The 2V-P,N polymer supported palladium catalyst for methoxycarbonylation of acetylene

Article abstract of DOI:10.1016/j.molcata.2015.12.025

Heterogenization of homogeneous catalyst by immobilizing complex on the surface of polymer supports promotes the design of the catalysts which combine the advantages of heterogeneous and homogeneous catalysts. The porous 2-vinyl-functional diphenyl-2-pyri

Full text of DOI:10.1016/j.molcata.2015.12.025

Accepted Manuscript
Title: The 2V-P,N polymer supported palladium catalyst for
methoxycarbonylation of acetylene
Author: Xingkun Chen Hejun Zhu Tao Wang Cunyao Li Li
Yan Miao Jiang Jia Liu Xueping Sun Zheng Jiang Yunjie Ding
PII:
S1381-1169(15)30188-6
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2015.12.025
MOLCAA 9728
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
22-8-2015
7-12-2015
29-12-2015
Please cite this article as: Xingkun Chen, Hejun Zhu, Tao Wang, Cunyao Li, Li
Yan, Miao Jiang, Jia Liu, Xueping Sun, Zheng Jiang, Yunjie Ding, The 2V-P,N
polymer supported palladium catalyst for methoxycarbonylation of acetylene, Journal
of Molecular Catalysis A: Chemical http://dx.doi.org/10.1016/j.molcata.2015.12.025
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The 2V-P,N polymer supported palladium catalyst for
methoxycarbonylation of acetylene
a,c
a*
a,c
a,c
a
a,c
Xingkun Chen , Hejun Zhu , Tao Wang , Cunyao Li , Li Yan , Miao Jiang , Jia
a,c
d
d
a,b*
Liu , Xueping Sun , Zheng Jiang , Yunjie Ding dyj@dicp.ac.cn
a
Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, Dalian 116023, PR China
b
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese
Academy of Sciences, Dalian 116023, PR China
c
University of Chinese Academy of Sciences, Beijing 100039, PR China
d
Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics,
Chinese Academy of Sciences, Shanghai 201204, China
*
Corresponding author.

Graphical Abstract

Highlights
-PyPPh2 ligand based porous organic polymer (POL-2V-P,N) was
2
successfully synthesized
The Pd/POL-2V-P,N catalyst exhibits higher activity than the
corresponding homogeneous complex
The reused catalyst exhibited similar activity as that of the fresh catalyst

Abstract
Heterogenization of homogeneous catalyst by immobilizing complex
on the surface of polymer supports promotes the design of the catalysts
which combine the advantages of heterogeneous and homogeneous
catalysts. The porous 2-vinyl-functional diphenyl-2-pyridylphosphine
(2V-P,N) polymer (POL-2V-P,N) was successfully synthesized under
solvothermal conditions. The POL-2V-P,N polymer was characterized by
nitrogen physisorption, thermogravimetry (TG), scanning electron
microscope (SEM) and transmission electron microscopy (TEM). The
heterogenized homogeneous Pd/POL-2V-P,N catalyst was synthesized by
immobilizing Pd(OAc) on the POL-2V-P,N, which was used as not only
2
31
support but also as ligands. The catalyst was investigated by means of P
NMR, X-ray absorption fine structure (EXAFS), X-ray photoelectron
spectroscopic (XPS) and FT-IR and tested for the methoxycarbonylation
3
1
of acetylene. According to the results of P NMR, XPS and EXAFS,
there existed coordination bonds between palladium and the exposed
phosphorous and nitrogen atoms of the porous POL-2V-P,N support. The
0
XPS and FT-IR results showed that Pd species were present on the
Pd/POL-2V-P,N catalyst. The heterogenized Pd/POL-2V-P,N palladium
complex catalyst with high surface area and large pore volume displayed
excellent activity for the methoxycarbonylation of acetylene as compared

with
the
corresponding
homogeneous
palladium
diphenyl-2-pyridylphosphine complex (Pd-P,N) under the same
conditions. The used Pd/POL-2V-P,N catalyst also exhibited excellent
activity under the same conditions. In addition, the hot filtration tests
indicated that the reaction occurred in a heterogeneous way.
Keywords: 2V-P,N Polymer; palladium; homogeneous reaction;
heterogenized catalyst; methoxycarbonylation of acetylene

