Carbonylative Suzuki coupling and alkoxycarbonylation of aryl halides using palladium supported on phosphorus-doped porous organic polymer as an active and robust catalyst

Article abstract of DOI:10.1002/aoc.4714

Developing highly active catalysts with the combined advantages of molecular and solid catalysis is considered as the “Holy Grail” in the area of catalysis research. Herein, a phosphorus-doped porous polymer-immobilized palladium was successfully developed as an efficient, robust, and recyclable catalyst for the carbonylative Suzuki coupling and alkoxycarbonylation reactions of aryl halides. Rather than just as an immobilizing molecular catalyst, palladium supported on phosphorus-doped porous organic polymer exhibits even better catalytic performances than that of its analogue homogeneous catalysts in both carbonylation reactions. Moreover, the catalyst can be easily separated and reused for at least 5 times without significant loss in reactivity. Importantly, the catalyst was highly stable under carbonylation reaction conditions, and no palladium nanoparticle was observed even after the 5th reuse.

Full text of DOI:10.1002/aoc.4714

Received: 31 August 2018
DOI: 10.1002/aoc.4714
Revised: 21 October 2018
Accepted: 25 October 2018
F U L L P A P E R
Carbonylative Suzuki coupling and alkoxycarbonylation of
aryl halides using palladium supported on phosphorus‐doped
porous organic polymer as an active and robust catalyst
1
,2
1
1
3
1
2
Yali Wan | Fangxiang Song | Tao Ye | Guangxing Li | Dingfu Liu
| Yizhu Lei
1
School of Chemistry and Chemical
Developing highly active catalysts with the combined advantages of molecular
and solid catalysis is considered as the “Holy Grail” in the area of catalysis
research. Herein, a phosphorus‐doped porous polymer‐immobilized palladium
was successfully developed as an efficient, robust, and recyclable catalyst for
the carbonylative Suzuki coupling and alkoxycarbonylation reactions of aryl
halides. Rather than just as an immobilizing molecular catalyst, palladium sup-
ported on phosphorus‐doped porous organic polymer exhibits even better cat-
alytic performances than that of its analogue homogeneous catalysts in both
carbonylation reactions. Moreover, the catalyst can be easily separated and
reused for at least 5 times without significant loss in reactivity. Importantly,
the catalyst was highly stable under carbonylation reaction conditions, and
no palladium nanoparticle was observed even after the 5th reuse.
Engineering, Guizhou University,
Guiyang, Guizhou 550025, China
2
School of Chemistry and Materials
Engineering, Liupanshui Normal University,
Liupanshui, Guizhou 553004, China
3
School of Chemistry and Chemical
Engineering, Huazhong University of
Science and Technology, Wuhan, Hubei
430074, China
Correspondence
Dingfu Liu, School of Chemistry and
Chemical Engineering, Guizhou University,
Guiyang, Guizhou, 550025 China.
Email: liudfgu@163.com
Yizhu Lei, School of Chemistry and
Materials Engineering, Liupanshui
Normal University, Liupanshui, Guizhou
KEYWORDS
aryl halide, carbonylation, palladium, porous organic polymer
553004 P.R. China.
Email: yzleiabc@126.com
Funding information
Liupanshui Key Laboratory of High Per-
formance Fibers and Advanced Porous
Materials, Grant/Award Number: 52020‐
2017‐02‐02; National Natural Science
Foundation of China, Grant/Award
Number: 1763017; Natural Science Foun-
dation of Guizhou Province, Grant/Award
Number: qian ke he ji chu [2016]1133 and
[2018]1414; Youth Talent Growth Project
of Educational Department of Guizhou
Province, Grant/Award Number: qian jiao
he KY [2016]264; Liupanshui Normal
University, Grant/Award Numbers:
LPSSYKJTD201501 and
LPSSYZDXK201602
1
| INTRODUCTION
versatile method for the synthesis of aromatic carbonyl
compounds, such as aromatic esters, amides, acids and
[
1–4]
Palladium catalyzed carbonylative coupling reactions of
aryl halides with various nucleophiles represents a
ketones.
