Benzimidazolic complexes of methyltrioxorhenium(VII): Synthesis and application in catalytic olefin epoxidation

Article abstract of DOI:10.1016/j.jorganchem.2012.11.006

Seven new Lewis base adducts of methyltrioxorhenium(VII) (MTO) with the general formula CH₃ReO₃·L (L = bidentate benzimidazolic ligands, namely (L = 2-(2-Pyridinyl)-1H-benzimidazole, 5-methyl-2-(2-pyridyl)benzimidazole, 5-Chloro-2-(2-pyridyl)benzimidazole, 2-(2-Pyridyl)-1H-imidazo-[4,5-b]-pyridine, 2-(2-Quinolyl)benzimidazole, 2-(5-methyl-1H-benzimidazol-2-yl)-quinoline, and 2-(5-chloro-1H-benzimidazol-2- yl)-quinoline)) were prepared. All the complexes were characterized by IR, ¹H, ¹³C NMR, MS and elemental analysis as well as tested as catalysts for olefin epoxidation using 35% aqueous hydrogen peroxide as oxidant under mild condition. The influence of different ligand concentrations was also examined. The results show that the complexes are highly selective in olefin epoxidation and good yields can be obtained when excess ligand is applied.

Full text of DOI:10.1016/j.jorganchem.2012.11.006

Journal of Organometallic Chemistry 730 (2013) 132e136
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Benzimidazolic complexes of methyltrioxorhenium(VII): Synthesis
and application in catalytic olefin epoxidation
*
Su Li, Bo Zhang, Fritz. E. Kühn
Chair of Inorganic Chemistry/Molecular Catalysis, Catalysis Research Center, Technische Universität München, Ernst-Otto-Fischer-Straße 1, D-85747 Garching bei München, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Seven new Lewis base adducts of methyltrioxorhenium(VII) (MTO) with the general formula CH3ReO3$L
(L ¼ bidentate benzimidazolic ligands, namely (L ¼ 2-(2-Pyridinyl)-1H-benzimidazole, 5-methyl-2-(2-
pyridyl)benzimidazole, 5-Chloro-2-(2-pyridyl)benzimidazole, 2-(2-Pyridyl)-1H-imidazo-[4,5-b]-pyridine,
2-(2-Quinolyl)benzimidazole, 2-(5-methyl-1H-benzimidazol-2-yl)-quinoline, and 2-(5-chloro-1H-benzi-
midazol-2-yl)-quinoline)) were prepared. All the complexes were characterized by IR, 1H, 13C NMR, MS and
elemental analysis as well as tested as catalysts for olefin epoxidation using 35% aqueous hydrogen peroxide
as oxidant under mild condition. The influence of different ligand concentrations was also examined. The
results show that the complexes are highly selective in olefin epoxidation and good yields can be obtained
when excess ligand is applied.
Received 8 October 2012
Received in revised form
2 November 2012
Accepted 5 November 2012
Keywords:
Methyltrioxorhenium(MTO)
Benzimidazolic
Epoxidation
Hydrogen peroxide
Olefin
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
latter, maintaining the interaction in the catalytically active species
[28,29]. Although numerous N-bases have been described [21e32],
Epoxides are versatile starting materials for value added prod-
ucts such pharmaceuticals, flavor and fragrance molecules [1e4]. A
broad variety of catalysts for olefin epoxidation has been described
over the years with organometallic complexes being very efficient
as catalysts for the synthesis for fine chemicals and for sophisti-
cated organic substrates [5e11]. Certainly one of the most widely
applied and well examined among them is methyltrioxo-
rhenium(VII) (MTO) [12e14]. MTO utilizes hydrogen peroxide as
oxidizing agent producing only water as by-product, making such
reaction environmentally benign [15e20]. A major drawback of this
system is the Lewis acidity of the catalyst in the presence of water:
it promotes ring opening reactions, leading to a mixture of epoxide
and diol instead of forming only one product with high selectivity
[12,13]. Although systems containing Lewis bases have been
examined early with respect to their ability to buffer the Lewis
acidity without reducing the catalyst activity, all these early
attempts did not prove successful [21e23].
adducts without N-donor functionalities and nevertheless leading
to good selectivity when applied with the MTO/H2O2-system
remained the exception [33e39].
