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CN113117754B - Flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst and preparation method and application thereof - Google Patents

Flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst and preparation method and application thereof Download PDF

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CN113117754B
CN113117754B CN202110398134.3A CN202110398134A CN113117754B CN 113117754 B CN113117754 B CN 113117754B CN 202110398134 A CN202110398134 A CN 202110398134A CN 113117754 B CN113117754 B CN 113117754B
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CN113117754A (en
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邓钦月
左彬
操兵兵
郑艳
李万方
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University of Shanghai for Science and Technology
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Abstract

The invention discloses a flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst and a preparation method and application thereof. The preparation method comprises the following steps: firstly, preparing flower-shaped core-shell type magnetic mesoporous microspheres, and then carrying out amination to load active amino target spots capable of reacting with N-heterocyclic carbene ligands on the magnetic mesoporous microspheres; then preparing a magnetic mesoporous microsphere immobilized N-heterocyclic carbene ligand, and finally reacting the ligand with palladium chloride to prepare the flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst. The flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst has high load and high catalytic activity, and can catalyze the cross-coupling reaction between aryl chloride and aryl phenylboronic acid with high difficulty by using a catalytic amount of 1 mol%. The catalyst is a superparamagnetic catalyst, can be separated magnetically and recycled, and has high economic value and wide application prospect.

Description

Flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst and preparation method and application thereof
Technical Field
The invention relates to a flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst, and a preparation method and application thereof, and belongs to the technical field of organic catalysis.
Background
Since Aduengo first isolated free N-heterocyclic carbenes in 1991, various N-heterocyclic carbene metal complexes have been reported. N-heterocyclic carbene (NHC) ligands have attracted considerable attention in transition metal catalysis due to their ease of preparation, strong sigma-donor capability and effective binding strength to transition metals. The types of the N-heterocyclic carbenes are few, and the found N-heterocyclic carbenes mainly have the following four structures: structural formulas 1-4. As homogeneous catalysts, particularly N-heterocyclic carbene cyclic palladium catalyst complexes have been widely used in organic catalysis, particularly in Suzuki-Miyaura cross-coupling reactions. Although a large number of homogeneous catalysts exhibit excellent catalytic activity, the homogeneous catalysts still have problems such as product contamination, complicated separation processes, and high operation costs. Various materials have been used to support azacyclo-carbene catalysts, including silica, carbon, magnetic nanoparticles, and the like. The use of recoverable heterogeneous catalysts is a necessary trend for green chemistry development.
Figure BDA0003019339750000011
The synthesis routes for the currently used aza-carbene target compounds in Suzuki-Miyaura coupling reactions are mainly: route one synthesis route disclosed in patent document CN 107880079A: the N-heterocyclic bis-carbene-palladium complex which takes 1, 4-bis (N-ethyl-benzimidazolium methyl) -2,3,5, 6-tetramethylbenzene arene salt as a precursor is mainly applied to the field of catalysis. Particularly, the catalyst is used for Suzuki-Miyaura coupling reaction of para-brominated aromatic hydrocarbon and phenylboronic acid, and the synthetic route of the route I is as follows:
Figure BDA0003019339750000021
route two is a synthetic route disclosed in patent document CN 108586345A: the 1,8-2[3- (N-ethylimidazolyl) propoxy ] anthraquinone hexafluorophosphate is mainly prepared by the reaction of 1, 8-bis (3-bromopropoxy) anthraquinone and N-ethyl-imidazole to generate 1,8-2[3- (N-ethylimidazolyl) propoxy ] anthraquinone halide and can also be prepared by the anion exchange reaction of ammonium hexafluorophosphate. Wherein, 1,8-2[3- (N-ethylimidazolyl) propoxy ] anthraquinone hexafluorophosphate reacts with a palladium compound to generate the N-heterocyclic carbene palladium complex, and the synthesis route of the second route is as follows:
Figure BDA0003019339750000022
the third synthetic route is disclosed in patent document CN 108579809A: mainly dissolving a N-heterocyclic carbene palladium compound and an amphiphilic polymer DSPE-PEG2000 in a small amount of dimethyl sulfoxide solution, slowly dripping the dimethyl sulfoxide solution into deionized water under the ultrasonic condition, and forming the nano-particle catalyst wrapping the N-heterocyclic carbene palladium compound through self-assembly of the amphiphilic polymer.
