The effect of PEGylated dendrimers on the catalytic activity and stability of palladium particles in the suzuki reaction

Article abstract of DOI:10.1007/s10562-013-0967-9

Stable dendrimer-coated Pd particles were synthesized using the wet-chemical borohydride reduction method of Pd(II) salts in the presence of low-generation (poly)ethylene glycol-terminated amidoamine-based dendrimers. The identity and structure of the Pd-

Full text of DOI:10.1007/s10562-013-0967-9

Catal Lett (2013) 143:317–323
DOI 10.1007/s10562-013-0967-9
The Effect of PEGylated Dendrimers on the Catalytic Activity
and Stability of Palladium Particles in the Suzuki Reaction
•
Christian Gabler Janine Jeschke Gulnar Nurgazina
•
•
•
¨
Sascha Dietrich Dieter Schaarschmidt Colin Georgi
•
•
•
Maik Schlesinger Michael Mehring Heinrich Lang
•
Received: 25 October 2012 / Accepted: 24 January 2013 / Published online: 20 February 2013
Ó Springer Science+Business Media New York 2013
Abstract Stable dendrimer-coated Pd particles were syn-
thesized using the wet-chemical borohydride reduction
method of Pd(II) salts in the presence of low-generation
(poly)ethylene glycol-terminated amidoamine-based den-
drimers. The identity and structure of the Pd-containing
colloids were analyzed by FT-IR spectroscopy, X-ray pow-
der diffraction, thermogravimetric analysis, atom absorption
spectroscopy and UV–Vis spectroscopy. Dynamic light
scattering experiments have been performed to determine
the hydrodynamic diameter of the particles (350–900 nm).
The performance of the thus obtained dendrimer-stabilized
Pd particles in Suzuki C,C cross-coupling reactions of aryl
halides and phenyl boronic acid was examined. Turn over
numbers of up to 930 could be achieved. The influence of the
dendritic stabilizers on the particle size along with the cat-
alytic performance is presented.
1 Introduction
Nanosized metallic particles exhibiting a large surface-
to-volume ratio gained considerable interest in the applica-
tion as effective catalysts for a variety of chemical trans-
formations [1–4]. Presently, scientific efforts are directed to
nanocatalysis, in the field of heterogeneous catalysis, in
which the nanoparticles (NPs) are supported on a solid sur-
face (e.g. silica [5, 6], alumina [7, 8]) and in homogeneous
catalysis applying colloidal NPs as catalytic active species,
respectively [9, 10]. Because metal NPs are thermodynam-
ically unstable with respect to agglomeration and precipita-
tion phenomena, the colloids tend to lose their catalytic
reactivity and selectivity [11]. Aggregation of NPs can be
avoided by surrounding the appropriate nanoparticle with an
electrical double layer of adsorbed ions (e.g. citrate and
chloride) or by adsorption of weakly bounded organic sur-
factant molecules (e.g. long-chain alkyl compounds, ten-
sides, polymers, dendrimers ) in the preparation progress,
thus providing a protective layer [12]. Common methods to
prepare metal colloids involve evaporation/condensation
processes of metal–organic and organometallic precursors as
well as chemical/electrochemical reduction of metal salts in
the presence of surfactants [13, 14].
Keywords Particles ꢀ Palladium ꢀ (Amidoamine)
dendrimers ꢀ (Poly)ethylene glycol
¨
C. Gabler ꢀ J. Jeschke ꢀ S. Dietrich ꢀ D. Schaarschmidt ꢀ
C. Georgi ꢀ H. Lang (&)
Department of Inorganic Chemistry, Faculty of Natural Sciences,
Institute of Chemistry, Chemnitz University of Technology,
Straße der Nationen 62, 09111 Chemnitz, Germany
e-mail: heinrich.lang@chemie.tu-chemnitz.de
Since the pioneering work of Crooks and Tomalia
[15, 16] the fascinating class of dendrimer molecules has
been successfully employed as templates and stabilizing
agents, respectively, for a variety of metal NPs, including
palladium and platinum [17]. Such particles exhibit a high
catalytic activity in hydrogenation reactions of olefins [18]
and several C,C cross-couplings, including Heck [19] and
Suzuki reactions [20]. One major advantage of stabilized
NPs compared to commonly used palladium phosphine
complexes lies in the convenient separation of the catalyst
that offers the possibility of recycling.
