An improved preparation of mesoporous silica-supported Pd as sustainable catalysts for phosphine-free Suzuki-Miyaura and Heck coupling reactions

Article abstract of DOI:10.1002/aoc.3036

An improved and eco-friendly procedure has been developed to generate mesoporous silica-supported palladium nanoparticles (SiO₂@PdNP) that could be used as a sustainable heterogeneous Pd catalyst for phosphine-free Suzuki-Miyaura and Heck coupling reactions with excellent turnover number and turnover frequency. The presence of Pd on the silica surface was detected by X-ray diffraction and the structural morphology of SiO₂@PdNP was obtained by transmission electron microscopy. The heterogeneous catalytic system is recyclable and leaching of the metal after the reaction is not apparently observed. Copyright

Full text of DOI:10.1002/aoc.3036

Full Paper
Received: 4 April 2013
Revised: 17 June 2013
Accepted: 26 June 2013
Published online in Wiley Online Library: 23 August 2013
(wileyonlinelibrary.com) DOI 10.1002/aoc.3036
An improved preparation of mesoporous
silica-supported Pd as sustainable catalysts
for phosphine-free Suzuki–Miyaura and Heck
coupling reactions
Basudeb Basu* and Susmita Paul
An improved and eco-friendly procedure has been developed to generate mesoporous silica-supported palladium
nanoparticles (SiO
and Heck coupling reactions with excellent turnover number and turnover frequency. The presence of Pd on the silica surface
was detected by X-ray diffraction and the structural morphology of SiO @PdNP was obtained by transmission electron micros-
2
@PdNP) that could be used as a sustainable heterogeneous Pd catalyst for phosphine-free Suzuki–Miyaura
2
copy. The heterogeneous catalytic system is recyclable and leaching of the metal after the reaction is not apparently observed.
Copyright © 2013 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: C―C coupling; Heck reaction; heterogeneous palladium; mesoporous silica; Suzuki–Miyaura reaction
supported Pd NPs have been prepared by different methodologies
in order to control and optimize metal NP sizes for effective cata-
Introduction
Catalysis is considered a foundational stone of green chemistry
and transition metal-catalysed organic reactions constitute the
central part of the contemporary organic synthesis. While
designing efficient heterogeneous catalyst systems, which are
often favoured for industrial uses both from economic and
environmental concerns, the major focuses include longer
lifetime, no leaching out from the surface and ease of achieving
the heterogeneous catalyst system. Since palladium (Pd) catalysts
systems are among the most widely used for the carbon–carbon
cross-coupling reactions, there are efforts by many chemists
throughout the globe for developing more efficient, versatile
and sustainable heterogeneous palladium catalysts for various
catalytic applications.
lytic applications.
The Suzuki–Miyaura and Heck reactions are unarguably
excellent tools for C―C coupling reactions of aryl halides with
suitable partners and, because of the great significance of these
reactions, they were recognized by the award of the Nobel Prize
in Chemistry in 2010. The Suzuki–Miyaura and Heck coupling
reactions have found widespread applications in academic
laboratories, fine chemical industries, synthesis of biologically
[
1,2]
active pharmaceuticals and several natural product syntheses.
[
1]
In view of some practical advantages of using heterogeneous
catalysts, such as easy separation and recycling, researchers have
immobilized palladium NPs on to various supports such as car-
[
4]
[5]
[6]
[7]
[8]
bon, magnetic materials, silica, hydroxyapatite, zeolites,
[
9]
[10]
With regard to heterogeneous supports. both organic polymers
and inorganic polymeric oxides have found ample uses. In the field
of heterogeneous catalysis, the size and nature of the interaction of
metal particles with an oxide support are critical in determining
metal–organic frameworks and organic polymers, and other
synthetic adsorbents like ion-exchange resins.
