Adhesive catalyst immobilization of palladium nanoparticles on cotton and filter paper: Applications to reusable catalysts for sequential catalytic reactions

Article abstract of DOI:10.1002/adsc.201300691

Palladium nanoparticles dispersed in ammonium salts of hyperbranched polystyrenes are adhesively immobilized on the surface of cotton or filter papers by simply heating with dicarboxylic acids or halide anions. The resulting Pd@cotton and Pd@filter paper

Full text of DOI:10.1002/adsc.201300691

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DOI: 10.1002/adsc.201300691
Adhesive Catalyst Immobilization of Palladium Nanoparticles on
Cotton and Filter Paper: Applications to Reusable Catalysts for
Sequential Catalytic Reactions
Takashi Nishikata,a Hironori Tsutsumi,b Lei Gao,a Keisuke Kojima,c
Katsumi Chikama,c and Hideo Nagashimab,*
a
Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
Institute for Materials Chemistry and Engineering, Kyushu University, and CREST, Japan Science and Technology
b
Agency (JST), Kasuga, Fukuoka 816-8580, Japan
Fax : (+81)-92-583-7819; e-mail: nagasima@cm.kyushu-u.ac.jp
Chemical Research Laboratories, Nissan Chemical Industries, LTD. 2-10-1, Tuboinishi, Funabashi-shi, Chiba 274-8507,
c
Japan
Received: August 1, 2013; Revised: November 30, 2013; Published online: March 11, 2014
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300691.
Abstract: Palladium nanoparticles dispersed in am-
monium salts of hyperbranched polystyrenes are
adhesively immobilized on the surface of cotton or
filter papers by simply heating with dicarboxylic
acids or halide anions. The resulting Pd@cotton and
Pd@filter paper behave as reusable catalysts; in par-
ticular, Pd@filter paper is useful as catalyst for ap-
plication to sequential cross-coupling and hydroge-
nation reactions to produce several different prod-
ucts with just one piece of the paper catalyst.
a number of catalysts showing high performance in
terms of catalyst recovery and reuse have been re-
ported, which include robust supported catalysts pre-
pared by conventional multi-step functionalization of
polymers,[1a–c] and easily accessible supported catalysts
by microencapsulation of metallic species to cross-
linked polymers.[1d–f] The catalytically active species in
these immobilized catalysts are not only molecular or-
ganometallic moieties but also metal nanoparti-
cles.[1g,3] Catalytic hydrogenation by late transition
metals[1,2] and palladium-catalyzed cross-coupling re-
actions[4] are excellent probes for performance of cat-
alyst immobilization on the solution and solid sup-
ports.
Keywords: cellulose; hyperbranched polymers; pal-
ladium; solid catalysts
As reported in our previous paper, a new polystyr-
ene having ammonium chloride as a functional group
+
(HPS-NR3 Clꢀ)[5] is easily accessible by chemical
With the increasing concern to develop environmen- modification of Ishizuꢀs hyperbranched polystyrene
tally friendly chemical processes, immobilization of bearing dithiocarbamate as the end group.[6,7] The re-
+
transition metal species for catalyst recovery and sulting polycationic salts, HPS-NR3 Clꢀ, behave as an
reuse has actively been investigated as a solution of efficient stabilizer of nanoparticles of late transition
residual metal problems in homogeneous catalysis.[1,2] metals by utilizing electrostatic and steric properties
Immobilization of the catalyst in water or a fluorous of the ammonium moieties. Both organo- and water-
phase results in solvent/solvent biphasic catalyst sys- dispersible
polymer-supported
nanoparticles,
+
tems that are useful for easy catalyst recycling by M@HPS-NR3 Clꢀ, can be prepared by judicious
phase separation.[2] Various catalytic reactions includ- choice of the R group. The resulting compounds,
ing industrial processes have been performed by bi- Pt@HPS-NR3 Clꢀ, are stable and can be stored over
+
phasic systems such as those composed of organic sol- months without change of the particle size. High dis-
vents/water[2b,c] and organic solvents/fluorinated sol- persibility in solvents and size of the metal particles
vents.[2d,e] Catalyst immobilization on solid materials are not changed upon heating at ~1008C either in so-
makes it possible to fix the catalytically active species lution or in the solid state. By taking advantage of
+
on the solid phase, which reacts with the substrate at these stabilities, the application of Pt@HPS-NR3 Clꢀ
the interface of the solution phase. This technology, in to biphasic hydrogenation was demonstrated.
