Synthetic strategies for the surface functionalisation of gold nanoparticles with metals and metal clusters

Article abstract of DOI:10.1039/c1dt10456j

The reaction of the new ditopic thiol-phosphine compound HS(CH ₂)₁₁OOCC₆H₄PPh₂ (L) with an excess of dodecanethiol-protected gold nanoparticles gave the asymmetric gold complex [CH₃(CH₂)₁₁SAuPPh₂C ₆H₄COO(CH₂)₁₁SH] (4), but no phosphine-protected gold nanoparticles were formed. However, by blocking the phosphine function in L with metal fragments, we have been able to produce gold nanoparticles functionalised with AuCl- and cluster [Fe₂(CO) ₇Au] units on the surface by the method of ligand-place exchange reaction.

Full text of DOI:10.1039/c1dt10456j

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PAPER
Synthetic strategies for the surface functionalisation of gold nanoparticles
with metals and metal clusters
a
a
a
a
b
Mario Friederici, Inmaculada Angurell,* Miquel Seco, Oriol Rossell* and Jordi Llorca
Received 17th March 2011, Accepted 13th May 2011
DOI: 10.1039/c1dt10456j
The reaction of the new ditopic thiol-phosphine compound HS(CH
excess of dodecanethiol-protected gold nanoparticles gave the asymmetric gold complex
CH (CH 11SAuPPh COO(CH 11SH] (4), but no phosphine-protected gold nanoparticles were
formed. However, by blocking the phosphine function in L with metal fragments, we have been able to
2
)
11OOCC
6
H
4
PPh
2
(L) with an
[
3
2
)
2
C
6
H
4
2
)
produce gold nanoparticles functionalised with AuCl- and cluster [Fe
the method of ligand-place exchange reaction.
2
(CO) Au] units on the surface by
7
Introduction
site of the chain. HS(CH
this purpose since the aryl protons could provide additional
spectroscopic information.
2
)
11OOCC
6
H
4
PPh (L) was chosen for
2
The functionalisation of gold nanoparticles with metal complexes
on the outermost surface is an area of increasing interest due the
1
2
potential use of these materials in catalysis, chemical sensors or
Synthesis of HS(CH
2
)
11OOCC
6
H
4
PPh (L)
2
3
medicine among others. The advantage of these nanoparticles
resides in the possibility of combining their stability with the
wealth of reactivity offered by metal species. Gold nanoparticles
functionalised by thiol-tethered transition metal moieties of Ru,
Ti, Cu, Rh, Fe, Co, Eu and Tb have been described along
L was obtained according to Scheme 1. The first step in-
volved the oxidation of the commercially available alkanethiol
HS(CH
ing disulphur compound 2. Next, this product was reacted with
Ph PC COOH in the presence of DCC and DMAP in CH Cl
at room temperature giving the di-ester 3. Finally, reduction
with PEt in THF/H O (9 : 1) allowed us to isolate the target
phosphinethiol compound L. The global yield was about 60.0%.
2
)11OH (1) with iodine in methanol, to give the correspond-
4
with their properties in some cases. Although no systematic
2
6
H
4
2
2
strategy to access these nanoparticles is known, very recently a
dithiocarbamated-based methodology has facilitated the forma-
3
2
5
6
tion of gold nanoparticles containing ruthenium or nickel on the
surface.
1
13
This reagent was characterized by elemental analysis, H, C and
3
1
The aim of the present paper has been to explore the possibility
of establishing a general method for the synthesis of functionalised
gold nanoparticles having metal fragments at the periphery.
Although we first focused our attention on the formation of gold
nanoparticles peripherally functionalised with free phosphine, the
impossibility of obtaining such kind of derivatives prompted us
to investigate new strategies and as a result we describe here the
first gold nanoparticles displaying an heterometallic cluster on the
surface.
P NMR, and MALDI-TOF-MS spectrometry.
