Bis[(2-methylacetatobenzyl)tri(p-tolyl)phosphonium]hexabromodipalladate(II); synthesis, characterization, structural study and application as a retrievable heterogeneous catalyst for the amination of aryl halides and Stille cross-coupling reaction

Article abstract of DOI:10.1016/j.ica.2016.02.045

The treatment of tri(p-tolyl)phosphine with 1,2-bis(bromomethyl)benzene results in (2-bromomethylbenzyl)tri(p-tolyl)phosphonium bromide. The resulted phosphonium salt reacts with palladium acetate(II) in a molar ratio of 1.5:1, respectively, to give [(CH₃C₆H₄)₃PCH₂C₆H₄CH₂OC(O)CH₃]₂[Pd₂Br₆], bis[(2-methylacetatobenzyl)tri(p-tolyl)phosphonium]hexabromodipalladate(II), as a dark brown powder. Characterization of the obtained compound was performed by elemental analysis (CHN), IR, ¹H, ³¹P, ¹³C NMR and X-ray crystallography techniques. This compound was found to be an efficient catalyst for the amination of aryl halides using aqueous ammonia to produce primary amines and for Stille cross-coupling reaction to produce biphenyl and its derivatives as well. Describe catalyst showed satisfactory results and could be recovered and reused without significant loss of its catalytic activity in both reactions.

Full text of DOI:10.1016/j.ica.2016.02.045

Inorganica Chimica Acta 446 (2016) 97–102
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Inorganica Chimica Acta
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Bis[(2-methylacetatobenzyl)tri(p-tolyl)phosphonium]
hexabromodipalladate(II); synthesis, characterization, structural study
and application as a retrievable heterogeneous catalyst for the amination
of aryl halides and Stille cross-coupling reaction
a
a
b
Arash Ghorbani-Choghamarani a, , Ali Naghipour , Fateme Heidarizadi , Roghayeh Shirkhani ,
⇑
Behrouz Notash c
a Department of Chemistry, Faculty of Science, Ilam University, P.O. Box 69315516, Ilam, Iran
b Faculty of Science, Omidiyeh Branch, Islamic Azad University, Omidiyeh, Iran
c Department of Chemistry, Shahid Beheshti University, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
The treatment of tri(p-tolyl)phosphine with 1,2-bis(bromomethyl)benzene results in (2-bromomethyl-
benzyl)tri(p-tolyl)phosphonium bromide. The resulted phosphonium salt reacts with palladium acetate
(II) in a molar ratio of 1.5:1, respectively, to give [(CH3C6H4)3PCH2C6H4CH2OC(O)CH3]2[Pd2Br6], bis[(2-
Received 24 December 2015
Received in revised form 19 February 2016
Accepted 22 February 2016
Available online 5 March 2016
methylacetatobenzyl)tri(p-tolyl)phosphonium]hexabromodipalladate(II), as
a dark brown powder.
Characterization of the obtained compound was performed by elemental analysis (CHN), IR, 1H, 31P,
13C NMR and X-ray crystallography techniques. This compound was found to be an efficient catalyst
for the amination of aryl halides using aqueous ammonia to produce primary amines and for Stille
cross-coupling reaction to produce biphenyl and its derivatives as well. Describe catalyst showed satis-
factory results and could be recovered and reused without significant loss of its catalytic activity in both
reactions.
Keywords:
Phosphonium salt
Palladium(II) acetate
Amination reaction
Stille cross-coupling reaction
Ó 2016 Elsevier B.V. All rights reserved.
1. Introduction
range of organic reactions including oxidation, polymerization
and cross-coupling reactions [5,6].
Triphenylphosphine and its derivatives are often used for the
preparation of organic phosphines. They can easily react as nucle-
ophiles with alkyl/aryl halides giving rise to phosphonium salts
which are attractive due to their enhanced thermal stability [1].
