2,6-Bis(imidazol-2-ylidene)pyridine Complexes of Lanthanoides: A Theoretical Study of the Bonding Situation and Selective Complexation

The coordination of a bis(NHC)pyridyl (NHC = N-heterocyclic carbene) ligand to d(0) fragments of group 3, lanthanide, and actinide series (M = Sc. Y, La, Sm, Lu, U, and Am) has been theoretically investigated at the DFT level. The influence of the pi-donation ability of the co-ligand has been emphasized by comparing the trichloro, trisamido fragments and bare ions. The coordination of the tridentate CNC ligand is dominated by the ligand -> metal sigma-donations, but unprecedented N-am -> C-carb back-bonding was evidenced in the trisamido complexes of La, Son, and Am. The ability of the bis(NHC)pyridine ligand B for lanthanide/actinide differentiation has been examined, substantiating the critical influence of the electronic properties of the co-ligand and carbene moieties.