Chemistry Reference
In-Depth Information
OH
2
OH
2
OH
2
N
OH
2
N
N
O
N
N
Cu
Cu
Cu
N
N
N
O
O
OH
2
N
N
d
n
4
r
4
n
g
|
0
O
A
B
C
OH
2
O
O
N
N
Cu
O
N
N
N
N
N
N
N
Cu
N
O
N
O
O
N
N
N
N
N
O
O
D
E
Figure 2.26 Copper complexes of phen (A, B), phendione (C) and phenfuroxan (D)
derivatives and furoxan derivative of 2,9-dimethyl-1,10-phenanthroline
(E) used in the aerobic oxidation of alcohols.
activities of Cu-bpy and Cu-TMEDA (TMEDA
¼
N,N,N
0
,N
0
-tetra-
methylethylenediamine) have been reported for the ecient oxidation of
alcohols.
113,114
A copper(
II
) meso-tetraphenylporphyrin (CuTPP) complex was
used for the selective oxidation of benzyl alcohols with molecular oxygen in
the presence of isobutyraldehyde as co-catalyst in o-xylene at 60 1C.
115
Ali-
phatic and alicyclic amine ligands in combination with copper salts exhibit
good catalytic activity. Repo and co-workers reported the oxidation of benzyl
alcohol and 3,4-dimethoxybenzyl alcohol (veratryl alcohol) by using copper
complexes of diamine-based ligands.
116
For this purpose, they utilized a
range of aliphatic, alicyclic and aromatic amines including ethylenediamine,
1,3-propanediamine, diethylenetriamine, TMEDA, 9,10-diaminophenan-
threne (DAPHEN), 1,2-diaminocyclohexane (DACH), etc. They also reported a
copper complex, bis(pyridine-2-carboxaldehyde oxime)copper(
II
) sulfate, as
the catalyst precursor for the aerobic oxidation of veratryl alcohol.
117
Kinetic
study of the oxidation reaction indicated the formation of a binuclear
hydroxyl-bridged complex (LCu-m-(OH)
2
-CuL)
21
in catalysis with a Cu-TMEDA
complex.
118
Studies on oxidation reactions with a copper-bisisoquinoline
catalyst revealed an increase in the catalytic yield of aldehydes and ketones by
using ionic liquids [bmim][PF
6
], [omim][BF
4
] and [hmim][BF
4
](omim
¼
1-octyl-3-methylimidazolium, hmim
¼
1-hexyl-3-methylimidazolium).
119
The catalytic cycle of GO has fuelled interest in developing copper
complexes supported by organic ligands, particularly nitrogen- and phenol-
containing ligands. Over the years, a number of copper complexes
employing multidentate ligands such as mono(pyridyl)-alkylamines,
bis(pyridyl)alkylamines, triazacyclononanes, salen and substituted tris(pyr-
azolyl)borates have been developed as structural and spectroscopic models
of GO.
120
The first catalytic functional model system for GO was reported even
before the structure of the enzyme was solved. The model complexes
.
Search WWH ::
Custom Search