Alkynylisocyanide gold mesogens as precursors of gold nanoparticles

Article abstract of DOI:10.1021/ic201210p

Gold nanoparticles (Au NPs) have been synthesized using simple thermolysis, whether from the mesophase or from toluene solutions, of mesogenic alkynyl-isocyanide gold complexes [Au(C=C-C₆H₄-C _mH_2m+1)(C=N-C₆H₄-O-C _nH_2n+1)]. The thermal decomposition from the mesophase is much slower than from solution and produces a more heterogeneous size distribution of the nanoparticles. Working in toluene solution, the size of nanoparticles can be modulated from ～2 to ～20 nm by tuning the chain lengths of the ligands present in the precursor. Different experimental conditions have been analyzed to reveal the processes governing the formation of the gold nanoparticles. Experiments on the effect of adding ligands or bubbling oxygen support that the thermal decomposition is a bimolecular process that starts by decoordination of the isocyanide ligand, producing an oxidative coupling of the akynyl group to [R-C=C-C=C-R] and reduction of gold(I) to gold(0) as nanoparticles. The nanoparticles obtained behave as a catalyst in the oxidation of isocyanide (CNR) to isocyanate (OCNR), which in turn cooperates to catalyze the decomposition.

Full text of DOI:10.1021/ic201210p

ARTICLE
pubs.acs.org/IC
Alkynylisocyanide Gold Mesogens as Precursors of Gold Nanoparticles
Rubꢀen Chico,† Eva Castillejos,‡ Philippe Serp,‡ Silverio Coco,*,† and Pablo Espinet*,†
†IU CINQUIMA/Química Inorgꢀanica, Facultad de Ciencias, Universidad de Valladolid, 47071 Valladolid, Castilla y Leꢀon, Spain
‡Laboratoire de Chimie de Coordination, UPR CNRS 8241 composante ENSIACET, Toulouse University, 4 Allꢀee Monso, B. P. 44362,
Toulouse Cedex 4, France
ABSTRACT: Gold nanoparticles (Au NPs) have been synthe-
sized using simple thermolysis, whether from the mesophase or
from toluene solutions, of mesogenic alkynylꢀisocyanide gold
complexes [Au(CtCꢀC6H4ꢀCmH2m+1)(CtNꢀC6H4ꢀOꢀ
CnH2n+1)]. The thermal decomposition from the mesophase is
much slower than from solution and produces a more hetero-
geneous size distribution of the nanoparticles. Working in
toluene solution, the size of nanoparticles can be modulated
from ∼2 to ∼20 nm by tuning the chain lengths of the ligands
present in the precursor. Different experimental conditions have been analyzed to reveal the processes governing the formation of
the gold nanoparticles. Experiments on the effect of adding ligands or bubbling oxygen support that the thermal decomposition is a
bimolecular process that starts by decoordination of the isocyanide ligand, producing an oxidative coupling of the akynyl group to
[RꢀCtCꢀCtCꢀR] and reduction of gold(I) to gold(0) as nanoparticles. The nanoparticles obtained behave as a catalyst in the
oxidation of isocyanide (CNR) to isocyanate (OCNR), which in turn cooperates to catalyze the decomposition.
’ INTRODUCTION
Au NPs were stabilized by coordination of the isocyanide ligand,
but no deeper studies were carried out at that moment on the
mechanism of formation of the nanoparticles and the possible
role of the alkynyl ligands in their stabilization.
Metal nanoparticles (MNPs) are of great interest in modern
materials chemistry due to their unique physical and chemical
properties.1,2 MNPs find applications in nanoelectronics,3 data
storage,4 catalysis,5 and other fields. Chemical reduction, thermal
decomposition, metal vapor deposition, photolysis, sonochem-
ical decomposition, and electrochemical synthesis have been
used for the synthesis of MNPs.6 The formation of MNPs
requires the presence of stabilizing ligands to control the particle
size and prevent massive agglomeration.7 To this end, stabilizers
with long alkyl or polymer chains are usually employed, which
attach to the MNP surface, hinder the access of the reactants
to the surface and modulate the structure and properties of
the MNP.
Gold nanoparticles (Au NPs) are probably the most studied
ones. Recent reviews show that most often they are stabilized by
organothiols. There are, however, reports on Au NPs stabilized
by other ligands such as isocyanides,8 aryl diazonium salts,9 aryl
iodoniums,10 thiocyanates,11 and alkynes.12
Two of these ligand types, alkynyls and isocyanides, happen
to make a part of the rod-like gold alkynyl complexes
[Au(CtCꢀR)(CtNꢀR0)] that have previously received atten-
tion as materials exhibiting liquid crystalline behavior13ꢀ17 or
luminescence,18ꢀ20 as building blocks for the synthesis of
nanoscale materials, or as materials for chemical vapor deposition
of gold.21,22 Very recently, we reported the synthesis and
selective deposition of Au NPs inside carbon nanotubes through
thermal decomposition of liquid crystalline complexes of the type
[Au(CtCꢀC6H4ꢀCmH2m+1)(CtNꢀC6H4ꢀOꢀCnH2n+1)], in
toluene at 110 °C. These materials are efficient catalysts for
selective CO oxidation.23 IR spectroscopy suggested that these
Although the shape-controlled synthesis of Au NPs has been
extensively studied,24 its mechanism of formation has received
little attention and remains partially unclear.1c,25ꢀ27 This is
particularly true in the case of Au NPs stabilized by less common
ligands such as isocyanides. Therefore, we decided to study in
more detail the thermal decomposition of our systems. Here, we
report a facile synthesis of gold nanoparticles by thermal
decomposition of mesogenic alkynylisocyanide gold complexes,
either in the mesophase or in solution. On the basis of some
experimental evidence, we suggest a bimolecular decomposition
pathway of the initial Au(I) complexes to Au NPs.
’ RESULTS AND DISCUSSION
Synthesis and Characterization of Precursors. Complexes
[Au(CtCꢀC6H4ꢀCmH2m+1)(CtNꢀC6H4ꢀOꢀCnH2n+1)]
were prepared as air-stable white solids at room temperature,
through the reaction of isocyanides with alkynylgold(I)
(Scheme 1), as reported for similar systems.14 C, H, N analyses;
yields; and relevant IR and NMR data for the complexes are given
in the experimental part. Their IR spectra show systematically
one ν(CtN) absorption in the range 2213ꢀ2224 cmꢀ1. As
reported previously for similar systems, the expected ν(CtC)
absorption is not observed.14 The 1H NMR spectra of all of the
Received: June 6, 2011
Published: August 04, 2011
r
2011 American Chemical Society
8654
dx.doi.org/10.1021/ic201210p Inorg. Chem. 2011, 50, 8654–8662
|

Inorganic Chemistry
ARTICLE
Scheme 1. Synthesis of AlkynylꢀIsocyanide Gold
Complexes
Figure 1. Polarized optical microscopic texture (ꢁ100) of the smectic
Table 1. Optical, Thermal, and Thermodynamic Data of
Complexes [Au(CtCꢀC6H4ꢀCmH2m+1)-
(CtNꢀC6H4ꢀOꢀCnH2n+1)]
A
mesophase observed for [Au(CtCꢀC6H4ꢀC14H29)(CtNꢀ
C6H4ꢀOꢀC2H5)] on heating at 150 °C.
