A polysalen based on polyacylamide stabilized palladium nanoparticle catalyst for efficient carbonylative Sonogashira reaction in aqueous media

Article abstract of DOI:10.1039/c7ra04910b

A highly cross-linked polymer matrix polysalen based on acrylamide and N,N'-methylene-bisacrylamide (NNMBA) was successfully prepared. It has been proved that this type of polysalen is an effective support for immobilizing palladium complex. The polysalen may provide coordination sites for conjugation with a palladium catalyst to produce polysalen-Pd catalyst. The polysalen-Pd was firstly applied in phosphine-free carbonylative Sonogashira coupling reactions of aryl iodides with terminal alkynes to produce α,β-alkynyl ketones in 81-95% yields in aqueous media, which was much higher than that of homogeneous Pd-salen in 52% yield. Furthermore, the catalyst showed excellent recyclability without any significant loss in its activity.

Full text of DOI:10.1039/c7ra04910b

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A polysalen based on polyacylamide stabilized
palladium nanoparticle catalyst for efficient
carbonylative Sonogashira reaction in aqueous
media†
Cite this: RSC Adv., 2017, 7, 31850
ab
Xiaolong Yang‡ and Jianqiang Yu*a
c
Yan Wang,
‡
0
A highly cross-linked polymer matrix polysalen based on acrylamide and N,N -methylene-bisacrylamide
NNMBA) was successfully prepared. It has been proved that this type of polysalen is an effective support
for immobilizing palladium complex. The polysalen may provide coordination sites for conjugation with
palladium catalyst to produce polysalen–Pd catalyst. The polysalen–Pd was firstly applied in
(
a
Received 2nd May 2017
Accepted 11th June 2017
phosphine-free carbonylative Sonogashira coupling reactions of aryl iodides with terminal alkynes to
produce a,b-alkynyl ketones in 81–95% yields in aqueous media, which was much higher than that of
homogeneous Pd–salen in 52% yield. Furthermore, the catalyst showed excellent recyclability without
any significant loss in its activity.
DOI: 10.1039/c7ra04910b
rsc.li/rsc-advances
the early reports, considerable efforts have been made towards
this reaction, and the most restricting aspect of these studies
Introduction
Alkynyl ketones are key structural motifs in organic synthesis as was that they focused on homogeneous and heterogeneous
11
they provide an easy access to various natural products and catalytic systems together with phosphine ligands. However,
1
2
3
heterocyclic derivatives such as pyrimidine, quinolone,
these phosphines were not considered to be the most desired
4
5
6
7
furan, pyrazole, pyrrole, and avone. Under physiological class of ligands for catalysis because of their high costs, envi-
conditions, alkynyl ketones exist in various biological active ronmentally unfriendly properties, complex synthesis, air and
molecules. So the synthesis of alkynyl ketones has attracted moisture sensitivity, inconvenient handing, and other prob-
considerable interest. Traditionally, alkynyl ketones were lems. Thus, an array of N-based ligands, such as N-heterocyclic
12
13
prepared by the coupling of acid chlorides with alkynyl organ- carbenes, and amines, has been employed successfully in
ometallic reagents such as copper, cadmium, lithium, silicon, phosphine-free carbonylative Sonogashira reactions.
8
sodium, silver, tin and zinc. However, these methods require
Salen ligands, one of the N-based ligands, have received
dry solvents under an inert atmosphere.
particular attention mainly due to their simple synthesis and
9
Since Tanaka reported the rst example of Pd-catalyzed high stability. Salen can be tuned easily by selecting suitable
carbonylative Sonogashira reaction of aryl halides with condensing aldehydes and amines. The salen ligands play an
terminal alkynes in the presence of carbon monoxide, this atom important role in the development of catalysis not only due to
economic route has become an alternative for the synthesis of varity of transition metals that can be incorporated, but also the
a,b-alkynones. Due to its great importance, promising devel- varity of ligand derivative from classics salen. Most of the re-
opment has been driven on and the scope of this reaction has ported metal salen complexes belong to the rst transition
10
14
also been extended for the synthesis of various heterocycles. In series, and the second series of these complexes are still rare.
