Palladium nanoparticles supported on silicadiphenyl phosphinite (SDPP) as efficient catalyst for Mizoroki-Heck and Suzuki-Miyaura coupling reactions

Article abstract of DOI:10.1016/j.jorganchem.2012.03.006

A very easy method is described for direct phosphorylation of silica gel to afford silica diphenylphosphinite (SDPP). This new phosphorylated silica contains higher amounts of P(III) moiety compared to the method based on the sol-gel technique. The phosphorylated silica reacts with Pd(II) to produce nano Pd(0)/SDPP which was characterized by different techniques. The obtained nano Pd(0) catalyst exhibited excellent reactivity and stability in the Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions with different aryl iodides and bromides. This heterogeneous catalyst can be easily recovered and reused in several runs.

Full text of DOI:10.1016/j.jorganchem.2012.03.006

Journal of Organometallic Chemistry 708-709 (2012) 118e124
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Palladium nanoparticles supported on silicadiphenyl phosphinite (SDPP) as
efficient catalyst for MizorokieHeck and SuzukieMiyaura coupling reactions
*
*
Nasser Iranpoor , Habib Firouzabadi , Somayeh Motevalli, Mohsen Talebi
Chemistry Department, College of Sciences, Shiraz University, Shiraz 71454, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A very easy method is described for direct phosphorylation of silica gel to afford silica diphenylphos-
phinite (SDPP). This new phosphorylated silica contains higher amounts of P(III) moiety compared to the
method based on the sol-gel technique. The phosphorylated silica reacts with Pd(II) to produce nano
Pd(0)/SDPP which was characterized by different techniques. The obtained nano Pd(0) catalyst exhibited
excellent reactivity and stability in the MizorokieHeck and SuzukieMiyaura cross-coupling reactions
with different aryl iodides and bromides. This heterogeneous catalyst can be easily recovered and reused
in several runs.
Received 2 June 2011
Received in revised form
27 February 2012
Accepted 6 March 2012
Keywords:
Palladium nanoparticle
Silicadiphenyl phosphinite
SuzukieMiyaura reaction
MizorokieHeck reaction
Heterogeneous catalyst
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
Normally, supported Pd catalysts show lower reactivity than
homogeneous ones and require more drastic reaction conditions
Formation of carbonecarbon bond is among the most funda-
mental reactions in organic chemistry. In many of these reactions,
transition metals or their complexes have been applied as catalyst
and promoter. Among different transition metals [1], Pd based
catalysts have been found enormous applications in these reactions
during the last decades. Carbonecarbon bond formation catalyzed
by Pd based catalysts in the MizorokieHeck [2], and the
SuzukieMiyaura reaction [3] has been recognized as powerful tools
and major area of interest in multiple organic transformations for
academic and industrial processes [4]. In this regard, the chemists
are faced the challenge of improving different aspects of Pd catalysts.
Although the homogeneous palladium catalysis in comparison
with the heterogeneous ones usually provides higher reaction rates
and turnover numbers (TON) and often affords higher selectivity
and yields, but suffer the problem of recycling of the catalyst [5]. In
order to overcome this problem, great efforts have been devoted to
develop recyclable heterogeneous catalysts. In this regard, Pd-
supported catalysts on organic or inorganic solid beds such as
polymers [6], activated carbon [7], zeolites and molecular sieves [8],
metal oxides [9], clays [10], and porous glass [11] have found
considerable synthetic applications.
but provide ease of separation and recycling of the catalyst. In
addition, they are relatively more stable and usually allow running
the reaction without the exclusion of air [12]. Some industrial
applications of heterogeneous catalysts have already been devel-
oped [13].
Phosphines and phosphinites as important phosphorous-based
ligands in organometallic chemistry are of current interest and
their metal complexes have been used in many catalytic reactions
[14]. However, phosphine ligands are comparatively difficult to
make or rather more expensive [15]. Also some of them are not easy
to handle and often lead to competitive degradation of the Pd
catalyst through the PeC bond cleavage of a coordinated phosphine
ligand [16].
Due to both economical and chemical reasons, phosphinite
ligands are under more develop and attention. There are a few
reports that these ligands have been applied as heterogeneous
ligands anchored on polymeric supports or silica gel [14].
In continuation of our studies on using phosphinite ligands [17],
we herein disclose the easy preparation of a stable, cheap and
efficient heterogeneous nano palladium silica based catalyst con-
taining the diphenylphosphinite group without the need of using
any reduction step and/or sol-gel technique. This new nano Pd
catalyst is characterized and used with excellent activity, stability
and recyclability in MizorokieHeck and SuzukieMiyaura cross-
coupling reactions with different aryl halides.
