Preparation of a nonleaching, recoverable and recyclable palladium-complex catalyst for Heck coupling reactions by immobilization on Au nanoparticles

Article abstract of DOI:10.1016/j.jcat.2010.04.005

The loading of a palladium complex immobilized on the surface of Au nanoparticles (NPs) was controlled through coordination to a supported spacer ligand (SL = S(CH₂)₁₁NHP(O)(2-py)₂) to yield catalyst particles of the composition (RS)_xAu(SL)_y(SL- PdCl₂)_z (SR = S(CH₂)₇CH₃; x:y:z = (0.31-2.3):1:(0.45-3.3)) with diameters of 3.1-4.9 nm. A fraction of the supported spacer ligands (23-69%) was left uncapped to capture any soluble Pd species resulting from leaching. These surface-bound Pd(II)-complex catalysts were highly effective for Heck reactions of iodobenzene and alkylacrylates, yielding a maximum turnover frequency (TOF) of 4.87 × 10⁴ h¹. Their catalytic activity was three- to tenfold higher than that of their unbound counterparts. These hybrid catalysts could be dissolved and precipitated. They could be quantitatively recovered and effectively recycled 15 times without significant loss of reactivity. The recovered Au NP-supported palladium could be also dissolved, precipitated and isolated. Various spectroscopic analyses were performed to determine a surface-structure composition of (RS)_xAu(SL)₁(SL-Pd⁰) _0.53.

Full text of DOI:10.1016/j.jcat.2010.04.005

Journal of Catalysis 272 (2010) 253–261
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Preparation of a nonleaching, recoverable and recyclable palladium-complex
catalyst for Heck coupling reactions by immobilization on Au nanoparticles
Jun-Nan Young, Tsao-Ching Chang, Shih-Chung Tsai, Lin Yang, Shuchun Joyce Yu *
Department of Chemistry and Biochemistry, National Chung, Cheng University, Ming Hsiung, Chia Yi 621, TAIWAN, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
The loading of a palladium complex immobilized on the surface of Au nanoparticles (NPs) was controlled
Received 19 February 2010
Revised 7 April 2010
Accepted 9 April 2010
Available online 15 May 2010
through coordination to a supported spacer ligand (SL = S(CH
cles of the composition (RS) Au(SL) (SL–PdCl (SR = S(CH
2
)
11NHP(O)(2-py)
2
) to yield catalyst parti-
x
y
)
2 z
2
)
7
CH ; x:y:z = (0.31–2.3):1:(0.45–3.3)) with
3
diameters of 3.1–4.9 nm. A fraction of the supported spacer ligands (23–69%) was left uncapped to cap-
ture any soluble Pd species resulting from leaching. These surface-bound Pd(II)-complex catalysts were
highly effective for Heck reactions of iodobenzene and alkylacrylates, yielding a maximum turnover fre-
Keywords:
Supported catalyst
Palladium
Heck reaction
Gold nanoparticles
Recyclable catalyst
4
1
quency (TOF) of 4.87 Â 10 h . Their catalytic activity was three- to tenfold higher than that of their
unbound counterparts. These hybrid catalysts could be dissolved and precipitated. They could be quan-
titatively recovered and effectively recycled 15 times without significant loss of reactivity. The recovered
Au NP-supported palladium could be also dissolved, precipitated and isolated. Various spectroscopic
analyses were performed to determine a surface-structure composition of (RS)
0
x
Au(SL)
1
(SL–Pd )0.53
.
Ó 2010 Elsevier Inc. All rights reserved.
1
. Introduction
for Heck coupling reactions over the past two decades [20–23].
However, most coupling protocols still rely on homogeneous
Pd-complex catalysts, in particular those with phosphorus donor
ligands; unfortunately, soluble palladium in such a form is not
recyclable and is difficult to separate from the products. Addition-
ally, significant PC bond cleavage has been observed with both
mono- and bidentate phosphine complexes, causing severe cata-
lyst decomposition at elevated temperatures [24–27]. In contrast,
heterogeneous palladium catalysts have been primarily developed
for their thermal stability, easy separation and feasibility of cata-
lyst recycling [28–30]. However, there have been several reports
indicating that the active form of palladium in many solid systems
is actually a soluble Pd species resulting from leaching at high
temperature [21]. Therefore, it would be very difficult to arrive at
general conclusions or mechanistic insights for such a system.
We describe herein the preparation and application of a highly effi-
cient, recoverable and recyclable Heck catalyst system composed
of Au NP cores with controlled amounts of Pd(II) complex function-
alized on their surfaces in a well-defined manner. These hybrid cat-
alysts can be dissolved and precipitated, so their structures and
reaction chemistry can be easily investigated by solution-phase
nuclear magnetic resonance (NMR) spectroscopy with a resolution
typically obtained for soluble systems.
Nanocatalysis is one of the most exciting and rapidly growing
subfields of nanoscience. Metal nanoparticle (MNP) catalysts can
mimic metal-surface activation and catalysis at the nanoscale
and are thought to be a bridge between homogeneous and hetero-
geneous systems, offering distinct and tunable chemical activity,
specificity and selectivity [1–7]. Gold nanoparticles are one of the
most studied MNPs in the field of nanocatalysis. Alkanethiolate-
protected Au NPs have been shown to possess solid surfaces
similar to the (1 1 1) surface of bulk gold [8,9]. These Au NPs also
behave like soluble molecules, exhibiting both dissolvability and
precipitability [10,11]. Therefore, alkanethiolate-protected Au
NPs are good candidates as supports for metal-complex catalysts,
with the MNP catalyst combining the advantages of both
supported and homogeneous catalysts. Several recent reports by
our group and others have demonstrated the successful use of Au
NP-supported metal-complex catalysts for various organic
transformations [12–18].
The Heck coupling reaction [19] is one of the most powerful
tools in synthetic chemistry for constructing aromatic carbon–
carbon bonds between complex organic molecules with potential
industrial or pharmaceutical applications. Various forms of palla-
dium have been reported to be useful catalysts or precatalysts
It has been noted that leaching is almost unavoidable for most
supported Pd catalysts. The leached Pd, in either soluble or solid
form, could contribute much of the activity for Heck reactions
[
(
31–33]. In this study, a flexible spacer ligand, HS(CH
2
)11NHP(O)
*
Corresponding author. Fax: +886 5 2721040.
E-mail address: chejyy@ccu.edu.tw (S.J. Yu).