Palladium(II) salen complexes have been reported as catalysts
15
for different C–C cross-coupling reactions, hydrogenation of
Laboratory of Clean Energy Chemistry and Materials, Lanzhou Institute of Chemical imines, and styrene polymerization. Hence, at rst we used
a
16
17
Physics, Chinese Academy of Sciences, No. 18 Tianshui Middle Road, Lanzhou 730000,
a simple Pd–salen (salicylaldehydoethylenediamine) in the
carbonylation of iodobenzene with phenylacetylene. Unfortu-
nately, the Pd–salen just gave the desired carbonylative
China. E-mail: yjq@licp.cas.cn
b
Qingdao Center of Resource Chemistry & New Materials, No. 36 Jinshui Road,
Qingdao 266000, China
18
c
coupling product in 52% yield. As previously reported, the
drawback of using metal salens in homogeneous solutions is
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education,
Ocean University of China, 238 Songling Road, Qingdao 266100, China
†
1
‡
Electronic supplementary information (ESI) available. See DOI: the formation of m-oxo dimers and other polymeric species
0.1039/c7ra04910b
leading to the irreversible catalyst deactivation. In principle,
this problem can be solved by immobilizing salen on supports
Y. Wang and X. Yang contributed equally to this work, both of them are the rst
authors.
31850 | RSC Adv., 2017, 7, 31850–31857
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to isolate the metal–salen complexes from each other. In recent
years, the immobilization of catalysts on suitable supports has
been a topic of special interest. The catalytic systems containing
immobilized organometallic compounds have several advan-
tages, e.g. the simple recycling of the catalysts by ltration,
preventing the loss of both ligands and metal, thus considerably
decreasing the environmental problems of waste materials,
19
compared with homogeneous catalysis. Much effort has been
focused on the immobilization of these salen ligands through
20
a variety of strategies till now. Immobilization of catalyst onto
salen containing polymers not only shows higher thermal
stability than corresponding salen monomer metal complexes
because of their polymeric network structure, but also more
active centers. Therefore, it is of interest to study the catalytic
21
activity of salen containing polymers. Tamami and co-works
synthesized copolymer polyacrylamide from acrylamide with
0
N,N -methylene-bisacrylamide (NNMBA), which was used for Fig. 1 FT-IR spectra of (a) crosslinked polyacylamide; (b) crosslinked
polyacrylohydrazide; (c) crosslinked polyacrylohydrazide-imino-
salicyaldehyde.
the immobilization of cobalt complex for selective oxidation of
olens and alkyl halides. However, to the best of our knowledge,
the carbonylation reactions catalyzed by salen containing
polymers supported palladium catalysts has not been reported
In order to conrm the components of the heterogeneous
up to now. In continuation to our previous study on heteroge- catalyst, the chemical structure of intermediate polymer was
22
neous carbonylation, in this paper, the noble metal Pd was analyzed by FTIR and the results are shown in Fig. 1. FT-IR
loaded on a polysalen support that was derived from the co- spectrum of the crosslinked polyacrylamide showed the char-
0
ꢀ1
polymerization
bisacrylamide (NNMBA). The polysalen–Pd was formed by carbonyl group (C]O) at 1666 cm
post-synthesis modication in the incorporation of Pd(II) in the acrylohydrazide was obtained by transamidation reaction of
of
acrylamide
and
N,N -methylene- acteristic absorbance of amide (N–H) group at 3384 cm , and
ꢀ1
(Fig. 1a). Poly-
polymer networks.
crosslinked polyacrylamide with excess of hydrazine hydrate.
The resultant polymer had a higher content of amino group of
the polymer than polyacrylamide (Fig. 1b). IR spectrum of the
polyacrylohydrazide showed the characteristic absorbance of
Results and discussion
ꢀ
1
amino
(N–H) group
at 3378
cm
.
