Catalytically active self-assembled silica-based nanostructures containing supported nanoparticles

Article abstract of DOI:10.1039/c0gc00282h

Self-assembled tubular silica-based nanostructures can be prepared using a simple, low-energy intensive and benign protocol under mild conditions (<100 °C) using microwave irradiation and conventional heating. These nanotubes were found to contain metal nanoparticles that are catalytically active in the microwave-assisted homocoupling of terminal alkynes. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c0gc00282h

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PAPER
www.rsc.org/greenchem | Green Chemistry
Catalytically active self-assembled silica-based nanostructures containing
supported nanoparticles
Camino Gonzalez-Arellano, Alina Mariana Balu, Rafael Luque* and Duncan J. Macquarriea
a
b
a,b
Received 2nd July 2010, Accepted 27th August 2010
DOI: 10.1039/c0gc00282h
Self-assembled tubular silica-based nanostructures can be prepared using a simple, low-energy
◦
intensive and benign protocol under mild conditions (<100 C) using microwave irradiation and
conventional heating. These nanotubes were found to contain metal nanoparticles that are
catalytically active in the microwave-assisted homocoupling of terminal alkynes.
Introduction
formation. Parameters such as the effect of the methodology of
preparation, different metals and metal salt precursors utilised
and the effect of the halide anions in the formation of the
nanostructures have been investigated as well as their appli-
cations in the heterogeneously catalysed microwave-assisted
homocoupling of terminal alkynes.
Nanomaterials have attracted a great deal of attention over the
last few decades due to the importance of miniaturisation and
nanotechnologies in key advances for a sustainable future. Sizes,
shapes and surface properties can be designed to evoke specific
nanomaterial functions with the aim to be utilised in a particular
1
2
application/end use such as chemical sensors, biomedicine,
optoelectronic devices and catalysis.
3
4
Experimental
Nanotubes are a particularly interesting example of nanoma-
terials. These nanostructures have been reported in a remarkable
number and variety of applications, using different chemical and
physicochemical synthetic methodologies (e.g. vapor-, solution-
Materials preparation
In the proposed synthesis of nanotubes (NT), 0.6 mmol
n-dodecylamine (0.14 mL), 2 mmol tetraethoxyorthosilicate
(TEOS, 0.45 mL), 0.2 g metal salt (i.e. FeCl ·4H O, RuCl ·xH O,
5–7
and supercritical fluid-liquid-solid systems, and surfactant-
2
2
3
2
8
CuCl ·2H O, NiCl ·6H O and CoCl ·6H O), 2 mL water and
mediated sol–gel methods ). Nevertheless, reports of simple,
2
2
2
2
2
2
2
mL acetonitrile were added to a microwave tube and mi-
low-energy intensive and benign methodologies are scarce, with
multiple-steps, organic solvent-mediated and energy intensive
methodologies being mostly reported for the preparation of
crowaved for 1 to 15 min at 200 W (maximum temperature
◦
reached 80–110 C depending on the material). Materials
5–9
were denoted as metal-Microwave Induced NanoTubes (metal-
MINT; e.g. Cu-MINT). Alternatively, the preparation of NT
was carried out under conventional heating (70 C), under iden-
tical conditions to those reported in the microwave protocol, to
compare results. These materials were simply denoted as metal-
NanoTubes (e.g. copper nanotubes). The resultant coloured
solid was filtered off, thoroughly washed with acetonitrile and
nanotubular structures. Well-developed silica nanotubes have
been prepared using copper sulfide nanocrystals under super-
◦
◦
9c
critical toluene (500 C, 10.3 MPa). In comparison to these
systems, we recently reported the preparation of self-assembled
nanotubular domains under both conventional heating and
10
microwave irradiation in aqueous surfactant solutions. To
the best of our knowledge, these findings were the first report
of the generation of such nanomaterials in water under mild
synthesis conditions (<100 C). These materials were also found
to contain (metal) nanoparticles into their nanostructures.
◦
acetone and dried overnight at 100 C before extracting the
◦
template in refluxing ethanol (5 h). Materials were then oven
◦
10
10
dried (100 C) overnight and further characterised.
Supported nanoparticles on nanotubes have also been the
subject of many investigations due to their important and
Characterisation
4,11
interesting applications in catalysis. However, most studies are
Materials were characterised by means of several techniques
including Scanning Electron Microscopy (SEM), Transmis-
sion Electron Microscopy (TEM), Nitrogen physisorption and
X-Ray Photoelectron Spectroscopy (XPS).
