Multifunctional Single-Site Catalysts for Alkoxycarbonylation of Terminal Alkynes

Article abstract of DOI:10.1002/cssc.201600660

A multifunctional copolymer (PyPPh₂–SO₃H@porous organic polymers, POPs) was prepared by combining acidic groups and heterogeneous P,N ligands through the copolymerization of vinyl-functionalized 2-pyridyldiphenylphosphine (2-PyPPh₂) and p-styrene sulfonic acid under solvothermal conditions. The morphology and chemical structure of the copolymer were evaluated using a series of characterization techniques. Compared with traditional homogeneous Pd(OAc)₂/2-PyPPh₂/ p-toluenesulfonic acid catalyst, the copolymer supported palladium catalyst (Pd–PyPPh₂–SO₃H@POPs) exhibited higher activity for alkoxycarbonylation of terminal alkynes under the same conditions. This phenomenon could be attributed to the synergistic effect between the single-site Pd centers, 2-PyPPh₂ ligands, and SO₃H groups, the outstanding swelling properties as well as the high enrichment of the reactant concentration by the porous catalyst. In addition, the catalyst could be reused at least 4 times without any apparent loss of activity. The excellent catalytic reactivity and good recycling properties make it an attractive catalyst for industrial applications. This work paves the way for advanced multifunctional porous organic polymers as a new type of platform for heterogeneous catalysis in the future.

Full text of DOI:10.1002/cssc.201600660

DOI: 10.1002/cssc.201600660
Full Papers
Multifunctional Single-Site Catalysts for
Alkoxycarbonylation of Terminal Alkynes
Xingkun Chen,[a, c] Hejun Zhu,*[a] Wenlong Wang,[a] Hong Du,[a, c] Tao Wang,[a, c] Li Yan,[a]
Xiangping Hu,[d] and Yunjie Ding*[a, b]
A multifunctional copolymer (PyPPh2–SO3H@porous organic
polymers, POPs) was prepared by combining acidic groups
and heterogeneous P,N ligands through the copolymerization
of vinyl-functionalized 2-pyridyldiphenylphosphine (2-PyPPh2)
and p-styrene sulfonic acid under solvothermal conditions. The
morphology and chemical structure of the copolymer were
evaluated using a series of characterization techniques. Com-
pared with traditional homogeneous Pd(OAc)2/2-PyPPh2/
p-toluenesulfonic acid catalyst, the copolymer supported palla-
dium catalyst (Pd–PyPPh2–SO3H@POPs) exhibited higher activi-
ty for alkoxycarbonylation of terminal alkynes under the same
conditions. This phenomenon could be attributed to the syner-
gistic effect between the single-site Pd centers, 2-PyPPh2 li-
gands, and SO3H groups, the outstanding swelling properties
as well as the high enrichment of the reactant concentration
by the porous catalyst. In addition, the catalyst could be
reused at least 4 times without any apparent loss of activity.
The excellent catalytic reactivity and good recycling properties
make it an attractive catalyst for industrial applications. This
work paves the way for advanced multifunctional porous or-
ganic polymers as a new type of platform for heterogeneous
catalysis in the future.
Introduction
Since the first report of alkoxycarbonylation of terminal alkynes
by Reppe and co-workers in 1939, this reaction has attracted
considerable attention[1] owing to its high atom economy pro-
cess (Scheme 1A) and the usefulness of a,b-unsaturated car-
boxylic acids and their derivatives in large-scale fine chemical
synthesis.[2] So far, palladium based homogeneous catalyst sys-
tems consisting of Pd(OAc)2, 2-PyPPh2 (Py=pyridine), and
acidic promoters exhibit high activity and selectivity for this re-
action at mild conditions.[3] Notably, 2-PyPPh2 plays a critical
dual role in achieving high catalytic efficiency through its abili-
ty to function as a bidentate P,N-coordinated ligand, whereas
a second P-coordinated N-protonated 2-PyPPh2 favors proton
transfer in the rate determining protonolysis step (Scheme 1
B).[3a,c] Moreover, the N atom of the pyridyl ring also works as
an acceptor of the alcoholic proton, thus favoring the cleavage
of the product. Replacement of 2-PyPPh2 by PPh3 or other het-
eroaromatic rings without N atoms results in a dramatic de-
crease in catalytic activity.[3b,4] Furthermore, Brçnsted acids,
which are normally employed as promoters, also play a key
role in the reaction; no product was obtained without the use
of Brçnsted acids in the reaction mixture. Therefore, soluble
acids with appropriate acidic strength and coordinative proper-
ties, such as methane sulfonate, trifluoromethane sulfonic acid,
and p-toluene sulfonic acid (TsOH), have often been employ-
ed.[3b,f]
[a] X. Chen, Prof. H. Zhu, Dr. W. Wang, H. Du, T. Wang, Prof. L. Yan,
Prof. Y. Ding
Such homogeneous catalytic systems play an extremely im-
portant role in the field of modern catalysis owing to their
high activity and selectivity. However, the recovery and reuse
of the homogeneous catalyst is still a major challenge that
needs to be addressed from the viewpoint of green and sus-
tainable chemistry. The use of precious organometallic cata-
lysts is not widespread owing to problems associated with
their recycling and metal contamination of the products.[5]Im-
mobilization of the homogeneous catalyst on an insoluble sup-
port (e.g., silica, alumina) definitely facilitates the recovery pro-
cedure using simple filtration, but their chemical nature limits
their potential for the chemical modification process.[6] In the
case of alkoxycarbonylation of terminal alkynes, Doherty and
co-workers have immobilized 2-PyPPh2 on an insoluble poly-
meric support. In such a catalytic system, additional soluble
acids need to be added to achieve high activity.[4] Minimizing
the liquid acidic corrosion of the reactor and pollution of the
Dalian National Laboratory for Clean Energy
Dalian Institute of Chemical Physics
Chinese Academy of Sciences
457 Zhongshan Road, Dalian, 116023 (China)
E-mail: zhuhj@dicp.ac.cn
dyj@dicp.ac.cn
[b] Prof. Y. Ding
The State Key Laboratory of Catalysis
Dalian Institute of Chemical Physics
Chinese Academy of Sciences
457 Zhongshan Road, Dalian, 116023 (China)
[c] X. Chen, H. Du, T. Wang
University of Chinese Academy of Sciences
Beijing 100049 (China)
[d] Prof. X. Hu
Dalian Institute of Chemical Physics
Chinese Academy of Sciences
457 Zhongshan Road, Dalian, 116023 (China)
Supporting Information for this article can be found under http://
dx.doi.org/10.1002/cssc.201600660.
