In most classical examples of homogeneous catalysis, the focus resides on the metal center, which is the one that carries out the reaction, while the ligands play mainly a spectator role. Thus, the initial approach applied to modify the reactivity of a system was the replacement of the metal. This has been the starting point of the majority of work in homogeneous organometallic catalysis. The tuning of the electronic or steric properties of the ligands affects the metal, and can have a huge impact on the reaction outcome such as higher yields, better selectivity or suppression of undesired side reactions. The concept has been taken one step further upon the realization that ligands may have a more active participation in the main steps of the catalytic cycle. These ligands are known as non-innocent ligands owing to their reactive nature during a chemical process. This behaviour differs with and complements that of innocent ligands which “only” contribute through tuning of the metal. In this Thesis we present three computational studies where the ligands have an active role on the outcome of the reaction. We have been able to study with DFT tools the features and particularities of each system. These studies will ultimately contribute on the development of new systems based on metal-ligand cooperation and improve the understanding of the mechanism governing this reactivity.