Chemistry Reference
In-Depth Information
9.3.1 Colloidal Cobalt Nanoparticles
The cobalt nanoparticles prepared by the thermal decomposition of Co
2
(CO)
8
were used in
the PKR.
12
The intramolecular PKR of an enyne has been studied under optimized reaction
conditions (Co NPs (25 mg, 45 wt% cobalt), enyne (0.42 mmol), 130
◦
C, THF, 5 atm of CO,
12 h) (Scheme 9.6).
EtO
2
C
EtO
2
C
Colloidal Cobalt (25 mg, 45 wt% Co)
O
5 atm CO, 130
°
C, 12 h, THF
EtO
2
C
EtO
2
C
CO(atm)
Yield(%)
Temp (
°
C)
130
110
130
130
5
5
3
1
97
26
45
0
Scheme 9.6
The cobalt nanoparticle catalyst is more active than other types of heterogeneous cata-
lysts such as metallic cobalt supported on mesoporous silica or charcoal.
11, 17
The catalyst
maintained its high activity even after five cycles of recycling and reuse. A TEM image
(Figure 9.2b) of the catalyst after running four reaction cycles showed that the particle size
of the cobalt nanoparticles was unchanged and confirmed that no particle agglomeration
was taking place.
9.3.2 Cobalt Nanoparticles on Charcoal
To combine the merits of conventional heterogeneous catalysts with those of cobalt nanopar-
ticles, such as the high catalytic activity, cobalt nanoparticles was immobilized on a support.
The first choice of catalyst support in the developmental stage for liquid-phase reactions
was charcoal because of its confirmed applicability in wide range.
28
Cobalt nanoparticles
on charcoal (
CNC
) were prepared by the thermal reduction of dicobalt octacarbonyl.
29
CNC
is quite stable even in air for several months.
9.3.2.1
CNC
-Catalyzed PKR
For the normal intramolecular PKRs, the
CNC
system gave almost the same result as the
cobalt nanoparticles (Scheme 9.7). The catalyst maintained its high activity even after being
MeO
2
C
MeO
2
C
"Co"
O
°
C, 12 h, THF
130
MeO
2
C
MeO
2
C
Co NP 97%
Co NP on charcoal 98%
Scheme 9.7
