Cobalt pyridine diimine complexes, processes for their preparation and processes for the preparation of 1-hexene

Abstract

This invention belongs to the field of catalytic materials technology, specifically relating to a pyridinediimide cobalt complex and its preparation method, as well as a method for preparing 1-hexene. A pyridinediimide cobalt complex has the structural formula: ; wherein, R... 1 Selected from fluorine, chlorine, bromine, ester, cyano, benzyl, and hydrogen; R 2 Selected from methyl, ethyl, isopropyl, fluorine, hydrogen, trifluoromethyl, methoxy, R 2 The positions are ortho, para, and meta of aniline; R 3 Selected from cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and hydrogen. This cobalt pyridine diimine complex, under the co-catalysis of methylaluminoxane (MAO), can catalyze the selective oligomerization of propylene to prepare 1-hexene. The oligomerization reaction conditions are mild, and the resulting polyethylene significantly reduces the symmetry and regularity of the polymer chain segments, thereby weakening its crystallinity. While maintaining mechanical strength, it also exhibits excellent flexibility, resistance to environmental stress cracking, and low-temperature impact resistance.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, specifically relating to a pyridine diimine cobalt complex and its preparation method, as well as a method for preparing 1-hexene. Background Technology

[0002] 1-Hexene is an α-olefin monomer and fine chemical intermediate with important industrial value. Its most prominent downstream application is as a comonomer to copolymerize with ethylene to produce linear low-density polyethylene (LLDPE). With the continued growth in global demand for high-performance polyolefins, the process route for the highly selective preparation of 1-hexene via catalytic dimerization of propylene has attracted much attention due to its high atom economy and low carbon footprint. Existing catalytic systems for propylene oligomerization have significant shortcomings: while heterogeneous catalytic systems exhibit high propylene conversion activity, the products contain a large amount of highly polymerized branched olefins and non-terminated olefins due to strong surface acidity, limited pore structure, and uneven distribution of active sites, resulting in low 1-hexene selectivity. This necessitates complex subsequent separation processes, leading to high energy consumption and equipment investment, thus limiting industrial application. Homogeneous catalytic systems, although capable of achieving highly selective oligomerization of propylene under mild conditions and with performance modifiable through ligand modification, are susceptible to the combined effects of the central metal electronic structure, ligand steric hindrance, and the softness and hardness of coordinating atoms. This can easily activate monomer insertion anomalies, β-H elimination, and isomerization pathways during chain growth, causing the product to deviate from the linear α-olefin target. In propylene dimerization, the selectivity of branched hexene isomers can reach 70%–90%, while the molar fraction of the target product, 1-hexene, is typically below 30%.

[0003] Therefore, there is an urgent need to develop a catalytic system for propylene oligomerization to meet the continued growth in global demand for high-performance polyolefins. Summary of the Invention

[0004] The purpose of this invention is to provide a cobalt pyridinediimide complex and its preparation method, as well as a method for preparing 1-hexene. Using this cobalt pyridinediimide complex in the presence of methylaluminoxane (MAO) as a co-catalyst, propylene can be selectively oligomeric to prepare 1-hexene. The catalyst used in this technique is simple to prepare, and the oligomeric reaction conditions are mild. The introduction of the prepared 1-hexene structural units into the polyethylene backbone can significantly reduce the symmetry and regularity of the polymer chain segments, thereby weakening its crystallinity. This allows the resulting LLDPE to maintain mechanical strength while also possessing excellent flexibility, resistance to environmental stress cracking, and low-temperature impact resistance.

[0005] A first aspect of the present invention is to provide a cobalt pyridine diimine complex, the structural formula of which is: Among them, R 1 Selected from fluorine, chlorine, bromine, ester, cyano, benzyl, and hydrogen; R2 Selected from methyl, ethyl, isopropyl, fluorine, hydrogen, trifluoromethyl, methoxy, R 2 The positions are ortho, para, and meta of aniline; R 3 Selected from cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and hydrogen.

[0006] A second aspect of the present invention provides a method for preparing a pyridinediimine cobalt complex, the method comprising the following steps: catalytically coupling cycloalkenylpinaborate with o-bromoaniline until the reaction is complete, followed by quenching, extraction, and separation to obtain cycloalkenylaniline; dissolving cycloalkenylaniline in ethyl acetate or ethanol and performing a reducing hydrogenation reaction to obtain cycloalkylaniline; dissolving cycloalkylaniline and 2,6-diacetylpyridine in ultra-dry toluene or tetrahydrofuran and performing a condensation reaction to obtain a pyridinediimine ligand; and controlling the coordination reaction between the pyridinediimine ligand and a cobalt salt to prepare the pyridinediimine cobalt complex.

[0007] In some embodiments of this application, the catalyst in the catalytic coupling reaction includes bis(triphenylphosphine)palladium dichloride, the base includes anhydrous cesium carbonate or potassium carbonate, the organic phase solvent includes ultra-dry 1,4-dioxane or tetrahydrofuran, and the co-solvent includes purified water.

