Pyridinium compounds with a low reduction potential and a persistent radical state.

Abstract

A series of pyridinium compounds, generally 2,6-dialkyl-4-arylpyridinum compounds, with low reduction potentials and highly persistent radical states for use as anolytes in redox flow batteries, thin-film metal-organic hybrid batteries, and all-organic batteries are disclosed. Related routes for the synthesis of the pyridinium compounds from pyrylium intermediates are also disclosed.

Description

[Technical Field]

[0001] Cross-reference of related applications

[0001] This application claims priority and interest in U.S. Provisional Patent Application No. 63 / 280,344, filed on 17 November 2021, the disclosure of which is incorporated herein by reference in whole.

[0002] Technical field of the present invention

[0002] This application relates to the preparation of pyridinium compounds and their derivatives in general. [Background technology]

[0003]

[0003] Many pyridinium compounds have been considered as anode liquids for redox flow batteries, but it has been difficult to achieve all the desired properties in a single system, namely a low reduction potential, high solubility, and an extremely stable radical state. Recent research (Non-Patent Literature 1) has shown that important structure / property relationships can be elucidated using predictive modeling, thereby generating new synthetic targets. Non-Patent Literature 1 points out that the properties of a certain pyridinium compound may be particularly attractive, but it has been found that such a substance is virtually impossible to synthesize through conventional routes. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004]

[0004] This application seeks to address these problems by identifying novel pyridinium compounds and related methods for forming them. [Means for solving the problem]

[0005]

[0005] The present invention has a low reduction potential (-1.54 to -1.83 V vs. Fc / Fc +The present invention provides a pyridinium compound that is in a highly persistent radical state. The present invention also provides a relevant high-yield and low-cost route for the synthesis of the compound.

[0006] In one embodiment, the pyridinium compound is given by the following formula (1A):

[0006] [ka] Regarding.

[0007] In formula (1A), R1 is selected from substituted aryl groups and unsubstituted aryl groups, as well as substituted and unsubstituted heteroaromatic groups.

[0008] In formula (1A), R2 is selected from substituted and unsubstituted aryl groups, unbranched and branched alkyl groups, haloalkyl groups, aralkyl groups, alkyl ether groups, alkyl nitro groups, alkyl nitrile groups, trialkylammonium alkyl groups, alkyl carboxylate groups, alkyl sulfonate groups, and alkyl phosphonate groups.

[0007]

[0009] In another embodiment, the pyridinium compound is given by the following formula (1B):

[0008] [ka] Regarding.

[0010] In formula (1B), R1 and R5 are independently selected from hydrogen, a methyl group, an ethyl group, a halide group, a halomethyl group, a perhalomethyl group, an alkoxy group, a nitrile group, and a nitro group. R2, R3, and R4 are independently selected from hydrogen, an unbranched alkyl group, a branched alkyl group, a haloalkyl group, an aralkyl group, an alkyl ether group, a nitro group, a nitrile group, a halide group, an acetyl group, a trialkylammonium alkyl group, an alkylcarboxylate group, an alkyl sulfonate group, and an alkylphosphonate group. Furthermore, R6 and R10 are independently selected from hydrogen, a methyl group, an ethyl group, a halide group, a halomethyl group, a perhalomethyl group, a hydroxyl group, an alkoxy group, a nitrile group, and a nitro group. Furthermore, R7 and R9 are independently selected from hydrogen, unbranched alkyl groups, branched alkyl groups, haloalkyl groups, perhaloalkyl groups, aryl groups, aralkyl groups, alkyl ether groups, nitro groups, nitrile groups, halide groups, acetyl groups, trialkylammonium alkyl groups, alkyl carboxylate groups, alkyl sulfonate groups, alkyl phosphonate groups, t-Bu (tert-butyl) groups, CF3 groups, -Br, N,N-dimethylaniline groups, and alkyl triether groups. R8 is independently selected from hydrogen, unbranched alkyl groups, branched alkyl groups, alkoxy groups, haloalkyl groups, perhalomethyl groups, aryl groups, aralkyl groups, alkyl ether groups, nitro groups, nitrile groups, halide groups, acetyl, trialkylammonium alkyl groups, alkyl carboxylate groups, alkyl sulfonate groups, alkyl phosphonate groups, t-Bu (tert-butyl) groups, CF3 groups, -Br, N,N-dimethylaniline groups, and alkyl triether groups. Furthermore, at least one of R1 to R10 is not hydrogen. In one embodiment, formula (1B) also has at least one of R1, R5, R6, or R10 that is not hydrogen.

