A phosphinylquinoline ligand, a phosphinylquinoline iron complex, and a preparation method and application thereof in catalyzing conjugated diene polymerization

Abstract

The application belongs to the technical field of conjugated diene polymerization, and particularly relates to a phosphine quinoline ligand, a phosphine quinoline iron complex, a preparation method thereof and application thereof in catalyzing conjugated diene polymerization. The phosphine quinoline ligand and the iron complex are respectively shown as formula I and formula II. The iron complex is a bidentate N, P-coordination catalyst, has a single catalytic active center, and can realize high-activity and high-selectivity polymerization of conjugated dienes by regulating ligand electronic effects, space effects and polymerization conditions. The iron complex only needs 5 equivalents of dry methylaluminoxane to be activated, and still maintains high activity at high temperature (100 DEG C). The obtained polyconjugated diene has narrow molecular weight distribution, and microstructure (cis-1, 4, trans-1, 4, 3, 4 or 1, 2) can be accurately regulated. The reaction system is green, environmentally friendly, low in cost and excellent in thermal stability, and is suitable for industrialized production of high-performance elastomer materials.

Description

Technical Field

[0001] This invention belongs to the field of conjugated diene polymerization technology, specifically relating to a phosphoquinoline ligand, a phosphoquinoline iron complex, their preparation method, and their application in catalytic conjugated diene polymerization. Background Technology

[0002] Isoprene (IP) and 1,3-butadiene (Bu), as typical conjugated dienes, produce polyisoprene (PIP) and poly1,3-butadiene (PB), which are essential raw materials for synthetic rubber and widely used in tire manufacturing (accounting for over 70% of global rubber consumption), medical consumables, high-end sealing materials, and low-temperature elastic components. Natural rubber's main component is cis-1,4 polyisoprene, but its production is limited by the geographical location and climate conditions of rubber tree cultivation, resulting in a large global supply-demand gap. Meanwhile, poly1,3-butadiene, as another high-performance synthetic rubber, especially high-cis-1,4 poly1,3-butadiene, is also in high demand due to its excellent low-temperature flexibility, abrasion resistance, and fatigue resistance in high-performance tires, sealing materials, and engineering vibration damping components. However, its synthesis relies entirely on petrochemical raw materials. Functionalized polyconjugated dienes, especially those modified by introducing functional groups (such as phenyl groups and long-chain hydroxyl groups) into polyisoprene and poly1,3-butadiene, can significantly improve the interfacial compatibility, adhesion, aging resistance, and interaction with inorganic fillers, thereby expanding their application potential in high-end composite materials, functional coatings, ion-conductive elastomers, and biomedical materials. Therefore, developing efficient catalytic systems to achieve structure-controlled polymerization of conjugated dienes not only helps alleviate the shortage of natural rubber but also promotes the diversification, customization, and independent controllability of high-performance synthetic rubbers, meeting the growing demands of industrial applications.

[0003] Traditional conjugated diene polymerization catalysts (such as titanium-based and rare earth-based catalysts) have significant drawbacks. Titanium-based catalysts (such as TiCl4 / AlR3) require a large amount of co-catalysts and have high residual metal toxicity, while rare earth-based catalysts rely on scarce metal resources and are expensive. Moreover, existing systems are difficult to control precisely in terms of the cis-1,4, trans-1,4 and 3,4 structural ratios, which limits the customized synthesis of high-performance elastomers. Traditional iron-based catalysts (such as N,N-bident ligand systems) experience a sharp drop in activity at high temperatures.

[0004] In recent years, iron-based catalysts have become a research hotspot due to their economic viability, biocompatibility, and unique electronic properties. However, existing N,N-bident iron complexes face numerous technical bottlenecks, such as unclear microstructure regulation mechanisms, an unclear structure-activity relationship between ligand design and polymerization selectivity, making precise structural control difficult. More importantly, the active species are unstable, requiring activation with high-equivalence dry methylaluminoxane (dMAO) (500–1000 equiv.), and are prone to deactivation at high temperatures (100 °C), failing to meet the demands of continuous industrial production. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a phosphoquinoline ligand, a phosphoquinoline iron complex, a method for preparing the same, and its application in the catalytic polymerization of conjugated dienes. The phosphoquinoline ligand provided by this invention, when combined with an iron-centered metal to form a phosphoquinoline iron complex, requires only 5 equivalents of dry methylaluminoxane (dMAO) for activation and maintains high activity even at high temperatures (100°C).

[0006] This invention provides a phosphoquinoline ligand with the structural formula shown in Formula I:

[0007]

[0008] In Equation I, R1 and R2 are independently selected. Or alkyl, R3 is selected from phenyl or hydrogen atom;

[0009] R4, R5, R6, R7 and R8 are independently selected from hydrogen atoms, alkoxy groups, dimethylamino groups, halogens, alkyl or substituted alkyl groups having 1 to 4 carbon atoms, phenyl or substituted phenyl groups.

[0010] Preferably, the alkoxy group is one of methoxy, isopropoxy, and cyclohexyloxy; and the alkyl group having 1 to 4 carbon atoms is one of methyl, ethyl, isopropyl, n-propyl, tert-butyl, sec-butyl, isobutyl, and n-butyl.

[0011] The present invention also provides a method for preparing the phosphoquinoline ligand described in the above technical solution, comprising the following steps:

[0012] R1(R2)PCl and lithium quinoline were mixed and subjected to a nucleophilic substitution reaction to obtain phosphinoquinoline ligands; the structural formula of the lithium quinoline is shown below:

[0013]

[0014] This invention provides a phosphinoquinoline iron complex with the structural formula shown in Formula II:

[0015]

[0016] In Equation II, R1, R2, and R3 are defined as in Equation I.

[0017] The present invention also provides a method for preparing the phosphoquinoline iron complex described in the above technical solution, comprising the following steps;

[0018] The phosphonoquinoline ligand shown in Formula I, FeCl2, and an organic solvent were mixed and subjected to a complexation reaction. After removing the organic solvent, the phosphonoquinoline iron complex was obtained.

[0019] Preferably, the molar ratio of the phosphoquinoline ligand to FeCl2 is 1:1 to 1:1.5; the temperature of the complexation reaction is -5 to 30°C, and the time is 10 to 50 h.

[0020] This invention also provides the application of the phosphoquinoline iron complex described in the above technical solution in the catalytic polymerization of conjugated dienes.

