Iridium or rhodium complex comprising k 2-( n,n)-pyridyl-1,2,3-triazole ligands and use thereof as a catalyst of a formic acid dehydrogenation and hydrogen production reaction
Patent Information
- Application Number
- PCT/ES2025/070107
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-03-04
- Filing Date
- 2025-03-04
- Publication Date
- 2025-10-02
AI Technical Summary
Current methods for hydrogen production from formic acid face challenges such as the need for high temperatures, formation of carbon monoxide byproducts, and catalyst deactivation, especially in the absence of solvents, limiting the efficiency and durability of hydrogen production systems.
Development of iridium(III) and rhodium(III) complexes with pyridyl-1,2,3-triazole ligands that catalyze the dehydrogenation of formic acid under mild conditions, allowing for high-purity hydrogen production without solvent, with notable activity and durability over multiple cycles.
The complexes achieve high turnover frequencies and cumulative turnover numbers, producing hydrogen and carbon dioxide without detectable carbon monoxide, demonstrating stability and efficiency in multiple dehydrogenation cycles.
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Figure ES2025070107_02102025_PF_FP_ABST
Abstract
Description
[0001] IRIDIUM OR RHODIUM COMPLEX COMPRISING K LIGANDS 2 -( / V / V)-PYRIDIL-1,2,3-TRIAZOLE AND ITS USE AS A CATALYST FOR THE DEHYDROGENATION REACTION OF FORMIC ACID AND HYDROGEN PRODUCTION
[0002] DESCRIPTION
[0003] TECHNICAL SECTOR
[0004] The present invention belongs to the technical field of the chemical industry and, in particular, relates to new types of metal catalysts for the dehydrogenation of formic acid, as well as to the method used to dehydrogenate formic acid and produce hydrogen using said catalysts.
[0005] BACKGROUND OF THE INVENTION
[0006] Currently, approximately 96% of global hydrogen (H2) production comes from fossil sources, primarily through natural gas reforming, hydrocarbons, or coal gasification processes. Although hydrogen is used in various industrial applications, the major challenge is to base the power supply on fuel cells powered by external hydrogen. However, the efficient storage and transportation of hydrogen poses significant challenges due to its low gravimetric and volumetric density. Solving these problems requires the development of safe and cost-effective technologies that guarantee a stable hydrogen supply. The use of fuel cells also faces the problem of the presence of variable amounts of carbon monoxide accompanying the hydrogen, which can be harmful to the electrode component materials.This fact implies the need for high purity hydrogen with a minimum carbon monoxide content, typically less than 10 ppm (IEA, Global Hydrogen Review 2022, Paris https: / / www.iea.org / reports / global-hydrogen-review-2022, License: CC BY 4.0).
[0007] Physical storage of H2 gas requires the use of materials with special characteristics, resistant to H2 corrosion and high pressures, which guarantee safety during transport. Liquid H2 storage is also not a competitive alternative, as it is a very energy-intensive process that uses extremely low temperatures and very high pressures, with daily losses of 3 to 6% due to vaporization. Chemical hydrogen storage offers an alternative that involves the use of materials with a high hydrogen content, easy to transport and store, and with the possibility of releasing their hydrogen content through a chemical process, generally catalyzed (Usman, MR, Renewable and Sustainable Energy Reviews).
[0008] Among the hydrogen-carrying liquids (LOHCs), formic acid stands out for being a biodegradable liquid, with a notable H2 content (4.4% by mass) and low toxicity, which can be obtained by hydrogenation of carbon dioxide, a greenhouse gas (Figure 1 A). The dehydrogenation of formic acid using heterogeneous catalysis is a process that normally requires high temperatures, which favors the secondary reaction of dehydration over dehydrogenation, and gives rise to the formation of CO as a byproduct (Figure 1 B).
