MnII complexes with tetradentate N4 ligands: Highly efficient catalysts for the epoxidation of olefins with H2O 2

Article abstract of DOI:10.1016/j.molcata.2011.11.024

A series of Mn-complexes with tetradentate N₄ ligands, introducing aromatic groups into 2-pyridylmethyl positions of N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine (mep), N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)cyclohexane-trans-diamine (mcp), have been synthesized and applied for epoxidation of olefins using H ₂O₂ as the oxidant. The Mn-complexes still possessed an octahedral mononuclear structure in a cis-α topology. These complexes showed good regioselectivity, high yields and turnover frequency (even up to 228,000 h^-1) with low catalyst loading (0.1-0.01 mol%) for epoxidation of a family of olefins (including internal aromatic olefins, internal and terminal aliphatic olefins and diolefins).

Full text of DOI:10.1016/j.molcata.2011.11.024

Journal of Molecular Catalysis A: Chemical 353–354 (2012) 185–191
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
II
Mn complexes with tetradentate N ligands: Highly efficient catalysts for the
4
epoxidation of olefins with H O
2
2
Songjie Yua,b, Cheng-Xia Miao , Daqi Wang , Shoufeng Wang , Chungu Xia , Wei Sun
a
c
a
a
a,∗
a
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
College of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng 252059, China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 September 2011
Received in revised form
A series of Mn-complexes with tetradentate N ligands, introducing aromatic groups into 2-pyridylmethyl
4
ꢀ
ꢀ
ꢀ
ꢀ
positions of N,N -dimethyl-N,N -bis(2-pyridylmethyl)ethane-1,2-diamine (mep), N,N -dimethyl-N,N -
bis(2-pyridylmethyl)cyclohexane-trans-diamine (mcp), have been synthesized and applied for
epoxidation of olefins using H2O2 as the oxidant. The Mn-complexes still possessed an octahedral
mononuclear structure in a cis-␣ topology. These complexes showed good regioselectivity, high yields
1
7 November 2011
Accepted 24 November 2011
Available online 4 December 2011
−1
and turnover frequency (even up to 228,000 h ) with low catalyst loading (0.1–0.01 mol%) for epoxida-
tion of a family of olefins (including internal aromatic olefins, internal and terminal aliphatic olefins and
diolefins).
Keywords:
N ligands
Manganese
Epoxidation
Hydrogen peroxide
Olefins
©
2011 Elsevier B.V. All rights reserved.
1
. Introduction
which exhibited excellent activity and selectivity in epoxidation
of olefins [17,18]. [Mn (DMEGqu) (ꢀ-CF SO ) (CF SO ) (H O) ]
2
2
3
3
2
3
3
2
2
2
Olefin epoxidation constitutes a very important reaction in
(DMEGqu = N-(1,3-dimethylimidazolidin-2-ylidene)quinolin-8-
organic synthesis because epoxides are valuable building blocks
for a number of subsequent transformations [1–4]. Many efforts
have been dedicated to the development of metal-catalyzed
epoxidation reaction effectively [5–8]. Notable in the non-heme
iron area is the report of Fe with mep (N,N -dimethyl-N,N -bis(2-
pyridylmethyl)ethane-1,2-diamine), that performs rapid, efficient
amine) also showed moderate catalytic activity in the epoxidation
of the terminal alkene, such as 1-octene [19]. Recently, our group
has successfully developed a series of Mn complexes of chi-
II
ral tetradentate nitrogen ligands derived from mcp that could
efficiently epoxidize electron-deficient olefins with nearly full con-
version and up to 89% ee using hydrogen peroxide as the oxidant in
the presence of AcOH [20]. Later, Bryliakov et al. prepared a series
of Mn-complexes based on mcp template and investigated their
performance in the epoxidation of olefins with various oxidants
(peroxycarboxylic acids, alkyl hydroperoxides, iodosylarenes,
etc.) [21,22]. Base on above mentioned, Mn-complexes based on
tetradentate nitrogen ligands have exhibited good performance in
the epoxidation. Taking into account the selectivity and efficiency
of the catalysts, however, the development of highly efficient
catalysts is still in high demand.
