JP2010208927A - Method for producing at least one of deuterium (d2) and hydrogen deuteride (hd) and formic acid decomposition catalyst to be used therein - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing hydrogen isotope gas safely, simply and easily, extremely efficiently and at a low cost. <P>SOLUTION: The method for producing at least one of deuterium (D<SB>2</SB>) and hydrogen deuteride (HD) includes: a preparation step of preparing a formic acid solution which contains formic acid, a solvent and a formic acid decomposition catalyst containing a dinuclear metal complex, its tautomer or stereoisomer or their salts and in which at least one of the formic acid and the solvent is deuterated; and a formic acid decomposition step of decomposing the formic acid by having the prepared solution left standing, heating the prepared solution or irradiating the prepared solution with light to generate at least one of deuterium (D<SB>2</SB>) and hydrogen deuteride (HD). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a method for producing at least one of deuterium (D ₂ ) and deuterated hydrogen (HD), and a formic acid decomposition catalyst used therefor.

Hydrogen (H ₂ ) is used in various applications such as synthesis of various substances, reduction, hydrodesulfurization of petroleum, hydrocracking, and is required in all industrial fields. Since hydrogen (H ₂ ) generates water by oxidation and does not generate harmful substances, it has recently been attracting attention as a clean next-generation fuel supply source in, for example, fuel cells, and the supply of hydrogen (H ₂ ) Storage and utilization technology is very important in industry.

Hydrogen (H) has two types of isotopes, D and T. As hydrogen (H) is regarded as important, interest in these isotopes is increasing. At present, deuterium (D) and tritium (T) are used, for example, as a fuel for a nuclear fusion reactor, an element for labeling a compound, and the like. In particular, deuterium (D) is non-radioactive, safe and stable, and its use is expected. Currently, deuterium (D) is used as a tracer in the form of deuterium labeled compounds, for example, in the form of deuterium labeled compounds in chemical reactions and mechanism / structure analysis of substances such as drug metabolism studies and catalytic activity measurements. Yes. In addition, it is difficult to determine the hydrogen (H) position of a compound containing hydrogen using single crystal X-ray diffraction, but by replacing hydrogen (H) with deuterium (D), a single crystal The spatial arrangement of deuterium (D) can be accurately determined using neutron diffraction. Deuterium (D) has also been confirmed to be useful as a hydrogen substitute in optical communication plastic fibers, a fluorine substitute in heat-resistant lubricating oils for aircraft, and an antibacterial effect on organic materials. Importance is also increasing in the industrial field. Furthermore, due to the increasing importance of hydrogen (H ₂ ) described above, it is certain that the use of deuterium (D) will increase further, for example, in technical development and research related to hydrogen (H ₂ ). Deuterium (D) can be stably stored in the form of deuterium (D ₂ ) and deuterated hydrogen (HD) molecules.

Deuterium (D ₂ ) can be produced, for example, by electrolyzing heavy water (D ₂ O) on a platinum electrode. However, such a conventional method for producing D ₂ is dangerous and costly.

In addition, deuterated hydrogen (HD) is, for example, a mixture of deuterium (D ₂ ) and hydrogen (H ₂ ), and deuterated hydrogen (HD) by an H / D exchange reaction using a metal-supported solid catalyst, to obtain a mixed gas of deuterium (D ₂₎ and hydrogen (H _2), only the hydrogen deuteride (HD) from the mixed gas can be produced by separating by cryogenic distillation separation method. For example, Patent Document 1 discloses a method for efficiently concentrating and recovering deuterated hydrogen (HD) from the mixed gas containing deuterated hydrogen (HD). In this method, an adsorbent having high deuterium hydrogen (HD) selectivity is used to adsorb deuterium hydrogen (HD) contained in the mixed gas, and then the deuterium is dehydrated under a predetermined low pressure condition. This is a method of desorbing and recovering hydrogen hydride (HD). However, in such a conventional HD production method, deuterated hydrogen (HD) must be isolated from the mixed gas in an equilibrium state, and only deuterated hydrogen (HD) can be obtained in a high yield. Because it can not be done, it takes time and money.

On the other hand, the present inventors decompose formic acid in an aqueous solution with a catalyst for formic acid decomposition using a rhodium mononuclear complex to generate one or both of deuterium (D ₂ ) and deuterated hydrogen (HD). And have found a method for producing them (Non-patent Document 1).

JP 2004-160294 A

Fukuzumi, S .; Kobayashi, T .; Suenobu, T. ChemSusChem 2008, 1, 827.

According to the formic acid decomposition method using the rhodium mononuclear complex of Non-Patent Document 1, deuterium (D ₂ ) or deuterium hydride (HD) can be produced safely, simply and efficiently. However, if deuterium (D ₂ ) or deuterated hydrogen (HD) can be produced more efficiently, it is possible to further reduce costs and contribute to further industrial development.

In view of this, the present invention reduces at least one of deuterium hydrogen (HD) and deuterium (D ₂ ) (hereinafter sometimes referred to as “hydrogen isotope gas”) safely, simply and extremely efficiently. It aims at providing the method for manufacturing at cost. Furthermore, the present invention also provides a formic acid decomposition catalyst used in the production method.

  As a result of intensive studies to solve the above problems, the present inventors have found that a binuclear metal complex represented by the following formula (1) is useful, and have reached the present invention.

More specifically, the production method of the present invention includes:
A formic acid decomposition catalyst containing a binuclear metal complex represented by the following formula (1), a tautomer or stereoisomer thereof, or a salt thereof, formic acid, and a solvent, wherein at least one of the formic acid and the solvent Preparing a formic acid solution, one of which is deuterated,
Formic acid decomposition step of decomposing formic acid by standing, heating or irradiating the solution to generate at least one of deuterium (D ₂ ) and deuterated hydrogen (HD),
This is a production method for producing at least one of deuterium (D ₂ ) and deuterium hydride (HD).

In the formula (1),
M ¹ and M ² are transition metals, which may be the same or different,
Ar is a ligand having aromaticity and may or may not have a substituent, and when it has a substituent, the substituent may be one or plural,
R ^{1 to} R ⁵ are each independently a hydrogen atom, an alkyl group, a phenyl group, or a cyclopentadienyl group,
R ^{12 to} R ²⁷ are each independently a hydrogen atom, an alkyl group, a phenyl group, a nitro group, a halogen group, a sulfonic acid group (sulfo group), an amino group, a carboxylic acid group (carboxy group), a hydroxy group, or an alkoxy group. Group,
Alternatively, R ¹⁵ and R ¹⁶ may be combined to form —CH═CH—, that is, R ¹⁵ and R ¹⁶ may be combined with their bound bipyridine ring to form a phenanthroline ring. The H in —CH═CH— is independently an alkyl group, a phenyl group, a nitro group, a halogen group, a sulfonic acid group (sulfo group), an amino group, a carboxylic acid group (carboxy group), or a hydroxy group. Or may be substituted with an alkoxy group,
R ²³ and R ²⁴ together may form -CH = CH-, that is, R ²³ and R ²⁴ together with their bound bipyridine ring may form a phenanthroline ring. H in -CH = CH- is independently an alkyl group, phenyl group, nitro group, halogen group, sulfonic acid group (sulfo group), amino group, carboxylic acid group (carboxy group), hydroxy group, or May be substituted with an alkoxy group,
L is any ligand or absent,
m is a positive integer, 0, or a negative integer.

  The formic acid decomposition catalyst of the present invention comprises at least one compound selected from the group consisting of a binuclear metal complex represented by the formula (1), a tautomer, a stereoisomer, and a salt thereof. And a formic acid decomposition catalyst used in the production method of the present invention.

According to the present invention, at least one of deuterium hydrogen (HD) and deuterium (D ₂ ) can be produced safely, simply and extremely efficiently at a low cost. For this reason, it can contribute further to the development of the industry in the technical field using deuterium (D ₂ ) or deuterated hydrogen (HD). According to the production method of the present invention, for example, at least one of deuterium (D ₂ ) and deuterium hydride (HD) can be produced in a necessary amount when necessary. It is possible to respond sufficiently to mass production of scale. In the present invention, “deuteration” means that at least one of hydrogen (H) in a compound such as formic acid or water is substituted with deuterium (D).

FIG. 1 is a graph showing the correlation between the abundance ratio of H ₂ and HD in Example 1 and pH. FIG. 2 is a scheme showing an example of a reaction mechanism that can be estimated in Example 1. FIG. 3 is another scheme showing an example of a reaction mechanism that can be estimated in Example 1. FIG. 4 is a graph showing the correlation between TOF and pH in Example 1. FIG. 5 is a diagram showing a part of an ESI-MS spectrum diagram of the aqua complex (8). Figure 6 shows the change in UV-Vis. Spectrum when [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ is added to [Ru (bpy) ₂ bpm] ²⁺ aqueous solution (1.2 × 10 ^-3 mol / L). It is a graph which shows. Fig. 7 shows the change in emission spectrum when 1 equivalent of [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ is added to [Ru (bpy) ₂ bpm] ²⁺ aqueous solution (2.0 × 10 ^-4 mol / L). It is a graph to show. FIG. 8 is a diagram showing a change in UV-Vis. Absorption spectrum when dilute sulfuric acid is added to an iridium monovalent complex (10) aqueous solution. FIG. 9A is a graph showing the relationship between absorbance at a wavelength of 512 nm and pH in FIG. FIG. 9B is a graph showing the relationship between log ([Ir-H] / [Ir]) and pH in the measurement of FIG. FIG. 10 is a graph showing a transient absorption spectrum diagram of the hydride complex (9) by nanosecond laser flash photolysis. FIG. 11 is a graph showing the deuterium isotope effect in nanosecond laser flash photolysis of the hydride complex (9). FIG. 12 is a graph showing a transient absorption spectrum diagram of the hydride complex (9) by femtosecond laser flash photolysis. FIG. 13 is a graph showing the deuterium isotope effect in femtosecond laser flash photolysis of the hydride complex (9). FIG. 14A is a graph showing the correlation between the concentration of the aqua complex (8) and the generation efficiency of H ₂ gas in the reference example. FIG. 14B is a graph showing the correlation between the formic acid concentration and the H ₂ gas generation efficiency in the reference example. FIG. 15 is a graph showing a correlation between pH and H ₂ gas generation efficiency in a reference example. FIG. 16 is a scheme showing an example of a reaction mechanism that can be estimated in the reference example.

  Hereinafter, embodiments of the present invention will be described.

[Dinuclear metal complex]
In the binuclear metal complex represented by the formula (1), the bridging ligand Ar is not particularly limited and may be any ligand.

  In the formula (1), when Ar has a substituent, the substituent is preferably independently an alkyl group, a phenyl group, or a cyclopentadienyl group, and the alkyl group has 1 carbon atom. More preferably, it is a -6 linear or branched alkyl group.

In the formula (1), in R ^{1 to} R ⁵ and R ^{12 to} R ²⁷ , the alkyl group is preferably a linear or branched alkyl group having 1 to 6 carbon atoms. In R ^{12 to} R ²⁷ , the alkoxy group is preferably a linear or branched alkoxy group having 1 to 6 carbon atoms, and particularly preferably a methoxy group. R ^{1 to} R ⁵ are particularly preferably all methyl groups, for example, and R ^{12 to} R ²⁷ are particularly preferably all hydrogen atoms, for example. In addition, when R ¹⁵ and R ¹⁶ or R ²³ and R ²⁴ together form —CH═CH—, H in the —CH═CH— is independently an alkyl group, phenyl, Group, nitro group, halogen group, sulfonic acid group (sulfo group), amino group, carboxylic acid group (carboxy group), hydroxy group, or alkoxy group, the alkyl group may have 1 to Preferably, the alkoxy group is a straight-chain or branched alkoxy group having 1 to 6 carbon atoms, and a methoxy group is particularly preferable.

  Moreover, it is preferable that the binuclear metal complex of said Formula (1) is a binuclear metal complex which has a structure represented by following formula (6).

In the formula (6),
R ^{6 to} R ¹¹ are each independently a hydrogen atom, an alkyl group, a phenyl group, a nitro group, a halogen group, a sulfonic acid group (sulfo group), an amino group, a carboxylic acid group (carboxy group), a hydroxy group, or an alkoxy group. Group,
M ¹ , M ² , R ^{1 to} R ⁵ , R ^{12 to} R ²⁷ , L and m are the same as those in the formula (1).

