Synthesis, crystal structural study and catalyst active of benzyloxycarbonylmethyl triphenylphosphonium hexabromopalladate (II) in amination of aryl halides and Suzuki cross-coupling reaction

Article abstract of DOI:10.1007/s13738-018-1406-z

In this study, palladium (II) chloride reacted with the phosphonium salt [PhCH₂COOCH₂P(Ph)₃]Br to give [PhCH₂COOCH₂P(Ph)₃]₂[Pd₂Br₆] (1). The characterization of synthesized compound was performed by elemental analysis, FT-IR, ¹H, ³¹P, ¹³C NMR and also X-ray crystallography. It was found that this compound works as an efficient catalyst for the amination of aryl halides to afford primary amines, the results of which were satisfactory. Furthermore, it was found that the catalyst showed a high activity for Suzuki carbon–carbon cross-coupling of aryl halides and phenylboronic acid. Interestingly, the catalyst can be recovered from the reaction mixture and recycled four consecutive runs without any significant loss in activity.

Full text of DOI:10.1007/s13738-018-1406-z

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-018-1406-z
ORIGINAL PAPER
Synthesis, crystal structural study and catalyst active
of benzyloxycarbonylmethyl triphenylphosphonium
hexabromopalladate (II) in amination of aryl halides and Suzuki cross-
coupling reaction
Arash Ghorbani‑Choghamarani1 · Ali Naghipour1 · Heshmatollah Babaee1 · Hayedeh Heidarnezhad1 ·
Behrouz Notash1
Received: 1 December 2017 / Accepted: 18 May 2018
© Iranian Chemical Society 2018
Abstract
In this study, palladium (II) chloride reacted with the phosphonium salt [PhCH2COOCH2P(Ph)3]Br to give
[PhCH2COOCH2P(Ph)3]2[Pd2Br6] (1). The characterization of synthesized compound was performed by elemental analy-
sis, FT-IR, 1H, 31P, 13C NMR and also X-ray crystallography. It was found that this compound works as an efficient catalyst
for the amination of aryl halides to afford primary amines, the results of which were satisfactory. Furthermore, it was found
that the catalyst showed a high activity for Suzuki carbon–carbon cross-coupling of aryl halides and phenylboronic acid.
Interestingly, the catalyst can be recovered from the reaction mixture and recycled four consecutive runs without any sig-
nificant loss in activity.
Keywords Crystal structure · Phosphonium · Palladium (II) chloride · Amination · Suzuki cross-coupling
Introduction
polymerization, oxidation and cross-coupling reactions [6,
7]. Furthermore, these compounds have numerous applica-
tions like the ability of the triphenylphosphonium group to
travel across cell membranes which leads to the use of phos-
phonium compounds such as anticancer agents [7], transport
vectors for targeting mitochondria [8, 9], and tumors diag-
nostic agents [10, 11].
Researchers often use triphenylphosphine and its deriva-
tives to prepare organic phosphines. Triphenylphosphine
and its derivatives easily react as nucleophiles with alkyl/
aryl halides and give rise to phosphonium salts which are
attractive, since they have enhanced thermal stability [1,
2]. Different types of phosphonium salts as precursors have
also been applied to prepare corresponding ylide complexes
of transition metals such as Pd(II), Au(I) and Hg(II) [3–5].
Phosphonium compounds have a range of advantages includ-
ing synthesis of a wide variety of organic derivatives and
functionalizing types of branches. Moreover, they have been
used as catalyst in a variety of organic reactions such as
The present study tries to investigate the synthesis
and the characterization of a crystal structure of a novel
phosphonium salt containing triphenylphosphonium and
hexabromodipalladate (II) moiety. This compound was
first tested successfully as a heterogeneous catalyst for
the amination reaction of various aryl halides by aqueous
ammonia as a source of nitrogen under air atmosphere
and solvent free conditions to produce aniline and other
primary aryl amines. Aniline and its derivatives are useful
intermediates in the production of pharmaceuticals, agro-
chemicals, pigments, dyes, etc. [13]. A desired approach
in the preparation of aniline and its derivatives is to use
ammonia directly due to its low cost and availability [14].
