A novel carbene ruthenium complex as reusable and selective two-electron catalyst for alkene epoxidation

Article abstract of DOI:10.1002/adsc.201000686

A new ruthenium aquo catalyst with the formula trans-[Ru(II)(CN-Me)(trpy) OH₂](PF₆)₂ [where trpy=2,2a:6′,2″- terpyridine and CN-Me=3-methyl-1-(pyridin-2-yl)-imidazolylidene] has been prepared and thoroughly characterized by spectroscopic and electrochemical techniques. The complex has been tested in epoxidation catalysis both in dichloromethane and dichloromethane:ionic liquid media, displaying excellent performances and selectivities. Reuse of the catalyst in ionic liquid:solvent media has been explored for the first time in ruthenium-mediated epoxidation catalysis and its performance is fully maintained for up to ten runs.

Full text of DOI:10.1002/adsc.201000686

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DOI: 10.1002/adsc.201000686
A Novel Carbene Ruthenium Complex as Reusable and Selective
Two-Electron Catalyst for Alkene Epoxidation
a,b
a
c
b
Mohamed Dakkach, Xavier Fontrodona, Teodor Parella, Ahmed Atlamsani,
a,
a,
Isabel Romero, * and Montserrat Rodrꢀguez *
Departament de Quꢀmica and Serveis Tꢁcnics de Recerca, Universitat de Girona, Campus de Montilivi S/N, E-17071
a
Girona, Spain
Fax : (+34)-972-418-150; phone: (+972)-418-262; e-mail: montse.rodriguez@udg.edu or marisa.romero@udg.edu
Laboratoire de Physico-Chimie des Interfaces et Environnement, Departement de Chimie, Facultꢂ des Sciences,
b
Universitꢂ Abdelmalek Essaadi, B.P. 2121, 93000 Tꢂtouan, Morocco
Servei de RMN and Departament de Quꢀmica, Universitat Autꢃnoma de Barcelona, Cerdanyola del Vallꢁs, E-08193
c
Barcelona, Spain
Received: September 5, 2010; Revised: November 19, 2010; Published online: February 8, 2011
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201000686.
Abstract: A new ruthenium aquo catalyst with the
formula trans-[Ru(II)(CN-Me)(trpy)OH ](PF )
where trpy=2,2’:6’,2’’-terpyridine and CN-Me=3-
In this sense, the use of N-heterocyclic carbene
(NHC) species as ligands for transition metal com-
plexes has experienced a growing interest throughout
A
H
U
G
R
N
U
A
H
U
G
R
N
U
ACHTUNGTRENNUNG
2
6 2
[
[
5,6]
methyl-1-(pyridin-2-yl)-imidazolylidene] has been
prepared and thoroughly characterized by spectro-
scopic and electrochemical techniques. The complex
has been tested in epoxidation catalysis both in di-
chloromethane and dichloromethane:ionic liquid
media, displaying excellent performances and selec-
tivities. Reuse of the catalyst in ionic liquid:solvent
media has been explored for the first time in ruthe-
nium-mediated epoxidation catalysis and its perfor-
mance is fully maintained for up to ten runs.
the last years given their particular electronic prop-
erties. A wide scope of carbenic d block metal com-
plexes have been tested as catalysts for a diversity of
[
7]
redox chemical transformations and, in the specific
case of ruthenium-NHC complexes, applications such
[
5c,8]
as olefin metathesis,
hydrogenation/transfer hydro-
[
9]
[10]
genation or alkylation have been extensively de-
veloped. However, the use of Ru-NHC species in oxi-
dative processes is still quite limited.
[
9d–e,11]
Olefin epoxidation is a key chemical transformation
for the synthesis of highly functionalized organic spe-
cies and the use of several transition metal complexes
Keywords: epoxidation; ionic liquids; reutilization;
ruthenium-carbene
[12]
for this type of process has been well documented.
Among these, the use of NHC as ligands for epoxida-
tion catalysts has been investigated mainly with Mo
[
13]
[14]
species and also with a few examples of Mn or
W
[
13a]
complexes but, although Ru complexes are
Polypyridyl ruthenium complexes have been widely powerful catalysts broadly studied for epoxidation
[
15]
developed during the past decades given their attrac- processes in homogeneous catalysis, a unique exam-
tive chemical, photochemical and electrochemical ple of epoxidation mediated by a Ru-NHC catalyst
[
1]
[11a]
properties that permit their application in a broad has been reported to date.
[
2]
scope of fields such as photochemistry/photophysics
On the other hand, heterogenization and reuse of
[3]
or bioinorganics[ as well as in a large diversity of cat- catalysts are fields of unquestionable importance es-
4]
alytic processes. In the specific field of redox cataly- pecially towards their application in large-scale pro-
[
16]
sis, the rationalization of catalyst performance on the cesses.
Room-temperature ionic liquids (RTIL)
basis of electronic and structural parameters is partic- have been broadly studied as alternative solvent or
[
17]
ularly complicated due to the involvement of distinct co-solvent media in catalysis given their ease of ma-
redox state species and so the development of new nipulation, high solubilization capacity and the possi-
metal complexes with novel properties is essential to bility of easily tuning the RTILꢄs properties by chang-
understand and optimize the mechanisms followed by ing the cation, the anion or the attached substituents.
such catalytic species.
Several oxidative catalytic processes have been tested
Adv. Synth. Catal. 2011, 353, 231 – 238
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
231

Mohamed Dakkach et al.
