Pyridine imine nickel (II) catalyst containing axial flexible naphthenic base and application of pyridine imine nickel (II) catalyst in synthesis of hyperbranched polyethylene lubricating oil

Abstract

The invention discloses a nickel pyridine imine (II) catalyst containing an axial flexible naphthenic base and application of the catalyst in synthesis of hyperbranched polyethylene lubricating oil. The pyridine imine nickel (II) catalyst disclosed by the invention shows remarkable innovation advantages. Firstly, the synthesis route is simpler and more efficient, and the production cost is remarkably reduced. More importantly, the catalyst greatly improves the total branch density of the polyethylene oil in the process of promoting the generation of the hyperbranched polyethylene oil, and the breakthrough directly promotes the liquidity and transparency of the lubricating oil to realize qualitative leap. Besides, through an elaborately designed low molecular weight strategy, the pour point of the lubricating oil is effectively reduced, the viscosity index performance of the lubricating oil is greatly enhanced, a wider prospect is developed for application of high-end synthetic lubricating oil base oil, and a solid foundation is laid.

Description

Technical Field

[0001] The invention belongs to the field of metal catalysis and olefin polymerization, and specifically relates to a pyridine imine nickel (II) catalyst containing an axially flexible cycloalkyl group and application thereof in the synthesis of hyperbranched polyethylene lubricating oil. Background Art

[0002] In recent years, with the rapid development of materials science, the exploration of late transition metal-catalyzed ethylene chain polymerization technology in the preparation of high-performance hyperbranched polyethylene oil has quietly become a research hotspot and frontier in the academic community. This type of unique hyperbranched polyethylene oil has shown great potential as a high-end synthetic lubricant base oil material with its extraordinary physical and chemical properties, such as excellent thermal stability, extremely low pour point and extraordinary viscosity index, indicating inestimable value in future industrial applications.

[0003] What is particularly noteworthy is that the excellent performance parameters of low molecular weight hyperbranched polyethylene oil directly point to broad commercial application prospects, including but not limited to long-term use of efficient lubrication of precision mechanical parts. However, research in this field also faces severe challenges: how to accurately control the catalyst system to achieve the fine design of the molecular structure of this type of low molecular weight polyethylene oil, especially to improve its fluidity, has become a key issue that needs to be solved urgently.

[0004] In this context, our scientific research team has successfully developed a series of innovative N-terphenylpyridine imine Ni (II) catalyst systems tailored for the synthesis of hyperbranched polyethylene oil (ACS Polymers Au, 2022, 2, 88-96). Although this achievement has taken an important step in promoting progress in the field, the prepared polyethylene product exhibits the characteristics of a solid-liquid transition state at room temperature and has a high viscosity, which limits its fluidity and practical application range. In-depth analysis shows that its molecular structure contains nearly 40% long-chain branches. Although it enriches the molecular configuration, it is not the dominant structural factor, which directly leads to a decrease in fluidity.

[0005] Looking back on past studies, we found that the clever introduction of flexible ortho-aryl substituents showed extraordinary effects in enhancing the branch density of polyethylene synthesized by α-diimine Ni(II) catalyst. Inspired by this, we are determined to further explore and design a new catalyst system, aiming to significantly improve the branch density and distribution of hyperbranched polyethylene by precisely controlling the catalytic mechanism, thereby effectively solving the problem of insufficient fluidity while maintaining its excellent physical and chemical properties, and opening up a broader world for the practical application of hyperbranched polyethylene oil. Summary of the invention

[0006] The present invention aims to address the major challenge faced by the preparation of polyethylene oil in the current technical field, namely, when using traditional catalysts for ethylene polymerization, the polyethylene oil products obtained have significant defects such as insufficient branching density and poor liquid properties. A pyridine imine nickel (II) catalyst containing an axially flexible cycloalkyl group and its application in the synthesis of hyperbranched polyethylene lubricating oil are provided.

[0007] The pyridine imine nickel (II) catalyst containing an axially flexible cycloalkyl group of the present invention has a general structural formula as shown below:

[0008]

[0009] Wherein R is selected from Ph or alkyl; R' is selected from H, Ph, Br or alkyl; X is selected from cycloalkyl, such as cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl and the like.

