Sulphonated "click" dendrimer-stabilized palladium nanoparticles as highly efficient catalysts for olefin hydrogenation and Suzuki coupling reactions under ambient conditions in aqueous media

Article abstract of DOI:10.1002/adsc.200700584

Water-soluble 1,2,3-triazolyl dendrimers were synthesized by "click chemistry" and used to stabilize palladium nanoparticles (PdNPs). These new "click" dendrimer-stabilized nanoparticles (DSN) are highly stable to air and moisture and are catalytically active for olefin hydrogenation and Suzuki coupling reaction, in aqueous media, under ambient conditions using a low amount of palladium (0.01 mol% Pd). Kinetic studies show high catalytic efficiency and high stability for the new "click" DSN in both reactions. The complexation of potassium tetrachloropalladate (K ₂PdCl₄) to the triazole ligands present in the dendritic structures was monitored by UV/vis and, after reduction, the nanoparticles were characterized by transmission electron microscopy (TEM).

Full text of DOI:10.1002/adsc.200700584

FULL PAPERS
DOI: 10.1002/adsc.200700584
Sulphonated “Click” Dendrimer-Stabilized Palladium
Nanoparticles as Highly Efficient Catalysts for Olefin
Hydrogenation and Suzuki Coupling Reactions Under
Ambient Conditions in Aqueous Media
a
a
b
a,
Cµtia Ornelas, Jaime Ruiz, Lionel Salmon, and Didier Astruc *
a
Institut des Sciences MolØculaires, UMR CNRS N8 5255, UniversitØ de Bordeaux 1, 351 Cours de la LibØration,
3
3405Talence Cedex, France
Fax : (+33)-5-4000-6994; e-mail: d.satruc@ism.u-bordeaux.fr
Laboratoire de Chimie de Coordination, UPR CNRS N8 8241, 205Route de Narbonne, 31077 Toulouse Cedex 04, France
b
Received: December 11, 2007; Published online: March 31, 2008
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: Water-soluble 1,2,3-triazolyl dendrimers in both reactions. The complexation of potassium tet-
were synthesized by “click chemistry” and used to rachloropalladate (K PdCl ) to the triazole ligands
2
4
stabilize palladium nanoparticles (PdNPs). These present in the dendritic structures was monitored by
new “click” dendrimer-stabilized nanoparticles UV/vis and, after reduction, the nanoparticles were
(
DSN) are highly stable to air and moisture and are characterized by transmission electron microscopy
catalytically active for olefin hydrogenation and (TEM).
Suzuki coupling reaction, in aqueous media, under
ambient conditions using a low amount of palladium
(
0.01 mol% Pd). Kinetic studies show high catalytic Keywords: catalysis; dendrimers; nanoparticles; pal-
efficiency and high stability for the new “click” DSN ladium; Suzuki reaction
Introduction
efficient catalysts in aqueous media even under ambi-
ent conditions using only 0.01% mol Pd catalyst. So
under ambient conditions is a far, the reported examples of dendrimer-stabilized NP
[
1,2]
Catalysis in water
highly challenging topic in the context of green catalysis in aqueous media were performed at high
[3]
chemistry. A promising ligandless approach is that temperatures using relatively high amounts of PdNPs
[
4]
using nanoparticle (NP) catalysis, in particular with catalyst (> 1%) only with PAMAM or PIP dendrim-
[
5–7]
dendrimer-stabilized NPs.
The catalytic applica- ers.
tions of such NPs were pioneered by Crooks using
PAMAM dendrimers for hydrogenation and CÀC
[
7]
[8]
coupling reactions. Recently, we reported “click”
Results and Discussion
[
9a]
dendrimers containing triazole ligands and showed
that they can stabilize PdNPs which efficiently cata- Synthesis of Water-Soluble 1,2,3-Triazolyl Dendrimers
[
9b]
lyse olefin hydrogenation and Suzuki coupling reac-
[9c]
tions in organic media using homeopathic amounts “Click” reactions of the known azido terminated den-
[9c,10]
[9b,11]
of PdNPs.
drimers
with sodium propargyl sulphonate in
A challenge was then to synthesize water-soluble water/THF (1:1) yielded the triazolyl sulphonate-ter-
triazolyl dendrimers to show that PdNPs stabilized by minated dendrimers [Eqs. (1)–(3)]. THF was evapo-
triazolyl dendrimers are also catalytically efficient in rated, and the dendrimers remained in aqueous solu-
aqueous media. We now report the first synthesis of tion. They were purified by dialysis against aqueous
water-soluble dendrimers containing triazole ligands ammonia solution for three days [in order to remove
in their structure, (water-soluble triazolyl sulphonate Cu(I) that remains trapped inside the dendrimer] and
“click” dendrimers) and the corresponding dendri- against water for one day. The aqueous solution
mer-stabilized PdNPs, and we show that they are very inside the membrane was recovered, water was re-
Adv. Synth. Catal. 2008, 350, 837 – 845ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Cµtia Ornelas et al.