2-py) (HSL), supported on the surface of Au colloids, was
2
0
021-9517/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcat.2010.04.005

2
54
J.-N. Young et al. / Journal of Catalysis 272 (2010) 253–261
designed to be less than fully palladated. A portion of the spacer
ligands (23–69%) remained uncapped to capture any soluble Pd
species if leaching occurs from one of the palladated surface spacer
ligands. In addition, these Au NP-supported palladium-complex
catalysts could be quantitatively recovered from the Heck reaction
mixture. Spectroscopic characterization of the recovered Pd-
2.3. Catalyst preparation
x y
Au NP-supported Pd(II)-complex catalyst, (RS) Au(SL)
(SL–PdCl
(RS)0.77Au–(SL)
Cl (8 mg). The reaction mixture was stirred for 8 h at ambient
2
)
z
(4): To a freshly prepared solution of Au NPs 3,
1
(60 mg) in CHCl (30 mL) was added Pd(CH CN)
3
3
2
2
containing Au NPs suggested
a
surface composition of
temperature. The supernatant obtained from the resulting mixture
was dried under vacuum. The crude product was washed with ace-
0
(
RS) Au(SL) (SL–Pd ) . Moreover, without the problem of Pd leach-
x y z
ing, these recovered Au NPs–SL–Pd(0) hybrid catalysts can be
effectively recycled 15 times without significant loss of activity.
tone (50 mL Â 3) to give 4 in the form of (RS)
1 1 2 0.57
Au(SL) (SL–PdCl )
as a black powder (40 mg).
2
2
.4. Catalyst characterization
2
. Experimental
.4.1. Transmission electron microscopy (TEM)
The catalyst particle size and morphology were examined by
2.1. General methods
brightfield and darkfield JEOL JEM-2010 microscopy operating at
an accelerating voltage of 200 kV and equipped with a Gatan
imaging filter (GIF). Supported Au NP Pd-complex catalysts were
All chemicals were used as supplied without further purifica-
tion. Methyl sulfoxide (DMSO), NEt
CaH ; CHCl was dried over CaCl and were freshly distilled under
a stream of nitrogen prior to use. Pd(CH CN) Cl was synthesized
by modification of previously reported procedure [34].
Ultraviolet–visible (UV–vis), infrared (IR) and electron-impact
EI) mass-spectral data were obtained in-house at Chung Cheng.
3 3
and NPr were dried over
2
3
2
3
dispersed in CHCl or DMSO before subsequent deposition onto a
3
2
2
copper grid coated with carbon followed by ambient drying. Histo-
grams of particle-size distributions were obtained by measuring at
least 120 randomly selected particles from at least five different
micrographs for each sample analyzed.
a
a
(
Chromatographic purifications were performed by flash chroma-
tography using silica gel (Aldrich 63–200 mesh). Yields of spacer
ligands and Pd catalysts refer to isolated products and are the
average of three runs.
1
2
.4.2. H NMR spectra of 4 and 5
1
The H NMR spectra were recorded at 27 °C in CDCl
d -DMSO on a Bruker DPK-400-MHz spectrometer; coupling con-
3
or
6
stants are reported in Hz. Chemical shifts are given in ppm relative
2.2. Materials
to TMS (tetramethyl silane).
1
H NMR analysis of the Au NPs, (RS)
x
Au(SL)
y
(SL–PdCl
2
)
z
(4):
The spacer ligand HS(CH
2
)
11NHP(O)(2-py)
2
(2) was synthesized
CDCl
3.22 (m, CH
3
: d = 0.84 (br, CH ), 1.15–1.53 (br, CH
3
2
), 2.98 (m, CH
2
NH),
II
according to our previously published procedures [12]. The com-
pound HS(CH (0.5 g, 2.1 mmol) was added to a solution of
P(2-py) (0.5 g, 1.9 mmol) in wet CH CN (30 mL). The mixture
2
NH–(Pd )), 4.51 (m, NH), 7.36 (m, py), 7.58 (m,
II
II
2
)
11
N
3
py-(Pd )), 7.78 (m, py), 8.07 (m, py), 8.32 (m, py-(Pd )), 8.73 (m,
py), 9.27 (m, py-(Pd )) ppm. The formula of (RS)
II
3
3
1
Au(SL)
1
1
was stirred for 16 h at 82 °C. The mixture was dried under vacuum
to give a light yellow solid. The solid was extracted with hot hex-
ane (4 Â 30 mL), and the extract was dried to obtain a white solid 4
(SL–PdCl
nance signals. d -DMSO: d = 2.76 (m, CH
2
)0.57 was calculated by integration of the H NMR reso-
6
2 2
NH), 2.92 (m, CH NH–
II
II
(Pd )), 5.46 (m, NH), 7.05 (m, NH–(Pd )), 7.49 (m, py), 7.77 (m,
II
(
0.68 g, 75% yield).
py-(Pd )), 7.95 (m, py), 8.25 (m, py), 8.67 (m, py), 9.10 (m, py-
II
Mixed thiolate-protected Au NPs, (RS)
x
Au(SL)
y
(3), were synthe-
(Pd )) ppm. The NMR signals of the terminal CH
3
protons of RS
sized according to a previously reported procedure [12]. Freshly
prepared octanethiolate-protected Au NPs (1, 75 mg) [35] were
dissolved in degassed CHCl (25 mL). To this solution was added
3
(d = 0.84 ppm), the pyridyl protons of SL (d = 8.73 ppm) and the
pyridyl protons of SLPdCl (d = 9.27 ppm) were integrated against
a 0.038 M internal standard iodoanisole to give the ratio of
RS:SL:SLPdCl = 1:1:0.57. Calculations based on the average parti-
cle size obtained by TEM (3.9 nm ± 0.4) and NMR integration gave
an average of 2382 ± 735 gold atoms for each Au core. Based on the
average diameter of Au particles obtained from TEM, the calculated
2
spacer ligand 2 (60 mg, 0.15 mmol), and the reaction mixture
was stirred for 16 h at 70 °C. The solution was concentrated to a
minimum amount (0.5 mL) then was washed with hexane (3 Â
2
5
0 mL). A degassed acetone solvent (150 mL) was added, and the
solution was allowed to sit at room temperature for 1 h to allow
gold colloid precipitation. Further precipitation from acetone was
performed continuously until no more free ligand 2 could be de-
tected by H NMR spectroscopy. Centrifugation gave the colloids
as black solid product 3 (60 mg).
2
numbers of 435 ± 134 RS, 435 ± 134 SL and 248 ± 76 SLPdCl per Au
particle were obtained.
1
H NMR analysis of the recovered Au NPs 5, (RS)
x
Au(SL)
1
1
0
(SL–Pd )0.53: CDCl
(SL)), 7.78 (m, py (SL)), 7.86 (m, py (Pd )), 8.20 (m, py (SL)), 8.30
(m, py (Pd )), 8.75 (m, py (SL)), 9.09 (m, py (Pd )) ppm. The NMR
3 3
: d = 0.85 (br, CH ), 4.46 (m, NH), 7.34 (m, py
0
0
0
The molecular palladium(II)-complex catalyst, HOLPdCl
was synthesized according to a previously published procedure
12]. Compound HO(CH 11NHP(O)(2-py) (0.5 g, 1.3 mmol) was
added to a solution of Pd(CH CN) Cl (0.34 g, 1.3 mmol) in CH CN
30 mL). The mixture was stirred for 6 h at ambient temperature.
