A tridentate phosphine ligand, its preparation method, and its application in ethylene oligomerization.

Abstract

This invention discloses a tridentate phosphine ligand, its preparation method, and its application in ethylene oligomerization, belonging to the field of organometallic catalyst technology. The structure of the ligand is shown in Formula I: wherein, C m Selected from alkylene, substituted alkylene, aromatic rings and their derivatives, where m represents the number of bridging carbon atoms, and m is 1~20; R 1 R 2 The compounds are independently selected from straight-chain alkyl groups, branched alkyl groups, cycloalkyl groups, substituted cycloalkyl groups, aromatic rings, and their derivatives. When the tridentate phosphine ligand of this invention is combined with a transition metal compound and a co-catalyst to form a catalytic system for the catalytic oligomerization of ethylene to prepare α-olefins, high catalytic activity, high selectivity for 1-hexene and 1-octene can be achieved, while reducing by-product polymers.

Description

Technical Field

[0001] This invention relates to the field of organometallic catalysts, and more specifically, to a tridentate phosphine ligand for ethylene oligomerization catalysis, a method for preparing the ligand, a catalytic system containing the ligand, and its application in the preparation of α-olefins from ethylene oligomerization. Background Technology

[0002] Linear alpha-olefins (LAOs) are a crucial class of organic raw materials and chemical intermediates, widely used in the synthesis of copolymer polyethylene, surfactants, advanced synthetic lubricants (polyalpha-olefins), plasticizers, and fine chemicals. 1-Hexene and 1-octene are two of the most valuable LAOs in terms of research and economics, primarily used in the production of linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and polyolefin elastomers (POE). Copolymers of 1-hexene or 1-octene exhibit excellent impact resistance, tear resistance, and tensile strength, properties unmatched by 1-butene copolymers, demonstrating broad development prospects.

[0003] Compared to traditional methods such as wax cracking, extraction separation, alkane catalytic cracking, alkane dehydrogenation, coal extraction, fatty alcohol dehydrogenation, and internal olefin isomerization, the selective oligomerization of ethylene to produce 1-hexene and 1-octene provides a clean and efficient route.

[0004] In 2004, Bollmann et al. of Sasol (J. AM. CHEM. SOC. 2004, 126, 14712-14713) first achieved the selective oligomerization of ethylene to 1-octene and 1-hexene. A Cr / PNP / MAO catalytic system was used, with the catalyst consisting of a trivalent chromium precursor and a PNP ligand, and MAO as a co-catalyst. Toluene or alkanes were used as solvents, the reaction temperature was 45 °C, and the ethylene pressure was 4.5 MPa. The selectivity for 1-octene was 70%, and for 1-hexene, it was 13%. The catalyst activity was approximately 300 kg / (g Cr). Subsequently, Sasol applied for a series of patents on ethylene oligomerization, including CN105263890A, CN104220402A, CN105228973A, CN105228974A, and CN101052605A, and in 2014, it achieved the industrial production of 1-octene by selective tetramerization of ethylene.

[0005] The ligand frameworks used in ethylene selective oligomerization catalysts mainly include PNP, PCCP, PCSiCP, PNCN, and various derivative ligands. The steric hindrance and electronic effects of the ligands have a significant impact on the catalyst activity and product selectivity. Patents such as US8609924B2, CN105562096A, CN105562095A, CN105562097A, CN105562099A, CN105566036A, CN105566045A, CN105566037A, CN105566046A, and CN104415790A disclose a series of oligomerization catalysts with PCCP framework ligands. The oligomerization activity of PCCP ligands is similar to that of Sasol's PNP ligands, but the products contain more isoolefins, which are difficult to separate, and more polymers are generated, which is not conducive to the long-term operation of industrial plants.

[0006] While maintaining catalyst activity, existing PNP, PCCP, and other catalytic systems only achieve a total selectivity of around 80% for 1-hexene and 1-octene, indicating significant room for improvement. Furthermore, these systems exhibit polymer selectivity exceeding 0.2 wt% and high activity durations of less than 60 minutes, severely impacting the long-term operation of industrial plants. To address the issues of low selectivity, short duration of high activity, and high byproduct polymer formation in existing ligand-structured catalysts, there is an urgent need to develop catalysts with novel ligand framework structures. Summary of the Invention

[0007] To address the aforementioned problems in the prior art, this invention is the first to develop a tridentate phosphine ligand bridged by o-phenylenediamine, and to formulate this ligand, along with a transition metal compound and a co-catalyst, into a catalytic system for catalyzing the oligomerization of ethylene to prepare 1-hexene and 1-octene.