In the formula (6), in R ^{1 to} R ²⁷ , the alkyl group is preferably a linear or branched alkyl group having 1 to 6 carbon atoms. In R ^{6 to} R ²⁷ , the alkoxy group is preferably a linear or branched alkoxy group having 1 to 6 carbon atoms, and particularly preferably a methoxy group. R ^{1 to} R ⁵ are particularly preferably all methyl groups, for example, and R ^{6 to} R ²⁷ are particularly preferably all hydrogen atoms, for example.

  Further, in the binuclear metal complex represented by the formula (1) or (6), a tautomer or stereoisomer thereof, or a salt thereof, in the formula (1) or (6), L is water. It is preferably a molecule, hydrogen atom, alkyloside ion, hydroxide ion, halide ion, carbonate ion, trifluoromethanesulfonate ion, sulfate ion, nitrate ion, formate ion, acetate ion, or absent. . The alkoxide ion is not particularly limited. For example, alkoxide ions derived from methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, etc. Can be mentioned.

  In addition, the ligand L in the formula (1) or (6) may be relatively easily substituted or eliminated depending on the type. As an example, the ligand L is a water molecule in a basic, neutral or weakly acidic aqueous solution, a hydrogen atom in a strongly acidic aqueous solution, an alkoxide ion in an alcohol solvent, Desorption may occur. However, this description is only an example of a possible mechanism and does not limit the present invention.

In the formula (1) or (6), M ¹ is preferably ruthenium, osmium, iron, manganese, chromium, cobalt, iridium, or rhodium, and ruthenium is particularly preferable. M ² is preferably iridium, ruthenium, rhodium, cobalt, osmium, nickel, or platinum, and iridium is particularly preferable. As a combination of M ¹ and M ² , it is particularly preferable that M ¹ is ruthenium and M ² is iridium.

  In the formula (1) or (6), m is, for example, preferably 0 to 5, and more preferably 2, 3 or 4.

  Among the binuclear metal complexes represented by the formula (1), for example, the binuclear metal complex represented by the following formula (7) is more preferable.

  In said Formula (7), L and m are the same as said Formula (6). Moreover, among the binuclear metal complexes represented by the formula (7), for example, the binuclear metal complexes represented by any of the following formulas (8) to (11) are particularly preferable.

In addition, among the binuclear complexes represented by the formula (1), the compounds other than the formula (7) are preferably represented by, for example, compound numbers (31) to (60) in the following Tables 1 to 5. A binuclear complex is mentioned. Each structure of the compounds (31) to (60) is represented by a combination of R ^{1 to} R ²⁷ , M ¹ , M ² and Ar in the formula (1) or (6). In the compounds (31) to (60), the ligand L is the same as the formula (1) or (6) and is not particularly limited. For example, the water molecule, hydrogen atom, methoxide ion, or water It is preferably an oxide ion or absent. m is the valence of M ^1, but determined by the valence of the valence and Kakuhaiiko of M ^2, for example, 0 to 5 is preferred. In addition, all the compounds in the following Tables 1 to 5 can be easily produced by those skilled in the art without undue trial and error based on the description in the present specification and common sense in the technical field to which the present invention belongs. is there.

If the binuclear complex represented by the formula (1) has isomers such as tautomers or stereoisomers (eg, geometric isomers, conformers and optical isomers), these isomers The body can also be used in the present invention. For example, when an enantiomer is present, both R and S isomers can be used. Furthermore, the binuclear complex represented by the formula (1) or an isomer salt thereof can also be used in the present invention. In the salt, the counter ion of the binuclear complex represented by the formula (1) is not particularly limited. Examples of the anion include hexafluorophosphate ion (PF ₆ ⁻ ), tetrafluoroborate ion (BF ₄ ^-), hydroxide ions (OH ^-), acetate ion, carbonate ion, phosphate ion, sulfate ion, nitrate ion, halide ion (e.g. fluoride ion (F ^-), chloride ion (Cl ^-), Bromide ion (Br ⁻ ), iodide ion (I ⁻ ), etc.), hypohalite ion (eg, hypofluorite ion, hypochlorite ion, hypobromite ion, hypoiodite ion, etc.), Halogenate ion (eg, fluorite ion, chlorite ion, bromite ion, iodate ion, etc.), halogenate ion (eg, fluorate ion, chlorate ion, bromate ion, iodate ion) Emissions, etc.), perhalogen acid ion (e.g., perfluorinated acid ion, perchloric acid ion, perbromic acid ion, periodic acid ion, etc.), trifluoromethanesulfonate ion (OSO ₂ CF ₃ ^-), tetrakis pentafluorophenyl borate And ions [B (C ₆ F ₅ ) ₄ ⁻ ] and the like. The cation is not particularly limited, but various metal ions such as lithium ion, magnesium ion, sodium ion, potassium ion, calcium ion, barium ion, strontium ion, yttrium ion, scandium ion, lanthanoid ion, hydrogen ion, etc. Can be mentioned. These counter ions may be one type, or two or more types may coexist.

  In the present invention, the alkyl group is not particularly limited. For example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group, Examples include pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, icosyl group, etc. It is done. The same applies to groups derived from alkyl groups and atomic groups (alkoxy groups and the like). Although it does not specifically limit as alcohol and an alkoxide ion, For example, the alcohol and alkoxide ion derived from each said alkyl group are mentioned. In the present invention, “halogen” refers to any halogen element, and examples thereof include fluorine, chlorine, bromine and iodine. Furthermore, in the present invention, when an isomer exists in a substituent or the like, any isomer may be used unless otherwise limited. For example, when simply referring to “propyl group”, either an n-propyl group or an isopropyl group may be used. When simply referred to as “butyl group”, any of n-butyl group, isobutyl group, sec-butyl group and tert-butyl group may be used.

[Production method of binuclear metal complex]
The production method of the binuclear metal complex represented by the formula (1), a tautomer or stereoisomer thereof, or a salt thereof (hereinafter sometimes simply referred to as “compound (1)”) is not particularly limited. Any method may be used. However, for example, a metal complex represented by the following formula (21), a tautomer or stereoisomer thereof, or a salt thereof (hereinafter sometimes simply referred to as the compound (21)) and the following formula (22) And a tautomer or stereoisomer thereof, or a salt thereof (hereinafter sometimes referred to simply as “compound (22)”) is dissolved in a solvent and reacted. It is preferable to do. This production method may, for example, merely produce the compound (1) by the reaction step, and may further include a step of isolating the compound (1) by an appropriate method thereafter. According to such a method, the compound (1) can be easily produced.

In the formula (21),
Ar, M ¹ and R ^{12 to} R ²⁷ are the same as those in the formula (1),
n is a positive integer, 0, or a negative integer;
In the formula (22),
M ² , L and R ^{1 to} R ⁵ are the same as those in the formula (1),
L ¹ and L ² are optional substituents or are not present and may be the same or different;
p is a positive integer, 0, or a negative integer.

In the formula (22), for example, L, L ¹ and L ² are preferably all water molecules. Further, when the metal complex (21) or the metal complex (22) or an isomer thereof forms a salt, the counter ion is not particularly limited. For example, the counter ion of the binuclear metal complex of the formula (1) is described above. The same as the specific example.

  In the production method of the compound (1), the solvent for dissolving the compound (21) and the compound (22) is not particularly limited. For example, water or an organic solvent may be used, or only one type may be used or two or more types may be used in combination. May be. For example, when both of the compound (21) and the compound (22) are soluble in water, it is preferable to use water because it is simple. The organic solvent is not particularly limited, but is preferably a highly polar solvent from the viewpoint of the solubility of the compound (21) and the compound (22). For example, acetonitrile, propionitrile, butyronitrile, nitriles such as benzonitrile, methanol, Primary alcohols such as ethanol, n-propyl alcohol, n-butyl alcohol, secondary alcohols such as isopropyl alcohol and s-butyl alcohol, tertiary alcohols such as t-butyl alcohol, ethylene glycol, propylene glycol, etc. Examples include polyhydric alcohol, ethers such as tetrahydrofuran, dioxane, dimethoxyethane, diethyl ether, amides such as dimethylformamide and dimethylacetamide, sulfoxides such as dimethyl sulfoxide, and esters such as ethyl acetate.

  When the compound (21) and the compound (22) are dissolved in a solvent, the concentration of the complex (21) molecule is not particularly limited, but is, for example, 0.001 to 50 mmol / L, preferably 0.005 to 20 mmol / L, more preferably 0.01. ~ 5mmol / L. The concentration of the complex (22) molecule is not particularly limited, and is, for example, 0.001 to 50 mmol / L, preferably 0.005 to 20 mmol / L, and more preferably 0.01 to 5 mmol / L. The mass ratio (number ratio) of the complex (21) molecule and the complex (22) molecule is not particularly limited, but is, for example, 1: 100 to 100: 1, preferably 1:50 to 50: 1, more preferably It is particularly preferable that the ratio is 1: 3 to 3: 1 and 1: 1 which is equal to the stoichiometric ratio.

  Further, the method for reacting the compound (21) and the compound (22) is not particularly limited. For example, the compound (21) may be allowed to stand at room temperature after being dissolved in a solvent, or may be heated as necessary. . Specifically, although reaction temperature is not specifically limited, For example, 4-100 degreeC, Preferably it is 20-80 degreeC, More preferably, it is 20-60 degreeC. The reaction time is not particularly limited, but is, for example, 5 seconds to 60 minutes, preferably 10 seconds to 10 minutes, and more preferably 10 seconds to 1 minute. Ideally, the reaction should be completed immediately after the compound (21) and the compound (22) are mixed.

  In the production method of the compound (1), the isolation method of the compound (1) is not particularly limited. For example, a method known as a metal complex isolation method such as a recrystallization method or a counter anion exchange precipitation method is appropriately applied. can do.

[Catalyst for formic acid decomposition of the present invention, method for producing hydrogen isotope gas and use thereof]
As described above, the formic acid decomposition catalyst of the present invention includes a dinuclear metal complex represented by the formula (1), a tautomer or stereoisomer thereof, or a salt thereof (compound (1)). Catalyst. For example, the compound (1) may be used as it is as the formic acid decomposition catalyst of the present invention, or other components may be added as appropriate. The formic acid decomposition catalyst of the present invention generates hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) by decomposing formic acid by its action. Therefore, the formic acid decomposition catalyst of the present invention can be used in the production method of the present invention for producing a hydrogen isotope gas from a formic acid solution in which at least one of formic acid and a solvent is deuterated as described above.

As described above, the production method of the present invention prepares a formic acid solution containing a formic acid decomposition catalyst containing compound (1), formic acid and a solvent, and at least one of the formic acid and the solvent is deuterated. And a formic acid decomposition in which at least one of deuterium (D ₂ ) and deuterium hydrogen (HD) is generated by decomposing formic acid by standing, heating, or irradiating light. And a process for producing at least one of deuterium (D ₂ ) and deuterium hydride (HD). The said preparatory process in the manufacturing method of this invention can be performed by adding formic acid to the solution of a compound (1), and making it a formic acid solution, for example. At this time, for example, prior to the addition of formic acid, it is preferable to sufficiently deoxygenate the solution of compound (1) from the viewpoint of the reaction efficiency in the formic acid decomposition step. The formic acid decomposition step can be performed by leaving the formic acid solution as it is or by heating or irradiating with light as necessary. In the case of heating, the temperature is not particularly limited, but is, for example, 4 to 100 ° C, preferably 10 to 80 ° C, more preferably 20 to 40 ° C. The method for collecting the generated hydrogen is not particularly limited, and a known method such as water replacement or upward replacement can be appropriately used.

  In the production method of the present invention, the solvent is not particularly limited. For example, water or an organic solvent may be used, or only one kind may be used or two or more kinds may be used in combination. For example, the solvent may contain water, and one or both of the water and the formic acid may be deuterated in the formic acid solution. The organic solvent is not particularly limited, but is preferably a highly polar solvent from the viewpoint of the solubility of the compound, nitrile such as acetonitrile, propionitrile, butyronitrile, benzonitrile, methanol, ethanol, n-propyl alcohol, n-butyl alcohol. Primary alcohols such as isopropyl alcohol, secondary alcohols such as s-butyl alcohol, tertiary alcohols such as t-butyl alcohol, polyhydric alcohols such as ethylene glycol and propylene glycol, tetrahydrofuran, dioxane, dimethoxyethane, Examples include ethers such as diethyl ether, amides such as dimethylformamide and dimethylacetamide, sulfoxides such as dimethyl sulfoxide, and esters such as ethyl acetate. For example, a mixed solvent of water and an organic solvent may be used as the solvent, but it is preferable to use only water because it is simple. Furthermore, the raw material formic acid may be in the form of, for example, a solution or a salt.

