Mesoporous SBA-15 modified with manganese pyrazolylpyridine complexes for the catalytic epoxidation of terminal alkenes

Article abstract of DOI:10.1016/j.molcata.2011.12.018

A manganese-based hybrid mesoporous material (denoted as 5) was synthesized by covalent grafting of [Mn^II(1)₂](OAc)₂ (3) (1 = [3-(2-pyridyl)pyrazol-1-yl]acetic acid amide) onto the surface of SBA-15, and characterized by m

Full text of DOI:10.1016/j.molcata.2011.12.018

Journal of Molecular Catalysis A: Chemical 355 (2012) 201–209
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Mesoporous SBA-15 modified with manganese pyrazolylpyridine complexes for
the catalytic epoxidation of terminal alkenes
Jianyuan Tanga, Yanhong Zua, Weitao Huoa, Lei Wanga,b, Jing Wanga, Mingjun Jiaa,∗, Wenxiang Zhanga,
Werner R. Thielb,∗∗
a State Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry, Jilin University, 130021 Changchun, China
b Technische Universität Kaiserslautern, Fachbereich Chemie, Erwin-Schrödinger-Str., Geb. 54, Kaiserslautern 67663, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
A manganese-based hybrid mesoporous material (denoted as 5) was synthesized by covalent grafting
of [MnII(1)2](OAc)2 (3) (1 = [3-(2-pyridyl)pyrazol-1-yl]acetic acid amide) onto the surface of SBA-15,
and characterized by means of XRD, N2 adsorption–desorption, FT-IR, Raman, EPR and UV–vis spec-
troscopic techniques. Catalytic tests showed that 5 could act as an efficient heterogeneous catalyst for
the epoxidation of a wide range of alkenes (including terminal ones) under mild reaction conditions when
peracids (e.g., meta-chloroperbenzoic acid) are used as oxidants. Moreover, the catalytic performance of
5 is solvent-dependent, it exhibits higher catalytic activity and selectivity to epoxides when the reaction
is carried out in aprotic solvent like CH3CN. UV–vis and electrochemical measurements revealed that
high-valent Mn species are easily formed during the reaction course, when meta-chloroperbenzoic acid
is used as oxidant and CH3CN is used as solvent, being probably the main reason for the high activity of
5 and its selectivity toward epoxide formation.
Received 30 September 2011
Received in revised form
11 December 2011
Accepted 12 December 2011
Available online 21 December 2011
Keywords:
Epoxidation
Hybrid materials
Manganese acetate
Pyrazolylpyridine
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
using meta-chloroperbenzoic acid (m-CPBA) as oxidant at room
temperature [13]. Stack et al. described a highly active homoge-
Epoxidation of alkenes is an important reaction since the
epoxides are key building blocks for the synthesis of fine chemi-
cals and modern industrial processes [1,2]. Particularly, terminal
alkenes are a challenging class of substrates to epoxidize owing
to their relatively electron-deficient nature [3,4]. By using oxi-
dants such as peracids, some electron-deficient and aliphatic
terminal alkenes can be epoxidized even without adding cata-
lysts. However, relatively high reaction temperatures (normally
accompanied with low epoxide selectivity) and extended reac-
tion times are usually required in this uncatalyzed process [5–7].
These drawbacks might be overcome if a suitable catalyst is
adopted into the reaction system [8–12]. It was reported that Mn-
containing complexes are active homogeneous catalysts for the
epoxidation of terminal alkenes with peracids as the oxidants.
neous epoxidation catalyst system with peracetic acids as oxidants
based on in situ prepared mononuclear manganese (II) complexes
by mixing Mn(CF3SO3)2 and aromatic bidentate nitrogen ligands
like 2,2ꢀ-bipyridyl or 1,10-phenanthroline [14,15].
Recently, more work has been focused on the heterogenization
of homogeneous Mn-complexes catalysts, since such heteroge-
neous systems are more environmentally benign with respect to
waste production and catalyst separation and recovery [16–20].
Moghadam et al. reported that Mn(porphyrin)Cl and Mn(saloph)Cl
complexes covalently grafted on multi-wall carbon nanotubes
showed moderate activity in the epoxidation of terminal olefins
when NaIO4 was used as oxidant [21,22]. Assis et al. designed a
polymer-supported catalyst by immobilizing Mn(salen)Cl onto chi-
tosan membrane, and found that this catalyst was active for the
epoxidation of cyclooctene and styrene with m-CPBA, although
obvious decrease in activity was observed after recovery [23]. In
another work reported by Stack et al., [MnII(phen)2](CF3SO3)2 was
immobilized onto mesoporous SBA-15 via a metal-template/metal-
exchange route [24]. This material could be used as efficient and
recyclable heterogeneous epoxidation catalyst with peracetic acid
as the oxidant, and exhibited a greater substrate scope, a more effi-
cient use of oxidant, and a higher reactivity than its homogeneous
analogues. In spite of these considerable progresses, it is still an
interesting and significant subject to develop novel heterogeneous
For example, Kim et al. reported that a catalyst, which is com-
4−
posed of [Re4Q4(CN)12
]
cluster anions (Q = Se or Te) surrounded
by saloph-MnIII (saloph= N,Nꢀ-o-phenylenebis-salicylidenaminato)
complexes through bridging CN ligands, exhibits very high activity
for the epoxidation of various alkenes (including terminal alkenes)
∗
Corresponding author. Tel.: +86 431 85155390; fax: +86 431 88499140.
Corresponding author. Tel.: +49 631 2052752; fax: +49 631 2054676.
E-mail addresses: jiamj@jlu.edu.cn (M. Jia), thiel@chemie.uni-kl.de (W.R. Thiel).
∗∗
1381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.12.018

202
J. Tang et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 201–209
systems based on inexpensive and non-toxic metal catalysts, allow-
ing an efficient epoxidation of electron-deficient alkenes under
mild conditions.
OAc
Mn
N
N
N
O
.
N
Mn(OAc)2 4H2O
2
Our previous work suggested that pyrazolylpyridine ligands
have special coordination ability allowing to generate active and
stable Mo- or W-based heterogeneous epoxidation catalysts with
t-BuOOH or H2O2 as the oxidant [25–27]. In this work, SBA-
15 supported manganese complexes of the type [MnII(1)2](OAc)2
(1 = pyrazolylpyridine ligand) are prepared by a post grafting
method. Their catalytic properties for the epoxidation of alkenes
(mainly for terminal alkenes) with peracids as oxidants are investi-
gated. Furthermore, the influence of different reaction parameters –
such as the oxidants and solvents – on the catalytic performance of
the grafted Mn-complexes has been studied and will be discussed.
