Palladium nanoparticles on amphiphilic carbon spheres: A green catalyst for Suzuki-Miyaura reaction

Article abstract of DOI:10.1002/adsc.201000940

We report the use of palladium nanoparticles stabilized on amphiphilic glucose-derived carbon spheres as heterogeneous catalysts for Suzuki-Miyaura reactions. Reactions of aryl halides with various boronic acids in the presence of different bases and solvents including organic polar, non-polar and water as sole solvent without the aid of phase-transfer catalysts, under phosphine-free and aerobic conditions have been studied. Especially, deactivated aryl bromides and activated aryl chlorides afforded good isolated yields in pure water. The catalyst was reused for up to four cycles without any marked loss in the activity. Copyright

Full text of DOI:10.1002/adsc.201000940

COMMUNICATIONS
DOI: 10.1002/adsc.201000940
Palladium Nanoparticles on Amphiphilic Carbon Spheres:
A Green Catalyst for Suzuki–Miyaura Reaction
a
a,
Chandra Babu Putta and Sutapa Ghosh *
a
Nanomaterials Laboratory, Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology,
Hyderabad – 500 607, India
Fax : (+91)-40-2716-0921; phone: (+91)-40-2719-1385; e-mail: sghosh@iict.res.in
Received: December 13, 2010; Revised: April 8, 2011; Published online: July 22, 2011
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adcs.201000940.
[
6]
Abstract: We report the use of palladium nanopar-
ticles stabilized on amphiphilic glucose-derived
carbon spheres as heterogeneous catalysts for
Suzuki–Miyaura reactions. Reactions of aryl halides
with various boronic acids in the presence of differ-
ent bases and solvents including organic polar, non-
polar and water as sole solvent without the aid of
phase-transfer catalysts, under phosphine-free and
aerobic conditions have been studied. Especially,
deactivated aryl bromides and activated aryl chlor-
ides afforded good isolated yields in pure water.
The catalyst was reused for up to four cycles with-
out any marked loss in the activity.
solvents or in pure water have been demonstrated.
In the past few years, a number of attempts and strat-
egies have been used to get a commercially viable,
active, recoverable, and reusable palladium catalyst
for Suzuki reactions. Usually, traditional Suzuki re-
actions were reported using phosphine based palladi-
um catalysts, and there has been considerable recent
interest in the development of new environmentally
benign and efficient catalysts. Some significant advan-
ces have been made in the use of palladium as the
[
7]
[
3]
[
8]
catalyst under phosphine-free conditions, microwave
technology, and so on. Particularly, palladium on
carbon has been most extensively studied for Suzuki
[
9]
[10]
[
11]
reactions so far.
Keywords: amphiphilic carbon spheres; green
chemistry; leaching; palladium nanoparticles;
Suzuki–Miyaura reaction
An issue of great importance is the leaching of Pd
from the support during the catalytic cycle, and recent
works has given evidence that the leached metal par-
ticles are the true catalytically active species in the
[
12]
coupling reactions. The palladium dissolution-rede-
position processes as well as catalytic activity are
[13]
strongly influenced by the reaction conditions. Sta-
Metal nanoparticles show different properties in com- bilization of the nanoparticles against agglomeration
[
14]
parison to their bulk materials and to isolated during the reaction is of special interest.
[1]
atoms.
In principle, the high surface area per
Synthesis of amphiphilic block copolymers needs
volume renders metal nanoparticles ideal candidates several steps. Besides, colloidal carbon micro- or
[
2]
[3]
for catalysis. The palladium-catalyzed Suzuki and nanospheres synthesized from glucose under hydro-
[4]
Heck reactions between aryl halides and boronic thermal conditions have been a hot topic and trend
acids or alkenes, respectively, are well-established for researches in the fields of nanoscience because of
[
15]
tools for CÀC bond formation in organic synthesis.
their unique functionality. The levulinic acid func-
In recent years, much attention has been focused tional groups were found to be highly abundant in the
on aqueous and heterogeneous switching of organic final carboneous material both as embedded mole-
[
16]
transformations using amphiphilic block copolymer- cules and as copolymerized compounds. Amphiphil-
supported transition metal complexes or metal nano- ic colloidal carbon spheres (CSP) derived from carbo-
particles. Especially water is genuinely useful for hydrates under hydrothermal conditions are readily
green chemistry as solvent itself, and has unique prop- dispersible in solvents of different polarity without
[5]
[
17]
erties in solvating organic molecules that can lead to any prior surface modifications.