Benzimidazole is a typical heterocyclic ligand with nitrogen as
the donor atom. In the case of 2-(2-pyridinyl)-1H-benzimidazole,
the bidentate ligand can be described as electron-donating due to
the two nitrogen atoms of the benzimidazole and pyridine moie-
ties. Studies about the coordination chemistry of benzimidazolic
ligands have been carried out with a variety of metal ions [40e42],
however, MTO complexes containing benzimidazole based ligands
have not been described until now. In this paper the synthesis,
characterization and catalytic application of bidentate MTO benz-
imidazole adducts are described.
2. Results and discussion
2.1. Synthesis and spectroscopic characterization
In the late 1990s Sharpless et al. discovered that a significant
excess of aromatic N-coordinating Lewis bases is needed to get high
selectivity towards epoxide without reduction of catalyst activity or
lifetime [24e27]. The effect was explained by shifting the equilib-
rium between free and Lewis base coordinated MTO towards the
The addition of one equivalent of MTO to the bidentate N-donor
benzimidazolic derivatives in dichloromethane at room tempera-
ture leads to the formation of the corresponding MTO-Lewis-base
complexes 1e7 (see Scheme 1), which can be easily isolated as
a yellow or orange solids in good yields. These bidentate complexes
have a good stability both in solid state and in solution at the room
temperature. In the solid state, all the complexes are not very
sensitive to air, but slightly sensitive to moisture. Therefore,
* Corresponding author. Tel.: þ49 89 289 13081; fax: þ49 89 289 13473.
E-mail address: fritz.kuehn@ch.tum.de (Fritz.E. Kühn).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.11.006

S. Li et al. / Journal of Organometallic Chemistry 730 (2013) 132e136
133
Scheme 1. Synthesis of MTO salen complexes 1e7.
a water-free atmosphere is needed to preserve the complexes over
prolonged periods of time.
Selected 1H NMR spectroscopic data of the benzimidazolic
ligands and the MTO complexes are shown in Table 3. Compared to
the spectra of the non-coordinated MTO, the proton signals origi-
nating from the ReeCH3 of the MTO complexes 1e4 are shifted to
higher magnetic field as reported in the literature [50,51]. With
regard to the MTO complexes 5e7, the proton signals from the Ree
CH3 group are not shifted much due to the influence of the quin-
oline ring. The magnitude of the shift is directly related to the
electron-donating capability of the ligands. For example, relative to
MTO itself, complexes 3 bearing an electron-withdrawing chlorine
atom on the phenyl moiety shows a chemical shift of the methyl
signal from 1.90 ppm to 1.76 ppm. However, in the case of complex
2, which has a methyl group on the phenyl moiety, the 1H shift
changes from 1.90 ppm to 1.55 ppm. Furthermore, the signals of the
NeH group on the imidazole ring of complexes 1, 2, 3, 4 and 7 are
slightly shifted to lower field compared to free benzimidazolic
ligands. The NeCH vibration in the pyridine ring is also slightly
shifted to a lower field in these cases.
The IR spectra of the complexes 1e7 show strong symmetric
Re]O stretching vibrations in the region of 946e958 cmꢀ1
whilst the asymmetric Re]O stretching vibration lies between
919 and 929 cmꢀ1 (see Table 1). The Re]O bands of the
complexes 1e7 are significantly red-shifted compared to the
vibrations (
n
sym ¼ 992 cmꢀ1
,
n
asym ¼ 965 cmꢀ1) of MTO alone
[43]. The vibration differences reflect the donating capacity of the
bidentate benzimidazolic ligands. The additional electron density
originating from the ligands significantly reduce the strength of
the Re]O bonds.
The main vibrational frequencies of the benzimidazolic ring,
namely the
imidazole, as well as the
n
(NeH),
n
(C]C),
n
(C]N) vibrations of pyridine and
(CeH) benzimidazolic ring
d
(CeN) and
d
out of plane vibrations are observed [44,45]. In all IR spectra of
compounds 1e7 peaks originating from these vibrations are
evident (Table 2). Interestingly, the bands are shifted towards
higher wave numbers as compared with the position in the free
ligands. These results are indicative of ligand coordination through
the benzimidazolic nitrogen. Moreover, the vibration of (NeH)
bands of the benzimidazolic ligands are seen in the range of
3000e3400 cmꢀ1 as a very broad band, and the ligands show
characteristic pyridine and imidazole C]N frequencies in the range
of 1563e1571 cmꢀ1 and 1590e1597 cmꢀ1. It is noteworthy that the
sharp band between 1454 and 1510 cmꢀ1 is due to the stretching
vibration of aromatic C]C. Another sharp band between 736 and
748 cmꢀ1 can be assigned to the out-of-plane CeH bending
vibrations of the di- and tri-substituted benzene ring [46].