Due to its inherent advantages, such as the
readily available substrates, high functional group
Appl Organometal Chem. 2018;e4714.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
1 of 10
https://doi.org/10.1002/aoc.4714

2
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WAN ET AL.
tolerance and good atom economy, this versatile method
has become growing importance in organic synthesis.
carbonylative cross‐coupling reactions of aryl halides
have been widely investigated in recently years,
[
5–8]
[24,28,30,31]
Carbon monoxide, an inexpensive and readily avail-
able C1 building block, is widely used as a carbonyl
source for palladium‐catalyzed carbonylation of aryl
studies of their catalytic applications in carbonylation of
aryl halides were relatively unexplored.
[
32]
To continue our ongoing efforts for exploring highly
efficient heterogeneous catalysts for carbonylation reac-
[1–4]
halides.
On the other hand, CO could also act as a
[
33–35]
strong π‐acidic ligand for the palladium metal, thus
resulting in a decrease of electron density for the palladium
center and making the oxidative addition of aryl halide
tions,
herein, we reported palladium supported on
phosphorus‐doped porous organic polymer (Pd@POP‐
Ph P) as an efficient, stable and recyclable catalyst for
3
[9,10]
difficult.
Meanwhile, under a CO atmosphere, palla-
carbonylative Suzuki coupling and alkoxycarbonylation
of aryl iodides and bromides.
dium atom is easily aggregated to form the catalytically
[11,12]
inactive species.
To address these problems, electron‐
rich ligands were usually added to the catalytic systems,
thus increasing electron density of the palladium center
and preventing the aggregation of palladium atoms.
Although homogeneous palladium complexes have
been demonstrated to be quite successful in many car-
2
| EXPERIMENTAL
.1 | Materials
[
13,14]
2
[
1–4,15,16]
4‐Bromostyrene, phosphorus trichloride, 2,2′‐azobis(2‐
methylpropionitrile) (AIBN), and palladium acetate (99%)
were got from Energy Chemical (Shanghai) Co. Ltd. Aryl
halides, arylboronic acids, alcohols, phenol, bases and
organic solvents were of analytical grade. Unless stated oth-
erwise, all materials were used as received. CO and Ar with
the purity of 99.99% were got from a local manufacturer.
Pd/C (palladium content, 5 wt%) was supplied by Shaanxi
Rock New Materials Co. Ltd (Baoji, China).
bonylation reactions,
while they still suffer from
[17]
some drawbacks including : (i) contamination of the
final products by the palladium and ligand residues; (ii)
problems of separation and reuse of the catalyst; and
(iii) destruction of palladium complex during the catalytic
reaction. Heterogeneous switching of a homogeneous pal-
ladium complex by immobilizing the complex onto a
solid support with a covalent bond has been expected to
[
18,19]
address these problems,
where traditional polymers
[
20]
and silicas are the most widely used support materials.
However, these traditional supports “anchored” molecular
2
.2 | Preparation of the porous polymers
catalysts often suffer from poor stability and
(POP‐ Ph P)
[21]
3
inhomogeneously distributed active sites.
Moreover,
under a CO atmosphere, palladium supported on these
traditional supports were easily aggregated to palladium
nanoparticles during the catalytic reactions, thus lowering
POP‐Ph P was obtained according to the reported syn-
3
[25]
thetic procedures by the literature
with slight modifi-
cations. The polymerization reaction was carried out in
a stainless‐steel autoclave (Teflon‐lined). Generally,
[12]
their stability and catalytic activities.
Therefore, devel-
oping heterogeneous catalytic system, which has high
catalytic activity and excellent stability, remains challeng-
ing for the carbonylation reactions of aryl halides.
tris(4‐vinylphenyl) phosphane (3 V‐PPh , 2.0 g) and
3
AIBN (50 mg) were dissolved in THF (20 ml) in a
100 mL Teflon lining. After replacing air in the Teflon
Porous organic polymers (POPs), which feature high
surface area, excellent framework stability, adjustable
chemical composition and flexible synthetic strategy,
have attracted tremendous interest recently because of
their potential to combine the advantages of heteroge-
lining with Ar for 5 min (1 L/min), the Teflon lining
was transferred into an autoclave, and heated still in an
oven at 100 °C for 24 hr. After the polymerization reac-
tion, the obtained white solid monolith was washed with
ethanol for five times, then dried under vacuum (60 °C).
