Preparation of nickel catalysts containing phosphine oxides with heteroatoms and their use in the polymerization of ethylene

Abstract

The application relates to the technical field of polyethylene catalysts, and discloses preparation of a nickel catalyst containing an oxygen heteroatom phosphine and application of the catalyst in ethylene polymerization, wherein the ligand contains a benz[d][1,3]dioxolane, 1,4-benzodioxane or 2,3-dihydrobenzofuran oxygen heterocycle structure; 2-tert-butyl phenol and 2-bromo-2,6-dimethoxy diphenyl are used as raw materials to prepare the oxygen heteroatom phosphine ligand L1-L3 through hydroxyl protection, lithiation, phosphination and acidolysis deprotection; then, under the protection of an inert gas, the ligand is stirred with a nickel precursor [Py2Ni(CH2SiMe3)2] in toluene at room temperature, and the target catalyst Ni1-Ni3 is obtained through n-hexane recrystallization. The catalyst has excellent thermal stability in ethylene homopolymerization, and the catalytic activity is as high as 2.08*10 6 g mol⁻¹ h⁻¹ at 120 DEG C.

Description

Technical Field

[0001] This invention relates to the field of polyethylene catalyst technology, specifically to the preparation of oxygen-containing heteroatom phosphonophenol nickel catalysts and their application in ethylene polymerization. Background Technology

[0002] Polyethylene is the world's most produced synthetic polymer, with an annual output exceeding 100 million tons. By controlling the degree of branching of the molecular chain, a series of products such as high-density polyethylene, low-density polyethylene, and polyolefin elastomers can be obtained. Traditional polyethylene production mainly relies on two routes: high-pressure free radical polymerization and copolymerization of ethylene and α-olefins. The former requires large equipment investment and high energy consumption, while the latter's cost is limited by the supply of α-olefin monomers.

[0003] The "chain-walking" mechanism of post-transition metal catalysts offers a new approach to solving the aforementioned problems. Unlike Ziegler-Natta catalysts, in the ethylene polymerization process, the alkyl chains at the metal centers of post-transition metals can undergo rapid β-hydrogen elimination and re-insertion reactions, allowing the active centers to "walk" along the polymer chains, thus enabling the direct synthesis of polyethylene using only ethylene as a single feedstock. α-Diimine nickel catalysts are a classic example in this field, capable of producing a full range of products from polyethylene waxes to polyolefin elastomers. However, these catalysts suffer from insufficient thermal stability at high temperatures (>80 °C) and their activity easily decays, limiting their industrial application.

[0004] Phosphophenol (P, O) neutral nickel catalysts are a promising system that has emerged in recent years. The chelated ligands composed of the "soft" phosphine (P) and the "hard" phenolic oxygen (O) endow the catalysts with unique electronic asymmetry and excellent thermal stability, maintaining high activity above 80 °C. Studies have shown that the catalytic efficiency is significantly increased by introducing a sterically hindered group at the ortho position of the phenolic oxygen. Introducing secondary coordinating groups containing heteroatoms (N, O, S) into the phosphophenol ligands can effectively regulate the competition between chain walk and chain transfer by utilizing the weak coordination interaction between the heteroatoms and the nickel center and the synergistic steric hindrance effect. Oxygen-containing groups, due to their moderate coordination ability, are preferred elements for designing secondary coordination structures. Summary of the Invention

[0005] The purpose of this invention is to provide the preparation of phosphonophenol nickel catalysts containing oxygen heteroatoms and their application in ethylene polymerization. By introducing secondary coordinating groups containing oxygen heteroatoms into the phosphine atom substituents, and utilizing the weak coordination interaction between the oxygen heteroatoms and the nickel center in conjunction with the steric hindrance effect, the chain walking behavior during ethylene polymerization can be precisely controlled, thereby preparing polyethylene materials.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a class of oxygen-containing heteroatom phosphine ligands, the ligands having the following structure: Ligand L1: 5-hydroxybenzo[d][1,3]dioxolane group; Ligand L2: 6-hydroxy-1,4-benzodioxane group; Ligand L3: 5-hydroxy-2,3-dihydrobenzofuran group.

