Mechanistic Studies of Ligand Fluxionality in [Mo(ç5-Cp)(ç1-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. © 2009 American Chemical Society.