A yolk-shell nanoreactor with a basic core and an acidic shell for cascade reactions

Article abstract of DOI:10.1002/anie.201204829

Smart yolk-shell nanoparticles (hollow nanoparticles with a movable core) with an acidic shell and a basic core were fabricated through an organosilane-assisted selective etching method and acted as efficient nanoreactors for catalyzing a deacetalization-Henry cascade reaction with high activity and high selectivity. This strategy is very promising for the design of multifunctional nanoreactors for cascade reactions. Copyright

Full text of DOI:10.1002/anie.201204829

Angewandte
Chemie
DOI: 10.1002/anie.201204829
Nanostructures
AYolk–Shell Nanoreactor with a Basic Core and an Acidic Shell for
Cascade Reactions**
Yan Yang, Xiao Liu, Xiaobo Li, Jiao Zhao, Shiyang Bai, Jian Liu,* and Qihua Yang*
Cascade reactions, which allow a consecutive series of
chemical reactions to proceed in a concurrent fashion, have
attracted intensive research attention owing to their high
and shell step-by-step by using the versatile sol–gel chemistry.
By using this method, the catalytic functionalities including
even incompatible groups, such as acidic and basic groups,
could be located in a controlled manner either in the core or
on the shell of YSNs. Herein, we present the fabrication of
YSNs with basic core (-NH ) and acidic shell (-SO H) by an
organosilane-assisted selective etching method. The catalytic
efficiency of these YSNs as nanoreactors for catalyzing the
deacetalization–Henry cascade reaction was demonstrated.
This synthetic method has been extended to the synthesis of
various functionalized YSNs and YSNs with multilayered
shells, thus providing a general approach for the fabrication of
multifunctional nanoreactors.
[
1]
atom economy, step-saving and biomimetic nature. For
efficiently catalyzing a cascade reaction, the fabrication of
solid catalysts with precise control over the location of
different functionalities is generally required but still a great
2
3
[
2]
challenge. In comparison with the solid catalysts without
well-defined morphology, the yolk–shell nanoparticles
(
YSNs) with unique core@void@shell nanostructure are
promising candidates as nanoreactors for cascade reactions
owing to the easy functionalization of both the core and the
shell, the high density of exposed active sites endowed by the
movable core, and the protection effect endowed by the shell,
The overall process for the synthesis of YSNs with basic
core and acidic shell is illustrated in Figure 1A (for synthesis
details see Section S4 of the Supporting Information).
Initially, spherical mesoporous silica nanospheres (MSNs)
[
3]
especially under harsh reaction conditions. Significantly,
since each core in the YSNs is isolated by a permeable shell
and has a relatively homogeneous environment, in principle,
the catalytically active sites could be accurately located in the
core or on the shell. This arrangement provides the possibility
to design and fabricate solid nanoreactors for cascade
[
4]
reactions.
However, the YSNs reported to date are generally
composed of a catalytically active core, such as metal, metal
oxide, and alloy nanoparticles, with inert shell, which limited
their further applications as nanoreactors in cascade reac-
tions. The synthesis of YSNs with precisely located active sites
both in the core and on the shell is no easy task and has rarely
been reported, though various synthesis methods have been
developed, including ship-in-bottle approach, soft templating
approaches, template-free approaches, Ostwald ripening or
galvanic replacement processes, and methods based on the
[5]
Kirkendall effect.
Recently, a facile organosilane-assisted etching method
has been developed by our group to fabricate YSNs based on
the in situ formation of the shell and partially or completely
[
6]
etching the predefined core. A unique feature of this
method is the possibility to precisely functionalize the core
[
*] Y. Yang, Dr. X. Liu, X. B. Li, Dr. J. Zhao, Dr. S. Y. Bai, Dr. J. Liu,
Prof. Q. H. Yang
State Key Laboratory of Catalysis
Dalian Institute of Chemical Physics
Chinese Academy of Sciences
Figure 1. A) Schematic illustration showing the general procedure for the
synthesis of YS-NHBoc@SH with NHBoc in the core and SH on the shell
NHBoc=NHOCOC(CH ) ); B,C) TEM images of NHBoc-functionalized
(
3
3
mesoporous silica nanospheres before (B) and after (C) coating with
a sacrificial silica layer; D) TEM image of YS-NHBoc@SH obtained by
treatment of the sample in (C) with BTME and MPTMS; E) FTIR spectrum
of YS-NHBoc@SH; F) HAADF-STEM image of YS-NHBoc@SH after treat-
ment with H PtCl and PdCl (before the treatment with PdCl , the sample
457 Zhongshan Road, Dalian 116023 (China)
E-mail: yangqh@dicp.ac.cn
Homepage: http://www.hmm.dicp.ac.cn
2
6
2
2
[
**] The authors would like to thank the National Natural Science
Foundation of China (20923001) and the National Basic Research
Program of China (2009CB623503) for the financial support.
