Grubbs-type catalysts immobilized on SBA-15: A novel heterogeneous catalyst for olefin metathesis

Article abstract of DOI:10.1016/j.molcata.2013.01.034

A series of novel heterogeneous olefin metathesis catalysts have been developed by immobilizing Ru species on SBA-15 mesoporous silica with tunable ordered pores and different textural properties. Various techniques such as X-ray diffraction, N₂ adsorption-desorption, high resolution transmission electron microscopy have been used to characterize the physicochemical properties of the catalysts. The catalytic activity of thus prepared Ru-based catalysts has been studied in ring closing metathesis (RCM) and other metathesis reactions. Among these immobilized catalysts, the SBA-15 support with the largest pore size gives rise to the highest catalytic activity because the large pores are benefit for the diffusion of reactants and products. The immobilized Ru catalysts prove to be reusable in RCM reactions. Their catalytic activity is closely related to the confinement effect and high hydrophobicity of SBA-15 mesopores.

Full text of DOI:10.1016/j.molcata.2013.01.034

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Journal of Molecular Catalysis A: Chemical 372 (2013) 35–43
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Grubbs-type catalysts immobilized on SBA-15: A novel heterogeneous catalyst
for olefin metathesis
Huan Zhang, Ying Li, Songxue Shao, Haihong Wu∗, Peng Wu∗
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, 3663 North Zhongshan Road, Shanghai 200062, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel heterogeneous olefin metathesis catalysts have been developed by immobilizing Ru
species on SBA-15 mesoporous silica with tunable ordered pores and different textural properties. Various
techniques such as X-ray diffraction, N2 adsorption–desorption, high resolution transmission electron
microscopy have been used to characterize the physicochemical properties of the catalysts. The catalytic
activity of thus prepared Ru-based catalysts has been studied in ring closing metathesis (RCM) and other
metathesis reactions. Among these immobilized catalysts, the SBA-15 support with the largest pore size
gives rise to the highest catalytic activity because the large pores are benefit for the diffusion of reactants
and products. The immobilized Ru catalysts prove to be reusable in RCM reactions. Their catalytic activity
is closely related to the confinement effect and high hydrophobicity of SBA-15 mesopores.
© 2013 Elsevier B.V. All rights reserved.
Received 15 September 2012
Received in revised form 18 January 2013
Accepted 19 January 2013
Available online 18 February 2013
Keywords:
Heterogeneous catalysis
Grubbs-type catalyst
SBA-15 mesoporous silica
Ring-closing olefin metathesis
Immobilization
1. Introduction
have been reported by using polymer supports including vinyl
polystyrene [5], polyethylene glycol [6], PEGA-NH2 resin [7], Poly
Olefin metathesis, a transition metal-catalyzed interexchange
reaction of alkylidene units between two substituted alkenes, is an
effective and useful method for constructing carbon–carbon dou-
ble bonds, which attracts growing research attentions in organic
synthesis in recent years [1]. It opens up new industrial routes
to synthesize valuable petrochemicals, polymers, oleochemicals
and specialty chemicals. As remarkable olefin metathesis catalysts,
ruthenium-based carbene complexes developed by Grubbs [2] have
significantly broadened the scope of the olefin metathesis reaction
(Scheme 1). Lately, several modified Grubbs-type catalysts have
also been developed and intensively studied [3].
Despite of the successes to ring construction, there is still a
large room to improve this general approach in terms of scope,
convenience and generality. Most of homogeneous Grubbs-type
catalysts are hard to be reused and recycled after reactions. Further-
more, the homogeneous systems suffer the difficulty of removing
residual ruthenium byproducts from the reaction products [4].
Nowadays, the use of environmentally friendly heterogeneous cat-
alysts has become an important research target for green chemistry.
Immobilizing homogeneous catalytic species on solid supports
and scavenging residual catalysts are the most effective ways to
solve the problems. Several immobilized Grubbs-type catalysts
(fluoroalkyl acrylate) [8], PolyHIPE [9], and so on [10]. The poly-
mers possess usually a relatively low thermal stability, making the
recovered catalysts less active in reuse.
