Reducing agent for synthesizing nitrogen-containing compound

Abstract

Disclosed is a reducing agent for synthesizing a nitrogen-containing compound, the reducing agent being composed of a metal complex that contains samarium and a multidentate ligand which is coordinated to samarium. The multidentate ligand has 4 to 8 coordinating atoms that are bonded to samarium, and the coordinating atoms are each independently an oxygen atom or a nitrogen atom.

Description

Reducing agent for synthesis of nitrogen-containing compounds

[0001] The present invention relates to a reducing agent, more specifically to a reducing agent for synthesizing nitrogen-containing compounds, a method for producing nitrogen-containing compounds using the same, and a catalyst composition.

[0002] Ammonia is an important chemical raw material used as a basic material for fertilizers and chemical products, and in recent years has also attracted attention for its use in coal-fired power generation and as an energy carrier. Conventionally, ammonia has been produced by the Haber-Bosch process, which is a method for producing ammonia by reacting nitrogen gas with hydrogen gas in the presence of an iron-based catalyst.

[0003] However, because the Haber-Bosch process synthesizes ammonia under high temperatures and pressures, it consumes a lot of energy and requires large equipment made of special materials. Furthermore, there is the problem that large amounts of carbon dioxide, a greenhouse gas, are emitted when hydrogen gas is obtained from natural gas, which is primarily composed of methane (CH4). Therefore, there is a need to develop a method for producing ammonia from nitrogen and water under mild reaction conditions.

[0004] Patent Document 1 discloses a method for producing ammonia from nitrogen molecules in the presence of a catalyst, a reducing agent, and a proton source using a specific molybdenum complex as an invention for inexpensively producing ammonia from nitrogen molecules. Patent Document 2 also discloses a method for producing a nitrogen-containing compound as an invention for further improving the production amount of ammonia, which includes a step of synthesizing a nitrogen-containing compound from nitrogen and a proton source in the presence of a nitrogen-activating catalyst and a reducing agent, while simultaneously reducing, by electrolysis, the reducing agent oxidized in the synthesis reaction of the nitrogen-containing compound.

[0005] International Publication No. 2019 / 168093 International Publication No. 2022 / 230898

[0006] However, the methods for producing nitrogen-containing compounds described in Patent Documents 1 and 2 leave room for further improvement in the production yield of nitrogen-containing compounds. For example, Patent Documents 1 and 2 use samarium iodide as a reducing agent (mediator), but this samarium iodide may cluster over the course of reaction time and become insoluble. For this reason, clustering of the reducing agent, which is a type of mediator, causes a decrease in the production yield of nitrogen-containing compounds, and therefore there is a strong demand for improving the production yield of nitrogen-containing compounds by developing a new reducing agent.

[0007] In order to solve the above-mentioned problems, an object of the present invention is to provide a reducing agent for synthesizing nitrogen-containing compounds, which can improve the production amount of nitrogen-containing compounds per amount of energy input, as well as a method for producing nitrogen-containing compounds using the same, and a catalyst composition.

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the production amount of a nitrogen-containing compound per amount of energy input in the synthesis of the nitrogen-containing compound can be improved by using a metal complex having a predetermined structure as a reducing agent (preferably a mediator).

[0009] That is, this embodiment includes the following aspects: <1> A reducing agent for synthesizing a nitrogen-containing compound, comprising a metal complex containing samarium and a multidentate ligand coordinated to the samarium, wherein the multidentate ligand has 4 to 8 coordinating atoms bonded to the samarium, and the coordinating atoms are each independently an oxygen atom or a nitrogen atom. <2> The reducing agent for synthesizing a nitrogen-containing compound according to <1>, wherein the metal complex has a structure represented by the following formula (1): (In formula (1), H represents the polydentate ligand and includes a structure represented by the following formula (1-1), formula (1-2), or formula (1-3).) (In formula (1-1), R1 and R2 each independently represent a hydrogen atom or a hydrocarbon group, A1 each independently represent an oxygen atom or a nitrogen atom, l represents an integer of 0 to 3, m represents the bonding position to n, n represents the bonding position to m, M1 represents an integer of 5 to 10, and * represents the bonding position to Sm in formula (1). In formula (1-2), R1 and R2 each independently represent a hydrogen atom or a hydrocarbon group, A1 and A2 each independently represent an oxygen atom or a nitrogen atom, l represents an integer of 0 to 3, M2 represents an integer of 1 to 5, N1 represents an integer of 1 to 3, and * represents the bonding position to Sm in formula (1). In formula (1-3), R1 and R2 each independently represent a hydrogen atom or a hydrocarbon group, A1 and A2 each independently represent an oxygen atom or a nitrogen atom, 1 represents an integer of 0 to 3, N2 represents an integer of 1 to 4, and * represents the bonding position with Sm in formula (1). <3> The reducing agent for synthesizing nitrogen-containing compounds according to <2>, wherein A2 is an oxygen atom in at least one of formulas (1-2) to (1-3). <4> The reducing agent for synthesizing nitrogen-containing compounds according to <2> or <3>, wherein R1 and R2 are hydrogen atoms in at least one of formulas (1-1) to (1-3). <5> The reducing agent for synthesizing nitrogen-containing compounds according to any one of <1> to <4>, wherein the multidentate ligand includes at least one selected from the group consisting of an aminoalcohol, a cryptand, 4,13-diaza-18-crown-6-ether, and binaphthol. <6> The reducing agent for synthesizing nitrogen-containing compounds according to any one of <1> to <5>, which is a solvate. <7> The reducing agent for synthesizing nitrogen-containing compounds according to any one of <1> to <6>, for synthesizing nitrogen-containing compounds by electrolytic reaction. <8> The reducing agent for synthesizing nitrogen-containing compounds according to any one of <1> to <7>, which is used in the synthesis of ammonia. <9> A method for producing a nitrogen-containing compound, comprising a step of synthesizing a nitrogen-containing compound from nitrogen and a proton source in the presence of a nitrogen-activating catalyst and the reducing agent for synthesizing nitrogen-containing compounds according to any one of <1> to <8>. <10> A method for producing a nitrogen-containing compound according to <9>, further carried out in the presence of an electrolyte. <11> A method for producing a nitrogen-containing compound according to <9> or <10>, further carried out in the presence of an organic solvent.<12> The method for producing a nitrogen-containing compound according to any one of <9> to <11>, wherein the nitrogen-containing compound is ammonia. <13> The method for producing a nitrogen-containing compound according to any one of <9> to <12>, wherein the proton source is water. <14> A catalyst composition for synthesizing a nitrogen-containing compound, comprising the following components (1) to (5): (1) a nitrogen-activating catalyst, (2) a reducing agent for synthesizing a nitrogen-containing compound according to any one of <1> to <8>, (3) an organic solvent, (4) an electrolyte, and (5) a proton source.

