Procédé Haber

Le procédé Haber est un procédé chimique servant à la synthèse de l'ammoniac (NH3) par hydrogénation du diazote (N2) gazeux atmosphérique par le dihydrogène () gazeux en présence d'un catalyseur. C'est en 1909 que le chimiste allemand Fritz Haber parvint à mettre au point ce procédé. Une équipe de recherche de la société BASF mit au point, en 1913, la première application industrielle du procédé Haber : c'est le procédé Haber-Bosch. Le responsable de son industrialisation, Carl Bosch, agissait à la fois comme superviseur de l'équipe et comme concepteur, apportant des solutions originales à certains problèmes posés lors de sa mise au point. Le procédé Haber-Bosch a une importance économique considérable, car il est difficile de fixer l'azote en grandes quantités et à un coût peu élevé, à l'aide des autres procédés mis au point. L'ammoniac peut ensuite être transformé en oxyde d'azote, puis en acide nitrique grâce au procédé Ostwald. Le sel d'am

Design, synthesis, reactivity, and magnetic properties of uranium based oxide and nitride complexes

Luciano Barluzzi

The activation of small molecules is a paramount challenge in modern chemistry. The use of cheap and abundant molecules such as N2, H2, CO2, or CO as energy supplies or as precursors for fine chemicals production is highly desirable. In particular, the only industrial process known so far that uses the ubiquitous molecule N2 is the Haber-Bosch process for the production of NH3, which consumes about 2% of the world energy yearly. Low valent uranium complexes have been proven to be ideal candidates in the field of small molecule activation such as N2. The activation of N2 in the Haber-Bosch process is thought to proceed through the formation of metal nitrides. The study of molecular nitride species, thus, is extremely important in light of the possibility to achieve N-functionalization processes. Uranium nitride species, indeed, are able to effect the activation of small molecules by N-functionalization. Low valent uranium species are of interest also for their magnetic properties. The magnetic anisotropy and the unpaired electron in U(III) species make them, indeed, ideal candidates as Single Molecule Magnets (SMM). The main objective of this thesis is to synthesize novel uranium species for the activation of small molecules and to synthesize low valent uranium species of interest for their magnetic properties. In the first part the synthesis of a dimeric U(III) complex bridged by an oxo linker and its reactivity with N2 will be reported. The functionalization of the activated N2 shows striking differences compared to previously reported complexes. The difference in reactivity is accompanied by a difference in the magnetic properties of the complexes, which reflects their different electronic structure and binding scheme. Since the full splitting of N2 could not be achieved so far with U(III) complexes, the synthesis of a bis-µ-nitride complex, which would serve as a model for cleaved N2, was targeted. Its synthesis and characterization are reported in Chapter 3. We proved that such a bis nitride complex is reactive and is able to activate small molecules, forming N-C bonds by reaction with molecules like CO2, CS2, or CO. More importantly, H2 is activated by the bis nitride complex in an unprecedented oxidative cleavage. While uranium nitride complexes supported by the siloxide ligand were reported to exhibit nucleophilic reactivity, other nitride complexes are instead unreactive or even electrophilic. In order to rationalize this behaviour, the synthesis of different uranium nitride complexes bearing different coligands has been targeted and their synthesis is described in Chapter 4. The importance of the coligand has been experimentally proven in closely related systems. Despite several bridging nitride complexes have been reported, a paucity of terminal uranium nitride complexes are, instead, isolable. In particular, the photochemical reactivity of terminal uranium azide complexes has so far failed to yield the desired terminal nitride species. In this work we report the first photochemical synthesis of an isolable uranium terminal nitride. The terminal nitride complex is remarkably stable and its functionalization with CO is reported. Lastly, the synthesis of low valent heteroleptic complexes is reported. These compounds can serve as starting materials for the synthesis of novel uranium complexes and are of interest for their magnetic properties.

EPFL2021

Four-electron Reduction and Functionalization of N₂ by a Uranium(III) Bridging Nitride

Marta Falcone, Marinella Mazzanti

N2 is a cheap and widely available but very unreactive molecule. Notably, the only industrial process for the conversion of dinitrogen is the Haber-Bosch process to form ammonia, but under very harsh conditions (high temperature and pressure). Here, we review our recent research leading to the reduction of dinitrogen by four electrons, under ambient conditions by a uranium(III) bridging nitride, K3 U-N-U, where two uranium(III) cations are linked by a nitride group and a flexible metal-ligand scaffold. We also show that the bound dinitrogen can be further functionalized under mild conditions: the addition of acid, hydrogen and protons or carbon monoxide to the uranium hydrazido complex yields to the cleavage of the N-N single bond and to the formation of new N-H and N-C bonds.

2018

Design, synthesis, reactivity, and magnetic properties of uranium based oxide and nitride complexes

Luciano Barluzzi

EPFL2021

Optimization of the Bosch process for micro-mold fabrication

Design, synthesis, reactivity, and magnetic properties of uranium based oxide and nitride complexes

Four-electron Reduction and Functionalization of N₂ by a Uranium(III) Bridging Nitride

Design, synthesis, reactivity, and magnetic properties of uranium based oxide and nitride complexes

Four-electron Reduction and Functionalization of N₂ by a Uranium(III) Bridging Nitride

Optimization of the Bosch process for micro-mold fabrication