Copper(II)-Schiff Base Complex-Functionalized Polyacrylonitrile Fiber as a Green Efficient Heterogeneous Catalyst for One-Pot Multicomponent Syntheses of 1,2,3-Triazoles and Propargylamines

Article abstract of DOI:10.1002/adsc.201701475

A series of copper(II)-Schiff bases-functionalized polyacrylonitrile fiber catalysts were successfully prepared using copper acetate as copper source and characterized by elemental analysis, fourier-transfer infrared spectroscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy and inductively coupled plasma analysis. Excellent physical strength and thermal stability of the fiber catalysts were demonstrated by scanning electron microscopy, X-ray diffraction, thermogravimetric/differential scanning calorimetry analysis and mechanical strength measurements. Furthermore, these catalysts were successfully applied to one-pot multicomponent copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction and aldehyde, alkyne, amine (A3) coupling reaction in which the influences of different substituent groups on the catalytic activities of fiber catalysts were investigated in detail. Among them, the bis[N-ethyl-3,5-di-tert-butyl-salicylideneiminato]copper(II)-functionalized polyacrylonitrile fiber (PAN_S2F?Cu) as a green, efficient catalyst exhibited the best catalytic activity for its high hydrophobic micro-environment can aggregate the reactants to the catalytic sites and accelerate the reaction. In addition, the PAN_S2F?Cu has performed well in scaled-up experiment and shown excellent recyclability (at least ten times), and these enable it to have great potential for further applications. (Figure presented.).

Full text of DOI:10.1002/adsc.201701475

Title: Copper(II)-Schiff Base Complex-Functionalized Polyacrylonitrile
Fiber as a Green Efficient Heterogeneous Catalyst for
One-Pot Multicomponent Syntheses of 1,2,3-Triazoles and
Propargylamines
Authors: Pengyu Li, Yuanyuan Liu, Lu Wang, Jian Xiao, and Minli Tao
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201701475
Link to VoR: http://dx.doi.org/10.1002/adsc.201701475

10.1002/adsc.201701475
Advanced Synthesis & Catalysis
FULL PAPER
DOI: 10.1002/adsc.201
Copper(II)-Schiff Base Complex-Functionalized
Polyacrylonitrile Fiber as a Green Efficient Heterogeneous
Catalyst for One-Pot Multicomponent Syntheses of 1,2,3-
Triazoles and Propargylamines
Pengyu Li,a Yuanyuan Liu,a Lu Wang,a Jian Xiaoa and Minli Taoa*
a
Department of Chemistry, School of Science Tianjin University
Collaborative Innovation Center of Chemical Science and Engineering.
Tianjin 300072, P. R. China.
E-mail: mltao@tju.edu.cn
Received:
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.
Abstract. A series of copper(II)-Schiff bases-functionalized catalytic activities of fiber catalysts were investigated in
polyacrylonitrile fiber catalysts were successfully prepared detail. Among them, the bis[N-ethyl-3,5-di-tert-butyl-
using copper acetate as copper source and characterized by salicylideneiminato]copper(II)-functionalized
elemental analysis, fourier-transfer infrared spectroscopy, polyacrylonitrile fiber (PANS2F-Cu) as a green, efficient
ultraviolet-visible spectroscopy, X-ray photoelectron catalyst exhibited the best catalytic activity for its high
spectroscopy and inductively coupled plasma analysis. hydrophobic micro-environment can aggregate the reactants
Excellent physical strength and thermal stability of the fiber to the catalytic sites and accelerate the reaction. In addition,
catalysts were demonstrated by scanning electron the PANS2F-Cu has performed well in scaled-up experiment
microscopy,
X-ray
diffraction,
thermogravimetric/ and shown excellent recyclability (at least ten times), and
differential scanning calorimetry analysis and mechanical these enable it to have great potential for further
strength measurements. Furthermore, these catalysts were applications.
successfully applied to two one-pot multicomponent copper-
catalyzed azide-alkyne cycloaddition (CuAAC) reaction and
aldehyde, alkyne, amine (A3) coupling reaction in which the
influences of different substituent groups on the
Keywords: Polyacrylonitrile fiber; Schiff base; Copper
catalyst; Triazoles; Propargylamines
syntheses. Among them, Click chemistry (often
synonymous with 1,3-dipolar cycloaddition to give
triazoles) was introduced by Sharpless in 2001,[9]
which is a set of powerful, highly reliable, selective
and atom-efficient reaction in organic synthesis.[10]
The products 1,2,3-triazoles have extensive
Introduction
In current chemistry, natural products and other
complicated organic compounds were synthesized by
multistep synthetic strategies according to their
complexity.[1] In such total synthesis procedures,
disadvantages of low yields, tedious operation, high
cost, environmental pollution, etc. restrict their large-
applications
in
pharmaceutical,[11]
chemical
sensors,[12] biodegradable polymers[13] and so on. And
A3 coupling reaction is a significant method to
synthesis the propargylamines, which is an important
skeleton structure of valuable intermediates[14] and
biologically active compounds,[15] etc. Therefore,
much attention has been paid to the MCRs of CuAAC
and A3 coupling reactions.
