Aromatic interactions in the synthesis and conformation of two collapsible tetracationic cyclophanes

The conformations of tetracationic paracyclophane and metacyclophane derivatives containing quaternary salts of para-2,2-diazaterphenyl were investigated. The molecules were synthesized as the bromide and hexafluorophosphate salts which allowed solubility in aqueous and organic solvents. Molecular mechanics led to the notion that these cyclophanes would populate collapsed and open conformations in water and only populate open conformers in organic solvent. VT NMR studies indicated that the open and the collapsed conformers did not exchange on the NMR timescale. Large, positively charged clefts in one of these conformers bound flat anions between pyridinium rings as would molecular-scale tweezers.