Preparation method of sulfur-bridged bimetallic alkyne complex and application thereof in dehydrogenative coupling to prepare 1,4-di-alkyne

Abstract

This invention belongs to the field of catalyst preparation and application technology, and discloses a method for preparing sulfur-bridged bimetallic alkyne complexes and their application in the dehydrogenation coupling synthesis of 1,4-diyne. The method uses thiols or thiophenol salts as bridging ligands, with each metal center coordinated with a cyclopentadienyl group or a substituted cyclopentadienyl group. This invention achieves coordination activation of the terminal alkyne by controlling the oxidation state of the metal center and altering the bonding mode of the terminal alkyne at the metal center. In this system, the sulfur-bridged ligand not only assists the metal center in activating the terminal alkyne but also stabilizes a key intermediate in the catalytic process. Subsequently, the coordinated-activated terminal alkyne undergoes a reductive elimination process to generate 1,4-diyne. This reaction can be carried out in a temperature range of -100℃ to 25℃, with a reaction time of 0.5 to 48 hours. This method can synthesize a series of novel sulfur-bridged bimetallic alkyne complexes with high yield and high selectivity, providing a novel catalytic system for the activation of C-H bonds in terminal alkynes mediated by inexpensive metals and the further synthesis of 1,4-diyne.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation and application technology, and relates to a method for preparing sulfur-bridged bimetallic alkyne complexes and their application in the dehydrogenation coupling synthesis of 1,4-diyne. Background Technology

[0002] Terminal alkyne dehydrogenation coupling dimerization combines 100% atom economy with the high efficiency of one-step C-C bond construction, making it an indispensable tool in modern synthetic chemistry. Based on differences in reaction mechanism and redox properties, terminal alkyne dimerization can be classified into three categories: redox neutral dimerization, oxidative dimerization, and reductive dimerization. Among these, oxidative dimerization is the most attractive due to its direct activation via CH bonds without requiring substrate pre-functionalization, but its mechanism complexity and practical application bottlenecks are also the most prominent. This reaction mainly involves the following steps: the terminal alkyne first coordinates to the metal center, followed by deprotonation to form a metal-alkynyl intermediate; the back-bonding π bond between the metal and alkyne stabilizes this intermediate, thereby lowering the reaction energy barrier. Although the above mechanism has been preliminarily established, oxidative dimerization still faces three key challenges in practical applications: firstly, the selection of the oxidant. While excessively strong oxidants can drive the reaction, they often lead to over-oxidation of the substrate or product and destruction of functional groups; conversely, excessively weak oxidants result in slow reaction kinetics, requiring high temperatures or long reaction times, and are prone to side reactions. Second, there is a contradiction in the electronic effects of substituents on aryl-terminated alkynes. While electron-rich aryl-terminated alkynes are beneficial for enhancing the acidity of CH, their strong electron-donating effect reduces the coordination ability of the metal and slows down the oxidative insertion step. Conversely, while electron-withdrawing substituents can activate coordination, they weaken the acidity of CH, making deprotonation difficult. Third, alkyne-metal intermediates have extremely short lifetimes and are difficult to detect using conventional techniques such as NMR and IR.

[0003] Current reports mainly focus on several metal complex systems: mononuclear rhodium complexes ( J. Am. Chem. Soc. 2012, 134 , 9276), binuclear copper complex ( J. Am. Chem. Soc. 2017, 139 , 5378) and mononuclear iron complexes ( ACS Catal. 2020 , 10, 4895). However, to date there have been no reports on binuclear metal complexes achieving coordination activation of terminal alkynes and further mediating the dehydrogenation coupling dimerization of terminal alkynes into 1,4-diyne compounds. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing sulfur-bridged bimetallic complexes and their application in the coordination activation and dehydrogenation coupling dimerization of alkynes into 1,4-diyne.

