Activation of hydrogen peroxide by ionic liquids: Mechanistic studies and application in the epoxidation of olefins

Article abstract of DOI:10.1002/chem.201203208

Imidazolium-based ionic liquids that contain perrhenate anions are very efficient reaction media for the epoxidation of olefins with H₂O ₂ as an oxidant, thus affording cyclooctene in almost quantitative yields. The mechanism of this reaction does not follow the usual pathway through peroxo complexes, as is the case with long-known molecular transition-metal catalysts. By using in situ Raman, FTIR, and NMR spectroscopy and DFT calculations, we have shown that the formation of hydrogen bonds between the oxidant and perrhenate activates the oxidant, thereby leading to the transfer of an oxygen atom onto the olefin demonstrating the special features of an ionic liquid as a reaction environment. The influence of the imidazolium cation and the oxidant (aqueous H₂O₂, urea hydrogen peroxide, and tert-butyl hydrogen peroxide) on the efficiency of the epoxidation of cis-cyclooctene were examined. Other olefinic substrates were also used in this study and they exhibited good yields of the corresponding epoxides. This report shows the potential of using simple complexes or salts for the activation of hydrogen peroxide, owing to the interactions between the solvent medium and the active complex. Copyright

Full text of DOI:10.1002/chem.201203208

FULL PAPER
DOI: 10.1002/chem.201203208
Activation of Hydrogen Peroxide by Ionic Liquids: Mechanistic Studies and
Application in the Epoxidation of Olefins
[
a]
[b]
[a, c]
[a]
Iulius I. E. Markovits, Wilhelm A. Eger, Shuang Yue,
Mirza Cokoja,
[
a]
[a]
[c, d]
[b]
Christian J. Mꢀnchmeyer, Bo Zhang, Ming-Dong Zhou,
Alexander Genest,
[
e, f]
[c, d]
[b, g]
[a]
Jꢁnos Mink,
Shu-Liang Zang,*
Notker Rçsch,*
and Fritz E. Kꢀhn*
Abstract: Imidazolium-based ionic liq-
uids that contain perrhenate anions are
very efficient reaction media for the
epoxidation of olefins with H O as an
oxidant, thus affording cyclooctene in
almost quantitative yields. The mecha-
nism of this reaction does not follow
the usual pathway through peroxo
complexes, as is the case with long-
known molecular transition-metal cata-
lysts. By using in situ Raman, FTIR,
and NMR spectroscopy and DFT cal-
culations, we have shown that the for-
mation of hydrogen bonds between the
oxidant and perrhenate activates the
oxidant, thereby leading to the transfer
of an oxygen atom onto the olefin
demonstrating the special features of
an ionic liquid as a reaction environ-
ment. The influence of the imidazolium
cation and the oxidant (aqueous H O ,
urea hydrogen peroxide, and tert-butyl
hydrogen peroxide) on the efficiency
of the epoxidation of cis-cyclooctene
were examined. Other olefinic sub-
strates were also used in this study and
they exhibited good yields of the corre-
sponding epoxides. This report shows
the potential of using simple complexes
or salts for the activation of hydrogen
peroxide, owing to the interactions be-
tween the solvent medium and the
active complex.
2
2
2
2
Keywords: density functional calcu-
lations · epoxidation · ionic liquids ·
peroxides · rhenium
Introduction
point, thermal stability, high polarity, and, at least in several
[4]
cases, low toxicity render ILs attractive and “green” alter-
[5]
Although the compound class of (room-temperature) ionic
liquids, henceforth denoted as (RT)ILs, has been known
since the middle of the 20th century, research on ILs has
experienced an extraordinary growth during the last
natives to conventional solvent systems. Pioneering contri-
[
6]
[7]
[8]
butions of the groups of Rogers, Wasserscheid, Seddon,
[1]
[9]
[10]
[11]
Welton, Dupont, among many others to the use of ILs
[12]
and SILPs
(supported ionic liquid phases) as reaction
[2]
decade. Thus far, more than 40000 research articles have
media for two-phase catalyzed reactions have made the cat-
[3]
[13]
been published on ionic liquids. Above all, their unique
chemical and physical properties, such as low miscibility
with non-polar, organic solvents, low volatility, low flash
alytic application of ILs a prominent research area.
In
several cases, ILs have already found applications as sol-
[14]
vents for extractants in industrial catalytic syntheses, such
+
+
[
a] I. I. E. Markovits, Dr. S. Yue, Dr. M. Cokoja, C. J. Mꢀnchmeyer,
B. Zhang, Prof. Dr. F. E. Kꢀhn
[d] Dr. M.-D. Zhou, Prof. Dr. S.-L. Zang
School of Chemical and Materials Science
Liaoning Shihua University
Chair of Inorganic Chemistry/Molecular Catalysis
Catalysis Research Center
Dandong Road, No.1, 113001 Fushun (P.R. China)
Technische Universitꢁt Mꢀnchen
Ernst-Otto-Fischer-Strasse 1
[
e] Prof. Dr. J. Mink
Hungarian Academy of Sciences
Chemical Research Center
8
5747 Garching bei Mꢀnchen (Germany)
Fax : (+49)89-289-13473
E-mail: fritz.kuehn@ch.tum.de
Pusztszeri u. 59-67, 1025 Budapest (Hungary)
[
f] Prof. Dr. J. Mink
Faculty of Information Technology
University of Pannonia
+
[
b] Dr. W. A. Eger, Dr. A. Genest, Prof. Dr. N. Rçsch
Department Chemie & Catalysis Research Center
Technische Universitꢁt Mꢀnchen
Egyetem u. 10 8200 Veszprꢂm (Hungary)
Lichtenbergstrasse 4
[
g] Prof. Dr. N. Rçsch
Institute of High Performance Computing
Agency of Science, Technology, and Research
8
5747 Garching bei Mꢀnchen (Germany)
E-mail: roesch@mytum.de
+
[
c] Dr. S. Yue, Dr. M.-D. Zhou, Prof. Dr. S.-L. Zang
Singapore 138362 (Singapore)
Institute of Rare and Scattered Elements Chemistry
Liaoning University
Chongshan Middle Road No. 66
+
[
] These authors contributed equally to this work.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203208.
1
10036 Shenyang (P.R. China)
E-mail: slzang@lnu.edu.cn
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[
15]
as the BASF-BASIL process. However, they also exhibit a
templating effect in the synthesis of inorganic materials
(
Table 1. Effect of the oxidant on the yield of cyclooctene oxide [%] in
imidazolium-based ILs with ReO
À
4
as an anion.
[a]
[16]
Entry
Ionic liquid
Oxidizing agent
UHP
nanoparticles, metal oxides, metal–organic frameworks).
H
2
O
2
/H
2
O
TBHP
The beneficial effect on a reaction in terms of reaction rate
is ascribed to a low degree of interactions (e.g., solvent
cages) with the dissolved molecules. Recently, many groups
have focused on the functionalization of ILs, in particular
those that contain imidazolium cations with Lewis acidic or
basic groups, which can act as organocatalysts.
