Cu(II)-anchored functionalized mesoporous SBA-15: An efficient and recyclable catalyst for the one-pot Click reaction in water

Article abstract of DOI:10.1016/j.molcata.2014.01.027

A new pyridine-imine functionalized mesoporus silica (SBA-15) has been synthesized through the Schiff-base condensation of 3-aminopropyl functionalized SBA-15 with 2-pyridinecarboxaldehyde followed by the grafting of Cu(II) onto it resulting a new Cu@PyIm-SBA-15 material. 2D-hexagonally ordered mesophases of the material are analyzed by small-angle powder X-ray diffractions (PXRD) and transmission electron microscopic (TEM) image analyses. The Cu(II)-anchored mesoporous material, Cu@PyIm-SBA-15 showed excellent catalytic activity towards the one pot click reaction between azides formed in situ from the corresponding amines and acetylenes in water at 0 C to room temperature resulting a wide variety of 1,4-disubstituted 1,2,3-triazoles. The catalyst has been recycled for five cycles without any appreciable loss of catalytic activity and also without any appreciable Cu-leaching, suggesting a future potential of this novel mesoporous catalyst for the synthesis of 1,4-disubstituted 1,2,3-triazoles.

Full text of DOI:10.1016/j.molcata.2014.01.027

Journal of Molecular Catalysis A: Chemical 386 (2014) 78–85
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Cu(II)-anchored functionalized mesoporous SBA-15: An efficient and
recyclable catalyst for the one-pot Click reaction in water
Susmita Roya,b,1, Tanmay Chatterjeec,1, Malay Pramanikd, Anupam Singha Roya,
Asim Bhaumikd,∗, Sk. Manirul Islama,b,∗
a Department of Chemistry, University of Kalyani, Nadia, 741235, West Bengal, India
b Department of Chemistry, Aliah University, Sector-V, Salt Lake, Kolkata 700099, West Bengal, India
c Department of Organic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700032, India
d Department of Material Science, Indian Association for the Cultivation of Science, Kolkata 700032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new pyridine-imine functionalized mesoporus silica (SBA-15) has been synthesized through the
Schiff-base condensation of 3-aminopropyl functionalized SBA-15 with 2-pyridinecarboxaldehyde fol-
lowed by the grafting of Cu(II) onto it resulting a new Cu@PyIm-SBA-15 material. 2D-hexagonally
ordered mesophases of the material are analyzed by small-angle powder X-ray diffractions (PXRD)
and transmission electron microscopic (TEM) image analyses. The Cu(II)-anchored mesoporous mate-
rial, Cu@PyIm-SBA-15 showed excellent catalytic activity towards the one pot click reaction between
azides formed in situ from the corresponding amines and acetylenes in water at 0 ◦C to room tempera-
ture resulting a wide variety of 1,4-disubstituted 1,2,3-triazoles. The catalyst has been recycled for five
cycles without any appreciable loss of catalytic activity and also without any appreciable Cu-leaching,
suggesting a future potential of this novel mesoporous catalyst for the synthesis of 1,4-disubstituted
1,2,3-triazoles.
Received 1 November 2013
Received in revised form 29 January 2014
Accepted 31 January 2014
Available online 10 February 2014
Keywords:
Mesoporous material
SBA-15
Cu(II) anchored
One-pot
Click reaction.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
received widespread attention since its discovery by Sharpless
and his co-workers in 2001 [28,29]. 1,2,3-Triazoles are found to
Organically functionalized mesoporous materials have received
considerable attention since past decades because these materi-
als have excellent potentiality as environmentally benign catalysts
[1–12], hosts of nanomaterials [13,14], sensors [15–17], optoelec-
tronic devices [18–22], drug delivery [23], etc. These organically
functionalized materials have gained particular importance as sup-
ports for various metal salts in designing novel heterogeneous
catalysts due to their exceptionally high surface area, wide and
controllable pore opening in nanoscale dimension, easy prod-
uct separation and excellent recycling efficiency [1–11]. Among
them mesoporous organosilicas and related nanomaterials have
been extensively used as heterogeneous catalysts through graft-
ing or immobilizing metal complexes within the nano channels
[24–27].
