Recyclable Acid–Base Bifunctional Core–Shell–Shell Nanosphere Catalyzed Synthesis of 5-Aryl-1H-1,2,3-triazoles through the “One-Pot” Cyclization of Aldehydes, Nitromethane, and Sodium Azide

Article abstract of DOI:10.1002/cctc.201700401

A magnetically separable core–shell–shell nanosphere, Fe₃O₄@nSiO₂-SO₃H@MS-NHCOCH₃ (n=nonporous, MS=microporous SiO₂), was fabricated as an acid–base collaborative catalyst for the three-component cyclization of aromatic aldehydes, nitroalkane, and sodium azide to afford 1H-1,2,3-triazoles. The bifunctional heterogeneous catalyst showed high activity for this transformation and good chemoselectivity, and toxic HN₃ was not released during the course of the reaction. A variety of aldehydes were transformed into the corresponding 5-aryl-1H-1,2,3-triazoles in up to 98 % yield. Furthermore, the catalyst could be recovered by using an external magnetic field and reused many times without any loss in activity. In contrast, a homogeneous catalyst system comprising ammonium acetate/acetic acid also worked in this three-component cyclization to afford 1H-1,2,3-triazoles.

Full text of DOI:10.1002/cctc.201700401

Accepted Article
Title: Recyclable Acid-Base Bifunctional Core-Shell-Shell Nanosphere
Catalyzed Synthesis of 5-Aryl-NH-1,2,3-triazoles via "One-Pot"
Cyclization of Aldehyde, Nitromethane and NaN3
Authors: Lei Liu, Yongjian Ai, Dong Li, Li Qi, Junjie Zhou, Zhike Tang,
Zixing Shao, Qionglin Liang, and Hong-bin Sun
This manuscript has been accepted after peer review and appears as an
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To be cited as: ChemCatChem 10.1002/cctc.201700401
Link to VoR: http://dx.doi.org/10.1002/cctc.201700401
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ChemCatChem
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COMMUNICATION
Recyclable Acid-Base Bifunctional Core-Shell-Shell Nanosphere
Catalyzed Synthesis of 5-Aryl-NH-1,2,3-triazoles via “One-Pot”
Cyclization of Aldehyde, Nitromethane and NaN
3
[a]
[a,b]
[a]
[a]
[a]
[a]
[b]
Lei Liu, Yongjian Ai,
Dong Li, Li Qi, Junjie Zhou, Zhike Tang, Zixing Shao, Qionglin
[b, ]
[a, ]
Liang, * and Hong-bin Sun *
Abstract: A magnetically separable core-shell-shell nanosphere
reagent, aldehyde, and NaN
and Chen individually developed the three-component reaction
was conducted.[10] Recently, Lin
3
3 4 2 3 3
Fe O @nSiO -SO H@MS-NHCOCH has been fabricated as an
acid-base collaborative catalyst for the three-component cyclization
of aromatic aldehyde, nitroalkane, and sodium azide to afford NH-
with aldehyde, nitroalkane and NaN
3
in the presence of excess
or catalytic amount of
[
11]
amounts of NaHSO
3
2 3
/Na SO .
aluminium(III) chloride.[
12]
These results not only make the
1
,2,3-triazoles. The bifunctional heterogeneous catalyst takes
advantages of high activity, good chemoselectivity and no toxic HN
releasing. variety of aldehydes have been transformed to
3
synthesis of NH-1,2,3-triazoles easier, but also reveal that the
three component condensation may be an acid-catalysed
procedure. Nowadays, the heterogenization of homogeneous
catalyst is in the trend of catalyst development, especially for the
solid acid-base bifunctional catalysts that take advantage of both
electrophile and nucleophile.[13] Following this guideline, we
developed the immobilized catalyst for the synthesis of 1,2,3-
triazoles via the MCR with aromatic aldehydes, nitroalkanes and
A
corresponding 5-aryl-NH-1,2,3-triazoles with up to 98% yield.
Furthermore, the catalyst could be recycled by an external magnetic
field and reused for many times without any activity lossing.
Contrastly,
a
homogeneous catalyst system ammonium
acetate/acetic acid also works to the three-component cyclization to
afford NH-1,2,3-triazoles.
