Chemoselective hydrogenation catalyzed by Pd on spherical carbon

Article abstract of DOI:10.1002/cctc.201300639

We have developed a highly chemoselective hydrogenation method using a novel palladium catalyst supported on spherical carbon (0.5 % Pd/SC). The 0.5 % Pd/SC exhibited a novel catalytic activity and could achieve the chemoselective hydrogenation of alkynes, alkenes, azides, nitro groups, and aliphatic O-tert-butyldimethylsilyl (TBS) ethers without hydrogenolysis of benzyl esters, benzyl ethers, nitriles, aromatic ketones, N-carbobenzyloxy (N-Cbz) protective groups, and aromatic O-TBS ethers. Highly selective spheres: The chemoselective hydrogenation of C-C multiple bonds, azides, nitro groups, and aliphatic O-tert-butyldimethylsilyl (TBS) ethers is achieved in the presence of benzyl esters, benzyl ethers, nitriles, aromatic ketones, N-carbobenzyloxy (Cbz) protective groups, and aromatic O-TBS ethers by a novel heterogeneous palladium catalyst supported on spherical carbon (0.5 % Pd/SC). Copyright

Full text of DOI:10.1002/cctc.201300639

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DOI: 10.1002/cctc.201300639
Chemoselective Hydrogenation Catalyzed by Pd on
Spherical Carbon
[a]
[b]
[b]
[a]
[c]
Hiroyoshi Esaki,* Tomohiro Hattori, Aya Tsubone, Satoko Mibayashi, Takao Sakata,
[b]
[b]
[c]
[a]
Yoshinari Sawama, Yasunari Monguchi, Hidehiro Yasuda, Kazuto Nosaka, and
Hironao Sajiki*
[b]
We have developed a highly chemoselective hydrogenation
method using a novel palladium catalyst supported on spheri-
cal carbon (0.5% Pd/SC). The 0.5% Pd/SC exhibited a novel
catalytic activity and could achieve the chemoselective hydro-
genation of alkynes, alkenes, azides, nitro groups, and aliphatic
O-tert-butyldimethylsilyl (TBS) ethers without hydrogenolysis of
benzyl esters, benzyl ethers, nitriles, aromatic ketones, N-carbo-
benzyloxy (N-Cbz) protective groups, and aromatic O-TBS
ethers.
Introduction
The transition-metal-catalyzed hydrogenation method in the
presence of hydrogen gas or a hydrogen transfer agent is
a powerful tool for functional group transformations in both
the laboratory and industrial syntheses. Palladium on activated
carbon (Pd/C) is one of the most widely used catalysts for hy-
drogenations owing to its stability, ease of the separation from
the reaction mixture, possible recyclability, and high catalyst
activity. Although the high catalyst activity of Pd/C leads to the
substrate’s versatility, it is incompatible with chemoselectivity
in the hydrogenation of specific functional groups among
other functionalities within the molecules. It is known that cat-
alytic hydrogenations are usually suppressed by so-called cata-
lyst poisons, such as sulfur- or nitrogen-containing materials,
based on covering the catalyst’s active sites by the strong co-
ordination of sulfur and nitrogen atoms to the catalyst
During the course of our studies involving the heterogene-
ous transition metal-catalyzed hydrogenation, we revealed that
the addition of an appropriate kind and quantity of the nitro-
gen- or sulfur-containing molecules as catalyst poisons to the
Pd/C-catalyzed hydrogenation system selectively suppressed
the catalyst activity toward the hydrogenation of the specific
[5]
functionalities. These findings led to the development of
novel catalysts, which contain a nitrogen or sulfur component,
for the chemoselective hydrogenations without any addition
of catalyst poisons; for example, the Pd/C–ethylenediamine
[6]
complex [Pd/C(en) (Wako: 169-21443)], fibroin (a protein pro-
duced by silkworms)-supported Pd catalyst [Pd/Fib (Wako:
[7]
163-22183)], Pd–polyethyleneimine complex [Pd/PEI (Wako:
[
8]
167-22223)], and Pd/C–diphenylsulfide complex [Pd/C(Ph S)
2
[9]
(N.E. Chemcat: SGS-10DR)]. Furthermore, palladium catalysts
[
1,2]
[10]
metal.
