Angewandte
Chemie
DOI: 10.1002/anie.201403425
Heterogeneous Catalysis
Hydrogenation of Sulfoxides to Sulfides under Mild Conditions Using
Ruthenium Nanoparticle Catalysts**
Takato Mitsudome, Yusuke Takahashi, Tomoo Mizugaki, Koichiro Jitsukawa, and
Kiyotomi Kaneda*
Abstract: The first demonstration of the hydrogenation of
sulfoxides under atmospheric H2 pressure is reported. The
highly efficient reaction is facilitated by a heterogeneous Ru
nanoparticle catalyst. The mild reaction conditions enable the
selective hydrogenation of a wide range of functionalized
sulfoxides to the corresponding sulfides. The high redox ability
of RuOx nanoparticles plays a key role in the hydrogenation.
The deoxygenation of sulfoxides to sulfides using molec-
ular hydrogen (H2) is a promising method which offers high
atom-efficiency since water is the sole by-product. However,
in early research on the hydrogenation of sulfoxides, the use
of RhCl3 for the hydrogenation of dimethyl sulfoxide
(DMSO) resulted in low yields of dimethyl sulfide in the
order of 0.4% together with low catalytic activity (turnover
numbers of 2) and an evidently limited range of applicable
[15]
T
he deoxygenation of sulfoxides to sulfides represents
substrates.[14] Pd/C[4] and MoO2Cl2
exhibited moderate
a fundamental and significant process within organic syn-
thesis[1] and biochemistry.[2] For example, during the asym-
metric synthesis of carbinols, chiral sulfoxides are introduced
to carbonyl compounds as a chiral auxiliary. Subsequent to
the asymmetric transformation of the carbonyl group to the
carbinol, the sulfoxide moiety is removed from the parent
molecule through deoxygenation followed by desulfidation.[3]
Deoxygenation is also useful in the one-carbon homologation
reaction of carbonyl compounds using active a-methylene
sulfoxides as carbon sources.[4] The stoichiometric deoxyge-
nation of sulfoxides has typically been carried out with excess
amounts of sacrificial agents such as metal hydrides,[5] gaseous
halogens,[6] hydrogen halides,[7] thiols,[8] and phosphines.[9]
These reaction systems, however, have significant drawbacks,
including the use of highly toxic reagents, the production of
large quantities of waste and low yields of sulfides.[3] To date,
many different catalytic sulfoxide deoxygenation reactions
have been reported, in which low-valent metals are combined
with reducing reagents such as PPh3,[10] silanes,[11] BH3,[12]
organosulfur compounds,[8c] and alcohols.[13] Although these
newer systems represent improvements, fundamental prob-
lems in terms of low atom-efficiency and difficulties in
separating catalysts from the reaction mixtures remain
challenges that have not yet been addressed.
catalytic activities for several sulfoxides but required harsh
reaction conditions including high H2 pressure (> 50 atm).
These severe conditions also preclude the use of these
catalysts for the selective hydrogenation of functionalized
sulfoxides containing other reducible or thermally labile
functional groups. As a result, the applicability of these
processes to different kinds of sulfoxide substrates is greatly
restricted. Therefore, the development of an efficient cata-
lytic system for the hydrogenation of diverse sulfoxides to
sulfides under mild conditions would represent a significant
advance.
Herein we report the first demonstration of the efficient
catalytic hydrogenation of sulfoxides under atmospheric H2
pressure, facilitated by a Ru nanoparticle catalyst. Even under
mild conditions, the catalytic activity of the Ru nanoparticle
catalyst is much greater than those of previously reported
catalyst systems requiring high H2 pressures. In addition, this
new process works under mild conditions and enables the
selective hydrogenation of a wide range of functionalized
sulfoxides while leaving other reducible or thermally labile
functional groups intact.
We initially screened various metal nanoparticle catalysts
supported on TiO2 (anatase) by evaluating the hydrogenation
of diphenyl sulfoxide (1) as a model substrate at 1008C under
an atmospheric H2 pressure (Table 1). Among the examined
TiO2-supported metal nanoparticles, Ru nanoparticles with
a mean diameter of 1.6 nm exhibited the highest catalytic
activity, affording diphenyl sulfide (2) in > 99% yield
(entry 1). The activity of Ru nanoparticles was significantly
higher than that of other metal nanoparticles; Rh, Pt, and Pd
nanoparticles showed very low activities (entries 2–4) while
Ni, Cu, Ag, and Au nanoparticles did not show any catalytic
activity at all (entries 5–8). The catalytic activity of Ru
nanoparticles was affected by the support material: TiO2 gave
the highest activity and SiO2 was also effective but inferior to
TiO2 (entry 1 versus 9), whereas the use of hydroxyapatite
(HAP) and Al2O3 supports resulted in moderate to low yields
of 2 (entries 10 and 11). The order of efficiency of the
supports was consistent with the size of the Ru nanoparticles
formed thereon (entries 1 and 9–11). The effect of the size of
[*] Dr. T. Mitsudome, Y. Takahashi, Dr. T. Mizugaki,
Prof. Dr. K. Jitsukawa, Prof. Dr. K. Kaneda
Department of Materials Engineering Science
Graduate School of Engineering Science, Osaka University
1-3 Machikaneyama, Toyonaka, Osaka 560-8531 (Japan)
E-mail: kaneda@cheng.es.osaka-u.ac.jp
Prof. Dr. K. Kaneda
Research Center for Solar Energy Chemistry, Osaka University
1-3, Machikaneyama, Toyonaka, Osaka 560-8531 (Japan)
[**] This work was supported by JSPS KAKENHI Grant Numbers
23686116, 23360357, 24246129, and 22360339. We thank Dr. Uruga,
Dr. Honma, Dr. Nitta, and Dr. Ina (SPring-8) for XAFS measure-
ments. TEM was performed at a facility of the Research Center for
Ultrahigh Voltage Electron Microscopy, Osaka University.
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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