Highly dispersed
beneficial effects in terms of both reaction rate and Pd NPs have been prepared on the surfaces of CSP
selectivity. Reusable palladium nanoparticles (Pd through an in situ reduction process in ethanol, which
NPs) that promote cross-coupling reactions in organic
Adv. Synth. Catal. 2011, 353, 1889 – 1896
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1889

Chandra Babu Putta and Sutapa Ghosh
COMMUNICATIONS
Scheme 1. Suzuki–Miyaura coupling of aryl halides with bor-
onic acids by Pd/CSP in H O.
2
[
18]
acted as the solvent and reducing agent. Pd NPs at-
[
18a]
tached to CSP have good catalytic properties.
We herein report the use of Pd NPs stabilized on
amphiphilic CSP as heterogeneous catalysts for
Suzuki–Miyaura reactions involving a wide range of
aryl halides and boronic acids (Scheme 1). Addition-
ally, the effects of the solvent polarity, base, tempera-
ture on yield, and evidence for the leaching of palladi-
um in the solution during the reaction and the recy-
cling potential of the amphiphilic CSP supported Pd
NPs (Pd/CSP) have all been assessed.
The TEM image in Figure 1 (a) shows that the syn-
thesized Pd NPs on amphiphilic CSP were of nearly
spherical shape with an average diameter of ~12 nm
and the size of CSP was typically 400–600 nm. The
degree of functionalization of CSP was determined by
atomic absorption spectroscopy (see Supporting Infor-
mation). This measurement was based on the ex-
change of the acidic protons using NaOH, followed
by dilution of Na salt of CSP with HNO solution at
3
+
pH 1. The acidification released Na , which could be Figure 1. Pd/CSP before use (a), and after three catalytic
cycles in H O (b).
quantified by atomic absorption. Based on the cali-
bration curve we found that 40 ppm, i.e., 4% (wt/wt)
of carboxylate groups were present on CSP. From
2
TGA analysis (Supporting Information, Figure S1), it Additionally, the products were separated by simple
has been observed that there is negligible loss in organic extraction and purified by crystallization. This
weight of the catalyst at reaction temperatures. The is significant because we eliminated the need to
catalytic activity of Pd/CSP was tested for various employ an organic solvent as reaction medium and
Suzuki coupling reactions. The conditions tolerated therefore could develop environmentally friendly pro-
the presence of a wide variety of functional groups, cesses. We obtained high yields with aryl chlorides
afforded good to excellent yields of the corresponding bearing a variety of substituents. It was also observed
products with different substrates starting from either that aryl iodides and bromides with hydrophilic sub-
aryl iodides or aryl bromides. Moreover, simple and stituents produced higher yields, while chlorides with
activated chlorides could also give the coupling prod- hydrophilic substituents gave moderate yields which
ucts in solvents of different polarity with satisfactory can be attributed to the nature of support (Table 1,
yields even in the absence of PTC such as tetrabuty- entries 3, 14 and 23). Optimum carboxylic groups
lammonium bromide (TBAB). The feasibility of recy- present on the hydrophobic surface are not only stabi-
cling of the catalyst was also examined over four runs. lizing the nanoparticles during the reaction, but also
Another limitation of the Suzuki–Miyaura reaction form hydrogen bonding with the hydrophilic substitu-
is that more economical aryl chlorides are less reac- ent of aryl halides and alcoholic groups of boronic
tive than aryl bromides and iodides, and protocols for acids. This therefore provides an environment for hy-
[
6-
such reactions conducted in pure water are very few.
drophobic guest molecules in water. The driving force
d,11b,c,12e,19]
Consequently, we tested the reaction be- for the hydrophobic guest molecules to diffuse onto
tween p-chlorobenzaldehyde and phenylboronic acid the sphere is mainly ascribed to the hydrophobic-hy-
in water, which delivered 85% isolated yield of the drophobic interactions in water. Interestingly, sub-
product in 13 hours at 908C in air (Table 1, entry 22). strates with hydrophobic substituents also afforded
1890
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 1889 – 1896

Palladium Nanoparticles on Amphiphilic Carbon Spheres: A Green Catalyst
Table 1. Suzuki–Miyaura coupling of aryl halides with bor- tion of aryl iodide in the presence of aryl bromide
[a]
onic acids by Pd/CSP in H O.
