Immobilization of a Molybdenum Complex on Bipyridine-Based Periodic Mesoporous Organosilica and Its Catalytic Activity for Epoxidation of Olefins

Article abstract of DOI:10.1021/acscatal.8b00809

The dichlorodioxomolybdenum(VI) complex (MoO₂Cl₂) is an efficient and low-cost homogeneous catalyst for a variety of organic reactions, but its activity usually decreases after immobilization on a solid support. This report describes the synthesis of heterogeneous Mo complex catalysts using a bipyridine-periodic mesoporous organosilica (BPy-PMO) as a solid chelating ligand and MoO₂Cl₂ as a precursor, and their catalysis in the epoxidation of olefins with tert-butyl hydroperoxide (TBHP). The MoO₂Cl(OH) complex could be immobilized on trimethylsilylated BPy-PMO (BPy-PMO-TMS), which was confirmed by Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray absorption fine-structure analysis. The Mo complex immobilized on BPy-PMO-TMS exhibited greater catalytic activity for the epoxidation of cis-cyclooctene compared with conventional heterogeneous Mo complex catalysts using mesoporous silica, polystyrene, and naked BPy-PMO as supports. A large amount (up to 0.72 mmol g^-1) of the Mo complex could be loaded on BPy-PMO-TMS, which resulted in 37% of the exposed bipyridine ligands on the surface forming Mo complexes. The turnover frequency relative to Mo was nearly constant, even with a high density of Mo complex on the pore surface. The Mo-BPy-PMO-TMS catalyst exhibited a solvent effect on the catalysis, and the presence of water in the reaction medium was detrimental for the catalysis. Under anhydrous conditions, Mo-BPy-PMO-TMS showed good catalytic activity for at least three reuse cycles in the epoxidation of cis-cyclooctene. A variety of olefins including aliphatic and aromatic olefins were successfully oxidized by Mo-BPy-PMO-TMS to give the desired epoxides in high yield.

Full text of DOI:10.1021/acscatal.8b00809

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Immobilization of a Molybdenum Complex on Bipyridine-Based Periodic
Mesoporous Organosilica and Its Catalytic Activity for Epoxidation of Olefins
Satoshi Ishikawa, Yoshifumi Maegawa, Minoru Waki, and Shinji Inagaki
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b00809 • Publication Date (Web): 03 Apr 2018
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Immobilization of a Molybdenum Complex on
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BipyridineꢀBased
Periodic
Mesoporous
Organosilica and Its Catalytic Activity for
Epoxidation of Olefins
Satoshi Ishikawa,†,‡, Yoshifumi Maegawa,†,∇ Minoru Waki,† Shinji Inagaki †,*
∇
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† Toyota Central R&D Labs., Inc., Nagakute, Aichi 480ꢀ1192, Japan
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Abstract
The dichlorodioxomolybdenum (VI) complex (MoO2Cl2) is an efficient and lowꢀcost homogeneous
catalyst for a variety of organic reactions, but its activity usually decreases after immobilization on a
solid support. This report describes the synthesis of heterogeneous Mo complex catalysts using a
bipyridineꢀperiodic mesoporous organosilica (BPyꢀPMO) as a solid chelating ligand and MoO2Cl2 as
a precursor, and their catalysis in the epoxidation of olefins with tertꢀbutyl hydroperoxide (TBHP).
The MoO2Cl(OH) complex could be immobilized on trimethylsilylated BPyꢀPMO
(BPyꢀPMOꢀTMS), which was confirmed by Fourierꢀtransform infrared spectroscopy, Raman
spectroscopy, and Xꢀray absorption fineꢀstructure analysis. The Mo complex immobilized on
BPyꢀPMOꢀTMS exhibited greater catalytic activity for the epoxidation of cisꢀcyclooctene compared
to conventional heterogeneous Mo complex catalysts using mesoporous silica, polystyrene polymer,
and naked BPyꢀPMO as supports. A large amount (up to 0.72 mmol gꢀ1) of the Mo complex could be
loaded on BPyꢀPMOꢀTMS, which resulted in 37% of the exposed bipyridine ligands on the surface
forming Mo complexes. The turnover frequency relative to Mo was nearly constant, even with a
high density of Mo complex on the pore surface. The MoꢀBPyꢀPMOꢀTMS catalyst exhibited a
solvent effect on the catalysis and the presence of water in the reaction medium was detrimental for
the catalysis. Under anhydrous conditions, MoꢀBPyꢀPMOꢀTMS showed good catalytic activity for at
least three reuse cycles in the epoxidation of cisꢀcyclooctene. A variety of olefins including aliphatic
and aromatic olefins were successfully oxidized by MoꢀBPyꢀPMOꢀTMS to give the desired epoxides
in high yield.
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KEYWORDS: Periodic mesoporous organosilica, bipyridine, immobilization, molybdenum,
epoxidation
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1. Introduction
The use of recoverable and reusable heterogeneous metal complex catalysts, instead of
homogeneous catalysts, for batch and flowꢀthrough systems is of interest in the development of
environmentally friendly chemical processes [1ꢀ2]. Flowꢀthrough reactions require highly active
catalysts because the contact time for column reactors is generally shorter than that for batch systems
[3]. Therefore, a large amount of active metal complex must be immobilized on a solid support to
prevent a loss of activity. However, the intrinsic catalytic activity of metal complexes usually
decreases after immobilization on conventional solid supports due to unfavorable interactions
between the active sites and the heterogeneous solid surface [1,4]. In addition, highꢀdensity
immobilization usually causes aggregation of the metal complex on the support, thus decreasing
activity [5].
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Recently, the synthesis of a new periodic mesoporous organosilica (PMO) containing
2,2’ꢀbipyridine (BPy) ligands within the framework (BPyꢀPMO) has been reported[6]. The
BPyꢀPMO had a molecularly wellꢀdefined pore surface structure in which bipyridine ligands were
regularly and densely arranged in the siloxane network. The neighboring BPyꢀBPy distance was
approximately 0.44 nm, estimated by a molecular mechanics simulation, which indicated that an
extremely high density of BPy ligands existed within the pore walls (elemental analysis indicated
that the total amount of BPy ligand in BPyꢀPMO was 3.18 mmol gꢀ1). Furthermore, BPyꢀPMO had a
large specific surface area (> 600 m2 gꢀ1) and large pore size (3.8 nm in diameter), which allowed the
smooth diffusion of reactant and product molecules in the mesochannels. Therefore, BPyꢀPMO was
expected to function as a unique solid support that could immobilize a large amount of metal
complexes without a loss of activity. Heterogeneous catalysis has been reported for precious metal
complexes formed on BPyꢀPMO such as Ir(OMe)(cod)(BPyꢀPMO) [6,7], Ru(bpy)2(BPyꢀPMO) [6],
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RuCl2(CO)2(BPyꢀPMO) [8], and IrClCp*(BPyꢀPMO) [9]. However, no report has described the
formation of base metal complexes, such as a Mo complex, on BPyꢀPMO.
