Hexakis(4-(N-butylpyridylium))benzene:: A six-electron organic redox system

[GRAPHICS] 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 (1(6+)), which can be reduced with Na/Hg in DMF to neutral 1(0). A single-crystal X-ray diffraction structure reveals that 1(0) has a chair-cyclohexane-like core and a [6]radialene structure. Cyclic voltammetry shows that 1(6+) is reversibly reduced to 1(2+) in one four-electron step and 1(2+) is reversibly reduced to 1(0) 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 1(6+) to 1(0) is responsible for the potential inversion in the cyclic voltammetry, and DFT calculations suggest a possible structure for the stable intermediate 1(2+). A comparison is made to the electrochemistry and structural transformations in a previously prepared [4]radialene analogue of 1(0).