SEM micrographs were recorded in a JEOL JSM-6490LV.
Samples were Au/Pd coated on a high resolution sputter SC7640
at a sputtering rate of 1500V per minute, up to 7 nm thickness.
TEM micrographs were recorded on a FEI Tecnai G2 fitted
with a CCD camera for ease and speed of use. The resolution
is around 0.4 nm. Samples were suspended in ethanol and
deposited straight away on a copper grid prior to analysis.
Nitrogen adsorption measurements were carried out at 77 K
using an ASAP 2010 volumetric adsorption analyzer from
12
limited to carbon nanotubes and other nanotubular structures
have rarely been reported to have broad catalytic applications.
In this work, we aim to report the structural and textural
properties of self-assembled tubular nanostructures from aque-
ous surfactant solutions as well as their plausible mechanisms of
a
Green Chemistry Centre Of Excellence, The University of York,
Heslington, York, UK, YO10 5DD
b
Departamento de Qu ´ı mica Org a´ nica, Universidad de C o´ rdoba, Campus
de Rabanales, Edificio Marie Curie, Ctra Nnal IV, Km 396, E14014,
C o´ rdoba, Spain. E-mail: q62alsor@uco.es; Fax: +34 957 212066;
Tel: +34 957 211050
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◦
Micromeritics. The samples were outgassed for 2 h at 100 C
tures similar to those utilised for the preparation of mesoporous
hexagonal silicas pointed to the generation of supported
-
2
15
under vacuum (p < 10 Pa) and subsequently analyzed. The
linear part of the BET equation (relative pressure between 0.05
and 0.22) was used for the determination of the specific surface
area. Materials were found to be mostly microporous.
nanoparticles on the surface of interestingly structured porous
materials. Further investigations on such materials using SEM
and TEM (Fig. 1 and Fig. 2) showed the formation of distinctive
self-assembled nanotubular domains from the original synthesis
gel, regardless of the metal precursor employed.
XPS (aka ESCA) measurements were performed in a ultra
high vacuum (UHV) multipurpose surface analysis system
TM
-10
(
Specs model, Germany) operating at pressures <10 mbar
using a conventional X-Ray source (XR-50, Specs, Mg-Ka,
253.6 eV) in a “stop-and-go” mode to reduce potential damage
1
due to sample irradiation. The survey and detailed Fe and Cu
high-resolution spectra (pass energy 25 and 10 eV, step size 1
and 0.1 eV, respectively) were recorded at room temperature
with a Phoibos 150-MCD energy analyser. Powdered samples
were deposited on a sample holder using double-sided adhe-
-
6
sive tape and subsequently evacuated under vacuum (<10
Torr) overnight. Eventually, the sample holder containing the
degassed sample was transferred to the analysis chamber for
XPS studies. Binding energies were referenced to the C1s line
at 284.6 eV from adventitious carbon. The curve deconvolution
of the obtained XPS spectra were obtained using the Casa XPS
program.
The metal content in the materials was determined using
Inductively Coupled Plasma (ICP) in a Philips PU 70000 sequen-
tial spectrometer equipped with an Echelle monochromator
(
0.0075 nm resolution). Samples were digested in HNO (Ru
3
was removed using aqua regia) and subsequently analysed by
ICP at the University of Newcastle.
Catalytic tests
In a typical catalytic experiment, 4 mmol phenylacetylene,
2
mmol di-azabicyclo [2.2.2] octane (DABCO) and 0.05 g
catalyst were microwaved in a CEM-DISCOVER microwave
reactor under air for 15 min at 300 W (maximum power output).
Dodecane was added to the mixture as internal standard. Upon
reaction completion, aliquots of the final mixture were sampled
and subsequently analysed by GCGC-MS using an Agilent 6980
N GC model fitted with a Petrocol capillary column and a
FID detector. Experiments were conducted on a closed vessel
Fig. 1 SEM micrographs of Ni-MINT (top) and Cu-MINT (bottom).
Nanotubular domains observed had sizes between 1 to several
micrometres long with diameters typically between 0.1 to 5 mm
(
pressure controlled) under continuous stirring. The microwave
(
Fig. 1). Tubular-shaped structures found in SEM were further
method was generally power controlled where samples were
irradiated with the maximum power output (300 W) and reached
different temperatures in the 140–170 C range.
confirmed in the TEM micrographs (Fig. 2). These images
evidenced the presence of rod/tube-like shapes in the materials
regardless of the mild synthetic methodology employed in their
preparation (see experimental). Clear nanotubular/nanofibres
exhibited in Fig. 2B pointed out these nanostructures were
typically 100–500 nm long with diameters typically between 10–
100 nm, in good agreement with those observed in the SEM
micrographs.