Since the discovery of the M41S family [11], ordered meso-
porous silica materials are widely investigated because of their
high surface area, large adsorption capacity, diverse morphologies
and tunable mesopores [12]. Thereafter, these ordered mesoporous
silica materials such as MCM-41 [13], siliceous mesocellular foam
[14], etc., are used as supports for the Grubbs-type catalysts. Among
these materials, SBA-15, a kind of important hexagonal mesoporous
silicas [15], has been developed and investigated in various appli-
cations as it has larger pore size, thicker silica walls and higher
hydrothermal stability [16]. Using these mesoporous materials as
supports, several generations immobilized Grubbs catalysts have
been reported [17]. In 2005, Shi and coworkers anchored first
generation of Grubbs catalyst on the inner pore surface of SBA-
15 through the N-heterocyclic carbene ligands, which effectively
prevented the decomposition of the catalytic species. SBA-15-
supported catalysts thus prepared achieved a durable catalytic
activity [17a].
The supported catalysts prepared from the second generation
Grubbs complex gave much higher reaction rates than those from
the first generation one. A second generation Hoveyda–Grubbs
catalyst was once immobilized on silica without any linkers but
simply by mixing the Ru complex with silica in a suspension [18].
Hoveyda–Grubbs-type complexes were also covalently bonded to
a silica matrix by sol-gel processes. They were shown to be superior
∗
Corresponding authors. Tel.: +86 21 62238510; fax: +86 21 62238510.
E-mail addresses: hhwu@chem.ecnu.edu.cn (H. Wu),
pwu@chem.ecnu.edu.cn (P. Wu).
1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.01.034

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H. Zhang et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 35–43
argon atmosphere. 1H spectra were acquired on a Bruker DRX500
spectrometer at 500 MHz in CDCl3. TMS was used as an internal
standard for 1H spectra. Flash column chromatography was per-
formed using silica gel 60 (230–400 mesh). The X-ray diffraction
(XRD) patterns were collected on a Bruker D8 ADVANCE instru-
Mes
Cl
Cl
N
N Mes
Ru
Mes
Cl
N
N Mes
Ru
PCy3
Ru
Cl
Cl
Cl
Ph
Ph
Ph
PCy3
PCy3
PCy3
˚
ment using Cu-K␣ radiation (ꢀ = 1.5418 A) at 40 kV and 40 mA.
Nitrogen adsorption–desorption isotherms were recorded on a
Quancachrome Autosorb-3B instrument. The specific surface areas
were evaluated using Brunauer–Emmett–Teller (BET) method. The
TEM images were recorded using a JEOL-JEM-2010 microscope.
IR analyses were obtained with Nicolet NEXUS 670 infrared spec-
trometer. N elemental analyses were performed on an Elementar
VarioEL III CHN elemental analyzer. The bulk loading amount of Ru
was determined by ICP (Thermo Electron Corporation IRIS Intrepid
II XSP).
3
1
2
PCy3
Mes
Cl
Cl
N
N Mes
Cl
Cl
Ru
O
Ru
O
4
5
2.2. Synthesis of SBA-15 mesoporous materials in different
conditions
Scheme 1. Grubbs-type catalysts.
to those prepared through anchoring the complexes to commercial
silica or meso-structured MCM-41 in the ring-closing metathesis
reactions of dienes (II) and enyne (IV) [19].
Four kinds of SBA-15 mesoporous materials with different pore
sizes were synthesized according to the literatures [15,21]. Both
the gel compositions and the condensation temperature were var-
ied changed in order to change pore size or surface. In a typical
synthesis, copolymer surfactant P123 was dissolved in deion-
ized water and 2 M HCl solution, followed by the addition of
TEOS. Four weight ratios of P123/H2O/HCl/TEOS actually used in
gram were 8.0/72/288/20.4, 6.0/45.2/180/12.3, 6.24/45/180/12.8
and 6.0/187.5/112.5/16.8. The four gels were first stirred at 35 ◦C
for 24 h, and then autoclaved for further condensation for 24 h at
60 ◦C,100 ◦C,130 ◦C and 180 ◦C, respectively. The products were col-
lected by filtration, dried and calcined at 550 ◦C for 6 h to remove
the surfactant. The samples were denoted as SBA-15-n (n = a, b, c
and d).
