The activation of small molecule is a topic of high current interest. A variety of homogeneous end heterogeneous catalysts have been studied to be able to promote chemical transformation of industrial relevance under mild condition and therefore decrease the costs. Often the most performant catalysts are composed by rare and precious metals such as Pd, Pt, Rh, Ir, making the catalyst expensive and not suitable for large scale reactions. Lots of effort is put in researching ways to substitute precious and rare metal while keeping catalytic efficiency and selectivity. F-elements have shown to be able to perform many chemical transformations that are common to d-metals, promoting also in some cases unusual chemical reactivity. Differently from transition metals, f-elements present a unique coordina-tion chemistry, governed by electrostatic interaction with the ligand environment and steric constrain. During my PhD I focused my attention on the synthesis of highly reactive, low valent metal complex-es based of f-elements for the activation of small molecules. In particular, two main pathways have been followed to promote the multi-electrons transfer necessary for the transformation of the substrate: The first approach consists in the use of redox active ligands to support the metal centre and act as electron reservoir in order to increase the number of electrons exchanged during the reaction. This method has been used for d-, f- and d- mixed f-elements complexes, resulting to be an elegant way for the preparation of multimetallic compounds capable of promoting multi-electron transfer reaction. In the second approach, divalent classic lanthanides have been stabilized thanks to the bulky tris(tert-butoxide)siloxide ligand that resulted a to be a useful tool for the formation of highly reactive bimetal-lic complexes. The reactivity of the synthetized complexes towards small molecules such as CO2, CS2 and arenes has been tested, proving the ability of those compounds to act as multielectron reducing reagents. Moreo-ver, we proved that multidentate Schiff base ligands are capable of stabilizing low valent d-metal com-plexes allowing the formation bonding interaction between different metals with the enhancement of the magnetic properties.