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Chemistry is the scientific study of the properties and behavior of matter. It is a physical science under natural sciences that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances. Chemistry also addresses the nature of chemical bonds in chemical compounds. In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant growth (botany), the formation of igneous rocks (geology), how atmospheric ozone is formed and how environmental pollutants are degraded (ecology), the properties of the soil on the moon (cosmochemistry), how medications work (pharmacology), and how to collect DNA

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

The fabrication of defined and high-quality metal nanostructures is an ongoing topic of research. Direct-write deposition of copper nanostructures is of great value for many fields of research and industrial applications. Focused electron beam induced deposition (FEBID) is an additive fabrication technique with extremely high resolution and versatility. Physisorbed, gaseous precursor molecules are locally dissociated by a finely focused electron beam resulting in volatile fragments which desorb and non-volatile fragments forming the deposit. When applying suitable deposition parameters, these deposits can be as small as the beam diameter and have ideally little to no contamination. For electron beam induced metal deposition, metal-organic compounds are chosen as precursors. However, organic ligand material is often co-deposited, which is detrimental to the depositâs properties. This work addresses the study of the perfluorinated copper carboxylate [Cu2(ÎŒ-O2CC2F5)4] (Cu2(pfp)4) and its aminated derivatives Cu2(EtNH2)2(pfp)4 and Cu2(tBuNH2)2(pfp)4 as viable FEBID precursors. 25 at.% of copper was achieved with the amine free compound, and 15 at.% with each of the two aminated complexes. Based on the chemical analysis of the deposits, electron-induced dissociation paths were proposed for the adsorbed species, demonstrating the influence of the ligand chemistry and fragmentation on the deposit composition. In parallel, the perfluorinated silver carboxylate Ag2(pfp)2 was reported and compared directly to its copper equivalent. The silver complex yielded up to 74 at.% metal content and exhibited strong susceptibility to varying electron beam densities throughout the deposit. Cu2(pfp)4 did not manifest the same electron sensitivity. Theoretical models, combining analytical solutions with Monte Carlo simulations of primary and backscattered electrons were successfully fitted to the cross sections of deposits from both carboxylates, determining the growth regimes within a single spot deposit. Additionally, two previously reported Î²-diketonates, Cu(hfac)2 and Cu(tbaoac)2, were directly compared to the other Cu(II) precursors with the aim to determine any dependence of the ligand size, electron density or dwell time on the deposit purity. The investigations concluded that the metal content rather depends on the chemistry of the metal-ligand bond than on the ligand size. This applies to both, the variation of ligands and the variation of the metal center. vii Furthermore, two copper complexes, Cu(hfac)2 and Cu2(pfp)4, were investigated in situ with a dedicated, custom-made setup. The âeQCMâ combines a low energy electron source (10- 100 eV) with a quartz crystal microbalance and serves to study fundamental processes occurring during FEBI deposition. First results yielded the total dissociation cross section for each precursor at varying electron energies. Finally, alternative approaches for the electron induced copper deposition from Cu2(pfp)4 were investigated. A two-step post-purification recipe of as-deposited material was reported to yield pure copper crystals (> 97 at.%). Additionally, direct electron beam lithography in a layer of condensed precursor was explored. This room temperature deposition approach yielded in lower metal contents but could potentially produce high resolution deposition.

EPFL2020

Stabilizing Unusual Oxidation States of Lanthanides in Molecular Complexes: Synthesis, Properties, and Reactivity