  Further, the formic acid solution may contain additives other than the formic acid decomposition catalyst, the formic acid and the solvent, but in the production method of the present invention, even if such other additives are not used, Hydrogen isotope gas can be generated easily and safely with high yield.

The activity of the formic acid decomposition catalyst of the present invention is not particularly limited, but is preferably higher than that of the conventional formic acid decomposition catalyst. Specifically, sodium hydroxide is added to an aqueous solution in which non-deuterated formic acid (HCOOH) is dissolved in non-deuterated water (H ₂ O) at a concentration of 0.83M to adjust the pH to 3.8. When the formic acid decomposition reaction is carried out at 298 K (25 ° C.) using the formic acid decomposition catalyst of the present invention, the TOF (Turn Over Frequency, the number of rotations of the catalyst per hour) is preferably 100 or more. The TOF under the reaction conditions is more preferably 200 or more, particularly preferably 400 or more, and the upper limit is not particularly limited, but is, for example, 500 or less. In addition, TOF in the said reaction conditions can be measured like the below-mentioned reference examples 1-3, for example. The TOF is a value obtained by dividing the number of hydrogen molecules generated per hour in the formic acid decomposition reaction by the number of molecules of the binuclear metal complex (1).

  The formic acid decomposition catalyst of the present invention preferably functions as a catalyst without any heating in an aqueous solution at room temperature, for example. In addition, although it does not restrict | limit especially with "room temperature", it is 5-35 degreeC, for example. In the production method of the present invention, for example, it is preferable to perform the formic acid decomposition step without heating at all, for the reason that the formic acid decomposition catalyst is hardly deteriorated. For example, in the formic acid decomposition step, the formic acid solution is preferably allowed to stand at room temperature until decomposition of formic acid starts, and further left at room temperature to perform the formic acid decomposition step. In this case, the time until the start of formic acid decomposition is not particularly limited, but is, for example, 10 to 20 minutes. In addition, it is not clear why the formic acid solution may be left standing and formic acid decomposition may not start for a while. For example, even in the case where the solution is sufficiently deoxygenated in the preparation step, the residual oxygen that cannot be completely removed reacts with the compound (1), and after the oxygen is consumed reductively, the compound (1) It is thought that there may be a case where the reaction of formic acid begins. However, this is merely an example of a mechanism that can be estimated, and does not limit the present invention. The reaction conditions in the formic acid decomposition step are not limited to the above conditions. For example, even when the formic acid decomposition catalyst of the present invention is sufficiently high in activity, for the purpose of further improving the reaction efficiency, it is appropriately heated as described above, or an organic solvent is used instead of water. Alternatively, water and an organic solvent may be used in combination.

  In the production method of the present invention, the concentration of the binuclear metal complex (1) molecule in the solution is not particularly limited. For example, 0.001 to 50 mmol / L, preferably 0.005 to 20 mmol / L, more preferably 0.005 to 5 mmol / L. It is. The mass ratio (number ratio) of the binuclear metal complex (1) molecule and formic acid molecule is not particularly limited, but is, for example, 100: 1 to 1: 5000, preferably 10: 1 to 1: 2000, more preferably 1: 1-1 to 1500.

The production method of the present invention can be used, for example, to obtain carbon dioxide as a by-product in the formic acid decomposition step. Further, according to the hydrogen isotope gas production method of the present invention, it is possible to obtain hydrogen without any toxic by-products without accompanying by-products other than carbon dioxide (CO ₂ ).

In the production method of the present invention, the pH or pD (initial pH or pD) of the formic acid solution before the start of the formic acid decomposition step is not particularly limited, but is, for example, in the range of 1.0 to 8.5. The initial pH or pD can be adjusted using a known pH adjuster, for example, a basic substance such as sodium hydroxide or potassium hydroxide, or an acidic substance such as hydrochloric acid, sulfuric acid or nitric acid. Further, as described later, by adjusting the initial pH or pD, it is possible to adjust the amount of each generated deuterated hydrogen (HD) and deuterium (D ₂ ). Note that hydrogen (H ₂₎ produced in the production method of the present invention, deuterium (D ₂₎ and deuterium from at least two types of mixed gas of hydrogen deuteride (HD) (D ₂₎ and hydrogen deuteride ( The method for obtaining HD) is not particularly limited, and for example, gas chromatography or the like can be used as appropriate.

In the production method of the present invention, as a result of the deuterium at least one of the formic acid and the solvent in the formic acid solution being involved in the formic acid decomposition reaction by the compound (1) as a deuterium source, deuterium (D ₂ ) And deuterated hydrogen (HD) are generated. In the production method of the present invention, for example, when the solvent of the formic acid solution contains D ₂ O, deuterium (D ₂ ) can be generated in the formic acid decomposition step. Thereby, for example, both deuterium (D ₂ ) and deuterated hydrogen (HD) can be obtained in good yield, or deuterium (D ₂ ) can be selectively produced. In this case, for example, it is particularly preferable that the solvent consists only of D ₂ O. In order to obtain both deuterium (D ₂ ) and deuterated hydrogen (HD) in good yield, heavy water (D ₂ O) is used, and the initial pH or pD is in the range of 1.0 to 8.0. Preferably, the range is 1.5 to 6.0, more preferably 2.0 to 4.0. In order to increase the generation amount of deuterium (D ₂ ), it is preferable to use heavy water (D ₂ O), and to set the initial pH or pD within the range of 1.0 to 6.0, 1.0 More preferably, it is in the range of ˜4.0, more preferably in the range of 1.0 to 3.0. When selectively producing deuterium (D ₂ ), the ratio of D ₂ in the total amount (mol) of H ₂ , HD and D ₂ obtained is not particularly limited, but is preferably 50 mol% or more. Preferably it is 60 mol% or more, More preferably, it is 70 mol% or more, More preferably, it is 80 mol% or more, Most preferably, it is 90 mol% or more. The upper limit of the D ₂ ratio is not particularly limited, but ideally 100 mol%.

In the production method of the present invention, for example, in the formic acid solution, the solvent contains water, and one of the water and the formic acid is deuterated, and the initial pH or initial value before the formic acid decomposition step is started. It is preferable that pD is 2.5 or more. According to this production condition, deuterated hydrogen (HD) is generated in the formic acid decomposition step, and it is easy to selectively produce deuterated hydrogen (HD). The initial pH or initial pD is preferably 2.5 or more, more preferably 3.0 or more, and particularly preferably 3.3 or more. The upper limit of the initial pH or initial pD is, for example, 6.0 or less, preferably 5.5 or less, more preferably 5.0 or less, and particularly preferably 4.5 or less. In addition, when using deuterated formic acid (DCOOH) and non-deuterated water (H ₂ O) under these production conditions, deuterated hydrogen (HD) is particularly easily produced, More preferred. In the case of selectively producing deuterated hydrogen (HD), the proportion of HD in the total amount (mol) of H ₂ , HD and D ₂ obtained is not particularly limited, but preferably 50 mol% or more, More preferably, it is 60 mol% or more, More preferably, it is 70 mol% or more, More preferably, it is 80 mol% or more, Most preferably, it is 90 mol% or more. The upper limit of the HD ratio is not particularly limited, but ideally 100 mol%.

In the present invention, deuterated formic acid refers to formic acid having a structure in which hydrogen (H) of the formyl group moiety (HCO-) in the formic acid molecule is substituted with deuterium (D). The hydrogen of the carboxy group moiety (—COOH) may be light hydrogen (H) or a structure substituted with deuterium (D). The deuterated water may be D ₂ O or HDO, but D ₂ O is preferable from the viewpoints of price, convenience, and the like. As described above, when deuterated formic acid (DCOOH) and water (H ₂ O) are used, particularly deuterated hydrogen (HD) can be selectively generated. When non-deuterated formic acid (HCOOH) and heavy water (D ₂ O) are used, both deuterated hydrogen (HD) and deuterium (D ₂ ) can be generated. The formic acid (HCOOH) can be appropriately produced with reference to a known formic acid production method or the like. For example, when it can be obtained as a commercial product, the commercial product may be used as it is. Deuterated formic acid (DCOOH) can be obtained by referring to known deuteration methods such as using a base or acid catalyst in the presence of deuterated formic acid (HCOOH) to deuterated water (D ₂ O). For example, when it can be obtained as a commercial product, the commercial product may be used as it is. The heavy water (D ₂ O) can be appropriately produced by concentrating water (H ₂ O). For example, when it can be obtained as a commercial product, the commercial product may be used as it is.

In the production method of the present invention, in the formic acid solution, at least one of the solvent and the formic acid may be tritiated instead of deuterated. Under such conditions, as a method for producing at least one of tritium (T ₂ ) and tritium hydride (HT) instead of at least one of deuterium (D ₂ ) and deuterated hydrogen (HD) Can also be used.

In the production method of the present invention, as described above, in the formic acid solution, at least one of the formic acid and the solvent is deuterated. However, if neither formic acid nor the solvent is deuterated, a method for producing light hydrogen (H ₂ ) instead of at least one of deuterium (D ₂ ) and deuterated hydrogen (HD) Can also be used. This light hydrogen (H ₂ ) production method can be carried out, for example, by applying the above-mentioned conditions in the production method of the present invention.

  According to the production method of the present invention, for example, a hydrogen isotope gas can be produced with high selectivity without using expensive equipment such as a multistage separation tower and a noble metal separation membrane. For example, if the manufacturing method of this invention is performed within an airtight container, a high-pressure hydrogen isotope gas can also be obtained. Therefore, according to the present invention, for example, it is possible to obtain a hydrogen isotope gas of any pressure from normal pressure to high pressure without using a gas compressor or the like.

The formic acid decomposition catalyst of the present invention can also be used in, for example, the following formic acid production and decomposition apparatus. In the following description of the formic acid production and decomposition apparatus, hydrogen (H ₂ ) is assumed to be at least partially D ₂ or HD. In the following description of the formic acid production and decomposition apparatus, for example, formic acid is deuterated formic acid, which may be used as a supply source of D in D ₂ or HD, or a deuterated solvent or the like is supplied as D. It may be used as a source.

The formic acid production and decomposition apparatus using the formic acid decomposition catalyst of the present invention includes, for example, a formic acid decomposition unit that decomposes formic acid to generate hydrogen (H ₂ ) and carbon dioxide (CO ₂ ), and hydrogen (H ₂ ). And a formic acid production unit that produces formic acid from carbon dioxide (CO ₂ ), the formic acid decomposition unit includes the formic acid decomposition catalyst of the present invention, and the formic acid production unit comprises hydrogen (H ₂ ) and carbon dioxide ( A formic acid production catalyst for producing formic acid by reacting CO ₂ ) is included. Although the specific structure of this apparatus is not specifically limited, For example, you may further provide the carbon dioxide supply part which supplies the carbon dioxide generated from the said formic acid decomposition | disassembly part to the said formic acid production part. In addition, for example, a formic acid supply unit that supplies the formic acid produced in the formic acid production unit to the formic acid decomposition unit may be further provided. According to this, formic acid can be produced again from carbon dioxide, which is a by-product of formic acid decomposition, and can be used cyclically without releasing carbon dioxide (CO ₂ ) into the atmosphere. In addition, the hydrogen storage and generation method using the formic acid production and decomposition apparatus may, for example, produce formic acid by reacting hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) with a formic acid production catalyst, It includes a hydrogen storage step of storing in the form of formic acid and a hydrogen generation step of generating hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) by decomposing formic acid with the formic acid decomposition catalyst of the present invention. The order of the hydrogen storage step and the hydrogen generation step is not particularly limited, and either may be first, or after each step is completed once, the process may return to the first step again. Although the apparatus for using the said hydrogen storage and generation | occurrence | production method is not specifically limited, For example, it can carry out using the said formic acid production and decomposition apparatus.