Phosphonium salts are used in the preparation of phosphorus
ylides, essential components in the Wittig reaction of alkenes syn-
thesis [2]. Certain phosphonium salts are also used in biological
researches as targeting agents and as pharmacological agents due
to their anti-microbial activity against gram negative and positive
bacteria [3]. These compounds have both lipophilic and cationic
character, allowing them facile transport through cell wall or
plasma membrane in order to accumulate in mitochondria of cells
or cytoplasm [4]. For this reason as anti-cancer agents, they show
great promise for diagnosis and treatment of tumor cells. Some of
the phosphonium salts have demonstrated catalytic activity in a
Herein we describe the synthesis and characterization of a
novel phosphonium salt containing tri(p-tolyl)phosphonium and
hexabromodipalladate(II) moiety. Initially, this compound was
successfully tested as a heterogeneous catalyst for the amination
reaction of various aryl halides by aqueous ammonia as a nitrogen
source under air atmosphere and solvent free conditions to pro-
duce aniline and other primary aryl amines. Aniline and its deriva-
tives are useful intermediates in producing dyes and pigments,
agrochemicals, pharmaceuticals, etc. [7]. Direct utilization of
ammonia in the preparation of aniline and its derivatives because
of its low cost and availability is a desired approach [8,9]. Using
this phosphonium salt containing hexabromodipalladate(II) as a
heterogeneous catalyst in amination reaction of aryl halides with
ammonia has several advantages, including direct utilization of
ammonia, but not ammonia equivalents with initial protection
and final deprotection [10], no need to argon or nitrogen atmo-
sphere, dry ice, high temperatures and pressures, autoclave, and
etc. [11,12], lack of by-products such as secondary and tertiary
amines.
⇑
Corresponding author. Tel./fax: +98 841 2227022.
E-mail
addresses:
arashghch58@yahoo.com,
a.ghorbani@mail.ilam.ac.ir
(A. Ghorbani-Choghamarani).
http://dx.doi.org/10.1016/j.ica.2016.02.045
0020-1693/Ó 2016 Elsevier B.V. All rights reserved.

98
A. Ghorbani-Choghamarani et al. / Inorganica Chimica Acta 446 (2016) 97–102
Catalytic activity of this phosphonium compound was then
with diethyl ether (10 mL) to give (2-bromomethylbenzyl)tri(p-
examined for Stille cross-coupling reaction. It showed remarkable
activity for catalyze carbon–carbon bond formation using triph-
enyltin chloride (Ph3SnCl) under green medium to obtain biphenyl
derivatives. It was demonstrate that biphenyls have wide range of
uses such as: antimicrobial, anti-inflammatory, anti-proliferative,
anti-diabetic and analgesic applications [13]. Construction of car-
bon–carbon bond via cross-coupling strategy is one of the most
fundamental transformations in chemistry which has gained con-
siderable attention particularly as a straightforward method in
order to C(sp2)–C(sp2) bond formation [14]. Various transition
metal-catalyzed cross-coupling reactions between aryl halides
and arylmetals involving Grignard reagents (Kumada–Tamao and
Corriu coupling), organostannanes (Kosugi–Migita–Stille cou-
pling), organozincs and –zirconiums (Negishi coupling) and
organoboranes (Suzuki–Miyaura coupling), have emerged as pow-
erful tools for the synthesis of biphenyls. Since organotin reagents
are stable in air and moisture and are compatible with a large vari-
ety of functional groups, they have been used by many research
groups through the world for this purpose [15]. In this study, we
present an account of our efforts in the cross-coupling of triph-
enyltin chloride with different aryl iodides and bromides in the
presence of our recently synthesized phosphonium compound as
a heterogeneous catalyst.
tolyl)phosphonium bromide, [(CH3C6H4)3PCH2C6H4CH2Br]Br, as a
white powder. Yield: 0.502 g (91%). M.p. 187 °C. IR (t
, cmꢀ1):
3045 (C–H stretch (aromatic)), 2955 (C–H stretch (alkyl)), 1447
(CH2–P).
The prepared (2-bromomethylbenzyl)tri(p-tolyl)phosphonium
bromide (0.828 g, 1.5 mmol) was dissolved in 5 mL of ethanol.
Then palladium(II) acetate (0.224 g, 1 mmol) in 5 mL of ethanol
was added to this solution and the mixture was stirred at room
temperature. After 4 h, the product was filtered off and washed
with diethyl ether (10 mL) to yield [(CH3C6H4)3PCH2C6H4CH2OC
(O)CH3]2[Pd2Br6] as a dark brown powder. The solid was recrystal-
lized in dichloromethane. Yield: 0.750 g (92%). M.p. 275 °C. IR (t,
cmꢀ1): 3064 (C–H stretch (aromatic)), 2969 (C–H stretch (alkyl)),
1731 (C@O stretch), 1462 (CH2–P), 1250, 1111 (C–O stretches).
