A novel six-coordinate magnesium complex, its preparation method and application

Abstract

The present invention provides a novel six-coordinate magnesium complex, a preparation method thereof and an application thereof, solving the technical problem that the existing disclosed magnesium complexes are still limited in actual catalytic applications. The present invention uses tert-butylmagnesium reagent to react with 4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy), in-situ reducing 4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy) to a radical anion, and then an addition reaction occurs to obtain the target product. The preparation method of the present invention is simple, the raw materials for preparation are simple and easily available, the yield is considerable, and the product has unique catalytic activity and can be truly applied as a catalyst in a catalytic reaction system.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnesium complex synthesis, and particularly relates to a novel six-coordinate magnesium complex, a preparation method thereof, and an application thereof. Background Art

[0002] In the periodic table of elements, magnesium is located in the second main group of the third period and is a typical alkaline earth metal. Currently, magnesium complexes applied in organic synthesis reactions can generally be divided into four categories (as shown in Figure 1 ). In the catalytic reaction system, inorganic magnesium salts have been widely used as Lewis acid catalysts (a in Figure 1 ). Under specific conditions, although inorganic magnesium salts have been proven to be able to catalyze addition and ring-opening reactions, etc., they have disadvantages such as high reaction temperature, poor solubility, weak coordination ability, and narrow substrate scope, resulting in low catalytic activity and poor selectivity of magnesium salts, and there is still a certain distance from actual application. In subsequent research, it was found that dialkylmagnesium and dialkoxymagnesium with stronger basicity were gradually applied to addition, ring-opening, and decarbonylation reactions (b in Figure 1 ), and the reports of these literatures further confirmed the certain universality of magnesium catalysts. In asymmetric synthesis, the research groups of Professor Wang Rui at Lanzhou University and Professor Feng Xiaoming at Sichuan University respectively reported that Lewis acidic metal magnesium salts were used as catalysts (d in Figure 1 ), and through the addition of different types of chiral ligands, the asymmetric reactions catalyzed by magnesium developed rapidly and efficiently. In 2007, the Jones research group first synthesized a stable monovalent magnesium complex. On this basis, more than 25 magnesium complexes with β-diketiminato (BDI) and its derivatives as ligands were synthesized. In 2021, the Harder group synthesized the first zero-valent magnesium complex with BDI derivatives as ligands on the basis of previous work. The reports of these complexes provided ideas for the development of novel magnesium complex catalysts. However, among the reported magnesium complexes, those truly applied in the catalytic reaction system are few.

[0003] Therefore, it is urgent to develop novel magnesium complex catalysts that not only have a novel skeleton structure but also possess unique catalytic activity. Summary of the Invention

[0004] The purpose of the present invention is to solve the deficiencies that the existing disclosed magnesium complexes are still limited in actual catalytic applications, and to provide a novel six-coordinate magnesium complex, a preparation method thereof, and an application thereof.

[0005] To achieve the above purpose, the technical solution provided by the present invention is:

[0006] A novel six-coordinate magnesium complex, characterized in that the structural formula is as follows:

[0007]

[0008] The preparation method of the above novel six-coordinate magnesium complex is characterized in that the steps are as follows:

[0009] 1) Under the protection of an inert gas in a dry environment, 4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy) is fully dissolved in an aromatic organic solvent to obtain Solution I; wherein, the aromatic organic solvent serves as a reaction solvent, and its amount only needs to be sufficient to fully dissolve 4,4′-di-tert-butyl-2,2′-bipyridine.

[0010] 2) After cooling the Solution I obtained in step 1) to 0 - 5 °C, a tetrahydrofuran solution of tert-butylmagnesium chloride (i.e., Grignard reagent) is added dropwise to Solution I, and the reaction is carried out with stirring at room temperature; after the reaction is completed, the solvent is removed under vacuum, the reaction product is extracted with an organic solvent multiple times, and filtered under the protection of an inert gas, and the filtrates are combined and concentrated to obtain a concentrated solution.

[0011] 3) The poor solvent is added dropwise to the concentrated solution obtained in step 2) to obtain a mixture, and the mixture is stored in an environment not higher than -15 °C for at least 72 hours to obtain a red crystal novel six-coordinate magnesium complex (Mg-Complex1), which is dried and stored in a sealed manner; the added volume of the poor solvent is greater than the volume of the concentrated solution, and its main purpose is to make the concentrated solution supersaturated at low temperature to facilitate crystal precipitation, and the dropwise addition is carried out slowly mainly to prevent precipitation in the solution.