Although chemoselective hydrogenations among
supported on molecular sieves (Pd/MS) and boron nitride
[11]
some reducible functionalities have been successfully achieved
by the addition of several catalyst poisons, these methods are
difficult to control and usually poorly reproducible except for
(Pd/BN) were developed for the chemoselective hydrogena-
tion of alkynes, alkenes, and azides leaving the coexisting
benzyl ester, aromatic carbonyl, N-carbobenzyloxy (N-Cbz), and
nitro functionalities intact, based on the characteristics of the
supports. The Pd/BN could also be used for the efficient semi-
hydrogenation of alkynes to the corresponding alkenes in the
[
3]
a few examples, such as the Lindlar catalyst and Rosenmund
[
4]
reaction.
[11]
presence of diethylenetriamine. Although the chemoselec-
tive hydrogenation of specific reducible functionalities has
been catalyst-dependently achieved, the further development
of new catalysts exhibiting different chemoselectivities will re-
inforce the versatility of the synthetic processes.
[
a] Dr. H. Esaki, S. Mibayashi, Prof. Dr. K. Nosaka
Department of Chemistry, Hyogo College of Medicine
1
-1 Mukogawa-cho, Nishinomiya, Hyogo 663-8501 (Japan)
Fax: (+81)798-45-6435
E-mail: esaki@hyo-med.ac.jp
[b] T. Hattori, A. Tsubone, Dr. Y. Sawama, Dr. Y. Monguchi, Prof. Dr. H. Sajiki
In the context of our ongoing study on the development of
new heterogeneous catalysts for hydrogenation reactions, we
found that a zero-valent palladium catalyst supported on
spherical carbon (Pd/SC from YMC Co., Ltd.), which was devel-
oped for a pre-packed catalyst cartridge for a continuous-flow
hydrogenation device, is useful for the chemoselective hydro-
genation using the batch reaction system without the addition
of catalyst poisons. We herein discuss the utility of the Pd/SC
Laboratory of Organic Chemistry, Gifu Pharmaceutical University
2
1-25-4 Daigaku-nishi, Gifu 501-1196 (Japan)
Fax: (+81)58-230-8109
E-mail: sajiki@gifu-pu.ac.jp
[
c] Dr. T. Sakata, Prof. Dr. H. Yasuda
Research Centre for Ultra-High Voltage Electron Microscopy
Osaka University
7
-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201300639.
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for the chemoselective hydrogenation, including detailed
scope and limitations among the reducible functionalities.
Results and Discussion
Characterization of Pd/SC
The SEM images of the spherical carbon (SC) and 0.5% Pd/SC
are shown in Figure 1 and Figure 2, respectively. Figure 1 re-
veals that the activated carbon is nearly spherical in shape and
Figure 3. a) Bright-field image of 0.5% Pd/SC at 60000ꢁ magnification.
b) The corresponding selected-area electron-diffraction pattern.
ters is 5.6 nm in diameter. The Pd metal surface area of 0.5%
2
À1
Pd/SC was found to be 152 m g -Pd by a surface area analysis
using the CO adsorption method.
Electron probe microanalysis (EPMA) of 0.5% Pd/SC clarified
that the Pd particles are exclusively located on the surface of
the SC (Figure 4).
Figure 1. a) SEM image of spherical carbon at 200ꢁ magnification. b) SEM
image of spherical carbon at 8500ꢁ magnification.
Figure 2. a) SEM image of 0.5% Pd/SC at 32ꢁ magnification. b) SEM image
of 0.5% Pd/SC at 500ꢁ magnification. c) SEM image of 0.5% Pd/SC at 8500ꢁ
magnification.
