9
6
B. Kodicherla et al. / Inorganica Chimica Acta 423 (2014) 95–100
(
100 mL). To this chloromethylated polystyrene (0.5 g, 2.25 mmol/
Cl), N,N-dimethylethylenediamine (2.3 mL, 22.5 mmol), and NaI
14.9 mg, 0.1 mmol) were added and the mixture was refluxed
for 48 h. The mixture was filtered, and the residue was washed
sequentially with CH OH–1 M aq K CO
CN (3 Â 20 mL), 1:1 CH
3 Â 20 mL), 1:1 CH OH–H O (3 Â 20 mL), and Et O (2 Â 20 mL),
and then dried in an oven.
Cl
N
NH2
N
N
H
(
NaI, CH CN,
Reflux, 48 h
3
3
3
2
3
1
2
(
3
2
2
Pd(CH CN) Cl
2
3
2
EtOH
Reflux, 12 h
2.2. Preparation of polystyrene-supported palladium complex 3
To the polystyrene-supported ligand, EtOH (100 mL) was added
and kept for 30 min. A solution of Pd(CH
3 2 2
CN) Cl (0.25 g) in EtOH
(
10 mL) was then added, and the mixture was refluxed for 12 h.
N
NH
Cl
The brown colored complex, impregnated with the metal, was fil-
tered, washed thoroughly with EtOH (3 Â 30 mL), and finally dried
in vacuum at 70 °C for 24 h.
Pd
Cl
3
Scheme 1. Preparation of polystyrene-supported Pd(II) complex 3.
2.3. General experimental procedure for Suzuki–Miyaura cross-
coupling reaction
ported ligand in the IR spectrum is 3427 cm–1, the NH group of
polystyrene-supported palladium complex 3 in the IR spectrum
is 3454 cm indicating the formation Pd–N bond (Fig. S1d).
Catalyst
0.75 mmol), aryl bromide (0.5 mmol), K
cetyltrimethylammonium bromide (36 mg, 0.1 mmol), and water
3 mL) were added to a reaction vessel. The resulting mixture
was stirred at 80 °C for 6 h, then cooled to room temperature and
catalyst was filtered, the crude residue was extracted with ethyl
acetate (3 Â 10 mL). The combined organic layers were extracted
with water, saturated brine solution, and dried over anhydrous
3
(10 mg, 0.004 mmol of Pd), arylboronic acid
–1
(
2
CO (138 mg, 1 mmol),
3
Morphological features of the polymeric ligand and Pd(II) com-
plex were investigated by making use of scanning electron micros-
copy. SEM–EDX of the polymeric ligand and their Pd(II) complex
are given in Fig. 1. The scanning electron micrographs (Fig. 1,
A&C) of the polymer supported ligand and Pd(II) catalyst clearly
show the morphological change which occurred on the surface of
polystyrene after loading of metal on it. SEM of the polymeric
ligand has rough surface. The voids/channels present in the poly-
meric ligand are responsible for the swelling of the polymer and
the active sites buried in the polymer matrix. For the polymeric
ligand and Pd(II) complex, the surface was found to be composed
of regions of white flake-like appearance. This white flake-like
appearance is higher in the case of DVB-crosslinked Pd(II) complex.
Also the voids present in the uncomplexed resin are more as com-
pared to the complexed resin. This may arise from the contraction
of the voids by the cooperative contribution of the ligands for com-
plexation with Pd(II) ions or the disappearance of the voids in the
rearrangement of polymer chains for complexation with metal
ions. Energy dispersive X-ray spectroscopy (EDX) analysis data
for the polymer anchored ligand and palladium catalyst are given
in Fig. 1 (B and D). The EDX data also infers the attachment of pal-
ladium metal on the surface of the polymer matrix.
(
2 4
Na SO . The organic layers were evaporated under reduced pres-
sure and the resulting crude product was purified by column chro-
matography by using ethyl acetate/hexane (1:9) as eluent to give
the corresponding product.
2.4. General procedure for catalyst recycling
After the completion of every repeated Suzuki–Miyaura cou-
pling reaction (bromobenzene with phenylboronic acid), the poly-
styrene-supported Pd catalyst was recovered from the reaction
mixture by filtration and washed with distilled water
(
2 Â 15 mL), ethanol (2 Â 15 mL) and diethyl ether (2 Â 15 mL).
The washed catalyst was dried at 60 °C under vacuum for 12 h.
3
. Results and discussion
The thermal stability of the complex was investigated by TG-
DTA. The negligible weight loss below 200 °C is due to the physi-
cally adsorbed solvent molecules. The complex 3 is stable up to
3.1. Catalyst characterization
2
2
86 °C and further weight loss at a higher temperature (above
86 °C) was attributed to the decomposition of complex Fig. S2
Firstly, polystyrene-supported N,N-dimethylethylenediamine 2
was prepared by treating chloromethylated polystyrene with an
appropriate quantity of N,N-dimethylethylenediamine 1 in reflux-
ing acetonitrile for 48 h. Product 2 was characterized by FTIR. Then,
the ligand-functionalized polystyrene-supported Pd(II) complex 3
(
supporting information). The catalytic activity of the diamine-
functionalized polystyrene-supported palladium complex 3 was
tested for the Suzuki–Miyaura cross-coupling reactions.
3 2 2
was prepared by a suspension of 2 in a solution of Pd(CH CN) Cl
in EtOH and was refluxed for 12 h (Scheme 1). The catalyst 3 was
characterized by FTIR, SEM–EDX, and AAS. The amount of palla-
dium incorporated into the polymer was determined by atomic
absorption spectroscopy (AAS), which showed a value of 4.23%
3.2. Catalytic Suzuki–Miyaura cross-coupling reaction
Initial studies were performed upon the Suzuki–Miyaura cross-
coupling reaction of 2-naphthylboronic acid with 4-bromoanisole
as a model reaction using 3 (10 mg, 0.004 mmol/Pd) as the catalyst
in water at 80 °C for 6 h (Table 1). The reaction was significantly
affected by the nature of base and the additive used. Of all the
(
0.39 mmol/g).
In the IR spectrum of chloromethylated polystyrene, the two
À1
characteristic peaks at 1263 and 670 cm were due to stretching
and bending vibrations of C–Cl group (Fig. S1a). They were practi-
cally eliminated after the introduction of N,N-dimethylethylenedi-
amine (Fig. S1b), and palladium onto the polymer (Fig. S1d).
2 3
bases and additives tested, the K CO -CTAB was found to be the
best combination (Table 1, entry 3). When the reaction was con-
ducted at room temperature, trace amount of product was
observed (Table 1, entry 11). Cross-coupling reaction of 2-naph-
thylboronic acid with 4-chloroanisole did not result in expected
yield (Table 1, entry 12). When the catalyst 3 loading was
Compared to the IR spectrum of Pd(CH
3
CN)
CN), and 2918 cm (C–H, CH
absent in the case of complex; as the NH group of polystyrene-sup-
2 2
Cl (Fig. S1c), the peaks
–
1
–1
at 2330 cm (CBN, CH
3
3
CN) are