1H NMR (400 MHz, DMSO-d6): d = 1.9 (s, 3H, –CO–CH3), 2.4(s, 9H,
–phenyl–CH3), 4.5 (s, 2H, –CH2–O–); 5.0 (d, 2H, –CH2–P–,
J = 15.2 Hz); 7.0–7.5 (m, Ph). 13C NMR (75.45 MHz, DMSO-d6):
d = 20.5 (s, –CH3 (acetate group)); 26.1 (d, –CH2–P–, J = 36.2 Hz);
62.3 (s, –CH2–O–); 113.9–146.0 (m, Ph); 169.9 (s, –C@O). 31P{1H}
NMR (121.50 MHz, DMSO-d6): d = 22.1. Anal. Calc. for
C62H64O4P2Br6Pd2: C, 45.7; H, 3.9. Found: C, 44.9; H, 3.8%.
2.4. General procedure for the amination of aryl halides
To a solution of aryl halide (1 mmol) and ammonium hydroxide
(28%) (1 mL, 0.003 mmol), 0.005 g (0.003 mmol) of [(CH3C6H4)3-
PCH2C6H4CH2OC(O)CH3]2[Pd2Br6] as catalyst was added and the
reaction mixture was stirred at 60 °C for its appropriate time.
The progress of the reaction is followed by TLC. After completion
of the reaction, the product was extracted with ethyl acetate
(3 ꢁ 10 mL). The combined ethyl acetate extracts were dried over
anhydrous sodium sulfate (1.5 g), filtered and evaporated to give
the pure product. The products were characterized by comparison
of their spectral (1H NMR and IR) and physical data with those of
authentic samples.
2. Experimental
2.1. Materials and physical measurements
All solvents and reactants were obtained from Merck, Aldrich
and Fluka Chemical Companies and used without further purifica-
tion. Elemental analysis was carried out with a CHNS–O Costech
ECS 4010 analyzer. Melting points were measured on a Stuart
SMP3 apparatus. NMR spectra (1H, 31P and 13C NMR) recorded on
a 400 MHz Bruker spectrometer in CDCl3 or DMSO-d6 as the sol-
vent at room temperature. IR spectra (in the range
4000–400 cmꢀ1) were recorded on a Shimadzu 435-U-04 spec-
trophotometer and samples were prepared as KBr pellets. Thin-
layer chromatography (TLC) was performed using Merck silica
gel 60 F254 precoated plates (0.25 mm) and visualized by UV flu-
orescence lamp.
2.5. General procedure for Stille cross-coupling reaction
A mixture of aryl halide (1 mmol), Ph3SnCl (0.4 mmol), K2CO3
(1.5 mmol), 0.005 g of [(CH3C6H4)3PCH2C6H4CH2OC(O)CH3]2
[Pd2Br6] (0.003 mmol) as catalyst and 1 mL polyethylene glycol
(PEG) as solvent was heated at 90 °C for its appropriate time. After
completion of the reaction based on TLC, the mixture was cooled to
room temperature. The reaction mixture was added to water
(10 mL), filtered (to remove the catalyst) and extracted three times
with diethyl ether (3 ꢁ 5 mL). The combined diethyl ether extracts
were dried over anhydrous sodium sulfate (1.5 g), filtered and
evaporated to give the pure product. The products were character-
ized by comparison of their spectral (1H NMR and IR) and physical
data with those of authentic samples.
2.2. X-ray crystallography
Crystal data of compound 1 were collected using graphite
monochromated Mo Ka radiation (k = 0.71073 Å) made on a STOE
IPDS-2T diffractometer at 120 K. The molecular structure was
solved by direct methods and then refined by full-matrix least-
squares on F2 using the X-STEP32 crystallographic software pack-
age [16]. All hydrogen atoms were added in their geometrically
idealized positions. Non-hydrogen atoms were refined with aniso-
tropic thermal parameters. Cell constants and orientation matrices
were obtained by least-squares refinement of diffraction data from
13453 unique reflections.
2.6. General procedure for the recovery of the catalyst
In the case of the both catalytic reactions, after completion of
the reaction based on TLC, the reaction mixture was cooled to room
temperature. Then water (5 mL) and the organic phase of the reac-
tion (5 mL), (ethyl acetate in the amination reaction or diethyl
ether in the Stille cross-coupling reaction) were added and the
mixture was filtered off to separate the catalyst. The catalyst was
dried at 100 °C and directly used for the next runs.