Reaction of gold nanoparticles with L
With L in our hands, we decided to carry out the ligand-exchange
reaction with dodecanethiol-protected gold nanoparticles in an
attempt to promote the exchange of dodecanethiol units for L.
However we were fully aware that this reaction could also proceed
through the phosphine group of L. In fact, although thiolate for
thiolate ligands replacement are the ligand-exchange reactions
7
more widely studied, phosphine for thiolate ligands replacements
Results and discussion
8
are well documented in the literature. Consequently, the proposed
reaction could illustrate the behaviour of the alkanethiol-protected
gold nanoparticles in front of the two potential active groups, thiol
and phosphine.
The formation of the free-phosphine functionalised gold nanopar-
ticles required the previous synthesis of a molecule containing a
terminal thiol function and a phosphine ligand at the opposite
The starting dodecanethiol-protected gold nanoparticles were
9
obtained by using the protocol described by Brust. A sample
a
Departament de Qu ´ı mica Inorg a` nica, Universitat de Barcelona, Mart ´ı i
of these nanoparticles was dissolved in CH Cl and reacted with
2
2
Franqu e` s 1-11, 08028, Barcelona, Spain. E-mail: oriol.rossell@qi.ub.es,
inmaculada.angurell@qi.ub.es
L in a 1 : 0.3 molar ratio at room temperature. We specifically
chose this molar ratio in order to avoid that excess of phosphine
could interchange with the resulting nanoparticles and mask the
b
Institut de T e` cniques Energ e` tiques i Centre de Recerca en Nanoenginyeria.
Universitat Polit e` cnica de Catalunya, Diagonal 647, 08028, Barcelona,
Spain
3
1
P NMR spectrum with broad bands. After 48 h of reaction,
7
934 | Dalton Trans., 2011, 40, 7934–7940
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Scheme 1 Synthesis of L.
3
1
13
the P NMR spectrum of the solution showed that the peak at
5.0 ppm due the PPh - group was not present and instead, a
to the gold nanoparticles are expected, was carefully examined
and no traces of bands were present nor at room temperature
-
2
1
new signal appeared at 39 ppm, along with another at 29 ppm
neither at low temperature. In addition, in the H NMR spectrum
which was attributed to L oxide. The lack of the peak at
of this solution no peaks appeared in the region of 7.0–8.0 ppm
(where the aryl protons of L are present) dismissing the attachment
of L on the surface of the nanoparticle. These results permit
therefore to establish that the reaction of L with gold nanoparticles
causes the release of gold atoms from the nanoparticle in the form
of the asymmetric gold thiolate/phosphine compound as already
proposed, but attachment of the phosphine ligand onto the surface
of the nanoparticle does not take place. A direct consequence
of this process is that the new gold nanoparticles should be
smaller than their parents. To check this point, both types
of nanoparticles were analyzed by high-resolution transmission
electron microscopy (HRTEM) (Fig. 1a and 1b).
-
5.0 ppm unambiguously revealed that L had reacted with gold
nanoparticles via phosphine. The key point was to know the nature
of the species responsible for the peak at 39.0 ppm. Taking into
10
account the paper by Foos, in which the asymmetric complex
CH (CH SAuPPh ] was reported to show a peak at 38 ppm, it
was thought that our unknown compound could be the similar
species [CH (CH 11SAuPPh COO(CH 11SH] (4) (Scheme
). To confirm this assumption, in a separate experiment we syn-
[
3
2
)
5
3
3
2
)
2
C
6
H
4
2
)
2
11
thesized 4 by reaction of [AuCl(tht)] (tht = tetrahydrothiophene)
with L, followed by treatment with dodecanethiol in presence of
NEt . The P NMR spectrum revealed the rapid appearance of
3
1
3
a unique resonance at 39 ppm, thus confirming that reaction of
the nanoparticles with L follows the previously proposed scheme
in which rapid formation of an asymmetric S–Au–P compound
takes place.
