Immobilized polytriazole complexes of copper(I) onto graphene oxide as a recyclable nanocatalyst for synthesis of triazoles

Article abstract of DOI:10.1002/aoc.3796

An efficient solid-supported catalyst for the Huisgen [3?+?2] cycloaddition reaction between azides and alkynes was prepared from copper(I) iodide and 1,2,3-triazole-functionalized graphene oxide. This catalyst was then used for the efficient synthesis of

Full text of DOI:10.1002/aoc.3796

Received: 11 December 2016
DOI: 10.1002/aoc.3796
Revised: 13 February 2017
Accepted: 14 February 2017
F U L L PA P E R
Immobilized polytriazole complexes of copper(I) onto graphene
oxide as a recyclable nanocatalyst for synthesis of triazoles
Hossein Naeimi
| Zahra Ansarian
Department of Organic Chemistry, Faculty of
Chemistry, University of Kashan, Kashan
87317IR, Iran
An efficient solid‐supported catalyst for the Huisgen [3 + 2] cycloaddition reaction
between azides and alkynes was prepared from copper(I) iodide and 1,2,3‐triazole‐
functionalized graphene oxide. This catalyst was then used for the efficient synthesis
of β‐hydroxy‐1,2,3‐triazoles giving access to these products in excellent yields. In
this protocol, the catalyst was shown to have high activity, air‐stability and
recyclability. The formation of copper triazolide is very straightforward and
energetically desirable. The catalyst can be isolated from copper‐catalysed
azide–alkyne cycloaddition reactions.
Correspondence
Hossein Naeimi, Department of Organic
Chemistry, Faculty of Chemistry, University
of Kashan, Kashan 87317, IR Iran.
Email: naeimi@kashanu.ac.ir
Funding Information
University of Kashan, Grant/Award Number:
grant number 159148/74
KEYWORDS
azides, catalyst, click reaction, graphene oxide, triazole
1 | INTRODUCTION
mechanical strength[19,20] and abundant hydrophilic oxygen‐
containing groups including hydroxyl, epoxy, carboxyl and
1,2,3‐Triazoles are nitrogen‐containing heterocyclic
molecules that have attracted increasing interest due to their
wide range of applications. These molecules are commonly
employed in many fields of chemistry such as drug
discovery,[1,2], fungicides, herbicides, corrosion‐retarding
agents, solar cells and dyes.[3,4]
carbonyl groups, leading to its easy modification and
widespread application.[21] The chemical modification of
GO has been demonstrated to be an efficient method which
renders it a more versatile precursor for a wide range of
applications.
Functionalization of GO is necessary for various applica-
tions such as carbocatalysis. In addition, carbocatalysts are
commonly inexpensive, stable and readily available. Another
advantage of carbocatalysts relates to their desirable surface
to volume ratio which increases the contact between
reactants and catalyst support and in turn enhances catalytic
activity.[22] Also, carbocatalysis provides a bridge to hetero-
geneous catalysis.[23]
Special ligands are often employed both to increase the
rate of reaction and to protect Cu(I) from oxidation in the
presence of adventurous oxygen.[24] These ligands containing
nitrogen atoms with special structure are able to chelate
copper. Oligotriazole ligands are advantageous in protecting
Cu(I) ions from aerobic aqueous conditions and therefore
improve the copper‐catalysed azide–alkyne cycloaddition
(CuAAC) reaction rate.[25,26] They are oligotriazole deriva-
tives branching from propargylamine cores. This new class
of ligands is capable of binding to metals by forming a
In 2002, Sharpless and co‐workers[5] and Meldal and
co‐workers[6] independently reported the Huisgen [3 + 2]
cycloaddition of terminal alkynes and organic azides
catalysed by homogeneous Cu(I) salts, the so‐called click
reaction. The click reaction can also be catalysed by hetero-
geneous Cu(I),[7] such as copper nanoparticles on activated
carbon,[8–11] copper zeolites,[12,13] CuBr on graphene
[14]
oxide/Fe3O4
and copper nitride nanoparticles supported
on mesoporous SiO2.[15,16] Also, CuI was applied in a highly
optimized protocol for repetitive triazole formation on a solid
support.[17,18]
Graphene is a typical solid support employed in the
preparation of heterogeneous catalysts. Graphene oxide
(GO), an oxidized form of graphene, has appeared as a
significant material owing to its unique nanostructure and a
diversity of fascinating characteristics such as very high
specific surface area with natural low mass, excellent
Appl Organometal Chem. 2017;e3796.
