Organorhenium(VII) and organomolybdenum(VI) oxides: synthesis and application in oxidation catalysis

Methyltrioxorhenium(VII) has found numerous applications in various catalyt ic processes. In olefin epoxidation its activity can be enhanced by the add ition of aromatic Lewis base nitrogen donor ligands, e.g. pyridines and pyr azoles, Due to the comparatively weak coordination of these ligands, a sign ificant excess has to be used. Therefore the MTO/chiral Lewis base/H2O2 sys tem is not very useful for chiral epoxidations. In contrast to this, dimeth yldioxomolybdenum (VI) MoO2(CH3)(2) undergoes a significantly stronger inte raction with Lewis bases and seems, despite its generally somewhat lower ac tivity, a reasonable candidate for application in chiral epoxidation reacti ons together with an appropriate chiral Lewis base ligand, Complexes of the type MoO2(CH3)(2)L are accessible via MoO2X2L (X = Cl, pr), These latter c ompounds are even more active in olefin epoxidation than MoO2(CH3)(2)L. Unf ortunately, however, all the Mo(VI) complexes mentioned above need t-butyl hydroperoxide as oxidizing agent and do not show activity in the presence o f H2O2 Copyright (C) 2001 John Wiley & Sons, Ltd.