Grafting of a chiral Mn(iii) complex on graphene oxide nanosheets and its catalytic activity for alkene epoxidation

Article abstract of DOI:10.1039/c4ra03047h

A chiral Mn(iii) complex supported by a covalent grafting method on modified graphene oxide was synthesized using 3-chloropropyltrimethoxysilane as a reactive surface modifier. The heterogeneous catalyst was characterized by X-ray diffraction, Fourier transform infrared spectra, thermogravimetric analysis, ultraviolet-visible spectra, nitrogen adsorption-desorption isotherms, transmission electron microscopy and atomic absorption spectroscopy. The catalytic potential of the heterogeneous catalyst and comparison with its homogeneous counterpart were studied for enantioselective epoxidation of various alkenes using m-chloroperbenzoic acid as an oxidant and it showed high selectivity and comparable catalytic reactivity with its homogeneous analogue. In addition, higher enantioselectivity and higher yield were observed in the presence of 4-methylmorpholine N-oxide and pyridine N-oxide, respectively. The catalyst was reused for several runs without significant loss of activity and selectivity.

Full text of DOI:10.1039/c4ra03047h

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Grafting of a chiral Mn(III) complex on graphene
oxide nanosheets and its catalytic activity for
alkene epoxidation†
Cite this: RSC Adv., 2014, 4, 26087
Mohammad Ali Nasseri,* Ali Allahresani and Heidar Raissi
A chiral Mn(III) complex supported by a covalent grafting method on modified graphene oxide was
synthesized using 3-chloropropyltrimethoxysilane as a reactive surface modifier. The heterogeneous
catalyst was characterized by X-ray diffraction, Fourier transform infrared spectra, thermogravimetric
analysis, ultraviolet-visible spectra, nitrogen adsorption–desorption isotherms, transmission electron
microscopy and atomic absorption spectroscopy. The catalytic potential of the heterogeneous catalyst
and comparison with its homogeneous counterpart were studied for enantioselective epoxidation of
various alkenes using m-chloroperbenzoic acid as an oxidant and it showed high selectivity and
comparable catalytic reactivity with its homogeneous analogue. In addition, higher enantioselectivity and
higher yield were observed in the presence of 4-methylmorpholine N-oxide and pyridine N-oxide,
respectively. The catalyst was reused for several runs without significant loss of activity and selectivity.
Received 5th April 2014
Accepted 28th May 2014
DOI: 10.1039/c4ra03047h
www.rsc.org/advances
heterogeneous Mn(III) complexes than homogenous counter-
parts. Therefore, novel and effective heterogeneous chiral
Introduction
18
The asymmetric epoxidation of alkenes into unique labile three- Mn(III) catalysts for asymmetric epoxidation of various olens
membered ether rings, which are useful organic building blocks are highly desirable.
for the synthesis of pharmaceuticals, agrochemicals and ne
chemicals, is one of the fundamental organic trans- SBA-15, graphene oxide (GO) has unique nanostructure
Compared to mesoporous silicates such as MCM-41 and
1–4
formations. From a synthesis point of view, the selective (monolayer) and hydrophilic nature owing to the wide range of
insertion of one oxygen atom into organic compounds, under oxygen carrying functional groups on its basal planes and
19
mild conditions, remains a difficult challenge in chemical edges. These functional groups allow GO to be readily func-
catalysis. Chiral Mn(III) salen complexes, rst reported by tionalized with various surfactants, polymeric materials, and
Jacobsen and Katsuki groups, as excellent catalysts have nanoparticles in order to provide enormous potential for
emerged as extremely efficient systems for the asymmetric applications in materials science and engineering. In addition,
5,6
epoxidation of unfunctionalized olens. Currently, much some studies have demonstrated that immobilization of tran-
attention is focused on the heterogenization of Mn(III) sition metal nanoparticles on GO nanosheets produced efficient
20–23
complexes from drawbacks such as difficult recovery and recy- catalysts.
