Cluster complex and method for producing the same, polymer catalyst having the cluster complex as constituent unit and method for producing the same, and electrode containing the polymer catalyst and method for producing the same

Abstract

To provide a novel compound which can be immobilized on a surface of an electrode in an electrolytic reaction and is prevented from being decomposed in a reduction reaction.SOLUTION: Provided is a cluster complex that comprises a predetermined cubane-type cluster containing a metal atom and one or more predetermined ligands coordinated to the cluster.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a cluster complex and a method for producing the same, a polymer catalyst having the cluster complex as a constituent unit and a method for producing the same, and an electrode including the polymer catalyst and a method for producing the same. [Background technology]

[0002] Electrocatalysts are used in various chemical reactions because they can convert "electrical energy" into "chemical energy," i.e., chemical bonds. New compounds for use as electrode catalysts are being actively developed.

[0003] For compounds used as electrode catalysts, the technology for immobilizing them on an electrode is also important. Non-Patent Document 1 discloses a compound that is a cluster complex containing a cubane-type cluster Co4O4 and a ligand containing a carbazole moiety that coordinates to the cluster. Non-Patent Document 1 discloses that the compound can be immobilized on the electrode surface by polymerizing via the carbazole moiety during an electrolytic reaction, and that the electrode can be used for HO oxidation. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Hikaru Iwami et al, "Electrochemical Polymerization Provides a Function-Integrated System for Water Oxidation", Angew. Chem. Int. Ed. 2021, 60, 5965-5969 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, technologies aimed at reducing carbon dioxide emissions have attracted attention, such as a method for synthesizing hydrocarbons such as methane by electrochemically reducing carbon dioxide using an electrode catalyst, and a method for synthesizing ammonia by electrochemically reducing nitrogen. Therefore, there is a strong demand for novel compounds suitable for these methods. Non-Patent Document 1 discloses a compound that can be used for HO oxidation, but it has been found that the compound may decompose during the reduction reaction described above, for example. The present disclosure has been made in view of the above circumstances, and one of its objectives is to provide a novel compound that can be immobilized on an electrode surface during an electrolysis reaction and that is inhibited from decomposing during a reduction reaction. Another objective is to provide an electrode using the novel compound and a method for producing the electrode. [Means for solving the problem]

[0006] Aspect 1 of the present invention is A cubane-type cluster containing a metal atom and one or more ligands coordinated to the cluster, The cubane cluster has the following formula (1): Mo3S4M x (1) (wherein M is a metal atom and x=0 to 1) is expressed as The ligand has the following formula (A): [ka] (In the formula, R 1 is an aliphatic hydrocarbon group having 3 to 5 carbon atoms, X 1 is expressed by the following formula (B): -CZ 1 (Z 2 )(Z 3 ) (B) (In the formula, Z 1 and Z 2 is a pyrazole group which may have a substituent, and Z 3is a pyrazole group, a carboxylic acid group, or hydrogen, which may have a substituent. is expressed as X 2 is expressed by the following formula (C): [ka] (In the formula, R 11 ~R 18 are each independently a hydrogen atom, a methyl group, a halogen atom, an alkoxy group, or a hydroxy group. It is a cluster complex represented by the formula:

[0007] Aspect 2 of the present invention is In the formula (A), R 1 is an alkylene group having 3 to 5 carbon atoms.

[0008] Aspect 3 of the present invention is In the formula (A), X 1 is the following formula: [ka] (In the formula, R 2 ~R 10 are each independently a hydrogen atom, a methyl group, a halogen atom, an alkoxy group, or a hydroxy group. The cluster complex according to embodiment 1 or 2 is represented by the following formula:

[0009] A fourth aspect of the present invention is In the formula (C), R 11 ~R 18 and are both hydrogen atoms.

[0010] A fifth aspect of the present invention is This is the cluster complex according to any one of Aspects 1 to 4, wherein in formula (1), M is any one selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Os, Ir, and Pt.

[0011] A sixth aspect of the present invention is The polymer catalyst has the cluster complex according to any one of Aspects 1 to 5 as a constituent unit.

[0012] A seventh aspect of the present invention is a conductive substrate; and a layer covering at least a portion of the surface of the conductive substrate and containing the polymer catalyst according to aspect 6.

