Encapsulation of Hoveyda-Grubbs2nd Catalyst within Yolk-Shell Structured Silica for Olefin Metathesis

Article abstract of DOI:10.1021/cs5015354

Through postreducing the pore size of a mesoporous shell, Hoveyda-Grubbs^2nd catalyst was successfully encapsulated within yolk-shell structured silica, leading to a heterogeneous catalyst for olefin metathesis. Such a catalyst exhibits much higher activity than the reported encapsulated catalysts in olefin ring-closing metathesis and cross metathesis. This excellent activity can be attributed to the combination of a hollow structure in the interior and permeable mesopores in the shells. This catalyst shows good recyclability, highlighted by eight cycles of reaction. This work not only supplies an excellent heterogeneous olefin metathesis catalyst but also demonstrates that yolk-shell structured silica materials can be used as an innovative scaffold to encapsulate homogeneous catalysts.

Full text of DOI:10.1021/cs5015354

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Article
Encapsulation of Hoveyda–Grubbs2nd Catalyst within
Yolk-Shell Structured Silica for Olefin Metathesis
Qibiao Li, Ting Zhou, and Hengquan Yang
ACS Catal., Just Accepted Manuscript • Publication Date (Web): 25 Feb 2015
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ACS Catalysis
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Encapsulation of Hoveyda–Grubbs Catalyst within Yolk-Shell
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Qibiao Li, Ting Zhou, and Hengquan Yang*
School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan, 030006, P.R. China.
2nd
ABSTRACT: Through postꢀreducing pore size of mesoporous shell, Hoveyda–Grubbs catalyst was successfully encapsulated
within yolkꢀshell structured silica, leading to a heterogeneous catalyst for olefin
metathesis. Such a catalyst exhibits much higher activity than the reported encapsulated
catalysts in olefin ringꢀclosing metathesis and cross metathesis. This excellent activity
should be attributed to the combination of hollow structure in the interior and permeable
mesopores in the shells. This catalyst shows good recyclability, highlighted by eight
times of reaction cycles. This work not only supplies an excellent heterogeneous olefin
metathesis catalyst, but also demonstrates that yolkꢀshell structured silica materials can
be used as an innovative scaffold to encapsulate homogeneous catalysts.
2nd
KEYWORDS: olefin metathesis, Hoveyda–Grubbs catalyst, encapsulation, yolk-shell structure, mesoporous silica
INTRODUCTION
Ru complexꢀcatalyzed olefin metathesis has become an
important tool to generate new C=C bonds. The commercial
method to encapsulate homogeneous catalysts, namely,
spatially confining metal complexes in the nanocages of
mesoporous silica by reducing the pore entrance size. With
this approach, our group and other groups succeeded in the
encapsulation of metal complexes such as Co(salen),
Cr(salen), VO(salen), Mn(salen), Ru–TsDPEN and Hoveyda–
2
nd
availability of Grubbs catalyst, Hoveyda–Grubbs catalysts,
their good functional group tolerance ability and mild reaction
conditions make this reaction accessible to a variety of olefins
1–4
even including polymer materials and natural products.
2nd
However, these well established elegant homogeneous
catalysts still suffer from difficulty in catalyst separation and
recycling, which constitutes a serious obstacle of large scale
industrial applications. To circumvent the obstacle, many
attempts have been made to immobilize these Ru complex
catalysts on insoluble solid materials through covalent linkage,
electrostatic adsorption and encapsulation, thereby achieving
Grubbs
materials SBAꢀ16 or SBAꢀ1.
catalyst in the nanocages of the mesoporous
26–32
These encapsulated catalysts
showed good activity, moderate to excellent recyclability and
interesting confinement effects. Although our series of work
sufficiently demonstrated that the obtained catalytic
performances are strongly dependent on the support structures,
our method is still limited in use of mesoporous cageꢀlike
SBAꢀ16 or SBAꢀ1 as support. Accordingly, to explore new
supports for encapsulating homogeneous catalysts so as to
achieve more efficient heterogeneous catalyst is desired.
5
–21
recoverable catalysts.
Alternatively, waterꢀsoluble Ru
complexes and light switchꢀtagged Ru complexes were
developed with aim to recycle the homogeneous catalyst by
2
2–25
virtue of biphasic systems.
Although encouraging and
Yolkꢀshell structured mesoporous materials containing a
void space between the core and the outer shell of the material
are emerging as an interesting family of new hollow nanoꢀ
interesting results have been obtained, these recyclable
catalysts either require relatively complicated preparation
procedures or show significantly decreased activity in
comparison to their homogeneous counterpart. In this context,
highly active and recyclable catalysts that can be prepared
with a simple procedure are desirable.
33–48
architectures.
The enclosed void space is expected to be
useful for accommodating various guest molecules or
nanoparticles, while the mesoporous shell allows reactant
molecules to permeate the shell to enter the void space. Such a
nanoꢀarchitecture is entirely different from the previously used
cageꢀlike mesoporous materials. Furthermore, their
dimensions of the void space and shell pore size are both
tunable. Despite these features that might lead to more
efficient heterogeneous catalysts, there are no reports on
encapsulation of homogeneous catalysts within yolkꢀshell
structured silica up to date.
