Carbon nanospheres with well-controlled nano-morphologies as support for palladium-catalyzed Suzuki coupling reaction

Article abstract of DOI:10.1002/aoc.3741

Uniform carbon nanospheres (UCS) with well-controlled nano-morphologies were fabricated by hydrothermal carbonization of sucrose in the presence of kayexalate. Highly dispersed and ultrafine palladium nanoparticles were supported on the UCS through a facile co-reduction process with NaBH₄ as reducing agent. The obtained Pd@UCS exhibited efficient catalytic activity for the Suzuki coupling reaction. Moreover, the as-prepared catalyst could be recycled and reused at least five times without significant loss of its catalytic activity.

Full text of DOI:10.1002/aoc.3741

Received: 9 November 2016
DOI 10.1002/aoc.3741
Revised: 5 December 2016
Accepted: 23 December 2016
F U L L PA P E R
Carbon nanospheres with well‐controlled nano‐morphologies as
support for palladium‐catalyzed Suzuki coupling reaction
Wenhuan Dong
| Saisai Cheng | Cheng Feng | Ningzhao Shang | Shutao Gao |
Chun Wang | Zhi Wang
College of Science, Agricultural University
of Hebei, Baoding 071001, China
Uniform carbon nanospheres (UCS) with well‐controlled nano‐morphologies were
fabricated by hydrothermal carbonization of sucrose in the presence of kayexalate.
Highly dispersed and ultrafine palladium nanoparticles were supported on the
UCS through a facile co‐reduction process with NaBH4 as reducing agent. The
obtained Pd@UCS exhibited efficient catalytic activity for the Suzuki coupling
reaction. Moreover, the as‐prepared catalyst could be recycled and reused at least
five times without significant loss of its catalytic activity.
Correspondence
Cheng Feng and Chun Wang, College of
Sciences, Agricultural University of Hebei,
Baoding 071001, China.
Email: chunwang69@126.com;
fengchengcctv@163.com
Funding information
Natural Science Foundation of Hebei Prov-
ince, Grant/Award Number: B2016204131.
B2015204003.National Natural Science
Foundation of China, Grant/Award Number:
21603054.
KEYWORDS
biomass, Pd, Suzuki coupling reaction, uniform carbon nanospheres
1 | INTRODUCTION
Carbon nanospheres not only possess the general advan-
tages of carbon supports including high stability in both
Palladium‐catalyzed Suzuki–Miyaura cross‐coupling reac-
tion has been one of the most powerful tools for constructing
unsymmetric biaryl compounds.[1] Over the past few
decades, homogeneous catalytic systems based on Pd have
served as effective strategic tools for organic transformation
and total synthesis.[2] However, the limited availability and
high price of Pd have also become a problem for homoge-
neous catalytic systems. In order to reduce the cost of the cat-
alyst and protect the environment, heterogeneous catalytic
systems, as excellent recyclable systems, have been devel-
oped rapidly in recent years. However, it is well known that
small metal nanoparticles tend to aggregate,[3] which may
reduce their catalytic activity and restrict their practical appli-
cation. In this context, scientists have developed various
materials such as silica,[4] zinc ferrite.[5] metal–organic
frameworks[6] and covalent organic frameworks[7] as sup-
ports for noble metals to address the aggregation problem.
Carbon materials, owing to their special high surface area
and excellent chemical, mechanical and thermal stabilities,[8]
have been widely used as supports in Pd‐catalyzed reactions,
such as fullerene,[9] graphene,[10] carbon nanotubes[11] and
porous carbon.[12]
acidic and basic environments, but also have the potential
to allow selective catalysis in some cases if faster mass trans-
fer and diffusion are performed in the domain of the carbon
nanospheres.[13] Moreover, carbon nanospheres can be sim-
ply prepared by the facile carbonization/activation route via
use of renewable biomass precursors as carbon source.[8b]
These strengths mean that biomass‐derived carbon nano-
spheres are promising, green and environmentally friendly
supports for noble metals. Recently, a carbon nanosphere‐
supported Pt nanocatalyst was synthesized by Zhou and co‐
workers[14] using a facile one‐pot hydrothermal synthesis
with sucrose as carbon source and P123 as stabilizer. The
results showed that the obtained Pt nanocatalyst could
enhance the electrochemical performance for CH3OH
oxidation. Xu and co‐workers[15] immobilized Pd nanoparti-
cles on carbon nanospheres, and the prepared catalyst
provided an average rate of CO‐free H2 generation up to
43 l H2 gPd min−1 and a turnover frequency (TOF) of
−1
7256 h−1 at 60 °C with 100% selective dehydrogenation from
aqueous formic acid. However, there is no report of the use of
carbon nanospheres as support in Pd‐catalyzed Suzuki cross‐
coupling reactions.
