Half-sandwich ruthenium complex containing nitrogen heterocyclic carbene ligand as well as preparation method and application of half-sandwich ruthenium complex

Abstract

The invention discloses a half-sandwich ruthenium complex containing a nitrogen heterocyclic carbene ligand and a preparation method and application thereof, the structural formula of the complex is # imgabs0 #, and X represents one of chloride ions, tetrafluoroborate ions, hexafluorophosphate ions or tetraphenylborate ions. The complex solves the problems that a transition metal complex catalyst for CO2 hydrogenation reaction is low in catalytic performance activity, rapid in inactivation, poor in water solubility, sensitive to air and water, difficult to synthesize and high in preparation cost, and a new thought is provided for resource utilization of CO2 and storage of hydrogen energy.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a half-sandwich ruthenium complex containing a nitrogen heterocyclic carbene ligand, a preparation method thereof, and an application thereof. Background Art

[0002] In recent decades, the consumption of fossil energy has been accompanied by the excessive emission of carbon dioxide (CO 2 ), leading to global warming and causing serious impacts on the ecological environment. From the perspective of the utilization and conversion of CO 2 and hydrogen storage, the field of CO 2 hydrogenation has received extensive attention. By using a catalyst to catalytically hydrogenate and reduce CO 2 to produce high-value-added chemicals such as formic acid, methanol and its derivatives, etc., while solving the problems of chemical fixation of CO 2 and hydrogen storage, and developing chemical substitutes for traditional energy sources to alleviate the global energy crisis. Formic acid is an important chemical raw material and also a good hydrogen storage medium. As a hydrogen carrier, formic acid can be easily converted into H 2 and CO 2 , which has attracted the attention of researchers. In addition, formic acid and formates are widely used in various industrial processes and are important products in people's daily lives. Therefore, the research on catalytic hydrogenation of CO 2 to formic acid has gradually received attention.

[0003] In recent years, the catalytic hydrogenation of CO 2 to formic acid by transition metal complexes has become an active research field. However, homogeneous catalysts for the catalytic hydrogenation reaction of CO 2 are mostly metal complexes containing phosphine ligands, which are sensitive to air and water, and the stability and water solubility of the complexes are poor. The catalytic hydrogenation reaction of CO 2 is mostly carried out in organic solvents with certain physiological toxicity, flammability and explosiveness. Therefore, it is of great significance to research and develop a new type of catalyst that is stable to air and water and apply it to efficiently catalyze the hydrogenation of CO 2 to formic acid in an aqueous solution system, which is in line with the green catalytic conversion of CO 2 . Summary of the Invention

[0004] Aiming at the above deficiencies in the prior art, the present invention provides a half-sandwich ruthenium complex containing a nitrogen heterocyclic carbene ligand, a preparation method thereof, and an application thereof. This complex solves the problems of low activity, fast deactivation, poor water solubility, sensitivity to air and water, difficult synthesis and high preparation cost of the transition metal complex catalyst for the CO 2 hydrogenation reaction, and provides a new idea for the resource utilization of CO 2 and the storage of hydrogen energy.

[0005] To achieve the above object, the technical solution adopted by the present invention to solve its technical problems is as follows:

[0006] A half-sandwich ruthenium complex containing a nitrogen heterocyclic carbene ligand, and the structural formula of the complex is:

[0007]

[0008] Among them, X represents one of a chloride ion, a tetrafluoroborate ion, a hexafluorophosphate ion, or a tetraphenylborate ion.

[0009] The preparation method of the above-mentioned half-sandwich ruthenium complex containing a nitrogen heterocyclic carbene ligand includes the following steps:

[0010] (1) Heat and reflux the nitrogen-nitrogen functionalized nitrogen heterocyclic carbene tridentate ligand and dichlorophenyl ruthenium (II) dimer in a first organic solvent, and then concentrate and recrystallize the reaction solution to obtain complex 1(Cl)

[0011] ([RuCl(η 6 -C 6 H 6 )(CNN)]Cl 2 );

[0012] (2) Mix complex 1(Cl)([RuCl(η 6 -C 6 H 6 )(CNN)]Cl 2 ) with a second organic solvent, add one of AgBF 4 , NaBF 4 , AgPF 6 , NaPF 6 and (C 6 H 5 ) 4 BNa thereto, stir and react, collect the precipitate, purify, and extract the product from the solution to obtain a half-sandwich ruthenium complex containing a nitrogen heterocyclic carbene ligand.

