Asymmetric hydrogenation by RuCl2(R-Binap)(dmf)n encapsulated in silica-based nanoreactors

Article abstract of DOI:10.1039/c4cy00228h

The Noyori catalyst RuCl₂(R-Binap)(dmf)_n has been successfully encapsulated in C-FDU-12 by using the active chlorosilane Ph₂Cl₂Si as the silylating agent. ³¹P-NMR results show that there is no strong interaction between the molecular catalyst and the solid support, thus the encapsulated molecular catalyst could move freely in the nanoreactor during the catalytic process. The solid catalyst exhibits high activity and enantioselectivity for the asymmetric hydrogenation of a series of β-keto esters due to the preserved intrinsic properties of RuCl₂(R-Binap)(dmf)_n encapsulated in the nanoreactor. The solid catalyst could be recycled by simple filtration and be reused at least four times.

Full text of DOI:10.1039/c4cy00228h

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Asymmetric hydrogenation by RuCl (R-Binap)(dmf)
2
n
encapsulated in silica-based nanoreactors†
Cite this: DOI: 10.1039/c4cy00228h
ab
a
ab
a
a
Juan Peng, Xuefeng Wang, Xiaoming Zhang, Shiyang Bai, Yaopeng Zhao,
a
a
Can Li* and Qihua Yang*
The Noyori catalyst RuCl
2
(R-Binap)(dmf)
n
has been successfully encapsulated in C-FDU-12 by using the
3
1
active chlorosilane Ph Cl
2
2
Si as the silylating agent. P-NMR results show that there is no strong interaction
Received 20th February 2014,
Accepted 12th April 2014
between the molecular catalyst and the solid support, thus the encapsulated molecular catalyst could
move freely in the nanoreactor during the catalytic process. The solid catalyst exhibits high activity and
enantioselectivity for the asymmetric hydrogenation of a series of β-keto esters due to the preserved
DOI: 10.1039/c4cy00228h
2 n
intrinsic properties of RuCl (R-Binap)(dmf) encapsulated in the nanoreactor. The solid catalyst could be
www.rsc.org/catalysis
recycled by simple filtration and be reused at least four times.
within pores have restricted their application for more compli-
Introduction
cated catalysts. Recently, our group has developed an efficient
strategy to encapsulate molecular catalysts in silica-based nano-
reactors with cage-like porous structures, such as SBA-16 and
FDU-12, by post-modification of the pore entrance through a
silylation method. With this method, several types of metal
Asymmetric catalysis is one of the most efficient approaches
for the production of chiral chemicals. Over the past decades,
huge progress has been made for homogeneous asymmetric
catalysis. Versatile and efficient asymmetric catalytic systems
have been developed for the synthesis of various enantiomers
which are important in both fine-chemical and pharmaceuti-
1
1–13
14
15
complex catalysts, such as Co(Salen),
VO(Salen), Fe(Salen),
16
17
18
Cr(Salen), Ru(Ts-DPEN) and (Binolate) Ti have been success-
2
1–5
cal industries. From the viewpoint of industrial application,
it is desirable to produce chiral compounds through the hetero-
geneous asymmetric catalytic approach due to its overwhelming
advantages in recycling and reuse of the expensive homoge-
neous asymmetric catalysts, easy purification of the products
and convenient manipulation for large scale production.
However, heterogeneous asymmetric catalysts which are often
prepared by simple immobilization of homogeneous asym-
metric catalysts onto solid supports always face the problems
fully trapped in the nanocages of mesoporous materials. It has
also been demonstrated that the encapsulated molecules could
31
move freely in the nanoreactor based on P-NMR characterization
using BINAPO (2,2′-bis(diphenylphosphinooxide)-1,1′-binaphthyl)
13
as the model molecule. The catalytic performance of the encap-
sulated molecular catalysts is comparable to, and in some cases
even higher than, those of the homogeneous counterparts.
