Mechanistic studies of Alkene/CO polymerization with palladium complexes promoted by B(C6F5)3

The reaction of Pd(dppp)(OAc)(2) [dppp = 1,3-bis(diphenylphosphino)propane] with B(C6F5)(3) in situ gives an efficient catalyst for alkene/CO polymerization in aprotic media. The borane is consumed during the polymerization, and its fluoroaryl groups are incorporated into the polymer chain ends. In the absence of the monomers the catalyst components react to give palladium(II)-pentafluoroaryl complexes formulated as Pd(dppp)(C6F5){[B(C6F5)(3)](y)OH} (y = 1, 3a; y = 2, 3b). Complex 3a can be isolated, albeit as an impure solid, and is itself a catalyst for the reaction. In light of these results a novel chain initiation process for the polymerization is proposed, involving insertion of monomers into a fluoroarylpalladium complex formed by aryl transfer from the borane to a palladium(II) complex. This facile initiation step, combined with the catalyst stability engendered by the presence of strong Bronsted acids, explains the effectiveness of this catalyst system in aprotic media.