Palladium supported on triphenylphosphine-functionalized porous organic polymer: An efficient heterogeneous catalyst for aminocarbonylation

Article abstract of DOI:10.1007/s11243-015-9990-6

An efficient route for the catalytic synthesis of aryl amides via the aminocarbonylation of aryl iodides with amines is described using palladium supported on triphenylphosphine-functionalized porous organic polymer (Pd@KAPs(Ph-PPh₃)) as the catalyst. Under low carbon monoxide pressure, the catalyst exhibited remarkable activity, and only 0.5 mol% palladium loading was required to achieve moderate to excellent yields (70-97 %) of aryl amides. The catalyst can be easily separated by a simple filtration process and recycled up to seven times with only minor loss of activity. The salient features of this protocol are the simplicity in handling of catalyst, low CO pressure, good functional group tolerance, high catalytic activity, negligible palladium leaching and effective catalyst recyclability.

Full text of DOI:10.1007/s11243-015-9990-6

Transition Met Chem
DOI 10.1007/s11243-015-9990-6
Palladium supported on triphenylphosphine-functionalized
porous organic polymer: an efficient heterogeneous catalyst
for aminocarbonylation
1
2
2
2
Yizhu Lei
Guangxing Li
•
Xuefeng Zhang
2
•
Yanlong Gu
•
Jianglin Hu
•
1
•
Kaiyi Shi
Received: 29 July 2015 / Accepted: 28 September 2015
Ó Springer International Publishing Switzerland 2015
Abstract An efficient route for the catalytic synthesis of
aryl amides via the aminocarbonylation of aryl iodides with
amines is described using palladium supported on triph-
enylphosphine-functionalized porous organic polymer
carboxylic acid derivatives and amines suffers from high
raw material costs and poor atom economy [1, 2]. Palla-
dium-catalyzed aminocarbonylation is a powerful and
alternative technique for the synthesis of amides, that has a
number of advantages over the traditional synthesis
method. This new technique has emerged in recent years as
the most promising route for the atom-economical and cost
effective synthesis of amides, producing the amides from
inexpensive and easily available feedstocks such as carbon
monoxide, organic halides and amines [3–7]. Much of the
recent research has focused on the development of highly
active palladium complexes [8–12]. These homogeneous
catalytic systems generally exhibit excellent activity and
selectivity, but they suffer from the practical problems such
as catalyst separation and recycling. In order to address
these problems, researchers have immobilized palladium
particles or complexes on various supports such as silica
[13, 14], MCM-41 [15], MOF-5 [16], ZIF-8 [17], organic
polymer [18, 19] and porous organic polymer (POP) [20] to
create heterogeneous catalysts for aminocarbonylation of
aryl halides. Nevertheless, key obstacles for practical
applications of these heterogeneous catalysts are their
catalytic activity and long-term stability [21, 22]. Hence, it
is necessary to develop highly active and stable heteroge-
neous catalysts for potential industrial applications.
(
Pd@KAPs(Ph-PPh )) as the catalyst. Under low carbon
3
monoxide pressure, the catalyst exhibited remarkable
activity, and only 0.5 mol% palladium loading was
required to achieve moderate to excellent yields (70–97 %)
of aryl amides. The catalyst can be easily separated by a
simple filtration process and recycled up to seven times
with only minor loss of activity. The salient features of this
protocol are the simplicity in handling of catalyst, low CO
pressure, good functional group tolerance, high catalytic
activity, negligible palladium leaching and effective cata-
lyst recyclability.
Introduction
Amides represent an important class of N-containing
organic chemicals that find many applications in the
chemical and pharmaceutical industries [1, 2]. However,
the traditional synthesis method of amides via coupling of
The combination of the advantageous properties of
molecular and solid catalysts was considered as the ‘‘Holy
Grail’’ in catalysis research. New opportunities have been
offered by porous polymers [23]. POPs emerged as a new
class of functional materials just in a few years ago. Due to
their extraordinarily high surface area, well-defined pore
structure, low skeletal density, and the ability to introduce
chemical functionalities within their porous frameworks,
POPs have been used as versatile materials for the devel-
&
&
1
Yizhu Lei
yzleiabc@126.com
Guangxing Li
ligxabc@163.com
Department of Chemistry and Chemical Engineering,
Liupanshui Normal University, Liupanshui 553004, Guizhou,
People’s Republic of China
2
School of Chemistry and Chemical Engineering, Huazhong
University of Science and Technology, Luoyu Road 1037,
Wuhan 430074, Hubei, People’s Republic of China
opment of catalysts [23]. Triphenylphosphine (PPh ) is one
3
123

