A mononuclear manganese complex of a tetradentate nitrogen ligand - Synthesis, characterizations, and application in the asymmetric epoxidation of olefins

Article abstract of DOI:10.1002/ejic.201402663

A new chiral manganese complex (C1) bearing a tetradentate nitrogen ligand containing chiral bipyrrolidine and benzimidazole moieties was prepared. The structure of C1 was confirmed by ESI-MS and crystallography. This manganese complex is an active catalyst for the asymmetric epoxidation of various olefins with excellent conversion (up to 99%) and high enantiomeric excess (up to 96%ee) with hydrogen peroxide as the oxidant in the presence of 2-ethylhexanoic acid or acetic acid. Compared with previous structurally similar manganese complexes with different diamine backbones (C2, cyclohexanediamine; C3, diamine from L-proline), C1 showed improved asymmetric induction, especially for simple olefins such as styrene derivatives and substituted chromene. The possible reasons for the improvement of the ee values are discussed in the text on the basis of the crystal structures of the manganese complexes.

Full text of DOI:10.1002/ejic.201402663

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DOI:10.1002/ejic.201402663
A Mononuclear Manganese Complex of a Tetradentate
Nitrogen Ligand – Synthesis, Characterizations, and
Application in the Asymmetric Epoxidation of Olefins
Duyi Shen,[a,b] Chengxia Miao, Shoufeng Wang, Chungu Xia,
[a]
[a]
[a]
[
a]
and Wei Sun*
Keywords: Homogeneous catalysis / Asymmetric catalysis / Bioinspired catalysis / Epoxidation / Manganese / N ligands
A new chiral manganese complex (C1) bearing a tetraden- acid or acetic acid. Compared with previous structurally sim-
tate nitrogen ligand containing chiral bipyrrolidine and
benzimidazole moieties was prepared. The structure of C1
ilar manganese complexes with different diamine backbones
(C2, cyclohexanediamine; C3, diamine from -proline), C1
L
was confirmed by ESI-MS and crystallography. This manga- showed improved asymmetric induction, especially for sim-
nese complex is an active catalyst for the asymmetric epoxid- ple olefins such as styrene derivatives and substituted
ation of various olefins with excellent conversion (up to 99%)
and high enantiomeric excess (up to 96%ee) with hydrogen
peroxide as the oxidant in the presence of 2-ethylhexanoic
chromene. The possible reasons for the improvement of the
ee values are discussed in the text on the basis of the crystal
structures of the manganese complexes.
[
6]
Introduction
polyamine backbones such as chiral triazacyclononane,
[
7]
[8]
cyclohexanediamine, amino-acid-derived amines, and
bipyrrolidine, were synthesized, characterized, and inten-
The catalytic asymmetric epoxidation of olefins is one of
the most important chemical transformations, because the
resulting epoxides are highly useful structural motifs or ver-
satile intermediates for organic synthesis.[ The seminal
studies of enantioselective epoxidation were started in the
late 1970s, and one of the major breakthroughs came in
the early 1980s with the discovery and development of the
Sharpless titanium-catalyzed asymmetric epoxidation of all-
[9]
sively studied.
