Amide-appended porphyrins as scaffolds for catenanes, rotaxanes and anion receptors

The synthesis of a porphyrin with an over-arching strap incorporating an isophthalamide unit produced both a porphyrin monomer with a potentially H-bonding receptor site, and a [2]catenane. Although both compounds exhibit fluxional behaviour, ¹H NMR and MS data was used to distinguish them, and was interpreted in terms of the dynamics of each system. The self-complementarity of the isophthalamide unit provides an ideal building block for assembling [2]pseudorotaxanes with similarly functionalised threads. This was illustrated by the self-assembly of a ruthenium–porphyrin stoppered rotaxane under thermodynamically controlled conditions, by simple mixing of the strapped porphyrin, a complementary thread unit containing an isophthalamide central unit and pyridine-attached ends, and a ruthenium carbonyl porphyrin. The strapped porphyrin was also shown to act as a receptor for chloride ion, and its binding ability with other H-bonding isophthalamide guests was found to be modulated by the presence of chloride ion. Chloride complexation was observed in both metallated and free base porphyrin monomers as well as the rotaxanes counterparts, but no anion binding was observed for the catenane.