JP2010083730A - Method for producing at least either deuterium (d2) or hydrogen deuteride (hd) and catalyst for formic acid decomposition used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for safely, easily and efficiently producing at least hydrogen deuteride (HD) or deuterium (D<SB>2</SB>) at low cost. <P>SOLUTION: The method for producing at least either deuterium (D<SB>2</SB>) or hydrogen deuteride (HD) comprises: a preparation step of preparing an aqueous formic acid solution containing a catalyst for formic acid decomposition, formic acid and water, provided that the catalyst contains at least one compound chosen from the group consisting of a specific mononuclear rhodium complex, a tautomer thereof, a stereoisomer thereof and a salt thereof and at least either the formic acid or the water is deuterated; and a formic acid decomposition step of decomposing formic acid by at least one step chosen from: a step of leaving the aqueous formic acid solution still; a step of heating the solution; and a step of exposing the solution to light. <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. Currently, deuterium (D) and tritium (T) are used, for example, as fuels for fusion reactors. Tritium (T) has safety problems due to its radioactivity, while deuterium (D) is safe and stable because it is non-radioactive, and its use is particularly 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. Currently, deuterium (D ₂ ) is produced by electrolyzing heavy water (D ₂ O) on a platinum electrode. In addition, deuterated hydrogen (HD) is a mixture of deuterium (D ₂ ) and hydrogen (H ₂ ) and deuterated hydrogen (HD) and deuterium by H / D exchange reaction using a metal-supported solid catalyst. (D ₂₎ and obtain a mixed gas of hydrogen (H _2), are prepared by separating only hydrogen deuteride (HD) at cryogenic distillation separation method from the mixed gas.

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 a high deuterium hydrogen (HD) selectivity is used to adsorb deuterium hydrogen (HD) contained in the mixed gas, and then the deuterium under a predetermined low pressure condition. This is a method of desorbing and recovering hydrogen hydride (HD).
JP 2004-160294 A

However, the conventional method for producing D ₂ is dangerous and costly. In addition, in the conventional HD production method, deuterated hydrogen (HD) must be isolated from the mixed gas in an equilibrium state, and only deuterated hydrogen (HD) cannot be obtained in high yield. , Costly and expensive. Therefore, a method capable of producing deuterium (D ₂ ) or deuterated hydrogen (HD) safely, simply and efficiently is desired.

Accordingly, the present invention provides at least one of deuterium hydrogen (HD) and deuterium (D ₂ ) (hereinafter sometimes referred to as “hydrogen isotope gas”) safely, simply and efficiently at low cost. The purpose is to provide a method for producing the product.

前記式（１）中、
Rhは、ロジウムの原子またはイオンであり、
Arは、芳香族性を有する配位子であり、置換基を有していても有していなくても良く、
置換基を有する場合、前記置換基は１でも複数でも良く、
R¹〜R⁵は、それぞれ独立に、水素原子または任意の置換基であり、
Lは、任意の配位子であるか、または存在せず、
mは、正の整数、０、または負の整数である。 As a result of diligent research to solve the above problems, the present inventors have used deuterium (D ₂ ) and deuterium hydrogen (D ₂ ) and deuterated hydrogen ( We have found that at least one of (HD) can be produced stably under mild conditions. More specifically, the production method of the present invention includes:
A method for producing at least one of deuterium (D ₂ ) and deuterium hydride (HD),
Formic acid decomposition catalyst, formic acid and water, comprising at least one compound selected from the group consisting of rhodium mononuclear metal complexes represented by the following formula (1), tautomers, stereoisomers and salts thereof Preparing a formic acid aqueous solution in which at least one of the formic acid and the water is deuterated, and
A formic acid decomposition step of decomposing formic acid by at least one step selected from the group consisting of a step of standing the formic acid aqueous solution as it is, a step of heating the solution, and a step of irradiating the solution with light.
In the formic acid decomposition step, at least one of deuterium (D ₂ ) and deuterated hydrogen (HD) is generated.

In the formula (1),
Rh is a rhodium atom or ion;
Ar is an aromatic ligand and may or may not have a substituent.
When having a substituent, the substituent may be one or plural,
R ^{1 to} R ⁵ are each independently a hydrogen atom or an arbitrary substituent,
L is any ligand or absent,
m is a positive integer, 0, or a negative integer.

According to the production method of the present invention, at least one of deuterium (D ₂ ) and deuterated hydrogen (HD) is safely, simply and efficiently under mild conditions from formic acid which is a stable and highly safe substance. In particular, it can be manufactured at low cost. According to the production method of the present invention, at least one of deuterium (D ₂ ) and deuterium hydride (HD) can be produced in a necessary amount when necessary. It can respond enough until it reaches mass production. 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).

  Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments.

[Rhodium mononuclear metal complex]
In the rhodium mononuclear metal complex represented by the formula (1), the ligand Ar is not particularly limited and may be any ligand. For example, 2,2′-bipyridine, 2 2,2 ', 6,6',-bipyrimidine, 2,2 ', 5,5'-bipyrazine, 1,10-phenanthroline and the like. Other substituents and the like are not particularly limited, but are as follows, for example.

In the formula (1), R ^{1 to} R ⁵ are preferably each independently a hydrogen atom, an alkyl group, a phenyl group, or a cyclopentadienyl group. The alkyl group is preferably a linear or branched alkyl group having 1 to 6 carbon atoms, and more preferably a methyl group, an ethyl group, or a butyl group. R ^{1 to} R ⁵ are particularly preferably all methyl groups. In addition, for example, it is also preferable that R ^{1 to} R ⁵ are all hydrogen atoms.

  In the 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, acetate ion. Or a hydride ion or preferably absent. Although it does not restrict | limit especially as an alkoxide ion, The alkoxide ion induced | guided | derived from a C1-C6 linear or branched alcohol is preferable, for example, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl Examples thereof include alkoxide ions derived from alcohol, sec-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, and the like.

  Note that the ligand L in the formula (1) may be relatively easily substituted or eliminated depending on the type. As an example, the ligand L is a hydroxide ion in a basic aqueous solution, a water molecule in a neutral, weakly acidic or strongly acidic aqueous solution, an alkoxide ion in an alcohol solvent, It may be desorbed by heat. However, this description is only an example of a possible mechanism and does not limit the present invention.

  In the formula (1), m is determined by the charge of the rhodium atom or ion and the charge of each ligand in the formula (1), and is preferably 0 to 6, for example, 0, 1 More preferably 2, 3, 4, or 5.

前記式（２）中、
R⁶〜R¹³は、それぞれ独立に、水素原子もしくは任意の置換基であり、
または、R⁹およびR¹⁰は、一体となって-CH=CH-を形成しても良く、前記-CH=CH-におけるHは、それぞれ独立に、任意の置換基で置換されていても良く、
Q⁶〜Q¹³は、それぞれ独立に、CまたはN⁺であり、
または、同一のX（Xは、６〜１３のいずれかの整数）を有するQ^XとR^Xのうち少なくとも一つが、一体となってNであっても良く、
Rh、R¹〜R⁵、Lおよびmは、前記式（１）と同じである。 The rhodium mononuclear metal complex represented by the formula (1) is preferably a rhodium mononuclear metal complex represented by the following formula (2).

In the formula (2),
R ^{6 to} R ¹³ are each independently a hydrogen atom or an arbitrary substituent,
Alternatively, R ⁹ and R ¹⁰ together may form —CH═CH—, and each H in —CH═CH— may be independently substituted with an arbitrary substituent. ,
Q ^{6 to} Q ¹³ are each independently C or N ⁺
Alternatively, at least one of Q ^X and R ^X having the same X (X is an integer of 6 to 13) may be N together,
Rh, R ^{1 to} R ⁵ , L and m are the same as in the above formula (1).

In the formula (2),
R ^{6 to} R ¹³ are each independently a hydrogen atom, alkyl group, phenyl group, benzyl group, nitro group, halogen group, sulfonic acid group (sulfo group), amino group, carboxylic acid group (carboxy group), hydroxy group Or an alkoxy group is more preferable. The alkyl group is preferably a linear or branched alkyl group having 1 to 6 carbon atoms, and more preferably a methyl group, an ethyl group, or a butyl group. The alkoxy group is preferably a linear or branched alkoxy group having 1 to 6 carbon atoms. Or, R ⁹ and R ¹⁰ together may form —CH═CH—, and each H in —CH═CH— independently represents an alkyl group, a phenyl group, a benzyl group, or 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. The alkyl group is preferably a linear or branched alkyl group having 1 to 6 carbon atoms, and more preferably a methyl group, an ethyl group, or a butyl group. The alkoxy group is preferably a linear or branched alkoxy group having 1 to 6 carbon atoms.

From the viewpoint of obtaining at least one of deuterium (D ₂ ) and deuterium hydride (HD) in a higher yield, it is a rhodium mononuclear metal complex represented by the formula (2), wherein the formula (2) Among them, it is more preferable that R ⁶ and R ¹³ are hydrogen. In the formula (2), it is more preferable that R ^{6 to} R ¹³ are all hydrogen atoms. In Formula (2), it is more preferable that Q ^{6 to} Q ¹³ are all C (carbon atoms).

前記式（３）中、
Rh、Lおよびmは、前記式（２）と同じである。 In the formic acid decomposition catalyst of the present invention, the rhodium mononuclear metal complex represented by the formula (2) is more preferably a rhodium mononuclear metal complex represented by the following formula (3).

In the formula (3),
Rh, L and m are the same as in the above formula (2).

Furthermore, the rhodium mononuclear metal complex represented by the formula (3) is particularly preferably a rhodium mononuclear metal complex represented by any of the following formulas (4) to (6). That is, in the rhodium mononuclear metal complex represented by the formula (3), the ligand L is a water molecule (rhodium mononuclear metal complex (4)) or a hydride ion (rhodium mononuclear metal complex (5)). Or is absent (rhodium mononuclear metal complex (6)). The ligand L of the complex represented by the formula (3) is not limited thereto, and is preferably, for example, a methoxide ion or a carbonate ion, a sulfate ion, a nitrate ion, or a formate ion. These ligands may be used.

