CN108126754B - Asymmetric N-H-pyridine-Ni metal catalyst and preparation method and application thereof - Google Patents

Asymmetric N-H-pyridine-Ni metal catalyst and preparation method and application thereof Download PDF

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CN108126754B
CN108126754B CN201810076277.0A CN201810076277A CN108126754B CN 108126754 B CN108126754 B CN 108126754B CN 201810076277 A CN201810076277 A CN 201810076277A CN 108126754 B CN108126754 B CN 108126754B
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CN108126754A (en
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康鹏
刘芳卫
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Technical Institute of Physics and Chemistry of CAS
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/16—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes
    • B01J31/18—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes containing nitrogen, phosphorus, arsenic or antimony as complexing atoms, e.g. in pyridine ligands, or in resonance therewith, e.g. in isocyanide ligands C=N-R or as complexed central atoms
    • B01J31/1805—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes containing nitrogen, phosphorus, arsenic or antimony as complexing atoms, e.g. in pyridine ligands, or in resonance therewith, e.g. in isocyanide ligands C=N-R or as complexed central atoms the ligands containing nitrogen
    • B01J31/181—Cyclic ligands, including e.g. non-condensed polycyclic ligands, comprising at least one complexing nitrogen atom as ring member, e.g. pyridine
    • B01J31/1815—Cyclic ligands, including e.g. non-condensed polycyclic ligands, comprising at least one complexing nitrogen atom as ring member, e.g. pyridine with more than one complexing nitrogen atom, e.g. bipyridyl, 2-aminopyridine
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
    • C07F15/00—Compounds containing elements of Groups 8, 9, 10 or 18 of the Periodic Table
    • C07F15/04—Nickel compounds
    • C07F15/045—Nickel compounds without a metal-carbon linkage
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2531/00—Additional information regarding catalytic systems classified in B01J31/00
    • B01J2531/02—Compositional aspects of complexes used, e.g. polynuclearity
    • B01J2531/0213—Complexes without C-metal linkages
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2531/00—Additional information regarding catalytic systems classified in B01J31/00
    • B01J2531/02—Compositional aspects of complexes used, e.g. polynuclearity
    • B01J2531/0238—Complexes comprising multidentate ligands, i.e. more than 2 ionic or coordinative bonds from the central metal to the ligand, the latter having at least two donor atoms, e.g. N, O, S, P
    • B01J2531/0241—Rigid ligands, e.g. extended sp2-carbon frameworks or geminal di- or trisubstitution
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J2531/00—Additional information regarding catalytic systems classified in B01J31/00
    • B01J2531/80—Complexes comprising metals of Group VIII as the central metal
    • B01J2531/84—Metals of the iron group
    • B01J2531/847—Nickel

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Abstract

the asymmetric N-H-pyridine-Ni metal catalyst of the invention introduces asymmetric ligand complex into the structure, satisfying the need of electrochemical system to require large pi-pi conjugated group to accept electron, and can be used for electrocatalytic reduction of carbon dioxide into carbon monoxide.

Description

Asymmetric N-H-pyridine-Ni metal catalyst and preparation method and application thereof
Technical Field
The invention relates to the technical field of electrochemistry. More particularly, relates to an asymmetric N-H-pyridine-Ni metal catalyst, a preparation method and an application thereof.
background
At present, the content of carbon dioxide artificially emitted in the atmosphere is increased year by year, which causes serious greenhouse effect, global warming, glacier thawing, sea level increase and the like. With the consumption of fossil fuel, CO in air2The discharge amount of the waste water is more and more, and great pressure is caused on the environment. CO22The reduction and conversion into liquid fuel can not only balance the global atmospheric carbon balance, but also convert the liquid fuel into useful fuel and relieve the environmental pressure. At present, both electrochemistry and photoelectrochemistry can reduce CO2Is CO or formic acid, but has many difficulties in regulating the specificity of the catalytic product. One main reason is CO2The reduction is a kinetic limitation, the reduction process needs a plurality of electron transfer participation, and the reduction process is accompanied by a highly competitive hydrogen production process. In addition, since formic acid can serve as a precursor for hydrogen storage fuels and methanol, many effective electrocatalysts selectively reduce CO2is formic acid.
In molecular catalysts, transition metal complexes avoid high overpotentials, store multiple electrons before reacting with carbon dioxide, thus avoid energetic carbon dioxide radical intermediates and allow intermediates based on multiple oxidation states of metals and ligands, which are characterized by reduction of CO2Has a certain effect in the reduction process. In the prior art, carbonyl-ruthenium and rhenium molecular catalysts based on bipyridine units are effective in reducing carbon dioxide to carbon monoxide and formic acid. However, the expensive price of rare metals limits the large-scale utilization of such catalysts.
In order to solve the problem of high price of rare metals, transition metal elements such as iron, nickel and the like are abundant in the earth, so that the method not only has environmental and economic advantages, but also provides opportunities for exploring new catalysts. In recent years, many scientists have made efforts to develop molecular catalysts using the above transition metal elements, and it is desired to obtain a highly efficient and highly selective carbon dioxide reducing agent.
At present, in the field of molecular electrocatalysis carbon dioxide reduction, more systems using noble metals as molecular catalysts are used, and the application of the noble metals is limited due to the scarcity and high price of the noble metals. In electrocatalysis of cheap metals, macrocyclic iron cobalt nickel is studied mostly, but in these systems, the reduction product is mainly CO product. Compared with alkyl nitrogen ligands, the electron transfer characteristics of the large conjugated nitrogen ligand are easier to adjust and more favorable for electrocatalytic reaction, and research of Jean-Michel savetant and the like shows that when substituents such as hydrogen bond-containing groups and the like are introduced into a macrocyclic nitrogen ligand coordination compound, the reactions are more favorable. Based on the characteristics, in the text, the large conjugated nitrogen-nickel complex is designed and synthesized, the influence of the hydrogen bond group of the complex and the introduction of an external proton source on the distribution of the product of the electrocatalytic reduction CO2 is researched, and the reaction mechanism and the catalytic activity of the complex are further explored.
However, few nickel-based nitrogen ligand molecular catalysts are effective in selectively reducing carbon dioxide to carbon monoxide.
accordingly, there is a need to provide an asymmetric nitrohydrogen-pyridine-nickel based metal catalyst that can efficiently electrocatalytically reduce carbon dioxide to carbon monoxide.
disclosure of Invention
An object of the present invention is to provide an asymmetric N-H-pyridine-Ni based metal catalyst.
The invention also aims to provide a preparation method of the asymmetric N-H-pyridine-Ni metal catalyst.
The third purpose of the invention is to provide the application of the asymmetric N-H-pyridine-Ni metal catalyst.
In order to achieve the first purpose, the invention adopts the following technical scheme:
an asymmetric N-H-pyridine-nickel metal catalyst, wherein the structure of the asymmetric N-H-pyridine-nickel metal catalyst is a six-coordination octahedral model structure, and the structural formula of the asymmetric N-H-pyridine-nickel metal catalyst is shown as the following formula I:
Wherein R1 and R2 are the same or different, and R1 and R2 each independently represent an alkyl, trimethylsilyl, amine, imine, alkoxy, benzyl, or halogen substituent; the halogen substituent is-F, -Cl, -Br or-I;
R3 represents a hydrogen atom, an alkyl group, an alkoxy group, a phenyl group, a benzyl group, an amino group, a pyridyl group, an oxazolyl group or biotin;
r4 and R5 are the same or different, and R4 and R5 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, an amino group, a nitrile group, an aryl group, or biotin;
L1、L2And L3each independently represents a halogen atom, an acetonitrile molecule, a carboxylate group, a methanol molecule, a water molecule, or a tetrahydrofuran group.