Within these versatile bioinspired manganese complexes,
the rational modification to the ligands, including the ma-
nipulation of the steric and electronic properties of the N
donors, led to dramatic changes of the efficiency and
enantioselectivity of the catalyst. An early example was the
improvement made by Costas and co-workers, who
1]
[
2]
ylic alcohols. Afterwards, substantial progress was made
in the development of catalysts for the asymmetric epoxid-
ation of a broad range of unfunctionalized olefins. Among
these methods, the Mn–salen-catalyzed asymmetric epoxid-
ation reaction, which was developed independently by Ja-
[
7f]
achieved better-defined chiral pockets by appending pi-
nene to the 4- and 5-positions of the two pyridine rings of
the ligand N,NЈ-dimethyl-N,NЈ-bis(2-pyridylmethyl)cyclo-
hexane-trans-1,2-diamine (MCP; Figure 1, 1 and 3);[ fur-
ther, they demonstrated that electron-rich groups such as
dimethylamine at the 4-position of the pyridine ring could
improve the ee values and reduce the amount of carboxylic
acid required to a substoichiometric level (Figure 1, 7).[
Very recently, Bryliakov et al. also undertook a systematic
investigation of the steric and electronic impacts of the
functional groups on the pyridine rings of (S,S)-bipyrrol-
idine-derived manganese catalysts in the epoxidation of
7a]
[
3]
[1a,4]
cobsen and Katsuki,
in particular, has drawn more
attention. In consideration of these pioneering achieve-
ments, growing interests and efforts were dedicated to man-
ganese-catalyzed epoxidation, owing to the low toxicity,
commercial availability, and biological role of manganese in
enzyme-catalyzed redox processes.[5] Thus, numerous man-
ganese complexes coordinated with well-designed polydent-
ate nitrogen-donating ligands, mainly based on enantiopure
9d]
[
9e]
electron-deficient alkenes (Figure 1, 8).
Pfaltz et al.
In addition,
creatively prepared a series of manganese
complexes of N,N,N,N ligands containing chiral oxazoline
rings rather than pyridine rings (Figure 1, 2). As steric con-
straints are generated by the substituents at the oxazoline
rings, different coordination modes existed in these metal
[
10]
[
a] State Key Laboratory for Oxo Synthesis and Selective
Oxidation, Lanzhou Institute of Chemical Physics, Chinese
Academy of Sciences,
Lanzhou, 730000, P. R. China
E-mail: wsun@licp.cas.cn
http://www.licp.cas.cn/swz/
[b] University of Chinese Academy of Sciences,
Beijing, 100049, P. R. China
complexes, but the enantioselectivities were relatively low
(
21%ee for trans-β-methylstyrene). Similarly, Gao et al.[
11]
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402663.
developed a highly efficient asymmetric epoxidation with
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Figure 1. Structures of previously synthesized tetradentate nitrogen ligands.
manganese catalysts generated in situ from a porphyrin-in-
spired ligand, which consisted of chiral oxazoline rings and
an achiral o-phenylenediamine moiety (Figure 1, 4).
On the other hand, Shul’pin et al.[ reported that the
carboxylic acid cocatalysts had an indispensable influence
on the initial reaction rate and the final selectivity of the
Mn-catalyzed alkene epoxidation through kinetic studies.
Recently, Bryliakov et al. and Costas et al. found that the
employment of a bulkier acid such as 2-ethylhexanoic acid
12]
(EHA) could successfully lead to a dramatic increase of
enantioselectivity relative to that with acetic acid (AA) for
asymmetric epoxidation.[
9a,9c–9e]
In 2009, our group devised and synthesized a family of
MCP-related manganese complexes with bulky aromatic
rings at the two 2-pyridylmethyl positions;[7c] these com-
plexes effectively increased the ee values for the epoxidation
of various α,β-enones under mild conditions. From another
aspect, we made one more modification by replacing the
Figure 2. Ligands studied in this work.
chiral cyclohexanediamine moiety of MCP with an l-pro- that a 6-Me -BPBP iron complex could promote the asym-
2
line-derived diamine, and the newly-prepared C -symmetric metric cis-dihydroxylation of alkenes with up to 97%ee
1
[
15]
manganese complex presented higher asymmetric induction (Figure 1, 6).
