Reducing agent for synthesizing nitrogen-containing compound

Abstract

The present disclosure relates to a reducing agent for synthesizing a nitrogen-containing compound, the reducing agent containing an electron supplying site and a proton accepting site that is bonded to the electron supplying site.

Description

Reducing agent for synthesis of nitrogen-containing compounds

[0001] The present disclosure relates to a reducing agent for synthesizing nitrogen-containing compounds.

[0002] Nitrogen-containing compounds such as ammonia are important chemical raw materials used as basic materials for fertilizers and chemical products, and in recent years have also attracted attention for their use in coal-fired power generation co-firing and as energy carriers. Conventionally, ammonia, an example of a nitrogen-containing compound, has been industrially produced by the Haber-Bosch process. The Haber-Bosch process is a method for producing ammonia by reacting nitrogen gas with hydrogen gas in the presence of an iron-based catalyst.

[0003] However, the Haber-Bosch process is a method for synthesizing ammonia under high temperature and pressure, which consumes a lot of energy and requires large equipment made of special materials. ４ When hydrogen gas is obtained from natural gas, which is mainly composed of carbon dioxide (CO ２ Therefore, there is a need for a new method for producing nitrogen-containing compounds such as ammonia from nitrogen under mild reaction conditions.

[0004] Patent Document 1 discloses a method for synthesizing a nitrogen-containing compound from nitrogen and a proton source in the presence of a nitrogen-activating catalyst and a reducing agent.

[0005] International Publication No. 2022 / 230898

[0006] However, there is room for further improvement in the production yield of nitrogen-containing compounds in the method for producing nitrogen-containing compounds described in Patent Document 1. The present disclosure has been made in view of the above circumstances, and provides a reducing agent for synthesizing nitrogen-containing compounds, which can improve the production yield of nitrogen-containing compounds, and a method for synthesizing nitrogen-containing compounds using the reducing agent.

[0007] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the production yield of nitrogen-containing compounds can be improved by using a reducing agent for synthesizing nitrogen-containing compounds having a predetermined structure in the synthesis of the nitrogen-containing compounds.

[0008] That is, this embodiment includes the following aspects. <1> A reducing agent for synthesizing nitrogen-containing compounds, comprising an electron donor moiety and a proton acceptor moiety bonded to the electron donor moiety. <2> The reducing agent for synthesizing nitrogen-containing compounds according to <1>, in which the proton acceptor moiety is a heterocycle. <3> The reducing agent for synthesizing nitrogen-containing compounds according to <2>, in which the heterocycle contains a nitrogen atom. <4> The reducing agent for synthesizing nitrogen-containing compounds according to <2> or <3>, in which the heterocycle is a pyridine ring. <5> The reducing agent for synthesizing nitrogen-containing compounds according to any one of <1> to <4>, in which the electron donor moiety is a moiety consisting of a metal atom and two saturated or unsaturated cyclic hydrocarbons coordinated to the metal atom. <6> The reducing agent for synthesizing nitrogen-containing compounds according to any one of <1> to <5>, in which the electron donor moiety is a metallocene structure which may have a substituent. <7> The reducing agent for synthesizing nitrogen-containing compounds according to <6>, wherein the metallocene structure is a cobaltocene structure which may have a substituent or a ferrocene structure which may have a substituent. <8> The reducing agent for synthesizing nitrogen-containing compounds according to <6> or <7>, wherein, in at least one of the two cyclopentadienyls which may have a substituent in the metallocene structure, one or more of the carbon atoms forming the ring are directly bonded to a substituent other than the proton-accepting site. <9> The reducing agent for synthesizing nitrogen-containing compounds according to any one of <6> to <8>, wherein, in at least one of the two cyclopentadienyls in the metallocene structure, one or more of the carbon atoms forming the ring are bonded to the proton-accepting site. <10> The reducing agent for synthesizing nitrogen-containing compounds according to any one of <1> to <9>, wherein the reducing agent is a compound represented by the following formula (1): (In formula (1), M is a metal atom, and R １ , R ２ , R ３ , R ４ , and R ５ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and R ６ , R ７ , R ８ , and R ９are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and R １０ is a heterocycle which may have a substituent, and R １１ is a saturated or unsaturated divalent cyclic hydrocarbon group having 3 to 21 carbon atoms which may have a substituent, a saturated or unsaturated divalent chain hydrocarbon group having 1 to 10 carbon atoms which may have a substituent, or a single bond.) <11> The reducing agent for synthesizing a nitrogen-containing compound according to any one of <1> to <10>, for synthesizing a nitrogen-containing compound by an electrolytic reaction. <12> A method for synthesizing a nitrogen-containing compound, comprising synthesizing a nitrogen-containing compound from nitrogen molecules in the presence of the reducing agent for synthesizing a nitrogen-containing compound according to any one of <1> to <11>, a catalyst, and a proton source. <13> The method for synthesizing a nitrogen-containing compound according to <12>, wherein the catalyst contains a molybdenum complex. <14> The synthesis method according to <12> or <13>, wherein the molar equivalent of the reducing agent for synthesizing a nitrogen-containing compound relative to the catalyst is 1 or more and 600 or less. <15> The synthesis method according to any one of <12> to <14>, wherein the proton source contains an organic acid. <16> The synthesis method according to <15>, wherein the organic acid includes a compound represented by the following formula (2): <17> The synthesis method according to <15> or <16>, wherein the molar equivalent of the organic acid relative to the reducing agent for synthesizing a nitrogen-containing compound is 10 or more and 300 or less.

[0009] According to the present disclosure, it is possible to provide a reducing agent for synthesizing nitrogen-containing compounds, which can improve the production yield of nitrogen-containing compounds, and a method for synthesizing nitrogen-containing compounds using the same.

[0010] The following describes in detail an embodiment of the present invention (hereinafter referred to as "the present embodiment"); however, the present invention is not limited to this embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0011] 1. Reducing Agent for Nitrogen-Containing Compound Synthesis The reducing agent for nitrogen-containing compound synthesis of this embodiment includes an electron donor moiety and a proton acceptor moiety bonded to the electron donor moiety. Here, "bond" refers not only to direct bonding of the proton acceptor moiety to the electron donor moiety, but also to indirect bonding via another moiety. The reducing agent of this embodiment may be a mediator. In this embodiment, a "mediator" refers to a substance having a structure that has the function of receiving electrons from an electrode or the like and then supplying the electrons to a catalyst or the like, and / or a structure that has the function of receiving protons from a proton source or the like and then supplying the protons to a catalyst or the like. The reducing agent of this embodiment may also be a PCET (proton-coupled electron transfer) mediator. In this embodiment, a "PCET mediator" refers to a substance having a structure that has the function of receiving electrons from an electrode or the like and then supplying the electrons to a catalyst or the like, and a structure that has the function of receiving protons from a proton source or the like and then supplying the protons to a catalyst or the like. The electron supply portion in this embodiment has a function of receiving electrons from the electrode and then supplying the electrons to the catalyst or the like.

[0012] SmI, a reducing agent that has been used in conventional synthesis reactions of nitrogen-containing compounds, ２ In the presence of a catalyst, reducing agents such as chromocene and cobaltocene can supply electrons to a nitrogen source such as nitrogen molecules, thereby reducing the nitrogen source. Such reducing agents have an electron donating site capable of supplying electrons to a substrate such as a nitrogen source. On the other hand, such reducing agents do not have a proton accepting site capable of accepting protons. Therefore, in a synthesis reaction of a nitrogen-containing compound using such reducing agents, it is thought that a reaction in which the reducing agent supplies electrons to the nitrogen source and a reaction in which the reducing agent supplies protons to the nitrogen source that has received the electrons occur separately.

