Magnetic nanoparticles entrapped in siliceous mesocellular foam: A new catalyst support

Article abstract of DOI:10.1002/chem.201102361

γ-Fe₂O₃ nanoparticles were formed inside the cage-like pores of mesocellular foam (MCF). These magnetic nanoparticles showed a uniform size distribution that could be easily controlled by the MCF pore size, as well as by the hydrocarbon chain length used for MCF surface modification. Throughout the entrapment process, the pore structure and surface area of the MCF remained intact. The resulting magnetic MCF facilitated the immobilization of biocatalysts, homogeneous catalysts, and nanoclusters. Moreover, the MCF allowed for facile catalyst recovery by using a simple magnet. The supported catalysts exhibited excellent catalytic efficiencies that were comparable to their homogeneous counterparts. Copyright

Full text of DOI:10.1002/chem.201102361

DOI: 10.1002/chem.201102361
Magnetic Nanoparticles Entrapped in Siliceous Mesocellular Foam:
A New Catalyst Support
Su Seong Lee,* Siti Nurhanna Riduan, Nandanan Erathodiyil, Jaehong Lim,
[
a]
Jian Liang Cheong, Junhoe Cha, Yu Han, and Jackie Y. Ying*
Abstract: g-Fe O3 nanoparticles were
ess, the pore structure and surface area
of the MCF remained intact. The re-
sulting magnetic MCF facilitated the
immobilization of biocatalysts, homo-
geneous catalysts, and nanoclusters.
Moreover, the MCF allowed for facile
catalyst recovery by using a simple
magnet. The supported catalysts exhib-
ited excellent catalytic efficiencies that
were comparable to their homogeneous
counterparts.
2
formed inside the cage-like pores of
mesocellular foam (MCF). These mag-
netic nanoparticles showed a uniform
size distribution that could be easily
controlled by the MCF pore size, as
well as by the hydrocarbon chain
length used for MCF surface modifica-
tion. Throughout the entrapment proc-
Keywords: catalyst
supports
·
foams · magnetic properties · nano-
particles · mesoporous materials
Introduction
covery. The immobilization of catalysts onto magnetic nano-
particles or nanocomposites has been reported previously.
[6]
Since ordered mesoporous silica was first reported in 1992,
Ideally, a magnetic catalyst support should possess a high
surface area to maximize catalyst loading and appropriate
magnetic properties for rapid and efficient separation from
the reaction media. These requirements can be met by the
construction of hierarchical magnetite/silica nanoassem-
[1]
they have been functionalized for various applications. For
example, the incorporation of nanoparticles into mesopo-
rous silica is of interest in catalysis, sensing, and in therapeu-
[2]
tics delivery. In particular, the encapsulation of magnetic
[3]
[7]
[8]
nanoparticles has attracted considerable attention.
blies and magnetic mesoporous materials.
A wide variety of heterogeneous catalysts have been de-
veloped by supporting nanoparticles onto mesoporous
Mesoporous silica possesses highly desirable properties as
a catalyst support, such as a high surface area and an ultra-
large pore size. Magnetic properties can be introduced into
mesoporous silica through the electrochemical synthesis of
magnetic nanoparticles within the walls of the silica sup-
[4]
silica. Heterogeneous catalysts can facilitate catalyst recov-
ery and reuse, minimize waste generation, and avoid the use
of toxic chemicals; these properties are important in the de-
[5]
[9]
velopment of sustainable chemical processes.
ports, such as the synthesis of g-Fe O within the pores of
2
3
Although a significant amount of effort has been devoted
to the immobilization of homogeneous catalysts onto poly-
meric and/or siliceous supports, these heterogenized cata-
lysts often require large-scale centrifugation and filtration in
their recycling. In contrast, the immobilization of catalysts
onto magnetic supports would enable catalyst recovery by
using magnetic separation. Such magnetic supports often in-
volve superparamagnetic nanoparticles, which are non-mag-
netic above their blocking temperature, thereby avoiding ag-
gregation in the reaction medium, whilst being responsive to
an applied external magnetic field to facilitate catalyst re-
SBA-15, MCM-41, MCM-48, and mesocellular foam (MCF)
[10]
by impregnation and exposure to organic acids. However,
such syntheses may lead to blockage of the pores in the
silica supports. To overcome this problem, magnetic cobalt
nanoparticles have been selectively deposited on the outer
[11]
surface of SBA-15. g-Fe O has also been grafted onto the
2
3
pore surface of hierarchically ordered mesocellular mesopo-
rous silica (HMMS), and the resulting support has been
used to immobilize ligands for asymmetric dihydroxylation
[12]
reactions. Magnetic nanoparticles with a diameter of 6 nm
have also been entrapped in HMMS by cross-linking the en-
[13]
zymes with the nanoparticles by using glutaraldehyde.
Monodispersed oleic acid-capped magnetite nanocrystals
have also been incorporated into thiol-functionalized SBA-
15.
[
a] Dr. S. S. Lee, S. N. Riduan, Dr. N. Erathodiyil, Dr. J. Lim,
J. L. Cheong, Dr. J. Cha, Dr. Y. Han, Prof. J. Y. Ying
Institute of Bioengineering and Nanotechnology
[14]
3
1 Biopolis Way
Herein, we report the entrapment of magnetic g-Fe O3
2
The Nanos 138669 (Singapore)
Fax : (+65)6478-9020
E-mail: sslee@ibn.a-star.edu.sg
jyying@ibn.a-star.edu.sg
nanoparticles into the unique cage-like pores of hydropho-
bic siliceous MCF. MCF possessed a highly organized 3D
array of ultralarge cell-like pores that were connected
[15]
through smaller window channels.
The magnetite nano-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201102361.
particles were incorporated into the siliceous MCF without
7394
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Chem. Eur. J. 2012, 18, 7394 – 7403

FULL PAPER
disrupting its pore connectivity. The resulting g-Fe O /MCF
2
3
was successfully used as a catalyst support for the immobili-
zation of nanoparticles, enzymes, and homogeneous cata-
lysts.
Results and Discussion
Scheme 1. Growth of iron nanoparticles within the cage-like pores of
MCF.
Entrapment of g-Fe O nanoparticles in the cage-like cells
2
3
of MCF: The spherical MCF microparticles were rendered
as hydrophobic by the reaction of the surface silanol groups
with hexamethyldisilazane (HMDS), chlorodimethyloctylsi-
lane (n-C H CHTUNGTRENNUNG( CH ) SiCl, C ) or chlorodimethyloctadecylsi-
17A
8
3 2 8
[16]
lane (n-C H
37A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(CH ) SiCl, C ).
Trimethysilane-capped
18
3
2
18
MCF (TMS-MCF) was obtained by vapor-phase grafting,
À1 [16]
which led to a very high TMS loading of 1.49 mmolg .
g-Fe O3 nanoparticles were easily entrapped inside the
2
cage-like pores of the hydrophobically modified MCF by
thermal decomposition of Fe(CO) in the presence of oleic
5
[17]
acid. In the formation of g-Fe O , iron and oleic acid were
2
3
complexed in the pores of hydrophobic MCF. The strong hy-
drophobic interactions between the modified silica surface
and the surfactant-capped magnetic nanoparticles have been
[18]
2 3
Figure 1. TEM images of g-Fe O /C18-MCF microparticles.
reported previously.
The hydrophobic environments in
the pores prevented Fe(CO) from decomposing on
5
the acidic surface of siliceous MCF. The nascent
small iron nanoparticles that were generated inside
the cell pores grew further under heat treatment.
Once the nanoparticles grew larger than the MCF
window size, they became entrapped in the cage-
like cells, whilst maintaining their spherical mor-
phology (Scheme 1). Repeated washing facilitated
the removal of oleic acid-stabilized iron nanoparti-
cles that were smaller than the window size of
MCF, as well as unused oleic acid. The resulting
iron species were firmly entrapped within the pores
and did not leach out from the support. The iron
Table 1. Characterization of g-Fe
particles that had different pore sizes and surface modifications.
