Wursterʹs crownophanes: an alternate topology for para-phenylenediamine-based macrocycles

Six redox-active cyclophane/crown hybrid molecules (crownophanes) were prepared via cyclization reactions involving N,N′-dimethyl-p-phenylenediamine and tosylated oligoethylene glycols of varying length. These new host molecules differ from other phenylenediamine-containing crown ethers in that the electron-rich π face is designed to be part of the ligating group. Their electrochemical properties were determined by cyclic voltammetry with a correlation found between macrocyclic architecture and ease of oxidation. The affinity of the smaller crownophanes for cations was studied by cyclic voltammetry with the result that these hosts show no electrochemical response to alkali metal cations, but, dependent on macrocycle size, modest selectivity for alkaline earth metal cations. This stands in contrast to previously reported phenylenediamine-containing crown ethers in which the redox centers are linked to guest ions through a macrocyclic amino group.