Among the many catalyzed processes that have been per-
formed in ionic liquids are epoxidation reactions.
1
2
3
A
T
N
T
E
N
G
4
8
mim]
mim]
A
T
N
T
E
U
G
4
4
]
]
99
99
99
42
66
80
5
6
5
A
H
N
T
E
N
G
ACHTUNGTRENNUNG
4
AHCTUNGTRENNUG[ C12mim] ACHTUNGTNERNUNG[ ReO ]
[
a] Reaction conditions: IL (1 mmol), cyclooctene (1 mmol), oxidizing
agent (2.5 mmol), 4 h, 708C.
[17]
[18]
The
H O was used as the oxidant (Table 1, entry 1 and
2
2
original purpose of applying ILs to this reaction was for
facile product/catalyst separation, which indeed could be
achieved more easily in several cases than in the original
processes. In addition, it was observed that ILs greatly af-
fected the activity of the epoxidation catalysts, thereby lead-
Figure 1). However, with UHP, the yield was lower and,
with TBHP, no significant yield of the epoxide was obtained.
[19]
ing to very active systems in several cases.
Surprisingly,
some typically catalytically inactive inorganic compounds,
such as perrhenates (the usual decomposition products of
well-examined epoxidation catalysts, such as methyltrioxo-
[20–22]
rhenium (MTO)),
displayed activity in olefin epoxida-
tion, when applied as anions of ILs, thus showing very good
yields of the epoxides and reusability of the IL. These obser-
vations led to the study reported herein. The activation of
hydrogen peroxide by perrhenate, which was enabled solely
by the ionic liquid environment, is, to the best of our knowl-
edge, reported for the first time. This new mode of activa-
tion allows for easy epoxidation of the olefins.
Figure 1. Plot of yield versus time in the reaction between cyclooctene
and aqueous
2 2 8 4
H O to afford cyclooctene oxide in [C mim] ACHTUNGTRENNUNG[ ReO ]
(
Table 1, entry 1).
Results and Discussion
Epoxidation in perrhenate-containing ionic liquids: Several
In the case of UHP, the yield of cyclooctene oxide was
higher when the alkyl moiety on the imidazolium cation was
longer. This effect can be attributed to increased solubility
perrhenate-containing ILs of the general formula [C mim]-
n
ACHTUNGTRENNUNG[ ReO ] (C mim=1-C H -3-methylimidazolium; C =butyl
4 n n 2n+1 n
(
C ), octyl (C ), dodecyl (C )) were synthesized and used to
of the oxidizing agent in [C mim] ACHNUTRTGENNUNG[ ReO ] (Table 1, entry 3).
12 4
4
8
12
study the epoxidation of cyclooctene with different oxidants:
Other substrates, such as cyclohexene, styrene, and
1-octene showed good conversions (100% selectivity in each
H O , urea hydrogen peroxide (UHP), tert-butyl hydroper-
2
2
oxide (TBHP; Scheme 1).
case) in [C mim] ACHTUNGTNERNUG[ ReO ] with UHP as the oxidant (see the
12 4
Supporting Information, Table S2). However, the solubility
of UHP in [C mim][ReO ] rendered the recycling of the IL
AHCTUNGTRENNUNG
1
2
4
more difficult than with hydrogen peroxide.
These promising findings of new peroxide chemistry were
a motivation to further experimentally examine whether the
addition of catalytic amounts of perrhenate to standard ILs
Scheme 1. Olefin epoxidation in ionic liquids with the perrhenate anion.
with different polarities, such as [C mim] ACHTUNGTRNENUG[ BF ] and [C mim]-
4 8
8
AHCTUNGTNERN[GU NTf ], would also lead to cyclooctene epoxidation
2
À
Equimolar amounts of the IL and cyclooctene, as well as
.5 equivalents of the oxidant, were mixed together at room
(Table 2). Notably, the cation of [ReO4] had a tremendous
effect on the activity. Whereas NH ReO does not provide a
2
4
4
temperature, thus giving a three-phase medium, which was
heated at 708C for 4 h under vigorous stirring. After the re-
action had been completed, the epoxide was dissolved in the
significant yield of the epoxide, with potassium perrhenate,
yields of up to 53% (Table 2, entry 2) can be achieved.
When the concentration of perrhenate is decreased to
10 mol% (relative to the substrate), the activity also drops
notably (Table 2, entry 3). From Table 2, it is clear that am-
monium ions inhibit the epoxidation of an olefin. Similarly
IL,
giving
a
two-phase
medium
IL+product/
water+H O . The epoxide was extracted with n-hexane (5ꢄ
2
2
1
mL) and the yield of the epoxide was determined by GC.
À
nearly quantitative conversion of cyclooctene and 100% se-
lectivity for cyclooctene oxide were obtained when aqueous
to peroxides, these cations interact with [ReO4] and/or the
IL ions. Presumably, this interaction causes the inactivity of
&
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Activation of Hydrogen Peroxide by Ionic Liquids
FULL PAPER
Table 2. Yields of cyclooctene oxide at various perrhenate concentrations
[
a]
(
PCs).
Mechanistic considerations of the activation of H O : The
2
2
Entry
Solvent
Perrhenate salt
–
PC [mol%]
Yield [%]
reactivity of the perrhenate-containing IL is intriguing. In
contrast, by using [C mim][BF ] without the addition of a
1
2
3
4
5
6
7
8
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[C
[C
[C
[C
[C
[C
[C
8
mim]
8
mim]
8
mim]
8
mim]
8
mim]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[BF
[BF
[BF
[BF
[BF
4
4
4
4
4
]
]
]
]
]
–
100
10
100
10
100
100
100
13
53
10
17
5
3
7
8
ACHTUNGTRENNUNG
8
4
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
KReO
KReO
4
metal oxide, cyclooctene oxide is obtained in 13% yield
Table 2, entry 1), thus pointing to the pivotal role of
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ACHTUNGTRENNUNG
4
(
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
NH
NH
4
ReO
ReO
4
4
perrhenate in the conversion of the olefin into the corre-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ACHTUNGTRENNUNG
4
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
8
mim]
mim]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[NTf
2
]
]
KReO
4
sponding epoxide. However, this fundamental—yet surpris-
À
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
8
A[ NTf
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
NH
NH
4
ReO
ReO
4
4
ing—activity of [BF ] can be rationalized by the formation
4
H
2
O
4
À
of hydrogen bonds between [BF ] and the hydroxide
4
[9b,23]
À
[
(
a] Reaction conditions: Solvent (0.5 mL), cyclooctene (1 mmol), H
2.5 mmol, 50% solution in water), 4 h, 708C.
2
O
2
groups.
