Novel palladium-on-carbon/diphenyl sulfide complex for chemoselective hydrogenation: Preparation, characterization, and application

Article abstract of DOI:10.1002/adsc.200700571

A diphenyl sulfide immobilized on palladium-on-carbon system, Pd/C[Ph ₂S], was developed to achieve the highly chemoselective hydrogenation of alkenes, acetylenes, azides, and nitro groups in the presence of aromatic ketones, halides, benzyl esters, and N-Cbz protective groups. Instrumental analyses of the heterogeneous catalyst demonstrated that diphenylsul fide was embedded on Pd/C via coordination of its sulfur atom to palladium metal or physical interaction with graphite layers of the activated carbon. The catalyst could be recovered and reused at least five times without any significant loss of the reactivity.

Full text of DOI:10.1002/adsc.200700571

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DOI: 10.1002/adsc.200700571
Novel Palladium-on-Carbon/Diphenyl Sulfide Complex for
Chemoselective Hydrogenation: Preparation, Characterization,
and Application
a
a,b
a
a
Akinori Mori, Tomoteru Mizusaki, Masami Kawase, Tomohiro Maegawa,
a
b
b
a,
Yasunari Monguchi, Shinobu Takao, Yukio Takagi, and Hironao Sajiki *
Laboratory of MedicinalChemistry, Gifu PharmaceuticalUniversity, 5-6-1 Mitahora-higashi, Gifu 502-8585, Japan
a
Fax : (+81)-58-237-5979; e-mail: sajiki@gifu-pu.ac.jp
N. E. Chemcat Corporation, 678 Ipponmatsu, Numazu, Shizuoka 410-0314, Japan
b
Received: December 7, 2007; Revised: December 28, 2007; Published online: February 5, 2008
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
[
6]
[7]
Abstract: A diphenyl sulfide immobilized on palla-
dium-on-carbon system, Pd/C[Ph S], was developed
nadium-promoted Raney nickel, Ir/C-MgO, and
[
7]
A
H
R
U
G
Pt/Al O -P(OPh) were also reported to give aniline
A
H
R
U
G
2
2
3
3
to achieve the highly chemoselective hydrogenation
of alkenes, acetylenes, azides, and nitro groups in
the presence of aromatic ketones, halides, benzyl
esters, and N-Cbz protective groups. Instrumental
analyses of the heterogeneous catalyst demonstrat-
ed that diphenylsu fl ide was embedded on Pd/C via
coordination of its sulfur atom to palladium metal
or physicalinteraction with graphite al yers of the
activated carbon. The catalyst could be recovered
and reused at least five times without any signifi-
cant loss of the reactivity.
derivatives which bear aromatic chlorides and aro-
matic carbonylgroups. Semihydrogenations of acety-
[8]
lenes to olefins was also achieved by use of nickel
[
9]
or gold nanoparticles. However, only a few catalyst
systems such as the Lindler and Rosenmund methods
[
10]
are practically useful.
During the course of our
study on the heterogeneous transition metal-catalyzed
chemoselective hydrogenation during the past decade,
we have established a chemoselective hydrogenation
[11]
method using a nitrogen-containing base and Pd/C,
which hydrogenates olefins, acetylenes, nitro groups
and so on, while leaving benzyl ethers untouched. Re-
cently, we reported that the addition of diphenyl sul-
Keywords: chemoselectivity; diphenyl sulfide; het-
erogeneous catalysis; hydrogenation; palladium
fide (Ph S) to the Pd/C-catalyzed hydrogenation
2
system achieved the chemoselective hydrogenation of
olefin, acetylene and azide functionalities in the pres-
ence of other functionalgroups, such as aromatic car-
bonyls, and halides, benzyl esters, N-Cbz (benzyloxy-
[12]
The development of chemoselective transformations carbonyl) protecting groups and cyano groups.
In
of functionalgroups has been of great importance in
synthetic organic chemistry. Chemoselective hydro- requires the removalof Ph S from the reaction mix-
spite of such unique chemoselectivities, this method
[
1]
2
genation, in particular, contributes to the synthesis of ture using silica gel column chromatography. There-
complicated natural products, pharmaceuticals, and fore, the development of a Pd/C-Ph S complex, Pd/C-
2
[
2]
[13]
functionalmateria sl .
A number of selective hydroge-
A
H
R
U
G
nation methods has been reported that minimize un- heterogeneous and chemoselective hydrogenation cat-
[
3]
desired reductions, e.g., platinum metal sulfides and alyst possessing a chemoselectivity similar to the addi-
[
4]
the ZnX -Pd/C or Pt/C systems have been applied tion of Ph S to the Pd/C-catalyzed hydrogenation
2
2
to the selective hydrogenation of nitro groups in the system was strongly desired.
presence of aromatic halides to obtain haloaniline de- Detailed investigations of Ph S on Pd/C led us to
rivatives. A recent study reported that a polymer-in- establish the preparation method of the Pd/C-Ph2S
carcerated platinum species worked for the selective complex (Pd/C[Ph S]). A suspension of 10% Pd/C
2
AHCTREUNG
2
reduction of olefins, acetylenes, and aromatic nitro and Ph S (2.0 equiv. vs. Pd metalof Pd/C) in metha-
2
groups while leaving benzyl ethers and aromatic hal- nolwas stirred for 5 days at room temperature under
[5]
ides untouched. Other methods for the chemoselec- an argon atmosphere, and then the resulting black
tive hydrogenation of aromatic nitro groups using va- powder was collected by filtration, washed successive-
406
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Adv. Synth. Catal. 2008, 350, 406 – 410