[0009] In this context, the development of catalytic precursors that allow the production of high-purity hydrogen from formic acid under milder conditions is a preferred line of research. Homogeneous catalysts are especially interesting because they are coordination compounds with broad structural versatility, allowing for the dehydrogenation of formic acid under milder conditions, facilitating the isolation of intermediate species and the study and control of reaction mechanisms. Ir(lll) complexes with applications as catalysts for the production of H2 from formic acid have been widely studied. The Himeda and Fujita groups developed derivatives of the Cp*lr fragment. IH , where Cp* is pentamethyl-r| 5-cyclopentadienyl, which also incorporate / ^-( N) ligands in their structure, and stand out for their activity and stability in aqueous medium (Sordakis, K. et al., Chem. Rev. 2018, 1 18, 372-433). Although 1,2,3-triazole heterocyclic rings have been used in the design of bidentate N,N and N,C type ligands, in most cases the nitrogen in position 2 (N2) does not interact with the metal center due to the greater donor character of the nitrogen in position 3 (N3) (Frutos, M. et al., Dalton Trans. 2018, 47, 9975-9979). The use of pyridyl-1,2,3-triazole ligands in organometallic chemistry has been restricted to a type of l -(N,C) coordination, derived from the use of mesoionic ligands (Maity, R.; Sarkar, B. JACS Au 2022, 2, 22-57). Only recently, He and collaborators have developed aqueous-complexes derived from Cp*lr IHwith pyridyl-1,2,4-triazole, pyridyl-1,2,3-triazole and bis(1H-1,2,4-thazol) ligands, with applications in the dehydrogenation of formic acid in aqueous solution (Ge, S. et al., Inorganic Chemistry
[0010] 2023, 62 (45), 18375-18383). Most of these homogeneous systems generate hydrogen efficiently without significant amounts of CO. Furthermore, dehydrogenation reactions carried out in aqueous media avoid the use of organic solvents and additives. However, they frequently present challenges related to the low activity and durability of the catalysts.
[0011] The dehydrogenation of formic acid in the absence of solvent and additives is an environmentally sustainable process, as it leads to the formation of H and CO as the only reaction products. The number of organometallic complexes capable of efficiently catalyzing the dehydrogenation of formic acid under these conditions is smaller. Among them, only the system of Fischmeister et al. is a derivative of the [Cp*lr] fragment. IH ], but in this case the dehydrogenation was explored only for 10 minutes to obtain initial TOFs (Wang, S. et al., ChemSusChem, 2019, 12 (1 ), 179-184).
[0012] In the state of the art, a series of patent applications and patents related to the use of organometallic complexes as homogeneous catalysts in formic acid dehydrogenation processes in the absence of a solvent have been located. Among them, the following should be mentioned: application WO2014134742 discloses the use of a RuCh / m-TPPTS (meta-trisulfonated triphenylphosphine) catalytic mixture in a heterogeneous / aqueous phase; application WO2022122522 refers to a method for the reversible storage of hydrogen. H2 is obtained by dehydrogenation of mixtures of C1 - C18 alcohols, formic acid and water in the presence of a transition metal hydride (Ru, Ir, Mn, Co, Mo, Fe, and Rh). The hydride complex contains b¡-, tri- and tetradentate PPPP type ligands; Patent JP2021016832 discloses a catalyst that is a derivative of the Cp*lr fragment IH, capable of carrying out the dehydrogenation of formic acid under high pressure conditions (160 MPa); application WO2018194537 describes systems derived from the Cp*lr fragment with N,N- bidentate ligands that catalyze FADH in aqueous solution; application WO2016057661 describes the dehydrogenation of formic acid catalyzed by metal complexes with P, N-type ligands (NHC); patent JP2015083544 describes the dehydrogenation of alcohols to obtain different carbonyl and carboxylic compounds, catalyzed by organometallic complexes based on a metal that can consist of Ru, Rh or Ir; application WO2015053317 refers to complexes of general formula [Cp*M(k 2 - (N, A / )-L)CI] +, where M is Ir, Rh, Ru, Co, Os, Ni, Fe, Pd or Pt (Figure 2). In these iridium complexes, all X atoms of the five-membered ring are substituted by an R group. These complexes catalyze the production of H2 by dehydrogenation of formic acid. The reactions are carried out in aqueous solution at different concentrations and in the presence of different bases, considering the HCOOH / HCOONa mixture; application WO2012070620 describes the preparation of complexes with the general formula MHm(CO)L n (where M = Ir, Fe, Rh, Ru; m = 3 and n = 2 and the ligands L are phosphines) and their use as catalysts for hydrogen production reactions in concentrated aqueous solutions of HCOOH; and application WO2011 108730 refers to a catalyst based on a fragment [Cp*lr IH] and a bidentate ligand CC or CN for the production of formic acid by hydrogenation of carbon dioxide, in water, at a pressure of 1 atm, and for the dehydrogenation of formic acid at room temperature.
