Benzimidazolyl based Schiff base palladium complex in an ionic liquid: an effective combination for Suzuki coupling

Article abstract of DOI:10.1080/00958972.2017.1311412

A new benzimidazole based Pd(II) Schiff base complex was prepared and its catalytic activity was evaluated for Suzuki cross-coupling reactions in ethyl-methyl imidazolium hexafluorophosphate [EMIM PF₆] ionic liquid at ambient temperature. The system provides a stable and reusable method for coupling reactions. Optimization for suitable reaction conditions were studied with respect to the effect of catalyst concentration, effects of additives, solvent and substituents on boronic acid. Good to excellent yields were achieved using a modest amount of the catalyst. The reaction time was less and the yield was more compared to previously reported results. In addition, the catalyst can be easily reused and recycled for six times without much loss in activity; this is an example of sustainable and green methodology.

Full text of DOI:10.1080/00958972.2017.1311412

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Benzimidazolyl based Schiff base palladium
complex in an ionic liquid: an effective
combination for Suzuki coupling
Vasantha Kumar Basappa Chidananda, Dileep Ramakrishna, Manpreet Kaur
& Revanasiddappa Hosakere Doddarevanna
To cite this article: Vasantha Kumar Basappa Chidananda, Dileep Ramakrishna, Manpreet Kaur
& Revanasiddappa Hosakere Doddarevanna (2017): Benzimidazolyl based Schiff base palladium
complex in an ionic liquid: an effective combination for Suzuki coupling, Journal of Coordination
Chemistry, DOI: 10.1080/00958972.2017.1311412
To link to this article: http://dx.doi.org/10.1080/00958972.2017.1311412
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Date: 18 April 2017, At: 23:37

Journal of Coordination Chemistry, 2017
http://dx.doi.org/10.1080/00958972.2017.1311412
Benzimidazolyl based Schiff base palladium complex in an
ionic liquid: an effective combination for Suzuki coupling
Vasantha Kumar Basappa Chidanandaa, Dileep Ramakrishnab, Manpreet Kaurc and
Revanasiddappa Hosakere Doddarevannaa
adepartment of Chemistry, manasagangotri, university of mysore, mysuru, india; bdepartment of Chemistry,
c
school of engineering Presidency university, Bengaluru, india; department of Chemistry, Keene state
College, Keene, nh, usa
ABSTRACT
ARTICLE HISTORY
received 18 november 2016
accepted 2 march 2017
A new benzimidazole based Pd(II) Schiff base complex was prepared
and its catalytic activity was evaluated for Suzuki cross-coupling
reactions in ethyl-methyl imidazolium hexafluorophosphate [EMIM
PF6] ionic liquid at ambient temperature. The system provides a stable
and reusable method for coupling reactions. Optimization for suitable
reaction conditions were studied with respect to the effect of catalyst
concentration, effects of additives, solvent and substituents on
boronic acid. Good to excellent yields were achieved using a modest
amount of the catalyst. The reaction time was less and the yield was
more compared to previously reported results. In addition, the catalyst
can be easily reused and recycled for six times without much loss in
activity; this is an example of sustainable and green methodology.
KEYWORDS
Benzimidazole; schiff base;
palladium; ionic liquid;
suzuki reaction
CONTACT revanasiddappa hosakere doddarevanna
hdrevanasiddappa@yahoo.com
supplemental data for this article can be accessed at http://dx.doi.org/10.1080/00958972.2017.1311412.
© 2017 informa uK limited, trading as taylor & francis Group