Using phosphonium salt which contains hexabromodipal-
ladate (II) as a heterogeneous catalyst in amination reac-
tion of aryl halides with ammonia has several advantages
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s13738-018-1406-z) contains
supplementary material, which is available to authorized users.
* Arash Ghorbani-Choghamarani
arashghch58@yahoo.com; a.ghorbani@mail.ilam.ac.ir
1
Department of Chemistry, Ilam University, P.O.
Box 69315516, Ilam, Iran
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
including direct utilization of ammonia, ammonia equiv-
alents with initial protection and final de-protection, no
need for argon or nitrogen atmosphere, high temperatures
and pressures, lack of by-products such as secondary and
tertiary amines [15, 17]. Moreover, we found the catalytic
activity of this phosphonium compound for C–C bond
formation by the Suzuki coupling reaction using phenyl
boronic acid to obtain biphenyl derivatives. A bundle of
activities of biphenyl derivatives includes: antifungal,
anti-proliferative, antimicrobial, anti-diabetic, immuno-
suppressant, analgesic, etc [18]. Phosphonium salts are
also used in biological studies as targeting and pharmaco-
logical agents due to their antimicrobial activity against
gram negative and positive bacteria [19].
samples were prepared as KBr pellets. NMR spectra (1H, 31
P
and 13C NMR) were recorded on a 400 MHz Bruker spec-
trometer in CDCl3 or DMSO-d6 as the solvent at room tem-
perature. Thin-layer chromatography (TLC) was performed
using Merck silica gel 60 F254 precoated plates (0.25 mm)
and visualized by UV fluorescence lamp.
X‑ray crystallography
The single crystal X-ray diffraction data of suitable crys-
tals was collected on a STOE IPDS-II diffractometer at
298 (2) K, using graphite monochromated Mo Ka radiation
(0.71073 Å). The data collection was performed using the
ꢀ-scan technique and using the STOE X-AREA software
package [20], whereas data diminution was carried out using
the program X-RED [21]. The structure was determined by
direct methods and subsequent difference Fourier maps and
then refined on F2 by full-matrix least-squares procedures
using the programs SHELX and SHELXL respectively [22],
and all refinements were performed using the XSTEP32
crystallographic software package [23]. All hydrogen atoms
were added in geometrically idealized positions.
Experimental
Materials and physical measurements
All starting materials were purchased from Merck and
Aldrich Chemical Companies and were used without any
additional purification. Mentioned microbial strains were
purchased from microbial collection of Iranian Research
Organization for Science and Technology. Melting points
were measured on a Stuart SMP3 apparatus. Elemental anal-
ysis was carried out with a CHNS-O Costech ECS 4010
analyzer. IR spectra (in the range 4000–400 cm−1) were
recorded on a Shimadzu 435-U-04 spectrophotometer and
Synthesis of bis](benzyloxycarbonylmethyl)tri
phenylphosphonium[hexabromopalladate (II),
[PhCH2COOCH2P(Ph)3]2[Pd2Br6]
To a solution of benzylbromoacetate (0.573 g, 2.5 mmol)
in benzene (5 mL), a solution of triphenylphosphine (PPh3)
Scheme 1 Synthesis of [PhCH2COOCH2P(Ph)3]2[Pd2Br6]
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Journal of the Iranian Chemical Society
Fig. 1 Asymmetric unit of [PhCH2COOCH2P(Ph)3]2[Pd2Br6]
(0.655 g, 2.5 mmol) in benzene (5 mL) was added and the
resulting mixture was stirred at room temperature for 3 h.