In the literature dealing with thiolate for phosphine ligand-
exchange processes it has been proposed proposed that after
formation of the asymmetric gold complexes, a fraction of
phosphine ligands was incorporated on the surface of the gold
10,12
nanoparticle.
In order to test the incorporation of L onto our
gold nanoparticles, these were carefully washed, recrystallised and
1
31
analyzed by H and P NMR spectroscopy. Contrarily to that
3
1
reported, no signals in the P NMR spectrum were detected. The
region at about 50–65 ppm, in which the resonances of P attached
Fig. 1 (a) HRTEM of the parent gold nanoparticles. (b) nanoparticles
after reaction with L.
3
1
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Scheme 2 Reaction of gold nanoparticles with L.
In the first case, the starting dodecanethiol-protected Au
New synthetic strategies
nanoparticles (NP1) were well-dispersed and reasonably homo-
geneous in size (~2.4 nm), whereas the new Au particles (NP2)
exhibited an average size of about 1.8 nm, and appeared to be much
less homogeneous. In addition to smaller particles, a few larger
nanoparticles were also present due to aggregation phenomena.
In all cases, lattice spacing (see insets) confirmed the nature of gold
nanoparticles. Fig. 2 shows core-size distribution histograms for
both samples.
The final confirmation of the lack of compatibility between
the alkanethiol-protected gold nanoparticles and the phosphine-
thiol L in solution arises from the complete degradation of
the gold nanoparticles after reaction with excess of L (1 : 1.5
molar ratio). Consequently, our attempts to prepare phosphine
functionalized-alkanethiols protected gold nanoparticles were not
successful and a new synthetic strategy for such species was
needed.
Our last results suggested that the phosphine group in L should
be blocked to prevent reaction with gold nanoparticles. With this
in mind, we made L to react with AuCl(tht) and the new metal
complex ClAuPPh
characterized, showing only one resonance at 33.0 ppm in the
2
C
6
H
4
COO(CH )11SH (5) was spectroscopically
2
3
1
P
NMR spectrum. Then, 5 was reacted with a sample of hexanethiol-
protected gold nanoparticles (formed by the Brust’s method)
which was chosen in order to promote facile thiol exchange ligands
reaction. After 24 h in dichloromethane, new gold nanoparticles
(NP3) were obtained and recrystallized in a mixture of CH
2
Cl
2
and hexane and purified by gel permeation chromatography using
thf as eluent. By integrating the methyl group signal of the
1
hexanethiol and the two a aromatic protons of L in the
H
NMR it was deduced that the hexane-thiol/5 ligand ratio on
the periphery of the nanoparticle was about 2 : 1. Furthermore,
Fig. 2 Size distribution histogram of gold nanoparticles before reaction with L (NP1) (a) and after reaction (NP2) (b).
936 | Dalton Trans., 2011, 40, 7934–7940
7
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3
two broad triplets assigned to the -CH
2
S group of both ligands
of the cluster to 57.1 and 117. 5 ppm ( J(P–P) = 22.9 Hz)
1
could be observed at 2.66 and 3.08 ppm, in agreement with
the proposed structure for NP3. The next step for the synthesis
of gold nanoparticles functionalised with transition metals was
to treat the bilayer gold nanoparticles with the binuclear iron
indicating that the reaction proceeded. The H NMR spectrum
was consistent with the presence of two different layers and the
thiol-hexane : 6 ratio of 2.7 : 1.0 was obtained by integrating the
methyl protons of hexanethiol and the a-aromatic protons of 6.
1
9
cluster [NEt
4
][Fe
2
(CO)
6
(m-CO)(m-PPh
2
)] in the presence of TlBF
4
The presence of the trinuclear Fe
by the IR spectrum, for which the pattern in the carbonyl region
was almost identical to that exhibited by the cluster [Fe (CO) (m-
2
Au cluster was also corroborated
salt as chloride abstractor, in thf. The purpose of this reaction
was to displace the chloride by the iron anion to form the
2
6
14
expected trinuclear Fe
2
Au cluster. However, we obtained a very
CO)(m-PPh
2
)(AuPPh )].