2.3. Synthesis of bis[(2-methylacetatobenzyl)tri(p-tolyl)phosphonium]
hexabromodipalladate(II), [(CH3C6H4)3PCH2C6H4CH2OC(O)
CH3]2[Pd2Br6]
The phosphonium salt was synthesized via following procedure
that described in the literature [17]. To a solution of 1,2-bis(bro-
momethyl)benzene (0.263 g, 1 mmol) in benzene (2 mL), a solution
of tri(p-tolyl)phosphine (P(p-tolyl)3) (0.304 g, 1 mmol) in benzene
(2 mL) was added and the resulting mixture was stirred for 6 h at
room temperature. The separated solid was filtered off and washed
2.7. Representative NMR and IR data
4-Nitroaniline: 1H NMR (400 MHz, CDCl3): d (ppm) = 8.12–8.10
(d, J = 9.2 Hz, 2H), 6.67–6.65 (d, J = 8.8 Hz, 2H), 4.43 (br, 2H). IR (t,

A. Ghorbani-Choghamarani et al. / Inorganica Chimica Acta 446 (2016) 97–102
99
Br
Br
P(p-tolyl)3Br
Br
benzene
r. t.
+
P(p-tolyl)3
P(p-tolyl)3Br
P(p-tolyl)3
EtOH
r. t.
3
+ 2 Pd(OAc)2
[Pd2Br6]2-
Br
O
CCH3
2
O
1
+ [(CH3C6H4)3PCH2C6H4CH2OCOCH3](CH3COO)
Scheme 1. Synthesis of [(CH3C6H4)3PCH2C6H4CH2OC(O)CH3]2[Pd2Br6].
Fig. 1. Asymmetric unit of [(CH3C6H4)3PCH2C6H4CH2OC(O)CH3]2[Pd2Br6].
cmꢀ1): 3419, 3391, 3096, 3061, 2958, 2927, 2856, 1921, 1733,
1600, 1568, 1515, 1472, 1436, 1398, 1356, 1344, 1306, 1276,
1173, 1120, 1106, 1066, 1011, 958, 853, 839, 738, 723, 693, 675,
620, 541, 522.
4-Methoxy-1,10-biphenyl: 1H NMR (400 MHz, CDCl3): d (ppm):
7.55–7.60 (m, 4H), 7.43–7.47 (m, 2H), 7.32–7.36 (m, 1H), 7.02
(m, 2H), 3.86 (s, 3H). IR (t
, cmꢀ1): 3061, 2997, 2926, 2844, 1600,
1524, 1482, 1280, 1248, 1191, 1032, 688.
4-Cyanoaniline: 1H NMR (400 MHz, CDCl3): d (ppm) = 7.65–7.68
(m, 2H), 7.54–7.58 (m, 2H), 4.26 (br, 2H). IR (t
, cmꢀ1): 3085, 3032,
3. Results and discussion
2965, 2929, 2860, 2288, 2221, 1915, 1728, 1655, 1580, 1475, 1397,
1277, 1176, 1121, 1066, 1010, 960, 823, 767, 746, 722, 699, 540,
430.
3.1. Synthesis of the catalyst
4-Cyano-1,10-biphenyl: 1H NMR (400 MHz, CDCl3): d (ppm)
= 7.78–7.76 (m, 2H), 7.72–7.68 (m, 2H), 7.65–7.62 (m, 2H), 7.53–
The treatment of 1,2-bis(bromomethyl)benzene with tri
(p-tolyl)phosphine in a molar ratio of 1:1 in benzene as a solvent
yielded the corresponding monophosphonium salt as an exclusive
product, because only the monophosphonium salts are insoluble in
benzene (their diphosphonium derivatives are dissolved in
7.49 (m, 2H), 7.49–7.45 (m, 1H). IR (t
, cmꢀ1): 3433, 3066, 2922,
2351, 2218, 1929, 1637, 1596, 1475, 1398, 1275, 1110, 953, 843,
767, 693, 559, 512.

100
A. Ghorbani-Choghamarani et al. / Inorganica Chimica Acta 446 (2016) 97–102
Table 1
NH2
X
Crystal data and structure refinement for compound 1.