Crosslinked
The designing procedure of the polysalen–Pd catalyst is shown
in Scheme 1. Polyacrylamide crosslinked with N,N -methylene-
bisacryl-amide (NNMBA) (5%) was prepared by polymerization
2 2 8
of acrylamide monomer in ethanol using K S O as an initiator.
The polar nature of the crosslinking agent makes it compatible
with the polymer backbone as well as the reaction medium. We
found that the polymer with less than 5% NNMBA was sticky
and not physically proper to be used in the further reactions.
The polysalen was synthesized by the addition of hydrazine
hydrate and then by aldimine condensation route with salicy-
polyacrylohydrazide-imino-salicylaldehyde was prepared by the
reaction of polyacrylohydrazide with salicylaldehyde in ethanol.
0
ꢀ1
The IR spectrum of the polymer showed peaks at 1636 cm
,
corresponding to the formation of imine group (C]N) and at
ꢀ
1
ꢀ1
1
268 cm and 750 cm due to C–OH stretching of aromatic
ring, respectively (Fig. 1c). The imine content was evaluated
ꢀ
1
from CHN analysis and was found to the 2.6 mmol g
.
Treating the solution of Pd(OAc) with the polysalen ligand
2
results in the formation of polysalen supported palladium
complex. In order to make the process completely heteroge-
neous, the catalyst was conditioned by washing thoroughly with
laldehyde. Followed by the addition of Pd(OAc) , polysalen–Pd
was produced.
2
Scheme 1 The synthesis of polysalen–Pd catalyst.
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2
+
3d3/2 of Pd (Fig. 3a). The results indicated that the polysalen–
Pd catalyst contains two types of Pd(II) species. In addition,
compared with the BE of Pd 3d5/2 of Pd(OAc) (338.6 eV), the
2
2
+
relatively large negative BE shi of Pd indicated that the cross-
linked polysalen support act as ligands stabilizing the Pd
species with a strong interaction. The XPS survey spectra of the
polysalen–Pd as shown in Fig. 3b–d, indicated the binding
energies of the C 1s, N 1s and O 1s correspond to different
components. The C 1s spectra can be deconvoluted into six
components which appeared at 284.1, 284.8, 285.4, 285.9, 286.7
and 288.1 eV, respectively, and were associated with C–OH, C–C,
23
24
C–N, C(C H –), C–O, C]O.
6
5
The N 1s spectra can be decovoluted into three peaks (Fig. 3c)
which appear at 398.8, 400.1 and 401.0 eV. The main peak at
4
3
00.1 eV was attributed to –NH–, the lower binding energy tail at
98.8 eV and the higher binding energy tail at 401.1 eV, which
2
3
25
Fig. 2 FT-IR spectra of polysalen and polysalen–Pd.
were assigned to N–sp C and N–sp C bonds. Deconvolution of
the O 1s spectrum results in three peaks located at 531.2, 532.4,
and 533.4 eV in Fig. 3d, respectively. The main peak at 532.4 eV
26
solvents to remove any loose Pd species. The metal content of which was consistent with standard spectrum O of O]C. The
the catalyst found by ICP was 1.98% of the resin. The IR spectra component at 531.2 eV and 533.4 eV were attributed to C–OH
of the polymer before and aer palladium loading (Fig. 2) bonding of polysalen and C–O–Pd of polysalen–Pd.
ꢀ
1
showed a shi in frequency from 1636 to 1603 cm for n(C]N)
Based on the XPS analysis above, we can speculate there may
ꢀ
1
and from 1268 to 1283 cm for n(C–O). In addition, IR spec- be an electrostatic interaction between the Pd atoms with N, O
trum of the polysalen–Pd showed two new absorption bands at of polyacrylohydrazide-imino-salicyaldehyde (polysalen) and
78 and 544 cm , which were attributed to the formation of the oxygen atoms of acetate. In other words, the Pd atom
ꢀ1
4
Pd–N and Pd–O, respectively. These variations conrmed the formed bond with the nitrogen atom, oxygen atom of the
coordination of palladium ion with the azomethine nitrogen support, the Pd particle was immobilized on the cross-linked
and phenolic oxygen of the polymeric salen ligand.