[0010] According to the present invention, it is possible to provide a reducing agent for synthesizing nitrogen-containing compounds, which can improve the production amount of nitrogen-containing compounds per amount of input energy, as well as a method for producing nitrogen-containing compounds using the same and a catalyst composition.

[0011] <<Reducing Agent for Nitrogen-Containing Compound Synthesis>> The reducing agent for nitrogen-containing compound synthesis according to this embodiment (hereinafter sometimes simply referred to as the "reducing agent of this embodiment") comprises a metal complex containing samarium and a multidentate ligand coordinated to the samarium, wherein the multidentate ligand has 4 to 8 coordinating atoms bonded to the samarium (hereinafter sometimes referred to as the "number of coordinating atoms"), and each of the coordinating atoms is independently an oxygen atom or a nitrogen atom. The reducing agent according to this embodiment may be a mediator for nitrogen-containing compound synthesis. In this specification, the term "mediator" encompasses all of the following: (1) a compound that accepts electrons and donates the electrons to a catalyst; (2) a compound that accepts protons and donates the protons to a catalyst; and (3) a compound that accepts electrons and protons and donates the electrons and protons to a catalyst. The reducing agent according to this embodiment may also be a PCET (proton-coupled electron transfer) mediator. In this embodiment, the "PCET mediator" is a compound that corresponds to the above (3).

[0012] Furthermore, "coordinating atom" refers to an atom in a multidentate ligand directly bonded to the metal atom samarium. Furthermore, "the number of coordinating atoms bonded to samarium (number of coordinating atoms)" refers to the number of bonds between samarium and the coordinating atoms, and does not include coordinate bonds between samarium and a solvent. Furthermore, "number of ligands" refers to the number of ligands coordinated to samarium. When one coordinating atom has a bonding form in which it is bonded to another coordinating atom directly or indirectly without going through samarium, the one coordinating atom and the other coordinating atom belong to the same ligand. On the other hand, when one coordinating atom does not have the above bonding form, the one coordinating atom and the other coordinating atom do not belong to the same ligand.

[0013] As described above, for example, samarium iodide (SmI) and the like may become insoluble due to the association or polynucleation of reducing agents (or mediators). When the reducing agent becomes insoluble, the amount of reducing agent that can contact the electrode decreases, thereby reducing the amount of electrons supplied from the electrode to the catalyst via the reducing agent. As a result, the production yield of nitrogen-containing compounds per applied energy amount decreases. Furthermore, if the electron acceptance capacity of the reducing agent decreases, small amounts of water molecules present at the cathode may accept electrons in place of the reducing agent, causing the hydrogen production reaction to proceed through water reduction. In contrast, the reducing agent of this embodiment has a multidentate ligand containing at least one of oxygen atoms and nitrogen atoms as a coordinating atom and has 4 to 8 coordinating atoms. Therefore, the reducing agent has a bulkier structure than, for example, samarium iodide (SmI). This makes it easier to suppress the association or polynucleation of reducing agents and makes it less likely to cluster. Therefore, when the reducing agent of this embodiment is used, the amount of insoluble matter generated is small, and the influence of the insoluble matter on the decrease in the amount of electrons supplied to the catalyst is small, so that the production amount of the nitrogen-containing compound per amount of energy input can be improved. The reducing agent for synthesizing a nitrogen-containing compound of this embodiment is preferably a reducing agent for synthesizing a nitrogen-containing compound by an electrolytic reaction.

[0014] (Metal Atom) Samarium in this embodiment is a type of rare earth lanthanide element, and is an element with atomic number 62, represented by the atomic symbol Sm. In the reducing agent of this embodiment, samarium serves as the metal atom in the metal complex. Although not particularly limited, the number of metal atoms in the metal complex can be 1 to 5, preferably 1 to 3, and from the viewpoints of stability, activity, and the like, more preferably 1 to 2. When the reducing agent of this embodiment has multiple samarium atoms, the number of coordination atoms for each samarium is 4 to 8. Furthermore, the number of ligands coordinated to each samarium (number of ligands) is preferably 1 to 5, more preferably 1 to 3, and even more preferably 1 or 2.

[0015] (Polydentate Ligand) The polydentate ligand in this embodiment is a compound that coordinates to samarium and has two or more coordinating atoms. The reducing agent in this embodiment may be a metal complex in which only one polydentate ligand is coordinated to samarium, or a metal complex in which two or more polydentate ligands are coordinated to samarium.

[0016] The coordinating atom is at least one of an oxygen atom and a nitrogen atom, and specific combinations of coordinating atoms include a combination of a nitrogen atom and an oxygen atom, a combination of only nitrogen atoms, and a combination of oxygen atoms. In addition, a hydrogen atom may be bonded to the coordinating atom, forming a state such as "-OH" or ">NH". Examples of the multidentate ligand include a bidentate ligand and a tridentate ligand.

