalyze the polymerization of isoprene.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyolefin catalysis, and particularly relates to a chiral oxazoline-pyridine-imine cobalt compound, a synthesis method and application thereof. BACKGROUND

[0002] Polyconjugated diene is widely used in industrial and agricultural, transportation and medical devices, etc. fields due to its good elasticity, flexibility and low temperature resistance. Nowadays, with the increasing demand for natural rubber, the development of high-performance synthetic rubber represented by polyisoprene has attracted extensive attention of researchers.

[0003] For isoprene polymerization, the catalyst plays a crucial role. The catalysts commonly used for isoprene polymerization include lithium system, titanium system, rare earth system and post-transition metal catalysts. Among them, cobalt catalysts can be prepared into polyconjugated dienes with different microstructures by adjusting the ligand structure, and exhibit high reactivity, gradually becoming a research hotspot in the field SUMMARY

[0004] The purpose of the present application is to provide a synthesis method and application of a chiral oxazoline-pyridine-imine cobalt compound. By changing the types of substituents, the electronic effect and steric hindrance effect of the metal compound can be significantly improved, further obtaining a chiral oxazoline-pyridine-imine cobalt catalyst with excellent performance, and successfully applied to the polymerization reaction of catalytic isoprene.

[0005] The present application achieves the above-mentioned purpose by using the following technology:

[0006] A chiral oxazoline-pyridine-imine cobalt compound, the structural formula of the compound is as follows:

[0007]

[0008] wherein, R 1 is isopropyl or diphenylmethyl; R 2 is methyl or hydrogen atom; R 3 is benzyl, isopropyl or tert-butyl.

[0009] As an example, the compound II shown in the present application has the following structures shown in formula II-1~II-4:

[0010]

[0011] The present application also provides a chiral oxazoline-pyridine ligand shown in the following formula I:

[0012]

[0013] wherein, R 1isopropyl or diphenylmethyl; R 2 is methyl or hydrogen atom; R 3 is benzyl, isopropyl or tert-butyl.

[0014] As examples, the ligands of formula I have the following structures of formulae I-1 to I-4:

[0015]

[0016] The synthesis method of the chiral oxazoline-pyridine-imine cobalt compound is as follows: 2-cyano-6-acetylpyridine and aniline derivatives are condensed under the action of p-toluenesulfonic acid to generate a pyridine-imine compound; then the compound is ring-closed with different chiral amino alcohols under the action of zinc trifluoromethanesulfonate to generate an oxazoline-pyridine-imine ligand. The ligand is reacted with anhydrous cobalt chloride to successfully prepare four chiral oxazoline-pyridine-imine cobalt compounds, and the specific steps are as follows:

[0017] (1) 2-cyano-6-acetylpyridine and aniline derivatives are heated and refluxed in toluene with p-toluenesulfonic acid as a catalyst, and a water trap is connected to remove water generated in the reaction system. After the reaction is completed, the crude product is purified by column chromatography to obtain the target compound.

[0018] (2) Under an argon atmosphere, the pyridine-imine compound, zinc trifluoromethanesulfonate and anhydrous toluene are mixed and stirred for 2-20 minutes, then the toluene solution of chiral amino alcohol is added, and refluxed for 12-72 hours. After the reaction is completed, the crude product is purified by column chromatography to obtain the corresponding chiral oxazoline-pyridine-imine cobalt compound.

[0019] (3) The obtained ligand is reacted with anhydrous cobalt chloride in tetrahydrofuran to obtain the corresponding chiral oxazoline-pyridine-imine cobalt catalyst.

[0020] Further, the synthesis method of the pyridine-imine compound in step (1) is as follows: 2-cyano-6-acetylpyridine and aniline derivatives are heated and refluxed in toluene with p-toluenesulfonic acid as a catalyst, and a water trap is connected to remove water generated in the reaction system. After the reaction is completed, the crude product is purified by column chromatography (PE / EA = 100 / 1-50 / 1) to obtain the target compound.