was treated in vacuum at 1508C to convert the NHBoc groups into NH2
groups); and G) EDX analysis along the line shown in (F) of a broken
nanosphere that was chosen intentionally. The upper, middle, and lower
traces correspond to Si, Pd (magnified by a factor of 9), and Pt (magnified
by a factor of 10), respectively.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201204829.
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

.
Angewandte
Communications
functionalized with 3-tert-butyloxycarbonylaminopropyl
groups were prepared by co-condensation of 3-tert-butyloxy-
carbonylaminopropyltriethoxysilane and tetraethoxysilane
YS-NH @SO H with basic core and acidic shell can be
2 3
facilely obtained through post-treatment of YS-NHBoc@SH
by oxidation of the SH to SO H groups using H O and
3
2
2
[2b,8]
(
TEOS) in the presence of cetyltrimethyl-ammonium bro-
deprotection of the NHBoc to NH groups
(for exper-
2
mide (CTAB) in NaOH aqueous solution according to
imental details see Section S6 of the Supporting Information).
The HRTEM image of YS-NH @SO H clearly shows the
uniform distribution of the monodispersed YSNs with a core
size of 100 nm, a void space between the core and the shell of
approximately 20 nm, and a shell thickness of approximately
20 nm (Figure 2A). 2-D hexagonal arrangement of the
[
7]
a modified Stçber method. The average particle size is
around 100 nm based on the transmission electron microsco-
py (TEM) image (Figure 1B). After the hydrolysis and
condensation of TEOS catalyzed by ammonia, the nano-
spheres were covered with a silica layer with a thickness of
2
3
2
2 nm (Figure 1C). The subse-
quent addition of 1,2-bis(trimeth-
oxysilyl)ethane (BTME) and (3-
mercaptopropyl)trimethoxysilane
(
MPTMS) into the synthesis
system resulted in the formation
of YS-NHBoc@SH with a yolk–
shell nanostructure. As shown in
Figure 1D, YS-NHBoc@SH has
a
2
shell thickness of around
0 nm and the void between core
and shell is approximately 24 nm,
thus suggesting that only the silica
layer around the parent NHBoc-
MSNs was selectively etched
during the organosilane-assisted
etching process. This finding sug-
gests that the silica layer acts as
a sacrificial layer to protect the
core and the dissolution of the
silica layer generates the void
space between the core and the
shell.
Figure 2. Characterization results of YSNs with basic cores and acidic shells (YS-NH @SO H). A) TEM
image, B) SEM image, C) FTIR spectrum, D) UV-Raman spectrum, and E) C cross-polarization magic-
2
3
13
The successful incorporation angle spinning (CP/MAS) NMR spectrum of YS-NH @SO H.
2
3
of NHBoc groups in YS-
NHBoc@SH was verified by
FTIR spectroscopy (Figure 1E). The location of the func-
tional groups in YS-NHBoc@SH after selective coordination
mesopores in the core and the existence of the open
mesopores on the shell are observed, which is quite important
to facilitate the mass diffusion of the guest molecules through
the YSNs. The appearance of one strong diffraction peak
between 1–38 in the XRD pattern proves that YS-NH @SO H
4
+
2+
of Pt and Pd ions to SH and NH groups, respectively, was
2
characterized by TEM, high angular annular dark-field
scanning transmission electron microscopy (HAADF-
STEM), and energy-dispersive X-ray spectrometry (EDX;
for experimental details see Section S5 of the Supporting
Information). The HAADF-STEM image (Figure 1F) of the
2
3
has an ordered mesostructure (Figure S1 in the Supporting
Information), which is consistent with the TEM result. The
SEM image verifies that YS-NH @SO H is composed of
2
3
2
+
4+
resulting YS-NH -Pd @SH-Pt provides a clear contrast of
uniform and monodispersed nanospheres with an average
particle size of 190 nm (Figure 2B). The nitrogen adsorption–
desorption isotherm of YS-NH @SO H displays a typical
2
the core, the hollow part, and the porous shell. The EDX
elemental analysis of a broken sample shows the hollow
region between the core and shell, with the core rich in Pd and
2
3
type-IV isotherm with a two-step capillary condensation in
the relative pressure range of 0.1–0.3 and 0.5–0.9 (Figure S2 in
the Supporting Information); this type of isotherm is in
agreement with the presence of a hierarchical porosity
the shell rich in Pt, thereby confirming that NH and SH
2
groups are mainly located in the core and on the shell,
respectively (Figure 1F and G). The successful location of
different types of functional groups in YSNs is attributed to
the separate steps for core and shell formation and the
protection effect of the sacrificial silica layer covering the
initial nanospheres. Thus, it is possible to precisely locate the
active sites in the core or on the shell of YSNs through
controlled addition of functional groups at different synthetic
steps.