The present invention introduces an asymmetric ligand complex into the structure, first, nickel is a transition metal element, and in molecular catalysts, the transition metal complex avoids high overpotentials, it can store multiple electrons before reacting with carbon dioxide, and therefore it can avoid high energy carbon dioxide radical intermediates, and intermediates based on multiple oxidation states of metals and ligands have been obtained, and have proven useful in this regard. Moreover, the introduction of the hydrogen bond can promote the coordination of the carbon dioxide, stabilize the intermediate and facilitate the process of electrocatalytic reduction of the carbon dioxide.
Preferably, said R1 and R2 each independently represent an alkyl group of 1 to 6 carbon atoms; wherein the introduction of alkyl groups increases the solubility of the system.
Preferably, said R3 represents an alkyl group of 1 to 10 carbon atoms; wherein R3 is connected with nitrogen hydrogen bond, and the steric hindrance is small, which is beneficial to reducing the reaction resistance and leading the reaction to be carried out smoothly.
Preferably, the R4 and R5 each independently represent a hydrogen atom, an aryl group or an alkyl group of 1 to 6 carbon atoms; wherein R4 and R5 are respectively positioned on pyridine ligands, such as alkyl, which can enhance the solubility of the system and ensure that the system is dissolved in the solution to the maximum extent; if aryl is used, the large conjugated system reduces the solubility of the aryl, so that the aryl is easy to be supported on the surface for catalytic reaction.
In order to achieve the second purpose, the invention adopts the following technical scheme:
The preparation method of the asymmetric N-H-pyridine-Ni metal catalyst comprises the following steps:
1) Dissolving the reactant A in tetrahydrofuran to obtain a mixed solution B;
Dissolving alkyl magnesium bromide in diethyl ether to obtain a mixed solution C;
Mixing the mixed solution C and the mixed solution B for reaction to obtain a mixed solution D;
Mixing the saturated ammonium-containing solution with the mixed solution D for quenching reaction to obtain a reactant E;
Wherein the structural formula of the reactant A is as follows:
2) Dissolving the reactant E in alcohol to obtain a mixed solution F;
Mixing the mixed solution F with acid to obtain a mixed solution G;
Mixing the mixed solution G and an aniline compound for reaction to obtain a reactant H;
3) dissolving a reactant H in alcohol to obtain a mixed solution I;
Mixing the mixed solution I and a reducing compound for reaction to obtain a reactant J;
4) Tetrahydrofuran, reactant J and nickel salt are mixed and reacted to obtain the asymmetric N-H-pyridine-nickel metal catalyst.
Preferably, the preparation method of the reactant A in the step 1) adopts literature (Tetranuclear Co)II,MnII,and CuII Complexes of a Novel Binucleating Pyrazolate Ligand Preorganized for the Self-Assembly of Compact[2×2]-Grid Structures van der Vlugt, j.i.; demeshko, s.; dechert, s.; meyer, f., inorg. chem.2008,47, 1576-.
Preferably, the alkyl magnesium bromide in step 1) is methyl magnesium bromide, ethyl magnesium bromide, butyl magnesium bromide or propyl magnesium bromide.
preferably, the saturated ammonium-containing solution in step 1) is a saturated aqueous ammonium chloride solution, a saturated aqueous ammonium bromide solution or a saturated aqueous ammonium hydroxide solution.
Preferably, the concentration of the reactant A in the mixed liquid B in the step 1) is 0.01-1 mol/L.
Preferably, the concentration of the alkyl magnesium bromide in the mixed liquid C in the step 1) is 1-2 mol/L.
Preferably, the volume ratio of the mixed solution B to the mixed solution C in the step 1) is 1-10: 1.
Preferably, the mixing manner of the mixed solution C and the mixed solution B in the step 1) is as follows: dropwise adding the mixed solution C into the mixed solution B, and stirring for reaction to obtain a mixed solution D; wherein the temperature during dripping is 0-10 ℃, the stirring reaction is carried out for 2-4h at-15 to-20 ℃, and then stirring is carried out for 3-4 h under the normal temperature condition. Wherein the stirring speed is not limited, and the reaction is not influenced; in addition, because the Grignard reagent is afraid of water and oxygen, the Grignard reagent and water oxygen can react violently to release a large amount of heat, so that splashing is caused or explosion is caused when the amount is large, and the mixed solution C is added into the mixed solution B dropwise at low temperature, so that the solution temperature cannot rise sharply, and accidents are prevented.
Preferably, the mixing manner of the saturated ammonium-containing solution and the mixed solution D in the step 1) is as follows: dropwise adding the saturated ammonium-containing solution into the mixed solution D until the surface of the reaction liquid does not smoke any more, and gradually changing the solution into orange red; wherein the dropwise addition is carried out under the ice bath condition of 0 to-10 ℃. Wherein, excessive Grignard reagent is afraid of water and oxygen, and can react with water and oxygen violently to release a large amount of heat, thereby causing splashing or explosion when the amount is large, and the Grignard reagent is added dropwise at low temperature, so that the temperature of the solution can not rise sharply, and accidents are prevented.
Preferably, the alcohol in step 2) is methanol, ethanol, propanol, butanol or ethylene glycol.
Preferably, the acid in step 2) is formic acid, acetic acid, propionic acid, butyric acid or oxalic acid.
preferably, the aniline compound in the step 2) is 2, 6-diisopropylaniline, aniline, 2, 6-dinitroaniline or 2, 6-dibromoaniline.
Preferably, the concentration of the reactant E in the mixed solution F in the step 2) is 0.01-0.2 mol/L.
Preferably, the mixing manner of the mixed solution F and the acid in the step 2) is: dropwise adding an acid into the mixed solution F (slowly dropwise adding the reactant E to be fully acidified); the volume ratio of the mixed solution F to the acid is 1: 0.001 to 0.01.
preferably, the mixing manner of the mixed solution G and the aniline compound in the step 2) is as follows: adding aniline compound into the mixed solution G for reaction; the molar ratio of the reactant E to the aniline compound in the mixed solution G is 0.8-1: 1, the reaction condition is heating reflux stirring for 22-24 hours, and the reflux temperature is 90-110 ℃. The stirring rate is not limited, and the reaction is not affected.
Preferably, the reducing compound in step 3) is a reagent for reducing imine; further, the reducing compound is sodium borohydride, sodium hydride or sodium cyanoborohydride.
Preferably, the concentration of the reactant H in the mixed solution I in the step 3) is 0.01-0.2 mol/L.
preferably, the mixing manner of the mixed solution I and the reducing compound in the step 3) is as follows: adding a reducing compound into the mixed solution I for reaction; the molar ratio of the reactant H to the reducing compound in the mixed solution I is 1-1: 10, stirring at normal temperature for 22-24 h.
Preferably, the molar ratio of the tetrahydrofuran, the reactant J and the nickel salt in the step 4) is 5-10: 1: 1.
Preferably, the nickel salt in step 4) is nickel tetraethyl cyanide trifluoromethanesulfonate, nickel acetate or nickel halide; the nickel halide is nickel chloride, nickel bromide or nickel fluoride and the like.
Preferably, the reaction in the step 4) is a stirring reaction for 2-4 hours. The stirring rate is not limited, and the reaction is not affected.
In order to achieve the third purpose, the invention adopts the following technical scheme:
An application of the asymmetric N-H-pyridine-Ni metal catalyst in electrocatalytic reduction of carbon dioxide.
preferably, the application is the application of the asymmetric nitrogen hydrogen-pyridine-nickel metal catalyst in electrocatalytic reduction of carbon dioxide into carbon monoxide. Electrochemical research shows that the asymmetric N-H-pyridine-Ni metal catalyst is used for CO2Has high responsiveness, and has regulating effect on electrolysis products when different external proton sources are introduced, wherein when the trifluoroethanol proton source is added, the trifluoroethanol proton source can effectively and selectively reduce carbon dioxide into carbon monoxide in acetonitrile, and the carbon monoxide accounts for 80% of all reduction products.
