WO2018194537A1

WO2018194537A1 - Iridium-based catalysts for highly efficient dehydrogenation and hydrogenation reactions in aqueous solution and applications thereof

Info

Publication number: WO2018194537A1
Application number: PCT/US2017/027844
Authority: WO
Inventors: Weiping Tang; Junrong Zheng
Original assignee: Tiger Instruments, Llc
Priority date: 2017-04-17
Filing date: 2017-04-17
Publication date: 2018-10-25

Abstract

A series of iridium-based catalysts for dehydrogenation of formic acid, and hydrogenation using formic acid as the hydrogen source, and the process using the catalyst(s) to produce hydrogen gas from formic acid solution, or to reduce aldehydes using formic acid, are disclosed and claimed. More specifically, the present invention relates to a group of pentamethylcyclopentadienyl (Cp*) iridium complexes with different Ν,Ν-bidentate ligands that catalyze dehydrogenation from formic acid, and chemo-selective hydrogenation of aldehydes, in the aqueous solution system in a highly efficient, and long life-time manner.

Description

A process for hydrogen production using iridium-based catalysts for dehydrogenation of formic acid and/or hydrogenation of aldehydes using formic acid as the hydrogen source in the aqueous solution, and its applications.

FIELD OF THE INVENTION

[0001] The present invention relates to a series of iridium-based organic-metallic catalysts that could either generate hydrogen gas from formic acid, and/or reduce aldehydes in aqueous solutions to primary alcohols, without any additives. More specifically, the present invention relates to a range of pentamethylcyclopentadienyl (Cp*) Iridium complexes with different N,N- bidentate ligands.

BACKGROUND OF THE INVENTION

[0002] Hydrogen has long been considered as a promising clean energy source.¹ However, it faces difficulties regarding the storage and transportation of hydrogen gas and safety issues to handle it that hindering its application in energy business. One approach to solve the challenge is chemical storage.² Formic acid (FA), because of its high volumetric hydrogen capacity (53g ¾ L^"1), being non-toxic and relatively safe to handle, is viewed as one of the most promising hydrogen chemical storage materials, especially in automotive applications.³ A secure and reliable energy storage and utilization system on a new generation hydrogen-driven automobile can be envisioned by carrying FA in liquid form and releasing hydrogen by selectively dehydrogenating FA and direct consuming hydrogen via fuel cell.⁴

[0003 ]In recent years, a variety of homogeneous catalysts based on rhodium, ruthenium, and iron have been reported for the selective dehydrogenation of FA in variable conditions.^5"7 However, for some of them, the catalysts were dissolved in organic solvent which would not be favorable in automobile considering the cost and toxicity; others will need the presence of additives such as amines or other organic bases in order to achieve high efficiency. Those catalytic systems could be problematic when scaling up and applying for practical use. Thus, a practical catalytic system which can take place in simple aqueous solutions without any additives such as organic base is favorable.

[0004] Catalysts reported in literature generally achieved moderate turnover frequencies (TOFs) and turnover numbers (TONs).^8"12 In addition, the methods used to measure the TON are not applicable for real applications in many cases.

Herein, we disclose and claim a group of iridium complexes Ν,Ν-bidentate ligands as a highly efficient, and long life-time catalyst(s) for dehydrogenation of formic acid in the aqueous solution system, without the addition of any additives. Some of catalysts reached reproducible high TON value and TOF values under conditions that can be used for real applications. The combination of both high TON value and high TOF value are critical in practice, because a high TOF value assures the fast reaction rate, while a high TON value guarantees the long-term stability of the catalyst.

Instead of generating hydrogen gas directly, the catalyst(s) can also be used to chemo-selectively reduce aldehydes to primary alcohols using formic acid as the hydrogen source.

The reduction of aldehydes to alcohols is a fundamentally important reaction in organic chemistry.¹³ For example, hydro formylation of alkenes followed by aldehyde reduction constitutes one of the most important industrial processes for the manufacture of alcohols.¹⁴ Different strategies have been developed for the reduction of aldehydes to alcohols and transition metal-catalysed hydrogenation is the most atom-economical and cleanest reduction method. However, it generally requires high pressure of hydrogen gas, which causes safety issues. The transfer hydrogenation (TH) has the potential to become an ideal green method for reduction.¹⁵ Various reducing agents for transition metal-catalysed TH reduction of aldehydes under neutral or basic conditions in organic solvents have been developed, such as z^'so-propanol, 1 ,4-butandiol, hydrosilane and ammonium formate.^16"19 However, an operationally simple and green reduction method that works for chemists in both academia and industry is still highly desirable. For example, organic solvents are employed in most of the above processes and water would be an ideal solvent for TH.²⁰ The waste generated from hydrogen donors can be further reduced. Being able to conduct the reactions in air and without complex purification procedures will deliver a green and practical procedure.