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Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3796

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NAEIMI AND ANSARIAN
chelate between the nitrogen atoms of the triazole and the
amine. The nitrogen atom of tertiary amine is supposed to
bind constantly to the metal centre, while the triazole ligands
might provisionally dissociate from the Cu(I) ion to permit
the formation of copper acetylide as starting point of the
catalytic cycle of the CuAAC reaction.[26] In continuation
of our ongoing work towards the synthesis of triazoles,[27,28]
herein we report a GO‐supported copper catalyst, containing
1,2,3‐triazoles as Cu(I)‐stabilizing ligands, for use in the
preparation of triazole derivatives.
15 min. Then deionized water (700 ml) and H2O2 (50 ml,
30%) were each added to the solution. The obtained suspen-
sion was filtered and washed with diluted HCl (5%) and
deionized water several times to eliminate excess acid and
dried for 12 h at 60 °C under vacuum. The graphite oxide
was dispersed in distilled water to get a concentration of
0.5 mg ml−1 and exfoliated by ultrasound to afford GO
nanosheets.
2.2.2 | Synthesis of 3‐chloropropyltrimethoxy-
silane‐functionalized GO (GO@CPTMS)
2 | EXPERIMENTAL
GO (1 g) was dispersed in 250 ml of dry toluene using
an ultrasonic probe. Subsequently, 3.0 ml of 3‐
chloropropyltrimethoxysilane (CPTMS) was diluted in
20 ml of dry toluene followed by dropwise addition to the
GO dispersion. The reaction vessel was heated to reflux
with continuous stirring for 48 h under nitrogen atmosphere.
After completion of the reaction, the functionalized GO
nanosheets were washed with toluene four times to remove
excess/non‐reacted CPTMS and then ethanol was used for
the final washing. The CPTMS‐coated GO nanosheets were
dried in an oven at 70 °C.[30,31]
2.1 | Materials and apparatus
The chemicals used in this work were purchased from Fluka
and Merck and used without purification. Fourier transform
infrared (FT‐IR) spectra were obtained as KBr pellets with
a PerkinElmer 781 spectrophotometer and a Nicolet Impact
400 FT‐IR spectrophotometer. 1H NMR and 13C NMR spec-
tra were recorded in CDCl3 solvent with a Bruker DRX‐400
spectrometer using tetramethylsilane as internal reference.
X‐ray diffraction (XRD) patterns were recorded using an
X'Pert Pro (Philips) instrument with an X‐ray beam of
1.54 Å wavelength and Cu anode material, at a scanning
speed of 2° min−1 from 10° to 80° (2θ). Scanning electron
microscopy (SEM) images of the prepared catalyst were
obtained with an FE‐SEM S4160 instrument (Hitachi).
Atomic force microscopy (AFM) images of GO nanosheets
and functionalized GO were measured using a scanning
probe microscope (SPM‐9600, Shimadzu). Thermogravimet-
ric analysis (TGA) was performed with a Mettler TA4000
system TG‐50 at a heating rate of 10 °C min−1 under a
nitrogen atmosphere. Melting points were obtained with a
Yanagimoto micro melting point apparatus. Purity
determination of substrates and reaction monitoring were
accomplished by TLC using silica‐gel Polygram SILG/UV
254 plates (Merck).
2.2.3 | Preparation of azide‐functionalized GO
(GO@PTMS‐N3)
In a 1000 ml round‐bottom flask, 1.0 g of GO@CPTMS was
added into deionized water (150 ml), followed by sonication
(35 W) for 5 min. Then, 2 g of NaN3 and 0.2 g of KI were
added into the round‐bottom flask, and heated at 60 °C for
48 h. After this step, the resulting product was washed with
water several times and dried at 50 °C in vacuum.
2.2.4 | Huisgen 1,3‐dipolar cycloaddition
between GO@PTMS‐N3 and tripropargylamine
GO@PTMS‐N3 was coupled to alkyne groups by a
copper‐catalysed azide–alkyne click reaction (Scheme 1).
GO@PTMS‐N3 (1 g) was dispersed in 250 ml of deionized
water using an ultrasonic probe. Subsequently,
tripropargylamine (0.6 g) and copper catalyst based on
CuSO4 and sodium ascorbate (0.05 and 0.1 equiv.,
respectively) were added. The reaction was performed for
48 h at room temperature. The resulting product was
washed with water several times and eventually dried under
vacuum overnight.
