Enantioselective epoxidation of nonfunctionalized alkenes catalyzed by recyclable new homochiral bis-diamine-bridged bi-Mn(salen) complexes

Article abstract of DOI:10.1007/s11426-012-4829-x

Three new homochiral bis-diamine-bridged bi-Mn(salen) complexes were synthesized. Their catalysis on asymmetric epoxidation of α-methylstyrene, styrene and indene was studied with NaClO and m-CPBA as oxidants respectively. This homogeneous catalyst exhibited comparable catalytic activity and enantioselectivity to the Jacobsen's catalyst in the asymmetric epoxidation of unfunctionalized olefins. Furthermore, the catalyst could be conveniently recovered and reused at least five times without significant losses of both activity and enantioselectivity. Specially, it also could be efficiently used in large-scale reactions with superior catalytic disposition being maintained at the same level, which provided the potential for the applications in industry. The effect of axial bases, temperature and solvent on activity and enantioselectivity of the catalytic system were also studied.

Full text of DOI:10.1007/s11426-012-4829-x

SCIENCE CHINA
Chemistry
May 2013 Vol.56 No.5: 604–611
doi: 10.1007/s11426-012-4829-x
• ARTICLES •
Enantioselective epoxidation of nonfunctionalized alkenes
catalyzed by recyclable new homochiral
bis-diamine-bridged bi-Mn(salen) complexes
HUANG XueMei1, 2, FU XiangKai1, 2, 3*, JIA ZiYong1, 2, MIAO Qiang1, 2 & WANG GuoMing1, 2
1College of Chemistry and Chemical Engineering, Research Institute of Applied Chemistry Southwest University,
Chongqing 400715, China
2The Key Laboratory of Applied Chemistry of Chongqing Municipality, Chongqing 400715, China
3The Key Laboratory of Eco-environments in Three Gorges Reservoir Region Ministry of Education, Chongqing 400715, China
Received August 28, 2012; accepted October 15, 2012; published online January 22, 2013
Three new homochiral bis-diamine-bridged bi-Mn(salen) complexes were synthesized. Their catalysis on asymmetric epoxida-
tion of α-methylstyrene, styrene and indene was studied with NaClO and m-CPBA as oxidants respectively. This homogeneous
catalyst exhibited comparable catalytic activity and enantioselectivity to the Jacobsen’s catalyst in the asymmetric epoxidation
of unfunctionalized olefins. Furthermore, the catalyst could be conveniently recovered and reused at least five times without
significant losses of both activity and enantioselectivity. Specially, it also could be efficiently used in large-scale reactions with
superior catalytic disposition being maintained at the same level, which provided the potential for the applications in industry.
The effect of axial bases, temperature and solvent on activity and enantioselectivity of the catalytic system were also studied.
homochiral bi-Mn(salen) complex, enantioselective, asymmetric epoxidation, unfunctionalized olefins
thetic chemistry and industrial processes. To address the
1 Introduction
issue, significant effort has been made to “heterogenize” the
Jacobsen chiral salen Mn(III) complex, such as grafting
chiral Mn(salen)Cl complexes monomeric catalyst systems
onto organic polymers [3], inorganic supports clays [4],
MCM-41 [5], SBA-15 [6], activated silica [7], zeolites [8]
and organic polymer-inorganic hybrid phosphate-phosphonate
materials [917]. Unfortunately, although the immobilized
catalysts showed the advantages of easy separation and re-
using, significant gaps still existed in the scope of these
methodologies. First, compared with the homogeneous coun-
terparts, the immobilized complexes generally need some
modifications of the supports which lead to the complicated
synthesis and high costs. Second, the leaching of salen
Mn(III) complexes during reaction is often troublesome.
