Iridium complex and preparation method and application thereof

Abstract

The present application discloses an iridium complex and its preparation method and application. The iridium complex has a structure shown in Formula I; wherein X is selected from one of sulfate, trifluoromethanesulfonate, tetrafluoroborate or hexafluorophosphate; when X is sulfate, n is 1; when X is trifluoromethanesulfonate, tetrafluoroborate or hexafluorophosphate, n is 2. It can decompose anhydrous pure formic acid and high-concentration formic acid with high activity and high stability. In addition to decomposing formic acid, it can activate hydrogen at room temperature or above to generate Ir-H active species, and then reduce different types of compounds containing unsaturated double bonds, such as aldehydes, ketones, imines, olefins, CO 2 and unsaturated bonds in compounds such as carboxylic acids; in addition, Ir-H active species can also be produced using hydrogen from formic acid, sodium formate, silicon hydride and 1,4-dihydropyridine compounds, which also have reducing properties and can also reduce different types of compounds containing unsaturated double bonds.

Description

Technical Field

[0001] The present application relates to an iridium complex and a preparation method and application thereof, belonging to the field of metal complex preparation. Background Art

[0002] As one of the liquid hydrogen storage materials, formic acid has attracted much attention in recent years. The homogeneous system currently developed can decompose formic acid with water efficiently and selectively. The highest reaction activity (TOF) reported in the literature can reach 485,000 / hour (Chem. Eur. J. 2015, 21, 12592–12595). The catalyst stability is also very good. The best stability reported in the literature is that 1 mole of catalyst can decompose 10 million moles of formic acid (TON) (Adv. Synth. Catal. 2019, 361, 289–296). However, for the decomposition of high-concentration or pure formic acid, there are currently few effective catalytic systems, and the activity and stability are far lower than the activity and stability of formic acid decomposition in aqueous solution. Many catalysts are unstable in high-concentration or pure formic acid, which may be the reason why there are few catalytic systems reported so far. Even if some catalysts can be stable in high-concentration or pure formic acid, they are more likely to be deactivated as the reaction proceeds, which may be the reason for the low activity and stability. The highest reported decomposition activity TOF in pure formic acid is 11,000 / hour (ACS Catal. 2017, 7, 8139-8146), and the TON value reaches 2.61 million (Nat. Commun. 2016, 7, 11308. DOI: 10.1038 / ncomms11308), which is much lower than the decomposition activity (TOF: 485,000) and stability (TON: 10 million) of formic acid in aqueous solution. Since the hydrogen content per unit volume of formic acid itself is not high, if water is added, the hydrogen content per unit volume will be further reduced. Therefore, the decomposition of pure formic acid has more practical application value, especially for the application of on-board formic acid fuel cells. Summary of the invention

[0003] The present application provides the following technical solution: to prepare a more structurally stable iridium catalyst, in which the NH structure of the bis-tetrahydropyrimidine ligand is protected, thereby avoiding the problem of NH being oxidized and causing the catalyst to decompose, and the iridium center is coordinated by a water molecule, and the coordinated anion uses OTf with weak coordination ability. - This structure makes it easy for the complex to generate empty coordination sites and bind to the substrate formic acid even under anhydrous conditions, thereby promoting the reaction.

[0004] According to one aspect of the present application, an iridium complex is provided, wherein the iridium complex has a structure shown in Formula I;

[0005]

[0006] Wherein X is selected from one of sulfate, trifluoromethanesulfonate, tetrafluoroborate or hexafluorophosphate;

[0007] When X is sulfate, n is 1;

[0008] When X is trifluoromethanesulfonate, tetrafluoroborate or hexafluorophosphate, n is 2.

[0009] According to another aspect of the present application, a method for preparing the above-mentioned iridium complex is provided, comprising at least the following steps:

[0010] The content of [(Cp*Ir(H 2 O) 3 )·nX] and the raw materials of the ligand L are mixed with a solvent and reacted to obtain the iridium complex;

[0011] The ligand L has a structure shown in formula II;

[0012]

[0013] The solvent is selected from at least one of water, methanol or ethanol.

[0014] The [(Cp*Ir(H 2 O) 3 )·nX] and the molar ratio of the ligand L is 1:1;

[0015] The [(Cp*Ir(H 2 O) 3 The volume ratio of the total molar amount of )·nX] and ligand L to solvent I is 0.01 to 0.1 mmol / mL.

[0016] The reaction temperature is 20-30°C;

[0017] The reaction time is 8 to 48 hours.

[0018] The iridium complex is separated by silica column chromatography.