COMMUNICATIONS
Scheme 1. Top, drawing of the carbene CN-Me ligand used. Bottom, schematic synthesis of catalyst trans-3.
in these media, among which olefin epoxidation,
[
18]
[19]
[20]
which has been investigated with Mn, Re, Fe
[21]
or Mo species. Nevertheless, it is surprising to see
that Ru-mediated oxidations in ionic liquids are prac-
[
22,23]
tically limited to alcohols.
In this paper we pres-
ent what is, to the best of our knowledge, the first
ruthenium complex applied to epoxidation catalysis in
ionic liquid:solvent media which also constitutes one
of the scarce carbenic Ru-complexes described for
this type of reaction.
The pyridylcarbene ligand (CN-Me) used together
with the schematic synthesis of the catalyst are out-
lined in Scheme 1. Reduction of the trichloro-complex
1
with triethylamine in the presence of the bidentate
carbene ligand leads to the major formation of com-
plex 2.
Due to the asymmetry of the CN-Me ligand, two
different isomers, trans and cis, can be obtained in the
synthesis (where the trans or cis notation refers to the
position of the imidazolate ring with regard to the
Figure 1. ORTEP plot for the X-ray structure of the cationic
part of complex trans-2.
monodentate ligand). The compound is predominant- and the trpy plane (see Supporting Information for a
ly obtained in its trans isomeric form with a minor space-filling scheme of the complex), as well as to the
amount of the cis complex and other by-products that formation of an H-bonding interaction between the
are easily separated by column chromatography. The chloro ligand and the H16 atom of the pyridyl ring
lesser occurrence of the cis isomer is probably due to situated in the cis position (the Cl1ÀH16 distance is
steric hindrance arising from the close situation of the 2.73 ꢆ).
methyl group of the CN-Me ligand and the monoden-
tate chloro ligand in this geometry. After purification somewhat longer than the ones found in other mono-
The RuÀCl bond distance of around 2.47 ꢆ is
of trans-2, the corresponding aquo complex trans-3 is chloro complexes of Ru with several heteroatom-
[
24]
obtained by substitution of the chloro ligand in 2 donor ancillary ligands that range between 2.34 and
through reaction with a silver salt in aqueous solu- 2.43 ꢆ, a behaviour that is presumably a consequence
tion.
of a considerable structural trans effect exerted by the
Both complexes have been thoroughly character- highly s-donating carbene ring. The arrangement of
ized by the usual spectroscopic techniques and the complex molecules in the crystalline network involves
corresponding data and spectra are gathered in the the establishment of intermolecular H-bonding be-
experimental section and in the Supporting Informa- tween the Cl ligand and three H atoms of neighbour-
tion. The X-ray structure of complex trans-2 is dis- ing molecules (see Supporting Information).
played in Figure 1. The complex presents a distorted
A complete 1D and 2D-NMR as well as UV-vis
octahedral geometry with a trans Cl1ÀRu1ÀC21 bond spectroscopic study of both complexes 2 and 3 has
angle of 170.38. The deviation with regard to the regu- been performed and the corresponding spectra are
lar 1808 geometry is probably due to the steric encum- gathered in the Supporting Information. All features
brance originating between the carbene methyl group observed are in complete agreement with octahedral
232
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ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 231 – 238

A Novel Carbene Ruthenium Complex as Reusable and Selective Two-Electron Catalyst
6
low spin d complexes as expected for Ru(II). Elec-
trochemical essays have also been carried out and
cyclic voltammetric experiments for both complexes
are also collected in the Supporting Information. For
the aquo complex trans-3, the presence of an aquo
ligand in the coordination environment of the metal
center allows a pH dependence of the redox potential
as expressed in Eq. (1) for the two general redox pro-
cesses [Ru ACHTUNGTRENNUNG( III/II) and Ru ACHTUNGTNERNUNG( IV/III)]:
Figure 3. Redox spectrophotometric titration performed
upon addition of small amounts of a Ce(IV) aqueous solu-
À4
tion (up to 2 equivalents) to a 2·10 M solution of complex
However, for trans-3, the Pourbaix diagram (plot of
E1/2 vs. pH, see Figure 2) shows the occurrence of a
unique redox process from pH approximately 3 to 11
with a slope value of roughly 56 mV per pH unit (in
accordance with the Nernst equation for the transfer
of an equal number of protons and electrons) that
trans-3 in HCl 0.1M. Isosbestic points are found at 575 and
39 nm thus indicating the net conversion between the
Ru(II)OH and the Ru(IV)=O species.
3
2
changes to a value of approximately 30 mV/pH unit PhI
corresponding to the transfer of two electrons and similar to those used for the catalytic essays described
only one proton) at higher pH. This behaviour is indi- below (see Supporting Information). The occurrence
cative of the occurrence of a bielectronic Ru(IV/II) of bielectronic processes in redox catalysts is of fun-
redox process and the change of slope at pH beyond damental importance since the simultaneous transfer
1 corresponds to the deprotonation of the reduced of two electrons avoids radical intermediates that
Ru(II) form of complex trans-3. This Ru(II)OH pK would lower the selectivity of the catalyzed reactions.