Transition Met Chem
of the most valuable phosphine ligands in homogeneous
catalysis. The introduction of triphenylphosphine ligand
into the porous organic frameworks would be an efficient
way to construct highly active catalytic supports and has
thus attracted considerable attention [21, 22, 24–26].
Recently, we reported palladium supported on triph-
A typical procedure for aminocarbonylation
reaction
Catalytic reactions were carried out in a Teflon-lined
stainless steel autoclave (50 mL) equipped with a magnetic
stirrer bar and an automatic temperature controller. In a
typical experiment, 0.5 mol% Pd, aryl iodide (1.0 mmol),
enylphosphine-functionalized POP (Pd@KAPs(Ph-PPh ))
3
having low levels of palladium loading as a highly active
and recyclable catalyst for the alkoxycarbonylation of aryl
iodides. Under atmospheric pressure of carbon monoxide,
the catalyst showed high catalytic activity and quantitative
yields of the corresponding esters were achieved [27].
To continue our interest on heterogeneous carbonylation
of organic halides [27–29] and extend the application of the
amine (3.0 mmol) and K CO (414.6 mg, 3.0 mmol) were
2 3
added to DMF (4 mL) and allowed to react under CO
atmosphere (1 bar) at 120 °C for 2–4 h. After the reaction,
the reactor was cooled to room temperature. The reaction
mixture was centrifuged at 5000 rpm for 10 min, and the
clear supernatant, to which was added ethyl phenylacetate
as an internal standard, was analyzed with GC. For the study
of substrate scope, after completion of the reaction, the
catalyst was centrifuged at 5000 rpm for 10 min and the
clear supernatant was diluted with 20 % HCl and extracted
with diethyl ether. The organic layer was washed with
active Pd@KAPs(Ph-PPh ) catalyst, in this paper, we
3
investigated the synthesis of valuable aryl amides via the
aminocarbonylation of aryl iodides using Pd@KAPs(Ph-
PPh ) as a heterogeneous catalyst (Scheme 1).
3
saturated NaHCO and NaCl solutions, respectively, dried
3
over anhydrous Na SO and evaporated under vacuum after
2
4
Experimental
filtration. The residue obtained was purified by column
chromatography (silica gel, 200–300 meshes; petroleum–
ethyl acetate, 20:1) to afford the pure products. All products
Reagents
1
13
were confirmed by H and C NMR analyses. For the
recycling experiment, the solid catalyst was separated by
centrifugation from the reaction mixture, washed three
times with the reaction solvent (DMF) and then engaged in
a new catalytic cycle under the same reaction conditions.
All the synthesized amides are known products, and we
have reported recently [28].
Benzene, triphenylphosphine, PdCl , FeCl (anhydrous), 1,2-
2
3
dichloroethane and acetonitrile were obtained from National
Medicines Corporation Ltd. of China, all of which were of
analytical grade and were used as received. Aryl iodides,
amines and bases were of analytical reagent grade and
commercially available. Formaldehyde dimethyl acetal (Alfa
Aesar, 98 %) was also used as received. Pd/Al O (5 wt%),
2
3
Pd/SiO (5 wt%) and Pd/C (5 wt%) were purchased from
2
Shaanxi Rock New Materials Co., Ltd (China). All solvents
were of analytical grade and distilled prior to use.
Results and discussion
Catalytic activity
Preparation of catalysts
To evaluate the catalytic activity of Pd@KAPs(Ph-PPh3)
catalyst for aminocarbonylation reactions, the aminocar-
bonylation of iodobenzene with diethylamine was selected
as a model reaction. Initially, the activities of several cat-
alysts were examined for the model reaction, and the
obtained results are summarized in Table 1. Under CO
Pd@KAPs(Ph-PPh ) [27] and PdCl (phen)@Y [28] were
3
2
prepared as we have reported recently, and the Pd content
was 0.8 and 2.1 wt%, respectively.
atmosphere (1 bar), 0.5 mol% Pd@KAPs(Ph-PPh ) gave
3
51 % yield of the desired amide in the presence of Et N as
3
the base (Table 1, entry 1). Ligand-free Pd catalysts, such
as PdCl , Pd/Al O , Pd/SiO and Pd/C, were also tested
2
2
3
2
under the same reaction conditions, but the yields of the
desired amide reached only to 14, 13, 12 and 13 %,
respectively (Table 1, entries 2–5). PdCl (phen)@Y, an
2
efficient and highly recyclable heterogeneous catalyst for
high-pressure aminocarbonylation [28], was also tested.
However, under low CO pressure, PdCl (phen)@Y affor-
2
Scheme 1 Aminocarbonylation of aryl iodides using Pd@KAPs(Ph-
PPh ) as the catalyst
ded the amide in only 8 % yield (Table 1, entry 6).
3
1
23

