259
initially as a potential and recyclable catalyst for the construction of biphenyl-2carboxamides using the ligand-free environment (Scheme 1) [58]. This protocol
involves ortho sp
2
C−H bond activation of benzamides accompanied by arylation
using aryl iodides employing the straightforward CONH 2 in the form of directing
group. The methodology has additional advantages of outstanding site-selectivity,
tolerance for various functional groups, predominance for the generation of monoarylated products, convenience to operate, recyclability for five successive runs
without substantial loss in activity as well as selectivity, and stability of catalyst
within the reaction standards.
Miura et al. developed a heterogeneous PPh 3 -modified Ru/CeO 2 catalyst which
exhibited outstanding catalytic activity for the arylation of aromatic substrates using
aryl halides in order to synthesize the arylated products with good selectivity as well
as yields (Scheme 2) [59]. However, both mono- and diarylated products could be
observed on performing the reaction with non-fused aromatic rings like
2- phenylpyridine or 1-phenyl-2-pyrazol. The recycling study of the catalyst was
performed and it was observed that this catalytic system found to be reusable with
negligible substantial decrease in activity.
2.2 Addition of C–H Bond to Vinylsilanes
The similar catalytic system, ruthenium immobilized on CeO 2 was then employed
effectively by Wada and co-workers in order to add a C–H bond of various aromatic
ketones to vinylsilanes (Scheme 3) [60]. For this, the main substrate was triethoxy(vinyl)
silane, despite ethoxydimethyl(vinyl)silane has also been described. This transformation could be carried out on a large amount under solvent less conditions to attain an
improved turnover number. Efforts for the complete recyclability of this catalytic
PS-3 (2-3 mol% Pd)
AgOAc, AcOH
120
o
C, 15-30 h
NH 2
O
R 1
I
R 2
NH 2
O
R 1
R 2
Scheme 1 Heterogeneous Pd-catalysed ortho arylation of amides
3PPh 3 -Ru/CeO 2
(5 mol% Ru)
K 2 CO 3 , NMP
120-140
o C, 2-12 h
X
R
N
N
R
Scheme 2 Arylation of aromatic substrates using heterogeneous PPh 3 -modified Ru/CeO 2 catalyst
Insights into Sustainable C–H Bond Activation
initially as a potential and recyclable catalyst for the construction of biphenyl-2carboxamides using the ligand-free environment (Scheme 1) [58]. This protocol
involves ortho sp
2
C−H bond activation of benzamides accompanied by arylation
using aryl iodides employing the straightforward CONH 2 in the form of directing
group. The methodology has additional advantages of outstanding site-selectivity,
tolerance for various functional groups, predominance for the generation of monoarylated products, convenience to operate, recyclability for five successive runs
without substantial loss in activity as well as selectivity, and stability of catalyst
within the reaction standards.
Miura et al. developed a heterogeneous PPh 3 -modified Ru/CeO 2 catalyst which
exhibited outstanding catalytic activity for the arylation of aromatic substrates using
aryl halides in order to synthesize the arylated products with good selectivity as well
as yields (Scheme 2) [59]. However, both mono- and diarylated products could be
observed on performing the reaction with non-fused aromatic rings like
2- phenylpyridine or 1-phenyl-2-pyrazol. The recycling study of the catalyst was
performed and it was observed that this catalytic system found to be reusable with
negligible substantial decrease in activity.
2.2 Addition of C–H Bond to Vinylsilanes
The similar catalytic system, ruthenium immobilized on CeO 2 was then employed
effectively by Wada and co-workers in order to add a C–H bond of various aromatic
ketones to vinylsilanes (Scheme 3) [60]. For this, the main substrate was triethoxy(vinyl)
silane, despite ethoxydimethyl(vinyl)silane has also been described. This transformation could be carried out on a large amount under solvent less conditions to attain an
improved turnover number. Efforts for the complete recyclability of this catalytic
PS-3 (2-3 mol% Pd)
AgOAc, AcOH
120
o
C, 15-30 h
NH 2
O
R 1
I
R 2
NH 2
O
R 1
R 2
Scheme 1 Heterogeneous Pd-catalysed ortho arylation of amides
3PPh 3 -Ru/CeO 2
(5 mol% Ru)
K 2 CO 3 , NMP
120-140
o C, 2-12 h
X
R
N
N
R
Scheme 2 Arylation of aromatic substrates using heterogeneous PPh 3 -modified Ru/CeO 2 catalyst
Insights into Sustainable C–H Bond Activation