The separated solid was filtered off and washed with diethyl
ether to give [PhCH2COOCH2P(Ph)3]Br as a white pow-
der. Yield: 0.246 g (83%). M.p.: 128 °C. Anal. Calc. for
C27H24BrO2P (491.36 g/mol): C, 66.00; H, 4.92. Found:
C, 65.72; H, 5.16%. IR (KBr disk, ν cm−1): 1705 (CO);
687–930 (C–H in Ph); 1588 (C=C in Ph); 1438 (P–CH2).
The prepared (benzyloxycarbonylmethyl)triphenylphos-
phonium bromide (0.737 g, 3.0 mmol) was dissolved in
10 mL of methanol. Then, palladium(II) chloride (0.265 g,
1.5 mmol) in 10 mL of methanol was added to this solution
and the mixture was stirred at room temperature for 6 h. The
suspension that formed was filtered off, washed with diethyl
ether and dried to give [PhCH2COOCH2P(Ph)3]2[Pd2Br6] as
an orange powder. Yield: 0. 67 g, 59%. M.p.: 218 °C. Anal.
Calc. for C54H50Br6O4P2Pd2 (1517.63 g/mol): C, 42.75; H,
3.32. Found: C, 43.02; H, 3.41%. IR (KBr disk, ν cm−1):
1725 (CO); 687–930 (C–H in Ph); 1445–1588 (C=C in Ph);
1456 (P–CH2). 1H NMR (400 MHz, CDCl3, δH ppm): 4.98
(s, 2H, CH2O); 5.32 (d, 2H, J=15.01 Hz, PCH2); 7.10–7.47
(m, 20H, PPh3, Ph). 13C NMR (100 MHz, CDCl3, δC ppm):
34.22 (d, J = 36.03 Hz, PCH2); 68.37 (s, CH2O); 117.21,
118.38, 119.27, 121.36, 129.74, 130.18, 133.13, 134.66
(Ph); 171.04 (s, CO). 31P NMR (162 MHz, CDCl3, δP ppm):
22.54 (s, PPh3).
General procedure for amination of aryl halides
In a typical procedure, a mixture of aryl halide (1 mmol),
ammonium hydroxide (28%) (1 mL), K2CO3 (1.5 mmol),
0.007 g of [PhCH2COOCH2P(Ph)3]2[Pd2Br6] as catalyst was
Fig. 2 Distorted square-planar geometry around Pd(II) central ions
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Journal of the Iranian Chemical Society
Table 1 Crystal data and structure refinement for [PhCH2COOCH2P
Table 2 Selected bond lengths (Å) and bond angles (º) for
(Ph)3]2[Pd2Br6]
[PhCH2COOCH2P(Ph)3]2[Pd2Br6]
Identification code
[PhCH2COOCH2P(Ph)3]2[Pd2Br6]
Bond lengths
Bond angles
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
α (°)
β (°)
C27H24O2P, 0.5 (Br6Pd2)
Pd(1)–Br(1)
Pd(1)–Br(2)
Pd(1)–Br(3)
P(1)–C(1)
P(1)–C(13)
P(1)–C(7)
P(1)–C(19)
O(1)–C(20)
O(2)–C(20)
O(2)–C(21)
C(19)–C(20)
2.3869 (15)
2.3887 (16)
2.4521 (14)
1.795 (9)
1.796 (9)
1.780 (9)
Br(1)–Pd(1)–Br(2)
Br(1)–Pd(1)–Br(3)
Br(2)–Pd(1)–Br(3)
C(1)–P(1)–C(19)
C(1)–P(1)–C(13)
C(7)–P(1)–C(1)
C(19)–P(1)–C(13)
C(7)–P(1)–C(19)
C(7)–P(1)–C(13)
C(20)–O(2)–C(21)
O(1)–C(20)–O(2)
91.09 (6)
91.27 (5)
176.02 (5)
110.9 (4)
111.3 (4)
108.4 (4)
109.5 (4)
107.8 (4)
108.9 (4)
116.7 (9)
125.1 (10)
757.53
298 (2)
0.71073
Triclinic
P-1
1.783 (9)
9.1369(18)
11.287 (2)
14.472 (3)
87.22 (3)
74.47 (3)
71.51 (3)
1362.7 (6)
2
1.166 (13)
1.318 (12)
1.480 (12)
1.508 (13)
ꢀ (°)
Volume (Å3)
Z
of [PhCH2COOCH2P(Ph)3]2[Pd2Br6] as catalyst and 2 mL
polyethylene glycol (PEG) as solvent were heated at 80 °C
and the progress of the reaction was followed by TLC. After
completion of the reaction, the mixture was cooled down to
room temperature. Water was added to the reaction mixture,
filtered to remove the catalyst and extracted three times with
diethyl ether. The combined ethyl acetate extracts were dried
over anhydrous sodium sulfate, filtered and evaporated to
give the pure product.