possess wide applications in several research fields like synthetic
organic chemistry [30–34], biological chemistry [35,36], medic-
inal chemistry [37–39] and material chemistry [40–42]. Hence
several methods have been developed for the synthesis of 1,2,3-
triazoles using various catalytic systems like copper nanoparticles
[43], copper nanoclustures [44], Cu(II)/Cu(0) comproportionation
[45], mixed Cu/Cu-oxide nanoparticles [46–48], in-situ reduction
of Cu(II) salts to Cu(I) salts [49,29,50–52] etc. But the major disad-
vantages associated with these homogeneous copper catalysts are
the difficulties to recover and reuse for successive reaction cycles
and the possibility of metal contamination with the end product.
To overcome these serious issues, various solid-supports like zeo-
lites [53], polymers [54,55], carbon [44], silica [56] etc. have been
employed to synthesize the corresponding heterogeneous copper
catalysts by immobilizing the active metal ions onto the solid sup-
ports.
On the other hand “Click” reaction between azides and alkynes
leading to the formation of 1,4-disubstituted 1,2,3-triazoles has
Herein, we report the synthesis of a new Cu(II) anchored
functionalized SBA-15 type mesoporous silica and utilized it
to catalyze the “Click” reaction. The mesoporous silica SBA-15
was first amine functionalized using 3-aminopropyltriethoxysilane
(3-APTES), which was then subjected to undergo Schiff base
condensation reaction with 2-pyridinecarboxaldehyde to form a
new imine functionalized mesoporous SBA-15. Grafting of copper
∗
Corresponding authors at: Corresponding author. Tel.: +91 33 2582 8750;
fax: +91 33 2582 8282.
E-mail addresses: msab@iacs.res.in (A. Bhaumik), manir65@rediffmail.com
(Sk.M. Islam).
1
These authors contributed equally to this manuscript.
1381-1169/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2014.01.027

S. Roy et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 78–85
79
acetate on the surface of this imine functionalized mesoporous
SBA-15 resulted in Cu@PyIm-SBA-15 material.
2.2.4. Synthesis of Cu@ImPy-SBA-15 (4)
One gram of SBA-15 supported imine material (3) was sus-
pended in absolute ethanolic (20 mL) solution of copper acetate
(0.2 g) and was kept under refluxing condition for 12 h. The reac-
tion mixture was cooled at room temperature. Then the resulting
brown material, Cu@ImPy-SBA-15 was filtered out, washed thor-
oughly with ethanol and dried under vacuum.
On the other hand one pot procedure for the synthesis of 1,2,3-
triazoles through the reaction between in-situ generated azides
from its corresponding amines and acetylenes is highly desirable
and economical as this avoids the isolation step of azides. Several
one pot procedures for the synthesis of 1,2,3-triazoles have been
developed using various copper catalysts [57–64]. Most of them
used alkyl halide as the starting material, but the main challenge
is to start with aromatic precursors like anilines, aryl halides or
aryl boronic acids. Few such methodologies have been developed
for the synthesis of 1,2,3-triazoles but, most of them uses costly
reagents or organic solvents/ligands/high temperature, etc., which
are not acceptable in the context of green chemistry. Here we report
a green one pot procedure for the synthesis of 1,2,3-triazoles by the
so-called click reaction between aryl azides formed in situ from ani-
lines and acetylenes over Cu@PyIm-SBA-15 catalyst at 0 ◦C to room
temperature (Scheme 1) to form a wide range of 1,4-disubstituted
1,2,3-triazoles.
2.3. Elemental analysis of the catalyst
The copper content in the Cu@ImPy-SBA-15 catalyst was
determined by using a Varian, USA, AA240 atomic absorption
spectrophotometer (AAS). The amount of metal was determined
by stripping the bound metal from the support followed by the
analysis of the metal ion by using an atomic absorption spectropho-
tometer. Copper content in the catalyst was 1.19 wt%. The copper
content in Cu@ImPy-SBA-15 after five reaction cycles has also been
measured.