[0007] A method for synthesizing an oxygen-containing heteroatom phosphine ligand includes the following steps: S1: 2-tert-butylphenol was reacted with 3,4-dihydro-2H-pyran under PPTS catalysis to prepare intermediate a with hydroxyl protected. S2: 2-Bromo-2,6-dimethoxybiphenyl was lithiated with n-butyllithium and then reacted with phosphorus trichloride to prepare the diarylphosphine intermediate Cl2PPh(Ar); S3: The bromine-containing oxygen-containing heterocyclic compound is lithiated with n-butyllithium and then reacted with Cl2PPh(Ar), followed by reaction with the lithiation product of intermediate a, and finally deprotected by acid to obtain the target ligands L1, L2 or L3.

[0008] A further provision of the present invention is that the bromine-containing oxygen-containing heterocyclic compound in step S3 is selected from 5-bromobenzo[d][1,3]dioxane, 6-bromo-1,4-benzodioxane, or 5-bromo-2,3-dihydrobenzofuran.

[0009] A further feature of the present invention is that the acid deprotection in step S3 is carried out using p-toluenesulfonic acid monohydrate in a deoxymethanol solvent; and the yields of the ligands L1, L2, and L3 are 65% to 68%.

[0010] A class of phosphonol nickel catalysts containing oxygen heteroatoms in secondary coordination structures, characterized in that they are used in the preparation of polyethylene; The Ni1 catalyst was prepared from catalyst ligand L1 and [Py2Ni(CH2SiMe3)2], as shown below: ; Ni2 was prepared from catalyst ligand L2 and [Py2Ni(CH2SiMe3)2], as shown below: ; Ni3 was prepared from catalyst ligand L3 and [Py2Ni(CH2SiMe3)2], as shown below: ; The oxygen heteroatom ligands are L1, L2, and L3; The L1 structure is: ; The L2 structure is: ; The L3 structure is: .

[0011] A further embodiment of the present invention is a method for synthesizing a phosphonophenol nickel catalyst with an oxygen-containing heteroatom secondary coordination structure, wherein, under inert gas protection, the ligand described in claim 1 and 1.2 to 1.5 equivalents of [Py2Ni(CH2SiMe3)2] are dissolved in toluene, the reaction is stirred at room temperature for 3 to 5 hours, the reaction solution is filtered, and then recrystallized with dry n-hexane to obtain a yellow solid target catalyst with a yield of 80%.

[0012] Application of phosphonol nickel catalysts with oxygen-containing heteroatom secondary coordination structures in olefin polymerization reactions.

[0013] A further provision of the present invention is that the olefin polymerization reaction includes an ethylene homopolymerization reaction; the temperature of the ethylene homopolymerization reaction is 70~150 °C, and the ethylene pressure is 4~10 atm.

[0014] A further provision of the present invention is that the olefin polymerization reaction includes a copolymerization reaction of ethylene with a polar monomer; the polar monomer is selected from acrylate compounds.

[0015] A further provision of the present invention is that the solvent for the polymerization reaction is a mixture of toluene and n-heptane.

[0016] In summary, the present invention has the following beneficial effects: 1. This invention provides a class of diarylphosphine ligands containing oxygen-containing heterocyclic substituents of benzo[d][1,3]dioxane, 1,4-benzodioxane, and 2,3-dihydrobenzofuran, enriching the structural types of phosphine-containing nickel catalysts. Furthermore, the synthetic routes for the ligands and complexes of this invention are very clear, simple to operate, and yield high yields in each step (ligand yield 65-68%, complex yield 80%), making them suitable for large-scale preparation. By introducing a ring structure containing oxygen-containing heteroatoms into the ligand, the electronic effects and steric hindrance of the ligand can be adjusted, thereby regulating the catalytic performance of the nickel complexes.

[0017] 2. In the case of homopolymerization, the present invention achieves the highest yield of Ni2 (up to 2.08 g) at 120 °C, and exhibits the best activity of Ni2 (up to 2.08 × 10⁻⁶). 6 g mol⁻¹ h⁻¹.

