Evaluation of the σ-Donating and π-Accepting Properties of N-Heterocyclic Boryl Anions

The relative σ-donating and φ-accepting capacities of a range of synthetically relevant boryl anions have been evaluated by examining the geometric, thermochemical, and electronic properties of their adducts to the Li cation and Se atom, as compared to the properties of the analogous neutral N-heterocyclic carbenes (NHCs), by theoretical methods. The results indicate that boryl anions have a weaker φ-accepting capability compared to NHCs, but it is still a non-negligible factor in the bonding contributions between boryl and the Se atom. The tunability of the φ-accepting capacity of boryl anions is similar to that of NHCs, indicating a potential for the modification of the electronic properties of metal complexes incorporating either boryl or NHC ligands. In all cases, the boryl ligands were found to be superior σ-donors to NHCs. +