CH3CN, RT
N
N
N
N
AcO
N
1
O
O
O
O
II 1
(3)
O
[Mn ( )2](OAC)2
Scheme 1. Synthesis of [MnII(1)2](OAc)2 (3).
diluted to 10 mL with deionized water. A 5 mL aliquot was acidi-
fied with 1 mL of concentrated HNO3 before diluted to 10 mL with
deionized water. Each solution was filtered through a polyether-
sulfone filter and then submitted for metal analysis [24].
2. Experimental
2.3. Preparation of catalysts
2.1. Materials
2.3.1. Synthesis of ligands
Triblock copolymer EO20–PO70–EO20 (P-123) (Aldrich),
[3-(2-Pyridyl)pyrazol-1-yl]aceticacid methylester (1) and
(3-triethoxysilylpropyl)[3-(2-pyridylpyrazol)-1-yl]acetamide (2)
were prepared according to procedures published in the literature
[25,28].
tetraethylorthosilicate
(TEOS,
Aldrich),
Mn(OAc)2·4H2O
(Acros), (3-aminopropyl)triethoxysilane (Sigma–Aldrich), meta-
chloroperbenzoic acid (m-CPBA, Acros), n-dodecane (Merck),
anhydrous acetonitrile (MeCN) (Aldrich), 1-octene (Acros),
cyclooctene (Acros), styrene (Alfa Aesar), a-methylstyrene (Alfa
Aesar), trans-stilbene (Alfa Aesar), were used as received without
any further pretreatment. Other commercially available chemicals
were laboratory-grade reagents from local suppliers.
2.3.2. Preparation of complex [MnII(1)2](OAc)2 (3)
Mn(OAc)2·4H2O (0.7 mmol) and ligand (1) (1.4 mmol) were dis-
solved in dry CH3CN (25 mL). The mixture was stirred at room
temperature for 4 h. The solvent was evaporated under vacuum
in a rotary evaporator at a bath temperature of 65 ◦C resulting in a
brown solid, which was washed with cold diethyl ether and dried
at 80 ◦C (see Scheme 1). Elemental analysis for complex 3 Found:
C, 50.8; H, 4.71; N, 13.6; Mn, 9.2%. Calcd.: C, 51.4; H, 4.6; N, 13.8;
Mn, 9.1%. FT-IR (KBr, cm−1, selected peaks): 2857, 2922, and 2963:
␯(CH2); 1750: ␯(C O); 1632: ␯(C N), 545: ␯(Mn N).
2.2. Characterization methods
Powder XRD diffraction patterns were recorded on a Shimadzu
XRD-6000 diffractometer (40 kV, 30 mA) using Ni-filtered Cu K␣
radiation. Microanalyses (C,H,N) were performed with a Perkin-
Elmer 2400. N2 adsorption/desorption isotherms were measured
at −196 ◦C using a Micromeritics ASAP 2010N analyzer. Samples
were degassed at 150 ◦C for 8 h before measurements. Specific sur-
face areas were calculated using the BET model. Pore volumes
are estimated at a relative pressure of 0.94 (P/Po), assuming full
surface saturation with nitrogen. Pore size distributions are eval-
uated from desorption branches of the nitrogen isotherms using
the BJH model. FT-IR spectra (KBr pellets) were recorded using a
Nicolet Impact 410 spectrometer. Raman spectra were recorded
on a Bruker RFS100/S FT instrument (Nd:YAG laser, 1064 nm exci-
tation, InGaAs detector). EPR spectra were recorded with a JEOL
JES-FA200 at X-band frequency (ꢀ ≈ 9.44 GHz, microwave power
1 mW, modulation frequency 100 kHz). The UV–vis spectra were
recorded on a Shimadzu 3600 instrument. The solution of sam-
ples in CH3CN (or CH3CH2OH) was poured into a 1 cm quartz cell
for UV–vis adsorption with CH3CN (or CH3CH2OH) as the refer-
ence. UV–vis spectra of the solid samples were recorded in the
spectrophotometer with an integrating sphere using BaSO4 as the
standard. Electrochemical measurements were performed with a
CHI660B electrochemical station in a conventional three-electrode
cell under nitrogen atmosphere at room temperature. In CH3CN
medium, the electrolyte was 0.1 M Bu4NClO4 and potentials were
referred to an Ag/10 mM AgNO3 reference electrode in CH3CN,
0.1 M Bu4NClO4 electrolyte. Potentials referred to that system can
be converted to the ferrocene/ferricinium couple by subtracting
87 mV. The working electrode was a platinum disk (5 mm in diam-
eter) polished with 2 ␮m diamond paste (Mecaprex Presi) for cyclic
voltammetry. Inductively Coupled Plasma Atomic Emission Spec-
troscopy (ICP-AES) analyses were conducted on a Perkin Elmer
emission spectrometer. Each 10–20 mg sample of vacuum-dried
material was dissolved in 1 mL of boiling 5% KOH solution and then
2.3.3. Preparation of the mesoporous SBA-15 Materials
Mesoporous SBA-15 was prepared according to the literature
using a triblock copolymer as the surfactant template [29]. In a typ-
ical synthesis, the triblock copolymer (P-123) (8.0 g) was dissolved
in distilled water (60 mL) and 2 M HCl (240 mL) with stirring at
40 ◦C. Once the solution was visibly homogeneous, TEOS (18 mL)
were added into that solution with stirring at 40 ◦C for 6 h. The
mixture was aged at 100 ◦C for 48 h without stirring. The resulting
material was filtered, washed with deionized water and ethanol,
air-dried, and finally calcined, first at 350 ◦C for 2 h and then at
550 ◦C for 6 h to remove the template.
2.3.4. Preparation of the hybrid material 5
Mn(OAc)2·4H2O (0.15 mmol) and (3-triethoxysilylpropyl)[3-(2-
pyridyl)pyrazol-1-yl]acetamide (2) (0.30 mmol) were dissolved in
dry CH3CN (25 mL) in a 150 mL Schlenk flask under N2. The solution
was stirred at room temperature for 12 h to form a brown solution.
Approximately 40 mL of toluene were added before the addition
of SBA-15 (1.0 g) (pre-activated by heating to 160 ◦C under vac-
uum for 3 h). The mixture was heated to reflux for 24 h under N2.
The resulting solid (denoted as 5) was filtered, washed, Soxhlet-
extracted with chloroform for 24 h, and dried in the vacuum at 70 ◦C
(see Scheme 2).
