Water-soluble metal nanoparticles with PEG-tagged 15-membered azamacrocycles as stabilizers

Article abstract of DOI:10.1039/b907705g

The synthesis of palladium, platinum and ruthenium nanoparticles stabilized by azamacrocycles bearing polyoxyethylenated chains has been achieved by decomposition of the corresponding organometallic precursors (Pd(dba) ₂, Pt₂(dba)₃ and Ru(COD)(COT)) under dihydrogen atmosphere, whereas gold and rhodium nanoparticles have been obtained in the presence of these ligands by reduction of HAuCl₄ and RhCl ₃, respectively. The metal nanoparticles were characterized by several techniques including IR, NMR, UV-vis, HRTEM, ED, and elemental analysis. The Pd nanoparticles have been used as recoverable catalyst in Suzuki cross-coupling in aqueous medium.

Full text of DOI:10.1039/b907705g

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www.rsc.org/dalton | Dalton Transactions
Water-soluble metal nanoparticles with PEG-tagged 15-membered
azamacrocycles as stabilizers†
Nereida Mej ´ı as, Anna Serra-Muns, Roser Pleixats,* Alexandr Shafir and Mar Tristany
Received 16th April 2009, Accepted 7th July 2009
First published as an Advance Article on the web 30th July 2009
DOI: 10.1039/b907705g
The synthesis of palladium, platinum and ruthenium nanoparticles stabilized by azamacrocycles
bearing polyoxyethylenated chains has been achieved by decomposition of the corresponding
organometallic precursors (Pd(dba)
whereas gold and rhodium nanoparticles have been obtained in the presence of these ligands by
reduction of HAuCl and RhCl , respectively. The metal nanoparticles were characterized by several
2
, Pt
2
(dba) and Ru(COD)(COT)) under dihydrogen atmosphere,
3
4
3
techniques including IR, NMR, UV-vis, HRTEM, ED, and elemental analysis. The Pd nanoparticles
have been used as recoverable catalyst in Suzuki cross-coupling in aqueous medium.
Introduction
Some years ago we reported that 15-membered triolefinic
macrocyles exemplified by compound 1 (Fig. 1) form stable
palladium(0) complexes such as 2, with the metal center co-
In the last decade, metal nanoparticles have attracted a great deal
of attention due to the particular physical and chemical properties
imparted by their size. They have found application in areas
as diverse as physics (optics, magnetism), chemistry (chemical
4
ordinated by the three olefinic double bonds. However, it was
discovered later on that metal nanoparticles are formed instead of
discrete complexes if polyoxyethylenated chains are incorporated
into the structure of the macrocycle. Thus, treatment of the
1
sensors, catalysis) as well as biology and medicine. The presence of
a stabilizing agent is required to prevent the facile agglomeration
of the particles and the formation of bulk metal. Furthermore,
the nature of the stabilizing shell also controls the solubility of the
nanoclusters in different media. Several kinds of stabilization have
triolefinic ligand 3 (Fig. 1) with Pd(dba) as palladium source,
2
following our standard methodology for complex formation, gave
5
rise to the nanoparticulate material. It was also found that
the triolefinic core was not essential for nanoparticle formation,
as polyoxyethylenated compound 4, devoid of the coordinating
1f ,l
been suggested, based on the protecting agents used: (i) steric
large adsorbed molecules); (ii) electrostatic (surface adsorbed
ions); (iii) electrosteric (ionic surfactants). Coordinating ligands
phosphines and other phosphorus based derivatives, thiols, sul-
(
olefins, was also able to produce palladium(0) nanoparticles by
5
reaction with Pd(dba)
2
, albeit with low metal content in the
(
resulting material. The procedure employed for the formation of
nanoparticles differed from those mentioned previously, and con-
fides, amines, alcohols, . . .) have been frequently employed and can
also be considered as electrosteric-type stabilizers, as in addition
to their coordination ability to the metal surface, they provide
some steric hindrance around the particles, particularly when they
bear long alkyl chains. Polymers stabilize metal nanoparticle not
only because of the steric bulk of their framework, but also by
weak binding to the nanoparticle surface by the heteroatoms
present in them. An entrapment mechanism is also envisioned for
dendrimers, block copolymers and cyclodextrins. Several methods
sisted of the ligand interchange between Pd(dba) , and triolefinic
2
macrocycle 3.
2
are available for the preparation of nanoparticles, the most
common being the chemical reduction of a metal salt with an
appropriate reducing agent in the presence of a stabilizer. The
reduction and subsequent displacement of a ligand from a zero-
3
valent organometallic precursor (organometallic approach ) in
the presence of the stabilizer constitutes a good alternative ap-
proach, providing well-controlled nanoparticles with tunable size,
morphology and surface state. Other methods include thermal,
sonochemical or photochemical decomposition, chemical vapor
deposition, and electrochemical reduction.
Department of Chemistry, Universitat Aut o` noma de Barcelona, Cerdanyola
del Vall e` s, 08193, Barcelona, Spain. E-mail: roser.pleixats@uab.cat;
Fax: +34 93 581 12 65
†
Electronic supplementary information (ESI) available: HR-TEM images,
particle size distribution diagrams and electron diffractograms for all
materials. See DOI: 10.1039/b907705g
Fig. 1 Structures of macrocycles and Pd(0) complexes 1–4.