Preferably, the specific steps of the asymmetric N-H-pyridine-Ni metal catalyst for electrocatalytic reduction of carbon dioxide into carbon monoxide comprise: dissolving tetrabutylammonium hexafluorophosphate in acetonitrile to obtain a mixed solution L, mixing the mixed solution L with an asymmetric N-H-pyridine-Ni metal catalyst to obtain a mixed solution M, introducing Ar to sweep the electrochemical CV, and exchanging carbon dioxide to sweep the electrochemical CV.
Preferably, the concentration of tetrabutylammonium hexafluorophosphate in the mixed solution L is 90-120 mM.
preferably, the concentration of the asymmetric ligand nickel metal catalyst in the mixed solution M is 1-3 mM.
Preferably, after the Ar is applied to sweep the electrochemical cyclic voltammetry curve, water is further added to the mixed solution M.
Preferably, the volume fraction of water is 1% vol to 3% vol.
preferably, the conditions for Ar-scanning electrochemical CV are: the sweep rate is 10-500 mV/s, the voltage is 0-minus 2V, the electrolysis electric quantity is about 1-3C, and the electrolysis time is obtained according to the electric quantity.
preferably, the carbon dioxide is introduced to sweep the electrochemical CV under the conditions of sweep speed of 10-500 mV/s, voltage of 0-2V and electrolytic electric quantity of 1-3C C, and the electrolysis time is obtained according to the electric quantity.
In addition, unless otherwise specified, all starting materials for use in the present invention are commercially available, and any range recited herein includes any value between the endpoints and any subrange between the endpoints and any value between the endpoints or any subrange between the endpoints.
The invention has the following beneficial effects:
(1) The asymmetric N-H-pyridine-nickel metal catalyst introduces an asymmetric ligand complex into a structure, meets the requirement that an electrochemical system needs a large pi-pi conjugated group to accept electrons, and can be used for electrocatalytic reduction of carbon dioxide into carbon monoxide.
(2) According to the asymmetric N-H-pyridine-Ni metal catalyst, two diisopropyl large steric hindrance groups are introduced to an asymmetric ligand to prevent a coordination compound from dimerization, so that reaction sites are exposed, and the catalyst can be used for electrocatalytic reduction of carbon dioxide into carbon monoxide.
(3) the asymmetric N-H-pyridine-Ni metal catalyst can effectively and selectively reduce carbon dioxide into carbon monoxide, has the selectivity up to 80 percent, and enriches the nickel catalyst system.
(4) unsaturated ligands are introduced into the asymmetric N-H-pyridine-Ni metal catalyst, and two electrocatalysis systems are compared.
drawings
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
FIG. 1 shows the synthetic route of the asymmetric N-H-pyridine-Ni-acetonitrile metal catalyst of example 1 of the present invention and the asymmetric unsaturated compound of comparative example 1.
Fig. 2 shows a schematic crystal structure of an asymmetric n-mh-pyridine-nickel-acetonitrile metal catalyst prepared in example 1 of the present invention.
fig. 3 shows a schematic of the crystal structure of the asymmetric imine-pyridine-nickel-acetonitrile metal catalyst prepared in comparative example 1 of the present invention.
Fig. 4 shows a schematic of the crystal structure of the asymmetric imine-pyridine-nickel-acetic acid metal catalyst prepared in comparative example 2 of the present invention.
Figure 5 shows an electrochemical cyclic voltammogram of an asymmetric N-H-pyridine-Ni-acetonitrile metal catalyst in example 2 of the present invention.
Fig. 6 shows the electrochemical cyclic voltammogram of the asymmetric imine-pyridine-nickel-acetonitrile metal catalyst prepared in comparative example 3 of the present invention.
Figure 7 shows one of the infrared spectra of the asymmetric N-H-pyridine-Ni-acetonitrile metal catalyst of example 3 of the present invention.
Figure 8 shows the second infrared spectrum of the asymmetric N-H-pyridine-Ni-acetonitrile metal catalyst of example 3 of the present invention.
FIG. 9 shows the electrochemical cyclic voltammogram of a 2mM asymmetric N-hydrogen-pyridine-nickel-acetonitrile metal catalyst in 0.1M ammonium tetrabutylammonium hexafluorophosphate in acetonitrile with addition of water in a volume fraction of 0 to 3% vol under an Ar atmosphere in example 4 of the present invention.
FIG. 10 shows CO in example 5 of the present invention2An electrochemical cyclic voltammetry curve of a 2mM asymmetric N-hydrogen-pyridine-nickel-acetonitrile metal catalyst in acetonitrile of 0.1M tetrabutylammonium hexafluorophosphate when water with a volume fraction of 0-3% vol is added under an atmosphere.
FIG. 11 shows CO in example 6 of the present invention2One of the cyclic voltammograms of 2mM asymmetric nitrogen hydrogen-pyridine-nickel-acetonitrile metal catalyst in 0.1M acetonitrile tetrabutylammonium hexafluorophosphate with different volume fractions of water addition under atmosphere.
FIG. 12 shows CO in example 6 of the present invention2two cyclic voltammogram of 2mM asymmetric nitrogen hydrogen-pyridine-nickel-acetonitrile metal catalyst in 0.1M acetonitrile tetrabutylammonium hexafluorophosphate with different volume fractions of water added under atmosphere.
FIG. 13 shows CO in example 7 of the present invention2one of the cyclic voltammograms of 2mM asymmetric nitrogen hydrogen-pyridine-nickel-acetonitrile metal catalyst in 0.1M acetonitrile tetrabutylammonium hexafluorophosphate with different volume fractions of deuterium water added under atmosphere.
FIG. 14 shows CO in example 7 of the present invention2Two cyclic voltammogram of 2mM asymmetric nitrogen hydrogen-pyridine-nickel-acetonitrile metal catalyst in 0.1M acetonitrile of tetrabutylammonium hexafluorophosphate with different volume fractions of deuterium water added.
FIG. 15 shows CO in example 8 of the present invention2One of the cyclic voltammograms of 2mM asymmetric N-H-pyridine-Ni-acetonitrile metal catalyst in 0.1M acetonitrile tetrabutylammonium hexafluorophosphate with different volume fractions of ethanol water added under atmosphere.
FIG. 16 shows CO in example 8 of the present invention2two cyclic voltammogram of 2mM asymmetric nitrogen hydrogen-pyridine-nickel-acetonitrile metal catalyst in 0.1M acetonitrile of tetrabutylammonium hexafluorophosphate with different volume fractions of ethanol water added.
FIG. 17 shows CO in example 9 of the present invention2Cyclic voltammogram of 2mM asymmetric nitrogen hydrogen-pyridine-nickel-acetonitrile metal catalyst in 0.1M tetrabutylammonium hexafluorophosphate in acetonitrile with different volume fractions of trifluoroethanol added under atmosphere.
FIG. 18 shows CO in example 9 of the present invention2Two cyclic voltammogram of 2mM asymmetric nitrogen hydrogen-pyridine-nickel-acetonitrile metal catalyst in 0.1M acetonitrile tetrabutylammonium hexafluorophosphate with different volume fractions of trifluoroethanol added under atmosphere.
FIG. 19 shows CO in examples 10 and 12 of the present invention2Potentiostatic electrolysis curve of 2mM asymmetric N-H-pyridine-Ni-acetonitrile metal catalyst in 0.1M tetrabutylammonium hexafluorophosphate in acetonitrile under atmosphere.