3
insoluble black residue resulting from the aggregation of the
gold nanoparticles. Consequently, a new strategy was attempted,
consisting in the partial replacement of hexanethiolate ligands
of preformed gold-hexanethiol nanoparticles for the new cluster-
functionalised thiolate 6 which previous synthesis was made
according to Scheme 3.
It is interesting to note that the same reaction carried out in a
molar ratio higher than 1 : 0.3 (gold-hexanethiol : 6) affords much
less soluble gold nanoparticles due the high polarity of the cluster-
functionalised thiolate. For the same reason attempts to prepare
directly the mixed thiolate gold nanoparticles were discarded.
The UV-vis spectrum of NP4 shows a continuous absorption,
which gradually disappears at higher wavelengths, and a weak
surface plasmon (SP) resonance at about 499 nm that confirms
3
The two doublets at 52.0 and 130.5 ppm ( J(P–P) = 25.1 Hz) in
3
1
the P NMR spectrum of 6 in thf are relevant for monitoring the
formation of the gold nanoparticles. The reaction of hexanethiol-
gold nanoparticles and 6 in a 1 : 0.3 molar ratio was performed
in thf at room temperature for 15 h. After this period, the
new nanoparticles NP4 were precipitated by adding hexane and
purified by gel permeation chromatography (Scheme 4). The most
interesting spectroscopic feature is the shifting of the two doublets
15
that the diameter of the gold nanoparticles is larger than 2 nm.
Nanoparticles NP4 were analysed by high-resolution transmis-
sion electron microscopy (HRTEM) and appeared well-dispersed
(Fig. 3). Fig. 4 shows the core-size distribution histogram.
Their average diameter is 2.89 nm so that the approximate
16
number of Au atoms in the core is 742. Taking into account the
Scheme 3 Synthesis of 6.
Scheme 4 Synthesis of NP4.
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Dalton Trans., 2011, 40, 7934–7940 | 7937

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Experimental
Materials. Hydrogen tetrachloroaurate (III) (Johnson Mat-
they), sodium borohydride (Sigma–Aldrich), tetraoctylammo-
nium bromide (TOAB; Aldrich), 1-dodecanethiol, 98 +%
(
Aldrich), 1-hexanethiol, 95% (Aldrich), 11-mercapto-
-undecanol, 97% (Aldrich), iodine (Panreac), sodium
bisulfite (Aldrich), 4-(diphenylphosphino)-benzoic acid, 97%
Aldrich), N,N¢-dicyclohexylcarbodiimide (DCC, Fluka), 4-
dimethylaminopyridine (DMAP, Aldrich), triethylphosphine,
9% (Aldrich), triethylamine (Aldrich), MgSO anhydrous
Panreac) were all used as received without further purification.
1
(
9
4
(
1
1
The materials [AuCl(tht)], TlBF
PPh
4
and [NEt
4
] [Fe
2
(CO) (m-CO)(m-
6
19
2
)] were synthesized as reported in the literature. Sephadex
LH-20 (GE Healthcare Bio-Sciences AB) was swollen in suitable
solvents and loaded into a glass column. Chromatographic
purifications were performed by flash chromatography using
silica gel (Fluka 0.063–0.2 mm). All solvents were distilled from
appropriate drying agents. Deionised water was obtained from
Millipore Milli-Q water purification system. All manipulations
were performed under purified nitrogen using standard Schlenk
techniques.
Fig. 3 HRTEM of the cluster-functionalised gold nanoparticles NP4.
1
13
1
31
Instrumentation. H, C{ H} and P NMR spectra were ob-
tained on Bruker DXR 250 and Varian Mercury 400 instruments.