[0021] This invention also provides a method for preparing a polyconjugated diene, comprising the following steps:

[0022] A conjugated diene monomer, a catalyst, and an organic solvent are mixed and polymerized to obtain a polyconjugated diene; the structural formula of the conjugated diene monomer is shown in Formula III:

[0023]

[0024] In Formula III, R9 is selected from hydrogen, alkyl, aryl, or functional group substituents containing heteroatoms;

[0025] The catalyst comprises the phosphoquinoline iron complex described in the above technical solution.

[0026] Preferably, the alkyl group is one of methyl, ethyl, isopropyl, n-propyl, tert-butyl, sec-butyl, isobutyl, n-butyl, and n-hexyl; the aryl group is one of phenyl, 3,5-dimethylphenyl, 2,6-dimethylphenyl, mesitylene, p-methoxyphenyl, o-methoxyphenyl, 3,5-dimethoxyphenyl, 2,6-dimethoxyphenyl, mesitylene, 3,5-diisopropylphenyl, and 2,6-diisopropylphenyl; and the substituent containing the heteroatom is one of phenoxy, hydroxyl, amino, methoxy, and dimethylamino.

[0027] Preferably, the molar ratio of the conjugated diene monomer to the phosphoquinoline iron complex is 10000:1 to 100; the polymerization reaction temperature is 0 to 100°C, and the time is 10 to 1440 min.

[0028] The catalyst further includes a co-catalyst, which is selected from one or more of aluminoxane, alkylaluminum and alkylaluminum chloride; the molar ratio of Al in the co-catalyst to Fe in the phosphoquinoline iron complex is (1-100):1.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention provides a phosphonoquinoline ligand with the structural formula shown in Formula I. A phosphonoquinoline iron complex is constructed using the specific phosphonoquinoline ligand of this invention and an iron-centered metal, which can be used as a catalyst for the polymerization of conjugated dienes. The iron complex catalyst has a single catalytic active center, and the molecular weight and microstructure of polyconjugated dienes (such as polyisoprene / poly1,3-butadiene) can be controlled by adjusting the ligand structure and polymerization conditions. The N,P-bident ligand can effectively stabilize the iron active center, exhibiting advantages such as high catalytic activity, good catalytic selectivity, low cost, and stable performance at high temperatures. The iron complex (Formula II) constructed using the phosphonoquinoline ligand of this invention was used to catalyze the polymerization of isoprene / 1,3-butadiene, demonstrating excellent high-temperature (100°C) catalytic activity. Moreover, only 5 equivalents of dMAO are needed to effectively activate the iron complex, achieving rapid polymerization of isoprene / 1,3-butadiene, which meets the requirements of green catalytic processes. This invention provides a novel catalyst that combines high activity, thermal stability, and solvent compatibility, enabling the controlled polymerization of isoprene / 1,3-butadiene structures. This breakthrough overcomes traditional technological bottlenecks and promotes the industrial application of green polymerization processes.

[0031] The method for preparing phosphoquinoline iron complexes provided by this invention has the advantages of mild reaction conditions, short cycle, and simple operation.

[0032] Application data shows that the iron complex / dMAO (molar ratio 1 / 5) system in Example 5 still possesses high conversion efficiency under high monomer loading (IP / iron complex molar ratio = 10000), providing experimental evidence for the development of industrial-grade high-concentration polymerization processes. This invention achieves precise control over the molecular weight and microstructure of polyisoprene and poly1,3-butadiene, catalyzing the production of polyisoprene M... n 2.4 × 10 4 g·mol -1 ~5.7×10 5 g·mol -1 It is predominantly composed of cis-1,4 and 3,4 structures (ca.cis-1,4 / 3,4 = 1 / 1), and its polymerization activity can reach 3431 kg / kg. PIP ·mol Fe -1 ·h -1 ; catalytically obtained polybutadiene M n1.8×10 4 g·mol -1 ~1.05×10 6 g·mol -1 It is predominantly cis-1,4 structured and has a polymerization activity of up to 347 kg. PB ·mol Fe -1 ·h -1 The iron complexes exhibited a strong ability to regulate the molecular weight of polyisoprene and poly1,3-butadiene. The iron complexes of this invention catalyze the polymerization of isoprene to prepare polyisoprene and the polymerization of 1,3-butadiene to prepare poly1,3-butadiene, demonstrating great potential for industrial application.

[0033] The preparation method of polyisoprene / poly1,3-butadiene provided by this invention is simple to operate, has mild reaction conditions, and yields polyisoprene / poly1,3-butadiene with controllable microstructure and molecular weight, which has good application prospects. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a molecular crystal structure diagram of the phosphinoquinoline iron complex when R1 = phenyl, R2 = phenyl, and R3 = hydrogen atom in this invention;

[0036] Figure 2 The crystal structure diagram of the phosphinoquinoline iron complex is shown when R1 = 1,1'-biphenyl-2-yl, R2 = phenyl, and R3 = hydrogen atom in this invention.

[0037] Figure 3 In this invention, when R1 = cyclohexyl, R2 = cyclohexyl, and R3 = hydrogen atom, the phosphinoquinoline iron complex... 1 HNMR spectrum;

[0038] Figure 4 The polyisoprene obtained by polymerizing isoprene with the complex 8-diphenylphosphinoquinoline and ferric chloride in this invention is... 1 H NMR spectrum;

[0039] Figure 5 The polyisoprene obtained by polymerizing isoprene with the complex 8-diphenylphosphinoquinoline and ferric chloride in this invention is... 13 C NMR spectrum. Detailed Implementation

[0040] This invention provides a phosphoquinoline ligand with the structural formula shown in Formula I:

[0041]

[0042] In Equation I, R1 and R2 are independently selected. Or alkyl, R3 is selected from phenyl or hydrogen atom;

[0043] R4, R5, R6, R7 and R8 are independently selected from hydrogen atoms, alkoxy groups, dimethylamino groups, halogens, alkyl or substituted alkyl groups having 1 to 4 carbon atoms, phenyl or substituted phenyl groups.

[0044] In this invention, R1 and R2 may be the same or different, and R4, R5, R6, R7 and R8 may be the same or different.

[0045] In this invention, the alkyl group preferably includes a cycloalkyl group, and the cycloalkyl group preferably includes a cyclohexyl group.

[0046] In this invention, the alkoxy group is preferably methoxy (-OMe) or isopropoxy (-O) i One of Pr and cyclohexyloxy (-OCy).

[0047] In this invention, the halogen is preferably a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom.