Third, most of modified catalysts are less efficient than their
corresponding unmodified catalysts, partly, because of the
inaccessibility of the reagents to the active centers in the
Asymmetric epoxidation of unfunctionalized olefins is
highly significant in synthesis of chiral epoxides which are
versatile intermediates in the pharmaceutical and various
fine chemicals fields. It’s still a challenge to get the excel-
lent enantioselectivity epoxides in high yields. Recently,
chiral salen Mn (III) complexes have been reported to give
high enantioselectivity in the epoxidation of unfunctional-
ized olefins. Among them, Jacobsen’s catalyst and its ana-
logues showed prominent advantages [1]. However, de-
composition of the catalyst and formation of inactive di-
meric -oxo-Mn(VI) [2] lead to the problems of separation
and recyclability of the catalyst, which limited the practical
applications of chiral Mn(III) salen catalysts in both syn-
*Corresponding author (email: fxk@swu.edu.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2013
chem.scichina.com www.springerlink.com

Huang XM, et al. Sci China Chem May (2013) Vol.56 No.5
605
heterogeneous reaction [18]. Thus, the development of a
novel class of catalyst with high activity, enantioselectivity
and easily separation from the reaction mixture is highly
desirable. As we known, appropriately increased the molec-
ular weight of the catalysts could lower their solubility in
certain solvents, thus opening a door for product isolation
and catalyst recovery [19]. Additionally, increasing the cat-
alytically active metal centers of the catalysts could enhance
the catalytic activities and recover the catalyst easily [20,
21]. Recently, a great number of dimeric [22–25] and pol-
ymeric homochiral Mn(III) salen complexes [26–28], linked
through side chain as homogenous catalysts, have been re-
ported. These dimeric or polymeric complexes, with in-
creased number of active reaction sites, showed higher ac-
tivities and turnover frequency compared with their corre-
sponding monomeric counterparts. Unfortunately, the enan-
tioselectivity was disappointed and the synthesized steps
were still problems. Zhang et al. [29] have reported that
axial coordination of the catalyst could improve the enanti-
oselectivities in the asymmetric epoxidation of unfunction-
alized olefins. According to this, we herein designed and
synthesized a series of bis-diamine-bridged bi-Mn(salen)
complexes as homogeneous catalysts (Scheme 1). The pre-
pared catalysts displayed superior catalytic activities and
enantioselectivities in the asymmetric epoxidation of
-methylstyrene and indene with m-CPBA and NaClO as
the oxidants, especially for -methylstyrene showed conv. up
to 99% and ee up to 99%. And the catalyst could be easily
recovered and reused five times without significant losses of
both activity and enantioselectivity. Furthermore, it could
also be efficiently used in large-scale reactions with the
enantioselectivity being maintained at the same level, which
provided the potential for applications in industry.
2 Experimental
2.1 Materials and methods
(1R,2R)-(-)-1,2-Diaminocyclohexane, indene, -methylstyrene,
n-nonane, N-methylmorpholine N-oxide (NMO), m-chloro-
perbenzoic acid (m-CPBA), NaClO and 4-PPNO were sup-
plied by Alfa Aesar. Other commercially available chemi-
cals were laboratory-grade reagents from local suppliers and
used as supplied without further purification. Chiral salen
ligand and chiral homogeneous catalyst salen Mn(III) were
synthesized according to the standard literature procedures
[30].
FT-IR spectra were recorded from KBr pellets using a
Bruker RFS100/S spectrophotometer (USA) and diffuse
reflectance UV-Vis spectra of the solid samples were rec-
orded in the spectrophotometer with an integrating sphere
1
using BaSO4 as standard. H NMR and 13C NMR were per-
Scheme 1 Synthesis of bis-diamine-bridged bi-Mn(salen) complexes (3a–3c).

606
Huang XM, et al. Sci China Chem May (2013) Vol.56 No.5
2c: Yield 88%; 1H NMR (300 MHz, DMSO-d6):  (ppm)
2.25 (s, 12H), 4.15 (s, 4H), 5.01 (s, 4H), 5.33 (s, 2H), 6.60
(d, J = 9.0 Hz, 4H), 6.74 (d, J=6.2 Hz, 4H), 7.24 (d, J=9.0
Hz, 4H), 7.30 (d, J = 6.2 Hz, 4H); IR (KBr, cm1): ν = 3391,
3324, 3210(N-H), 2982, 2920, 2860(C–H), 1609, 1508(–C6H5),
1384–1349(C–N), 825(N–H) cm1; Anal. Calcd. for
C24H30N4: C, 76.97; H, 8.07; N, 14.96%. Found: C, 76.95;
H, 8.04; N, 14.95%.
formed on AV-300 NMR instrument at ambient temperature
of 300 and 121 MHz. All of the chemical shifts were re-
ported downfield in ppm relative to the hydrogen resonance
of TMS. The conversions (with n-nonane as internal stand-
ard) and the ee values were analyzed by gas chromatog-
raphy (GC) with a Shimadzu GC2010 (Japan) instrument
equipped using a chiral column (HP19091G-B233, 30 m ×
25 m × 0.25 m) and FID detector, injector 230 °C, detector
230 °C. The column temperature was in the range of
80–150 °C.
