The effect of silica-coating on catalyst recyclability in ionic magnetic nanoparticle-supported Grubbs-Hoveyda catalysts for ring-closing metathesis

Article abstract of DOI:10.1016/j.tet.2014.12.024

The Grubbs-Hoveyda type ruthenium-carbene complexes have been covalently immobilized on both silica coated and uncoated magnetic nanoparticles utilizing an imidazolium salt linker. These MNP-supported catalysts showed comparable catalytic activity to the

Full text of DOI:10.1016/j.tet.2014.12.024

Tetrahedron xxx (2014) 1e6
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
The effect of silica-coating on catalyst recyclability in ionic magnetic
nanoparticle-supported GrubbseHoveyda catalysts for ring-closing
metathesis
Shu-Wei Chen , Zhi-Cheng Zhang , Ning-Ning Zhai , Chong-Min Zhong ,*,
Sang-gi Lee
a
a
,
b
a
a
a
b
,
*
Department of Applied Chemistry, College of Science, Northwest A&F University, Yangling 712100, PR China
Department of Chemistry and Nano Science (BK Plus), Ewha Womans University, Seoul 120-750, Republic of Korea
b
a r t i c l e i n f o
a b s t r a c t
Article history:
The GrubbseHoveyda type rutheniumecarbene complexes have been covalently immobilized on both
silica coated and uncoated magnetic nanoparticles utilizing an imidazolium salt linker. These MNP-
supported catalysts showed comparable catalytic activity to the homogeneous imidazolium salt-
tagged ruthenium catalyst in the ring-closing metathesis (RCM) of dienes, and could effectively cata-
lyze RCM reactions in the presence of only 0.85 mol % Ru. The MNP-supported ruthenium catalysts could
be easily recovered using an external magnet. The recyclability of the silica-coated MNP-supported
catalysts was superior to silica uncoated MNP-supported catalysts allowing reuse 14 times, due to the
increased compatibility of the silica-coated MNPs with the reaction medium.
Received 6 November 2014
Received in revised form 5 December 2014
Accepted 6 December 2014
Available online xxx
Keywords:
Metathesis
Ruthenium
Immobilization
Magnetic nanoparticles
Ionic materials
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
Compatibility issues regarding the interactions among the
support material, the catalyst and the reaction medium is integral
Widely utilized in natural product synthesis, pharmaceutical
research and development, and in polymer chemistry, ruthenium-
catalyzed olefin metathesis has become indispensable for estab-
lishing the requisite carbonecarbon double bonds of target mole-
to the stability, activity, and recyclability of supported catalysts.
Therefore, it is important to the field of supported catalysis that
new support materials and immobilization methods are developed.
Accordingly, we recently developed ionic nanomaterials via the
covalent surface modification of nanomaterials such as silica
nanoparticles, carbon nanotubes (CNTs), and nanodiamonds with
imidazolium salt-based ionic liquid moieties for use as new
1
cules. To allow for greener and more cost-effective production by
enabling the recovery and reuse of the catalysts, significant effort
has been directed towards the development of supported catalysts
by immobilizing the homogeneous catalysts and using a ‘release
and return’ metathesis mechanism with the GrubbseHoveyda ru-
thenium catalyst.2 During the last decade, various support mate-
rials such as polymers, silica, ionic liquids, and per-fluorinated
hydrocarbons have been investigated as a means to immobilize
4
supports. These ionic nanomaterials combine the important
characteristics inherent to both ionic liquids and nanomaterials, i.e.,
the anion-directed tunable physiochemical properties of ionic liq-
5
uids and the high surface area of nanomaterials. In addition, the
use of ionic nanomaterial functionalized imidazolium salts can fa-
cilitate the immobilization of palladium and gold nanoparticle
3
these Ru-metathesis catalysts. However, because of the significant
6
leaching of the ruthenium species, many of the recyclability tests
required a relatively larger amount of the ruthenium catalyst
catalysts with increased stability. During our continuing
studies directed towards the development of supported
7
(
generally 2.5e5.0 mol % compared to less than 1.0 mol % required
ruthenium-metathesis catalysts,
we recently immobilized
for homogeneous reactions) limiting the practical application of
these immobilized catalysts. Therefore, a supported metathesis
catalyst with high activity and good recyclability due to facile re-
covery is still a challenging goal.
a
GrubbseHoveyda Ruecarbene complex on imidazolium-
functionalized ionic CNTs with excellent catalytic activity toward
7
e,f
olefin metathesis.