FIG. 20 showsCO in example 11 of the present invention2Electrolytic faradaic efficiency and product distribution for varying potentials of 2mM asymmetric nitrogen hydrogen-pyridine-nickel-acetonitrile metal catalyst in 0.1M tetrabutylammonium hexafluorophosphate in acetonitrile under atmosphere.
FIG. 21 shows CO in example 13 of the present invention2Under the atmosphere, a certain amount of trifluoroethanol is added into 2mM asymmetric nitrogen hydrogen-pyridine-nickel-acetonitrile metal catalyst in acetonitrile of 0.1M tetrabutylammonium hexafluorophosphate to transform the electrolysis Faraday efficiency and product distribution of different potentials.
FIG. 22 shows CO in example 14 of the present invention2Electrolytic faradaic efficiencies and product distributions of 2mM asymmetric nitrogen hydrogen-pyridine-nickel-acetonitrile metal catalyst in 0.1M acetonitrile tetrabutylammonium hexafluorophosphate with different volume fractions of trifluoroethanol added.
FIG. 23 shows CO in example 15 of the present invention2Transformation of 2mM asymmetric imine-pyridine-nickel-acetonitrile metal catalyst in 0.1M tetrabutylammonium hexafluorophosphate in acetonitrile under atmosphere faradaic efficiency and product distribution for different potentials electrolysis.
Detailed Description
In order to more clearly illustrate the invention, the invention is further described below with reference to preferred embodiments and the accompanying drawings. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
In the present invention, the preparation methods are all conventional methods unless otherwise specified. The starting materials used are, unless otherwise specified, available from published commercial sources, and the percentages are, unless otherwise specified, percentages by mass.
In the invention, the preparation methods are all conventional methods if no special description is provided, the percentages are mass percentages if no special description is provided, the unit M is mol/L if no special description is provided, the reaction conditions are normal temperature and normal pressure conditions if no special description is provided, the used medicines and solvents are commercially available, except that the solvent needing drying is particularly mentioned in the text, and the medicines and the solvents are directly used without treatment if no description is provided.
In the invention, the dried dichloromethane, tetrahydrofuran and acetonitrile are obtained by a solvent purification system; the material used for column chromatography is 200-300 mesh silica gel or aluminum oxide; the nuclear magnetic resonance spectrum hydrogen spectrum and carbon spectrum are measured by a Bruker Avance400M nuclear magnetic resonance instrument at room temperature, and Trimethylsilane (TMS) is used as an internal standard; high resolution mass spectra were determined on a BruKer Apex IV Fourier Transform mass spectrometer; 4,4 '-dimethyl-2, 2' -bipyridine was purchased from Acros; deionized Water was obtained from an ultra-pure Water machine Master-S15 UV Water Purification system.
In addition, compounds 3, 4 and nickel tetranitrile triflate in the present invention were synthesized by literature methods, namely: synthesis of compounds 3, 4: tetranuclear CoII,MnII,and CuII Complexes of a Novel Binucleating Pyrazolate Ligand Preorganized for the Self-Assembly of Compact[2×2]-Grid Structures van der Vlugt, j.i.; demeshko, s.; dechert, s.; meyer, f., inorg. chem.2008,47, 1576-. Compound 3 is consistent with the pyridine nitrogen-oxygen synthesis method in this document; compound 4 is consistent with the pyridine nitrogen-ketone synthesis method in this document with nickel tetraacetonitrile triflate: iron (II) Triflate Salts as transgenic substrates for Perchlorine Salts of Crystal Structures of [ Fe (H2O)6](CF3SO3)2 and Fe (MeCN)4(CF3SO3)2 Hagen, K.S., Inorg. chem.2000,39, 5867-. Which is consistent with the synthesis of ferric tetra-ethylnitrile-triflate in this document.
the synthesis of compound 3 in the invention specifically comprises the following steps:
adding 4, 4-dimethyl-2, 2-bipyridine (3.68g,20mmol) into a 100mL round-bottom flask, adding 10mL trifluoroacetic acid into a reaction flask at normal temperature, dropwise adding 30% hydrogen peroxide (3.00mL,30mmol) into the reaction flask, fully stirring for 2-4h at room temperature, performing dot-plate detection, after the reaction is finished, dropwise adding 5M sodium hydroxide solution under ice bath, and adjusting the pH to be neutral. The mixture was extracted three times with 50mL of chloroform, combined, washed three times with saturated sodium chloride brine, dried over anhydrous sodium sulfate, and the organic phases were combined, filtered, rotary evaporated, and dried under vacuum to give 3.5g of Compound 3.
The synthesis of compound 4 in the present invention specifically comprises the following steps:
Compound 3(15.26g,88.6mmol) and trimethylsilanoxane (50mL,375mmol) were added dropwise carefully to 250mL of dry dichloromethane under ice-bath under nitrogen (2equiv,20.4mL,177.2mmol) and stirred overnight. 10% aqueous sodium carbonate (200mL) was added slowly under ice bath conditions and the reaction was quenched. The organic phase was washed three times with saturated brine, dried over anhydrous magnesium sulfate, filtered and spin-dried. This gave 12.45g,68.7mmol, 77.5% as a pure white solid powder.
The above synthetic steps are referred to the reported literature, and the nuclear magnetic characterization of the product is consistent with the literature. It will be appreciated by those skilled in the art that the compound 3 is an existing compound, and the compound 3 can also be prepared by other existing methods, and the above preparation method is not limiting, and should not limit the scope of the present invention.
Electrochemical experiments in the present invention all used the CHI 601E electrochemical workstation (CH Instruments, inc., TX). The three-electrode system comprised a glassy carbon working electrode, a platinum wire counter electrode and a silver/silver nitrate reference electrode (BASi,10mM silver nitrate, 0.1M solution of tetrabutylammonium hexafluorophosphate in acetonitrile, 0.55V vs NHE), gas filled in two separate cells. Before each test, a glassy carbon electrode (BASi,7.1mm2) was polished with 0.05 μm aluminum paste to give a mirror surface, followed by sonication with ultrapure water and acetone. For cyclic voltammetry experiments, one side of the working and counter electrodes and the other side of the reference electrode. For the electrolysis experiments, the reference and counter electrodes were on one side and the working electrode on the other side. Ferrocene was added as a calibration substance and converted to the standard hydrogen potential NHE by adding 0.55V. The gas phase product was detected by Varian 8610C-GC, equipped with molecular sieves and a PDHID detector. The electrochemical tests are carried out under mild conditions, and unexpected conditions such as severe temperature rise and the like can be avoided if no special statement is made.
example 1
An asymmetric N-H-pyridine-Ni-acetonitrile metal catalyst, i.e. 2MeCNthe structural formula is as follows:
The synthesis route of the catalyst is shown in figure 1, and the preparation comprises the following steps:
1) synthesis of Compound 5:
Methylmagnesium bromide (3.0M in ether solution, 0.85mL, 2.5 equiv., 12.5mmol) was added dropwise to compound 4(1.05g,5.0mmol) in dry tetrahydrofuran at-15 deg.C, and the reaction was stirred at-15 deg.C for 1h, then at ambient temperature for 2h to give an orange-red liquid. After the reaction, saturated ammonium chloride is added dropwise under the ice-bath condition to quench the reaction, organic phases are extracted by tetrahydrofuran and dichloromethane respectively, the organic phases are combined, washed by saturated common salt for three times, dried by anhydrous sodium sulfate, the organic phases are combined, filtered and evaporated in a rotary manner, and dried in vacuum to obtain a white solid compound 5(735mg,3.25mmol, 65.0%).1H NMR(400MHz,CDCl3):δ8.55(d,J＝5.0Hz,1H),8.44(s,1H),8.33(s,1H),7.88(s,1H),7.17(d,J＝4.9Hz,1H),2.83(s,3H),2.49(d,J＝4.3Hz,6H)。
2) 226mg (i.e., 1.00mmol) of Compound 5 was dissolved in 10mL of ethanol solution, ten drops of acetic acid were added, followed by 0.38mL (i.e., 2.00mmol) of 2, 6-diisopropylaniline, and the mixture was stirred under reflux for 72 hours. After cooling to room temperature, the solvent was distilled off under reduced pressure. The precipitate was dissolved in chloroform, washed with saturated sodium bicarbonate water, washed with saturated sodium chloride, dried over anhydrous sodium sulfate, filtered and spin-dried. Column dichloromethane and methanol (100:3 by volume) were passed to give 308mg of the product, ligand L1.
