Rational size control of gold nanoparticles employing an organometallic precursor [Au-C≡C-t-Bu]4 and tunable thiolate-functionalized ionic liquids in organic medium

Article abstract of DOI:10.1139/v11-146

Gold nanoparticles (Au NPs) stabilized with six different thiolate-functionalized ionic liquids (TFILs) were synthesized in an organic solvent. The size and optical properties of the TFIL-stabilized Au NPs can be rationally controlled by altering the N-alkyl chain length and (or) the counteranion of the TFIL-stabilizing ligand. Au NPs were prepared from the reduction of a gold precursor (HAuCl₄ or [Au-C≡C-t-Bu] ₄) employing NaBH₄ in the presence of the different disulfide precursors. A model, based on Israelachvili theory, is proposed to account for the dependence of NP size on the N-alkyl chain length and the counteranion of the surfactantlike TFIL stabilizers.

Full text of DOI:10.1139/v11-146

145
Rational size control of gold nanoparticles employing
an organometallic precursor [Au-CꢀC- t-Bu]4 and
tunable thiolate-functionalized ionic liquids in
organic medium
Kylie L. Luska and Audrey Moores
Abstract: Gold nanoparticles (Au NPs) stabilized with six different thiolate-functionalized ionic liquids (TFILs) were syn-
thesized in an organic solvent. The size and optical properties of the TFIL-stabilized Au NPs can be rationally controlled by
altering the N-alkyl chain length and (or) the counteranion of the TFIL-stabilizing ligand. Au NPs were prepared from the
reduction of a gold precursor (HAuCl4 or [Au-CꢀC-t-Bu]4) employing NaBH4 in the presence of the different disulfide pre-
cursors. A model, based on Israelachvili theory, is proposed to account for the dependence of NP size on the N-alkyl chain
length and the counteranion of the surfactantlike TFIL stabilizers.
Key words: gold nanoparticles, functionalized ionic liquids, gold(I) complexes, surface plasmon band, imidazolium salts.
Résumé : Des nanoparticules d’or (NPAu) stabilisées par six ioniques liquides fonctionnalisés par un thiolate (ILFT) ont été
synthétisées dans un solvant organique. La taille et les propriétés optiques de ces NPAu stabilisées par des ILFT peuvent
être contrôlées rationnellement en modifiant la longueur de la chaine N-alkyle et (ou) le contre-anion du ILFT. Les NPAu
ont été préparées par réduction d’un précurseur d’or, HAuCl4 ou [Au-CꢀC-t-Bu]4, à l’aide de NaBH4, en présence de cha-
cun des six précurseurs de disulfure. Un modèle, basé sur la théorie de Israelachvili, est avancé pour rendre compte de la re-
lation entre la taille des NPAu et la longueur de la chaine N-alkyle et la taille du contre-anion du ILFT, qui agit comme
stabilisant de la NP et surfactant.
Mots‐clés : nanoparticules d’or, liquides ioniques fonctionnels, complexe d’or(I), bande plasmon de surface, sels d’imidazo-
lium.
be accomplished that do not involve changing the metal-
binding moiety (i.e., N-alkyl chain length or counteranion),
and thus preserve the electronic nature of the NP. Kim et al.12
previously employed TFILs in the synthesis of Au and Pt NPs
and demonstrated that the position and number of thiol moi-
eties present in either the cation or anion of the TFIL ligands
impacted the size of the Au and Pt NPs. Such ligand altera-
tions dramatically influence both the electronic properties of
the metal core and the organization of the ligand sphere, pa-
rameters that are proposed to remain constant in this study. Re-
cent reports on Au NP synthesis have featured novel gold
precursors (e.g., AuX (for X = Cl or Br),13 [AuN(SiMe3)2]4,14
and [NMe4][Au(CF3)2]15) in an effort to complement the
Introduction
Gold nanoparticles (Au NPs) are subject to intensive re-
search because of their application in optical sensing,1 sur-
face-enhanced Raman spectroscopy,2 and catalysis.3,4
Optical1 and catalytic4 properties are governed by various
factors including, among others, the size and shape of the
NPs and the nature of the stabilizing ligand. Correlations be-
tween NP size and the properties of NPs are challenging to
establish as different ligands are most often employed to
achieve variance in the NP size,5 which alter not only the
size but also the electronics of the metal core. To establish
such a relationship, it would be desirable to develop a family
of stabilizing ligands, employed under identical reaction con-
ditions,6,7 that can control particle size. To reach this goal,
we synthesized Au NPs of tunable size using the same class
of ligand, thiolate-functionalized ionic liquids (TFILs), based
on an imidazolium structure. This class of Au NP ligand was
first proposed by Itoh et al.8 and used for anion sensing.