However, the final recovery of the supported
catalysts from the reaction mixture by the conventional methods of
extraction, filtration or centrifugation was problematic. This chal-
lenge could be addressed by supporting the catalyst on the emer-
gent magnetic nanoparticles (MNPs), which can be easily separated
*
Corresponding
authors.
E-mail
addresses:
zhongcm@nwsuaf.edu.cn
(
C.-M. Zhong), sanggi@ewha.ac.kr (S.-g. Lee).
http://dx.doi.org/10.1016/j.tet.2014.12.024
040-4020/Ó 2014 Elsevier Ltd. All rights reserved.
0
Please cite this article in press as: Chen, S.-W.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.12.024

2
S.-W. Chen et al. / Tetrahedron xxx (2014) 1e6
8
from the reaction mixture using an external magnet. Despite the
advantages of MNPs as support materials, only three recent ex-
amples of MNP-supported Ru-metathesis catalysts (A-C) have been
reported (Fig. 1).9
isopropoxy group showed excellent catalytic activities for the RCM
7
d
of dienes in ionic liquids. However, the recyclability of the cata-
lysts was dependent largely on the tether length, the structure of
the imidazolium tag and the ionic liquid, as well as the composition
Fig. 1. The MNP-supported Ru-metathesis catalysts.
The sugar-coated MNP-supported GrubbseHoveyda catalyst A
showed excellent catalytic activity, functioning with 0.05 mol % Ru
and was reusable 5 times with minimal leaching of the Ru species
of the ionic solvent system. Thus, complex 2 with a 1,2-dimethyl
imidazolium salt moiety and a long tether length showed supe-
rior recyclability to the catalysts in which the imidazolium salt had
a 2-methine proton or was attached with a shorter tether length.
On the basis of these observations, we anticipated that the MNP-
supported GrubbseHoveyda Ruecarbene complexes 1 with the
imidazolium salt tether that had been utilized for 2 could provide
an effective recyclable metathesis catalyst. In order to compare the
catalytic activity between homogeneous and supported catalysts,
the imidazolium salt-functionalized Ruecarbene complex 2 was
synthesized by the reaction of chlorinated ether 3, which can be
readily prepared according to our previous protocol starting from
9
a
(
3.0 ppm) in the cross metathesis (CM) of methyl oleate. Although
a relatively larger amount of the Ru-catalyst (2.5 mol %) was used,
catalyst B, which is covalently immobilized on uncoated MNPs, can
be reused up to 22 times in ring-closing metathesis (RCM) reac-
9
b
tions. More recently, Robinson and co-workers also reported
new type of electrostatically immobilized MNP-supported
a
GrubbseHoveydatype Ru-catalyst C, which catalyzed RCM re-
actions in the presence of 0.68 mol % of Ru and could be magneti-
9
c
cally recovered and reused 5 times. However, due to the weak
electrostatic interactions, significant amounts of the Ru species
were leached out (ca. 519 ppm) decreasing catalytic activity upon
reuse. This catalyst could be restored, however, by addition of the
fresh Ruecarbene complex bearing a quaternary ammonium moi-
ety. We envisioned that immobilization of the GrubbseHoveyda
type Ruecarbene complex onto imidazolium salt-functionalized
ionic MNPs could be useful as a new highly efficient MNP-
supported metathesis catalyst with high recyclability. In a pre-
liminary communication, it was found that the imidazolium salt-
functionalized ionic MNP-supported GrubbseHoveyda type
Ruecarbene 1a, in which the surface hydroxyl group of the MNPs
was used to anchor the trialkoxy silyl-functionalized chelating li-
gand, exhibited excellent catalytic activity in RCM and CM of olefins
in the presence of 0.85 mol % of Ru, and the magnetically recovered
7
d
commercially available 2-propenylphenol, with 1,2-dimethyl-1H-
imidazole, followed by anion exchange with NaPF . For the im-
6
mobilization of the imidazolium salt-functionalized Ruecarbene
complex onto the MNPs, ligand 5 functionalized with trimethox-
ysilylpropyl imidazolium chloride was synthesized by the sequen-
tial reaction of chlorinated ether 3 with 2-methyl-1H-imidazole
and 3-chloropropyltrimethoxysilane. Ligand 5 was then thermally
grafted onto the surfaces of two different MNPs, silica-uncoated
and silica-coated MNPs, which were prepared according to the
11
6
reported procedures. Anion exchange with NaPF , followed by
metathesis with Grubbs second-generation catalyst in the presence
of CuCl afforded the desired MNP-supported Ruecarbene com-
plexes 1a and 1b, respectively (Scheme 1). Inductively coupled
plasma mass spectrometry (ICP-MS) analysis indicated that the Ru
10
catalyst could be reused 7 times. Herein, we report the details and
expand on our studies of silica-coated ionic MNP-supported Ru-
metathesis 1b, which significantly increased the recyclability of this
catalyst in olefin metathesis allowing 14 times reuse.