In this study, we report design and characteriza-
cling of the catalysts, product contamination and deactivation tion of the covalent attachment of homogeneous Mn(III)
of homogeneous catalysts through the formation of dimeric complex onto GO and its catalytic properties in the epoxidation
7
peroxo and m-oxo species. To overcome these drawbacks, of alkenes using m-CPBA as an oxidant.
heterogeneous Mn(III) complexes prepared by immobilizing the
homogeneous analogue onto insoluble solid supports such as
mesoporous materials, zeolites, polymer supports, organic
Results and discussion
Characterization of the heterogeneous catalyst
polymer-inorganic hybrid materials, clays, MCM-41, SBA-15 and
8
–17
activated silica have been developed.
Unfortunately, despite Synthesis of the heterogeneous Mn(III) complex and the inter-
their excellent performance in separation and reuse, immobi- mediate steps were examined and monitored by XRD, FT-IR,
lization oen decreased enantioselectivities or efficiencies of TEM, TGA, UV-vis, AAS and nitrogen adsorption at room
temperature.
3
-Chloropropylterimethoxysilane which plays the role of
Department of Chemistry, Faculty of Science, University of Birjand, P. O. Box
7175-615, Birjand, Iran. E-mail: manaseri@birjand.ac.ir; Fax: +98-561-2502065;
Tel: +98-561-2502065
coupling agent, merely providing a large surface to anchor the
active complex and increase the efficiency of heterogeneous
catalyst was used for anchoring the homogeneous Mn(III) cata-
9
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c4ra03047h
24–26
1
lyst onto GO.
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 26087–26093 | 26087

View Article Online
RSC Advances
Paper
FT-IR analysis
The FT-IR spectrum of GO (Fig. 1a) shows a broad peak appeared
ꢀ
1
at 3446 cm , assigned to the stretching mode of an O–H bond,
reveals the abundance of hydroxyl groups in GO. The strong band
ꢀ
1
at 1716, 1619, 1224 and 1059 cm revealed the presence of
C]O, C]C, C–OH and C–O (epoxy) functional groups in GO.
Fig. 1b which is assigned to CPGO aer reaction with 3-chlor-
opropyltrimethylsilane shows an obvious decrease in intensities
ꢀ
1
of peaks such as 3446, 1728 and 1395 cm which are corre-
sponding to the OH, C]O stretching vibration and O–H defor-
ꢀ1
mation peak, respectively. Also, the bands at 2880 and 2920 cm
are corresponding to the aliphatic C–H bonds. The IR spectra of
ꢀ
1
the ligand salen showed a strong band at 1614 cm which is
Fig. 2 The XRD patterns of (a) GO (b) CPGO and (c) heterogeneous
catalyst.
assigned to stretching vibration of C]N group (Fig. 1e). This
ꢀ
1
band shis to lower position (30 cm ) in homogeneous Mn(III)
complex (B) that suggests coordination of Mn through C]N
functional groups (Fig. 1d). The new stretching vibration bands at
ꢀ
1
2
930, 2880, 1580 and 1190 cm suggest the graing of homo-
geneous Mn(III) complex on the CPGO (Fig. 1c).
XRD analysis
Fig. 2 shows XRD patterns of GO, CPGO and heterogeneous
catalyst. Upon oxidation of graphite, the basal reection (002)
ꢁ
27
peak appeared at 2q ¼ 26.6 (d spacing ¼ 0.335 nm) shis to a
ꢁ
lower angle (2q ¼ 11.79 , d spacing ¼ 0.79 nm) Fig. 2(a). The
increase in d spacing is due to the intercalation of water mole-
cules and the formation of oxygen-containing functional groups
between the layers of the graphite. By immobilization of CPGO, a
ꢁ
broad peak appeared at 2q ¼ 15–27 depending on amorphous
silica (Fig. 2b). The decrease in the intensity of 002 reection
Fig. 3 The TG curve of (a) GO (b) CPGO and (c) heterogeneous
peak of GO and the appearance of a broad peak appeared at 2q ¼ catalyst.
ꢁ
1
5–27 in the CPGO indicated the immobilization of 3-
chloropropyltrimethoxysilane on the GO. By immobilization of
the homogeneous Mn(III) complex on graphene oxide, 002 attributed to the loss of adsorbed water in the TGA curve of GO
reections peak of GO was completely disappeared (Fig. 2c).
