Preparation of microporous polymer-encapsulated Pd nanoparticles and their catalytic performance for hydrogenation and oxidation

Article abstract of DOI:10.1016/j.tet.2014.04.049

Palladium nanoparticles (Pd NPs) encapsulated by conjugated microporous polymers (CMPs) were prepared by the Pd-catalyzed polymerization followed by a thermal treatment with N₂or H₂. The Pd catalysts were embedded in the porous network during polymerization and used as a precursor for the generation of Pd NPs in CMP. Although no Pd NPs were formed in the as-synthesized Pd/CMPs, Pd NPs with 1.6-3.5 nm size were formed after the thermal treatment. The obtained Pd/CMP-N₂and -H₂catalysts were highly selective in the hydrogenation of 4-nitrostyrene to 4-ethylnitrobenzene, whereas Pd NPs supported on carbon (Ketjen black) gave a fully reduced product, 4-ethylaniline. Substituents in CMP framework could change the catalytic activity of Pd NPs; hydroxy-substituted CMP encapsulated Pd NPs showed higher catalytic activity than Pd/CMP-H₂for benzyl alcohol oxidation.

Full text of DOI:10.1016/j.tet.2014.04.049

Tetrahedron xxx (2014) 1e6
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Preparation of microporous polymer-encapsulated Pd nanoparticles
and their catalytic performance for hydrogenation and oxidation
Tamao Ishida a , Yuta Onuma , Kota Kinjo , Akiyuki Hamasaki , Hironori Ohashi ,
,
b
a
a
c
*
e
d
a
a
Tetsuo Honma , Tomoki Akita , Takushi Yokoyama , Makoto Tokunaga ,
Masatake Haruta
Department of Chemistry, Graduate School of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
Department of Applied Chemistry, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji,
b
a
b
Tokyo 192-0397, Japan
c
Faculty of Arts and Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
Research Institute for Ubiquitous Energy Devices, National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorigaoka, Ikeda, Osaka
d
5
63-8577, Japan
e
Japan Synchrotron Radiation Research Institute (JASRI)/SPring-8, 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Palladium nanoparticles (Pd NPs) encapsulated by conjugated microporous polymers (CMPs) were
Received 3 February 2014
Received in revised form 11 April 2014
Accepted 15 April 2014
Available online xxx
2 2
prepared by the Pd-catalyzed polymerization followed by a thermal treatment with N or H . The Pd
catalysts were embedded in the porous network during polymerization and used as a precursor for the
generation of Pd NPs in CMP. Although no Pd NPs were formed in the as-synthesized Pd/CMPs, Pd NPs
2 2
with 1.6e3.5 nm size were formed after the thermal treatment. The obtained Pd/CMP-N and -H cat-
alysts were highly selective in the hydrogenation of 4-nitrostyrene to 4-ethylnitrobenzene, whereas Pd
NPs supported on carbon (Ketjen black) gave a fully reduced product, 4-ethylaniline. Substituents in CMP
framework could change the catalytic activity of Pd NPs; hydroxy-substituted CMP encapsulated Pd NPs
Keywords:
Palladium nanoparticles
Microporous conjugated polymer
Heterogeneous catalyst
Selective hydrogenation
showed higher catalytic activity than Pd/CMP-H
2
for benzyl alcohol oxidation.
Ó 2014 Elsevier Ltd. All rights reserved.
4
1. Introduction
immobilization. Cooper et al. have reported the synthesis of CMP
by Pd-catalyzed SonogashiraeHagihara coupling reaction of 1,4-
5
,8
Nanoporous materials such as metal-organic frameworks
MOFs) are currently of great interest owing to their potential ap-
dihalobenzenes with 1,3,5-triethynylbenzene.
deposited Pd NPs in CMP by impregnation using Pd(acac)
a precursor in supercritical CO as a solvent, followed by thermal
They have also
(
2
as
plications to gas sorption, separation, and heterogeneous catalysis.
They are also expected to be efficient supports for the confinement
of metal nanoparticles (NPs) with controlled size in their porous
structures.1 Recently, well-defined nanoporous organic polymers
constructed by only covalent bonds have also attracted growing
interest because of tunable building units and high thermal and
2
5
decomposition of Pd complex to form Pd NPs. However, relatively
large (5e10 nm) Pd NPs were also formed.
