G-/C-rich oligonucleotides stabilized pd nanocatalysts for the Suzuki coupling reaction under mild conditions

Article abstract of DOI:10.1007/s10562-013-0989-3

Pd nanoparticles with narrow size distributions between 1.3 and 3.3 nm are prepared using G-/C-rich oligonucleotide as the template. These DNA-Pd nanoparticles efficiently catalyze the Suzuki coupling reaction and exhibit highly catalytic activities under mild conditions, which are greatly dependent upon the particle size of Pd nanoparticles besides the DNA sequence. For the coupling reaction of iodobenzene and phenylboronic acid at 60 C in the presence of KOH, it can be achieved high TOF value of 2646 mol biphenyl (mol Pd × h)^-1 over AG22-Pd and 3640 mol biphenyl (mol Pd × h) ^-1 over CT22-Pd. Under the optimal experimental conditions, the yield of 100 % in biphenyl is obtained with only 0.0055 mol% AG22-Pd at 60 C for 1 h in the solvent of EtOH/H₂O (1:2) using Na₂CO₃ or K₂CO₃ as the base. It is illustrated that G-/C-rich oligonucleotides are promising templates to modulate easily the morphology of Pd nanoparticles in aqueous solution with high catalytic activity.

Full text of DOI:10.1007/s10562-013-0989-3

Catal Lett (2013) 143:578–586
DOI 10.1007/s10562-013-0989-3
G-/C-rich Oligonucleotides Stabilized Pd Nanocatalysts
for the Suzuki Coupling Reaction Under Mild Conditions
Wei Li
Jinli Zhang
•
Yingming Fu
•
Yan Fu
•
Xian Wang
•
Received: 24 January 2013 / Accepted: 3 March 2013 / Published online: 13 March 2013
Ó Springer Science+Business Media New York 2013
Abstract Pd nanoparticles with narrow size distributions
between 1.3 and 3.3 nm are prepared using G-/C-rich oli-
gonucleotide as the template. These DNA-Pd nanoparticles
efficiently catalyze the Suzuki coupling reaction and exhibit
highly catalytic activities under mild conditions, which are
greatly dependent upon the particle size of Pd nanoparticles
besides the DNA sequence. For the coupling reaction of
iodobenzene and phenylboronic acid at 60 °C in the presence
of KOH, it can be achieved high TOF value of 2646 mol
1 Introduction
Suzuki cross-coupling reaction, one of the most widely
used protocols for the formation of carbon–carbon bonds,
has presented wide applications in the production of
polymers, agrochemicals, pharmaceutical intermediates
and high-tech materials [1, 2], which are generally cata-
lyzed by soluble palladium complexes with various ligands
such as phosphines, N-heterocyclic carbenes [3]. Owing to
high surface-to-volume ratio and highly active surface
atoms, palladium nanoparticles (Pd NPs) catalyzed Suzuki
cross-coupling reactions have been extensively studied
recently [1, 2, 4], indicating that a critical nanoparticle size
exist in the Suzuki cross-coupling reaction with high cat-
alytic activities while small clusters were found to be less
catalytically active. El-Sayed and co-workers investigated
the catalytic activity of different-sized poly(vinylpyrroli-
done)-capped Pd nanoparticles in Suzuki cross-coupling
between iodobenzene and phenylboronic acid at 80 °C in
the solvent of CH CN/H O (3:1) using NaOAc as the base,
-
1
biphenyl (mol Pd 9 h)
over AG22-Pd and 3640 mol
-
1
biphenyl (mol Pd 9 h) over CT22-Pd. Under the optimal
experimental conditions, the yield of 100 % in biphenyl is
obtained with only 0.0055 mol% AG22-Pd at 60 °C for 1 h
in the solvent of EtOH/H O (1:2) using Na CO or K CO as
2
2
3
2
3
the base. It is illustrated that G-/C-rich oligonucleotides are
promising templates to modulate easily the morphology of
Pd nanoparticles in aqueous solution with high catalytic
activity.