1
13
Bidimensional NMR spectra (HSQC H- C) were recorded on
a Varian Mercury 400 apparatus. Chemical shifts are reported
1
13
in ppm relative to external standards (SiMe
4
for H and C, H
3
PO
4
3
1
for P), and coupling constants are given in Hz. MS MALDI-
TOF spectra were recorded in a VOYAGER-DE-RP (Applied
Biosystems) spectrometer. UV-visible samples were placed in
quartz cuvettes (Suprasil, Hellma; path length of 1 cm) and
analyzed using a spectrophotometer (Cary 100 SCAN, Varian).
Infrared spectra were carried out in a spectrophotometer FT-IR
NICOLET Impact 400 or on a NICOLET 520 FT-IR in the region
between 4000 and 400 cm and KBr has been used as dispersing
medium. To designate the intensity of the bands of spectrum have
used the following abbreviations: s, strong; m, medium; w, weak
and vs, very strong. It is noteworthy that only IR bands which
give us information about the structure of the compounds have
been assigned. Elemental analyses were carried out on Thermo
Finnigan-1108 instrument. High-resolution transmission electron
microscopy (HRTEM) measurements were performed at 200 kV
with a JEOL 2100 microscope (point-to-point resolution of 0.21
nm). Samples were prepared by placing a drop of toluene solution
on a holey-carbon-coated Cu grid and allowing the solvent to
evaporate in air.
-
1
Fig. 4 Size distribution histogram of NP4.
elemental analysis of C, H and S and the thiolate hexane/6 ratio,
obtained by integrating the methyl protons of hexanethiol and
the a-aromatic protons of 6 it is deduced that the total number
of ligands is 242, including 65 ligands of 6. Similar results are
17
obtained by applying the size core model. To the best of our
knowledge this is the first heterometallic cluster grafted on the
periphery of gold nanoparticles. It should be noted that a similar
5
species containing the homometallic iron cluster [Fe(h -C
5
H
5
)(m -
3
18
CO)] has been recently reported by Astruc.
4
Synthesis of ditopic ligand HS(CH
0.165 g, 60.0%). This ligand was synthesized in three steps. First
2
)
11OOCC
6
H
4
PPh
2
(L).
Conclusions
(
Free phosphine derivatives and alkanethiolate-protected gold
nanoparticles are not compatible in solution. However, thiol
molecules containing the phosphine function previously blocked
with metal units such as AuCl or the metal cluster fragment
step: Synthesis of compound 2 (0.924 g, 92.2%). A methanol solu-
tion (80 mL) containing 11-mercapto-1-undecanol (1.002 g, 4.90
mmol) (1) was titrated by 1 M iodine methanol solution until the
solution turned light yellow, and then the reaction was quenched
with sodium bisulfite. The reaction mixture was evaporated to
dryness under reduced pressure at room temperature and then the
[Fe
2
(CO)
6
(m-CO)(m-PPh
2
)(AuPPh )] have shown to be suitable for
2
the surface functionalisation of gold nanoparticle through ligand-
place exchange reactions. We believe that this strategy can be
extended to other metal fragments to give new gold nanoparticles
functionalised with a plethora of metals and/or transition metal
clusters on the periphery.