polymer through covalent bonding as supported palladium
The X-ray photoelectron spectroscopy (XPS) measurements salen complex.
were carried out to investigate the chemical environment and
surface stoichiometry of the elements of samples. The catalyst
polysalen–Pd was also characterized by XPS before reaction, and
the results are shown in Fig. 3. It can be seen that the Pd 3d
spectrum was resolved into two spin–orbit pairs with binding
energies of 335.9 eV, 338.4 eV and 341.4 eV, 343.7 eV, respec-
tively, which were assigned to electron transitions of 3d5/2 and
Fig. 4 TEM and HRTEM images of the polysalen (a, b) and fresh pol-
ysalen–Pd (c–e), recovered catalyst (f). Insert in (b) was selected-area
Fig. 3 XPS spectrum of the polysalen–Pd: Pd 3d (a), C 1s (b), N 1s (c), O diffraction (SEAD) pattern. Insert in (d) was histogram of Pd particles'
1
s (d).
size. Insert in (e) was HRTEM image.
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The morphology and structure of the polysalen and poly- 78% (Table 1, entries 1–3), respectively. It is found that when
salen–Pd were characterized by transmission electronic toluene and H O were used as solvent, a,b-alkynyl ketones will
2
microscopy (TEM). Selected area electron diffraction (SAED) be formed in an excellent yield.
pattern of the polysalen is shown in the insert of Fig. 4b.
The appearance of the diffused rings indicated that the best mediate. Using H
polysalen was in polycrystalline phase. From the TEM micro- the inuence of alkalinity on the carbonylative Sonogashira
graphs of the polysalen–Pd, it was clearly observed that Pd coupling reaction. Noteworthy, Et N was the most suitable base
Therefore, H O was chosen as a non-toxic solvent to be the
2
2
O as the solvent, we further investigated
3
species are dispersed granularly and uniformly on the surface of for the water system while the use of NaOH and pyridine
polysalen, the average size of Pd nanoparticles was measured delivered the product in low yields (Table 1, entries 6, 7).
about 5.2 nm. The histogram of Pd particles' size was shown in Increasing the reaction temperature and time also had a posi-
insert in (d). From the HRTEM image of Fig. 4e, it can be seen tive effect on the catalytic activity. For comparison, when
that the interplanar space is 0.225 nm, corresponding to the homogeneous Pd–salen (salicylaldehydoethylenediamine) was
(
111) plane of face centered cubic Pd (JCPDS 46-1043).
The crystalline nature of polysalen–Pd was further conrmed reaction is proceeded in a homogeneous catalysis (Scheme 2).
by powder X-ray diffraction (XRD) (Fig. 5). The peaks at about The improvement in the activity using polysalen–Pd as catalyst
used as the catalyst, only 52% yield was obtained, although the
ꢁ ꢁ ꢁ
4
0.0 , 46.4 and 68.0 correspond to the (111), (200) and (220) might be attributed to the interactions between the polymeric
lattice planes of the face center cubic crystalline structure of Pd, support with palladium, and the polysalen ligands stabilized
respectively. The peak positions and relative intensities match the Pd nanoparticles to isolate the metal–salen complexes from
well with the standard XRD pattern for face centered cubic Pd each other.
(JCPDS 46-1043), agreeing well with that observed by HRTEM.
As a result of these studies, we were encouraged to examine
Obviously, both TEM and XRD results conrm that the Pd the reaction with a broad range of substrates to determine the
nanoparticles in a narrow size range are successfully prepared. specicity and scope of substrates for this system. Thus, using
The formation of the small Pd nanoparticles might be attrib- water as the solvent, 0.5 mmol% Pd catalyst loading, starting
uted to the following facts: (1) the N–, O– on the surface of with terminal alkynes and aryl iodides, we carried out the car-
polysalen coordinate to Pd cations are benecial for the bonylative Sonogashira coupling reaction under 2.0 MPa CO
dispersion of Pd nanoparticles, and (2) the interactions between with Et N as the base. To explore the generality and scope of the
3
the polymeric support with palladium and the salen ligands carbonylative coupling reaction, we evaluated various aryl
stabilized the Pd nanoparticles also contributes to the iodides and terminal alkynes as substrates. The results are
dispersibility.