3
NaN . Considering Sengupta reported in 2008 the proline-
catalyzed three-component reaction of β-alkyl nitroalkene to
1,2,3-triazoles are a class of artificially synthesized five-
[14]
synthesize 1,2,3-NH-triazoles,
we recognize that an acid-
membered heterocyclic compounds, which have been widely
applied in medicinal chemistry and material science.[1] The
synthesis of 1,2,3-triazoles has attracted extensive attention. So
far, the most popular synthetic route is the Cu(I)-catalyzed
azide-alkyne cycloaddition (CuAAC).[2] Besides of Cu, some
other metal complexes also work, such as Ru and Ir, to give
corresponding RuAAC and IrAAC reaction, respectively.[3] To
avoid the heavy metal residue in the products, non-toxic metal
catalyst [4] and organocatalyst have been also developed.[5]
In recent years, nitroolefin has been applied as an alternative
of the terminal alkyne for the synthesis of 1,2,3-triazole.[6] In
base bifunctional catalyst will has good performance.
The designation of the target catalyst includes the following
aspects: high efficiency, recoverability and easiness of catalyst
[15]
preparation.
Particularly, the chemoselectivity should be
carefully considered. This is because that the selectivity of the
condensation of aldehyde, nitroalkane with NaN is not as good
3
as the cycloaddition of alkyne with organic azides, which is well
known as a “click reaction” and even heterogeneous catalyst
such as Cu
2
O and Au nanocrystals gives good chemoselectivity
under mild conditions.[ Following these demands, we designed
16]
a
Fe
core-shell-shell
structured
heterogeneous
(n stands for non-porous
). It includes the combined
highlights of the literatures.[17] The core is the Fe
sphere that
give the catalyst magnetic separablity, the inner layer silica shell
is grafted with –SO H that generates from the oxidation of -SH
group, and the outer shell is functionalized with the acetylated –
NH . The outer shell is punched to porous so that the reactant
catalyst
many cases, the [3+2] cycloaddition of nitroolefin with NaN
3
3
O
4
@nSiO -SO H@MS-NHCOCH
2
3
3
gives the N-unsubstituted 1,2,3-triazoles, which have extensive
applications in synthesizing various 1,2,3-triazoles by post-N-
functionalization.[7] However, the rare availability of nitroolefin
drives the development of the “one pot” synthesis of 1,2,3-
triazoles with aldehydes, nitroalkanes and azides. What’s more,
the multicomponent reaction (MCR) is step-economical, and the
separation of the intermediates is avoidable.[8] In 2014,
Dehaen’s group detailed the synthesis of 1,2,3-triazole via the
cascade reaction of organocatalyzed Henry condensation of the
aldehyde with the nitro compound and the 1,3-dipolar
cycloaddition of the azide to the in-situ generated nitroarene.[9]
After that, a three-component reaction based upon the Julia
and MS stands for microporous SiO
2
3
O
4
3
2
can reach the acid site. As expected, this core-shell-shell
nanoparticles catalyse the synthesis of 1,2,3-triazole smoothly
under mild conditions and the products are obtained with high
yield..
The final bifunctional material Fe
NHCOCH was systematically characterized by TEM, EDS
analysis, vibrating sample magnetometer (VSM), XRD, FTIR
and N -adsorption-desorption.
As shown in the TEM images (Figure 1), the Fe
SO H@MS-NHCOCH is uniform egg-like nanosphere with the
3 4 2 3
O @nSiO -SO H@MS-
3
2
[
a]
B. S. L. Liu, M. S. Y. Ai, M. S. D. Li, B. S. L. Qi, B. S. J. Zhou, M. S.
Z. Tang, A. P. Dr. H. Sun.
3
4 2
O @nSiO -
Department of Chemistry
3
3
Northeastern University
average size of about 400 nm, and the three-layer structure is
distinguishable. A selected particle (about 500 nm) is detailed
with EDS analysis.
Shenyang 110819, People’s Republic of China
E-mail: sunhb@mail.neu.edu.cn
M. S. Z. Shao, A. P. Dr. Q. Liang.
Department of Chemistry
[
b]
Tsinghua University
Beijing 100084, People’s Republic of China
Supporting information for this article is given via a link at the end of
the document.