Subsequently, several manganese catalysts
[
8a]
for chalcones. On this basis, we further modified this C1- containing tetradentate aminopyridine ligands derived from
symmetric complex by switching the pyridine rings to benz- bipyrrolidine showed improved asymmetric inductions in
imidazole moieties (homolog of L3, Figure 2), and great im- the epoxidation compared with the manganese catalysts
provements to both the efficiency [turnover frequency bearing chiral cyclohexanediamines. As mentioned above,
TOF) = 59000 h ] and the enantiomeric excesses (up to the N,N,N,N ligands with a bipyrrolidine backbone had en-
[
9]
–
1
(
9
[
8b]
5% ee)
were achieved for the asymmetric epoxidation joyed increasing use in target-oriented synthesis. To develop
compared with those for the two examples mentioned even more efficient bioinspired catalysts, the N,N,N,N li-
above. In addition, the use of a C -symmetric manganese gand-merging bipyrrolidine and benzimidazole moieties is
2
catalyst bearing a cyclohexanediamine–benzimidazole li- considered to be an ideal choice for the Mn-catalyzed asym-
gand (L2, Figure 2) also afforded high enantioselectivities metric epoxidation of olefins. Herein, we present the syn-
[
7g]
for chalcones.
thesis of such a ligand, L1, containing bipyrrolidine and
The chiral bipyrrolidine framework was first used in benzimidazole moieties, its manganese complex, and in-
asymmetric catalysis by Hirama for the osmylation of alk- vestigations of the performance for the epoxidation of ole-
[
13]
enes. White and Chen reported that the iron(II) complex fins. Furthermore, we make comparisons of the asymmetric
[
Fe(S,S-PDB)(MeCN) ][SbF6]2 based on a bipyrrolidine epoxidation abilities of the three manganese complexes con-
2
[
7g]
moiety could efficiently catalyze aliphatic C–H or methyl- taining bipyrrolidine, cyclohexanediamine,
and the di-
ene oxidation (Figure 1, 5).[ Que et al. also demonstrated amine from l-proline.
14]
[16]
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Results and Discussion
2.215(3) Å], consistent with those of the analogs C2 and
[
7g,16]
C3.
The ligand L1 could be readily prepared in good yield
through the direct alkylation of (R,R)-bipyrrolidine with 2-
chloromethyl-1-methylbenzimidazole according to a con-
[9c]
On the basis of the discoveries of Bryliakov et al. and
Costas et al., we first explored the new catalyst C1 in the
[9d]
asymmetric epoxidation of cis-β-methylstyrene with EHA
as the additive and hydrogen peroxide as the oxidant. Grati-
fyingly, full conversion and a high ee (73%) were achieved
with 1.0 mol-% of catalyst and 3.0 equiv. of EHA in half an
hour at –20 °C (Table 1, Entry 2). The same results could
also be obtained with a 0.3 mol-% catalyst loading (Table 1,
Entries 3 and 4). In addition, several carboxylic acids such
as AA, (S)-ibuprofen [(S)-IBU], and 4-methylvaleric acid
[
7g,8b]
ventional method.
The corresponding manganese
complex C1 was synthesized by reacting equimolar
amounts of ligand L1 and Mn(OTf) (OTf = trifluorome-
thanesulfonate), and the single-crystal X-ray structure of
the acetonitrile solvate of Mn(L1)(OTf) was determined
2
2
(Figure 3, C1).
(MVA) were also evaluated, but EHA was the most efficient
for conversion and enantioselectivity (Table 1, Entries 5–8).
The optimal conditions were then established, and the high-
est ee (81%) was accomplished with 2.0 equiv. of EHA and
1
.2 equiv. of H O at –30 °C (Table 1, Entries 9–11). How-
2 2
ever, under the optimized conditions, the analogous manga-
nese complexes C2 and C3 with different diamines pre-
sented poorer activities both in conversion and in asymmet-
Table 1. Screening the reaction conditions with cis-β-methylstyr-
ene.[
a]
Entry Catalyst
x]
H
[y]
2
O
2
Additive
[equiv.]
