Chemistry Reference
In-Depth Information
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
N
NN
N
N
NN
N
N
NN
N
Ph
N
N
N
+
+
N
H
N
Ph
Ph
Ph
N
Ph
Ph
N
Ph
38+
38
46
45
Scheme 7.15
reaction - reduction
of
verdazyls
to
leuco
compounds - has
been
documented
extensively
as
well.
70 kcal/mol)
99
; accordingly, many of the
The N-H bond in the leuco compounds is relatively weak (
∼
hydrogenating reagents - hydrogen/palladium,
12
sodium dithionite,
12
thiols,
12,100
1,4-dihydropyridines,
101
hydrazines,
102
secondary phosphines,
103
and ascorbic acid
104
- are good hydrogen atom donors/reducing
agents.
Leuco versions of 6-oxoverdazyls (
47
) are relatively rare. They have been made by hydrogen reduction
of the radicals,
41,42
and there is one report of oxidation of a tetrazane
17
to give a leuco compound
(Scheme 7.16).
44
As is the case with the leuco compounds
11, 47
are readily converted to radicals by
atmospheric oxygen. 6-Oxoverdazyls can also be reduced to the leuco compounds with ascorbic acid,
although the reaction is rather sluggish compared to the reduction of nitroxides by this method.
105
1,3,5-Triphenylverdazyl
38
undergoes
redox
reactions
with
a
variety
of
organometallic
reagents
Mg, Li, Al).
106
(Scheme 7.17; M
=
The verdazyl is initially reduced by the carbanion, producing a
O
O
O
R'
R"
R'
R"
R'
R"
NaIO
4
H
2
/Pd
N
NN
N
N
N
N
N
HN
N
H
NH
R
R
R
H
47
7
17
Scheme 7.16
Ph
Ph
Ph
Ph
N
NN
N
N
NN
N
+
R
+
R[M]
[M]
Ph
Ph
38
48
a
O
2
H
+
Ph
Ph
Ph
Ph
N
N
N
N
NN
N
H
R
Ph
Ph
46
49
Scheme 7.17
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