To stabilize metal NPs, the introduction of functional groups
containing heteroatoms into their porous frameworks has often
been exploited. Prati et al. demonstrated that Pd/CTF showed
2
4
chemical stability. Several kinds of nanoporous organic polymers,
higher catalytic performance than Pd/C did. They concluded that
3
such as covalent-organic frameworks (COFs), covalent triazine
the incorporation of N atoms in the framework enhanced the in-
teractions between Pd and supports, preventing the aggregation of
Pd NPs during immobilization and improving catalyst durability.
However, aggregation of Pd NPs on the CTF surface was observed
after catalytic reactions. Thus, post-loading method cannot com-
pletely prevent the aggregation of metal NPs on the outer support
surface, in particular for organic polymers without coordination
sites to metal precursors.
frameworks (CTFs),4 and conjugated microporous polymers
5
(
CMPs), have been reported to be useful as metal NPs supports.
To deposit metal NPs into the porous structures, post-loading
methods, in which metal precursors or metal NPs are loaded into
the porous materials, are commonly used, e.g., chemical
vapor deposition,3
c,6
solid grinding, impregnation, and sol
7
5
On the other hand, Ogasawara and Kato have reported the one-
pot entrapping of Pd NPs in polymer matrices by the
polymerization-induced phase separation technique, in which Pd
*
Corresponding author. Tel./fax: þ81 92 642 7528; e-mail address: tishida@
chem.kyushu-univ.jp (T. Ishida).
0
040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.04.049
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T. Ishida et al. / Tetrahedron xxx (2014) 1e6
ꢁ1
NPs formation concurrently occurs with the synthesis of polymer
matrices. However, Pd precursors have to be stabilized by amide-
backbone. For Pd/CMP-1-N
internal alkynes remained.
2 2
and -H , the peaks at 2195 cm of
9
containing dendritic monomer units before the polymerization
reactions. Thus, in situ loading of metal source during polymeri-
zation of monomers without coordinating groups to metal ions and
size control of metal NPs confined in nanoporous polymers without
coordination sites are still challenging research targets.
As mentioned above, Cooper’s CMPs are prepared by Pd-
catalyzed cross-coupling reaction. Their polymers inspired us to at-
tempt that Pd catalysts, which were used for the polymerization,
were exploited as the precursors for the generation of Pd NPs. In this
work, we synthesized CMP-1 in the presence of Pd catalysts without
The construction of aryleneeethynylene structure was also
13
confirmed by C CP-MAS NMR, based on the peak at 90.6 ppm,
which corresponded to the internal alkyne carbons (Fig. S2). Small
peaks at 78 and 82 ppm indicated the presence of terminal alkyne
in the polymer backbone. The peaks at 123.9 and 131.8 ppm were
ascribed to the aromatic carbons. After thermal treatment,
a shoulder peak at around 137 ppm was observed, and the peak of
Pd/CMP-1-H
partial decomposition of the polymer network or the reduction of
the internal alkyne by H . Taking into account the absence of alkane
2
was more obvious. This was probably due to the
2
Cu co-catalysts and treated in N
formed and highly dispersed in CMP framework even heteroatoms
were not contained in the porous framework. We examined the
2
or H
2
. As a result, Pd NPs were
peaks at around 30 ppm, it could be suggested that some part of
alkyne groups was not fully reduced to alkyl chains.
2 2
The N adsorption isotherms of Pd/CMP-1, Pd/CMP-1-N , and
catalytic performance of the obtained Pd/CMP-1-N
2
and -H
2
and
2
-H showed the type I isotherms by IUPAC classifications, sug-
found that they were active for selective hydrogenation of 4-
nitrostyrene to 4-ethylnitrobenzene. We also studied the effect on
the functional groups of CMP backbone to a Pd NPs-catalyzed
reaction.
gesting that all the three had microporous structures (Fig. S3). The
BrunauereEmmetteTeller (BET) surface area of Pd/CMP-1 was
2
calculated to be 744 m /g, which was almost consistent with the
2
8a
reported value (834 m /g), suggesting that the absence of Cu co-
catalysts did not strongly affect the polymerization. The BET surface
2
areas of Pd/CMP-1-N
2
and -H
2
decreased to 521 and 458 m /g, re-
2
2
. Results and discussion
spectively. This was probably due to a partial collapse of porous
structures by thermal treatment or blocking the pores by the for-
mation of Pd NPs.
