What difference one double bond makes: Electronic structure of saturated and unsaturated n-heterocyclic carbene ligands in Grubbs 2nd generation-type catalysts

N-heterocyclic carbene (NHC) ligands are a versatile and useful class of ligands that have enjoyed much success over the past few decades in organometallic chemistry. This fact is exemplified most convincingly in Grubbs 2nd generation olefin metathesis catalysts. We explore the electronic impact of the NHC-ligand by decoupling electronic and steric effects through simplified model N-heterocyclic carbenes. Saturated and unsaturated N-heterocyclic carbene ligands give rise to fundamentally different frontier orbitals in these catalysts, suggesting a need to classify them as two electronically distinct ligand classes.

Graphical abstractWe explore the impact of the N-heterocyclic carbene (NHC) ligand on the electronic structure of the Ruthenium center in Grubbs olefin metathesis catalyst. Electronic and steric effects were decoupled through simplified model carbenes and the electronic difference between saturated and unsaturated NHC ligands was highlighted.Figure optionsDownload full-size imageDownload as PowerPoint slide