Published on the web March 31, 2011
405
Highly Efficient Pd/SiO2-Dimethyl Sulfoxide Catalyst System
for Selective Semihydrogenation of Alkynes
Yusuke Takahashi,1 Norifumi Hashimoto,1 Takayoshi Hara,2 Shogo Shimazu,2 Takato Mitsudome,1
Tomoo Mizugaki,1 Koichiro Jitsukawa,1 and Kiyotomi Kaneda*1,3
1Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531
2Graduate School of Engineering, Chiba University, 1-33 Yayoi, Inage-ku, Chiba 263-8522
3Research Center for Solar Energy Chemistry, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531
(Received January 27, 2011; CL-110066; E-mail: kaneda@cheng.es.osaka-u.ac.jp)
Table 1. Hydrogenation of 1-phenyl-1-propyne catalyzed by
Pd/SiO2 in the presence of various sulfur compoundsa
Silica-supported Pd nanoparticles (Pd/SiO2) with dimethyl
sulfoxide (DMSO) show excellent catalytic activity and
selectivity for the semihydrogenation of alkynes. Small amounts
of DMSO drastically suppress the overhydrogenation and
isomerization of alkenes. This catalyst system is also applicable
to both internal and terminal alkynes. Furthermore, the Pd/SiO2
catalyst was separable from the reaction mixture after the
hydrogenation and reusable without loss of its high catalytic
activity or selectivity.
Pd/SiO2
+ H2
+
additive
1
2
3
Sel. of 2
/%b
Time
/min
Conv.
/%b
Entry
Additive
Z:E
98:2
98:2
O
1
2
90
90
100
100
98
96
S
O
S
O
S
The selective hydrogenation of alkynes to (Z)-alkenes is of
great importance for the construction of a variety of valuable
compounds such as bioactive molecules, natural products, and
industrial materials.1 Lindlar catalyst has been widely employed
for a long time for this purpose.2 However, Lindlar catalyst must
be pretreated with environmentally harmful Pb compounds
during the preparation of the catalyst and also requires
considerable amounts of quinoline as an additive to achieve
the selective semihydrogenation. Moreover, Lindlar catalyst
suffers from substrate limitations in that only internal alkynes
are selectively hydrogenated into the desired alkenes whereas
terminal alkynes are generally overhydrogenated into alkanes.3
From the perspective of green chemistry and other practical
concerns, the development of more environmentally benign and
efficient catalyst systems for the semihydrogenation of alkynes
is highly desired. There have been some successful catalytic
methods for the semihydrogenation of alkynes using H2.4-9 For
example, Sajiki and co-workers have developed a polyethyl-
eneimine-supported Pd catalyst that promoted highly selective
hydrogenation of a wide range of alkynes to alkenes without
any additives.7 Ohkuma and co-workers also have reported
an efficient catalytic system using colloidal Pd nanoparticle-
tetrabutylammonium borohydride that showed good turnover
frequency (5000 min¹1) under a pressurized atmosphere of H2.8
Herein, we report that silica-supported Pd nanoparticles
(Pd/SiO2) with dimethyl sulfoxide (DMSO) show excellent
catalytic activity and selectivity for the semihydrogenation of
alkynes. Small amounts of DMSO drastically suppress the over-
hydrogenation and isomerization of alkenes.10 This catalyst
system is also applicable to terminal alkynes as well as internal
ones.
3
90
100
95
98:2
S
S
4
5
80
90
100
100
92
95
98:2
98:2
S
6
70
100
95
98:2
O
O
O
O
7c
8c
15
15
100
100
72
75
95:5
93:7
S
S
O
O
9c
15
15
100
100
70
72
96:4
95:5
S
No
10
aReaction conditions: Pd/SiO2 (0.010 g, Pd; 0.46 ¯mol), 1-
phenyl-1-propyne (0.5 mmol), additive (10 ¯mol), n-hexane
(5 mL), 30 °C, H2 (1 atm). bDetermined by GC using an
c
internal standard. In THF.
species as a white powder. Next, the obtained solid was treated
with ethanol at 85 °C for 2 h under an argon atmosphere to give
Pd/SiO2 as a grayish-brown powder. The loading amount of
Pd in Pd/SiO2 was determined by elemental analysis to be
0.046 mmol g¹1. The TEM image of Pd/SiO2 revealed that Pd
nanoparticles were formed on SiO2 whose mean diameter was
estimated as 5.3 nm.11
The hydrogenation of 1-phenyl-1-propyne (1) was carried
out using Pd/SiO2 under 1 atm of H2 at 30 °C in the presence
of various sulfur compounds such as sulfides, sulfoxides, and
sulfones.12 The results are summarized in Table 1. Among the
sulfur compounds tested, sulfoxides and sulfides were found to
be effective additives (Entries 1-6) to afford 1-phenyl-1-propene
(2) in >92% yields. DMSO provided the best efficiency in the
semihydrogenation of 1, giving 2 in 98% yield with 98% (Z)-
selectivity. In contrast, the addition of sulfones improved neither
the yield nor the selectivity of 2 (Entries 7-9 vs. 10).
The SiO2-supported Pd catalyst was synthesized as follows.
Silica (CARiACT Q-30:FUJI Silysia Chemical, Ltd.) was added
to an aqueous solution of [Pd(NH3)4Cl2]¢H2O (1.0 mM), and
then the mixture was stirred for 12 h in air at 30 °C. The resulting
slurry was filtered, washed with deionized water, and dried in
vacuo at room temperature to yield a silica-supported PdII
Chem. Lett. 2011, 40, 405-407
© 2011 The Chemical Society of Japan
Takahashi, Yusuke