Keywords DNA Á Palladium nanoparticles Á Suzuki
3
2
cross-coupling
and showed that Pd NPs with a particle size of 4–5 nm
exhibit the highest turnover frequency (TOF) [5, 6].
Therefore, the controllable synthesis of Pd NPs with tun-
able and uniform size play a critical role for the design of
efficient catalysts in these important reactions. On the other
hand, compared with Pd nanocatalysts based on conven-
tional supports involving silica [7], metal oxide [8, 9],
carbon nanotube [10, 11], and polymeric microsphere [12],
Pd NPs stabilized by dendrimer [13, 14], cyclodextrin [15],
peptide [16–18], etc., have attracted much attention in C–C
coupling reactions owing to the advantage of conveniently
controlling the shape and size distribution of particles. For
example, Knecht and coworkers reported that peptide
selected by phage display has the ability to finely tune the
size, surface structure and functionality of single-crystal Pd
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-013-0989-3) contains supplementary
material, which is available to authorized users.
W. Li (&) Á Y. Fu Á Y. Fu Á X. Wang Á J. Zhang
Key Laboratory of Systems Bioengineering MOE, Key
Laboratory for Green Chemical Technology MOE, School of
Chemical Engineering & Technology, Tianjin University,
Tianjin 300072, People’s Republic of China
e-mail: liwei@tju.edu.cn
1
23

G-/C-rich Oligonucleotides Stabilized Pd Nanocatalysts
579
NPs between 1.9 and 3.1 nm, and the peptide-Pd NPs with
the critical particle size exhibit high reactivity in Stille
coupling reaction [19]. Therefore, exploration of novel
polymer stabilizer to control the particle size is promising
for enhancing the catalytic activities in C–C coupling
reactions as well as achieving more environmental-benign
synthetic processes.
of 4-phenylbenzoic acid gives the highest yield with
0.11 mol% AG22-Pd in the presence of NaOH.
2 Experimental
2.1 Chemicals
Nucleic acids, which enrich nitrogen and oxygen func-
tional groups that coordinate with metallic nanoparticles,
have emerged as promising biotemplates for the construc-
tion of nanomaterials [20–22]. A number of reports sug-
gested that the sequence composition of nucleic acids can
greatly influence morphologies [23, 24] or electric prop-
erties [25, 26] of palladium nanomaterials. Considering
green and sustainable organic synthesis, natural DNA
molecules extracted from salmon sperm or calf thymus
with low toxicity have been performed as a catalytic sup-
port to control the dispersibility of Pd NPs, which has been
successfully assessed in a series of organic reactions
involving oxidation, reduction or C–C cross-coupling [27].
For instance, Pd NPs templated by salmon DNA with a
distribution of 5–8 nm were found to be effective in the
Suzuki reaction between aryl halides and phenylboronic
acid, i.e., 4-nitrophenyl iodide was produced in a high yield
of 93 % at 60 °C for 48 h using Na CO as the base [28].
Oligonucleotides d[AG (T AG ) ] and d[(C TA ) C T]
3
2
3 3
3
2 3 3
(denoted as AG22 and CT22 respectively) were purchased
from Japanese Takara Bio (Dalian) with the purity higher than
98 % measured by high performance liquid chromatography
(HPLC). Na PdCl (99.95 %), 4-iodobenzoic acid (97 %) and
2
4
4-phenylbenzoicacid(98 %)werepurchasedfromAlfaAesar.