Route four is represented by a document published in ChemComm, 2017, 53, 13063: the cheap aza carbene ligand is synthesized by taking 10-undecene-1-alcohol as a raw material through simple reactions such as bromination, etherification, ammoniation, hydrosilylation and the like. Then preparing the aza-carbene nanometer particle by corresponding triethoxy-silicon-based functionalization, wherein the synthesis route of the fourth route is as follows:
Figure BDA0003019339750000031
the above synthetic routes all have certain disadvantages:
1) The homogeneous N-heterocyclic carbene-palladium compound is not easy to separate in the product, causes secondary pollution and does not accord with the concept of green environmental protection;
2) The central palladium of the N-heterocyclic carbene cyclic palladium catalyst is easily lost in the catalysis process, so that the catalyst is inactivated.
3) The prepared magnetic microspheres are easy to agglomerate, so that the heterogeneous N-heterocyclic carbene-palladium catalyst is too low in load, the utilization rate of the catalyst is reduced, and the TOF (amount of converted reactants in unit time) of the catalyst is reduced.
These disadvantages limit the industrial application of the existing synthetic routes to a certain extent. Therefore, the existing method for synthesizing the N-heterocyclic carbene ring palladium magnetic microsphere catalyst needs further improvement.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the N-heterocyclic carbene ring palladium magnetic microsphere synthesized in the prior art is easy to agglomerate, so that the heterogeneous N-heterocyclic carbene ring palladium catalyst has too low load, the utilization rate of the catalyst is reduced, and the TOF of the catalyst is reduced.
In order to solve the technical problem, the invention provides a flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst, wherein the flower-shaped core-shell magnetic mesoporous microsphere is loaded with the N-heterocyclic carbene ring palladium catalyst shown as a formula I:
Figure BDA0003019339750000041
preferably, the flower-shaped core-shell magnetic mesoporous microsphere comprises magnetic Fe in a core shell 3 O 4 SiO outside the particle and core-shell 2 And (4) mesoporous.
The invention also provides a preparation method of the flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst, which comprises the following steps:
step 1: preparation of Fe from iron source and silicon source 3 O 4 @SiO 2 Magnetic microspheres;
and 2, step: mixing Fe 3 O 4 @SiO 2 Dispersing magnetic microspheres in water to obtain magnetic microsphere dispersion, and treating the magnetic microsphere dispersion with a template agent to obtain flower-shaped core-shell magnetic mesoporous microspheres Fe 3 O 4 @mSiO 2
And step 3: flower-shaped core-shell type magnetic mesoporous microsphere Fe 3 O 4 @mSiO 2 Amination of (a);
and 4, step 4: reacting the aminated flower-shaped core-shell magnetic mesoporous microsphere with an N-heterocyclic carbene ligand to prepare a flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ligand;
and 5: atmosphere of inert gasThen, flower-shaped core-shell magnetic mesoporous microspheres are immobilized with N-heterocyclic carbene ligands and PdCl 2 Adding the mixture into a solvent, stirring to obtain a mixed solution, adding carbonate into the mixed solution, performing reflux reaction, washing and drying a product after the reaction is finished, and preparing the flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst.
Preferably, the iron source in the step 1 is at least one of ferric chloride and ferric sulfate; the silicon source is organic siloxane; the template agent in the step 2 comprises cetyl trimethyl ammonium bromide and fluorine surfactant FS-66.
