Chemistry Reference
In-Depth Information
O
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41
42
43
Scheme 14 Cage networks with benzene units and amide linkers
Spherical and prismatic networks can be constructed by amide linkers
(Scheme
14
). Spherical network 41 consisting of four benzene units and six
amide linkers was synthesized by cyclization between a cyclic triamide and
1,3,5-benzenetricaboxylic acid [
81
]. This molecule is chiral depending on the
direction of unsymmetrical amide linkers. The enantiomers were resolved by chiral
HPLC. Various prismatic structures can be constructed by formation of amide
linkages between a linear diamine and a triangular tricaboxylic acid in a 3:2 ratio.
The geometrical shapes are controllable by the length of wall diamine units and the
size of cap tricarboxylic acids. Compound 42 with long
p
-terphenyl units takes a
helically twisted triangular prism structure due to C-H
interactions [
82
,
83
]
between the wall
p
-phenylene units [
84
]. In contrast, when large 1,3,5-
triphenylphenyl units and short
m
-phenylene units are combined, a flat prismatic
structure is formed as compound 43 [
85
].
Garcia-Garibay et al. designed molecular gyroscopes consisting of a 1,4-bis
(tritylethynyl)benzene framework where a
p
-phenylene rotor rotated about acety-
lene axle attaching to two terminal trityl stators [
86
,
87
]. The introduction of three
bridges between phenyl groups across the central axle is a rational modification
toward facile rotation of the central rotor in the solid state. Triply-bridged deriva-
tive 44 with benzophenone-derived chains was synthesized by macrocyclization
(Scheme
15
)[
88
]. The central phenylene group is surrounded by the spherical cage
with 12 benzene units.
A triptycene has rigid bicyclic structure, where three benzene units are
connected by two bridgehead carbons. This structural feature has been utilized
to construct 3D molecular cages [
89
]. Compound 45 was synthesized by
Eglinton-Glaser coupling of 2,7,14-tris[(3-ethynylphenyl)ethynyl]triptycene [
90
].
Its NMR spectra were consistent with the
D
3h
structure, whereas the X-ray structure
was slightly twisted from the regular
D
3h
structure. The distance between the inner
bridgehead carbons in the two triptycene units reaches 13.0
˚
. In the solid state, the
p