In most cases, only catalyzed by appropriate catalysts
can organic reactions take place smoothly with
satisfactory yields.[16] Numerous homogeneous and
heterogeneous catalysts have been designed and
applied in various simple organic reactions or MCRs.
However, homogeneous catalysis has the intrinsic
disadvantage of complicated separation, which will
cause resource consumption, environmental pollution
and hinder its further application in industrial circle.
scale
applications
in
synthetic
chemistry.
Multicomponent reactions (MCRs), generally the
one-pot reactions employing more than two starting
materials, are reactions where most of the atoms of
the starting materials are incorporated in the final
products.[2] They are the most useful synthetic routes
to generate great structural and skeletal complexes
with advantages of simplicity, synthetic efficiency
and atom-economy over conventional chemical
syntheses.[3] For the advantages above, many MCRs
such as Biginelli reaction,[4] Cu-catalyzed azide-
alkyne cycloaddition (CuAAC) reaction,[5] Mannich
reaction,[6] carbometallation-Michael reaction[7] and
A3 coupling reaction,[8] have been applied in organic
1
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10.1002/adsc.201701475
Advanced Synthesis & Catalysis
Compared to homogenous catalysts, heterogeneous
ones have much advantages of facile separation and
reusability of the catalysts and simple isolation of the
product, which is a green strategy for sustainable
chemistry. Immobilizing catalysts on solid supports is
a common method to synthesize heterogeneous
catalysts. Various organic materials like polymer,[5]
cellulose,[17] chitosan,[18] starch,[19] resin,[20] and
inorganic materials like SBA,[21] silica,[22] metallic
oxide,[23] graphene,[24] activated carbon,[25] have been
used as supports for heterogeneous catalysts. Due to
the unique micro-environment, polymer supported
catalysts often display superior catalytic activity, high
regioselectivity
and
many
other
special
performances.[26]
Polyacrylonitrile fiber (PANF), an industrial product
of low cost, high strength, light density and mildew
resistant, has been widely used in industry and our
daily life. Because it has abundant cyano groups
which can be easily transformed into carboxyl,
aminocarbonyl and other functional groups.[27] More
distinctively, the modification will reach hundred
layers deep inside the fiber surface, which constructs
a special soft micro-environment in favor of the
accumulation of reactants and there by promoting the
reaction.[26] Various PANF materials have been
developed and applied to remove heavy metal ions[28]
and organic compounds[29] from waste water or air, to
prepare phase change material,[30] pH sensitive
material,[31] antimicrobial material,[32] heterogeneous
catalyst,[33] and so on. In our previous work, PANF
not only has been modified to synthesize heavy metal
ions adsorbent or sensory material[34] and acid-base
sensory material,[27] but also been prepared into
heterogeneous base catalyst,[35] acid catalyst,[36] phase
transfer catalyst,[35b, 37] bifunctional catalyst,[38] metal
catalyst[39] and chiral catalyst,[40] which indicate that
the PANF is an ideal multipurpose support for
heterogeneous catalyst.
Scheme 1. Preparation of the fiber catalysts.
formed PANS1-5F were coordinated with Cu(OAc)2 to
obtain the green fiber catalysts PANS1-5F-Cu. On the
other hand, the PANEF can coordinate with Cu(OAc)2
directly to synthesize the PANEF-Cu as another fiber
catalyst. The extents of functionalization of the fibers
were determined by weight gain and ICP analysis
which were summarized in Table 1.
The Schiff base contents are approximately double
that of the copper (Table 1, entries 1-3), which
indicates that one copper ion chelates with two Schiff
base units (Scheme 1). While for PANS4F-Cu and
PANS5F-Cu, rarely coppers are anchored on the fiber.
This result has been proved by the elemental analysis,
FTIR and UV-vis spectra. That may be explained by
the low coordination abilities of the Schiff bases due
to the strong electron-withdrawing group or large
conjugate aromatic ring (Table 1, entries 5 and 6).
Elemental analysis (EA)
Due to the economic and environmental friendly
properties, copper catalyst has attracted the
widespread attention of chemists. Numerous copper
catalysts have been developed to efficiently catalyze
various organic reactions.[41] In the present study,
combining the advantages of copper catalyst and
PANF, and several Cu(II)-Schiff base complexes-
functionalized PANFs have been prepared and
applied to MCRs of CuAAC and A3 coupling
reactions as efficient green reusable heterogeneous
catalysts.
The EA data of PANF and modified fibers are
displayed in Table 2 and Table S1. With the
introduction of amide oxygen atom and the
aminoethyl group, the PANEF has lower carbon and
nitrogen contents (62.87% and 23.09%, respectively)
and higher hydrogen content (6.263%) (Table 2, entry
2). Because the Schiff base moieties in PANS2F have
Table 1. The modified degree of fiber catalysts.