* Corresponding authors. Tel.: þ98 711 2287600; fax: þ98 711 2280926.
E-mail addresses: iranpoor@chem.susc.ac.ir (N. Iranpoor), firouzabadi@
chem.susc.ac.ir (H. Firouzabadi).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.03.006

N. Iranpoor et al. / Journal of Organometallic Chemistry 708-709 (2012) 118e124
119
2. Experimental
2.4. General procedure for the SuzukieMiyaura coupling reaction
X-Ray diffraction data obtained with XRD, D8, Advance, Bruker,
axs. TEM analyses were performed on a Philips model CM 10
instrument. Scanning electron micrograph was obtained by SEM,
XL-30 FEG SEM, Philips, at 20 kV. The plate silica gel type 60
Pd(0)/SDPP (1.5 mol%, 6 mg), NaOH (1.5 mmol, 60 mg), phe-
nylboronic acid (1.5 mmol, 180 mg), aryl halide (1.0 mmol), and
EtOH (2.0 mL) were placed in a 50 mL flask equipped with
a magnetic stirring bar under reflux. The completion of the reaction
was monitored by TLC. After completion of the reaction, the catalyst
was removed by filtration. The obtained solution was then
concentrated and purified by column chromatography over silica
gel using n-hexane/ethyl acetate (5:1) as eluent to afford the
product with high purity. The products were identified by their
spectral data and comparison with authentic samples
(Supplementary section).
(15e40 mm) was used for the preparation of phosphorylated silica
and was preactivated by refluxing in HCl (aq. 37%) for 4 h. It was
then filtered and washed several times with distilled water to
remove the produced HCl and dried in a vacuum oven at 200 ꢀC for
24 h before use.
2.1. Preparation of silicadiphenyl phosphinite (SDPP)
2.5. General procedure for recycling of the catalyst
Under an argon atmosphere, to a flask containing activated
dried plate silica gel (0.3 g, 5 mmol) ClPPh2 (2 mL, 10 mmol) was
added at room temperature and stirred with a mechanical stirrer
for 30 min. The mixture was then heated to 60 ꢀC for 3 h to remove
the produced HCl. The reaction mixture was then washed with
10 mL of diethyl ether and dried under vacuum. SDPP was obtained
as a white solid (0.6 g), which was stored in a capped bottle without
The reaction mixture of either Heck or Suzuki reaction was
cooled down to room temperature and the solvent was removed by
evaporation. Ethyl acetate was then added to the reaction mixture
and centrifuged. This process was repeated again with water and
then the catalyst was dried under vacuum and reused without any
pretreatment for the repeating cycles.
any change for months. IR, KBr disk,
n
(cmꢁ1): 3425, 1435, 1160,
1126, 964, 725, 694. In order to determine the amount of active
phosphorous content of the reagent, silicaphosphinite was reacted
with the excess of iodine in acetonitrile and stirred for 5 h at room
temperature. On the basis of titration (three runs) of the unreacted
iodine with an aqueous solution of sodium thiosulfate (0.01 M), the
amount of active phosphorous content was found to be 2.25 mmol
per 1 g of SDPP.
3. Results and discussion
3.1. Synthesis and characterization
In this work we report a very easy method for the synthesis of
palladium(0)-silica diphenylphosphinite; Pd(0)/SDPP complex
(Scheme 1). The surface of silica, type 60 Å (15e40
mm) was first
activated by refluxing in aq. HCl (37%) for 4 h. It was then covalently
functionalized by treatment with ClPPh2 under argon atmosphere
at room temperature. The phosphorous content of the functional-
ized silica was obtained by iodometric titration method and was
found to be 2.25 mmol per 1 g. The Pd(0) complex was easily
obtained by mixing Pd(OAc)2 with SDPP in DMF at 90e100 ꢀC as
described in the experimental section. The active Pd(0) catalyst was
formed initially by coordination of P atoms to Pd(II) center, fol-
lowed by the reduction to Pd(0) by another phosphinite group and
eventually the catalyst as a black insoluble mass was obtained. We
have recently reported this reduction pathway for Pd(II) in an ionic
liquid carrying -OPPh2 group [17a,b]. Determination of the Pd
content was carried out by inductively coupled plasma (ICP) anal-
ysis on the digested catalyst in refluxing aq. HCl (37%). The obtained
results revealed that 2.6 mmol per 1 g of Pd is immobilized on SDPP,
which is much higher than that reported for the method which is
based on sol-gel technique (0.118 mmol/g) [18].
