Premium
Negative Charge as a Lens for Concentrating Antiaromaticity: Using a Pentagonal “Defect” and Helicene Strain for Cyclizations
Author(s) -
Zhou Zheng,
Kawade Rahul Kisan,
Wei Zheng,
Kuriakose Febin,
Üngör Ökten,
Jo Minyoung,
Shatruk Michael,
GershoniPoranne Renana,
Petrukhina Marina A.,
Alabugin Igor V.
Publication year - 2020
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201911319
Subject(s) - helicene , antiaromaticity , deprotonation , delocalized electron , chemistry , aromaticity , crystallography , ring (chemistry) , photochemistry , conjugated system , stereochemistry , molecule , organic chemistry , polymer , ion
Incorporation of a five‐membered ring into a helicene framework disrupts aromatic conjugation and provides a site for selective deprotonation. The deprotonation creates an anionic cyclopentadienyl unit, switches on conjugation, leads to a >200 nm red‐shift in the absorbance spectrum and injects a charge into a helical conjugated π‐system without injecting a spin. Structural consequences of deprotonation were revealed via analysis of a monoanionic helicene co‐crystallized with {K + (18‐crown‐6)(THF)} and {Cs + 2 (18‐crown‐6) 3 }. UV/Vis‐monitoring of these systems shows a time‐dependent formation of mono‐ and dianionic species, and the latter was isolated and crystallographically characterized. The ability of the twisted helicene frame to delocalize the negative charge was probed as a perturbation of aromaticity using NICS scans. Relief of strain, avoidance of antiaromaticity, and increase in charge delocalization assist in the additional dehydrogenative ring closures that yield a new planarized decacyclic dianion.