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 and geometric features of YOOH species (Y = H, CH3, t-But, CF3, CH3CO, (PH3)2Pt(CF3), (PH3)2PtCl) have been evaluated and compared. Coordination of the OOH group to platinum induces an inversion of the polarity of the O-O bond when compared to any organic hydroperoxide; parallelly it favours the isomerisation of the OOH group from a hydroperoxo to an oxywater-like structure. This latter effect could be an important factor in favouring the reaction of the platinum coordinated OOH group with ethylene to form ethylene oxide. In fact, calculations on the energetics of the interaction between H2O2 and C2H4 have shown that isomerisation of HOOH to H2OO oxywater structure is the rate determining step for the epoxidation process.