To verify whether the [BF ] anions are respon-
4
sible for the activation of hydrogen peroxide, or whether
19
they even react with the peroxide or water, in situ F NMR
spectra of the ionic liquid, [C mim][BF ] (see the Supporting
AHCTUNGTRENNUNG
4
4
+
NH ReO4 (Table 2, entries 4 and 5), whereas K ions
Information, Figures S4 and S5), were recorded in the pres-
ence of perrhenate and hydrogen peroxide. Notably, no
changes in the fluorine signals during epoxidation were ob-
4
behave very differently (Table 2, entries 2 and 3). This com-
parison also highlights the role of the IL as an environment,
which is able to dissolve polar species, such as perrhenate
salts, without the need to include a protic solvent shell (e.g.,
water; Table 2, entry 8) which would disturb the perrhen-
ateÀperoxide complexation. This argument allows a ration-
À
served, thus showing that [BF ] did not react with H O or
4
2
2
was hydrolyzed by water. Therefore, we can conclude that
À
the [BF ] anion is not (or only to a minor degree) responsi-
4
À
ble for the activation in the presence of ReO , as also cor-
4
alizing of why perrhenates are inactive in aqueous medium,
where the hydration “shell” passivates the complex.
By comparing the use of two ILs, [C mim]
roborated by vibrational spectroscopy.
Welton and co-workers reported the formation of hydro-
[24]
A
H
U
G
R
N
U
G
gen bonds between the IL anions and water molecules.
Mele et al. observed weak hydrogen bonding between the
8
2
[
C mim] ACHTUNGTRENNUNG[ BF ], as solvent (Table 2, entries 2, 4, 6, and 7), we
8 4
[25]
can clearly conclude that the solubility of the perrhenate
salt in the respective IL has a significant influence on the ac-
tivity towards epoxidation. A more-polar IL, such as
imidazolium cation and water molecules.
Hence, in
Table 2, entry 1, H O is presumably associated with the IL
2
2
anion. Hydrogen bonds to the cation probably do not form
in the presence of a potent H-bond acceptor, such as a
[
C mim] ACHTUNGTRENNUNG[ BF ], can facilitate the solubility of the perrhenate
8 4
salt, thus leading to formation of hydrogen bonds between
perrhenate and H O . A reciprocal observation is made with
perrhenate anion. The addition of metalÀoxo complexes,
À
such as [ReO ] , accelerates the reaction, presumably
2
2
4
[
C mim]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
[NTf ], wherein NH ReO and KReO are entirely
through the formation of O ReÀO···HÀOÀOH species,
8
2
4
4
4
3
insoluble, thus leading to yields of 7% and 3%, respectively.
Recycling experiments were carried out on samples of IL
[
were obtained for at least eight runs, which demonstrates
the high stability of the IL under oxidative conditions, thus
rendering it a good candidate for efficient olefin epoxida-
tion.
which activate the peroxide and, hence, enable epoxidation.
Seemingly, metalÀoxide-mediated olefin epoxidation in ILs
C mim]
8
A[ ReO ] (Figure 3). Consistent yields of 98–99%
C
H
T
U
N
G
T
R
E
N
N
U
N
G
follows a different reaction mechanism to that with the
4
[11]
usual metal catalysts, in which (hydro)peroxo ligands act
as catalytically active species in transferring an oxo moiety
[26]
to the olefin. The activation of peroxides with the carbo-
nate anion and the subsequent epoxidation of olefins were
[27]
reported by Yao and Richardson.
However, their reac-
tions were performed in water and, thus, the substrates had
to contain functional groups (carboxylate, sulfonate, ester)
that would render them soluble; hence, the reactions of
simple olefins were not undertaken. The mechanism has
also not been examined in detail. Therefore, to shine some
light onto the activation of peroxide with perrhenate, the re-
action mechanism was also examined by using DFT calcula-
tions.
Spectroscopic and DFT studies of the activation of H O2
2
with perrhenate and subsequent epoxidation: Recent publi-
cations have presented elaborate schemes for modeling
[28,29]
ILs.
The scope of the calculations reported herein was
to elucidate and support the proposed catalytic mechanisms,
in particular in terms of the trends in crucial activation bar-
riers. Therefore, as a first approximation, we refrained from
directly including the effects of ILs that are often described
Figure 2. Yields of cyclooctene oxide after eight reaction runs in
[C mim] ACHTUNGTRENNUNG[ ReO ].
8 4
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S.-L. Zang, N. Rçsch, F. E. Kꢀhn et al.
by using molecular modeling approaches. We relied on ILs
to provide a reaction cavity and we assumed that gas-phase
models correctly helped to identify any trends. Thus, the ab-
solute values of barrier heights should be taken with cau-
tion. Three complexes from which the oxidation may start
were considered (Scheme 2), that is, encounter complex 1
À
between hydrogen peroxide and [ReO ] , hydroxoÀhydro-
4
peroxo rhenium species 3, and bis-hydroxoÀperoxo complex
[
30]
5
.
8 4
Figure 3. Raman and mid-IR spectra of [C mim] ACHTUNTRGENNUNG[ ReO ] (Re=O asymmet-
4À
ric stretching vibration) after the addition of peroxide. Calculated spectra
Scheme 2. Calculated equilibrium structures for the reaction of ReO
with H
monoanions. Thin dashed lines indicate hydrogen bonds; thick dashed
are of encounter complex 1, hydroxoÀhydroperoxo complex 3, and
2
2
O , including transition states (ts). All of the complexes are
peroxo complex 5; experimental spectra are the (a) measured and (b)
second derivative of the spectra. Peak broadening is indicated as horizon-
tal bars (see text).
ACHTUNGTRENNUNG
lines indicate bonds to be broken or formed during a reaction step. Free
reaction energies (in kJmol ) are relative to structure 1; activation barri-
À1
ers are relative to the preceding initial state. Color coding of the atomic
spheres: Re white, large; O gray; H white, small.
À1
Information, Figure S9) is broadened to 885–930 cm
(
Figure 3, spectrum a). Again, this finding is supported by
Before exploring the actual mechanism, it is important to
identify any active species that are formed with peroxide in
the IL. Therefore, the reactions were monitored by in situ
IR and Raman spectroscopy. Upon the addition of the oxi-
dant, the asymmetric stretching vibration splits in both the
Raman and IR spectra (Figure 2, spectrum a). Point-group
analysis shows that this result is consistent with a decrease
the calculated spectrum of encounter complex 1, which ex-
hibits a broadening to 875–930 cm . The splitting patterns
À1
in the Raman spectra of structures 3 and 5 are also signifi-
À1
À1
cantly broadened (3: 840–985 cm ; 5: 875–990 cm ). The
calculated spectrum of structure 1 has a slightly different
peak pattern to the second derivative of the experimental
spectrum (spectrum b, extended view). The simulated IR
and Raman spectra of structures 3 and 5 show an additional
À
in the local symmetry of [ReO ] from T to C .
4
d
2v
À1
These changes can be assigned to a distortion of the local
symmetry of the anion by weak coordination, for example,
through hydrogen bonds. This assignment is supported by
the calculated vibrational spectra of the key intermediates
peak at about 980 cm , which is assigned to the hydroxy
groups but is not observed experimentally, thus corroborat-
ing the dominance of structure 1 in the reaction. Far-IR
measurements do not indicate any additional ReÀO vibra-
tions, excluding the formation of rheniumÀperoxo species.