2.4. Characterizations of Cu@ImPy-SBA-15
2. Experimental
Powder X-ray diffraction patterns of the pure SBA-15 and
functionalized materials were recorded on a Bruker D-8 Advance
diffractometer operated at 40 kV voltage and 40 mA current using
Cu K␣ (␭ = 0.15406 nm) radiation. TEM analysis was carried out
by using a JEOL 2010 TEM operated at 200 kV. The EPR (electron
paramagnetic resonance) spectra of the fresh and used Cu@PyIm-
SBA-15 catalyst were recorded for the solid sample at room
temperature using a JES-FA200 ESR spectrometer (JEOL).
2.1. General
Pluronic
P123
(EO20PO70EO20,
EO = ethylene
oxide,
PO = propyleneoxide, Mav = 5800), tetraethoxyorthosilicate (TEOS),
3-aminopropyl triethoxysilane (3-APTES), copper acetate and all
acetylene derivatives were purchased from Sigma-Aldrich. All
the reagents were analytical grade and used as such without
further purification. Solvents were purified and dried according to
standard procedures. Thin layer chromatography was carried out
by using commercial (MERCK) plates with silica gel 60 F254
2.5. Experimental procedure for the synthesis of 1,4-disubstituted
1,2,3-triazole
2.2. Synthesis of catalyst
Aniline (0.5 g, 5.4 mmol) was placed into a 25 mL round bot-
tomed flask which was then put in an ice water bath (0–5 ◦C).
Subsequently, a mixture of conc. HCl–H2O (1.3 mL: 1.3 mL) was
added to it and the mixture was stirred for 1 min. NaNO2 (0.392 g,
5.7 mmol), dissolved in 1 mL of water, was first cooled at 0–5 ◦C
and then added to the reaction mixture drop wise. After 2 min stir-
ring, sodium azide (0.416 g, 6.4 mmol) was added and stirred for
5 min. Then phenylacetylene (0.46 g, 4.6 mmol) and Cu@PyIm-SBA-
15 (0.025 g, 0.1 mol%) were added to the reaction mixture followed
by stirring at room temperature for 6 h (TLC). When the reaction
was over, the water layer was decanted off and the reaction mixture
was dissolved in ethanol. Then the catalyst was filtered through
a sintered glass-bed (G-4), and washed with water (3 × 4 mL) fol-
lowed by ethanol (3 × 3 mL) and acetone (2 × 4 mL). The product
was purified by a simple crystallization from ethanol to furnish the
corresponding triazole, 1,4-diphenyl-1H-[1,2,3]triazole, as a white
solid (Yield = 98%), TOF = 163 h−1, mp 183–185 ◦C; IR (KBr) 3120,
The reaction pathways for the synthesis of mesoporous
Cu@PyIm-SBA-15 is outlined in Scheme 2.
2.2.1. Synthesis of mesoporous SBA-15 (1)
Mesoporous SBA-15 was synthesized by following the reported
procedure [18]. P123 (4 g), 2.0 (M) aq. HCl (120 mL) and distilled
water (15 mL) were stirred at room temperature for 4 h. Then TEOS
(8.5 g) was added drop wise to the solution of P123 at 40 ◦C for 24 h.
Then, a synthesized gel was thus formed, which was then loaded
in a 500 mL scaled polypropylene bottle using Teflon tape and was
kept at 100 ◦C for 24 h under static condition. Solid white prod-
uct was formed and separated by filtration, washed with distilled
water, dried in air. Then the product was calcined at 500 ◦C for 5 h.
2.2.2. Synthesis of 3-amino propyl functionalized SBA-15 (2)
The calcined SBA-15 (2 g) was refluxed with 3-
aminopropyltriethoxysilane (3-APTES) (3.6 g) in toluene for
18 h. The resulting white solid was filtered, washed thoroughly
with ethanol and finally dried in air.
