Alkene oxidation by platinum (II) oxo/hydroxo complexes

Abstract

The facile reaction between tetranuclear Pt-oxo complex [(COD)4Pt4([mu]2-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).