meso‐Substituted Aromatic 34π Core‐Modified Octaphyrins: Syntheses, Characterization and Anion Binding Properties

Abstract

Modified octaphyrins with 34pi electrons have been synthesized and characterized following a simple synthetic methodology. An acid-catalyzed alpha,alpha coupling of tetrapyrranes containing furan, thiophene and selenophene rings resulted in the formation of the respective octaphyrins in relatively good yield. Solution studies by (1)H NMR and 2D NMR methods and single crystal Xray structural characterization reveal an almost flat structure with two heterocyclic rings inverted. Specifically, in 14 two selenophene rings (one on each biselenophene unit) are inverted while in 15 two furan rings (one on each bifuran unit) are inverted when the meso substituent are mesityl groups. On changing the mesityl substituent to m-xylyl group as in 19, the location of ring inversion shifts to pyrrole rings (one on each bipyrrole unit) indicating the dependence of structure on the meso substituents. UV/Vis studies, both in freebase and protonated forms reveal typical porphyrinic character and the aromatic nature of the octaphyrins. The Deltadelta values evaluated by (1)H NMR spectroscopy also support their aromatic nature. The protonated forms of octaphyrins bind TFA anion in a 1:2 ratio. The TFA anions are located one above and below the plane of the octaphyrin macrocycle and they are held by weak electrostatic NH-O interactions similar to that observed for protonated rubyrins. However, in the present case, there is an additional non-electrostatic CH-O interaction involving beta-CH of the inverted heterocyclic ring and the carbonyl oxygen of the TFA. Furthermore, inter molecular interactions between the Cbond;H of the meso-mesityl group and the fluorine of CF(3) group of bound TFA leads to the formation of one-dimensional supramolecular arrays with interplanar distance of 13 A between two octaphyrins.

Core-Modified Expanded Porphyrins: New Generation Organic Materials

“…29 Specifically, the TFA anion complex of 77‚(TFA) 2 displays a fairly flat structure similar to that of tetrathia octaphyrin 75 ( Figure 10). The planarity of the macrocycle is slightly disrupted, probably Of the above four interactions, the first two are typical electrostatic interactions.…”

Figure Eights, Möbius Bands, and More: Conformation and Aromaticity of Porphyrinoids

“…[256] In another system, containing biselenophene and quaterthiophene subunits (84 d), the two selenophene rings are inverted (T0 C,D conformer). [61] Compounds 83d-H 2 and 84 d contain [34]annulenoid CPs and are both aromatic.…”

Figure‐Eight‐Strukturen, Möbius‐Bänder und mehr: Konformation und Aromatizität von Porphyrinoiden

“…A,E -Konformation und weisen zwei im Makrocyclus schräg gegenüberliegende, invertierte nichtpyrrolische Untereinheiten auf. [256] In einem anderen System mit Biselenophen-und Quaterthiophen-Untereinheiten (84 d) sind die beiden Selenophenringe invertiert (T0 C,D -Konformer). [61] Die Verbindungen 83d-H 2 und 84 d, die beide aromatisch sind, enthalten [34]Annulen-CPs.…”