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Dichlorodioxomolybdenum (VI) complexes, such as [MoO2Cl2(L)n] (L: neutral ligand),
have attracted attention as efficient and lowꢀcost homogeneous catalysts for a variety of organic
reactions including epoxidation, acylation, hydrosilylation, reduction, and oxidation [10ꢀ17]. Due to
their attractive catalytic properties and the potential for environmentally friendly (“green”) chemistry,
attempts have been made to heterogenize MoO2Cl2(L)n using solid supports such as metalꢀorganic
frameworks (MOF), mesoporous silica, and hydrotalcite [18ꢀ22]. However, in most cases, the
catalytic activity of MoO2Cl2(L)n decreased significantly after immobilization.
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The present report describes the immobilization of MoO2Cl2 on BPyꢀPMO, and its catalysis for
the epoxidation of olefins using tertꢀbutyl hydroperoxide (TBHP). The Moꢀimmobilized BPyꢀPMO
complexes were formed successfully using BPyꢀPMO endꢀcapped with trimethylsilyl (TMS) groups
on the silanol groups, without changing the ordered mesoporous and pore wall structures. The
obtained MoꢀBPyꢀPMOꢀTMS exhibited catalytic activity for the epoxidation of cisꢀcyclooctene,
which was significantly greater than the activity of heterogeneous MoO2Cl2(bpy) catalysts prepared
by a conventional immobilization approach using bipyridineꢀgrafted mesoporous silica, polystyrene,
or nonꢀtrimethylsilylated (naked) BPyꢀPMO as solid supports. The relationship between the loading
amount and catalytic activity, which has not been well studied for BPyꢀPMO [6ꢀ8], was also
investigated. The Mo complexes could be formed on up to 37% of the BPy ligands exposed on the
pore surface without a loss of catalytic activity. A hotꢀfiltration experiment clearly indicated that the
catalytic reaction proceeded without leaching of Mo species from BPyꢀPMO. MoꢀBPyꢀPMOꢀTMS
showed good recyclability for the epoxidation of cisꢀcyclooctene for at least three times and could be
used for the epoxidation of a variety of olefins such as cyclic, terminal and internal aliphatic olefins,
and aromatic olefins.
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2. Experimental
2.1. Chemicals and characterization
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All chemicals were purchased from commercial suppliers (SigmaꢀAldrich, Tokyo Chemical
Industry Co., Ltd., and Wako Pure Chemical Industries, Ltd.) and used without further purification.
The BPyꢀPMO and BPyꢀPMO endꢀcapped with trimethylsilyl groups (BPyꢀPMOꢀTMS) were
prepared according to a previously reported procedure [4]. Gas chromatography (GC) mass analyses
were performed using an Agilent 6890GC/5973MSD instrument equipped with a capillary column
(HPꢀ5MS, 0.25 mm × 30 m) and a flame ionization detector. 1H NMR spectra were obtained using a
Jeol ECXꢀ400 spectrometer operating at 400 MHz. Chemical shifts are reported in δ parts per
million referenced to tetramethylsilane as an internal standard. For the NMR experiments, the
product yield was determined using the integral value of internal standards such as mesitylene or
1,4ꢀdioxane. Xꢀray diffraction (XRD) profiles were recorded by a Rigaku RINTꢀTTR diffractometer
using CuꢀKα radiation (50 kV, 300 mA). Nitrogen adsorption/desorption isotherms were obtained
using a Quantachrome Nova3000e sorptometer at liquid nitrogen temperature (ꢀ196 °C).
BrunauerꢀEmmettꢀTeller (BET) surface areas were calculated from the linear sections of BET plots
(P/P0 = 0.1–0.25). Poreꢀsize distributions were calculated using the DFT method (DFT kernel: N2 at
ꢀ196 °C on silica, cylindrical pores, nonlinear density functional theory (NLDFT) equilibrium
model). Pore volumes were estimated using the tꢀplot method. Scanning electron microscopy (SEM)
and energy dispersive Xꢀray spectrometry (EDX) were performed using a Hitachi Sꢀ3600N
instrument. Fourierꢀtransform infrared spectroscopy (FTꢀIR) was performed using a Thermo Fisher
Scientific Nicolet Avatarꢀ360 FTꢀIR with an attenuated total reflection attachment. Raman analysis
was conducted on a Jasco NRSꢀ3300 instrument using an Ar laser (532 nm). Xꢀray absorption fine
structure (XAFS) measurements at the Mo Kꢀedge were conducted using a quick XAFS (QXAFS)
method in transmission mode at BL14B2 of SPringꢀ8. Xꢀrays from the synchrotron were
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monochromatized using a Si(311) doubleꢀcrystal monochromator. An ion chamber was used to
detect I0 (intensity of incident Xꢀrays), and another placed behind the samples was used to detect I
(intensity of transmitted Xꢀrays). Background subtraction was performed with an Autobk and Spline
smoothing algorithm. The extended Xꢀray absorption fine structure (EXAFS) was analyzed with
Athena and Artemis using IFEFFIT. k3ꢀWeighted Mo Kꢀedge EXAFS oscillations (20ꢀ130 nmꢀ1)
were Fourier transformed into Rꢀspace and curve fitting was carried out in Rꢀspace. The fitting
parameters were the coordination number (CN), interatomic distance (R), DebyeꢀWaller factor (σ2),
and correctionꢀofꢀedge energy (ꢀE0). The phase shift and backscattering amplitudes were calculated
using the FEFF6 code.
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2.2. Immobilization of dichlorodioxomolybdenum (VI) complex
For preparation of MoꢀBPyꢀPMOꢀTMS, reagentꢀgrade acetonitrile (> 99.5%, undried) was used.
First, a 10 mM MoO2Cl2 solution was prepared using acetonitrile as the solvent (Caution! MoO2Cl2
is hydroscopic and highly reactive with metals to form insoluble materials. We rapidly weighed
MoO2Cl2 by using a PTFE spatula). Next, 1, 2, 4, or 6 mL of MoO2Cl2 solution were added to a
solution containing BPyꢀPMOꢀTMS (68.5 mg, 0.20 mmol) dispersed in 9, 8, 6, or 4 mL, respectively,
of acetonitrile. The solution obtained was stirred at room temperature for 24 h. After filtration and
washing with acetonitrile, the obtained powder was dried under reduced pressure to give x%
MoꢀBPyꢀPMOꢀTMS, where x represents the molar ratio of Mo against the bipyridine in
BPyꢀPMOꢀTMS, and was determined by ICP analysis (x = 5, 10, 20, 23). The MoO2Cl2 was
immobilized over bipyridineꢀgrafted mesoporous silica, polystyrene, and nonꢀtrimethylsilylated
BPyꢀPMO using the same procedures.