Yield: 80 percent.1H NMR(400MHz,CDCl3):δ8.57(d,J＝4.9Hz,1H,Py-CH),8.38(d,J＝6.0Hz,2H,Py-CH),8.24(s,1H,Py-CH),7.20(d,J＝7.6Hz,2H,Ar-CH),7.18–7.10(t,1H,Ar-CH),7.15(d,J＝4.0Hz,1H,Py-CH)2.91–2.74(m,2H,CH3CHCH3),2.48-2.55(d,6H,CH3-Py),2.36(s,3H,CH3C＝N),1.24–1.12(m,12H,CH3CHCH3)。13C NMR(400MHz,CDCl3):δ167.5(Cq,s,C＝N-Ar),156.1(Cq,s,Py-C),155.7(Cq,s,Py-C),155.1(Cq,s,Py-C),149.1(CH,s,Py-C),148.7(Cq,s,Py-C),148.1(Cq,s,Py-C),146.7(Cq,s,Ar-C-N),136.1(Cq,s,Ar-C),124.9(CH,s,Py-C),123.7(Cq,s,Ar-C),123.2(CH,s,Py-C),123.1(CH,s,Ar-C),122.1(CH,s,Ar-C),121.9(CH,s,Py-C),28.4(CH,s,CH3CHCH3),23.2-23.4(CH,d,CH3CHCH3),21.5(CH,s,CH3-Py),17.6(CH,s,CH3-C＝N).HR-ESI-MS:m/z calcd for[M]+C26H32N3:386.259074；found:386.259151,error:0.2ppm；calcd for[M+Na]+C26H31N3Na:408.241019；found:408.240803,error:0.5ppm.
3) Synthesis of compound L2: ligand L1(386mg,1.00mmol) was dissolved in 10mL of anhydrous methanol solution, sodium borohydride (380mg,10.00mmol) was added, stirring was performed at room temperature, and spotting was performed. After the reaction is finished, the solvent is removed by reduced pressure distillation. The precipitate was dissolved in chloroform, washed with saturated sodium chloride, dried over anhydrous sodium sulfate, filtered and spin-dried. CH (CH)2Cl2/CH3OH (100:3, v/v) is passed through the column to obtain the product. The yield is 90%.1H NMR(400MHz,CDCl3):8.55(d,J＝4.9Hz,1H),8.37(s,1H),8.14(s,1H),7.15(d,J＝4.8Hz,1H),7.08(d,J＝6.8Hz,2H),7.02(dd,J＝8.6,6.3Hz,1H),6.94(s,1H),4.34(q,J＝6.6Hz,1H),3.52–3.38(m,2H),2.48-2.38(d,6H),1.45(d,J＝6.7Hz,3H),1.28-1.13(m,12H).13C NMR(400MHz,CDCl3):δ162.7(Cq,s,C＝N-Ar),156.4(Cq,s,Py-C),155.6(Cq,s,Py-C),149.0(CH,s,Py-C),148.5(Cq,s,Py-C),147.9(Cq,s,Py-C),142.3(Cq,s,Ar-C-N),142.1(Cq,s,Ar-C),124.7(CH,s,Py-C),123.5(CH,s,Ar-C),123.1(CH,s,Py-C),122.6(CH,s,Ar-C),122.0(CH,s,Ar-C),120.4(CH,s,Py-C),60.3(CH,s,Py-C),27.9(CH,s,CH3CHCH3),24.3-24.2(CH,d,CH3CHCH3),22.5(CH,s,CH3-Py),21.4-21.3(CH,d,CH3-C＝N).HR-ESI-MS:m/z calcd for[M]+C26H34N3:388.274725；found:388.274769,error:0.1ppm；calcd for[M+Na]+C26H33N3Na:410.256669；found:410.256827,error:0.4ppm.
4) Compound 2MeCNIn a 50mL round-bottomed flask, 20mL of tetrahydrofuran, L2(77mg,0.20mmol) and Ni (CF) were added3SO3)2(CH3CN)4(104mg,0.20mmol), and stirred at room temperature overnight. The solution was spun dry and washed three times with ether to give 92mg of solid yellow product, 95% yield HR-ESI-MS, M/z calcd for 1/2[ M-CH ]3CN-2H2O]2+C26H31NiN3:222.600847；found:222.600873,error:-0.1ppm；m/z calcd for 1/2[M-2H2O]2+C28H34NiN4:242.106296；found:242.106330,error:0.1ppm.
The solid green productthe product is the asymmetric N-H-pyridine-Ni-acetonitrile metal catalyst 2MeCN。
To the prepared 2MeCNSubjecting to X-ray single crystal diffraction, and analyzing Compound 2 as shown in FIG. 2MeCNIs a pure green crystal obtained by slow diffusion of cyclohexane into tetrahydrofuran at room temperature, and has a crystal structure of 1MeCNThe medium nickel atom is coordinated in a horizontal position by three nitrogen atoms of the ligand L1, three water molecules, two axial coordination and one horizontal coordination. Although no water molecules are introduced during the growth of the single crystal, three water molecules are de-coordinated due to the small amount of water that may be present in tetrahydrofuran or the extremely easy coordination of water molecules, and it is demonstrated that water molecules are extremely easy to coordinate to the nickel center.
Comparative example 1
Asymmetric compound 1MeCNThe structural formula is as follows:
The preparation method comprises the following steps:
1) Synthesis of ligand L1: in accordance with the synthesis procedure of L1 in example 1.
2) Compound 1MeCNIn a 50mL round-bottomed flask, 20mL of tetrahydrofuran, L1(77mg,0.20mmol) and Ni (CF) were added3SO3)2(CH3CN)4(104mg,0.20mmol), and stirred at room temperature overnight. The solution was spun dry and washed three times with ether to give 92mg of solid yellow product, 95% yield HR-ESI-MS, M/z calcd for 1/2[ M-2H ]2O]2+C28H34NiN4:242.106296；found:242.106387,error:-0.2ppm.
For the obtained 1MeCNsubjecting to X-ray single crystal diffraction, and analyzing Compound 1 as shown in FIG. 3MeCNIs a pure green crystal obtained by slowly diffusing diethyl ether into acetonitrile solution at room temperature, and the crystal structure shows 1MeCNThe middle nickel atom is coordinated by three nitrogen atoms of a ligand L1 in a horizontal position, one acetonitrile molecule, two water molecules, one is coordinated in an axial direction, and the other is coordinated in a horizontal directiona bit. Although no water molecules were introduced during the growth of the single crystal, three water molecules were de-coordinated due to the small amount of water that may be present in the acetonitrile or the extreme ease of coordination of the water molecules, and this suggests that the water molecules are extremely easy to coordinate to the nickel center.