Our previous encapsulation method always required an
organic base, such as pyridine, as a silylation catalyst during
the silylation process to reduce the pore entrance size. How-
ever, due to its strong coordination ability, pyridine may dete-
riorate some metal complexes. It is therefore desirable to
develop new methods for the encapsulation of special types
of catalysts, for example, RuCl (R-Binap)(dmf) (abbreviated
6
,7
of low enantioselectivity and catalytic activity. This is partly
because the molecular catalysts lose their mobility after immo-
bilization, which may alter their intrinsic properties. Great
efforts have been made in trying to keep the intrinsic proper-
ties of molecular catalysts after immobilization; for example,
encapsulating the metal complex catalyst in a zeolite through
2
n
as Ru-(R-Binap) in the following paragraphs; as for the struc-
tural formula, RuCl (R-Binap)(dmf) (n = 2) is taken as the
8–10
the “ship-in-bottle” method.
Unfortunately, the small pore
2
2
size of zeolites and the uncontrollable coordination process
representative), which has been widely used in asymmetric
hydrogenation after being reported by Noyori and Takaya in
19
1980. Ru-(R-Binap) is air sensitive and loses its catalytic activ-
a
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics,
ity in the presence of pyridine. Many efforts have been made
to immobilize Binap onto different types of supports, such as
Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China.
E-mail: yangqh@dicp.ac.cn, canli@dicp.ac.cn; Fax: +86 0411 84694447
2
0,21
22,23
24
b
zirconium phosphonate,
Fe
3
O
4
,
PMOs,
graphite
Graduate School of the Chinese Academy of Sciences, Beijing 100049, China
2
5
26
27–29
oxide, polymers, ionic liquids,
etc.; however, the immo-
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4cy00228h
bilization of Ru-(R-Binap) through non-covalent interactions
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has rarely been reported. Herein, we describe a new method
for encapsulating this organic base sensitive catalyst in the
nanocages of mesoporous silica C-FDU-12 without deteriorating
its activity. Based on the characterization results of nitrogen
adsorption–desorption analysis, XRD and TEM, the ordered
mesoporous structure of the cage-like material is maintained
31
after the encapsulation of Ru-(R-Binap). Furthermore, P-NMR
spectroscopic studies show that the encapsulated Ru-(R-Binap)
could move freely in the nanocages, which was seldom reported
by other immobilization methods. To evaluate the catalytic per-
formance of Ru-(R-Binap)@C-FDU-12, the asymmetric hydroge-
nation of β-keto esters was chosen as the model reaction. The
influence of the loading amount of Ru-(R-Binap) on the cata-
lytic performance of Ru-(R-Binap)@C-FDU-12 and the cycling
stability of Ru-(R-Binap)@C-FDU-12 were also investigated.
Fig. 1 (a) The N
2
sorption isotherm and (b) the TG curve of C-FDU-12.
−
1
−1
−1
810 cm , 743 cm , 697 cm for C(naphthalene)–H, and
−
1
1
434 cm for P–C(aryl). The UV–vis diffused reflectance spec-
trum of Ru-(R-Binap)@C-FDU-12 clearly shows the bands at
338 nm, similar to that of Ru-(R-Binap) dissolved in CH Cl
Results and discussion
Encapsulation of the Ru-(R-Binap) complex in the nanocage
2
2
(
Fig. S3†). The results of FT-IR and UV–vis spectroscopy con-
firm the successful encapsulation of Ru-(R-Binap) in the
nanocage of C-FDU-12.
of C-FDU-12
As illustrated in Scheme 1, Ru-(R-Binap) was first introduced
into the nanocage of C-FDU-12 (obtained by carbonization of
the as-made FDU-12 at 550 °C under a nitrogen atmosphere
for 6 h, the carbon content is 4.8 wt%, Fig. 1b) under vacuum.
Then the pore entrance size was reduced using Ph Cl Si as
the silylating agent at room temperature under vacuum. After
being thoroughly washed with dichloromethane in a glove
box, the solid catalyst, Ru-(R-Binap)@C-FDU-12, was obtained.
