Palladium supported hybrid cellulose-aluminum oxide composite for Suzuki-Miyaura cross coupling reaction

Article abstract of DOI:10.1016/j.tetlet.2012.11.140

A cellulose-aluminum oxide composite was prepared and modified with organo-functional groups by reacting with the coupling reagent (CH ₃O)₃Si(CH₂)₃NH₂ through Al-O-Si bonds. The amino groups confined in the composite were found to be efficient for palladium entrapment, leading to a highly active and reusable heterogeneous catalyst (Pd@Al₂O₃-CELL) for Suzuki-Miyaura cross coupling reaction in water and H₂O/DMF (8:2) mixture at 80 °C. Copyright

Full text of DOI:10.1016/j.tetlet.2012.11.140

Tetrahedron Letters 54 (2013) 1331–1337
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Palladium supported hybrid cellulose–aluminum oxide composite
for Suzuki–Miyaura cross coupling reaction
⇑
Arjun Kumbhar, Sanjay Jadhav, Santosh Kamble, Gajanan Rashinkar, Rajashri Salunkhe
Department of Chemistry, Shivaji University, Kolhapur, 416004 MS, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A cellulose–aluminum oxide composite was prepared and modified with organo-functional groups by
reacting with the coupling reagent (CH3O)3Si(CH2)3NH2 through Al–O–Si bonds. The amino groups con-
fined in the composite were found to be efficient for palladium entrapment, leading to a highly active and
reusable heterogeneous catalyst (Pd@Al2O3–CELL) for Suzuki–Miyaura cross coupling reaction in water
and H2O/DMF (8:2) mixture at 80 °C.
Received 15 October 2012
Revised 26 November 2012
Accepted 28 November 2012
Available online 5 December 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Suzuki–Miyaura coupling reaction
Heterogeneous catalysis
Composite materials
Palladium
Biodegradable
Nowadays, an important part of synthetic chemistry is based
on the use of precious transition metal catalysis,1 mainly palla-
dium which is widely used expensive metal with a high demand.
Palladium plays a versatile role in organic synthesis, especially in
a variety of reactions, such as Mizoroki–Heck, Suzuki–Miyaura,
Stille, Sonogashira, and Buchwald–Hartwig couplings.2 Among
these Suzuki–Miyaura reaction is one of the most effective for
the construction of biaryl units, which are molecular components
in pharmaceuticals.3 They are also present in many herbicides,
alkaloids like ancistrocladine as well as in engineering materials
such as conducting polymers, molecular wires, and liquid
crystals.4
Since, palladium complexes are highly expensive and some-
times responsible to contamination of the products, recovery and
reuse of palladium by alternative benign process are of prime
importance. One such method exploits immobilization of palla-
dium on solid support,5 and typical ligands employed for this pur-
pose are phosphine, imine, acetylacetonate, and amine moieties.
Among them, amine moieties are advantageous in tuning of their
electronic characters, and its easy availability. From this point of
view, various organic and inorganic solid supports bearing amine
groups were developed for ligation with palladium.6
monly used solvents, because the hydroxyl groups, which are
responsible for the majority of the reactions are involved in inter
and intra-molecular hydrogen bonding. The properties of cellulose
may be modified by changing both physical and chemical struc-
ture. Grafting onto cellulose is possible by growing polymer chain
on active sites of the cellulose backbone. Surface hydroxyl groups
of cellulose could be used to tether with the organofunctionalized
alkoxysilane coupling reagents resulting in functionalized cellulose
surfaces with C–O–Si bonds. However, this chemical bond can be
easily hydrolyzed by water when the material is immersed in
aqueous solution. Hence to make cellulose more reactive, surface
modification has been carried out with metal oxides like cellu-
lose–Al2O3 composite in which the aluminum oxide can be ob-
tained highly dispersed on the surface with a good degree of
adhesion.8 The use of silane coupling agents for surface modifica-
tion is an important and well-established field,9 as these agents
are useful for immobilizing specific chemical species on surfaces
in organized monolayer assemblies. In the cellulose–Al2O3 com-
posite, Al–OH groups present on the surface can easily react
with Si–OMe groups of
c-aminopropyl trimethoxy silane (APTS)
forming a very stable Al–O–Si bond with a high degree of
organofunctionalization.
