Chemistry Reference
In-Depth Information
Scheme 15 M¨ llen's synthesis of HBC derivatives [
101
-
103
]
Scheme 16 Synthesis of HBC derivatives with low symmetry [
104
,
105
]
hexaphenylbezene into HBC because FeCl
3
possesses an oxidation potential suffi-
cient for the C-C bond formation [
101
-
103
]. The significance of this synthetic
sequence lies not only in the large enhancement of the reaction yields, but also
allows introduction of various substituents in the periphery, thus realizing increased
solubility, processability, and controllable self-assembly.
The HBC derivatives 141 with low symmetry were synthesized by an alternative
route, following a synthetic route including Diels-Alder cycloaddition between
tetraphenylcyclopentadienone derivatives 138 and diphenylacetylene derivatives
139, and subsequent oxidative cyclodehydrogenation of low symmetric precursor
140 with FeCl
3
(Scheme
16
)[
104
,
105
]. Based on this synthetic strategy, HBCs
possessing solubilizing chains and one or several bromine atoms with different
symmetries were synthesized. The presence of bromine atoms allows further
functionalizations by transition metal-catalyzed coupling reactions such as
Kumada, Suzuki, Hagihara, Negishi, and Buchwald coupling reactions. The attach-
ment of different functionalities leads to a more exact control of the order of HBC
molecules in the bulk state, the alignment of the discs on the surface, and the
intramolecular binary energy/electron transport. In addition, both of the above-
mentioned synthetic methods are quite versatile and are applicable for a large
variety of precursors, which makes the preparation of extended graphene fragments
practically possible.