[0048] In this invention, the alkyl group having 1 to 4 carbon atoms is preferably methyl, ethyl (Et), or isopropyl (-). i Pr), n-propyl (- n Pr), tert-butyl (- t Bu), sec-butyl (- s Bu), isobutyl (- i Bu) and n-butyl (- n One of Bu); the substituted alkyl group is preferably trifluoromethyl, perfluoroethyl, perfluoron-propyl, and perfluoroisopropyl (- i One of C3F8).

[0049] In this invention, R1 and R2 are independently preferably one of pentahalophenyl, mestrihalophenyl, 2,6-dihalophenyl, para-halophenyl, meta-halophenyl, ortho-halophenyl, 3,4,5-trihalophenyl, and 3,5-dihalophenyl; the halogenation is preferably fluorination, chlorination, bromination, or iodination.

[0050] In this invention, the substituted phenyl group is preferably one of 3,5-dimethylphenyl, 2,6-dimethylphenyl, mesitylene, p-methoxyphenyl, o-methoxyphenyl, 3,5-dimethoxyphenyl, 2,6-dimethoxyphenyl, mesitylene, 3,5-diisopropylphenyl, and 2,6-diisopropylphenyl.

[0051] In this invention, the phosphoquinoline ligand is preferably any one of 8-diphenylphosphoquinoline, 8-dicyclohexylphosphoquinoline, 8-bis(3,5-dimethylphenyl)phosphoquinoline, or 8-bis(3,5-dimethoxyphenyl)phosphoquinoline. The structural formulas of 8-diphenylphosphoquinoline and 8-bis(3,5-dimethylphenyl)phosphoquinoline are shown below:

[0052]

[0053] The present invention also provides a method for preparing the phosphoquinoline ligand described in the above technical solution, comprising the following steps:

[0054] R1(R2)PCl and lithium quinoline were mixed and subjected to a nucleophilic substitution reaction to obtain phosphinoquinoline ligands; the structural formula of the lithium quinoline is shown below:

[0055]

[0056] In the formula, R1 and R2 in R3, R1(R2)PCl are defined as in formula I.

[0057] Unless otherwise specified, all materials and equipment used in this invention are commercially available products in the field.

[0058] When R1 and R2 are the same:

[0059] The bromide of R1 was mixed with n-butyllithium and subjected to a lithium halide substitution reaction to obtain the lithium salt R1(R2)Li;

[0060] The lithium salts R1(R2)Li and PCl3 were mixed and subjected to a nucleophilic substitution reaction to obtain R1(R2)PCl.

[0061] When R1 and R2 are not the same:

[0062] The bromides of R1 and R2 were mixed with n-butyllithium and subjected to lithiation to obtain R1Li and R2Li;

[0063] The R1Li and R2Li were mixed with PCl3 and subjected to a nucleophilic substitution reaction to obtain R1(R2)PCl.

[0064] When R3 is a hydrogen atom:

[0065] 8-Bromoquinoline and n-butyllithium were mixed and subjected to a lithium halide substitution reaction to obtain lithium quinoline, with the following structural formula:

[0066]

[0067] When R3 is a phenyl group:

[0068] Mixing 8-bromo-1H-2-quinolinone with phosphorus oxychloride yields 2,8-dibromoquinoline;

[0069] The 2,8-dibromoquinoline and phenylboronic acid were mixed to obtain 8-bromo-2-phenylquinoline;

[0070] The 8-bromo-2-phenylquinoline and n-butyllithium were mixed and subjected to a lithium halide substitution reaction to obtain lithium quinoline.

[0071] This invention provides a phosphinoquinoline iron complex with the structural formula shown in Formula II:

[0072]

[0073] In Equation II, R1, R2, and R3 are defined as in Equation I.

[0074] In this invention, the phosphoquinoline iron complex is preferably any one of the following structures:

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081] The present invention also provides a method for preparing the phosphoquinoline iron complex described in the above technical solution, comprising the following steps;

[0082] The phosphonoquinoline ligand shown in Formula I, FeCl2, and an organic solvent were mixed and subjected to a complexation reaction. After removing the organic solvent, the phosphonoquinoline iron complex was obtained.

[0083] In this invention, the molar ratio of the phosphoquinoline ligand to FeCl2 is preferably 1:1 to 1.5, specifically 1:1; the temperature of the complexation reaction is preferably -5 to 30°C, specifically room temperature; the time is preferably 10 to 50 hours, specifically 48 hours; the complexation reaction is preferably carried out under stirring conditions. The complexation reaction is preferably carried out under anaerobic conditions, for example, under the protection of an inert gas such as nitrogen.

[0084] In this invention, the organic solvent is preferably a hydrocarbon solvent or an ether solvent. The hydrocarbon solvent is preferably n-hexane, dichloromethane, or toluene, and the ether solvent is preferably diethyl ether or tetrahydrofuran (THF), more preferably THF.

[0085] In this invention, the removal of organic solvent is preferably achieved through vacuum concentration; the process after solvent removal preferably includes washing and drying, wherein the washing reagent is preferably n-hexane.

[0086] Taking R3 as a hydrogen atom as an example, the preparation reaction formula of the phosphinoquinoline iron complex is shown below:

[0087]

[0088] This invention also provides the application of the phosphoquinoline iron complex described in the above technical solution in the catalytic polymerization of conjugated dienes.

[0089] This invention also provides a method for preparing a polyconjugated diene, comprising the following steps:

[0090] A conjugated diene monomer, a catalyst, and an organic solvent are mixed and polymerized to obtain a polyconjugated diene; the structural formula of the conjugated diene monomer is shown in Formula III:

[0091]

[0092] In Formula III, R9 is selected from hydrogen, alkyl, aryl, or functional group substituents containing heteroatoms;

[0093] The catalyst comprises the phosphoquinoline iron complex described in the above technical solution.

[0094] In this invention, the alkyl group is preferably one of methyl, ethyl, isopropyl, n-propyl, tert-butyl, sec-butyl, isobutyl, n-butyl, and n-hexyl.

[0095] In this invention, the aryl group is preferably one of phenyl, 3,5-dimethylphenyl, 2,6-dimethylphenyl, mesitylene, p-methoxyphenyl, o-methoxyphenyl, 3,5-dimethoxyphenyl, 2,6-dimethoxyphenyl, mesitylene, 3,5-diisopropylphenyl, and 2,6-diisopropylphenyl.

[0096] In this invention, the functional group substituent containing heteroatoms is preferably one of phenoxy, hydroxy, amino, methoxy, and dimethylamino groups.

[0097] In this invention, the conjugated diene monomer is preferably isoprene, 1,3-butadiene, 2-phenyl-1,3-butadiene, or ((4-methylenehex-5-en-1-yl)oxy)benzene.