[0013] In view of the state of the art, we can conclude that the use of systems derived from the organometallic fragment [Cp*lr IH ] in formic acid dehydrogenation reactions is well known. The complexes developed by the Himeda group allow obtaining truly competitive TOF and accumulated TON values. However, their usefulness is limited to their use in aqueous solution. In turn, the complexes derived from [Cp*lr IH ] developed by Fischmeister and collaborators catalyze the dehydrogenation of neat formic acid, but their activity has been explored for short periods of time and the reported TOF values are limited to the initial moments of the reaction.
[0014] The present invention offers a new system of catalysts that are highly active over several cycles and without signs of deactivation in a method of dehydrogenation of formic acid in the absence of solvent, for the production of H2 / CO2 without detectable amounts of CO.
[0015] DESCRIPTION OF THE INVENTION
[0016] A first object of the invention is a new iridium (III) or rhodium (III) complex characterized in that it has the general formula (1): and stoichiometric formula [Cp'M(k 2 -A / ,A / )Y] n+ [A ]n comprising a Cp'M fragment bound to a ligand l^-(N,N), where the ligand k 2 -( / V,A / ) is a pyridyl-1,2,3-triazole derivative that is linked to the metal center M through two non-adjacent nitrogen atoms, the pyridyl nitrogen and the nitrogen in position 2 (N2) of the triazole, leaving free the more basic nitrogen in position 3 (N3) of the triazole ring, and where:
[0017] M represents a metal consisting of iridium or rhodium;
[0018] Cp', in its stoichiometric formula, represents a g ligand 5 -substituted or unsubstituted cyclopentadienyl, where R 1 to R 5 represent, independently, a hydrogen atom; or an alkyl group (preferably, CH3, CH(CH3)2 or C(CH3)3), or an aryl group (preferably, CeH5), or a silyl group (preferably, Si(CH3)3)-or a perfluoroalkyl group (preferably, CF3), and where Cp' is designated Cp* when R 1 to R 5 are methyl;
[0019] R 6 to R 9 independently represent a hydrogen atom; or a carbon chain; or a fluorocarbon chain; or an alkoxyalkane group. Preferably, R 6 to R 9 They represent, independently, a hydrogen atom; or a carbon chain (-(CH2) n-CH3, where, preferably, n= 0, 1, 2 or 3); or a fluorocarbon chain (-(CF2) n -CF3, , where, preferably, n= 0, 1, 2 or 3); or an alkoxyalkane group (-O-(CH2) n -CH3, where, preferably, n= 0, 1, 2 or 3); and where R 6 and R 7 (radicals of the carbons adjacent to the nitrogen of the pyridyl ring), may form part of a ring with -CH=CH- bonds where each hydrogen of said ring may be substituted, independently, preferably by a methyl or by a trifluoromethyl or by a methoxy or by a phenyl; n is 1 or 2, and represents the ionic charge of the complex;
[0020] Y represents an F, Cl, Br, or I atom; or, for n = 1, an OH or OTf functional group; or, for n = 2, H2O;
[0021] A represents a counterion selected from the group consisting of F, Cl, Br, I, OH, OTf, BF4, BAr4, and PF6;
[0022] R 10 is a CO2R group 11 ; where R 11represents a hydrogen, or an alkyl group (preferably CH3, CH2CH3, CH(CH3)2 or C(CH3)3) or an aryl group (preferably CeH5). In a particular embodiment of the invention, R 10 It may be a salt [-COO] [Z] + ; where [Z] + may be preferably selected from a group consisting of a cation [NR'4] + , [PR'4] + , K + and Na + where, preferably, R' is selected from a group consisting of H, methyl, ethyl, propyl, butyl and phenyl.