[
5k]
organization of the yolk–shell nanostructure.
YS-
2
À1
NH @SO H has a BET surface area of 178 m g , a pore
2
3
3
À1
volume of 0.30 cm g , and a pore diameter of 2.4 nm
(Table S1 in the Supporting Information). The above charac-
terizations suggest that the morphology, structure, and
physical parameters of YS-NH @SO H are identical to
2
3
those of YS-NHBoc@SH (Figure 1D; Figure 2A; Table S1
in the Supporting Information), thus showing that YS-
2
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
NHBoc@SH is robust enough to survive the post-treatment
process.
The chemical composition of YS-NH @SO H was verified
2
3
by FTIR, UV-Raman, and NMR spectroscopy (Figure 2C–
E). The FTIR spectrum of YS-NH @SO H displays character-
2
3
À1
istic peaks at 2958–2854 cm assigned to CH vibrations of
bridging ethylene and propyl groups, and 1596 cm attrib-
uted to NH vibration of amine groups (Figure 2C). The
existence of sulfonic acid groups was confirmed by the
vibration at 1045 cm in the UV-Raman spectrum of YS-
À1
[9]
À1
[
8]
13
NH @SO H (Figure 2D). The C CP/MAS NMR spectrum
2
3
of YS-NH @SO H displays the signals at d = 53.4 and
2
3
4
2.0 ppm assigned to the carbon atoms bonded to sulfonic
[2b]
acid and amine groups, respectively (Figure 2E), thereby
confirming the existence of amine and sulfonic acid groups.
The solid-state Si NMR spectrum of YS-NH @SO H (Fig-
2
9
2
3
ure S3 in the Supporting Information) shows the character-
istic resonances in the range of d = À103 to À112 ppm and d =
À57 to À67 ppm, which are attributed to Q and T silicon
species, respectively. The above characterizations further
Figure 3. Synthetic process and TEM characterizations of YSNs with
one and two shells. A) Schematic illustration showing the strategy to
YSNs with one and two shells; TEM images of B) YS-silica@ethanesil-
ica with a single shell and C) YS-silica@ethanesilica@ethanesilica with
two shells (the inset shows the SEM image, scale bar is 200 nm).
confirm the successful incorporation of NH2 and SO H
3
functional groups in the YSNs. YS-NH @SO H exhibits an
2
3
À1
amino content of 240 mmolg and acidic exchange capacity of
0 mmolg . This result shows that YS-NH @SO H has both
À1
8
Information and Figure 3B). A control experiment shows
that the direct addition of BTME to the synthesis medium of
the MSNs (without deposition of a silica layer) can result in
the formation of yolk–shell nanostructures with rough
surfaces and disorderly structured cores (Figure S8 in the
Supporting Information). The presence of the silica sacrificial
layer is an essential element that ensures the core retains the
original mesostructure and remains discrete.
2
3
acidic and basic functionalities (Table S1 in the Supporting
Information).