Textural properties of Ru-(R-Binap)@C-FDU-12
The N2 sorption isotherms of Ru-(R-Binap)@C-FDU-12 are
of type IV with an H2 hysteresis loop similar to that of parent
C-FDU-12, indicating that the solid catalyst still maintains
the cage-like porous structure (Fig. 1a and 3A). In compari-
son with C-FDU-12, an obvious decrease in the BET surface
area and cage size is observed due to the occupation of the
Ru-(R-Binap) catalyst in the nanocages (Table 1). As the con-
tent of Ru-(R-Binap) increases, the BET surface area and pore
volume of Ru-(R-Binap)@C-FDU-12 decrease gradually.
2
2
3
0
2 2
In this case, we chose the very active chlorosilane Ph Cl Si
instead of alkoxysilanes as the silylating agent, thus the silylation
could be performed at room temperature without any silylation
catalysts. This will help in keeping the intrinsic properties of
Ru-(R-Binap) during the encapsulation process.
FT-IR spectra of Ru-(R-Binap) and Ru-(R-Binap)@C-FDU-12
are presented in Fig. 2. Ru-(R-Binap)@C-FDU-12 displays the
The XRD patterns of Ru-(R-Binap)@C-FDU-12 (0.71 wt% Ru)
exhibit two well-resolved diffraction peaks (Fig. 3B), which can
be indexed to the (111) and (311) reflections of a fcc structure
−
1
characteristic vibration bands of Ru-(R-Binap) at 3050 cm ,
31
(
Fm3m), similar to C-FDU-12. The TEM images also show that
the ordered distribution of the mesopores of C-FDU-12 remains
invariable after the encapsulation of Ru-(R-Binap) (Scheme 1).
The above results confirm that Ru-(R-Binap)@C-FDU-12 has a
Scheme 1 Schematic illustration of encapsulating Ru-(R-Binap) in the
nanocage of C-FDU-12 and TEM images of C-FDU-12 (a) before and
Fig. 2 FT-IR spectra of (a) Ru-(R-Binap) and (b) Ru-(R-Binap)@C-FDU-12
(
b) after encapsulation of Ru-(R-Binap).
(0.71 wt% Ru).
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Fig.
2
3 (A) The N sorption isotherms of Ru-(R-Binap)@C-FDU-12
at different Ru content: (a) 0.12 wt%, (b) 0.28 wt%, (c) 0.37 wt%,
(
(
d) 0.5 wt% and (e) 0.71 wt%. (B) XRD patterns of (a) C-FDU-12 and
b) Ru-(R-Binap)@C-FDU-12 (0.71 wt% Ru).
3
1
Fig. 4 (A) (a) Liquid P-NMR spectrum obtained under an inert
atmosphere using degassed CHCl as the solvent and (b) the solid-
3
31
state magic-angle spinning (MAS) P-NMR spectrum of Ru-(R-Binap).
B) Static P-NMR spectra of Ru-(R-Binap)@C-FDU-12 (0.71 wt% Ru)
a) in the solid state and (b) in suspension with degassed CHCl as
31
(
well ordered cage-like porous structure and the encapsula-
tion of Ru-(R-Binap) does not damage the porous structure
of C-FDU-12.
(
3
the solvent.
3
1
Investigation of the movement freedom of Ru-(R-Binap)
static P-NMR spectra of Ru-(R-Binap)@C-FDU-12 in the pres-
encapsulated in C-FDU-12
ence of different amounts of solvent are summarized in Fig. 5.
The peak firstly appears in the presence of 20 μl of CHCl , cor-
responding to 40% of the cage volume filled with the solvent
3
In our previous work, the degree of movement free-
dom of the molecule encapsulated in the nanocages
of mesoporous silica was detected using BINAPO
(
based on the N sorption results). As the amount of CHCl
2 3
increases, the peak at 56 ppm becomes sharper, and the
intensity of the signal increases and reaches a maximum with
(
2,2′-bis(diphenylphosphinooxide)-1,1′-binaphthyl) as a model
1
3
molecule. However, the movement freedom of the real cata-
lysts was not detected. In this work, the movement freedom
of the molecular catalyst, Ru-(R-Binap), in the nanocages of
a CHCl amount of 50 μl, corresponding to 100% of the cage
3
volume filled with the solvent. It is worth mentioning that the
3
1
peak at −16.2 ppm which belongs to R-Binap could hardly be
C-FDU-12 was investigated by P-NMR characterization.
