Evaluation of Extensive Sets of p-Block-Atom-Based Lewis Acids

Philipp Erdmann, Manuel Schmitt, Andreas Albers, Lukas M. Sigmund, Lutz Greb

The quantification and comparison of Lewis acidity is a fundamental concept in chemistry. A convenient comparison, however, is hindered by challenges in addressing the influence of molecular charge and solvation effects. In this study, we present a systematic analysis of 784 cationic Lewis acids, encompassing monocationic, dicationic, and tricationic species, alongside 149 neutral Lewis acids. The fluoride ion affinity (FIA) scale, a widely used metric, is evaluated with and without solvation correction [1,2] Our results reveal a charge-dependent clustering of FIA values, necessitating an altered approach for a unified acidity ranking. Solvation-corrected FIA_solv emerges as a robust metric that overcomes charge sensitivity, allowing for a coherent evaluation of Lewis acids. Further analysis demonstrates the significant impact of molecular volume on solvation-induced FIA damping, providing valuable insights for designing strong neutral and cationic Lewis acids. Exploring alternative scales such as ammonia, LiF, and NMe₄F affinity and counter anion effects highlight their limitations and reaffirms the advantages of solvation-corrected FIA_solv as a versatile and charge-independent metric for Lewis acidity. The general evaluation of Lewis Acidity is further extended by affinity datasets with other reference Lewis bases than F^– and compared with experimental data.[3]

Figure 1.

1. K. O. Christe, D. A. Dixon, D. McLemore, W. W. Wilson, J. A. Sheehy, J. A. Boatz, Fluorine Chem. 2000, 101, 151-153.
2. P. Erdmann, J. Leitner, J. Schwarz, L. Greb, ChemPhysChem 2020, 21, 987-994.
3. P. Erdmann, L. Greb, ChemPhysChem 2021, 22, 935-943.

 Philipp Erdmann