T
[°C]
Conv./GC yield ee
[
[%]
[%]
Figure 3. Molecular structures of the MnII complexes C1 (top), C2
(
left), and C3 (right) with key atoms labeled. The hydrogen atoms
1
2
3
4
5
6
7
8
9
1
C1 (1.0)
C1 (1.0)
C1 (0.3)
C1 (0.2)
C1 (0.3)
C1 (0.3)
C1 (0.3)
C1 (0.3)
C1 (0.3)
C1 (0.3)
C1 (0.3)
C2 (0.3)
C3 (0.3)
C2 (0.3)
C3 (0.3)
C3 (1.0)
1.6
1.6
1.6
1.6
1.6
1.6
1.6
1.6
1.6
1.6
1.2
1.2
1.2
1.6
1.6
1.6
–
–20
–20
–20
–20
–30
trace
99/89
99/88
55/50
97/87
80/68
69/52
99/83
78/66
99/89
99/89
70/40
25/15
85/54
52/41
99/90
–
have been omitted for clarity.
EHA (3.0)
EHA (3.0)
EHA (3.0)
EHA (3.0)
(S)-IBU (3.0) –30
AA (3.0)
MVA (3.0)
EHA (1.5)
EHA (2.0)
EHA (2.0)
EHA (2.0)
EHA (2.0)
EHA (2.0)
EHA (2.0)
EHA (3.0)
73
73
73
81
45
60
65
81
81
81
75
74
75
74
69
The structure reveals that the ligand L1 adopts a cis-α
conformation around the distorted octahedral manganese
–30
–30
–30
–30
–30
–30
–30
–30
–30
–20
center, in which the nitrogen atoms of the two benzimid-
azole donors are trans to each other.[17] The same patterns
are also found in the structures of the related complexes
0
C2[ and C3
7g]
[16]
with different diamine backbones. In C1, 11
the Mn–N (benzimidazole donors) bonds tilt into the vac- 12
13
14
15
16
ant space between Mn1–N4 and Mn1–O4. The N1–Mn1–
N5 angle is significantly distorted [166.73(12)°] from the
180° associated with an ideal octahedral coordination. The
distortion of C1 is larger than those of C2 [168.46(10)°] and
C3 [168.44(10)°] as a result of the more-rigid bipyrrolidine
[
7g,16]
framework.
metrical distortion manifested in the N1–Mn1–N5 angle
benzimidazole donors) is also larger than that of amino-
It is worth mentioning here that the geo-
(
pyridine manganese complex featuring a bipyrrolidine moi-
ety [N4–Mn1–N1, 171.94(9)°].[9a] As shown in Table S1, the
Mn–N bond lengths of C1 are apparently close to those
found in C2 and C3, except that the Mn–N5 bond length
in C3 is slightly shorter (by ca. 0.02–0.03 Å) owing to its
[
a] Reaction conditions: hydrogen peroxide (50% aqueous solution)
C -symmetric nature. For C1, the Mn–N bond lengths of
1
diluted with MeCN (0.5 mL) was delivered through a syringe pump
over 0.5 h to a stirred solution of catalyst (0.2–1.0 mol-%), carb-
oxylic acid (1.5–3.0 equiv.), internal standard (decane), and sub-
the bipyrrolidine nitrogen atoms [Mn–N(3) = 2.304(3) and
Mn–N(4) = 2.325(3) Å] are clearly longer than those of the
benzimidazole nitrogen atoms N(1) and N(2) [both are strate (0.4 mmol) in MeCN (1.0 mL) in the air.
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ric induction (Table 1, Entries 12 and 13). The substrate because of the electronegative halogen groups (Table 2, En-
could be fully epoxidized only when larger amounts of the tries 4 and 5). For other styrene derivatives such as cyclic
catalysts, oxidants, and additives were employed (Table 1, 1-phenyl-1-cyclohexene, very low ee values (12%) were de-
Entries 14–16).
