PdII and PtII Metal-Directed Self-Assembly of Supramolecular Structures Based on N-Monoalkyl-4,4¢-Bipyridinium Derivatives - Molecular Self-Assembly: Advances and Applications - page 376

to check the regioselectivity with acyclic guests such as S1a,b and

S2a,b . Thus, the addition of acyclic guests to a solution of M6a ·6NO

3

O resulted in the partial or total reorganization
of the “incorrect” metallocycle

and M ′ 6a ·6NO in D

3 2

M ′ 6a ·6NO to yield the 1:2 inclusion

3

. Obviously, the mechanism
requires, as in the case of catenanes, the dissociation of the N atoms
from the Pd

complexes derived from M6a ·6NO

3

II

centers. In contrast to catenanes, in these cases the
inclusion equilibrium between the complexed species and their
separated components is fast in

1

H NMR time scale so only averaged

signals are detected.

Figure 11.12 Regioisomeric metalocycles , which result from

two possible orientations of the starting materials.

M6 and M'6

, and
other guests allowed us to draw some conclusions. First, cyclic guests
(in acetonitrile solution) seem to favor higher regioselectivities than
their acyclic counterparts (e.g.,

The comparison of the results obtained from S1a,b , S2a,b

BPP34C10 and S1a,b ). Assuming a

similar π-donor capacity for the dioxoaryl rings of BPP34C10 and

S1a,b and almost identical entropic costs for all the self-assembly

processes, then the number and strength of the π-interactions
with the metallocycles determine the regioselectivity. Thus, the
ratio of π-interaction energies between M ′ 6a

( BPP34C10 ) /

2

M6a ( BPP34C10 ) is smaller than those of the inclusion complexes

2

M ′ 6a resulting in a higher regioselectivity for the

former. Second, naphthalenic substrates achieve higher selectivities
than phenylenic derivatives owing to their better π-donor character.
Finally, the presence of the polyether chains in the acyclic guest (e.g.,

( S1a ) / M6a ( S1a ) 2 2