[0023] In a particular embodiment where M= Ir; R 1 to R 5 = CH3 (Me); R 6 to R 9 = H, Y = Cl, A = OTf, R 10 = COsEt (hereinafter Complex 1a, comprising the ligand L a ), the complex is represented according to the following general formula:
[0024] In another particular embodiment in which M= Ir; R 1 to R 5 = CH3; R 6 , R8 and R 9 = H; R 7 = CH3O (MeO); Y = Cl, A = OTf, R 10 = COsEt (hereinafter Complex 1 b, comprising the ligand L b ), the complex is represented according to the following general formula:
[0025] In another particular embodiment in which M= Ir; R 1 to R 5 = CH3; R 6 , R 8 and R 9 = H; R 7 = CH3; Y = Cl, A = OTf, R 10 = COsEt (hereinafter Complex 1c, comprising the ligand L c ), the complex is represented according to the following general formula:
[0026] In another particular embodiment in which M= Ir; R 1 to R 5 = CH3; R 6 , R 8 and R 9 = H; R 7 = CF3; Y = Cl, A = OTf, R 10 = COsEt (hereinafter Complex 1 d, comprising the ligand L d ), the complex is represented according to the following general formula:
[0027] Another object of the invention is the use of the iridium (III) or rhodium (III) complex described above as a catalyst.
[0028] Additionally, the object of the invention is the use of said catalyst to dehydrogenate formic acid and produce hydrogen, free of CO and in the absence of solvent. In particular, the developed complexes have shown notable activity in the dehydrogenation reactions of neat formic acid, in the absence of solvent, requiring minimal quantities of sodium formate (NaOCH2) to initiate the reaction. Specifically, it has been demonstrated that the claimed complex allows obtaining average turnover frequency values (TOF50, defined as moles of H2 / (moles of catalyst*!)) of up to 11,000 h -1and a cumulative Turnover Number (TON, defined as moles of H2 / moles of catalyst) of up to 14134 over several dehydrogenation cycles.
[0029] BRIEF DESCRIPTION OF THE FIGURES
[0030] To complement the description and in order to help better understand the characteristics of the invention, the following figures are attached as an integral part of said description, in which, for illustrative and non-limiting purposes, the following has been represented:
[0031] Figure 1 (State of the art):
[0032] Figure 1 A. Hydrogen storage cycle in the form of formic acid; Figure 1 B. Decomposition reaction of formic acid by dehydration, generating H2O and CO.
[0033] Figure 2. (State of the art). Structure defined in international application WO2015053317, where X 9 to X 16 They can be C or N and R atoms7 to R 13 are selected from H, alkyl, OH, OR, NO2, halogen, RSO2, COOR, NR2 and Ph, with the proviso that in the six-membered ring, when X' = N (where, i = 13-16), R' (i = 10-13) is absent.
[0034] Figure 3. Synthesis of the complex [Cp*lr( 2 -A / ,A / )CI] + by reaction of the pyridyl-1,2,3-triazole ligand (L) with [lrCl2Cp*]2.
[0035] Figure 4. (State of the art). General method used for the preparation of L ligands.
[0036] Figure 5. Gas production graphs. Measurements of the variation in relative pressure inside the reactor corresponding to inlets 1 -C1, 1 -C2, 1 -C3 of Table 1. The pressures are relative to the initial pressure at the time of formic acid injection. The reactor was depressurized on successive occasions before its interior exceeded the safety pressure.
[0037] Figure 6. Gas production graphs. Measurements of relative pressure variation inside the reactor corresponding to inlets 1-C4, 1-C5, 1-C6 of Table 1. The pressures are relative to the initial pressure at the time of formic acid injection. The reactor was depressurized several times before its interior exceeded the safety pressure.
[0038] Figure 7. Gas production graphs. Measurements of the variation in relative pressure inside the reactor corresponding to inlets 2-C1 and 2-C2 of Table 1. The pressures are relative to the initial pressure at the time of formic acid injection. The reactor was depressurized on several occasions before its interior exceeded the safety pressure.
[0039] Figure 8. Gas production graphs. Measurements of the variation in relative pressure inside the reactor corresponding to inlets 1 -C1 and 1 -C2 of Table 3. The pressures are relative to the initial pressure at the time of formic acid injection. The reactor was depressurized on several occasions before its interior exceeded the safety pressure.
[0040] Figure 9. Gas production graphs. Measurements of relative pressure variation inside the reactor corresponding to inlets 1 - C3, 1 - C4 of Table 3. The pressures are relative to the initial pressure at the time of formic acid injection. The reactor was depressurized several times before its interior exceeded the safety pressure.