(
1, 3, and 5; Figure 3). Indeed, in the IR spectra, the experi-
À1
mentally observed splitting (890–920 cm ; Figure 3, spec-
Thus, structure 1 can be safely addressed as the predominant
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
trum a) of the former asymmetric stretching mode of the
equilibrium structure. The formation of encounter complex
À1
À1
pure ionic liquid, which is found at about 900 cm (see the
Supporting Information, Figure S9),
the simulated spectra (Figure 3). For structure 1, a small
splitting is calculated, with three peaks within the range
1
is calculated to be exothermic by À20 kJmol
[31]
is also reflected in
(Scheme 2), owing to the newly formed H bonds. Compound
1 can be considered as an initial state of all of the reaction
pathways. Thus, all of the free reaction energies shown are
ACHTUNGTRENNUNG
À1
À1
8
65–910 cm , whereas the ligands on the metal center of
given relative to structure 1. A barrier of 112 kJmol (2_ts)
structures 3 and 5 induce a significant larger broadening of
the spectra (3: 840–985 cm ; 5: 875–990 cm ). Both the
shift and splitting of this band, as observed experimentally
has to be overcome to arrive at the endothermic hydroxoÀ
À1
À1
À1
hydroperoxo complex (3, 82 kJmol ). The strongly endo-
À1
thermic peroxo complex (5, 156 kJmol ) is reachable over
À1
(
spectrum a), are best reproduced by the simulated spec-
a barrier of 79 kJmol (4_ts). Hence, these latter alterna-
trum for complex 1. Thus, from the IR data, structure 1 is
expected to be predominantly formed.
tives to structure 1 are both thermodynamically and kineti-
cally disfavored. These computational results, together with
the vibrational spectra, indicate that the equilibrium of the
ionic liquid and hydrogen peroxide will be predominantly
In the Raman spectra, the asymmetric stretching mode of
À1
the pure ionic liquid at about 916 cm (see the Supporting
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Activation of Hydrogen Peroxide by Ionic Liquids
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À1
shifted towards complex 1. As a consequence, during the re-
action was calculated to be 355 kJmol ; hence, the reverse
À
action, [ReO4] can be assumed to be coordinated by H O
step is highly unlikely. Direct insertion, starting from struc-
ture 1, encounters a notably higher barrier (256 kJmol ;
2
2
À1
through hydrogen bonds, thus activating the peroxide bond
and making it susceptible to attack by an olefin. In contrast
to MTO, the stable delocalized electronic structure of
perrhenate implies a chemical inertness that requires a sig-
nificant amount of energy to be disturbed, for example, by
inserting H O to yield structures 3 and 5.
see the Supporting Information, Figure S12). In agreement
with experimental findings that identify structure 1 as the
prevailing species, alternative epoxidation pathways, starting
from structures 3 or 5, are far less likely (Scheme 2). The
barriers of such alternative oxygen-transfer pathways, rela-
tive to structure 1, that is, neglecting the energy change
owing to coordination of the olefin, are at least 254 kJmol
(see the Supporting Information, Figure S12). To elucidate
the origin of the oxygen atom in the epoxide product, the
2
2
Further computational efforts addressed the question of
whether a single perrhenate moiety or peroxide-bridged ag-
glomerates of such anions may act as active species (see the
Supporting Information, Figure S10). Simulated Raman
spectra did not exclude the action of such agglomerates (see
the Supporting Information, Figure S11). The formation of
such structures will depend on the size and content of the
reaction cavity that is provided by the IL, specifically on the
size of the counterion. Mono-perrhenates that contain two
peroxide moieties are also conceivable as active species,
thus enhancing the possibility for epoxidation.
À1
17
epoxidation of cyclooctene was repeated by using O-la-
beled [C mim][ReO ] and H O as the oxidant. After work-
AHCTUNGTRENNUNG
8
4
2
2
1
7
up and product isolation, the recorded O NMR spectrum
of cyclooctene oxide does not show any signals, even after
24 h of acquisition time (see the Supporting Information,
Figures S7 and S8). This result clearly excludes the forma-
tion of ReÀhydroperoxo (3) or ReÀperoxo species (5), that
Although our spectroscopic studies show that the equili-
brium is shifted almost completely towards complex 1, epox-
idation might involve one of the minor intermediates.
Therefore, we examined various plausible transition states
is, a transfer of oxo ligands from Re onto the olefin. Thus,
the oxygen has to originate from H O , without prior direct
2
2
coordination at the metal center, thus suggesting that the
pathway starts from structure 1.
(
ts). Accordingly, among all of the reaction channels stud-
Thus far, we have only discussed the mechanistic aspects
with regard to H O as the oxidant. It is the question, which
ied, the rate-limiting barrier (relative to structure 1) was by
far the lowest for direct oxidation by complex 1 (see the
Supporting Information, Figure S12). Transition state 7_ts
2
2
effects are responsible for the poor epoxide yields when
using UHP and TBHP as the oxidants (Table 1). Analogous
to structure 1 with oxidant H O (Scheme 2), we examined
À1
lies 171 kJmol above the preceding intermediate state
2
2
(
IS), structure 6 (Scheme 3). A second hydrogen bond does
the H-bonded encounter complexes (1a and 1b) of perrhen-
ate and oxidants UHP and TBHP, respectively (Figure 3).
Oxidant UHP, viewed as an adduct of H O and urea (1a),
À
not necessarily have to form to the same ReO4 unit.
2
2
exhibits H bonds between the hydroxy groups of H O and
2
2
[34]
the carbonyl and amino groups of urea. In structure 1b,
the tert-butyl group of TBHP shields the oxygen center to
be transferred. In contrast to structure 1, both structures 1a
and 1b can only form a single H bond to perrhenate
(
Figure 4). According to the calculated activation barriers,
À
Figure 4. Encounter complexes of [ReO
4
]
with UHP (1a) and TBHP
Scheme 3. Calculated reaction pathway for direct epoxidation through
À1
(1b). Color coding of the atomic spheres: N dark gray, small; the rest as
H-bonded complex 1. Gibbs free energies (in kJmol ) are relative to the
À
in Scheme 3.
separated substrates, [ReO
4
]
and H
2
O
2
. All of the complexes are mono-
anions. Free energies were calculated as in Scheme 2. Color coding of the
atomic spheres: C black, small; the rest as in Scheme 2.
relative to the corresponding ISs (1, 1a, or 1b; Scheme 3
and Figure 4), direct epoxidation with UHP (7a_ts,
À1
We were unable to identify an alternative structure for
product 8 that involved a water molecule that was bound
through H bonds to the perrhenate anion. A water ligand,
which was coordinated at the perrhenate through its oxygen
atom, analogous to structures that have previously been
173 kJmol ) is favored over the reactions of alternative oxi-
À1
À1
dants (H O : 7 ts, 192 kJmol ; TBHP: 7b_ts, 189 kJmol ).