particular, immobilized catalysts on polymer supports,
In our further studies, the palladium analogues of
+
has been a hot topic in current organic chemistry; Pt@HPS-NR3 Clꢀ were also prepared, which were
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well-dispersible in solvents, and stable enough to for cross-coupling reactions and hydrogenations.
store over months or upon heating at 1008C in the so- From the advantage of the easy handling of Pd@cot-
lution or the solid state. Applications of Pd@HPS- ton and Pd@filter papers, which were transferrable by
+
NR3 Clꢀ to the homogeneous or biphasic catalytic hy- tweezers from one reaction solution to another, se-
drogenation of alkenes were possible. In this paper, quential reactions were achieved to prepare several
we wish to report our unprecedented discovery during compounds by using the same piece of the catalyst.
+
these studies on the catalysis of Pd@HPS-NR3 Clꢀ
In a typical example, the preparation of Pd@HPS-
that some of the Pd@HPS-NR3 Clꢀ well dispersible
N
N
ACHTUNGTRENNUNG
A
+
+
+
in common organic solvents, typically those of R=
(C12H25)3 Clꢀ with Pd
N
C12H25 or C8H17, became insoluble in contact with Iꢀ, 708C (Scheme 1). As shown in Figure 1, a TEM
Brꢀ, or certain dicarboxylic acids. Moreover, the reac- image showed that palladium nanoparticles of around
+
tions in the presence of cellulose materials, typically 3 nm size were well-dispersed in HPS-N
N
commercially available cotton and filter paper, led to TG analysis showed that 32.6 wt% of Pd was included
+
adhesive immobilization of the palladium species on in Pd@HPS-NACHTUGNTERNUNNG
their surface. The resulting Pd@cotton and Pd@filter
(C12H25)3 Clꢀ. Similar to Pt@HPS-N-
+
+
(C12H25)3 Clꢀ, Pd@HPS-N(C12H25)3 Clꢀ is well disper-
ACHUTGTNRENNUG CAHTUNGTRENNUGN
papers were robust enough to be reusable catalysts sible in common organic solvents including hydrocar-
bon and polar aprotic solvents. When Pd@HPS-
+
N
N
in the presence of laboratory used cotton, an initial
black colored homogeneous dispersion of Pd@HPS-
+
N
N
while white cotton was changed to black. Since the re-
+
action of Pd@HPS-N
occurs at 1008C to give insoluble black materials, it is
(C12H25)3 Clꢀ with KI in DMF
ACHTUNGTRENNUNG
+
likely that Pd@HPS-NACTHNUTRGNEUNG
(C12H25)3 Clꢀ turned to be in-
soluble in contact with KI, and the resulting insoluble
materials were adhered on the surface of the cotton.
It was confirmed that similar results were obtained
when KBr or dicarboxylic acids were added to the re-
action mixture instead of KI, whereas no color
change occurred by heating a DMF solution of
+
Pd@HPS-N
tive.
N
SEM and TEM analyses of the formed ꢂblack
cottonꢀ provided supporting evidence for the adhesion
+
of clusters of Pd@HPS-N
N
+
(C12H25)3 Clꢀ and b)
ACHTUNGTRENNUNG
of cotton. As shown in Figure 2, SEM images showed
that resinous materials are located on the surface of
Scheme 1. a) Preparation of Pd@HPS-N
its immobilization onto cotton or filter paper.
+
Figure 1. TEM image of Pd@HPS-NACHTUNGTRNEUNG
(C12H25)3 Clꢀ (average particle size is 3.0 nm).