[0041] Figure 10. Gas production graphs. Measurements of relative pressure variation inside the reactor corresponding to inlets 1-C5, 1-C6, 1-C7 of Table 3. The pressures are relative to the initial pressure at the time of formic acid injection. The reactor was depressurized on several occasions before its interior exceeded the safety pressure.
[0042] Figure 11. Gas production graphs. Measurements of relative pressure variation inside the reactor corresponding to inlets 1-C8, 1-C9, 1-C10 of Table 3. The pressures are relative to the initial pressure at the time of formic acid injection. The reactor was depressurized on several occasions before its interior exceeded the safety pressure.
[0043] DETAILED DESCRIPTION OF THE INVENTION
[0044] In a particular embodiment of the invention, the synthesis process of the claimed complex is carried out as shown in Figure 3, by reacting one equivalent of [lrCl2Cp*]2 with two equivalents of the pyridyl-1,2,3-triazole ligand (L) and 2.1 equivalents of sodium triflate (NaOTf), in methylene chloride as solvent. The process is carried out at room temperature (20 to 25 °C). e C) for 18 hours, with a loading of the metal precursor of 100 to 200 mg. In Figure 3, R is selected from a group consisting of H, CH3O, CH3, and CF3. The complexes 1a-1d are isolated by precipitation with diethyl ether or hexane.
[0045] In a further particular embodiment of the invention, the process may comprise an additional preliminary step of preparing the pyridyl-1,2,3-triazole ligand. To this end, the click chemistry methodology, previously described in the literature for the ligand L, may be carried out. a and Lb (Sabater, S. et al., Organometallics 2016, 35, 2256-2266; Olivares, M. et al., Eur. J. Inorg. Chem. 2020, 801-812), as shown in Figure 4. Again in this case, R is selected from a group consisting of H, CH3O, CH3, and CF3.
[0046] A series of tests carried out to test the effectiveness of the developed catalysts are described below:
[0047] First, the ligands L were prepared a -L d according to the methodology described in Sabater, S. et al., Organometallics 2016, 35, 2256-2266 and Olivares, M. et al., Eur. J. Inorg. Chem. 2020, 801-812, with yields of 60-90%.
[0048] The reagent [lrCl2Cp*]2 was prepared as described in Ball, RG et al., Inorg. Chem. 1990, 29, 2023-2025.
[0049] The solvents (dichloromethane, diethyl ether, toluene, tetrahydrofuran, acetonitrile, and hexane) were dried by passing through columns of a solvent purification system or by dehydrating agents and distillation. Triethylamine (NET) was dried and distilled over calcium hydride (CaH2). All other reagents were purchased commercially and used without further purification.
[0050] The preparations of the metal complexes were carried out under an inert atmosphere (argon). Thus, once the reagents were prepared, complexes 1a, 1b, 1c and 1d were synthesized. To do this, one equivalent of [lrCl2Cp*]2, two equivalents of the corresponding pyridyl-1,2,3-triazole ligand (L) and 2.1 equivalents of sodium triflate (NaOTf) were dissolved in 10 mL of CH2Cl2 in a 25 mL Schlenk flask. The reaction mixture was stirred at room temperature (20 to 25 °C). eC) for 18 hours and then filtered through a layer of diatomaceous earth. The filtrate was dried under reduced pressure, and the resulting residue was washed and precipitated with diethyl ether.
[0051] Experiment 1. Obtaining Complex 1 a
[0052] For the synthesis of complex 1a, 109.5 mg (0.502 mmol) of L were dissolved a , 200 mg (0.251 mmol) of [lrCl2Cp*]2 and 90.7 mg (0.527 mmol) of NaOTf in dry CH2Cl2 (10 mL). Complex 1a was isolated as a yellow solid, with a yield of 310.2 mg (85%).