[(CH3C6H4)3PCH2C6H4CH2OC(O)CH3]2[Pd2Br6] (Cat.)
Solvent free, 60 0
NH4OH
+
Identifier
Chemical formula
Formula weight
T (K)
Khc652b
31H32O2P, 0.5(Br6Pd2)
813.64
120
C
C
R
R
X= I, Br
k (Å)
0.71073
triclinic
Scheme 2. Amination of various aryl halides in the presence of compound 1.
Crystal system
Space group
a (Å)
b (Å)
c (Å)
ꢀ
P1
10.268(2)
12.562(3)
14.137(3)
92.29(3)
109.00(3)
113.40(3)
1551.9(8)
1.741
Table 5
Optimization of the amount of compound 1 for the synthesis of biphenyl.
a
(°)
b (°)
Entry
Compound 1 (g)
Time (min)
Yield (%)
c
(°)
V (Å3)
1
2
3
4
0.00
10
10
10
10
0
75
95
96
Dcalc (g/cm3)
0.002
0.005
0.007
Z
2
Absorption coefficient (mmꢀ1
Crystal size (mm3)
Crystal F(000)
Goodness-of-fit (GOF) on F2
)
4.883
0.35 ꢁ .25 ꢁ 0.05
Reaction conditions: iodobenzene: 1 mmol, Ph3SnCl: 0.4 mmol, K2CO3: 1.5 mmol,
1 mL PEG, at 90 °C, 15 min.
800
0.972
Table 6
Table 2
Selected bond distances and bond angles for compound 1.
Effect of solvent on the synthesis of biphenyl.
Entry
Solvent
Time (min)
Yield (%)
Bond length (Å)
Bond angles (°)
1
2
3
4
Ethanol
N,N-Dimethylformamide
Water
PEG
10
10
10
10
75
80
50
95
Pd(1)–Br(2)
Pd(1)–Br(1)
Pd(1)–Br(3)
P(1)–C(25)
P(1)–C(11)
P(1)–C(18)
P(1)–C(10)
O(1)–C(2)
O(2)–C(2)
O(2)–C(3)
C(1)–C(2)
2.4089(15)
2.4076(17)
2.4565(17)
1.774(9)
1.777(10)
1.799(9)
Br(3)–Pd(1)–Br(2)
Br(3)–Pd(1)–Br(1)
Br(2)–Pd(1)–Br(1)
C(25)–P(1)–C(11)
C(25)–P(1)–C(18)
C(11)–P(1)–C(18)
C(2)–O(1)–C(3)
91.28(6)
174.12(6)
91.66(6)
111.0(5)
107.3(4)
108.8(5)
110.3(4)
116.2(8)
Reaction conditions: iodobenzene: 1 mmol, Ph3SnCl: 0.4 mmol, K2CO3: 1.5 mmol, at
90 °C, 15 min.
1.821(9)
(1) as a dark brown solid as shown in Scheme 1. Since palladium
acetate is soluble in diethyl ether [18], the resulting solid was
washed with diethyl ether to give a product free of palladium acet-
ate. The observed singlet and sharp peak at d = 22.1 ppm in 31P
NMR spectrum of the compound confirmed its purity.
1.242(14)
1.256(14)
1.545(12)
1.471(15)
P(1)–C(10)–H(10)
Table 3
Effect of solvent on amination of iodobenzene by aqueous ammonia.
3.2. X-ray crystallographic study of compound 1
Entry
Solvent
Time (h)
Yield (%)
Several Suitable crystals of bis[(2-methylacetatobenzyl)tri(p-
tolyl)phosphonium]hexabromodipalladate(II) were obtained by
slow evaporation from its dichloromethane solution over several
days and its structure was determined by X-ray diffraction. The
asymmetric unit of the compound is shown in Fig. 1. Compound
1
2
3
4
Ethanol
N,N-Dimethylsulfoxide
Water
6
6
6
6
65
50
60
95
Solvent free
Reaction conditions: iodobenzene: 1 mmol, aqueous ammonia: 1 mL, catalyst:
0.005 g, at 60 °C, 7 h.
