Effect of methyl substituents on the preferred conformations of Bis(pentadienyl) open metallocenes

Abstract

Density functional theory (DFT) methods indicated that the preferred geometries, spin states, and energetics of unsubstituted bis(pentadienyl)metal open sandwich complexes (C5H7)2M of the first row transition metals (M = Ti to Ni) are similar to those of the corresponding substituted and more stable (2,4-Me2C5H5)2M open sandwich complexes with 2,4-dimethylpentadienyl ligands. Structures with two fully bonded pentahapto η5-C5H7 ligands are energetically preferred for iron and for the transition metals to the left of iron in the Periodic Table. However, for the electron-rich first-row transition metals cobalt and nickel, structures with at least one trihapto η3-C5H7 ligand are preferred in order to prevent the electron configuration of the central metal atom from exceeding the favored 18-electrons. For the manganese systems (C5H7)2Mn and (2,4-Me2C5H5)2Mn the presence of the two methyl substituents is found to have little effect on the complicated potential energy surface with low-energy structures in the doublet, quartet, and sextet spin states.