Among the various methods to transfer homogeneous
catalysts to heterogeneous ones, encapsulation may be
preferable because it does not require chemical modification
of the initially perfect catalyst structure on which the catalytic
performances strongly depend, and negative effects caused by
supports can be decreased owing to the absence of direct
covalent linkage or electrostatic interaction with supports.
Along this line, we have recently developed an efficient
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Herein, we first demonstrate encapsulation of Hoveyda– dichlorodiphenylsilane and 0.018 g of pyridine. After stirring
2nd
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Grubbs catalysts within yolkꢀshell structured mesoporous
silica by reducing the shell pore size through silylation
for 6 h at 35 ºC under N atmosphere, the resultant solid was
2
collected through centrifugal separation, repeatedly washed
with dichloromethane (4.5 mL × 6) and dried under vacuum,
eventually leading to the Ru@YꢀS catalysts. All used
dichloromethane solutions were collected and analyzed with
UV/Vis spectrophotometer to estimate the residual amount of
2
nd
method. The encapsulated Hoveyda–Grubbs catalyst shows
much higher activity and recyclability than its analogous
heterogeneous catalysts. Moreover, this work demonstrates
that yolkꢀshell structured materials can be used as an
innovative scaffold to encapsulate homogeneous catalysts.
2nd
Hoveyda–Grubbs catalyst. Based on the difference between
the initially used amount and the residual amount, The
2
nd
EXPERIMENTAL PROCEDURES
Hoveyda–Grubbs
9
catalyst loading was determined as
.57×10 mmol·g . This result is in agreement with the ICPꢀ
ꢀ
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Chemicals. Tetraethyl orthosilicate (TEOS, AR) was
purchased from Alfa Aesar. Ammonia solution (25–28%),
Dodecyltrimethylammonium bromide (DTAB, AR), ethanol,
acetone (AR), toluene (AR), hexane (AR), pyridine (AR),
dichloromethane (AR) and sodium carbonate (AR) were
purchased from Sinopharm Chemical Reagent Co. (Shanghai,
AES result.
Catalyst characterization. TEM micrographs were taken
with
a JEMꢀ2000EX transmission electron microscope
(operated at 120 kV). Smallꢀangle Xꢀray powder diffraction
analysis was performed on a Rigaku D/max rA Xꢀray
2nd
China). HoveydaꢀGrubbs catalyst (CAS No.: 301224ꢀ40ꢀ8),
diffractometer (at 40 kV and 30 mA with CuKa radiation). N
2
dichlorodiphenylsilane (>95%) and the substrates were
purchased from Aldrich Co. Deionized water was used in all
experiments.
physical adsorption was performed on a micrometritics ASAP
2020 volumetric adsorption analyzer (before the
measurements, samples were outgassed at 398 K for 8 h). The
BET specific surface areas were evaluated from data in the
relative pressure range from 0.05 to 0.25. The total pore
volume was estimated from the amount adsorbed at the
Preparation of yolk-shell structured mesoporous silica (Y-
S). SiO2 nanospheres were synthesized according to a
49
modified Stöber method. 16 mL of aqueous ammonia, 200
highest P/P (above 0.99). UV/Vis spectra were recorded on
0
mL of ethanol and 12.2 mL of deionized water were mixed.
After stirring for 0.5 h (1500 rpm), into this mixture 12.4 mL
of TEOS was dropwise added. Further stirring for 12 h at
room temperature resulted in a white silica colloidal
suspension. The silica particles were collected through
centrifugal separation, then washed with deionized water (30
mL × 6) and ethanol (20 mL × 2), and finally dried at 60 ºC
the JASCOVꢀ550 UV/Vis spectrophotometer. Diffuseꢀ
reflectance UV/Vis spectra were also recorded on the
13
CARY300 spectrophotometer (Varian Co.). C CP–MAS
NMR spectra were recorded on an Infinity plus 300 MHz
spectrometer experiments (75.4 MHz resonant frequency, 4
kHz spin rate, 4 s pulse delay, 1.0 ms contact time,
hexamethyl benzene as a reference compound). Thermal
gravimetric (TG) experiments were carried out with a
NETZSCH TG analyzer (Germany) under nitrogen
atmosphere from room temperature to 950 ºC with a heating
rate of 10 ºC /min. The leached Ru was analyzed by
inductively coupled plasmaꢀatomic emission spectrometry
for 4 h under air, leading to SiO nanospheres.
2
The above silica nanospheres (1.0 g) were dispersed in 500
mL of deionized water by ultrasonication. DTAB (1.27 g),
ethanol (300 mL) and concentrated ammonia solution (5.5
mL) were added into this suspension. After the mixture was
stirred for 0.5 h at room temperature, 2.35 g of TEOS was
added dropwise. After further stirring for 7 h, the solid was
collected by centrifugation, washed with deionized water and
ethanol, and dried at room temperature. The resultant solid
powder was dispersed in 200 mL of water containing 4.24 g of
Na CO by ultrasonication. After stirring for 4 h at 50 ºC, the
(
ICPꢀAES, AtomScan16, TJA Co.). GC analysis was
conducted on an Agilent 7890A.
