Existence and stability of lanthanide-main group element multiple bonds.: New paradigms in the bonding of the 4f elements.: A DFT study of CP2CeZ (Z = F+, O, NH, CH-, CH2 and the ligand adduct CP2Ce(CH2)(NH3)

We theoretically investigate the stability and nature of metal-ligand multiple bonding between the tetravalent lanthanide element cerium and a number of different ligand sets that commonly form metal-ligand multiple bonds in transition element chemistry. A comparison of electronic structure and bonding in a homologous series of bent metallocene complexes CP2CeF+, CP2CeO, CP2Ce(NH), CP2Ce(CH2), and CP2Ce(CH)(-) and the Lewis base adduct CP2Ce(CH2)(NH3) is presented. A direct comparison of bonding between CP2CeO and the transition element analogue CP2HfO is also discussed. We present an analysis of the Ce 4f and 5d orbital contribution to metal-ligand sigma and pi bonding interactions in Cp(2)CeZ complexes and suggest the types of ligand systems that might support metal-ligand multiple bonds between 4f series and main group elements. In Cp(2)CeZ systems, we find that the Ce-Cp interactions are best described as largely ionic in nature, whereas the Ce-Z interactions have a stronger covalent component. The optimized Ce-Z bonds are short, and the bonding analysis indicates the formation of metal-ligand a and pi bonds. Our theoretical studies suggest that a unique hybridization of Ce 4f, 5d, and 6p valence orbitals results in formation of very covalent metal-ligand sigma bonds when compared to the transition element analogue. In contrast, the hybridization of Ce 4f and 5d valence orbitals in pi bonds results in weaker metal-ligand pi bonding than in the transition element analogue. The main result of the present computational study is the recognition that species with terminal multiple bonds between lanthanide ions (such as tetravalent cerium) and main group elements appear to be legitimate synthetic targets.