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Adhesive Catalyst Immobilization of Palladium Nanoparticles
Figure 2. a) SEM and b) EDX analysis of Pd@cotton. c) and d) TEM images of Pd@cotton.
the cotton fiber (Figure 2a), EDX analysis of this image comes from the aggregation of the ꢂegg-shellꢀ
+
sample clearly demonstrated the existence of palladi- moieties from clusters of Pd@HPS-NR3 Clꢀ.
um (Figure 2b). It was confirmed that no palladium
The results strongly suggest that palladium nano-
was present on the cotton surface in the absence of particles are immobilized on the surface of ꢂblack
resinous material. TEM analysis of the resinous mate- cottonꢀ (Pd@cotton). Since cotton is chemically
rials on a cotton fiber provided an image of dry slabs robust, Pd@cotton has a potential as a reusable cata-
on the human skin (Figure 2c), and increased magnifi- lyst. In fact, Pd@cotton made from Pd@HPS-
+
cation provided an image that the slab looks like the
N
N
ovary of fishes composed of many eggs, of which the for hydrogenation and Mizoroki–Heck reactions.
yolk is a palladium nanoparticle of 2–3 nm size and Treatment of iodobenzene with tert-butyl acrylate in
+
the white is HPS- NR3 Clꢀ (Figure 2d). This corre- DMF at 808C gave tert-butyl cinnamate by catalysis
sponds to the ꢂegg-shellꢀ structure proposed in our of Pd@cotton (S/C=512). After 12 h, the reaction
+
previous paper as an image of Pt@HPS-NR3 Clꢀ,[5] was not complete, but the TON reached 200. The re-
where a metal nanoparticle was surrounded by several covered catalyst was active enough to promote anoth-
+
molecules of HPS-NR3 Clꢀ. The ovary of fishes-like er run of the reaction under the same conditions
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Takashi Nishikata et al.
(TON=122). Also Pd@cotton is robust enough to
perform catalyst recycling experiments over 10 runs.
A mixture of 3-(MeO)C6H4I and tert-butyl acrylate
(S/C=32) was treated with Pd@cotton at 808C for
12 h. After the reaction, the black cotton was re-
moved by a tweezers from the reaction mixture,
washed with diethyl ether, water, and acetone consec-
utively, and reused in another run of the Mizoroki–
Heck reaction. The experiments can be repeated up
to 16 times without loss of catalytic activity (conver-
sion was >99% in all of runs), and another 4 times
with lower activity; the total TON reached 600.
Leaching of a small amount of Pd to the solution was
observed; that was 1.1 ppm in the first run, and
3.3 ppm at the fifth run. The loss of catalytic activity
was accompanied by a fading of the black color of
Pd@cotton. It is likely that adhesion is not mechani-
+
cally strong and Pd@HPS-N
N
off during the repeated experiments. Nevertheless,
the result that the black cotton was recyclable over 16
times showed that the adhesive immobilization of
+
Pd@HPS-N
N
that is far more robust than we expected. Hydrogena-
tion of stilbene (PH =2 atm, S/C=535) proceeded at
2
room temperature, for which the TON reached 310
after 5 h. The recovered catalyst was active enough to
promote another run of the reaction under the same Scheme 2. Examples of test reactions for the catalyst recy-
cle.
conditions (TON=535 after 12 h). For catalyst recy-
cling, five repeated experiments with S/C=49 pro-
ceeded without loss of catalytic activity. In both the 5 runs. ICP-MS analysis of the reaction solution
Mizoroki–Heck reaction and hydrogenation, TEM showed no or small leaching of Pd (<0.5 ppm) to the
images showed no significant difference in the particle solution was observed in most cases, though it was sig-
size before and after 5 repeated experiments as sum- nificant in a few cases (0.6–2 ppm). We consider that
marized in detail in the Supporting Information.
