Hydration of Polycationic [5]Radialene with Quintuple 1,3-Dithiol-2-ylidenes Leads to a New Class of π-Extended Tetrathiafulvalene Scaffold.

[5]Radialene with quintuple 4,5-benzo-1,3-dithiol-2-ylidenes (DTs) easily forms a stable polycationic salt (1)4+ (BF4 - )4 owing to its aromatic character in the central cyclopentadienide ring. In this work, it was found that the polycationic salt (1)4+ underwent a hydration reaction in moist polar solvent to give several unexpected products, namely, an oxygen adduct dicationic salt (2)2+ , a tetrathiafulvalene (TTF) vinylogue (3) with 1,4-dithiine-2(3H)-one moieties, and an oxygen adduct of π-extended TTF with a cyclopentenone core (4). Their molecular structures were fully determined by X-ray crystal-structure analysis. In this reaction, irreversible hydration to the polycationic salt might either initiate the ring expansion and lead to the successive hydration at the specific cationic DT ring (for 3), or promote the transannular reactions to the next DT ring followed by elimination of the DT ring (for 4). Cyclic voltammetry and differential pulse voltammetry measurements for compound 3 indicated the occurrence of multi redox process resulting from electronic delocalization on the vinylogous TTF moiety. The electronic structures of the cationic species of 3 were also investigated by electronic spectra.