Scalable synthesis of catalysts for the Mizoroki-Heck cross coupling reaction: Palladium nanoparticles assembled in a polymeric nanosphere

Article abstract of DOI:10.1039/c0nj00898b

Palladium nano-spheres 160 nm in diameter, as an assembly of uniform 5 nm nanoparticles, are accessible using a facile one step method under continuous flow on a spinning disc with hydrogen gas as the reducing agent. The stable colloidal system is an effe

Full text of DOI:10.1039/c0nj00898b

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PAPER
Scalable synthesis of catalysts for the Mizoroki–Heck cross coupling
reaction: palladium nanoparticles assembled in a polymeric nanospherew
a
a
b
a
Jianli Zou, K. Swaminathan Iyer,* Scott G. Stewart* and Colin L. Raston
Received (in Victoria, Australia) 15th November 2010, Accepted 6th January 2011
DOI: 10.1039/c0nj00898b
Palladium nano-spheres 160 nm in diameter, as an assembly of uniform 5 nm nanoparticles,
are accessible using a facile one step method under continuous flow on a spinning disc with
hydrogen gas as the reducing agent. The stable colloidal system is an effective catalyst for the
Mizoroki–Heck reaction, as established for the reaction between several aryl halides and n-butyl
acrylate, and can be readily recycled without a change in their catalytic activity.
in a variety of Suzuki reactions. More recently, Wan et al.
Introduction
reported 3 nm palladium nanoparticles supported on ordered
mesoporous silica–carbon nano-composites exhibiting high
22
Heterogeneous catalytic systems have an advantageous
practical convenience over homogeneous systems because of
their ease of separation which is usually through simple
catalytic activity for coupling reactions. However, the
problem of catalytic recovery is not completely resolved using
the aforementioned supported-heterogeneous systems. An
inherent challenge in using supported palladium nano-
particles is their disassociation from the substrate support,
resulting in catalyst leaching from the substrate over time. This
leaching is often associated with a drop in catalytic activity
and reusability.
1
–3
filtration. The recovery and reusability of catalysts is a very
important factor especially in the case of noble metal (Pd)
catalysed C–C coupling reactions like the Mizoroki–Heck and
Suzuki cross coupling reactions, and heterogeneous systems
also dispense with the need for the design and synthesis of
often expensive ligands that feature in homogeneous
4
–12
systems.
The interest and study of supported palladium
The use of palladium nanoparticles as heterogeneous
catalysts in C–C coupling reactions is an area of current
interest due to the possibility of fine tuning the shape and size
of the colloidal system to control the catalytic efficacy. The
first well-known case for the use of colloidal Pd catalysts was
independently reported by Beller et al. and Reetz et al. in 1996.
In the former case palladium nano-particles were stabilized by
catalysts for applications in C–C cross coupling reactions had
its origins in 1990’s, where initially palladium was often
embedded on or in to supporting materials such as zeolite
2 3
and inorganic oxides, including graphite oxide, MgO, Al O
1
.
3–18
and SiO
2
With nano-materials exhibiting unique physical
and chemical properties relative to their larger counterparts,
the synthesis and application of these supported palladium
23
tetra-octyl ammonium chloride, whereas in the latter they
24
were stabilized in propylene carbonate. More recently
1
9–22
catalysts is attracting ever increasing interest.
Bradley
et al. have recently developed amino modified resins as
supported materials for in situ reduction of Pd(OAc) to
nm Pd nano-particles, which are stable and can be reused
1
9
palladium clusters stabilized in polymer micelles, dendrimers
2
and ionic liquids have been widely studied as recyclable
25–27
7
catalysts.
The synthesis of colloidal palladium systems
usually avoids the multi-step method for generating supported
systems with their associated leaching problem, but they
are thermodynamically unstable leading to aggregations,
especially at high temperatures. Such aggregations can result
in the loss of active surface area for effective catalysis, thereby
diminishing their potential for recycling.
a
Centre for Strategic Nano-Fabrication, School of Biomedical,
Biomolecular and Chemical Sciences, The University of Western
Australia M313, 35 Stirling Highway, Crawley, WA 6009, Australia.