Bis-diamine-bridged bi-Mn(salen) complexes (3a3c)
Bis-diamine derivative axially coordinated ligands 2a–2c
(1.5 mmol), chiral Jacobsen’s catalyst (4.5 mmol, 3 equiv)
and NaOH (4.5 mmol) in THF (25 mL) was vigorously
stirred for 24 h under reflux. The dark brown powder was
collected by filtration and washed thoroughly with ethanol,
and deionized water respectively, then dissolved in CH2Cl2,
filtrated, and the filtrate was collected, evaporated under
reduced pressure, dried under vacuum.
2.2 Synthesis of bis-diamine-bridged bi-Mn(salen) com-
plexes
1,4-Bis(bromomethyl)-2,3,5,6-tetramethylbenzene (1)
1,2,4,5-Tetramethylbenzene (8.04 g, 6.0 mmol), paraform-
aldehyde (5.4 g, 180 mmol, 3 equiv) and potassium bromide
(23.42 g, 180 mmol, 3 equiv) were mixed with 80 mL acetic
acid at room temperature. Then the mixed solution of 10
mL concentrated sulfuric acid (180 mmol, 3 equiv) and 10
mL acetic acid (180 mmol, 3 equiv) was added dropwise.
The solution was vigorously stirred with mechanical agita-
tion overnight at 95 °C. The grey solid was collected by
filtration and extracted with CH2Cl2. The yellow solid was
obtained by evaporation of the filtrate under reduced pres-
sure. The crude product was crystallized by ethyl acetate to
3a: Yield 90%; IR (KBr, cm1): ν = 3393(NH), 2914,
2871(C–H), 1630(C=N), 1605, 1510(–C6H5), 1350–1245
(C–N), 820(N–H), 519(Mn–O) cm1 (Figure S1 in the Sup-
porting Information); UV-Vis: (CH2Cl2) max 330, 421, 503;
Anal. Calcd. for C96H132Mn2N8O4: C, 73.35; H, 8.46; N,
7.13%. Found: C, 73.31; H, 8.44; N, 7.10%.
3b: Yield 84%; IR (KBr, cm1): ν = 3410(N–H), 2982,
2864(C–H), 1630(C=N), 1613 1502(–C6H5), 1350–1239
(C–N), 809(N–H), 505(Mn–O) cm1 (Figure S1); UV-Vis:
(CH2Cl2) max 340, 429, 512 (Figure S2 in the Supporting
Information); Anal. Calcd. for C108H140Mn2N8O4: C, 75.23;
H, 8.18; N, 6.50%. Found: C, 75.20; H, 8.15; N, 6.48%.
3c: Yield 86%; IR (KBr, cm1): ν = 3397(N–H), 2923,
2868(C–H), 1629(C=N), 1607, 1501(–C6H5), 1349–1250
(C–N), 872(N–H), 510(Mn–O) cm1 (Figure S1); UV-Vis:
(CH2Cl2) max 321, 415, 496. Anal. Calcd. for C96H132Mn2N8O4:
C, 73.35; H, 8.46; N, 7.13%. Found: C, 73.32; H, 8.43; N,
7.11%.
1
obtain white needle crystal 1 in a yield of 87%. H NMR
(300 MHz, CDCl3):  (ppm) = 2.33 (s, 12H), 4.60 (s, 4H);
13C NMR (75 MHz, CDCl3):  = 134.4, 133.8, 30.7, 15.6;
IR (KBr, cm1): ν = 2921.2, 1618.8, 1433.4, 507.4 cm1.