ACHTUNGTNERNGNU( OAc) as oxidant, under experimental conditions
2
(
AHCTUNGTRENNUNG
1
2
a
value has been corroborated through acid-base spec- However, only a few Ru aquo complexes have been
trophotometric titrations carried out on the complex reported to undergo such redox processes up to
[
11a,24a,25]
(
see experimental details in the Supporting Informa- date.
tion). Also, a spectrophotometric redox titration per- The performance of the aquo complex trans-3 has
formed upon the progressive addition of 2 equivalents been tested in the epoxidation of a series of substrates
of Ce(IV) to an aqueous solution of the complex in homogeneous phase at room temperature (see
(
Figure 3) confirms the direct conversion from the Table 1). In most cases high conversions and selectivi-
Ru(II) to the Ru(IV) species. ties are obtained. For the case of styrene, total con-
This bielectronic process has also been confirmed sumption of the substrate is attained with a selectivity
to take place in dichloromethane and using among the highest obtained with ruthenium com-
[
15a–d,26]
plexes as catalysts.
It is also remarkable that
the cis configuration in cis-b-methylstyrene epoxida-
tion (entry 3) is fully maintained which is consistent
with a potential O-transfer mechanism favoured by
the bielectronic nature of the catalyst. Complex trans-
3
is also regiospecific for epoxidation of the ring
double bond in 4-vinylcyclohexene.
A comparison between the values of initial con-
sumption rates n for the family of substrates tested
i
indicates that trans-stilbene, with two electron-with-
drawing substituents on the double bond, is epoxi-
dized faster, followed by the two monosubstituted al-
kenes. This seems to indicate a nucleophilic character
of the Ru=O species that in turn is in accordance with
the presence of a strong s-donor carbene group in
trans position with regard to the active site. Previous
Figure 2. Pourbaix diagram for complex trans-3. The stability
regions for the different redox species are indicated sche- examples of similar complexes have shown more elec-
matically.
trophilic character for catalysts containing anionic
Adv. Synth. Catal. 2011, 353, 231 – 238
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
233

Mohamed Dakkach et al.
COMMUNICATIONS
Table 1. Epoxidation tests performed with complex trans-3. Conditions: substrate (50 mM), catalyst (0.5 mM), oxidant
PhI(OAc) (100 mM), CH Cl (2.5 mL), 258C, 24 h. Conversions and yields are evaluated by GC analysis with biphenyl as in-
ternal standard.
ACHTUNGTRENNUNG
2
2
2
[a]
6
À1
Entry
1
Substrate
Product
Conversion [%]
Selectivity [%]
61
10 ꢇn (mol·h )
i
>99.9
–
2
90
89
13.6
[b]
3
4
81
94
95
6.1
8.4
>99.9
5
6
98
99
80
97
8.6
[c]
10.9
[
[
a]
b]
Calculated as [epoxide yield/substrate conversion]ꢇ100.
Specific for cis epoxide. Epoxidation exclusively at the cyclohexene ring.
[c]
trans ligands when compared to neutral pyrazine li-
[24a]
gands.
Given the efficacy of the catalyst, we proceeded to
test its performance and reusability in ionic liquid:sol-
vent media. The ionic liquid used was the commer-
cially available [bmim]PF and the reaction conditions
6
were initially optimized using different solvents, oxi-
dants and [bmim]PF :solvent ratios with cyclooctene
6
as test substrate (see Supporting Information). Opti-
mal using
performance
was
obtained
[
bmim]PF :CH Cl 0.8:1.2 as solvent and PhI AHCTUNTGERG(NNUN OAc)
6
2
2
2
as oxidant and these conditions were used for the ep-
oxidation of different alkenes (Table 2).
We then tested the recyclability of the catalytic
system using cyclooctene (see Experimental Section Figure 4. Yields and conversions obtained throughout ten
for a detailed description of the procedure followed). consecutive reuses of catalyst trans-3 in the epoxidation of
cyclooctene.
The results obtained throughout ten consecutive runs
are displayed in Figure 4. As can be seen, the catalyst
maintains excellent performance and selectivity right
through all runs thus giving an overall turnover lizing effect on the catalyst that allows its reuse with-
number close to 1000. out loss of activity. This positive influence could arise
A similar recycling procedure has also been investi- from a role as “ionic dilutor” of [bmim]PF6 that
gated in CH Cl as single solvent (see Supporting In- would keep the catalyst molecules away from each
2
2
formation) but the conversion dropped to 35% at the other thus preventing auto-deactivation. To verify this
second run (although keeping selectivity for the epox- point, the experiments were reproduced in the pres-
ide at over 99%). Thus, the ionic liquid exerts a stabi- ence of a high concentration of an ionic salt (tetrabu-
234
asc.wiley-vch.de
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 231 – 238

A Novel Carbene Ruthenium Complex as Reusable and Selective Two-Electron Catalyst
Table 2. Epoxidation tests performed with complex trans-3 in [bmim]PF :CH Cl 0.8:1.2. Conditions: substrate (50 mM), cat-
6
2
2
alyst (0.5 mM), PhI
ACHTUNGTRENNUNG( OAc) (100 mM), solvent (2 mL), 258C, 24 h. Conversions and yields are evaluated by GC analysis with
2
biphenyl as internal standard.
[a]
Entry
1
Substrate
Product
Conversion [%]
62
Selectivity [%]
57
2
3
4
>99.9
>99.9
>99.9
>99.9
[b]
99
>99.9
5
6
45
90
98
59
[c]
7
73
93
[a]
[b]
[c]
Calculated as [epoxide yield/substrate conversion]ꢇ100.
Specific for cis epoxide.
