Chemistry Reference
In-Depth Information
6+
Pt
R
Pt
a
:
R =
X = B(C
6
F
5
)
4
N
N
b
:
R =
X = NO
3
N
N
R
Pt
Pt
PPh
2
N
N
Pt
=
Ph
2
P
Pt
6 X
-
Pt
R
Pt
57
Scheme 20 Cage networks with trigonal prism frameworks
positions [
108
]. This molecular cage furnished an inner space sufficient for the
rotation of the triptycene paddle wheels. Actually, no restricted rotation was
observed even at
90
C by NMR spectroscopy.
5.3 Cage Networks with Hydrogen Bonds
Although a large number of aromatic cage networks assembled by hydrogen bonds,
such as carcerands and calixarenes, have been explored [
26
,
109
], we introduce
resorcinarene capsules as a typical example in this section [
110
,
111
]. Compound
58 is a bowl-shaped cavitand consisting of a calix[4]resorcinarene core and four
peripheral imide moieties (Scheme
21
). Two cavitand molecules form cylindrical
capsule 59 via hydrogen bond networks at the imide moieties. A wide range of
cylindrical molecules can be encapsulated within the cavity. For long linear alkanes
a single guest molecule enters into the capsule and tends to take a helical confor-
mation rather than an extended conformation to fit into the cavity [
112
,
113
]. The
capsule size can be extended by the insertion of glycoluril spaces between the two
cavitand molecules, leading to encapsulation of longer alkanes and other long
molecules [
113
-
115
]. Two resorcinarene cavitands can be held together by ordi-
nary covalent linkers, boronic ester linkers, and metal-ligand coordination linkers
[
116
,
117
].
6 Topologically Fascinating Aromatic Networks
Topological isomers refer to isomers with the same connectivities but different
topologies. Typical examples are catenanes, knots, and rotaxanes, in which
molecules are interlocked by mechanical bonds rather than ordinary chemical