Calculated density, Mg/m3
F(000)
1.846
736
2.35 to 25.00
Theta range for data collec-
tion, (°)
Limiting indices
− 10≤h ≤ 10, − 12≤k ≤ 13,
− 16≤l ≤ 17
99.5%
Numerical
5.161
Completeness to theta=25
Absorption correction
Absorption coefficient
(mm−1
)
Selected spectral data
Crystal size (mm3)
0.35×0.18×0.15
Aniline: 1H NMR (400 MHz, CDCl3, ppm): δ=7.22–7.26
(m, 2H), 6.83–6.87 (tt, J = 7.3, 1 Hz, 1H), 6.75–6.77 (m,
2H), 3.66 (s, 2H).
Reflections collected/unique
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2 ꢀ (I)]
R indices (all data)
10,064/4776 [R(int)=0.1061]
0.5116 and 0.2653
Full-matrix least-squares on F2
4776/0/301
1
4-Nitroaniline: H NMR (400 MHz, CDCl3. ppm):
0.919
δ = 8.092–8.115 (d, J = 9.3 Hz, 2H); 6.649–6.671 (d,
J=8.8 Hz, 2H); 4.43 (br, 2H).
R1 =0.0623, WR2 =0.1400
R1 =0.1232, WR2 =0.1594
1.305 and −0.791
1
4- Chloroaniline: H NMR (400 MHz, CDCl3. ppm):
Largest diff. peak and hole,
δ=7.12–7.15 (d, J=8.7 Hz, 2H); 6.64–6.67 (m, 2H); 3.59
e Å−3
(br, 2H).
1
4-methoxy-1,1′-biphenyl: H NMR (400 MHz, CDCl3,
ppm): δ=7.56–7.60 (m, 4H); 7.44–7.49 (m, 2H); 7.32–7.37
added and the reaction mixture was stirred at 80 °C and the
progress of the reaction was followed by TLC. When the reac-
tion completed, the product was extracted with ethyl acetate.
The combined ethyl acetate extracts were dried over anhydrous
sodium sulfate, filtered and evaporated to give the pure product.
(m, 1H); 7.03–7.7.05 (m, 2H); 3.89 (s, 3H).
1
4-Nitro-1, 1′-biphenyl: H NMR (400 MHz, CDCl3,
ppm): δ = 8.32–8.35 (d, J = 8.7 Hz, 2H), 7.75–7.78 (dt,
J = 7.8 Hz, 2H), 7.65–7.67 (m, 2H), 7.50–7.55 (m, 2H),
7.57–7.50 (m, 1H).
1
4-Cyano-1,1′-biphenyl: H NMR (400 MHz, CDCl3,
ppm): δ=7.76–7.79 (m, 2H); 7.70–7.73 (m, 2H); 7.61–7.64
General procedure for Suzuki cross‑coupling
reaction
(m, 2H); 7.50–7.54 (m, 2H); 7.44–7.48 (m, 1H).
