Synthesis of DMF-protected Au NPs with different size distributions and their catalytic performance in the Ullmann homocoupling of aryl iodides

Article abstract of DOI:10.1039/c4dt01856g

DMF-stabilized Au nanoparticles (NPs) with three different particle sizes were prepared by controlling the reaction temperatures and times. In the absence of any additional ligands, these Au NPs showed high catalytic activity in the Ullmann homocoupling of aryl iodides in DMF. The effects of Au particle size on the coupling reaction were investigated by the use of three Au catalysts with mean particle sizes of ca. 1.0 nm, 2.5 nm, and 5.5 nm, respectively. The catalytic activity of the Au NPs was found to be in the order of Au (2.5 nm) > Au (<1.0 nm) > Au (5.5 nm), indicating that surface Au atoms do not have the same catalytic activity toward such a homocoupling reaction.

Full text of DOI:10.1039/c4dt01856g

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Synthesis of DMF-protected Au NPs with different
size distributions and their catalytic performance
in the Ullmann homocoupling of aryl iodides†
Cite this: Dalton Trans., 2014, 43,
15752
a
a
a
a
a
Wang Yao, Wei-Jie Gong, Hong-Xi Li,* Fei-Long Li, Jun Gao and
a,b
Jian-Ping Lang*
DMF-stabilized Au nanoparticles (NPs) with three different particle sizes were prepared by controlling the
reaction temperatures and times. In the absence of any additional ligands, these Au NPs showed high
catalytic activity in the Ullmann homocoupling of aryl iodides in DMF. The effects of Au particle size on
the coupling reaction were investigated by the use of three Au catalysts with mean particle sizes of ca.
Received 21st June 2014,
Accepted 18th August 2014
1
.0 nm, 2.5 nm, and 5.5 nm, respectively. The catalytic activity of the Au NPs was found to be in the order
DOI: 10.1039/c4dt01856g
of Au (2.5 nm) > Au (<1.0 nm) > Au (5.5 nm), indicating that surface Au atoms do not have the same cataly-
tic activity toward such a homocoupling reaction.
www.rsc.org/dalton
1
4
reaction. These auxiliary stabilizers play an important role in
preventing aggregation of the metal NPs and controlling the
Introduction
Biaryl compounds play a major role in industrial production concentration of active catalytic species, but increase the com-
1
15
and pharmaceutical synthesis. To date, transition metal-cata- plexity of the reaction system and the cost. To this end, the
lyzed coupling reaction of aryl halides is one of the most development of a simple and environmentally benign metal
2
efficient and powerful methods for the synthesis of biaryls.
NP catalyst without any additional coating agents for such C–C
The copper-mediated Ullmann homocoupling reactions of aryl bond formations would be necessary. N,N-Dimethylformamide
halides have some potential limitations because these reac- (DMF) is well known as a solvent with polarity and a wide solu-
tions need high temperatures (over 200 °C) and the consump- bility range for both organic and inorganic compounds. In
3
16
tion of a stoichiometric amount of copper salt. In the past addition, DMF also acts as a reducing agent in wet chemical
4
5
6
decades, palladium, nickel and other metal catalysts
bearing various N-, O- or P-donor ligands could catalyze DMF has been used to reduce Ag , Ni , Co , Cu ,
Ullmann homocoupling reactions of aryl halides under mild Pd , Pt , and Au
synthesis of metal NPs. In recent years, initiated by Marzán,
+
17
2+
2+ 18
2+ 19
2
+ 20
2+ 21
3+ 22
ions into the corresponding metal
conditions. But these coupling reactions need additional redu- NPs at the appropriate temperatures. Moreover, Cu and Pd
4
h
cing agents such as poly(ethylene glycol) (PEG), tetrakis(di- NPs stabilized by DMF showed high catalytic activities in the
4
i
4j
19,20
methylamino)ethylene (TDAE),
glucose
or
a
fluoride coupling reactions.
Gold NPs stabilized by thiolate
4
k
23
24
reagent. In recent years, metal nanoparticles (NPs) in the ligands and phosphine ligands have also displayed high
presence of auxiliary stabilizers such as surfactants, functio- catalytic activity towards various organic reactions. However, to
nalized polymers, inorganic solids or organic ligands have our knowledge, the catalytic activity of DMF-protected Au NPs
7
8
9
10
been proven to be effective catalysts for organic transform- in the coupling reactions has not yet been explored.
1
1
ations such as the Ullmann coupling reaction, Heck reac-
Furthermore, the particle size of metal NPs plays an impor-
1
2
8c,13
25
tion,
Suzuki–Miyaura reaction,
and Sonogashira tant role in determining their catalytic activity. For example,
El-Sayed et al. investigated the effects of particle size on the
catalytic Suzuki–Miyaura reaction over PVP-Pd (PVP = poly-
2
5e
a
vinylpyrrolidone) nanocatalysts and found that the catalytic
activity of the Pd NPs towards this reaction followed the order
of Pd (3.9 nm) > Pd (3.0 nm) ≈ Pd (5.2 nm) > Pd (6.6 nm).
Thus, the synthesis of gold NPs with various precise particle
sizes is of major importance. Up to now, the size of reported
College of Chemistry, Chemical Engineering and Materials Science, Soochow
University, Suzhou 215123, People’s Republic of China. E-mail: jplang@suda.edu.cn;
Fax: +86 512 65880328; Tel: +86 512 65882865
b
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, Shanghai 200032, People’s Republic of
China
†
2
2a
1
13
DMF-stabilized Au NPs is less than 1 nm. In this article, we
report the synthesis of DMF-stabilized Au NPs with three par-
Electronic supplementary information (ESI) available: H and C NMR Spectra
of homocoupling products. See DOI: 10.1039/c4dt01856g
15752 | Dalton Trans., 2014, 43, 15752–15759
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
ticle sizes (<1 nm, 2.5 nm, and 5.5 nm diameter), which
showed high catalytic activity in the Ullmann homocoupling of
aryl iodides. The Au NPs of 2.5 nm diameter exhibit an excel-
lent catalytic performance for such a coupling reaction.