2.3.5. Preparation of reference sample 6
The mesoporous support SBA-15 (1.0 g), was first pre-activated
by heating to 160 ◦C under vacuum for 3 h. After cooling and release
of the vacuum, 2 (0.21 mmol in 40 mL of toluene) was added under
a N2 atmosphere and the mixture was heated to reflux for 24 h.

J. Tang et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 201–209
203
OAc
OAc
Mn
OAc
Mn
N
N
N
N
N
N
N
.
N
Mn
Mn(OAc)2 4H2O
-15
SBA
N
N
N
N
N
CH3CN, RT
N
toluene,reflux
N
N
N
AcO
O
N
AcO
H
N
H
N
N
N
AcO
H
H
H
H
N
N
O
O
O
O
(EtO)3Si
O
Si(OEt)3
Si
Si
Si
Si
N
EtO
O
EtO
EtO
EtO
O
O
O
O
O
O
O
N
N
5
2
H
N
O
OAc
Si(OEt)3
N
N
N
N
N
N
N
Mn
.
5
A-1
Mn(OAc)2 4H2O
CH3CN, RT
SB
N
N
N
N
N
N
N
N
N
N
flux
e,re
en
tolu
N
N
AcO
O
H
N
H
N
H
H
H
H
N
N
N
O
O
O
O
O
Si
Si
Si
Si
Si
Si
EtO
EtO
EtO
EtO
EtO
EtO
O
O
O
O
O
O
O
O
O
O
O
O
6
4
Scheme 2. Preparation of hybrid mesoporous materials 5 and 6.
The resulting solid (denoted as 4) was filtered, washed, Soxhlet-
extracted with chloroform for 24 h, and dried in the vacuum at
70 ◦C. After that, hybrid material 4 (1.0 g) was stirred with 0.040 g
Mn(OAc)2·4H2O (dissolved in 60 mL of CHCl3) at room temperature
for 24 h. The resulting sample 6 was filtered off, Soxhlet-extracted
with CHCl3 to remove untethered species and dried in vacuum
(see Scheme 2). The composition of the grafted samples 5 and 6
is summarized in Table 1.
evaporator. The crude product was purified by a silica gel column
with dichloromethane as the eluent to give the desired epoxides
as a colorless liquid. The epoxides were characterized by GC–MS or
1H NMR spectrum, and compared with the known compounds.
3. Results and discussion
3.1. Catalyst Characterization
2.4. Representative epoxidation conditions
The FT-IR spectra of SBA-15, complex 3, the hybrid materials
5 and 6 are shown in Fig. 1. In the 2800–4000 cm−1 region, the
sharp band at 3740 cm−1 in the spectrum of the SBA-15 support
is assigned to free surface Si OH groups (Fig. 1b). For the hybrid
materials 5 and 6, the relative intensities of these Si OH vibrations
obviously decrease compared with the neat SBA-15, indicating that
Epoxidation of alkenes was typically performed according to
the following procedure: substrate(0.5 mmol), the heterogeneous
catalyst (25 mg, equiv. to 0.0035 mmol of Mn, 0.7 mol% relative
to the alkene) suspended in the solvent (2 mL), and n-dodecane
(0.5 mmol, internal standard) were combined in a 10-mL glass flask
with a stir bar. The mixture was pre-cooled to the indicated temper-
ature, and then oxidant (1.0 mmol, e.g., m-CPBA) was added in four
roughly equal portions over a 2 min period, the mixture was stirred
for an additional 28 min. Gas chromatography was employed to
monitor the progress of the epoxidation reaction. After comple-
tion of the reaction, the catalyst was removed by filtration, washed
with acetone, and dried in air. The remaining catalyst used in subse-
quent trials was assumed to fully retain all of the initial manganese.
Isolated epoxides: The epoxide product was extracted into pentane
(3 mL × 4 mL), washed with 1 M NaHCO3 (aq) and dried over sodium
sulfate. The organic solvent was removed under vacuum by rotary
the condensation reaction to form Si
O Si bonds between the
organosilane moieties and the surface Si OH groups of SBA-15
has occurred under our experimental conditions [27]. The bands
at 2857, 2922, and 2963 cm−1, being absent in the spectrum of the
neat support but present in the spectra of the hybrid materials 5
and 6, are attributed to ␯(CH2) of the propyl arm of the ligand.
In the region of 1250–1800 cm−1, SBA-15 support exhibited a
broad band at around 1635 cm−1 due to the ␯(O H) of adsorbed
water. The C N groups in the hybrid materials, should give a char-
acteristic band overlapped by this O H bending vibration band
[30]. The bands centered at around 1635 cm−1 in the spectra of
the hybrid materials shifted slightly to higher wavenumbers and
increased in intensity. Moreover, some additional weak peaks,
appearing at 1550, 1437, 1403 and 1360 cm−1, are due to the pres-
ence of the organic ligands in the hybrid materials. Compared with
the complex 3, hybrid materials 5 and 6 show less and weaker bands
related to the complex. The relatively low resolution for the intro-
duced complex in the hybrid materials should be due to the strong
IR absorbance of the siliceous base materials in a similar region.
Raman spectroscopy characterization has also been carried out
on 5 and 6. However, the resolution of the Raman spectra is very
poor owing to the relatively low loading of ligand and complex in
Table 1
Characteristics of support and catalysts, specific surface area, SBET (m2 g−1); pore
volume VBJH (cm3 g−1); pore diameter DBJH (nm) the C, H, N analyses of the hybrid
materials; C(Mn), initial concentration of Mn species (mmol g−1).
Entry
Materials
SBET
VBJH
DBJH
Ligand 1
C(Mn)
(mmol g−1
)
(mmol g−1
)
1
2
3
SBA-15
5
6
1160
629
702
1.72
1.04
1.16
6.8
6.4
6.3
–
0.28
0.20
–
0.14
0.14

204
J. Tang et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 201–209
a
b
3740
c
d
a
b
c
1
2
3
4
2θ (degree)
Fig. 3. Powder XRD patterns of SBA-15 (a); 5 (b) and 6 (c).
framework and organic moieties which are located inside the chan-
nels of SBA-15.
400036003200 1800 1600 1400
Warenumber(cm-1)
The N2 adsorption/desorption isotherms of the hybrid materials
5, 6 and SBA-15 are shown in Fig. 4. Obviously, the hybrid mate-
rials 5 and 6 maintain the characteristics of type IV isotherms and
show a uniform pore size distribution in the mesoporous region.