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2.3. Catalytic reaction
Epoxidation of cisꢀcyclooctene was carried out under both undried and anhydrous conditions.
The former condition was applied to a variety of Moꢀimmobilized heterogeneous catalysts and a
homogeneous MoO2Cl2(bpy) complex as a benchmark reaction. These reactions used reagentꢀgrade
solvent and TBHP solution in decane (undried). The latter condition was applied to
MoꢀBPyꢀPMOꢀTMS for experiments concerning the solvent effect and substrate scope and
limitations. These reactions were conducted using anhydrous solvent and TBHP solution in decane
dried over molecular sieves 4A.
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2.3.1 Epoxidation of cis-cyclooctene under undried conditions
A 20ꢀmL twoꢀnecked flask, with a stir bar and septum, was charged with a reaction solution of
cisꢀcyclooctene (0.65 mL, 5.0 mmol, substrate), 5ꢀ6 M TBHP solution in decane (0.96 mL, 5 mmol,
oxidant), toluene (3.19 mL, 30 mmol, internal standard, > 99.5%), and decane (5.20 mL, solvent, >
99.0%). The heterogeneous catalyst (20 mg) or MoO2Cl2(bpy) (2.1 mg, 5.8 ꢁmol Mo) was added to
the reaction solution, and the flask was placed in an oil bath heated to 45–90 °C. The reaction time
was measured from the time the flask was placed in the oil bath. Samples of the reaction solution
were collected at regular intervals and centrifuged to separate the solid catalyst. After centrifugation,
the reaction solution was analyzed by GC using a Shimadzu GCꢀ8A equipped with a capillary
column (HPꢀ5, 0.53 mm × 30 m) and FID. After the reaction was completed, the catalyst was filtered
and washed with hexane before drying under reduced pressure. The used catalyst was subjected to
another reaction under the same reaction conditions.
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2.3.2 Epoxidation of cis-cyclooctene under anhydrous conditions
A 20ꢀmL test tube, with a stir bar, was equipped with a twoꢀneck gas adaptor. The side neck was
connected to a vacuum/argon manifold. The main neck was capped with a rubber septum. The test
tube was charged with 10% MoꢀBPyꢀPMOꢀTMS (20 mg, 5.8 ꢁmol Mo), then evacuated and
backfilled with argon three times. To the test tube were added cisꢀcyclooctene (0.65 mL, 5 mmol),
dry mesitylene (1 mmol, internal standard), dry solvent (9.0 mL), and dry 5ꢀ6 M TBHP solution in
decane (0.96 mL, 5 mmol). The test tube was placed in an aluminum block preꢀheated to 75 °C. The
reaction time was measured from the time the test tube was placed in the aluminum block. Samples
of the reaction solution were collected at regular intervals and diluted with chloroformꢀd. The
sample solution was passed through a membrane filter (0.20 ꢁm) to separate the solid catalyst. The
obtained sample solution was analyzed by 1H NMR spectroscopy. After the reaction was completed,
the catalyst was filtered and washed with diethyl ether (30 mL) before drying under reduced pressure.
The used catalyst was subjected to another reaction under the same reaction conditions. For the
recharging system, cisꢀcyclooctene (0.65 mL, 5 mmol) and dry 5ꢀ6 M TBHP solution in decane
(0.96 mL, 5 mmol) were added to the reaction test tube and another reaction was carried out at the
same reaction temperature.
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2.3.3 Epoxidation of olefins
A 20ꢀmL test tube, with a stir bar, was equipped with a twoꢀneck gas adaptor. The side neck was
connected to a vacuum/argon manifold. The main neck was capped with a rubber septum. The test
tube was charged with 10% MoꢀBPyꢀPMOꢀTMS (35 mg, 10 ꢁmol Mo), then evacuated and
backfilled with argon three times. To the test tube were added olefin (2.5 mmol), dry mesitylene or
dry 1,4ꢀdioxane (1 mmol, internal standard), dry 1,2ꢀdichloroethane (4.3 mL), and dry 5ꢀ6 M TBHP
solution in decane (0.72 mL, 3.75 mmol). The test tube was placed in an aluminum block preꢀheated
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to 75 °C. The reaction time was measured from the time the test tube was placed in the aluminum
block. Samples of the reaction solution were collected at regular intervals and diluted with
chloroformꢀd. The sample solution was passed through a membrane filter (0.20 ꢁm) to separate the
solid catalyst. The obtained sample solution was analyzed by 1H NMR spectroscopy.
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3. Results and discussion
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3.1 Synthesis and characterization
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To immobilize the dioxomolybdenumꢀbipyridine complex over the pore surface of
BPyꢀPMOꢀTMS, commercially available MoO2Cl2 was used as a precursor. A MoO2Cl2 solution in
acetonitrile was added to a suspension of BPyꢀPMOꢀTMS in acetonitrile and stirred at room
temperature for 24 h. After filtration and washing with acetonitrile followed by drying under reduced
pressure, MoꢀBPyꢀPMOꢀTMS was obtained in quantitative yield as a white powder (Figure 1).
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Figure 1. Schematic for direct Moꢀcomplex formation on the pore surface of BPyꢀPMOꢀTMS.
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The loading amount of the Mo complex on BPyꢀPMOꢀTMS could be controlled simply by
varying the concentration of the MoO2Cl2 solution. Figure 2 shows the relationship between
preparative Mo/BPy molar ratios in the reaction mixtures and the observed Mo/BPy molar ratios in
BPyꢀPMOꢀTMS. The Mo/BPy molar ratios in BPyꢀPMOꢀTMS were determined from the Mo/Si
ratios measured by ICP analysis, with the assumption that the ratio of Si/BPy was 10/3 because the
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pore walls were composed of three layers of SiꢀBPyꢀSi units, and the silanol groups (SiꢀOH) at the
inner and outer pore surface (2/3 of the total Si) were almost completely trimethylsilylated [6].