[0005] The technical solution of the present invention is as follows: Sulfur-bridged bimetallic alkyne complexes have the following structures: In structural formulas I and II: R 1 Selected from C2-C4 aliphatic hydrocarbon groups or C6-C 11 aryl, R 3 Also selected from C2~C4 aliphatic hydrocarbon groups or C6~C 11 aryl; R 2 Selected from cyclopentadiene ligand Cp and monomethylcyclopentadiene ligand Cp 1 dimethylcyclopentadiene ligand Cp 2 Trimethylcyclopentadiene ligand Cp 3 Tetramethylcyclopentadiene ligand Cp 4 Any one of pentamethylcyclopentadiene ligand Cp* and 1,2,4-tritert-butylcyclopentadiene ligand Cp'; Where: Cp, Cp 1 Cp 2 Cp 3 Cp 4 Cp* and Cp' represent the following structures: ; M 1 Selected from any one of Co, Fe, Ru, Rh, Cr, Ni, and Mn, M 2 It can also be selected from any one of Co, Fe, Ru, Rh, Cr, Ni, and Mn; n is 0, 1, or 2; When n is 1 or 2, X - Selected from Cl - ,Br - I - PF6 - SbF6 - BF4 - BPh4 - CF3SO3 - B(C6F5)4 - and B(3,5-(CF3)2C6H3)4 - At least one of them.

[0006] Table 1 lists some specific coordination compound structures: Table 1. Specific structures of sulfur-bridged bimetallic complexes In a preferred embodiment of the present invention, M 1 For Fe or Co, M 2 For Fe or Co, R 1 For bdt, and R 2 For Cp*, R 3 The complexes of the present invention are selected from H, Ph, or Tol, and more preferably, the complexes of the present invention are selected from: 1:R 1 = bdt, R 2 = Cp*, R 3 = H, M 1 = M 2 = Co, n = 1; 2: R 1 = bdt, R 2 = Cp*, R 3 = Ph, M 1 = M 2 = Co, n = 1; 3: R 1 = bdt, R 2 = Cp*, R 3 = H, M 1 = M 2 = Fe, n = 0; 4: R 1 = bdt, R 2 = Cp*, R 3 = Ph, M 1 = M 2 = Fe, n = 0; 5:R 1 = bdt, R 2 = Cp*, R 3 = Ph, M 1 = M 2= Co, n = 2; 6:R 1 = bdt, R 2 = Cp*, R 3 = Tol, M 1 = M 2 = Co, n = 2; 7:R 1 = bdt, R 2 = Cp*, R 3 = H, M 1 = M 2 = Fe, n = 1; 8:R 1 = bdt, R 2 = Cp*, R 3 = Ph, M 1 = M 2 = Fe, n = 1.

[0007] Table 2. Specific structures of preferred thiol-bridged bimetallic alkynyl complexes A method for preparing a sulfur-bridged bimetallic alkyne complex, following the route shown below: The specific preparation method is as follows: At -100~50℃, the complex [Cp*M] was subjected to […]. 1 ( m -bdt)M 2 Add 1 to 5 times the amount of ferrocene hexafluorophosphate (Fc·PF6) to a dichloromethane solution of Cp*], maintain this temperature and react for 0.5 to 2 h, then add alkynes (HC≡CR). 3 After the temperature rises to room temperature, the reaction continues for 1-24 hours. The solvent is removed under vacuum, the solid is washed with diethyl ether, and then the solvent is removed again under reduced pressure to finally obtain the sulfur-bridged bimetallic alkyne complex, M. 1 With M 2 The definition is the same as above.

[0008] Furthermore, the amount of alkyne used is the complex [Cp*M] 1 ( m -bdt)M 2 The amount of substance is 1 to 5 times that of [Cp*], ultimately yielding [Cp*M]. 1 ( m - or 1 : or 2-bdt)( m - or 2 : or 1 -HC-CR 3 M 2 Cp*][PF6].