[0013] Aspect 8 of the present invention is The following formula (B'): CH-Z 1 (Z 2 )(Z 3 ) (B') (In the formula, Z 1 and Z 2 is a pyrazole group which may have a substituent, and Z 3 is a pyrazole group, a carboxylic acid group, or hydrogen, which may have a substituent. preparing a first solution at −75° C. to −65° C. containing a first compound represented by the formula: subjecting the first solution to a first temperature increase of −40° C. to 5° C.; After the first temperature increase, cooling to −75° C. to −65° C.; After cooling, the compound represented by the following formula (C'): [ka] (In the formula, R 1 is an aliphatic hydrocarbon group having 3 to 5 carbon atoms, and R 11 ~R 18 are each independently a hydrogen atom, a methyl group, a halogen atom, an alkoxy group, or a hydroxy group; Y 1 is iodine or bromine.) and then subjecting the mixture to a second temperature increase to 0°C to 30°C. removing the solvent after the second temperature increase to obtain a ligand; The ligand and the following formula (1'): Mo3S4M x (tu)9(1') (In the formula, M is a metal atom, x=0 to 1, and tu is thiourea.) and preparing a second solution comprising a third compound represented by the formula: maintaining the second solution at a temperature of 25°C to 150°C; The present invention relates to a method for producing a cluster complex, comprising the steps of:

[0014] A ninth aspect of the present invention is A method for producing a polymer catalyst includes applying a voltage to an electrolyte solution containing the cluster complex according to any one of the first to fifth aspects.

[0015] A tenth aspect of the present invention is A method for producing an electrode includes placing at least a part of a working electrode made of a conductive substrate and at least a part of a counter electrode in an electrolyte solution containing the cluster complex according to any one of aspects 1 to 5, and applying a positive voltage to the working electrode to precipitate a polymer of the cluster complex on the surface of the working electrode. [Effects of the Invention]

[0016] According to the present disclosure, it is possible to provide a novel compound that can be immobilized on an electrode surface during an electrolysis reaction and that is inhibited from decomposing during a reduction reaction. Furthermore, according to the present disclosure, it is possible to provide an electrode using the novel compound and a method for producing the electrode. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of an example of the polymer catalyst according to this embodiment. [Figure 2] FIG. 2 shows the results of NMR measurement of the ligand of the example. [Figure 3] FIG. 3 shows the results of NMR measurement of the cluster complex of the example. [Figure 4] FIG. 4 is a schematic diagram illustrating a method for producing an electrode according to an embodiment of the present invention. [Figure 5]FIG. 5 is a schematic diagram illustrating a CO2 reduction reaction test method of the example. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present inventors conducted extensive research to develop a novel compound that can be immobilized on an electrode surface during an electrolytic reaction and that is inhibited from decomposing during a reduction reaction. As a result, they discovered a cluster complex containing a specific cubane-type cluster and a specific ligand that coordinates to the cluster. This cluster complex can be immobilized on an electrode surface during an electrolytic reaction and inhibited from decomposing during a reduction reaction. The cluster complex according to this embodiment will be described in detail below.

[0019] [1. Cluster complexes] The cluster complex according to this embodiment is A cubane-type cluster containing a metal atom and one or more ligands coordinated to the cluster, The cubane cluster has the following formula (1): Mo3S4M x (1) (wherein M is a metal atom and x=0 to 1) is expressed as The ligand has the following formula (A): [ka] (In the formula, R 1 is an aliphatic hydrocarbon group having 3 to 5 carbon atoms, X 1 is expressed by the following formula (B): -CZ 1 (Z 2 )(Z 3 ) (B) (In the formula, Z 1 and Z 2 is a pyrazole group which may have a substituent, and Z 3 is a pyrazole group, a carboxylic acid group, or hydrogen, which may have a substituent. is expressed as X 2 is expressed by the following formula (C): [ka] (In the formula, R 11 ~R 18 are each independently a hydrogen atom, a methyl group, a halogen atom, an alkoxy group, or a hydroxy group. It is expressed as: The cluster complex can be immobilized on the electrode surface during the electrolytic reaction and can also be prevented from decomposing during the reduction reaction. Each component will be described in detail below.

[0020] (Cubane cluster) In this embodiment, the basic structure of a "cubane-type cluster" is a polynuclear skeleton having a hexahedral structure similar to the regular hexahedron of cubane (C8H8), and has a tetranuclear polynuclear skeleton composed of four metal atoms and four bridging atoms (atoms that form bridges). In this embodiment, the "cubane-type cluster" is a polynuclear skeleton obtained by removing one atom from the above skeleton, and also includes a trinuclear polynuclear skeleton (also referred to as an "incomplete cubane-type cluster") structure composed of three metal atoms and four bridging atoms. In the above formula (1), Mo and M are metal atoms, and S corresponds to a bridging atom. Such a structure can be chemically stable under reduction reactions (compared to, for example, Co4O4 as disclosed in Non-Patent Document 1), and decomposition of the cluster complex according to this embodiment can be suppressed.

