A method for catalyzing reactions of organic compounds based on visible light

Abstract

The application relates to a method for visible light catalytic synthesis of organic compounds based on low-toxicity ZnSe@ZnS core-shell quantum dots. ZnSe@ZnS quantum dots are used as a sensitizer, the surface of the quantum dots is chelated with 4-benzoylbenzoic acid (BP), N,N-diisopropylethylamine (DIPEA) molecules are added to the solution as an electron sacrificial reagent and a substrate organic molecule to construct a quantum dot sensitized electron reduction system. The photocatalytic reduction product can be obtained under 405nm visible light excitation. In the system, the electron transfer and transmission process is studied through a transient absorption spectrum.

Description

Technical Field

[0001] This invention relates to a method for organic synthesis reactions using low-toxicity ZnSe@ZnS core-shell quantum dots as strong reducing agents. Background Technology

[0002] In recent years, methods using inorganic quantum dots as photosensitizers to reduce organic molecules have emerged, producing strong reducing agents that can be used in organic catalysis, photodynamic therapy, and other fields. A crucial element in this process is the use of inorganic quantum dots as the photosensitizer. Commonly used quantum dots often contain heavy metals, such as cadmium selenide (CdSe), cadmium sulfide (CdS), lead selenide (PbSe), lead sulfide (PbS), and lead-based inorganic perovskites (CsPbX3, X=Cl, Pb, I). The toxic Pb and Cd elements limit their use. Therefore, some heavy metal-free quantum dots have also emerged, including silicon quantum dots (Si), core-shell zinc sulfide-coated copper indium sulfide (CuInS2@ZnS) quantum dots, and core-shell zinc sulfide-coated zinc selenide-coated indium phosphide (InP@ZnSe@ZnS) quantum dots.

[0003] These non-toxic quantum dot-based photoreduction systems all utilize absorption in the green light band. Sensitizers in the blue light band are crucial because they can sensitize molecules with strong reducing properties, allowing them to directly participate in organic catalytic reactions for photocatalysis or environmental remediation. However, current applications of blue quantum dots as photosensitizers are still limited to those containing heavy metals such as CdS and CsPbBr(Cl).

[0004] Core-shell ZnSe@ZnS quantum dots and their similar derivatives are the only non-toxic quantum dots that emit blue light, attracting much research attention in recent years for applications in light-emitting devices. Here, we have invented a method using ZnSe@ZnS quantum dots as a molecular reducing agent, which can sensitize and reduce -2.8 V vs. SCE benzoylbenzoic acid with fluorescence quenching efficiencies exceeding 89%. When N,N-diisopropylethylamine (DIPEA) is added as an electron sacrificial agent, under 405 nm visible light excitation, aryl dehalogenation, carbon-carbon coupling, additive-free photoreduction polymerization, and organic reactions are achieved, with reaction yields reaching 60-90%. Summary of the Invention

[0005] The purpose of this invention is to provide a strong electron reduction organic reaction system based on low-toxicity ZnSe@ZnS quantum dots for visible light catalysis, thereby solving the problem of toxicity of photosensitive materials in this organic reaction.

[0006] The ZnSe@ZnS quantum dots were prepared using methods known in the art. A preferred method for preparing the ZnSe@ZnS-BP inorganic-organic hybrid system is the direct stirring and filtration method, which is simple to prepare and holds promise for future applications in low-toxicity organic synthesis reactions.

[0007] A reaction method for organic compounds based on visible light catalysis is characterized by: using ZnSe@ZnS core-shell quantum dots as sensitizers in an organic solvent, chelating 4-benzoylbenzoic acid (BP) on the surface of the quantum dots, and using N,N-diisopropylethylamine (DIPEA) molecules as electron sacrificial reagents, and achieving one or both of aryl dehalogenation or carbon-carbon coupling of organic compounds under visible light excitation at a wavelength of 400-420 nm.

[0008] ZnSe@ZnS core-shell quantum dots, used as light absorbers, have ZnSe as the core and ZnS wrapped around the outer surface. The first exciton absorption peak should ideally be controlled around 400-420 nm.

[0009] The shell quantum dots need to have a strong quantum confinement effect. The ZnSe particle size is 3~4 nm, and the shell thickness should not be too thick, preferably 1-2 layers (0.3~0.9 nm thick) of ZnS.

[0010] The organic solvent is one or more of n-hexane, toluene, and N,N-dimethylformamide (DMF).

[0011] The specific process is as follows: 1) In 1-2 mL, 3.04×10 -5 2 mg of 4-benzoylbenzoic acid (BP) was directly added to a nonpolar n-hexane solution of M ZnSe@ZnS quantum dots. After stirring until homogeneous, the solution was filtered through a membrane with a pore size of 0.22-0.25 µm. The filtrate obtained was the QD-BP complex solution, in which the amount of BP was 23250 L mol. -1 cm -1 ; Diisopropylethylamine (DIPEA), the organic compound to be reacted, and a QD-BP complex solution were added to an organic solvent; finally, the solution was placed in a transparent sealed container and subjected to an organic reaction under 400-420 nm light for 3 minutes to 24 hours.