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Poly(ethylene oxide) units are present in some block copolymers
and in some surfactants which have been used as stabilizers of
discrete palladium complexes for 1 or metallic palladium for MeO-
PEG-OH (Scheme 1).
6
7
metal nanoparticles (Au, Pd, Pt). PEG-modified dendrimers
8
and PEG derivatives immobilized on silica have also been
described as stabilizers for gold and palladium nanoparticles,
respectively. Although preparation or in situ generation of metal
nanoparticles (Au, Pd, Pt, Fe, Ag, Co) dispersed in unfunc-
tionalized poly(ethylene glycols) of different average molecular
weights (with or without the addition of other protecting agents)
Scheme 1 Effect of the stabilizer structure on the outcome of hydrogena-
tion of Pd(dba)2.
9
10
11
have been reported, the incorporation of thiol or amino
Thus, the synthesis of metal nanoparticles (Pd, Pt, Ru) using
the organometallic approach was achieved through the room-
functional groups in the PEG matrix tends to impart improved
stabilizing capacity to the polymers used for the synthesis of gold
nanoparticles. In particular, the amino group was found essential
to avoid the formation of metal conglomerates when gold vapor
temperature hydrogenation (H , 3 bar) of the THF solution of the
2
14
15
corresponding organometallic precursors Pd(dba)
2
,
Pt
2
(dba)
3
16
or Ru(COD)(COT) in the presence of the stabilizers (L)
11a
11b
deposition or salt reduction methods were employed. The
attempted preparation of PEG-stabilized ruthenium nanoparticles
(
Scheme 2, Table 1) (COD = 1,5-cyclooctadiene, COT = 1,3,5-
cyclooctatriene).
12
by reduction of RuCl failed. A few reports are available on PEG-
3
13
tagged compounds such as bipyridines, bisphenol A derivatives,
phosphine oxides, Fischer carbenes and oxime carbapalladacycles
as capping agents or metal sources for palladium and gold clusters.
The presence of polyoxyethylenated chains results in water
solubility of the ligands and the metal nanoparticles derived
from them. Solubility in aqueous medium may be advantageous
for potential applications of metal nanoparticles in catalysis or
Scheme 2 Synthesis of Pd, Pt and Ru nanoparticles by decomposition of
organometallic precursors under dihydrogen atmosphere.
5
biomedicine. Encouraged by our previous results we decided
In the case of the palladium and platinum precursors, the
homogeneous black suspensions obtained overnight were filtered
through Celite or through a Milli-Pore filter to eliminate residual
bulk metal and the solvent was evaporated. To purify the crude
mixtures we took advantage of the fact that, like the parent
polyoxyethylenated stabilizer, the newly formed nanoparticulated
materials are soluble in water, tetrahydrofuran, dichloromethane
and ethyl acetate and are insoluble in diethyl ether. Thus, the result-
ing black solid residues were washed with diethyl ether to eliminate
the reduction product of dibenzylideneacetone, and the remaining
insoluble materials were examined by high resolution transmission
electron microscopy (HR-TEM). Alternatively, the isolation and
purification of the nanoparticulated Pd and Pt materials were
performed as indicated in the two following procedures: (a) the
solid residues obtained after evaporation of the filtered THF
solution were taken in water and filtered to eliminate the reduction
derivative of the dibenzylideneacetone; the water from the filtrate
was evaporated and the residues taken in dichloromethane, dried
5
5
to expand the scope of the PEG-tagged macrocyles 3 and 4
as stabilizers for water-soluble metal nanoparticles following
the standard methods of synthesis. We report hereafter the
preparation of palladium, platinum and ruthenium nanoparticles
following the organometallic approach and the formation of
gold and rhodium nanoparticles by the metal salt reduction
3
procedure. To our knowledge, the organometallic synthesis has
not been previously applied to the preparation of water-soluble
nanoparticles with PEG-derived compounds as protecting agents.
Results and discussion
As was the case for the ligand exchange method mentioned above,
in the organometallic approach the combination of both the
macrocyclic core and the polyoxyethylenated chains within the
structure were necessary to induce the formation of palladium
nanoparticles, with individual components leading either to
Table 1 Preparation of Pd, Pt and Ru nanoparticles stabilized by polyoxyethylenated compounds L by decomposition of a zero-valent organometallic
a
precursor under H
2
atmosphere (3 bar)
b
c
Entry
Metal precursor
Initial mol ratio L : metal
f/ nm
Atoms per particle
% Metal (by ICP)
2
1
2
3
4
5
6
7
8
Pd(dba)
Pd(dba)
Pd(dba)
Pd(dba)
Pd(dba)
2
2
2
2
2
4 : Pd = 0.6 : 1
4 : Pd = 1.1 : 1
4 : Pd = 2.5 : 1
3 : Pd = 1.0 : 1
2.9 ± 0.6
4.8 ± 0.6
2.9 ± 0.6
3.2 ± 0.5
8.6 ¥ 10
0.98
0.25
0.27
1.44
—
3.64
0.845
2.82
d
3
3.9 ¥ 10
2
8.6 ¥ 10
3
e
1.2 ¥ 10
f
g
5 : Pd = 2.0 : 1
—
—
2
Pt
Pt
2
(dba)
(dba)
3
3
4 : Pt = 0.5 : 1
4 : Pt = 2.0 : 1
4 : Ru = 0.25 : 1
2.9 ± 0.6
2.2 ± 0.3
11 ± 3
8.4 ¥ 10
2
2
3.7 ¥ 10
4
Ru(COD)(COT)
5.2 ¥ 10
2
1
.6 ± 0.3
1.6 ¥ 10
3
9
Ru(COD)(COT)
3 : Ru = 0.25 : 1
1.9 ± 0.4
2.2 ¥ 10
3.03
a
b
c
d
In THF at room temperature overnight, [Metal] = 1.5–6.0 mM Mean diameter determined by TEM. Determined as (Vnano/Vatom) ¥ 0.74. Smaller
e
nanoparticles (< 1 nm) have not been taken into account. The protecting shell was constituted by 4 formed from 3 under hydrogenation conditions.