Results and discussion
Synthesis and characterization of DMF-protected Au NPs
The DMF-protected Au NPs of less than 1 nm in diameter were
2
2a
prepared according to the literature method.
.1 M aqueous HAuCl (150 μL) was added to preheated DMF
5 mL, 140 °C). The mixture was refluxed for 6 h at 140 °C with
A solution of
0
(
4
Fig. 3 TEM images and the corresponding particle size distribution his-
tograms of Au NPs 2 (a, c) and Au NPs 3 (d, f). HRTEM images of a single
Au NP 2 (b) and Au NP 3 (e).
vigorous stirring. The resulting yellow solution contained
photoluminescent Au NPs 1. The DMF background was elimi-
nated before each fluorescence measurement. The DMF solu-
tion of HAuCl4 did not show any luminescence upon
excitation at 200–400 nm. Upon excitation at 380 nm, Au NPs 1
exhibited strong photoluminescence with emission maxima at
around 465 nm (Fig. 1a), which was very similar to that of the
resulting gold nanoparticles (Au NPs 1) was below 1 nm, which
22
is similar to that of the reported ones.
It has been reported that higher reaction temperatures can
27
enlarge the size of nanoparticles. When the reaction temp-
2
2a
reported Au nanoclusters (smaller than
1
nm).
We
erature was close to the boiling point of DMF, the DMF mole-
cules were desorbed from the surface of Au NPs, thereby
inducing the growth of particles. Thus, a similar reaction was
carried out at 150 °C for 2 h to produce Au NPs 2. No signal of
a SPR band at about 520 nm is observed according to the UV-
vis spectrum (Fig. 2b). Upon excitation at 380 nm, the DMF
solution of Au NPs 2 exhibited strong photoluminescence with
an emission maxima at 475 nm (Fig. 1b), which was red-
shifted relative to that of the Au NPs 1. This implied that the
attempted to obtain an image of Au NPs 1 through high-resolu-
tion transmission electron microscopy (HRTEM). Unfortu-
nately, no ideal result was obtained, which may be due to the
fact that 1 was too small to be detected. The UV-vis spectrum
(
Fig. 2a) showed no surface plasmon resonance (SPR) band in
2
6
the range of 500–550 nm, suggesting that the size of the
2
8
size of Au NPs 2 may be larger than that of Au NPs 1. The
HRTEM image of the Au NPs 2 showed gold nanoparticles of
approximately 2.5 nm in size (Fig. 3a and 3c). The lattice
fringes of the as-prepared Au NPs are consistent with metallic
gold having a discerned lattice spacing of 2.37 Å (Fig. 3b),
which corresponds to the d-spacing of the (111) crystal plane
2
9
of fcc Au.
To further explore the temperature effects, the reaction was
carried out at 160 °C to obtain larger Au NPs. Unfortunately, a
Fig. 1 Normalized fluorescence spectra of as-prepared Au NPs 1 (a)
and Au NPs 2 (b). Inset to (b): photograph of the fluorescence of the Au large amount of gold metal was precipitated out of the solu-
NPs 2 under ambient light (left) and UV light of 365 nm (right).
tion (Fig. S1†), which indicates that the formation of gold
metal began at 160 °C and the DMF-protected Au NPs were
2
2a
stable up to about 150 °C.
Extending the reaction time was
also a useful method to generate large Au NPs. Thus, we pro-
longed the refluxing time to 8 h at 150 °C. The resulting dark
yellow solution of Au NPs 3 exhibited no photoluminescence
under the UV light with a wavelength of 365 nm. Its UV-visible
spectrum (Fig. 2c) showed the SPR band at 521 nm, which
means that the size of the Au NPs 3 was larger than that of the
Au NPs 2. The TEM image (Fig. 3d) showed a homogeneous
distribution of Au nanoparticles with an average particle size
of 5.5 nm (Fig. 3f). The HRTEM (Fig. 3e) image revealed a
typical lattice of gold with a d-spacing of 2.36 Å, corresponding
29
to the (111) plane of Au. The XPS Au (4f7/2) spectra of the
dried Au NPs 1, 2 and 3 are shown in Fig. 4. Their main peaks,
located at 85.0 eV, 84.7 eV and 84.5 eV, respectively, were of
Fig. 2 The UV-vis absorption spectra of solutions containing Au NPs 1
(
a), Au NPs 2 (b) and Au NPs 3 (c).
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 15752–15759 | 15753

View Article Online
Paper
Dalton Transactions
Table 1 Optimization of reaction conditions for the Ullmann homo-
a
coupling of aryl iodides catalyzed by DMF-protected Au NPs
Cat.
loading
(mol%) Solvent
Fig. 4 XPS Au (4f2/7) spectra of Au NPs 1 (a), Au NPs 2 (b) and Au NPs 3
b
Yield
T/°C (%)
(
c).
Entry Cat.
Base
1
2
3
4
5
6
7
8
9
1
1
1
Au NPs 1
3
3
3
3
3
3
3
3
3
5
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
NMP
Toluene
THF
K
K
K
Na
Na
Cs
Li
K
K
K
K
K
K
K
K
K
K
2
2
2
CO
CO
CO
3
130
130
130
130
130
130
130
130
130
130
130
120
110
140
130
130
130
34
43
25
28
39
30
n.r.
46
57
90
89
80
46
91
73
12
n.r.
Au NPs 2
Au NPs 3
Au NPs 2
Au NPs 2
Au NPs 2
Au NPs 2
Au NPs 2
Au NPs 2
Au NPs 2
3
higher binding energy than that of bulk Au (83.9 eV), and were
of lower binding energy than that of Au (87.3 eV). The peaks
in the XPS spectra seem asymmetric, which may be caused by
3
3
+
CO
2 3
3
PO
4
0
+
30
2
CO
CO
3
Au NPs coupled with the superficial Au ion. Furthermore,
it is known that the binding energy of metal nanoparticles
2
3
3
PO
PO
PO
PO
PO
PO
PO
PO
PO
PO
4
4
4
4
4
4
4
4
4
4
2
·3H O
3
1
increases with the decrease in size, which is in agreement
with our results described above (Fig. 4). Au NPs 1–3 are
further confirmed by powder X-ray diffraction (PXRD)
3
3
3
3
3
3
3
3
3
0
1
2
Au NPs 2 10
Au NPs 2
Au NPs 2
Au NPs 2
Au NPs 2
Au NPs 2
Au NPs 2
5
5
5
5
5
5
(
(
Fig. S3†). All of the diffraction peaks could be indexed to Au 13
1
1
1
4
5
6
JCPDS, 04-0784), which revealed the formation of monodis-
persed Au NPs. The lattice constants of the three kinds of Au
1
7b
NPs were very similar.