The above synthetic approach provides an easy route
towards the fabrication of YSNs with precise control over the
location of various active sites. The synthesis of YS-silica@-
SO H (pure silicate core with SO H groups on the shell) and
3
3
of YS-NH @ethanesilica (amine groups in the core and
2
ethylene-bridged organosilica shell) has been successfully
demonstrated (for experimental details see Section S7 of the
Supporting Information). The TEM images show that both
samples have a similar yolk–shell nanostructure and identical
particle size and core size as YS-NH @SO H (Figure S4 in the
A repetition of the synthesis process would yield yolk–
shell nanoparticles with multiple shells (Figure 3C). To
prepare YSNs with two shells (YS-silica@ethane-
silica@ethanesilica), YS-silica@ethanesilica was selected as
seed, and the addition of TEOS and BTME was repeated as
shown in Figure 3A (for synthesis details see Section S8 of the
Supporting Information). YS-silica@ethanesilica@ethanesil-
ica with a particle size of 240 nm is composed of two
mesoporous shells with shell thicknesses of 40 nm and an
interlayer space of 5–6 nm, a void space between the core and
shell, and the mesoporous core with highly ordered structure
(Figure 3C). The SEM image of the broken nanosphere that
was chosen intentionally after mechanical fracturing, further
confirms the double-shelled nanostructure (inset of Fig-
ure 3C). The existence of the strong diffraction peak in the
XRD pattern confirms the ordered organization of the
mesopores in the core; this result is consistent with the
TEM result (Figure S9 in the Supporting Information). The
nitrogen sorption isotherm shows a type-IV isotherm with two
2
3
Supporting Information). The successful incorporation of
sulfonic acid and amine groups in YS-silica@SO H and YS-
3
NH @ethanesilica, respectively, was further confirmed by
2
FTIR and UV-Raman spectroscopy (Figure S5 in the Sup-
porting Information), thereby showing the generality of this
method for the fabrication of YSNs with precise location of
the functional groups. YS-silica@SO H and YS-
3
NH @ethanesilica have identical pore diameters of 2.4 nm
2
2
À1
with BET surface areas of 157 and 239 m g , respectively
(
Table S1 in the Supporting Information).
Similar to the synthesis of YS-NH @SO H, YS-silica@-
2
3
ethanesilica (pure silica core and ethylene-bridged organo-
silica shell; for synthesis details see Section S8 of the
Supporting Information) can also be obtained by using
mesoporous silica nanospheres as initial material (MSNs)
and BTME as the organosilane source (Figure 3A). YS-
silica@ethanesilica has an average particle size of 190 nm,
a core size of 110 nm, and a void space between the core and
the shell of approximately 20 nm based on the SEM and TEM
images (Figure S6 in the Supporting Information and Fig-
ure 3B). The spherical core of YS-silica@ethanesilica has
a highly ordered 2-D hexagonal mesostructure as evidenced
by XRD and TEM results (Figure S7 in the Supporting
hysteresis loops at relative pressure values P/P of 0.2–0.4 and
0
0.5–0.8 that correspond to the mesopores of 2.4 nm in the core
and shell and the interlayer space of 5.8 nm, respectively
(Figure S10 in the Supporting Information); this result further
confirms the double-shelled structure. The doubled-shelled
2
À1
YSNs exhibit high BET surface areas of 708 m g with a total
3
À1
pore volume of 0.81 cm g (Table S1 in the Supporting
Information). It is believed that YSNs with an ordered
mesoporous core and multiple shells can also be synthesized
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

.
Angewandte
Communications
by repeating the coating and etching steps. Hence, the
versatility of this synthesis strategy towards the fabrication
of YSNs with well-located active sites, controllable shell
layers and compositions, and complex hollow structures has
been successfully demonstrated.
The catalytic performance of YS-NH @SO H was tested
2
3
in the deacetalization–Henry cascade reaction and compared
with that of YS-NH @ethanesilica and YS-silica@SO H
2
3
(
Table 1). The deacetalization reaction is firstly catalyzed by
Figure 4. Catalytic performance of the YSN nanoreactor. A) The reac-
the SO H groups, followed by the Henry reaction catalyzed
3
tion profiles of YS-NH @SO H (a), and the mixture (b) of
2
3
YS-NH @ethanesilica and YS-silica@SO H for the deacetalization–
2
3
Table 1: Deacetalization–Henry cascade reaction catalyzed by different
Henry cascade reaction. B) Schematic illustration of the cascade
reaction in a YS-NH @SO H nanoreactor.
[
a]
catalysts.
Catalyst
2
3
basic functional groups in one nanoreactor could shorten the
reaction pathway. Thus the much lower catalytic activity of
the physical mixture than of YS-NH @SO H is mainly due to
Conv.