2
V. K. BASAPPA CHIDANANDA ET AL.
1. Introduction
Immobilization of transition metal Schiff base complexes onto zeolite, polymeric or clay
matrices has been adopted to prepare heterogeneous catalysts [1]. A prominent achieve-
ment in this field is the use of ionic liquids as homogeneous immobilization of organocat-
alysts in organic synthesis [2a–d]. Ionic liquid (IL) immobilized catalysts can induce organic
reactions, and such reactions were carried in polar solvents, which results in a homogeneous
system. After completion of the reaction, a non-polar solvent such as diethyl ether is added
and the IL immobilized catalyst can be separated easily from the polar phase due to the
difference in solubility. Consequently, the IL immobilized catalyst is regenerated and can be
used for further reactions [2e].
Many biaryls have industrial applications, for the synthesis of drugs, conducting polymers,
liquid crystal materials, and natural products [3, 4]. In 2010, the Nobel Prize was shared
between Richard F. Heck, Ei-ichi Negishi and Akira Suzuki for their discovery and develop-
ment of C–C coupling with arylboronic acids (Suzuki coupling) [5]. The development of
improved reaction conditions for the Pd-catalyzed Suzuki reaction has received much atten-
tion [6–8]. The choice of ligand is crucial to the success of such a catalytic reaction.
Benzimidazole-containing ligands have proven to be good candidates for complexation
with metals due to their exceptional coordination ability and versatile conformations [9].
Benzimidazole with rigid structure and high electron transfer capability can provide nitro-
gens to coordinate with transition metals. Many palladium complexes with N-donor ligands
have been employed as catalysts for C–C coupling reactions [10]. However, recyclable and
reusable homogeneous catalytic systems of palladium complex with benzimidazole Schiff
base ligand are rarely studied. There is demand for development of a robust, efficient, and
cost-effective catalyst that can circumvent the limitations of existing catalysts [11–13].
Environmental concerns and economic considerations make it essential to develop catalytic
systems that can be recovered and recycled, especially when noble transition metals are
involved [14–16]. Recently, Wei Cao et al. [17] and Zhuang Liao et al. [18] showed that copper
and zinc aided in the ring opening of benzimidazo [1,2-c]quinazoline yielding Schiff base
complexes. Herein, we focus our interest on the synthesis of palladium benzimidazole Schiff
base complex via ring opening of benzimidazo [1,2-c]quinazoline by palladium benzonitrile
precursor and its application in Suzuki coupling reactions in ionic liquid as a robust and
recyclable catalytic system.
2. Experimental
2.1. Materials and methods
All solvents were of analytical reagent grade. Solvents were dried and purified before use
according to standard procedures. The metal content was determined by a gravimetric
method using dimethylglyoxime as precipitating agent. Melting points of the compounds
were determined on an ELICO-3210 apparatus and are uncorrected. Elemental analysis
(CHNO) of the compounds were determined using a Perkin-Elmer 240 elemental analyzer.
Infrared spectral measurements were made using Perkin-Elmer Spectrum Version 10.03.09.
from 4000 to 200 cm−1. 1H and 13C NMR spectra for the ligand and its palladium compound
were taken using an Agilent-NMR spectrophotometer at 400 MHz employing TMS as a ref-
erence and DMSO-d6 as solvent at ambient temperature. XRD crystal data were collected

