Hexakis(4-(<i>N</i>-butylpyridylium))benzene: A Six-Electron Organic Redox System

The cobalt-catalyzed cyclotrimerization of bis(4-pyridyl)acetylene affords hexakis(4-pyridyl)benzene in moderate yield. Alkylation with n-butyltriflate gives hexakis(4-(N-butylpyridylium))benzene triflate (16+), which can be reduced with Na/Hg in DMF to neutral 10. A single-crystal X-ray diffraction structure reveals that 10 has a chair-cyclohexane-like core and a [6]radialene structure. Cyclic voltammetry shows that 16+ is reversibly reduced to 12+ in one four-electron step and 12+ is reversibly reduced to 10 in one two-electron step. A reduction by four electrons at one potential is unprecedented for a molecule in which the electrochemically active centers are in electronic communication. The large structural transformation from 16+ to 10 is responsible for the “potential inversion” in the cyclic voltammetry, and DFT calculations suggest a possible structure for the stable intermediate 12+. A comparison is made to the electrochemistry and structural transformations in a previously prepared [4]radialene analogue of 10.