Preferably, the step 2 specifically comprises: cetyl trimethylammonium bromide, triethanolamine and ultrapure water were mixed at a ratio of 0.6g:0.1mL:30 mL-0.7 g:0.2mL: mixing the components in a proportion of 40mL, and stirring the mixture for 15 to 30 minutes at a temperature of between 60 and 70 ℃ to prepare CTAB template solution; then weighing template agent FS-66 according to the mass ratio of FS-66 to hexadecyl trimethyl ammonium bromide being 0.1-0.25, dissolving the template agent FS-66 in isopropyl ketone to prepare a solution with the concentration of 0.0375-0.15 g/mL, adding the solution into the CTAB template solution, continuously stirring for 1-2 hours, adding TEOS according to the ratio of 6-10 mL TEOS/g hexadecyl trimethyl ammonium bromide, and stirring for 60-80 seconds to obtain a double-template solution; mixing the double-template solution and the magnetic microsphere dispersion according to the ratio of 2-3 to 1, then carrying out ultrasonic treatment for 2-3 minutes, then oscillating for 30-40 minutes on a circumferential oscillator at the r = 600-700 r/min, and then shaking for 6 hours at the r = 200-300 r/min; finally, separating the product and removing the template solution, adding an ethanol solution of saturated ammonium nitrate, oscillating and washing for 10-15 h, washing the washed solid product for 2-3 times by using absolute ethanol and water respectively, and drying to obtain the flower-shaped core-shell magnetic mesoporous microspheres; in the magnetic microsphere dispersion, fe 3 O 4 @SiO 2 The concentration of the magnetic microspheres is 0.005-0.01 g/mL.
Preferably, the amination in the step 3 is specifically: and (3) adding the flower-shaped core-shell magnetic mesoporous microspheres prepared in the step (2), amino alkyl siloxane and a cation trapping agent into cyclohexane, performing ultrasonic treatment to obtain a dispersion liquid, stirring the obtained dispersion liquid at room temperature for reaction, washing a product with n-hexane and ethanol after the reaction is finished, and drying to obtain the aminated flower-shaped core-shell magnetic mesoporous microspheres.
More preferably, the aminoalkyl siloxane is 3-aminopropyltrimethoxysilane; the cation trapping agent is dodecylamine; in the dispersion, the concentration of the flower-shaped core-shell magnetic mesoporous microspheres is 0.005-0.01 g/mL, the concentration of 3-aminopropyltrimethoxysilane is 1-3 v/v%, and the concentration of dodecylamine is 1-5 v/v%; the ultrasonic treatment time is 5-10 min, and the stirring reaction time is 4-6 h.
Preferably, the mass ratio of the aminated flower-shaped core-shell magnetic mesoporous microsphere in the step 4 to the azacyclo-carbene ligand is 1: methanol is used as a solvent, the reaction temperature is 50-60 ℃, and the reaction time is 2-3 days; the molar ratio of the carbonate to the flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene ligand to the palladium chloride in the step 5 is (1.4); in the mixed solution, the concentration of the flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene ligand is 0.02-0.03 mol/L; the solvent is acetonitrile, and the carbonate is potassium carbonate; the time of the reflux reaction is 20 to 30 hours.
The invention also provides application of the flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst.
Preferably, the use comprises use in a Suzuki-Miyaura coupling reaction.
Compared with the prior art, the invention has the beneficial effects that:
1. the magnetic mesoporous silica is prepared by two templates, namely hexadecyl trimethyl ammonium bromide and FS-66 (fluorinated surfactant), and the aperture is adjustable, so that the magnetic mesoporous silica with larger specific surface area can be prepared to be used as a carrier, and the mass transfer of reactant molecules is more facilitated; in the amination process of the core-shell magnetic mesoporous microspheres, dodecylamine forms micelles on the surfaces of the core-shell magnetic mesoporous microspheres, so that the prepared aminated core-shell magnetic mesoporous microspheres are more uniformly dispersed;
2. the load of palladium in the magnetic mesoporous palladium catalyst prepared by the invention is very high and reaches 0.20mmol/g, the prepared magnetic microspheres are not easy to agglomerate, and the catalytic efficiency of the catalyst is greatly improved;
3. the center palladium of the N-heterocyclic carbene cyclic palladium catalyst is connected with a structure of two independent groups, one end of the catalyst is introduced with an aliphatic long chain at an N atom, and the N-heterocyclic carbene is connected to a cyclic palladium ligand in a molecule; in order to coordinate and ring-palladate, groups at two ends of palladium need to be pulled by virtue of the stability of long-chain palladium molecules, so that the loss of a catalytic center in the catalytic process is avoided, therefore, the flower-shaped core-shell N-heterocyclic carbene ring target catalyst has higher stability, and two ends of a ligand are anchored on the palladium by virtue of a flexible aliphatic long chain; the catalyst can be recycled through magnetic separation and recovery, the catalytic activity of the catalyst is basically kept unchanged after 12 times of recycling, and the catalyst has higher economic value and wide application prospect.
