Porphyrin/Quinoidal‐Bithiophene‐Based Macrocycles and Their Dications: Template‐Free Synthesis and Global Aromaticity. (19th December 2019)

• Record Type: Journal Article
• Authors: Ren, Longbin; Gopalakrishna, Tullimilli Y.; Park, In‐Hyeok; Han, Yi; Wu, Jishan
• Is Part Of: Angewandte Chemie. Volume 132:Number 6(2020)
• Page Start: 2250
• Page End: 2254
• Publication Date: 2019-12-19
• Subjects: Globale Aromatizität -- Makrocyclen -- Porphyrine -- Chinoide -- Thiophen; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.201911269
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: We report the template‐free synthesis and characterization of a new type of porphyrin/quinoidal‐bithiophene‐based conjugated macrocycle. X‐ray crystallographic analysis of the dimer (2MC ) revealed a cyclophane‐like geometry with large dihedral angles between the porphyrin and the neighboring thiophene rings, and NMR measurements and theoretical calculations confirmed a localized aromatic character of the porphyrin/thiophene rings and quinoidal character of the bithiophene linkers. Restricted rotation of the thiophene rings linked to the porphyrin unit was observed by variable‐temperature NMR measurements. The dication (2MC 2+ ) adopts a chair‐shaped conformation to facilitate π‐electron delocalization around the whole macrocycle. As a result, the molecule is globally aromatic, with a dominant 54 π conjugation pathway. The trimer (3MC ) also shows localized aromatic character of porphyrin rings and conformational flexibility, but its dication (3MC 2+ ) is rigid and globally aromatic with a dominant 82 π conjugation pathway. Abstract : Anpassungsfähige Porphyrin‐Makrozyklen : Makrozyklen, die aromatisches Porphyrin und chinoide Bithiopheneinheiten enthalten, wurden durch eine templatfreie Methode synthetisiert. Die Moleküle nehmen eine verzerrte Konformation mit lokaler Aromatizität im neutralen Zustand ein sowie eine mehr planare Geometrie mit globaler Aromatizität im dikationischen Zustand (siehe Bild).