Full exploration of the Diels-Alder cycloaddition on metallofullerenes M _3N@C _(80) (M=Sc, Lu, Gd): The D _(5h) versus I _h isomer and the influence of the metal cluster

摘要

In this work a detailed investigation of the exohedral reactivity of the most important and abundant endohedral metallofullerene (EMF) is provided, that is, Sc _3N@I _h-C _(80) and its D _(5h) counterpart Sc _3N@D _(5h)-C _(80), and the (bio)chemically relevant lutetium- and gadolinium-based M _3N@I _h/D _(5h)-C _(80) EMFs (M=Sc, Lu, Gd). In particular, we analyze the thermodynamics and kinetics of the Diels-Alder cycloaddition of s-cis-1,3-butadiene on all the different bonds of the I _h-C _(80) and D _(5h)-C _(80) cages and their endohedral derivatives. First, we discuss the thermodynamic and kinetic aspects of the cycloaddition reaction on the hollow fullerenes and the two isomers of Sc _3N@C _(80). Afterwards, the effect of the nature of the metal nitride is analyzed in detail. In general, our BP86/TZP//BP86/DZP calculations indicate that [5,6] bonds are more reactive than [6,6] bonds for the two isomers. The [5,6] bond D _(5h)-b, which is the most similar to the unique [5,6] bond type in the icosahedral cage, I _h-a, is the most reactive bond in M _3N@D _(5h)-C _(80) regardless of M. Sc _3N@C _(80) and Lu _3N@C _(80) give similar results; the regioselectivity is, however, significantly reduced for the larger and more electropositive M=Gd, as previously found in similar metallofullerenes. Calculations also show that the D _(5h) isomer is more reactive from the kinetic point of view than the I _h one in all cases which is in good agreement with experiments.