[0009]

[0011] In some further embodiments, the pyridinium compound is given by the following formula (1C):

[0010] [ka] Regarding.

[0012] In formula (1C), R1 and R5 are independently selected from hydrogen, a methyl group, a methoxy group, an ethyl group, a halide group, a halomethyl group, a hydroxyl group, an alkoxy group, a nitrile group, and a nitro group. Furthermore, R2, R3, and R4 are independently selected from hydrogen, an unbranched alkyl group, a branched alkyl group, an alkoxy group containing a methoxy group, a haloalkyl group, an aryl group, an aralkyl group, an alkyl ether group, a nitro group, a nitrile group, a halide group, an acetyl group, a trialkylammonium alkyl group, an alkyl carboxylate group, an alkyl sulfonate group, and an alkyl phosphonate group. Furthermore, R' is selected from unbranched and branched alkyl groups, a haloalkyl group, an aralkyl group, an alkyl ether group, an alkyl nitro group, an alkyl nitrile group, a trialkylammonium alkyl group, an alkyl carboxylate group, an alkyl sulfonate group, and an alkyl phosphonate group. In these embodiments, if R' has two or more carbon atoms, one or more of R1, R2, R3, R4, and R5 may be a methoxy group. In one embodiment, formula (1C) also has at least one of R1 or R5 that is not hydrogen.

[0011]

[0013] In a further embodiment, the pyridinium compound may or may not include one or more of formulas (1A), (1B), or (1C), such as the following pyridinium compounds (1D)~(1Z) and (1AA)~(1LL):

[0012] [ka] Selected from JPEG0007870565000005.jpg249161.

[0013]

[0014] In particular, this application provides an extremely diverse range of 2,6-dialky-4-arylpyridinum compounds, available via pyririum intermediates, comprising one or more of the formulas (1A)-(1Z) and (1AA)-(1LL).

[0015] Some of these pyridinium compounds corresponding to any one or more of Formulas (1A) to (1Z) and (1AA) to (1LL) have been found to exhibit excellent solubility in polar organic solvents. Further, in certain embodiments, by introducing a simple methyl group to R3 of Formula (1B) to form the 2,6-dialkyl-4-tolylpyridinum compound according to the present application, compared with a pyridinium compound containing the same other substituents except that R3 does not contain methyl, the solubility is more than three times higher, which suggests that a non-aqueous flow battery with a significantly high energy density can be achieved. Further, these pyridinium compounds according to any one or more of Formulas (1A) to (1Z) and (1AA) to (1LL) have a diffusion coefficient (usually on the order of 1.1 to 1.5×10 -5 cm 2 / s), which is significantly high and can thereby promote a high power density.

[0016] The 2,6-dialkyl-4-arylpyridinum compounds according to any one or more of Formulas (1A) to (1Z) and (1AA) to (1LL) of the present application undergo a chemically and electrochemically reversible one-electron reduction at a low potential (about -1.54 to -1.83 V vs. Fc / Fc + ). The reaction rate of the electrode is favorable in all cases, as shown in the typical cyclic voltammogram of 1 mM pyridinium salt described in FIG. 2 below. Further, the compound is extremely soluble in polar organic solvents (more than 1 M in acetonitrile for some derivatives) and exhibits a significantly high diffusion coefficient.

[0014]

[0017] Furthermore, the synthesis of the compound according to Formula (1B) when R6 and / or R10 is not hydrogen is unexpectedly sterically crowded and was unforeseen. Similarly, considering the fact that the π overlap is substantially reduced by the restricted rotation around the pyridinium-(4-aryl) bond, the formation of a persistent radical state in the compound according to Formula (1B) when R1 and / or R5 is not hydrogen is also unexpected.

