Why do cycloaddition reactions involving C60 prefer [6,6] over [5,6] bonds?

Area of Science:

• Computational Chemistry
• Organic Chemistry
• Physical Chemistry

Background:

• Fullerenes, specifically C60, exhibit regioselectivity in cycloaddition reactions.
• Experimental data shows a preference for [6,6] bond formation over [5,6] bonds.

Purpose of the Study:

• To computationally investigate the origin of the experimentally observed regioselectivity in C60 cycloadditions.
• To determine the key factors governing the preference for [6,6] over [5,6] bond formation.

Main Methods:

• Activation Strain Model (ASM) of reactivity.
• Energy Decomposition Analysis (EDA).
• Analysis of transition state aromaticity.

Main Results:

• The [6,6] reaction pathway exhibits more stabilizing interactions between deformed reactants compared to the [5,6] pathway.
• This stabilizing interaction is consistent along the entire reaction coordinate.
• Aromaticity of transition states was also considered.

Conclusions:

• The dominant factor controlling regioselectivity in C60 cycloadditions is the superior stabilizing interaction in the [6,6] pathway.
• Computational methods like ASM and EDA provide insights into reaction mechanisms and selectivity.