Aminocarbonylation of aryl iodides with primary and secondary amines in aqueous medium using polymer supported palladium-N-heterocyclic carbene complex as an efficient and heterogeneous recyclable catalyst

Article abstract of DOI:10.1016/j.cattod.2012.03.039

Aminocarbonylation of aryl iodides with primary and secondary aromatic/aliphatic amines to corresponding amides using polymer supported palladium-N-heterocyclic carbene complex (PS-Pd-NHC) as an efficient heterogeneous, recyclable catalyst is described. The catalytic system was optimized with respect to various reaction parameters to give excellent yield of desired products. The catalyst can be easily separated by simple filtration process and recycled further up to four consecutive recycle without loss in any activity and selectivity. The protocol is advantageous due to the ease in handling of the catalyst, simple workup procedure, and environmentally benign water as solvent and effective catalyst recyclability.

Full text of DOI:10.1016/j.cattod.2012.03.039

Catalysis Today 198 (2012) 148–153
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Catalysis Today
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Aminocarbonylation of aryl iodides with primary and secondary amines in
aqueous medium using polymer supported palladium-N-heterocyclic carbene
complex as an efficient and heterogeneous recyclable catalyst
Ziyauddin S. Qureshi, Santosh A. Revankar, Mayur V. Khedkar, Bhalchandra M. Bhanage∗
Department of Chemistry, Institute of Chemical Technology, N. Parekh Marg, Matunga, Mumbai, 400 019, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 12 April 2012
Aminocarbonylation of aryl iodides with primary and secondary aromatic/aliphatic amines to corre-
sponding amides using polymer supported palladium-N-heterocyclic carbene complex (PS-Pd-NHC) as
an efficient heterogeneous, recyclable catalyst is described. The catalytic system was optimized with
respect to various reaction parameters to give excellent yield of desired products. The catalyst can be
easily separated by simple filtration process and recycled further up to four consecutive recycle with-
out loss in any activity and selectivity. The protocol is advantageous due to the ease in handling of the
catalyst, simple workup procedure, and environmentally benign water as solvent and effective catalyst
recyclability.
Keywords:
Aminocarbonylation
Aryl iodides
Heterogeneous catalysis
Palladium
Primary–secondary amine
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
[11,12], because of its effective binding ability to any transition
metal irrespective of their oxidation states. NHC ligand reveals
The synthesis of carbonyl compounds including carboxylic
acids [1], amides [2], esters [3], aldehydes [4], and ketones
[5] are of basic importance in organic chemistry. Palladium-
catalyzed carbonylation of aryl halides for the synthesis of such
compounds is one of the highly efficient protocols. In context,
aminocarbonylation is one of the promising methods used for the
direct one step synthesis of amides via carbonylative coupling
of aryl, alkenyl, and heterocyclic halides with primary/secondary
amines [6]. Various palladium-based catalytic systems such as
PdBr2(PPh3)2/PdCl2(PPh3)2 [7], silica-supported bidentate arsine-
palladium complex [8], silica-supported bidentate sulfur and
phosphine mixed palladium complex [9], and Pd(OAc)2/PPh3 in
ionic liquid [10], and so on for has been explored for this reac-
tion. However, these catalytic systems have several limitations like
requirement of air and moisture-sensitive phosphine-containing
ligands, high carbon monoxide pressure, higher catalyst loading,
limited substrate compatibility, and the use of organic solvents.
Therefore, the efforts to develop a heterogeneous, reusable and
phosphine free catalytic system which can efficiently catalyze
aminocarbonylation of aryl halides are highly desirable.
very high dissociation energies compared to phosphine ligands,
which have been quantified via theoretical calculation for differ-
ent metals. Therefore, the binding between the NHC and transition
metal is much stronger, as well as being chemically and thermally
more inert toward cleavage than that of other metal complexes.
Recently, polymer-supported palladium-N-heterocyclic carbene
(PS-Pd-NHC) catalyst have been explored for Suzuki and carbonyla-
tive Suzuki coupling reactions [13], as it offers several advantages
like reuse of expensive transition metals and ligands with a possi-
bility to prevent the contamination of ligand residue in products.
However, to the best of our knowledge, no such polymer-supported
catalytic system has yet been explored for the simple aminocar-
bonylation of aryl iodides with primary and secondary amines.
In continuation of our interest on phosphine-free carbonyla-
tion reactions [14], herein we report an facile protocol for the
aminocarbonylation of aryl iodides with primary and secondary
amines using polymer supported palladium-NHC complex (PS-Pd-
NHC) as a phosphine free, heterogeneous and recyclable catalyst
(Scheme 1).
Recently, N-heterocyclic carbene (NHC) as a ligand has found
potential applications in homogeneous transition metal catalysis
2. Experimental
All chemicals were procured from firms of repute. Various
substrates of aryl iodides and amines were purchased from
Sigma–Aldrich. All the chemicals were used as received without any
further purification. Polymer-supported Palladium-N-heterocyclic
∗
Corresponding author. Tel.: +91 22 3361 1111; fax: +91 22 24145614.
E-mail addresses: bm.bhanage@ictmumbai.edu.in, bm.bhanage@gmail.com
(B.M. Bhanage).
0920-5861/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2012.03.039

