The mechanism of transition metal catalyzed carbonylation of allyl halides: A theoretical investigation

Abstract The mechanism of the carbonylation reaction of allyl halides catalyzed by nickel (Ni(CO) 4 ) and palladium (Cl 2 Pd(PPh 3 ) 2 ) complexes is theoretically investigated at the DFT level using the hybrid B3LYP functional. The favored reaction path to carbonylation corresponds, for both catalysts, to a direct attack of the halogen on the metal. This affords η 1 intermediates that can undergo the final carbonylation step. It is also possible to obtain the acyl product (β,γ-unsaturated acyl halides) from η 2 and/or η 3 intermediates. However, in this case, the barrier of the rate-determining step to carbonylation is much higher. Since a channel on the potential surface connects rather easily the η 2 or η 3 intermediates to the η 1 intermediates, an alternative and competitive path leading to the acyl products can originate from the η 2 or η 3 intermediates, follow the η 2 /η 3  → η 1 transformation, then undergo the final carbonylation step.