Entry Fiber
CS (mmol/g)a) CCu (mmol/g)b)
PANS1F-Cu 2.0 1.25
1
2
3
4
5
Results and Discussion
PANS2F-Cu 1.97
1.11
1.13
0.02
0.05
0.55
PANS3F-Cu 1.80
PANS4F-Cu 2.27
PANS5F-Cu 2.18
PANEF-Cu ----
Synthesis of the fiber catalysts
The fiber catalysts PANEF-Cu and PANS1-5F-Cu were
prepared as shown in scheme 1. In the first step,
PANF was refluxed with ethylenediamine aqueous to
get the PANEF (modified degree = 2.4 mmol/g)
which was treated with different aldehydes to give
the Schiff base modified PANS1-5F. Finally, the
6
a)
CS: Schiff base contents of different fibers, which
determined by weight gain. Weight gain = [(W2-W1)/W1]
×100%, where W1 and W2 are the weights of unmodified
b)
and modified fibers. CCu: Cu contents of different fibers,
which determined by ICP.
2
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10.1002/adsc.201701475
Advanced Synthesis & Catalysis
Table 2. EA data of different fibers.
Entry Fiber
C (%) H (%) N (%) S (%)
1
2
3
4
5
PANF
PANEF
PANS2F
PANS2F-Cu 60.76 6.48
PANS2F-1a)
60.95 6.51
PANS2F-10b) 61.81 6.63
70.75 5.94
62.87 6.26
66.94 7.10
26.12 0.09
23.09 0.01
16.29 0.01
15.43 0.01
15.81 0.01
16.55 0.01
6
a)
b)
The PANS2F-Cu was used once in CuAAC reaction.
The PANS2F-Cu was used ten times in CuAAC reaction.
higher carbon and hydrogen contents and lower
nitrogen content, the carbon and hydrogen contents
rise to 66.94% and 7.10% respectively, and the
nitrogen content of PANS2F declined to 16.29%
(Table 2, entry 3). When Schiff base moieties in
PANS2F coordinate with copper ions, all the carbon,
hydrogen and nitrogen contents of the fiber catalyst
PANS2F-Cu declined (Table 2, entry 4). After the
fiber catalyst was used once in CuAAC reaction, the
PANS2F-Cu-1 remained almost the same EA data
with that of the fresh fiber catalyst (Table 2, entry 5).
While, when the fiber catalyst is reused ten times, the
carbon and nitrogen contents of PANS2F-Cu-10
respectively increased to 61.81% and 16.55%, which
may be attributed to the absorption of organic
compounds during the reaction process (Table 2,
entry 6). The EA data of fiber catalysts PANS1F-Cu
and PANS3F-Cu are listed in table S1 which are
similar with that of PANS2F-Cu. However, because of
the poor chelate abilities of PANS4F and PANS5F, the
EA data of PANS4F-Cu and PANS5F-Cu are almost no
changes compared to that of PANS4F and PANS4F,
respectively (Table S1, entries 5-8).
Figure 1. FTIR spectra of (a) PANF, (b) PANEF, (c)
PANS2F, (d) PANS2F-Cu, (e) PANS2F-Cu-1, (f) PANS2F-
Cu-10.
of PANS1F-Cu (Figure S2d) and PANS3F-Cu (Figure
S2f) have similar red-shift phenomena. Therefore, the
Cu-Schiff base complexes are proved to be grafted
onto the fiber successfully. However, the spectrum of
PANS4F-Cu and PANS5F-Cu are nearly the same with
PANS4F and PANS5F, which indicate the copper ions
and Schiff base complexes are almost no coordinating
(Figure S2g-j). After the PANS2F-Cu was reused one
or ten times, the FTIR spectra of PANS2F-Cu-1 and
PANS2F-Cu-10 only have minor changes, which
suggests the excellent recoverability of the fiber
catalyst (Figure 1e and f).
Solid UV-Vis spectroscopy
The fiber catalysts are also investigated by solid UV-
Vis technique and the results are shown in Figure 2.
Compared with PANF and PANEF, the UV-Vis
spectrum of PANS2F shows a distinct new peak
around 360 nm which is due to the π→π* and n→π*
transitions of the Schiff base moiety.[42] New bands
Fourier-transfer infrared spectroscopy (FTIR)
Samples of PANF, PANEF, PANS2F, PANS2F-Cu,
PANS2F-Cu-1 and PANS2F-Cu-10 were pulverized by
cutting and then prepared into KBr pellets, and their
FTIR spectra are shown in Figure 1. For PANF, the
distinctive absorption band at 2244 cm-1 is attributed
to C≡N stretching vibrations. Due to the existence of
methyl acrylate units in PANF, there is C=O
stretching vibration peak at 1737 cm-1. Moreover, the
strong absorption band at 1455 cm-1 is assigned to the
C-H bending vibrations (Figure 1a). After being
modified by ethylenediamine (Figure 1b),
methoxycarbonyl and cyano groups react with -NH2,
and the bands at 1733 cm-1 and 2245 cm-1 are
weakened apparently and two strong bands appeared
at 1654 cm-1 and 1561 cm-1 which are attributed to
the amide I and II bands, respectively. Besides, the
new broad band at 3650-3150 cm-1 is stretching
vibration peak of N-H in -NH2. In the spectrum of
PANS2F-EA (Figure 1c), the peak at 1644 cm-1 is
enhanced which is caused by the formation of C=N
bond. The spectrum of PANS2F-Cu (Figure 1d) shows
a red shift to 1622 cm-1 due to the coordination of the
C=N band with copper ions.[24, 42] The FTIR spectra
Figure 2. UV-vis spectra of (a) PANF, (b) PANEF, (c)
PANS2F, (d) PANS2F-Cu, (e) PANS2F-Cu-1, (f) PANS2F-
Cu-10.