Cellulose has unlimited availability as a renewable agro-based
resource and is biodegradable having interesting structure related
properties with many commercial applications in various fields.7
The polymer is relatively inert to treatment with almost all com-
In continuation of our work associated in the direction of heter-
ogeneous catalysis,10 the aim of the present study is to carry out
synthesis and characterization of the amino groups attached palla-
dium incorporated into hybrid cellulose–Al2O3 based Pd@Al2O3–
CELL catalyst (Fig. 1), which could function as heterogeneous cata-
lyst for Suzuki–Miyaura cross coupling reaction having potentially
high catalytic activity.
⇑
Corresponding author. Tel.: +91 231 260 9240; fax: +91 231 269 2333.
E-mail address: rss234@rediffmail.com (R. Salunkhe).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.11.140

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A. Kumbhar et al. / Tetrahedron Letters 54 (2013) 1331–1337
Synthesis of Pd@Al2O3–CELL catalyst 4 was achieved in a three
step fashion as described in Scheme 1. The cellulose–aluminum
oxide composite (Al2O3–CELL) 2, and the experiment to modify 2
with
c-aminopropyl trimethoxy silane affording 3 was carried
out as described in the literature.11 The palladium was loaded on
composite through the interaction of amino groups by slowly add-
ing solution of palladium acetate in dry acetone18 and stirring the
resulting suspension for 48 h at room temperature. The gray col-
ored catalyst 4 (Pd@Al2O3–CELL) obtained was filtered, washed
with dry acetone, and dried under vacuum at 25 °C for 8 h. The
Pd content on 4 as determined by ICP-AES was suggested to be
0.070 mmol gꢀ1
.
Our initial effort was focused on the characterization of the
resulting solid material, which would be used as the heteroge-
neous catalyst in the Suzuki–Miyaura cross coupling reaction. A
good adhesion is expected on composite, since the free aluminol
groups, Al–OH on the alumina surface has a high affinity by the ter-
minal silanol group of APTS.12 The amount of aluminum was deter-
mined by calcining 0.300 g of 2 to 600 °C for 8 h and the residue
weighed as Al2O3, which was found to be 3.27 wt %, corresponding
to 0.31 mmol gꢀ1 aluminium, which was also supported by TGA
analysis (3.44 wt %). The elemental analysis showed that,
0.56 mmol gꢀ1 of organic groups was attached on the 3.
Thermal stability of the catalyst has a great effect on its catalytic
activity and recyclability because the Suzuki–Miyaura coupling
reaction is carried out under high temperature conditions. TGA–
DSC profile (Fig. 2) of 4 indicated that the catalyst is stable up to
270 °C. Weight loss from 25 to 110 °C temperature was assigned
to the loss of loosely bound water on the support (4.0%). The large
weight loss of around 89% at temperature between 225 and 278 °C
was due to the oxidative decomposition of polymer carrier. The
sharp exothermic peak exhibited by DSC at the temperature
Figure 1. The conceptual illustration of Pd@Al2O3–CELL catalyst.
Scheme 1. Synthesis of Pd@Al2O3–CELL catalyst.

A. Kumbhar et al. / Tetrahedron Letters 54 (2013) 1331–1337
1333
Figure 2. TGA–DSC spectrum of Pd@Al2O3–CELL catalyst.
when the temperature was raised to 278 °C and the 3.44 wt % of
oxide Al2O3 and SiO2 with some palladium oxide remained as
residue.
2000
1500
1000
500
0
Powder XRD patterns of the three materials are displayed in Fig-
ure 3. The XRD pattern shows the reflection only due to the cellu-
losic phase. The appearance of reflections in the XRD pattern due to
Pd and Al2O3 phases is far away from the detection limit of the sen-
sitivity of the detector used in the present study (detection limit 5%
by weight). However, the decrease in the intensity of the reflec-
tions of cellulosic phase after loading of Al2O3 and Pd reveals that
the structural disorders are formed in cellulose after the loading.