In a typical procedure, a mixture of aryl halide (1 mmol),
phenylboronic acid (1 mmol), K2CO3 (1.5 mmol), 0.010 g
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Journal of the Iranian Chemical Society
Fig. 3 The Br1⋯H interactions between Pd(II) complexes and phosphonium cations
the monophosphonium salts are insoluble in benzene and
Results and discussion
their diphosphonium derivatives are dissolved in benzene
afterwards, the reaction of the phosphonium bromide with
palladium(II) chloride in a molar ratio of 2:1 in methanol at
room temperature led to the formation of compound 1 as an
orange solid (Scheme 1). The 31P NMR spectra of the com-
pound displayed a significant singlet signal range 22.54 ppm
implying some local electron density reduction in the P–C
bonds in comparison with that in the literature for PPh3.
Catalyst preparation
Compound bis (benzyloxycarbonylmethyl)triphenylphos-
phonium hexabromopalladate (II) (1) was synthesized as
follows: the treatment of benzylbromoacetate with triph-
enylphosphine in benzene as a solvent yielded the corre-
sponding phosphonium salt as an exclusive product, because
Fig. 4 The Br1⋯H and Br1⋯π interactions between Pd(II) complexes and phosphonium cations
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Journal of the Iranian Chemical Society
Fig. 5 The Br2⋯H interactions between Pd(II) complexes and phosphonium cations
Fig. 6 The H⋯H bonding and C–H⋯π interaction between adjacent phosphonium units
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Journal of the Iranian Chemical Society
Fig. 7 The packing diagram of title compound along c axis
intermolecular noncovalent interactions between various
units help in stabilization of the crystal structure in three
dimensions. The Br⋯H [24] (Br1⋯H5, Br1⋯H19A and
Br2⋯H19B interactions with distances 2.92, 2.86 and
2.96 Å, respectively) and Br⋯π interactions [25] between
Br1 and Cg1 (Cg1: C1–C6) with distance 3.527 Å that
is smaller than Van der Waals radii of carbon and bro-
mine (3.55 Å), are formed between neighbour Pd(II) com-
plexes and phosphonium cations (see Figs. 3, 4, 5). In
addition, C–H⋯π interaction between C–H26 group and
Cg2 (Cg2: C13–C18) with distance 2.974 Å and also H–H
bonding with H⋯H distance equal to 2.361 Å that is less
than sum of Van der Waals radii of H atoms (2.4 Å), are
created between adjacent phosphonium units (see Fig. 6).
X‑ray crystallographic study of compound 1
Suitable crystals of [PhCH2COOCH2P(Ph)3]2[Pd2Br6]
(1) were gained by slow evaporation from chloroform/
methanol solutions over several days and its structure was
determined by X-ray diffraction. The crystallization of
compound was done in the triclinic space group P-1 with
two molecules in the unit cell. Figure 1 shows asymmetric
unit of the compound. The crystal structure of this com-
pound consists of binuclear anionic complexes of Pd(II),
namely Pd2Br62−, and triphenylphosphonium cations for
charge neutrality. In the bromopalladate(II) unites, the
geometry around metal ion centres are slightly distorted
square-planar. The central metal ions are out of plan and
the Br2–Pd–Br1 and Br2–Pd–Br2 angels are smaller than
180 degree (see Fig. 2). The Pd–Br bonds distances are
within a range typical for other structures containing
bromopalladate(II). The Br3 atoms act as bridge ligands
and thus the Pd–Br3 bond length is longer than terminate
Pd–Br length. Significant crystallographic data are sum-
marized in Table 1 and selected bond distances and angles
are summarized in Table 2.