◦
Results and discussion
Following our recently developed microwave protocol to syn-
thesize a variety of supported nanoparticles on mesoporous
13,14
materials at mild conditions,
we were prompted to investigate
Promisingly, the use of other metals including Ru, Ni and
to some extent Co also rendered similarly developed tubular
whether a direct one-pot synthesis involving simultaneous co-
precipitation of the metal precursor and the silica gel could
lead to embedded nanoparticles on a porous network. Having
the possibility to explore a range of metal precursors, our
preliminary aims were focused on cheap, readily available and
environmentally friendly precursors such as Fe and Cu chlorides
10
nanostructures. The degree of development of the nanotubes
network was found to follow the order:
Cu > Ru > Ni > Fe ꢀ Co with reasonably developed Cu,
Ru and Ni MINT (Fig. 2). Nanoparticles on the nanostructures
could be clearly observed in many cases (Fig. 3).
(
FeCl
Thus, preliminary results of the simultaneous co-precipitation
of these metal salts in n-dodecylamine/TEOS/water/ACN mix-
2
and CuCl
2
).
Metal content (as determined by elemental analysis) showed a
ca. 0.5 wt% metal loading irrespective of the synthesis conditions
and the metal employed (Table 1).
1
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2
-1
Table 1 Textural properties [surface area (SBET, m g ), pore diameter
-1
(
DBJH, nm), pore volume (VBJH, mL g ) and metal loading (wt%,
measured by ICP/AES) of different metal loaded nanostructures
Surface area Pore diameter Pore volume Metal content
2
-1
-1
Material
(SBET, m g ) (DBJH, nm)
(VBJH, mL g ) (wt%)
Fe-MINT 97
<2
<2
<2
<2
<2
<2
0.38
0.21
0.25
0.20
0.43
0.26
0.49
0.54
0.51
0.55
0.42
0.58
Fe-NT
181
Cu-MINT 586
Copper-NT 192
Ni-MINT 165
Ru-MINT 88
Fig. 4 TEM micrographs of A) Fe-MINT prepared under microwave
◦
irradiation (200 W, 60–100 C, 15 min) compared to B) Fe-NT prepared
◦
under conventional heating (70 C, 2 h).
respect to those found under microwave irradiation (1–15 min).
In contrast, typically reported spherical particle morphologies
were observed when no metal chlorides were added to the syn-
thesis methodology under the same conditions (both microwave
irradiation and conventional heating, Fig. 5A). These findings
pointed to the direct involvement of metal chlorides in the
formation of such nanostructures.
Table 1 summarises the textural properties of the investigated
materials. All nanotubular structures were found to have high
surface areas (90–500 m g ), being mostly microporous in
nature (Table 1) regardless of the methodology employed for
their synthesis.
Fig. 2 TEM micrographs of A) Ni-MINT; B) Cu-MINT (bottom)
nanostructures.
2
-1
Of note was the significantly higher surface area of Cu-
MINT compared to other nanomaterials. This interesting fact
is related to the inherent superior microporosity present in
this material that can be clearly demonstrated in the nitrogen
absorption/desorption curves included in Fig. 6.
Cu-MINT isotherm (Fig. 6, top) is completely different to
those obtained, with similar profiles, for Fe-MINT and Cu
and Fe-NT (Fig. 6, bottom), showing a remarkably superior
microporosity that is likely to be the case for the increase
of the surface area. It is well-known that an increase in the
microporosity of the materials considerably increases their
surface areas (e.g. micro-mesoporous carbons, zeolites and so
on). However, there may be other reasons for such difference
in surface areas and microporosity that will be discussed in more
detail later on.
According to all obtained results, in particular to the influence
of the metal and precursor in the formation of the nanostruc-
tures, there were two key parameters which could also influence
the generation of nanotubes that needed further investigation.
These are the formation of supported nanoparticles that could
act as in situ generated catalytic seeds to build-up the nanotube
network and the anions from the metal precursor.
Fig. 3 TEM micrographs of Cu-MINT material. Nanoparticles can be
clearly seen as small dark spots present within the nanostructure.
16
Having proved the successful formation of nanotubular
structures under microwave irradiation, the next step was to
further broaden the scope of the protocol trying to prepare
similar nanotubes under conventional heating.