[0015]

[0018] This application also discloses a redox flow battery comprising a charge transport electrolyte comprising a pyridinium compound according to any one or more of Formulas (1A)-(1Z) and (1AA)-(1LL) provided herein.

[0019] Other features and advantages of the present invention will be readily understood from the following description in conjunction with the accompanying drawings, which will be better understood.

[0020] The advantages of the present invention will be readily understood when considered in connection with the accompanying drawings and will be better understood by reference to the following detailed description. It should be understood that the drawings are for illustrative purposes only and are not necessarily drawn to scale.

Brief Description of the Drawings

[0016] [Figure 1]

[0021] It is a schematic diagram of a redox flow battery according to an embodiment of the present invention. [Figure 2]

[0022] It is a graph showing a cyclic voltammogram of a representative pyridinium compound (1 mM pyridinium salt) according to the present invention.

Mode for Carrying Out the Invention

[0017]

[0023] This application provides a pyridinium compound having a desired reduction potential (i.e., about -1.54 to -1.83 V relative to Fc / Fc + For example, 1.54 to -1.83 V relative to Fc / Fc + ), which is low and in a highly persistent radical state, as well as a related high-yield and low-cost route for the synthesis of the compound.

[0024] As used herein, when the terms "ca." or "about" relate to a reduction potential or a yield (%), a variability of 5% of the number or numerical range as described herein is allowed.

[0025] Furthermore, the description of the “R” group in any of the representative formulas may be expressed herein with or without the term “group,” but is intended to be equivalent. As a non-restrictive example, where a particular R group is described as being “selected from methyl,” the term “methyl” is used interchangeably with the phrase “methyl group,” and is understood to mean the CH3 group at the position indicated by R in each formula. The same applies to any group described in one or more of the following formulas (1A) to (1Z) and (1AA) to (1LL).

[0026] Due to their low reduction potential, high solubility, and highly persistent radical state, pyridinium compounds are ideally suited for use as anode liquids in redox flow batteries.

[0018]

[0027] In one embodiment, the pyridinium compound is given by the following formula (1A):

[0019] [ka] Regarding.

[0028] In formula (1A), R1 is selected from substituted aryl groups, unsubstituted aryl groups, and substituted and unsubstituted heteroaromatic groups. More specific R1 groups that can be used include aryl or substituted aryl groups (e.g., phenyl, 4-tolyl, 4-fluorophenyl, 4-methoxyphenyl, 3,4-dimethoxyphenyl, 2,4-dimethylphenyl, 4-dimethylaminophenyl, 4-(t-Bu)phenyl, 4-trifluoromethylphenyl, and 4-(alkoxyether)phenyl groups).

[0029] In formula (1A), R2 is selected from substituted and unsubstituted aryl groups, unbranched and branched alkyl, haloalkyl, aralkyl, alkyl ether, alkylnitro, alkylnitrile, trialkylammonium alkyl, alkylcarboxylate, alkyl sulfonate, and alkylphosphonate groups.

[0020]

[0030] In certain further embodiments, the pyridinium compound is given by the following formula (1B):

[0021] [ka] Regarding.