ongoing project towards developing various polymer-supported
transition metal catalysts,
[
11]
As part of our
[
11a]
we have developed a very simple,
[
2]
catalytic activity and selectivity. Among the inorganic oxides,
the majority of the novel heterogeneous catalysts are based on
silica supports. This is primarily because of some advantageous
properties that silica displays, such as excellent stability (chemical
and thermal), mechanical robustness, good accessibility and poros-
ity, and the fact that organic groups can be covalently attached to
the surface to provide catalytic centres. The major thrust to achiev-
ing success in designing and developing a heterogeneous Pd
catalyst includes improved stability, increased selectivity for the
reactions, phosphine-free catalyst system and reusability of the
heterogeneous catalyst. Palladium nanoparticles (NPs), highly
dispersed on various supports, have been widely studied over the
last few years owing to their various interesting properties, includ-
eco-friendly and practical technique to prepare palladium NPs
having been soaked onto commercially and chiefly available
silica gel in the presence of formic acid. To the best of our
knowledge, this is the first report for preparing highly dispersed
palladium metal NPs on to the silica gel surface by direct use of
formic acid as the reducing source. The resulting ‘SiO @PdNP’
2
was tested for its catalytic activity in Suzuki–Miyaura and Heck
coupling reactions. The results are promising, with the lowest
catalyst requirement as low as 0.006 mol% in small-scale
*
Correspondence to: Basudeb Basu, Department of Chemistry, North Bengal
University, Darjeeling 734013, India. E-mail: basu_nbu@hotmail.com
[
3]
ing catalysis in diverse organic reactions. Mesoporous silica-
Department of Chemistry, North Bengal University, Darjeeling734013, India
Appl. Organometal. Chem. 2013, 27, 588–594
Copyright © 2013 John Wiley & Sons, Ltd.

Silica-supported Pd catalyst for Suzuki–Miyaura and Heck reactions
Suzuki–Miyaura reactions and turnover number/turnover frequency
known to reduce palladium salts with the liberation of carbon di-
–1
[15]
(TON/TOF) (15 833/880 (h ), Table 1, entry 11); it can be recycled
oxide.
Previously, we developed a potential technique to im-
for several runs without any appreciable loss of activities and can also
be used efficiently under on-water conditions (Scheme 1). We report
our results, which in effect constitute an extremely low-cost but
highly efficient phosphine ligand-free and sustainable heteroge-
neous Pd catalyst for C―C cross-coupling reactions.
mobilize palladium onto poly-ionic Amberlite resins in the
À
[11a]
presence of formate (HCOO ) as the counter anion.
In this
work, we prepared SiO @PdNP in a very simple eco-friendly way
2
using formic acid as the reducing source. Thus, to a suspension
of commercially available silica gel (Source: SRL, India; mesh size:
325) (1 g) and palladium chloride (10 mg) in water (4 mL) was
added formic acid (85%, 20 μL). The mixture was then stirred
under an open atmosphere for 1 h at room temperature and then
evaporated to dryness. The solid mass was washed successively
Results and Discussion
Metal nanoparticles are usually prepared from its salts in the
2 2 2
with CH Cl and Me CO, and then dried under vacuum to afford
[
12]
presence of some reducing agents such as borohydride
black free-flowing silica. The presence of palladium embedded
with silica was confirmed by X-ray diffraction (XRD) measurement
(Fig. 1). The surface morphology of the newly prepared
[13]
[14]
and hydrazine
or by electrochemical reduction.
In the
case of immobilizing metal NPs on to insoluble polymeric
surface, one of the basic problems of using such reducing
agents is associated with the problem of formation of by-products
that either require additional steps for removal or are still retained
with the polymeric supports. Formic acid or its salts are also
2
SiO @PdNP was seen by using transmission electron microscopy
(TEM) (Fig. 2a, b). The TEM image clearly revealed that the nano-
sized palladium particles (mean size 3.5 nm ± 1 nm) were depos-
ited on to the spherical silica surfaces (Fig. 2c).
