Computational QM/MM study on the structure and energetics of species involved in the activation of the C-H and C-S bonds of thiophene by Cp* RhPMe3

The hybrid quantum mechanics/molecular mechanics (QM/MM) method IMOMM is applied to the calculation of the reaction of thiophene with Cp*RhPMe3, which is a good experimental model for homogeneous catalytic hydrodesulfurization (HDS). The validity of the results is checked by comparison with previously reported full QM calculations on the same system. The geometries obtained with IMOMM are in good agreement with those obtained with full QM. Concerning the energies of the reaction path, differences from full QM results are found for steps involving a change in the oxidation state of the Rh atom. The effect of the methyl substituents on each reaction step is quantified and separated into steric and electronic contributions.