Figure 4. EPMA of 0.5% Pd/SC.
has dents in places on the surface (Figure 1a and b, respective-
ly). The average diameter of SCs is 0.36 mm, and the average
pore size is 1.7 nm. The BET specific surface area of the activat-
2
À1
ed carbon was determined to be 1371 m g . It is shown in
Figure 2 that small white Pd metal particles of 0.5% Pd/SC are
preferentially located in the pores of the spherical carbon.
The palladium metal supported on SC was also observed by
TEM measurements (Figure 3). In Figure 3a and b, a bright-
field image of Pd particles formed on an SC and the corre-
sponding selected-area electron diffraction pattern are shown,
respectively. The Debye–Scherrer rings in the selected-area
electron diffraction pattern are consistently indexed as those
of face-centered cubic Pd. The mean size of the palladium clus-
The X-ray photoelectron spectra and XRD pattern of 0.5%
and 5% Pd/SCs are shown in Figure 5 and Figure 6, respective-
ly. Figure 5 reveals large Pd3d3/2 and Pd3d5/2 peaks at approxi-
mately 340 eV and 335 eV, respectively, both of which are de-
0
rived from the Pd . Although a clear XRD spectrum of 0.5%
Pd/SC could not be obtained with 0.5% Pd/SC, owing to the
low palladium concentration, the peaks of 5% Pd/SC were
found to be identical to the reported Pd peaks of Pd/C
[12]
(Figure 6). The peaks at 2q=40.18, 46.78, 68.38, and 82.38 in
Figure 6 correspond to the Pd planes (111), (200), (220), and
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as an over-hydrogenation product together with a 92% recov-
1
ery of the substrate 1 ( H NMR data, Table 2, entry 1), whereas
EtOAc, THF, and acetonitrile indicated comparatively suppres-
sive effects (Table 2, entries 2–4), and the benzyl ether com-
pletely survived in 1,4-dioxane (Table 2, entry 5). Equally good
results have been achieved for the hydrogenation of a variety
of benzyl ethers by using 1,4-dioxane instead of methanol
(
Table 1, entries 7–9). No hydrogenolysis of the benzyl ester
could be accomplished in 1,4-dioxane or acetonitrile as the sol-
vent (Table 1, entries 9–11 and 28). Unexpectedly, the nitro and
benzyl ester functionalities were completely tolerated even in
methanol in the presence of an azido functionality within the
molecule (Table 1, entries 2–4). This is probably owing to the
catalyst’s poisonous effect of the liberated amine moiety pro-
duced by the reduction of the coexisting azide group.
Figure 5. X-ray photoelectron spectra of Pd/SCs. 0.5% Pd/SC (–), 5% Pd/SC
(
–).
Although it is well-known that aromatic carbonyls are easily
reduced to the corresponding methylene compounds through
the formation of intermediary benzyl alcohols under Pd/C-cata-
lyzed hydrogenation conditions, the carbonyl groups of the
benzophenone derivatives were untouched under the present
conditions (entries 15 and 16). On the other hand, reduction of
the aromatic carbonyls of acetophenone or acetonaphthone
derivatives proceeded in part, but the use of 1,4-dioxane as
a solvent resulted in the complete suppression (entries 12 and
13). In the case of 4-acetylbenzonitrile, no hydrogenation of
the carbonyl group took place even in methanol as the sol-
vent, probably because the catalytic poisonous effect of the ni-
trile group within a molecule is similar to the above-mentioned
solvent effect of acetonitrile (entry 14).
Figure 6. XRD patterns of Pd/SCs. 0.5% Pd/SC (–), 5% Pd/SC (–).
tert-Butyldimethylsilyl (TBS) ether, which is one of the widely
used protecting groups of hydroxyl groups, is generally re-
moved by an acid treatment. We previously demonstrated that
Pd/C smoothly catalyzed the hydrogenolysis of O-TBS ethers
[
13]
(311), respectively.