[0008] In some embodiments of this application, the molar ratio of o-bromoaniline, cycloalkenylpinaborate, catalyst, and base is 1:(1.2~2):(0.5%~5%):(1.5~3); in the catalytic coupling reaction, the concentration of the reaction system is 0.1M~1M, and the volume ratio of organic solvent to co-solvent water is 5:1~10:1.

[0009] In some embodiments of this application, the conditions for the catalytic coupling reaction are: 80℃±2℃, and the reaction time is 16 hours±0.5 hours.

[0010] In some embodiments of this application, in the reductive hydrogenation reaction, the hydrogenation catalyst includes a carbon-supported catalyst with a palladium loading of 10%; the molar ratio of cycloalkenylaniline to the hydrogenation catalyst is 1:5% to 1:20%.

[0011] In some embodiments of this application, the conditions for the reducing hydrogenation reaction are: 25℃±2℃, and the reaction time is 48 hours±0.5 hours.

[0012] In some embodiments of this application, the condensation agent in the condensation reaction includes one or more of alkylaluminum supported silica (SiO2 / MAO) and p-toluenesulfonic acid; the molar ratio of cycloalkylaniline, 2,6-diacetylpyridine, and the condensation agent is 1:(2.5~3):(1~2).

[0013] In some embodiments of this application, the conditions for the condensation reaction are: 55℃±2℃, and the reaction time is 24 hours±0.5 hours.

[0014] In some embodiments of this application, the cobalt salt includes anhydrous cobalt chloride; the molar ratio of cobalt salt to pyridine diimide ligand is 1:1 to 1:1.5.

[0015] A third aspect of the present invention is to provide a method for preparing 1-hexene, wherein 1-hexene is prepared using the cobalt pyridine diimine complex provided in the first aspect or the cobalt pyridine diimine complex prepared by the method provided in the second aspect.

[0016] The beneficial effects of the present invention include at least one of the following: Compared with the prior art, the pyridine diimine cobalt complex provided by the present invention is obtained through R 1 R 2 R 3 The synergistic regulation of three types of substituents, catalyzing the selective oligomerization of propylene to 1-hexene under the co-catalysis of methylaluminoxane (MAO), not only achieved a high 1-hexene selectivity of 90%–93.1%, significantly improving upon the selectivity of less than 30% in existing homogeneous catalytic systems, but also achieved a maximum catalytic activity of 4.32 × 10⁻⁶. 5 g / (mol·h), successfully breaking the industry dilemma of "high activity and high selectivity are difficult to achieve at the same time".

[0017] The preparation process of pyridinediimide cobalt complex requires only four steps: catalytic coupling, reductive hydrogenation, condensation, and coordination. The raw materials are readily available, the process is simple, the reaction conditions in each step are mild, no special equipment is required, the yield of the complex is as high as 90%~99%, and it can be stored stably at room temperature and pressure, making storage and transportation convenient. The catalytic system has strong tolerance to fluctuations in reaction conditions, few side reactions, and low purification difficulty, which significantly reduces energy consumption and equipment investment in industrial production. At the same time, the 1-hexene prepared can be used as a comonomer to effectively improve the flexibility, environmental stress cracking resistance, and low-temperature impact resistance of linear low-density polyethylene (LLDPE). It has strong compatibility with existing propylene processing and LLDPE production systems, high atom economy, and low carbon footprint, and has outstanding industrial application value and significant economic benefits. Attached Figure Description

[0018] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention.

[0019] Figure 1 The gas chromatographic (GC) detection chromatogram of 1-hexene prepared using the cobalt pyridine diimine complex provided in Example 4 of this invention. Detailed Implementation

[0020] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0022] In the description of the embodiments of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "multiple" means two or more, unless otherwise explicitly defined.

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] With the continued growth in global demand for high-performance polyolefins, the process route for the highly selective catalytic dimerization of propylene to prepare 1-hexene has attracted much attention due to its high atom economy and low carbon footprint. Existing catalytic systems used for propylene oligomerization can be mainly divided into the following two categories: (1) Heterogeneous catalytic systems: using metal-supported solid phosphoric acid (SPACs), polyoxometalates (POMs), and catalysts containing metal ions (such as Ni). 2+ Co 2+ Zn 2+Modified microporous or mesoporous molecular sieves (such as ZSM-5, MCM-41, and SBA-15) are representative examples. These catalysts typically exhibit high propylene conversion activity, but due to their strong surface acidity, limited pore structure, and uneven distribution of active sites, the products contain a large amount of branched olefins with trimer, tetramer, or even higher degrees of polymerization. Furthermore, the proportion of non-terminal olefins is high, and the selectivity for 1-hexene is low. Subsequent complex separation processes such as multi-tower distillation, extractive distillation, or molecular sieve adsorption are required, significantly increasing energy consumption and equipment investment, thus limiting their industrial application.