1598, 1502, 1481, 1451, 1228, 1056, 758 cm−1 1H NMR (500 MHz,
;
CDCl3) ␦ 7.37 (t, J = 7.5 Hz, 1H), 7.44–7.47 (m, 3H), 7.54 (t, J = 7.5 Hz,
2H), 7.79 (d, J = 8 Hz, 2H), 7.92 (d, J = 8 Hz, 2H), 8.2 (s, 1H).
3. Results and discussion
2.2.3. Synthesis of SBA-15 supported imine ligand (3)
2-Pyridinecarboxaldehyde (3 mL) was added to a mixture of 3-
amino propyl functionalized SBA-15 (1.8 g) in super dry ethanol
(90 mL) in a 250 mL round bottomed flask. The reaction mixture
was stirred at 60 ◦C for 24 h. Then it was filtered. The resulting light
yellow solid was washed with toluene and then further washed
with ethanol to remove any unreacted aldehyde. It was dried in
a hot-air oven at 90 ◦C for overnight to furnish the corresponding
SBA-15 supported imine material (3).
3.1. Characterizations of Cu@ImPy-SBA-15
The heterogeneous catalyst, Cu@PyIm-SBA-15 was synthesized
via surface functionalization of mesoporus SBA-15 with 3-
aminopropyltriehoxysilane (3-APTES) followed by Schiff-base con-
densation of surface–NH2 group with 2-pyridinecarboxaldehyde.
Then Cu(OAC)2 was subjected to react with Schiff-base anchored
SBA-15 catalyst to yield Cu@PyIm-SBA-15 as shown in Scheme 2.

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S. Roy et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 78–85
1. Conc. HCl:H2O (1:1)
NaNO
2. NaN3
N
R'
2 (0 o-5 oC)
N
R
N
R-N3
R-NH2
Cu@PyIm-SBA-15
(0.1 mol%)
6-8 h, rt
R'
Yield = 90-98%
R = aryl and benzyl
R' = aryl, benzyl and alkyl
Scheme 1. Cu@PyIm-SBA-15 catalyzed one-pot Click reaction.
Scheme 2. Synthesis of Cu@PyIm-SBA-15 catalyst.
3.1.1. Nanostructure of Cu@PyIm-SBA-15
ca. 9.80 nm. Considerable increase in the pore wall thickness in the
Cu@PyIm-SBA-15 material compared to pure SBA-15 is observed.
This could be attributed to the homogeneous grafting of organic
moiety and Cu(II) at the surface of the mesopore.
The small angle X-ray diffraction pattern of Cu@PyIm-SBA-15
material has been shown in Fig. 1. Very strong intensity peak
centred at 2␪ = 0.92 is due to the diffraction of 1 0 0 plane of
mesostructure is very clearly observed. This is followed by other
two weak intensity peaks, corresponding to the 2 0 0 and 2 1 0
planes of 2D-hexagonal planes of the ordered mesophase of the
SBA-15 type material [65,66]. The intensity of the latter diffraction
planes decreased from pure mesoporous silica SBA-15 material due
to the disturbance of ordered mesostructure after grafting of the
organic scaffold and copper. The d spacing for the mesophase is
3.1.2. TEM studies
The TEM image of Cu@PyIm-SBA-15 is shown in Fig. 2. As seen
from the Image 2D array of pore channels are quite clear together
hexagonal arrangement of pores (white spots) of dimension ca.
7.0 nm, which are uniformly spread throughout the specimen. Fur-
ther, no agglomeration of metallic Cu is observed in the entire grid,
4000
3000
2000
1000
0
1
2
3
4
5
2θ
in degrees
Fig. 1. Small angle X-ray diffraction pattern of Cu@PyIm-SBA-15.
Fig. 2. TEM image of Cu@PyIm-SBA-15.

S. Roy et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 78–85
81
Fig. 4. The X-band EPR spectrum of Cu+2 in (a) fresh and (b) used catalyst.