[0017] The metal complex to be used may include a structure represented by the following formula (1):

[0018] (In formula (1), H represents the polydentate ligand and includes a structure represented by the following formula (1-1), formula (1-2), or formula (1-3).)

[0019] In formula (1-1), R1 and R2 each independently represent a hydrogen atom or a hydrocarbon group, A1 each independently represent an oxygen atom or a nitrogen atom, l represents an integer of 0 to 3, m represents the bonding position to n, n represents the bonding position to m, M1 represents an integer of 5 to 10, and * represents the bonding position to Sm in formula (1).

[0020] In formula (1-2), R1 and R2 each independently represent a hydrogen atom or a hydrocarbon group, A1 and A2 each independently represent an oxygen atom or a nitrogen atom, l represents an integer of 0 to 3, M2 represents an integer of 1 to 5, N1 represents an integer of 1 to 3, and * represents the bonding position with Sm in formula (1).

[0021] In formula (1-3), R1 and R2 each independently represent a hydrogen atom or a hydrocarbon group, A1 and A2 each independently represent an oxygen atom or a nitrogen atom, l represents an integer of 0 to 3, N2 represents an integer of 1 to 4, and * represents the bonding position with Sm in formula (1).

[0022] In formulas (1-1) to (1-3), each 1 is independently preferably an integer of 0 to 2, more preferably an integer of 0 to 1. M1 is preferably an integer of 6 to 9. M2 is preferably an integer of 1 to 3, more preferably an integer of 1 to 2. N1 is preferably an integer of 1 to 2. N2 is preferably an integer of 1 to 3.

[0023] A1 and A2 each independently represent either an oxygen atom or a nitrogen atom. Specific combinations include, in formula (1-2) and formula (1-3), a combination in which one of A1 and A2 is a nitrogen atom and the other is an oxygen atom; 1 and A 2 In view of the activity against nitrogen-containing compounds, it is preferable that A2 is an oxygen atom. In addition, a combination in which A1 is a nitrogen atom and A2 is an oxygen atom, A 1 and A 2 is an oxygen atom. In addition, in formulas (1-1) to (1-3), the number of oxygen atoms is preferably greater than the number of nitrogen atoms.

[0024] R1 and R2 each independently represent either a hydrogen atom or a hydrocarbon group. R1 and R2 may be linked to form a ring structure. Examples of the hydrocarbon group represented by R1 and R2 include an alkyl group and an aryl group. The alkyl group is preferably an alkyl group having 1 to 20 carbon atoms, and more preferably an alkyl group having 1 to 10 carbon atoms. The alkyl group includes linear, branched, and cyclic alkyl groups. The aryl group is preferably an aryl group having 6 to 20 carbon atoms, and more preferably an aryl group having 6 to 10 carbon atoms. Furthermore, R1 and R2 may be linked to form a ring structure. Examples of the ring structure formed by linking R1 and R2 include a benzene structure and a naphthalene structure.

[0025] From the viewpoint of the activity of the nitrogen-containing compound, it is preferable that R1 and R2 are hydrogen atoms.

[0026] Specific examples of the polydentate ligand include amino alcohol, cryptand, 4,13-diaza-18-crown-6-ether, binaphthol, ethylenediamine, phenanthroline, porphyrin, and dimercaprol. From the viewpoint of activity toward nitrogen-containing compounds, it is preferable to include at least one selected from amino alcohol, cryptand, 4,13-diaza-18-crown-6-ether, and binaphthol.

[0027] When the reducing agent of the present embodiment is positively charged, the counter anion is not particularly limited, but examples thereof include trifluoromethanesulfonate (OTf), NO, and Br. - , Cl - , I - , PF6 - , BF4 - , N(CN)2 - , bis(trifluoromethylsulfonyl)amide, and the like.

[0028] The reducing agent of this embodiment may form a solvate. Examples of solvents that form solvates include water, and organic solvents such as methanol, ethanol, isopropanol, phenol, bisphenol, naphthol, binaphthol, diethyl ether, dimethoxyethane, and tetrahydrofuran (THF). When the reducing agent of this embodiment forms a solvate, the solvent is coordinated to samarium.

[0029] Specific examples of the reducing agent of this embodiment include the following: However, the present invention is not limited to the following compounds.

[0030]

[0031] The reducing agent of this embodiment, together with a nitrogen activation catalyst described later, is suitably used in a method for producing a nitrogen-containing compound, particularly in the synthesis of ammonia, which includes a step of synthesizing a nitrogen-containing compound from nitrogen and a proton source.

[0032] (Method for Producing Reducing Agent) The reducing agent of this embodiment (which may also function as a mediator) can be produced by a known synthesis method, for example, by reacting a samarium halide with a compound corresponding to a multidentate ligand in a solvent.

[0033] From the viewpoint of reaction efficiency, the reaction temperature is preferably 10 to 50°C, more preferably 15 to 45°C, and even more preferably 20 to 40°C. From the viewpoint of reaction efficiency, the reaction time is preferably 6 to 20 hours, more preferably 10 to 16 hours. The reaction time may be overnight. "Overnight" means 13 to 16 hours overnight. The samarium halide and the compound corresponding to the multidentate ligand can be reacted in a ratio ranging from an excess of the compound corresponding to the multidentate ligand per 1 mole of samarium halide to an excess of samarium halide per 1 mole of the compound corresponding to the multidentate ligand. From the viewpoint of reaction efficiency, preferably, about 1 to 6 moles (preferably 1 to 3 moles, more preferably 1 to 2 moles) of the compound corresponding to the multidentate ligand can be reacted per 1 mole of samarium halide.

[0034] The solvent that can be used in producing the reducing agent is preferably an organic solvent such as hexane, heptane, toluene, acetone, diethyl ether, dimethoxyethane, tetrahydrofuran (THF), or a mixture thereof, more preferably tetrahydrofuran (THF).