f
g
MeO-PEG-OH 2000. Bulk Pd.
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with anhydrous sodium sulfate and the solvent evaporated; (b)
the solid residues obtained after evaporation of the filtered THF
solution were dissolved in ethyl acetate and diethyl ether was added
to precipitate the nanoparticles. In the case of the ruthenium
nanoparticles the work-up procedure involved concentration of
the THF suspension to one-third of its volume and subsequent
addition of degassed anhydrous diethyl ether to precipitate the
nanoparticles as a black solid, which was filtered off and washed
with diethyl ether under argon atmosphere. IR in solid state (ATR)
1
and H NMR analysis in solution of all the samples showed the
presence of the stabilizer in the protecting shield. No significant
differences were found between the spectra of the free stabilizers
and those of the nanoparticles formed from them. We have
assumed a mechanism of stabilization based on entrapment of the
metal nanoparticles within the solid framework of the mentioned
Fig. 3 Electron diffraction pattern for 4-Pd (Table 1, entry 1).
5
5
compounds. In our previous report we had performed powder
X-ray diffraction of polyoxyethylenated triolefinic macrocycle 3
and of the Pd nanoparticles derived from it. Compound 3 exhibited
diffraction peaks indicating a long-range ordered structure and
the same crystalline phases of this polyoxyethylenated compound
existed in the related Pd nanoparticles. These ordered structures
should be at the origin of the ability of the compounds to act as
stabilizers.
Three different molar ratios L : Pd were tested with ligand
4
(entries 1–3, Table 1). A ratio of 4 : Pd of 0.6 : 1 (entry 1)
gave more agglomerated nanoparticulated material than ratios
: Pd of 1.1 : 1 and 2.5 : 1 (entries 2 and 3). For entry 2, two
4
distributions of nanoparticles were observed, one with an average
size of 4.8 and another one of very small nanoparticles (< 1 nm) the
diameter of which could not be measured (Fig. 2). An experiment
with triolefinic ligand 3 was also performed (Table 1, entry 4).
The protecting shell of the resulting nanoparticles (mean diameter
of 3.2 nm) was formed by the saturated macrocycle 4 formed
under hydrogenation conditions. When the monomethyl ether of
polyethylenglycol-2000 (MeO-PEG-OH), 5, was tested as ligand
Fig. 4 (a) HR-TEM image and particle size distribution diagram; (b)
electron diffraction pattern for 4-Pt (Table 1, entry 7).
Treatment of Ru(COD)(COT) under the conditions of Scheme 2
in the presence of macrocycle 4 in a molar ratio 4 : Ru of 0.25 :
1 yielded very well separated nanoparticles of two different size
distributions centered at 11 and 1.6 nm, respectively, as observed
by HRTEM (Table 1, entry 8 and Fig. 5).
(
Table 1, entry 5), bulk metal precipitated and nanoparticles were
not observed. Electron diffraction (ED) confirmed the presence of
face centered cubic (fcc) palladium(0) in all the samples (Fig. 3).
Although the preparation of this material was performed under
an inert atmosphere, the electron diffraction pattern suggests
the presence of a mixture of Ru metal and Ru oxide. Similarly,
hydrogenation of Ru(COD)(COT) in the presence of triolefinic
macrocycle 3 led to the formation of nanoparticles (entry 9,
Table 1) with the electron diffraction pattern characteristic of Ru
oxide. Although the source of oxygen is currently under investiga-
tion, the oxidation likely takes place during the preparation of the
sample for the TEM analysis. Noteworthy is that unlike entry 4,
1
the H NMR analysis of the material in entry 9 reveals the presence
of the stabilizer 3 in its non-hydrogenated olefinic form.
Next, we undertook the preparation of gold and rhodium
nanoparticles by the metal salt reduction method (Scheme 3). Gold
nanoparticles were generated by treatment of tetrachloroauric
Fig. 2 HR-TEM image and particle size distribution diagram for 4-Pd
(
Table 1, entry 2).
Platinum nanoparticles of similar size (2.3–2.9 nm) were ob-
tained with two different 4 : Pt ratios of 0.5 : 1 and 2.0 : 1 (entries
and 7 of Table 1) which showed some aggregation (Fig. 4(a)).
6
Electron diffraction (ED) confirmed the presence of face centered
cubic (fcc) platinum(0) (Fig. 4(b)).
Scheme 3 Preparation of gold and rhodium nanoparticles.
