Chemistry Reference
In-Depth Information
Fig. 35 Crystal packing of [6]CPP showing tubular arrangement [
49
]
This has obvious implications in the synthesis of extended nanotube structures.
Most recently, Itami reported the selective syntheses of [9]CPP, [10]CPP,
[11]CPP, and [13]CPP using modifications of previously reported methods [
45
].
This is notable in that it contains the first example of intramolecular
macrocyclizations to offer [9]CPP, [11]CPP, and [13]CPP precursors (Fig.
36
).
These strategies yield approximately 5 mg of the desired hydrocarbons in good
to moderate yields [
45
].
4.5 Host-Guest Behavior of [10]CPP·C
60
, a Fullerene Peapod
The first and only example of a host-guest complex with cycloparaphenylene was
assembled by Yamago and coworkers [
37
]. In this work, solid fullerene C
60
was
ingeniously added to an NMR sample of the product mixture from the “shotgun”
synthesis of [8-13]CPP in CDCl
3
. The monitored proton spectrum showed the
downfield shift of only the signal corresponding to [10]CPP (Fig.
37
).
Yamago concluded that this shift indicated the size-selective encapsulation of the
fullerene guest by [10]CPP. Similar NMR trends were seen in the CPPA·C
60
experiments [
18
,
22
]. Yamago was able to confirm by optical data a 1:1 complex
of [10]CPP with C
60
with a dissociation energy of 14.1 kcal/mol, identical to
Kawase's
-extended CPPA 18 with C
60
. Moreover, computational analysis showed
that the CPP-fullerene intermolecular distance was 3.35
˚
, which corresponds with
the interlayer distance in graphene and multi-walled carbon nanotubes, as well as
CNT-fullerene peapods and CPPA·C
60
. Unlike CNTs, the discrete synthesis of
single sizes of CPP made possible the application of their inward-facing
π
π
-system
to offer a single length of fullerene peapod in high purity.
