Understanding the Binding Properties of N-heterocyclic Carbenes through BDE Matrix App

The interaction of N-heterocyclic carbene (NHC) ligands with transition metal centers is analyzed with a set of descriptors derived from the statistical treatment of density functional theory (DFT) computational results. These descriptors, labeled as hidden descriptors (HD), had been previously defined in our group and here are applied with the help of a user-friendly web application developed for that purpose: BDE Matrix App. Five HDs are computed with little computational effort for each NHC under consideration. Expectations are confirmed in that the binding to the metal center is largely ruled by the first two descriptors, suitably associated to sigma donation and pi backdonation, and the approach leads to a straightforward comparison of their quantitative values. The study is extended beyond NHCs, and other neutral ligands, such as cyclopropenylidenes, phosphines, and amines are considered. The procedure is shown to be well suited to provide a unified framework for the comparison of these diverse ligands.