tected even though excellent conversion and selectivity were
To test the applicability of this manganese catalyst, a achieved (Table 2, Entry 6); trans-stilbene was transformed
broad range of olefins, including aromatic alkenes, unfunc- into the epoxide with 50% yield and 36%ee (Table 2, En-
tionalized aliphatic alkenes, and electron-deficient α,β-un- try 7) in the presence of 5.0 equiv. of AA (almost no reac-
saturated ketones and esters, were studied under the opti- tion with EHA). On the contrary, for the asymmetric epox-
mal conditions. In most cases, the asymmetric epoxidation idation of 2,2-dimethyl-2H-chromene-6-carbonitrile, 75%ee
proceeded rapidly with good-to-excellent conversion, selec- was obtained with AA, which was nearly consistent with
tivity, and enantioselectivity in the presence of small the results with C2 and C3 under the same conditions.
amounts of carboxylic acid (Ͻ5 equiv.). For example, styr- However, high yields (90%) and excellent ee values (93%)
ene was epoxidized with high conversions and a good ee of were obtained with the bulkier EHA (Table 2, Entries 8 and
[
9d]
5
6% (Table 2, Entries 2 and 3), which was even a little 9), which was the carboxylic acid chosen by Costas et al.
[7c,7g]
[9e]
higher than the value we reported previously.
for the reaction of 4-Cl- and 4-Br-substituted styrenes, more
However, and Bryliakov et al.
For α,β-unsaturated ketones, similarly, a slightly higher
catalyst was needed, but moderate ee values were achieved ee was gained for chalcone with EHA than with AA, but a
2 2
Table 2. Asymmetric epoxidation of olefins with H O
and catalyst C1.[a]
[
a] Unless stated, the reaction conditions are: cat. (C1, 0.3 mol-%), EHA (2 equiv.), and H
2 2
O (1.2 equiv.) in MeCN at –30 °C for 0.5 h.
[
b] EHA (3 equiv.), 1 h. [c] Cat. (C1, 0.6 mol-%), EHA (3 equiv.), H (1.6 equiv.), 1 h. [d] HOAc (5 equiv.), H
2
O
2
2
O
O
2
(2 equiv.), 1 h. [e]
(2 equiv.). [i] Cat.
HOAc (2 equiv.). [f] Cat. (C2, 0.3 mol-%). [g] Cat. (C3, 0.3 mol-%). [h] Cat. (C1, 1.5 mol-%), EHA (3 equiv.), H
2
2
(
C1, 0.3 mol-%), HOAc (3 equiv.), H (1.6 equiv.).
2 2
O
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larger catalyst loading was required (Table 2, Entries 12 and Experimental Section
FULL PAPER
13). Substrates bearing electron-donating groups such as
General: All chemicals were purchased from commercial sources
and used as received, unless noted otherwise. Anhydrous solvents
para-Me on the phenyl rings on the olefin or carbonyl side,
both presented high α,β-epoxy ketone yields and ee values
[22]
1
13
were purified by standard methods. The H and C NMR spec-
tra were recorded with a Bruker Avance III 400 MHz spectrometer.
(up to 96%). Meanwhile, electron-withdrawing groups such
as para-Cl had an undesirable impact on the yields; how-
1
13
The H and C NMR spectroscopic chemical shifts (δ) are given
ever, the stereocontrol was not bad (Table 2, Entries 14–17). in ppm relative to tetramethylsilane as an internal standard or to
1
3
Furthermore, trace amounts of product were formed in the the solvent signal (for H: CDCl , δ = 7.26 ppm). The ESI-MS
II
epoxidation of methyl cinnamate even with 5 equiv. of spectra were collected with a Bruker Daltonics micrOTOF-Q
mass spectrometer. Optical rotations were recorded with a Perkin–
Elmer 341 polarimeter (sodium lamp, 1 dm cuvette, c in g/100 mL,
EHA. Thus, AA was employed, and good yields (close to
90%) were obtained, and the ee values increased slightly in
20 °C). GC analysis for ee values and yields were performed with
the order iPrϾBnϾEtϾMe (Table 2, Entries 18–21).