Epoxidation exclusively at the cyclohexene ring.
tylammonium hexafluorophosphate, see Supporting Experimental Section
Information) and the catalyst could be reused for sev-
eral times but also encountered a decrease in perfor- Synthesis of trans-[Ru(II)Cl ACHTUNGTRENUNGN( CN-Me) ACHTNUREGTNNUNG( trpy)] ACHUNTGTRENNUNG( PF )·
6
mance after the third run. Consequently, the role of 0.5CH Cl , trans-2·0.5CH Cl
2
2
2
2
the ionic liquid in the reaction media is not limited to
stabilizing “bulk” but other electronic parameters
such as the influence of the p-cation interaction of IL
with cationic catalysts, as postulated by several stud-
A sample of 1 (100 mg, 0.218 mmol) and LiCl (18.5 mg,
.436 mmol) was dissolved in a 3:1 EtOH:H O mixture
0
2
(
40 mL) under an N2 atmosphere. NEt3 (0.06 mL,
0
3
.436 mmol) was added and the mixture was stirred for
0 min at room temperature. At this point the CN-Me
[17e,27]
ies,
must be taking place.
In conclusion, we have investigated the first ruthe- ligand (52.3 mg, 0.218 mmol) dissolved in 2 mL of 3:1
nium-based system for epoxidation catalysis in ionic EtOH:H O was added and the resulting solution was re-
2
liquid:solvent media, that has displayed a highly re- fluxed overnight. Upon cooling to room temperature the so-
lution was filtered on a frit to eliminate small amounts of
undesired by-products and, afterwards, 2 mL of a saturated
NH PF aqueous solution were added. The volume was re-
duced under low pressure until a precipitate appeared and
the resulting dark-brown solid was filtered on a frit, washed
with water and diethyl ether and dried in vacuum. The solid
was purified by chromatography over alumina using di-
chloromethane as eluent and an increasing gradient of meth-
anol (0–1%). The final product was further purified by re-
crystallization from a mixture of dichlomethane and ether
markable effectiveness and selectivity for the epoxide
product as well as excellent reusability. Complex
trans-3 is also the second example of a carbenic Ru
complex successfully applied to this type of reaction
thus manifesting that carbene ligands are a promising
choice to tune catalysts properties in oxidation pro-
cesses that has been barely investigated to date.
4
6
(
1:1, v/v) and suitable crystals for the resolution of its X-ray
diffraction structure were obtained (CCDC 799291);
yield: 59 mg (40.2%); anal. found (calcd.) for
Adv. Synth. Catal. 2011, 353, 231 – 238
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
235

Mohamed Dakkach et al.
COMMUNICATIONS
C H N ClRuPF ·0.5CH Cl :
C
41.39 (41.08),
N
11.30
then analyzed by GC) and the oxidant by-products, and the
remaining mixture was dried under vacuum. A new load of
substrate and oxidant dissolved in dichloromethane was
then added and the mixture left for an additional 24 h run.
This procedure was repeated up to ten times.
24
20
6
6
2
2
1
(
11.72), H 2.91 (2.95); H NMR (600 MHz, acetone-d6,
2
8
58C): d=10.15 (ddd, J=5.7, 1.6, 0.9 Hz, H-16), 8.67 (d, J=
.1 Hz, H-7, H-9), 8.58 (dt, J=8.1, 0.9 Hz, H-4, H-12), 8.31
(
(
m, H-19), 8.30 (m, H-20), 8.25 (d, J=2.3 Hz, H-23), 8.15
td, J=8.1, 0.8 Hz, H-8), 7.99 (td, J=6.0, 1.4 Hz, H-3, H-18),
7
0
7
.77 (tq, J=7.2, 5.7, 1.7 Hz, H-17), 7.71 (ddd, J=5.5, 1.5,
.8 Hz, H1, H-15), 7.38 (tq, J=7.4, 5.8, 1.3 Hz, H-2, H-14),
1
3
.07 (d, J=2.3 Hz, H-22), 2.90 (s, H-24, 3H); C NMR Acknowledgements
(
151 MHz, acetone-d , 258C): d=192.32 (C-21), 159.26 (C-5,
6
C-11), 158.57 (C-6, C-10), 154.33 (C-20), 153.25 (C-1, C-15),
This project has been financed by MICINN of Spain through
projects CTQ2007-60476/PPQ, CTQ2010-21532-C02-01 and
CTQ2009-08328. Johnson & Matthey Ltd. are acknowledged
for a RuCl ·nH O loan. MD thanks AECID (MAEC) of
1
8
1
2
53.03 (C-16), 139.35 (C-19), 137.47 (C-3, C-18), 133.99 (C-
) , 128.01 (C-2, C-14), 125.68 (C-22), 124.15 (C-4, C-12),
23.29 (C-7, C-9), 122.78 (C-17), 117.17 (C-23), 112.15 (C-
0), 35.26 (C-24), for the NMR assignment we have used
3
2
Spain for the allocation of an MAEC-AECID grant.
the same numbering Scheme as for the X-ray displayed in
Figure 1; IR: nmax =1610 (m), 1494 (m), 1251 (m), 1091 (w),
À1
8
82 (m), 836 (s), 771 (m) 555 cm (s); E1
A
H
U
G
R
N
U
G
/2
2
2
References
0
M
.1M TBAH): 0.87 V vs. SSCE; UV-vis (CH Cl ): l
(e,
2
2
max
À1
À1
cm )=267 (16636), 279 (sh 12768), 316 (17314), 372
À
[1] a) J. L. Boyer, J. Rochford, M. K. Tsai, J. T. Mucker-
man, E. Fujita, Coord. Chem. Rev. 2010, 254, 309–330;
b) I. Dixon, E. Lebon, P. Sutra, A. Igau, Chem. Soc.