JOURNAL OF COORDINATION CHEMISTRY
3
from a Bruker, Microstar Proteum 8 diffractometer at 296 K. Electronic spectra of the com-
pounds in the UV–visible region (200–800 nm) were measured using an ELICO SL 117 double
beam spectrophotometer with quartz cells. Thermogravimetric measurement for the com-
plex was recorded in nitrogen on a NETZCH Proteus Thermal Analysis system keeping final
temperature at 600°C at a heating rate of 10°C/min. The ESI mass spectra were recorded from
an LC-MS/MS Synapt G2 HDMS Mass Spectrometer.
2.2. Preparation of 2-(5,6-dihydro-benzo[4,5]imidazo[1,2-c]quinazolin-6-yl)-6-
methoxy-phenol (1)
To an ethanolic solution of 2-(1H-benzoimidazol-2-yl)-phenylamine (5 mmol, 1.04 g)
ortho-vanillin (5 mmol, 0.76 g) and a catalytic amount of glacial acetic acid were added. Then
the reaction mixture was refluxed on a water bath for 4 h. The pale yellow solid that formed
upon cooling was filtered off and dried under vacuum at room temperature. The synthetic
route of 1 is depicted in scheme 1.
Ligand 1: yield: 89%. M.P 180–184°C. IR ν (cm−1): 3313, m (C=N, benzimidazole), 3320 (NH,
benzimidazole), 3386 (Ph–OH), ESI–LCMS m/z: 343.38 [M + 1]+. Anal Calcd for [C21H17N3O2]
(%): C, 73.46; H, 4.99; N, 12.24. Found: C, 73.64; H, 5.12; N, 12.54. 1H NMR 9.364 (S, 1H, OH);
7.915 (d, 1H, J = 7.5 Hz, ArH); 7.60 (d, 1H, J = 7.5 Hz ArH); 7.252–7.039 (m, 5H, ArH); 7.188
(s, 1H, NH); 6.872–6.747 (m, 3H, ArH); 6.558 (t, 1H, J = 7.9 Hz, ArH); 6.279 (d, 1H, J = 7.59 Hz,
CH); 3.777 (s, 3H, OCH3). 13C NMR 148.186, 147.564, 144.301, 143.800, 143.671, 133.297,
131.924, 127.988, 124.988, 122.529, 122.354, 119.691, 118.977, 118.249, 118.211, 115.138,
112.421, 111.844, 110.546, 63.072, 56.470.
2.3. Preparation of palladium catalyst [Pd(1)Cl]·H2O (2)
Palladium catalyst (2) was prepared by stirring a mixture of bis(benzonitrile)palladium(II)
chloride (1 mmol, 0.383 g) with 1 (1 mmol, 0.343 g) in CH2Cl2 for 1 h at room temperature
under nitrogen. Instantaneous coordination occurred since there was a change in color from
a pale yellow to brick red solid formation. The solid was filtered off, washed with CH2Cl2 and
dried in vacuo. The synthetic route of new palladium catalyst 2 is depicted in scheme 2.
Compound 2: yield: 73%. M.P 285–287°C. IR ν (cm−1): 1617 (HC=N), 3320 (NH, benzimi-
dazole), ESI–LCMS m/z: 503.0450 [M + 1]+. Anal Calcd for [C21H18ClN3O3] (%): C, 50.22; H, 3.61;
N, 8.37. Found: C, 50.89; H, 4.02; N, 8.91. 1H NMR 14.082 (s, NH, 1Himi); 8.607 (d, 1H, J = 8.39 Hz,
ArH); 8.119 (d, 1H, J = 7.59 Hz, ArH); 8.107 (s, 1H, HC = N–); 7.684 (t, 2H, J = 8.39 Hz, ArH); 7.573
(d, 2H, J = 7.19 Hz, ArH); 7.32 (d, 1H, J = 7.59 Hz, ArH); 7.273 (d, 1H, J = 7.99 Hz, ArH); 7.144 (d,
1H, J = 8.39 Hz, ArH); 6.901 (d, 1H, J = 7.9 Hz, ArH); 6.532 (d, 1H, J = 7.59 Hz, ArH); 3.777 (s, 3H,
Scheme 1. i) ethanol, 2 drops of acetic acid, reflux 4 h.

4
V. K. BASAPPA CHIDANANDA ET AL.
Scheme 2. i) Pd[(PhCn)2Cl2], dichloromethane, rt, 1 h.
OCH3). 13C NMR 177.752, 148.414, 147.488, 147.169, 146.775, 146.539, 145.090, 140.506,
133.935, 131.347, 129.989, 127.340, 124.396, 124.168, 123.242, 119.448, 118.719, 116.025,
115.859, 111.973, 56.477.
2.4. X-ray crystallographic analysis
Crystals suitable for X-ray crystallographic measurements were obtained by slow diffusion
of diethyl ether into solution of the palladium complex in methanol at room temperature.
The crystal was mounted on a glass fiber. X-ray diffraction data of 2 were collected on a
Bruker Microstar Proteum 8 diffractometer at 296 K [26]. Data were collected using Cu-Kα
radiation (λ = 1.54178 Å) at 296 K with the ψ and ω scan method. The structure of 2 was
solved by direct methods using SHELXS and all non-hydrogen atoms were refined aniso-
tropically by full-matrix least squares based on F2 using SHELXL [27]. Hydrogens were placed
in calculated positions and included in the refinement using the riding model.
2.5. Catalytic activity
To a 50 mL round bottom flask, aryl halide (1.0 mmol), arylboronic acid (1.0–1.2 mmol), 2
(0.1 mol%), K2CO3 (2.0 mmol), and EMIM [PF6]-water mixture (1:1, 2 mL) were added and
continuously stirred at room temperature (25°C). The progress of the reaction was monitored
at regular 5 min intervals byTLC. After completion of the reaction, the crude reaction mixture
was diluted with water (20 mL) and extracted with a mixture of hexane and ethyl acetate
(1:1 v/v, 3 × 10 mL). Diethyl ether was used for extraction in the cases of some substrates.
The organic layer was dried over anhydrous Na2SO4, and then the solvent was removed
under reduced pressure. The resulting crude residue was purified by column chromatography
over silica gel (mesh 60–120), using n-hexane–ethyl acetate as eluent, to give the pure prod-
uct. The products were analyzed by NMR spectroscopy.
3. Results and discussion
IR spectra of 2-(5,6-dihydro-benzo[4, 5]imidazo[1,2-c]quinazolin-6-yl)-6-methoxy-phenol (1)
and its palladium complex (2) were compared (figure S1). A medium peak at 1720 cm−1 of
1 was assigned to the C=N of the benzimidazole ring [19]. A characteristic absorption band
for benzimidazo [1,2-c]quinazoline ring with a tertiary nitrogen at 1360 cm−1 and absence
of peak corresponding to –NH of imidazolyl ring and CH=N group supports the