[0010] The pyridine imine nickel (II) catalyst containing an axially flexible cycloalkyl group is preferably of the following structure:

[0011]

[0012] The preparation method of the pyridine imine nickel (II) catalyst containing an axially flexible cycloalkyl group of the present invention comprises the following steps:

[0013] Step 1: Preparation of ligand

[0014] 2-Acetyl-6-bromopyridine or 2-acetyl-6-methylpyridine (1 mmol, 0.5 eq), aromatic amine (2 mmol, 1 eq), zinc chloride (1.0 eq) and acetic acid (4 mL) were added to a round-bottom flask, and the system was heated to 90°C and refluxed for reaction for 4 h. After the reaction, the solution was cooled to room temperature, and a large amount of ether was added, the solution became turbid, and a light yellow precipitate was produced. After filtration, the precipitate was washed with ether (3×10 mL) and dried. The obtained solid powder was placed in a round-bottom flask, 20 mL of dichloromethane was added to dissolve, and then an aqueous solution (20 mL) of potassium oxalate (1.0 eq) was added and mixed and stirred for 1 h. The organic phase was separated, washed with water (3×20 mL), and dried over anhydrous magnesium sulfate. The dried filtrate was concentrated under reduced pressure, and ethanol was added to precipitate the desired solid. After filtration and vacuum drying, the ligand (L1-L3) was obtained as a yellow powder.

[0015] Step 2: Preparation of catalyst

[0016] Under a nitrogen atmosphere, a mixture consisting of 0.2 mmol of ligand and 1 equivalent of (DME)NiBr2 was added to 5 mL of dichloromethane and stirred at room temperature for 12 h. After the reaction was completed, part of the solvent was evaporated under reduced pressure, and the remaining mixture was diluted with 20 mL of anhydrous ether to obtain an orange-red solid precipitate, which was then separated by filtration, washed with ether, and dried in vacuo to obtain the catalyst Ni1-Ni3.

[0017] The synthetic route is as follows:

[0018]

[0019] The pyridine imine nickel (II) catalyst containing axially flexible cycloalkyl groups of the present invention uses 6-substituted 2-acetylpyridine as the catalyst skeleton, and introduces a large sterically hindered flexible cycloalkyl imine group into the skeleton, thereby more effectively promoting the catalytic system to generate a hyperbranched polyethylene oil with a higher branching degree and excellent fluidity. Due to its low molecular weight, it has the characteristics of low pour point and high viscosity index, which makes it have unlimited possibilities in commercial utilization.

[0020] The invention discloses an application of a pyridine imine nickel (II) catalyst containing an axially flexible cycloalkyl group in catalyzing ethylene polymerization to prepare a hyperbranched polyethylene lubricant.

[0021] Specifically, during the ethylene polymerization process, the catalyst and the co-catalyst alkyl aluminum form a composite catalytic system for reaction at a reaction temperature of 30-90° C. and a reaction time of 30-360 minutes.

[0022] Experiments have shown that in the ethylene polymerization reaction, when the reaction temperature is controlled at 30-70°C, the reaction time is 60 min, and the catalyst dosage is 10 μmol, under the activation of the cocatalyst MAO, the catalytic activity of the ethylene polymerization of the catalytic system is moderate, reaching 4.90×10 5 g mol -1 h -1 The rate is low, and the polyethylene oil obtained has a low molecular weight (325-478 g / mol) and a high branching density (139-167 / 1000C).

[0023] The molar ratio of the catalyst to the co-catalyst MAO is 1:200 to 1:1000, preferably 1:300.

[0024] The beneficial effects of the present invention are embodied in:

[0025] The catalyst of the present invention uses 6-substituted 2-acetylpyridine as the skeleton, and by precisely introducing a large sterically hindered flexible cycloalkyl group in the metal center axis, the catalytic efficiency is significantly optimized, and a hyperbranched polyethylene oil with high branching degree and outstanding lubrication performance is successfully driven to be generated. The prepared hyperbranched polyethylene oil exhibits three core advantages: first, the branch density is significantly improved and the structure is more refined; second, the branch morphology is diverse and mainly long-chain branching, which gives the material unique properties; third, the molecular weight is effectively controlled, achieving the goal of low molecular weight. Compared with the currently widely used electron-rich N-triaryl neutral salicylaldehyde imine nickel catalyst, small sterically hindered cationic asymmetric α-diimine palladium catalyst and 5-aryl neutral pyrroimine nickel catalyst, the pyridine imine nickel (II) catalyst proposed in the present invention exhibits significant innovative advantages. First, its synthetic route is simpler and more efficient, which significantly reduces the production cost. More importantly, the catalyst greatly improves the total branch density of polyethylene oil in the process of promoting the generation of hyperbranched polyethylene oil. This breakthrough directly promotes the fluidity and transparency of lubricating oil to achieve a qualitative leap. In addition, through a carefully designed low molecular weight strategy, the present invention not only effectively reduces the pour point of the lubricant, but also greatly enhances its viscosity index performance, opening up broader prospects for the application of high-end synthetic lubricant base oils and laying a solid foundation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The yield (a), molecular weight (b) and branch density (c) of hyperbranched polyethylene oil prepared by the catalysts of Examples 1 to 3 at 30°C-70°C.