2
2
Thus, the electronic activation of the peroxide does not cor-
relate with the measured trend in terms of yields (Table 1).
Notably, the yields are affected by: 1) Steric shielding of
the activated center, 2) competition between the substrates,
and 3) the thermodynamic driving force, in particular the ac-
[32,33]
found in MTO chemistry,
immediately reoriented to
form structure 8. The barrier of the corresponding back re-
Chem. Eur. J. 2013, 00, 0 – 0
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www.chemeurj.org
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S.-L. Zang, N. Rçsch, F. E. Kꢀhn et al.
tivation barrier of the back reaction. Whilst the calculated
free reaction energies for the overall reaction with H O
opens up new possibilities for the epoxidation of olefins
with compounds that are very stable, readily accessible, and
cheap. These compounds have several advantages over the
commonly used Re, Mo, Ti, and Mn compounds, which are
expensive and often quite sophisticated. Further studies of
this reaction system are worthwhile, particularly in view of
affording longer-term stability and performance in the epox-
idation of cyclooctene.
2
2
À1
À1
(
À192 kJmol ) and UHP (À190 kJmol ) are similar, the
À1
reaction is far less exothermic with TBHP (À170 kJmol ).
Furthermore, the tert-butyl group of TBHP that is coordi-
nated to the perrhenate anion shields the active oxygen
center, thus (together with the slightly lower reaction free
energy) rationalizing the poor yields (Table 1). Other factors
may contribute to the differing activities of UHP and H O .
2
2
For instance, urea does not need to stay close to the com-
plex of perrhenate and H O , but may coordinate to another
perrhenate ion. According to calculated energies of the
2
2
Experimental Section
H bonds between perrhenate and various substrates, urea
General remarks: All syntheses and catalytic reactions were carried out
in air. 1-Methylimidazole, 1-bromobutyl bromide, 1-bromooctyl bromide,
and 1-bromododecyl bromide imidazole, fluoroboric acid (50%), hydro-
gen peroxide (50% in water), n-hexane, MeCN, and EtOAc were pur-
chased from Acros Organics. NaOH pellets were purchased from J. T.
Baker. Cyclooctene (95%), tert-butyl hydroperoxide (5.0–6.0m solution
in n-decane), Amberlite IRA-400 (OH), and acetone were purchased
from Sigma–Aldrich. O-enriched water (10 wt.%) was purchased from
Deutero GmbH. All chemicals were used as received without further pu-
rification.
À1
(
(
34 kJmol ) binds more strongly to perrhenate than H O
20 kJmol ), whilst water binds the weakest (8 kJmol ).
2
À1
2
À1
System 1 (H O ) contains notable amounts of water because
2
2
the oxidant is available in aqueous solution, whereas system
a (UHP) only incorporates urea and H O . Thus, the epox-
1
2
2
1
7
idation yields can be rationalized as the result of competi-
tion between forming a perrhenate complex with either urea
or H O . Notably, ammonium ions almost completely sup-
2
2
Microanalysis of the obtained products was performed in the Mikroana-
press the reaction (Table 2) because they form very strong
1
lytisches Labor of the Technische Universitꢁt Mꢀnchen in Garching. H,
À1
1
3
17
H bonds with perrhenate anions (404 kJmol ).
C, and O NMR spectra were recorded in CDCl on a 400 MHz Bruker
3
The cations of the IL, not accounted for in our simple
models, are obviously not innocent (Table 1). Despite its
simplicity, this computational approach demonstrates the
feasibility of the discussed mechanism. Clearly, more elabo-
Avance DPX-400 spectrometer. In situ Mid-IR spectra were recorded on
a Mettler Toledo ReactIRTM; ex situ spectra were recorded on a Varian
IR FT670 that was equipped with an ATR cell (diamond crystal). Raman
spectra were recorded on a Bio-Rad FTS-60A. Thermogravimetry cou-
pled with mass spectroscopy (TG-MS) was performed on a Netzsch
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
rate modeling of the environment that is set up by the IL
TG209 system; typically, each sample (10 mg) was heated from 258C to
À1
1
0008C at a rate of 10 Kmin . Differential scanning calorimetry (DSC)
will be desirable. With such more realistic modeling, the cal-
culated activation barriers would be expected to be lower.
Because the high activation barrier of 173 kJmol is at
odds with the good observed yields (at least 50%), the rate-
limiting step has been recalculated with the experimentally
used substrate (cyclooctene), which is known to be more
easily epoxidized than the model olefin (ethene). The re-
sulting activation barrier of 143 kJmol
better agreement between the chosen computational model
and the experimental data, as well as the far better reactivi-
ty of cyclooctene in comparison to ethene. Assuming a first-
was performed on a Q2000 series DSC instrument; typically, each sample
À1
(
2 mg) was heated from À1008C to 1508C at a rate of 10 Kmin . Densi-
À1
ty was measured on an Anton Paar DMA4500 densimeter. Catalytic runs
were monitored by using GC methods on a Hewlett–Packard HP 5890
Series II instrument that was equipped with a FID, a Supelco column Al-
phadex 120, and a Hewlett–Packard integration unit HP 3396 Series II.
[35]
Synthesis of perrhenate-based ILs: The original synthesis of the per-
AHCTUNGTRENNUNGr henates involved a mixture of imidazolium bromide and [NH ] ACHTUNGTRENNUNG[ ReO ] in
4 4
À1
demonstrates
acetone, which was stirred for 48 h at room temperature and subsequent
work-up. Elemental analysis showed that a significant amount of the bro-
mide was present in the ionic liquid after purification. Because the purity
of the new ILs has a dramatic effect on the epoxidation of olefins, a new
strategy was used for the synthesis of the IL perrhenates, which involved
the exchange of bromide by hydroxide on an ion-exchange resin and the
1
3
À1
order reaction and a pre-exponential factor of 10 s , we
estimate a barrier of about 110 kJmol based on the ob-
À1
4 4
subsequent addition of NH ReO with stirring at 708C for 24 h. The only
served 50% yield after 4 h.
byproducts were ammonia and water, which were easily removed in va-
cuo at elevated temperatures. The ionic liquids were characterized by
FTIR, Raman, H, C, and O NMR spectroscopy and elemental analy-
sis. In addition, physical data, such as density, melting point, and decom-
position temperature, were determined. According to the differential
1
13
17
Conclusions
scanning calorimetry (DSC) data, compounds [C
[C mim][ReO ] were liquid and contain a glass-transition temperature
below room temperature. Owing to its high molecular mass, [C12mim]-
[ReO ] showed a melting point at 488C. Thermogravimetric analysis
TGA) indicated that all of the ionic liquids showed negligible volatility
4 4
mim] ACHTUNGETRNNUNG[ ReO ] and
A new synthetic concept that is based on the solvent effect
of ionic liquids on polar compounds, such as perrhenate
salts, is presented. NMR, IR, and Raman spectroscopy, as
well as DFT studies, indicate that simple anionic metalÀoxo
8
A
H
U
G
E
N
N
4
A
T
N
T
E
N
G
4
and high thermal stability with a decomposition onset temperature of
almost 4008C (see the Supporting Information, Table S1).
