Monocyclisches (CH)9+ – ein Heilbronner-Möbius-Aren

Abstract

Fast dreißig Jahre unerkannt blieb das wahrscheinlich schon Anfang der siebziger Jahre als reaktive Zwischenstufe erzeugte monocyclische, C2‐symmetrische Kation (CH)9+ 1: Es ist das erste der bereits 1964 von Heilbronner vorhergesagten Möbius‐aromatischen [4n]Annulene.

Metalation of Expanded Porphyrins: A Chemical Trigger Used To Produce Molecular Twisting and Möbius Aromaticity

“…The concept of Möbius aromaticity, a postulate that states that aromatic characteristics will be observed for [4 n ]annulenes lying in a twisted Möbius strip, is a time‐honored concept that is fascinating from both the theoretical and experiment standpoints,1, 2 since it provides a natural complement to the well‐recognized idea of Hückel aromaticity that governs the properties of planar [4 n +2]annulenes (Figure 1). Although first suggested by Heilbronner for a ground‐state system early in 1964,1 and later put forth as being relevant to certain transition states3 and reactive intermediates,4 real Möbius aromatic systems proved elusive until the recent seminal report by Herges and co‐workers,5 wherein the first example of a Möbius aromatic hydrocarbon was disclosed. This system was obtained by the strategic lateral combination of a normal, planar conjugated segment with a belt‐shaped conjugated segment.…”

Möbius Antiaromatic Bisphosphorus Complexes of [30]Hexaphyrins

“…The concept of Möbius aromaticity, first proposed by Heilbronner in 1964,2 is simple and elegant, and has considerably stimulated both experimental and theoretical approaches toward Möbius aromatic molecules 1b,c. 3 However, the realization of Möbius aromatic systems is difficult, since the implementation of two conflicting structural features, that is, cyclic full π conjugation and a singly twisted topology, within a single macrocycle is not easy. Despite this difficulty, a seminal report by Herges and co‐workers described the synthesis and moderate aromaticity of a twisted [16]annulene molecule 4.…”

Expanded Porphyrin with a Split Personality: A Hückel–Möbius Aromaticity Switch

“…Even though Möbius aromaticity was first considered over 40 years ago,3 it is still more easily demonstrated in silico than in vitro. While Möbius‐type structures were proposed as transition states5–8 and reactive intermediates,9 the first examples of stable, neutral Möbius π systems have been synthesized only recently 10. 11 In those carefully designed molecules, developed by Herges and co‐workers, the twist was achieved by combining normal and in‐plane conjugation.…”