Mechanistic studies of ligand fluxionality in [M(eta(5)-Cp)(eta(1)-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(eta(5)-Cp)(eta(1)-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(eta(5)-Cp*)(eta(1)-Cp)(CO)(2)] and [Fe(eta(5)-Cp)(eta(1)-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 eta(1)-eta(5) interconversion of the Cp binding mode is shown to be a high-energy process, consistent with experimental observations. The L substitution reactions by eta(1)-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.