FULL PAPERS
moved under vacuum, and the poly-1,2,3-triazolyl ure S1). These dendrimers were characterized by
sulphonate dendrimers 4-G , 5-G and 6-G were ob- size-exclusion chromatography (SEC) showing mono-
0
1
2
1
tained as colorless waxy products. Their H NMR dispersity (polydispersity: 1.00 for 4-G and 1.01 for
0
spectra, recorded in D O, confirmed the structures 5-G and 6-G ). The infrared spectra confirm the ab-
2
1
2
clearly showing all the expected peaks, especially the sence of unreacted azido groups. Dynamic light scat-
triazole protons at 7.8 ppm and the CH SO Na pro- tering experiments for the poly-1,2,3-triazolyl sulpho-
2
3
tons at 4.2 ppm (see Supporting Information, Fig- nate dendrimer 6-G reproducibly give the very large
2
838
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Sulphonated “Click” Dendrimer-Stabilized Palladium Nanoparticles
FULL PAPERS
[
9b]
value of the hydrodynamic diameter of 25.8Æ0.7 nm by several dendrimers, DSNs, Figure 2).
On the
in water, which reflects an enormous amount of water other hand, TEM data now show that, in all cases, the
solvation in the corona due to the peripheral sulpho- size of the NPs obtained is much larger than the size
nate termini.
expected for DENs (G : 2.8Æ0.4 nm instead of
1
0
.9 nm; G : 3.0Æ0.6 nm instead of 1.3 nm) (Figure 4
2
[
12]
and Figure 5).
In fact, the sulphonate groups are
Complexation of K PdCl and Stabilization of PdNPs
by the 1,2,3-Triazolylsulphonate Dendrimers
not bulky enough to encapsulate the NPs by the den-
drimers, thus DSNs are obtained for the three genera-
2
4
tions. The TEM data also show that, in this series of
we showed that 1,2,3-triazolyl- dendrimers, the higher dendrimers forms NPs with
[
9b,c]
In previous reports,
ferrocenyl dendrimers are able to complex Pd(II) in larger polydispersity than the smaller dendrimers.
the form of [Pd(MeCN) ][BF ] and Pd(OAc) by in- Contrary to dendrimers with bulky termini that
A
C
H
T
R
E
U
N
G
A
H
R
U
G
ACHTREUNG
4
4 2
2
[12]
teraction with the triazole ligands, using cyclic voltam- usually form relative monodisperse NPs (DENs), in
1
metry, UV/vis and H NMR spectroscopy. We now this series of dendrimers the polydispersity increases
show the interaction of K PdCl with the 1,2,3-triazo- with the dendrimer size (Figure 3, Figure 4, and
2
4
lylsulphonate dendrimers by UV/vis spectroscopy. In Figure 5). Indeed, in the present case (triazolylsulpho-
Figure 1, we can observe that the spectrum of nate termini), G is the optimal generation because it
0
K PdCl , that presents two absorption bands at 208 forms the smaller NPs with low dispersity (Figure 3).
2
4
and 235nm, changes upon addition of dendrimer 4-G0
214 and 227 nm). This change in the UV/vis spec-
trum can be attributed to the coordination of Pd(II) Use of the New “Click” DSN as Catalysts in
(
to the triazole ligands in the dendrimer.
Hydrogenation Reactions
The three generations of 1,2,3-triazolylsulphonate
dendrimers (4-G , 5-G and 6-G ) were used to stabi- The DSNs formed with the new poly-1,2,3-triazolyl-
0
1
2
lize PdNPs. Upon addition of the classic reducing sulphonate dendrimers are highly stable to air and
agent, NaBH , to an aqueous solution of 1,2,3-triazo- moisture, and proved to be efficient catalysts for hy-
4
lylsulphonate dendrimers and K PdCl (1 equiv. per drogenation of allyl alcohol at 0.01% mol Pd [Eq.
