N-Heterocyclic silylenes as ambiphilic activators and ligands

Abstract

This frontiers article highlights recent developments of the use of N-heterocyclic silylenes (NHSis), the higher homologues of the Arduengo-carbenes, as ambiphilic activators and ligands in organometallic chemistry and provides a comparison of five-membered ring NHSi ligands with ubiquitous N-heterocyclic carbene (NHC) and phosphine ligands. The frontier orbital region of NHSis differs considerably from that of NHCs which results in different ligation properties. The donor properties of NHSis are closer to those of phosphines than to those of NHCs. NHSis reveal a much stronger tendency to act as bridging ligands between two metal centres than NHCs or phosphines and NHSi insertion reactions into metal–ligand bonds are more facile to achieve compared to similar insertion reactions of NHCs. These interesting properties clearly distinguish NHSi ligands from their NHC or phosphine counterparts and should provide novel reactivities in basic organometallic chemistry and catalysis.