The information about the surface of catalyst was obtained by
the scanning electron microscopy (SEM) image as presented in
Fig.1. The SEM image shows particles with diameters in the range of
nanometers.
Transmission electron microscopy (TEM) image of the catalyst
shows that Pd nanoparticles are formed and dispersed in the silica
matrix with a size w 7 nm (Fig. 2).
2.2. Preparation of palladium catalyst
To a mixture of Pd(OAc)2 (0.25 mmol, 56 mg) in DMF (10 mL)
was added SDPP (0.1 g). The mixture was heated at 90e100 ꢀC for
24 h. The reaction mixture was allowed to cool and then centri-
fuged. The resulting black powder was washed with ethyl acetate
(5 ꢂ 5 mL) and distilled water (5 ꢂ 5 mL) and centrifuged after each
washing. Finally, it was dried under vacuum to give 0.121 g of Pd(0)/
SDPP catalyst. The content of palladium(0) was determined by ICP
to be 2.6 mmol per 1 g.
2.3. General procedure for the MizorokieHeck coupling reaction
Pd(0)/SDPP (0.5 mol%, 2 mg), nPr3N (1.5 mmol, 0.28 mL), olefin
(1.5 mmol), aryl halide (1.0 mmol) were placed in a 25 mL flask
equipped with a magnetic stirring bar under solvent-free condition
and heated at 130 ꢀC. The completion of the reaction was monitored
by TLC analysis. After completion of the reaction, the reaction
mixture was cooled to room temperature and purified by column
chromatography over silica gel using n-hexane/ethyl acetate (5:1)
as eluent to afford the highly pure products. The products were
identified by their spectral data and comparison with authentic
samples (Supplementary section).
The X-ray diffraction (XRD) pattern of the Pd catalyst shows the
(111) (2 0 0) (2 2 0) (3 11) and (2 2 2) crystallographic planes of the
SiO2
SiO2
SiO2
1. rt, 30 min
under N2
Pd(OAc)2/ DMF
ClPPh2
OH
Pd(0)
n
OPPh2
OPPh2
°
2. 60 C,3h
90-100 oC, 24 h
Activated
Scheme 1. Synthesis of Pd(0)/SDPP.

120
N. Iranpoor et al. / Journal of Organometallic Chemistry 708-709 (2012) 118e124
Fig. 3. Histogram of Pd-doped SDPP based on the TEM image.
preprepared nano Pd(0) catalyst immobilized on SDPP (Table 1,
entry 2) and nPr3N under solvent free condition. Comparison of the
results obtained by these two routs clearly shows that the immo-
bilized Pd(0)/SDPP complex as a heterogeneous catalytic system for
this reaction is more efficient than using Pd(OAc)2 and SDPP
separately. In the absence of Pd catalyst, the reaction time is 20 h
under the same reaction condition. The completion of the reaction
is due to the Pd contamination of nPr3N which was found by ICP
analysis to be 5.61 ppm.
Fig. 1. Scanning electron micrograph (SEM) image of Pd-supported SDPP.
Pd(0) nanoparticles according to the literature [19] (Fig. 4). The Pd
nanoparticle size was estimated from the XRD pattern using the
Scherrer equation [20] to be 8 nm which is in good harmony with
the results obtained from TEM (Fig. 2) and histogeram (Fig. 3)
analysis.
Choosing the nano Pd(0)/SDPP immobilized catalyst as the
preferred catalyst, we then studied the effects of different solvents
and bases and also solvent-free condition. It was observed that the
model cross-coupling reaction occurred less efficiently in organic
solvents compared to the solvent-free condition (Table 1, entries
11e14). In addition, comparison of the obtained results (Table 1,
entries 2, 3 and 11) also shows that, the reaction occurs more
effieciently under solvent-free condition. If the reaction is per-
fomed using unimmobilized catalyst (Table 1, entry 15), the reac-
tion time is slightly shorter. This could possibly be due to the
solubility of Pd(OAc)2 in DMF which can perform the reaction under
homogeneous condition. In general, the use of organic solvents is
the major problem in chemical industries [21], therefore the
solvent-free condition which is rarely used for CeC bond formation
[22], was considered as the most suitable condition for our study.
Using organic and inorganic bases showed that nPr3N is the most
suitable one for this reaction (Table 1, entries 2, 7e9).
