Enhanced N-directed electrophilic C-H borylation generates BN-[5]- and [6]helicenes with improved photophysical properties

Kang Yuan, Daniel Volland, Sven Kirschner, Marina Uzelac, Gary S. Nichol, Agnieszka Nowak-Król, Michael J. Ingleson

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22 Citations (SciVal)

Abstract

Helicenes are chiral polycyclic aromatic hydrocarbons (PAHs) of significant interest, e.g. in supramolecular chemistry, materials science and asymmetric catalysis. Herein an enhanced N-directed electrophilic C-H borylation methodology has been developed that provides access to azaborine containing helicenes (BN-helicenes). This borylation process proceeds via protonation of an aminoborane with bistriflimidic acid. DFT calculations reveal the borenium cation formed by protonation to be more electrophilic than the product derived from aminoborane activation with BBr3. The synthesised helicenes include BN-analogues of archetypal all carbon [5]- and [6]helicenes. The replacement of a CC with a BN unit (that has a longer bond) on the outer helix increases the strain in the BN congeners and the racemization half-life for a BN-[5]helicene relative to the all carbon [5]helicene. BN incorporation also increases the fluorescence efficiency of the helicenes, a direct effect of BN incorporation altering the distribution of the key frontier orbitals across the helical backbone relative to carbo-helicenes.

Original languageEnglish
Pages (from-to)1136-1145
Number of pages10
JournalChemical Science
Volume13
Issue number4
DOIs
Publication statusPublished - 28 Jan 2022

Bibliographical note

Funding Information:
This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 769599 – MJI). We acknowledge SIRCAMS at University of Edinburgh for performing mass spectrometry and Dr Richard Brewster and Dr Ektoras Yiannakas (both University of Edinburgh) for their kind assistance with chiral HPLC analysis. A. N. -K. thanks the German Research Foundation (DFG) for the Emmy-Noether fellowship (No. 1459/1-1) and the Hector Fellow Academy for nancial support.

Data availability
Data associated with this article, including synthetic and computational details and compound characterization are available in the ESI.†

ASJC Scopus subject areas

  • General Chemistry

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