[0025] (2) Homogeneous catalytic system: Based on group IVB (Zr, Hf), group VB (V) and group VIII (Fe, Co, Ni) transition metal complexes, and using cyclopentadienyl, α-diimine, phosphine-nitrogen-phosphine (PNP), phosphine-oxygen-phosphine (POP), nitrogen-nitrogen-nitrogen (NNN), nitrogen heterocyclic carbene (NHC), and bis(phosphine)-amine (PNP / NPN) as ligands, single-center catalytically active species are constructed through precise modification of ligands with tunable electronic and steric effects. This type of catalytic system can achieve highly selective oligomerization of propylene under mild reaction conditions (temperature 0℃~50℃, pressure 0.5MPa~5.0MPa). By systematically optimizing the electronic effects (e.g., electron-donating / electron-withdrawing groups) and steric hindrance (e.g., volume and rigidity of ortho-substituents) of the ligand substituents, the electron density, coordination environment, and chain growth / chain transfer rate constant of the active center of the catalytic system can be finely controlled, thereby achieving a synergistic improvement in catalytic activity and product selectivity. However, homogeneous catalytic systems are limited by the synergistic effect of the central metal electronic structure, ligand steric hindrance, and the softness and hardness of coordinating atoms, affecting the monomer insertion mode during chain growth. β -H elimination and isomerization pathways are easily activated, causing the product distribution to deviate significantly from the linear α-olefin target. Specifically, propylene dimerization tends to generate branched hexene isomers such as 2-methyl-1-pentene, 4-methyl-1-pentene, and 2,3-dimethyl-1-butene, with a branching product selectivity as high as 70% to 90%, while the molar fraction of the target product 1-hexene is usually less than 30%.

[0026] To overcome the shortcomings of the prior art, the present invention provides a cobalt pyridine diimine complex, which can be used to catalyze the selective oligomerization of propylene to prepare 1-hexene under the co-catalysis of methylaluminoxane (MAO).

[0027] A first aspect of the present invention is to provide a cobalt pyridine diimine complex, the structural formula of which is: Among them, R 1 Selected from fluorine, chlorine, bromine, ester, cyano, benzyl, and hydrogen; R 2 Selected from methyl, ethyl, isopropyl, fluorine, hydrogen, trifluoromethyl, methoxy, R 2The positions are ortho, para, and meta of aniline; R 3 Selected from cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and hydrogen.

[0028] The pyridinediimide cobalt complex is obtained through R 1 R 2 R 3 Synergistic regulation of three types of substituents optimizes catalytic performance; R 1 Electron-withdrawing groups such as fluorine and chlorine, or hydrogen and benzyl groups, finely adjust the coordination strength between the ligand and the cobalt ion through electronic effects. Larger substituents such as benzyl can also form moderate steric hindrance to inhibit β-H elimination; R 2 The flexible distribution of (methyl, trifluoromethyl, etc.) and aniline at the ortho / para / meta positions allows for a fine balance between activity and selectivity through the adaptation of electronic effects and steric hindrance. Strong electron-withdrawing groups enhance monomer activation, while electron-donating groups strengthen the stability of the active site. R 3 When the cycloalkyl group is cyclopropyl, cyclopentyl, or other cycloalkyl groups, its rigid cyclic structure creates a specific spatial environment, forcing propylene to linearly insert and oligomerize. The 1-hexene prepared using this pyridine diimine cobalt complex exhibits stable selectivity exceeding 90% (R...). 3 =93.1% when cyclopentyl), with a maximum catalytic activity of 4.32×10. 5 The yield per mol·h is significantly higher than that of existing catalytic systems. Furthermore, the combination of substituents is flexible and can be adapted to different industrial needs. The complex can be stored stably at room temperature and pressure, providing a high-performance and process-feasible technical solution for the high-selectivity preparation of 1-hexene by propylene oligomerization.

[0029] In some embodiments of this application, the structural formula of the pyridine diimine cobalt complex can be, for example: , , wait.

[0030] In some embodiments, with For example, n can be 3 to 12, such as any value from 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or any combination of both.

[0031] In some embodiments, with For example, R 1 It can be fluorine, chlorine, bromine, ester, cyano, benzyl, or hydrogen.

[0032] In some embodiments, with For example, R 2 The positions are ortho, para, and meta of aniline; R 2 It can be methyl, ethyl, isopropyl, fluorine, hydrogen, trifluoromethyl, or methoxy.

[0033] A second aspect of the present invention provides a method for preparing a pyridinediimine cobalt complex, the method comprising the following steps: catalytically coupling cycloalkenylpinaborate with o-bromoaniline until the reaction is complete, followed by quenching, extraction, and separation to obtain cycloalkenylaniline; dissolving cycloalkenylaniline in ethyl acetate and performing a reducing hydrogenation reaction to obtain cycloalkylaniline; dissolving cycloalkylaniline and 2,6-diacetylpyridine in ultra-dry toluene and performing a condensation reaction to obtain a pyridinediimine ligand; and controlling the coordination reaction between the pyridinediimine ligand and a cobalt salt to prepare the pyridinediimine cobalt complex.

