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 degrees C in a chlorinated solvent/H2O two-phase system. All the investigated catalysts performed better than the corresponding dimeric complexes of general formula [Pt(mu-OH)(P-P)]2[BF4]2 as a consequence of the positive effect imparted by the triflate counter-anion on catalysts speciation. (C) 2007 Elsevier B.V. All rights reserved.