EPFL Doctorate Award 2020 – Marta Falcone
Small Molecule Activation by Multimetallic Uranium Complexes
EPFL thesis n°9539 (2019)
Thesis director: Prof. M. Mazzanti
For outstanding contributions to fundamental uranium chemistry and its application in dinitrogen conversion to ammonia.
The development of new processes for the selective and sustainable transformation of abundant small molecules constitutes one of the major research areas in inorganic and organometallic chemistry. These molecules such as CO2, CO, N2 and H2 are abundant reservoirs of chemical energy, readily available sources of carbon, nitrogen and hydrogen. In a patent from 1909, Haber reported that uranium and uranium nitride were very efficient catalysts for ammonia synthesis. In order to perform multielectron transfer, multimetallic complexes need to be designed. Reactivity of uranium bridging nitrides remained unexplored since we investigated the nitride-based reactivity of a dinuclear uranium(IV) complex. Beyond the nitride-ligand based reactivity, we were interested in accessing the diuranium(III) bridging nitride complex, combining the high reducing power of U(III) with the high flexibility of the siloxides. This approach led to the four-electron reduction of dinitrogen, followed by the complete cleavage upon addition of CO or H2. The nitride linker is nonetheless, too reactive to act as a spectator and it is involved in reactivity. Hence, we target the isolation of the analogue dinuclear U(III) complex with an oxide ligand as linker. This complex led to different reactivity, related to the more ionic character of the U-O bond.