Transition Met Chem
Table 1 Effect of catalyst
Table 2 Effect of base and solvent
O
a
Entry Base
Solvent
Conversion (%) Yield (%)
I
Pd (0.5 mol%)
CO (1 bar)
NEt2
+
HNEt2
1
2
3
4
5
6
7
8
9
1
1
1
Et N
3
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
52
98
51
96
80
95
88
44
6
K
2
CO
KHCO
Na CO
PO
HPO
3
a
Entry
Catalyst
Conversion (%)
Yield (%)
3
89
2
3
96
1
2
3
4
5
6
Pd@KAPs(Ph-PPh
PdCl
Pd/Al
3
)
52
51
14
13
12
13
8
K
3
2
4
99
2
21
24
23
20
11
K
4
47
2 3
O
KOH
20
Pd/SiO
Pd/C
2
CH
CH
3
COOK Toluene
70
59
68
16
97
95
42
77
30
–
3
OK
Toluene
Toluene
DMF
94
2
PdCl (phen)@Y
0
1
2
DBU
84
Reaction conditions Pd (0.5 mol%), PhI (40.8 mg, 0.2 mmol), Et
2
NH
2
K CO
2
K CO
2
K CO
2
K CO
2
K CO
2
K CO
2
K CO
3
3
3
3
3
3
3
[99
[99
69
(
(
a
43.9 mg, 0.6 mmol), CO (1 bar), Et N (60.6 mg, 0.6 mmol), toluene
3
DMAc
4 mL), 120 °C, 2 h
GC yield
13
1,4-Dioxane
Anisole
DMSO
14
15
16
17
90
42
Carbonylation of aryl iodides with amines usually
H
2
O
–
gives rise to mixtures of mono- and dicarbonylated
products [30]. Chemoselectivity and catalytic activity of
the aminocarbonylation reaction are greatly dependent on
the reaction conditions [31]. Therefore, the influences of
various reaction parameters such as bases, solvents,
temperature and pressure were studied. Firstly, the reac-
tion was carried out with various inorganic bases, such as
K CO (96 %) and K PO (88 %), and organic bases,
b
DMF
64
62
Reaction conditions Pd@KAPs(Ph-PPh
3
) (13.3 mg, 0.5 mol%), PhI
(
(
a
40.8 mg, 0.2 mmol), Et NH (43.9 mg, 0.6 mmol), CO (1 bar), base
2
0.6 mmol), solvent (4 mL), 120 °C, 2 h
GC yield
b
0
3
.25 mol% Pd@KAPs(Ph-PPh )
2
3
3
4
such as Et N (51 %) and CH OK (68 %). Because K CO
3
the selectivity of a-ketoamide (Table 3, entries 9–13).
When the reaction was carried out at 2 MPa CO pressure
for 24 h, a-ketoamide could be obtained in 72 % yield
(Table 3, entry 13). Heterogeneous catalysts for double
carbonylation have been scarcely reported [34], and the
3
3
2
provided the maximum yield of the desired product, it was
used for a further study (Table 2, entry 2). With K CO as
2
3
the base, screening of solvents was carried out (Table 2,
entries 11–16). Among all the solvents screened, DMF
displayed the best performance, with which 97 % yield
could be obtained (Table 2, entry 11). Then, the effect of
catalyst loading was also studied. A catalyst loading of
results suggested that Pd@KAPs(Ph-PPh ) might be an
3
accessible catalyst for the double carbonylation of aryl
iodides.
0
.5 mol% was found to be optimal as decreasing the
catalyst loading to 0.25 mol% reduced the yield to 62 %
Substrate scope
(
Table 2, entry 17).
We next tested the effect of temperature and CO pres-
With the optimized conditions in hand, we turned our focus
to the scope and limitations of the system (Table 4).
Firstly, we extended the scope of this aminocarbonylation
reaction to a wide range of aryl iodides with diethylamine
as the amine (Table 4, entries 1–8). The para-, meta- and
ortho-methyl-substituted aryl iodides were successfully
transformed into the corresponding amides in good yields
(87–91 %; Table 4, entries 1–3). Various electron-donating
and electron-withdrawing groups on the aryl iodide such as
p-OMe, p-NO , p-COCH , p-Br and p-Cl were also well
sure (Table 3). Increasing the temperature favored selec-
tivity to the desired amide and afforded satisfactory yields
without significant dehalogenation (Table 3, entries 1–8).
At lower temperatures, the double carbonylation occurred
and yielded a-ketoamide (N,N-diethyl-2-oxo-2-phenylac-
etamide) as the main by-product. These results are con-
sistent with the literature [32, 33] in which other groups
reported that low temperature (60–80 °C) favored the
double carbonylation reaction of aryl iodide, while up to
2
3
1
00 °C the main products are the amides. a-Ketoamide is
tolerated and gave the desired tertiary amides in good to
excellent yields (Table 4, entries 4–8). Next, the
aminocarbonylation reactions of iodobenzene with various
amines were carried out. The reaction of iodobenzene with
an important motif in many biologically active compounds
and also a valuable starting material to synthesize several
families of heterocycles [34]. Hence, we tried to improve
123