G. Nurgazina
Department of Chemistry, Faculty of Natural Sciences,
L.N.Gumilyov Eurasian National University, Munaitpasov
Street 5, 010008 Astana, Kazakhstan
M. Schlesinger ꢀ M. Mehring
Department of Coordination Chemistry, Faculty of Natural
Sciences, Institute of Chemistry, Chemnitz University of
Technology, Straße der Nationen 62, 09111 Chemnitz, Germany
123

¨
C. Gabler et al.
318
Previously, Li and El-Sayed reported on the application of
Zetasizer Nano Series S 90 and UV–Vis spectroscopy was
recorded with a THERMO Genesys 6 spectrometer. Ther-
mogravimetric experiments were performed with a MET-
TLER-TOLEDO TGA/DSC1 1100 system with an UMX1
balance, and atomic absorption spectroscopy was performed
on a Thermo Scientific iCE 3000 system.
hydroxyl-terminated (poly)amidoamine (PAMAM) dendri-
mers of second to fourth generation as effective stabilizers for
catalytically active Pd NPs in the Suzuki reaction concluding
that G4 provides the best protection against Pd black forma-
tion [20]. However, these NPs are strongly encapsulated
within the dendrimer resulting in a pronounced loss of cata-
lytic activity. For the preparation of effective catalysts, the
usage of low generation dendrimers may be advantageous,
which in addition are much easier to synthesize. Recently, the
synthesis of gold [21] and Fe3O4 NPs, [22] stabilized by low-
generation PEGylated PAMAM-dendrimers, has been
reported by our group. The particle size can be influenced by
both the dendrimer and the dendrimer-to-metal ratio.
2.2 Synthesis Procedure for Pd Particles
In a typical experiment, dendrimer stabilized Pd particles
were formed in a wet-chemical process, applying stock
solutions of the stabilizers 1 or 2, respectively, in methanol,
sodium tetrachloropalladate(II) as palladium source and
sodium borohydride in H2O as reducing agent. An appro-
priate volume of the respective stabilizer stock solution
was mixed with aqueous Na2[PdCl4] (molar ratio stabi-
lizer-to-Pd = 1:10, 1:50, 1:100, 1:150, 1:200, 1:250, 1:500,
1:1,000) at ambient temperature, filled up to 3 mL with
water and stirred vigorously for 5 min. Subsequent addi-
tion of the Na[BH4] stock solution resulted in the imme-
diate formation of black-colored Pd colloids, which were
applied as catalysts in the Suzuki C,C cross-coupling
reaction after removal of the organic solvent without fur-
ther purification. (For further information see ESI.)
In continuation of our recent studies in the field of
(metallo)dendrimers, [21, 22] the generation of NPs
[23–27] and in homogeneous C,C cross-coupling, [28–35]
we here report on the generation of Pd particles from
Na2[PdCl4] using the wet-chemical borohydride reduction
method. As stabilizer for colloidal Pd particles low-
generation (poly)ethylene glycol-terminated amidoamine-
based dendrimers are applied. The appropriate Pd particles
were used as catalyst in the Suzuki reaction of diverse aryl
halides with phenyl boronic acid. The identity and com-
position of the Pd colloids has been confirmed by X-ray
powder diffraction (XRPD), ultraviolet–visible spectros-
copy (UV–Vis), thermogravimetric analysis (TGA) along
with atom absorption spectrometry (AAS). Dynamic light
scattering (DLS) measurements were performed to deter-
mine the hydrodynamic diameter of the particles. The
influence of the stabilizer used as well as the stabilizer-
to-Pd ratio onto the particle size along with the conse-
quences for the catalysts performance will also be discussed.