The storage and generation of hydrogen can be performed, for example, as follows. That is, first, the formic acid production and decomposition apparatus is prepared. The apparatus includes a carbon dioxide supply unit that supplies carbon dioxide generated from the formic acid decomposition unit to the formic acid production unit, a formic acid supply unit that supplies formic acid produced by the formic acid production unit to the formic acid decomposition unit, and the formic acid A hydrogen supply unit for supplying hydrogen to the manufacturing unit is provided. Next, hydrogen is supplied from the hydrogen supply unit to the formic acid production unit, and carbon dioxide generated from the formic acid decomposition unit is supplied to the formic acid production unit via the carbon dioxide supply unit. In the formic acid production section, hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) are reacted with the formic acid production catalyst to produce formic acid, and the hydrogen is stored in the form of formic acid. This formic acid can be used after storage for an arbitrary period, but may be used immediately if necessary. Then, the formic acid is supplied to the formic acid decomposition section through the formic acid supply section, and the formic acid is decomposed by the formic acid decomposition catalyst of the present invention to generate hydrogen (H ₂ ) and carbon dioxide (CO ₂ ). This hydrogen can be used for any application such as a fuel cell, for example, as necessary. And the carbon dioxide of a by-product is supplied to the said formic acid production part via the said carbon dioxide supply part, and is utilized again for formic acid production. Although the hydrogen supply part which supplies hydrogen to the said formic acid production part is not specifically limited, For example, you may provide a well-known hydrogen cylinder etc. If the hydrogen storage and generation method or the formic acid production and decomposition apparatus is used, hydrogen can be stored and transported as formic acid or formate, and can be safely used at the necessary place as necessary. This is advantageous in terms of safety and the like rather than transporting a hydrogen cylinder or the like and supplying hydrogen directly from the hydrogen cylinder or the like when necessary.

The formic acid production catalyst used in the hydrogen storage and generation method or the formic acid production and decomposition apparatus is not particularly limited, and is described in, for example, the following documents (a) to (c) according to the inventors' invention. Formic acid production catalysts are preferred. This formic acid production catalyst is represented by the following formula (23) or (24). In the following formula (23), X ¹ is H ₂ O (water molecule) or H (hydrogen atom), Q is 3 when X ¹ is H ₂ O, and Q when X ¹ is H. Is 2. R ¹⁰⁰ and R ²⁰⁰ are each independently a hydrogen atom or a methoxy group. In the following formula (24), X ² is H ₂ O (water molecule) or H (hydrogen atom), T is 2 when X ² is H ₂ O, and T when X ² is H. Is 1. R ³⁰⁰ and R ⁴⁰⁰ are each independently a hydrogen atom or a methoxy group. However, in the following formulas (23) and (24), X ¹ , X ² , R ¹⁰⁰ , R ²⁰⁰ , R ³⁰⁰ and R ⁴⁰⁰ are replaced with other atomic groups as long as the function as a catalyst for producing formic acid is not impaired. For example, R ¹⁰⁰ , R ²⁰⁰ , R ³⁰⁰ or R ⁴⁰⁰ may be another alkoxy group or an alkyl group. Further, in the pentamethylcyclopentadienyl group in the formula (23) or the hexamethylbenzene group in the formula (24), each methyl group is replaced with another atomic group unless the function as a catalyst for producing formic acid is impaired. For example, each may independently be another alkyl group, an alkoxy group, a hydrogen atom, or the like. The formic acid production catalyst represented by the following formulas (23) and (24) is characterized by high activity under acidic conditions, unlike conventional formic acid production catalysts. Thereby, since the manufactured formic acid can be utilized in the form of a free acid instead of a salt, it is preferable from the viewpoint of ease of operation. Further, the production method of the formic acid production catalyst represented by the following formulas (23) and (24) is not particularly limited, but those skilled in the art can easily produce it based on the description and technical common sense in the present specification. is there. The following formulas (23) and (24) may be produced, for example, according to the method for producing a formic acid decomposition catalyst of the present invention. That is, for example, in the following formula (23), the aqua complex is mixed with a bipyridine ligand in an aqueous solution of [Cp ^* Ir (OH ₂ ) ₃ ] ²⁺ (Cp ^* is a pentamethylcyclopentadienyl group). The hydride complex can be generated by adding formic acid or H ₂ to the aqua complex. These production methods are described in detail in the following documents (a) to (c) and the like.

(a) Hideki Hayashi, Seiji Ogo, and Shunichi Fukuzumi, Chem. Commun. 2004, 2714−2715
(b) Seiji Ogo, Ryota Kabe, Hideki Hayashi, Ryosuke Harada and Shunichi Fukuzumi, Dalton Trans. 2006, 4657-4663
(c) Hideki Hayashi, Seiji Ogo, Tsutomu Abura, and Shunichi Fukuzumi, Journal of American Chemical Society, 2003, 125, 14266-14267

  As an example of the method for producing the catalyst for producing formic acid represented by the formula (23) or (24), the method described in the literature (b) is described below.

[(η ⁶ -C ₆ Me ₆ ) Ru ^II (4,4′-OMe-bpy) (OH ₂ )] ²⁺ (In the above formula (24), X ² is H ₂ O (water molecule), R ³⁰⁰ And R ⁴⁰⁰ is a methoxy group, a catalyst for formic acid production with T = 2) [(η ⁶ -C ₆ Me ₆ ) Ru ^II (4,4'-OMe-bpy) (OH ₂ )] SO ₄ It can be manufactured as follows. That is, first, 4,4′-dimethoxy-2,2′-bipyridine (105 mg, 0.486 mmol) was converted into [(η ⁶ -C ₆ Me ₆ ) Ru ^II (OH ₂ ) ₃ ] SO ₄ (200 mg, 0.484 mmol). ) In an aqueous solution (20 cm ³ ). The solution is stirred at room temperature for 24 hours to give a light brown solution. Trace amounts of impurities were removed by filtration, and the filtrate was evaporated under reduced pressure to obtain the desired [[η ⁶ -C ₆ Me ₆ ) Ru ^II (4,4'-OMe-bpy) (OH ₂ )] SO ₄ Get. It is used after vacuum drying (98% yield calculated on the basis of [(η ⁶ -C ₆ Me ₆ ) Ru ^II (OH ₂ ) ₃ ] SO ₄ ). The instrumental analysis value of [(η ⁶ -C ₆ Me ₆ ) Ru ^II (4,4′-OMe-bpy) (OH ₂ )] SO ₄ is shown below.

[(η ⁶ -C ₆ Me ₆ ) Ru ^II (4,4'-OMe-bpy) (OH ₂ )] SO ₄ :
¹ H NMR (300 MHz, H ₂ O, 25 ° C) δ (TSP in D ₂ O, ppm) 2.12 (s, η ⁶ -C ₆ (CH ₃ ) ₆ , 18H), 4.08 (s, OCH ₃ , 6H) , 7.42 (dd, J = 6.6, 2.6Hz, bpy, 2H), 7.86 (d, J = 2.6Hz, bpy, 2H), 8.91 (d, J = 6.6Hz, bpy, 2H).

Further, NaPF ₆ was added to an aqueous solution (5 cm ³ ) of this sulfate [(η ⁶ -C ₆ Me ₆ ) Ru ^II (4,4'-OMe-bpy) (OH ₂ )] SO ₄ (64.7 mg, 0.10 mmol). When (168 mg, 1.00 mmol) of an aqueous solution (1 cm ³ ) is added, orange powder hexafluorophosphate [(η ⁶ -C ₆ Me ₆ ) Ru ^II (4,4′-OMe-bpy) (OH ₂ )] (PF ₆ ) ₂ is precipitated. This powder is recrystallized with methanol to obtain crystals of hexafluorophosphate [(η ⁶ -C ₆ Me ₆ ) Ru ^II (4,4'-OMe-bpy) (OH ₂ )] (PF ₆ ) ₂ . The elemental analysis value of this hexafluorophosphate is shown below.

[(η ⁶ -C ₆ Me ₆ ) Ru ^II (4,4'-OMe-bpy) (OH ₂ )] (PF ₆ ) ₂ :
Elemental analysis: [(η ⁶ -C ₆ Me ₆ ) Ru ^II (4,4'-OMe-bpy) (OH ₂ )] (PF ₆ ) ₂ · H ₂ O: C ₂₄ H ₃₄ N ₂ F ₁₂ O ₄ P ₂ Ru: Theoretical value: C, 35.79; H, 4.25; N, 3.48%. Observed value: C, 35.85; H, 4.31; N, 3.44%.

^{[Cp * Ir III (4,4'-} OMe-bpy) (OH 2)] in ^{2 +} (Formula (23), X ¹ is H ₂ O (water molecules), R ¹⁰⁰ and R ²⁰⁰ is a methoxy group, Q = 2 of sulfate formic acid catalyst for the ^{production) [Cp * Ir III (4,4'} -OMe-bpy) (OH 2)] sO 4 may be prepared as follows. That is, first, 4,4′-dimethoxy-2,2′-bipyridine (324 mg, 1.50 mmol) was added to an aqueous solution (25 cm ³ ) of [Cp ^* Ir ^III (OH ₂ ) ₃ ] SO ₄ (717 mg, 1.50 mmol). Add to. The solution is stirred at room temperature for 12 hours to give a yellow solution. The precipitate traces removed by filtration, the filtrate the desired product was evaporated under reduced pressure ^{[Cp * Ir III (4,4'-} OMe-bpy) (OH 2)] to obtain a SO _4. It is used to vacuum drying ^{([Cp * Ir III (OH} 2) 3] 96% yield calculated on the basis of SO _4). The instrumental analytical values are indicated below in ^{[Cp * Ir III (4,4'-} OMe-bpy) (OH 2)] SO 4.

[Cp ^* Ir ^III (4,4'-OMe-bpy) (OH ₂ )] SO ₄ :
¹ H NMR (300 MHz, H ₂ O, 25 ° C.) δ (TSP in D ₂ O, ppm): 1.67 (s, η ⁵ -C ₅ (CH ₃ ) ₅ , 15H), 4.11 (s, OCH ₃ , 6H ), 7.40 (dd, J = 6.6, 2.6Hz, bpy, 2H), 7.97 (d, J = 2.6Hz, bpy, 2H), 8.89 (d, J = 6.6Hz, bpy, 2H).

Further, an aqueous solution (0.5 mg) of sodium trifluoromethanesulfonate NaOTf (172 mg, 1.5 mmol) was added to an aqueous solution (1 cm ³ ) of this sulfate [Cp ^* Ir ^III (4,4′-OMe-bpy) (OH ₂ )] SO _4. the addition of cm ^3), yellow powder trifluoromethanesulfonate ^{[Cp * Ir III (4,4'-} OMe-bpy) (OH 2)] (OTf) 2 is precipitated. This powder was recrystallized from water trifluoromethanesulfonate ^{[Cp * Ir III (4,4'-} OMe-bpy) (OH 2)] (OTf) obtaining a _second single crystal. Hereinafter, trifluoromethanesulfonate ^{[Cp * Ir III (4,4'-} OMe-bpy) (OH 2)] (OTf) shows a _second elemental analysis.

[Cp ^* Ir ^III (4,4'-OMe-bpy) (OH ₂ )] (OTf) ₂ :
Elemental ^{analysis: [Cp * Ir III (4,4'} -OMe-bpy) (OH 2)] (OTf) 2: C 24 H 29 N 2 F 6 O 9 S 2 Ir: theoretical value: C, 33.53; H , 3.40; N, 3.26%. Observations: C, 33.47; H, 3.36; N, 3.37%.

^{[Cp * Ir III (4,4'-} OMe-bpy) H] + ( In the above formula (23), X ¹ is a hydrogen atom (hydride ligand), R ¹⁰⁰ and R ²⁰⁰ is a methoxy group, Q = 1 of hexafluorophosphate ^{[Cp * Ir III (4,4'-} OMe-bpy) H] formic acid catalyst for the production) PF ₆ can be produced as follows. That is, ^{first, [Cp * Ir III (4,4'} -OMe-bpy) (OH 2)] SO 4 (13.1mg, 20.0μmol) citrate buffer solution (pH 3.0, 20 cm ^3, light yellow) to Maintain pressure condition (5.5 MPa) while blowing H ₂ . Under this condition, the mixture is reacted at 40 ° C. for 12 hours to obtain a red solution of [Cp ^* Ir ^III (4,4′-OMe-bpy) H] ⁺ .

