Olefin epoxidations in the ionic liquid [C(4)mim][PF6] 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)]center dot H2O

摘要

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(4)mim][PF6]. 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 MoO3 dissolved in aqueous hydrogen peroxide afforded [Mo(O)(O-2)(2)(4-MepyO)(2)]center dot H2O (1) as yellow crystals. Compound 1, an active epoxidation catalyst, was subsequently characterised and its structure determined by X-ray crystallography.