SEM analysis (Fig. 4) was undertaken to study the morphology
of the catalyst 4. Fibrous morphology was observed with diameters
in the range of several hundreds of nanometers up to a few
micrometers.
The formation of 4 was confirmed by detecting Pd species using
energy dispersive X-ray spectroscopy (EDS). The EDS spectrum of
the catalyst 4 was taken at random points on the surface for qual-
itative analysis of elements (Fig. 5). The spectrum confirmed the
deposition of alumina on cellulose, grafting of APTS on alumina,
and presence of palladium on composite material.
CELL
CELL-Al2O3
Pd@Al2O3-CELL
10
20
30
40
50
60
2θ°
Figure 3. XRD patterns of cellulose, Al2O3–CELL and Pd@Al2O3–CELL catalyst.
270 °C could be assigned to the decomposition of carbohydrates of
cellulosic support. The decomposition of composite was completed
Figure 4. SEM images for Pd@Al2O3–CELL catalyst (a) normal view and (b) magnified view.

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A. Kumbhar et al. / Tetrahedron Letters 54 (2013) 1331–1337
Table 2
Screening of various bases in Suzuki–Miyaura cross coupling reactiona
Entry
Base
Time
Yieldb (%)
1
2
3
4
5
K2CO3
Na2CO3
K3PO4
TEA
20 min
2.0 h
45 min
2.5 h
97
93
95
73
70
DBU
2.5 h
a
Reaction conditions: 4-Bromobenzophenone (1.0 mmol), phenylboronic acid
(1.2 mmol), 4 (1 mol %), base (2.0 mmol), H2O/DMF (8:2) (5 mL) at 80 °C, under
aerobic conditions.
b
Isolated yields after purification.
Table 3
Effect of loading and temperature on Suzuki–Miyaura cross coupling reactiona
Figure 5. EDS spectrum of Pd@Al2O3–CELL catalyst.
Entry Amount of catalyst (mol %) Time
Temperature (°C) Yieldb (%)
1
2
3
4
5
0.5
1.0
1.5
1.0
1.0
50 min 80
20 min 80
20 min 80
78
97
97
10
80
5 h
2 h
25
60
a
Reaction conditions: 4-Bromobenzophenone (1.0 mmol), phenylboronic acid
(1.2 mmol), 4 (1 mol %), K2CO3 (2.0 mmol), H2O/DMF (8:2) (5 mL) at 80 °C, under
Scheme 2. Pd@Al2O3–CELL catalyzed Suzuki–Miyaura cross coupling reaction.
aerobic conditions.
b
Isolated yields after purification.
Table 1
Effect of solvents on Suzuki–Miyaura cross coupling reactiona
entries 7–9). This effect is probably due to the fine dispersibility
of cellulose in water14 and higher solubility of organic substrates
in DMF. As the drastic rate enhancement was observed in a H2O/
DMF (8:2) mixture, it was chosen as reaction solvent for further
study.
The influence of nature of bases has also been investigated by
performing model reaction with varying organic and inorganic
bases in H2O/DMF (8:2) mixture at 80 °C. It was observed that inor-
ganic bases were more effective (Table 2, entries 1–3) as that of or-
ganic bases (Table 2, entries 4 and 5).
Entry
Solvent
Time
Yieldb (%)
1
2
3
4
5
6
7
8
9
EtOH
95% EtOH
CH3CN
Toluene
DMF
1.0 h
1.5 h
2.0 h
2.5 h
1.5 h
2.0 h
30 min
20 min
45 min
96
95
94
96
97
96
96
97
94
H2O
H2O/DMF (5:5)
H2O/DMF (8:2)
H2O/DMF (9:1)
The effect of concentration of catalyst on the percentage con-
version of the model reaction has been studied and the results
are shown in Table 3. Thus among the different loadings 1 mol %
proved to be the best affording desired product in 20 min with
97% yield in H2O/DMF (8:2) mixture (Table 3, entry 2).
a
Reaction conditions: 4-Bromobenzophenone (1.0 mmol), phenylboronic acid
(1.2 mmol), 4 (1 mol %), K2CO3 (2.0 mmol), solvent (5 mL) at 80 °C, under aerobic
conditions.
b
Isolated yields after purification.
