Effect of water in fabricating copper nanoparticles onto reduced graphene oxide nanosheets: Application in catalytic ullmann-coupling reactions

Article abstract of DOI:10.1246/BCSJ.20200115

Copper nanoparticles fabricated onto reduced graphene oxide (Cu NPs/rGO) were successfully synthesized via a one-pot dimethylformamide (DMF) reduction approach with an addition of nominal water. This small amount of water can significantly decrease the de

Full text of DOI:10.1246/BCSJ.20200115

Advance Publication Cover Page
Effect of water in fabricating copper nanoparticles onto reduced graphene oxide
nanosheets: application in catalytic Ullmann-coupling reactions
Pattira Suktanarak, Tatsuya Tanaka, Tatsuki Nagata, Ryota Kondo, Takeyuki Suzuki,
Thawatchai Tuntulani, Pannee Leeladee,* and Yasushi Obora*
Advance Publication on the web May 28, 2020
doi:10.1246/bcsj.20200115
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2020 The Chemical Society of Japan
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Publication manuscripts.

Effect of water in fabricating copper nanoparticles onto reduced graphene oxide
nanosheets: application in catalytic Ullmann-coupling reactions
Pattira Suktanarak,1,2,3 Tatsuya Tanaka, Tatsuki Nagata, Ryota Kondo, Takeyuki Suzuki, Thawatchai Tuntulani,
4
4
4
5
2
Pannee Leeladee,*1,2 and Yasushi Obora*4
1Research Group on Materials for Clean Energy Production STAR, Department of Chemistry, Faculty of Science, Chulalongkorn University,
Bangkok 10330, Thailand. E-mail: pannee.l@chula.ac.th
2Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.
3Faculty of Sport and Health Sciences, Thailand National Sports University Lampang Campus, Lampang, 52100, Thailand.
4Department of Chemistry and Materials Engineering, Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita, Osaka
5
64-8680, Japan. E-mail: obora@kansai-u.ac.jp
5Comprehensive Analysis Center, The Institute of Scientific and Industrial Research (ISIR), Osaka University, 8-1 Mihogaoka, Ibaraki,
Osaka 567-0057, Japan.
E-mail: <obora@kansai-u.ac.jp>
Yasushi Obora
Yasushi Obora received Ph.D. degree from Gifu University (1995) and worked as a postdoctoral fellow at Northwestern University (Prof.
Tobin J. Marks). In 1997, he moved to National Institute of Materials and Chemical Research, AIST. He joined the research group of Prof.
Yasushi Tsuji at Hokkaido University as Research Associate and he was appointed to Associate Professor at Kansai University in 2006.
Since 2013, he has been a full Professor at Kansai University. His current research interests include organometallic chemistry and their use
as catalyst in organic reactions.
E-mail: <pannee.l@chula.ac.th>
Pannee Leeladee
Pannee Leeladee received her B.S. degree in chemistry from Chulalongkorn University (2006) and Ph.D. in chemistry under supervision of
Prof. David P. Goldberg from The Johns Hopkins University (2012). Currently, she is an Assistant Professor at Department of Chemistry,
Faculty of Science, Chulalongkorn University. Her research focuses on development of bio-inspired transition metal complexes and
materials for biomedical and energy-related applications.
Abstract
Copper nanoparticles fabricated onto reduced graphene
arylation of 3,5-dimethylphenol with 86% yield and turnover
number of 2,642).
oxide (Cu NPs/rGO) were successfully synthesized via a
one-pot dimethylformamide (DMF) reduction approach with an
addition of the nominal water. This small amount of water can
significantly decrease the degree of GO reduction by DMF. As
a result, the remaining oxygen-containing functionality on rGO
can still interact with the copper cation precursor leading to the
high Cu content fabricated onto the support material, which
was evidenced by X-ray photoelectron spectroscopy (XPS).