All volatiles were removed to give 6 as a yellow solid (0.70 g,
2
(6),
signals of the pyridyl protons of SL (d = 8.75 ppm) and the pyridyl
[
2
)
2
protons of SLPd0 (d = 9.09 ppm) were integrated against
a
3
2
2
3
0.038 M internal standard iodoanisole to give the ratio of
0
(
SL:SLPd = 1:0.53. Calculations based on the average size obtained
by TEM (14.1 nm ± 3.4) and NMR integration gave an average of
112,592 gold atoms for each Au core. The average numbers of sur-
face thiolate molecules per Au core were about 7570 SL and 4012
9
5% yield).
3 2
The silica-supported Pd(II)-complex catalyst (O) Si–L–PdCl (7)
0
was synthesized according to our previously published procedure
36]. PdCl (94 mg, 0.525 mmol) was added to a solution of
NHP(O)(2-py) -functionalized polysiloxane (200 mg, 0.966 mmol
of py) in CH CN (15 mL). The mixture was stirred at reflux for
4 h. All volatile substances were removed, and the residue was
extracted with CHCl
(2 Â 10 mL). The extract was dried to give 7
as a yellow solid with a yield of 260 mg (91% based on py).
SLPd .
[
2
2
2.4.3. X-ray photoelectron spectroscopy (XPS) of 4 and 5
3
The XPS spectra were obtained with a Kratos AXIS ULTRA DLD
2
spectrometer equipped with a monochromatized Al K
source (h = 1486.69 eV) at 75 W and 5 mA. The survey spectra
and high-resolution spectra were obtained at analyzer pass-energy
a X-ray
3
m

J.-N. Young et al. / Journal of Catalysis 272 (2010) 253–261
255
values of 160 and 20 eV, respectively. All spectra were charge com-
pensated using the C component peak of the carbon 1s spectra
2.6. Catalyst-recycling experiments
x
H
y
at a binding energy (BE) of 285.00 eV as the reference peak [37].
XPS spectroscopic analysis can be utilized to measure the elec-
tronic state of a certain element that exists within a material.
The binding energies of the 3d3/2 and 3d5/2 levels of palladium
A
mixture of iodobenzene (0.04 mmol), n-butyl acrylate
(0.049 mmol), NPr
3
8
1 1 2 0.57
(0.08 mmol) and (RS) Au(SL) (SL–PdCl )
(4, 11.05 mg) in d -toluene (0.1 mL) was reacted at 108 °C for
30 min. The resulting mixture was centrifuged. The precipitate
thus obtained was washed with dried hexane (0.5 mL Â 5) to give
Au NPs–Pd0 as a black solid to be used in the following catalytic
II
were found to be 343 and 337 eV, respectively, for Pd in 4, and
0
3
41 and 335 eV for Pd in 5. The binding energies of the 4f5/2 and
4
f
7/2 levels of gold were found to be 88 and 84 eV, respectively,
cycle. Recycling of Pd(CH
procedures. The detailed reaction conditions were as follows:
iodobenzene, 0.375 mmol; n-butyl acrylate, 0.45 mmol; NPr
3 2 2
CN) Cl was performed under similar
for the Au NP core in both 4 and 5.
3
,
0
.75 mmol; 8 mol% Pd(CH
3 2 2
CN) Cl ; toluene, 0.1 mL; 110 °C; 6 h.
2
1 1 2
.4.4. Palladium loadings on (RS) Au(SL) (SL–PdCl )0.57 (4) obtained
1
from H NMR, atomic absorption (AA) and inductively coupled
plasma-mass (ICP-MS) spectroscopy
3
. Results and discussion
AA spectra were recorded on a Perkin Elmer Analyst 200 spec-
trometer, and ICP-MS spectra were recorded on a PE-SCIEX ELAN
6
3
.1. Partial palladation on the surface of Au NPs
100 DRC spectrometer. Integration of the 1H NMR signals of 4
The incomplete metallation of the surface spacer ligand
(SL = S(CH2)11NHP(O)(2-py) ) on Au NPs, (RS) Au(SL) (3) (SR =
S(CH ) CH ; x:y = 1.43–0.77:1; D = 3.9 ± 0.4–4.7 ± 1.4 nm), was
2 7 3
(
iodoanisole as internal standard) gave the Pd loading of (RS)
1
1
II
2
x
y
Au(SL)
1
(SL–PdCl
2
)
0.57 as 2.899 Â 10 mmol Pd /g. AA analysis on
1 II
the same sample gave a Pd loading of 2.821 Â 10 mmol Pd /g.
1
II
3
achieved by direct reaction with a limiting amount of (CH CN)2
ICP-MS gave a Pd loading of 2.827 Â 10 mmol Pd /g.
PdCl
RS)
2
(0.2–0.8 equivalent to SL) to give the desired Au colloids,
Au(SL) (SL–PdCl (4), (x:y:z = 0.31–2.3:1:0.45–3.3; D = 3.1 ±
(
x
y
2 z
)
2
.5. General procedure for catalytic Heck reactions
0.9–4.9 ± 0.8 nm) (Scheme 1). Leaving a portion (23–69%) of the
supported ligands uncapped made the target hybrid system very
soluble in many organic solvents, ranging from the relatively less
x
The colloidal gold-surface-bound palladium catalyst (RS) Au
(
SL)
y
(SL–PdCl
2
)
z
(4) was dissolved in DMSO (20 mL) to make a
3
polar CHCl to the very polar DMSO. This made it very easy to man-
À3
stock solution (2.36 Â 10 mmol Pd). To 0.85 mL of the stock
age when using solution-phase spectroscopy for quantitative or
structural analysis. In contrast, fully palladated Au NPs are only
partially soluble in DMSO [12], thus methods for their character-
ization and their application as supported catalysts for organic
À4
solution (containing 1.0 Â 10 mmol Pd) was added 0.15 mL of
DMSO, iodobenzene (2.04 g, 10 mmol), n-butyl acrylate (1.28 g,
1
3
0 mmol) and NEt
h at 115 °C. After the reaction, the resulting tarry mixture was
3
(1.5 mL). The reaction mixture was stirred for
transformations have been limited.
1
extracted with hexane (3 Â 40 mL). The combined hexane extracts
The H NMR analyses of 4 were performed in both CDCl
3
and
were washed with H
2
O (3 Â 40 mL) to remove salt by-products. All
DMSO to give spectra with resolutions typically obtained with sol-
1
volatiles were removed under vacuum. The Heck product was
further purified on a short silica plug to remove the catalyst
uble systems. As shown in Fig. 1d, the H NMR spectra of 4 clearly
showed two sets of spacer pyridyls: one from the uncapped spacer
ligand (Au–SL) and the other from the palladated spacer ligand
(
63–200 mesh; eluted with ethyl acetate). The product was used
directly for NMR analysis.