[0098] In this invention, the molar ratio of the conjugated diene monomer and the phosphoquinoline iron complex is preferably 10000:1 to 100, specifically 1000:1, 2000:1 or 10000:1.

[0099] In this invention, the catalyst preferably further includes a co-catalyst, which is preferably selected from one or more of aluminoxanes, alkylaluminum, and alkylaluminum chlorides. The aluminoxane is preferably selected from methylaluminoxane (MAO) or dried methylaluminoxane (dMAO). The alkylaluminum is preferably selected from trimethylaluminum, triethylaluminum, or triisobutylaluminum. The alkylaluminum chloride is preferably selected from one or more of dimethylaluminum chloride (Me₂AlCl), sesquidiethylaluminum chloride (EASC), and sesquidimethylaluminum chloride (MASC).

[0100] When the catalyst further includes a co-catalyst, the molar ratio of Al in the co-catalyst to Fe in the phosphoquinoline iron complex is preferably (1-100):1, more preferably (3-50):1, and specifically can be 1:1, 2:1, 3:1, 5:1, 10:1, 30:1, or 50:1. The molar ratio described in this invention results in high polymerization activity.

[0101] In this invention, the polar organic solvent is preferably selected from one or more of alkanes, aromatics and alcohols, specifically toluene.

[0102] In this invention, the polymerization is preferably carried out under anaerobic conditions, for example, under the protection of an inert gas such as nitrogen.

[0103] In this invention, the temperature of the polymerization reaction is preferably 0 to 100°C, specifically 25°C, 30°C or 50°C, and the time is preferably 10 to 1440 min, more preferably 5 to 240 min, specifically 10 min or 20 min.

[0104] In this invention, the polymerization reaction preferably further includes: quenching the resulting reaction solution and precipitating it, and then washing and drying the precipitate. The quenching agent is preferably methanol acidified with hydrochloric acid, wherein the volume percentage of hydrochloric acid in the acidified methanol is preferably 10%, and the mass fraction of the hydrochloric acid is preferably 36%–38%; the precipitating agent is preferably methanol; the washing agent is preferably methanol; and the drying temperature is preferably 60°C, and the drying time is preferably until constant weight is achieved.

[0105] The microstructure (cis-1,4, trans-1,4, 3,4) of the polyisoprene obtained by this invention is regulated by phosphonoquinoline ligand substituents, wherein the content of cis-1,4 is 38.2%–53.5%, the content of trans-1,4 is 0–17.8%, and the content of 3,4 is 43.7%–52.5%. The molecular weight of the polyisoprene is 2.4 × 10⁻⁶. 4 g·mol -1 ~5.7×10 5 g·mol -1 g·mol -1 The molecular weight distribution (PDI) is 1.11–1.96. The iron complex requires only 5 molar equivalents of dMAO for effective activation, and exhibits a catalytic activity of 654 kg at 100 °C. PIP ·mol -1 Fe ·h -1 .

[0106] The microstructure (cis-1,4, trans-1,4, 1,2) of poly(1,3-butadiene) is regulated by phosphonoquinoline ligand substituents, wherein the content of cis-1,4 is 61.6%–73.0%, the content of trans-1,4 is 11.7%–17.9%, and the content of 1,2 is 14.5%–24.6%. The molecular weight of the poly(1,3-butadiene) is 1.8 × 10⁻⁶. 4 g·mol -1 ~1.05×10 6 g·mol -1 The molecular weight distribution (PDI) is 1.17–2.48. The iron complex requires only 5 equivalents of dMAO for activation and exhibits a catalytic activity of 347 kg at room temperature. PB ·mol -1 Fe ·h -1 .

[0107] To further illustrate the present invention, the following detailed description, in conjunction with the accompanying drawings and embodiments, describes the phosphoquinoline ligands, phosphoquinoline iron complexes, their preparation methods, and their applications in the catalytic polymerization of conjugated dienes provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0108] In the following embodiments or application examples, the English words or abbreviations used have the following meanings: n BuLi - n-Butyllithium, Ph₂PCl - Diphenylphosphine chloride, DCM - Dichloromethane, THF - Tetrahydrofuran, hexane - n-Hexane, dMAO (drymethylaluminoxane), Al i Bu3-triisobutylaluminum, AlMe3-trimethylaluminum, AlEt3-triethylaluminum.

[0109] In the following examples or application examples, unless otherwise specified, all concentrations are molar concentrations.

[0110] In the following examples of isoprene / 1,3-butadiene polymerization applications, the molecular weight and molecular weight distribution of the polymers obtained were determined by conventional room-temperature GPC method, the glass transition temperature was determined by conventional DSC method, and the polymerization activity of the polymers was calculated by the following formula: Polymer activity = Polymer yield / (Catalyst amount × Polymerization time).

[0111] The compounds synthesized below were confirmed by nuclear magnetic resonance spectroscopy (NMR) and X-ray single crystal diffraction (XRSCD).

[0112] Example 1

[0113] When R1 = phenyl, R2 = phenyl, and R3 = hydrogen atom, the structural formula of the phosphinoquinoline ligand is as follows:

[0114]

[0115] The specific synthetic steps for phosphoquinoline ligands are as follows:

[0116] In a 200 mL Schlenk tube, 8-bromoquinoline (8.24 g, 40.0 mmol, 1.00 equiv.) was dissolved in 60 mL THF. After the system cooled to -78 °C, the solution was slowly added dropwise. n BuLi (16.8 mL, 2.5 M in hexane, 42.0 mmol, 1.05 equiv.) was stirred at this temperature for 3 h to obtain reaction solution A.

[0117] In a 100 mL Schlenk tube, Ph₂PCl (9.71 g, 44.0 mmol, 1.10 equiv.) was dissolved in 20 mL THF; this is reaction solution B.

[0118] Using a 20 mL syringe, reaction solution B was added dropwise to reaction solution A. After the addition was complete, refrigeration was stopped, and the reaction system was allowed to gradually return to room temperature overnight with stirring. After the reaction was complete, the THF was evaporated to dryness, and an appropriate amount of DCM and saturated NH4Cl aqueous solution were added. The mixture was then transferred to a separatory funnel. The organic matter in the aqueous phase was thoroughly extracted with DCM, and the organic phase was separated. The organic phase was washed with water and finally dried with anhydrous sodium sulfate for 30 min. The solvent in the solution was evaporated to dryness to obtain the crude product. The crude product was separated by silica gel column chromatography (developing solvent: petroleum ether / ethyl acetate volume ratio = 5 / 1) to obtain 8.34 g of white solid 8-diphenylphosphinequinoline, with a yield of 66.7%.