[0012] The molar ratio of the organic compound to DIPEA is 1:2-10, preferably 1:35, and more preferably 1:3-4; QD-BP complexes are organic compounds with a molar content of 0.2-0.4 mol%.

[0013] Reaction time: 3 minutes to 24 hours.

[0014] The organic compound is one or more of the following: 4-bromoacetophenone, 4-bromobenzaldehyde, 4-bromobenzonitrile, 2-bromobenzonitrile, 4-bromophenethyl ether, 4-iodobenzonitrile, 2-iodobenzonitrile, 4-iodobenzaldehyde, 4-iodoacetophenone, or 4-iodophenyl methyl ether.

[0015] This invention utilizes ZnSe@ZnS quantum dots as a sensitizer, with 4-benzoylbenzoic acid (BP) chelated on its surface. N,N-diisopropylethylamine (DIPEA) molecules are added to the solution as an electron sacrificial agent and substrate organic molecule to construct a quantum dot-sensitized electron reduction system. Photocatalytic reduction products can be obtained under 405 nm visible light excitation. The electron transfer process within this system was investigated using transient absorption spectroscopy. Attached Figure Description

[0016] Figure 1 Electron micrograph of ZnSe@ZnS quantum dots.

[0017] Figure 2 Absorption fluorescence spectra of QD and QD-BP systems.

[0018] Figure 3 (a) Chemical reaction diagram of arylation debromination in QD-BP; (b) Expanded substrate diagram of reductive dehalogenation reaction in the QD-BP system. Figure 4 (a) Structural diagram of QD-BP single electron transfer (SET) reduction arylation dechlorination reaction; (b) Structural diagram of QD-BP single electron transfer (SET) reduction carbon-carbon coupling; (c) Structural diagram of QD-BP single electron transfer (SET) photocatalytic polymerization without initiator addition.

[0019] Figure 5 NMR spectrum of reduction products by single electron transfer (SET). Detailed Implementation

[0020] To demonstrate the feasibility of this invention and its fundamental principles, the verification technology employed in this invention is as follows: The shell thickness of quantum dots was determined using electron microscopy. The basic light absorption and emission characteristics of the QD and QD-BP systems were determined using steady-state absorption and fluorescence spectroscopy. The electron transfer mechanism from QD to BP was determined using transient absorption spectroscopy. The organic reaction efficiency was determined using gas chromatography and nuclear magnetic resonance, and the structure of the organic reaction products was determined.

[0021] The present invention will be further described with reference to the accompanying drawings.

[0022] The preparation process of ZnSe@ZnS core-shell quantum dots is as follows: Preparation of ZnSe cores: 20 mL of oleylamine (OAm) was placed in a flask and degassed under vacuum (0.9 MPa) at 90 °C for 30 min. The solution was heated to 295 °C under nitrogen, and then 3.0 mL of TOP-Se (a tri-n-octylphosphine solution of selenium powder, with a selenium concentration of 0.5 M) was slowly added. When the temperature returned to 295 °C, 3.75 mL of a 0.5 M diethylzinc TOP (tri-n-octylphosphine) solution was rapidly injected into the flask with vigorous stirring. The growth temperature was maintained at 290 °C. The core size was monitored by absorption spectroscopy sampling. After 30 min of growth, another 20 mL of ODE was slowly added to the flask.

[0023] To obtain larger ZnSe quantum dots, TOP solutions of 0.5 M TOP-Se and 0.55 M diethylzinc were injected separately at 3 mL / h using a syringe pump at 300 °C. After 3 hours, ZnSe quantum dots of the target size (first exciton absorption peak at 400 nm, average particle size 3.5 nm, particle size distribution 3.5 ± 0.5 nm) were obtained. The reaction was quenched by cooling the solution to room temperature with compressed air. Ethanol was used as the antisolvent to precipitate the ZnSe quantum dots, and the precipitate was dissolved in n-hexane. The entire purification process was carried out in a nitrogen-filled glove box. The purified zinc selenide quantum dots were stored in the glove box.

