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OsO
4
(1 mol %) - CuCl (1.5 mol %)
Pyridine (5 mol %)
OH
O
(7.4)
MS 4Å, toluene, O
2
(1 atm), 100 °C
MeO
MeO
15
16
, 1 h, 96%
OsO
4
-quinuclidine (2 mol %)
Cu(2-ethylhexanoate)
2
(1 mol %)
O
O
O
O
OH
O
(7.5)
allyl ethyl ether (18 mol %)
MeCN, 25 °C, O
2
(1 atm)
17
18
, 8h, 97%
In the case of the Os-Cu bimetallic complex 19, mechanistic studies, in-
cluding kinetic and labeling studies, were conducted on the oxidation of
benzyl alcohol (4) to benzaldehyde (5) (Scheme 7.10).
20
The first step in-
volved the coordination of alcohol 4 to osmium complex 19, followed by
proton transfer from the coordinated alcohol to the bridging oxo group.
A concerted b-hydrogen elimination oxidized the alkoxide intermediate to
N
O
R
O
O
Os
Cr
R
Ph
O
4
19
OH
R = (CH
3
)
3
SiCH
2
-
N
N
R
O
Cr
O
2
O
R
O
Os
N
Os
Cr
R
O
R
O
O
R
O
O
O
O
Os
Cr
O
R
O
V
VI
OH
Ph
- H
2
O
- PhCHO
5
N
O
O
N
R
O
HO
Os
Cr
R
O
Cr
OH
O
R
Os
O
O
R
H
O
Ph
Ph
Scheme 7.10 Proposed mechanism of the catalytic aerobic oxidation of alcohols
with the Os-Cr bimetallic catalyst.
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