A transition metal bis-silylene carbene complex, a preparation method thereof, and an application thereof

Abstract

The present invention provides a transition metal bis(silylene)carbene complex, a preparation method thereof, and an application thereof. The transition metal bis(silylene)carbene complex includes a central transition metal, two silylene carbene ligands, and an outer ligand, where the outer ligand is a six-coordinate benzene ring or tert-butyl isocyanate, and the transition metal is selected from one of Co, Fe, and Mn. The transition metal bis(silylene)carbene complex of the present invention uses an azasilacyclopropenylidene as a stabilizing group and a transition metal as a central atom to form a bis(silylene)carbene coordination mode with a zero-valent transition metal center, has excellent hydrosilylation catalytic performance, and can achieve structural diversification by changing the ligands connected to the metal center; the synthesis method is efficient, has low energy consumption, a single product, is easy to purify, and has high selectivity. The transition metal bis(silylene)carbene complex obtained by using this synthesis method can be used as a catalyst in hydrosilylation reactions.

Description

Technical Field

[0001] The present invention relates to the technical field of metal silylcarbene, and particularly to a transition metal bis(silylcarbene) complex, a preparation method thereof, and an application thereof. Background Art

[0002] Silylcarbene has become an important ligand in metal coordination chemistry due to its strong electron-donating ability. At the same time, due to the high yield, simple equipment, and easy industrialization of the hydrosilylation reaction process, in order to carry out hydrosilylation applications more efficiently, the preparation of good hydrosilylation carbene reagents has become an important topic for hydrosilylation. Since hydrosilylation carbene is not easily obtained and usually needs to be stabilized by Lewis acid or Lewis base, when hydrosilylation carbene complexes with metals, especially transition metal groups, stable hydrosilylation carbene metal complexes can be formed. The silicon-hydrogen bond in such complexes exists stably and can be well applied to the hydrosilylation catalytic reaction of organic compounds.

[0003] The methods for synthesizing hydrosilylation carbene metal complexes mainly include: 1) direct complexation of azacyclic silylcarbene with metals (Inorg. Chem. 2017, 56, 10061 - 10069), and 2) obtaining stable hydrosilylation metal complexes by using hydrosilylation reagents such as LiBHEt3 for metal silylcarbene complexes (Chem. Eur. J. 2012, 18, 13355). However, the above methods have many limitations, such as difficult access to reaction raw materials, low stability of hydrogenation products, low reaction yields, etc., which greatly limit the synthesis and application of hydrosilylation carbene metal complexes. Since transition metals play an important role in metal chemistry, especially in organometallic catalysis, and the application of transition metals in similar substances is extremely rare, the synthesis of stable transition metal-complexed hydrosilylation carbene and the realization of the green chemistry concept of efficient development have important research significance. Summary of the Invention

[0004] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a transition metal bis(silylcarbene) complex, a preparation method thereof, and an application thereof, which are used to solve the problems of difficult access to reaction raw materials, low stability of hydrogenation products, and low reaction yields of hydrosilylation carbene metal complexes in the prior art.

[0005] To achieve the above object and other related objects, the present invention is obtained by including the following technical solutions.

[0006] The present invention provides a transition metal bis(silylcarbene) complex, which includes a central transition metal, two silylcarbene ligands, and an outer ligand. The outer ligand is a hexacoordinate benzene ring or tert-butyl isocyanate, and the transition metal is selected from one of Co, Fe, and Mn.

[0007] Preferably, the silylcarbene ligand is an azacyclic silylcarbene.

[0008] Preferably, the aza - cyclic silylene is 1,3 - di - tert - butyl - 4 - phenyl bis(aza - cyclic silylene).

[0009] Preferably, the structural formula of the transition metal bis(silylene) carbene complex is as shown in Formula I:

[0010]

[0011] In Formula I, M is the central transition metal, and the transition metal is selected from one of Co, Fe, and Mn;

[0012] L is the external ligand, and the external ligand is a six - coordinated benzene ring or tert - butyl isocyanate;

[0013] t Bu is tert - butyl, and Ph is phenyl.