[0018] 3. The nickel complex of the present invention can be used as an olefin polymerization catalyst and is expected to be applied in the fields of ethylene polymerization and copolymerization of ethylene with polar monomers. Attached Figure Description

[0019] Figure 1 This is the synthetic route for the nickel-based catalyst of the present invention; Figure 2 This is the 1H NMR spectrum of catalyst ligand L1 of this invention; Figure 3 This is the phosphorus NMR spectrum of catalyst ligand L1 of the present invention; Figure 4 This is the carbon NMR spectrum of catalyst ligand L1 of this invention; Figure 5 This is the mass spectrum of catalyst ligand L1 of the present invention; Figure 6 This is the 1H NMR spectrum of the catalyst Ni1 of this invention; Figure 7 The NMR phosphorus spectrum of the catalyst Ni1 of this invention; Figure 8 This is the 1H NMR spectrum of catalyst ligand L2 of this invention; Figure 9 This is the phosphorus NMR spectrum of catalyst ligand L2 of the present invention; Figure 10 This is the carbon NMR spectrum of catalyst ligand L2 of this invention; Figure 11 This is the mass spectrum of catalyst ligand L2 of the present invention; Figure 12 This is the 1H NMR spectrum of the Ni2 catalyst of this invention; Figure 13 This is the phosphorus NMR spectrum of the Ni2 catalyst of this invention; Figure 14 This is the 1H NMR spectrum of catalyst ligand L3 of this invention; Figure 15 This is the phosphorus NMR spectrum of catalyst ligand L3 of the present invention; Figure 16 This is the carbon NMR spectrum of catalyst ligand L3 of this invention; Figure 17 This is the mass spectrum of catalyst ligand L3 of the present invention; Figure 18 This is the 1H NMR spectrum of the Ni3 catalyst of this invention; Figure 19 This is the NMR phosphorus spectrum of the Ni3 catalyst of this invention. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings in the embodiments of the present invention.

[0021] Example 1: Synthesis of compound a 1.0 eq. of 2-tert-butylphenol was added to a Schlenk flask, followed by a suitable amount of dichloromethane, and then 0.5 eq. of pyridine 4-methylbenzenesulfonic acid (PPTS). The flask was purged with air using a double-row tube, and 5 eq. of 3,4-dihydro-2H-pyran was slowly added after inserting a nitrogen balloon. The reaction was carried out at room temperature for 12 hours. After the reaction was completed, post-treatment and column chromatography were performed to obtain an oily product a with a yield of 80%.

[0022] Example 2: Synthesis of Cl2PPh(Ar) intermediate In a Schlenk flask, n-BuLi (220 mmol, 2.5 M) was added to an ultradry tetrahydrofuran (300 mL) solution of 2-bromo-2,6-dimethoxybiphenyl (200 mmol) and incubated at -78 °C. After stirring the reaction mixture for 3 hours, the resulting suspension was slowly added dropwise to an ultradry tetrahydrofuran (200 mL) solution of phosphorus(III) chloride (600 mmol) while maintaining the temperature at -78 °C. After the addition was complete, the mixture was slowly heated to room temperature and stirred overnight. After the reaction was complete, the solvent was removed by double-row tube drying, and the product was recrystallized from dry n-hexane. The crystals were filtered through a glove box to obtain a white solid product, Cl2PPh(Ar), which was dried and stored in a glove box for later use.

[0023] Example 3: Synthesis of ligand L1 In a Schlenk flask, 5-bromobenzo[d][1,3]dioxolane (10 mmol) was dissolved in ultradry tetrahydrofuran (30 mL). n-BuLi (11 mmol, 2.5 M) was slowly added dropwise at -78 °C. After reacting for 3 hours, the reaction solution was introduced into a suspension of Cl2PPh(Ar) (10 mmol) in ultradry tetrahydrofuran (30 mL), and reacted at -78 °C for 3 hours to obtain a mixed suspension.

[0024] In a separate Schlenk flask, compound a (10 mmol) was dissolved in ultra-dry tetrahydrofuran (20 mL), and n-BuLi (11 mmol, 2.5 M) was slowly added dropwise at 0 °C. After reacting for 3 hours, the reaction solution was added to the suspension of the above mixture, and the temperature was naturally raised from 0 °C to room temperature for 12 hours.