1
. Introduction
Acrylic esters are important bulk chemicals which are widely used in
textile, leather finishes, polymer synthesis etc[1-3]. Since Reppe and
co-works reported alkoxycarbonylation of terminal alkynes firstly in 1939,
carbonylation of acetylene with CO and alcohol, a non-petroleum
approach, has been extensively studied as potential route for direct
synthesis of acrylic esters[4]. In addition, as a highly versatile process of
high atom economy (Scheme 1), acrylic acid and their derivatives could
be synthesized in one step[5-7].
So far, the homogeneous palladium catalyst system consisting of
2
-pyridyl-diphenylphosphine (2-PyPPh ), palladium acetate (Pd(OAc) )
2
2
and a sulfonic acid have received great attention due to their high activity
and selectivity in the carbonylation of alkynes under mild
conditions[8-13]. Drent et al. employed the complex catalysts for
methoxycarbonylaiton of propyne giving turn over numbers as high as
-
1
-1
4
0,000 molproduct molcat h [14, 15]. Tang and co-workers reported
that the catalyst exhibited high activity for hydrocarbonylation of
acetylene[16, 17]. It is especially worth mentioning that the organic
ligand 2-PyPPh is of critical importance in the reaction that replacement
2
of it by a phenyl group or a heteroaromatic ring without N atoms results
in a dramatic decrease in catalytic activity[14, 15, 18]. This is attributed
to that 2-PyPPh functions as a bidentate ligand, and this type of
2

P-coordinated N-promoted 2-PyPPh ligand facilities rapid proton
2
transfer in the rate determining protonlysis step. In addition, the N atom
of the pyridyl ring can also work as acceptor of the alcoholic proton, thus
favouring the cleavage[18].
Such kind of above homogeneous catalytic system play an extremely
important role in the field of modern catalysis due to their high activity
and selectivity. However, the difficulties of recovery and recycling
restrict their more extensive application[19]. A series of approaches have
been developed to solve this problem[20], the main one is to heterogenize
the metal complex, where silica-based materials and magnetic
nanoparticles are the most commonly used materials for such
supports[21-25]. However, their chemical nature limits their potential for
chemical modification process. Moreover, the catalytic moieties are
usually in homogeneously distributed and pendent into the pore volume
thus deactivating the catalytic system[26]. Recently, porous organic
polymers (POPs) have emerged as a versatile platform for the
development of highly efficient catalysts due to their porous nature and
high surface area [27-29]. Recently, we developed a porous organic
ligand (POL-PPh ) supported Rh catalysts with high activities and
3
stabilities for hydroformylation of olefins[30, 31]. Sun et al. reported a
hierarchical porous ionic organic polymer as a new platform for
heterogeneous phase transfer catalysis[32]. Therefore, the POPs

supported catalysts have great potential to be developed using in
industrial fields. Doherty et al. immobilized 2-PyPPh to an insoluble
2
solid support, but the process they employed for copolymerization is
difficult to operate[33]. Inspired by the POPs material, we have
successfully synthesized a POL-2V-P,N porous organic polymer under
solvothermal conditions and prepared the insoluble POPs supported
palladium complex catalyst. The synthesized heterogenized homogeneous
catalyst showed high activity for the methoxycarbonylation of acetylene
with CO and CH OH to produce methyl acrylate.
3
2
2
. Experimental
.1. Materials
All materials (A.R. grade) were obtained from commercial sources
and used without further purification unless otherwise stated.
Tetrahydrofuran（THF）was distilled from sodium and pyridine (py) from
calcium hydride under argon. Acetone was refluxed with 4A zeolite and
methanol with magnesium and iodine under argon.
2
.2. Preparation of POL-2V-P,N
All operations were carried out under anaerobic anhydrous
conditions. The synthesis of POL-2V-P,N is shown in Scheme 2.
2-C H NZnCl • C H N] was prepared according to the method of
[
5
4
5
5
2
Budzelaar et al.[34]. The prepared [2-C H NZnCl•C H N] was dissolved
5
4
5
5
2

