Chemistry Reference
In-Depth Information
DDQ, TfOH
40%
50
171
Scheme 55 Synthesis of warped nanographene 171 [
181
]
6 The Smallest Carbon Nanotube
The structural properties of the corannulene-based series (C
10
)
n
H
10
were theoreti-
cally studied [
179
]. The transition from a bowl to a tube increases with molecular
size. Whereas corannulene (1) and C
30
H
10
are seen as bowl-shaped compounds,
C
40
H
10
marks the onset of the tube regime, and C
50
H
10
ends the character of the
bowl regime. Recently, compound 170 (C
50
H
10
) has been synthesized in the Scott's
laboratory (Scheme
54
)[
180
]. The key precursor 50 was prepared by fivefold
Negishi coupling of 46 with 2,6-dichlorophenylzinc chloride as shown in
Scheme
13
. Under FVP conditions, 50 was converted to 170 in 2-3% yield.
Based on the crystallographic analysis, 170 has a nanotube structure with the
bowl depth (tube length) of 5.16
. The average POAV pyramidalization angle
of the central pentagon was observed to be 12.3
Å
[
180
], which is very close to the
computational result (12.2
)[
179
].
7 A Warped Nanographene
Nanographene 171 was prepared by cyclodehydrogenation of 1,3,5,7,9-pentakis
(2-biphenylyl)corannulene 50, which was synthesized by a Suzuki coupling of
the resulting 1,3,5,7,9-pentakis(Bpin)corannulene (47) with 2-bromobiphenyl
(Scheme
55
)[
181
]. Based on X-ray crystallography, 171 adopts a warped structure,
and the central corannulene moiety is very shallow with a bowl depth of 0.37
.
The presence of five helical hexa[7]circulene moieties causes 171 to be chiral.
Theoretical analysis indicated that activation energies for the inversion and the
racemization are 1.7 and 18.9 kcal/mol, respectively.
Å