The peaks derived from other metals
[6g,14]
were not detected in the XRD spectra.
under neutral conditions.
When 0.5% Pd/SC was used for
the hydrogenolysis of 1-tert-butyldimethylsilyloxy-3-phenylpro-
pane, the hydrogenolysis of the O-TBS group readily proceed-
ed and the corresponding 3-phenylpropane was obtained in
91% isolated yield (entry 17). Other alkyl TBS ethers also un-
derwent a similar smooth hydrogenolysis, together with the
hydrogenation of the alkene moieties (entries 18 and 20),
while the aryl TBS ethers were tolerant to their cleavage, lead-
ing to the chemoselective reduction of alkenes and nitro
groups to the corresponding alkanes and amines, respectively
(entries 21 and 22). The pH value of the filtrate after stirring of
the aqueous suspension of 0.5% Pd/SC (500 mg in 5.0 mL of
0
.5% Pd/SC as a hydrogenation catalyst
0.5% Pd/SC was used as a catalyst for the hydrogenation of
a variety of reducible functionalities (Table 1) and indicated an
excellent catalyst activity for the hydrogenation of azide (en-
tries 1–4 and 16), nitro (entries 5, 6, and 22), olefin (entries 7,
10, 11, 13, 18, 20, 21, and 24–26), and acetylene (entry 23)
functionalities. On the other hand, benzyl ethers and benzyl
esters were found to partially undergo the hydrogenolysis in
methanol. We have reported that the choice of solvent was an
important factor to control the selective suppression under the
H O) under a hydrogen atmosphere at room temperature for
2
[
5e–g,6a,d,f,h,i,7,8,14a]
hydrogenation conditions.
Thus, several solvents
24 h was measured to be 5.96, which is roughly equal to the
[15]
possessing a weak coordinative ability as a bulk configuration,
such as EtOAc, THF, acetonitrile, and 1,4-dioxane, could mildly
and appropriately decrease the catalyst activity, and the che-
moselective hydrogenations would be achieved if using such
solvents. With the expectation of the complete suppression of
the hydrogenolysis of benzyl ether, the hydrogenation reaction
in a wide variety of solvents was investigated (Table 2). The re-
action of 4-benzyloxyphenylacetic acid 1 in methanol by using
the general procedure for the chemoselective hydrogenation
resulted in the formation of 8% 4-hydroxyphenylacetic acid 2
pH value of ordinary purified water and would not be acidic
[14b,c]
enough to cleave the O-TBS groups.
Furthermore, the silyl
group of the aliphatic O-TBS ether, 1-tert-butyldimethylsilyloxy-
3-phenyl-2-propene, was found to be never cleaved in metha-
nol at room temperature under an argon atmosphere even
after 48 h (entry 19). These results indicated that 0.5% Pd/SC
possesses a catalyst activity toward the hydrogenolysis of the
alkyl O-TBS ethers.
The N-Cbz protecting group is widely used for the protec-
tion of amino groups in organic synthesis because of their
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[
a]
Table 1. Chemoselective hydrogenation.