Moreover, small particle sizes and high dispersion of Cu NPs
on rGO were confirmed by scanning transmission electron
microscopy (STEM). In addition, our Cu NPs/rGO was
competent to catalyze the Ullmann-coupling reaction (i.e.,
Keywords: Copper nanoparticles fabricated onto
reduced
graphene
oxide,
Effect
of
water,
Ullmann-coupling reaction
1. Introduction
Copper (Cu) is an abundant and low-cost transition metal
that also serves as an active site for various catalytic reactions.
Among an extensive variety of chemical syntheses, Ullmann
condensation for arylation of phenols is one of the attractive
methods for organic transformations because of a wide range of
substrate applicability in polymers, pharmaceutical molecules

and life science industries.1-4 Further extending the advantages
of Cu, copper cations can be fashioned into nanoparticles,
which have unique properties and large surface areas.
Nanoparticles typically exhibit high catalytic activity. However,
they can easily aggregate into larger agglomerates and rapidly
on the rGO and catalytic activity toward the Ullmann-coupling
reaction was also examined.
5
deactivate, especially under harsh reaction conditions.
Recently, a wealth of interdependent research has focused on
6
-9
stabilizing nanoparticles (NPs) with functionalized polymers,
1
0-13
Scheme 1. Synthesis of copper nanoparticles fabricated
onto reduced graphene oxide (Cu NPs/rGO) using a CuCl
2
dendrimers,
inorganic solids (silica, alumina, zeolite,
1
4-20
redox metal (Au)21 and carbonaceous materials.
22-26
etc.),
2
precursor in N,N-Dimethylformamide (DMF)/H O (50/4
v/v).
Graphene oxide (GO) and graphene derivatives are a
current fascinating class of carbon because of their remarkable
and unique chemical, physical and mechanical properties e.g.
high mechanical strength, fast 2D electron-transfer kinetics,
promising chemical and thermal stability and large specific
surface areas, which demonstrate promising use as supports for
2
. Experimental
.1 Materials and methods
All commercially available chemicals and solvents were
2
2
7-32
purchased from Acros Organics, Wako Chemical Co., TCI and
Sigma Aldrich, and used without further purification unless
otherwise stated. For Cu NPs/rGO syntheses and catalytic
activity studies, DMF of high purity grade was purchased from
Wako Chemical Co. Catalytic activity was investigated by GC
coupled to a flame ionization detector (FID) using a 0.22 mm ×
heterogonous catalytic systems.
Furthermore, GO and GO
composites demonstrate high adsorption capacities with metal
ions and have also found use in applications for metal removal
owing to a number of surface functionalized groups and high
3
3-36
specific surface areas.
Hence, GOs are considered to easily
interact with metals, presumably due to the presence of oxygen
functionalities including hydroxyl and epoxide groups, and
therefore, should allow for reasonable fabrication with metal
NPs (M NPs). The syntheses of hybrid materials between M
NPs and graphene-based materials are potentially applicable in
2
5 m capillary column (BP-5). GC-FID response factors for the
products were compared with n-tridecane as an internal
standard. For STEM (JEOL JEM-ARM200F), the Cu NPs/rGO
was dispersed in EtOH and dropped onto a carbon-coated Mo
grid, with imaging performed at an acceleration voltage of 200
kV. IR measurements were recorded using a Thermo Nicolet
6700 FT-IR spectrometer. ICP-AES data was determined using
a Shimadzu ICPS-8100 spectrometer. XPS was recorded using
a ULVAC-PHI PHI5000 VersaProbe instrument with Al K
radiation.
3
7
38-42
numerous fields including energy storage,
medical therapy,
sensors,
4
3,
44
and particularly in catalysis
electrocatalysis45 and chemical catalysis46-50). Hybrid
(
nanocatalysts are likely to offer combined properties of both
homogeneous and heterogeneous catalytic systems—exhibiting
high activity and selectivity of homogeneous catalysts, whilst
2
8
being reusable like heterogeneous catalysts.