ꢀ
1 crystallizes in the triclinic space group P1 with two molecules
in the unit cell. The geometry of [Pd2Br6] moiety is nearly planar
and the structure around the phosphorus atom is close to tetrahe-
dral. The bromo group attached to CH2 in the ligand structure is
replaced by acetate group in the final compound structure. The Sig-
nificant crystallographic data are given in Table 1 and some
selected bond distances and angles are summarized in Table 2.
benzene). Then, the reaction of the obtained phosphonium bro-
mide with palladium(II) acetate in a molar ratio of 3:2 in ethanol
at room temperature for 4 h led to the formation of bis[(2-methy-
lacetatobenzyl)tri(p-tolyl)phosphonium]hexabromodipalladate(II)
Table 4
The amination of various aryl halides.
Entry
Aryl halide
Product
Yielda (%)
Time (h)
M.p. (°C)
1
2
3
4
5
6
7
8
9
10
C6H5I
C6H5Br
C6H5NH2
C6H5NH2
95
93
96
90
88
92
90
90
87
92
6
13
4
15
5
3
5
8
7
5
Colorless oil [19]
Colorless oil [19]
145–147 [20]
43–44 [19]
68–70 [19]
87–89 [21]
136–137 [22]
55–58 [20]
56–58 [20]
4-NO2–C6H4Br
4-CH3–C6H4Br
4-CHO–C6H4Br
4-CN–C6H4Br
4-NH2–C6H4Br
4-OCH3–C6H4Br
4-OCH3–C6H4I
2-COOH–C6H4I
4-NO2–C6H4NH2
4-CH3–C6H4NH2
4-CHO–C6H4NH2
4-CN–C6H4NH2
4-NH2–C6H4NH2
4-OCH3–C6H4NH2
4-OCH3–C6H4NH2
2-COOH–C6H4NH2
143–145 [19]
Reaction conditions: aryl halide: 1 mmol, aqueous ammonia: 1 mL, catalyst: 0.005 g, at 60 °C.
a
Isolated yield.

A. Ghorbani-Choghamarani et al. / Inorganica Chimica Acta 446 (2016) 97–102
101
Table 7
the products were obtained in very good to excellent yields. The
products were characterized by spectral techniques (1H NMR
and IR).
The effect of temperature on the synthesis of biphenyl.
Temperature (°C)
Compound 1 (g)
Time (min)
Yield (%)
25
60
90
0.005
0.005
0.005
0.005
10
10
10
10
0
65
97
96
3.3.2. Stille cross-coupling reaction
The other studied reaction in this work was Stille cross-cou-
pling reaction. The influence of the amount of catalyst, solvent
and temperature on the reaction times and yields were studied
in order to determine the most appropriate reaction conditions.
For this purpose, the reaction of iodobenzene, triphenyltin chloride
and potassium carbonate in polyethylene glycol at 90 °C was
selected as a model reaction and different amounts of catalyst were
investigated. The results are shown in Table 5.
According to Table 5, the reaction without catalyst was per-
formed to prove the true effectiveness of the heterogeneous cata-
lyst. It was found that biphenyl was not obtained in the absence
of the catalyst.
100
Reaction conditions: iodobenzene: 1 mmol, Ph3SnCl: 0.4 mmol, K2CO3: 1.5 mmol,
1 mL PEG, 15 min.
Table 8
Optimization of base in Stille cross-coupling reaction.
Base
Time (min)
Yield (%)
Potassium carbonate (K2CO3)
Potassium hydroxide (KOH)
Triethylamine (Et3N)
10
10
10
10
96
92
60
80
Sodium bicarbonate (NaHCO3)
It was necessary to choose a suitable solvent before tempera-
ture and base optimization. Thus several solvents including etha-
nol, water, N,N-dimethylformamide and polyethylene glycol
(PEG) were used. The results are present in Table 6. Polyethylene
glycol was chosen as the optimal solvent reaction because it is a
green solvent and also is cheaper than other organic solvents.
Next the effect of temperature on the rate of the reaction was
studied using the reaction of iodobenzene, triphenyltin chloride
and potassium carbonate in the presence of the optimum quantity
of catalyst (Table 7). It was found that the reaction did not proceed
at room temperature. The reaction proceeded to give the corre-
sponding product in good yield at 90 °C. The temperature of reac-
tion was kept at 90 °C as optimal temperature because further
increase in temperature to 100 °C had little effect on the rate of
reaction.
At the end, optimization of base was performed. According to
Table 8, potassium carbonate could be selected as the optimum
base among the used bases.
The best result was obtained with 1:0.4:1.5 ratios of aryl
halides: triphenyltin chloride: potassium carbonate with 0.005 g
of catalyst at 90 °C.