Rev. 2009, 38, 1621–1634; c) J. Wing-Sze Hui, W.-T.
Wong, Coord. Chem. Rev. 1998, 172, 389–436; d) M. J.
Clarke, Coord. Chem. Rev. 2002, 232, 69–93; e) T. J.
Meyer, M. H. V. Huynh, Inorg. Chem. 2003, 42, 8140–
(
5341), 490 nm (4316); ESI-MS: m/z=529.1 [MÀPF ].
6
Synthesis of trans-[Ru(II)
.5H O, trans-3·0.5H O
ACHTUNGTRENNGN(U CN-Me) ACHTUNTGRENNUG( trpy)OH ] AHCTGNRUETNNUG( PF ) ·
2 6 2
0
2
2
A 25 mg (0.037 mmol) sample of trans-2 and a 12.57 mg
0.074 mmol) sample of AgNO3 were placed in a round-
(
8
1
169; f) W. P. Griffith. Chem. Soc. Rev. 1992, 21, 179–
85; g) A. G. Lappin, R. A. Marusak, Coord. Chem.
bottom flask together with 15 mL of H O and the resulting
2
mixture was refluxed in the dark for 3 h. Afterwards the so-
lution was cooled on ice to completely precipitate the AgCl
formed which was filtered over celite. A saturated aqueous
solution of NH PF (1 mL) was added to the filtrate and the
solvent was reduced in a rotary evaporator until precipita-
tion of a green solid that was filtered, washed with ether
and pentane and dried under vacuum; yield: 23 mg (77.6%);
anal. found (calcd.) for C H N OP F Ru·0.5H O: C 35.32
Rev. 1991, 109, 125–180.
2] a) M. J. Rose, P. K. Mascharak, Coord. Chem. Rev.
[
2
008, 252, 2093–2114; b) J. P. Sauvage, J. P. Collin, J. C.
4
6
Chambron, S. Guillerez, C. Coudret, V. Balzani, F. Bar-
igelletti, L. Decola, L. Flamigni, Chem. Rev. 1994, 94,
9
93–1019; c) L. C. C. Sun, L. Hammarstrom, B. Aker-
mark, S. Styring, Chem. Soc. Rev 2001, 30, 36–49; d) R.
Martin, L. Jimenez, M. Alvaro, J. Scaiano, H. Garcia,
Chem. Eur. J. 2010, 16, 7282–7292; e) L. J. Nurkkala,
R. O. Steen, H. K. J. Friberg, J. A. Hꢈggstrçm, P. V.
Bernhardt, M. J. Riley, S. J. Dunne, Eur. J. Inorg.
Chem. 2008, 4101–4110.
2
4
22
6
2
12
2
1
(
35.57), N 10.28 (10.37), H 2.63 (2.86); H NMR (600 MHz,
acetone-d /10% D O, 25 8C): d=9.46 (d, J=5.3 Hz, H-16),
8
8
6
2
.74 (d, J=8.0 Hz, H-4, H-9), 8.62 (d, J=7.9 Hz, H-4, H-12),
.37 (t, J=7.7 Hz, H-18), 8.32 (m, H-19), 8.30 (m, H-8), 8.25
(
d, J=1.7 Hz, H-23), 8.10 (t, J=7.7 Hz, H-3, H-13), 7.85 (t,
[
3] a) S. O. Kelley, J. K. Barton, Science 1999, 283, 375–
J=6.3 Hz, H-17), 7.79 (d, J=5.1 Hz, H-1, H-15), 7.46 (t, J=
3
81; b) D. B. Hall, R. E. Holmlin, J. K. Barton, Nature
6
3
1
.3 Hz, H-2, H-14), 7.08 (d, J=1.5 Hz, H-22), 2.92 (s, H-24,
13
1
996, 384, 731–735; c) C. J. Burrows, J. G. Muller,
H); C NMR (151 MHz, acetone-d /10% D O, 25 8C): d=
6
2
Chem. Rev. 1998, 98, 1109–1151; d) S. C. Weatherly,
I. V. Yang, H. H. Thorp, J. Am. Chem. Soc. 2001, 123,
90.03 (C-21), 159.51 (C-5, C-11), 159.29 (C-6, C-10), 153.97
(
1
(
1
C-1, C-15), 153.83 (C-20), 150.55 (C-16), 140.07 (C-19),
39.02 (C-3, C-18), 136.40 (C-8), 128.81 (C-2, C-14), 126.09
C-22), 124.74 (C-4, C-12), 124.05 (C-7, C-9), 123.55 (C-17),
17.73 (C-23), 112.89 (C-20), 35.30 (C-24); IR:nmax =3326
1
236–1237.
[
4] a) S. I. Murahashi, H. Takaya, T. Naota, Pure Appl.
Chem. 2002, 74, 19–24; b) T. Naota, H. Takaya, S. I.