[0021] Further, the molar ratio of 2-cyano-6-acetylpyridine, aniline derivatives and p-toluenesulfonic acid is 1:1.2:0.05; the reaction temperature is 90-200°C, and the reaction time is 12-72 hours.

[0022] Further, the synthesis method of the oxazoline-pyridine-imine ligand in the step (2) is as follows: under argon atmosphere, the pyridine-imine compound, zinc trifluoromethanesulfonate and anhydrous toluene are mixed, stirred for 2-20 minutes, then the toluene solution of chiral amino alcohol is added, refluxed for 12-72 hours, the reaction is completed, the crude product is purified by column chromatography to obtain the corresponding chiral oxazoline-pyridine-imine cobalt compound.

[0023] Further, the molar ratio of the pyridine-imine compound, chiral amino alcohol and zinc trifluoromethanesulfonate is 1:1.5:0.05.

[0024] Further, the molar ratio of the chiral oxazoline-pyridine-imine ligand and anhydrous cobalt chloride in the step (3) is 1:1-1:3, and the reaction is carried out at room temperature for 3-48 hours; after the reaction is completed, the solvent is removed, and the chiral oxazoline-pyridine-imine cobalt compound is obtained by washing with anhydrous diethyl ether for three times.

[0025] Further, in the step (2), petroleum ether and ethyl acetate are used as eluents for column chromatography separation, and the volume ratio of petroleum ether and ethyl acetate is 10:1-5:1.

[0026] Further, the solvent in the step (3) is heavy-boiled tetrahydrofuran, and the washing agent used for separation is heavy-boiled diethyl ether.

[0027] The application also provides the application of the chiral oxazoline-pyridine-imine cobalt compound as a catalyst in the polymerization reaction of isoprene. The catalyst prepared by the application shows high catalytic activity in the polymerization reaction of isoprene. Within 60 minutes, the complete conversion of isoprene monomer can be realized by using compound II-1, compound II-2, compound II-3 and compound II-4 as catalysts, and the molecular weight of the polyisoprene obtained by using compound II-2 is the highest, which is 4.69×10 4 g·mol -1 , and the PDI is relatively narrow, which is 2.07.

[0028] The application relates to the synthesis and application of a chiral oxazoline-pyridine-imine cobalt catalyst. By changing the types of substituents, the electronic effect and steric hindrance effect of the metal center can be influenced, and the catalytic performance of the catalyst can be further improved. The prepared catalysts can all catalyze the polymerization of isoprene with high activity, and the highest reaction activity of the catalyst for catalyzing the polymerization of isoprene can reach 1.70×10 5 g·mol -1 ·h -1 . BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a single crystal structure diagram of the chiral oxazoline-pyridine-imine cobalt compound II-2. DETAILED DESCRIPTION

[0030] The application will be further described in conjunction with specific examples. It should be understood that the following examples are used to illustrate but not limit the scope of the present application, and those skilled in the art can make some non-essential improvements and adjustments to the application according to the above description.

[0031] Example 1

[0032] The structural formula of the chiral oxazoline-pyridine-imine cobalt compound Co1 in this example is as follows

[0033]

[0034] The synthesis method is as follows:

[0035] (1) In a 100 mL round-bottom flask, 2-cyano-6-acetylpyridine (1.45 g, 10.0 mmol), 2,6-diisopropylaniline (2.26 mL, 12.0 mmol), p-toluenesulfonic acid (0.18 g, 0.5 mmol) and 30 mL of toluene were added, the reaction was heated to reflux for 48 hours, and a water separator was connected to remove the water generated in the reaction system. After the reaction was completed, it was cooled to room temperature, the solvent was concentrated under vacuum, and the crude product was purified by column chromatography (petroleum ether / ethyl acetate = 100 / 1 to 50 / 1) to obtain 2.60 g of yellow solid with a yield of 85%. 1 HNMR (600 MHz, CDCl3): δ 8.59 (dd, J = 8.1, 1.1 Hz, 1H, ArH), 7.95 (t, J = 7.8 Hz, 1H, ArH), 7.80 (d, J = 7.6 Hz, 1H, ArH), 7.19-7.15 (m, 2H, ArH), 7.12 (dd, J = 8.5, 6.8 Hz, 1H, ArH), 2.70-2.62 (m, 2H, CH(CH3)2), 2.21 (s, 3H, N=CCH3), 1.15 (d, J = 6.1 Hz, 6H, CH(CH3)2), 1.13 (d, J = 5.9 Hz, 6H, CH(CH3)2) ppm. 13 C{ 1 H}NMR (151 MHz, CDCl3): δ 166.0, 157.8, 146.0, 137.6, 135.7, 132.9, 129.5, 124.6, 124.2, 123.2, 117.4, 28.5, 23.3, 22.9, 17.2 ppm.