Aurélien René Willauer

The chemistry of divalent lanthanides has generated increasing interest in the past years due to their redox properties and unique reaction pathways. Notably, molecular complexes of low-valent lanthanides have been shown to be suitable one-electron reductants that are able to activate inert small molecules such as heteroallenes and dinitrogen in mild conditions. Lanthanide(II) complexes usually undergo mono-electron transfer, but multi-electron transfer can be achieved through multiple one-electron processes in polymetallic complexes. The first part of this thesis describes attempts to expand the redox chemistry of lanthanide complexes and lays the basis for a wider understanding of the chemical and reductive properties of low-valent polynuclear lanthanide complexes. Thus, Chapter 2, 3, and 4, reports the synthesis and characterization of different polynuclear lanthanides(II) complexes of various siloxide ligands. In Chapter 2, the outcome of carbon dioxide reduction (oxalate versus carbonate) by dinuclear Ln(II) tris(tert-butoxy)siloxide complexes, depending on the solvent polarity and on the nature of the Ln ions, was investigated. Furthermore, unprecedented reduction products could be isolated from the reaction with CS2, providing the first example of acetylenedithiolate ligand formation from metal reduction of carbon disulphide. In all cases, it has been shown that cooperative binding of the substrate plays an important role in the outcome of the reaction. Chapter 3 describes a rational route to the first metallasilsesquioxane of a dinuclear divalent lanthanide which can selectively effect the reductive disproportionation of CO2 and the two-electron reduction of azobenzene. In an attempt to confer increased reductive reactivity to Eu(II) ions, Chapter 4 describes the use of the tetraphenyldisiloxanediolate ligand to form polynuclear complexes of Eu(II) that can initiate for the first time carbon dioxide activation by Eu(II) ions in an isolated complex.Differently, until 2019, the +IV oxidation state of lanthanide in molecular complexes remained limited to a single lanthanide ion, cerium. It is only recently that the terbium ion was shown to be able to access the +IV oxidation state in molecular complexes. However, given the broad applications of cerium(IV), the discovery of other molecular complexes of Ln(IV) is of great interest for chemists. Chapter 5 describes the synthesis of the third example of a Tb(IV) complex displaying an open coordination sphere and the very first report of a molecular complex of praseodymium in the +IV oxidation state. The novel Ln(IV) complexes were characterized by UV-Visible, NMR, EPR and IR spectroscopy, magnetometry, single-crystal X-ray diffraction analysis, cyclic voltammetry, and computational studies. In particular, this provided an opportunity to measure and study the luminescent spectra of Pr(IV) for the first time, which upon binding to the siloxide ligand results in a large shift of the ligand triplet state. Furthermore, these complexes have been shown to be appropriate starting materials for the synthesis of Ln(IV) phosphine oxide adducts. Preliminary studies directed towards the isolation of Nd(IV) molecular complexes are discussed.

EPFL2022

Synthetic methodologies for C-C and C-N bond formation involving alkyl radicals

Guido Barzanò

C-C and C-N bonds are some of the most common structures in molecules ranging from drugs to catalysts and to food additives. Many coupling reactions were developed to form these types of bonds with excellent selectivity and good performance. Still, the synthesis of some of those species either depends on traditional methods or requires expensive and rare reagents and catalysts. The use of precious metals in chemistry, and particularly in the industry, can make molecular synthesis expensive and energy-intensive since the extraction of those materials is costly. Moreover, in homogeneous catalysis, the recovery of metal-based catalysts is almost impossible, making these processes unsustainable for the future. Thus, the discovery of chemical reactions that donât involve precious materials is indispensable. This thesis concentrates on the development of two chemical transformations, one performing an sp2-sp3 radical reductive coupling, one performing a photocatalyzed alkyl amination, involving inexpensive reagents and catalysts. The first chapter reviews the existing methodologies which use alkyl radicals to form carbon-carbon and carbon-nitrogen bonds. Alkyl radicals are formed from alkyl halides and pseudo-halides (Acids, esters, tosylates, etc.) via oxidation or reduction performed by metal or photoredox catalyst. The wide variety of available methodologies was illustrated, highlighting the advantages and weaknesses of each reaction. The second chapter of this dissertation is devoted to the development of a new iron-based catalytic method to form stereoselectively Z-alkene boron species from the corresponding boron-alkyne. This novel stereoselective method opens a new way to obtain these types of molecules with cheap reagents, in high yields, with excellent stereoselectivity (Z:E ratio >10:1), and with good tolerance of functional group. The reaction is radical based, avoiding the problem of beta-hydride elimination, which usually occurs in ionic reactions involving metal centers. In order to prove the versatility of this method, the vinyl boron compound formed from this reaction was used for further functionalizations. The formal total synthesis of a 5-HT2c receptor agonist was successfully performed, improving the overall yield of the process, and avoiding the use of expensive and polluting chemicals. The third chapter of this thesis is concentrated on the development of a tandem photoredox/metal base catalyzed functionalization of anilines and imines with alkyl carboxylic esters. In this reaction, no late transition metal is used, and the traditional metal-based photocatalyst is substituted with an inexpensive and more efficient organic dye. The alkylation of amines is a challenging topic in organic chemistry and classical nucleophilic substitution lacks selectivity and scope. Harvesting visible light with a photoredox catalyst opens the possibility to a radical pathway, making this coupling easy and with high tolerance for functional groups. In order to understand the catalytic cycle of the reaction, additional mechanistic studies were conducted, leading to some insight on how this reaction works.

EPFL2020

Synthetic methodologies for C-C and C-N bond formation involving alkyl radicals

Guido Barzanò

EPFL2020

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

EPFL2020

Stabilizing Unusual Oxidation States of Lanthanides in Molecular Complexes: Synthesis, Properties, and Reactivity

Aurélien René Willauer

EPFL2022