C2-symmetrical bis-diamine ligands (2a2c)
Diamine (25 mmol, 2.5 equiv) and sodium hydroxide (1 g,
25 mmol, 2.5 equiv) in 50 mL absolute THF, and 1,4-
bis(bromomethyl)-2,3,5,6-tetramethylbenzene (3.17 g, 10
mmol) in 20 mL absolute THF was added dropwise. The
mixture was then vigorously stirred for 24 h at 65 °C under
N2 protection. After cooled to room temperature, the precip-
itate was filtered off, washed with ethanol, distilled water,
Na2CO3 (5%), respectively, and the product 2 was obtain
after dried under vacuum.
2.3
Synthesis of arylamine modified chiral salen
Mn(III) catalyst 4
The arylamine modified chiral salen Mn(III) catalyst were
prepared according to similar procedure to bis-diamine-
bridged bi-Mn(Salen) catalysts [16] (Scheme 2).
2a: Yield 82%; 1H NMR (300 MHz, DMSO-d6):
 (ppm) 2.22 (s, 12H), 4.00 (s, 4H), 4.47 (s, 6H), 6.37–6.62
(m, 8H); IR (KBr, cm1): ν = 3427, 3391, 3348(N–H), 2969,
2894, 2874(C–H), 1612, 1501(–C6H5), 1350–1241(C–N),
810(N–H) cm1; Anal. Calcd. for C24H30N4: C, 76.97; H,
8.07; N, 14.96%. Found: C, 76.94; H, 8.03; N, 14.94%.
2b: Yield 85%; 1H NMR (300 MHz, DMSO-d6):  (ppm)
2.22 (s, 12H), 4.05 (s, 4H), 4.73 (s, 4H), 4.93 (s, 2H), 6.01
(m, 6H), 6.74 (t, J = 6.2 Hz, 2H); IR (KBr, cm1): ν = 3418,
3378, 3309(N–H), 2982, 2869(C–H), 1612, 1501 (–C6H5),
1360–1241(C–N), 810(N–H) cm1 (in Figure S1); Anal.
Calcd. for C36H30N4: C, 82.09; H, 7.27; N, 10.64%. Found:
C, 82.06; H, 7.25; N, 10.61%.
2.4 General procedures for enantioselective epoxida-
tion
All catalytic reactions were performed under laboratory
atmosphere. The course of the product formation was mon-
itored by GC analysis. A working model of the bis-diamine-
bridged bi-Mn(salen) complex was showed in Figure 1.
Epoxidation of olefins were carried out in two methods.
Method A. A solution of 1.0 mmol of olefin in 4.0 mL of
CH2Cl2, the homogeneous diamine-bridged bi-Mn(salen)

Huang XM, et al. Sci China Chem May (2013) Vol.56 No.5
607
Scheme 2 Synthesis of arylamine modified chiral salen Mn(III) catalyst 4.
was added to the reaction mixture after the reactions.
Thereafter, the organic phase was separated, and the catalyst
was washed with hexane and deionized water, and dried
over vacuum at 60 °C for subsequent use without further
purification.
2.6 Large-scale asymmetric epoxidation
In order to see the catalyst’s potential industrial applications,
we performed large-scale asymmetric epoxidation reactions.
The amount of reagents was -methylstyrene (25 mmol),
n-nonane (12.5 mmol), catalyst 3b (0.375 mmol), NaClO
(92.5 ml, 50 mmol, 0.55 M, pH = 11.3), 4-PPNO (12.5
mmol). The organic layer was dried over sodium sulfate.
The catalyst was precipitated out from the solution by add-
ing hexane and kept for subsequent use without further
purification. The conversion and ee values of the epoxide
were determined by GC.
Figure 1 A working model of diamine-bridged dimeric Mn(salen) com-
plex.
complexes 3a–3c (0.015 mmol), n-nonane (internal standard,
1 mmol) and 4-PPNO (0.50 mmol) was cooled to the de-
sired temperature. Pre-cooled NaClO solution (3.7 mL, 2.0
mmol, 0.55 M, pH = 11.3) was added to the solution. When
the reaction was completed (as monitored by TLC), the
phases were separated and the aqueous layer was extracted
with CH2Cl2 (2.0 mL × 3). The combined organic layers
were washed with brine (2.0 mL × 3) and dried over anhy-
drous Na2SO4. The conversion and ee values of the epoxide
were determined by GC.