[0019] The silica used in the silica column chromatography separation is 200-300 mesh; the eluent is a mixture of dichloromethane and methanol, and the ratio of dichloromethane to methanol in the mixture is 50 / 1-3 / 1.

[0020] Further, the preparation process is as follows:

[0021] [(Cp*Ir(H 2 O) 3 )·2OTf], ligand L and solvent are mixed and stirred, and TLC is used to detect whether the reaction is complete. After the raw materials react completely, the solvent is removed and the residue is washed with SiO2 Column chromatography was performed to obtain pure iridium complex I.

[0022] Among them, due to (Cp*Ir(H 2 O) 3 The optimal molar ratio of 2OTf to ligand L is 1:1. Reducing iridium or reducing the amount of ligand will reduce the yield of I.

[0023] The amount of solvent has little effect on the reaction. The minimum amount is the amount that can dissolve the ligand and is suitable for stirring. The maximum amount can be unlimited. (Cp*Ir(H 2 O) 3 )·The optimal concentration range of 2OTf and ligand L in the solvent is 0.01-0.1 mmol / mL. Since the reaction can be carried out at room temperature (20-30 degrees), it is not necessary to increase the temperature;

[0024] The solvent may be a single protic polar solvent such as methanol, water, ethanol, or a mixture of any two or more thereof;

[0025] The reaction time is not limited and is determined according to the amount of the reaction raw materials and the results of TLC, generally 8 to 48 hours;

[0026] SiO for column chromatography 2 It is generally 200-300 mesh, and the elution solvent is a mixture of dichloromethane and methanol, with the ratio generally being 50 / 1 to 3 / 1.

[0027] According to another aspect of the present application, a method for dehydrogenating formic acid is provided, comprising at least the following steps: mixing a catalyst with formic acid to react to obtain carbon dioxide and hydrogen;

[0028] The catalyst contains the iridium complex mentioned above or the iridium complex prepared by the above preparation method.

[0029] The beneficial effects produced by the present application include: being able to decompose anhydrous pure formic acid and aqueous formic acid with high activity and high stability.

[0030] In addition to decomposing formic acid, iridium complexes can activate hydrogen at room temperature or above to generate Ir-H active species, which are reductive and can reduce different types of compounds containing unsaturated double bonds, such as aldehydes, ketones, imines, olefins, CO 2 and unsaturated bonds in compounds such as carboxylic acids; in addition, since iridium complexes can also utilize hydrogen from formic acid, sodium formate, silicon hydride and 1,4-dihydropyridine compounds to produce Ir-H active species, they also have reducing properties and can also reduce different types of compounds containing unsaturated double bonds. DETAILED DESCRIPTION

[0031] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0032] Unless otherwise specified, the raw materials and catalysts in the examples of this application were purchased through commercial channels.

[0033] In the embodiments, the nuclear magnetic resonance analysis was performed using a 400 MHz or 700 MHz instrument from Bruker Avance, at room temperature, and the solvent used was deuterated water (D 2 O); high-resolution mass spectrometry (HRMS) was performed using Finnigan MAT 95 system, tested at room temperature, and the samples were dissolved in secondary water or methanol; formic acid, methanol, and ethanol were from Tianjin Komiou Chemical Reagent Co., Ltd.; [(Cp*IrCl 2 ) 2 ] was purchased from Suzhou Xinjiayuan Chemical Technology Co., Ltd., and silver trifluoromethanesulfonate (AgOTf) was purchased from Anaiji. Ligand L was prepared according to the method of Inorganica Chimica Acta, 2010, 364, 185-194.

[0034] Cp* refers to pentamethylcyclopentadienyl;

[0035] TOF refers to the number of turnovers per unit time, which refers to the number of moles of substrate converted per mole of catalyst per unit time.

[0036] TLC refers to thin layer chromatography.

[0037] TON is calculated according to the following equation eq.1:

[0038]

[0039] H 2 The molar volume at 20 degrees is calculated according to the following equation:

[0040]

[0041] R:8.3145m 3 Pa mol -1 K -1

[0042] T:298.15K

[0043] p:101325Pa

[0044] b:26.7·10 -6 m 3 ·mol -1

[0045] a:2.49·10 -10·Pa·m 3 ·mol -2

[0046] CO 2 The molar volume at 20 degrees is calculated according to the following equation:

[0047]

[0048] R:8.3145m 3 Pa mol -1 K -1

[0049] T:298.15K

[0050] p:101325

[0051] a:36.5·10 -10 ·Pa·m 3 ·mol -2

[0052] b:42.7·10 -6 m 3 ·mol -1

[0053] The initial reactivity was calculated as follows.