[0027] Figure 2 The catalyst of Example 3 was used to synthesize hyperbranched polyethylene oil at 30°C. 1 H NMR spectra and 13 C NMR spectral analysis assignment.

[0028] Figure 3 This is a state diagram of the catalyst in Example 3 synthesizing hyperbranched polyethylene oil at 30°C. DETAILED DESCRIPTION

[0029] In order to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with the embodiments. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0030] The synthesis steps involved in the examples are preferred catalyst synthesis steps.

[0031] Reagents and raw materials used in the examples: All metal organic reactions were carried out under nitrogen protection, and all solvents were dried and deoxygenated. Ethanol was analytical grade and used directly.

[0032] Embodiment 1:

[0033] 1. Synthesis of ligand L1

[0034] In a round-bottom flask, 2-acetyl-6-bromopyridine (1 mmol, 0.5 eq) was added together with 2,4,6-tricyclopentyl-1-aniline (2 mmol, 1 eq). Zinc chloride (1.0 eq) and acetic acid (4 mL) were then added, and the mixture was refluxed for reaction for 4 hours. After the reaction was completed, the solution was cooled and mixed with a large amount of diethyl ether to produce a turbid solution and form a light yellow precipitate. This precipitate was then filtered, rinsed with diethyl ether (3×10 mL), and dried to produce a powder. Subsequently, the powder was dissolved in dichloromethane (20 mL) in the same flask. 20 mL of potassium oxalate (1.0 eq) aqueous solution was added to the flask and stirred for 1 hour. The organic layer was then separated, rinsed with water (3×20 mL), and dried over anhydrous magnesium sulfate. Subsequently, the dried filtrate was concentrated under reduced pressure. Ethanol was introduced to precipitate the target solid, and a yellow powder (L1) was obtained after filtration and vacuum drying with a yield of 50%.

[0035] The reaction route is as follows:

[0036]

[0037] NMR analysis: 1 H NMR (400MHz, CDCl3) δ8.33(d,J=7.6Hz,Ar-H,1H),7.66(t,J=7.7Hz,Ar-H,1H),7.57(d,J=7.7Hz,Ar-H,1H),7.02(s,Ar-H,2H),2.97(m,-CH-,1H), 2.79–2.67(m,-CH-,2H).2.18(s,-CH3,3H),2.12–2.03(m,-CH2-,2H),1. 96(m,-CH2-,2H),1.86–1.66(m,-CH2-,10H),1.63–1.47(m,-CH2-,10H). 13 C NMR (101MHz, CDCl3) δ166.19(-C=N),157.54,145.46,141.26,140.94,138.74,133.14,129.09,122.21,120.05,45. 98(-CH-),40.43(-CH-),34.74(-CH2-),33.84(-CH2-),25.68(-CH2-),25.66(-CH2-),25.46(-CH2-),17.40(-CH3).

[0038] Mass spectrometry analysis: APCI-MS (m / z): calcd for C52H41N2+: 479.2062, Found, 479.2006, [M+H]+.

[0039] 2. Synthesis of Catalyst Ni1

[0040] Under nitrogen atmosphere, a mixture containing 0.2mmol ligand L1 and an equal amount of (DME)NiBr2 was introduced into a flask containing 20mL dichloromethane. The mixture was stirred at room temperature for 12 hours. After the reaction, the solvent was partially evaporated under reduced pressure. Subsequently, the residual mixture was diluted with 20mL ether to precipitate an orange-red solid. The solid was then separated by filtration, strictly washed with ether, and finally dried under vacuum to obtain the Ni1 complex. The yield was 70%.

[0041] The reaction route is as follows:

[0042]

[0043] Mass spectrometry: MALDI-TOF-MS (m / z): calculate for C 28 H 35 Br2N2Ni:615.0515,Found,615.0486,[M-Br]+.

[0044] Embodiment 2:

[0045] 1. Synthesis of ligand L2

[0046] The 2,4,6-tricyclopentyl-1-aniline in step 1 of example 1 was replaced by 2,4,6-tricyclohexyl-1-aniline, and the remaining operations were the same as step 1 of example 1, with a yield of 63%.

