Freigabe ab 11.05.2018 Iron Complexes with Nitrogen Ligands for Catalytic Hydrogenation of Olefins

The aim of this thesis was the investigation of different approaches towards the development of hydrogenation catalytic systems based on iron as cheap and environmentally friendly metal. The first chapter offers an overview of the last developments in the field of iron-catalyzed hydrogenation systems, special attention has been devoted on catalysts based on non-innocent ligand containing iron complexes, with the description of selected examples. The implementation of this redox active moieties granted to these complexes unseen properties resulting in astonishing results. In the second chapter a practical and simple hydrogenation system was described, the use of widespread available iron trichloride and lithium aluminumhydride as precursors allow facile implementation of this methodology in synthetic laboratories. Mono- and di-substituted olefins were converted under mild reaction conditions. Different functional groups were tolerated and mechanistic investigations indicated the presence of a homogeneous catalyst in the early stage of the reaction, less reactive nanoparticles are subsequently formed as result of aggregation. A different hydrogenation protocol was described in chapter 3. This catalyst, based on iron(II) bis(1,1,1,3,3,3-hexamethyl-disilazan-2-ide) or on a most friendly in situ generated iron amide, upon activation with diisobuthylaluminum hydride, resulted in an unprecedented active system. Tri- and tetra-substituted alkenes were efficiently hydrogenated under mild reaction conditions. Novel low-valent nanoclusters with planar Fe4, Fe6, and Fe7 geometries were isolated during the study. These structures standing on the border between homogeneous and heterogeneous catalysts furnish new insights about the growth of metal nanoparticles. In the fourth chapter the easy synthesis of novel iron complexes coordinated to non-innocent bis(imino)acenaphthene ligands was described. The morphology of the resulting complex can be predicted on the basis of the sterical hinderance of the selected BIAN ligand. Sterically demanding backbones led to the formation of high-spin tetrahedral complexes while less bulky ligands resulted in the creation of low-spin octahedral complexes. The electrochemical properties of both the set of iron species were investigated, showing interesting ligand centered reduction events.The potential catalytic application of these Fe complexes coordinated to redox-active BIAN scaffolds was investigated and described in the fifth chapter. Tetrahedral iron(II) species did not show any hydrogenation capacity, nevertheless, activation of these complexes with different reducing agents led to an active species able to catalyze olefins hydrogenation. Different reductants have been screened and hydrogenation of mono-, di-, tri- and even tetra-substituted olefins was observed employing the optimized conditions. Preliminary mechanistic studies indicated in a reduced anionic iron complex, a ferrate, the competent active catalyst operating in these transformations. Intrigued by the redox properties of bis(imino)acenaphthene moieties further studies were carried on aiming at the isolation of aluminum hydride complexes coordinated to pre-reduced BIAN ligand. The results were described in chapter 6. The synthesis of novel aluminum complexes was efficiently achieved in a single step, mixing the desired ligand and lithium aluminumhydride. In the last chapter an analysis of the different hydroamination approaches known in literature was proposed. The remarkable results obtained in this field thanks to iron-catalyzed hydrogen atom transfer were then discussed