Copper-γ-cyclodextrin complexes immobilized on hexagonal boron nitride as an efficient catalyst in the multicomponent synthesis of 1,2,3-triazoles

Article abstract of DOI:10.1016/j.jcat.2016.09.022

A copper-γ-cyclodextrin complex immobilized on hexagonal boron nitride (h-BN@γ-CD@Cu(OAc)₂) has been prepared for the first time. This recoverable and reusable heterogeneous catalyst can be used in the click synthesis of 1,2,3-triazoles via a one-pot three-component reaction of boracic acid, terminal alkynes, and sodium azide at room temperature in water. FT-IR, XRD, SEM, XPS, TG, and ICP-AES techniques were used to characterize the catalyst. In general, this reaction, with the aid of this new catalyst, afforded the corresponding products with good yields and excellent tolerance of the functional groups.

Full text of DOI:10.1016/j.jcat.2016.09.022

Journal of Catalysis 344 (2016) 286–292
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Copper-
c-cyclodextrin complexes immobilized on hexagonal boron
nitride as an efficient catalyst in the multicomponent synthesis of
1,2,3-triazoles
⇑
Ruifang Nie, Rui Sang, Xiaojun Ma, Yang Zheng, Xu Cheng, Weijian Li, Li Guo, Hui Jin, Yong Wu
Key Laboratory of Drug-Targeting of Education Ministry and Department of Medicinal Chemistry, West China School of Pharmacy, Sichuan University, Chengdu 610041,
People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
A copper-c-cyclodextrin complex immobilized on hexagonal boron nitride (h-BN@c-CD@Cu(OAc)2) has
Received 27 July 2016
Revised 17 September 2016
Accepted 20 September 2016
been prepared for the first time. This recoverable and reusable heterogeneous catalyst can be used in
the click synthesis of 1,2,3-triazoles via a one-pot three-component reaction of boracic acid, terminal
alkynes, and sodium azide at room temperature in water. FT-IR, XRD, SEM, XPS, TG, and ICP-AES tech-
niques were used to characterize the catalyst. In general, this reaction, with the aid of this new catalyst,
afforded the corresponding products with good yields and excellent tolerance of the functional groups.
Ó 2016 Elsevier Inc. All rights reserved.
Keywords:
Hexagonal boron nitride
c
-Cyclodextrins
Click chemistry
1,2,3-Tiazoles
Recyclable
Water
1. Introduction
being hard to be recover and separate, cytotoxic, and easily
destroyed during the course of the reaction. To overcome these
In the past two decades of organic chemistry, ‘‘click chemistry”
has attracted a significant amount of attention in both academia
and industry, given its ability to efficiently create complex prod-
ucts from simple substrates [1–3]. Among all the click reactions,
the copper-catalyzed azide–alkyne cycloaddition reaction (CuAAC),
which was independently described by Sharpless and Meldal in
2002, has proven to be the primal and best-known example of such
reactions [4,5]. The CuAAC is a highly regioselective, biocompati-
ble, and efficient method of synthesis for 1,2,3-triazole derivatives
under mild conditions and has been widely used in many kinds of
organic synthesis. Since then, considerable effort has been devoted
to the CuAAC reaction, aiming to discover new and more powerful
synthetic strategies [6–10].
In CuAAC reactions, copper plays a vital role in the construction
of 1,2,3-triazole derivatives. On the basis of Sharpless and Medal’s
work, different copper sources such as CuI [11], Cu(OAc)2 [12],
CuOTfÁC6H6 [13], [Cu(CH3CN)4]PF6 [14], and [Cu(phen)(PPh3)2]
NO3 [15] have been applied to the reaction. Although those homo-
geneous catalysts have proven efficient in triazole synthesis, their
applications are also limited due to some difficulties, such as their
issues, much attention has been given to the heterogeneous cata-
lysts, which have more advantages than homogenous ones in that
they are easy to separate and recover and are low-toxic in nature
[16–18]. By immobilizing copper ions onto insoluble supports,
the advantages of both homogeneous and heterogeneous catalysts
can be combined. During the past few years, copper ions have been
immobilized onto a large variety of solid supports, such as agarose
[19], clay [20], chitosan [21], silica [22], and graphene [23]. These
catalysts have been applied to CuAAC reactions for the synthesis
of 1,2,3-triazoles.