2.2 | Preparation of catalyst
2.2.1 | Preparation of GO
GO was synthesized from natural graphite using the
Hummers method.[29] Graphite powder (5.0 g) was stirred
in the presence of sodium nitrate (2.5 g) and concentrated
sulfuric acid (115 ml) in a 1000 ml round‐bottom flask
placed in an ice bath. Then, potassium permanganate
(15 g) was slowly added to the mixture and stirred for 2 h.
The mixture solution was transferred to a water bath
(35 °C) and stirred for 30 min. Afterwards, deionized water
(230 ml) was added to the solution slowly and the solution
temperature was monitored at about 98 °C and stirred for
2.2.5 | Preparation of copper complex catalyst
immobilized on GO (GO@PTA‐Cu)
1,2,3‐Triazole‐functionalized GO (1 g) was dispersed in
250 ml of dry acetonitrile using an ultrasonic probe. In the

NAEIMI AND ANSARIAN
3 of 11
7.80–7.79 (m, 3H), 7.70 (s, 1H), 7.42–7.38 (m, 6H) 7.33 (s,
3
1H), 5.69 (dd, 3J(H–H) = 8 Hz,
J = 3.9 Hz, 1H),
3
3
4.67–4.60 (dd, 1H, J(H–H) = 12.4 Hz, J(H–H) = 7.6),
4.27–4.22 (dd, 1H, J(H–H) = 14.4 Hz, J(H–H) = 3.6),
3.21 (t, J(H, H) = 6.8 Hz; 1H, OH).
3
3
2‐(4‐Phenyl‐1H‐1,2,3‐triazol‐1‐yl)‐2‐p‐tolylethanol
(3b)
Yellow solid; m.p. 125.0–127.0 °C (lit.[32] 124.0–126.0 °C).
FT‐IR (KBr, ν, cm−1): 697, 726, 757, 1047, 1075, 1008,
1
1185, 1221, 1380, 1457, 1497, 2927, 3028, 3092, 3417. H
NMR (400 MHz, CDCl3, δ, ppm): 7.69–7.65 (m, 3H),
7.39 (m, 3H), 7.27–7.20 (m, 3H), 5.68–5.65 (dd, 3J(H,
3
H) = 8 Hz,
J = 3.2 Hz, 1H), 4.65–4.61 (dd, 1H,
3J(H–H) = 12.6 Hz, J(H–H) = 8.4), 4.25–4.20 (dd, 1H,
3
3J(H–H) = 9 Hz, J(H–H) = 3.6), 2.38 (s, 3H), 2.37
3
(t, J(H, H) = 2.8 Hz; 1H).
SCHEME 1 Preparation of GO@PTA‐Cu organocatalyst
1‐(4‐Phenyl‐1H‐1,2,3‐triazol‐1‐yl)butan‐2‐ol (3c)
subsequent step, CuI (0.26 mmol, 0.05 g) was added to the
stirring mixture. The resulting mixture was refluxed for
24 h. After completion of the reaction, the immobilized
catalyst was filtered and washed with CH3CN and dried
under vacuum overnight.
White solid; m.p. 110.0–112.0 °C (lit.[28] 110.0–111.0 °C).
FT‐IR (KBr, ν, cm−1): 697, 763, 981, 1079, 1136, 1228,
1456, 1617, 2926, 2962, 3138, 3254, 3419. 1H NMR
(400 MHz, CDCl3, δ, ppm): 7.87 (s, 1H), 7.80–7.79 (m,
2H), 7.43–7.40 (m, 2H), 7.34 (m, 1H), 4.55–4.50 (dd, 1H,
3
3J(H–H) = 14 Hz),4.33–4.28 (dd, 1H, J(H–H) = 13.8 Hz,
2.3 | General procedure for preparation of
β‐Hydroxy‐1,2,3‐triazoles catalysed by
GO@PTA‐Cu under thermal conditions
2
J(H–H) = 7.6), 2.66–2.65(d, 3J(H–H) = 4.4, 1H),
1.66–1.53 (m, 2H), 1.09–1.05 (t, 3H).
In a 25 ml round‐bottom flask equipped with a magnetic stir
bar and condenser, a mixture of NaN3 (72 mg, 1.1 mmol),
epoxide (1 mmol), alkyne (1 mmol) and GO@PTA‐Cu
(10 mg, 0.017 mol%) was heated at 60 °C in water (5 ml)
for a suitable time period. The progress of the reaction was
monitored using TLC.
After the end of reaction, in order to separate the catalyst,
the product was dissolved in hot methanol and the mixture
was filtered under reduced pressure using a vacuum pump
over sintered glass. The solution was recovered via evapora-
tion using a rotary evaporator. The crude solid product was
recrystallized from ethanol to afford the β‐hydroxy‐1,2,3‐
triazoles as pure product. All products were confirmed using
spectral data and physical data and compared and verified
with authentic samples.