[0034] The preparation method of this pyridine diimine cobalt complex involves a four-step continuous reaction process: catalytic coupling, reductive hydrogenation, condensation, and coordination. The catalytic coupling reaction uses palladium dichloride as a catalyst and anhydrous cesium carbonate as a base, achieving efficient coupling between cycloalkenyl pinaborate and o-bromoaniline in a mixed solvent of ultra-dry 1,4-dioxane and pure water, precisely introducing the cycloalkenyl group. The reductive hydrogenation reaction can use a 10% Pd / C catalyst to selectively reduce the carbon-carbon double bond of the cycloalkenyl group in anhydrous ethyl acetate, yielding a stable cycloalkylaniline. The condensation reaction uses SiO2 / MAO as a condensing agent, promoting the formation of a pyridine diimine ligand between cycloalkylaniline and 2,6-diacetylpyridine in ultra-dry toluene, avoiding hydrolysis side reactions caused by moisture. In the coordination reaction, the pyridine diimine ligand can coordinate with anhydrous cobalt chloride in a 1:1 molar ratio, forming a structurally uniform single-center catalytically active species. This method solves the problems of low product purity, poor stability, and complex processes in existing preparation methods, and provides an efficient and feasible technical path for industrial production.

[0035] In some embodiments of this application, the pyridine diimine cobalt complex can be synthesized using the following preparation route:

[0036] In some embodiments, for example, cycloalkenylaniline can be obtained by catalytic coupling of o-bromoaniline and cycloalkenylpinaborate as raw materials, followed by reduction hydrogenation to obtain cycloalkylaniline, which is then further condensed with 2,6-diacetylpyridine to obtain a pyridinediimine ligand, and finally coordinated with anhydrous cobalt chloride (CoCl2) to obtain a pyridinediimine cobalt complex.

[0037] In some embodiments, R 1 Derived from the difference in the substituent at the 4-position of the 4-X-2,6-diacetyl group; R 2 o-Bromoaniline derived from different substituted groups; R 3 The difference stems from the ring size of cycloalkenylpinaborates.

[0038] In some embodiments of this application, the catalyst in the catalytic coupling reaction includes bis(triphenylphosphine)palladium dichloride, the base includes anhydrous cesium carbonate, the organic solvent includes ultra-dry 1,4-dioxane, and the co-solvent includes purified water.

[0039] In the catalytic coupling reaction, palladium dichloride of bis(triphenylphosphine) acts as a catalyst. The synergistic effect of palladium ions and the triphenylphosphine ligand efficiently activates the C-Br bond in o-bromoaniline and the BC bond in cycloalkenylpinaborate, promoting the transmetalation and reductive elimination steps and ensuring the directional progress of the coupling reaction. Anhydrous cesium carbonate acts as a base, reacting with cycloalkenylpinaborate to promote transmetalation while maintaining an alkaline environment in the reaction system and inhibiting side reactions such as hydrolysis of the reactants. 1,4-Dioxane acts as an organic solvent, fully dissolving the reactants. Pure water acts as a co-solvent, promoting mass transfer between the water and organic phases, improving the mixing homogeneity of the reaction system, and accelerating the reaction process. This results in a high conversion rate for the coupling reaction of cycloalkenylpinaborate and o-bromoaniline, with a yield of 70%–80% of the target product, cycloalkenylaniline, and high product purity. Simple post-processing is sufficient to meet the requirements of subsequent reactions. Furthermore, the reaction conditions are mild and the operation is simple, laying the foundation for the efficient preparation of cobalt pyridinediimide complexes.

[0040] In some embodiments of this application, the molar ratio of o-bromoaniline, cycloalkenylpinaborate, catalyst, and base is 1:(1.2~2):(0.5%~5%):(1.5~3). It should be noted that in some embodiments, the molar ratio of o-bromoaniline, cycloalkenylpinaborate, catalyst, and base can be, for example, 1:1.2:0.05:1.5, 1:1.5:0.03:2, 1:2:0.05:3, or any two of these values, or other values ​​selected from the above ranges. A slight excess of cycloalkenylpinaborate ensures complete reaction of o-bromoaniline, avoiding unreacted raw material residue; a suitable amount of catalyst provides sufficient active centers to ensure coupling efficiency while avoiding cost waste and subsequent separation burden due to excessive catalyst; a suitable amount of base fully extracts protons from the boron reagent to form active species, maintaining the alkalinity of the system to suppress side reactions; the organic solvent and co-solvent, in an appropriate volume ratio, provide a homogeneous reaction environment, ensuring sufficient contact between all materials. This ratio enables the catalytic coupling reaction to be highly directional, resulting in a high yield of the target product, cycloalkenylaniline. The purity can be met by simple post-treatment to meet the requirements of subsequent reactions, while avoiding material waste and the increase of by-products. This provides a stable and reliable reaction basis for the efficient preparation of pyridine diimine cobalt complexes.

[0041] In some embodiments of this application, the catalytic coupling reaction conditions are: 80℃±10℃, and the reaction time is 16 hours±1 hour. The temperature of approximately 80℃ matches the kinetics of the Suzuki-Miyaura coupling reaction catalyzed by bis(triphenylphosphine)palladium dichloride, ensuring efficient catalyst activation of the C-Br bond of o-bromoaniline and the BC bond of cycloalkenylpinaborate, accelerating the transmetalation and reductive elimination steps, while avoiding oxidation of the raw materials and increased side reactions due to high temperatures. The reaction time of approximately 16 hours, combined with TLC monitoring, ensures complete conversion of o-bromoaniline. These reaction conditions achieve high yields and high purity of cycloalkenylaniline, effectively suppressing side reactions such as self-polymerization and thermal decomposition of the raw materials. Furthermore, the conditions are mild and easily controllable, requiring no extreme equipment, providing high-purity intermediates for subsequent reductive hydrogenation, condensation, and coordination reactions, and ensuring the catalytic stability of the final pyridinediimide cobalt complex.