given in Table 2. Generally, a wide range of aryl iodides bearing
To assess the catalytic performance of the prepared catalyst, an electron-withdrawing group or an electron-donating group
the carbonylative Sonogashira coupling reaction between all gave corresponding carbonyl products in excellent yields
iodobenzene and phenylacetylene in the presence of CO was when react with phenylacetylene (entry 1–13). The aryl iodides
chosen as model reaction. The effects of various reaction with electron-donating groups, such as methoxy, methyl and
parameters such as catalyst loading, solvent, base, temperature, ethyl, gave excellent yields (Table 2, entries 2–4, 7–9). Even the
reaction time and CO pressure on the catalytic performance
were thoroughly examined. The solvent plays an important role
in the reaction: when the reaction was performed in acetoni-
trile, acetone and THF, the isolated yields reached 57%, 39%,
Table 1 Carbonylative coupling of iodobenzene with phenylacetylene
under different reaction condition
ꢁ
a
Entry
Solvent
CH CN
Acetone
THF
Base
T ( C)
t (h)
Yield (%)
1
2
3
4
5
6
7
8
9
3
NEt
NEt
NEt
NEt
NEt
3
3
3
3
3
130
130
130
130
130
130
130
120
100
130
130
130
6
6
6
6
6
6
6
6
6
2
3
6
57
39
78
91
90
21
46
85
56
70
82
52
Toluene
H
2
H
2
H
2
H
2
H
2
H
2
H
2
H
2
O
O
O
O
O
O
O
O
NaOH
Pyridine
NEt
NEt
NEt
NEt
NEt
3
3
3
3
3
1
1
1
0
1
2
b
a
Iodobenzene 1.0 mmol, phenylacetylene 1.2 mmol, solvent 5.0 mL,
base 2.0 mmol, CO 2.0 MPa, polysalen–Pd 0.5 mol%, isolated yield.
b
Pd–salen (salicylaldehydoethylenediamine) 0.5 mol%.
Fig. 5 XRD patterns of polysalen–Pd.
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Table 2 Carbonylative Sonogashira coupling of aryl iodides with
a
terminal alkynes to form a,b-alkynyl ketones
Scheme 2 Homogeneous Pd–salen catalyzed carbonylative Sono-
gashira coupling of iodobenzene with phenylacetylene.
b
0
Entry
R
R
Product
Yield (%)
1
2
H
H
H
90
95
reaction of sterically hindered 2-iodoanisole with phenyl-
acetylene gave the desired coupling product in 81% yield (Table
1, entry 3). The reactions of 4-chloro-iodobenzene and 4-bromo-
4-CH
3
O
O
iodobenzene with phenylacetylene also afforded the corre-
sponding products in satisfactory yield (Table 2, entry 5–6). The
reaction of a-iodonaphthalene with phenylacetylene afforded
the corresponding alkynyl ketone in 85% yield (Table 2, entry
3
4
2-CH
3-CH
3
H
H
81
88
11). We also investigated three acetylenes containing different
groups for the reaction. The reactions of the substituted phe-
nylacetylenes, such as 4-methoxy-phenylacetylene, 4-tertiary-
butyl-phenylacetylene and 4-bromo-phenylacetylene with iodo-
benzene, also proceeded effectively under the same conditions
to yield 94%, 90% and 87% of the desired a,b-alkynyl ketones,
respectively (Table 2, entries 12–14).
