Epoxidation versus Baeyer−Villiger Oxidation: The Possible Role of Lewis Acidity in the Control of Selectivity in Catalysis by Transition Metal Complexes

Abstract

AbstractThe synthesis of a series of cationic complexes of PtII containing triphos or triphosPO and either a solvent, a hydroxo or a hydroperoxo as the fourth ligand is reported. The complexes are characterized by IR and 31P{1H} NMR spectroscopy and by molar conductivity data, and their Lewis acid characteristics determined by NMR techniques. All complexes are good catalysts for the epoxidation of olefins and the Baeyer−Villiger oxidation of ketones under mild conditions using hydrogen peroxide as oxidant. The latter reaction is more Lewis‐acid demanding in terms of the electronic characteristics of the catalysts. The use of Lewis‐acidic metal centers allows the selective oxidation of unsaturated ketones to the corresponding unsaturated esters without oxidation of the carbon‐carbon double bond, indicating that a strong Lewis‐acid character of the catalyst can be an important feature in the design of catalysts capable of separating the two processes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)