To study the effect of temperature on catalytic activity the mod-
el reaction was carried out at room temperature. The reaction was
sluggish (Table 3, entry 4) indicating that the temperature of reac-
tion is crucial for the catalytic efficiency of 4. Increasing the reac-
tion temperature from 25 to 80 °C, the yield of the product was
enhanced remarkably. We have concluded that, excellent result
was obtained when the coupling reaction was carried out with
1 mol % of the catalyst using K2CO3 as a base in H2O/DMF (8:2)
mixture at 80 °C.
To explore the scope and generality of the catalyst, the opti-
mized protocol was applied for reactions of a variety of differently
substituted aryl bromides and arylboronic acids.19 Both activated
and deactivated aryl bromides were completely converted into
the corresponding products in 70–97% yields within 20 min–4 h
(Table 4). The reaction showed good diversity in the presence of
both electron withdrawing and donating groups. For the highly
sterically hindered, deactivated 2,4,6-trimethylbromobenzene, a
satisfactory yield could be obtained within 9 h (Table 4, entry 8).
We have also evaluated the coupling ability of aryl chlorides under
the optimized conditions. The low reactivity of aryl chlorides in
cross-coupling reactions is due to their reluctance to oxidatively
add to Pd(0). It was interesting to note that both chlorobenzene
and 4-chlorobenzophenone reacted with phenylboronic acid, albeit
Next, we investigated the catalytic activity of Pd@Al2O3–CELL
(4) in Suzuki–Miyaura cross-coupling reaction (Scheme 2). To ob-
tain a more accurate assessment of catalytic activity, electronically
deactivated aryl bromides were chosen rather than the more easily
coupled aryl iodides.
Our initial investigation started with the cross coupling reaction
of 4-bromobenzophenone
5 (1 mmol), phenylboronic acid 6
(1.2 mmol), and K2CO3 as base using catalyst 4 (1 mol %) at 80 °C.
Various bases, solvents, and solvent mixtures were screened in or-
der to establish ideal coupling parameters. The model reaction was
performed in a protic solvent (Table 1, entries 1 and 2) as well as in
aprotic solvents (Table 1, entries 3–5). In all the cases there was
complete conversion of substrates with quantitative yield of the
product in 1–2.5 h. Then we tried to conduct the same reaction
in aqueous medium, and it was observed that the catalyst was also
active in aqueous medium with excellent yield of the desired prod-
uct in comparatively same reaction time as in organic solvents (Ta-
ble 1, entry 6).
It was observed that addition of water in DMF had a dramatic
effect on reaction.13 When the reaction was carried out in H2O/
DMF mixture, the time required for reaction was drastically
reduced to 20 min with excellent yield of the product (Table 1,

A. Kumbhar et al. / Tetrahedron Letters 54 (2013) 1331–1337
1335
Table 4
The Suzuki–Miyaura cross coupling reaction of various aryl halides and arylboronic acids over Pd@Al2O3–CELL catalysta
Entry
Aryl halides
Arylboronic acids
Product
Solvent
Time (h)
Yieldb (%)
O
BOH)2
O
H2O/DMF
(8:2)
H2O
20 min
2
97
96
1
Br
Br
O
O
BOH)2
2
H2O
2
94
F
F
Br
Br
BOH)2
H2O/DMF
(8:2)
3
4
1.5
2
95
94
BOH)2
BOH)2
F
H2O/DMF
(8:2)
F
Br
O
5
H2O
2
94
O
BOH)2
BOH)2
Br
H2O/DMF
(8:2)
6
7
6
8
94
79
Br
H2O/DMF
(8:2)
Br
BOH)2
H2O/DMF
(8:2)
8
9
9
5
70
40
Cl
BOH)2
BOH)2
H2O/DMF
(8:2)
O
O
H2O/DMF
(8:2)
10
4
45
Cl
a
Reaction conditions: Aryl halide (1.0 mmol), arylboronic acid (1.2 mmol), 4 (1 mol %), K2CO3 (2.0 mmol), solvent (5 mL) at 80 °C, under aerobic conditions.