3 Results and discussion
3.1 Asymmetric epoxidation of non-functionalized ole-
fins catalyzed by 3a–3c with m-CPBA and NaClO as
oxidants
Method B. A solution of 1.0 mmol of olefin, the homo-
geneous diamine-bridged bi-Mn(salen) complexes 3a–3c
(0.015 mmol), n-nonane (internal standard, 1 mmol) and
NMO (N-methylmorpholine N-oxide) (5.0 mmol) in 4 mL
CH2Cl2, was cooled to the appropriate temperature, after
which pre-cooled solid m-CPBA (2.0 mmol) was added in
portions over 5 minutes. When the reaction was completed
(as monitored by TLC), NaOH (4 mL, 1.0 M) was added,
the phases were separated and the aqueous layer was ex-
tracted with CH2Cl2 (2.0 mL × 3). The combined organic
layers were washed with brine (2 mL × 2) and dried over
anhydrous Na2SO4. The conversion and ee values of the
epoxide were determined by GC.
Enantioselective epoxidations of indene, styrene, -methy-
lstyrene by the prepared catalysts 3a3c were studied with
m-CPBA/NMO or NaClO/PPNO as an oxidant system in
CH2Cl2 at defined temperature. Jacobsen’s catalyst and
monomer chiral salen Mn(III) catalysts 4a–4b were also
examined for comparison purposes. Conversions and enan-
tiomeric excess values were determined by gas chromatog-
raphy. The results were presented in Table 1. As described
in Table 1, in the two oxidant system, the bi-Mn(salen) cat-
alysts showed higher conversions and ee values than Jacob-
sen’s catalyst 2 and the monomeric catalysts 4a and 4b in
the asymmetric epoxidation of indene, styrene and α-meth-
ylstyrene under identical reaction conditions. For example,
in the m-CPBA/NMO oxidant system, 98% conversion and
99% ee were obtained in the asymmetric epoxidation of
indene. In the NaClO/PPNO oxidant system, 99% conver-
sion and 94% ee were obtained in the asymmetric epoxida-
tion of α-methylstyrene (Figure S3 in the Supporting Infor-
2.5 Recycling of the bis-diamine-bridged bi-Mn(salen)
complexes
In a typical recycle experiment, the equal volume of hexane

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Huang XM, et al. Sci China Chem May (2013) Vol.56 No.5
Table 1 Asymmetric epoxidation of alkenes catalyzed by 3a–3c with m-CPBAa) and NaClOb) as oxidants
Entry
1
Substrate
Catalyst
Oxidant
T (°C)
20
20
20
20
20
20
20
20
Time (h)
Conv. (%)
95
97
95
96
78
98
99
90
95
67
97
99
92
90
92
93
95
98
90
92
94
97
87
86
90
92
98
99
84
88
90
93
ee (%) c)
57
64
72
85
53
90
92
47
89
52
90
94
65
78
72
87
90
99
72
80
87
91
31
35
42
45
50
62
42
51
55
67
2-methylstyrene
2-methylstyrene
2-methylstyrene
2-methylstyrene
2-methylstyrene
2-methylstyrene
2-methylstyrene
2-methylstyrene
2-methylstyrene
2-methylstyrene
2-methylstyrene
2-methylstyrene
Jacobsen
m-CPBA/NMO
m-CPBA/NMO
m-CPBA/NMO
m-CPBA/NMO
m-CPBA
4
4
4
4
4
4
4
6
6
6
6
6
4
4
4
4
4
4
6
6
6
6
4
4
4
4
4
4
6
6
6
6
2
4a
3
4b
4
3a
5
3a
6
3b
m-CPBA/NMO
m-CPBA/NMO
NaClO/PPNO
NaClO/PPNO
NaClO
7
3c
8
Jacobsen
9
3a
20
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
3a
20
3b
NaClO/PPNO
NaClO/PPNO
m-CPBA/NMO
m-CPBA/NMO
m-CPBA/NMO
m-CPBA/NMO
m-CPBA/NMO
m-CPBA/NMO
NaClO/PPNO
NaClO/PPNO
NaClO/PPNO
NaClO/PPNO
m-CPBA/NMO
m-CPBA/NMO
m-CPBA/NMO
m-CPBA/NMO
m-CPBA/NMO
m-CPBA/NMO
NaClO/PPNO
NaClO/PPNO
NaClO/PPNO
NaClO/PPNO
20
3c
20
indene
indene
indene
indene
indene
indene
indene
indene
indene
indene
styrene
styrene
styrene
styrene
styrene
styrene
styrene
styrene
styrene
styrene
Jacobsen
20
20
20
20
20
20
20
4a
4b
3a
3b
3c
Jacobsen
3a
20
3b
20
3c
20
Jacobsen
4a
20
20
20
20
20
20
20
4b
3a
3b
3c
Jacobsen
3a
20
3b
20
3c
20
a) Reactions were carried out at desired temperature in CH2Cl2 (4 mL) with alkene (1.0 mmol), m-CPBA(2.0 mmol), NMO (5.0 mmol, if necessary),
