Chiral Mn(III) salen complexes immobilized directly on pyrolytic waste tire char for asymmetric epoxidation of unfunctionalized olefins

Article abstract of DOI:10.1016/j.inoche.2012.09.001

Two kinds of chiral Mn(III) salen complexes were synthesized and directly immobilized on pyrolytic waste tire char (PWTC) without modification of any organosilicon, which was an economic support, having rich oxy functionalized groups inherently. The as-pr

Full text of DOI:10.1016/j.inoche.2012.09.001

Inorganic Chemistry Communications 25 (2012) 65–69
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Chiral Mn(III) salen complexes immobilized directly on pyrolytic waste tire char for
asymmetric epoxidation of unfunctionalized olefins
Runan Ji a,b, Kai Yu c, Lan-Lan Lou a,b, Cui Zhang a,b, Yan Han a,b, Sheng Pan a,b, Shuangxi Liu a,b,
⁎
a
Institute of New Catalytic Materials Science, College of Chemistry, Nankai University, Tianjin 300071, China
Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of Chemistry, Nankai University, Tianjin 300071, China
b
c
College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 July 2012
Accepted 1 September 2012
Available online 11 September 2012
Two kinds of chiral Mn(III) salen complexes were synthesized and directly immobilized on pyrolytic waste
tire char (PWTC) without modification of any organosilicon, which was an economic support, having rich
oxy functionalized groups inherently. The as-prepared heterogeneous catalysts were characterized by X-ray
photoelectron spectra (XPS), N2 sorption, Fourier transform infrared spectra (FT-IR) and thermogravimetric
analysis (TG), and possessed of good catalytic performance in asymmetric epoxidation of unfunctionalized
olefins. They obtained higher enantiomeric excess (ee) values than that of homogeneous catalysts for asym-
metric epoxidation of 1-phenylcyclehexene and could be recycled three times.
Keywords:
Chiral Mn(III) salen complex
Pyrolytic waste tire char
Heterogeneous catalysts
Asymmetric epoxidation
© 2012 Elsevier B.V. All rights reserved.
Chiral epoxides are useful organic building blocks in the synthesis
of pharmaceuticals and agrochemicals. Chiral Mn(III) salen complexes
are one of the most efficient successful catalysts in the asymmetric
epoxidation of unfunctionalized olefins [1–3]. In recent decades, the
heterogenization of Mn(III) salen complexes has attracted substan-
tial attention as a result of the advantage of easy separation and sim-
ple recycling [4–8] of heterogeneous catalysts. The supports are
adopted for the immobilization of Mn(III) salen complexes, includ-
ing mesoporous silica [9–13], polymers [14–17] and activated carbon
[18–20]. Generally, organosilicons are necessary for the heteroge-
neous Mn(III) salen catalysts immobilized on inorganic supports.
Very few examples [21,22] existed for the achiral transition metal
salen complexes that are anchored directly on activated carbon. To date,
the heterogeneous Mn(III) salen catalyst supported on carbonous mate-
rials, has not been applied in asymmetric epoxidation of unfunctionalized
olefins.
With the rapid development of automobile industry, an enormous
number of waste tires cause a series of environmental problems. How
to deal with these waste tires is common challenge for human beings.
Compared with other technologies of disposing waste tires such as in-
cineration and landfill, pyrolysis of waste tires proves to be a high-
value-added and environmentally friendly technology in numerous
technologies of disposing waste tires. During the pyrolyzing process,
pyrolytic waste tire char (PWTC) as one of the main products is
obtained. It possesses similar structure of carbon black, owning gen-
eral properties of carbonous materials such as high thermal stability,
great corrosion resistance in acid/base and low cost in economy. Spe-
cially, compared with commercial activated carbon, which needs ox-
idation disposal to increase its oxygen content, the surface of PWTC
has rich oxy functional groups inherently without any oxidation pro-
cess, which makes PWTC anchor the catalysts conveniently. Hence,
the PWTC has great potential application in catalysis. In this work,
this novel support was employed and two kinds of chiral Mn(III)
salen complexes were immobilized on PWTC directly without any
silane coupling agent as an anchor for asymmetric epoxidation of
unfunctionalized olefins.
The PWTC needed to be extracted by toluene before using [23]. The
synthesis of heterogeneous catalysts was shown in Scheme 1. The
chiral Mn(III) salen complexes (1 and 2) [24] and PWTC were refluxed
in anhydrous toluene for 24 h under stirring. After the evaporation
of solvent, the obtained catalysts were extracted by dichloromethane
for 12 h. The synthesized heterogeneous Mn(III) salen catalysts were
marked as PWTC-1 and PWTC-2 and evaluated by the epoxidation of
unfunctionalized olefins. The content of Mn was detected by ICP-AES
and the results were 0.167 mmol/g for PWTC-1 and 0.206 mmol/g
for PWTC-2.
PWTC and prepared catalyst PWTC-2 were characterized by X-ray
photoelectron spectra (XPS). The XPS spectrum of PWTC in O1s re-
gion is presented in Fig. 1, and the XPS results are listed in Table 1.
As shown in Fig. 1, the XPS spectrum of PWTC in O1s region could
be deconvoluted into four components, and according to the litera-
ture [25], the peaks of O1s region at 531.2 eV (1) and 534.0 eV (4)
were due to the groups of ketone and carboxylic acid, and other
⁎
Corresponding author at: Institute of New Catalytic Materials Science, College of
Chemistry, Nankai University, Tianjin 300071, China. Tel./fax: +86 22 23509005.
E-mail address: sxliu@nankai.edu.cn (S. Liu).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.inoche.2012.09.001