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Scheme 1. (A) Palladium catalyzed hydrocarbonylation of terminal alkynes. (B) Mechanism of the alkoxycarbonylation of alkynes in the presence of the
Pd(OAc)2/2-PyPPh2/acidic promoters catalytic system. (C) Syntheses of Pd–PyPPh2–SO3H@POPs catalyst. Reagents and conditions: i) H2O, THF, AIBN, 1208C;
ii) 1m H2SO4; iii) Pd(OAc)2, THF.
environment has become an important factor to be addressed
for commercial exploitation.[7]
ported palladium catalyst Pd–PyPPh2–SO3H@POPs and used it
for alkoxycarbonylation of terminal alkynes. Compared with
the soluble acids, the immobilization of the ÀSO3H group on
the heterogeneous Pd–PyPPh2–SO3H@POPs catalyst prevented
the corrosion of the equipment and environmental pollution.
From the viewpoint of atom economy and green chemistry,
the heterogeneous POPs catalyst, which combines excellent re-
activity and reductive corrosion as well as facile product sepa-
ration, has potential applications in chemical industry. Further-
more, the excellent activity and stability of the Pd–PyPPh2–
SO3H@POPs heterogeneous catalyst pave the way towards the
design of sustainable, efficient, and reliable catalysts.
Recently, porous organic polymers (POPs) have emerged as
a versatile platform for the deployment of catalysts owing to
their porous nature, high stability, and flexibility in building
block design.[8] Generally, catalytic POPs can be divided into
two major classes: POPs that are self-polymerized with only
one monomer and POPs that are co-polymerized by two (or
more) different monomers. Compared with self-polymerized
POPs, copolymerized POPs have a clear advantage of integrat-
ing two (or more) active sites into one multifunctional material
and playing a synergistic role during catalysis. In addition,
compared with the homogeneous system, ligands, and other
active groups are greatly concentrated by confining them in
the heterogeneous space of POPs, which will further enhance
their synergistic effects.[9] Moreover, it has been recognized
that polymers that are polymerized through vinyl-functional-
ized monomers exhibit excellent mobility of the active sites,
which plays an important role in the improvement of the cata-
lytic performance.[10]
Results and Discussion
The Pd–PyPPh2–SO3H@POPs catalyst was prepared according
to Scheme 1C. The monomer of 2-vinyl-functionalized diphen-
yl-2-pyridylphosphine (2V-P,N) was synthesized according to
the method described in Scheme 2.[11] The copolymer of 2-
vinyl-functionalized 2-PyPPh2 with p-styrene sulfonic acid
(PyPPh2–SO3H@POPs) was prepared by solvothermal copoly-
merization of 2V-P,N with sodium p-styrene sulfonate below
1208C, followed by treating with H2SO4. After drying at 808C
under reduced pressure, PyPPh2–SO3H@POPs was obtained as
a white powder. The Pd–PyPPh2–SO3H@POPs catalyst was pre-
pared by impregnating PyPPh2–SO3H@POPs using a solution of
As far as we know, multifunctional POPs catalysts are rare
owing to the difficulty of functionalizing the building blocks.
Therefore, in this work, we report the preparation of a novel
co-polymerized multifunctional POPs material (PyPPh2–
SO3H@POPs) through an elegant design of vinyl-functionalized
ligand (which contain both P and N) and vinyl-functionalized
benzene sulfonic acid (Scheme 1). Palladium is immobilized
onto PyPPh2–SO3H@POPs as the active metal center through
impregnation. According to the mechanism in the alkoxycarbo-
nylation of terminal alkynes, the synergistic effect of the Pd
active sites, 2-PyPPh2 ligands, and ÀSO3H groups plays a key
role in accelerating the reaction rates. Bearing this requirement
in mind, and given the extraordinary advantage of co-polymer-
ized POPs, which could concentrate several active sites in
a confined pore field to strengthen the synergistic effect, we
firstly prepared the multifunctional PyPPh2–SO3H@POPs sup-
Scheme 2. Synthesis of 2V-P,N. Reagents and conditions: (i) BuLi, ZnCl2, Py,
THF, À408C; (ii) PCl3, THF, Py, À108C; (iii) Styryl magnesium bromide, THF,
08C.
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Pd(OAc)2 in tetrahydrofuran (THF). For comparison, three other
POPs, porous 2-vinyl-funtionalized 2-PyPPh2 polymer
phosphine atom in the copolymer carrier was investigated by
31P solid state NMR (Figure 1F). A single peak at À4.53 ppm
was detected, which was attributed to the P atoms of the
PyPPh2–SO3Na@POPs support.[4] For Pd–PyPPh2–SO3H@POPs, in
addition to the peak of À4.53 ppm assigned to the uncoordi-
nated P in PyPPh2–SO3H@POPs, a peak at 21.5 ppm was also
identified, which was attributed to the P atoms coordinated
with PdII species. The results indicated that there was a strong
coordinative bond between the Pd atoms and the exposed
phosphorous atoms on the surface of the porous PyPPh2–
SO3H@POPs support. Extended X-ray absorption fine structure
(EXAFS) analysis results also supported the presence of coordi-
nation bonds.[11]
(PyPPh2@POPs),
3-vinyl-funtionalized
PPh3
polymer
(PPh3@POPs), and PPh3 with p-styrene sulfonic acid (PPh3–
SO3H@POPs), which have only one or two functionalized sites,
were also synthesized and used as supports to prepare the
corresponding catalysts, denoted as Pd–PyPPh2@POPs, Pd–
PPh3@POPs, and Pd–PPh3–SO3H@POPs, respectively, using the
same procedure as for Pd–PyPPh2–SO3H@POPs.