[22,23]
neous and homogeneous catalysis.
In recent years,
a series of POPs containing PPh ligand and its deriva-
3
tives, have been successfully prepared and applied as
the catalysis supports for immobilizing transition metal
2.3 | Preparation of catalysts
[24–28]
species.
Due to the strong interaction between tran-
In a typical experiment, palladium acetate (0.043 g) was
dissolved in 30 ml acetone. Subsequently, POP‐Ph3P
(1.0 g) was added. After stirring at room temperature for
sition metals and phosphine ligands, these catalysts usu-
ally exhibited high catalytic activities, long‐term
[
24–31]
reusability and excellent leaching resistant ability.
24 hr, the pale yellow Pd@POP‐Ph P was collected via fil-
3
Some of them even outperformed the activities of their
tration, washed with methanol, purified by Soxlet‐
extraction with acetone for 24 hr, and then dried under
vacuum (60 °C). ICP analysis suggested that the
[24,29–31]
homogeneous analogues.
Although the applica-
tions of phosphine functionalized POPs in non‐

WAN ET AL.
3 of 10
palladium content of Pd@POP‐Ph P was 2.0 wt%. Palla-
dium supported on crosslinked polymer of benzene and
triphenylphosphine with a 0.8 wt% palladium loading,
before the measurements. The surface area and pore
size distribution were calculated by the Brunauer–
Emmett–Teller (BET) and nonlocal density functional
theory (NLDFT) methods, respectively. Fourier trans-
form infrared (FTIR) spectra were recorded on a Bruker
Equinox 55 FTIR spectrophotometer. The morphology
of the sample was observed with a TESCAN MIRA3
field emission scanning electron microscope (FE‐SEM)
and a FEI Tecnai G2 F30 transmission electron micros-
copy (TEM). X‐ray photoelectron spectroscopy (XPS)
experiments were carried out over a VG multilab 2000
spectrometer fitted with a Mg‐AlKa X‐ray source. The
amount of palladium loading and leaching were deter-
mined by inductively coupled plasma atomic emission
spectroscopy (ICP, PerkinElmer Optima 8000). Gas
chromatography (GC) was performed on a Scientific™
TRACE™ 1310 equipped with a TRACE TR‐WAX capil-
3
Pd@KAPs (Ph‐PPh ), was obtained as our previously
3
[32]
reported.
2
.4 | Typical procedure for carbonylative
Suzuki coupling reaction
In a 50 ml Teflon‐lined stainless‐steel autoclave, aryl
halide (2 mmol), aryl boronic acid (3 mmol), K CO3
2
(
4 mmol) and Pd@POP‐Ph P were added. After purging
3
four times with CO, the autoclave was pressurized with
CO to 5 atm. Then, the reaction was reacted at the setting
temperature for a definite time. After that, the autoclave
was cooled to room temperature and carefully
depressurized. The catalyst was separated by centrifuga-
tion at 12000 rpm for 10 min and washed with anisole.
For the model reaction, the resulting mixture was quanti-
tatively analyzed with GC by using N‐methyl pyrrolidone
as an internal standard. For the investigation of substrate
scope, the organic solution was collected, concentrated,
and purified by preparative thin‐layer chromatography
1
lary column and a FID. H NMR spectra were collected
on a Bruker AVANCE III NMR spectrometer operating
at 400 MHz.
(PTLC) using petroleum ether‐ethyl acetate as the eluting
solvent. All of the biaryl ketones are known products, and
1
analyzed by H NMR.