3.2. Catalytic activity of the catalyst in CeC coupling reactions
Firstly, the efficiency of catalyst was evaluated in the Heck
reaction as a versatile method for CeC bond formation in organic
synthesis. We initially studied the coupling of 1-bromo-4-
nitrobenzene with n-butyl acrylate as a model reaction under
two different reaction conditions (Table 1). We performed the
reaction using (i) Pd(OAc)2 as a homogeneous catalyst in the
presence of silicadiphenyl phosphinite (SDPP) as ligand and nPr3N
as the base (Table 1, entry 1) and also (ii) in the presence of
Under our optimized reaction conditions (1.0 mmol of aryl
halide, 1.5 mmol of nPr3N, 1.5 mmol of n-butyl acrylate, 2 mg
(0.5 mol%) SDPP supported Pd(0) under solvent-free conditions at
130 ꢀC), the desired products were obtained in good to excellent
yields for a wide array of aryl iodides and bromides (Scheme 2). The
results are shown in Table 2.
250
(111)
200
150
100
(200)
(220)
70
(311)
50
0
(222)
90
20
30
40
50
60
80
100
2-Theta-Scale
Fig. 2. Transmission electron microscopy (TEM) of Pd-supported SDPP.
Fig. 4. XRD pattern of Pd-supported SDPP.

N. Iranpoor et al. / Journal of Organometallic Chemistry 708-709 (2012) 118e124
121
Table 1
Table 2
Optimization of different parameters for coupling of 1-bromo-4-nitrobenzene and
Heck reaction of n-butyl acrylate or styrene with aryl halidesa
n-butyl acrylate in the Heck reactiona
X
Y
nPr3N, Pd(0)/SDPP
Y
Br
CO2Bu-n
Base, Catalyst
Solvent, Temp.
°
CO2Bu-n
Solvent- free, 130 C
R
R
O2N
O2N
.
.
Entry
1
substrate
Y
Time (h)
1
Isolated yield (%)
99
Entry Catalyst (mg)
Base
nPr3N
Solvent Time (h) Temp (ꢀC) Yield (%)b
1
Pd(OAc)2/SDPP
(2:2)
none
6
130
100
I
-CO2Bu-n
2
3
4
SDPP/Pd(0) (4)
SDPP/Pd(0) (2)
SDPP/Pd(0) (1)
SDPP/Pd(0) (4)
SDPP/Pd(0) (4)
SDPP/Pd(0) (4)
SDPP/Pd(0) (4)
SDPP/Pd(0) (4)
SDPP/Pd(0) (4)
SDPP/Pd(0) (4)
SDPP/Pd(0) (4)
SDPP/Pd(0) (4)
SDPP/Pd(0) (4)
Pd(OAc)2/SDPP
(2:2)
nPr3N
nPr3N
nPr3N
nPr3N
nPr3N
K2CO3
Cs2CO3
none
none
none
none
none
none
none
2
130
130
130
130
130
130
130
130
110
130
130
110
80
100
100
100
80
85
5
10
20
80
90
87
e
1.5
2.5
6
6
2
2
2
12
6
6
5c
6d
7
2
3
4
-CO2Bu-n
-CO2Bu-n
-CO2Bu-n
1
1
2
94
91
90
8
9
Morpholine none
10
11
12
13
14
15
nPr3N
nPr3N
nPr3N
nPr3N
nPr3N
nPr3N
none
DMF
DMSO
Toluene 24
EtOH
DMF
24
1
e
130
100
a
Reaction conditions: (a) 1-bromo-4-nitrobenzene (1.0 mmol), n-butyl acrylate
5
-CO2Bu-n
1
85
(1.5 mmol), base (1.5 mmol), Pd(0)/SDPP, no solvent and (b) 1-bromo-4-
nitrobenzene (1.0 mmol), n-buthyl acrylate (1.5 mmol), nPr3N (1.5 mmol), Pd(0)/
SDPP, and solvent (2 mL).
b
Conversion yield based on GC analysis.
c
The amount of n-butyl acrylate was 1.0 mmol.
The amount of nPr3N was 1.0 mmol.
d
6
7
-CO2Bu-n
-CO2Bu-n
0.1
1.5
92
60
I
The cross-coupling reaction proceeded smoothly for iodo-
benzene and iodobenzenes bearing either electron-withdrawing or
electron-donating groups at the para position and activated bro-
mobenzenes with n-butyl acrylate (Table 2, entries 1e3, 6e7,
9e10). The ortho-methyl iodobenzene which has some steric
effect also produced the desired coupled product in excellent yield
(Table 2, entry 4). Also, the Heck reaction of sterically hindered 1-
iodonaphthalene afforded a good yield of the corresponding
coupled product (Table 2, entry 8). nBu4NBr salt, the so-called
Jeffery conditions, as an additive [23,24] was applied to the cross-
coupling of deactivated aryl bromides with n-butyl acrylate
(Table 2, entries 12e16). In general, the efficiency of the coupling
reactions were observed to be lower when the reaction proceeds
with the less reactive styrene compared to n-butyl acrylate (Table 2,
entries 17e24).