[0014] More preferably, in Formula I, L is a six - coordinated benzene ring, and M is Fe, and its structural formula is as shown in Formula II:

[0015]

[0016] In Formula II, t Bu is tert - butyl, and Ph is phenyl.

[0017] More preferably, in Formula I, L is tert - butyl isocyanate, and M is Fe, and its structural formula is as shown in Formula III:

[0018]

[0019] In Formula III, t Bu is tert - butyl, and Ph is phenyl.

[0020] The second object of the present invention is to provide a method for synthesizing a transition metal bis(silylene) carbene complex. The compound shown in Formula IV and lithium tri - sec - butylborohydride are subjected to a substitution reaction in a reaction medium to obtain the transition metal bis(silylene) carbene complex;

[0021]

[0022] In Formula IV, X is Cl or Br;

[0023] M is the central transition metal, and the central transition metal is selected from one of Co, Fe, and Mn;

[0024] L is the external ligand, and the external ligand is a six - coordinated benzene ring or tert - butyl isocyanate;

[0025] t Bu is tert - butyl, and Ph is phenyl.

[0026] More preferably, in the compound represented by Formula IV, M is Fe, L is tert-butyl isocyanate, and X is Cl, and its structural formula is as shown in Formula V:

[0027]

[0028] The synthesis method of the compound represented by Formula V is as follows: reacting the compound represented by Formula VI and tert-butyl isocyanate in a reaction medium to obtain the compound represented by Formula V;

[0029]

[0030] In Formulas V and VI, t Bu is tert-butyl, and Ph is phenyl.

[0031] Preferably, the reaction medium is diethyl ether.

[0032] Preferably, the molar ratio of the compound represented by Formula IV to lithium tri-sec-butylborohydride is 1:(2-3); more preferably 1:2.1.

[0033] Preferably, the molar ratio of the compound represented by Formula VI to tert-butyl isocyanate is 1:(3-5); more preferably 1:4.

[0034] Preferably, the reaction is carried out at 25-35 °C.

[0035] Preferably, the reaction further includes a purification process.

[0036] The third object of the present invention is to provide an application of a transition metal bis(silyl)carbene complex as a catalyst in a hydrosilylation reaction.

[0037] As described above, the transition metal bis(silyl)carbene complex of the present invention, its preparation method and application have the following beneficial effects: the transition metal bis(silyl)carbene complex of the present invention uses a N-heterocyclic silylene (NHSi) as a stabilizing group and a transition metal as a central atom to form a bis(silylene) coordination mode with a zero-valent transition metal center, has excellent hydrosilylation catalytic performance, and can achieve structural diversification by changing the ligands connected to the metal center; the synthesis method is efficient, has low energy consumption, a single product, is easy to purify, and has high selectivity. The transition metal bis(silyl)carbene complex obtained by this synthesis method can be used as a catalyst in a hydrosilylation reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It shows a single crystal diffraction structural diagram of the transition metal bis(silyl)carbene complex represented by Formula II prepared in Example 1.

[0039] Figure 2It shows the 1H NMR spectrum of the transition metal bis-silylene carbene complex shown in Formula II prepared in Example 1.

[0040] Figure 3 It shows the single crystal X-ray diffraction structural diagram of the dichlorosilylene isocyanide coordinated iron complex shown in Formula V prepared in Example 2.

[0041] Figure 4 It shows the single crystal X-ray diffraction structural diagram of the transition metal bis-silylene carbene complex shown in Formula III prepared in Example 2.

[0042] Figure 5 It shows the 1H NMR spectrum of the transition metal bis-silylene carbene complex shown in Formula III prepared in Example 2.

[0043] Figure 6 It shows the effect diagrams of the hydrosilylation reaction with different catalyst dosages in Example 1. Detailed implementation manners

[0044] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0045] It should be noted that the process equipment or devices not specifically noted in the following examples all adopt the conventional equipment or devices in the art.