Among the rhodium mononuclear metal complexes represented by the formula (1), the compounds other than the formula (3) are preferably represented by the compound numbers (7) to (25) in the following Table 1 and Table 2, for example. And rhodium mononuclear metal complexes. The individual structures of the compounds (7) to (25) are represented by combinations of R ^{1 to} R ⁵ , M ¹ , M ² and Ar in the formula (1). Furthermore, the compounds which can be represented by the formula (2) represents also R ⁶ to R ¹³ and Q ⁶ to Q ^13. In the rhodium mononuclear metal complexes (7) to (25), the ligand L is the same as that in the formula (1) or (2) and is not particularly limited. For example, a water molecule, a hydrogen atom, a methoxide ion, It is preferred that they are hydroxide ions, carbonate ions, formate ions, nitrate ions or are absent. m is determined by the charge possessed by the rhodium atom or ion and the charge possessed by each ligand, but is preferably 0 to 5, for example. In addition, rhodium mononuclear complex complexes, tautomers and stereoisomers thereof, and salts thereof shown in Table 1 and Table 2 below are all described in the present specification and belong to the present invention by those skilled in the art. It can be manufactured easily without undue trial and error based on common sense in the technical field.

In the catalyst for formic acid decomposition of the present invention, the rhodium mononuclear metal complex represented by the above formula (1) is a tautomer or stereoisomer (eg, geometric isomer, conformer and optical isomer). In the case where isomers such as these are present, any of them can be used for the formic acid decomposition catalyst of the present invention. For example, when an enantiomer is present, both R and S isomers can be used. Furthermore, the rhodium mononuclear metal complex represented by the formula (1) or a salt of an isomer thereof can also be used for the formic acid decomposition catalyst of the present invention. In the salt, the counter ion of the rhodium mononuclear metal complex represented by the formula (1) is not particularly limited. Examples of the anion include hexafluorophosphate ion (PF ₆ ⁻ ) and 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.), hypohalous acid ion (e.g. hypofluorite ion, hypochlorite ion, hypobromous acid ion, hypoiodous acid ion Etc.), halite ion (eg, fluorite ion, chlorite ion, bromate ion, iodate ion, etc.), halogenate ion (eg, fluorate ion, chlorate ion, bromate ion) Etc. iodate ion), 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 pentafluoro And phenylborate ion [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. For example, a linear or branched alkyl group having 1 to 6 carbon atoms is preferable. 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 Rhodium Mononuclear Metal Complex]
The production method of the rhodium mononuclear 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 particularly limited. However, it may be manufactured by any method. Compound (1) can be appropriately produced with reference to, for example, a known method for producing a metal complex. Moreover, for example, when the compound (1) can be obtained as a commercial product, the commercial product may be used as it is.

Compound (1) can be synthesized (produced) according to Scheme 1 below, for example.

  The scheme 1 can be performed as follows, for example. Various reaction conditions, such as reaction temperature, reaction time, and solvent, are examples, are not limited thereto, and can be changed as appropriate.

(Process 1)
In the above scheme 1, in step 1, for example, reaction conditions are appropriately set with reference to documents such as Kenichi Fujita, Yoshinori Takahashi, Maki Owaki, Kazunari Yamamoto, and Ryohei Yamaguchi, Organic. Letters. 2004, 6, 2785-2788. Can be done. Specifically, it is as follows, for example. That is, first, RhX ₃ (compound (101), X is halogen) is dissolved in an alcohol solvent (methanol, ethanol, etc.) to obtain a solution. RhX ₃ may be, for example, a hydrate. The concentration is not particularly limited, but is, for example, 0.01 to 10 mol / L, preferably 0.01 to 5 mol / L, and more preferably 0.1 to 1 mol / L. Cp ^R (compound (102), the structure is as shown in Scheme 1) was added to this solution under an inert gas (nitrogen, argon, etc.) atmosphere, and the reaction was carried out to give the target complex [Cp ^R RhX ₂ ] ₂ (103) is obtained. The substance amount (number of moles) of Cp ^R is not particularly limited, but is, for example, 1 to 20 times, preferably 1 to 10 times, more preferably 1 to 5 times the amount of substance (number of moles) of RhX _3. . Although reaction temperature in particular is not restrict | limited, For example, it is 30-64 degreeC, Preferably it is 50-64 degreeC, More preferably, it is 55-62 degreeC. Although the reaction time is not particularly limited, it is, for example, 1 to 30 hours, preferably 10 to 24 hours, and more preferably 15 to 24 hours. After completion of the reaction, the obtained complex (103) may be isolated, purified, etc. as necessary. If there is no problem, the complex (103) is used as it is in the next reaction step without isolation, purification, etc. Also good. The method of isolation, purification, etc. is not particularly limited and can be carried out according to a conventional method. For example, methods such as evaporation, filtration, washing, column chromatography, recrystallization method, etc. can be used alone or in appropriate combination. Can be used.

(Process 2)
In the scheme 1, the step 2 is performed by, for example, Andrew Nutton, Pamela M. Bailey, and Peter M. Maitlis. Journal of the Chemical Society, Dalton Transactions. 1981, 9, 1997-2002 and Moris S. Eisen, Ariel Haskel. , Hong Chen, Marilyn M. Olmstead, David P. Smith, Marcos F. Maestre, and Richard H. Fish. Organometallics, 1995, 14, 2806-2812 Can do. Specifically, it is as follows, for example. That is, first, an aqueous solution of a silver salt (for example, Ag ₂ SO ₄ etc.) is prepared. The concentration is not particularly limited, but is, for example, 0.1 to 28 mmol / L, preferably 1 to 27 mmol / L, and more preferably 10 to 27 mmol / L. To this aqueous solution, the complex [Cp ^R RhX ₂ ] ₂ (103) produced in Step 1 above is added in an inert gas (nitrogen, argon, etc.) atmosphere and reacted to react with the target complex [Cp ^R Rh (OH ₂ ). ₃ ] ²⁺ (104) is obtained. For example, this reaction is preferably performed in the dark, but is not limited thereto. The reaction temperature is not particularly limited and can be set as appropriate. Although the reaction time is not particularly limited, for example, it is 0.5 to 10 hours, preferably 0.5 to 5 hours, and more preferably 2 to 5 hours. Further, the amount of the silver salt (number of moles) is not particularly limited, but is, for example, 1 to 2 times, preferably 1 to the amount of the amount of the complex [Cp ^R RhX ₂ ] ₂ (103) (number of moles). 1.5 times, more preferably 1 to 1.05 times. After completion of the reaction, the obtained complex (104) may be isolated, purified, etc. as necessary. If there is no problem, the complex (104) is used as it is in the next reaction step without isolation, purification, etc. Also good. The method of isolation, purification, etc. is not particularly limited, and can be carried out according to a conventional method, for example, methods such as evaporation, filtration, washing, column chromatography, recrystallization method, counter-anion exchange precipitation method, It can be used alone or in appropriate combination.

(Process 3)
In the scheme 1, the step 3 is performed by, for example, Seiji Ogo, Hideki Hayashi, Keiji Uehara, and Shunichi Fukuzumi, Applied Organometallic Chemistry, 2005, 19, 639-643 and H. Christine Lo, Carmen Leiva, Olivier Buriez, John B The reaction conditions can be appropriately set with reference to documents such as Kerr, Marilyn M. Olmstead, and Richard H. Fish, Inorganic Chemistry, 2001, 40, 6705-6716. Specifically, it is as follows, for example. That is, first, an aqueous solution of Ar (the ligand in the chemical formula (1)) is prepared. The concentration is not particularly limited, but is, for example, 0.01 to 0.4 mol / L, preferably 0.1 to 0.4 mol / L, and more preferably 0.1 to 0.3 mol / L. To this aqueous solution, a salt of the complex [Cp ^R Rh (OH ₂ ) ₃ ] ²⁺ (104) produced in Step 2 above (for example, sulfate) is added under an inert gas (nitrogen, argon, etc.) atmosphere, and the reaction is performed. To obtain the target rhodium mononuclear metal complex (1A). For example, this reaction is preferably performed in the dark, but is not limited thereto. The reaction temperature is not particularly limited and can be set as appropriate. The reaction time is not particularly limited, but is, for example, 1 to 30 hours, preferably 3 to 25 hours, and more preferably 5 to 20 hours. Further, material of the Ar (moles) is not particularly limited, amount of substance of the complex _{^{[Cp R Rh (OH 2)}} 3] 2+ (104) to (moles), for example 1 to 2 times, Preferably it is 1-1.5 times, More preferably, it is 1-1.05 times.

  After completion of the reaction, the product (1A) may be isolated and purified as necessary, or may be used as it is without isolation and purification if there is no problem. The method of isolation, purification, etc. is not particularly limited, and can be carried out according to a conventional method, for example, methods such as evaporation, filtration, washing, column chromatography, recrystallization method, counter-anion exchange precipitation method, It can be used alone or in appropriate combination. The rhodium mononuclear metal complex (1A) is a complex in which the ligand L is a water molecule in the rhodium mononuclear metal complex (1). Therefore, this rhodium mononuclear metal complex (1A) may be used in the present invention as it is, or may be used after appropriate ligand exchange or the like, if necessary. The method for ligand exchange is not particularly limited, and an appropriate method may be used.

  The target compound (1) (or (1A)) can be produced as described above.

The counter ion of the complex [Cp ^R Rh (OH ₂ ) ₃ ] ²⁺ (104) is not particularly limited, but for example, the counter ion of the rhodium mononuclear metal complex (1) is the same as the specific example described above. The same applies to counter ions of other ionic substances. Moreover, in each process of the said processes 1-3, the reaction solvent is not limited above, For example, water or a suitable organic solvent may be used, and it may use only 1 type or may use 2 or more types together. However, when water can be used as a reaction solvent, for example, when all of the reactants (raw materials) are soluble in water, it is particularly preferable to use water for reasons such as economy and ease of reaction. . For the same reason, alcohol solvents such as methanol and ethanol are also preferable as the reaction solvent. The organic solvent is not particularly limited, but a highly polar solvent is preferable from the viewpoint of the solubility of the reactant (raw material), for example, nitrile such as acetonitrile, propionitrile, butyronitrile, benzonitrile, methanol, ethanol, n Primary alcohols such as propyl alcohol and n-butyl alcohol, secondary alcohols such as isopropyl alcohol and s-butyl alcohol, tertiary alcohols such as t-butyl alcohol, and polyhydric alcohols such as ethylene glycol and propylene glycol , Ethers such as tetrahydrofuran, dioxane, dimethoxyethane, diethyl ether, amides such as dimethylformamide and dimethylacetamide, sulfoxides such as dimethyl sulfoxide, esters such as ethyl acetate, and the like.

