Speculations on new mechanisms for Heck reactions

Abstract

A mechanism for the olefination reaction is proposed, involving PdII/PdIV, in which a key step is reversible nucleophilic attack on the PdII-coordinated olefin to give an electron-rich σ-alkyl- or, with carbonate, a chelated σ-dialkyl-complex, which then oxidatively adds the organic halide e.g. ArX. Loss of nucleophile, migration of Ar from PdIV to coordinated olefin, β-hydrogen elimination and loss of HX then gives the product of olefination and regenerates the PdII catalyst.