The ion–ion attraction between anionic complexes
and triphenylphosphonium cations is the most important
intermolecular force in this crystal structure. Moreover,
Scheme 2 [PhCH2COOCH2P(Ph)3]2[Pd2Br6] catalyzed the amination
of aryl halides
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Journal of the Iranian Chemical Society
Table 3 Optimization of various
parameters for the amination
of iodobenzene with aqueous
ammonia
Entry
Cat (mg)
Solvent
Base
Temp (°C)
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
5
5
5
5
5
5
5
5
5
5
5
–
7
10
EtOH
NH3·H2O
H2O
PEG
DMF
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
KHCO3
Et3N
60
60
60
60
60
60
60
60
r.t
80
100
80
80
80
6
6
6
6
6
6
6
6
6
6
6
24
6
6
57
84
64
71
75
80
76
82
–
87
90
–
94
95
KOH
9
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
10
11
12
13
14
aYields refer to those of pure isolated products
Yield (%)a
94
Table 4 Preparation of aniline
derivatives from aryl halides in
the presence of catalytica
Entry
1
Aryl halide
I
product
Time (h)
6
M.P. ( C)
NH2
Yellow oil
[15]
Br
NH2
Yellow oil
[15]
2
3
12
10
90
91
NH2
I
42–45 [13]
Me
Me
Me
Br
NH2
NH2
NH2
NH2
4
5
6
7
13
8
88
89
87
85
42–45 [26]
57–59 [13]
57–59 [15]
69–71 [26]
Me
I
MeO
MeO
OHC
MeO
MeO
Br
Br
9
7
OHC
O2N
Br
Br
Br
NH2
NH2
NH2
8
9
5
4
6
93
87
86
147–149 [13]
84–86 [13]
O2N
NC
NC
10
135–137 [15]
H2N
H2N
Reaction conditions: aryl halide (1 mmol), NH4OH (1 mmol), K2CO3 (1.5 mmol), 7 mg catalyst at 80 °C
aIsolated yield
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Journal of the Iranian Chemical Society
Optimal conditions for the reaction were defined as fol-
lows: 1 mL of aqueous ammonia, 1 mmol of iodobenzene,
1.5 mmol of K2CO3 as base and 0.007 g of catalyst at 80 °C
of catalyst in solvent free conditions. When the reaction con-
ditions are optimized, the coupling reaction proceeds easily
with aryl bromides and iodides with aqueous ammonia. The
results are summarized in Table 4. In all cases, the yields of
products were in a good to an excellent range.
Scheme 3 Carbon–carbon coupling reaction using phenyl boronic
acid in the presence of [PhCH2COOCH2P(Ph)3]2[Pd2Br6]
For better vision, packing diagram of crystal structure in
direction of c axis is shown in Fig. 7.
The other studied reaction in this work was Suzuki cross-
coupling reaction. we were interested in finding a simple and
efficient method for the carbon–carbon coupling reaction in
the presence of complex [PhCH2COOCH2P(Ph)3]2[Pd2Br6]
(Scheme 3).
Catalytic studies
To extend applications of the catalytic activity of
[PhCH2COOCH2P(Ph)3]2[Pd2Br6], this catalyst was inves-
tigated in the direct amination of aryl halides using aqueous
ammonia (Scheme 2).
T o e x a m i n e t h e c a t a l y t i c a c t i v i t y
[PhCH2COOCH2P(Ph)3]2[Pd2Br6] in the Suzuki reaction,
the reaction between iodobenzene with phenyl boronic
acid in presence of catalyst was chosen as model reaction.
Influences of different parameters including base, solvent,
temperature, and catalyst concentration were examined to
obtain the best possible combination (Table 5). Unsur-
prisingly, no product was observed in the absence of the
catalyst (Table 5, entry 1). At first, the model reaction
was carried out in several solvents such as polyethyl-
ene glycol 400 (PEG-400), dimethyl formamide (DMF),
dimethyl sulfoxide (DMSO) and ethanol (EtOH), and
it was found that PEG gave the best yield, and in other
solvents lower yields were observed (Table 5, entries 3
and 5–7). The reaction was significantly affected by the
nature of base and the additive used. Therefore, a variety
of bases were tested (Table 5, entries 3 and 8–10). As
shown in Table 5, K2CO3 was selected as the optimum
base among the used bases. Therefore, the best results
were achieved in water at 80 °C in the presence of 5 mg
of [PhCH2COOCH2P(Ph)3]2[Pd2Br6] using 1.5 mmol of
K2CO3 (Table 5, entry 3).