[0013] On the other hand, the reducing agent for synthesizing nitrogen-containing compounds of this embodiment (hereinafter also simply referred to as "reducing agent") contains an electron donor moiety and a proton acceptor moiety bonded to the electron donor moiety. Therefore, in a nitrogen-containing compound synthesis reaction in the presence of the reducing agent, the reducing agent supplies electrons and protons to the nitrogen source. That is, a reaction of supplying electrons to the nitrogen source and a reaction of supplying protons to the nitrogen source that has received the electrons occur in concert. Therefore, the nitrogen-containing compound synthesis reaction proceeds more easily than if these reactions occurred separately. As a result, the production yield of nitrogen-containing compounds per amount of input energy tends to be improved. However, the factors that can improve the production yield of nitrogen-containing compounds per amount of input energy are not limited to those described above.

[0014] Furthermore, in the presence of the reducing agent of this embodiment, the nitrogen-containing compound synthesis reaction tends to proceed more easily, and therefore the nitrogen-containing compound synthesis reaction tends to proceed under milder conditions. Milder conditions include, for example, conditions in which the temperature is closer to room temperature and the pressure is closer to atmospheric pressure. The reducing agent for synthesizing nitrogen-containing compounds of this embodiment is preferably a reducing agent for synthesizing nitrogen-containing compounds by electrolytic reaction.

[0015] Hereinafter, each component of the reducing agent for synthesizing nitrogen-containing compounds according to this embodiment will be described in detail.

[0016] 1.1. Proton Acceptor Site The reducing agent for synthesizing nitrogen-containing compounds of this embodiment contains one or more proton acceptor sites bonded to an electron donor site described below. The proton acceptor site refers to a site capable of accepting a proton. Here, the proton acceptor site is a concept that includes an atom capable of suitably accepting a proton, a portion of a functional group, the entire functional group, a portion of the main skeleton, the entire main skeleton, a portion of a compound, and the like. The proton acceptor site may accept a proton by containing, for example, an atom having an unshared electron pair. The atom having an unshared electron pair is not particularly limited, but examples include a nitrogen atom, an oxygen atom, a phosphorus atom, a sulfur atom, and a selenium atom, and among these, a nitrogen atom is preferred. The proton acceptor site is preferably a heterocycle. The heterocyclic ring is not particularly limited, but for example, it can be mentioned saturated or unsaturated 3-membered ring containing one or two heteroatoms; saturated or unsaturated 4-membered ring containing one or two heteroatoms; saturated or unsaturated 5-membered ring containing one, two or three heteroatoms; saturated or unsaturated 6-membered ring containing one, two or three heteroatoms; saturated or unsaturated 7-membered ring containing one or two heteroatoms; saturated or unsaturated 8-membered ring containing one heteroatom; saturated or unsaturated 9-membered ring containing one heteroatom.It should be noted that aromatic ring is included in unsaturated ring.In addition, heterocyclic ring can be bonded to a substituent.

[0017] As the heteroatom contained in the heterocycle, an atom having an unshared electron pair is preferred from the viewpoint of improving the proton acceptance of the heterocycle.When the heterocycle has an atom having an unshared electron pair, a proton is bonded to the heterocycle via the unshared electron pair, so that the proton acceptance of the heterocycle tends to be improved.Examples of the atom having an unshared electron pair include the above-mentioned atoms having an unshared electron pair.

[0018] The heterocycle is not particularly limited, and examples thereof include an aziridine ring, an azirine ring, a diaziridine ring, a diazirine ring, an oxaziridine ring, an azetidine ring, an azeto ring, a diazetidine ring, a diazeto ring, a pyrrolidine ring, a pyrrole ring, an imidazolidine ring, a pyrazolidine ring, an imidazole ring, a pyrazole ring, an oxazolidine ring, an isoxazolidine ring, an oxazole ring, an isoxazole ring, a thiazolidine ring, an isothiazolidine ring, a thiazole ring, an isothiazole ring, a triazole ring, a furazan ring, and an oxadiazo ring. Examples of heterocyclic rings include a pyridine ring, a thiadiazole ring, a dioxazole ring, a dithiazole ring, a tetrazole ring, an oxatetrazole ring, a thiatetrazole ring, a pentazole ring, a piperidine ring, a pyridine ring, a piperazine ring, a diazine ring, a morpholine ring, an oxazine ring, a thiomorpholine ring, a thiazine ring, a hexahydro-1,3,5-triazine ring, a triazine ring, a tetrazine ring, a pentazine ring, an azepane ring, an azepine ring, a diazepane ring, a diazepine ring, an azocane ring, an azocine ring, an azonane ring, and an azonine ring. For example, 2,6-dimethylpyridine has a pyridine ring, and ε-caprolactam has an azepane ring (lactam ring). Preferred heterocyclic rings containing a nitrogen atom include a pyridine ring and a diazine ring, and more preferably a pyridine ring. In addition to heterocyclic rings, the proton-accepting site may also be a nitrogen-containing substituent such as an amino group.

[0019] 1.2. Linking Group The proton acceptor moiety in this embodiment may be bonded to the electron donor moiety via a linking group. The proton acceptor moiety in this embodiment is bonded directly or indirectly to the electron donor moiety described below. An example of a mode in which the proton acceptor moiety is indirectly bonded to the electron donor moiety is when the proton acceptor moiety is bonded to the electron donor moiety via another moiety. An example of such another moiety is a linking group. The linking group in this embodiment connects the electron donor moiety and the proton acceptor moiety. Note that the linking group in this embodiment does not have a structure capable of accepting a proton. The linking group is not particularly limited, but is preferably a divalent linking group, and more preferably a divalent hydrocarbon group. The divalent hydrocarbon group preferably has 1 to 21 carbon atoms, more preferably 3 to 18 carbon atoms, even more preferably 4 to 12 carbon atoms, and particularly preferably 5 to 10 carbon atoms. The divalent hydrocarbon group may include at least one of a cyclic structure and a chain structure. The cyclic structure preferably has 3 to 10 carbon atoms, more preferably 4 to 8 carbon atoms, and even more preferably 5 to 7 carbon atoms. Examples of the cyclic structure include a cycloalkylene group and an arylene group, with a phenylene group and a diphenylene group being preferred. The chain structure may be a straight chain or a branched chain. The chain structure preferably has 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, even more preferably 3 to 7 carbon atoms, and particularly preferably 4 to 6 carbon atoms. Examples of the chain structure include an alkylene group, an alkenylene group, and an alkynylene group.

[0020] Examples of the linking group include a substituted or unsubstituted o-phenylene group, m-phenylene group, p-phenylene group, 2-methyl-1,4-phenylene group, 2,5-dimethyl-1,4-phenylene group, 1,2-naphthylene group, 1,4-naphthylene group, 1,5-naphthylene group, 9,10-anthrylene group, 9,10-phenanthrylene group, and 4,4′-diphenylene group.