Murahashi, Chem. Rev. 1998, 98, 2599–2660; c) M. Ro-
drꢀguez, I. Romero, A. Llobet, A. Deronzier, M. Biner,
T. Parella, H. Stoeckli-Evans, Inorg. Chem. 2001, 40,
(
w), 3203 (s), 1625 (m), 1450 (s), 1251 (w), 1197 (m), 831 (s),
À1
7
0
67 (s), 551 cm (s); E1/2 (IV/II), phosphate buffer pH 7:
À1
À1
.57 V vs. SSCE; UV-vis (CH Cl ): l (e, M cm )=272
2
2
max
4
150–4156; d) U. J. Jauregui-Haza, M. Dessoudeix,
P. H. Kalck, A. M. Wilhelm, H. Delmas, Catal. Today
001, 66, 297–302.
(
18306), 315 (21670), 362 (5250), 463 nm (4494); ESI-MS:
+
À
m/z=513.1 [M+H À2PF ].
6
2
[
5] a) A. J. Arduengo, H. V. R. Dias, F. Davidson, R. L.
Harlow, J. Organomet. Chem. 1993, 462, 13–18; b) M.
Poyatos, E. Mas-Marzꢉ, M. Sanaffl, E. Peris, Inorg.
Chem. 2004, 43, 1793–1798; c) R. H. Grubbs, Angew.
Chem. 2006, 118, 3845–3850; Angew. Chem. Int. Ed.
2006, 45, 3760–3765; d) W. A. Herrmann, Angew.
Chem. 2002, 114, 1342–1363; Angew. Chem. Int. Ed.
2002, 41, 1290–1309; e) J. A. Mata, M. Poyatos, E.
Catalytic Epoxidation in Ionic Liquid:Solvent Media
Catalyst trans-3 (0.5 mM), substrate (50 mM) and
PhI
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(OAc)
(75 mM) were dissolved in 2 mL of
2
[
bmim]PF :CH Cl (0.8:1.2) and the solution was stirred at
6
2
2
room temperature for 24 h. After completion, CH Cl was
2
2
rotavaporated and the resulting suspension washed with di-
ethyl ether (3ꢇ5 mL) to extract the epoxide (which was
236
asc.wiley-vch.de
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 231 – 238

A Novel Carbene Ruthenium Complex as Reusable and Selective Two-Electron Catalyst
Peris, Coord. Chem. Rev. 2007, 251, 841–859; f) P. de
Fremont, N. Marion, S. P. Nolan, Coord. Chem. Rev.
[12] a) E. M. McGarrigle, D. G. Gilheany, Chem. Rev. 2005,
105, 1563–1602; b) B. S. Lane, K. Burgess, Chem. Rev.
2003, 103, 2457–2473; c) T. Katsuki, Adv. Synth. Catal.
2002, 344, 131–147; d) K. Matsumoto, T. Oguma, T.
Katsuki, Angew. Chem. 2009, 121, 7568–7571; Angew.
Chem. Int. Ed. 2009, 48, 7432–7435; e) H. Egami, T.
Oguma, T. Katsuki, J. Am. Chem. Soc. 2010, 132, 5886–
5895; f) K. Schroeder, S. Enthaler, B. Bitterlich, T.
Schulz, A. Spannenberg, M. K. Tse, K. Junge, M.
Beller, Chem. Eur. J. 2009, 15, 5471–5481; g) K.
Schroeder, S. Enthaler, B. Join, K. Junge, M. Beller,
Adv. Synth. Catal. 2010, 352, 1771–1778.
2
009, 253, 862–892.
[
6] a) Y. Canac, M. Soleilhavoup, S. Conejero, G. Bertrand,
J. Organomet. Chem. 2004, 689, 3857–3865; b) S. Burl-
ing, M. K. Whittlesey, J. M. J. Williams, Adv. Synth.
Catal. 2005, 347, 591–594; c) S. Dꢀez-Gonzꢉlez, N.
Marion, S. P. Nolan, Chem. Rev. 2009, 109, 3612–3676;
d) M. Poyatos, J. A. Mata, E. Peris, Chem. Rev. 2009,
1
09, 3677–3707; e) W. A. Herrmann, J. Schutz, G. D.
Frey, E. Herdtweck, Organometallics 2006, 25, 2437–
2
448; f) N. Marion, S. P. Nolan, Acc. Chem. Res. 2008,
4
1, 1440–1449.
[
13] a) V. V. K. M. Kandepi, J. M. S. Cardoso, B. Royo,
Catal. Lett. 2010, 136, 222–227; b) S. Li, C. W. Kee,
K. W. Huang, T. S. A. Hor, J. Zhao, Organometallics
[
7] a) W. L. Duan, M. Shi, G. B. Rong, Chem. Commun.
2
003, 2916–2917; b) H. Clavier, L. Coutable, L.
Toupet, J. C. Guillemin, M. Mauduit, J. Organomet.
Chem. 2005, 690, 5237–5254; c) P. L. Arnold, S. Pear-
son, Coord. Chem. Rev. 2007, 251, 596–609; d) D.
Pugh, A. Danopoulos, Coord. Chem. Rev. 2007, 251,
2
010, 29, 1924–1933; c) V. V. K. M. Kandepi, A. P. da
Costa, E. Peris, B. Royo, Organometallics 2009, 28,
544–4549.
4
[
[
14] T. Yagyu, K. Yano, T. Kimata, K. Jitsukawa, Organo-
metallics 2009, 28, 2342–2344.
15] a) C. M. Che, J. S. Huang, Chem. Commun. 2009, 3996–
6
10–641; e) J. W. Ogle, S. A. Miller, Chem. Commun.