TEM micrographs of such investigations demonstrated anal-
ogous nanotubular arrays could be successfully prepared under
conventional heating using Fe and Cu chlorides (Fig. 4B).
Nevertheless, significantly longer times of heating (1 h and over)
were required to obtain similarly developed nanostructures with
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Fig. 5 TEM micrographs of materials prepared under A) under
◦
microwave irradiation (200 W, 60–100 C, 15 min) in the absence of
a metal precursor compared to B) Fe-MINT under the same conditions
prepared using FeCl as a metal precursor.
2
An interesting difference in the oxidation state of metal/metal
oxide nanoparticles was also observed in the materials regardless
of the type of metal. XPS spectra showed a significant shift
in the XPS bands that corresponded to a higher content of
reduced copper species in the Cu-MINT materials compared to
10
the copper nanotubes (Table 2). This evidence correlated well
with the more developed nanotubes in Cu-MINT with respect to
copper nanotubes. Interestingly, the relatively similar content of
metallic Fe in both Fe-MINT and Fe-NT was in good agreement
with relatively similar nanotubes developed for both materials
Fig. 6 Isotherm profiles of Cu-MINT (top) and copper-NT (bottom).
10
(
Table 2). In the particular case of Ni materials, reduced species
were only present at relatively low proportions as compared to
Ni species (possibly NiO).
However, the nature of the anions in the metal precursor were
found to be the critical parameter in the formation of nanostruc-
2
+
-
tures. While the presence of halides [e.g. Cl (Fig. 2, Fig. 3, Fig. 4
-
-
Table 2 Data of XP spectra [reduced and non reduced species (% of
total metal content in the materials) as well as their corresponding bands]
for different metal loaded nanostructures
and Fig. 7) and to a lesser extent Br (Fig. 7A) and I (Fig. 7D)]
had a clear effect in the formation of nanorod/nanofibre-like
domains, other anions including carbonates (Fig. 7B), sulfates
(Fig. 7C), and even acetates rendered typical materials with
Non reduced species
Material
Reduced species (%)
(metal oxides)
spherical morphologies as well as heterogeneous structures
(
Fig. 7).
◦
Fe-MINT
Fe-NT
Cu-MINT
12 (Fe , 706.2 eV)
86 (hematite, Fe
94 (hematite, Fe
40 (CuO, 940-945 eV
shake-up peak)
2
2
O
O
3
3
)
)
◦
The generation of tubular nanostructures under the investi-
6 (Fe , 706.5 eV)
60 (932.8 eV)
a
gated conditions is therefore a complex process in which many
different parameters seem to be involved. Nevertheless, based on
further studies of these systems, we can propose two plausible
mechanisms for the formation of nanotubular/fibre domains in
the materials. These are based on several facts that were observed
as follows:
a
Copper-NT
15 (933.0 eV)
85 (CuO, 940–945 eV
shake-up peak)
◦
2+
Ni-MINT
Ni-NT
45 (Ni , 852.6 eV)
55 (Ni , 855.8 eV)
◦
2+
28 (Ni , 853.1 eV)
72 (Ni , 856.3 eV)
a
◦
2
Including Cu and Cu O as these species can only be distinguished by
17
-The addition of metal salts (e.g. CuCl
2
, FeCl ) to a
2
examination of their Auger spectra.
n-dodecylamine/water/ACN solution causes an immediate
1
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In fact, oxide surfaces can be very versatile ligands and thus
we believe properties in our system can be described in the
framework of coordination chemistry.
The first proposed mechanism (Scheme 1) is the coordination
of the metal/metal oxide to the n-dodecylamine to give ML X
n
complexes (where L is the amine and X are the halides). This
coordination will increase the charge density of the micelles
when formed, making them straighter. Furthermore, metal
coordination to the head group of the micelle would increase
its head volume, resulting in a dramatic shrinkage of the micelle,
hence no mesopores will be observed, in good agreement with
the porosity data obtained for the microporous materials (Table
1
). Likewise, metal species may strongly interact with the silica
precursor that will polymerise around the micelles to give the
observed individual cylindrical-like nanotubes (cf. MCM-41
channels). However, a switch in the mechanism of hydrolysis
cannot be ruled out.
Scheme 1 Proposed mechanism of formation of tubular nanostructures
2
+
with different possibilities of interaction including the reduction of M
(
2+
in this example Cu ) by OH groups on the surface of the material
promoted by microwave irradiation.
