The Field of Main Group Lewis Acids and Lewis Superacids: Important Basics and Recent Developments

Abstract

New developments in the field of Lewis acidity are highlighted, with the focus of novel Lewis acids and Lewis superacids of group 2, 13, 14, and 15 elements. Several important basics, illustrated by modern examples (classification of Donor‐Acceptor (DA) complexes, amphoteric nature of any compound in terms of DA interactions, reorganization energies of main group Lewis acids and the role of the energies of frontier orbitals) are presented and discussed. It is emphasized that the Lewis acidity phenomena are general and play vital role in different areas of chemistry: from weak “atomophilic” interactions to the complexes of Lewis superacids.

Coordination of Al(C6F5)3vs. B(C6F5)3 on group 6 end-on dinitrogen complexes: chemical and structural divergences

“…We have shown that a two-channel activation by the means of a strongly electrophilic bis(borane) C 6 F 4 {B(C 6 F 5 ) 2 } 2 ( B 2 CF ) imparts significant activation to the diatomic molecule, up to the diazene-diide (N 2 2− ) state. 40 In the continuation of this work, we decided to study the coordination of the aluminium analogue of BCF , tris(pentafluorophenyl)alane – Al(C 6 F 5 ) 3 ( AlCF ) 47–56 – to group 6 dinitrogen complexes, in order to assess how the resulting Lewis pairs differ or not in terms of structure and reactivity with respect to BCF .…”

“…In ascending order, the latter has an FIA higher than B 2 CF (523 kJ mol −1 ), SbF 5 (490 kJ mol −1 ) (the reference of the LSA scale), and much higher than BCF (450 kJ mol −1 ). 53,56,62–65…”

“… 53 This singular aspect to form adducts with very weak donors ( vide infra ) suggests indeed higher electrophilic properties of AlCF vs. BCF, and it is now widely accepted that AlCF has a much stronger Lewis acid character than BCF. 56 From computational studies and compiled experimental data, AlCF is considered as an LSA, having a Fluoride Ion Affinity (FIA) 61 – acknowledged to be a way to estimate Lewis acidity – of 530 kJ mol −1 . In ascending order, the latter has an FIA higher than B 2 CF (523 kJ mol −1 ), SbF 5 (490 kJ mol −1 ) (the reference of the LSA scale), and much higher than BCF (450 kJ mol −1 ).…”