Appl Organometal Chem. 2017;e3741.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
1 of 6
https://doi.org/10.1002/aoc.3741

2 of 6
DONG ET AL.
In the work reported herein, uniform size carbon nano-
2.3 | Synthesis of Pd@UCS
spheres (UCS) were prepared via novel and simple hydro-
thermal carbonization (HTC) of sucrose at 180 °C with the
help of kayexalate. After activation in air, UCS possessed a
high surface area of 1346 m2 g−1. Palladium metal nanopar-
ticles were successfully immobilized on UCS by a facile
co‐reduction process. For the first time, the prepared
Pd@UCS was used to catalyze the Suzuki coupling
reaction, with the catalyst exhibiting efficient catalytic
activity for this reaction. Furthermore, it could be
recycled by simple centrifugation and reused at least five
times without significant loss of its catalytic activity. To
the best of our knowledge, this is the first report of
UCS‐supported Pd nanoparticles for the Suzuki coupling
reaction.
UCS (100 mg) was dispersed in 8.335 ml of H2PdCl4
(1 mg ml−1) solution and stirred at room temperature for
12 h. Then, 5 ml of NaBH4 (4 mg ml−1) was added into
the mixture solution drop by drop in 5 min under vigorous
stirring. After 2 h of sustaining stirring, the resulting solid
was washed with water and ethanol two times each. Finally,
the product was dried in vacuum at 60 °C overnight.
2.4 | General Procedure for Suzuki–Miyaura
Reaction
Typically, a mixture of aryl halide (0.5 mmol), phenylboronic
acid (0.75 mmol), solvent (5 ml) and Pd@UCS (2.6 mg,
0.12 mol%) was stirred at 50 °C in a round‐bottom flask for
the desired reaction time. Subsequently, the mixture was
diluted with water (10 ml), and extracted with ethyl acetate
(10 ml) three times. After drying using anhydrous MgSO4,
the product was concentrated by vacuum and purified by
flash chromatography on silica gel with petroleum ether–
ethyl acetate as eluent.
2 | EXPERIMENTAL
2.1 | Materials and Methods
All chemicals were used as received without any purification.
Palladium chloride (PdCl2) and kayexalate were obtained
from Aladdin Reagent Company Limited. Sucrose, sodium
borohydride (NaBH4), ethanol and other reagents were
purchased from Huaxin Co. Ltd (Baoding, China).
2.5 | Recyclability Test
For the recycling test, after the reaction of bromobenzene and
phenylboronic acid was completed, the catalyst was isolated
from the reaction solution by centrifugation and washed with
water, then dried in a vacuum at 60 °C overnight. The dried
catalyst was used again to catalyze the reaction of
bromobenzene and phenylboronic acid.
The morphologies and sizes of samples were observed
using transmission electron microscopy (TEM) with an FEI
Tecnai f20 at 200 kV and scanning electron microscopy
(SEM) with an S‐4800 SEM instrument. X‐ray diffraction
(XRD) patterns were recorded using a Dandong TD‐3500
X‐ray diffractometer with Cu Kα irradiation at 40 kV and
150 mA. Brunauer–Emmett–Teller (BET) surface areas of
samples were measured at 77 K by nitrogen adsorption using
a V‐Sorb 2800 surface area and porosity analyzer. X‐ray
photoelectron spectroscopy (XPS) was performed using a
Thermo ESCALAB 250Xi spectrometer with a monochro-
matic Al Kα X‐ray source at 15 kV. The Pd content was
determined by means of inductively coupled plasma atomic
emission spectroscopy (ICP‐AES) with a Thermo Elemental
IRIS Intrepid II.