Drawings
FIG. 1 is a schematic diagram of a preparation process of a flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst;
FIG. 2 is a transmission electron micrograph of flower-like core-shell magnetic mesoporous microspheres prepared with different amounts of templating agent FS-66 (a: FS-66=0.075g, b FS-66=0.10g, c FS-66=0.125g, d FS-66= 0.15g);
fig. 3 is a transmission electron microscope image of flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene annular palladium catalyst, wherein, a and b are transmission electron microscope images of flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene annular palladium catalyst freshly prepared in example 1 under low multiple and high multiple respectively, and c and d are transmission electron microscope images of magnetic mesoporous microsphere immobilized N-heterocyclic carbene annular palladium catalyst recovered last time in application example 1 under low multiple and high multiple respectively;
FIG. 4 is a nuclear magnetic hydrogen spectrum of 4-methoxybiphenyl prepared by application example 1;
FIG. 5 is a nuclear magnetic carbon spectrum of 4-methoxybiphenyl prepared in application example 1;
FIG. 6 is a result chart of the verification of the recycling performance of the flower-shaped core-shell magnetic mesoporous microsphere immobilized aza-ring captivity palladium catalyst.
Detailed Description
In order to make the invention more comprehensible, preferred embodiments are described in detail below with reference to the accompanying drawings.
Example 1
The preparation process of the flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst is shown in figure 1, and comprises the following steps:
s1, preparation of flower-shaped core-shell magnetic mesoporous microspheres (a 1-a 3):
1) 1.3g of ferric chloride hexahydrate and 60mL of ethylene glycol are used as reducing agents, and 4.5g of anhydrous sodium acetate, 1.5g of poly (4-styrenesulfonic acid-co-maleic acid) sodium salt and 0.5g of calcium fluoride are added simultaneously to prepare Fe with uniform appearance 3 O 4 Magnetic microspheres.
2) 0.50g of Fe was taken 3 O 4 Magnetic microspheres, sonicated in 60mL of ultrapure water for 2 minutes, added with 4.5ml of 1% naf solution, and then stirred on a stirrer (r =500 r/min). A mixture of 1.98mL TEOS (tetraethylorthosilicate) and ethanol (1.8mL EtOH +0.18mL TEOS) was added dropwise every 30 minutes for a total of 10 additions. After all additions were complete, rapid stirring was continued for 15 hours. Washing the product twice with absolute ethyl alcohol and twice with water, drying for 24 hours at 60 ℃ to obtain Fe 3 O 4 @SiO 2
3) 0.64g of cetyltrimethylammonium bromide (CTAB) was weighed by an electronic balance, mixed with 0.12mL of Triethanolamine (TEA) and 33.3mL of ultrapure water, and stirred in a magnetic stirrer at 60 ℃ for 15 minutes to prepare a CTAB template solution. Then, template FS-66 (a: FS-66=0.075g, b. 20mL of the dual template solution was added to 10mL of ultrasonically dispersed 0.08g Fe 3 O 4 @SiO 2 In aqueous solution, then sonicated for 2 minutes, then rapidly shaken (r =700 r/min) on a circular shaker for 30 minutes, then slowly shaken (r =250 r/min) for 6 hoursWhen the user wants to use the device. After 6 hours, the product was isolated and the template solution was removed. Then, a saturated ethanol solution of ammonium nitrate was added thereto, and the mixture was washed with shaking for 12 hours. Washing the product twice with absolute ethyl alcohol and twice with water, and then drying the product for 24 hours at 60 ℃ to obtain the flower-shaped core-shell magnetic mesoporous microspheres (Fe) with different apertures and specific surface areas 3 O 4 @mSiO 2 ) FIG. 2 shows a transmission electron micrograph of the compound.