[0021] In the above formula (1), M is a metal atom. Since M can be a reaction site during the reduction reaction, from the viewpoint of promoting the reduction reaction, it is preferable that x=1 in the above formula (1). This can further promote the reduction reaction. M is preferably any one selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Os, Ir, and Pt, which can promote the reaction of reducing carbon dioxide to synthesize hydrocarbons such as methane and / or the reaction of reducing nitrogen to synthesize ammonia. M is preferably any one selected from the group consisting of Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Os, Ir, and Pt, which can promote the reaction of reducing carbon dioxide to synthesize hydrocarbons such as methane. M is preferably any one selected from the group consisting of Cr, Mn, Fe, Co, Mo, Ru, and Os, which can promote the reaction of reducing nitrogen to synthesize ammonia.

[0022] (ligand) In the above formula (A), R 1 is an aliphatic hydrocarbon group having 3 to 5 carbon atoms. When the carbon number is 3 or more, chemical stability is improved. When the carbon number is 5 or less, electronic conductivity is improved. Preferably, R 1 is an alkylene group having 3 to 5 carbon atoms.

[0023] In this embodiment, the ligand represented by the formula (A) has a polypyrazolylmethane moiety (X 1 ) and can be coordinated to the cubane type cluster. By having such a structure, the cluster complex according to this embodiment can be chemically stabilized during a reduction reaction, and decomposition of the cluster complex can be suppressed. One or two or more (four or less) ligands represented by the above formula (A) may be coordinated to the cubane type cluster. From the viewpoint of promoting the reduction reaction, it is preferable that three or less ligands represented by the above formula (A) be coordinated to the cubane type cluster.

[0024] In the above formula (B), Z 1 and Z 2 The substituents of Z may be, for example, methyl, halogen, alkoxy or hydroxy groups.3 is preferably a pyrazole group which may have a substituent (e.g., a methyl group, a halogen group, an alkoxy group, or a hydroxy group), and for example, X in the above formula (1) 1 is the following formula: [ka] (In the formula, R 2 ~R 10 are each independently a hydrogen atom, a methyl group, a halogen atom, an alkoxy group, or a hydroxy group. It is preferable that the formula be represented by the following formula:

[0025] The carbazole moiety in the formula (A) is X 2 (Formula (C)), R 11 ~R 18 are preferably each independently hydrogen or a methyl group.

[0026] [2. Polymer catalyst] The polymer catalyst according to this embodiment has the cluster complex as a constituent unit. In this embodiment, the constituent unit has, for example, a carbazole moiety (X 2 At least a part of the polymer catalyst according to this embodiment preferably has, for example, the following structure: [ka] (In the formula, R 1 is an aliphatic hydrocarbon group having 3 to 5 carbon atoms, and R 11 ~R 15 , R 17 ~R 18 , R 21 ~R 27 are each independently a hydrogen atom, a methyl group, a halogen atom, an alkoxy group, or a hydroxy group.

[0027] The polymer catalyst according to this embodiment may have a structure as shown in Fig. 1. Fig. 1 is a schematic diagram of an example of the polymer catalyst according to this embodiment (polymer catalyst 1), and the polymer catalyst 1 comprises a cubane-type cluster 2 (for example, the large sphere in Fig. 1 is a metal atom M) represented by the above formula (1) and a carbazole moiety X 2 The ligand 3 (represented by the above formula (A)) containing the following is coordinated, and the carbazole moiety X 2 It is multimerized via

[0028] The cluster complex and polymer catalyst according to this embodiment can be used as an electrode catalyst for reduction reactions, such as the reduction of carbon dioxide to synthesize hydrocarbons such as methane, and the reduction of nitrogen to synthesize ammonia.

[0029] [3. Electrode] The electrode according to this embodiment includes a conductive substrate and a layer that covers at least a portion of the surface of the conductive substrate and contains the polymer catalyst. Each of the components will be described in detail below.

[0030] (Conductive substrate) The conductive substrate contains a conductive material that allows the electrolytic reaction described below to occur. Examples of conductive materials include carbon materials, conductive oxide materials, and metal (alloy) materials. The conductive substrate preferably has a large surface area and may be, for example, plate-shaped or even porous. Suitable substrates include glassy carbon, carbon paper, and ITO substrates.

[0031] (Layer containing polymer catalyst) In this embodiment, the layer containing the polymer catalyst may cover at least a portion of the surface of the conductive substrate, or may cover the entire surface. The surface may be the portion that comes into contact with the electrolyte solution in the manufacturing method described below. The thickness of the layer containing the polymer catalyst may be, for example, 1 nm to 200 μm.