3 | RESULTS AND DISCUSSION
The morphologies and sizes of samples were observed using
SEM and TEM. Because of the presence of kayexalate, UCS
with sizes ranging from 50 to 100 nm are obtained by HTC
(Figure 1a,b). From the TEM image of the catalyst
(Figure 1c), it can be seen that highly dispersed Pd
(2–3.5 nm) nanoparticles are immobilized on the surface
of UCS. The Pd content of the catalyst was determined by
means of ICP‐AES, amounting to 2.92%.
Figure 2 shows the XRD patterns of samples. The broad
peak at 24° and weak peak at 45° belong to (002) and
(100) reflections of the graphite‐type lattice, respectively,
which result from UCS. The pattern of Pd@UCS exhibits
peaks at 40.1° and 46.9° arising from Pd. The diffraction
peaks of reused Pd@UCS are similar to those of fresh
Pd@UCS, which demonstrates that the catalyst maintains
its original structure after being used in catalytic reactions.
The presence of Pd metal was further confirmed using
XPS. In Figure 3, the characteristic peaks of Pd 3d3/2 and
2.2 | Synthesis of UCS
In a typical synthesis, 8 g of sucrose and 40 mg of kayexalate
were added into 50 ml of deionized water. After
ultrasonication for 10 min, the mixture was transferred into
a Teflon‐lined stainless steel autoclave, and heated at
180 °C for 8 h. After cooling naturally, the material was
washed with water and ethanol several times, and dried in a
vacuum at 60 °C overnight. The resultant product was
activated in air (0.01 MPa) at 800 °C for 1 h.

DONG ET AL.
3 of 6
FIGURE 2 XRD patterns of UCS, Pd@UCS and recycled Pd@UCS
FIGURE 3 XPS analysis of Pd@UCS
Pd 3d5/2 are seen at 341.3 and 336.1 eV, which could confirm
that Pd on UCS is present in the metallic state. However, the
presence of PdO species is confirmed by the peaks at 337.8
and 343.2 eV, which is probably due to the oxidation of
metallic Pd left in an oxygen‐containing environment.
The N2 adsorption–desorption isotherms of UCS and
Pd@UCS are shown in Figure 4. The BET surface areas of
UCS and Pd@UCS are 1345.7 and 934.6 m2 g−1, respec-
tively. The slight decrease in surface area could be attributed
to the fact that the majority of Pd nanoparticles are supported
on the surface of UCS, and a small number within UCS.
The synthesized Pd@UCS material was investigated as a
catalyst for typical Suzuki–Miyaura carbon–carbon coupling
reaction. In the optimization experimental study, the reaction
FIGURE 1 (a) SEM image of UCS. TEM images of (b) UCS, (c)
Pd@UCS and (d) recycled Pd@UCS (recovered after five recycles)

4 of 6
DONG ET AL.
nanoparticles have a key role in the reaction. The reaction
could be carried out at room temperature; however, the
reaction time is 4 h with a yield of 95% (Table 1, entry 3).
With the reaction temperature increasing to 50 °C, the
reaction can be completed after 1 h with a yield of 99%
(Table 1, entry 4).
It is well known that the base has a great influence on
Suzuki reactions. Various bases including organic and inor-
ganic ones have been considered. The screening experiments
show that K2CO3 as a base affords the coupling product in
the highest yield (99%) at 50 °C in 1 h (Table 1, entries 4–9).
The dosage of Pd@UCS and type of solvent were also
studied, and the results show that 0.12 mol% Pd@UCS is
sufficient to guarantee complete conversion with EtOH–
H2O (5 ml, 3:2 v/v) as the solvent (Table 2, entries 4 and
10–15).