2
Table 1. Optimization of Suzuki–Miyaura coupling reaction in the presence of SiO @PdNP
a
b
Entry
Solvent
Toluene
Base
Additive
Pd@silica
Temp. (°C)
Time
% yield
1
2
3
4
5
6
7
K
K
K
2
2
2
CO
CO
CO
3
3
3
Nil
10 mg
10 mg
10 mg
10 mg
10 mg
10 mg
10 mg
10 mg
10 mg
100 mg
1 mg
75
75
75
75
90
90
75
50
90
35
90
75
12 h
5.5 h
5 h
95
90
93
92
85
92
90
65
85
92
95
94
Ethanol
Nil
Water–ethanol
Water–acetone
Water
Nil
K
2
CO
3
Nil
5 h
K
K
K
K
2
2
2
2
CO
CO
CO
CO
3
Nil
8 h
Water
3
TBAB
TBAB
TBAB
Nil
3 h
Water
3
3
5.5 h
12 h
8 h
c
8
Water
9
Water
KOH
CO
CO
Cs CO
1
0
Water–acetone
Water–acetone
Water
K
2
3
TBAB
Nil
5 h
d
1
1
1
2
K
2
3
18 h
9 h
2
3
Nil
10 mg
a
0
.01 mol% of TBAB was used.
b
Yield represents pure product obtained after column chromatography.
c
Yield calculated on the basis of unreacted starting iodoarene isolated.
d
3
2 3
equiv. of K CO was used.
Scheme 1. Suzuki-Miyaura and Heck reactions using SiO
Appl. Organometal. Chem. 2013, 27, 588–594
2
@PdNP
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

B. Basu and S. Paul
Miyaura and Heck coupling reactions. The Suzuki–Miyaura cou-
pling reaction was indeed found to be effective using our
catalyst and we turned our attention to optimizing the reaction
conditions with a model case 4-idotoluene and phenylboronic
acid. The results are presented in Table 1. Initial studies in
non-polar or polar organic solvents (toluene or ethanol) afforded
the desired biphenyl in 90–95% yield (entries 1 and 2). Further
studies in a mixture of water–organic solvents (acetone or etha-
nol) in the presence of different bases – tetraalkylammonium
salts, which are often employed in aqueous Suzuki–Miyaura
[
16a,b]
coupling
is by and large effective in a broad range of reaction conditions
entries 3–10). However, reducing the quantity of the catalyst
– at varying temperatures revealed that the catalyst
(
needs a higher temperature and longer reaction time and also
requires an excess amount of the base (entry 11). Although
Suzuki–Miyaura coupling in the model study afforded excellent
yields of the cross-coupled product under various conditions, we
considered optimal reaction conditions (as in entry 4) and
applied these to a wide variety of haloarenes and aryl boronic
acids. The results are presented in Table 2. Aryl iodides bearing
both electron-donating and electron-withdrawing groups such
as OMe, Me, F and COMe underwent a smooth coupling reac-
tion, affording the corresponding unsymmetrical biphenyls in
85–92% yields (Table 2, entries 1–6). Mechanistically, the oxidative
2
Figure 1. XRD of Pd@SiO .
Catalytic Activity of SiO
Coupling Reactions
2
@PdNP in Suzuki–Miyaura and Heck
Since the metal particle size has a prominent impact on the
catalytic performance and as the sizes of the Pd NPs are relatively
uniform in this case, it might be worth investigating Pd-catalysed
C―C cross-coupling reactions in the presence of SiO
catalytic activity of the resulting SiO @PdNP was tested in Suzuki–
2
@PdNP. The
2
(
a)
(b)
(c)
2
Figure 2. TEM images of Pd@SiO after preparation: (a) scale bar 10 nm; (b) SAED picture; (c) average particle size distribution.
