More importantly, both complexes Ru16 and Ru17 were shown to be significantly less susceptible towards decomposition than the known BIPh-supported complex Ru5. This enhanced stability gain was rationalised through a DFT study of the involved decomposition pathways. Although the aromatic rings of the second decker cannot prevent the rotation of the N-phenyl groups in Ru16 and Ru17, they strongly contribute to increase the energy of the rate-determining step, by imposing a strong distortion of the carbenic heterocycle through steric constraints. Among the transition states of the decomposition profile, those that show the most marked Gibbs free energy difference between the Ru5 complex and the Ru16 and Ru17 counterparts are TS-1 (28.8 vs 33.8 and 33.4 respectively), TS-4 (28.1 vs 35.1 and 36.1 respectively) and TS-5 (29.7 vs 33.7 and 34.7 respectively), involving, respectively, a Berry pseudo-rotation (TS-1), the proton transfer from one of the ortho positions of the N-phenyl groups to the nearby carbon atom of the benzylidene moiety (TS-4) and the migration of the benzylic proton to ruthenium with the simultaneous carboncarbon bond formation (TS-5). The observed increased stability of the ruthenium precursors Ru16 and Ru17 was also translated to the active species and enabled their implementation as highly efficient, stable pre-catalysts in challenging olefin metathesis reactions for the formation of tri-and tetra-substituted C-C double bonds. Complex Ru16, bearing the more electron-donating and trans effect inducting BI*Ph ligand, revealed more active than its Ru17 counterpart bearing the less electron donating BIF*Ph ligand.