α-Metallocenylmethylium Ions and Their Isoelectronic Congeners: A Comparison Based on DFT Calculations

The geometrical parameters, net natural charges, and Wiberg bond indices of a series of alpha-metallocenylmethylium ions with 18 valence electrons were calculated using density functional theory. The transition metals considered were Cr, Mn, Fe, Mo, Re, W, Ru, and Os. As coligands to the fulvene-metal fragment we used benzene, cyclopentadienyl, and three CO units. We also examined the fulvene-metal fragments for Co, Rh, and Ir using a cyclobutadiene coligand. Trends in bond order between the exo-carbon atom of the fulvene unit (C6) and the metal atom as well as the bending angle of C6, alpha, and the net charges at C6 and the metal centers were analyzed. We found good correlation between alpha and the metal-C6 distance (d(1)). A comparison of the calculated values of alpha and d(1) with experimental data shows good agreement in cases where steric effects do not hamper the C6-metal interaction.