[
b]
[b]
Entry
Substrate
Product
Yield [%]
100
Entry
15
Substrate
Product
recovery
Yield [%]
[
g]
96
[c]
1
[d,j]
[
96]
99
91
2
96
16
9
98]
5
[
[
k]
l]
3
4
17
18
[
d,e]
[
8
[
7
–]
96
[
m]
[
[
l,n]
k]
[g]
[o]
5
6
95
19
20
recovery
98
82
100
98
[
f]
[l]
[l]
7
21
94
[
f]
f]
[g]
[g]
8
9
1
recovery
recovery
100
93
22
23
24
25
100
1
[
00
[
[
d,p]
22]
[
h]
[q]
[q]
[r]
0
99
97
93
[
h]
11
86
[
f]
[g]
[s]
1
2
recovery
recovery
97
92
26
–
[f]
[g]
[g]
1
3
27
28
recovery
recovery
95
97
[
g]
9
9
[
h]
1
4
[
d,i]
[
92]
[a] Unless otherwise noted, the reactions were performed by using substrate (1.0 mmol) in methanol (1.0 mL) with 0.5% Pd/SC (0.05 mol% of the sub-
strate) with stirring under ordinary hydrogen pressure and at room temperature for 24 h. [b] Isolated yield. [c] Methanol (3 mL) of was used. [d] 0.5% Pd/C
was used instead of 0.5% Pd/SC. The yield of the desired product [or recovered starting material (entries 14 and 15)] in the mixture was determined by
1
the calculation based on the H NMR ratio, total weight of the mixture, and molecular weight of each material. [e] A 98:2 mixture of 4-nitroaniline and
p-phenylenediamine was obtained. [f] 1,4-Dioxane was used as the solvent. [g] Yield of recovered starting material. [h] Acetonitrile was used as the solvent.
[i] A 94:3:3 mixture of 4’-cyanoacetophenone, 4-(1-hydroxyethyl)benzonitrile, and 1-[4-(aminomethyl)phenyl]ethanone was obtained. [j] A 98:2 mixture of
benzophenone and benzhydrol was obtained. [k] The reaction time for was 72 h. [l] The reaction time was 48 h. [m] 0.5% Pd/C was used instead of 0.5%
Pd/SC. A complex mixture including the substrate and 3-phenyl-1-propanol was obtained. [n] The reaction was performed under an argon atmosphere.
[o] 9% of 4-(tert-butyldimetylsilyloxy)butyl propionate was obtained. [p] A 40:60 mixture of N-(benzyloxycarbonyl)-4-ethylaniline and 4-ethylaniline was ob-
tained. [q] The reaction time was 3 h. [r] A 98:2 mixture of N-benzyloxycarbonyl-N-propylaniline and N-propylaniline was obtained. The yield of the desired
1
product in the mixture was determined by the calculation based on the H NMR ratio, total weight of the mixture, and molecular weight of each material.
3
[s] CD OD was used as the solvent, owing to the low boiling point of the products.
easy introduction as well as easy removal under the Pd/C-cata-
lyzed mild hydrogenolysis conditions. Therefore, the develop-
ment of the hydrogenation method of alkynes and alkenes
without the hydrogenolysis of the N-Cbz groups would in-
crease the utility of the N-Cbz protective group and offer new
possible synthetic routes. The results in entries 23–25 demon-
strate that the selective hydrogenation of olefins and acetylene
can be achieved by using 0.5% Pd/SC under ordinary hydro-
gen pressures and temperatures in the presence of the N-Cbz
group within the molecules.
We next investigated the hydrogenation of aromatic chlor-
ides. Aromatic chlorides are partially hydrodehalogenated
[16]
under the Pd/C-catalyzed conditions, whereas 0.5% Pd/SC
has no catalytic activity toward the hydrodechlorination
(entries 26–28).
The 0.5 wt% palladium catalyst supported on activated
carbon powder (0.5% Pd/C) was also used for the hydrogena-
tion for comparison with 0.5% Pd/SC. Although 0.5% Pd/C in
general exhibited weak catalyst activity compared with more
highly Pd-loaded 5% or 10% Pd/C, the complete chemoselec-
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The reuse of the heterogeneous catalysts is one of the most
important properties owing to cost-performance and environ-
mental considerations. We then investigated the reuse test of
Table 2. The effect of solvent on the hydrogenolysis.