The anions seemed also to have an important effect in the
formation of the nanostructures. We believe the halides may also
coordinate/bind (that is the reason of the proposed ML X) and
n
modify the structure of the complexes, and therefore the silica,
whereas the other anions do not coordinate/bind (as much). In
-
-
-
this regard, the order of coordination will be Cl >Br >I , that
will correlate well with the size of the anion (bigger electronic
-
-
cloud I anions will not coordinate/bind as well as smaller Cl
anions).
2
Fig. 7 TEM micrographs of materials prepared using A) CuBr ; B)
CuCO ; C) CuSO and D) CuI under conventional heating (2 h, 70 C).
3 4
◦
With regards to the observation of metal nanoparticles, the
hydroxyl groups on the silicate material have been reported
to reduce metal ions in solution, and this process is favoured
precipitate to form (blue and dark orange for the case of Cu
and Fe, respectively).
18
by gentle heating. Thus, the differences in reduced nanopar-
ticle species found between MINT and NT materials can
be attributed to the fast and homogeneous heating achieved
-
The precipitate formed is not soluble in ethanol at room
temperature, which again points to the strong interaction
between Cu and/or Fe to the amine.
19
under microwave irradiation, as well as its demonstrated
improved reducing properties compared to conventional heating
-
Surprisingly, the colour of the precipitate also changes when
13,14,18
the pH is raised (by adding small quantities of NaHCO -CO
3
2
on solution containing metals.
Another alternative lies in the idea that the ML X complex
given off), which might suggest that there may be a formation
of some oxidic species containing amine ligands, and the effect
is not just due to the amine changing the pH.
n
is not the structure directing agent, and the precipitate found in
the absence of TEOS could be functioning as a template in the
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Table 3 Catalytic performance [total conversion and selectivity to
Table 4 Catalytic performance of Ni-MINT in the microwave-assisted
a
homocoupling product (Shomocoupling)] of M-MINT and M-NT materials
homocoupling of a range of terminal alkynes
a
in the homocoupling of phenylacetylene under microwave irradiation
Conversion
(mol%)
S
homocoupling
(mol%)
Entry
1
Susbtrate
Time/min
15
>95
70
2
3
4
5
30
30
30
45
>99(86)
>99(90)
>99(92)
85
>99
>99
>99
60
Conversion
(mol%)
S
homocoupling
(mol%)
Entry Catalyst
Time/min
1
2
3
3
4
5
6
7
8
No catalyst
Conventional silica
CuI (5 mol%)
Fe-MINT
Fe-NT
Cu-MINT
Copper-NT
Ni-MINT
Ru-MINT
60
60
30
30
30
30
30
15
30
—
—
30
<30
<20
>90
80
>95
<10
—
—
>99
>99
>99
75
85
70
>99
6
30
15
>90
80
60
b
c
b
Reused
89
c
c
a
Reaction conditions 4 mmol susbtrate, 2 mmol DABCO, 0.05 g catalyst,
a
Reaction conditions: 4 mmol phenylacetylene, 2 mmol DABCO, 0.05 g
◦
b
microwaves, 300 W, 140–170 C. Activity of reused recovered catalyst
in the 4th reaction cycle. Isolated yields, where appropriate, are given in
brackets.
◦
b
c
catalyst, 300 W, 140–170 C. Neat CuI was employed as catalyst. The
difference to 100 corresponds to the formation of enynes.
solid state or even reorganising under microwave/conventional
heating to reform the amine and then templating.
◦
CuI; >99% conversion in 12 h adding 10 mol% CuI at 100 C).
With regards to the potential application of the prepared
nanomaterials, materials from this work were tested in the
microwave-assisted homocoupling of terminal alkynes. Cou-
pling processes have recently received a great deal of attention
Comparatively, microwave-assisted reactions provided excellent
conversions of starting materials for Cu and Ni nanomaterials,
compared to the poor activity found for similar catalytic
quantities of CuI (Table 3, entry 3). Fairly high selectivities to
the homocoupling product were observed at very short times
of reaction (typically 15–30 min) and low catalyst quantities.
The main by-products in the reaction were the enynes showed
in Table 3. Ni-MINT material appeared to be the most active
in the reaction and a complete conversion to products could be
20–22
as highly desirable protocols in organic synthesis.