Tb
ΔH
m
n
transitiona
(°C)
(kJ/mol)
2
2
2
CfI
CfC2
C2fC3
C3fC4
C4fI
183c (dec)
91.7
8
12.0
2.3
105.2
115.6
1.3
172.7 (dec)
25.9
13.2
4.2
2
14
CfC2
C2fC3
C3fC4
C4fC5
C5fSmA
SmAfI
CfC2
C2fSmA
SmAfI
CfC1
C1fC2
C2fSmA
SmAfI
CfC2
C2fC3
C3fC4
C4fSmA
SmAfI
CfC2
46.6
11.0
2.0
60.2
113.0
5.3
140.8
159c (dec)
15.0
d
8
14
2
36.4
10.2
21.1
1.7
145.6
150.2 (dec)
79.4
14
19.9
3.0
Figure 2. Polarized optical microscopic textures (ꢁ100) observed for
[H29C14C6H4CCtCꢀCtCC6H4C14H29]. (a) Schlieren texture of the
N phase, at 74 °C on cooling from the isotropic liquid. (b) Fan-shaped
texture of the SmA phase at 70 °C, on cooling from the isotropic liquid.
(c) Broken fan-shaped texture of the SmC phase at 58 °C formed on
cooling from the fan-shaped focal-conic area of the SmA phase.
95.1
141.9
32.8
d
160 (dec)
23.6
14
14
8
9.7
81.3
4.4
96.7
8.5
139.9
156c (dec)
17.4
d
Coordination to gold enhances the intermolecular interactions,
compared to the nonmesomorphic free ligands, giving rise to
mesomorphic gold complexes. They display smectic A (SmA)
mesophases characterized by typical homeotropic textures, re-
organizing to the fan-shaped texture at temperatures close to the
clearing point (Figure 1). The compounds with the shortest or
the longest chains (m = 2, n = 2 and 8, and m = n = 14) are not
mesomorphic. Several complexes show one or more crystal-to-
crystal transitions before melting, and all of them undergo
decomposition to a gold mirror upon reaching the clearing point.
It is interesting to note that, at a heating rate of 10 °C minꢀ1, the
decomposition temperature of the complex decreases as the total
length of its two ligands (Cm + Cn) increases.
14
41.1
1.9
C2fC3
C3fC4
C4fI
61.9
30.5
1.4
126.9
135.2
23.3
a C = crystal; Sm = smectic; I = isotropic liquid. b Data referred to the first
DSC cycle. The transition temperatures are given as peak onsets.
c Optical microscopy data. d Decomposition precludes measurement.
complexes are very similar and show, as expected, four reso-
nances in the range 6.9ꢀ7.5 ppm (two AA0XX0 spin systems) for
the aryl protons. In addition, the first methylene group of the
alkoxy and alkyl chains is observed as a pseudotriplet (quartet for
the ethoxy group) at ca. 4.0 and 2.5 ppm, respectively. The
remaining hydrogen chains appear in the range 0.8ꢀ1.8 ppm.
Mesomorphic Behavior of the Precursors. The thermotro-
pic behavior of the complexes is summarized in Table 1.
The diacetylene with C14, H29C14C6H4CCtCꢀCtCC6H4-
C14H29, which had not been reported before, is a white solid that
displays liquid crystal behavior upon heating, showing smectic C,
smectic A, and nematic mesophases (see Experimental Section
for details). The N mesophase displays a Schlieren texture
8655
dx.doi.org/10.1021/ic201210p |Inorg. Chem. 2011, 50, 8654–8662

Inorganic Chemistry
ARTICLE
Table 2. ParticleSize(Diameterinnm) ofAuNPsObtainedfrom
[Au(CtCꢀC6H4ꢀCmH2m+1)(CtNꢀC6H4ꢀOꢀCnH2n+1)]
(m = 2, 8, 14; n = 2, 8, 14) after the Indicated Time at 110 °C in
Toluene Solution, in the Air
Table 3. Particle Size (Diameter in nm) of Au NPs Obtained
by Thermal Decomposition of [Au(CtCꢀC6H4ꢀC14H29)-
(CtNꢀC6H4ꢀOꢀCnH2n+1)] in Toluene Solution, at
110°C, in the Air after Different Times
entry
m
n
2 h heating
14 h heating
time (h)
n = 2
n = 14
1
2
3
4
5
6
2
2
no decomposition
2.4 ( 0.1
gold mirror
gold mirror
gold mirror
gold mirror
18.7 ( 0.5
20.9 ( 0.4
2
7.8 ( 0.2
13.6 ( 0.2
16.6 ( 0.3
18.7 ( 0.5
8.6 ( 0.2
13.4 ( 0.2
15.9 ( 0.2
20.9 ( 0.4
2
8
5
2
14
2
2.2 ( 0.1
8
8
3.3 ( 0.1
14
14
14
2
7.8 ( 0.2
14
8.6 ( 0.2
showing singularities with two and four associated brushes
(Figure 2a). The SmA mesophase was identified in optical
microscopy by its focal-conic fan texture produced on cooling
from the nematic mesophase (Figure 2b). The SmC mesophase
shows the typical broken fan-shaped texture on cooling from the
a SmA phase (Figure 2c).
Thermal Decomposition Studies. The gold complexes re-
ported here, most of them giving rise to mesophases and to
isotropic liquids at moderate temperatures, have in common with
the typical stabilizers of NPs that they contain long alkyl or alkoxy
chains. Thus, the generation of gold nanoparticles from these
complexes in solution, in the absence of added external stabi-
lizers, was studied. The thermolysis of the gold compounds was
carried out through heating toluene solutions of [Au(Ct
CꢀC6H4ꢀCmH2m+1)(CtNꢀC6H4ꢀOꢀCnH2n+1)] (m = 2,
8, 14; n = 2, 8, 14) in the air at 110 °C for 2 and 14 h. The
resulting solids were analyzed by TEM, and the results are
collected in Table 2. It seems that the characteristics of
the complexes and the nanoparticles are more influenced by
the length of the alkynyl chain than by the length of the
isocyanide chain: Shorter alkynyls lead to smaller nanoparti-
cles at shorter times and produce gold mirrors at longer
times; long alkynyls produce larger nanoparticles at shorter
times, which grow in size at longer times but resist better the
formation of gold mirrors. It is interesting to note that the rate
of decomposition of the complexes under these conditions is
low (as seen by IR monitoring of some of these decomposi-
tions, see later), so a high percentage of the starting complex is
still unaltered after 14 h under decomposition conditions.
In other words, there is a source (the starting Au(I) complex)
of new Au(0) atoms available throughout the monitoring of
the decomposition process.