Ullmann homocoupling of aryl iodides catalyzed by DMF-
17
a
Reaction conditions: iodobenzene (0.2 mmol), base (0.4 mmol),
protected Au NPs. As mentioned above, the (111) planes of Au solvent (2 ml) and each catalyst was stirred at reflux temperature
b
(
130 °C for DMF) for 48 h. GC yield. n.r. = no reaction.
NPs 2 and 3 were demonstrated to be an active catalytic site for
many reactions since the low index plane (111) has low surface
3
2
energy. To examine the catalytic activity of Au NPs 1–3
towards the Ullmann homocoupling reaction of aryl iodides, from 57% to 90% when the catalyst loading was changed from
each (3 mol%) is mixed with phenyl iodide (0.2 mmol) and 3 mol% to 5 mol% in DMF at 130 °C (entry 10). However,
K CO (0.4 mmol) in DMF (2 mL) at 130 °C for 48 h (Table 1, when the catalyst loading for this reaction was increased from
2 3
entries 1–3). A standard work-up produced the desired biphe- 5 mol% to 10 mol%, the yield of 5a was not improved (entry
nyl product in 34%, 43% and 25% yield, respectively. These 11). The reaction temperature usually exerts a great impact on
preliminary results revealed that the homocoupling reaction of such a coupling reaction. At lower temperatures (120 °C or
aryl iodides might be efficiently catalyzed by DMF-protected 110 °C), the reaction afforded the product 5a in lower yields
Au NPs and the catalytic activity of the gold nanoparticles (entries 12, 13) while at the higher reaction temperature
decreased in the order of Au NPs 2 (2.5 nm) > Au NPs 1 (140 °C) the yield of 5a was enhanced. For the solvents used,
(<1.0 nm) > Au NPs 3 (5.5 nm). In general, the catalytic activity the Au NPs 2 catalyst worked the best in DMF (Table 1, entry
increases with the decrease of the particle size because the 10), while it gave a relatively bad performance in other solvents
low-coordination number vertex and edge atoms on the par- such as NMP and toluene and did not work in THF. Thus, the
3
3
ticle surface are active sites for coupling reactions. However, optimized reaction conditions were fixed to be 5 mol% of Au
it is Au NPs 2 (2.5 nm) not Au NPs 1 (<1.0 nm) which exhibit NPs 2, K PO as a base at 130 °C in DMF.
3
4
the highest catalytic activity in our catalytic systems. Compared
with the Au NPs 2 (2.5 nm), the smaller metal particles scope of the reaction and found that a variety of functional
<1.0 nm) absorbed the reaction intermediates more strongly, groups could be tolerated for aryl iodides including methyl,
which may poison the reaction and reduce the catalytic activi- methoxyl, bromide, chloride, carbonyl, cyano and nitryl
With the optimized conditions in hand, we examined the
(
2
5e,34
ty.
Therefore, 2.5 nm Au NPs 2 and iodobenzene were groups. As shown in Table 2, the coupling reactions were per-
chosen as a model system to optimize the reaction conditions formed well for all the substrates examined, and the desired
such as bases, solvents, catalyst loadings, and temperatures. products were isolated in moderate to excellent yields. It
We employed various bases such as K
2
CO
3
, Na
2
CO
3
, Na
3
PO
4
,
appeared that the steric hindrance of aryl iodides affected the
Cs CO , Li CO , K PO ·3H O and K PO for this homo- catalytic activity of the homocoupling reaction. The homocou-
2
3
2
3
3
4
2
3
4
coupling reaction. It seemed that K
3
PO
4
was the best one for pling reaction of 1-iodo-4-methoxybenzene afforded 4,4′-
this reaction with 3 mol% Au NPs 2 in DMF (Table 1, entry 9). dimethoxy-1,1′-biphenyl in 85% yield. However, the reaction of
The yield using K PO ·3H O (entry 8) as a base was lower than 1-iodo-3-methoxybenzene or 1-iodo-2-methoxybenzene pro-
3
4
2
that using K
pling reaction was sensitive to H
also affect the product yield. The yield of 5a was increased yield; entry 5) in lower yields. The electronic nature of substitu-
3 4
PO (entry 9). This indicated that the homocou- duced the corresponding products 3,3′-dimethoxy-1,1′-biphe-
4
c
2
O. The catalyst loading may nyl (63% yield; entry 4) and 2,2′-dimethoxy-1,1′-biphenyl (43%
15754 | Dalton Trans., 2014, 43, 15752–15759
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Table 2 Ullmann homocoupling of various aryl iodides using the DMF- ents on the aryl iodides might also influence the yields of the
a
protected Au NPs 2
coupling products. The electron-deficient substituted aryl
iodides were found to proceed in higher yields than those with
b
Entry
1
Aryl iodide
Product
Yield (%)
electron-donating substituent groups. For example, higher
yields (entries 6 and 7) were obtained for 1-chloro-4-iodoben-
zene and 1-bromo-4-iodobenzene relative to 1-iodo-4-methyl-
benzene and 1-iodo-4-methoxybenzene (entries 2 and 3).
These results were consistent with those obtained by Au-cata-
91
2
3
4
88
85
63
4
a
lyzed homocoupling reactions reported previously. The reac-
tions of heterocycle iodide-like 2-iodopyridine gave the
corresponding product in a good yield (50% yield; entry 13).