[0013] Further, in step (1), the molar ratio of the nitrogen-nitrogen functionalized nitrogen heterocyclic carbene tridentate ligand to the dichlorophenyl ruthenium (II) dimer is 1:0.4 - 0.6.

[0014] Further, in step (1), the first organic solvent is one of tetrahydrofuran, dichloromethane, toluene, acetonitrile, acetone, and methanol.

[0015] Further, in step (1), the heating reaction temperature is 40 - 80 °C, and the reaction time is 3 - 8 h.

[0016] Further, in step (2), the second organic solvent is methanol or ethanol.

[0017] Further, the stirring reaction time in step (2) is 24 - 48 h.

[0018] Use of the above-mentioned half-sandwich ruthenium complex with a nitrogen-containing heterocyclic carbene ligand in the preparation of a catalyst for carbon dioxide hydrogenation reduction reaction.

[0019] The beneficial effects produced by the present invention are as follows:

[0020] 1. The synthesized half-sandwich nitrogen heterocyclic carbene ruthenium complexes in the present invention are all new compounds. Their synthesis method is simple and efficient, without the harsh synthesis conditions of water and oxygen removal. The post-treatment and purification method is simple, and the yield is moderate.

[0021] 2. The synthesized half-sandwich nitrogen heterocyclic carbene ruthenium complexes in the present invention are stable to water and air and are easy to store, overcoming the disadvantages that the current homogeneous catalytic CO 2 hydrogenation catalyst is prone to deterioration and inactivation and is difficult to store; it has good water solubility, and the catalytic reaction can be carried out in an aqueous solution system, avoiding environmental pollution caused by the use of organic solvents.

[0022] 3. In the catalytic CO 2 hydrogenation reaction of the synthesized half-sandwich ruthenium complex, the selectivity of the product formate is high, no other by-products are generated in the reaction, the catalytic activity is good, and the TON (turnover number) of formate formation can reach 72,600.

[0023] 4. Using abundant CO 2 as a carbon source to synthesize high-value formate effectively realizes the conversion and utilization of greenhouse gas CO 2 and the storage of H 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 1H NMR spectrum of the half-sandwich ruthenium complex 1(Cl) with a nitrogen-containing heterocyclic carbene ligand;

[0025] Figure 2 1H NMR spectrum of the half-sandwich ruthenium complex 1(BF 4 4);

[0026] Figure 3 1H NMR spectrum of the half-sandwich ruthenium complex 1(BF 4 4); DETAILED DESCRIPTION OF THE INVENTION

[0027] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0028] Therefore, the following detailed description of the provided embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0029] It should be noted that relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "comprising a..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the element.

[0030] The features and performance of the present invention will be further described in detail below in conjunction with embodiments and drawings.

[0031] Example 1

[0032] A half-sandwich ruthenium complex with a nitrogen-containing heterocyclic carbene ligand, and its preparation method includes the following steps:

[0033] (1) Place the nitrogen-nitrogen functionalized nitrogen heterocyclic carbene tridentate ligand (0.3 mmol) and dichlorophenyl ruthenium (II) dimer (0.15 mmol) in a 100 mL dry two-necked round-bottom flask, add 40 mL of acetonitrile solution, and heat under reflux at 80 °C for 5 h. Then, evaporate the solvent under reduced pressure, concentrate the reaction solution to 15 mL, and then slowly add 20 mL of ether to it. Let the mixture stand overnight. A large amount of solid precipitates at the bottom of the round-bottom flask. Discard the upper mother liquor. Wash the solid precipitate with a small amount of ether twice and dry it under vacuum to obtain ruthenium complex 1 (Cl)([RuCl(η 6 -C 6 H 6 )(CNN)]Cl 2 ), which is a yellow-brown solid powder with a yield of 68%;