[0032] [4. Method for producing cluster complexes] The method for producing a cluster complex according to this embodiment includes the steps of: The following formula (B'): CH-Z 1 (Z 2 )(Z 3 ) (B') (In the formula, Z 1 and Z 2 is a pyrazole group which may have a substituent, and Z 3 is a pyrazole group, a carboxylic acid group, or hydrogen, which may have a substituent. preparing a first solution at −75° C. to −65° C. containing a first compound represented by the formula: subjecting the first solution to a first temperature increase of −40° C. to 5° C.; After the first temperature increase, cooling to −75° C. to −65° C.; After cooling, the compound represented by the following formula (C'): [ka] (In the formula, R 1 is an aliphatic hydrocarbon group having 3 to 5 carbon atoms, and R 11 ~R 18 are each independently a hydrogen atom, a methyl group, a halogen atom, an alkoxy group, or a hydroxy group; Y 1 is iodine or bromine.) and then subjecting the mixture to a second temperature increase to 0°C to 30°C. removing the solvent after the second temperature increase to obtain a ligand; The ligand and the following formula (1'): Mo3S4M x (tu)9(1') (In the formula, M is a metal atom, x=0 to 1, and tu is thiourea.) and preparing a second solution comprising a third compound represented by the formula: maintaining the second solution at a temperature of 25°C to 150°C; Each step will be described in detail below.

[0033] (A: Prepare the first solution at -75℃ to -65℃) The first solution contains a first compound, n-butyllithium, and a solvent. The first compound can constitute a polypyrazolylmethane moiety of the ligand in the cluster complex according to this embodiment. n-butyllithium functions as a base. The first compound and n-butyllithium may be prepared by a known method. The solvent is not particularly limited as long as it can dissolve the first compound and n-butyllithium. One or more solvents may be used.

[0034] The solvent may include a first solvent and a second solvent, and the first solution may be prepared by preparing a solution A containing the first compound and the first solvent and a solution B containing n-butyllithium and the second solvent, and mixing them. The first solvent may be, for example, THF, etc. The second solvent may be, for example, hexane, etc.

[0035] The concentration of the first compound in the first solution may be 100 to 500 mM. The concentration of n-butyllithium in the first solution is preferably about 1 equivalent (for example, 1.0 to 1.5 equivalents) relative to the first compound, but is not limited thereto.

[0036] The first solution is cooled to −75° C. to −65° C. (also referred to as “first cooling”). This makes it possible to suppress side reactions and heat generation due to the addition of n-butyllithium.

[0037] (B: First temperature increase of the first solution from -40°C to 5°C) The first solution is heated to -40°C to 5°C (also referred to as "first heating"). This can promote the reaction between the first compound and n-butyllithium. Stirring may be performed appropriately during or after the temperature is raised. The temperature may be maintained for, for example, 30 minutes or more and 2 hours or less after the temperature is raised.

[0038] (C: After the first temperature rise, cool to -75℃ to -65℃) After the first temperature increase of the first solution, the first solution is cooled again to −75° C. to −65° C. (also referred to as “second cooling”), which makes it possible to suppress the reaction heat generated by the addition of the second compound.

[0039] (D: After the second cooling, mix the second compound and perform a second heating to 0°C to 30°C) After the second cooling, a second compound is further mixed in. The second compound may constitute the carbazole moiety and the aliphatic hydrocarbon group of the ligand in the cluster complex according to this embodiment. The second compound may be prepared by a known method.

[0040] When mixing the second compound with the first solution, a solution (also referred to as "solution C") in which the second compound is dissolved in a solvent (also referred to as "third solvent") may be mixed with the first solution. Examples of the third solvent include THF. The mixing method is not particularly limited. When mixing the first solution with the solution C, the solution C may be cooled to the second cooling temperature before mixing.

[0041] The concentration of the second compound in the solution after mixing (also referred to as "first solution") is preferably about 1 equivalent (for example, 1.0 to 1.5 equivalents) relative to the first compound, but is not limited to this. The first solution after the above mixing is subjected to a second temperature increase to 0°C to 30°C. This promotes the reaction for obtaining the ligand according to this embodiment. The second temperature increase from the second cooling temperature may be carried out gradually, for example, over a period of 1 hour to 6 hours. The solution may also be stirred as needed during the temperature increase.

[0042] (E: After the second temperature increase, the solvent is removed to obtain the ligand.) After the second temperature increase, the solvent (for example, the first to third solvents) is removed to obtain the ligand according to this embodiment. After the solvent removal, drying and / or purification may be carried out as appropriate.

[0043] (F: Preparing a second solution containing a ligand, a third compound, and a solvent) The second solution contains the ligand, a third compound, and a solvent (also referred to as a "fourth solvent"). The third compound may constitute a cubane-type cluster of the cluster catalyst according to this embodiment. The fourth solvent is not particularly limited as long as it can dissolve the ligand and the third compound, and may be, for example, DMF, DMSO, acetonitrile, etc. The fourth solvent may be one type or two or more types. The third compound may be prepared by a known method.

[0044] The concentration of the third compound in the second solution may be 1 to 20 mM. The concentration of the ligand in the second solution is preferably about 3 equivalents (for example, 2.5 to 3.5 equivalents) relative to the third compound, but is not limited thereto.

