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meso ‐Substituted Aromatic 34π Core‐Modified Octaphyrins: Syntheses, Characterization and Anion Binding Properties
Author(s) -
Anand Venkataramanarao G.,
Venkatraman Sundararaman,
Rath Harapriya,
Chandrashekar Tavarekere K.,
Teng Weijie,
RuhlandtSenge Karin
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200204537
Subject(s) - chemistry , protonation , substituent , thiophene , aromaticity , furan , pyrrole , ring (chemistry) , crystallography , proton nmr , crystal structure , stereochemistry , molecule , ion , organic chemistry
Abstract Modified octaphyrins with 34π electrons have been synthesized and characterized following a simple synthetic methodology. An acid‐catalyzed α , α 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 Δ δ 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 β ‐CH of the inverted heterocyclic ring and the carbonyl oxygen of the TFA. Furthermore, inter molecular interactions between the CH 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 Å between two octaphyrins.