Oxidation of a Dithieno[3,4‐b:3′,4′‐d]thiophene Cyclic Dimer Containing a Planar Cyclooctatetraene Ring: Retention of High Antiaromaticity During Reactions

Abstract

One‐electron and peracid oxidations of dithieno[3,4‐b : 3’,4’‐d]thiophene cyclic dimer, which contains an antiaromatic planar cyclooctatetraene (COT) core, were conducted. The reaction of the cyclic dimer with SbCl5 produced isolable radical cation salts. Density functional theory (DFT) calculations showed that the spin density of the radical cation resides not on the COT ring but on the peripheral sulfur and carbon atoms in the thiophene unit with retention of high antiaromaticity based on the nucleus‐independent chemical shift (NICS). The peracid oxidation of the cyclic dimer was found to proceed not on the COT ring but on the bridging sulfur atom in the dithienothiophene moiety. The retention of the high antiaromaticity of the COT ring after the sulfoxide formation was experimentally confirmed based on the relative hardness, and also was theoretically supported by NICS calculations. Interestingly, the DFT calculations suggested that the high antiaromaticity does not enhance the reactivity towards the epoxidation on the COT ring.

On-Surface Synthesis of Square-Type Porphyrin Tetramers with Central Antiaromatic Cyclooctatetraene Moiety

“…By nuclear magnetic resonance analysis, a unique downfield shift was assigned to a paratropic current at the COT moiety . Indeed, an antiaromatic character is anticipated for COT that has its planarity enforced, e.g., by substituents. − From a theoretical perspective, the electron delocalization, the role of antiaromatic junctions, and spectroscopic properties were detailed for porphyrin arrays hosting Zn or Mg centers. ,, Thus, square-type porphyrin tetramers are model systems to address fundamental concepts such as global and local (anti)­aromaticity, which are intricate for porphyrinoids and large polycyclic arrays. ,− Furthermore, they present building blocks for extended two-dimensional crystals and heterocyclic polymers, with intriguing electronic, magnetic, and optical properties predicted from theoretical studies that evaluated infinite sheets with Zn and V at the porphyrin centers, − and an experimental realization reported very recently …”

Graphene‐induced planarization of cyclooctatetraene derivatives

“…In this context, we note that another approach for planarizing COT is oxidation or reduction. [27][28][29][30][31][32][33] While this planarization approach has more typically employed metal ions, recently, Cohen and co-workers studied the nanomechanical response of COT to application of an external gate voltage on a graphene device, predicting planarization upon electron-and hole-doping. 31 Closer to the context of the present work, it was further recently found that COT-derived π-extended diaza [8]circulenes planarize on a gold surface.…”