[0034] The structure of complex 1(Cl)([RuCl(η Figure 1 ) was characterized by nuclear magnetic resonance spectroscopy( 6 -C 6 H 6 )(CNN)]Cl 2 ), and the NMR data are as follows: 1 1H NMR(400MHz,DMSO-d 6 )δ9.47(d,J=8.3Hz,1H),9.35-9.25(m,2H),8.04-7.95(m,2H),7.76(t,J=1.76Hz,1H),7.55-7.47(m,2H),6.09(s,6H),4.69-4.58(m,1H),4.55-4.45(m,1H),4.33(dd,J=15.9,5.5Hz,1H),3.88(s,3H),3.86-3.66(m,3H).

[0035] (2) Complex 1(Cl)([RuCl(η 6 -C 6 H 6 )(CNN)]Cl 2 )(0.2mmol) and 30mL of methanol were added to a 100mL single-necked round-bottom flask, and AgBF 4 (0.45mmol) was added thereto. The reaction was stirred at room temperature for 24h. After the reaction was completed, the brown-yellow solid precipitate was collected, washed successively with methanol and n-hexane, and dried under vacuum to obtain a solid powder. The solid powder was added to 30mL of acetonitrile, stirred at room temperature for 30min, the filtrate was collected by filtration, the solvent was removed under reduced pressure, and the ruthenium complex 1(BF 4 )

[0036] ([RuCl(η 6 -C 6 H 6 )(CNN)](BF 4 ) 2 ) was obtained as a yellow-brown solid powder with a yield of 69%. By the gas-liquid diffusion method, ether was diffused into the acetonitrile solution of ruthenium complex 1(BF 4 )([RuCl(η 6 -C 6 H 6 )(CNN)](BF 4 ) 2 ) to obtain bright yellow-brown granular crystals of complex 1(BF 4 ) that can be used for X-ray single crystal diffraction analysis.

[0037] The structure of complex 1 (BF Figure 2 ) was characterized by nuclear magnetic resonance spectroscopy ( Figure 3 ) and single-crystal X-ray diffraction ( 4 ). The NMR data are as follows:

[0038] ([RuCl(η 6 -C 6 H 6 )(CNN)](BF 4 ) 2 ) 1 1H NMR (400 MHz, DMSO-d 6 ) δ 9.31 (d, J = 5.7 Hz, 1H), 9.19 (s, 1H), 8.09 - 7.92 (m, 2H), 7.88 (s, 1H), 7.78 (s, 1H), 7.56 (t, J = 6.7 Hz, 1H), 7.51 (d, J = 7.9 Hz, 1H), 6.01 (s, 6H), 4.45 (t, J = 7.1 Hz, 2H), 4.28 (dd, J = 15.9, 5.4 Hz, 1H), 4.02 - 3.74 (m, 5H), 3.68 - 3.57 (m, 1H). 1 1H NMR and single-crystal X-ray diffraction indicate that the ruthenium complex coordinated with the nitrogen-functionalized N-heterocyclic carbene tridentate ligand (CNN ligand) and phenyl ligand with very high purity can be successfully synthesized by the method of the present invention.

[0039] Crystal structure determination of the half-sandwich ruthenium complex with N-heterocyclic carbene ligand:

[0040] Single crystals of appropriate size were selected under a microscope, and X-ray single-crystal diffraction data were collected at 293.15 K using an Xcalibur Eos X-ray single-crystal diffractometer (Mo-Kα radiation) from Oxford Instruments. The structure of the complex was solved by direct methods using the ShelXS structure solution program in the Olex2 software, and refined by full-matrix least-squares using the ShelXL refinement package. The crystal structure of complex 1(BF4)([RuCl(η 6 -C 6 H 6 )(CNN)](BF 4 ) 2 ) is shown in Figure 3 , and some of the crystallographic parameters are listed in Table 1.

