Palladium(IV) monohydrocarbyls: Mechanistic study of the ligand-enabled oxidation of palladium(II) complexes with H2O2 in water

Williamson N. Oloo, Peter Y. Zavalij, Andrei N. Vedernikov

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A detailed mechanistic study of the di(2-pyridyl)ketone (dpk)-enabled oxidation with H2O2 in water of a series of monohydrocarbylpalladium(II) complexes derived from cyclopalladated 2-(3-R-benzoyl)pyridines (R = H, Me) and 2-(p-R′-phenyl)pyridines (R′ = H, Me, MeO, F) to produce corresponding PdIV monohydrocarbyl hydroxo complexes has been carried out, and the PdIV hydrocarbyls have been characterized in detail. The study involves kinetics, isotopic labeling experiments, and the DFT calculations. A reaction mechanism has been proposed for the oxidation of dpk-supported PdII complexes in water that includes elimination of water from the hydrated dpk ligand of the monohydrocarbylpalladium(II) species as the rate-limiting step. Subsequent reversible addition of H2O2 across the resulting ketone Cî - -O bond leads to the formation of two diastereomeric hydroperoxoketals, one of which can rapidly produce a PdIV monohydrocarbyl and the second is unreactive in this type of transformation. All the monohydrocarbyl PdIV complexes undergo clean C-O reductive elimination to form the corresponding phenols or derived palladium(II) phenoxides. The kinetics of the C-O reductive elimination of the Pd(IV) monohydrocarbyls derived from cyclopalladated 2-(p-R-phenyl)pyridines was studied at 22 C; the corresponding first-order rate constants were found to be only weakly dependent on the nature of the substituent R (H, Me, OMe, F). To account for these observations, a detailed DFT analysis of plausible C-O reductive elimination mechanisms in water was carried out. A direct elimination mechanism of six-coordinate complexes resulting from the oxidation above was proposed to be operational that involves an "early" C-O coupling transition state whose structure varies insignificantly among the substrates studied.

Original languageEnglish (US)
Pages (from-to)5601-5614
Number of pages14
Issue number19
StatePublished - Oct 14 2013


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