Great wonders of f-chemistry: Synthetic, structural and reactivity investigation of low valent f-block metal complexes

The inspiration behind the synthesis and reactivity studies of the f-block metal complexes generally originated from several well defined basic purposes. The main goals in the field of lanthanide and actinide centered chemistry could be separated onto: (i) exploration of the fondamental chemistry of f-block elements with their reactivity and coordination behavior; (ii) understanding the nature of the bonding interactions between the metal centers and the ligands as well as between different metal centers within the same heterometallic complex; and finally, (iii) exploration of the possibility to use new complexes in catalytic or sensor related applications. This thesis is manly focused on the investigation of the preparation and the reactivity investigation of the several low valent compounds of Sm, Tm, U and Th with non-cyclopentadienyl ligands. Despite exceptionally high reactivity and rather unpredicted transformations demonstrated by some of the species in this class, an overall picture of the chemical activity remained rather scattered and considerably poorly investigated. In attempt to contribute to the understanding of the reactivity patterns in the field of f-block metal chemistry Chapter 2 of this thesis explored the chemical behavior of Sm complexes supported by the bulky aryloxides ligands. Application of the aluminum alkyls led to the appearance of a new coordination mode of aryloxide ligands to lanthanide, affording an unusually stable Sm(II) compounds. Attempted insertion reactions afforded several new complexes and provided more information about the stabilization influence of Lewis acids in zwitterionic compounds. The application of similar strategy to Sm(III) species resulted in the isolation of rare non-cyclopentadienyl single component ethylene polymerization catalyst. In Chapter 3 the reaction of Tm complexes supported by the combination of dimethyl-pyrrole with aluminum alkyl produced a very unusual product of C-H bond activation by the Tm metal center. Utilization of the Lewis acidic aluminum alkyls enforced the ligand to thulium pi-bonding and a formation of Zwitterionic structure. Upon treatment with hydrogen or PhSiH3 as hydrogenating agent the initial species exhibited a series of very unusual transformations, leading to the isolation of rare case of SiH3 coordination to thef-block metal center. Chapter 4 discovered unexpected reactivity of uranium complex with bulky amido-ligand in halogen replacement alkylation processes or during the reduction of the metal center. The alkylation reactions yielded extensive gamma-deprotonation and formation of cluster compounds. Two first structurally characterized uranium carbines were discovered and documented in the course of this exploratory work. Reduction of the mixed Uranium amido-halogenates proceeded with the formation of transient low valent species and immediate re-oxidation at the expense of the ligand, affording new amido-imino- or amido-alkyl-complexes of U(V). Multiple attempts of lowering the oxidation state of uranium metal center supported by new bis-amido-benzene ligand, presented in Chapter 5, resulted in the isolation of several new solvent fragmentation products. The reactivity displayed by the related ligand systems together with the additional support, provided by the isolation of complexes of this type, suggested the presence of highly reactive low valent synthons. Reduction reactions afforded the new uranium complex with the lowest reported oxidation state of the metal centers. However, the DFT calculations revealed that all the excessive electron density was situated on the ligand delocalized pi-systems, forcing the ligand to act as electron storage. Chapter 6 discussed the possibility of sterically enforcing pi-bonding ligands to stabilize the low valent oxidation state of Th metal center. Utilization of the bis-pyrrolide base ligand allowed the isolation of the thorium complex with significant pi-interaction of the metal center with the aromatic system of the ligand. Reduction of this system afforded the isolation of the rare example of Th(III) complex. Similarly to the complexes of U reported in the previous chapter, DFT calculation displayed significant presence of the electronic density on the pi-system of the ligand fragment. Nevertheless, it was demonstrated by the reactivity examples that stored electronic density could be delivered back to the metal center, initiating the transformations expected for low valent f-block element compounds