Cr(CO)3 activated Diels-Alder reaction on single-wall carbon nanotubes: a DFT investigation

The reaction mechanism and the effect of Cr(CO)3 on the Diels– Alder reaction of butadiene on (5,5) carbon nanotube sidewalls have been investigated by high-level DFT calculations. We investigated both concerted and stepwise reaction pathways on closed-shell and open-shell potential energy surfaces. In agreement with recent experimental evidence, we found the Cr(CO)3 metal fragment to considerably reduce the reaction energy barrier, both for the concerted and stepwise reaction mechanisms. The latter mechanism, previously found to be higher in energy with traditional substrates, appears to compete with the concerted mechanism on the carbon nanotube sidewalls. An analysis of the frontier molecular orbitals on the pristine and Cr(CO)3 -complexed carbon nanotubes allowed us to identify the reason for this inverted reactivity pattern and the role of the transition metal on the addition of the diene.