complexes are able to activate hydrogen peroxide through
only hydrogen-bonding interactions, thus enabling olefin ep-
oxidation through an outer-sphere mechanism, which does
not involve the Re center. This method was shown to be
very efficient, even with substoichiometric amounts of the
metal salts, which were easily separated from the product
and reused without any loss of activity. This reaction type
Preparation of 3-alkyl-1-methyl imidazolium bromide: Equimolar
amounts of alkyl bromide and 1-methylimidazole (0.5 mol) were heated
for 1 h at 408C in THF (40 mL). Afterwards, the mixture was heated at
reflux for 24 h. After cooling to room temperature, a mixture of EtOAc
and MeCN (40 mL, 3:1 v/v) were added and the mixture was heated at
reflux for 1 h to afford the pure product after drying at 808C under high
vacuum for 8 h.
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Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Activation of Hydrogen Peroxide by Ionic Liquids
FULL PAPER
Preparation of 3-alkyl-1-methyl imidazolium perrhenate: A solution of
ionic liquid (IL) will not prevent the formation of weak hydrogen bonds
between the perrhenate anion and peroxide (typically about
1.5 kJmol ). These H bonds are not stable in common organic solvents,
3
-alkyl-1-methyl imidazolium bromide (0.08 mmol) in water (10 mL) was
À1
slowly added onto the ion-exchange resin (pH 7). The product was slowly
washed off the column with water until the pH value of the eluent re-
owing to strong coordination of the substrate by a solvent, and such sol-
À1
+
mained at 7, thus affording the desired product (c=0.26 molL ). Subse-
vent effects are assumed to be absent in an IL. C
n
Rmim counterions,
[
40]
quently, NH
08C for 24 h, followed by the complete removal of the residual water
under reduced pressure. Excess NH ReO was removed by extraction of
the ionic liquid with CH Cl (30 mL) to afford the pure product after re-
moval of the solvent under reduced pressure (98% yield).
-Butyl-1-methyl-1H-imidazolium perrhenate:
4
ReO
4
(1.2 equiv) was added and the solution was heated to
known as H-bond donors, are not expected to participate as H-bond
acceptors in the reaction mechanism, such as the complexation and acti-
vation of peroxides, in view of their cationic character and the complete
7
4
4
[
41]
2
2
lack of lone-pair-bearing atoms.
3
C
8
H
15
N
2
O
4
Re (389.42);
, 400 MHz, RT): d=8.92 (s, 1H), 7.32 (d, 1H), 7.34 (d,
H), 4.30 (t, 2H), 3.68 (s, 3H), 1.75 (q, 2H), 1.26–1.17 (m ,2H), 0.79 ppm
1
H NMR (CDCl
1
3
Acknowledgements
1
3
(
t, 3H); C NMR (CDCl
3
, 100 MHz, RT): d=135.9, 123.6, 122.3, 49.7,
3
6.3, 31.7, 19.1, 13.2 ppm; IR (ATR, diamond crystal, neat): n˜ =900 (Re=
I.I.E.M. and B.Z. thank the TUM Graduate School for financial support.
N.R. is grateful for generous access to the computing resources at the
Leibniz Rechenzentrum Mꢀnchen and the Fonds der Chemischen Indus-
trie. F.E.K. thanks the DFG (Ku 1265/10-1) for financial support. S.-L.Z.,
S.Y., and M.-D.Z. thank the National Science Foundation of China
(21071073, 21101084, 21101085, and 21003068), the Key Projects in the
National Science and Technology Pillar Program (2012BAF03B02), and
the Cooperation Project (21111130584) for financial support.
À1
O asymmetric), 916 cm (Re=O symmetric); elemental analysis calcd
%) for C Re: C 24.67, H 3.88, N 7.19, O 16.43, Re 47.82; found:
C 25.19, H 4.05, N 7.29, Re 46.50.
-Octyl-1-methyl-1H-imidazolium perrhenate:
(
8 15 2 4
H N O
3
C
12
H
23
N
2
O
4
Re (445.53);
, 400 MHz, RT): d=8.82 (s, 1H), 7.40 (d, 1H), 7.36 (d,
H), 4.16 (t, 2H), 3.95 (s, 3H), 1.84 (t, 2H), 1.27–1.19 (m, 10H),
1
H NMR (CDCl
3
1
0
1
1
3
.79 ppm (t, 3H); C NMR (CDCl
3
, 100 MHz, RT): d=136.1, 123.9,
1
7
22.4, 50.3, 36.5, 31.6, 30.1, 28.9, 28.8, 26.2, 22.5, 13.98 ppm; O NMR
(
CDCl
3
, 100 MHz, RT): d=564 ppm; IR (ATR, diamond crystal, neat):
À1
n˜ =916 (Re=O asymmetric), 900 (Re=O symmetric), 320 cm (Re=O
[1] J. S. Wilkes, J. A. Levisky, R. A. Wilson, C. L. Hussey, Inorg. Chem.
1982, 21, 1263–1264.
[2] J. S. Wilkes, M. Zaworotko, J. Chem. Soc. Chem. Commun. 1992,
965–967.
[3] Thomson ISI Web of Science topic search “Ionic liquids”, Septem-
ber 7th 2012.
[4] a) J. Ranke, S. Stolte, R. Stçrmann, J. Arning, B. Jastorff, Chem.
Rev. 2007, 107, 2183–2206; b) M. Matzke, S. Stolte, K. Thiele, T. Juf-
fernholz, J. Arning, J. Ranke, U. Welz-Biermann, B. Jastorff, Green
Chem. 2007, 9, 1198–1207; c) S. Stolte, J. Arning, U. Bottin-Weber,
M. Matzke, F. Stock, K. Thiele, M. Uerdingen, U. Welz-Biermann,
B. Jastorff, J. Ranke, Green Chem. 2006, 8, 621–629; d) R. P. Swat-
loski, J. D. Holbrey, R. D. Rogers, Green Chem. 2003, 5, 361–363.
[5] J. G. Huddleston, A. E. Visser, W. M. Reichert, H. D. Willauer,
G. A. Broker, R. D. Rogers, Green Chem. 2001, 3, 156–164.
deform.) Raman: n˜ =959 (Re=O symmetric), 908 (Re=O asymmetric)
À1
3
31 cm
(Re=O deform.); elemental analysis calcd (%) for
Re: C 32.35, H 5.20, N 6.29, O 14.36, Re 41.79; found:
C 31.85, H 5.31, N 6.29, Re 40.03.