[0024] Preparation of ZnSe@ZnS core-shell quantum dots: 1.5 mL of 1-octadecene (ODE), 1.5 mL of oleic acid (OA), and 1.5 mL of oleylamine (OAm) were added to a three-necked flask in a nitrogen-filled glove box, followed by the injection of ZnSe QDs (300 nmol). The solution was degassed under vacuum (0.9 MPa) at 90 °C for 1 hour, then purged with nitrogen and heated to 310 °C. When the temperature of the solution in the flask reached 240 °C, 0.13 M 1-octylthiol solution (prepared by diluting 204 μL of 1-octylthiol in 8.8 mL ODE) and 0.1 M zinc oleate (prepared by reacting ZnAc2 and OA in a 5:1 molar ratio at 200 °C and diluted to 0.1 M with ODE) were added to the flask separately using a syringe pump at a rate of 3 mL / hour. After injecting approximately 5.6 mL of each precursor solution (1-octylthiol and zinc oleate), the injection was stopped, and the solution was incubated at 310 °C for 5 minutes. The solution was then cooled to 80–90 °C with compressed air. The resulting ZnSe@ZnS QDs were washed by centrifugation with a (20:1) volume ratio of hexane and ethanol, and then dispersed in hexane. All centrifugation and washing procedures were performed in a glove box. The purified ZnSe / ZnS core / shell quantum dots were stored in a glove box.

[0025] The obtained core-shell quantum dots had an average particle size of 5.3 nm and a particle size distribution of 5.3 ± 0.9 nm. The average thickness of the ZnS shell was 0.9 nm, and the shell thickness distribution was 0.9 ± 0.2 nm. Electron micrographs of the core-shell quantum dots are shown below. Figure 1 As shown.

[0026] Example 1 The low-toxicity core-shell ZnSe@ZnS quantum dots obtained above can be used for visible light-catalyzed organic synthesis reactions. Their preparation method includes the following steps: In a glove box, at 1 mL, 3.04 × 10 -5 2 mg of 4-benzoylbenzoic acid (BP) was directly added to a hexane solution of ZnSe@ZnS quantum dots. After stirring for 20 minutes, the solution was filtered through a 0.25 µm pore size polytetrafluoroethylene (PTFE) membrane to remove excess undissolved molecular powder, yielding a QD-BP complex solution containing 23250 L mol of BP. -1 cm -1 (Absorbance unit, represented by symbol A, A=abc, where a is the absorptivity coefficient in L / (g·cm), b is the distance the light travels in the sample (usually the thickness of the sample in the cuvette) in cm, and c is the solution concentration in g / L). 4-Bromoacetophenone (40 mg, 0.2 mmol) and DIPEA (106 μL, 0.6 mmol) were added to a small, transparent glass vial containing dry N,N-dimethylformamide (DMF, 3 mL) and a QD-BP complex solution (QD-BP in 0.2 mol% of 4-bromoacetophenone). The vial containing the mixture was then sealed in a transparent tube and transferred out of the glove box for irradiation under a 405 nm LED. After 8 hours, the reaction was complete, and 0.5 mL of deionized water was added to the vial to quench the light reaction. The reaction conversion rate (98%) was measured by gas chromatography (GC-MS), and the reaction product (acetophenone, yield 95%) was identified by nuclear magnetic resonance.

[0027] The verification and detection of visible light photocatalytic organic synthesis methods are mainly carried out from the following two aspects: (1) Detection of product conversion rate in visible light catalytic organic synthesis reaction system.

[0028] The conversion rates of feedstock and product in the QD-BP reduced aryl dehalogenation system were tested using gas chromatography-mass spectrometry (GC-MS).

[0029] (2) Detection of product structure in visible light catalytic organic synthesis system.

[0030] The NMR spectrum of the single electron transfer (SET) reduction product was obtained using NMR detection, as shown in Figure 6.

[0031] Example 2 The process and conditions are the same as in Example 1, except that: 4-Bromoacetophenone was replaced by equimolar amounts of 4-bromobenzaldehyde, 4-bromobenzonitrile, 2-bromobenzonitrile, 4-bromophenethyl ether, 4-iodobenzonitrile, 2-iodobenzonitrile, 4-iodobenzaldehyde, 4-iodoacetophenone, or 4-iodoanisole.

[0032] The reaction conversion rates were 80% for 4-bromobenzaldehyde, 90% for 4-bromobenzonitrile, 89% for 2-bromobenzonitrile, 92% for 4-bromophenethyl ether, 96% for 4-iodobenzonitrile, 92% for 2-iodobenzonitrile, 90% for 4-iodobenzaldehyde, 86% for 4-iodoacetophenone, and 80% for 4-iodoanisole. The corresponding reaction products and yields were benzaldehyde (70-86%), benzonitrile (82-90%), acetophenone (80-96%), phenethyl ether (90%), and anisole (76%), respectively. The chromatograms are shown below. Figure 3 As shown in Figure 5.

