Rate and mechanism of the heck reactions of arylpalladium complexes ligated by a bidentate P,P ligand with an electron-rich alkene (isobutyl vinyl ether)

Two main intermediate complexes, PhPd(OAc)(dppp) and PhPdI(dppp), are generated in palladium-catalyzed Heck reactions performed from PhI and an acetate salt used as a base, in DMF. Both complexes react with the electron-rich alkene isobutyl vinyl ether (CH2 =(HOBu)-Bu-i) exclusively by an ionic mechanism, i.e., via the cationic complex [PhPd(dppp)(DMF)](+) formed by dissociation of AcO- or I- from the parent complexes, as already established for the reaction of PhPd(OAc)(dppp) with styrene and methyl acrylate and the reaction of PhPdI(dppp) with styrene. A mechanism is proposed which rationalizes the regioselectivity observed when reacting the electron-rich isobutylvinyl ether in palladium-catalyzed Heck reactions.