[0012] Furthermore, the molar ratio of 4,4′-di-tert-butyl-2,2′-bipyridine to tert-butylmagnesium chloride is 1.1 - 1.5∶1.0 - 1.2.

[0013] Furthermore, in step 2), the reaction time is 18 - 24 h.

[0014] Furthermore, because the target product is extremely sensitive to air and water, all operations after the reaction in step 2) are carried out in a glove box.

[0015] Furthermore, in step 2), the dropping rate of tert-butylmagnesium chloride is 0.8 ml - 1.2 ml per minute;

[0016] In step 3), the dropping rate of the poor solvent is 0.8 ml - 1.2 ml per minute.

[0017] It can be added dropwise using a syringe.

[0018] Furthermore, in step 1), the aromatic organic solvent is toluene, o-xylene or benzene;

[0019] In step 3), the poor solvent is n-hexane, cyclohexane or petroleum ether.

[0020] Further, in step 3), the organic solvent is toluene, ether, ethyl acetate, chlorobenzene or benzene;

[0021] Extract three times with an organic solvent, combine the filtrates and concentrate to 1 / 3 of the total volume.

[0022] Further, the inert gas is nitrogen or argon.

[0023] Meanwhile, the present invention also provides the application of the above-mentioned novel six-coordinate magnesium complex as a catalyst for addition, ring-opening and decarbonylation reactions.

[0024] Advantages of the present invention:

[0025] The present invention designs a novel six-coordinate magnesium complex. The reaction of tert-butylmagnesium reagent with 4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy) is used to in-situ reduce 4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy) to a radical anion, and then an addition reaction occurs to obtain the target product. The preparation method of the present invention is simple, the raw materials for preparation are simple and easy to obtain, the yield is considerable, and the product has unique catalytic activity and can be truly applied as a catalyst in the catalytic reaction system. The chemical equation is as follows:

[0026] Description of the drawings

[0027] Figure 1 Common current magnesium catalyst types and representative structures;

[0028] Figure 2 Crystal structure obtained by characterizing the product of Example 1 through X-ray single crystal diffraction;

[0029] Figure 3 X-ray photoelectron spectroscopy diagram of the product of Example 1;

[0030] Figure 4 Electron paramagnetic resonance diagram of the product of Example 1;

[0031] Figure 5 Ultraviolet absorption spectrum diagram of the product of Example 1. Detailed implementation manners

[0032] The following further describes the content of the present invention in detail with reference to the drawings and specific examples:

[0033] Example 1

[0034] Preparation of the six-coordinate magnesium complex, the steps are as follows:

[0035] In a dry Schlenk tube, dtbpy (4,4′-di-tert-butyl-2,2′-bipyridine, 1.33 mmol) was added under nitrogen atmosphere and dissolved thoroughly in 3 mL of toluene solution. After cooling to 0 °C, a solution of tert-butylmagnesium chloride in tetrahydrofuran (1.1 mL, 1.0 M THF solution, 1.1 mmol) was added dropwise via a syringe, and the resulting solution was stirred at room temperature for 18 hours. After removing the solvent under vacuum in the glove box, the residue was extracted with toluene (3 × 5 mL), then filtered under nitrogen atmosphere. The combined solution was concentrated to 5 mL, and then 10 mL of n-hexane was added dropwise above the concentrated solution. The mixture was stored in a refrigerator at -30 °C. After 3 days, red crystals were obtained.

[0036] Since the red sample is extremely sensitive to air and water, all operations after the reaction was completed were carried out in the glove box.

[0037] Example 2

[0038] In a dry Schlenk tube, dtbpy (4,4′-di-tert-butyl-2,2′-bipyridine, 1.4 mmol) was added under nitrogen atmosphere and dissolved thoroughly in 5 mL of o-xylene solution. After cooling to 5 °C, a solution of tert-butylmagnesium chloride in tetrahydrofuran (1.0 mL, 1.0 M THF solution, 1.0 mmol) was added dropwise via a syringe, and the resulting solution was stirred at room temperature for 20 hours. After removing the solvent under vacuum in the glove box, the residue was extracted with diethyl ether (3 × 7 mL), then filtered under nitrogen atmosphere. The combined solution was concentrated to 7 mL, and then 15 mL of cyclohexane was added dropwise above the concentrated solution. The mixture was stored in a refrigerator at -15 °C. After 3 days, red crystals were obtained.