E-mail: swaminatha.iyer@uwa.edu.au; Fax: +61 8 6488 1005;
Tel: +61 8 6488 4470
School of Biomedical, Biomolecular and Chemical Sciences,
The University of Western Australia M313, 35 Stirling Highway,
Crawley, WA 6009, Australia. E-mail: sgs@ uwa.edu.au;
Tel: +61 8 6488 3180
b
Poly(vinylpyrrolidone) (PVP) has been shown to be an
effective matrix in stabilising palladium nanoparticles as
28–31
w Electronic supplementary information (ESI) available: Schematic of
spinning disc processor, TEM image of as-prepared palladium nano-
particles using hydrazine as the reducing reagent, TEM image of a
typical palladium nanomaterials synthesized using PVP with a mole-
cular weight of 360 000, TEM images of palladium–PVP spheres
synthesized via mechanical stirring, EDS data of palladium nano-
catalyst for cross coupling reactions.
Here we report the
synthesis of novel palladium composite nano-spheres using
spinning disc processing (SDP) as a facile one step process
with hydrogen gas as the reducing agent for scalable size
controlled synthesis of heterogeneous catalysts. The nano-
spheres herein are held together by a PVP scaffold. We
1
spheres, H NMR data and GC-MS data of the product of
Mizoroki–Heck reactions in Table 1–5. See DOI: 10.1039/c0nj00898b
8
54 New J. Chem., 2011, 35, 854–860
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anticipated that the PVP scaffold is likely to prevent catalytic
leaching with time, with the prospect of maintaining high
colloidal stability, structural integrity and reusability.
Results and discussion
Synthesis and characterization of palladium composite
nano-spheres
SDP is a microfluidic process intensification strategy with a
continuous flowing film (1 to 200 mm) on a rapidly rotating
disc surface (usually up to 3000 rpm) (Fig. S1, ESIw). It
facilitates controlled nucleation and growth of nanoparticles
3
2,33
for the fabrication of different nano-materials,
and has
potential for the large scale synthesis of a range of nano-
materials/nanoparticles. Such a microfluidic platform offers an
alternative approach in alleviating the obstacles and limita-
tions of the relaxed fluid dynamic regimes associated with
conventional batch processing. In essence SDP offers
improved micromixing environments on a rapidly rotating
surface which ensures that there is a very high surface area
to volume ratio for the reacting fluid, resulting in supersatura-
tion of the gas phase reagents and nanocrystal nucleation and
growth at room temperature. The mixing for SDP is achieved
by feeding the reagents close to the centre of a rapidly rotating
disc. The behavior of a thin film on a rapidly rotating disc can
be associated with two zones: (i) The injection zone where the
reagents hit the surface close to the centre of the spinning disc
forming a spin-up pool with the flow of liquid from the pool
controlled by viscous drag associated with centrifugal forces
where rapid nucleation and instantaneous growth initiation
occur. (ii) The acceleration and synchronized flow zone where
the fluid film initially experiences an increase in the radial flow
velocity with the liquid then rotating close to the disc velocity
Fig. 1 (a) TEM image, (b) cross-section TEM image, (c) high
resolution TEM image, (d) X-ray diffraction pattern of the typical
palladium nano-spheres used in Mizoroki–Heck cross coupling reactions.
The use of hydrogen gas as the reducing agent is noteworthy
for the following reasons: (1) high purity palladium catalysts
are accessible void of reaction by-products associated with
traditional reducing agents and (2) it presumably influences
the growth of this unique nanostructure of palladium nano-
spheres in the present case, noting that other reducing agents
such as hydrazine result in individual nanoparticles (Fig. S2,
ESIw) rather than nano-spheres. It is noteworthy that the wavy
thin film generated on the spinning disc surface has been
3
4
35
with the flow becoming similar to the Nusselt model. The
shear forces and viscous drag between the moving fluid layer
and the disc surface create turbulence and ripples which gives
rise to highly efficient mixing within the thin fluid layer. The
turbulent waves thereby provide a high degree of growth
control in zone (ii).
demonstrated to enhance the hydrogen gas uptake, which
in turn is important for effective and rapid reduction of
H PdCl .
