A green approach for copper-free sonogashira reaction of aryl halides with phenylacetylene in the presence of Nano-Pd/Phosphorylated Silica (SDPP/Pd0)

Article abstract of DOI:10.1071/CH14332

Silicadiphenyl phosphinite (SDPP) is used as the solid support for the generation of nano SDPP/Pd(0) from PdII as pre-catalyst. This nano catalyst was used for the efficient copper-free Sonogashira reaction of aryl halides in PEG-200 as a solvent. The nan

Full text of DOI:10.1071/CH14332

CSIRO PUBLISHING
Aust. J. Chem. 2015, 68, 926–930
Full Paper
http://dx.doi.org/10.1071/CH14332
A Green Approach for Copper-Free Sonogashira Reaction
of Aryl Halides with Phenylacetylene in the Presence
0
of Nano-Pd/Phosphorylated Silica (SDPP/Pd )
A
,
B
A
,
B
A
Nasser Iranpoor,
HAabib Firouzabadi,
Somayeh Motevalli,
and Khashayar Rajabi
A
Department of Chemistry, Shiraz University, Shiraz, 71454, Iran.
B
Corresponding authors. Email: iranpoor@susc.ac.ir; firouzabadi@susc.ac.ir
II
Silicadiphenyl phosphinite (SDPP) is used as the solid support for the generation of nano SDPP/Pd(0) from Pd as pre-
catalyst. This nano catalyst was used for the efficient copper-free Sonogashira reaction of aryl halides in PEG-200 as a
solvent. The nano Pd(0) that can be used as pre-prepared or as in situ-generated catalyst exhibited excellent reactivity and
stability in the Sonogashira cross-coupling reactions with different aryl iodides, bromides, and also chlorides. This
heterogeneous catalyst can be easily recovered and reused in several runs. The use of PEG as solvent and K CO as
2
3
inorganic base together with the heterogeneous nature of the reaction can be considered as green conditions for this
reaction.
Manuscript received: 29 May 2014.
Manuscript accepted: 4 September 2014.
Published online: 24 November 2014.
Introduction
studies on heterogeneous catalysis based on nano palladium
[
13]
One of the most straightforward methods for the preparation of
aryl alkynes and conjugated enynes is the palladium-catalyzed
coupling of terminal alkynes with aryl or alkenyl halides that
supported on silica for C–C bond formation, we herein report
the excellent efficiency, stability, and recyclability of nano
Pd(0)/SDPP catalyst in the Sonogashira cross coupling reaction
with different aryl iodides, bromides, and also chlorides.
[
1]
was described for the first time by Sonogashira et al. in 1975.
The most common competitive pathway as side reaction that
can affect the efficiency and yield of the Sonogashira coupling
is homocoupling of the alkynes to diynes (Glaser-type cou-
Results and Discussion
[
2]
Preparation of the Catalyst
pling). Hence, since 1992, for the cross-coupling reaction of
alkynes with aryl- or vinyl-halides, several improvements
have been reported. One of the most important solutions from
industrial points of concern is efficient copper-free Sonogashira
The Pd(0) metal complex of silicadiphenyl phosphinite
(SDPP), Pd(0){PPh O-SiO } , was prepared according to our
2
2 n
[
13]
previous report.
We have shown that P atoms are coordi-
[
3]
II
reaction in the presence of homogeneous catalytic systems.
CuI can induce homocoupling reactions of terminal alkynes to
nated initially to the Pd centre, followed by the reduction to
Pd(0) by another phosphinite group, and eventually the active
Pd(0) catalyst as a black insoluble mass is obtained. According
to inductively coupled plasma (ICP) analysis of several sam-
ples on the digested catalyst in refluxing aqueous HCl (37 %),
a Pd content of 2.5–27 mmol per 1 g of Pd immobilized on
SDPP was obtained. The scanning electron microscopy (SEM)
image shows particles with diameters in the nanometer scale as
presented in Fig. 1. Further information about the size of the
Pd particles was obtained by transmission electron microscopy
(TEM) analysis of the catalyst that showed that Pd nano-
particles (size: 7 nm) formed and dispersed in the silica matrix
(Fig. 2). As observed from the X-ray diffraction (XRD) pat-
tern, the Pd catalyst shows the (111), (200), (220), (311), and
(222) crystallographic planes of the Pd(0) nanoparticles
(Fig. 3). The Pd nanoparticle size from the XRD pattern was
estimated to be 8 nm which is in good agreement with the
results obtained from TEM (Fig. 2) and histogram (Fig. 4)
analysis.
