A novel layered organic polymer-inorganic hybrid zinc poly (styrene-phenylvinylphosphonate)-phosphate immobilized chiral salen Mn(III) catalyst large-scale asymmetric epoxidation of unfunctionalized olefins

Article abstract of DOI:10.1016/j.jorganchem.2011.04.027

A novel layered organic polymer-inorganic hybrid zinc poly (styrene-phenylvinylphosphonate)-phosphate (ZnPS-PVPA) has been synthesized under mild conditions and diphenol-modified ZnPS-PVPA was used to successfully immobilize the chiral salen Mn(III) by axial coordination. The obtained heterogeneous chiral catalysts exhibited excellent activities and enantioselectivities using sodium periodate as an oxidant for asymmetric epoxidation of unfunctionalized olefins, especially for the epoxidation of α-methylstyrene (conversion: up to 97%; ee: exceed 99%). Moreover, these synthesized catalysts were relatively stable and could be expediently separated from the reaction system, and could be recycled at least ten times without obvious loss of activity and enantioselectivity. These novel catalysts could be efficiently used in large-scale reactions with the enantioselectivity being maintained at the same level, which offer a great possibility for application in industry.

Full text of DOI:10.1016/j.jorganchem.2011.04.027

Journal of Organometallic Chemistry 696 (2011) 2797e2804
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
A novel layered organic polymer-inorganic hybrid zinc poly
(
styrene-phenylvinylphosphonate)-phosphate immobilized chiral salen Mn(III)
catalyst large-scale asymmetric epoxidation of unfunctionalized olefins
a
a
,
b
,
, Jiangwei Xu , Changwei Wang a
a
*
Xiaoyan Hu , Xiangkai Fu
a
College of Chemistry and Chemical Engineering Southwest University, Research Institute of Applied Chemistry Southwest University, The Key Laboratory of Applied Chemistry of
Chongqing Municipality, Chongqing 400715, PR China
The Key Laboratory of Eco-environments in Three Gorges Reservoir Region, Ministry of Education, Chongqing 400715, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 February 2011
Received in revised form
A novel layered organic polymer-inorganic hybrid zinc poly (styrene-phenylvinylphosphonate)-phos-
phate (ZnPS-PVPA) has been synthesized under mild conditions and diphenol-modified ZnPS-PVPA was
used to successfully immobilize the chiral salen Mn(III) by axial coordination. The obtained heteroge-
neous chiral catalysts exhibited excellent activities and enantioselectivities using sodium periodate as an
oxidant for asymmetric epoxidation of unfunctionalized olefins, especially for the epoxidation of
18 April 2011
Accepted 26 April 2011
a
-methylstyrene (conversion: up to 97%; ee: exceed 99%). Moreover, these synthesized catalysts were
Keywords:
relatively stable and could be expediently separated from the reaction system, and could be recycled at
least ten times without obvious loss of activity and enantioselectivity. These novel catalysts could be
efficiently used in large-scale reactions with the enantioselectivity being maintained at the same level,
which offer a great possibility for application in industry.
Layered zinc poly (styrene-
phenylvinylphosphonate)-phosphate
Diphenol-modified
Heterogeneous chiral salen Mn(III) catalysts
Asymmetric epoxidation
Large-scale reaction
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
example, salen Mn(III) complexes have been immobilized onto
inorganic supports such as clays [12], SBA-15 [13], MCM-41 [14];
The asymmetric epoxidation of unfunctionalized olefins takes
a great importance in synthesis of chiral epoxides, which are widely
used in the manufacture of drugs, vitamins, fragrances and other
optical materials [1e3]. Chiral Jacobsen-type salen Mn(III)
complexes as homogeneous catalysts have emerged extremely
efficient systems for the asymmetric epoxidation of the unfunc-
tionalized olefins [4] in the presence of terminal oxidants such as
iodosylbenzene, sodium hypochlorite, m-Chloroperbenzoic acid,
hydrogen peroxide and so on [5e8]. However, the recycle of the
expensive homogeneous catalysts is so difficult that limit the
practical applications of chiral salen Mn(III) catalysts in both
synthetic chemistry and industrial processes [9]. Consequently, the
last decades have witnessed an intense research effort to Jacobsen-
type salen Mn(III) complexes on supports to make them recyclable
and enhance their stability, activity, and selectivity [10,11]. For
organic poly-systems such as PS [15], p-divinylbenzene [16]; and
organic polymer-inorganic hybrid solids as zirconium phosphate-
phosphonate materials reported in our group: ZPSeIPPA [17];
ZPSePVPA [18] and ZSPP [19]. By contrast, the inorganic materials
and organic polymers which were employed for the immobilization
of homogeneous catalysts generally exhibited higher or lower
catalytic activities than their corresponding homogeneous coun-
terparts, whereas the organic polymer-inorganic hybrid materials
as very promising support which were used to immobilize chiral
salen Mn(III) complexes and obtained heterogeneous catalysts
displayed comparable or even higher conversions and enantiose-
lectivities than those reported in the relevant literatures [17e20].