[0042] In some embodiments of this application, the hydrogenation catalyst in the reductive hydrogenation reaction includes a carbon-supported catalyst with a palladium loading of 10% or 20%; the molar ratio of cycloalkenylaniline to the hydrogenation catalyst is 1:5 to 1:20. In some embodiments of this application, the conditions for the reductive hydrogenation reaction are: 25℃±2℃, and the reaction time is 48 hours±0.5 hours.

[0043] In the reductive hydrogenation reaction, using a palladium loading of 10% Pd / C ensures catalytic activity while avoiding cost waste. The carbon support disperses the active sites of palladium, preventing aggregation and deactivation. The appropriate ratio of its dosage to cycloalkenylaniline ensures complete reduction of the cycloalkenyl carbon-carbon double bond without initiating side reactions such as benzene ring hydrogenation. The amount of anhydrous ethyl acetate used is determined by fully dissolving the cycloalkenylaniline; its anhydrous nature prevents moisture from affecting catalyst activity, and its low boiling point facilitates subsequent separation. Ambient temperature conditions of 25℃±2℃ eliminate the need for extreme equipment, preventing product structure damage. A reaction time of 48 hours±0.5 hours combined with TLC monitoring ensures complete conversion of the raw materials, adapting to industrial-scale parameter fluctuations. This approach is beneficial for the reduction conversion rate of cycloalkenylaniline, producing a high-purity cycloalkylaniline product with no significant byproducts. It eliminates the need for complex purification to meet the requirements of subsequent condensation reactions, balancing reaction efficiency, cost control, and product quality stability. This provides a reliable high-purity intermediate for the efficient preparation of pyridinediimide cobalt complexes.

[0044] In some embodiments of this application, the condensation agent in the condensation reaction includes SiO2 / MAO; the molar ratio of cycloalkylaniline, 2,6-diacetylpyridine, and the condensation agent is 1:(2.5~3):(1~2). In some embodiments of this application, the conditions for the condensation reaction are: 55℃±2℃, and the reaction time is 24 hours±0.5 hours.

[0045] In the condensation reaction, SiO2 / MAO can be used as a condensing agent to simply and efficiently dehydrate and condense cycloalkylaniline with 2,6-diacetylpyridine. A slight excess of cycloalkylaniline ensures complete reaction of 2,6-diacetylpyridine, while the anhydrous nature of ultra-dry toluene avoids ligand hydrolysis. Its dosage is adapted to the reaction system to provide a homogeneous environment. A temperature of 55℃±2℃ accelerates the imidization reaction rate, and a reaction time of 24 hours±0.5 hours combined with TLC monitoring ensures complete conversion of the raw materials, adapting to industrial-scale parameter fluctuations. The pyridine diimine ligand yield is high, with good structural uniformity and high purity, and no obvious hydrolysis or polymerization byproducts. It can meet the requirements of subsequent coordination reactions without complex purification, and the reaction conditions are mild and easy to control, providing a high-purity ligand guarantee for the efficient preparation of pyridine diimine cobalt complexes.

[0046] In some embodiments of this application, the cobalt salt includes anhydrous cobalt chloride; the molar ratio of cobalt salt to pyridine diimide ligand is 1:1 to 1:1.5. The Co in anhydrous cobalt chloride... 2+ The N atom of the ion exhibits excellent coordination compatibility with the pyridine diimine ligand, forming a stable single-center coordination structure (catalytically active core). Its anhydrous nature prevents water from interfering with the coordination reaction, leading to coordination disorder or ligand hydrolysis. The 1:1 molar ratio ensures the ligand's interaction with Co. 2+ Complete ion coordination avoids both the increased burden of subsequent separation due to excessive ligands and the impact on the selectivity of the final catalyst due to residual metal ions caused by excessive cobalt salts. The resulting benefits include: highly directional coordination reactions; yields of the target pyridinediimide cobalt complex reaching 90%–99%; uniform structure and high purity; stable storage at room temperature and pressure; and good selectivity and high activity for 1-hexene during propylene oligomerization, providing a stable and high-quality catalyst for the efficient preparation of 1-hexene.

[0047] A third aspect of the present invention is to provide a method for preparing 1-hexene, wherein 1-hexene is prepared using the cobalt pyridinediimide complex provided in the first aspect or the cobalt pyridinediimide complex prepared by the method provided in the second aspect. Based on the aforementioned characteristics of the cobalt pyridinediimide complex, the introduction of the prepared 1-hexene structural unit into the polyethylene backbone can significantly reduce the symmetry and regularity of the polymer chain segments, thereby weakening its crystallinity. This allows the resulting LLDPE to maintain mechanical strength while also possessing excellent flexibility, resistance to environmental stress cracking, and low-temperature impact resistance.

