Chemistry Reference
In-Depth Information
Tab l e 9 . 1
Substrate
Time (h)
Product (%)
TsN
6.5
88
TsN
O
Me
EtO
2
C
Me
EtO
2
C
18
92
O
EtO
2
C
EtO
2
C
Ph
Ph
O
18
98
O
O
O
+
6.5
11
Ph
Ph
O
+
Ph
6.5
36
Ph
low activity in the intermolecular PKR. The bulk metallic cobalt on mesoporous silica was
easily recovered and reused without loss of activity.
When the support was charcoal, the catalytic system (
Co/C
) exhibited an excellent
catalytic performance for intra- and intermolecular PKRs (Table 9.2).
17
However, an
n
-
alkyl halide substituted substrate was found to be inappropriate for the
Co/C
system. The
optimum cobalt loading on charcoal was about 12 wt%. The catalytic system is stable and
can be reused at least 10 times without losing any catalytic activity. The use of other carbon
supports such as graphite and mesoporous carbon showed almost the same catalytic activity
as that of cobalt on charcoal even though they have different surface areas and structures.
The metallic cobalt showed ferromagnetism and was thus easily recovered by filtration or
by using a magnet.
9.2.3 Raney Cobalt
14a
Recently, skeletal metal catalysts
18
have attracted a lot of attention especially due to their
microscopic spongy network of pores. One of the famous groups of skeletal catalysts is
Raney catalysts. Recently, Leitner et al. reported
14a
on the use of the commercially available
Raney cobalt in catalytic intra- and intermolecular PKRs. According to their report, their
reaction conditions (the substrate/Co
17.0, 23 bar CO, 130
◦
C; the substrate/Co ratio
=
6.0, 35 bar CO, 130
◦
C) were quite similar to those of bulk metallic cobalt on charcoal,
=