[0009] Furthermore, the amount of alkyne used is the complex [Cp*M] 1 ( m -bdt)M 2 The amount of substance is 5 to 7 times that of [Cp*], ultimately yielding [Cp*M]. 1 ( m -bdt)( m - or 2 : or 2 -HC≡CR 3 M 2 Cp*][PF6 2。

[0010] In [Cp*M 1 ( m - or 1 : or 2 -bdt)( m - or 2 : or 1 -HC-CR 3 M 2 [Cp*][PF6] was added in an amount equal to that of cobalt dicene (CoCp2), and the reaction was continued for 1–24 h after the temperature was raised to room temperature. The solvent was removed under vacuum, and the product was extracted with n-hexane. The solvent was then removed under reduced pressure to obtain the complex [Cp*M]. 1 ( m - or 1 : or 2 -bdt)( m - or 2 : or 1 -HC-CR 3 M 2 Cp*].

[0011] Furthermore, the alkyne is preferably any one of phenylacetylene, methylphenylacetylene, and acetylene.

[0012] Furthermore, the reaction occurs at carbon number C 10 The following ethers and benzenes have a carbon number of C10 The following alkylbenzenes have the following carbon number (C): 10 The following alkanes and halogenated hydrocarbons are subjected to this process.

[0013] An application of a sulfur-bridged bimetallic alkyne complex for the synthesis of 1,4-diphenylbutyne, the method comprising the following steps: In a nitrogen atmosphere, the sulfur-bridged bimetallic yne complex was added to a Schlenk flask and dissolved in dichloromethane. The atmosphere was then replaced with air to allow the reaction to proceed. The solution gradually turned dark green. The reaction system was then placed at -100°C to 25°C, and 1 to 2 times the amount of CoCp2 was added to react for 0.5 to 48 h. The solvent was removed under vacuum, and the low-polarity product was extracted with n-hexane. The target product, 1,4-diphenylbutyne, was then separated by column chromatography.

[0014] The product was qualitatively analyzed by gas chromatography-mass spectrometry (GC-MS), and the yield of 1,4-diphenylbutyne was determined by proton nuclear magnetic resonance (NMR) characterization, with ferrocene as an internal standard.

[0015] Compared with the prior art, the advantages of the present invention are as follows: (1) This invention discloses for the first time a novel method for preparing sulfur-bridged bimetallic alkyne complexes, providing a new approach for designing and developing catalysts that synergistically activate alkynes with bimetals.

[0016] (2) This invention successfully prepared 1,4-diyne compounds by using sulfur-bridged bimetallic complexes to achieve terminal alkyne dimerization, providing a new opportunity for constructing a synergistic catalytic alkyne functionalization system.

[0017] Its structural innovation and diversity provide rich structural models for the field of organometallic chemistry, helping to understand the nature of interactions and chemical bonds; the preparation methods are highly controllable, enabling the synthesis of complexes with different structures, facilitating the study of structure-property relationships; the reaction conditions are mild, reducing equipment requirements, energy consumption, and improving safety; the wide range of raw material choices facilitates the development of complexes with different functions; the broad applicability of solvents allows for the selection of appropriate solvents based on reactant conditions to improve yield and selectivity; its high application value provides new pathways for the synthesis of important organic compounds, enriching organic synthesis methodologies; the relatively simple synthesis steps reduce operational difficulty and cost, facilitating industrial production; the high purity of the products meets the needs of high-purity applications; the advantages of catalyst compositions are significant, improving reaction rates and yields, and the selection and optimization of co-catalysts provide room for optimizing reaction conditions; it can also expand the field of organic synthesis, opening up new reaction pathways and methods, and helping to discover new reactions and synthesize unique organic molecules. Attached Figure Description

[0018] Figure 1 The crystal structure of complex 1 in Example 1 is shown. Figure 2The crystal structure of complex 2 in Example 2; Figure 3 The crystal structure of complex 3 in Example 3 is shown. Figure 4 The crystal structure of complex 4 in Example 4 is shown. Detailed Implementation

[0019] The following embodiments are intended to provide a more comprehensive understanding of the present invention by those skilled in the art, but do not limit the invention in any way. Unless otherwise specified, the experimental methods used in this invention are conventional methods, and the experimental equipment, materials, reagents, etc. used are all commercially available.