1‐Phenoxy‐3‐(4‐phenyl‐1H‐1,2,3‐triazol‐1‐yl)
propan‐2‐ol (3d)
Pale yellow solid; m.p. 125.0–127.0 °C (lit.[33]
125.5–126.0 °C). FT‐IR (KBr, ν, cm−1): 692, 756, 981,
1043, 1245, 1494, 1595, 2866, 2927, 3087, 3429. 1H
NMR (400 MHz, CDCl3, δ, ppm): 7.89 (s, 1H), 7.75–7.73
(m, 2H),7.40–7.38 (m, 2H), 7.31–7.27 (m, 3H), 7.02–6.94
(m, 1H), 6.93–6.91(m, 2H), 4.75–4.73 (m, 1H), 4.56–4.54
(m, 2H), 4.22–4.04 (m, 2H), 3.94–3.76 (m, 1H).
1‐Isopropoxy‐3‐(4‐phenyl‐1H‐1,2,3‐triazol‐1‐yl)
propan‐2‐ol (3e)
Yellow solid; m.p. 62.0–64.0 °C (lit.[28] 61.0–63.0). FT‐IR
(KBr, ν, cm−1): 697, 765, 923, 975, 1078, 1127, 1228,
1373, 1466, 2867, 2973, 3062, 3137, 3425. 1H NMR
(400 MHz, CDCl3, δ, ppm): 7.91 (s, 1H), 7.79–7.78 (m,
2H),7.42–7.37 (m, 2H), 7.34–7.31 (m, 1H), 4.60–4.57 (dd,
2‐Phenyl‐2‐(4‐phenyl‐1H‐1,2,3‐triazol‐1‐yl)etha-
nol (3a)
3
2
1H, J(H–H) =12 Hz, J(H–H) = 2.8), 4.64–4.40 (dd, 1H,
Pale yellow solid; m.p. 125.0–127.0 °C lit.[9]
125.5–127.0 °C). FT‐IR (KBr, ν, cm−1): 690, 758, 1047,
1080, 1241, 1438, 1463, 1493, 1593, 2928, 3065, 3089,
3140, 3345. 1H NMR (400 MHz, CDCl3, δ, ppm):
3J(H–H) = 14 Hz, J(H–H) = 4), 4.21 (m, 1H), 3.64–3.57
2
(m, 1H), 3.53–3.51 (dd, 1H, 3J(H–H) = 8 Hz, 3 J(H–H) = 4.4),
3.41–3.36 (dd, 1H, 3J(H–H) =10 Hz, 3J(H–H) = 4),
1.15–1.17 (t, 6H).

4 of 11
NAEIMI AND ANSARIAN
2925, 3087, 3426. 1H NMR (400 MHz,CDCl3, δ, ppm):
7.91 (s, 1H), 7.79–7.78 (m, 1H), 7.43–7.41 (m,
2H),7.35–7.30 (m, 2H), 7.02–6.98 (t, 1H), 6.92–6.91 (m,
2H), 4.22 (m, 1H), 3.64–3.57 (m, 1H), 4.08–3.98 (m, 1H),
3.38–3.37 (m, 1H).
2‐(4‐Phenyl‐1H‐1,2,3‐triazol‐1‐yl)cyclohexanol
(3f)
Yellow solid; m.p. 168.0–172.0 °C (lit.[9] 168.0–171.0 °C).
FT‐IR (KBr, ν, cm−1): 698, 768, 713, 1052, 1083, 1234,
1441, 2858, 2938, 3118, 3307. 1H NMR (400 MHz, CDCl3,
δ, ppm): 7.78 (s, 1H), 7.74–7.71 (m, 2H), 7.41–7.37 (m, 2H)
7.33–7.29 (s, 1H), 4.19–4.08 (m, 3H), 4.01–1.91 (m, 4H),
2.25–2.22 (m, 2H), 1.51–1.25 (m, 2H).
1,3‐Bis(4‐phenyl‐1H‐1,2,3‐triazol‐1‐yl)propan‐
2‐ol (3h)
Green solid; m.p. 233.0–236.0 °C (lit.[34] 233.0–236.0 °C).
