A DFT Computational Study of the Mechanism of Allyl Halides Carbonylation Catalyzed by Palladium Complexes

A theoretical DFT (B3LYP) investigation on the carbonylation reaction of allyl chloride catalyzed by Cl2Pd(PH3)(2) is discussed. The computational results show the following. (i) The favored reaction channel leading to the beta,gamma-unsaturated acyl chloride product is a direct attack of the chlorine atom on the metal (sigma pathway). (ii) The carbonylation pathway involving the formation of pi-allyl complexes is highly disfavored. (iii) In the pi complexes the ligand is not eta(3)-coordinated to the metal, as usually assumed, but eta(2)-coordinated. (iv) The presence of a favored or pathway seems to be a common feature of this class of reactions (i.e. metal-catalyzed carbonylation of allyl halides). (v) The Cl2Pd(CO)(2) complex, which forms from Cl2Pd(PH3)(2), can behave as an "active" catalytic species. In the presence of high CO pressures, it initiates an alternative pathway that can be competitive with the main a pathway.