content (22.5
mmol/g) of silica-coated MNP-supported 1b was
greater than that of silica-uncoated MNP-supported 1a (18.3
mmol/
g). This difference is ascribed to the limited surface hydroxyl groups
of the silica-uncoated MNPs. The X-ray photoelectron spectroscopy
(XPS) analysis of 1b also confirmed the anion exchange and suc-
2
2
. Results and discussion
cessful immobilization of the Ruecarbene complex based on the
observed binding energies at 686.3 eV for F1s, and at 463.2 eV and
485.8 eV for Ru3p(3/2) and Ru3p(1/2), respectively (Fig. 2). The
morphology and magnetic behavior of the MNPs were measured by
transmission electron microscopy (TEM) and a magnetic properties
measurement system (MPMS-squid VSM-094) magnetometer be-
fore and after-silica coating. As shown in Fig. 3, the morphology of
.1. Design, synthesis and characterization of MNP-supported
Ruecarbene complexes 1a and 1b
Previously, we found that GrubbseHoveyda Ruecarbene com-
plexes having an imidazolium salt tag attached to the chelating
Please cite this article in press as: Chen, S.-W.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.12.024

S.-W. Chen et al. / Tetrahedron xxx (2014) 1e6
3
Scheme 1. Synthesis of ionic MNP-supported Ruecarbene complexes.
the MNPs was not significantly altered after silica-coating, and the
magnetism was only slightly diminished.
2.2. Catalytic activity and recyclability of MNP-supported 1a
and 1b in RCM reactions
We first compared the catalytic activity of the MNP-supported
Ruecarbene complexes 1a and 1b with the homogeneous
Ruecarbene complex 2 in the RCM of N,N-bisallyl p-toluenesulfo-
namide 6a in methylene chloride (Scheme 2). It has been found that
all these catalysts exhibited extremely high catalytic activity.
Moreover, the catalytic activity of the MNP-supported Ruecarbene
complexes 1a and 1b is quite comparable with that of the homo-
geneous 2. Consequently, the RCM reactions with 1a and 1b went to
completion within 30 min at room temperature in the presence of
Fig. 2. XPS spectrum of 1b (right: Ru 3p and F 1s regions).
0.85 mol % Ru-catalysts. We also compared the catalytic activity of
1a and 1b in the RCM of various dienes 6 that are frequently used as
standard substrates to test the catalytic activity of supported me-
tathesis catalysts. As shown in Table 1, the silica-coated MNP-sup-
ported catalyst 1b showed higher catalytic activity than that of the
uncoated MNP-supported 1a. For example, the RCM of dienes 6d
and 6e with catalyst 1b was completed in shorter reaction times
than when utilizing catalyst 1a (Table 1, entries 4 and 5). In addi-
tion, catalyst 1b enabled complete conversion of the RCM reactions
of trisubstituted 6f and tetrasubstituted diene 6g, whereas the RCM
with catalyst 1a did not go to completion (Table 1, entries 6 and 7).
Fig. 3. TEM images and magnetisms for 1b: (A) before silica-coating (B) after silica-
coating.
Scheme 2. RCM with MNP-supported 1a,1b, and homogeneous Ruecarbene complex 2.