JOURNAL OF COORDINATION CHEMISTRY
5
benzimidazoquinazoline ring structure [20]. In the spectrum of 2, new peaks at 1600 cm−1
and 3230 cm−1 corresponding to azomethine group coordinated to metal and NH stretching
vibration of benzimidazole ring, respectively [21], and absence of peak at 1360–1380 cm−1
confirms the opening of benzimidazo [1,2-c]quinazoline ring during coordination. The peak
at 3470 cm−1 indicates the presence of water. The peak corresponding to phenolic ν(C–O)
at 1270 cm−1 for 1 shifted to slightly higher frequency in the IR spectrum of 2, confirming
the involvement of phenolic OH in the M–O bond formation.
The 1H NMR and 13C NMR spectral data of 1 and 2 provide insight to their structure and
are in agreement with those obtained from IR and X-ray crystal studies (tables 1, 2a, and 2b).
The 1H NMR spectrum of 1 (figure S2) shows a singlet at δ 6.279 ppm (d, –HC–N) correspond-
ing to sp3 carbon in benzimidazo [1,2-c]quinazoline or dihydropyrimidine ring [22]. This
disappeared in the spectrum of 2 (figure S3). A new signal at δ 8.107 ppm (s, –HC=N) corre-
sponding to imine proton and at δ 14.097 ppm (s, –NH) due to benzimidazole –NH proton
clearly indicates the opening of benzimidazo [1,2-c]quinazoline ring and coordination of
1
azomethine in 2. Furthermore, H NMR results are supported by 13C NMR spectrum of 1
(figure S4) and show a signal at δ 63.072 ppm corresponding to sp3 carbon in benzimidazo
[1,2-c]quinazoline ring which disappeared in the spectrum of 2 (figure S5). Appearance of
a new signal at δ 177.752 ppm indicates formation of complex with azomethine via ring
opening of benzimidazoquinazoline. Further, mass spectra help elucidate the structure. The
ESI mass spectrum of 1 (figure S6) shows a molecular ion peak at m/z = 344.1921 (ES+). The
positive ion mass spectrum of 2 (figure S7) shows the base peak at m/z = 503.0450 which is
an isotopic peak with the most abundant isotope of palladium of 105.9 Da (27.3%). However,
the fragment ion peaks are observed at m/z = 448.0099 (M–Cl) and yet another peak at
m/z = 344.1250 corresponding to the mass of 1.
The UV–vis spectra of 1 and 2 were recorded in 10−3M solutions of DMSO (figure S8). The
UV–vis spectrum of 1 shows a π → π* transition at 255 nm. A broad absorption from 340 to
383 nm may be assigned to the electronic transition of n → π*, while in the electronic spectra
of 2, n → π* transitions are slightly shifted to lower wavelength at 328 and 372 nm. However,
in addition 2 also displayed a band at 481 nm corresponding to a spin allowed transition
Table 1. Crystal data and structure refinement for 2.
Formula
C
21H18ClN3O3Pd
fW
502.23
orthorhombic
P212121
Crystal system
space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
7.6461(2)
12.7333(3)
19.0395(5)
90
90
γ (°)
90
Volume (Å3)
1853.69(8)
4
Z
Calculated density (g cm−3
F (0 0 0)
)
1.800 mg m−3
1008
reflections collected/unique
7821
1.039
Goodness-of-fit on F2
final R indices [I > 2σ(I)]
R1 = 0.0259
wR2 = 0.0598
R1 = 0.0265
wR2 = 0.0601
R indices (all data)