[0046] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combined steps or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated; it should also be understood that the combined connection relationship between one or more devices / devices mentioned in the present invention does not exclude the existence of other devices / devices before and after the combined devices / devices or the insertion of other devices / devices between these two explicitly mentioned devices / devices, unless otherwise stated. Moreover, unless otherwise stated, the numbers of each method step are only convenient tools for identifying each method step, rather than limiting the arrangement order of each method step or the scope in which the present invention can be implemented. The change or adjustment of their relative relationship, without substantial change in technical content, should also be regarded as the scope in which the present invention can be implemented.

[0047] In an embodiment of the present application, a specific transition metal bis(silylene)carbene complex is provided. The transition metal bis(silylene)carbene complex includes a central transition metal, two silylene carbene ligands, and an outer ligand. The outer ligand is a hexacoordinated benzene ring or tert-butyl isocyanate, and the transition metal is selected from one of Co, Fe, and Mn.

[0048] In a specific embodiment, the silylene carbene ligand is a N-heterocyclic silylene carbene.

[0049] In a specific embodiment, the N-heterocyclic silylene carbene is 1,3-di-tert-butyl-4-phenyl bis(N-heterocyclic silylene) carbene.

[0050] In a specific embodiment, the structural formula of the transition metal bis(silylene)carbene complex is shown in Formula I:

[0051]

[0052] In Formula I, M is the central transition metal, and the transition metal is selected from one of Co, Fe, and Mn;

[0053] L is the outer ligand, and the outer ligand is a hexacoordinated benzene ring or tert-butyl isocyanate;

[0054] t Bu is tert-butyl, and Ph is phenyl.

[0055] In a more specific embodiment, in Formula I, L is a hexacoordinated benzene ring, M is Fe, and its structural formula is shown in Formula II:

[0056]

[0057] In Formula II, t Bu is tert-butyl, and Ph is phenyl.

[0058] In a more specific embodiment, in Formula I, L is tert-butyl isocyanate, M is Fe, and its structural formula is shown in Formula III:

[0059]

[0060] In Formula III, t Bu is tert-butyl, and Ph is phenyl.

[0061] The embodiment of the present application also provides a synthesis method of a transition metal bis(silylene)carbene complex. The compound shown in Formula IV and lithium tri-sec-butylborohydride are subjected to a substitution reaction in a reaction medium to obtain the transition metal bis(silylene)carbene complex;

[0062]

[0063] In Formula IV, X is Cl or Br;

[0064] M is a central transition metal, and the transition metal is selected from one of Co, Fe, and Mn;

[0065] L is an external ligand, and the external ligand is a six-coordinate benzene ring or tert-butyl isocyanate;

[0066] t Bu is tert-butyl, and Ph is phenyl.

[0067] In a more specific embodiment, lithium tri-sec-butylborohydride is used to prepare a solution in a tetrahydrofuran solvent with a concentration of 1 M / L.

[0068] In a more specific embodiment, in the compound shown in Formula IV, M is Fe, L is tert-butyl isocyanate, and X is Cl, and its structural formula is shown in Formula V:

[0069]

[0070] The synthesis method of the compound shown in Formula V is: reacting the compound shown in Formula VI and tert-butyl isocyanate in a reaction medium to obtain the compound shown in Formula V;

[0071]

[0072] In Formulas V and VI, t Bu is tert-butyl, and Ph is phenyl.

[0073] In a more specific embodiment, the synthesis route of the transition metal disilylcarbene complex shown in Formula II is as follows:

[0074]

[0075] Reacting the compound shown in Formula VI and lithium tri-sec-butylborohydride in a reaction medium to obtain the transition metal disilylcarbene complex shown in Formula II. The reaction mechanism is that lithium tri-sec-butylborohydride acts as a reducing agent and a source of hydride ions. After reacting with the Si-Cl bond, a hydrogen atom replaces the Cl atom, and LiCl and B(s-Bu)3 are formed.

[0076] In a more specific embodiment, the compound shown in Formula VI is prepared according to the preparation method described in Dalton Trans., 2020, 49, 12586–12591.