2
4
triazole, 10 equivalents of NaBH as in literature re- (4)].
4
[7]
ports ), black homogeneous solutions were obtained
and analyzed by TEM.
In our previous studies, it was shown that the type
of stabilization of the NPs by the dendrimers mostly
depends on the dendrimer size and type of terminal
groups (dendrimers with bulky terminal groups en-
capsulate the NPs forming DENs, and for dendrimers
with non-bulky terminal groups the NPs are stabilized
Crooks et al. reported the hydrogenation of allylic
alcohols in aqueous solutions, presenting catalytic effi-
À1
À1
ciencies around 500 mol H2 (mol Pd )h (TOF,
[13]
turnover frequency) for monometallic Pd DENs.
The turnover frequencies (TOF) obtained for the hy-
drogenation of allyl alcohol using the new “click”
DSN (0.01% mol Pd) is about sixteen times higher
À1 À1
[
DSN-G : 8 088 mol H (mol Pd) h ] than those re-
0 2
[13]
ported for NPs stabilized by PAMAM. The stability
of the new “click” DSN catalysts was tested by
adding the substrate to the catalytic solutions until
the catalyst was no longer active. Thus, the new DSNs
are highly stable in the catalytic conditions, being re-
used for more than 10 catalytic cycles at 0.01% mol
Pd (TON >100,000). The most efficient catalyst is
DSN-G , confirming the trend according to which the
0
catalytic activity is a function of the size of the
PdNPs, that is, the catalytic reactions are faster for
the smaller NPs than for the larger ones (Table 1).
Figure 1. a) UV/vis spectrum obtained for K PdCl in water;
2
4
b) UV/vis spectrum obtained for a mixture of K PdCl and
2
4
dendrimer 4-G in water (one equiv. of K PdCl per tria-
0
2
4
zole).
Adv. Synth. Catal. 2008, 350, 837 – 845ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Cµtia Ornelas et al.
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Figure 2. Representation of DSN-G0.
Use of the New “Click” DSN as Catalysts in Suzuki
Coupling Reactions
These studies showed evidence for the atom-leaching
mechanism in Suzuki coupling reaction catalyzed by
PdNPs at room temperature, a mechanism analogous
There are a few reports of the use of PdNPs stabilized to that proposed earlier by de Vries for the high-tem-
[
10]
by dendrimers to catalyze the Suzuki coupling reac- perature Heck reaction.
tion, but in all cases the reactions were performed
[14]
The DSNs formed with the new poly-1,2,3-triazolyl-
at high temperatures using relative large amounts of sulphonate dendrimers were tested as catalysts in the
PdNP catalyst. The PdNPs stabilized by poly-1,2,3-tri- Suzuki coupling reaction at 258C, in aqueous media
azolylferrocenyl dendrimers, recently reported by our [Eq. (5)].
group, were shown to be catalytically active in the
In order to compare the catalytic efficiencies of the
Suzuki coupling reaction, in organic solvents, at room new “click” DSNs using different amounts of catalyst,
temperature using low catalyst amounts (between the reactions were carried out using 0.1% mol Pd and
0
.1% and 1 ppm), although these NPs are air-sensitive 0.01% mol Pd. Thus, in aqueous media, the Suzuki
[
9b,c]
and the yields were never quantitative (<70%).
coupling reaction appears to follow the atom-leaching
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Sulphonated “Click” Dendrimer-Stabilized Palladium Nanoparticles
FULL PAPERS
Figure 3. DSN-G : a) TEM image and b) size distribution.
0
Figure 4. DSN-G : a) TEM image and b) size distribution.
1
Figure 5. DSN-G : a) TEM image and b) size distribution.
2
Adv. Synth. Catal. 2008, 350, 837 – 845ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Table 1. Catalytic efficiency (TOF values) and stability media for allylic alcohol hydrogenation and Suzuki
(
TON values) of the new “click” DSNs in the hydrogenation
reactions between PhB(OH) and PhX (X=I or Br).
2
of allyl alcohol using 0.01% mol Pd.
