Quantifying the Donor−Acceptor Properties of Phosphine and N-Heterocyclic Carbene Ligands in Grubbs’ Catalysts Using a Modified EDA Procedure Based on Orbital Deletion

Abstract

The σ-donation and π-acceptor properties of phosphine and N-heterocyclic carbene (NHC) ligands in first- and the second-generation Grubbs’ catalysts have been theoretically evaluated by means of a modified version of the energy decomposition analysis (EDA). According to the calculations, the NHC ligand is significantly more tightly bonded than the phosphine ligand as a consequence of the larger energetic contributions of the σ-donation, π-back-donation, and synergic effects. Despite its larger σ-donor strength, the NHC ligand is a slightly poorer charge σ-donor and better π-acceptor than phophine, explaining the recently observed overall poorer charge donation of the NHC ligand.