The permanent porosity of PyPPh2–SO3H@POPs was con-
firmed by N2 sorption isotherms (Figure 1A). The curve collect-
ed at 77 K revealed that the copolymer possessed a surface
area of 44.3 m2 gÀ1 and a total pore volume of 0.133 m3 gÀ1.
The scanning electron microscopy (SEM) and the transmission
electron microscopy (TEM) images of PyPPh2–SO3H@POPs are
shown in Figure 1B and C, which indicate that the copolymer
has rough surfaces and a considerable number of pores. Fur-
thermore, thermogravimetric analysis shows that PyPPh2–
SO3H@POPs has superior thermal stability, with an initial de-
composition temperature of 3108C(Figure 1D), which is com-
parable to that of Nafion NR50 (3308C), one of the most stable
resins.[6d] 13C magic angle spinning (MAS) NMR spectra were
used to characterize the PyPPh2–SO3H@POPs polymer (Fig-
ure 1E). The new peak at 31.5 ppm was assigned to the poly-
merized vinyl groups. The interaction between Pd and exposed
The high-angle annular dark-field scanning transmission
electron microscopy (HAADF-STEM) images of Pd–PyPPh2–
SO3H@POPs clearly show the isolated individual Pd species (in-
dicated by the arrows) uniformly dispersed within the porous
structures of the PyPPh2–SO3H@POPs support (Fig-
ure 2A and B). In addition, scanning electron microscopy–
energy-dispersive X-ray spectroscopy (SEM-EDS) mapping
images (Figure 2C, D, E, and F) reveal the highly dispersed
character of all the functional elements (P, S, N, and Pd), which
are well integrated in our material.
The XPS spectra of Pd–PyPPh2–SO3H@POPs catalysts (fresh
and used) are shown in Figure 3. Clearly, Figure 3A shows the
Figure 1. (A) N2 sorption isotherms and pore size distributions, (B) SEM image and (C) TEM image, (D) TG curve and (E) 13C NMR of PyPPh2–SO3H@POPs,
(F) 31P NMR of PyPPh2–SO3Na@POPs (top) and 31P NMR of Pd–PyPPh2–SO3H@POPs (bottom). Spinning side bands are denoted by asterisks (*).
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catalysts. It is interesting to find that both 2-PyPPh2 and
Brçnsted acid promoters play a significant role in the reaction.
Pd catalysts with a pyridyl ligand exhibited much higher activi-
ties (Table 1, entries 1, and 9) than the corresponding triphe-
nylphosphine (PPh3) counterparts without
a pyridyl ring
(Table 1, Entries 3, 7, and 10). This is attributed to the critical
role of 2-PyPPh2, which serves not only as a bidentate P,N-coor-
dinated ligand but also as a mono-coordinated ligand in the
protonolysis step of the catalytic cycle.[3c,4] No desired products
were found in the reaction mixture without acid (Table 1, En-
tries 2, 4, 5, and 8), which is in accordance with literature re-
ports. This could be explained by the fact that the Brçnsted
acid initiates the formation of the active PdÀH complex and
accelerates the coordination process of alkyne to the Pd cen-
ter.[3b,f,g,17] Both the P,N-coordinated bidentate ligand and the
Brçnsted acid activate the catalytic cycle. Generally speaking,
heterogeneous catalysts exhibit lower activities than homoge-
neous catalysts owing to the low degree of exposure of the
catalytic active sites. However, the heterogeneous Pd–PyPPh2–
SO3H@POPs catalyst (Table 1, Entry 9) showed higher activity
than the homogeneous counterpart (Entry 1). This phenomen-
on could be attributed to the following reasons: 1) The forma-
tion of a catalytically active PdÀH species is the rate controlling
step during the catalytic reaction process in alkoxycarbonyla-
tion of terminal alkynes.[3a] In our catalyst system, the different
functional centers of the Pd center, 2-PyPPh2 ligand, and SO3H
group were adjacent on the same copolymer, which favored
the formation of a catalytically active PdÀH species, resulting
in a catalytic synergistic effect to improve the reaction rate.
2) The PyPPh2–SO3H@POPs solid has outstanding solvation and
swelling properties in the presence of organic solvents.[9] For
example, when the polymer was added into the THF solvent,
the volume was remarkably enlarged because of the absorp-
tion of THF and then swelling of the PyPPh2–SO3H@POPs poly-
mer (see Figure S4). The outstanding swelling properties of the
catalyst make the active sites on the framework flexible and
movable, which play an important role in the improvement of
the catalytic performance. 3) The interface between the hetero-
geneous catalyst and the reaction system favors the enrich-
ment of the reactants on the catalyst surface, which acceler-
ates the reaction rate.[18] To understand this phenomenon, we
measured the adsorption of methanol and phenylacetylene on
the Pd–PyPPh2–SO3H@POPs catalyst. The methanol and phe-
nylacetylene could be remarkably adsorbed on the catalyst
with 3.95 ggÀ1 and 4.38 ggÀ1 catalyst, respectively.
Figure 2. HAADF STEM image of (A) the fresh and (B) the used Pd–PyPPh2–
SO3H@POPs catalyst; SEM-EDS mapping of Pd–PyPPh2–SO3H@POPs. (C) P
with green color, (D) S with yellow color, (E) N with cyan color, (F) Pd with
dark-red color.
signals of P, N, S, C, and O, indicating the presence of sulfonic
group and a pyridyl ring in PyPPh2–SO3H@POPs. Figure 3B
shows the C1s peaks at 284.6, 285.3, 286.2, and 287.7 eV,
which were attributed to CÀC, CÀP, CÀS, and CÀN bonds, re-
spectively.[12] The O1s peak at 532.5 eV and S2p peak at
168.2 eV were associated with the ÀSO3H (Figure 3C and 3D).