0.5% Pd/SC for the hydrogenation of cinnamyl alcohol
(
Table 3). The 0.5% Pd/SC could be reused at least until the
[
a]
Entry
Solvent
1:2
second run without any loss of catalyst activity, although it sig-
1
2
3
4
5
MeOH
EtOAc
THF
MeCN
1,4-dioxane
92:8
95:5
97:3
97:3
100:0
[17]
nificantly decreased after the third run.
Table 3. Reuse of Pd/SC.
1
[
a] Determined by using H NMR spectroscopy.
[
a]
tivity was not achieved and the over-reduction proceeded (see
the brackets in entries 3, 14, 15, 18, and 23, and footnotes). In
particular, the hydrogenation of N-benzyloxycarbonyl-4-
ethynylaniline afforded a 40:60 mixture of N-(benzyloxycarbon-
yl)-4-ethylaniline and 4-ethylaniline product (brackets in
entry 23). The difference in the catalyst activity between 0.5%
Pd/SC and 0.5% Pd/C would be presumably arisen from that
of their structural characteristics, such as the Pd distribution on
the support and morphology.
Run
Recovered Pd/SC [%]
1:2
1st
2nd
100
91
99
0:100 [92]
0:100 [98]
79:21
3
4
rd
th
95
99:1
1
[
a] The ratio was determined by H NMR spectroscopy. Isolated yield is
indicated in parentheses.
A summary table comparing the activity of Pd/SC and other
chemoselective hydrogenation catalysts developed by us is
shown in Figure 7. The 0.5% Pd/SC can catalyze the hydroge-
nation of unsaturated CÀC multiple bonds, azido groups, and
The leaching of Pd metal from 0.5% Pd/SC was next investi-
gated. After completion of the 0.5% Pd/SC-catalyzed hydroge-
nation of cinnamyl alcohol in methanol (12 h), the catalyst was
removed by filtration by using a membrane filter (Millipore;
Millex-LG, 0.20 mm) and the Pd concentration in the filtrate was
measured by inductively coupled plasma atomic emission
spectrometry (ICP–AES). As no leached Pd was detected within
the limit of detection (<1 ppm), the reduced catalyst activity
of 0.5% Pd/SC during the reuse would be attributed to the
mechanical damage of the catalyst during the vigorous stirring.
The mechanical damage of the catalyst was confirmed by the
observation of many small cracked particles of the catalyst in
the SEM image measured after the 2nd reuse test (Figure 8).
Conclusions
In summary, we have developed a mild and chemoselective
hydrogenation method using commercially available 0.5% Pd/
SC as a catalyst, which is applicable for the reduction of
alkyne, alkene, azido, nitro, and alkyl O-TBS functionalities leav-
Figure 7. Comparison of catalytic activities of various catalysts for the
chemoselective hydrogenation: functional groups of the framework could
be reduced by each captioned catalyst.
nitro groups in the presence of benzyl ethers, benzyl esters, ni-
triles, aromatic ketones, N-Cbz protective, and aromatic chlo-
ride functionalities. The significant future of the 0.5% Pd/SC is
the catalytic ability regarding the hydrogenolysis of alkyl O-TBS
ethers, as shown in Figure 7, for the chemoselective hydroge-
nation. Another characteristic of Pd/SC is the distinction be-
tween the azido and nitro groups within the same molecule. If
azido groups coexist in the nitro compounds, only azides
could be reduced to the corresponding amines derived from
the hydrogenation of azides with the nitro groups intact
caused by the suppressive effect of the amine.
Figure 8. SEM image of 0.5% Pd/SC after 2nd reuse test at 200ꢁ
magnification.
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ing the benzyl ether, benzyl ester, nitrile, aromatic ketones, aro-
matic chlorides, N-Cbz, and aryl O-TBS groups intact. The pres-
ent method could be expected to be of practical use as a gen-
eral chemoselective hydrogenation process in synthetic and
process chemistries.