[
2]
diynes in the presence of oxygen. Though these examples
contributed to the improvement of the Sonogashira reaction, the
use of homogeneous Pd catalysts has several drawbacks, in
particular, its limited thermal stability, the precipitation of pal-
ladium black, which limits the lifetime of the active species, and
problems associated with catalyst recycling. This leads to a loss
of expensive metal and ligands, formation of impurities in the
[
4]
products, and the need to remove residual metals. To over-
come these problems, heterogeneous catalysts have been
[
5]
developed for the Sonogashira cross-coupling reactions.
Chemists have made considerable achievements in heteroge-
[6]
neous catalysis and, recently, nanocatalysis. Heterogeneous
[
catalysts supported on a solid support, such as CNs, metal
7]
[
oxides mainly silica, clays, organic polymers, such as
8]
[9]
[
10]
polymeric N-heterocyclic carbene ligand-grafted silica,
[12]
and
have found
[11]
gelatin and agarose as bioorganic supports,
considerable synthetic applications. In continuation of our
Journal compilation Ó CSIRO 2015
www.publish.csiro.au/journals/ajc

Sonogashira Reaction in the Presence of Pd(0)/SDPP
927
6
5
4
3
2
1
0
0
0
0
0
0
0
3.5
4
7
9
10.5
Average diameter of Pd nanoparticles [nm]
[13]
Fig. 4. Pd size histogram of Pd-doped SDPP based on the TEM image.
Table 1. Study of different parameters on the reaction of iodobenzene
A
and phenylacetylene
500 nm
Fig. 1. Scanning electron microscopy (SEM) image of Pd-supported
[13]
SDPP.
Entry
Solvent
Base
mmol]
Temperature
Time
[h]
Conversion
B
[%]
[
[8C]
1
2
3
4
5
6
7
8
9
None
NMP
NMP
NMP
NMP
NMP
NMP
TBAB
EtOH
PEG 200
n-Pr
NaOH
CO
NaOAc
Cs CO
3
N
130
130
130
130
130
130
80
20
6
70
75
K
2
3
4.25
5.5
2.5
4
100
100
100
100
95
2
3
Morpholine
Morpholine
20
20
20
20
20
20
20
3
K
K
K
2
2
2
CO
CO
CO
3
3
3
80
50
80
80
10
11
12
13
14
15
16
17
18
80
90
PEG 200 NaOH
80
60
PEG 200 Morpholine
80
45
PEG 200 n-Pr
PEG 200 CO
PEG 200 Cs CO
3
N
80
73
K
2
3
100
100
100
100
100
100
70
2
3
20
2
C
C
D
PEG 200
PEG 200
PEG 200
K
K
K
2
CO
CO
CO
3
3
3
100
100
80
2
2
1
20
A
Reactionconditions: iodobenzene(0.5mmol), phenylacetylene(0.75 mmol),
base (0.75 mmol), catalyst (0.001 mg, 0.5 mol-%), solvent (1mL).
B
Conversion based on gas chromatography analysis.
C
The amounts of catalyst Pd(0)/SDPP used in entries 16 and 17 are 0.002 g
(
D
1 mol-%) and 0.003 (1.5 mol-%), respectively.
Applied catalysts: Pd(0)/SDPP (0.001 g, 0.5 mol-%) and CuI (0.002 g).
30 nm
Catalytic Activity of the Catalyst in C–C
Coupling Reaction
Fig. 2. Transmission electron microscopy (TEM) image of Pd-supported
[13]
SDPP.
In order to examine the efficiency of SDPP-supported nano-
particles of palladium as the catalyst, we decided to further our
studies on the Sonogashira reaction.
Preliminary screening was performed to compare different
systems in the Sonogashira reaction using different solvents and
bases as well as by changing the reaction temperature for the
reaction of iodobenzene with phenylacetylene as a model
reaction. Under solvent-free conditions, 1308C, and n-Pr N
3
(n-tripropylamine) as an amine base, the reaction was not
completed after 20 h and the conversion yield was only 70 %
2
2
1
1
50
00
50
00
(111)
(200)
(220)
(311)
50
(222)
(
Table 1, entry 1). Then, the effect of various solvents was
0
2
0
30
40
50
60
70
80
90
100
investigated. In N-methylpyrrolidone (NMP), as a polar aprotic
solvent, this reaction was examined in the presence of different
inorganic and organic bases using 0.001 g Pd(0)/SDPP at 1308C.