Besides the efficient catalytic activity, the stable recyclability
is also crucial for an outstanding heterogeneous catalyst from
the viewpoint of both academic research and industrial appli-
cations. To evaluate the recyclability of polysalen–Pd in car-
bonylative Sonogashira coupling reaction, the continuous
carbonylative coupling reaction of iodobenzene with phenyl-
acetylene in water was investigated and the results are pre-
sented in Fig. 6. The catalyst could be reused ve times only
with a slight loss of activity (the 5th recycle yield still can obtain
3
O
5
6
7
4-Cl
H
H
H
92
92
93
4-Br
4-CH
3
3
8
9
2-CH
H
89
4-C
2
H
5
H
H
91
82
84%). The aggregation of the Pd particles in the used catalyst
was not obvious from the TEM photograph in Fig. 4f. The
ꢀ1
content of Pd in the catalyst was 1.76 wt% (0.229 mmol g ), as
determined by the AAS analysis. Accordingly, the coordination
bond of polysalen–Pd(II) lead to its better catalytic activity and
recycle stability.
1
1
1
0
1
2
4-CH
3
CO
Naphthyl
H
85
To get the deeper insight into the active sites for the sup-
ported polysalen–Pd catalyzed the carbonylative Sonogashira
reaction, the hot ltration test was performed. Aer 1 h of
reaction, the catalyst was isolated by ltration without cooling
the reaction mixture and the conversion of iodobenzene was
detected by in 43% GC. Moreover, the ltrate was maintained
H
H
4-CH
3
O
94
90
under the reaction condition and the mixture was analyzed aer 13
an additional hour by GC. The conversion of iodobenzene was
detected in 48%. The hot ltration test proved that the catalytic
4-tBu
1
4
H
4-Br
87
activity could be attributed to the heterogeneous catalyst and
the leached species in the solution. The TEM images of the
reaction mixture and the catalyst aer 1 h of reaction by ltra-
a
Reaction condition: aryl iodide (1 mmol), terminal alkyne (1 mmol),
tion was also investigated in Fig. 7. Fig. 7a was the TEM image of polysalen–Pd (30 mg, 0.005 mmol Pd), Et N (0.4 mL), distilled water (5
3
ꢁ
b
mL), temperature: 130 C, time: 6 h, CO pressure: 2.0 MPa. Isolated
yield.
the reaction mixture by ltration and no Pd particle was found
in the mixture, this result showed that the leached species in the
2
+
solution was the water-soluble Pd . Fig. 7b was the TEM image
of the catalyst aer 1 h reaction, it was clearly observed that Pd
species are dispersed granularly and uniformly on the surface of
polysalen. The histogram of Pd particles' size was shown in
insert in (b), the average size of Pd nanoparticles was measured
about 5.2 nm. The nanoparticles size was the same as the fresh
catalyst. According to the result above, we proposed that the
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salen complexes from each other. In addition, the catalyst
offered practical advantages such as easy separation from the
products and was reused without loss in the activity. The
heterogeneous salen–Pd catalyzed carbonylation reaction
provides a practical and environmentally friendly procedure for
the synthesis of a,b-alkynyl ketone.
Experimental
Materials and techniques
All chemicals were of reagent grade and used as purchased. All
solvents were puried according to standard procedures before
use. The products were puried by ash chromatography on
silica gel and characterized by comparison of their spectra and
physical data with authentic samples. The 1H and 13C NMR
spectra were recorded on a Bruker Avance 400 MHz NMR
spectrometer (400 and 100 MHz, respectively) in ppm with
reference to tetramethylsilane (TMS) internal standard in
Fig. 6 Recycle test of polysalen–Pd in the carbonylative Sonogashira
coupling reaction.
CDCl . GC-MS were measured on an Agilent 6890/5973 GC-MS.
3
Elemental analyses were carried out on a Vario EL analyzer.