For the later reaction, they show impressive TOFs
and TONs in aqueous media at room temperature for
iodobenzene and at 1008C for bromobenzene. Finally,
[a]
[b]
PdNPs
Diameter
nm]
TOF
TON
À1 À1
[
[mol H (mol Pd) h ]
2
[
9c,10]
the Pd-atom leaching mechanism
disclosed with
DSN-G0
2.3Æ0.2
2.8Æ0.4
3.0Æ0.6
8 088
7 742
5173
123 500
100 000
86 000
triazolylferrocenyl click-DSNs in organic solvent is
also operating in aqueous media with the new DSNs,
but the yields in Suzuki heterocoupling are quantita-
tive at 0.01% mol Pd with these water-soluble DSNs
DSN-G1
DSN-G2
[
[
a]
b]
Diameter of the DSNs, obtained by TEM.
The catalytic activity of the DSNs was investigated for whereas they were never so with the organic DSNs
the hydrogenation of allyl alcohol at 0.01% mol Pd, in whatever the DSN catalyst loading. In our previous
H O, 25 8C and 1 atm H . Reactions were followed by
2
2
study with analogous “click” dendrimers containing
ferrocenyl and other hydrophobic termal groups,
intra- vs. inter-dendritic PdNP stabilization was shown
to depend on the dendrimer generation. On the other
hand, the stablilization of the PdNPs is always inter-
dendritic with sulphonate-terminated dendrimers in
the present study. It is remarkable that, although the
stabilization of the PdNPs is not intradendritic but
outside the dendrimers, the catalysis is so efficient. It
is probable that the environment of the PdNP surface
by several dendrimers is optimal concerning the
PdNP stabilization without inhibition of the surface
GPC and TOF values were determined on the basis of
the yield of formation of propanol.
Table 2. Catalytic efficiency (TOF) and stability (TON) of
the water-soluble “click” DSNs in Suzuki coupling reactions
of iodobenzene, at 258C, using 0.1 and 0.01% mol Pd.
[a]
%
Pd
PdNPs
t [h]
Yield [%]
TOF
TON
0
.1%
DSN-G0
DSN-G1
DSN-G2
DSN-G0
DSN-G1
6 h
6 h
6 h
6 h
6 h
6 h
96%
95%
70%
92%
94%
70%
167
158
117
1 533
1 567
1 167
960
950
700 Pd atoms. The PdNP is a reservoir of catalytically
9 200 active Pd atoms, and this combination of outer-den-
9 400 dritic stabilization and lack of surface inhibition ap-
0
.01%
DSN-G2
7 000
pears to be essential for the efficient delivery of cata-
[
a]
À1 À1
lytically active Pd atoms. It is this very situation that
affords the invaluable ligandless approach for the use
of Pd catalysis. This efficient ligandless catalysis
TOFs are expressed in mol PhI (mol Pd) h . The cata-
lytic activity of the DSNs was investigated for iodoben-
zene, at 258C, in H O/ethanol (1:1). Reactions were fol-
2
lowed by GPC and TOF values were determinated on under ambient conditions in an aqueous solvent com-
the basis of the yield of biphenyl.
pares favourably with other more classic approaches
of dendritic palladium catalysis.
[
16]
mechanism, because there is no significant difference Experimental Section
between the TOFs obtained for NPs of different sizes
(
comparing DSN-G with DSN-G and DSN-G ) and General Data
0 1 2
the catalytic efficiency is higher for lower concentra-
tion of catalyst (Table 2).
Bromobenzene was also used as the substrate to
test our new “click” DSN catalysts in aqueous condi-
tions. A quantitative yield was obtained for the reac-
The chloromethylsilyl dendrimers were prepared according
[11]
to ref. and sodium propargyl sulphonate was prepared ac-
[15]
cording to ref. Dialysis membranes were purchased from
Aldrich.
tion carried out at 1008C, using the DSN-G (0.01%
0
Transmission Electron Microscopy (TEM)
mol Pd) which showed an impressive catalytic effi-
À1 À1
ciency [TOF: 8,700 mol H (mol Pd) h ] and high The samples were prepared by setting a drop of a 4.41”
2
À4
1
0
M water solution of PdNPs (concentration in mol Pd)
stability (TON: 10,000).
on a holey-carbon-coated Cu TEM grid. The size of the
nanoparticles was measured using the software sigmascan-
pro (for each sample, about 100 nanoparticles were mea-
sured).