2
(Au–SLPdCl ). The IR spectra of 4 also showed that the
m
asym(SH)
H
O
+
-
S
1
. [CH3(CH2)7]4N Br /CHCl3/rt/1h
S
S
HS(CH2)11N P(2-py)2
(HSL, 2)
HAuCl4 3H2O/H2O
S Au S
S
2
3
. CH3(CH2)7SH/CHCl3
. NaBH4/H2O/12h
o
S
S
CHCl , 70 C,16 h
3
H O
O H
H O
1
N
P(2-py)2
(2-py)2P
N
N
P(2-py)2PdCl2
Pd(CH3CN)2Cl2
LS:Pd = 1:0.4 ~0.6)
CHCl3, rt, 3 h
S
SS
S
S
S
(
S Au S
S
S Au S
S
S
S
S
S
O
O
O
O
(
2-py)2P
N
H
N
H
P(2-py)2
Cl2Pd(2-py)2P N
H
N
H
P(2-py)2
3
4
(
RS)xAu(SL)y
(RS)xAu(SL)y(SL-PdCl2)z
(
x:y = 1.43-0.77:1)
(x:y:z = 0.31-2.3:1:0.45-3.3)
Heck conditions
O H
H O
N
(
2-py)2P
N
P(2-py)2Pd0
SR = S
SL = S
S(CH2)7CH3
SS
S
N
P(2-py)2
O
S(CH2)11NHP(O)(2-py)2
S Au S
S
S
H
S
O
O
0
Pd (2-py)2P
N
H
N
H
P(2-py)2
5
0
(
RS)xAu(SL)y(SL-Pd )z
x y 2 z
Scheme 1. Synthesis of Pd(II)-functionalized Au NPs, (RS) Au(SL) (SL–PdCl ) (4).

2
56
J.-N. Young et al. / Journal of Catalysis 272 (2010) 253–261
Fig. 1. The 400-MHz 1H NMR (27 °C) spectra of (a) unbound spacer ligand HSL (2) in CDCl
, (b) RS–Au–SL NPs (3) in CDCl
recovered from the 4-catalyzed reaction of iodobenzene and n-butyl acrylate, (f)
3
3 3
, (c) molecular Pd complex 6 in CDCl , (d)
0
(
RS)1.7Au(SL)
1
(SLPdCl
2
)
0.57 NPs (4) in CDCl
3
, (e) (RS)
x
Au(SL)
1
(SLPd )0.53 NPs (5) in CDCl
3
6
6
(
RS) Au(SL) (SLPdCl
1
1
2
)
0.57 NPs (4) in d -DMSO, and (g) fully PdCl
2
-metallated Au NPs (RS–Au–SLPdCl
2 3
) in d -DMSO (Ã is CDCl , # is the internal standard iodoanisole, d is
6
water, and N is d -DMSO).
À1
bands at 2569 cm
2
of the free n-octanethiol (HSR) and at
Pd(II)-functionalized Au NPs were obtained, ranging in size from
3.1 ± 0.9 nm to 4.9 ± 0.8 nm, (Fig. 4 and Table 1). The XPS spectro-
scopic analysis of 4 (Fig. 5) showed the BE of the palladium 3d3/2
and 3d5/2 levels at 343 and 337 eV, respectively; these values are
consistent with previously reported data for Pd(II) complexes
[38]. The BE of the gold 4f5/2 and 4f7/2 levels of the Au core in 4
were found at 88 and 84 eV, respectively.
À1
576 cm of the unbound free ligand (HSL, 2) disappeared after
their immobilization onto Au NPs (Fig. 2b). Moreover, a shift of
the pyridyl ring stretching
its covalent binding to palladium [12,36]. The UV–vis spectra of 4
gave the characteristic Au surface-plasmon resonance peak at
520 nm (Fig. 3). The TEM images of 4 showed that partially
À1
m
py from 1574 to 1590 cm indicated
ꢀ

J.-N. Young et al. / Journal of Catalysis 272 (2010) 253–261
257
acquire a 1H NMR spectrum (Fig. 1), we chose solution-phase
NMR spectroscopy as the routine method for quantitative mea-
surements and for in situ monitoring of reaction chemistry.
3.2. Catalytic Heck reactivity of the partially palladated Au NPs
(
RS) Au(SL) (SL–PdCl (4)
x
y
2 z
)
We found that both partially and fully palladated Au NPs were
extremely effective catalysts for Heck reactions with iodobenzene
and alkyl acrylates. The catalyses were carried out in DMSO or in
a mixture of CHCl
the reactions of 10 mmol of iodobenzene and
3
and o-xylene at 115 °C. As shown in Table 2,
C = CHR
3
R = COOMe, COOEt, COO Bu, or COO Bu) with NEt (1.5 mL) and
H
2
n
t
(
À4
II
catalyst 4 (1 Â 10 mmol of Pd ) proceeded most efficiently in
DMSO, giving Heck products with 89.3–97.3% yields in two hours
1
and with TOFs of 44,700–48,700 h . Even with a nonactivated
substrate such as styrene, the TOF was still as high as 18,700 h .
1
The use of a less polar solvent also became convenient when
trialkylamine was used as the organic base. However, the same
catalyses gave lower TOFs in a mixture of CHCl and o-xylene un-
3
Fig. 2. IR spectra of (a) recovered catalyst Au NP 5, (b) precatalyst Au NP 4, and (c)
ligand HSL (HS(CH)11NHP(O)(2-py) ).
2
der similar reaction conditions (Table 2, entries 6 and 7). This was
possibly because a better homogeneity could be achieved for the
Pd-complex catalyst in a more polar media. In addition, a TOF of
À1
2
34 h could still be obtained even for the more difficult reaction
of bromobenzene and n-butylacrylate. The best known TOF of
6
À1
1
0 h
reported for the Heck reaction of iodobenzene and
methylacrylate was catalyzed by the Pd-complex containing a
six-membered CNN-pincer palladacyle [39]. However, it is
interesting to note that this palladacycle was difficult to be
recycled and was far less effective for the Heck reactions between
bromobenzene and acrylic esters.
It has been reported that transition-metal complexes attached
to monolayered-alkanethiolates on Au colloids exhibit catalytic
properties similar to those of the corresponding homogeneous
catalysts [14–18]. In the current study, HO(CH 11N(H)(O)P
2
)
(
2-py) PdCl (6) [12] (Scheme 2) and Pd(CH CN) Cl were used
2
2
3
2
2
as controls to study the effect of the immobilization of molecular
Pd(II) on the surface of Au NPs. As demonstrated in Table 2, both
Pd(II) complexes had similar reactivities. However, it is interesting
to note that a significant increase in TOFs was observed when
Pd(II) was immobilized onto the surface of Au NPs. When the gold
core was covered only with octanethiolates (RS–Au NPs (1)), it was
found to be noncatalytically active for Heck reactions. Addition of 1
to the Heck system containing molecular catalyst 6 did not provoke
any further reactivity. Conversely, it reduced the TOFs of 6 from
4100–14,400 h to 1100–2800 h . This drop in reactivity was
probably due to competitive substrate binding between the sup-
ported Pd centers and the relatively large number of surface Au
atoms [12,40]. However, with the Pd(II) complex immobilized on
Fig. 3. UV spectra of Au NPs 1, 4 and 5.