-Dodecyl-1-methyl-1H-imidazolium perrhenate: C16
12 23 2 4
C H N O
3
H
31
N
2
O
4
Re (501.64);
, 400 MHz, RT): d=8.85 (s, 1H), 7.40 (d, 1H), 7.34 (d,
H), 4.21 (t, 2H), 4.01 (s, 3H), 1.89 (t, 2H), 1.33–1.24 (m, 18H),
1
H NMR (CDCl
3
1
0
1
1
9
1
3
3
.86 ppm (t, 3H); C NMR (CDCl , 100 MHz, RT): d=136.4, 123.9,
22.4, 50.6, 36.7, 32.0, 30.3, 29.7, 29.7, 29.6, 29.5, 29,4, 29.1, 26.4, 22.8,
4.2 ppm; IR (ATR, diamond crystal, neat): n˜ =900 (Re=O asymmetric),
À1
16 cm
(Re=O symmetric); elemental analysis calcd (%) for
Re: C 38.31; H 6.23, N 5.58, O 12.76, Re 37.12; found:
C 38.19, H 6.16, N 5.63, Re 36.84.
16 31 2 4
C H N O
1
7
17
Preparation of the O-labeled ionic liquid: O-labeled water (100 mL,
0 atom%) was added to 1,3-methyl-octyl imidazolium perrhenate
3.7 mmol) and the solution was stirred at room temperature for 16 h. Af-
[
6] a) J. G. Huddleston, H. D. Willauer, R. P. Swatlowski, A. E. Visser,
R. D. Rogers, Chem. Commun. 1998, 1765–1766; b) K. E. Gutowski,
G. A. Broker, H. D. Willauer, J. G. Huddleston, R. P. Swatlowski,
J. D. Holbrey, R. D. Rogers, J. Am. Chem. Soc. 2003, 125, 6632–
1
(
terwards, water was removed under reduced pressure.
Oxidation of cyclooctene into cyclooctene oxide in ILs: The ionic liquid
6
633.
(
1 mmol) was placed in a round-bottomed flask that was equipped with a
[
[
7] P. Wasserscheid, W. Keim, Angew. Chem. 2000, 112, 3926–3945;
Angew. Chem. Int. Ed. 2000, 39, 3772–3789.
8] a) M. J. Earle, P. B. McCormac, K. R. Seddon, Green Chem. 1999, 1,
magnetic stirrer bar, followed by the addition of the substrate (1 mmol).
Finally, the oxidant (2.5 mmol) was added and the reaction mixture was
heated at 708C for 4 h. Afterwards, the epoxide was extracted with n-
hexane (5ꢄ1 mL) and a solution of the epoxide in n-hexane (100 mL)
was mixed with an internal standard (1000 mL) and analyzed by GC.
Apart from the epoxidation of cyclooctene, other substrates, that is, cis-
cyclohexene, styrene,
2
3–25; b) C. J. Adams, M. J. Earle, G. Roberts, K. R. Seddon,
Chem. Commun. 1998, 2097–2098; c) M. J. Earle, K. R. Seddon,
Pure Appl. Chem. 2000, 72, 1391–1398.
[
9] a) T. Welton, Chem. Rev. 1999, 99, 2071–2083; b) J. P. Hallett, T.
Welton, Chem. Rev. 2011, 111, 3508–3576; c) T. Welton, Coord.
Chem. Rev. 2004, 248, 2459–2477.
1
-methyl cyclohexene, and 1-octene, were tested in the oxidation reaction
to afford their corresponding epoxides with UHP as an oxidizing agent
see the Supporting Information, Table S2).
[
10] J. Dupont, R. F. de Souza, P. A. Z. Suarez, Chem. Rev. 2002, 102,
667–3691.
(
3
Recycling experiments were performed by the extraction of cyclooctene
[
11] a) R. Sheldon, Chem. Commun. 2001, 2399–2407; b) Q. Zhang, S.
Zhang, Y. Deng, Green Chem. 2011, 13, 2619–2637; c) S. Liu, J.
Xiao, J. Mol. Catal. A 2007, 270, 1–43.
12] a) C. P. Mehnert, Chem. Eur. J. 2005, 11, 50–56; b) H.-P. Steinrꢀck,
J. Libuda, P. Wasserscheid, T. Cremer, C. Kolbeck, M. Laurin, F.
Maier, M. Sobota, P. S. Schulz, M. Stark, Adv. Mater. 2011, 23,
2571–2587.
[13] V. I. Pꢅrvulescu, C. Hardacre, Chem. Rev. 2007, 107, 2615–2665.
[14] N. V. Plechkova, K. R. Seddon, Chem. Soc. Rev. 2008, 37, 123–150.
[15] R. D. Rogers, K. R. Seddon, Science 2003, 302, 792–793.
[16] Z. Ma, J. Yu, S. Dai, Adv. Mater. 2010, 22, 261–285.
oxide with n-hexane (5ꢄ1 mL) and the subsequent removal of residual
À2
n-hexane, water, and hydrogen peroxide in vacuo (10 mbar) at 508C for
4
h. This procedure was repeated after each run.
[
Computational details: All electronic-structure calculations were per-
[
36]
formed by using the Gaussian 03 program package
with the hybrid
[
37]
DFT functional B3LYP.
MWB-60 energy-averaged Stuttgart/Dresden pseudopotential;
For the rhenium atoms, we employed the
[
38]
all
other atoms were represented by using the 6-311+G AHCTUNGTERNNG(UN d,p) basis set. In
[
39]
general, we invoked simple models that focused on perrhenate. These
models did not account for the environment that was provided by the
ionic liquid; in particular, all of the effects of the (1R)-3-methylimidazoli-
[17] Z.-Z. Yang, Y.-N. Zhao, L.-N. He, RSC Adv. 2011, 1, 545–567.
[18] a) M. Crucianelli, R. Saladino, F. De Angelis, ChemSusChem 2010,
3, 524–540; b) D. Betz, P. Altmann, M. Cokoja, W. A. Herrmann,
+
um (C
n
Rmim ) counterions (R=butyl, octyl, or dodecyl) were neglected.
This model approach assumes that the environment provided by the
Chem. Eur. J. 2013, 00, 0 – 0
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
7
&
ÞÞ
These are not the final page numbers!

S.-L. Zang, N. Rçsch, F. E. Kꢀhn et al.
F. E. Kꢀhn, Coord. Chem. Rev. 2011, 255, 1518–1540; c) L. Graser,
D. Betz, M. Cokoja, F. E. Kꢀhn, Curr. Inorg. Chem. 2011, 1, 166–
[31] a) L. A. Woodward, H. L. Roberts, Trans. Faraday Soc. 1956, 52,
615–619; b) M. R. Mohammad, W. F. Sherman, J. Phys. C 1981, 14,
283–288.
[32] a) C. C. Rom¼o, F. E. Kꢀhn, W. A. Herrmann, Chem. Rev. 1997, 97,
3197–3246; b) F. E. Kꢀhn, A. M. Santos, M. Abrantes, Chem. Rev.
2006, 106, 2455–2475.
1
81.
19] a) D. Betz, A. Raith, M. Cokoja, F. E. Kꢀhn, ChemSusChem 2010, 3,
59–562; b) D. Betz, W. A. Herrmann, F. E. Kꢀhn, J. Organomet.