3
1
3
1
observed in the P-NMR spectrum of Ru-(R-Binap)@C-FDU-12,
The liquid P-NMR spectrum of Ru-(R-Binap) and its
3
1
indicating that the silylation with Ph Cl Si is very efficient and
2
2
solid-state magic-angle spinning
P-NMR spectrum are
allows controllable modification of the pore entrance of C-FDU-12.
The NMR spectroscopic studies further confirm that Ru-
shown in Fig. 4A. The isotropic chemical shifts at 56 ppm
and −16.2 ppm could be identified by magic-angle spinning
(
R-Binap) has been successfully encapsulated in the nanocage
(Fig. 4Ab), which could be respectively assigned to the signals
of C-FDU-12. Moreover, the confined Ru-(R-Binap) can move
freely in the nanocages during a liquid phase catalytic pro-
cess. Thus, Ru-(R-Binap)@C-FDU-12 is a solid catalyst as a
whole, but has homogeneous properties on the nanoscale.
of the Ru-(R-Binap) and R-Binap ligand residues (excess
R-Binap ligand was used for the synthesis of Ru-(R-Binap)
3
2
according to
a previous report ). An asymmetric and
3
1
broad peak was observed in the static P NMR spectrum of
Ru-(R-Binap)@C-FDU-12 due to chemical-shift anisotropy of
the P nucleus (Fig. 4Ba). Interestingly, the static P NMR
3
1
31
Asymmetric hydrogenation of β-keto esters
spectrum of Ru-(R-Binap)@C-FDU-12 displays a sharp peak at
The catalytic performance of Ru-(R-Binap)@C-FDU-12 was
investigated in the asymmetric hydrogenation of methyl
acetoacetate. As shown in Table 2, no product was detected
5
6 ppm in the presence of solvent (Fig. 4Bb), indicating that
Ru-(R-Binap) could move in the nanocages of C-FDU-12. The
Table 1 The textural parameters of C-FDU-12 and Ru-(R-Binap)@C-FDU-12 at different Ru content
2
−1
a
p
3
−1
b
Catalysts
Ru content/wt%
S
BET/m g
V
/cm g
Cage size /nm
Ru-(R-Binap)@C-FDU-12-0
Ru-(R-Binap)@C-FDU-12-0.12
Ru-(R-Binap)@C-FDU-12-0.28
Ru-(R-Binap)@C-FDU-12-0.37
Ru-(R-Binap)@C-FDU-12-0.5
Ru-(R-Binap)@C-FDU-12-0.71
0
381
26.4
17.9
18.1
8.2
0.49
9.1
8.0
8.0
8.0
8.0
8.0
0.12
0.28
0.37
0.5
0.048
0.034
0.038
0.017
0.016
0.71
6.6
a
b
Estimated from the amounts adsorbed at a relative pressure (P/P
0
) of 0.99. The pore size distribution calculated from the N
2
adsorption
branch using the BJH method.
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Fig. 6 TOF and ee values of MAA hydrogenation in the presence of
Ru-(R-Binap)@C-FDU-12 with different numbers of Ru-(R-Binap)
molecules in each nanocage.
3
1
Fig.
Ru-(R-Binap)@C-FDU-12 (0.71 wt% Ru) in the presence of different
amounts of CHCl
5
P-NMR spectra measured under static conditions of
3
.
As shown in Table 1, the BET surface area and pore volume
of Ru-(R-Binap)@C-FDU-12 decrease as the Ru-(R-Binap) load-
ing increases. Thus, the decreased activity is probably due to
the crowded microenvironment in the nanocages caused by
the high content of Ru-(R-Binap), which makes the diffusion
of reactants and products difficult. The maintained enantio-
selectivity indicates that the properties of Ru-(R-Binap) remain
unchanged regardless of the number of molecular catalyst
encapsulated in the nanocages. Fig. 7 gives the kinetic plots
of the asymmetric hydrogenation of methyl acetoacetate by
Ru-(R-Binap)@C-FDU-12 with Ru content of 0.5 wt%. After the
reaction was carried out for 3 h, the solid catalyst was filtered
off, while the filtrate was stirred under the same conditions
for another 21 h. However, the yield of the product remains
almost the same as that measured at 3 h, confirming that the
solid catalyst actually is responsible for the catalytic reaction.