Typically, M NPs deposited on graphene sheets are
2
.2 Preparation of GO
4
0
GO was synthesized according to a modified Hammers
synthesized via electrodeposition or chemical reduction
6
2
5,
41, 51
method, , in which graphite powder was chemically oxidized
by KMnO in the presence of NaNO and H SO . In brief,
graphite powder (0.8 g) and NaNO (0.4 g) were suspended in
conc. H SO (25 mL) at 0 C. After being stirred in an ice bath
for 20 min, KMnO (2.45 g) was added to the reaction. The
reaction was allowed to stir for 6 h prior to the addition of
KMnO (2.66 g). Subsequently, another portion of H SO (10
processes in the presence of a reducing agent.
4
3
2
4
N,N-Dimethylformamide (DMF) is well-known for exhibiting
3
high chemical and thermal stability and demonstrates reducing
5
2-55
2
4
properties for the preparation of M NPs
and M NPs/reduced
5
6
4
GO (rGO). In the approach herein, DMF can be substituted
for strong reducing agents, which are hazardous reductants (i.e.
4
2
4
hydrazine, NaBH
4
). Additionally, DMF enhances the stability
mL) was added, and the reaction was further stirred for 18 h.
The crude product was poured into the ice bath in the presence
of M NPs, which prevents the graphene nanosheets from
5
6
aggregating and restacking as a result of - interactions.
of H
product was centrifuged at 4,000 rpm for 10 min and washed
with de-ionized (DI) water, a K HPO /KH PO buffer solution
pH ~7), and again with DI water (×2). The product was dried
2 2
O (30%, 5 mL) and continuously stirred for 1 h. The GO
Challenges associated with improved catalytic activity and
reducing catalyst consumption are to be circumvented if the
hybrid catalyst materials can be designed with high dispersion,
precise particle size control and improved recyclability.
2
4
2
4
(
under vacuum for at least 6 h before further analysis was
conducted.
Nonetheless, oxygen-derived GO functionalities can be
5
7-59
directly reduced to rGO during dispersion in DMF,
which
may result in negatively-charged materials having low
interactions with copper cations, which also negatively impacts
Cu NP deposition onto rGO. Previous reports have attempted to
enhance the interaction upon the addition of a base to
deprotonate, to yield GOs having increased numbers of
2
.3 Preparation of Cu NPs
DMF (50 mL) was pre-heated at 140 C for 5 min before
the addition of CuCl
solution was vigorously stirred at 140 C, 1,500 rpm for 24 h.
The blue CuCl solution turned yellow, which is indicative of
Cu NP formation.
2
2
2H O (0.1 M, 0.5 mL). Thereafter, the
5
,
60
2
negatively-charged oxygen sites.
Similarly, efforts have
been made to decrease the dosage of reducing agents by
dividing the reduction processes into two steps to protect full
6
1
2.4 Synthesis of Cu NPs/rGO
In a typical procedure, GO (40 mg) was dispersed in
DMF (25 mL) by sonication for 3 h. Prior addition of a metal
GO reduction.
Herein, we introduced a new approach to decrease the reducing
power of DMF upon dispersion of GO during Cu NPs/rGO
preparation by addition of a nominal amount of water (Scheme
precursor (CuCl
were added to the mixture solution and pre-heated at 140 C for
min. The solution was vigorously stirred at 1,500 rpm for 24
2
or Cu NPs), and additional DMF (25 mL)
1
). This led to a significant enhancement of the Cu
5
concentration on rGO. The increased number of Cu active sites
retained on the support material resulted in enhanced catalytic
activity and product yield. The correlation of Cu concentration
h. Thereafter, the solvent was removed in vacuo and the
product was washed with MeOH (×3).

To enhance Cu NP deposition onto rGO, the solvent
mixture comprising DMF and a varying nominal amount of
water was employed to study the effect of water in the synthetic
process. First, GO (40 mg) was dispersed in DMF (25 mL) by
sonication for 1 h prior to the addition of a nominal amount of
water (0.5–8 mL). The solution was then sonicated for an
GO,59 and in addition, influence particle dispersion by
improving the GO dispersion in the solvent. Markedly, it was
demonstrated that oxygen functionality on GO can be directly
5
7-59
reduced by DMF, especially, under heating.