[
[
5
Chem. 2009, 694, 3320–3324.
20] a) W. A. Herrmann, R. W. Fischer, D. W. Marz, Angew. Chem. 1991,
[33] W. A. Herrmann, J. D. G. Correia, F. E. Kꢀhn, G. R. J. Artus, C. C.
Rom¼o, Chem. Eur. J. 1996, 2, 168–173.
1
03, 1706–1709; Angew. Chem. Int. Ed. Engl. 1991, 30, 1638–1641;
[
[
[
34] J. A. Dobado, J. Molina, D. Portal, J. Phys. Chem. A 1998, 102, 778–
84.
35] P. Altmann, M. Cokoja, F. E. Kꢀhn, J. Organomet. Chem. 2012, 701,
1–55.
b) J. Rudolph, K. L. Reddy, J. P. Chiang, K. B. Sharpless, J. Am.
Chem. Soc. 1997, 119, 6189–6190; c) F. E. Kꢀhn, A. M. Santos, P. W.
Roesky, E. Herdtweck, W. Scherer, P. Gisdakis, I. V. Yudanov, C. Di
Valentin, N. Rçsch, Chem. Eur. J. 1999, 5, 3603–3615; d) P. Ferreira,
W.-M. Xue, E. Bencze, E. Herdtweck, F. E. Kꢀhn, Inorg. Chem.
7
5
36] Gaussian 03 (Revision C.01), M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery,
Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar,
J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R.
Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross,
V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y.
Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg,
V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O.
Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Fores-
man, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski,
B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Na-
nayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wallingford
CT, 2004..
2
001, 40, 5834–5841; e) M.-D. Zhou, J. Zhao, J. Li, S. Yue, C.-N.
Bao, J. Mink, S.-L. Zang, F. E. Kꢀhn, Chem. Eur. J. 2007, 13, 158–
66.
21] a) A. M. Al-Ajlouni, J. H. Espenson, J. Org. Chem. 1996, 61, 3969–
976; b) J. H. Espenson, Chem. Commun. 1999, 479–488; c) M. M.
Abu-Omar, P. J. Hansen, J. H. Espenson, J. Am. Chem. Soc. 1996,
18, 4966–4974.
1
[
[
3
1
22] F. E. Kꢀhn, A. M. Santos, I. S. GonÅalves, C. C. Rom¼o, A. D.
Lopes, Appl. Organomet. Chem. 2001, 15, 43–50.
23] Y. Wang, H. Li, S. Han, J. Phys. Chem. B 2006, 110, 24646–24651.
24] L. Cammarata, S. G. Kazarin, A. P. Salter, T. Welton, Phys. Chem.
Chem. Phys. 2001, 3, 5192–5200.
[
[
[
25] A. Mele, C. D. Tran, S. H. De Paoli Lacerda, Angew. Chem. 2003,
1
15, 4500–4502; Angew. Chem. Int. Ed. 2003, 42, 4364–4366.
[
26] W. A. Herrmann, R. W. Fischer, W. Scherer, M. U. Rauch, Angew.
Chem. 1993, 105, 1209–1212; Angew. Chem. Int. Ed. Engl. 1993, 32,
1
157–1160.
[
[
[
37] R. Bauernschmitt, R. Ahlrichs, Chem. Phys. Lett. 1996, 256, 454–
[
[
27] H. Yao, D. E. Richardson, J. Am. Chem. Soc. 2000, 122, 3220–3221.
28] M. Klꢁhn, A. Seduraman, P. Wu, J. Phys. Chem. B 2008, 112, 10989–
4
64.
38] D. Andrae, U. Haussermann, M. Dolg, H. Stoll, H. Preuss, Theor.
Chim. Acta 1990, 77, 123–141.
39] a) A. J. H. Wachters, J. Chem. Phys. 1970, 52, 1033–1036; b) P. J.
Hay, J. Chem. Phys. 1977, 66, 4377–4384; c) A. D. McLean, G. S.
Chandler, J. Chem. Phys. 1980, 72, 5639–5648; d) R. Krishnan, J. S.
Binkley, R. Seeger, J. A. Pople, J. Chem. Phys. 1980, 72, 650–654.
1
1004.
29] M. Klꢁhn, C. Stꢀber, A. Seduraman, P. Wu, J. Phys. Chem. B 2010,
14, 2856–2868.
[
[
1
30] a) P. Gisdakis, S. Antonczak, S. Kçstlmeier, W. A. Herrmann, N.
Rçsch, Angew. Chem. 1998, 110, 2333–2336; Angew. Chem. Int. Ed.
1
998, 37, 2211–2214; b) C. Di Valentin, R. Gandolfi, P. Gisdakis, N.
[40] K. Fumino, T. Peppel, M. Geppert-Rybczy n´ ska, D. H. Zaitsau, J. K.
Lehmann, S. P. Verevkin, M. Kçckerling, R. Ludwig, Phys. Chem.
Chem. Phys. 2011, 13, 14064–14075.
Rçsch, J. Am. Chem. Soc. 2001, 123, 2365–2376; c) N. Rçsch, C. Di
Valentin, I. V. Yudanov in Computational Modeling of Homoge-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
neous catalysis, Vol. 25 (Eds: F. Maseras, A. Lledꢆs), Springer, Hei-
[41] A. Aggarwal, N. L. Lancaster, A. R. Sethi, T. Welton, Green Chem.
2002, 4, 517–520.
delberg, 2002, pp. 289; d) D. V. Deubel, G. Frenking, P. Gisdakis,
W. A. Herrmann, N. Rçsch, J. Sundermeyer, Acc. Chem. Res. 2004,
Received: September 9, 2012
3
7, 645–652.
Published online: && &&, 0000
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8
&
www.chemeurj.org
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Activation of Hydrogen Peroxide by Ionic Liquids
FULL PAPER
Media savvy: Imidazolium-based ionic
liquids that contain perrhenate are
very efficient reaction media for the
epoxidation of olefins with H O as an
oxidant, thus affording cyclooctene in
almost quantitative yields. In situ
Raman, FTIR, and NMR spectroscopy
and DFT calculations showed hydro-
gen-bonding interactions between the
oxidant and perrhenate, which acti-
vated the oxidant and led to the trans-
fer of an oxygen atom onto the olefin.
Ionic Liquids
I. I. E. Markovits, W. A. Eger, S. Yue,
M. Cokoja, C. J. Mꢀnchmeyer,
B. Zhang, M.-D. Zhou, A. Genest,
J. Mink, S.-L. Zang,* N. Rçsch,*
F. E. Kꢀhn* ................... &&&& — &&&&
2
2
Activation of Hydrogen Peroxide by
Ionic Liquids: Mechanistic Studies and
Application in the Epoxidation of
Olefins
Chem. Eur. J. 2013, 00, 0 – 0
ꢃ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
9
&
ÞÞ
These are not the final page numbers!