In 2000, Bryson reported an aqueous TH reduction of aldehydes with sodium formate at high temperature and high pressure in low to moderate yields.²¹ In 2004, Ajjou realized a Rh- catalyzed aqueous TH of aldehydes with isopropanol as hydrogen donor and 0.2 equivalent of sodium carbonate as additive under nitrogen atmosphere.²² A breakthrough was made in 2006 by Xiao and co-workers by using iridium catalysts (Ir-1 or Ir-2) with N-sulfonyl ethanediamines as ligand.²³ In their work, the aldehydes were reduced in high efficiency (TOF up to 50,000)^§ on water and in air under neutral conditions by using 5 equivalents of sodium formate as the hydrogen source.

We disclose and claim a greener procedure employing the catalyst to reduce aldehydes. By replacing sodium formate with formic acid, a more environmentally friendly procedure to reduce aldehydes in water under acidic conditions can be realized. The reduction reaction with some of the catalysts features not only high efficiency (TOF up to 73,800) and low catalyst loading (0.005 mol%), but also low waste and excellent chemoselectivity. SUMMARY OF THE INVENTION

This invention relates to an iridium-based organometallic catalyst that catalyzes i) , the dehydrogenation reaction of formic acid in the aqueous solution and the process to produce hydrogen gas and/or ii) , the hydrogenation reactions of aldehydes using formic acid as the hydrogen source in the aqueous solution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows gas generating rate depending on the reaction time

FIG. 2 shows the effect of temperature on the catalytic activity of hydrogen gas generation

FIG. 3 shows the effect of the concentration of formic acid on the catalytic activity of hydrogen gas generation

FIG. 4 shows the effect of pH on the catalytic activity of hydrogen gas generation

FIG. 5 shows the effect of the counter ion on the catalytic activity of hydrogen gas generation

FIG. 6 shows the effect of pH on the catalytic activity of hydrogenation of aldehydes

DETAILED DESCRIPTION OF THE INVENTION

The present invention is related to a group of iridium complexes Ν,Ν-bidentate ligands as the catalyst(s) for dehydrogenation of formic acid. Some of catalysts achieved reproducible high TON value, and high TOF values. In addition, our catalyst generates no detectible amount of CO which would be highly toxic towards a fuel cell.

The following examples describe the procedures used for the preparation of various catalysts claimed in this invention.

Synthesis of catalyst cat-6:

To the solution of 4-methoxypyridine-2-carbaldehyde (3.00 g, 21 mmol) in 50 ml of

dichloromethane was dropwise added ethylenediamine (23 mmol, 1.6 ml) in an ice-water bath. The mixture was stirred for 1 h. Then N-bromosuccinimide (4.1 g, 23 mmol) was added at 0 °C, The mixture was slowly warmed to room temperature and stirred overnight. Washing the reaction mixture with 5% NaOH solution (50 mL) and then saturated Na₂S₂0₃ solution (50 mL), drying with Na₂S0₄ and removal of the dichloromethane under vacuum directly gave the desired crude product 2-(4,5-dihydro-lH-imidazol-2-yl)-4-methoxypyridine (3.55 g, yield 95%), which could be used directly in the next step.

To a suspension of [Cp*IrCi₂]₂ (4.451 g, 5.6 mmol) in 50 ml of DCM was dropwise added the solution of 2-(4,5-dihydro-lH-imidazol-2-yl)-4-methoxypyridine (2.052 g, 12 mmol). After stirring overnight, DCM was removed under reduced pressure, and the resultant yellow solid was dissolved in minimum amount of DCM. Then a large amount of EtOAc was added to precipitate an orange solid as desired product cat-6, which was isolated by reduced-pressure filtration and further dried under vacuum at room temperature. Yield: 6.445 g, yield 98%. 1H NMR (400 MHz,

CDC1₃): δ 1.75 (s, 15 H), 3.92-3.97 (m, 1H), 4.14 (s, 6H), 7.12 (dd, J= 2.8, 6.5 Hz, 1H), 8.43 (d, J= 6.5 Hz, 1H), 9.06 (d, J= 2.7 Hz, 1H), 10.50 (brs, 1H); ¹³C NMR (100 MHz, CDC1₃): δ 9.2, 46.1, 51.9, 58.2, 87.1, 112.9, 116.9, 148.8, 150.6, 168.4, 169.7; IR(powder): v = 1597, 1479, 1254, 1043, 1025, 840 cm^"1; HRMS (ESI) for Ci^NsClOIr (M⁺), (Calc.) 540.1394, found 540.1386.