[0021] 1.3. Electron Donor Moiety The reducing agent for synthesizing nitrogen-containing compounds of this embodiment contains one or more electron donor moieties. The electron donor moiety refers to a moiety that can donate electrons to an oxidizing agent such as a nitrogen source. Here, the electron donor moiety is a concept that includes an atom that can donate electrons to an oxidizing agent such as a nitrogen source, a part of a functional group, the entire functional group, a part of the main skeleton, the entire main skeleton, a part of a compound, and the like. The electron donor moiety is not particularly limited, but examples thereof include Fe ２＋ , Cr ２＋ , Co ２＋ Metal ions such as [Fe(CN) ６ ] ４－ [Cr(NH ３ ) ６ ] ３＋ , Co(ηC ５ H ５ ) ２ Metal complex structures such as H ２ , C ２ H ２ O ４ , C.H. ３ Examples of suitable organic molecules include those that do not have metal atoms, such as CHO. When the electron donor site has a metal complex structure, the electron donor site is a site consisting of a metal and a molecule that directly coordinates with the metal. For example, [Fe(CN) ６ ] ４－ In the formula, the electron donating site is [Fe(CN) ６ ] ４－ In addition, [Co(ηC ５ H ５ ) ２ ] ＋ In the formula, the electron donating site is [Co(ηC ５ H ５ ) ２ ] ＋ The whole.

[0022] The electron donor moiety is preferably a metal complex structure. A preferred example of the metal complex structure is a sandwich compound structure. A sandwich compound is a compound consisting of a metal atom and two saturated or unsaturated cyclic hydrocarbons, and a sandwich compound structure is a structure consisting of a metal atom and two saturated or unsaturated cyclic hydrocarbons. The electron donor moiety is preferably a moiety consisting of a metal atom and two saturated or unsaturated cyclic hydrocarbons coordinated to the metal atom. The metal atom is not particularly limited, but examples thereof include Ti (titanium), Zr (zirconium), Hf (hafnium), V (vanadium), Nb (niobium), Ta (tantalum), Mo (molybdenum), W (tungsten), Fe (iron), Ru (ruthenium), Co (cobalt), Rh (rhodium), Ir (iridium), Ni (nickel), Pd (palladium), Pt (platinum), and Sm (samarium). Among these, Cr, Mo, W, Fe, Ru, Co, Rh, Ir, and Sm are preferred, and Co is more preferred. The sandwich compound structure may be a mononuclear metal sandwich compound structure having one central metal atom, or a polynuclear metal sandwich compound structure having two or more central metal atoms.

[0023] The saturated or unsaturated cyclic hydrocarbon in the sandwich compound structure is not particularly limited, and examples thereof include cyclopentadienyl, benzene, and cyclooctatetraenyl, with cyclopentadienyl being preferred. In this embodiment, in the saturated or unsaturated cyclic hydrocarbon, one or more of the carbon atoms forming the ring may be directly bonded to a substituent other than the proton-accepting moiety. One or more of the carbon atoms forming the ring may be directly or indirectly bonded to the proton-accepting moiety. In this embodiment, the substituent is different from the proton-accepting moiety described above. The substituent is not particularly limited, but an electron-donating group is preferred from the viewpoint of improving the ability to supply electrons from the metal center to the catalyst, etc., and an electron-withdrawing group is preferred from the viewpoint of adjusting the redox potential of the metal center.

[0024] In this embodiment, the electron-donating group is not particularly limited, but examples thereof include alkyl groups such as a methyl group, an ethyl group, and a butyl group; aryl groups such as a phenyl group, a tolyl group, a xylyl group, and a naphthyl group; an alkoxy group, a hydroxyl group, an amino group, and an alkylamino group.

[0025] The number of carbon atoms in the alkyl group is preferably 1 to 5, more preferably 1 to 4, and even more preferably 1 to 3. The number of carbon atoms in the aryl group is preferably 6 to 15, more preferably 6 to 12, and even more preferably 6 to 10. The number of carbon atoms in the alkoxy group is preferably 1 to 5, more preferably 1 to 4, and even more preferably 1 to 3. The number of carbon atoms in the alkylamino group is preferably 1 to 5, more preferably 1 to 4, and even more preferably 1 to 3.

[0026] The electron-donating group is preferably a methyl group or an ethyl group, more preferably a methyl group.

[0027] In this embodiment, the electron-withdrawing group is not particularly limited. For example, —NH ３ ＋ , -CF ３ , -CCl ３ , -NO ２ , -CN, -CHO, -COCH ３ , -COOC ２ H ５ , -COOH, -SO ２ CH ３ , -SO ３ H and the like.

[0028] When the saturated or unsaturated cyclic hydrocarbon is cyclopentadinyl and one or more of the carbon atoms forming the ring are directly bonded to an electron-donating group other than the proton-accepting site, the number of carbon atoms forming the ring to which the electron-donating group is directly bonded is preferably 1 to 5, more preferably 2 to 5, even more preferably 3 to 5, particularly preferably 4 to 5, and even more preferably 5.

[0029] In this embodiment, it is preferred that one of the two saturated or unsaturated cyclic hydrocarbons in the sandwich compound structure is bonded to a proton-accepting site, and the other is bonded directly to an electron-donating group other than the proton-accepting site.

[0030] The sandwich compound structure is preferably a metallocene structure in which the two saturated or unsaturated cyclic hydrocarbons are both cyclopentadienyls and which is a mononuclear metal sandwich compound structure, and more preferably a cobaltocene structure or a ferrocene structure.

[0031] In a metallocene structure such as a cobaltocene structure, it is preferred that in at least one of the two cyclopentadienyls, one or more of the carbon atoms forming the ring be directly bonded to an electron-donating group other than the proton-accepting site. Also, in a metallocene structure such as a cobaltocene structure, it is preferred that in one of the two cyclopentadienyls, one or more of the carbon atoms forming the ring be directly bonded to a proton-accepting site, and in the other of the two cyclopentadienyls, one or more of the carbon atoms forming the ring be directly bonded to an electron-donating group other than the proton-accepting site.

[0032] In a metallocene structure such as a cobaltocene structure, when one or more of the carbons forming the ring in one of the two cyclopentadienyls is bonded to a proton-accepting site, the proton-accepting site may be directly bonded to the carbon forming the ring or indirectly bonded via another site.

[0033] As described above, in the synthesis reaction of a nitrogen-containing compound in the presence of the reducing agent for synthesizing a nitrogen-containing compound of this embodiment, a reaction of donating electrons to the nitrogen source and a reaction of donating protons to the nitrogen source occur in concert. Therefore, in the reducing agent of this embodiment, the synthesis reaction of a nitrogen-containing compound tends to proceed more easily when the electron donor site and the proton acceptor site are physically close to each other. From this perspective, the reducing agent of this embodiment is preferably a compound represented by the following formula (1):

[0034]

[0035] where M is a metal atom, and R１ , R ２ , R ３ , R ４ , and R ５ (Hereinafter referred to as “R １ ~R ５ ") are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and R ６ , R ７ , R ８ , and R ９ (Hereinafter referred to as “R ６ ~R ９ ") are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and R １０ is a heterocycle which may have a substituent, and R １１ is a linking group or a single bond.

[0036] The metal atom is preferably Cr, Mo, W, Fe, Ru, Co, Rh, Ir, or Sm, and more preferably Co. １１ Specific examples, preferred embodiments, and other details of the linking group in R are the same as those described above in the section on linking groups. １１ may be a saturated or unsaturated divalent cyclic hydrocarbon group having 3 to 21 carbon atoms which may have a substituent, or a saturated or unsaturated divalent chain hydrocarbon group having 1 to 10 carbon atoms which may have a substituent.

[0037] R １ ~R ５ are each independently preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, still more preferably a methyl group or an ethyl group, and particularly preferably a methyl group.

[0038] R ６ ~R ９ are each independently preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, still more preferably a methyl group or an ethyl group, and particularly preferably a methyl group.