[0119] 1 H NMR (400MHz, Benzene-d6): δ8.83 (dd, J=4.2, 1.7Hz, 1H), 8.12 (d, J=8.3Hz, 1H), 7.77 (d ,J=8.1Hz,1H),7.43-7.32(m,2H),7.30-7.20(m,10H),7.08ppm(dd,J=7.0,4.0Hz,1H).

[0120] 31 P{ 1 H}NMR (162MHz, Benzene-d6): δ-14.99ppm.

[0121] Example 2

[0122] The only difference from Example 1 is that Ph2PCl is replaced with dicyclohexylphosphine chloride, while all other conditions remain the same. This yields 8-dicyclohexylphosphinoquinoline.

[0123] 1 H NMR (400MHz, Benzene-d6): δ8.79(d,J=4.1Hz,1H),7.99(t,J=7.2Hz,1H),7.50(d,J=8.2Hz,1H),7.37(d,J=8.1Hz,1H),7.21(t,J=7.5Hz,1H),6.7 3(dd,J=8.3,4.2Hz,1H),2.68(m,2H),2.19(m,2H),1.73(m,4H),1.62-1. 41(m,6H),1.33(m,2H),1.22(q,J=9.7,8.6Hz,4H),1.16-1.02ppm(m,2H).

[0124] 13 C{ 1H}NMR (101MHz, Benzene-d6): δ151.62,149.48,138.07,137.02,136.27,129.13,128.72,125.96, 121.02,34.65,34.50,31.77,31.59,30.83,30.73,27.69,27.66,27.58,26.91,23.06,14.37ppm.

[0125] 31 P{ 1 H}NMR (162MHz, Benzene-d6): δ-1.76ppm.

[0126] Example 3

[0127] The only difference from Example 1 is that Ph2PCl is replaced with bis(3,5-dimethylphenyl)phosphine chloride, while all other conditions remain the same. This yields 8-bis(3,5-dimethylphenyl)phosphinoquinoline.

[0128] 1 H NMR (400MHz, Benzene-d6): δ8.60 (dd, J=4.2, 1.8Hz, 1H), 7.53 (ddd, J=7.1, 3.4, 1.4Hz, 1H), 7.46 (dd, J=8.3, 1.8Hz, 1H), 7.3 5(d,J=7.1Hz,1H),7.31(d,J=9.5Hz,4H),7.11(t,J=7.6Hz,1H),6.76(s,2H),6.64(dd,J=8.2,4.2Hz,1H),1.99ppm(s,12H).

[0129] 13 C{ 1 H}NMR (101MHz, Benzene-d6): δ157.79,150.39,150.22,149.71,141.03,140.87,137.99,137.9 1,135.88,134.61,132.81,132.61,130.70,128.63,128.17,126.71,121.41,114.08,21.29ppm.

[0130] 31 P{ 1 H}NMR (162MHz, Benzene-d6): δ-13.38ppm.

[0131] Example 4

[0132] The only difference from Example 1 is that Ph2PCl is replaced with bis(3,5-dimethoxyphenyl)phosphine chloride, while all other conditions remain unchanged. This yields 8-bis(3,5-dimethoxyphenyl)phosphinoquinoline.

[0133] 1 H NMR (400MHz, Benzene-d6): δ8.60(d,J=4.1Hz,1H),7.57(dd,J=7.2,3.3Hz,1H),7.44(d,J=8.3Hz,1H),7.32(d ,J=8.2Hz,1H),7.07(t,J=7.7Hz,1H),6.95(s,4H),6.62(dd,J=8.5,3.8Hz,1H),6.55(s,2H),3.17ppm(s,12H).

[0134] 13 C{ 1 H}NMR (101MHz, Benzene-d6): δ161.57,161.48,150.30,150.13,149.74,141.09,14 0.95,135.82,134.54,128.86,126.78,121.43,112.60,112.38,101.66,54.73ppm.

[0135] 31 P{ 1 H}NMR (162MHz, Benzene-d6): δ-10.10ppm.

[0136] Example 5

[0137] When R1 = phenyl, R2 = phenyl, and R3 = hydrogen atom, the structural formula of the phosphinoquinoline iron complex is as follows:

[0138]

[0139] The specific synthetic steps for phosphinoquinoline iron complexes are as follows:

[0140] In a glove box, FeCl2 (0.1276 g, 1.00 mmol, 1.00 equiv.) and 5 mL THF were added to a 50 mL round-bottom flask and stirred vigorously until homogeneous. 8-Diphenylphosphinoquinoline (0.3133 g, 1.00 mmol, 1.00 equiv.) was dissolved in 10 mL THF in a 25 mL round-bottom flask and transferred dropwise to the 50 mL round-bottom flask. The reaction system was then stirred at room temperature. After 48 h, all solvent was removed under reduced pressure. 10 mL of n-hexane was added, and all volatiles were removed under reduced pressure. This process was repeated three times. 30 mL of n-hexane was added, the mixture was filtered, and the filter cake was washed with n-hexane. The filter cake was collected to obtain 0.41 g of orange powder 8-diphenylphosphinoquinoline ferric chloride, with a yield of 94.0%.

[0141] 1 H NMR (400MHz, Chloroform-d): δ39.36, 21.21, 17.91, 12.40, 10.24, 4.19, 1.24, -3.89, -6.41, -19.17ppm.

[0142] Example 6

[0143] The only difference from Example 5 is that 8-diphenylphosphinoquinoline is replaced with 8-dicyclohexylphosphinoquinoline, while all other conditions remain the same. This yields 8-dicyclohexylphosphinoquinoline ferric chloride.

[0144] 1 H NMR (400MHz, Chloroform-d): δ164.77,92.92,42.31,23.64,16.50,12.96,12.40,3.65,3.10,1.59,0.83,0.35,-13.24,-19.56ppm.

[0145] Example 7

[0146] The only difference from Example 5 is that 8-diphenylphosphinoquinoline is replaced with 8-bis(3,5-dimethylphenyl)phosphinoquinoline, while all other conditions remain the same. 8-bis(3,5-dimethylphenyl)phosphinoquinoline ferric chloride is obtained.

[0147] 1 H NMR (400MHz, Chloroform-d): δ94.85, 41.48, 21.08, 13.75, 10.78, 3.91, 2.28, 1.98, -1.87, -4.81, -6.49, -18.78ppm.