Two peaks at approximately 399.0 and 400.1 eV were ascribed
to N atoms in CÀN and CÀNÀPd, respectively, indicating that N
coordinated with the Pd species (Figure 3E).[13] The P2p gives
two peaks at approximately 131.4 and 133.8 eV, which corre-
spond to P atoms in CÀP and CÀPÀPd, respectively (Fig-
ure 3F).[14] The above XPS results reveal that both 2-PyPPh2
ligand and SO3H group were successfully immobilized on the
same copolymer. In addition, the XPS spectra (Figure 3G
and H) of Pd show that the binding energy of PdII (337.8 eV)
and Pd0 (336.0 eV) in the catalyst are higher than their typical
value (PdII (337.0 eV) and Pd0 (335.0 eV)[15] as well as our results
of Pd binding energy in the Pd–PyPPh2–SO3Na@POPs sample
(see Figure S3), probably originating from the PdÀH species,
which are considered as the active species of the reaction. The
presence of ÀSO3H in the copolymer was also verified by FTIR
spectroscopy. Figure 3I shows the FTIR spectra of the porous
PyPPh2@POPs and PyPPh2–SO3H@POPs. Compared with
PyPPh2@POPs, the bands at 1037, 1009, and 673 cmÀ1 were at-
tributed to the ÀSO3H group in the PyPPh2–SO3H@POPs.[16]
Table 1 presents the reaction performance for the methoxy-
carbonylation of phenylacetylene and acetylene over various
It showed that the activity of Pd–PyPPh2@POPs with a homo-
geneous acid for carbonylation of acetylene and phenylacety-
lene are 3591 and 1907 hÀ1 (Table 1, Entries 6 and 16), respec-
tively, which were higher than those of the homogeneous
Pd(OAc)2/2-PyPPh2/TsOH as well as the heterogeneous Pd–
PyPPh2–SO3H@POPs catalysts. To understand this phenomen-
on, we firstly measured the adsorption of TsOH on
PyPPh2@POPs and found that TsOH can be remarkably ad-
sorbed on the polymer with 1.7 ggÀ1 polymer. It is reasonable
to propose that the increase in the TsOH concentration in the
PyPPh2@POPs leads to an enhancement of the activity. Then,
the S content on the surface of the Pd–PyPPh2–SO3H@POPs
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Figure 3. (A) XPS spectra of PyPPh2–SO3H@POPs, XPS spectra of (B) C1s, (C) O1s, (D) S2p, (E) N1s, (F) P2p and (G) Pd in the fresh Pd–PyPPh2–SO3H@POPs cata-
lyst, (H) XPS spectra of Pd in the used Pd–PyPPh2–SO3H@POPs catalyst. (I) FTIR spectra of (a) PyPPh2@POPs and (b) PyPPh2–SO3H@POPs.
catalyst was measured by XPS. Only 0.37 mmolgÀ1 S content
on the surface of the catalyst was detected, which was lower
than 0.93 mmolgÀ1 of the total S content of the Pd–PyPPh2–
SO3H@POPs catalyst. This suggested that the low exposure of
SO3H group on the heterogeneous catalyst affected the cata-
lytic performance. Although the Pd–PyPPh2@POPs catalyst en-
riched by homogeneous TsOH acid exhibited higher catalytic
activity, a part of TsOH is still present in the methanol solution,
which could lead to corrosions of the reactor and pollution of
the environment.
mately 4.8 MPa (Figure 5). The Pd loading and amount of SO3H
in the polymer also had a significant influence on the activity
of Pd–PyPPh2–SO3H@POPs. No ester product was found in the
absence of palladium (Table 2, Entry 1) whereas the appropri-
ate Pd loading benefited the reaction, and an excess loading
of Pd(OAc)2 causes the aggregation of palladium nanoparticles,
which eventually deactivated the reaction system. Figure S5
shows that the palladium particles emerged on the surface of
the catalyst (with Pd loading of 0.35%) after the reaction pro-
cess. The presence of a sufficient amount of SO3H is essential
in the polymer to form the PdÀH active species (Table 2,
Entry 5).[3f]
In an attempt to glean further information about the me-
thoxycarbonylation, acetylene was also examined as a substrate
(Table 1, Entries 11–20). Similar results were observed as for the
methoxycarbonylation of phenylacetylene. These results clearly
indicate that both the bidentate P,N-coordinated ligand and
the Brçnsted acid play a key role in the alkoxycarbonylation of
terminal alkynes. The effects of reaction temperature, carbon
monoxide (CO) pressure, Pd loading, and the amount of SO3H
on the turnover numbers (TON) of the methoxycarbonylation
of phenylacetylene were investigated. A plot of TON value
versus reaction temperature showed that 858C was the opti-
mal reaction temperature (Figure 4). The pressure of CO
strongly impacted on the TON value of the methoxycarbonyla-
tion of phenylacetylene, and the optimal pressure was approxi-
The catalytic efficiency of Pd–PyPPh2–SO3H@POPs was also
investigated by employing various aliphatic alcohols. To our
delight, the linear alcohols (Table 3, Entries 1, 2, 5, and 6) react-
ed with alkynes to give the desired products with good cata-
lytic activities. Slightly lower activity was obtained in the case
of branched alcohols. This may be attributed to the steric hin-
drance of branched alcohols, which restricts the nucleophilic
attack in the reaction process.[3g] The stability of the supported
complex during the carbonylation reaction is of great concern
for most anchored catalysts. Thus, the recovery and reuse of
the heterogeneous Pd–PyPPh2–SO3H@POPs catalyst was inves-
tigated for the methoxycarbonylation of phenylacetylene
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Table 1. Methoxycarbonylation of phenylacetylene and acetylene.[a]
Entry
Catalyst system
Substrate[b]
Acid[c]
TON[d]
1
2
3
4
5
6
7
8
Pd(OAc)2/2-PyPPh2
Pd(OAc)2/2-PyPPh2
Pd(OAc)2/PPh3
PhÀCꢀCH
PhÀCꢀCH
PhÀCꢀCH
PhÀCꢀCH
PhÀCꢀCH
PhÀCꢀCH
PhÀCꢀCH
PhÀCꢀCH
PhÀCꢀCH
PhÀCꢀCH
HCꢀCH
TsOH
no
TsOH
no
955
no
30
no
no
1907
45
no
1242
21
862
no
no
no
no
3591
14
no
1136
5
Pd(OAc)2/PPh3
Pd–PyPPh2@POPs
Pd–PyPPh2@POPs
Pd–PPh3@POPs
no
TsOH
TsOH
no
no
no
TsOH
no
TsOH
no
Pd–PPh3@POPs
9
Pd–PyPPh2–SO3H@POPs
Pd–PPh3–SO3H@POPs
Pd(OAc)2/2-PyPPh2
Pd(OAc)2/2-PyPPh2
Pd(OAc)2/PPh3
10
11[e]
12[e]
13[e]
14[e]
15[e]
16[e]
17[e]
18[e]
19[e]
20[e]
HCꢀCH
HCꢀCH
Figure 5. The effect of the pressure of CO on the catalytic activity of the Pd–
PyPPh2–SO3H@POPs catalyst for methoxycarbonylation of phenylacetylene.