FT‐IR (KBr, ν, cm−1): 687, 724, 763, 1074, 1126, 1278,
1464, 1729, 2861, 2928, 2959. 1H NMR (400 MHz, DMSO,
δ, ppm): 8.55 (s, 1H), 7.84 (m, 2H), 7.44–7.42 (m, 2H),
2‐Hydroxy‐3‐(4‐phenyl‐1H‐1,2,3‐triazol‐1‐yl)
propyl acrylate (3g)
Livid solid; m.p. 102.0–104.0 °C (lit.[28] 101.0–103.0 °C).
FT‐IR (KBr, ν, cm−1): 695, 756, 1044, 1245, 1494, 1596,
FIGURE 1 FT‐IR spectra of (a) graphite, (b) GO, (c) GO@CPTMS,
(d) GO@PTMS‐N3 and (e) GO@PTA
FIGURE 2 XRDpatternsof(a)graphite,(b)GOand(c)GO@PTA‐Cu
FIGURE 3 SEM images of (a) GO and (b) GO@PTA‐Cu

NAEIMI AND ANSARIAN
5 of 11
7.32–7.30 (m, 1H), 5.81 (m, 1H), 4.61–4.56 (d, 1H), 4.40 (m,
2H). 13C NMR (400 MHz, DMSO, δ, ppm): 147.71, 132.42,
130.51, 129.68, 129.41, 127.11, 126.72, 124.12, 69.91,
54.84.
GO is a notable support for the immobilization of
organocatalysts as a result of its mechanical and thermal
stability. These reasons prompted us to develop our work
for the linking of an organocatalyst onto GO. The preparation
1‐(4‐Phenyl‐1H‐1,2,3‐triazol)hexan‐2‐ol (3i)
Cream solid; m.p. 92.0–94.0 °C (lit.[32] 91.0–93.0 °C). FT‐IR
(KBr, ν, cm−1): 693, 764, 1087, 1138, 1228, 1463, 2862,
2925, 2959, 3142, 3248, 3407. 1H NMR (400 MHz, CDCl3,
δ, ppm): 7.85 (s, 1H), 7.78–7.75 (m, 2H), 7.42–7.41 (m, 2H),
7.35–7.32 (m, 1H), 4.52–4.49 (m, 2H), 4.29–4.23 (m, 1H),
4.15–4.13 (m, 1H), 1.57–1.50 (m, 3H), 1.45–1.37 (m, 3H),
0.95–0.91 (t, 3H). 13C NMR (400 MHz, CDCl3, δ, ppm):
147.27, 130.33, 128.78, 128.06, 125.53, 121.16, 70.44,
56.34, 34.17, 30.77, 28.01, 22.59, 13.99.
2‐Phenyl‐2‐(4‐propyl‐1H‐1,2,3‐triazol‐1‐yl)etha-
nol (3j)
Pale yellow solid; m.p. 62.0–64.0 °C. FT‐IR (KBr, ν, cm−1):
697, 761, 1070, 1280, 1455, 1726, 2853, 2925, 3061, 3367.
1H NMR (400 MHz, CDCl3, δ, ppm): 7.80 (s, 1H), 7.72
(m, 1H), 7.55–7.53 (m, 1H), 7.46–7.33 (m, 3H), 4.24–4.17
(m, 2H), 1.68–1.8 (t, 1H), 1.44–1.40 (m, 1H), 1.32–1.25
(m, 4H), 0.94 (m, 3H).
3 | RESULTS AND DISCUSSION
3.1 | Preparation and characterization of
catalyst
Synthesis of the heterogeneous Cu(I) complex and the
intermediate steps were examined and monitored using
FT‐IR spectroscopy, AFM, SEM, XRD, inductively
coupled plasma (ICP) analysis and energy‐dispersive
X‐ray (EDX) analysis.
FIGURE 4 TGA curve of GO@PTA‐Cu
FIGURE 5 AFM images of (a) GO nanosheets and (b) GO@PTA‐Cu

6 of 11
NAEIMI AND ANSARIAN
of the GO‐immobilized copper complex consists of the
following steps, as shown in Scheme 1.
spectrum of natural graphite powder exhibits peaks charac-
teristic of C═C groups of which the peak related to C═C
double bonds at 1573 cm−1 is not sharp (Figure 1a).
Figure 1(b) shows the FT‐IR spectrum of GO powder. The
stretching vibration at 3398 cm−1 corresponds to the OH
group. The absorption band at 1717 cm−1 corresponds to
C═O group. The absorption peaks at 1640 and 1056 cm−1
are assigned to carbon–carbon double bonds and C─O,
respectively. The various functional groups on the GO
provide active sites for the bonding between GO sheets
and silane.