Among
them, alkyne homocoupling or dimerisation to 1,3-diynes is
particularly important in the synthesis of a wide chemical
23
spectra ranging from natural products to polymers. However,
most reported systems for these homocoupling processes involve
homogeneous conditions and employ metal salts and/or com-
2
+
obtained after 15 min of microwave irradiation. Ni species in
the Ni-materials are likely to be responsible for the activity in
the systems but more detailed studies are required to unravel
the mechanism of the reaction and its similarity (or not) as
20,22,24
25
26
27
plexes including Pd,
Cu and/or Ni as well as Ru, with
only few truly heterogeneously catalysed protocols having been
reported up to date dealing with highly active and/or reusable
28
29
26,30
heterogeneous Pd or Cu systems.
compared to the reported homogeneous systems.
Recent reports highlighted the possibility of using Ni-based
protocols for the effective oxidative coupling of terminal alkynes
The scope of the protocol was then extended to a range
of terminal alkynes for the most active Ni-MINT material as
shown in Table 4. Quantitative conversion and selectivity to the
corresponding homocoupling products were obtained under the
investigated reaction conditions (Table 4), generally short times
of irradiation (<30 min) and low catalyst quantities (0.05 g).
Microwave irradiation reduced the times of reaction needed
for reaction completion from 6–18 h (under conventional
heating) to a few minutes (15–30 min). The methodology was
therefore amenable toawiderange of substrates andsusbtituents
under mild reaction conditions.
Most importantly the catalyst was also highly recyclable under
the investigated conditions, preserving almost 90% of its initial
activity and selectivity after 3 reuses (Table 4, entry 1 vs. reused).
These materials have also been compared to similar literature
reports (Table 5). While the majority of the reports to date
deal with conventionally heated systems that required long times
of reaction (>3 h), our system allowed quantitative conversion
26,30
promoted by oxygen or air,
in good agreement with our latest
results on alkyne homocoupling catalysed reactions by sup-
31
ported Ni(II) complexes on biopolymers (e.g. chitosan). This
2
+
reaction seems to be promoted by Ni species and a remarkable
increase to the homocoupling products was observed when CuI
26,31
was added as co-catalyst.
Results obtained for the M-MINT and M-NT materials in the
heterogeneously-catalysed homocoupling of phenylacetylene
under microwave irradiation have been included in Table 3. The
conventionally heated reactionprogressed smoothlyto give com-
plete conversions and selectivity to the homocoupling product
◦
after 12–18 h reaction at 100 C (not shown). Interestingly, the
addition of small quantities of CuI in the absence of catalyst
was found to be sufficient to achieve complete formation of
the phenylacetylene dimer in 6–18 h depending on the quantity
added of CuI (e.g. >95% conversion in 18 h employing 2 mol%
2
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Table 5 Comparison of the catalytic performance of state-of-the-art catalysts with the reported metal-MINT systems in the homocoupling of
phenylacetylene under similar reaction conditions
Reference
This work
Reaction conditions
Time/min
15
Conversion (mol%)
4 mmol substrate, 0.05 g Ni-MINT
>95
(
3
5 mol% Ni), 2 mmol DABCO,
00 W, 170 C, microwaves
◦
This work
4 mmol substrate, 0.05 g Cu-MINT
30
>90
96
(
3
6 mol% Cu), 2 mmol DABCO,
00 W, 160 C, microwaves
◦
2
2
5a
5c
5 mmol substrate, 2 mol% CuCl,
300
180
◦
1
0 mol% piperidine, 60 C,
conventional heating
1 mmol susbtrate, 1 mmol CuI,
99
◦
1
mmol I
2 2 3
, 2 mmol Na CO , 80 C,
conventional heating
2
2
5d
6
1 mmol substrate, 4.4 mol% Cu,
180
60
91
◦
O
2
, 100 C, conventional heating
2 mmol substrate, 1 equiv. n-BuLi,
>99
1
8
equiv. NiCl
0 C, conventional heating
2
.DME, 2 equiv. CuI,
◦
2
9c
1 mmol substrate, 30 mol%
Cu-USY zeolite, no base, 110 C,
conventional heating
900
97
◦
and selectivity to the corresponding diyne in 15–30 min under
microwave irradiation conditions. The reported work describes
a novel family of nanomaterials that give comparable and/or
improved activities to those already reported at comparatively
shorter reaction times and catalyst loadings (Table 5). This also
constitutes the first report to date of a highly active and reusable
heterogeneously Ni catalysed homocoupling of terminal alkynes
under microwave irradiation.
