(N-salicylidene)aniline derived Schiff base complexes of methyltrioxorhenium(VII): ligand influence and catalytic performance.

Methyltrioxorhenium(VII) (MTO) readily forms 1:1 adducts with several N-(salicylidene)aniline derived Schiff bases. If the aromatic rings of the N-(salicylidene)aniline ligands display non-donating or electron withdrawing substituent groups, the resulting MTO adducts show good activities in olefin epoxidations. However, steric effects seem to play a major role, leading often to instable o- and m-Schiff base-MTO adducts, while p-substituted Schiff bases usually lead to more stable adducts. In catalysis, electron-withdrawing substituents on the aniline moiety lead to better catalysts than electron donating ones. The gap between good catalysts and instable or non-existing compounds, however, is small. The general tendency, however, that good donors on the Schiff base ligands lead to shorter Re-O(Schiff base) bridges and lower catalytic activity, while the opposite is true with acceptor ligands on the Schiff bases, seems to be quite clear.

Immobilization of monomeric organometallic molybdenum oxo and carbonyl complexes and their application in epoxidation reactions.

Various oxomolybdenum complexes are efficient and selective homogeneous catalysts in the presence of organic hydroperoxides. The increasing interest in the heterogenisation of such catalysts has led to an increased interest in finding suitable support materials for the complexes. These supports include ionic liquids, mesoporous materials and zeolites to name a few. Several methods are used to anchor the catalyst depending on the nature of the carrier material. The supported catalysts combine properties of homogeneous catalysts such as reactivity, control and selectivity with those of heterogeneous catalysts such as enhanced stability and recyclability.

Ansa-bridged eta5-cyclopentadienyl molybdenum and tungsten complexes: synthesis, structure and application in olefin epoxidation.

Ansa-bridged eta(5)-cyclopentadienyl molybdenum and tungsten tricarbonyl complexes of formula [M(eta(5)-C(5)H(4)(CH(2))(3)-eta(1)-CH(2))(CO)(3)] (M=Mo or W) were synthesized and the X-ray crystal structure of the tungsten complex is reported. In the epoxidation of cyclooctene the molybdenum compound shows a high catalytic activity, approaching the observed activities for the most reactive unbridged complexes of composition CpMo(CO)(3)X (X=Cl, CH(3)). The activity of the tungsten complex is also amongst the highest catalytic activities for the olefinic epoxidation of complexes with the composition CpW(CO)(3)X and WO(2)X(2)L(2), reported so far. The low ring strain of the ansa-bridged system improves the stability of the complexes under oxidative conditions considerably in comparison to derivatives with a shorter bridge and therefore paves the way to introduction of chirality in these systems.