2 3 3 4
O - and Fe O -entrapped MCFs with MCF micro-
Material Composition [(wt.%)]
Cell
size [nm]
Window
size [nm]
Magnetic particle
[a]
[a]
[b]
size [nm]
[c]
A
B
C
D
E
F
G
H
I
TMS-MCF
TMS-MCF
TMS-MCF
14.0
22.3
26.3
23.3
13.9
20.0
26.2
23.7
21.6
4.5
7.7
14.9
11.2
3.9
–
–
–
[
[
d]
e]
[
e]
C
18-MCF
–
[
c]
g-Fe
g-Fe
g-Fe
2
2
2
O
O
O
3
3
3
/TMS-MCF (5.89)
/TMS-MCF (10.04)
/TMS-MCF (15.47)
12
18
24
15
17
[
d]
6.5
[e]
11.6
11.3
6.9
[
e]
g-Fe O /C -MCF (9.87)
2
3
18
[
d]
Fe
3
O
4
/TMS-MCF (5.88)
precursors could be quantitatively converted into [a] Calculated from the nitrogen-adsorption/desorption isotherms; [b] measured from
TEM images that were obtained after grinding magnetic MCF microparticles with a
entrapped iron nanoparticles by performing chemi-
pestle and mortar; [c] MCF was synthesized without the addition of NH
cined at 9008C; [d] MCF was synthesized without the addition of NH F and calcined
at 5508C; [e] MCF was synthesized with the addition of NH F and calcined at 5508C.
4
F and cal-
cal reactions with the surfactants in the hydropho-
bic microenvironment. The entrapped iron nanopar-
ticles were subsequently oxidized into g-Fe O
4
4
2
3
nanoparticles by using trimethylamine N-oxide in
dioctyl ether.
entrapped in the 26.2 nm cells of MCF (Table 1). The high-
resolution SEM images clearly showed the pores on the sur-
face of materials D and H, thus confirming that the magnet-
ic nanoparticles in the latter material were entrapped within
the pores of the MCF microparticles (see the Supporting In-
formation, Figure S7).
TEM images of the resulting magnetic MCF materials
showed the formation of highly monodispersed magnetic
nanoparticles that were entrapped within the cage-like pores
of MCF (Figure 1). The size of the g-Fe O nanoparticles
2
3
was controlled by the MCF cell-size, and by the chain length
of the hydrophobic groups that were used in the surface
modification of MCF (see Table 1). After the entrapment of
the magnetic nanoparticles, the surface area and pore size of
MCF did not change significantly (Table 1, also see the Sup-
porting Information). A high loading of g-Fe O nanoparti-
This method was also used for the entrapment of Fe O4
3
nanoparticles, which were synthesized through similar
[19]
metal–surfactant interactions.
Table 1 shows that this
method can be widely applied to the entrapment of nano-
particles in the cage-like pores of MCF through the thermal
decomposition of metal–surfactant complexes. The relatively
large g-Fe O nanoparticles and their effective entrapment
2
3
cles (>15 wt.%) only decreased the size of the window cell,
but hardly affected the cell size of MCF. For example, mate-
rial G consisted of 24 nm magnetic nanoparticles that were
2
3
within the porous MCF microparticles facilitated the mag-
Chem. Eur. J. 2012, 18, 7394 – 7403
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7395

S. S. Lee, J. Y. Ying et al.
netic separation of the catalytic materials from the reaction
shown to boost the esterification activity of the immobilized
lipases in organic media by five orders of magnitude as com-
medium, even at a low loading of about 7 wt.% of g-Fe O3
2
[21,22]
on MCF. The g-Fe O loading could be controlled by the
pared to free enzymes in solution.
The access of the
2
3
amounts of iron precursor, surfactant, and solvent used.
substrates to the catalytic sites was promoted by the hydro-
phobicity of the support, and the hydrophobic interactions
between the enzyme and the support prevented enzyme
leaching and allowed the enzyme to maintain its active con-
The g-Fe O /MCF materials were used as supports for a
2
3
variety of catalysts. g-Fe O /TMS-MCF was calcined at
2
3
4508C for 5 h to remove the TMS groups (material J) prior
[22]
to its use in the immobilization of nanoclusters and homoge-
neous catalysts. Elemental analysis of the calcined MCF
showed the complete removal of TMS groups. X-ray diffrac-
tion (XRD) confirmed the presence of g-Fe O nanocrystals
formation.
Methods of immobilizing enzymes onto hydrophobic mes-
oporous silica have been developed, including the conven-
[23]
tional stirring of porous silica in an enzyme solution and
2
3
[16]
in g-Fe O /MCF both before and after calcination (see the
the pressure-driven method for enzyme entrapment. Low
enzyme loadings and serious leaching problems have been
reported when enzymes were immobilized onto mesoporous
silica by using the conventional stirring method. In contrast,
the pressure-driven entrapment of enzymes in MCF has led
to high enzyme loading, high catalytic activity, improved
2
3
Supporting Information); the XRD pattern also showed a
broad band (2q=11–298) that was associated with amor-
phous silica.
Previous attempts to derive magnetically modified MCF
adversely impacted the surface area and porosity of the
MCF support. In contrast, the BET surface area and pore
volume of our C -MCF material only decreased slightly
[16]
thermal stability, and reduced enzyme leaching.
We immobilized the CALB enzyme onto the magnetic hy-
18
[
16]
after the loading of about 7 wt.% g-Fe O nanoparticles,
drophobic MCF by using our pressure-driven method.
2
3
2
À1
3
À1
À1
À1
that is, from 238 to 228 m g and from 1.22 to 1.17 cm g ,
Enzyme loadings of 143–200 mgg and 129 mgg were
achieved on magnetic C -MCF and magnetic C -MCF, re-
respectively. Figure 2 shows the N -adsorption/desorption
2
8
18
spectively (Table 2). Although the enzyme loading on mag-
Table 2. Enzyme loading and characteristics of the catalysts.
Catalyst Support [(wt.%; mm)]
Enzyme
Cell
size
[nm]
Window
size
[nm]
loading
À1 [a]
[b]
[b]
[
mgg
]
[
[
[
[
c]
c]
c]
c]
1
2
3
4
g-Fe
g-Fe
g-Fe
2
2
2
O
O
O
3
3
3
/C
/C
/C
8
8
8
-MCF (7.22; 5)
-MCF (6.62; 5)
-MCF (6.79; 2)
200
22.3
22.1
21.4
20.9
8.3
8.4
8.9
8.6
143
143
129
2 3
g-Fe O /C18-MCF (7.76; 5)
[
a] Calculated by elemental analysis and change in weight. [b] Calculated
from nitrogen-adsorption/desorption isotherms. [c] Average size of MCF
microparticles that were obtained by SEM.
Figure 2. Nitrogen-adsorption/desorption isotherms of
wt.% g-Fe
/C18-MCF (&), and catalyst 4 (*).
C
18-MCF (~),
netic C -MCF was not as high as on C -MCF
1
8
8
7
2 3
O
À1 [16]
(
275 mgg ), it was still considerably higher than that at-
tained by C -MCF by the conventional stirring method
8
À1
isotherm of C -MCF before and after the incorporation of
(92 mgg ). The lower enzyme loading on magnetic C -
18
18
magnetic nanoparticles. The cell and window sizes of C -
MCF as compared to C -MCF was presumably due to the
1
8
8
MCF remained essentially unchanged after entrapping
decrease of the support pore volume owing to g-Fe O load-
2
3
about 7 wt.% of g-Fe O .
ing. The loading of magnetic nanoparticles in catalysts 2 and
3 were similar, which gave rise to the identical enzyme load-
ing in these two catalysts.
2
3
The magnetic moments of the materials were measured
by superconducting quantum interference device (SQUID;
see the Supporting Information, Figure S8); these data cor-
related well with the loading amount and size of the mag-
netic nanoparticles as determined by ICP-MS measurements
and TEM, respectively.
Catalyst 4 was also subjected to nitrogen-sorption charac-
terization before and after enzyme immobilization
(Figure 2). It had a slightly lower BET surface area
2
À1
2
À1
(210 m g ) than C -MCF (238 m g ) and g-Fe O /C -
1
8
2
3
18
2
À1
MCF (228 m g ). The cell size of g-Fe O /C -MCF was
2
3
18
Immobilization of candida antarctica lipase B (CALB): One
of the major limitations in enzyme entrapment is the lack of
affinity between the enzyme and the inorganic support sur-
face, thereby causing the enzyme to leach out from the sup-
port. This problem could be resolved by grafting long-
chained hydrocarbons onto the surface of siliceous sup-
slightly smaller (20.9 nm from 22.1 nm) after enzyme load-
ing. This result indicated that the pores were not substantial-
ly blocked by the presence of enzymes, thereby facilitating
the diffusion of substrates in organic transformations.