2.2. Application as epoxidation catalysts
Compounds 1e7 were examined as catalysts for the epoxidation
of cyclooctene with 35% H2O2 as oxidant in dichloromethane at
room temperature. A catalyst: oxidant: substrate ratio of 1:100:50
was applied in all experiments. The results are summarized in
Table 4. Among all the catalysts, compound 4 appears to be the best
for epoxidation of cis-cyclooctene. The yield reaches 99% and the
Table 2
The strong band around 1300e1320 cmꢀ1 in the spectra of the
ligands is shifted towards higher energy and splitted upon chela-
tion, indicating coordination through the pyridine-nitrogen atom
[47,48]. In case of complex 1, the split band appears at 1323 cmꢀ1
and 1301 cmꢀ1 whereas it is at 1312 cmꢀ1 in the spectrum of L1 as
a strong band. In addition to this, differences are observed in the
band character due to the effect of metal complexation. For
example, the medium strong (C]N) bands are changed to
a shoulder or weak bands in some complexes [49].
Selected IR spectroscopic data of ligands and MTO complexes.
Compound
n
(NeH)
n
(C]N)
n
(C]C)
d
(CeN)
d (CeH)
(cmꢀ1
)
(cmꢀ1
)
(cmꢀ1
)
(cmꢀ1
)
(cmꢀ1
)
L1
1
L2
2
L3
3
L4
4
L5
5
L6
6
L7
7
3042
3078
3056
3075
3050
3068
3060
3087
3043
3074
3048
3063
3055
3062
1590, 1564
1608, 1591
1590, 1568
1607, 1593
1593, 1569
1602, 1589
1595, 1568
1589
1595, 1571
1596
1597, 1566
1603, 1594
1597, 1563
1602, 1593
1465
1497
1458
1547
1454
1547
1465
1539
1496
1510
1508
1553
1497
1506
1439, 1397
1457, 1440
1441, 1396
1490, 1452
1443, 1400
1491, 1442
1446, 1414
1481, 1454
1442, 1413
1475, 1456
1447, 1405
1480, 1428
1442, 1412
1471, 1428
740
745
744
749
736
752
741
760
740
761
748
748
741
756
Table 1
Characteristic IR vibrations of CH3ReO3 fragments (cmꢀ1) in 1e7.
MTO
1
2
3
4
5
6
7
Assignment
992
965
943
919
946
922
950
925
950
926
958
929
956
929
955
925
ReO3 sym str
ReO3 asym str

134
S. Li et al. / Journal of Organometallic Chemistry 730 (2013) 132e136
H
N
Table 3
N
N
Selected 1H and 13C NMR spectroscopic data for complexes 1e7 in d6-DMSO.
NeCH(Py) NeCH(Py) NH ligand NH complex ReeCH3,
ReeCH3,
N
N
N
N
complex, 1H
[ppm]
d
[ppm] 1H
d
[ppm] 1H
d
[ppm] 13C
d
[ppm]
N
H
ligand,
d
4
4'
1H [ppm] 1H
d
Scheme 2. Resonance structures 4 and 40.
MTO
1.90
1.77
1.55
1.76
1.87
25.39
25.79
25.90
25.58
25.52
1
2
3
4
8.74
8.73
8.75
8.78
8.41
e
8.77
8.80
8.77
8.80
8.78
e
13.09
12.96
13.32
13.52
13.29
13.53
13.46
13.75
1 h with a TOF of ca. 750 hꢀ1 and ca. 920 hꢀ1 when the molar ratio
of L1:MTO was raised to 20:1 and 50:1 (line f and g). The results
show that large excesses of benzimidazolic ligands lead to higher
catalytic activity for olefin epoxidation. This observation is in
contrast to previous observations with modentate pyridine-derived
ligands, where the activity and yield did not change significantly
when ratios higher than 1:10 (MTO: Lewis base) were reached. The
reason for the observed behavior may be as follows: the NH groups
in the benzimidazolic ligands may form hydrogen bonds with the
oxidant leading to an activity decrease. The amount of active
species present, however, increases with increasing amounts of the
ligand due to a favorable shift of the equilibrium. The large excesses
of the ligands help to maintain the activity by providing the cata-
lytically active species in a significant enough concentration.