Reaction conditions: Pd–PyPPh2–SO3H@POPs (0.36 mmol Pd), phenylacety-
lene (0.1 g), CH3OH (15 mL), T=808C.
Pd(OAc)2/PPh3
HCꢀCH
Pd–PyPPh2@POPs
Pd–PyPPh2@POPs
Pd–PPh3@POPs
Pd–PPh3@POPs
Pd–PyPPh2–SO3H@POPs
Pd–PPh3–SO3H@POPs
HCꢀCH
no
HCꢀCH
TsOH
TsOH
no
no
no
HCꢀCH
HCꢀCH
HCꢀCH
HCꢀCH
Table 2. Catalytic performance for the methoxycarbonylation of phenyla-
cetylene under different Pd loading and content of ÀSO3H.[a]
[a] Reaction conditions: 15 mL methanol, 4.8 MPa CO, 0.28 mmol ligand,
theoretical catalyst loading equal to 0.0019 mmol Pd(OAc)2, 0.0078 mmol
TsOH, 508C, 1 h; [b] 5 mmol phenylacetylene or 0.12 MPa acetylene;
[c] TsOH: p-toluenesulfonic acid, SO3H content was analyzed by element
analysis. “No” means the reaction was carried out without TsOH being
added. [d] Calculated by GC analysis, l/r=2–20%. [e] 20 mL acetone, 5 mL
methanol, 0.55 mmol ligand, 0.0036 mmol Pd(OAc)2, 0.016 mmol TsOH.
Entry
Pd Loading[b]
[wt%]
TON
b/l[c]
Selectivity[d]
[%]
1
0
0
–
–
2
3
4
5[e]
0.1
851.7
995.2
347.6
145.6
22.7
23.8
24.8
17.0
>99
>99
>99
>99
0.19
0.35
0.23
[a] Reaction conditions: 15 mL methanol, 4.8 MPa CO, 0.02 g catalyst,
1 mmol phenylacetylene, 808C,1 h. [b] Pd loading was calculated by the
amount used in preparing the catalyst. [c] Molar ratio of branched to
linear ester. [d] The amount of unsaturated ester in the product. [e] The
theoretical content of S in Pd–PyPPh2–SO3H@POPs is 0.50 mmolgÀ1
.
Table 3. Alkoxycarbonylation of various substrates catalyzed by Pd–
PyPPh2–SO3H@POPs.[a]
Entry
Alkyne[b]
Alcohol
t [h]
TON[c]
1
2
3
4
5
6
7
PhÀCꢀCH
PhÀCꢀCH
PhÀCꢀCH
PhÀCꢀCH
HCꢀCH
ethanol
2
4
4
4
1
1
3
475
842
145
442
949
588
402
propanol
isopropanol
isobutanol
ethanol
butanol
isobutanol
Figure 4. The effect of the reaction temperature on the catalytic activity of
the Pd–PyPPh2–SO3H@POPs catalyst for methoxycarbonylation of phenylace-
tylene. Reaction conditions: Pd–PyPPh2–SO3H@POPs (0.36 mmol Pd), phenyl-
acetylene (0.1 g), CH3OH (15 mL), P(CO)=4.8 MPa.
HCꢀCH
HCꢀCH
[a] Reaction conditions: 25 mL alcohol, 4.8 MPa CO, theoretical catalyst
loading equal to 3.5ꢁ10À4 mmol Pd(OAc)2, 508C; [b] 5 mmol phenylacety-
lene or 0.12 MPa acetylene; [c] Calculated by GC analysis.
(Figure 6). The catalyst was readily separated by simple centri-
fugation and then reused for the next reaction. The catalyst
showed good stability and could be reused at least 4 times
without a significant loss of activity. This might be associated
with the stability of the polymer network and a strong coordi-
nation between Pd and P ligand in the polymer. To investigate
the metal leaching problem, inductively coupled plasma
atomic emission spectroscopy (ICP-OES) was used to detect
the content of metal in the reaction solution. It was found that
the amount of Pd that leached in the first reaction solution
was 0.081 ppm, and 0.114 ppm in the second cycle, which
showed a negligible amount of leaching. This might be re-
sponsible for the slight loss of activity of the catalyst after
5 cycles. To test the stability of the catalyst Pd–PyPPh2–
SO3H@POPs and ensure the heterogeneous nature of the cata-
lytic process, a hot filtration test was conducted. When the in-
soluble catalyst was removed from the hot reaction mixture by
filtration, the reaction stopped and no additional products
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ic efficiency. All these results demonstrated that this novel mul-
tifunctional single-site POPs catalyst could be a powerful po-
tential catalyst for a sustainable industrial process for the al-
koxycarbonylation of terminal alkynes.