Hexagonal boron nitride (h-BN) is similar in many ways to gra-
phene, with a wide band gap independent of morphology, high
thermal conductivity, and excellent mechanical strength [24].
Moreover, h-BN is more stable than graphene at high tempera-
tures. Due to its outstanding performance, h-BN has been widely
applied in aluminum matrix composites [25], refractory materials
[26], hydrogen storage [27–29], and water cleanup [30]. In addi-
tion, h-BN has also served as a catalyst support applied in chemical
reactions. For instance, boron nitride-supported Pd has been used
as a selective oxidant for lactose [31].
On the other hand, there is growing interest in using environ-
mentally benign substances as heterogeneous catalysts [32–34].
Recently, cyclodextrins (CD) were found to be a compatible
⇑
Corresponding author.
E-mail address: wyong@scu.edu.cn (Y. Wu).
http://dx.doi.org/10.1016/j.jcat.2016.09.022
0021-9517/Ó 2016 Elsevier Inc. All rights reserved.

R. Nie et al. / Journal of Catalysis 344 (2016) 286–292
287
material to form many metal ion complexes. Also recently, the
2.3. Preparation of amino-functionalized h-BN (h-BN@APTMS)
copper-b-cyclodextrin (CD) complex was reported as a phase
transfer catalyst in CuAAC reactions [35–37]. On the other hand,
even if the h-BN-supported heterogeneous catalysts have also been
used, such catalysts often show a broad size distribution and
limited reusability. The limited reusability might be due to the
stability of the h-BN and the metal ions. Therefore, increasing the
binding affinity by functionalizing the BN may solve those prob-
lems. In this article, we employ functionalized h-BN as a stable
The h-BN@OH particles (3 g) were dispersed in dry toluene
(120 mL) and stirred at 25 °C for 20 min. Then, to the resulting
solution, 1.6 mL of (3-aminopropyl)trimethoxysilane (APTMS)
was added dropwise. Then the mixture was stirred for 24 h at
120 °C under Ar. The resulting particles (h-BN@APTMS) were fil-
tered and washed several times with toluene. Finally, the obtained
white solid (3.05 g) was dried under reduced pressure at 80 °C for
6 h.
substance for supporting copper-c-cyclodextrin complexes
(Fig. 1, h-BN@ -CD@Cu(OAc)2), serving as a recoverable and reusa-
c
ble catalyst in the multicomponent one-pot synthesis of 1,2,3-
triazoles in water. To the best of our knowledge, this is the first
2.4. Preparation of carboxylic acid-functionalized h-BN
time for the synthesis of the immobilized Cu (II)-c-cyclodextrin
complex on h-BN and this is also the first report for h-BN-based
heterogeneous catalysts in click chemistry.
The prepared particles of h-BN@APTMS (2 g) were added into
0.1 M succinic anhydride in DMF (71.4 mL) at 25 °C and the mix-
ture was stirred for 24 h. The resulting carboxylic group-
functionalized h-BN (h-BN@APTMS@COOH) was filtered and
washed with DMF. Finally, the obtained white solid (2.01 g) was
dried under reduced pressure at 50 °C for 6 h.
2. Experimental
2.1. Materials and instrumentation
2.5. Preparation of
c
-cyclodextrin-conjugated h-BN (h-BN@
c
-CD)
The h-BN powder (99.9%) was obtained from Micxy Regent Co.
Ltd. (Chengdu, China). (3-Aminopropyl)trimethoxysilane (APTMS,
97%) was purchased from Aladdin Reagent Co. Ltd. (Shanghai,
China). Succinic anhydride (99.0%) was supplied by Tianjin Yuan-
h-BN@APTMS@COOH particles (1 g) and
1.56 g, 2.74 mmol) were stirred in dry DMF (25 mL) at 60 °C for
7 h. The resulting particles (h-BN@ -CD) were filtered and washed
c-cyclodextrin (c-CD,
c
hang Chemicals Co. Ltd. (Tianjin, China).
c-Cyclodextrin (c-CD,
with DMF and DCM, each for three times. Then the product (0.98 g)
99.0%) was provided by Chengdu Kelong Chemicals Co. Ltd.