The results obtained in this solvent are shown in Table 1, entries
2
Theta [Њ]
[13]
Fig. 3. X-Ray diffraction pattern of Pd-supported SDPP.

9
28
N. Iranpoor et al.
2
–6. Decreasing the temperature from 130 to 808C in the
presence of morpholine as the base and NMP as the solvent,
5 % conversion of the starting material within 20 h was
Table 2. Sonogashira reaction of phenylacetylene with selected
A
organic halides
9
X
observed (Table 1, entry 7). The catalyst was inefficient when
it was used in ethanol (EtOH) and/or molten tetrabutylammo-
nium bromide (TBAB) using K CO as a base at 808C (Table 1,
Nano-Pd(0)/SDPP (1.5 mol-%)
ϩ
K CO , PEG 200
R
2
3
2
3
R
entries 8 and 9). The cross-coupling reaction was also screened
in polyethylene glycol (PEG) by using different organic and
X: I, Br, Cl, CH:CH-Br (R: H)
R: H, OCH , CH , NO , OH, NH , Cl, CN
3
3
2
2
1
4
inorganic bases at 808C. According to the literature, PEG is
regarded as a green solvent because it has several benign
characteristics, for example, low molecular weight liquid PEGs
are non-volatile and the vapour density for such PEGs is greater
than 1 relative to air according to available MSDS data, and is
consistent with the industry standard for replacement of volatile
B
Entry
Substrate
Product
Temperature Time Yield
[
8C]
[h]
[%]
I
Ph
1
2
100
100
1.5
95
1
4
organic solvents with PEG. PEG also has low flammability
and is biodegradable. In order to have green conditions for the
reaction, PEG 200 was selected. The use of n-Pr N, morpholine,
I
Ph
2.5
2.5
91
91
3
NaOH, and Cs CO was less efficient in comparison with the
2
3
use of K CO as a base at 808C (Table 1, entries 10–13, 15). We
2
3
H CO
Ph
3
4
3
100
100
therefore selected K CO as the most appropriate base. Hence,
3
2
H CO
3
the reaction progressed very well at 1008C within 3 h (Table 1,
entry 14). In all the above-performed reactions, the amount of
palladium supported on SDPP was 0.001 g (0.5 mol-%). When
the catalyst amount increased from 0.001 to 0.002 and 0.003 g,
the reaction time decreased from 3 to 2 and 1 h, respectively
I
I
H N
Ph
Ph
2
20
53
H N
2
(
Table 1, entries 16, 17). The effect of CuI on the reaction was
H2
N
5
6
7
120
100
100
5
4
73
90
65
also investigated. When CuI was used as the co-catalyst in the
Sonogashira reaction, the reaction proceeded achieving 80 %
conversion after 20 h (Table 1, entry 18). Hopefully, the use of
Pd(0)/SDPP provides a very suitable condition for conducting
the reaction in the absence of copper by using K CO as a cheap
H N
2
I
Ph
2
3
and available inorganic base in PEG as a green solvent.
Applying the optimized conditions i.e. 0.003 g (1.5 mol-%)
Pd(0)/SDPP, 0.75 mmol phenylacetylene, 0.75 mmol K CO ,
I
O N
Ph
2
1.5
O N
2
2
3
1
.0 mL PEG 200, a variety of aryl iodides and activated aryl
Br
Br
bromides at 1008C, and also less reactive and deactivated aryl
bromides and chlorides at 1208C were examined. The results are
illustrated in Table 2. Iodobenzene and iodobenzenes substitu-
ted with an electron-donating group at the para-position were
applied in this cross-coupling reaction, and the starting materials
were completely converted into the coupled products (Table 2,
entries 1–3, 5). In the case of nitro compounds, the dehaloge-
nated products were also observed in the mixture of the reaction.
The product of cross-coupling of 2-iodo-5-nitrotoluene with
phenylacetylene was obtained in moderate yields after 1.5 h.
O N
Ph
8
9
2
100
100
100
120
120
5
2
81
58
49
83
78
O N
2
NC
Ph
NC
Br
Br
Ph
Ph
1
1
0
1
28
4
N
N
(
Table 2, entry 7). Remarkably, the catalytic system was also
N
efficient for the aryl bromides. The coupling of 1-bromo-4-
nitrobenzene and 4-bromobenzonitrile with phenylacetylene
produced the desired product within 5 and 2 h, respectively.