.1. Preparation and characterization of Pd/CMPs
The presence and the size of Pd particles were evaluated by high
angle annular dark-field scanning transmission electron micros-
copy (HAADF-STEM) observations. For Pd/CMP-1, the formation of
Pd NPs was not observed (Fig. 1a). In contrast, Pd NPs were ob-
served as white spots and highly dispersed in Pd/CMP-1 network
CMP-1 was prepared from 1,3,5-triethynylbenzene and 1,4-
diiodobenzene in a similar manner established by Cooper et al.
with minor modifications in the presence of Pd(PPh ) without
3 4
8
a
copper co-catalysts (Scheme 1). The as-synthesized polymer was
abbreviated as Pd/CMP-1. The Pd content in Pd/CMP-1 was mea-
sured by atomic absorption spectrometry (AAS) and 0.9 wt % of Pd
was contained. This was almost consistent with the reported val-
2 2
for both Pd/CMP-1-N (Fig. 1b) and -H (Fig. 1c). These results
suggested that thermal treatment caused the formation of mono-
dispersed Pd NPs. Large Pd NPs located outside of the porous net-
work were not observed, indicating that Pd NPs were confined in
the porous network. The mean diameters were calculated to be
8
a
ue. It can be assumed that ca. 50% of Pd remained in the CMP
network during the polymerization. The obtained Pd/CMP-1 was
ꢀ
dried and then treated in a flow of N
CMP-1-N and -H , respectively.
2
or H
2
at 250 C to give Pd/
1
.6ꢂ0.4 and 3.5ꢂ0.8 nm for Pd/CMP-1-N
2 2
and Pd/CMP-1-H , re-
2
2
spectively (Fig. S4). It was assumed that hydrogen treatment of Pd/
Scheme 1. Synthesis of Pd/CMPs.
Structures of Pd/CMP-1, Pd/CMP-1-N
ized by FT-IR, N adsorption isotherms, and C CP-MAS NMR. FT-IR
spectrum of Pd/CMP-1 revealed that the disappearance of the peaks
2 2
, and -H were character-
13
2
ꢁ
1
at 1068 and 3280 cm corresponded to the CeI stretching vibra-
tions of 1,4-diiodobenzene and to the CeH stretching vibration of
terminal alkynes of 1,3,5-triethynylbenzne, respectively (Fig. S1). In
ꢁ
1
addition, a new peak was observed at 2195 cm , which corre-
sponded to CeC stretching vibrations of the internal alkyne. These
results suggested the construction of aryleneeethynylene polymer
Fig. 1. HAADF-STEM images of (a) Pd/CMP-1, (b) Pd/CMP-1-N
(d) Pd/CMP-2-H
2 2
, (c) Pd/CMP-1-H , and
2
.
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T. Ishida et al. / Tetrahedron xxx (2014) 1e6
3
CMP-1 facilitated the aggregation of Pd atoms. According to the
energy dispersive X-ray spectrometry analysis, P was detected in
Pd/CMP-1 (Fig. S5), indicating that phosphine ligands also partially
remained in the porous network. Elemental analysis of P proved
that 0.8 wt % of P was contained in Pd/CMP-1 and Pd/CMP-1-H
To further evaluate the chemical state and the size of Pd in Pd/
CMP-1 and Pd/CMP-1-H , X-ray absorption fine structure (XAFS)
2
.
2
measurements were performed. In the Pd K-edge X-ray absorption
near edge structure (XANES) spectra and the absorption edges of
Pd/CMP-1 and Pd/CMP-1-H
that Pd in both samples exist as Pd(0) (Fig. 2). The Pd K-edge k -
weighted EXAFS oscillation patterns of Pd/CMP-1 and Pd/CMP-1-H
were also similar to that of Pd foil but different from those of PdO
Fig. S7). It is inferred that the PdeO bonds do not exist as a major
2
resembled that of Pd foil, suggesting
3
2
(
species in those two samples. In addition, the amplitude of EXAFS
oscillations was much smaller than that of Pd foil. This suggests that
the size of Pd particles was very small. In the radial structure
ꢀ
functions (RSF), two peaks were observed at 1.81 and 2.42 A
(
phase-uncorrected) in Pd/CMP-1 (Fig. 3d). By the comparison with
ꢀ
those of Pd foil (2.52 A) (Fig. 3b), the latter peak corresponded to
PdePd bond. The decrease in the FT magnitude indicated that the
decrease in the particle size, since it is known that metalemetal
bond length decreases with a decrease in the size of metal particles
smaller than 3 nm.10 When compared to the RSF of Pd(PPh
3
)
4
Fig. 3. Pd K-edge radial structure functions of (a) PdO, (b) Pd foil, (c) Pd(PPh
3
)
4
, (d) Pd/
ꢀ
(Fig. 3c), the peak at 1.81 A implied that PdeP bond may be in-
2
CMP-1, and (e) Pd/CMP-1-H .