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750 | Dalton Trans., 2009, 7748–7755

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a
Table 2 Preparation of Au nanoparticles stabilized by polyoxyethylenated compounds L by reduction of HAuCl
4
·3H
2
O in alkaline methanol
b
c
Entry
L
Initial mol ratio Au : L : NaOH
f /nm
UV-Vis/nm
Atoms per particle
% Metal (by ICP)
d
4
1
2
3
4
3
4
6
3
2 : 1 : 8
9.5 ± 2.3
2.3 ± 0.5
22.5 ± 8.2
6.0 ± 2
—
—
553
—
2.7 ¥ 10
0.18
0.05
1.6
2
2.1 : 1 : 8.3
2 : 1 : 8.2 f
2 : 1.4 : 28
3.8 ¥ 10
e
3
3.5 ¥ 10
3
7.0 ¥ 10
0.143
a
b
c
d
At room temp. in MeOH in the dark, [Au] initial = 5.4–13.0 mM. Mean diameter determined by TEM. Determined as (Vnano/Vatom) ¥ 0.74. A small
e
f
amount of larger nanocluster was also observed.
2
H N-PEG-OH 3000. Using a 0.75 M solution of NaOH in methanol.
UV-visible absorption spectrum of the material of entry 3 of
Table 2 exhibited a broad band with a maximum at 553 nm due
to the surface plasmon resonance of gold. Electron diffraction of
the samples showed gold to be in face centered cube (fcc) form
(
Fig. 6). IR and NMR spectra of the materials confirmed the
presence of the ligands in the stabilizing shields. No improvement
could be achieved by the use of other reducing agents such as
13b
18
NaBH
4
and triethylamine. Nanoparticles were not observed
by HR-TEM in the former case, the reduction process was too
fast and bulk metal was obtained, while poor reproducibility was
found in the latter case.
Fig. 5 HR-TEM image and particle size distribution diagrams for 4-Ru
Table 1, entry 8).
(
17
acid with alkaline methanol in the presence of the stabilizers
, 4 and commercial O-(2-aminoethyl)polyethylene glycol 3000
N-PEG-OH), 6 (Table 2). All the reactions were performed
3
(
H
2
in methanol as solvent at room temperature under stirring in
the dark. After slow addition (in six portions over a period of
3
0 min) of a solution of NaOH in methanol (0.108 M), the
mixtures were left for 7 h, filtered through a Milli-Pore filter
and the solvent was evaporated. The solid residue was taken in
dichloromethane, washed with water, dried and evaporated. The
residue was dissolved in THF and diethyl ether was added to
precipitate the nanoparticles. In all cases, a molar ratio Au : L of
Fig. 6 (a) HR-TEM image and particle size distribution diagram;
(
b) electron diffraction pattern for 3-Au (Table 2, entry 1).
2
: 1 and a stoichiometric amount of NaOH were used (entries 1–3,
Table 2). With the macrocycle 3, nanoparticles with an average
diameter of 9.5 nm were observed by TEM along with a small
amount of larger nanoclusters. The metal content in the material
determined by ICP was lower than expected (entry 1). This can
be attributed to some bulk metal formation. Ligand 4, on the
other hand, gave small monodispersed nanoparticles of 2.3 nm
albeit with a lower percentage of metal (entry 2). The presence
of the coordinating amino group in 6 resulted in the formation
of a nanoparticulated material with a higher percentage of gold,
but, unexpectedly, the mean size of the particles increased and the
monodispersion decreased (22.5 ± 8.2 nm (entry 3). An experiment
performed with the stabilizer 3 and a great excess of NaOH of
higher concentration (0.75 M) favoured the monodispersion and
the formation of smaller nanoparticles (entry 4, Table 2). The
Preparation of Rh nanoparticles was achieved by reduction
of rhodium trichloride with an excess of sodium borohydride
19
in a degassed aqueous solution which contained the stabilizer
(3, 4 and 6) (Scheme 3, Table 3). The residue obtained after
water evaporation was taken in THF, filtered through a Milli-Pore
filter and the filtrate evaporated. The resulting solid was taken
in dichloromethane, washed with water, dried and the solvent
evaporated to give the materials as black solids. Two molar ratios
Rh : 3 of 2.2 : 1 and 5 : 1 were tested (entries 1 and 2 in Table 3). Not
a very significant difference in the size of nanoparticles (2.6 and
2.2) was observed by varying these ratios, although the percentage
of metal in the nanoparticulate material was higher in the later
case. HR-TEM images showed that these small nanoparticles form
cauliflower-shaped aggregates of irregular size (Fig. 7(a)). Similar
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a
Table 3 Preparation of Rh nanoparticles stabilized by polyoxyethylenated compounds L by reduction of RhCl
3
·3H
2
O with NaBH
4
b
c
Entry
L
Initial mol ratio Rh : L : NaBH
4
[Rh]/mM
[L]/mM
f /nm
Atoms per particle
% Metal (by ICP)
2
1
2
3
4
5
6
3
3
4
4
4
2.2 : 1 : 6.3
5 : 1 : 15
1 : 1 : 6.7
2 : 1 : 13.4
10 : 1 : 24.3
2 : 1 : 9.9
0.33
1.5
0.31
0.6
2.3
0.71
0.15
0.30
0.30
0.30
0.23
0.34
2.6 ± 0.6
2.2 ± 0.4
2.2 ± 0.5
2.4 ± 0.5
2.4 ± 0.5
2.5 ± 0.6
6.6 ¥ 10
0.12
1.9
0.26
0.07
0.96
0.18
2
4.0 ¥ 10
2
4.0 ¥ 10
2
5.2 ¥ 10
2
5.2 ¥ 10
d
2
6
5.9 ¥ 10
a
b
c
d
At room temp. in degassed H
000.