66
R. Ji et al. / Inorganic Chemistry Communications 25 (2012) 65–69
Scheme 1. The synthesis of heterogeneous chiral Mn(III) salen catalysts.
two peaks at 532.3 eV (2) and 533.3 eV (3) were attributed to the
oxygen atoms of anhydride, lactone or hydroxyl group. As a result of
high temperature during pyrolyzing process, the surface of PWTC was
apt to the synthesis of anhydride. The group of anhydride was an active
esterification agent, which could react with the hydroxyl of Mn(III)
salen complexes, and that was the proposed way of immobilizing
homogeneous catalysts [21]. From Fig. 1 and Table 1, the PWTC was a
born material with rich oxy function groups, especially for the group
of anhydride, so it was very convenient for the immobilization of the
synthesized chiral Mn(III) salen complexes (1 and 2).
Fig. 2 presents the XPS spectra of the heterogeneous catalysts
PWTC-2 in N1s and Mn 2p regions. As shown in Fig. 2(A) and (B),
the peaks at 339.2 eV in N1s region and at 642.1 eV in Mn 2p region
were both characteristic of Mn(III) salen complexes, which was in
agreement with the previous report [26]. It indicated that the struc-
ture of Mn(III) salen complex 2 was kept well after immobilization.
Additionally, the content of Ototal of the heterogeneous catalysts
PWTC-2 increased (seen in Table 2), implying that the Mn(III) salen
complex was anchored.
PWTC and the catalysts PWTC-1 were characterized by N2 sorp-
tion. Fig. 3 shows the isotherms of PWTC and PWTC-1 and the struc-
ture parameters of samples are listed in Table 2. The isotherm of
PWTC in the range of low relative pressure (P/P0 b0.3) is type I iso-
therm, indicating that the supports PWTC possessed microporous
structure. However, because of the rareness of microporous structure,
the N2 quantity absorbed of PWTC was not high and the BET area
of PWTC was only 85 m2/g. In the range of high relative pressure
(P/P0 >0.95), as a result of the cumulation of the pellets of PWTC,
the adsorption quantity of N2 increased sharply, which implied that
the stacking of PWTC grains formed macroporous structure. The sim-
ilar isotherm was obtained for the heterogeneous catalyst PWTC-1,
which accounted for no obvious change in the structure of support.
As shown in Table 2, compared with PWTC, the BET area and pore
(1) 531.2 eV
(2) 532.3 eV
(3) 533.3 eV
(2)
(4) 534.0 eV
(4)
(3)
(1)
Table 1
XPS results of PWTC and PWTC-2 for O1s regions (atom %).
Sample
O1s binding energy (eV)
Ototal (%)
526 528 530 532 534 536 538 540 542
Binding Energy (eV)
531.2
532.3
533.3
534.0
PWTC
PWTC-2
0.4
1.5
2.1
4.5
2.8
3.9
2.5
2.0
7.8
11.9
Fig. 1. The XPS spectrum of PWTC in O1s region.