(Chengdu, China). Sodium hydroxide (NaOH, 96%) and cupric
acetate (Cu(OAc2), 99.0%) were collected from Tianjin Ruijinte
Chemicals Co. Ltd. (Tianjin, China). All other materials were
commercially available and used without further purification.
Fourier transform infrared (FT-IR) spectra were determined on a
Nicolet 6700 FI-IR spectrometer (Nicolet), using KBr pellets. X-ray
photoelectron spectroscopy (XPS) measurements were carried out
on an AXIS Ultra spectrometer (KRATOS). X-ray diffractometry
(XRD) spectra were recorded with an EMPYREAN spectrometer
(Panalytical). The morphologies of the h-BN catalyst were observed
using scanning electron microscopy (SEM, JSM-7500F). Thermo-
gravimetric analysis (TGA) was performed with a thermal analyzer
(TGA/DSC2, METTLER TOLEDO) at a rate of 10 °C/min under N2. The
loading content was determined by inductively coupled plasma
optical emission spectroscopy (ICP-OES, SPECTRO ARCOS).
was dried under a vacuum desiccator at room temperature for 6 h.
2.6. Preparation of h-BN@c-CD@ Cu(OAc)2
h-BN@APTMS@ -CD (1.0 g) and Cu(OAc)2 (396 mg, 1.98 mmol)
c
was mixed in methanol (100 mL) at room temperature and stirred
for 24 h under Ar. The resulting mixture was filtered and washed
with methanol five times to remove unreacted Cu(OAc)2. Finally,
the pale-blue solid (1.07 g) was dried under vacuum at room tem-
perature for 5 h.
2.7. General procedure (4a as an example)
Phenylboronic acid 1a (1.5 mmol), NaN3 (1.5 mmol), and cata-
lyst (0.03 mmol) were added to a solution of H2O (5 ml). The mix-
ture was stirred at ambient temperature for 7 h a corresponding
time. The progress was monitored by TLC. After this, pheny-
lacetylene 3a (1.0 mmol) was added, and the mixture was stirred
at ambient temperature until complete. The reaction mixture
was adjusted to pH 12 with 1 M NaOH and then filtered. The filter
cake was washed with EtOAc and THF twice each. The filtrate was
diluted with water and extracted with EtOAc several times. The
organic layer was separated, washed with saturated brine, and
dried over anhydrous sodium sulfate and the solvent was removed
under vacuum. The crude residue was purified by flash chromatog-
raphy on silica gel to give the final product, 4a.
2.2. Preparation of hydroxide-functionalized h-BN (h-BN@OH)
First, h-BN (4 g) was dispersed in 5 M sodium hydroxide solu-
tion (500 mL) and stirred at 120 °C for 24 h. Then the particles were
filtered and washed with D.I. water (3 Â 150 mL) to adjust the pH
from basic to neutral. Finally, the obtained white solid (3.50 g) was
dried under reduced pressure at 80 °C for 6 h and stored in a des-
iccator at room temperature.
3. Results and discussion
3.1. Catalyst preparation
As shown in Scheme 1, the immobilization of Cu (II) onto the
c-CD-functionalized hexagonal boron nitride was performed in
four steps. First, pristine h-BN was treated with hydroxide anions,
resulting in the formation of free hydroxyl groups on the edges of
BN sheets. Second, h-BN@OH was reacted with aminopropyl
trimethoxysilane (APTMS) to afford amino-functionalized boron
: B
: N
:
: APTMS-Amber Acid
-CD@Cu(OAc)2
γ
nitride. Third,
c-cyclodextrin was attached to h-BN@APTMS via
Fig. 1. The structure of h-BN@c-CD@Cu(OAc)2.
the butanedioic anhydride-promoted condensation reactions.