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ChemCatChem
10.1002/cctc.201700401
COMMUNICATION
3 4 2 3 3
Figure 3. XRD and FTIR of Fe O @nSiO -SO H@MS-NHCOCH .
3 4 2
In order to further study the characteristics of Fe O @nSiO -
SO
3
H@MS-NHCOCH
3
, the powder X-ray diffraction (XRD) was
o
also conducted (Figure 3a). The diffraction peaks at 2θ= 18.6 ,
3
0.2o, 35.8o, 37.4o, 42.3o, 53.8o, 57.1o, 62.9o and 74.3o
correspond to the (111), (220), (311), (222), (400), (422), (511)
440) and (622) planes of cubic phase of Fe (JCPDS: 00-
03-0862). And a wide diffusion peak at 2θ= 15-19〫(marked
(
0
3 4
O
with asterisk) generally was considered as the diffusion peak of
amorphous silica. [18]
Table 1. Optimization of the heterogeneous catalytic reaction
[
a]
conditions .
Figure 1. (a and b) TEM images, (c, d, e and f) EDS elemental mappings of
core-shell-shell structured catalyst
The distribution of Fe indicates that the Fe
ball, while the distribution of Si shows that the silica matrix is a
hollow ball that is bigger than Fe core. The N sphere is a bit
3 4
O core is a solid
3
O
4
larger than the S sphere, this clearly presents that N locates in
the outer silica shell and S is in the inner layer. The average
thickness of silica shell is several tens of nanometres.
Figure 2. (a) Magnetization curves at 302 k of the catalyst. (b) Magnetic
separation of the catalyst in ethanol.
The magnetic properties of the catalyst are shown in Figure 2.
With an applied field of 10000 Oe, the saturation magnetization
value is up to 50.004 emu/g (figure 2a). This indicates the high
magnetization of the sample. The absence of hysteresis
phenomenon demonstrates the superparamagnetic behavior of
the material at room temperature. Figure 2b also shows that the
well dispersed nanoparticles can be easily collected with an
external magnetic field.
The surface chemical structure of the synthesized materials
was characterized by FTIR spectroscopy (Figure 3b). The
characteristic peak at 640 cm-1 is due to the presence of Fe-O
bond, and the peaks around 1087 and 509 cm-1 are assigned to
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ChemCatChem
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the characteristic SiO
2
bands. The presence of the sulfonyl
was used to inhibit the formation of corresponding tetrazole, as
both of the aldehyde group and the cyano group can react with
sodium azide in the presence of acid to generate triazole and
tetrazole respectively. Considering the formation of triazole is
group is confirmed in the spectrum because the peaks at 1309
cm-1 was assigned to the stretching vibrations of the S=O. The
-1
peak at 1862 cm was assigned to imide asymmetrical carbonyl
C=O) absorbance. The bands around 2937 cm-1 was assigned
to the stretching vibrations of the CH group. The broad peak
(
faster than tetrazole, a small amount of NaN
Especially, acquiring the product 3n was very exciting, because
it couldn’t be obtained by using HOAc/NH OAc as catalyst. No
3
was used.
2
centered around 3436 cm-1 was an envelope of stretching
vibrations for O-H of the silanol groups and the sulfonyl groups.
These FT-IR spectra indicated that the sulfonyl groups and the
4
matter whatever the reaction conditions changed, the TLC
always showed us that a large amount of impurities existed in
the reaction solution and no main product. Generally, the
HOAc/NH OAC catalyzed three-component reaction (conditions
4
B) was also an acceptable method for the synthesis of 5-aryl-
NH-1,2,3-triazoles via the multicomponent reaction of aldehyde,
amide groups were successfully grafted onto Fe
We conducted the experiment of benzaldehyde, nitromethane
and NaN with the acid-base bifunctional catalyst in DMF, and
the 1,2,3-triazole was obtained in excellent yield (table 1, entry
). Because the catalyst contains amide that may acted the
3 4 2
O @nSiO .
3
1
3
nitromethane and NaN , because the catalyst is easily
similar role towards DMF, we tried to replace the solvent with a
low boiling point one so that the work-up could be easier. To our
disappointment, the best solvent was still confined to DMF (entry
accessible and the functional group tolerance is wide.
Table 2. Substrate scope of the catalytic reaction to afford NH-1,2,3-triazoles.
