Synthesis and electrochemical properties of cavitands functionalized with 4,4′-bipyridinium units

Four new brominated resorcinarene cavitand derivatives () and the already known tetrakis(bromomethyl)cavitand have been synthesized, starting from the tetramethylcavitand . These brominated cavitands constitute excellent building blocks for the covalent assembly of new structures containing one (), two ( and ), three () and four () monoquaternized bipyridine units attached to the upper rim of the cavitand bowl. The free terminal nitrogens in these structures can be methylated to yield compounds with one to four 4,4′-bipyridinium (viologen) units attached to the cavitand (), or treated with monobromocavitand to produce oligomeric structures containing from two to five cavitand units connected by viologen residues (). Compounds , and show the electrochemical reactivity anticipated from their reducible units (mono- or diquaternized bipyridines) with no detectable level of electronic communication between them. Surprisingly, compounds , and exhibit more complicated electrochemical behavior, which simplifies and becomes more reversible as the temperature increases.