For this purpose, aqueous ammonia was used as the
amine group supplier. First, the reaction of iodobenzene
with aqueous ammonia was performed in various organic
solvents the results of which are shown in Table 3. On the
basis of the achieved results, the reaction in the presence
of NH3·H2O as solvent proceeded much better than other
solvents with a good yield in short reaction time (Table 3,
entry 2). Then, amount of catalyst optimization was con-
ducted and the optimal amount was found to be 0.007 g
(Table 3, entry 13). After that the effect of temperature on
the rate of the reaction was examined. It was observed that
at room temperature, the reaction did not proceed (Table 3,
entry 9). At 80 °C, the reaction proceeded and gave the
corresponding product a good yield (Table 3, entry 10).
Increasing the temperature to 100 °C had little effect on
the rate of reaction (Table 3, entry 11). Therefore, we kept
reaction temperature at 80 °C as the optimal temperature.
Finally, base optimization was carried out in this study
(Table 3, entries 2 and 6–8). As shown in Table 3, K2CO3
was selected as the optimum base among used bases.
Table 5 The optimization of
reaction parameters for the
Suzuki reaction of iodobenzene
with phenyl boronic acid
Entry
Cat (mg)
Solvent
Base
Temp (°C)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
–
3
5
7
5
5
5
5
5
5
5
5
PEG
PEG
PEG
PEG
DMF
DMSO
EtOH
PEG
PEG
PEG
PEG
PEG
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Et3N
80
80
80
80
80
80
80
80
80
80
r.t.
60
120
120
35
30
35
35
35
35
35
35
35
35
–
92
95
95
79
73
66
54
81
85
Trace
69
9
KOH
10
11
12
KHCO3
K2CO3
K2CO3
aIsolated yields
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Journal of the Iranian Chemical Society
Table 6 Reaction of structurally
different aryl halides with
phenyl boronic acid in the
presence of catalyst
Aryl halide
Product
Entry
Time (min) Yield (%)a
Mp (°C)
Ph
Ph
I
I
1
35
95
66–68 [27]
2
30
91
45–47 [27]
H3C
H3C
I
Ph
3
4
5
35
40
35
89
90
88
85–88 [28]
66–68 [27]
45–47 [27]
H3CO
H3CO
Ph
Ph
Br
Br
Br
H3C
H3C
Ph
Ph
6
45
30
86
93
83–85 [28]
H3CO
H3CO
O2N
NC
111–113
[27]
7
O2N
NC
Cl
Br
Br
Ph
Ph
8
9
35
40
55
50
90
87
89
86
82–84 [28]
76–78 [28]
66–68 [27]
Cl
Ph
Ph
10
11
111–112
[27]
O2N
NC
Ph
12
65
90
83–84 [28]
Reaction conditions: aryl halide (1 mmol), phenyl boronic acid (1 mmol), K2CO3 (1.5 mmol), PEG (1
mL) and 5 mg catalyst at 80 °C
bIsolated yield
After the optimization of the reaction conditions, the
various aryl halides with and phenylboronic acid compris-
ing several functional groups have been reacted in opti-
mum conditions. The results are summarized in Table 6.
As illustrated in Table 6, biphenyl reactions were gained
in short reaction times with good to excellent yields. How-
ever, aryl bromides and aryl iodides show lower reaction
times compared to those corresponding aryl chlorides.
Reusability of the catalyst
Reusability is an advantage of catalysts that makes them sig-
nificant from a commercial point of view. Therefore, the recov-
ery and recyclability of [PhCH2COOCH2P(Ph)3]2[Pd2Br6] was
studied in the coupling reaction of iodobenzene with aqueous
ammonia and phenylboronic acid under the optimal condi-
tions. The reaction mixture was cooled to room temperature
after the completion of the reaction. Then, the mixture was
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Journal of the Iranian Chemical Society
efficiently without using toxic organic solvents and this cata-
lyst also is a suitable catalyst in terms of stability, price and
easy separation.