Yield
Yield
TOF
[
b]
[b]
À1
of 1 [%]
of 2 [%]
of 3 [%]
[h
]
2
3
the long diffusion route from one acidic nanoreactor to the
other basic one. Furthermore, YS-NH @SO H shows 100%
YS-silica@SO H
100
trace
>99
trace
trace
trace
–
–
3
YS-NH @ethanesilica
2
2
3
YS-NH @ethanesilica
2
conversion with quantitative yield of the final product for 4-
methyl and 4-nitro-benzaldehyde dimethyl acetal and 77%
conversion with 65% yield of the final product for 4-chloro-
benzaldehyde dimethyl acetal (Table S2 in the Supporting
Information). The high yield and selectivity of YS-
NH @SO H suggest that the appropriate location of the
+
55
trace
55
6
[
c]
YS-silica@SO H
3
YS-NH @SO H
100
100
100
trace
12
28
>99
88
72
13
–
–
2
3
[
d]
YS-NH @SO H 2nd
2
3
[
d]
YS-NH @SO H 3rd
2
3
2
3
[a] Reaction conditions: benzaldehyde dimethyl acetal (0.5 mmol), solid
active sites in the YSNs is essential to make different kinds of
functional groups work efficiently during the catalytic pro-
cess, especially for the ones that are incompatible with each
other.
catalyst (0.025 mmol of amine), CH NO (5 mL), 908C, 22 h. [b] Deter-
3
2
mined by GC analysis using nitrobenzene as internal standard.
c] Physical mixture of YS-NH @ethanesilica and YS-silica@SO H con-
[
2
3
taining the same amount of amine and acid as YS-NH @SO H. [d] The
second or third recycled catalysts.
2
3
YS-NH @SO H can be recycled and exhibits 100%
2
3
conversion with 88% and 72% yield of nitrostyrene for the
second cycle and third cycle, respectively (Table 1). The TEM
characterization (Figure S11 A in the Supporting Informa-
tion) shows that the used YS-NH @SO H still has a well-
by the amine groups. Thus only the co-existence of acidic and
basic groups could catalyze the reaction smoothly. No
2
3
reaction occurs in the presence of YS-NH @ethanesilica,
and only the deacetalization product is observed using YS-
defined yolk–shell nanostructure but the structural order of
the core was deteriorated. The slight decrease in the yield of
nitrostyrene (catalyzed by amine groups) is probably due to
the deteriorated structural order of the core.
2
silica@SO H. As expected, the cascade reaction can be
3
efficiently catalyzed by YS-NH @SO H with high activity
2
3
(
100% conversion) and selectivity (100%). This finding
In summary, we demonstrated the facile synthesis of YSNs
with controllable chemical compositions, spatial locations of
functional groups, and tuneable shell layers. Through the
organosilane-assisted selective etching method, various func-
tionalized YSNs with well-located active sites, both in the core
and on the shell, that included the active functional groups
-NH , -SH, and -SO H, were synthesized, and the location of
suggested that acid on the shell and base in the core are
efficiently separated by the unique yolk–shell nanostructure,
without neutralization. The mixture of YS-NH @ethanesilica
and YS-silica@SO H can also catalyze the reaction with 55%
conversion under the same reaction conditions (the content of
NH and SO H in different catalysts is shown in Table S1 in
2
3
2
3
2
3
the Supporting Information). Based on the reaction profiles,
the mixture of YS-NH @ethanesilica and YS-silica@SO H
the functional groups was clearly characterized. By introduc-
ing amine and sulfonic acid groups into the cores and onto the
shells, respectively, the yolk–shell nanoreactors with isolated
acidic and basic active sites in one nanoreactor were obtained
for the first time, and showed high catalytic activity in a one-
pot deacetalization–Henry cascade reaction. It can be envi-
sioned that YSNs with various well-located active sites,
controllable shell layers and chemical compositions could
also be synthesized through this strategy. The spatial isolation
effect presented herein may open up new opportunities for
the applications of multiple functionalized YSNs as efficient
nanoreactors for catalysis.
2
3
exhibits a much lower reaction rate than YS-NH @SO H
2
3
À1
(
turnover frequency (TOF): 6 versus 13 h ; Figure 4A). The
reaction route to explain the high activity of YS-NH @SO H
2
3
is depicted in Figure 4B. The reactant (benzaldehyde
dimethyl acetal) diffuses through the porous shell, and its
conversion into benzaldehyde is catalyzed by -SO H groups
3
on the shell. The intermediate benzaldehyde diffuses further
into the core and is converted into the final product,
nitrostyrene; this reaction is catalyzed by the -NH groups
2
located in the core. The integration of both the acidic and
4
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
Received: June 20, 2012
Published online: && &&, &&&&
G. A. Somorjai, Nat. Mater. 2009, 8, 126 – 131; d) Q. Zhang, I. Lee,
J. P. Ge, F. Zaera, Y. D. Yin, Adv. Funct. Mater. 2010, 20, 2201 –
214; e) B. Liu, W. Zhang, H. L. Feng, X. L. Yang, Chem.