FIGURE 4 N2 adsorption–desorption isotherms of UCS and
With the optimized conditions in hand, the catalytic
activity of Pd@UCS for Suzuki coupling reactions was
investigated with various aryl halides and arylboronic
acids, and the results are summarized in Table 2. High
catalytic activities are observed for bromobenzene and
both electron‐rich and electron‐poor aryl bromide,
affording the corresponding biphenyl compounds in good
yields under the optimized reaction conditions. It is worth
noting that the reaction of 3‐methylbenzeneboronic acid
with bromobenzene needed less reaction time (Table 2,
entry 8) than that of phenylboronic acid, indicating that
benzeneboronic acid containing electron‐donating group is
beneficial for the reaction. However, 2‐methylbenzeneboronic
acid needs a relatively long reaction time, which can be
ascribed to the steric hindrance effect (Table 2, entry 7).
Unfortunately, a low yield was obtained with the reaction of
aryl chloride (Table 2, entry 9) because of the strength of
the C─Cl bond.
In order to evaluate the catalytic activity of the
Pd@UCS catalyst for the reaction of bromobenzene and
phenylboronic acid, it was compared with other reported
Pd catalysts in terms of dosage of catalysts, reaction time
and temperature, yield of product and TOF of the reac-
tion (Table 3). The Pd@UCS catalyst could efficiently
catalyze the Suzuki coupling reaction giving the highest
yield without using any additive and toxic solvent.
The recycling and reusability of the Pd@UCS catalyst
were further investigated because they are very important
characters for heterogeneous catalysts. The reaction of
bromobenzene with phenylboronic acid was carried out
under optimized conditions. It can be seen in Figure 5
that the catalyst maintains high catalytic activity after five
reaction runs, indicating good stability. A TEM image of
the recovered catalyst after five recycles is shown in
Figure 1(d), where there is no aggregation phenomenon
occurring, which demonstrates that the Pd nanoparticles
remain well dispersed after five runs.
Pd@UCS
of phenyl bromide and phenylboronic acid was selected as
a model reaction. As is evident from Table 1, the reaction
does not proceed either when the Pd@UCS catalyst is
absent (Table 1, entry 1) or when pure UCS is used as
catalyst (Table 1, entry 2), which demonstrates that Pd
TABLE 1 Optimization of factors influencing the Suzuki–Miyaura
reaction of bromobenzene with phenylboronic acida
Entry
Solvent
Base
Pd (mol%)
Yield (%)
1b
2c
3d
4
EtOH–H2O (3:2)
EtOH–H2O (3:2)
EtOH–H2O (3:2)
EtOH–H2O (3:2)
EtOH–H2O (3:2)
EtOH–H2O (3:2)
EtOH–H2O (3:2)
EtOH–H2O (3:2)
EtOH–H2O (3:2)
EtOH–H2O (3:2)
EtOH–H2O (3:2)
EtOH–H2O (3:2)
EtOH–H2O (4:1)
EtOH–H2O (1:4)
EtOH–H2O (2:3)
EtOH–H2O (3:2)
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
KOH
—
—
—
95
99
90
10
10
13
10
87
94
99
73
5
—
0.12
0.12
0.12
0.12
0.12
0.12
0.12
0.06
0.09
0.15
0.12
0.12
0.12
0.12
5
6
7
NaOH
Et3N
8
9
NaAc
10
11
12
13
14
15
16e
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
83
83
aReaction conditions: bromobenzene (0.5 mmol), phenylboronic acid
(0.75 mmol), base (1.5 mmol), solvent (5 ml), 50 °C, 1 h.
bIn absence of catalyst.
cCatalyzed by UCS.
d30°C, 6 h.
e0.5 h.

DONG ET AL.
5 of 6
TABLE 2 Suzuki coupling reactions catalyzed by Pd@UCSa
Entry
Aryl halide
Arylboronic acid
Time (h)
Yield (%)
1
1
99
91
94
2
3
2
3
4
5
6
7
3
90
98
96
89
1
1
0.67
8
0.67
98
9
12
4
19
98
10
11
12
4
4
97
90
aReaction conditions: aryl bromide (0.5 mmol), phenylboronic acid (0.75 mmol), K2CO3 (1.5 mmol), EtOH–H2O (3:2, 5 ml) and Pd@UCS (0.12 mol%), 50 °C.
