Olefin epoxidations in the ionic liquid [C 4mim][PF 6] catalysed by oxodiperoxomolybdenum species in situ generated from molybdenum trioxide and urea–hydrogen peroxide: The synthesis and molecular structure of [Mo(O)(O 2) 2(4-MepyO) 2]·H 2O

Abstract

Commercially available molybdenum(VI) compounds, including molybdenum trioxide, were successfully employed as catalyst precursors in the epoxidation of olefins with urea–hydrogen peroxide adduct (UHP) in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [C 4mim][PF 6]. After oxidation, the corresponding epoxides were isolated by extraction with diethyl ether. Additionally the ionic liquid–catalyst mixture was recycled and reused in further catalytic cycles. The catalytic species is assumed to be an oxodiperoxomolybdenum species which forms in situ. A representative complex of this type was thus isolated and characterised. Reaction of excess 4-methylpyridine-1-oxide (4-MepyO) with MoO 3 dissolved in aqueous hydrogen peroxide afforded [Mo(O)(O 2) 2(4-MepyO) 2]·H 2O ( 1) as yellow crystals. Compound 1, an active epoxidation catalyst, was subsequently characterised and its structure determined by X-ray crystallography.