100
80
60
40
20
0
Aniline reaction
Suzuki reaction
Conclusion
The present study describes the synthesis and the char-
acteristics of new compound derived from reaction of
palladium chloride and (benzyloxycarbonylmethyl)triph-
enylphosphoniumh salt. The physicochemical and spec-
troscopic data indicate that crystal structure of the title
compound contains two crystallographically independent
phosphonium cations and binuclear anionic complexes of
Pd(II), namely Pd2Br62−. A new phosphonium salt con-
taining hexabromodipalladate(II) moiety was used as an
efficient catalyst for the amination of aryl halides by aque-
ous ammonia in the absence of any organic solvent. This
method enables direct synthesis of a number of primary
amines with very good to excellent yields. Furthermore,
it was demonstrated that this compound can act as an effi-
cient catalyst for Suzuki cross-coupling reaction using
commercially available and cheap reagent (phenyl boronic
acid). The catalyst turned out to be highly active, and its
reusability was tested in up to four consecutive cycles in
both reactions.
1
2
3
4
Number of cycles
Fig. 8 Reuse of the catalyst in Aniline and Suzuki cross-coupling
reactions
filtered off to separate the catalyst. In the end, the catalyst was
dried at 120 °C and directly used for the next run. After four
consecutive runs, a negligible reduction in the activity of the
catalyst indicated that the catalyst was not only very active, but
also very stable (Fig. 8).
Comparison of the catalyst
To examine the efficiency of these procedures, we compared
the results of the coupling of iodobenzene with phenylboronic
acid (Table 7) with some reported C–C coupling reactions in
the presence of other catalysts. As illustrated in Table 7, the
achieved results indicate the superiority of the present cata-
lyst in terms of yield or reaction time to the other catalysts
reported in previous literatures. Mainly the reaction catalyzed
by [PhCH2COOCH2P(Ph)3]2[Pd2Br6] can be performed
Table 7 Comparison results of [PhCH2COOCH2P(Ph)3]2[Pd2Br6] with other catalysts for the coupling of iodobenzene with phenylboronic acid
Entry
Catalyst
Condition
Time (min)
Yield (%)a
Refs.
1
2
3
4
5
6
7
[PhCH2COOCH2P(Ph)3]2[Pd2Br6]
{Pd[P(Ph)(CH2Ph)(Ph-4-CH3)]((µ-Br)Br)}
PCP-pincer palladium complex
[Ph2PCH2PPh2CH=C(O)(C10H7)] PdCl2
CA/Pd(0)
PEG, K2CO3, 80 °C
PEG, K2CO3, 100 °C
DMF, K2CO3, 80 °C
H2O, Cs2CO3, 80 °C
H2O, K2CO3, 100 °C
DMF, K2CO3, 80 °C
35
25
1 h
20
120
5 h
180
95
96
96
93
94
100
97
This work
[29]
[30]
[31]
[32]
[33]
[34]
Polymer anchored pd(II)
N,N′-bis(2-pyridinecarboxamide)-1,2-benzene H2O, K2CO3, 100 °C
palladium complex
8
9
PVP–PdNPs
K2PO4, EtOH/H2O, 90 °C
H2O/EtOH, K2CO3, 82 °C
120
6 h
94
97
[35]
[36]
N2,N6-dibenzylpyridine-
2,6-dicarboxamidopalladium(II)triph-
enylphosphine
10
PANI-Pd
K2CO3, 1,4-dioxane: H2O (1:1), 95 °C
4 h
91
[37]
aIsolated yield
1 3

Journal of the Iranian Chemical Society
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Acknowledgements Authors thank the research facilities of Ilam Uni-
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