Ist das [9]Annulenkation ein Möbius‐Annulen?

Bucher, Götz; Huenerbein, Robert; Auer, Alexander A.; Mucke, Eva; Köhler, Felix; Siegwarth, Jan; Herges, Rainer

doi:10.1002/ange.200900886

Cited by 5 publications

(2 citation statements)

References 42 publications

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“…According to Heilbronner’s model, organic compounds which possess 4 n π electrons may show aromatic character when p orbitals forming the π‐electron basis set lie on the surface of Möbius band 1. Although the Möbius aromaticity concept was used for the description of possible transition states7–9 and reactive intermediates,10, 11 the first example of a stable Möbius aromatic molecule was provided by the synthesis of the Herges annulene,12, 13 which was published almost forty years after Heilbronner’s article. Although the Heilbronner–Hückel theory was originally developed for monocyclic annulene systems, many examples of Möbius aromatics have been found among porphyrin‐like macrocycles 14–39…”

Section: Introductionmentioning

confidence: 99%

Hückel and Möbius Expanded para‐Benziporphyrins: Synthesis and Aromaticity Switching

Szyszko

Sprutta

Chwalisz

et al. 2014

Chemistry A European J

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The four expanded p-benziporphyrins A,C-di-p-benzi[24]pentaphyrin(1.1.1.1.1), N-fused A-p-benzi[24]pentaphyrin, A,D-di-p-benzi[28]hexaphyrin(1.1.1.1.1.1), and A,C-di-p-benzi[28]hexaphyrin(1.1.1.1.1.1) were obtained in three-component Lindsey-type macrocyclizations. These compounds were explored as macrocyclic ligands and as potential aromaticity switches. A BODIPY-like difluoroboron complex was obtained from the A,C-di-p-benzi[24]pentaphyrin, whereas A,C-di-p-benzi[28]hexaphyrin yielded a Möbius-aromatic Pd(II) complex containing fused pyrrole and phenylene subunits. Conformational behavior, tautomerism, and acid-base chemistry of the new macrocycles were characterized by means of NMR spectroscopy and DFT calculations. Free base N-fused A-p-benzi[24]pentaphyrin showed temperature-dependent Hückel-Möbius aromaticity switching, whereas the A,C-di-p-benzi[28]hexaphyrin formed a Möbius-aromatic dication.

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Section: Introductionmentioning

confidence: 99%

Hückel and Möbius Expanded para‐Benziporphyrins: Synthesis and Aromaticity Switching

Szyszko

Sprutta

Chwalisz

et al. 2014

Chemistry A European J

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“…Ähnlich schwer tun sich DFT‐Methoden bei hochdelokalisierten Strukturen, wie anhand der Isomere des [9]Annulene‐Kations (68) gezeigt wurde: aromatische Strukturen sind gegenüber nichtaromatischen bevorzugt. So zeigt sich unter Verwendung hochwertiger Ab‐initio‐Methoden in Verbindung mit Blitzlichtphotolysestudien, dass die günstigste Struktur von (68) am besten als leicht anti‐aromatisches oder nichtaromatisches Hückel‐Annulen zu betrachten ist; die Möbius‐Struktur (69) ist zwar rechnerisch isoenergetisch, wurde aber experimentell nicht beobachtet (Abbildung 44) 80…”

Section: Computational Organic Chemistryunclassified

Organische Chemie 2010

Bräse¹

2011

Nachr Chem

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Viability of Möbius Topologies in [26]‐ and [28]Hexaphyrins

Alonso

Geerlings

Proft

2012

Chemistry A European J

101

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Recently, hexaphyrins have emerged as a promising class of π-conjugated molecules that display a range of interesting electronic, optical, and conformational properties, including the formation of stable Möbius aromatic systems. Besides the Möbius topology, hexaphyrins can adopt a variety of conformations with Hückel and twisted Hückel topologies, which can be interconverted under certain conditions. To determine the optimum conditions for viable Möbius topologies, the conformational preferences of [26]- and [28]hexaphyrins and the dynamic interconversion between the Möbius and Hückel topologies were investigated by density functional calculations. In the absence of meso substituents, [26]hexaphyrin prefers a planar dumbbell conformation, strongly aromatic and relatively strain free. The Möbius topology is highly improbable: the most stable tautomer is 33 kcal mol(-1) higher in energy than the global minimum. On the other hand, the Möbius conformer of [28]hexaphyrin is only 6.5 kcal mol(-1) higher in energy than the most stable dumbbell conformation. This marked difference is due to aromatic stabilization in the Möbius 4n electron macrocycle as opposed to antiaromatic destabilization in the 4n+2 electron system, as revealed by several energetic, magnetic, structural, and reactivity indices of aromaticity. For [28]hexaphyrins, the computed activation barrier for interconversion between the Möbius aromatic and Hückel antiaromatic conformers ranges from 7.2 to 10.2 kcal mol(-1), in very good agreement with the available experimental data. The conformation of the hexaphyrin macrocycle is strongly dependent on oxidation state and solvent, and this feature creates a promising platform for the development of molecular switches.

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Ist das [9]Annulenkation ein Möbius‐Annulen?

Cited by 5 publications

References 42 publications

Hückel and Möbius Expanded para‐Benziporphyrins: Synthesis and Aromaticity Switching

Hückel and Möbius Expanded para‐Benziporphyrins: Synthesis and Aromaticity Switching

Organische Chemie 2010

Viability of Möbius Topologies in [26]‐ and [28]Hexaphyrins

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