Platinum(II) mediated oxidation of remote CH bonds in functionalized organic molecules

The oxidation of remote CH bonds of aliphatic alcohols, carboxylic acids, sulfonic acids and phosphonic acids by the Pt^II ion in water was examined. The reactions were very specific with respect to the degree of oxidation: only hydroxylation (or its equivalent) was observed and further oxidation to the corresponding aldehyde or carboxylic acid functionally did not occur. The order of reactivity was σ-CH ≪ β-CH < γ-CH < δ-CH for alcohols and σ-CH ≪ β-CH < γ-CH {slanted equal to or greater-than} δ-CH for the acids. The reactions are thought to proceed by the initial coordination of the functional group followed up the formation of an intermediate platinacylce upon CH activation. The observed regioselectivity arises from the tendency to form the metallacycle with the least ring strain. It was possible to make the oxidations catalytic in Pt^II by the addition of a reoxidant, such as K₂PtCl₆.