Alkene oxidation by platinum (II) oxo/hydroxo complexes
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The facile reaction between tetranuclear Pt-‐oxo complex [(COD)4Pt4(μ2-‐O)2Cl2]2[BF4]2 (1) and norbornene (NB) yields the stable platinaoxetane [(COD)2Pt2(OC7H10)Cl][BF4] (2) in quantitative yield. A rapid reaction between NB and the novel (1,5-‐COD)Pt(II)-‐hydroxo complex [(COD)2Pt(OH)2]2+ (4) is observed and the protonated platinaoxetane [(COD)Pt(OH)C7H10)]+ (5) is formed in quantitative yield. Both Pt-‐hydroxo complex 4 and protonated platinaoxetane 5 are found to be important species in the formation of platinaoxetane 2. Mechanisms for formation of platinaoxetanes 2 and 5 are proposed. Pt-‐hydroxo complex 4 reacts readily with ethylene, propylene and 1-‐butene. All three reactions, resembling Wacker chemistry, yield alkene oxidation products: acetaldehyde, acetone and ethyl-‐methyl ketone, respectively. Pt-‐ethyl alkyl complexes are yielded as the only Pt containing complexes. A proposed mechanism for these alkene oxidations is described. Pt-‐hydroxo complex 4 also reacts with cyclohexene. In this case the reaction takes an allylic C-‐H activation pathway to produce the cyclohexyl allyl complex [(COD)Pt(C6H9)]+ (55).