[0053] Experiment 2. Obtaining Complex 1 b
[0054] For the synthesis of complex 1 b, 93.8 mg (0.376 mmol) of L were dissolved b , 150 mg (0.186 mmol) of [lrCl2Cp*]2 and 68.1 mg (0.395 mmol) of NaOTf in dry CH2Cl2 (10 mL). Complex 1 b was isolated as a yellow solid, with a yield of 205.5 mg (71%). For the synthesis of complex 1 c, 58.3 mg (0.251 mmol) of L were dissolved c , 100 mg (0.126 mmol) of [lrCl2Cp*]2 and 45.3 mg (0.263 mmol) of NaOTf in dry CH2Cl2 (10 mL). After 18 hours of reaction, the mixture was washed with water and subjected to an extraction process with CH2Cl2. The organic phase was dried over MgSO4, after which the solvent was removed in vacuo. The residue obtained was precipitated and washed with diethyl ether. Complex 1 c was obtained as a yellow solid, with a yield of 144.4 mg (77%).
[0055] Experiment 4. Obtaining Complex 1d
[0056] For the synthesis of complex 1d, 78.1 mg (0.251 mmol) of L was dissolved d, 100 mg (0.126 mmol) of [lrCl2Cp*]2 and 43.2 mg (0.251 mmol) of NaOTf in dry CH2Cl2 (10 mL). After 18 hours of reaction, the mixture was washed with water and subjected to an extraction process with CH2Cl2. The organic phase was dried over MgSO4 after which, the solvent was removed in vacuo. The residue obtained was precipitated and washed with hexane. Complex 1 d was obtained as a yellow solid, with a yield of 159.0 mg (79%).
[0057] The 1 aa 1d complexes were used as catalysts in the dehydrogenation of formic acid in the absence of solvent, according to equation 1: (Equation 1)
[0058] Experiment 5. Dehydrogenation reaction
[0059] The general procedure followed to carry out the dehydrogenation reactions and measurement of the generated gas is described below:
[0060] The experiment requires the prior preparation of a 10:1 mixture of formic acid (M = 46.03 g / mol; w = 1.2183 g / mL) / sodium formate (M = 68.01 g / mol). To do this, 360 mg (5.29 mmol) of HCOONa is dissolved in 2 mL (52.9 mmol) of HCOOH.
[0061] The experiments were carried out in a 20 mL reactor equipped with a pressure transducer (“Man on the Moon” gas evolution measurement kit, model X103). The reactor was charged with the required amount of catalyst under an argon atmosphere and then heated to operating temperature (90 °C). Once a constant pressure reading was reached, the pressure transducer and stopwatch were reset to zero, and a 10:1 mixture of formic acid / sodium formate (91 pL of mixture, 2.35 mmol of HCOOH) or neat formic acid (100 pL, 2.64 mmol) was injected through a septum. The relative pressure of the reactor was recorded thereafter at regular 15 s intervals. To avoid exceeding the safety pressure of the reactor, the relief valve was opened whenever the absolute pressure inside the reactor exceeded approximately 0.25 MPa.
[0062] Subsequent processing of these data with a spreadsheet allowed obtaining the TON and TOF values, which are a measure of the catalyst activity in terms of stability and process speed, respectively. The chemical amount of dihydrogen (n(H2)) in moles was first calculated, considering an ideal gas behavior for the 1:1 mixture of CO2 and H2: n(mixture) = VP / (RT) ; n(H2) = n(mixture) / 2 where AP is the accumulated pressure increase at the time of measurement, V the volume of the flask, R the ideal gas constant (8.3145 m 3 Pa K -1 mol -1 ), the temperature of the system and n(H2) the moles of H2 obtained.
[0063] The calculation of TON and TOF was performed as follows: n(H2)
[0064] TON = - - ; TOF = TON / t float where n ca t is the moles of catalyst used and í is the time elapsed from the addition of the catalyst until the time of measurement (h).
[0065] As an example, Table 1 shows the reaction conditions, times, yield, conversions, TON and TOF, corresponding to different dehydrogenation experiments catalyzed by complex 1d.
[0066] Table 1. Dehydrogenation of net HCOOH catalyzed by complex 1d
[0067] 91 pL (2.35 mmol of HCOOH) of a 10:1 mixture of HCOOH / HCOONa was taken.
[0068] The yield was calculated taking into account the amount of HCOOH injected and the final accumulated pressure, with 1:1 being the stoichiometry of the process (Equation 1). max is the maximum TOE value. The time corresponding to this maximum value is indicated in parentheses. TOF5o is the TOF value corresponding to 50% conversion. TOF is the TOF value at the end of the reaction (maximum conversion value).