They were chosen here as (i) TFILs provide both electrostatic
and covalent stabilization to metal NPs increasing their long-
term stability9–11 and (ii) alterations to the TFIL structure can
16
well-established methodologies based on HAuCl4 and to
provide insight into the Au NP formation mechanism.17
[AuN(SiMe3)2]4 and [NMe4][Au(CF3)2] are interesting pre-
cursors as they eliminate the presence of halides in the reac-
tion mixture, which have been shown to affect the properties
of NPs.18 For instance, a recent DFT study by Janiak and co-
workers19 demonstrated that the interaction between chloride
anions and Au clusters possesses a large binding energy and
thus Cl– will play a role in stabilizing Au NPs if present in
Received 25 May 2011. Accepted 8 September 2011. Published at www.nrcresearchpress.com/cjc on 25 November 2011.
K.L. Luska and A. Moores. Department of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, QC H3A 2K6, Canada.
Corresponding author: Audrey Moores (audrey.moores@mcgill.ca).
This article is part of a Special Issue dedicated to Professor Tak-Hang Chan.
Can. J. Chem. 90: 145–152 (2012)
doi:10.1139/V11-146
Published by NRC Research Press

146
Can. J. Chem. Vol. 90, 2012
the synthetic mixture. Furthermore, in the context of IL
chemistry, it was even more important to select a metal pre-
cursor that does not produce any ionic by-products that can
undergo ion exchange with either of the IL ions.
Scheme 1. Ionic liquid disulfides 1–6 employed as precursors in the
synthesis of thiolate-stabilized gold nanoparticles.8
R1
Recently, the groups of Roucoux,20 Hou,21 and Dyson22
studied the influence of various structural parameters of func-
tionalized ionic liquid (FIL)-stabilized Rh and Pd NPs. Spe-
cifically, the concept of “supramolecular” arrangement of
FILs at the surface of stabilized NPs was explored and
evoked to rationalize such NP properties as catalytic activity.
Herein, we propose the use of a family of disulfide TFIL
precursors 1–6 (Scheme 1) in the formation of stable Au
NPs with control of the NP size (Scheme 2) by reduction of
gold precursors using NaBH4. The TFILs act as surfactants,
which stabilize the NPs through the anchoring of the thiol
moiety to the metal surface. We also introduce a model to ra-
tionalize this control and study the impact of the ligands 1–6
onto the optical properties of the synthesized Au NPs. We
also introduced a novel organometallic Au NP precursor,
[Au-CꢀC-t-Bu]4,23 to avoid the presence of halides during
the NP synthesis and compared its performance with the
more commonly used halide-based precursor, HAuCl4.
[Au-CꢀC-t-Bu]4 is expected to decompose under reducing
conditions into Au(0) and volatile organic by-products, thus
leaving the NP surface and the IL free of unwanted contam-
inants. Overall, our study suggests that FILs can act as sur-
factants to stabilize metal NPs and exert some level of size
control over the final NP size.
N
N
+
S
n
X-
2
R1 = H; X = Cl-; n = 5 (Itoh et al. precursor)
R1 = CH3; X = -OSO2CF3 (-OTf); n = 5 (1), n = 8 (2), n = 10 (3)
R1 = CH3; X = -N(SO2CF3)2 (-NTf2); n = 5 (4), n = 8 (5), n = 10 (6)
Scheme 2. Synthesis of thiolate-stabilized gold nanoparticles.
HAuCl4
Disulfide 1-6
or
N
N
+
[Au]0
NaBH4, Solvent, rt, 1 h
[Au-C?C-tBu]4
S
n
X-
to the development of a useful anion sensor; however, the
extent of the full counteranion replacement within the NP
ligand sphere, as well as the anion’s impact during the syn-
thesis of the NPs, was not determined. The present work
used TFIL precursors composed of a known counterion and
explored their influence on the properties of the resulting
Au NPs.
Nanoparticle synthesis and characterization
Synthesis of Au NPs was achieved by combining an organic
solution of an Au precursor (HAuCl4 or [Au-CꢀC-t-Bu]4,
0.100 and 0.025 mmol, respectively) with a methanol solu-
tion of one of disulfides 1–6 (0.20 mmol) and reducing the
mixture with NaBH4 (Scheme 2). The solution instantly
changed colour from pale yellow to purple, indicating the
formation of Au NPs. TEM analysis of the reaction mix-
tures showed the presence of well-dispersed Au NPs having
mean diameters ranging from 3.0 to 4.3 nm depending on n
and X– (Fig. 1 and Table 1; see the Supplementary data for
size and distribution data, Figs. S1 and S2). X-ray photo-
electron spectrometry (XPS) analysis of the Au NPs (for
HAuCl4 and disulfide 1) indicated the presence of gold, sul-
fur, carbon, nitrogen, oxygen, and fluorine, which signified
the TFIL stabilization of the NPs (Supplementary data Figs.
