SYNTHESIS AND ELECTROCHEMICAL PROPERTIES OF REDOX-ACTIVE [2]ROTAXANES BASED ON THE INCLUSION COMPLEXATION OF 1,4-PHENYLENEDIAMINE AND BENZIDINE BY CYCLOBIS(PARAQUAT-P-PHENYLENE)

The inclusion complexation of 1,4-phenylenediamine (2) by the host cyclobis(paraquat-p-phenylene) (1(4+)) was used as the core interaction for the template-directed synthesis of a new redox-active [2]rotaxane (5(4+)) in high yield. The half-wave potentials for both monoelectronic oxidations of the 1,4-phenylenediamine subunit in this rotaxane exhibit remarkable anodic shifts as compared to the values typically observed in 1,4-phenylenediamine derivatives. These shifts result from the hindrance imposed by the rotaxane's tetracationic macrocyclic bead on the generation of additional positive charges. The electrostatic field created by the bead also slows down the kinetics of electron transfer, especially for the second oxidation process. Qualitatively similar effects were observed on the electrochemistry of a comparable rotaxane (7(4+)) built around the interactions between a benzidine subunit and host 1(4+), but the magnitude of the effects on the voltammetric parameters was smaller than in 5(4+).