2
Table 2. Suzuki-Miyaura reaction of aryl boronic acid and aryl halides using SiO @PdNP
a
Entry
Haloarene
―I
Arylboronic acid
Conditions Temp. (°C)/time (h)
Product
% yield
1
2
3
4
5
6
7
8
9
4-Me―C
6
H
4
C
C
C
C
C
C
C
C
C
C
C
C
6
6
6
6
6
6
6
6
6
6
6
6
H
5
H
5
H
5
H
5
H
5
H
5
H
5
H
5
H
5
H
5
H
5
H
5
―B(OH)
―B(OH)
―B(OH)
―B(OH)
―B(OH)
―B(OH)
―B(OH)
―B(OH)
―B(OH)
―B(OH)
―B(OH)
―B(OH)
2
2
2
2
2
2
2
2
2
2
2
2
75 / 5
75 / 6
4-Me―C
4-OMe―C
3-OMe―C
2-F―C
6
H
H
H
H
4
4
4
4
2
4
4
3
2
2
―C
―C
―C
―C
―C
―C
―C
―C
―C
―C
6
6
6
6
6
6
6
6
6
6
H
H
H
H
H
H
H
H
H
H
5
5
5
5
4
5
5
5
4
3
92
91
92
86
82
85
92
92
84
86
4-OMe―C
3-OMe―C
6
H
H
4
―I
―I
6
6
6
6
4
75 / 6
2-F―C
1,3-C
4-MeCO―C
3-Me―C ―Br
4-OMe―3―Me―C
1,3-C ―Br
4-OMe―1,3― C
4-OH―C ―Cl
4-NO ―C ―Cl
6
H
4
―I
75 / 12
75 / 24
75 / 7
6
H
4
―I
2
6 5
1,3-(C H )
6
H
4
―I
4-MeCO―C
3-Me―C
6
6
6
H
H
H
6
H
4
75 / 11
90 / 11
90 / 26
90 / 28
100 / 20
100 / 20
90 / 8
6
H
3
―Br
4-OMe―3―Me―C
6
H
4
2
1,3-(C
6
H
H
5
)
)
10
11
12
13
14
15
16
6
H
3
Br
2
4-OMe―1,3―(C
6
5
6
H
4
No reaction
No reaction
2
6 4
H
4-OMe―C
4-OMe―C
6
H
4
―I
―I
3-Me―C
6
H
H
H
4
4
4
―B(OH)
―B(OH)
―B(OH)
2
4-OMe―C ―3′-Me―C
6
H
4
6
6
H
H
4
86
90
78
89
6
H
4
4-OMe―C
3-Me―C
6
2
2
90 / 8
6 4
4-OMe―C H ―4′-OMe―C
4
3-Bromoquinoline
2-Iodothiophene
6
90 / 24
75 / 8
3-(3―tolyl)―quinoline
2-(4―Methoxyphenyl)
thiophene
6 4 2
4-OMe C H ―B(OH)
a
Yield represents pure product isolated after column chromatography.
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Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2013, 27, 588–594

Silica-supported Pd catalyst for Suzuki–Miyaura and Heck reactions
Table 3. Optimization of Heck reaction in the presence of SiO
2
@PdNP
a
Entry
Solvent
Base
Additive
SiO2@PdNP
Temp. (°C)
Time
% yield
1
2
Water
Water
Water
KOH
CO
CO
Nil
10 mg
10 mg
10 mg
10 mg
1 mg
90
90
90
90
90
75
75
75
8 h
8 h
Nil
Nil
K
2
3
Nil
b
3
K
2
3
CTAB
Nil
14 h
18 h
30 h
12 h
5 h
87
4
Water–acetone (1:1)
K
K
K
2
2
2
CO
CO
CO
3
15
[b]
5
6
Water
DMF
DMF
DMF
3
CTAB
Nil
Trace
Nil
3
10 mg
10 mg
1 mg
7
Et
Et
3
N
Nil
92
8
3
N
Nil
30 h
89
a
Yield represents pure product obtained after column chromatographic separation.
b
0.1 mmol CTAB was used.