2
Commun. 2011, 47, 11727 – 11729; f) X. L. Fang, Z. H. Liu, M.-
F. Hsieh, M. Chen, P. X. Liu, C. Chen, N. F. Zheng, ACS Nano
Keywords: cascade reactions · yolk–shell nanoparticles · acid–
base nanoreactors · nanostructures
.
2012, 6, 4434 – 4444; g) D. A. Wilson, R. J. M. Nolte, J. C. M.
van Hest, Nat. Chem. 2012, 4, 268 – 274; h) S. Wu, J. Dzubiella, J.
Kaiser, M. Drechsler, X. H. Guo, M. Ballauff, Y. Lu, Angew.
Chem. 2012, 124, 2272 – 2276; Angew. Chem. Int. Ed. 2012, 51,
[
1] a) C. Grondal, M. Jeanty, D. Enders, Nat. Chem. 2010, 2, 167 –
178; b) M. Climent, A. Corma, S. Iborra, M. Mifsud, J. Catal. 2007,
247, 223 – 230; c) K. C. Nicolaou, J. S. Chen, Chem. Soc. Rev. 2009,
38, 2993 – 3009; d) R. J. R. W. Peters, I. Louzao, J. C. M. van Hest,
2
229 – 2233.
5] a) K. Kamata, Y. Lu, Y. N. Xia, J. Am. Chem. Soc. 2003, 125,
384 – 2385; b) Y. D. Yin, R. M. Rioux, C. K. Erdonmez, S.
Hughes, G. A. Somorjai, A. P. Alivisatos, Science 2004, 304,
11 – 714; c) D. M. Cheng, X. D. Zhou, H. B. Xia, H. S. O. Chan,
[
2
Chem. Sci. 2012, 3, 335 – 342; e) D. M. Vriezema, M. C. Aragones,
J. Elemans, J. Cornelissen, A. E. Rowan, R. J. M. Nolte, Chem.
Rev. 2005, 105, 1445 – 1489; f) C. Zhao, J. A. Lercher, Angew.
Chem. 2012, 124, 6037 – 6042; Angew. Chem. Int. Ed. 2012, 51,
7
Chem. Mater. 2005, 17, 3578 – 3581; d) Y. Vasquez, A. K. Sra,
R. E. Schaak, J. Am. Chem. Soc. 2005, 127, 12504 – 12505;
e) H. M. Chen, R. S. Liu, K. Asakura, J. F. Lee, L. Y. Jang, S. F.
Hu, J. Phys. Chem. B 2006, 110, 19162 – 19167; f) D. K. Yi, S. S.
Lee, G. C. Papaefthymiou, J. Y. Ying, Chem. Mater. 2006, 18, 614 –
5935 – 5940.
[
2] a) A. Katz, M. E. Davis, Nature 2000, 403, 286 – 289; b) J.
Alauzun, A. Mehdi, C. Reye, R. J. P. Corriu, J. Am. Chem. Soc.
2006, 128, 8718 – 8719; c) N. T. S. Phan, C. S. Gill, J. V. Nguyen,
619; g) H. X. Li, Z. F. Bian, J. Zhu, D. Q. Zhang, G. S. Li, Y. N.
Z. J. Zhang, C. W. Jones, Angew. Chem. 2006, 118, 2267 – 2270;
Angew. Chem. Int. Ed. 2006, 45, 2209 – 2212; d) D. M. Vriezema,
P. M. L. Garcia, N. Sancho Oltra, N. S. Hatzakis, S. M. Kuiper,
R. J. M. Nolte, A. E. Rowan, J. C. M. van Hest, Angew. Chem.
Huo, H. Li, Y. F. Lu, J. Am. Chem. Soc. 2007, 129, 8406 – 8407;
h) X. W. Lou, C. Yuan, L. A. Archer, Adv. Mater. 2007, 19, 3328 –
3332; i) X. J. Wu, D. S. Xu, J. Am. Chem. Soc. 2009, 131, 2774 –
2775; j) Y. Chen, H. R. Chen, L. M. Guo, Q. J. He, F. Chen, J.