[0031] In formula (1B), R1 and R5 are independently selected from hydrogen, a methyl group, an ethyl group, a halide group, a halomethyl group, a hydroxyl group, an alkoxy group, a methoxy group, a nitrile group, and a nitro group. R2, R3, and R4 are independently selected from hydrogen, an unbranched alkyl group, a branched alkyl group, an alkoxy group, a haloalkyl group, an aralkyl group, an alkyl ether group, a nitro group, a nitrile group, a halide group, an acetyl group, a trialkylammonium alkyl group, an alkylcarboxylate group, an alkyl sulfonate group, and an alkylphosphonate group. Furthermore, R6 and R10 are independently selected from hydrogen, a methyl group, an ethyl group, a halide group, a halomethyl group, a hydroxyl group, an alkoxy group, a nitrile group, and a nitro group. Furthermore, R7 and R9 are independently selected from hydrogen, unbranched alkyl groups, branched alkyl groups, haloalkyl groups, perhaloalkyl groups, aryl groups, aralkyl groups, alkyl ether groups, nitro groups, nitrile groups, halide groups, acetyl groups, trialkylammonium alkyl groups, alkyl carboxylate groups, alkyl sulfonate groups, alkyl phosphonate groups, t-Bu (tert-butyl) groups, CF3 groups, -Br, N,N-dimethylaniline groups, and alkyl triether groups. R8 is independently selected from hydrogen, unbranched alkyl groups, branched alkyl groups, alkoxy groups, haloalkyl groups, perhalomethyl groups, aryl groups, aralkyl groups, alkyl ether groups, nitro groups, nitrile groups, halide groups, acetyl groups, trialkylammonium alkyl groups, alkyl carboxylate groups, alkyl sulfonate groups, alkyl phosphonate groups, t-Bu (tert-butyl) groups, CF3 groups, -Br, N,N-dimethylaniline groups, and alkyl triether groups. Furthermore, at least one of R1 to R10 is not hydrogen.

[0032] In one embodiment, formula (1B) also has at least one of R1, R5, R6, or R10 that is not hydrogen.

[0022]

[0033] In yet another embodiment, the pyridinium compound is given by formula (1C):

[0023] [ka] Regarding.

[0034] In formula (1C), R1 and R5 are independently selected from hydrogen, a methyl group, a methoxy group, an ethyl group, a halide group, a halomethyl group, a hydroxyl group, an alkoxy group such as a methoxy group, a nitrile group, and a nitro group. Furthermore, R2, R3, and R4 are independently selected from hydrogen, an unbranched alkyl group, a branched alkyl group, an alkoxy group including a methoxy group, a haloalkyl group, an aryl group, an aralkyl group, an alkyl ether group, a nitro group, a nitrile group, a halide group, an acetyl group, a trialkylammonium alkyl group, an alkyl carboxylate group, an alkyl sulfonate group, and an alkyl phosphonate group. Furthermore, R' is selected from unbranched and branched alkyl groups, a haloalkyl group, an aralkyl group, an alkyl ether group, an alkyl nitro group, an alkyl nitrile group, a trialkylammonium alkyl group, an alkyl carboxylate group, an alkyl sulfonate group, and an alkyl phosphonate group. In this embodiment, if R' has two or more carbon atoms, one or more of R1, R2, R3, R4, and R5 may be a methoxy group.

[0035] In one embodiment, formula (1C) also has at least one of R1 or R5 that is not hydrogen.

[0024]

[0036] In a further embodiment, the pyridinium compound may or may not include one or more of formulas (1A), (1B), or (1C), such as the following pyridinium compounds (1D)~(1Z) and (1AA)~(1LL):

[0025] [ka] Selected from JPEG0007870565000010.jpg181161.

[0026]

[0037] The present application also discloses synthetic routes for forming pyridinium compounds according to formulas (1A), (1B), and (1C), as well as other individual pyridinium compounds according to the above formulas (1D)-(1Z) and (1AA)-(1LL).

[0038] In general, a wide range of 2,6-dialkyl-4-arylpyridinum compounds according to formula (1A) (and, in some cases, formulas (1B) and (1C)), and other individual pyridinium compounds according to formulas (1D) to (1Z) and (1AA) to (1LL) are available via pyririum intermediate (III), and the following reaction scheme (A):

[0027] [ka] It can be formed as shown by

[0039] In reaction scheme (A), possible N-substituents (i.e., R2 substituents) of formula (1A) provided via NH2-R2 include any group that is essentially compatible with the terminal amine, including alkyl, aralkyl, alkyl ether, haloalkyl, trialkylammonium alkyl, aryl, and substituted aryl groups, among other N-substituents.

[0040] Examples of R1 groups include phenyl, tolyl, methoxyphenyl, xylyl, mesityl, perfluorophenyl, and trifluoromethylphenyl groups.