[0039] R １０is preferably a heterocycle which may have a nitrogen atom and which may have a substituent, more preferably a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a heterocycle which may have a nitrogen atom and which may have a substituent, and even more preferably a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a piperidine ring which may have a substituent, a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a pyridine ring which may have a substituent, a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a piperazine ring which may have a substituent, a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a diazine ring which may have a substituent, a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from an optionally substituted morpholine ring, a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from an optionally substituted oxazine ring, a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from an optionally substituted thiomorpholine ring, a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from an optionally substituted thiazine ring, a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from an optionally substituted hexahydro-1,3,5-triazine ring, or a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from an optionally substituted triazine ring. １０ is particularly preferably a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a piperidine ring which may have a substituent, a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a pyridine ring which may have a substituent, a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a piperazine ring which may have a substituent, or a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a diazine ring which may have a substituent. １０is even more preferably a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a pyridine ring which may have a substituent, or a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a diazine ring which may have a substituent, and even more preferably a monovalent group obtained by removing one hydrogen atom bonded to a carbon atom forming the ring from a pyridine ring which may have a substituent.

[0040] Examples of the substituent include an alkyl group, an alkynyl group, an alkenyl group, a halogen atom, an imino group, an amino group, a thiol group, a hydroxy group, an acyl group, a nitrile group, a formyl group, an amide group, and an acryl halide group (—CH ２ CH ２ Examples of the substituent include —C(═O)—X (where X is a halogen atom), ester group, carboxy group, alkoxy group, thioalkoxy group, nitro group, and nitroso group. Among these, a methyl group is preferred as the substituent. The pyridine ring which may have a substituent is not particularly limited, but examples thereof include an unsubstituted pyridine ring, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, and 2,6-dimethylpyridine.

[0041] Specific examples of the reducing agent for synthesizing nitrogen-containing compounds according to this embodiment include compounds represented by the following formulae (1-1) to (1-7), in which M represents a metal atom.

[0042] In the above formula (1-3), R １２ , R １３ , R １４ , R １５ and R １６ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. １７ is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

[0043] In addition, when the reducing agent for synthesizing a nitrogen-containing compound of this embodiment is positively charged, the counter anion is not particularly limited, but for example, trifluoromethanesulfonate (OTf － ), Br － , Cl － , I－ , P.F. ６ － , B.F. ４ － , N (CN) ２ － , NO ３ － , bis(trifluoromethylsulfonyl)amide, and the like.

[0044] 2. Method for Producing Reducing Agent for Nitrogen-Containing Compound Synthesis The reducing agent for nitrogen-containing compound synthesis of this embodiment can be produced, for example, by the following synthesis method.

[0045]

[0046] Synthesis method 1: Under an Ar atmosphere, a THF solution (18 mL) of 4-(4-bromophenyl)-2,6-lutidine (297.2 mg, 1.13 mmol, 1 eq.) was cooled to −78° C. ｎ To the mixture was added ca. 800 μL (1.24 mmol, 1.1 eq.) of a 1.56 M hexane solution of BuLi, and the mixture was stirred for 3 hours. In addition, 4-(4-bromophenyl)-2,6-lutidine can be synthesized according to the method described in Reference 1 (R. Feng, L. Zhang, H. Ruan, Y. Zhao, G. Tan, X. Wang, Angew. Chem. Int. Ed. volume 58, pages 6084-6088 (2019), A Main-Group Element Radical Based One-Dimensional Magnetic Chain, https: / / doi.org / 10.1002 / ane.201901177). The resulting green-yellow solution of the lithiated product was cooled to −78° C. [CoCp*(CpMe ４ ) ](PF ６) (517.9 mg, 1.13 mmol, 1 eq.) in THF solution (12 mL) was added dropwise over about 5 minutes. After stirring for 3 hours, the mixture was stirred overnight while slowly returning to room temperature. The solvent was distilled off from the resulting dark green solution, and the filtrate was extracted with pentane and Celite until the filtrate became colorless. The extract was dried under reduced pressure to obtain a dark green oil. The entire amount of the dark green oil was dissolved in 2 mL of THF, and the solution was added dropwise to a suspension of 281.1 mg (0.84 mmol) of triflate ferrocene (ferrocenium triflate) in 18 mL of THF. After stirring for 30 minutes at room temperature, the resulting suspension was evaporated to dryness under reduced pressure, and the ferrocene was removed by washing with hexane until the color disappeared. ２ The resulting yellow solid was passed through a short column of basic alumina (developing solvent: MeCN / Et ２ 0, v / v=2 / 1) was performed twice, and the yellow oil obtained under reduced pressure was ２ After adding 5 mL of HCl and allowing the mixture to stand at room temperature overnight, yellow needles containing the target reducing agent for synthesizing nitrogen-containing compounds were obtained as the main product. Synthesis Method 2: Under an Ar atmosphere, 24 mL of a THF solution of 4-(4-bromophenyl)-2,6-lutidine (412.6 mg, 1.57 mmol, 1.1 equivalents) was cooled to -78°C, and a hexane solution of n-BuLi (1.72 mmol) (1.56 M, 1.1 mL, 1.1 equivalents) was added and the mixture was stirred for 3 hours. 4-(4-bromophenyl)-2,6-lutidine was synthesized according to the method described in Reference 1 (R. Feng, L. Zhang, H. Ruan, Y. Zhao, G. Tan, X. Wang, Angew. Chem. Int. Ed. volume 58, pages 6084-6088 (2019), A Main-Group Element Radical Based One-Dimensional Magnetic Chain, https: / / doi.org / 10.1002 / ane.201901177). The resulting green-yellow solution of the lithiated product was cooled to −78° C. [CoCp*(CpMe ４ ) ](PF ６) (687.3 mg, 1.50 mmol, 1 equivalent) was added dropwise to a 16 mL THF suspension over about 5 minutes. After stirring for 3 hours, the mixture was slowly returned to room temperature and stirred overnight. The resulting dark green solution was distilled off the solvent, and then extracted with pentane and Celite until the filtrate became colorless. The extract was dried under reduced pressure to obtain a dark green oil. The entire amount of the dark green oil was dissolved in 14 mL of THF, and 460.4 mg (1.38 mmol) of triflate ferrocene (ferrocenium triflate) was added thereto. After stirring for 30 minutes at room temperature, the resulting suspension was evaporated to dryness under reduced pressure and washed with hexane until the ferrocene was removed, followed by further rinsing with Et ２ The resulting yellow solid was washed with 10 mL of basic alumina. ２ 0, v / v = 2 / 1) twice and then reduced pressure to give a yellow oil. ２ The target yellow needles were obtained by liquid-liquid recrystallization (-30°C) of O. The yield was 99.7 mg (0.154 mmol), and the yield was 10%. １ The results of H-NMR were as follows: (CD3CN, 400 MHz) δ 7.86 (2H, d, J = 8.0 Hz), 7.51 (2H, d, J = 8.4 Hz), 7.35 (2H, s), 2.55 (6H, s), 1.84 (6H, s), 1.80 (6H, s), 1.69 (15H, s). １９ F-NMR (CD3CN, 376 MHz) δ -79.3. Elemental analysis gave the following results: Calcd(C33CoH39F3NO3S.1.5H2O): C, 58.92; H, 6.29; N, 2.08. Found: C, 59.04; H, 6.22; N, 2.24.

