Marschner-Baumgartner Research Group

Main Group Organometallic Chemistry

Institut für Anorganische Chemie Technische Universität Graz / Institut für Chemie Universität Graz

Current FWF-Projects


Tuning Reduced States of Group 4 and Rare Earth Metals (P 30955)


Some 65 years ago a new chapter of chemistry was opened by the incidental discovery of ferrocene. While in the initial publications the compound's structure was not assigned correctly, later scientists at Harvard University and at the TU Munich recognized that ferrocene constitutes the first member of a completely new class of compounds, the metallocenes. At that time the bonding interaction in ferrocene between a metal atom (iron) and an organic π-bond was completely new and it revolutionized the way of our perception of the bonding between metal atoms and organic groups. The organic group in ferrocene is the cyclopentadienyl ligand which nowadays can be found in numerous interesting compounds, many of them being catalysts for industrially important reactions. Interestingly enough the popularity of the cyclopentadienyl ligand is not caused by its spectacular reactivity. The group is valued much more as a spectator ligand, which constitutes part of a metal complex by providing electron density but does not interfere directly with the actual reaction. Cyclopentadienyl complexes of all transition metals (metallocenes) and lanthanides (lanthanocenes) are known. However, the chemistry of the metallocenes was studied in much more detail due to the fact that transition metals were considered of superior value for chemical transformations compared to lanthanides. The latter were thought to be chemically incapable because of their strong preference for the oxidation state +3. However, over the last years several studies emerged which showed that both lanthanide complexes and group 4 metallocenes in reduced oxidation states are able to form complexes with dinitrogen and other notoriously non-reactive small molecules. Careful analysis of these complexes shows that their reactivity is intimately connected to the energy levels of the highly reactive reduced oxidation states of these metals which can be manipulated by proper choice of substituted cyclopentadienyl ligands. Recent work by Evans and co-workers has shown that it is possible to prepare stable cyclopentadienyl complexes of all lanthanide complexes in the oxidation state +2. Given the redox properties of naked lanthanide ions this should be impossible. However, Evans' work suggests that the additional electron of several of the Ln(II) compounds is not located in an f-orbital but rather in a d-orbital. The energetic accessibility of this d-orbital is caused by the ligand field of a silylated cyclopentadienyl ligand. The main intention of the current proposal is therefore to study the effect of silylated cyclopentadienyl ligands and of the related silole, germole and stannole ligands on the energy levels of d-orbitals in the pursuit of understanding whether this is a general effect and how it can be exploited for new reactions. ....


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