6
V. K. BASAPPA CHIDANANDA ET AL.
Table 2a. hydrogen bonds for 2 [Å and °].
D–H⋯A
d(D–H)
d(H⋯A)
2.00(5)
2.26
d(D⋯A)
<(DHA)
n(3)–h(3)⋯o(1W)#
o(1W)–h(1WB)⋯Cl(1)
o(1W)–h(1Wa)⋯o(2)
0.76(4)
0.85
0.85
2.748(5)
3.082(3)
2.825(4)
173(4)
162.5
170.0
1.98
symmetry transformations used to generate equivalent atoms: #−x + 1/2, −y + 1, z + ½.
Table 2b. selected bond distances (Å) and angles (°) for 2.
Pd(1)–n(1)
Pd(1)–o(1)
Pd(1)–n(2)
1.987(3)
1.993(3)
2.008(3)
Pd(1)–Cl(1)
2.3312(9)
90.86(11)
88.76(12)
175.39(12)
171.86(10)
87.97(7)
n(1)–Pd(1)–o(1)
n(1)–Pd(1)–n(2)
o(1)–Pd(1)–n(2)
n(1)–Pd(1)–Cl(1)
o(1)–Pd(1)–Cl(1)
n(2)–Pd(1)–Cl(1)
93.04(9)
from 1A1g → 1B1g indicating a slightly distorted square planar geometry for 2 [23]. Furthermore,
the thermal behavior of 2 has been studied as a function of temperature from room tem-
perature to 700°C under nitrogen at a heating rate of 10°C/min (figure S8). The thermal
decomposition pattern of 2 reveals that degradation takes place in three steps, a small weight
loss of 10.44% (10.67%) from 30 to 90°C which is associated with loss of a lattice water along
with loss of a chloride, a small weight loss at 250°C which may be due to some reductions
and phase transitions and a sharp weight loss of 68.50% (68.48%) from 400 to 460°C corre-
sponding to ligand loss leaving behind metal oxide above 600°C.
The single-crystal X-ray diffraction study shows that 2 crystallizes in the orthorhombic
space group P212121. The asymmetric unit consists of one independent metal complex and
a water molecule (figure 1). Pd exhibits a slightly distorted square planar coordination geom-
etry. The mean planes of the benzimidazole (C14/N3/C15-C20/N2), methoxyphenyl (C2-C7),
and the phenyl (C8-C13) are twisted away from the Pd center in a similar fashion with dihedral
angles of 30.5(2)°, 33.0(1)°, and 36.5(3)°, respectively. The chloride attached to Pd lies trans
to the nitrogen of the imine and is slightly bent away from the benzimidazole and meth-
oxyphenyl moieties owing to steric repulsion. The benzimidazole and the bonded phenyl
are essentially planar with a dihedral angle of 9.6(9)° while the dihedral angle between the
benzimidazole and methoxyphenyl is 57.6(1)°. The bond lengths and angles around the Pd
center were comparable to related structures [24, 25]. The water molecule interacts with O2
of the methoxy group and the chloride via O1W–H1WA⋯O2 and O1W–H1WB⋯Cl1 inter-
molecular hydrogen bonds, respectively. In the crystal, N–H⋯O intermolecular hydrogen
bonds involving the water molecule and the free NH group on the benzimidazole form
infinite 1-D chains along [0 0 1] (figure 2). Thus, water plays a dual acceptor/donor role as a
bridge between Pd ions and a major role in stabilizing the crystal packing. In addition, π–π
stacking interactions influence the crystal packing.
3.1. Catalytic activity
Our next focus was on exploring the catalytic applications of the complex for carbon–carbon
bond forming (Suzuki) reactions in ionic liquid media. Suzuki reaction can be affected by

