AbstractHigh valent molybdenum(VI) dioxo complexes in oxygen atom transfer reactionsMag. rer. nat. Martina E. JudmaierThis thesis focuses on the syntheses of high valent monomeric [MoO2(L)2], [MoOCl(L)] and dimeric [MoO2(L)]2(-O) complexes and their application in oxygen atom transfer (OAT) reactions, either as functional model compounds for molybdoenzymes or as catalysts in epoxidation reactions. The high valent [MoO2]2+ metal center is ligated by bi- and tridentate phenol based ligands. These ligands contain alkyl side chains with (D = OMe, NMe2 or NEt2) or without (tBu, nBu) donor groups. Steric and electronic properties are modulated by different substituents in ortho and para position on the aromatics.Monomeric [MoO2(L)2] complexes exhibit OAT reactivity to tertiary phosphines (PMe3 and PPh3). Sterically demanding substituents in the ligand backbone allow the isolation of reduced [MoO(L)2] and [MoO(PMe3)(L)2] complexes. The free coordination site after the OAT is usually captured by donor atom in the side chain or by a residual PMe3 molecule in cis position to the Mo=O metal core. Sterically demanding substituents in the ligand backbone (tBu on the aromatics and tBu in the side chain) allows the isolation of an uncommon trans-[MoO(PMe)]2+ complex.Reaction of [MoO(PMe3)(L)2] complexes with O2 results in the formation of [MoO(O2)(L)2] complexes. Only a limited number of metal complexes can be found in the literature, capable of activating molecular oxygen.Both monomeric and dimeric complexes have proven to be highly active catalysts in the epoxidation of internal and terminal alkenes. The activity as well as the selectivity are influenced by the donor group in the alkyl side chain. In both complex types the OMe based complexes are more active than complexes with NMe2 donor groups or without donor atoms. In the epoxidation of styrene, complexes with donor atoms have proven to be more selective than complexes without.