Encouraged by the high efficiency for the reactions of aryl
iodides described above, we also examined whether the cata-
lyst system worked well with aryl bromides. Surprisingly, reac-
tion of bromobenzene in the presence of 5 mol% catalyst was
rather reluctant. Table 3 lists a comparison of the results for
the homocoupling reactions using different catalysts. Com-
5
43
6
7
8
9
95
93
59
90
parative runs with Cu (82% yield), CuI–PEt
Ni(cod) (71% yield), Ni powder (73% yield), In (78% yield)
CoBr (67% yield), Pd(dba) (86% yield) and Pd/C (85.8% yield)
3
(66% yield),
2
2
2
indicated that Au NPs 2 exhibited a better catalytic perform-
ance (91% yield). In the presence of reducing agents such as
hydroquinone and PEG (Table 3, entries 7 and 8), some Pd cat-
alysts showed higher activity than that of the Au NPs 2.
Reusability of catalyst. The reusability of the Au NP 2 cata-
lyst was examined under the optimized conditions using iodo-
benzene as the model substrate in the Ullmann homocoupling
reaction. As shown in Table 4, the homocoupling reaction of
1
1
1
0
1
2
94
96
15
4a with 5 mol% catalyst loading formed 1,1′-biphenyl 5a in
91% yield. After the completion of the first cycle, the organic
product and the catalyst were separated. The isolated catalyst
Au NPs 2 was used for catalyzing the second cycle by adding 4a
1
1
3
4
50
3 4
and K PO . This catalyst still exhibited activity in the homo-
coupling reaction of iodobenzene (Table 4, entry 2). The cataly-
tic activity went down gradually with the increase of reaction
cycles (Table 4, entries 3–5), which may be ascribed to the loss
of Au NPs, which are being absorbed by the base. After the
fifth cycle, the remaining Au NP catalyst was directly employed
to prepare the samples for TEM. As shown in Fig. S2,† aggrega-
Trace
a
Reaction conditions: iodobenzene (1 mmol), base (2 mmol), DMF
(
5 mL) and catalyst (5 mol%) was stirred at reflux temperature (130 °C
b
for DMF) for 48 hours. Isolated yield.
Table 3 Catalytic characteristics of conventional catalysts for the Ullmann homocoupling of iodobenzene
a
Entry
Cat.
Cat. loading (mol%)
Addition
Solvent
Yield (%)
Ref.
1
2
3
4
5
6
7
8
9
Cu
CuI–PEt
Ni(cod)
Ni powder
Pd(dba)
Pd/C
Pd(OAc)
Pd(OAc)
Pd(dppf)Cl
Indium metal
CoBr
Zn
Au NPs 2
>100
200
≈50
67
10
5
2–4
2
10
100
10
100
5
—
—
82
66
71
73
86
85.8
96
95
3c
3d
5d
5e
4k
4d
4a
4h
4g
6a
6d
6b
3
Lithium naphthalide
—
KI
TBAF
Ethanol
As(o-tol)
PEG4000
—
—
Mn, C
DME
DMF
DMF
DMF
DMSO
DMA
—
DMSO
—
CH
2
2
b
2
3
, hydroquinone
2
b
2
96.7
10
11
12
13
78
67
96
91
2
3
H
5
Cl
3
CN
HCOONH
—
4
MeOH
DMF
This work
a
b
Isolated yield. GC yield.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 15752–15759 | 15755

View Article Online
Paper
Dalton Transactions
Table 4 Recyclability studies on the Ullmann homocoupling of iodo- HITACHI HT-7700 electron microscope operating at 120 kV.
a
benzene using DMF-protected Au NPs 2
High-resolution transmission electron microscopy (HRTEM)
was performed on a FEI Tecnai G20 (USA) electron microscope
b
Cycle
Yield (%)
operating at 200 kV. X-ray photoelectron spectra (XPS) were
recorded with an X-ray photoelectron spectrometer (AXIS Ultra
DLD, USA). The binding energies were referenced to C 1s at
1
2
3
4
5
91
83
75
61
43
284.6 eV from hydrocarbon to compensate for the charging
effect. Powder X-ray diffraction (PXRD) patterns were recorded
on an X’Pert PRO SUPERrA rotation anode X-ray diffractometer
with Ni-filtered Cu-Kα radiation (λ = 1.5418 Å).
a
Reaction conditions iodobenzene (1 mmol), K
3
PO
4
(2 mmol), DMF
(
5 mL) and catalyst (5 mol%) were stirred at reflux temperature (130 °C
b
for DMF) for 72 hours. Isolated yield.
Preparation of Au NPs (1) (less than 1 nm). A solution of
4
150 μL of 0.1 M aqueous HAuCl was added to 5 mL of DMF
that was preheated to 140 °C. The resulting DMF solution was
refluxed by simply heating with vigorous stirring for 6 h. The
as-prepared gold nanoparticles were dispersed in DMF.
Preparation of Au NPs (2) (2.5 nm). A solution of 150 μL of
tion of the Au NPs was not observed, which indicated that the
DMF-protected Au NPs were stable during the reaction. Cata-
lyst deactivation was witnessed during each run, which was
consistent with other metal NP catalysts reported in the litera-
0
.1 M HAuCl dissolved in DMF was added to 5 mL of DMF
4
j,6c,11f
4
ture.
of iodobenzene, the product yields decreased gradually from
4% (initial run) to 21% (the fourth cycle) as the number of
When Pd NPs catalysed the homocoupling reaction
that was preheated to 150 °C. The resulting DMF solution was
refluxed by simply heating with vigorous stirring for 2 h. The
DMF-protected Au NPs were dispersed in DMF.
6
c
9
cycles increased.
Preparation of Au NPs (3) (5.5 nm). A solution of 150 μL of
4
0.1 M HAuCl dissolved in DMF was added to 5 mL of DMF
that was preheated to 150 °C. The resulting DMF solution was
refluxed by simply heating with vigorous stirring for 8 h. The
DMF-protected Au NPs were dispersed in DMF.
Conclusions
In summary, we have demonstrated a DMF reduction method
for the synthesis of DMF-protected Au NPs. The size of the Au
NPs could be controlled through changing the reaction temp-
eratures and reaction times. These Au NPs can be used as an
efficient catalyst for the Ullmann homocoupling reaction of
aryl iodides without addition of any other organic ligand.