The ^{[Cp * Ir III (4,4'-} OMe-bpy) H] + red solution (pH 3.0 aqueous solution) to NaPF ₆ (16.7 mg, 0.1 mmol) the addition of a stable hexafluorophosphate in air salt ^{[Cp * Ir III (4,4'-} OMe-bpy) H] PF 6 is precipitated as a yellow powder. This is used to vacuum drying ^{([Cp * Ir III (4,4'} -OMe-bpy) (OH 2)] 77% yield calculated on the basis of SO _4). Hereinafter, hexafluorophosphate ^{[Cp * Ir III (4,4'-} OMe-bpy) H] shows the instrumental analytical values of PF _6.

Hexafluorophosphate [Cp ^* Ir ^III (4,4'-OMe-bpy) H] PF ₆ :
¹ H NMR (300 MHz, DMSO-d ₆ , 25 ° C) δ (TMS, ppm): -11.25 (s, Ir-H, 1H), 1.79 (s, η ⁵ -C ₅ (CH ₃ ) ₅ , 15H) , 4.06 (s, OCH ₃ , 6H), 7.33 (dd, J = 6.6, 2.6Hz, bpy, 2H), 8.33 (d, J = 2.6Hz, bpy, 2H), 8.65 (d, J = 6.6Hz, bpy, 2H).
ESI-MS (in H ₂ O), m / z 545.2 {[Cp ^* Ir ^III (4,4'-OMe-bpy) H] ⁺ ; relative intensity (I) = 100 in the range m / z 100-2000 %}.
FT-IR (KBr, cm ^-1 ) 2030 (Ir-H).

Furthermore, the method for using the formic acid production catalyst represented by the formulas (23) and (24) is not particularly limited. For example, formic acid can be produced by dissolving these catalysts in an appropriate solvent and supplying hydrogen and carbon dioxide into the solution to cause a catalytic reaction. Therefore, for example, the formic acid production section in the formic acid production and decomposition apparatus of the present invention is constructed by filling a suitable container with the solution of the formic acid production catalyst represented by the above formulas (23) and (24). You can also. The said solvent is not specifically limited, For example, water or an organic solvent can be used, and it may be individual or a mixed solvent. The solvent is particularly preferably water from the viewpoints of the solubility of the formic acid production catalyst represented by the formulas (23) and (24), the simplicity of the reaction, the reactivity of hydrogen and carbon dioxide, and the like. Although the reaction temperature in the said catalytic reaction is not specifically limited, For example, 4-100 degreeC, Preferably it is 10-80 degreeC, Most preferably, it is 20-60 degreeC. Although the reaction time is not particularly limited, for example, it is 1 to 80 minutes, preferably 2 to 30 minutes, particularly preferably 2 to 10 minutes. The internal pressure of hydrogen (H ₂ ) in the reaction system is not particularly limited, but is, for example, 0.1 to 10 MPa, preferably 0.1 to 8 MPa, and particularly preferably 0.1 to 6 MPa. The internal pressure of carbon dioxide (CO ₂ ) is not particularly limited, but is, for example, 0.1 to 10 MPa, preferably 0.1 to 8 MPa, and particularly preferably 0.1 to 6 MPa. The method for using the formic acid production catalyst represented by the above formulas (23) and (24) is described in detail in the above-mentioned documents (a) to (c) and the like. It can be easily implemented from the description and technical common sense.

As an example of the method for using the formic acid production catalyst represented by the above formulas (23) and (24), the method for catalytic hydrogenation of CO ₂ in an acidic aqueous solution described in the above-mentioned document (b) will be described. That is, first, a Parr BenchTop Micro Reactor (trade name, cylinder volume 50 cm ³ ) is prepared as a reaction vessel (pressure vessel). The material of the reaction vessel is an alloy called Hastelloy (registered trademark of Haynes International, Inc.). Next, the formic acid production catalyst (20.0 μmol) represented by the above formula (23) or (24) is dissolved in a citrate buffer solution (20 cm ³ ) of pH 3.0 and sealed in the pressure vessel. Then, the solution is heated to 40 ° C., and CO ₂ and H ₂ are appropriately blown and pressurized to react for an appropriate time. After returning the internal pressure of the container to normal pressure, the solution is quickly cooled in an ice bath. Formic acid HCOOH is produced, for example, by ¹ H NMR using TSP (deuterated sodium 3- (trimethylsilyl) propionate, (CH ₃ ) ₃ Si (CD ₂ ) ₂ CO ₂ Na) as an internal standard in D ₂ O. It can be confirmed by measurement.

  Examples of the present invention will be described below. However, the present invention is not limited to the following examples.

[Measurement conditions]
In the following examples, the reaction was traced by UV-visible absorption spectrum, ESI-Mass, GC and ¹ H-NMR. All chemicals are reagent grade. Cis-bis (2,2′-bipyridine) dichlororuthenium Ru (bpy) ₂ Cl ₂ dihydrate was purchased from Strem Chemicals. 2,2′-Bipyrimidine was purchased from Aldrich. Formic acid was purchased from Wako Pure Chemical Industries. The ultraviolet-visible absorption spectrum (UV-Vis. Spectrum) measurement was performed using Shimadzu Corporation equipment (trade name UV-3100PC). Shimadzu equipment (trade name RF-5300PC) was used for fluorescence spectrum measurement. ESI-MS data was collected in positive detection mode using an API-150EX mass spectrometer (trade name, manufactured by PE-Sciex) equipped with an ion spray interface. The spray device maintained the voltage at +5.0 kV, and pressurized N ₂ was used to assist the liquid spray. ^{For the 1} H-NMR measurement, a device nuclear magnetic resonance spectrometer (trade name JNM-AL300, 300.4 MHz at the time of ¹ H-NMR measurement) manufactured by JEOL Ltd. was used. ^{For the 13} C-NMR measurement, an instrument nuclear magnetic resonance spectrometer (trade name UNITY INOVA600, 599.9 MHz at the time of ¹³ C-NMR measurement) manufactured by Varian was used. For GC analysis, Shimadzu Corporation equipped with Shimadzu equipment (trade name GC-14B) and hydrogen isotope gas separation column (trade name Hydro Isopack (2.0m, 4.0mm id, GTR TEC Co., Ltd.) The transient absorption spectrum was observed by the laser flash photolysis method, and the femto and nanosecond laser flash photolysis measurement was performed using a femto and nanosecond time-resolved spectrometer (Unisoku). For the elemental analysis, the product name CHN-Corder (MT-2 type) of Yanagimoto Seisakusho was used for the elemental analysis.The amount of hydrogen generated in the formic acid decomposition reaction was passed through 5 mol / L NaOH water. Carbon dioxide was removed, and only the remaining hydrogen was collected in a measuring cylinder by the water displacement method and measured.

[Complex production example 1: Production of binuclear metal complex (aqua complex)]
In the following manner, an iridium-ruthenium dinuclear aqua complex (8), which is a compound of the present invention (binuclear metal complex), was produced (synthesized). That is, first, commercially available reagent bis (2,2′-bipyridine) dichlororuthenium Ru (bpy) ₂ Cl ₂ dihydrate (3.1 g, 6 mmol, manufactured by Strem Chemicals) was added to water (20 ml). To this was added Ag ₂ SO ₄ (1.87 g, 6 mmol), and the mixture was stirred at room temperature for 12 hours. The precipitate AgCl is filtered off with a glass filter (G4), the filtrate is further filtered through a membrane filter (ADVANTEC, PTFE (polytetrafluoroethylene)), and the filtrate is dehydrated under reduced pressure in the air. A stable red solid [Ru (bpy) ₂ (H ₂ O) ₂ ] ²⁺ sulfate (SO ₄ ²⁻ ) salt was obtained. A ruthenium aqua complex [Ru (bpy) ₂ (H ₂ O) ₂ ] ²⁺ sulfate (0.6 g, 1.1 mmol) was dissolved in 40 mL of water to obtain an aqueous solution. When 1 equivalent of 2,2'-bipyrimidine (Johnson Matthey) is added to this solution, it immediately reacts with [Ru (bpy) ₂ (H ₂ O) ₂ ] ²⁺ and has a bridging ligand An aqueous solution of ruthenium complex [Ru (bpy) ₂ bpm] ²⁺ (bpm = 2,2′-bipyrimidine) was obtained. Furthermore, water was distilled off from this aqueous solution (removed by evaporation), and [Ru (bpy) ₂ bpm] ²⁺ sulfate (bpm = 2,2′-bipyrimidine) was isolated. The instrumental analysis data of [Ru (bpy) ₂ (H ₂ O) ₂ ] ²⁺ sulfate and [Ru (bpy) ₂ bpm] ²⁺ sulfate are shown below.

Ruthenium Aqua Complex Sulfate [Ru (bpy) ₂ (H ₂ O) ₂ ] SO ₄ :
¹ H-NMR (D ₂ O, 298K) δ (TSP, ppm) 7.06 (t, J = 7Hz, 2H, bpy), 7.70 (d, J = 6Hz, 2H, bpy), 7.74 (t, J = 8Hz , 2H, bpy), 7.88 (t, J = 7Hz, 2H, bpy), 8.23 (t, J = 8 Hz, 2H, bpy), 8.34 (d, J = 8Hz, 2H, bpy), 8.56 (d, J = 8Hz, 2H, bpy), 9.36 (d, J = 5Hz, 2H, bpy) ¹³ C-NMR (D ₂ O, 298K) δ (TSP, ppm) 126.09, 126.26, 128.43, 129.73, 138.62, 140.28, 154.43, 157.23, 161.13, 163.37
UV-Vis. (Nm): 243, 290, 339, 481, 647 (sh)
Elemental analysis: [Ru (bpy) ₂ (H ₂ O) ₂ ] SO ₄・ H ₂ O: C ₂₀ H ₂₂ N ₄ O ₇ SRu; Theoretical value: C, 42.63; H, 3.93; N, 9.94. : C, 42.53; H, 3.67; N, 9.95.
Mass spectrometry (ESI-MS): m / z [M -2H ₂ O -SO ₄ + PF ₆ ] ⁺ 559.0 Theoretical value C ₂₀ H ₁₆ N ₄ F ₆ PRu 559.0

Ruthenium sulfate [Ru (bpy) ₂ bpm] SO ₄ :
¹ H-NMR (D ₂ O, 298K) δ (TSP, ppm) 7.41 (t, J = 7Hz, 2H, bpy), 7.45 (t, J = 7Hz, 2H, bpy), 7.60 (t, J = 5Hz , 2H, bpm), 7.80 (d, J = 5Hz, 2H, bpy), 7.94 (d, J = 5Hz, 2H, bpy), 8.09 (t, J = 8Hz, 2H, bpy), 8.12 (t, J = 8Hz, 2H, bpy), 8.24 (dd, J = 6, 2Hz, 2H, bpm), 8.57 (d, J = 8Hz, 2H, bpy), 8.58 (d, J = 7Hz, 2H, bpy), 9.09 (dd, J = 5, 2Hz, 2H, bpm) ¹³ C-NMR (D ₂ O, 298K) δ (TSP, ppm) 124.40 (bpy), 124.44 (bpy), 124.51 (bpm), 127.48 (bpy), 127.65 (bpy), 138.39 (bpy), 138.53 (bpy), 151.72 (bpy), 151.89 (bpy), 157.04 (bpy), 157.09 (bpy), 157.70 (bpm), 159.98 (bpm), 163.11 (bpm)
UV-Vis. (Nm): 244, 283, 415
Elemental analysis: [Ru (bpy) ₂ bpm] SO ₄ · 4H ₂ O: C ₂₈ H ₃₀ N ₈ O ₈ SRu; Theoretical value: C, 45.46; H, 4.09; N, 15.15. Observed value: C, 45.39; H, 4.06; N, 15.36.
Mass spectrometry (ESI-MS): m / z [M -SO ₄ + PF ₆ ] ⁺ 717.0 Theoretical C ₂₈ H ₂₂ N ₈ F ₆ PRu 717.1

On the other hand, sulfuric acid (SO ₄ ^2- ) salt of organometallic iridium aqua complex [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ was converted to Ogo, S .; Makihara, N .; Watanabe, Y., Organometallics 1999, 18 , 5470-5474. And Ogo, S .; Nakai, H .; Watanabe, Y., J. Am. Chem. Soc. 2002, 124, 597-601. Cp ^* represents a pentamethylcyclopentadienyl group. The operation of synthesis and isolation is specifically as follows. That is, first, Ag ₂ SO ₄ (1.87) was added to a suspension solution (20 mL) of pentamethylcyclopentadienyldichloroiridium dimer [Cp ^* IrCl ₂ ] ₂ (2.4 g, 3 mmol, Strem Chemicals, Inc.), which is a commercially available reagent. g, 6 mmol) was added and stirred at room temperature for 12 hours. Then, the precipitate AgCl is filtered off with a glass filter, the filtrate is further filtered through a membrane filter (manufactured by ADVANTEC PTFE), and the filtrate is dehydrated under reduced pressure to remove a stable yellow solid [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ SO ₄ was obtained. In addition, the instrumental analysis values of the products are described in the above documents Ogo, S .; Makihara, N .; Watanabe, Y., Organometallics 1999, 18, 5470-5474. And Ogo, S .; Nakai, H .; Watanabe, Y Compared with the values described in J. Am. Chem. Soc. 2002, 124, 597-601., Organometallic iridium aqua complex [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ was confirmed. That is, the instrumental analysis values of the product [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ SO ₄ are as follows, which is in good agreement with the values described in the above literature.