volved in Pd/CMP-1, although the fraction of PdeP bond is small. In
the RSF of Pd/CMP-1-H , two peaks were observed at 1.92 and
.52 A (phase-uncorrected), and these spectral features resembled
that of Pd foil (Fig. 3e). Significant lower FT magnitude of both Pd/
CMP-1 and Pd/CMP-1-H than that of Pd foil also supports the fact
2
ꢀ
2
Table 1
a
EXAFS fit parameters of Pd/CMP-1 and Pd/CMP-1-H
2
CNb
f
ꢀ
c
s2 (A )
ꢀ
2
d
e
2
Shells
R (A)
Rfactor (%)
that Pd exists as very small clusters.
Pd foil
PdePd 12
2.741ꢂ0.003 0.0054ꢂ0.0004 0.1
2.406ꢂ0.013 0.0092ꢂ0.0017 2.5
g
Pd(PPh
3
)
4
PdeP
4
Pd/CMP-1
PdePd 3.7ꢂ0.7 2.689ꢂ0.006 0.0070ꢂ0.0010 0.4
PdeP
1.4ꢂ0.6 2.261ꢂ0.035 0.0089ꢂ0.0042
h
Pd/CMP-1-H
2
PdePd 5.7ꢂ0.8 2.713ꢂ0.006 0.0100ꢂ0.0008 0.6
ꢀ
ꢁ1
a
3
ꢀ
k :k-range¼2e12 A , r-range¼1.3e2.9 A
b
2
First shell coordination number. Intrinsic loss factor, S ¼0.826 (PdePd) and
0
0
.777 (PdeP) from Pd foil and Pd(PPh
3
)
4
data, respectively.
c
Bond length.
DebyeeWaller factor.
Goodness-of-fit index.
CN was fixed as that of fcc lattice.
CN was fixed.
r-Range¼1.8e2.9 A.
d
e
f
g
h
ꢀ
consisting of only PdePd bond fitted well. It implied that the
phosphine ligands were removed from Pd atoms and aggregated to
Pd nanoparticles during H
Pd/CMP-1-H was calculated to be 5.7, which corresponds to ca.
Pd13 clusters in average. Significant small size of Pd NPs for Pd/
CMP-1-H , as compared to 3.5 nm obtained from HAADF-STEM
2
treatment. The CN of PdePd bond for
2
2
observation, indicated that a large amount of small Pd clusters
exist in CMP network but they could not be identified by HAADF-
STEM.
8
a
The CMP with biphenyl moieties (Pd/CMP-2)
was also
0
prepared from 1,3,5-triethynylbenzene and 4,4 -diiodobiphenyl
instead of 1,4-diiodobenzene, followed by the H
2
treatment at
2
Fig. 2. Pd K-edge XANES spectra of (a) Pd/CMP-1 and (b) Pd/CMP-1-H . Solid blue line:
ꢀ
Pd foil, dash-dotted black line: PdO, dashed red line: Pd/CMP-1 (a) and Pd/CMP-1-H
b).
2
250 C to give Pd/CMP-2-H
2
. The size of Pd NPs in Pd/CMP-2-H
2
(
was estimated to be 2.5ꢂ1.6 nm, which was slightly smaller than
that of Pd/CMP-1-H , whereas the pore size of Pd/CMP-2 is
2
larger than that of Pd/CMP-1. This indicates that the pore size
does not significantly affect to the size of Pd NPs (Fig. 1d). It is
reasonable because the pore size distribution did not signifi-
cantly alter except for ultramicropore (<0.7 nm) between Pd/
The extended XAFS (EXAFS) fit parameters are shown in Table 1.
The coordination number (CN) of PdePd bond for CMP-1 was cal-
1
1
culated to be 3.7, which corresponds to ca. Pd
The PdeP bond also exists in Pd/CMP-1 and the CN was estimated
to be 1.4. Fitting analysis of Pd/CMP-1-H was failed when both the
PdePd and PdeP bonds were considered, while the model
5
clusters in average.