S2, aminated magnetic mesoporous microsphere Fe 3 O 4 @mSiO 2 -NH 2 Synthesis of (a 4):
the amount of the template FS-66 prepared from S1 above was 0.15g of Fe 3 O 4 @mSiO 2 (0.5 g), 2% v/v APTMS (3-aminopropyltrimethoxysilane) and 3% v/v dodecylamine to 20ml cyclohexane, sonicated for 5min, stirred at room temperature for 5h, then the product washed once with n-hexane, once with ethanol and dried under vacuum at 50 ℃ for 24 hours to give aminated magnetic mesoporous microspheres Fe 3 O 4 @mSiO 2 -NH 2
S3 preparation of (2, 6-diisopropyl) imidazole (a 5):
50mmol of 2, 6-diisopropylaniline and 50mmol of glyoxal are dissolved in 20mL of MeOH and stirred at 20 ℃ for 12 hours. Then 100mmol of ammonium dichloride and 10mmol of formaldehyde (37% aqueous formaldehyde) were added to the system and the system was diluted with 10 times of MeOH. Heating the system at 65 deg.C under reflux for 1 hr, and adding dropwise 7mL 86% 3 PO 4 Reflux for 8 hours. At the end of the reaction, the system was rotary evaporated to 30-40mL, transferred to a beaker, ice was added and the pH was adjusted to 9 with 8M NaOH solution. The solution was extracted with EA, washed with water, and then with saturated brine. The pure product was then isolated by silica gel chromatography. The product was collected, dried and weighed. Nuclear magnetic analysis of the product: 1 H NMR(400MHz,CDCl 3 ,298K):δ=7.50-7.42(m,2H),7.28(s,3H),6.96(s,1H),2.42(dt,J=13.7,6.9Hz,2H),1.15(d,J=6.8Hz,12H); 13 C NMR(101MHz,CDCl 3 ,298K):δ=146.51,138.44,132.81,129.77,129.32,123.71,121.52,28.06,24.39,24.31。
s4.preparation of 4- (12-bromododecyloxy) benzaldehyde (a 6):
adding 5mmol of p-hydroxybenzaldehyde into 11mmol of 1, 12-dibromododecane dissolved in 75mL of acetone, adding 20mmol of anhydrous potassium carbonate into the system, condensing and refluxing at 65 ℃, stirring for 3 hours, adding 3mmol of p-hydroxybenzaldehyde into the system, continuing to react for 3 hours, finally adding 2mmol of p-hydroxybenzaldehyde into the reaction system, and continuing to react for 15 hours. The pure product is then isolated by chromatography on silica gel. The product was collected, dried by cooling by removing the solvent by rotary evaporation and weighed. Nuclear magnetic analysis of the product: 1 H NMR(400MHz,CDCl 3 ,298K):δ=9.88(s,1H),7.83(d,J=8.0Hz,2H),6.99(d,J=8.0Hz,2H),4.04(t,J=6.5Hz,2H),3.41(t,J=6.8Hz,2H),1.90-1.76(m,4H),1.44(dt,J=15.3,7.5Hz,4H),1.29(s,12H); 13 C NMR(101MHz,CDCl 3 ,298K):δ=190.80,164.29,131.99,129.79,114.77,68.44,34.02,32.84,29.51,29.42,29.32,29.06,28.76,28.17,25.96。
s5, preparing an imidazole salt (a 7):
3mmol of 4- (12-bromododecyloxy) benzaldehyde and 3.5mmol of 2, 6-diisopropyl) imidazole were dissolved in 8mL of 1, 4-dioxane, the reaction system was placed in an oil bath at 100 ℃, concentrated and refluxed, and the reaction was stirred for 18 hours. After the reaction was complete, the pure product was isolated by silica gel chromatography. Nuclear magnetic analysis of the product: 1 H NMR(400MHz,CDCl 3 ,298K):δ=10.24(s,1H),9.84(s,1H),8.19(s,1H),7.81(d,J=8.6Hz,2H),7.52(t,J=7.8Hz,1H),7.33-7.27(m,3H),6.99(d,J=8.6Hz,2H),4.71(t,J=6.8Hz,2H),4.04(t,J=6.4Hz,2H),2.32-2.22(m,2H),1.99(s,2H),1.87-1.75(m,2H),1.45(d,J=7.2Hz,3H),1.33(s,6H),1.25(s,7H),1.19(d,J=6.8Hz,6H),1.15(d,J=6.7Hz,6H); 13 C NMR(101MHz,CDCl 3 ,298K):δ=160.18,145.27,138.09,132.59,131.80,130.08,124.56,124.25,123.15,115.04,67.99,55.45,50.36,45.99,30.53,29.38,29.25,28.97,28.88,28.64,25.99,25.76,24.35,24.04,8.84。