Comparative example 2
An asymmetric N-H-pyridine-Ni-carboxylate ion metal catalyst with carboxylate anions introduced, namely 1OActhe structural formula is as follows:
the preparation method is the same as 2 in example 1MeCNThe synthesis methods are consistent, and the difference is that: in catalyst 1OAcIn the preparation step 1), the reactant acetonitrile nickel triflate Ni (CF)3SO3)2(CH3CN)4And replacing the nickel acetate with equal amount of the substances.
For the obtained 1OAcPerforming X-ray single crystal diffraction, as shown in FIG. 4, Compound 1OAcThe carboxylate anion is used as a counter ion, and the crystal structure of the counter ion shows that two carboxylate counter ions are coordinated to the compound, one water molecule is coordinated to the compound, and the acetonitrile molecule is not subjected to de-coordination.
Example 2
For 2 obtained in example 1MeCNPerforming electrochemical performance characterization:
2.5mL of 0.1M tetrabutylammonium hexafluorophosphate in acetonitrile was added to the mixture of 2M tetrabutylammonium hexafluorophosphate obtained in example 1MeCNTo obtain a mixture solution, wherein the concentration of the mixture solution is 2mM (i.e. 2mmol of 1 per L of acetonitrile of tetrabutylammonium hexafluorophosphate)MeCN) After Ar is introduced for 10min, sweeping the electrochemical CV at a sweeping speed of 50 mV/s; after that, the electrochemical CV was swept at a sweep rate of 50mV/s after 10min of carbon dioxide was switched on.
The characterization results are shown in FIG. 5, and the Cyclic Voltammograms (CV) of the compounds in acetonitrile are shown in Ar or CO2Obtaining the product; wherein, Ar is lower than the compound 1MeCNShows two reversible electrochemical peaks E1/2-0.35V (peak I) and1.03V (Peak II), Peak I being electrochemically reversible, and being ascribed to the Ni (II)/Ni (I) electrochemical reduction electron pair, Peak II being at E1/2Nhe belongs to a reduction process at the center of the azahydro-pyridine ligand.
However, at 1 atmosphere CO2Next, peak I retained the diffusion characteristic and peak II became the electrocatalytic peak. After normalization, the normalized peak II current gradually increased as the sweep rate decreased from 500 to 10mV s-1, which corresponds to the electrocatalytic process.
Comparative example 3
1 obtained in comparative example 1MeCNPerforming electrochemical performance characterization:
To 2.5mL of 0.1M tetrabutylammonium hexafluorophosphate in acetonitrile was added 1 prepared in comparative example 1MeCNTo obtain a mixture solution, wherein the concentration of the mixture solution is 2mM (i.e. 2 mmol/L acetonitrile of tetrabutylammonium hexafluorophosphate)MeCN) After Ar is introduced for 10min, sweeping the electrochemical CV at a sweeping speed of 50 mV/s; after that, the electrochemical CV was swept at a sweep rate of 50mV/s after 10min of carbon dioxide was switched on.
the characterization results are shown in FIG. 6, 1MeCNShows an electrochemical CV of 2MeCNSimilar peaks, but with the peak shifted to a more positive position, respectively corresponding to E1/2The peak position was shifted up due to the stronger electron donating ability of ligand L1 than ligand L2 for-0.38V peak I 'and-1.37V peak II'.
Combine FIGS. 5 and 6 to pair 1MeCNAnd 2MeCNComparison of electrochemical performance: as shown in fig. 5, for 2MeCNWhen the solution was saturated with carbon dioxide gas, peak I remained almost unchanged and peak II intensity increased by a factor of 2.4.
As shown in FIG. 6, Compound 1MeCNThe current enhancement was also shown at the position of peak II', but the enhancement was lower, up to 1.4 times that of the original, indicating Compound 2MeCNRatio 1MeCNthe reaction activity is high.
Example 3
The influence of the generation of the intermediate compound on the electrochemical performance of the asymmetric N-H-pyridine-Ni-acetonitrile metal catalyst is tested, and the method comprises the following steps:
2.5mL of 0.1M tetrabutylammonium hexafluorophosphate in acetonitrile was added to the mixture of 2M tetrabutylammonium hexafluorophosphate obtained in example 1MeCNto obtain a mixture solution, wherein the concentration of the mixture solution is 5mM (i.e. 2mmol of 1 per L of acetonitrile of tetrabutylammonium hexafluorophosphate)MeCN) After 20min of Ar introduction, saturation, electrolysis was carried out for 4h at-1.45V vs. NHE. And (5) measuring the infrared of the liquid and observing the result. Comparing the electrolysis results before non-electrolysis and under Ar with CO2And (4) performing lower electrolysis.
The results are shown in FIGS. 7 and 8, 2 under ArMeCNThree new peaks appear, corresponding to carbon dioxide coordinated C ═ O double bond oscillations and C — O single bond oscillations. Description of Ni Compound and CO2The reaction takes place.
example 4
Examination of 2 from example 1 with different volume fractions of water under Ar atmosphereMeCNThe electrochemical performance of (a) is as follows:
2.5mL of 0.1M tetrabutylammonium hexafluorophosphate in acetonitrile was added to the mixture of 2M tetrabutylammonium hexafluorophosphate obtained in example 1MeCNTo obtain a mixture solution, wherein the concentration of the mixture solution is 2mM (i.e. 2 mmol/L acetonitrile of tetrabutylammonium hexafluorophosphate)MeCN) After 10min Ar, the electrochemical CV is swept at a sweep rate of 50 mV/s. Then adding water with different volume fractions to the mixed solution, wherein the water respectively accounts for 0% vol, 1% vol, 2% vol and 3% vol of the volume of the mixed solution, and sweeping the electrochemical CV at a sweeping speed of 50 mV/s.
FIG. 9 shows 2mM 2 under ArMeCNCV in acetonitrile with 0-3% water. The position of peak I hardly shifts compared to the dry case. Probably due to the coordination of water to the nickel centre, buffering the effect. Peak II shows almost no change in peak height after addition of water, indicating 2MeCNIs not a hydrogen-producing catalyst.
example 5
Testing CO2Addition of different volume fractions of water under atmosphere for 2 from example 1MeCNThe electrochemical performance of (a) is as follows:
2mM of 2 obtained in example 1 was added to 2.5mL of 0.1M acetonitrile containing tetrabutylammonium hexafluorophosphateMeCNThen adding 0% vol1%, 2% vol, 3% vol of water, after passing 10min of carbon dioxide, the electrochemical CV is swept at a sweep rate of 50 mV/s.
The results are shown in FIG. 10:
In CO2In this case, when the water fraction increased from 0 to 3%, peak II 26%, indicating that the addition of water promoted CO2The effective reduction of (2).
example 6
Testing CO2Addition of different volume fractions of water under atmosphere for 2 from example 1MeCNThe electrochemical performance of (a) is as follows:
2mM of 2 obtained in example 1 was added to 2.5mL of 0.1M acetonitrile containing tetrabutylammonium hexafluorophosphateMeCNAnd 2mM ferrocene is added as an internal standard, then 0% vol, 1% vol, 2% vol, 3% vol, 5% vol, 10% vol and other water are respectively added, and after 10min of carbon dioxide is introduced, the electrochemical CV is swept at a sweep rate of 50 mV/s.
The results are shown in FIGS. 11 and 12:
In CO2In the case where the water fraction increased from 0 to 10% vol, peak II increased to 1-1.9 times the peak current in pure carbon dioxide, eventually reaching an equilibrium current, indicating that the addition of water promoted CO2Reduction of (2).