Among these Au NPs, the 2.5 nm Au NPs showed the highest
catalytic activity. In this catalytic coupling reaction, DMF
behaved as an interesting multi-functional molecule and
served as a stabilizer, a reductant, and a reaction solvent. This
approach could also tolerate a variety of functional groups and
the catalytic system could be reused several times. The DMF-
stabilized Au NPs may be applied to catalyse other organic
reactions like C–H activation. Studies in this area are under
way in our laboratory.
Typical procedure for the Ullmann homocoupling reactions
(
Table 2, entry 1). A mixture containing iodobenzene
(
1 mmol), Au NPs (5 mol%), K PO (2 mmol), and DMF (5 mL)
3
4
was loaded into a 25 mL round bottomed flask. The mixture was
stirred at 130 °C for 48 h in air. Then, it was cooled to ambient
temperature, and extracted three times with diethyl ether (3 ×
1
1
5 mL). The combined organic layer was washed with brine (3 ×
5 mL), dried over anhydrous Na SO and concentrated under
2
4
reduced pressure. The crude product was purified by flash
column chromatography using petroleum ether as the eluent.
1
Biphenyl: white solid; H NMR (CDCl
3
, ppm, 400 Hz):
δ 7.59–7.57 (d, 4H, J = 8.0 Hz, aromatic CH), 7.44–7.40 (t, 4H,
1
3
aromatic CH), 7.34–7.31 (t, 2H, aromatic CH). C NMR
(
CDCl
,4′-Dimethyl-biphenyl: white solid; H NMR (CDCl
00 Hz): δ 7.52–7.50 (d, 4H, J = 8.0 Hz, aromatic CH), 7.28–7.26
3
, ppm, 100 MHz): 141.4, 128.9, 127.4, 127.3.
1
4
3
, ppm,
4
1
3
(
(
d, 4H, J = 8.0 Hz, aromatic CH), 2.42 (s, 6H, CH
CDCl , ppm, 100 MHz): 138.3, 136.7, 129.4, 126.8, 21.1.
,4′-Dimethoxy-biphenyl: white solid; H NMR (CDCl , ppm,
3
). C NMR
Experimental section
General procedures
3
1
4
3
All solvents and HAuCl
Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). (d, 4H, J = 8.0 Hz, aromatic CH), 3.84 (s, 6H, CH
Other reagents were obtained from TCI and J & K and were used (CDCl , ppm, 100 MHz): 158.7, 133.5, 127.7, 114.1, 55.3.
4 2
·4H O (99.9%) were obtained from 400 Hz): δ 7.48–7.46 (d, 4H, J = 8.0 Hz, aromatic CH), 6.96–6.94
1
3
3
). C NMR
3
1
13
1
without further purification. The H and C NMR spectra
3,3′-Dimethoxy-biphenyl: pale yellow oil liquid; H NMR
, ppm, 400 Hz): δ 7.39–7.35 (t, 2H, aromatic CH),
were recorded at ambient temperature on a Varian UNITYplus- (CDCl
3
1
13
4
00 spectrometer. The H and C NMR chemical shifts were 7.21–7.19 (d, 2H, J = 8.0 Hz, aromatic CH), 7.15 (s, 2H, aro-
referenced to the solvent signal in CDCl . UV-vis absorption matic CH), 6.93–6.91 (d, 2H, J = 8.0 Hz, aromatic CH), 3.87 (s,
spectra were obtained using HITACHI U-2810 spectrometer 6H, CH
with 1 cm optical path length. Fluorescence emission spectra 129.7, 119.7, 112.9, 112.8, 55.3.
were measured on a Varian Cary Eclipse fluorescence spectro- 2,2′-Dimethoxy-biphenyl: white solid; H NMR (CDCl
3
1
3
3
3
). C NMR (CDCl , ppm, 100 MHz): 159.9, 142.6,
1
3
,
photometer equipped with a continuous xenon lamp. Trans- ppm, 400 Hz): δ 7.38–7.34 (t, 2H, aromatic CH), 7.29–7.27 (d,
mission electron microscopy (TEM) was performed on a 2H, J = 8.0 Hz, aromatic CH), 7.06–7.00 (m, 4H, aromatic CH),
15756 | Dalton Trans., 2014, 43, 15752–15759
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
1
3
3
1
.81 (s, 6H, CH
3
). C NMR (CDCl
3
, ppm, 100 MHz): 157.05,
2 (a) N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457;
(b) C. Amatore and A. Jutand, Acc. Chem. Res., 2000, 33,
314; (c) D. Alberico, M. E. Scott and M. Lautens, Chem.
Rev., 2007, 107, 174; (d) K. Huang, C. L. Sun and Z. J. Shi,
Chem. Soc. Rev., 2011, 40, 2435; (e) F. S. Han, Chem. Soc.
Rev., 2013, 42, 5270; (f) S. C. Matthew, B. W. Glasspoole,
P. Eisenberger and C. M. Crudden, J. Am. Chem. Soc., 2014,
136, 5828.
3 (a) F. Ullmann and J. Bielecki, Chem. Ber., 1901, 34,
2174; (b) A. P. Degnan and A. I. Meyers, J. Am. Chem.
Soc., 1999, 121, 2762; (c) F. Ullmann, G. M. Meyer,
O. Loewenthal and E. Gilli, Liebigs Ann. Chem., 1972,
41, 1046; (d) G. W. Ebert and R. D. Rieke, J. Org.
Chem., 1988, 53, 4482.
31.48, 128.6, 127.8, 120.4, 111.1, 55.7.
