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C. Singh et al. / Catalysis Communications 69 (2015) 11–15
iodides or triflates (or vinyl iodides/triflates) and activated alkene in the
presence of base and palladium catalyst [15].
reactions such as Suzuki, Sonogashira and Hiyama cross-coupling reac-
tions. The reactivity of catalyst was investigated under the optimized con-
ditions for the respective reactions (see Tables 1–4). To our delight the
catalyst displayed excellent reactivity with a very low catalytic loading
(0.62 mmol%) yielding the desired products in good to excellent yields.
For the Heck coupling, the model reaction was carried using iodo-
benzene and ethyl acrylate as a starting materials using DMF as solvent
and triethyl amine as base at 120 °C. Under this optimal reaction condi-
tion the reaction went smoothly to furnish desired product, ethyl
cinnamate in excellent yield. To examine the scope of catalyst various
substituted aryl iodides, acrylates and styrenes were also employed in
the reaction under the optimized conditions. In case of aryl iodides the
substituents showed little or no effect on the outcome of reactions.
The reaction proceeded well with both the electron withdrawing and
electron donating groups. Under the same reaction conditions we ex-
amined bromo benzene and chloro benzene for the Heck reaction. It
was observed that the products were obtained in prolonged reaction
time (24 h for bromobenzene and 30 h for chlorobenzene). In case of
bromobenzene and chlorobenzene the electron withdrawing substitu-
ents produced an accelerating effect on the rate of reaction although
the yields were found to be similar in both the cases. While studying
the effect of substitution on other coupling partners i.e. styrenes and ac-
rylates it was found that the catalyst works well with both electron
withdrawing and electron donating substituents. Another interesting
observation of these studies was that in case of α-methyl styrene the re-
action took longer time for the completion (Table 1, entry 1o). This is
probably due to the steric bulk of methyl group.
The Suzuki reaction employs aryl iodides and various phenyl boronic
acids as coupling partners leading to formation of substituted biaryls
[16]. In case of Sonogashira reaction various acetylenes are formed
employing phenyl acetylenes and aryl iodides as coupling partners in
the presence of base [17]. The Hiyama reaction also provides biaryls
but it involves phenyltrimethoxysilanes and aryl iodide as the coupling
partners [18]. A variety of modifications in the palladium catalyst in-
volving both homogeneous and heterogeneous palladium catalyst has
resulted in much broader range of acceptors and donors being amena-
ble to these reactions. As a part of our keen interest in palladium cata-
lyzed reactions we have explored the SBA-15-TAT-Pd(II) catalyst for
its catalytic activity in the Heck, Suzuki, Sonogashira and Hiyama cou-
pling reactions.
The synthesis of SBA-15-TAT-Pd(II) catalyst was carried out by the
procedure described by Singh and Sharma [13]. The procedure involves
stirring and refluxing a mixture of organofunctionalized SBA-15, 2,4,6-
triallyloxy-1,3,5-triazine and azobisisobutyronitrile (AIBN) (initiator)
in DMF at 100 °C for 24 h under nitrogen atmosphere. The solid obtained
was filtered and purified by soxhlet extraction using DCM and then vac-
uum dried. For anchoring of palladium on triazine modified SBA-15, a
solution of Pd(OAc)2 and triazine modified SBA-15 in DMSO was stirred
and resultant product was purified by washing with THF and soxhlet
extraction using DCM (Scheme 1). The catalyst was well characterized
for its texture, structure of mesoporous channel and other physico-
chemical properties using analytical techniques such as CP-OES, XRD, N2
sorption measurement isotherm, TGA & DTA, solid state 13C, 29Si NMR
spectroscopy, FT-IR, XPS, DRS UV–Visible, SEM and TEM [13].
We then further investigated the compatibility of SBA-15-TAT-Pd(II)
catalyst for Sonogashira reaction. The reaction was optimized using
iodobenzene and phenylacetylene as coupling partners. To study the ef-
fect of CuI on Sonogashira reaction, the reaction was carried out both in
presence and in absence of CuI. It was found that the CuI was required
only when inorganic bases like K2CO3 were used for reaction. When
triethyl amine was used as a base in reaction the desired product was
We examined the catalytic activity of SBA-15-TAT-Pd(II) catalyst
initially for Heck reaction using iodobenzene and ethyl acrylate. The
reaction proceeded smoothly in 1 h to afford the desired product, ethyl
cinnamate in 98% yield. Encouraged by this result we considered extend-
ing the application of the catalyst for other carbon\\carbon bond forming
OH
OH
OH
8h, Toluene, 90oC
O
H3CO
OH
OH
Scheme 1(A)
O
O
OH
OH
Si
SH
H3CO Si
SH
H3CO
OH
OH
SBA-15-SH
SBA-15
3-mercaptopropyl
trimethoxysilane
HO
HO
O
OH
O
OH
O
O
O
S
N
O
S
O
S
O
Si
SH
O
AIBN, DMF
2 atm, 24 h
Si
O
O
O
O
OH
OH
N
N
N
N
N
OH
OH
HO
O
N
O
SBA-15-TAT
Scheme 1(B)
2,4,6-Triallyloxy-
1,3,5-triazine
SBA-15-SH
O
O O
HO
HO
O
(OAc)2
Pd
OH
O
HO
OH
O
HO
O
O
S
N
O
S
O
S
O
Si
O
O
Pd(OAc)2, DMSO
90oC, 24 h
O
O
S
O
O
N
O
S
O
S
Si
O
O
N
N
OH
OH
HO
N
N
OH
OH
Pd(OAc)2
HO
(AcO)2Pd
Scheme 1(C)
SBA-15-TAT
SBA-15-TAT-Pd
O
O O
O
O O
Scheme 1. Synthesis of SBA-15-TAT-Pd(II) catalyst.