REACTIVITY OF ORGANOPALLADIUM COMPOUNDS TOWARD MOLYBDENUM PEROXIDES - OXYGEN INSERTION VERSUS C-CL AND C-O COUPLING - EVIDENCE FOR PALLADIUM(IV) MOLYBDATE INTERMEDIATES

The molybdenum peroxide [MoO(O2)2.HMPT-H2O] (1) reacts with organopalladium compounds preferentially to give products derived from coupling of nucleophiles (halide or alkoxide) to the palladated carbon atom. Oxygen insertion into the Pd-C bond is only of minor importance for this peroxide. No other oxidants were able to effect this type of transformation as efficiently as 1. The C-0 coupling mediated by 1 comprises the first method for the direct alkoxylation of organopalladium compounds and constitutes the basis for a very selective one-pot conversion of a C-H bond into an ether function by a sequence of cyclopalladation and alkoxylation. Evidence was found that the reaction can be described as an oxidatively induced SN2 reaction, which proceeds via a palladium(IV) intermediate formed by oxidative addition of the O-O bond to the organopalladium(II) substrate. Steric hindrance either in the alkyl group attached to palladium or in the alkoxide nucleophile suppresses the alkoxylation and leads to oxygenation of the organopalladium compound. This oxygen insertion probably proceeds via the same Pd(IV) intermediate as the nucleophilic substitution. The mechanism of the oxidative addition, in which a Pd-Mo interaction may be a critical step, is discussed.