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

Four new brominated resorcinarene cavitand derivatives (3-6) and the already known tetrakis(bromomethyl)cavitand 2 have been synthesized, starting from the tetramethylcavitand 1. These brominated cavitands constitute excellent building blocks for the covalent assembly of new structures containing one (8), two (9 and 10), three (11) and four (7) 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 (12-16), or treated with monobromocavitand 3 to produce oligomeric structures containing from two to five cavitand units connected by viologen residues (17-21). Compounds 8-16, 18 and 20 show the electrochemical reactivity anticipated from their reducible units (mono- or diquaternized bipyridines) with no detectable level of electronic communication between them. Surprisingly, compounds 17, 19 and 21 exhibit more complicated electrochemical behavior, which simplifies and becomes more reversible as the temperature increases.