Hexakis(4-(N-butylpyridylium))benzene:  A Six-Electron Organic Redox System

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 (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.

Guanidines as Reagents in Proton-Coupled Electron-Transfer Reactions and Redox Catalysts

“…The aromatic stabilization in the monocationic and dicationic forms was made responsible for their increased reduction power. 54 Another family of strong and neutral organic electron donors comprises viologens, which are easily oxidized to bipyridinium derivatives, and related compounds (like 'extended viologen' 55 and the reduced form of the hexacation hexakis [4-(N-butylpyridylium)]-benzene 56 (Figure 1). Murphy et al also synthesized bispyridinylidene compounds for use in the dehalogenation of aryl halides and other reactions.…”

Organic Electron Donors as Powerful Single‐Electron Reducing Agents in Organic Synthesis

“…[142] Recently, cyclic voltammetry of six-electron redox system 201 showed that 201 6+ is reversibly reduced to 201 2+ in one four-electron transfer and 201 2+ is reversibly reduced to 201 0 in one twoelectron transfer [E 1/2 (THF) = À0.58 and À0.69 V versus SCE; calibrated using Fc/Fc + ]. [143] Cyclic voltammetry of 202 showed a two-electron wave [E 1/2 (CH 3 CN) = À0.32 V versus SCE], although computational studies suggested that 202 could be a stronger two-electron reducing agent than 152 c in nonpolar solvents. [144] In other solvents, 152 c should be superior.…”

Expanded Pyridiniums: Bis‐cyclization of Branched Pyridiniums into Their Fused Polycyclic and Positively Charged Derivatives—Assessing the Impact of Pericondensation on Structural, Electrochemical, Electronic, and Photophysical Features

“…Fine‐tuning of the electrochemical properties of the dimers can be achieved by varying the following parameters:18a, 19 1) The interannular dihedral angle (that is, the degree of π delocalization),20 2) the connection scheme of the pyridinium rings, 3) the nature of the N pyridinio substituent (alkyl or aryl),14 and 4) the nature of the intervening linker (if any),21 which can even be switchable 22. The same approaches also hold for higher oligomers, even incorporating intervening spacers19 like star‐shaped tris‐23 and hexakis( p ‐ N ‐alkylpyridinium)benzene24 or other discrete entities like linear polypyridinium wires,25, 26 polyviologen dendrimers27 and rod‐like (1D) polymers 28. 29…”