Molecular Borromean Rings Based on Dihalogenated Ligands

A series of Cp* Rh- and Cp* Ir-based molecular Borromean rings (BRs) have been prepared with dihalogenated ligands (fluoranilic acid, chloranilic acid, and bromianilic acid) and 4,4'-bipyridylacetylene. The halogen atoms play a crucial role in forming BRs. The strength of the interaction among the rings for different BRs is not the same and can be adjusted by changes in the halogen atoms on the precursor. We took advantage of this dissimilarity in the interactions to realize selective reversible conversion between BRs and a monomeric rectangle by the use of different p-dihalobenzenes. Subsequently, a stepwise separation method for p-dichlorobenzene, p-dibromobenzene, and p-diiodobenzene at ambient temperature was developed. The BRs used in the separation are recoverable and recyclable.