2
4
The molar ratio of PVP to palladium was varied in order to
optimise the synthesis of the palladium nano-spheres. SEM
2 4
images show that a molar ratio (PVP : H PdCl ) of 20 : 1 gave
In a typical experiment aqueous solutions of H
2
PdCl
4
were
a more uniform shape than for a ratio of 10 : 1, for a fixed disc
speed of 2000 rpm. For a molar ratio of 30 : 1, the mono-
dispersity of the nano-spheres decreased compared to the ratio
of 20, due to coalescence in the presence of excess of polymer
(Fig. 2a–c). Varying the disc spinning speed also affected the
size and distribution of the nano-spheres when investigating
the fixed molar ratio (Fig. 2d and e). A disc speed of 1500 rpm
with a molar ratio of 10 resulted in a more uniform and
separated nano-spheres than for disc speeds of 2000 rpm and
2500 rpm. This phenomenon is attributed to shorter residence
times on the disc with increasing speed, resulting in a decrease
in the time for the reacting mixture to equilibrate.
mixed with PVP at various molecular ratios of PVP relative to
palladium, and then fed through a jet feed onto the spinning
disc. Simultaneously the hydrogen gas reducing agent was fed
through another jet feed slightly above ambient pressure,
which resulted in the formation of palladium nano-spheres
of uniform size and shape (Fig. 1). The nano-spheres result
from the spontaneous assembly of a large number of 5 nm
palladium particles within the dynamic thin films on the
surface of the disc in the presence of PVP, rather than discrete
individual palladium nanoparticles. The role of the PVP is
multifunctional, in acting as a scaffold preventing leaching of
palladium during catalysis from the confines of the nano-
spheres into the solution and in acting as a stabiliser main-
taining high colloidal stability thereby preventing loss of
activity due to agglomeration. TEM images (Fig. 1a–c) reveal
an assembly of palladium nano-particles with a mean diameter
of 5 nm. The XRD pattern (Fig. 1d) shows that the palladium
nanoparticles are highly crystalline.
The effect of varying the average molecular weight of the
PVP polymer was also investigated. Using a lower average
molecular weight of PVP (10 000) resulted in smaller nano-
spheres, as expected with a shorter scaffolding structure, with
the average size of 120 nm (Fig. 3), in contrast to 160 nm
(Fig. 2d) for an average molecular weight of 40 000 for the
PVP. Increasing the speed resulted in a decrease in size
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Fig. 3 SEM images of palladium nano-spheres: (a)–(c) disc speed
1
500, 2000 and 2500 rpm, respectively (10 : 1 molar ratio of PVP to
Pd; 10 000 MW PVP). Scale bar indicated is 200 nm.
not provide the intense micro-mixing associated with SPD,
and moreover the reaction time using SDP is much shorter
which relates to the high mass transfer of hydrogen gas
associated with the breakdown of surface tension arising from
waves and ripples on the dynamic thin films.
Catalytic activity
Fig. 2 SEM images of palladium nano-sphere hybrids: (a)–(c) molar
ratio of PVP to palladium 10, 20 and 30, respectively (disc speed
The catalytic activity of the optimised 160 nm palladium nano-
spheres was first trialled for the Mizoroki–Heck cross coupling
reaction between iodobenzene and n-butyl acrylate. All
reactions were carried out at 60 1C overnight with a range of
catalyst loading, as indicated in mol%. In each case the
isolated yield of 1,2-disubstituted olefinic product 1 is shown
in Table 1.
2
2
4
000 rpm; 40 000 MW PVP), (d) and (e) disc speeds of 1500 rpm and
500 rpm, respectively (molar ratio of PVP to palladium 10;
0 000 MW PVP). Scale bar indicated is 200 nm.
3
6
distribution, with uniform nano-spheres obtained at 2500 rpm.
