Baeyer-Villiger oxidation of ketones catalyzed by platinum(II) Lewis acid complexes containing coordinated electron-poor fluorinated diphosphines

The synthesis and characterization of new hydroxo-bridged platinum(II) complexes of the type [P(mu-OH)(P-P)]2[BF4]2 (1-4), where P-P = (C6H5-nFn)2PCH2CH2P(C6H5-nFn)2 (n = 2 (2Fdppe) (1), 3 (3Fdppe) (2), 4 (4Fdppe) (3), 5 (dfppe) (4), are reported. These compounds have been used in the Baeyer-Villiger oxidation of 2-methylcyclohexanone using 35% hydrogen peroxide as oxidant. The reactions were performed at 25, 50, and 70 °C in a chlorinated solvent/H2O two-phase system. Among the fluorinated catalysts, complex 4 was found to be the best one in the oxidation of cyclic ketones; however, it is ineffective toward acyclic ketones. The Lewis acidity of the platinum(II) complexes with coordinated fluorinated diphosphines was investigated through the determination of the wavenumber shift Delta(v) over bar = (v) over bar (CN)(coord) - (v) over bar (CN)(free) of the isocyanide group in complexes of the type [PtCl(CN-2,6-(CH3)2C6H3)(P-P)] [BF4] (P-P = 2Fdppe, 3Fdppe, 4Fdppe, dfppe, dppe). This latter parameter, which represents a measure of the electrophilicity of the metal center, was then correlated to the catalytic activity of complexes 1-4 in the Baeyer-Villiger oxidation of ketones.