Reaction conditions: iodobenzene: 1 mmol, Ph3SnCl: 0.4 mmol, base: 1.5 mmol,
1 mL PEG, catalyst: 0.005 g, 15 min, at 90 °C.
3.3. Catalytic study
3.3.1. Amination of aryl halides
Amination reaction of aryl halides is a reaction that does not
proceed in the absence of a catalyst. So this reaction was selected
to study the catalytic activity of the synthesized compound (1).
Aqueous ammonia was used as a supplier of the amine group for
this purpose. At the beginning of work, the heterogeneous catalyst
optimization was carried out and the optimal amount was found to
be 0.005 g (0.3 mol%). Then, the reaction of iodobenzene with
aqueous ammonia was performed in various organic solvents.
The results are shown in Table 3.
The optimal conditions reaction determined as follows: 1 mmol
of aryl halide, 1 mL of aqueous ammonia and 0.005 g (0.3 mol%) of
catalyst in solvent free conditions. To investigate the efficiency of
this method, various aryl iodides and bromides were applied and
the results are summarized in Table 4 (Scheme 2). As can be seen,
X
R
[(CH3C6H4)3PCH2C6H4CH2OC(O)CH3]2[Pd2Br6] (Cat.)
K2CO3,PEG, 90 0
Ph3SnCl
+
C
R
X= I, Br
Scheme 3. Synthesis of biaryls in the presence of [(CH3C6H4)3PCH2C6H4CH2OC(O)CH3]2[Pd2Br6].
Table 9
Stille cross-coupling for the synthesis of biaryls from aryl halides.
Entry
Aryl halide
Product
Yielda (%)
Time (min)
M.p. (°C)
1
2
3
4
5
6
7
8
9
10
11
12
13
C6H5I
C6H5Br
C6H5–C6H5
C6H5–C6H5
96
95
94
90
93
97
90
92
95
96
95
91
90
8
10
5
20
6
60–62 [23]
62–64 [23]
107–110 [15]
41–44 [15]
55–57 [15]
83–84 [15]
49–51 [15]
82–84 [15]
82–84 [15]
115–117 [24]
75–76 [15]
43–45 [15]
Colorless oil [15]
4-NO2–C6H4Br
4-CH3–C6H4Br
4-CHO–C6H4Br
4-CN–C6H4Br
4-NH2–C6H4Br
4-OCH3–C6H4Br
4-OCH3–C6H4I
2-COOH–C6H4I
4-Cl–C6H4Br
4-CH3–C6H4I
3-CF3–C6H4Br
4-NO2–C6H4–C6H5
4-CH3–C6H4–C6H5
4-CHO–C6H4–C6H5
4-CN–C6H4–C6H5
4-NH2–C6H4–C6H5
4-OCH3–C6H4–C6H5
4-OCH3–C6H4–C6H5
2-COOH–C6H4-C6H5
4-Cl–C6H4–C6H5
4-CH3–C6H4–C6H5
3-CF3–C6H4-C6H5
8
35
23
18
16
10
30
13
Reaction conditions: iodobenzene: 1 mmol, Ph3SnCl: 0.4 mmol, K2CO3: 1.5 mmol, PEG: 1 mL, catalyst: 0.005 g, at 90 °C.
a
Isolated yield.

102
A. Ghorbani-Choghamarani et al. / Inorganica Chimica Acta 446 (2016) 97–102
Series2
Series1
require inert or dry atmosphere. The catalyst showed high activity,
and its reusability was tested up to four consecutive cycles in both
reactions.
95
94
93
90
90 90
90
88
Acknowledgement
This work was supported by the research facilities of Ilam
University, Ilam, Iran.
Appendix A. Supplementary material
1
2
3
4
CCDC 1030178 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif. Supplementary data associated with this arti-
cle can be found, in the online version, at http://dx.doi.org/10.
1016/j.ica.2016.02.045.
CYCLE
Fig. 2. Reuse of the catalyst in amination reaction (series 1) and Stille
cross-coupling reaction (series 2).
Using several types of aryl halides having electron donating and
electron withdrawing groups, the generality of the reaction was
evaluated (Scheme 3). In all cases, the corresponding products
were obtained in good to excellent yield (Table 9). The products
were characterized by spectral techniques (1H NMR and IR).
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