Electrophilic C–H Borylation of Aza[5]helicenes Leading to Bowl-Shaped Quasi-[7]Circulenes with Switchable Dynamics

The intrinsic relationship between helicenes and circulenes is of fundamental interest and importance in molecular engineering. Herein, electrophilic borylation of phenanthroline-derived aza[5]­helicenes is presented, resulting in the incorporation of a boryl unit into two termini of helicenes to af...

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Published inJournal of the American Chemical Society Vol. 144; no. 48; pp. 22316 - 22324
Main Authors Zhang, Xiaolei, Rauch, Florian, Niedens, Jan, da Silva, Ramon B., Friedrich, Alexandra, Nowak-Król, Agnieszka, Garden, Simon J., Marder, Todd B.
Format Journal Article
LanguageEnglish
Published United States American Chemical Society 07.12.2022
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Summary:The intrinsic relationship between helicenes and circulenes is of fundamental interest and importance in molecular engineering. Herein, electrophilic borylation of phenanthroline-derived aza[5]­helicenes is presented, resulting in the incorporation of a boryl unit into two termini of helicenes to afford quasi-[7]­circulenes. Their bowl-shaped structures were determined by X-ray diffraction. UV–vis absorption and fluorescence spectroscopy, as well as electrochemical measurements and DFT calculations, gave insight into their electronic properties. Variable-temperature NMR studies and DFT calculations revealed bowl-to-bowl inversion at room temperature and bowl-to-helix equilibria at elevated temperature, highlighting the important role of B ← N bond strength in tuning their dynamic properties.
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ISSN:0002-7863
1520-5126
DOI:10.1021/jacs.2c10865