TABLE 3 Suzuki coupling reaction of bromobenzene with phenylboronoic acid catalyzed by various catalysts
Entry
Catalyst
Pd/Nf‐G
Dosage (mol%)
Temp. (°C)
Time (h)
Yield (%)
TON
293.3
TOF (h−1
)
Ref.
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
1
2
3
4
5
6
7
8
9
10
0.3
80
90
3
1
88
95
94
90
59
50
65
90
98
99
97.8
950
Fe3O4@PUNP‐Pd
MOF‐253‐Pd
Pd‐MCM‐41
0.1
950
0.23
0.05
0.054
1.3
100
80
10
12
8
408.7
40.9
1 800
150
Pd/Y‐MOF
80
1 092.6
38.5
136.6
1.6
Pd/PMA‐MIL‐101
Pd@p‐SiO2
130
200
60
24
3
0.003
0.25
0.5
21 666.7
360
7 222.2
720
Pd/UiO‐66‐NH2
Pd/H2P‐Bph‐COF
Pd@UCS
0.5
1.5
1
110
50
196
130.7
825
0.12
825
This study

6 of 6
DONG ET AL.
[4] A. Martínez, J. L. Krinsky, I. Peñafiel, S. Castillón, K. Loponov, A.
Lapkin, C. Godard, C. Claver, Catal. Sci. Technol. 2015, 5, 310.
[5] A. S. Singh, U. B. Patil, J. M. Nagarkar, Catal. Commum. 2013, 35, 11.
[6] (a) M. Zhang, J. Guan, B. Zhang, D. Su, C. T. Williams, C. Liang,
Catal. Lett. 2012, 142, 313. (b) L. Chen, Z. Gao, Y. Li, Catal.
Today 2015, 245, 122.
[7] S. Y. Ding, J. Gao, Q. Wang, Y. Zhang, W. G. Song, C. Y. Su, W.
Wang, J. Am. Chem. Soc. 2011, 133, 19816.
[8] (a) D. Krishnan, K. Raidongia, J. Shao, A. J. Huang, ACS Nano
2014, 8, 449. (b) Y. Fan, P.‐F. Liu, Z.‐J. Yang, T.‐W. Jiang, K.‐L.
Yao, R. Han, X.‐X. Huo, Y.‐Y. Xiong, Electrochim. Acta 2015,
163, 140. (c) A. D. Roberts, X. Li, H. Zhang, Chem. Soc. Rev.
2014, 43, 4341.
[9] H. Veisi, R. Masti, D. Kordestani, M. Safaei, O. Sahin, J. Mol.
Catal. A 2014, 385, 61.
[10] (a) Y. Li, X. Fan, J. Qi, J. Ji, S. Wang, G. Zhang, F. Zhang, Nano
Res. 2010, 3, 429. (b) A. R. Siamaki, A. E. R. S. Khder, V.
Abdelsayed, M. S. El‐Shall, B. F. Gupton, J. Catal. 2011, 279, 1.
FIGURE 5 Recyclability of Pd@UCS for Suzuki reaction
[11] X. Chen, Y. Hou, H. Wang, Y. Cao, J. He, J. Phys, Chem. C 2008,
112, 8172.
4 | CONCLUSIONS
[12] (a) L. Zhang, C. Feng, S. Gao, Z. Wang, C. Wang, Catal. Commun.
2015, 61, 21. (b) L. Zhang, W.‐H. Dong, N.‐Z. Shang, C. Feng,
S.‐T. Gao, C. Wang, Chin. Chem. Lett. 2015. (c) C. Feng, Y.
Hao, L. Zhang, N. Shang, S. Gao, Z. Wang, C. Wang, RSC Adv.
2015, 5, 39878.
