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Ethylene Oxidation by a Platinum(II) Hydroxo Complex. Insights into the Wacker Process

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journal contribution
posted on 08.10.2012 by Nandita M. Weliange, Paul R. Sharp
The ethylene reaction of hydroxo complex [Pt­(COD)­(μ-OH)]2(OTf)2 (4) yields acetaldehyde and an equilibrium mixture of Pt­(COD)­(C2H5)­(OTf) (6) and [Pt­(COD)­(C2H5)­(η2-C2H4)]­OTf (7). Dinuclear [Pt2(COD)2(μ-OH)­{μ-κ2C,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.