For characterization purposes the colloids have been
isolated. Therefore, the particles were evaporated to dry-
ness and subsequently washed with water and methanol to
remove inorganic salts as well as excess surfactant.
2.3 General Procedure for the Suzuki Reaction
The respective aryl halide (2.0 mmol), phenyl boronic acid
(365 mg, 3.0 mmol), acenaphthene (308 mg, 2.0 mmol) as
well as the corresponding base K2CO3 (830 mg, 6.0 mmol)
or K3PO4 (1.27 g, 6.0 mmol) were dissolved in 7 mL of a
1,4-dioxane/water mixture (ratio 2:1, v/v) and loaded with
the dendrimer-stabilized Pd catalyst 1:Pd or 2:Pd (Pd
loading = 1.0, 0.25, 0.1 mol%). The colloidal suspensions
were stirred at 100 °C for 3 h. The organic phase was fil-
tered through a pad of silica with diethyl ether as eluent.
All volatiles were evaporated under reduced pressure. The
yields were determined by 1H NMR spectroscopy applying
acenaphthene as internal standard and are an arithmetic
average of three independent runs.
2 Materials and Methods
2.1 Materials and Instruments
All synthesis procedures were performed under a dry and
deoxygenated dinitrogen atmosphere using standard
Schlenk techniques. Distilled water was deoxygenated prior
to use. All starting materials were obtained from commercial
suppliers and were used without further purification. Den-
drimers 1 [21] and 2, [36] 1-bromo-2-methylnaphthalene
[37] and 1-bromo-2-methoxynaphthalene [38] were syn-
thesized according to previously published procedures.
The structure of the powder samples was identified by
X-ray powder diffraction on a STOE-STAD IP diffractom-
3 Results and Discussion
3.1 Preparation and Characterization of Dendrimer-
Stabilized Pd Particles
˚
eter with Cu Ka (1.5405 A) radiation. The surface coating
was examined by FT-IR spectroscopy recorded with a FT
Nicolet IR 200 instrument. Dynamic light scattering (DLS)
measurements were accomplished with a MALVERN
End-grafted ethylene glycol ether-functionalized amido-
amine-based low-generation dendrimers 1 [21] and 2 [36]
123

PEGylated Dendrimers and Palladium Particles
319
Et
Et
O
O
O
O
Et
O
O
Et
O
O
O
N
Et
O
N
O
O
Et
O
O
O
O
O
O
O
O
O
NH
Et
Et
O
O
O
O
O
O
O
N
O
O
Et
Et
O
O
O
O
O
N
O
N
O
O
NH
H
O
O
N
O
O
O
O
N
O
N
O
O
O
N
N
O
N
N
HN
H
H
HN
NH
O
N
O
N
N
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Et
O
O
Et
Et
Et
Et
Et
1
2
Scheme 1 Ethylene glycol-functionalized PAMAM dendrimers 1 and 2 [21, 36]
(Scheme 1) were prepared according to published proce-
dures. The obtained PEGylated dendritic molecules of the
type N(CH2CH2C(O)NHCH2CH2NR2)3 (1, R = CH2CH2
C(O)O(CH2CH2O)2C2H5), and (R2NCH2CH2NHC(O)CH2
CH2)N[CH2CH2N(CH2CH2C(O)NHCH2CH2NR2)2]2 (2, R =
CH2CH2C(O)O(CH2CH2O)2C2H5) were applied as sur-
factants for the stabilization of Pd particles generated by
the controlled wet-chemical borohydride reduction of
Na2[PdCl4] (Scheme 2).
these transitions are bathochromic shifted by 7 nm. Fur-
thermore, a ligand-to-metal-charge transfer band (LMCT)
of the [PdCl4]2- ions at 235 nm is observed [39]. After
wet-chemical reduction with Na[BH4] this LMCT disap-
pears and the spectrum is dominated by an intensive
background absorbance, characteristic for Pd particles
(Fig. 2) [40].