[0039] Example 3

[0040] In a dry Schlenk tube, dtbpy (4,4′-di-tert-butyl-2,2′-bipyridine, 1.5 mmol) was added under argon atmosphere and dissolved thoroughly in 8 mL of benzene solution. After cooling to 3 °C, tert-butylmagnesium chloride (1.2 mL, 1.0 M THF solution, 1.2 mmol) was added dropwise via a syringe, and the resulting solution was stirred at room temperature for 2 April 2024 16:24:44 24 hours. After removing the solvent under vacuum in the glove box, the residue was extracted with chlorobenzene (3 × 8 mL), then filtered under argon atmosphere. The combined solution was concentrated to 10 mL, and then 20 mL of petroleum ether was added dropwise above the concentrated solution. The mixture was stored in a refrigerator at -25 °C. After 3 days, red crystals were obtained.

[0041] The following structural characterizations were performed on the hexacoordinate magnesium complex prepared in Example 1:

[0042] 1. X-ray single crystal diffraction

[0043] The research team of the present invention characterized the structure of the obtained red crystal by X-ray single crystal diffraction and obtained the crystal structure as shown in Figure 2 and the data in Table 1 and Table 2.

[0044] Table 1 Crystal data of magnesium complex

[0045]

[0046]

[0047] Table 2 Bond lengths of magnesium complex and angles (°)

[0048]

[0049]

[0050] From Figure 2 Table 1 and Table 2, it can be analyzed that the magnesium complex crystallizes in the triclinic space group P-1. The central metal magnesium ion is coordinated by six neutral nitrogen atoms to form a distorted geometric octahedron. Two tert-butyl groups are inserted into the meta positions of N3 and N5 atoms, resulting in the deformation of these two pyridine rings. It can be clearly seen from the crystal structure that two pyridine rings are damaged, and tert-butyl addition occurs on the damaged pyridine rings, and the damaged pyridine rings are severely distorted.

[0051] 2. X-ray photoelectron spectroscopy (XPS)

[0052] After obtaining the magnesium complex, the research team of the present invention hoped to confirm the valence state of the central metal atom. Therefore, the energies of its 1s and 2p orbitals were characterized by XPS, and the results are as shown in Figure 3 It can be found that the energy of its 2p orbital is significantly smaller than that of tert-butylmagnesium chloride.

[0053] 3. Electron paramagnetic resonance (EPR)

[0054] The research team of the present invention characterized it by EPR, and the results are as shown in Figure 4As shown, the team tested the electron paramagnetic resonance of magnesium complexes at different frequencies and found the presence of free radicals. Subsequently, through the analysis of 170 GHz EPR, a complete set of spin Hamiltonian parameters including D, E, and g values were obtained by fitting the single spectrum of the complex (at 170 GHz) at 2K. The HF-EPR spectrum allows the extraction of all spin parameters of the standard spin Hamiltonian function. Here, higher-order Zeeman interactions are not considered, and the best fit was obtained with parameters S = 1, |D| = 3.41(2) cm-1, E = 0.05(1) cm-1, and g = 2.00. During the fitting process, it was found that the positive D value matched the experiment, while applying a negative D parameter led to a worse fit, thus proving the existence of two free radicals and the divalent positive state of the magnesium element.

[0055] 4. Ultraviolet spectrum (uv)

[0056] The research team of the present invention also analyzed the ultraviolet spectrum of the magnesium complex and obtained the results as Figure 5 shown. It can be clearly seen that there are obvious absorptions beside 300 nm and 400 nm, indicating the presence of a conjugated system in the complex.

[0057] 5. Catalytic application

[0058] The research team of the present invention believes that the magnesium complex prepared in Example 1 has catalytic activity and can be used as a catalyst. The performance was verified here:

[0059] Using Mg-Complex 1 as a catalyst, the reaction of phenylacetylene 1a with pinacol borane 2a gave the addition product in 65% yield;

[0060] Meanwhile, reactions with styrene 1b and 1-phenyl-1,3-butadiene 1c as substrates were also carried out separately, and the corresponding hydroboration products could be obtained under the same reaction conditions.

[0061] The chemical equation for the hydroboration reaction of unsaturated carbon-carbon bonds catalyzed by the specific magnesium complex and the product characterization results are as follows:

[0062]

[0063] 1 H NMR (500 MHz, CDCl3) δ 7.49 (d, J = 7.2 Hz, 2H), 7.40 (d, J = 18.4 Hz, 1H), 7.33 (t, J = 7.1 Hz, 2H), 7.29 (d, J = 7.0 Hz, 1H), 6.17 (d, J = 18.4 Hz, 1H), 1.31 (s, 12H). 13CNMR(125 MHz, CDCl3) δ 149.5, 137.5, 128.9, 128.6, 127.1, 83.4, 24.8.