Reuse test of 0.5% Pd/SC
Five test tubes were prepared. Each test tube was charged with
cinnamyl alcohol (134 mg, 1.00 mmol), 0.5% Pd/SC (16.7 mg,
0
.500 mmol, 0.05 mol%), and methanol (1.00 mL). Each mixture was
stirred at RT under a hydrogen atmosphere for 24 h, then passed
through a filter paper (Kiriyama, No. 5C (1 mm), diameter=8 mm).
The catalyst on the filter paper was washed with methanol (3ꢁ
1
0 mL) and used for the 2nd run (83.4 mg, 100%). The combined
filtrates were concentrated in vacuo to give 3-phenyl-1-propanol
627 mg, 92%) as the single product.
Experimental Section
(
General experimental
Four test tubes were prepared for the 2nd run. Each test tube was
charged with cinnamyl alcohol (134 mg, 1.00 mmol), 0.5% Pd/SC
(16.7 mg, 0.500 mmol, 0.05 mol%), and methanol (1.00 mL). Each
mixture was stirred at RT under a hydrogen atmosphere for 24 h,
then passed through a filter paper (Kiriyama, No. 5C (1 mm), diame-
ter=8 mm). The catalyst on the filter paper was washed with
methanol (3ꢁ10 mL) and used for the 3rd run (60.6 mg, 91%). The
combined filtrates were concentrated in vacuo to give 3-phenyl-1-
propanol (528 mg, 98%) as the single product.
The novel 0.5% Pd/SC catalyst (wet-type, containing 36.3 wt%
H O) is commercially available from YMC Co., Ltd. (Kyoto, Japan).
2
The XRD patterns were recorded by a Rigaku RINT2000 using mon-
ochromatic CuKa radiation at 40 kV and 20 mA. The 2q/q range
from 10 to 1008 was converted at a scan speed of 0.18min . The
À1
XPS spectrum was recorded by a Shimadzu AXIS-165 using a non-
monochromatic AlKa X-ray source (1486.6 eV) and collected in the
binding energy range of 331.89–347.01 eV. The SEM images were
captured by a Hitachi SU1510 microscope operated at 30 kV. The
TEM images were obtained with a Hitachi H-800 microscope oper-
ated at 200 kV. EPMA was performed by using a JEOL JXA-8100.
Three test tubes were prepared for the 3rd run. Each test tube was
charged with cinnamyl alcohol (134 mg, 1.00 mmol), 0.5% Pd/SC
(16.7 mg, 0.500 mmol, 0.05 mol%), and methanol (1.00 mL). Each
mixture was stirred at RT under a hydrogen atmosphere for 24 h,
then passed through a filter paper (Kiriyama, No. 5C (1 mm), diame-
ter=8 mm). The catalyst on the filter paper was washed with
methanol (3ꢁ10 mL) and used for the 4th run (49.4 mg, 99%). The
combined filtrates were concentrated in vacuo to give a 79:21
1
13
The H and C NMR spectra were recorded by a JEOL JNM-ECX
1
4
1
00P or JNM-ECA 400 spectrometer (400 MHz for H NMR and
00 MHz for C NMR).
1
3
ratio mixture of cinnamyl alcohol and 3-phenyl-1-propanol
General procedure for the chemoselective hydrogenation
1
(
H NMR).
After three vacuum/H2 cycles to replace air inside the test tube
with hydrogen, the mixture of the substrate (1.00 mmol) and 0.5%
Pd/SC (16.7 mg, 0.500 mmol, 0.05 mol% of the substrate) in metha-
nol (1.00 mL) was stirred under ordinary hydrogen pressure (bal-
loon) and at RT for 24 h. After dilution with an appropriate solvent,
which can dissolve the product, the reaction mixture was filtered
by using a membrane filter (Millipore Corporation, Billerica, MA,
USA; Milex-LG, 0.20 mm), and then the collected catalyst was
washed with the solvent (3ꢁ10 mL). The combined filtrates were
concentrated under reduced pressure to give the analytically pure
Two test tubes were prepared for the 4th run. Each test tube was
charged with cinnamyl alcohol (134 mg, 1.00 mmol), 0.5% Pd/SC
(16.7 mg, 0.500 mmol, 0.05 mol%), and methanol (1.00 mL). Each
mixture was stirred at RT under a hydrogen atmosphere for 24 h,
then passed through a filter paper (Kiriyama, No. 5C (1 mm), diame-
ter=8 mm). The catalyst on the filter paper was washed with
methanol (3ꢁ10 mL), and 31.6 mg (95%) of the catalyst was recov-
ered. The combined filtrates were concentrated in vacuo to give
a 99:1 ratio mixture of cinnamyl alcohol and 3-phenyl-1-propanol
1
1
( H NMR analysis).
