Lewis Acidic Boranes, Lewis Bases, and Equilibrium Constants: A Reliable Scaffold for a Quantitative Lewis Acidity/Basicity Scale

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 degrees C. Analysis with the linear free energy relationship log K-B=LA(B)+LBB allows equilibrium constants, K-B, to be calculated for any type of borane/Lewis base combination through the sum of two descriptors, one for Lewis acidity (LA(B)) 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 (Delta HBF3 ). Furthermore, this experimental platform can be utilized for the rational development of borane-catalyzed reactions.

Automated summary

A quantitative Lewis acidity/basicity scale has been established for boron-centered Lewis acids based on experimental equilibrium constants, allowing the calculation of equilibrium constants for borane/Lewis base combinations. The scale is independent of fixed reference acids/bases and applicable to various types of trivalent boron-centered Lewis acids. The scale is easily extendable through linear relationships with quantum-chemically calculated or common physical-organic descriptors and known thermodynamic data. This experimental platform can be used for the rational development of borane-catalyzed reactions.