A Combined Experimental and Theoretical Study Examining the Binding of N-Heterocyclic Carbenes (NHC) to the CpRuCl (Cp = η5-C5Me5) Moiety:  Insight into Stereoelectronic Differences between Unsaturated and Saturated NHC Ligands

Combined solution calorimetric and quantum mechanics studies of reactions involving saturated and unsaturated N-heterocyclic carbene (NHC) ligands show that the difference in their relative bond dissociation energies is very small (1 kcal·mol-1). Structural and computational studies reveal small metric parameter differences. These observations in conjunction with relative reactivity profiles of NHC-modified ruthenium-based olefin metathesis catalysts suggest that very small changes in the donor properties of the NHC ligands can translate into significant differences in catalytic properties.