To the best of our knowledge, there are no reports on hybrid
zinc phosphate-phosphonate materials immobilized chiral salen
Mn(III) catalysts for the asymmetric epoxidation reaction. Mean-
while, there are relatively few reports using sodium periodate
as an oxidant in the system of asymmetric epoxidation. Hence, we
have designed and synthesized a novel layered organic polymer-
inorganic hybrid-zinc poly (styrene-phenylvinylphosphonate)-
phosphate (ZnPS-PVPA) based on our previous work. This layered
compound was prepared under mild conditions in the absence of
*
Corresponding author. The Key Laboratory of Eco-environments in Three
Gorges Reservoir Region, Ministry of Education, Chongqing 400715, PR China.
Tel.: þ86 23 6825 3704; fax: þ86 23 6825 4000.
E-mail address: fxk@swu.edu.cn (X. Fu).
0
022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.04.027

2798
X. Hu et al. / Journal of Organometallic Chemistry 696 (2011) 2797e2804
organic template. Noteworthy features of this new compound as
support for immobilization of chiral salen Mn(III) complexes are:
spectra of the solid samples were recorded in the spectrophotom-
eter with an integrating sphere using BaSO as standard. TG anal-
ysis was performed on a SBTQ600 thermal analyzer (USA) with the
heating rate of 15 C$min from 25 to 1000 C. The Mn content of
the catalysts was determined by a TASe986G (Pgeneral, China)
atomic absorption spectroscopy (AAS). XRD powder pattern
4
(
1) the hybrid material possesses adjustable of functional organic
ꢀ
ꢁ1
ꢀ
groups, which allows us to tailor their density, chemical reactivity,
and thermal stability [18]; (2) this compound with abundant
framework as well as the layers of the phosphates [21e24]are
separated on either side by the pendent organic moieties of the
phosphonate groups; (3) the compound can be prepared easily and
economically from commercially available sources. Founded on
these advantages, the chiral salen Mn(III) complexes were immo-
bilized onto the diphenol-modified layered ZnPS-PVPA through
axial coordination for the first time and showed significantly higher
was collected on D/MAX-3C diffractometer using graphite-
ꢀ
monochromatic Cu K
a
radiation in the angular range 2
q
¼ 2e50
ꢀ
with a step size of 0.02 . Atomic Force Microscope (AFM) was
performed on NanoScope Quadrex (USA). The BET surface area was
2
determined with the use of N sorption data measured at 77 K
(Quantachrome Autosorb-1). The conversion (with n-nonane
as internal standard) and the ee value were analyzed by gas
chromatography (GC) with Shimadzu GC2014 (Japan) instru-
enantioselectivities with NaIO
4
as an oxidant system at room
temperature for asymmetric epoxidation of unfunctionalized
olefins, furthermore, the catalysts could be recycled at least ten
times without significant loss of activity and enantioselectivity.
Such excellent catalytic effect is likely to attribute to the specific
frameworks of ZnPS-PVPA which could provide the advantaged
reaction microenvironment for the asymmetric epoxidation. In
addition, these novel heterogeneous catalysts could be efficiently
used in large-scale reactions with the enantioselectivity being
maintained at the same level. As far as our information goes, there
are scarcely any reports about large-scale reactions in the asym-
metric epoxidation of unfunctionalized olefins, which offer a great
possibility for application in industry.
ment equipped using
a
chiral column (HP 19091GeB213,
m) or high performance liquid
30 m ꢂ 30 m ꢂ 0.32 mm ꢂ 0.25
m
chromatography (HPLC) with Agilent 1200 instrument using Chir-
alcel OD-H (4.6 mm ꢂ 250 mm) columns.
2.2. Synthesis of zinc poly (styrene-phenylvinylphosphonate)-
phosphate (ZnPS-PVPA)
The synthesis and characterization of PS-PVPA were accorded to
the literature [18] (Scheme 1).
PS-PVPA (6.0 g, 8.5 mmol) was dissolved in 100 ml THF.
Hydrated sodium orthophosphate (2.66 g, 17 mmol) dissolved with
deionized water was slowly added and vigorously stirred for 1 h.