Catalysis reaction and catalyst recycling. 1 mL of dry
dichloromethane, 0.1 mmol of substrate and a given amount of
the solid catalyst containing 0.001 mmol of Ru were added
2
3
into a tube. This tube was sealed under N atmosphere for
2
solid were isolated by centrifugation and thoroughly washed
with deionized water (60 mL × 6) and ethanol (20 mL× 2).
Also, the obtained solid was subjected to calcination to
remove the template DTAB (the temperature was raised from
room temperature to 550 ºC at a rate of 1 ºC/min and further
maintained for 5 h under air atmosphere). The finally obtained
yolkꢀshell material was denoted as YꢀS. For comparison, YꢀS
materials with thinner shell and thicker shell were also
prepared only by changing the amount of TEOS used for shell
growth. 1.76 and 2.94 g of TOES were used for the former and
latter, respectively. In parallel, the completely hollow
mesoporous silica was prepared only by prolonging the
etching time to 12 h.
reaction at given temperature. At the end of the reaction, the
liquid was withdrawn after centrifugation and diluted with
dichloromethane for GC analysis. The collected solid catalyst
was washed thoroughly with dichloromethane (2 mL × 3), and
dried under vacuum for the next reaction cycle.
Filtrate activity test. 2 mL of dry dichloromethane, 0.2 mmol
of diethyl diallyl malonate and a given amount of solid
catalyst (containing 0.002 of mmol Ru complexes) were
mixed. The mixture was stirred at 25 ºC under N atmosphere.
2
After 15 min, the reaction was stopped. After rapid
centrifugation, one half of filtrate (without solid catalyst) was
transferred to a new tube and continuously stirred at 25 ºC
2
nd
under N atmosphere. The other half of filtrate containing the
2
Encapsulation of Hoveyda–Grubbs catalyst. 1.0 g of YꢀS
solid catalyst was also continuously stirred under the same
conditions. These two reactions were monitored with GC
every 30 min.
was dispersed in a mixture of 10 mL of toluene containing
2
nd
0
.02 g of HoveydaꢀGrubbs catalyst. After stirring for 4 h at
room temperature under N atmosphere, the solid was dried
2
under vacuum. The obtained solid was dispersed in a mixture
RESULTS AND DISCUSSION
of 8.0 mL of dry hexane containing 0.38
g
of
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the shell pores of yolkꢀshell silica were reduced through
Catalyst preparation and characterization. Based on the
optimized geometries, the threeꢀdimensional size of Hoveyda–
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silylation of dichlorodiphenylsilane. After thoroughly washing
2nd
2nd
Grubbs catalyst is estimated to be 1.76 nm × 1.35 nm × 1.05
with dichloromethane to remove Hoveda–Grubbs catalyst
3
0
nm. To allow this complex to pass through the shell and
enter the interior of yolkꢀshell structured silica, we synthesized
yolkꢀshell mesoporous silica material with shell pore size of
located on the external surface, the Ru@YꢀS catalyst was
obtained. The whole preparation process is very simple in
2
nd
comparison to other immobilized Hoveyda–Grubbs
2
.2 nm (the N sorption isotherms and pore size distribution
catalysts. Since the molecular size of grafted diphenylsilane is
estimated as 0.6 nm, the pore size of yolkꢀshell structured
silica was estimated as 1.0 nm (2.2ꢀ2×0.6), which is smaller
2
calculated by DFT method are provided in Figure S1 in
Supporting Information), slightly larger than the size of the
complex. The procedure for encapsulating Hoveyda–Grubbs
2nd
2nd
than the size of Hoveyda–Grubbs catalyst molecule. As a
2nd
catalyst within yolkꢀshell structured silica consists of two steps
the diagram is shown in Scheme 1. The yolkꢀshell structured
silica was first impregnated with toluene solution containing
Hoveyda–Grubbs catalyst, allowing Ru complexes to enter
the interior of yolkꢀshell structured silica. In the followed step,
result, Hoveyda–Grubbs catalyst was spatially confined in
the void space of yolkꢀshell silica. The amount of Ru complex
entrapped in the inner of yolkꢀshell structured material is
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ꢀ3
ꢀ1
about 9.57×10 mmol·g . About 30% of the initially added Ru
complex was encapsulated within the yolkꢀshell silica. In
contrast, it was found that only 9% and 15% of the initially
added Ru complex were encapsulated within coreꢀshell silica
(without etching) and the completely hollow silica
respectively (Table S1 and Figure S2, Supporting Information).
