Dinaphtho[2′,3′:5,6][1,4]dithiino[2,3-b:2,3-e]pyridine, its 16-butyl derivative and dinaphtho[2′,3′:5,6][1,4]dioxo[2,3-b:2,3-e]pyridine: novel heterocycles as electron donor compounds

Abstract

Dinaphtho[2′,3′:5,6][1,4]dithiino[2,3-b:2,3-e]pyridine (4a), its 16-butyl derivative (4b), and dinaphtho[2′,3′:5,6][1,4]dioxo[2,3-b:2,3-e]pyridine (5) have been prepared and fully characterized. The electrochemical properties of 4a, 4b and 5 have been studied by cyclic voltammetry in CH₂Cl₂∶trifluoroacetic acid (1∶1); in agreement with their donor character, they exhibit a first reversible oxidation wave to their radical cations with very similar potential peak values and a second irreversible wave to their dications, the lowest potential peak value of this second oxidation corresponding to 5. Their radical cations, generated by oxidation of the parent compounds, are relatively stable and have been analyzed in liquid solution by electron paramagnetic resonance (EPR). Spin density distributions in the SOMO have been calculated by the semiempirical MNDO method. Electronic spectra of 4a and 4b in trifluoroacetic acid show peaks at 417 and 401 nm, respectively, and in the presence of thallium(III) trifluoroacetate two characteristic peaks at λ_max 411 and 868 nm for 4a˙⁺, and at 411 and 872 nm for 4b˙⁺. X-Ray analysis of 4b shows a molecular structure with a stable chair-shaped conformation with interplanar angles between naphthalenes and the pyridine ring of 139.0(1) and 146.4(1)°.