The ratio of polystyrene-phenylvinyl phosphonate parts to inor-
ganic phosphate parts is 0.35: 0.65 in mol stoichiometric. After-
2
. Experimental
2.1. Material and instruments
(
1R, 2R)-1, 2-diaminocyclohexane, chloromethyl methyl ether
2 2
ward, this solution of Zn(Ac) $2H O (5.61 g, 25.6 mmol) was slowly
(
toxic compound), 1-octene, styrene, -methylstyrene, 4-
a
added to the reactants with vigorously stirring, accompanied with
ꢀ
chlorostyrene, indene, n-nonane and sodium periodate were
supplied by Alfa Aesar. Other commercially available chemicals
were laboratory-grade reagents from local suppliers. Styrene was
passed through a pad of neutral alumina before use.
FT-IR spectra was recorded from KBr pellets using a Bruker
RFS100/S spectrophotometer (USA), and diffuse-reflectance UVevis
a step by step temperature rise to 65 C. The reaction mixture was
ꢀ
kept at 65 C for 72 h. After cooling down to room temperature, the
pH of the reaction mixture was adjusted to neutral by addition of
triethylamine and then washed with distilled water and ethanol
and subsequently dried under vacuum. Primrose yellow solid ZnPS-
PVPA was obtained in 90% yield.
PO(OH)2
PO(OH)2
BPO
H
H
C
2
H
C
2
*
C
C
*
Zn(OAc) 2H O
2
2
n
m
NaH PO4
2
EtOAc/reflux
St
PVPA
PS-PVPA
Cl
Cl
CH
2
CH
n
2
CH OCH Cl
3
2
Zn(NaPO4)0.65[O PCHCH (CHCH ) ]
xH O
CH2
Cl
CH2
Cl
3
2
2 n 0.35
2
ZnCl2
n
1
ZnCMPS-PVPA
ZnPS-PVPA
= ZnPS-PVPA
2
a R =
b R =
2c R =
d R =
O
O
OH
OH
R
R
CH2
2
diphenol, NaOH
N , reflux
n
CH
2
CH2
R
CH2
2
R
O
O
OH
OH
n
2
2
ZnPMPS-PVPA
Scheme 1. Synthesis of the support.

X. Hu et al. / Journal of Organometallic Chemistry 696 (2011) 2797e2804
2799
2.3. Synthesis of diphenol-modified zinc poly (styrene-
phenylvinylphosphonate)-phosphate (ZnPMPS-PVPA)
The synthesis of ZnPMPS-PVPA was accorded to the literature
[20].
2.4. Grafting chiral salen Mn(III) catalyst onto ZnPMPS-PVPA
The route for preparing the heterogeneous chiral salen Mn(III)
catalysts was outlined in Scheme 2. After preswelled in 10 ml of THF
for 30 min, ZnPMPS-PVPA (0.50 g) was mixed with chiral salen
Mn(III) [4] (1.5 g, 2.36 mmol), sodium hydroxide (adequate
amount). And this suspension was stirred for 24 h under reflux.
Finally the obtained catalysts were filtered and rinsed thoroughly
2 2
with THF, CH Cl , distilled water until the extraction liquid became
colorless. The filtrates were collected to be detected until no
manganese by atomic absorption spectrometry. After dried in
vacuum, the catalysts were yielded with 90e93%. Meanwhile, the
manganese contents of the supported catalysts were determined
Fig. 1. UVeVis spectra of ZnPS-PVPA (a), chiral salen Mn(III) (b) and immobilized
catalyst (3d) (c).
ꢁ
1
by AAS, which showed values about 0.52e0.65 mmol$g based on
the Mn.
organic phase was separated and purified on a silica gel column,
and then analyzed by GC.
2.5. Asymmetric epoxidation of unfunctionalized alkenes
To a mixture of olefins (1 mmol), n-nonane (internal standard,
3
. Results and discussion
1
.0 mmol), heterogeneous catalysts (4.7 mol% of the catalysts, based
on the Mn amount in the catalyst) in THF (8 ml) was added
a solution of NaIO (2 mmol) in H O (4 ml). The reaction mixture
3.1. Catalysts characterization
4
2
was stirred magnetically at room temperature for 24 h. The catalyst
was precipitated from the reaction mixture by adding hexane
The diffuse-reflectance UVevis spectra (Fig. 1) can provide
evidence for the successful immobilization of salen Mn(III) onto the
support. The band at 510 nm is due to the ded transition of salen
Mn(III) complex [25]. For the immobilized salen Mn(III) catalysts,
all the characteristic bands appeared in their spectra exhibite a blue
shift from 259, 335, 433 and 510 nm to 253, 325, 420 and 503 nm,
which indicate that an interaction existed between the salen
Mn(III) complex and the diphenol-modified ZnPS-PVPA support.