Preparative Mo/BPy ratios less than 0.20 agreed well with observed Mo/BPy molar ratios, but Mo
amounts greater than 0.20 resulted in saturation. The maximum Mo/BPy ratio of 0.246,
corresponding to 0.72 mmol Mo gꢀ1, was achieved when the total amount of BPy ligand in
BPyꢀPMOꢀTMS was 2.92 mmol gꢀ1 by elemental analysis [6]. This indicates that 37% of the surface
BPy ligands were coordinated with Mo in three layers of pore walls, and that a high density of Mo
complex could be loaded on BPyꢀPMOꢀTMS. Four Moꢀloaded BPyꢀPMOꢀTMS with Mo/BPy ratios
of 0.05, 0.10, 0.20, and 0.23 were used to evaluate catalysis (denoted x% MoꢀBPyꢀPMOꢀTMS,
where x = 5, 10, 20 and 23). The Cl/Mo ratios of MoꢀBPyꢀPMOꢀTMS were 1.2–1.5, which were less
than that of the MoO2Cl2 precursor (Cl/Mo = 2), indicating that some Cl was released from MoO2Cl2
during the immobilization process. This is not surprising because Cl in MoO2Cl2 undergoes easy
substitution with polar anion species such as CH3CH2Oꢀ [23]. The acetonitrile solvent or a small
amount of water contaminating the solvent may have promoted the replacement of the chloride
ligand from MoO2Cl2 on BPyꢀPMOꢀTMS.
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Figure 2. Relationship between preparative and observed Mo/BPy ratios determined by ICP
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The mesoporous and pore wall structures of MoꢀBPyꢀPMOꢀTMS were investigated by
XRD and nitrogen adsorption/desorption analyses (Figures 3 and 4). The XRD diffraction patterns
for MoꢀBPyꢀPMOꢀTMS showed a peak at 2θ = 1.78°, attributed to the periodicity of the mesoporous
structure. Peaks at 2θ = 7.54°, 15.2°, 22.9, and 30.8° were attributed to the molecularꢀscale
periodicity of bipyridine ligands in the pore walls, similar to that of the parent BPyꢀPMOꢀTMS [6].
No additional peaks corresponding to impurities, such as inorganic salts of MoO2Cl2, were observed.
These results indicate that the ordered structure of the parent BPyꢀPMOꢀTMS was maintained after
immobilization of the Mo complex on the pore surface. The nitrogen adsorption/desorption
isotherms for MoꢀBPyꢀPMOꢀTMS were typeꢀIV isotherms, similar to those for the parent
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BPyꢀPMOꢀTMS,
which
indicates
preservation
of
uniform
mesoporosity.
The
BrunauerꢀEmmettꢀTeller surface area (SBET), mesopore volume (Vp) and density functional theory
pore diameter (dDFT) are listed in Table 1. The SBET and Vp values decreased gradually with
increasing Mo complex loading amount due to the increase in sample weight. No change in dDFT was
found after immobilization of the Mo complex on the pore surface.
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2θ/degree(CuꢀKα)
(b)
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2θ/degree(CuꢀKα)
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Figure 3. (a) Lowꢀangle and (b) highꢀangle XRD patterns for BPyꢀPMOꢀTMS (black lines) and x%
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MoꢀBPyꢀPMOꢀTMS (5%, gray lines; 10%, blue lines; 20%, red lines; 23%, green lines).
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Figure 4. Nitrogen adsorption/desorption isotherms for BPyꢀPMOꢀTMS (black line) and x%
MoꢀBPyꢀPMOꢀTMS (5%, gray line; 10%, blue line; 20%, red line; 23%, green line). Closed
symbols: adsorption; open symbols: desorption.
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Table 1. Physicochemical properties of x% MoꢀBPyꢀPMOꢀTMS
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Mo amount /mmol gꢀ1
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SBET /m2 gꢀ1a
Vp /cc gꢀ1 a
dDFT /nm a
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Preparative
―
ICP
―
BPyꢀPMOꢀTMS
5% Mo
654
657
647
608
585
0.41
0.41
0.39
0.37
0.36
3.8
3.8
3.8
3.8
3.8
0.14
0.15
0.30
0.58
0.67
10% Mo
0.29
20% Mo
0.58
23% Mo
0.87
a
2
3
Determined from nitrogen adsorptionꢀdesorption isotherms at liquidꢀnitrogen temperature and
calculated using the BET method (SBET), tꢀplot method (Vp) or density functional theory (dDFT).
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The molecular structures of the Mo complexes formed on BPyꢀPMOꢀTMS were
characterized by FTꢀIR spectroscopy (Figure 5a), Raman spectroscopy (Figure 5b), and XAFS
analysis. The x% MoꢀBPyꢀPMOꢀTMS showed an additional three bands at 945 cmꢀ1 and 917 cmꢀ1 in
the IR spectrum and at 953 cmꢀ1 in the Raman spectrum, compared to the parent BPyꢀPMOꢀTMS.
Band intensities increased with the loading amount of Mo. MoO2Cl2(bpy), which was prepared as a
model complex, showed Mo=O symmetric stretching at 932 cmꢀ1 in the IR spectrum and 935 cmꢀ1 in
the Raman spectrum, and a Mo=O asymmetric stretching band at 902 cmꢀ1 in the IR [14,24]. Thus,
the additional bands observed in x% MoꢀBPyꢀPMOꢀTMS were assigned to symmetric and
asymmetric Mo=O stretching in the MoO2Cl2(bpy) complex. However, the wavenumbers of these
bands were blueꢀshifted compared with those of the model complex MoO2Cl2(bpy). Kühn et al.
reported that an electronꢀdeficient Mo center due to coordination of the electronꢀwithdrawing
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bipyridine ligand increased the Mo=O bond strength [14, 24]. Therefore, the silicon attached to the
bipyridine ligand (SiꢀbpyꢀSi) could promote greater electron withdrawal than the bpy ligand alone.
The FTꢀIR spectra of x% MoꢀBPyꢀPMOꢀTMS also showed absorption bands derived from TMS
groups and no absorption bands related to silanol groups, indicating that TMS was strongly attached
during the MoO2Cl2 immobilization process (Figure S1). The XAFS measurements revealed the
electronic state and local structure of the Mo center in x% MoꢀBPyꢀPMOꢀTMS. The Xꢀray
absorption near edge structure (XANES) spectra of 10% MoꢀBPyꢀPMOꢀTMS showed a
characteristic shoulder at 20004 eV, which is typically observed for hexavalent Mo compounds such
as MoO2Cl2(bpy), MoO2Cl2, and MoO3 (Figure S2). The spectral shape for 10%
MoꢀBPyꢀPMOꢀTMS was slightly different to that for model complex MoO2Cl2(bpy). In order to
elucidate the local structure of the Mo complex in 10% MoꢀBPyꢀPMOꢀTMS, an EXAFS analysis
was carried out. Figures S3a and S3b show Mo Kꢀedge EXAFS oscillations and their Fourier
transforms with MoO2Cl2 and MoO3 as references. The radial structure functions for 10%
MoꢀBPyꢀPMOꢀTMS were different from those for MoO2Cl2(bpy). This presumably stems from
elimination of the chloride ligand from the Mo complex in 10% MoꢀBPyꢀPMOꢀTMS as observed by
EDX analysis. Thus, the EXAFS curve fitting of 10% MoꢀBPyꢀPMOꢀTMS was carried out using
MoO2Cl(OEt)(bpy) as a model complex where one chloride ligand in MoO2Cl2(bpy) was replaced
with ethoxide (Figures S4 and S5). The fitted curve was consistent with Mo coordinated to two
oxygen centers at 1.68 Å (Mo=O), an oxygen center at 1.83 Å (MoꢀO), a bipyridine unit by two
nitrogen centers at 2.23 Å (MoꢀN), and a chloride center at 2.43 Å (MoꢀCl) (Tables S1 and S2).