S3–S7). The S2p(3/2) binding energies (BEs) for disulfide 1
and the corresponding stabilized Au NPs are 163.7 and
162.3 eV respectively; a shift (–1.4 eV) that was in agree-
ment with the binding of the thiolate functionality to the
surface of the Au NPs.27 Additional evidence for the presence
Results and discussion
Synthesis of TFILs
Compounds 1–6 are characterized by four parameters: (1)
a thiolate function that binds to the Au particle, (2) an imidazo-
lium unit, (3) an alkyl chain playing the role of spacer be-
tween the metal binding and imidazolium moiety, and (4) a
counteranion (Scheme 2). In this study we altered both com-
ponents (3) and (4) to impact the size of the particle while
preserving (1) and (2) to have constant electronic and molec-
ular structure, respectively. The procedure employed for the
synthesis of 1–6 was adapted from that reported by Itoh et
al.8 (R1 = H, n = 5, and X = Cl–; Scheme 1) to prepare a
series of TFIL precursors having differing N-alkyl chains (n =
5, 8, and 10) and counteranions (X–
=
–OTf and –NTf2)
(Scheme 3). Synthesis of the disulfide precursors 1–6 was
achieved through the quaternization of u-bromodisulfides
with 1,2-dimethylimidazole, followed by an ion exchange
of Br– with either –OTf or –NTf2. 1,2-Dimethylimidazole
was selected here instead of 1-methylimidazole, to ensure
the stabilization of the NPs was provided solely by the
TFILs 1–6. NPs stabilized by 1-alkyl-3-methylimidazolium
ILs may involve the formation of N-heterocyclic carbenes,
which primarily occur at the C2 position on the imidazo-
lium ring.24–26 Thus, TFILs based on the 1-alkyl-2,3-di-
methylimidazolium moiety were employed in this study to
restrict the formation of carbene stabilizing species. Further-
more, ion exchange of Br– to form disulfides 1–6 prior to
NP synthesis allows for a better control of the properties of
both the TFIL stabilizers and the resulting Au NPs. This
contrasts with the work of Itoh et al.8 as anion exchange
was performed directly on the Au NPs. Their technique led
of an Au–S bond was provided by the BEs of Au (4f(7/2)
=
84.0 eV and 4f(5/2) = 87.7 eV).27,28 The Au:disulfide ratio
was optimal at 1:2, affording small and well-dispersed NPs,
whereas a smaller ratio (1:1) formed large Au aggregates
and a larger ratio (1:4) produced clusters of small Au NPs
that were not monodispersed. This ratio (1:2) was kept con-
stant in all of the subsequent studies.
Size analysis and supporting model
The nature of the disulfide precursor, in terms of n and X–,
was found to influence the size of the Au NPs synthesized
from [Au-CꢀC-t-Bu]4 (Table 1, entries 1–6). These results
showed an increase in the NP size with an increase in the
length of the N-alkyl chain (n) and a decrease in the NP size
with an increase in the molecular volume of the counteranion
Published by NRC Research Press

Luska and Moores
Scheme 3. Synthetic pathway for the preparation of disulfide ionic liquids 1–6 (for n = 5, 8, and 10 and X– = OTf and NTf2).
147
–
–
I2
1. Thiourea, EtOH, ?
SH
n
Br
n
S
n
HO
HO
HO
2. NaOH(aq)
EtOH, rt
2
1. PPh3, THF
2. NBS
1.
, CH CN, 70 °C
3
N
N
S
n
N
N
Br
+
S
2. LiX, H2O, rt
2
n
X-
2
Fig. 1. Transmission electron micrograph of thiolate-stabilized gold
nanoparticles, employing [Au-CꢀC-t-Bu]4 and disulfide 6.
ume of the counteranions employed here are 0.131 and
–
–
0.232 nm3 for OTf and NTf2, respectively.30 Therefore, the
–
larger NTf2 anion would increase a0 and thus decrease the
NP size. A comparison of the TEM data for thiolate-stabilized
–
–
NPs with OTf (Table 1, entries 1–3) and NTf2 (Table 1,
entries 4–6) counteranions showed a consistently smaller
size for the NTf2 species.
–
The relationship between NP size and the TFIL counteran-
ion was investigated already by Janiak and co-workers30–32 in
metal NPs synthesized directly in IL solvents. In their sys-
tem, the relationship is opposite to what we observe, with an
increase in NP diameter when the molecular volume of the
anion was increased. Their results provided evidence that the
NPs were stabilized by a classical electric double layer where
anionic species stabilize the metal surface and thus govern
the size of the NPs.30 For our system, the size variation
trends observed and the XPS measurements are both consis-
tent with a covalent binding of the thiolate to the metal sur-
face (as suggested by Itoh et al.8 and shown in Scheme 2)
and a global arrangement where the IL anion and cation pair
are localized at the periphery of the ligand shell. These re-
sults, and especially the compliance to the Israelachvili
model, suggest that there is a high level of organisation in
the ligand shell resulting from the surfactant nature of the
TFIL stabilizers. This is in accordance to what is expected
from both imidazolium moieties33 through electrostatic inter-
actions and the N-alkyl chains through van der Waals interac-
tions; the later being a similar phenomenon to that observed
in the formation of self-assembled monolayers (SAMs) of
long-chain alkanethiol on Au NPs.34
(X–). The dependence of n and X– on the size of the Au NPs
can be justified by adapting the geometric theory proposed
by Israelachvili29 for the formation of spherical micelles
(Scheme 4). This theory was adapted because of the intrinsic
surfactant nature of the TFILs and their ability to bind
strongly to the Au surface through their thiolate functionality.