[0069] Entries 1-C1 to 1-C6 in the table show results from the same experiment (same catalyst). According to the general procedure described, a 10:1 HCOOH / HCOONa mixture was used in entry 1-C1. Entries 1-C-2 to 1-C6 show successive dehydrogenation cycles of neat formic acid (Figures 5 and 6). Entries 2-C1 and 2-C2 correspond to the same experiment (same catalyst sample) (Figure 7).
[0070] In addition to the data shown in Table 1, the catalyst durability was tested in an additional experiment in which 0.1 mol% of catalyst was used to dehydrogenate formic acid in 10 cycles (ca. 1 mL of HCOOH), over a period of three days. The results are shown in Table 2:
[0071] Table 2
[0072] Specifically, a 10:1 mixture of HCOOH / NaOCHO (91 pL) was added to a conditioned MoM system (100 eC) containing complex 1d (0.11 mol% relative to HCOOH). This catalytic test showed an activation period and reached a maximum TOE value of 1749 h'. 1 In a second dehydrogenation cycle, a new charge of neat formic acid (100 µL) was added. In this cycle, a TOE value of 4253 h was reached. -1 (Figure 8). The system was then conditioned to 90 e C and two more formic acid charges were added consecutively (2x100 pL; Figure 9). The experiment continued with the addition of three new formic acid charges (3x100 pL; Figure 10), followed by three more (Figure 11). In total, the addition of approximately 1 mL of formic acid was completed. The TOF5o values remained between 2000 and 4000 h -1in all cases, and only the last cycle showed a lower activity, probably due to the consumption of sodium formate throughout the ten catalytic cycles, after which a cumulative TON of 7702 was reached. Table 3 shows a selection of these results and compares them with those published by other authors:
[0073] Table 3. Comparative table of activity of different active metal catalysts in the dehydrogenation of HCOOH in the absence of solvent. a The gas mixture contains CO amounts of 150 to 5000 ppm. b Initial charge of HCOOH / HCOONa (10:1).
[0074] C Cumulative TON (three days); initial HCOOH / NaO2O2 loading (91 pL) and 9 HCOOH loadings (100 pL). d Cumulative TON (two days); initial HCOOH / NaO2O2 charge (91 pL) and 5 HCOOH charges (100 pL). e Accumulated TON in 90 minutes; initial HCOOH / NaOCHO charge (91 pL) and one HCOOH charge (100 pL).
[0075] The required amount of catalyst was taken from a solution of known concentration in dichloromethane. Once this amount was added to the reaction flask, the dichloromethane was removed under vacuum before setting up the equipment.
[0076] Entry 8 shows an example of the activity of catalyst 1a in the presence of the NEts base (11 mol%) instead of HCOONa. In this case, maximum TOE values greater than 18000 h were reached. -1 .
[0077] As can be seen in Table 3, experiments performed with ruthenium complexes described by Mistein (entry 1, Catal. 2021, 4, 193-201) or iridium complexes described by Williams (entry 3, Nat. Commun. 2016, 7, 11308) show significant presence of carbon monoxide. In turn, experiments using iridium systems described by Fischmeister et. al (entry 2, ChemSusChem 2019, 12 (1 ), 179-184), or those studied by Gelman et. al (entry 4, ACS Catal. 2017, 7, 8139-8146), only provide initial TOF values (10 min or less), but do not offer information on the rate of the process over a long period of time. Studies conducted by Oro et al. (entry 5, Green Chem. 2018, 20, 4875–4879) using iridium systems show that the maximum TOF value occurs at 5 h. However, they require the addition of 30 mol% sodium formate and 100 mol% water. Finally, experiments conducted by Casado et al.al (entries 6 and 7, Inorg. Chem. Front. 2022, 9, 4538-4547), using rhodium systems, were shown to have lower maximum TOF values than those previously observed with iridium systems.
[0078] The catalysts that are part of this invention demonstrate TOF values competitive with those published and TON values that support their durability to the extent that it has been explored.
[0079] Experiment 6. CO detection
[0080] The analysis of the gases generated during catalysis was performed on an Agilent 490 Micro GC. The equipment used was a gas chromatograph with three independent modules, with a sensitivity of up to 1 ppm and optimized with an Agilent Technologies standard for refinery gas. Gas samples corresponding to entries 9 and 10 of Table 3 were measured. In both cases, the amount of CO formed was below the detection limit of the chromatograph used.