[0008] In a first aspect of the present invention, a tridentate phosphine ligand is provided, the structural formula of which is shown in Formula I:

[0009] Among them, C m Selected from alkylene, substituted alkylene, aromatic rings and their derivatives, where m represents the number of bridging carbon atoms, and m is 1~20; R 1 R 2 Each is independently selected from straight-chain alkyl, branched-chain alkyl, cycloalkyl, substituted cycloalkyl, aromatic ring and its derivatives.

[0010] In some embodiments of the first aspect of the invention, the alkylene comprises C1 to C6 alkylene, the substituted alkylene comprises C3 to C18 substituted alkylene, and the aromatic ring and its derivatives comprise C6 to C18 aryl groups.

[0011] In some embodiments of the first aspect of the invention, C m Selected from –CH2–, –CH2–CH2–, –CH(CH3)–CH2–, –CH(CH3)–CH(CH3)–, –CH(Ph)–CH2–, –CH(Ph)–CH(Ph)–, –C6H4–, –C6H4–CH2–, –CH2–CH2–CH 2-, -CH(CH3)-CH2-CH2-, -CH(Ph)-CH2-CH2-, -CH(Ph)-CH(Ph)-CH2-, preferably -CH2-, -CH2-CH2-, -C6H4-, -C6H4-CH2-, -CH2-CH2-CH2-.

[0012] In some embodiments of the first aspect of the invention, R 1 R 2 The compounds are independently selected from straight-chain alkyl and branched alkyl groups from C1 to C6, cycloalkyl and substituted cycloalkyl groups from C4 to C10, and aromatic rings and their derivatives from C6 to C18.

[0013] In some embodiments of the first aspect of the invention, R 1 R 2 The compounds are selected from methyl, ethyl, isopropyl, n-butyl, isobutyl, tert-butyl, cyclohexyl, phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2,6-dimethylphenyl, 2,6-diethylphenyl, 2,6-diisopropylphenyl, 2,4,6-trimethylphenyl, 2-methoxyphenyl, 4-methoxyphenyl, 2,6-dimethoxyphenyl, 2,6-diethoxyphenyl, 2,4,6-trimethoxyphenyl, naphthyl, and biphenyl, with methyl, ethyl, isopropyl, n-butyl, tert-butyl, cyclohexyl, phenyl, and naphthyl being preferred.

[0014] In some embodiments of the first aspect of the invention, the tridentate phosphine ligand has one of the following structural formulas:

[0015] In a second aspect of the invention, a method for preparing the tridentate phosphine ligand of the first aspect of the invention is provided, the method comprising the following steps: Step 1: Synthesize an intermediate having the structure shown in formula (a) by reacting according to the following reaction formula:

[0016] Among them, C m Selected from alkylene, substituted alkylene, aromatic rings and their derivatives, where m represents the number of bridging carbon atoms, and m is 1~20; R 1 R 2Each is independently selected from straight-chain alkyl, branched-chain alkyl, cycloalkyl, substituted cycloalkyl, aromatic ring and their derivatives; X is a halogen; Step 2: React PhPCl2 with the intermediate obtained in Step 1 to form a tridentate phosphine ligand with the structure shown in Formula I.

[0017] In some embodiments of the second aspect of the invention, the reaction in step 2 is carried out in the presence of Et3N.

[0018] In some embodiments of the second aspect of the present invention, the synthetic reaction route for the tridentate phosphine ligand with the structure shown in Formula I is as follows:

[0019] In the first stage, phosphonamine compounds (R) 1 R 2 PC m Using NH2 and o-dihalobenzene (e.g., o-dibromobenzene) as raw materials, in a trialkylamine (e.g., diisopropylethylamine) i The reaction was carried out in the presence of Pr2EtN or triethylamine to obtain the ligand intermediate shown in formula (a). The synthesis reaction was carried out at a temperature of 120-150°C under reflux with stirring. After the reaction was completed, the reaction product was post-processed and purified, including extraction, drying, filtration, rotary evaporation, and recrystallization, to obtain the ligand intermediate shown in formula (a).