This could
lead to an inefficient fabricating Cu NPs onto rGO since
oxygen-containing functional groups on GO play an important
role to absorb the transition metal via non-covalent
additional 2 h. CuCl
pre-heated GO solution (5 min for pre-heating) and stirred at
,500 rpm for 24 h. The solvent was removed in vacuo and the
2
(0.1 M, 0.5 mL) was then added to the
6
3, 64
interaction.
Therefore, we hypothesized that using a
O) may also help to decrease
1
mixture of solvent (i.e. DMF/H
2
product was washed with MeOH (×3).
the degree of GO reduction by DMF, resulting in a higher
copper content deposited on rGO.
The copper loading on rGO was determined by ICP-AES.
The Cu NPs/rGO samples were dispersed in a 3 M HNO
3
From our experimental data, the presence of a nominal
amount of water can improve the Cu deposition on the support
materials. Both XRF and inductively coupled plasma-atomic
emission spectroscopy (ICP-AES) results revealed that the Cu
concentration on the graphene sheets was obviously enhanced
in the presence of a nominal amount of water in DMF. Notably,
28 ppm of Cu on rGO in pure DMF could be increased to 100
solution to extract the copper from the support material prior to
ICP-AES analysis. The ICP-AES data for each sample were
compared with a standard copper solution to obtain correct and
reliable results.
2
.5 Catalytic activity studies toward the Ullmann-coupling
reaction
In a typical reaction, Cu NPs/rGO (1 mg), Cs
2
ppm in 4:50 (v/v) H O/DMF (Fig. 1).
2
3
CO (2
mmol), iodobenzene (1.5 mmol) and 3,5-dimethylphenol (1
mmol) were added into a pressure tube and dispersed in DMF
(
1 mL) by sonication for 10 min. The mixture solution was
deoxygenated under Ar for a 2-3 minutes and then stirred at
10, 120 or 130 C for 24 h. For quantitative analysis, the
1
products were extracted with ethyl acetate, hexane and
n-tridecane as an internal standard prior to GC analysis. TON
values were calculated from the number of moles of the
obtained product per mole of copper active sites on the catalyst.
3
. Results and Discussion
Fig. 1 Quantitative analysis of Cu fabricated on rGO by
inductively coupled plasma-atomic emission spectroscopy. The
3
.1 Fabrication of Cu NPs onto rGO
Initially, Cu NPs deposited on rGO were chemically
Cu NPs/rGO was prepared under various conditions (use of
Cu NPs precursor in DMF, CuCl precursor in DMF and
CuCl precursor in 4:50 (v/v) H O/DMF.
◼
◼
synthesized using a one-pot reduction approach with DMF as a
pure solvent. DMF is demonstrated to play three important
functions including serving as solvent, a reducing agent and a
◼
2
2
2
5
3, 55, 56
stabilizer.
To prepare the efficient fabrication of Cu NPs
and
3
.2 Effect of water on the synthesis of hybrid CuNPs/rGO
materials
To understand the key role of water, structural prediction
of GO, after dispersion in pure DMF or H O/DMF (4:50 (v/v)),
was elucidated from the x-ray photoelectron spectroscopy
XPS) binding energies. The findings determined that the GO
onto rGO, the influence of copper precursor types (CuCl
2
Cu NPs) on the Cu deposition onto rGO was examined. From
the Cu concentration, analyzed by X-ray fluorescence (XRF),
2
the use of CuCl
enhancement of Cu on the rGO, when compared with the Cu
NPs precursor (Fig. S2). However, from naked-eye
2
as a Cu precursor provided a significant
(
a
oxygen functionalities (i.e. hydroxyl, epoxide, carbonyl and
carboxyl) nearly disappeared in the case of pure DMF.