2
(Table 1, entry 6). Reactions with boronic acid other
than PhB(OH) also gave good yields (Table 1, en-
1
2
2
Entry
R
X
R
Yield
Time
[h]
[b]
tries 5, 9, 10, 11 and 12). Since the coupling of 2-pyr-
idyl halides is not as straightforward as coupling of
[%]
[
22]
1
2
3
4
5
6
7
8
9
H
p-Me
I
I
I
I
I
I
I
I
I
I
I
I
Br
Br
Br
Br
Br
Br
H
H
H
H
p-NO2
H
95
93
95
95
92
98
85
95
83
92
70
75[
95
90
1.5
1.5
2
1.5
1.5
1
2.5
2
3.5
1.5
4
most aryl halides. We performed these catalytic re-
actions with 2-iodopyridine and 2-bromopyridine. It
was found that a high isolated yield was obtained in
both the cases (Table 1, entries 7 and 20). Further-
more, sterically hindered aryl halides could be cou-
pled with substituted phenylboronic acids to give
moderate to good yields of 45–75% of products
p-OH
p-OMe
p-NO2
p-Br
2-pyridyl
m-I
H
H
(
Table 1, entries 11, 12 and 19). The sterically de-
p-Me
2,3,4-(OMe)
3
[c]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
p-OMe
2,6-(Me)2
2,6-(Me)2
H
p-OH
p-CHO
p-NO2
p-OMe
p-Me
2,6-(Me)2 Br p-OMe
2-pyridyl
H
p-CHO
p-OH
p-Me
H
manding 2,6-tolylbromide (Table 1, entry 19), howev-
er, proved to be a difficult substrate. After extended
reaction times, the product was isolated in a modest
p-CN
p-OMe
4
3.5
d]
[d]
H
H
H
H
H
H
45% yield. Substituted aryl iodides could be coupled
8
with less sterically hindered boronic acids and led to
required product in high yields (Table 1, entry 9).
In standardizing the reaction conditions in dime-
thylformamide (DMF) for the reaction of bromoben-
zene with phenylboronic acid, we used several bases
to obtain the best possible conditions (Scheme 2).
[
e]
[e]
90, 86
90
80
85
45
2.5, 3
1.5
9
8.5
12
5
Br
Cl
Cl
Cl
Cl
Cl
H
H
H
H
H
H
85
[f]
[f]
70, 80[
13, 10
g]
g]
[g]
85, 90
13, 9
20, 15
18
[
[g]
30, 55
30
90
p-NO2
13
[
a]
Reaction conditions: aryl halide (0.47 mmol), boronic
acid (0.70 mmol), K CO (1.40 mmol), Pd/CSP (0.2 mol%
2
3
vs. halide) in 3 mL of H O, under air, heated at 908C.
Isolated yield.
2
[
[
[
[
[
[
b]
c]
d]
e]
f]
Scheme 2. Suzuki–Miyaura coupling of aryl halides with bor-
2-Naphthylboronic acid was used instead of PhB(OH)2.
onic acids by Pd/CSP in DMF/H O.
Using Et N as base.
Isolated yield and time at 3 cycle.
TBAB was used (0.47 mmol).
2
3
rd
K CO , Et N and Bu N gave good yields but use of
g]
2
3
3
3
1
mol% of catalyst loading was used.
NaOAc as base afforded poor yields (Table 2,
entry 8). This may be due to the lower stability of Pd
good to excellent yields (Table 1, entries 2, 4, 9–12, nanoparticles in the increased ionic strength of
1
5, 17, 18 and 22). These good yields might be due to NaOAc solution resulting in ineffective protection of
[5d]
a combination of the hydrophobic effect of water and CSP to Pd nanoparticles.
the nature of the support,
leached Pd reactive species in water.