2
Table 4. Heck reaction of iodoarenes with alkyl acrylates in the presence of catalytic SiO @PdNP
a
b
Entry
1
[A] Haloarene
[B] Alkyl acrylate
Conditions
[C] % yield
1
2
3
n
n
n
n
R = 4-Me, R = H, X = I
R = Bu
[A] / 75 °C / 5 h
[B] / 90 °C / 14 h
[A] / 75 °C / 6 h
[A] / 75 °C / 8 h
[A] / 75 °C / 7 h
92
87
87
91
86
83
81
83
93
90
77
72
Nil
Nil
c
1
2
3
2
R = 4-Me, R = H, X = I
R = Bu
1
2
3
3
4
R = 3-Me, R = H, X = I
R = Bu
1
2
3
R = 4-COMe, R = H, X = I
R = Bu
c
1
2
3
5
R = 4-OMe, R = H, X = I
R = Et
[
B] / 90 °C / 12 h
c
1
2
3
6
R = 2-F, R = H, X = I
R = Et
[A] / 75 °C / 8 h
[A] / 75 °C / 6 h
[A] / 75 °C / 6 h
1
2
3
7
8
R = 3-Cl, R = H, X = I
R = Et
1
2
3
R = 2-OMe, R = 5-Br, X = I
R = Et
[
B] / 90 °C / 11 h
[A] / 75 °C / 20 h
B] / 90 °C / 26 h
[A] / 140 °C / 24 h
B] / 140 °C / 26 h
c
1
2
3
9
R = 2-NH
2
, R = H, X = I
R = Et
[
1
2
3
n
10
R = 4-Me, R = H, X = Br
R = Bu
[
a
À1
À1
Condition [A]: Catalyst 10 mg mmol iodoarene in DMF; [B] catalyst 10 mg mmol iodoarene in water, CTAB 0.1 mmol.
b
Yield represents pure product isolated after column chromatography.
c
Starting iodoarenes were isolated in (7–9%) yield.
addition of aryl halides to Pd(0) depends on the nature of the
halogens and occurs in the descending order of I > Br> Cl.
points of view. We therefore began our studies on the Heck
reaction using 4-iodotoluene with n-butyl acrylate as the model
case, using water as the solvent (Table 3). Although the cross-
[
16c,d]
We therefore examined the coupling of other aryl electrophiles
bearing bromide and chloride. While aryl bromides underwent
smooth coupling with phenylboronic acids (entries 7–10), aryl chlo-
rides showed reluctance to undergo Suzuki–Miyaura coupling reac-
tion (entries 11 and 12) under the given reaction conditions.
Changing the coupling partner phenylboronic acid with m-tolyl
phenylboronic acid and p-anisyl phenylboronic acid did work effi-
ciently with bromo- and iodoarenes (Table 2, entries 13–16).
Heteroaryl halides (I and Br) also undergo Suzuki–Miyaura
coupling reactions, affording corresponding unsymmetrical
biphenyl in good yields (entries 15 and 16).
