Self-Assembled Multi-Component Catenanes: Structural Insights into an Adaptable Class of Molecular Receptors and [2]-Catenanes

Under acidic conditions (50 equiv of TFA), combinations
of hydrazide
A-B monomers self-assemble into octameric [2]-catenanes with high
selectivity for [132]2, where 1 is a d-Pro-X (X = Aib, Ac4c, Ac6c, l-4-Cl-PhGly)-derived monomer and 2 is an l-Pro′-l-arylGly (Pro′
= Pro, trans-F-Pro, trans-HO-Pro,
aryl = naphthyl, phenyl)-derived monomer. Five different combinations
of monomers were studied by X-ray crystallography. In each case, the
unique aryl glycine unit is located in the core of the structure where
the aryl ring templates a CH−π–CH sandwich. Analysis
of metrical parameters indicates that this core region is highly conserved,
while the more peripheral zones are flexible. 1H NMR spectroscopy
indicate that the solid-state structures are largely retained in solution,
though several non-C2-symmetric compounds
have a net C2-symmetry that indicates
accessible dynamic processes. Catenane dynamic processes were additionally
probed through H/D exchange, with the core being inflexible relative
to the peripheral structure. Mass spectrometry was utilized to identify
the constitutional isomerism in the minor asymmetric [1523] catenanes.