Hexakis(4-(N-butylpyridylium))benzene: A Six-Electron Organic
Redox System
Zhenfu Han,Thomas P. Vaid,* andArnold L. Rheingold
Department of Chemistry and Center for Materials Innovation, Washington University, St. Louis, Missouri
63130, and Department of Chemistry and Biochemistry, University of California, San Diego,
La Jolla, California 92093
vaid@wustl.edu
Received September 4, 2007
Abstract:
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.