Isolated yields after purification.
b
giving the corresponding biaryls in slightly lower yields (Table 4,
entries 9 and 10).
coupling 9,10-dibromoanthracene with phenylboronic acid (Ta-
ble 5, entry 2) in 85% yield.
To further extend the scope of this methodology, we carried out
reactions of dibromoarenes with phenylboronic acid. The results of
these reactions were of particular interest since their outcome in-
volves the formation of products which are extensively used in the
synthesis of molecular wires. The reactions of dibromoarenes with
arylboronic acids afforded desired products in quantitative yields
(Table 5). Diphenylanthracene which is used as a fluorescer in a
peroxyoxalate chemiluminescence system15 was also obtained by
In order to evaluate the heterogeneity of catalyst, hot filtration
test was performed by coupling bromobenzophenone with phenyl-
boronic acid in the presence of the catalyst in H2O/DMF (8:2) mix-
ture.16 After 50% of the cross-coupling reaction was completed
(10 min, GC), the catalyst was filtered off and filtrate was allowed
to react further. No further reaction was observed even after a pro-
longed reaction time (GC) suggesting that the palladium catalyst
remains on the support during the reaction.

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A. Kumbhar et al. / Tetrahedron Letters 54 (2013) 1331–1337
Table 5
The Suzuki–Miyaura cross coupling reaction of various aryl dihalides and phenylboronic acid over Pd@Al2O3–CELL catalysta
Entry
1
Aryl halide
Arylboronic acid
Product
Solvent
Time (h)
8
Yieldb (%)
92
BOH)2
Br
Br
H2O/DMF
(8:2)
BOH)2
Br
Br
H2O/DMF
(8:2)
2
3
4
85
BOH)2
H2O
3
94
N
Br
N
Br
a
Reaction conditions: Aryl halide (0.5 mmol), phenylboronic acid (1.2 mmol), 4 (1 mol %), K2CO3 (2.0 mmol), solvent (5 mL) at 80 °C, under aerobic conditions.
Isolated yields after purification.
b
Table 6
References and notes
Recyclability of the Pd@Al2O3–CELL catalyst in Suzuki–Miyaura cross coupling
reactiona
1. (a) Beller, M.; Bolm, C. In Transition Metals for Organic Synthesis; Wiley-VCH:
Weinheim, 2004; Vol. 1,; (b) Seregin, I V.; Gevorgyan, V. Chem. Soc. Rev. 2007,
36, 1173.
Entry
Aryl halide
Cycle
Time (h)
Yieldb (%)
2. (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457; (b) Beletskaya, I. P.;
Cheprakov, A. V. Chem. Rev. 2000, 100, 3009.
O
1
2
1
2
20 min
2
97
92
3. (a) Chemler, S. R.; Trauner, D.; Danishefsky, S. J. Angew. Chem., Int. Ed. 2001, 40,
4544; (b) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun. 1981, 11, 513; (c)
Corbet, J. P.; Mignani, G. Chem. Rev. 2006, 106, 2651; (d) Martin, R.; Buchwald, S.
L. Acc. Chem. Res. 2008, 41, 1461.
4. (a) Wilkins, C. K.; Bohn, B. A. Phytochemistry 1976, 15, 211; (b) Boren, J.;
Cascante, M.; Marin, S.; Comin-Anduix, B.; Centelles, J. J.; Lim, S.; Bassilian, S.;
Ahmed, S.; Lee, W. N.; Boros, L. G. J. Biol. Chem. 2001, 276, 37747; (c) Rosowsky,
A.; Chen, H.; Fu, H.; Queener, S. F. Bioorg. Med. Chem. 2003, 11, 59; (d) Long, Y.
Q.; Jiang, X. H.; Dayam, R.; Sachez, T.; Shoemaker, R.; Sei, S.; Neamati, N. J. Med.
Chem. 2004, 47, 2561.
3
4
5
3
4
5
3.5
4
7
84
83
81
Br
a
Reaction conditions: 4-Bromobenzophenone (1.0 mmol), phenylboronic acid
(1.2 mmol), 4 (1 mol %), K2CO3 (2.0 mmol), H2O/DMF (8:2) (5 mL) at 80 °C, under
aerobic conditions.
b
Isolated yields after purification.