Further, among the rhodium mononuclear metal complexes (1), for example, the rhodium mononuclear metal complex represented by the chemical formula (4), a tautomer or stereoisomer thereof, or a salt thereof is represented by, for example, the following scheme 2 Can be manufactured according to Scheme 2 below can be carried out in the same manner as in Scheme 1 except that the reactant is selected according to the structure of the final target product (compound (4)).

[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 is at least selected from the group consisting of a rhodium mononuclear metal complex represented by the formula (1), a tautomer, a stereoisomer, and a salt thereof. It is a formic acid decomposition catalyst containing one compound. For example, the compound 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 aqueous solution in which at least one of formic acid and water is deuterated as described above.

  The formic acid decomposition catalyst of the present invention can be used in a formic acid decomposition method. The formic acid decomposition method is selected from the group consisting of, for example, a step of leaving the solution for formic acid decomposition of the present invention and formic acid as it is, a step of heating the solution, and a step of irradiating the solution with light. At least one step. That is, for example, formic acid may be added to the solution of the compound and left as it is, or may be heated or irradiated 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 formic acid decomposition method, 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. When the compound is 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, 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. Furthermore, the raw material formic acid may be in the form of, for example, a solution or a salt.

  Conventional formic acid decomposition catalysts have a low activity and, for example, have a problem that they do not function as a catalyst unless they are heated in an organic solvent, in a strongly acidic or strongly basic aqueous solution, or in a mixture thereof. It was. The binuclear metal complex containing iridium and ruthenium described in Non-Patent Documents 8 to 10 is highly active and functions as a catalyst for formic acid decomposition even in an aqueous solution at room temperature, but requires preheating. 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. For example, it is particularly preferable that the formic acid decomposition catalyst of the present invention functions as a catalyst without heating at all in an aqueous solution at room temperature. However, the present invention is not limited to this. 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 formic acid decomposition method, the concentration of the rhodium mononuclear metal complex (1) molecule in the solution is not particularly limited, but is, for example, 0.001 to 50 mmol / L, preferably 0.005 to 20 mmol / L, more preferably 0.005 to 5 mmol. / L. The substance ratio (number ratio) of the rhodium mononuclear metal complex (1) molecule and formic acid molecule is not particularly limited, but is, for example, 100: 1 to 1: 1000, preferably 10: 1 to 1: 500, more preferably 1: 1 to 1: 500.

The formic acid decomposition catalyst of the present invention using the rhodium mononuclear metal complex (1) can be used in a method for producing hydrogen (H ₂ ). The method for producing hydrogen (H ₂ ) includes, for example, a step of decomposing formic acid by the formic acid decomposing method to generate hydrogen (H ₂ ). This makes it possible to supply hydrogen stably using, for example, formic acid, which is a safe substance, under mild conditions at room temperature, for example. If an aqueous solution in which one of formic acid and water in the formic acid aqueous solution is deuterated is used, the present invention can be carried out as the production method of the present invention for producing D ₂ or HD. When hydrogen (H ₂ ) is generated by formic acid decomposition, carbon dioxide (CO ₂ ) is generated as a by-product. Therefore, the formic acid decomposition method of the present invention can also be used in a carbon dioxide (CO ₂ ) production method. That is, this carbon dioxide (CO ₂ ) production method includes a step of decomposing formic acid by the formic acid decomposition method of the present invention to generate carbon dioxide (CO ₂ ). According to the method for producing hydrogen (H ₂ ) of the present invention, it is possible to obtain hydrogen without toxic by-products without accompanying by-products other than carbon dioxide (CO ₂ ).

Next, the manufacturing method of the present invention will be described more specifically.
As described above, the production method of the present invention is a group comprising a step of leaving a reaction solution containing a formic acid decomposition catalyst, formic acid and water as it is, a step of heating the reaction solution, and a step of irradiating the reaction solution with light. Wherein the initial compound is selected from the group consisting of a rhodium mononuclear metal complex represented by the formula (1), a tautomer, a stereoisomer, and a salt thereof. And at least one of the formic acid and the water is deuterated. In the production method of the present invention, deuterium (D ₂ ) is produced as a result of the deuteration of at least one of the formic acid and the water in the reaction solution involved in the decomposition reaction of the formic acid by the compound as a deuterium source. And / or deuterated hydrogen (HD).

An example of the production method of the present invention is a method for producing deuterium (D ₂ ) by the production method, wherein the water is D ₂ O in the aqueous formic acid solution. In the above production method, 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, more preferably 60 mol% or more, and further preferably It is 70 mol% or more, more preferably 80 mol% or more, and particularly preferably 90 mol% or more. The upper limit of the ratio of D2 is not particularly limited, but ideally is 100 mol%.

Another example of the production method of the present invention is a method for producing deuterated hydrogen (HD) by the production method, wherein one of formic acid and water is deuterated in the aqueous formic acid solution, and the pH or A production method in which pD is 4.0 or less can be mentioned. The pH or pD is preferably 3.0 or less, more preferably 2.5 or less, still more preferably 2.2 or less, and particularly preferably 2.0 or less. The lower limit of the pH or pD is not particularly limited, but is −1.0 or more, for example. In the above production method, the ratio of HD in the total amount (mol) of H ₂ , HD and D ₂ obtained is not particularly limited, but is preferably 50 mol% or more, more preferably 60 mol% or more, and further preferably 70 mol. % Or more, more preferably 80 mol% or more, particularly preferably 90 mol% or more. The upper limit of the HD ratio is not particularly limited, but ideally 100 mol%.

The mechanism of generation of the hydrogen isotope gas by the production method of the present invention is considered as follows, for example. However, these are examples of mechanisms that can be estimated, and do not limit the present invention.
Using the rhodium mononuclear metal complex represented by the formula (1) as a catalyst for formic acid decomposition, as shown in FIG. 1, the complex existing as an aqua complex reacts with a formate anion in an aqueous solution, A formic acid complex is formed, becomes a hydride complex through elimination of carbon dioxide, and then the hydride complex reacts with protons in the aqueous solution to generate hydrogen (H ₂ ). On the other hand, as shown in FIG. 2, when deuterated formic acid (DCOOH) is used, the deuteride complex that has undergone the elimination of carbon dioxide from the formic acid complex is combined with protons in the reaction solution and H / H. It is thought that a process of generating a hydride complex by performing D exchange is newly generated.

FIG. 3 shows an example of a presumed reaction mechanism in the present invention. When deuterated formic acid (DCOOH) is used, deuteride hydrogen (HD) is generated when the deuteride complex reacts with protons (H ⁺ ) in the reaction solution, as shown in FIG. . In this case, since the H / D exchange reaction of the deuteride complex also proceeds at the same time, the generated hydride complex reacts with protons (H ⁺ ) in the reaction solution, and hydrogen (H ₂ ) is also generated. Here, when heavy water (D ₂ O) is included in the aqueous solution, the hydride complex can further generate deuterated hydrogen (HD) by reacting with deuteron (D ⁺ ) in the reaction solution. . When formic acid (HCOOH) is used as the formic acid and the aqueous solution contains heavy water (D ₂ O), as shown in FIG. 4, the hydride complex that has undergone the elimination of carbon dioxide from the formic acid complex becomes a proton (H ⁺ ) To produce deuterated hydrogen (HD). In this case, at the same time, the hydride complex undergoes H / D exchange with deuteron (D ⁺ ) in the reaction solution to form a deuteride complex, so that the deuteride complex is deuterated with deuteron (D ⁺ ) in the reaction solution. The reaction also generates deuterium (D ₂ ).

The reaction step in the production method of the present invention includes, for example, preparing the reaction solution in advance by dissolving the compound in the water to obtain an aqueous solution, and then adding the formic acid to the aqueous solution, and allowing the compound to stand as it is. Alternatively, it can be carried out by heating or light irradiation as necessary. The pH or pD (initial pH or pD) before the formic acid decomposition reaction of the reaction solution is, for example, in the range of 1.5 to 8.5, and hydrogen isotope gas can be reliably generated in this range. it can. By adjusting the initial pH or pD, the amount of each of deuterated hydrogen (HD) and deuterium (D ₂ ) generated can be adjusted. In order to selectively produce the amount of deuterated hydrogen (HD) generated, for example, deuterated formic acid (DCOOH) is used as the formic acid, and the initial pH or pD is adjusted to 1.5 to 4.0. Preferably, the range is 1.5 to 3.0, more preferably 1.5 to 2.0. 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 1.5 to 4.0. Preferably, the range is 1.5 to 3.0, more preferably 1.5 to 2.0. 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 in the range of 4.0 to 8.5, More preferably, it is in the range of -8.0, and more preferably in the range of 6.0-7.0. The initial pH or pD can be adjusted using a known pH adjusting agent, 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.

The influence of the initial pH or pD on the generation of isotope gas by the production method of the present invention can be considered as follows, for example. However, this is also an example of a presumable reaction mechanism, and does not limit the present invention.
The inventors previously analyzed the formic acid decomposition reaction using ESI-MS and UV-visible absorption spectrum with respect to the influence of the initial pH on the reaction rate of the formic acid decomposition reaction. As a result, the formic acid decomposition reaction shown in FIG. In the case of high-pH conditions, the reaction between hydride complexes and protons (H ⁺ ) becomes the rate-limiting process, whereas under low-pH conditions, the process of forming hydride complexes from formic acid complexes becomes the rate-limiting process. It was. Next, in the process of making the present invention, the inventors analyzed the formic acid decomposition reaction by changing the pH of the aqueous solution using formic acid (HCOOH) and deuterated formic acid (DCOOH), respectively. As shown in FIG. 6, it was recognized that the value of the kinetic deuterium isotope effect was significantly reduced when the pH of the aqueous solution was high (FIG. 5) than when the pH was low (FIG. 5). In FIGS. 5 and 6, the upper line is when formic acid (HCOOH) is used, and the lower line is when deuterated formic acid (DCOOH) is used. According to the previous knowledge, when the pH of the reaction solution is low, the process from the formic acid complex to the hydride complex is the rate-limiting process, whereas when the pH of the reaction solution is high, the hydride complex is in the aqueous solution. It can be explained that the process of generating hydrogen (H ₂ ) by reacting with the protons of the catalyst is rate-limiting.