3
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10.1002/adsc.201701475
Advanced Synthesis & Catalysis
around 420 nm and 730 nm appeared in spectrum of
PANS2F-Cu are attributed to the ligand to metal
transfer (LMCT) and d→d transition band of the
Cu(II), respectively.[43] The UV-Vis spectra of
PANEF-Cu (Figure S3a), PANS1F-Cu (Figure S3c)
and PANS3F-Cu (Figure S3e) are similar to PANS2F-
Cu which indicate the successful anchoring of Cu(II)
Schiff base complexes on PANF. As well as FTIR
spectra, the UV-Vis spectra of PANS4F-Cu and
PANS5F-Cu (Figure S3g and i) don’t show similar
peak as PANS2F-Cu. After reused one or ten times in
CuAAC reaction, the PANS2F-Cu shows excellent
stability because the spectra of PANS2F-Cu-1 (Figure
2e) and PANS2F-Cu-10 (Figure 2f) are basically
consistent.
Figure 4. XPS spectra of PANS2F-Cu: (a) survey spectrum,
(b) Cu2p spectrum.
around 942.8 eV could be assigned to the
characteristic binding energies of Cu(II) (Figure
4b) which shows the successful immobilization
of Cu(II).[44]
Scanning electron microscopy (SEM)
The SEM images of PANF, PANEF, PANS2F,
PANS2F-Cu, PANS2F-Cu-1 and PANS2F-Cu-10 are
shown in Figure 3. The diameter of PANF is around
25 μm and the surface is smooth (Figure 3a). After
modified succeedingly by ethylenediamine, aldehyde
and Cu(OAc)2, the surface of the fiber becomes
slightly rough, and the diameter increases remarkably
(Figure 3b, c and d), which indicates the successful
grafting of Schiff base-Cu. When the fiber catalyst
was used once, very few changes occur on the fiber
catalyst surface (Figure 3e). While, after being reused
ten times, the surface of the PANS2F-Cu-10 becomes
more roughly and the diameter becomes more slender
(Figure 3f). In the end, the basic structure of fiber
catalyst is retained with considerable mechanical
strength which will be confirmed by further research
(Table 3), for example, the PANS2F-Cu-10 still keeps
72% mechanical strength as the original PANF
(Table 3, entry 6).
X-ray diffraction (XRD).
Different fibers were also studied by XRD, and the
spectra of PANF, PANEF, PANS2F and PANS2F-Cu
are given in Figure 5. For PANF, two peaks (2θ=17º,
30º) are shown in Figure 5a which correspond to
strong diffraction of (100) face and weak diffraction
of (110) face, respectively. The intense peak at
2θ=17º is due to the hexagonal lattice formed by the
parallel close packing of the molecule rods.[45] The
peak at 17º in Figure 5b is stronger than that of PANF
because that some ethylenediamine molecules
crosslink between the fiber skeletons to stabilize the
structure of PANF. For spectra of PANS2F, PANS2F-
Cu and PANS2F-Cu-10 (Figure 5c-e), the peaks at 17º
are weaker than that of PANF and PANEF, which
indicates that part of the crystalline phase of the fibers
have been changed after being heated during the
modification process.
X-ray photoelectron spectroscopy (XPS)
Thermal Stability Analysis
The XPS spectra of PANS2F-Cu are shown in Figure
4. The surface content of copper calculated by XPS is
0.78 mmol/g, which is less than the total copper
content of 1.11 mmol/g tested by ICP. The result
illustrates that the fiber catalyst is not modified on
shallow surface but a goes deep to multilayers which
further contribute to the formation of catalytic micro-
environments on the fiber catalyst. High intensity
peaks at 933.4 eV, 953.1 eV and satellite peaks
TG/DSC curves of different fibers are presented in
Figure 6. The maximum thermal decomposition
Figure 3. SEM images of (a) PANF, (b) PANEF, (c)
PANS2F, (d) PANS2F-Cu, (e) PANS2F-Cu-1, (f) PANS2F-
Cu-10.
Figure 5. X-ray diffraction spectra of (a) PANF, (b)
PANEF, (c) PANS2F, (d) PANS2F-Cu, (e) PANS2F-Cu-10.
4
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10.1002/adsc.201701475
Advanced Synthesis & Catalysis
Table 3. The mechanical properties of different fibers.
