Chiral Molecular Propellers of Triarylborane Ammonia Adducts. Issue 6 (10th December 2020)

• Record Type: Journal Article
• Authors: Kemper, Michael; Engelage, Elric; Merten, Christian
• Is Part Of: Angewandte Chemie international edition. Volume 60:Issue 6(2021)
• Page Start: 2958
• Page End: 2962
• Publication Date: 2020-12-10
• Subjects: chirality -- circular dichroism -- molecular propeller -- stereochemistry -- vibrational spectroscopy; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202014130
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Chiral molecular propeller conformations have been induced to various triaryl structures including trityl derivatives and triaryl boranes. For borane–amine adducts, such induced propeller chirality has not been reported yet due to the low energy barrier for racemization in common triarylboranes such as B(C6 H5 )3 or B(C6 F5 )3 . Herein, we demonstrate that point chirality in side chains of chiral triarylborane–ammonia adducts, which feature intramolecular hydrogen bonds in addition to the dative N→B bond, can efficiently be transferred to triarylborane propeller chirality. Employing X‐ray crystallography and ECD/VCD spectroscopy for structural characterizations, we investigate three examples with different steric demands of the incorporated chiral alkoxy side groups. We elucidate the conformational preferences of the molecular propellers. Furthermore, we show that computationally predicted conformational preferences obtained for the isolated, only implicitly solvated molecules are actually opposite to the experimentally observed ones. Abstract : Using VCD spectroscopy as key analytical tool, it was found that point chirality in side chains of chiral triarylborane–ammonia adducts, which feature intramolecular hydrogen bonds in addition to the dative N→B bond, can efficiently be transferred to triarylborane propeller chirality.