(Fig. 3a). Two more degradation steps were observed in GO; the
ꢁ

rst commencing at 165–250 C, due to the loss of hydroxyl,
Thermogravimetric analysis
epoxy functional groups and remaining water molecules and
the second degradation step (250–650 C) depend on the
ꢁ
The TGA curve of pure GO, CPGO and heterogeneous catalyst
are shown in Fig. 3. A small mass loss (3 wt%) at ca. 100 C is
ꢁ
pyrolysis of the remaining oxygen-containing groups as well as
the burning of ring carbon. In the TGA curve of CPGO a weight
ꢁ
loss over a wide range of temperature (170–600 C) was observed
(Fig. 3b). In the TGA curve of heterogeneous catalyst three
stepwise weight losses are observed. The rst step with a weight
ꢁ
loss of 4.59% at 60–170 C is attributed to the loss of the surface
ꢁ
or interstitial water. In the temperature range of 170–600 C, a
weight loss of 33% is corresponded to the decomposition of the
appended organic groups. In comparison, a 42.5% weight loss
ꢁ
is experienced by pure GO up to 600 C. The thermogram of the
heterogeneous catalyst shows that the heterogeneous catalyst is
27,28
ꢀ1
stable.
The loading of Mn(III) complex is 0.31 mmol g
based on the difference in the weight losses for GO and
heterogeneous catalyst. The molar ratio of ligand to metal in
homogeneous Mn(III) catalyst is 1 : 1 in immobilized complex
catalyst, indicating that the molar ratio of Mn element is 0.31
ꢀ
1
ꢀ1
mmol g . The content of Mn is 0.35 mmol g estimated by
Fig. 1 The FT-IR spectra of (a) GO (b) CPGO (c) heterogeneous
catalyst (d) Mn(III) complex and (e) salen.
26088 | RSC Adv., 2014, 4, 26087–26093
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
AAS, respectively. Moreover, these results suggest that metal
complex has been anchored onto CPGO.
UV-vis analysis
The UV-vis spectrum of GO shows a strong absorption peak at
230 nm and a shoulder at about 300 nm, which are attributed to
the p / p* transition of graphitic C–C bonds and to the n /
p* transitions of C]O bonds, respectively (Fig. 4a). For CPGO,
all absorption peaks are disappeared and a new absorption peak
appeared at 280 nm which is attributed to Si (Fig. 4b). The UV-
vis spectrum of heterogeneous catalyst (Fig. 4c) can provide
evidence for the immobilization of Mn(III) complex onto the
support. All the characteristic bands appeared in its spectrum
Fig. 6 TEM image of heterogeneous catalyst.
(325, 380 and 490 nm) indicated that an interaction took place
between the homogeneous Mn(III) complex and the CPGO.
The BET specic surface area of the heterogeneous catalyst
which is determined at room temperature by nitrogen phys-
2
ꢀ1
isorption was 18.6 m g . The loading of homogeneous Mn(III)
ꢀ
1
TEM analysis
complex (B) in the heterogeneous catalyst was 0.35 mmol g
based on Mn element analysis by AAS.
The high magnication TEM image of GO exhibits a completely
amorphous and disordered structure (Fig. 5). Fig. 6 shows the
nanoscopic features of the heterogeneous Mn(III) complex with Catalyst activity
amorphous nature.
The catalytic activity of heterogeneous chiral Mn(III) complex
was studied for the oxidation of alkenes by using m-CPBA as the
oxygen source. The catalytic tests for the heterogeneous chiral
Mn(III) complex was compared with homogeneous Mn(III)
complex under identical reaction conditions. In this content, a-
methylstyrene was chosen as model substrate to investigate the
activity of heterogeneous chiral Mn(III) complex. Various olens
such as cyclic and linear terminal olens were tested by this
catalyst and in all cases high catalytic activity and selectivity
were observed. To optimize the amount of catalyst, the reaction
was carried out in the presence of different amounts of
heterogeneous chiral Mn(III) complex (0.5–3 mol% based on Mn
ꢁ
element) at 0 C. It was found that by increasing the amount of
catalyst from 0.5 to 2 mol% the yields were increased from 30 to
93% and additional increasing the amount of catalyst did not
show any signicant effect on the conversion of the products
Fig. 4 The UV-vis spectra of (a) GO (b) CPGO and (c) heterogeneous
catalyst.