Entry Fiber
BS (cN) RBS (%)
1
2
3
4
5
PANF
PANS2F
PANS2F-Cu
PANS2F-Cu-1
PANS2F-Cu-10 7.9
11.0
9.1
8.7
100
83
79
79
72
8.7
applied to the CuAAC reaction of benzyl chloride,
phenyl acetylene and sodium azide once, the RBS of
the PANS2F-Cu-1 is the same with that of PANS2F-Cu
(Table 3, entries 4 and 5). After reused ten times, 72%
RBS of PANS2F-Cu-10 is still reserved (Table 3,
entry 6). That shows the PANS2F-Cu has good
mechanical strength for further researches.
Figure 6. TG/DSC spectra of (a) PANF, (b) PANEF, (c)
PANS2F, (d) PANS2F-Cu.
Catalytic activities
Initially, the Cu(II)-Schiff base-functionalized fibers
Table 4. Optimization of the CuAAC reaction conditions.a)
temperature (DSCmax) of the PANF is determined to
be 309.4 (Figure 6a). After modified by
ethylenediamine, the DSCmax of PANEF is slightly
o
declined to 293.1 C, which indicates very little
damage happening on the fiber. In addition, the
decreasing rate of the PANEF’s TG curve is slower
than that of PANF (Figure 6b) due to the crosslinking
of ethylenediamine with PANF. The PANS2F
Entry Catalyst
Solvent
T (oC) Time
(h)
Yield
(%)b)/TON
o
exhibites a main transient of weight loss at 288.8 C,
1
----
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
CH3OH
60
60
60
60
60
60
60
60
60
60
60
60
60
80
50
60
60
60
60
60
60
2
2/----
which shows similar thermal stability with that of
PANEF (Figure 6c). Although the DSCmax of
PANS2F-Cu further declines to 228.2 oC (Figure 6d),
it is enough for the application in CuAAC and A3
coupling reactions. Furthermore, when the fiber is
heated to 800 oC, the PANS2F-Cu has a mass residue
of 57.4%, which is 10.5% higher than that of the
PANS2F (46.9%). The higher mass residue of
PANS2F-Cu shoud be attributed to the immobilization
of copper. The copper content by the mass residue is
1.64 mmol/g which higher than the copper content
tested by ICP (1.11 mmol/g), which may be because
part of copper ions are coordinate with Schiff base
moieties as a ratio of 1:1 (Scheme S1) and
systematic errors of different methods. In
summary, all experiment results can prove the
successful immobilization of copper on the fiber.
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16d)
17e)
18f)
19g)
20g)
21
22
23
24
PANF
Cu(OAc)2
S2-Cuc)
2
2
2
2
2
2
2
2
2
3
3.5
4
3.5
3.5
3.5
3.5
3.5
3.5
24
3.5
3.5
3.5
3.5
2/----
41/20.5
67/33.5
51/25.5
66/33.0
32/16.0
11/5.5
13/6.5
51/25.5
85/42.5
97/48.5
97/48.5
97/48.5
84/42.0
96/19.6
91/93.0
78/156
18/360
98/1960
19/9.5
4/2
PANS1F-Cu
PANS2F-Cu
PANS3F-Cu
PANS4F-Cu
PANS5F-Cu
PANEF-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
PANS2F-Cu
Mechanical strength
The breaking strength (BS) is an important
application indicator for the fiber catalysts. Higher
mechanical strength will make the fiber catalyst more
suitable for the application as fixed bed material in
industry. The testing results of breaking strength (BS)
and retention of breaking strength (RBS) of different
fibers are listed in Table 3. After grafting with the
Schiff base, the breaking strength of PANS2F
decreases to 9.1 cN with 83% RBS (Table 3, entry 2).
The processes of anchoring copper ion have less
impact on the mechanical strength of fiber catalysts,
so PANS2F-Cu almost keep its break strength with 79%
RBS (Table 3, entry 3). When the fiber catalyst was
C2H5OH 60
CH3CN
1,4-
Dioxane
AcOEt
60
60
1/0.5
0/0
25
a)
PANS2F-Cu
60
3.5
0/0
Reaction conditions: benzyl chloride (1 mmol),
phenylacetylene (1 mmol), NaN3 (1.2 mmol), L- sodium
ascorbate (10 mol%), catalyst (2 mol%, calculate base on
Cu ) and solvent (5 mL). b) Yield by HPLC. c) The structure
of S2-Cu was shown in supporting information. d) With 5
mol% catalyst. e) With 1 mol% catalyst. f) With 0.5 mol%
catalyst. g) With 0.05 mol% catalyst.
5
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10.1002/adsc.201701475
Advanced Synthesis & Catalysis
were used to catalyze the CuAAC reaction and the
results are listed in Table 4.When the reaction was
carried out without catalyst or in the presence of
PANF, only 2% yield was obtained (Table 4, entries
1 and 2). In the case of Cu(OAc)2 or S2-Cu as
catalysts, the yield were raised to 41% and 67%,
respectively (Table 4, entries 3 and 4). With PANS1-
3F-Cu as catalysts, yields of 32-66% were obtained
(Table4, entries 5-7). And the PANS2F-Cu shows the
same catalytic activity with S2-Cu (Table 4, entry 6).