nonane (internal standard, 1.0 mmol) and catalysts (0.015 mmol). The conversion and the ee value were determined by GC with chiral capillary columns
(HP19091G-B233, 30 m × 25 m × 0.25 m); b) reactions were carried out at desired temperature in CH2Cl2 (4 mL) with alkene (1.0 mmol), NaClO (3.7 ml,
2.0 mmol, 0.55 M, pH = 11.3), 4-PPNO (0.5 mmol, if necessary), nonane (internal standard, 0.5 mmol) and catalysts (0.015 mmol). The conversion and the
ee value were determined by GC with chiral capillary columns (HP19091G-B233, 30 m × 25 m × 0.25 m); c) (S)-form.
mation). However, Hu et al. [31] reported that the ethyldia-
mine-bridged bi-Mn(salen) complexes catalyzed enantiose-
lective epoxidation of α-methylstyrene only got 33% yield
and had no enantiomeric excess values. The results were
also better than the previously reported -CH2- linked dimeric
Mn(III) salen complex [24] with the ee values only 20–30%
for epoxidation of α-methylstyrene. To the best of our
knowledge, the highest ee value of α-methylstyrene is 78%
known from the literatures [5] with heterogeneous Mn(salen)
catalysts immobilized in inorganic support via multi-step
grafting. The excellent results in this text were due to the
increased local concentration of the active sites for the
bis-diamine-bridged bi-Mn(salen) complexes, and the co-
operative interaction [18, 21] between the two metal centers
presented in the catalysts that were not working in isolation.
Moreover, diamine group in bis-diamine-bridged bi-Mn(salen)
complexes can facilitate the electron transfer between the
Mn(salen) complexes [31]. Meanwhile, the monomeric cat-
alysts 4a and 4b also showed higher ee values than the
Jacobsen’s catalyst with the same level of conversions.
Based on above, it indicates that the rigid linker, coordina-
tion method and increased active metal centers were devot-
ed to the increase of ee values. Moreover, catalyst 3c got the
better results than 3a and 3b in both the two oxidation sys-
tems. It was probably due that the axial coordinating ligand
2c has stronger electron-donating character than 2a and 2b,
and the olefins can approach to the Mn-oxo center more
expediently with the increase of linkage lengths. The same
results were also obtained by Li et al. [32].
Chiral Mn(III) salen complexes are sensitive to the
choice of the solvent and it has been reported [33] that 15
mol% monomeric Jacobsen catalyst loading resulted in cy-
anochromene epoxide yield 67%, ee’s 85% in 15 min and
yield 61%, ee’s 19.8% in 12 h in acetonitrile and CH2Cl2

Huang XM, et al. Sci China Chem May (2013) Vol.56 No.5
609
Table 2 Data for the enantioselective epoxidation of indene with NaClO a)
catalyzed by the catalyst 3b using different solvents at 20 °C
respectively. In view of this, the effect of solvents using
complex 3b as catalyst in the epoxidation of indene was
studied (Table 2). The considerable decrease of enantiose-
lectivity caused by the use of toluene and hexane as solvents
may be due to the polarity of these solvents in comparison
with dichloromethane. Acetonitrile and tetrahydrofuran
which moderately dissolves complex 3b, can take part in
coordination on the Mn centre, competing with indene co-
ordination, hence leading to the lower yields observed
compared with dichloromethane as solvent. The solvent
dichloromethane dissolves complex 3b completely yielded
94% conversion with 87% ee’s. Hence, dichloromethane
turned out to be the most suitable solvent for the present
epoxidation studies.