[0041] Exemplary embodiments of this application according to formula (1B) (and optionally formula (1C)) are shown in the following reaction scheme (B) and Table (1):

[0028] [ka]

[0029] [Table 1]

[0030] [ka]

[0031] [Table 2] It can be formed by [this method].

[0042] In the above reaction scheme (B), dimethyl-γ-pyrone is reacted with R1-magnesium bromide (for example, phenylmagnesium bromide or methoxyphenylmagnesium bromide as shown in Table 1) to form a pyryllium intermediate. Then, the pyryllium intermediate is reacted with an amine-containing compound represented by NH2-R2 to obtain a pyridinium compound according to formula (1B).

[0043] Possible N-substituents provided via NH2-R2 in reaction scheme (B) include any group that is essentially compatible with the terminal amine, such as alkyl, aralkyl, alkyl ether, haloalkyl, trialkylammoniumalkyl, aryl, substituted aryl, and each of the specific groups listed in Table 1 above.

[0044] As described above, the pyridinium compounds according to this application (including formulas (1A), (1B), and (1C)) and the other individual pyridinium compounds according to formulas (1D) to (1Z) and (1AA) to (1LL) described above are suitable for use as an anode in redox flow batteries.

[0032]

[0045] Figure 1 shows a redox flow battery 10 according to one embodiment of the present invention. The redox flow battery 10 may be described as an energy storage device that generates energy using redox (reduction and oxidation) reactions, and the energy is stored in an electrolyte solution that flows through the battery 10. During the discharge of the battery 10, electrons are released during oxidation reactions on the negative (or anode) side of the battery 10. The electrons move through an external circuit to perform useful work and are then received during reduction reactions on the positive (or cathode) side of the battery 10. The direction of the current and the chemical reactions are reversed during charging. The energy generated by the redox flow battery 10 is often used for grid storage applications. However, it should be understood that the redox flow battery 10 can be scaled up or down to suit the needs of any suitable application.

[0046] Referring to Figure 1, the redox flow cell 10 has an electrochemical cell 12 including a positive (cathode) side 14 and a negative (anode) side 16. The positive electrode side 14 has a first container 18 that houses a charge-carrying electrolyte and an oxidized form of the electroactive material (referred to herein as the active material), and the negative electrode side 16 has a second container 20 that houses a charge-carrying electrolyte and a reduced form of the electroactive material. The positive electrode side 14 further includes a cathode 22, and the negative electrode side further includes an anode 24. The net charge of each container is zero. Any positively charged species is balanced by a negatively charged species, and vice versa.

[0047] During charging and discharging of the redox flow battery 10, the electrolyte carrying the positive charge 14 is circulated by the first pump 26 from the first receptacle 18 through the cathode 22. The electrolyte carrying the negative charge 16 is circulated by the second pump 28 from the second container 20 through the anode 24. The cathode 22 and anode 24 may be electrically connected to an external load 30 via a current collector. As the electrolyte passes through the cathode 22 and anode 24, the electroactive material reacts (via oxidation-reduction reactions) to generate energy.

[0033]

[0048] The cathode 22 may be one or a pair of electrodes or an array of electrodes. The anode 24 may be one or a pair of electrodes or an array of electrodes. The cathode 22 and anode 24 are not particularly limited and may be known in the art. In non-limiting examples, one or more of the cathode 22 and anode 24 are carbon-based electrodes, metallic electrodes, and combinations thereof. Non-limiting examples of carbon-based electrodes include electrodes made or formed from porous carbon (e.g., carbon felt, carbon paper, and graphite felt), carbon nanotubes, carbon nanowires, graphene, and / or combinations thereof. Non-limiting examples of metallic electrodes include electrodes made or formed from gold, steel, nickel, platinum-clad gold, platinum-clad carbon, and / or combinations thereof. In other non-limiting examples, the cathode 22 and / or anode 24 are porous. The cathode 22 and / or anode 24 may further contain additives such as carbon black and flake graphite. Each of the cathode 22 and anode 24 may be in any convenient form including foil, plate, rod, screen, paste, or as a composite material made by coating an electrode material onto a conductive current collector or other suitable support.