These results strongly suggest the formation of a MoO2Cl(OR)(bpy) complex. Since the preparation
solvent contained a small amount of water, the MoO2Cl(OH)(bpy) complex would be formed on the
surface of the BPyꢀPMOꢀTMS. XAFS measurements were also carried out for other compositions of
x% MoꢀBPyꢀPMOꢀTMS (x = 5, 20, and 23). The Mo Kꢀedge XANES, EXAFS oscillations, and
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EXAFS Fourier transforms for x% MoꢀBPyꢀPMOꢀTMS (x = 5, 20, and 23) were similar to those for
10% MoꢀBPyꢀPMOꢀTMS (Figures S6 and S7), suggesting the same electronic state and local
structure for the Mo complexes even at low and high packing densities.
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950
850
750
650
550
Wavenumber / cmꢀ1
(b)
1100
900
700
500
300
Raman shift / cmꢀ1
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Figure 5. (a) FTꢀIR and (b) Raman spectra of BPyꢀPMOꢀTMS (black lines), x%
MoꢀBPyꢀPMOꢀTMS (5%, gray lines; 10%, blue lines; 20%, red lines; 23%, green lines), and
MoO2Cl2(bpy) (purple lines).
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3.2 Catalytic activity in epoxidation of cis-cyclooctene under undried conditions
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Epoxidation reactions of cisꢀcyclooctene (5 mmol) were conducted using TBHP (5 mmol)
in a solvent of undried decane. Figure 6 shows the yield of 1,2ꢀepoxycyclooctane (Ecyo) as a
function of reaction time over 10% MoꢀBPyꢀPMOꢀTMS, homogeneous MoO2Cl2(bpy), and
Moꢀbipyridine complexes supported on various supports at 75 °C. The TON values were calculated
as moles of product (Ecyo)/moles of Mo in the catalysts. Initial turnover frequencies (TOF, hꢀ1)
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based on the amounts of Ecyo per unit of Mo for the first 30 min were calculated and are listed in
Table 2 along with Ecyo yields after 7–8 h.
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The 10% MoꢀBPyꢀPMOꢀTMS showed high catalytic activity with an Ecyo yield of 67%
and TON of 609 at 75 °C, while homogeneous MoO2Cl2(bpy) showed greater activity with an Ecyo
yield of 90% and TON of 819 under identical conditions (Table 2, entries 1 and 2). BPyꢀPMOꢀTMS
without a Mo complex was used as a blank reaction. The experiment showed negligible conversion
of cisꢀcyclooctene (< 1%) after 24 h at 75 °C. In order to confirm whether leaching of Mo species
from 10% MoꢀBPyꢀPMOꢀTMS occurred during the reaction, a hot filtration experiment was
conducted. The PMO catalyst was removed by filtration after 30 min of reaction, and the resulting
clear solution was allowed to react under identical conditions for another 7.5 h (Figure S8). No
significant change in product yield was observed, which clearly indicated that the reaction was
catalyzed by the Mo complex fixed on BPyꢀPMO, and not leached Mo. An increase in reaction
temperature to 90 °C improved the Ecyo yield to 84% and the TON to 797 for 10%
MoꢀBPyꢀPMOꢀTMS (Table 2, entry 3), values comparable to those for homogeneous MoO2Cl2(bpy)
at 75 °C. However, a decrease in reaction temperature to 60 °C reduced the Ecyo yield to 51% and
the TON to 485 (Table 2, entry 4). For comparison, conventional catalyst supports, a mesoporous
silica (FSM) grafted with bipyridine ligands using a molecular linker followed by trimethylsilylation
(denoted as BPyꢀFSMꢀTMS) and polystyrene grafted with bipyridine ligands (denoted as
BPyꢀPolymer), were used for immobilization of the Mo complex (Figures 7, S9 and S10).
MoꢀBPyꢀFSMꢀTMS produced a lower product yield of 48% and a TON of 409 compared to 10%
MoꢀBPyꢀPMOꢀTMS at 75 °C even with the same Mo amount (Table 2, entry 5), perhaps due to
undesirable interactions between the Mo active center and the pore surface of FSM in the presence
of a flexible linker. The MoꢀBPyꢀPolymer produced a much lower product yield of 22% and a TON
of 275 (Table 2, entry 6), due to the flexible nature of the polymer matrix. Interestingly, 11%
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MoꢀBPyꢀPMO without trimethylsilylation possessed very low catalytic activity (TOF of 43 hꢀ1 at
~75 °C, Table 2, entry 7). Silanol groups inside the mesopores interact with oxygenated compounds,
such as TBHP and epoxide, due to their hydrophilic nature, and prevent smooth diffusion of these
compounds inside the mesopores [25,26]. Therefore, the treatment of silanol groups with
hydrophobic TMS groups is sometimes effective for catalysis, and has been reported for mesoporous
silicaꢀbased oxidation catalysis [25ꢀ28]. Thus, BPyꢀPMOꢀTMS is a very good support for
immobilization of Mo complexes, and minimizes the loss of the original activity of the
homogeneous MoO2Cl2(bpy) catalyst.
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Figure 6. Epoxidation of cisꢀcyclooctene with TBHP under undried conditions catalyzed by various
Moꢀbipyridine complex catalysts at 75 °C. ×, MoO2Cl2(bpy); ●, 10% MoꢀBPyꢀPMOꢀTMS; ◆,
MoꢀBPyꢀFSMꢀTMS; ■, MoꢀBPyꢀPolymer; ○, 11% MoꢀBPyꢀPMO.
