title: Computational study of a new heck reaction mechanism catalyzed by palladium(II/IV) species.
abstract: In this theoretical study on the Heck reaction we explore the feasibility of an alternative pathway that involves a PdII/PdIV redox system. Usually, the catalytic cycle is formulated based on a Pd0/PdII mechanism. We performed quantum chemical calculations using density functional theory on a model system that consisted of diphosphinoethane (DPE) as a bidentate ligand and the substrates ethylene and phenyl iodide to compare both mechanisms. Accordingly, the PdII/PdIV mechanism is most likely to occur in the equatorial plane of an octahedral PdIV complex. The energy profiles of both reaction pathways under consideration are largely parallel. A major difference is found for the oxidative addition of the C-I bond to the palladium centre. This is a rate-determining step of the PdII/PdIV mechanism, while it is facile for a Pd0 catalyst. The calculations show that intermediate ligand detachment and reattachment is necessary in the course of the oxidative addition to PdII. Therefore, we expect the PdII/PdIV mechanism to be only feasible if a weakly coordinating ligand is present.
authors.affiliation: Department of Organic Chemistry, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: A
authors.initials: A
authors.lastname: Sundermann
authors.forename: O
authors.initials: O
authors.lastname: Uzan
authors.forename: J M
authors.initials: JM
authors.lastname: Martin