2 3
coupling did not occur in the presence of KOH or K CO as the
base at 90 °C (Table 3, entries 1 and 2), use of a catalytic amount
of phase transfer catalysts (cetyltrimethylammonium bromide,
CTAB) did work efficiently for the Heck coupling reaction, affording
the desired cross-coupled product in 87% yield (entry 3). Change in
the solvent, i.e. use of a mixture of water–acetone (1:1) or reduction
in the amount of catalyst, did not result in a satisfactory yield of the
cross-coupled product (entries 4 and 5). On the other hand,
conducting the reaction in dimethylformamide (DMF) and NEt as
3
the base showed excellent conversion, though reduction in the
amount of catalyst afforded similar results requiring a much longer
reaction time (entries 6–8). Such observation, however, indicates that
the catalyst has a pronounced effect in controlling the kinetics of the
reaction. The general applicability of the reaction conditions was
The catalytic efficiency of this SiO @PdNP was further
2
explored in another widely applicable Heck coupling reaction
between aryl iodide and alkene. In recent years, on-water Heck
reaction has drawn interest from ecological and economic
Appl. Organometal. Chem. 2013, 27, 588–594
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

B. Basu and S. Paul
looked into by taking other iodoarenes, as shown in Table 4. Basically,
two conditions were employed, viz. condition [A] and condition [B];
both were found to be suitable for the Heck coupling of iodoarenes,
but not for bromoarenes. Thus 4-bromo-2-iodoanisole, when
subjected to condition [A] or [B], afforded only iodo-coupled
product ((E)-ethyl 3-(4-bromo-2-methoxyphenyl)acrylate (entry 8)
or 4-bromotoluene failed to undergo Heck reaction with acrylate
ester, even after heating the reaction mixture at 145 °C under
condition [A] or [B] (entry 10). This selectivity in coupling, however,
could be important for further functionalization. It may be noted
that exclusive trans-selectivity in the coupled product was
observed in each case, as seen from the value of the coupling
constant (J) in the range 15.6–16.2 Hz.
Conclusion
In summary, we have developed an improved and eco-friendly
procedure for the preparation of quite uniformly dispersed sil-
ica-supported palladium nanoparticles (SiO @PdNP) that showed
2
excellent catalytic activity in phosphine-free Suzuki–Miyaura and
Heck coupling reactions. However, the catalyst was not effective
in the Suzuki–Miyaura reaction of chloroarenes or in the Heck
reaction of bromoarenes, even at higher temperature. Other
notable features are: use of as low as 0.006 mol% of Pd, high
TON/TOF (15 833/880 (h ), on-water conditions and recyclabil-
ity. In addition, the catalyst (SiO
heterogeneous catalyst in C―C cross-coupling reactions, which
is not often found in literature reports.
of TON/TOF, which are much higher than those reported for
À1
@PdNP) is likely to act as a true
2
[
17c] [18a] [19]
Leaching of the palladium remains a crucial parameter to
measure the efficiency of a heterogeneous catalyst. Several ex-
,
,
High values
[
17]
[19a,20]
periments have been designed and reported in the literature.
other silica-supported Pd systems,
the heterogeneous cata-
In an attempt to determine any leaching of the palladium after
the reaction, the Suzuki–Miyaura reaction between 4-iodotolune
and phenylboronic acid (1:1.2) in water–acetone (1:1) was
lytic activity and reuse might be useful for industrial applications.
stopped after 20 min (5.2% conversion; high-performance liquid Experimental
chromatography, HPLC) and the catalyst was filtered off. The fil-
All the coupling reactions were carried out under open atmo-
sphere. All the aryl halides were purchased from Aldrich
Chemicals, and used as received. PdCl was purchased from
trate (reaction mixture) was then heated at 75 °C for 7 h and then
monitoring by HPLC showed no appreciable conversion (6.2%).
17c,18
Following the literature procedure,
we also performed an
2
Fluka, Switzerland, and used as received. Silica used for immobi-
lization: source, SRL, India; particle size 325 mesh. The palla-
dium-impregnated silica was stored after drying without any
precautions (absence of oxygen). Column chromatography:
silica (60-120 mesh) (SRL, India), thin-layer chromatography on
Merck plates coated with silica gel 60, F254. Solution NMR spec-
tra of the organic compounds were recorded with a Bruker AV
Hg(0) poisoning experiment. Thus the reaction of 4-iodotolune
and phenylboronic acid (1:1.2) in water–acetone (1:1) was
stopped after 1 h, when about 31% conversion to the
corresponding biphenyl was measured by HPLC analysis. Then,
Hg(0) (100 mg) was added to the reaction mixture and the
reaction allowed to continue for another 5 h. After work-up, HPLC
analysis showed 94% conversion to the corresponding biphenyl.