NaBH (98 %), sodium acetate trihydrate (99 %), K CO
4
2
3
(99 %), Cs CO (99.5 %), KOH (82 %), iodobenzene
2
3
(98.5 %), bromobenzene (98.5 %), chlorobenzene (99.0 %),
4-chlorobenzoic acid (99.5 %) and dimethylformamide
(DMF, 99.5 %) were purchased from Tianjin Guangfu Fine
Chemical Research Institute. Glacial acetic acid (99.5 %),
Na CO (99.8 %), NaOH (96 %) and ethanol (EtOH, 99.7 %)
2
3
were purchased from Tianjin Fengchuan Chemical Reagent
Science And Technology Co., Ltd. K PO Á3H O (99 %),
3
4
2
4-bromobenzene acid (99 %) and N-methyl pyrrolidone
(NMP, 98 %) were purchased from Sinopharm Chemical
Reagent Co., Ltd. Phenylboronicacidwaspurchasedfrom TCI
Shanghai. Biphenyl (99.5 %) was purchased from J&K Sci-
2
3
Furthermore, the yield in the reaction between phenylbo-
ronic acid and iodobenzene can reach as high as 100 % at
1
00 °C for 4 min catalyzed by ctDNA-capping Pd NPs on
entific Ltd. Acetonitrile (CH CN, 99.9 %)waspurchasedfrom
3
graphene in the range of 4–6 nm [29]. Electron-rich
nitrogen atoms in DNA bases especially N1, N7 sites of
guanine (G) and N3 site of cytosine (C), provide active
Merck KgaA. N,N-dimethyl acetamide (DMAC, 99.5 %) was
purchased from Tianjin Kemiou Chemical Reagent Co., Ltd.
All reagents were used as received without purification.
?
sites coordinating with transition metal ions including Ag ,
2?
[30]. G-/C-rich oligonucleotides have been
2
Pt , Pd
?
2.2 Characterizations
reported to synthesize silver nanoclusters and regulate their
fluorescent properties [31–33]. However, few reports focus
on the synthesis of Pd NPs using G-/C-rich oligonucleotide
as the template to modulate the catalytic characteristics in
organic reactions such as Suzuki cross-coupling.
UV spectroscopy were recorded on a Cary-300 Bio UV–
Visible spectrophotometer (Varian Ltd.) using a 1 mm path
quartz cuvette at 25 °C. Transmission Electron Microscopy
(TEM) were performed on JEM-2010FEF equipment (JEOL,
Japan). Electron microscopy samples were prepared by
applying 10 lL samples on a carbon-coated grid for 10 min,
and then excess liquid was removed with filter paper. HPLC
was carried out at ambient temperature on a Agilent 1200
system equipped with a UV detector. Analysis of the products
of Suzuki coupling reaction was performed on a Agilent
Eclipse XDB-C18 column (5 lm, 150 9 4.6 mm). The
product of biphenyl was analyzed using acetonitrile/water
mixture (60/40, v/v) as mobile phase at a flow rate of 1 mL/
min at the detection wavelength of 254 nm and the product of
4-phenylbenzoic acid was detected using acetonitrile/glacial
acetic acid (0.1 %) mixture (40/60, v/v) as mobile phase at the
detection wavelength of 270 nm. Quantitative analysis was
calculated by using external standard method.
In the present study, G-rich oligonucleotide d[AG3
(
T AG ) ] and C-rich d[(C TA ) C T] are used as the tem-
2 3 3 3 2 3 3
plates to synthesize monodispered Pd NPs. These DNA-Pd
NPs exhibit highly catalytic activities in the Suzuki coupling
reactions in aqueous solution, which are greatly dependent
upon the particle size of Pd NPs. Effects of reaction solvents,
base species and different types of aryl halides are studied in
order to optimize the catalytic performance of DNA-tem-
plated Pd NPs under mild conditions. It is illustrated that G-/
C-rich oligonucleotides are promising templates to modulate
easily Pd NPs with high catalytic activity. The yield of
1
00 % in biphenyl is obtained with only 0.0055 mol%
AG22-Pd at 60 °C for 1 h in the solvent of EtOH/H O (1:2)
2
using Na CO or K CO as the base, while the production
2
3
2
3
123

5
80
W. Li et al.
Fig. 1 UV–Vis spectra of the
Na PdCl in the absence of
DNA (a). UV–Vis spectra of the
2
4
II
AG22-Pd complexes (b) and
0
AG22-Pd after reduction with
4
NaBH at different Pd/base
ratios (c). UV–Vis spectra of the
II
CT22-Pd complexes (d) and
0
CT22-Pd after reduction with
4
NaBH at different Pd/base
ratios (e)
2
.3 Preparation and Catalytic Performance of DNA-
templated Pd NPs
phenylboronic acid and 0.25 mmol base in the presence of a
certain amount of DNA-Pd catalyst in 2 mL solvent. After
stirring at 60 °C for 1 h, the reaction mixture was cooled in a
water–ice bath to stop the reaction, and then 6 mL of aceto-
nitrile–water mixture was added to dissolve the reaction
mixture. The product diluted with mobile phase was analyzed
with the HPLC.