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Table 2. Catalytic activity of heterogeneous and homogeneous Moꢀbipyridine catalysts for
epoxidation of cisꢀcyclooctene with TBHP. a
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Entry
Mo catalyst
Mo loading
(mmol Mo/g)
―
T
(°C)
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75
90
60
75
75
75
Time
Yield
(%)b
90
TONc
TOFd
(h)
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MoO2Cl2(bpy)
819
609
797
485
409
275
75
881
382
1155
175
141
96
10% MoꢀBPyꢀPMOꢀTMS
10% MoꢀBPyꢀPMOꢀTMS
10% MoꢀBPyꢀPMOꢀTMS
MoꢀBPyꢀFSMꢀTMSe
MoꢀBPyꢀPolymerf
0.30
8
67
0.30
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84
0.30
8
51
0.30
8
48
0.13
8
22
11% MoꢀBPyꢀPMO
0.35
8
12
43
4
5
aReactions were conducted with cisꢀcyclooctene (5 mmol), TBHP (5 mmol), and toluene (30 mmol,
internal standard) in the presence of heterogeneous (2.6ꢀ5.8 ꢁmol Mo) or homogeneous
b
6
Moꢀbipyridine catalysts (5.8 ꢁmol Mo) in decane (total volume: 10 mL) GC yields based on
c
7
internal standard. TON was calculated as moles of product/moles of Mo in the Moꢀbipyridine
d
8
catalyst. TOF (hꢀ1) was calculated as moles of product within the first 30 min/moles of Mo in
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Moꢀbipyridine catalysts. eMo/BPy ratio was 0.08. fMo/BPy ratio was 0.64.
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Figure 7. Schematic representations of MoꢀBPyꢀFSMꢀTMS and MoꢀBPyꢀPolymer.
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In order to compare the catalytic activity to previously reported Moꢀbipyridineꢀbased
heterogeneous catalysts, the catalytic reactions were conducted under the same conditions as the
reported ones. First, the activity was compared to Moꢀimmobilized bipyridine MOF (MoꢀBPyꢀMOF),
where the reaction was conducted at 50 ºC with a molar ratio of cisꢀcyclooctene/TBHP/Mo = 140:
280:1 [18]. 10% MoꢀBPyꢀPMOꢀTMS showed an initial TOF of 170 hꢀ1 and a TON of 90 after 45
min, while the MOF catalyst showed an initial TOF of 12 hꢀ1 and a TON of 82 after 24 h. The higher
catalytic activity of 10% MoꢀBPyꢀPMOꢀTMS compared to MoꢀBPyꢀMOF can be ascribed to the
smooth diffusion of substrate/product molecules owing to the larger pore diameter (ca. 3.8 nm for
BPyꢀPMO and > 1 nm for BPyꢀMOF). Second, we adopted reaction conditions of the
Moꢀimmobilized bipyridineꢀgrafted mesoporous silica (MoꢀBPyꢀMCMꢀ41) catalyst [20].
MoꢀBPyꢀMCMꢀ41 shows an initial TOF of 16 hꢀ1 and a TON of 36 at 55 °C under neat conditions
after 24 h at a molar ratio of cisꢀcyclooctene/TBHP/Mo = 48:72:1. In contrast, 10%
MoꢀBPyꢀPMOꢀTMS showed a higher TOF of 5200 hꢀ1 and a TON of 1850 after 3 h, although the
amount of PMO catalyst was reduced to 40 times that for MoꢀBPyꢀMCMꢀ41 due to difficulty in
stirring the reaction mixture. These results indicate that the catalytic activity of 10%
MoꢀBPyꢀPMOꢀTMS is greater than those of previously reported Moꢀbipyridineꢀbased heterogeneous
catalysts.
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Next, the effect of Mo loading amount (5, 10, 20, or 23%) for MoꢀBPyꢀPMOꢀTMS on
catalysis was examined. As the loading amount increased, the reaction rate within the first 30 min
also increased (Figure S11). Figure 8a shows TOF values in x% MoꢀBPyꢀPMOꢀTMS as a function of
Mo loading. The TOF value relative to Mo loading in MoꢀBPyꢀPMOꢀTMS remained nearly constant
between 300 and 400 hꢀ1. Catalytic activity was almost completely preserved, indicating that the Mo
complex acts as a singleꢀsite catalyst for the epoxidation even with a high density of Mo complex on
BPyꢀPMOꢀTMS. For comparison, the effect of Mo loading amount of MoꢀBPyꢀPolymer was
examined since it had the greatest bipyridine loading amount (up to 2.0 mmol BPy/g) among
commercially available solid supports. The results showed that immobilization of MoO2Cl2 over
BPyꢀPolymer was difficult when the loading amount of Mo exceeded 0.2 mmol Mo/g, indicating
low coordination ability. The four MoꢀBPyꢀPolymer catalysts obtained were then evaluated in the
epoxidation of cisꢀcyclooctene. The TOF values for MoꢀBPyꢀPolymer decreased as the Mo amount
increased perhaps due to an increase of undesirable interactions among Mo complex centers in the
polymer matrix upon an increase in loading amount of MoO2Cl2. These results indicate that
BPyꢀPMOꢀTMS is a unique chelating support that can accept a high density of Moꢀbipyridine
complex (up to 0.67 mmol gꢀ1) on the pore surface without a loss of activity for the epoxidation of
cisꢀcyclooctene (Figure 8b). From a practical viewpoint, this is an attractive feature for flowꢀthrough
systems because the same catalysis can be achieved using a much lower amount of catalyst, meaning
that the column reactor size can be minimized.
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Figure 8. (a) TOF value per Mo in MoꢀBPyꢀPMOꢀTMS (●) and MoꢀBPyꢀPolymer (■).
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Immobilized Mo amounts were determined by ICP analysis. (b) CG image of pore surface of
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MoꢀBPyꢀPMOꢀTMS with Mo/BPy molar ratio of approximately 23% (Mo/BPysurface
=
5
approximately 35%). Mo: sky blue; Cl: pink; O: red; Si: orange; C: light gray; N: purple; H: omitted
except for hydrogen atoms of OH ligands in Mo complexes.
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3.3 Catalytic activity in epoxidation of cis-cyclooctene under anhydrous conditions
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We investigated the catalytic reactions in different solvents under anhydrous conditions
(Figure 9). Gonçalves et al. previously reported enhanced catalysis by a solvent effect on the
epoxidation of cisꢀcyclooctene catalyzed by Mo(CO)3ꢀimmobilized phenyleneꢀbridged PMO [29].
The report also demonstrated that the presence of water was detrimental to the reaction rate, possibly
due to undesired coordination to the active Mo complex center. When the epoxidation of
cisꢀcyclooctene was carried out using anhydrous TBHP dried over molecular sieves 4A in dry decane,
the initial TOF for 10% MoꢀBPyꢀPMOꢀTMS was dramatically improved to 2030 hꢀ1 at 75 °C, and
the Ecyo yield was 89% after 3 h. This indicates that a small amount of water in the reaction solvent
and/or reagent is very detrimental to the catalysis with the Mo complex. In fact, addition of a small
amount of water (5 mmol) to the reaction media severely suppressed the catalysis.