In summary, UCS were synthesized using a renewable bio-
mass – sucrose – with HTC and activation methods. The
as‐prepared catalyst, Pd@UCS, showed highly efficient cata-
lytic activity for the Suzuki coupling reaction. Moreover, the
catalyst could be recovered by simple centrifugation and
reused for at least five times without significant loss of its
catalytic activity. The use of UCS as a catalyst support might
bring new opportunities in the development of efficient het-
erogeneous Pd catalysts. Studies aimed at extending the
scope of Pd@UCS to other Pd‐catalyzed reactions are cur-
rently underway in our laboratories.
[13] P. Zhang, Z.‐A. Qiao, S. Dai, Chem. Commun. 2015, 51, 9246.
[14] Y. Yang, L.‐M. Luo, J.‐J. Du, S.‐S. Li, R.‐H. Zhang, Z.‐X. Dai, X.‐
W. Zhou, Int. J. Hydrogen Energy 2016, 41, 12062.
[15] Q. L. Zhu, N. Tsumori, Q. Xu, J. Am. Chem. Soc. 2015, 137, 11743.
[16] S. S. Shendage, U. B. Patil, J. M. Nagarkar, Tetrahedron Lett. 2013,
54, 3457.
[17] J. Yang, D. Wang, W. Liu, X. Zhang, F. Bian, W. Yu, Green Chem.
2013, 15, 3429.
[18] L. Chen, Z. Gao, Y. Li, Catal. Today 2015, 245, 122.
[19] S. Jana, S. Haldar, S. Koner, Tetrahedron Lett. 2009, 50, 4820.
[20] J. Huang, W. Wang, H. Li, ACS Catal. 2013, 3, 1526.
ACKNOWLEDGMENTS
Financial support from the National Natural Science Founda-
tion of China (21603054), the Natural Science Foundation of
Hebei Province (B2015204003, B2016204131), the Young
Top‐notch Talents Foundation of Hebei Provincial Universi-
ties (BJ2016027) and the Natural Science Foundation of
Agricultural University of Hebei (LG201404, ZD201506,
ZD201613) is gratefully acknowledged.
[21] J. Juan‐Alcaniz, J. Ferrando‐Soria, I. Luz, P. Serra‐Crespo, E.
Skupien, V. P. Santos, E. Pardo, F. X. L. Xamena, F. Kapteijn, J.
Gascon, J. Catal. 2013, 307, 295.
[22] J. C. Park, E. Heo, A. Kim, M. Kim, K. H. Park, H. Song, J. Phys.
Chem. C 2011, 115, 15772.
[23] R. Kardanpour, S. Tangestaninejad, V. Mirkhani, M. Moghadam, I.
Mohammadpoor‐Baltork, A. R. Khosropour, F. Zadehahmadi,
J. Organometal. Chem. 2014, 761, 127.
REFERENCES
[24] Y. Hou, X. Zhang, J. Sun, S. Lin, D. Qi, R. Hong, D. Li, X. Xiao, J.
Jiang, Micropor. Mesopor. Mater. 2015, 214, 108.
[1] (a) F. S. Han, Chem. Soc. Rev. 2013, 42, 5270. (b) A. S. Singh, U.
B. Patil, J. M. Nagarkar, Catal. Commun. 2013, 35, 11. (c) W.
Dong, L. Zhang, C. Wang, C. Feng, N. Shang, S. Gao, C. Wang,
RSC Adv. 2016, 6, 37118.
How to cite this article: Dong W, Cheng S, Feng C.
et al. Carbon nanospheres with well‐controlled nano‐
morphologies as support for palladium‐catalyzed
Suzuki coupling reaction. Appl Organometal Chem.
2017;e3741. https://doi.org/10.1002/aoc.3741
[2] Y. Ma, X. Ma, Q. Wang, J. Zhou, Catal. Sci. Technol. 2012, 2,
1879.
[3] (a) M. Zhao, K. Deng, L. He, Y. Liu, G. Li, H. Zhao, Z. Tang,
J. Am. Chem. Soc. 2014, 136, 1738. (b) Z. Dong, X. Le, Y. Liu,
C. Dong, J. Ma, J. Mater. Chem. A 2014, 2, 18775.