Size and Morphology of the Au NPs. The decomposition
produces predominantly spherical Au NPs, although triangular
or hexagonal shapes are occasionally observed. In general,
increasing the heating time from 2 to 14 h produces progressive
growth in size of the nanoparticles, and eventually the formation
of gold mirrors. The complexes [Au(CtCꢀC6H4ꢀC14H29)-
(CtNꢀC6H4ꢀOꢀCnH2n+1)], with the longest alkynyl chain
(m = 14), give more stable Au NPs, of essentially identical size for
the two isocyanide chain lengths, and allow for 14 h Au NPs
monitoring. Table 3 and Figure 3 show the progressive and
steady increase in size of the nanoparticles with heating time.
On the other hand, TEM monitoring of [Au(CtCꢀC6H4ꢀ
C14H29)(CtNꢀC6H4ꢀOꢀC2H5)] after 2, 5, 8, and 14 h of
heating affords histograms where the mean size of the nanoparticle
increases with time, while the smaller sizes are progressively lost
(Figure 4). This suggests that the growth of the nanoparticles is
Figure 3. Nanoparticle size (diameter, nm) obtained from [Au(Ct
CꢀC6H4ꢀC14H29)(CtNꢀC6H4ꢀOꢀCnH2n+1)] (n = 2, 14) as a
function of heating time.
occurring not only by Ostwald ripening at the expense of redis-
solving the smaller particles but also by capturing the proto-
nanoparticles that are continuously being formed by decomposi-
tion of the Au(I) precursor.28,29 In other words, nucleation seems
to be negligible or moderate during this growing process.
To the best of our knowledge, there is no previous report of
formation of metal nanoparticles in a thermotropic mesophase
that is itself generated by the molecular precursor of the metal.
Thus, especially in order to check for possible morphological
modifications influenced by the orientation of the molecules in the
precursor phase, we studied additionally the thermal decomposi-
tion of [Au(CtCꢀC6H4ꢀC14H29)(CtNꢀC6H4ꢀOꢀC2H5)]
at 155 °C for 14 h. At thistemperature, the material displays a SmA
mesophase. The gold nanoparticles obtained from the mesophase
(Figure 5) have a smaller average diameter(12.6 ( 0.6) than those
obtained from toluene solutions (18.7 ( 0.5). Moreover, they are
more polydisperse and, in spite of the higher decomposition
temperature used (155 °C in LC mesophase vs 110 °C in toluene
solution), the rate of decomposition is smaller. It is worth noting
that often the mesophases of metallomesogens are viscous, asis the
case here. Clearly, the higher polydispersity of the NPs produced
from the mesophase must arise from the negative effect of the high
viscosity on diffusion, thus reducing the rate of Ostwald ripening.
Depending on the mechanism of decomposition of the precursor
molecules, the reduction of mobility caused by viscosity could also,
as discussed later, cause slower decomposition rates in the
mesophase compared to solution.
Studies of the Thermal Decomposition of [Au(CtCꢀC6H4ꢀ
C14H29)(CtNꢀC6H4ꢀOꢀC2H5)]. Gold catalyzed oxidative CꢀC
couplings occurring in dimerizations and other organic synth-
eses mediated by gold complexes30ꢀ34 are well documented to
8656
dx.doi.org/10.1021/ic201210p |Inorg. Chem. 2011, 50, 8654–8662

Inorganic Chemistry
ARTICLE
Figure 4. TEM pictures and histograms of NP size distribution obtained by thermal decomposition of [Au(CtCꢀC6H4ꢀC14H29)-
(CtNꢀC6H4ꢀOꢀC2H5)] after (a) 2, (b) 5, (c) 8, and (d) 14 h of reaction.
occur on Au(III) intermediates and require the use of strong
oxidants such as Selectfluor or PhI(OAc)2 in order to produce
these Au(III) intermediates. Obviously, these are not the condi-
tions under which we observe alkynyl dimerization, and a different
mechanism should operate. The species clearly observed in our
studies of the thermal decomposition of the alkynyl isocyanide
gold(I) complexes are Au(0), eitherin the form of nanoparticlesor
as a mirror; the remaining initial isocyanide; and the dimer of the
alkynyl radical, either free or coordinated to the nanoparticles
(Scheme 2). The homocoupling product [H29C14ꢀC6H4ꢀ
CtCꢀCtCꢀC6H4ꢀC14H29] was identified by comparison
with an independently prepared authentic sample.
To gain further insight into the process, thermal decompositions
of [Au(CtCꢀC6H4ꢀC14H29)(CtNꢀC6H4ꢀOꢀC2H5)] in
toluene solution were monitored by IR spectroscopy under differ-
ent conditions (Figure 6). Interesting observations were made,
which are discussed below by blocks in order to facilitate the
conclusions.
1. In the absence of any additive (Figure 6, left), the color of
the toluene solution changed from yellow to red as the sample
was heated. Successive IR spectra of the reaction mixture in
toluene show an intense ν(CtN) absorption corresponding to
the remaining gold precursor (2205 cmꢀ1), and a second
ν(CtN) absorption at 2128 cmꢀ1, progressively increasing in
8657
dx.doi.org/10.1021/ic201210p |Inorg. Chem. 2011, 50, 8654–8662

Inorganic Chemistry
ARTICLE
Figure 5. TEM pictures and histogram with size distribution of gold NPs obtained by decomposition of [Au(CtCꢀC6H4ꢀC14H29)-
(CtNꢀC6H4ꢀOꢀC2H5)] by heating for 14 h in the liquid crystal state at 155 °C.
Scheme 2. Stoichiometry of the Thermal Decomposition
intensity, corresponding to free isocyanide. After 14 h, the IR
spectrum of the nanoparticles extracted in hexane (where the
gold precursor is insoluble) shows, in addition to the free
isocyanide band at 2128 cmꢀ1, a weak ν(CtN) absorption at
2195 cmꢀ1 (Figure 6, left, spectrum labeled as 14 h (hexane)).
This weak absorption was not observable in the toluene solution
because it was overlapped by the strong absorption of the
precursor at 2205 cmꢀ1 and has been assigned to p-alkoxyphenyl
isocyanide bonded to Au NPs.35 These observations suggest that
part of the isocyanide released upon decomposition of the
precursor gold compound is involved in the stabilization of the
Au NP.8
Figure 6. Left: IR monitoring of the decomposition of [Au(Ct
CꢀC6H4ꢀC14H29)(CtNꢀC6H4ꢀOꢀC2H5)] in toluene, as a func-
tion of heating time: 2, 5, 8, and 14 h. Down, in green, spectrum of a
sample heated for 14 h and extracted in hexane, where the remaining
precursor is insoluble. Right: IR monitoring of the decomposition of
[Au(CtCꢀC6H4ꢀC14H29)(CtNꢀC6H4ꢀOꢀC2H5)] with [H29C14ꢀ
C6H4ꢀCtCꢀCtCꢀC6H4ꢀC14H29] as additive (1:5), dissolved in
toluene, as a function of heating time (2, 5, 8, and 14 h).