[0081] In view of the tests carried out, it can be concluded that the Ihdio(lll) complexes of stoichiometry [Cp*lr( 2 -A / ,A / )CI] + developed show a remarkable activity in the dehydrogenation of formic acid, both in solution and in the absence of solvent, for the production of H2 / CO2 without detectable amounts of CO.
[0082] It has also been demonstrated that it is possible to carry out several dehydrogenation cycles without the catalyst showing signs of deactivation, even using small amounts of sodium formate. The TOF values obtained (Tables 1 and 2) correspond to TOF50 values (measured at 50% conversion) and, unlike the initial TOF values, provide a realistic approximation of the catalyst's activity.
[0083] In conclusion, the tests carried out demonstrate that the developed catalytic precursors are an alternative to the currently limited number of systems capable of performing the dehydrogenation of neat formic acid. Unlike the iridium-based systems studied to date, the catalysts object of the invention exhibit high TOF values over several catalysis cycles. Obtaining the gas mixture at high pressures offers the possibility of physically storing H2 from the chemical decomposition of formic acid. Thus, the catalysts described could be used in stationary devices that require H2 for operation, without the need to transport the gas in any of its physical storage formats. The stream obtained can be enriched in H2 by cooling (liquefaction and storage of CO2) or alkalization (removal of CO2 in the form of carbonates) of the dehydrogenation mixture.
Claims
CLAIMS 1. Iridium (III) or rhodium (III) complex characterized by having a general formula: and stoichiometric formula [Cp'M(k 2 -A / ,A / )Y] n+ [A ]n comprising a Cp'M fragment bound to a ligand l^-(N,N), where the ligand k 2 -( / V,A / ) is a pyridyl-1,2,3-triazole derivative that binds to the metal center M through two non-adjacent nitrogen atoms, the pyridyl nitrogen and the nitrogen in position 2 (N2) of the triazole ring, leaving the more basic nitrogen in position 3 (N3) of the triazole free, and where: Cp' represents an r -cyclopentadienyl ligand, where R 1 to R 5 represent, independently, a hydrogen atom or an alkyl group or an aryl group or a silyl group or a perfluoroalkyl group; R 6 to R 9represent, independently, a hydrogen atom; or a carbon chain; or a fluorocarbon chain; or an alkoxyalkane group; n is 1 or 2; Y represents an atom selected from a group consisting of F, Cl, Br, and I; or, for n = 1, an OH or OTf functional group; or, for n = 2, H2O; A represents a counterion selected from the group consisting of F, Cl, Br, I, OH, OTf, BF4, BAr4, and PF6; R 10 is a CO2R group 11 ; where R 11 represents a hydrogen, or an alkyl group or an aryl group.
2. Iridium (III) or rhodium (III) complex according to claim 1, wherein M is Ir; R 1 to R 5 are CH3; R 6 to R 9 are H; Y is Cl; A is OTf and R 10 is CO2Et, and the complex is represented according to the following general formula:
3. Iridium (III) or rhodium (III) complex according to claim 1, wherein M is Ir; R 1 to R5 are CH3; R 6 , R 8 and R 9 are H; R 7 is CH3O; Y is Cl; A is OTf and R 10 is CO2Et, and the complex is represented according to the following general formula:
4. Iridium (III) or rhodium (III) complex according to claim 1, wherein M is Ir; R 1 to R 5 are CH3; R 6 , R 8 and R 9 are H; R 7 is CH3; Y is Cl; A is OTf and R 10 is CO2Et and the complex is represented according to the following general formula:
5. Iridium (III) or rhodium (III) complex according to claim 1, wherein M is Ir; R 1 to R 5 are CH3; R 6 , R 8 and R 9 are H; R 7 is CF3; Y is Cl; A is OTf and R 10 is CO2Et and the complex is represented according to the following general formula:
6. Use of an iridium (III) or rhodium (III) complex according to any one of claims 1 to 5 as a catalyst.
7. Use according to claim 6, wherein the catalyst is used to dehydrogenate formic acid and produce hydrogen, free of CO and in the absence of solvent.