The Pd(II) loadings on 4 as determined by either AA or ICP-MS
spectroscopy were systematically smaller (<3%) than those
obtained by H NMR spectroscopy. One specific sample of 4 was
1
1
1
II
À1
À1
analyzed by H NMR to give a Pd loading of 2.899 Â 10 mmol Pd
per gram of Au NPs, while AA analysis on the same sample gave a
1
II
Pd loading of 2.821 Â 10 mmol Pd /g; ICP-MS analysis gave a Pd
1
II
loading of 2.827 Â 10 mmol Pd /g. As it required only 10 min to
(
a)
(b)
(c)
1
00 nm
100 nm
100 nm
0
(
RS)
1
Au(SL)
1
(SL-PdCl
2
)0.57 (4) (RS)
1
Au(SL-PdCl
2
)
1.2 (4) (RS)
x
Au(SL)
1
(SL-Pd )0.53 (5)
D = 3.9 ± 0.4 nm
D = 4.6 ± 0.86 nm
D = 14.1 ± 3.4 nm
1 1 2 1 2 x 1
Fig. 4. TEM images of Au NPs; (a) the partially palladated 4, (RS) Au(SL) (SL–PdCl )0.57; (b) the fully palladated 4, (RS) Au(SL–PdCl )1.2; (c) the recovered (RS) Au(SL)
0
(
SL–Pd )0.53 (5).

2
58
J.-N. Young et al. / Journal of Catalysis 272 (2010) 253–261
Table 1
Analytical data of spacer ligand- and Pd-complex-functionalized Au NPs 3, 4 and 5.
2
Pd/SL/SRa mole ratio
b
Ausurface atom%c
Pd/SL/SRd (molecule/core)
Surface areae
Au NPs (m /core)
Particle size (nm)
Pd/Autotal (wt.%)
À17
(
(
(
(
RS)
RS)
RS)
RS)
1
1
1
Au(SL)1.1 (3)
Au(SL) (SL–PdCl
Au(SL–PdCl
Au(SL)
4.1 ± 0.8
3.9 ± 0.4
4.6 ± 0.86
14.1 ± 3.4
0/1/1.1
0.57/1/1
1.2/0/1
–
28.4
29.9
25.4
8.3
0/542/484
248/435/435
415/351/0
5.28 Â 10
À17
1
2
)
0.57 (4)
5.61 (5.46)
5.73 (5.51)
(1.93)
4.77 Â 10
À17
2
)
1.2 (4)
(SL–Pd )0.53 (5)
6.64 Â 10
0
0
0
À16
x
1
0.53/1 (Pd /SL)
4012/7570 (Pd /SL)
6.24 Â 10
a
b
c
Pd = Pd(II) complex on Au surface; SR = octanethiolate on Au surface.
Weight percent of Pd(II)-to-total Au as determined by NMR; numbers in parentheses were obtained by atomic absorption analysis.
o
2
Defined as the number of surface Au atoms (ns)/total number of Au atoms per particle (n)  100%, where ns = S/p  (r ) .
d
e
The average number of Pd(II) and octanethiol molecules per Au particle.
 (r )  n , where r = atomic radius of Au; n = average number of Au atoms per particle; r = r  n1/3, where
o
2
2/3
o
o
Average surface area (S) of Au particles calculated by S = 4
p
r = average radius of Au particles.
Fig. 5. Palladium 3d photoelectron spectra of (a) a 1:1 mixture of Au NPs (RS)
1
Au(SL)
1
2
(SLPdCl )0.57 (4) and (RS)
x
Au(SL)
1
(SLPd0)0.53 (5); (b) Au NPs (RS)
1
1 2 0.57
Au(SL) (SLPdCl )
(4); and (c) the gold 4f photoelectron spectra of the central Au core of 4 and 5.
Table 2
a
Catalytic Heck-type coupling reactions mediated by Pd(II) in various forms.
Cat.
0.001 mol%)
I
R
(
R
+
o
1
15 C; 2-3 h
TOF (h )/(yield (%))f
À1
Entry
Catalyst system (Cat.)
R=
n
t
COOMe
COOEt
COO Bu
COO Bu
Ph
4
4
4
4
4
1
2
3
4
5
6
7
8
9
(RS)
(RS)2.3Au(SL)
(RS) Au(SL)
1
Au(SL)
0
(SL–PdCl
2
)
1.2 (4)b
4.73 Â 10 (94.7)
4.87 Â 10 (97.3)
4.60 Â 10 (92.0)
4.47 Â 10 (89.3)
1.87 Â 10 (37.3)
b
4
4
4
4
4
1
(SL–PdCl
2
)
3.3 (4)
3.79 Â 10 (75.8)
3.94 Â 10 (78.7)
3.67 Â 10 (73.4)
3.65 Â 10 (72.9)
1.50 Â 10 (30.1)
c
4
4
4
4
4
1
1
(SL–PdCl
2
)
0.57 (4)
1.12 Â 10 (33.7/3 h)
1.20 Â 10 (35.9/3 h)
1.05 Â 10 (31.4/3 h)
1.03 Â 10 (30.8/3 h)
0.44 Â 10 (13.2/3 h)
d
RS-Au NPs (1)
0
0
0
0
0
1
(6)b
4
4
4
4
4
HO(CH
2
)
1
HNOP(2-py)
2
PdCl
2
1.08 Â 10 (21.5)
1.44 Â 10 (28.7)
1.13 Â 10 (22.5)
1.24 Â 10 (24.8)
0.41 Â 10 (8.2)
b
4
4
4
4
4
Pd(CH
Pd(CH
1 + 6
3
CN)
CN)
2
Cl
Cl
2
1.11 Â 10 (22.2)
1.50 Â 10 (30.0)
1.45 Â 10 (29.0)
1.32 Â 10 (26.3)
0.43 Â 10 (8.5)
c
g
4
3
2
2
ND
ND
0.10 Â 10 (3.2/3 h)
ND
ND
d
4
4
4
4
4
0.22 Â 10 (6.5/3 h)
0.28 Â 10 (8.3/3 h)
0.24 Â 10 (7.1/3 h)
0.22 Â 10 (6.5/3 h)
0.11 Â 10 (3.4/3 h)
(O)
3
Si-L-PdCl
2
(7)e
0.90 Â 10 (27.0/3 h)
4
1.0 Â 10 (30.0/3 h)
4
0.71 Â 10 (21.3/3 h)
4
0.97 Â 10 (29.0/3 h)
4
0.44 Â 10 (13.1/3 h)
4
a
b
c
d
e
f
Iodobenzene = 10 mmol; CH
Pd = 1 Â 10 mmol; DMSO = 1 mL; 2-h reaction time.