Anyway, this encapsulation method enables the precise
control of the loading amount of metal complexes in the
nanocages to meet different needs. For some particular asym-
metric catalytic system, the number of encapsulated metal
complexes should be precisely adjusted to obtain high activity,
e.g., one molecule per nanocage for the catalyst which may be
with only C-FDU-12, showing that C-FDU-12 is not active
for this reaction. Under the same reaction conditions,
Ru-(R-Binap)@C-FDU-12-0.12 (0.12 wt% Ru) exhibits 99% yield
with 96.5% ee, very close to those of its homogeneous counter-
part. The high ee of Ru-(R-Binap)@C-FDU-12 suggests that
the current encapsulation method does not cause damage
to Ru-(R-Binap) during the silylation process. The TOF of
Ru-(R-Binap) is still lower than that of the homogeneous
Ru-(R-Binap). This is due to the mass diffusion limitation
of the reactants and products through the nanocages. When
the S/C increases to 2000, the yield and enantioselectivity of
methyl-3-hydroxybutyrate do not significantly alter, while the
TOF value becomes a little higher, as shown in entry 4. The
influence of the catalyst loading amount on the catalytic per-
formance of Ru-(R-Binap)@C-FDU-12 was also investigated
(entries 3, 5–9). With the metal loading increasing from 0.12 wt%
to 0.82 wt%, the molecular number of the metal complex
in each cage increases from 7 to 45, and the TOF value of
−
1
−1
Ru-(R-Binap)@C-FDU-12 decreases from 299 h to 82 h ,
while the enantioselectivity nearly remains the same (Fig. 6).
Table 2 Asymmetric hydrogenation of methyl acetoacetate (MAA) catalyzed by Ru-(R-Binap)@C-FDU-12 at different Ru loadingsa
b
−1
c
c
Entry
Catalysts
Number of cat. per cage
S/C
TOF /h
Yield /%
Ee /%
1
2
3
4
5
6
7
8
9
C-FDU-12
Ru-(R-Binap)
—
—
7
—
—
1101
299
382
227
152
127
100
82
0
99
99
97
99
99
99
99
99
—
1000
1000
2000
1000
1000
1000
1000
1000
97.1
96.5
93.0
96.7
96.9
97.3
96.7
97
Ru-(R-Binap)@C-FDU-12-0.12
Ru-(R-Binap)@C-FDU-12-0.12
Ru-(R-Binap)@C-FDU-12-0.28
Ru-(R-Binap)@C-FDU-12-0.37
Ru-(R-Binap)@C-FDU-12-0.5
Ru-(R-Binap)@C-FDU-12-0.71
Ru-(R-Binap)@C-FDU-12-0.82
7
16
21
28
39
45
a
b
All of the reactions were carried out under a hydrogen pressure of 4 MPa in 1.0 mL methanol at 50 °C for 24 h. TOFs were calculated at the
c
initial 1 h. Yield and ee values were determined by GC on a Supelco g-DEX 225 capillary column.
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Fig.
7
Kinetic plots of the asymmetric hydrogenation of methyl
Fig. 8 (a) Recycling test of Ru-(R-Binap)@C-FDU-12 (0.12 wt% Ru) in
the asymmetric hydrogenation of methyl acetoacetate, (b) the TEM
image and (c) N2 sorption isotherms of Ru-(R-Binap)@C-FDU-12
(0.12 wt% Ru) after cycling 4 times.
acetoacetate by Ru-(R-Binap)@C-FDU-12 with Ru content of 0.5 wt%.