As a part of our ongoing interest in the developing novel cat-
alysts for oxidation reaction [20,23–26], herein we reported the
synthesis of tetradentate N4 ligands and their corresponding Mn-
complexes by introducing aromatic groups into 2-pyridylmethyl
positions derived from various diamine backbones (Scheme 1)
and investigated their performance in the epoxidation. To our
delighted, the simply prepared manganese complexes C1 and C3
derived from mep and mcp could efficiently epoxidize a family of
II
ꢀ
ꢀ
epoxidations of terminal olefins using H O2 as the oxidant in
2
the presence of acetic acid [9]. On the other hand, manganese
complexes have been also attracting significant attention [10],
especially after the breakthroughs of asymmetric epoxidation of
unfunctionalized olefins catalyzed by Mn(III)-salen complexes
developed by Jacobsen and Katsuki groups [11–14]. In recent
II
years, Stack and co-workers developed Mn complexes bear-
ing tridentate and tetradentate nitrogen based ligands (mcp,
ꢀ
ꢀ
N,N -dimethyl-N,N -bis(2-pyridylmethyl)cyclohexane-trans-
diamine)in combination with peracetic acid as very fast and
efficient epoxidation system [15,16]. Subsequently, Costas and co-
II
workers exploited a series of Mn (PyTACN)(CF SO ) complexes
3
3 2
∗ Corresponding author. Tel.: +86 931 496 8278; fax: +86 931 827 7088.
E-mail address: wsun@licp.cas.cn (W. Sun).
1
381-1169/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2011.11.024

1
86
S. Yu et al. / Journal of Molecular Catalysis A: Chemical 353–354 (2012) 185–191
N
N
C6, L1Zn(OTf)2
Zn
TfO OTf
N
N
R
R
PhMgBr
THF
MeI
Mn(OTf)2
MeCN
N
N
N
N
THF
Mn
N
N
N
N
TfO OTf
R
L1, R = 1,2-Diaminoethane
L2, R = 1,3-Diaminopropane
L3, R = 1,2-Diaminocyclohexane
C1, L1Mn(OTf)2
C2, L2Mn(OTf)2
C3, L3Mn(OTf)2
N
N
N
N
A
R
R
N
N
N
N
Mn(OTf)2
MeCN
NaBH4
MeOH
3
7% HCHO
Mn
N
TfO OTf
N
N
N
MeOH
L4, R = 1,2-Diaminoethane
L5, R = 1,3-Diaminopropane
C4, L4Mn(OTf)2
C5, L5Mn(OTf)2
Scheme 1. Synthesis of ligands L1–L5 and complexes C1–C6.
olefins (including internal aromatic olefins, internal and terminal
aliphatic olefins and diolefins) with 0.1–0.01 mol% catalyst loading
within 5 min using hydrogen peroxide as the terminal oxidant. The
CH Cl and organic phase was dried over anhydrous Na SO4 and
2
2
2
concentrated in vacuo to yield the product as a brown solid. To a
solution of the brown solid in THF (15 mL) was added NaH (ca. 60%
−
1
◦
turnover frequency (TOF) can be reached up to 228,000 h
.
in oil, 0.32 g, 8 mmol) at 0 C. After stirring for 1 h, MeI (3.0 mmol)
was added to the mixture and stirred for 12 h. The reaction mixture
was quenched by saturated NH4Cl and extracted with CH2Cl2. The
organic phase was dried over anhydrous Na SO . The crude prod-
2
. Experimental
2
4
2
.1. General
uct was purified by chromatography on silica gel to afford yellow
solids in 70% isolated yields L1 [20,27]. And the synthetic procedure
of L2 or L3 was the same as the procedure for L1, both are yellow
solid in 65% yield, 85% yield respectively.
The 1H and 13C NMR spectra were recorded on a Bruker Avance
III 400 MHz spectrometer. The chemical shifts (ı) are reported in
ppm and coupling constants (J) in Hz. HRMS were obtained on
a Bruker Daltonics micrOTOF-Q mass spectrometer. X-ray crys-
For the synthesis of L4: NaBH4 (2.48 g, 10 mmol) was added
into the compound A (5 mmol) dissolved in MeOH (50 mL), and
the mixture was stirred for 30 min at room temperature. Aque-
ous HCl (3 M, 15 mL) was added slowly with stirring, and then the
MeOH was removed in vacuo. Aqueous NaOH (20%) was added until
the solution reached pH > 10. After that, the product was extracted
with CH2Cl2, washed with H2O and brine (50 mL), and then dried
over Na2SO4. Following filtration and concentration, the diamine
was obtained as yellow oil. Then, the oil was dissolved in abso-
lute methanol (10 mL). 37% aqueous formaldehyde solution diluted
with methanol (2 mL) was added, and the mixture was stirred for
II
tallographic data were collected on a Bruker SMART CCD1000
diffractometer with graphite-monochromated Mo K␣ radiation
(
ꢁ = 0.71073 A˚ ) at 298(2) K. GC analysis was performed on Agilent
6
820 or 7890A equipment. Column chromatography was generally
performed on silica gel (200–300 mesh) and TLC inspections were
on silica gel GF254 plates.
