Synthesis and characterization of a paramagnetic receptor based on cyclobis(paraquat-p-phenylene) tetracation

Synthesis of a new class of π-electron-deficient tetracationic cyclophane ring, cyclobis(paraquat-p-phenylene), carrying one or two paramagnetic side-arms based on 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) moiety has been achieved in five steps starting from 2,5-dimethyl benzoic acid. The possibility of exploiting the proposed cyclophanes as hosts in rotaxane-like structures was tested preparing the monoradical receptor by the clipping procedure in the presence of 1,5-dimethoxynaphthalene (DMN). The addition of template allows the isolation of the monoradical complex with DMN.