Transition Met Chem
Table 3 Effect of temperature and CO pressure
O
O
I
+
NEt2
Pd@KAPs(Ph-PPh3)
NEt2
HNEt + CO
+
2
O
A
B
a
Entry
T (°C)
P
CO (bar)
Conversion (%)
Selectivity (%)
Yield (%)
A
B
A
B
1
2
3
4
5
6
7
8
60
70
1
1
32
42
19
21
54
80
93
94
95
94
16
19
16
19
14
75
74
40
15
5
6
24
31
25
14
5
9
34
74
90
93
97
95
8
80
1
63
90
1
92
100
110
120
130
60
1
97
1
99
2
2
1
[99
[99
50
0
–
1
0
–
b
9
1
76
80
81
81
85
38
47
51
52
72
b
1
1
1
1
0
1
2
3
60
10
20
30
20
59
11
10
12
12
b
b
c
60
63
60
64
60
85
Reaction conditions Pd@KAPs(Ph-PPh
0
3
) (13.3 mg, 0.5 mol%), PhI (40.8 mg, 0.2 mmol), Et
2
NH (43.9 mg, 0.6 mmol), K CO
2
3
(82.9 mg,
.6 mmol), DMF (4 mL), 2 h
a
GC yield
b
c
Pd@KAPs(Ph-PPh
Pd@KAPs(Ph-PPh
3
) (26.6 mg, 1.0 mol%), 4 h
3
) (26.6 mg, 1.0 mol%), 24 h
aniline provided a 70 % yield of the desired product under
the optimized reaction conditions (Table 4, entry 9). Ali-
phatic amines, such as dipropyl amine and cyclohexyl
amine, provided good yields of the desired amides
after 1 h, when the yield reached to 67 %. A rapid sep-
aration of the Pd@KAPs(Ph-PPh ) catalyst was performed
3
immediately by a high-speed centrifugation (20,000 r/min,
3 min), and then, the hot liquid mixture was allowed to
react further 1 h under the same conditions. However, the
yield (69 %) was scarcely changed. We also tested Pd
content in the filtrate by means of AAS, and the result
showed that palladium leaching is very low, to be ca.
(
Table 3, entries 10–12). The substrate scope was further
extended to the unreactive aryl bromide and chloride. But
unfortunately, no desired products were observed.
0.4 ppm. These results suggested that all the palladium
Hot filtration test and catalyst recycling
species were strongly absorbed on the support and no
significant quantity of metal was lost to the reaction liquid
during the process.
When a supported metal catalyst is used in a liquid-phase
reaction, two points need to be clarified. The first one is
the metal leaching that sometimes is partially responsible
for the observed good catalytic activity in a reaction in
liquid phase. In order to determine whether the catalytic
The second one is the recyclability of the catalyst. To
this end, at the end of the model reaction, Pd@KAPs(Ph-
PPh ) was separated by a simple centrifugation and
3
extracted with copious DMF and then subjected to the next
run. As shown in Fig. 1, the catalyst exhibited good
reusability and could be reused for seven times. Only a
slight decrease in its activity was observed, which can be
attributed partially to a physical loss of the catalyst during
the operation.
recycle was derived from Pd@KAPs(Ph-PPh ) or from
3
leaching palladium released from the solid catalyst
during the reaction, we performed a hot filtration test.
A
Pd@KAPs(Ph-PPh )-catalyzed aminocarbonylation
3
reaction of iodobenzene with diethylamine was stopped
1
23