[0034]

[0049] Examples of charge-transporting electrolytes include a charge-transporting medium (i.e., a solvent or gel), an electrolyte salt, and one or more redox active materials (i.e., a pyridinium compound relating to any one of formulas (1A), (1B), (1C), (1D) to (1Z) or (1AA) to (1LL)) and ions. The charge-transporting medium may be one or more liquids and / or gels. Furthermore, the charge-transporting medium may be used over a wide temperature range, e.g., about -30°C to about 70°C, without freezing or boiling, and is usually stable within the electrochemical window in which cathode 22 and anode 24 operate.

[0050] In certain embodiments, the charge transport medium is present in amounts of 10% to 100% by mass, for example 40% to 99% by mass, for example 60% to 99% by mass, for example 65% to 95% by mass, or for example 70% to 90% by mass, based on the total mass of the charge transport electrolyte. All values ​​and ranges within the above ranges are expressly intended herein in various non-limiting embodiments.

[0035]

[0051] While pyridinium compounds are suitable for use in redox flow batteries as described above, the potential applications of these materials can be expanded to a wider range of applications beyond those in redox flow batteries. Possible further applications include, but are not limited to, redox catalysts, chemical reducing agents (from reduced form), additives for conventional batteries, or applications in molecular electronics.

[0052] In certain exemplary embodiments, pyridinium compounds according to any one of the above formulas (1A), (1B), (1C), (1D)-(1Z) or (1AA)-(1LL) may also be coupled to an oxidizable moiety for subsequent use in the above system. Exemplary oxidizable moieties include, but are not limited to, ferrocene, carbazole, phenazine, phenoxazine, phenothiazine, phenothiazine-5-oxide, phenothiazine-5,5-dioxide, benzoquinone, TEMPO, and / or cyclopropenium.

[0053] In another embodiment, the redox-active pyridinium compounds described herein may be bonded to a polymer backbone or be components of a polymer backbone. Such redox-active polymers can then be used as soluble anodelites in redox flow batteries, in which case their large size and high charge help to reduce crossover.

[0036]

[0054] In further embodiments, any one of the pyridinium compounds according to formulas (1A), (1B), (1C), (1D)-(1Z), or (1AA)-(1LL) may also be used in metal-organic hybrid or all-organic thin-film (i.e., "jelly roll") batteries. Such batteries utilize established low-cost manufacturing methods such as roll-to-roll processing and addition methods, but utilize redox-active organic compounds or polymers as active materials in one or both electrodes. In these batteries, the redox-active pyridinium compound may be bonded to or a component of the polymer backbone. Alternatively, the pyridinium compounds according to formulas (1A), (1B), (1C), (1D)-(1Z), or (1AA)-(1LL), or polymers incorporating them, may be covalently bonded to the above-mentioned metal or carbon, carbon surface, or other electrodes. In non-limiting examples, the electrodes may be carbon-based electrodes, metal-based electrodes, or combinations thereof. Non-limiting examples of carbon-based electrodes include electrodes made from or formed from porous carbon (e.g., carbon felt, carbon paper, and graphite felt), carbon nanotubes, carbon nanowires, graphene, and / or combinations thereof. Non-limiting examples of metallic electrodes include electrodes made from or formed from gold, steel, nickel, platinum-clad gold, platinum-clad carbon, and / or combinations thereof. The electrodes may further contain additives such as carbon black, flake graphite, and graphene. The electrodes may be in any convenient form, including foil, plate, rod, screen, and paste, or as a composite material made by coating the electrode material onto a conductive current collector or other suitable support. The battery also includes an electrolyte that carries charge. The charge-carrying electrolyte includes a charge-carrying medium (i.e., a solvent or gel, and an electrolyte salt). It may also contain other electroactive materials, stabilizers, or other additives to improve battery performance and / or service life. The charge-carrying medium may be one or more liquids and / or gels. Furthermore, the charge transport medium can be used over a wide temperature range, for example, from about -30°C to about 70°C, without freezing or boiling, and is usually stable within the electrochemical window in which the battery operates.

