Chemistry Reference
In-Depth Information
copper(
II
) complex of 4,6-O-ethylidene-b-
D
-glucopyranosylamine (A in
Figure 2.17) has been used as a catalyst in the TEMPO-mediated selective
oxidation of primary and secondary alcohols under mild conditions.
84
A
cupric acetate selective receptor of an N
2
O
2
donor ligand derived from ala-
nyl-4,6-O-ethylidene-b-
D
-glucopyranosylamine exhibited catalytic properties
in the TEMPO-assisted oxidation of alcohols in anionic liquid.
85
Contel et al. reported a copper(
II
) complex, [Cu(C
8
F
17
(CH
2
)
2
CO
2
)
2
(R
f
-tacn)],
where R
f
ΒΌ
-(CH
2
)
3
C
8
F
17
, as an e
cient and recoverable precatalyst for
the aerobic oxidation of 4-nitrobenzyl alcohol to 4-nitrobenzaldehyde with
TEMPO at 90 1C. The catalyst can be recycled after five runs without a
decrease in activity.
86
They also reported the use of fluorocarbon-soluble
copper(
II
) carboxylate complexes of ligands, i.e. N-1,4,7-Me
3
TACN and
N-1,4,7-pentamethyldiethylenetriamine (PMDETA), in the aerial oxidation of
p-nitrobenzyl alcohol to p-nitrobenzaldehyde in chlorobenzene-toluene using
TEMPO at 90 1C in the thermomorphic mode (Figure 2.23).
87
Moreover, a
series of copper complexes of fluorinated alkoxide-derived bipyridine ligands
have been reported to perform as an ecient catalytic system under the
aforementioned experimental conditions.
88
Poly(ethylene glycol) (PEG), an environmentally benign solvent, produces
a recyclable catalyst for the oxidation of alcohols upon functionalization
with TEMPO.
89
d
n
4
r
4
n
g
|
0
2.2.2 Heterogeneous Catalysts
Compared with homogeneous-phase catalysts, examples of Cu-TEMPO
catalytic systems for the aerobic oxidation of alcohols in the heterogeneous
phase are limited. Yang et al. reported a recyclable Cu-Mn mixed oxide
supported on active carbon for the aerobic oxidation of various alcohols in
the presence of TEMPO in dichloromethane at 80 1C.
90
The catalyst is
effective with a low loading of TEMPO (0.5 mol%) and can be recycled after
five runs without any detectable decrease in activity and selectivity. An
immobilized TEMPO derivative, (TEMPO-4-oxymethyl)polystyrene, has been
.
R
Me
Me
R
O
O
O
O
N
N
Me
Me
Me
N
N
N
Me
N
Cu
Cu
Me
Me
O
O
O
O
O
O
Cu
R
Cu
R
R
R
O
O
O
O
O
O
R
R
A
B
C
C
8
F
17
C
8
F
17
R =
Figure 2.23 Fluorocarbon-soluble copper complexes (A, B and C) of ligands N-1,4,7-
Me
3
TACN (B) and N-1,4,7-pentamethyldiethylenetriamine (C) used as
oxidation catalysts.
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