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In-Depth Information
Reedijk and co-workers used pyrazole-pyridine and pyrazole-naphthol
ligands for the Cu-TEMPO catalytic oxidation of benzyl alcohol in the
presence of dioxygen under mild conditions. Whereas pyrazole-naphthol
ligands inhibit the catalytic ability of the corresponding copper complexes,
the copper(
II
) complex of pyrazole-pyridine ligands can oxidize benzyl al-
cohol in acetonitrile.
59
Reedijk's group further developed copper complexes
of bifunctional triazine-based ligands (Figure 2.13) by combining a pyrazole-
pyridine group or substituted bpy and TEMPO on a triazine ring for the
oxidative transformation of benzyl alcohol and 1-octanol to the aldehydic
products under mild conditions in air.
60,61
Repo and co-workers reported the catalytic aerobic oxidation of substi-
tuted benzyl alcohols by using copper(
II
) complexes of 2-N-arylpyrrole-
carbaldimine ligands and TEMPO in the presence of potassium carbonate in
aqueous medium.
62
A comparative study of catalytic conversion with elec-
tronically and sterically variable aryl-substituted ligands was performed
(Figure 2.14). A catalytic system containing N-benzylidene-N,N-dimethylethane-
1,2-diamine, CuBr
2
and TEMPO has been reported to oxidize various benzylic
alcohols in the absence of any base in acetonitrile-water solvent mixture
at 80 1C.
63
Repo and co-workers also developed an ecient catalytic system
based on N
2
O
2
donor 3,5-di-tert-butylsalicylaldimine ligands and TEMPO
d
n
4
r
4
n
g
|
0
N
N
.
N
N
N
N
N
N
N
N
HN
N
O
O
N
NH
N
N
N
O
N
O
N
R = H, CH
3
N
N
O
N
NH
N
R
N
N
O
Figure 2.13 Bifunctional triazine-based ligands used in the Cu-TEMPO-catalyzed
aerobic oxidation of alcohols.
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