1
The IR assignments were confirmed and completed by H
NMR in CDCl3 on samples obtained evaporating to dryness the
toluene solutions and dissolving the dry residues in CDCl3. The
1H NMR spectrum of the material obtained after heating
[Au(CtCꢀC6H4ꢀC14H29)(CtNꢀC6H4ꢀOꢀC2H5)] for 14 h
confirms the presence of an unaltered gold precursor, and also
the presence of the bis-alkyne homocoupling product [H29C14ꢀ
C6H4ꢀCtCꢀCtCꢀC6H4ꢀC14H29], which had not been
observed in the IR spectrum.36 This assignment was made
comparing its 1H NMR spectrum with that of an original sample
of [H29C14ꢀC6H4ꢀCtCꢀCtCꢀC6H4ꢀC14H29], prepared
independently.
bonding energy of 0.67 eV (15.45 kcal molꢀ1) for acetylene
bonded to an Au19 nanoparticle.39
2. Heating for very long times (up to 64 h) produces
aggregation of the Au NPs, leading to gold mirrors. However,
aggregation is not complete, and some groups of nanoparticles
can still be observed (Figure 7).
After 30 h of heating, the IR spectra show small amounts of
free isocyanide, the disappearance of the precursor complex, a
weak ν(CtN) absorption at 2195 cmꢀ1, which is characteristic
of p-alkoxyphenyl isocyanidesꢀb1onded to gold nanoparticles,35
and a strong band at 2275 cm (Figure 8). The appearance of
this strong band at 2275 cmꢀ1 as that of free isocyanide
disappears suggests oxidation of the isocyanide to the corre-
sponding isocyanate [C2H5ꢀOꢀC6H4ꢀNdCdO], which was
fully identified by mass spectroscopy [MS (CI, methane) m/z
(relative intensity, %): 164 ([M + H]+, 100); calcd. for [M + H]+:
164.07]. Once this characteristic band had been identified, the
presence of isocyanate could be noted also in Figure 6 (left), at
least at the late stages of the reaction. Both the oxidation of RNC
Evaporation of the reactions and extraction in hexane of the
dry residues extracted only the nanoparticles and the homo-
coupling product. So the unaltered remains of starting materi-
als were filtered off, and evaporation of the hexane extracts
afforded purified materials containing Au NPs. Again, these
purified materials did not show CtC stretching bands
associated with the alkyne group in the IR spectra (neither
in solution nor in the solid state), but the presence of
1
bis-alkynes was confirmed by H NMR, which also showed
bands associated with isocyanide. The absence of CtC bands
has been reported to occur for alkynyl groups bonded to
nanoparticles.37,38 In this regard, DFT calculations predict a
8658
dx.doi.org/10.1021/ic201210p |Inorg. Chem. 2011, 50, 8654–8662

Inorganic Chemistry
ARTICLE
Figure 7. TEM pictures and histograms with size distribution of Au NPs obtained through thermolysis of [Au(CtCꢀC6H4ꢀC14H29)(CtNꢀ
C6H4ꢀOꢀC2H5)] after (a) 30 and (b) 64 h of heating.
decomposition process (Figure 6, right). Thus, after 2 h of
heating, the IR spectrum of the crude reaction displays three
absorption bands, at 2128, 2145, and 2205 cmꢀ1, corresponding
respectively to ν(CtN) (free isocyanide), ν(CtC) (free dia-
cetylene), and ν(CtN) from the remaining gold precursor. The
amount of free isocyanide formed after 2 h is larger than observed
in the experiment without added diacetylene; moreover, the
ν(CtN) band of the precursor is completely lost after 14 h of
heating, that is, at a much faster rate than in the experiment
carried out in the absence of added bis-alkyne; this allows for the
additional observation of the band at 2216 cmꢀ1 of the bis-alkyne
and the ν(CtN) absorption at 2195 cmꢀ1 of isocyanide bonded
to Au NP. An additional observation that turns out to be
interesting is the appearance, already at early stages of the
reaction, of the band at 2275 cmꢀ1, revealing the presence of
isocyanate OCNR (see later for details).
4. In contrast, no decomposition is observed upon heating for
Figure 8. IR spectra (compensated toluene) of [Au(CtCꢀC6H4ꢀ
14 h [Au(CtCꢀC6H4ꢀC14H29)(CtNꢀC6H4ꢀOꢀC2H5)]
in toluene in the presence of added [CtNꢀC6H4ꢀOꢀC2H5]
(1:10). The fact that added [CtNꢀC6H4ꢀOꢀC2H5] blocks
so efficiently the decomposition process suggests that ligand
dissociation is required for the decomposition mechanism.
Associated with this, since free isocyanide is a decomposition
product, its progressive formation should have a detrimental
effect on the rate of decomposition as the reaction progresses,
although this may be counterbalanced by the oxidation effect
discussed in entry 5.
5. When the decomposition is carried out under slow O2
bubbling through the solution, a faster decomposition is ob-
served, as shown in Figure 9 where a direct comparison of the
ratio of the IR bands can be easily made. The band of free iso-
cyanide at 2128 cmꢀ1 is an indirect measure of decomposition,
and the band for coordinated isocyanide, at 2205 cmꢀ1, measures
the remaining gold precursor. It is clear that the ratio of these two
C
14H29)(CtNꢀC6H4ꢀOꢀC2H5)] as function of heating time
(14, 18, 24, and 30 h).
to RNCO and the disappearance of the starting gold(I) complex
seem to occur at higher rates as the decomposition progresses.
The fact that the oxidation appears to become faster at the later
stages of decomposition (in contrast, the free isocyanide remains
almost unaltered after refluxing for 14 h in toluene) suggests that
isocyanide oxidation is favored by coordination to nanoparticles,
as reported for other isocyanides bonded to metal surfaces,40 and
the consumption of isocyanide is, in turn, favoring the decom-
position of the starting complex.
3. Interestingly, in a separated experiment, the thermal
decomposition of [Au(CtCꢀC6H4ꢀC14H29)(CtNꢀC6H4ꢀ
OꢀC2H5)] in the presence of added [H29C14ꢀC6H4ꢀCtCꢀ
CtCꢀC6H4ꢀC14H29] (1:5) showed a clear acceleration of the
8659
dx.doi.org/10.1021/ic201210p |Inorg. Chem. 2011, 50, 8654–8662

Inorganic Chemistry
ARTICLE
Scheme 3. Proposed Mechanism for the Thermal Decom-
position of AlkynylꢀIsocyanide Gold Complexes to Give
Gold Nanoparticles: (i) without Addition of External Dia-
lkynyl, (ii) Caytalyzed by Large Excess of Added Dialkynyl
Figure 9. IR spectra for direct comparison of the rate of decomposition
of [Au(CtCꢀC6H4ꢀC14H29)(CtNꢀC6H4ꢀOꢀC2H5)] (a) in the
air and (b) under O2 bubbling.
bands (an indirect measure of decomposed vs starting materials)
increases more rapidly under O2 bubbling (Figure 9b).
Interestingly, when the decomposition was carried out under
N2, the IR monitoring hardly showed any difference with the
reaction under air. This suggests that isocyanide dissociation is
the main route for decomposition, whereas isocyanide oxidation
(which helps to this dissociation) is relatively inefficient and
occurs only in small or catalytic amounts when O2 bubbling
is used.
The complexity and physical conditions of the system under
study do not allow for a controlled quantitative kinetic study.