Table 1 Screening the quantity of the catalyst in the epoxidation of a-
methylstyrene with m-CPBA in EtOAC
a
b
Entry
Catalyst mol%
Yield (%)
1
2
3
4
5
6
7
8
0.5
1
1.5
2
2.5
3
30
45
70
93
94
96
8
No catalyst
Homogeneous chiral Mn(III)
complex
96
a
Reaction conditions: a-methylstyrene (1 mmol), m-CPBA (2 mmol) in 3
ꢁ
ml EtOAC. The reactions were run at 0 C for 6 h except for entry 7 which
was run for 12 h. The reaction was sonicated for 20 min before addition
b
of oxidant. Determined by GC with a CBP1 column (Shimadzu 30 m ꢂ
Fig. 5 TEM image of GO nanosheets.
0.32 mm ꢂ 0.25 mm).
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 26087–26093 | 26089

View Article Online
RSC Advances
Paper
Then, the effect of different additives was studied (Fig. 8). In
the epoxidation reactions, despite the conversion increase in
the presence of PNO, higher ee was observed in the presence of
MNO as an additive (Fig. 9). When NH OAC is used in EtOAC,
4
low yield (15%) with only 30% ee was obtained (Fig. 9).
In addition, different amounts of oxidants were tested, and
the results showed that the higher catalytic activity was
obtained with 2 equivalents of the oxidant (Fig. 10). Conse-
quently, the optimum molar ratio of olen to oxidant is 1 : 2.
We also performed the model reaction at different temper-
atures in EtOAC in the presence of heterogeneous catalyst (ꢀ78,
Fig. 7 The effect of different solvents on the epoxidation of a-
methylstyrene (1 mmol) using 2 mmol m-CPBA in 3 ml EtOAC cata-
ꢁ
2
5, 40 and 60 C) (Table 2, entries 1 and 3–5). Temperature plays
ꢁ
lyzed by heterogeneous Mn(III) complex (2 mol% based on Mn) at 0 C. an important role in the yield and ee of the reaction. There was a
(Table 1, entry 4). For comparison, the homogeneous chiral
Mn(III) complex (B) was also investigated under the same reac-
tion conditions, but shortening the reaction time to 3 h (Table 1,
entry 8). Blank experiment showed that the heterogeneous
chiral Mn(III) complex alone is inactive towards epoxidation of
a-methylstyrene (Table 1, entry 7).
The effect of different solvents in the epoxidation of a-
methylstyrene
Fig. 9 The effect of different additives on the epoxidation of a-
The choice of solvent is crucial in the asymmetric epoxidation of
olens. In this study, a systematic examination of the solvent lyzed by heterogeneous Mn(III) complex (2 mol% based on Mn) at 0 C.
methylstyrene (1 mmol) using 2 mmol m-CPBA in 3 ml EtOAC cata-
ꢁ
nature was performed in different solvents, namely acetonitrile,
ethyl acetate, tetrahydrofuran, dichloromethane, chloroform,
methanol, ethanol, ethanol–water and water, using 2 mol% of
heterogeneous Mn catalyst (Fig. 7). The best enantioselectivity
ꢁ
and moderate yield were obtained in ethyl acetate at 0 C.
The effect of different oxidants and axial additives on the
asymmetric epoxidation of a-methylstyrene
The effect of various oxidants such as H
2 2 4
O , NaIO , t-BuOOH, m-
CPBA, UHP, PhIO, PhI(OAC) and oxone are investigated in the
2
asymmetric epoxidation of a-methylstyrene. To choose the best
oxygen source, suitable axial additive (PNO) was added to the
reaction. As the results show in Fig. 8, m-CPBA was the best
Fig. 10 The effect of different amount of m-CPBA on the epoxidation
oxygen source for alkenes oxidation in the presence of hetero- of a-methylstyrene (1 mmol) in 3 ml EtOAC catalyzed by heteroge-
ꢁ
neous Mn(III) complex (2 mol% based on Mn) at 0 C.
geneous chiral Mn(III) complex.