[0035] [Method for producing nitrogen-containing compounds] The reducing agent of this embodiment can be used as a reducing agent for synthesizing nitrogen-containing compounds in a method for producing nitrogen-containing compounds, which includes a step of synthesizing a nitrogen-containing compound from nitrogen and a proton source in the presence of a nitrogen-activating catalyst and a reducing agent for synthesizing nitrogen-containing compounds. The method for producing nitrogen-containing compounds can proceed with the synthesis reaction while suppressing clustering of the reducing agent, so that it consumes less energy, does not require large-scale equipment made of special materials, and is therefore excellent in industrial productivity.

[0036] (Nitrogen-Containing Compound) Examples of the nitrogen-containing compound produced by the method for producing a nitrogen-containing compound include ammonia and hydrazine, and ammonia is preferred.

[0037] (Nitrogen) As nitrogen, it is preferable to use nitrogen gas at normal pressure. Since nitrogen gas is inexpensive, it may be used in large excess relative to the other reagents.

[0038] (Proton Source) Examples of proton sources include alcohols such as water, methanol, ethanol, propanol, butanol, trifluoroethanol, phenol, and ethylene glycol; protonated forms of lutidines such as 2,6-dimethylpyridinium triflate; protonated forms of picolines such as 2-methylpyridinium triflate; and protonated forms of collidines such as 2,4,6-trimethylpyridinium triflate, with water being preferred. When water is used as the proton source, the step of obtaining hydrogen gas from natural gas primarily composed of methane (CH4), as in the conventional Haber-Bosch process, can be omitted, thereby significantly reducing emissions of carbon dioxide, a greenhouse gas. The amount of proton source used is preferably 0.5 to 300 moles, more preferably 5 to 50 moles, per mole of nitrogen activation catalyst.

[0039] (Mediator) The reducing agent of this embodiment is used as the mediator. The amount of the mediator used is preferably 0.5 to 300 moles, more preferably 5 to 50 moles, per mole of the nitrogen-activated catalyst.

[0040] (Nitrogen Activation Catalyst) The catalyst in the synthesis method of this embodiment is not particularly limited, and examples thereof include metal complexes. The catalyst is preferably a metal complex capable of cleaving the triple bond of a nitrogen molecule, and more preferably a metal complex capable of cleaving the triple bond of a nitrogen molecule and soluble in a solvent such as an organic solvent. Here, the term "soluble in a solvent" is not particularly limited, and examples thereof include mixing the catalyst in an amount to give a concentration of 0.1 mmol / L with a solvent and visually confirming dissolution. The catalyst may be used alone, or two or more types may be used in combination.

[0041] Examples of the central metal of the metal complex include titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), zirconium (Zr), molybdenum (Mo), ruthenium (Ru), rhodium (Rh), hafnium (Hf), tungsten (W), rhenium (Re), osmium (Os), and iridium (Ir). More preferred are chromium (Cr), molybdenum (Mo), and rhenium (Re), and even more preferred is molybdenum (Mo). A metal complex in which the central metal is Mo is also called a molybdenum complex.

[0042] Examples of the ligand of the metal complex include halide ions and tertiary phosphines. The ligand is preferably a combination of a pincer ligand (i.e., a ligand in which three coordinating atoms are bonded from three directions on the same plane containing the central metal) and a halide ion, more preferably a combination of a PCP (phosphorus-carbon-phosphorus) type pincer ligand or a PNP (phosphorus-nitrogen-phosphorus) type pincer ligand and a halide ion, and even more preferably a combination of a PCP type pincer ligand and a halide ion.

[0043] The metal complex is not particularly limited, and examples thereof include metal complexes each combining the central metal and the ligand described above. As the metal complex, a molybdenum complex having a pincer ligand and a halide ion as the ligand is more preferred, a molybdenum complex having a PCP-type pincer ligand or a PNP-type pincer ligand and a halide ion as the ligand is even more preferred, and a molybdenum complex having a PCP-type pincer ligand and a halide ion as the ligand is even more preferred.

[0044] Examples of molybdenum complexes having a PNP-type pincer ligand and a halide ion as the ligand include molybdenum complexes represented by the following formula (3-1) or (3-2): Examples of molybdenum complexes having a PCP-type pincer ligand and a halide ion as the ligand include molybdenum complexes represented by the following formula (3-3) or (3-4): Other examples of molybdenum complexes include molybdenum complexes represented by the following formula (3-5):

[0045]

[0046] In the formulas (3-1) to (3-5), R 18 , R 19 , R 20 , and R 21 (Hereinafter referred to as “R 18 ~R 21 ") each independently represents a hydrogen atom or a linear, cyclic or branched monovalent hydrocarbon group having 1 to 14 carbon atoms. 18 and R 19 , and / or R 20 and R 21 may be bonded to each other to form a ring, and PR 18 R 19 and PR 20 R 21 may be the same as or different from each other, and R 18 ~R 21 may all be the same or at least some may be different. 22represents a hydrogen atom or a linear, cyclic or branched monovalent hydrocarbon group having 1 to 14 carbon atoms. m1 is an integer of 0 to 3. m2 is an integer of 0 to 4, preferably an integer of 0 to 2. In addition, R 22 When two or three R 22 may be bonded to each other to form a ring. 22 When two or three R are present, they may all be the same or at least some may be different. 18 ~R 21 and R 22 The "linear, cyclic or branched monovalent hydrocarbon group having 1 to 14 carbon atoms" in the formula (I) can be selected from the group consisting of alkyl groups having 1 to 6 carbon atoms, alkenyl groups having 2 to 6 carbon atoms, alkynyl groups having 2 to 6 carbon atoms, cycloalkyl groups having 3 to 6 carbon atoms, cycloalkenyl groups having 3 to 6 carbon atoms, cycloalkynyl groups having 3 to 6 carbon atoms, aryl groups having 6 to 14 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, and phenyl or naphthyl groups which may have at least one substituent selected from the group consisting of a hydroxy group, a halogen atom, and a perfluoromethyl group. 18 ~R 21 As the alkyl group, an alkyl group having 1 to 6 carbon atoms is preferable, and an alkyl group having 1 to 4 carbon atoms is more preferable. 18 ~R 21 Z is more preferably a butyl group, and particularly preferably a tert-butyl group. Z represents a structure represented by the following formulas (i) to (iii).