The filtrate test was performed by removing the solid catalyst from the
reaction system after 3 h.
deactivated by dimer formation (such as Ir-Binap), and two
molecules or above for catalysts which show the cooperative
activation effect (such as CoSalen).
mesoporous structures of the fresh Ru-(R-Binap)@C-FDU-12
(Fig. 8b and c). The slight decrease in activity and enantio-
selectivity during the recycle process is considered to be partly
caused by the air sensitivity of the catalytically active Ru-hydride
The encapsulated catalyst was also used to catalyze the
asymmetric hydrogenation of a wide range of β-keto esters for
the production of different β-hydroxy esters, which are impor-
tant intermediates in the fine chemical and pharmaceutical
industries. As shown in Table 3, all of these substrates can
be efficiently converted into the corresponding chiral alcohol
by Ru-(R-Binap)@C-FDU-12 in high yield (91–99%) and high
enantioselectivity (87–99% ee).
20,33
species and partly due to the leaching of metal complexes.
Conclusions
In summary, we have developed an efficient method for the
encapsulation of organic base sensitive metal complexes in the
nanocages of mesoporous silica. With highly active chlorosilane,
Ru-(R-Binap)@C-FDU-12 exhibits good catalytic stability
and could be easily recycled by a simple filtration method.
For the hydrogenation of methyl acetoacetate, the yield and
enantioselectivity of the solid catalyst remain above 90% after
four cycles (Fig. 8a). After the first cycle, 0.98 wt% Ru was
found in the reaction filtrate by ICP analysis. After the second
cycle, the amount of leaching species dropped down to 0.26 wt%,
and a little amount of Ru species could be detected after the
third cycle. The recycled solid catalyst could still maintain the
2 2
Ph Cl Si, as a silylating agent, the encapsulation could be
performed at room temperature without any silylation cata-
lysts. This method is proved to be available for the encapsula-
tion of the Noyori catalyst Ru-(R-Binap) in the nanocages of
3
1
C-FDU-12 without damaging Ru-(R-Binap). P-NMR results
show that the encapsulated molecular catalyst could move
freely in the nanocages during a liquid phase catalytic process.
Thus, the intrinsic properties of Ru-(R-Binap) are preserved.
Ru-(R-Binap)@C-FDU-12 exhibits excellent enantioselectivity
which is comparable with that of its homogeneous counter-
part for the asymmetric hydrogenation of β-keto esters and
could be reused at least four times. We could expect that this
encapsulation strategy would be generally applicable for the
design of various high-efficient nanoreactors for the produc-
tion of fine chemicals and pharmaceuticals.
Table
3
Catalytic performance of Ru-(R-Binap)@C-FDU-12a and
homogeneous Ru-(R-Binap) for asymmetric hydrogenation of various
b
β-keto esters
c
c
Entry
R
Yield /%
Ee /%
Experimental section
Material information
1
2
1
2
3
4
5
6
7
R = R = Me
99 (99)
97 (97.1)
98.8 (97.7)
99 (99)
99 (99)
99 (99)
1
2
R = Et, R = Me
99 (98.4)
94.2 (97.8)
99 (99)
99 (99)
99 (99)
1
2
R = i-Pr, R = Me
Pluronic
copolymer
F127
(EO106PO70EO106)
and
1
2
R = t-Bu, R = Me
[
RuCl (benzene)] were purchased from Sigma-Aldrich Com-
2
2
1
2
R = –CH
2
–Ph, R = Me
1
2
pany, USA. Dichlorodiphenylsilane (Ph
from Beijing Coupling Technology Company Ltd, China.
,2′-Bis(diphenylphosphino)-1,1′-binaphthyl ((R)-Binap) was obtained
2 2
Cl Si) was purchased
R = Me, R = Et
99 (99)
87 (97)
1
2
R = Me, R = i-Pr
91 (99)
2
a
b
Ru-(R-Binap)@C-FDU-12 with Ru content of 0.12 wt%. All of
the reactions were carried out under a hydrogen pressure of 4 MPa
in 1.0 mL methanol at 50 °C with S : C = 1000 : 1. The data in
parentheses are for homogeneous Ru-(R-Binap).
from Shijiazhuang Shengjia Chemical Co, Ltd., China. Tetra-
ethoxysilane (TEOS) was purchased from Shanghai Chemical
Reagent Company of the Chinese Medicine Group. Methyl
c
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acetoacetate and other β-keto esters were purchased from Alfa
Aesar Company. All of the solvents were of analytical grade
and deoxygenated by standard methods before use.
corresponding products hydrogenated by various β-keto esters
were given in the ESI† (Fig. S4).
