Mechanistic studies of ligand fluxionality in [M(η-Cp)(ηC-Cp)(L) ₂]ⁿ

Density functional theory has been used to provide a thorough investigation of the mechanistic factors affecting Cp ligand fluxionality in a series of organometallic complexes, [M(η⁵-Cp)(η¹-Cp)(L) ₂]ⁿ, involving different metals, different oxidation states, and different ligands. Excellent agreement with experiment for the barrier heights for the 1,5-shift were obtained for the complexes [Fe(η⁵-Cp*)(η¹-Cp)(CO)₂] and [Fe(η⁵-Cp)(η¹-Cp)- (CO)₂]. For the range of complexes studied, the barriers have been successfully rationalized in terms of hyperconjugation, metal-Cp bond strength, and steric effects. In addition, the η¹-η⁵ interconversion of the Cp binding mode is shown to be a high-energy process, consistent with experimental observations. The L substitution reactions by η¹-Cp are quite sensitive to the nature of the metal center and ancillary ligand. A detailed theoretical explanation of the factors involved in all of these transformations is provided.