Pushing the Lewis Acidity Boundaries of Boron Compounds With Non‐Planar Triarylboranes Derived from Triptycenes

Bending the planar trigonal boron center of triphenylborane by connecting its aryl rings with carbon or phosphorus linkers gave access to a series of 9‐boratriptycene derivatives with unprecedented structures and reactivities. NMR spectroscopy and X‐ray diffraction of the Lewis adducts of these non‐...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2019-11, Vol.58 (47), p.16889-16893
Main Authors: Ben Saida, Ali, Chardon, Aurélien, Osi, Arnaud, Tumanov, Nikolay, Wouters, Johan, Adjieufack, Abel I., Champagne, Benoît, Berionni, Guillaume
Format: Article
Language:English
Subjects:
Acidity
Adducts
Aromatic compounds
Boron
Boron compounds
Carbon
Covalent bonds
Lewis acid
Lewis acids
Lewis base
Lewis superacid
Magnetic resonance spectroscopy
NMR
NMR spectroscopy
non-planar
Nuclear magnetic resonance
Phosphorus
triarylboranes
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Summary:Bending the planar trigonal boron center of triphenylborane by connecting its aryl rings with carbon or phosphorus linkers gave access to a series of 9‐boratriptycene derivatives with unprecedented structures and reactivities. NMR spectroscopy and X‐ray diffraction of the Lewis adducts of these non‐planar boron Lewis acids with weak Lewis base revealed particularly strong covalent bond formation. The first Lewis adduct of a trivalent boron compounds with the Tf2N− anion illustrates the unrivaled Lewis acidity of these species. Increasing the pyramidalization of the boron center and using a cationic phosphonium linker resulted in an exceptional enhancement of Lewis acidity. Introduction of a phosphorus and a boron atom at each edge of a triptycene framework, allowed access to new bifunctional Lewis acid‐base 9‐phospha‐10‐boratriptycenes featuring promising reactivity for the activation of carbon‐halogen bonds. Pyramid power: Owing to the drastic pyramidalization around the trivalent boron atom and the presence of a cationic phosphonium back‐side bridge, the Lewis acidity of the cage‐shaped 9‐bora‐10‐phosphonium triptycenes surpasses that of all trivalent boron Lewis acids generated to date.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201910908