[0033] Example 3 In a glove box, at 1 mL, 3.04 × 10 -5 2 mg of 4-benzoylbenzoic acid (BP) was directly added to a hexane solution of ZnSe@ZnS quantum dots. After stirring for 20 minutes, the solution was filtered through a 0.25 µm pore size polytetrafluoroethylene (PTFE) membrane to remove excess undissolved molecular powder, yielding a QD-BP complex solution containing 23250 L mol of BP. -1 cm -1 Add 40 mg (0.2 mmol) of 2-chlorobenzonitrile and 40 μL (0.23 mmol) of DIPEA to a small, clear glass vial containing dry N,N-dimethylformamide (DMF, 3 mL) and a QD-BP complex solution (QD-BP amounting to 0.2 mol% of 2-chlorobenzonitrile). Then add N-methyl-2,5-dihydropyrrole (…). The glass vial containing the mixture was then sealed in a transparent sealed tube and transferred out of the glove box for irradiation under a 405 nm LED. After 8 hours, the reaction was complete, and 0.5 mL of deionized water was added to the small glass vial to quench the light reaction. The reaction conversion rate (48%) was measured by gas chromatography-mass spectrometry (GC-MS), and the reaction products were analyzed by nuclear magnetic resonance (NMR). The yield was 44%, and the sample was identified. The chromatogram is shown below. Figure 4 As shown.

[0034] Example 4 In a glove box, at 1 mL, 3.04 × 10 -52 mg of 4-benzoylbenzoic acid (BP) was directly added to a hexane solution of ZnSe@ZnS quantum dots. After stirring for 20 minutes, the solution was filtered through a 0.25 µm pore size polytetrafluoroethylene (PTFE) membrane to remove excess undissolved molecular powder, yielding a QD-BP complex solution containing 23250 L mol of BP. -1 cm -1 296 mg (1 mmol) of trimethylolpropane triacrylate was added to a small, transparent glass vial containing 3 mL of dried N,N-dimethylformamide (DMF) and a QD-BP complex solution (0.2 mol% of trimethylolpropane triacrylate). The vial containing the mixture was then sealed in a transparent tube and transferred out of the glove box for irradiation under a 405 nm LED. The polymerization of trimethylolpropane triacrylate ended after 3 minutes, yielding a gel-like polymerization product. Mn = 21389 g / mol and Mw = 26380 g / mol. The spectrum is as follows: Figure 4 As shown In summary, our invented electron transfer sensitization system based on low-toxicity ZnSe@ZnS quantum dots can effectively utilize visible light to catalyze organic reactions. This invention provides a new approach for designing low-toxicity quantum dot-sensitized organic reaction systems.

Claims

1. A reaction method for organic compounds based on visible light photocatalysis, characterized in that: In an organic solvent, ZnSe@ZnS core-shell quantum dots are used as sensitizers, 4-benzoylbenzoic acid is chelated on the surface of the quantum dots, and N,N-diisopropylethylamine is used as an electron sacrificial reagent. Under visible light excitation at a wavelength of 400-420 nm, one or two of the following can be achieved: aryl dehalogenation or carbon-carbon coupling of organic compounds. The organic compounds are one or more of the following: 4-bromoacetophenone, 4-bromobenzaldehyde, 4-bromobenzonitrile, 2-bromobenzonitrile, 4-bromophenethyl ether, 4-iodobenzonitrile, 2-iodobenzonitrile, 4-iodobenzaldehyde, 4-iodoacetophenone, or 4-iodoanisole.

2. The method according to claim 1, characterized in that: ZnSe@ZnS core-shell quantum dots, used as light absorbers, have ZnSe as the core and ZnS wrapped around the outer surface, with the first exciton absorption peak controlled at 400-420 nm.

3. The method according to claim 2, characterized in that: ZnSe has a particle size of 3~4 nm and a thickness of 1-2 layers of ZnS.

4. The method according to claim 1, characterized in that: The organic solvent is one or more of n-hexane, toluene, and N,N-dimethylformamide.

5. The method according to any one of claims 1-4, characterized in that: The specific process is as follows: In 1-2 mL, 3.04×10 -5 2 mg of 4-benzoylbenzoic acid was directly added to a nonpolar n-hexane solution of M ZnSe@ZnS quantum dots, stirred evenly, and then filtered through a membrane with a pore size of 0.22-0.25 µm. The filtrate obtained was the QD-BP complex solution. Add N,N-diisopropylethylamine and the organic compound to be reacted, as well as a QD-BP complex solution, to an organic solvent; finally, place the solution into a transparent sealed container and allow it to react under 400-420 nm light for 3 minutes to 24 hours.

6. The method according to claim 5, characterized in that: The molar ratio of the organic compound to N,N-diisopropylethylamine is 1:2-10. QD-BP complexes are organic compounds with a molar content of 0.2-0.4 mol%.

7. The method according to claim 5, characterized in that: Reaction time: 3 minutes to 24 hours.

8. The method according to claim 5, characterized in that: The molar ratio of the organic compound to N,N-diisopropylethylamine is 1:3-5.

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