Conclusions
In conclusion, we have synthesized the first-water
soluble “click” dendrimers, and shown that they can
form PdNPs that are stable DSNs with three dendri-
Gas Chromatography
GPC data were recorded on a Hewlett Packard 5890 Series
mer generations. These new “click” DSNs are very ef- II gas chromatograph, equipped with a Stabilwaxꢁ (Cross-
ficient catalysts down to 0.01% mol Pd in aqueous bandꢁ Carbowaxꢁ-PEG) column and a flame ionization
842
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Adv. Synth. Catal. 2008, 350, 837 – 845

detector. Helium was used as the carrier gas for all the sub-
stratres. The injector and detector temperatures were
162H, Si
A
H
E
U
G
Sulphonated “Click” Dendrimer-Stabilized Palladium Nanoparticles
FULL PAPERS
1
3
159.2 (OC ), 139.1 (arom. C of the dendron), 127.2 and
Ar
q
2408C.
113.6 (arom. CH of the dendron), 60.3 (SiCH O), 43.1 (ben-
2
zylic Cq of the core and dendron), 41.1 (CH CH CH Si),
2
2
2
2
0
9.8 (SiCH N ), 17.6 (CH CH CH Si), 15.0 (CH CH CH Si),
2 3 2 2 2 2 2 2
29
.0023 [Si
A
H
R
U
G
A
H
R
U
G
3
2
2
General Synthesis of Azido-Dendrimers
(CDCl , 59.6 MHz): d=3.33 (SiCH N ), 0.52 (SiCH O); IR:
3
2
3
2
À1
n =2093 cm ; anal. calcd. for C288H543O N Si : C 54.94, H
N3
9
81 36
The chloroalkyl-dendrimer and sodium azide (2 equiv. per
branch) were heated at 808C for 16 h in dry DMF. The sol-
vent was removed under vacuum, the crude product was dis-
solved in dichloromethane, washed twice with water, dried
with sodium sulphate, filtered under paper, and the solvent
was removed under vacuum. The dendrimer was precipitat-
ed using dichloromethane/methanol.
8
.69; found: C 54.16, H 8.54.
Synthesis of 3
The 81-azido-dendrimer 3 was synthesized from the 81-
chloromethylsilyl-dendrimer (0.100 g, 0.0050 mmol) using
the general procedure for azido-dendrimers. The product
[
11]
was obtained as a colorless waxy product; yield: 0.102 g
1
(
0.0049 mmol, 99%). H NMR (CDCl , 300 MHz): d=7.16
General Procedure for the “Click” Reactions
3
and 6.86 (double d, 144H, p-C H ), 3.53 (s, 72H, SiCH O),
6
4
2
The azido-dendrimer (1 equiv.) was dissolved in 10 mL of
tetrahydrofuran (THF), and 5mL of an aqueous solution of
sodium propargyl sulphonate (1.5equiv. per branch) was
2
(
0
.71 (d, 162H, CH N ), 1.62 (s, 234H, CH CH CH Si), 1.09
2 3 2 2 2
s, 234H, CH CH CH Si), 0.55 (s, 234H, CH CH CH Si),
2 2 2 2 2 2
.0062 [s, 216H, Si(CH ) CH O], 0.039 [s, 486H, Si-
A
T
U
G
3 2 2
1
3
added. CuSO was added (1 equiv. per branch, 1M aqueous
4
A
H
R
U
G
C NMR (CDCl3, 75.0 MHz): d=159.5
OC ), 139.0 (arom. C of the dendron), 127.4 and 113.9
arom. CH of the dendron), 60.6 (SiCH O), 43.4 (benzylic
Cq of the core and dendron), 41.4 (CH CH CH Si), 30.1
3
2
2
3
solution) at 08C, followed by dropwise addition of a freshly
prepared solution of sodium ascorbate (2 equiv. per branch,
(
(
Ar
q
2
1
M aqueous solution). Water was added, giving a 1:1 THF/
2
2
2
H O solution that was allowed to stir for 1 hour at room
2
(SiCH N ), 17.9 (CH CH CH Si), 15.6 (CH CH CH Si),
2 3 2 2 2 2 2 2
29
temperature. After removing THF under vacuum, the den-
drimers remained dissolved in the aqueous solution. The
dendrimers were purified by dialysis against 1 L of aqueous
ammonia solution for three days [in order to remove Cu(I)
that remains trapped inside the dendrimer] and against 1 L
of water for one day (the dialysis solutions were changed
twice a day). After removing water, the poly-1,2,3-sulpho-
nate dendrimers were obtained as colorless waxy products.