[0020] In the second stage, intermediate (a) and phenylphosphine dichloride (PhPCl2) were dissolved in a solvent and subjected to a salt elimination reaction in the presence of triethylamine to generate a new NP-N structure (i.e., the tridentate phosphine ligand shown in Formula I) and the byproduct triethylamine hydrochloride. After the reaction was completed, the reaction product was post-processed and purified to obtain the tridentate phosphine ligand shown in Formula I.

[0021] In a third aspect of the invention, a catalytic system is provided, comprising: a tridentate phosphine ligand of the first aspect of the invention, a transition metal compound, and a cocatalyst.

[0022] In some embodiments of the third aspect of the invention, the transition metal compound is selected from chromium trichloride, chromium trichloride tetrahydrofuran complex, chromium dichloride, chromium dichloride tetrahydrofuran complex, chromium acetylacetonate, chromium tri(2-ethylhexanoate), chromium methyl dichloride tetrahydrofuran complex, triphenylchromium tetrahydrofuran complex, and carbonyl chromium, preferably chromium trichloride tetrahydrofuran complex, chromium acetylacetonate, and chromium tri(2-ethylhexanoate).

[0023] In some embodiments of the third aspect of the present invention, the co-catalyst is an alkylaluminum co-catalyst or an organoboron co-catalyst, wherein the alkylaluminum co-catalyst is selected from one or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, methylaluminoxane (MAO), modified methylaluminoxane (MMAO, triisobutylaluminum modified), ethylaluminoxane, isobutylaluminoxane, diethylaluminum chloride, ethylaluminum dichloride, and tris(pentafluorophenyl)aluminum; and the organoboron co-catalyst is selected from one or more of tris(pentafluorophenyl)boron, tetrafluoroborate, and tetra(pentafluorophenyl)borate.

[0024] In a fourth aspect of the invention, the application of the catalytic system described in the third aspect of the invention in the preparation of α-olefins by ethylene oligomerization is provided.

[0025] In a fifth aspect of the invention, a method for preparing α-olefins by ethylene oligomerization is provided, the method employing the catalytic system of the third aspect of the invention.

[0026] In some embodiments of the fifth aspect of the present invention, a method for preparing α-olefins by ethylene oligomerization includes the following steps: under an ethylene atmosphere, a solvent mixture of a co-catalyst, a tridentate phosphine ligand, and a transition metal compound in a catalytic system is sequentially added to an organic solvent, and then hydrogen and ethylene are sequentially introduced to carry out an oligomerization reaction; wherein the molar concentration of the tridentate phosphine ligand is 0.002~1 mmol / L, the molar concentration of the transition metal compound is 0.002~1 mmol / L, and the molar concentration of the co-catalyst is 0.1~1000 mmol / L.

[0027] In some embodiments of the fifth aspect of the present invention, the molar concentration of the ligand is 0.005 to 0.1 mmol / L; the molar concentration of the transition metal compound is 0.005 to 0.1 mmol / L; and the molar concentration of the co-catalyst is 2.5 to 50 mmol / L.

[0028] In some embodiments of the fifth aspect of the present invention, the oligomerization reaction is carried out at a temperature of 10-150 °C, a reaction pressure of 0.5-5 MPa, and a reaction time of 0.1-48 h.

[0029] In some embodiments of the fifth aspect of the invention, the organic solvent is selected from toluene, xylene, mesitylene, pentane, cyclopentane, methylcyclopentane, hexane, cyclohexane, methylcyclohexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, 1-hexene, 1-octene, 1-decene, dichloromethane, dichloroethane, chlorobenzene, o-dichlorobenzene, m-dichlorobenzene, and p-dichlorobenzene.

[0030] The present invention has the following beneficial technical effects compared with the prior art: This invention is the first to develop a tridentate phosphine ligand bridged by o-phenylenediamine and use it for ethylene oligomerization catalysis. This ligand forms a catalytic system in situ with a transition metal compound and a co-catalyst, without the need for pre-reaction to form an organometallic complex.