2007, 119, 7522 – 7526; Angew. Chem. Int. Ed. 2007, 46, 7378 –
7382; e) A. L. Miller, N. B. Bowden, Adv. Mater. 2008, 20, 4195 –
4199; f) F. Zhang, G. H. Liu, W. H. He, H. Yin, X. S. Yang, H. Li, J.
Zhou, J. W. Feng, J. L. Shi, ACS Nano 2010, 4, 529 – 539; k) J. Liu,
S. Z. Qiao, S. B. Hartono, G. Q. Lu, Angew. Chem. 2010, 122,
5101 – 5105; Angew. Chem. Int. Ed. 2010, 49, 4981 – 4985; l) X. J.
Zhu, H. X. Li, Y. F. Lu, Adv. Funct. Mater. 2008, 18, 3590 – 3597;
g) S. Shylesh, A. Wagener, A. Seifert, S. Ernst, W. R. Thiel,
Angew. Chem. 2010, 122, 188 – 191; Angew. Chem. Int. Ed. 2010,
Wu, D. S. Xu, Adv. Mater. 2010, 22, 1516 – 1520; m) M. IbꢁÇez, J.
Fan, W. Li, D. Cadavid, R. Nafria, A. Carrete, A. Cabot, Chem.
Mater. 2011, 23, 3095 – 3104; n) L. Kuai, S. Wang, B. Geng, Chem.
Commun. 2011, 47, 6093 – 6095.
49, 184 – 187; h) K. Motokura, N. Fujita, K. Mori, T. Mizugaki, K.
Ebitani, K. Kaneda, J. Am. Chem. Soc. 2005, 127, 9674 – 9675.
3] a) X. W. Lou, L. A. Archer, Z. Yang, Adv. Mater. 2008, 20, 3987 –
[
[
6] Y. Yang, J. Liu, X. B. Li, X. Liu, Q. H. Yang, Chem. Mater. 2011,
[
23, 3676 – 3684.
4019; b) J. Liu, S. Z. Qiao, J. S. Chen, X. W. Lou, X. Xing, G. Q.
7] J. Kim, H. S. Kim, N. Lee, T. Kim, H. Kim, T. Yu, I. C. Song, W. K.
Moon, T. Hyeon, Angew. Chem. 2008, 120, 8566 – 8569; Angew.
Chem. Int. Ed. 2008, 47, 8438 – 8441.
8] J. S. Gao, J. Liu, S. Y. Bai, P. Wang, H. Zhong, Q. H. Yang, C. Li, J.
Mater. Chem. 2009, 19, 8580 – 8588.
Lu, Chem. Commun. 2011, 47, 12578 – 12591; c) J. Liu, S. Z. Qiao,
Q. H. Hu, G. Q. Max Lu, Small 2011, 7, 425 – 443; d) R. Ghosh
Chaudhuri, S. Paria, Chem. Rev. 2012, 112, 2373 – 2433; e) F. Q.
Tang, L. L. Li, D. Chen, Adv. Mater. 2012, 24, 1504 – 1534.
[
[
4] a) P. M. Arnal, M. Comotti, F. Schꢀth, Angew. Chem. 2006, 118,
[
9] L. Zhang, J. Liu, J. Yang, Q. H. Yang, C. Li, Microporous
Mesoporous Mater. 2008, 109, 172 – 183.
8
404 – 8407; Angew. Chem. Int. Ed. 2006, 45, 8224 – 8227; b) Q.
Zhang, T. R. Zhang, J. P. Ge, Y. D. Yin, Nano Lett. 2008, 8, 2867 –
871; c) S. H. Joo, J. Y. Park, C.-K. Tsung, Y. Yamada, P. Yang,
2
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Nanostructures
Smart yolk–shell nanoparticles (hollow
nanoparticles with a movable core) with
an acidic shell and a basic core were
fabricated through an organosilane-
assisted selective etching method and
acted as efficient nanoreactors for cata-
lyzing a deacetalization–Henry cascade
reaction with high activity and high
selectivity. This strategy is very promising
for the design of multifunctional nano-
reactors for cascade reactions.
Y. Yang, X. Liu, X. B. Li, J. Zhao, S. Y. Bai,
J. Liu,* Q. H. Yang*
&&&& — &&&&
A Yolk–Shell Nanoreactor with a Basic
Core and an Acidic Shell for Cascade
Reactions
6
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!