288
R. Nie et al. / Journal of Catalysis 344 (2016) 286–292
HO
HOHO
HOHO
HOHO
HOHO
HOHO
HO
H
H
H
H
H
H
H
O
O
O
O
O
O
OO
H
OH
OH
OH
OH
OH
OH
5N N OH 120 oC 24h
a
,
,
OH
OH
OH
OH
OH
OH
Step
1
OH
OH
OH
OH
HO OHHO OHHO OHHO OHHO OHHO OHHO OHHO OH
-
BN
h
h-BN @ OH
APTMS, Tol, Ar, reflux, 24h
(1) Butanedioic anhydride,
DMF, Ar, rt, 24h
-CD, DMF, Ar, 60 oC 7h
¨
(2)
,
Step
3
@
-CD
h-BN
h-BN @ APTMS
MeOH, Ar, rt, 24h
Cu(OAc)2,
:
:
N
B
: APTMS-Amber Acid
O
O
Si
O
H
N
:
-CD
O
O
O
:
-CD @ Cu(OAc)2
+
u2
C
h-BN @ -CD @ Cu(OAc)2
h-BN @ -CD @ Cu(OAc)2
Scheme 1. The synthetic strategy for the synthesis of h-BN@
c
-CD@Cu(OAc)2.
Ultimately, the attachment of Cu(OAc)2 onto
heterogeneous Cu(II) catalyst.
c-CD generated the
927 cmÀ1 that were also observed in spectrum of h-BN@
c-CD with
little shift (Fig. 3d). The results provide direct evidence that the
conjugation occurs.
3.2. Catalyst characterization
For quantitative analysis, the as-prepared h-BN@OH, h-
BN@APTMS, and h-BN@c-CD were further observed via TGA, and
The synthesized nanocatalyst was characterized using several
different microscopic and spectroscopic techniques including FT-
IR, SEM, TGA, ICP, XRD, and XPS analysis.
these results are shown in Fig. 4. The experiments were performed
at up to 700 °C under N2 at a heating rate of 10 °C minÀ1. Under
these conditions, a weight loss of about 1.67% was observed for
h-BN@OH, which should be ascribed to the removal of physically
adsorbed solvents and surface hydroxyl groups. Weight losses of
about 3.45% and 5.57% were observed for h-BN@APTMS and h-
BN@c-CD, respectively. These should be mainly attributed to the
thermal degradation of organic components on the BN complex.
Moreover, around 2.12% weight loss was observed when these
Scanning electron microscopy (SEM) has been used to study the
presence, distribution, and dimensions of the prepared hybrid
nanomaterials. As shown in Fig. 2a and b, no obvious morphologi-
cal difference can be found between h-BN and h-BN@OH. They all
exhibit schistose structures with smooth edges and flat surfaces.
And it can be clearly seen that the size of copper (II)-loaded
nanocatalyst is in the range 20–400 nm. Notably, after functional-
ization, the h-BN nanosheets are still arranged in schistose struc-
tures and appeared more broken and aggregated (Fig. 2c).
two samples were compared. This suggests that
successfully conjugated to h-BN@APTMS particles. In the curve of
h-BN@ -CD, the first step is associated with the loss of water mole-
c-CD was
c
Infrared spectroscopy was used to characterize the organic
components bound to the surface of h-BN (Fig. 3). The characteris-
tic absorption bands of B–N bonds were observed at 1395 and
799 cmÀ1 (Fig. 3a), and were slightly shifted to 1391 cmÀ1 and
806 cmÀ1 after the conjugations with APTMS (Fig. 3a vs. Fig. 3b).
All the functionalized h-BN showed a strong band at around
3420 cm-1, which was attributed to the stretching vibrations of
O–H bonds (Fig. 3a, b, and d). Comparison studies on h-BN@OH
and h-BN@APTMS reveal additional strong bands at 1120 and
1033 cmÀ1 corresponding to characteristic absorption of S–O
bonds formed through the silylation process. Also, the
h-BN@APTMS peak at 2928 cmÀ1 was assigned to stretching vibra-
tion of C–H bonds of the propylamine groups (Fig. 3b). The spec-
cules (below 200 °C). The second weight loss, starting at 200 °C,
disintegrates the supported organic parts with a calculated loss
of 4.27%. Notably, the amount of copper (1.7%) in h-BN@
c-CD@Cu(OAc)2 was determined by inductively coupled plasma
(ICP) analysis. In all, these results corroborate the FT-IR data.