Oligonucleotide AG22 and CT22 were chosen as the tem-
plate to synthesize Pd NPs in 10 mM KH PO –K HPO
4
2
4
2
potassium phosphate buffer (10 mM, pH 5.0) and they were
carried out in open air. All DNA samples were annealed by
heating the sample cuvette to 95 °C for 5 min and then
cooling to 4 °C. The Pd NPs were synthesized through
-
reduction of Na PdCl by BH4 . Oligonucleotides dis-
3 Results and Discussion
2
4
solved in KH PO –K HPO buffer were firstly incubated
2
4
2
4
with Na PdCl at Pd/base ratio of 0.5, 1, 2, 5 for 0.5 h, and
2
3.1 Preparation and Characterization
of Oligonucleotide-Capping Pd NPs
4
then adding NaBH (2 equiv) to Na PdCl to start the
4
4
2
reduction reaction for 0.5 h.
II
As shown in the UV–Vis spectra of the AG22-Pd com-
2
.4 Suzuki Coupling Reaction
plexes (Fig. 1b), a ligand-to-metal charge-transfer (LMCT)
II
band is observed around 215 nm for the AG22-Pd prior to
II
reduction, which contributes to the interaction of Pd ions
All the reactions were carried out in a 10 mL ground glass
stoppered flask containing 0.1 mmol aryl halide, 0.125 mmol
with nitrogen atoms in guanine bases [34]. As the Pd/base
1
23

G-/C-rich Oligonucleotides Stabilized Pd Nanocatalysts
581
Fig. 2 TEM images of Pd
nanoparticles templated by
AG22 at Pd/base ratio of 0.5 (a),
1 (b), 2 (c), 5 (d), as well as Pd
NPs templated by CT22 at Pd/
base ratio of 0.5 (e), 1 (f), 2 (g),
5
(h)
123

5
82
W. Li et al.
Fig. 3 a The yield of biphenyl
with AG22-Pd NPs loadings of
0
.0055–0.22 mol% at different
Pd/base ratios, yield = (moles
of biphenyl)/(moles of
iodobenzene) 9 100 %; b TOF
analysis of AG22-Pd NPs
prepared at Pd/base ratio of 0.5,
1
, 2, 5 respectively, the yields of
biphenyl at different reaction
times (3 min, 6 min, 9 min,
1
2 min or 15 min) are plotted as
the mol biphenyl/mol Pd, and
the slope derived from linear
fitting represents the TOF value;
c TOF comparison of four
AG22-Pd NPs (y-axis
units = mol biphenyl (mol
-
1
Pd 9 h) ), a catalyst loading
of 0.033 mol% is employed in
TOF determination
ratio increasing, the intensity of the LMCT band also
increases; however, a slight red-shift to 220 nm is observed
increasing significantly with the Pd/base ratio of 0.5–2, i.e.,
the product yield can reach to 92.4 % with only
0.033 mol% Pd using the AG22-Pd NPs of 2.7 nm (Pd/
base = 2). However, the catalytic activity decreases with
the Pd NPs of 3.3 nm, suggesting a critical particle size of
2.7 nm for the Pd NPs templated by G-rich AG22 in the
Suzuki coupling. Furthermore, the highest TOF value of
II
at the Pd/base ratio of 5 due to the free Pd ions in solution
II
Fig. 1a). After reduction of the DNA-Pd complex, the
(
LMCT band disappears and a broad absorbance band
II
appears in this region, indicating that Pd are reduce into
0
Pd NPs (Fig. 1c). Similar spectral changes are also
-
1
observed for the synthesis of Pd NPs templated by C-rich
oligonucleotide (Fig. 1d, e).