The entrapped enzyme in magnetic hydrophobic MCF
was characterized by photoacoustic FTIR spectroscopy (PA-
[20]
À1
ports.
Such hydrophobic surface moieties have been
FTIR, see the Supporting Information). NÀH (3300 cm )
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Nanoparticles Entrapped in Siliceous Mesocellular Foam
FULL PAPER
À1
and C=O stretching bands (1650 cm ), which were associat-
for the higher reaction rate in catalyst 3 as compared to cat-
alyst 2. Catalysts 1 and 2 were similar in size and surface hy-
drophobicity, but the former had higher enzyme loading,
which gave rise to higher catalytic activity. The higher
enzyme loading also led to higher catalytic activity for cata-
lyst 1 as compared to catalyst 3. Catalysts 1–4 demonstrated
higher activity than free CALB in an organic reaction
medium. These results could be attributed to the uniform
dispersion of CALB in the magnetic hydrophobic MCF,
thereby allowing the enzymes to remain free from aggrega-
tion, and hence retaining their active conformation.
ed with the peptide bonds in the enzymes, were observed
for the CALB/g-Fe O /C -MCF catalyst, thereby confirming
2
3
8
enzyme incorporation. The CÀH stretching band (2800–
À1
3
000 cm ) was also noted in the spectra of g-Fe O /C -MCF
2
3
8
before and after CALB loading, which was attributed to the
hydrophobic modification of the MCF surface.
The activity of the resulting enzyme catalyst was tested
for the acylation of 1-phenylethanol with isopropenyl ace-
tate (Scheme 2). A fixed amount of CALB was introduced
The enantioselectivity of the reaction was not affected by
the entrapment of CALB in the magnetic hydrophobic
MCF using the pressure-driven method. Over 99% ee for
(
R)-1-phenylethyl acetate was obtained over catalysts 1–4.
Recycling studies were conducted with catalyst 4 (see the
Supporting Information). The activity and enantioselectivity
remained excellent up to 5 runs. Interestingly, after the first
hour, the catalytic activity decreased from 39% to 30%
over 5 runs, whilst the decrease in the conversion of the
product after 8 h was minimal over 5 runs (from 50% to
47%). The drop in catalyst activity in the first hour for the
subsequent runs might have been due to the partial inactiva-
tion and denaturation of the enzymes after catalyst washing
and drying in vacuo. These enzymes seemed to restore their
native structure during the course of the reaction. After
Scheme 2. Kinetic resolution of 1-phenylethanol with isopropenyl acetate
over CALB.
for the acylation of 1-phenylethanol with isopropenyl ace-
tate. Catalysts 1–4 all achieved complete conversion of (R)-
1-phenylethanol into (R)-1-phenylethyl acetate within 8 h
(
Figure 3). After 1 h, catalysts 1 and 4 achieved superior
conversion as compared to CALB that was entrapped in
5
runs, catalyst 4 did not show any change in its powder
XRD pattern (see the Supporting Information, Figure S12).
Immobilization of Pd nanoparticles: Palladium-catalyzed re-
actions have become an important tool in organic synthesis
[24]
owing to their high efficiency and selectivity.
However,
despite their high activity, homogeneous palladium-based
catalysts suffer from low stability and high cost, which hin-
ders their application in industrial processes. To overcome
these challenges, various heterogeneous and heterogenized
[25]
catalysts have been developed. Palladium has been sup-
ported on materials such as carbon, zeolites, silicas, and pol-
[26]
ymers for catalytic applications. Although these supported
palladium catalysts have allowed for facile recovery, palladi-
um leaching remains a serious problem.
Figure 3. Acylation of 1-phenylethanol as a function of time over: cata-
lyst 1 (^),catalyst 2 (
&
),catalyst 3 (~),catalyst 4 (*), and free CALB (*).
[27]
To facilitate the recovery of the supported palladium cata-
lysts, palladium was immobilized on magnetic MCF by using
urea ligands (Scheme 3). Our earlier work on supported pal-
MCF, whilst catalyst 3 showed similar conversion to the
[16]
[28]
latter. Nitrogen-sorption experiments were performed on
all four catalysts, and we found that the cell and window
sizes of all four catalysts were similar. Catalyst 4 (C -modi-
ladium on urea-MCF prompted us to examine the efficacy
of g-Fe O /MCF as a catalyst support. The urea groups were
2
3
introduced onto the pore surface of the siliceous support by
18
fied) had a higher catalytic activity than catalyst 1 (C -modi-
reacting
(CH O) Si
A
H
U
G
R
N
U
G
or
(CH O) Si-
8
3
3
2
3
2
3
3
fied); the difference could stem
from the degree of hydropho-
bicity of the silica support. A
similar trend has been observed
[16]
previously. Catalysts 2 and 3
had similar enzyme loadings,
but the latter had a smaller par-
ticle size. The shorter substrate
diffusion length might account Scheme 3. Immobilization of palladium nanoclusters on magnetic urea-MCF.
Chem. Eur. J. 2012, 18, 7394 – 7403
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7397

S. S. Lee, J. Y. Ying et al.
[
a]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(CH ) NHCONH
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(CH ) CH with magnetic MCF in toluene
Table 3. Transfer hydrogenation of ketones.
2
3
2
2
3
at 808C for 24 h. The loading of the urea ligands in the re-
sulting magnetic urea-MCF was determined by elemental
À1
analysis to be 1.7 mmolg . Pd
A
H
U
G
R
N
U
G
2
solved in CH Cl and mixed with magnetic urea-MCF (2 g).
2
2
Entry
Ketone
t [h]
Yield
[%]
[
b]
The mixture was stirred at room temperature for 30 min and
then heated at 608C for 24 h. The initially dark-brown palla-
dium acetate solution was reduced to elemental palladium,
which was deposited onto the magnetic urea-MCF support
through the urea ligands. The supernatant was colorless
after the reaction, thereby indicating the complete immobili-
zation of palladium onto the support. The resulting Pd/g-
Fe O /urea-MCF (5) was filtered, washed, and dried.
2
8
4
92
82
[c]
1
[
d]
2
3
4
5
6
24
88
2
3
2
8
4
84
80
The palladium nanoclusters had a size distribution in the
range 3–5 nm (Figure 4) and were dispersed uniformly over
magnetic urea-MCF, as confirmed by TEM. X-ray photo-
[
d]
18
96
2
8
4
92
94
[
d]
24
12
96
99
7
8
12
99
Figure 4. TEM and high-resolution TEM (inset) images of palladium
nanoclusters deposited onto g-Fe O /urea-MCF.
2 3
[
5
a] Reaction conditions: 5 wt.% Pd/g-Fe
nm palladium nanoclusters (10 mol%), ketone (1 mmol), formic acid/
2
O
3
/urea-MCF catalyst with 3–
triethylamine (5 mmol, molar ratio=1:1), EtOAc (5 mL), 258C. [b] Yield
of isolated product. [c] Recycled 3 times without any significant loss in
activity or selectivity. [d] Ammonium formate and water were used as the
hydrogen source and solvent, respectively, at 608C.
electron spectroscopy (XPS) indicated that the surface palla-
dium species were mostly present as Pd( ), and the peaks
0
with binding energies (BE) of 334.6 eV and 339.6 eV were
0
0
assigned to Pd 3d5 and Pd 3d , respectively (see the Sup-
/2
3/2
porting Information, Figure S11).
Excellent yields were achieved for the transfer hydrogena-
tion reactions of various ketones over Pd/g-Fe O /urea-
10 wt.% Pd/C catalyst was brown in color after just 1 run
owing to about 90% palladium leaching. Interestingly, when
the transfer hydrogenation of various ketones was per-
formed in water at 608C with ammonium formate as the hy-
drogen source instead of formic acid/triethylamine, the reac-
tion proceeded faster, giving an excellent yield of the corre-
sponding alcohol in just 8 h. The size of Pd nanoclusters
slightly increased after 5 runs from 1–2 nm to 3–5 nm (see
the Supporting Information, Figure S13). However, the over-
all size and shape of the iron oxide nanoparticles were not
affected by the catalytic reactions, as confirmed by the
powder XRD patterns (see the Supporting Information, Fig-
ure S12).