The time needed for forming uniform nano-spheres decreased
(
higher speed) for shorter chains (2500 rpm for PVP 10 000
Given the success of using one mole percent of the catalyst
for iodobenzene and n-butyl acrylate, this loading was chosen
in studying the Mizoroki–Heck cross coupling reaction with a
range of iodobenzenes (Table 2). Excellent catalytic activity
was established for both activated (containing a para-electron
withdrawing group) and deactivated iodobenzene derivatives
and 1500 rpm for PVP 40 000). This establishes that the time
needed to equilibrate in forming uniform nano-spheres using
SDP is a function of the polymer chain length. Indeed, using a
much higher molecular weight, PVP360 (MW 360 000),
resulted in non-uniform and poorly-dispersable nano-spheres
for all accessible disc speeds, r2500 rpm (Fig. S3, ESIw). High
colloidal stability and uniformity in size is an important
parameter to test catalytic efficacy. The 160 nm nano-spheres
Table 1 Isolated yield of the Mizoroki–Heck reaction involving
iodobenzene and butyl acrylate as the mole percent of the catalyst is
varied
(
Fig. 2d, PVP to palladium 10, disc speed 1500 rpm,
0 000 MW PVP) were used in Mizoroki–Heck cross coupling
4
reactions.
In further studying the effect of the use of SDP in fabricat-
ing the nano-spheres, a control batch experiment was under-
taken whereby hydrogen gas was bubbled into a rapidly stirred
aqueous mixture of H
0 seconds. During this time the solution turned from yellow
to black which is indicative of reduction of H PdCl , with the
2 4
PdCl and PVP 40 000 for 30 to
Entry
Mol% of Pd catalyst
Yield (%)
6
1
2
3
4
5
3.3
1
0.67
0.33
0.1
97
96
96
93
89
2
4
resulting palladium/polymer composite spheres varying in
size from several hundred nano-metres to micro-metres
(
Fig. S4, ESIw). Thus rapid stirring in batch processing does
8
56 New J. Chem., 2011, 35, 854–860
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a
Table 2 Mizoroki–Heck reaction of iodobenzene derivatives with
n-butyl acrylate
Table 4 Mizoroki–Heck reaction of bromobenzene derivatives
a
Isolated
yield (%)
Entry
1
Aryl halide
Product
Entry
1
Aryl halide
Time/h
24/48
Conversion (%)
25/30
94
2
3
95
98
b
2
3
4
4
100
24
11
4
95
95
24/48
24
9/40
c
42
5
5
a
0
DMF, K
.98 mmol bromobenzene, 1.47 mmol n-butyl acrylate (1.5 eq.), 2 mL
CO 2.45 mmol (2.5 eq.), tetra-n-butyl ammonium chloride
a
Reaction conditions: Iodobenzene derivatives (0.98 mmol, 1 eq.),
N (2.45 mmol, 2.5 eq.), and
mol% Pd nano-sphere catalyst in DMF (2 mL), 60 1C, overnight.
2
3
b
n-butyl acrylate (1.18 mmol, 1.2 eq.), Et
3
TBAC 0.98 mmol (1 eq.), 135 1C. Methyl acrylate was used.
Isolated yield.
c
1
1
2–6). In all cases the products (7–11) were characterized by H
(
reaction has been thoroughly studied by Jeffery et al. in
4
2–44
NMR and GC-MS, and the isolated yield was reported. As
expected none of the 1,1-disubstituted product was observed.
The palladium/PVP nano-sphere catalyst showed a lower
catalytic activity in the bromobenzene system, as normally
phosphine free systems.
The improved reaction efficiency
of TBAC relative to the bromide analogue (TBAB) was also
observed in our system. This effect of the quaternary ammonium
salt is consistent with previous work, which depends both on
the nature of the anion and the cation. Using sodium acetate
or sodium carbonate as the base failed to improve the reaction
conditions even in the presence of TBAC.
3
7–41
observed in the Mizoroki–Heck reactions,
using the
identical conditions to the study of iodobenzene. Additionally,
there was a little effect on increasing the reaction temperature
from 60 1C to 135 1C. However, greater activity was evident
After optimizing the reaction conditions for bromobenzene,
several bromobenzene and chlorobenzene derivatives (12–16)
were investigated, Table 4. As expected, for electron poor aryl
bromides (13) the yields were very high, and conversely for
electron rich bromobenzenes (12, 14–16) the yields were
relatively low. There was no activity detected in the case of
chlorobenzenes.