[Cp ^* Ir (H ₂ O) ₃ ] ²⁺ SO ₄ :
¹ H NMR (D ₂ O, pH 2.3, 25 ° C.) δ (DSS, ppm): 1.61 (s; Cp ^* ).
¹ H NMR (DMSO-d ₆ , 25 ° C.) δ (see DMSO-d ₆ residual hydrogen as 2.50 ppm): 1.68 (s; Cp ^* ), 3.31 (br; H ₂ O).
¹³ C NMR (D ₂ O, pH 2.3, 25 ° C) δ (DSS, ppm) 11.09 (s; η ⁵ -C ₅ ( C H ₃ ) ₅ ), 86.94 (s; η ⁵ - C ₅ (CH ₃ ) ₅ ).
Elemental analysis: [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ SO ₄ : C ₁₀ H ₂₁ Ir ₁ O ₇ S ₁ ; Theoretical value: C, 25.15; H, 4.43. Observed value: C, 25.39; H, 4.48.

Furthermore, [Ru (bpy) ₂ bpm] ²⁺ sulfate synthesized and isolated as described above reacts with 1 equivalent of organometallic iridium aqua complex [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ in water at room temperature. The target iridium-ruthenium dinuclear aqua complex (8) was obtained (Scheme 1 below). In the following scheme 1, Formula (101) represents [Ru (bpy) ₂ bpm] ²⁺ , and Formula (102) represents [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ .

Specifically, the operation of Scheme 1 was performed as follows. That is, first, the [Ru (bpy) ₂ bpm] ²⁺ sulfate (162.7 mg, 0.22 mmol) was dissolved in 10 mL of water to obtain an aqueous solution. On the other hand, an organometallic iridium aqua complex [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ sulfate (105.1 mg, 0.22 mmol) was dissolved in 10 mL of water to obtain an aqueous solution. When these two aqueous solutions were mixed, a reaction immediately occurred, and an aqueous solution of iridium-ruthenium dinuclear aqua complex (8) was obtained. Then, water was distilled off from this aqueous solution to isolate the iridium-ruthenium dinuclear aqua complex (8) sulfate, and the structure was confirmed by ¹ H-NMR, UV-Vis. And ESI-MS. ^{As a} solvent for ¹ H-NMR measurement, heavy water (D ₂ O) was used, and TSP-d ₄ (sodium trimethylsilylpropionate) was used as a reference substance. Water was used as a solvent for measurement of UV-Vis. Methanol was used as a solvent for ESI-MS measurement. FIG. 5 shows a part of the ESI-MS spectrum diagram of the aqua complex (8). As shown in the figure, in this ESI-MS spectrum, a methoxide complex (11) [Ru (bpy) ₂ bpmIrCp in which a water molecule (aqua ligand), which is a ligand of the aqua complex (8), is substituted with a methoxide ion. ^* (OCH ₃ ) SO ₄ ] ⁺ was observed as the parent ion peak with the maximum m / z (m / z = 1027). Since the sulfate of the water-soluble iridium-ruthenium dinuclear aqua complex (8) is hygroscopic, potassium hexafluorophosphate (Tokyo Chemical Industry Co., Ltd.) is added to the sulfate aqueous solution of the iridium-ruthenium dinuclear aqua complex (8). A few drops of a saturated aqueous solution (made by the company) was dropped, and the dark green solid precipitated as hexafluorophosphate of the iridium-ruthenium dinuclear aqua complex (8), which is sparingly soluble in water by counterion exchange, was vacuum filtered and then vacuum dried This was subjected to elemental analysis. The measurement results of the ¹ H-NMR, UV-Vis., Mass spectrometry, and elemental analysis are shown below.

Iridium-ruthenium dinuclear aqua complex (8): [Ru (bpy) ₂ bpmIrCp * (OH ₂ )] (SO ₄ ) ₂ :
¹ H-NMR (D ₂ O, 298K) δ (TSP, ppm) 1.71 (s, 15H, Cp ^* ), 7.42 (t, J = 7Hz, 2H, bpm), 7.50 (t, J = 7Hz, 1H, bpy), 7.55 (t, J = 7Hz, 1H, bpy), 7.70 (d, J = 5Hz, 1H, bpy), 7.75 (d, J = 7Hz, 1H, bpy), 7.95 (t, J = 6Hz, 1H, bpy), 7.97 (t, J = 6Hz, 1H, bpy), 8.09-8.14 (m, 5H, bpm, bpy), 8.18 (t, J = 8Hz, 1H, bpy), 8.47 (d, J = 5Hz, 1H, bpy), 8.53 (d, J = 6Hz, 1H, bpy), 8.54-8.62 (m, 4H, bpm, bpy), 9.45 (td, J = 5, 2Hz, 2H, bpm)
¹³ C-NMR (D ₂ O, 298K) δ (TSP, ppm) 10.97 ( C H ₃ ), 93.54 (η ⁵ - C ₅ (CH ₃ ) ₅ ), 127.26, 127.31, 127.39, 127.58, 130.00, 130.25, 130.32, 130.52, 130.79, 131.03, 154.49, 154.61, 155.15, 156.31, 159.03, 159.75, 159.76, 159.88, 160.20, 160.49, 164.56, 164.77, 169.08, 169.23
UV-Vis. (Nm): 246, 279, 412, 575
Elemental analysis: [Ru (bpy) ₂ bpmIrCp * (OH ₂ )] (PF ₆ ) ₄ : C ₃₈ H ₃₉ N ₈ OF ₂₄ P ₄ RuIr; Theoretical value: C,
30.49; H, 2.63; N, 7.49. Observations: C, 30.28; H, 2.58; N, 7.52.
Mass spectrometry (ESI-MS): m / z [M -SO ₄ + CH ₃ O] ⁺ 1027.0 Theoretical C ₂₈ H ₂₂ N ₈ F ₆ PRu 1027.2

In addition, UV-Vis. Spectrum when [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ was added to [Ru (bpy) ₂ bpm] ²⁺ aqueous solution (1.2 × 10 ^-3 mol / L) Cp ^* Ir (H ₂ O) ₃ ] ²⁺ concentration was measured with various changes from 0 to 1.7 × 10 ⁻³ mol / L. The optical path length was 1 mm. The UV-Vis. Spectrum diagram is shown in the graph of FIG. In the figure, the vertical axis represents absorbance, and the horizontal axis represents wavelength. The curve in the figure shows the UV-Vis. Spectrum at various [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ concentrations, and the arrow indicates the increase in [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ concentration. The state of the increase or decrease in the absorbance of each absorption band is shown. As shown in the figure, the absorption bands at the absorption maximum wavelengths of 412 nm and 575 nm increase in absorbance as the concentration of [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ increases, and the absorption band at the maximum absorption wavelength of 470 nm is [Cp ^* On the contrary, the absorbance decreased with increasing Ir (H ₂ O) ₃ ] ²⁺ concentration. However, in any of the absorption bands, after the concentration of [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ exceeds 1 equivalent to 1.2 × 10 ⁻³ M, that is, [Ru (bpy) ₂ bpm] ²⁺ No change was seen. Furthermore, the graph in the inset of FIG. 6 shows the absorbance at the wavelength of 575 nm and the concentration ratio of [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ / [Ru (bpy) ₂ bpm] ²⁺ , that is, the substance amount ratio. ([Ir] / [Ru]). In the figure, the vertical axis represents absorbance at a wavelength of 575 nm, and the horizontal axis represents [Ir] / [Ru]. As shown in the figure, the absorbance at a wavelength of 575 nm is 1 for [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ concentration of 1.2 × 10 ⁻³ mol / L, that is, [Ru (bpy) ₂ bpm] ^2+. until equivalent was increased in proportion to the concentration of _{^{[Cp * Ir (H 2 O}} ) 3] 2+ , but did not change at higher _{^{[Cp * Ir (H 2 O}} ) 3] 2+ concentration. This indicates that [Ru (bpy) ₂ bpm] ²⁺ and [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ reacted at a 1: 1 mass ratio in aqueous solution to form a binuclear complex. It has been shown.

_{Incidentally, [Ru (bpy) 2 bpm} ] to ²⁺ solution ^{(2.0 × 10 -4 mol / L} ) [Cp * Ir (H 2 O) 3] 2+ 1 equivalent when added [Ru (bpy) ₂ The emission spectrum of bpm] ²⁺ was measured. For the measurement, a 1 cm square four-sided transparent quartz cell was used. The graph of FIG. 7 shows the emission spectrum change diagram. In the figure, the vertical axis represents the emission intensity, and the horizontal axis represents the wavelength. The upper curve in the figure shows the emission spectrum of [Ru (bpy) ₂ bpm] ²⁺ , and the lower curve after adding 1 equivalent of [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ An emission spectrum is shown. The arrow indicates a nearly complete decrease in emission intensity with the addition of [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ . This indicates that [Ru (bpy) ₂ bpm] ²⁺ and [Cp ^* Ir (H ₂ O) ₃ ] ²⁺ reacted at a 1: 1 mass ratio in aqueous solution to form a binuclear complex. It has been shown.

[Complex production example 2: Production of binuclear metal complex (hydride complex)]
The aqua complex (8) synthesized in Example 1 was reacted with an excess amount of formic acid in water (pH 2.0). Specifically, dilute sulfuric acid is added to 0.4 mL of water to adjust the pH to 2.0, and the aqua complex (8) sulfate (1.0 mg, 8.8 × 10 ⁻³ mmol) synthesized as described above is added thereto. Then, argon gas was passed through the aqueous solution to deoxygenate, then formic acid (8.3 mL, 2.2 × 10 ⁻¹ mol) was added and reacted at 333K. When the UV-Vis. Absorption spectrum of the aqueous solution after the reaction was measured, the spectrum of the iridium hydride complex (9) in which the aqua ligand of the aqua complex (8) was replaced with hydride was confirmed. The structure of the iridium hydride complex (9) is as shown in the chemical formula (9). The instrumental analysis data of the iridium hydride complex (9) is shown below.

Iridium hydride complex (9):
¹ H-NMR (H ₂ O, 298K) δ (TSP / D ₂ O, ppm) -11.4 (s, Ir-H), 1.91 (s, 15H, Cp *), 7.41-7.55 (m, 4H, bpm , bpy), 7.65-7.75 (m, 2H, bpm, bpy), 7.86 (d, J = 5Hz, 1H, bpy), 7.98 (d, J = 7Hz, 1H, bpy), 8.05-8.20 (m, 5H , bpm, bpy), 8.32 (m, 1H, bpm, bpy), 8.45-8.65 (m, 6H, bpm, bpy), 9.27 (d, J = 5Hz, 2H, bpm)
UV-Vis. (Nm): 391 (sh), 409, 518, 590

[Complex Production Example 3: Production of Binuclear Metal Complex (Iridium Monovalent Complex)]
Aqua complex (8) was reacted with formic acid in the same manner as in Complex Production Example 2 except that sodium hydroxide was added to water and the pH of water was changed to 4.0 instead of 2.0. When the UV-Vis. Absorption spectrum of the aqueous solution after the reaction was measured, spectra having several absorption maxima (λ _max = 453, 512, 723 nm) extending to the near infrared region (λ> 900 nm) were observed. This spectrum is considered to be derived from the iridium monovalent complex represented by the chemical formula (10). As a reaction mechanism, for example, the aqua complex (8) reacts with 1 equivalent of formic acid to produce an iridium hydride complex (9), and further thermally deprotonated to produce an iridium monovalent complex (10). It is possible that However, this is an example of a mechanism that can be estimated, and does not limit the present invention. The instrumental analysis data is shown below.