[0077] In a more specific embodiment, the synthesis route of the transition metal disilylcarbene complex shown in Formula III is as follows:

[0078]

[0079] 1) React a compound with the structural formula shown in Formula VI and tert-butyl isocyanate in a reaction medium to obtain a compound with the structural formula shown in Formula V;

[0080] 2) Carry out a substitution reaction on the compound with the structural formula shown in Formula V and lithium tri-sec-butylborohydride in a reaction medium to obtain the transition metal disilylcarbene complex shown in Formula III. The reaction mechanism is that lithium tri-sec-butylborohydride acts as a reducing agent and a source of hydride ions. After reacting with the Si-Cl bond, a hydrogen atom replaces the Cl atom, and LiCl and B(s-Bu)3 are formed.

[0081] In a specific embodiment, the reaction medium is diethyl ether.

[0082] In a specific embodiment, the molar ratio of the compound with the structural formula shown in Formula IV to lithium tri-sec-butylborohydride is 1:(2 - 3); specifically 1:2.1.

[0083] In a specific embodiment, the molar ratio of the compound with the structural formula shown in Formula VI to tert-butyl isocyanate is 1:(3 - 5); specifically 1:4.

[0084] In a specific embodiment, the reactions are all carried out at 25 - 35 °C.

[0085] In a specific embodiment, the reaction also includes a purification process after the reaction.

[0086] In a more specific embodiment, the purification process includes draining, redissolving in a solvent, and filtering; the solvent is n-pentane.

[0087] The embodiments of the present application also provide an application of a transition metal disilylcarbene complex as a catalyst in a hydrosilylation reaction.

[0088] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0089] In the following embodiments of the present application, the compound shown in Formula VI is prepared according to the preparation method described in Dalton Trans., 2020, 49, 12586 - 12591.

[0090] Example 1

[0091] This example provides a transition metal disilylcarbene complex with the structural formula shown in Formula II:

[0092]

[0093] In formula II, t Bu is tert-butyl and Ph is phenyl.

[0094] This example also provides a synthetic route for the transition metal disilylcarbene complex shown in formula II:

[0095]

[0096] The specific synthesis method includes the following steps: Take 1 mL of lithium tri-sec-butylborohydride and dissolve it in 4.68 mL of tetrahydrofuran solvent to prepare a 1 M / L solution of lithium tri-sec-butylborohydride in tetrahydrofuran; Take 160 μL of the lithium tri-sec-butylborohydride tetrahydrofuran solution and add it to a 10 mL ether solution of the compound shown in formula VI (55 mg, 0.076 mmol); Under the action of a magnetic stirrer, stir the reaction at room temperature for 3 h; After the reaction is completed, evacuate the solvent and all volatile substances under reduced pressure to obtain a solid. Redissolve the above solid with n-hexane solvent and filter off the insoluble substances. Collect the solution part, repeat evacuating the solvent and drying at room temperature to obtain a solid; Redissolve the solid obtained in step 4) with 5 mL of n-pentane and 1 mL of a mixed solvent, concentrate it, and let it stand in a -30 °C refrigerator for 10 days to obtain a red wine-colored transition metal disilylcarbene complex with the structural formula shown in formula II, and the yield is 75%.

[0097] The single crystal diffraction structure diagram of the transition metal disilylcarbene complex shown in formula II prepared in this example is as Figure 1 shown, and the 1H NMR spectrum is as Figure 2 shown. It can be clearly seen from the figure that a Si-H characteristic peak appears at δ = 6.6 ppm, indicating that the transition metal disilylcarbene complex has been successfully synthesized.

[0098] This example also provides an application of a specific transition metal disilylcarbene complex shown in formula II as a catalyst in the hydrosilylation reaction,

[0099] Using acetophenone and triethylsilane as reaction raw materials, tetrahydrofuran as the reaction solvent, and the transition metal bis(silyl)carbene complex shown in Formula II as the catalyst, the hydrosilylation reaction is carried out to synthesize 1-phenylethanol compounds. The specific steps are as follows: Select 1 equivalent of acetophenone reagent and 1.5 equivalents of triethylsilane as raw materials. Based on the total amount of acetophenone, the transition metal bis(silyl)carbene complex shown in Formula IV with different catalyst dosages (0.5 mol%, 1 mol%, 2.5 mol%) is used to heat and react in a tetrahydrofuran solution at 70 °C for 30 minutes; after the reaction is completed, it is quenched with a 2 M sodium hydroxide solution for 1 hour. After quenching, 10 mL of ethyl acetate solution is added for extraction; 10 μL of the ethyl acetate extract obtained after extraction is mixed in 2 mL of ethyl acetate solution and loaded for gas chromatography-mass spectrometry testing. The catalytic results with different catalyst dosages are as Figure 6 shown.

