Chemistry Reference
In-Depth Information
NITRENO RADICALS
D
IRK
G
ROTE AND
W
OLFRAM
S
ANDER
9.1 Introduction
9.2 Theory
9.3 EPR Spectroscopy on Iodophenyl Nitrenes
9.4 Nitrene Rearrangement as Competition to The Formation of Nitreno Radicals
9.5 Matrix Isolation and Spectroscopic Characterization of Nitreno Radicals
9.5.1 Phenyl Nitrene-4-yl
9.5.2 Phenyl Nitrene-2-yl
Acknowledgments
References
9.1
INTRODUCTION
Phenyl nitrene has a robust triplet ground state with a singlet-triplet splitting of
16 kcal/mol,
1
and is therefore an interesting building block for the construction of
organic high-spin molecules. One of the unpaired electrons of phenyl nitrene is
localized in the
s
plane at the nitrogen atom, whereas the other unpaired electron is
delocalized in the
system with large coefficients in the
ortho
and
para
positions,
similar to a benzyl radical. Introducing an additional unpaired
p
electron in the
ortho
and
para
positions results in strong coupling and quinoid low-spin systems, whereas
meta
coupling results in non-Kekul
p
e high-spin systems. Thus, the coupling of two
nitrene centers in the
para
position as in
1
results in low-spin triplet dinitrenes,
whereas coupling in the
meta
position as in
results in high-spin quintet ground state
molecules (Scheme 9.1).
2-4
Similar high-spin quintet systems can be constructed by
the combination of nitrene and carbene centers coupled via
meta
phenylene units.
5
2
