<p>Since the discovery of cisplatin, metal complexes have been widely explored as anticancer agents. Ruthenium complexes stand out for their selectivity toward cancer cells, and some of them have reached human clinical trials. The broad availability of different ligands and metals enable detailed structure/activity relationship studies. In this work, we have studied a Ru complex containing a N-heterocyclic carbene (NHC) ligand, which are also very promising ligands by their chemical versatility and reduced side effects. This Ru-NHC complex, with an additional stabilizing tethered pyridine moiety, was modified to change the hydrophobic/hydrophilic balance and has been incorporated into nanosystems, as carbosilane (CBS) dendrimers, to play also with the size and multivalency of the new metallodendrimers. The antitumoral activity of these mono- and polymetallic systems was evaluated, and assays to identify their ROS or hydride-transfer properties were performed. Moreover, mitochondrial membrane potential and apoptosis were assessed using TMRM and Annexin V flow-cytometry assays to further explore the mechanism of action of dendrimers as model compounds. The results pointed out that hydrophobic chains and multivalency are key factors to improve anticancer activity.</p> Graphical Abstract <p></p>