Terthiophene Radical Cations End-Capped by Bicyclo[2.2.2]octene Units: Formation of Bent π-Dimers Mutually Attracted at the Central Position

Citations Over TimeTop 10% of 2006 papers

Abstract

A terthiophene fused with bicyclo[2.2.2]octene units only at both ends was newly synthesized. Since there is no steric hindrance at the central position, this terthiophene has a possibility to interact only at the central position. One-electron oxidation of this terthiophene afforded a highly stable radical-cation salt as deep blue crystals. The result of X-ray crystal structural analysis demonstrated a characteristically bent pi-dimereric structure, which is formed by mutual attraction of single radical-cation species at the central position to minimize the steric repulsion. Remarkably short intermolecular distances between the central thiophene rings of each unit of the dimeric pair, that is, 2.976(10) A for Cbeta-Cbeta, 3.091(10) A for Calpha-Calpha, and 3.779(3) A for S-S, are good indication of the existence of attracting interaction, which was confirmed by theoretical calculations. This interaction was experimentally demonstrated by the reversible formation of the pi-dimer in CH2Cl2 solution using ESR and UV-vis-NIR spectroscopy. The crystal of the pi-dimer is in its singlet state and ESR silent in the solid state at 300 K, but the signal of a triplet state of the pi-dimer was observed by heating the solid at 400 K. This indicates that this pi-dimer has a quite small triplet-singlet enegy gap and the triplet state is thermally accessible.

Related Papers

• → Bicyclo[3.3.0]octanone formation by Fe(III) mediated ring expansion-transannular cyclisation reactions of cyclopropyl ethers(1998)12 cited
• → New β-ketophosphonates for the synthesis of prostaglandin analogues. 2 Phosphonates with bicyclo[3.3.0]octene and bicyclo[3.3.0]octane scaffolds linked to the β-keto group(2020)6 cited
• → Borontrifluoride-etherate induced rearrangement of bicyclo[2.2.2]octene-7,8-diones: An efficient synthesis of bicyclo[3.2.1]octene-2,8-diones(1996)11 cited
• → A novel skeletal rearrangement of bicyclo(2.2.2)octenes through bicyclo(3.2.1)octene system: synthesis of (±)-hinesol and (±)-10--hinesol(1988)5 cited
• → The stereochemistry of bicyclo[3.2.1]-octane—XII(1967)12 cited