These comparisons may suggest that the internal cavity is
helpful to accommodate the metal complex and the core of
yolkꢀshell structure serves as a support to adsorb the metal
complex to prevent from escaping during silylation. Moreover,
only 15% of the initially added Ru complex was retained in
the yolkꢀshell materials without silylation modification (most
of Ru complexes were observed to be removed during the
course of washing with polar solvent). This set of comparison
confirms that our encapsulation protocol with the yolkꢀshell
structures mesoporous silica is effective at trapping Hoveyda–
N
N
=
Cl
Cl
=
Si
Ru
O
O
O
2nd
Scheme 1. The process for encapsulating Hoveyda–Grubbs
catalyst within a yolkꢀshell structured silica through silylation.
2nd
Grubbs catalyst.
a
b
100
C
d
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Ru@Y-S
Ru@Y-S
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0.0
0.2
0.4
0.6
0.8
1.0
2θ
(degree)
Relative pressure (P/P )
0
Figure 1. Structural characterization of the Ru@YꢀS catalyst. (a) TEM image, less magnified; scale bars is 100 nm. (b) TEM
image, more magnified; scale bar is 20 nm. (c) XRD pattern. (d) N sorption isotherm.
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The structures of the Ru@YꢀS catalyst were characterized
Page 4 of 8
loss in the range of 100 to 800 ºC, which is due to the SiꢀOH
condensation accompanied with dehydration. For
dipenylsilane modified yolkꢀshell structured silica without
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with transmission electron microscope (TEM), XꢀRay
diffraction (XRD) and N physical sorption. As the TEM
2
2nd
Images shows (Figure 1a), the Ru@YꢀS catalyst consists of
monodisperse yolkꢀshell structured spherical particles. There
is a void space between the shell and core, which is a typical
yolkꢀshell structure. The diameter of the whole yolkꢀshell
silica is ca. 540 nm. The shell thickness and core diameter are
ca. 70 and 320 nm, respectively. From the high resolution
TEM image (Figure 1b), one can clearly find that the ordered
mesopores are present on the shell of Ru@YꢀS and their
diameters are ca. 2 nm. Interestingly, the mesopores in the
shell are radially aligned (oriented to the outer shell
boundary). The lowꢀangle XRD pattern of Ru@YꢀS displays a
broad diffraction peak at 2θ=2.9º (Figure 1c), indicating the
encapsulation of Hoveyda–Grubbs
catalyst, there is
significantly increased weight loss from 490 to 800 ºC in
comparison to the bare yolkꢀshell silica, which is attributed to
diphenyl moiety decomposition. Notably, different from the
dipenylsilane modified yolkꢀshell silica without encapsulation
of Hoveyda–Grubbs catalyst, the Ru@YꢀS catalyst exhibits
two steps of weight loss curve in the range of 490 to 800 ºC.
There is a relatively sharp loss from 490 to 530 ºC, followed
by a slow loss from 530 to 800 ºC. The former sharp loss may
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be caused mainly by the decomposition of Hoveyda–Grubbs
catalyst while the latter is mainly due to diphenyl moiety
decomposition.
mesopores structures in the shell. The N sorption isotherms of
2
Catalytic activity evaluation. The Ru@YꢀS catalyst was first
examined with ringꢀclosing metathesis (RCM) of diethyl
diallylmalonate with 1mol% Ru (with respect to substrate) at
room temperature, using dichloromethane as solvent. The
kinetic profile was monitored with GC, as shown in Figure S6
in Supporting Information. The conversion of diethyl
diallylmalonate increased with the extension of time, and
reached 82% within 105 min and 96% within 180 min. Under
the same conditions, the reaction rate over the Ru@YꢀS
catalyst is slower than that over the homogeneous Hoveyda–
Ru@YꢀS exhibit a type of IV isotherm (Figure 1d). Notably, a
pronounced hysteresis with delayed capillary evaporation at a
relative pressure of 0.43ꢀ0.99 was observed. This feature
4
1, 50
indicates that there is a void structure,
which is in good
agreement with the TEM observations. Compared with YꢀS,
the surface area and pore volume are progressively decreased
2
ꢀ1
3
ꢀ1
from 401 to 129 m ·g , and 0.26 to 0.15 cm ·g respectively.
Such changes are caused by the silylation modification and
2
nd
location of Hoveyda–Grubbs
void.
catalyst inside the interior
2nd
Grubbs
catalyst. The decreased reaction rate may be
attributed to the diffusion resistance of mesoporous shell.
However, the reaction rate over Ru@YꢀS is much higher than
1.0
2
nd
those obtained with the Hoveyda–Grubbs
catalyst
encapsulated in coreꢀshell structured silica (62%) and hollow
mesoporous silica (87%) (Table S1, Supporting Information).
To further clarify the diffusion effects, we compared its
reaction rate with those of the Ru@YꢀS catalyst with thinner
shell and thicker shell (Figure S7, Supporting Information).
The reaction rate slightly increases with decreasing the shell
thickness, which confirms that there actually is diffusion
resistance for the yolkꢀshell catalysts. However, the reaction
rate over the Ru@YꢀS catalyst is much faster than that of our
0.9
0.8
0.7
0.6
258nm
377nm
Ru@Y-S
3
2
previously reported Ru@SBAꢀ1catalyst (50% conversion
within 105 min, Figure S6, Supporting Information), which is
the
0
.5
2
00
300
400
λ
500
600
700
(nm)
2nd
Hoveyda–Grubbs
catalyst
encapsulated
with
mesoporous material SBAꢀ1.