The mechanical strength to solve the leaching prob- collision of the filter paper with a stirring bar.
lem was improved by changing the support from In Table 2 are shown representative examples of
the leaching took place mechanically by an accidental
cotton to more porous filter paper; no significant three to four repeated reactions using the same piece
fading of the black color of Pd@filter paper was ob- of Pd@filter paper, in which the substrates were
served in repeated experiments for catalyst recycling. changed in each run. In all cases, the reactions pro-
As examples, we selected four reactions, Suzuki– ceeded smoothly and the product was obtained quan-
Miyaura coupling, Mizoroki–Heck reaction, intramo- titatively. Some leaching of Pd was observed, but it
ꢀ
lecular coupling via C H bond activation, and hydro- was not very significant. The results clearly show that
genation of alkenes and alkynes as shown in simple manipulation, transfer of the filter-paper cata-
Scheme 2, Eq. (1)–Eq. (4). In Table 1 are shown rep- lyst by a tweezers from one reaction flask to another,
resentative results for each reaction including catalyst provides a way to synthesize several different com-
recycling experiments. Immobilization of Pd@HPS- pounds with ease. We also examined experiments
+
N
N
the conditions shown in the table captions and the lyst to carry out four sequential reactions starting
Supporting Information, the reactions shown in en- from Mizoroki–Heck reaction, Suzuki–Miyaura cou-
ꢀ
tries 1–9 gave the corresponding products in quantita- pling, and intramolecular coupling via C H bond acti-
tive yields. Similar to the experiments using Pd@cot- vation. Different solvent systems from those used for
ton, Pd@filter paper was removed from the reaction the experiments shown in Table 2 were employed for
mixture by a tweezers, washed with acetone, water, the former two reactions to check that the Pd@filter
and ether, and transferred to the new reaction vessel. paper is useful in other solvents, too. As shown in
In the reactions shown in entries 1, 3, 5, and 7, the Scheme 3, it was confirmed that the four successive
catalyst was recyclable five times. In all of the experi- reactions gave the desired four products quantitative-
ments, no loss of catalytic activity was observed after ly.
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Adhesive Catalyst Immobilization of Palladium Nanoparticles
Table 1. Reactions catalyzed by Pd@filter paper including catalyst recycling experiments.
Run[a]
Reactants
Conditions[b]
Yield [%]/Pd [ppm][c]
Suzuki–Miyaura coupling [Eq. (1)]
1: 1st
2nd
3rd
4th
Ph-I
Ph-B(OH)2
A
A
A
A
A
A
99/0.29
99/0.15
99/0.25
99/0
99/0
99/0
5th
2
Ph-I
3,5-Me2C6H3-B(OH)2
Mizoroki-Heck reaction [Eq. (2)]
3: 1st
2nd
3rd
4th
Ph-I
CH2=CHCO2-t-Bu
B
B
B
B
B
B
99/0.79
99/1.2
99/0.25
99/0.51
99/0.50
99/0
5th
4
Ph-I
CH2=CHPh
ꢀ
Intramolecular coupling via C H bond activation [Eq. (3)]
5: 1st
2nd
3rd
4th
compound 1 (Y=3-OMe; 1a)
C
99/0.72
C99/0.34
C99/0.34
C99/0.34
C99/3.0
C
5th
6
Compound 1 (Y=4-CN; 1b)
99/0
Hydrogenation of alkenes [Eq. (4)]
7: 1st
2nd
3rd
4th
5th
8
trans-stilbene
D
99/2.0
D99/0.60
D99/0.60
D99/0.45
D99/0.45
D
styrene
99/0.20
99/0
9
cis-RO2CCH=CHCO2R {2, R=[(CH2)2O]2Me}
D
[a]
In runs 1, 3, 5, 7 are described the results of the catalyst reuse by five times.
[b]
A: Conducted at 508C for 24 h in water (2 mL) with PhI (0.25 mmol), ArB(OH)2 (0.38 mmol), catalyst (S/C=40) and
K2CO3 (2 mmol). B: Conducted at 808C for 24 h in water (2 mL) with PhI (0.25 mmol), olefin (1 mmol), catalyst (S/C=
68) and K2CO3 (2 mmol). C: Conducted at 1208C for 24 h in N,N-dimethylacetamide (2 mL) with ArI (0.25 mmol), cata-
lyst (S/C=66), and KOAc (0.75 mmol),. D: Conducted at room temperature for 5 h in EtOAc (2 mL) with olefin
(0.25 mmol), catalyst (S/C=150), and hydrogen (2 atm).
