Platinum(II) diphosphine complexes as catalysts for the Baeyer–Villiger oxidation of ketones: Is it possible to increase the concentration of the active species?

The synthesis and characterization of new bis-aquo platinum(II) complexes of the type [Pt(H2O)(P–P)][OTf]2 (OTf = triflate anion), in which the diphosphine P–P is a series of 1,n-bis-diphenyphosphinoalkanes (1a–d, with n = 1–4), 1,2-bis-(di-n-fluorophenylphosphino)ethanes (2a–c, with n = 2, 4–5) and 1,2-bis-dialkylphosphinoethanes (3a–e), where the alkyl substituents at phosphorus have been systematically changed (dmpe) (3a), (depe) (3b), (dippe) (3c), (dcype) (3d) are reported. These complexes were used as catalysts in the Baeyer–Villiger oxidation of 2-methylcyclohexanone, 2-methylcyclopentanone and cyclobutanone with 35% hydrogen peroxide as an environmentally friendly oxidant. The reactions were performed at 25 °C in a chlorinated solvent/H2O two-phase system. All the investigated catalysts performed better than the corresponding dimeric complexes of general formula [Pt(μ-OH)(P–P)]2[BF4]2 as a consequence of the positive effect imparted by the triflate counter-anion on catalysts speciation.