To study the composition of the dendrimer-coated Pd
particles 1ꢀPd (1:150) thermo-gravimetric experiments
Upon addition of the reducing agent, black colored
solutions were obtained. The particles do not precipitate in
the methanolic/aqueous solution within days and can be
maintained upon removal of the solvent and addition of
1,4-dioxane. This indicates that the glycol-functionalized
PAMAM-based dendrimers 1 and 2 are efficient stabilizing
agents as reported earlier [21, 22].
were performed in a dinitrogen atmosphere (60 mL min-1
)
in the temperature range of 40–800 °C applying a heating
rate of 10 K min-1. Decomposition of the organic stabi-
lizer occurs in various steps between 50 and 630 °C
resulting in an overall mass diminution of 7.3 wt%
(Fig. 3). After cooling to ambient temperature the sample
was heated to 800 °C (10 K min-1) with a gas flow of
40 mL min-1 N2 and 20 mL min-1 O2. As no further mass
diminution could be detected, the formation of carbon
during the decomposition of the surfactant can be excluded
and the residual mass of 92.7 wt% corresponds to the
amount of Pd in the colloid.1 This result could be validated
by AAS measurements (93.3 wt% Pd). For a surfactant-
to-Pd ratio of 1:150, 91.5 wt% Pd would be expected, the
isolated colloids exhibit a 1:Pd ratio of 1:178.
As an evidence for chemical bonding between Pd and
surfactant FT-IR spectroscopy of the organic–inorganic
hybrid material was performed. As expected, 1ꢀPd
(1:Pd = 1:150) revealed no definite absorption, due to the
low concentration of the stabilizer. Figure 1 exemplarily
shows the FT-IR spectra of 1 and 1-stabilized Pd colloids at
a surfactant-to-palladium ratio of 1:10. The bands of 1
coated on Pd particles attributing to the C–O–C vibrations
are bathochromically shifted by 25 cm-1 (1,093 and
1,025 cm-1) and 5 cm-1 (1,175 cm-1), respectively, when
compared to the parent dendrimer 1. This indicates the
dendritic stabilization of the Pd particles.
The phase and crystalline nature of the dendrimer-
stabilized Pd particles were confirmed by XRPD experi-
ments on 1ꢀPd colloids (molar ratio of 1:Pd = 1:150) as
shown in Fig. 4. The powder diffraction pattern is consis-
tent with standard Pd reflections reported in literature
(JCPDS Card No. 46-1043) confirming the formation of Pd
The formation of Pd particles was investigated by UV–
Vis spectroscopy (Fig. 2) with 1:Pd = 1:150 as represen-
tative example. For molecule 1, absorptions were observed
at 213 and 267 nm, respectively, which can be assigned to
p-p* and n-p* transitions. Upon addition of Na2[PdCl4]
1
Due to the partial formation of PdO a slight increase in weight of
1.5 wt% was observed.
123

¨
C. Gabler et al.
320
1. Na2[PdCl4],
MeOH/H2O, 25 °C
2. Na[BH4], H2O, 25 °C
H
N
=
=
N
O
O
O
Et
n
O
= Pd aggregates
n = 2
Scheme 2 Schematic illustration of dendrimer-stabilized Pd particle formation by the wet-chemical borohydride method in methanol as solvent
with space group Fd-3m. The characteristic diffraction
100
Molecule 1
1 • Pd
peaks could be well indexed. The crystallite size of the
colloids as calculated by the Scherrer formula was found to
be 6–7 nm [41].
