Synthesis of bis-2H and 4H-chalcogenapyrans and benzochalcogenapyrans via Pd catalyzed dimerization of Fischer type carbene complexes: redox properties and electronic structure of these new extended electron rich molecules

Extended electron rich bis-chalcogenapyrans and bis-benzochalcogenapyrans have been synthesized by Pd⁰ catalyzed dimerization of α- and γ-methylene chalcogenapyran and benzochalcogenapyran Fischer type carbene complexes. Voltammetric studies performed on these molecules show a single two-electron wave around 0 V versus SCE, which is ascribed to the oxidation of the neutral form in radical and dipyrylium cations. DFT calculations show that the oxidation leads to a rotating movement around the central C-C bond and suggest that the solvent plays a major role in the observation of the two one-electron systems. Furthermore, according to the structure, these molecules are likely to be reduced at very low potential (E=−1.5 V vs SCE) via a two-electron transfer reaction.