s6, immobilizing an N-heterocyclic carbene ligand (a 8) by using the magnetic mesoporous microsphere:
aminated magnetic mesoporous microspheres a4 (0.40 g) prepared in S2 were added to dry methanol (20 ml) for sonication for 15 minutes, followed by addition of imidazolium salt a7 (0.044 g) prepared in S5 and heating at 50 ℃ for 2 days. After the reaction, separating the product by magnetic separation, washing the product with methanol for 3 times, and drying the product in vacuum at 50 ℃ for 24 hours to obtain the magnetic mesoporous microsphere of the immobilized N-heterocyclic carbene ligand.
S7, preparation of flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst (a 9= Fe) 3 O 4 @mSiO 2 @NHC-Pd):
Under nitrogen, 0.24mmol of imidazolium salt and 0.21mmol of PdCl 2 Added to 10ml of acetonitrile solvent and stirred at 80 ℃ for 0.5 hour under nitrogen protection. Then adding K 2 CO 3 (0.12 mmol), cooling and refluxing for 24 hours, washing the product twice with water, washing with ethanol for 2 times, and vacuum drying at 50 ℃ for 24 hours to obtain flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst Fe 3 O 4 @mSiO 2 @ NHC-Pd, its transmission electron micrograph is shown in figure 3a and 3b, the palladium loading in the catalyst prepared is 0.2mmol/g.
And (3) verification of catalytic performance:
in order to verify the catalytic activity and the recycling performance of the catalyst prepared in example 1 in the coupling reaction, the flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst Fe prepared in example 1 is applied 3 O 4 @mSiO 2 The @ NHC-Pd is used as a catalyst to prepare 4-methoxybiphenyl, and the catalyst is recovered through magnetic separation to verify the recycling performance of the catalyst.
Application example 1
In the nitrogen atmosphere, 4-methoxyphenylboronic acid (0.75 mmol) and the flower-shaped core-shell type magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst (1 mol%) prepared in the step 1 are added, and K 2 CO 3 (1.5 equivalents) and EtOH/H in a volume ratio of 2 2 O (2.0 mL) was added to the Schlenk reaction tube, followed by chlorobenzene (0.5 mmol). The mixture was stirred at 60 ℃ for 12h, then extracted with EtOAc, and the organic phase was collected and purified over anhydrous Na 2 SO 4 Drying, filtration and purification by flash column chromatography gave the pure product in 95% yield. 4-methoxybiphenyl nuclear magnetic analysis: 1 H NMR(400MHz,CDCl 3 ,298K):δ=7.59-7.52(m,4H),7.42(dd,J=10.8,4.5Hz,2H),7.34-7.28(m,1H),6.99(d,J=8.8Hz,2H),3.86(s,3H); 13 C NMR(101MHz,CDCl 3 ,298K):δ=159.12,140.81,133.77,128.70,128.13,126.72,126.63,114.18,55.33)。
to verify Fe 3 O 4 @mSiO 2 The reusability of the @ NHC-Pd catalyst. After the catalytic reaction is completed, fe is recovered by magnetic separation 3 O 4 @mSiO 2 The reaction was continued with ethanol and water to prepare 4-methoxybiphenyl (the reaction conditions were the same) using the catalyst of @ NHC-Pd and continuously washing with ethanol and water, and the yield of the obtained 4-methoxybiphenyl was as shown in FIG. 5, and after 12 cycles of use, fe 3 O 4 @mSiO 2 The @ NHC-Pd still has high catalytic activity, the yield of 4-methoxybiphenyl can still reach 90%, and the transmission electron microscope images of the catalyst obtained by the last recovery are shown in figures 3c and 3 d.
