Ethylene oxidation by a platinum(II) hydroxo complex. Insights into the wacker process

The ethylene reaction of hydroxo complex [Pt(COD)(ì-OH)]2(OTf)2 (4) yields acetaldehyde and an equilibrium mixture of Pt(COD)(C2H5)(OTf) (6) and [Pt(COD)(C2H5)(ç2-C2H4)]OTf (7). Dinuclear [Pt2(COD)2(ì-OH){ì-ê2C,O-CH2C(O)H}](OTf)2 (10) and mononuclear Pt(COD)(CH2C(O)H)(OTf) (11) are detected as intermediates during the reaction. The reaction displays three phases: (1) an induction period, (2) an accelerating reaction yielding intermediate 11, water, and 6 plus 7, and (3) a linear decrease in the concentration of 11 with simultaneous formation of acetaldehyde and more 6 plus 7. The reaction is proton catalyzed, and phases 1 and 2 are attributed to autocatalytic behavior resulting from the acidic complex of 6 with water, [Pt(COD)(C2H5)(OH2)]OTf. Phase 3 is initiated by the complete consumption of basic 4 and the resulting release of protons to catalyze the reaction of 11 with water and ethylene to give acetaldehyde and 6 plus 7.