3
2-3). However, we found there was undissolved NaN in DMF,
and this might be a main reason that cause the incomplete
conversion. When the solvent was pure methanol, sodium azide
was completely dissolved but the problem was the serious
impurities. We utilized the mixed solvent of DMF/methanol (5/1),
which can fully dissolve sodium azide and maintain good
conversion (entry 4-5). Raising the reaction temperature to 140
o
C and shortening reaction time to 1 h led to a greatly increased
yield (entry 6). The subsequent experiments revealed that the
acidic group played a main role and acid-base synergy could
obviously improve the catalytic effect. Under the same
conditions,
Fe @nSiO
the
monofunctionalized
magnetic
sphere
3
O
4
2
-SO H offered relatively low yield of 90% 5-
3
phenyl-NH-1,2,3-triazole (entry 7). If the amide group was
directly grafted on the Fe @nSiO , the nanosphere was
3
O
4
2
almost inactive without the existence of sulfonyl acid (entry 8). In
the case of entry 9, its catalytic activity was equivalent to the one
that contained only amide, because there was no pore in the
outer imide grafted silica layer so that the reactants couldn’t
reach the acid sites. As the silicon matrix has amorphous hole
by itself, the yield was actually a little higher than in entry 8.
Obviously, a reaction in the absence of any catalyst gave a poor
3 4 2 3
yield (entry 10). Treating the Fe O @nSiO -SO H@MS-NHAc in
HCl to remove the protecting group –Ac gave no improvement,
so we confirmed that the final catalyst should be the N-protected
one, which provided better chemo compatibility than the N-
unprotected catalyst.
To further evaluate the core-shell-shell nanosphere, we also
4
explored the homogeneous AcOH/NH OAc catalysed the same
reaction as a comparison. The optimization of the homogeneous
conditions was concluded in the table S1.
Under the optimized reaction conditions, various aldehydes
were subjected to this one-pot reaction with nitromethane and
sodium azide. The results are summarized in table 2. All
substrates afforded the target product in excellent yields. The
effect of electron-withdrawing or electron-donating group on the
reaction was not apparent.
Comparing
heterogeneous catalyst Fe
showed many advantages such as high yield, excellent
selectivity and safety. In most cases, the bifunctional solid
4
catalyst gave higher yield than the HOAc/NH OAc. We could
with
the
HOAc/NH
@nSiO
4
OAc
-SO
systems,
H@MS-NHCOCH
the
3
O
4
2
3
3
For most aldehydes, the corresponding NH-1,2,3-triazoles
were obtained with more than 90% yield according to the
general procedure (3a, 3b, 3c, 3g, 3h, 3i, conditions A), and the
others gave more than 80% product (3d, 3f, 3j~3n), except the
obtain excellent yields when we adopt 10 wt% catalyst that is
only 10-20 mg/mmol, and the amount of catalyst is insensitive.
That embodied remarkable performance of the catalyst. Again,
the acid center is grafted on the inner silica sphere, this prevent
the release of hydrazoic acid, which generates in situ and is a
cyano benzaldehyde that gave 3e. This is because 1 mmol NaN
3
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ChemCatChem
10.1002/cctc.201700401
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highly toxic substance that can inhibit enzyme activity and cause
nerve change. That reflects the safety of heterogeneous catalyst.
Figure 4. (a) The crystallization of 5-(4-isopropylphenyl)-1H-1,2,3-triazole. (b)
The recyclability of the catalyst.
Figure 5. Nitrogen adsorption-desorption curve.
Another advantage of our heterogeneous catalyst is that less
impurities generates than homogeneous catalytic system, which
can be proved in the work-up process. As quite a few
byproducts could format during the cyclization of nitroolefin with
sodium azide, the previous reports have alleged that NH-1,2,3-
triazoles can’t be crystallized out.[6a] Good chemoselectivity that
was observed on TLC and HPLC interested us to challenge the
crystalizing ability of the reaction mixture, as it is well accepted
that less impurities offer better crystal ability. We chose the
reaction of p-isopropylbenzaldehyde as the objective reaction.