[0047] 3. Method for synthesizing nitrogen-containing compounds In the method for synthesizing nitrogen-containing compounds of this embodiment (hereinafter also simply referred to as the "synthesis method"), a nitrogen-containing compound is synthesized from nitrogen molecules in the presence of the reducing agent for synthesizing nitrogen-containing compounds of this embodiment, a catalyst, and a proton source. The synthesis method of this embodiment tends to improve the production amount of nitrogen-containing compounds. Specifically, the Faraday efficiency (FE) (%), which is obtained by dividing the amount of ammonia produced by a value corresponding to the amount of electricity input, tends to improve. FE is calculated using the following formula: FE (%) = Amount of ammonia produced (mol) ÷ (Amount of electricity input (C) ÷ Faraday constant (C / mol) ÷ 3) × 100

[0048] The amount of the reducing agent used in the method for synthesizing a nitrogen-containing compound of this embodiment is not particularly limited, but is, for example, 0.5 mM to 3.0 mM, or 1.0 mM to 2.5 mM, 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.

[0049] Hereinafter, each component used in the method for synthesizing a nitrogen-containing compound according to the present embodiment will be described in detail.

[0050] 3.1 Nitrogen-Containing Compound Examples of the nitrogen-containing compound produced by the synthesis method of this embodiment include ammonia and hydrazine, with ammonia being preferred.

[0051] 3.2. Nitrogen Molecules In the synthesis method of this embodiment, the nitrogen molecular source is not particularly limited, but is, for example, nitrogen gas. Nitrogen gas may be supplied at high pressure or at normal pressure. Because nitrogen gas is inexpensive, it may be used in large excess relative to other compounds.

[0052] 3.3. Catalyst The catalyst used 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. One type of catalyst may be used alone, or two or more types may be used in combination.

[0053] Examples of the central metal of the metal complex include Ti, V, Mo, Fe, Mn (manganese), Co, Pt, Ir, and W, and preferably Mo. A metal complex having Mo as the central metal is also called a molybdenum complex.

[0054] 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.

[0055] The metal complex is not particularly limited, and examples thereof include metal complexes each combining the central metal and the ligand. 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.

[0056] 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):

[0057]

[0058] In the above 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. ２２ represents 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 ２２The "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).

[0059]

[0060] 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. In the structures represented by formulas (i) to (iii), Mo may be positively or negatively charged, or may not be charged.

[0061] The amount of catalyst used in the synthesis method of this embodiment is not particularly limited, but is, for example, 0.5 mM to 3.0 mM, or 1.0 mM to 2.5 mM, 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.

[0062] 3.4. Proton Source The proton source is not particularly limited, but examples thereof include water; alcohols such as methanol, ethanol, propanol, butanol, trifluoroethanol, phenol, and ethylene glycol; organic acids such as protonated lutidines such as 2,6-dimethylpyridinium triflate, protonated picolines such as 2-methylpyridinium triflate, protonated collidines such as 2,4,6-trimethylpyridinium triflate, and carboxylic acids such as acetic acid; and inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid. One proton source may be used alone, or two or more may be used in combination. Among the above proton sources, organic acids are preferred, and protonated collidines are more preferred. Specifically, for example, it is preferable to use a compound represented by the following formula (2):

[0063]

[0064] In the synthesis method of this embodiment, when a nitrogen-containing compound is synthesized by an electrochemical reduction reaction described below, protons are generated by the reaction at the anode, and these protons may participate in the reaction of nitrogen molecules.

[0065] In the synthesis method of this embodiment, when an acid is used as a proton source, the pKa of the acid in a THF solution at 25° C. and 1 atmosphere is preferably 5.0 to 15.0, and more preferably 8.0 to 12.0. In the synthesis method of this embodiment, by using the reducing agent of this embodiment, the synthesis reaction of the nitrogen-containing compound can proceed under milder conditions, and therefore, even when a weak acid having a pKa in the above range is used, the synthesis reaction of the nitrogen-containing compound tends to proceed.

[0066] The amount of the proton source used in the synthesis method of this embodiment is not particularly limited, but is, for example, 5 mM to 30 mM, or 10 mM to 25 mM, 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.

[0067] In the synthesis method of this embodiment, the molar equivalent of the reducing agent for synthesizing nitrogen-containing compounds relative to the catalyst introduced into the system is preferably 1 to 600, 1 to 500, 1 to 400, 1 to 300, 1 to 200, 1 to 100, 1 to 50, 1 to 25, 1 to 10, or 1 to 5. The upper limit of the molar equivalent of the reducing agent relative to the catalyst introduced into the system tends to be determined from the perspective of solubility in the solvent, and even if the molar equivalent is near the upper limit, the production amount of nitrogen-containing compounds per amount of energy introduced tends to be sufficiently high. From the viewpoint of more effectively and reliably achieving the effects of this embodiment, the lower limit is preferably 1.

[0068] In the synthesis method of this embodiment, the molar equivalent of the organic acid relative to the reducing agent for synthesizing nitrogen-containing compounds introduced into the system is preferably 10 to 300, 15 to 200, 20 to 100, 25 to 80, or 30 to 60. The upper limit of the molar equivalent of the organic acid relative to the reducing agent introduced into the system tends to be determined from the perspective of solubility in the solvent, and even if the molar equivalent is near the upper limit, the production amount of nitrogen-containing compounds per amount of energy introduced tends to be sufficiently high. From the viewpoint of more effectively and reliably achieving the effects of this embodiment, the lower limit of the range is preferably as described above.

[0069] 3.5. Solvent A solvent may be used in the synthesis method of this embodiment. The solvent is not particularly limited as long as it can dissolve or disperse the reducing agent, catalyst, and proton source for synthesizing a nitrogen-containing compound of this embodiment. Examples of the solvent include cyclic ether compounds, chain ether compounds, nitrile compounds, aromatic hydrocarbon compounds, and saturated hydrocarbon compounds. Examples of the cyclic ether compounds include, but are not limited to, tetrahydrofuran, 4-methyltetrahydropyran, tetrahydropyran-4-methanol, and 1,4-dioxane. Examples of the chain ether compounds include, but are not limited to, diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, and cyclopentyl methyl ether. Examples of the nitrile compounds include, but are not limited to, acetonitrile and propionitrile. Examples of the aromatic hydrocarbon compounds include, but are not limited to, toluene and o-xylene. Examples of the saturated hydrocarbon compounds include, but are not limited to, hexane, heptane, and petroleum ether. The solvents may be used alone or in combination.

[0070] 3.6. Electrolyte In order to promote the synthesis reaction of the nitrogen-containing compound, an electrolyte may be added to the solvent. 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(SO ２ CF ３ ) ２ ), 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 (Li ２ SO ４ ), sodium sulfate (Na ２ SO ４), potassium sulfate (K ２ SO ４ ), lithium hydrogen sulfate (LiHSO ４ ), sodium hydrogen sulfate (NaHSO ４ ), potassium hydrogen sulfate (KHSO ４ ), lithium phosphate (Li ３ P.O. ４ ), sodium phosphate (Na ３ P.O. ４ ), potassium phosphate (K ３ P.O. ４ ), lithium hydrogen phosphate (Li ２ HPO ４ ), sodium hydrogen phosphate (Na ２ HPO ４ ), potassium hydrogen phosphate (K ２ HPO ４ ), lithium dihydrogen phosphate (LiH ２ P.O. ４ ), sodium dihydrogen phosphate (NaH ２ P.O. ４ ), potassium dihydrogen phosphate (KH ２ P.O. ４ ), ammonium triflate (NH ４ OTf), tetraethylammonium perchlorate, tetraethylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate, tetrabutylammonium perchlorate, tetrabutylammonium tetrafluoroborate, and tetrabutylammonium hexafluorophosphate. The electrolyte may be used alone or in combination of two or more.

[0071] The concentration of the electrolyte is not particularly limited, but is, for example, 0.01 M (mol / L) or more and 5.00 M or less, and 0.20 M or more and 2.00 M or less.