Table 2 The effect of temperature on the epoxidation of a-methyl-
styrene (1 mmol) in 3 ml EtOAC catalyzed by heterogeneous Mn(III)
a
complex (2 mol% based on Mn)
ꢁ
b
Entry
T ( C)
Yield (%)
ee (%)
1
2
3
4
5
ꢀ78
0
25
40
60
55
93
95
97
99
92
90
84.6
65
40
a
Reaction conditions: a-methylstyrene (1 mmol), m-CPBA (2 mmol),
Fig. 8 The effect of different oxidants on the epoxidation of a-
catalyst (2 mol% based on Mn) in 3 ml EtOAC. The reactions were run
b
methylstyrene (1 mmol) using 2 mmol oxidant in 3 ml EtOAC catalyzed for 6 h for entries 1 and 2 and 4 h for entries 3–5. Determined by
ꢁ
by heterogeneous Mn(III) complex (2 mol% based on Mn) at 0 C.
GC with a CBP1 column (Shimadzu 30 m ꢂ 0.32 mm ꢂ 0.25 mm).
26090 | RSC Adv., 2014, 4, 26087–26093
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
ꢁ
decrease in the yield at ꢀ78 C and no signicant change in the (minor enantiomer)] where A stands for the area of the chro-
ee values (Table 2, entry 1). The reaction proceeded faster (4 h) matographic peak.
ꢁ
ꢁ
at 25 C compared with 0 C and gave higher TOF (11.5–12.1
The performed study on the catalytic transformation of
ꢀ1
h
). It is notable that a drop in the selectivity was not observed alkenes by m-CPBA in the presence of heterogeneous chiral
when the reaction carried out at 25 C. However, when
temperature is higher than room temperature (40 and 60 C), an
ꢁ
ꢁ
obvious decreasing in enantioselectivity was observed (Table 2,
entries 4 and 5).
Under optimized conditions, the catalytic activity of hetero-
geneous chiral Mn(III) complex was investigated for the asym-
metric epoxidation of various olens using m-CPBA. Table 2
shows that the heterogeneous chiral Mn(III) complexes effec-
tively catalyze the epoxidation of various olens. Conditions
ꢁ
used: injector temperature, 220 C; detector temperature,
ꢁ
ꢁ
2
50 C, injection volume, 0.2 ml, and column, isothermal 90 C
ꢁ
for styrene and 80 C for a-methyl styrene. The following
formulas were used for calculation of TON, TOF and % ee: TON
¼
mmol of converted alkene per mmol Mn; TOF ¼ TON per
Fig. 11 The recycles of the catalyst for asymmetric epoxidation of a-
time of reaction; and % ee ¼ [A (major enantiomer) ꢀ A methylstyrene (1 mmol), m-CPBA (2 mmol) and MNO (0.25 mmol) in 3
(minor enantiomer)]
ꢂ
100/[A (major enantiomer)
+
A
ml EtOAC catalyzed by heterogeneous Mn(III) complex (2 mol% based
ꢁ
on Mn) at 0 C.
a
Table 3 Epoxidation of different alkenes using m-chloroperbenzoic acid catalyzed by heterogeneous Mn(III) complex
ꢁ
b
c
d
ꢀ1
Entry
Alkene
T ( C)
Time (h)
Selectivity (%)
Yield (%)
ee (%)
TON
TOF (h )
0
5
6
4
99
98
93
95
90
84.6
46.5
48
7.75
12.1
2
1
0
5
6
4
98
97
90
93
65
61.5
45
46.5
7.5
11.6
2
2
0
25
6
4
99
99
92
95
85.1
80.2
46
47.5
7.66
11.87
3
4
0
25
6
4
99
98
90
94
55.6
55
46
47
7.66
7.8
0
5
6
4
99
98
92
96
60.9
58.6
46
48
7.66
12.0
2
5
0
5
6
4
98
98
85
90
53
50
42.5
46
7.1
11.5
6
7
2
0
25
6
4
99
99
94
95
86
80
48
48.5
8.0
12.1
0
5
6
4
99
99
95
96
88
84.7
44
48
7.33
12.0
2
8
9
0
5
6
4
99
98
90
93
62
60
45
46.5
7.5
11.62
2
a
b
Reaction conditions: substrate (1 mmol), DCM (3 ml), oxidant (2 mmol) and catalyst (2 mol% based on Mn). Selectivity based on alkenes
c
d
conversion. Determined by GC with a Shimadzu CBP5 column (30 m ꢂ 0.32 mm ꢂ 0.25 mm). ee% was performed by GC with a Agilent HP
column (19091G-B213, 30 m ꢂ 0.25 mm ꢂ 0.25 mm).