All reactions were carried out under argon in dried glassware.
All chemicals and solvents were used as received unless otherwise
stated. Tetrahydrofuran, ethyl ether (Na, benzophenone), acetoni-
◦
trile (CaH ) were distilled under argon prior to use.
6 h at 45 C. Finally, the product was concentrated in vacuo and
2
purified by chromatography on silica gel to give yellow oil L4 in
90% yield. And the synthetic procedure of L5 was the same with L4,
L5 was obtained as yellow oil in 87% yield.
2
.2. Synthetic procedure and characterization of L1–L5 and
C1–C6
Complex 1 (C1): Under argon atmosphere, Mn(OTf) (0.1 mmol)
2
A solution of ligand A (0.48 g, 2 mmol) in THF was added drop-
wise to a vigorously stirred Grignard reagent (10 mmol) in THF
20 mL) at room temperature and then the reaction mixture was
was added into a stirred solution of ligand 1 (0.1 mmol) in ace-
tonitrile (2.0 mL). The mixture was stirred for 12 h and then was
concentrated in vacuo to yield the product as a brown powder. The
powder was washed with cold Et2O and dried in vacuo. Crystals of
C1 suitable for X-ray diffraction was obtained by slow diffusion of
(
stirred at same temperature for 12 h. Saturated NH Cl was added
4
to quench the reaction. After that, the mixture was extracted with

S. Yu et al. / Journal of Molecular Catalysis A: Chemical 353–354 (2012) 185–191
187
Et O into its concentrated MeCN solution. And the synthetic proce-
2
dropwise 1.3 equiv of 30% H O2 dissolved in CH CN 1:1 (V:V) over
2 3
dures of C2–C6 were the same with procedure for C1. CCDC 754024,
a period of 30 min. And 5 extra minutes of stirring was allowed
at 0 C. Then the reaction mixture was quenched by saturated
◦
8
08616 and 808615 contain the supplementary crystallographic
data of C1, C5 and C6 for this paper respectively. Crystallographic
Na CO3 and extracted with Et O. The corresponding epoxides and
2
2
data can be obtained free of charge from the Cambridge Crystallo-
the side-products were determined by GC–MS. Yields were further
determined by GC using nitrobenzene as internal standard.
graphic Data Center via www.ccdc.cam.ac.uk/data request/cif.
1
L1 H NMR (400 MHz, CDCl ): ı = 8.48 (d, J = 4.8 Hz, 2H, ArH),
3
7
4
.60–7.52 (m, 4H, ArH), 7.44 (d, J = 7.6 Hz, 4H, ArH), 7.28–7.24 (m,
H, ArH), 7.19 (t, J = 7.6 Hz, 2H, ArH), 7.09–7.06 (m, 2H, ArH), 4.52
2
.4. General procedure for epoxidation reactions with AcOOH as
oxidant
13
(
(
s, 2H, CH), 2.63–2.52 (m, 4H, CH ), 2.06 (s, 6H, CH ). C NMR
100 MHz, CDCl ): ı = 162.8, 149.0, 141.8, 136.5, 128.4, 128.2, 127.1,
2 3
3
To
a mixture of the substrate (1.0 mmol), nitrobenzene
1
22.1, 121.8, 77.8, 53.1, 41.1.
(0.20 mmol), and catalyst 0.25 mol% in 1.5 mL CH CN under Ar
1
3
L2 H NMR (400 MHz, CDCl ): ı = 8.48 (dd, J = 0.8 Hz, J = 4.8 Hz,
3
1
2
atmosphere was rapidly added 1.2 equiv of 8% AcOOH. And 5 extra
min of stirring was allowed at room temperature. Then the reac-
tion mixture was quenched by saturated Na CO3 and extracted
with Et O. The corresponding epoxides and the side-products were
determined by GC–MS. Yields were further determined by GC using
nitrobenzene as internal standard.