For a conventional micelle, (Scheme 4A) the radius (R) of a
spherical micelle is dependent on the properties of the surfac-
tant molecule such that R = 3v/a0, where v is the volume of
the hydrocarbon chain and a0 is the area of the headgroup.
This relationship can be extended to the formation of spheri-
cal NPs stabilized by TFILs 1–6 such that R ∝ v/a0, where R
is now the radius of the structure containing the particle and
the ligand shell, v is the volume of the hydrocarbon chain,
including the thiolate moiety, and a0 is the area of the imida-
zolium headgroup, including both the cation and the anion
(Scheme 4B). According to this relationship, an increase in n
would increase v, thus increase R, and ultimately the NP size.
The TEM data obtained for Au NPs stabilized by thiolate li-
gands 1–6 (Table 1, entries 1–6) showed an increase in NP
size when comparing n = 5, 8, and 10. In terms of the influ-
ence of X–, this relationship predicts that an increase in a0
would decrease the diameter of the NP. The molecular vol-
Influence of the gold precursor
Au NPs synthesized from [Au-CꢀC-t-Bu]4 were compared
23
with NPs prepared employing HAuCl4. [Au-CꢀC-t-Bu]4 is
expected to decompose under reducing conditions to Au(0)
and volatile organic by-products. TEM analysis of the thio-
late-stabilized Au NPs showed well-dispersed NPs for the
syntheses with either precursor, although slightly larger NPs
were obtained from HAuCl4 (Table 1, entries 7–12) com-
pared with those from [Au-CꢀC-t-Bu]4 (Table 1, entries 1–6).
This difference was attributed to the presence of Cl– ions in
the Au precursor, which may exchange with the counteran-
ion of the TFIL stabilizer. According to our proposed
–
–
model (Scheme 3), exchange of either OTf or NTf2 with
the smaller Cl– species would decrease a0 and increase the
size of the resulting Au NPs. It was also observed that the
trend between NP size and the properties of the disulfide
ligand (n and X–) were not as clear for particles synthesized
from HAuCl4. This discrepancy was most pronounced when
Published by NRC Research Press

148
Can. J. Chem. Vol. 90, 2012
Table 1. Influence of the gold and disulfide precursors on the size and size dis-
tribution of thiolate-stabilized gold nanoparticles (Au NPs).
Stabilizing ligand
Au NP size
(nm) (standard
Entry
1
2
3
4
5
6
7
8
Au precursor
[Au-CꢀC-t-Bu]4
Disulfide
n
X–
deviation s)a
1
2
3
4
5
6
1
2
3
4
5
6
5
8
10
5
8
10
5
8
10
5
8
10
–OTf
–OTf
–OTf
–NTf2
–NTf2
–NTf2
–OTf
–OTf
–OTf
–NTf2
–NTf2
–NTf2
2.9( 0.6)
3.2( 0.6)
3.3( 0.6)
2.7( 0.5)
2.9( 0.4)
3.2( 0.6)
3.3( 0.6)
4.2( 0.7)
4.3( 0.7)
3.0( 0.4)
3.0( 0.3)
3.1( 0.5)
HAuCl4
9
10
11
12
Note: Reaction conditions: [Au] = 0.1 mmol, disulfide = 0.2 mmol (2 equiv), NaBH4 =
1.0 mmol (10 equiv), solvent = CH3OH (for HAuCl4), CH3OH–CH2Cl2 (3:2, for
[Au-CꢀC-t-Bu]4).
aDetermined by TEM, measurement of >200 spherical particles.
comparing disulfides 2 (4.2 nm) to 3 (4.3 nm) (Table 1,
entries 8 and 9) and 4 (3.0 nm) to 5 (3.0 nm) (Table 1,
entries 10 and 11) as very little difference in size was ob-
served for these NPs. The lack of correlation within the
HAuCl4 data was again accredited to anion exchange of the
TFIL anion and thus emphasizes the importance of having
well-defined systems in the synthesis of nanomaterials, in-
cluding the use of halide-free metal precursors such as
[Au-CꢀC-t-Bu]4.