From its first report, the Suzuki coupling reaction is the most
investigated cross-coupling reaction in the synthesis of unsym-
metrical biaryls. Due to the importance of biaryls, we applied our
new catalytic system to this coupling reaction. We initially used 1
and 1.5 mol% of the Pd(0)/SDPP for the coupling of 1-bromo-4-
nitrobenzene with phenylboronic acid at 80 ꢀC. The effect of polar
protic and aprotic solvents, and also different bases were also
studied on the progress of the reaction (Table 3).
HO
I
8
-CO2Bu-n
1
78
9
-CO2Bu-n
-CO2Bu-n
1.5
6
83
79
Br
10
NC
N
Br
11
-CO2Bu-n
-CO2Bu-n
-CO2Bu-n
-CO2Bu-n
2.6
7
85
70
89
68
N
Br
12b
13b
14b
N
Br
5
Cl
Br
Br
X
Y
24
nPr3N, Pd(0)/SDPP
Y
°
Solvent- free, 130 C
R
R
15b
16b
-CO2Bu-n
-CO2Bu-n
24
24
60
52
X: Br, I
Y: CO2Bu-n, Ph
R: H, CH3, OCH3, NO2, OH, Cl, CN
Scheme 2. MizorokieHeck cross-coupling reaction.
(continued on next page)

122
N. Iranpoor et al. / Journal of Organometallic Chemistry 708-709 (2012) 118e124
Table 2 (continued )
Entry
substrate
Y
Time (h)
0.5
Isolated yield (%)
80
X
B(OH)2
SDPP/Pd(0), NaOH
R'
°
R'
EtOH, 80 C
R
17
-Ph
R
X: Br, I
R: H, NO2, CN, Cl,CH3, OCH3, NH2, OH
R': H, F
18
19
20
21
-Ph
-Ph
-Ph
-Ph
4
4
75
75
70
73
Scheme 3. SuzukieMiyaura cross-coupling reaction.
reaction described above, the Suzuki reaction was performed under
milder reaction condition (80 ꢀC in EtOH). The results are shown in
Table 4.
10
9
3.3. Heterogeneity test and catalyst reuse
I
I
The importance of using heterogeneous catalyst is due to their
application in industry and the reusability of catalyst is the major
area of interest. Therefore, the recovery and reusability of our
supported catalyst was investigated in the Heck reaction of iodo-
benzene with n-butyl acrylate which required higher temperature
than the Suzuki reaction. The results are tabulated in Table 5.
22
23
-Ph
1.5
90
-Ph
-Ph
6
6
70
50
Table 4
Br
Suzuki reaction of phenylboronic acid with aryl halidesa
24
NC
X
B(OH)2
a
Reaction conditions: aryl halide (1.0 mmol), n-butyl acrylate or styrene
SDPP/Pd(0), NaOH
R'
(1.5 mmol), nPr3N (1.5 mmol), SDPP/Pd(0) (0.5 mol%, 2 mg).
°
b
Reaction conditions: aryl halide (1.0 mmol), n-butyl acrylate (1.5 mmol), nPr3N
R'
EtOH, 80 C
R
R
(1.5 mmol), SDPP/Pd(0) (0.5 mol%, 2 mg), TBAB (0.5 g, 1.5 mmol).
.
Entry
Ar-X
AreAr
Time (h) Isolated
It was found that the best solvent for this reaction was ethanol in
the combination with NaOH as base, which yielded a 100%
conversion of 1-bromo-4-nirobenzene to 4-nitrobiphenyl within
45 min using 1.5 mol% of the Pd catalyst (Table 3, entry 11). The
reaction of different aryl halides with phenylboronic acid was
studied under the obtained optimized conditions, under which,
aryl iodides and activated bromides produced high to excellent
yields of the coupled products (Scheme 3). Compared to the Heck
yield (%)
Ph
I
1
2
3
3
99
Ph
93
93
89
72
95
H3C
Table 3
Ph
Optimization of different parameters of 4-nitrobromobenzene and phenylboronic
3
4
5
6
1
acid in the Suzuki reactiona
H3CO
Br
I
Ph
B(OH)2
SDPP/Pd (0), Base
1.5
1
°
Solvent, 80 C, 45 min
CH3
CH3
O2N
O2N
.