[0031] The ethylene oligomerization catalytic system of the present invention is used for the oligomerization of ethylene to prepare α-olefins, and it has high catalytic activity. In an exemplary embodiment, the catalytic activity can reach up to 18 × 10⁻⁶. 7 g / (mol Cr·h); at the same time, 1-hexene and 1-octene can be produced with high selectivity, and in an exemplary embodiment, the total selectivity of 1-hexene and 1-octene exceeds 88%.

[0032] Furthermore, when using the catalytic system of the present invention for ethylene oligomerization, the amount of by-product polymer generated is effectively reduced. In an exemplary embodiment, the amount of by-product polymer generated is as low as 0.08%, which effectively avoids blockage of the production equipment pipeline and is beneficial for long-term operation of the equipment. Attached Figure Description

[0033] Figure 1 The nuclear magnetic resonance of the tridentate phosphine ligand with the structure shown in Formula V in Embodiment 4 of the present invention. 31 P-spectrum.

[0034] Figure 2 This is a gas chromatogram of the ethylene oligomerization product in Example 4 of the present invention (internal standard is n-heptane). Detailed Implementation

[0035] The present invention will be described in detail below with reference to specific embodiments. These specific embodiments are only used to illustrate the present invention and do not constitute a limitation on the scope and substance of the present invention.

[0036] Example 1 1. Preparation of ligands:

[0037] This embodiment relates to the tridentate phosphine ligand shown in Formula II, and its preparation steps are as follows: Step 1: Synthesizing intermediates Using Ph₂PCH₂CH₂NH₂ and o-dibromobenzene as precursors, in i The intermediate was synthesized by reaction in the presence of Pr2EtN, and the synthetic route for this step is shown below:

[0038] Specifically, an anhydrous and oxygen-free operating system, namely the Schlenk double-row system, was used. Ph₂PCH₂CH₂NH₂ (2.30 g, 10 mmol) and o-dibromobenzene (1.18 g, 5 mmol) were added in a round-bottom flask. i Pr₂EtN (1.7 mL, 10 mmol) was mixed thoroughly and refluxed with stirring at 138 °C for 5 h. Subsequently, it was cooled to room temperature and extracted with a mixture of deionized water (20 mL) and dichloromethane (15 mL). KOH (0.5 M, 15 mL) solution was added to the aqueous phase, followed by extraction with dichloromethane (15 mL). The combined organic phases were dried over anhydrous MgSO₄ and filtered through a diatomaceous earth column, followed by rotary evaporation to remove volatiles. The residual solid was recrystallized from ethanol to give a white solid intermediate. The yield was 1.48 g, or 56%. The NMR data for this intermediate are as follows: 31 P NMR (162 MHz, C6D6): -21.65.

[0039] Step 2: Prepare the tridentate phosphine ligand of Formula II from the intermediate obtained in Step 1. The intermediate reacts with PhPCl2 to generate the tridentate phosphine ligand shown in Formula II. The synthetic route for this step is shown below:

[0040] Specifically, the reaction was carried out in an anhydrous and oxygen-free environment in a glove box. The intermediate obtained in step 1 (1.06 g, 2 mmol) and PhPCl2 (0.27 mL, 2 mmol) were dissolved in THF, and then Et3N (0.56 mL, 4 mmol) was slowly added dropwise at room temperature. The reaction mixture immediately became turbid, and was stirred overnight to ensure complete reaction. The solvent was removed under vacuum, and the remaining solid was extracted with toluene and filtered through a diatomaceous earth column. The solvent was removed under vacuum to obtain the product. The product weighed 1.10 g, with a yield of 86%. The structure of the product was determined by... 31 P NMR characterization, combined with its preparation process, confirmed that it is the target ligand shown in Formula II.

[0041] The NMR data are as follows: 31 P NMR (162 MHz, C6D6): 75.06, -17.95.

[0042] 2. Ethylene oligomerization:

[0043] After the 1L high-pressure reactor was installed and debugged, it was preheated to 120 °C, vacuum dried for 5 h, purged with nitrogen three times, and then cooled to room temperature. 200 mL of dry methylcyclohexane solution was added, and the stirring speed was controlled. 0.39 g of MMAO-3A (7wt% Al, methylcyclohexane solution, co-catalyst), 1.30 mg of the ligand shown in Formula II, and 0.70 mg of chromium acetylacetone (transition metal compound) in methylcyclohexane solution were added sequentially. The mixture was rapidly heated to 45 °C, and hydrogen was first introduced to 0.1 MPa, followed by ethylene to 4.5 MPa. The stirring speed was 200 rpm and maintained for 90 min.