Synthesis of catalyst cat-1:

To a mixture of [Cp*IrCi2]2 (80 mg, 0.1 mmol) in 10 ml of CH2CI2 was slowly added the solution of ligand 2-(4,5-dihydro-lH-imidazol-2-yl)pyridine (28 mg, 0.2 mmol) in 5 ml of DCM. The mixture was stirred at room temperature overnight. Similar workup as described before afforded cat-1 as a yellow solid. Yield: 105 mg, 98%. 1H NMR (600 MHz, CDC1₃, TMS): δ 1.76 (s, 15 H), 3.92-3.97 (m, 1H), 4.14-4.22 (m, 3H), 7.61 (t, J= 6.6 Hz, 1H), 8.13 (t, J= 7.8 Hz, 1H), 8.67 (d, J= 5.4 Hz, 1H), 9.38 (d, J= 7.8 Hz, 1H), 10.93 (brs, 1H); ¹³C NMR (150 MHz, CDC1₃): δ 9.2, 46.3, 51.9, 87.6, 128.6, 128.7, 140.4, 147.5, 150.4, 169.5; IR(powder): v = 1592, 1460, 1287, 1051, 1030, 758 cm^"1; HRMS (ESI) for Cis^^ClIr (M⁺), (Calc.) 510.1288, found 510.1274. Synthesis of catalyst cat-2:

To the solution of pyridine-2-carboxaldehyde (107 mg, 1 mmol) in dichloromethane (10 mL) was dropwise added N-methylethylenediamine (78 mg, 1.05 mmol) in 5 mL of DCM. The mixture was stirred for 1 h, and then was cooled to 0 °C. N-Bromosuccinimide (196 mg, 1.1 mmol) was added and the mixture was stirred overnight. Washing the reaction mixture with 5% NaOH solution (10 mL) and then saturated Na₂S₂0₃ solution (10 mL), drying with Na₂S0₄ and removal of the dichloromethane under vacuum directly gave the desired crude product 2-(l- methyl-4,5-dihydro-lH-imidazol-2-yl)pyridine. Yield: 146 mg, 91%.

To a mixture of [Cp*IrCi₂]₂ (80 mg, 0.1 mmol) in 10 ml of CH₂C1₂ was slowly added the solution of ligand (39 mg, 0.24 mmol) in 5 ml of DCM. The mixture was stirred at room temperature overnight. Similar workup as described before afforded cat-2 as a yellow solid.

Yield: 92 mg, 82%. 1H NMR (600 MHz, CDC1₃, TMS): δ 1.79 (s, 15 H), 3.66 (s, 3H), 3.87-3.91 (m, 1H), 4.07-4.12 (m, 1H), 4.28-4.34 (m, 2H), 7.76 (t, J= 6.6 Hz, 1H), 8.29 (t, J= 7.8 Hz, 1H), 8.63 (d, J= 7.8 Hz, 1H), 8.86 (d, J= 5.4 Hz, 1H); ¹³C NMR (150 MHz, CDC1₃): δ 9.2, 36.2, 50.6, 55.8, 88.2, 127.5, 129.3, 140.6, 146.7, 152.2, 167.4; IR(powder): v = 1583, 1453, 1288, 1030, 756 cm^"1; HRMS (ESI) for Ci₉H₂₆N₃ClIr (M⁺), (Calc.) 524.1444, found 524.1446.

Synthesis of catalyst cat-7:

To the solution of 6-methoxypyridine-2-carboxaldehyde (300 mg, 2.1 mmol) in dichloromethane (20 mL) was dropwise added ethylenediamine (0.16 mL, 2.3 mmol). The mixture was stirred for 1 h, and then was cooled to 0 °C. N-Bromosuccinimide (410 mg, 2.3 mmol) was added and the mixture was stirred overnight. Washing the reaction mixture with 5% NaOH solution (20 mL) and then saturated Na₂S₂0₃ solution (20 mL), drying with Na₂S0₄ and removal of the

dichloromethane under vacuum directly gave the desired crude product 2-(l-methyl-4,5-dihydro- lH-imidazol-2-yl)pyridine. Yield: 346 mg, 93%.

To a solution of ligand (200 mg, 1.13 mmol) in 10 ml of DCM was added the powder of

[Cp*IrCl₂]₂ (0.5 mmol, 400 mg). The resultant orange solution was stirred overnight. Similar workup as described before afforded cat-7 as a yellow solid. Yield: 465 mg, 80%. ^JH NMR (400 MHz, CDC1₃, TMS): δ 1.73 (s, 15 H), 3.86-3.95 (m, 1H), 4.15 (s, 6H), 7.17 (d, J= 8.4 Hz, 1H), 8.08 (t, J= 8.1 Hz, 1H), 8.87 (d, J= 7.4 Hz, 1H), 10.5 (brs, 1H); ¹³C NMR (100 MHz, CDC1₃): δ 10.0, 46.2, 52.5, 58.0, 87.8, 110.7, 121.4, 143.8, 145.7, 163.9, 170.2; IR(powder): v = 1593, 1479, 1307, 1065, 1052, 805 cm^"1; HRMS (ESI) for

(M⁺), (Calc.) 540.1394, found 540.1383.

The following examples describe the catalytic properties of various catalyst(s) for

dehydrogenation of formic acid to generate hydrogen gas under different conditions in the process.