Experimental Section
General
All reagents were of analytical grade and used as purchased with-
out further purification unless otherwise stated. Tetrahydrofuran
(THF) was distilled from sodium and methanol was distilled from
magnesium and iodine under argon. Acetone was refluxed with
4 A zeolite under argon.
Figure 6. Recyclability of Pd–PyPPh2–SO3H@POPs catalyst in the methoxycar-
bonylation of phenylacetylene. Reaction conditions: phenylacetylene (0.1 g,
0.98 mmol), methanol (15 mL), substrate/Pd=550, 508C, P(CO)=4.8 MPa,
b: branched prducts, l: linear products.
Synthesis of PyPPh2–SO3H@POPs copolymer
All operations were performed under argon. According to
Scheme 2, 1.17 g 3 was added into a solution containing 0.11 g
azobisisobutyronitrile (AIBN) and 15 mL THF, followed by the addi-
tion of 1.2 mL H2O, and 0.3 g p-styrene sulfonate. After stirring at
room temperature for 3 h, the solution was heated to 1208C with
stirring. The resulting white solid was dried under reduced pres-
sure at room temperature to give PyPPh2–SO3Na@POPs. A 0.5 g
sample of PyPPh2–SO3Na@POPs was treated with 50 mL 1m H2SO4
and stirred for 24 h at room temperature. PyPPh2–SO3H@POPs was
obtained after drying under reduced pressure at 808C.
Synthesis of PyPPh2@POPs polymer
PyPPh2@POPs was synthesized according to our previous report.[11]
Synthesis of PPh3–SO3H@POPs copolymer
Figure 7. Hot filtration test for the Pd–PyPPh2–SO3H@POPs catalyst in the
methoxycarbonylation of phenylacetylene. Reaction conditions: 15 mL meth-
anol, 4.8 MPa CO, 0.02 g catalyst, 1 mmol phenylacetylene, temperature:
808C.
All operations were performed under argon. 3-vinyl-functionalized
PPh3 was synthesized according to the method reported previous-
ly.[6d] 2.28 g of 3-vinyl-functionalized PPh3 was added into a solution
containing 0.19 g AIBN and 26 mL THF, followed by the addition of
2.2 mL H2O and 0.3 g p-styrene sulfonate. After stirring at room
temperature for 3 h, the solution was heated to 1208C with stir-
ring. The resulting white solid was dried under reduced pressure at
room temperature to give PPh3–SO3Na@POPs. A 0.5 g sample of
PPh3–SO3Na@POPs was treated with 50 mL 1m H2SO4 and stirred
for 24 h at room temperature. PPh3–SO3H@POPs was obtained
after drying under reduced pressure at 808C.
were generated (Figure 7). This indicated that the reaction oc-
curred in a true heterogeneous manner.
Conclusions
We have successfully synthesized for the first time, a copolymer
(PyPPh2–SO3H@POPs) that combines an active solid acid site (À
SO3H) and a bidentate P,N-coordinated ligand (2-PyPPh2) as an
environmentally benign support. The copolymer-supported
Pd–PyPPh2–SO3H@POPs catalyst exhibited higher activities
than the corresponding homogeneous Pd(OAc)2/2-PyPPh2/
TsOH catalytic system for alkoxycarbonylation of terminal al-
kynes under the same conditions, which could be explained by
the synergistic effect among different functional centers on
the restricted micropore environment of the co-polymerized
POPs. Furthermore, the outstanding swelling properties and
high enrichment of the reactants of the catalyst also play a sig-
nificant role in accelerating the reaction rates. Moreover, the
heterogeneous Pd–PyPPh2–SO3H@POPs catalyst could be
reused at least four times without any apparent loss of catalyt-
Synthesis of PPh3@POPs polymer
PPh3@POPs was prepared according to the method reported pre-
viously.[6d]
Preparation of Pd–PyPPh2–SO3H@POPs catalyst
All operations were performed under argon. The Pd–PyPPh2–
SO3H@POPs catalyst was prepared by immobilizing Pd(OAc)2 onto
the PyPPh2–SO3H@POPs support. The procedure was as follows.
1.2 g PyPPh2–SO3H@POPs was added into a solution of 0.0046 g
Pd(OAc)2 in 12 mL THF. After stirring for 24 h at room temperature,
the mixture was dried under reduced pressure at 658C, and then
the Pd–PyPPh2–SO3H@POPs catalyst was obtained. In addition, the
Pd–PyPPh2–SO3H@POPs catalyst could be prepared by using POL-
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2V-P,N–SO3Na as a support to immobilize Pd(OAc)2. After drying at
658C, the sample was treated with H2SO4 (1m) with stirring for
24 h at room temperature and then dried at 808C.
isolate the catalyst, and analyzed offline by Agilent 7890 A gas
chromatography with a HP-5 capillary column and FID detector
using benzene as an internal standard.
PyPPh2@POPs, PPh3–SO3H@POPs, PPh3@POPs were loaded with
Pd(OAc)2 according to the procedure describe above to prepare
Pd–PyPPh2@POPs, Pd–PPh3–SO3H@POPs, and Pd–PPh3@POPs cata-
lysts, respectively.
Homogeneous methoxycarbonylation of acetylene
The procedure of homogeneous methoxycarbonylation of acety-
lene was the same as that of the heterogeneous methoxycarbony-
lation of acetylene except that Pd(OAc)2 (0.0036 mmol), ligand
(0.55 mmol), and p-toluenesulfonic acid (0.016 mmol) were used as
a homogeneous catalyst.