Transition Met Chem
Table 4 Aminocarbonylation of aryl iodides with various amines
O
I
Pd@KAPs(Ph-PPh3)
K CO , DMF
NR1R2
1
2
+
R R NH
R
R
2
3
1
bar CO,120 °C
a
Entry
1
R
R
1
, R
2
Products
t (h)
Yield (%)
91
p-Me
R
1
=R
2
=Et
2
O
Et
N
Et
2
m–Me
R
1
=R
2
=Et
O
2
85
Et
N
Et
3
4
o-Me
R
R
1
=R
=R
2
=Et
=Et
O
4
2
87
86
Et
N
Et
p-OMe
1
2
O
Et
Et
N
Et
MeO
5
6
p-NO
2
R
R
1
=R
2
=Et
O
O
4
2
82
93
N
Et
O N
2
p-COCH
3
1
=R
2
=Et
Et
N
Et
O
7
8
p-Br
p-Cl
R
R
1
=R
2
=Et
3
4
91
89
O
Et
Et
N
Et
Br
1
=R
2
=Et
O
N
Et
Cl
9
H
H
R
R
1
=H, R =Ph
2
4
2
70
82
O
N
H
1
0
1 2
=R =n-Pr
O
nPr
N
nPr
123

Transition Met Chem
Table 4 continued
a
Entry
R
H
R
1
, R
2
Products
t (h)
Yield (%)
1
1
–(CH
2
)
5
–
4
75
O
O
N
1
2
H
–(CH
2
)
4
–
4
72
N
Reaction conditions Pd@KAPs(Ph-PPh
DMF (4 mL), 120 °C
3 2 3
) (66.5 mg, 0.5 mol%), aryl halide (1 mmol), amine (3 mmol), CO (1 bar), K CO (414.6 mg, 3 mmol),
a
Isolated yields
(
NC2010 MA0137). The authors thank for financial support from the
National Natural Science Foundation of China (51504134), Guizhou
‘125 Plan’’ Key Project of Science and Technology Project [Qian jiao
‘
he zhong da zhuang xiang zi (2013) 026] and Liupanshui normal
university creative team (LPSSYKJTD201401).
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