[0048] In some embodiments, a cobalt pyridine diimide complex, methylaluminoxane, and liquid propylene are sequentially added to a 500 mL stainless steel reactor that has been fully purged with nitrogen. Stirring is then initiated, and the reaction is carried out at a set temperature for a specified period to obtain the target product, 1-hexene. The methylaluminoxane can be, for example, a toluene solution of methylaluminoxane, preferably a 30 wt% toluene solution. The molar ratio of methylaluminoxane to the cobalt pyridine diimide complex can be 100:1 to 500:1. The liquid propylene is of polymerization grade with a purity greater than 99.6%. The amount of propylene added can be 40 g to 150 g, such as 50 g, 100 g, etc. The reaction temperature can be -5 °C to 50 °C, such as 10 °C, room temperature (25 °C), 30 °C, etc. The reaction time can be 0.5 hours to 5 hours, such as 1 hour, 2.5 hours, 4 hours, etc.

[0049] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are all conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or through existing methods; unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations; unless otherwise specified, the experimental methods are all conventional methods.

[0050] Example 1 Add solid Cs₂CO₃ (7.3 g, 22.5 mmol) and (PPh₃)₂PdCl₂ (0.53 g, 0.75 mmol) to a 250 mL two-necked flask, purge with nitrogen three times, then inject 100 mL of 1,4-dioxane, o-bromoaniline (2.6 g, 15 mmol), and 1-cyclopentenylpinaboryl ester (3.7 g, 18 mmol), followed by 10 mL of purified water. Heat to 80 °C and react for 16 hours, monitoring the reaction progress by TLC. After the o-bromoaniline reacts completely, cool to room temperature, quench with water, and extract three times with ethyl acetate. Combine the organic phases. Wash the organic phase twice with brine, dry with anhydrous sodium sulfate, evaporate the solvent, and then purify by column chromatography using a 30:1 (v / v) petroleum ether:ethyl acetate eluent, yielding a pale yellow oil. o -Cyclopentenylaniline. It was redissolved in ethyl acetate, and 10% Pd / C (1.4 g, 1.3 mmol) was added. Hydrogen was purged twice, and the mixture was stirred at room temperature for 48 hours. The reaction progress was monitored by TLC. The mixture was filtered, and the filtrate was evaporated to dryness to obtain o-cyclopentenylaniline. NMR characterization: 1 H NMR (300 MHz, CDCl3) δ7.21 (dd, J = 7.7, 1.5 Hz, 1H), 7.08 (td, J= 7.6, 1.5 Hz, 1H), 6.89 – 6.79 (m,1H), 6.73 (dd, J = 7.8, 1.3 Hz, 1H), 3.14 – 2.93 (m, 1H), 2.22 – 2.02 (m, 2H), 1.93 – 1.64 (m, 6H). 13 C10 NMR (101 MHz, CDCl3) δ 144.03, 141.28, 128.32, 128.23, 127.64, 118.29, 115.86, 36.38, 33.95, 24.90, 23.24. Mass spectrometry characterization: HRMS (ESI) C10 NMR (101 MHz, CDCl3) δ 144.03, 141.28, 128.32, 128.23, 127.64, 118.29, 115.86, 36.38, 33.95, 24.90, 23.24. 11 H 15 N[M+H] + Theoretical value: 162.1283, Detected value: 162.1278.

[0051] In a 250 mL flask placed in a glove box, 3.0 g of SiO2 / MAO was added, followed by 30 mL of ultra-dry toluene for thorough dispersion. Separately, in a side-arm flask, 0.5 g (3.0 mmol) of 2,6-diacetylpyridine and 1.5 g (9.0 mmol) of o-cyclopentylaniline were added. The mixture was purged with nitrogen three times, dissolved in 20 mL of ultra-dry toluene, and heated to 55 °C for 24 hours. The reaction progress was monitored by TLC. After the 2,6-diacetylpyridine had completely reacted, the mixture was cooled to room temperature, filtered, and the filtrate was evaporated to dryness. Recrystallization with methanol yielded pyridine diimine ligands in 60%–85% yield. NMR characterization: 1 H NMR (400 MHz, CDCl3) δ 8.42 (d, J = 7.8 Hz, 2H), 7.91 (t, J = 7.8 Hz, 1H), 7.35 (d, J = 7.7 Hz, 2H), 7.20 (t, J = 7.5 Hz, 2H), 7.11 (t, J = 7.5 Hz, 2H), 6.65 (d, J = 7.6 Hz, 2H), 3.04 – 3.09 (m, J = 8.3 Hz, 2H), 2.39 (s, 6H), 1.95 (q, J = 6.8 Hz, 4H), 1.78 (s, 4H), 1.63 (q, J = 6.1, 5.0 Hz, 8H). 13C10 NMR (101 MHz, CDCl3) δ 166.61, 155.51, 149.53, 136.84, 135.87, 126.24, 126.12, 123.88, 122.25, 118.26, 40.59, 33.33, 25.66, 16.50. Mass spectrometry characterization: HRMS (ESI): C10 NMR (101 MHz, CDCl3) δ 166.61, 155.51, 149.53, 136.84, 135.87, 126.24, 126.12, 123.88, 122.25, 118.26, 40.59, 33.33, 25.66, 16.50. 31 H 35 N3[M+H] + Theoretical value: 450.2909, Detected value: 450.2904.

