Bis(3-methylthio-1-azulenyl)phenylmethyl Cations and Dications Connected by a 1,4-Phenylene Spacer: Synthesis and Their Electrochemical Properties

The preparation of bis(3-methylthio-1-azulenyl)phenylmethyl cations and 1,4-phenylenebis[bis(3,6-di-tert-butyl-1-azulenyl)methyl] dications was accomplished by the hydride abstraction of the corresponding hydride derivatives, which were synthesized by the acid-catalyzed condensation of 1-azulenyl methyl sulfide with benzaldehyde and terephthalaldehyde with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. The intramolecular charge transfer among the azulene ring and the methylium moieties of these cations and dications was investigated by UV–Vis spectroscopy and electrochemical analyses. The pKR+ values of the cations were examined for their thermodynamic stability spectrophotometrically. The voltammetry experiments of these cations revealed their reversible reduction waves on their cyclic voltammograms. Moreover, a notable spectral change of cations was observed by spectroelectrochemistry during electrochemical reduction conditions.

Azulene Moiety as Electron Reservoir in Positively Charged Systems; A Short Survey

The non-alternant aromatic azulene, an isomer of alternant naphthalene, differs from the latter in peculiar properties. The large polarization of the π-electron system over the seven and five rings gives to azulene electrophile property a pronounced tendency to donate electrons to an acceptor, substituted at azulene 1 position. This paper presents cases in which azulene transfers electrons to a suitable acceptor as methylium ions, positive charged heteroaromatics and examples of neutral molecules that can accept electrons. The proposed product synthesis was outlined and the expected electron transfer was highlighted by analyzing the NMR, UV-Vis spectra and the pKR+ values.

Charge delocalization and enhanced acidity in tricationic superelectrophiles

This Article presents the results from studies related to the chemistry of tricationic superelectrophiles. A series of triaryl methanols were ionized in Brønsted superacids, and the corresponding tricationic intermediates were formed. The trications are found to participate in two types of reactions; both are characteristic of highly charged organic cations. One set of reactions occurs through charge migration. A second set of reactions occurs through deprotonation of an unusually acidic site on the tricationic species. One of the tricationic intermediates has been directly observed by low temperature NMR spectroscopy. These highly charged ions and their reactions have also been studied using density functional theory calculations. As a result of charge migration, electron density at a carbocation site is found to increase with progression from monocationic to pentacationic structures.

Synthesis, properties, and redox behavior of di(1-azulenyl)(2- and 3-thienyl)methyl cations and dications composed of two di(1-azulenyl)methylium units connected with 2,5-thiophenediyl and 2,5-thienothiophenediyl spacers

The titled stable monocations, di(1-azulenyl)(2- and 3-thienyl)methyl cations 7a,b and 8a,b and dications composed of two di(1-azulenyl)methylium units connected with 2,5-thiophenediyl and 2,5-thieno[3,2-b]thiophenediyl spacers 9a,b and 10a,b were prepared by hydride abstraction of the corresponding methane derivatives. These mono- and dications 7a,b, 8a,b, 9a,b, and 10a,b showed high stability with large pK(R)+ values. The values of monocations 7a,b and 8a,b were 11.2-11.8 +/- 0.1 and 11.4-12.4 +/- 0.1, respectively. Two cation units in dications 9a,b and 10a,b were neutralized via one step at the pH of 11.1-11.7 +/- 0.1, which corresponds to the average of the pK(R)+ values of the dications and half-neutralized monocations. Electrochemical behavior of 7a,b, 8a,b, 9a,b, and 10a,b was examined by cyclic voltammetry (CV). Formation of the thienoquinoid products 18a,b and 19a,b from 9a,b and 10a,b was characterized by UV-vis spectroscopy under electrochemical reduction conditions. Chemical reduction of 9a,b and 10a,b with Zn powder in acetonitrile afforded 18a,b and 19a,b as deep-colored crystals, which exhibited rather high electron-donating ability.