[0045] (G: Maintaining the second solution at a temperature of 25°C to 150°C) The second solution is maintained at a temperature of 25° C. to 150° C. This promotes the reaction for obtaining the cluster catalyst according to this embodiment. The maintenance time can be, for example, 5 hours or more and 100 hours or less. After the retention, the fourth solvent is removed to obtain the cluster complex according to this embodiment. After the solvent removal, drying and / or purification may be carried out as appropriate.

[0046] [5. Method for producing polymer catalysts] The method for producing a polymer catalyst according to this embodiment includes applying a voltage to an electrolyte solution containing the cluster complex according to this embodiment.

[0047] The electrolyte solution (also referred to as "first electrolyte solution") contains the cluster complex according to this embodiment, an electrolyte, and a solvent (also referred to as "fifth solvent"). Examples of the electrolyte include tetrabutylammonium hexafluorophosphate (TBAPF6), tetrabutylammonium perchlorate (TBAP), and tetraethylammonium hexafluorophosphate (TEAPF6). Examples of the fifth solvent include dichloromethane. The electrolyte and / or the fifth solvent may be one or more types. The concentration of the cluster complex in the electrolyte solution may be 0.2 to 1.0 mM. The concentration of the electrolyte in the first electrolyte solution may be 0.1 to 0.2 M.

[0048] By applying a voltage to the first electrolyte solution, the polymer catalyst according to this embodiment, which is a polymer of the cluster complex, can be obtained. The polymer of the cluster complex can be deposited, for example, on the side where a positive voltage is applied (for example, the surface of the electrode).

[0049] [6. Electrode manufacturing method] The method for manufacturing an electrode according to this embodiment includes placing at least a portion of a working electrode made of a conductive substrate and at least a portion of a counter electrode in an electrolyte solution containing the cluster catalyst according to this embodiment, and applying a positive voltage to the working electrode to precipitate a polymer of the cluster complex on the surface of the working electrode.

[0050] The electrolyte solution is the same as that described above in [5. Electrode manufacturing method]. The conductive substrate may be any of those described above in [3. Electrode]. As the counter electrode, a known electrode may be used, for example, a Pt wire.

[0051] The positive voltage applied to the working electrode is preferably 0.8 to 1.6 V. The voltage application time is preferably 10 seconds to 1 hour. By applying the voltage, for example, the cluster complex according to this embodiment forms a carbazole moiety (X 2) and a layer containing the polymer catalyst according to the present embodiment is formed so as to cover the contact portion, thereby obtaining the electrode according to the present embodiment. After the electrode is produced, it can be washed as appropriate.

[0052] In the above-mentioned electrode production, it is also possible to later introduce (and / or substitute) a metal M into the cubane type clusters in the electrode. The introduction method includes placing at least a portion of the electrode according to this embodiment and at least a portion of the counter electrode in an electrolyte solution containing ions of metal M (also referred to as the "second electrolyte solution"), and applying a negative voltage to the electrode according to this embodiment.

[0053] The second electrolyte solution contains ions of metal M, an electrolyte, and a solvent (also referred to as "sixth solvent"). The sixth solvent is not particularly limited as long as it can dissolve the metal M ions and the electrolyte, and examples thereof include acetonitrile, THF, DMF, etc. Examples of the electrolyte include tetrabutylammonium hexafluorophosphate (TBAPF6), tetrabutylammonium perchlorate (TBAP), tetraethylammonium hexafluorophosphate (TEAPF6), etc. The electrolyte and / or the sixth solvent may be one type or two or more types. The metal M ion concentration in the second electrolyte solution may be 0.5 to 50 mM. The electrolyte concentration in the second electrolyte solution may be 0.1 to 0.2 M. The second electrolyte solution may be prepared by, for example, mixing a metal M ion solution with the electrolyte solution. The metal M ion solution may be prepared by, for example, mixing a salt of metal M with a solvent.

[0054] A known electrode can be used as the counter electrode, for example, a Pt wire. The negative voltage applied to the working electrode (i.e., the electrode according to this embodiment) is preferably −1.5 to −2.5 V. The voltage application time is preferably 10 seconds to 1 hour. By applying the voltage, the metal M is introduced into, for example, the cubane clusters in the polymer catalyst according to the present embodiment at the portion of the electrode that contacts the second electrolyte solution. In this introduction method, for example, by using an electrode containing a polymer catalyst in which x = 0 in the above formula (1), the metal M is introduced, and an electrode in which x = 1 can be obtained. [Example]

[0055] (Synthesis of the first compound (trispyrazolylmethane)) Trispyrazolylmethane was synthesized as follows according to the literature (DL Reger et al., J. Organomet. Chem. 2000, 607, 120). Pyrazole (20 g, 294 mmol), tetrabutylammonium bromide (4.7 g, 14.7 mmol), and sodium carbonate (187 g, 1.8 mol) were dispersed in 300 mL of water, and 150 mL of chloroform was added to the dispersion. The mixture was refluxed for 3 days, cooled to 25 °C, and filtered to remove excess sodium carbonate. The filtrate was extracted with diethyl ether (500 mL) and water (300 mL), and the organic phase was recovered. The aqueous phase was then extracted with diethyl ether (200 mL), and the same procedure was repeated twice. The combined organic phases were washed with brine, and the recovered organic phase was treated with activated carbon. After filtering to remove the activated carbon, the filtrate was evaporated to give a solid. The resulting solid was extracted with boiling hexane and cooled to 25 °C, yielding trispyrazolylmethane as white crystals.