Compared to SBA-15, a pronounced decrease in BET surface area,
pore volume, and pore size of the hybrid materials occurs. This
should be mainly caused by the introduction of ligand and/or the
manganese complexes (Table 1). It should be mentioned here that,
the ratio of ligand/Mn ratio in 6 is less than 2:1, which is slight
lower than that of 5 (2:1). In this case, a considerable amount of
mono-ligand coordinated Mn-complexes should be present in 6,
while bis-ligand coordinated Mn-complexes are dominant in 5, as
showed in Scheme 2.
Fig. 1. FT-IR spectra of complex 3 (a); SBA-15 (b); 5 (c) and 6 (d).
the hybrid materials. The complexation of ligand with Mn species
can be confirmed by comparing the Raman spectra of ligand 1 and
complex 3 (Fig. 2), in which significant changes can be observed
in the region between 1630 and 1430 cm−1 in the bands assigned
to ring skeletal stretching modes of the ligand N
[31–33].
C C N fragment
The powder XRD patterns of the hybrid materials 5, 6 and of neat
SBA-15 are shown in Fig. 3. The SBA-15 sample shows three peaks,
indexed as the (1 0 0), (1 1 0) and (2 0 0) diffraction peaks associated
with typical two-dimensional hexagonal symmetry of the SBA-15
material (Fig. 3a) [29].
For the hybrid materials 5 and 6 the relative intensities of the
prominent diffraction peak (1 0 0) decreased somewhat after intro-
ducing the chelate ligand and the manganese complex. However,
the main reflections of the XRD pattern can still be observed.
According to the related references [29,34], the intensity reduc-
tion may be mainly due to contrast matching between the silicate
3.2. Catalysis
The catalytic properties of 5 and 6 in the epoxidation of styrene
are shown in Table 2. For comparison, the reaction results of the
homogeneous manganese(II) acetate complex [MnII(1)2](OAc)2 (3)
are also given. When m-CPBA was used as oxidant in combination
with CH3CN as solvent, all catalysts were active for the epoxida-
tion of styrene. The complex 3 was found to be the most active
catalyst for epoxidation of styrene with a TOF of 841 h−1, which
was much higher than that of homogeneous manganese(II) acetate
(TOF 531 h−1). The hybrid catalysts 5 and 6 were also quite active,
with TOFs of 583 and 612 h−1, respectively. Besides, 5 showed very
high selectivity to styrene epoxide, and a 96% selectivity of styrene
Table 2
Epoxidation reactivity of various catalysts with styrene.a
Entry
Catalysts
Conv. (%)
TOF (h−1
)
Product sel. (%)b
a
b
SO
BA
13
PA
1
2
3
4
Mn(OAc)2·4H2O
90
>99
>99
95
531
841
612
583
83
93
96
94
4
2
1
1
3
5
6
5
3
5
1620 1600 1580 1560 1540 1520 1500 1480 1460 1440
Wavenumber cm-1
a
Reaction conditions: 0.5 mmol of olefin, 1.0 mmol of m-CPBA, 0.5 mmol of n-
dodecane (internal standard), 0.7 mmol% of Mn, and 2 mL of CH3CN; reaction
temperature 0 ◦C; reaction time (30 min); TOF, average turnover frequency in the
first 10 min per active site.
Fig. 2. Selected region of the Raman spectra of the free ligand 1 (a) and the corre-
sponding manganese complex 3 (b).
b
SO, styrene oxide; BA, benzaldehyde; PA, phenylacetaldehyde.

J. Tang et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 201–209
205
Table 3
1200
1000
800
600
400
200
0
Effect of oxidant on the epoxidation of styrene catalyzed by 5.a
16
14
12
10
8
6
4
2
0
Entry Oxidant
T (◦C) t (h) Conv. (%) TOF (h−1
)
Product sel. (%)b
SO
BA
PA
1
2
3
4
5
6
7
m-CPBA
m-CPBA
0
25
0.5 >99
0.5 >99
612
771
5c
96
91
22
52
65
3
6
78
42
32
1
3
n.d.
6
5
tert-BuOOH 25
48
95
99
92
n.d.
96
NaClOd
25
25
25
25
12
24
24
24
16c
8c
n.d.
10c
e
NaIO4
0 2 4 6 8 101214161820
H2O2
H2O2
n.d. n.d. n.d.
96
f
Pore diameter (nm)
1
2
a
Reaction conditions: olefin (0.5 mmol), oxidant (1.0 mmol), n-dodecane (internal
standard, 0.5 mmol), catalyst (0.7 mmol% of Mn, 25 mg), and CH3CN (2 mL); TOF,
average turnover frequency in first 10 min per active site.
b
SO, styrene oxide; BA, benzaldehyde; PA, phenylacetaldehyde.
TOF, average turnover frequency in first hour per active site.
NaClO (pH 11.5, 0.55 M) [30].
NaIO4 [21,22].
c
a
d
e
0.0
0.2
0.4
0.6
0.8
1.0
f
H2O2 (1.0 mmol); imidazole (0.07 mmol), NaHCO3 (0.5 mmol) [36].
Relative pressure
1200
1000
800
600
400
200
0
by-products (benzaldehyde and phenylacetaldehyde) were pro-
duced in these systems. Similar results have been reported for
Mn(porphyrin)- and Mn(salen)-based heterogeneous epoxidation
catalysts [21–23]. When H2O2 (30%) was used as the oxygen source,
no detectable conversion of styrene could be observed after 24 h
reaction. This might be due to the fact that 5 possess a strong ability
for the decomposition of H2O2 to water and oxygen [35]. Notably,
the rapid decomposition of hydrogen peroxide could be effectively
inhibited over catalyst 5 when some additives like imidazole and
NaHCO3 were introduced into the reaction system, thus very high
styrene conversion and epoxide selectivity could be achieved under
the same reaction conditions (Table 3, entry 6). It should be men-
tioned here that the selectivity of epoxide decrease somewhat
(from 96% to 91%) with m-CPBA as the oxidant when the reaction
temperature increases from 0 ◦C to 25 ◦C (Table 3, entry 2).
The effect of various solvents on the epoxidation of styrene was
also investigated for catalyst 5. Table 4 summarizes the results of a
comparative study on the epoxidation of styrene with the catalyst
of 5 and m-CPBA in protic (CH3OH and C2H5OH) and aprotic sol-
vents (CH3COOC2H5, CH2Cl2 and CH3CN). As expected, the catalytic
activity was related to the solvent. It is found that the conversion of
styrene was much higher in aprotic than in protic solvents (Table 4).
The catalytic properties of 5 and 6 were explored for the epoxi-
dation of different alkenes using m-CPBA as oxidant at 0 ◦C (Table 5).