[0041] Table 1: Complex 1(BF 4 )([RuCl(η 6 -C 6 H 6 )(CNN)](BF 4 )2 ) Crystallographic and structure refinement data

[0042]

[0043] In the above technical solution, when X = tetrafluoroborate ion, the complex 1 (BF 4 )([RuCl(η 6 -C 6 H 6 )(CNN)](BF 4 ) 2 ) is specifically a half-sandwich ruthenium complex coordinated with a CNN ligand and a phenyl ligand. Its experimental formula is: C 18 H 23 B 2 ClF 8 N 4 Ru, with a molecular weight of 605.54. The crystal of this complex belongs to the orthorhombic system, the space group is Pna21, and the unit cell parameters are: Unit cell volume Z = 4. In the crystal, the Ru(II) metal center of the complex coordinates with two N coordination atoms of the CNN ligand, a Cl ion, and a phenyl ligand to form a pseudo-octahedral half-sandwich geometry.

[0044] Example 2

[0045] A half-sandwich ruthenium complex containing a nitrogen heterocyclic carbene ligand, and its preparation method includes the following steps:

[0046] (1) Put the nitrogen-nitrogen functionalized nitrogen heterocyclic carbene tridentate ligand (0.3 mmol) and dichlorophenyl ruthenium(II) dimer (0.12 mmol) into a 100 mL dry two-necked round-bottom flask, add 40 mL of tetrahydrofuran solution, heat and reflux at 40 °C for 8 h. Then, evaporate the solvent under reduced pressure, concentrate the reaction solution to 15 mL, and then slowly add 20 mL of ether to it. Let the mixture stand overnight. A large amount of solid precipitates at the bottom of the round-bottom flask. Discard the upper mother liquor, wash the solid precipitate with a small amount of ether twice, and dry it under vacuum to obtain the ruthenium complex 1(Cl)([RuCl(η 6 -C 6 H 6 )(CNN)]Cl 2 ), which is a yellow-brown solid powder with a yield of 71%;

[0047] (2) For the complex 1(Cl)([RuCl(η 6 -C 6 H 6 )(CNN)]Cl 2)(0.2 mmol) and 30 mL of ethanol were added to a 100 mL single-necked round-bottom flask, and AgPF 6 (0.45 mmol) was added thereto. The reaction was stirred at room temperature for 48 h. After the reaction was completed, the brownish-yellow solid precipitate was collected, washed successively with ethanol and n-hexane, and dried under vacuum to obtain a solid powder. The solid powder was added to 30 mL of acetonitrile, stirred at room temperature for 30 min, the filtrate was collected by filtration, the solvent was removed under reduced pressure, and the ruthenium complex 1 (PF 6 )

[0048] ([RuCl(η 6 -C 6 H 6 )(CNN)](PF 6 ) 2 ) was obtained as a yellowish-brown solid powder with a yield of 64%.

[0049] Example 3

[0050] A half-sandwich ruthenium complex containing a nitrogen heterocyclic carbene ligand, and its preparation method includes the following steps:

[0051] (1) The nitrogen-nitrogen functionalized nitrogen heterocyclic carbene tridentate ligand (0.3 mmol) and dichlorophenyl ruthenium (II) dimer (0.18 mmol) were placed in a 100 mL dry two-necked round-bottom flask, 40 mL of toluene solution was added, and the reaction was heated under reflux at 70 °C for 6 h. Then, the solvent was removed by distillation under reduced pressure, the reaction solution was concentrated to 15 mL, then 20 mL of ether was slowly added thereto, the mixture was allowed to stand overnight, a large amount of solid precipitated at the bottom of the round-bottom flask, the upper mother liquor was discarded, and the solid precipitate was washed twice with a small amount of ether and dried under vacuum to obtain ruthenium complex 1 (Cl)([RuCl(η 6 -C 6 H 6 )(CNN)]Cl 2 ) as a yellowish-brown solid powder with a yield of 63%;