2
3
MCF. Typically, the reactions were performed with 10 mol%
of the 5 wt.% Pd/g-Fe O /urea-MCF catalyst (5) and 5 equiv
2
3
of a formic acid/triethylamine mixture as the hydrogen
source in EtOAc at room temperature. The heterogeneous
catalyst was easily recovered by using an external magnetic
field, and was reused several times without any loss in reac-
tivity or selectivity (Table 3). After 3 runs of the transfer hy-
drogenation reaction of acetophenone (Table 3, entry 1), the
palladium nanoclusters remained highly dispersed and the
catalyst demonstrated negligible loss in activity. The filtrate
of the reaction system was colorless; inductively coupled
plasma mass spectrometry (ICP-MS) confirmed that only
Pd/g-Fe O /urea-MCF was also examined for the hydroge-
2
3
nation of activated olefins (Table 4), such as dimethyl itaco-
nate (Table 4, entry 1) under low pressure (40 psi). The hy-
drogenated product, 1-methyldimethyl succinate, was ob-
tained in 98% yield, and the catalyst was successfully recy-
1
% of the palladium that had been loaded in g-Fe O /urea-
2 3
MCF had leached out after 3 runs. In contrast, the filtrate
from the reaction that contained the commercially available
7398
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 7394 – 7403

Nanoparticles Entrapped in Siliceous Mesocellular Foam
FULL PAPER
[a]
Table 4. Hydrogenation of olefins.
Entry Olefin
Product
t [h] Yield
[
b]
[
%]
[
c]
1
2
8
8
98
98
Scheme 5. Hydrogenation of nitrobenzene.
The catalytic efficacy of Pd/g-Fe O /urea-MCF was also
2
3
tested for the asymmetric hydrogenation of a-methylcin-
namic acid (Scheme 6). Pd/g-Fe O /urea-MCF was modified
3
4
8
8
99
99
2
3
with cinchonidine (Cd) alkaloid by adsorption in CH Cl ,
2
2
followed by drying, and used directly in the asymmetric hy-
5
6
18
18
95
96
Scheme 6. Enantioselective hydrogenation of a-methylcinnamic acid over
cinchonidine-modified Pd/g-Fe O /urea-MCF.
2 3
7
8
24
24
94
97
drogenation reaction. a-Methylcinnamic acid was hydrogen-
ated into the corresponding a-methylhydrocinnamic acid in
quantitative yield and 38% ee. The optimization of the cata-
lyst system and reaction conditions to improve the enantio-
selectivity is underway.
[
5
1
a] Reaction conditions: 5 wt.% Pd/g-Fe
2
O
3
/urea-MCF catalyst with 3–
nm palladium nanoclusters (1 mol%), olefin (1 mmol), hydrogen (40 or
00 psi, for entries 1–6 and 7–8, respectively), MeOH (5 mL), 258C.
[
b] Yield of isolated product. [c] Recycled 5 times without any loss in
yield.
In the transfer hydrogenation, hydrogenation, and reduc-
tive amination reactions, the total palladium leaching after
6
runs was determined by ICP-MS to be <2.5% of the total
cled and reused without any loss in activity over 5 runs. The
hydrogenation of a variety of olefins also proceeded with
excellent yields and catalyst recyclability (Table 4).
palladium loading in the catalyst. The supernatant of the
heterogeneous reaction systems that contained Pd/g-Fe O /
2
3
urea-MCF was colorless at the end of the reactions as there
was negligible leaching of palladium. Thus, this catalyst was
easily isolated and recycled without much loss in activity.
Next, the catalytic activity of Pd/g-Fe O /urea-MCF for
2
3
the reductive amination of aldehydes and amines was exam-
ined. This reaction was very important for producing secon-
dary amines in the pharmaceutical and fine chemicals indus-
tries. Excellent conversions and yields of the corresponding
amines were achieved under mild conditions, and the cata-
lyst was recycled 3 times without any significant loss in reac-
tivity or selectivity (Scheme 4; also see the Supporting Infor-
mation, Table S1).
Immobilization of the ring-closing metathesis (RCM) cata-
lysts: Although RCM reactions are of great interest in the
chemical and pharmaceutical industries, the conventional
ruthenium catalysts suffer from several drawbacks, such as
[29]
high cost and metal leaching.
The immobilization of homogeneous catalyst offers an at-
[30]
Pd/g-Fe O /urea-MCF was found to catalyze the reduction
tractive alternative for industrial applications. Taking ad-
vantage of the robust and orthogonal nature of the click
2
3
of nitro groups into amines. For example, nitrobenzene was
hydrogenated at 100 psi to provide aniline in 98% yield
[
31]
chemistry reaction,
triazole 8 was readily formed from
I
(
Scheme 5; also see the Supporting Information, Table S2).
alkyne 6 and azide 7 over a Cu catalyst (Scheme 7). The
Hoveyda-type ligand was then smoothly grafted onto g-
Fe O /MCF at elevated temperature to provide immobilized
2
3
ligand 9. The green powder (10) was smoothly generated by
treatment with the second-generation Grubbs catalyst in the
I [32]
presence of Cu .
An excellent yield of >90% was ach-
1
3
29
ieved over three steps. FTIR and C and Si cross-polariza-
tion magic angle spinning nuclear magnetic resonance (CP-
MAS NMR) spectra confirmed the immobilization of well-
dispersed Hoveyda-type ligands on the surface of MCF. Ele-
Scheme 4. Reductive amination of aldehydes.
Chem. Eur. J. 2012, 18, 7394 – 7403
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7399

S. S. Lee, J. Y. Ying et al.
Conclusions
Magnetic MCF has been synthesized and used as a versatile
catalyst support. Maghemite nanoparticles (g-Fe O ) were
2
3
incorporated into the siliceous MCF without disrupting its
D pore connectivity. The magnetic nanoparticles were not
3
embedded or grafted onto the pore walls, but rather were
entrapped in the cage-like pores of MCF like a ball in a
rattle. The maghemite particle size could be tuned by chang-
ing the cell size of MCF and the synthesis conditions. The
resulting system was effectively applied to the immobiliza-
tion of CALB enzyme catalysts, palladium nanoclusters, and
homogeneous Grubbs catalysts. The immobilized CALB
demonstrated excellent activity and enantioselectivity in the
kinetic resolution of the acylation of 1-phenylethanol with
isopropenyl acetate. The heterogenized catalysts were easily
separated from the reaction medium by using magnetic
force for reuse. Active palladium nanoclusters were deposit-
ed with high dispersion onto g-Fe O /urea-MCF. They were
Scheme 7. Immobilization of the second-generation Grubbs–Hoveyda
catalyst on g-Fe /MCF by using click chemistry. a) CuI, N,N-diisopro-
pylethylamine (DIPEA), THF, 258C. b) g-Fe /MCF, toluene, 1008C,
then HMDS, 808C. c) Second-generation Grubbs catalyst, CuCl, CH Cl
08C.
2
O
3
2
O
3
2
2
,
5
2
3
mental analysis revealed that the ruthenium loading was
formed by the reduction of Pd ACHTUNREGTNNUNG( OAc) and were stabilized by
2
À1
0.088 mmolg in compound 10.
urea ligands on the MCF surface. The ultralarge MCF pores
facilitated the reaction of bulky substrates. The resulting Pd/
g-Fe O /urea-MCF catalyst demonstrated excellent activity
In the catalyst studies, the diene in Figure 5 was reacted
in CH Cl2 at room temperature. The RCM reaction pro-
2
2
3
ceeded smoothly and was complete within 75 min over
for transfer-hydrogenation and hydrogenation reactions, and
were superior to the commercially available 10 wt.% Pd/C
in terms of both activity and recyclability. A homogeneous
ring-closing metathesis catalyst was also successfully immo-
bilized on the magnetic MCF. The resulting heterogenized
catalyst showed high reactivity and excellent recyclability.