Probably the elongation of the reaction time for 1-bromo-4-
nitrobenzene relates to its reduced solubility in PEG 200
N
Br
Cl
Ph
12
5
Cl
(
Table 2, entries 8 and 9). Heterocyclic bromides, such as 3-
Br
Br
Ph
Ph
bromopyridine and 3-bromothiophene, led to the corresponding
bi-functionalized acetylene indesirable yields at 1208C(Table2,
entries 11 and 16). The Sonogashira reaction of 4-chlorobromo-
benzene produced the coupled product in good yields with high
selectivity (Table 2, entry 12). The reaction between the steri-
cally hindered 1-bromonaphthalene and phenylacetylene was
not completed after 11 h and gave the desired product in 58 %
yield (Table 2, entry 13). Complete conversion was obtained for
the reaction of bromobenzene and 4-bromotoluene with pheny-
lacetylene, affording good yields (Table 2, entries 14 and 15).
The coupling reaction of ortho-substituted iodotoluene and
1
3
120
11
58
1
1
4
5
120
120
3
6
72
72
Br
Ph
(Continued)

Sonogashira Reaction in the Presence of Pd(0)/SDPP
929
Table 2. (Continued)
Table 3. Recycling of Pd catalyst for the Sonogashira reaction of
A
idobenzene and phenylacetylene
B
Entry
Substrate
Product
Temperature Time Yield
B
C
TOF [min
ꢁ1
[
8C]
[h]
[%]
Run
Time [h]
Isolated yield [%]
TON
]
Br
1
2
3
4
5
6
7
8
1.5
1.5
1.5
1.6
1.6
1.8
2.2
2.5
95
95
93
92
93
90
87
74
61
61
60
59
60
58
56
47
0.7
Ph
Ph
0.7
16
17
18
120
120
120
6
71
S
0.66
0.61
0.63
0.53
0.42
0.31
S
Br
7
72
64
Ph
Br
A
Reaction conditions: iodobenzene (0.5 mmol), phenylacetylene
CO (0.75 mmol), Pd(0)/SDPP (1.5 mol-%, 0.003 g), and
5.5
(
0.75 mmol), K
2
3
PEG 200 (1 mL) at 1008C.
B
TON (turn over number) ¼ mmol of products/mmol of catalyst.
Br
Cl
C
HO
Ph
TOF (turn over frequency) ¼ TON/time.
1
2
2
9
0
1
120
120
120
4
70
75
51
HO
Table 3. This investigation showed the excellent recyclability of
the catalyst in the Sonogashira reaction.
O N
Ph
Ph
2
7.5
O N
2
Conclusions
Cl
In this work, SDPP (silicadiphenyl phosphinite) as the solid
II
support for the generation of nano SDPP/Pd(0) from Pd has
NC
15
NC
been used for the efficient copper-free Sonogashira reaction of
aryl halides in PEG-200 as a green solvent. The obtained SDPP
can be used as a stable solid to immobilize nanoparticles of Pd
Cl
Ph
2
2
2
3
120
120
15
15
83
74
(0). The introduced catalyst can be used efficiently for the
Cl
coupling of aryl iodides, bromides, and chlorides. The recy-
clability of the catalyst can also be regarded as an advantage of
this method.
Ph
A
Reaction conditions: aryl halide (0.5 mmol), phenylacetylene (0.75 mmol),
CO (0.75 mmol), Pd(0)/SDPP (1.5 mol-%, 0.003 g), PEG 200 (1.0 mL)
Experimental
K
2
3
X-Ray diffraction data were collected on D8 Advance Bruker
AXS. TEM analyses were performed on a Philips CM 10
instrument. SEM images were obtained on a Philips XL-30 FEG
at 1008C for aryl iodides and 1208C for aryl bromides and chlorides.
B
Isolated yield.
C
[14–23]
Products are known compounds.