100
50
0
98
96
94
92
90
88
86
To investigate the effective size of the Pd-containing
colloids in solution the hydrodynamic diameter was mea-
sured by dynamic light scattering (DLS). The colloids
analyzed by DLS were generated following the synthesis
protocol as used for the colloids applied in the Suzuki
reactions. The smallest particles were observed for a sur-
factant-to-Pd ratio of 1:150 with 357 ( 50) nm (Table 1,
entry 4). Both, increase or decrease of the amount of 1
causes the formation of Pd particles with larger hydrody-
namic diameters. In case of low surfactant-to-Pd ratios
(entries 7 and 8) the increase in particle size can be
explained by agglomeration originating from insufficient
stabilization of the particles by 1. For high amounts of
surfactant (entries 1 and 2) the formation of larger particles
may be due to a decrease in the nucleation rate, which may
2000
1500
1000
500
Wavenumber / cm-1
Fig. 1 FT-IR spectra of molecule 1 and 1ꢀPd (KBr, 25 °C)
Molecule 1
1 • Pd2+
1 • Pd
100
98
96
94
92
200
300
400
500
Wavelength / nm
200
400
600
800
Fig. 2 UV–Vis spectra of 1 (c = 0.2 mmol L-1), 1ꢀPd2? (cPd2þ
=
Temperature / °C
1.14 mmol L-1 c1 = 0.0076 mmol L-1) and 1ꢀPd (1:Pd = 1:150,
cPd2þ = 0.285 mmol L-1 c1 = 0.0019 mmol L-1) in a mixture of
H2O–MeOH of ratio 1:0.77 (v/v) at 25 °C
Fig. 3 Thermogravimetric analysis of 1ꢀPd (1:150) under dinitrogen
(60 mL min-1) using a heating rate of 10 K min-1
123

PEGylated Dendrimers and Palladium Particles
321
The applied surfactant impacts the behavior of the Pd
colloids in two ways. On the one hand it acts as stabilizing
agent that prevents formation of catalytically inactive
Table 1 Hydrodynamic diameters of 1-stabilized Pd particles with
varying molar stabilizer-to-Pd ratios determined by DLS (cPd2þ
=
0.2 mmol L-1, 1,4-dioxane:H2O = 2:1, 20 °C)
Entry
Surfactant-to-palladium ratio
Particle size (nm)
1
2
3
4
5
6
7
8
1:10
898 ( 142)
780 ( 55)
370 ( 73)
357 ( 50)
391 ( 18)
418 ( 49)
593 ( 114)
614 ( 105)
1:50
1:100
1:150
1:200
1:250
1:500
1:1,000
40
60
80
2 Theta (°)
Fig. 4 X-ray powder diffraction pattern derived from 1ꢀPd particles
(1:Pd = 1:150)
be explained by strong interactions between the dendritic
molecules and Pd clusters prior to nucleation. It is
instructive to note that the hydrodynamic diameter is much
higher than the crystallite size measured by XRPD which
Table 2 Suzuki C,C cross-coupling of 2-bromotoluene and phenyl
boronic acid with stabilized Pd colloids generated by 1 and 2 at
varying molar surfactant-to-palladium ratios
2
points to a fast agglomeration process of the particles.
Both the use of different reducing agents (polymethylhy-
drosiloxane, lithium triethylborohydride as thf solution) as
well as performing the reducing step at lower temperatures
(-20 – 0 °C) did not result in the formation of smaller
particles. Noteworthy, the Pd particles discussed here are
by far larger than the Au (5.0–60.0 nm) [21] and Fe3O4
(5.0–10.0 nm) [22] particles generated in the presence of
the same dendritic stabilizer.
Entry
Surfactant
Surfactant-to-palladium ratio
Yield (%)
1
–
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
–
22a
56b
30
2
1:10
3
1:50
4
1:100
1:150
1:200
1:250
1:500
1:1,000
1:150
1:10
61
3.2 Suzuki C,C Cross-Coupling with Dendrimer-
Stabilized Pd Particles
5
93
6
87
7
82
To enrich the family of existing C,C cross-coupling cata-
lysts and in order to determine the low-generation dendri-
mers’ impact on the catalytic activity of Pd particles, we
applied the appropriate dendrimer-stabilized Pd colloids in
Suzuki reactions. In comparative studies the newly syn-
thesized organic–inorganic hybrid materials showed to be
efficient catalysts in palladium-mediated transformations
of aryl halides with phenyl boronic acid to give biphenyls.