Therefore, our magnetic MCF support has the potential to
be broadly applied to the immobilization of enzyme cata-
lysts, metal and oxide nanoclusters, and homogeneous orga-
nometallic complexes and organocatalysts. The entrapment
method that was developed for the synthesis of g-Fe O /
2
3
MCF could also be extended to the derivation of other mag-
netic nanocomposite systems for functional and biological
applications.
Experimental Section
Figure 5. a) Catalytic activity at 258C with 2.5 mol% (~) and 5.0 mol%
catalyst 10 (
5
&
). b) Recyclability studies of 5.0 mol% of catalyst 10 at
Materials and methods: Spherical MCF microparticles were synthesized
according to our published procedure. They were rendered hydropho-
08C (45 min/run). Substrate concentration=0.05m.
[16]
bic by the reaction of the surface silanol groups with HMDS, n-C
8 17
H -
A
H
U
G
R
N
U
G
3
)
2
H
37
A
H
U
G
R
N
U
3 2
)
chased from Roche. Iron pentacarbonyl, oleic acid, trimethylamine N-
oxide, anhydrous toluene, and isopropenyl acetate were obtained from
Aldrich, and dioctyl ether and 1-phenylethanol were purchased from
Fluka. Solvents, such as cyclohexane, acetone, and toluene, were obtained
from J. T. Baker (A.C.S. grade). SEM and TEM images were obtained on
JEOL JSM-7400F (5 kV) and JEOL JEM-3010 (300 kV) electron micro-
scopes, respectively. Nitrogen-sorption isotherms were obtained on a Mi-
cromeritics ASAP 2020M system and the samples were degassed at
1008C for 24 h before analysis. Analysis of the g-Fe O loading in the ma-
terials was conducted at the Chemical, Molecular, and Materials Analysis
Centre, the National University of Singapore. The enzyme loadings in
the catalysts were determined by elemental analyses on a CE440 CHN
analyzer. PA-FTIR spectra were recorded on a Digilab FTS 7000 FTIR
spectrometer that was equipped with a MTEC-300 photoacoustic detec-
tor.
5
2
mol% of compound 10, but was incomplete after 2 h over
.5 mol% of compound 10 (Figure 5a). The substrate con-
1
centration was 0.05m and the H NMR spectrum indicated
no trace of by-product formation. Next, the recyclability of
compound 10 was investigated in the RCM of the diene in
CH Cl2 at 508C (Figure 5b). The reaction time was kept
2
constant at 45 min to monitor any changes in catalytic activi-
ty over multiple runs. The catalysts were reused after their
facile recovery by applying a magnetic force, and >90%
conversion was obtained, even after 11 runs.
2
3
7400
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Chem. Eur. J. 2012, 18, 7394 – 7403

Nanoparticles Entrapped in Siliceous Mesocellular Foam
FULL PAPER
Entrapment of g-Fe
2.0 g) were dispersed in a mixture of oleic acid (2.0 g, 7.12 mmol) and di-
octyl ether (8 mL), and the slurry was dried under high vacuum at 808C
overnight. The dried mixture was heated to 1008C before Fe(CO) was
injected. For material F, Fe(CO) (0.6 mL) was added to a mixture of
oleic acid (2.0 g) and dioctyl ether (8 mL). The mixture was slowly
heated to 3008C and kept at that temperature for 3 h. The color of the
mixture gradually changed from orange to black. The mixture was then
allowed to cool to ambient temperature and then filtered. The filtrate
was thoroughly washed with hexanes and then transferred into a 100 mL
2
O
3
nanoparticles: Hydrophobic MCF microparticles
through a sintered glass funnel, washed with EtOAc (5 mLꢁ5), and dried
under reduced pressure. The catalyst was recycled 3 times.
(
General procedure for the hydrogenation of olefins: An oven-dried reac-
tion vial was charged with olefin (1 mmol), catalyst (1 mol%), and
MeOH (5 mL) under argon atmosphere. The mixture was pressurized
with hydrogen (100 psi) and stirred at ambient temperature for 16 h. The
progress of the reaction was monitored by GC. After completion of the
reaction, the mixture was filtered through a sintered glass funnel, washed
with MeOH (5 mLꢁ5), and dried under reduced pressure. The catalyst
was recycled 5 times.
5
5
flask. Dioctyl ether (10 mL) and dehydrated (CH
3 3
) NO (1.02 g,
General procedure for the reductive amination of aldehydes under hy-
drogen atmosphere: An oven-dried reaction vial was charged with alde-
hyde (1.0 mmol), primary amine (1.01 mmol), catalyst (1 mol%), and
MeOH (5 mL) under argon atmosphere. The resulting reaction mixture
was pressurized with hydrogen (100 psi) and was stirred at ambient tem-
perature for 16 h. The progress of the reaction was monitored by GC.
After completion of the reaction, the mixture was filtered through a sin-
tered glass funnel, washed with MeOH (5 mLꢁ5), and dried under re-
duced pressure. The catalyst was recycled 3 times.
1
3.68 mmol) were added to the flask. The mixture was heated to 2008C,
and kept at that temperature for 90 min, before being subsequently
heated to 3008C, and refluxed for 1 h before being cooled to ambient
temperature. The resulting suspension was filtered and thoroughly
washed with hexanes. The particles were then thoroughly washed with
MeOH and acetone before being dried under reduced pressure. For the
removal of TMS groups, g-Fe
h. The resulting g-Fe /MCF (J) foam was used for the immobilization
of palladium particles and of the ring-closing metathesis catalyst.
Entrapment of Fe nanoparticles: Oleic acid (1.25 g) and TMS-MCF
2.0 g) were added to a 100 mL 3-necked round-bottomed Schlenk flask.
2 3
O /TMS-MCF was calcined at 4508C for
5
2 3
O
Hydrogenation of nitrobenzene: An oven-dried reaction vial was charged
with nitrobenzene (1 mmol), catalyst (1 mol%), and MeOH (5 mL)
under argon atmosphere. The mixture was pressurized with hydrogen
(100 psi) and stirred at ambient temperature for 16 h. The progress of the
reaction was monitored by GC. After completion of the reaction, the
mixture was filtered through a sintered glass funnel, washed with MeOH
(5 mLꢁ5), and dried under reduced pressure. The catalyst was recycled
5 times.
3
O
4
(
Next, dibenzyl ether was added until the MCF was sufficiently wet.
Oleylamine (0.7 mL) was then subsequently introduced. The reaction
mixture was heated at 608C by using a Digisense apparatus setup and
dried overnight under argon atmosphere. After drying, hexanediol (2 g,
9
2
0%) and Fe ACHTUNGTRENNUNG( acac) (1 g) were weighed in a glove box, and added into
the round-bottomed flask. The Digisense apparatus was then configured
as follows: ramping to 2008C and soaking for 2 h, followed by ramping to
Asymmetric hydrogenation of a-methylcinnamic acid: An oven-dried re-
action vial was charged with a-methylcinnamic acid (1 mmol), cinchoni-
dine-adsorbed catalyst (2 mol%), and THF (5 mL). The mixture was
pressurized with hydrogen (100 psi) and stirred at ambient temperature
for 16 h. The progress of the reaction was monitored by GC. After com-
pletion of the reaction, the mixture was filtered through a sintered glass
funnel, washed with MeOH (5 mLꢁ5), and dried under reduced pres-
sure. The catalyst was recycled 3 times.
3
008C and soaking for 1 h. After the reaction, the solution was filtered
and washed before drying under reduced pressure overnight.
Catalytic enzymatic reaction: In typical reaction, an appropriate
a
amount of heterogenized catalyst (total CALB loading: 2 mg) was dis-
persed in dry toluene (1.5 mL). An aliquot (1.5 mL) of 1-phenylethanol
À1
stock solution in toluene (1.44 mmolmL ) was added at ambient temper-
ature, followed by isopropenyl acetate. A small aliquot was withdrawn
from the reaction mixture every hour, and the reaction was monitored by
GC until complete conversion had occurred, as indicated by the disap-
pearance of the (R)-1-phenylethanol peak. After 8 h, the enantiomeric
excess was determined by HPLC using a chiral Daicel OD-H column.