2
009, 5728–5730; f) V. Dragutan, I. Dragutan, I. De-
laude, A. Demonceau, Coord. Chem. Rev. 2007, 251,
65–794; g) W. A. Herrmann, G. D. Frey, E. Herdt-
weck, M. Steinbeck, Adv. Synth. Catal. 2007, 349,
677–1691.
4
015; b) W. Magerlein, C. Dreisbach, H. Hugl, M. K.
Tse, M. Klawonn, S. Bhor, M. Beller, Catal. Today
007, 121, 140–150; c) D. Chatterjee, Coord. Chem.
7
2
1
Rev. 2008, 252, 176–198; d) M. K. Tse, S. Bhor, M. Kla-
wonn, G. Anilkumar, H. Jiao, A. Spannenberg, C.
Dobler, W. Magerlein, H. Hugl, M. Beller, Chem. Eur.
J. 2006, 12, 1875–1888; e) J. Benet-Buchholz, P.
Comba, A. Llobet, S. Roeser, P. Vadivelu, H. Wade-
pohl, S. Wiesner, Dalton Trans. 2009, 5910–5923; f) O.
Hamelin, S. Menage, F. Charnay, M. Chavarot, J. L.
Pierre, J. Pecaut, M. Fontecave, Inorg. Chem. 2008, 47,
[
8] a) T. Weskamp, F. J. Kohl, W. Hieringer, D. Gleich,
W. A. Herrmann, Angew. Chem. 1999, 111, 2573–2576;
Angew. Chem. Int. Ed. 1999, 38, 2416–2419; b) T. Ung,
A. Hejl, R. H. Grubbs, Y. Schrodi, Organometallics
2
004, 23, 5399–5401; c) S. P. Nolan, H. Clavier, Chem.
Soc. Rev. 2010, 39, 3305–3316; d) F. Ragone, A. Poater,
L. Cavallo, J. Am. Chem. Soc. 2010, 132, 4249–4258;
e) M. Lichtendheldt, D. R. Wang, K. Vehlow, I. Rein-
hardt, C. Kuhnel, U. Decker, S. Blechert, M. R. Buch-
meiser, Chem. Eur. J. 2009, 15, 9451–9457; f) A. Furst-
ner, L. Ackermann, B. Gabor, R. Goddard, C. W. Leh-
mann, R. Mynott, F. Stelzer, O. R. Thiel, Chem. Eur. J.
6
413–6420; g) X. Sala, N. Santana, I. Serrano, E. Plan-
talech, I. Romero, M. Rodrꢀguez, A. Llobet, S. Jansat,
M. Gómez, X. Fontrodona, Eur. J. Inorg. Chem. 2007,
5
207–5214; h) I. Serrano, X. Sala, E. Plantalech, M.
Rodrꢀguez, I. Romero, S. Jansat, M. Gómez, T. Parella,
H. Stoeckli-Evans, X. Solans, M. Font-Bardia, B. Vid-
jayacoumar, A. Llobet, Inorg. Chem. 2007, 46, 5381–
2
001, 7, 3236–3253.
[
9] a) S. Enthaler, R. Jackstell, B. Hagemann, K. Junge, G.
Erre, M. Beller, J. Organomet. Chem. 2006, 691, 4652–
5
389; i) G. A. Barf, R. A. Sheldon, J. Mol. Catal. A
4
659; b) F. Zeng, Z. Yu, Organometallics 2008, 27,
1
995, 102, 23–39.
6
025–6028; c) N. Gurbuz, S. Yasar, E. O. Ozcan, I. Oz-
[
[
16] a) G. Centi, S. Perathoner, in: Methods and Tools of
Sustainable Industrial Chemistry: Catalysis, in: Sustaina-
ble Industrial Chemistry, (Eds.: F. Cavani, G. Centi, S.
Perathoner, F. Trifiró), Wiley-VCH, Weinheim, Germa-
ny, 2009,chap 2; b) N. V. Plechkova, K. R. Seddon,
Chem. Soc. Rev. 2008, 37, 123–150.
17] a) M. Earle, P. Wasserscheid, P. Schulz, H. Olivier-
Bourbigou, F. Favre, M. Vaultier, A. Kirschning, V.
Singh, A. Riisager, R. Fehrmann, S. Kuhlmann, in: Or-
ganic Synthesis, in: Ionic Liquids in Synthesis, 2nd edn.,
demir, B. Cetinkaya, Eur. J. Inorg. Chem. 2010, 3051–
056; d) S. Burling, L. J. L. Haller, E. Mas-Marza, A.
3
Moreno, S. A. Macgregor, M. F. Mahon, P. S. Pregosin,
M. K. Whittlesey, Chem. Eur. J. 2009, 15, 10912–10923;
e) M. Poyatos, J. A. Mata, E. Falomir, R. H. Crabtree,
E. Peris, Organometallics 2003, 22, 1110–1114.
[
10] a) S. Yasar, I. Ozdemir, B. Cetinkaya, J. L. Renaud, C.
Bruneau, Tetrahedron Lett. 2006, 47, 535–538; b) M.
Viciano, M. Sanau, E. Peris, Organometallics 2007, 26,
6
050–6054; c) D. Gnanamgari, E. L. O. Sauer, N. D.
(
Eds.: P. Wasserscheid, T. Welton), Wiley-VCH, Wein-
Schley, C. Butler, C. D. Incarvito, R. H. Crabtree, Orga-
nometallics 2009, 28, 321–325; d) S. Burling, B. M.
