Unusually Stable Palladium(IV) Complexes: Detailed Mechanistic Investigation of C−O Bond-Forming Reductive Elimination

This communication describes the synthesis of a family of unusually stable palladium(IV) complexes containing two chelating 2-phenylpyridine ligands and two benzoates. These complexes undergo clean C−O bond-forming reductive elimination upon heating, and the mechanism of this catalytically relevant process has been studied in detail. Solvent effects, crossover experiments, Eyring plots (which show ΔS⧧ of −1.4 ± 1.9 and 4.2 ± 1.4 in CDCl3 and DMSO, respectively), and Hammett analysis (which shows ρ = −1.36 ± 0.04 upon substitution of the para-benzoate substituent) all suggest that reductive elimination does not proceed via initial dissociation of a benzoate ligand. Instead, an unusual mechanism involving pre-equilibrium dissociation of the N-arm of the phenylpyridine ligand is proposed.