Chemistry Reference
In-Depth Information
O
N
aBH
3
C
N
NH
H
2
NNHBoc
N
N
H
Boc
N
H
Boc
20
21
COCl
2
pyridine
O
O
O
iPr
iPr
iPr
iPr
N
N
N
iPr
iPr
HCl
EtOH
N
NH
N
N
NH
2
N
N
HN
NH
2
Boc
Boc
R
2
8
23
22
Scheme 7.8
X
X
X
R'
H
R'
R'
R"
R'
R"
COCl
2
R"NHNH
2
NEt
3
N
N
N
Cl
[ox]
N
N
N
N
HN
N
N
H
H
N
NH
pyridine
R
R
H
R
R
7
X=O
8
X=S
24
25
26
Scheme 7.9
shorter than the Cp-to-Cp distance of 3.30 A). The molecule is diamagnetic, indicating that spin pairing
is complete via
dimerization. Notably, the solution characterization data indicate that the two verdazyls
are very weakly interacting, suggesting that in solution the diradical does
not
adopt the
π
π
-dimer structure.
Me
Ph
N
N
O
N
N
NN
N
(CH
2
)
8
O
O
Me
Fe
Me
NN
N
N
Br
O
Ph
NN
Me
27
28
Not surprisingly, verdazyl radicals are highly coloured compounds. Kuhn verdazyls
6
are typically
green, with low energy absorptions between 700 - 750 nm (extinction coefficients
10
3
M
−
1
cm
−
1
.
12
∼
)
In
comparison, 6-oxoverdazyls have their longest wavelength absorption maximum (
λ
max
) between 400 and
560 nm and thus are yellow to red in solution.
42,47
For both of these verdazyl types the C3 substituent has
a significant influence on the absorption wavelength: radicals with R
=
hydrogen or alkyl generally have
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