2
.5 | Typical procedure for
alkoxycarbonylation reaction
In a typical run, Pd@POP‐Ph P, aryl halides (2 mmol),
3
DBU (4 mmol) and alcohol were added to a 10 ml reac-
tion flask which equipped with a reflux condenser and
carbon monoxide balloon. After complete replacement
of air by CO, the reaction flask was reacted under a CO
atmosphere for a definite time. After the reaction, the
reaction flask was cooled to room temperature and the
balloon was removed. The catalyst was separated by cen-
trifugation at 12000 rpm for 10 min and washed with
alcohol. The organic solution was collected, concentrated,
and purified by PTLC using petroleum ether and ethyl
acetate as the eluting solvent. The products were ana-
1
lyzed by H NMR and yields were based on aryl halides.
All the synthesized aromatic esters are known products,
[32]
and we have reported previously.
2.6 | Characterization
Nitrogen physisorption measurements were carried out
at 77 K on a Micrometrics ASAP 2020 system, the sam-
ples were treated under vacuum at 90 °C for 10 hr
FIGURE 1 Nitrogen adsorption (square)‐desorption (circle)
isotherms and pore size distribution curves (insert): (a) POP‐Ph P,
3
3
(b) Pd@ POP‐Ph P

4
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WAN ET AL.
3
3
| RESULTS AND DISCUSSION
.1 | Characterization of the catalyst
Nitrogen adsorption–desorption analysis of POP‐PPh3
and Pd@POP‐Ph P showed that the samples have high
3
BET surface areas and large pore volumes (Table S1).
The sorption isotherms of the samples (Figure 1) exhib-
ited the combined type I and type IV sorption behaviour.
The steep increase at low relative pressure (P/P < 0.01)
0
indicates the filling of micropores, the hysteresis loop at
the relative pressure of 0.7–1.0 implies the presence of
mesopores, while the sharp rise at the relative pressure
of 0.8–1.0 indicates the presence of macropores. Corre-
spondingly, pore size distribution curves (inset) of the
samples also indicate their hierarchical pore structure.
FIGURE 3 FTIR spectra of 3 V‐Ph
3
P (a) and POP‐Ph
3
P (b)
The morphology of POP‐Ph P was further characterized
and C elements are present in the two samples. Com-
3
by SEM and TEM. The images in Figure 2 suggested that
the sample was comprised of loosely packed and
irregular‐shape nanoparticles. Representative TEM
pared with POP‐Ph P polymer, two additional Pd and O
bands were observed in the XPS full spectrum of
3
Pd@POP‐Ph P. XPS spectrum of Pd 3d revealed that Pd
3
images of POP‐Ph P further confirmed the presence of
mesopores in the polymer.
was present in a + 2 oxidation state. As shown in
Figure 4a, the binding energy of Pd 3d5/2 was about
337.3 eV, which was about 1.1 eV lower than that of free
3
FTIR spectra of 3 V‐PPh3 and POP‐Ph P were
3
[
36]
depicted in Figure 3. The results revealed that the
Pd (OAc) (338.4 eV).
Simultaneously, the P 2p bind-
2
−
1
stretching band of C=C (1627 cm ) was disappeared
after the polymerization reaction. It indicated that the
polymerization of vinyl groups was finished.
ing energy of Pd@POP‐Ph P was about 0.7 eV higher
3
than that (131.7 eV) of POP‐Ph P (Figure 4b). These
3
results indicated that there was a strong coordination
[
24,30,31]
XPS analysis was used to study the composition of
POP‐Ph P and Pd@POP‐Ph P. As shown in Figure S1, P
effect between P and Pd species.
Scanning elec-
3
3
tron microscopy (SEM) elemental mapping was also used
3
FIGURE 2 SEM and TEM images of POP‐Ph P with different magnifications: SEM for (a) and (b), TEM for (c) and (d)

WAN ET AL.
5 of 10
3.2 | Carbonylative Suzuki coupling of
aryl halides
Biaryl ketones are important structural building blocks in
many natural products, pharmaceuticals and mate-
[
37,38]
rials.
Palladium catalyzed carbonylative Suzuki cou-
pling of aryl halides represents one of the pivotal
[
1–4]
reactions for the synthesis of biaryl ketones.