Preparation of alkyne 6: A 100 mL one-necked flask was charged with
potassium carbonate (7.00 mmol), propargyl bromide (6.00 mmol), the
known phenol (5.00 mmol) and dried MeCN (50 mL). The mixture was
heated at 658C for 15 h, cooled to ambient temperature, and then rough-
ly concentrated under reduced pressure. Et
the organic layer was washed with water (50 mLꢁ2) and brine (50 mLꢁ
), followed by drying over magnesium sulfate. After filtration, the sol-
vent was removed under reduced pressure and the crude product was pu-
rified by column chromatography on silica gel (hexanes/Et O=20:1 to
0:1) and dried under reduced pressure for 24 h to produce the product
2
O (100 mL) was added and
Synthesis of g-Fe
4 h and then cooled to ambient temperature under argon atmosphere.
Dry toluene (20 mL) was added to the particles. Next, a solution of 1-[3-
trimethoxysilyl)propyl]urea (2.2 mmol) in toluene (2 mL) was added.
2 3 2 3
O /urea-MCF: g-Fe O /MCF was dried at 1008C for
1
2
2
(
1
The mixture was stirred under argon atmosphere for 10 min, and then
heated at 808C for 24 h. The mixture was cooled to ambient temperature,
filtered, and washed several times with toluene, EtOH, acetone, and
CH Cl to remove any unreacted precursor. The resulting material was
2 2
suspended in EtOH, and heated at 608C overnight, filtered, washed, and
1
as a colorless oil (4.70 mmol, 94%). H NMR (400 MHz, CDCl
3
): d=1.33
(
d, 6H, J=6.0 Hz), 2.54 (t, 1H, J=2.4 Hz), 4.42 (septet, 1H, J=6.0 Hz),
5
2
1
1
.27 (dd, 1H, J=11.2, 1.4 Hz), 5.72 (dd, 1H, J=17.6, 1.4 Hz), 6.85 (d,
H, J=1.6 Hz), 7.05 (dd, 1H, J=17.6, 11.2 Hz), 7.14 ppm (t, 1H, J=
13
.6 Hz); C NMR (100 MHz, CDCl
3
): d=22.2, 56.5, 72.1, 75.4, 78.8,
dried. Elemental analysis showed a loading of 1.70 mmol of urea per
12.7, 114.4, 115.2, 116.5, 129.2, 131.6, 150.1, 151.8 ppm.
gram of g-Fe
Synthesis of Pd/g-Fe
pended in dry toluene (20 mL), and a solution of palladium acetate (1.10
or 0.55 mmol) in CH Cl (2 mL) was added dropwise. The mixture was
2
O
3
/urea-MCF.
Preparation of azide 7: A 100 mL Schlenk flask was charged with 3-bro-
mopropyltrimethoxysilane (10 mmol), sodium azide (12 mmol), and THF
2
O
3
/urea-MCF: g-Fe
2 3
O /urea-MCF (1 g) was sus-
(
25 mL) under argon atmosphere. The mixture was heated at 658C with
2
2
the valve closed for 15 h, and then cooled to ambient temperature. Hex-
anes (25 mL) was added, and the precipitate was removed by centrifuga-
tion. The liquid was then concentrated under reduced pressure and dried
for 24 h under reduced pressure to give the product as a colorless oil
heated at 608C under argon atmosphere until the supernatant became
colorless (24 h). The mixture was cooled to ambient temperature, filtered,
washed, and dried to obtain Pd/g-Fe
black solid. Elemental analysis showed 1.10 or 0.55 mmol of Pd loading
per gram of g-Fe /urea-MCF, which corresponded to 10 and 5 wt.%
Pd/g-Fe /urea-MCF, respectively.
2 3
O /urea-MCF as a dark-brownish–
(
about 10 mmol, quantitative yield), which was pure enough to be used
O
3
1
2
without further purification. H NMR (400 MHz, CDCl
): d=0.68–0.72
3
2
O
3
(m, 2H), 1.68–1.75 (m, 2H), 3.27 (t, 2H, J=7.2 Hz), 3.58 ppm (s, 9H);
1
3
General procedure for the transfer hydrogenation of ketones: An oven-
dried reaction vial was charged with ketone (1 mmol), a formic acid/trie-
thylamine mixture (molar ratio=1:1) or ammonium formate (5 mmol),
3
C NMR (100 MHz, CDCl ): d=6.29, 22.44, 50.6, 53.7 ppm; MS (FAB):
+
m/z (%): 206 (25) [M+H] , 174 (100), 147 (26).
Preparation of triazole 8: A 50 mL flask was charged with alkyne 6
I
catalyst (10 mol% of 5 wt.% Pd/g-Fe
2
O
3
/urea-MCF), and EtOAc or
(1.00 mmol), azide
7
(1.00 mmol), Cu iodide (0.01 mmol), DIPEA
water (5 mL) under argon atmosphere. The mixture was stirred at ambi-
ent temperature for 24 h and the progress of the reaction was monitored
by GC. After completion of the reaction, the mixture was filtered
(2.00 mmol), and THF (15 mL). The mixture was stirred for 15 h at ambi-
ent temperature, and then concentrated and further dried under reduced
pressure for 24 h to afford the product as a colorless oil (1.00 mmol,
Chem. Eur. J. 2012, 18, 7394 – 7403
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7401

S. S. Lee, J. Y. Ying et al.
quantitative yield), which was pure enough to be used without further
Giri, I. I. Slowing, V. S.-Y. Lin, Chem. Commun. 2007, 3236–3245;
e) Q. Meng, X. Zhang, C. He, G. He, P. Zhou, C. Duan, Adv. Funct.
Mater. 2010, 20, 1903–1909; f) I. I. Slowing, J. L. Viviero-Escoto, C.-
W. Wu, V. S.-Y. Lin, Adv. Drug Delivery Rev. 2008, 60, 1278–1288;
g) T. Xia, M. Kovochich, M. Liong, H. Meng, S. Kabehie, S. George,
J. I. Zink, A. E. Nel, ACS Nano 2009, 3, 3273–3286; h) Z. Luo, K.
Cai, Y. Hu, L. Zhao, P. Liu, L. Duan, W. Yang, Angew. Chem. 2011,
1
purification. H NMR (400 MHz, CDCl
3
): d=0.61–0.65 (m, 2H), 1.32 (d,
6
4
5
1
H, J=6.0 Hz), 2.00–2.08 (m, 2H), 3.57 (s, 9H), 4.37 (t, 2H, J=7.2 Hz),
.40 (septet, 1H, J=6.0 Hz), 5.20 (s, 2H), 5.25 (dd, 1H, J=11.2, 1.4 Hz),
.72 (dd, 1H, J=17.6, 1.4 Hz), 6.85 (dd, 2H, J=4.0, 1.4 Hz), 7.04 (dd,
H, J=17.6, 11.2 Hz), 7.14 (d, 1H, J=2.8 Hz), 7.62 ppm (s, 1H);
1
3
C NMR (100 MHz, CDCl
3
): d=6.16, 22.2, 24.0, 50.7, 52.5, 62.7, 72.1,
1
12.5, 114.4, 114.9, 116.7, 122.6, 129.3, 131.6, 144.3, 149.8, 152.5 ppm; MS
1
23, 666–669; Angew. Chem. Int. Ed. 2011, 50, 640–643.
+
(
FAB): m/z (%): 422 (16) [M+H] , 371 (9), 155 (100).
Preparation of immobilized ligand 9: A 100 mL Schlenk flask was charg-
ed with g-Fe /MCF (1.00 g) and placed under reduced pressure for
4 h at 1208C. The flask was purged with argon at ambient temperature
[
3] a) T. Sen, A. Sebastianelli, I. J. Bruce, J. Am. Chem. Soc. 2006, 128,
7130–7131; b) M. Arruebo, W. Y. Ho, K. F. Lam, X. Chen, J. Arbiol,
J. Santamarꢂa, K. L. Yeung, Chem. Mater. 2008, 20, 486–493; c) J.
Kim, Y. Piao, N. Lee, Y. I. Park, I.-H. Lee, J.-H. Lee, S. R. Paik, T.
Hyeon, Adv. Mater. 2010, 22, 57–60; d) H.-A. Lin, C.-H. Liu, W.-C.
Huang, S.-C. Liou, M.-W. Chu, C.-H. Chen, J.-F. Lee, C.-M. Yang,
Chem. Mater. 2008, 20, 6617–6622; e) W. Zhao, J. Gu, L. Zhang, H.