2
O overnight under Ar. Mean diameter determined from TEM. Determined as (Vnano/Vatom) ¥ 0.74.
H
2
N-PEG-OH
3
Scheme 4 Suzuki–Miyaura coupling using 4-Pd.
although somewhat lower isolated yields were obtained for the
same reaction time in the subsequent runs.
Conclusions
In summary, this contribution describes the synthesis and charac-
terization (IR, NMR, UV-Vis, HR-TEM, ED, elemental anal-
yses) of Pd, Pt, Ru, Au and Rh nanoparticles stabilized by
polyoxyethylenated macrocycles 3 and 4 and the amine H N-
2
PEG-OH, 6. The preparation of Pd, Pt and Ru nanoparticles
has been performed by decomposition of the corresponding
zero-valent organometallic precursors (Pd(dba)
2
, Pt
2
(dba) and
3
Ru(COD)(COT)) under dihydrogen atmosphere in THF at room
temperature. The formation of Au and Rh nanoparticles in
the presence of these ligands has been achieved by reduction
Fig. 7 (a) HR-TEM image and particle size distribution diagram; (b)
electron diffraction pattern for 4-Rh (Table 3, entry 5).
of HAuCl
4
with alkaline methanol and of RhCl with sodium
3
results were obtained with stabilizer 4 with three different Rh :
borohydride, respectively. The versatility of PEG-tagged macro-
cycles 3 and 4 as stabilizers for the formation of water-soluble
nanoparticles of several metals using two different synthetic
approaches have been demonstrated. Both the macrocyclic and
PEG moieties are required for the nanoparticle formation. The
solubility of the nanoparticulated materials in aqueous medium
offers some advantages for their potential applications in the fields
of catalysis or biomedicine. In this sense, palladium nanoparticles
are efficient recoverable catalysts for the Suzuki reaction in
aqueous medium.
4
molar ratios (1 : 1, 2 : 1 and 10 : 1) (entries 3–5 of Table 3).
In this case, however, the increase in the initial metal : stabilizer
ratio did not result in a notable increase of metal content in the
final materials. This fact suggests that this ligand leads to higher
losses in the form of bulk metal. Polyoxyethylenated amine 6 in
a molar ratio Rh : 6 of 2 : 1 gave similar results to macrocycle 3
in terms of percentage of metal (compare entry 6 with entry 1 in
Table 3), indicating that the presence of coordinating amino group
offers no clear advantage. In all cases face-centered cubic (fcc) Rh
nanoparticles were obtained as determined by electron diffraction
(
ED) (Fig. 7(b)). IR and NMR spectra of the materials showed
Experimental
the presence of the ligands in the surrounding shell.
An important aspect of employing PEG-tagged stabilizer is the
potential for increased water solubility of the resulting nanomate-
rial. To test this concept, Pd nanoparticles corresponding to entry
General procedures and reagents
5
Compounds 3 and 4 were reported previously. PEG derivatives
1
4
15
1
in Table 1 were tested as a catalyst for the Suzuki–Miyaura
5 and 6 were purchased from Fluka. Pd(dba)
2
,
Pt
2
(dba)
3
and
16
coupling of iodobenzene with p-methoxybenzeneboronic acid in
Ru(COD)(COT) were synthesized as described in the literature
and the amounts of Pd, Pt and Ru were determined by elemental
water (Scheme 4). Thus, the use of 0.25 mol% Pd led, after 4 h at
◦
1
00 C to a 98% isolated yield of the desired p-methoxybiphenyl.
analyses. HAuCl
4
·3H
2
O and RhCl
3
·3H
2
O were purchased from
TEM analysis of the catalyst after the first run showed the presence
of nanoparticles with the average diameter of 5.6 nm, which is
somewhat larger than the size of the nanoparticles in the original
material. The catalyst was reused for a total of three cycles,
Aldrich. The synthesis of organometallic precursors was carried
out using standard Schlenk line and glovebox techniques. The
preparation of Pd, Pt and Ru nanoparticles was carried out
in a Fischer–Porter glassware. Water Milli-Q was used for the
7
752 | Dalton Trans., 2009, 7748–7755
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preparation and purification of metal nanoparticles. THF has
been dried over Na-benzophenone and distilled before use in the
organometallic approach for metal nanoparticles.
cycles. Ru(COD)(COT) (23.7 mg, 0.075 mmol) was introduced
in a Schlenk under nitrogen atmosphere in a glove-box and
anhydrous deoxygenated THF (20 mL) was added. This solution
was transferred under argon to the Fischer–Porter flask. The
bottle was filled with hydrogen (3 atm) and the mixture was
stirred at room temperature for 15 h. A black homogeneous
suspension was formed. The hydrogen was evacuated and the
solution was transferred under argon to a Schlenk flask and
the solvent was partially evaporated to one third of its volume.
