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An Experimental Acidity Scale for Intramolecularly Stabilized Silyl Lewis Acids
Author(s) -
Künzler Sandra,
Rathjen Saskia,
Merk Anastasia,
Schmidtmann Marc,
Müller Thomas
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201903241
Subject(s) - silylation , lewis acids and bases , chemistry , scale (ratio) , organic chemistry , catalysis , physics , quantum mechanics
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 19 F NMR chemical shifts and the 1 J (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.