[0047]

[0048] In the formula, X H represents a halogen atom. A wavy line represents a bond to an adjacent atom. The halogen is one selected from the group consisting of fluorine, chlorine, bromine, and iodine.

[0049] The amount of catalyst used in the synthesis method of this embodiment is not particularly limited, but may be, for example, 0.5 mmol / L to 3.0 mmol / L, and preferably 1.0 mmol / L to 2.5 mmol / L, relative to the volume of the solvent in the system. For example, when a nitrogen-containing compound is synthesized in the cathode compartment by an electrochemical reduction reaction using an electrolysis reaction cell in which the anode compartment and the cathode compartment are separated by a separator that preferentially allows ions to permeate, the volume of the solvent in the system refers to the volume of the solvent in the cathode compartment.

[0050] In this embodiment, the amount of the reducing agent for synthesizing a nitrogen-containing compound may be 20 mmol / L to 300 mmol / L, preferably 50 mmol / L to 200 mmol / L, and more preferably 70 mmol / L to 150 mmol / L, relative to the volume of the solvent in the system.

[0051] In the method for producing a nitrogen-containing compound according to the present embodiment, the reaction for synthesizing a nitrogen-containing compound from nitrogen and a proton source is presumed to proceed according to the following mechanism when water is used as the proton source. The synthesis of ammonia will be described as an example. In the formula, the pincer ligand in the nitrogen-activating catalyst is represented by L. The synthesis of ammonia is presumed to proceed according to formulas <1> to <3>.

[0052]

[0053] Specifically, the central metal Mo of the nitrogen activation catalyst is reduced from trivalent to monovalent by the reducing agent Red (Equation <1>). Next, nitrogen N2 is converted by the reduced nitrogen activation catalyst to give a nitride complex (LMo(I)-N) accompanied by cleavage of the nitrogen triple bond (Equation <2>). Then, the proton and electron source generated by the reaction of the reducing agent Red with water react with this nitride complex (LMo(I)-N), which is reduced to imide (LMo(I)-NH) and amide (LMo(I)-NH2), ultimately producing ammonia (Equation <3>). As a result, the nitrogen triple bond of nitrogen N2 is dissociated by the action of the nitrogen activation catalyst, producing ammonia.

[0054] (Reaction Conditions, etc.) According to the method for producing a nitrogen-containing compound of this embodiment, the synthesis of the nitrogen-containing compound can be carried out under relatively mild conditions, for example, in the range of −80° C. to 100° C. and 0.10 MPa to 0.20 MPa. The temperature is preferably −60° C. to 70° C., more preferably −40° C. to 60° C.

[0055] In the method for producing a nitrogen-containing compound according to the present embodiment, the production of the nitrogen-containing compound can be carried out in the presence of an organic solvent. Examples of the solvent include cyclic ethers such as tetrahydrofuran and dioxane, chain ethers such as diethyl ether and dimethoxyethane, nitrile compounds such as acetonitrile, aromatic solvents such as benzene, toluene and xylene, and alcohols such as methanol, ethanol and isopropanol. Among these, the solvent is preferably a cyclic alcohol, more preferably tetrahydrofuran.

[0056] <Electrochemical Reduction Reaction> In another preferred aspect of the method for producing a nitrogen-containing compound according to this embodiment, a nitrogen-containing compound is synthesized from nitrogen and a proton source under an electrochemical reduction reaction. Specifically, a nitrogen-activating catalyst is introduced into the cathode side of an electrolysis reaction cell, and reacted with nitrogen and protons supplied from the anode side to produce the nitrogen-containing compound. It is presumed that the proton source is water, the reducing agent acts as a proton-coupled electron transfer mediator, and nitrogen-containing compounds such as ammonia are continuously produced by the mechanism shown in reaction formulas (1) to (6) or reaction formulas (7) to (12).

[0057]

[0058] Here, "Red" represents a reducing agent (which may be a mediator), Ox-OH represents an oxidized reducing agent (which may be a mediator), and Cat represents a nitrogen-activating catalyst. + can be provided from a proton source added in the cathode compartment or from the anode compartment through the diaphragm.

[0059] (Electrolyte) In the method for producing a nitrogen-containing compound according to the present embodiment, the production of the nitrogen-containing compound can be carried out in the presence of an electrolyte. In order to promote the synthesis reaction of the nitrogen-containing compound, an electrolyte may be added to the cathode fluid or the anode fluid. The electrolyte is not particularly limited as long as it is an additive that does not inhibit the synthesis reaction of the nitrogen-containing compound and can improve electrical conductivity. Examples of such electrolytes include lithium trifluoromethanesulfonate (LiOTf), lithium bis(trifluoromethanesulfonyl)imide (LiN(SOCF)), lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), lithium bromide (LiBr), sodium bromide (NaBr), potassium bromide (KBr), lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), lithium sulfate (LiSO), sodium sulfate (NaSO), potassium sulfate (KSO), lithium hydrogen sulfate (LiHSO), sodium hydrogen sulfate (NaHSO), potassium hydrogen sulfate (KHSO), lithium Examples of electrolytes include lithium phosphate (LiPO), sodium phosphate (NaPO), potassium phosphate (KPO), lithium hydrogen phosphate (LiHPO), sodium hydrogen phosphate (NaHPO), potassium hydrogen phosphate (KHPO), lithium dihydrogen phosphate (LiHPO), sodium dihydrogen phosphate (NaHPO), potassium dihydrogen phosphate (KHPO), ammonium triflate (NHOTf), tetraethylammonium perchlorate, tetraethylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate, tetrabutylammonium perchlorate, tetrabutylammonium tetrafluoroborate, and tetrabutylammonium hexafluorophosphate. The electrolyte may be used alone or in combination. The amount of electrolyte used is 0.01 mol / L or more and 5 mol / L, and more preferably 0.2 to 2 mol / L.