[0056] (Synthesis of the second compound (iodopropylcarbazole)) Iodopropylcarbazole was synthesized according to the literature (X. Hu et al., Org. Lett. 2014, 16, 2566) as follows. Carbazole (5.0 g, 30 mmol) was dissolved in 20 mL of DMF and added to a solution of sodium hydride (11.8 g, 75 mmol) in 20 mL of DMF while cooling at 0 °C. After stirring at 25 °C for 2 hours, 200 mL of water was added to quench the reaction. 50 mL of dichloromethane was added and extracted, and the organic phase was recovered (this procedure was repeated twice). The recovered organic phase was dried over sodium sulfate, filtered to remove the solids, and the filtrate was evaporated. The resulting product was dissolved in 50 mL of acetone, sodium iodide was added, and the mixture was heated to reflux overnight. The reaction mixture was added to 50 mL of dichloromethane / 400 mL of water, extracted, and the organic phase was recovered. The aqueous phase was then subjected to the same procedure with 50 mL of dichloromethane (this procedure was repeated twice). The solvent was distilled off from the collected organic phase, and the resulting solid was extracted with boiling hexane and cooled to 25°C to obtain iodopropylcarbazole as a white solid.

[0057] (Synthesis of the Ligand According to the Present Embodiment) The first compound (trispyrazolylmethane; 3.8 g, 17.9 mmol) was dissolved in 150 mL of THF (tetrahydrofuran), and the solution was cooled to -70°C. A hexane solution of n-butyllithium (2.69 M, 6.65 mL, 17.9 mmol) was added at -70°C, and the mixture was then heated to 0°C and stirred for one hour. After stirring was complete, the reaction mixture was cooled to -70°C, and the second compound (iodopropylcarbazole; 6.0 g, 17.9 mmol) dissolved in 80 mL of THF was added. The mixture was gradually heated to 25°C over three hours and stirred at 25°C for three days. After the reaction was complete, the solvent was evaporated to dryness. The resulting solid was purified using a silica gel column (solvent: ethyl acetate:hexane = 1:4) to obtain 6.3 g of Ligand A (formula: [ka] The product was obtained as a white solid (yield: 74.6%). 1 This was confirmed by 1 H NMR measurement (Figure 2).

[0058] (Synthesis of the third compound (Mo3S4(tu)9)) The third compound was synthesized as follows according to the literature (T. Shibahara, H. Akashi, Inorg. Synth. 1992, 29, 254, and AL Gushchin et al., Eur. J. Inorg. Chem. 2014, 4093). Sodium molybdate (28.8 g, 120 mmol) was dissolved in 400 mL of water, and 20 mL of concentrated hydrochloric acid was added. Sodium sulfide (60 g, 252 mmol) was added, and the mixture was heated at 90°C for 30 minutes. L-cysteine ​​hydrochloride (36 g, 205 mmol) was added, and the reaction solution was concentrated by heating above 90°C. The concentrated solution was cooled at 0°C overnight, and orange crystals precipitated. The precipitated crystals were collected by filtration, washed with methanol and diethyl ether, and dried to obtain Intermediate 1. Intermediate 1 (48.9 g) was dissolved in 1.2 L of water, and 60 mL of concentrated hydrochloric acid was added. Sodium borohydride (19.4 g) and sodium sulfide (20.4 g) were added, followed by concentrated hydrochloric acid (250 mL). The mixture was heated at 90°C or higher for 2 days and concentrated. After the reaction, the solid was removed by filtration, and the filtrate was purified using a Sephadex column to obtain the compound represented by the following formula: [ka] (wherein L is chlorine or water) (The developing solvent was a 1 M aqueous hydrochloric acid solution.) The purity and concentration of the column-purified intermediate 2 were confirmed by ultraviolet-visible absorption spectroscopy.

[0059] Thiourea (1.8 g, 24 mmol) was added to a solution of intermediate 2 in hydrochloric acid (~30 mM, 20 mL), stirred thoroughly, and then allowed to stand at 25 °C. The resulting crystals were collected by filtration, washed with a cooled ethanol / water mixture (1:1, v / v), 2-propanol, and diethyl ether, and then dried under reduced pressure to obtain Mo3S4(tu)9 as brown crystals.