A varity of aryl halides
and stabilization of has been used in the reactions. The catalytic reactions
[
20]
[12b]
Deactivated of 3-iodopyridine with 4-formylphenylboronic acid
aryl bromides, and simple, activated aryl chlorides af- gave high isolated yields (Table 2, entry 3). Sterically
forded good yields in pure water (Table 1, entries 14, hindered aryl iodides reacted actively with substituted
17, 18, 21, 22 and 25). However, deactivated aryl phenylboronic acids; whereas sterically hindered aryl
chlorides gave lower yields of ~30% after 18 or 20 h, bromides reacted sluggishly (Table 2, entries 6, 7 and
with traces of homocoupling product (Table 1, en- 13). Reactions with boronic acids other than
tries 23 and 24). Simple aryl chlorides also gave the PhB(OH) also gave good yields (Table 2, entries 1, 2,
2
coupling product with excellent yield in the presence 3, 6, 7 and 15). Substituted aryl iodides could be cou-
of TBAB (Table 1, entry 21). The increase of activity pled with less sterically hindered boronic acids and
in the presence of TBAB may be also due to stabiliza- led to the required product in high yields in DMF as
tion of leached palladium species in the reaction mix- well (Table 1, entry 2). The solvent system DMF:H O
2
[21]
[12b]
ture. An increase in the catalyst loading for the ac- (9:1) was used in the reactions.
Just as expected,
tivated chlorides afforded good to excellent yield of the Suzuki reactions of activated aryl bromides with
the required products (Table 1, entries 22 and 23). phenylboronic acid at room temperature were unsatis-
Complete chemoselectivity was achieved for the reac- factory and lower yields were observed (Table 2,
Adv. Synth. Catal. 2011, 353, 1889 – 1896
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1891

Chandra Babu Putta and Sutapa Ghosh
COMMUNICATIONS
[a]
Table 2. Suzuki–Miyaura coupling of aryl halides with boronic acids by Pd/CSP in DMF/H O.
2
1
2
[b]
Entry
R
X
R
Yield [%]
Time [h]
1
2
3
4
5
6
7
8
9
H
p-Me
I
I
I
I
I
I
I
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
m-OMe, p-F
2,3,4-(OMe)3
p-CHO
H
90
80
95
90, 80
95
1
3
2
3-pyridyl
p-NO2
m-I
2,6-(Me)2
2,4,6-(Me)3
H
p-CHO
p-NO2
p-OMe
p-Me
2,6-(Me)2
p-NO2
p-NO2
H
[
c]
[c]
1.5, 10
H
2
4
6
p-OMe
p-OMe
H
H
H
H
H
p-CN
H
p-NO2
H
75
60
[d]
[e] [f]
[d]
[e] [f]
92, 94,[ 90,
7
3, 3, 3,
2.5, 3, 48 , 96,
1.5, 15
8
8
12
10, 20
12
12
13
3
g]
[h]
[h]
[i]
[g]
[h]
[h] [i]
92, 87, 20, 50, 25
2
[c]
[c]
10
11
12
13
14
15
16
17
95, 55
80
85
40
80, 45
70
[c]
[c]
65
20
p-Me
H
[
a]
Reaction conditions: aryl halide (0.47 mmol), boronic acid (0.70 mmol), K CO (1.40 mmol), Pd/CSP (0.2 mol% vs. halide)
2
3
in 3 mL of DMF: H O (9:1), under air, heated at 908C.
Isolated yield.
2
[
[
[
[
[
[
[
[
b]
c]
d]
e]
f]
10 wt% of Pd/C (3 mg, 0.6 mol% vs. halide) was used.
Using Et N as base.
3
Using Bu N as base.
3
Using NaOAc as base.
Isolated yield and time at 3 cycle.
g]
h]
i]
rd
Reaction performed at room temperature.
Reaction performed in toluene instead of DMF, using TEA as base.
entry 9). A comparison of catalytic activity of Pd/CSP
We verified that the Pd/CSP are recyclable for the
using commercial Pd on charcoal (10 wt%) was car- reaction of 4-bromobenzaldehyde with phenylboronic
ried out, which showed lower activity. The coupling acid in pure water and DMF invidually, and could be
reaction of activated aryl halides and phenylboronic reused in up to four cycles (Figure 2). Maintenance of
acid with commercial Pd/C catalyst took 10–20 h, the catalytic activity can be explained by the redepo-
whereas with Pd/CSP the reaction was completed in sition of most of the palladium nanoparticles on the
1
.5–10 h with a relatively low Pd loading under simi- CSP as the reaction ends and the system cools
[
24]
lar experimental conditions (Table 2, entries 4, 10 and down. Conversion as a function of reaction time for
4). The catalyst exhibited good catalytic activity with
1
À1
À1
TONs and TOFs of 441 and 294 h , 465 and 310 h ,
À1
392 and 29 h , respectively, for the reactions of 1-
iodo-4-nitrobenzene,
1-bromo-4-nitrobenzene,
1-
chloro-4-nitrobenzene, with simple phenylboronic
acid, respectively, in contrast to the TONs and TOFs,
À1
À1
À1
1
34 and 13.4 h , 92 and 6 h , 76 and 3.8 h , respec-
tively, for the same reaction conditions using the com-
mercial Pd/C catalyst.