Example 1, the catalytic property of dehydrogenation: the TOF value and TON value

The catalyst was dissolved in DI water, then the pure formic acid was added to the catalyst aqueous solution at a constant rate. During the reaction, the solution was maintained at 80°C using a heating device. TOF was calculated by averaging the gas generation rate in the first 10 minutes. The TOF was measured to be 60,000 h^"1. TON was calculated by totalizing the overall gas generation volume. The TON was measured to be 620,000. In this example, both TOF and TON increased with temperature. To the best of our knowledge, this is the highest reproducible TON achieved under the condition that is desired for practical fuel cell applications. In typical industrial setting, TON is the most important value as long as TOF is not too low.

Fig.l

Example 2, the catalytic property of dehydrogenation under 60°C in formic acid solution

The catalyst was dissolved in 1M formic acid aqueous solution under 60°C. The TOF value was measured to be 16,000 h^"1 and the TON was measured to be 1,016,753.

Example 3, temperature dependence of the catalytic activity of dehydrogenation

The process describe in Example 1 was repeated under 50°C and 70°C. Together with the TOF values measured Example 2, an Arrheniu plot (Fig. 2) can be plotted. From analyzing it, the activation enthalpy of this catalyst was calculated to be 14.3 ± 1.0 kcal/mol.

Fig.2 Example 4, the catalytic activity of dehydrogenation of a few different catalysts

The process describe in Example 1 was repeated with a few other catalysts. The results were reported in Table 1.

Example 5, concentration dependence of the catalytic activity of dehydrogenation

The process describe in Example 1 was repeated using formic acid with different concentrations ranging from pure FA (>98%) to very dilute FA solution (0.1M). The result indicated that 5M is close to the optimal concentration. Too concentrated or too dilute FA solution wouldn't yield good catalytic activity of cat-6.

Fig.3 Example 6, pH dependence of the catalytic activity of dehydrogenation

The process described in Example 1 was repeated using sulfuric acid or sodium hydroxide to control the pH. The result indicated that pH = 2 is close to the optimal concentration. Too high or too low pH value would lower the catalytic activity.

Example 7, counterion dependence of the catalytic activity of dehydrogenation

The process describe in Example 6 was repeated using HCl, H₂SO₄, and H₃PO₄ control the counterion. In the figure, Black solid line, adding HCl; blue solid line, adding H3P04; red solid line, H2S04. The result showed a non-coordinating ion, such as S04 is the better choice when optimizing the catalytic activity.

Fig.5 The following examples describe the catalytic properties of various catalyst(s) for

dehydrogenation of formic acid to reduce aldehydes under different conditions in the process.

Example 8, the catalytic activity of hydrogenation of aldehydes

Table 2 describes the hydrogenation reaction of aldehydes using 4-Methoxybenzaldehyde as an example.

Table 2. Optimization of Reaction Conditions

Example 9, pH dependence of the catalytic activity of hydrogenation

The process described in Example 8 was repeated using sulfuric acid or sodium hydroxide to control the pH. The result indicated that pH = 3 is close to the optimal concentration. Too high or too low pH value would lower the catalytic activity.

Fig. 6

The following examples describe the catalytic properties for dehydrogenation of formic acid to reduce various aldehydes to corresponding alcohols, as listed in Table 3. All the products synthesized were known compounds, and their NMR spectra are identical with those reported. Catalyst loading was at 0.05 mol%. Isolated yields by extraction with ethyl acetate, drying over Na₂S0₄, and concentration at vacuum.

Table 3. Scope of Substrates

Example 10, hydrogenation to produce 4-Methoxybenzyl alcohol(2a)

The product is a yellowish oily liquid. As shown in Table 3, the yield is 273mg, 99%. 1H NMR (400 MHz, CDC1₃) δ 7.23 (d, J= 8.8 Hz, 2H), 6.85 (d, J= 8.7 Hz, 2H), 4.52 (s, 2H), 3.76 (s, 3H). ¹³C NMR (101 MHz, CDC1₃) δ 159.07, 133.23, 128.63, 113.89, 64.73, 55.30, 55.26.

Example 11, hydrogenation to produce 4-(Pentyloxy)benzenemethanol(2b)

The product is a yellowish solid. As shown in Table 3, the yield is 368mg, 95%>. H NMR (400 MHz, CDC1₃) δ 7.27 (d, J= 8.5 Hz, 2H), 6.90 (d, J= 8.6 Hz, 2H), 4.58 (s, 2H), 3.98 (t, J = 6.6 Hz, 2H), 2.52 (s, 1H), 1.97 - 1.68 (m, 2H), 1.64 - 1.26 (m, 4H), 0.98 (t, J= 7.0 Hz, 3H). ¹³C NMR (101 MHz, CDC1₃) δ 158.70, 132.98, 128.63, 114.52, 68.08, 64.85, 29.00, 28.24, 22.52, 14.07.