Anhydrous and deoxygenated diethyl ether (30 mL) was added
resulting in the precipitation of a black solid, which was filtered
IR spectra were determined by the Attenuated Total Reflectance
(
ATR) mode. HR-TEM analyses were performed in the Servei de
Microsc o` pia of the Universitat Aut o` noma de Barcelona in a JEOL
˚
JEM-2010 model at 200 kV with a resolution point of 2.5 A. A drop
of the colloidal suspension of the nanoparticulated material in
THF was placed on a copper grid covered by a specially produced
structureless carbon support film having a thickness of 4–6 nm,
and it was dried before observation. The size distributions were
determined through a manual analysis of enlarged micrographs
by measuring a high number of particles on a given grid to obtain
a statistical size distribution and a mean diameter (Gatan Digital
Micrograph Program).
off, washed with diethyl ether (2 ¥ 20 mL) and dried in vacuo
1
(128 mg, 48% with respect to initial ruthenium); IR and
H
NMR spectra were coincident with those of ligand 4. Found:
C, 49.03 and 49.08; H, 7.85 and 7.91; N, 0.75 and 0.68; Ru,
2
.82% (ICP).
Synthesis of Pd nanoparticles by the organometallic approach
(
entry 4 of Table 1).
Synthesis of Au nanoparticles by the reduction method (entry 1 of
Table 2).
Ligand 3 (101 mg, 0.015 mmol) and Pd(dba)
2
(15.5% wt of Pd by
ICP) (10.2 mg, 0.015 mmol of Pd) were introduced in a Fischer–
Porter flask and the system was degassed by three pump–refill
cycles. Anhydrous and deoxygenated THF (10 mL) was added.
The flask was filled with hydrogen (3 atm) and the mixture was
allowed to stir at room temperature for 18 h. A black homogeneous
suspension was formed. The hydrogen was evacuated and the
solution was filtered through a Milli-Pore filter. The solvent from
the filtrate was evaporated and the resulting black solid residue was
washed with diethyl ether and dried to afford the nanoparticulate
material (70 mg, 68% yield with respect to initial palladium). IR
To a stirred mixture of 3 (100 mg, 0.015 mmol), hydrogen tetra-
chloroaurate(III) trihydrate (11.7 mg, 0.030 mmol) and methanol
(
5 mL) kept in the dark, a solution of sodium hydroxide (0.108 M in
MeOH, 1.12 mL, 0.121 mmol) was slowly added (in six portions
during 30 min). The mixture was stirred for 7 h at room tem-
perature, then filtered through a Milli-Pore filter and the solvent
was evaporated. The residue was taken in dichloromethane and
washed with water. The organic phase was dried with anhydrous
sodium sulfate and evaporated. The solid residue was dissolved
in THF and upon addition of diethyl ether the nanoparticulate
material precipitated as a purple solid (84.2 mg, 2.6% yield with
-
1
1
(
ATR, neat) n: 2879, 1594, 1466, 1341, 1103 cm . H NMR
CDCl , 250 MHz): d 1.60 (apparent s, 12H), 3.0 (apparent s,
2H), 3.40 (s, 9H), 3.55–3.73 (m, 383 H), 3.80–3.92 (m, 12H), 4.19
m, 6H), 7.00 (d, J = 9.0 Hz, 6H), 7.70 (d, J = 9.0 Hz, 6H) ppm.
Found: C, 52.22 and 52.39; H, 8.42 and 8.52; N, 0.47 and 0.48; Pd,
.44% (ICP).
(
3
1
respect to initial gold); IR and H NMR spectra were coincident
1
(
with those of ligand 3. Found: C, 55.23, 56.08 and 55.10; H,
9
0
.54, 9.94 and 9.33; N, 0.67 and 0.68; S, 1.61, 1.34 and 1.23; Au,
.18% (ICP).
1
Synthesis of Pt nanoparticles by the organometallic approach
entry 6 of Table 1).
Synthesis of Rh nanoparticles by the reduction method (entry 4 of
Table 3).
(
Ligand 4 (160 mg, 0.024 mmol) and Pt
2
(dba) (25.3% wt of Pt by
3
Ligand 4 (100 mg, 0.015 mmol) and sodium borohydride (7.7 mg,
ICP) (37 mg, 0.048 mmol of Pt) were introduced in a Fischer–
Porter flask and the system was degassed by three pump–refill
cycles. Anhydrous and deoxygenated THF was added (8 mL). The
bottle was filled with hydrogen (3 atm) and the mixture was stirred
at room temperature for 18 h. A black homogeneous suspension
was formed. The hydrogen was evacuated and the solution was
filtered through a Milli-Pore filter. The solvent from the filtrate
was evaporated, the solid residue was dissolved in the minimal
amount of ethyl acetate and diethyl ether was added to precipitate
the nanoparticulate material as a grey solid (133 mg, 52% yield
0
.20 mmol) were introduced in a Schlenk flask, the system
was degassed by three pump–refill cycles and degassed Milli-Q
water was added (45 mL). In a second Schlenk was introduced
rhodium trichloride trihydrate (8.1 mg, 0.030 mmol), the system
was degassed with three pump–refill cycles and degassed Milli-
Q water was added (5 mL). The ligand solution was added
under argon to the RhCl solution at room temperature leading
3
to a color change from red to black. The mixture was stirred
at room temperature under argon for 15 h. The solvent was
evaporated; the residue was taken in THF and filtered through
a Milli-Pore filter. The solvent from filtrate was evaporated, the
residue was dissolved in dichloromethane, washed with water,
dried with anhydrous sodium sulfate and the solvent evaporated,
1
with respect to initial platinum); IR and H NMR spectra were
coincident with those of ligand 4. Found: C, 50.35 and 50.12; H,
8
.53 and 8.47; N, 0.69 and 0.69; S, 0.79 and 0.98; Pt, 3.64% (ICP).