During
the past few decades, great efforts have been devoted to
develop highly efficient catalytic systems for this transfor-
[
39–41]
mation. Various homogeneous
molecular catalysts
and immobilized
[
42–46]
have been developed. However,
most of the immobilized molecular catalysts suffered
from either the formation of less active palladium nano-
[
12]
particles or the obvious palladium leaching.
Therefore,
developing highly active, stable and recyclable catalytic
system is imperative and worthy of further investigation.
To this end, the activity of the prepared Pd@POP‐Ph3P
was tested over this important reaction. We started our
investigation with the carbonylative Suzuki coupling of
iodobenzene and phenylboronic acid as a model reaction.
For comparison, the catalytic activities of different cata-
lysts were also tested. As shown in Table 1, Pd@POP‐
Ph P afforded the highest yield (93%) of the target
3
diphenylmethanone with an excellent selectivity
(
Table 1, entry 1). Under the same reaction conditions,
its homogenous counterpart and analogue, Pd (OAc)2/
FIGURE 4 XPS spectra of POP‐Ph3P and Pd@POP‐Ph3P: (a) Pd
3 V‐PPh and PdCl (PPh ) , afforded the desired product
in only 43% and 37% yields, respectively (Table 1, entries
3
2
3 2
3
d XPS spectrum of Pd@POP‐Ph3P; (b) P 2p XPS spectra
2
and 3). Other heterogeneous catalysts, Pd@KAPs (Ph‐
to investigate the composition of Pd@POP‐Ph P catalyst.
PPh ) and the ligand free Pd/C also provided the low cat-
3
3
As shown in Figure S2, Pd was well distributed in the
alytic performances (Table 1, entries 4 and 5). With the
optimal catalyst in hand, we then studied the effects of
CO pressure and catalyst usage (Table 1, entries 6 and
7). The results showed that the selectivity was slightly
decreased with a lower CO pressure. Interestingly,
POP‐Ph P polymer with a high degree of dispersion.
3
Moreover, Pd, P, C, and O were clearly observed from
these images, which suggested that they were the main
elements for the Pd@POP‐Ph P catalyst.
3
a
TABLE 1 Effect of the catalyst on the model carbonylative Suzuki coupling reaction
b
b
Entry Catalyst
Catalyst usage (mol%)
CO pressure (bar)
Diphenylmethanone (mol%)
Biaryl (mol%)
1
2
3
4
5
6
7
Pd@POP‐Ph
Pd (OAc) /3 V‐PPh
PdCl (PPh
3
P
0.5
0.5
0.5
0.5
0.5
0.5
0.25
5
5
5
5
5
2
5
93
43
37
28
19
92
87
4
11
9
2
3
2
3 2
)
Pd@KAPs (Ph‐PPh
3
)
6
Pd/C
17
5
Pd@POP‐Ph
Pd@POP‐Ph
3
3
P
P
3
a
2 2 3
Reaction conditions: iodobenzene (2.0 mmol), PhB (OH) (3.0 mmol), K CO (4.0 mmol), toluene (5 ml), 6 h, 80 °C, stirring speed (600 rpm).
b
GC yields.

6
of 10
WAN ET AL.
lowering the catalyst usage to 0.25 mol%, 87% yield of
diphenylmethanone was still obtained.
1–8). Moderately hindered aryl iodides, such as 3‐Me
and 2‐Me substituted iodobenzenes, could also react
smoothly with a prolonged reaction time (Table 3, entries
9 and 10). The catalytic system was also highly effective
for various substituted arylboronic acids, and high yields
of desired diaryl ketones were obtained within 9 hr
(Table 3, entries 11–16). Interestingly, Pd@POP‐Ph3P
can also be used in the carbonylation reactions of aryl
bromides bearing both electron‐donating and electron‐
withdrawing groups (Table 3, entries 17–21). And moder-
ate yields of desired diaryl ketones could be obtained
(Table 3, entries 18–21), though higher catalyst usage,
prolonged reaction times and elevated reaction tempera-
ture were needed.
Then, the effect of solvent and base were investigated.