Conversely, the H O/DMF (4:50 (v/v)) system exhibited
2
enhanced oxygen functional groups despite a lesser starting GO
content (Fig. 2). When comparing the carbon/oxygen (C/O)
observation, the solution color after washing the Cu NPs/rGO
product still retained an intense yellow color indicating a low
Cu content fabricated onto the rGO leading to a yellow solution
of free Cu (Cu NPs). Particularly in the case of the Cu NPs
precursor, a more intense yellow color was observed after
washing the product with MeOH, which is in agreement with
XRF and ICP (vide infra) results. Thus, CuCl was appropriate
2
as a Cu precursor for the preparation of Cu NPs/rGO.
From this hypothesis, the higher number of active sites
ratio, the GO dispersed in H
significantly lower ratio than pure DMF (GO C/O = 1.95 in
O/DMF; GO C/O = 5.37 in DMF) suggesting a higher
degree of GO oxygen functional groups in H O/DMF. The
2
O/DMF (4:50 (v/v)) exhibited a
H
2
2
addition of a nominal amount of water appears to hinder DMF
reduction leading to an enhanced concentration of oxygen
functionalities. Increased negatively-charged oxygen functional
groups are likely to interact more strongly with Cu(II) cations,
therefore, enhancing the number of Cu NPs onto rGO. These
findings are consistent with previous studies, which show that
(
Cu NPs), on the support materials are expected to enhance the
catalytic activity and reduce catalyst consumption. The
aforementioned design strategy led to a new idea to improve
the fabrication method. The architecture, shape, size, properties
and functionalization of NPs is influenced by several synthetic
conditions including the starting materials, reaction time,
temperature and solvent. Additionally, varying the ratio of a
5
7-59
GO can be directly reduced to graphene sheets by DMF.
The results also imply that the interaction between the Cu(II)
ions and GO oxygen functional groups might be a key step to
enhance the adhesion of Cu(II) onto GO prior to the DMF
reduction process.
2
mixture of solvents (i.e. DMF/H O) influenced the
6
2
nanostructure, however, there are no reports detailing the
fabrication of active NPs onto support materials via this method.
Herein, the influence of the solvent mixture ratio, between
2
DMF and H O, on the synthesis of such hybrid materials was
investigated. The rationale was that the addition of water may
assist facile exfoliation of the graphite oxide to a monolayer of

Fig. 3 Comparison of the FT-IR spectra of GO (red line) and
Cu NPs/rGO (black line).
The chemical structure of Cu NPs/rGO was further
explored using XPS by identifying the signals from carbon,
oxygen and copper. The narrow XPS spectra (Fig. 4) in the C1s
region exhibited C-C/C=C, C-OH/C-O, C=O and (C=O)-OH
peaks at 284.8, 286.0, 288.1 and 290.0 eV, respectively.
Likewise, the binding energies in the O1s region at 532.3 and
5
32.6 eV, corresponding to oxygen-carbon bonds, were also
observed. The findings may infer that the Cu NPs/rGO
structure still comprises oxygen functionalities despite a lesser
starting GO content. Additionally, data fitting of the Cu 2p3/2
0
and Cu 2p1/2 regions showed Cu and Cu(II) signals at 932.5
and 952.4 eV, and 934.1 and 954.0 eV, respectively.
Nonetheless, both valence states can serve as efficient active
species toward catalytic processes. Furthermore, Cu NPs/rGO
2
prepared under 4:50 (v/v) H O/DMF is observed to exhibit
Fig.
2
X-ray photoelectron spectroscopy (XPS) survey
higher catalytic activity than Cu NPs/rGO prepared under pure
DMF regardless of the presence of a lower Cu /Cu(II) ratio
(vide infra). Consideration should also be given to the
possibility that the number of Cu active sites on the support
material influences the catalysis more than the oxidation state
of Cu.