Comparing the IR spectra of heterogeneous salen Mn(III) complexes
with the neat chiral salen Mn(III) in Fig. 2, it is found that the main
characteristic bands of the heterogeneous catalysts were similar to
the neat chiral salen Mn(III). The heterogeneous catalysts and chiral
(
10 ml), then the organic phase was separated and purified on
a silica gel column, and then analyzed by GC. The progress of the
reaction was monitored by GC to find the optimal conversion and
selectivity.
2.6. Large-scale asymmetric epoxidation of a-methylstyrene
In order to detect whether the heterogeneous catalysts have the
potential of industrial applications, we performed large-scale
asymmetric epoxidation reactions with 40 mmol of -methylstyr-
a
ꢁ
1
ene. The corresponding catalysts (1.88 mmol, respectively),
salen Mn(III) have the same absorption peak at 1623 cm ascribed
n-nonane (internal standard, 40 mmol) were added in THF (320 ml)
to the stretching vibration of C]N bond in the salen ligand, and the
ꢁ1
in turn, and then the solution of NaIO
4
(80 mmol) in H
2
O (160 ml)
strong absorption peak at 530 cm assigned to MneN bond of the
salen ligand [26,18]. Hence, the observations suggest that the neat
chiral salen Mn(III) has been successfully immobilized onto
diphenol-modified ZnPS-PVPA support.
was added and stirred continuously at room temperature for 36 h.
Afterward the catalysts were precipitated from the reaction
mixture by adding adequate amount of hexane, and then the
Scheme 2. Synthetic route for the supported catalysts.

2800
X. Hu et al. / Journal of Organometallic Chemistry 696 (2011) 2797e2804
Fig. 2. FT-IR spectra of chiral salen Mn(III) and immobilized catalysts(3aw3d).
The TG curves for the supported catalyst 3d (as a representative
Fig. 4. XRD patterns of ZnPS-PVPA (a) and immobilized catalyst 3d (b).
catalyst) are shown in Fig. 3. There are three stepwise weight losses
in the DTG trace for catalyst 3d. The first section with a weight loss
diameter of Mn(salen)Cl complex is about 16.1 Å [29] which
revealed that the chiral salen Mn(III) could easily introduce in the
support. The introduction of salen Mn(III) complexes is the most
probable cause to make the zinc layer stretched and become
broader. The X-ray diffraction patterns of the heterogeneous cata-
lysts (3aw3c) are not shown here, because their diffractograms
are similar to the diffraction pattern of the heterogeneous catalyst
ꢀ
of 4.59% at 60 e200 C is corresponded to the loss of the surface or
ꢀ
interstitial water. In the temperature range 200e600 C, the DSC
ꢀ
curve shows a sharp endothermic peak at 420 C with weight loss
of 38.49%, which is attributed to the decomposition of the appen-
ded organic groups and decomposition of the immobilized
heterogeneous complex. The third weight loss is with 11.2% because
of the dehydrolysis of ZnHPO
range of 650e1000 C. The result showed that the temperature for
4
to Zn
2
P
2
O
7
[27] in the temperature
(3d).
ꢀ
The Nitrogen adsorptionedesorption isotherms of immobilized
decomposition of the supported catalyst were much higher than
catalyst 3d exhibit representative type IV isotherms with hysteresis
loops (Fig. 5.), confirming that the typical catalyst owns different
pore size distribution centered around 23.2 Å. The specific surface
area and pore volume of the immobilized catalyst 3d are
ꢀ
2
00 C. Generally, organic reactions of heterogeneous catalysis
ꢀ
were carried out below 200 C, therefore, these heterogeneous
catalysts had favorable thermal stability.
The X-ray diffraction patterns of the pure support ZnPS-PVPA (a)
and immobilized catalyst 3d (b) are compared in Fig. 4. XRD data
shows that the crystalline ZnPS-PVPA and immobilized catalyst 3d
are layered complexes whose interlayer distances calculated
2
ꢁ1
3
ꢁ1
6
2.3 m $g and 0.19 cm $g , respectively. Compared with ZnPS-
PVPA, the surface area and pore volume of immobilized catalyst 3d
apparently increased, whereas pore size decreased unnoticeably
(Table 1). Different results have been reported [30,31], where the
according to the formula of Bragg equation (n
l
¼ 2d sin
q) are about
pore sizes, surface areas, and pore volumes all decreased compared
to those of the supports after the immobilization of the chiral salen
Mn(III). From Fig. 4, we know that the layers of immobilized cata-
lyst are stretched observably. Therefore, it could be deduced that
21.12 and 40.87 Å [28], respectively. As also can be seen from the
XRD patterns, after the diphenol-modified ZnPS-PVPA was used to
immobilize the chiral salen Mn(III) complexes, the intensity of
diffraction peaks were significantly lower and the diffraction peaks
shifted slightly to lower angle with the increase of the interlayer
distance remarkably. There has been reported that the molecule
Fig. 3. DSC-DTG curves of immobilized catalyst 3d.