[0052] Weigh 0.5 mmol of pyridine diimide ligand and dissolve it in 5 mL of redistilled tetrahydrofuran (sodium, benzophenone reflux). Add the ligand solution dropwise to 0.9 mol / L CoCl2 solution, stir at room temperature for 24 hours, filter, and wash with diethyl ether to obtain a light green solid pyridine diimide cobalt complex, designated CAT-1, with a yield of 90-99%. CAT-1 was characterized by mass spectrometry: MALDI-TOF-MS:C 31 H 35 Cl2N3Co, [M-Cl] + Theoretical value: 578.1540, Detected value: 578.1543.

[0053] Examples 2 to 12 Compared with Example 1, the preparation methods of pyridine diimine cobalt complexes in Examples 2 to 12 are different as shown in Table 1 below.

[0054] Table 1

[0055] The pyridine diimine cobalt complexes in Examples 1 to 12 are designated as CAT-1 to CAT-12, respectively, and their structures are characterized as follows: The structural formulas of the cobalt pyridine diimine complexes in Examples 1-4 are as follows:

[0056] In Example 1, n is 5; in Example 2, n is 4; in Example 3, n is 3; and in Example 4, n is 6.

[0057] The structural formulas of the pyridine diimine cobalt complexes in Examples 5-8 are as follows:

[0058] In Example 5, R 1 It is chlorine (Cl), R in Example 6 1 For bromine (Br), R in Example 71 It is cyano (CN), R in Example 8 1 It is benzyl (Bn).

[0059] The structural formulas of the pyridine diimine cobalt complexes in Examples 9-12 are as follows:

[0060] In Example 9, R 2 It is fluorine (F), R in Example 10 2 It is trifluoromethyl (CF3), R in Example 11 2 It is a methoxy group (OMe), R in Example 12 2 It is a methoxycarbonyl group (COOMe).

[0061] It can be seen that R 1 The difference lies in the substituent at the 4-position of the 4-X-2,6-diacetyl group; R 2 o-Bromoaniline with different substituted groups; R 3 For different ring sizes of cycloalkenyl pinaborates.

[0062] Preparation of 1-hexene 1-Hexene was prepared using the pyridine diimine cobalt complexes CAT-1 to CAT-12 provided in Examples 1 to 12, respectively.

[0063] The preparation method of 1-hexene is as follows: To a thoroughly dried 500 mL stainless steel reactor, 40 μmol of pyridine diimide cobalt complex CAT-1, 0.9 mL (4 mmol) of methylaluminoxane in toluene (4.5 M), and finally 50 g of polymer-grade propylene liquid were added sequentially. All valves were closed, the reaction temperature was set to 25 °C, and stirring was started. The reaction was allowed to proceed for 0.5 hours. After the reaction was complete, the vent valve was slowly opened to drain any unreacted propylene. The oligomers were collected, weighed, and their composition and content were analyzed using gas chromatography-mass spectrometry. The experimental results are shown in Table 2.

[0064] Table 2

[0065] Figure 1 The gas chromatogram (GC) of 1-hexene prepared using the pyridinediimide cobalt complex provided in Example 4 of this invention is shown. As can be seen, the selectivity for 1-hexene reaches 93.1%. The experimental results of the effect of the pyridinediimide cobalt complex on the reactivity and selectivity are shown in Table 3.

[0066] Comparative Example 1 The reaction conditions were basically the same as in Example 4, except that the pyridine diimide was substituted with the cobalt complex ligand R.1 =H,R 2 =H,R 3 The experimental results of the effect of ethylpyridinediimide cobalt complex on the reactivity and selectivity are shown in Table 3.

[0067] Comparative Example 2 The reaction conditions were basically the same as in Example 4, except that the pyridine diimide was substituted with the cobalt complex ligand R. 1 =H,R 2 =H,R 3 =Isopropyl. The experimental results of the effect of cobalt complexes of pyridine diimide on the reactivity and selectivity are shown in Table 3.

[0068] Table 3. Effect of catalyst structure on reaction activity and selectivity

[0069] Referring to Examples 1-12 and Tables 1-3, it can be seen that the pyridinediimine cobalt complex provided by the present invention, especially when R 3 It is cyclopentyl, and R 1 R 2 When independently selected from hydrogen, halogens (fluorine, chlorine, bromine), or other functional groups (cyano, benzyl, methoxy, trifluoromethyl, methoxycarbonyl, etc.), it exhibits superior catalytic performance even under mild reaction conditions of only 25°C: the catalytic activity can reach up to 4.32 × 10⁻⁶. 5 The selectivity for the target product 1-hexene was stably maintained at 90%~93.1% with g / (mol·h), which significantly broke through the technical bottleneck of the existing homogeneous catalytic system with a selectivity of less than 30% for 1-hexene.

