Bonding of N-Heterocyclic Carbenes on Metal Nanoparticles

This work studied the bonding of N-heterocyclic carbenes (NHCs) with systematic modifications to their structures, including their wingtips, functional groups, back- bones, metal surfaces, and orientation. We apply two separate analysis methods: en- ergy decomposition analysis with natural orbitals for chemical valence (EDA-NOCV) and intrinsic bonding orbitals (IBOs). We determined that the binding energy of these systems is described almost entirely by the orbital interaction energy as obtained by EDA-NOCV due to the dispersion being cancelled by the steric repulsion. We further explore the σ and π orbitals and how they change across systems. Finally, bis- complexes were explored via IBO, EDA-NOCV, and energy differences as compared to the monomeric versions. The two σ bonds connected the NHCs to the central Au atom are proposed to be 4-electron, 3-center bonds. We note that this is likely an accurate way to view bonds of monomeric NHCs on metal surfaces as well.