Fig. 5. Isotherms and distribution of pore diameter of immobilized catalyst 3d.

X. Hu et al. / Journal of Organometallic Chemistry 696 (2011) 2797e2804
2801
Table 1
height of immobilized catalyst have become smaller than those of
the pure support, which may be ascribed to the effect of the
entrapment of salen Mn(III) molecules inside the pores. But
the average diameters of these pores and secondary channels
among the layers of the catalyst are far greater than substrates, it is
deduced that more chances will be able to offer substrates to
transfer to the internal catalytic active sites.
The BET surface areas, pore volumes and average pore sizes ZnPS-PVPA and
immobilized catalyst 3d.a
Sample
Surface
area (m /g)
Pore volume
(ꢂ10 cm /g)
0.1
1.9
Average
2
b
ꢁ1
3
b
pore size (Å)b
ZnPS-PVPA
4.9
62.3
27.3
23.2
3d
a
ꢀ
The samples were out gassed at 150 C for 6 h.
Surface area, Pore volume, Pore size based on the adsorption data of BJH
b
method.
3.2. Asymmetric epoxidation
the chiral salen Mn(III) complex are located on the external surfaces
or between the layers of ZnPS-PVPA by the increase of surface area
and pore volume. Moreover, the increase the surface area of the
catalyst can provide enough chance for substrates to access to the
catalytic active sites.
To gain a better catalytic effect, the catalyst 3d was selected as
the typical catalyst to investigate the effects of various reaction
parameters such as catalyst amount, solvent, oxidant and axial
additive on the asymmetric epoxidation of
a-methylstyrene.
The atomic force microscopy (AFM) was used to illustrate the
morphologies and particle sizes of the pure support ZnPS-PVPA and
immobilized catalyst 3d. From Fig. 6, the 3D AFM image of the pure
support ZnPS-PVPA has shown that the surface is uneven on
account of the aggregation of polystyrene segments. Every thin
granule of the support is an aggregation of a mass of smaller
particulates to some extent [18]. The 2D photograph of the support
clearly indicates that the support has various sizes of channels,
pores and caves, and the diameters of the pores are ranged in
3.2.1. The effect of the catalyst amount in the asymmetric
epoxidation of -methylstyrene
In order to optimize the catalyst amount, different amounts of
catalyst 3d were used in the asymmetric epoxidation of -meth-
a
a
ylstyrene with NaIO as an oxidant. The best results were obtained
4
with 80 mg (0.047 mmol) of the catalyst (Table 2).
3.2.2. The effect of solvent on the asymmetric epoxidation of
a-methylstyrene
10e20 nm. Upon the immobilization of chiral salen Mn(III) on the
In the asymmetric epoxidation of olefins the choice of reaction
support, the morphologic have greatly changed. The surface of the
media is crucially important. Among the mixture of acetonitrile,
immobilized catalyst 3d has become regularly, and the diameter or
acetone, tetrahydrofuran, N, N-dimethylformamide, methanol,
Fig. 6. The AFM images of the pure support ZnPS-PVPA and immobilized catalyst 3d.

2802
X. Hu et al. / Journal of Organometallic Chemistry 696 (2011) 2797e2804
Table 2
Optimization of the catalyst 3d amounts in the asymmetric epoxidation of
a
Table 4
The effect of various oxidants on the asymmetric epoxidation of
catalyzed by the catalyst 3d at room temperature.
a-methylstyrene
-methylstyrene.a
a
Entry
Catalyst amount
Time (h)
Conv. (%)
ee (%)b
Oxidant
Solvent
Conv. (%)
ee (%)b
(
mg, mmol)
NaIO
NaIO
NaIO
4
4
4
(2 mmol)
(1 mmol)
(2 mmol)/imidazole
(2 mmol)
THF/H
THF/H
THF/H
THF
2
2
2
O
O
O
97
77
70
16
10
95
77
37
>99
>99
>99
89
88
74
60
63
16
20
20
7
1
2
3
4
5
0 (0)
50 (0.029)
80 (0.047)
24
24
24
24
24
8
12
97
98
98
5
92
>99
98
H
H
2
O
O
2
2
100 (0.059)
120 (0.07)
2
(2 mmol)/imidazole
THF
97
NaOCl (2 mmol)
NaOCl (2 mmol)/4-PPNO
tert-BuOOH (2 mmol)
m-CPBA
CH
CH
CH
CH
CH
2
Cl
2
Cl
2
Cl
2
Cl
2
Cl
2
a
2
2
2
2
a
-methylstyrene (1 mmol), NaIO
O (4 ml), rt. The conversion and the ee value were deter-
with chiral capillary columns HP 19091G-B213
30 m ꢂ 0.32 mm ꢂ 0.25 m).