Z.S. Qureshi et al. / Catalysis Today 198 (2012) 148–153
149
Table 1
Optimization of the aminocarbonylation reaction using PS-Pd-NHC catalyst.a
Entry
Solvent
Base
Temperature (◦C)
CO pressure (psi)
Time (h)
Yield (%)b
Effect of solvent
1
2
3
Toluene
THF
None
Water
Water
Water
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
100
100
100
100
100
100
100
100
100
100
100
100
8
8
8
8
8
8
74
90
14
92
96
88
4c
5d
6e
Effect of base
7
8
9
Water
Water
Water
–
100
100
100
100
100
100
8
8
8
–
90
89
K2CO3
Et3N
Effect of temperature
10
11
Water
Water
Na2CO3
Na2CO3
80
110
100
100
8
8
81
88
Effect of CO pressure
12
13
Water
Water
Na2CO3
Na2CO3
100
100
150
200
8
8
94
94
Effect of time
14
15
Water
Water
Na2CO3
Na2CO3
100
100
100
100
6
10
84
94
a
Reaction conditions = iodobenzene (1 mmol), aniline (2 mmol), Na2CO3 (2 mmol), PS-Pd-NHC (50 mg, 14.2 ␮mol), water (10 mL), CO pressure (100 Psi), temperature
(100 ◦C), time (8 h).
b
GC yield.
TOF = 8.2 h−1
.
c
d
e
Catalyst = Pd(OAc)2 and TOF = 8.5 h−1
Catalyst = (5%) Pd/C.
.
Scheme 1. Aminocarbonylation reaction of aryl iodides with primary and secondary amines.
carbene complex (PS-Pd-NHC) used was prepared according to the
reported procedure in literature [15].
with 100 psi of CO and the mixture was heated at 100 ◦C for
8 h. The progress of the reaction was monitored using GC analy-
sis (PerkinElmer, Clarus 400) (BP-10 GC column, 30 m × 0.32 mm
ID, film thickness 0.25 mm). After completion of the reaction, the
mixture was cooled to room temperature. The catalyst was fil-
tered off and products were extracted with ethyl acetate, dried
2.1. Characterization of polymer-supported Pd-N-heterocyclic
carbene complex (PS-Pd-NHC)
Prepared PS-Pd-NHC was characterized by solid state 13C NMR
(Bruker AvanceIII 700 MHz); ı 14 (CH3 aliphatic acetate skele-
ton), 38 (N CH3 skeleton), 41 (aliphatic polystyrene skeleton),
128 (NCH, NCH, aromatic polystyrene skeleton), 147 (NCN, aro-
matic polystyrene skeleton), 187 (C O acetate skeleton). Loading
of palladium catalyst on chloromethyl polystyrene resin support
was evaluated by ICP-AES analysis and was found to be about
0.29 mmol g−1 of support.
100
80
60
40
20
0
2.2. Typical procedure for aminocarbonylation of aryl iodides
with primary and secondary amines in aqueous medium
1
2
3
4
Number of Recycles
To a 100 mL autoclave were added aryl iodides (1.0 mmol),
amines (2 mmol), PS-Pd-NHC (50 mg, 14.5 ␮mol), H2O (10 mL),
and Na2CO3 (2.0 mmol). The reaction mixture was first stirred
for 10 min and then flushed several times with CO, then filled
Fig. 1. Catalyst recyclability study for aminocarbonylation reaction of iodobenzene
with aniline.Reaction conditions = iodobenzene (1 mmol), aniline (2 mmol), Na2CO3
(2 mmol), PS-Pd-NHC (50 mg, 14.2 ␮mol), water (10 mL), CO pressure (100 psi), tem-
perature (100 ◦C), time (8 h), GC yield.