5. (a) Molnar, A. Chem. Rev. 2011, 111, 2251; (b) Balanta, A.; Godard, C.; Claver, C.
Chem. Soc. Rev. 2011, 40, 4973; (c) Budarin, V. L.; Clark, J. H.; Luque, R.;
Macquarrie, D. J.; White, R. J. Green Chem. 2008, 10, 382.
6. (a) Jin, M. J.; Lee, D. H. Angew. Chem., Int. Ed. 2010, 49, 1119; (b) Lee, D. H.; Jung,
J. Y.; Jin, M. J. Green Chem. 2010, 1, 2024; (c) Fukaya, N.; Ueda, M.; Onozawa, S.;
Bando, K. K.; Miyaji, T.; Takagi, Y.; Sakakura, T.; Yasud, H. J. Mol. Catal. A: Chem.
2011, 342–343, 58.
7. (a) Godinho, M. H.; Martins, A. F.; Figueirinhas, J. L. Opt. Mater. 1998, 9, 226; (b)
Fischer, S.; Thummler, K.; Volkert, B.; Hettrich, K.; Schmidt, I.; Fischer, K.
Macromol. Symp. 2008, 262, 89.
8. (a) Filho, U. P. R.; Gushikem, Y.; Fujiwara, F. Y.; de Castro, S. C.; Torriani, I. C. L.;
Cavalcanti, L. P. Langmuir 1994, 10, 4357; (b) Bhattacharya, A.; Misra, B. N. Prog.
Polym. Sci. 2004, 29, 767.
For practical applications of heterogeneous systems, the life-
time of the catalyst and its level of reusability are very important
features. The recyclability of 4 was investigated with consecutive
Suzuki–Miyaura reactions of 4-bromobenzophenone with phenyl-
boronic acid in H2O/DMF (8:2) mixture. After first cycle, the cata-
lyst was recovered by filtration and extensively washed with
water, dichloromethane, and acetone. The catalyst was then dried
under vacuum before performing the reusability test. The recycling
results of 4 are summarized in Table 6. Investigations of the cata-
lyst recycling showed a decrease of the total yield in every run.
Additionally, the catalyst exhibited high stability in air.
9. (a) Yoshino, N.; Nakaseko, H.; Yamamoto, Y. React. Polym. 1994, 23, 157; (b)
Wu, L.; Guo, Z.; Meng, S.; Zhong, W.; Du, Q.; Chou, L. L. Appl. Mater. Interfaces
2010, 2, 2781.
In conclusion, the composite containing amino groups has been
prepared as a robust catalyst for Suzuki–Miyaura coupling reaction
in water and H2O/DMF (8:2) mixture. This catalyst significantly ex-
pands the scope of Pd-catalyzed cross-couplings by enabling the
use of various arylboronic acids for the coupling of aryl bromides.
The prepared catalyst presents good recyclability, with coupling
yields maintained over five catalytic cycles.
10. Kumbhar, A.; Kamble, S.; Jadhav, S.; Rashinkar, G.; Salunkhe, R. Catal. Lett. 2012,
142, 1388.
11. Lazarin, A. M.; Gushikem, Y.; de Castro, S. C. J. Mater. Chem. 2000, 10, 2526.
12. Alfaya, R. V. S.; Gushikem, Y. J. Colloid Interface Sci. 1999, 213, 438.
13. Liu, C.; Ni, Q.; Bao, F.; Qiu, J. Green Chem. 2011, 13, 1260.
14. Quignard, F.; Choplin, A. Chem. Commun. 2001, 21.
15. Zhi, Z.; Yang, X.; Lu, L.; Wang, X. Chem. Educ. 2000, 5, 187.
16. Gruber-Woelfler, H.; Radaschitz, P. F.; Feenstra, P. W.; Haas, W.; Khinast, J. G. J.
Catal. 2012, 286, 30.