Please cite this article in press as: Chen, S.-W.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.12.024

4
S.-W. Chen et al. / Tetrahedron xxx (2014) 1e6
Table 1
activity and recyclability of the silica-coated MNP-supported cata-
a
RCM of dienes with MNP-supported Ru-catalysts 1a and 1b
lyst 1b suggested that the surface silicate may not only accelerate
the dissociation of the Ru-complex, increasing the concentration of
the catalytically active Ru-species, but may also increase the effi-
ciency of its return to the stable complex via the chelating ligand
attached to the surface of the silica-coated MNPs. The increased
recyclability and decreased leaching of the Ru species of the silica-
coated MNP-supported 1b is ascribed to the grafting of an increased
amount of the chelating ligand moiety onto the surface. In silica-
uncoated MNPs, there is a relatively smaller amount of hydroxyl
functional groups that can be utilized for the grafting of trime-
thoxypropylimidazolium salt 5.
Entry
1
6
7
Cat
Time (h)
Conv (%)b
1a
0.5
0.5
>99
>99
1b
2
3
4
5
6
1a
0.5
0.5
>99
>99
1b
1a
0.5
0.5
>99
>99
1b
3. Conclusion
The second generation GrubbseHoveyda Ruecarbene catalyst
1a
1.0
0.5
>99
>99
was successfully immobilized on magnetically separable ionic
magnetic nanoparticles having an imidazolium-based ionic liquid
moiety as a linker. The MNP-supported Ru-catalyst could effectively
catalyze RCM reactions in the presence of only 0.85 mol % Ru. In
particular, the silica-coated MNP-supported catalyst could easily be
recovered by applying an external magnet and could be reused 14
times without significant loss of the catalytic activity due to the
minimal leaching of Ru and high compatibility of the ionic support
material with the reaction medium. These results suggest that the
surface properties of the supporting material can significantly in-
fluence catalyst recyclability.
1b
1a
1.5
1.0
>99
>99
1b
1a
6.0
4.0
97
>99
1b
1
1
a
b
3.0
3.0
91
>99
7c
4. Experimental section
a
Reactions were carried out with substrate 6 (0.14 mmol, c¼0.28 M) and catalyst
(Ru¼0.85 mol %) at room temperature. The data for 1a reported in reference 10
4.1. Materials and analysis
1
and used here for comparative purpose.
Dienes were synthesized and purified according to literature
b
Determined by GC or 1H NMR analysis.
Reactions were carried out in toluene at 90 C.
12
c
ꢀ
procedures. The imidazolium salt-functionalized Ruecarbene 2
and chlorinated ether 3 were synthesized according to our previous
7
d
After confirming the high catalytic activity of the MNP-
supported Ru-catalysts 1a and 1b, we next compared the recycla-
bility of these supported catalysts by using diene 6a. Both sup-
ported catalysts 1a and 1b dispersed well in methylene chloride to
form a quasi-homogeneous brown solution, and, upon completion
of the reaction, they could be collected by applying an external
magnet yielding a clear solution (Fig. 4). After decanting the
supernant solution, the catalyst was washed three times with
methylene chloride, and fresh solvent and substrate 6a were added
for the next run. As shown in Table 2, the silica-coated MNP-sup-
ported catalyst 1b showed superior recyclability compared to the
silica uncoated 1a, and thus, the catalytic activity of the recovered
catalyst 1b was completely retained during the first 6 runs. Al-
though the catalytic activity gradually decreased after the 7th run,
the recovered catalyst could be reused a total of 14 times. ICP-MS
analyses suggested that, although the effects were not significant,
leaching of the Ru species into the product was influenced by the
silica-coating: during the first three runs, ca. 130 ppm from 1a and
ca. 101 ppm from 1b were leached out. Even though there are still
arguments regarding the release-return mechanism of
methods. The MNPs were prepared according to the reported
13
procedures or purchased from Aladdin. Toluene was dried over
sodium metal and distilled under argon. Dichloromethane was
dried over calcium hydride and distilled under argon. All others
chemical reagents and solvents were obtained from commercial
sources and used without further purification. Nuclear magnetic
resonance (NMR) spectra were recorded on Bruker Avance spec-
1
13
trometers working at 500 MHz and 125 MHz for H and C, re-
spectively. Gas chromatographic analyses were conducted on
a Shimadzu GC-2014C equipped with a flame ionization detector.