in THF/pyridine mixture (3:1, 240 ml), then the solution was cooled to
10℃ and then added dropwise to a THF/pyridine (1:1, 120 ml) solution
of PCl (0.12 mol). Finally, the reaction mixture was warmed up to room
-
3
temperature,
-pridyldichlorophosphine.
The p-styrylmagnesium bromine was synthesized as described by
stirred
for
25
h
and
filtered
to
give
2
Leebrick et al[35]. 2-pridyldichlorophosphine was added to the solution
of the p-styrylmagnesium bromine at 0 ℃ and stirred for 2 h[36]. Then
the reaction mixture was quenched by adding 200 ml of H O, extracted
2
by 500 ml of ethyl acetate and the products were purified by column
chromatography (petroleum ether, silica gel). Then 2-vinyl-functional
diphenyl-2-pyridylphosphine was obtained.
The
polymerization
reaction
of
2-vinyl-functionalized
diphenyl-2-pyridylphosphine (1.0 g, 3.18 mmol) in THF solution (10ml)
was induced with AIBN (1 mol%，0.05 g, 0.03 mmol) and the solution
was heated to 100℃ and held for 24 h. The resulting white solid was
dried under reduced pressure at 65℃ to synthesize the polymer of
2
-vinyl-functional diphenyl-2-pyridylphosphine (hereafter referred to as
POL-2V-P,N).
2
.3. Preparation of Pd/POL-2V-P,N catalyst
The heterogenized Pd/POL-2V-P,N catalyst was prepared by stirring

a solution of Pd(OAc) (0.0053 g) in 15 ml of THF containing 1.0 g
2
POL-2V-P,N polymer solid at room temperature for 24 h. The solvent was
removed under vacuum, and the resulting solid washed with CH OH at
3
room temperature with a Soxhlet apparatus and dried under reduced
pressure to obtain the Pd/POL-2V-P,N catalyst.
2
.4. Carbonylation reactions
The carbonylation reactions were carried out in a 140 ml autoclave
which was made of Hastelloy NS334 material following by a procedure
similar to that described by Tang[16]. In a typical run, Pd/POL-2V-P,N
catalyst (0.0046 mmol), and p-toluenesulfonic acid monohydrate (0.0115
mmol), were dissolved in a mixture of 20 ml acetone and 5 ml CH OH
3
and transferred to the autoclave. After replaced three times with argon,
the reactor was pressured to 0.12 MPa with C H and then to 4.92 MPa
2
2
with CO at room temperature. The autoclave was heated to 50 ℃ within
min and stirred at 800 rpm for 1h. Afterwards the reactor was cooled to
5
room temperature, and the gas samples and liquid samples were analyzed
online by Agilent 7890A gas chromatography with a TDX-01 packed
column and off-line with a HP-5 capillary column, respectively.
2
.5. Hot filtration test
Two parallel reactions were carried out under the same reaction
conditions (see 2.4), and one of the reaction mixtures was filtered off at

the reaction temperature after 1 h (the content of methacrylate is 0.28 g).
The filtrate was then transferred into the autoclave and the reaction was
restarted under the same conditions as the original reaction. The result
catalyzed by the filtrate was compared with that of the parallel reaction.
2
.6. Characterization
The BET surface area, pore volume, and BJH pore distribution were
measured by adsorption-desorption of N at 77 K using an AutoSorb-1
2
instrument. 53.8 mg sample was degassed under vacuum at 120 ℃ for
2
1 h prior to measurement. The thermal stability of POL-2V-P,N was
-
1
detected in N flow (20 ml min ) using a STA 449 F3 TG-DSC
2
-
1
instrument, with a heating rate of 10℃.min up to 1000 ℃. SEM study
was carried out on a JSM-7800F scanning electron microscope. TEM
measurement was performed on a JEM-2100 transmission electron
microscopy. Pd leaching was determined by ICP-OES on a Perkin-Elmer
3
1
optima 7300DV instrument. Solid-state P NMR experiments were
carried out on an Infinity plus 400 spectrometer operating at 161 MHZ.
The FT-IR spectra were measured on a NICOLET iS50 Fourier transform
-
1
infrared spectrometer in the range of 4000-400 cm . All spectra were
-
1
recorded with 32 scans with a resolution of 4 cm . XPS spectra were
performed on an ESCALAB 250Xi AIα radiation. Pd K-edge X-ray
absorption fine structure (EXAFS) spectra of the prepared catalysts were
obtained at the BL14W1 beamline of SSRF, SINAP (Shanghai, China)