[c]
Leaching amount of Pd to the solution (ppm).
In summary, the above described results demon- in solvents – are fixed on the surface of cellulose ma-
strate that unique reusable catalysts are easily pre- terials simply by treatment with Brꢀ, Iꢀ, or dicarbox-
pared by adhesive immobilization of Pd@HPS- ylic acids. It is worthwhile to refer to a report by
+
N
G
chemists daily used in their laboratory.[8] Similar treatment of metal nanoparticles stabilized by organic
ꢂblack cottonꢀ or ꢂblack filter paperꢀ can also be ammonium salts with alumina and other solid sup-
+
formed from Pd@HPS-N
(C8H17)3 Clꢀ; this suggests ports resulted in their immobilization on the surface
that the adhesive immobilization is a general property of the supports.[11] Further studies on the immobiliza-
of Pd@HPS-NR3 Clꢀ. High catalytic activity is contra- tion are described in a review by Bçnnemann;[3b]
+
ry to robustness of the catalyst for repeated catalyst nanoparticles stabilized by organic or polymer sup-
recycling. Pd@cotton is not reactive enough to acti- ports produce an “egg-shell” structure, in which the
vate bromo- and chlorobenzenes, but is advantageous metal particle is the egg and the stabilizer is the shell.
with sufficient robustness to perform repeated catalyst The egg-shell materials are adsorbed on the surface
recycling and sequential reactions as shown in Table 2 of solid metal oxide and carbon supports through the
and Scheme 3. Like conventional silk-protein and cel- solid-shell interaction to form the precursor of ꢂcortex
lulose fibers, cotton and filter papers have a merit of catalystsꢀ. A similar mechanism can be proposed for
+
being bio-degradable.[9,10]
the immobilization of Pd@HPS-NR3 Clꢀ presented in
The mechanism of adhesive immobilization is of in- this paper. However, a question is that cotton and
+
terest, because Pd@HPS-NR3 Clꢀ – well-dipsersible filter paper are not a good adsorbent. Furthermore,
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Table 2. Sequential reactions changing the substrates catalyzed by one piece of Pd@filter paper.
Run[a]
Reactants
Conditions[b]
Yield [%]/Pd [ppm][c]
Suzuki–Miyaura coupling [Eq. (1)]
1: 1st
2nd
Ph-I
Ph-B(OH)2
Ph-B(OH)2
Ph-B(OH)2
3,5-(MeO)2C6H3B(OH)2
A
A
A
A
99/0.3
99/0.5
99/0
4-MeO-(C6H4)I
compound 1
Ph-I
3rd
4th
99/0
Mizoroki-Heck reaction [Eq. (2)]
2: 1st
2nd
Ph-I
4-MeO-(C6H4)I
compound 1a
Ph-I
CH2=CHCO2-t-Bu
CH2=CHCO2-t-Bu
CH2=CHCO2-t-Bu
CH2=CHPh
B
B
B
B
99/0.7
99/0.9
99/0.5
99/0
3rd
4th
ꢀ
Intramolecular coupling via C H bond activation [Eq. (3)]
3: 1st
2nd
compound 1a
compound 1b
compound 1 (Y=3,5-Me2; 1c)
C
C
C
99/0.7
99/0
52/0
3rd
Hydrogenation of alkenes and alkynes [Eq. (4)]
4: 1st
2nd
diphenylacethylene
compound 2
trans-stilbene
D
D
D
99/0.2
99/0
99/1.9
3rd
[a]
Three to four reactions of different substrates using the same piece of Pd@filter paper were listed.
A: Conducted at 508C for 24 in water (2 mL) with PhI (0.25 mmol), ArB(OH)2 (0.38 mmol), catalyst (S/C=65) and
K2CO3 (2 mmol). B: Conducted at 808C for 24 in water (2 mL) with ArI (0.25 mmol), olefin (1 mmol), catalyst (S/C=71)
and K2CO3 (2 mmol). C: Conducted at 1208C for 24 in N,N-dimethyl acetoamide (2 mL) with ArI (0.25 mmol), catalyst
(S/C=83), and KOAc (0.75 mmol). D: Conducted at room temperature for 5 h in EtOAc (2 mL) with olefin (0.5 mmol),
catalyst (S/C=129), and hydrogen (2 atm).