Mesitylene was used as an internal standard. High-resolution mass
spectra (HRMS) were recorded on a Micromass TOF-Q II (Bruker)
spectrometer. Inductively Coupled Plasma Mass Spectrometry (ICP-
MS) analysis was carried out using an Agilent 725 ICp-OES or ICP-
MS spectrometer (Agilent TeChnoLogies Corporation). Magnetic
Properties Measurement System (MPMS) was measured with
MPMS-squid VSM-094 magnetometer.
4.2. Synthesis of MNP-supported 1a and 1b
2
GrubbseHoveyda type catalysts, the observed higher catalytic
4.2.1. 2-Methyl-1-{4-[2-(2-propenylphenoxy)-propoxy]-butyl}-1H-
imidazole (4). To a solution of NaH (0.44 g, 18.27 mmol, 60 wt %
suspension in mineral oil, washed 3 times with anhydrous n-hex-
ane) in anhydrous DMF (30 mL) was added 2-methyl-1H-imidazole
ꢀ
ꢀ
(
(
1.2 g, 14.61 mmol) at 0 C. After stirring for 20 min at 0 C, the (E)/
Z)-mixture of chloride 3 (2.1 g, 7.31 mmol) was added, and then the
mixture was stirred at room temperature for 12 h. After concen-
tration under vacuum, the residue was purified by flash chroma-
tography on silica gel (MeOH/CH
as a yellowish oil. Spectral data of the major isomer: H NMR
(500 MHz, CDCl
7.40 (dd, J¼7.8, 1.2 Hz, 1H), 7.18e7.11 (m, 1H),
2
Cl
2
¼2:25) to give 4 (2.1 g, 86.2%)
1
Fig. 4. Magnetic separation of MNP-supported catalyst 1.
3
) d
Please cite this article in press as: Chen, S.-W.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.12.024

S.-W. Chen et al. / Tetrahedron xxx (2014) 1e6
5
Table 2
Catalyst recycling experiments in the RCM of 6a with catalysts 1a and 1b
a
Cat.
Run
1
2
3
4
5
6
7
8e9
10
11
12
13
14
1
a
Time (h)
0.5
>99
50
0.5
>99
69
0.5
>99
49
0.5
>99
19
0.5
98
32
0.5
>99
13
0.75
98
1.0
96
1.5
96
2
76
Conv (%)b
Ru (ppm)c
Time (h)
1
b
0.5
>99
11
0.5
>99
0.5
>99
0.75
98
0.75
95
0.75
90
1.0
90
1.0
85
1.0
75
24
92
Conv (%)b
Ru (ppm)c
a
b
c
Reactions were carried out with 6a (0.14 mmol) at room temperature in CH
Determined by GC using mesitylene as an internal standard.
Residual Ru from the separated product determined by ICP-MS.
2
Cl
2
(0.5 mL). The data for 1a reported in reference 10 and used here for comparative purpose.
6
(
.94e6.89 (m, 2H), 6.88 (d, J¼1.1 Hz, 1H), 6.77 (d, J¼1.1 Hz, 1H), 6.71
dd, J¼15.9, 1.6 Hz, 1H), 6.20 (dq, J¼15.9, 6.6 Hz, 1H), 4.50 (sextet,
J¼4.9, 1H), 3.81 (t, J¼7.3 Hz, 2H), 3.64e3.48 (m, 4H), 2.33 (s, 3H),
.87 (dd, J¼6.6, 1.6 Hz, 3H), 1.80e1.75 (m, 2H), 1.60e1.54 (m, 2H),
1b was separated with a magnet and washed with anhydrous
CH Cl 5 times before being dried under vacuum at room temper-
2 2
ature for 1 h.
1
13
1
1
7
C
.32 (d, J¼6.2 Hz, 3H) ppm; C NMR (125 MHz, CDCl
44.4, 130.4, 128.5, 127.7, 127.1, 126.5, 125.9, 121.3, 119.1, 114.8, 74.4,
4.3, 71.0, 46.0, 27.8, 26.9, 19.0, 17.4, 13.1 ppm; HRMS Calcd for
: 329.2224. Found 329.2205.