Moreover, the main products of decomposition (bis-alkyne and
isocyanide) should have opposite effects on the rate of decom-
position but are at the same time involved (in unknown
proportions) in the stabilization of the Au NP. Hence, a simple
kinetic dependence cannot be expected. This difficulty reduces
the available information to support a mechanistic proposal for
the decomposition, but at least we know that the proposal should
account for the qualitative observations just discussed; namely,
(i) an excess of bis-alkyne induces a faster decomposition and
consequently accelerates the formation of nanoparticles; (ii) an
excess of isocyanide quenches the decomposition process; (iii)
O2 bubbling shows some accelerating effect.
could occupy the vacant site as a π ligand not needing to
displace a strongly coordinated isocyanide ligand.
A plausible mechanism operating for the decomposition of
these complexes to eventually give nanoparticles, consistent with
all the observations, is depicted in Scheme 3. The decomposition
patway is proposed to be bimolecular. The transmetalation
intermediate (highlighted in red) leading to the confluence of
the two alkynyl groups on the same atom (a prerequisite for
CꢀC coupling to occur) involves a bridging alkynyl group, and
its formation might be helped by aurophillic interactions. Alkynyl
transmetalations in transition metals are very well documented.45
From that intermediate, the coupling of the two alkynyls
produces a dinuclear complex of Au(0) precariously stabilized
by isocianyde and the bisalkyne, which is the protoparticle to be
incorporated to others, with partial release of the stabilizing
ligands.
Mechanistic Proposal for the Thermal Decomposition of
[Au(CtCꢀR)(CtNꢀR0)] Complexes. It is well-known that
CtC bonds can π-coordinate gold. A representative example
is the polymeric complex [Au(CtCꢀBut)]n, where the alkynyl
ligand adopts both η1 and η2 coordination modes.41,42 These
polymeric alkynyl complexes react with Lewis bases (L) to give a
variety of [Au(CtCꢀR)L] complexes. However, for ligands
with hard donor atoms and lower bonding ability toward gold,
the mixed alkynyl-L gold(I) complexes are often formed only in
the presence of a large excess of ligand.43 Therefore, it is not
unexpected that a large excess of a relatively poorly coordinating
fragment (the bis-alkyne, or the triple bond of a second molecule
of the starting isocyanideꢀalkynylgold precursor) can promote
decoordination of isocyanide from the starting gold complex,
producing a faster decomposition, as observed. In this regard, it is
interesting to note that the stability of π-alkyne complexes
increases with increasing the electron-withdrawing character
of X in [XCtCX] alkynes.44 Thus, the coordination strength
of RꢀCtCꢀCtCꢀR through one CtC bond should be
higher than that of an isolated RꢀCtCꢀR group. Moreover,
dissociation of isocyanide in catalytic amounts could be
produced by its oxidation to isocyanate, so that a CtC bond
In summary, alkynylꢀisocyanide gold complexes are useful
precursors of stable gold nanoparticles in the absence of added
stabilizers. The decomposition can be produced from the
mesophase or from solutions of these metallomesogens but
is noticeably faster from solutions and produces more homo-
geneous particle sizes. The thermal decomposition probably
starts by decoordination of an isocyanide ligand (either by
itself or assisted in part by its slow oxidation to isocyanate)
followed by alkynyl transmetalation from the less electrophillic
to the more electrophilic gold center created upon isocyanide
decoordination. This transmetalation leads to oxidative cou-
pling of the two akynyl groups to RꢀCtCꢀCtCꢀR and
reduction of gold(I) to gold(0) dimers, which eventually
agglomerate into nanoparticles. The NP obtained would
catalyze the oxidation of isocyanide (CNR) to isocyanate
(OCNR), which explains the observed acceleration of the
decomposition as the reaction progresses. The slower decom-
position rates observed in the thermotropic mesophase, as
compared to the solution, should be mostly due to the slower
molecular diffusion in that viscous medium, which is detri-
mental for a bimolecular decomposition process.
8660
dx.doi.org/10.1021/ic201210p |Inorg. Chem. 2011, 50, 8654–8662

Inorganic Chemistry
ARTICLE
’ EXPERIMENTAL SECTION
6.4 Hz, CtNC6H4OCH2CH2), 6.93 (d, 2H, J = 9.2 Hz, CtNC6H4Oꢀ),
7.06 (d, 2H, J = 8.3 Hz, CtCC6H4), 7.39 (d, 2H, J = 8.3 Hz, CtCC6H4),
7.45 (d, 2H, J = 9.2 Hz, CtNC6H4Oꢀ). IR ν(CtN)/cmꢀ1: 2218 (KBr),
2214 (CH2Cl2). Analysis calculated for C37H54NOAu (%): C, 61.23; H,
7.49; N, 1.93. Found: C, 61.18; H, 7.22; N, 2.00.
Combustion analyses were performed with a Perkin-Elmer 2400
microanalyzer. IR spectra were recorded on a Perkin-Elmer FT BX
instrument and 1H NMR spectra on Bruker AC 300 or ARX 300
instruments in CDCl3. Mass spectra were recorded using an Agilent
Technologies 5973 inert mass selective detector spectrometer. Microscopy
studies were carried out using a Leica DMRB microscope provided with a
Mettler FP82HT hot stage and a Mettler FP90 central processor, at a
heating rate of 10°Cminꢀ1. For differentialscanningcalorimetry(DSC), a
Perkin-Elmer DSC7 instrument was used, which was calibrated with water
and indium; the scanning rate was 10 °C minꢀ1. The samples were sealed
in aluminum capsules in the air, and the holder atmosphere was dry
nitrogen. TEM observations were performed on a Hitachi HF2000
(200 kV) or a JEOL 1011 (110 kV) electron microscope. At least
200 particles were used to determine the mean diameter of the Au NP.
m = 14, n = 8. Yield: 89%. 1H RMN (CDCl3, 300 MHz): δ, 0.89
(m, 6H, CH3), 1.26ꢀ1.81 (m, 36H, alkyl chain), 2.57 (t, 2H, J = 7.0 Hz,
CtCC6H4CH2), 3.99 (t, 2H, J = 6.6 Hz, CtNC6H4OCH2), 6.93
(d, 2H, J = 9.2 Hz, CtNC6H4Oꢀ), 7.06 (d, 2H, J = 7.9 Hz,
CtCC6H4), 7.39 (d, 2H, J = 7.9 Hz, CtCC6H4), 7.44 (d, 2H, J =
9.2 Hz, CtNC6H4Oꢀ). IR ν(CtN)/cmꢀ1: 2213 (KBr), 2214
(CH2Cl2). Analysis calculated for C37H54NOAu (%): C, 61.23; H,
7.50; N, 1.93. Found: C, 61.23; H, 7.18; N, 1.84.
m = 14, n = 14. Yield: 91%. 1H RMN (δ, CDCl3, 300 MHz): 0.89
(m, 6H, CH3), 1.26ꢀ1.80 (m, 48H, alkyl chain), 2.57 (t, 2H, J = 7.5 Hz,
CtCC6H4CH2), 3.98 (t, 2H, J = 6.6 Hz, CtNC6H4OCH2), 6.93 (d,
2H, J = 8.8 Hz, CtNC6H4Oꢀ), 7.06 (d, 2H, J = 7.9 Hz, CtCC6H4),
7.39 (d, 2H, J = 7.9 Hz, CtCC6H4), 7.44 (d, 2H, J = 8.8 Hz,
CtNC6H4Oꢀ). IR ν(CtN)/cmꢀ1: 2220 (KBr), 2214 (CH2Cl2).