Expoxide configuration S.
4
(2 mmol), n-nonane (internal standard,
1
mmol), THF (8 ml), H
by GC
2
mined
m-CPBA/NMO
(
m
b
a
a
-methylstyrene (1 mmol), axial additives (0.2 mmol), heterogeneous catalyst
O (4 ml),
(8 ml), 24 h, rt. The conversion and the ee value were determined by GC with
3
d (0.047 mmol), n-nonane (internal standard, 1 mmol), THF (8 ml), H
CH Cl
2
2
2
chiral capillary columns HP 19091G-B213 (30 m ꢂ 0.32 mm ꢂ 0.25
mm).
dichloromethane, chloroform and carbontetrachloride with water
were all examined, at the same time, different ratios of tetrahy-
drofuran/water mixture were also examined. The results are dis-
played in Table 3, and the data demonstrated that the 2:1
tetrahydrofuran/water mixture was chosen as the best reaction
medium, because the higher ee was observed. That is due to our
support, which contains hydrophobic segments of polystyrene and
hydrophilic segments of PVPA in the copolymer [18], make the
catalyst possess dual properties which are hydrophobic and
hydrophilic. In other words, the heterogeneous catalyst used in
mixed solvent has better swelling than either in aqueous solution
or in organic solvent. In addition, the heterogeneous catalyst is
more readily swelled in tetrahydrofuran than in other solvents, so
that they exhibited the higher catalytic activity in tetrahydrofuran/
water mixture solvent.
b
Expoxide configuration S.
7e74% ee values of
a-methylstyrene were obtained. The results
showed that NaIO is the best oxygen source because this oxidant
4
can give better conversion (97%) and ee value (excess 99%). In
addition, different equivalents of the oxidant were tested, and the
data showed that the higher catalytic activity obtained with 2
equivalents of the oxidant than that with 1 equivalent of the
oxidant. From Table 3, the 2:1 tetrahydrofuran/water mixture was
chosen as the best reaction medium. This is because the oxidant
sodium periodate only has certain solubility in tetrahydrofuran.
The more ratios we add, the more sodium periodate will dissolve.
4
When 2 equivalents NaIO was used, the oxidant could provide
moderate source of oxygen for the catalytic reaction, and excellent
activity and enantioselectivity were obtained. Consequently, the
optimum molar ratio of olefin to oxidant is 1: 2.
3
.2.3. The effect of the oxidant and axial additive on the asymmetric
epoxidation of -methylstyrene
The effect of various oxidants such as NaOCl, NaIO
, and tert-BuOOH was investigated in the asymmetric epox-
idation of -methylstyrene catalyzed by the heterogeneous cata-
a
4
, m-CPBA,
3.2.4. Enantioselective epoxidation of unfunctionalized olefins
2 2
H O
The catalytic activity and selectivity of catalysts (3aw3d) were
a
explored for the asymmetric epoxidation of various olefins using
NaIO as an oxidant system under optimized conditions (with
lyst 3d. The results are summarized in Table 4. In order to
investigate the best oxygen source, we added the suitable axial
additive to the reaction mixture for comparison. These axial
additives are 4-PPNO for NaOCl, NMO for m-CPBA, imidazole for
4
n-nonane as internal standard). The optimum conditions used for
the asymmetric epoxidation of olefins with this heterogenized
system were catalyst, oxidant and substrate in a molar ratio of
H
2
O
2
and NaIO
conversions and ee values apparently increased in the absence of
the axial additives in the asymmetric epoxidation of -methyl-
4
[6,7,32e35]. However, it was also found that the
0.047: 2: 1. Meanwhile, in order to investigate the effect of the
support on the catalytic activity of these supported catalysts, the
homogeneous chiral salen Mn(III) catalyst 3 was examined for
comparison under the same conditions. The catalytic results,
summarized in Table 5, show that the heterogeneous catalysts
a
styrene. These phenomena are not in agreement with other earlier
literature reported, in which a good catalytic activity needs an
extra axial ligand. When NaOCl, H O and m-CPBA are used as
2 2
(3aw3d) effectively catalyze the epoxidation of the various olefins
oxygen source, either in tetrahydrofuran or dichloromethane, only
in comparable or even higher conversion and enantioselectivity
than those of homogeneous catalyst.