I
Ph
Entry Catalyst (mg) Base
Solvent
GC conversion (%)
1
2
3
4
5
6
7
8
4
4
4
4
4
4
4
4
4
4
6
4
K2CO3
NaOH
Et3N
EtOH
EtOH
EtOH
EtOH
80
85
10
30
75
15
66
18
24
8
H2N
H2N
Ph
KOAc
0.1
Na3PO4.12H2O EtOH
(NH4)2CO3
Cs2CO3
NaOH
EtOH
EtOH
DMSO
DMF
None
EtOH
O2N
Ph
I
9
NaOH
10
11
12
nPr3N
CH3
CH3
NaOH
NaOH
100
20
7
0.15
85
EtOH:H2O (2:1)
a
Reaction conditions: 1.0 mmol of 1-bromo-4-nitrobenzene, 1.5 mmol of phe-
NO2
NO2
nylboronic acid, base (1.5 mmol), catalyst (4, 6 mg) and 2 mL of solvent.

N. Iranpoor et al. / Journal of Organometallic Chemistry 708-709 (2012) 118e124
123
Table 4 (continued )
Entry Ar-X
Table 5
Recycling of Pd catalyst for the Heck reaction of iodobenzene with n-butyl acrylatea
AreAr
Time (h) Isolated
yield (%)
Run
Time (min)
Yield (%)b
Pd-leaching %c
TONd
1
2
3
4
5
6
60
60
60
65
75
99
97
96
95
94
94
3.5
3.6
3.6
3.9
4.2
4.3
198
194
192
190
188
188
Ph
I
8
1
76
75
220
a
Reaction conditions: iodobenzene (1.0 mmol), n-butyl acrylate (1.5 mmol),
I
Ph
nPr3N (1.5 mmol), Pd(0)/SDPP (2 mg, 0.5 mol%) at 130 ꢀC.
9
11
9
b
Isolated yield.
The analysis was performed by ICP technique.
TON ¼ mmol of products/mmol of catalyst.
c
HO
HO
d
Ph
Br
10b
11
91
DMF at 130 ꢀC was cooled down to room temperature after 10 min.
GC analysis of the reaction mixture showed that 45% of iodo-
benzene has been converted to its corresponding coupled product.
The reaction mixture was then filtered to remove the catalyst and
the obtained filtrate was left to react more at 130 ꢀC. GC analysis of
the reaction after 24 h showed that 90% conversion has been
occurred. Comparison of this result with the data of Table 2, entry 1
(99% isolated yield after 1 h), indicates that the reaction has been
catalyzed mainly by the heterogeneous catalyst although the
possibility of homogeneous catalysis by the leaching catalyst can
not be ruled out. In order to see if the leaching palladium can re-
adsorbed on SDPP, we performed two more experiments. In this
study, the coupling reaction of iodobenzene and n-butyl acrylate
was stopped once after 10 min and the other reaction after
completion (1 h) and both reaction mixtures were filtered. Both
filtrates were analyzed by ICP for palladium leaching. The amount
of palladium-leaching was found to be 17.7 and 3.5% respectively
indicating that part of the leached palladium is absorbed again on
the surface of the silicaphosphinite support and behave heteroge-
neously as Pd(0)/SDPP. Considering the above observations, it can
be concluded that the supported catalyst is more responsible than
the leached palladium for the occurrence of the reaction. The
demonstrated data of Table 1, entries 2 and 11, also supports this
conclusion, since the coupling reaction of 1-bromo-4-nitrobenzene
with n-butyl acrylate in the presence of Pd(0)/SDPP in DMF which
has considerable leaching (17.7%) is more slowly than the reaction
under solvent-free condition.
Br
Ph
0.75
100
O2N
NC
O2N
NC
Br
Ph
12
13
0.75
1.5
93
90
Ph
Br
N
N
N
N
Br
Ph
14
15
4
2
80
86
N
N
Ph
Br
Cl
Cl
Br
Ph
16b
17
9
1
85
73
H3C
H3C
Ph
Br
4. Conclusion
Br
Ph
18b
15
20
90
In this work a very easy and cheap method is described for
phosphorylation of silica gel without the need to use any sol-gel.