Example 12, hydrogenation to produce 4-(2-Propen-l-yloxy)benzenemethanol(2c)

The product is a yellowish oily liquid. As shown in Table 3, the yield is 301mg, 92%>. 1H NMR (400 MHz, CDC1₃) δ 7.26 (d, J= 8.4 Hz, 2H), 7.05 - 6.72 (m, 2H), 6.08 (ddt, J= 17.2, 10.5, 5.3 Hz, 1H), 5.38 (ddq, J= 46.7, 10.5, 1.5 Hz, 2H), 4.54 (dd, J = 4.1, 2.8 Hz, 4H). ¹³C NMR (101 MHz, CDC1₃) δ 158.09, 133.39, 133.32, 128.62, 117.70, 117.65, 114.74, , 68.85, 64.68, 64.66.

Example 13, hydrogenation to produce 2,5-Dimethoxybenzenemethanol (2d)

The product is a yellowish solid. As shown in Table 3, the yield is 332 mg, 99%>. 1H NMR (400 MHz, CDC1₃) δ 6.92 (d, J= 1.4 Hz, 1H), 6.78 (d, J= 7.6 Hz, 2H), 4.63 (d, J= 15.0 Hz, 2H), 3.85 - 3.66 (m, 6H), 3.09 (s, 1H). 13C NMR (101 MHz, CDC13) δ 153.60, 151.29, 130.33, 114.44, 112.82, 111.10, ,61.28, 55.73, 55.68.

Example 14, hydrogenation to produce 2,4,6-trimethoxy-Benzenemethanol (2e).

The product is a yellowish solid. As shown in Table 3, the yield is 392 mg, 99%>. 1H NMR (400 MHz, CDC1₃) δ 6.10 (s, 2H), 4.67 (s, 2H), 3.77 (d, J= 1.3 Hz, 9H), 2.50 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 161.01, 159.18, 109.90, 90.46, 55.61, 55.24, 54.09.

Example 15, hydrogenation to produce Benzyl alcohol (2f)

The product is a yellowish oily liquid. As shown in Table 3, the yield is 214 mg, 99%>. 1H NMR (400 MHz, CDC1₃) δ 7.45 - 7.09 (m, 5H), 4.57 (s, 2H), 2.60 (s, 1H).

1³C NMR (101 MHz, CDC1₃) δ 140.93, 128.55, 127.61, 127.04, 65.14.

Example 16, hydrogenation to produce 4-Methylbenzyl alcohol (2g)

The product is a white solid. As shown in Table 3, the yield is 241 mg, 99%. ^lR NMR (400 MHz, CDC1₃) δ 7.30 - 7.22 (m, 2H), 7.17 (d, J= 7.9 Hz, 2H), 4.64 (s, 2H), 2.35 (s, 3H), 1.61 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 137.92, 137.43, 129.26, 127.13, 65.32, 21.17. Example 17, hydrogenation to produce 4-(l,l-Dimethylethyl)benzenemethanol (2h).

The product is a yellowish oily liquid. As shown in Table 3, the yield is 324 mg, 99%. 1H NMR (400 MHz, CDC1₃) δ 7.46 (d, J= 8.2 Hz, 2H), 7.35 (d, J= 8.4 Hz, 2H), 4.67 (s, 2H), 1.40 (d, J= 0.7 Hz, 9H). ¹³C NMR (101 MHz, CDC1₃) δ 150.63, 137.95, 126.98, 125.48, 65.00, 64.96, 64.93, 34.60, 31.44.

Example 18, hydrogenation to produce 2,4,6-Trimethylbenzenemethanol (2i)

. Colorless oil. As shown in Table 3, the yield is 291 mg, 97%. 1H NMR (400 MHz, CDC1₃) δ 6.86 (s, 2H), 4.69 (s, 2H), 2.38 (s, 6H), 2.26 (s, 3H). ¹³C NMR (101 MHz, CDC1₃) δ 137.74, 137.31, 133.72, 129.16, 59.19, 21.00, 19.38.

Example 19, hydrogenation to produce 4-Fluoro-3-phenoxybenzenemethanol (2j)

The product is a yellowish oily liquid. As shown in Table 3, the yield is 427 mg ,98%>. H NMR (400 MHz, CDC1₃) δ 7.43 - 7.31 (m, 2H), 7.21 - 7.11 (m, 2H), 7.10 - 6.98 (m, 4H), 4.56 (s, 2H), 3.95 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 157.23, 154.85, 152.38, 143.77, 143.65, 137.65, 137.61, 129.83, 123.35, 123.18, 123.11, 120.31, 117.44, 117.11, 116.93, 64.07.

Example 20, hydrogenation to produce 4-Bromobenzenemethanol (2k)

The product is a white solid. As shown in Table 3, the yield is 344 mg, 92%. ^lR NMR (400 MHz, CDC1₃) δ 7.46 (d, J= 8.4 Hz, 2H), 7.21 (d, J= 8.3 Hz, 2H), 4.61 (s, 2H), 2.17 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 139.75, 131.62, 128.60, 121.44, 64.51.