Example 7
Testing CO2Under atmosphere, adding deuterium water with different volume fractions to the mixture 2 prepared in example 1MeCNThe electrochemical performance of (a) is as follows:
2mM of 2 obtained in example 1 was added to 2.5mL of 0.1M acetonitrile containing tetrabutylammonium hexafluorophosphateMeCNand 2mM ferrocene is added as an internal standard, then deuterium water with the volume of 0%, 1%, 2%, 3%, 5%, 10% and the like is respectively added, and after carbon dioxide with the volume of 10min is introduced, the electrochemical CV is swept at the sweep speed of 50 mV/s.
The results are shown in fig. 13 and 14:
In CO2Under the condition, when the deuterium water fraction is increased from 0 to 10 percent, the peak II is increased to be 1.20-1.48 times of the peak current under the high-purity carbon dioxide, and finally the equilibrium current is reached, which indicates that the addition of the deuterium water promotes CO2Reduction of (2).
Example 8
Testing CO2Addition of different volume fractions of ethanol to 2 from example 1 under an atmosphereMeCNthe electrochemical performance of (a) is as follows:
2mM of 2 obtained in example 1 was added to 2.5mL of 0.1M acetonitrile containing tetrabutylammonium hexafluorophosphateMeCNAnd 2mM ferrocene is added as an internal standard, then 0% vol, 2% vol (0.28M), 4% vol (0.56M) and other ethanol are respectively added, and after 10min of carbon dioxide is introduced, the electrochemical CV is swept at a sweep rate of 50 mV/s.
Results are shown in fig. 15 and 16:
In CO2Under the condition, when the ethanol fraction is increased from 0 to 410 percent, the peak II is increased to be 1.11 to 1.21 times of the peak current under pure carbon dioxide, and finally the equilibrium current is reached, which indicates that the addition of ethanol promotes CO2Reduction of (2).
example 9
Testing CO2Under atmosphere, different volume fractions of trifluoroethanol were added to the reaction mixture 2 obtained in example 1MeCNThe electrochemical performance of (a) is as follows:
2mM of 2 obtained in example 1 was added to 2.5mL of 0.1M acetonitrile containing tetrabutylammonium hexafluorophosphateMeCNAnd 2mM ferrocene is added as an internal standard, then trifluoroethanol with the concentration of 0% vol, 2% vol (0.28M), 4% vol (0.56M), 6% vol (0.84M), 8% vol (1.12M) and the like is respectively added, and after carbon dioxide with the concentration of 10min is introduced, the electrochemical CV is swept at the sweep rate of 50 mV/s.
The results are shown in fig. 17 and 18:
In CO2Under the condition, when the fraction of the trifluoroethanol is increased from 0 to 9 percent, the peak II is increased to be 1.35 to 2.21 times of the peak current under pure carbon dioxide, and finally the equilibrium current is reached, which indicates that the addition of the trifluoroethanol promotes CO2The effective reduction of (2).
example 10
Controlled potential electrolysis experiments:
2.5mL of 0.1M tetrabutylammonium hexafluorophosphate in acetonitrile was added to the mixture of 2M tetrabutylammonium hexafluorophosphate obtained in example 1MeCNto obtain a mixed solutionWherein the concentration of the mixture is 2mM (i.e., 2mmol of 2 per L of acetonitrile of tetrabutylammonium hexafluorophosphateMeCN) After 15min of carbon dioxide is introduced, closing the electrolytic cell for electrolysis, stopping the electrolysis when the electrolytic capacity reaches 1.0-2.0 ℃, extracting 2mL of gas phase gas by using a sample injection needle, injecting the gas phase gas into a gas phase chromatograph, and detecting a gas phase electrolysis product; then taking 1mL of liquid phase liquid, spin-drying, adding 10 microliter of 100mM acetonitrile solution of N, N-dimethylformamide as a standard sample, carrying out hydrogen spectrum nuclear magnetism, and detecting the liquid phase product.
Controlled Potential Electrocatalytic (CPE) experiments were performed at-1.45V vs NHE, which showed reasonably stable current densities over 10h of electrolysis.
as shown in FIG. 19, the average density of the catalytic current was maintained at 0.8mA/cm in average throughout the electrolysis2. This shows that, throughout the catalytic process, Compound 2MeCNIs stable. Carbon monoxide is generated by detecting gas phase products generated by electrolysis.
Example 11
The effect of different potentials was examined, i.e. the method steps were the same as in example 10, except that: the control potentials were respectively: NHE, -1.05V vs. NHE, -1.15V vs. NHE, -1.25V vs. NHE, -1.35V vs. NHE.
The gases generated in the electrochemical cell were analyzed by gas chromatography and the liquid phase solution was characterized by nuclear magnetic NMR.
The results are shown in FIG. 20, the best results were electrolysis at-1.05V vs. NHE for 6h (glassy carbon electrode, 7.1 mm)2) The selectivity of carbon monoxide generation reaches 25%, and the selectivity of formic acid reaches 65%. As the electrolysis potential becomes negative, the production of products is dominated by hydrogen.
Example 12
The potential controlled electrolysis experiment, i.e. the process steps, were the same as in example 10, except that:
Controlled Potential Electrocatalytic (CPE) experiments were performed at-1.45V vs NHE, which showed reasonably stable current densities over 10h of electrolysis.
As shown in FIG. 19, the average density of the catalytic current was maintained at 1.5mA/cm on average throughout the electrolysis2. This shows that, throughout the catalytic process, Compound 2MeCNIs stable. Carbon monoxide is mainly generated by detecting gas phase products generated by electrolysis.
Example 13
The effect of the addition of the same volume fraction of trifluoroethanol on the electrolysis products subjected to different potentials was examined, i.e. the procedure was the same as in example 10, except that: trifluoroethanol was added to the mixture at 4 vol% (0.56M) and then electrolyzed with carbon dioxide.
Controlled Potential Electrocatalytic (CPE) experiments were performed at-1.45V vs NHE and the results are shown in fig. 21, where in the dry case, the faradaic efficiency of carbon monoxide increased as the electrolytic potential was progressively negative, indicating that CO is the major product. The addition of trifluoroethanol increases the production of CO products.
Example 14
The effect of the addition of different volume fractions of trifluoroethanol on the electrolysis products was examined, i.e. the process steps were the same as in example 10, except that: trifluoroethanol water was added to the mixture in respective volumes of 0% vol, 2% vol (0.28M), 4% vol (0.56M), 6% vol (0.84M) and 8% vol (1.12M), followed by electrolysis with carbon dioxide.
Controlled Potential Electrocatalytic (CPE) experiments were performed at-1.45V vs NHE and the results are shown in fig. 22, where faradaic efficiency of carbon monoxide increased with increasing negative electrolytic potential in the dry case, indicating that CO is the major product. The addition of trifluoroethanol increased the CO product.
Comparative example 4
The potential electrolysis experiment and the method steps are the same as the example 10, and the difference is only that:
Adding a compound of nickel tetraethyl nitrile triflate into 2.5mL of acetonitrile containing 0.1M tetrabutylammonium hexafluorophosphate to obtain a mixed solution, wherein the concentration of the mixed solution is 2mM (namely, 2mmol of nickel tetraethyl nitrile triflate is contained in each L of acetonitrile containing tetrabutylammonium hexafluorophosphate), and adding no compound 2 in the stepMeCN。
Only the nickel tetraacetonitrile trifluoromethanesulfonate is electrolyzed and electrifiedHydrogen is produced by decomposition, the faradic efficiency of the hydrogen is f H296% and fco<2%, the average current density at electrolysis is significantly lower than the current density (j) at the time of including the catalyst<0.10mA cm-2). Comparative experiments confirmed that the molecular nickel catalyst did participate in the catalytic process.