[0044] After the reaction is complete, stop the ethylene supply, rapidly cool the reaction system to 10 °C, slowly depressurize, and discharge the liquid material mixed with polymer particles from the bottom valve of the reactor, weighing it. After standing for 30 minutes, take 10 g of the supernatant, add 2 g of n-heptane internal standard, dry with anhydrous Na₂SO₄, and perform gas chromatography analysis to obtain the mass of the liquid product and the selectivity of each component. In addition, filter out the settled polymer particles, air-dry them in a fume hood, and then dry them in a 100 °C oven to constant weight before weighing. Open the reactor and scrape off the white flocculent polymer scale formed on the reactor internal components (including the agitator, internal coil, and thermometer), air-dry them in a fume hood, and then dry them in a 100 °C oven to constant weight before weighing. The total product mass includes the sum of the liquid product mass and the solid by-product mass. The by-product polymer mass includes both the flocculent polymer on the reactor internal components and the polymer particles mixed in the liquid material. In this embodiment, the amount of by-product polymer generated in the ethylene oligomerization product is the ratio of the mass of the two solid polymers to the total product mass, which is 0.12 wt%. The results are summarized in Table 1.

[0045] The catalyst activity was calculated to be 9.3 × 10⁻⁶ using the internal standard method. 7 The specific composition of the ethylene oligomerization products is recorded in Table 1, with g / (mol Cr·h).

[0046] Example 2 The difference between Example 2 and Example 1 lies in the structure of the tridentate phosphine ligand. The structure of the tridentate phosphine ligand in Example 2 is shown in Formula III below:

[0047] The preparation steps of the tridentate phosphine ligand shown in Formula III of this embodiment are as follows: Step 1: Synthesizing intermediates The intermediate was prepared using a synthetic method similar to that in Example 1, except that the precursor Ph2PCH2CH2NH2 used in the intermediate preparation of Example 1 was replaced with... t Bu2PCH2CH2NH2, the intermediate formed by...31 P NMR characterization, its NMR data are as follows: 31 P NMR (162 MHz, C6D6): 18.36. The structural formula of this intermediate is as follows:

[0048] Step 2: Prepare the tridentate phosphine ligand of Formula III from the intermediate obtained in Step 1. This step is similar to step 2 in Example 1, and the obtained product is subjected to... 31 P NMR characterization and, combined with the preparation process, confirmed that it is the target ligand shown in Formula III. The NMR data are as follows: 31 P NMR (162 MHz, C6D6): 82.36, 21.52.

[0049] 1.15 mg of the tridentate phosphine ligand shown in Formula III was used to form a catalytic system with chromium acetylacetone (a transition metal compound) and MMAO-3A (a cocatalyst). This catalytic system was used for ethylene oligomerization. In the ethylene oligomerization reaction of this embodiment, except for the ligand, all other conditions were the same as in Example 1.

[0050] The catalyst activity in this embodiment was calculated to be 15.6 × 10⁻⁶ using internal standard gas chromatography quantitative analysis. 7 The specific composition of the ethylene oligomerization products is recorded in Table 1, with g / (mol Cr·h).

[0051] In this embodiment, the amount of by-product polymer generated in the ethylene oligomerization product was 0.10 wt%, and the results are summarized in Table 1.

[0052] Example 3 The difference between Example 3 and Example 1 lies in the structure of the tridentate phosphine ligand. The structure of the tridentate phosphine ligand in Example 3 is shown in Formula IV below:

[0053]

[0054] The preparation steps of the tridentate phosphine ligand shown in Formula IV of this embodiment are as follows: Step 1: Synthesizing intermediates The intermediate was prepared using a synthetic method similar to that in Example 1, except that the precursor Ph2PCH2CH2NH2 used in the intermediate preparation of Example 1 was replaced with... i Pr2PCH2CH2NH2, the intermediate formed by... 31 P NMR characterization, its NMR data are as follows: 31 P NMR (162 MHz, C6D6): -6.72. The structural formula of this intermediate is as follows:

[0055] Step 2: Prepare the tridentate phosphine ligand of formula IV from the intermediate obtained in Step 1. This step is similar to step 2 in Example 1, and the obtained product is subjected to... 31 P NMR characterization, combined with the preparation process, confirmed that it is the target ligand shown in Formula IV.