[0060] When a nitrogen-containing compound is synthesized by an electrochemical reduction reaction, the reaction is presumed to proceed according to the following mechanism. Here, the synthesis of ammonia as the nitrogen-containing compound will be described as an example.

[0061] The reducing agent for synthesizing a nitrogen-containing compound of this embodiment, a catalyst, and a proton source are introduced into the cathode compartment of an electrolysis reaction cell, the anode compartment and the cathode compartment of which are separated by a separator that preferentially allows ions to pass through. A compound to be oxidized by electrolysis is introduced into the anode compartment of the cell, and the nitrogen-containing compound is produced from nitrogen molecules in the cathode compartment.

[0062] In the synthesis method of this embodiment, the synthesis of the nitrogen-containing compound can be carried out under relatively mild conditions, for example, in a temperature range of −80° C. to 100° C. and a pressure of 0.10 MPa to 0.20 MPa. This temperature is preferably −60° C. to 70° C., and more preferably −40° C. to 60° C.

[0063] In the synthesis method of this embodiment, when a nitrogen-containing compound is synthesized by an electrochemical reduction reaction, the potential applied to the cathode is not particularly limited, but is, for example, −3.0 to −0.5 V (vs. Ag / Ag + ), and may be −2.0 to −1.0 V (vs. Ag / Ag + ) may be used. + ) is Ag / Ag + represents the potential when used as a reference electrode.

[0064] In another embodiment of the method for synthesizing a nitrogen-containing compound, the nitrogen-containing compound may be synthesized by a normal reduction reaction instead of an electrochemical reduction reaction.

[0065] <Batch Reaction> One aspect of the method for producing a nitrogen-containing compound according to this embodiment is a batch reaction in which each component is charged into a vessel and reacted. Nitrogen is circulated through the vessel, and a solvent is added and stirred, thereby supplying nitrogen from the gas phase. A gas trap containing dilute sulfuric acid is installed at the nitrogen outlet to capture the gaseous nitrogen-containing compound that is produced. A nitrogen activation catalyst, a reducing agent, and a proton source are placed in the vessel. The nitrogen activation catalyst activates the nitrogen, and the reducing agent reacts with protons from the proton source. The reduction reaction and the proton reaction may be simultaneous or sequential. The reduction of the nitrogen activation catalyst and the proton reaction are repeated to synthesize a nitrogen-containing compound. The nitrogen-containing compound is dissolved in a solvent and captured in a gas trap, and then recovered.

[0066] In conventional methods for producing nitrogen-containing compounds using SmI, SmI(OH) is generated as an oxidized reducing agent after the reaction is completed. However, this substance can undergo a precipitation reaction due to polynucleation, making it difficult to continuously produce nitrogen-containing compounds while regenerating SmI(OH) through an electrolytic reaction. The reducing agent of the present embodiment has a bulky structure, which is thought to easily suppress association and polynucleation of the reducing agents, making insolubilization due to clustering less likely to occur, and preventing the precipitation reaction from proceeding. This is thought to improve the efficiency of continuous production of nitrogen-containing compounds and increase the productivity of nitrogen-containing compounds.

[0067] Furthermore, suppression of the precipitation reaction may ultimately contribute to the productivity of the nitrogen-containing compound in some cases. For example, when a precipitate is generated from the reaction solution after production, the accumulated precipitate may clog pipes, etc., and therefore, extra steps such as removal of the precipitate and cleaning of the precipitate adhering to the equipment are required, resulting in extra costs.

[0068] The suppression of the precipitation reaction is particularly remarkable when, in the compound represented by formula (I) or a solvate thereof, R represents an alkyl group having 1 to 20 carbon atoms, a perfluoroalkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, a perfluorocycloalkyl group having 3 to 20 carbon atoms, or an aromatic group which may have a substituent.

[0069] [Catalyst Composition] The catalyst composition for synthesizing a nitrogen-containing compound of the present invention contains the following components (1) to (5): (1) a nitrogen-activating catalyst, (2) a reducing agent in this embodiment, (3) an organic solvent, (4) an electrolyte, and (5) a proton source.

[0070] The catalyst composition is preferably used in a method for producing a nitrogen-containing compound, which comprises a step of synthesizing a nitrogen-containing compound from nitrogen and a proton source while simultaneously reducing, by electrolysis, a reducing agent oxidized in the synthesis reaction of the nitrogen-containing compound. Specifically, the catalyst composition is used as a first electrode solution in the method for producing a nitrogen-containing compound by electrochemical reduction.

[0071] The preferred embodiments of each component are the same as those described above. The preferred content of each component in the catalyst composition can be the preferred amount used described above.

[0072] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0073] (1) Ammonia Measurement Method Ammonia was quantified using an ion chromatograph (Tosoh Corporation, IC-8100EX equipped with a TSKgel SuperIC-Cation HS II column). A commercially available ammonium ion standard solution was diluted to 1 to 4 ppm with ultrapure water and measured by ion chromatography to create a calibration curve. The reaction solution to be measured was diluted with ultrapure water or a dilute sulfuric acid aqueous solution, and the ammonia in the reaction solution was converted to ammonium ions. The reaction solution was then measured by ion chromatography, and the ammonium ion concentration of the reaction solution was measured from the previously prepared calibration curve. The obtained ammonium ion concentration was used as the ammonia concentration of the reaction solution, and the amount of ammonia produced was calculated by multiplying it by the volume of the reaction solution and the dilution ratio.