2
7
H, ArH), 7.59–7.54 (m, 2H, ArH), 7.42 (q, J = 8.0 Hz, 6H, ArH),
.27–7.23 (m, 4H, ArH), 7.18 (t, J = 7.2 Hz, 2H, ArH), 7.08–7.05 (m, 2H,
2
ArH), 4.48 (s, 2H, CH), 2.40–2.23 (m, 4H, CH ), 2.13 (s, 6H, CH ), 1.74
2
3
13
2
(
t, J = 7.2 Hz, 2H, CH ). C NMR (100 MHz, CDCl ): ı = 162.9, 148.9,
2
3
1
41.8, 136.5, 128.4, 128.3, 127.1, 122.1, 121.8, 77.7, 53.3, 40.2, 24.0.
1
L3 [20] H NMR (400 MHz, CDCl ): ı = 8.48 (dd, J = 0.8 Hz,
3
1
J2 = 4.8 Hz, 2H, ArH), 7.90 (d, J = 8.0 Hz, 2H, ArH), 7.76–7.72 (m,
2
7
2
H, ArH), 7.49 (d, J = 7.2 Hz, 4H, ArH), 7.26 (t, J = 8.0 Hz, 4H, ArH),
.21–7.17 (m, 2H, ArH), 7.14–7.11 (m, 2H, ArH), 5.02 (s, 2H, CH),
.58 (dd, J = 3.2 Hz, J = 6.0 Hz, 2H, CH), 2.19 (s, 6H, CH ), 1.78 (d,
3. Results and discussion
According to our previous reported methods [20], the ligands
L1–L3 can be prepared in good yields through Grignard reaction
and subsequent methylation with MeI from compound A. And the
ligands L4 and L5 were synthesized with about 90% yields as shown
in Scheme 1 from compound A through reduction with NaBH4 and
cyclization with 37% aqueous formaldehyde solution [28]. Addi-
tionally, the corresponding Mn- or Zn-complexes 1–6 (C1–C6) were
prepared by reactions of Mn(OTf)2 or Zn(OTf)2 with equivalent of
ligands in acetonitrile and then treated with diethyl ether. All the
complexes were obtained in nearly quantitive yields.
1
2
3
J = 12.8 Hz, 2H, CH ), 1.51 (t, J = 3.6 Hz, 2H, CH ), 1.09 (d, J = 8.8 Hz,
2
2
13
2
H, CH ), 0.78 (d, J = 9.6 Hz, 2H, CH ). C NMR (100 MHz, CDCl ):
2
2
3
ı = 164.3, 149.0, 141.4, 136.5, 129.0, 128.3, 127.1, 121.9, 121.7, 75.4,
5
9.9, 34.2, 25.4, 25.0.
1
L4 H NMR (400 MHz, CDCl ): ı = 8.54 (d, J = 4.8 Hz, 2H, ArH), 7.65
3
(
t, J = 7.6 Hz, 2H, ArH), 7.46 (d, J = 8.0 Hz, 2H, ArH), 7.17–7.14 (m, 2H,
13
ArH), 3.91 (s, 4H, CH ), 3.61 (s, 2H, CH ), 2.95 (s, 4H, CH ). C NMR
2
2
2
(
100 MHz, CDCl ): ı = 159.1, 149.1, 136.6, 122.7, 122.0, 76.6, 61.1,
3
5
2.5.
1
L5 H NMR (400 MHz, CDCl ): ı = 8.52 (dd, J = 0.4 Hz, J = 4.8 Hz,
It has been known that linear tetradentate N Py ligands can
3
1
2
2
2
II
2
7
H, ArH), 7.61 (t, J = 7.6 Hz, 2H, ArH), 7.47 (d, J = 7.6 Hz, 2H, ArH),
.14–7.11 (m, 2H, ArH), 3.75 (s, 4H, CH ), 3.35 (s, 2H, CH ), 2.66 (t,
coordinate to an octahedral Mn center in three possible topologies
(cis-␣, cis-␤, and trans) depending on the way they wrap around the
metal center [29,30]. The solid state structures of metal-complexes
could be established by X-ray analysis. For the present complexes,
crystals of C1, C5 and C6 for suitable for X-ray diffraction were
obtained by slow diffusion of diethyl ether into their MeCN solu-
tion. Then the data were collected using a Bruker APEX-II CCD and
the structures were solved by the direct method using the SHELX-
97 program. The crystallographic data for C1, C5 and C6 were listed
in Table 1 and the crystal structures of the three metal-complexes
were shown in Fig. 1.