For the catalyst 5, cyclooctene was oxidized with >99% of conver-
sion and >99% selectivity to the epoxide after 10 min (TOF 856 h−1).
Oxidation of a-methylstyrene produced 78% of a-methylstyrene
epoxide and 22% of acetophenone at the similar reaction conditions.
Moreover, the terminal alkene 1-octene was also readily epoxidized
with m-CPBA as the oxidant and 5 as the catalyst: 91% of conver-
sion with >99% selectivity to epoxide and 87% isolated yield could
be obtained at 0 ◦C after 30 min reaction time (entry 7). Besides,
trans-stilbene could be epoxidized in a stereospecific manner with
16
14
12
10
8
6
4
2
0
0 2 4 6 8 101214161820
Pore diameter (nm)
b
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure
1200
1000
800
600
400
200
0
16
14
12
10
8
6
4
2
0
0 2 4 6 8 101214161820
Pore diameter (nm)
c
Table 4
0.0
0.2
0.4
0.6
0.8
1.0
Effect of solvent on the epoxidation of styrene catalyzed by 5 at 0 ◦C.a
Relative pressure
Entry
Solvent
Conv. (%)
TOF (h−1
)
Product sel. (%)b
Fig. 4. N2 adsorption/desorption isotherms at 77 K and pore size distribution pro-
files (inset) of SBA-15 (a); 5 (b) and 6 (c).
SO
BA
PA
1
2
3
4
5
CH3OH
49
34
74
91
>99
284
257
465
573
612
93
94
93
94
96
4
4
7
5
3
3
2
n.d.
1
1
C2H5OH
CH3COOC2H5
CH2Cl2
epoxide (with >99% conversion of styrene) could be achieved after
30 min reaction.
The catalytic activity of 5 was further studied in the epoxida-
tion of styrene using different oxidants, including NaClO, NaIO4,
t-BuOOH and H2O2 (30%). When t-BuOOH, NaClO and NaIO4 were
used as oxidants, 5 also showed high activity for the epoxida-
tion of styrene at room temperature. However, large amounts of
CH3CN
a
Reaction conditions: styrene (0.5 mmol), m-CPBA (1.0 mmol), n-dodecane (inter-
nal standard, 0.5 mmol), 5 (0.7 mmol% Mn, 25 mg), and solvent (2 mL); reaction
temperature (0 ◦C); TOF, turnover frequency in first 10 min per active site.
b
SO, styrene oxide; BA, benzaldehyde; PA, phenylacetaldehyde.

206
J. Tang et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 201–209
Table 5
Epoxidation of various olefins with m-CPBA catalyzed by 5 and 6.a
Entry
Substrate
Catalysts
t (min)
Conv. (%)
>99
TOF (h−1
)
Epoxide sel. (%)
1
2
5
6
10
10
856
856
>99
>99
>99
3
4
5
6
10
10
>99
>99
856
856
78
71
5
6
5
6
30
30
>99
95
612
583
96
94
7
8
9
5
6
5
6
30
30
60
60
91
80
66
54
446
427
94b
77b
>99
>99
>99
>99
10
a
Reaction conditions: olefin (0.5 mmol), m-CPBA (1.0 mmol), n-dodecane (internal standard, 0.5 mmol), the heterogeneous catalyst (0.7 mmol% of Mn, 25 mg), and CH3CN
(2 mL); reaction temperature (0 ◦C); TOF, turnover frequency in first 10 min per active site.
b
Turnover frequency in first hour per active site.
complete retention of configuration (66% conversion with >99%
selectivity to the major product after 60 min, TOF 94 h−1). Com-
pared with 5, the catalytic activity and/or epoxide yield of catalyst
6 was usually lower under the same reaction conditions.
The recycling experiments of 5 and 6 for the epoxidation of 1-
octene were also carried out with m-CPBA as the oxidant and CH3CN
as the solvent (Table 6). After each experiment, the filtered catalysts
were washed with CH3CN and dried at 60 ◦C, then reused without
further treatment. The catalyst 5 showed very good recyclability,
no obvious change in activity could be observed with the increase
of recyclable number, and the conversion of 1-octene still remains
at around 90% after six reaction cycles (Table 6); while the catalyst
6 demonstrated a gradual decrease in activity with increasing the
numbers of recycling experiments. The results of the ICP analysis
provide a further evidence that Mn species in 5 were very sta-
ble during the reaction process, since the Mn content for the used
catalyst of 5 (after the 6th reaction) just decreased slightly (from
0.14 mmol g−1 to 0.13 mmol g−1) compared with the fresh one. As
for 6, an obvious decrease of the Mn content (from 0.14 mmol g−1
to 0.10 mmol g−1) can be observed after the 6th reaction.
Our previous work has shown that pyrazolylpyridines are suit-
able to form active and stable Mo- and W-based epoxidation
catalysts due to their special coordination abilities [26,27]. As men-
tioned above, the main difference between 5 and 6 is: bis-ligand
coordinated Mn-complexes are dominant in 5, while a consider-
able amount of mono-ligand coordinated Mn-complexes should be
present in 6. Hence, we may conclude here that that the perfect cat-
alytic features of 5 should be mainly assigned to the presence of a
strong coordinative interaction between the chelate ligand and the
Mn species.
Fig. 5A shows the kinetic profiles of epoxidation of 1-octene
with CH3CN as the solvent over 5 and 6. In a duplicate reaction, the
leaching test was also performed to verify the heterogeneity of the
catalytic process (Fig. 5B). It should be mentioned firstly that a blank
reaction (without adding any catalyst) using the mixed solvent gave
a conversion of 1-octene of about 4.5% after a reaction time of 2 h,.
With 5 as the catalyst, the conversion of 1-octene reached 31% after
5 min. After removing the catalyst by filtration, the conversion of
1-octene increased to 36% during the following 115 min. In the case
of 6 as the catalyst, the conversion of 1-octene increased from 28
to 47% after removing the catalyst. Taking the result of the blank
reaction into account, it can be concluded here that 5 is truly hetero-
geneous catalyst under the test condition and no obvious leaching
of active catalytic species occurs during the reaction. On the other
hand, a small part of active Mn actives should be leached from the
hybrid 6 catalyst during the reaction course.