Based on these findings, the influence of pH or pD of the aqueous solution on gas generation by the production method of the present invention can be explained as follows. For example, referring to FIG. 3, when deuterated formic acid (DCOOH) is used as the formic acid, the process from the formic acid complex to the deuteride complex becomes a rate-limiting process under low pH or pD conditions. Reacts with protons (H ⁺ ) in the reaction solution to generate deuterated hydrogen (HD), and the deuterated hydrogen (HD) can be generated in high yield. In contrast, under high pH or pD conditions, the deuteride complex reacts with protons (H ⁺ ) in an aqueous solution to generate hydrogen (H ₂ ), which is the rate-determining process. Generation of hydrogen (H ₂ ) proceeds faster than the deuteride complex undergoes H / D conversion, rather than reacting with protons (H ⁺ ) in solution to produce deuterated hydrogen (HD). The amount increases and the amount of deuterated hydrogen (HD) generated decreases . When non-deuterated formic acid (HCOOH) is used as formic acid and deuterated water (D ₂ O) is used as water, referring to FIG. 4, the hydride complex is deuterated in the reaction solution (under low pH or pD conditions). D ⁺ ) reacts with D ⁺ ) to generate deuterium hydride (HD) faster than the H / D exchange reaction of the hydride complex, deuterium (D ₂ ) In contrast to the rate at which the hydride complex reacts with deuteron (D ⁺ ) in the reaction solution to generate deuterated hydrogen (HD) under high pH or pD conditions. The H / D conversion reaction of the hydride complex proceeds faster, the amount of deuterium (D ₂ ) generated increases, and the amount of deuterated hydrogen (HD) generated decreases.

In the production method of the present invention, when the reaction solution is heated, 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. A method for collecting the generated deuterium (D ₂ ) and deuterium hydrogen (HD) is not particularly limited, and a known method such as water displacement or upward displacement can be appropriately used. Hydrogen (H _2), deuterium (D ₂₎ and a method for obtaining at least two deuterium from a gas mixture of (D ₂₎ and the respective hydrogen deuteride (HD) of the hydrogen deuteride (HD) is also limited For example, a column separation method can be used as appropriate. Thus, the production method of the present invention can generate hydrogen isotope gas very easily and stably under mild conditions.

As described above, the formic acid decomposition catalyst used in the production method of the present invention is composed of the rhodium mononuclear metal complex represented by the formula (1), a tautomer, a stereoisomer, and a salt thereof. At least one compound selected from. As described above, the compound is a catalyst that reacts with formic acid to generate hydrogen, and when deuterated formic acid (DCOOH) is added to the compound in water, the deuteride complex reacts with protons in the reaction solution. Thus, deuterated hydrogen (HD) can be selectively generated through the process of generating deuterated hydrogen (HD). In particular, when heavy water (D ₂ O) is contained in the reaction solution, a reaction occurs in which the hydride complex reacts with deuteron (D ⁺ ) in the reaction solution to generate deuterated hydrogen (HD), The amount of deuterated hydrogen (HD) generated can be increased. On the other hand, when formic acid (HCOOH) is added to the above compound in deuterated water (D ₂ O), deuterium hydride is produced by the reaction of hydride complex that has undergone elimination of carbon dioxide from the formic acid complex and deuteron (D ⁺ ) in the reaction solution. In addition, a deuteride complex is formed by H / D exchange of the hydride complex, and deuterium is generated by a reaction with deuteron (D ⁺ ) in the reaction solution of the deuteride complex. (D ₂ ) can also be generated. The method for producing the formic acid decomposition catalyst of the present invention, the preferred chemical structural formula, the preferred ligand, the use conditions, and the like are as described above. In particular, in the above formula (2), when a rhodium mononuclear metal complex in which R ⁶ and R ¹³ are hydrogen, deuterium (D ₂ ) and deuterated hydrogen (HD) Although at least one can be obtained, the said compound is not limited to this.

The influence of the three-dimensional structure of the ligand on the generation of hydrogen isotope gas by the production method of the present invention is considered as follows, for example. However, this is also an example of a presumable reaction mechanism, and does not limit the present invention.
The inventors considered the reason for the difference in gas generation rate for three types of hydride complexes having ligands with different steric structures based on the DFT calculation results. As a result, in the H / D exchange reaction, the deuteri complex is first deprotonated to become an I-valent complex, which is presumed to be protonated by water molecules in the vicinity thereof, thereby becoming a hydride complex. The present inventors have found that the H / D exchange reaction is likely to occur when there is a space where deprotonation and protonation reaction are likely to occur. Therefore, for example, when the compound in which R ⁶ and R ¹³ in the ligand are hydrogen atoms is used, a sufficient space for the deprotonation and protonation reaction can be secured in the deuteride complex. The generation yield of hydrogen isotope gas can be obtained.

  In the production method of the present invention, the concentration of the compound is not particularly limited. In particular, the concentration of the rhodium mononuclear metal complex (1) molecule in the reaction solution is, for example, 0.001 to 50 mmol / L, preferably 0.005 to 20 mmol. / L, more preferably 0.005 to 5 mmol / L. The substance ratio (number ratio) of the rhodium mononuclear metal complex (1) molecule and formic acid molecule is not particularly limited, but is, for example, 100: 1 to 1: 1000, preferably 10: 1 to 1: 500, more preferably 1: 1 to 1: 500.

Since at least one of the formic acid and the water used in the production method of the present invention is a deuterium (D) supply source, at least one of them must be deuterated. 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.

  The reaction solution may contain an additive other than the formic acid decomposition catalyst, the formic acid and the water, as long as the generation efficiency of the hydrogen isotope gas is not impaired. Without using any other additive, hydrogen isotope gas can be generated in a high yield, and the reaction solution preferably does not contain an organic solvent from the viewpoint of safety of operation and simplicity.

The formic acid decomposition catalyst of the present invention can be suitably used for, for example, a formic acid production and decomposition apparatus as described below. Such production of formic acid and cracking devices, for example, hydrogen is decomposed formic acid (H ₂₎ and carbon dioxide and formic acid decomposition section to (CO ₂₎ generating, hydrogen (H ₂₎ and carbon dioxide (CO ₂₎ A formic acid production section for producing formic acid from the formic acid decomposition section, the formic acid decomposition section includes the formic acid decomposition catalyst of the present invention, the formic acid production section reacts hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) A formic acid production catalyst for producing formic acid is included. In this case, for example, if a formic acid aqueous solution in which water is D ₂ O is used, at least one of D _{2 and} HD can be repeatedly generated by the production method of the present invention. That is, at least a part of the generated hydrogen (H ₂ ) becomes at least one of D ₂ or HD (hydrogen isotope gas). 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. The formic acid decomposition catalyst of the present invention can also be used in hydrogen storage and generation methods. The hydrogen storage and generation method includes, for example, a hydrogen storage step of producing formic acid by reacting hydrogen (H ₂ ) and carbon dioxide (CO ₂ ) with a formic acid production catalyst, and storing the hydrogen in the form of formic acid; It includes a hydrogen generation step in which formic acid is decomposed by the formic acid decomposition catalyst of the present invention to generate hydrogen (H ₂ ) and carbon dioxide (CO ₂ ). 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. Thus, the apparatus for using the hydrogen storage and generation method is not particularly limited. For example, it can be performed using the formic acid production and decomposition apparatus.

The hydrogen storage and generation method can be performed, for example, as follows. That is, first, the formic acid production and decomposition apparatus of the present invention 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 of the present invention or the formic acid production and decomposition apparatus of the present invention is used, hydrogen can be stored and transported as formic acid or formate, and used safely at the necessary place when necessary. it can. 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.

(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 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 (109) or (110). In the following formula (109), 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 (110), 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 (109) and (110), 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 (109) or the hexamethylbenzene group in the formula (110), each methyl group is replaced with another atomic group as long as the function as a formic acid production catalyst is not 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 (109) and (110) 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 (109) and (110) is not particularly limited, but those skilled in the art can easily produce the catalyst based on the description and technical common sense in the present specification. is there. The following formulas (109) and (110) 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 (109), 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 (109) or (110), 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 formula (110), X ² is H ₂ O (water molecule), R ³⁰⁰ And R ⁴⁰⁰ is a methoxy group, a catalyst for producing formic acid 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: C, 35.85; H, 4.31; N, 3.44%.

^{[Cp * Ir III (4,4'-} OMe-bpy) (OH 2)] in ^{2 +} (Formula (109), 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 formula (109), 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 in the range m / z 100-2000 (I) = 100%}. FT-IR (KBr, cm ^-1 ) 2030 (Ir-H).

Furthermore, the method for using the formic acid production catalyst represented by the formulas (109) and (110) 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 unit 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 (109) and (110). 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 (109) and (110), the ease of 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 (109) and (110) is described in detail in the above-mentioned documents (a) to (c). 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 (109) and (110), 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 formula (109) or (110) is dissolved in a pH 3.0 citrate buffer (20 cm ³ ) 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 monitored by ¹ H-NMR, ¹³ C-NMR, FAB-MS and GC. All chemicals are reagent grade. The commercially available reagents were of the highest purity and were used without further purification unless otherwise specified: trichlororhodium RhCl ₃ trihydrate (Tanaka Kikinzoku Kogyo Co., Ltd.), pentamethylcyclopentadiene (Kanto) Chemical Co., Ltd.), 2,2'-bipyrimidine (Wako Pure Chemical Industries, Ltd.), formic acid (Wako Pure Chemical Industries, Ltd.), sodium hydroxide (Wako Pure Chemical Industries, Ltd.), sodium deuteroxide D ₂ O solution (40wt% NaOD, 99.5% D ;. Aldrich Chemical Co), D 2 O (99.9% D), DCOOH (> 99.5%, 98% D), DCOOD (> 99.5%, 98% D; Cambridge Isotope Laboratories) , H ₂ gas (99.99%), standard gas (H ₂ 1.07%, CO ₂ 1.07%, CO 1.06%, N ₂ 96.8%, GL Sciences Co., Ltd.), D ₂ gas (99.5%; Sumitomo Seika Chemicals Co., Ltd.) and HD gas (HD 97%, H ₂ 1.8%, D ₂ 1.2%; Isotec Inc.). Water generation (18.2 mΩcm) was performed using a Milli-Q system (Millipore; Milli-Q Jr and Direct-Q 3 UV). ¹ H-NMR measurement was performed by using a Varian instrument nuclear magnetic resonance spectrometer (trade name UNITY INOVA600, 59 HMHz for ¹ H-NMR measurement) and a device manufactured by JEOL (trade name JNM-AL300, ¹ H-NMR measurement 300.4 MHz) was used. ¹ H NMR test in D ₂ O, dissolved in D ₂ O for Dew tape helium lock [2,2 ', 3,3'-D4] -3- ( trimethylsilyl) propionic acid sodium salt ( In a D ₂ O in NMR tube (diameter: 5.0 mm) using a sealed capillary tube (diameter: 1.5 mm) containing TSP; 100 mM, as a control using methyl proton resonance set at δ = 0.00 ppm This was done by dissolving the sample. Electrospray ionization mass spectrometry (ESI-MS) data was acquired using an API 150EX quadrupole mass spectrometer (PE-Sciex) in positive detection mode with an ion spray interface. The sprayer was held at a potential of +5.0 kB and liquid spray was assisted using compressed N ₂ . Orifice potential was recorded using a Hewlett Packard 8453 diode array spectrometer using a crystal cuvette (path length: 1 mm or 1 cm) at 298K.