(Cu@PyIm-SBA-15) for the one-pot Click reaction. We first chose
water as the reaction medium as it is environmentally benign for
the one pot click reaction between phenyl azides formed in situ
from anilines and phenyl acetylene at 50 0C using high Cu loaded
sample (5 mol% Cu). To our delight the reaction was successful
leading to the formation of the 1,4-diphenyl 1,2,3-triazole in 98%
yield. To optimize the reaction conditions in water a series of
experiments varying the mol% of Cu in the catalyst, temperature
and time for the representative reaction were carried out. The
results are summarized in Table 1. Progress of the reaction for
the preparation of 1,4-diphenyl 1,2,3-triazole with time at differ-
ent temperatures has been given in supporting information, Figure
S3.
Fig. 3. A: N2 adsorption/desorption isotherms of Cu@PyIm-SBA-15 (a), and used
Cu@PyIm-SBA-15 (b). Adsorption points are marked with filled triangles or cir-
cles whereas those for desorptions are marked by empty triangles or circles. B:
Respective pore size distributions employing NLDFT model.
suggesting uniform anchoring of Cu(II) species at the surface of the
pyridine-imine functionalized SBA-15 material.
3.1.3. Surface area and porosity
N2 adsorption/desorption isotherms of the Cu@PyIm-SBA-15
before and after the catalytic reactions are shown in Fig. 3. These
sorption isotherms are typical type IV. A large hysteresis loop in
the 0.5 to 0.8 P/Po range is observed for the fresh sample. The BET
surface areas of the fresh and reused Cu@PyIm-SBA-15 samples
were 21.0 m2 g−1 and 13.5 m2 g−1, respectively. Their respective
pore size distributions using non-local density functional theory
(NLDFT) method shown in Fig. 3B, which suggests that mesopores
with peak pore dimensions of ca. 4.5 nm and 2.5 nm, respectively.
Decrease in the BET surface area and peak pore size is observed for
the reused catalyst, however mesostructure has been preserved.
The best result was obtained using 0.1 mol% of Cu in the cata-
lyst Cu@PyIm-SBA-15 at room temperature for 6 h for the second
step (Table 1, entry 8). No product was obtained in absence of
Table 1
Optimization of the reaction conditions for the synthesis of 1,4-disubstituted 1,2,3-
triazolesa.
Entry cat.
(Cu mol%)
Temperature ( ◦C)b
Time (h)
Yieldc (%)
3.1.4. EPR data
1
2
3
4
5
6
7
8
5
2
1
0.1
0.05
0.1
0.1
0.1
0.1
–
50
50
50
50
50
40
rt
rt
rt
–
40
8
8
8
8
8
8
8
6
5
6
6
98
98
98
98
92
98
98
98
85
–
The X-band EPR spectra of the fresh and used Cu@PyIm-SBA-15
catalyst are shown in Fig. 4. The spectrum shows four well-defined
hyperfine lines which arises due to the coupling of the unpaired
electron with the nuclear spin of copper(II). Moreover, it was also
clear that the EPR spectrum of the used catalyst was very similar to
that of the fresh catalyst which indicates that Cu remains in the +2
oxidation state throughout the reaction.
9
10
11
0.1
98
3.2. Catalytic activity
a
Reaction conditions: Aniline (5.4 mmol), conc. HCl:H2O = 1:1, NaNO2
5.7 mmol, NaN3 = 6.4 mmol, alkyne = 4.6 mmol, Cu@PyIm-SBA-15 = 0.1 mol% of Cu
=
b
Detailed catalytic investigations were carried out using
this Cu(II)-anchored functionalized mesoporous SBA-15 catalyst
Temperatures refer to the second step
Yields refer to those of isolated pure products
c

82
S. Roy et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 78–85
catalyst, Cu@PyIm-SBA-15. At first diazotization of aniline was car-
ried out using conc. HCl and NaNO2 in water medium at 0–5 ◦C,
then sodium azide (NaN3) was added to form the correspond-
ing phenyl azide. After 5 min of stirring, phenyl acetylene and
Cu@PyIm-SBA-15 catalyst were added and the reaction mixture
was stirred at room temperature for additional 6 h (progress of
the reaction was monitored through TLC). After the completion
of reaction, water was decanted and the solid product was crys-
tallized from environmentally benign ethanol to provide the pure
product (NMR). Thus the use of huge amount of hazardous organic
solvents in the work-up and column chromatography stages was
avoided.
