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are adequate to carry out this kind of study
because they represent a dynamic system of two regioisomeric
square hosts (Fig. 11.12). The self-assembly of
Metallocycles
M6a,b
II
L6
and the Pd
or
II
Pt
complexes leads to a 1:1 mixture of the metallocycles
M6
and
M
′
6
[34,35]. Although both metallocycles own quite similar cavity
dimensions, only the squares
present the correct disposition
of the bipyridinium units to maximize the π
M6a,b
stacking interactions,
which are expected to be stronger with the bipyridinium moieties
than with the phenylpyridine subunits. This assumption was
supported by DFT calculations. As expected from these results,
the addition of a π-complementary aromatic guest (
-
π
BPP34C10
or
DN38C10)
in acetonitrile
induced the regioselective formation of the [3]catenane structures
derived from
to a solution of
M6a
·6PF
and
M
′
6a
·6PF
6
6
M6
(Scheme 11.5). Similar results were obtained with
II
Pt
. In both cases the presence of only
one regioisomer was verified by a careful NMR study and X-ray
crystallography.
metallocycles
M6b
and
M
′
6b
Scheme 11.5
Regioselective synthesis of [3]catenanes.
Although the structure of catenanes was unambiguously
characterized, the reason of the observed regioselectivity should
be addressed. With the aim of clarifying this issue, we carried out
a series of experiments to establish what interactions between the
components govern the preferred formation of the [3]catenanes
M6a
(
BPP34C10
)
·6PF
and
M6a
(
DN38C10
)
·6PF
. We decided
2
6
2
6
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