Scheme 4. Schematic representation of (A) the size dependence of
micelles on surfactant properties and (B) the size dependence of
gold nanoparticles (Au NPs) on thiolate-functionalized ionic liquids
(TFIL) properties.29
(A) Formation of Spherical Micelles: R = 3v /a0
Headgroup Area (a0)
Radius (R)
Hydrocarbon Volume (v)
Optical properties analysis
Surfactant
The optical properties of the synthesized Au NPs were an-
alyzed using UV–vis spectroscopy. A surface plasmon band
(SPB) was observed for Au NPs stabilized by TFILs 1–6
(lmax(MeOH) = 535–650 nm) and was dependent on the na-
ture of the thiolate employed (Fig. 2). The length of the alkyl
chain was observed to influence the SPB as the longer chain
thiolates, n = 8 and 10 (Fig. 2, curves b, c, e, and f), showed
lmax = 535 nm, whereas Au NPs synthesized from the
shorter chain disulfides, n = 5 (Fig. 2, curves a and d),
caused the lmax to red shift to >535 nm. For TFIL 1 and 4
(n = 5) stabilized NPs, the distance between the particle sur-
face and the IL environment is smaller than in the case of the
longer chain TFIL-stabilized NPs. This shorter distance re-
sulted in the NP perceiving a more polar environment and
thus a globally higher dielectric medium at its surrounding.
The theory predicts that the position of the SPB shifts toward
the lower energy region as the surrounding medium refractive
index increases,1,35 which is consistent with the observed
trend. A shorter chain disulfide (n = 2) was desired to further
test this hypothesis; however, the synthesis of this disulfide
could not be achieved. Aggregation of the NPs in solution
could also be envisaged as the cause of this shift, in which
case a red-shift is expected when the mean distance between
particles decreases;1,36 however, the TEM images obtained
for all NPs are not consistent with significant aggregation in
solution (Supplementary data Figs. S1 and S3). These results
Micelle
(B) Formation of Thiolate Stabilized Au NPs: R a v/a0
X?
+
+
X?
X?
X?
+
+
Headgroup Area (a0)
+
X?
[Au]0
X?
Hydrocarbon Volume (v)
Radius (R)
+
+
X?
X?
[Au]0
+
+
X?
Thiolate Ligand
Thiolate
Stabilized Au NPs
are supporting the idea that TFILs organize around the par-
ticle. Indeed, in the case of the longest alkyl spacers (n = 8
and 10), the respective blue-shift observed proves that the al-
kyl portion of the TFIL resides close to the surface of the
particle, whereas the imidazolium cation and anion are main-
tained at the periphery of the ligand sphere. Moreover, the
results obtained for n = 8 and 10 are virtually identical. This
can be explained by the fact that changes happening far from
the surface will not impact the perceived dielectric medium
of the particle significantly. When the alkyl spacer is short
(n = 5), the dielectric medium perceived by the Au NP is al-
tered by the presence of the imidazolium cation and anion.
Published by NRC Research Press

Luska and Moores
149
Fig. 2. UV–vis spectra of lmax(MeOH) for gold nanoparticles (Au
Conclusions
NPs) synthesized employing (A) HAuCl4 and (B) [Au-CꢀC-t-Bu]4
In conclusion, this report has outlined the synthesis of sta-
ble, well-dispersed Au NPs employing an organometallic Au
precursor [Au-CꢀC-t-Bu]4 and TFIL stabilizers in a molecu-
lar solvent. This halogen-free Au complex allowed for the
recognition of a relationship between the properties of the
Au NPs, in terms of NP size and SPB, and two properties of
the thiolate-stabilizing ligand, namely the length of the N-alkyl
chain and the counteranion. A model, based on Israelachvili
theory, was employed to explain the correlation between the
size of Au NPs and the properties of the thiolate ligands.
This model and XPS data evidenced a high level of organ-
ization inside these NPs where the TFILs interact with the
particle surface through their thiolate functionalities. Func-
tionalized ionic liquids act as surfactants for the synthesis of
metal NPs with controlled properties leading to a novel bottom-
up approach to the design of functional nanomaterials, as
well as models to measure the influence of small size changes
on the properties of NPs. Furthermore, [Au-CꢀC-t-Bu]4 has
been shown to be an effective precursor in the synthesis of
NPs featuring increased compositional purity and opens new
opportunities for gaining an understanding in the role vari-
ous stabilizing ligands play in the formation of Au NPs.
–
as gold precursors stabilized by thiolates (a) n = 5, X– = OTf; (b)
–
–
–
n = 8, X– = OTf; (c) n = 10, X– = OTf; (d) n = 5, X– = NTf2;
(e) n = 8, X– = NTf2; and (f) n = 10, X– = NTf2.