2646 ± 152 mol biphenyl (mol of Pd 9 h) is achieved
at Pd/base of 2 with the average size of 2.7 nm (Fig. 3b, c).
These results suggest that the smallest particle size can not
result in an increased reaction rate in the Suzuki reaction.
Adopting the oligonucleotide AG22 (Fig. 2a–d), the
average size gradually increases from 1.4 nm to 3.3 nm
with the Pd/base ratio ranging from 0.5 to 5. Moreover,
CT22-Pd NPs show smaller particle size ranging from
II
Most of Pd anticipates in the coordination with nitrogen
atoms in DNA bases at the ratio of 0.5, thus, the sample is
0
most difficult to reduce and less reactive Pd is presented.
1
.3 nm to 2.8 nm at the same Pd/base ratio (Fig. 2e–h).
II
As the part of DNA coordinating Pd decreases with
Compared with the polynucleotide template of natural fish
sperm DNA, which prepared Pd nanohybrids with an
average diameter of 7–8 nm [27], it is indicated that G-/C-
rich oligonucleotides are superior to control efficiently and
easily the size contribution of Pd NPs.
II
increasing the Pd/base ratio, more Pd is reduced to active
0
Pd to generate high TOFs [34]. Therefore, it is clear that
there is a balance between the protection of Pd NPs against
further agglomeration and either the Pd leaching or the free
access for the reactants to the PdNP surface. Similarly, the
catalytic activities of PVP-stabilized Pd NPs have been
reported to decrease in the order of Pd (3.9 nm) [ Pd
3
.2 Suzuki Reactions in Aqueous Medium Catalyzed
by DNA-Pd NPs
(3.0 nm) & Pd (5.2 nm) [ Pd (6.6 nm) on the Suzuki
Suzuki reactions of iodobenzene and phenylboronic acid to
produce biphenyl are firstly performed using AG22-Pd NPs
with different particle size (illustrated in Fig. 2a–d). As
shown in Fig. 3a, the catalytic activities of the Pd NPs
reaction between phenylboronic acid and iodobenzene [5].
In the case of C-rich oligonucleotide CT22, the TOF
-
1
value of 3640 mol biphenyl (mol Pd 9 h)
can be
achieved at the Pd/base ratio of 2 under similar conditions
1
23

G-/C-rich Oligonucleotides Stabilized Pd Nanocatalysts
583
Table 1 Effect of solvent on the Suzuki reaction between aryl halide and phenylboronic acid catalyzed by AG22-Pd NPs
Entry
R
Solvent (v/v)
Pd (mol%)
Yield (%)
1
2
3
4
5
6
7
8
9
H
H
2
O
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.033
0.11
92.4
100
100
9.8
H
EtOH/H
EtOH/H
2
2
O = 1:2
O = 1:1
H
H
CH
CH
3
CN/H
CN/H
2
O = 1:2
O = 1:1
H
3
2
2.9
H
DMF/H
DMF/H
NMP/H
NMP/H
2
2
2
2
O = 1:2
O = 1:1
O = 1:2
O = 1:1
0.3
H
0.2
H
2.3
H
0.4
10
11
12
13
14
15
16
17
18
19
20
21
22
H
DMAC/H
DMAC/H
2
O = 1:2
O = 1:1
10.9
2.5
H
2
COOH
COOH
COOH
COOH
COOH
COOH
COOH
COOH
COOH
COOH
COOH
H
2
O
92.7
96.9
96.5
72.8
74.5
0.5
EtOH/H
EtOH/H
2
2
O = 1:2
O = 1:1
0.11
0.11
CH
CH
3
CN/H
CN/H
2
O = 1:2
O = 1:1
0.11
3
2
0.11
DMF/H
DMF/H
NMP/H
NMP/H
2
2
2
2
O = 1:2
O = 1:1
O = 1:2
O = 1:1
0.11
0.11
0.4
0.11
70.1
29.2
71.1
48.7
0.11
DMAC/H
DMAC/H
2
O = 1:2
O = 1:1
0.11
2
0.11
Reaction conditions: aryl halide (0.1 mmol, 1 equiv), PhB(OH)2 (0.125 mmol, 1.25 equiv), KOH (0.25 mmol, 2.5 equiv), solvent (2 mL), 60 °C,
h. AG22-Pd NPs (Pd/base = 2) was used here as the catalyst. Each sample was repeated at least three times
1
(
Fig. S1c). Therefore, it is suggested that the critical par-
the chemical reactions [35]. Similarly, the yield of 96.9 %
for 4-phenylbenzoic acid at 0.11 mol% Pd can be achieved
ticle size is around 2.7 nm for AG22-Pd while 2.3 nm for
CT22-Pd both at the Pd/base of 2.