100
80
60
40
20
0
100
80
60
40
20
0
A
B
To understand the nature of catalyst 5, EPR and UV–vis mea-
surements were carried out for fresh and used catalyst 5 (after
5
6
5
6
No catalyst
Table 6
Recyclability of 5 and 6 in the epoxidation of 1-octene with m-CPBA oxidant.a
Run
5
6
C(Mn)
Conv. (%)
C(Mn)
Conv. (%)
b
b
(mmol g−1
)
(mmol g−1
)
0
1
2
3
4
5
6
0.14
0.14
91
85
89
90
92
89
90
80
79
77
75
72
0
10 20 30 40 50 60
0
20 40 60 80 100 120
Time (min)
0.13
0.10
Fig. 5. (A) Kinetic profiles of the epoxidation of 1-octene with m-CPBA over 5 and 6
in the presence of CH3CN. (B) Leaching experiments of two Mn-containing catalysts
(dashed lines indicate the conversions after the removal of the catalysts). Reaction
conditions are analogous to Table 5.
a
Reaction conditions: olefin (2.0 mmol), m-CPBA (4.0 mmol), heterogeneous cat-
alyst (0.7 mmol% of Mn, 100 mg), and CH3CN (8 mL); reaction temperature (0 ◦C).
b
Determined by ICP-AES analysis.

J. Tang et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 201–209
207
1.65
50 µA
0.97
a
b
a
1.52
0.73
b
c
0
100 200 300 400 500 600 700 800
B/mT
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
E/V vs Ag/AgCl
Fig. 6. EPR spectra of the fresh 5 (a) and the used 5 after the 6th reaction (b).
Recording temperature: T = 20 ◦C.
Fig. 8. (a) Cyclic voltammograms of a 1 mM acetonitrile solution of complex 3
in the presence of 0.1 M tetrabutylammonium perchlorate (T = 25 ◦C, scan rate
100 mV s−1); (b) after addition 2 equiv. of t-BuOOH per molecule of 3; (c) after
addition 2 equiv. of m-CPBA per molecule of 3.
the 6th reaction). EPR spectra of the two samples were recorded
at room temperature using the conventional perpendicular detec-
tion mode (Fig. 6). Both spectra present features between 0 and
800 mT. The fresh 5 presents three main transitions at geff ≈ 5.7,
2.9, and 2.0 (Fig. 6a). 55Mn hyperfine lines (I = 5/2) are observed
on the geff ≈ 2.0 transition and are separated by 8.5 mT, which is
consistent with a high-spin (S = 5/2) mononuclear Mn(II) species
[37,38]. The appearance of a weak signal at lower field geff ≈ 8.7
in spectrum of used 5 implies the presence of a trace amount of
high-valent Mn species. The diffuse reflectance UV–vis spectra of
fresh and used 5 are given in Fig. 7. Strong bands at 248 and 285 nm
can be attributed to the charge transfer transition of pyrazolylpyri-
dine ligand (Fig. 7a). The appearance of weak and broad bands at
about 330 and 400 nm in the spectrum of the used 5 should be also
related to the presence of a small amount of high-valent Mn species
[39], thus providing a further evidence that a part of Mn(II) species
has been oxidized to a high-valent state by the oxidant during the
reaction course.
oxidants (i.e., tert-BuOOH and m-CPBA) are used for epoxidation
reaction. The oxidation processes of the homogeneous complex 3
in acetonitrile at room temperature, measured by Cyclic voltam-
metry (CV) are shown in Fig. 8a. For the CV of 3 in CH3CN, two
oxidation processes are detected, which located at Epa = 0.90 V
and 1.65 V vs. Ag/Ag+ 10−2 M. The shape of the CV of 3 are quite
similar to that of [(L)MnIICl(OH2)] (L = N,Nꢀ-dimethyl-N,Nꢀ-bis(2-
pyridylmethyl)propane-1,3-diamine) [37], and [Mn(tolylterpy)2]2+
[40]. Hence, the two oxidation waves can be assigned to the suc-
cessive one-electron abstraction from Mn(II), leading to Mn(III),
and from Mn(III), generating Mn(IV), respectively. The absence of
reversibility of the two processes might be due to the potential high
reactivity of the high valent manganese cation [41].
When two equiv. of t-BuOOH was added into the 3 solution, the
two oxidation waves potential (Epa = 0.90 V and 1.65 V vs. Ag/Ag+
10−2 M) shift considerably toward lower positive potential located
at 0.7 V and 1.5 V vs. Ag/Ag+ 10−2 M after 30 min (Fig. 8b). The
observed changes in the cyclic voltammograms of the Mn-complex
might be due to fact that the original anionic ligands of metal center
have been replaced (at least partially) by t-BuOO−, and the higher
donor capacity of the ligand t-BuOO− may result in an easy oxida-
tion of the metal center (Mn cation) [42,43]. It should be mentioned
that the solution color changed from light yellow to yellow in a few
minutes after the addition of t-BuOOH, indicating that only a small
amount of high-valent manganese species appeared in the solution.
Fig. 8c shows that the oxidation waves turn to very weak (nearly
disappear) when two equiv. m-CPBA was added into acetonitrile
solution of 3. Besides, it was found that the solution color changed
from light yellow to brown in a few minutes after the addition of
m-CPBA. Hence, the change in the cyclic voltammograms might
be due to the fact that a great number of high-valent Mn species
have already appeared in the presence of m-CPBA oxidant (before
electrochemical experiments).
Furthermore, electrochemical measurements were carried out
to monitor the formation of reactive intermediates over the
homogeneous complex Mn(1)2(OAc)2(3) catalyst when different
a
b
UV–vis spectroscopy was also used to monitor the formation of
reactive intermediates of the homogeneous catalyst 3 (dissolved
in CH3CN or CH3CH2OH). First, a small amount of freshly prepared
complex 3 was dissolved in CH3CN (or CH3CH2OH), then 20 equiv.
of oxidant were added to the solution at room temperature. The
250
300
350
400
450
500
550
600
Wavelength (nm)
Fig. 7. The solid reflectance UV–vis spectra of fresh 5 (a) and used 5 after the 6th
reaction (b).

208
J. Tang et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 201–209
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
1.0
0.8
0.6
0.4
0.2
C
A
B
0.0
0.0
300
400
500
600 300
400
500
600 300
400
500
600
Wavelength (nm)
Fig. 9. UV–vis spectral changes during the reaction of complex 3 (4 × 10−5 M) with 20 equiv. of oxidant in different solvents at room temperature. The spectra at 0, 5, 10, 20,
30 min after the addition of oxidant are shown. (A) oxidant: t-BuOOH, solvent: CH3CN; (B) oxidant: m-CPBA; solvent: CH3CN; (C) oxidant: m-CPBA; solvent: CH3CH2OH.