17. (a) Mohanthy, S.; Suresh, D.; Balkrishna, M. S.; Mague, J. T. Tetrahedron 2008,
64, 240; (b) Basu, B.; Das, P.; Bhuiyan, M. H.; Jha, S. Tetrahedron Lett. 2003, 44,
3817; (c) Peng, Y. Y.; Liu, J.; Lei, X.; Yin, Z. Green Chem. 2010, 12, 1072; (d) Bulut,
H.; Artok, L.; Yilmaz, S. Tetrahedron Lett. 2003, 44, 289; (e) Borhade, S. R.;
Waghmode, S. B. Beilstein J. Org. Chem. 2011, 7, 310; (f) Li, S.; Lin, Y.; Cao, J.;
Zhang, S. J. Org. Chem. 2007, 72, 4067.
18. Synthesis of Pd@Al2O3–CELL (4): In a small Schlenk tube compound 3 (1.0 g) was
mixed with Pd(OAc)2 (22.6 mg, 0.1 mmol) in dry acetone (20 mL). The mixture
was stirred at room temperature for 48 h. The solid product was filtered by
suction, washed with acetone, distilled water, and acetone successively, and
Acknowledgment
Financial support provided by the Department of Science and
Technology and the University Grants Commission, New Delhi, In-
dia are warmly acknowledged with thanks. One of the authors A.K.
thanks UGC, New Delhi, India for the award of Teacher Fellowship
under the F. I. P. of the XIth Plan.

A. Kumbhar et al. / Tetrahedron Letters 54 (2013) 1331–1337
1337
dried under vacuum at room temperature for 8 h to afford 1.0 g of gray
palladium complex (4).
19. General procedure for the Suzuki–Miyaura reaction: An oven-dried Schlenk flask,
equipped with a magnetic stir bar, septum, and a condenser was charged with
2H), 7.50–7.56 (m, 4H); 13C NMR (75 MHz, CDCl3, d ppm): 115.2, 115.4, 127.0,
127.3, 128.5, 128.6, 128.9, 137.1, 137.2, 140.0, 161.2, 163.7; MS (ESI): m/z 172.
4-Acetyl biphenyl (Table 4, entry 5): White solid, mp 126–127 °C17 1H NMR
;
(300 MHz, CDCl3, d ppm): 2.66 (s, 3H), 7.40–7.50 (m, 3H), 7.62–7.70 (m, 4H),
8.00–8.07 (m, 2H); 13C NMR (75 MHz, CDCl3, d ppm): 26.6, 127.2, 127.9, 128.8,
128.9, 135.8, 139.8, 145.7, 197.7; MS (ESI): m/z 196.
aryl halide (1.0 mmol), arylboronic acid (1.2 mmol), K2CO3 (2 mmol),
4
(0.143 g, 1 mol %), and 5 mL of solvent. The flask was immersed in an oil
bath and stirred at 80 °C. Upon complete consumption of starting materials as
determined by TLC analysis, the reaction mass was filtered and the solid
washed with water (2 ꢁ 5 mL), and extracted with diethyl ether (3 ꢁ 5 mL).
The combined organic layers were collected, dried over anhydrous Na2SO4, and
concentrated in vacuum to afford product which was purified by silica gel
column chromatography (n-hexane/EtOAc = 9:1).
1,4-Diphenylbenzene (Table 4, entry 6): White solid, mp 126–127 °C17 1H NMR
;
(300 MHz, CDCl3, d ppm): 7.35–7.38 (m, 2H), 7.46–7.50 (m, 4H), 7.60 (d, 4H,
J = 7.1 Hz), 7.63–7.65 (m, 4H); 13C NMR (75 MHz, CDCl3, d ppm): 126.6, 127.4,
127.9, 128.2, 140.1, 140.6; MS (ESI): m/z 230.
2-Phenyl-9H-fluorene (Table 4, entry 7): White solid, mp 295–297 °C; 1H NMR
(300 MHz, CDCl3, d ppm): 3.97 (s, 2H), 7.29–7.38 (m, 2H), 7.40–7.47 (m, 2H),
7.53–7.65 (m, 4H), 7.79 (d, 2H, J = 7.0 Hz), 7.84 (s, 1H); 13C NMR (75 MHz,
CDCl3, d ppm): 36.9, 119.9, 120.0, 123.7, 124.9, 125.9, 126.6, 126.7, 127.0,
127.1, 128.6, 139.9, 140.9, 141.4, 141.5, 143.2, 143.6; MS (ESI): m/z 242.