The obtained silicadiphenyl phosphinite (SDPP) can be used as
a stable solid to immobilize nanoparticles of Pd(0). This new
phosphorylated silica contains higher amounts of P(III) moiety
compared to the method based on the sol-gel technique which
allows higher loading of nano Pd(0). The introduced catalyst can be
used efficiently for the coupling of aryl iodides and bromides. The
recyclability of the catalyst can also be regarded as an advantageous
of this method.
HO
NC
HO
NC
Br
19
1
F
a
Reaction conditions: 1.0 mmol of aryl halide, 1.5 mmol of phenylboronic acid or 4-
fluoroboronic acid, 6 mg of Pd(0)/SDPP (1.5 mol%), 1.5 mmol of NaOH, and 2 mL EtOH.
b
Reaction conditions: 1.0 mmol of aryl halide, 1.5 mmol of phenylboronic acid,
Pd(0)/SDPP (1.5 mol%, 6 mg), 3.0 mmol of NaOH, and 2 mL of DMF at 110 ꢀC.
Acknowledgments
To investigate the palladium-leaching in these reactions, the
filtrate of the Heck reaction between iodobenzene and n-butyl
acrylate after completion was analyzed by ICP technique. Due to the
observation of low palladium concentration in the filtrate (3.5%), it
can be concluded that the catalyst has high stability for recycling.
In order to know whether the reaction takes place at the surface
of solid Pd as a truly heterogeneous reaction or the Pd-leaching acts
as catalyst, the hot filtration test was done [25]. The reaction of
iodobenzene and n-butyl acrylate in the presence of Pd(0)/SDPP in
We are grateful to Shiraz university research council for the
partial support of this work.
Appendix A. Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2012.03.006.

124
N. Iranpoor et al. / Journal of Organometallic Chemistry 708-709 (2012) 118e124
[13] V.M. Wall, A. Eisenstadt, D.J. Ager, S.A. Laneman, Platinum Met. Rev. 43 (1999)
References
138e145.
[14] (a) A. Mansour, M. Portnoy, J. Mol. Catal. A: Chem. 250 (2006) 40e43;
(b) G. Singh, S. Bali, A.K. Singh, Polyhedron 26 (2007) 897e903;
(c) D.E. Bergbreiter, A.M. Kippenberger, G. Tao, Chem. Commun. (2002)
2158e2159;
(d) M. Guino, K.K. Hii, Tetrahedron Lett. 46 (2005) 6911e6913;
(e) R. Chanthateyanonth, H. Alper, J. Mol. Catal. A: Chem. 201 (2003) 23e31;
(f) B. Tamami, S. Ghasemi, J. Mol. Catal. A: Chem. 322 (2010) 98e105;
(g) H. Kosslick, I. Mönnich, E. Paetzold, H. Fuhrmann, R. Fricke, D. Müller,
G. Oehme, Micropor. Mesopor. Mater. 44-45 (2001) 537e545;
(h) E. Paetzold, G. Oehme, H. Fuhrmann, M. Richter, R. Eckelt, M.M. Pohl,
H. Kosslick, Micropor. Mesopor. Mater. 44-45 (2001) 517e522.
[15] B. Punji, C. Ganesamoorthy, M.S. Balakrishna, J. Mol. Catal. A: Chem. 259
(2006) 78e83.
[1] (a) P.M. Maitlis, A. Haynes, in: G.P. Chiusoli, P.M. Maitlis (Eds.), Metal-catalysis
in Industrial Organic Processes, RSC Publishing, Cambridge, UK, 2006, pp.
146e162;
(b) F. Calderazzo, M. Catellani, G.P. Chiusoli, in: G.P. Chiusoli, P.M. Maitlis
(Eds.), Metal-catalysis in Industrial Organic Processes, RSC Publishing, Cam-
bridge, UK, 2006, pp. 163e175.
[2] (a) R.F. Heck, J.P. Nolley Jr., J. Org. Chem. 37 (1972) 2320e2322;
(b) H.A. Dieck, R.F. Heck, J. Am. Chem. Soc. 96 (1974) 1133e1136;
Palladium-catalyzed conjugated diene synthesis from vinylic halides and
olefinic compounds, J. Org. Chem. 40 (1975) 1083e1090.
[3] N. Miyaura, K. Yamada, A. Suzuki, Tetrahedron Lett. 20 (1979) 3437e3440.
[4] (a) M. Larhed, A. Hallberg, in: E. Negishi (Ed.), Handbook of Organo-
palladium Chemistry for Organic Synthesis, WileyeInterscience, New York,
2002;
(b) I.P. Beletskaya, A.V. Cheprakov, Chem. Rev. 100 (2000) 3009e3066.
