Chemistry Reference
In-Depth Information
5 mol% (Phen)CuCl
5 mol%
t-
BuOK
5 mol%
-BuO
2
CN(H)N(H)CO
2
t
-Bu
t
OH
H
O
7 mol%
-Methylimidazole
O
2
, C
6
H
5
F
N
(a)
R
H
R
H
d
n
4
r
4
n
g
|
0
COO
t
Bu
DBADH
2
:
HN
NH
t
Bu
OOC
E
E
N
N
LCu
II
H
O
O
(b)
O
Cu
I
L
O
2
H
Cu
II
L
1/2
Cu
II
L
NN
H
H
E
E
NN
NN
E
E
E
E
I
II
L = 1,10-phenanthroline
R = alkyl, aryl
E = CO
2
t
- RCHO
Bu
R
R
O
H
O
OH
OH
H
RCH
2
OH
- H
2
O
Cu
II
Cu
II
Cu
I
L
Cu
I
L
L
L
H
H
NN
NN
NN
NN
E
E
E
E
E
E
E
E
IV
III
Figure 2.25
(a) Aerobic oxidation of alcohols catalyzed by Cu-phen catalyst in the
presence of DBADH
2
and (b) the proposed catalytic mechanism.
.
Copper-phen complexes have also been utilized in the oxidation of
veratryl alcohol (3,4-dimethoxybenzyl alcohol) to veratraldehyde with O
2
in
alkaline aqueous solutions by Repo and co-workers.
110
Recently, Das and
Paine reported a series of copper complexes supported by different phen
derivatives for the aerobic oxidation of primary alcohols in the presence of a
base (tetrabutylammonium methoxide) under ambient conditions
(Figure 2.26).
111
The catalysts exhibit high selectivity towards primary alco-
hols. The copper complexes of phen (A and B in Figure 2.26) are found to be
better catalysts than other complexes. In the catalytic cycle, a copper(
II
)-
superoxo species is proposed to abstract the hydrogen atom of the metal-
bound alcoholate. The effect of structural and electronic factors of the
supporting ligand on the catalytic eciencies was reported.
In addition to copper-phen complexes, numerous catalytic systems with
nitrogen donor ligands have been reported. In 1980, Munakata et al. used a
series of binary copper(
I
) complexes of 2,2
0
-bipyridine, 4,4
0
-dimethyl-2,2
0
-
bipyridine, 2,2
0
,2
00
-terpyridine and ethylenediamine and ternary copper(
I
)
complexes of 2,2
0
-bipyridine and b-diketonates for the oxidation of primary
and secondary alcohols in the presence of O
2
at 15 1C.
112
The catalytic
Search WWH ::
Custom Search