Entry
Solvent
toluene
hexane
THF
Time (h)
Con. (%)
ee (%) b)
45
1
2
3
4
5
6
6
6
6
6
89
72
46
28
94
36
69
CH3CN
DCM
76
87
a) The reactions were carried out using the same method with Table 1.
The conversion and the ee value were determined by GC with chiral capil-
lary columns (HP19091G-B233, 30 m × 25 m × 0.25 m); b) (S)-form.
a)
Table 3 Effect of temperature on epoxidation of indene with m-CPBA
catalyzed by the catalyst 3b
We further researched the effect of the temperature for
the epoxidation of α-methylstyrene using m-CPBA as the
oxidant (Table 3). A decrease of reaction temperature from
0 to 78 °C led to the decrease of the conversion from 99 to
90%. However, an increase of enantioselectivity (86% to
99%) was observed, which was consistent with the conclu-
sion reported in reference [25]. The reaction rate was de-
creased with the decrease of temperature.
Entry
T (°C)
0
Time (h)
Conv. (%)
ee (%) b)
86
1
2
3
4
4
5
99
98
95
90
90
20
40
78
7
93
10
99
a) Reactions were carried out at desired temperature in CH2Cl2 (4 mL)
with alkene (1.0 mmol), m-CPBA(2.0 mmol), NMO (5.0 mmol), nonane
(internal standard, 1.0 mmol) and catalysts (0.015 mmol). The conversion
and the ee value were determined by GC with chiral capillary columns
(HP19091G-B233, 30 m × 25 m × 0.25 m); b) (S)-form.
It is well known that the axial base acts as an additional
donor ligand by forming a strong bond with the transition-
meter center, which endows it with a dual role in activating
the catalyst and stabilizing the oxo intermediate [34, 35].
The effects of various axial bases, such as PyNO, NMO,
4-PhPyNO and 4-PPPyNO, as well as their different
amounts on the asymmetric epoxidation of indene in the
presence of the complex 3b were investigated and the re-
sults were listed in Table 4. As expected, a rather low yield
of the epoxide with a relatively low enantioselectivity was
obtained in the absence of additive axial base (entry 1),
whereas the addition of axial base led to the increase of the
yield and enantioselectivity of the epoxide (entries 2–9),
suggesting that the presence of axial base is essential to the
asymmetric epoxidation of indene. Also, the amount of
various axial bases had a crucial influence on the yield and
enantioselectivity of the epoxide. In general, with an in-
creased amount of the axial base, the yield of the epoxide
reached a maximum level then decreased and the enanti-
oselectivity increased until a constant level was reached
(entries 2–6). When adding 1 mmol of 4-PhPyNO or
4-PPPyNO in the reaction system, the maximum yield and
enantioselectivity of target product was obtained (entries 8,
9). An excess of axial base would lower the activity of the
catalyst, thus resulting in a decrease of the yield of target
product, but with no effect on the enantioselectivity. As a
result, adding 0.5 mmol 4-PPNO to the NaClO oxidant sys-
tem could obtain the best results.