3
)
d
154.8,
4.3. A typical procedure for RCM using the MNP-supported
Ru-catalyst 1b
H
20 29
N
2
O
2
A solution of diene 6a (35.2 mg, 0.14 mmol) and MNP-supported
2 2
catalyst 1b (52 mg, Ru is 22.5 mmol/g) in anhydrous CH Cl (0.5 mL)
4
.2.2. 2-Methyl-1-{4-[2-(2-propenylphenoxy)-propoxy]-butyl}-3-(3-
trimethoxysilyl propyl)-1H-imidazolium chloride (5). To a solution of
compound 4 (100 mg, 0.304 mmol) in anhydrous toluene (150 L)
was stirred at room temperature until complete conversion was
observed by GC. The catalyst was separated with a magnet and
washed with anhydrous CH Cl (5ꢁ2 mL). The combined CH Cl
m
2
2
2
2
was added 3-chloropropyltrimethoxysilane (121 mg, 0.608 mmol).
The reaction mixture was stirred at 95 C for 72 h. After cooling to
room temperature, the mixture was dissolved in toluene (0.5 mL),
washed with diethyl ether 4e5 times to remove impurities, and
washings were evaporated and the residue was subjected to either
GC or NMR analysis to determine the conversion. For catalyst
recycling experiments, the magnetically separated MNP-supported
catalyst 1b was reused by the addition of fresh diene 6a and solvent.
ꢀ
ꢀ
then dried under vacuum at 90 C to give the desired compound 5
(
158.6 mg, 99%) as a yellow solid. Spectral data of the major isomer:
Acknowledgements
1
H NMR (500 MHz, CDCl
m, 2H), 6.69 (dd, J¼15.9, 1.6 Hz, 1H), 6.20 (dq, J¼15.9, 6.6 Hz, 1H),
.53 (m, 1H), 4.35e4.23 (m, 4H), 3.57 (m, 13H), 2.66 (s, 3H),
.90e1.82 (m, 7H), 1.64 (s, 2H), 1.29 (d, J¼6.2 Hz, 3H), 0.74e0.65 (m,
H) ppm; 13C NMR (125 MHz, CDCl
154.8, 143.1, 127.8, 126.4,
26.2, 125.8, 121.9, 121.6, 121.2, 114.6, 74.7, 74.3, 70.9, 50.8, 50.6,
3
) d 7.65 (m, 1H), 7.51e7.03 (m, 3H), 6.89
(
4
1
2
This work was supported by the National Natural Science
Foundation of China (No. 21202131), the Scientific Research Foun-
dation for the Returned Overseas Chinese Scholars, State Education
Ministry (No. K308021305), the Foundation of Northwest A&F
University (No. Z109021114), the Fundamental Research Funds for
the Central Universities (No. 2014YB026), and the Korea Research
Foundation (2011-0016344 and 2012-0000908 for S.-g. Lee). We
thank Dr. Kris Rathwell at the NanoBio Institute at Ewha Womans
University for his critical reading of this manuscript.
3
) d
1
4
8.7, 27.4, 26.1, 23.7, 19.1, 17.1, 10.2, 6.0 ppm.
4
.2.3. Preparation of silica-coated MNPs. Iron oxide MNPs (0.8 g)
were dispersed into 400 mL of 0.1 M aqueous HCl, and stirred
vigorously for 10 min. The MNPs were separated with a magnet,
washed with deionized water 3 times, and then homogeneously
dispersed in a mixture of ethanol (640 mL), deionized water
References and notes
1. For selected reviews on olefin metathesis, see: (a) Trnka, T. M.; Grubbs, R. H.
(
160 mL) and aqueous ammonia (28 wt %, 8.0 mL). To this solution
Acc. Chem. Res. 2001, 34, 18e29; (b) Schrock, R. R.; Hoveyda, A. H. Angew.
Chem., Int. Ed. 2003, 42, 4592e4633; (c) Grubbs, R. H. Handbook of Metath-
esis; Wiley-VCH: Weinheim, Germany, 2003; (d) Connon, S. J.; Blechert, S.
Angew. Chem., Int. Ed. 2003, 42, 1900e1923; (e) Astruc, A. New J. Chem. 2005,
was added TEOS (0.8 g) at room temperature, and the mixture was
vigorously stirred with a mechanical stirrer at 50 C for 6 h. The
product was separated with a magnet and washed with deionized
water and ethanol 3 times before being dried under vacuum at
ꢀ
29, 42e56.
