Influence of the Transition-Metal Fragment on the Reactivity of Metallaanthracenes.

The influence of the nature of the transition-metal fragment on the Diels-Alder reactivity of metallaanthracenes has been explored computationally within the Density Functional Theory framework. It is found that the cycloaddition reactions with maleic anhydride become kinetically less favored for those processes involving metallaanthracenes compared with the analogous reaction involving the parent anthracene. The origins of this reduction in the Diels-Alder reactivity have been quantitatively analyzed in detail by using the activation strain model of reactivity in combination with the energy decomposition analysis method. In general, the transition-metal fragment makes the interaction energy between the reactants significantly lower, particularly at the transition state region, which is translated into a higher activation barrier. In addition, the influence of the aromaticity strength of the metallabenzene present in the considered metallaanthracenes on the barriers of the cycloaddition reactions has also been assessed.