to give the nanoparticulate material as a black solid (93 mg,
Synthesis of Ru nanoparticles by the organometallic approach
entry 8 of Table 1).
1
2
.3% yield with respect to initial rhodium); IR and H NMR
(
spectra were coincident with those of ligand 4. Found: C, 54.41
and 54.82; H, 9.35 and 9.58; N, 0.65 and 0.68; S, 0.33 and 0.27; Rh,
0.07% (ICP).
Ligand 4 (125 mg, 0.019 mmol) was introduced in a Fischer–
Porter bottle and the system was degassed by three pump–refill
This journal is © The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7748–7755 | 7753

View Article Online
Suzuki–Miyaura coupling of iodobenzene with
p-methoxyphenylboronic acid (Scheme 4).
Chem., 2005, 9, 173–204; (j) D. Astruc, F. Lu and J. R. Aranzaes, Angew.
Chem., Int. Ed., 2005, 44, 7852–7872; (k) A. Roucoux, K. Philippot,
in Handbook of Homogeneous Hydrogenations, ed. J. G. de Vries and
C. J. Elsevier, Wiley-VCH, Weinheim, 2007, vol. 9, pp. 217–255; (l) L.
Starkey Ott and R. G. Finke, Coord. Chem. Rev., 2007, 251, 1075–
A screw-top sealable tube was charged with a magnetic stirbar,
iodobenzene (61 mg, 0.3 mmol), p-methoxyphenylboronic acid
1
100; (m) P. K. Jain, X. Huang, I. H. El-Sayed and M. A. El-Sayed,
(
70 mg, 0.45 mmol, 1.5 equiv), K
2
CO
3
(105 mg, 0.75 mmol,
Acc. Chem. Res., 2008, 41, 1578–1586.
2
3
See ref. 1 and B. L. Cushing, V. L. Kolesnichenko and C. J. O’Connor,
Chem. Rev., 2004, 104, 3893–3946.
2
1
.5 equiv) and Pd-4 (from Table 1, entry 1, 8.2 mg, 7.5 ¥
-
4
0
mmol Pd, 0.25 mol%). Water (Milli-Q; 4.5 mL) was added,
(a) K. Philippot, B. Chaudret, in Comprehensive Organometallic
Chemistry III, ed. R. H. Crabtree and M. P. Mingos, Elsevier, 2007,
vol. 12, ch. 12.03, pp. 71–99; (b) M. Tristany, B. Chaudret, P. Dieudonn e´ ,
Y. Guari, P. Lecante, V. Matsura, M. Moreno-Ma n˜ as, K. Philippot and
R. Pleixats, Adv. Funct. Mater., 2006, 16, 2008–2015; (c) M. Tristany, M.
Moreno-Ma n˜ as, R. Pleixats, B. Chaudret, K. Philippot, P. Dieudonn e´
and P. Lecante, J. Mater. Chem., 2008, 18, 660–666.
◦
the tube was sealed and heated to 100 C for 4 h. The tube
was then allowed to cool to room temperature, and the prod-
uct was extracted with Et
aqueous fraction for subsequent runs. The ether fraction was
evaporated and the residue partitioned between water and CH Cl
The resulting organic fraction was separated and washed with
additional H O, dried with anhydrous Na SO and evaporated.
Product 4-methoxybiphenyl was obtained as a white solid (for
yields see Scheme 4). The aqueous fraction was reused for two
more cycles, adding each time iodobenzene (61 mg, 0.3 mmol),
2
O, reserving the catalyst-containing
2
2
.
4 For reviews, see: (a) M. Moreno-Ma n˜ as, R. Pleixats, A. Roglans, R. M.
Sebasti a´ n and A. Vallribera, Arkivoc, 2004, iv, 109–129; (b) M. Moreno-
Ma n˜ as, R. Pleixats, R. M. Sebasti a´ n, A. Vallribera and A. Roglans,
J. Organomet. Chem., 2004, 689, 3669–3684.
5 A. Serra-Muns, R. Soler, E. Badetti, P. de Mendoza, M. Moreno-
Ma n˜ as, R. Pleixats, R. M. Sebasti a´ n and A. Vallribera, New J. Chem.,
2
2
4
2
006, 30, 1584–1594.
p-methoxyphenylboronic acid (70 mg, 0.45 mmol), and K
41 mg, 0.3 mmol). After each cycle, the reaction mixture was
treated in a manner analogous to the first run.
2
CO
3
6
(a) S. N. Sidoreov, L. M. Bronstein, P. M. Valetsky, J. Hartmann, H.
