ALKENE EPOXIDATION CATALYZED BY CAMPHOR-DERIVED BETA-KETOPHOSPHONATE COMPLEXES OF MOLYBDENUM(VI)

New beta-ketophosphonates (L) have been prepared from (R)- or (S)-camp hor with various substituents on the phosphorus atom [EtO, (R)- or (S) -Bu(s)O, Ph or binaphthoxy] and reacted with [MoO2Cl2] to form complex es [MoO(2)Cl(2)L]. These complexes have been used to give highly activ e catalysts for epoxidation of alkenes by Bu(t)OOH. Very fast initial rates (ca. 400 catalyst turnovers in the first minute) gave way to muc h slower rates because the hemi-labile beta-ketophosphonate is displac ed by a diol ligand. In the presence of molecular sieves, the fast ini tial stage of the reaction is extended and for styrene, which gives lo w conversions followed by degradation in the absence of molecular siev es, styrene oxide can be formed with 98% conversion and 94% selectivit y. It is demonstrated that both the Bu(t)OOH and the catalyst bind to the molecular sieves. the latter with loss of the beta-ketophosphonate ligand.