A variety of substituted azides formed in situ from the cor-
responding amines were reacted with a variety of acetylenes to
produce the corresponding 1,4-disubstituted 1,2,3-triazoles. The
results are summarized in Table 2. A wide range of diversely substi-
tuted azides formed in situ from their corresponding amines were
subjected to react with phenyl acetylenes (Table 2, entries 1–5).
Both electron withdrawing (4-NO2) and donating (4-OMe) group
substituted anilines reacted to equal extent with phenyl acetylene
under the said reaction conditions (Table 2, entries 2 and 4). Steri-
cally hindered (2-I) aniline reacted smoothly with phenyl acetylene
(Table 2, entry 3). Benzyl amine also reacted with phenyl acetylene
without any difficulty to produce the corresponding 1-benzyl-4-
phenyl 1,2,3-triazole (Table 2, entry 5).
100
80
60
40
20
0
Run 1
Run 2
Run 3
Run 4
Run 5
0
1
2
3
4
5
6
7
8
Time (h)
Fig. 5. Kinetic plot of recycling test of catalyst (Cu@PyIm-SBA-15) in the Click reac-
tion of phenyl azide formed from aniline with phenyl acetylene.
3.2.1.1. 4-(Biphenyl-4-yl)-1-(3-chlorophenyl)-1H-1,2,3-triazole
(Table 2, entry 8)
White solid (92%), mp 210–212 ◦C, IR (KBr) 3109, 1593, 1479,
1450, 1394, 1226, 1037, 885, 840, 815, 783, 761, 678 cm−1 1H
;
A variety of substituted acetylenes were also employed to
react with different substituted azides formed in situ from the
corresponding amines (Table 2, entries 6–14). Both electron with-
drawing (CN, F) (Table 2, entries 6 and 7) and electron donating
(OMe) (Table 2, entry 10) group substituted phenyl acetylene
reacted smoothly with variety of azides to form the corresponding
triazoles. Biphenyl acetylene (Table 2, entries 8 and 9) and napthyl
acetylene (Table 2, entry 10) also participated in the click reac-
tion. Interestingly, when 2-nitro-phenylazide formed in situ from
2-nitro-aniline was subjected to react with excess (1.5 equiv) of
1,4-diethynyl benzene, only the mono triazole product was formed
keeping the other acetylene moiety intact (Table 2, entry 11). This
implies that the reaction is chemoselective. Heteroaryl substituted
acetylene, 2-ethynyl pyridine also reacted smoothly with benzyl
azide formed in situ from benzyl amine to form the corresponding
triazole containing pyridine moiety (Table 2, entry 12). Significantly
aliphatic acetylene, propergyl alcohol also reacted with 3-chloro
aniline and 4-nitro aniline without any difficulty (Table 2, entries
13 and 14). Both the electron donating and electron withdraw-
ing substituents on both the amine and acetylene moieties do not
show any significant influence on the outcome of the reaction and
they all were competable with the reaction condition. All ortho,
meta and para substituted anilines reacted almost uniformly with
acetylenes. Generally, the reactions are quite clean and high yield-
ing. Most significantly no column chromatography was required for
the purification of products as they can be easily crystallized from
ethanol. Thus the use of hazardous organic solvents in the entire
process could be avoided. Atomic absorption spectroscopy (AAS)
showed that the final product does not contain even a trace amount
of copper, suggesting strongly bound Cu(II) sites at the surface of
Cu@PyIm-SBA-15.