Fig. 5 shows the wide-angle XRD patterns of h-BN@APTMS and
h-BN@c-CD@Cu(OAc)2 nanomaterials. These two samples show
the same diffraction peaks at 2h = 30.1°, 35.6°, 43.1°, 53.5°, 57.1°,
and 62.7°, which correspond to the (220), (311), (400), (422),
(511), and (440) lattice planes of a typical hexagonal boron nitride
structure (JCPDS No. 45-896). This suggests that the crystal
structure of the h-BN has not been compromised by the reaction.
In the process of the coordination between the h-BN@
c-CD and
trum of c-CD (Fig. 3c) displayed characteristic peaks at 1050 and
copper ions, the formation of Cu nanoparticles was completely

R. Nie et al. / Journal of Catalysis 344 (2016) 286–292
289
h-BN@OH
a
100
80
60
40
20
0
3420 O-H
799
B-N
B-N 1395
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm -1
)
h-BN@APTMS
b
100
80
60
40
20
0
1033
Si-O
2928 C-H
3427
O-H
1120
Si-O
806 B-N
B-N 1391
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm -1
)
γ-CD
c
100
80
60
40
20
0
1724
3124
1449
1050
4000 3500 3000 2500 2000 1500 1000 500
752
2609
2784
927
658
Wavenumber (cm -1
)
h-BN@ γ-CD
d
100
80
60
40
20
0
Fig. 2. SEM of (a) pristine h-BN, (b) h-BN@OH, and (c) h-BN@c-CD@Cu(OAc)2.
929
γ-CD
Si-O
2928
C-H
3425
O-H
1025
1051 γ-CD
avoided. No characteristic peaks of copper particles were found in
the XRD pattern of h-BN@ -CD@Cu(OAc)2, which implies that all of
c
the catalytic activity can be attributed to divalent copper. More-
over, no peaks corresponding to any other impurity were observed.
Detailed surface information of h-BN@APTMS and h-BN@
800
B-N
Si-O
1122
c
-CD@Cu(OAc)2 was collected by X-ray photoelectron spec-
troscopy (XPS) and the corresponding results are presented in
Fig. 6. The new peaks of O1s, C1s, and Si2p can be assigned in
Fig. 6a, indicating that (3-aminopropyl)trimethoxysilane (APTMS)
has successfully attached to the surface and edges of pristine BN
1394
B-N
4000 3500 3000 2500 2000 1500 1000 500
0
Wavenumber (cm -1
)
particles. The spectrum of h-BN@
increase in the signal intensity of the O1s and C1s peaks, which
is attributed to -CD covalently grafted to the h-BN@APTMS.
The B1s spectra of h-BN@ -CD@Cu(OAc)2 showed a strong bind-
c-CD@Cu(OAc)2 shows a large
Fig. 3. FT-IR spectra of (a) h-BN@OH, (b) h-BN@APTMS, (c) c-CD, and (d) h-BN@c-
c
CD.
c
ing energy peak for the B–N bond and a weak binding energy peak
for the B–OH bond at 190.1 eV and 192.0 eV, respectively (Fig. 6b)
[38]. The B–OH peak resulted from the introduction of a hydroxyl
group by the base treatment. In order to provide clearer evidence

290
R. Nie et al. / Journal of Catalysis 344 (2016) 286–292
100
99
98
97
96
95
94
h-BN@APTMS
(a)
h-BN@γ-CD@Cu(OAc)
1.3 %
2
1.6 %
1.7 %
Cu 2p
h-BN@OH
2.1 %
700
h-BN@APTMS
h-BN@γ-CD
1000
800
600
400
200
100
200
300
400
500
600
Binding Energy (eV)
Temperature (oC)
(b)
B-N 190.1 eV
B 1s
12000
Fig. 4. TGA thermograms of h-BN@OH, h-BN@APTMS, and h-BN@c-CD.