product, 11-hydroxyundecyldisulfide (2) was extracted in CH
2
Cl
2
as a white solid. Second step: Synthesis of compound 3 (0.232 g,
91.8%). To a stirred solution of 2 (0.253 g, 0.62 mmol) in 40 mL
CH
2
Cl
2
was added 4-(diphenylphosphino)-benzoic acid (0.377 g,
7
938 | Dalton Trans., 2011, 40, 7934–7940
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1
0
.23 mmol), DCC (0.277 g, 1.34 mmol) and DMAP (0.014 g,
.11 mmol) successively. The resulting mixture was allowed to stir
TlBF
4
(0.126 g, 0.43 mmol), and [NEt
4
] [Fe
2
(CO)
6
(m-CO)(m-PPh )]
2
(0.270 g, 0.43 mmol) were stirred in THF (50 mL) for 1 h at
◦
overnight at room temperature under nitrogen. When the reaction
was finished, the white solid was removed by filtration, solvent was
removed under reduced pressure, and the residue was purified by
flash chromatography on silica using a mixed eluent (hexane:ethyl
acetate, 10 : 1), obtaining 3 as a colourless to light-yellow oil. Third
step: Synthesis of compound L (0.165 g, 71.0%). Compound 3
-20 C. The solution obtained, after filtration, was evaporated to
dryness under reduced pressure. Then the product was extracted
in thf. Elemental analysis: Found: C, 49.75; H, 4.0%. Calc. for
-
1
C
49
H
47AuFe
2
O
9
P
2
S: C, 49.8; H, 4.0%. IR: nmax/cm 3052 w (arC-
), 2926 m and 2848 m (CH ), 2061 m, 2043 m,
2013vs, 1974vs and 1774 m (CO), 1721 m (C O) and 1430 m (S–
CH ). NMR: d (400 MHz; THF-d ; Me Si) 8.15–8.02 (2H, m,
H), 2956 w (CH
3
2
(
0.232 g, 0.24 mmol) was dissolved in THF/H
2
O (9 : 1, 20 mL) and
2
H
8
4
(
73.1 mL, 0.50 mmol) of triethylphosphine was added to it at room
CHPh), 7.91–7.43 (12H, m, CHPh), 7.41–7.11 (10H, m, CHPh), 4.32
20
3
temperature. The mixture was stirred for 30 min and the solvent
was then removed under a vacuum. CH Cl (20 mL) was added
and washed with H O (3 ¥ 10 mL). The compound was extracted
with CH Cl . The combined organic layers were dried over MgSO
anhydrous. Removal of solvent followed by flash chromatography
on silica using a mixed eluent (hexane:ethyl acetate, 4 : 1) yielded
the final product L. Elemental analysis: Found: C, 73.0; H, 7.5%.
Calc. for C30
CDCl ; Me
CHPh) 4.32 (2H, t, JHH = 8.0, CH
(2H, t, J(HH) = 8.0, CH
2
COOAr), 2.46 (2H, pq, J
). d (101.2 MHz; THF-d
(d, JPP = 25.1), 52.0 (d, JPP = 25.1).
ª
8.0, HSCH
2
),
2
2
1.78–1.13 (18H, m, CH
2
P
8
; H PO ) 130.5
3
4
3
3
2
2
2
4
Ligand-Exchange reaction of dodecanethiol-capped gold
nanoparticles with ligand L (NP2). The gold nanoparticles
stabilized with dodecanethiol were prepared using the method
of Brust. A sample of these nanoparticles (0.100 g) was dissolved
H
37
O
2
PS: C, 73.1; H, 7.5%. NMR: d (400 MHz;
H
in 10 mL of CH
2
2
Cl and reacted with L in a 1 : 0.3 molar ratio at
3
4
Si) 8.02–7.96 (2H, m, CHPh), 7.37–7.30 (12H, m,
3
room temperature for 48 h. The reaction mixture was concentrated
under a vacuum and by addition of hexane, gold nanoparticles
were precipitated. The nanoparticles were washed with hexane,
filtered and dried. UV-Vis: lmax = 530 nm.