That may be because the special flexible micro-
environment of the fiber catalyst can efficiently
aggregate the reactants to the catalytic active center
and accelerate the reaction. Especially, the
hydrophobic micro-environment constructed by the
Schiff base with two tertiary butyl groups will
promote the reaction more efficiently.[46] The
catalytic activity of PANS3F-Cu is lower than that of
PANS1F-Cu and PANS2F-Cu (Table 4, entries 5-7)
due to the electron donating effect of the -OCH3 in
PANS3F-Cu, which declines the reaction activity of
alkyne-copper intermediate with iminium ion
intermediate generated from aldehyde and secondary
amine.[47] Because of the low contents of Cu, there
has few valid catalytic active sites on PANS4F-Cu and
PANS5F-Cu, only 11% and 13% yields were obtained
(Table 4, entries 8 and 9). For PANEF-Cu, although a
medium yield 51% was obtained, the fiber changed
color from green to yellow after reaction, which
indicates the Cu has dissociated from the fiber (Table
4, entry 10). When the reaction time was prolonged
from 2 h to 3.5 h with PANS2F-Cu as catalyst, the
yields increased from 66% to 97% (Table 4, entries 6,
11 and 12). Reducing the reaction temperature to
50ºC will cause yield fall down to 84% (Table 4,
entry 15). However, there has no obvious yield
improvement with longer reaction time or higher
temperature (Table 4, entries 13 and 14). When
increasing the catalyst amount to 5 mol%, a yield of
96% was obtained. If the catalyst amount was
decreased to 1 mol%, 0.5 mol% and 0.05 mol%, the
yields were declined to 91%, 78% and 18 %
respectively (Table 4, entries 16-19). Nevertheless,
the reaction can also be finished with catalyst amount
of 0.05 mol% when the reaction time was prolonged
to 24 h (Table 4, entry 20). And the highest TON of
1960 was attained with 0.05 mol% catalyst amount.
Furthermore, the solvent effect on the CuAAC
reaction had also been explored. The yields obviously
decreased as lowering the solvent polarities (Table 4,
entries 21-25). With solvent polarities lower than
CH3CN, the reaction even failed to take place (Table
4, entries 24 and 25). All in all, the optimal
conditions with PANS2F-Cu as catalyst are 3.5 h at
60ºC in water.
Table 5. The substrate scope CuAAC reaction catalyzed
by PANS2F-Cu.a)
Time
(h)
Yield
(%)b)
Entry
X
R1
R2
1
2
3
4
5
6
7
8
9
Cl
Br
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
3.5
2
3.5
3.5
3.5
2
3.5
5
3
1a 95
1a 97
1b 94
1c 95
1d 95
1d 98
1e 96
1f 90
1f 92
Cl 4-MeC6H5
Cl 4-ClC6H5
Cl 4-CNC6H5
Br 4-CNC6H5
Cl 2-CNC6H5
Under the optimal conditions, we probed the scope of
the reaction with different halohydrocarbons and
Table 6. PANS2F-Cu catalyzed synthesis of bis-and tris-
triazoles.a)
Cl
Br
EtOOC
EtOOC
3-CHO-2-
OHC6H3
4-BrC6H5
10
Cl
C6H5
3.5
1g 89
11
12
13
14
15
Br
C6H5
C6H5
C6H5
C6H5
C6H5
2
2
2
3
5
1h 96
1i 97
1j 97
1k 91
1l 94
Br 4-NO2C6H5
Br 3-NO2C6H5
Br
Br
C6H5CO
n-C3H7
16
17
18
19
20
21
Br
Br
C6H5
5
4
5
5
4
5
1m 95
1n 93
1o 97
1p 90
1q 95
1r 93
4-BrC6H5
Br 4-CNC6H5
Br
Br
C6H5
4-BrC6H5
Br 4-CNC6H5
a) Reaction conditions: halohydrocarbon (1 mmol), alkynes
(2 mmol), NaN3 (2.5 mmol), L-sodium ascorbate (10 mol%
based on alkynes), catalyst (2 mol%, calculate base on Cu )
and solvent (5 mL). Isolate yield.
a) Reaction conditions: halohydrocarbon (1 mmol), alkynes
(1 mmol), NaN3 (1.2 mmol), L-sodium ascorbate (10
mol%), catalyst (2 mol%, calculate base on Cu ) and
solvent (5 mL). b) Isolate yield.
6
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10.1002/adsc.201701475
Advanced Synthesis & Catalysis
alkynes. As shown in Table 5, the activities of
bromo-hydrocarbons are higher than that of chloro-
ones (Table 5, entries 1-15). Excellent yields are
obtained whether the substituents are electron-
donating or electron-withdrawing groups on phenyl
groups which coincied with literature results.[25] In
addition, the scope of different alkynes can also
obtain excellent yields of 93-97% (Table 5, entries
16-21).