[0025] After the reaction was complete, the mixture was concentrated under vacuum. The residue was dissolved in 50 mL of deoxyethanol and 2 mL of concentrate, and 0.3 g of p-toluenesulfonic acid monohydrate (PTSA) was added. The mixture was stirred at room temperature for 3 hours. After vacuum concentration, the mixture was extracted and subjected to column chromatography (petroleum ether / ethyl acetate = 20 / 1) to obtain a pure white solid (I) with a yield of 68%.

[0026] (I) Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the compound prepared in Example 3 of this disclosure.

[0027] like Figure 2 As shown, its proton spectrum data is as follows: 1 H NMR (400 MHz, CDCl3) δ 7.43 (s, 1H), 7.30 (t, J = 8.1 Hz, 2H), 7.21 (d, J = 13.2 Hz, 2H), 6.88 – 6.83 (m, 1H), 6.81 – 6.67(m, 4H), 6.53 (d, J = 21.9, 8.3 Hz, 2H), 5.93 (s, 2H), 3.58 (s, 3H, -OC H 3), 3.41 (s, 3H, -OC) H 3), 1.35 (s, 9H, -C(C H 3)3). Figure 3 This is the phosphorus NMR spectrum of the compound prepared in Example 3 of this disclosure.

[0028] like Figure 3 As shown, its phosphorus spectrum data are as follows: 31 p NMR (162 MHz, CDCl3) δ -37.7. Example 4: Synthesis of ligand L2 The same synthetic method as in Example 3 was used, except that 5-bromobenzo[d][1,3]dioxane (10 mmol) was replaced with 6-bromo-1,4-benzodioxane (10 mmol), to obtain the following (II) ligand L2, a pure white solid, in 65% yield.

[0029] (II) Figure 9 This is the 1H NMR spectrum of the compound prepared in Example 4 of this disclosure.

[0030] like Figure 9 As shown, its proton spectrum data is as follows: 1 H NMR (600 MHz, CDCl3) δ 7.43 (t, J = 8.2 Hz, 1H), 7.29 (d, J= 12.2, 8.6 Hz, 2H), 7.25 – 7.17 (m, 3H), 6.89 – 6.85 (m,1H), 6.78 (q, J = 7.6, 7.0 Hz, 2H), 6.72 (d, J = 8.1 Hz, 2H), 6.56 (d, J =8.3 Hz, 1H), 6.49 (d, J = 8.4 Hz, 1H), 4.23 (d, J = 12.1 Hz, 4H), 3.60 (s,3H, -OC H 3), 3.38 (s, 3H, -OC H 3), 1.35 (s, 9H, -C(C H 3)3). Figure 10 This is the phosphorus NMR spectrum of the compound obtained in Example 4 of this disclosure.

[0031] like Figure 10 As shown, its phosphorus spectrum data are as follows: 31 p NMR (162 MHz, CDCl3) δ -38.89. Example 5: Synthesis of ligand L3 The same synthetic method as in Example 3 was used, except that 5-bromobenzo[d][1,3]dioxolane (10 mmol) was replaced with 5-bromo-2,3-dihydrobenzofuran (10 mmol), to obtain the following (III) ligand L3, a pure white solid, with a yield of 67%.

[0032] (III) Figure 16 This is the hydrogen nuclear magnetic resonance spectrum of the compound prepared in Example 5 of this disclosure.

[0033] like Figure 16 As shown, its proton spectrum data is as follows: 1 H NMR (400 MHz, CDCl3) δ 7.47 – 7.39 (m, 1H),7.29 (d, J = 8.3 Hz, 2H), 7.23 (d, J = 9.7 Hz, 3H), 7.05 (d, J= 7.6 Hz, 1H),7.02 – 6.93 (m, 1H), 6.86 (s, 1H), 6.83 – 6.74 (m, 1H), 6.72 (d, J = 8.2 Hz, 1H), 6.53 (d, J = 20.3, 9.3 Hz, 2H), 4.56 (t, J = 8.7 Hz, 2H, -C H 2), 3.56 (d, J = 2.0 Hz, 3H, -OC H 3), 3.42 (s, 3H,-OCH3), 3.18 – 3.09 (m, 2H, -C H 2), 1.35(s, 9H, -C(C H 3)3).