2
COOAr), 2.51 (2H, pq, J ª
). d (100.6 MHz; CDCl
Si) 166.4 (s, COOAr), 143.8 (d, JCP = 14.1 CPh–P), 136.2 (d,
8
.0, HSCH
2
), 1.81–1.25 (18H, m, CH
2
C
3
;
1
Me
4
1
2
2
J
CP = 10.0, CPh–P), 133.9 (d, JCP = 20.1, CPh), 133.2 (d, JCP
=
3
1
1
(
2
9.1, CPh), 130.4 (s, CPh), 129.3 (d, JCP = 6.0, CPh), 129.1 (s, CPh),
Ligand-Exchange reaction of hexanethiol-capped gold nanopar-
ticles with ligand 5 (NP3). The gold nanoparticles stabilized with
hexanethiol were prepared using the method of Brust. A sample
3
28.7 (d, J = 7.0, CPh), 65.2 (s, CH
2
COOAr), 34.0 (s, CH
), 28.7 (s, CH ), 28.4 (s, CH
(101.2 MHz; CDCl ; H PO
Cl ): calc.: m/z = 493.23 [M +
2
), 29.5
s, CH
2
), 29.3 (s, CH
6.0 (s, CH ), 24.6 (s, CH
5.1 (s). MS (MALDI-TOF) (CH
2
), 29.1 (s, CH
2
2
2
),
2
2
SH). d
P
3
3
4
)
of these nanoparticles (0.100 g) was dissolved in 10 mL of CH
2
Cl
2
-
2
2
and reacted with 5 in a 1 : 0.3 molar ratio at room temperature
for 24 h. The reaction mixture was concentrated under a vacuum
and by addition of hexane, gold nanoparticles were precipitated.
The nanoparticles were washed with hexane and then filtered
and dried. Further purification was achieved by gel permeation
+
+
H] ; found: m/z = 493.3 (100) [M + H] .
Synthesis of the compound HS(CH
2
)
11OOCC
6
H
4
PPh
2
AuCl (5).
(
1.6 g, 91%). To a solution of L (1.2 g, 2.44 mmol) in 40 mL of
11
CH
(
2
Cl with stirring at room temperature [AuCl(tht)] was added
2
-
1
chromatography (GPC) using thf as eluting solvent. IR: nmax/cm
057 w (arC-H), 2948 w (CH ), 2917 m and 2848 m (CH ), 1717
m (C O) and 1430 m (S–CH ). NMR: d (400 MHz; CD Cl
0.764 g, 2.38 mmol). The stirring was maintained for 30 min.
3
3
2
Thereafter, the solution was evaporated to dryness under reduced
pressure obtaining a colorless to light-yellow oil that was washed
with hexane to extract the tht liberated in the reaction. Elemental
2
H
2
2
;
Me
4
Si) 8.2–7.92 (2H, m, CHPh), 7.80–7.21 (12H, m, CHPh), 4.30
3
(
2H, m, CH
2
COOAr), 3.08 (0.14H*, t, JHH = 8.0, SCH
2
), 2.66
), 0.96 (6H,
). *The integrations were not the expected ones due to
the environment of the nanoparticles. d (101.2 MHz; CD Cl
PO ) 33.1 (s). UV-Vis: lmax = 508 nm. HRTEM: The average
diameter of NP3 = 2.51 nm
analysis: Found: C, 49.6; H, 5.1%. Calc. for C30
H
37AuClO
9.7; H, 5.1%. IR: nmax/cm 3074 w (arC-H), 3052 w (CH
s and 2843 s (CH ), 1717vs (C O) and 1430 s (S–CH ). NMR: d
Cl ; Me Si) 8.15–8.02 (2H, m, CHPh), 7.69–7.43
12H, m, CHPh), 4.31 (2H, t, JHH = 8.0, CH
, HSCH ), 1.82–1.18 (18H, m, CH ). d (100.6 MHz; CD
2
PS: C,
), 2922
3
-
1
(0.2H*, t, JHH = 8.0, SCH
m, CH
2
), 2.10–0.99 (27H*, m, CH
2
4
3
3
2
2
H
P
2
2
;
(400 MHz; CD
2
2
4
3
H
3
4
(
s
2
COOAr), 2.50 (2H,
Cl
b
2
2
2
C
2
2
;
Me
4
Si) 165.6 (s, COOAr), 134.7 (d, JCP = 14.1, CPh), 134.4 (d,
CP = 14.1, CPh), 134.0 (s, CPh), 132.7 (s, CPh), 130.2 (d, JCP
Ligand-Exchange reaction of hexanethiol-capped gold nanopar-
ticles with ligand 6 (NP4). The gold nanoparticles stabilized with
hexanethiol were prepared using the method of Brust. A sample
of these nanoparticles (0.070 g) was dissolved in 10 mL thf and
reacted with 6 in a 1 : 0.3 molar ratio at room temperature for 15 h.