[0054] For example, at 90°C, 0.001 mol% (0.5 μmol) of iridium complex I was reacted in 5.0 M formic acid solution, and the volume of gas released in the first 30 seconds was 105 mL.

[0055]

[0056] Example 1

[0057] Preparation of Iridium Complex I

[0058] [(Cp*Ir(H 2 O) 3 )·2OTf] (0.2 mmol), ligand L (0.42 mmol) and water (10 mL) were mixed in a 50 mL reaction bottle and stirred at room temperature for 30 minutes. The reaction was monitored by TLC. After the reaction of the raw materials was complete, the solvent was removed and the residue was washed with SiO 2 Column chromatography was performed with dichloromethane / methanol as the eluent to obtain pure iridium complex I as an orange solid with a yield of 60%.

[0059] The characterization data of I obtained are as follows: 1 H NMR (400 MHz, D 2O): δ (ppm) = 3.77 (t, J = 4.0Hz, 4H), 3.41 (t, J = 6.0Hz, 4H), 3.40 (s, 4H), 1.97-2.00 (m, 4H), 1.60 (s, 15H); 13 C{ 1 H}NMR (174 MHz, D 2 O): δ (ppm) = 145.42 [122.31, 120.51, 118.71, 116.91, (q, J = 315Hz)], 86.67, 48.70, 46.06, 45.85, 20.53, 8.19; ESI-HRMS calcd.for C 20 H 31 Ir 4 [MH 2 O-2OTf] 2+ :520.2178,Found 260.1082

[0060] Test Example 1

[0061] Iridium complex I (10 μmol) was dissolved in water (10 mL) to prepare a catalyst aqueous solution. 10.0 mL of 5 mol / L formic acid solution was placed in a reaction bottle. After heating in a 90-degree water bath for 1-2 minutes, 0.05 mL of the prepared catalyst solution was added to the reaction bottle. At this temperature, the reaction of decomposing formic acid started immediately and ended after 15 minutes. The initial reaction activity calculated based on the volume of gas released in the first 30 seconds (125 mL) was 625,000 / hour.

[0062] Test Example 2

[0063] Iridium complex I (5.2 μmol) was dissolved in pure formic acid (1.0 mL), and the mixture was heated in a 90-degree water bath. The timing started, and the reaction of decomposing formic acid started immediately, and the reaction ended after 22 minutes. The initial reaction activity calculated based on the volume of gas released in the first 2 minutes was 11,000 / hour. In this reaction, the reaction activity gradually increased, and the fastest reaction rate could reach 16,000 / hour.

[0064] Comparative Example 1

[0065]

[0066] The reaction results of using formula III as a catalyst to decompose anhydrous formic acid are as follows:

[0067] Iridium complex III (5.2 μmol) was dissolved in anhydrous formic acid (1.0 mL) and heated in a 90-degree water bath. The reaction of decomposing formic acid started immediately, and the reaction rate gradually decreased. The reaction stopped after 45 minutes, and the formic acid reaction was incomplete.

[0068] The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for dehydrogenating formic acid, It is characterized in that The method comprises at least the following steps: mixing a catalyst with formic acid to obtain carbon dioxide and hydrogen through dehydrogenation; The catalyst is an iridium complex having a structure shown in Formula I; Formula I; The X is trifluoromethanesulfonate, and n is 2; The preparation method of the iridium complex comprises at least the following steps: The content of [(Cp*Ir(H 2 O) 3 )ˑnX] and the raw materials of the ligand L are mixed with a solvent and reacted to obtain the iridium complex; The ligand L has a structure shown in formula II; Formula II.

2. The method according to claim 1, It is characterized in that The solvent is selected from at least one of water, methanol or ethanol.

3. The method according to claim 1, It is characterized in that The molar ratio of the [(Cp*Ir(H 2 O) 3 )ˑnX] to the ligand L is 1:1; The [(Cp*Ir(H 2 O) 3 The volume ratio of the total molar amount of )ˑnX] and ligand L to solvent I is 0.01~0.1mmol / mL.

4. The method according to claim 1, It is characterized in that In the preparation method of the iridium complex, the reaction temperature is 20-30°C; The reaction time is 8 to 48 hours.

5. The method according to claim 1, It is characterized in that The iridium complex is separated by silica column chromatography.

6. The method according to claim 5, It is characterized in that The silica used in the silica column chromatography separation is 200-300 mesh; the eluent is a mixture of dichloromethane and methanol, and the ratio of dichloromethane to methanol in the mixture is 50 / 1-3 / 1.

7. The method according to claim 1, It is characterized in that The formic acid is anhydrous formic acid or aqueous formic acid.

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