[0056] The NMR data are as follows: 31 P NMR (162 MHz, C6D6): 73.78, 1.65.

[0057] Using 1.04 mg of the ligand shown in Formula IV, a catalytic system was formed with chromium acetylacetone (a transition metal compound) and MMAO-3A (a cocatalyst). This catalytic system was used for ethylene oligomerization. In the ethylene oligomerization reaction of this embodiment, except for the different ligand, all other conditions were the same as in Example 1.

[0058] The catalyst activity was quantitatively calculated to be 12.4 × 10⁻⁶ using gas chromatography with internal standard method. 7 g / (mol Cr·h), the specific composition of the products is recorded in Table 1.

[0059] In this embodiment, the amount of by-product polymer generated in the ethylene oligomerization product was 0.08 wt%, and the results are summarized in Table 1.

[0060] Example 4 The difference between Example 4 and Example 1 lies in the structure of the tridentate phosphine ligand. The ligand structure of Example 4 is shown in Formula V below:

[0061] The preparation steps of the tridentate phosphine ligand shown in Formula V of this embodiment are as follows: Step 1: Synthesizing intermediates The intermediate was prepared using a synthetic method similar to that of Example 1, except that the precursor Ph2PCH2CH2NH2 in the intermediate preparation of Example 1 was replaced with Ph2PCH2CH2CH2NH2. The resulting intermediate was then processed... 31 P NMR characterization, NMR data are as follows: 31 P NMR (162 MHz, C6D6): -16.42. The structural formula of this intermediate is as follows:

[0062] Step 2: Prepare the tridentate phosphine ligand of formula V from the intermediate obtained in Step 1. This step is similar to step 2 in Example 1, and the obtained product is subjected to... 31P NMR characterization and, combined with the preparation process, confirmed that it is the target ligand shown in Formula V, and its NMR... 31 P spectrum as shown Figure 1 As shown.

[0063] The NMR data are as follows: 31 P NMR (162 MHz, C6D6): 71.65, -16.20.

[0064] Using 1.35 mg of the ligand shown in Formula V, a catalytic system was formed with chromium acetylacetone (a transition metal compound) and MMAO-3A (a co-catalyst). This catalytic system was used for ethylene oligomerization. In the ethylene oligomerization reaction of this embodiment, except for the ligand, all other conditions were the same as in Example 1.

[0065] The catalyst activity was quantitatively calculated to be 18.5 × 10⁻⁶ using gas chromatography with internal standard method. 7 g / (mol Cr·h), the specific composition of the product is recorded in Table 1, and the gas chromatographic analysis spectrum of the product is shown in Figure 1. Figure 2 As shown.

[0066] In this embodiment, the amount of by-product polymer generated in the ethylene oligomerization product was 0.08 wt%, and the results are summarized in Table 1.

[0067] Example 5 The difference between Example 5 and Example 1 lies in the structure of the tridentate phosphine ligand. The ligand structure of Example 5 is shown in VI below:

[0068] The preparation steps of the tridentate phosphine ligand shown in Formula VI of this embodiment are as follows: Step 1: Synthesizing intermediates The intermediate was prepared using a synthetic method similar to that of Example 1, except that the precursor Ph2PCH2CH2NH2 in the intermediate preparation of Example 1 was replaced with 2-Ph2PC6H4NH2. The resulting intermediate was then processed... 31 P NMR characterization, NMR data are as follows: 31 P NMR (162 MHz, C6D6): -21.85. The structural formula of this intermediate is as follows:

[0069] Step 2: Prepare the tridentate phosphine ligand of formula VI from the intermediate obtained in Step 1. This step is similar to step 2 in Example 1, and the obtained product is subjected to... 31 P NMR characterization, combined with the preparation process, confirmed that it is the target ligand shown in formula VI, and its NMR data are as follows: 31P NMR (162 MHz, C6D6): 82.56, -17.45.

