Theoretical studies of pi-loading and structural diversity in Cp3MX (M = Zr, Hf; X = H, CH3, OR, NR2) compounds

摘要

Density functional theory has been used to explore the bonding and geometric preferences of tris-Cp zirconium and hafnium compounds of the type Cp3MX. In most cases, two primary isomers were found: a "3-5" isomer, which contains three eta(5)-cp ligands, and a "2-5,1-1" isomer, which contains two eta(5)-Cp and one eta(1)-Cp ligands. The relative energies of these isomers are dependent upon the pi-donor ability of the X ligand. For the tris-Cp methyl compounds, the "3-5" isomers are more stable by 1-4 kcal/ mol. The "2-5,1-1" isomers of the tris-Cp alkoxide and amido compounds are more stable by 3-6 and 6-11 kcal/mol, respectively. Bonding analyses show these binding preferences can be understood in terms of pi-competition between the tris-Cp ligand set and the lone pair of the X ligand. pi-loading on the X ligand decreases the pi-donor ability of the "3-5" tris-Cp ligand set, which increases the preference for the "2-5,1-1" ground state geometry in the complexes with strong pi-donors. In addition, molecular orbital theory provides evidence for destabilization effects arising from filled-filled interactions between the "3-5" Cp3M fragment and the X lone pair. (c) 2005 Elsevier Ltd. All rights reserved.