Analysis calculated for C43H66NOAu (%): C, 63.76; H, 8.21; N, 1.73.
Found: C, 63.51; H, 7.99; N, 2.01.
Synthesis of Au NP. Gold nanoparticles were prepared by decom-
position of [Au(CtCꢀC6H4ꢀCmH2m+1)(CtNꢀC6H4ꢀOꢀCnH2n+1)]
complexes. A typical procedure is as follows: 0.072 mmol of the correspond-
ing gold complex was dissolved in 6 mL of toluene in a 25 mL flask
connected to a condenser. The flask was placed in a previously thermostatted
oil bath at 110 °C, under aerobic conditions for 2 or 14 h. The solvent was
removed under vacuum conditions, and the residue extracted with hexane,
which was evaporated to obtain the product as a brown solid.
Literature methods were used to prepare [HCtCꢀC6H4ꢀ
46
CmH2m+1
]
and [CtNꢀC6H4ꢀOꢀCnH2n+1].14 The isocyanide
[CtNꢀC6H4ꢀOꢀC14H29] had not been described before, and its
spectroscopic data are as follows: MP = 40.0 °C. IR (CH2Cl2),
ν(CtN)/cmꢀ1: 2127 (s). 1H NMR (CDCl3, 300 MHz): δ 0.89
(t, 3H, J = 6.6 Hz, CH3), 1.27ꢀ1.78 (24H, alkyl chains), 3.96 (t, 2H,
J = 6.6 Hz, CH2ꢀO), 6.86 (d, 2H, J = 8.8 Hz, H-aryl), 7.30 (d, 2H,
J = 8.8 Hz, H-aryl).
All new complexes [Au(CtCꢀC6H4ꢀCmH2m+1)(CtNꢀC6H4ꢀ
OꢀCnH2n+1)] were prepared as reported for similar complexes.14
A
sample preparation is given: [CtNꢀC6H4ꢀOꢀCnH2n+1] (1.90 mmol)
was added to [Au(CtCꢀC6H4ꢀCmH2m+1)]n (1.27 mmol) suspended
in toluene (40 mL). The resulting solution was stirred for 15 min. Then,
the solvent was eliminated under reduced pressure, and a white residue
was obtained. Recrystallization from CH2Cl2/hexane afforded white
crystals of the product, 60ꢀ90% yield. Spectroscopic and analytical data
are as follows:
For the decomposition in the liquid crystal state, [Au(CtCꢀC6H4ꢀ
C14H29)(CtNꢀC6H4ꢀOꢀC2H5)] (0.072 mmol) was heated in an
open vial in the air for 14 h at 155 °C. At this temperature, the compound
displays a SmA mesophase.
m = 2, n = 2. Yield: 60%. 1H RMN (CDCl3, 300 MHz): δ 1.21 (t,
3H, J = 7.8 Hz, CH3, alkynyl), 1.44 (t, 3H, J = 6.3 Hz, CH3, isocyanide),
2.62 (q, 2H, J = 7.6 Hz, CtCC6H4CH2), 4.07 (q, 2H, J = 7.0 Hz,
CtNC6H4OCH2), 6.92 (d, 2H, J = 8.9 Hz, CtNC6H4Oꢀ), 7.07 (d,
2H, J = 8.4 Hz, CtCC6H4), 7.39 (d, 2H, J = 8.4 Hz, CtCC6H4), 7.44
(2H, d, J = 8.9 Hz, CtNC6H4Oꢀ). IR ν(CtN)/cmꢀ1: 2209 (KBr),
2214 (CH2Cl2). Analysis calculated for C19H18NOAu (%): C, 48.22; H,
3.83; N, 2.96. Found: C, 48.27; H, 3.89; N, 3.02.
Synthesis of H29C14C6H4CC;CꢀC;CC6H4C14H29. This
compound was prepared as reported for similar 1,3-diines.47 To a
solution of CuCl (7 mg, 0.07 mmol) and TMEDA (19 μL, 0.21 mmol)
in 10 mL of acetone was added 4-tetradecylphenylacetylene (0.1 g,
0,34 mmol). Oxygen was bubbled in the solution for 2 h, giving rise the
desired product as a white solid that was filtered and washed with
acetone (3 ꢁ 10 mL). Yield: 46 mg, 46%. IR ν(CtC)/cmꢀ1: 2140
(KBr). 1H NMR (δ, CDCl3, 300 MHz): 0.88 (m, 6H, CH3), 1.25 (m,
44H, CH2), 1.59 (m, 4H, CtCC6H4CH2CH2), 2.60 (t, 4H,
CtCC6H4CH2), 7.14 (d, 4H, H-aryl), 7.43 (d, 4H, H-aryl). DSC/°C
(kJmolꢀ1): CꢀC0 12 (13.9); C0-SmC 59 (29); SmC-SmA 70
(microscopic data); SmAꢀN-I 73 (16.9, combined enthalpies).
m = 2, n = 8. Yield: 80%. 1H RMN (CDCl3, 300 MHz): δ 0.89 (t,
3H, J = 7.6 Hz, CH3, isocyanide), 1.21 (t, 3H, J = 7.7 Hz, CH3, alkynyl),
1.30 (m, 8H, CH2, isocyanide), 1.45 (2H, m, CH2, isocyanide), 1.78 (m,
2H, CtNC6H4OCH2CH2), 2.62 (q, 2H, J = 7.6 Hz, CtCC6-
H4CH2CH3), 3.98 (t, 2H, J = 6.4 Hz, CtNC6H4OCH2CH2), 6.93
(d, 2H, J = 9.0 Hz, CtNC6H4Oꢀ), 7.08 (d, 2H, J = 8.3 Hz,
CtCC6H4ꢀ), 7.40 (d, 2H, J = 8.3 Hz, CtCC6H4ꢀ), 7.43 (d, 2H,
J = 8.9 Hz, CtNC6H4Oꢀ). IR ν(CtN)/cmꢀ1: 2210 (KBr), 2214
(CH2Cl2). Analysis calculated for C25H30NOAu (%): C, 53.86; H, 5.42;
N, 2.51. Found: C, 53.95; H, 5.28; N, 2.55.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: scoco@qi.uva.es (S.C.); espinet@qi.uva.es (P.E.).
m = 2, n = 14. Yield: 79%. 1H RMN (CDCl3, 300 MHz): δ 0.89
(t, 3H, J = 7.0 Hz, CH3, isocyanide), 1.22 (t, 3H, J = 7.7 Hz, CH3,
alkynyl), 1.27 (m, 20H,CH2, isocyanide), 1.45 (m, 2H, CH2, iso-
cyanide), 1.81 (m, 2H, CtNC6H4OCH2CH2), 2.63 (q, 2H, J =
7.7 Hz, CtCC6H4CH2CH3), 3.99 (t, 2H, J = 6.4 Hz, CtNC6-
H4OCH2CH2), 6.94 (2H, d, J = 8.9 Hz, CtNC6H4Oꢀ), 7.09 (d, 2H,
J = 8.0 Hz, CtCC6H4), 7.41 (d, 2H, J = 8.0 Hz, CtCC6H4), 7.45 (d,
2H, J = 8.9 Hz, CtNC6H4Oꢀ). IR ν(CtN)/cmꢀ1: 2211 (KBr), 2214
(CH2Cl2). Analysis calculated for C31H42NOAu (%): C, 58.03; H, 6.60;
N, 2.18. Found: C, 57.86; H, 6.32; N, 2.29.