2
2
13
J = 5.2 Hz, 4H, CH ), 1.76 (t, J = 4.8 Hz, 2H, CH ). C NMR (100 MHz,
CDCl ): ı = 158.8, 148.9, 136.4, 123.0, 121.9, 75.4, 60.8, 52.3, 22.7.
2
2
3
1
C6 H NMR (400 MHz, CDCl ): ı = 9.19 (d, J = 4.8 Hz, 2H, ArH),
3
7
4
7
2
.91 (t, J = 7.6 Hz, 2H, ArH), 7.66–7.57 (m, 4H, ArH), 7.56–7.48 (m,
H, ArH), 7.43 (t, J = 7.6 Hz, 2H, ArH), 7.21 (d, J = 8.0 Hz, 2H, ArH),
.10 (d, J = 7.6 Hz, 2H, ArH), 5.92 (s, 2H, CH), 2.85 (d, J = 10.4 Hz,
13
H, CH ), 2.40 (s, 6H, CH ), 1.97 (d, J = 10.4 Hz, 2H, CH ). C NMR
2
3
2
(
100 MHz, CDCl ): ı = 156.4, 148.9, 140.2, 134.8, 131.1, 129.8, 129.5,
3
1
28.8, 128.6, 125.7, 124.8, 71.2, 48.6, 40.1.
C1 HRMS: calcd. for C29H30F MnN O S m/z 626.1371, found
The result revealed that C1 possessed a distorted octahedral
mononuclear structure with the ligands adopting a cis-␣ topol-
ogy. The two pyridine rings as nitrogen donors to the metal center
are disposed in trans position. The Zn-complex C6 also adopted a
cis-␣ topology. Interestingly, C5 formed a seven-coordinate struc-
ture in topology containing an acetonitrile molecule because of a
loose spatial environment correspondingly. Importantly, the bond
lengths of Mn N reflect the different electronic effect of coordi-
nation atoms and also influence the catalytic activity of the metal
complexes. And the results in Table 2 showed that the bond lengths
of Mn1 to the pyridyl nitrogens for C1, C3 [20] and C5 are notice-
ably shorter than to the aliphatic amine nitrogens. The average
3
4
3
6
4
26.1358. Anal. calcd. For C30H30F MnN O S ·2H O: C, 44.39; H,
6
4
6
2
2
.22; N, 6.90. Found: C, 44.71; H, 3.89; N, 6.99.
C2 HRMS: calcd. for C30H32F MnN O S m/z 640.1528, found
3
4
3
6
4
40.1523. Anal. calcd. For C31H32F MnN O S ·1.5H O: C, 45.59; H,
6
4
6
2
2
.32; N, 6.86. Found: C, 45.74; H, 4.16; N, 6.74.
C3 HRMS: calcd. for C33H36F MnN O S m/z 680.1841, found
3
4
3
6
4
80.1847. Anal. calcd. For C34H36F MnN O S ·0.9H O: C, 48.27; H,
6
4
6
2
2
.50; N, 6.62. Found: C, 48.60; H, 4.48; N, 6.74.
C4 HRMS: calcd. for C16H18F MnN O S m/z 458.0432, found
3
4
3
4
3
58.0419. Anal. calcd. For C17H18F MnN O S ·2H O: C, 31.73; H,
6
4
6
2
2
.45; N, 8.71. Found: C, 31.38; H, 3.20; N, 8.36.
C5 HRMS: calcd. for C17H20F MnN O S m/z 472.0589, found
bond length of pyridyl nitrogens and Mn atom for complex C1 is
2.22 A˚ , similar with the previous reported complex C3 [20]. For the
3
4
3
4
3
72.0576. Anal. calcd. For C18H20F MnN O S ·2H O: C, 32.88; H,
6
4
6
2
2
.68; N, 8.52. Found: C, 32.98; H, 3.35; N, 8.42.
seven-coordinate Mn-complex C5, all the lengths of Mn N bond
II
are longer than those of [Mn (mcp)(CF SO ) ], C1 and C3, due to
3
3 2
2
.3. General procedure for epoxidation reactions with H O as
the additional coordinated acetonitrile [15].