The catalytic reactions of the appropriate organic coupling
reagents were performed in a 1,4-dioxane-water mixture of
ratio 2:1 (v/v) in presence of a base. (Pre)catalyst loadings
of 1.0, 0.25 and 0.1 mol% palladium at 100 °C were
applied. For the optimization of the reaction conditions the
conversion of 2-bromotoluene with phenyl boronic acid
was chosen (Table 2).
8
28
9
21
10
11
12
13
14
15
16
17
18
14c
9a
1:50
16a
58a
22a
32a
40a
35a
26a
1:100
1:150
1:200
1:250
1:500
1:1,000
2.0 mmol of 2-bromotoluene, 3.0 mmol of phenyl boronic acid,
6.0 mmol of K2CO3, 0.1 mol% Pd, 1,4-dioxane:water (2:1, 7 mL),
100 °C, 3 h
a
1.0 mol% Pd
b
0.25 mol% Pd
c
The reaction mixture was extracted with n-hexane and water, after
evaporation to dryness the black precipitate obtained was used as the
catalyst in a second run
2
This agglomeration process was complete in the time required for
the acquisition of the DLS measurements (approx. 5 minutes).
123

¨
C. Gabler et al.
322
palladium black (Table 2, entry 1). On the other hand it
shields the active catalyst from the substrate molecules
[20]. Therefore, the surfactant-to-palladium ratio has to be
optimized (Table 2, entries 2–9). A surfactant-to-palladium
ratio of 1:150 for surfactant 1 provides the best results
(Table 2, entry 5) which corresponds to the particles
exhibiting the smallest hydrodynamic diameter (vide
supra). Most likely this result is due to the relatively high
surface to volume ratio of these particles and consequently
the highest number of Pd atoms accessible for substrate
molecules. Investigations to reuse the Pd colloids revealed
that this is possible in principle (entry 10), however, being
associated with a significant diminution of the catalytic
productivity. The reason for this behaviour is most proba-
bly due to a partial decomposition of the Pd colloid and
consequently the formation of catalytically inactive palla-
dium black in course of the catalytic transformation. When
changing from surfactant 1 to 2 the catalytic productivity is
considerably decreased (Table 2, entry 5 vs. 14) even
though a higher Pd loading is applied. Thus, we concen-
trated on 1 for further investigations.
particles synthesized by Diallo et al. [42] significantly
higher conversions and excellent yields even with less
reactive bromoarenes could be achieved. However, a major
drawback of the as-prepared Pd particles is the lower cat-
alytic activity towards the conversion of ortho-substituted
substrates (Table 3, entries 8–10) and chloroarenes
(Table 3, entries 11 and 12).
Similar results for the transformation of diverse bro-
´
moarenes have recently been reported by Mejıas et al. [43]
applying Pd NPs (2–5 nm) stabilized with PEG-tagged
material. In case of deactivated bromo and activated
chloroarenes a decrease in catalytic activity is observed
even though the reaction temperature is increased up to
130 °C. In contrast Han et al. [44] demonstrated the use of
in situ generated PEG-400-stabilized Pd NPs (2–3 nm) in
an oxygen-promoted ligand-free Suzuki coupling of acti-
vated and non-activated chloroarenes.
