Chemistry Reference
In-Depth Information
a
b
2.8
°
0
°
122°
174
°
149
°
Si
Si
A
B
122°
1.40
1.38
142
°
1.36
129°
112°
1.46
1.39
0
°
90°
120°
1.45
cove
Si
Si
C
1.48
136
°
122°
118°
120°
c
d
b
a
c
Fig. 9 Structure of 52:(a) X-ray crystal structure of major contributor (methyl groups and H
atoms omitted for clarity), (b) calculated geometry, (c) disorder in the crystal, and (d) crystal
packing. Reprinted with permission from [
66
]. Copyright 2009 John Wiley and Sons
results reflect the complexities of materials designs and difficulties in translating
molecular properties to solid-state and device properties.
Nonbenzenoid rings in graphitic structures induce curvature, the most classic
example being the 12 5-membered rings that allow the spherical shape of C
60
.
The [n]circulenes are a class of PAHs derived from the fusion of benzenoid rings to
the corresponding [n]radialene frame [
65
]. The curvature and bowl-to-bowl inver-
sion barrier of these materials is expected to increase with decreasing size of the
central ring. The first synthesis of benzannulated [4]circulene, quandrannulene (52)
was reported by King and coworkers in 2010 [
66
]. The four-membered ring is
derived from the photodimer of naphthoquinone (50). The authors take advantage
of the Co-catalyzed cyclotrimerization's well-established ability to form highly-
strained rings to form the bridges in going from tetrayne 51 to 52.
The X-ray crystal structure and calculated geometry (B3LYP/6-311G**) of 52
are shown in Fig.
9
. Calculated bond lengths and NICS value support the radialene-
structure as depicted in Scheme
14
, with ring A having an NICS value of 4.5 ppm.
The bowl depth, the distance between the plane containing ring A and the plane
formed by the eight atoms that fuse rings B and C, is 1.36
˚
, significantly deeper
than a depth of 0.87
˚
for [5]circulene.
