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

摘要

The synthesis of a series of cationic complexes of Pt~(II) 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 ~(31)P{~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.