Figure 2. Diffusion reflectance UV/Vis spectrum of the
Ru@YꢀS catalyst.
The catalytic performances of Ru@YꢀS were examined
with RCM of other dienes. The results are summarized in
Table 1. The conversion of diethyl diallylmalonate reached
Composition of the Ru@YꢀS catalyst was characterized by
diffusion reflectance UVꢀVis spectrum. The solid catalyst
exhibits a remarkable absorbance bands at 377 nm (Figure 2),
which is the characteristic absorbance of Hoveyda–Grubbs
catalyst (as shown in Figure S3, Supporting Information). This
9
6% within 3 h (entry 1). Diallyl acetylacetone was
transformed to a cyclic product with excellent conversion
97%, entry 2). For diallyl sulfonamide (entry 3), a conversion
2
nd
(
of 99% was obtained within 4 h. The cyclization of N, Nꢀ
diallylbenzamide afforded a conversion of 89% within 4 h
2
nd
finding confirms that Hoveyda–Grubbs
catalyst was
(entry 4). Diallyl ether was converted to a cyclic product with
successfully encapsulated within the yolkꢀshell structured
1
3
a 99% conversion within 3 h (entry 5). 1,7ꢀoctadiene was
transformed to cyclohexene with a 90% conversion (entry 6).
Di(4ꢀbutenyl)ꢀsubstituted diethylmalonate could be also
smoothly cyclized with a conversion of 99% within 5 h (entry
silica. The C crossꢀpolarization magicꢀangle spinning (CPꢀ
MAS) NMR spectrum of the Ru@YꢀS catalyst exhibits strong
signals at 128 and 134 ppm, which are attributed to benzene
ring. The signals for the Ru complex such as those of the
isopropyl groups (at 15ꢀ30 ppm) were not detected because the
loading of the Ru complex loading was relatively low (Figure
S4, Supporting Information). The thermal gravimetric (TG)
curves are provided in Figure S5 (Supporting Information).
The yolkꢀshell structured silica is subjected to 2.0% weight
7
). In these investigated reactants, the Ru@YꢀS catalyst
showed much higher activity than Ru@SBAꢀ1 (the
comparisons of their TOFs are showed in Table S2 in
Supporting Information). These results demonstrate the
superiority of yolkꢀshell structured materials over the
3
1, 32
mesoporous materials such as SBAꢀ1.
The excellent
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2.5mol% Ru, also using dichloromethane as solvent. The
reactivity of Ru@YꢀS should be related to the unique yolkꢀ
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shell mesoporous structure. Due to
results are summarized in Table 2. Within 5 h, styrene was
smoothly converted to 1,2ꢀdiphenylethene with a conversion
of 99% (entry1); methoxyꢀsubstituted styrene obtained a
conversion of 86% (entry 2); For 4ꢀbromostyrene and 4ꢀ
fluorostyrene, the conversions were up to 74% and 95%,
respectively (entries 3 and 4); the conversion of allylbenzene
reached as high as 96% (entry 5). The experiments
demonstrate a functional group tolerance for the Ru@YꢀS
catalyst.
Table 1. RCM reactions of various dienes over the Ru@YꢀS
a
catalyst.
b
Entry
Substrates
Products
Time/h Conv.%
1
3
96
2
3
4
3
4
4
97
99
89
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Table 3. The recycling results of RCM over the Ru@YꢀS
a
catalyst.
O
O
O
O
O
Catalyst (2.5 mol%)
CH Cl , 35
O
O
o
2
2
C
O
5
6
3
4
99
90
6
3
7
5
8
7
Reaction
cycles
1
2
2
2
3
2
4
2
5
Time/h
2
b
Conv.%
99 96 91 87 66 69 64 50
7
5
99
a
Reaction conditions: 0.1 mmol diethyl diallylmalonate (0.1
ꢀ
1
a
ꢀ1
mmol·mL ), 2.5mol% Ru with respect to substrate, 1 mL
dichloromethane as solvent, 35 ºC. Determined with GC.
Reaction conditions: 0.1 mmol substrate (0.1 mmol
·mL ),
b
1
mol% Ru with respect to substrate, 1 mL dichloromethane as
b
solvent, 25 ºC. Determined with GC.
The recyclability of the Ru@YꢀS catalyst was tested with
consecutive RCM of diethyl diallylmalonate reaction. The
results are listed in Table 3. The fresh solid Ru@YꢀS catalyst
gave 99% conversion of diethyl diallylmalonate within 2 h at
35 ºC (using 2.5mol% Ru with respect to substrate). After the
first reaction cycle, the catalyst could be recovered by
centrifugation. After being washed with dichloromethane (2
mL × 3) and dried under vacuum, the recovered catalyst was
directly used for the next reaction cycle. In the second and
third reaction cycle, the conversion kept 96% and 91%,
respectively. Although the catalytic activity began to decrease
from the fourth reaction cycle on, 87% and 66% of
conversions were still obtained in the fourth and fifth reaction
cycles, respectively. To obtain good conversions, the reaction
time was prolonged in the followed reaction cycles. For the
eighth reaction cycle, 50% conversion was still achieved. The
Ru contents in the filtrate of the first reaction cycle and the
eighth reaction cycle were determined as ca. 4 ppm and 1 ppm,
respectively. These results probably indicates that the
deactivation of our catalyst may be mainly due to the change
the presence of void space in the interior of support, the
reactant molecules can faster transport inside the catalyst
particle than the cageꢀlike mesoporous material SBAꢀ1.