in the 1:2 mixture of EtOH/H O, and other solvents in the
2
reaction system also inhibit the catalytic activities.
Next, in order to study the reactivities and specificities
of DNA-Pd NPs, Suzuki reactions of various aryl halide
with phenylboronic acid are carried out as shown in
Table 2. Substitution of the halide for bromide or chloride
functionalities result in a decrease in reactivity, i.e., the
yield of biphenyl decreases to 87.9 % for bromobenzene
while 1.6 % for chlorobenzene even with high catalyst
loading of 0.033 mol% Pd. These results are well consis-
tent with previous studies on the Stille C–C coupling
reactions using peptide stabilized Pd NPs (1.9 nm) due to
the lesser activity of the lighter halides [35]. In the case of
4-halobenzoic acids, substitution of the halide similarly
resulted in decreased reaction yields. A significant
decrease in the yield of 4-phenylbenzoic acid is also
observed especially for the substitution of the halide for
chloride.
3
.3 Optimization of Catalytic Activities of DNA-Pd
NPs in Suzuki Coupling Reactions
Effects of reaction solvents, base species and different
types of aryl halides are studied in order to optimize the
catalytic performance of DNA-templated Pd NPs under
mild conditions. Firstly, we attempt to use the mixtures of
water with a series of organic solvents as the reaction
medium to improve the solubility of the initial reactants.
As listed in Table 1, the yield of 100 % for biphenyl at
0
.033 mol% Pd with AG22-Pd NPs synthesized at Pd/base
of 2 is produced in the 1:2 and 1:1 mixture of EtOH/H O
2
(
v/v). In contrast, these water-soluble DNA-Pd NPs are not
compatible with other organic solvents including CH CN,
3
DMF, NMP, or DMAC, which might cause changes to the
particle surface to alter the specific interactions that drive
123

5
84
W. Li et al.
Table 2 The coupling reactions between various aryl halides and phenylboronic acid catalyzed by AG22-Pd NPs
Entry
R
X
Pd (mol%)
Yield (%)
1
2
3
4
5
6
7
H
I
0.0088
0.033
0.033
0.088
0.11
100
87.9
1.6
H
Br
Cl
I
H
COOH
COOH
COOH
COOH
94.9
96.9
94.7
2.3
I
Br
Cl
0.11
0.11
Reaction conditions: aryl halide (0.1 mmol, 1 equiv), PhB(OH)2 (0.125 mmol, 1.25 equiv), KOH (0.25 mmol, 2.5 equiv), EtOH/H2O (2 mL,
v/v = 1:2), 60 °C, 1 h. The AG22-Pd NPs (Pd/base = 2) was used here as the catalyst. Each sample was repeated at least three times
Table 3 Effect of various bases on the Suzuki reaction between aryl halide and phenylboronic acid catalyzed by AG22-Pd NPs
Entry
R
Base
Pd (mol%)
Yield (%)
1
2
3
4
5
6
7
8
9
H
NaOAc
0.033
0.0022
0.0055
0.0022
0.0055
0.0022
0.0055
0.0088
0.0022
0.0055
0.0088
0.11
1.7
92.3
100
H
Na
Na
2
CO
CO
3
3
H
2
H
K
2
CO
CO
3
3
89.0
100
H
K
2
H
NaOH
NaOH
NaOH
KOH
69.8
92.9
100
H
H