Furthermore, the strong electron-donating ability of the ligand may
contribute to an acceleration of the formation of the active species,
leading to a better catalytic activity. Calculations are under way to
prove these assumptions.
5
6
7
13.20
13.06
13.20
13.19
13.03
13.35
1.91
1.91
1.91
25.42
25.43
25.42
e
e
e
e
TOF is 236 hꢀ1 (Entry 4). The other complexes show only moderate
or low conversions during the first hour and no significant
improvement even after 24 h (Entries 1e3, 5e7). The better
performance of 4 may be due to its enhanced stability due to
electron delocalization (Scheme 2) and its stronger Lewis basicity.
On the other hand, this poor conversion may be also due to the
presence of NH groups in the benzimidazolic ligands [52]. They
may interfere with the catalytic cycle by forming hydrogen bonds
with produced H2O during the reaction. In summary, the strong
coordination capacity of the di-nitrogen benzimidazolic ligands can
slightly increase the epoxidation selectivity but reduce the
conversion of the epoxidation reaction. A similar situation is also
known of other related literature described systems [53,54].
MTO complex 4 was also tested as catalyst for the epoxidation of
various other olefins including cyclic olefins and long-chain olefins
with H2O2 as oxidant. The results are given in Table 5. It has to be
noted here that 1-octene is readily epoxidized into its epoxide the
3. Conclusions
Several bidentate N-donor benzimidazolic adducts of MTO were
synthesized, characterized and applied for catalytic olefin epoxi-
dation using H2O2 as oxidant in CH2Cl2 at room temperature. The
benzimidazolic MTO compounds show good stability and can be
exposed to air for several days. Most complexes exhibit good
selectivity but relatively low activity. A large excess of the benzi-
midazolic ligands however, is able to increase the catalytic activity
significantly.
yield being 99% (Entry 2). For trans-b-methylstyrene (Entry 3),
limonene (Entry 4) and (þ)-camphene (Entry 5), usually more
challenging substrates for epoxidation, still relatively high yields
(>70%) can be obtained (Entries 3e5).
2.3. Influence of the ligands concentration
4. Experimental
L1 was used to investigate the influence of the ligands concen-
tration on the epoxidation reaction. The epoxidation results in the
first hour are summarized in Fig. 1. Application of free MTO (line d)
4.1. Materials
leads to a yield 88% after 1 h reaction time and a TOF of 280 hꢀ1
.
All preparation and manipulations were performed using stan-
dard Schlenk techniques under an Argon atmosphere. All the
chemicals for syntheses were obtained commercially and used
without further purification. Solvents were dried by standard
procedures (n-hexane over Na/benzophenone; CH2Cl2 over CaH2),
distilled under argon and used immediately or kept over 4 Å
molecular sieves. Elemental analyses were performed with a Flash
EA 1112 series elemental analyzer. 1H and 13C NMR were measured
in d6-DMSO with a mercury-VX 300 spectrometer and a 400-MHz
Bruker Avance DPX-400 spectrometer. IR spectra were recorded
using a Perkin Elmer FT-IR spectrometer with KBr pellets as the IR
matrix. CI-MS spectra were measured on a Finnigan MAT 90 mass
spectrometer. Catalytic runs were monitored by GC methods on
a HewlettePackard instrument HP 5890 Series II equipped with
a FID, a Supelco column Alphadex 120 and a HewlettePackard
integration unit HP 3396 Series II. MTO was synthesized accord-
ing to the literature procedures [16,17].
Compared to this, the epoxide yield was only 25%,15% and 28% after
1 h with no further changes even after 24 h when the molar rate of
L1:MTO was 0.5:1, 1:1 and 2:1(line a, b, c). The activity of the
catalytic system increased when the ratio of L1:MTO was raised to
10:1. The reaction displayed a TOF of nearly 700 hꢀ1 and a yield of
57% after 5 min and reached to 98% after 1 h (line e). With higher
ligands concentrations, the epoxide yield slightly increased to 63%
and 76% after 5 min reaction time and reached almost 100% after
Table 4
Epoxidation of cis-cyclooctene with different catalyst using H2O2 as oxidant.a
Entry
Catalyst
Yieldb (%)
Selectivityb (%)
TOFc (hꢀ1
)
1
2
3
4
5
6
7
1
2
3
4
5
6
7
29
23
34
99
25
31
33
99
99
99
99
99
99
99
137
149
211
236
132
176
152
4.2. Synthesis of the ligands
a
Reaction condition: cis-cyclooctene (2 mmol); H2O2 (35%)(4 mmol), catalyst
(2 mol%), CH2Cl2 (1.2 mL) at room temperature, t ¼ 1 h.