2
= CHCOOR = 10 mmol; NEt
3
= 1.5 mL; 115 °C.
II
II
À4
À4
Pd = 1 Â 10 mmol; CHCl
3
/o-xylene = 1 mL (v:v = 1:1); 3-h reaction time.
Pd = 1 Â 10 mmol; DMSO = 1 mL; 0.2 mg of 1; 3-h reaction time.
II
II
À4
À4
Pd = 3 Â 10 mmol; DMSO = 0.5 mL; 3-h reaction time.
Isolated products were purified by flash chromatography, and TOF was determined by 1H NMR spectroscopy.
ND = not determined.
g

J.-N. Young et al. / Journal of Catalysis 272 (2010) 253–261
259
O H
H O
(
2-py) P
N
N P(2-py) PdCl2
2
2
H
O
P
S
N
N
S
S
S Au S
S
HOCH (CH ) CH N
PdCl2
2
2 9
2
S
S
O
O
Cl Pd(2-py) P
N
H
N P(2-py)2
2
2
6
4
H
molecular HOLPdCl2
(
RS) Au(SL) (SL-PdCl )
x y 2 z
OTMS
TMS O Si CH (CH )
H
N
O
P
N
N
PdCl2
2
2 10
p
O
O
TMS O Si O Si O
O H
n
m
H
N
O
Cl Pd(2-py) P N(CH ) CH2 CH (CH )
P(2-Py) PdCl2
2
2
2 10
2
2 10
2
7
Silica supported (O) Si-L-PdCl2
3
Scheme 2. Molecular and surface-supported palladium precatalysts.
ated through immobilization in such a way as to give overall activ-
ities higher than either metal alone. However, as with most other
reported occurrences, the promotional role of Au in our system
has not yet been elucidated.
1
00
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
It is noteworthy that the TOFs observed with a fully palladated
Au NP catalyst having no free Pd-binding ligand (Table 2, row 1)
are about 25% greater than those from the partially palladated
Au NP catalyst with free Pd-binding sites. The higher value does
not seem attributable to leached Pd species, which are apparently
less active than the bound ones. The exact cause for the higher
TOFs observed for the fully palladated Au NP catalyst when com-
pared with the partially palladated Au NP catalyst is not yet clear.
However, it was noted in the catalyses that the fully palladated Au
NP catalysts formed flocculates in DMSO, while the partially
palladated Au NP catalyst formed a regular suspension in DMSO.
The formation of flocculates may somehow have a positive influ-
ence on the catalytic performance of palladium. The study of the
correlation between catalytic activity and flocculates formation is
currently in progress.
4
Pd(CH CN) Cl
3
2
2
0
2
4
6
8
10
12
14
16
Number of Cycles
Fig. 6. Comparative recycling and reuse of precatalysts (RS)
and Pd(CH
toluene.
1
Au(SL)
1 2
(SLPdCl )0.57 (4)
8
3 2 2
CN) Cl in the reaction of iodobenzene and n-butyl acrylate in d -
the surface of Au NPs, substrate binding to the surface Au atoms
may possibly increase the local concentration of reactants around
the supported Pd center and facilitate the catalysis. To verify the
reactivity promotion of Au on Pd, we also studied the catalyses
3.3. Recovery of palladium and catalyst recycling
It is generally known that most current applications of homoge-
neous Pd catalysts cope with difficulties in quantitative separation,
catalyst recovery and catalyst deactivation into inactive colloidal
species at higher temperatures [46,47], while most heterogeneous
Pd catalysts suffer from low TOFs and poor reusability due to either
particle aggregation or leaching [48–54]. In the current study,
filtration and split tests [23] were performed at the end of the 4-
catalyzed reaction of iodobenzene and butyl acrylate. The filtrate
obtained after centrifugation and filtration of the reaction mixture
was tested and found to have no residual Heck reactivity and no
sign of palladium or gold content on AA spectroscopic analysis.
Both results suggested that Pd leaching into either the active or
inactive form did not occur. On the contrary, when fully palladated
on a different surface. The SiO
PdCl (7) (Scheme 2), was prepared according to our previously re-
ported procedures [36]. In contrast to the case on the Au surface,
the same Pd(II) complex supported on SiO did not cause reactivity
2 3
-bound Pd(II) complex, „(O) SiL-
2
2
enhancement and only provided TOFs similar to those of its
unbound free forms (Table 2).
It has been documented that composites of Pd/Au in various
forms can greatly enhance the catalytic activity, selectivity and
stability of Pd [12,41–43]. For example, adding gold to palladium
in a bimetallic Pd–Au alloy system can significantly increase Pd
catalytic activity in the acetoxylation of ethylene through an
ensemble effect, in which the orientation of the Pd on Au surface
favors formation of the product [44]. In addition, similar effects
have also been demonstrated for gold colloids and gold-coated
glass-slide-bound Ru(III) catalysts for the ring-opening metathesis
polymerization of norbornene [45]. It was clearly seen in our case
that the tethered Pd(II) complex and the surface Au atoms cooper-
Au NPs (RS)
1 0 2
Au(SL) (SL–PdCl )1.2 were used in the recycling exper-
iment, the filtrate obtained from the Heck reaction mixture still
afforded a ꢀ4% further conversion. This result suggested that a
small amount of soluble Pd species was leached from the surface
of the fully palladated Au NPs.

2
60
J.-N. Young et al. / Journal of Catalysis 272 (2010) 253–261
Table 3
1
Au(SL)
1
(SL–PdCl
2 3 2 2
)0.57 (4) and Pd(CH CN) Cl
in the Heck coupling reaction of iodobenzene and n-butyl acrylate.a
Comparative recycling and reuse of precatalysts (RS)
Precatalyst
Cycle (% yieldb)
1
2
3
4
5
6
7
8
9
10
91
11
90
12
88
13
85
14
83
15
79
4a
97
99
99
93
99
85
99
71
97
68
96
44
95
94
92
c
3 2 2
Pd(CH CN) Cl
a
8
3
Reaction conditions: iodobenzene = 0.0401 mmol; n-butyl acrylate = 0.0488 mmol; NPr = 0.0802 mmol; catalyst loading = 11.05 mg (8 mol% Pd(II)); solvent = d -toluene
(
0.1 mL); reaction temperature = 108 °C; reaction time for each cycle = 30 min.
b
Determined by 1H NMR spectroscopy analysis.
c
n
3 3 2 2
Reaction conditions: iodobenzene = 0.375 mmol; n-butyl acrylate = 0.45 mmol; NPr = 0.75 mmol; and 8 mol% Pd(CH CN) Cl in 0.1 mL toluene at 110 °C for 6 h.