However, most of supported catalysts exhibit a lower activity in
comparison to homogeneous counterparts and suffer substantial
leaching of the ruthenium species. The supported catalytic species
should have suitable interactions with the surface, whether func-
tionalized or not, in order to obtain a desired catalytic activity [20].
Therefore, a proper understanding of the nature on inorganic sup-
port surface would provide deep insights into the activity of the
supported metathesis catalysts. Polarz et al. proved that the cov-
ering of surface silanols may stabilize the Grubbs catalyst [17c].
Recently, Fontaine and coworkers further demonstrated the pore
surface functionalities of mesoporous SBA-15 silica influenced the
stability of first generation Grubbs catalyst. The presence of sur-
face silanols significantly decreases the longevity of the ring-closing
metathesis catalyst, whereas total passivation of the surface with
trimethylsilyl groups prevents the catalyst from deactivating, but
slows down the reaction rate [17d].
2.3. Synthesis of amino-functionalized SBA-15 mesoporous
materials (1a–1d)
Compared to organic polymers, mesoporous silica material is
a common support for immobilization due to its higher thermal
and chemical stability. It has already been discussed that a confin-
ing reaction field affects intermolecular equilibrium reactions very
strongly [17c]. In this context, we design new method for immo-
bilization and use SBA-15 with different pore sizes as supports for
the heterogenization of the first-generation or second-generation
Grubbs catalyst. The surface hydrophilicity/hydrophobicity of SBA-
15 with variable pore sizes is quite different because of the various
synthesis conditions. It will allow a different loading of these large
catalytic species throughout the matrix, which results in different
catalytic conversions of bulky organic reactants.
In this study, with purpose to prepare active and stable het-
erogeneous Grubbs catalysts, we synthesized a series of SBA-15
ordered mesoporous silica materials with variable pore sizes, and
then immobilized the Grubbs-type catalysts on them. We prepared
a series of new supported catalysts and studied the catalytic activ-
ity of them in ring-closing metathesis (RCM), self-metathesis and
cross-metathesis (CM) reactions.
SBA-15-a (2.0 g) mesoporous materials were evacuated at 90 ◦C
for 4 h in a three-necked flask, into which dry toluene (60 mL) and
3-aminopropyl triethoxysilane (0.9 g, 4 mmol) were added through
a syringe. The mixture was then refluxed at 110 ◦C for 24 h. After
cooling to room temperature, the mixture was filtrated and washed
repeatedly with toluene, ethanol and acetone in turns to afford 1a as
a light yellow solid 2.2 g. 1b–1d were obtained by the same method.
2.4. Immobilization of Hoveyda-type ligand on SBA-15 (6a–6d)
To
a solution of 3-(3-vinyl-4-isopropoxyphenyl) propionic
Acid 5 (0.80 g, 3.42 mmol) in 50 mL of DMF was added DCC
(0.78 g, 3.76 mmol), DMAP (0.125 g, 1.03 mmol) and TsOH (65.0 mg,
0.342 mmol). This solution was stirred at room temperature for 1 h
and then amino-functionalized SBA-15-a mesoporous materials 1a
(800 mg) were added in one portion. The mixture was stirred at
70 ◦C for 72 h. The resulting suspension was filtered and washed
repeatedly with CH2Cl2, DMF and acetone in turns to afford 6a as a
yellow solid 0.96 g. 6b–6d were obtained by the same method.