Paine, N. Devendrababu, V. S. Brown, M. F. Mahon,
J. T. Prior, P. S. Pregosin, M. K. Whittlesey, J. M. J. Wil-
liams, J. Am. Chem. Soc. 2007, 129, 1987–1995.
heim, Germany, 2008, chap 5; b) V. Gauchot, W. Krou-
til, A. R. Schmitzer, Chem. Eur. J. 2010, 16, 6748–6751;
c) Y. Gu, G. Li, Adv. Synth. Catal. 2009, 351, 817–847;
d) V. Parvulescu, C. Hardacre, Chem. Rev. 2007, 107,
2615–2655; e) T. Welton, Coord. Chem. Rev. 2004, 248,
2459–2477; f) J. M. Fraile, J. I. Garcia, J. A. Mayoral,
Coord. Chem. Rev. 2008, 252, 624–646; g) E. Ochsner,
K. Schneiders, K. Junge, M. Beller, P. Wasserscheid,
Appl. Catal. A 2009, 364, 8–14.
[
11] a) E. Masllorens, M. Rodrꢀguez, I. Romero, A. Ro-
glans, T. Parella, J. Benet-Buchholz, M. Poyatos, A.
Llobet, J. Am. Chem. Soc. 2006, 128, 5306–5307;
b) R. A. Diggle, S. A. Macgregor, M. K. Whittlesey, Or-
ganometallics 2004, 23, 1857–1865.
Adv. Synth. Catal. 2011, 353, 231 – 238
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
237

Mohamed Dakkach et al.
COMMUNICATIONS
[
18] a) C. E. Song, E. J. Roh, Chem. Commun. 2000, 837–
Inorg. Chem. 2010, 49, 7072–7079; b) J. Mola, I.
Romero, M. Rodrꢀguez, F. Bozoglian, A. Poater, M.
Solà, T. Parella, J. Benet-Buchholz, X. Fontrodona, A.
Llobet, Inorg. Chem. 2007, 46, 10707–10716; c) I. Ser-
rano, M. Rodrꢀguez, I. Romero, A. Llobet, T. Parella,
J. M. Campelo, D. Luna, J. M. Marinas, J. Benet-Buch-
holz, Inorg. Chem. 2006, 45, 2644–2651.
8
2
38; b) Z. Li, C. G. Xia, M. Ji, Appl. Catal. A 2003,
52, 17–21; c) C. Basheer, M. Vetrichelvan, V. Suresh,
H. K. Lee, Tetrahedron Lett. 2006, 47, 957–961.
[
19] a) G. S. Owens, M. M. Abu-Omar, Chem. Commun.
2
000, 1165–1166; b) G. S. Owens, Z. Durazo, M. M.
Abu-Omar, Chem. Eur. J. 2002, 8, 3053- 3059; c) G.
Soldaini, F. Cardona, A. Goti, Tetrahedron Lett. 2003,
[
25] a) A. Gerli, J. Reedijk, M. T. Lakin, A. L. Spek, Inorg.
Chem. 1995, 34, 1836–1843; b) X. Hua, M. Shang,
A. G. Lappin, Inorg. Chem. 1997, 36, 3735–3740; c) J. J.
Concepcion, J. W. Jurss, J. L. Templeton, T. J. Meyer, J.
Am. Chem. Soc. 2008, 130, 16462–16463.
4
4, 5589–5592.
[
[
[
[
[
20] a) N. Jain, A. Kumar, S. M. S. Chauhan, Tetrahedron
Lett. 2005, 46, 2599–2602; b) K. A. Srinivas, A. Kumar,
S. M. S. Chauhan, Chem. Commun. 2002, 2456–2457.
21] F. E. Kuhn, J. Zhao, M. Abrantes, W. Sun, C. A. M.
Afonso, L. C. Branco, I. S. GonÅalves, M. Pillinger,
C. C. Romao, Tetrahedron Lett. 2005, 46, 47–52.
22] a) S. V. Ley, C. Ramarao, M. D. Smith, Chem.
Commun. 2001, 2278–2279; b) V. Farmer, T. Welton,
Green Chem. 2002, 4, 97–102.
[
[
26] a) M. K. Tse, C. Dçbler, S. Bhor, M. Klawonn, W. Mꢈ-
gerlein, H. Hugl, M. Beller, Angew. Chem. Int. Ed.
2
004, 43, 5255–5260; b) D. Chatterjee, J. Mol Cat. A:
Chem. 2009, 310, 174–179;.
27] a) J. C. Ma, D. A. Dougherty, Chem. Rev. 1997, 97,
1
303–1324; b) S. RiaÇo, D. Fernandez, L. Fadini, Catal.
23] A. Wolfson, S. Wuyts, D. E. De Vos, I. F. J. Vankele-
Commun. 2009, 10, 1282–1285; c) C. G. Hanke, A. Jo-
hansson, J. B. Harper, R. M. Lynden-Bell, Chem. Phys.
Lett. 2003, 374, 85–90; d) S. Chowdhury, R. S. Mohan,
J. L. Scott, Tetrahedron 2007, 63 2363–2389.
com, P. A. Jacobs, Tetrahedron Lett. 2002, 43, 8107–
8
110.
24] a) M. Dakkach, M. I. López, I. Romero, M. Rodrꢀguez,
A. Atlamsani, T. Parella, X. Fontrodona, A. Llobet,
238
asc.wiley-vch.de
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 231 – 238