Polystyrene and polymethacrylate resin-supported Jacobsen's alkene epoxidation catalyst

Polystyrene and polymethacrylate-based resin supported Jacobsen's chiral Mn salen complexes have been prepared. The resins are of defined molecular st ructure and morphology, and the complexes have been attached primarily in a pendant fashion. The loadings of Mn(III) are in the range approximate to 0 .08-0.35 mmol g(-1) to maximise the likelihood of site-isolation. The polym er-supported complexes have been used as enantioselective catalysts in the epoxidation of 1,2-dihydronaphthalene, indene, 1-phenylcyclohex-1-ene and 1 -phenyl-3,4-dihydronaphthalene using m-chloroperbenzoic acid as the oxidant and 4-methylmorpholine N-oxide as the co-oxidant. Though the activities of the polymer catalysts are reduced relative to the soluble homogeneous anal ogue, the catalysts are sufficiently active to be useful. The corresponding reduction in enantioselectivity is more significant, and is both substrate and polymer resin dependent. However, in the case of 1-phenylcyclohex-1-en e and a macroporous polymethacrylate-based resin the enantioselectivity is equivalent to that of the soluble complex (91-92% ee). This is the first re port of a polymer-supported analogue of Jacobsen's catalyst being as select ive as the homogeneous species. The catalysis data is discussed in detail i n the context of the design of the polymer-supported system, and the existi ng data already available in the literature. Attempts have also been made to recycle the polymer catalysts with and with out re-loading of Mn. In fact the level of leaching of Mn is very low, but the catalysts show a very rapid fall off in both activity and selectivity i n the first and second cycles. Overall therefore it seems that the intrinsi c stability of the chiral Mn(II) salen complex itself is too low to allow v iable recycling, and the development of other more stable supported chiral metal salen complexes for use in other enantioselective reactions seems a b etter future option.