[0100] As can be seen from Figure 6 , within the same time, when the catalyst dosage is 0.5 mol%, there is still acetophenone residue after the reaction ends, because the catalyst dosage is too low and acetophenone is not completely converted. When the catalyst dosage is increased to 1 mol% or 2.5 mol%, acetophenone has been completely converted into the reduction product 1-phenylethanol. Therefore, when the dosage of the transition metal bis(silyl)carbene complex shown in Formula II as the catalyst is only 1 mol%, a relatively high catalytic efficiency can be achieved.

[0101] Example 2

[0102] This example provides a transition metal bis(silyl)carbene complex with the structural formula shown in Formula III:

[0103]

[0104] In Formula III, t Bu is tert-butyl and Ph is phenyl.

[0105] This example also provides a synthesis route of a transition metal bis(silyl)carbene complex with the structural formula shown in Formula III:

[0106]

[0107] The specific synthesis method includes the following steps:

[0108] 1) Use a pipette to add 27 μL of tert-butyl isocyanate to an ether solution of 50 mg (0.070 mmol) of the compound shown in Formula VI (the preparation method refers to Dalton Trans., 2020, 49, 12586–12591). Under the action of a magnetic stirrer, stir the reaction at room temperature for 12 h. After the reaction is completed, evacuate the solvent and all volatile substances under reduced pressure. Redissolve the solid obtained after evaporation in n-hexane solvent and filter off the insoluble substances. Collect the solution part; evacuate the solvent under reduced pressure and dry at room temperature to obtain a solid; redissolve the above solid in 5 mL of n-pentane, concentrate it, and let it stand in a -30 °C refrigerator for 3 days to obtain the red-brown dichlorosilylene isocyanide coordinated iron complex shown in Formula V with a yield of 97%. The single crystal X-ray diffraction pattern is as shown in Figure 3 shown;

[0109] 2) Dissolve 1 mL of lithium tri-sec-butylborohydride in 4.68 mL of tetrahydrofuran solvent to prepare a 1 M / L solution of lithium tri-sec-butylborohydride in tetrahydrofuran; add 140 μL of the lithium tri-sec-butylborohydride tetrahydrofuran solution to an ether solution of 60 mg (0.067 mmol) of the compound described in Formula V; under the action of a magnetic stirrer, stir the reaction at room temperature for 3 h. After the reaction is completed, evacuate the solvent and all volatile substances under reduced pressure. Redissolve the solid obtained after evaporation in n-hexane solvent and filter off the insoluble substances. Collect the solution part, evacuate the solvent under reduced pressure and dry at room temperature to obtain a solid. Redissolve the above solid in 5 mL of n-pentane, concentrate it, and let it stand in a -30 °C refrigerator for 10 days to obtain the red-brown transition metal bis-silylene complex shown in Formula III with a yield of 82%.

[0110] The single crystal X-ray diffraction pattern of the transition metal bis-silylene complex shown in Formula III prepared in this example is as shown in Figure 4 shown, and the 1H NMR spectrum is as shown in Figure 5 shown. It can be clearly seen from the figure that a Si-H characteristic peak appears at B: δ = 7.34 ppm, indicating the successful synthesis of the transition metal bis-silylene complex.

[0111] Examples 3-5

[0112] The differences between Examples 3-5 and Example 1 are that the types of central transition metals are different and the halogenated groups of the compounds shown in Formula VI are different. Specifically, refer to Table 1, and the rest of the processes are exactly the same.

[0113] Examples 6-8

[0114] The differences between Examples 6-8 and Example 2 are that the types of central transition metals are different and the halogenated groups of the compounds shown in Formula VI and Formula V are different. Specifically, refer to Table 1, and the rest of the processes are exactly the same.