2
2
II
oxidant
The NMR spectra of Zn complex can reveal considerable infor-
mation about the structure of complex with N4 ligand [31]. The
II
To
a
mixture of the substrate (2.0 mmol), nitrobenzene
Zn complex of L1 (C6) was prepared in order to study the sta-
(
1
0.20 mmol), catalyst 0.1 mol%, and acetic acid (20 mmol,
bility of complex in solution. X-ray structure of C6 indicates that
ligand also coordinates the zinc center in a cis-␣ topology (Fig. 1).
0.0 equiv) in 1.5 mL CH CN under Ar atmosphere was added
3

1
88
S. Yu et al. / Journal of Molecular Catalysis A: Chemical 353–354 (2012) 185–191
Table 1
Details of structure determination, refinement, and experimental parameters for C1, C5 and C6.
L1–Mn·0.5MeCN
L5–Mn
L1–Zn·0.5MeCN
Formula
Formula
C31H31.5F6MnN4.5O6S2
796.17
C20H23F6MnN5O6S2
662.49
C31H31.5F6ZnN4.5O6S2
806.60
Crystal system
Space group
Monoclinic
P21/n
Monoclinic
P21/c
Monoclinic
P21/n
Crystal size/mm
a/A˚
b/A˚
0.32 × 0.28 × 0.26
9.0508(9)
25.808(2)
16.1004(18)
90
105.693(11)
90
3629.0(6)
4
0.32 × 0.30 × 0.22
19.473(17)
8.876(7)
16.687(16)
90
105.24(4)
90
2783(4)
4
0.46 × 0.42 × 0.39
9.0415(4)
25.6007(10)
16.0329(7)
90
105.841(2)
90
3570.2(3)
4
c/A˚
◦
˛
/
◦
◦
ˇ/
ꢂ/
V/A˚
3
Z
−
3
Dc/mg m
m/mm
1.457
0.557
1.581
0.709
1.501
0.884
−
1
F(0 0 0)
ꢃrange/
Reflns. collected
Reflns. unique
Parameters
Goodness-of-fit on F
R1,wR2
R1,wR2 [all data]
Largest diff. peak and hole [e A˚ −3]
1632
1.53–25.50
19,502
6725
575
1348
2.17–24.20
12,485
4333
362
1652
1.54–25.50
19,156
6638
555
◦
2
1.024
1.012
1.045
0.0543, 0.1410
0.0804, 0.1620
0.542, −0.395
0.0909, 0.2192
0.1834, 0.2637
0.627, −0.708
0.0445, 0.1127
0.0635, 0.1239
0.410, −0.913
The 1H NMR spectrum indicates that there is only one isomer in
Table 3
Reactivity of complexes in epoxidation of 1-octene.
a
solution even at room temperature (5.92 ppm. S, 2H. Fig. 2, also
see Figure S1 in the supplementary data for details). Taking into
b
Entry
Complex
Yield /%
II
account the NMR spectra and X-ray structure, the Zn complex
1
2
3
4
5
C1
C2
C3
C4
C5
99
<10
99
<10
<10
C6 still retain its ligand topology in solution. The result also sug-
gests that the corresponding Mn-complex seems to adopt a cis-␣
topology in solution.
Que et al. have determined that iron with N4 ligands could cat-
a
Reaction conditions: alkene (1.0 mmol), complex (0.5 mol%) and CH3COOH
10.0 equiv) dissolved in 1.5 mL CH3CN, and 30% H2O2 (1.5 equiv) dissolved in CH3CN
V:V = 1:1) was added at 0 C over a period of 30 min, and the mixture was stirred
alyze in situ formation of AcOOH from H O2 and AcOH [32]. Costas
2
(
(
and our group also explored H O /AcOH system for the epoxida-
2
2
◦
tion of olefins [16,20]. And in preliminary studies we evaluated
the catalytic property of C1–C5 in the epoxidation of 1-octene
with H O as terminal oxidant (1.5 equiv) in the presence of acetic
for additional 30 min.
b
Determined by GC using nitrobenzene as internal standard.
2
2
acid (10.0 equiv). Fortunately, C1 and C3 exhibited excellent cat-
alytic activities affording the corresponding epoxides in 99% yields
substrates, such as internal aromatic olefins, internal and terminal
aliphatic olefins and diolefins. The results were shown in Table 5.