H
42.0
87.7
100
1
1
1
1
1
1
1
0
1
2
3
4
5
6
H
KOH
H
KOH
COOH
COOH
COOH
COOH
COOH
NaOAc
Na CO
CO
1.1
2
3
0.11
97.0
86.6
99.8
96.9
K
2
3
0.11
NaOH
KOH
0.11
0.11
Reaction conditions: aryl halide (0.1 mmol, 1 equiv), PhB(OH)2 (0.125 mmol, 1.25 equiv), Base (0.25 mmol, 2.5 equiv), EtOH/H2O (2 mL,
v/v = 1:2), 60 °C, 1 h. The AG22-Pd NPs (Pd/base = 2) was used here as the catalyst. Each sample was repeated at least three times
Finally, a series of bases involving NaOAc, Na CO ,
2
mol Pd NPs in the presence of NaOH and KOH. For the
reaction of 4-iodobenzoic acid and phenylboronic acid, the
highest product yield (99.8 %) occurs in the presence of
NaOH, and the yields decrease with the bases in the following
order: NaOH[ KOH & Na CO [ K CO [ NaOAc.
3
K CO , NaOH, and KOH, are investigated to enhance the
2
3
catalytic performance in the Suzuki coupling reactions
Table 3). For the reaction of iodobenzene and phenylbo-
(
ronic acid, the yield of biphenyl can reach to 100 % with the
catalyst loading of 0.0055 % in the presence of Na CO and
2
3
2
3
As shown in Table 4, compared with the other four Pd
2
3
K CO , while the yield of 100 % is obtained with 0.0088 %
2
catalysts, DNA-Pd nanocatalyst used in this study exhibit
3
1
23

G-/C-rich Oligonucleotides Stabilized Pd Nanocatalysts
585
Table 4 Suzuki reaction of iodobenzene with phenylboronic acid via different Pd catalysts
Entry Catalyst (mean diameter)
Pd loading (mol%) Solvent
Base
Temp (°C) Time (h) Yield (%)
1
2
3
4
5
AG22-Pd (2.7 nm)
0.0055
0.3
EtOH/H
EtOH/H
EtOH/H
2
2
2
O (1:2, v/v) Na
2
3
3
CO
3
60
1
100
95
PVP-Pd [36] (3.6 nm)
O (2:3, v/v) Na
O (2:3, v/v) Na
PO
PO
4
Reflux
Reflux
60
12
24
24
5
G3-OHdendrimer-Pd [37] (1.4 nm) 1.5
4
71
a-HPCD-Pd [15] (3.7 nm)
0.01
0.2
H
2
O
O
K
2
CO
CO
3
100
99
PNIPAM-Pd [38] (3 nm)
H
2
K
2
3
90
high efficiency for the Suzuki reaction between iodoben-
zene and phenylboronic acid under mild conditions. For
example, the yield of 95 % in biphenyl was obtained with
templates to modulate easily the morphology of Pd NPs in
aqueous solution with high catalytic activity.
Acknowledgments This work was supported by NSFC (21276179,
20836005), and the Special Funds for Major State Basic Research
Program of China (2012CB720300).
0
2
.3 mol% PVP-Pd NPs (3.6 nm) at reflux for 12 h in the
:3 mixture of EtOH/H O using Na PO as the base [36].
2
3
4
Moreover, in the case of a-HPCD-Pd NPs of 3.7 nm, the
yield of biphenyl reaches to 100 % with 0.01 mol% Pd
loading at 60 °C for 24 h in H O using K CO as the base
2
2
3
[
15]. In this study, the yield of 100 % in biphenyl is
obtained with only 0.0055 mol% AG22-Pd at 60 °C for 1 h
in the 1:2 mixture of EtOH/H O using Na CO or K CO .
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