Table 3
As can be seen from Table 5, when nonactivated terminal 1-
octene was used as a substrate, there was a significant improve-
ment in enantioselectivity (ee: 50e75%, entries 2e5) over the
homogeneous system (ee: 40%, entry 1). In the epoxidation of
aromatic olefins, the catalytic system showed excellent catalytic
performance. Obviously, the enantioselectivity for styrene (ee:
The effect of solvent on the asymmetric epoxidation of
catalyzed by the catalyst 3d at room temperature.
a
-methylstyrene with NaIO
4
a
Solvent
Time (h)
Conv. (%)
ee (%)b
THF/H
THF/H
THF/H
2
2
2
O (2:1)
O (1:1)
O (1:2)
24
24
24
24
24
24
24
24
24
97
48
21
10
66
20
60
12
10
>99
95
94
99
70
91
90
76
30
60e67%, entries 7e10) and 4-chlorostyrene (ee: 62e79%, entries
CH
3 2
CN/H O (2:1)
17e20) were higher with immobilized catalysts compared with
DMF/H
2
O
CH
CH
CH
3
3
2
COCH
OH/H
Cl /H
/H
/H
3 2
O
homogeneous catalyst (ee: 49, 48%, entries 6, 16; respectively)
under identical reaction conditions. Especially, in the case of
2
O
O
2
2
a-methylstyrene, the conversion could reach 97% and ee values
CCl
4
2
O
could exceed 99% (Table 5, entry 15), in which the ee values are
outstanding higher than 34% ee for the homogeneous catalyst.
Notably, the influence of the support could not be ignored to the
chiral induction for the asymmetric epoxidation. Furthermore,
a few similar results have been reported to give higher ee values
a
a
4
-methylstyrene (1 mmol), NaIO (2 mmol), heterogeneous catalyst 3d
(
0.047 mmol), n-nonane (internal standard, 1 mmol), rt. The conversion and the ee
value were determined by GC with chiral capillary columns HP 19091G-B213
30 m ꢂ 0.32 mm ꢂ 0.25 m).
Expoxide configuration S.
(
m
b

X. Hu et al. / Journal of Organometallic Chemistry 696 (2011) 2797e2804
2803
Table 5
Asymmetric epoxidation of alkenes catalyzed by homogeneous and heterogeneous
Table 6
The recycles of catalyst 3d in the asymmetric epoxidation of a
-methylstyrene.a
a
catalysts (3aw3d) with NaIO
4
as oxidant systems.
Run
Time (h)
Conv. (%)
ee (%)b
Mn leached (%)c
Entry Substrate
Catalyst Time (h) Conv. (%)b ee (%)c
1
2
3
4
5
6
7
8
9
24
24
24
24
24
24
24
24
24
24
97
97
96
95
95
93
92
90
90
88
>99
>99
>99
99
97
97
96
95
93
92
0.6
0.3
0
0
0
0
0
0
0
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
3
3a
3b
3c
3d
3
3a
3b
3c
3d
3
3a
3b
3c
3d
3
3a
3b
3c
3d
3
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
90
87
92
95
96
72
71
81
83
94
90
89
95
93
97
99
85
90
91
92
79
87
71
83
90
40d
d
59
50
67
75
49
60
67
65
61
65
99
99
d
d
d
e
e
e
e
10
0
e
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
a
e
a
-methylstyrene (1 mmol), NaIO
4
(2 mmol), catalyst 3d (0.047 mmol), n-nonane
O (4 ml), rt. The conversion and the ee
value were determined by GC with chiral capillary columns HP 19091G-B213
m).
e
(internal standard, 1 mmol), THF (8 ml), H
2
e
e
(30 m ꢂ 0.32 mm ꢂ 0.25
m
99
b
>99e
Expoxide configuration S.
Determined by atomic absorption spectrometry.
c
e
48
67
62
75
79
61
65
52
e
e
Zou’s catalyst were not satisfactory. Hence, the different types of
supports obviously affected the reaction performance for the
heterogeneous asymmetric epoxidation. Further studies concerning
the mechanism of this novel behavior for these immobilized cata-
lysts are currently in progress.
e
e
Cl
f
f
3a
3b
3c
3d
f
f
63
f
73
3.3. The recycling of the supported chiral salen Mn(III) catalyst
a
4
alkenes (1 mmol), NaIO (2 mmol), homogeneous catalyst 3 and heterogeneous
catalysts (0.047 mmol, respectively), n-nonane (internal standard, 1 mmol), THF
8 ml), H O (4 ml), rt.