Mn-containing catalysts, such as MnIII(salen), MnIII(porphyrin) and
MnIII(nonheme). It was reported that when a peroxidic oxygen
donor such as H2O2, t-BuOOH or m-CPBA was used as the oxidant,
an ROO MnIII-adduct was initially formed, which could epoxidize
olefins directly by a Lewis acid mechanism. Besides, the O O bond
of the ROO MnIII-adduct may also be cleaved either heterolyti-
cally to form O MnV species or homolytically to yield HO MnIV
species (actually the HO MnIV radical cation). It was believed that
the O MnV species is an active intermediate and responsible for
alkene epoxidation, whereas the HO MnIV complex is invoked in
radical-type oxidations to account for the formation of ring-opened
or aldehyde products in the MnIII(salen) catalyzed epoxidation
reactions [13,48].
On the basis of these reports and our results, we can say that
the epoxidation of alkenes over catalyst 5 could also occur in dif-
ferent ways when different oxygen donors (oxidants) or solvents
are used (Scheme 3). When m-CPBA was used as the oxidant for the
epoxidation of styrene (with CH3CN as the solvent), very high selec-
tivity (ca. 96%) to epoxystyrene can be obtained with 5, suggesting
that pathway a or b should give significant contribution. When
t-BuOOH was used as the oxidant, a large number of by-product
UV–vis spectra were recorded after the addition of the oxidant
(see Fig. 9). When CH3CN was used as the solvent, no obvious
change could be observed after the addition of t-BuOOH for 30 min
(Fig. 9A). It was supposed that the reactive intermediates might
not be spectroscopically observable due to their low concentration
and/or short lifetime. When m-CPBA was added into the 3 solution,
it could be observed that the solution color changed from light yel-
low to brown in a few minutes, while an absorption band appeared
at 410 nm, and its intensity grew rapidly with time (Fig. 9B). On
the basis of related literatures [44,45] as well as the above elec-
trochemical results, the appearance of 410 band might be mainly
assigned to the formation of a great number of high-valent Mn
species (e.g., O MnIV) after the addition of m-CPBA. Besides, if apro-
tic solvent (CH3CN) was replaced by protic solvent (CH3CH2OH),
the absorption band at around 410 nm is nearly undetectable in
the m-CPBA/CH3CH2OH system (Fig. 9C), this might be due to the
fact that alcohol could act as a reducing solvent, which can easily
react with the high valent manganese species upon its forma-
tion.
In previous reports [45–47], several groups have studied
the reaction mechanism of the epoxidation in the presence of
Scheme 3. Proposed mechanism of the oxygen activation for m-CPBA or t-BuOOH.

J. Tang et al. / Journal of Molecular Catalysis A: Chemical 355 (2012) 201–209
209
(benzaldehyde) was obtained (see Table 3, entry 2), implying that a
greater contribution should come from the radical route (pathway
c).
[11] E.M. McGarrigle, D.G. Gilheany, Chem. Rev. 105 (2005) 1565–1602.
[12] K.P. Ho, W.L. Wong, K.M. Lam, C.P. Lai, T.H. Chan, K.Y. Wong, Chem. Eur. J. 14
(2008) 7988–7996.
[13] S.H. Lee, L. Xu, B.K. Park, Y.V. Mironov, S.H. Kim, Y.J. Song, C. Kim, Y. Kim, S. Kim,
Chem. Eur. J. 16 (2010) 4678–4685.
These contrasting mechanistic behaviors can be rationalized on
[14] A. Murphy, A. Pace, T.D.P. Stack, Org. Lett. 6 (2004) 3119–3122.
[15] A. Murphy, T.D.P. Stack, J. Mol. Catal. A 251 (2006) 78–88.
[16] R.I. Kureshy, N.H. Khan, S.H.R. Abdi, I. Ahmad, S. Singh, R.V. Jasra, J. Catal. 221
(2004) 234–240.
[17] R.I. Kureshy, I. Ahmad, N.H. Khan, S.H.R. Abdi, S. Singh, P.H. Pandia, R.V. Jasra, J.
Catal. 235 (2005) 28–34.
[18] R.I. Kureshy, I. Ahmad, N.H. Khan, S.H.R. Abdi, K. Pathak, R.V. Jasra, J. Catal. 238
(2006) 134–141.
[19] N.J. Schoenfeldt, A.W. Korinda, J.M. Notestein, Chem. Commun. 46 (2010)
1640–1642.
[20] F. Song, C. Wang, J.M. Falkowski, L. Ma, W. Lin, J. Am. Chem. Soc. 132 (2010)
15390–15398.
[21] M. Moghadam, I. Mohammadpoor-Baltork, S. Tangestaninejad, V. Mirkhani, H.
Kargar, N. Zeini-Isfahani, Polyhedron 28 (2009) 3816–3822.
[22] S. Tangestaninejad, M. Moghadam, V. Mirkhani, I. Mohammadpoor-Baltork,
M.S. Saeedi, Appl. Catal. A: Gen. 381 (2010) 233–241.
the basis of the physical parameters of the substitutes on O
O
bond in these two oxidants (t-BuOOH and m-CPBA). The chloro-
phenyl group of m-CPBA has a stronger ability to withdraw electron
density from the peroxo unit alkyl group in t-BuOOH. This fea-
ture may result in an easy homolytic cleavage of the O O bond
(radical pathway) after the formation of a t-BuOO-MnII fragment,
while a heterolytic cleavage of the O O bond is dominant in the m-
CPBA case. This point can be confirmed by the rapid formation of
high valent Mn species (e.g., O MnIV intermediate) when m-CPBA
is used as oxidant (as suggested by the UV–vis results). Besides,
the type of solvent should be another key factor in influencing the
catalytic performance of 5. In our case, aprotic solvent like CH3CN
seems more suitable for the improvement of the catalytic perfor-
mance of 5.
[23] T.C.O. Mac Leod, V. Palaretti, V.P. Barros, A.L. Faria, T.A. Silva, M.D. Assis, Appl.
Catal. A: Gen. 361 (2009) 152–159.
[24] T.J. Terry, T.D.P. Stack, J. Am. Chem. Soc. 130 (2008) 4945–4953.
[25] M. Jia, A. Seifert, W.R. Thiel, Chem. Mater. 15 (2003) 2174–2180.
[26] M. Jia, A. Seifert, W.R. Thiel, J. Catal. 221 (2004) 319–324.
[27] J. Tang, L. Wang, G. Liu, Y. Liu, Y. Hou, W. Zhang, M. Jia, W.R. Thiel, J. Mol. Catal.
A: Chem. 313 (2009) 31–37.