[0020] Example 1: Preparation of o-benzenedithiophenol-bridged binuclear cobalt acetylene complex 1 Under an argon atmosphere at 25 °C, complex A (50 mg, 0.09 mmol) was dissolved in dichloromethane (5 mL). One equivalent of ferrocene hexafluorophosphate (35 mg, 0.11 mmol) was added to the solution. After reacting for 5 min, acetylene was introduced at 1 atm, and the reaction was continued for 10 h. The solvent was removed under reduced pressure, and the mixture was washed with n-hexane (3 mL × 3). After vacuum drying, complex 1 (65 mg, 0.09 mol) was obtained, with a yield of 93%. 1 ¹H NMR (400 MHz, CD₂Cl₂, ppm): d 9.48 (br,30H, Cp*-C H 3). HRMS (ESI, m / z ) calcd. for C 28 H 36 Co2S2 [1-PF6] + , 554.9026, found554.9022. IR (KBr, cm -1 ): 3040, 2978, 2920, 1577, 1477, 1427, 1378, 1340,1260, 1141, 842, 762, 733, 706, 609. Example 2 Preparation of o-phenyldithiophenol-bridged binuclear cobalt phenylacetylene complex 2 Under an argon atmosphere at 25 °C, complex A (200 mg, 0.38 mmol) was dissolved in dichloromethane (20 mL). Ferrocene hexafluorophosphate (153 mg, 0.23 mmol) was added to the solution. After reacting for 5 min, excess phenylacetylene (50 mL) was added. mThe solvent was removed under reduced pressure, and the mixture was washed with n-hexane (10 mL × 3). After vacuum drying, complex 2 (255 mg, 0.33 mmol) was obtained, with a yield of 87%. 1 ¹H NMR (400 MHz, CD₂Cl₂, ppm): d 9.08 (br, 30H, Cp*-C H 3). HRMS (ESI, m / z ) calcd. for C 34 H 39 Co2S2 [2-PF6] + ,630.1235; found 630.1236. IR (KBr, cm -1 ): 3057, 2959, 2923, 2858, 1603, 1447,1378, 1266, 1082, 1021, 839, 767, 558. Example 3 Preparation of o-dithiophenol-bridged diferethyne complex 3 Under an argon atmosphere at -50 °C, complex B (94 mg, 0.18 mmol) was dissolved in dichloromethane (5 mL). Ferrocene hexafluorophosphate (90 mg, 0.27 mmol) was added to this solution, and after reacting for 5 min, 1 atm of acetylene was added. The temperature was raised to room temperature, and the reaction was continued for 12 h. Subsequently, the temperature was lowered to -50 °C, and an equal amount of cobalt dicene (40 mg, 0.21 mmol) was added, and the reaction was carried out for 10 h. The solvent was removed under reduced pressure, and the product was extracted with n-hexane (3 mL × 3), washed with n-pentane (3 mL × 3), and dried under vacuum to obtain complex 3 (106 mg, 0.15 mmol), with a yield of 85%. 1 H NMR (400MHz, C6D6, ppm): d 12.37 (d, J = 3.18 Hz, 1H, C2H2- H ), 8.24 (d, J = 7.63 Hz, 1H, Ph- H ), 6.86 (t, J = 7.50 Hz, 1H, Ph- H ), 6.81 (d, 1H, J = 7.43 Hz, 1H, Ph- H ), 6.56 (t, 1H, J= 7.34 Hz, 1H, Ph- H ), 6.24 (d, J = 3.16 Hz, 1H, C2H2- H ),1.65 (s, 15H, Cp*-C H 3), 1.49 (s, 15 H, Cp*-C H 3). 13 C6D6 NMR (400 MHz, C6D6, ppm): d 181.8 (s, C 2H2), 135.3 (s, C 2H2), 137.1 (s, Ph- C ), 130.7 (s, Ph- C ), 129.8(s, Ph- C ), 127.7 (s, Ph- C ), 124.3 (s, Ph- C ), 91.0 (s, Ph- C ), 87.8 (s, Cp*- C ),86.6 (s, Cp*- C ), 10.8 (s, Cp*- C H3), 10.6 (s, Cp*- C H3). Anal. Calcd. ForC 28 H 36 Fe2S2: C, 61.32; H, 6.62. Found: C, 61.40, H, 6.97. Example 4 Preparation of o-phenyldithiophenol-bridged binuclear iron phenylacetylene complex 4 Under an argon atmosphere at -50 °C, complex B (550 mg, 1.05 mmol) was dissolved in dichloromethane (20 mL). An equivalent of ferrocene hexafluorophosphate (350 mg, 1.06 mmol) was added to this solution. After reacting for 5 min, phenylacetylene (120 mL) was added. m L, 1.02 mmol), the reaction was continued for 12 h after the temperature was raised to room temperature, then cooled to -50 °C and cobalt dicene (200 mg, 1.06 mmol) was added and reacted for 10 h to remove the solvent under reduced pressure. The mixture was then washed with n-hexane (15 mL × 3) and dried under vacuum to obtain complex 4 (453 mg, 0.59 mmol), with a yield of 56%. IR (KBr, cm⁻¹) –1): 3433, 3062,2979, 2910, 1633, 1431, 1378, 1083, 761. Anal. Calcd For C 34 H 40 Fe2S2BF4: C,57.41; H, 5.67. Found: C, 57.66; H, 5.76. The structures of coordinations 1, 2, 3, and 4 were characterized by X-ray single-crystal diffraction (instrument used: Bruker Smart Apex CCD single-crystal diffractometer). Important crystallographic data are shown in Tables 3 and 4, and their crystal structures are as follows: Figure 1-4 As shown, the main structural parameters are shown in Table 5-8.