8
a
CMP-1 and -2.
2
To study whether functional groups affected the catalytic per-
formance, hydroxy groups were introduced into the CMP backbone
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4
T. Ishida et al. / Tetrahedron xxx (2014) 1e6
(
Pd/CMP-OH). The Pd/CMP-OH was prepared from 1,3,5-
triethynylbenzene and 1,4-dihydroxy-2,5-diiodobenzene, fol-
lowed by the H treatment to give Pd/CMP-OH-H . The mean di-
ameter of Pd NPs of Pd/CMP-OH-H was estimated to be
Table 3
a
Hydrogenation of 4-nitrostyrene
2
2
2
3
.9ꢂ0.9 nm by HAADF-STEM (Fig. S8).
Entry
Catalyst
Conv.b (%)
4b (%)
5b (%)
6b (%)
1
2
3
Pd/CMP-1
Pd/CMP-1-H
Pd/KB
4
>99
>99
>99
0
>99
0
0
0
0
0
0
0
93
56
2
.2. Pd/CMP-catalyzed hydrogenation
2
c
Catalytic performance of Pd/CMP-1-N
2
and -H
2
was examined
4
Pd/KB
42
using hydrogenation of N-benzylideneaniline as a model reaction
a
4
-Nitrostyrene (0.5 mmol), Pd cat. (Pd 1 mol %), dehydrated toluene (3 mL), H
2
(
(
Table 2). For the comparison, Pd NPs supported on Ketjen black
KB), which has similar BET surface area (700 m /g), was used. N-
ꢀ
(
0.3 MPa), 50 C, 1 h.
2
b
Calculated on the basis of GC analysis using anisole as an internal standard.
H (0.1 MPa), rt, 30 min.
2
c
Benzylideneaniline was converted into N-benzylaniline (1) over
Pd/CMP-1, whereas the hydrolysis of imine also proceeded to give
aniline and benzaldehyde as major products due to the presence
of a trace amount of H O (entry 1). When Pd NPs were formed in
2
the CMP framework, the catalytic performance was remarkably
et al. have reported that zeolite (MS-3A and MS-5A) supported Pd
NPs showed selectivity to olefin, and they catalyzed the hydroge-
nation of 4-nitrostyrene to give 4-ethylnitrobenzene (4) with ex-
improved, and N-benzylaniline was obtained as a major product
13
2
cellent selectivity. Pd/CMP-1-H also showed excellent selectivity
(
entries 2 and 3). Moreover, Pd/CMP-1-H
NPs, exhibited higher catalytic activity and selectivity than Pd/
CMP-1-N did. It is likely that terrace Pd atoms work as active
2
, which has larger Pd
to 4 (entry 2), whereas the complete hydrogenation of 4-
nitrostyrene to 4-ethylaniline (6) could not be suppressed over
Pd/KB even under mild reaction conditions (entry 4). Baiker et al.
have reported that the chemoselectivity for the 3-nitrostyrene
hydrogenation could be controlled by reaction media. In their
report, CeC double bond was preferentially hydrogenated in acidic
media. Taking into account the fact, acidic sites of supports would
play an important role for Pd-catalyzed selective hydrogenation.
Interestingly, Pd/CMP-1-H exhibited olefin selectivity, although
2
CMP framework has neither acidic nor basic sites.
Although the catalytic performance of Pd/CMP-OH-H
alter from Pd/CMP-1-H
neaniline (Table 2, entry 7), Pd/CMP-OH-H
lytic activity than Pd/CMP-1-H for the oxidation of benzyl alcohol
Table 4). Pd/CMP-1-H slightly improved the benzaldehyde yields
from Pd/CMP-1 (entries 1 and 2). In contrast, Pd/CMP-OH-H re-
2
sites, as previously observed in the Pd NP-catalyzed alkene hy-
drogenation, in which terrace Pd atoms showed higher catalytic
14
activity than edge and corner Pd atoms did.11b,12 Another possi-
bility is ascribed to the removal of phosphine ligands from the
surface Pd atoms by H
atoms, which can dissociate H
2
treatment, giving the bare surface Pd
. Hexane was more beneficial sol-
2
vent and N-benzylaniline could be obtained in 87% yield (entry 4).