Espa n˜ a for the provision of a Ramon y Cajal contract (ref RYC-
2009-04199). AMB and RLA gratefully acknowledge current
funding from projects P09-FQM-4781 and CTQ2008-01330.
Notes and references
1
Y. Cui, Q. Q. Wei, H. K. Park and C. M. Lieber, Science, 2001, 293,
289–1292.
1
2
H. M. Fan, J. B. Yi, Y. Yang, K. W. Kho, H. R. Tan, Z. X. Shen, J.
Ding, X. W. Sun, M. C. Olivo and Y. P. Feng, ACS Nano, 2009, 3,
2
798–2808.
Conclusions
3
4
Y. Huang, X. F. Duan and C. M. Lieber, Small, 2005, 1, 142–147.
(a) A. G. S. Prado and L. L. Costa, J. Hazard. Mater., 2009, 169,
Self-assembled tubular nanostructures can be prepared from
aqueous surfactant-mediated systems both under conventional
heating and microwave irradiation. Further studies about the
effect of the anions/cations, metal nanoparticles, porosity
and structural properties showed such nanostructures may be
generated through the coordination of the metals (Cu, Fe, Ni)
and/or halides to the amine (ML
phase thus influencing the formation of straighter micelles that
lead to microporous materials or alternatively via ML X tem-
plating in the solid state/restructured material under microwave
irradiation. In any case, the MINT/NT materials were found to
have interesting catalytic properties and were proved to be very
active and selective in the microwave-assisted homocoupling
of terminal alkynes. We envisage the supported systems can
greatly contribute to advance the development of active and
selective supported materials owing to their wide availability,
ease of preparation and low cost as well as promoting the green
credentials of future catalytic protocols in terms of sustainability
and environmentally friendliness.
2
97–301; (b) C. J. Lin, W. Y. Yun, Y. T. Lu and S. H. Chien, Chem.
Commun., 2008, 6031–6033.
5
6
7
J. T. Hu, T. W. Odom and C. M. Lieber, Acc. Chem. Res., 1999, 32,
435–445.
F. D. Wang, A. G. Dong, J. W. Sun, R. Tang, H. Yu and W. E. Buhro,
Inorg. Chem., 2006, 45, 7511–7521.
P. S. Shah, T. Hanrah, K. P. Johnston and B. A. Korgel, J. Phys.
Chem. B, 2004, 108, 9574–9587.
H. P. Lin, C. Y. Mou and S. B. Liu, Adv. Mater., 2000, 12, 103–106.
(a) D. C. Lee, F. V. Mikulec and B. A. Korgel, J. Am. Chem. Soc.,
2
Chem. Mater., 2006, 18, 3356–3364; (c) H. Y. Tuan, A. Ghezelbach
and B. A. Korgel, Chem. Mater., 2008, 20, 2306–2313.
0 C. Gonzalez-Arellano, R. Luque and D. J. Macquarrie, Chem.
Commun., 2009, 4581–4583.
1 (a) N. Y. Hsu, C. C. Chien and K. T. Jeng, Appl. Catal., B, 2008, 84,
196–203; (b) L. M. Sikhwivhilu, S. S. Ray and N. J. Coville, Diffusion
Defect Data–Solid State Phenomena, 2008, 140, 61–68.
2 (a) X. Pan and X. Bao, Chem. Commun., 2008, 6271–6281; (b) W.
Chen, Z. Fan, X. Pan and X. Bao, J. Am. Chem. Soc., 2008, 130,
9
n
X complexes) in the liquid
8
9
n
004, 126, 4951–4957; (b) D. K. Smith, D. C. Lee and B. A. Korgel,
1
1
1
414–9419.
13 J. M. Campelo, T. D. Conesa, M. J. Gracia, M. J. Jurado, R. Luque,
J. M. Marinas and A. A. Romero, Green Chem., 2008, 10, 853–858.
1
1
1
4 C. Gonz a´ lez-Arellano, J. M. Campelo, D. J. Macquarrie, J. M.
Marinas, A. A. Romero and R. Luque, ChemSusChem, 2008, 1,
746–750.
Acknowledgements
5 D. J. Macquarrie, B. C. Gilbert, L. J. Gilbey, A. Caragheorgheopol,
F. Savonea, D. B. Jackson, B. Onida, E. Garrone and R. Luque, J.
Mater. Chem., 2005, 15, 3946–3951.