[0034] Figure 17 This is the phosphorus NMR spectrum of the compound obtained in Example 5 of this disclosure.

[0035] like Figure 17 As shown, its phosphorus spectrum data are as follows: 31 p NMR (162 MHz, CDCl3) δ -39.75. Example 6: Synthesis of Catalyst Ni1 Under a nitrogen atmosphere in a glove box, ligand L1 (515 mg, 1 mmol) and 1.3 equivalents of [Py2Ni(CH2SiMe3)2] were dissolved in a suitable amount of toluene solution (10 mL), and stirred at room temperature for 4 hours. The toluene solution was removed by filtration, and the solution was recrystallized from dry n-hexane to give a yellow solid Ni1 in 80% yield. Example 7: Synthesis of Ni2 catalyst Using the same synthesis method as in Example 6, but replacing ligand L1 with ligand L2, catalyst Ni2 was obtained. Example 8: Synthesis of Ni3 catalyst Using the same synthesis method as in Example 6, but replacing ligand L1 with ligand L3, catalyst Ni3 was obtained. Example 9: Ethylene Homopolymerization Data Sheet In a glove box, 10 μmol of nickel catalyst was weighed and dissolved evenly in 10 mL of toluene. 18 mL of n-heptane was added to a pressure vessel, which was then sealed and taken out of the glove box. The vessel was placed on a stirrer and connected to a high-pressure line. Once the pressure vessel was heated to the required temperature, 2 mL of the catalyst toluene solution was injected into the pressure vessel using a syringe. The pressure vessel was then closed, and the ethylene pressure was rapidly increased to 8 atm. After 30 min of polymerization, the ethylene valve was closed. The pressure was slowly released, the polymerization vessel was disassembled, and ethanol was added to precipitate the polymer. The polymer was then filtered and dried to obtain polyethylene. The results are shown in Table 1.

[0036] Table 1 Results of ethylene polymerization at 120 °C a

[0037] a Conditions: 2 µmol nickel catalyst; 2 mL toluene; 18 mL heptane; rotation speed 350 rpm; ethylene pressure 8 atm; reaction time t = 30 min.

[0038] b 10 active units 6 g mol -1 h -1 .

[0039] c Number average molecular weight is in units of 10 4 g mol -1 ; M n The molecular weight distribution was determined by gel permeation chromatography in 1,2,4-trichlorobenzene at 160 °C.

[0040] d The determination was performed using differential scanning calorimetry (second heating curve).

[0041] Example 10: Ethylene / Polar Monomer Copolymerization In a glove box, 10 μmol of nickel catalyst was weighed and dissolved evenly in 2 mL of toluene. 18 mL of n-heptane and a polar monomer were added to a pressure vessel, which was then sealed and taken out of the glove box. The vessel was placed on a stirrer and connected to a high-pressure line. Once the pressure vessel was heated to the required temperature, 2 mL of the catalyst toluene solution was injected into the pressure vessel using a syringe. The pressure vessel was then closed, and the ethylene pressure was rapidly increased to 8 atm. After 30 min of polymerization, the ethylene valve was closed. The pressure was slowly released, the polymerization vessel was disassembled, and ethanol was added to precipitate the polymer. The polymer was then filtered and dried to obtain polyethylene. The results are shown in Table 2.

[0042] Table 2 Results of copolymerization of ethylene with polar monomersa

[0043] a Conditions: 10 µmol nickel catalyst; temperature = 120 ℃; ethylene pressure = 8 atm; 2 mL toluene; 18 mL heptane and polar monomer; rotation speed = 350 rpm; reaction time = 30 min.

[0044] b 10 active units 5 g mol -1 h -1 .

[0045] c Determined by ¹H NMR analysis.

[0046] d The determination was performed using differential scanning calorimetry (second heating curve).

[0047] e Number average molecular weight unit 10 4 g mol -1 Number-average molecular weight and molecular weight distribution were determined by gel permeation chromatography in 1,2,4-trichlorobenzene at 160 °C.

