Organorhenium(VII) and organomolybdenum(VI) oxides: Syntheses and application in olefin epoxidation

The first members of the classes of the organorhenium(VII) oxides and organomolybdenum(VI) oxides were described during the 1960s and 1970s. However, despite the fact that methyltrioxorhenium(VII) (MTO) is probably the best examined organometallic oxide known, many of its derivatives as well as the Mo congeners were not tested for any application. Nevertheless, it is known that several organomolybdenum oxides, particularly those of formula η⁵-(C₅R₅)MoO₂Cl and η⁵-(C₅R₅)MoO₂R' are powerful epoxidation catalysts if applied together with tert-butylhydroperoxide (TBHP). MTO catalyzes a broad variety of organic reactions, among them being olefin epoxidation - in this case with the "green" oxidant H ₂O₂ - the most thoroughly examined. The heterogenization of the molybdenum compounds as well as of MTO both on carrier materials and in ionic liquids has already been achieved and it is to be expected that a suitable modification of the organic ligands will lead to applications in chiral catalysis in the near future.