These observations apparently suggest that the metal might not
get leached out after the reaction, though the probability of
homogeneous catalysis by the leached palladium cannot be
3
00 spectrometer using Tetramethylsilane as the internal
standard. Centrifugation was carried out using Superspin R-V/
F
M
. HPLC was performed using ZORBAX RX-SIL, 5 μm, 4.6 ×
1
50 mm column and eluent was n-hexane (flow rate 4 mL
2
ruled out. The recyclability of the catalytic system SiO @PdNP
À1
min ). X-ray diffraction technique was performed with a
Rigaku SmartLab X-ray diffractometer operating at 9 kW
was explored again in the model case of Suzuki–Miyaura reaction
between 4-iodotoluene and phenylboronic acid. The catalyst
was found to be active for four consecutive runs tested without
any appreciable loss of activity, and the results are shown
in Table 5.
(
200 mA and 45 kV) using Cu Kα (λ = 1.5406 Å) radiation. Low-an-
gle XRD was done in continuous θ/2θ scanning mode with a
À1
scanning speed of 1° min using a step size of 0.02°, whereas
for high-angle XRD studies 2θ scanning mode with the same
speed and step size was used, maintaining the grazing
incidence angle (ω) at 0.3°. TEM studies of the samples were
done using a JEM 2010 electron microscope operating at an
accelerating voltage of 200 kV.
Catalyst recovery and use
After the reaction, the mixture was centrifuged at 10 000 rpm for
1
0 min and the supernatant liquid was removed. Similar centrifu-
gation and subsequent removal of the supernatant liquid was
performed by adding acetone (1 mL each, three times) and then
diethyl ether (1 mL each, three times) and finally the catalyst
Representative Procedure for Suzuki–Miyaura
Coupling Reaction
2
SiO @PdNP was air dried for use in the next run.
A mixture of 4-iodotoluene (218 mg, 1.0 mmol), phenylboronic
acid (145.2 mg, 1.2 mmol) and potassium carbonate (207 mg,
1
1
.5 mmol) was made in water–acetone (1:1, 2 mL) and then
0 mg of SiO @PdNP (0.06 mol%) was added. The mixture
Table 5. Recycling of the catalyst SiO
2
@PdNP for Suzuki–Miyaura re-
2
action between 4-iodotoluene and phenylboronic acid
was heated at 75 °C under refluxing conditions for 5 h. After
cooling, the reaction mixture was subjected to centrifugation
Run
1st
2nd
3rd
4th
(
10 000 rpm, 10 min × 3), followed by filtration through a mem-
Time (h)
5
5
5
5
brane filter (200 nm). The filtrate was diluted with water and
Temperature
75 °C
92
75 °C
89
75 °C
91
75 °C
88
extracted with ether (3 × 5 mL) and the combined organic layer
a
Yield (%)
was dried over anhydrous Na
residue, which was purified by column chromatography on silica gel
light petroleum) to give a colourless solid (170 mg, 92%). The com-
2 4
SO . Removal of the solvent left a solid
a
Yield represents pure product obtained after column chromatographic
separation.
(
pound was characterized as 4-phenyltoluene from its melting point
wileyonlinelibrary.com/journal/aoc
Copyright © 2013 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2013, 27, 588–594

Silica-supported Pd catalyst for Suzuki–Miyaura and Heck reactions
[
21]
1
13
[
3] a) V. L. Budarin, J. H. Clark, R. Luque, D. J. Macquarrie, R. J. White,
(
m.p. 46–47 °C; lit. 46–48 °C), spectral data (IR, H and C NMR
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spectra), and comparison to literature values. Characterizations of
other compounds were made by spectral data and are given in the
supporting information.
1
9, 2818; c) B. Karimi, S. Abedi, J. H. Clark, V. Budarin, Angew. Chem.