On completion of the reaction, the catalyst was separated out
and the solution was mixed with double volume of water then
was refrigerated overnight. The product was crystallized out in
the end as we can see in Figure 4a. This may because the bulky
byproducts is limited by the microtunnel of the catalyst, which
Because we found the intermediate nitroolefins present both
in homogeneous and heterogeneous catalytic system, we
speculated that the reaction path is a one-pot two-steps pathway
that includes
a
Henry condensation and
a
1,3-dipolar
cycloaddition cascade reaction as described in the earlier
literature.[
19]
The heterogeneous reaction was expected to
proceed through the following pathway (Scheme 1). The acid
site activates the benzaldehyde through the hydrogen bond
between the carbonyl group and the proton of sulfonyl acid,
while the amide-activated nitromethane attacks the activated
benzaldehyde to form the β-nitro-alcohol, which converts to
nitroolefin by eliminating one molecular water under heating.
The second step is that the triazoline is formed via the
matched with the N
2
-adsorption-desorption experimental results
adsorption of the
cycloaddition of the olefin and azide. The elimination of HNO
2
(
Figure 5). The curve indicates the low N
2
gives the triazole as the ultimate product. The bifunctional
catalyst was involved in all of the reaction process and
participated in the next run with its original form. In order to
verify the reaction process, we carried out DSC testing with the
HOAc/NH OAc catalyzed model reaction (Figure S2). The curve
4
shows two exothermic peaks, this indirectly verified the
mechanism of two steps.
catalyst, and this reveals that there was almost no mesopores or
macropores in the nanoparticles. Considering the result of
cyclization using a non-porous catalyst (table 1, entry 9), there
must be pores in the outer silica shell, therefore the pores
should be in microscale. This may be mutually deduced from the
low CTAB loading in the preparation of the outer shell.
The main advantage of the heterogeneous catalyst is that can
be reused many times without any loss of the catalytic activity.
The recyclability of our catalyst was investigated in the synthesis
of 5-phenyl-NH-1,2,3-triazole at the optimized reaction
conditions. The catalyst can be retrieved via magnetic
separation, lavation with ethanol and drying, then used for next
reaction cycle. The recycling test showed that the catalyst was
robust and could be reused up to 10 times without any loss in
catalytic activity (Figure 4b).
As we concluded, the good reusability located in two aspects:
one is that the active centers of the catalyst are organic
functional groups that are linked to the silica matrix through the
strong covalent bond, so no active component leaches out
during the reactions. The other one is that our catalyst is robust
enough and can be retrieved by a magnet bar at the end of
reaction, so it can be thoroughly recovered without any losing.
The TEM image of the recovered catalyst in Figure S1 confirmed
that the morphology of the sample was almost unchanged.
Scheme 1. Proposed reaction pathway for the synthesis of 5-aryl-NH-1,2,3-
triazoles in heterogeneous catalytic system.
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ChemCatChem
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COMMUNICATION
In conclusion, we have developed an efficient heterogeneous Acknowledgements
catalyst
Fe
3
O
4
@nSiO
2
-SO
3
H@MS-NHCOCH
3
for
the
multicomponent condensation of aldehyde, nitroalkane and
sodium azide. This process gives 5-aryl-NH-1,2,3-triazoles with
excellent yields and has showed a wide substrate scope. A
This work was financially supported by National Natural Science
Foundation of China (21235004, 21175080) and the Ministry of
Science and Technology (2013ZX09507005)
4
homogeneous catalytic system HOAc/NH OAc also works, but
the heterogeneous catalyst provides better yield because the
micro tunnel of the silica shell limits the generation of by-
products. Moreover, the application of the silica matrix wrapped
acid enhances the operating security. In addition, its good
magnetism and structure stability can guarantee catalytic activity
does not decline even after it is used repeatedly for many times.
Keywords: Magnetically Recyclable Nanosphere • Bifunctional
Catalyst • Acid-Base Synergy • NH-1,2,3-triazole • Three-
Component Condensation
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Preparation of Fe
.1 mol/L HCl solution (60 mL) under ultrasonic condition for 10 minutes.