JOURNAL OF COORDINATION CHEMISTRY
7
Figure 1. orteP diagram of 2 showing the atom labeling scheme with 30% probability displacement
ellipsoids. dashed lines indicate o–h⋯o and o–h⋯Cl intermolecular hydrogen bonds.
the amount of catalyst and the type of base used. Hence, we optimized the reaction condi-
tions using the reaction between iodobenzene and phenylboronic acid to give biphenyl as
a model reaction. The results from various experiments are summarized in table 3. Initially
the reaction was carried out in the presence of palladium acetate as catalyst (table 3, entry
1), maintaining all the other reaction conditions. The reaction yielded only 67% of the cou-
pled product. From the optimization experiment, it was found that using 0.1 mol% of the
complex in the presence of K2CO3 as the base were the most suitable conditions for efficient
conversion at room temperature with an excellent yield of product (table 3, entry 4). The
yield of the product was not affected much by increasing the concentration of the catalyst
up to 2.0 mol% (table 3, entries 6 and 7). Although the product was obtained in excellent
yield (80%) using 0.05 mol% of the catalyst (table 3, entry 3), it was not possible to recycle
the catalyst after two cycles under these conditions. Thus, we determined that the optimum
loading for the catalyst was 0.1 mol% for the Suzuki reaction.
Another important role in the palladium-catalyzed Suzuki reaction is by the solvent. The
influence of solvent in the present system was therefore evaluated first (table 4); according
to the green solvent selection guide, ethyl-methyl imidazolium hexafluorophosphate [EMIM
PF6] ionic liquid was the best solvent in our screening experiments (table 4, entries 5 and 6).
A major advantage is that both base and the catalyst are soluble in the ionic liquid, giving
a solution that is completely homogeneous with water. With ethanol and THF, only low to
moderate results were obtained (table 4, entries 2 and 4). Good yield was observed when
methanol was used as a solvent, but the time and temperature conditions were more drastic
during this reaction compared to using ionic liquid as solvent. Moreover, the recycling of

8
V. K. BASAPPA CHIDANANDA ET AL.
Figure 2. molecular packing for 2 viewed along the a axis. dashed lines indicate o–h⋯o, o–h⋯Cl,
and n–h⋯o hydrogen bonds forming 1-d chains along [0 0 1]. hydrogens not involved in hydrogen
bonding have been removed for clarity.
the ionic liquid immobilized catalyst was better in EMIM [PF6]-water [1:1] system than in
EMIM [PF6] alone.
The scope of the Suzuki reaction catalyzed by the palladium complex in ionic liquid
medium was investigated by employing various aryl halides and arylboronic acids. The results
are summarized in table 5. Reaction of substituted halobenzenes with arylboronic acids
gave the corresponding coupled products in good to excellent yields (70–94%) without
formation of homocoupled product. However, the time required for completion of the reac-
tions for bromobenzene and chlorobenzene was longer than that for iodobenzene. The
method is equally applicable for aryl iodides substituted with either electron-withdrawing
or electron-donating groups. For example, 4-nitro-, 4-methyl-, 4-methoxy-, and 2-amino-
iodobenzenes were converted to the corresponding coupled products in high yields. A
comparison with previously reported results shows that the present catalytic system is pre-
ferred in terms of catalyst loading, temperature range, and reaction time [28].
The recycled palladium catalyst in EMIM [PF6] showed comparable activity even after 6–7
runs in the reaction of iodobenzene with phenyl boronic acid (figure 3). However, the addi-
tion of excess base to the reaction mixture resulted in degradation of catalyst. ILs are not