4 Conclusion
In order to screen the substrate scope of the dendrimer-
stabilized Pd particles different aryl halides were reacted
with phenyl boronic acid under the optimized reaction
conditions. It can be seen that activated, non-activated and
deactivated bromoarenes can be coupled at a catalyst
loading of 0.25 mol% Pd, the respective biaryls are formed
in good to excellent yields after only 3 h (Table 3, entries
1–7). In comparison with PAMAM dendrimer-stabilized
The preparation and characterization of palladium particles
coated with low-generation PEGylated dendritic molecules
of the type N(CH2CH2C(O)NHCH2CH2NR2)3 (1, R = CH2
CH2C(O)O(CH2CH2O)2C2H5), and (R2NCH2CH2NHC(O)
CH2CH2)N[CH2CH2N(CH2CH2C(O)NHCH2CH2NR2)2]2
(2, R = CH2CH2C(O)O(CH2CH2O)2C2H5), respectively,
and their application in the Suzuki C,C cross-coupling
reaction of aryl halides with phenyl boronic acid is repor-
ted. The identity and elemental composition of the Pd
particles was investigated by XRPD, TGA and AAS
demonstrating the presence of surfactant even in case of the
isolated particles. The observation of an intensive back-
ground absorbance in the UV–Vis spectra indicates the
formation of Pd particles. A bathochromic shift of the
C–O–C vibrations measured by FT-IR could be observed,
due to an interaction between surfactant and Pd particles.
Their hydrodynamic diameters, which strongly depend on
the surfactant-to-Pd ratio, have been determined by
dynamic light scattering to be in the range of 350–900 nm.
The smallest Pd colloids were observed for a surfactant-
to-Pd ratio of 1:150. Both, increase or decrease of the
amount of 1 causes the formation of Pd particles with
larger hydrodynamic diameters. Compared to previously
reported dendrimer-stabilized Au particles (5.0–60.0 nm)
[21] and Fe3O4 particles (5.0–10.0 nm) [22] the size of the
Pd particles is clearly increased. The dendrimer-coated Pd
particles were applied in the palladium-catalyzed Suzuki
C,C cross-coupling. The reaction of 2-bromotoluene and
phenyl boronic acid with potassium carbonate as base was
chosen for a pre-screening and to optimize the catalysis
conditions. It was found that at a 1-to-Pd ratio of 1:150 the
highest catalytic productivity is observed, which most
Table 3 Suzuki C,C cross-coupling of various aryl halides with
phenyl boronic acid using 1ꢀPd as catalyst
Entry
Aryl halide
Yield
(%)
Entry
Aryl halide
Yield
(%)
1
2
100
99
7
8
74
35
3
4
98
60
9
27
10
10
5
6
71
70
11
12
26
17
2.0 mmol of aryl halide, 3.0 mmol of phenyl boronic acid, 6.0 mmol
of K3PO4, 1:Pd = 1:150, 0.25 mol% Pd, 1,4-dioxane:water (2:1,
7 mL), 100 °C, 3 h
123

PEGylated Dendrimers and Palladium Particles
323
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activated and deactivated bromoarenes have successfully
been coupled with phenyl boronic acid at 100 °C and a
0.25 mol% Pd loading (1:Pd = 1:150) within 3 h. However,
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5 Supporting Information
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Detailed information concerning the preparation of the Pd
particles and results of further Suzuki reactions are avail-
able in electronic supplementary information (ESI).
25. Tuchscherer A, Schaarschmidt D, Schulze S, Hietschold M, Lang
H (2011) Inorg Chem Commun 14:676–678
26. Tuchscherer A, Schaarschmidt D, Schulze S, Hietschold M, Lang
H (2011) Eur J Inorg Chem 2011:4421–4428
27. Steffan M, Jakob A, Claus P, Lang H (2009) Catal Commun
10:437–441
Acknowledgments This study was generously supported by the
Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie,
and the State of Saxony (Landesgraduierten fellowship SD).
28. Schaarschmidt D, Lang H (2011) ACS Catalysis 1:411–416
29. Schaarschmidt D, Lang H (2010) Catal Commun 11:581–583
30. Jakob A, Milde B, Ecorchard P, Schreiner C, Lang H (2008)
J Organomet Chem 693:3821–3830
31. Lohan M, Milde B, Heider S, Speck JM, Krauße S, Schaarsch-
midt D, Ru¨ffer T, Lang H (2012) Organometallics 31:2310–2326
32. Milde B, Lohan M, Schreiner C, Ru¨ffer T, Lang H (2011) Eur J
Inorg Chem 2011:5437–5449
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