with the use of a Si(311) crystal monochromator. The storage ring was
operated at 3.5 GeV with injection currents of 200 mA. Pd foil was used
as reference samples, and all the X-ray absorption spectra were measured
in the transmission mode. All spectra of the as-synthesized catalysts were
conducted in the fluorescence mode. The raw data were energy-calibrated
(Pd K-edge energy of Pd foil) at 24,350 eV, first inflection point,
background-corrected, and normalized using the IFEFFIT software.
Fourier transformation of the EXAFS data was applied to the
k3-weighted functions. For the curve-fitting analysis, Pd-C, Pd-P, Pd-N
path parameters were obtained from the ab initio multiple scattering
codes FFEF6.
3
3
3
. Results and discussion
.1. Characterization
.1.1. Characterization of POL-2V-P,N
Fig.1. shows the TG curve of the POL-2V-P,N sample, N sorption
2
isotherms, SEM and TEM images. TG analysis was utilized to examine
the thermal stability of the POL-2V-P,N. The TG curve showed a minute
weight loss at about 200 ℃ owing to the removal of physically absorbed
solvent in Fig. 1A). The biggest weight loss was observed in the range of
4
00-500 ℃ due to the decomposition of the polymer. It indicated that
the POL-2V-P,N was a highly thermally stable material. As shown in Fig.

1
B), the N sorption isotherms exhibited a hysteresis loop at a relative
2
pressure(P/P ) of 0.45-0.95, suggesting that the polymer is filled with
0
mesopore. Accordingly, the BET surface area, pore volume, and BJH
2
-1
3
-1
average pore size of POL-2V-P,N were 475 m .g , 0.64 cm .g , and
about 2.7 nm, respectively. It implied that the polymer possessed high
surface area and large pore volume. The morphologies of the polymer
were further characterized by SEM and TEM (Fig. 1 C) and D)). Both of
the SEM and TEM images also showed the presence of mesopore, which
was consistent with the result of N sorption isotherm (Fig. 1B)).
2
3
.1.2. Characterization of Pd/POL-2V-P,N catalyst
31
Solid-state
P NMR for the POL-2V-P,N support and the
heterogenized Pd/POL-2V-P,N catalyst were carried out to detect the
interaction between Pd and the polymer, and the result was shown in Fig.
2
. A single peak at -4.53 ppm belonged to uncoordinated P atoms was
detected for the polymer support. For the Pd/POL-2V-P,N, except for
4.53 ppm peak, a new peak at 19.77 ppm appeared, which was attributed
-
to P atom coordinated with palladium (Fig. 2 b). It implied that there was
truly an interaction between palladium and the exposed phosphorous
atoms on the surface of porous POL-2V-P,N support, and the
POL-2V-P,N was used as not only support but also ligands
simultaneously.
To determine the chemical environment of Pd, the spent

