Chemistry Reference
In-Depth Information
Table 9.12
MeO
2
C
Me
MeO
2
C
Me
Pd NP
OAc
+
MeO
2
C
MeO
2
C
Solvent
THF
THF
THF
THF
THF
DMF
CH
2
Cl
2
Base
Time (h)
Yield (%)
NaH
NaH
K
2
CO
3
BSA
NaHCO
3
NaH
NaH
10
6
6
6
6
6
6
88
89
N.R.
23
78
87
60
9.5.3
Palladium and Cobalt Nanoparticles-Catalyzed Tandem Allylic
Alkylation and PKRs
63
Most of the known combinations of bimetallic nanoparticles have been used as catalysts
for specific single reactions utilizing the synergistic effect between the different metal
species;
61
the combination of bimetallic nanoparticles for a sequential reaction of two
specific reactions corresponding to two different metals is relatively rare.
62
The
Chung
group
prepared
palladium
and
cobalt
nanoparticles
immobilized
on
silica
(
PCNS
)
and
used
them
in
the
sequential
allylic
alkylation
and
PKRs
(Scheme 9.26).
27
R
R
"Pd"
R
"Co"
OAc
Z
+
Z
O
HZ
Base
CO
Scheme 9.26
They first prepared palladium nanoparticles immobilized on silica (1 wt % of Pd) by the
reaction of Pd(OAc)
2
with colloidal silica in a solvent mixture of ethanol and toluene (v/v,
6:94) and used them for the study of the allylic alkylation (Table 9.12). This was the first
palladium nanoparticle catalyzed-allylic alkylation.
Then the palladium and cobalt nanoparticles immobilized on silica (
PdCNS
) (14.5 wt%
of Co and 1 wt% of Pd) were prepared by heating Pd on silica with colloidal cobalt in
ethanol at reflux (Figure 9.5). The HRTEM revealed that the bimetallic nanoparticles are
in a cluster-in-cluster structure.
Using
PdCNS
as a catalyst, they studied the sequential allylic alkylation and PKR
(Scheme 9.27). The
PdCNS
was very efficient but the reaction was highly sensitive to the