R. Ji et al. / Inorganic Chemistry Communications 25 (2012) 65–69
67
(A)
300
250
200
150
100
50
A
B
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure(P/P0)
390
395
400
405
410
Binding Energy (eV)
Fig. 3. The N2 sorption isotherms of PWTC and PWTC-1.
(B)
of PWTC. The C\H deformation vibrations of the functionalized
groups on the surface of PWTC were observed between 1450 and
1400 cm−1. In the FT-IR spectrum of PWTC-2 (Fig. 4), the heteroge-
neous catalyst PWTC-2 possessed of all absorption bands of Mn(III)
salen complex 2 and PWTC except that slight shifts were presented
in Fig. 4. It confirmed that the Mn(III) salen complex was anchored
on PWTC successfully.
The thermogravimetry (TG) curves of the samples PWTC and
PWTC-1 are presented in Fig. 5. The weight loss of parent support
PWTC was 22.8% when the temperature got to 1100 °C under the
atmosphere of nitrogen, while the percentage of weight loss of het-
erogeneous catalyst PWTC-1 reached 27.5%. The additional weight
loss of PWTC-1 was attributed to the decomposition of Mn(III) salen
complex 1. It also confirmed that the homogeneous catalyst 1 was
immobilized on the support PWTC.
635
640
645
650
Binding Energy (eV)
The prepared heterogeneous catalysts were evaluated in asym-
metric epoxidation of unfunctionalized olefins. The oxidant was the
solution of NaClO and the substrates were styrene, α-methylstyrene,
indene and 1-phenylcyclohexene. The conversions and enantiomeric
excess (ee) values were determined by gas chromatography (GC).
The results of epoxidation of unfunctionalized olefins catalyzed by
homogeneous and heterogeneous catalysts are shown in Table 3. The
Fig. 2. The XPS spectra of PWTC-2 in (A) N1s region and (B) Mn2p region.
volume of PWTC-1 decreased, due to the blockage of Mn(III) salen
complex 1 at the entrance of micropore of PWTC.
The FT-IR spectra of Mn(III) salen complex 2, the support PWTC
and heterogeneous catalyst PWTC-2 are shown in Fig. 4. For Mn(III)
salen complex 2 and the support PWTC (Fig. 4), the absorption
bands around 2900 cm−1 were due to the C\H stretching vibrations
of alkyl groups. The band at 1547 cm−1 in Fig. 4 was the characteristic
IR absorption band of Mn(III) complexes, attributed to the stretching
vibration of azomethine groups (H\C_N). The C\H deformation
vibrations of Mn(III) complex 2 were located at 1426 cm−1 and
1390 cm−1. In the spectra of parent support PWTC (Fig. 4), the
peaks in the range of 1540–1480 cm−1 were assigned to the C_C
stretching vibrations of polynuclear aromatics structure on the surface
(a)
(a)
(b)
(b)
(c)
(c)
Table 2
The structure parameters of PWTC and heterogeneous Mn(III) salen catalysts PWTC-1
and PWTC-2.
3000 2950 2900 2850
1550
1500
1450
1400
Sample
SBET (m2g−1
)
Pore volume (cm3g−1
)
Wavenumber(cm-1)
PWTC
PWTC-1
PWTC-2
85
68
57
0.28
0.14
0.22
Fig. 4. The FT-IR spectra of (a) Mn(III) salen complex 2, (b) the support PWTC and (c) the
heterogeneous catalyst PWTC-2.