JOURNAL OF COORDINATION CHEMISTRY
9
Table 3. optimization of reaction conditions for the reaction catalyzed by Pd complex.a
Pd Catalyst
(HO)2B
I
+
Base, EMIMPF6
Room temperature
Yield (%)b
Entry
Catalyst concentration (mol %)
1
2
3
4
5
6
7
Pd(CooCh3)2, 0.1
67
64
80
92
92
91
91
0.01
0.05
0.1
0.2
1.5
2.0
aunless otherwise indicated, all reactions were carried out with 1 mmol of iodobenzene, 1 mmol of phenylboronic acid, x
mmol of catalyst, 2 mmol K2Co3, 2 ml emim [Pf6]-water mixture, 30 min, room temperature.
bisolated yield after column chromatography.
Table 4. effect of solvents on the reaction catalyzed by Pd complex.a
Yield (%)b
Entry
Solvent
Temperature (°C)
Time (min)
1
2
3
4
5
6
Water
ethanol
methanol
80
80
80
80
25
25
120
120
120
120
30
36
75
83
12
94
93
thf
emim [Pf6]
emim [Pf6]-water [1:1]
30
aunless otherwise indicated, all reactions were carried out with 1 mmol of iodobenzene, 1 mmol of phenylboronic acid,
0.1 mol% of catalyst, 2 mmol K2Co3, 2 ml solvent.
bisolated yield after column chromatography.
Table 5. suzuki reactions between aryl halides and arylboronic acids catalyzed by Pd complex in emim
Pf6.a
Yield (%)b
Entry
Aryl halides
Arylboronic acid
Time (min)
1
2
3
4
5
6
7
8
C6h5i
C6h5Br
C6h5Cl
C6h5i
C6h5Br
C6h5Cl
C6h5i
C6h5i
C6h5i
C6h5i
C6h5i
C6h5B(oh)2
C6h5B(oh)2
C6h5B(oh)2
30
90
90
30
90
90
30
30
30
30
30
90
30
90
90
94
88
84
85
82
79
87
70
89
89
82
80
85
80
78
3,4,5-(oCh3)3C6h2B(oh)2
3,4,5-(oCh3)3C6h2B(oh)2
3,4,5-(oCh3)3C6h2B(oh)2
4-Ch3C6h4B(oh)2
2-C4h3sB(oh)2
2-nh2C6h4B(oh)2
4-no2C6h4B(oh)2
4-oCh3C6h4B(oh)2
4-oCh3C6h4B(oh)2
2-Ch3C6h4B(oh)2
2-Ch3C6h4B(oh)2
2-Ch3C6h4B(oh)2
9
10
11
12
13
14
15
C6h5Br
oCh3C6h5i
oCh3C6h5Br
oCh3C6h5Cl
aall reactions were carried out with 1 mmol of iodobenzene, 1 mmol of phenylboronic acid, 0.1 mol% of catalyst, 2 mmol
K2Co3, 2 ml emim [Pf6]-water mixture, room temperature (30°C).
bisolated yield after column chromatography.
intrinsically“green”with most of them as toxic as organic solvents. Recently, biodegradability
and toxicity of ILs have become of interest. The toxicity of 1-alkyl-3-methyl imidazolium ionic
liquids increases with increase in the size of the alkyl group. This is due to the ionic nature

10
V. K. BASAPPA CHIDANANDA ET AL.
Figure 3. effect of recycling on conversion.
decreasing as the bulkiness of the organic cation increases. Ionic liquids like EMIM [PF6] have
a simple alkyl group which gives good ionic character and hence their toxicity levels are low.
The complete ionic liquid-catalyst mixture was recovered and reused.
3.2. Reusability and recovery of the catalyst
After the first run of the reaction was completed, the product was directly extracted into the
organic layer; the catalyst which remained in the aqueous layer was reused for the next cycle
of the reaction following the same procedures as mentioned above for the Suzuki
reactions.
4. Conclusion
We have synthesized and systematically characterized a benzimidazole Schiff base palladi-
um(II) complex and explored its application in Suzuki coupling reaction in ethyl-methyl
imidazolium-hexafluorophosphate [EMIM PF6] ionic liquid, which provides a robust air stable
system for the Suzuki reaction. The palladium catalyzed Suzuki reaction was highly active
in EMIM [PF6]-water [1:1] system in our screening experiment and the reusability of the
catalyst was efficient in the above system. The present work can be an approach to green
chemistry as the catalyst is immobilized on an ionic liquid medium and hence the catalytic
system (catalyst + ionic liquid) can be completely recycled by solvent extraction and then
reused effectively.
Acknowledgements
The authors would like to thank the Institute Of Excellence, University of Mysore, Mysuru, Karnataka for
NMR, mass spectrometry, XRD facility and other minor equipment. Also, the author B.C. Vasantha Kumar
acknowledges the Council for Scientific and Industrial Research-University Grants Commission (CSIR-
UGC) for senior research fellowship [grant number DV. 5/176/UGC-FS/2012-13, DATED: 23-08-2012].

JOURNAL OF COORDINATION CHEMISTRY
11
CCDC: 1485219 contains supplementary crystallographic data for 2 in 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, by emailing data_request@ccdc.cam.ac.uk, or by contacting the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44 1223 336033.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the University Grants Commission [grant number ORDER NO. DV. 5/176/
UGC-FS/2012-13, DATED: 23-08-2012].
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