[0052] (2) Complex 1 (Cl)([RuCl(η 6 -C 6 H 6 )(CNN)]Cl 2 )(0.2 mmol) and 30 mL of methanol were added to a 100 mL single-necked round-bottom flask, and (C 6 H 5 ) 4BNa (0.45 mmol), stirred at room temperature for 36 h. After the reaction, the brownish-yellow solid precipitate was collected, washed successively with methanol and n-hexane, and dried under vacuum to obtain a solid powder. The solid powder was added to 30 mL of acetonitrile, stirred at room temperature for 30 min, the filtrate was collected by filtration, the solvent was removed under reduced pressure, and the ruthenium complex 1 (BPh 4 )

[0053] ([RuCl(η 6 -C 6 H 6 )(CNN)](BPh 4 ) 2 ) was obtained as a yellowish-brown solid powder with a yield of 60%.

[0054] In the above scheme, the nitrogen-nitrogen functionalized N-heterocyclic carbene tridentate ligand (CNN) is named: 1-methyl-3-{2-{(pyridin-2-ylmethylene)-amino}-ethyl}imidazolium chloride, and its structural formula is Its synthesis method is as follows:

[0055] Weigh chloroethylamine hydrochloride (0.05 mol, 5.8 g) and 1-methylimidazole (0.1 mol, 8.2 g) into a 100 mL two-necked flask, add 50 mL of acetonitrile, reflux and stir at 90 °C for 12 h, cool to room temperature, the solid precipitate was filtered, washed twice with EtOH, the solid was dissolved in a small amount of water, the pH value was adjusted to 8 - 9 with KOH solution, stirred for 30 min, then the aqueous solution was evaporated under reduced pressure, and then a mixed solution of THF / ethanol (1:4, 50 mL) was added, the insoluble matter was filtered off, the filtrate was collected, and the solvent was removed under reduced pressure to obtain a pale yellow viscous liquid, which is 1-methyl-3-(2-aminoethyl)imidazolium chloride (yield 70%).

[0056] The 1H NMR data of 1-methyl-3-(2-aminoethyl)imidazolium chloride are as follows: 1 H NMR (400.1 MHz, DMSO-d 6 , δ) 9.28 (s, 1H), 7.78 (s, 1H), 7.74 (s, 1H), 4.16 (t, 2H, J = 6.0 Hz), 3.87 (s, 3H), 2.93 (t, 2H, J = 6.0 Hz).

[0057] The structure of 1-methyl-3-(2-aminoethyl)imidazolium chloride is as follows:

[0058]

[0059] 1-Methyl-3-(2-aminoethyl)imidazolium chloride (1.62 g, 10 mmol) was dissolved in 30 mL of anhydrous methanol, and pyridine-2-carboxaldehyde (1.07 g, 10 mmol) was added. The mixture was stirred at room temperature for 12 h. After the reaction was completed, a red-brown methanol solution was obtained. Under an ice-water bath condition, the red-brown methanol solution was added to a two-necked flask containing NaBH 4 (378 mg, 10 mmol). Subsequently, the mixture solution was stirred at room temperature for 12 h. After the reaction was completed, it was cooled to room temperature. 10% dilute HCl aqueous solution was added to the mixed solution to adjust the solution to acidic. After stirring for 1 h, the pH of the obtained mixed solution was adjusted to 7 with saturated NaHCO 3 aqueous solution. All solvents were removed under reduced pressure. The crude product of the ligand was extracted with CH 2 Cl 2 . The crude product of the ligand was separated and purified by column chromatography on a silica gel column. The eluent was dichloromethane:ethanol (volume ratio 10:1), and the ligand CNN was obtained as a light yellow viscous substance (yield 70%).

