Quantum chemical study of the structures and dynamic behavior of tricarbonyl complexes of Group 6 metals (Cr, Mo, W) with polyaromatic hydrocarbons using the density functional theory

Abstract

The quantum chemical study of the mechanism was performed for tricarbonyl η⁶-complexes of coronene I-M and kekulene II-M (M = Cr, Mo, W) by the density functional method. The activation barriers of η⁶,η⁶-interring haptotropic rearrangements (IHR), being the migration of the metaltricarbonyl group M(CO)₃ from one six-membered aromatic ring to another, were determined. The processes of η⁶,η⁶-IHR in the metal tricarbonyl complexes with relatively high polycyclic aromatic hydrocarbons (PAH) I and II occur with close energy barriers (ΔG^≠ ≈ 20—25 kcal mol^–1), which are lower than the barriers (ΔG^≠ ~ 30 kcal mol^–1) of similar transformations measured or calculated earlier for the chromium tricarbonyl complexes of naphthalene and its derivatives and other PAH. For the molybdenum tricarbonyl complexes the activation barriers of η⁶,η⁶-IHR decrease additionally by ~ 5 kcal mol^–1 compared to those for the chromium tricarbonyl complexes, whereas for the tungsten tricarbonyl complexes they increase again and become approximately equal to the activation barriers of similar chromium tricarbonyl complexes. All stationary states on the potential energy surface determining the mechanism of η⁶,η⁶-IHR are characterized by a decrease in hapticity compared to the initial and final complexes.