[0036] (2) Under argon atmosphere, a 100 mL Schlenk flask was charged with the compound from step (1) (1.22 g, 4.0 mmol), zinc trifluoromethanesulfonate (73 mg, 0.2 mmol) and anhydrous toluene (20 mL), stirred for 10 min, then a toluene solution (20 mL) of L-phenylalaninol (0.91 g, 6.0 mmol) was added, and refluxed for 48 h. Upon completion of the reaction, the solvent was concentrated in vacuo, and the crude product was purified by column chromatography (petroleum ether / ethyl acetate = 30 / 1) to give yellow solid I-1 (0.80 g, 45%). 1 H NMR (600 MHz, CDC13): δ 8.52 (dd, J = 7.9, 1.1 Hz, 1H, ArH), 8.17 (dd, J = 7.7, 1.1 Hz, 1H, ArH), 7.90 (t, J = 7.8 Hz, 1H, ArH), 7.33 (t, J = 7.5 Hz, 2H, ArH), 7.29-7.22 (m, 3H, ArH), 7.16 (d, J = 7.6 Hz, 2H, ArH), 7.13-7.07 (m, 1H, ArH), 4.73-4.65 (m, 1H, OxH), 4.47 (t, J = 9.0 Hz, 1H, OxH), 4.28 (dd, J = 8.6, 7.6 Hz, 1H, OxH), 3.33 (dd, J = 13.8, 5.0 Hz, 1H, CH2Ph), 2.81-2.70 (m, 3H, CH2Ph and CH(CH3)2), 2.29 (s, 3H, N=CCH3), 1.14 (d, J = 6.9 Hz, 12H, CH(CH3)2) ppm. 13 C{ 1 H} NMR (151 MHz, CDC13): δ 166.8, 163.3, 156.4, 146.4, 146.0, 137.9, 137.1, 135.8, 129.3, 128.7, 126.7, 125.4, 123.8, 123.3, 123.1, 72.6, 68.3, 41.8, 28.3, 23.3, 22.9, 17.4 ppm.

[0037] (3) Under argon atmosphere, a 25 mL Schlenk flask was charged with ligand I-1 (0.21 g, 0.5 mmol), anhydrous cobalt chloride (65 mg, 0.5 mmol) and 10 mL of freshly distilled tetrahydrofuran, stirred at room temperature for 12 h. Upon completion of the reaction, the solvent was concentrated, anhydrous diethyl ether was added, filtered, the obtained solid was washed with anhydrous diethyl ether for three times, and dried in vacuo to constant weight to give 256 mg of dark green solid with a yield of 90%. FT-IR (cm -1): 1644, 1581, 1445, 1389, 1366, 1273, 1261, 1202, 928, 821, 807, 750, 712. Anal. Cacld for C 29 H 33 Cl2CoN3O:C,61.17;H,5.84;N,7.38.Found C,61.64;H,6.23;N,7.26.HRMS(MALDI-TOF)m / z:[M-Cl] + calcd for C 29 H 33 ClCoN3O + :533.1639,found:533.1632.