68
R. Ji et al. / Inorganic Chemistry Communications 25 (2012) 65–69
100
95
90
85
80
75
70
Table 4
The recycle results of asymmetric epoxidation of styrene catalyzed by heterogeneous
catalysts PWTC-1.
A
B
Catalyst
PWTC-1
Substrate
Styrene
Time (h)
48
Conv. (%)
ee (%)
1st
2nd
3rd
>99
>99
72.1
49.0 (1R)
51.2 (1R)
44.8 (1R)
aReactions were carried out in CH2Cl2 (3 mL) with substrate (1 mmol), toluene (internal
standard, 1 mmol), PPNO (0.38 mmol), catalysts (1.5 mol%) and NaClO (3 mmol) at 273 K.
bThe conversion was determined by gas chromatography using toluene as internal
standard and calculated by ([substrate]0-[substrate])/[substrate]0×100%.
cThe ee value was determined by gas chromatography with chiral β-cyclodextrin cap-
illary column (RESTEK RT-BetaDEXse, 30 m×0.25 mm×0.25 μm) and was calculated
by |([R]−[S])|/([R]+[S])×100%.
Weight loss:22.8%
Weight loss:27.5%
200
400
600
800
1000
the fourth recycling the conversion decreased to 17.2%, which may be
due to the loss of PWTC-1 during the process of filtrating and the cover-
age of active species by the salt produced in the reaction. So the catalyst
could not be reused further.
o
Temperature( C)
Fig. 5. The curves of TG analysis of PWTC and PWTC-1.
In summary, two kinds of Mn(III) salen complexes 1 and 2 were
immobilized on PWTC without any organosilane. The structure of
supports was kept well and the property of Mn(III) complex did not
change during the preparation of heterogeneous catalyst (PWTC-1
and PWTC-2). The synthesized heterogeneous catalysts obtained
high conversions and enantioselectivities in the asymmetric epoxida-
tion of unfunctionalized olefins, and notably, they obtained higher
enantioselectivity than the homogeneous catalysts in the epoxidation
of 1-phenylcyclohexene. The heterogeneous catalysts could be reused
three times.
heterogeneous catalysts PWTC-1 and PWTC-2 obtained high conver-
sions, and the conversions of substrates were all >90% after 48 h. In
the epoxidation of styrene and indene, PWTC-1 obtained almost the
same ee values as the homogeneous catalyst 1 (entries 1, 2, 7 and 8),
while PWTC-2 showed slightly lower enantioselectivities compared
with the homogeneous catalyst 2 (entries 3, 4, 9 and 10). Particularly,
in the epoxidation of 1-phenylcyclohexene, the heterogeneous cata-
lysts PWTC-1 and PWTC-2 catalyzed this reaction with 61.9% and
66.1% ee values, respectively (entries 12 and 14), which were higher
than the results obtained by the homogeneous catalysts (50.4% and
60.9%). The increase of ee values might be attributed to the positive
confinement effect of the surface of PWTC [27]. In other words, the
size of 1-phenylcyclohexene was comparable with the space which
was built by Mn(III) salen complex and the surface of PWTC [28].
The recycle results of asymmetric epoxidation of styrene catalyzed
by heterogeneous catalyst PWTC-1 are listed in Table 4. As shown
in Table 4, the catalysts possessed the ability of recycling, and the cat-
alyst PWTC-1 could be reused three times. The filtrate was analyzed
by ICP-AES, and a little Mn leaching (3%) was detected. However, in
More details about the experiment and characterizations of het-
erogeneous catalysts can be seen in supporting information (SI).
Acknowledgements
We acknowledge the support from the National Natural Science
Foundation of China (grants 21203102 and 21003077), Key Program
of Municipal Natural Science Foundation of Tianjin (08JCZDJC21400),
the Specialized Research Fund for the Doctoral Program of Higher
Education (grant 20100031120029) and the Fundamental Research
Funds for the Central Universities.
Table 3
The results of asymmetric epoxidation of unfunctionalized olefins catalyzed by homogeneous and heterogeneous catalysts.a
Entry
Catalyst
Substrate
Styrene
Time (h)
Conv. (%)b
ee (%)c
Sele. (%)d
TOFe×10-4 (s-1
)
1
2
3
4
5
6
7
8
1
2
48
2
48
2
48
2
48
2
48
2
48
2
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
48.8 (R)
49.0 (R)
33.7 (R)
29.1 (R)
42.3 (1R)
39.3 (1R)
66.9 (1R,2S)
68.4 (1R,2S)
71.1 (1R,2S)
65.6 (1R,2S)
50.4 (1S,2S)
61.9 (1S,2S)
60.9 (1S,2S)
66.1 (1S,2S)
96.9
97.2
96.9
96.3
94.4
91.1
88.9
50.3
66.9
85.8
95.2
>99
93.2
>99
34.7
1.45
34.7
1.45
34.7
1.45
34.7
1.45
34.7
1.45
34.7
1.45
34.7
1.45
PWTC-1
2
PWTC-2
2
PWTC-2
1
PWTC-1
2
PWTC-2
1
PWTC-1
2
α-Methylstyrene
Indene
9
10
11
12
13
14
1-Phenylcyclohexene
PWTC-2
48
a
Reactions were carried out in CH2Cl2 (3 mL) with substrate (1 mmol), toluene (internal standard, 1 mmol), PPNO (0.38 mmol), catalysts (1.5 mol%) and NaClO (3 mmol) at
273 K.
b
c
The conversion was determined by GC using toluene as internal standard and calculated by ([substrate]0-[substrate])/[substrate]0×100%.
The ee value was determined by GC with chiral β-cyclodextrin capillary column (RESTEK RT-BetaDEXse, 30 m×0.25 mm×0.25 μm) and was calculated by |([R]−[S])|/
([R]+[S])×100%.
d
The selectivity of epoxide was determined by GC and calculated by [epoxide]/[product]×100%.
TOF was calculated by [product]/([catalyst]×time).
e

R. Ji et al. / Inorganic Chemistry Communications 25 (2012) 65–69
69
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Appendix A. Supplementary material
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