0
spectrum in the C1s region of: (a) the GO starting material, (b)
GO dispersed in DMF and (c) GO dispersed in 4:50 (v/v)
H
2
O/DMF. Intensity of XPS was reported in counts per second
(CPS).
Although the role of water is important to protect the
oxygen functionalities, an excessive amount inhibits the
reduction of Cu(II) to Cu NPs, which can lead to aggregation of
the Cu NPs to larger agglomerates or deactivation by oxidation.
Varying the H
XRF and ICP-AES results in supporting info). No H
2
O ratio in DMF supports this hypothesis (see
O, or a
2
nominal amount, is observed to yield a yellow solution of Cu
NPs after washing the Cu NPs/rGO product with MeOH, which
thereafter, displays fluorescence properties (NP properties),
while an excessive H
ions).
2
O ratio yields a blue solution (Cu(II)
3
.3 Characterization of the hybrid Cu NPs/rGO materials
Above all, the addition of a suitable H O content in DMF
4:50 (v/v)) successfully improves the fabrication of the hybrid
2
(
Cu NPs/rGO material via a one-pot DMF reduction approach.
Next, Cu NPs/rGO was characterized by various techniques
including IR, XPS and scanning transmission electron
microscopy (STEM).
Fig. 3 shows the IR spectra of the starting GO and Cu
NPs/rGO synthesized under 4:50 (v/v) H
2
O/DMF. The GO
revealed IR vibrations related to oxygen functionalities
−
1
−1
including C-O (1106 cm ), O-H (1231 cm ), C=O (1699
−1
2
−1
cm ) as well as sp -hybridized C=C at ~1500–1600 cm ,
which are consistent with previous works
the intense oxygen vibrational bands at ~1,000 ‒ 1,800 cm
4
7, 60, 65-69
. Conversely,
−1
are weakened in Cu NPs/rGO indicating the incomplete
reduction of GO (reduced graphene oxide form, rGO). Some
oxygen functionalities retained their structures because of the
inhibition for GO to be fabricated with Cu NPs.
Fig. 4 XPS survey spectra of Cu NPs/rGO (synthesized under
4
:50 (v/v) H
2
O/DMF) in the (a) C1s, (b) O1s and (c) Cu 2p1/2
and Cu 2p3/2 regions.

aCu NPs were fabricated onto rGO under 4:50 (v/v) H
utilizing the CuCl precursor.
O/DMF
2
2
b
Cu NPs were fabricated onto rGO under DMF utilizing the Cu
NPs precursor.
c
Cu NPs were fabricated onto rGO under DMF utilizing the
CuCl
2
precursor.
In addition to the observed high dispersion, precise
narrow size distribution and high stability, the number of Cu
active sites (Cu NPs) fabricated onto the support material was
also important to improve catalytic activity. All of the Cu
2
NPs/rGO materials prepared in 4:50 (v/v) H O/DMF exhibited
a higher Cu loading on rGO when compared with the other
reaction conditions, and in addition, provided higher activity
toward the Ullmann-coupling reaction. First, the optimal
catalytic conditions were studied as a function of temperature
Fig. 5 Scanning transmission electron microscopy image of Cu
NPs/rGO exhibiting a high degree of Cu NP dispersion on rGO.
Inset: size distribution histogram indicating an average particle
size of ~3–5 nm.
(110–130 °C), Entries 6–8. The results show that product yield
increased at higher reaction temperatures with the optimum
temperature at 130 C. As shown in Table 1, the catalytic
activity data are in good agreement with the hypothesis that Cu
NPs/rGO prepared in 4:50 (v/v)
2
H O/DMF exhibited
Additionally, STEM observations revealed a narrow and
precise nano-sized distribution of Cu on rGO (~3–5 nm), Fig. 5.
The small particle diameter implied a high specific surface area,
which is a prerequisite for improved catalytic activity. The
results also suggest that the Cu NPs are highly dispersed on
rGO and are not aggregated to larger sizes, resulting in
stabilizing of the Cu NPs with the support material (rGO) and
DMF.
significantly higher efficiency for the catalytic arylation of
phenols than for Cu NPs/rGO prepared in pure DMF in the
presence of the same precursor or the Cu NPs precursor.