,4′-Dichloro-biphenyl: white solid; H NMR (CDCl
00 Hz): δ 7.51–7.49 (d, 4H, J = 8.0 Hz, aromatic CH), 7.44–7.42
1
4
3
, ppm,
4
(
1
1
3
d, 4H, J = 8.0 Hz, aromatic CH). C NMR (CDCl , ppm,
3
00 MHz): 138.4, 133.7, 129.1, 128.2.
,4′-Dibromo-biphenyl: white solid; H NMR (CDCl
00 Hz): δ 7.60–7.58 (d, 4H, J = 8.0 Hz, aromatic CH), 7.45–7.43
1
4
3
, ppm,
4
(
1
1
3
d, 4H, J = 8.0 Hz, aromatic CH). C NMR (CDCl
00 MHz): 138.9. 132.0, 128.5, 122.0.
,1′-Biphenyl,4,4′-bis(1,1-dimethylethyl): white solid;
NMR (CDCl
matic CH), 7.50–7.48 (d, 4H, J = 8.0 Hz, aromatic CH), 1.40 (s,
3
, ppm,
1
1
H
3
, ppm, 400 Hz): δ 7.58–7.56 (d, 4H, J = 8.0 Hz, aro-
1
3
6
H, CH3). C NMR (CDCl , ppm, 100 MHz): 149.9. 138.2,
3
1
26.7, 125.6. 34.5, 31.4.
4 (a) D. D. Henning, T. Iwama and V. H. Rawal, Org. Lett.,
1999, 1, 1205; (b) M. Kuroboshi, Y. Waki and H. Tanaka,
J. Org. Chem., 2003, 68, 3938; (c) D. Albanese, D. Landini,
M. Penso and S. Petricci, Synlett, 1999, 199; (d) L. J. Shao,
Y. J. Du, M. F. Zeng, X. D. Li, W. T. Shen, S. F. Zuo, Y. Q. Lu,
X. M. Zhang and C. Z. Qi, Appl. Organomet. Chem., 2010,
24, 421; (e) S. Nadri, E. Azadi, A. Ataei, M. Joshaghani and
E. Rafiee, J. Organomet. Chem., 2011, 696, 2966; (f) J. H. Li,
Y. X. Xie and D. L. Yin, J. Org. Chem., 2003, 68, 9867;
(g) C. Z. Qi, X. D. Sun, C. Y. Lu, J. Z. Yang, Y. J. Du, H. J. Wu
and X. M. Zhang, J. Organomet. Chem., 2009, 694, 2912;
(h) L. Wang, Y. H. Zhang, L. F. Liu and Y. G. Wang, J. Org.
Chem., 2006, 71, 1284; (i) M. Kuroboshi, Y. Waki and
H. Tanaka, J. Org. Chem., 2003, 68, 3938; ( j) A. Monopoli,
V. Calò, F. Ciminale, P. Cotugno, C. Angelici, N. Cioffi and
A. Nacci, J. Org. Chem., 2010, 75, 3908; (k) W. M. Seganish,
M. E. Mowery, S. Riggleman and P. D. Shong, Tetrahedron,
2005, 61, 2117.
1
4
,4′-Diacetyl-biphenyl: white solid; H NMR (CDCl
3
, ppm,
4
00 Hz): δ 8.07–8.05 (d, 4H, J = 8.0 Hz, aromatic CH), 7.74–7.72
1
3
(
(
d, 4H, J = 8.0 Hz, aromatic CH), 2.66 (s, 6H, CH
CDCl , ppm, 100 MHz): 170.7. 117.5, 109.7, 102.2, 100.6.
,4′-Dinitro-biphenyl: yellow solid; H NMR (CDCl , ppm,
3
). C NMR
3
1
4
3
4
00 Hz): δ 8.40–8.38 (d, 4H, J = 8.0 Hz, aromatic CH), 7.82–7.80
1
3
3
(d, 4H, J = 8.0 Hz, aromatic CH). C NMR (CDCl , ppm,
1
00 MHz): 148.1. 145.0, 128.3, 124.4.
,4′-Dicyano-biphenyl: white solid; H NMR (CDCl
00 Hz): δ 7.82–7.80 (d, 4H, J = 8.0 Hz, aromatic CH), 7.73–7.71
1
4
3
, ppm,
4
1
3
(d, 4H, J = 8.0 Hz, aromatic CH). C NMR (CDCl , ppm,
3
1
00 MHz): 143.5. 132.9, 127.9, 118.4, 112.5.
,3′,5,5′-Tetramethyl-biphenyl: white solid; H NMR (CDCl
ppm, 400 Hz): δ 7.23 (s, 4H, aromatic CH), 7.02 (s, 2H, aro-
1
3
3
,
1
3
matic CH), 2.41 (s, 12H, CH
3
).
3
C NMR (CDCl , ppm,
1
00 MHz): 141.5, 138.1, 128.7, 125.1, 21.4.
1
2
,2′-Bipyridyl: white solid; H NMR (CDCl , ppm, 400 Hz):
3
δ 8.72–8.70 (d, 2H, J = 8.0 Hz, heterocyclic CH), 8.43–8.41 (d,
H, J = 8.0 Hz, heterocyclic CH), 7.85–7.84 (m, 2H, heterocyclic
CH), 7.35–7.32 (m, 2H, heterocyclic CH). C NMR (CDCl3,
5 (a) G. Q. Lin and R. Hong, J. Org. Chem., 2001, 66, 2877;
(b) J. Peng, X. Liu and Y. Kishi, Tetrahedron Lett., 2011, 52,
2172; (c) V. Percec, J. Y. Bae, M. Y. Zhao and D. H. Hill,
J. Org. Chem., 1995, 60, 176; (d) M. F. Semmelhack,
P. M. Helquist and L. D. Jones, J. Am. Chem. Soc., 1971, 93,
2
1
3
ppm, 100 MHz): 156.1, 149.2, 137.0, 123.8, 121.1.
5908; (e) C. S. Chao, C. H. Cheng and C. T. Chang, J. Org.
Chem., 1983, 48, 4904.