Chen, J. Shi, J. Am. Chem. Soc. 2005, 127, 8916–8917; f) C. R.
Thomas, D. P. Ferris, J.-H. Lee, E. Choo, M. H. Cho, E. S. Kim, J. F.
Stoddart, J. S. Shin, J. Cheon, J. I. Zink, J. Am. Chem. Soc. 2010,
2
O
3
2
and charged with triethylamine (0.22 mL), dry toluene (20 mL), and tria-
zole 8 (0.15 mmol). The mixture was stirred for 15 h at 808C. The white
solid was thoroughly washed with toluene, CH
2 2 2 2
Cl , MeOH, and CH Cl
(
50 mL each), transferred to a 100 mL Schlenk flask, and dried under re-
duced pressure for 12 h at 808C. After being cooled to ambient tempera-
ture, the flask was placed in a liquid nitrogen bath for 10 min and HMDS
(
1 mL) was added under reduced pressure. The flask was sealed and kept
at 808C for 5 h. The solid was cooled to ambient temperature, washed
thoroughly with CH Cl (100 mL), and then dried under reduced pressure
1
32, 10623–10625.
[
4] a) N. Madhavan, C. W. Jones, M. Weck, Acc. Chem. Res. 2008, 41,
2
2
1
2
153–1165; b) N. Mizuno, M. Misono, Chem. Rev. 1998, 98, 199–
18; c) A. Corma, H. Garcꢂa, Chem. Rev. 2003, 103, 4307–4366;
for 24 h to give the product as a white powder.
Preparation of catalyst 10: A 50 mL two-necked flask that was equipped
with a reflux condenser was charged with ligand 9 (0.18 mmol), second-
generation Grubbs catalyst (0.18 mmol), Cu chloride (0.18 mmol), and
dried CH Cl (20 mL) under argon atmosphere. The reaction mixture
2 2
was heated to reflux for 5 h under argon atmosphere and gradually
changed from dark brown to deep green. After cooling to ambient tem-
d) D. Astruc, F. Lu, J. R. Aramzaes, Angew. Chem. 2005, 117, 8062–
8083; Angew. Chem. Int. Ed. 2005, 44, 7852–7872.
[5] a) D. Macquarrie, Handbook of Green Chemistry and Technology,
Blackwell Science Ltd., Oxford, 2002; b) M. Poliakoff, J. M. Fitzpa-
trick, T. R. Farren, P. T. Anastas, Science 2002, 297, 807–810; c) R.
Noyori, Chem. Commun. 2005, 1807–1811.
6] a) T. Hirakawa, S. Tanaka, N. Usuki, H. Kanzaki, M. Kishimoto, M.
Kitamura, Eur. J. Org. Chem. 2009, 789–792; b) B. Panella, A.
Vargas, A. Baiker, J. Catal. 2009, 261, 88–93; c) L. M. Rossie, F. P.
Silva, L. L. R. Vono, P. K. Kiyohara, E. L. Duarte, R. Itri, R. Land-
ers, G. Machado, Green Chem. 2007, 9, 379–385; d) A. Schꢃtz, M.
Hager, O. Reiser, Adv. Funct. Mater. 2009, 19, 2109–2115; e) D. K.
Yi, S. S. Lee, J. Y. Ying, Chem. Mater. 2006, 18, 2459–2461; f) Y.
Deng, D. Qi, C. Deng, X. Zhang, D. Zhao, J. Am. Chem. Soc. 2008,
I
2 2
perature, the fine powder was washed thoroughly with CH Cl (100 mL)
and dried under reduced pressure for 24 h to give the product as a green
[
powder. Elemental analysis found (%) for 10: C 11.60, H 2.01, N 1.17,
À1
Fe 3.96, Ru 0.89. Loading of ruthenium: 0.088 mmolg
.
Catalytic activity of the RCM catalyst: The reactions were performed in
a vial that contained a magnetic stirrer bar under argon atmosphere. The
vial was charged with catalyst 10 (2.5 or 5.0 mmol) and CH
substrate (0.10 mmol) was injected and the conversion was monitored by
GC or LC after filtration through a short pad of silica gel by CH Cl
2 2
Cl (2 mL). A
2
2
.
1
30, 28–29; g) Y. Deng, Y. Cai, Z. Sun, J. Liu, C. Liu, J. Wei, W. Li,
Recyclability of the RCM catalyst: The reactions were run in a similar
manner as described above. On completion of each run, a magnet was
applied to the reaction vial for 5 min and the supernatant was character-
ized by GC. After discarding the solution, the vial was charged with a
C. Liu, Y. Wang, D. Zhao, J. Am. Chem. Soc. 2010, 132, 8466–8473;
h) Y. Deng, Y. Cai, Z. Sun, D. Gu, J. Wei, W. Li, X. Guo, J. Yang, D.
Zhao, Adv. Funct. Mater. 2010, 20, 3658–3665; i) Y. Deng, Y. Cai, Z.
Sun, D. Zhao, Chem. Phys. Lett. 2011, 510, 1–13.
fresh aliquot of CH
again. Two further rinse cycles were performed before the next run was
conducted with fresh substrate.
2
Cl
2
, stirred for 1 min, and catalyst 10 was collected
[7] J. Ge, T. Hyunh, Y. Hu, Y. Yin, Nano Lett. 2008, 8, 931–934.
[8] A.-H. Lu, W. Schimdt, N. Matoussevitch, H. Bçnnemann, B. Splieth-
off, B. Tesche, E. Bill, W. Kiefer, F. Schꢄth, Angew. Chem. 2004, 116,
4
403–4406; Angew. Chem. Int. Ed. 2004, 43, 4303–4306.
9] P. Wang, Y. Zhu, X. Yang, C. Li, Colloids Surf. A 2007, 294, 287–
91.
10] a) M. Frçba, R. Kçhn, G. Bouffaud, Chem. Mater. 1999, 11, 2858–
865; b) A. B. Bourlinos, A. Simopoulos, N. Boukos, D. Petridis, J.
[
2
[
Acknowledgements
2
Phys. Chem. B 2001, 105, 7432–7437; c) J.-S. Jung, K.-H. Choi, Y.-K.
Jung, S. H. Lee, V. O. Golub, L. Malkinski, C. J. OꢅConnor, J. Magn.
Magn. Mater. 2004, 272, E1157–E1159.
This work was supported by the Institute of Bioengineering and Nano-
technology (Biomedical Research Council, Agency for Science, Technol-
ogy, and Research, Singapore).
[
[
[
11] A.-H. Lu, W.-C. Li, A. Kiefer, W. Schmidt, E. Bill, G. Fink, F.
Schꢄth, J. Am. Chem. Soc. 2004, 126, 8616–8617.
12] D. Lee, J. Lee, H. Lee, S. Jin, T. Hyeon, B. M. Kim, Adv. Synth.
Catal. 2006, 348, 41–46.
13] J. Kim, J. Lee, H. B. Na, B. C. Kim, J. K. Youn, K. M. Kwak, E. Lee,
J. Kim, J. Park, A. Dohnalkova, H. G. Park, M. B. Gu, H. N. Chang,
J. W. Grate, T. Hyeon, Small 2005, 1, 1203–1207.
14] R. P. Hodgkins, A. Ahniyaz, K. Parekh, L. M. Belova, L. Bergstrçm,
Langmuir 2007, 23, 8838–8844.
[15] a) P. Schmidt-Winkel, W. W. Lukens, Jr., D. Zhao, P. Yang, B. F.
Chmelka, G. D. Stucky, J. Am. Chem. Soc. 1999, 121, 254–255; b) P.
Schmidt-Winkel, W. W. Lukens, Jr., P. Yang, D. I. Margolese, J. S.
Lettow, J. Y. Ying, G. D. Stucky, Chem. Mater. 2000, 12, 686–696;
c) J. S. Lettow, Y. J. Han, P. Schmidt-Winkel, P. Yang, D. Zhao, G. D.
Stucky, J. Y. Ying, Langmuir 2000, 16, 8291–8295; d) J. S. Lettow,
T. M. Lancaster, C. J. Glinka, J. Y. Ying, Langmuir 2005, 21, 5738–
[
1] a) X. Feng, G. E. Fryxell, L.-Q. Wang, A. Y. Kim, J. Liu, K. M.