Pd/KB also catalyzed the hydrogenation, but the hydrogenolysis of
2
did not
1
to toluene and/or the reduction of benzaldehyde to benzyl al-
2
for the hydrogenation of N-benzylide-
cohol and the further hydrogenolysis of benzyl alcohol to toluene
also occurred (entry 5). Inductively coupled plasma atomic emis-
sion spectroscopy (ICP-AES) analysis proved that leaching Pd into
the reaction solution was below detection limit (<0.1 ppm) for Pd/
CMP-1-H , whereas 5.3% Pd from the initial Pd loading leached
2
into the reaction solution for Pd/KB. From these results, CMP
frameworks appeared to be effective supports for metal clusters.
2
exhibited higher cata-
2
(
2
2
markably improved the catalytic activity from that of Pd/CMP-OH,
and gave benzaldehyde in 73% yield, which was even higher than
that for Pd/CMP-1-H (entry 4). It is likely that hydroxy groups in
2
Pd/CMP-2-H
2
2
and Pd/CMP-OH-H showed similar catalytic activity
the CMP framework affected the catalytic activity of Pd NPs.
to that of Pd/CMP-1-H
2
(entries 6 and 7), probably due to the
similar or smaller size of Pd NPs.
Table 4
a
Oxidation of benzyl alcohol
Table 2
a
Hydrogenation of N-benzylideneaniline
Entry
Catalyst
Conv.b (%)
Benzaldehydeb (%)
1
2
3
4
Pd/CMP-1
Pd/CMP-1-H
Pd/CMP-OH
37
35
42
74
20
34
27
73
2
Entry
Catalyst
Conv.b (%)
1b (%)
2b (%)
3b (%)
Pd/CMP-OH-H
2
1
2
3
4
5
Pd/CMP-1
23
57
79
4
32
72
87
57
77
73
14
21
5
3
31
5
15
19
4
2
0
a
Benzyl alcohol (0.25 mmol), Pd cat. (Pd 2 mol%), dehydrated toluene (3 mL), O
2
Pd/CMP-1-N
Pd/CMP-1-H
Pd/CMP-1-H
Pd/KB
Pd/CMP-2-H
Pd/CMP-OH-H
2
2
2
ꢀ
(
1.0 MPa), 150 C, 4 h.
b
Calculated on the basis of GC analysis using dodecane as an internal standard.
c
91
d
>99
>99
82
e
6
7
2
Trace
8
3. Conclusions
2
8
a
N-Benzylideneaniline (0.5 mmol), Pd cat. (Pd 1 mol %), dehydrated toluene
ꢀ
2
3 mL), H (0.5 MPa), 100 C, 4 h.
In summary, we have prepared the Pd NPs encapsulated by
microporous polymer networks, CMPs, by the Pd-catalyzed poly-
merization followed by thermal treatment. The Pd catalysts were
fixed in the CMP porous structures during the polymerization and
aggregated to form Pd NPs by the thermal treatment. Palladium NPs
were highly dispersed in the porous structures, even though CMP
frameworks had no interaction sites with Pd. Once Pd NPs were
formed, the catalytic activity was significantly improved for hy-
(
b
Calculated on the basis of GC analysis using dodecane as an internal standard.
Hexane (3 mL) was used instead of toluene.
c
d
e
1
H
h.
2
(1.5 MPa), 5 h.
2
The catalytic performance of Pd/CMP-1-H was further exam-
ined by the hydrogenation of 4-nitrostyrene and results are shown
in Table 3. Heterogeneous Pd NP-catalyzed selective hydrogena-
tions of alkenes in the presence of nitro groups are limited. Sajiki
drogenations and oxidations. In addition, Pd/CMP-1-H was active
2
for the selective hydrogenation of 4-nitrostyrene into 4-
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T. Ishida et al. / Tetrahedron xxx (2014) 1e6
5
ethylnitrobenzene, while Pd/KB gave 4-ethylaniline even at mild
reaction conditions.
dried under vacuum to obtain Pd/CMP-1. The obtained Pd/CMP-1
was placed in a U-shaped glass reactor and treated in a flow of N
2
ꢀ
(
50 mL/min) at 250 C for 4 h to give Pd/CMP-1-N
2
. To give Pd/CMP-
4
4
. Experimental section
1-H
2
, 20 vol% H
2
in N
2
(50 mL/min) was used.