Powder X-ray diffraction (XRD) measurements were performed
using an X'Pert Pro multipurpose diffractometer (PANalytical,
Inc.) with Ni-ltered Cu Ka radiation (0.15046 nm) at room
ꢁ
ꢁ
temperature from 10.0 to 80.0 (wide angle). The ESI-MS was
performed on Micro-QOF-II mass instrument. The X-ray
photoelectron spectra (XPS) were obtained using a VG ESCA-
LAB 210 spectrometer equipped with a Mg Ka X-ray radiation
source (hn ¼ 1253.6 eV) and charge referencing was measured
against adventitious carbon (C 1s at 284.6 eV). High resolution
transmission electron microscope (HRTEM) experiments were
conducted in a JEM-2010 TEM with an accelerating voltage of
Fig. 7 TEM images of reaction mixture (a) and catalyst (b) by after 1 h
reaction. Insert in (d) was histogram of Pd particles' size.
polysalen–Pd complex was corresponding to the Pd nano-
particles with the Pd5/2 binding energy 335.9 eV, and the
200 KV. The Fourier transform infrared spectra (FTIR) of the
samples were recorded using an NEXUS 870 FTIR spectrometer
released water-soluble Pd was corresponding to the Pd(OAc)
2
ꢀ1
by the KBr pellet method in the range of 400 to 4000 cm
.
attracted to the surface with the Pd5/2 binding energy 338.4 eV.
The catalytic activity could be attributed to the Pd nanoparticles
and the leached species in the solution. Meanwhile, we use ESI-
MS to examine the liquid phase of the reaction of iodobenzene
and phenylacetylene catalysed by polysalen–Pd (Fig. S1†). The
Pd containing anionic species, [PdPhCOI]- and [PhCOPd(OAc)
CCPh]-were detected in the solution. The Pd anionic species
desorbed from the supports can explain the Pd loss of poly-
salen–Pd in a certain extent.
16b
Preparation of Pd–salen (salicylaldehydoethylenediamine)
To a stirred solution of 2-hydroxybenzaldehyde (1 mmol) in 5
mL of methanol, 1,2-ethylenediamine (0.5 mmol) was added
dropwise and the reaction stirred for 20 min at room temper-
ature. N,N -Bis(salicylidene)-ethylenediamine was obtained by
ltration. Dichloromethane (DCM) (5 mL) was added to dissolve
0

the formed precipitate. To this solution Pd(OAc) (0.5 mmol) in
2
DCM (5 mL) was added dropwise. The resulting reaction
mixture was stirred for 18 to 20 h at room temperature. The
product was ltered and washed with DCM and methanol to
remove the unreacted ligand.
Conclusions
In summary, a highly cross-linked polymer matrix polysalen
0
based on acrylamide and N,N -methylene-bisacrylamide
Preparation of 5% NNMBA-crosslinked polyacrylamide (PAA)
(NNMBA) was successfully synthesized. It can be proved that
0
the polysalen is an effective support for immobilizing palladium N,N -Methylene-bis-acrylamide (NNMBA) (1.14 g, 7.4 mmol) and
complex. The resulted polysalen–palladium catalyst exhibited acrylamide (10 g, 0.14 mol) were dissolved in methanol (250
2 2 8
high efficiency for the carbonylative Sonogashira coupling of mL). K S O (62 mg, 0.23 mmol) was added to the solution and
aryl iodides with terminal alkynes in aqueous media without stirred. The polymer began to precipitate within 30–40 min. The
ꢁ
the addition of phosphine ligands, which is much higher than suspension was stirred at 70–75 C for additional 5 h. The
that of the homogeneous Pd–salen catalyst. The improvement polymer formed was collected by ltration, washed several
ꢁ
in the activity might be attributed to the interactions between times with water and methanol and dried at 60 C under
the polymeric supports with palladium that isolate the metal– reduced pressure over night.
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Preparation of crosslinked poly(acrylohydrazide) (PAH)
Notes and references
PAA (1 g) was added in small portions to an excess of well-stirred
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PAH (1 g, 2.6 mmol NH
2
) was added to salicyaldehyde (1.9 g,
49, 10642.
ꢁ
15.6 mmol) in methanol (50 mL) stirred at 60 C for 12 h. The
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ꢁ
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2
(0.5 mmol, 112 mg).
ꢁ
ꢁ
should be noted that a decrease in the coloration of the solu-
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Acknowledgements
2
This work was nancially supported by the National Natural
Science Foundation of China (No. 21503243, 21403257) and the
Independent Innovation Plan Foundations of Qingdao City of
China (No. 16-5-1-36-jch).
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