[0038] Example 2

[0039] The structural formula of the chiral oxazoline-pyridine-imine cobalt compound Co2 of this example is as follows:

[0040]

[0041] The synthesis method is as follows:

[0042] (1) The same as Example 1 step (1), replace 2,6-di(diphenylmethyl) -p-toluidine with 2,6-diisopropylaniline. Yellow solid 4.09 g, yield 72%. 1 H NMR (600 MHz, CDC13): δ 8.19 (d, J = 8.2 Hz, 1H, ArH), 7.83 (t, J = 7.9 Hz, 1H, ArH), 7.73 (d, J = 8.7 Hz, 1H, ArH), 7.25-7.16 (m, 12H, ArH), 7.03-6.96 (m, 8H, ArH), 6.68 (s, 2H, ArH), 5.19 (s, 2H, CHPh2), 2.18 (s, 3H, CH3), 1.10 (s, 3H, N=CCH3) ppm. 13 C{ 1 H} NMR (151 MHz, CDC13): δ 168.4, 157.5, 145.5, 143.6, 142.5, 137.2, 132.7, 132.2, 132.0, 129.9, 129.5, 129.4, 128.9, 128.5, 128.2, 126.5, 126.2, 124.6, 117.4, 52.3, 21.5, 16.8 ppm.

[0043] (2) Under an argon atmosphere, the compound obtained in step (1) (1.76 g, 4.0 mmol), zinc trifluoromethanesulfonate (73 mg, 0.2 mmol), and anhydrous toluene (20 mL) were added to a 100 mL Shrek flask. The mixture was stirred for 10 minutes, and then a toluene solution (20 mL) of L-phenylalanine (0.91 g, 6.0 mmol) was added. The mixture was refluxed for 48 hours. After the reaction was completed, the mixture was cooled to room temperature, the solvent was concentrated under vacuum, and the crude product was purified by column chromatography (petroleum ether / ethyl acetate = 30 / 1) to give a yellow solid I-2 (0.67 g, 24%). [α] 25 D = -46.26 (c 0.51, CH2Cl2). 1 H NMR (600MHz, CDCl3): δ8.13-8.07(m,1H,ArH),7.76(t,J=7.8Hz,1H,ArH),7.32(t,J=7.5Hz,2H,ArH),7 .29-7.26(m,2H,ArH),7.25-7.13(m,13H,ArH),7.00(d,J=7.4Hz,8H,ArH),6.68(s,2H,ArH),5.24(s,2 H,CHPh2),4.69-4.62(m,1H,OxH),4.45(t,J=9.0Hz,1H,OxH),4.25(t,J=8.0Hz,1H,OxH),3.30(dd,J=1 3.8,5.1Hz,1H,CH2Ph),2.78(dd,J=13.8,9.1Hz,1H,CH2Ph),2.17(s,3H,CH3),1.45(s,3H,N=CCH3)ppm. 13 C{ 1 H}NMR (151MHz, CDCl3): δ168.8,163.4,156.0,145.81,145.78,143.53,143.52,142.71,142.68,137.9,136.6,132.1,132.0,131.7,129.77 ,129.75,129.4,129.3,128.63,128.61,128.3,128.0,126.6,126.2,126.0,125.2,123.2,72.5,68.1,52.0,41.7,21.3,17.0ppm.FT-IR(cm -1 ):1638,1491,1448,1372,1237,1102,1074,1029,966,825,763,740,697,604.HRMS(ESI-TOF)m / z:[M+H] + calcd for C50 H 44 N3O + :702.3479,found:702.3489.

[0044] (3) Same as step (3) in Example 1. Replace I-1 with I-2. A dark green solid (254 mg, 61%) is obtained. [α] 30 D =+87.40(c 0.25,CH2Cl2).FT-IR(cm -1 ):1647,1580,1494,1447,1388,1263,1211,1030,933,750,702,603.Anal.Cacld for C 50 H 43 Cl2CoN3O:C,72.20;H,5.21;N,5.05.Found C,72.38;H,5.07;N,4.63.HRMS(MALDI-TOF)m / z:[M-Cl] + calcd for C 50 H 43 Cl2CoN3O + :795.2421,found:795.2388.

