PREPARATION OF NEW CHIRAL DIOXOMOLYBDENUM COMPLEXES HETEROGENIZED ON MODIFIED USY-ZEOLITES - EFFICIENT CATALYSTS FOR SELECTIVE EPOXIDATION OF ALLYLIC ALCOHOLS

A series of dioxomolybdenum(VI) complexes were synthesised by reaction of Mo(VI) complexes with new chiral ligands derived from (2S,4R)-4-hy droxyproline. The complexes bearing a Si(OEt)(3) group were heterogeni sed to a modified USY-zeolite by covalent bonding. All catalysts, homo geneous and heterogenised, are active and regioselective in the epoxid ation of allylic alcohols at room temperature using tert-butyl hydrope roxide as terminal oxidant. The catalytic activity of the heterogenise d complexes is generally comparable with the corresponding homogeneous ones, yielding epoxyalcohols with excellent yields and selectivity an d moderate enantioselectivity. Life time of heterogenised catalysts ha s been examined by repeated use of the complexes leading similar rates and yields of epoxide, whilst no appreciable loss of metal has been o bserved over several runs.