AN AB-INITIO MO-LCAO INVESTIGATION OF THE ELECTRONIC-STRUCTURE OF ORGANIC HYDROPEROXIDES AND PLATINUM(II) HYDROPEROXO COMPLEXES - A CONTRIBUTION TO THE KNOWLEDGE OF THE MECHANISM OF OLEFIN EPOXIDATION

A possible new process of activation of the OOH group in the mechanism of ethylene epoxidation catalysed by Pt(II) diphosphine complexes has been investigated by ab initio MO-LCAO calculations. The electronic a nd geometric features of YOOH species (Y = H, CH3, t-But, CF3, CH3CO, (PH3)(2)Pt(CF3), (PH3)(2)PtCl) have been evaluated and compared. Coord ination of the OOH group to platinum induces an inversion of the polar ity of the O-O bond when compared to any organic hydroperoxide; parall elly it favours the isomerisation of the OOH group from a hydroperoxo to an oxywater-like structure. This latter effect could be an importan t factor in favouring the reaction of the platinum coordinated OOH gro up with ethylene to form ethylene oxide. In fact, calculations on the energetics of the interaction between H2O2 and C2H4 have shown that is omerisation of HOOH to H2OO oxywater structure is the rate determining step for the epoxidation process. (C) 1998 Elsevier Science S.A.