[0055] See also: “High-Power-Density Organic Radical Batteries”, C. Friebe and USSchubert, Top Curr Chem(Z)(2017)375:19, “Sustainable Energy Storage: Recent Trends and Developments toward Fully Organic Batteries”, C. Friebe, A. Lex-Balducci, and USSchubert, ChemSusChem(2019), 12, 4093-4115, or “Organic Batteries Based on Just Redox Polymers”, N. Goujon, N. Casada, N. Patil, R. Marcilla, and D. Mecerreyes, Prog. Polymer Sci(2021), 122, 101449.

[0056] The 2,6-dialky-4-arylpyridinum compounds of any one or more of the formulas (1A)~(1Z) and (1AA)~(1LL) of this application exhibit low potential (approximately -1.54 to -1.83 V vs. Fc / Fc + It undergoes chemically and electrochemically reversible one-electron reduction. As shown in the typical cyclic voltammogram of the 1 mM pyridinium salt in Figure 2, the electrode dynamics are favorable in all cases. Referring to Figure 2, the cyclic voltammogram of the 1 mM pyridinium salt was performed at 22°C and in a pure N2 atmosphere using a 3 mm diameter glassy carbon electrode with 100 mM Bu4NBF4 as the supporting electrolyte in acetonitrile at a variable scanning speed. The invariance of the peak oxidation potential and peak reduction potential at different scanning speeds shown in Figure 2 corresponds to the heterogeneous electron transfer rate constant k 0 The value is greater than 1 cm / second, indicating that this value is fast enough to be suitable for use with redox flow batteries.

[0057] Furthermore, the pyridinium compounds of this application are extremely soluble in polar organic solvents (more than 1 M in acetonitrile for some derivatives) and have remarkably high diffusion coefficients.

[0058] Furthermore, the synthesis of compounds according to formula (1B) when R6 and / or R10 are not hydrogen was unexpectedly stereoconstricted. Similarly, considering the fact that the π superposition is substantially reduced due to the restriction of rotation around the pyridinium-(4-aryl) bond, the formation of persistent radical states in compounds according to formula (1B) when R1 and / or R5 are not hydrogen is also unexpected. [Examples]

[0037] Synthesis of 2,6-dimethyl-4-phenylpyrlium tetrafluoroborate (1a) and its derivatives (1b, 1c, and 1d)

[0059] 2,6-dimethyl-4-phenylpyrlium tetrafluoroborate (1a) was synthesized by adapting the procedure reported by DiMauro and Kozlowski, as shown in the following reaction scheme (C) (DiMauro, EF and Kozlowski, MC, Phosphabenzenes as electron withdrawing phosphine ligands in catalysis. J. Chem. Soc., Perkin Trans. 1 2002, 439-444). A magnetic stirring rod was placed in an oven-dried 250 ml round-bottom flask, and 2,6-dimethyl-γ-pyrone (2.0 g, 0.016 mol) was dissolved in tetrahydrofuran (THF, 75 ml) under nitrogen. Phenylmagnesium bromide (16 ml, 0.016 mol) as a 1 mol solution in THF was added to the addition funnel via a cannula. After cooling the solution to 5°C in an ice bath, the contents of the addition funnel were added dropwise to the solution. The resulting crude solution was heated to room temperature over 1 hour. Subsequently, the crude solution was poured into boron trifluoride diethyl etherate (BF4-, 5.92 ml, 0.048 mol) to obtain a yellow precipitate, which was filtered and washed with diethyl ether. After recrystallization in methanol, the product according to formula (1a) shown below was isolated as a yellow solid (3.0157 g, 0.011 mol) in 69% yield.

[0038] Reaction scheme (C)

[0039] [ka]

[0060] Using the corresponding Grignard reagent, the following derivatives (1b - j) were synthesized according to the above procedure of the reaction scheme (C).

[0040]

Chem.

