Chemistry Reference
In-Depth Information
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ยท
58
)
58
R = (CH
2
)
10
CH
3
59
(= 2
Scheme 21 Resorcinarene cavitand 58 and dimeric capsule 59 (partly adapted from [
113
])
bonds. These molecules are fascinating in terms of not only synthetic challenges but
also application to functional materials due to their unique geometry [
118
-
123
].
Because catenanes and knots have at least one crossing of the ring chain, these
molecules have nonplanar topologies. For the selective synthesis of such
compounds, aromatic units have often been utilized as rigid building blocks to
regulate structural flexibility. In addition, the interactions of aromatic units with
other aromatic or nonaromatic units play important roles in preorganizing cycliza-
tion steps via
interactions, as well as other weak
interactions. In this section we will introduce some examples of catenanes and
topologically fascinating networks mainly from recent examples.
p
p
, C-H
p
, and cation
p
6.1 Catenanes
Recent advances in chemistry of catenanes, in which two or more macrocycles are
mechanically interlocked, are attributed to effective synthesis by intelligent
approaches. Template synthesis is the most promising approach, where two or
more fragments are organized before cyclization to form catenanes. Such
preorganization is occasionally performed by metal coordination [
124
] or aromatic
donor-acceptor interactions [
125
]. In the former approach, aromatic multidentate
ligands such as bipyridines, terpyridines, and phenanthrolines are preferably used to
fix the geometry. In the latter approach, for example, interactions between electron
deficient and electron rich aromatic units can effectively preorganize building units.
It is interesting that [2]catenane 61 (the number of ring components in brackets)
is formed by self-assembly of two isolated rings 60 consisting of two
p-
bis(4-
pyridylmethyl)benzene ligands and two Pt(II) ions (Scheme
22
)[
126
]. These
methods enabled us to construct not only simple [2]catenanes but also very com-
plicated catenanes with more than two rings or high ordered crossings [
127
].
Recently, template dynamic synthesis of a [3]catenane was reported by Sanders
et al. (Scheme
23
)[
128
]. Two kinds of acyclic units, 63 with two acceptor units