[0148] Example 8

[0149] The only difference from Example 5 is that 8-diphenylphosphinoquinoline is replaced with 8-bis(3,5-dimethoxyphenyl)phosphinoquinoline, while all other conditions remain unchanged. 8-bis(3,5-dimethoxyphenyl)phosphinoquinoline ferric chloride is obtained.

[0150] 1 H NMR (400MHz, Chloroform-d): δ97.90,38.53,21.17,14.29,10.87,3.78,1.93,-2.49,-5.79,-18.72ppm.

[0151] Application Example 1

[0152] The polymerization of isoprene in toluene was catalyzed using the phosphoquinoline iron complex of Example 5, and the specific steps are as follows:

[0153] a) Isoprene polymerization was carried out at room temperature in a glove box. In a 10 mL penicillin bottle, phosphoquinoline iron complex (4.40 mg, 10.0 μmol, 1.00 equiv.) was dissolved in 2 mL toluene, and 50.0 μmol Al ( i After adding Bu3 (co-catalyst), stirring continued. Finally, 1 mL of toluene solution of isoprene (0.681 g, 10.0 mmol, 1000 equiv.) was rapidly added to the penicillin bottle, and stirring was carried out at room temperature. After 10 min, the penicillin bottle was removed from the glove box, and the reaction was quenched with methanol acidified with hydrochloric acid (10% v / v). The reaction solution was poured into a large amount of methanol to precipitate the polymer, which was washed several times with methanol and dried under vacuum at 60 °C to constant weight.

[0154] Thermal analysis and molecular weight characterization were performed on the obtained product. The test results showed that the polymerization activity was 136 kg. PI ·mol Fe -1 ·h -1 Polymer T g = -27.1℃ (T) g (The glass transition temperature of the polymer is obtained by DSC measurement), and the polymer molecular weight M is... n =42×10 3 g·mol -1 PDI = 1.60 (M n The number-average molecular weight (NMR) of the polymer is given by PDI (Polymer density distribution), obtained from room-temperature GPC testing. The ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 46.7 / 8.2 / 45.1 (obtained through GPC testing at room temperature). 1 HNMR and 13 (obtained from C NMR testing).

[0155] b) is basically the same as a), the difference being: the addition of 10 μmol Al i Bu3, at this time the Al / Fe molar ratio is 1:1.

[0156] Polymerization activity: 18kg PI ·mol Fe -1 ·h -1 Polymer T g = -26.5℃. Polymer molecular weight M n =24×10 3 g·mol -1 PDI = 1.55, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 46.4 / 7.1 / 46.5.

[0157] c) is basically the same as a), the difference being: the addition of 20 μmol Al i Bu3, at this time the Al / Fe molar ratio is 2:1.

[0158] Polymerization activity: 88kg PI ·mol Fe -1 ·h -1 Polymer T g = -26.6℃. Polymer molecular weight M n =40×10 3 g·mol -1 PDI = 1.80, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 48.2 / 6.3 / 45.5.

[0159] d) is basically the same as a), except that 30 μmol Al is added. i Bu3, at this time the Al / Fe molar ratio is 3:1.

[0160] Polymerization activity: 125kg PI ·mol Fe -1 ·h -1 Polymer T g = -26.9℃. Polymer molecular weight M n =46×10 3 g·mol -1 PDI = 1.67, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 46.8 / 8.3 / 44.9.

[0161] e) is basically the same as a), the difference being: the addition of 100 μmol Al i Bu3, at this time the Al / Fe molar ratio is 10:1.

[0162] Polymerization activity: 136kg PI ·mol Fe -1 ·h -1 Polymer T g = -26.7℃. Polymer molecular weight M n =41×10 3 g·mol -1 PDI = 1.56, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 49.6 / 5.3 / 45.1.

[0163] f) is basically the same as a), except that the added co-catalyst is AlMe3.

[0164] Polymerization activity: 136kg PI ·mol Fe -1 ·h -1 Polymer T g = -25.8℃. Polymer molecular weight M n =62×10 3 g·mol -1 PDI = 1.64, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 48.4 / 5.9 / 45.7.

[0165] g) is basically the same as a), except that the added co-catalyst is AlEt3.

[0166] Polymerization activity: 136kg PI ·mol Fe -1 ·h -1 Polymer T g = -27.3℃. Polymer molecular weight M n =25×10 3 g·mol -1 PDI = 1.52, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 50.0 / 4.5 / 45.5.

[0167] h) is basically the same as a), except that the added co-catalyst is dMAO.

[0168] Polymerization activity: 409kg PI ·mol Fe -1 ·h -1 Polymer T g = -24.5℃. Polymer molecular weight M n =130×10 3g·mol -1 PDI = 1.19, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 51.5 / 0 / 48.5.

[0169] i) is basically the same as h), except that 30 μmol dMAO is added.

[0170] Polymerization activity: 368kg PI ·mol Fe -1 ·h -1 Polymer T g = -24.6℃. Polymer molecular weight M n =102×10 3 g·mol -1 PDI = 1.29, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 51.4 / 0 / 48.6.

[0171] j) is basically the same as h), except that 100 μmol dMAO is added.

[0172] Polymerization activity: 409kg PI ·mol Fe -1 ·h -1 Polymer T g = -24.7℃. Polymer molecular weight M n =89×10 3 g·mol -1 PDI = 1.13, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 51.8 / 0 / 48.2.

[0173] k) is basically the same as h), except that 300 μmol dMAO is added.

[0174] Polymerization activity: 409kg PI ·mol Fe -1 ·h -1 Polymer T g = -24.3℃. Polymer molecular weight M n =83×10 3 g·mol -1 PDI = 1.15, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 51.7 / 0 / 48.3.

[0175] l) is basically the same as h), except that 500 μmol dMAO is added.

[0176] Polymerization activity: 409kgPI ·mol Fe -1 ·h -1 Polymer T g = -24.3℃. Polymer molecular weight M n =69×10 3 g·mol -1 PDI = 1.11, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 51.5 / 0 / 48.5.

[0177] m) is basically the same as h), except that 100 mmol of isoprene is added.

[0178] Polymerization activity: 3431kg PI ·mol Fe -1 ·h -1 Polymer T g = -24.6℃. Polymer molecular weight M n =570×10 3 g·mol -1 PDI = 1.84, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 53.5 / 0 / 46.5.