The above-described embodiments are intended to be preferred embodiments of the present invention only, and not to limit the invention in any way and in any way, it being noted that those skilled in the art will be able to make modifications and additions without departing from the scope of the invention, which shall be deemed to also encompass the scope of the invention.

Claims (9)

1. A flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst is characterized in that the flower-shaped core-shell magnetic mesoporous microsphere is loaded with the N-heterocyclic carbene ring palladium catalyst shown as a formula I:
Figure 320736DEST_PATH_IMAGE001
formula I;
the flower-shaped core-shell type magnetic mesoporous microsphere consists of magnetic Fe in a core shell 3 O 4 SiO outside the particle and core-shell 2 Mesoporous composition;
the preparation method of the flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst comprises the following steps:
step 1: fe preparation from iron source and silicon source 3 O 4 @SiO 2 Magnetic microspheres;
and 2, step: mixing Fe 3 O 4 @SiO 2 Dispersing magnetic microspheres in water to obtain magnetic microsphere dispersion, and treating the magnetic microsphere dispersion with a template agent to obtain flower-shaped core-shell magnetic mesoporous microspheres Fe 3 O 4 @mSiO 2
And 3, step 3: flower-shaped core-shell type magnetic mesoporous microsphere Fe 3 O 4 @mSiO 2 Amination of (a);
and 4, step 4: reacting the aminated flower-shaped core-shell magnetic mesoporous microsphere with an N-heterocyclic carbene ligand to prepare a flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ligand;
and 5: immobilizing the flower-shaped core-shell magnetic mesoporous microspheres with N-heterocyclic carbene ligands and PdCl in an inert gas atmosphere 2 Adding the mixture into a solvent, stirring to obtain a mixed solution, adding carbonate into the mixed solution, performing reflux reaction, washing and drying a product after the reaction is finished, and preparing the flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst.
2. The preparation method of the flower-like core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst according to claim 1 comprises the following steps:
step 1: preparation of Fe from iron source and silicon source 3 O 4 @SiO 2 Magnetic microspheres;
step 2: mixing Fe 3 O 4 @SiO 2 Dispersing magnetic microsphere in water to obtain magnetic microsphere dispersion, and using templateTreating the magnetic microsphere dispersion with an agent to obtain flower-shaped core-shell magnetic mesoporous microspheres Fe 3 O 4 @mSiO 2
And step 3: flower-shaped core-shell type magnetic mesoporous microsphere Fe 3 O 4 @mSiO 2 Amination of (2);
and 4, step 4: reacting the aminated flower-shaped core-shell magnetic mesoporous microsphere with an N-heterocyclic carbene ligand to prepare a flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ligand;
and 5: immobilizing the flower-shaped core-shell magnetic mesoporous microspheres with N-heterocyclic carbene ligands and PdCl in an inert gas atmosphere 2 Adding the mixture into a solvent, stirring to obtain a mixed solution, adding carbonate into the mixed solution, performing reflux reaction, washing and drying a product after the reaction is finished, and preparing the flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst.
3. The method for preparing the flower-like core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclopalladated catalyst according to claim 2, wherein the iron source in the step 1 is at least one of ferric chloride and ferric sulfate; the silicon source is organic siloxane; the template agent in the step 2 comprises hexadecyl trimethyl ammonium bromide and a fluorine surfactant FS-66.