Conversions were determined by GC, by integration of product peaks against an
To study the stability and reusability of the supported chiral
(
2
b
salen Mn(III) catalysts, we chose catalyst 3d in repeated epoxida-
tion reactions with -methylstyrene as a model substrate. The
a
internal quantitative standard (nonane), correcting for response factors.
c
Determined by GC with chiral capillary columns HP 19091G-B213
catalyst was separated form the reaction mixture after each
experiment by simple filtration, washed with water and hexane,
dried carefully before using it in the subsequent run. Furthermore,
the filtrates were collected for determination of Mn leaching. No
manganese was detected in the filtrates after the first two runs by
atomic absorption spectrometry. The data in Table 6 indicate only
a slightly decrease in activity and enantioselectivity after ten
consecutive times (conversion: from 97% to 88%; ee: from excess
99% to 92%). The decrease in the conversion and enantioselectivity
for more cycles might be caused by a physical loss during the
recovery process and/or by a gradual degradation of catalysts under
the epoxidation condition and continuous stirring. Moreover,
because channels, pores and cavums with various sizes and shapes
of catalysts were partly plugged after several recycle epoxidations,
it can induce the decrease of the activity.
(
30 m ꢂ 0.32 mm ꢂ 0.25 m) or HPLC with chiral OD (4.6 mm ꢂ 250 mm) column.
m
d
Epoxide configuration R.
Expoxide configuration S.
Epoxide configuration 1S,2R.
e
f
than the homogeneous ones for the asymmetric epoxidation and
this was attributed to the confinement effect of supports [36]. The
support ZnPS-PVPA was regularly layered structure, which still kept
good layered structure after the immobilization of salen Mn(III)
catalyst and owned larger surface area, various sizes of pores,
micropores, and channels as compared with the support. Accord-
ingly, the increase in enantiomeric excess may be attributed to the
microenvironment effect and confinement effect differing from
either pure polystyrene or inorganic supports, these effects are
provided by the layered structure and micropores of ZnPS-PVPA
and the balance adjustment between the hydrophobic of poly-
styrene parts and the hydrophilic of phosphate parts [19].
3.4. Preparation for large-scale asymmetric epoxidation of
-methylstyrene
a
In addition, the asymmetric epoxidation of the relatively bulkier
olefin like indene were also tested by these heterogeneous catalysts.
Whereas, the catalytic system showed a lower or comparable cata-
lytic performance (ee: 52e73%, entries 22e25) than that of
homogenous catalyst 3 (ee: 61%, entries 21), the reason may be that
indene is too large to accommodate into the micropores or between
the layers of ZnPS-PVPA. So that indene may merely react with a few
active sites on the external surface of the ZnPS-PVPA. These results
are different from Zou [20] reported, where the chiral salen Mn(III)
catalyst immobilized onto zirconium phosphonate and showed an
eevalue of 99.5%for the asymmetric epoxidation of indene. The most
probable explanation is that the support of zirconium phosphonate
is amorphous with bigger nanopore sizes, surface areas, and pore
volumes [18] compared to those of the support ZnPS-PVPA. More-
over, there are more chances for the bulkier indene to approach the
catalytic active sites in the microporous and channels of the Zou’s
catalyst. However, in the case of small olefin like styrene and
We further performed large-scale asymmetric epoxidation
reactions with 40 mmol of a-methylstyrene (Table 7). The corre-
sponding catalyst loading as in the experimental scale was used.
The large-scale experiments can be facilely carried out using the
Table 7
Large-scale asymmetric epoxidation of
a-methylstyrene catalyzed by heterogeneous
a
catalysts (3aw3d) with NaIO as oxidant systems.
4
Entry
Substrate
Catalyst
Time (h)
Conv. (%)
ee (%)b
1
2
3
4
3a
3b
3c
3d
36
36
36
36
85
89
88
90
97
98
98
99
a
4
a-methylstyrene (40 mmol), NaIO (80 mmol), heterogeneous catalysts
(
H
1.88 mmol, respectively), n-nonane (internal standard, 40 mmol), THF (320 ml),
O (160 ml), rt. The conversion and the ee value were determined by GC with chiral
2
capillary columns HP 19091G-B213 (30 m ꢂ 0.32 mm ꢂ 0.25
mm).
b
a-methylstyrene, the enantiomeric excess values obtained by the
Expoxide configuration S.

2804
X. Hu et al. / Journal of Organometallic Chemistry 696 (2011) 2797e2804
same procedure as for the experimental scale reactions. As can be
seen from the result, delightfully, the enantioselectivity maintained
at the same level for the large-scale reactions.
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2
(
[
[
1
(
4
. Conclusions
8
[
[
Chiral salen Mn(III) complex has been first immobilized on
diphenol-modified layered of ZnPS-PVPA by axial coordination,
which was incorporated into the interlayer space of support, and
1
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was able to transfer an oxygen atom from NaIO
4
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much higher ee values than that observed in the homogeneous
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epoxidation reactions for the first time, which may carry out the
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