2. Experimental
2.1. General
All reagents were commercially available (Aldrich) and were
directly used without further purification. All reactions were car-
ried out in Argonaut advantage seriesTM 2410 personal screening
synthesizer. All non-aqueous reactions were performed under an

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H. Zhang et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 35–43
37
2.5. Preparation of SBA-15 supported Hoveyda–Grubbs 1st type
catalyst (7a–7d)
(100)
(110)
6a (400 mg) and CuCl (24 mg, 0.24 mmol) was charged to a
50 mL tube-flask. In the glove box, Grubbs Catalyst 1st Generation
(198 mg, 0.24 mmol) was added to the above tube flask, and the
flask was evacuated and charged with N2 for three times. Then,
15 mL of CH2Cl2 was added and the reaction mixture was stirred
at 40 ◦C for 24 h. After the reaction, the mixture was filtrated and
washed repeatedly with CH2Cl2 to afford 7a as a gray green solid
0.5 g. 7b–7d was obtained by the same method.
(200)
SBA-15-d
SBA-15-c
SBA-15-b
SBA-15-a
1
2
3
4
2Theta(deg)
2.6. Preparation of SBA-15 supported Hoveyda–Grubbs 2nd type
catalyst (8a–8d)
Fig. 1. Small angle XRD patterns for SBA-15 samples.
The N2 adsorption/desorption isotherms of four calcined SBA-15
samples are shown in Fig. 2. All four SBA-15 samples have typ-
ical type IV isotherms with the H1-type hysteresis loop, clearly
indicating that these materials possess a mesoporous structure.
The relative pressure position for the mutilayer adsorption step
increases gradually with synthesis temperature, suggesting an
enlargement of pore size.
As listed in Table 1, the pore size of SBA-15 samples increased
with an increase in hydrothermal temperature. SBA-15-a synthe-
sized at 80 ◦C has the smallest pore size of 3.7 nm, while SBA-15-d
at 180 ◦C has the biggest pore size of 10.1 nm. These results are in
agreement with those of microwave-assisted synthesis of SBA-15
reported by Jaroniec et al. [22]. At the same time, the BET surface
area and pore volume varied with the hydrothermal temperature.
The synthesis of amino-functionalized SBA-15 ordered meso-
porous materials is illustrated in Scheme 2. The silylation of four
SBA-15 samples, including SBA-15-a, SBA-15-b, SBA-15-c and SBA-
15-d, with 3-(triethoxysilyl) propan-1-amine correspondingly gave
rise to four amino-functionalized SBA-15 ordered mesoporous
materials 1a–1d [23]. Scheme 2 also illustrates the novel route
to synthesize the new SBA-15 supported Grubbs-type catalysts,
where the commercially available Methyl-3-(4-hydroxyphenyl)
6a (400 mg), CuCl (24 mg, 0.24 mmol) was charged to a 50 mL
tube-flask. In the glove box, Grubbs Catalyst 2nd Generation
(204 mg, 0.24 mmol) was added to the above tube flask, and the
flask was evacuated and charged with N2 for three times. Then,
15 mL of CH2Cl2 was added and the reaction mixture was stirred
at 40 ◦C for 24 h. After the reaction, the mixture was filtrated and
washed repeatedly with CH2Cl2 to afford 8a as a yellow green solid
0.49 g. 8b–8d was obtained by the same method.
2.7. Typical procedure for RCM reaction
In a typical experiment, a mixture of olefins (0.5 mmol) and 7a
(5 mol%) in CH2Cl2 (5 mL) was stirred at 38 ◦C under Ar. The reaction
was monitored by TLC. After the completion of the reaction, the
catalyst was filtered off and washed with CH2Cl2. The filtrate was
evaporated under vacuum and the residue was purified by column
chromatography on silica gel to give the pure RCM product. The
catalyst was dried and reused without any further activation.
propionate
2 start the esterification of carboxylic acid with
methanol in the presence of acid and the etherification of phenol
group with isopropyliodide offered 3, followed by bromination of
the aromatic ring and then introduction of the vinyl group by a Pd-
catalyzed Still coupling offered 4. 5 was accomplished by hydrolysis
2.8. Typical procedure for other metathesis reaction
In a typical experiment, a mixture of styrene (1 mmol) or styrene
(0.5 mmol) and ethyl acrylate (0.5 mmol) and 8d (5 mol%) in CH2Cl2
(5 mL) was stirred at 38 ◦C under Ar. The reaction was monitored by
TLC. After the completion of the reaction, the catalyst was filtered
off and washed with CH2Cl2. The filtrate was evaporated under vac-
uum and the residue was purified by column chromatography on
silica gel to give the pure product.