Moreover, the radially aligned mesopores in the shell is
favorable for reactant molecule to permeate the shell to access
directly the Ru complexes.
Table 2. CM reactions of various substrates over the Ru@YꢀS
a
catalyst.
b
Entry Substrates
1
Products
Time/h Conv.%
5
5
5
99
86
74
2
3
2nd
of Hoveyda–Grubbs catalyst itself such as the isomerization
4
5
5
95
96
or dimerization instead of Ru complex leaching, which is
preliminarily supported by the catalyst color change from
51, 52
green to gray.
Under the same conditions, for the Ru
5
complexꢀloaded yolkꢀshell structured silica without silylation
as catalyst, the first reaction cycle gave only 72% conversion
of diethyl diallylmalonate (Table S3 in Support Information);
in the second and third reaction cycles, the conversion rapidly
declined to 27% and 5%, respectively. These remarkable
contrasts indicate that reducing pore size through silylation is
crucial to prevent Ru complex leaching from the support.
a
ꢀ1
Reaction conditions: 0.1 mmol substrate (0.1 mmol·mL ),
2
.5mol% Ru with respect to substrate, 1 mL dichloromethane
b
as solvent, 35 ºC. Determined with GC.
The Ru@YꢀS catalyst also showed good activity towards
olefin cross–metathesis (CM). The CM over the Ru@YꢀS
catalyst was also conducted at 35 ºC in the presence of
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The Hoveyda–Grubbs
Page 6 of 8
catalyst encapsulation fractions of
2
nd
In order to check the heterogeneity nature of reaction in the
presence of the Ru@YꢀS catalyst, the activity of the filtrate
was examined. When the reaction proceeded for a period of 15
min, the RCM reaction of diethyl diallylmalonate was stopped.
1
2
3
4
5
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9
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coreꢀshell structured silica and the completely hollow
structured silica, the comparison of TOF over Ru@YꢀS and
Ru@SBAꢀ1 catalyst for different dienes, the recycling results
of the Ru complexꢀloaded in yolkꢀshell structured silica
without silylation in RCM, N sorption isotherm and pore size
2
100
distribution of yolkꢀshell structured silica (YꢀS), TEM images
of coreꢀshell structured silica and image of the completely
hollow silica, UV/Vis absorbance spectra of Hoveyda–
80
60
40
20
0
Over Ru@Y-S
2nd
Grubbs catalyst and diffusion reflectance UV/Vis of YꢀS
(ph) which is only silylated without entrapping Ru complex,
13
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
C CP–MAS NMR spectrum of the Ru@YꢀS catalyst,
In filtrate
thermal gravimetric curves of YꢀS, YꢀS (ph) and Ru@YꢀS,
kinetic profiles of diethyl diallylmalonate RCM over
2nd
Hoveyda–Grubbs
catalyst, Ru@YꢀS and Ru@SBAꢀ1
catalysts, kinetic profiles of diethyl diallylmalonate RCM over
the Ru@YꢀS catalysts with different shell thickness. This
material is available free of charge via the Internet at
http://pubs.acs.org.
0
20
40
60
Time(min)
80
100
120
AUTHOR INFORMATION
Corresponding Author
Figure 3. Profiles of the conversions versus time for the RCM
of diethyl diallylmalonate over the Ru@YꢀS catalyst and in
the filtrate (1mol% Ru with respect to substrate,
dichloromethane as solvent, 25 ºC).
*Phone: +86ꢀ351ꢀ7018371. Fax: +86ꢀ351ꢀ7011688. Eꢀmail:
hqyang@sxu.edu.cn
Notes
The authors declare no competing financial interest.
After rapid centrifugation, one portion of upper filtrate
(
without solid catalyst) was immediately transferred into
ACKNOWLEDGMENTS
another reaction vessel and further stirred like the standard
RCM reaction procedure. The residual mixture containing the
Ru@YꢀS catalyst was also continuously stirred for further
reaction. Their conversions versus time over the Ru@YꢀS
catalyst and in the filtrate are monitored by GC (Figure 3). In
the presence of the Ru@YꢀS catalyst the conversion increases
with time, while the conversion in the filtrate does not show
any increase. These results are in good agreement with the
aforementioned determination results of the Ru contents in the
filtrate. These results also revealed that the conversion was
indeed contributed to the solid catalyst instead of the leached
Ru complex in the filtrate, further confirming the effectiveness
of our encapsulation protocol.