[0070] Using 1.48 mg of the ligand shown in Formula VI, a catalytic system was formed with chromium acetylacetone (a transition metal compound) and MMAO-3A (a co-catalyst). This catalytic system was used for ethylene oligomerization. In the ethylene oligomerization reaction of this embodiment, except for the different ligand, all other conditions were the same as in Example 1.

[0071] The catalyst activity was calculated to be 7.5 × 10⁻⁶ using quantitative analysis by gas chromatography with internal standard method. 7 g / (mol Cr·h), the specific composition of the products is recorded in Table 1.

[0072] In this embodiment, the amount of by-product polymer generated in the ethylene oligomerization product was 0.19 wt%, and the results are summarized in Table 1.

[0073] Example 6 The difference between Example 6 and Example 1 lies in the structure of the tridentate phosphine ligand. The ligand structure of Example 6 is shown in Formula VII below:

[0074] The preparation steps of the tridentate phosphine ligand shown in Formula VII of this embodiment are as follows: Step 1: Synthesizing intermediates The intermediate was prepared using a synthetic method similar to that of Example 1, except that the precursor Ph2PCH2CH2NH2 in the intermediate preparation of Example 1 was replaced with 2-Ph2PC6H4CH2NH2. The resulting intermediate was then processed... 31 P NMR characterization, NMR data are as follows: 31 P NMR (162 MHz, C6D6): -15.96. The structural formula of this intermediate is as follows:

[0075] Step 2: Prepare the tridentate phosphine ligand of formula VII from the intermediate obtained in Step 1. This step is similar to step 2 in Example 1, and the obtained product is subjected to... 31 P NMR characterization, combined with the preparation process, confirmed that it is the target ligand shown in formula VII, and its NMR data are as follows: 31 P NMR (162 MHz, C6D6): 79.68, -14.59.

[0076] A catalytic system was formed by using 1.55 mg of the ligand shown in Formula VII, chromium acetylacetone (a transition metal compound), and MMAO-3A (a cocatalyst). This catalytic system was used for ethylene oligomerization. In the ethylene oligomerization reaction of this embodiment, all conditions were the same as in Example 1 except for the ligand.

[0077] The catalyst activity was calculated to be 10.9 × 10⁻⁶ using quantitative analysis by gas chromatography with internal standard method. 7 g / (mol Cr·h), the specific composition of the products is recorded in Table 1.

[0078] In this embodiment, the amount of by-product polymer generated in the ethylene oligomerization product was 0.18 wt%, and the results are summarized in Table 1.

[0079] Table 1: Results of catalytic reactions in Examples 1-6

[0080] As shown in Table 1, the in-situ catalytic system composed of the tridentate phosphine ligand, transition metal compound, and co-catalyst of this invention can catalyze the oligomerization of ethylene to prepare 1-hexene and 1-octene with high activity and selectivity, and the catalytic activity of both is higher than 7 × 10⁻⁶. 7 (mol Cr·h), exceeding 18×10 7 g / (mol Cr·h), and the total selectivity of 1-hexene and 1-octene can exceed 88%, with the amount of by-product polymer generated as low as 0.08%.

[0081] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0082] The above embodiments are only used to illustrate the technical solutions of the present invention and should not be used to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments or equivalent substitutions can be made to some of the technical features without departing from the essence and scope of the present invention. Such modifications or equivalent substitutions still fall within the scope of the present invention.

Claims

1. A tridentate phosphine ligand, characterized in that, The structure of the ligand is shown in Formula I: Among them, C m Selected from alkylene, substituted alkylene, aromatic ring and their derivatives, m represents the number of bridging carbon atoms, m is 1~20; R 1 R 2 Each is independently selected from straight-chain alkyl, branched-chain alkyl, cycloalkyl, substituted cycloalkyl, aromatic ring and its derivatives.

2. The tridentate phosphine ligand as described in claim 1, wherein, The alkylene group includes C1 to C6 alkylene groups, the substituted alkylene group includes C3 to C18 substituted alkylene groups, and the aromatic ring and its derivatives include C6 to C18 aryl groups.

3. The tridentate phosphine ligand as described in claim 1, wherein, Said C m Selected from –CH2–, –CH2–CH2–, –CH(CH3)–CH2–, –CH(CH3)–CH(CH3)–, –CH(Ph)–CH2–, –CH(Ph)–CH(Ph)–, –C6H4–, –C6H4–CH2–, –CH2–CH2–CH2–, –CH(CH3)–CH2–CH2–, –CH(Ph)–CH2–CH2–, –CH(Ph)–CH(Ph)–CH2–.