SBA-15-d
SBA-15-c
3. Results and discussion
SBA-15-b
SBA-15-a
According to the literatures [15,21], four kinds of SBA-15 meso-
porous materials with different pore sizes were synthesized by
changing the condensation temperature. The four samples were
denoted as SBA-15-n (n = a, b, c or d), corresponding to the conden-
sation temperature of 80, 100, 130 and 180 ◦C, respectively.
As shown in small-angle XRD patterns (Fig. 1), four SBA-15 sam-
ples all exhibit three peaks, which can be indexed to (1 0 0), (1 1 0)
and (2 0 0) reflections that associated with a 2D hexagonal (p6mm)
structure.
0.0
0.2
0.4
0.6
0.8
1.0
P/P0
Fig. 2. The Nitrogen adsorption–desorption isotherms for SBA-15 samples.

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H. Zhang et al. / Journal of Molecular Catalysis A: Chemical 372 (2013) 35–43
Table 1
Nitrogen adsorption–desorption for SBA-15 samples.a
Sample
P123/H2O/HCl/TEOSb
Condensation temp. (◦C)
SBET (m2/g)
Vp (cm3/g)
dp (nm)
SBA-15-a
SBA-15-b
SBA-15-c
SBA-15-d
8.0:72:288:20.4
60
100
130
180
469
567
679
450
0.50
0.84
1.40
1.20
3.70
6.18
8.06
10.1
6.0:45.2:180:12.3
6.24:45:180:12.8
6.0:187.5:112.5:16.8
a
Given by N2 sorption at 77 K.
Weight ratios.
b
Scheme 2. Synthesis of SBA-15 supported Grubbs-type catalysts.
with KOH and then acidification with HCl [24,2f], then was cou-
pled to the 1a–1d by amidation and thus offered precursor 6a–6d.
6a–6d was then treated with the first-generation Grubbs catalyst
or second-generation Grubbs catalyst in the presence of CuCl to
provide the desired heterogeneous catalysts 7a–7d or 8a–8d [25].
The key step of the synthesis is to prepare amidation 6a–6d,
which is confirmed by FT-IR and elemental analysis. Fig. 3 shows
the IR spectra of amino-functionalized SBA-15 1b and 6b. The peak
at 3302 cm−1 assigns as stretching vibration absorption of N H,
meanwhile the characteristic peaks at 1656 cm−1 could be related
to the stretching vibration absorption of C O, indicating that the
product of amidation was obtained.
Results of elemental analysis are shown in Table 2. After amida-
tion, nitrogen content of the samples all has a reduction between
0.15 mmol/g and 0.19 mmol/g. It indicates that 4 products of ami-
dation were obtained in success.
Ruthenium content in catalytic materials is determined by
inductively coupled plasma (ICP) analysis, summarized in Table 3.
All immobilized catalysts contain a certain amount of Ru with some
differences. Ruthenium content of immobilized catalysts prepared
from the second generation Grubbs complexes gave much lower
Ru content than those prepared from the first generation Grubbs
complexes. As reported by Polarz et al. [17c] and Staub et al. [17d]
Table 3
Ruthenium content in catalytic materials of 7a–7d and 8a–8d.a
Table 2
Nitrogen content of 1a–1d and 6a–6d.
Substrate
Ru (mmol/g)
Substrate
Ru (mmol/g)
Substrate
N (mmol/g)
Substrate
N (mmol/g)
7a
7b
7c
7d
0.0935
0.1452
0.1656
0.1208
8a
8b
8c
8d
0.0504
0.0630
0.1050
0.0828
1a
1b
1c
1d
1.15
1.58
1.49
0.92
6a
6b
6c
6d
1.00
1.39
1.32
0.77
a
Determined by ICP.