The reaction of 4-bromobenzaldehyde with phenyl-
boronic acid in toluene and Et N as the base yielded
3
~
25% of the product under similar catalytic condi-
tions as for DMF or pure water (Table 2, entry 9, foot-
note [i]). The extent of leaching was significantly
lower when the reaction was carried out in toluene in-
stead of water or DMF (30% in toluene as compared
to 100% in DMF). Obviously, the nature of the sol-
vent played a crucial role in the occurrence and Figure 2. Recycling experiments for the Suzuki–Miyaura re-
[
23]
extent of leaching.
action of 4-bromobenzaldehyde and phenylboronic acid.
1892
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Adv. Synth. Catal. 2011, 353, 1889 – 1896

Palladium Nanoparticles on Amphiphilic Carbon Spheres: A Green Catalyst
Figure 3. Plot of conversion vs. reaction time for the recy-
cling of Pd/CSP for the coupling reaction of 4-bromobenzal-
Figure 4. XPS narrow scan for Pd (a) in fresh Pd/CSP and
dehyde and phenylboronic acid. Reaction conditions: 4-bro-
mobenzaldehyde (0.47 mmol), phenylboronic acid
0.70 mmol), K CO (1.40 mmol), Pd/CSP (0.2 mol% vs.
nd
(
b) in used (after 2 cycle) Pd/CSP.
(
2
3
halide) in 3 mL of H O, under air, heated at 908C. The con-
2
version was monitored by GC.
also attributed to the weak reducing nature of etha-
[
18c]
nol,
rendering it less susceptible to reduction.
Therefore, it was not a surprise that the unreduced Pd
the recycling of Pd/CSP is illustrated in Figure 3, for ions in addition to Pd(0) were found on the CSP sur-
the reaction of 4-bromobenzaldehyde with phenylbor- face based on their XPS results. XPS analysis of the
onic acid. A slight gradual decrease in activity was ob- catalyst recovered after two cycles, showed 3d5/2 and
served during four successive runs. Probable reasons 3d3/2 binding energies at 335.69 eV and 340.96 eV, re-
for the loss of activity were loss of leached palladium spectively, with a D=5.27 eV, which indicated the
active species in each cycle and somewhat lower pal- zero oxidation state of the metal. The marginal in-
ladium dispersion after re-deposition.
crease in the intensity of the shoulders at slightly
To test the leaching of palladium from the support higher binding energies at 337.03 eV and 342.53 eV
during the reaction, a hot filtration test was per- (D=5.5 eV) were corresponding to 3d5/2 and 3d3/2 of
formed in DMF and pure water individually for the Pd(II), respectively [Figure 4 (b)]. This revealed that
reaction of 4-bromobenzaldehyde with phenylboronic the oxidation of Pd(0) to Pd(II) was marginal under
acid which yielded ~70% of the product in both the the reaction conditions, but most of the Pd NPs were
cases with increased reaction times of up to ~20 h. redeposited on the support in Pd(0) form. The oxida-
ICP-AES analysis showed that ~3.3 ppm of Pd was tion of the Pd(0) and slight loss of the leached species
found in the filtrate; the solid was filtered at half of may account for the slightly diminished activity of the
the reaction time in hot conditions. A TEM image of catalyst over extending recycling. The reaction carried
catalyst after three cycles showed small agglomeration out in toluene underlined the importance of leaching
of nanoparticles [Figure 1 (b)]. The high-resolution of metal nanoparticles for better conversion of start-
[
23]
XPS narrow scan investigation of the fresh Pd/CSP ing materials to the required product.
