Coordination's preference and electronic structure of N-heterocyclic carbene-monometallic complexes: DFT evaluation of sigma-bonding and pi-backbonding interactions

摘要

The geometrical parameters, the electronic structures and the nature of the chemical bonding for complexes of the type (NqMes)M[Cl(CO)(2)] (NqMes=naphtoquinone-annulated NHC ligand and M=V, Mn, Re, Co, Rh, Cu) which possess even electron counts have been investigated at the BP86 and B3LYP levels of theory using orbital molecular and energy decomposition analyses. The coordination of the six-membered ring is strongly disfavoured (structures A), while the structures B1 and B2 which differ by the orientation of the M[Cl(CO)(2)] unit are in competition with regard to the metal's nature and the spin state. The carbene-metal bonds are governed chiefly by electrostatic attractions contributing 65-75% of the bonding attractive interactions. The carbene-metal bonds are strong in electron-moderately rich Re element and weak in electron-rich Cu metal. In the most cases, orbital interactions are more important in symmetrical species than in the unsymmetrical ones, which are mainly described by sigma -bonding with the pi -backbonding part less than 20%.