We acknowledge the Natural Science Foundation of China
(20903064, 21173137), Program for the Top Young Academic
Leaders of Higher Learning Institutions of Shanxi (2011002)
and Middleꢀaged Innovative Talents of Higher Learning
Institutions of Shanxi (20120202).
REFERENCES
(
1) Schrock, R. R. Angew. Chem. Int. Ed. 2006, 45, 3748–
759.
2) Grubbs, R. H. Angew. Chem. Int. Ed. 2006, 45, 3760–
765.
3) Hoveyda, A. H.; Zhugralin, A. R. Nature 2007, 450, 243–
50.
3
3
2
4
(
(
(4) Schmidt, B.; Geissler, D. ChemCatChem 2010, 2, 423–
CONCLUSIONS
29.
2
nd
The
Hoveyda–Grubbs
catalyst
was
successfully
(
(
5) Buchmeiser, M. R. Chem. Rev. 2009, 109, 303–321.
6) Burtscher, D.; Grela, K. Angew. Chem. Int. Ed. 2009, 48,
encapsulated within yolkꢀshell structured silica by postꢀ
reducing the pore size through silylation. The obtained
Ru@YꢀS catalyst exhibited excellent activity and recyclability
in the RCM and CM of various olefins. Its activity proved
much higher than the analogous encapsulated Hoveyda–
Grubbs catalyst. The high activity should be attributed to the
unique yolkꢀshell mesoporous structures, in which the void
spaces in the interior and permeable mesopores in the shell are
favorable for the reactant and product molecule transports.
Our work suggests that yolkꢀshell structured materials can be
used as an innovative and efficient scaffold to encapsulate
homogeneous catalysts with the silylation protocol.
4
42–454.
(7) Van Berlo, B.; Houthoofd, K.; Sels, B. F.; Jacobs, P. A.
Adv. Synth. Catal. 2008, 350, 1949–1953.
(8) Liu, G. Y.; He, H. Y.; Wang, J. H. Adv. Synth. Catal.
2009, 351, 1610–1620.
2nd
(
9) Clavier, H.; Grela, K.; Kirschning, A.; Mauduit, M.;
Nolan, S. P. Angew. Chem. Int. Ed. 2007, 46, 6786–6801.
10) Lim, J.; Lee, S. S.; Ying, J. Y. Chem. Commun. 2010,
6, 806–808.
11) Bek, D.; Balcar, H.; Zilkova, N.; Zukal, A.; Horacek,
M.; Cejka, J. ACS Catal. 2011, 1, 709–718.
12) Marciniec, B.; Rogalski, S.; Potrzebowski, M. J.;
Pietraszuk, C. ChemCatChem 2011, 3, 904–910.
(
4
(
(
ASSOCIATED CONTENT
Supporting Information
6
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Page 7 of 8
ACS Catalysis
(41) Liu, J.; Yang, H. Q.; Kleitz, F.; Chen, Z. G.; Yang, T.;
(
13) Bru, M.; Dehn, R.; Teles, J. H.; Deuerlein, S.; Danz, M.;
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Müller, I. B.; Limbach, M. Chem. Eur. J. 2013, 19, 11661–
11671.
(14) Cabrera, J.; Padilla, R.; Bru, M.; Lindner, R.; Kageyama,
T.; Wilckens, K.; Blof, S. L.; Schanz, H. J.; Dehn, R.; Teles,
J.H.; Deuerlein, S.; Muller, K.; Rominger, F.; Limbach, M.
Chem. Eur. J. 2012, 18, 14717–14724.
Strounina, E.; Lu, G. Q.; Qiao, S. Z. Adv. Funct. Mater. 2012,
22, 591–599.
(42) Fang, X. L.; Liu, Z.H.; Hsieh, M. F.; Chen, M.; Liu,
P.X.; Chen, C.; Zheng, N.F. ACS Nano 2012, 6, 4434–4444.
(43) Liang, X.; Li, J.; Joo, J. B.; Gutierrez, A.; Tillekaratne,
A.; Lee, I.; Yin, Y.; Zaera, F. Angew. Chem. Int. Ed. 2012, 51,
8034–8036.
(44) Zhang, Q.; Lee, I.; Joo, J. B.; Zaera, F.; Yin, Y. Acc.
Chem. Res. 2013, 46, 1816–1824.
(45) Sun, Q.; Guo, C. Z.; Wang, G. H.; Li, W. C.; Bongard,
H. J.; Lu, A. H. Chem. Eur. J. 2013, 19, 6217–6220.
(46) Shmakov, S. N.; Jia, Y.; Pinkhassik, E. Chem. Mater.
2014, 26, 1126–1132.
(47) Shakeri, M.; Roiban, L.; Yazerski, V.; Prieto, G.;
Gebbink, R. J. M. K.; Jongh, P. E.; Jong, K. P. ACS Catal.
2014, 4, 3791–3796.
(48) Zhang, H.; Jin, R.; Yao, H.; Tang, S.; Zhuang, J.; Liu,
G.; Li, H. X. Chem. Commun. 2012, 48, 7874–7876.