0
(
.0027 [Si
A
H
R
U
G
A
T
E
N
3
2
2
CDCl , 59.6 MHz): d=3.32 (SiCH N ), 0.51 (SiCH O); IR:
3
2
3
2
À1
n =2093 cm ; anal. calcd. for C963H1785O N243Si117: C 56.06,
H 8.72; found: C 55.31, H 8.62.
N3
36
Synthesis of 4
The 9-SO Na-dendrimer 4 was synthesized from 9-azido-
3
dendrimer 1 (0.100 g, 0.066 mmol) and sodium propargyl
sulphonate (0.126 g, 0.89 mmol) using the general procedure
Synthesis of 1
for “click” reactions. The product was obtained as a color-
1
The 9-azido-dendrimer 1 was synthesized from the 9-chloro-
less waxy product; yield: 0.133 g (72%). H NMR (D O,
2
[
11]
methylsilyl-dendrimer
general procedure for azido-dendrimers. The product 1 was
obtained as colorless waxy product; yield: 0.196 g
(0.190 g, 0.130 mmol) using the
300 MHz): d=7.83 (s, 9H, CH of triazole), 6.96 (s, 3H, CH
of arom. core), 4.19 (s, 18H, CH SO Na), 3.98 (s, 18H,
2
3
a
SiCH -triazole), 1.61 (s, 18H, CH CH CH Si), 1.07 (s, 18H,
2
2
2
2
1
(
0.129 mmol, 99%). H NMR (CDCl , 300 MHz): d=6.94 (s,
CH CH CH Si), 0.56 (s, 18H, CH CH CH Si), À0.013 [s,
13
ACHTREUNG
3
2
2
2
2
2
2
3
H, arom. CH), 2.72 (s, 18H, CH N ), 1.62 (s, 18H,
54H, Si(CH ) ]; C NMR (D O/MeOD, 75.0 MHz): d=
3 2 2
2
3
SiCH CH CH ), 1.07 (s, 18H, SiCH CH CH ), 0.58 (s, 18H,
145.5 (C of triazole), 127.9 (CH of arom. core), 122.1 (CH
2
2
2
2
2
1
2
q
3
SiCH CH CH ), 0.042 [Si
A
H
R
U
G
C NMR (CDCl3,
of triazole), 51.2 (CH SO Na), 43.9 (SiCH CH CH ), 41.9
2
2
2
3
2
2
3
2
2
2
75.0 MHz): d=145.7 (arom. C ), 121.5(arom. CH), 43.9
(benzylic Cq), 35.2 (SiCH -triazole), 22.1 (SiCH CH CH ),
q
2
2
2
2
(
SiCH CH CH ),
41.9
(Cq),
41.1
(CH N ),
17.7
17.3 (SiCH CH CH ), À4.0 [Si
A
T
E
N
2
2
2
2
3
2
2
2
(
SiCH CH CH ), 15.0 (SiCH CH CH ), À4.04 [Si
A
H
R
U
G
C H O S N Si Na : C 38.65, H 5.62; found: C 37.62, H
90 156 27 9 27 9 9
2
2
2
2
2
2
3
2
2
9
Si NMR (CDCl , 59.62 MHz): d=3.33 (Si
A
H
R
U
G
5.41. Polydispersity index obtained by SEC: 1.00.
3
À1
3
2
2
3
IR: n =2093 cm ; anal. calcd. for C H N Si : C 49.86, H
N3
63 129 27
9
8.57; found: C 49.31, H 8.30.