Iridium monovalent complex (10):
UV-Vis. (Nm): 409, 453 (sh), 512, 723, 795 (sh)

[Complex Production Example 4: Formation of iridium monovalent complex by deprotonation of iridium hydride complex]
In Complex Production Example 2, deoxygenated 1.5 × 10 ⁻⁴ mol / L dilute sulfuric acid was added to the aqueous solution of iridium hydride complex (9) after reacting aqua complex (8) with formic acid at pH 2.0. The pH was changed from 2.1 to 3.9, and the UV-Vis. absorption spectrum at each pH was measured. The spectrum diagram is shown in the graph of FIG. In the figure, the horizontal axis represents wavelength (nm) and the vertical axis represents absorbance. Moreover, the arrow shows the change of the light absorbency accompanying decrease in pH (increase in acidity). As shown in the figure, with decreasing pH (increasing acidity), the absorbance at the maximum absorption wavelengths of 409 nm and 591 nm increased, while the absorbance at 512 nm and 723 nm decreased. Further, the graph of FIG. 9A shows the relationship between the absorbance at a wavelength of 512 nm and pH in FIG. In the figure, the horizontal axis is pH, and the vertical axis is absorbance. As shown, the absorbance at a wavelength of 512 nm gradually decreased from about 0.8 to about 0.4 as the pH decreased from about 4 to about 2. Further, in the graph of FIG. 9B, the logarithm log ([Ir-H] / [Ir]) of the value obtained by dividing the iridium hydride complex (9) concentration by the iridium monovalent complex (10) concentration, pH, The relationship is shown. In the figure, the horizontal axis represents pH, and the vertical axis represents log ([Ir-H] / [Ir]). As shown in the figure, a straight line having an inclination of −1.0 and an intercept of 3.2 was obtained. log from ([Ir-H] / [ Ir]) is equal to pK _a -pH, pK _a of the iridium hydride complex (9) was confirmed to be 3.2.

Further, nanosecond laser flash photolysis of an aqueous solution of the iridium hydride complex (9) with a visible light laser was performed. As described above, the aqueous solution was prepared by reacting the aqua complex (8) with formic acid at pH 2.0, and then the aqueous solution of iridium hydride complex (9) (sulfuric acid, iridium hydride complex (9) concentration 1.8 × 10 ⁻⁴ M, pH 2. 8) was used. The irradiation light output was 7 mJ / pulse. As the excitation wavelength, a wavelength (420 nm) corresponding to the characteristic absorption band (λ _max = 409 nm) of the iridium hydride complex (9) was used. This absorption band is considered to be an MLCT absorption band derived from the ruthenium (II) complex site of the iridium hydride complex (9). FIG. 10 shows a transient absorption spectrum by the nanosecond laser flash photolysis. In the figure, the horizontal axis represents wavelength (nm) and the vertical axis represents optical density difference (ΔO.D.). The arrow indicates the change in optical density difference after irradiation. A transient absorption spectrum was observed at intervals of 3 milliseconds after the excitation laser pulse irradiation. As shown, the optical density difference decreased after absorption at wavelengths of 510 nm and 720 nm immediately after irradiation, while the optical density difference increased after 410 nm and 600 nm bleaching. That is, the absorption maximum wavelength immediately after irradiation coincided with λ _max of the iridium monovalent complex (10). This indicates that when the iridium hydride complex (9) was excited by a visible light laser, the Ir—H bond was cleaved to cause deprotonation and acted as an acid generator.

Furthermore, a transient absorption spectrum derived from the iridium monovalent complex (10) was obtained even when laser light irradiation was carried out at 600 nm instead of the excitation wavelength of 409 nm. That is, it was confirmed that the iridium hydride complex (9) can be photodeprotonated from the metal-hydride bond with light having a longer wavelength than that of the conventional hydride complex. In the conventional organometallic iridium hydride complex [Cp ^* Ir (bpy) H] ⁺ (Cp ^* = pentamethylcyclopentadienyl, bpy = 2,2′-bipyridine), the wavelength capable of photodeprotonation is 500 nm. Was less than. The organometallic iridium hydride complex [Cp ^* Ir (bpy) H] ⁺ is disclosed in JP-A-2005-104880, Suenobu, T .; Guldi, DM; Ogo, S .; Fukuzumi, S., Angew. Chem. , Int. Ed. 2003, 42, 5492-5495. And Abura, T .; Ogo, S .; Watanabe, Y .; Fukuzumi, S., J. Am. Chem. Soc. 2003, 125, 4149-4154. It is described in.

Further, the same nanosecond laser flash photolysis was carried out by replacing water with heavy water, and the rate constant of the protonation reaction of the iridium (I) metal center of the iridium monovalent complex (10) in water and heavy water (rate in water comparing the rate constant k _D) of the constant k _H and deuterium. The vertical axis of the graph in FIG. 11 shows the optical density difference at a wavelength of 512 nm, and the horizontal axis shows the laser irradiation time. In the figure, the curve indicated as “Ir-H” indicates the spectrum when irradiated with underwater laser, and the curve indicated as “Ir-D” indicates the spectrum when irradiated with laser in heavy water. Further, the inset of FIG. 11 is obtained by converting the vertical axis of FIG. 11 into ln [(A _inf −A) / (A _inf −A ₀ )]. A is the optical density difference at the irradiation time, A _inf is the optical density difference at infinite time after laser pulse irradiation, and A ₀ is the optical density difference immediately after irradiation. As shown in the figure, the relationship between ln [(A _inf −A) / (A _inf −A ₀ )] and irradiation time was obtained as a linear line in both water and heavy water. From this, it was calculated that k _H = 1.1 × 10 ² s ^−1, and further the kinetic deuterium isotope effect (k _H / k _D = 1.4) was confirmed. This deuterium isotope effect indicates that proton (or deuterium) desorption occurs in the nanosecond laser flash photolysis. This also indicates that the product in Complex Production Example 2 is a hydride complex.

  In addition, femtosecond laser flash photolysis was performed under the same conditions. The excitation wavelength was 420 nm. The graph of FIG. 12 shows a spectrum diagram of femtosecond laser flash photolysis in water. In the figure, the horizontal axis represents wavelength (nm) and the vertical axis represents the optical density difference. Arrows on the right and left sides of the numbers representing the time after laser pulse irradiation indicate an increase in time. Furthermore, in the curve (spectrum) indicating the absorbance, the arrow near the wavelength of 512 nm indicates that the absorbance near the maximum absorption wavelength of 512 nm continuously increased from 90 picoseconds to 700 picoseconds. Formation of iridium monovalent complex (10) was confirmed from the absorbance near the maximum absorption wavelength of 512 nm. That is, it shows that the Ir—H bond of the iridium hydride complex (9) was cleaved to cause deprotonation and acted as an acid generator. As a detailed mechanism, a transition between excited states occurs from time 0 to 70 picoseconds, and from the time 90 picoseconds to 700 picoseconds, the cleavage of the Ir—H bond (desorption) of the iridium hydride complex (9) occurs. It is considered that the generation of the iridium monovalent complex (10) by protonation occurs. However, this is an example of a mechanism that can be estimated and does not limit the present invention.

Furthermore, the same femtosecond laser flash photolysis was performed in place of heavy water, and the rate constant of the deprotonation reaction from the iridium-hydride bond of the iridium hydride complex (9) in water and heavy water (rate constant in water) k _H and the rate constant k _D ) in heavy water were compared. The vertical axis of the graph in FIG. 13 shows the optical density difference at a wavelength of 512 nm, and the horizontal axis shows the time after pulse laser irradiation. In the figure, the curve indicated as “Ir-H” indicates the spectrum when irradiated with underwater laser, and the curve indicated as “Ir-D” indicates the spectrum when irradiated with laser in heavy water. In the measurement of the figure, the initial concentration of the iridium hydride complex (9) was 9.0 × 10 ⁻⁴ mol / L, and the optical path length was 2 mm. Further, the inset of FIG. 13 is obtained by converting the vertical axis of FIG. 13 into ln [(A _inf −A) / (A _inf −A ₀ )]. A is the optical density difference at that time after irradiation, A _inf is the optical density difference at infinite time after irradiation, and A ₀ is the optical density difference immediately after irradiation. As shown in the figure, the relationship between ln [(A _inf −A) / (A _inf −A ₀ )] and irradiation time was obtained as a linear line in both water and heavy water. From this, it was calculated that k _H = 6.6 × 10 ⁹ s ⁻¹ and k _H / k _D = 1.0, and it was confirmed that femtosecond laser flash photolysis does not show deuterium isotope effect.

[Reference Example 1: Formic acid decomposition and hydrogen production using formic acid decomposition catalyst]
The iridium-ruthenium dinuclear aqua complex (8) produced in Complex Production Example 1 was dissolved in 2 mL of water to obtain an aqueous solution. The aqueous solution was purged with an argon gas stream for 20 minutes for deoxygenation, 0.83 mol / L formic acid was added to water, and sodium hydroxide was added to adjust the pH to 3.8. All the above operations were performed at room temperature (298K). When this aqueous solution was allowed to stand at 298 K for 10 to 20 minutes as it was, the generation of gas that could be clearly confirmed visually started, and the gas was continuously generated. As a result of GC analysis of this gas, it was a 1: 1 mixed gas of hydrogen and carbon dioxide. That is, hydrogen and carbon dioxide could be produced by decomposing formic acid with a catalytic amount of aqua complex with respect to formic acid.

Furthermore, operations similar to those described above were carried out by varying the concentration of the aqua complex (8), and the amount of H ₂ gas generated was measured. The result is shown in the graph of FIG. In the figure, the horizontal axis represents the concentration of the aqua complex (8) in the aqueous solution. The vertical axis represents the amount of H ₂ gas generated per 60 minutes of reaction time, and is a calculated value from the amount of H ₂ gas generated from the time 15 minutes after the start of the reaction until 45 minutes have passed. As shown in the figure, the concentration of the aqua complex (8) and the amount of H ₂ gas generated show a proportional relationship (linear relationship), and one molecule of the aqua complex (8) catalyzes the decomposition reaction of one molecule of formic acid. confirmed.

The reason why the aqueous solution was allowed to stand at 298 K and it took 10 to 20 minutes to start generation of H ₂ gas is not clear. This is because, for example, residual oxygen that cannot be removed by purging with an argon gas stream reacts with the aqua complex (8), and after the oxygen is consumed reductively, the reaction between the aqua complex (8) and formic acid starts. it is conceivable that. However, this is merely an example of a mechanism that can be estimated, and does not limit the present invention.

[Reference Example 2: Formic acid concentration dependence in formic acid decomposition and hydrogen production]
Fixing the aqua complex concentration (8) to 0.5 mM, perform decomposition of the formic acid formic acid concentration, except for adjusting to 3.8 pH with sodium hydroxide causes variously changed in the same manner as in Reference Example 1, the H ₂ gas The amount generated was measured. The result is shown in the graph of FIG. In the figure, the horizontal axis represents the formic acid concentration (mol / L). The vertical axis represents the number of rotations of the catalyst per hour (TOF, Turn Over Frequency). TOF is a value obtained by dividing the number of hydrogen molecules generated per hour by the number of molecules of the aqua complex (8) (the same applies hereinafter). As shown in the figure, the relationship between formic acid concentration and TOF showed a saturation curve. From this, it is considered that the reaction between the aqua complex (8) and formic acid is an equilibrium reaction.

[Reference Example 3: pH dependence in formic acid decomposition and hydrogen production]
And fixing the concentration of aqua complex (8) to 0.5 mM, except that pH was changed variously by changing the amount of addition of sodium hydroxide performs decomposition of formic acid in the same manner as in Reference Example 1, the H ₂ gas The amount generated was measured. The result is shown in the graph of FIG. In the figure, the horizontal axis represents the initial pH of the formic acid aqueous solution. The vertical axis represents the number of rotations of the catalyst per hour (TOF, Turn Over Frequency). As shown in the figure, TOF reached its maximum at pH = 3.8, and its maximum value was 426h ⁻¹ . This value is the world's highest value known as the TOF of the formic acid decomposition reaction in room temperature water until the filing date of the present application.