[0074] (2) Calculation method of Faraday efficiency (%) A potentiostat (HZ-Pro, manufactured by Hokuto Denko Corporation) was used for the electrolytic synthesis test. The cathode applied potential was −1.5 V vs. Ag / Ag. +The reaction was carried out for 4 hours, and the amount of coulombs was recorded. The faradaic efficiency was calculated from the amount of coulombs and the amount of ammonia in the electrolyte solution using the following formula: Faraday efficiency (%) = amount of ammonia / (amount of coulombs / Faraday constant / 3) x 100

[0075] (3) Compound Structure The compound structure was determined using a nuclear magnetic resonance spectrometer under the following conditions: 1 The H-NMR measurement was carried out and confirmed. Frequency: 400 MHz Solvent: THF-d8 Measurement temperature: 298 K

[0076] Synthesis Example 1 A reducing agent for synthesizing nitrogen-containing compounds, which is the compound shown below, was synthesized by the following method: This reducing agent for synthesizing nitrogen-containing compounds is referred to as "Med1".

[0077]

[0078] Sm(OTf)3 (2.03 g, 3.34 mmol) and 50 mL of THF were added to a Schlenk flask under an Ar atmosphere to obtain a colorless solution. Triethanolamine (0.88 mL, 6.69 mmol, 0.998 g) was added via syringe and stirred at room temperature for 12 hours. The resulting insoluble matter was removed, and the solvent was then removed under reduced pressure to obtain a viscous colorless solid. The solid was washed multiple times with diethyl ether (5 mL) to obtain a white powder. The powder was dissolved in tetrahydrofuran and recrystallized at -20 °C for 1 week to obtain colorless crystalline Med1 in 92% yield (3.01 g). The H NMR results are shown below, and the structure of Med1 was confirmed by single-crystal X-ray structural analysis of the obtained crystals. 1H NMR (400 MHz, CD3CN, 298 K): H 8.13 (br), 4.75 (br s, 2H), 4.33 (br s, 8H), 3.84 (br s, 4H), 3.65 (m, 4H), 3.37 (br s, 4H), 2.49 (br s, 8H), 1.81 (m, 4H). 19F[1H] NMR (376 MHz, CD3CN, 298 K): δF -79.40 (s).

[0079] Synthesis Example 2 A reducing agent for synthesizing nitrogen-containing compounds, which is the compound shown below, was synthesized by the following method: This reducing agent for synthesizing nitrogen-containing compounds is referred to as "Med2".

[0080]

[0081] Sm(NO)3·6H2O (1.03 g, 2.25 mmol) and 8 mL of THF (undiluted) were added to a Schlenk flask under an Ar atmosphere to obtain a colorless solution. Triethanolamine (0.60 mL, 4.49 mmol, 0.67 g, undistilled) was added and stirred overnight under an inert atmosphere to obtain a white suspension. After removing the supernatant, the solvent was removed under reduced pressure to obtain a white solid. The solid was washed three times with diethyl ether (5 mL), dried under vacuum, and recrystallized from a saturated methanol solution at room temperature to obtain colorless crystalline Med2 in 70% yield (1.04 g). HNMR results are shown below, and the structure of Med2 was confirmed by single-crystal X-ray structural analysis of the obtained crystals. 1H NMR (400 MHz, DMSO-d6): H 4.36 (br), 3.41 (m, 12H), 2.56 (m, 12H).

[0082] Synthesis Example 3 A reducing agent for synthesizing nitrogen-containing compounds, which is the compound shown below, was synthesized by the following method: This reducing agent for synthesizing nitrogen-containing compounds is referred to as "Med3".

[0083]

[0084] A 300 ml Schlenk tube was charged with 1.5 g (2.5 mmol) of Sm(OTf), 941 mg (2.4 mmol) of cryptand, and 150 mL of THF, and the mixture was stirred overnight. The mixture was then filtered to obtain a clear solution. This solution was concentrated to approximately 50 ml and placed in a freezer to obtain 877 mg of white crystals in a 36% yield.

[0085] The resulting compound was subjected to NMR measurement under the above-mentioned conditions, and the following peaks were observed, confirming that it had the chemical structure of Med3. δ (ppm) (THF-d8): 3.97 (t, 12H) 3.41 (s, 12H), 3.04 (t, 12H)

[0086] Synthesis Example 4 A reducing agent for synthesizing nitrogen-containing compounds, which is the compound shown below, was synthesized by the following method: This reducing agent for synthesizing nitrogen-containing compounds is referred to as "Med4".

[0087]

[0088] A 300 ml Schlenk tube was charged with 1.5 g (2.4 mmol) of Sm(OTf), 630 mg (2.4 mmol) of 4,13-Diaza-18-Crown-6, and 150 mL of THF, and the mixture was stirred overnight and then filtered. The solution was concentrated to approximately 40 ml, and 3 ml of methanol was added and heated to 50°C. The solution was allowed to stand in a freezer, yielding 1.38 g of white crystals in a 64% yield.

[0089] The resulting compound was subjected to NMR measurement under the above-mentioned conditions, and the following peaks were observed, confirming that it had the chemical structure of Med4. δ (ppm) (THF-d8): 5.04 (br, 4H), 4.52 (br, 4H), 4.37 (br, 4H), 4.21 (br, 4H), 3.39 (br, 2H), 3.17 (br, 4H), 2.42 (br, 4H).

[0090] [Examples 1 and 2, Comparative Example 1] An electrolysis reaction cell was used in a nitrogen atmosphere, in which the anode chamber and the cathode chamber were separated by a separator through which ions preferentially permeate. Carbon felt was used as the electrode in the anode chamber and the electrode in the cathode chamber. Four Nafion 117 membranes hot-pressed together were used as the separator. Nafion 117 is a product name of DuPont, and "Nafion" is a registered trademark.