The reaction mixture was concentrated in vacuo and by addition of
hexane, gold nanoparticles were precipitated. The nanoparticles
were washed with hexane and then filtered and dried. Further
purification was achieved by gel permeation chromatography
2
3
J
=
3
1
1
6
2
2.1, CPh), 129.8 (d, JCP = 12.1, CPh), 128.6 (d, JCP = 61.4, CPh–P),
6.0 (s, CH COOAr), 34.6 (s , CH ), 29.9 (s, CH ), 29.6 (s, CH ),
9.2 (s, CH ), 29.0 (s, CH ), 28.8 (s, CH ), 26.4 (s, CH ), 25.0 (s
SH). d (101.2 MHz; CD Cl ; H PO ) 33.6 (s).
2
b
2
2
2
2
2
2
2
b
,
CH
2
P
2
2
3
4
SynthesisofthecomplexCH
3
(CH
2
)
11SAuPPh
2
C
6
H
4
COO(CH
2
)
11
SH (4). (0.0904 g, 0.12 mmol) of the compound 5 was dissolved
in 20 mL of CH Cl . To this stirring solution was added (30 mL,
.12 mmol) of dodecanethiol followed by (17 mL, 0.12 mmol) of
2
2
(
GPC) using THF as eluting solvent. Elemental analysis: Found:
0
Et
-
1
3
1
C, 20.66; H, 2.38; S, 3.08%. IR: nmax/cm 3048 w (arC-H), 2948 w
CH ), 2913 m and 2843 m (CH ), 2030 s, 1961 s and 1917 m (CO),
717 m (C O) and 1435 m (S–CH ). NMR: d (400 MHz; THF-
Si) 8.24–7.98 (2H, m, CHPh), 7.96–6.79 (22H, m, CHPh),
COOAr), 3.08 (0.13H*, m, SCH ), 2.68 (0.3H*,
), 1.61–0.98 (31H*, m, CH ), 0.89 (9H, m, CH ). *The
3
N. The reaction was monitored by P NMR and after 2 h of
(
3
2
stirring, one only signal at 39 ppm was observed.
1
2
H
Synthesis of the compound [Fe
Au(PPh COO(CH
11SH)}] (6). (0.291 g, 57%). The com-
pounds HS(CH PPh AuCl (0.314 g, 0.43 mmol),
2
(CO)
6
(l-CO)(l-PPh
2
){l-
d
8
; Me
4
2
C
6
H
4
2
)
4.32 (2H, m, CH
m, SCH
2
2
2
)
11OOCC
6
H
4
2
2
2
3
This journal is © The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7934–7940 | 7939

View Article Online
integrations were not the expected ones due to the environment
of the nanoparticles. d (101.2 MHz; THF-d ; H PO ) 117.5 (d,
PP = 22.9), 57.1 (d, JPP = 22.9). UV-Vis: lmax = 499 nm.
7 Selected examples: (a) A. C. Templeton, W. P. Wuelfing and R. W.
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P
8
3
4
3
3
J
2
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Financial support from MICINN projects CTQ2009-08795
and CTQ2009-12520 is acknowledged. J. L. is grateful to
ICREA Academia program and M. F. to IFARHU-SENACYT
program.
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940 | Dalton Trans., 2011, 40, 7934–7940
This journal is © The Royal Society of Chemistry 2011