The ligands L1-L7 were prepared according to literature proce-
dures [55]. All the ligands were characterized by IR, 1H NMR and
elementary analysis.
b
Yield and selectivity are calculated based on GC analysis.
c
Determined after 5 min.

S. Li et al. / Journal of Organometallic Chemistry 730 (2013) 132e136
135
Table 5
Epoxidation of different olefins with complex 4 as catalyst using H2O2 as oxidant in CH2Cl2.a
Entry
Substrate
Product
Time (h)
1
Conversion (%)b
99
Yield (%)b
1
99
O
O
2
3
24
4
99
96
99
96
O
O
4
3
73
77
73
77
5
0.5
O
a
Reaction condition: olefins (2 mmol); H2O2 (35%)(4 mmol), catalyst 4 (2 mol%), CH2Cl2 (1.2 mL) at room temperature.
The yield and selectivity are calculated by GC analysis.
b
4.3. Synthesis of MTO complexes
Compound 1: yellow powder, Yield: 85%. C13H12N3O3Re (445),
elemental analysis: Theory (C: 35.13; H: 2.72; N: 9.45), Found (C:
All MTO complexes were synthesized according to a general
procedure: a solution of MTO (0.05 g, 0.2 mmol) in CH2Cl2 (2 mL)
was drop-wise added to an equally concentrated solution of ligand
(L1eL7) in CH2Cl2 (5 mL) under stirring at room temperature. For 1,
2, 5 a yellow precipitate formed rapidly. The precipitate was iso-
lated by filtration, washed with n-hexane and dried under reduced
pressure. For 3, 4, 6, 7, the reaction mixture was stirred for 1 h at
room temperature before removing the solvent in vacuum. The
remaining solid was washed with n-hexane twice and dried under
reduced pressure.
35.38; H: 2.72; N: 9.48); IR (KBr,
n
cmꢀ1):3078, 1608, 1591, 1457,
1440, 943, 919, 745; 1H NMR (d6-DMSO, 400 MHz, r.t.):
d
(ppm) ¼ 13.29 (1H, s, NH), 8.77, 8.76 (1H, d, Py), 8.36, 8.37 (1H, d,
Py), 8.04, 8.06, 8.07 (1H, t, Py), 7.66 (2H, s, Ph), 7.55, 7.56 7.57 (1H, t,
Py), 7.26e7.28 (2H, m, Ph), 1.77 (3H, s, MTOeCH3); 13C NMR (d6-
DMSO, 100 MHz, r.t.):
d
(ppm) ¼ 150.45, 149.64, 147.49, 138.73,
126.80, 123.69, 122.47, 116.91, 26.79; MS (CI): m/z
¼
430.8
[M ꢀ CH3]þ, 195.8 [M ꢀ MTO]þ, 234.8 [ReO3]þ.
Compound 2: yellow powder, Yield: 83%. C14H14N3O3Re (459),
elemental analysis: Theory (C: 36.67; H: 3.08; N: 9.16), Found (C:
37.22; H: 3.09; N: 9.25); IR (KBr,
n
cmꢀ1): 3075, 1607, 1593, 1490,
1452, 946, 922, 749; 1H NMR (d6-DMSO, 400 MHz, r.t.):
d
(ppm) ¼ 13.53 (1H, s, NH), 8.80, (1H, s, Py), 8.39, 8.38 (1H, d, Py),
8.15e8.09 (1H, m, Py), 7.61, 7.60 (2H, d, Ph), 7.50 (1H, s, Py), 7.16, 7.14
(1H, d, Ph), 2.46 (3H, s, CH3), 1.55 (3H, s, MTOeCH3); 13C NMR (d6-
DMSO, 100 MHz, r.t.):
d
(ppm) ¼ 150.42, 149.64, 149.51, 139.04,
138.77, 133.65, 125.95, 125.83, 123.73, 122.60, 122.49, 116.00, 25.90,
21.80; MS (CI): m/z ¼ 460.8 [M]þ, 447.8 [M ꢀ CH3]þ,446.9 [M ꢀ O]þ,
210.1 [M ꢀ MTO]þ, 250.0 [MTO]þ.