Table 4 Effect of donor ligands on the on epoxidation of indene with
NaClO a) catalyzed by the catalyst 3b at 20 °C
Entry
Axial base (mmol)

ee (%) b)
48
Conv. (%)
1
2
3
4
5
6
7
8
9
65
86
94
92
87
75
89
78
84
4-PPNO(0.2)
4-PPNO(0.5)
4-PPNO(1.0)
4-PPNO(1.5)
4-PPNO(2.0)
PyNO (0.5) c)
4-PhPyNO (1) c)
4-PPPyNO (1) c)
74
87
85
86
88
58
74
82
a) Reactions were carried out at desired temperature in CH2Cl2 (4 mL)
with alkene (1.0 mmol), NaClO (3.7 ml, 2.0 mmol, 0.55 M, pH = 11.3),
different axial base, nonane (internal standard, 0.5 mmol) and catalysts
(0.015 mmol). The conversion and the ee value were determined by GC
with chiral capillary columns (HP19091G-B233, 30 m × 25 m × 0.25 m).
b) (S)-form; c) the optimum amount.
plexes were very soluble in dichloromethane, but almost
insoluble in hexanes and diethyl ether. Based on the solubil-
ity of our bi-Mn(salen) complexes mentioned above, the
catalysts was precipitated in hexane for recovery from the
concentrated reaction mixture (Figure 2). The solid can be
conveniently isolated by filtration, and then dissolved in
dichloromethane for another reaction. Experimental study
of the recovery and recyclability was conducted using com-
plex 3b as the catalyst, the epoxidation of α-methylstyrene
with aqueous NaClO/4-PPNO as an oxidant under opti-
mized reaction conditions.
3.2 The recycling of the chiral bi-Mn(salen) complexes
We are also interested in recycling the catalysts in the ee’s
of the epoxidation. It was found that the bi-Mn(salen) com-
Despite the possible loss of catalyst during the recovery

610
Huang XM, et al. Sci China Chem May (2013) Vol.56 No.5
Table 6 Large-scale asymmetric epoxidation reaction of -methylstyrene a)
and reuse process, the recycling experiments were success-
fully carried out up to five times. The recycling data were
listed in Table 5. As can be seen, 87% conversion and 86%
ee value were obtained in the fifth reaction with only a
small decrease in catalytic activity compared to the fresh
catalyst. Slightly decreased conversion and ee values were
attributed to the minor physical losses of the catalyst in the
post-epoxidation work up. The amount of Mn in catalyst 3b
was calculated by AAS after five runs. The result indicated
that 15% of the Jacobsen salen Mn gradually degradated
from the catalyst 3b under the epoxidation conditions.
Entry
1 b)
2 c)
Time (h)
Conv. (%)
ee (%) d)
92
6
6
97
95
90
a) Same as in Table 2; b) the usage amounts of reagents were
α-methylstyrene (25 mmol), n-nonane (12.5 mmol), catalyst 3b (0.375
mmol), NaClO (92.5 ml, 50 mmol, 0.55 M, pH = 11.3), 4-PPNO (12.5
mmol) at 20 °C for 6 h; c) the usage amounts of reagents were
α-methylstyrene (50 mmol), n-nonane (25 mmol), heterogeneous catalyst
3b (0.75 mmol), NaClO (185 ml, 100 mmol, 0.55 M, pH = 11.3), 4-PPNO
(25 mmol) at 20 °C for 6 h; d) (S)-form.
level for the large-scale reactions under the corresponding
condition although the large scale was 25 or 50 times bigger
than the experimental scale.
3.3 Large-scale asymmetric epoxidation reaction
We further performed various proportions of large-scale
asymmetric epoxidation reactions with α-methylstyrene as a
model substrate using NaClO/PPNO as oxidation system.
The large-scale experiments proceeded smoothly under the
same procedure with the experimental-scale. As can be seen
from the results summarized in Table 6, delightfully, the
conversion and enantioselectivity maintained at the same
4 Conclusions
In summary, three new bis-diamine-bridged bi-Mn(salen)
complexes have been synthesized and characterized. They
were efficient catalysts for asymmetric epoxidation of un-
functionalized alkenes with good-to-excellent chemical
yields and enantioselectivity. Moreover, those catalysts
were relatively stable, could be recycled five times in the
asymmetric epoxidation reactions, and could also be effi-
ciently used in large-scale reactions with the enantioselec-
tivity being maintained at the same level, which provided
the potential for applications in industry.
This work was financially supported by National Ministry of Science and
Technology Innovation Fund for High-tech Small and Medium Enterprise
Technology (09C26215112399) and National Ministry of Human Re-
sources and Social Security Start-up Support Projects for Students Re-
turned to Business, Office of Human Resources and Social Security Issued
2009 (143).
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