Novel Palladium-on-Carbon/Diphenyl Sulfide Complex
COMMUNICATIONS
Figure 2. EPMA analysis of Pd/C[Ph S].
A
H
R
U
G
2
Figure 1. XRD analysis of Pd/C[Ph S].
A
H
R
U
G
2
ly with methanol and ether, and finally dried under
reduced pressure to give a complex which consists of
Pd/C and Ph S. The elemental analysis of the complex
2
indicated that the ratio of Pd metaland Ph S was
2
1
:1.27. As the result of the XRD (X-ray diffraction)
[14]
analysis, it was observed that the (0,0,2) face of the
activated carbon of this complex was shifted to a
lower angle compared to that of commercial Pd/C
(
Figure 1). This result means that a certain amount of
Ph S penetrates into the graphite layers of the activat-
2
[15]
ed carbon.
micro analyzer ) data (Figure 2) showed that Ph2S
and the Pd metal are not necessarily evenly distribut- Figure 3. XPS analysis of Pd/C
[Ph S].
2
Furthermore, EPMA (electron probe
[16]
A
H
R
U
G
ed on the carbon support.
The XPS (X-ray photoelectron spectroscopy) spec-
trum of Pd 3d of Pd/C
A
H
R
U
G
partialinteraction of Ph S with the Pd metal. One of were selectively hydrogenated without any reduction
2
the binding energy peaks of the Pd metalof Pd/C-
of the aromatic ketones by Pd/C[Ph S] (entries 1, 3–
A
H
R
U
G
2
A
C
H
T
R
E
U
N
G
[Ph S] was observed at 337.7 eV which is obviously 5), although aromatic ketones are very smoothly hy-
2
higher than that of the Pd(0) standard (335.1– drogenolyzed to methylene compounds via the forma-
[
17]
3
35.5 eV) (Figure 3),
should be derived from the Pd–S complex, and a por- mercialPd/C as a cat ay lst (entry 2).
tion of the Pd metalis strong yl bound to Ph 2S. Fur- known that aromatic chlorides are partially hydrogen-
thermore, a comparison of the effective Pd metalsur- ated under the Pd/C-catalyzed hydrogenation condi-
suggesting that the peak tion of the intermediary benzyl alcohols using com-
[13b,h]
It is well
[18]
[2a]
face area, determined by measurement of the CO tions. In contrast, Pd/C
absorbability, between Pd/C and Pd/C[Ph S] indicated hydrogenolysis of aromatic chlorides at all (entry 6),
that 47% of the active sites on the Pd surface of Pd/ and the selective hydrogenation of olefins with reten-
[Ph S] were covered by Ph S. These results indicated tion of the aromatic chlorides was available (en-
A
H
R
U
G
AHCTREUNG
2
C
ACHTREUNG
2
2
that about one-half of the fresh Pd(0) surface (active tries 7–9). Benzylesters and N-Cbz protecting groups
sites) of the originalPd/C st il lr emained intact and
are widely used in organic synthesis as protecting
[19]
the other half had interacted with Ph S by the PdÀS groups,
because of their easy introduction to car-
2
bond based upon the moderately-occluded sulfur lone boxylic acids and amines, respectively, as well as easy
pair. Therefore, Pd/C[Ph S] should possess a very deprotection using the Pd/C-catalyzed hydrogenation,
A
H
R
U
G
2
weak catalyst activity and was expected to produce therefore, it is extremely difficult to keep such groups
chemoselective hydrogenation among some reducible intact during a synthetic process including the hydro-
functionalities.
genation steps. If these protecting groups survive
[Ph S], the under the hydrogenation conditions, Pd/C[Ph S]
To explore the catalyst activity of Pd/C
A
H
R
U
G
ACHTREUNG
2
2
hydrogenation of various substrates was carried out would provide new applications. We then examined
Adv. Synth. Catal. 2008, 350, 406 – 410
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407