[b]
[c]
Leaching amount of Pd to the solution (ppm).
adhesive immobilization did not take place without lized catalysts of various metal nanoparticles dis-
+
the additives, Brꢀ, Iꢀ, or dicarboxylic acids. A clue for persed in HPS-NR3 Clꢀ are underway.
+
understanding this is that Pd@HPS-NR3 Clꢀ well-dis-
persed in solvents is able to form insoluble resinous
material in contact with the additives.
Experimental Section
It is well-known that cross-linking of polymers
gives an insoluble gel.[1d] Since Pd@HPS-NR3 Clꢀ General Methods
+
contains a large number of ammonium salts as the
All reactions were carried out under a nitrogen or argon at-
functional group, replacement of Clꢀ by the dicarbox-
ylate could result in cross-linking of Pd@HPS-
1
mosphere unless otherwise noted. H and 13C NMR spectra
were measured on JEOL GSX-270 (270 MHz) and ECA-
600 (600 MHz) spectrometers, and chemical shifts (d values)
are given in ppm relative to the solvent signal. TG (Shimad-
zu DTG-60), SEM (JEOL, JSM7400F), EDS (Oxford In-
struments, INCAEnergy), TEM (Hitachi, H-8000, V=
200 kV), ICP-MS and HR-MS analysis were performed at
the Analytical Center in Institute for Materials Chemistry
and Engineering, Kyushu University or Nissan Chemical In-
dustry. IR spectra were measured on JASCO FT/IR-550 and
4200 spectrometers. Filter paper was purchased from AD-
+
NR3 Clꢀ. In the cross-linking by Brꢀ or Iꢀ, relatively
large ionic radii and electrons at the outer-sphere
may behave similarly to dicarboxylates. There is the
electrostatic interaction of ionic ammonium groups in
+
Pd@HPS-NR3 Clꢀ with surface hydroxy groups of
cotton and filter paper made by cellulose. The large
number of ionic ammonium groups in Pd@HPS-
+
NR3 Clꢀ and many OH groups on the surface of cel-
lulose form multiple electrostatic interactions be-
VANTEC (size No. 1). Cotton was purchased from
+
+
tween the NR3 Clꢀ group in HPS-NR3 Clꢀ and
+
SANSYO (No. 94–1847). HPS-N
G
OdꢀHd+; this could realize a tight adhesion of resinous
by the procedure reported previously.[5] Representative ex-
periments are described below in the experimental section,
and full details including actual photos and spectral charts
are described in the Supporting Information.
HPS-NR3 Clꢀ on the surface of cotton or filter paper.
+
The proposed mechanism is shown in Figure 3. Char-
+
acteristic features of HPS-NR3 Clꢀ, the existence of
a large number of ammonium groups and spheroidal
structures, should be responsible for this facile adhe-
sive immobilization. Further investigations on prepa-
ration, homogeneous catalysis, and use as the immobi-
+
Preparation of Pd@HPS-N
N
A
mixture of HPS-N
(dba)3·CHCl3 (200 mg) in CHCl3 (3 mL) was heated at
(C12H25)3 Clꢀ (200 mg), and
ACHTUNGTRENNUNG
Pd
2A
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Adhesive Catalyst Immobilization of Palladium Nanoparticles
Scheme 3. A sequential procedure ([a]![b]![c]![a]) consisting of three cross-coupling reactions using one piece of Pd@fil-
ter paper. [a] Conducted at 808C for 24 in DMF (2 mL) with ArI (0.25 mmol), olefin (1 mmol), catalyst and K2CO3
(1.5 mmol). [b] Conducted at 508C for 24 h in THF/water (2 mL/0.4 mL) with ArI (0.25 mmol), ArB(OH)2 (0.38 mmol), cat-
alyst and K2CO3 (2 mmol). [c] Conducted at 1208C for 24 h in N,N-dimethyl acetamide (2 mL) with ArI (0.25 mmol), cata-
lyst, and KOAc (0.75 mmol).