Synthesis of 5
The 27-SO Na-dendrimer 5 was synthesized from the 27-
3
Synthesis of 2
azido-dendrimer 2 (0.070 g, 0.011 mmol) and sodium prop-
argyl sulphonate (0.064 g, 0.45mmol) using the general pro-
cedure for “click” reactions. The product was obtained as a
The 27-azido-dendrimer 2 was synthesized from the 27-
chloromethylsilyl-dendrimer (0.100 g, 0.0163 mmol) using
the general procedure for azido dendrimers. The product
[11]
1
colorless waxy product; yield: 0.075g (66%). H NMR
was obtained as a colorless waxy product; yield: 0.101 g
(D O/MeOD, 300 MHz): d=7.82 (s, CH of triazole), 7.12
2
1
(
0.0161 mmol, 99%). H NMR (CDCl , 300 MHz): d=7.16
and 6.76 (s, arom. CH of dendron), 4.19 (s, CH SO Na), 3.94
3
2
3
and 6.89 (double d, 36H, p. C H of dendron), 3.53 (s, 18H,
(s, SiCH -triazole), 3.59 (s, SiCH O), 1.52 (s, CH CH CH Si),
6
4
2 2 2 2 2
SiCH O), 2.71 (d, 54H, CH N ), 1.62 (s, 72H,
1.02 (s, CH CH CH Si), 0.49 (s, CH CH CH Si), À0.074 [s,
2
2
3
2
3
2
2
2
2
2
1
CH CH CH Si), 1.09 (s, 72H, CH CH CH Si), 0.55 (s, 72H,
Si
A
H
E
N
(CH ) ]; C NMR (D O/MeOD, 75.0 MHz): d=145.5 (C
2
2
2
2
2
2
3
2
2
q
CH CH CH Si), 0.0061 [s, 54H, Si
A
H
R
U
G
of triazole), 128.2 and 114.6 (arom. CH of the dendron),
2
2
2
3
2
2
Adv. Synth. Catal. 2008, 350, 837 – 845ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
843

Cµtia Ornelas et al.
FULL PAPERS
1
4
22.1 (CH of triazole), 60.3 (SiCH O), 50.5 (CH SO Na), Acknowledgements
2
2
3
3.9 (SiCH CH CH ), 41.9 (benzylic Cq), 34.2 (SiCH -tria-
2
2
2
2
zole), 21.1 (SiCH CH CH ), 17.3 (SiCH CH CH ), À4.0 [Si-
We are grateful to Fundażo para a CiÞncia e a Tecnologia
(FCT), Portugal (Ph.D. grant to CO), the Institut Universi-
taire de France (IUF, DA), the CNRS and the UniversitØ Bor-
deaux I for financial support.
2
2
2
2
2
2
A
C
H
T
R
E
U
N
G
(CH ) ]. Polydispersity index obtained by SEC: 1.01.
3 2
Synthesis of 6
The 81-SO Na-dendrimer 6 was synthesized from the 81-
3
azido-dendrimer 3 (0.050 g, 0.0024 mmol) and sodium prop-
argyl sulphonate (0.042 g, 0.29 mmol) using the general pro-
cedure for “click” reactions. The product was obtained as a
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colorless waxy product; yield: 0.041 g (53%). H NMR
(
D O/MeOD, 300 MHz): d=7.89 (s, CH of triazole), 7.09
2
and 6.83 (s, arom. CH of dendron), 4.10 (s, CH SO Na), 3.94
2
3
(
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C
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T
R
E
U
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2
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C
H
T
R
E
U
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[
General Procedure for the Preparation of the PdNPꢀs
The procedure is described using the preparation of DSN-
À4
G as an example: 1 mL of a 3.6”10 M water solution of
0
À4
dendrimer 4-G (1.0 mg, 3.6”10 mmol) was introduced in
0
À3
a Schlenk flask. 1.1 mL of a 2.9”10 M water solution of
À3
K PdCl (1.1 mg, 3.2”10 mmol, 1 equiv per triazole) was
added. Water was added, providing a 8.82”10 M (in Pd)
2
4
À4
solution that was stirred for 5min, then NaBH (1 mg, 3.2”
4
À2
10
mmol, 10 equiv. per Pd) was added, and the light yellow
solution turned to black indicating the nanoparticle forma-
tion.
Hydrogenation Reactions
The nanoparticles were freshly prepared in a Schlenk flask
À4
in an aqueous solution (8.82”10
M
in Pd), and
10,000 equiv. of the substrate was added. The Schlenk flask
was filled with H (1 atm), and the solution was allowed to
2
stir at 258C. For re-use of the catalyst, the substrate was
added to the reaction solution until the catalyst was no
longer active. Calculation of the turnover frequency (TOF)
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were extracted at different reaction times and analyzed. Cal-
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using the sum of substrate that reacted in all the catalytic
cycles, after analyzing the final reaction solution.
2
007.
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3
4
nylboronic acid and iodobenzene or bromobenzene were
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2
zene.
844
asc.wiley-vch.de
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2008, 350, 837 – 845

Sulphonated “Click” Dendrimer-Stabilized Palladium Nanoparticles
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