[0091] The compounds placed in the anode and cathode compartments were as follows: (Anode) First electrolyte: 0.5M KSO 4 Water (HO, 6 mL) (cathode) Second electrolyte: 1.0 M LiOTf Tetrahydrofuran (THF, 6 mL) [MoI(PCP)] (0.01 mmol) Reducing agent (0.6 mmol) shown in Table 1 below

[0092] In the above structure, a potentiostat was used, and the cathode potential was −1.5 V vs. Ag / Ag + The liquid flow rate at both electrodes was set to 20 mL / min, and ammonia production was carried out for 4 hours, and the amount of ammonia produced was confirmed using an ion chromatograph. The results are shown in the table below.

[0093]

[0094] The reducing agent (mediator) of the example had a superior faradaic efficiency compared to the reducing agent of Comparative Example 1, which did not have a multidentate ligand. As a result, the production amount of nitrogen-containing compounds per input energy amount was improved.

[0095] [Examples 3 and 4, Comparative Example 2] The same procedure as in Example 1 was carried out except for the following changes. A potentiostat was used, and the cathode applied potential was −1.5 V vs. Ag / Ag. + The liquid flow rate at both electrodes was set to 20 mL / min, and ammonia production was carried out for 3 hours, and the amount of ammonia produced was confirmed using an ion chromatograph. The results are shown in the table below.

[0096] (Anode) First electrolyte: 0.5 M K2SO4 (Cathode) Second electrolyte: 1.0 M LiOTf Tetrahydrofuran (THF, 6 mL) [MoI3(PCP)] (0.01 mmol) Reducing agent (0.6 mmol) shown in Table 2 below

[0097]

[0098] The reducing agent (mediator) of the example had a superior faradaic efficiency compared to the reducing agent of Comparative Example 2, which did not have a multidentate ligand. As a result, the production amount of nitrogen-containing compounds per input energy amount was improved.

[0099] The disclosure of Japanese Patent Application No. 2024-031594, filed on March 1, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A reducing agent for synthesizing nitrogen-containing compounds, comprising a metal complex containing samarium and a multidentate ligand that coordinates to the samarium, wherein the multidentate ligand has 4 to 8 coordinating atoms bonded to the samarium, and the coordinating atoms are each independently an oxygen atom or a nitrogen atom.

2. The reducing agent for synthesizing nitrogen-containing compounds according to claim 1, wherein the metal complex comprises a structure represented by the following formula (1): (In formula (1), H represents the polydentate ligand and includes a structure represented by the following formula (1-1), formula (1-2), or formula (1-3).) In formula (1-1), R1 and R2 each independently represent a hydrogen atom or a hydrocarbon group, A1 each independently represent an oxygen atom or a nitrogen atom, l represents an integer of 0 to 3, m represents the bonding position with n, n represents the bonding position with m, M1 represents an integer of 5 to 10, and * represents the bonding position with Sm in formula (1). In formula (1-2), R1 and R2 each independently represent a hydrogen atom or a hydrocarbon group, A1 and A2 each independently represent an oxygen atom or a nitrogen atom, l represents an integer of 0 to 3, M2 represents an integer of 1 to 5, N1 represents an integer of 1 to 3, and * represents the bonding position with Sm in formula (1). In formula (1-3), R1 and R2 each independently represent a hydrogen atom or a hydrocarbon group, A1 and A2 each independently represent an oxygen atom or a nitrogen atom, l represents an integer of 0 to 3, N2 represents an integer of 1 to 4, and * represents the bonding position with Sm in formula (1).

3. The reducing agent for synthesizing nitrogen-containing compounds according to claim 2, wherein A2 in at least one of the formulas (1-2) to (1-3) is an oxygen atom.

4. The reducing agent for synthesizing nitrogen-containing compounds according to claim 2 or 3, wherein R1 and R2 in at least one of the formulas (1-1) to (1-3) are hydrogen atoms.

5. The reducing agent for synthesizing nitrogen-containing compounds according to any one of claims 1 to 4, wherein the multidentate ligand comprises at least one selected from the group consisting of amino alcohol, cryptand, 4,13-diaza-18-crown-6-ether, and binaphthol.

6. The reducing agent for synthesizing nitrogen-containing compounds according to any one of claims 1 to 5, which is a solvate.

7. The reducing agent for synthesizing nitrogen-containing compounds according to any one of claims 1 to 6, for synthesizing nitrogen-containing compounds by electrolytic reaction.

8. The reducing agent for synthesizing nitrogen-containing compounds according to any one of claims 1 to 7, which is used in the synthesis of ammonia.

9. A method for producing a nitrogen-containing compound, comprising a step of synthesizing a nitrogen-containing compound from nitrogen and a proton source in the presence of a nitrogen-activating catalyst and a reducing agent for synthesizing a nitrogen-containing compound according to any one of claims 1 to 8.

10. The method for producing a nitrogen-containing compound according to claim 9, further carried out in the presence of an electrolyte.

11. The method for producing a nitrogen-containing compound according to claim 9 or 10, further carried out in the presence of an organic solvent.

12. The method for producing a nitrogen-containing compound according to any one of claims 9 to 11, wherein the nitrogen-containing compound is ammonia.

13. The method for producing a nitrogen-containing compound according to any one of claims 9 to 12, wherein the proton source is water.

14. A catalyst composition for synthesizing nitrogen-containing compounds, comprising the following components (1) to (5): (1) a nitrogen-activating catalyst; (2) a reducing agent for synthesizing nitrogen-containing compounds according to any one of claims 1 to 8; (3) an organic solvent; (4) an electrolyte; and (5) a proton source.

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