Fortunately, a broad of olefins were rapidly epoxidized in high
conversions and yields. The activities of terminal aliphatic olefins
were almost not influenced by the steric hindrance and chain
length (Table 5, entries 1–9), especially using C3 as the catalyst
with TOF even up to 228,000 h (entry 6). Additionally, steric hin-
drance and chain length also did not affect the activities of internal
aliphatic olefins (entries 10–14). Besides, the epoxidation of aro-
matic olefins such as 1, 2-diphenylethene and methyl cinnamate
was also accomplished with good yield and high selectivity employ-
ing C3 as catalyst (entries 15, 16). However, slight low yields were
obtained using C1 as catalyst. The epoxidation of electron-deficient
(
Table 3, entries 1, 3). However, the catalytic activities of other
complexes were very low (entries 2, 4, 5). Subsequently, reaction
conditions were screened using C1 as model catalyst and the results
were summarized in Table 4. Obviously, acetic acid loading has sig-
nificant influence on the catalytic activity. When acetic acid loading
increased to 10.0 equiv, high yield was achieved with 0.1 mol% cat-
alyst loading (Table 4, entry 5). According to the previous reports,
acetic acid may enhance the electrophilicity of the peroxide moiety
or assist heterolytic O O bond cleavage of the Mn peroxide inter-
mediate [17,18]. And the optimal conditions are as follow: 0.1 mol%
−
1
◦
C1, 1.3 equiv of H O , 10.0 equiv of CH COOH, 0 C for 5 min.
2
2
3
To demonstrate the versatility of the reaction system, C1
and C3 were applied to the epoxidation of a series of olefins
Table 4
a
Table 2
Screening of reaction conditions in the epoxidation of 1-octene.
Selected bond lengths and angles for C1, C3 and C5.
b
Entry
C1/mol%
H2O2/equiv
CH3CO2H/equiv
T/min
Yield /%
C1
C3
C5
2.343
2.425
2.408
2.273
2.219
2.244
1
2
3
4
5
6
0.25
0.25
0.25
0.25
0.1
1.5
1.5
1.5
1.3
1.3
1.3
1.0
5.0
10.0
10.0
10.0
10.0
30
30
30
30
30
5.0
2
78
99
96
92
90
Mn1–N1/A˚
Mn1–N2/A˚
Mn1–N3/A˚
Mn1–N4/A˚
Mn1–O1/A˚
Mn1–O2/A˚
N1–Mn1–N4/
N2–Mn1–N3/
O–Mn1–O/
2.225
2.284
2.311
2.216
2.13
2.20b
171
81
90
2.241
2.287
2.287
2.241
2.17
2.17
165
82
a
0.1
a
Reaction conditions: alkene (2.0 mmol), C1 (0.1–0.25 mol%) and CH3COOH
◦
◦
89
58
86
(
1.0–10.0 equiv) dissolved in 1.5 mL CH3CN, 30% H2O2 (1.3–1.5 equiv) dissolved in
◦
CH3CN (V:V = 1:1) was added at 0 C over a period of 30 min.
◦
92
b
Determined by GC using nitrobenzene as internal standard.

S. Yu et al. / Journal of Molecular Catalysis A: Chemical 353–354 (2012) 185–191
189
Table 5
Epoxidations of different substrates using C1 and C3.a
Entry
Alkenes
Cat./mol%
0.1
H2O2/equiv
1.3
C1
C3
b
b
Conv./yield /%
Conv./yield /%
1
97/92
99/99
2
3
C
3
H
7
0.1
0.1
1.3
1.3
96/94
99/98
C
4
H
9
92/90
–c
99/97
56/54
4
5
6
0.01
0.01
0.01
1.3
1.3
1.3
c
d
–
64/60
c
40/38e
–
7
8
C
6
H
13
17
0.1
0.1
1.3
1.3
94/91
89/87
99/97
C
H
99/95
8
9
0.1
0.1
0.1
1.3
1.3
1.3
89/89
96/94
100/95
99/99
97/88
100/92
1
0
1
1
1
1
2
3
0.1
0.1
1.3
1.3
100/75
97/96
100/80
97/96
1
4
0.1
1.3
100/97
100/95
Ph
1
5
6
Ph
Ph
Ph
0.1
0.1
1.3
1.3
57/55f,g
74/70h,i
100/99/90g,h
97/94/87h
O
1
O
O
1
7
0.1
1.3
90/88/85h
100/99/96h
95/91/90h
Ph
h
1
1
2
2
8
9
0
1
0.1
0.1
0.25
0.25
1.3
3.0
1.2
3.0
90/88/88
94/92/90
92/90/88
96/90/88
O
h
h
100/96/94
j
j
h
h
97/92/89
h
h
99/94/92
a
Reaction conditions: alkene (2.0 mmol), complex (0.1 mol%) and CH3COOH (10.0 equiv) dissolved in 1.5 mL CH3CN, 30% H2O2 (1.3 equiv) dissolved in CH3CN (V:V = 1:1)
◦
was added dropwise at 0 C over a period of 30 min and 5 extra min of stirring were allowed.
