In TS-1, the increase of the energy from , ongoing from Ru5 to Ru17 to Ru16 respectively, is mainly due to the insertion of additional phenyl or pentafluorophenyl planes parallel to the N-aryl rings, which constrains the Berry rotation process. This increased steric constrain is geometrically traduced by an out-of-plane distortion of the bicyclic benzimidazolylidene ligand, with the N1-C2-C3-C4 and N2-C7-C6-C5 dihedral angles deviating more and more from the expected 180° on going from Ru5 (-179.3 and 179.6°) to Ru17 (177.7 and -177.1°) and to Ru16 (175.1 and -174.7°) (Figure ). On the other hand, as displayed in Figures and, the analysis of the frontier MOs and NPA charges does not show any significant difference between the three species.