Synthesis and post-assembly modification of some functionalised, neutral π-associated [2]catenanes

Two diaryl crown ethers bearing methyl ester functionality on one of the aromatic components of the macrocycle have been used as templates for the cyclodimerisation of acetylenic aromatic diimides, thereby achieving assembly of several functionalised neutral pi-associated [2]catenanes. Post-assembly synthetic modification of some of these interlocked structures, and of some previously reported [2]-lcatenanes, by hydrogenation of the butadiyne linkers in the diimide macrocycle has also been achieved. In contrast to their parent systems, these modified catenanes give room temperature H-1 NMR spectra which are poorly resolved; at elevated temperatures the constituent rings of the catenanes are in fast exchange on the chemical shift timescale leading to simplification of the spectra. The crystal structure of one of the ester-derivatised [2]catenanes is also presented. The ester functionality present in these interlocked systems provides options for potential chemical modification via surface attachment or metal-ion complexation.