With K CO as a base, several organic solvents were
2
3
investigated for this carbonylation reaction (Table 2,
entries 1–6). Among the solvents screened, anisole was
identified as optimal, providing 96% yield of
diphenylmethanone (Table 2, entry 5). With anisole as
the solvent, evaluation of the base was carried out
(
Table 2, entries 7–13), and K CO exhibited the best per-
2
3
formance (Table 2, entry 5). Further lowering the catalyst
loading to 0.125 mol%, 79% yield of diphenylmethanone
−
1
with a TOF of 105 hr was obtained (Table 2, entry
1
4). The catalytic activity of Pd@POP‐Ph P outperformed
3
[42,44–47]
most of the immbolized palladium complexes
as
Then, the reusability and stability of Pd@POP‐Ph3P
was evaluated on the model reaction. To rigorously test
well as some homogeneous triphenylphosphine
[41]
derivatives.
TABLE 3 Carbonylative Suzuki coupling of aryl halides catalysed
Next, various aryl halides and arylboronic acids were
used to investigate the scope and limitation of Pd@POP‐
a
3
by Pd@POP‐Ph P
Ph P catalyst for this carbonylative Suzuki coupling reac-
3
tion (Table 3). The results showed that aryl iodides bear-
ing both electron‐donating and electron‐withdrawing
groups at the para position participated in the reactions
readily at 80 °C, affording the corresponding diaryl
ketones in moderate to excellent yields (Table 3, entries
b
Entry
R
1
R
2
X
Time (h) Yield (%)
1
2
3
4
5
6
7
8
9
4‐F
H
I
6
6
91
89
85
94
96
92
80
91
95
90
93
96
87
91
94
98
11
78
49
75
64
4‐Cl
4‐Br
H
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
H
6
TABLE 2 Effect of base and solvent on the model carbonylative
4‐NO
2
H
6
a
Suzuki coupling reaction
4‐COMe
4‐OMe
H
6
Base
ketone (mol%)
Diphenylmethanone Biaryl
H
6
b
b
Entry Solvent
(mol%)
4‐NH
4‐Me
3‐Me
2‐Me
H
2
H
6
1
2
3
4
5
6
7
9
1
1
1
1
1
DMF
K
K
K
K
K
2
2
2
2
2
2
3
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
21
25
48
12
96
81
41
58
85
21
8
11
2
H
6
DMAc
DMSO
MeCN
Anisole
H
8
10
11
12
13
14
15
16
17
18
19
20
21
H
12
6
15
3
4‐Me
4‐OMe
3‐OMe
2‐OMe
4‐COMe
4‐Me
H
H
6
1,4‐dioxane K
19
56
39
13
18
8
H
6
Anisole
Anisole
Anisole
Anisole
Anisole
Anisole
Anisole
K
PO
CO
CO
NaHCO
4
H
9
Cs
2
3
H
6
0
1
2
3
4
Na
2
3
4‐Me
H
6
3
Br 24
Br 24
Br 24
Br 24
Br 24
DABCO 89
c
c
c
c
H
H
DBU
CO
50
79
6
4‐COMe
4‐NO
4‐OMe
H
c,d
K
2
3
2
2
H
a
Reaction conditions: Pd@POP‐Ph
PhB (OH) (3.0 mmol), K CO (4.0 mmol), solvent (5 ml), CO (5 bar), 6 hr,
0 °C, stirring speed (600 rpm).
3
P (0.25 mol%), iodobenzene (2 mmol),
H
2
2
3
8
a
Reaction conditions: Pd@POP‐Ph
3
P (0.25 mol%), aryl halide (2 mmol), ArB
b
GC yields.
(OH) (3 mmol), K CO (4.0 mmol), anisole (5 ml), CO (5 bar), 6 hr, 80 °C,
2
2
3
c
stirring speed (600 rpm).
Pd@POP‐Ph
3
P (0.125 mol%).
Turnover frequency (TOF): moles of diphenylmethanone obtained per mole
of palladium per hour.
b
d
GC yields.
c
3
Pd@POP‐Ph P (2.5 mol%), 120 °C.

WAN ET AL.
7 of 10
the recyclability of Pd@POP‐Ph P, recycling reaction was
porous structure favours the high dispersion of palladium
species.