Kemner, Science 2000, 276, 923–926; b) D. Margolese, J. A. Melero,
S. C. Christensen, B. F. Chmelka, G. D. Stucky, Chem. Mater. 2000,
1
2, 2448–2459; c) F. de Juan, E. Ruiz-Hitzky, Adv. Mater. 2000, 12,
4
30–432; d) D. S. Shephard, W. Zhou, T. Maschmeyer, J. M. Matters,
[
C. L. Roper, S. Parsons, B. F. G. Johnson, M. J. Duer, Angew. Chem.
998, 110, 2847–2851; Angew. Chem. Int. Ed. 1998, 37, 2719–2723;
e) J. Y. Ying, C. P. Mehnert, M. S. Wong, Angew. Chem. 1999, 111,
8–82; Angew. Chem. Int. Ed. 1999, 38, 56–77.
2] a) W. A. Cavalho, M. Wallau, U. Schuchardt, J. Mol. Catal. A 1999,
44, 91–99; b) H.-T. Chen, S. Huh, J. W. Wiench, M. Pruzski, V. S.-
1
5
[
1
Y. Lin, J. Am. Chem. Soc. 2005, 127, 13305–13311; c) G. Matteo, C.
Pirovano, N. Ravasio, B. Lazaro, J. M. Fraile, J. A. Mayoral, C. Coq,
A. Galaneau, Green Chem. 2009, 11, 1421–1427; d) B. G. Trewyn, S.
7402
www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 7394 – 7403

Nanoparticles Entrapped in Siliceous Mesocellular Foam
FULL PAPER
5
746; e) Y. Han, J. Y. Ying, Angew. Chem. 2005, 117, 292–296;
Catal. 2005, 347, 161–171; d) K. Kçhler, R. G. Heidenreich, J. G. E.
Krauter, J. Pietsch, Chem. Eur. J. 2002, 8, 622–631.
Angew. Chem. Int. Ed. 2005, 44, 288–292.
[
[
16] Y. Han, S. S. Lee, J. Y. Ying, Chem. Mater. 2006, 18, 643–649.
17] T. Hyeon, S. S. Lee, J. Park, Y. Chung, H. B. Na, J. Am. Chem. Soc.
[26] a) A. L. Dantas Ramos, P. da Silva Alves, D. A. G. Aranda, M.
Schmal, Appl. Catal. A 2004, 277, 71–81; b) C. P. Mehnert, J. Y.
Ying, Chem. Commun. 1997, 2215–2216; c) C. P. Mehnert, D. W.
Weaver, J. Y. Ying, J. Am. Chem. Soc. 1998, 120, 12289–12296;
d) M. K. Richmond, S. L. Scott, H. Alper, J. Am. Chem. Soc. 2001,
123, 10521–10525; e) K. Okumura, K. Nota, K. Yoshida, M. Niwa,
J. Catal. 2005, 231, 245–253; f) H.-U. Blaser, A. Indolese, A.
Schnyder, H. Steiner, M. Studer, J. Mol. Catal. A 2001, 173, 3–18.
[27] a) F. Zhao, B. M. Bhanage, M. Shirai, Y. Ikushima, M. Arai, J. Mol.
Catal. A 2002, 180, 211–219; b) B. H. Lipshutz, S. Tasler, W. Chris-
man, B. Spliethoff, B. Tesche, J. Org. Chem. 2003, 68, 1177–1189.
[28] N. Erathodiyil, S. Ooi, A. M. Seayad, Y. Han, S. S. Lee, J. Y. Ying,
Chem. Eur. J. 2008, 14, 3118–3125.
2
001, 123, 12798–12801.
[
[
18] T. R. Sathe, A. Agrawal, S. Nie, Anal. Chem. 2006, 78, 5627–5632.
19] J. Xie, S. Peng, N. Brower, N. Pourmand, S. X. Wang, S. Sun, Pure
Appl. Chem. 2006, 78, 1003–1014.
[
20] a) M. T. Reetz, P. Tielmann, W. Wiesenhçfer, W. Kçnen, A. Zonta,
Adv. Synth. Catal. 2003, 345, 717–728; b) S. Maury, P. Buisson, A. C.
Pierre, J. Mol. Catal. B 2002, 19, 269–278.
[
21] a) M. T. Reetz, J. Simpelkamp, A. Zonta, German Patent DE
4
408152 A1, 1995; b) M. T. Reetz, Adv. Mater. 1997, 9, 943–954;
c) L. Veum, U. Hanefeld, A. Pierre, Tetrahedron 2004, 60, 10419–
0425; d) R. B. Bhatia, C. J. Brinker, C. S. Ashley, T. M. Harris,
1
Mater. Res. Soc. Symp. Proc. 1998, 519, 183–188.
22] T. Gitlesen, M. Bauer, P. Adlercreutz, Biochim. Biophys. Acta
Lipids Lipid Metab. 1997, 1345, 188–196.
23] a) H. Takahashi, B. Li, T. Sasaki, C. Miyazaki, T. Kajino, S. Inagaki,
Chem. Mater. 2000, 12, 3301–3305; b) H. H. P. Yiu, C. H. Botting,
N. P. Botting, P. A. Wright, Phys. Chem. Chem. Phys. 2001, 3, 2983–
[29] a) P. A. Evans, J. Cui, S. J. Gharpure, A. Polosukhin, H.-R. Zhang, J.
Am. Chem. Soc. 2003, 125, 14702–14703; b) A. Deiters, S. F. Martin,
Chem. Rev. 2004, 104, 2199–2238; c) T. Nicola, M. Brenner, K.
Donsbach, P. Kreye, Org. Process Res. Dev. 2005, 9, 513–515.
[30] a) Q. W. Yao, Angew. Chem. 2000, 112, 4060–4062; Angew. Chem.
Int. Ed. 2000, 39, 3896–3898; b) J. Lim, S. S. Lee, S. N. Riduan, J. Y.
Ying, Adv. Synth. Catal. 2007, 349, 1066–1076; c) J. Lim, S. N.
Riduan, S. S. Lee, J. Y. Ying, Adv. Synth. Catal. 2008, 350, 1295–
1308; d) J. Lim, S. S. Lee, J. Y. Ying, Chem. Commun. 2008, 4312–
4314; e) J. Lim, S. S. Lee, J. Y. Ying, Chem. Commun. 2009, 46, 806–
808.
[
[
2
2
985; c) H. H. P. Yiu, P. A. Wright, N. P. Botting, J. Mol. Catal. B
001, 15, 81–92; d) E. Dumitriu, R. Secundo, J. Patarin, I. Fechete,
J. Mol. Catal. B 2003, 22, 119–133; e) J. He, X. Li, D. G. Evans, X.
Duan, C. Li, J. Mol. Catal. B 2000, 11, 45–53; f) Y. Wang, F. Caruso,
Chem. Mater. 2005, 17, 953–961.
[
24] a) T. Mizoroki, K. Mori, A. Ozaki, Bull. Chem. Soc. Jpn. 1971, 44,
[31] J.-F. Lutz, Angew. Chem. 2007, 119, 1036–1043; Angew. Chem. Int.
Ed. 2007, 46, 1018–1025.
[32] J. S. Kingsbury, J. P. A. Harrity, P. J. Bonitatebus, Jr., A. H. Hoveyda,
J. Am. Chem. Soc. 1999, 121, 791–799.
5
2
81–581; b) R. F. Heck, J. P. Nolley, J. Org. Chem. 1972, 37, 2320–
322; c) A. Suzuki, Chem. Commun. 2005, 4759–4763; d) A. Zapf,
M. Beller, Chem. Commun. 2005, 431–440; e) M. T. Reetz, J. G.
de Vries, Chem. Commun. 2004, 1559–1563.
[
25] a) C. Rocaboy, J. A. Gladysz, Org. Lett. 2002, 4, 1993–1996; b) D. E.
Bergbreiter, P. L. Osburn, J. D. Frels, Adv. Synth. Catal. 2005, 347,
Received: July 29, 2011
Revised: February 28, 2012
Published online: May 15, 2012
1
72–184; c) K. Yu, W. Sommer, M. Weck, C. W. Jones, Adv. Synth.
Chem. Eur. J. 2012, 18, 7394 – 7403
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7403