Comparative example 5
The potential electrolysis experiment and the method steps are the same as the example 10, and the difference is only that:
In 2.5mL of 0.1M ammonium tetrabutyl hexafluorophosphate in acetonitrile, only 0.56M trifluoroethanol was added to obtain a mixture solution, wherein the concentration of the mixture solution was 4% vol, and Compound 2 was not added in this stepMeCN。
Electrolyzing only trifluoroethanol to generate hydrogen with the faradic efficiency of f H295% and fco<5%, the average current density at electrolysis is significantly lower than the current density (j) at the time of including the catalyst<0.10mA cm-2). Comparative experiments confirmed that the molecular nickel catalyst did participate in the catalytic process.
Example 15
1 obtained in comparative example 2MeCNThe electrochemical properties were characterized as in example 10, except that 2MeCNIs replaced by 1MeCNThe results are shown in FIG. 23.
The control potential electrolysis result is shown in fig. 23, and the asymmetric conjugated system mainly comprises hydrogen and carbon monoxide, and the electrolysis effect is good after the reduction.
It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it will be obvious to those skilled in the art that other variations or modifications may be made on the basis of the above description, and all embodiments may not be exhaustive, and all obvious variations or modifications may be included within the scope of the present invention.

Claims (25)

1. The asymmetric N-H-pyridine-nickel metal catalyst is characterized in that the structure of the asymmetric N-H-pyridine-nickel metal catalyst is a six-coordination octahedral model structure, and the structural formula of the asymmetric N-H-pyridine-nickel metal catalyst is shown as the following formula I:
Wherein R1 and R2 each independently represent an alkyl, trimethylsilyl, amino, imino, alkoxy, benzyl or halogen substituent; the halogen substituent is-F, -Cl, -Br or-I;
R3 represents a hydrogen atom, an alkyl group, an alkoxy group, a phenyl group, a benzyl group, an amino group, a pyridyl group, an oxazolyl group or biotin;
R4 and R5 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, an amino group, a nitrile group, an aryl group or biotin;
L1、L2And L3Each independently represents a halogen atom, an acetonitrile molecule, a carboxylate group, a methanol molecule, a water molecule, or a tetrahydrofuran group.
2. The asymmetric N-H-pyridine-nickel based metal catalyst according to claim 1, wherein R1 and R2 each independently represent an alkyl group of 1-6 carbon atoms.
3. the asymmetric N-H-pyridine-nickel based metal catalyst according to claim 1, wherein R3 represents an alkyl group of 1-10 carbon atoms.
4. The asymmetric N-H-pyridine-nickel based metal catalyst according to claim 1, wherein R4 and R5 each independently represent a hydrogen atom, an aryl group or an alkyl group of 1 to 6 carbon atoms.
5. a method for preparing the asymmetric N-H-pyridine-nickel metal catalyst as claimed in any one of claims 1 to 4, comprising the steps of:
1) Dissolving the reactant A in tetrahydrofuran to obtain a mixed solution B;
Dissolving alkyl magnesium bromide in ether to obtain a mixed solution C;
Mixing the mixed solution C and the mixed solution B for reaction to obtain a mixed solution D;
Mixing the saturated ammonium-containing solution with the mixed solution D for quenching reaction to obtain a reactant E;
Wherein the structural formula of the reactant A is as follows:
2) Dissolving the reactant E in alcohol to obtain a mixed solution F;
mixing the mixed solution F with acid to obtain a mixed solution G;
Mixing the mixed solution G and an aniline compound for reaction to obtain a reactant H;
3) Dissolving a reactant H in alcohol to obtain a mixed solution I;
mixing the mixed solution I and a reducing compound for reaction to obtain a reactant J;
4) Tetrahydrofuran, reactant J and nickel salt are mixed and reacted to obtain the asymmetric N-H-pyridine-nickel metal catalyst.
6. The method according to claim 5, wherein the alkyl magnesium bromide in step 1) is methyl magnesium bromide, ethyl magnesium bromide, butyl magnesium bromide or propyl magnesium bromide.
7. The method according to claim 5, wherein the saturated ammonium-containing solution in step 1) is a saturated aqueous ammonium chloride solution, a saturated aqueous ammonium bromide solution or a saturated aqueous ammonium hydroxide solution.
8. the method according to claim 5, wherein the concentration of the reactant A in the mixed solution B in the step 1) is 0.01 to 1 mol/L.
9. The method according to claim 5, wherein the concentration of the alkyl magnesium bromide in the mixed solution C in the step 1) is 1 to 2 mol/L.
10. The preparation method according to claim 5, wherein the volume ratio of the mixed solution B to the mixed solution C in the step 1) is 1-10: 1.
11. The method according to claim 5, wherein the mixed solution C and the mixed solution B in the step 1) are mixed in a manner that: dropwise adding the mixed solution C into the mixed solution B, and stirring for reaction to obtain a mixed solution D; wherein the temperature during dripping is 0-10 ℃; the stirring reaction is carried out for 2-4h at the temperature of-15 to-20 ℃, and then stirring is carried out for 3-4 h under the condition of normal temperature.
12. The method according to claim 5, wherein the saturated ammonium-containing solution and the mixed solution D in the step 1) are mixed in a manner that: dropwise adding the saturated ammonium-containing solution into the mixed solution D until the surface of the reaction liquid does not smoke any more, and gradually changing the solution into orange red; wherein the dropwise addition is carried out under ice bath conditions.
13. The method according to claim 5, wherein the alcohol in step 2) is methanol, ethanol, propanol, butanol, or ethylene glycol.
14. the method according to claim 5, wherein the acid in step 2) is formic acid, acetic acid, propionic acid, butyric acid or oxalic acid.
15. The method according to claim 5, wherein the aniline compound in the step 2) is 2, 6-diisopropylaniline, aniline, 2, 6-dinitroaniline, or 2, 6-dibromoaniline.
16. The method according to claim 5, wherein the concentration of the reactant E in the mixed solution F in the step 2) is 0.01 to 0.2 mol/L.
17. The method according to claim 5, wherein the mixed solution F and the acid in the step 2) are mixed in a manner that: dripping acid into the mixed solution F; the volume ratio of the mixed solution F to the acid is 1: 0.001 to 0.01.
18. The preparation method according to claim 5, wherein the mixed solution G and the aniline compound in the step 2) are mixed in a manner that: adding aniline compound into the mixed solution G for reaction; the molar ratio of the reactant E to the aniline compound in the mixed solution G is 0.8-1: 1, the reaction condition is heating reflux stirring for 22-24 hours, and the reflux temperature is 90-110 ℃.
19. The method according to claim 5, wherein the alcohol in step 3) is methanol, ethanol, propanol, butanol, or ethylene glycol.
20. The preparation method according to claim 5, wherein the reducing compound in step 3) is sodium borohydride, sodium hydride or sodium cyanoborohydride.
21. The method according to claim 5, wherein the concentration of the reactant H in the mixed solution I in the step 3) is 0.01 to 0.2 mol/L.
22. The method according to claim 5, wherein the mixing of the mixed solution I and the reducing compound in step 3) is performed in a manner that: adding a reducing compound into the mixed solution I for reaction; the molar ratio of the reactant H to the reducing compound in the mixed solution I is 1-1: 10, stirring at normal temperature for 22-24 h.
23. the preparation method according to claim 5, wherein the molar ratio of the tetrahydrofuran, the reactant J and the nickel salt in the step 4) is 5-10: 1: 1.
24. the preparation method according to claim 5, wherein the reaction in the step 4) is a stirring reaction for 2-4 hours.
25. the application of the asymmetric N-H-pyridine-nickel metal catalyst as claimed in any one of claims 1 to 4 in electrocatalytic reduction of carbon dioxide.
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