3
carried out at a shorter reaction time, together with a
[48]
lower conversion.
After each run, the catalyst was
recovered by centrifugation and washed with H O, THF,
2
and anisole. The obtained liquid was quantitatively
analysed using GC. As shown in Figure 5a, the catalyst
could be effectively reused for at least 5 times with only
slight loss in its activity, and the slight loss of activity
might be mainly attributed to the inevitable physical loss
of the catalyst during the operation. Moreover, the Pd
leaching in the filtrate as determined by ICP is undetect-
able during the recycling experiment. XPS and TEM
results (Figure 5b‐d) of the recovered catalyst after the
3.3 | Alkoxycarbonylation of aryl halides
Aryl esters constitute integral parts of natural products,
pharmaceutical intermediates and polymers. Among var-
ious
synthetic
methods,
palladium
catalyzed
alkoxycarbonylation of aryl halides represents a valuable
[
1–4]
alternative.
The excellent catalytic performance of
Pd@POP‐Ph P in the carbonylative Suzuki coupling of
3
aryl halides prompted us to further investigate its applica-
1
st and 5th reuse suggested that the palladium was still
tion in the alkoxycarbonylation of aryl halides. Our previ-
in the +2 oxidation state and no palladium nanoparticle
was observed even after reusing for 5 times. These results
were also consistent with the observed experimental phe-
nomena that the recovered catalyst kept a light brown
colour during the recycling (Figure S3). The above results
were different from the general immobilized palladium
complexes, in which palladium species were usually par-
tially reduced to palladium nanoparticles during the car-
ously
reported
reaction
conditions
for
the
alkoxycarbonylation of aryl iodides with Pd@KAPs (Ph‐
[
32]
PPh ) as a catalyst,
was adopted to evaluate the cata-
3
lytic efficiency. Interestingly, with iodobenzene and etha-
nol as the substrates, 0.25 mol% of Pd@POP‐Ph P could
give a 99% yield of target aryl ester in 4 hr (Table 4, entry
1). However, our previously reported Pd@KAPs (Ph‐
3
[
32]
PPh3),
gave only 36% yield of target aryl ester under
[12,34,43,46,49,50]
bonylation reaction.
Considering the
similar conditions (Table 4, entry 2). Running the reac-
tion with homogeneous PdCl (PPh ) , likewise, showed
inferior result (Table 4, entry 3). With these results in
hand, we started assessing the scope and efficacy of the
catalytic system. Iodobenzene with different primary or
structure of the catalyst, the good performance could be
attributed to the high ligand concentration and excellent
porous structure. The high ligand concentration provides
the abundant coordination sites, while the excellent
2
3 2
FIGURE 5 (a) Reuse of Pd@POP‐Ph
the reaction time, reaction conditions of the recycling experiments were the same as that of entry 5 in Table 2, and the reaction time for each
recycling run was 3 hr; (b) Pd 3d XPS spectra of recycling Pd@POP‐Ph P after the 1st and 5th recycle; (c) TEM image of the recovered
Pd@POPPh P after the 1st recycle; (d) TEM image of the recovered Pd@POP‐Ph P after the 5th recycle
3
P catalyst for the carbonylative Suzuki coupling of iodobenzene with phenylboronic acid. Except for
3
3
3

8
of 10
WAN ET AL.
secondary alcohols could react readily, affording excellent
yields of corresponding benzoates in 5 hr (Table 4, entries
As representative examples of aryl bromides, the reactiv-
ity of bromobenzene, 4‐NO2 and 4‐OMe substituted
bromobenzene was also investigated (Table 4, entries
17–19). The results showed that the yields were signifi-
cantly influenced by the electronic property of the substit-
uent groups. Aryl bromides bearing electron‐withdrawing
nitro group afforded the target aryl ester in 78% yield at
130 °C for 24 hr (Table 4, entry 18). While aryl bromides
bearing electron‐donating methoxyl group failed to afford
the target ester (Table 4, entry 20).