2 3
when switching the base from triethylamine to K CO in the
presence of a phase transfer agent, namely tetra-n-butyl-
ammonium chloride (TBAC) (entry 5, Table 3). The use of
tetraalkylammonium salts in general as phase transfer agents
in increasing the reaction rate in the Mizoroki–Heck type
Table 3 Outcome of the Mizoroki–Heck reaction involving bromo-
benzene and n-butyl acrylate, and the effect of various bases and phase
transfer agents
Kinetic and recycling studies
a
Recycling the palladium nano-sphere catalyst was investi-
gated, along with the kinetics of the reaction of iodobenzene
with n-butyl acrylate. After each reaction, the catalyst was
recovered by centrifugation, washed by DMF three times,
stored under argon and used for the next reaction without
further treatment. We have established that the Pd nano-
sphere catalyst can be recycled five times involving 16 hour
reactions, without losing any catalytic activity, Table 5, and
can be easily re-dispersed in DMF or water after each reaction.
The size of palladium nanoparticle within the nano-spheres
slightly increases after the first run, and remains the same size
from the second to fifth recycle, Fig. 4. The reason for the
particle growth is widely postulated that the Ostwald ripening
effect at elevated temperatures may be a dominant force
resulting in a slight increase in the particle size in the initial
Entry
Base
(Et)
Phase transfer agent
Time/h
Yield (%)
1
2
3
3
N
24
24
24
24
24
20
24
24
48
24
48
Trace
20
25
K
2
K
2
K
2
K
2
K
2
K
2
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
TBAB
TBAB
TBAC
b
4
26
76
c
5
6
7
8
9
e
TBAA
34
38
b,d
TBAC
TBAC
TBAC
TBAC
TBAC
b
c
NaOAc
NaOAc
NaHCO
NaHCO
4
b
c
5
b
c
1
1
0
1
3
3
9
15
b
c
a
0.98 mmol bromobenzene, 1.47 mmol n-butyl acrylate (1.5 eq.), 2 mL
DMF, base 2.45 mmol (2.5 eq.), tetra-n-butylammonium bromide
(
TBAB) or tetra-n-butyl ammonium chloride (TBAC) 0.98 mmol (1 eq.),
b
c
d
1
35 1C. 2.0 eq. n-butyl acrylate. GC-MS yield. Recycled catalyst
e
from entry 5 was used. Tetra-n-butyl ammonium acetate (TBAA).
4
5,46
catalytic cycles.
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Table 5 Recycling of palladium nano-spheres for the Mizoroki–Heck
cross coupling reaction of iodobenzene with n-butyl acrylate
a
Conversion determined
by GC-MS (%)
Reaction number
Time/h
1
2
3
4
5
st
16
16
16
16
16
100
100
99
96
100
nd
rd
th
th
a
Reaction conditions: Iodobenzene (0.98 mmol, 1 eq.), n-butyl acrylate
N (2.45 mmol, 2.5 eq.), and 1 mol% Pd
(1.18 mmol, 1.2 eq.), Et
3
nano-sphere catalyst in DMF (2 mL), 60 1C.
Fig. 5 Kinetic and recycling studies for the Mizoroki–Heck cross
coupling reaction involving iodobenzene and n-butyl acrylate
(
reaction conditions are defined in Table 2).
Fig. 6 Curve-fitting of the Pd 3d spectra obtained for pristine nano-
spheres (a), and after being recycled five times (b).
4
,
9
of PdI
2
which is consistent with the formation of palladium
iodide species in the catalytic cycle, including hydrido-
palladium iodide.
We have established that the catalytic activity of the nano-
spheres does not change after the first cycle for at least another
four cycles. The small palladium nano-particles in the nano-
spheres retain their high volume-to-surface ratio, with no
apparent agglomeration of the nano-particles and formation
of palladium black, and with no significant leaching of the
metal in any form (determined by using ICP-AAS). For
reactions involving 1 mol% palladium, 2.5 ppm palladium
was found in the undiluted mixtures for the first cycle, and less
than 2.0 ppm for subsequent cycles, the overall leaching being
less than 0.05% of palladium.