The palladium in (RS)
1
Au(SL)
1
(SLPdCl
2
)
0.57 (4) could be quanti-
can be imbued with a solubility generally obtained for the molec-
ular system. As a result, the structural details and reaction chemis-
try of the hybrid catalyst systems can be easily studied and closely
monitored. Consequently, more general conclusions and funda-
mental insights can be readily obtained. Leaving a certain portion
of the surface-spacer-linkers uncapped allowed them to stably trap
the active Pd(0) centers and to tightly bind leached Pd species dur-
ing each catalytic cycle. This approach opens up a new avenue for
the immobilization of metal-complex catalysts on the surface of
MNPs in a well-defined manner. This method can also minimize
the problem of metal leaching. In addition, adding Au NPs to the
molecular Pd complex through a step-wise immobilization pro-
cesses can promote further reactivity and can offer the advantages
of quantitative recovery, effective recyclability and easy separa-
tion. We believe that the results of this study can serve as an
important reference work for scientists active in organic synthesis,
green catalysis, nanoscience and related areas, and it is expected
that many applicable catalysts of this form can be made by tether-
ing various metal complexes or even organocatalysts onto MNPs in
a well-defined and controllable way so as to promote chemical
reactions in a greener and more manageable fashion.
tatively recovered as a soluble black colloid 5 with an average core
diameter of 14.1 ± 3.4 nm (Fig. 4 and Table 1). The large change in
particle size of the recovered catalyst 4 was believed due to the
Ostwald ripening phenomenon [55] observed at elevated tempera-
ture. These recovered particles were not only dissolvable but also
precipitable, so they could be easily studied by solution-phase
spectroscopy such as NMR and UV–vis; the solid form was studied
by TEM, IR and XPS spectroscopy. The H NMR spectra of 5 (Fig. 1e)
clearly showed two different sets of supported pyridyls (i.e., of the
uncapped Au–SL and the Pd -capped Au–SL–Pd ) in a ratio of
:0.53. Expectedly, the pyridyl protons of Au–SL–Pd were shifted
1
0
0
0
1
upfield to the Pd(II)-capped pyridyls of Au–SL–PdCl in 4. As eluci-
dated earlier for 4, the IR spectra of 5 (Fig. 2a) also gave a pyridyl
2
À1
ring stretching of
m
py at 1590 cm , which indicated its covalent
binding to palladium. The UV–vis spectra of 5 (Fig. 3) gave the
characteristic Au surface-plasmon resonance peak at about
30 nm. The XPS spectroscopic analysis of a 1:1 mixture of 4 and
5
5
clearly gave two sets of BE for the Pd 3d3/2 and 3d5/2 levels,
II
whereas the Pd BE levels of 4 were located at 343 and 337 eV,
0
and the Pd levels of 5 were located at 341 and 335 eV; these data
are all consistent with previously reported values [38]. The BE of
the gold 4f5/2 and 4f7/2 levels of the Au core in 5 were found at
Acknowledgments
8
8 and 84 eV, respectively. The combined spectral analyses of the
recovered colloids 5 established that active palladium in the form
Funding for this work was provided by the National Science
Council of Taiwan (NSC-97-2113-M-194-010-MY2), for which the
authors are grateful. The authors are also grateful to the NSC South
Precision Instrument Centers at National Chung Cheng University
for performing the XPS experiments and at National Chung Hsing
University for performing the ICP-MS spectral analysis.
0
of Pd was bound to the Au NP surface dipyridyls. We therefore cal-
0
culated the surface composition of 5 as (RS)
x
Au(SL)
1
(SL–Pd )0.53
according to its XPS and 1H NMR spectra, where the ratio x of
octanethiolate (RS) was not determined as its NMR signal over-
lapped with the protons of the NPr
These results are theoretically consistent with the Pd(0)/Pd(II) cat-
3
ÁHI salt formed during catalysis.
alytic cycle proposed for Heck reactions in the literature [56–59].
References
0
In addition, the recovered (RS)
x
1
Au(SL) (SL–Pd )0.53 was nonle-
aching and could be consecutively recycled in toluene with conver-
sions maintained at >90% for the first 11 cycles, gradually dropping
to 82% at the 15th cycle (Fig. 6 and Table 3). More importantly, the
catalyst-recycling procedures for 5 were easy and sustainable,
comprising only centrifugation and filtration. In contrast, the recy-
cling of a molecular Pd(CH CN) Cl catalyst requires multiple cy-
3 2 2
cles of extraction with organic solvents followed by evaporation
of organic volatiles. Under similar recycling conditions, the conver-
[1] C.-B. Hwang, Y.-S. Fu, Y.-L. Lu, S.-W. Jang, P.-T. Chou, C.-R.C. Wang, S.J. Yu, J.
Catal. 195 (2000) 336.
[
[
2] D. Astruc, F. Lu, J. Ruiz Aranzaes, Angew. Chem. Int. Ed. 44 (2005) 7399.
3] J.G. De Vries, Dalton Trans. (2006) 421.
[4] D. Astruc, Inorg. Chem. 46 (2007) 1884.
[5] G.A. Somorjai, A.M. Contreras, M. Montano, R.M. Rioux, Proc. Natl. Acad. Sci.
USA 103 (2006) 10577.
[
[
6] D. Astruc, F. Lu, J.R. Aranzaes, Angew. Chem. Int. Ed. 44 (2005) 7852.
7] N. Toshima, Y. Shiraishi, T. Teranishi, M. Miyake, T. Tominaga, H. Watanabe, W.
Brijoux, H. BJnnemann, G. Schmid, Appl. Organomet. Chem. 15 (2001) 178.
8] G. Schmid, Chem. Rev. 192 (1992) 1709.
9] R. Terril, T. Postlethwaite, C. Chen, C. Poon, A. Terzis, A. Chen, J. Hutchinson, M.
Clark, G. Wignall, J. Londono, R. Superfine, M. Falvo, C.S. Johnson Jr., E.
Samulski, R. Murray, J. Am. Chem. Soc. 117 (1995) 12537.
[
[
3 2 2
sion for a system using Pd(CH CN) Cl as the catalyst dropped from
9
9% to 85% on the 3rd cycle and to 44% on the 6th cycle. Fully
palladated Au NP–Pd could also be reused many times; however,
a gradual drop in conversion due to the small amount of Pd leach-
ing during consecutive recycling procedures was noticed.
[
[
10] M. Brust, D. Bethell, D.J. Schiffrin, C.J. Kiely, Adv. Mater. 7 (1995) 795.
11] R.L. Whetten, J.T. Khoury, M.M. Alvarez, S. Murthy, I. Vezmar, Z.L. Wang, P.W.
Stephens, C.L. Cleveland, W.D. Luedtke, U. Landmann, Adv. Mater. 8 (1996)
428.
[
[
[
[
12] Y.-Y. Lin, S.-C. Tsai, S.J. Yu, J. Org. Chem. 73 (2008) 4920.
13] Y. Uozumi, Y.M.A. Yamada, C.K. Jin, Synfacts 9 (2008) 995.