[0048] The above description is only a preferred embodiment of the present invention. Therefore, all equivalent changes or modifications made to the structure, features and principles described in the claims of this patent application are included in the scope of this patent application.

Claims

1. A class of oxygen-containing heteroatom phosphine ligands, characterized in that, The ligand has the following structure: Ligand L1: 5-hydroxybenzo[d][1,3]dioxolane group; Ligand L2: 6-hydroxy-1,4-benzodioxane group; Ligand L3: 5-hydroxy-2,3-dihydrobenzofuran group.

2. A method for synthesizing the oxygen-containing heteroatom phosphine ligand according to claim 1, characterized in that, Includes the following steps: S1: 2-tert-butylphenol was reacted with 3,4-dihydro-2H-pyran under PPTS catalysis to prepare intermediate a with hydroxyl protected. S2: 2-Bromo-2,6-dimethoxybiphenyl was lithiated with n-butyllithium and then reacted with phosphorus trichloride to prepare the diarylphosphine intermediate Cl2PPh(Ar); S3: The bromine-containing oxygen-containing heterocyclic compound is lithiated with n-butyllithium and then reacted with Cl2PPh(Ar), followed by reaction with the lithiation product of intermediate a, and finally deprotected by acid to obtain the target ligands L1, L2 or L3.

3. The method for synthesizing oxygen-containing heteroatom phosphine ligands according to claim 2, characterized in that, The bromine-containing oxygen-containing heterocyclic compound mentioned in step S3 is selected from 5-bromobenzo[d][1,3]dioxane, 6-bromo-1,4-benzodioxane, or 5-bromo-2,3-dihydrobenzofuran.

4. The method for synthesizing oxygen-containing heteroatom phosphine ligands according to claim 2, characterized in that, The acid deprotection in step S3 is carried out using p-toluenesulfonic acid monohydrate in deoxymethanol solvent; the yields of ligands L1, L2, and L3 are 65% to 68%.

5. A class of phosphonophenol nickel catalysts containing oxygen heteroatom secondary coordination structures, characterized in that, Used in the preparation of polyethylene; The Ni1 catalyst was prepared from catalyst ligand L1 and [Py2Ni(CH2SiMe3)2], as shown below: ； Ni2 was prepared from catalyst ligand L2 and [Py2Ni(CH2SiMe3)2], as shown below: ； Ni3 was prepared from catalyst ligand L3 and [Py2Ni(CH2SiMe3)2], as shown below: ； The oxygen heteroatom ligands are L1, L2, and L3; The L1 structure is: ； The L2 structure is: ； The L3 structure is: 。 6. A method for synthesizing the phosphonophenol nickel catalyst with an oxygen-containing heteroatom secondary coordination structure as described in claim 5, characterized in that, Under inert gas protection, the ligand described in claim 1 and 1.2 to 1.5 equivalents of [Py2Ni(CH2SiMe3)2] were dissolved in toluene and stirred at room temperature for 3 to 5 hours. After filtration, the reaction solution was recrystallized from dry n-hexane to obtain a yellow solid target catalyst with a yield of 80%.

7. The application of the phosphonol nickel catalyst with oxygen-containing heteroatom secondary coordination structure as described in claim 5 in olefin polymerization reactions.

8. The application of the phosphonophenol nickel catalyst with an oxygen-containing heteroatom secondary coordination structure according to claim 7 in olefin polymerization, characterized in that, The olefin polymerization reaction includes ethylene homopolymerization; the temperature of the ethylene homopolymerization reaction is 70~150 ℃, and the ethylene pressure is 4~10 atm.

9. The application of the phosphonophenol nickel catalyst with an oxygen-containing heteroatom secondary coordination structure according to claim 7 in olefin polymerization, characterized in that, The olefin polymerization reaction includes a copolymerization reaction of ethylene with a polar monomer; the polar monomer is selected from acrylate compounds.

10. The application of the phosphonophenol nickel catalyst with an oxygen-containing heteroatom secondary coordination structure according to claim 7 or 8 in olefin polymerization, characterized in that, The solvent for the polymerization reaction is a mixture of toluene and n-heptane.

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