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 h ^-1. 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.