0
For the preparation of Pd/CMP-2, 4,4 -diiodobiphenyl (0.81 g,
2 mmol) was used instead of 1,4-diiodobenzene, and the poly-
.1. General experimental
3
merization was performed in toluene (5 mL) and NEt (5 mL) at
ꢀ
ꢀ
2 2
in N at 250 C for 4 h to
All reagents and solvents, including dehydrated toluene and
80 C. Pd/CMP-2 was treated in a flow of H
give Pd/CMP-2-H
THF, were purchased and used without further purifications.
FT-IR spectra were obtained by JASCO FT/IR-620. The metal
content of Pd/CMP-1 was estimated by atomic absorption spec-
2
.
For the preparation of Pd/CMP-OH, 1,4-dihydroxy-2,5-
diiodobenzene (0.73 g, 2 mmol), which was prepared according
to the literature, was used instead of 1,4-diiodobenzene. The
polymerization was carried out at 80 C. Pd/CMP-OH was treated in
a flow of H
18
trometry (AAS) using
a
SHIMADZU AA-6800. The Bru-
ꢀ
nauereEmmetteTeller (BET) surface areas were calculated from N
2
ꢀ
adsorption isotherms obtained by Bell Japan, BELSORP-Mini II. The
2
in N
2
at 250 C for 4 h to give Pd/CMP-OH-H
2
.
ꢀ
samples were pretreated under vacuum at 105 C for 7 h and then
13
N
2
adsorption isotherms were obtained at 77 K. C CP-MAS NMR
4.3. Typical experiments for hydrogenations
spectra were obtained by JEOL JNM-ECP400 at the Center of Ad-
vanced Instrumental Analysis, Kyushu University. High angle an-
nular dark-field scanning transmission electron microscopic
An autoclave was charged with substrate, catalyst, solvent, and
a magnetic stirring bar. The autoclave was purged and filled with
(
3
HAADF-STEM) observations were performed using a JEOL JEM-
000F at AIST, JEM-3200FS equipped with energy dispersive X-
ray spectrometry at Tokyo Metropolitan University, and JEM-ARM
00F at the Research Laboratory for High Voltage Electron Mi-
H . After the reaction mixture was stirred, the mixture was filtered
by Celite and the filtrate was analyzed by GC.
2
2
Acknowledgements
croscopy (HVEM), Kyushu University. Elemental analysis of phos-
phorous was performed at the Organic Elemental Analysis Research
Center, Kyoto University. ICP-AES analysis was performed by Biko
Chemical Company, Limited.
This work was financially supported by Hayashi Female Foun-
dation and Tokuyama Science Foundation. The synchrotron radia-
tion experiments were performed at the BL14B2 of the SPring-8
with approval of the JASRI (proposal No. 2011B1001). C CP-MAS
NMR measurements were performed at the Center of Advanced
Instrumental Analysis, Kyushu University. HAADF-STEM observa-
tions were partly performed at the Research Laboratory for High
Voltage Electron Microscopy (HVEM), Kyushu University.
13
X-ray absorption fine structure (XAFS) measurements were
15
carried out at BL14B2 of SPring-8 (Hyogo, Japan). The XAFS
samples were ground with boron nitride or cellulose in an agate
mortar and made as pellets. The storage ring energy was 8 GeV with
a typical current of 99.5 mA. Pd K-edge (24.3 keV) XAFS spectra
were measured using a Si(3 1 1) double crystal monochromator in
transmission mode. Ionization chambers were used to measure the
intensity of the incident and transmitted X-rays and the Quick scan
technique (QXAFS) was used in this measurement. The spectral
analysis was carried out by the XAFS analysis software, Athena and
Artemis.16 The extraction of the extended X-ray absorption fine
structure (EXAFS) oscillation from the spectra, normalization by
edge-jump, and Fourier transformation were performed by Athena.
The curve-fitting analysis was carried out in R-space by Artemis. In
the curve-fitting analysis, the backscattering amplitude, the phase
shift, and the mean-free path of the photoelectron were calculated
by FEFF8.4,17 and then the other parameters, i.e., the number of
neighboring atoms, the interatomic distance between the absorbed
atom to the neighboring atom, the DebyeeWaller factor, and the
absorption edge energy were treated as fitting parameters. The
intrinsic loss factor was obtained by the curve-fitting analysis of the
Supplementary data
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2014.04.049.
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