Chemistry Reference
In-Depth Information
Fig. 21 Summarizing scheme of cycloaddition reactions on carbon nanotubes
Cycloadditions
The group of cycloadditions comprises a large number of reactions that are largely
employed for CNTs sidewall functionalization. Among the first developed with this
aim we find carbene addition, which is shown to yield the derivative depicted in
Fig.
21
after the addition of phenyl (bromodichloromethyl) mercury to previously
oxidized tubes [
81
]. The resulting saturation of the carbon atoms replaced with a
cyclopropane ring functionality provoked dramatic changes in the optical spectra
and at the Fermi level transitions. In this case, thermal treatment of the derivative
above 300
C determined the rupture of the Cl-Cl bonds, but the electronic structure
of the initial tubes was not restored.
In a similar fashion, the Bingel-Hirsch [2 + 1] cyclopropanation reaction
describes the use of diethylbromomalonate as a carbene precursor in order to obtain
a cyclopropane ring bearing two ester appendages, both available for subsequent
modifications on the tubes (Fig.
21
). The degree of functionalization was estimated
to be about 2% [
82
-
84
].
Other reactive species suitable for sidewall modification are nitrenes, as
reported by Hirsch and co-workers who reacted SWCNTs with different alkyl
azidoformates at 160
C leading to N
2
extrusion and subsequent formation of
alkoxycarbonylaziridino-modified tubes [
85
].
Impressive work based on nitrene cycloaddition was reported by Yinghuai et al.,
who functionalized SWCNTs with C
2
B
10
carborane cages and found specific
tumor-targeting activity after administration of the derivative to mice [
86
].