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 26087–26093 | 26091

View Article Online
RSC Advances
Paper
˚
Mn(III) complex showed that the system with the heterogeneous X-ray diffractometer with Cu K
a
radiation (k ¼ 1.5406 A). The
catalyst exhibits high catalytic efficiency with TON (42.5–46.5). TEM measurements were obtained using Philips CM10 instru-
Also, the catalytic activity of heterogeneous chiral Mn(III) ment. The UV-vis spectra were carried out by using a Shimadzu
complex showed good catalytic performance reaching a TOF of UV-160A spectrophotometer. The surface area was carried out by
ꢀ
1
7
.1–7.8 h at conversion of 85–95% and selectivity higher than
2
N adsorption using Quanta chrome (Chem. Bet-3000). TGA
9
8% in the epoxidation of different alkenes (Table 3). The analysis was performed by heating the samples in an Argon ow
ꢀ
1
catalytic activity of heterogeneous chiral Mn(III) complex was at a rate of 100 ml min using a Perkin-Elmer Diamond TG/DTA
also investigated for the asymmetric epoxidation of various thermal analyzer with a heating rate of 10 C min . The Mn
olens using m-CPBA at 25 C. In all the cases, the oxidation content of the catalysts was determined by Shimadzu AA-6300
reactions were done faster (4 h) at 25 C compared with 0 C and Atomic absorption spectroscopy (AAS). The yields were deter-
ꢁ
ꢀ1
ꢁ
ꢁ
ꢁ
ꢀ1
gave higher TOF (11.5–12.1 h ) (Table 3).
mined by Shimadzu GC-17A gas chromatograph (GC) equipped
with a ame ionization detector with a capillary column (CBP-1,
3
0 m ꢂ 0.25 mm ꢂ 0.25 mm), using helium as carrier gas. The
enantioselectivity was determined in a chiral GC column (HP
9091G-B213, 30 m ꢂ 0.25 mm ꢂ 0.25 mm).
Reusability of the catalyst
To access the recyclability of the heterogeneous chiral Mn(III)
complex, the heterogeneous catalyst was completely washed by
ethanol and dichloromethane and used in repeated epoxidation
reactions with a-methylstyrene by adding fresh reactants. In
each run, no manganese was detected in the ltrates by AAS. As
shown in Fig. 11, it is obvious that the catalyst worked well for
up to ve cycles with no considerable decrease in reactivity and
enantioselectivity (conversion: from 93% to 88%; ee: from
excess 90% to 87%).
1
Synthesis of 3-chloropropyltrimethoxysilane functionalized
GO (CPGO, A)
27,30
GO was prepared as described in the literature.
powder of GO (1 g) was dispersed in 70 ml of dry toluene for 20
min followed by dropwise addition of 3 ml of 3-chloropropyl-
trimethoxysilane, which was diluted in 20 ml dry toluene. The
resulting mixture was heated to reux with continuous stirring
for 24 h under nitrogen atmosphere (Fig. 12). Aer cooling the
mixture, the black powdery sample was ltered, washed with
toluene four times and then washed with EtOH. The solid was
Brown
29
Conclusions
Chiral Mn(III) salen complex was anchored onto CPGO and
characterized by XRD, FT-IR, UV-vis and nitrogen adsorption at
room temperature. The catalyst exhibited high catalytic activity
and selectivity towards the epoxidation of olens. Catalytic tests
ꢁ
dried at 70 C under vacuum for 6 h.
Synthesis of Mn(III) complex immobilized on CPGO
0
showed that the heterogeneous Mn(III) complex is the most (R,R)-N,N -Bis(2,4-di-hydroxybenzaldehyde)-1,2-cyclohexanedi-
31
32
active with m-CPBA as the oxidant in EtOAC. Moreover, the amine and Mn(III) salen complex were prepared as described
heterogeneous Mn(III) complex showed higher yield and enan-
tioselectivity with PNO and MNO, respectively. The catalyst can
be recovered and reused ve runs without any signicant
decrease in reactivity.