Fortunately, this manganese complex was also an active
catalyst for aliphatic olefins with full conversions and epox-
ide selectivities (Table 2, Entries 22–31). Surprisingly, rela-
tively large amounts of catalyst (1.5 mol-%) were required
TM
an Agilent 6820GC instrument with a Beta dex
a 7890 GC instrument with a CP-Chirasil-Dex CB column. HPLC
analysis for ee values was performed with a Waters-Breeze system
120 column or
(
2487 Dual λ Absorbance Detector and 1525 Binary HPLC Pump).
Chiralpak OD, OB, OJ, AS, and IC columns were purchased from
with EHA as the additive, probably because of the steric Daicel Chemical Industries, Ltd. The X-ray crystallographic data
effect of this bulkier acid. In contrast, the epoxidation pro- were collected with a Bruker SMART CCD1000 diffractometer
ceeded smoothly in the presence of 3.0 equiv. of AA with with graphite-monochromated Mo-K
96(2) K.
enantioselectivities are a tough problem that remains to be Synthesis of the Ligand L1 and Complexes C1-C3: The ligand L1
α
radiation (λ = 0.71073 Å) at
2
only 0.3 mol-% of catalyst loading. However, the fairly low
II
resolved.
and the corresponding Mn complex C1 were synthesized from
In addition, with respect to the role of the additive in (R,R)-bipyrrolidine by the same procedures as we reported pre-
viously.[ Complexes C2 and C3 were prepared according to
8b]
[7g]
[16]
manganese-catalyzed asymmetric epoxidation systems, Talsi
et al. concluded by the EPR analysis that the acid might
our previous methods.
act as an auxiliary ligand in the possible intermediate [(5) Ligand L1: Yield 0.9 g, 70%. [α]2
0
= –23 (c = 0.2, CHCl
): δ = 7.72 (dd, J = 6.3, 1.9 Hz, 2 H), 7.33–7.20
m, 6 H), 4.24 (d, J = 13.3 Hz, 2 H), 3.79 (s, 6 H), 3.65 (d, J =
1
D
3
). H NMR
V
[9c]
Mn =O] in the enantioselectivity-determining step.
(400 MHz, CDCl
3
(
Compared with those for manganese catalyst systems, the
accounts of the effect of the acid in iron-catalyzed oxi-
1
1.6 Hz, 2 H), 2.86 (s, 2 H), 2.74 (s, 2 H), 2.34 (d, J = 3.4 Hz, 2
H), 1.90–1.55 (m, 8 H) ppm. C NMR (101 MHz, CDCl
52.4, 142.2, 136.2, 122.4, 121.9, 119.6, 109.0, 65.3, 55.5, 52.5, 29.9,
6.3, 24.0 ppm. HRMS (ESI): calcd. for C26
29.2767; found 429.2793.
1
3
[
18]
3
): δ =
dations seem to be relatively extensive,
and an acid-as-
1
2
4
[
19]
sisted mechanism
has already been proposed. Very re-
synthesized and fully characterized a
+
H
33
N
6
[M + H]
[
20]
cently, Que et al.
low-spin acylperoxoiron(III) intermediate, of which the de-
gradation product was assigned to be an oxoiron(V) species
and the true powerful oxidant. Their findings were sug-
Complex C1: HRMS (ESI-MS): calcd. for C27
H
32
F
3
MnN
6
O
3
S
[
M – OTf]+ 632.1589; found 632.1605. X-ray-quality crystals were
grown from the layer interface between diethyl ether and MeCN.
CCDC-979540 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[9b,21]
gested to apply to other non-heme iron models
and
will perhaps be quite helpful in further understanding the
synergistic cooperation of carboxylic acids with non-heme
manganese catalysts.