The pH or pD was adjusted as follows. In the pH range of 0.9 to 11.9, the pH value of the solution was measured with a pH meter (TOA, HM-20J) equipped with a pH combination electrode (TOA, GST-5725C). The pH of the solution was adjusted using 1.00 M HNO ₃ / H ₂ O and 1.00-10.0 M NaOH / H ₂ O without buffer. The pD value was corrected by adding 0.4 to the observed value (pD = pH meter recorded value + 0.4).

^{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. Chemical shifts are expressed in parts per million (ppm). Tetramethylsilane (TMS) and deuterated sodium 3- (trimethylsilyl) propionate (TSP-d ₄ ) were used for the internal standard of 0 ppm. Coupling constants (J) are in hertz, and the abbreviations s, d, t, q, m, and br are singlet, doublet, triplet, quadruple, respectively. Represents a quartet, a multiplet, and a broad line. FAB-MS data was measured using a device manufactured by JEOL (trade name JMS-DX300). For GC analysis, a Shimadzu gas chromatograph (trade name GC-8A) equipped with a hydrogen isotope gas separation column (Hydro Isopack (2.0 m, 4.0 mm id, GTR TEC Co., Ltd.)) was used.

  Rhodium mononuclear aqua complexes 1 to 10 shown in FIG. 7 were produced, or formation in the system was confirmed. Below, the specific manufacturing method of these rhodium mononuclear aqua complexes is demonstrated using the manufacture example of the rhodium mononuclear aqua complex 1 shown in FIG. The rhodium mononuclear aqua complex (4) shown below corresponds to the rhodium mononuclear aqua complex 1 shown in FIG. 7, and the rhodium mononuclear aqua complex (4-1) is the rhodium mononuclear aqua complex shown in FIG. The rhodium mononuclear aqua complex (4-2) corresponds to the complex 6 shown in FIG.

[Complex production example 1: Production of rhodium mononuclear aqua complex (4)]
According to the scheme 2, a rhodium mononuclear aqua complex (4) was synthesized (manufactured). Details are as follows.

(Step 1: [Cp ^* RhCl ₂ ] ₂ (complex (107)) production)
First, trichlororhodium RhCl ₃ trihydrate (0.510 g, 1.95 mmol), which is a commercially available reagent, was added to methanol (13 mL) to prepare a solution. To this was added pentamethylcyclopentadiene (0.5 mL) under an argon atmosphere. And it heated with stirring under argon atmosphere as it was, and was made to recirculate | reflux for 21 hours. After stirring, the mixture was allowed to cool to room temperature. The resulting precipitate was filtered off with a glass filter (G4) and washed with ether to obtain the desired complex (107), that is, [Cp ^* RhCl ₂ ] ₂ (0.430 g, yield 72.5%). It was confirmed that the product was the target compound (107) because the instrumental analysis values agreed with the literature values. FIG. 8 shows a ¹ H-NMR spectrum of the product of this step (complex (107)). The measurement in the figure was performed in deuterated chloroform (CDCl ₃ ), and TMS was used as a reference substance.

(Step 2: Production of sulfuric acid (SO ₄ ^2- ) salt of [Cp ^* Rh (OH ₂ ) ₃ ] ²⁺ (complex (108)))
Ag ₂ SO ₄ (0.450 g, 1.50 mmol) was dissolved in water (54 mL) to give an aqueous solution. To this aqueous solution, the complex (107) prepared in Step 1 above, that is, [Cp ^* RhCl ₂ ] ₂ (0.415 g, 1.04 mmol), is added under argon atmosphere, and 4.5% at room temperature (25 ° C.) in the dark. Stir for hours. After stirring, the precipitate (AgCl) is filtered off with a glass filter (G4), and the filtrate is further filtered through a membrane filter (ADVANTEC, manufactured by PTFE (polytetrafluoroethylene)), and water is evaporated from the filtrate by evaporation. Was removed. The obtained residue was dissolved in water and purified by reverse phase chromatography through a Sephadex G-10 (Pharmacia trade name) column. Water was removed from the liquid that passed through the Sephadex column by evaporation. The obtained solid was dried under reduced pressure at 25 ° C. for 10 hours to obtain the desired complex (108), ie, sulfuric acid (SO ₄ ²⁻ ) salt of [Cp ^* Rh (OH ₂ ) ₃ ] ²⁺ (0.455 g, yield 87.6%). It was confirmed that the product was the sulfate of the target compound (108) because the instrumental analysis values agreed with the literature values. FIG. 9 shows a ¹ H-NMR spectrum of the product of this step (complex (108) sulfate). The measurement in the figure was performed in deuterated dimethyl sulfoxide (DMSO-d ₆ ), and TMS was used as a reference substance.

(Step 3: [Cp ^* Rh (bpy) (OH ₂ )] ²⁺ (Production of sulfuric acid (SO ₄ ^2- ) salt of rhodium mononuclear aqua complex (4)))
2,2′-bipyridine (0.12 g, 0.77 mmol) was added to water (7.5 mL) to give an aqueous solution. To this aqueous solution, the sulfuric acid (SO ₄ ²⁻ ) salt (0.29 g, 0.75 mmol) of the complex (108) [Cp ^* Rh (OH ₂ ) ₃ ] ²⁺ prepared in Step 2 was added under an argon atmosphere. The mixture was stirred at room temperature (25 ° C.) for 16 hours in the dark. After stirring, water was removed from the reaction solution by evaporation. The obtained residue was dissolved in water and purified by reverse phase chromatography through a Sephadex G-10 (Pharmacia trade name) column. Water was removed from the liquid that passed through the Sephadex column by evaporation. The obtained solid was dried under reduced pressure at 25 ° C. for 5 hours, and the desired rhodium mononuclear aqua complex (4), ie, [Cp ^* Rh (bpy) (OH ₂ )] ²⁺ sulfuric acid (SO ₄ ^2- ) salt (0.32 g, yield 84.0%) was obtained.

It is to be noted that the product is a target rhodium mononuclear aqua complex (4), that is, a sulfate (SO ₄ ^2- ) salt of [Cp ^* Rh (bpy) (OH ₂ )] ^2+. Was confirmed from the literature value. ^{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. ^{As a} solvent for ¹³ C-NMR measurement, heavy water (D ₂ O) was used, and TSP-d ₄ (sodium trimethylsilylpropionate) was used as a reference substance. The measurement results of ¹ H-NMR, ¹³ C-NMR, and mass spectrometry (FAB-MS) are shown below. FIG. 10 shows a ¹ H-NMR spectrum. (A) is an overall view of the ¹ H-NMR spectrum, and (B) is a partially enlarged view. In addition, the pH titration curve of the rhodium mononuclear aqua complex (4) separately obtained by measurement using NaOH is shown in FIG.

[Cp ^* Rh (bpy) (OH ₂ )] ²⁺ (Rhodium mononuclear aqua complex (4)) sulfate (SO ₄ ^2- ) salt:
¹ H-NMR: (600MHz, in D ₂ O, reference to TSP in D ₂ O, 298K): δ 1.72 (s, Cp ^* , 15H), 7.94 (t, J = 6.3Hz, 2H, bpy), 8.35 (t, J = 7.2Hz, 2H, bpy), 8.49 (d, J = 8.4Hz, 2H, bpy), 9.15 (d, J = 4.8Hz, 2H, bpy) ¹³ C-NMR: (600MHz, in D ₂ O, reference to TSP in D ₂ O, 298K): δ 8.03 (s, C ₅ (CH ₃ ) ₅ ), 98.0 (d, J _Rh-C = 36Hz, C ₅ (CH ₃ ) ₅ ), 124, 129, 142, 152, 155 (s, bpy) FAB-MS: [Cp ^* Rh (bpy) (OH ₂ )] PF ₆ ⁺ , m / z 539.1; [Cp ^* Rh (bpy) (OH ₂ )] ( Elemental analysis (%) for SO ₄ ) · 3H ₂ O (C ₂ 0H ₂₅ N ₂ O ₅ SRh · 3H ₂ O): Theoretical value C42.71, H5.55, N4.98; Observed value C42.47, H5 .27, N5.08.

[Detection of intermediate complex in decomposition reaction of formic acid with rhodium mononuclear aqua complex (4)]
The intermediate complex in the formic acid decomposition reaction with the produced rhodium mononuclear aqua complex (4), formic acid complex [Rh ^III (Cp ^* ) {OC (O) H} (bpy)] ⁺ is electrospray ionized mass spectrometry ( ESI-MS). peak at m / z439.2 (Figure 12a) is, corresponding to the complex of formic acid ^{[Rh III (Cp *) {} OC (O) H} (bpy)] +, distribution of isotopomers estimated isotope distribution (Fig. 12b). Replacing formic acid (HCOOH) with deuterated formic acid (DCOOH), the ESI mass peak is at m / z 430.2 due to [Rh ^III (Cp ^* ) {OC (O) D} (bpy)] ⁺ Shifted. That is, [Rh ^III (Cp ^* ) {OC (O) H} (bpy)] due to hydride transfer from HCOO ^- or DCOO ^- to [Rh ^III (Cp ^* ) (bpy) (H ₂ O)] ^{2+ +} Or [Rh ^III (Cp ^* ) {OC (O) D} (bpy)] ⁺ occurs respectively.