Example 21, hydrogenation to produce 3-Bromobenzenemethanol(21)

The product is a white solid. As shown in Table 3, the yield is 344 mg, 92%. ^lR NMR (400 MHz, CDC1₃) δ 7.46 (s, 1H), 7.41 - 7.35 (m, 1H), 7.19 (d, J= 7.5 Hz, 2H), 4.58 (d, J= 2.1 Hz, 2H), 3.76 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 142.95, 130.62, 130.13, 129.89, 125.40, 122.61, 64.23.

Example 22, hydrogenation to produce 2-Bromo-5-hydroxybenzenemethanol (2m)

The product is a yellowish solid. As shown in Table 3, the yield is 381 mg, 94%. 1H NMR (400 MHz, CDCl₃) 6 8.18 (s, 1H), 7.42 (d, J= 8.6 Hz, 1H), 6.94 (d, J= 3.0 Hz, 1H), 6.71 (dd, J = 8.6, 3.0 Hz, 1H), 5.24 (s, 2H). ¹³C NMR (101 MHz, DMSO) δ 157.46, 142.43, 132.92, 115.90, 115.56, 109.47, 63.01, 40.49, 40.29, 40.08, 39.87, 39.66, 39.45, 39.24.

Example 23, hydrogenation to produce 4-Chlorobenzenemethanol (2n)

The product is a white solid. As shown in Table 3, the yield is 255 mg, 90%. ^lR NMR (400 MHz, CDC1₃) δ 7.38 - 7.18 (m, 4H), 4.65 (s, 2H), 2.08 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 139.24, 133.37, 128.69, 128.29, 64.55. Example 24, hydrogenation to produce 3-Cyanobenzenemethanol (2o)

The product is a yellowish oily liquid. As shown in Table 3, the yield is 255 mg, 96%. 1H NMR (400 MHz, CDC1₃) δ 7.66 (td, J= 1.7, 0.9 Hz, 1H), 7.62 - 7.53 (m, 2H), 7.46 (t, J= 7.7 Hz, 1H), 4.73 (s, 2H), 2.51 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 142.41, 131.12, 131.11, 130.17, 129.28, 118.86, 112.35, 63.85.

Example 25, hydrogenation to produce 1,4-Benzenedimethanol (2p)

The product is a white solid. As shown in Table 3, the yield is 262 mg, 95%. H NMR (400 MHz, DMSO) δ 7.25 (s, 4H), 5.12 (t, J= 5.7 Hz, 2H), 4.47 (d, J= 5.7 Hz, 4H). ¹³C NMR (101 MHz, DMSO) δ 141.31, 126.68, 63.23.

Example 26, hydrogenation to produce 4-Acetylbenzyl alcohol (2q)

The product is a yellowish solid. As shown in Table 3, the yield is 294 mg, 98%. 1H NMR (400 MHz, CDC1₃) δ 7.92 (d, J= 8.5 Hz, 2H), 7.52 - 7.34 (m, 2H), 4.76 (d, J= 3.0 Hz, 2H), 2.59 (s, 3H). ¹³C NMR (101 MHz, CDC1₃) δ 198.11, 146.38, 136.26, 128.61, 126.62, 64.53, 26.65.

Example 27, hydrogenation to produce 4-(Carbomethoxy)benzyl alcohol (2r)

The product is a yellowish solid. As shown in Table 3, the yield is 325 mg, 98%>. 1H NMR (400 MHz, CDC1₃) δ 7.99 (d, J= 8.4 Hz, 2H), 7.40 (dd, J= 8.0, 0.6 Hz, 2H), 4.73 (s, 2H), 3.90 (s, 3H), 2.54 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 167.06, 146.10, 129.81, 129.20, 126.45, 64.59, 52.13.

Example 28, hydrogenation to produce 4-Nitrobenzenemethanol (2s)

The product is a yellowish solid. As shown in Table 3, the yield is 302 mg, 99%>. 1H NMR (400 MHz, CDC1₃) δ 8.26 - 8.11 (m, 2H), 7.59 - 7.43 (m, 2H), 4.83 (s, 2H), 2.35 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 148.29, 127.01, 123.72, 63.97.

Example 29, hydrogenation to produce 2-Chloro-6-nitrobenzenemethanol (2t)

The product is a yellowish solid. As shown in Table 3, the yield is 336 mg, 90%>. 1H NMR (400 MHz, CDC1₃) 6 7.80 (dd, J= 8.2, 1.2 Hz, 1H), 7.69 (dd, J= 8.1, 1.2 Hz, 1H), 7.43 (t, J = 8.1 Hz, 1H), 4.92 (s, 2H). ¹³C NMR (101 MHz, CDC1₃) δ 151.24, 136.91, 134.57, 132.59, 129.55, 123.18, 58.52.