Fig. 4 TEM images of reused palladium nano-spheres (a and b, after
first run; c and d, after fifth run).
Tracking the conversions for each recycling provides an
insight into the catalytic system. Although the final conver-
sions of recycling is at the same level, there is a significant
change in the catalytic activity between the 1st run and
subsequent runs during the first several hours, as can be seen
from GC-MS analysis, Fig. 5. Energy dispersive spectroscopy
(
EDS) shows the presence of iodine in the recycled catalyst
(
Fig. S5, ESIw), and iodine is retained even after vigorous
washing. It is assumed this hydrido-palladium iodide species
4
7
Conclusions
does not react with the base, triethylamine, so still remains on
the surface after reaction completion. Therefore, it’s likely that
the residual iodine hinders the oxidative addition of iodo-
benzene in the next recycling. XPS studies were undertaken on
the pristine catalyst and on the catalyst recovered from the
reactions after recycling. The as-prepared material shows a
dominant Pd(0) peak (BE = 335.5 ꢀ 0.1 eV) in the Pd 3d5/2
region, and an additional Pd(II) peak (BE = 336.7 ꢀ 0.1 eV),
We have established a simple method for preparing novel
palladium-polyvinylpyrrolidone (Pd–PVP) composite nano-
spheres of uniform size using a microfluidic spinning disc
platform under an atmosphere of hydrogen. This processing
platform is ideal for large scale synthesis of uniform Pd nano-
catalysts under continuous flow conditions. The turbulent
mixing within the dynamic thin films arising from the high
centrifugal forces results in the long chains of PVP forming a
compact scaffold which entangles and traps a large number
of 5 nm palladium nano-particles within the composite. We
have established that these nano-spheres are effective recyclable
colloidal catalysts for Mizoroki–Heck cross coupling
3
0,48
Fig. 6. The latter presumably corresponds to PdO,
noting
that the palladium nano-spheres were exposed to an oxygen-
containing atmosphere before the XPS test. The peak at
3
38.0 ꢀ 0.1 eV only appears in the recycled catalyst, and
according to the literature data, it can be assigned to the peak
8
58 New J. Chem., 2011, 35, 854–860
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reactions. The polymeric scaffold maintains the morphology
and integrity by minimising catalytic loss caused by leaching of
the precious metal.
The ensuing reaction mixture was centrifuged and the palla-
dium nano-sphere catalyst washed three times with DMF
(3 ꢂ 5 mL). The combined DMF were washed by HCl (0.1 M)
and ethyl acetate (V : V = 1 : 4) once and water and
ethyl acetate (V : V = 1 : 4) twice. The ethyl acetate layers
were collected and concentrated under reduced pressure
and the resulting mixture subjected to column chromato-
graphy (2%, 10%, 5%, 3%, 6%, and 4%, ethyl acetate in
hexane for iodobenzene, 4-iodotoluene (2), 4-iodophenol (3),
Experimental section
Reagents and conditions
Polyvinylpyrrolidone (PVP, average molecular weight 10 000,
4
4
4
4
0 000, and 360 000), 4-iodotoluene, methyl 4-iodobenzoate,
0
0
methyl 4-iodobenzoate (4), 4 -iodoacetophenone (5), and
-iodoacetophenone, 4-iodoanisole, bromobenzene, methyl
0
4
-iodoanisole (6), respectively). The products (7–11) were
1
-bromobenzoate, 4-bromoanisole, 4 -bromoacetophenone,
0
characterized by H NMR (for data see ESIw) and GC-MS
for data see ESIw), and matched authentic samples found in
-bromo-N,N-dimethylaniline, chlorobenzene, and 4 -chloro-
(
acetophenone, tetrabutylammonium bromide (TBAB),
tetrabutylammonium acetate (TBAA), butyl acrylate, and
iodobenzene were purchased from Sigma-Aldrich. Triethyl-
51–55
the literature.
The isolated yield is reported. For recycling
studies, the palladium nano-sphere catalyst was separated by
centrifugation, washed by DMF three times, and stored in
DMF under argon prior to the next catalytic run. (b) Aryl
bromides: The same procedure was carried out for the reaction
between aryl bromides (bromobenzene and 12–16) and
acrylates except the reaction temperature and the reaction
time varied (135 1C for the designated time). For 4-bromo-
N,N-dimethylaniline (16), the mobile phase of 5% ethyl
acetate in hexane was used.
amine (Et
ammonium chloride (TBAC) were purchased from Fluka.