(A)
(b)
–
–
(e)
(d)
(c)
(a)
(f)
400
450
500
550
600
650
700
750
800
Wavelength (nm)
(e)
(f)
(B)
(c)
Experimental section
(b)
General remarks
All syntheses of ILs and NPs were carried out under an
argon atmosphere employing Schlenk techniques. 6-Mercapto-
1-hexanol,37,38 9-mercapto-1-nonanol,37,39,40 11-mercapto-1-
undecanol,37,41,42 bis(6-hydroxyhexyl)disulfide,41 bis(11-
hydroxyundecyl)disulfide,37,41 bis(6-bromohexyl)disulfide,42,43
and [Au-CꢀC-t-Bu]423,44 were prepared following known liter-
ature procedures. Tetrahydrofuran (distillation over Na and
benzophenone) and acetonitrile (dried over 4 Å molecular
sieves) were purified prior to use. All other chemicals and sol-
vents were purchased from commercial sources and used with-
out further purification. Melting points (mp) were determined
on a Gallenkamp melting point apparatus and are uncorrected.
Nuclear magnetic resonance (NMR) spectra were recorded on
a 300 MHz Varian Mercury spectrometer. Mass spectra (MS)
were recorded in positive electrospray mode with an IonSpec
7.0 tesla FTMS (IonSpec Corp., Lake Forest, California).
TEM was performed on a Phillips CM 200 microscope. UV–
vis spectra were recorded on a Jasco V-660 spectrophotometer.
XPS was performed on a VG ESCALAB 3 MKII spectrome-
ter (VG, Thermo Electron Corporation, UK) equipped with an
Mg Ka source.
(a)
(d)
400
450
500
550
600
650
700
750
800
Wavelength (nm)
NaHSO3(aq) and extracted with CH2Cl2 (3 × 50 mL). The
organic phase was washed with 10% NaHSO3(aq) and H2O
and dried over MgSO4. The solvent was removed and the
product was dried in vacuo to yield a white solid. Yield:
1
7.09 g (92%); mp 65–66 °C. H NMR (300 MHz, CDCl3,
ppm) d: 3.61(t, J = 6.2 Hz, 4H), 2.65 (t, J = 7.3 Hz, 4H),
1.64–1.28 (m, 30H). 13C NMR (75.5 MHz, CDCl3, ppm) d:
63.2, 39.4, 33.0, 29.7, 29.6, 29.4, 29.4, 28.7, 25.9. MS (ESI+)
m/z: 351.2386 (M+ = [C18H39O2S2]+ requires 351.2385).
Bis(9-bromononyl)disulfide
Bis(9-hydroxynonyl)disulfide (3.55 g, 10.1 mmol) and
PPh3 (5.56 g, 21.2 mmol) were dissolved in 100 mL of dis-
tilled THF under an argon atmosphere. NBS (4.50 g,
25.3 mmol) was added in portions over 30 min. The mixture
was stirred at rt for 1 h then heated to 50 °C for 18 h. The
solvent volume was reduced, EtO2 was added, and the mix-
ture was cooled for 30 min to cause the precipitation of white
solids. Upon filtration and solvent evaporation, the crude
mixture was purified on silica employing EtOAc–hexanes.
Bis(9-bromononyl)disulfide was obtained as a colourless
Synthesis of TFILs
The synthesis of disulfide ILs 1–6 followed a similar path-
way to that reported by Itoh et al. (Scheme 1).8 The synthesis
and characterization data for all novel compounds are re-
ported.
Bis(9-hydroxynonyl)disulfide
9-Mercapto-1-nonanol (7.81 g, 58.2 mmol) was dissolved
in 12 mL MeOH and titrated with 0.5 mol/L methanolic io-
dine until the reaction turned from colourless to a persistent
yellow colour. The mixture was allowed to stir at room tem-
perature (rt) for 1 h. The reaction was quenched with 10%
1
liquid. Yield: 3.56 g (74%). H NMR (300 MHz, CDCl3,
ppm) d: 3.38 (t, J = 6.8 Hz, 4H), 2.65 (t, J = 7.4 Hz, 4H),
1.82 (pentet, J = 7.4 Hz, 4H), 1.64 (pentet, J = 7.1 Hz, 4H),
Published by NRC Research Press

150
Can. J. Chem. Vol. 90, 2012
1.46–1.22 (m, 20H). 13C NMR (75.5 MHz, CDCl3, ppm) d:
(pentet, J = 7.4 Hz, 4H), 1.68 (pentet, J = 7.1 Hz, 4H),
1.54–1.30 (m, 8H). 13C NMR (75.5 MHz, (CD3)2CO, ppm)
d: 145.5, 123.3, 121.8, 120.9 (q, JCF = 321.6 Hz), 49.1,
38.8, 35.5, 30.3, 29.5, 28.5, 26.4, 9.7. MS (ESI+) m/z:
212.1342 (M2+ = [C22H40N4S2]2+ requires 212.1345).
39.3, 34.2, 33.0, 29.7, 29.3, 29.3, 28.9, 28.6, 28.3.