Pd/POL-2V-P,N catalyst (0.247 wt%) was characterized by EXAFS (Fig.
.). The curve-fitting analysis for the EXAFS Fourier-transformed spectra
3
at Pd-K edge for the catalyst revealed the existence of a Pd-P bond at 2.35
Å, a Pd-N bond at 2.15 Å and Pd-C bonds at 2.03 Å (Table 2). All the
observations above revealed clearly that coordination bonds were formed
between Pd and the exposed P and N atoms of POL-2V-P,N support[37].
It also demonstrated a similar bonding characteristics to that of the
corresponding homogeneous catalysts [38, 39] in the coordination sphere
around Pd in the catalyst. This result was consistent with those obtained
3
1
from P NMR.
X-ray photoelectron spectroscopic (XPS) analysis was performed for
the fresh and spent catalysts (Fig. 4.). Two peaks at 338.0 and 343.2 eV
2
+
for fresh catalyst were assigned to 3d and 3d for Pd species, while
5
/2
3/2
the other two peaks at 336.2 and 341.3 eV were assigned to 3d and 3d
5
/2
3/2
0
for Pd species, respectively[40]. The corresponding binding energies of
the spent catalysts were lower than that of the fresh catalyst, probably due
to the electron donating effect of CO on the Pd species[41]. The relative
0
Pd percentage was 7.6 % for the fresh catalyst, which was calculated
0
from the area of the 3d peak. However, the Pd percentage enhanced to
5
/2
2
+
2
2.0 % for the spent catalyst. It implied that Pd species were reduced to
0
Pd species during the catalytic reactions. This result was analogous
2
+
with those reported in literature [18, 40]. It is well known that Pd

species acted as catalytic active sites for methoxycarbonylation of
0
acetylene [16, 17]. Meanwhile, it has also been shown that Pd species
are involved in catalytic cycle[18].
XPS spectra of P of the fresh catalyst were shown in Fig. 5. Two peaks
at about 131.4 and 133.8 eV were ascribed to P atoms in C-P and C-P-Pd,
respectively, indicating that P coordinated with Pd species[42]. The result
3
1
was coincident with those obtained from P NMR and EXAFS.
To glean further information about the carbonylation reaction process,
the Pd/POL-2V-P,N catalysts were characterized with FT-IR by CO probe
molecule (Fig. 6.). According to the literature[43, 44], ligand has a big
-
1
influence on the palladium carbonyls. The bands at 2002 cm and 1946
-
1
0
cm were assignable to Pd (CO) /POL-2V-P,N species, which were close
n
t
0
to that reported for the (d bpe)Pd (CO) [44]. Importantly, Willner’s report
2
0
2+
has revealed that substitution of Pd with Pd caused a lower electron
density, thus decreasing the back-donation to the carbonyl ligand and
leading a blue shift in the carbonyl stretching frequency[45]. Therefore,
-
1
the bands at 2071 and 1987cm could probably ascribed to
2
+
Pd (CO) /POL-2V-P,N species. This was coincident with the results of
n
0
2+
XPS which indicated both Pd and Pd species were present during the
catalytic cycle.
3
3
.2．Catalytic tests
.2.1. Comparison between homogeneous and heterogenized catalyst

For a comparison, both of the homogeneous Pd-N,P catalyst and the
heterogenized Pd/POL-2V-P,N catalyst were employed in the
methoxycarbonylation of acetylene under the same conditions, as shown
-3
in Table 1. The Pd-N,P complex (4.6×10 mmol Pd(OAc) , 0.63 mmol
2
-1
2
-pyPPh ) gave 1238.8 h TOF (Entry 1). The result was lower than
2
Tang’s report [17] which pointed out that higher activity was obtained at
lower pressure. The initial partial pressure was 1.0 MPa in Tang’s study,
while it was 4.8 MPa in this experiment. Thus, the lower TOF (1238.8
-
1
h ) was ascribed to the higher initial partial CO pressure. Higher activity
-1
(
TOF 2983.3 h ) was achieved over Pd/POL-2V-P,N catalyst with 4.6×
-3
1
0 mmol Pd(OAc) and 0.63 mmol POL-2V-P,N (Entry 2).
2
It was found that the molar ratio of P ligand to Pd has a significant
role on catalytic activity [16, 17]. The effect of different ratio of P/Pd of
the two types of catalyst was investigated in our study. When the content
of Pd(OAc) increased, the molar ratio of P/Pd decreased. It led to drop
2
of the catalytic activity of the heterogenized Pd/POL-2V-P,N catalyst as
well as the homogeneous Pd/N,P catalyst. The similar observation has
been reported in the Pd-catalyzed carbonylation of aryl
arenesulfonates[46].
It was obvious that the heterogenized Pd/POL-2V-P,N catalysts
exhibited excellent activity with the molar ratio of P/Pd ranging from 90
to 137, which were higher than that of the corresponding Pd/N,P