In the first step, GO was functionalized using CPTMS
according to previously reported methods.[30,31] The chloro‐
functionalized GO was allowed to react with sodium azide
to form GO@PTMS‐N3. The azide‐functionalized GO was
then coupled to tripropargylamine to form 1,2,3‐triazole‐
functionalized GO via a copper‐catalysed azide–alkyne click
reaction. 1,2,3‐Triazole‐functionalized GO formed a complex
with CuI, affording the immobilized Cu complex catalyst
(GO@PTA‐Cu). The nitrogen‐donating ligands of 1,2,3‐tri-
azole are particularly promising as they form stable Cu(I)
complexes.
Figure 1(c) shows the FT‐IR spectrum of CPTES‐coated
GO. The absorption peak at 1045 cm−1 corresponds to the
Si─O─C bond. The vibrational bands at 2926 and
2854 cm−1 are attributed to CH2 and the peak at 695 cm−1
Figure 1 shows the FT‐IR spectra of graphite, GO,
GO@CPTMS, GO@PTMS‐N3 and GO@PTA. The FT‐IR
FIGURE 6 EDX patterns of (a) GO and (b) GO@PTA‐Cu

NAEIMI AND ANSARIAN
7 of 11
representing the C─Cl bond indicates the successful coating
of the CPTES onto GO through chemical bonding. After the
reaction between sodium azide with GO@CPTMS, azide
groups were attached to the surfaces of GO, which is evident
from the appearance of the characteristic FT‐IR absorption
peak of azide groups at 2098 cm−1 and disappearance of the
peak at 695 cm−1 corresponding to C─Cl bond (Figure 1d).
Figure 1(e) shows the FT‐IR spectrum of 1,2,3‐triazole‐
functionalized GO. Disappearance of the peak at 2098 cm
The SEM images of GO and GO@PTA‐Cu are shown in
Figure 3. Different morphologies are observed for GO nano-
sheets and the prepared catalyst. The images confirm that
two‐dimensional GO nanosheets can be produced via exfoli-
ation of suspended graphite oxide.
TGA was used to verify the anchoring of organic groups
on the surface of GO. As shown in Figure 4, there is a mass
loss (42%) below 260 °C attributed to the removal of
adsorbed water firstly and oxygen‐containing functional
groups on the GO surface. There is a decrease of weight
(24%) when the temperature is between 260 and 610 °C that
is attributed to the covalency of organic groups.
AFM was employed to observe the morphology of GO
nanosheets and measure their thickness. The AFM images
of GO and GO@PTA‐Cu easily confirm the wrinkled two‐
dimensional characteristic of the GO nanosheets. The images
indicate that the thickness of GO is approximately 0.9 to
1.5 nm, corresponding to structures with one to two layers
(Figure 5a). After surface functionalization, the thickness of
sheets is increased to 4.3 nm (Figure 5b). The increase in
thickness of functionalized GO nanosheets is perhaps caused
by the organic compounds grafted on the GO sheets, indicat-
ing the successful functionalization of GO.
−1
indicates the successful azide–alkyne coupling reaction
on the surface of GO. The N═N stretching absorption for
triazole compounds appears at around 1457 cm−1 which is
assigned within the same absorption region of the C…C
stretching for GO.
XRD patterns were analysed to determine the phase
structure of GO. Figure 2 shows XRD patterns of graphite,
GO and GO@PTA‐Cu. The pattern of graphite powder
shows a sharp peak at 2θ = 26° (Figure 2a), corresponding
to an interlayer spacing (d‐spacing) of 0.335 nm. The
exfoliated GO shows a broad peak at about 2θ = 26.5° and
a peak at 2θ = 12° (d‐spacing =0.78 nm) (Figure 2b). The
enhancement in d‐spacing is due to the intercalation of water
molecules and the formation of oxygen‐containing functional
groups between the layers of the graphite. After the surface
covalent functionalization of GO with CPTMS, click
coupling process and finally production of the GO@PTA‐
Cu catalyst, the diffraction peak at 2θ = 12° in the GO pattern
disappears, indicating an increase the interlayer distances.
Furthermore, because of the small amount of copper in
GO@PTA‐Cu, the signals pertaining to copper are not
clearly detected in the XRD pattern (Figure 2c).
The Cu content for GO@PTA and GO@PTA‐Cu catalyst
was determined using ICP analysis. According to the
TABLE 2 Optimization of GO@PTA‐Cu catalyst amount in the
model reactiona
Entry Catalyst (mg) Cu (mmol) Time (min) Yield (%)b
1
2
3
4
5
0
2
—
120
50
35
35
40
—
75
90
94
90
0.00034
0.00086
0.0017
0.0026
5
10
15
aReaction conditions: styrene oxide (1 mmol), phenylacetylene (1 mmol), NaN3
(1.1 mmol), H2O, 60 °C, GO@PTA‐Cu (0.017%).
bIsolated yield.