Acknowledgements
6
(a) B. C. Ranu, P. Dutta and A. Sarkar, Tetrahedron Lett.,
1998, 39, 9557; (b) K. Abiraj, G. R. Srinivasa and
D. C. Gowda, Tetrahedron Lett., 2004, 45, 2081;
(c) K. Narasimharaoa, E. Al-Sabban, T. S. Saleh,
A. G. Gallasteguib, A. C. Sanfiz, S. Basahel, S. Al-Thabaiti,
A. Alyoubi, A. Obaid and M. Mokhtar, J. Mol. Catal. A:
Chem., 2013, 379, 152; (d) A. Moncomble, P. L. Floch and
C. Gosmini, Chem. – Eur. J., 2009, 15, 4770.
7 (a) L. Strimbu, J. Liu and A. E. Kaifer, Langmuir, 2003, 19,
483; (b) H. M. Song, B. A. Moosa and N. M. Khashab,
J. Mater. Chem., 2012, 22, 15953; (c) R. Genç, G. Clergeaud,
M. Ortiz and C. K. O’Sullivan, Langmuir, 2011, 27, 10894;
The authors thank the National Natural Science Foundation of
China (21171124 and 21171125), State Key Laboratory of Orga-
nometallic Chemistry, Shanghai Institute of Organic Chem-
istry, Chinese Academy of Sciences (201201006) for financial
support. J. P. Lang also highly appreciates the support for the
Qin-Lan Project and the “333” Project of Jiangsu Province, the
Priority Academic Program Development of Jiangsu Higher
Education Institutions, and the “SooChow Scholar” Program of
Soochow University.
(
d) Y. W. Lee, M. J. Kim, Z. H. Kim and S. W. Han, J. Am.
References
Chem. Soc., 2009, 131, 17036.
1
(a) F. Mikes and G. Boshart, J. Chromatogr., 1978, 149, 455;
b) A. F. Littke and G. C. Fu, Angew. Chem., Int. Ed., 2002,
1, 4176; (c) A. Molnár, Chem. Rev., 2011, 111, 2251.
8 (a) S. Ogasawara and S. Kato, J. Am. Chem. Soc., 2010, 132,
4608; (b) Y. Li and M. A. El-Sayed, J. Phys. Chem. B, 2001,
105, 8938; (c) J. Han, Y. Liu and R. Guo, J. Am. Chem. Soc.,
(
4
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 15752–15759 | 15757

View Article Online
Paper
Dalton Transactions
2
009, 131, 2060; (d) W. G. Li, Q. X. Jia and H. L. Wang, 20 M. Hyotanishi, Y. Isomura, H. Yamamoto, H. Kawasaki and
Polymer, 2006, 47, 23. Y. Obora, Chem. Commun., 2011, 47, 5750.
(a) R. Abu-Reziq, H. Alper, D. Wang and M. L. Post, J. Am. 21 H. Kawasaki, H. Yamamoto, H. Fujimori, R. Arakawa,
9
Chem. Soc., 2006, 128, 5279; (b) R. J. White, R. Luque,
V. L. Budarin, J. H. Clark and D. J. Macquarrie, Chem. Soc.
M. Inada and Y. Iwasaki, Chem. Commun., 2010, 46,
3759.
Rev., 2009, 38, 481; (c) M. Haruta, Cattech, 2002, 6, 102; 22 (a) H. Kawasaki, H. Yamamoto, H. Fujimori, R. Arakawa,
(
d) J. L. Long, H. L. Liu, S. J. Wu, S. J. Liao and Y. W. Li,
Y. Iwasaki and M. Inada, Langmuir, 2010, 26, 5926;
(b) X. F. Liu, C. H. Li, J. L. Xu, J. Lv, M. Zhu, Y. B. Guo,
S. Cui, H. B. Liu, S. Wang and Y. L. Li, J. Phys. Chem. C,
2008, 112, 10778; (c) H. Yamamoto, H. Yano, H. Kouchi,
Y. Obora, R. Arakawa and H. Kawasaki, Nanoscale, 2012, 4,
4148.
ACS Catal., 2013, 3, 647; (e) H. L. Jiang, T. Akita, T. Ishida,
M. Haruta and Q. Xu, J. Am. Chem. Soc., 2011, 133, 1304.
1
0 (a) T. Yonezawa and T. Kunitake, Colloids Surf., A, 1999,
49, 193; (b) E. Oh, K. Susumu, R. Goswami and
H. Mattoussi, Langmuir, 2010, 26, 7604; (c) M. Zhu,
1
E. Lanni, N. Garg, M. E. Bier and R. C. Jin, J. Am. Chem. 23 (a) W. P. Wuelfing, S. M. Gross, D. T. Miles and
Soc., 2008, 130, 1138; (d) K. K. R. Datta, B. V. Subba,
K. Ariga and A. Vinu, Angew. Chem., Int. Ed., 2010, 49, 5961.
1 (a) M. Samim, N. K. Kaushik and A. Maitra, Bull. Mater.
Sci., 2007, 30, 535; (b) B. Karimi and F. K. Esfahani, Chem.
Commun., 2011, 47, 10452; (c) G. Li, C. Liu, Y. Lei and
R. C. Jin, Chem. Commun., 2012, 48, 12005; (d) R. N. Dhital,
C. Kamonsatikul, E. Somsook, K. Bobuatong, M. Ehara,
S. Karanjit and H. Sakurai, J. Am. Chem. Soc., 2012, 134,
R. W. Murray, J. Am. Chem. Soc., 1998, 120, 12696;
(b) Y. Zhu, H. F. Qian, B. A. Drake and R. C. Jin,
Angew. Chem., Int. Ed., 2010, 122, 1317; (c) J. Luo,
V. W. Jones, M. M. Maye, L. Han, N. N. Kariuki and
C. J. Zhong, J. Am. Chem. Soc., 2002, 124, 13988;
(d) S. Link, A. Beeby, S. FitzGerald, M. A. El-Sayed,
T. G. Schaaff and R. L. Whetten, J. Phys. Chem. B,
2002, 106, 3410.
1
2
0250; (e) X. L. Wu, L. F. Tan, D. Chen, X. W. Meng and 24 (a) M. Turner, V. B. Golovko, O. P. H. Vaughan,
F. Q. Tang, Chem. Commun., 2014, 50, 539; (f) K. Layek,
H. Maheswaran and M. L. Kantam, Catal. Sci. Technol.,
P. Abdulkin, A. Berenguer-Murcia, M. S. Tikhov,
B. F. G. Johnson and R. M. Lambert, Nature, 2008, 454, 981;
(b) V. Maraval, R. Laurent, A. M. Caminade and
J. P. Majoral, Organometallics, 2000, 19, 4025;
(c) J. Kilmartin, R. Sarip, R. Grau-Crespo, D. D. Tommaso,
G. Hogarth, C. Prestipino and G. Sankar, ACS Catal., 2012,
2, 957.