Example 30, hydrogenation to produce 4-(Trifluoromethyl)benzenemethanol (2u)

The product is a yellowish oily liquid. As shown in Table 3, the yield is 344 mg, 98%>. H NMR (400 MHz, CDC1₃) δ 7.56 (d, J= 8.1 Hz, 2H), 7.46 - 7.33 (m, 2H), 4.66 (s, 2H), 3.04 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 144.63, 129.88, 129.56, 129.24, 128.22, 126.80, 125.52, 125.41, 125.37, 122.81, 64.26, 64.22, 64.19.

Example 31, hydrogenation to produce 4-Carboxybenzyl alcohol (2v) The product is a white solid. As shown in Table 3, the yield is 282 mg, 93%. 1H NMR (400 MHz, DMSO) δ 7.90 (d, J= 8.2 Hz, 2H), 7.42 (d, J= 8.3 Hz, 2H), 4.57 (s, 2H). ¹³C NMR (101 MHz, DMSO) δ 167.90, 148.08, 129.84, 129.63, 126.59, 62.91, 40.57, 40.36, 40.15, 39.94, 39.73, 39.53, 39.32.

Example 32, hydrogenation to produce l-Naphthylenemethanol( 2w)

The product is a white solid. As shown in Table 3, the yield is 300 mg, 95%. 1H NMR (400 MHz, CDC1₃) δ 8.09 (dd, J= 6.6, 3.0 Hz, 1H), 7.96 - 7.90 (m, 1H), 7.88 - 7.81 (m, 1H), 7.63 - 7.53 (m, 2H), 7.53 - 7.40 (m, 2H), 5.06 (s, 2H), 3.26 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 136.30, 133.81, 131.25, 128.71, 128.49, 126.34, 125.90, 125.48, 125.30, 123.71, 63.31, 63.26.

Example 33, hydrogenation to produce 4-Methoxy-2-pyridinemethanol (2x)

The product is a yellowish solid. As shown in Table 3, the yield is 264 mg, 95%. 1H NMR (400 MHz, CDCI3) δ 8.28 (d, J= 5.8 Hz, 1H), 6.82 (d, J= 2.5 Hz, 1H), 6.68 (dd, J= 5.8, 2.5 Hz, 1H), 4.68 (s, 2H), 3.81 (s, 3H). ¹³C NMR (101 MHz, CDC1₃) δ 166.44, 161.72, 149.66, 108.99, 106.05, 64.44, 64.39, 64.35, 55.22, 55.17.

Example 34, hydrogenation to produce 2-Thienylmethanol (2y)

The product is a yellowish oily liquid. As shown in Table 3, the yield is 225 mg, 99%>. H NMR (400 MHz, CDC1₃) δ 7.27 (dd, J= 5.0, 1.3 Hz, 1H), 7.02 - 6.99 (m, 1H), 6.97 (dd, J= 5.0, 3.5 Hz, 1H), 4.81 (s, 2H), 2.05 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 143.99, 126.89, 125.64, 125.51, 59.99.

Example 35, hydrogenation to produce 2-Furanmethanol (2z)

The product is a yellowish oily liquid. As shown in Table 3, the yield is 186 mg, 95%>. H NMR (400 MHz, CDC1₃) δ 7.38 (dt, J= 1.8, 0.9 Hz, 1H), 6.40 - 6.18 (m, 2H), 4.54 (s, 2H), 2.82 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 154.08, 142.50, 110.35, 107.72, 57.21.

Example 36, hydrogenation to produce 3-Phenyl-2-propen-l-ol (2aa)

The product is a yellowish solid. As shown in Table 3, the yield is 254 mg, 95 %. 1H NMR (400 MHz, CDCI3) δ 7.43 - 7.15 (m, 5H), 6.60 (d, J= 15.9 Hz, 1H), 6.35 (dt, J= 15.9, 5.7 Hz, 1H), 4.31 (dd, J= 5.7, 1.5 Hz, 2H), 1.77 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 136.70, 131.13, 128.62, 128.54, 127.71, 126.49, 63.72.

Example 37, hydrogenation to produce 2-Methyl-3-phenyl-2-propen-l-ol (2ab)

The product is a yellowish solid. As shown in Table 3, the yield is 269 mg, 91%. 1H NMR (400 MHz, CDCI3) δ 7.41 - 7.05 (m, 5H), 6.50 (s, 1H), 4.14 (d, J= 0.9 Hz, 2H), 1.86 (d, J= 1.4 Hz, 3H). ¹³C NMR (101 MHz, CDC1₃) δ 154.67, 137.73, 137.68, 128.95, 128.21, 126.46, 124.98, 124.94, 68.81, 68.79, 15.35.

