343329-33-9Relevant articles and documents
Dication species stabilized by heteroazulenes: Synthesis and properties of 1,3- and 1,4-bis[bis(2-oxo-2H-cyclohepta[b]furan-3-yl)methyliumyl]-, bis[bis(1,2-dihydro-N-methyl-2-oxocyclohepta-[b]pyrrol-3-yl)methyliumyl]benzene, and their related dications
Naya, Shin-Ichi,Nitta, Makoto
, p. 275 - 281 (2007/10/03)
A general synthetic route to a novel type of heteroazulene analogue of exceptionally stable dimethyliumbenzenes (16a-c·2PF6- and 17a-c·2PF6-) bearing 1,3-di- and 1,4-dimethylium groups substituted with four 2H-cyclohepta-[b]furan-2-one 9a, four 1,2-dihydro-N-methylcyclohepta[b]pyrrol-2-one 9b, and two 9a and two 9b, is reported. The synthetic method is based on a single and stepwise TFA-catalyzed electrophilic aromatic substitution on the heteroazulenes 9a and 9b with isophthalaldehyde and terephthalaldehyde to afford the corresponding 1,3- and 1,4-dimethylbenzene derivatives, followed by oxidative hydrogen abstraction with DDQ, and subsequent exchange of the counter-anion by using aq. HPF6 solution. In spite of the dicationic nature of 16a-c and 17a-c, they exhibited high stability with large pKR+ values due to the stabilizing effect of the heteroazulene units; however, we could not determine pkR+ and pKR++ values separately. Thus, the pKR+ values correspond to the average of the pH used to form neutralized dications and half-neutralized monocations. The electrochemical reduction of the cations exhibits irreversible waves and low reduction peak potentials upon cyclic voltammetry (CV); the values are discussed on the basis of the comparison with those of the related monocation species.