NMR (300 MHz, CDCl3) ␦ 7.30 (d, J = 5 Hz, 1H), 7.37 (t, J = 5 Hz, 1H),
7.44–7.50 (m, 4H), 7.51–7.53 (m, 2H), 7.58–7.61 (m, 1H), 7.64–7.73
(m, 2H), 7.90 (s, 1H), 8.05 (d, J = 5 Hz, 1H), 8.22 (s, 1H); 13C NMR
(75 MHz, CDCl3) ␦ 120.9, 125.6, 126.4 (2C), 127.1 (2C), 127.7, 127.8
(2C), 128.1, 129.0 (2C), 129.1, 130.5, 131.0, 135.8, 138.0, 140.6. Anal.
Calcd for C20H14ClN3: C, 72.40; H, 4.25; N, 12.66%. Found: C, 72.46;
H, 4.22; N, 12.67%.
3.2.1.2. 4-(Biphenyl-4-yl)-1-(2-nitrophenyl)-1H-1,2,3-triazole
(Table 2, entry 9)
Yellow solid (93%), mp 203–205 ◦C, IR (KBr) 3134, 1604, 1591,
1537, 1479, 1423, 1359,1311, 1240, 1029, 850, 802, 767, 746,
727 cm−1 1H NMR (400 MHz, CDCl3) ␦ 7.35–7.38 (m, 1H), 7.47 (t,
;
J = 8 Hz, 2H), 7.69–7.75 (m, 4H), 7.80–7.85 (m, 1H), 7.98 (d, J = 7 Hz,
2H), 8.10 (s, 1H), 8.12 (s, 1H); 13C NMR(100 MHz, CDCl3) 121.1,
125.7, 126.5 (2C), 127.2 (2C), 127.7, 127.8 (2C), 128.1, 128.8, 129.0
(2C), 130.4, 130.9, 133.9, 140.7, 141.6, 144.6, 148.3. Anal. Calcd for
C20H14N4O2: C, 70.17; H, 4.12; N, 16.37%. Found: C, 70.12; H, 4.26;
N, 16.35%.
3.3. Recycling of catalyst
For a heterogeneous catalyst, it is important to examine its
ease of separation, recoverability and reusability. The reusability
of the mesoporous Cu@PyIm-SBA-15 catalyst was investigated in
“Click” reaction between phenyl azide formed in situ from aniline
and phenyl acetylene (Table 2, entry 1). After the first cycle of the
reaction catalyst was recovered by simple filtration through a sin-
tered glass-bed (G-4) and washed with ethanol followed by acetone
which was then dried in an oven at 100 ◦C. The performance of the
recycled catalyst for the representative reaction was tested with
time (h) up to five successive runs and the corresponding kinetic
plot is shown in Fig. 5. This diagram clearly suggests that the cat-
alytic efficacy of the recovered catalyst remained almost the same
for several reaction cycles.
The IR, 1H NMR spectroscopic data of the triazole products are in
good agreement with those of the authentic compounds reported
earlier. Reaction in gram scale also provided the uniform result.
This procedure was followed for all the reactions in Table 2. Most
of these products are known compounds and are identified by
a comparison of their spectroscopic data with those previously
reported (see references in Table 2). The products which are not
We have also compared the recyclability of the Cu@PyIm-
SBA-15 catalyst with Cu@SBA-15, which bear no surface grafted
Schiff-base imine ligand for the representative synthesis of 1,4-
diphenyl-1H-[1,2,3]triazole. It was found that over Cu@SBA-15 the
catalytic activity start reducing from the second cycle itself and
reported earlier were characterized through FT IR, 1H NMR and 13
C
NMR spectroscopic analysis (Table 2, entries 8 and 9, supporting
information).

S. Roy et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 78–85
83
Table 2
One pot click reaction between azides formed in situ from corresponding amines and acetylenes catalyzed by Cu@PyIm-SBA-15 in [68,69] water.