homogeneous catalyst under the same conditions. According to the results
31
of P NMR, XPS, EXAFS and FT-IR, the Pd species of the
Pd/POL-2V-P,N catalyst was coordinated with the exposed phosphorous
and nitrogen atoms of the POL-2V-P,N, and its bonding characteristics
was similar to that of the corresponding homogeneous catalysts. It means
that both of the catalytic active species of the heterogenized
Pd/POL-2V-P,N catalyst and Pd/N,P homogeneous catalyst are Pd/N,P
complex. However, the former was located on the surface of the
POL-2V-P,N support, but the latter was soluble species in the reaction
solutions. Thus, the excellent catalytic performance of the
Pd/POL-2V-P,N catalyst might originate from the high surface area (475
2
-1
3
-1
m g ) and large pore volume (0.64 cm g ) of the POL-2V-P,N polymer,
which allowed the substrates more accessible to the active metal sites.
3
.2.2 Effect of initial partial pressure of carbon monoxide
Fig. 7. shows the effect of initial partial pressure of CO to the
catalytic activity of the heterogenized Pd/POL-2V-P,N catalyst. The
reaction rate increased rapidly with the increasing of CO partial pressure
from 1.11 MPa to 4.96 MPa, then the increasing of TOF value slowed
down when CO partial pressure was further raised to 5.83 MPa. However,
the TOF value decreased when the CO partial pressure is above 5.83 MPa.
This result was distinguished from the result of the homogeneous Pd-P,N
catalyst with high activity at low initial partial pressure of CO (1.0 MPa)

reported by Tang[17]. It could be speculated that high pressure of CO
favored for the CO coordination with Pd active species located in the pore
of the POL-2V-P,N support, thus improving the reaction rate. Meanwhile,
too high CO pressure suppressed coordination of other reactant such as
C H and CH OH with the catalytic active species, and thus inhibited the
2
2
3
reaction process.
3
.2.3 Effect of p-toluenesulfonic acid concentration
Fig. 8. shows the effect of p-toluenesulfonic acid concentration
+
(
H /Pd) to the behavior of methoxycarbonylation of acetylene reaction
over Pd/POL-2V-P,N catalyst. The catalytic activity enhanced rapidly
+
when the p-toluenesulfonic acid concentration increased to an H /Pd ratio
+
of 23. Nevertheless, keep increasing the ration of H /Pd from 23 to 51,
there was only a slight improving of catalytic activity. And the catalytic
+
activity decreased when the H /Pd ratio was higher than 51, which
indicated that the appropriate amount of p-toluenesulfonic acid facilitated
methoxycarbonylation of acetylene.
3
.2.4. Effect of temperature to catalytic performance
The effect of temperature to the catalytic performance is shown in
Fig. 9. The catalytic activity increased rapidly when the reaction
temperature was raised, and then it reached a maximum TOF value at
6
3℃. However, the catalytic activity decreased with further increase of

temperature. It is probably due to that the interaction between Pd species
and POL-2V-P,N support weakened at higher temperature, and even led
to decomposition of catalyst with the further increase of temperature[17].
3
.3. Catalyst reusability
The reusability of the Pd/POL-2V-P,N catalyst for the
methoxycarbonylation of acetylene was investigated (Fig. 10.). After
completion of the reaction (1h), the catalyst was separated by
centrifugation, which kept the catalyst away from the air[47]. After
recycling three times, a conversion of 77.9 % was obtained with the
recycled catalyst, which is a little higher than the first cycle of 72.3 %.
This might be attributed to the formation of the Pd-H active species in the
reaction. Pd leaching of the heterogenized Pd/POL-2V-P,N catalyst in
reaction solution was detected by ICP-OES. It was found that after the
first run the amount of Pd leaching was about 0.16%, and after the second
and third runs it was about 0.097% and 0.12% of the initial Pd,
respectively. This indicated that the Pd/POL-2V-P,N catalyst could be
reused in the methoxycarbonylation of acetylene reaction. The stability of
the catalyst might be attributed to the stable structure of palladium
coordination with the exposed phosphorous and nitrogen atoms of the
porous POL-2V-P,N support.
3
.4 Hot filtration test