C o¨ lfen, H. Schnablegger and M. Antonietti, J. Colloid Interface Sci.,
1999, 212, 197–211; (b) L. Bronstein, E. Kr a¨ mer, B. Berton, C. Burger,
S. F o¨ rster and M. Antonietti, Chem. Mater., 1999, 11, 1402–1405;
(
(
c) L. M. Bronstein, S. N. Sidorov, P. M. Valetsky, J. Hartmann, H.
Attempted hydrogenation of Pd(dba)
macrocycle 1
2
in the presence of
C o¨ lfen and M. Antonietti, Langmuir, 1999, 15, 6256–6262; (d) L. M.
Bronstein, D. M. Chernyshov, G. I. Timofeeva, L. V. Dubrovina, P. M.
Valetsky, E. S. Obolonkova and A. R. Khokhlov, Langmuir, 2000,
16, 3626–3632; (e) H. H a¨ relind Ingelsten, R. Bagwe, A. Palmqvist,
M. Skoglundh, C. Svanberg, K. Holmberg and D. O. Shah, J. Colloid
Interface Sci., 2001, 241, 104–111; (f) Z. Liu, J. Y. Lee, M. Han, W.
Chen and L. M. Gan, J. Mater. Chem., 2002, 12, 2453–2458; (g) P. H.
Wang and C.-Y. Pan, J. Appl. Polym. Sci., 2002, 86, 2732–2736; (h) H.
Nishikawa, T. Morita, J. Sugiyama and S. Kimura, J. Colloid Interface
Sci., 2004, 280, 506–510; (i) T. Sakai and P. Alexandridis, Langmuir,
A Fischer–Porter apparatus equipped with a magnetic stirbar
was charged with macrocycle 1 (main section, Fig. 1, 100 mg,
0
.146 mmol) and Pd(dba) (44.6 mg, 0.073 mmol). The apparatus
2
was closed and the contents were subjected to three evacuate–refill
cycles with argon. THF (anhydrous, 30 mL) was added, the system
was purged with H
to 3 atm. The dark mixture was allowed to stir for 15 h at room
temperature. The resulting mixture was filtered through a Milli-
Pore sheet, and the volatile fraction was removed. The residue was
washed with hexane, to remove dba, giving a white solid. H NMR
analysis shows a 1 : 1 mixture of macrocycle 1 and the palladium
complex 2 described previously.
2
three times and bringing the pressure of H
2
2
004, 20, 8426–8430; (j) M. Mandal, S. Kundu, S. K. Gosh and T.
Pal, J. Photochem. Photobiol. A: Chem., 2004, 167, 17–22; (k) N. V.
Semagina, A. V. Bykov, E. M. Sulman, V. G. Matveeva, S. N. Sidorov,
L. V. Dubrovina, P. M. Valetsky, O. I. Kiselyova, A. R. Khokhlov, B.
Stein and L. M. Bronstein, J. Mol. Catal. A: Chem., 2004, 208, 273–
1
2
1
84; (l) R. Nakao, H. Rhee and Y. Uozumi, Org. Lett., 2005, 7, 163–
65; (m) M. Vamvakaki, L. Papoutsakis, V. Katsamanis, T. Afchoudia,
20
P. G. Fragouli, H. Iatrou, N. Hadjichristidis, S. P. Armes, S. Sidorov, D.
Zhirov, V. Zhirov, M. Kostylev, L. M. Bronstein and S. H. Anastasiadis,
Faraday Discuss., 2005, 128, 129–147; (n) K. Okamoto, R. Akiyama,
H. Yoshida, T. Yoshida and S. Kobayashi, J. Am. Chem. Soc., 2005,
Acknowledgements
1
27, 2125–2135; (o) S. Chen, C. Guo, G.-H. Hu, J. Wang, J.-H. Ma,
X.-F. Liang, L. Zheng and H.-Z. Liu, Langmuir, 2006, 22, 9704–9711;
p) Y. M. A. Yamada, T. Arakawa, H. Hocke and Y. Uozumi, Angew.
Financial support from MEC and MICINN of Spain (Projects
CTQ2005-04968/BQU and CTQ2006-04204/BQU, predoctoral
scholarship to A. S-M. and a Ramon y Cajal contract
for A. Shafir), Generalitat de Catalunya (Projects SGR2005-
(
Chem., Int. Ed., 2007, 46, 704–706; (q) Y. Uozumi, R. Nakao and
H. Rhee, J. Organomet. Chem., 2007, 692, 420–427; (r) X. Wang, H.
Kawanami, N. M. Islam, M. Chattergee, T. Yokoyama and Y. Ikushima,
Chem. Commun., 2008, 4442–4444.
(a) R. C. Hedden, B. J. Bauer, A. P. Smith, F. Gr o¨ hn and E. Amis,
Polymer, 2002, 43, 5473–5481; (b) Y. Haba, C. Kojima, A. Harada,
T. Ura, H. Horinaka and K. Kono, Langmuir, 2007, 23, 5243–5246;
0
0305 and SGR2009-1441), and from Consolider Ingenio 2010
7
(
CSD2007-00006) is gratefully acknowledged.
(
c) E. Boisselier, A. K. Diallo, L. Salmon, J. Ruiz and D. Astruc, Chem.
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This journal is © The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7748–7755 | 7755