The activated magnetic nanoparticles were dispersed in the
homogeneous solution of deionized H O (40 ml), ethanol (160 mL), and
5% NH ·H O (4 mL). After TEOS (1 mL) was added dropwise, the
3 4 2
3 4
O @nSiO -SH.First, Fe O (0.2 g) was treated by
0
2
2
3
2
solution was stirred vigorously at ambient temperature for 6 h. Then, the
solid was separated from the suspension then reacted with MPTMS (1
mL) in isopropanol (200 mL) at 80 oC for 3 h to functionalize the silica
3 4 2
surface with thiol groups. Finally, the Fe O @nSiO -SH nanocomposite
was segregated by an external magnet and washed with ethanol for a
few times
[3]
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Preparation of Fe
addition of TEOS (1.5 mL), the Fe
of ethanol (160 mL), deionized water (40 mL) and CTAB (0.3 g) at room
temperature for 6 h. After the liquid was removed, the residue was
blended with isopropanol (200 mL) and APTES (1.5 mL) at 80 C for 3 h.
3
O
4
@nSiO
2
-SH@nSiO -NHCOCH3. Along with the
2
@nSiO -SH was stirred in a mixture
2
O
3 4
8
Soc. 2007, 129, 12670-12671; d) S. Ding, G. Jia, J. Sun, Angew.
Chem.-Int. Edit. 2014, 53, 1877-1880.
o
[
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Xie, X. Deng, Heterocycles 2016, 92, 423-430.
As the solution was cooled to room temperature, the solid was attracted
by a magnet to remove the liquid and washed with little CCl
4
. Eventually,
the Fe @nSiO -SH@nSiO -NHCOCH was prepared by reacting the
O
3 4
2
2
3
a) Q. Jia, G. Yang, L. Chen, Z. Du, J. Wei, Y. Zhong, J. Wang, Eur. J.
Org. Chem. 2015, 3435-3440; b) H. Singh, G. Khanna, J. M. Khurana,
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above obtained magnetic materials with acetic anhydride (4 mL) in CCl
4
at 80 ℃ for 4h.
Preparation
of
Fe
3 4 2 3
O @nSiO -SO H@MS-NHCOCH3.
The
Fe @nSiO -SH@nSiO
3
O
4
2
2
-NHCOCH
3
is firstly stirred vigorously in
ethanol (100 mL) for 12 h to form the pores via the dissolution of CTAB.
After the material was collected, the thiol group was oxidized to the
sulfonic acid group by hydrogen peroxide (80 mL, 35 wt%) for 12 h at
2016, 1886-1890; g) R. Nagarajan, J. Jayashankaran, L. Emmanuvel,
Tetrahedron Lett. 2016, 57, 2612-2615.
ambient temperature. Finally, the Fe
3 4 2 3 3
O @nSiO -SO H@MS-NHCOCH
[
6]
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Habib, B. R. Raju, V. Kavala, C.-W. Kuo, C.-F. Yao, Tetrahedron 2009,
was dried at 333 k for 6 h to wait for further use.
6
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Typical Procedure for the synthesis of NH-1,2,3-triazoles. The
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o
stirred in a sealed tube at 140 C. After 60-80 min (as monitored by TLC),
the solution was quenched with H
4×10 mL). The combined organic layers were dried through adding
anhydrous Na SO , and the solvent was evaporated in vacuo. The
resulting mixture was purified by flash column chromatography on silica
gel (SiO , petroleum ether/EtOAC) to afford the NH-1,2,3-triazoles.
2
O (20 mL) and extracted with EtOAc
[
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COMMUNICATION
COMMUNICATION
[
a]
[a,b]
[a]
Lei Liu, Yongjian Ai,
Dong Li, Li
Qi,[ Junjie Zhou, Zhike Tang, Zixing
a]
[a]
[a]
Shao,[b] Qionglin Liang, * and Hong-bin
[b, ]
Sun [a,*]
Page No. – Page No.
Recyclable Acid-Base Bifunctional
Core-Shell-Shell Nanosphere
Text for Table of Contents
Catalyzed Synthesis of 5-Aryl-NH-
1
,2,3-triazoles via “One-Pot”
Cyclization of Aldehyde,
Nitromethane and NaN
3
•
•
•
•
Fe
3 4 2 3 3
O @nSiO -SO H@MS-NHCOCH as an recyclable heterogeneous catalyst
The reaction is safe to be handled as no dangerous hydrazoic acid releases.
The NH-1,2,3-triazoles are synthesized from aromatic aldehydes, nitromethane and sodium azide with less byproducts.
The catalyst can be reused for ten times without any loss of the catalytic activity.
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