[0179] Application Example 2

[0180] The polymerization of isoprene in toluene was catalyzed using the phosphoquinoline iron complex of Example 5, and the specific steps are as follows:

[0181] The high-temperature polymerization of isoprene was carried out in a Schlenk flask under a nitrogen atmosphere. In a 25 mL Schlenk flask, a phosphinoquinoline iron complex (4.40 mg, 10.0 μmol, 1.00 equiv.) was dissolved in 2 mL of toluene. Then, a 2 mL toluene solution of dMAO (8.70 mg, 50.0 μmol, 5.00 equiv.) was added to the solution with stirring. After the addition was complete, the flask was placed in a 100 °C oil bath. A 1 mL toluene solution of isoprene (0.681 g, 10.0 mmol, 1000 equiv.) was rapidly added to the Schlenk flask, and polymerization was carried out with thorough stirring. After 10 min, the reaction was quenched with hydrochloric acid-acidified methanol (10% v / v). The reaction solution was then poured into a large volume of methanol to precipitate the polymer, which was washed several times with methanol and dried under vacuum at 60 °C to constant weight.

[0182] Thermal analysis and molecular weight characterization were performed on the obtained product. The test results showed that the polymerization activity was 654 kg. PI ·mol Fe -1 ·h-1 Polymer T g = -22.5℃, polymer molecular weight M n =122×10 3 g·mol -1 PDI = 1.96, and the ratio of cis-1,4 / trans-1,4 / 3,4 structural units is 50.4 / 5.9 / 43.7.

[0183] It can be seen that the iron complex constructed using the phosphoquinoline ligand of this invention exhibits excellent high-temperature (100°C) catalytic activity in the polymerization of isoprene. Furthermore, only 5 equivalents of dMAO are required to effectively activate the iron complex, enabling rapid polymerization of isoprene and meeting the requirements of green catalytic processes.

[0184] Application Example 3

[0185] The polymerization of 1,3-butadiene in toluene was catalyzed using the phosphinoquinoline iron complexes of Examples 5-8, and the specific steps are as follows:

[0186] a) The polymerization of 1,3-butadiene was carried out at room temperature in a glove box. In a 10 mL penicillin bottle, 8-diphenylphosphinoquinoline ferric chloride complex (main catalyst, 4.40 mg, 10.0 μmol, 1.00 equiv.) was dissolved in 2 mL of toluene, and 50.0 μmol dMAO was added with continuous stirring. Finally, 1 mL of a toluene solution of 1,3-butadiene (0.54 g, 10.0 mmol, 1000 equiv.) was rapidly added to the penicillin bottle, and the mixture was stirred at room temperature. After 10 min, the penicillin bottle was removed from the glove box, and the reaction was quenched with hydrochloric acid-acidified methanol (10% v / v). The reaction solution was poured into a large amount of methanol to precipitate the polymer, which was then washed several times with methanol and dried under vacuum at 60 °C to constant weight.

[0187] Thermal analysis and molecular weight characterization were performed on the obtained product. The test results showed that the polymerization activity was 347 kg. PI ·mol Fe -1 ·h -1 Polymer T g = -35.6℃, polymer molecular weight M n =104.5×10 4 g·mol -1 PDI = 1.17, and the ratio of cis-1,4 / trans-1,4 / 1,2 structural units is 70.0 / 12.7 / 17.3.

[0188] b) is basically the same as a), except that the main catalyst is the complex 8-dicyclohexylphosphinoquinoline ferric chloride.

[0189] Polymerization activity: 253kg PI ·mol Fe -1 ·h -1 Polymer T g = -31.2℃. Polymer molecular weight M n =18×10 3 g·mol -1 PDI = 2.48, and the ratio of cis-1,4 / trans-1,4 / 1,2 structural units is 57.5 / 17.9 / 24.6.

[0190] c) is basically the same as a), except that the main catalyst is the complex 8-bis(3,5-dimethylphenyl)phosphinoquinoline ferric chloride.

[0191] Polymerization activity: 306kg PI ·mol Fe -1 ·h -1 Polymer T g = -22.5℃. Polymer molecular weight M n =72×10 3 g·mol -1 PDI = 1.39, and the ratio of cis-1,4 / trans-1,4 / 1,2 structural units is 70.7 / 12.7 / 16.6.

[0192] d) is basically the same as a), except that the main catalyst is the complex 8-bis(3,5-dimethoxyphenyl)phosphinoquinoline ferric chloride.

[0193] Polymerization activity: 334kg PI ·mol Fe -1 ·h -1 Polymer T g = -10.8℃. Polymer molecular weight M n =85×10 3 g·mol -1 PDI = 1.84, and the ratio of cis-1,4 / trans-1,4 / 1,2 structural units is 71.7 / 11.7 / 16.6.

[0194] Application Example 4

[0195] The polymerization of conjugated dienes in toluene was catalyzed using the phosphoquinoline iron complexes of Examples 5-8, and the specific steps are as follows:

[0196] a) The polymerization of 2-phenyl-1,3-butadiene was carried out in a glove box at room temperature. In a 10 mL penicillin bottle, 8-diphenylphosphinoquinoline ferric chloride complex (main catalyst, 4.40 mg, 10.0 μmol, 1.00 equiv.) was dissolved in 2 mL of toluene, and 50.0 μmol dMAO was added with continuous stirring. Finally, 1 mL of a toluene solution of 2-phenyl-1,3-butadiene (1.3 g, 10 mmol, 1000 equiv.) was rapidly added to the penicillin bottle, and the mixture was stirred at room temperature. After 10 h, the penicillin bottle was removed from the glove box, and the reaction was quenched with hydrochloric acid-acidified methanol (10% v / v). The reaction solution was poured into a large amount of methanol to precipitate the polymer, which was washed several times with methanol and then dried under vacuum at 60 °C to constant weight.

[0197] Thermal analysis and molecular weight characterization of the obtained product showed that the polymerization activity was 6.5 kg. PI ·mol Fe -1 ·h -1 Polymer molecular weight M n =182.7×10 3 g·mol -1 PDI = 1.59, and the ratio of cis-1,4 / trans-1,4 / 1,2 structural units is 60.0 / 15.7 / 22.3.