150
Z.S. Qureshi et al. / Catalysis Today 198 (2012) 148–153
Table 2
Aminocarbonylation of aryl iodides with various aliphatic and aromatic primary amines.a
Entry
Aryl iodide
Amine
Product
Yield (%)b
1
90
2
3
88
79
4
5
6
94
90
87
7
8
9
80
89
78

Z.S. Qureshi et al. / Catalysis Today 198 (2012) 148–153
151
Table 2 (Continued)
Entry
Aryl iodide
Amine
Product
Yield (%)b
10
11
14
72
12
82
75
13
a
Reaction conditions = aryl iodide (1 mmol), amine (2 mmol), Na2CO3 (2 mmol), PS-Pd-NHC (50 mg, 14.2 ␮mol), water (10 mL), CO pressure (100 Psi), temperature (100 ◦C),
time (8 h).
b
Isolated yield.
over Na2SO4 and the solvent was evaporated under vacuum. The
residue obtained was purified by column chromatography (silica
gel, 60–120 mesh; PE-EtOAc, 90:10) to afford the desired aminocar-
bonylated product. All the products are well known and were
confirmed by GC–MS analysis.
Firstly, the influence of solvents on aminocarbonylation reac-
tion was investigated (entries 1–4). Non-polar solvent like toluene
furnishes lower yield of desired product (entry 1). Whereas polar
aprotic solvent like THF provides excellent yield (90%) of desired
product (entry 2). With this observation, to make a synthetic
protocol greener we screened water as a reaction solvent and it
provided excellent yield of desired product (entry 4). To confirm
the role of solvent in reaction outcome, we attempted reaction
in neat condition, but poor yield of corresponding product was
observed (entry 3). Therefore further reactions were carried out
using water as a solvent. To check the activity of developed catalytic
system, TOF values of PS-Pd-NHC is compared with homoge-
neous Palladium catalyst (Pd(OAc)2) (entries 5 and 6) and it was
observed that homogeneous catalyst gave somewhat higher TOF
i.e. 8.5 h−1 than that of PS-Pd-NHC catalyst which gave TOF of
8.2 h−1. This is observed due to the soluble nature of homoge-
neous catalyst. Also it should be noted that PS-Pd-NHC catalyst is
giving nearly similar performance with additional benefit of cat-
alyst product separation and recycle. Heterogeneous catalyst like
Pd/C (5%) was also screened for aminocarbonylation reaction but
it gave lower yield of desired product (entry 6) as compared to
both of above mentioned catalysts. To confirm the influence of
base in reaction progress, initially reaction was tried in absence
of base, but no desired product was observed that indicates vital
role of base in the reaction (entry 7). Consequently inorganic and
organic bases were screened, and Na2CO3 was found to be best
base for reaction (entries 4, 8–9). In order to examine the effect
of temperature, reactions were carried out at different temper-
atures ranging from 80 to 110 ◦C (entries 4, 10–11). At 100 ◦C
maximum yield of expected product was observed. The influence
of CO pressure was also studied and 100 psi of CO pressure was
found to be optimum for the reaction (entries 3, 12–13). When
reaction was carried out for 6 h lower yield of corresponding
product was observed (entry 14), while with the increase in reac-
tion time improved yield of corresponding amide was observed
(entries 3, 15).
2.3. Recyclability study of PS-Pd-NHC complex for
aminocarbonylation reaction of iodobenzene with aniline in water
After completion of reaction, the reaction mixture was cooled
to room temperature, and the catalyst was collected by filtration.
The product was extracted in ethyl acetate and the aqueous layer
containing catalyst was filtered (catalyst particles are suspended
in aqueous layer), the filtered catalyst was washed vigorously with
distilled water (3 × 10 mL) and methanol (3 × 10 mL) to remove all
traces of product or reactant present. The filtered catalyst was then
dried under reduced pressure and kept for activation at 80 ◦C for a
period of 4 h prior to the next recycle. The dried catalyst was then
used for catalyst recyclability experiment and it was observed that
the recovered catalyst could be reused for four consecutive cycles
for the aminocarbonylation reaction of iodobenzene with aniline
(product yield = 92%, 90%, 90%, 88%, respectively Fig. 1). To check the
palladium metal leaching, we performed the ICP-AES analysis of the
1st and 4th recycle run; where below detectable level (0.01 ppm) of
palladium in solution was observed thus indicating no significant
leaching of the palladium catalyst.
3. Results and discussion
In concern to development of efficient, phosphine free and
heterogeneous protocol for aminocarbonylation, the reaction of
iodobenzene with amines in the presence of PS-Pd-NHC as a cata-
lyst was chosen as a model reaction, and the influence of various
reaction parameters such as nature of solvent, base, temperature,
CO pressure and time were studied (Table 1).