Encouraged by the excellent results above, the
activity of this catalytic system was further tested by
catalyzing the synthesis of several bis- and tris-
triazoles. In Table 6, 1,2-bisbromomethylbenzens and
1,4-bisbromomethylbenzene can both react smoothly
with different alkynes catalyzed by fiber PANS2F-Cu
to achieve 82-92% yields (Table 6, 6a-f). The activity
of 1,2-bisbromomethylbenzene is lower than that of
1,4-bisbromomethylbenzene which may be caused by
the yields improved from 53% to 95% gradually
(Table 7, entries 9-12). The yield no longer increased
when reaction time was prolonged to 7 h (Table 7,
entry 13).
Universality of the fiber catalyst PANS2F-Cu in three-
component coupling reaction was determined by
different combinations of aldehydes, amines and
alkynes and the results are shown in Table 8.
Comparing different amines, pyrrolidine has higher
yield than diethylamine and dibutylamine (Table 8,
entries 1-3) since the iminium ion produced from
alicyclic amine is more stable than that of dialkyl
amine.[48] Because of the low activities of aromatic
aldehydes caused by conjugate effect, the yields of
aromatic aldehydes are lower than that of aliphatic
aldehydes (Table 8, entries 4-13). Besides, aromatic
aldehydes with electron-withdrawing groups have
higher yields than that of aromatic aldehydes with
the larger steric hindrance of the former. Furthermore, electron-donating groups (Table 8, entries 7-13).
the tris-triazoles were synthesized successfully with
yields of 80-82% in 5 h at 80ºC (Table 6, 8a-b).
However, only 32% yield was obtained for the 1,4-
dibromobutane due to the low activity of the
bromoalkane (Table 6, 9a).
To further widen the applicability of the present
methodology, the catalytic activity of this catalytic
system was also examined by the A3 coupling
reaction which is an important reaction in organic
synthesis.[8] In the first place, the A3 reaction was
carried out in different solvents. From Table 7 we can
see that, high polarity solvent is beneficial for the A3
reaction especially in CH3CN (with a yield of 53% in
3 h). When the temperature was raised to 80ºC, the
yield increased obviously to 68% in 3 h (Table 7,
entry 9). Prolonging the reaction time from 3 h to 6 h,
Possible mechanisms of the CuAAC reaction and A3
coupling reaction catalyzed by PANS2F-Cu were
depicted in Scheme 2. Both of the two reactions have
some parallel procedures. Initially, the Cu(II) on the
fiber catalyst was reduced by sodium ascorbate to
PANS2F-Cu(I) which can efficiently activate the C-H
bond of alkyne to form the intermediate A. For A3
reaction, the intermediate A was then reacted with the
iminium ion intermediate B generated from aldehyde
and secondary amine to give the propargylamines. In
terms of CuAAC reaction, the corresponding 1,2,3-
triazoles were produced after the reaction of
intermediate A with azides C generated from
halohydrocarbons and NaN3. After the above
processes, the fiber catalyst was regenerated for
further reaction.
Table 7. Optimization of the A3 coupling reaction
Table 8. The substrate scope of PANS2F-Cu catalyzed A3
conditions.a)
coupling reaction conditions.a)
Entry Solvent
T (oC) Time (h) Yield (%)b)
Entry R3
Amine
R4
Yield (%)b)
1
H2O
60
60
60
60
60
60
60
3
3
3
3
3
3
3
3
3
4
5
6
7
27
26
37
53
16
2
1
H
Pyrrolidine
Diethylamine
Dibutylamine
Pyrrolidine
Pyrrolidine
Pyrrolidine
Pyrrolidine
Pyrrolidine
Pyrrolidine
H
H
H
H
5a 96
5b 92
5c 92
5d 94
2
3
4
5
CH3OH
C2H5OH
CH3CN
THF
2
H
3
H
4
5
6
7
Isopropyl
Isopropyl
Isobutyl
Ph
CH3 5e 93
H
H
6
7
EtOAc
Toluene
5f 95
5g 83
13
3
8
Cyclohexane 60
8
Ph
CH3 5h 84
9
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
80
80
80
80
80
68
85
92
95
95
9
4-CH3C6H4
H
H
H
H
H
5i 80
5j 78
5k 75
5l 85
5m 88
10
11
12
13
10
11
12
13
4-CH3OC6H4 Pyrrolidine
4-PhC6H4
4-BrC6H4
4-ClC6H4
Pyrrolidine
Pyrrolidine
Pyrrolidine
a)
Reaction conditions: isobutyraldehyde (1 mmol),
a) Reaction conditions: aldehyde (1 mmol), amine (1 mmol),
alkyne (1.2 mmol), L-sodium ascorbate (10 mol%),
catalyst (2 mol%, calculate base on Cu ) and CH3CN (5
mL) at 80oC for 6 h. b) Isolate yield.
pyrrolidine (1 mmol), phenylacetylene (1.2 mmol), L-
sodium ascorbate (10 mol%), catalyst (2 mol%, calculate
base on Cu ) and solvent (5 mL). b) Yield by HPLC.
7
This article is protected by copyright. All rights reserved.

10.1002/adsc.201701475
Advanced Synthesis & Catalysis
Scheme 2. Possible mechanisms of CuAAC reaction and
A3 coupling reaction.
Figure 8. Recyclability of PANS2F-Cu in the CuAAC
reaction.