Formic acid decomposition using the aqua complex (8), the iridium hydride complex (9) or iridium monovalent complex (10) produced by the reaction of the aqua complex (8) with formic acid acts as a catalyst. It is considered that the hydrogen generation rate increases with the increase. More specifically, for example, as shown in the scheme of FIG. 16, a formate complex is generated by the reaction of an aqua complex and a formate anion, and after the elimination of carbon dioxide, a hydride complex is formed, and the hydride complex reacts with a proton to generate hydrogen. Is considered to occur. However, this is only an example of a mechanism that can be estimated, and does not limit the present invention. In the scheme of FIG. 16, “Ir ^III ” and “Ir ^I ” mean structures obtained by removing the ligand L from the binuclear metal complex represented by the chemical formula (7), and “Ir ^III ” An iridium atom represents a trivalent structure, and “Ir ^I ” represents a structure in which the iridium atom is monovalent.

[Example 1: Decomposition of formic acid and production of deuterated hydrogen with formic acid decomposition catalyst]
Formic acid was decomposed under various pH conditions in the same manner as in Reference Example 3 except that deuterated formic acid DCOOH was used instead of normal formic acid HCOOH. The formic acid decomposition reaction was performed until all the formic acid was consumed and no hydrogen was generated, and the abundance ratio of H ₂ and HD in the generated hydrogen gas was measured by gas chromatography. The results are shown in the graph of FIG. In the figure, the horizontal axis represents the initial pH of the formic acid aqueous solution. The vertical axis represents the abundance ratio (molar ratio,%) of H ₂ or HD in the generated hydrogen gas. In the figure, the white circle (◯) line graph shows the pH dependence of the HD abundance ratio, and the black circle (●) line shows the pH dependence of the H ₂ abundance ratio. As shown in the figure, the H ₂ abundance ratio was high in the low pH region near pH 2, but the HD abundance ratio was high in the region where the pH was about 2.5 or higher. In the vicinity of pH 3.5, the HD abundance ratio was 79% of the maximum value (H ₂ abundance ratio 21%). That is, according to the present example, deuterated hydrogen HD could be produced with extremely high selectivity in a wide pH range using deuterated formic acid DCOOH.

In the decomposition of deuterated formic acid DCOOH using aqua complex (8), as in the decomposition of HCOOH, for example, the reaction of aqua complex and formate anion produces a complex of deuterated formic acid DCOOH, and carbon dioxide. It can be considered that a deuterated hydride complex is formed through the elimination of. Further, it is presumed that this deuterated hydride complex becomes a hydride complex by the H / D exchange reaction, and deuterated ion D ⁻ reacts with protons to generate deuterated hydrogen HD. The presumed reaction mechanism is shown in the schemes of FIGS. In the schemes of FIGS. 2 and 3, “Ir ^III ” represents a structure obtained by removing the ligand L from the trivalent iridium atom in the binuclear metal complex represented by the chemical formula (7). And As described later, since the value of the kinetic deuterium isotope effect between the formic acid HCOOH decomposition reaction and the deuterated formic acid DCOOH decomposition reaction was 2.0, as shown in the scheme of FIG. It is considered that the stage where becomes a deuterated hydride complex is the rate-determining stage. The reason why the H ₂ gas is selectively generated at a low pH is presumably because, for example, the hydride of the hydride complex accelerates the process of H / D exchange with protons in the solvent. However, these are merely examples of mechanisms that can be estimated, and do not limit the present invention.

Furthermore, the graph of FIG. 4 shows the pH dependence of TOF in Example 1 above. In the figure, the horizontal axis represents the initial pH of the formic acid aqueous solution. The vertical axis represents the number of rotations of the catalyst per hour (TOF, Turn Over Frequency). In the figure, the broken line indicated by the solid line indicates the pH dependence of TOF in the deuterated formic acid DCOOH decomposition reaction of Example 1. The broken line shown by the dotted line shows the pH dependence of TOF in the formic acid HCOOH decomposition reaction of Reference Example 3, which is the same as FIG. As shown in the figure, the TOF of the deuterated formic acid DCOOH decomposition reaction in Example 1 was maximum at pH 3.8, and the maximum value was 215 h ⁻¹ . This value was about half of the maximum TOF value (426 h ⁻¹ ) of the formic acid HCOOH decomposition reaction in Reference Example 3, but is extremely high as the TOF of the formic acid decomposition reaction in water at room temperature. In addition, as shown in the figure, the pH dependence of TOF shows the same tendency between the deuterated formic acid DCOOH decomposition reaction and the formic acid HCOOH decomposition reaction, and the deuterated formic acid DCOOH decomposition reaction TOF is the same formic acid HCOOH at the same pH. About half of the decomposition reaction. From this, it was confirmed that the value of the kinetic deuterium isotope effect between the formic acid HCOOH decomposition reaction and the deuterated formic acid DCOOH decomposition reaction is 2.0.

[Example 2]
Deuterium D ₂ could be obtained with high selectivity in the same manner as in Example 1 except that heavy water (D ₂ O) was used as a solvent. It was possible to obtain deuterium D ₂ with high selectivity both when deuterated formic acid DCOOH was used and when non-deuterated formic acid HCOOH was used.

  As described above, according to this example, an iridium-ruthenium binuclear complex was used as a catalyst for formic acid decomposition, deuterated formic acid was decomposed under mild conditions in room temperature water, and expensive deuterated hydrogen (HD) gas Can be produced with high pH selectivity, high efficiency and high selectivity.

As described above, according to the present invention, at least one of deuterated hydrogen (HD) and deuterium (D ₂ ) can be safely, simply and extremely efficiently produced at low cost from stable and highly safe formic acid. Can be manufactured. According to the production method of the present invention, for example, a hydrogen isotope gas can be produced inexpensively and easily without using a large-scale apparatus or the like. As a result, for example, at least one of deuterium (D ₂ ) and deuterium hydride (HD) can be produced in the necessary amount when needed, from laboratory production to industrial scale mass production. It is also possible to respond sufficiently. The present invention is useful in, for example, research on the mechanism of a fuel cell, synthesis of various compounds including organic compounds, determination of a hydrogen position by structural analysis, and the like. According to the present invention, hydrogen isotope gas can be obtained without toxic by-products, and a great energy saving effect can be obtained as compared with conventional method examples.

  Since the formic acid decomposition catalyst of the present invention has good rotational efficiency, it can contribute to environmental load suppression and resource saving. In addition, the formic acid decomposition catalyst of the present invention may be used by dissolving it in an organic solvent, for example, but if the hydrogen isotope gas is generated using only water as a solvent, the undesirable influence on the environment is further reduced. can do.

  Since hydrogen isotope gas is in demand in a wide range of fields, the scope of application of the present invention is also wide. For example, a hydrogen isotope is an indispensable strategic material for use in the nuclear industry, and a technique for producing a high-purity hydrogen isotope gas is required. Hydrogen isotopes are also used for research on isotope labeling for product identification in pharmaceutical synthesis, enzyme reaction activation mechanisms such as hydrogenases, and structures and functions of metal hydrides in oxygen-hydrogen fuel cells and secondary battery negative electrodes. Is also used. Therefore, the production method of the present invention and the formic acid decomposition catalyst of the present invention are also useful for these. Furthermore, the application range of the present invention is not limited to the above, and can be used in all technical fields that require hydrogen isotope gas.

Claims (14)

A formic acid decomposition catalyst containing a binuclear metal complex represented by the following formula (1), a tautomer or stereoisomer thereof, or a salt thereof, formic acid, and a solvent, wherein at least one of the formic acid and the solvent Preparing a formic acid solution, one of which is deuterated,
Formic acid decomposition step of decomposing formic acid by standing, heating or irradiating the solution to generate at least one of deuterium (D ₂ ) and deuterated hydrogen (HD),
A production method for producing at least one of deuterium (D ₂ ) and deuterium hydride (HD).

In the formula (1),
M ¹ and M ² are transition metals, which may be the same or different,
Ar is a ligand having aromaticity and may or may not have a substituent, and when it has a substituent, the substituent may be one or plural,
R ^{1 to} R ⁵ are each independently a hydrogen atom, an alkyl group, a phenyl group, or a cyclopentadienyl group,
R ^{12 to} R ²⁷ are each independently a hydrogen atom, an alkyl group, a phenyl group, a nitro group, a halogen group, a sulfonic acid group (sulfo group), an amino group, a carboxylic acid group (carboxy group), a hydroxy group, or an alkoxy group. Group,
Alternatively, R ¹⁵ and R ¹⁶ may be combined to form —CH═CH—, that is, R ¹⁵ and R ¹⁶ may be combined with their bound bipyridine ring to form a phenanthroline ring. The H in —CH═CH— is independently an alkyl group, a phenyl group, a nitro group, a halogen group, a sulfonic acid group (sulfo group), an amino group, a carboxylic acid group (carboxy group), or a hydroxy group. Or may be substituted with an alkoxy group,
R ²³ and R ²⁴ together may form -CH = CH-, that is, R ²³ and R ²⁴ together with their bound bipyridine ring may form a phenanthroline ring. H in -CH = CH- is independently an alkyl group, phenyl group, nitro group, halogen group, sulfonic acid group (sulfo group), amino group, carboxylic acid group (carboxy group), hydroxy group, or May be substituted with an alkoxy group,
L is any ligand or absent,
m is a positive integer, 0, or a negative integer.   The method according to claim 1, wherein in the formula (1), the substituents on Ar are each independently an alkyl group, a phenyl group, or a cyclopentadienyl group.   In the above formula (1), L is a water molecule, hydrogen atom, alkyloside ion, hydroxide ion, halide ion, carbonate ion, trifluoromethanesulfonate ion, sulfate ion, nitrate ion, formate ion, or acetic acid. The manufacturing method of Claim 1 or 2 which is an ion or does not exist. M ¹ is, ruthenium, osmium, iron, manganese, chromium, cobalt, The method according to any one of iridium or claims 1 rhodium, 3. The production method according to any one of claims 1 to 4, wherein M ² is iridium, ruthenium, rhodium, cobalt, osmium, nickel, or platinum.   m is 2, 3 or 4, The manufacturing method as described in any one of Claim 1 to 5. The production method according to any one of claims 1 to 6, wherein the binuclear metal complex of the formula (1) is a binuclear metal complex having a structure represented by the following formula (6).

In the formula (6),
R ^{6 to} R ¹¹ are each independently a hydrogen atom, an alkyl group, a phenyl group, a nitro group, a halogen group, a sulfonic acid group (sulfo group), an amino group, a carboxylic acid group (carboxy group), a hydroxy group, or an alkoxy group. Group,
M ¹ , M ² , R ^{1 to} R ⁵ , R ^{12 to} R ²⁷ , L and m are the same as those in the formula (1). The production method according to claim 7, wherein the binuclear metal complex represented by the formula (6) is a binuclear metal complex having a structure represented by the following formula (7).

In said Formula (7), L and m are the same as said Formula (6). The production method according to claim 8, wherein the binuclear metal complex represented by the formula (7) is a binuclear metal complex having a structure represented by any of the following formulas (8) to (11).

  The manufacturing method according to any one of claims 1 to 9, wherein in the formic acid solution, the solvent contains water, and at least one of the water and the formic acid is deuterated.   In the formic acid solution, one of the water and the formic acid is deuterated, the initial pH or initial pD before the formic acid decomposition step is 2.5 or more, and deuterated hydrogen (HD) in the formic acid decomposition step The production method according to claim 10, wherein deuterated hydrogen (HD) is produced. In the formic acid solution, water is the D ₂ O, the formic acid decomposition step to generate deuterium (D ₂₎ in, to produce a deuterium (D _2), The method according to Claim 10. In the formic acid solution, at least one of the solvent and the formic acid is tritiated instead of deuteration, and tritium instead of at least one of deuterium (D ₂ ) and deuterated hydrogen (HD). The production method according to claim 1, wherein at least one of (T ₂ ) and tritium hydride (HT) is produced.   The compound includes at least one compound selected from the group consisting of the binuclear metal complex represented by the formula (1), a tautomer, a stereoisomer, and a salt thereof, A catalyst for formic acid decomposition used in the production method according to the item.

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