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DOI: 10.1002/cctc.201402042
High Catalytic Synergism between the Components of the
Rhenium Complex@Silver Hybrid Material in Alkene
Epoxidations
[
a]
[b]
[b]
[b]
[c]
Arindam Indra, Mark Greiner, Axel Knop Gericke, Robert Schlçgl, David Avnir,* and
[
a]
Matthias Driess*
The immobilization of a water-soluble rhenium complex in
metallic silver matrices has resulted in a highly efficient catalyst
for epoxidation, which has better epoxidation catalytic activity
than the individual components. This unprecedented syner-
gism could be obtained only by using the novel immobiliza-
tion methodology, and not by using the standard adsorption
process. The composite catalyst has been fully characterized
(by using XRD, TEM, SEM, energy-dispersive X-ray spectroscopy,
and atomic X-ray mapping), and the synergism has originated
as a result of the proximity of the two components. Photoem-
ission spectroscopic studies confirm the presence of +6 and
+7 oxidation states of rhenium in metallic silver in the active
catalyst.
Introduction
[
2b]
The immobilization of dopant molecules in metal matrices has
the pinacol–pinacolone rearrangement and RhCl(cod)(Ph P-
2
[1]
led to the formation of a new family of functional materials.
(C H SO Na))@Ag used for the hydrogenation of styrene or di-
6
4
3
[4]
Methods for the effective immobilization of various organic
molecules and polymers in silver, copper, palladium, and gold
phenylacetylene (cod=1,5-cyclooctadiene). Improved conver-
sions, enhanced stabilities, altered product ratios, and obtain-
ing new products were all observed in these studies.
[
2]
matrices have been developed. Such methods can change
the properties of the dopant molecules or of the metal or give
Another development is to use the metal not only as a heter-
ogenization matrix but also as a catalyst by itself. Two direc-
tions are then possible: the first is that the dopant and the
metal catalyze different reactions, so that the catalyst@metal
can activate two consecutive steps. This direction was con-
firmed with Nafion@Pd, which activated consecutive catalytic
dehydrations followed by disproportionation or hydrogena-
[
3,4]
rise to synergism between the two components.
A useful
property of these materials is that the mesoporous metallic
matrix binds the dopant molecules strongly while leaving
them accessible to external reagents and substrates.
These properties have opened the possibility of using
metals as heterogenizing matrices for homogeneous catalysts:
catalytic dopant@metal. An example is the immobilization of
[6]
tion. The second direction, which is the focus of this article, is
to explore the possibility of a synergetic, mutual enhancement
of the same reaction catalyzed both by the dopant and by the
metal.
phosphomolybdic
acid
and
phosphotungstic
acid
[
5]
(
H [P(M O ) ], M=Mo/W) in metallic silver, which proved to
3
3
10 4
be highly efficient in the Friedel–Crafts adamantylation of sub-
stituted benzenes. Other examples of the use of this new het-
erogenization approach include Nafion@Ag used to catalyze
Herein, we report the use of the latter concept in the cata-
lytic epoxidation of alkenes. We recall here the central role of
epoxides as starting materials used for many industrial fine
[7]
[a] Dr. A. Indra, Prof. Dr. M. Driess
chemicals and large-volume processes and that ever better
heterogeneous catalysts for these processes are always in
Department of Chemistry
Technische Universitꢀt Berlin
Strasse des 17. Juni 135, Sekr. C2, 10623 Berlin (Germany)
Fax: (+49)030-314-29732
[8]
need. The two catalysts working in synergism—the first im-
mobilized within the other—are 1) the rhenium complex ReO-
E-mail: matthias.driess@tu-berlin.de
(
DPBS) Cl (ReOD in short; DPBS=3-(diphenylphosphino)ben-
2 3
[
b] Dr. M. Greiner, Dr. A. K. Gericke, Prof. Dr. R. Schlçgl
Fritz Haber Institute of the Max Planck Society
Department of Inorganic Chemistry
zenesulfonic acid sodium salt) and 2) silver metals. Of other
catalysts, rhenium complexes catalyze the epoxidation of al-
[9–12]
5+/7+
[7,11]
kenes
with Re
as the catalytic species
and silver
Faradayweg 4-6, 14195 Berlin (Germany)
nanoparticles catalyze the epoxidation of alkenes with organic
[
c] Prof. Dr. D. Avnir
[13]
Institute of Chemistry and the Center for Nanoscience and Nanotechnology
The Hebrew University of Jerusalem
Jerusalem 91904 (Israel)
Fax: + +972-2-6520099
E-mail: david.avnir@mail.huji.ac.il
peroxides. Through the immobilization of ReOD in silver ma-
trices (denoted as ReOD@Ag), a highly efficient epoxidation
catalyst is obtained, which has better catalytic activity than the
individual components. Instead of using the common hydro-
[11]
gen peroxide as a sacrificial oxidant (it is decomposed by
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201402042.
ꢀ
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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