Behaviour of dimeric methylrhenium(vi) oxides in the presence of hydrogen peroxide and its consequences for oxidation catalysis

Abstract

Avoiding the use of toxic methyltin precursors to synthesize methyltrioxorhenium (MTO) and its mono- and bis-peroxo derivatives, applicable as oxidation catalysts, dimethyl zinc might be considered a promising alternative alkylating agent. However, the methylrhenium(VI) dimers, formed as reduction products alongside MTO during the reaction of dimethyl zinc with Re₂O₇, are not as straightforwardly transformed into the epoxidation catalysts as MTO itself in the presence of excess H₂O₂. In the case of red (μ-oxo)bis[trimethyloxorhenium(VI)], the main reaction product with H₂O₂ is the catalytically inactive trimethyldioxorhenium(VII). In the case of bis[dimethyl(μ-oxo)oxorhenium(VI)], slow conversion to the monomeric mono- and bis-peroxo congenes of MTO occurs. Furthermore, part of the Re(VI) starting complex is transformed into inactive perrhenate. While bis[dimethyl(μ-oxo)oxorhenium(VI)] might be applied (also in a mixture with MTO) as an oxidation catalyst precursor, (μ-oxo)bis[trimethyloxorhenium(VI)] can be applied as a useful precursor for the synthesis of trimethyldioxorhenium(VII), which was previously only accessible by less convenient synthetic pathways.