Hexakis(4-(N-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 (1 6+), which can be reduced with Na/Hg in DMF to neutral 10. 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.
Han
Zhenfu
Z
Department of Chemistry and Center for Materials Innovation, Washington University, St. Louis, Missouri 63130, USA.
Vaid
Thomas P
TP
Rheingold
Arnold L
AL
D001555:Benzene Derivatives / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003500:Cyclization; D004563:Electrochemistry; D004583:Electrons; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011726:Pyridinium Compounds / Q000138:chemical synthesis / Q000737:chemistry*
D001555:Benzene Derivatives; D011726:Pyridinium Compounds; C527424:hexakis(4-(N-butylpyridylium))benzene