SCHEME 2 Synthesis of 2‐phenyl‐2‐(4‐phenyl‐1H‐1,2,3‐triazol‐1‐
yl)ethanol (3a)
TABLE 1 Solvent optimization for the synthesis of 3a in the model
reactiona
TABLE 3 Temperature optimization for synthesis of 3a in the model
reactiona
Entry
Solvent
Time (min)
Yield (%)b
Entry
Temperature (°C)
Time (min)
Yield (%)b
1
2
3
4
5
6
H2O
35
35
75
60
60
40
94
60
35
20
15
55
EtOH
1
2
3
4
5
r.t.
40
50
60
80
120
60
—
—
30
94
94
PhCH3
CH2Cl2
n‐hexane
DMF
120
35
35
aReaction conditions: styrene oxide (1 mmol), phenylacetylene (1 mmol), NaN3
aReaction conditions: styrene oxide (1 mmol), phenylacetylene (1 mmol), NaN3
(1.1 mmol), GO@PTA‐Cu (10 mg, 0.017 mol%), 60 °C.
bIsolated yield.
(1.1 mmol), H2O, GO@PTA‐Cu (10 mg, 0.017 mol%).
bIsolated yield.

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NAEIMI AND ANSARIAN
TABLE 4 Synthesis of β‐hydroxytriazoles catalysed by GO@PTA‐Cua
Entry
Alkyne (R2)
Epoxide
Product
Time (min)
Yield (%)b
TONc
TOF (h−1 d
)
1
Ph
35
94
543
936
936
481
2
3
Ph
Ph
35
65
94
90
543
520
4
5
Ph
Ph
70
85
92
90
531
520
454
366
6
Ph
60
90
520
520
189
7
Ph
Ph
150
55
82
85
473
491
8e
534
(Continues)

NAEIMI AND ANSARIAN
9 of 11
TABLE 4 (Continued)
Entry
Alkyne (R2)
Epoxide
Product
Time (min)
Yield (%)b
TONc
TOF (h−1 d
)
9e
Ph
90
80
462
308
10
11
Ph
80
50
89
89
514
514
395
619
aGeneral reaction conditions: 1 (1 mmol), 2 (1 mmol), NaN3 (1.1 mmol), GO@PTA‐Cu (0.017 mol%, 10 mg), H2O, 60 °C.
bIsolated yield.
cTON: moles of formed β‐hydroxy‐1,2,3‐triazole per mole of catalyst.
dTOF: (mmol of product/mmol of active site of catalyst)/time of reaction (h).
eReaction conducted with 1:2:2 mole ratio of epoxide, alkyne and NaN3, respectively.
obtained results from ICP analysis, the Cu content in the
catalyst is 1.1%, while no Cu content was indicated in the
GO@PTA species. Also, to support the mentioned observa-
tion, the catalyst was subjected to EDX analysis. The EDX
analysis of GO and GO@PTA‐Cu catalyst confirms the
presence of organosilane and copper (Figure 6).
and the catalyst afforded 94% yield of product 3a in 35 min in
water under reflux conditions. No product was formed in the
absence of the catalyst.
For optimization of temperature of the reaction, an
increase in temperature of the reaction (room temperature to
80 °C) led to decreased time of the reaction and increased
yields of the desired product (Table 3). No significant
increase in the yield of product was observed as the reaction
temperature was raised from 60 to 80 °C. Therefore, 60 °C
was chosen for this reaction.
After optimization of the reaction conditions, we used
these conditions for the reaction of a series of different aryl‐
and alkyl‐substituted oxiranes (1a–j) and terminal alkynes
(2a and 2b) to investigate the versatility of the protocols
under GO@PTA‐Cu catalysis. The results are summarized in
Table 4. We first studied the reaction of aryl‐substituted
epoxides with phenylacetylene (Table 4, entries 1 and 2).
The aryl‐substituted epoxides 1a and 1b reacted rapidly,
affording triazoles 3a and 3b, respectively, in high yield
and short reaction time and with reverse regioselectivity to
that displayed by the alkyl‐substituted epoxides. Subse-
quently, we examined the reaction between aliphatic epoxides
and phenylacetylene (Table 4, entries 3–10). In these cases,
we observed a decrease in yield and increase in reaction time
compared with the aryl‐substituted epoxides. The formation
3.2 | Investigation of catalyst activity
Initially, the reaction parameters were optimized in the reac-
tion of styrene oxide (1 mmol), phenylacetylene (1 mmol)
and NaN3 (1.1 mmol), in the presence of catalytic amounts
of catalyst, as the model reaction (Scheme 2).