’ ACKNOWLEDGMENT
This work was sponsored by the DGI (Project CTQ2008-
03954/BQU and INTECAT Consolider Ingenio-2010 CSD2006-
0003) and the Junta de Castilla y Leꢀon (Projects VA248A11-2 and
VA281A11-2). R.C. and E.C. gratefully acknowledge financial
support from the Spanish Ministerio de Ciencia e Innovaciꢀon.
’ REFERENCES
m = 8, n = 14. Yield: 82%. 1H RMN (CDCl3, 300 MHz): δ, 0.88
(m, 6H, CH3), 1.26ꢀ1.58 (m, 34H, alkyl chain), 1.81 (m, 2H,
CtNC6H4OCH2CH2), 2.57 (t, 2H, 7.4 Hz,CtCC6H4CH2), 3.99 (t, 2H,
(1) (a) Schmid, G. Chem. Rev. 1992, 92, 1709–1727. (b) Murray,
R. W. Chem. Rev. 2008, 108, 2688–2720. (c) Daniel, M. C.; Astruc, D.
Chem. Rev. 2004, 104, 293–346.
8661
dx.doi.org/10.1021/ic201210p |Inorg. Chem. 2011, 50, 8654–8662

Inorganic Chemistry
ARTICLE
(2) Burda, C.; Chen, X.; Narayanan, R.; El-Sayed, M. A. Chem. Rev.
2005, 105, 1025–1102.
(20) Vicente, J.; Chicote, M.-T.; Abrisqueta, M.-D.; Jones, P. G.
Organometallics 1997, 16, 5628–5636.
(3) (a) Chen, W.; Chen, S. W.; Ding, F. Z.; Wang, H. B.; Brown,
L. E.; Konopelski, J. P. J. Am. Chem. Soc. 2008, 130, 12156–12162.
(b) Andres, R. P.; Bein, T.; Dorogi, M.; Feng, S.; Henderson, J. I.;
Kubiak, C. P.; Mahoney, W.; Osifchin, R. G.; Reifenberger, R. Science
1996, 272, 1323–1325. (c) Chen, S. W.; Ingram, R. S.; Hostetler, M. J.;
Pietron, J. J.; Murray, R. W.; Schaaff, T. G.; Khoury, J. T.; Alvarez,
M. M.; Whetten, R. L. Science 1998, 280, 2098–2101. (d) Berven, C. A.;
Clarke, L.; Mooster, J. L.; Wybourne, M. N.; Hutchison, J. E. Adv.
Mater. 2001, 13, 109–113. (e) Kamat, P. V. J. Phys. Chem. B 2002,
106, 7729–7744.
(21) Siemeling, U.; Rother, D.; Bruhn, C. Organometallics 2008,
27, 6419–6426.
(22) Puddephatt, R. J.; Treurnicht, I. J. Organomet. Chem. 1987,
319, 129–137.
(23) Castillejos, E.; Chico, R.; Bacsa, R.; Coco, S.; Espinet, P.; Pꢀerez-
Cadenas, M.; Guerrero-Ruiz, A.; Rodríguez-Ramos, I.; Serp, P. Eur.
J. Inorg. Chem. 2010, 5096–5102.
(24) (a) Sau, T. K.; Murphy, C. J. J. Am. Chem. Soc. 2004,
126, 8648–8649. (b) Shukla, S.; Priscilla, A.; Banerjee, M.; Bhonde,
R. R.; Ghatak, J.; Satyam, P. V.; Sastry, M. Chem. Mater. 2005,
17, 5000–5005. (c) Wu, H. Y.; Chu, H. C.; Kuo, T. J.; Kuo, C. L.;
Huang, M. H. Chem. Mater. 2005, 17, 6447–6451.
(25) (a) Sakai, T.; Alexandridis, P. J. Phys. Chem. B 2005,
109, 7766–7777. (b) J. Kimling, J.; Maier, M.; Ovenke, B.; Kotaidis,
V.; Ballot, H.; Plech, A. J. Phys. Chem. B 2006, 110, 15700–15707.
(c) Pong, B. K.; Elim, H. I.; Chong, J. X.; Trout, B. L.; Lee, J. Y. J. Phys.
Chem. C 2007, 111, 6281–6287. (d) Ji, X. H.; Song, X. N.; Li, J.; Bai,
Y. B.; Yang, W. S.; Peng, X. G. J. Am. Chem. Soc. 2007, 129,
13939–13948.
(26) Pileni, M. P. Metal Particles Made in Various Colloidal Self-
Assemblies: Syntheses and Properties. In Fine Particles: Synthesis,
Characterization, and Mechanisms of Growth; Sugimoto, T., Ed.; Marcel
Dekker: New York, 2000.
(4) (a) Sun, S. H.; Murray, C. B.; Weller, D.; Folks, L.; Moser, A.
Science 2000, 287, 1989–1992. (b) Sun, T.; Seff, K. Chem. Rev. 1994,
94, 857–870.
(5) (a) Mallik, K.; Witcomb, M. J.; Scurrell, M. S. Appl. Phys. A:
Mater. Sci. Process. 2005, 80, 797–801. (b) Zaera, F. J. Phys. Lett. 2010,
1, 621. (c) Li, Y.; Somorjal, G. A. Nano Lett. 2010, 10, 2289.
(6) (a) Lewis, L. N. Chem. Rev. 1993, 93, 2693–2730. (b) Bradley,
J. S. In Clusters and Colloids, From Theory to Applications; Schmid, G., Ed.;
VCH: Weinheim, Germany, 1994; pp 523ꢀ536. (c) Edwards, P. P.;
Johnston, R. L.; Rao, C. N. R. In Metal Clusters in Chemistry; Braunstein,
P., Oro, L. A., Raithby, P. R., Eds.; Wiley-VCH: Weinheim, Germany,
1998. (d) Nanoparticles and Nanostructured Films, Preparation, Char-
acterization and Applications; Fendler, J. H., Ed.; Wiley-VCH: Weinheim,
Germany, 1998. (e) Aiken, J. D.; Finke, R. G. J. Mol. Catal. A 1999,
145, 1–44. (f) Rao, C. N. R.; Kulkarni, G. U.; Thomas, P. J.; Edwards,
P. P. Chem. Soc. Rev. 2000, 29, 27–35.
(27) Polte, J.; Ahner, T. T.; Delissen, F.; Sokolov, S.; Emmerling, F.;
Th€unemann, A. F.; Kraehnert, R. J. Am. Chem. Soc. 2010, 132,
1296–1301.