[0064]

[0065] 1 H NMR(500 MHz, CDCl3) δ 7.23 (dt, J=15.4, 7.5 Hz, 4H), 7.14 (t, J=7.2 Hz, 1H), 2.77–2.72 (m, 2H), 1.21 (s, 12H), 1.16–1.12 (m, 2H). 13 C NMR(125 MHz, CDCl3) δ 144.3, 128.1, 127.9, 125.4, 83.0, 29.9, 24.8, 13.0.

[0066]

[0067] 1 H NMR(500 MHz, CDCl3) δ 7.32 (d, J=7.8 Hz, 2H), 7.26 (dd, J=13.7, 6.1 Hz, 2H), 7.17 (t, J=7.1 Hz, 1H), 6.37 (d, J=15.9 Hz, 1H), 6.28 (dt, J=15.8, 6.4 Hz, 1H), 2.34 (dd, J=14.5, 7.3Hz, 2H), 1.24 (s, 12H), 0.98 (t, J=7.7Hz, 2H). 13 CNMR(125MHz, CDCl3) δ 138.0, 132.7, 128.8, 128.4, 126.6, 125.9, 83.0, 27.3, 24.8, 10.7.

[0068] Thus, it can be seen that the hydroboration of unsaturated bonds can be achieved by using the magnesium complex of the present invention, further proving that the synthesized magnesium complex of the present invention has catalytic activity.

[0069] The research team of the present invention believes that by changing the structures of the Grignard reagent and bipyridine, this synthesis principle can also be extended to the preparation of novel skeleton magnesium complexes using bipyridine and its derivatives and Grignard reagents as raw materials. The general formula is as follows:

[0070]

[0071] Similarly, the prepared magnesium complex should have catalytic activity.

[0072] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A novel six-coordinate magnesium complex, characterized in that, The structural formula is as follows:

2. The preparation method of the novel six-coordinate magnesium complex according to claim 1, characterized in that, The steps are as follows: 1) Under a dry environment protected by an inert gas, 4,4'-di-tert-butyl-2,2'-bipyridine is fully dissolved in an aromatic organic solvent to obtain Solution I; 2) After cooling the Solution I obtained in step 1) to 0 - 5 °C, a tetrahydrofuran solution of tert-butylmagnesium chloride is added dropwise to Solution I, and the reaction is carried out with stirring at room temperature; after the reaction is completed, the solvent is removed under vacuum, the reaction product is extracted with an organic solvent multiple times, and filtered under the protection of an inert gas. The filtrates are combined and concentrated to obtain a concentrated solution; 3) A poor solvent is added dropwise to the concentrated solution obtained in step 2) to obtain a mixture, and the mixture is stored in an environment not higher than -15 °C for at least 72 hours to obtain a novel hexacoordinate magnesium complex, which is dried and stored in a sealed manner.

3. The preparation method of the novel hexacoordinate magnesium complex according to claim 2, characterized in that: The molar ratio of 4,4'-di-tert-butyl-2,2'-bipyridine to tert-butylmagnesium chloride is 1.1 - 1.5∶1.0 - 1.

2.

4. The preparation method of the novel hexacoordinate magnesium complex according to claim 3, characterized in that: In step 2), the reaction time is 18 - 24 h.

5. The preparation method of the novel hexacoordinate magnesium complex according to any one of claims 2 - 4, characterized in that: All operations after the reaction in step 2) are carried out in a glove box.

6. The preparation method of the novel hexacoordinate magnesium complex according to claim 5, characterized in that: In step 2), the dropping rate of tert-butylmagnesium chloride is 0.8 ml - 1.2 ml per minute; In step 3), the dropping rate of the poor solvent is 0.8 ml - 1.2 ml per minute.

7. The preparation method of the novel hexacoordinate magnesium complex according to claim 6, characterized in that: In step 1), the aromatic organic solvent is toluene, o-xylene or benzene; In step 3), the poor solvent is n-hexane, cyclohexane or petroleum ether.

8. The preparation method of the novel hexacoordinate magnesium complex according to claim 7, characterized in that: In step 3), the organic solvent is toluene, ether, ethyl acetate, chlorobenzene or benzene; The extraction is carried out three times with an organic solvent, and the filtrates are combined and concentrated to 1 / 3 of the total volume.

9. The preparation method of the novel hexacoordinate magnesium complex according to claim 2, characterized in that: The inert gas is nitrogen or argon.

10. The application of the novel hexacoordinate magnesium complex according to claim 1 as a catalyst.

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