Example 38, hydrogenation to produce Benzenepropanol (2ac) The product is a colorless oily liquid. As shown in Table 3, the yield is 263 mg, 97%. 1H NMR (400 MHz, CDC1₃) δ 7.38 - 7.08 (m, 5H), 3.65 (t, J= 6.5 Hz, 2H), 2.82 - 2.57 (m, 2H), 2.00 - 1.76 (m, 2H), 1.63 (s, 1H). ¹³C NMR (101 MHz, CDC1₃) δ 141.86, 128.46, 128.43, 125.89, 62.27, 34.25, 32.11.

Example 39, hydrogenation to produce 1-Pentanol (2ad)

The product is a colorless oily liquid. As shown in Table 3, the yield is 109 mg, 62%. H NMR (400 MHz, CDC1₃) δ 3.62 (s, 2H), 2.26 (s, 1H), 1.70 - 1.46 (m, 2H), 1.42 - 1.22 (m, 4H), 0.91 (ddd, J= 7.1, 4.0, 2.0 Hz, 3H). ¹³C NMR (101 MHz, CDC1₃) 562.81, 32.41, 27.91, 22.47, 14.00.

Example 40, hydrogenation to produce 1-Octanol(2ae)

The product is a colorless oily liquid. As shown in Table 3, the yield is 257 mg, 99%>. 1H NMR (400 MHz, CDC1₃) δ 4.83 (t, J= 5.3 Hz, 1H), 1.78 - 1.57 (m, 2H), 1.49 - 1.12 (m, 11H), 0.88 (t, J= 6.9 Hz, 3H). ¹³C NMR (101 MHz, CDC1₃) δ 101.72, 34.44, 31.79, 29.35, 29.18, 23.59, 22.66, 14.09.

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Claims

Claims (15) We claim:

1. A series of iridium-based organometallic catalysts that catalyzes the dehydrogenation of formic acid in aqueous solution, and hydrogenation of aldehydes using formic acid as the hydrogen source. The structures of the catalysts are shown below.

Y = any anion, particularly N0₃ ^", C10₄ ^", BF₄ ^", S0₄ ^", SbF₆ ^", PF₆ ^", CI^", acetate;

X = any anionic ligand, particularly X could be CI^", Br^", T, F^", OH^";

Z = any neutral ligand, particularly water, methanol, alcohol, tetrahydrofuran, or null

(non-existent);

n= 1 or 2;

R = any substitution group(s), particularly electron donating groups such as MeO, R'O, Me₂N, or R'₂N. R' = any alkyl, cycloalkyl, aryl group.

2. The catalyst(s) with the structure shown in claim 1, wherein R = any electron donating group(s), particularly R = OR¹, R¹ = any alkyl, cycloalkyl, aryl groups. Catalyst 3 is an example.

3. The catalyst(s) with the structure shown in claim 1, wherein R = NR^XR², R¹ or R²= alkyl, cycloalkyl, aryl, where R¹ or R² could be linked such as . Catalyst 4 is an example.

4. A process for producing hydrogen gas through dehydrogenation of formic acid solution utilizing one of the catalysts with the structures, the process comprising:

preparing an aqueous solution of the catalyst in a reaction container or chamber; adding formic acid continuously or intermittently, as a pure liquid or as aqueous solution;

generating H₂/C0₂ mixture;

collecting the mixture gas and removing it from the reaction container/chamber; feeding the gas, with or without purification, to other applications downstream, such as a fuel cell.

5. The process of claim 4, wherein the catalyst concentration of the aqueous-phase system is within 0. 0001-5.0 mol /L.

6. The process of claim 4, wherein the aqueous system contains formic acid with the concentration ranging from 0.001 mol/L to near pure formic acid (-28 mol/L under room temperature and pressure) with or without other additives.

7. The process of claim 4, wherein the temperature of the reactive system maintained within 0-100 °C and the pH of the reactive system maintained between 0-14.

8. A process to reduce aldehydes, using formic acid as the hydrogen source utilizing one of the catalysts with the structures, the process comprising:

preparing an aqueous solution of the catalyst in a reaction container or chamber; adding a solution of mixture of formic acid and aldehyde, continuously or intermittently;

running the reaction for a period of time;

purifying the reaction product(s).

9. The process of claim 8, wherein the catalyst concentration of the aqueous-phase system is within 0. 0001-5.0 mol /L.

10. The process of claim 8, wherein the solution system contains formic acid with the

concentration ranging from 0.001 mol/L to 25 mol/L.

11. The process of claim 8, wherein the solution system contains an aldehyde with the

concentration ranging from 0.001 mol/L to 10 mol/L.

12. The process of claim 8, wherein the solution system contains formic acid and aldehyde with the molar ratio ranging from 1 : 1 to 10: 1.

13. The process of claim 8, wherein the reaction time ranges from 0.1 minute to 24 hours.

14. The process of claim 8, wherein the temperature of the reactive system maintained within 0-100 °C and the pH of the reactive system maintained between 0-14.

15. The process of claim 8, wherein the aldehyde is an aliphatic or aromatic aldehyde

including alpha, beta-unsaturated aldehydes.