708C for 6 h with stirring. The title product was obtained
after filtration followed by drying (yield: 147 mg). TEM
analysis showed existence of palladium nanoparticles with
an average particle size of 2.97 nm. TG analysis showed the
palladium content of 32.6 wt%. Elemental analysis: C 65.5,
H 9.3, N 1.4, Cl 5.4, Pd 12.2.
be 0.767 mg. The ꢂblack cottonꢀ was subjected to analysis by
TEM, SEM, SEM-EDX as shown in the Supporting Infor-
mation.
Filter Paper as a Support (Pd@filter paper)
+
A mixture of Pd@HPS- N
N
Pd), KI (8 mg; 8 mg of KBr can be alternatively used), and
a piece of filter paper (the initial color was white, ca. 70 mg)
was placed in a reaction vessel, and DMF (2 mL) was
added. After stirring for 2 h at 1008C, the initial black color
of the solution part of the reaction mixture turned to pale
brown, and color of the filter paper turned from white to
Cotton as a Support (Pd@cotton)
+
A mixture of Pd@HPS-N
N
Pd), KI (15 mg or 15 mg of KBr) and cotton (the initial
color was white, ca. 55 mg) was placed in a reaction vessel,
to which DMF (2 mL) was added. After stirring for 2 h at
1008C, the initial black color of a solution part of the reac-
tion mixture turned to pale red, and ꢂblack cottonꢀ was
formed. The ꢂblack cottonꢀ was separated by a tweezers, and
washed with water, acetone and Et2O consecutively. ICP-
MS analysis of ꢂblack cottonꢀ showed the content of Pd to
black. The resulting black filter paper embedding Pd@HPS-
+
N
N
water, acetone and Et2O consecutively. Alternatively, the so-
lution was removed by a pipette from the mixture, and the
black filter paper was washed with water, acetone, and Et2O
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Takashi Nishikata et al.
Figure 3. A proposed mechanism of adhesive immobilization.
in the reaction vessel. The content of Pd (0.17 mg) in the
Representative Examples for Catalysis of Pd@filter
paper
Pd@filter paper was determined by ICP-MS analysis. Adhe-
+
sive immobilization of Pd@HPS- N
N
Suzuki–Miyaura coupling [Scheme 2, Eq. (1), Table 1 Run
1]: A mixture of iodobenzene (0.25 mmol), phenylboronic
acid (0.38 mmol), K2CO3 (2.0 mmol), and Pd@filter paper
(0.662 mg of Pd, S/C=40) prepared by the procedure using
citric acid as the immobilizer were placed in a reaction tube
equipped with a stirring bar and a septum under air. Water
(2.0 mL) was added by syringe and the resulting mixture
was heated at 508C for 24 h. After Pd@filter paper was re-
moved by a tweezers, water was added, and the reaction
mixture was extracted with Et2O. The ethereal layers were
combined, and then concentrated under vacuum. The resi-
due was purified by flash chromatography eluting with
hexane/EtOAc to afford the product. The desired product
was obtained quantitatively, and the purity (>99%) was
paper was also achieved by treatment with several dicarbox-
ylic acids examined, although the immobilization was slower
than the reaction with KBr or KI. Among the dicarboxylic
acids, citric acid was the most effective.
Mizoroki–Heck Reaction Catalyzed by Pd@cotton
In a reaction tube equipped with a stirring bar and
a septum, meta-iodoanisole (0.5 mmol), tert-butyl acrylate
(2.0 mmol), K2CO3 (3.0 mmol), and Pd@cotton (1.65 mg of
Pd contained; S/C=32) prepared by the procedure shown in
above were placed under air, and then, DMF (2.0 mL) was
added by syringe. The resulting mixture was kept at 808C
for 12 h. The cotton was removed by a tweezers, and water
was added. Then the mixture was extracted with EtOAc.