10000
8000
6000
4000
2000
0
h-BN@APTMS
h-BN@γ-CD@Cu(OAc)
2
B-O
192.0 eV
194
193
192
191
190
189
188
Binding Energy (eV)
(c)2200
Si 2p
Si-O-B
102.1 eV
2000
1800
1600
1400
1200
102.5 eV
Si-OH
16 20 24 28 32 36 40 44 48 52 56 60 64 68 72
2 θ
Fig. 5. XRD patterns of h-BN@APTMS and h-BN@c-CD@Cu(OAc)2.
Si-C
100.8 eV
1000 103.3 eV
Si-O-Si
800
600
400
of chemical bonding between the BN particles and the silane curing
agent, the Si2p peak can be fitted by a curve with several compo-
nent peaks (Fig. 6c). In the deconvoluted Si2p spectra, the strong
peak at binding energy 102.1 eV represents the bond between
silicon and oxygen originating from the BN particles (B–O–Si), indi-
cating that the surface curing agent and BN particles are connected
through the hydroxyl groups. The peak at 103.3 eV is attributed to
siloxane (Si–O–Si) resulting from the partial hydrolysis of the
silane curing agent molecules during the silanization reaction.
Moreover, the peak at 100.8 eV is attributed to Si–C bonding in
the silane curing agent molecules. These results are in agreement
with the reaction mechanism of silane, including the hydrolysis
of –OCH3, condensation to oligomers, hydrogen bonds between oli-
gomer and hydroxyl groups on the substrate, and the formation of
the covalent linkage between silane and the substrate. The peak at
102.5 eV is attributed to Si–OH bonding, indicating that some
hydroxyl groups did not hydrolyze and a small amount of hydroxyl
group remained [39,40].
106 105 104 103 102 101 100 99 98
Binding Energy (eV)
(d) 12000
934.1 eV
Cu 2p
11000
10000
9000
8000
7000
6000
954.0 eV
970
960
950
940
930
The XPS spectrum of the Cu2p core level region for the h-BN@
-CD@Cu(OAc)2 nanocomposite displays main peaks at 934.1 and
954.0 eV, which can be attributed to the binding energy of
Cu2p3/2 and Cu2p1/2, respectively (Fig. 6d). These values corre-
spond to the Cu(II) binding energies of Cu(OAc)2.
Binding Energy (eV)
c
Fig. 6. Full-range XPS spectra of h-BN@APTMS and h-BN@
c
-CD@Cu(OAc)2 (a), and
the B1s (b), Si2p (c), and Pd3d (d) core-level region XPS spectra of the h-BN@
-CD@Cu(OAc)2 nanocomposite.
c

R. Nie et al. / Journal of Catalysis 344 (2016) 286–292
291
Table 1
Table 2
Optimization of the reaction conditions.a
h-BN@c
-CD@Cu(OAc)2-catalyzed synthesis of 1,4-disubstituted 1,2,3-triazoles.a
Entry R1
R2
Time
(h)b
Products
Yield
Entry
Solvent
Catalyst (equiv.)
T (°C)
Yield (%)b
(%)c
1
2
3
4
5
6
7
8
H2O
0.03
0.03
0.03
0.03
0.03
0.01
0.02
0.04
0
0.03
0.03
0.03
0.03
0.03
25
25
25
25
25
25
25
25
25
40
60
25
25
25
90
85
75
60
50
75
80
90
0
90
90
65
90
90
1
2
C6H5
C6H5
10 + 7
90
H2O:EtOH(1:1)
EtOH
CH3CN
THF
H2O
H2O
H2O
H2O
H2O
H2O
3-CH3-C6H4 C6H5
9 + 7
91
72
9
3
4-C(CH3)3- C6H5
C6H4
13 + 5
10
11
12c
13d
14e
H2O
H2O
H2O
4
5
6
4-OCH3-
C6H4
C6H5
C6H5
C6H5
6 + 4
90
91
71
a
Reaction condition: phenylboronic acid (1.5 mmol), NaN3 (292.5, 4.5 mmol),
phenylacetylene (1.0 mmol), catalyst (the contents of Cu2+
complete.