[0070] In Comparative Examples 1 and 2, when the cyclopentyl group at the 2-position of the complex ligand was replaced with acyclic substituents such as ethyl or isopropyl, the selectivity of 1-hexene decreased to 46.3%–55.2% under the same reaction system and operating conditions, a significant difference compared to cyclopentyl substitution. This demonstrates the decisive role of the cycloalkyl skeleton provided in this application in the selectivity of propylene oligomers. Its rigid cyclic structure can construct a specific steric environment, forcing the propylene monomer to participate in the reaction via linear insertion, effectively suppressing β-H elimination and isomerization side reactions, thereby ensuring high selectivity for 1-hexene.

[0071] Introducing strong electron-withdrawing substituents (such as -F, -CF3, -Cl, -Br, -CN) or weak electron-donating substituents (such as -OMe) at the fitting sites of the cyclopentyl skeleton can increase polymerization activity by up to 340% (e.g., R). 1 For Cl, R 3 When the cyclopentyl group is present, the activity reaches 4.32 × 10⁻⁶. 5g / (mol·h), which is 340% higher than the basic cyclopentyl-substituted complex, while the fluctuation of 1-hexene selectivity is always controlled within ±2%, which fully demonstrates the excellent electronic effect tolerance and process robustness of the pyridine diimine cobalt complex provided by this invention as a component in the catalytic system.

[0072] In summary, this invention not only achieves for the first time the synergistic effect of "ultra-high catalytic activity and high 1-hexene selectivity" in propylene oligomerization under mild conditions, but also constructs a catalytic system with "finely adjustable activity and basically stable selectivity" through the flexible combination of cyclopentyl and electronically modulated substituents. This characteristic provides a broad operating window for subsequent industrial-scale production, adapting to activity regulation under different production capacity requirements while ensuring product quality stability, significantly reducing process integration difficulty and production costs. It provides a high-quality monomer source for the preparation of high-performance linear low-density polyethylene (LLDPE), possessing outstanding industrial application value and significant economic benefits.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. 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 or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A pyridinediimine cobalt complex, characterized in that, Its structural formula is: Among them, R 1 Selected from fluorine, chlorine, bromine, ester, cyano, benzyl, and hydrogen; R 2 Selected from methyl, ethyl, isopropyl, fluorine, hydrogen, trifluoromethyl, methoxy, R 2 The positions are ortho, para, and meta of aniline; R 3 Selected from cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and hydrogen.

2. A method for preparing a cobalt pyridinediimine complex, characterized in that, Includes the following steps: Cycloalkenylpinaboronic acid ester was catalytically coupled with o-bromoaniline. After the reaction was completed, the mixture was quenched, extracted, and separated to prepare cycloalkenylaniline. The cycloalkenylaniline was dissolved in ethyl acetate or ethanol and then subjected to a reducing hydrogenation reaction to prepare cycloalkylaniline. The cycloalkylaniline and 2,6-diacetylpyridine were dissolved in ultra-dry toluene or tetrahydrofuran and then subjected to a condensation reaction to prepare the pyridine diimine ligand. The pyridinediimide ligand was controlled to undergo a coordination reaction with the cobalt salt to prepare a pyridinediimide cobalt complex.

3. The preparation method according to claim 2, characterized in that, In the catalytic coupling reaction The catalyst includes bis(triphenylphosphine)palladium dichloride, the base includes anhydrous cesium carbonate or potassium carbonate, the organic solvent includes 1,4-dioxane or tetrahydrofuran, and the co-solvent includes purified water; The molar ratio of o-bromoaniline, the cycloalkenylpinaborate, the catalyst, and the base is 1:(1.2~2):(0.5%~5%):(1.5~3); In the catalytic coupling reaction, the concentration of the reaction system is 0.1M to 1M, and the volume ratio of organic solvent to co-solvent water is 5:1 to 10:

1.

4. The preparation method according to claim 2, characterized in that, The conditions for the catalytic coupling reaction are: 80℃±10℃, and the reaction time is 16 hours±1 hour.

5. The preparation method according to claim 2, characterized in that, In the reductive hydrogenation reaction, the hydrogenation catalyst includes a carbon-supported catalyst with a palladium loading of 10% or 20%. The molar ratio of the cycloalkenyl aniline to the hydrogenation catalyst is 1:5 to 1:

20.

6. The preparation method according to claim 2, characterized in that, The conditions for the reducing hydrogenation reaction are: 25℃±2℃, and the reaction time is 48 hours±0.5 hours.

7. The preparation method according to claim 2, characterized in that, In the condensation reaction, the condensing agent includes one or more of alkylaluminum supported silica and p-toluenesulfonic acid; The molar ratio of the cycloalkylaniline, the 2,6-diacetylpyridine, and the condensing agent is 1:(2.5~3):(1~2).

8. The preparation method according to claim 2, characterized in that, The conditions for the condensation reaction are: 55℃±2℃, and the reaction time is 18 hours±5 hours.

9. The preparation method according to claim 2, characterized in that, The cobalt salt includes anhydrous cobalt chloride; The molar ratio of the cobalt salt to the pyridine diimide ligand is 1:1 to 1:1.

5.

10. A method for preparing 1-hexene, characterized in that, 1-Hexene is prepared using the cobalt pyridine diimide complex according to claim 1 or the cobalt pyridine diimide complex prepared by any one of claims 2 to 9.

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