Akinori Mori et al.
COMMUNICATIONS
Table 1. Chemoselective hydrogenation of olefin or acetylene in the presence of aromatic
[a]
ketone using Pd/C[Ph S].
A
H
R
U
G
2
[a]
Unless otherwise noted, the reaction was carried out using 500 mmolof the substrate in
MeOH (1.0 mL) with 10% Pd/C[Ph S] (10 wt% of the substrate) with vigorous stirring at
AHCTREUNG
2
room temperature (ca. 208C) under ordinary hydrogen pressure (balloon) for 24 h.
Isolated yield.
The reaction was carried out using 10% Pd/C (10 wt% of the substrate) instead of Pd/C
[
[
[
b]
c]
d]
A
H
R
N
[Ph S].
2
1
The reaction was carried out in CD OD (1.0 mL) and the yield was determined by H NMR
3
because of the low-boiling point property of the product.
the application of Pd/C
A
H
R
U
G
hydrogenation of olefin and acetylene functionalities plete hydrogenation and produced a complex mix-
[
12]
in the presence of benzylester and N-Cbz protecting
groups (entries 10–17). No hydrogenolysis of either lowed by dimerization probably took place.
the benzylester or N-Cbz protecting groups was ob- the other hand, Pd/C[Ph S] was able to be applied to
served during the smooth hydrogenation of olefin or the hydrogenation of the nitro groups without any
ture,
because hydroxylamine-accumulation fol-
[6,7,21]
On
AHCTREUNG
2
[
20]
acetylene moieties.
side reaction. The desired amine was obtained in a
While nitro groups are easily reduced to amines nearly quantitative yield as the sole product (en-
[
2a]
under the Pd/C-catalyzed hydrogenation conditions,
tries 18–21) with the coexisting aromatic carbonyl(en-
408
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Novel Palladium-on-Carbon/Diphenyl Sulfide Complex
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Table 2. Reuse test of Pd/C
A
H
R
U
G
stored in a regular reagent bottle at room temperature with-
out any special handling and alternation of the catalyst ac-
tivity.
2
General Procedure for the Chemoselective
Hydrogenation using Pd/C[Ph S]
A
H
R
U
G
2
A substrate (0.50 mmol), Pd/C[Ph S] (10 wt% of the sub-
A
H
R
U
G
2
strate), and MeOH (1 mL) were added to a test tube con-
taining a stir bar and sealed with a septum. After two
Run Ratio of
:2:3
Yield of
2
Yield of Recovered Pd/C-
[Ph S]
[
a]
1
ACHTREUNG
2
vacuum/H cycles to replace the air inside with hydrogen,
2
the mixture was vigorously stirred at room temperature
under ordinary hydrogen pressure (balloon) for 24 h. The
reaction mixture was filtered using a membrane filter (Milli-
pore, Millex -LH, 0.45 mm) and the filtrate was concentrat-
ed under vacuum to provide the pure product without fur-
ther purification.
1
2
3
4
5
0:100:0
0:100:0
0:100:0
0:100:0
0:100:0
100
92
97
99
99
99
98
97
100
100
ꢂ
[
a]
Isolated yield.
References
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A
H
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A
H
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A
H
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A
H
R
U
G
2
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2
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A
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T
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Adv. Synth. Catal. 2008, 350, 406 – 410
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
409

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A
C
H
T
R
E
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N
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410
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Adv. Synth. Catal. 2008, 350, 406 – 410