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Figure 9. Solvent effect on epoxidation of cisꢀcyclooctene with TBHP at 75 °C in dry
1,2ꢀdichloroethane (●), dry acetonitrile (▲), dry toluene (◆), dry decane (*), dry ethanol (■),
undried decane (○), and decane containing water (5 mmol) (+).
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Under anhydrous conditions, we examined the influence of solvent polarity on the
epoxidation of cisꢀcyclooctene with anhydrous TBHP at 75 °C. The reactions were performed in
1,2ꢀdichloroethane, acetonitrile, toluene, and ethanol. The initial TOF values (hꢀ1) followed the order
of acetonitrile (2760) > 1,2ꢀdichloroethane (2480) ≈ toluene (2440) > decane (2030) >> ethanol
(520), indicating no clear relationship between the dielectric properties and initial TOF values. The
use of 1,2ꢀdichloroethane completed the reaction within 1.5 h to afford Ecyo quantitatively.
Although the use of acetonitrile and toluene also achieved high TOF, slightly prolonged reaction
times were required for completing the reaction. These solvents showing high TOF likely stabilized
the Moꢀactive intermediate and also promoted diffusion of the substrate/product molecules in the
mesopores. The lowered reaction rate observed for ethanol may be due to the coordination of ethanol
to the Moꢀactive intermediate. A similar detrimental effect of ethanol was observed for the catalytic
system using Mo(CO)3ꢀimmobilized phenyleneꢀbridged PMO [29].
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3.4 Scope and limitations of Mo-BPy-PMO-TMS for epoxidation of olefins
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The scope and limitations of 10% MoꢀBPyꢀPMOꢀTMS were evaluated in the epoxidation
of a variety of olefins 1aꢀ1h. The reactions were carried out in the presence of olefin (2.5 mmol),
anhydrous TBHP solution in decane (3.75 mmol), and 10% MoꢀBPyꢀPMOꢀTMS (0.4 mol% Mo
relative to olefin) in dry 1,2ꢀdichloroethane at 75 °C, and the results are summarized in Table 3.
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Table 3. Epoxidation of olefins with TBHP catalyzed by MoꢀBPyꢀPMOꢀTMS a
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Entry
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Olefins
Epoxides (%)b
Yield (%)c
100 (100)
1a
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96 (98)
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a All reactions were conducted with olefin (2.5 mmol), TBHP (3.75 mmol), and dry mesitylene or
dry 1,4ꢀdioxane (1.0 mmol, internal standard) in the presence of 10% MoꢀBPyꢀPMOꢀTMS (35 mg,
10 ꢁmol Mo) or MoO2Cl2(bpy) (3.6 mg, 10 ꢁmol Mo) in dry 1,2ꢀdichloroethane (4.3 mL) at 75 °C. b
The reaction was carried out at 50 °C. c 1H NMR yields based on internal standard. 1H NMR yields
for homogeneous catalytic system using MoO2Cl2(bpy) are given in parentheses.
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The epoxidation of cyclohexene (1a) proceeded efficiently and gave
1,2ꢀepoxycyclohexane (2a) quantitatively after 3 h (Table 3, entry 1). The epoxidation of internal
aliphatic olefins such as cisꢀ2ꢀoctene (1b) and transꢀ2ꢀoctene (1c) occurred stereoselectively to
afford desired epoxides 2b and 2c quantitatively, respectively (Table 3, entries 2 and 3). In contrast,
the reaction of terminal aliphatic olefin 1ꢀoctene (1d) showed moderate conversion to give
1,2ꢀepoxyoctane (2d) in 61% yield (Table 3, entry 4). MoꢀBPyꢀPMOꢀTMS also catalyzed the
epoxidation of styrene (1e), giving styrene oxide (2e) as the main product in 78% yield along with
unidentified side products (Table 3, entry 5). When limonene (1f) was used as a substrate,
regioselective oxidation was observed at the endocyclic double bond to give
1,2ꢀepoxyꢀpꢀmenthꢀ8ꢀene (limonene oxide, 2f) in 87% yield after full conversion of 1f (Table 3,
entry 6). Small amounts of side products such as diepoxide and carveol were detected by GCꢀMS
analysis, suggesting that the epoxidation of the terminal double bond and overꢀoxidation occurred.
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We also examined the epoxidation of the double bonds of cisꢀstilbene (1g) and transꢀstilbene (1h).
The cisꢀisomer was perfectly consumed after 24 h and transformed into cisꢀstilbene oxide (2g) in
96% yield (Table 3, entry 7). On the other hand, the transꢀisomer showed a lower conversion after
24 h to give transꢀstilbene oxide (2h) in 82% yield (Table 3, entry 8). This may be due to the steric
hindrance of the diphenyl groups of the transꢀisomer against the immobilized Mo complex on the
pore surface. In order to compare the catalytic activity of MoꢀBPyꢀPMOꢀTMS and homogeneous
MoO2Cl2(bpy), epoxidation of olefins 1aꢀ1h was performed using the homogeneous catalyst under
the same conditions, and these results are also summarized in Table 3. The product yields for the
10% MoꢀBPyꢀPMOꢀTMS system were comparable with those for homogeneous systems. These
results indicated that 10% MoꢀBPyꢀPMOꢀTMS is a good heterogeneous catalyst for the epoxidation
of olefins.
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3.5 Reusability of Mo-BPy-PMO-TMS
To investigate the reusability of 10% MoꢀBPyꢀPMOꢀTMS for the epoxidation of
cisꢀcyclooctene, the recovered catalyst was reused in a recycling experiment (Figure 10). Under
undried conditions, the catalytic activity gradually decreased after repeated reactions. The TOF of
382 hꢀ1 for fresh catalyst decreased to 73 and 26 hꢀ1 for the first and second reuse cycles. The yields
of Ecyo for the first and second reuse cycles after 8 h were 35% and 18%, respectively. However,
under anhydrous conditions, the recovered 10% MoꢀBPyꢀPMOꢀTMS still maintained good catalytic
activity at least three more times in the epoxidation of cisꢀcyclooctene, although the reaction rate and
product yield were gradually decreased (1st recycle: 90% after 1.5 h; 2nd recycle: 84% after 3 h; 3rd
recycle: 94% after 8 h). The decrease in activity was attributed to a change in the coordination
structure of the Mo complex fixed on BPyꢀPMO. The change in the Cl/Mo ratio of
MoꢀBPyꢀPMOꢀTMS was measured by EDX after the first reaction. Under undried conditions, the
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Cl/Mo ratio decreased from 1.5 to 0.33 after 2 h, suggesting a change in the coordination structure of
Mo. However, the Cl/Mo ratio was only slightly reduced from 1.5 to 1.1 under anhydrous conditions,
indicating that chloride elimination was effectively suppressed. These results suggest that
elimination of the chloride ligand may occur as a side reaction with residual water in solvent and/or
tꢀBuOH formed in situ. The decomposition of the MoꢀCl complex would be accelerated by the
filtration process since it removed liberated chloride ion from the reaction media. Thus, in order to
prevent loss of chloride ion from the reaction media, cisꢀcyclooctene and TBHP were recharged in
the reaction test tube after the reaction. In this system, > 95% yield of Ecyo was obtained within 4 h
for at least three reuse cycles. This result confirms that preservation of the MoꢀCl complex is
essential to maintaining the catalytic activity.