Compound 3: yellow powder, Yield: 74%. C13H11ClN3O3Re (479),
elemental analysis: Theory (C: 32.60; H: 2.32; N: 8.77), Found (C:
32.62; H: 2.33; N: 8.70); IR (KBr,
n
cmꢀ1): 3068, 1602, 1589, 1491,
1442, 950, 925, 752; 1H NMR (d6-DMSO, 400 MHz, r.t.):
d
(ppm) ¼ 13.44 (1H, s, NH), 8.77, 8.76 (1H, d, Py), 8.36, 8.33 (1H, d,
Py), 8.07, 8.06, 8.03 (1H, t, Py), 7.68 (2H, s, Ph), 7.58, 7.57 7.56 (1H, t,
Py), 7.29, 7.27 (1H, d, Ph), 1.78 (3H, s, MTOeCH3); 13C NMR (d6-
DMSO, 100 MHz, r.t.):
d
(ppm) ¼ 152.22, 149.84, 147.98, 138.36,
127.54, 125.71, 123.54, 122.28, 26.68; MS (CI): m/z ¼ 462.7
[M ꢀ CH3]þ, 229.9 [M ꢀ MTO]þ.
Compound 4: orange powder, Yield: 81%. C12H11N4O3Re (446),
elemental analysis: Theory (C: 32.36; H: 2.49; N: 12.58), Found (C:
33.05; H: 2.56; N: 12.63); IR (KBr,
n
cmꢀ1): 3079, 1589, 1481, 1454,
Fig. 1. Influence of the ligand concentration on the yield, L1:MTO ¼ 1:1 (a), 0.5:1 (b),
1
2:1 (c), 10:1 (e), 20:1 (f), 50:1 (g), MTO (d).
952, 927, 784; H NMR (d6-DMSO, 400 MHz, r.t.):
d
(ppm) ¼ 13.75

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S. Li et al. / Journal of Organometallic Chemistry 730 (2013) 132e136
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8.03 (2H, t, Py), 7.57e7.60 (1H, m, Py), 7.27e7.30 (1H, m, Py), 1.87
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(2008) 442e446.
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Technol. 2 (2012) 722e724.
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P. Kiprof, W. Scherer, Chem. Ber. 126 (1993) 45e50.
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196.8 [M ꢀ MTO]þ.
Compound 5: yellow powder, Yield: 80%. C17H14N3O3Re (495),
elemental analysis: Theory(C:41.29;H:2.85;N:8.50), Found(C:41.11;
H:2.84;N:8.49);IR(KBr,
n
cmꢀ1):3072,1597,1475,1461, 958,929, 761;
1H NMR (d6-DMSO, 400 MHz, r.t.):
d
(ppm) ¼ 13.19 (1H, s, NH), 8.57,
8.56 (1H, d, Py), 8.50, 8.48 (1H, d, Ph), 8.19, 8.16 (1H, d, Ph), 8.09, 8.07
(1H, d, Ph), 7.90, 7.88, 7.86 (1H, t, Ph), 7.78, 7.76 (1H, d, Ph), 7.71, 7.69,
7.67 (1H, t, Ph), 7.64, 7.62 (1H, d, Py), 7.24e7.32 (2H, m, Ph),1.90 (3H, s,
MTOeCH3); 13C NMR (d6-DMSO, 100 MHz, r.t.):
d
(ppm) ¼ 151.09,
149.03, 147.65, 137.90, 130.95, 129.21, 128.70, 128.55, 127.80, 123.37,
119.67, 25.42; MS (CI): m/z ¼ 250.6 [MTO]þ, 245.8 [M ꢀ MTO]þ.