, 0.03 mmol), until
4-F-C6H4
3-Cl-C6H4
14 + 6
11 + 7
b
Isolated yield.
c
Phenylboronic acid (1.0 mmol), NaN3 (292.5, 1.0 mmol), phenylacetylene
(1.0 mmol).
d
Phenylboronic acid (1.5 mmol), NaN3 (292.5, 1.5 mmol), phenylacetylene
(1.0 mmol).
Phenylboronic acid (1.5 mmol), NaN3 (292.5, 3.0 mmol), phenylacetylene
(1.0 mmol).
e
7
3,5-Cl-C6H3 C6H5
8.5 + 2
20 + 10
4.5 + 2.5
10 + 5
75
88
51
94
8
3,5-CF3-
C6H3
C6H5
9
3-Pyridinyl C6H5
10
C6H5
N-octyl
11
12
C6H5
C6H5
2-
11 + 5
11 + 6
84
87
hydroxyethyl
Fig. 7. Plots of the yield against reuse times for 4a.
Isobutanol
3.3. Catalytic studies
13
C6H5
Aminomethyl 8 + 5
80
At the beginning of our investigation, the syntheses of triazoles
was carried out using phenylboronic acid 1a and phenylacetylene
3a as the prototypical substrate. Solvents played an important role:
When the reaction was performed in water, 90% yield of products
was obtained (Table 1, entry 1), and the use of solvents other than
H2O led to lower yields (Table 1, entries 2–5). Next, we varied the
a
Reaction conditions: phenylboronic acid (1.5 mmol), NaN3 (1.5 mmol), pheny-
lacetylene (1.0 mmol), and catalyst (the contents of Cu2+, 0.03 mmol) for indicated
time.
amount of catalyst and found that 0.03 equiv. of h-BN@c-CD@Cu
b
Time of synthesis for aryl azide and triazoles.
Isolated yield.
c
(OAc)2 gave the best result, and neither larger nor smaller amounts
showed better yields (Table 1, entries 6–8). Moreover, in the
absence of catalyst, no products were detected (Table 1, entry 9).
Encouraged by this result, we further optimized the temperature
of the reaction conditions. When the temperature was increased
to 40 and 60 °C, there was no increment in the yield (Table 1,
entries 10 and 11). With regard to green chemistry, the reaction
was carried out at room temperature. Finally, we searched for
the optimal ratio of the reaction substrate in this reaction and

292
R. Nie et al. / Journal of Catalysis 344 (2016) 286–292
1.5:1.5:1 equivalent weights of 1a, NaN3, and 3a was the best pro-
portion for preparing triazoles (Table 1, entries 12–14). Above all,
phenylacetylene (1 mmol), phenylboronic acid (1.5 mmol), sodium
azide (1.5 mmol), and catalysis 0.03 equivalent in water at room
temperature were considered to be the ideal reaction conditions.
After the optimization of the reaction conditions, we examined
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water, dichlormethane, and acetone until no residual products
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recovered directly under the same reaction conditions.
After it has been reused seven times, there is almost no signif-
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4. Conclusions
We have successfully developed a novel and green heteroge-
neous catalytic system for the multicomponent 1,3-dipolar
cycloaddition reaction using h-BN@c-CD@Cu(OAc)2 as the catalyst.
The h-BN@ -CD@Cu(OAc)2 catalyst showed high catalytic activity
c
in water, offered the corresponding products with good yields,
and had excellent functional group tolerance. Moreover, this cata-
lyst can be separated easily by filtration and used directly in new
reactions after recycling, at least seven times. Therefore, h-BN@
c
-CD@Cu(OAc)2 can serve as a highly active, mild, and
environment-friendly catalyst in the synthesis of the 1,2,3-
triazole derivatives. Further studies of the catalyst are ongoing in
our laboratory to expand its applications to different organic
reactions.
Acknowledgment
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We are grateful for financial support from the National Natural
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jcat.2016.09.022.