Experimental
Materials
3 2 2 2
Tetraethoxysilane (TEOS), FeCl $6H O, FeCl $4H O, styrene, 4-
chlorostyrene, cyclohexene, a-methyl styrene, indene, cis & trans
stilbene, m-chloroperbenzoic acid (m-CPBA), pyridine N-oxide
(PNO), pyridine (Py), 4-methylmorpholine N-oxide (MNO), 1-
methyl imidazole (MI), imidazole (IM), dichloromethane (DCM),
ethyl acetate (EtOAC), ethanol (EtOH), H O , NaIO , NH OAC, t-
2
2
4
4
BOOH, PhI(OAC)2 and oxone were purchased from Merck
Company and used without purication. Graphite powder was
obtained from Aldrich. The resulting GO and heterogeneous
chiral Mn(III) complex (C) were characterized by X-ray diffraction
(XRD), Fourier transform infrared spectra (FT-IR), thermogravi-
metric analysis (TGA), ultraviolet-visible spectra (UV-vis), trans-
mission electron microscopy (TEM), nitrogen adsorption–
desorption isotherm and Atomic absorption spectroscopy (AAS).
The FT-IR experiments were carried out on a Bruker Vector-22 FT-
IR spectrometer (AVATR-370) in a KBr pellet. The XRD
measurements were carried out by using a Bruker D
8
-advance Fig. 12 Schematic illustration for preparation of catalyst.
26092 | RSC Adv., 2014, 4, 26087–26093
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
RSC Advances
in the literature. The synthesized Mn(III) complex (B) was
chemically anchored to the CPGO (A) as described in Fig. 1.
Briey, CPGO (2 g) was dispersed in 140 ml dry toluene for 20
min. Then, 0.6 g of homogeneous Mn(III) complex was added to
the stirring mixture. The resulting suspension was reuxed for
8 H. Zhang, Y. M. Wang, L. Zhang, G. Gerritsen,
H. C. L. Abbenhuis, R. A. Van Santen and C. Li, J. Catal.,
2008, 256, 226–236.
9 R. I. Kureshy, I. Ahmad, N. H. Khan, S. H. R. Abdi, K. Pathak
and R. V. Jasra, J. Catal., 2006, 238, 134–141.
19
2
4 h under inert atmosphere. Aer completion of the reaction, 10 R. I. Kureshy, I. Ahmad, N. H. Khan, S. H. R. Abdi, K. Pathak
the immobilized catalyst was washed with dry toluene, EtOH and R. V. Jasra, Tetrahedron: Asymmetry, 2005, 16, 3562–3569.
and extracted repeatedly on a Soxhlet extractor with methanol 11 H. Zhang, S. Xiang, J. Xiao and C. Li, J. Mol. Catal. A: Chem.,
and dichloromethane until the washing becomes colorless. The
solid was dried at 70 C under vacuum for 6 h. The immobilized 12 V. Mirkhani, M. Moghadam, S. Tangestaninejad,
2005, 238, 175–184.
ꢁ
chiral Mn(III) complex was characterized by XRD, TEM, UV-vis,
FT-IR, AAS, TGA and nitrogen adsorption at room temperature.
B. Bahramian and A. Mallekpoor-Shalamzari, Appl. Catal.,
A, 2007, 321, 49–57.
1
1
3 K. Smith and C. H. Liu, Chem. Commun., 2002, 886–887.
4 X. C. Zou, X. K. Fu, Y. D. Li, X. B. Tu, S. D. Fu, Y. F. Luo and
X. J. Wu, Adv. Synth. Catal., 2010, 352, 163–170.
Catalytic measurements
In a typical procedure, catalyst (2 mol% based on Mn element)
1
1
1
1
1
2
2
2
5 I. Kuzniarska-Biernacka, C. Pereira, A. P. Carvalho, J. Pires
and C. Freire, Appl. Clay Sci., 2011, 53, 195–203.