4–7). Phenol, as a representative example of phenols,
could also react with iodobenzene smoothly (Table 4,
entry 8). With ethanol as a nucleophile, aryl iodides bear-
ing different functional groups at the para position could
react smoothly, affording the corresponding aryl esters in
excellent yields in 4 hr (Table 4, entries 9–14). Moderately
hindered aryl iodides, such as 3‐OMe, 2‐OMe substituted
iodobenzene, could also react readily, although prolonged
reaction times were needed (Table 4, entries 15 and 16).
The reusability and stability of Pd@POP‐Ph P in the
3
alkoxycarbonylation reaction were also tested. The reac-
tion conditions of the recycling experiment were
described in the entry 21 of Table 4. After each run, the
catalyst was recovered by centrifugation and washed with
ethanol. The obtained liquid was analysed using GC. To
our delight, 99% yield of target aryl ester was still pre-
served even after reusing for 5 times (Table 4, entry 21).
The morphology of the recovered catalyst after reusing
for 5 times was also investigated by TEM (Figure 6).
TEM results suggested that no palladium nanoparticle
was observed after reusing for 5 times. This suggested
TABLE 4 Alkoxycarbonylation of aryl halides with various
alcohols
a
1
2
b
Entry
R
R
X
Time (h)
Yield (%)
c
1
H
Et
I
4
99
36
58
95
97
92
96
99
94
86
98
92
99
97
95
92
7
c,d
2
H
Et
I
4
e
3
H
Et
I
4
that Pd@POP‐Ph P was highly stable during the recycling
3
4
5
6
7
H
n‐Pr
i‐Pr
n‐Bu
Cy
Ph
Et
I
4
experiment.
H
I
5
H
I
4
H
I
4
f
8
H
I
8
9
4‐COMe
4‐COOMe
I
4
10
11
12
13
14
15
16
17
18
19
20
21
Et
I
4
4‐NO
4‐Cl
4‐F
2
Et
I
4
Et
I
4
Et
I
4
4‐OMe
3‐OMe
2‐OMe
H
Et
I
4
Et
I
6
Et
I
10
24
24
24
24
4
Bu
Bu
Bu
Bu
Et
Br
Br
Br
Br
I
g
H
49
78
trace
99
g
NO
2
g
OMe
H
c,h
a
3
Reaction conditions: Pd@POP‐Ph P (0.25 mol%), aryl halide (2 mmol), DBU
(
4 mmol), alcohol (4 ml), 80 °C, CO (1 atm), stirring speed (600 rpm).
b
Isolated yield.
c
GC yields.
d
Pd@KAPs (Ph‐PPh
3
) (0.25 mol% Pd) as a catalyst.
e
f
0
.25 mol% PdCl
2
(PPh as a catalyst.
3 2
)
DMAc (3 ml), PhOH (3 mmol).
g
Pd@POP‐Ph
3
P (2.5 mol%), 130 °C.
FIGURE 6 TEM images of the recovered Pd@POP‐Ph3P after
the 5th recycle
h
Resued for 5 times.

WAN ET AL.
9 of 10
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4
| CONCLUSIONS
7520.
In conclusion, we have developed an active, stable and
recyclable catalyst for the carbonylation of aryl halides.
The solid catalyst displayed high catalytic activity and
reusability in the carbonylative Suzuki coupling and
alkoxycarbonylation reactions of aryl iodides/bromides.
Importantly, the catalyst is highly robust. Negligible
metal leaching and no aggregation of palladium species
were observed during the recycling reactions. Thus, this
protocol not only provides an active heterogeneous cata-
lyst for the carbonylative Suzuki coupling and
alkoxycarbonylation of aryl halides, but also provides
some clues to develop stable catalysts for other carbonyl-
ation reactions.
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This work is financial supported by the National Natural
Science Foundation of China (No. 21763017), the Youth
Talent Growth Project of Educational Department of Gui-
zhou Province (qian jiao he KY [2016]264), the Natural
Science Foundation of Guizhou Province (qian ke he ji
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Porous Materials (52020‐2017‐02‐02), and the Funds of
Liupanshui Normal University (LPSSYKJTD201501 and
LPSSYZDXK201602).
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