Chemistry Reference
In-Depth Information
While the redox chemistry of verdazyls is fairly extensive, there are only a few reports in which the
redox activity of verdazyls is exploited in electron transfer reactions (i.e., without bond making/breaking).
Nakatsuji prepared charge transfer salts of verdazylium cations (
5
+
) and radical anions of the acceptor
molecules TCNQ
40
, tetrafluoroTCNQ
41
, and DDQ
42
by reaction of the two neutral reagents.
89
Hynes
has studied the kinetics of outer sphere electron transfer reactions between Kuhn verdazyl radicals and
coordination complexes of Co
3
+
,Ru
3
+
,Fe
3
+
and Fe
3
clusters.
92
O
F
F
Cl
CN
NC
CN
NC
CN
NC
CN
NC
CN
Cl
CN
F
F
O
40
41
42
Reactions of verdazyls
6
with oxidizing agents (halogens,
12
metal-based reagents such as FeCl
3
, AuCl
3
,
PtCl
4,
93
tetranitromethane
93
) normally give the corresponding verdazylium cations
12
. Oxidations with
peracids
94
or peroxides,
95
or heating verdazyls in oxygenated solutions containing activated charcoal,
96
induce ring opening to form either 1,2,4-triazoles
43
or N-formylformazans
44
(Scheme 7.13). 1,2,4-
Triazoles are also produced by simple thermolysis of verdazyls, either by heating the radical as a solid to
200
◦
C
12
or in solution at 80
◦
C.
97
There have been a few studies on the chemistry of verdazylium cations. They undergo a complex reaction
with hydroxide to ultimately give the corresponding radicals and N-formyl formazans
44
(Scheme 7.14).
23
Heating mixtures of verdazylium cations and verdazyl radicals produces C6-N2 coupled products
45
along
with one equivalent of leuco verdazyl (Scheme 7.15).
98
7.2.3.2 Hydrogenation and related reductions
Leuco verdazyls
11
, the initial cyclic product from formazan alkylation reactions (Schemes 7.1
and 7.2) are oxidized (most commonly by atmospheric oxygen) to produce radicals
6
. The reverse
Ph
Ph
CHO
Ph
N
NN
N
Ph
Ph
N
NN
N
N
N
+
Ph
N
Ph
Ph
38
43
44
Scheme 7.13
CHO
Ph
Ph
Ph
Ph
Ph
Ph
N
NN
N
N
NN
N
3NaOH
N
NN
N
3
2
+
Ph
Ph
Ph
38+
38
44
Scheme 7.14
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