Organocerium(IV) Chemistry

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Among the rare-earth elements cerium deserves special attention since it has access to the oxidation states +2, +3, and crucially +4. Because of their high oxidation potential, Ce(IV) compounds are routinely applied in organic synthesis, bioinorganic chemistry, materials science, and industrial catalysis (three-way catalytic converters, oxygen storage, etc.). Primary goal of this research project comprises the synthesis and full characterization of novel coordination compounds and organometallics of tetravalent cerium. Phenyliodine(III) dichloride is to be established as an innovative oxidant in rare-earth metal chemistry. Cerium(IV) amidinates and (silyl)amides as well as novel organocerium(IV) complexes bearing cyclopentadienyl and cyclooctatetraenyl ligands are relevant targets. In particular cases, the corresponding uranium(IV) amidinates will be synthesized to allow for the first time for a comparative study of a series of analogous cerium(IV) and uranium(IV) complexes with respect to their structure and reactivity. The reaction of metal chloride precursors with non-reducing alkylating agents such as ZnMe2 or SnMe4 might give access to the first organocerium(IV) complexes featuring sigma-bonded alkyl ligands. Furthermore, direct oxidation of cerium(III) alkyl derivatives will be systematically investigated as an alternative synthesis protocol. In order to prevent possible ligand oxidation, particular (ancillary) ligand sets will be employed. It can be foreseen that a moderate topical success already could have major implications for the development of organocerium(IV) chemistry. The research project also aims at the surface organometallic chemistry of the Ce(III)/Ce(IV) redox couple. The utilization of periodic mesoporous silicas as support material as well as the heterogenized silylamide route will be crucial criteria for studying the stability and reactivity of such molecular Ce(IV) surface species.