product. The product ratio was determined by H NMR analysis.
1
The H NMR spectra of all products were identical to those in the
literature or commercial sources (see the Supporting Information).
Assay of residual palladium in the reaction mixture
A suspension of cinnamyl alcohol (671 mg, 5 mmol) and 0.5% Pd/
SC (83.5 mg, 2.50 mmol, 0.05 mol%) in methanol (5 mL) was stirred
at RT under a hydrogen (balloon) atmosphere for 12 h, then
passed through a membrane filter (Millipore; Millex-LH, 0.20 mm).
The filtrate was diluted with methanol to 20 mL of total volume
and the residual palladium was assayed using a Shimadzu ICP-
Procedure for the confirmation of the catalytic activity of
0.5% Pd/SC toward the hydrogenolysis of aryl O-TBS ethers
pH measurement of the filtrate obtained from the aqueous sus-
pension of 0.5% Pd/SC: A suspension of 0.5% Pd/SC (500 mg) in
8
001 (Shimadzu, Kyoto, Japan). No palladium species were detect-
H O (5.00 mL) under a hydrogen atmosphere was stirred at RT for
2
ed within the detection limit (<1 ppm).
2
4 h, then the mixture was filtered by using a membrane filter (Mil-
lipore; Milex-LG, 0.20 mm). The pH value of the aqueous filtrate was
measured by using a Horiba pH meter F-21 and found to be 5.96.
Acknowledgements
Treatment
under an argon atmosphere: 1-tert-Butyldimethylsilyloxy-3-phenyl-
-propene (248 mg, 1.00 mmol) was treated with 0.5% Pd/SC
16.7 mg, 0.500 mmol) in a manner similar to that described in the
of
1-tert-butyldimethylsilyloxy-3-phenyl-2-propene
This work was supported by JSPS KAKENHI Grant Number
2
(
24790031 and Grant-in-Aid for Researchers, Hyogo College of
Medicine, 2010. We thank the YMC Co., Ltd., for the kind gift of
the catalysts and their structural analysis. We also sincerely
thank the N.E. Chemcat Corporation for the ICP-AES, EPMA, and
metal surface area measurements and kind gift of 0.5% Pd/C.
general procedure for the chemoselective hydrogenation except
for stirring under an argon atmosphere instead of a hydrogen at-
mosphere. No reaction took place and the unchanged 1-tert-butyl-
dimethylsilyloxy-3-phenyl-2-propene (243 mg, 98%) was recovered.
ꢀ
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 3629 – 3635 3634

CHEMCATCHEM
FULL PAPERS
www.chemcatchem.org
We are grateful to Associate Professor Takuya Maeda (Hyogo Uni-
versity of Health Science) for the SEM analysis, and to Professor
Hideto Miyabe, Assistant Professor Eito Yoshioka, and Assistant
Professor Koji Tsukamoto for their kind help with the NMR ease-
ments at the Hyogo University of Health Science.
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Keywords: chemoselectivity
·
heterogeneous catalysis
·
6
hydrogenation · palladium · solvent effects
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Received: August 1, 2013
Published online on September 25, 2013
ꢀ
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2013, 5, 3629 – 3635 3635