152
Z.S. Qureshi et al. / Catalysis Today 198 (2012) 148–153
Table 3
Aminocarbonylation of aryl iodides with various secondary amines.a
Entry
Aryl iodide
Amine
Product
Yield (%)b
1
91
2
88
3
81
4
5
6
7
–
88
91
86
79
8
a
Reaction conditions = aryl iodide (1 mmol), amine (2 mmol), Na2CO3 (2 mmol), PS-Pd-NHC (50 mg, 14.2 ␮mol), water (10 mL), CO pressure (100 Psi), temperature (100 ◦C),
time (8 h).
b
Isolated yield.
Hence the optimized reaction conditions were, iodobenzene
as a dehalogenation product). There was no other side product
was observed. Primary aromatic amines such as 4-methyl and 4-
chloro aniline were found to react with iodobenzene providing
88% and 79% yield of respective amides products (entries 2–3).
The reaction of aryl iodide bearing strong electron-withdrawing
group such as COMe permits the aminocarbonylative coupling
reaction with aniline giving 4-acetyl-N-phenyl-benzamide (94%)
in excellent yield (entry 4). Aminocarbonylation of aliphatic pri-
mary amine such as benzylamine was found to react smoothly with
iodobenezene and 4-iodotoluene providing 90% and 87% yields
of respective N-benzylbenzamides (entries 5–6). Furthermore
different aliphatic primary amines such as cyclohexylamine
and butylamine were found to undergo the aminocarbony-
lation reaction with different substituted aryl iodides giving
(1 mmol), amine (2 mmol), CO pressure (100 psi), PS-Pd-NHC
(2 mol%), Na2CO3 (2 mmol) in water (10 mL) at 100 ◦C for 8 h.
These optimized reaction conditions were then used for
aminocarbonylation of various aryl iodides with different aliphatic
and aromatic primary amines results obtained are summarized in
Table 2.
The aminocarbonylation of iodobenzene with aniline pro-
vided the corresponding amide product in good yields (entry 1)
and it was observed that both electron-donating and electron-
withdrawing groups under present reaction conditions smoothly
underwent aminocarbonylation reaction giving desired products
with appreciable yields. In all cases, we observed that aryl halide
consumes completely giving amide and benzene (to small extent

Z.S. Qureshi et al. / Catalysis Today 198 (2012) 148–153
153
78–89% yields of amide products (entries 7–9). Encouraged
References
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(entries 10–12). It was noticed that bicyclic heteroaryl iodide such
as 5-iodoindole smoothly undergoes aminocarbonylative coupling
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4. Conclusion
In conclusion, an efficient, phosphine-free protocol for the
aminocarbonylation reaction of aryl iodides with primary and sec-
ondary amines in aqueous medium using PS-Pd-NHC complex as
a heterogeneous and recyclable catalyst has been developed. The
reaction was optimized with respect to various parameters and
enabled aminocarbonylation reaction of different aryl iodides with
variety of primary and secondary amines affording good to excel-
lent yield of desired products thus illustrating broad application of
the methodology. The catalyst can be easily recycled by simple fil-
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activity and selectivity. The developed protocol with use of water
as a solvent and recyclable catalytic system introduces a success
toward green approach in organic synthesis.
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The financial assistance from Indira Gandhi Centre for Atomic
Research (IGCAR) Kalpakkam, India is kindly acknowledged.