[0061] Alternatively, derivative (1a) can be synthesized according to the procedure of Breit et al. as shown in the following reaction scheme (D) (Breit, B.; Winde, R.; Mackewitz, T.; Paciello, R.; Harms, K., Phosphabenzenes as Monodentate π - Acceptor Ligands for Rhodium - Catalyzed Hydroformylation. Chem. Eur. J. 2001, 7(14), 3106 - 3121) and was carried out as follows. Reaction scheme (D)

[0041]

Chem.

[0062] First, acetic anhydride (3.5 milliliters, 37 millimoles) was mixed with diethyl ether complex of tetrafluoroboric acid (0.572 milliliters, 4.2 millimoles) in a dry 25 - mL round - bottom flask equipped with a magnetic stir bar. After cooling to 0 °C (0 degrees Celsius) via an ice bath, α - methylstyrene (0.546 milliliters, 4.2 millimoles) was added and the solution was stirred at 0 °C (0 degrees Celsius) for 2 hours. After warming to room temperature overnight, the reaction mixture was poured into diethyl ether and the crude purple solid was isolated by filtration. By recrystallization from hot water, the product (1a) was obtained as yellow crystals (0.1215 g, 0.45 mmol) in a yield of 10%.

[0063] Pyrilium compounds (1a) - (1j) with BF4 -Although prepared as a salt, conversion to other salts, such as halides, hexafluorophophates, perchlorates, triflates, and bis(trifluoromethanesulfonyl)imide (trifluimide), can be achieved by simple anionic metathesis. For example, the conversion of (1b) to the bis(trifluoromethanesulfonyl)imide salt was achieved by first adding 35 g of (1b)(BF4) to a 2 L flask with 600 ml of desalted water and 600 ml of methanol. 181 g of lithium bis(trifluoromethanesulfonyl)imide was added, the mixture was brought to a low boiling point, and the methanol was slowly evaporated over several hours. Once most of the methanol had evaporated, heating was stopped and the flask was transferred to a refrigerator. After cooling overnight, colorless / slightly yellow crystals were collected by vacuum filtration (isolation yield, 55.7 g, 95%).

[0042]

[0064] 2,6-dimethyl-1,4-diphenylpyridine-1-ium tetrafluoroborate (shown below as (2a)) was synthesized according to the procedure of Huifeng et al. shown in the reaction scheme (E) below (Huifeng, Y,; Zhu, C.; Shen, L.; Geng, Q.; Hoch, K.; Yuan, T.; Cavallo, L.; Rueping, M., Nickel-catalyzed CN bond activation: Activated primary amines as alkylating reagent in reductive cross-couplings. Chem. Sci. 2019, 10(6), 4430-4435). Reaction scheme (E)

[0043] [ka]

[0065] First, 2,6-dimethyl-4-phenylpyrlium tetrafluoroborate (0.3 g, 1.1 mmol) was suspended in ethanol (20 mL) in a 50 ml round-bottom flask equipped with a magnetic stirring rod and a condenser. Aniline (0.12 ml, 1.3 mmol) was added, and the mixture was refluxed under nitrogen at reflux temperature, in this case 88 °C, for 4 hours. The solution was cooled to room temperature overnight and diluted with diethyl ether. The precipitate was isolated by filtration and dried under vacuum to obtain a white solid (0.325 g, 0.94 mmol) as the product according to formula (2a) in 85% yield.

[0066] Other pyridinium compounds listed in Table 1 above were synthesized using appropriate amines or aniline reactants following the same procedure.

[0067] In light of the above teachings, many modifications and variations of this application are possible. Therefore, the present invention can be carried out in ways other than those specifically described.

Claims

1. below: 【Chemistry 1】 【change】 【change】 A pyridinium compound selected from the group consisting of the following.

2. The reduction potential of 2,6-dialkyl-4-allylpyridinium compounds is -1.54 to -1.83 V vs. Fc / Fc ＋ The pyridinium compound according to claim 1.

3. below, (I) Cathode; (II) Anode; and (III) A charge transport electrolyte comprising the pyridinium compound according to claim 1, Redox flow batteries, including those mentioned above.

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