Next, the protonicity of the hydride complex was confirmed based on the change in the UV / Vis spectrum due to the reaction with the base. The results are shown in FIG. Formic acid HCOOH / HCOONa (12 mM) and [Rh ^III (Cp ^* ) (bpy) (H ₂ O)] ²⁺ (0.24 mM, solid line in the figure) were reacted for 6 minutes to give [Rh ^III (Cp ^* ) (H ) (bpy))] ²⁺ (broken line in the figure), and when reacted in the presence of NaOH (0.48 mM), new absorption bands were observed at λ = 560, 690, 765 and 856 nm (in the figure) , Dash-dot line). These multiple bands represent [Rh ^I (Cp ^* ) (bpy)]. The complex [Rh ^I (Cp ^* ) (bpy)] reacts with HCOOH (0.48 mM) and again in [Rh ^III (Cp ^* ) (H) in 298 K degassed H ₂ O (1 mm path length) (bpy))] ²⁺ (broken line in the figure) is generated. FIG. 14 shows a UV / Vis absorption spectrum generated by reduction of [Rh ^III (Cp ^* ) (bpy)-(H ₂ O)] ²⁺ (2.5 M, solid line in the figure) with (nBu ₄ ) NBH _4. . This property is consistent with the results observed in the reaction of HCOOH with [Rh ^III (Cp ^* ) (bpy) (H ₂ O)] ²⁺ in the presence of NaOH (FIG. 13).

[Temperature dependence of reaction efficiency of formic acid decomposition reaction by rhodium mononuclear aqua complex (4)]
The temperature dependence of the reaction efficiency of the decomposition reaction of formic acid (HCOOH) by the produced rhodium mononuclear aqua complex (4) was investigated. The results are shown in FIG. From the Arrhenius plot FIG. 15b, this rhodium mononuclear aqua complex (4) is much smaller than the activation energy of the non-catalytic hydrogen generation reaction, and this complex has a high catalytic activity in a wide temperature range including room temperature. You can see that

Next, as in Reference Examples 1 to 3 below, this rhodium mononuclear aqua complex (4) sulfate was used as a catalyst for formic acid decomposition, and the hydrogen (H ₂ ) performance was evaluated.

[Reference Example 1: Formic acid decomposition and hydrogen production using formic acid decomposition catalyst]
The rhodium mononuclear aqua complex (4) sulfate (2.54 mg, 5 μmol) prepared in Complex Production Example 1 was dissolved in water (1.1 mL) to give an aqueous solution (4.5 mM). Formic acid (450 mM, 100 times the number of moles of rhodium mononuclear aqua complex (4)) was added to this aqueous solution under deoxygenated (anaerobic) conditions. The initial pH of the aqueous solution at this time (pH before the formic acid decomposition reaction occurred) was measured and found to be 2.0. When this aqueous solution was allowed to stand at 293 K (20 ° C.) in the dark, a gas that could be clearly confirmed visually was generated. As a result of analyzing this gas by GC (gas chromatography), it was a 1: 1 mixed gas of hydrogen and carbon dioxide. That is, formic acid was decomposed with a catalytic amount (1 mol%) of rhodium mononuclear aqua complex (4) with respect to formic acid in an aqueous solution at room temperature and normal pressure to produce hydrogen and carbon dioxide. Further, preheating was not necessary.

[Reference Example 2: Formic acid decomposition and hydrogen production in repeated use of catalyst]
Formic acid was decomposed and hydrogen was produced by the rhodium mononuclear aqua complex (4) in the same manner as in Example 1 except that the initial pH of the aqueous solution (pH before the formic acid decomposition reaction) was adjusted to 3.7. That is, first, rhodium mononuclear aqua complex (4) sulfate (5.08 mg, 10 μmol) was dissolved in water (2.2 mL) to obtain an aqueous solution (4.5 mM). To this aqueous solution, a mixed aqueous solution of 1.0 M formic acid aqueous solution and 1.0 M sodium hydroxide aqueous solution was added under deoxygenated (anaerobic) conditions to adjust the pH to 3.7 (the formate anion concentration was 450 mM, rhodium mononuclear aqua 100 times the number of moles of complex (4)). This was left still in the dark at 293 K (20 ° C.) to decompose formic acid and generate hydrogen. At this time, the gas generated by the decomposition of formic acid was passed through a 1.0 M aqueous sodium hydroxide solution to remove carbon dioxide. Then, only the remaining hydrogen was collected in a graduated cylinder by the water displacement method, and the hydrogen generation amount was measured.

  Further, when the formic acid was completely consumed and the generation of hydrogen was completed, formic acid was added again to a concentration about 100 times that of the rhodium mononuclear aqua complex (1), and the amount of hydrogen generated was measured by the above method. . This was repeated 4 times. The additional amounts of formic acid were 6.7 μL (first time), 5.1 μL (second time), 8.4 μL (third time), and 6.9 μL (fourth time), respectively.

The graph of FIG. 23 shows the measurement result of the hydrogen generation amount in this reference example. In the figure, the horizontal axis is the elapsed time from the first addition of formic acid, and the vertical axis is the mass ratio of the generated hydrogen (H ₂ ) to the catalyst (rhodium mononuclear aqua complex (4)) ( Molar ratio). As shown in FIG. 23, after the first addition of formic acid, the amount of hydrogen generated increases with the elapsed time (reaction time), and in about 60 minutes, 17 times the number of moles of hydrogen of the rhodium mononuclear aqua complex (4) is generated did. That is, hydrogen generation was confirmed in the presence of 100 equivalents of formic acid under the reaction conditions of room temperature and pressure using rhodium mononuclear aqua complex (4) as a catalyst. After that, when formic acid was added again four times so that the concentration of the rhodium mononuclear aqua complex (4) was about 100 times the molar amount (100 equivalents), as shown in FIG. Hydrogen was generated efficiently while maintaining substantially the same catalytic activity. Thus, the rhodium mononuclear aqua complex (4) could be repeatedly used as a catalyst for formic acid decomposition at an extremely low concentration (about 1 mol%).

In this reference example (reference example 2), the average catalyst rotation efficiency (TOF) for 10 minutes from the beginning of formic acid addition determined using the water displacement method was 31 h ⁻¹ . Furthermore, in Reference Example 2, formic acid was decomposed over about 6 hours, and TON (turnover number, number of formic acid decomposed per mol of catalyst) exceeded 90. That is, (catalyst rotations per hour) Average TOF in formic acid degradation of 6 hours has exceeded 15h ^-1. These TOF and TON values are extremely high, indicating that the formic acid decomposition catalyst used is highly active.

As described above, according to Reference Examples 1 and 2, by using water-soluble rhodium aqua complex (4) sulfate ([Cp ^* Rh (bpy) (OH ₂ )] SO ₄ ) as a catalyst, In this water, formic acid was decomposed without requiring any heating, and hydrogen could be generated efficiently (production of hydrogen). Even when such a rhodium mononuclear complex is used in the production of a hydrogen isotope gas (at least one of D ₂ and HD) as a catalyst for formic acid decomposition of the present invention, as described later, with a high yield and a catalyst rotation speed. Hydrogen isotope gas can be produced.

[Complex Production Example 2: Production of Rhodium Mononuclear Aqua Complex (4-1)]
In Step 3 of Complex Preparation Example 1, 4,4′-methyl-2,2′-pipyridine (0.12 g, 0.77 mmol) was used instead of 2,2′-pipyridine (0.12 g, 0.77 mmol). Except for the above, a rhodium mononuclear aqua complex (4-1) represented by the following chemical formula was synthesized (produced) in the same manner as in Complex Production Example 1. The measurement results of the ¹ H-NMR are shown.

¹ H NMR (300MHz, in D ₂ O, reference to TSP inD2O, 298K): δ = 1.69 (s, 15H, η ⁵ -C ₅ (CH ₃ ) ₅ ), 2.61 (s, 6H, Me), 7.74 ( d, J = 5.7 Hz, 2H, bpy), 8.29 (s, 2H, bpy), 8.93 ppm (d, J = 6.0 Hz, 2H, bpy).

[Complex Production Example 3: Production of Rhodium Mononuclear Aqua Complex (4-2)]
In Step 3 of Complex Production Example 1, 6,6′-methyl-2,2′-pipyridine (0.12 g, 0.77 mmol) was used instead of 2,2′-pipyridine (0.12 g, 0.77 mmol). Except for the above, a rhodium mononuclear aqua complex (4-2) represented by the following chemical formula was synthesized (produced) in the same manner as in Complex Production Example 1. The measurement results of the ¹ H-NMR are shown below. In addition, FIG. 16 shows a pH titration curve of the rhodium mononuclear aqua complex (4-2) obtained by measurement using NaOH separately.

¹ H NMR (300MHz, D ₂ O, reference to TSP in D ₂ O, 298K): δ = 1.49 (s, 15H; η ⁵ -C ₅ (CH ₃ ) ₅ ), 3.02 (s, 6H, Me), 7.81 (d, J = 7.8Hz, 2H; bpy), 8.18 (t, J = 8.0Hz, 2H; bpy), 8.29ppm (d, J = 8.1Hz, 2H; bpy).

Similar to the rhodium mononuclear aqua complex (4) described above, an intermediate complex in the decomposition reaction of formic acid by the rhodium mononuclear aqua complex (4-2), [Rh ^III (Cp ^* ) {OC (O) H} (6, 6′-Me ₂ -bpy)] ⁺ was detected by electrospray ionization mass spectrometry (ESI-MS). The results are shown in FIG. The peak at m / z 467.2 (FIG. 17a) corresponds to [Rh ^III (Cp ^* ) {OC (O) H} (6,6′-Me ₂ -bpy)] ⁺ and the isotopomer distribution is It is in good agreement with the estimated isotope distribution. When formic acid (HCOOH) is replaced with deuterated formic acid (DCOOH), the peak of ESI mass is [Rh ^III (Cp ^* ) {OC (O) D} (6,6'-Me ₂ -bpy)] ⁺ To m / z 468sss.2 (FIG. 17b). That is, [Rh ^III (Cp ^* ) {OC (by hydride movement from HCOO ^- or DCOO ^- to [Rh ^III (Cp ^* ) (6,6'-Me ₂ -bpy) (H ₂ O)] ²⁺ O) H} (6,6′-Me ₂ -bpy)] ⁺ or [Rh ^III (Cp ^* ) {OC (O) D} (6,6′-Me ₂ -bpy)] ⁺ respectively. In addition, as a result of decomposition of formic acid (HCOOH) using [Rh ^III (Cp ^* ) (6,6'-Me ₂ -bpy) (H ₂ O)] ²⁺ at pH 6.1, it was measured after 20 minutes. and ¹ H NMR spectrum, in addition to the ^{[Rh III (Cp *) {} OC (O) H} (6,6'-Me 2 -bpy)] peaks corresponding to ^+, with δ = -7.1ppm, [ Rh ^III (Cp ^* ) (H) (6,6′-Me ₂ -bpy)] ⁺ showed a hydride peak (FIG. 18).