4. The tridentate phosphine ligand as described in claim 1, wherein, The C m Selected from –CH2–CH2–, –CH2–CH2–CH2–, –C6H4–, –C6H4–CH2–.

5. The tridentate phosphine ligand as described in claim 1, wherein, R 1 R 2 The compounds are independently selected from straight-chain alkyl and branched alkyl groups from C1 to C6, cycloalkyl and substituted cycloalkyl groups from C4 to C10, and aromatic rings and their derivatives from C6 to C18.

6. The tridentate phosphine ligand as described in claim 1, wherein, R 1 R 2 The compounds are selected from methyl, ethyl, isopropyl, n-butyl, isobutyl, tert-butyl, cyclohexyl, phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2,6-dimethylphenyl, 2,6-diethylphenyl, 2,6-diisopropylphenyl, 2,4,6-trimethylphenyl, 2-methoxyphenyl, 4-methoxyphenyl, 2,6-dimethoxyphenyl, 2,6-diethoxyphenyl, 2,4,6-trimethoxyphenyl, naphthyl, and biphenyl, respectively.

7. The tridentate phosphine ligand as described in claim 1, wherein, The ligand has one of the following structural formulas: 。 8. The method for preparing the tridentate phosphine ligand according to any one of claims 1 to 7, characterized in that, The method includes the following steps: Step 1: Synthesize an intermediate having the structure shown in formula (a) by reacting according to the following reaction formula: Among them, C m Selected from alkylene, substituted alkylene, aromatic rings and their derivatives, where m represents the number of bridging carbon atoms, and m is 1~20; R 1 R 2 Each is independently selected from straight-chain alkyl, branched-chain alkyl, cycloalkyl, substituted cycloalkyl, aromatic ring and their derivatives; X is a halogen; Step 2: React PhPCl2 with the intermediate obtained in Step 1 to form a tridentate phosphine ligand with the structure shown in Formula I.

9. The preparation method according to claim 8, wherein, The reaction in step 2 is carried out in the presence of Et3N.

10. A catalytic system, characterized in that, The catalytic system comprises: a tridentate phosphine ligand as described in any one of claims 1 to 8, a transition metal compound, and a co-catalyst.

11. The catalytic system of claim 10, wherein, The transition metal compound is selected from chromium trichloride, chromium trichloride tetrahydrofuran complex, chromium dichloride, chromium dichloride tetrahydrofuran complex, chromium acetylacetone, chromium tri(2-ethylhexanoate), chromium methyl dichloride tetrahydrofuran complex, triphenylchromium tetrahydrofuran complex, and carbonyl chromium.

12. The catalytic system of claim 10, wherein, The cocatalyst is an alkylaluminum cocatalyst or an organoboron cocatalyst. The alkylaluminum cocatalyst is selected from one or more of trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, methylaluminoxane (MAO), modified methylaluminoxane (MMAO, triisobutylaluminum modified), ethylaluminoxane, isobutylaluminoxane, diethylaluminum chloride, ethylaluminum dichloride, and tris(pentafluorophenyl)aluminum. The organoboron cocatalyst is selected from one or more of tris(pentafluorophenyl)boron, tetrafluoroborate, and tetra(pentafluorophenyl)borate.

13. The use of the catalytic system according to any one of claims 10 to 12 in the preparation of α-olefins by ethylene oligomerization.

14. A method for preparing α-olefins via ethylene oligomerization, characterized in that, The method employs the catalytic system as described in any one of claims 10 to 12.

15. The method of claim 14, wherein, The method includes the following steps: In an ethylene atmosphere, a solvent mixture of the co-catalyst, tridentate phosphine ligand, and transition metal compound in the catalytic system is sequentially added to an organic solvent, and then hydrogen and ethylene are sequentially introduced to carry out an oligomerization reaction. The molar concentration of the tridentate phosphine ligand is 0.002~1 mmol / L, the molar concentration of the transition metal compound is 0.002~1 mmol / L, and the molar concentration of the co-catalyst is 0.1~1000 mmol / L.

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