1
13
scanning electron microscope operating at 20 kV. H and
C
NMR spectra were recorded on a Bruker Avance DPX-250 MHz
spectrometer using tetramethylsilane as internal standard. For
gas chromatography analysis of the reaction mixture, n-heptane
was used as internal reference to calculate the conversion yield.
bromotoluene with phenylacetylene produced the desired pro-
ducts in excellent isolated yields (Table 2, entries 6 and 17). We
applied our protocol for the reaction of b-bromostyrene,
a vinylic bromide, and phenylacetylene under similar reaction
conditions. The reaction proceeded well within 5.5 h (64 %) in
PEG 200 (Table 2, entry 18). The catalytic system was efficient
for the coupling reaction of 4-bromophenol and phenylacetylene
at 1208C after 4 h to give the corresponding product in 70 %
yield (Table 2, entry 19). The coupling reaction of 1-chloro-
Synthesis of Pd(0)/SDPP Nanocatalyst
[13]
The catalyst was prepared according to our previous report
with modification as follows. To a 50 mL round bottom flask,
56 mg (0.25 mmol) Pd(OAc) and 0.1 g SDPP in 10 mL DMF
2
were added, and the mixture was heated at 90–1008C for 2 h. The
4
-nitrobenzene with phenylacetylene gave the product in
reaction mixture was allowed to cool and then centrifuged at
2
good yields (Table 2, entry 20). However, the reaction of 4-
chlorobenzonitrile with phenylacetylene produced the desired
product in moderate yields together with any unidentified side
product (Table 2, entry 21). The coupling reaction of chloro-
benzene and 4-chlorotoluene with phenylacetylene was per-
formed at 1208C. The desired products were obtained in very
good yields (Table 2, entries 22 and 23).
.236 g for 5 min. The resulting black powder was washed with
ethyl acetate (5 ꢀ 5 mL) and distilled water (5 ꢀ 5 mL)
and centrifuged at 2.236 g for 5 min after each wash. Finally,
it was dried under vacuum to give 0.12 g Pd(0)/SDPP catalyst.
The content of palladium(0) was determined by ICP to be
2
.6 mmol per 1 g.
General Procedure for the Sonogashira Coupling
Reaction of Aryl Halides and Phenylacetyene
in the Presence of Pd(0)/SDPP
Heterogeneity Test and Catalyst Reusability Test
The recoverability of the catalyst was examined for the reaction
of iodobenzene with phenylacetylene. After completion of the
reaction, the catalyst was recovered and used in eight successive
cycles. During this experiment, the Pd catalyst exhibited only a
slight loss in activity and required a slightly longer time in the
eighth run to achieve full conversion. The results are shown in
A round-bottom flask was charged with phenylacetylene
(0.75 mmol, 0.08 mL), K CO (0.75 mmol, 100 mg), PEG 200
2 3
(1 mL), and aryl halide (0.5 mmol). To this mixture, Pd(0)
nano-catalyst supported on SDPP (1.5 mol-%, 3.0 mg) prepared
[
13]
according to our previous report was added. In the case of aryl

9
30
N. Iranpoor et al.
iodides and activated aryl bromides, the reaction mixture was
placed in a 1008C oil bath; and in the case of the less active and
deactivated aryl bromides and chlorides, the reaction mixture
was placed in a 1208C oil bath. After completion of the reaction,
the catalyst was removed by centrifugation and the remaining
mixture was extracted with ethyl acetate (3 ꢀ 10 mL) and water
several times and dried over anhydrous Na SO . The organic
layer was evaporated under reduced pressure, and then purified
by column chromatography over silica gel 60 (230–240 mesh;
Merck) using petroleum ether/ethyl acetate (5 : 1) as eluent to
afford the product with high purity in 51–95 % yield. Note: This
procedure can also be used, but the catalyst is prepared in situ by
adding the appropriate amounts of SDPP and Pd(OAc)2.
(c) B.-N. Lin, S.-H. Huang, W.-Y. Wu, C.-Y. Mou, F.-Y. Tsai,
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1
2
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General Procedure for Recycling of the Catalyst
(
The reaction mixture of the Sonogashira reaction between
iodobenzene and phenyl acetylene was cooled to room tem-
perature, and water/ethyl acetate (1 : 1) was added to the reaction
mixture. After centrifuging at 2.236 g for 5 min the reac-
tion mixture and separating the upper phase, SDPP/Pd(0) cata-
lyst remained at the bottom of the vessel. The obtained catalyst
was washed with ethyl acetate to dissolve any residual organic
materials. Then, the recovered catalyst was used in eight suc-
cessive cycles.
(
(
(
01)81946-7
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TCR.10003
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0
03685001783238925
Supplementary Material
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Acc. Chem. Res. 2003, 36, 20. doi:10.1021/AR990017Q
Spectral data of the products are available on the Journal’s
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[
[
Acknowledgements
6
3. doi:10.1016/J.JORGANCHEM.2013.06.021
We would like to acknowledge the support of this work by Shiraz University
Research Council and a grant from Iran National Elite Foundation.
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