Scaled-up experiment of the CuAAC and A3
reactions catalyzed by PANS2F-Cu
Recyclability of the PANS2F-Cu was investigated
using CuAAC reaction with benzyl chloride,
phenylacetylene and NaN3 as template and A3
coupling reaction with isobutyraldehyde, pyrrolidine
and phenylacetylene as template, and the results are
listed in Figure 8. After completion of each reaction,
the fiber catalyst was separated out with tweezers and
washed with ethyl acetate to remove the adsorbed
Under the optimal reaction conditions, the CuAAC
reaction and A3 reaction catalyzed by PANS2F-Cu
were amplified to 50 times. The two one-pot
multicomponent reactions were completed without
any extension of the reaction time and high product
yields of 96% (11.3 g) and 95% (10.8 g), respectively.
That shows a potential application in industry of the
PANS2F-Cu.
Table 9. The compares of different heterogeneous catalytic
Leaching experiment and recyclability test
systems.a)
The CuAAC reaction of benzyl chloride, phenyl
acetylene and sodium azide was chosen as the model
reaction to verify the heterogeneity of the PANS2F-Cu.
The fiber catalyst was filtrated out at 2 h and then the
filtrate continued to stir for next 3 h. As can be seen
from Figure 7, the extent of yield was found to
remain almost unchanged, indicating no significant
leaching of copper ions. Moreover, ICP test confirm
that there are no copper ions in the filtrate. These
results indicate that the reaction follows
heterogeneous pathway.
One of the highlights of the heterogeneous catalyst is
the recyclability which is an important factor from
the view of economical and sustainable chemistry.
Entry
Catalyst
Condition
Yield (%)/TOF (h-1)
Runb)
H2O, 100oC, 0.6
1[49]
2[25]
Cu/C
91/151.7
98/65.3
10
5
h
CuNPs/C
H2O, 70oC, 3 h
H2O,
120oC, Power
MW,
Nano-
3[50]
94/228.3
3
FGT-Cu
100Watt,
min
10
HMS-
DP-Cu
P[imCu/I
L][Cl]
PANS2F-
Cu
4[51]
5[52]
6c)
EtOH, 80oC, 8 h 99/2.5
6
a
H2O/t-BuOH,
99/495
12
10
55oC, 2 h
H2O, 60oC, 2 h
97/24.3
Cu-PS-
ala
H2O, Reflux, 6
h
THF, 60oC, 20 h 95/15.8
7[53]
8[19]
9[54]
89/23.7
10
5
Cu@NPs
Toluene, 100oC,
Cu/G
97/8.1
4 h
4
polymer-
10[55]
11[56]
supported H2O, 80oC, 24 h 98/81.7
7
gold NPs
SiO2-Py-
CuI
MeCN, 90oC, 6
93/3.1
83/6.9
5
h
PANS2F-
Cu
MeCN, 80oC, 6
12c)
10
h
a)
Take the CuAAC reaction of benzyl bromide and
phenylacetylene (entries 1-6) and the A3 coupling reaction
of benzaldehyde, pyrrolidine and phenylacetylene (entries
b)
7-12) as template reactions.
work.
Run: Reused time. c) This
Figure 7. Leaching experiment.
8
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10.1002/adsc.201701475
Advanced Synthesis & Catalysis
phase was collected and the crude product was purified by
product. Then the recycled catalyst was used directly
for the next cycle. After used ten times, the reaction
can still reach a yield of 93% and 86%, respectively
(Figure 8), which indicates that the PANS2F-Cu has
an excellent recoverability.
column chromatography (petroleum ether/ethyl acetate).
Acknowledgements
This was financially supported by the National Natural Science
Foundation of China (Nos. 21777111 and 21572156)
Comparison of the FANS2F-Cu with different
heterogeneous catalytic systems
Different heterogeneous catalystic systems are
compared with this work and the results are listed in
Table 9. The PANS2F-Cu has overwhelming
advantages such as low-cost commercial raw material,
easy preparation processes, simpl separation of the
catalyst with reaction system, high catalytic activity,
performing well in scaled-up production and
excellent reusability and so on. The PANS2F-Cu has
much potential for further applications
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Taking advantage of low-cost Cu(OAc)2 as copper
source, different Cu(II)-Schiff bases-functionalized
polyacrylonitrile fiber catalysts have been prepared
and applied to catalyze the CuAAC reaction and A3
coupling reaction. The structures of fiber catalysts
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Experimental Section
General procedure for the CuAAC reaction
A mixture of halohydrocarbon (1 mmol), alkyne (1 mmol),
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9
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10.1002/adsc.201701475
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Advanced Synthesis & Catalysis
FULL PAPER
Copper(II)-Schiff Base Complex-Functionalized
Polyacrylonitrile Fiber as a Green Efficient
Heterogeneous Catalyst for One-Pot
Multicomponent Syntheses of 1,2,3-Triazoles and
Propargylamines
Adv. Synth. Catal. Year, Volume, Page – Page
Pengyu Li,a Yuanyuan Liu,a Lu Wang,a Jian Xiao,a
Minli Taoa*
11
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