In conclusion, we have computed by DFT calculations the full decomposition profile of the precatalytic species Ru5, Ru16 and Ru17. Interestingly, compounds Ru16 and Ru17 display higher kinetic barriers than their analogue Ru5, indicating a slower decomposition process of Ru16 and Ru17, in accordance with the experimental data reported in Figure . This behaviour is likely due to the steric hindrance of the additional second decker phenyl-and pentafluorophenyl groups, which induces a distortion of the bicyclic benzimidazolylidene scaffold and the consequent increase of the energies of the corresponding rate-determining steps (TS-1, TS-4 and TS-5). The similar energetic profiles obtained for the Ru16 and Ru17 species underlines the little effect of the aromatic-aromatic interaction, observed in Ru17, in the stabilisation of its potential energy surface with respect to Ru16.