14] T. Belser, M. Stöhr, A. Pfaltz, J. Am. Chem. Soc. 127 (2005) 8720.
15] F. Ono, S. Kanemasa, J. Tanaka, Tetrahedron Lett. 46 (2005) 7623.
4
. Conclusions
The main purpose of using Au NPs as a metal-complex catalyst
[16] M. Bartz, J. Küther, R. Seshadri, W. Tremel, Angew. Chem. 110 (1998) 2646.
[
[
17] H. Li, Y.-Y. Luk, M. Mrksich, Langmuir 15 (1999) 4957.
18] K. Marubayashi, S. Takizawa, T. Kawakusu, T. Arai, H. Sasai, Org. Lett. 5 (2003)
support is to provide a good quality surface for the immobilization
of metal complexes. By controlling the amount of palladium com-
plex immobilized on the Au surface, the resulting hybrid catalyst
4409.
[19] R.F. Heck, J. Am. Chem. Soc. 90 (1968) 5518.

J.-N. Young et al. / Journal of Catalysis 272 (2010) 253–261
261
[
[
[
[
[
20] A. Fihri, P. Meunier, J.-C. Hierso, Coord. Chem. Rev. 251 (2007) 2017.
21] L. Yin, J. Liebscher, Chem. Rev. 107 (2007) 133.
22] J.P. Knowles, A. Whiting, Org. Biomol. Chem. 5 (2007) 31.
23] N.T.S. Phan, M. Van Der Sluys, C.W. Jones, Adv. Synth. Catal. 348 (2006) 609.
24] W.A. Herrmann, C. Brobmer, K. Öfele, M. Beller, H. Fischer, J. Organomet. Chem.
[39] M.S. Yoon, D. Ryu, J. Kim, K.H. Ahn, Organometallics 25 (2006) 2409.
[40] C.-G. Yang, C. He, J. Am. Chem. Soc. 127 (2005) 6966.
[41] R. Abel, P. Collins, K. Eichler, I. Nicolau, D. Peters, in: G. Ertl, H. Knözinger, J.
Weitkamp (Eds.), Handbook of Heterogeneous Catalysis, vol. 5, Wiley VCH,
Germany, 1997, p. 2298.
4
91 (1995) C1.
[42] A.M. Venezia, V. La Parola, V. Nicoli, G. Deganello, J. Catal. 212 (2002) 56.
[43] D.L. Trimm, Z.I. Onsan, Catal. Rev. 43 (2001) 31.
[44] M. Chen, D. Kumar, C.-W. Yi, D.W. Goodman, Science 310 (2005) 291.
[45] M. Bartz, J. Küther, R. Seshadri, W. Tremel, Angew. Chem. Int. Ed. 37 (1998)
2466.
[
[
[
[
25] P. Nilsson, O.F. Wendt, J. Organomet. Chem. 690 (2005) 4197.
26] F. d’Orlye, A. Jutand, Tetrahedron 61 (2005) 9670.
27] K. Yu, W. Sommer, M. Weck, C.W. Jones, J. Catal. 226 (2004) 101.
28] X.-S. Zhou, Z.-R. Dong, H.-M. Zhang, J.-W. Yan, J.-X. Gao, B.-W. Mao, Langmuir
2
3 (2007) 6819.
[46] M. Beller, H. Fisher, K. Kuhlein, C.-P. Reisinger, W.A. Herrmann, J. Organomet.
Chem. 520 (1996) 257.
[47] J. Tsuji, Palladium Reagents and Catalysts, Wiley, New York, 1995. p.125
(Chapter 4).
[
[
29] Y.-F. Han, Z. Zhong, K. Ramesh, F. Chen, L. Chen, T. White, Q. Tay, S.N. Yaakub, Z.
Wang, J. Phys. Chem. C 111 (2007) 8410.
30] F.H.B. Lima, J. Zhang, M.H. Shao, K. Sasaki, M.B. Vukmirovic, E.A. Ticianelli, R.R.
Adzic, J. Phys. Chem. C 111 (2007) 404.
31] L. Djakovitch, K. Köhler, J. Am. Chem. Soc. 123 (2001) 5990.
32] K. Köhler, R.G. Heidenreich, J.G.E. Krauter, M. Pietsch, Chem. Eur. J. 8 (2002)
[48] I.P. Beletskaya, A.V. Cheprakov, Chem. Rev. 100 (2000) 3009.
[49] M. Albrecht, G. van Koten, Angew. Chem. Int. Ed. 40 (2001) 3750.
[50] B.M. Choudary, S. Madhi, N.S. Chowdari, M.L. Kantam, B. Sreedhar, J. Am. Chem.
Soc. 124 (2002) 14127.
[51] P. Mehnert, D.W. Weaver, J.Y. Ying, J. Am. Chem. Soc. 120 (1998) 12289.
[52] A.F. Shmidt, L.V. Mametova, Kinet. Catal. 37 (1996) 406.
[53] F. Zhao, B.M. Bhanage, M. Shirai, M. Arai, Chem. Eur. J. 6 (2000) 843.
[54] A. Biffis, A.M. Zecca, M. Basato, Eur. J. Inorg. Chem. (2001) 1131.
[55] L. Ratke, P.W. Voorhees, Growth and Coarsening: Ostwald Ripening in Material
Processing, Springer, 2002, ISBN 3-540-42563-2. pp. 117–118.
[56] G.T. Crisp, Chem. Soc. Rev. 27 (1998) 427.
[
[
6
22.
33] S.S. Prockl, W. Kleist, M.A. Gruber, K. Köhler, Angew. Chem. Int. Ed. 43 (2004)
881.
[
[
1
34] S. Komiya, Synthesis of Organometallic Compounds: A Practical Guide, John
Wiley and Sons, NY, USA, 1997. p. 249.
[
[
[
35] D.V. Leff, C. Ohara, J.R. Heath, W.M. Gelbart, J. Phys. Chem. 99 (1995) 7036.
36] Y.-S. Fu, S.J. Yu, Angew. Chem. Int. Ed. Engl. 40 (2001) 437.
37] G. Beamson, D. Briggs, High Resolution XPS of Organic Polymers. The Scienta
ESCA 300 Database, J. Wiley & Sons, Chichester, New York, Brisbane, Toronto,
Singapore, 1992, ISBN 0-471-93592-1. p. 278.
[57] C. Amatore, A. Jutand, Acc. Chem. Res. 33 (2000) 314.
[58] M. Buback, T. Perkovic, S. Redlich, A. de Meijere, Eur. J. Org. Chem. (2003) 2375.
[59] C.S. Consorti, F.R. Flores, J. Dupont, J. Am. Chem. Soc. 127 (2005) 12054.
[
38] G. Kumar, J.R. Blackburn, R.G. Albrtdge, W.E. Moddeman, M.M. Jones, Inorg.
Chem. 11 (1972) 296.