[5] C.E. Garrett, K. Prasad, Adv. Synth. Catal. 346 (2004) 889e900.
[6] A. Biffis, M. Zecca, M. Basato, J. Mol. Catal. A: Chem. 173 (2001) 249e274.
[7] (a) M. Seki, Synthesis (2006) 2975e2992;
[16] N.J. Whitcombe, K.K. Hii, S.E. Gibson, Tetrahedron 57 (2001) 7449e7476.
[17] (a) N. Iranpoor, H. Firouzabadi, R. Azadi, Eur. J. Org. Chem. 13 (2007)
2197e2201;
(b) N. Iranpoor, H. Firouzabadi, R. Azadi, J. Organomet. Chem. 693 (2008)
2469e2472;
(c) N. Iranpoor, H. Firouzabadi, A. Tarassoli, M. Fereidoonnezhad, Tetrahedron
66 (2010) 2415e2421;
(d) H. Firouzabadi, N. Iranpoor, M. Gholinejad, J. Mol. Catal. A: Chem. 321
(2010) 110e116;
(e) N. Iranpoor, H. Firouzabadi, R. Azadi, J. Organomet. Chem. 695 (2010)
887e890.
(b) F. Zhao, B.M. Bhanage, M. Shirai, M. Arai, Chem. Eur. J. 6 (2000) 843e848;
(c) H. Hagiwara, Y. Shimizu, T. Hoshi, T. Suzuki, M. Ando, K. Ohkubo,
C. Yokoyama, Tetrahedron Lett. 42 (2001) 4349e4351;
(d) F. Zhao, M. Shirai, M. Arai, J. Mol. Catal. A: Chem. 154 (2000) 39e44.
[8] (a) M.L. Toebes, J.A. van Dillen, K.P. de Jong, J. Mol. Catal. A: Chem. 173 (2001)
75e98;
[18] W. Chen, P. Li, L. Wang, Tetrahedron 67 (2011) 318e325.
[19] S. Martinez, A. Vallribera, C.L. Cotet, M. Popovici, L. Martin, A. Roig,
M. Moreno-Manas, E. Molins, New J. Chem. 29 (2005) 1342e1345.
[20] B.-Q. Xu, J.-M. Wei, H.-Y. Wang, K.-Q. Sun, Q.-M. Zhu, Catal. Today 68 (2001)
217e225.
[21] R.A. Sheldon, Chem. Tech. 24 (1994) 38e47.
[22] (a) N.E. Leadbeater, V.A. Williams, T.M. Barnard, M.J. Collins, Synlett (2006)
2953e2958;
(b) A. Diazortiz, P. Prieto, E. Vazquez, Synlett (1997) 269e270.
[23] (a) T. Jeffery, J.C. Galland, Tetrahedron Lett. 35 (1994) 4103e4106;
(b) T. Jeffery, Tetrahedron 52 (1996) 10113e10130.
[24] C.S. Consorti, F.R. Flores, J. Dupont, J. Am. Chem. Soc. 127 (2005)
12054e12065.
(b) C.P. Mehnert, D.W. Weaver, J.Y. Ying, J. Am. Chem. Soc. 120 (1998)
12289e12296;
(c) L. Djakovitch, K. Koehler, J. Am. Chem. Soc. 123 (2001) 5990e5999;
(d) L. Djakovitch, K. Koehler, J. Mol. Catal. A: Chem. 142 (1999) 275e284;
(e) L. Djakovitch, H. Heise, K. Köhler, J. Organomet. Chem. 584 (1999) 16e26.
[9] (a) A. Biffis, M. Zecca, M. Basato, Eur. J. Inorg. Chem. 2001 (2001) 1131e1133;
(b) K. Köhler, M. Wagner, L. Djakovitch, Catal. Today 66 (2001) 105e114.
[10] (a) R.K. Ramchandani, B.S. Uphade, M.P. Vinod, R.D. Wakharkar,
V.R. Choudhary, A. Sudalai, Chem. Commun. (1997) 2071e2072;
(b) R.S. Varma, K.P. Naicker, P.J. Liesen, Tetrahedron Lett. 40 (1999)
2075e2078.
[11] J. Li, A.W.H. Mau, C.R. Strauss, Chem. Commun. (1997) 1275e1276.
[12] R.G. Heidenreich, J.G.E. Krauter, J. Pietsch, K. Köhler, J. Mol. Catal. A: Chem.
182-3 (2002) 499e509.
[25] L. Yin, J. Liebscher, Chem. Rev. 107 (2007) 133e173.