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Representative Procedure for Heck Reaction in DMF
106; f) S. Mandal, D. Roy, R. V. Chaudhari, M. Sastry, Chem. Mater. 2004,
To a suspension of SiO
were added 4-bromo-2-iodo anisole (313 mg, 1 mmol), ethyl acrylate
220 mg, 1.5 mmol) and triethylamine (150 mg, 1.5 mmol), and the re-
2
@PdNP (10mg, 0.06mol%) in DMF (2mL)
16, 3714; g) D. Astruc, Inorg. Chem. 2007, 46, 1884; h) J. C. Garcia-Martinez,
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(
action mixture was heated under an open atmosphere with gentle
magnetic stirring at 75 °C for 7 h. After cooling, the reaction mixture
was subjected to centrifugation (8000 rpm,10 min), followed by filtra-
tion through a membrane filter (200 nm) to isolate the catalyst. The
filtrate was diluted with water and extracted with ether (3 × 5 mL)
and the combined organic layer was dried over anhydrous Na SO .
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4] a) S. M. Chergui, A. Ledebt, F. Mammeri, F. Herbst, B. Carbonnier, H. B.
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2
4
The combined washings were concentrated under reduced pressure
leaving a residue, which was purified by column chromatography on
silica gel. Elution with ethyl acetate–light petroleum (1:10) afforded
ethyl-3-(5-bromo-2-methoxyphenyl)acrylate as a colourless solid
2
011, 3174; b) S. Paul, J. H. Clark, Green Chem. 2003, 5, 635; c) C.
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1
2
(256 mg, 90% yield). The compound was characterized as (E)-ethyl
3
-(5-bromo-2-methoxyphenyl)acrylate from its melting point (m.p.
[11a]
1
13
4
2
64–65 °C; lit.
63–64 °C), spectral data (IR, H and C NMR spectra)
and comparison to literature values. Characterizations of other
compounds were made by spectral data and are given in the
supporting information.
Crudden, J. Catal. 2007; 252, 97; i) M. Cai, Q. Xu, Y. Huang, J. Mol.
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Representative Procedure for Heck Reaction in Water
To a suspension of SiO @PdNP (10 mg, 0.06 mol%) in water (2 mL)
2
were added 4-bromo-2-iodo anisole (313 mg, 1 mmol), ethyl acrylate
(220 mg, 1.5 mmol), potassium carbonate (207 mg, 1.5 mmol) and
CTAB (36.4 mg, 0.1 mmol), and the reaction mixture was heated un-
der an open atmosphere using refluxing conditions with gentle mag-
netic stirring at 90 °C for 11 h. After cooling, the reaction mixture was
diluted with water and extracted with ethyl acetate (3 × 5 mL) and
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9] a) K. Kaneda, M. Higuchi, T. Imanaka, J. Mol. Catal. 1990, 63, L33; b)
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2 4
the combined organic layer was dried over anhydrous Na SO . The
combined washings were concentrated under reduced pressure,
leaving a residue, which was purified by column chromatography
on silica gel. Elution with ethyl acetate–light petroleum (1:10)
afforded ethyl-3-(5-bromo-2-methoxyphenyl)acrylate as a colourless
1
4127; d) M. L. Kantam, S. Roy, M. Roy, M. S. Subhas, P. R. Likhar, B.
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[11a]
solid (241 mg, 85% yield; m.p. 64–65 °C; lit.
63–64 °C). A similar
procedure was employed for other reactions, as shown in Table 4.
Supporting information
[
11] a) B. Basu, S. Das, P. Das, B. Mandal, D. Banerjee, F. Almqvist,
Synthesis 2009, 1137; b) Y. Monguchi, K. Saki, K. Endo, Y.
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Supporting information may be found in the online version of
this article.
Acknowledgements
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A. Desforges, R. Backov, H. Deleuze, O. Mondain-Monval, Adv. Funct.
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We are grateful to the Department of Science and Technology, New
Delhi, for financial support (Grant No. SR/S1/OC–86/2010 (G)) and to
Dr Goutam De, Central Glass and Ceramic Research Institute, Kolkata,
India, for help with XRD measurements. We wish to thank the
reviewers for extending useful comments to improve the manuscript.
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