-Iodophenol is from Alfa Aesar. Potassium carbonate
CO ), sodium acetate (NaOAc), sodium bicarbonate
NaHCO ), and magnesium sulfate (dried) are from Ajax
3
N), 4-bromphenol, 4-bromotoluene, and tetrabutyl-
4
(
K
2
3
(
3
Finechem Pty Ltd. Palladium precursor solution (palladium
dissolved in aqua regia) was provided by AGR Matthey. All
chemicals were used without further purification except
N,N-dimethylformamide (DMF) which was purified by
5
0
Kinetic studies
approved procedures.
To monitor the reaction, 10 mL samples were taken at regular
intervals, washed with 0.1 M HCl, diluted with ethyl acetate,
centrifuged to remove the palladium nano-sphere catalyst,
and analyzed by gas chromatography and mass spectrometry
(GC-MS).
Synthesis of palladium composite nano-spheres
In typical experiment H PdCl solution (50 mL,
.6 mmol L ) was mixed with PVP40 (34 mg, molecular
weight is 40 000) (molar ratio of PVP monomer to palladium is
a
2
4
ꢁ
1
0
ꢁ1
1
0 : 1) and then fed into a jet feed at a flow rate of 0.7 mL s
onto the spinning disc for which the speed was set at
500 rpm, with hydrogen gas fed into another jet feed,
X-Ray photoelectron spectra (XPS) measurements
1
High resolution XPS measurements were preformed on a
Kratos Axis-Ultra spectrometer using a Dual anode Mg Ka
X-ray source (1253.6 eV) with 12 kV operational voltage and
affording a colloidal suspension of composite nano-materials.
Products were collected from beneath the disc through an
exit port. The as-synthesised palladium composite nano-
spheres were washed using MilliQ water (>18 MO) three
times and then freeze dried. The nanoparticles were highly
stable for several months and could be used as catalyst
directly.
1
2 mA emission current. The working pressure in the analysing
ꢁ10
chamber was better than 10
Torr. The pass energies were
8
0 eV for the survey scan and 20 eV for the Pd 3p, Pd 3d, O 1s
and C 1s in the high resolution scans. A hybrid lens mode
with a top lens set at 01 was utilised. Samples were mounted
horizontally by the double side sticky carbon tape and the
external surfaces were examined as introduced without
any further treatment. All spectra were processed by using a
Powell peak-fitting algorithm provided by the spectrometer
software.
Characterization of the composite nano-materials
The freeze dried materials were re-dispersed in water and the
size and morphology of the samples were determined using
transmission electron microscopy (TEM, JEOL 3000F)
operating at 300 kV and scanning electron microscopy
(
SEM, Zeiss 1555) applying with an acceleration voltage of
kV, respectively. Powder XRD patterns were measured using
2
Acknowledgements
an Oxford Diffraction Gemini-R CCD diffractometer (using
˚
Cu Ka = 1.54178 A radiation).
The authors are grateful for the financial support for this work
by the Australian Research Council and The University of
Western Australia, and for the palladium precursors provided
by AGR Matthey. The microscopy analysis was carried out
using facilities in the Centre for Microscopy, Characterization
and Analysis, The University of Western Australia, which are
supported by University, State and Federal Government
funding. The authors would also like to thank Dr L. Byrne
for NMR spectra acquisition.
General procedure for Mizoroki–Heck reaction
(a) Aryl iodides: Iodobenzene or an iodobenzene derivative
(0.98 mmol, 1 eq.), butyl acrylate (1.18 mmol, 1.2 eq.), Et
(2.45 mmol, 2.5 eq.) in DMF (2 mL) were treated in one
3
N
portion with the palladium nano-sphere catalyst (varying mol%).
The reaction mixture was degassed (freeze–pump–thaw
method) before heating to 60 1C for the designated time.
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011
New J. Chem., 2011, 35, 854–860 859

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