[0045] The structure of the chiral oxazoline-pyridine-imine cobalt compound Co2 was further confirmed by X-ray single-crystal diffraction, and its specific structure is as follows: Figure 1 As shown.

[0046] Example 3

[0047] The structural formula of the chiral oxazoline-pyridine-cobalt imine compound Co3 in this embodiment is as follows:

[0048]

[0049] The synthesis method is as follows:

[0050] (1) Same as step (1) in Example 1.

[0051] (2) Same as step (2) in Example 1. Replace L-phenylalanine with L-valine. Obtain yellow solid I-3 (0.66 g, 42%). 1H NMR (600MHz, CDCl3): δ8.50(d,J=7.9Hz,1H,ArH),8.19(d,J=7.7Hz,1H,ArH),7.89(t,J=7.8Hz,1H,ArH),7.16( d,J=7.6Hz,2H,ArH),7.10(dd,J=8.4,6.9Hz,1H,ArH),4.55(dd,J=9.7,8.3Hz,1H,OxH),4.26(t,J=8.4Hz,1H,Ox H),4.23-4.16(m,1H,OxH),2.75-2.68(m,2H,PhCH(CH3)2),2.29(s,3H,N=CCH3),1.95-1.88(m,1H,CH(CH3)2),1 .13(dd,J=6.9,2.0Hz,12H,PhCH(CH3)2),1.09(d,J=6.8Hz,3H,CH(CH3)2),0.97(d,J=6.8Hz,3H,CH(CH3)2)ppm. 13 C{ 1 H}NMR (151MHz, CDCl3): δ166.9,162.8,156.3,146.5,146.3,137.1,135.9,135.8,1 25.5,123.8,123.2,123.1,73.1,71.0,33.0,27.9,23.4,23.0,19.3,18.4,17.4ppm.

[0052] (3) Same as step (3) in Example 1. Replace I-1 with I-3. 224 mg of dark green solid was obtained, with a yield of 86%. FT-IR (cm²) -1 ):1648,1582,1446,1383,1369,1269,1202,1103,1084,1058,1025,943,824,762,747.Anal.Cacld for C 25 H 33 Cl2CoN3O:C,57.59;H,6.38;N,8.06.Found C,57.35;H,5.99;N,8.01.HRMS(MALDI-TOF)m / z:[M-Cl] + calcd for C 25 H 33 ClCoN3O + :485.1644,found:485.1632.

[0053] Example 4

[0054] The structural formula of the chiral oxazoline-pyridine-cobalt imine compound Co4 in this embodiment is as follows:

[0055]

[0056] The synthesis method is as follows:

[0057] (1) Same as step (1) in Example 1.

[0058] (2) Same as step (2) in Example 1, except that L-phenylalanine is replaced with L-tert-leucine. Yellow solid I4 (0.57 g, 35%) is obtained. 1 H NMR (600MHz, CDCl3): δ8.51 (dd, J=7.9, 1.1Hz, 1H, ArH), 8.23 ​​(dd, J=7.7, 1.1Hz, 1H, ArH), 7.88 ( t,J=7.8Hz,1H,ArH),7.17(d,J=7.6Hz,2H,ArH),7.10(dd,J=8.4,6.9Hz,1H,ArH),4.50(dd,J=1 0.2,8.7Hz,1H,OxH),4.35(t,J=8.5Hz,1H,OxH),4.16(dd,J=10.2,8.3Hz,1H,OxH),2.78-2.66( m,2H,CH(CH3)2),2.29(s,3H,N=CCH3),1.16-1.11(m,12H,CH(CH3)2),1.00(s,9H,C(CH3)3)ppm. 13 C{ 1 H}NMR (151MHz, CDCl3): δ166.7,162.6,156.1,146.4,146.2,136.9,135.71,135.69,1 25.4,123.6,123.1,123.0,76.4,69.5,34.1,28.24,28.21,26.0,23.2,22.9,17.2ppm.