Sample characterization
Nitrogen sorption isotherms were measured using an AutoSorb-
1 instrument. The samples were outgassed for 24 h at 1208C
before measurements. The thermal stability of PyPPh2–SO3H@POPs
was detected in a N2 flow (20 mLminÀ1) using a Diamond TG/DTA
instrument, with a heating rate of 108CminÀ1 up to 10008C. SEM
and SEM-EDS mapping studies were performed on a JSM-7800F
scanning electron microscope. The TEM study was performed on
a JEM-2100 transmission electron microscope. HAADF STEM was
performed on a JEM-ARM200F. Solid-state 31P NMR experiments
were performed on an Infinity plus 400 spectrometer operating at
161 MHz. The FTIR spectra were measured on a NICOLET iS50 Four-
Hot filtration test
Two parallel reactions were performed under the same conditions.
One reaction was performed in the presence of the catalyst for 1 h,
and then the solid catalyst was filtered off at the reaction tempera-
ture. The resulting filtrate was placed under the same reaction con-
ditions as the original reaction and analyzed by GC. The other reac-
tion was performed in the presence of the catalyst during the
entire reaction process.
ier transform infrared spectrometer in the range 4000–400 cmÀ1
.
All spectra were recorded with 32 scans with a resolution of
4 cmÀ1. XPS spectra were performed on a ESCALAB 250Xi AIa radia-
tion.
Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (21273227 and 21303190) and the Strategic Pri-
ority Research Program of the Chinese Academy of Sciences,
Grant No XDB17020400.
Heterogeneous methoxycarbonylation of phenylacetylene
In a typical run, a 140 mL autoclave made of Hastelloy NS334 ma-
terial was charged with 0.1 g Pd–PyPPh2–SO3H@POPs catalyst,
0.1 g phenylacetylene, 15 mL CH3OH, and then the reactor was
sealed. After purging three times with argon, the reactor was pres-
surized to 4.8 MPa with CO at room temperature. The contents
were heated to 508C within 5 min and stirred at 800 rpm for 1 h.
Afterward, the reactor was cooled to room temperature with ice–
water, the liquid samples were centrifuged to isolate the catalyst,
and then the solution was analyzed offline by Agilent 7890A gas
chromatography with a HP-5 capillary column and FID detector
using cumene as an internal standard.
Keywords: alkoxycarbonylation
· multifunctional catalyst ·
palladium · porous organic polymers · solid acid
[1] a) W. Reppe, Experientia 1949, 5, 93–110; b) A. Brennfꢂhrer, H. Neu-
mann, M. Beller, ChemCatChem 2009, 1, 28–41; c) P. Kalck, M. Urrutigoı-
ty, O. Dechy-Cabaret in Catalytic Carbonylation Reactions, Springer,
2006, pp. 97–123; d) G. Kiss, Chem. Rev. 2001, 101, 3435–3456.
[2] a) C. Bird, Chem. Rev. 1962, 62, 283–302; b) R. Chinchilla, C. Najera,
Chem. Rev. 2014, 114, 1783–1826; c) A. Scrivanti, V. Beghetto, E. Campa-
gna, U. Matteoli, J. Mol. Catal. A 2001, 168, 75–80; d) A. Scrivanti, V. Be-
ghetto, M. Zanato, U. Matteoli, J. Mol. Catal. A 2000, 160, 331–336;
e) A. A. NfflÇez Magro, L.-M. Robb, P. J. Pogorzelec, A. M. Z. Slawin, G. R.
Eastham, D. J. Cole-Hamilton, Chem. Sci. 2010, 1, 723; f) J. J. de Pater,
B. J. Deelman, C. J. Elsevier, G. van Koten, Adv. Synth. Catal. 2006, 348,
1447–1458.
¨
Other polymer supported Pd–PyPPh2@POPs, Pd–PPh3@POPs, Pd–
PPh3–SO3H@POPs catalysts were used in the reaction according to
the same procedure described above for the Pd–PyPPh2–
SO3H@POPs catalyst.
Homogeneous methoxycarbonylation of phenylacetylene
[3] a) E. Drent, P. Arnoldy, P. Budzelaar, J. Org. Chem. 1993, 455, 247–253;
b) E. Drent, P. Arnoldy, P. Budzelaar, J. Org. Chem. 1994, 475, 57–63;
c) A. Scrivanti, V. Beghetto, E. Campagna, M. Zanato, U. Matteoli, Orga-
nometallics 1998, 17, 630–635; d) P. Edwards, P. Newman, R. Tooze, S.
Coles, M. Hursthouse, J. Chem. Soc. Dalton Trans. 1998, 3771–3776; e) J.
Liu, C. Jacob, K. J. Sheridan, F. Al-Mosule, B. T. Heaton, J. A. Iggo, M. Mat-
thews, J. Pelletier, R. Whyman, J. F. Bickley, A. Steiner, Dalton Trans.
2010, 39, 7921–7935; f) C.-M. Tang, Y. Zeng, X.-G. Yang, Y.-C. Lei, G.-Y.
Wang, J. Mol. Catal. A 2009, 314, 15–20; g) C.-M. Tang, X.-L. Li, G.-Y.
Wang, Korean J. Chem. Eng. 2012, 29, 1700–1707.
[4] S. Doherty, J. G. Knight, M. Betham, Chem. Commun. 2006, 88–90.
[5] a) D. J. Cole-Hamilton, Science 2003, 299, 1702–1706; b) A. L. Robinson,
Science 1976, 194, 1261–1263.
[6] a) Z. Wang, G. Chen, K. Ding, Chem. Rev. 2009, 109, 322–359; b) Y. R.
µde Miguel, J. Chem. Soc. Perkin Trans. 1 2000, 4213–4221; c) C. E. Song,
S.-g. Lee, Chem. Rev. 2002, 102, 3495–3524; d) Q. Sun, M. Jiang, Z.
Shen, Y. Jin, S. Pan, L. Wang, X. Meng, W. Chen, Y. Ding, J. Li, F.-S. Xiao,
Chem. Commun. 2014, 50, 11844–11847.
The procedure of homogeneous methoxycarbonylation of phenyla-
cetylene was the same as that of the heterogeneous methoxycar-
bonylation of phenylacetylene except that Pd(OAc)2 (0.0019 mmol),
ligand (0.28 mmol,) and p-toluenesulfonic acid (0.0078 mmol) were
used as the homogeneous catalyst.