[0021] Table 3 Crystallographic data of coordinations 1 and 2 Table 4 Crystallographic data of coordinations 3 and 4 Table 5. Main bond lengths, bond angles, and dihedral angles of complex 1 Table 6. Main bond lengths, bond angles, and dihedral angles of complex 2 Table 7. Main bond lengths, bond angles, and dihedral angles of complex 3 Table 8. Main bond lengths, bond angles, and dihedral angles of complex 4 Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A sulfur-bridged bimetallic alkyne complex, characterized in that, It has the following structure I or II: ， R 1 Selected from C2-C4 aliphatic hydrocarbon groups or C6-C 11 aryl, R 3 Also selected from C2~C4 aliphatic hydrocarbon groups or C6~C 11 aryl; R 2 Selected from cyclopentadiene ligand Cp and monomethylcyclopentadiene ligand Cp 1 dimethylcyclopentadiene ligand Cp 2 Trimethylcyclopentadiene ligand Cp 3 Tetramethylcyclopentadiene ligand Cp 4 Any one of pentamethylcyclopentadiene ligand Cp* and 1,2,4-tritert-butylcyclopentadiene ligand Cp'; Where: Cp, Cp 1 Cp 2 Cp 3 Cp 4 Cp* and Cp' represent the following structures: ； M 1 Selected from any one of Co, Fe, Ru, Rh, Cr, Ni, and Mn, M 2 It can also be selected from any one of Co, Fe, Ru, Rh, Cr, Ni, and Mn; n is 0, 1, or 2.

