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Updated: Nov 29, 2025

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
Published on: February 20, 2020
Lewis Acidic Boranes, Lewis Bases, and Equilibrium Constants: A Reliable Scaffold for a Quantitative Lewis
Robert J Mayer1, Nathalie Hampel1, Armin R Ofial1
1Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377, München, Germany.
Abstract:
A quantitative Lewis acidity/basicity scale toward boron-centered Lewis acids has been developed based on a set of 90 experimental equilibrium constants for the reactions of triarylboranes with various O-, N-, S-, and P-centered Lewis bases in dichloromethane at 20 °C. Analysis with the linear free energy relationship log KB =LAB +LBB allows equilibrium constants, KB , to be calculated for any type of borane/Lewis base combination through the sum of two descriptors, one for Lewis acidity (LAB ) and one for Lewis basicity (LBB ). The resulting Lewis acidity/basicity scale is independent of fixed reference acids/bases and valid for various types of trivalent boron-centered Lewis acids. It is demonstrated that the newly developed Lewis acidity/basicity scale is easily extendable through linear relationships with quantum-chemically calculated or common physical-organic descriptors and known thermodynamic data (ΔH ). Furthermore, this experimental platform can be utilized for the rational development of borane-catalyzed reactions.
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