[0047] NMR analysis: 1 H NMR (400MHz, CDCl3) δ8.30 (d, J=7.6Hz, Ar-H, 1H), 7.67 (t, J=7.7Hz, Ar-H, 1H), 7 .58(dd,J=7.9,1.0Hz,Ar-H,1H),6.95(s,Ar-H,2H),2.52–2.42(m,-CH-,1H),2. 23(m,-CH-,2H),2.17(s,-CH3,3H),1.95–1.82(m,-CH2-,7H),1.79–1.69(m,-CH 2-,5H),1.67–1.60(m,-CH2-,4H),1.43(m,-CH2-,8H),1.33–1.21(m,-CH2-,6H). 13C NMR (101MHz, CDCl3) δ166.09(-C=N),157.65,143.91,143.14,141.08,138.87,134.48,129.21,122.06,120.02,44.56(-CH-),39.3 6(-CH-),34.83(-CH2-),33.71(-CH2-),33.38(-CH2-),27.23(-CH2-),27.18(-CH2-),27.16(-CH2-),26.39(-CH2-),17.42(-CH3).

[0048] Mass spectrometry analysis: ACPI-MS (m / z): calcd for C52H39F2N2+: 521.2508, Found, 521.2546, [M+H]+

[0049] 2. Synthesis of Catalyst Ni2

[0050] L1 in step 2 of Example 1 was replaced by L2, and the remaining operations were the same as step (2) of Example 1, with a yield of 73%.

[0051] Mass spectrometry analysis: MALDI-TOF-MS (m / z): calcd for C31H41Br2N2Ni: 657.0984, Found, 657.0977, [M-Br]+

[0052] Embodiment 3:

[0053] 1. Synthesis of ligand L3

[0054] The 2-acetyl-6-bromopyridine in step 1 of Example 2 was replaced with 2-acetyl-6-methylpyridine, and the remaining operations were the same as those in step 1 of Example 2, with a yield of 59%.

[0055] NMR analysis: 1 H NMR (400MHz, CDCl3) δ8.12(d,J=7.8Hz,Ar-H,1H),7.68(t,J=7.7Hz,Ar-H,1H),7.23(d,J=7.6Hz,Ar-H,1H),6.95(s,Ar-H,2H ),2.64(s,-CH3,3H),2.47(m,-CH-,1H),2.35–2.26(m,-CH-,2H),2.18(s,-CH3,3H),1.96–1.81(m,-CH2-,6H),1.79–1.59(m,

[0056] -CH2-,9H),1.52–1.37(m,-CH2-,6H),1.36–1.18(m,-CH2-,9H). 13 C NMR (101MHz, CDCl3) δ167.39(-C=N),157.24,156.20,144.22,142.56,136.50,134.49,124.05,121.85,118.08,44.44(-CH),39.15(- CH),34.75(-CH2),33.62(-CH2),33.33(-CH2),27.15(-CH2),27.07(-CH2),26.34(-CH2),26.30(-CH2),24.58(-CH3),17.37(-CH3).

[0057] Mass spectrometry analysis: ACPI-MS (m / z): calcd for C52H39Br2N2 + :457.3583,Found,457.3549,[M+H] +

[0058] 2. Synthesis of Catalyst Ni3

[0059] L1 in step 2 of Example 1 was replaced by L3, and the remaining operations were the same as step 2 of Example 1, with a yield of 72%.

[0060] Mass spectrometry analysis: MALDI-TOF-MS (m / z): calcd for C32H44BrN2Ni: 593.2036, Found, 593.2047, [M-Br] +

[0061] Example 4: Application of Ni1-Ni3 in catalytic ethylene polymerization

[0062] In the standard experimental procedure, a 350 mL thick-walled glass pressure vessel was dried in a hot air circulating oven at 60 °C for 2 h. Once cooled to room temperature, the vessel was filled with cyclohexane (40 mL) and MAO (300 eq.) under a nitrogen atmosphere. Ni(II) catalyst (10 μmol) was dissolved in CH2Cl2 (2 mL) and carefully injected into the polymerization system using a syringe. Under vigorous stirring at 320 RPM, the reactor was pressurized to maintain a steady 6 atm of ethylene. After 1 h, the reactor pressure was reduced to atmospheric pressure and the resulting hyperbranched polyethylene oil was then concentrated under reduced pressure.