[0060] The 1H NMR data of ligand CNN are as follows: 1H NMR (400 MHz, DMSO-d6, δ): 9.19 (s, 1H), 8.49 (m, 1H), 7.77 (t, J = 1.8 Hz, 1H), 7.74 (dd, J = 7.7, 1.8 Hz, 1H), 7.70 (t, J = 1.8 Hz, 1H), 7.35 (d, J = 7.7 Hz, 1H), 7.25 (m, 1H), 4.26 (t, J = 5.7 Hz, 2H), 3.87 (s, 3H), 3.80 (s, 2H), 2.91 (t, 1H, J = 5.7 Hz, 2H).

[0061] Test Example

[0062] Taking the complex prepared in Example 1 as an example, it was used as a catalyst for carbon dioxide hydrogenation test. The specific operation was as follows: Under nitrogen protection, 20 mmol of K 2 CO 3 and 10 mL of an aqueous solution of 0.01 μmol / mL ruthenium complex 1 (BF 4 )([RuCl(η 6 -C 6 H 6 )(CNN)](BF 4 ) 2 ) were successively added to a high-pressure reaction kettle. The reaction kettle was tightened, and H 2 / CO 2(3:1) After the mixed gas was replaced three times, it was then pressurized to 6 MPa. Under stirring conditions, the reaction kettle was placed at a reaction temperature of 170 °C and catalytic reaction was carried out for 30 h. After the reaction was completed, it was cooled to room temperature to obtain the product.

[0063] The above reaction solution was analyzed by NMR, and the TON of formate generated was calculated to reach 72600 by the internal standard method.

Claims

1. A half-sandwich ruthenium complex of a nitrogen-containing heterocyclic carbene ligand, characterized in that: The structural formula of the complex is: Here, X represents one of a chloride ion, a tetrafluoroborate ion, a hexafluorophosphate ion or a tetraphenylborate ion.

2. The method for preparing the half-sandwich ruthenium complex of the nitrogen-containing heterocyclic carbene ligand according to claim 1, characterized in that: The following steps are involved: (1) heating a nitrogen-functionalized nitrogen heterocyclic carbene tridentate ligand and a dichlorophenylruthenium (II) dimer in a first organic solvent for reflux reaction, and then concentrating and recrystallizing the reaction solution to obtain a complex 1(Cl) ([RuCl(η 6 -C6H6(CNN)]Cl2); (2) The complex 1(Cl)([RuCl(η 6 -C6H6)(CNN)]Cl2) and a second organic solvent are mixed, one of AgBF4, NaBF4, AgPF6, NaPF6 and (C6H5)4BNa is added thereto, the reaction is stirred, the precipitate is collected, purified, and the product is extracted with a solution to obtain a semi-sandwich ruthenium complex of a nitrogen-containing heterocyclic carbene ligand.

3. The method for preparing a half-sandwich ruthenium complex of a nitrogen-containing heterocyclic carbene ligand according to claim 1, characterized in that: In step (1), the molar ratio of the nitrogen-nitrogen functionalized nitrogen heterocyclic carbene tridentate ligand to the dichlorophenylruthenium (II) dimer is 1:0.4-0.

6.

4. The method for preparing a half-sandwich ruthenium complex of a nitrogen-containing heterocyclic carbene ligand according to claim 1, characterized in that: In step (1), the first organic solvent is one of tetrahydrofuran, dichloromethane, toluene, acetonitrile, acetone and methanol.

5. The method for preparing a half-sandwich ruthenium complex of a nitrogen-containing heterocyclic carbene ligand according to claim 1, characterized in that: In step (1), the heating reaction temperature is 40-80° C. and the reaction time is 3-8 h.

6. The method for preparing a half-sandwich ruthenium complex of a nitrogen-containing heterocyclic carbene ligand according to claim 1, characterized in that: The second organic solvent in step (2) is methanol or ethanol.

7. The method for preparing a half-sandwich ruthenium complex of a nitrogen-containing heterocyclic carbene ligand according to claim 1, characterized in that: The stirring reaction time in step (2) is 24-48h.

8. Use of the half-sandwich ruthenium complex of the nitrogen-containing heterocyclic carbene ligand as claimed in claim 1 in the preparation of a catalyst for the hydrogenation reduction reaction of carbon dioxide.

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