The combined extracts were concentrated, and the residue
was purified by flash chromatography eluting with hexane/
EtOAc to afford the product. The cotton catalyst was
reused for another run of the reaction, after washing with
acetone, water, and Et2O.
1
confirmed by H NMR. The Pd leaching to the solution was
determined by ICP-MS analysis. After washing with ace-
tone, water, and Et2O, the recovered Pd@filter paper was
subjected to the catalyst recycle experiments for 5 times.
Mizoroki–Heck Reaction [Scheme 2, Eq. (2), Table 1
Run 3): A mixture of iodobenzene (0.25 mmol), tert-butyl
acrylate (1.0 mmol), K2CO3 (1.5 mmol), and Pd@filter paper
(0.389 mg of Pd, S/C=68) prepared by the procedure using
citric acid as the immobilizer were placed in a reaction tube
equipped with a stirring bar and a septum under air. Water
958
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Adhesive Catalyst Immobilization of Palladium Nanoparticles
(2.0 mL) was added by syringe and the resulting mixture References
was heated at 808C for 24 h. After Pd@filter paper was re-
moved by a tweezers, the reaction mixture was extracted
with Et2O. The ethereal layers were combined, and then
concentrated under vacuum. The residue was purified by
flash chromatography eluting with hexane/EtOAc to afford
the product. The desired product was obtained quantitative-
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ly, and the purity (>99%) was confirmed by H NMR. The
Pd leaching to the solution was determined by ICP-MS anal-
ysis. After washing with acetone, water, and Et2O, the recov-
ered Pd@filter paper was subjected to the catalyst recycle
experiments for 5 times.
ꢀ
Intramolecular coupling via C H bond activation
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[Scheme 2, Eq. (3), Table 1 Run 5]: A mixture of 1-iodo-2-
[(3-methoxyphenoxy)methyl]benzene (0.25 mmol), KOAc
(0.75 mmol), and Pd@filter paper (0.401 mg of Pd, S/C=66)
prepared by the procedure using citric acid as the immobil-
izer was placed in a reaction tube equipped with a stirring
bar and a septum under air. DMA (N,N-dimethylacetamide)
(2.0 mL) was added by syringe and the resulting mixture
was heated at 1208C for 24 h. After Pd@filter paper was re-
moved by a tweezers, water was added, and the reaction
mixture was extracted with Et2O. The ethereal layers were
combined, and then concentrated under vacuum. The resi-
due was purified by flash chromatography eluting with
hexane/EtOAc to afford the product. The desired product
was obtained quantitatively, and the purity (>99%) was
1
confirmed by H NMR. The Pd leaching to the solution was
determined by ICP analysis. After washing with acetone,
water, and Et2O, the recovered Pd@filter paper was subject-
ed to the catalyst recycle experiments for 5 times.
Hydrogenation of alkenes [Scheme 2, Eq. (4), Table 1
Run 7): A mixture of trans-stilbene (0.5 mmol), and Pd@fil-
ter paper (0.353 mg of Pd, S/C=150) prepared by the proce-
dure using citric acid as the immobilizer was placed in
a glass tube, and AcOEt (2.0 mL) was added by syringe.
The glass tube was moved into a stainless steel autoclave,
and the reaction was performed at room temperature for 5 h
under hydrogen atmosphere (2 atm). After Pd@filter paper
was removed by a tweezers, the solvent was removed by
a rotary evaporator. The residue was purified by flash chro-
matography eluting with hexane/EtOAc to afford the prod-
uct. The desired product was obtained quantitatively, and
the purity (>99%) was confirmed by 1H NMR. The Pd
leaching to the solution was determined by ICP analysis.
After washing with acetone, water, and Et2O, the recovered
Pd@filter paper was subjected to the catalyst recycle experi-
ments for 5 times.
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Acknowledgements
This work was financially supported by the Core Research
Evolutional Science and Technology (CREST) Program of
Japan Science and Technology Agency (JST) Japan. We are
thankful to Mr. Yuki Nohara and Mr. Shun Fujita (Nissan
Chemical Co. Ltd.) for SEM and TEM measurements.
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ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2014, 356, 951 – 960