To choose the medium of the reaction, the model reaction
was performed in various solvents: water, EtOH, PhCH3,
CH2Cl2, n‐hexane and dimethylformamide (DMF). The
results are summarized in Table 1. The reaction in water as
solvent gave the best result (Table 1, entry 1). This is proba-
bly due to the high solubility of sodium azide in water.
Furthermore, the reactions were clean in water compared to
those in organic solvents. Therefore, in continuation of the
process, water was chosen as the reaction medium.
The effect of the amount of GO@PTA‐Cu as catalyst on
the synthesis of 3a is presented in Table 2. The best result
was observed with 10 mg (0.0017 mmol of Cu) of the catalyst

10 of 11
NAEIMI AND ANSARIAN
of bis‐triazole 3 h from 1 h and 1i in this reaction can be due
to the existence of good leaving groups (OTs, Cl) in the pri-
mary epoxides (Table 4, entries 8 and 9). Furthermore, the
1
structures of these products were confirmed from H NMR
and 13C NMR spectra.
3.3 | Proposed reaction mechanism
The proposed mechanism for the formation of β‐hydroxy‐
1,2,3‐triazoles includes two routes,[28] in which GO@PTA‐
Cu has a two‐fold catalytic effect as a bifunctional catalyst,
which combines one‐pot ring‐opening and 1,3‐dipolar cyclo-
addition. Firstly, GO@PTA‐Cu catalyses the formation of
organoazide (II) from epoxide and sodium azide (Scheme 3).
Also, a π‐complex is formed between phenylacetylene and
GO@PTA‐Cu to afford the copper(I) acetylide intermediate
(III), the generation and disappearance of the organoazide
intermediate being monitored by TLC. Coordination of the
organoazide to the copper centre of the acetylide enhances
the nucleophilicity of the triple bond and begins a sequence
of steps which finally results in the formation of the new
C─N bond between the nucleophilic β‐carbon atom of the
acetylide and the terminal electrophilic nitrogen atom of the
azide.[35] Ultimately, after protonation of intermediate (IV),
β‐hydroxy‐1,2,3‐triazole is obtained in high yield and short
reaction time.
FIGURE 7 Reusability of GO@PTA‐Cu catalyst in synthesis of 3a
FIGURE 8 SEM image of GO@PTA‐Cu after recycling
3.4 | Recycling the catalyst
The possibility of recycling the catalyst was examined
through the reaction of styrene oxide, phenylacetylene and
NaN3 catalysed by GO@PTA‐Cu under the optimized condi-
tions. Upon completion of the reaction, the catalyst was
separated by filtration, washed with methanol and dried at
80 °C in an oven for 8 h. The recycled catalyst could be
reused five times without significant loss of its catalytic
activity, with yields ranging from 94 to 85% (Figure 7). An
SEM image of the catalyst after recycling from the reaction
was obtained, which does not show any considerable change
in the morphology (Figure 8). demonstrating the retention of
the catalytic activity with recycling.
4 | CONCLUSIONS
We have established that GO@PTA‐Cu is a robust, reusable
and heterogeneous solid catalyst for the synthesis of
β‐hydroxy‐1,2,3‐triazoles in water under thermal conditions.
We have reported the preparation of a tetradentate nitrogen
ligand on the surface of functionalized GO support using click
SCHEME 3 Proposed mechanism for synthesis of β‐hydroxy‐1,2,3‐
triazoles

NAEIMI AND ANSARIAN
11 of 11
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Cu(I) intermediates but also advances the catalytic process.
Also, the prepared catalyst was characterized using some
spectroscopic and microscopic techniques such as FT‐IR
spectroscopy, SEM, TGA, ICP analysis, EDX analysis,
AFM and XRD. The spectroscopic and microscopic
analyses confirmed that the functionalization of GO was
successful. This method has several advantages, including
high to excellent yields of products, green reaction solvent,
reusability of catalyst and simple work‐up process.
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supporting this work via grant no. 159148/74.
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How to cite this article: Naeimi H, Ansarian Z.
Immobilized polytriazole complexes of copper(I)
onto graphene oxide as a recyclable nanocatalyst for
synthesis of triazoles. Appl Organometal Chem.
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