Bis(11-bromoundecyl)disulfide
Bis(11-bromoundecyl)disulfide was obtained as a white
solid. Yield: 2.93 g (52%). 1H NMR (300 MHz, CDCl3,
ppm) d: 3.39 (t, J = 6.9 Hz, 4H), 2.66 (t, J = 7.5 Hz, 4H),
1.83 (pentet, J = 7.2 Hz, 4H), 1.65 (pentet, J = 7.2 Hz, 4H),
1.45–1.21 (m, 28H). 13C NMR (75.5 MHz, CDCl3, ppm) d:
39.4, 34.3, 33.0, 29.7, 29.7, 29.6, 29.4, 29.4, 29.0, 28.7,
28.4.
Disulfide 5
The product was obtained as an amber oil. Yield: 3.90 g
1
(79%). H NMR (300 MHz, (CD3)2CO, ppm) d: 7.62 (d, J =
2.1 Hz, 2H), 7.58 (d, J = 2.1 Hz, 2H), 4.27 (t, J = 7.5 Hz,
4H), 3.93 (s, 6H), 2.77 (s, 6H), 2.70 (t, J = 7.2 Hz, 4H), 1.83
(pentet, J = 7.4 Hz, 4H), 1.66 (pentet, J = 7.2 Hz, 4H),
1.50–1.24 (m, 20H). 13C NMR (75.5 MHz, (CD3)2CO, ppm)
d: 145.6, 123.4, 121.9, 121.0 (q, JCF = 321.4 Hz), 49.1, 39.2,
35.5, 30.5, 30.0, 29.8, 29.8, 29.7, 29.1, 26.9, 9.8. MS (ESI+)
m/z: 254.1811 (M2+ = [C28H52N4S2]2+ requires 254.1813).
Disulfide 1
1,2-Dimethylimidazole (1.37 g, 14.3 mmol) was dissolved
in 10 mL of MeCN. Bis(6-bromohexyl)disulfide (2.74 g,
6.99 mmol) was added and the mixture was stirred at 70 °C
for 48 h. The solvent was removed in vacuo and the residual
solid was washed with Et2O (3 × 20 mL). Lithium trifluoro-
methanesulfonate (2.23 g, 14.3 mmol) was added in small
portions to a solution of the crude product in 15 mL of
H2O. The mixture was stirred at rt for 1 h and 25 mL of
CH2Cl2 was added. The organic phase was washed with
H2O and dried over MgSO4. The solvent was removed and
the product was dried in vacuo to yield a white solid. Yield:
3.63 g (72%); mp 104–106 °C. 1H NMR (300 MHz, (CD3)2CO,
ppm) d: 7.65 (d, J = 2.0 Hz, 2H), 7.60 (d, J = 2.0 Hz,
2H), 4.28 (t, J = 7.5 Hz, 4H), 3.93 (s, 6H), 2.77 (s, 6H),
2.70 (t, J = 7.5 Hz, 4H), 1.88 (pentet, J = 7.5 Hz, 4H),
1.68 (pentet, J = 7.5 Hz, 4H), 1.52–1.28 (m, 8H). 13C NMR
Disulfide 6
The product was obtained as a pale yellow oil. Yield:
1
3.39 g (58%). H NMR (300 MHz, (CD3)2CO, ppm) d: 7.62
(d, J = 2.1 Hz, 2H), 7.58 (d, J = 2.1 Hz, 2H), 4.27 (t, J =
7.5 Hz, 4H), 3.93 (s, 6H), 2.77 (s, 6H), 2.71 (t, J = 7.5 Hz,
4H), 1.88 (pentet, J = 7.2 Hz, 4H), 1.67 (pentet, J = 7.2 Hz,
4H), 1.45–1.25 (m, 28H). 13C NMR (75.5 MHz, (CD3)2CO,
ppm) d: 145.6, 123.4, 121.9, 121.0 (q, JCF = 321.6 Hz), 49.1,
39.3, 35.5, 30.5, 30.2, 30.2, 30.2, 30.2, 29.8, 29.8, 29.1, 26.9,
9.8. MS (ESI+) m/z: 282.2124 (M2+ = [C32H60N4S2]2+ re-
quires 282.2128).
(75.5 MHz, (CD3)2CO, ppm) d: 145.6, 123.4, 122.3 (q, JCF
=
Synthesis of gold nanoparticles
322.1 Hz), 122.0, 49.0, 38.9, 35.5, 30.4, 29.6, 28.5, 26.4,
9.8. MS (ESI+) m/z: 212.1342 (M2+ = [C22H40N4S2]2+ re-
quires 212.1344).
