Fluorinated Solvents in Methyltrioxorhenium-Catalyzed Olefin Epoxidations

Epoxidations with methyltrioxorhenium(VII) (MTO) as catalyst precursor and additives are examined in fluorinated solvents under various conditions. These fluorinated solvents have a strong influence on the 1H NMR, 13C NMR, and 17O NMR spectroscopic data of the catalyst precursor, apparently contributing significantly to the catalytic activity of such systems. Accordingly, the highest turnover frequencies (TOF) obtained with MTO-containing systems have been determined, reaching up to 39000 h1. Despite the high initial activity, such systems show a pronounced sensitivity to water leading also to faster catalyst decomposition. The high activity as well as the high sensitivity of the catalyst may be due to its solvent-enhanced higher Lewis acidity, leading to quantitative epoxide yields only when quite stable epoxides are the end products and very high amounts of Lewis base additives are applied.