Alkene epoxidation catalysed by camphor-derived β-ketophosphonate complexes of molybdenum(VI)
New β-ketophosphonates (L) have been prepared from (R)- or (S)-camphor with various substituents on the phosphorus atom [EtO, (R)- or (S)-BusO, Ph or binaphthoxy] and reacted with [MoO2CI2] to form complexes [MoO2CI2L]. These complexes have been used to give highly active catalysts for epoxidation of alkenes by ButOOH. Very fast initial rates (ca. 400 catalyst turnovers in the first minute) gave way to much slower rates because the hemi-labile β-ketophosphonate is displaced by a diol ligand. In the presence of molecular sieves, the fast initial stage of the reaction is extended and for styrene, which gives low conversions followed by degradation in the absence of molecular sieves, styrene oxide can be formed with 98% conversion and 94% selectivity. It is demonstrated that both the ButOOH and the catalyst bind to the molecular sieves, the latter with loss of the β-ketophosphonate ligand.