The result of hot filtration test for the Pd/POL-2V-P,N catalyst in
methoxycarbonylation of acetylene is shown in Fig. 11. The results
revealed that no additional methacrylate was generated after the solid
catalyst was filtered off, which confirmed that the catalytic active species
came from the surface of heterogeneous catalysts rather than the leaching
Pd species in solution, suggested that the reaction occurred in a truly
heterogeneous manner[33, 37].
3
.5 Proposed mechanism
3
1
P NMR and EXAFS experiments results revealed that there was a
strong interaction between Pd and POL-2V-P,N support. Usually, two
mechanisms, namely the “metal-carbalkoxy” and “metal-hydride”, were
proposed [13, 15, 17, 18, 48]. The reaction mechanism of the
Pd/POL-2V-P,N catalysts for methoxycarbonylation of acetylene was
proposed, as shown in Scheme 3, which was similar to that of the
homogeneous Pd(OAc) /2-PyPPh complex[13, 18]. The Pd-H active
2
2
species ( Ⅰ) were formed when Pd/POL-2V-P,N was treated with
Br nsted acid. Then the alkyne inserted into a Pd-H bond to give a
σ-vinyl)-palladium complex (Ⅲ). Following that, CO adsorbed on
Ö
(
palladium and inserted into the Pd-C bond to afford an acylpalladium
complex (Ⅴ). Subsequently, alcoholysis of the acylpalladium complex
yielded the expected ester, simultaneously regenerating the Pd-H active
species. In the above catalytic process, Pd active sites were located in the

POL-2V-P,N support with high surface area and large pore volume,
which might facilitate substrates like C H , CO and CH OH to interact
2
2
3
with Pd active sites, thus leading to higher catalytic activity for
methoxycarbonylation of acetylene.
4
. Conclusions
In summary, POL-2V-P,N was successfully synthesized by
polymerizing 2-vinyl-functional diphenyl-2-pyridylphosphine. And the
heterogenized homogeneous Pd/POL-2V-P,N catalyst was prepared by
31
immobilizing Pd(OAc) on the POL-2V-P,N support. The results of P
2
NMR, XPS, EXAFS and FT-IR of the Pd/POL-2V-P,N catalyst indicated
that Pd was coordinated with the exposed P and N atoms of the 2V-P,N
polymer. The heterogenized Pd/POL-2V-P,N catalyst showed higher
activity for methoxycarbonylation of acetylene than that of the
corresponding Pd-P,N complex under the same conditions. It might
originate from the high surface area and large pore volume of the
2
V-P,N-POL polymer, which allowed the substrates more accessible to
the Pd active sites. The recovered Pd/2V-P,N-POL catalyst also displayed
excellent activity under the same conditions. Our approach provides a
method for the preparation of highly efficient heterogenized
homogeneous catalytic system with characteristic of easy separation and
recycling.

Acknowledgements
We thank Prof. Xiangping Hu and Mr. Xianchun Liu for useful
discussions and contributions. We are also grateful for Mr. Yimin Li, Miss.
Huimin Gong and Mr. Jike Jiang for technical assistance. This work was
supported by the National Natural Science Foundation of China
(
21273227).

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1

Figure Captions
Fig. 1. A) TG curves, B) N sorption isothermes, C) SEM image, and D)
2
TEM image of POL-2V-P,N

3
1
Fig. 2. Solid-state P NMR spectra. (a) POL-2V-P,N
(b)Pd/
POL-2V-P,N catalyst. Spinning side bands are denoted by asterisks (*).

Fig. 3. EXAFS spectra of the spent Pd/POL-2V-P,N catalyst.

Fig. 4. XPS spectra of Pd in (a) the fresh Pd/ POL-2V-P,N catalyst, (b)
the spent catalyst

Fig. 5. XPS spectra of P of the fresh Pd/ POL-2V-P,N catalyst