4. The preparation method of the flower-like core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst according to claim 3, wherein the step 2 specifically comprises the following steps: cetyl trimethylammonium bromide, triethanolamine and ultrapure water were mixed at a ratio of 0.6g:0.1mL:30 mL-0.7 g:0.2mL:40 mixing the components in a ratio of mL, and stirring the mixture for 15 to 30 minutes at a temperature of between 60 and 70 ℃ to prepare a hexadecyl trimethyl ammonium bromide template solution; then weighing a template agent FS-66 according to the mass ratio of FS-66 to hexadecyl trimethyl ammonium bromide being 0.1 to 0.25, dissolving the template agent FS-66 in isopropanol to prepare a solution with the concentration being 0.0375 to 0.15g/mL, adding the solution into the hexadecyl trimethyl ammonium bromide template solution, continuously stirring for 1 to 2 hours, then adding TEOS according to the ratio of 6 to 10mL TEOS/g hexadecyl trimethyl ammonium bromide, stirring for 60 to 80 seconds, and then, adding the TEOS into the mixtureObtaining a double-template solution; mixing the double-template solution and the magnetic microsphere dispersion liquid according to the proportion of 2-3, carrying out ultrasonic treatment for 2-3 minutes, then oscillating for 30-40 minutes at the speed of r = 600-700 r/min on a circumferential oscillator, and then shaking for 6 hours at the speed of r = 200-300 r/min; finally separating the product, removing the template solution, adding a saturated ethanol solution of ammonium nitrate, oscillating and washing for 10-15h, washing the washed solid product for 2-3 times respectively by using absolute ethanol and water, and drying to obtain the flower-shaped core-shell magnetic mesoporous microspheres; in the magnetic microsphere dispersion, fe 3 O 4 @SiO 2 The concentration of the magnetic microspheres is 0.005 to 0.01g/mL.
5. The preparation method of the flower-like core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclic palladium catalyst according to claim 2, wherein the amination in the step 3 specifically comprises: adding the flower-shaped core-shell magnetic mesoporous microspheres prepared in the step 1, amino alkyl siloxane and a cation trapping agent into cyclohexane, performing ultrasonic treatment to obtain a dispersion liquid, stirring the obtained dispersion liquid at room temperature for reaction, washing a product with n-hexane and ethanol after the reaction is finished, and drying to obtain the aminated flower-shaped core-shell magnetic mesoporous microspheres.
6. The preparation method of the flower-like core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst according to claim 5, wherein the amino alkyl siloxane is 3-aminopropyl trimethoxysilane; the cation trapping agent is dodecyl amine; in the dispersion liquid, the concentration of the flower-shaped core-shell type magnetic mesoporous microspheres is 0.005 to 0.01g/mL, the concentration of 3-aminopropyltrimethoxysilane is 1 to 3v/v%, and the concentration of dodecylamine is 1 to 5v/v%; the ultrasonic treatment time is 5 to 10min, and the stirring reaction time is 4 to 6h.
7. The method for preparing the flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene cyclopalladated catalyst according to claim 2, wherein the mass ratio of the aminated flower-shaped core-shell magnetic mesoporous microsphere to the N-heterocyclic carbene ligand in the step 4 is 1 to 1.2, and the reaction conditions are as follows: methanol is used as a solvent, the reaction temperature is 50 to 60 ℃, and the reaction time is 2 to 3 days; the molar ratio of the carbonate to the flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ligand to the palladium chloride in the step 5 is (1.4); in the mixed solution, the concentration of the immobilized N-heterocyclic carbene ligand of the flower-shaped core-shell type magnetic mesoporous microsphere is 0.02 to 0.03mol/L; the solvent is acetonitrile, and the carbonate is potassium carbonate; the time of the reflux reaction is 20 to 30 hours.
8. The application of the flower-shaped core-shell magnetic mesoporous microsphere immobilized N-heterocyclic carbene ring palladium catalyst of claim 1.
9. Use according to claim 8, comprising use in a Suzuki-Miyaura coupling reaction.
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