[0115] Table 1. Structural formula substituents of transition metal disilylcarbene complexes in Examples 1-8

[0116] Central transition metal M External ligand Halogenated group in Formula VI Example 1 Fe Six-coordinate benzene ring Cl Example 2 Fe tert-Butyl isocyanate Cl Example 3 Co Six-coordinate benzene ring Br Example 4 Mn Six-coordinate benzene ring Cl Example 5 Mn Six-coordinate benzene ring Br Example 6 Co tert-Butyl isocyanate Br Example 7 Mn tert-Butyl isocyanate Cl Example 8 Fe tert-Butyl isocyanate Br

[0117] The effects of the transition metal disilylcarbene complexes prepared in Examples 2-8 when used as catalysts in hydrosilylation reactions are equivalent to those in Example 1 and will not be elaborated here.

[0118] In summary, the transition metal disilylcarbene complexes of the present invention use N-heterocyclic silylene (NHSi) as a stabilizing group and a transition metal as the central atom to form a bis-silylene coordination mode with a zero-valent transition metal center. They have excellent hydrosilylation catalytic performance and can achieve diverse structures by changing the ligands connected to the metal center; the synthesis method is efficient, with low energy consumption, a single product, and easy purification, and has high selectivity. The transition metal disilylcarbene complexes obtained by this synthesis method can be used as catalysts in hydrosilylation reactions. Therefore, the present invention effectively overcomes various drawbacks in the prior art and has high industrial utilization value.

[0119] The above examples are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above examples without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A transition metal bis-silylene carbene complex, characterized in that, The structural formula of the transition metal disilylcarbene complex is shown in Formula I: ， In Formula I, M is the central transition metal, and the transition metal is selected from one of Co, Fe, and Mn; L is the external ligand, and the external ligand is a six-coordinate benzene ring or tert-butyl isocyanate; t Bu is tert-butyl and Ph is phenyl.

2. The transition metal disilylcarbene complex according to claim 1, characterized in that: In Formula I, L is a six-coordinate benzene ring and M is Fe, and its structural formula is shown in Formula II: ， In formula II, t Bu is a tert-butyl group and Ph is a phenyl group.

3. The transition metal disilylcarbene complex according to claim 1, wherein: In Formula I, L is tert-butyl isocyanate and M is Fe, and its structural formula is shown in Formula III: ， In formula III, t Bu is tert-butyl and Ph is phenyl.

4. A method for synthesizing a transition metal bis-silylcarbene complex as described in any one of claims 1-3, characterized in that: The transition metal disilylcarbene complex is prepared by carrying out a substitution reaction on the compound shown in Formula IV and lithium tris(sec-butyl)borohydride in a reaction medium; ， In Formula IV, X is Cl or Br; M is the central transition metal, and the transition metal is selected from one of Co, Fe, and Mn; L is the external ligand, and the external ligand is a six-coordinate benzene ring or tert-butyl isocyanate; t Bu is tert-butyl and Ph is phenyl.

5. The synthesis method according to claim 4, wherein: In the compound shown in Formula IV, M is Fe, L is tert-butyl isocyanate, and X is Cl, and its structural formula is shown in Formula V: ， The synthesis method of the compound shown in Formula V is: reacting the compound shown in Formula VI and tert-butyl isocyanate in a reaction medium to obtain the compound shown in Formula V; ， In Formula V and Formula VI, t Bu is a tert-butyl group, and Ph is a phenyl group.

6. The synthesis method according to claim 5, wherein: The reaction medium is diethyl ether; and / or, the molar ratio of the compound shown in Formula IV to lithium tris(sec-butyl)borohydride is 1:(2 - 3); and / or, the molar ratio of the compound shown in Formula VI to tert-butyl isocyanate is 1:(3 - 5); and / or, the reaction is carried out at 25 - 35 °C; and / or, a purification process is also included after the reaction.

7. Use of the transition metal disilylcarbene complex as claimed in any one of claims 1 - 3 as a catalyst in a hydrosilylation reaction.

Images