During the
catalyst at the Pd 3d level showed 3d5/2 and 3d3/2 bind- reaction, the base transforms the (COOH) to carbox-
À
ing energies at 335.67 eV and 340.94 eV, respectively, ylate ligand (COO ), which acts as a strong chelating
with a D=5.27 eV, which clearly indicated the zero ligand for the active Pd species and prevented it from
oxidation state of the metal. The shoulders at slight aggregation during the course of the reaction. We
higher binding energies at 337.19 eV and 342.67 eV found that small amounts of palladium species
(
D=5.48 eV), were corresponding to 3d and 3d3/2 of (~0.19 ppm of Pd) remained in the filtrate after each
5
/2
[25]
Pd(II), respectively [Figure 4 (a)].
This indicated cycle; the catalyst exhibited only a marginal loss in
that most of the Pd was in the reduced form. The activity and required a slightly longer time to achieve
presence of a small amount of Pd as the unreduced similar results. And the cold filtrate led to product
metal ions on the surface of the support might be due formation in about ~6% yield after 30 hours of reac-
to the complexation of Pd(II) with the ketonic group tion time. The catalyst exhibited a loss in activity
of the levulinic acid. The unreduced form of Pd was after the fourth cycle because of the slower decompo-
Adv. Synth. Catal. 2011, 353, 1889 – 1896
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1893

Chandra Babu Putta and Sutapa Ghosh
COMMUNICATIONS
sition of support during the reaction. However, the Reusability Study of the Catalyst
decomposition of CSP is slower in water than in
After completion of the first cycle as described above, the
catalyst was recovered by filtration over a Teflon membrane
PTFE, 0.2 mm pore size) and used again in the next cataly-
sis cycle, after sufficient washing with dichloromethane,
DMF. This catalyst is air stable, and all the reactions
can be conducted in air and under phosphine-free
conditions.
(
Thus, it can be concluded that the carboxylate water (necessary to remove salts in the form of excess base),
groups present on the CSP are effective for prevent- acetone and subsequent drying at 608C.
ing the aggregation of the leached active palladium
species during the reaction. We did notice a decline in Supporting Information
the dissolution of the CSP support over extended re-
General remarks, procedure for the determination of the
cycling. Better performance of Pd/CSP in terms of ac-
degree of functionalization of CSP, TG-DTA thermograms
tivity and reusability has been obtained compared to
activated carbon or other inorganic support sys-
1
13
for the Pd/CSP catalyst, H NMR and C NMR spectra of
products are available in the Supporting Information.
[8c,26]
tems.
Experimental Section
Acknowledgements
Synthesis of CSP
P.C.B. acknowledges CSIR, New Delhi for providing research
fellowship. This work was supported by funding from DBT,
Government of India. The authors thank Dr. J. S. Yadav, Di-
rector, and Dr. M. Lakshmi Kantam, Head, I&PC division,
IICT for their kind support and encouragement. The authors
also acknowledge Dr. B. Sreedhar and Dr. R. K. Rana for
their support.
The procedure for preparing carbon spheres was in accord-
[17a]
ance with the reported method by Sun et al.
4 g) was dissolved in distilled water (40 mL) by stirring for
.5 h, and then the solution wase placed in a 40-mL Teflon-
Glucose
(
0
sealed autoclave and maintained at 1808C for 6 or 8 hrs.
The final product was isolated by centrifugation, washed by
three cycles of centrifugation/washing/redispersion in water
and in ethanol, and oven-dried at 608C for 8 h.
References
Synthesis of CSP-Supported Pd Nanoparticle
Catalysts
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[
[
[
2] M. Haruta, T. Kobayashi, H. Sano, N. Yamada, Chem.
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3] N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457–
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[17a,18a]
available elsewhere.
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were dispersed in absolute ethanol (25 mL) by sonicating
2
483.
for 30 min. Then PdCl (11 mg) was added into the above
2
4] a) R. F. Heck, J. P. Nolley, J. Org. Chem. 1972, 37,
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fuged, washed with distilled water twice, and dried at 608C
for 12 h. ICP-AES analysis showed that 3.42 wt% of Pd was
found in the CSP supported Pd nanoparticle catalyst.
2
1
320–2322; b) R. F. Heck, Acc. Chem. Res. 1979, 12,
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5] a) R. Nakao, H. Rhee, Y. Uozumi, Org. Lett. 2005, 7,
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Adv. Synth. Catal. 2011, 353, 1889 – 1896
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asc.wiley-vch.de
1895

Chandra Babu Putta and Sutapa Ghosh
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 1889 – 1896