4. Conclusion
Hybrid manganese-based mesoporous material, prepared by
covalent grafting of [MnII(1)2](OAc)2 (3) onto the surface of SBA-15,
is an efficient heterogeneous catalyst for the epoxidation of alkenes
(including terminal alkenes) with m-CPBA as the oxidant under
mild conditions. The catalytic performance of this hybrid catalyst
is solvent-dependent, relatively high catalytic activity and selec-
tivity to epoxides could be obtained when an aprotic solvent (e.g.,
CH3CN) is present. UV–vis measurements of the reaction of oxidant
in solution with homogeneous the [MnII(1)2](OAc)2 (3), revealed
that high-valent Mn species, which are easily formed when CH3CN
is used as the solvent, should be the main active intermediates for
the epoxidation reaction with m-CPBA as the oxidant.
[28] W.R. Thiel, M. Angstl, T. Priermeier, Chem. Ber. 127 (1994) 2373–2379.
[29] D. Zhao, Q. Huo, J. Feng, B.F. Chmelka, G.D. Stucky, J. Am. Chem. Soc. 120 (1998)
6024–6036.
[30] H. Zhang, Y. Wang, L. Zhang, G. Gerritsen, H.C.L. Abbenhuis Rutger, A. van San-
ten, C. Li, J. Catal. 256 (2008) 226–236.
[31] S. Gago, Y. Zhang, A.M. Santos, K. Köhler, F.E. Kühn, J.A. Fernandes, M. Pillinger,
A.A. Valente, T.M. Santos, P.J.A. Ribeiro-Claro, I.S. Gonc¸ alves, Micropor. Mesopor.
Mater. 76 (2004) 131–136.
[32] S.M. Bruno, J.A. Fernandes, L.S. Martins, I.S. Gonc¸ alves, M. Pillinger, P. Ribeiro-
Claro, J. Rocha, A.A. Valente, Catal. Today 114 (2006) 263–271.
[33] S. Gago, J.A. Fernandes, J.P. Rainho, R.A. Sá Ferreira, M. Pillinger, A.A. Valente,
T.M. Santos, L.D. Carlos, P.J.A. Ribeiro-Claro, I.S. Gonc¸ alves, Chem. Mater. 17
(2005) 5077–5084.
[34] A. Stein, M.H. Lim, Chem. Mater. 11 (1999) 3285–3295.
[35] S. McCann, M. McCann, R.M.T. Casey, M. Jackman, M. Devereux, V. McKee, Inorg.
Chim. Acta 279 (1998) 24–29.
[36] H.H. Monfared, V. Aghapoor, M. Ghorbanloo, P. Mayer, Appl. Catal. A: Gen. 372
(2010) 209–216.
Acknowledgment
[37] C. Hureau, G. Blondin, M. Charlot, C. Philouze, M. Nierlich, M. Césario, E.
Anxolabéhère-Mallart, Inorg. Chem. 44 (2005) 3669–3683.
[38] S. Groni, P. Dorlet, G. Blain, S. Bourcier, R. Guillot, E. Anxolabéhère-Mallart,
Inorg. Chem. 47 (2008) 3166–3172.
Financial support from the National Natural Science Foundation
of China (20773050, 21173100) is gratefully acknowledged.
[39] T. Kurahashi, A. Kikuchi, Y. Shiro, M. Hada, H. Fujii, Inorg. Chem. 49 (2010)
6664–6672.
References
[40] S. Romain, C. Duboc, F. Neese, E. Rivière, L.R. Hanton, A.G. Blackman, C. Philouze,
J.-C. Leprêtre, A. Deronzier, M.-N. Collomb, Chem. Eur. J. 15 (2009) 980–988.
[41] M. Hoogenraad, K. Ramkisoensing, W.L. Driessen, H. Kooijman, A.L. Spek, E.
Bouwman, J.G. Haasnoot, J. Reedijk, Inorg. Chim. Acta 320 (2001) 117–126.
[42] S. Biswas, K. Mitra, S.K. Chattopadhyay, B. Adhikary, Transition Met. Chem. 30
(2005) 393–398.
[43] R. van Gorkum, J. Berding, D.M. Tooke, A.L. Spek, J. Reedijk, E. Bouwman, J. Catal.
252 (2007) 110–118.
[44] R. Giovannetti, L. Alibabaei, F. Pucciarelli, Inorg. Chim. Acta 363 (2010)
1561–1567.
[45] J.T. Groves, M.K. Stern, J. Am. Chem. Soc. 110 (1988) 8628–8638.
[46] D. Feichtinger, D.A. Plattner, Angew. Chem. Int. Ed. Engl. 36 (1997) 1718–1719.
[47] W. Adam, K.J. Roschmann, C.R. Saha-Möller, D. Seebach, J. Am. Chem. Soc. 124
(2002) 5068–5073.
[48] K.P. Bryliakov, D.E. Babushkin, E.P. Talsi, J. Mol. Catal. A: Chem. 158 (2000)
19–35.
[1] Z. Xi, N. Zhou, Y. Sun, K. Li, Science 292 (2001) 1139–1141.
[2] G. Sienel, R. Rieth, K.T. Rowbottom, Ulmann’s Encyclopedia of Industrial Chem-
istry, 6th ed., Verlag Chemie, Weinheim, 2003, p. 269.
[3] A. Ansmann, R. Kawa, M. Neuss, Cosmetic composition containing hydrox-
yethers, US Patent 7,083,780 B2, Aug. 1, 2006, To Cognis Deutschland, Gmbh &
Co. KG.
[4] A.H. Hoveyda, Chem. Rev. 93 (1993) 1307–1370.
[5] D. Swern (Ed.), Organic Peroxides, vol. 1, J. Wiley & Sons, Inc., 1970, p. 654.
[6] W. Ye, R. Sangaiah, D.E. Degen, A. Gold, K. Jayaraj, K.M. Koshlap, G. Boysen, J.
Williams, K.B. Tomer, V. Mocanu, N. Dicheva, C.E. Parker, R.M. Schaaper, L.M.
Ball, J. Am. Chem. Soc. 131 (2009) 6114–6123.
[7] S. Quideau, G. Lyvinec, M. Marguerit, K. Bathany, A. Ozanne-Beaudenon, T. Buf-
feteau, D. Cavagnat, A. Chénedé, Angew. Chem. Int. Ed. 48 (2009) 4605–4609.
[8] B. Meunier, Chem. Rev. 92 (1992) 1411–1456.
[9] J.T. Groves, M.K. Stern, J. Am. Chem. Soc. 109 (1987) 3812–3814.
[10] M. Palucki, P.J. Pospisil, W. Zhang, E.N. Jacobsen, J. Am. Chem. Soc. 116 (1994)
9333–9334.