[0060] (Synthesis of Cluster Complex According to This Embodiment) The third compound (Mo3S4(tu)9) (200 mg, 0.16 mmol) and ligand A (202.3 mg, 0.48 mmol) were dissolved in 20 mL of DMF and heated at 110°C for 36 hours. After the reaction was completed, the mixture was cooled to 25°C and concentrated to a solvent volume of approximately 5 mL. An excess amount of saturated lithium bis(trifluoromethanesulfonyl)imide aqueous solution and water were added to the concentrated solution, and the precipitated solid was collected by filtration and washed with an excess amount of water. The obtained solid was extracted with acetone, and an excess amount of diethyl ether was added to the extracted solution to precipitate a solid, which was then collected by filtration. The collected solid was dried to obtain the compound of the following formula: [ka] The cluster complex A according to this embodiment, represented by the formula: 1 This was confirmed by 1 H NMR measurement (Figure 3).

[0061] (Fabrication of the electrode according to this embodiment) Prepare an electrolyte solution (0.1 M TBAPF6 / dichloromethane) containing 0.2 mM cluster complex A, and measure the potential in the range from the open circuit potential to the oxidation side (1.15 V vs. Ag / Ag). + ) and performed cyclic voltammetry measurements. FIG. 4 shows a schematic diagram for explaining the electrode fabrication method. As shown in FIG. 4, at least a part 11a of the working electrode 11, at least a part of the counter electrode 13, and the reference electrode 14 were placed in the electrolyte solution 12, and a positive voltage was applied to the working electrode 11, thereby depositing a polymer of cluster complex A on the surface of the working electrode 11 (at least a part 11a of the working electrode 11). After the reaction was completed, the working electrode 11 was washed with dichloromethane and dried under reduced pressure to obtain an electrode A according to this embodiment. Note that the above conditions were as follows: working electrode 11: carbon paper, reference electrode 14: Ag / Ag + Counter electrode 13: Pt wire, number of cycles: 50 cycles, scan rate: 100 mV / s. It is believed that a layer containing polymer catalyst A (corresponding to polymer catalyst 1 in FIG. 1 without metal atom M) is formed on the surface of electrode A.

[0062] Using an experimental system similar to that shown in Figure 4, Fe ions were introduced into polymer catalyst A as follows. 10 mg of FeCl2·TMEDA (tetramethylethylenediamine) was dissolved in a 0.1 M TBAPF6 / acetonitrile solution to form electrolyte solution 12, and electrode A was used as the working electrode 11. At least a portion 11a of working electrode 11, at least a portion of counter electrode 13, and a reference electrode 14 were placed in the electrolyte solution 12. Potential electrolysis was performed by applying a potential of -2.2 V (vs. Ag / AgCl) to the working electrode 11 (reaction time: 1 hour). After the reaction was completed, the working electrode was washed with acetonitrile and dried under reduced pressure to prepare electrode A', in which Fe ions had been introduced into polymer catalyst A. (Working electrode 11: electrode A; reference electrode 14: Ag / AgCl; counter electrode 13: Pt wire; applied potential: -2.2 V vs. Ag / AgCl; reaction time: 1 hour) It is believed that a layer containing polymer catalyst A' (corresponding to polymer catalyst 1 in FIG. 1) is formed on the surface of electrode A'.

[0063] (Reduction reaction test) Figure 5 shows a schematic diagram illustrating the test procedure. One side of an H-shaped cell 20 separated by a DSV membrane 25 contained 10 mL of reaction solution 22 (containing TBAPF / acetonitrile and a proton source, HO), a working electrode 21, and a reference electrode 24. The other side contained 10 mL of the same reaction solution 22 and a counter electrode 23, which were then sealed. When using electrode A or electrode A' according to this embodiment as the working electrode 21, the portion 21a containing the layer containing polymer catalyst A or A' was immersed in the reaction solution 22. CO2 gas was bubbled through both sides of the cell 20 for 30 minutes to fill the cell with CO2. Potential electrolysis was performed at -1.9 V for 1 hour while stirring. After the reaction, the gas phase on the working electrode 21 side was analyzed by gas chromatography to qualitatively and quantitatively characterize the product. The conditions for the above test are as follows: Working electrode 21: Electrode A' (Test No. 1), Electrode A (Test No. 2), or Carbon Paper (Test No. 3) ·Reference electrode 24:Ag / AgCl Counter electrode 23: Pt wire Reaction solution 22: 0.1M TBAPF6 / acetonitrile Proton source in reaction solution 22: H2O (5%, v / v) ·Applied potential: -1.9V vs.Ag / AgCl Response time: 1 hour H-type cells 20, cells separated by DSV membrane 25 The reaction solution 22 and the gas phase in the cell 20 are filled with carbon dioxide Experimental Procedure: The results are shown in Table 1.