Next, using the sulfates of this rhodium mononuclear aqua complex (4), (4-1) and (4-2), deuterium (HD) and deuterium (D ₂ ) At least one was produced.

[Example 1: Decomposition of deuterated formic acid and production of hydrogen isotope gas (HD) with catalyst for decomposition of formic acid (rhodium mononuclear aqua complex (4) sulfate)]
A 2.8M DCOOH / DCOONa solution (0.74 mL, 2.1 mmol) was added to an aqueous solution (1.66 mL) of the rhodium mononuclear aqua complex (4) sulfate (8.54 mg, 16.8 μmol) prepared in Complex Preparation Example 1. The initial pH of the aqueous solution (pH before the formic acid decomposition reaction) was measured and found to be 2.9. When this aqueous solution was allowed to stand at 298 K (25 ° C.) in the dark, a gas that could be clearly confirmed visually was generated. As a result of analyzing this gas by GC (gas chromatography), it was a 28%: 72% mixed gas of hydrogen (H ₂ ) and deuterated hydrogen (HD). In other words, deuterated formic acid (DCOOH) is decomposed in a catalytic amount (0.80 mol%) of rhodium mononuclear aqua complex (4) in deuterated formic acid in an aqueous solution at room temperature and normal pressure to produce deuterated hydrogen (HD ) Could be selectively produced in high yield. Further, preheating was not necessary.

[Example 2: Decomposition of deuterated formic acid using formic acid decomposition catalyst (rhodium mononuclear aqua complex (4) sulfate), production of hydrogen isotope gas (HD), and measurement of TON]
Example except that HCOOH / HCOONa solution was used at 0.87M, rhodium mononuclear aqua complex (4) was used at 7.0mM, and the initial pH of the aqueous solution (pH before deuterated formic acid decomposition reaction) was adjusted to 3.6 Decomposition of deuterated formic acid (DCOOH) and production of hydrogen isotopes using rhodium mononuclear aqua complex (4) in the same manner as in 1 above, together with the addition of HCOOH / HCOONa solution for 60 minutes The TON (number of turnover, number of moles of H ₂ and HD generated per mole of catalyst) of the complex (4) was measured. The results are shown in FIG. TON for H ₂ and HD generation is proportional to time, the ratio of H ₂ and HD generated is constant, and there is no change in H / D exchange rate of deuteride complex, which is an intermediate complex. I understand.

[Example 3: Decomposition of deuterated formic acid and production of hydrogen isotope gas (HD) under pH change]
Decomposition of deuterated formic acid (DCOOH) by rhodium mononuclear aqua complex (4) in the same manner as in Example 1 except that the initial pH of the aqueous solution (pH before deuterated formic acid decomposition reaction) was adjusted to 5.2. And hydrogen isotopes were produced. As a result of analyzing the generated gas by GC (gas chromatography), it was a 78%: 22% mixed gas of hydrogen (H ₂ ) and deuterated hydrogen (HD). That is, deuterated formic acid (DCOOH) is decomposed by deuterated formic acid (DCOOH) in a catalytic amount (0.80 mol%) of rhodium mononuclear aqua complex (4) in an aqueous solution at normal temperature and pressure. Hydrogen (HD) could be produced. Further, preheating was not necessary.

[Example 4: Decomposition of deuterated formic acid and production of hydrogen isotope gas (HD) under pH change]
Rhodium mononuclear aqua complex (4) 26.5M deuterated formic acid aqueous solution and 10.0M sodium hydroxide aqueous solution are mixed with sulfate aqueous solution, and various initial pH (pH before formic acid decomposition reaction) varies. Deuterated formic acid (DCOOH) was decomposed to generate hydrogen isotopes in the same manner as in Example 1 except that an aqueous solution (initial pH 2.0 or more) was prepared. In addition, hydrogen isotopes were generated in the same manner except that 1.0M nitric acid aqueous solution was used instead of the 10.0M sodium hydroxide aqueous solution and various aqueous solutions having different initial pH (initial pH 2.0 or less) were prepared. It was. FIG. 20 shows the result of comparing the ratio of hydrogen (H ₂ ) generated at these various pHs (initial pH) and deuterated hydrogen (HD) in this example. In the figure, the horizontal axis represents pH (initial pH), and the vertical axis represents the ratio of each of generated hydrogen (H ₂ ) and hydrogen isotope (HD). As shown in FIG. 20, the hydrogen and hydrogen isotope ratio determined by GC analysis is reversed at pH 4.0, and deuterated hydrogen (HD) is selectively generated at pH lower than pH 4.0. It was confirmed that hydrogen (H ₂ ) was selectively generated at a pH higher than pH 4.0.

[Example 5: Decomposition of deuterated formic acid and production of hydrogen isotope gas (HD) with a catalyst for formic acid decomposition (rhodium mononuclear aqua complex (4-1) sulfate) under pH change]
Rhodium mononuclear aqua complex (4) Same as Example 4 except that rhodium mononuclear aqua complex (4-1) sulfate (9.01 mg, 16.8 μmol) was used instead of sulfate (8.54 mg, 16.8 μmol) Then, deuterated formic acid (DCOOH) was decomposed to generate hydrogen isotope gas. FIG. 21 shows the result of comparing the ratio of hydrogen and hydrogen isotope gas generated at these various pHs (initial pHs) in this example. The horizontal and vertical axes in the figure are the same as those in FIG. As shown in FIG. 21, the ratio of hydrogen (H ₂ ) and deuterated hydrogen (HD) determined by GC analysis is reversed at pH 4.0, and at pH lower than 4.0, deuterated hydrogen ( HD) was selectively generated, and it was confirmed that hydrogen (H ₂ ) was selectively generated at a pH higher than pH 4.0. Also, deuterated hydrogen (HD) could be produced with higher selectivity than Example 4 at the lowest pH in the tested pH range (pH 1.6). However, it was performed at 300.5 K (27.5 ° C.) under pH 1.6 conditions.

[Example 6: Decomposition of deuterated formic acid and production of hydrogen isotope gas (HD) with catalyst for formic acid decomposition under the change of pH (rhodium mononuclear aqua complex (4-2) sulfate)
Rhodium mononuclear aqua complex (4) Same as Example 4 except that rhodium mononuclear aqua complex (4-2) sulfate (9.01 mg, 16.8 μmol) was used instead of sulfate (8.54 mg, 16.8 μmol) Then, deuterated formic acid (DCOOH) was decomposed to generate hydrogen isotope gas. FIG. 22 shows the result of comparing the ratio of hydrogen (H ₂ ) generated at these various pHs (initial pH) and hydrogen isotope gas in this example. The horizontal and vertical axes in the figure are the same as those in FIG. As shown in FIG. 22, when rhodium mononuclear aqua complex (4-2) sulfate was used, hydrogen (H ₂ ) was generated in a larger amount even at pH 2.0. That is, in the rhodium mononuclear aqua complex (4-2) sulfate, the selectivity of deuterated hydrogen (HD) was not as high as that of complex (4) and complex (4-1). (HD) could be manufactured.

[Example 7: Decomposition of non-deuterated formic acid (HCOOH) in heavy water using formic acid decomposition catalyst (rhodium mononuclear aqua complex (4) sulfate) and production of hydrogen isotope gas (HD and D ₂ )]
A 2.8 M HCOOH solution (0.74 mL, 2.1 mmol) was added to an aqueous solution (1.66 mL) of the rhodium mononuclear aqua complex (4) sulfate (9.01 mg, 16.8 μmol) prepared in Complex Preparation Example 1. The initial pD (pD before the formic acid decomposition reaction) of the aqueous solution was measured and found to be 2.1. When this aqueous solution was allowed to stand at 298 K (25 ° C.) in the dark, a gas that could be clearly confirmed visually was generated. As a result of analyzing this gas by GC (gas chromatography), it was a 10%: 72%: 18% mixed gas of hydrogen (H ₂ ), hydrogen isotope (HD) and hydrogen isotope (D ₂ ). That is, formic acid (HCOOH) is decomposed with a catalytic amount (0.80 mol%) of rhodium mononuclear aqua complex (4) with respect to formic acid (HCOOH) in heavy aqueous solution at normal temperature and pressure, and hydrogen (H ₂ ), deuterium Hydrogen fluoride (HD) and deuterium (D ₂ ) could be produced. Further, preheating was not necessary.

[Example 8: Decomposition of non-deuterated formic acid (HCOOH) in heavy water using formic acid decomposition catalyst (rhodium mononuclear aqua complex (4) sulfate) and production of hydrogen isotope gas (HD and D ₂ )]
Decomposition of formic acid (HCOOH) by rhodium mononuclear aqua complex (4) and hydrogen isotope gas in the same manner as in Example 7 except that the initial pD of the aqueous solution (pD before the formic acid decomposition reaction) was adjusted to 2.9. Manufactured. As a result of analyzing the generated gas by GC (gas chromatography), it was a 9%: 51%: 40% mixed gas of hydrogen (H ₂ ), hydrogen isotope (HD) and hydrogen isotope (D ₂ ). That is, formic acid (HCOOH) is decomposed with a catalytic amount (0.80 mol%) of rhodium mononuclear aqua complex (4) with respect to formic acid (HCOOH) in heavy aqueous solution at normal temperature and pressure, and hydrogen (H ₂ ), deuterium Hydrogen fluoride (HD) and deuterium (D ₂ ) could be produced. Further, preheating was not necessary.