6 K. Yu, Z. C. Gu, R. N. Ji, L. L. Lou and S. X. Liu, Tetrahedron,
was dispersed in 3 ml of ethyl acetate for 20 min and cooled to
ꢁ
0
C followed by addition of a-methyl styrene as substrate (1
mmol), toluene (internal standard, 40 ml), m-CPBA (2 mmol) as
oxidant and MNO (0.5 mmol) as additive. The mixture was
magnetically stirred at 0 C for appropriate time. The progress
of the reaction was monitored by TLC. Aer completion of the
reaction, the catalyst was separated by centrifugation. The
supernatant was washed with NaOH (1 M, 8 ml), brine (8 ml),
dried over MgSO4 and concentrated to 1 ml. Finally, the
conversion and enantioselectivity values of products were
determined by GC. The catalyst was washed twice with ethanol
and reused.
2009, 65, 305–311.
7 S. Sahoo, P. Kumar, F. Lefebvre and S. B. Halligudi, Appl.
Catal., A, 2009, 354, 17–25.
8 D. A. Annis and E. N. Jacobsen, J. Am. Chem. Soc., 1999, 121,
147–4154.
9 T. Szabo, E. Tombacz, E. Illes and I. Dekany, Carbon, 2006,
4, 537–545.
0 M. Zhou, A. Zhang, Z. Dai, C. Zhang and Y. P. Feng, J. Chem.
Phys., 2010, 132, 194704.
1 M. Stein, J. Wieland, P. Steurer, F. Tolle, R. Mulhaupt and
B. Breit, Adv. Synth. Catal., 2011, 353, 523–527.
2 S. Donner, H. W. Li, E. S. Yeung and M. D. Porter, Anal.
Chem., 2006, 78, 2816–2822.
ꢁ
4
4
Acknowledgements
The authors are grateful to the University of Birjand for nan- 23 S. Pei and H.-M. Cheng, Carbon, 2012, 50, 3210–3228.
cial support.
24 M. Lazghab, K. Saleh and P. Guigon, Chem. Eng. Res. Des.,
010, 88, 686–692.
2
2
2
2
2
2
3
3
3
5 C. Baleiz ˜a o, B. Gigante, M. J. Sabater and H. Garcia, Appl.
Catal., A, 2002, 228, 279–288.
6 B. Jarrais, C. Pereira, A. Rosa Silva, A. P. Carvalho, J. Pires
and C. Freire, Polyhedron, 2009, 28, 994–1000.
7 F. Liu, J. Sun, L. Zhu, X. Meng, C. Qi and F.-S. Xiao, J. Mater.
Chem., 2012, 22, 5495–5502.
8 M. R. Maunja, K. Kumar, S. J. J. Titinchi, H. S. Abbo and
S. Chad, Catal. Lett., 2003, 86, 97–105.
9 H. P. Mungse, S. Verma, N. Kumar, B. Sain and O. P. Khatri,
J. Mater. Chem., 2012, 22, 5427–5433.
References
1
2
3
4
5
6
7
Q. H. Fan, Y. M. Li and A. S. C. Chan, Chem. Rev., 2002, 102,
385–3465.
L. Canali and D. C. Sherrington, Chem. Soc. Rev., 1999, 28,
5–93.
W. Zhang, J. L. Loebach, S. R. Wilson and E. N. Jacobsen,
J. Am. Chem. Soc., 1990, 112, 2801–2803.
3
8
W. Zhang and E. N. Jacobsen, J. Org. Chem., 1991, 56, 2296–
2298.
0 W. S. Hummers and R. E. Offeman, J. Am. Chem. Soc., 1958,
W. Zhang, J. L. Loebach, S. R. Wilson and E. N. Jacobsen,
J. Am. Chem. Soc., 1990, 112, 2801–2803.
R. Irie, K. Noda, Y. Ito, N. Matsumoto and T. Katsuki,
Tetrahedron Lett., 1990, 31, 7345–7348.
K. J. Balkus Jr, A. Khanmamedova, K. Dixon and F. Bedioui,
Appl. Catal., A, 1996, 143, 159–173.
8
0, 1339.
1 J. Lopez, S. Liang and X. R. Bu, Tetrahedron Lett., 1998, 39,
199–4202.
2 H. Vezin, E. Lamour and J. P. Catteau, J. Inorg. Biochem.,
002, 92, 177–182.
4
2
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 26087–26093 | 26093