Unveiling M?bius/Hckel Topology and Aromaticity in A Core-Expanded [10]Annulene at Different Oxidation States

The exploration of annulene's conformation, electronic properties and aromaticity has generated enduring interest over the years, yet it continues to present formidable challenges for annulenes with more than ten carbon atoms. In this study, we present the synthesis of a stable [10]cyclo-para-phenylmethine derivative (1), which bears a resemblance to [10]annulene. 1 can be readily oxidized into its respective cations, wherein electrons are effectively delocalized along the backbone, resulting in different conformations and aromaticity. Both 1 and its tetracation (14+ & sdot; 4SbF6-) exhibit a nearly planar conformation with a rectangular shape, akin to the E,Z,E,Z,Z-[10]annulene. In contrast, the radical cation (1 & sdot;+ & sdot; SbCl6-) possesses a doubly twisted Huckel topology. Furthermore, the dication (12+ & sdot; 2SbCl6-) displays conformational flexibility in solution and crystalizes with the simultaneous presence of Mobius-twisted (1a2+ & sdot; 2SbCl6-) and Huckel-planar (1b2+ & sdot; 2SbCl6-) isomers in its unit cell. Detailed experimental measurements and theoretical calculations reveal that: (1) 1 demonstrates localized aromaticity with an alternating benzenoid/quinoid structure; (2) 1a2+ & sdot; 2SbCl6- and 1b2+ & sdot; 2SbCl6- with 48 pi electrons are weakly Mobius aromatic and Huckel antiaromatic, respectively; (3) 14+ & sdot; 4SbF6- exhibits Huckel aromaticity (46 pi) and open-shell diradical character. A core-expanded [10]annulene analog was synthesized and oxidized to its cationic states. These compounds exhibit notable structural flexibility, allowing for topological twisting. The dication displays a simultaneous presence of singly twisted and planar isomers within the crystal structure, distinguished by Mobius aromaticity and Huckel antiaromaticity, respectively. The tetracation shows Huckel aromaticity and open shell diradical nature. image