(7) Dellinger, T. M.; Braun, P. V. Chem. Mater. 2004, 16, 2201–2207.
(8) (a) Ontko, A. C.; Angelici, R. J. Langmuir 1998, 14, 1684–1691.
(b) Horinouchi, S.; Yamanoi, Y.; Yonezawa, T.; Mouri, T.; Nishihara, H.
Langmuir 2006, 22, 1880–1884. (c) Swanson, S. A.; McClain, R.;
Lovejoy, K. S.; Alamdari, N. B.; Hamilton, J. S.; Scott, J. C. Langmuir
2005, 21, 5034–5039. (d) Kim, H. S.; Lee, S. J.; Kim, N. H.; Yoon, J. K.;
Park, H. K.; Kim, K. Langmuir 2003, 19, 6701–6710. (e) Horswell, S. L.;
O’Neil, I. A.; Schiffrin, D. J. J. Phys. Chem. B 2001, 105, 941–947.
(f) Henderson, J. I.; Feng, S.; Bein, T.; Kubiak, C. P. Langmuir 2000,
16, 6183–6187.
(28) Shevchenko, E. V; Talapin, D. V.; Schnablegger, H.; Kornowski,
A.; Festin, O.; Svelindh, P.; Haase, M.; Weller, H. J. Am. Chem. Soc. 2003,
125, 9090–9101.
(29) Alloyeau, D.; Prꢀevot, G.; Le Bouar, Y.; Oikawa, T.; Langlois, C.;
Loiseau, A.; Ricilleau, C. Phys. Rev. Lett. 2010, 105, 255901–255904.
(30) Wegner, H. A. Chimia 2009, 63, 44–48.
(31) Cui, L.; Zhang, G.; Zhang, L. Bioorg. Med. Chem. Lett. 2009,
19, 3884–3887.
€
(32) Brenzovich, W. E., Jr; Brazeau, J.-F.; Toste, F. D. Org. Lett. 2010,
12, 4728–4731.
(9) Stewart, M. P.; Maya, F.; Kosynkin, D. V.; Dirk, S. M.; Stapleton,
J. J.; McGuiness, C. L.; Allara, D. L.; Tour, J. M. J. Am. Chem. Soc. 2004,
126, 370–378.
(10) Dirk, S. M.; Pylypenko, S.; Howell, S. W.; Fulghum, J. E.;
Wheeler, D. R. Langmuir 2005, 21, 10899–10901.
(33) Kar, A.; Mangu, N.; Kaiser, H. M.; Beller, M.; Tse, M. K. Chem.
Commun. 2008, 386–388.
(34) Shao, Z.; Peng, F. Angew. Chem., Int. Ed. Engl. 2010, 49, 9566–8.
(35) Kim, S.; Ihm, K.; Kang, T.-H.; Hwang, S.; Joo, S.-W. Surf.
Interface Anal. 2005, 37, 294–299.
(11) Ciszek, J. W.; Keane, Z. K.; Cheng, L.; Stewart, M. P.; Yu, L. H.;
Natelson, D.; Tour, J. M. J. Am. Chem. Soc. 2006, 128, 3179–3189.
(12) (a) Patterson, M. L.; Weaver, M. J. J. Phys. Chem. 1985,
89, 5046–5051. (c) Feilchenfeld, H.; Weaver, M. J. J. Phys. Chem.
1989, 93, 4216–4282. (d) Zhang, S.; Chandra, K. L.; Gorman, C. B.
J. Am. Chem. Soc. 2007, 129, 4876–4877.
(36) 1,4-Diphenylbutadiyne C6H5ꢀCtCꢀCtCꢀC6H5 displays
two IR bands in solution associated with the triple bonds: 2145 cmꢀ1
(strong), Ag mode; 2216 cmꢀ1 (medium), Bu mode. See: Nyquist, R. A.;
Putzig, C. L. Vib. Spectrosc. 1992, 4, 35–38.
(37) Zhang, S.; Chandra, K. L.; Gorman, C. B. J. Am. Chem. Soc.
2007, 129, 4876–4877.
(13) (a) Metallomesogens; Serrano, J. L., Ed.; VCH: Weinheim,
Germany, 1996. (b) Donnio, B.; Guillon, D.; Bruce, D. W.; Deschenaux,
R. Metallomesogens, Comprehensive Organometallic Chemistry III: From
Fundamentals to Applications; Crabtree, R. H., Mingos, D. M. P., Eds.;
Elsevier: Oxford, U.K.; Vol. 12, 2006; Applications III: Functional
Materials, Environmental and Biological Applications; O’Hare, D., Ed.;
Elsevier: Oxford, U.K.; ch. 12.05, pp 195ꢀ294.
(38) Markovich, N.; Volinsky, R.; Jelinek, R. J. Am. Chem. Soc. 2009,
131, 2430–2431.
(39) Segura, Y.; Lꢀopez, N.; Pꢀerez-Ramírez, J. J. Catal. 2007, 247,
383–386.
(40) Angelici, R. J.; Lazar, M. Inorg. Chem. 2008, 47, 9155–9165.
(41) Coates, G. E.; Parkin, C. J. Chem. Soc. 1962, 3220–3226.
(42) Mingos, D. M. P.; Yau, J.; Menzer, S.; Williams, D. J. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1894–1895.
(43) Kilpin, K. J.; Horvath, R.; Jameson, G. B.; Telfer, S. G.; Gordon,
K. C.; Crowley, J. D. Organometallics 2010, 6186–6195.
(44) Elchenbroich, C.; Salzer, A. Organometallics, 2nd ed.; VCH:
Weinheim, Germany, 1992. ISBN: 3-527-28164-9.
(45) Berenguer, J. R.; Lalinde, E.; Moreno, M. T. Coord. Chem. Rev.
2010, 254, 832–875.
(14) Alejos, P.; Coco, S.; Espinet, P. New J. Chem. 1995, 19,
799–805.
(15) Espinet, P. Gold Bull. 1999, 32, 127–134.
(16) Ferrer, M.; Mounir, M.; Rodríguez, L.; Rossell, O.; Coco,
S.; Gꢀomez-Sal, P.; Martín, A. J. Organomet. Chem. 2005, 690, 2200–
2208.
(17) Kaharu, T.; Ishii, R.; Adachi, T.; Yoshida, T.; Takahashi, S.
J. Mater. Chem. 1995, 5, 687–692.
(46) Praefcke, K.; Khone, B.; Guthier, K.; Johnen, N.; Singer, D. Liq.
(18) Xiao, H.; Cheung, K.-K.; Che, C.-M. J. Chem. Soc., Dalton Trans.
1996, 3699–3703.
Cryst. 1989, 5, 233–249.
(47) Hay, A. S. J. Org. Chem. 1962, 27, 3320–3321.
(19) Irwin, J.; Vittal, J. J.; Puddephatt, R. J. Organometallics 1997,
3541–3547.
8662
dx.doi.org/10.1021/ic201210p |Inorg. Chem. 2011, 50, 8654–8662