Chemistry Reference
In-Depth Information
113
77
1) CH
2
Cl
2
,60ºC
2) Ti(0)
55%
C
60
@
114
114
Scheme 34 Synthesis of corannulene clip 114 [
108
]
2.6.4 Corannulene Clip
Two concave corannulene substituents fused to a tether make it possible to form
a molecular catcher [
108
]. The designed molecule 114 was synthesized by
the twofold Diels-Alder reactions of isocorannulenofuran 77 with
dibenzocyclooctadiyne 113 and subsequently by deoxygenation with low-valent
titanium (Scheme
34
). Due to the non-planar shape of two corannulenyl moieties,
114 could have several conformations. A
1
H NMR titration experiment indicated
that buckycatcher 114 has a high binding affinity with C
60
. The strong interaction
between 114 and C
60
was also confirmed by the formation of crystals of inclusion
complex C
60
@114, which was generated from an approximately equimolar solu-
tion of both compounds in toluene. Based on X-ray crystallographic analysis, 114 in
C
60
@114 acts as a molecular clip for the guest C
60
.
2.7 The Correlations Between Structures and Bowl-to-Bowl
Inversion Barriers
The correlations between structures and the bowl-to-bowl
inversion barriers
(
ʔ
G
{
inv
) can be simply described as in Scheme
35
with a focus on bowl depth
being directly related to the height of
G
{
inv
. Compounds of Class IA and Class IB
(with a benzene ring fused to a rim of corannulene), where the bowl is shallower
than that found for 1, lead in general to a decrease of
ʔ
G
{
inv
relative to 1. In contrast
compounds of Class II lead in general to an increase of
ʔ
G
{
inv
relative to 1. As the
distance between two methylene groups in Class II decreases, the additional ring is
more strained in the transition state to bowl inversion, which in part explains the
observation that the value of
ʔ
G
{
inv
increases. Cyclopentacorannulene (67) and
acecorannulene (69), with a direct connection between the
peri
carbon atoms, have
the highest
ʔ
G
{
inv
s within the simple annulated-corannulene family. The lower
ʔ
G
{
inv
for 1,2-dihydrocyclopenta[
b,c
]dibenzo[
g,m
]corannulene (90) and
indenocorannulenes 98/100 compared to those of 67/69 is consistent with the
principle of Class I, i.e., the shallower bowl gives rise to the lower inversion barrier.
In order to develop a quantitative structure-energy relationship, Siegel and
co-workers investigated the correlation between bowl depth and barrier energy
values of
ʔ