[0064] [Table 1]

[0065] The results in Table 1 will be considered. The electrodes of Test Nos. 1 and 2 used a cluster complex that satisfied all of the requirements of this embodiment, and the cluster complex was immobilized on the electrode surface during the electrolytic reaction to form a layer containing a polymer catalyst (a polymer of the cluster complex). CO2 was reduced to hydrocarbons, CO, etc., and no decomposition of the polymer catalyst immobilized on the electrode was observed during the reduction reaction; in other words, the decomposition was suppressed. Among these, Test No. 1 was one in which Fe was introduced as the metal M (x = 1 in the above formula (1)), and CO2 was reduced to a large extent by industrially useful hydrocarbons. In Test No. 3, cluster complex A was not immobilized on the electrode surface, and almost no charge was generated during the test. [Explanation of symbols]

[0066] 1 Polymer catalyst 2. Cubane clusters 3 Ligand 11 Working electrode 11a At least a part of the working electrode 12 Electrolyte solution 13 Counter electrode 14 Reference electrode 20 H-type cells 21 Working electrode 21a: A portion of the working electrode on which a layer containing polymer catalyst A (or A') is formed 22 Reaction solution 23 Counter electrode 24 Reference electrode 25 DSV membrane

Claims

1. A cubane-type cluster containing a metal atom and one or more ligands coordinated to the cluster, The cubane cluster has the following formula (1): Mo ３ S ４ M ｘ (1) (wherein M is a metal atom and x=0 to 1) is expressed as The ligand has the following formula (A): 【Chemical 1】 (In the formula, R １ is an aliphatic hydrocarbon group having 3 to 5 carbon atoms, X １ is represented by the following formula (B): -C-Z １ (Z ２ )(Z ３ ) (B) (In the formula, Z １ and Z ２ is a pyrazole group which may have a substituent; Z ３ is a pyrazole group, a carboxylic acid group, or hydrogen, which may have a substituent. is expressed as X ２ is represented by the following formula (C): 【Chemistry 2】 (In the formula, R １１ ~R １８ are each independently a hydrogen atom, a methyl group, a halogen atom, an alkoxy group, or a hydroxy group. A cluster complex represented by

2. In the formula (A), R １ The cluster complex according to claim 1, wherein is an alkylene group having 3 to 5 carbon atoms.

3. In the formula (A), X １ is the following formula: 【Chemistry 3】 (In the formula, R ２ ~R １０ are each independently a hydrogen atom, a methyl group, a halogen atom, an alkoxy group, or a hydroxy group. The cluster complex according to claim 1, wherein the cluster complex is represented by the formula:

4. In the formula (C), R １１ ~R １８ The cluster complex according to claim 1 , wherein each of

5. 2. The cluster complex according to claim 1, wherein in formula (1), M is any one selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Rh, Pd, Os, Ir, and Pt.

6. A polymer catalyst having the cluster complex according to any one of claims 1 to 5 as a constituent unit.

7. a conductive substrate; An electrode comprising: a layer covering at least a portion of the surface of the conductive substrate and containing the polymer catalyst according to claim 6.

8. The following formula (B'): CH-Z １ (Z ２ )(Z ３ ) (B') (In the formula, Z １ and Z ２ is a pyrazole group which may have a substituent; Z ３ is a pyrazole group, a carboxylic acid group, or hydrogen, which may have a substituent. preparing a first solution at −75° C. to −65° C. containing a first compound represented by the formula: subjecting the first solution to a first temperature increase from −40° C. to 5° C.; After the first temperature increase, cooling to −75° C. to −65° C.; After cooling, the compound represented by the following formula (C'): 【Chemistry 4】 (In the formula, R １ is an aliphatic hydrocarbon group having 3 to 5 carbon atoms, and R １１ ~R １８ are each independently a hydrogen atom, a methyl group, a halogen atom, an alkoxy group, or a hydroxy group; Y １ is iodine or bromine.) and then subjecting the mixture to a second temperature increase to 0°C to 30°C; removing the solvent after the second temperature increase to obtain a ligand; The ligand and the following formula (1'): Mo ３ S ４ M ｘ (tu) ９ (1') (wherein M is a metal atom, x=0 to 1, and tu is thiourea.) and preparing a second solution containing a third compound represented by the formula: maintaining the second solution at a temperature of from 25°C to 150°C; A method for producing a cluster complex, comprising:

9. A method for producing a polymer catalyst, comprising applying a voltage to an electrolyte solution containing the cluster complex according to any one of claims 1 to 5.

10. A method for producing an electrode, comprising: placing at least a part of a working electrode made of a conductive substrate and at least a part of a counter electrode in an electrolyte solution containing the cluster complex according to any one of claims 1 to 5; and applying a positive voltage to the working electrode to precipitate a polymer of the cluster complex on the surface of the working electrode.

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