2. The sulfur-bridged bimetallic alkyne complex according to claim 1, characterized in that, When n is 1 or 2, X - Selected from Cl - ,Br - I - PF6 - SbF6 - BF4 - BPh4 - CF3SO3 - B(C6F5)4 - and B(3,5-(CF3)2C6H3)4 - At least one of them.

3. A process for the preparation of a sulfur-bridged dimetallal yne complex, characterized in that, Prepared according to the route shown below: ， The specific preparation method is as follows: At -100~50℃, the complex [Cp*M] was subjected to […]. 1 ( μ -bdt)M 2 Add 1 to 5 times the amount of ferrocene hexafluorophosphate (Fc·PF6) to a dichloromethane solution of Cp*], maintain this temperature and react for 0.5 to 2 h, then add alkynes (HC≡CR). 3 After the temperature rises to room temperature, the reaction continues for 1-24 hours. The solvent is removed under vacuum, the solid is washed with diethyl ether, and then the solvent is removed again under reduced pressure to finally obtain the sulfur-bridged bimetallic alkyne complex, M. 1 With M 2 The definition is the same as in claim 1.

4. The method for preparing the sulfur-bridged bimetallic alkyne complex according to claim 3, characterized in that, The amount of alkyne used is the complex [Cp*M] 1 ( μ -bdt)M 2 The amount of substance is 1 to 5 times that of [Cp*], ultimately yielding [Cp*M]. 1 ( μ - η 1 : η 2 -bdt)( μ - η 2 : η 1 -HC-CR 3 M 2 Cp*][PF6].

5. The method for preparing the sulfur-bridged bimetallic acetylene complex according to claim 3, characterized in that, The amount of alkyne used is the complex [Cp*M] 1 ( μ -bdt)M 2 The amount of substance is 5 to 7 times that of [Cp*], ultimately yielding [Cp*M]. 1 ( μ -bdt)( μ - η 2 : η 2 -HC≡CR 3 M 2 Cp*][PF6 2。 6. The method for preparing the sulfur-bridged bimetallic alkyne complex according to claim 4, characterized in that, In [Cp*M 1 ( μ - η 1 : η 2 -bdt)( μ - η 2 : η 1 -HC-CR 3 M 2 [Cp*][PF6] was added in an amount equal to that of cobalt dicene (CoCp2), and the reaction was continued for 1–24 h after the temperature was raised to room temperature. The solvent was removed under vacuum, and the product was extracted with n-hexane. The solvent was then removed under reduced pressure to obtain the complex [Cp*M]. 1 ( μ - η 1 : η 2 -bdt)( μ - η 2 : η 1 -HC-CR 3 M 2 Cp*].

7. The method for preparing a sulfur-bridged dimetallaldehyde complex according to claim 3, characterized by, Furthermore, the alkyne is preferably any one of phenylacetylene, methylphenylacetylene, and acetylene.

8. The method for preparing the sulfur-bridged bimetallic alkyne complex according to claim 3, characterized in that, Furthermore, the reaction occurs at carbon number C 10 The following ethers and benzenes have a carbon number of C 10 The following alkylbenzenes have the following carbon number (C): 10 The following alkanes and halogenated hydrocarbons are subjected to this process.

9. An application of a sulfur-bridged bimetallic alkynyl complex, characterized in that, Used for the synthesis of 1,4-diphenylbutyne.

10. The application of the sulfur-bridged bimetallic alkynyl complex according to claim 9, characterized in that, The method for synthesizing 1,4-diphenylbutyne includes the following steps: In a nitrogen atmosphere, the sulfur-bridged bimetallic yne complex was dissolved in dichloromethane, and then the atmosphere was replaced with air to allow the reaction to proceed. The solution gradually turned dark green. The reaction system was then placed at -100°C to 25°C, and 1 to 2 times the amount of CoCp2 was added to react for 0.5 to 48 h. The solvent was removed under vacuum, and the low-polarity product was extracted with n-hexane. The target product, 1,4-diphenylbutyne, was then separated by column chromatography.

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