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d
n
4
r
4
n
g
|
0
N
N
N
PhCH
2
O
N
Cu
II
O
Cu
II
t
t
O
t
Bu
O
Bu
Bu
O
Bu
O
PhS
SPh
PhS
SPh
Ph
H
2
O
2
H
H
[Cu(II)BSP]
PhCH
2
OH
RDS
N
N
PhCHO
O
2
N
N
Cu
II
Cu
I
HO
t
t
O
Bu
Bu
Bu
O
Bu
O
O
O
PhS
PhS
SPh
O
SPh
Ph
H
H
Figure 2.28 Proposed mechanism for the catalytic aerobic oxidation of alcohols by
the copper complex [Cu
II
(BSP)].
.
mononuclear copper complex with an N
2
O
2
coordination environment. The
complexes were shown to catalyze the oxidation of benzyl alcohol, 1-phe-
nylethanol and cinnamyl alcohol in the presence of catalytic amount of KOH
under O
2
at 22 1C in acetonitrile. The catalyst exhibited high TON with a low
catalyst loading (0.01-0.06 mol%). The catalytic oxidation operates through
a GO pathway involving cycling between copper(
II
)-phenoxyl radical and
copper(
I
)-phenolate intermediate (Figure 2.28).
Chaudhuri and co-workers reported a number of excellent synthetic
models for GO.
17,124-128
Copper complexes of phenolate ligands containing
N, S and Se hetero-donor atoms are capable of catalyzing the aerobic oxi-
dation of alcohols. A range of different primary alcohols could be oxidized
using these catalysts. The copper(
II
) complex with selenobis(2,4-di-tert-
butylphenol) ligand (F in Figure 2.27) selectively oxidizes benzyl alcohol to
benzaldehyde with 95 turnovers in 24 h under ambient conditions.
127
The
copper complex of the sulfur analog (E in Figure 2.27) has been reported to
oxidize secondary alcohols and also to effect oxidative C-C bond coupling
reactions. The copper complex of the tetradentate ligand N,N
0
-bis(3,5-di-tert-
butyl-2-hydroxyphenyl)-1,2-phenylenediamine (D in Figure 2.27) is capable
of oxidizing methanol and ethanol under ambient conditions in
organic solvents or in pure substrates.
125
The copper complex derived from
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