Heterogeneous methoxycarbonylation of acetylene
In a typical run, a 140 mL autoclave made of Hastelloy NS334 ma-
terial was charged with 0.1 g Pd–PyPPh2–SO3H@POPs catalyst,
20 mL acetone, 5 mL CH3OH, and then the reactor was sealed. It
was purged three times with argon and then pressurized to
0.12 MPa with C2H2 and to 4.92 MPa with CO at room temperature.
The contents were heated to 508C within 5 min and stirred at
800 rpm for 1 h. Afterward, the autoclave was cooled to room tem-
perature with ice—water, the liquid products were centrifuged to
[7] a) H. Ooka, T. Inoue, S. Itsuno, M. Tanaka, Chem. Commun. 2005, 1173–
1175; b) W. Y. Lou, Q. Guo, W. J. Chen, M. H. Zong, H. Wu, T. J. Smith,
&
ChemSusChem 2016, 9, 1 – 10
www.chemsuschem.org
8
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Papers
ChemSusChem 2012, 5, 1533–1541; c) P. Wang, S. Bai, J. Zhao, P. Su, Q.
Yang, C. Li, ChemSusChem 2012, 5, 2390–2396; d) L. Vilcocq, P. C. Castil-
ho, F. Carvalheiro, L. C. Duarte, ChemSusChem 2014, 7, 1010–1019.
[8] a) P. Kaur, J. T. Hupp, S. T. Nguyen, ACS Catal. 2011, 1, 819–835; b) N. B.
McKeown, P. M. Budd, Chem. Soc. Rev. 2006, 35, 675–683; c) A. I.
Cooper, Adv. Mater. 2009, 21, 1291–1295; d) A. Trewin, A. I. Cooper,
Angew. Chem. Int. Ed. 2010, 49, 1533–1535; Angew. Chem. 2010, 122,
1575–1577; e) J. X. Jiang, F. Su, A. Trewin, C. D. Wood, N. L. Campbell,
H. Niu, C. Dickinson, A. Y. Ganin, M. J. Rosseinsky, Y. Z. Khimyak, Angew.
Chem. Int. Ed. 2007, 46, 8574–8578; Angew. Chem. 2007, 119, 8728–
8732; f) Y. Zhang, S. N. Riduan, Chem. Soc. Rev. 2012, 41, 2083–2094;
g) Q. Sun, Z. Dai, X. Meng, F.-S. Xiao, Chem. Soc. Rev. 2015, 44, 6018–
6034; h) F. Liu, W. Li, Q. Sun, L. Zhu, X. Meng, Y. H. Guo, F. S. Xiao, Chem-
SusChem 2011, 4, 1059–1062.
[12] a) F. Liu, W. Kong, C. Qi, L. Zhu, F.-S. Xiao, ACS Catal. 2012, 2, 565–572;
b) F. Liu, R. K. Kamat, I. Noshadi, D. Peck, R. S. Parnas, A. Zheng, C. Qi, Y.
Lin, Chem. Commun. 2013, 49, 8456–8458.
[13] M. Soorholtz, L. C. Jones, D. Samuelis, C. Weidenthaler, R. J. White, M.-M.
Titirici, D. A. Cullen, T. Zimmermann, M. Antonietti, J. Maier, ACS Catal.
2016, 6, 2332–2340.
[14] D. C. Phillips, S. J. Sawhill, R. Self, M. E. Bussell, J. Catal. 2002, 207, 266–
273.
[15] Z. He, Z. Hou, Y. Luo, Y. Dilixiati, W. Eli, Catal. Sci. Technol. 2014, 4,
1092–1103.
[16] L. Wang, H. Wang, F. Liu, A. Zheng, J. Zhang, Q. Sun, J. P. Lewis, L. Zhu,
X. Meng, F. S. Xiao, ChemSusChem 2014, 7, 402–406.
[17] A. Dervisi, P. G. Edwards, P. D. Newman, R. P. Tooze, S. J. Coles, M. B.
Hursthouse, J. Chem. Soc. Dalton Trans. 1999, 1113–1120.
[18] F. Liu, L. Wang, Q. Sun, L. Zhu, X. Meng, F.-S. Xiao, J. Am. Chem. Soc.
2012, 134, 16948–16950.
[9] Q. Sun, Z. Dai, X. Liu, N. Sheng, F. Deng, X. Meng, F.-S. Xiao, J. Am.
Chem. Soc. 2015, 137, 5204–5209.
[10] T. Iwai, T. Harada, K. Hara, M. Sawamura, Angew. Chem. Int. Ed. 2013, 52,
12322–12326; Angew. Chem. 2013, 125, 12548–12552.
Received: May 17, 2016
[11] X. Chen, H. Zhu, T. Wang, C. Li, L. Yan, M. Jiang, J. Liu, X. Sun, Z. Jiang, Y.
Ding, J. Mol. Catal. A 2016, 414, 37–46.
Revised: July 2, 2016
Published online on && &&, 0000
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X. Chen, H. Zhu,* W. Wang, H. Du,
T. Wang, L. Yan, X. Hu, Y. Ding*
Multifunctional catalyst! A novel multi-
functional copolymer [(PyPPh2–
SO3H@porous organic polymers (POPs),
Py=pyridine] is used as a support to
prepare a heterogeneous palladium cat-
alyst (Pd–PyPPh2–SO3H@POPs). The mul-
tifunctional catalyst exhibits higher ac-
tivity than the corresponding homoge-
neous catalyst for alkoxycarbonylation
of terminal alkynes. The high efficiency
is attributed to the synergistic effect of
the Pd center, 2-PyPPh2, ligand and
SO3H group, which was strengthened
by the high concentration of the ligand
and SO3H groups on the copolymer.
&& – &&
Multifunctional Single-Site Catalysts
for Alkoxycarbonylation of Terminal
Alkynes
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