[Example 9: Decomposition of non-deuterated formic acid (HCOOH) under heavy water and production of hydrogen isotope gases (HD and D ₂ )]
Decomposition of formic acid (HCOOH) by rhodium mononuclear aqua complex (4) and hydrogen isotope gas in the same manner as in Example 7 except that the initial pD of the aqueous solution (pD before the formic acid decomposition reaction) was adjusted to 5.2. Manufactured. As a result of analyzing the generated gas by GC (gas chromatography), it was a 3%: 24%: 73% mixed gas of hydrogen (H ₂ ), hydrogen isotope (HD) and hydrogen isotope (D ₂ ). That is, formic acid is decomposed by a rhodium mononuclear aqua complex (4) in a catalytic amount (0.80 mol%) with respect to deuterated formic acid in an aqueous solution at normal temperature and pressure, and hydrogen (H ₂ ), deuterated hydrogen (HD ) And deuterium (D ₂ ) could be produced. Further, preheating was not necessary.

As described above, according to Examples 1 to 6, by using the water-soluble rhodium aqua complex (4), (4-1) and (4-2) sulfate as a catalyst, Deuterated formic acid (DCOOH) was decomposed without any heating, and deuterated hydrogen (HD) could be selectively produced efficiently. In addition, according to Examples 7 to 9, by using a water-soluble rhodium aqua complex (4) sulfate ([Cp ^* Rh (bpy) (OH ₂ )] SO ₄ ) as a catalyst, In water, formic acid (HCOOH) was decomposed without any heating, and hydrogen isotope gas (HD and D ₂ ) was generated efficiently (production of hydrogen isotope gas). In particular, in Example 7, it is possible to obtain a hydrogen deuteride (HD) in high yields, in Example 9, it was possible to obtain a deuterium (D ₂₎ in high yield.

As described above, according to the present invention, at least one of deuterium (D ₂ ) and deuterium hydride (HD) can be easily and appropriately controlled at an appropriate speed from a stable and highly safe formic acid. Can be manufactured safely and at low cost. The method of the present invention can be adequately adapted from laboratory research to industrial scale mass production. 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.

  The catalyst for formic acid decomposition of the present invention can generate the hydrogen isotope gas using only water as a solvent without using an organic solvent, and has high rotational efficiency, so that it is possible to suppress and save environmental load. It can also contribute to resources. Since the catalyst for formic acid decomposition of the present invention uses a mononuclear metal complex, the amount of noble metal used can be reduced as compared to a binuclear metal complex, and low-cost and highly efficient production of a hydrogen isotope element can be realized. The use of the formic acid decomposition catalyst of the present invention is not limited to the above, and can be used, for example, in any technical field that requires the supply of a hydrogen isotope gas.

FIG. 1 is a diagram illustrating a reaction mechanism of a formic acid decomposition reaction by a formic acid decomposition catalyst. FIG. 2 is a diagram illustrating the reaction mechanism of H / D exchange of the hydride complex of the catalyst for formic acid decomposition. FIG. 3 is a diagram illustrating a reaction mechanism of hydrogen isotope gas generation according to the present invention. FIG. 4 is a diagram illustrating a reaction mechanism of hydrogen isotope gas generation according to the present invention. FIG. 5 is a graph illustrating the kinetic deuterium isotope effect in the formic acid decomposition reaction using the formic acid decomposition catalyst. FIG. 6 is a graph illustrating the kinetic deuterium isotope effect in the formic acid decomposition reaction using the formic acid decomposition catalyst. FIG. 7 is a diagram illustrating the chemical structure of the rhodium mononuclear aqua complex produced in the example. FIG. 8 is a ¹ H-NMR spectrum of a rhodium aqua complex (4) synthetic intermediate. FIG. 9 is a ¹ H-NMR spectrum of a rhodium aqua complex (4) synthetic intermediate. FIG. 10 is a ¹ H-NMR spectrum of rhodium aqua complex (4). FIG. 11 is a graph illustrating the pH titration curve of the rhodium mononuclear aqua complex (4). FIG. 12 is a diagram exemplifying detection by ESI-MS of an intermediate complex in a decomposition reaction of formic acid by a rhodium mononuclear aqua complex (4). FIG. 13 is a diagram illustrating a UV / Vis spectrum illustrating the protonicity of the rhodium mononuclear hydride complex (4). FIG. 14 is a diagram illustrating a UV / Vis absorption spectrum of [RhI (Cp ^* ) (bpy)] generated by reduction of the rhodium mononuclear hydride complex (4). FIG. 15 is a diagram illustrating the temperature dependence of the formic acid decomposition reaction efficiency by the rhodium mononuclear aqua complex (4). FIG. 16 is a graph illustrating a pH titration curve of a rhodium mononuclear aqua complex (4-2). FIG. 17 is a diagram illustrating an ESI-MS detection result of an intermediate complex in a formic acid decomposition reaction by a rhodium mononuclear aqua complex (4-2). FIG. 18 is a diagram illustrating a ¹ HNMR spectrum of a reaction mixture of rhodium mononuclear aqua complex (4-2) and formic acid. FIG. 19 is a graph illustrating a TON relating to generated hydrogen (H ₂ ) and deuterated hydrogen (HD) in the decomposition reaction of formic acid by the rhodium mononuclear aqua complex (4). FIG. 20 is a graph illustrating the hydrogen isotope gas generation ratio when the formic acid decomposition reaction is performed by changing the initial pH of the reaction solution in the formic acid decomposition reaction by the rhodium mononuclear aqua complex (4). FIG. 21 is a graph illustrating the hydrogen isotope gas generation ratio when the formic acid decomposition reaction is performed by changing the initial pH of the reaction solution in the decomposition reaction of formic acid by the rhodium mononuclear aqua complex (4-1). FIG. 22 is a graph illustrating the generation ratio of hydrogen isotope gas when the formic acid decomposition reaction is performed by changing the initial pH of the reaction solution in the decomposition reaction of formic acid by the rhodium mononuclear aqua complex (4-2). . FIG. 23 is a graph illustrating the amount of hydrogen generation (TON) when the catalyst is repeatedly used in the formic acid decomposition reaction by the rhodium mononuclear aqua complex (4).

Claims (15)

A method for producing at least one of deuterium (D ₂ ) and deuterium hydride (HD),
Formic acid decomposition catalyst, formic acid and water, comprising at least one compound selected from the group consisting of rhodium mononuclear metal complexes represented by the following formula (1), tautomers, stereoisomers and salts thereof Preparing a formic acid aqueous solution in which at least one of the formic acid and the water is deuterated, and
A formic acid decomposition step of decomposing formic acid by at least one step selected from the group consisting of a step of standing the formic acid aqueous solution as it is, a step of heating the solution, and a step of irradiating the solution with light.
A production method for generating at least one of deuterium (D ₂ ) and deuterated hydrogen (HD) in the formic acid decomposition step.

In the formula (1),
Rh is a rhodium atom or ion;
Ar is an aromatic ligand and may or may not have a substituent.
When having a substituent, the substituent may be one or plural,
R ^{1 to} R ⁵ are each independently a hydrogen atom or an arbitrary substituent,
L is any ligand or absent,
m is a positive integer, 0, or a negative integer. In the formula (1),
R ¹ to R ⁵ are each independently a hydrogen atom, an alkyl group, a phenyl group or a cyclopentadienyl group, The process according to claim 1, wherein,. In the formula (1),
The production method according to claim 1 or 2, wherein R ^{1 to} R ⁵ are all methyl groups. In the formula (1),
Whether L is a water molecule, hydrogen atom, alkyloside ion, hydroxide ion, halide ion, carbonate ion, trifluoromethanesulfonate ion, sulfate ion, nitrate ion, formate ion, acetate ion, or hydride ion Or the production method according to any one of claims 1 to 3, which is absent. In the formula (1),
The manufacturing method according to any one of claims 1 to 4, wherein m is 0, 1, 2, 3, 4, 5 or 6. The production method according to any one of claims 1 to 5, wherein the rhodium mononuclear metal complex represented by the formula (1) is a rhodium mononuclear metal complex represented by the following formula (2).

In the formula (2),
R ^{6 to} R ¹³ are each independently a hydrogen atom or an arbitrary substituent,
Alternatively, R ⁹ and R ¹⁰ together may form —CH═CH—, and each H in —CH═CH— may be independently substituted with an arbitrary substituent. ,
Q ^{6 to} Q ¹³ are each independently C or N ⁺
Alternatively, at least one of Q ^X and R ^X having the same X (X is an integer of 6 to 13) may be N together,
Rh, R ^{1 to} R ⁵ , L and m are the same as in the above formula (1). In the formula (2),
R ^{6 to} R ¹³ are each independently a hydrogen atom, alkyl group, phenyl group, benzyl group, nitro group, halogen group, sulfonic acid group (sulfo group), amino group, carboxylic acid group (carboxy group), hydroxy group Or an alkoxy group,
Alternatively, R ⁹ and R ¹⁰ together may form —CH═CH—, and each H in —CH═CH— independently represents an alkyl group, a phenyl group, a benzyl group, or a nitro group. The production method according to claim 6, which may be substituted with 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. In the formula (2),
The method according to claim 6 or 7, wherein R ⁶ and R ¹³ are hydrogen atoms. In the formula (2),
The production method according to any one of claims 6 to 8, wherein R ^{6 to} R ¹³ are all hydrogen atoms. In the formula (2),
The process according to Q ⁶ to Q ¹³ are all C any one of claims 6 a (carbon atoms) 9. The production method according to claim 6, wherein the rhodium mononuclear metal complex represented by the formula (2) is a rhodium metal complex represented by the following formula (3).

In the formula (3),
Rh, L and m are the same as in the above formula (2). The production method according to claim 11, wherein the rhodium mononuclear metal complex represented by the formula (3) is a rhodium mononuclear metal complex represented by any one of the following formulas (4) to (6).

A method for producing deuterium (D ₂ ) by the production method according to claim 1, wherein water is D ₂ O in the formic acid aqueous solution. A method for producing deuterated hydrogen (HD) by the production method according to any one of claims 1 to 12, wherein in the aqueous formic acid solution, one of formic acid and water is deuterated, and pH Or the manufacturing method whose pD is 4.0 or less. The rhodium mononuclear metal complex represented by the formula (1), tautomers thereof, stereoisomers, and at least one compound selected from the group thereof, comprising any one of claims 1 to 14 A catalyst for decomposing formic acid used in the production method according to claim 1.

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