Additionally, the data show that the desired product was not
obtained in the absence of any catalyst or in the presence of GO
only, implying an insignificant number of any active sites (Cu),
Entries 1–3.
To further increase the turn over number (TON) and test
the robustness of the Cu NPs/rGO catalyst, the substrate
3
.4 Catalytic activity of copper nanoparticles fabricated onto
(
5
3,5-dimethylphenol and iodobenzene) was increased up to
-fold under the same amount of the Cu NPs/rGO catalysts
prepared in 4:50 (v/v) H O/DMF. The findings show that 86%
reduced graphene oxide (Cu NPs/rGO) toward the
Ullmann-coupling reaction.
2
of the product was still obtained, with TON increased to 2,642
implying the degree of robustness of the Cu NPs/rGO catalysts
prepared in 4:50 (v/v) H
reaction.
2
O/DMF toward the Ullmann-coupling
4
. Conclusion
Table 1 Cu NPs/rGO-catalyzed arylation of phenol1
Herein, a new approach is presented to improve the
fabrication of Cu NPs/rGO upon addition of a nominal amount
of water in DMF via a one-pot DMF reduction approach. Water
decreases the reducing properties of DMF and further protects
the GO oxygen functional groups, which are important for the
adhesion of Cu on rGO. The influence of water content on the
fabrication of Cu NPs on rGO was examined by XRF and
ICP-AES analyses of the Cu concentrations. XPS elucidates the
structural properties of the functional groups of the support and
hybrid materials and provides an explanation for the synthetic
mechanism. Furthermore, Cu NPs/rGO exhibited a narrow and
precise nano-sized distribution (3–5 nm) with highly dispersed
Cu on rGO, as observed by STEM. The analytical data reported
herein demonstrates the successful synthetic approach for Cu
NPs/rGO. Finally, to show an example for practical application
toward Ullmann-coupling reaction, Cu NPs/rGO was
demonstrated to catalyze arylation of 3,5-dimethylphenol with
high yield (86% yield and turnover number = 2,642).
3
4
Entry
Catalyst
Temp.(

C)
Yield (%)
TON
1
2
3
4
5
6
7
8
9
-
130
110
130
110
130
110
120
130
130
110
130
110
130
1
-
GO
1
-
GO
1
-
Cu NPs
17
40
49
57
89
86
8
1662
3866
237
353
549
2642
47
Cu NPs
a
Cu NPs/rGO
Cu NPs/rGO
Cu NPs/rGO
Cu NPs/rGO
Cu NPs/rGO
Cu NPs/rGO
Cu NPs/rGO
Cu NPs/rGO
a
a
a,2
b
1
1
1
1
0
1
2
3
b
21
33
68
135
214
428
c
c
1Reaction conditions: 3,5-dimethylphenol (1 mmol),
iodobenzene (1.5 mmol), Cs CO (2 mmol), catalysts: Cu
2
3
NPs/rGO or GO (1 mg/1 mL DMF) or Cu NPs (0.1 mM, 1mL),
reactions were performed under heating for 24 h.
Reaction conditions: 3,5-dimethylphenol (5 mmol),
Acknowledgement
We thank the members of the Comprehensive Analysis
Center, SANKEN (ISIR), Osaka University, for TEM analyses.
P. S. gratefully acknowledges Ratchadapisek Somphot Fund,
Chulalongkorn University for Postdoctoral Fellowship. P. L.
thanks the Asahi Glass Foundation for partially supported this
research.
2
2 3
iodobenzene (7.5 mmol), Cs CO (10 mmol), catalysts: Cu
NPs/rGO (1 mg/1 mL DMF), reactions were performed under
heating for 24 h.
3
Quantitative product analysis by GC.
TON = turnover number.
4

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