6 (a) V. Budarin, J. H. Clark, J. J. E. Hardy, R. Luque, K. Millkowski,
S. Tavener and A. Wilson, Angew. Chem., Int. Ed., 2006, 45, 3782–
3
CG-A would like to thank Ministerio de Educaci o´ n y Ciencia
and Fundaci o´ n Espa n˜ ola para la Ciencia y Tecnolog ´ı a for a
funded fellowship and Ministerio de Ciencia e Innovaci o´ n for
a Ramon y Cajal contract (ref RYC-2010-06268). RL is also
grateful to Ministerio de Ciencia e Innovaci o´ n, Gobierno de
786; (b) W. Liu, Y. Soneda, M. Kodama, J. Yamashita and H.
Hatori, Mater. Lett., 2008, 62, 2766–2768; (c) D. Carriazo, S. Lima,
This journal is © The Royal Society of Chemistry 2010
Green Chem., 2010, 12, 1995–2002 | 2001

View Article Online
C. Martin, M. Pillinger, A. A. Valente and V. Rives, J. Phys. Chem.
Solids, 2007, 68, 1872–1880.
7 Z. W. Huang, F. Cui, H. X. Kang, J. Chen, X. Z. Zhang and C. G.
Xia, Chem. Mater., 2008, 20, 5090–5099.
8 (a) T. Tuval and A. Gedanken, Nanotechnology, 2007, 18, 255601;
25 (a) Q. Zheng, R. Hua and Y. Wan, Appl. Organomet. Chem., 2010,
24, 314–316; (b) S. Adimurthy, C. C. Malakar and U. Beifuss, J.
Org. Chem., 2009, 74, 5648–5651; (c) D. F. Li, K. Yin, J. Li and
X. S. Jia, Tetrahedron Lett., 2008, 49, 5918–5919; (d) K. Kamata,
S. Yamaguchi, M. Kotani, K. Yamaguchi and N. Mizuno, Angew.
Chem., Int. Ed., 2008, 47, 2407–2410.
26 J. D. Crowley, S. M. Goldup, N. D. Gowans, D. A. Leigh, V. E.
Ronaldson and A. M. Z. Slawin, J. Am. Chem. Soc., 2010, 132,
6243–6248.
1
1
(
b) P. Mukherjee, C. R. Patra, A. Ghosh, R. Kumar and M. Sastry,
Chem. Mater., 2002, 14, 1678–1684.
1
2
9 C. O. Kappe, Chem. Soc. Rev., 2008, 37, 1127–1139.
0 Handbook of organopalladium chemistry for organic synthesis, ed. E.
Negishi, 1st edn, Wiley-Interscience, New York, 2002.
1 Handbook of C-H transformations, Ed. G. Dyker, 1st edn, Wiley-
VCH, Weinheim, 2005.
2 J. Tsuji, Palladium reagents and catalysts: new perspectives for the 21st
century, 1st edn, John Wiley & Sons, Chichester, 2004.
3 (a) J. M. Tour, Chem. Rev., 1996, 96, 537–553; (b) R. E. Martin and
F. Diederich, Angew. Chem., Int. Ed., 1999, 38, 1350–1377.
4 (a) P. Siemsen, B. Felber, Handbook of C–H transformations, Ed. G.
Dyker, 1st edn, Wiley-VCH, Weinheim, 2005, 53–62, 83–84; (b) A.
S. Batsanov, J. C. Collings, I. J. S. Fairlamb, J. P. Holland, J. A. K.
Howard, Z. Y. Lin, T. B. Marder, A. C. Parsons, R. M. Ward and J.
Zhu, J. Org. Chem., 2005, 70, 703–706.
27 K. Melis, D. De Vos, P. Jacobs and F. Verpoort, J. Organomet. Chem.,
2
2
2
2
2003, 671, 131–136.
28 S. N. Chen, W. Y. Wu and F. Y. Tsai, Green Chem., 2009, 11, 269–
274.
29 (a) D. Wang, J. H. Li, N. Li, T. T. Gao, S. H. Hou and B. H.
Chen, Green Chem., 2010, 12, 45–48; (b) T. Oishi, T. Katayama,
K. Yamaguchi and N. Mizuno, Chem.–Eur. J., 2009, 15, 7539–7542;
(c) P. Kuhn, A. Alix, M. Kumarraja, B. Louis, P. Pale and J. Sommer,
Eur. J. Org. Chem., 2009, 423–429.
30 W. Y. Yin, C. He, M. Chen, H. Zhang and A. W. Lei, Org. Lett., 2009,
11, 709–712.
31 R. Luque, unpublished results.
2
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