[0072] 3.7. Reaction Pathway In the synthesis method of this embodiment, a nitrogen-containing compound may be synthesized by an electrochemical reduction reaction. When a nitrogen-containing compound is synthesized by an electrochemical reduction reaction, the reaction is presumed to proceed according to the following mechanism. Here, an example will be described in which ammonia is synthesized as the nitrogen-containing compound.

[0073] 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.

[0074] When the compound introduced into the anode chamber is ethylene glycol or water, it is presumed that ammonia, a nitrogen-containing compound, is continuously produced by the mechanism shown in reaction formulas <1> to <3>.

[0075] Formula <1>: Med+H ＋ +e － →H-Med Formula <2>: Cat+1 / 2N ２ →(Cat≡N) compound Formula <3>: (Cat≡N) compound+3[H-Med]→Cat+NH ３ +3Med

[0076] Here, "Med" is the reducing agent for synthesizing nitrogen-containing compounds of this embodiment, "H-Med" is the reducing agent for synthesizing nitrogen-containing compounds of this embodiment in a state in which it has accepted a proton and an electron, "Cat" is a catalyst, and "(Cat≡N) compound" is a compound in which a nitrogen atom is triple-bonded to the catalyst.

[0077] The protons in formula <1> may be protons provided from the anode compartment through the separator to the cathode compartment, or may be protons from a proton source introduced into the cathode compartment.

[0078] In the reaction of formula <3>, protons and electrons are provided to the (Cat≡N) compound from the reducing agent for synthesizing a nitrogen-containing compound of this embodiment. That is, a reaction of supplying electrons to the catalyst and a reaction of supplying protons to the catalyst that has received the electrons occur in concert.

[0079] 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., more preferably −40° C. to 60° C.

[0080] 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 -2.0 to -1.0 V (vs. Ag / Ag ＋ ) may be used. ＋ ) is Ag / Ag ＋ represents the potential when used as a reference electrode.

[0081] 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.

[0082] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to the following examples. Unless otherwise specified, the operations of each example and comparative example were carried out at room temperature (25°C), 10 ５ I went with Pa.

[0083] 1. Synthesis of reducing agent for synthesizing nitrogen-containing compounds [Synthesis Example 1] A reducing agent for synthesizing nitrogen-containing compounds, which is a compound represented by the following formula (4-1), was synthesized by the following method. This reducing agent for synthesizing nitrogen-containing compounds is referred to as "Med1".

[0084]

[0085]

[0086] The first-stage reaction represented by the above reaction formula was carried out. Specifically, under an argon atmosphere, 21 mL of a THF (tetrahydrofuran) solution of 4-(4-bromophenyl)-2,6-lutidine (338.3 mg, 1.29 mmol, 1 equivalent) was cooled to -78°C, and a hexane solution (1.57 M, 850 μL, 1 equivalent) of n-BuLi (1.33 mmol) was added thereto and stirred for 3 hours. 4-(4-bromophenyl)-2,6-lutidine was synthesized according to the method described in Reference 1 (R. Feng, L. Zhang, H. Ruan, Y. Zhao, G. Tan, X. Wang, Angew. Chem. Int. Ed. 2019, 58, 6084.).

[0087] The resulting yellow-green solution of the lithiated product was cooled to −78° C. [CoCpCp ＊ ](PF ６ The mixture was added dropwise to 14 mL of a THF solution of 519.7 mg (1.29 mmol, 1 equivalent) of cyclopentadienyl (Cp) over a period of about 5 minutes. ＊ means 1,2,3,4,5-pentamethylcyclopentadienyl.

[0088] After the dropwise addition was completed, the mixture was stirred at -78°C for 3 hours. After the stirring was completed, the mixture was slowly returned to room temperature and further stirred overnight. The resulting dark red solution was evaporated to dryness under reduced pressure, and extracted with pentane and Celite until the filtrate became colorless. The resulting extract was evaporated to dryness under reduced pressure to obtain a dark red viscous solid. This was dissolved in a minimum amount of pentane and cooled to -78°C to obtain the target red precipitate. The yield was 252.3 mg (0.571 mmol), a yield of 44%. １ The H-NMR results were as follows (C6D6, 400 MHz): δ 7.38 (2H, d, J = 8.4 Hz), 7.05 (2H, d, J = 8.0 Hz), 6.96 (2H, s), 4.57 (2H, s), 3.80 (1H, s), 2.49 (8H, m), 2.23 (2H, s), 1.79 (15H, s).

[0089] １ ​From the results of H-NMR, the target substance was [CoCp ＊ (η ４ -C ５ H ５ -C ６ H ４ -C ７ H ８ N)] was identified.

[0090]

[0091] Next, the second stage reaction represented by the above reaction formula was carried out. ＊ (η ４ -C ５ H ５ -C ６ H ４ -C ７ H ８ A red solution was obtained by dissolving 252.3 mg (571 μmol) of ferrocene triflate in 12 mL of THF, and the resulting solution was added dropwise to a blue suspension obtained by adding 214.9 mg (641 μmol) of ferrocene triflate to 36 mL of THF, whereby the suspension turned brown-black.

[0092] After stirring the brown-black suspension for 15 minutes, 207.7 mg (470 μmol, 2 equivalents in total) of triflate ferrocene was added and stirred for an additional 30 minutes. This gave a yellow-green suspension. The solvent was distilled off from this suspension, and the filtrate was washed with pentane until it no longer had any color, thereby removing the ferrocene produced after the reaction and the raw materials.

[0093] The resulting reddish-yellowish green solid was dried under reduced pressure and then purified by elution with a short column of basic alumina gel (developing solvent: acetonitrile (MeCN) / diethyl ether (Et ２ The brown component was removed using a solvent mixture of MeCN / Et (v / v = 2 / 1), and the obtained fraction was evaporated to dryness under reduced pressure. ２ The red impurity was removed by liquid-liquid recrystallization (-30°C) of O to obtain the target yellow-orange needle crystals. The yield was 165.7 mg (281 µmol), and the yield was 49%. １The results of H-NMR were as follows: (CD3CN, 400 MHz) δ 7.88 (2H, d, J = 9.2 Hz), 7.77 (2H, d, J = 8.4 Hz), 7.38 (2H, s), 5.72 (2H, s), 5.38 (2H, s), 2.55 (6H, s), 1.77 (15H, s). １９ The results of F-NMR were as follows: (CD3CN, 376 MHz) δ -79.3. The results of elemental analysis were as follows: Calcd(C29CoH31F3NO3S.0.5H2O): C, 58.19; H, 5.39; N, 2.38. Found: C, 58.38; H, 5.24; N, 2.45. The results of ESI MS were as follows: (cation): m / z = 440.4 ([CoCp * Cp C6H4Lut ] + , Sim: 440.5 )). (anion) : m / z = 149.0 (OTf-).

[0094] From the results of 1H-NMR, 19F-NMR and ESI MS, the target yellow-orange needle crystals were identified as the compound represented by the above formula (4-1).

[0095] Synthesis Example 2 A reducing agent for synthesizing nitrogen-containing compounds, which is a compound represented by the following formula (4-2), was synthesized by the following method: This reducing agent for synthesizing nitrogen-containing compounds is referred to as "Med2".