Compound 6: yellow powder, Yield: 84%. C18H16N3O3Re (509),
elemental analysis: Theory (C: 42.51; H: 3.17; N: 8.26), Found (C:
42.18; H: 3.35; N: 7.53); IR (KBr,
n
cmꢀ1): 3063, 1603, 1594, 1511,
1480, 1428, 955, 929, 748; 1H NMR (d6-DMSO, 400 MHz, r.t.):
d
(ppm) ¼ 13.06 (1H, s, NH), 8.55, 8.53 (1H, d, Py), 8.17, 8.15 (1H, d,
Ph), 8.08, 8.06 (1H, d, Py), 7.89, 8.87, 7.85 (1H, t, Ph), 7.70, 7.68, 7.66
(1H, t, Ph), 7.69 (1H, s, Ph), 7.47 (1H, s, Ph), 7.11, 7.09 (1H, d, Ph), 2.46
(3H, s, CH3) 1.91 (3H, s, MTOeCH3); 13C NMR (d6-DMSO, 100 MHz,
r.t.):
d
(ppm) ¼ 150.71, 149.03, 147.55, 137.84, 132.90, 130.93, 129.16,
128.69, 128.50, 127.73, 124.97, 119.63, 25.43, 21.86; MS (CI): m/
z ¼ 509.5 [M]þ, 258.9 [M ꢀ MTO]þ, 250.9 [MTO]þ, 234.9 [ReO3]þ.
Compound 7: orange powder, Yield: 71%. C17H13ClN3O3Re (529),
elemental analysis: Theory (C: 38.60; H: 2.48; N: 7.94), Found (C:
39.20; H: 3.30; N: 6.71); IR (KBr,
n
cmꢀ1): 3062, 1593, 1506, 1471,
1428, 955, 925, 756; 1H NMR (d6-DMSO, 400 MHz, r.t.):
[30] M.D. Zhou, K.R. Jain, A. Günyar, P.N.W. Baxter, E. Herdtweck, F.E. Kühn, Eur. J.
d
(ppm) ¼ 13.37 (1H, s, NH), 8.57, 8.54 (1H, d, Py), 8.19, 8.17 (1H, d,
Inorg. Chem. (2009) 2907e2914.
[31] S.A. Hauser, V. Korinth, E. Herdtweck, M. Cokoja, W.A. Herrmann, F.E. Kühn,
Eur. J. Inorg. Chem. (2010) 4083e4090.
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Inorg. Chem. (2012) in press.
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118 (1997) 33e45.
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(2007) 158e166.
[35] M.D. Zhou, S.L. Zang, E. Herdtweck, F.E. Kühn, J. Organomet. Chem. 693 (2008)
2473e2477.
[36] A. Capapé, M.D. Zhou, S.L. Zang, F.E. Kühn, J. Organomet. Chem. 693 (2008)
3240e3244.
Ph), 8.09, 8.07 (1H, d, Py), 7.90, 8.88, 7.86 (1H, t, Ph), 7.67e7.72 (3H,
m, Ph), 7.27e7.31 (1H, m, Ph), 1.91 (3H, s, MTOeCH3); 13C NMR (d6-
DMSO, 100 MHz, r.t.):
d
(ppm) ¼ 152.43, 151.07, 148.98, 147.66,
138.03, 137.90, 131.03, 130.96, 129.21, 128.70, 128.64, 128.56, 127.96,
127.81, 123.40, 119.67, 25.42; MS (CI): m/z ¼ 529.7 [M]þ, 279.8
[M ꢀ MTO]þ, 250.8 [MTO]þ.
4.4. Catalytic reactions
[37] M.D. Zhou, Y. Yu, A. Capapé, K.R. Jain, E. Herdtweck, X.R. Li, J. Li, S.L. Zhang,
F.E. Kühn, Chem. Asian J. 4 (2009) 411e418.
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205e208.
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(1994) 2039e2057.
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All catalytic reactions were carried out under continuous stir-
ring in a glass flask in a water bath at room temperature. General
procedure: 2 mmol of substrate, 1.2 mL of CH2Cl2 and 0.04 mmol of
the catalyst were mixed in a flask. The reaction started when
aqueous H2O2 (35%, 4 mmol, 0.35 mL) was added. The course of the
reaction was monitored by quantitative GC analysis. Samples were
taken at regular time intervals, diluted with n-hexane, then treated
with a catalytic amount of MgSO4 and MnO2 to remove water and
to destroy the excess of peroxide. The resulting slurry was filtered
and the filtrate injected into a GC column. The conversion of
cyclooctene and the formation of the according oxide were calcu-
lated from calibration curves (r2 > 0.999) recorded prior to the
reaction course.
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Acknowledgments
[49] A.Tavman, B.Ülküseven, S.Birteksöz, G. Ötük, FoliaMicrobiol. 48 (2003)479e483.
[50] S.M. Nabavizadeh, A. Akbari, M. Rashidi, Dalton Trans. (2005) 2423e2427.
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Inorg. Chem. Acta 304 (2000) 230e236.
SL and BZ thank the TUM graduate School for financial support.
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