2
3
. There are still arguments on the “release-return” mechanism, see: (a) Bieniek,
M.; Michrowska, A.; Usanov, D. L.; Grela, K. Chem.dEur. J. 2008, 14, 806e818;
ꢀ
6
0 C for 12 h.
(b) Bates, J. M.; Lummiss, J. A. M.; Bailey, G. A.; Fogg, D. E. ACS Catal. 2014, 4,
2387e2394.
4
.2.4. Preparation of MNP-supported Ruecarbene complex 1b. In
. For reviews on supported Ru catalysts, see: (a) Clavier, H.; Grela, K.; Kirschning,
a glove box, compound 5 (120 mg, 0.227 mmol), silica-coated MNPs
1.2 g), and anhydrous toluene (3.8 mL) were placed in a screw-
A.; Mauduit, M.; Nolan, S. P. Angew. Chem., Int. Ed. 2007, 46, 6786e6801; (b)
Cop eꢀ ret, C.; Basset, J. M. Adv. Synth. Catal. 2007, 349, 78e92; (c) Sledz, P.;
Mauduit, M.; Grela, K. Chem. Soc. Rev. 2008, 37, 2433e2442; (d) Buchmeiser, M.
R. Chem. Rev. 2009, 109, 303e321; (e) Vougioukalakis, G. C.; Grubbs, R. H. Chem.
Rev. 2010, 110, 1746e1787; (f) Lwin, S.; Wachs, I. E. ACS Catal. 2014, 4,
2505e2520.
ꢀ
ꢀ
(
capped reaction vial. The vial was moved out of the glove box,
and the mixture was stirred at 135 C for 72 h. After cooling to room
temperature, the MNPs were separated with a magnet and washed
with anhydrous acetonitrile 4 times. The separated MNPs were
dried under vacuum at room temperature for 2 h. For anion ex-
change, a solution of MNPs (1.25 g) and NaPF (67.18 mg, 0.4 mmol)
6
in acetonitrile (4.0 mL) was stirred at room temperature for 12 h.
The MNPs were separated again with a magnet and washed with
ꢀ
4
5
6
. Selected papers, see: (a) Park, M. J.; Lee, J. K.; Lee, B. S.; Lee, Y. W.; Choi, I. S.; Lee,
S.-g Chem. Mater. 2006, 18, 1546e1551; (b) Shin, J. Y.; Lee, B. S.; Jung, Y.; Kim, S.
J.; Lee, S.-g Chem. Commun. 2007, 5238e5240; (c) Chun, Y. S.; Shin, J. Y.; Song, C.
E.; Lee, S.-g Chem. Commun. 2008, 942e944; (d) Kim, Y. S.; Shin, J. Y.; Jeon, H. J.;
Cha, A.; Lee, C.; Lee, S.-g Chem.dAsian J. 2013, 8, 232e237.
. (a) P a^ rvulescu, V. I.; Hardacre, C. Chem. Rev. 2007, 107, 2615e2665; (b) Lee, J. W.;
Shin, J. Y.; Chun, Y. S.; Jang, H. B.; Song, C. E.; Lee, S.-g Acc. Chem. Res. 2010, 43,
985e994; (c) Dupont, J.; Scholten, J. D. Chem. Soc. Rev. 2010, 39, 1780e1804; (d)
Zhang, P.; Wu, T.; Han, B. Adv. Mater. 2014, 26, 6810e6827; (e) Polshettiwar, V.;
Varma, R. S. Green. Chem. 2010, 12, 743e754.
. (a) Kim, Y. S.; Cha, A.; Shin, J. Y.; Jeon, H. J.; Shim, J. H.; Lee, C.; Lee, S.-g Chem.