2
013, 3, 1147.
1
2 (a) C. C. Cassol, A. P. Umpierre, G. Machado, S. I. Wolke
and J. Dupont, J. Am. Chem. Soc., 2005, 127, 3298;
(b) H. M. Song, B. A. Moosa and N. M. Khashab, J. Mater.
Chem., 2012, 22, 15953; (c) A. Corma, S. Iborra,
F. X. Llabrés i Xamena, R. Montón, J. J. Calvino and 25 (a) M. Haruta, Catal. Today, 1997, 36, 153; (b) S. Panigrahi,
C. Prestipino, J. Phys. Chem. C, 2010, 114, 8828.
3 (a) R. Narayanan and M. A. El-Sayed, J. Am. Chem. Soc.,
S. Basu, S. Praharaj, S. Pande, S. Jana, A. Pal, S. K. Ghosh
and T. Pal, J. Phys. Chem. C, 2007, 111, 4596; (c) N. T. Khoa,
S. W. Kim, D. H. Yoo, E. J. Kim and S. H. Hahn, Appl.
Catal., A, 2014, 469, 159; (d) H. Tsunoyama, H. Sakurai,
Y. Negishi and T. Tsukuda, J. Am. Chem. Soc., 2005, 127,
9374; (e) Y. Li, E. Boone and M. A. El-Sayed, Langmuir,
2002, 18, 4921.
1
2
003, 125, 8340; (b) Y. Wu, D. S. Wang, P. Zhao, Z. Q. Niu,
Q. Peng and Y. Li, Inorg. Chem., 2011, 50, 2046;
c) P. P. Fang, A. Jutand, Z. Q. Tian and C. Amatore, Angew.
(
Chem., Int. Ed., 2011, 123, 12392.
4 (a) S. K. Beaumont, G. Kyriakou and R. M. Lambert, J. Am.
1
Chem. Soc., 2010, 132, 12246; (b) S. U. Son, Y. Jang, J. Park, 26 I. Hussain, S. Graham, Z. X. Wang, B. Tan,
H. B. Na, H. M. Park, H. J. Yun, J. Lee and T. Hyeon, J. Am.
Chem. Soc., 2004, 126, 5026; (c) L. A. Aronica,
D. C. Sherrington, S. P. Rannard, A. I. Cooper and M. Brust,
J. Am. Chem. Soc., 2005, 127, 16398.
A. M. Caporusso, G. Tuci, C. Evangelisti, M. Manzoli, 27 (a) D. Vorkapic and T. Matsoukas, J. Am. Ceram. Soc., 1998,
M. Botavina and G. Martra, Appl. Catal., A, 2014, 480, 1.
5 Z. Q. Niu and Y. Li, Chem. Mater., 2014, 26, 72.
81, 2815; (b) M. Tiemann, F. Marlow, J. Hartikainen,
Ö. Weiss and M. Lindén, J. Phys. Chem. C, 2008, 112, 1463.
1
1
6 (a) F. Ahmad and V. S. Baswani, Polyhedron, 1984, 3, 977; 28 Y. Negishi, K. Nobusada and T. Tsukuda, J. Am. Chem. Soc.,
b) G. H. Hugar and S. T. Nandibewoor, Indian J. Chem., 2005, 127, 5261.
Sect. A: Inorg., Bio-inorg., Phys., Theor. Anal. Chem., 1993, 29 (a) P. A. Buffat, M. Flüeli, R. Spycher, P. Stadelmann
(
3
2, 1056; (c) G. H. Hugar and S. T. Nandibewoor, Transition
and J. P. Borel, Faraday Discuss., 1991, 92, 173;
(b) J. Majimel, M. Lamirand-Majimel, I. Moog, C. Feral-
Martin and M. Tréguer-Delapierre, J. Phys. Chem. C,
2009, 113, 9275.
Met. Chem., 1994, 19, 215; (d) Z. Khan and Kabir-Ud-Din,
Int. J. Chem. Kinet., 1999, 31, 409.
7 (a) I. Pastoriza-Santos and L. M. Liz-Marzán, Langmuir,
1
1
999, 15, 949; (b) L. P. Jiang, S. Xu, J. M. Zhu, J. R. Zhang, 30 (a) A. V. Gaikwad, P. Verschuren, S. Kinge, G. Rothenberg
J. J. Zhu and H. Y. Chen, Inorg. Chem., 2004, 43, 5877.
8 Z. Zhang, X. Chen, X. Zhang and C. Shi, Solid State
Commun., 2006, 139, 403.
9 Y. Isomura, T. Narushima, H. Kawasaki, T. Yonezawa and 31 G. K. Wertheim and S. B. DiCenzo, Phys. Rev. B: Condens.
Y. Obora, Chem. Commun., 2012, 48, 3784. Matter, 1988, 37, 844.
and E. Eiserz, Phys. Chem. Chem. Phys., 2008, 10, 951;
(b) I. P. Santos and L. M. Liz-Marzán, Adv. Funct. Mater.,
2009, 19, 679.
1
1
15758 | Dalton Trans., 2014, 43, 15752–15759
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
3
2 (a) M. Valden, X. Lai and D. W. Goodman, Science, 1998, 33 J. L. Bars, U. Specht, J. S. Bradley and D. G. Blackmond,
81, 1647; (b) N. Lopez, T. V. W. Janssens, B. S. Clausen, Langmuir, 1999, 15, 7621.
Y. Xu, M. Mavrikakis, T. Bligaard and J. K. Nørskov, 34 (a) M. Crespo-Quesada, A. Yarulin, M. S. Jin, Y. N. Xia
2
J. Catal., 2004, 223, 232; (c) V. K. Kanuru, G. Kyriakou,
S. K. Beaumont, A. C. Papageorgiou, D. J. Watson and
R. M. Lambert, J. Am. Chem. Soc., 2010, 132, 8081.
and L. Kiwi-Minsker, J. Am. Chem. Soc., 2011, 133,
12787; (b) M. Pérez-Lorenzo, J. Phys. Chem. Lett., 2012,
3, 167.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 15752–15759 | 15759