[0198] b) The copolymerization of isoprene and ((4-methylenehex-5-en-1-yl)oxy)benzene was carried out in a glove box at room temperature. In a 10 mL penicillin bottle, 8-diphenylphosphinoquinoline ferric chloride complex (main catalyst, 4.40 mg, 10.0 μmol, 1.00 equiv.) was dissolved in 2 mL of toluene, and 50.0 μmol dMAO was added with continuous stirring. Finally, a 1 mL toluene solution of isoprene (0.34 g, 5 mmol, 500 equiv.) and ((4-methylenehex-5-en-1-yl)oxy)benzene (0.94 g, 5 mmol, 500 equiv.) was rapidly added to the penicillin bottle and stirred at room temperature. After 10 minutes, the penicillin bottle was removed from the glove box, and the reaction was quenched with methanol acidified with hydrochloric acid (10% v / v). The reaction solution was poured into a large amount of methanol to precipitate the polymer. The polymer was washed several times with methanol and then dried under vacuum at 60°C to constant weight.

[0199] Thermal analysis and molecular weight characterization of the obtained product showed that the polymerization activity was 11.77 kg. PI ·mol Fe -1 ·h -1 Polymer molecular weight M n =171.7×103 g·mol -1 PDI = 1.77, polyisoprene structure: cis-1,4 / trans-1,4 / 1,2 structural unit ratio is 51.2 / 4.1 / 44.7, ((4-methylenehex-5-en-1-yl)oxy)benzene structure is 1,2 structural unit.

[0200] Figure 1 This is a molecular crystal structure diagram of the phosphinoquinoline iron complex when R1 = phenyl, R2 = phenyl, and R3 = hydrogen atom in this invention; Figure 2 This is a crystal structure diagram of the phosphinoquinoline iron complex when R1 = 1,1'-biphenyl-2-yl, R2 = phenyl, and R3 = hydrogen atom in this invention.

[0201] Figure 3 In this invention, when R1 = cyclohexyl, R2 = cyclohexyl, and R3 = hydrogen, the phosphinoquinoline iron complex... 1 H NMR spectrum; Figure 4 The polyisoprene obtained by polymerizing isoprene with the complex 8-diphenylphosphinoquinoline and ferric chloride in this invention is... 1 H NMR spectrum; Figure 5 The polyisoprene obtained by polymerizing isoprene with the complex 8-diphenylphosphinoquinoline and ferric chloride in this invention is... 13 C NMR spectrum; the horizontal axis unit is ppm.

[0202] This invention provides a highly active and thermally stable phosphine-based quinoline iron complex that enables the structurally controlled polymerization of isoprene / 1,3-butadiene, thereby reducing the amount of co-catalyst required.

[0203] The iron complex of this invention catalyzes polyisoprene, maintaining high activity (654 kg) even at high temperature (100°C). PIP ·mol Fe -1 ·h -1 It requires only 5 equivalents of dMAO to activate. The resulting polyisoprene has a narrow molecular weight distribution (PDI = 1.11–1.96) and its microstructure (cis-1,4, trans-1,4, 3,4) can be precisely controlled.

[0204] The iron complex of this invention is used to catalyze poly(1,3-butadiene), exhibiting high activity (347 kg). PB ·mol Fe -1 ·h -1 It requires only 5 equivalents of dMAO for activation. The resulting poly-1,3-butadiene has a narrow molecular weight distribution (PDI = 1.17–2.48) and its microstructure (cis-1,4, trans-1,4, 1,2) can be precisely controlled.

[0205] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on the present invention without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A phosphonoquinoline ligand, characterized in that, The structural formula is shown in Formula I: In Equation I, R1 and R2 are independently selected. Or alkyl, R3 is selected from phenyl or hydrogen atom; R4, R5, R6, R7 and R8 are independently selected from hydrogen atoms, alkoxy groups, dimethylamino groups, halogens, alkyl or substituted alkyl groups having 1 to 4 carbon atoms, phenyl or substituted phenyl groups.

2. The phosphoquinoline ligand according to claim 1, characterized in that, The alkoxy group is one of methoxy, isopropoxy, and cyclohexyloxy; the alkyl group having 1 to 4 carbon atoms is one of methyl, ethyl, isopropyl, n-propyl, tert-butyl, sec-butyl, isobutyl, and n-butyl.

3. The method for preparing the phosphoquinoline ligand according to claim 1 or 2, characterized in that, Includes the following steps: R1(R2)PCl and lithium quinoline were mixed and subjected to a nucleophilic substitution reaction to obtain phosphinoquinoline ligands; the structural formula of the lithium quinoline is shown below:

4. A phosphinoquinoline iron complex, characterized in that, The structural formula is shown in Formula II: In Equation II, R1, R2, and R3 are defined as in Equation I.

5. The method for preparing the phosphoquinoline iron complex according to claim 4, characterized in that, Includes the following steps; The phosphonoquinoline ligand shown in Formula I, FeCl2, and an organic solvent were mixed and subjected to a complexation reaction. After removing the organic solvent, the phosphonoquinoline iron complex was obtained.

6. The preparation method according to claim 5, characterized in that, The molar ratio of the phosphoquinoline ligand to FeCl2 is 1:1 to 1:1.5; the temperature of the complexation reaction is -5 to 30°C, and the time is 10 to 50 h.

7. The application of the phosphoquinoline iron complex according to claim 4 in the catalytic polymerization of conjugated dienes.

8. A method for preparing a polyconjugated diene, characterized in that, Includes the following steps: A conjugated diene monomer, a catalyst, and an organic solvent are mixed and polymerized to obtain a polyconjugated diene; the structural formula of the conjugated diene monomer is shown in Formula III: In Formula III, R9 is selected from hydrogen, alkyl, aryl, or functional group substituents containing heteroatoms; The catalyst comprises the phosphoquinoline iron complex of claim 4.

9. The preparation method according to claim 8, characterized in that, The alkyl group is one of methyl, ethyl, isopropyl, n-propyl, tert-butyl, sec-butyl, isobutyl, n-butyl, and n-hexyl; the aryl group is one of phenyl, 3,5-dimethylphenyl, 2,6-dimethylphenyl, mesitylene, p-methoxyphenyl, o-methoxyphenyl, 3,5-dimethoxyphenyl, 2,6-dimethoxyphenyl, mesitylene, 3,5-diisopropylphenyl, and 2,6-diisopropylphenyl; the functional group substituent containing a heteroatom is one of phenoxy, hydroxyl, amino, methoxy, and dimethylamino.

10. The preparation method according to claim 8, characterized in that, The molar ratio of the conjugated diene monomer to the phosphoquinoline iron complex is 10000:1 to 100; the polymerization reaction temperature is 0 to 100°C, and the time is 10 to 1440 min. The catalyst further includes a co-catalyst, which is selected from one or more of aluminoxane, alkylaluminum and alkylaluminum chloride; the molar ratio of Al in the co-catalyst to Fe in the phosphoquinoline iron complex is (1-100):1.

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