b
Yields determined by GC using nitrobenzene as internal standard.
c
“
–” means that the reaction was not carried out.
d
e
f
◦
H2O2 dissolved in CH3CN (V:V = 1:1) was added dropwise at 0 C in 60 min.
H2O2 dissolved in CH3CN (V:V = 1:1) is added dropwise at 0 C rapidly and total reaction time is 1 min, and the corresponding TOF was up to 228,000 h
◦
−1
.
C1 0.5 mol%.
Dissolved in 15 mL CH3CN.
Isolated yields.
g
h
i
C1 0.25 mol%.
j
Reaction conditions: alkene (1.0 mmol) and complex (0.25 mol%) dissolved in 1.5 mL CH3CN, 8% AcOOH (1.2–3.0 equiv) added at room temperature in one time and stirred
for 5 min.

1
90
S. Yu et al. / Journal of Molecular Catalysis A: Chemical 353–354 (2012) 185–191
9
.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
Fig. 2. 1H NMR spectrum of Zn L1(CF3SO3)2 in CDCl3 at ambient temperature.
II
the regioselectivity of C1 or Mn complex with mep ligand was
poorer than that of C3. We presumed that the phenyl group intro-
duced into the 2-pyridylmethyl positions of mep and mcp changed
the steric hindrance and electronic effect, which was beneficial for
achieving perfectly selective monoepoxidation in the epoxidation
of R(−)-carvone. Additionally, the addition time of hydrogen per-
oxide was examined and the yield just increased a little when the
time was prolonged to 60 min (Table 5, entry 5). The efficiency of
these Mn-complexes also was tested. The hydrogen peroxide was
added one-offly with 0.01 mol% catalyst loading, the yield reached
−
1
3
8% within 1 min. And the TOF was 228,000 h (Table 5, entry 6).
4. Conclusion
In summary, the present work describes an efficient approach
for the synthesis of a family of N4 tetradentate ligands and their
II
corresponding Mn complexes which provided opportunities for
the screening of a broad range of epoxidation catalysts. And the
influence of the topologies of the ligands including the steric hin-
drance and the electronic effect on the catalytic activities was
systematically examined, which provided important information
for designing new efficient ligand. Fortunately, C1 and C3 exhibited
excellent selectivity, high yields and TOF with low catalyst load-
ing (0.1–0.01 mol%) for epoxidation of a family of olefins, including
internal aromatic olefins, internal and terminal aliphatic olefins
−
1
and diolefins. Notably, the TOF was even up to 228,000 h . And
diolefins R(−)-carvone could be epoxidized with excellent regios-
electivity using H O or AcOOH as the terminal oxidant. Further
2
2
developing new synthetic strategy toward the nitrogen ligands and
further mechanistic studying on these highly active systems are
currently underway.
Acknowledgements
Fig. 1. X-ray structures of C1, C5 and C6 (hydrogen atoms are omitted for clarity).
We are grateful for the financial support from the Chinese
Academy of Sciences and the National Natural Science Foundation
of China (20873166, 21073210, 21133011).
olefins such as chalcone also proceeded well with good yield and
selectivity (entry 17).
Importantly, an excellent regioselectivity of C1 or C3 was also
demonstrated by the monoepoxidations of the terminal olefin
site of R(−)-carvone (entries 18–21). Different from the previ-
ous report [15], the same monoepoxide was attained when the
amount of hydrogen peroxide (entries 18–19) or peracetic acid
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molcata.2011.11.024.
[
33] (entries 20–21) was increased to 3.0 equiv of R(−)-carvone.
Furthermore, a 1:1 mole mixture of cyclooctene and trans-4-
octene was used in the present catalytic system to testify the
regioselectivity (Table S1). Interestingly, excellent results were
obtained using C3 as the catalyst (yields of cyclooctene epoxide and
trans-4-octene epoxide were 65% and 4.6% respectively). However,
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