[0096]

[0097] Under argon atmosphere, CrCp ＊ ２ (807 mg, 2.5 mmol; Cp ＊ = η ５ -C ５ Me ５ ) and [FeCp ２ ]OTf (821 mg, 2.5 mmol; Cp = η ５ -C ５ H ５ , OTf = OSO ２ CF３ To the mixture of (25 mL) and (30 mL) was added THF to form a solution, which was then stirred at room temperature for 18 hours. After the reaction, the solid was filtered off using a Kiriyama funnel, and the resulting solid was dissolved in THF (2 mL x 2) and Et ２ The precipitate was washed with 2 mL of HCl (2 mL x 3) and dried under vacuum to obtain [CrCp ＊ ２ ]OTf was obtained as an orange solid (1106 mg, 2.4 mmol, 96%). １ H NMR ((CD ３ ) ２ CO): δ 5.8 (br-s).

[0098] Synthesis Example 3 A reducing agent for synthesizing nitrogen-containing compounds, which is a compound represented by the following formula (4-3), was synthesized by the following method: This reducing agent for synthesizing nitrogen-containing compounds is referred to as "Med3".

[0099]

[0100]

[0101] The first-stage reaction represented by the above reaction formula was allowed to proceed. Specifically, under an argon atmosphere, 18.5 mL of a THF solution of 4-(4-bromophenyl)-2,6-lutidine (315.1 mg, 1.2 mmol, 1 equivalent) was cooled to -78°C, and a hexane solution of n-BuLi (1.3 mmol) (1.56 M, 840 μL, 1.1 equivalent) was added and stirred for 3 hours. 4-(4-bromophenyl)-2,6-lutidine was synthesized according to the method described in the above-mentioned literature 1.

[0102] The resulting yellow-green solution of the lithiated product was cooled to −78° C. [CoCp ２ ](PF ６ The resulting suspension was added dropwise to a 7.5 mL THF solution of 402.4 mg (1.2 mmol), 1 equivalent (1 equiv.) over about 5 minutes, whereupon the yellow suspension quickly turned red.

[0103] The mixture was further stirred at -78°C for 3 hours, and the resulting red solution was returned to room temperature and then evaporated to dryness under reduced pressure. The filtrate was extracted with pentane and Celite until the filtrate became colorless. The resulting extract was evaporated to dryness under reduced pressure to obtain an orange solid. The yield of the orange solid was 330.4 mg (0.89 mmol), a 74% yield. １ H-NMR results were as follows: (C6D6): δ 7.34 (2H, d, J = 8.4 Hz), 6.96-6.92 (4H, m), 5.10 (2H, t, J = 2.0 Hz), 4.64 (4H, s), 3.94 (1H, t, J = 2.6 Hz), 2.86 (2H, q, J = 2.0 Hz), 2.53-2.47 (6H, m).

[0104] １ From the results of H-NMR, the orange solid was found to be [CoCp(η ４ -C ５ H ５ -C ６ H ４ -C ７ H ８ N)] was identified.

[0105]

[0106] Next, the second-stage reaction represented by the above reaction formula was carried out. Under a nitrogen atmosphere, [CoCp(η ４ -C ５ H ５ -C ６ H ４ -C ７ H ８ N)] (213.6 mg, 575 μmol) was dissolved in 72 mL of a methylcyclohexane / benzene mixed solution (v / v=5 / 1), and the resulting red solution was heated under reflux for 72 hours.

[0107] The resulting dark blue solution was allowed to cool to room temperature, the solvent was distilled off, and the resulting black solid was extracted five times with 15 mL of pentane to remove brownish-black insoluble matter. 242.3 mg of a black solid was then obtained by evaporation under reduced pressure.

[0108] ​242.3 mg of the obtained black solid was dissolved in 18.5 mL of THF, and the obtained dark blue solution was added dropwise to 9 mL of a THF suspension of 166.4 mg (500 μmol) of triflate ferrocene while stirring, to obtain a reddish orange solution.

[0109] After stirring at room temperature for 30 minutes, the solvent was distilled off. After that, the filtrate was washed with pentane until it was no longer colored, and the remaining [CoCp(η ４ -C ５ H ５ -C ６ H ４ -C ７ H ８ N)], ferrocene, and [CoCp(η ４ -C ５ H ５ -C ６ H ４ -C ７ H ８ The by-products formed in the reaction of the ferrocenium ion with the methyl group were then removed by THF / Et ２ Liquid-liquid recrystallization (-30°C) was carried out at 0 to obtain a reddish-orange powder.

[0110] The reddish-orange powder was passed through a short column of basic alumina (developing solvent: MeCN / Et ２ 0, v / v=2 / 1) and evaporated to dryness under reduced pressure to give a yellow powder.

[0111] Then, recrystallization (MeCN / Et ２ The target product was obtained as a yellow-orange block crystal in an amount of 35.7 mg (68.7 μmol), with a yield of 11%. １ H-NMR results were as follows: (CDCN) δ 7.85 (2H, d), 7.79 (2H, d), 7.33 (2H, s), 6.21 (2H, t), 5.77 (2H, t), 5.49 (4H, s), 2.51 (6H, s). １９F-NMR gave the following results: (CD3CN): δ -79.3. Elemental analysis gave the following results: Calcd(C24CoH21F3NO3S): C, 55.50; H, 4.08; N, 2.70. Found: C, 55.71; H, 4.34; N, 2.61. ESI MS gave the following results: (cation): m / z = 370.1 ([CoCpCp C6H4Lut ] + , Sim: 370.3 (anion) : m / z =149.0 (OTf)

[0112] １ H-NMR, １９ From the results of F-NMR, elemental analysis, and ESI MS, the target substance was identified as the compound represented by the above formula (4-3).

[0113] 2. Catalyst Synthesis [Synthesis Example 4] A catalyst, which is a compound represented by the following formula (5-1), was synthesized according to the method described in Nature Synthesis volume 2, pages 635-644 (2023), "Catalytic production of ammonia from dinitrogen employing molybdenum complexes bearing N-heterocyclic carbene-based PCP-type pincer ligands," https: / / doi.org / 10.1038 / s44160-023-00292-9. This catalyst is referred to as Cat1.

[0114]

[0115] Synthesis Example 5 A catalyst, which is a compound represented by the following formula (5-2), was synthesized by the following method: This catalyst is referred to as "Cat2".

[0116]

[0117]

[0118] The reaction represented by the above reaction formula was allowed to proceed. ３ (CF​３ -PCP)] was synthesized according to the method described in Nature Synthesis volume 2, pages 635-644 (2023), Catalytic production of ammonia from dinitrogen employing molybdenum complexes bearing N-heterocyclic carbene-based PCP-type pincer ligands, https: / / doi.org / 10.1038 / s44160-023-00292-9. Next, [MoI ３ (CF ３ -PCP)] 197 mg (0.20 mmol) of CoCp in 10 mL of THF ＊ ２ 145 mg (0.44 mmol) of hexane was added to obtain a mixture. The resulting mixture was then stirred at room temperature for 18 hours. After removing the volatile components in vacuo, the resulting yellow-brown solid was washed three times with 5 mL of hexane to obtain a residue. The residue was then extracted with 15 mL of THF to obtain an extract. Next, 45 mL of hexane was slowly added to the extract to obtain yellow-brown crystals. The crystals were collected by filtration, washed three times with 3 mL of hexane, and dried in vacuo to obtain the compound represented by formula (5-2). The yield was 88.8 mg (0.12 mmol), a 60% yield. １ H-NMR results were as follows: (THF-d8): δ 8.14 (s, 1H), 7.94 (d, J = 8.0 Hz, 1H), 7.72 (dd, J = 1.2, 8.0 Hz, 1H), 4.93-4.67 (m, 4H), 1.62 (d, J = 12.4 Hz, 9H), 1.60 (d, J = 12.8 Hz, 9H), 1.20 (d, J = 12.0 Hz, 9H), 1.14 (d, J = 12.4 Hz, 9H). １９ The results of F-NMR were as follows: (THF-d8): δ −63.0 (s). ３１P{H}-NMR results were as follows: (THF-d): δ 114.0 (d, J = 99.7 Hz), 112.0 (d, J = 99.7 Hz). Anal Calcd for C26H43F3IMoN3P2: C, 42.23; H, 5.86; N, 5.68. Found: C, 42.16; H, 5.81; N, 5.66.