[0063] The following table shows the experimental conditions for ethylene polymerization using the catalyst provided by the present invention, including complex, temperature, yield, catalytic activity, and b.), polymer molecular weight (M n c ), degree of branching (brs d ), viscosity index (VI) and other polymerization result data.

[0064] Table 1 Ethylene polymerization

[0065]

[0066] a Polymerization conditions: catalyst 10 μmol, dichloromethane = 2 mL, [Al] / [Ni] = 300, cyclohexane = 40 mL, ethylene pressure 6 atm, time = 60 min;

[0067] b The unit of activity is 10 5 gmol -1 h -1 ;

[0068] c Polymer molecular weight M n Depend on 1 HNMR nuclear magnetic resonance determination;

[0069] d The degree of branching refers to the number of branches per 1000 carbon atoms, which is 1 HNMR nuclear magnetic resonance determination;

[0070] e The viscosity index of polyethylene oil was measured by automatic kinematic viscometer TP825;

[0071] As shown in Table 1, the catalyst Ni1-Ni3 of the present invention can achieve medium activity (range 0.94~4.90×10 5 g mol -1 h -1 ), and at the same time, a polymer with a low molecular weight (338-478 g / mol) and a high degree of branching (up to 139-167 branches / 1000C) was prepared, and the polymer was a polyethylene oil with a high viscosity index (170.1-217.9). Further analysis using nuclear magnetic resonance technology confirmed the diversity of branch structures in polyethylene oil, a considerable portion of which showed hyperbranched motifs. The high degree of branching, excellent liquefaction performance, low pour point due to its low molecular weight and high viscosity index add unlimited commercial value to it, and also show its potential as a synthetic lubricant base oil.

[0072] The above is a detailed introduction to a preferred compound, complex catalyst, catalyst composition and method for preparing an olefin polymer provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention, but the present invention is not limited to the specific implementation methods described herein. It is understood by those skilled in the art that other changes and modifications may be made without departing from the scope of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A pyridine imine nickel (II) catalyst containing an axially flexible cycloalkyl group, characterized in that Its general structure is shown below: wherein R is selected from Ph or alkyl; R' is selected from H, Ph, Br or alkyl; and X is selected from cycloalkyl.

2. The pyridine imine nickel (II) catalyst containing an axially flexible cycloalkyl group according to claim 1, characterized in that Its general structure is shown below: R'=Br, X=Cp(Ni1); or R'=Br, X=Ch(Ni2); or R'=Me, X=Ch(Ni3).

3. The method for preparing the pyridine imine nickel (II) catalyst containing an axially flexible cycloalkyl group as claimed in claim 2, characterized in that The steps include: Step 1: Preparation of ligand Add 2-acetyl-6-bromopyridine or 2-acetyl-6-methylpyridine, aromatic amine, zinc chloride and acetic acid to the reactor, and heat the system to reflux for 4 hours; after the reaction, cool the solution to room temperature, add ether to precipitate, filter, wash the precipitate with ether and dry, place the obtained solid powder in a round-bottom flask, add dichloromethane to dissolve, then add an aqueous solution of potassium oxalate to mix and stir, separate the organic phase, wash with water, dry with anhydrous magnesium sulfate, concentrate under reduced pressure, add ethanol to precipitate the desired solid, filter and vacuum dry to obtain the ligand; Step 2: Preparation of catalyst Under a nitrogen atmosphere, a mixture of the ligand and (DME)NiBr2 is added to dichloromethane and stirred at room temperature for reaction; after the reaction is completed, part of the solvent is evaporated under reduced pressure, and the remaining mixture is diluted with anhydrous ether to obtain an orange-red solid precipitate, which is then separated by filtration, washed with ether, and dried in vacuo to obtain the catalyst Ni1-Ni3; The synthetic route is as follows:

4. Use of the pyridine imine nickel (II) catalyst containing an axially flexible cycloalkyl group as claimed in claim 1 in catalyzing ethylene polymerization to prepare hyperbranched polyethylene lubricant.

5. The use according to claim 4, characterized in that: During the ethylene polymerization process, the catalyst and the co-catalyst alkyl aluminum form a composite catalyst system to carry out catalytic polymerization reaction.

6. The use according to claim 5, characterized in that: The molar ratio of the catalyst to the co-catalyst is 1:200 to 1:1000.

7. The use according to claim 6, characterized in that: The molar ratio of catalyst to co-catalyst is 1:

300.

8. The use according to claim 5, characterized in that: The reaction temperature is 30-90°C, and the reaction time is 30-360 minutes.

9. The use according to claim 8, characterized in that: The reaction temperature is 30-70°C.

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