1. Conc. HCl:H2O (1:1)
N
(0 o-5 oC)
N
R'
NaNO2
2. NaN3
R
N
R-N3
R-NH2
Cu@PyIm-SBA-15
(0.1 Cu mol%)
6-8 h, rt
R'
Yield = 90-98%
Entry
1
R
R'
Product
Yielda (%)
Ref
52
Time
N
N
N
C6H5-
C6H5-
N
6
7
7
98
N
N
N
O2N
N
N
C6H5-
C6H5-
4-NO2-C6H4-
2-I-C6H4-
2
3
98
62
52
97
I
N
MeO
N
N
N
C6H5-
C6H5-
4-OMe-C6H4-
C6H5CH2-
4
5
95
98
8
6
57
57
N
N
N
N
MeO
N
4-OMe-C6H4- 4-CN-C6H4-
3-Cl-C6H4- 4-F-C6H4-
6
7
8
8
7
7
96
94
92
68
55
CN
N
N
N
N
Cl
F
N
N
3-Cl-CH4-
4-Ph-C6H4-
Cl
N
N
N
2-NO2-C6H4- 4-Ph-C6H4-
9
93
7
NO2
N
N
N
N
2-NO2-C6H4- 6-OMe-C10H6-
2-NO2-C6H4-
55
55
10
11
8
96
96
NO2
OMe
N
N
8
NO2
N
N
N
N
C6H5CH2-
12
13
7
6
92
90
52
69
N
N
N
N
N
3-Cl-C6H4-
-CH2OH
-CH2OH
OH
OH
Cl
N
O2N
N
4-NO2-C6H4-
14
6
96
65
aYield refers to those of isolated pure products.

84
S. Roy et al. / Journal of Molecular Catalysis A: Chemical 386 (2014) 78–85
explored as catalyst in the one-pot synthesis of triazole derivatives
starting from amines and hence we believe that this result would
make an important contribution to the existing methods for triazole
synthesis.
Acknowledgement
SMI acknowledges the Council of Scientific and Industrial
Research (CSIR) and Department of Science and Technology (DST),
New Delhi, India for funding. We acknowledge DST for providing
support to the University of Kalyani under Purse and FIST pro-
gramme. AB wishes to thank DST-SERB, New Delhi for extramural
project grant and DST Unit on Nanoscience for providing instru-
mental facilities. MP wishes to thank CSIR, New Delhi for Senior
Research Fellowships.
Fig. 6. Comparison of recyclability between Cu@PyIm-SBA-15 and Cu@SBA-15.
after third cycle there is a drastic reduction of product yield (Fig. 6).
This result suggested the superiority of our Cu-grafted functional-
ized mesoporous material over Schiff-base ligand free Cu@SBA-15
catalyst. Retention of the catalytic activity could be largely due to
strong binding of the catalytically active Cu(II) sites at the mesopore
surface via coordination bonds through imine-N and pyridine-N
donor sites (Scheme 2).
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.molcata.
2014.01.027.
3.4. Heterogeneity test
To examine whether copper was being leached out from the
solid support to the solution, a typical test was performed in
the click reaction between aniline and phenyl acetylene with our
supported Cu@PyIm-SBA-15 catalyst. For the various proof of het-
erogeneity, a test was carried out by filtering catalyst from the
reaction mixture after 4 h and the filtrate was allowed to react
up to the completion of the reaction (6 h). In this case no change
in conversion was observed, which suggests that the catalyst is
heterogeneous in nature. No evidence for leaching of copper or
decomposition of the complex catalyst was observed during the
catalytic reaction. It was noticed that after filtration of the catalyst
from the reaction mixture, reaction do not proceed further. Atomic
absorption spectrometric analysis of the supernatant solution of
the reaction mixture thus collected by filtration also confirmed the
absence of copper ions (below detection limit of AAS) in the liquid
phase. Thus, results of the above test suggested that Cu was not
being leached out from the solid catalyst during the reactions.
It is also evident from the electron paramagnetic resonance
(EPR) spectrum of the fresh and used Cu@PyIm-SBA-15 catalyst
(Fig. 4) that copper remains in +2 oxidation state throughout the
reaction. Moreover we also did not found the formation of even
a trace amount of dimer of alkyne in any reaction which generally
forms via Cu(I) catalysis. Hence, it can be assumed that our reaction
may proceed in a similar pathway catalyzed by Cu+2, postulated by
Pitchumani et al. [67].
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