For recycling of the catalyst, the autoclave was opened in
the glove box. After centrifugation under N , the liquid was
2
Preparation methods
decanted, and the residual catalyst was washed thoroughly
2 2
with CH Cl , dried under vacuum and used directly for the
next catalytic reaction.
The Ru-(R-Binap) complex was synthesized according to the lit-
erature method and was fully characterized by FT-IR (Fig. 2a),
3
1
1
13
UV–vis (Fig. S3†), P-NMR (Fig. 4), H-NMR and
C-NMR
32
spectroscopy (Fig. S1–S3†).
The mesoporous material FDU-12 was synthesized according
to the literature method. C-FDU-12 was obtained by carboni-
zation of the as-made FDU-12 at 550 °C under a nitrogen
atmosphere for 6 h.
Characterization
N2 sorption isotherms were recorded on a Micromeritics
ASAP2020 volumetric adsorption analyzer. Before the sorption
measurements, the samples were degassed at 393 K for 6 h.
X-Ray powder diffraction (XRD) patterns were recorded on a
Rigaku RINT D/Max-2500 powder diffraction system using
Cu Kα radiation (λ = 0.1541 nm). Transmission electron
microscopy (TEM) was performed using a FEI Tecnai G2
Spirit at an acceleration voltage of 120 kV. FT-IR spectra were
collected using a Nicolet Nexus 470 IR spectrometer. All liquid
34
The encapsulation was performed in a glove box. A typical
process for the encapsulation of Ru-(R-Binap) in the nanocages
of C-FDU-12 was as follows: C-FDU-12 (0.2 g) was evacuated at
room temperature for 0.5 h. CH Cl (0.5 mL) containing a
2 2
given number of Ru-(R-Binap) was injected into the C-FDU-12
material under vacuum conditions with vigorous stirring. After
31
and solid P-NMR spectroscopy experiments were carried out
evaporation of CH
resultant solid, followed by 0.5 ml of Ph Cl Si (12 mmol g ).
2
Cl
2
, 1 ml of dry hexane was injected into the
31
at 9.4 T on a Varian Infinity Plus 400 spectrometer with a
P
−1
2
2
frequency of 161.83 MHz using a 5 mm Chemagnetic probe.
After reaction for 8 h under low pressure at room tempera-
ture, the resulting solid catalyst was isolated by filtration and
thoroughly washed with CH Cl . The Ru content of the encap-
31
One pulse sequence was used to collect P liquid and solid
NMR data, using a π/2 pulse width of 1.9 μs and a recycle
delay of 10 s. The spinning rates in solid NMR experiments
are 6 kHz and 7 kHz. The chemical shifts were referenced to
2
2
sulated catalysts varied from 0.12 to 0.82 wt%. The number of
Ru-(R-Binap) in each cage (n, Table 2) was calculated using
the following equation:
(
4 2 4
NH ) HPO .
Ru-(R-Binap) (100 mg) in dried form was measured by MAS
3
1
23
and static P NMR spectroscopy. With the addition of different
NRu  6.0210

1g

n 
volumes of CHCl (5 μL to 300 μL), the sample was kept for
3
Vmesopore
31
3
0 min before it was subjected to detection by P static NMR.
3
4
 D 
 2 



3
Acknowledgements
N
Ru(1 g) is the mole of Ru-(R-Binap) per gram of the solid
The authors would like to thank the Natural Science Founda-
tion of China (21325313, 21232008 and 21273226) for finan-
cial support.
catalyst.
V
mesop. = Vtotal − Vmicrop., where Vtotal means the total pore
volume, Vmesop. refers to the pore volume attributed by the
mesopore and Vmicrop. refers to the pore volume of the
micropore.
Notes and references
D is the cage size of C-FDU-12.
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