Commun. 2012, 8940e8942; (b) Li, J.; Shi, X.-Y.; Bi, Y.-Y.; Wei, J.-F.; Chen, Z.-G.
anhydrous CH
0.5 g), Grubbs 2nd generation catalyst (33.96 mg, 40
CuCl (7.92 mg, 80 mol) in anhydrous CH Cl (1.8 mL) was stirred at
room temperature for 3 h. After the reaction, the MNP-supported
2
Cl
2
5 times. A solution of the anion-exchanged MNPs
(
mmol) and
m
2
2
Please cite this article in press as: Chen, S.-W.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.12.024

6
S.-W. Chen et al. / Tetrahedron xxx (2014) 1e6
ACS Catal. 2011, 1, 657e664; (c) Li, S.; Dong, Z.; Yang, H.; Guo, S.; Gou, G.; Ren,
9. (a) Zhu, Y.; Loo, K.; Ng, H.; Li, C.; Stubbs, L. P.; Chia, F. S.; Tan, M.; Peng, S. C. Adv.
Synth. Catal. 2009, 351, 2650e2656; (b) Che, C.; Li, W.; Lin, S.; Chen, J.; Zheng, J.;
Wu, J.-C.; Zheng, Q.; Zhang, G.; Yang, Z.; Jiang, B. Chem. Commun. 2009,
5990e5992; (c) Byrnes, M. J.; Hilton, A. M.; Woodward, C. P.; Jackson, W. R.;
Robinson, A. J. Green. Chem. 2012, 14, 81e84.
10. Chen, S.-W.; Zhang, Z.-C.; Ma, M.; Zhong, C.-M.; Lee, S.-g Org. Lett. 2014, 16,
4969e4971.
11. (a) Shao, M.; Ning, F.; Zhao, J.; Wei, M.; Evans, D. G.; Duan, X. J. Am. Chem. Soc.
2012, 134, 1071e1077; (b) Deng, Y.; Qi, D.; Deng, C.; Zhang, X.; Zhao, D. J. Am.
Chem. Soc. 2008, 130, 28e29.
12. (a) Terada, Y.; Arisawa, M.; Nishida, A. Angew. Chem., Int. Ed. 2004, 43,
4063e4067; (b) Kim, A.; Hong, J. H. Arch. Pharm. Chem. Life Sci. 2005, 338,
522e527; (c) Yao, Q.; Zhang, Y. Angew. Chem., Int. Ed. 2003, 42, 3395e3398.
13. (a) Deng, H.; Li, X.; Peng, Q.; Wang, X.; Chen, J.; Li, Y. Angew. Chem., Int. Ed. 2005,
44, 2782e2785; (b) Yu, X.; Wan, J.; Shan, Y.; Chen, K.; Han, X. Chem. Mater.
2009, 21, 4892e4898.
R.; Zhu, Z.; Jin, J.; Ma, J. Chem.dEur. J. 2013, 19, 2384e2391; (d) Li, S.; Guo, S.;
Yang, H.; Gou, G.; Ren, R.; Li, J.; Dong, Z.; Jin, J.; Ma, J. J. Hazard. Mater. 2014, 270,
1
1e17; (e) Yang, H.; Li, S.; Zhang, X.; Wang, X.; Ma, J. J. Mater. Chem. A 2014, 2,
2060e12067.
. (a) Lee, B. S.; Namgoong, S. K.; Lee, S.-g Tetrahedron Lett. 2005, 46, 4501e4503;
b) Chen, S.-W.; Kim, J. H.; Song, C. E.; Lee, S.-g Org. Lett. 2007, 9, 3845e3848; (c)
Chen, S.-W.; Kim, J. H.; Shin, H.; Lee, S.-g Org. Biomol. Chem. 2008, 6,
676e2678; (d) Chen, S.-W.; Kim, J. H.; Ryu, K. Y.; Lee, W. W.; Hong, J.; Lee, S.-g
1
7
(
2
Tetrahedron 2009, 65, 3397e3403; (e) Lee, S.; Shin, J. Y.; Lee, S.-g Tetrahedron
Lett. 2013, 54, 684e687; (f) Lee, S.; Shin, J. Y.; Lee, S.-g Chem.dAsian J. 2013, 8,
1990e1993.
8
. (a) Polshettiwar, V.; Luque, R.; Fihri, A.; Zhu, H.; Bouhrara, M.; Basset, J.-M.
Chem. Rev. 2011, 111, 3036e3075; (b) Wang, D.; Astruc, D. Molecules 2014, 19,
4635e4653; (c) Cheng, T.; Zhang, D.; Li, H.; Liu, G. Green. Chem. 2014, 16,
3401e3427.
Please cite this article in press as: Chen, S.-W.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.12.024