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Number of reactions
Number of reactions
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Figure 10. Reusability of 10% MoꢀBPyꢀPMOꢀTMS for epoxidation of cisꢀcyclooctene (a) under
undried conditions and (b) under anhydrous conditions. For (a), the recovered catalyst was reused for
the recycle reaction under the same conditions. For (b), after the reaction, cisꢀcyclooctene and TBHP
were recharged.
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In order to evaluate the mesoporous structure, the recovered MoꢀBPyꢀPMOꢀTMS under
undried conditions was analyzed by XRD and nitrogen adsorption/desorption isotherm
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measurements. The XRD pattern for MoꢀBPyꢀPMOꢀTMS changed little after the reaction,
suggesting the preservation of periodic mesoporous and pore wall structures due to the strong
covalent siloxane networks (Figure S12). The BET surface area and pore volume remained nearly
unchanged after the 4th reaction, clearly indicating robust mesoporous structures (Figure S13).
Preservation of TMS groups on the pore surface was also confirmed by IR analysis, which showed
that the TMS groups on BPyꢀPMO were not eliminated (Figure S14).
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4. Conclusions
Heterogeneous Mo complex catalysts were prepared using BPyꢀPMO as a solid support and
MoO2Cl2 as a precursor, and were evaluated for their ability to catalyze the epoxidation of a variety
of olefins by TBHP. The formation of MoO2Cl(OH) complexes on BPyꢀPMO was confirmed by
FTꢀIR spectra, Raman spectra, and XAFS analysis. A high density of Mo complex could be loaded
on BPyꢀPMO, in which 37% of the surface BPy ligands formed Mo complexes. The
MoꢀBPyꢀPMOꢀTMS exhibited greater catalytic activity for epoxidation compared to the activity of
heterogeneous Mo complex catalysts supported on mesoporous silica or BPyꢀPolymer. The
trimethylsilylation of the surface silanol groups of BPyꢀPMO was very effective at improving the
catalytic activity, perhaps due to the smooth diffusion of oxygenated compounds, such as TBHP and
epoxide products, in the mesochannels. The TOF for MoꢀBPyꢀPMOꢀTMS was nearly constant up to
high loading amounts of Mo complex, while the TOF decreased for MoꢀBPyꢀPolymer. A significant
solvent effect was observed for the MoꢀBPyꢀPMOꢀTMSꢀcatalyzed epoxidation of cisꢀcyclooctene.
The presence of water in the reaction medium was found to strongly influence the catalysis.
MoꢀBPyꢀPMOꢀTMS was found to catalyze a variety of aliphatic and aromatic olefins and showed
good recyclability for at least three reuse cycles in the epoxidation of cisꢀcyclooctene. The high
loading and good recyclability indicate that this supported catalyst has the potential for application to
a flowꢀthrough reactor that requires a solid catalyst containing a large number of active centers and a
small loss of activity.
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ASSOCIATED CONTENT
Supporting Information
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FTꢀIR spectra of BPyꢀPMO, BPyꢀPMOꢀTMS and x% MoꢀBPyꢀPMOꢀTMS (x = 5%, 10%, 20%, and
23%); Mo Kꢀedge XANES spectra of 10% MoꢀBPyꢀPMOꢀTMS, MoO2Cl2(bpy), MoO2Cl2, and
MoO3; Mo Kꢀedge EXAFS oscillations and EXAFS Fourier transforms (κ = 20ꢀ130 nmꢀ1) of 10%
MoꢀBPyꢀPMOꢀTMS, MoO2Cl2(bpy), MoO2Cl2, and MoO3; Curve fitting of Mo Kꢀedge EXAFS
Fourier transform for MoO2Cl2(bpy) using the crystal data of MoO2Cl2(bpy); Curveꢀfitting
parameters for Mo Kꢀedge EXAFS Fourier transform of MoO2Cl2(bpy); Curve fitting of Mo Kꢀedge
EXAFS Fourier transform for 10% MoꢀBPyꢀPMOꢀTMS using the crystal data of
MoO2Cl(OEt)(bpy); Curveꢀfitting parameters of Mo Kꢀedge EXAFS Fourier transform of 10%
MoꢀBPyꢀPMOꢀTMS; Mo Kꢀedge XANES spectra of x% MoꢀBPyꢀPMOꢀTMS (x = 5%, 10%, 20%,
and 23%); Mo Kꢀedge EXAFS oscillations and EXAFS Fourier transforms (κ = 20ꢀ130 nmꢀ1) of x%
MoꢀBPyꢀPMOꢀTMS (x = 5%, 10%, 20%, and 23%); Hot filtration experiment for epoxidation
catalyzed by 10% MoꢀBPyꢀPMOꢀTMS; Mo Kꢀedge XANES spectra of 10% MoꢀBPyꢀPMOꢀTMS,
MoꢀBPyꢀFSMꢀTMS, MoꢀBPyꢀPolymer, and MoO2Cl2(bpy); Mo Kꢀedge EXAFS oscillations and
EXAFS Fourier transforms (κ = 20ꢀ130 nmꢀ1) of 10% MoꢀBPyꢀPMOꢀTMS, MoꢀBPyꢀFSMꢀTMS,
MoꢀBPyꢀPolymer, and MoO2Cl2(bpy); Yield of 1,2ꢀepoxycyclooctane as a function of reaction time
and yield changes of 1,2ꢀepoxycyclooctane up to 30 min from the start of the reaction using x%
MoꢀBPyꢀPMOꢀTMS (x = 5%, 10%, 20%, and 23%); XRD patterns of 10% MoꢀBPyꢀPMOꢀTMS
before and after the 1st reaction run and after the 2nd reaction run; Nitrogen adsorption/desorption
isotherms of 10% MoꢀBPyꢀPMOꢀTMS before and after the 1st reaction run and after the 4th reaction
run; IR spectra at 2500 – 3500 cmꢀ1 and 1200 – 1400 cmꢀ1 of BPyꢀPMOꢀTMS, 10%
MoꢀBPyꢀPMOꢀTMS before and after the 1st reaction run and after the 2nd reaction run.
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