[0059] (3) Same as step (3) in Example 1. Replace I-1 with I-4. A dark green solid (209 mg, 78%) is obtained. FT-IR (cm²) -1 ):1650,1583,1460,1385,1366,1275,1252,1199,1105,1081,1057,1024,945,920,824,808,765,749.Anal.Cacld for C 26 H 35Cl2CoN3O:C,58.33;H,6.59;N,7.85. Found C,58.65;H,6.82;N,7.49.

[0060] Example 5

[0061] The polymerization of isoprene was catalyzed by compound Co1 and diethylaluminum chloride, and the specific steps are as follows:

[0062] (1) In a glove box, add Co1 (4.56 mg, 8 μmol), 5 mL toluene, 2.4 mmol AlEt2Cl and 2 mL isoprene to a 25 mL Shrek bottle in sequence. At this time, Al / Co = 300 / 1. React at room temperature for 1 hour. Quench the reaction by adding hydrochloric acid-acidified ethanol solution dropwise to the reaction system to obtain polymer precipitate. Wash with ethanol several times, dry to constant weight and weigh.

[0063] Polymerization activity: 1.70 × 10 5 g·mol -1 ·h -1 Polymer molecular weight: 1.90 × 10⁻⁶ 4 g·mol -1 PDI = 2.73.

[0064] (2) The operation steps are the same as (1), the difference being that Al / Co = 50 / 1, and the polymerization activity is 1.70 × 10⁻⁶. 5 g·mol -1 ·h -1 Polymer molecular weight: 2.10 × 10⁻⁶ 4 g·mol -1 PDI = 2.51.

[0065] (3) The operation steps are the same as (1), the difference being that Al / Co = 10 / 1, and the polymerization activity is 3.6 × 10⁻⁶. 4 g·mol -1 ·h -1 Polymer molecular weight: 7.1 × 10⁻⁶ 3 g·mol -1 PDI = 3.70.

[0066] By screening the Al / Co molar ratio, the optimal molar ratio Al / Co = 50 / 1 was determined when Co1 was the main catalyst and AlEt2Cl was the co-catalyst. At this ratio, the polymerization activity was 1.70 × 10⁻⁶. 5 g·mol -1 ·h -1 Polymer molecular weight: 2.10 × 10⁻⁶ 4 g·mol -1 PDI = 2.51.

[0067] In Examples 6-8, diethylaluminum chloride was used as a co-catalyst, and different catalysts were used instead of Co1 to catalyze the polymerization of isoprene (Al / Co = 50 / 1, reaction at room temperature for 1 hour, other conditions the same as in Example 5). The polymerization results are as follows:

[0068]

[0069] The polyisoprene obtained from the catalyst Co2 had the highest molecular weight, at 4.69 × 10⁻⁶. 4 g·mol -1 The PDI is relatively narrow, at 2.07.

[0070] In Examples 9-20, diethylaluminum chloride was used as a co-catalyst, and different catalysts were used to catalyze the polymerization of isoprene at different reaction temperatures (Al / Co = 50 / 1, reaction time 1 hour, other conditions the same as in Example 5). The polymerization results are as follows:

[0071]

[0072]

[0073] In summary, the prepared catalysts exhibited high catalytic activity for the polymerization of isoprene, achieving complete monomer conversion within 60 minutes at room temperature. The polyisoprene obtained from Co2 had the highest molecular weight, 4.69 × 10⁻⁶. 4 g·mol -1 The PDI is relatively narrow, at 2.07.

[0074] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. Use of a chiral oxazoline-pyridine-imine cobalt compound as a catalyst in the polymerization of isoprene, said chiral oxazoline-pyridine-imine cobalt compound being of the structure shown in formulae II-1 to II-4: ###0001### II-1 II-2 II-3 II-4 。 2. Use according to claim 1, characterized in that: Within 60 minutes, compound II-1, compound II-2, compound II-3 and compound II-4 can all realize the complete conversion of isoprene monomer as catalyst, wherein the molecular weight of the polyisoprene obtained by compound II-2 is 4.69 x 10 4 g·mol -1 , and the PDI is 2.07.

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