Carbon dioxide as a C1 building block. Mechanism of palladium-catalyzed carboxylation of aromatic halides

The reduction of aryl halides in the presence of stoichiometric amounts of carbon dioxide and catalytic amounts of Pd II Cl 2 (PPh 3 ) 2 has been previously reported to result in the formation of the corresponding carboxylic acids. It is shown here that the mechanism proceeds via a catalytic cycle initiated by the one-step, two-electron reduction of the divalent palladium complex followed by oxidative addition of the aryl halide to the resulting poorly ligated zerovalent palladium center «Pd 0 (PPh 3 ) 2 », to afford the corresponding σ-arylpalladium(II) intermediate