An Experimental Acidity Scale for Intramolecularly Stabilized Silyl Lewis Acids

A new NMR‐based Lewis acidity scale is suggested and its application is demonstrated for a family of silyl Lewis acids. The reaction of p‐fluorobenzonitrile (FBN) with silyl cations that are internally stabilized by interaction with a remote chalcogenyl or halogen donor yields silylated nitrilium io...

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Bibliographic Details
Published in:Chemistry : a European journal 2019-11, Vol.25 (66), p.15123-15130
Main Authors: Künzler, Sandra, Rathjen, Saskia, Merk, Anastasia, Schmidtmann, Marc, Müller, Thomas
Format: Article
Language:English
Subjects:
Acidity
Acids
Cations
chalcogens
Chemistry
Ions
Lewis acids
NMR
NMR spectroscopy
Nuclear magnetic resonance
Organic chemistry
Probes
silicon
silyl cation
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Summary:A new NMR‐based Lewis acidity scale is suggested and its application is demonstrated for a family of silyl Lewis acids. The reaction of p‐fluorobenzonitrile (FBN) with silyl cations that are internally stabilized by interaction with a remote chalcogenyl or halogen donor yields silylated nitrilium ions with the silicon atom in a trigonal bipyramidal coordination environment. The 19F NMR chemical shifts and the 1J(CF) coupling constants of these nitrilium ions vary in a predictable manner with the donor capability of the stabilizing group. The spectroscopic parameters are suitable probes for scaling the acidity of Lewis acids. These new probes allow for the discrimination between very similar Lewis acids, which is not possible with conventional NMR tests, such as the well‐established Gutmann–Beckett method. The basis of natural sciences is to measure complex parameters, such as Lewis acidity. A new NMR‐based probe is suggested, which allows for the scaling of stabilized Lewis acids and complements the toolbox of methods for gauging Lewis acidity.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201903241