From [Au-CꢀC-t-Bu]4
[Au-CꢀC-t-Bu]4 (27 mg, 0.025 mmol) was dissolved in
10 mL of degassed CH2Cl2 and the disulfide IL (0.20 mmol)
was dissolved in 10 mL of degassed MeOH. Upon addition
of the disulfide solution, the mixture was stirred for 30 min
to form a light yellow solution. NaBH4 (38 mg, 1.0 mmol)
in 5 mL MeOH was added dropwise and stirred for 1 h. The
precipitate was isolated via centrifugation (7500 rpm for
10 min), washed with acetone–pentane (2:1) (3 × 10 mL),
and dried in vacuo. The crude mixture was employed for
UV–vis and TEM analyses, while purified NPs were used
for XPS.
Disulfide 2
The product was obtained as an amber oil. Yield: 3.19 g
1
(80%). H NMR (300 MHz, (CD3)2CO, ppm) d: 7.65 (d, J =
2.0 Hz, 2H), 7.60 (d, J = 2.1 Hz, 2H), 4.27 (t, J = 7.5 Hz,
4H), 3.92 (s, 6H), 2.76 (s, 6H), 2.70 (t, J = 7.5 Hz, 4H), 1.86
(pentet, J = 7.5 Hz, 4H), 1.66 (pentet, J = 7.5 Hz, 4H),
1.48–1.25 (m, 20H). 13C NMR (75.5 MHz, (CD3)2CO, ppm)
d: 145.6, 123.4, 122.3 (q, JCF = 322.1 Hz), 121.9, 49.0, 39.3,
35.5, 30.5, 30.0, 29.8, 29.8, 29.7, 29.0, 26.8, 9.8. MS (ESI+)
m/z: 254.1811 (M2+ = [C28H52N4S2]2+ requires 254.1809).
From HAuCl4
Disulfide 3
HAuCl4·3H2O (34 mg, 0.10 mmol) and the disulfide IL
(0.20 mmol) were separately dissolved in 10 mL of degassed
MeOH. Upon addition of the disulfide, the mixture was
stirred for 30 min to form a light yellow solution. NaBH4
(38 mg, 1.0 mmol) in 5 mL MeOH was added dropwise and
stirred for 1 h. The precipitate was isolated via centrifugation
(7500 rpm for 10 min), washed with acetone–pentane (2:1)
(3 × 10 mL), and dried in vacuo. The crude mixture was em-
ployed for UV–vis and TEM analyses, while purified NPs
were used for XPS.
The product was obtained as an amber oil. Yield: 2.20 g
1
(79%). H NMR (300 MHz, (CD3)2CO, ppm) d: 7.64 (d, J =
2.0 Hz, 2H), 7.61 (d, J = 2.0 Hz, 2H), 4.28 (t, J = 7.5 Hz,
4H), 3.93 (s, 6H), 2.77 (s, 6H), 2.71 (t, J = 7.5 Hz, 4H), 1.87
(pentet, J = 7.2 Hz, 4H), 1.67 (pentet, J = 7.2 Hz, 4H),
1.45–1.25 (m, 28H). 13C NMR (75.5 MHz, (CD3)2CO, ppm)
d: 145.6, 123.4, 122.3 (q, JCF = 322.1 Hz), 121.9, 49.1, 39.3,
35.5, 30.5, 30.2, 30.2, 30.2, 30.2, 29.8, 29.8, 29.1, 26.9, 9.8.
MS (ESI+) m/z: 282.2124 (M2+ = [C32H60N4S2]2+ requires
282.2128).
Transmission electron microscopy
Disulfide 4
TEM of Au NPs was obtained on a Phillips CM 200 mi-
croscope operating at an accelerating voltage of 200 kV with
a point resolution of 0.24 nm. Sample preparation included
dilution of 10 drops of the Au NP solution in 20 drops of
The product was obtained as an amber oil. Yield: 2.91 g
1
(90%). H NMR (300 MHz, (CD3)2CO, ppm) d: 7.60 (d, J =
2.1 Hz, 2H), 7.56 (d, J = 2.1 Hz, 2H), 4.27 (t, J = 7.5 Hz,
4H), 3.92 (s, 6H), 2.76 (s, 6H), 2.70 (t, J = 7.2 Hz, 4H), 1.89
Published by NRC Research Press

Luska and Moores
151
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Spectra were recorded on a Jasco V-660 spectrophotome-
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Supplementary data
Supplementary data are available with the article through
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Acknowledgments
We acknowledge the Natural Sciences and Engineering
Research Council of Canada (NSERC), the Canada Founda-
tion for Innovation (CFI), the Fonds de recherche sur la na-
ture et les technologies (FQRNT), the Canada Research
Chairs, the Centre for Green Chemistry and Catalysis
(CGCC), and McGill University for financial support. We
also thank Dr. A. LeSimple (McGill University) for HRMS
analysis and Dr. S. Poulin (École Polytechnique de Montréal)
for XPS measurements. Drs. R.B. Lennox and I.S. Butler are
acknowledged for fruitful comments.
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