(49) Stober, W.; Fink, A. J. Colloid Interface Sci. 1968, 26,
62–69.
(50) Deng, Y.; Liu, C.; Gu, D.; Yu, T.; Tu, B.; Zhao, D. J.
Mater. Chem. 2008, 18, 91–97.
(51) Hong, S. H.; Wenzel, A. G.; Salguero, T. T.; Day, M.
W.; Grubbs, R. H. J. Am. Chem. Soc. 2007, 129, 7961–7968.
(52) Copéret, C.; Basset, J. M. Adv. Synth. Catal. 2007, 349,
78–92.
(
15) Balcar, H.; Čejka, J. Coord. Chem. Rev. 2013, 257,
107–3124.
16) Zelin, J.; Trasarti, A. F.; Apesteguía, C. R. Catal.
Commun. 2013, 42, 84–88.
17) Pastva, J.; Skowerski, K.; Czarnocki, S. J.; Žilková, N.;
Čejka, J.; Bastl, Z.; Balcar, H. ACS Catal. 2014, 4, 3227–
236.
18) Staub, H.; Kleitz, F.; Fontaine, F. G. Microporous
Mesoporous Mater. 2013, 175, 170–177.
19) Staub, H.; GuilletꢀNicolas, R.; Even, N.; Kayser, L.;
3
(
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
3
(
(
Kleitz, F.; Fontaine, F. G. Chem. Eur. J. 2011, 17, 4254–4265.
(20) MongeꢀMarcet, A.; Pleixats, R.; Cattoen, X.; Man, M.
W. C. J. Mol. Catal. A: Chem. 2012, 357, 59–66.
(21) Chen, S. W.; Zhang, Z. C.; Ma, M.; Zhong, C. M.; Lee,
S. G. Org. Lett. 2014, 16, 4969–4971.
(
22) Ferraz, C. P.; Autenrieth, B.; Frey, W.; Buchmeiser, M.
R. ChemCatChem 2014, 6, 191–198.
23) Tomasek, J.; Schatz, J. Green Chem. 2013, 15, 2317–
338.
24) Matsugi, M.; Kobayashi, Y.; Suzumura, N.; Tsuchiya,
Y.; Shioiri, T. J. Org. Chem. 2010, 75, 7905–7908.
25) Liu, G.; Wang, J. Angew. Chem. Int. Ed. 2010, 49,
425–4429.
26) Yang, H. Q.; Zhang, L.; Zhong, L.; Yang, Q. H.; Li, C.
Angew. Chem. Int. Ed. 2007, 46, 6861–6865.
27) Yang, H. Q.; Zhang, L.; Wang, P.; Yang, Q. H.; Li, C.
(
2
(
(
4
(
(
Green Chem. 2009, 11, 257–264.
(28) Bai, S. Y.; Yang, H. Q.; Wang, P.; Gao, J. S.; Li, B.;
Yang, Q. H.; Li, C. Chem. Commun. 2010, 46, 8145–8147.
(29) Ma, Z. C.; Yang, H. Q.; Qin, Y.; Hao, Y. J.; Li, G. J.
Mol. Catal. A: Chem. 2010, 331, 78–85.
(
30) Hao, Y. J.; Chong, Y. Z.; Li, S. R.; Yang, H. Q. J. Phys.
Chem. C 2012, 116, 6512–6519.
31) Yang, H.Q.; Ma, Z. C.; Wang, Y.K.; Wang, Y.W. Chem.
Commun. 2010, 46, 8659–8661.
32) Yang, H. Q.; Ma, Z. C.; Zhou, T.; Zhang, W.J.; Chao,
J.B.; Qin, Y. ChemCatChem 2013, 5, 2278–2287.
33) Yang, Y.; Liu, J.; Li, X.; Liu, X.; Yang, Q. Chem.
Mater. 2011, 23, 3676–3684.
34) Chen, Y.; Chen, H. R.; Shi, J. L. Acc. Chem. Res. 2014,
7, 125–137.
35) Yao, K. X.; Zeng, H, C, Chem. Mater. 2012, 24, 140–
148.
(36) Zhang,T,; Zhang, Q.; Ge, J.; Goebl, J.; Sun, M.; Yan,
(
(
(
(
4
(
Y.; Liu, Y.; Chang, C.; Guo, J.; Yin, Y. J. Phys. Chem. C
2009, 113, 3168–3175.
(
37) Ha, T. L.; Kim, J. G.; Kim, S. M.; Lee, I. S. J. Am.
Chem. Soc. 2013, 135, 1378–1385.
38) Park, J. C.; Bang, J. U.; Lee, J.; Ko, C. H.; Song, H. J.
Mater. Chem. 2010, 20, 1239–1246.
39) PérezꢀLorenzo, M.; Vaz, B.; Salgueiriño, V.; Correaꢀ
Duarte, M. A. Chem. Eur. J. 2013, 19, 12196–12211.
40) Goebl, J.; Yin, Y. D.; ChemCatChem 2013, 5, 1287–
288.
(
(
(
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