A computational study of cycloaddition reactions of d8 metal tetroxide (Iron, Ruthenium, Osmium) complexes with C60

Abstract

The potential energy surfaces of the cycloaddition reactions MO₄(NC₅H₅)₂ + C₆₀ → MO₄(NC₅H₅)₂(C₆₀) (M = Fe, Ru, and Os) have been studied at the B3LYP/LANL2DZ level of theory. It has been found that there should be two competing pathways in these reactions, which can be classified as a [6,5]-attack (path A) and a [6,6]-attack (path B). Our theoretical calculations indicate that, given the same reaction conditions, the cycloaddition reaction of C₆₀via [6,6]-attack is more favorable than that via [6,5]-attack both kinetically and thermodynamically. This is in good agreement with the available experimental observations. A qualitative model, which is based on the theory of Pross and Shaik, has been used to develop an explanation for the barrier heights. As a result, our theoretical findings suggest that the singlet–triplet splitting ΔE_st (= E_triplet − E_singlet) of the d⁸MO₄(NC₅H₅)₂ and C₆₀ species can be a guide to predict their reactivity towards cycloaddition. Our model results demonstrate that the reactivity of d⁸ metal tetroxide cycloaddition to C₆₀ decreases in the order FeO₄(NC₅H₅)₂ > RuO₄(NC₅H₅)₂ > OsO₄(NC₅H₅)₂. In consequence, we show that both electronic and geometric effects play a decisive role in determining the energy barriers as well as the reaction enthalpy.