[0119] Synthesis Example 6 A catalyst, which is a compound represented by the following formula (5-3), was synthesized by the following method: This catalyst is referred to as "Cat3".

[0120]

[0121]

[0122] The reaction represented by the above reaction formula was allowed to proceed. The Mo complex, which is the reactant, was synthesized according to the method described in Nature Communications, 8, 14874 (2017), "Remarkable catalytic activity of dinitrogen-bridged dimolybdenum complexes bearing NHC-based PCP-pincer ligands toward nitrogen fixation." THF is manufactured by Kanto Chemical Co., Ltd., and pyridine is manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. １ The H-NMR results were as follows: (THF-d8): δ 8.06-8.03 (m, ArH, 2H), 7.51-7.48 (m, ArH, 2H), 5.33 (dt, J=13.6, 3.6 Hz, CH2P, 2H), 4.65 (d, J=13.6 Hz, CH2P, 2H), 1.64 (pseudo t, 7.0 Hz, P t Bu2, 18H), 1.42 (pseudot, 6.2 Hz, P t Bu2, 18H) ３１ P{ １H}NMR gave the following results: (THF-d8): δ 75.8(s) ESI-MS gave the following results: (THF): 675.3 (m / z)

[0123] 3. Synthesis of Ammonia [Example 1] An electrolysis reaction cell was used in which the anode chamber and the cathode chamber were separated by a separator that preferentially allowed ions to 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.

[0124] The compounds placed in the anode and cathode compartments were as follows: Anode compartment: ethylene glycol LiOTf (1.0 M) as an electrolyte Cathode compartment: Med1 (0.010 mmol, 1.7 mM): a reducing agent for synthesizing nitrogen-containing compounds synthesized in Synthesis Example 1 Catalyst: Cat1 (0.010 mmol, 1.7 mM): a proton source compound represented by the following formula (2) (organic acid (pKa in THF: 10.4), 0.10 mmol, 17 mM) Tetrahydrofuran as a solvent LiOTf (1.0 M) as an electrolyte

[0125]

[0126] Room temperature (25°C), normal pressure (1 atmosphere), cathode applied potential -1.5V (vs Ag / Ag ＋ ) for 4 hours to obtain ammonia.

[0127] [Examples 2 to 7 and Comparative Examples 1 to 3] In Examples 2 to 7 and Comparative Examples 1 to 3, ammonia was synthesized in the same manner as in Example 1, except that the type and amount of catalyst, the type and amount of reducing agent for synthesizing a nitrogen-containing compound, the amount of proton source, and the applied potential at the cathode were changed as shown in Table 1.

[0128]

[0129] 4. Evaluation 4.1. Faraday Efficiency In each Example and Comparative Example, the Faraday efficiency was calculated by the following method. A potentiostat (HZ-Pro, manufactured by Hokuto Denko Corporation) was used to record the amount of coulombs during the reaction in each Example and Comparative Example. The Faraday efficiency FE (%) was calculated from the amount of coulombs and the number of moles of ammonia obtained using the following formula: FE (%) = Amount of ammonia produced (mol) ÷ (Amount of electricity input (C) ÷ Faraday constant (C / mol) ÷ 3) × 100 When FE is 30% or more, the amount of nitrogen-containing compound produced per amount of energy input is excellent. FE is preferably 40% or more, and more preferably 50% or more.

[0130] It can be said that the higher the Faraday efficiency, the higher the production amount of nitrogen-containing compounds per amount of energy input. Here, when comparing each Example with each Comparative Example, it is found that each Example has a higher Faraday efficiency. In other words, it is found that each Example has a higher production amount of nitrogen-containing compounds per amount of energy input.

[0131] The disclosure of Japanese Patent Application No. 2024-031592, 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 a nitrogen-containing compound, comprising: an electron donor moiety; and a proton acceptor moiety bound to the electron donor moiety.

2. The reducing agent for synthesizing nitrogen-containing compounds according to claim 1, wherein the proton-accepting site is a heterocycle.

3. The reducing agent for synthesizing nitrogen-containing compounds according to claim 2, wherein the heterocycle contains a nitrogen atom.

4. The reducing agent for synthesizing nitrogen-containing compounds according to claim 2 or 3, wherein the heterocycle is a pyridine ring.

5. The reducing agent for synthesizing nitrogen-containing compounds according to any one of claims 1 to 4, wherein the electron donating moiety is a moiety consisting of a metal atom and two saturated or unsaturated cyclic hydrocarbons coordinated to the metal atom.

6. The reducing agent for synthesizing nitrogen-containing compounds according to any one of claims 1 to 5, wherein the electron donating moiety is a metallocene structure which may have a substituent.

7. The reducing agent for synthesizing nitrogen-containing compounds according to claim 6, wherein the metallocene structure is a cobaltocene structure which may have a substituent or a ferrocene structure which may have a substituent.

8. The reducing agent for synthesizing nitrogen-containing compounds according to claim 6 or 7, wherein in at least one of the two cyclopentadienyls in the metallocene structure, which may have a substituent, one or more of the carbon atoms forming the ring are directly bonded to a substituent other than the proton-accepting site.

9. The reducing agent for synthesizing nitrogen-containing compounds according to any one of claims 6 to 8, wherein one or more of the carbon atoms forming the ring in at least one of the two cyclopentadienyls in the metallocene structure is bonded to the proton-accepting site.

10. The reducing agent for synthesizing nitrogen-containing compounds according to any one of claims 1 to 9, wherein the reducing agent for synthesizing nitrogen-containing compounds is a compound represented by the following formula (1): (In formula (1), M is a metal atom, and R １ , R ２ , R ３ , R ４ , and R ５ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and R ６ , R ７ , R ８ , and R ９ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and R １０ is a heterocycle which may have a substituent, and R １１ is a saturated or unsaturated divalent cyclic hydrocarbon group having 3 to 21 carbon atoms which may have a substituent, a saturated or unsaturated divalent chain hydrocarbon group having 1 to 10 carbon atoms which may have a substituent, or a single bond.

11. The reducing agent for synthesizing nitrogen-containing compounds according to any one of claims 1 to 10, for synthesizing nitrogen-containing compounds by electrolytic reaction.

12. A method for synthesizing a nitrogen-containing compound, comprising synthesizing the nitrogen-containing compound from nitrogen molecules in the presence of the reducing agent for synthesizing a nitrogen-containing compound according to any one of claims 1 to 11, a catalyst, and a proton source.

13. The method for synthesizing a nitrogen-containing compound according to claim 12, wherein the catalyst comprises a molybdenum complex.

14. The synthesis method according to claim 12 or 13, wherein the molar equivalent of the reducing agent for synthesizing nitrogen-containing compounds relative to the catalyst is 1 or more and 600 or less.

15. The method of any one of claims 12 to 14, wherein the proton source comprises an organic acid.

16. The synthesis method according to claim 15, wherein the organic acid comprises a compound represented by the following formula (2):

17. The synthesis method according to claim 15 or 16, wherein the molar equivalent of the organic acid relative to the reducing agent for synthesizing nitrogen-containing compounds is 10 or more and 300 or less.

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