2,4,6-Trimethylbiphenyl (Table 4, entry 8): Colorless liquid; 1H NMR (300 MHz,
CDCl3, d ppm): 2.27 (s, 3H), 2.41 (s, 6H), 6.91 (d, 2H, J = 2.5 Hz), 7.14–7.16 (m,
1H), 7.33–7.48 (m, 4H); 13C NMR (75 MHz, CDCl3, d ppm): 20.7, 23.7, 127.1,
128.0, 128.3, 128.6, 129.0, 129.2, 135.6, 135.9, 136.1, 137.7; MS (ESI): m/z 196.
Spectral data of synthesized compounds: 4-Phenyl benzophenone (Table 4, entry
1): White solid, mp 99–100 °C17 1H NMR (300 MHz, CDCl3, d ppm): 7.37–7.41
;
(m, 1H), 7.47–7.53 (m, 4H), 7.58 (d, 1H, J = 1.5 Hz), 7.59–7.65 (m, 2H), 7.70 (d,
2H, J = 8.4 Hz), 7.83 (d, 2H, J = 8.4 Hz), 7.91 (d, 2H, J = 8.4 Hz); 13C NMR
(75 MHz, CDCl3, d ppm):126.8, 127.2, 128.0, 128.2, 128.9, 129.9, 130.6, 132.1,
136.2, 137.8, 140.0, 145.1, 196.1; MS (ESI): m/z 258.
4-(40-Fluoro-phenyl) benzophenone (Table 4, entry 2): White solid, mp 145–
148 °C; 1H NMR (300 MHz, CDCl3, d ppm): 7.13–7.21 (m, 2H), 7.48–7.53 (m,
2H), 7.58–7.66 (m, 5H), 7.82 (d, 2H, J = 6.9 Hz), 7.90 (d, 2H, J = 8.1 Hz); 13C NMR
(75 MHz, CDCl3, d ppm): 116.0, 126.7, 128.2, 128.8, 128.9, 129.9, 130.7, 132.2,
136.1, 136.2, 137.7, 144.1; MS (ESI): m/z 276.
9,10-Biphenyl anthracene (Table 5, entry 2): White solid, mp 249–251 °C17 1H
;
NMR (300 MHz, CDCl3, d ppm): 7.33 (d, 4H, J = 3.3 Hz), 7.50 (d, 4H, J = 7.5 Hz),
7.56–7.64 (m, 6H), 7.70 (d, 4H, J = 3.3 Hz), 13C NMR (75 MHz, CDCl3, d ppm):
124.9, 126.9, 127.4, 128.3, 129.8, 131.3, 137.0, 139.1; MS (ESI): m/z 330.
2,6-Diphenylpyridine (Table 5, entry 3): White solid, mp 73–75 °C; 1H NMR
(300 MHz, CDCl3, d ppm): 7.50–7.59 (m, 6H), 7.70–7.86 (m, 3H), 8.19–8.25 (m,
4H); 13C NMR (75 MHz, CDCl3, d ppm): 118.4, 127.0, 128.5, 128.9, 137.2, 139.4,
156.8; MS (ESI): m/z 231.
Biphenyl (Table 4, entry 3): White solid; mp 68–69 °C17 1H NMR (300 MHz,
;
CDCl3, d ppm): 7.31–7.41(m, 2H), 7.40–7.46 (m, 4H), 7.66 (d, 4H, J = 8.0 Hz); 13
NMR (75 MHz, CDCl3, d ppm): 127.1, 127.4, 128.5, 140.2; MS (ESI): m/z 154.
C
4-Fluro biphenyl (Table 4, entry 4): White solid mp 87–90 °C17 1H NMR
;
(300 MHz, CDCl3, d ppm): 7.15–7.17 (m, 2H), 7.33–7.35 (m, 1H), 7.40–7.42 (m,