General Procedure for the Asymmetric Epoxidation of cis-β-Methyl-
styrene: A MeCN (1.0 mL) solution of the substrate (0.4 mmol),
catalyst (0.3 mol-%), and carboxylic acid (1.5–3.0 equiv.) was pre-
pared in a 10 mL flask at room temperature. Then, a H
2 2
O solution
Conclusions
(
1.2–1.6 equiv., diluted from a 50% aqueous solution in 0.5 mL of
MeCN) was added with a syringe pump over 30 min with stirring
at –20 or –30 °C. At this point, decane was added to the mixture as
an internal standard. The reaction was quenched with a saturated
NaHCO aqueous solution and a saturated Na S O aqueous solu-
3 2 2 3
tion and then extracted with diethyl ether; the yields and ee values
A new chiral manganese complex of a N,N,N,N ligand
with a bipyrrolidine and benzimidazole framework has been
synthesized and characterized. This manganese complex ex-
hibits good control of asymmetric induction (up to 96%ee)
in the asymmetric epoxidation of various olefins, including
α,β-unsaturated olefins and aromatic olefins, with 2.0–
were determined by GC analysis. The enantiomeric purity was de-
termined with an Agilent 6820 GC instrument with a Beta dex
TM
1
5
20 column (80 °C isothermal for 2 min, 3 °C/min, 170 °C for
min, t = 25.449 and 25.793 min).
5.0 equiv. of EHA or AA as the additive and 1.2–2.0 equiv.
r
of H O as the oxidant. Nevertheless, the enantioselectivit-
2
2
General Procedure for the Asymmetric Epoxidation of 2,2-Dimethyl-
H-chromene-6-carbonitrile: A MeCN (1.0 mL) solution of the sub-
strate (0.4 mmol), catalyst (0.3 mol-%), and carboxylic acid
2 equiv.) was prepared in a 10 mL flask at room temperature.
ies for simple aliphatic alkenes are very low, although the
conversions and selectivities for epoxidation are excellent.
Further studies on the reaction mechanism as well as the
2
(
development of even more efficient non-heme systems for Then, a H O solution (1.2 equiv., diluted from a 50% aqueous
2
2
oxidations are underway in our laboratory.
solution in 0.5 mL of MeCN) was added with a syringe pump over
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3
0 min with stirring at –30 °C. The reaction was quenched with
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a saturated NaHCO aqueous solution and a saturated Na S O
3
2 2 3
aqueous solution and then extracted with diethyl ether. The solvent
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corresponding epoxide 2,2-dimethyl-2,7b-dihydro-1aH-oxireno[2,3-
c]chromene-6-carbonitrile as a colorless solid. H NMR (400 MHz,
3
CDCl ): δ = 7.66 (d, J = 2.0 Hz, 1 H), 7.53 (dd, J = 8.5, 2.1 Hz, 1
2
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1
1
5
=
(
1
4.4 Hz, 1 H), 1.60 (s, 3 H), 1.30 (s, 3 H) ppm. 13C NMR
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04.3, 74.7, 62.3, 49.8, 25.5, 23.0 ppm. The enantiomeric purity was
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Received: July 15, 2014
Published Online: ᭿
Eur. J. Inorg. Chem. 0000, 0–0
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I42663
/KAP1
Date: 07-10-14 13:01:34
Pages: 7
www.eurjic.org
FULL PAPER
Asymmetric Epoxidation
D. Shen, C. Miao, S. Wang, C. Xia,
W. Sun* ............................................ 1–7
A Mononuclear Manganese Complex of a
Tetradentate Nitrogen Ligand – Synthesis,
Characterizations, and Application in the
Asymmetric Epoxidation of Olefins
A chiral manganese complex bearing a
tetradentate nitrogen ligand with chiral bi-
pyrrolidine and benzimidazole moieties is
an active catalyst for the asymmetric epox-
idation of various olefins with excellent
conversions (up to 99%) and up to 96%ee
with hydrogen peroxide as the oxidant in
the presence of 2-ethylhexanoic acid or
acetic acid.
Keywords: Homogeneous catalysis / Asym-
metric catalysis / Bioinspired catalysis /
Epoxidation / Manganese / N ligands
Eur. J. Inorg. Chem. 0000, 0–0
7
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim