C-H ACTIVATION BY AQUEOUS PLATINUM COMPLEXES - A MECHANISTIC STUDY

Detailed mechanistic studies are reported on the oxidation of alkanes by aqueous [PtCl6](2-)/[PtCl4](2-) to alcohols plus alkyl chlorides, v ia proposed (alkyl)Pt-II and (alkyl)Pt-IV intermediates. Reactions of [PtCl4](2-) with RI (R=CH3, CH2CH2OH) in water yield [PtCl(5)R](2-), w hich were isolated as their NMe(4) salts. Kinetic rate laws of their d ecomposition in aqueous chloride solution to ROH and RCl support S(N)2 displacement by Cl- or H2O as the mechanism of the last step. erythro - and threo-[PtCl5(CHDCHDOH)](2-) are obtained by oxidation of [PtCl3( trans- and cis-CHD=CHD)](-) respectively, and react with Cl- with inve rsion of stereochemistry at carbon, consistent with the S(N)2 mechanis m. [PtCl5(CH2CH2OH)](2-) is also obtained by oxidation of Zeise's salt with [PtCl6](2-). Kinetics indicate that attack of water on coordinat ed ethylene to give a beta-hydroxyethyl group precedes oxidation of Pt -II to Pt-IV, rather than the reverse order, and that this reaction is a model for the oxidation of(alkyl)Pt-II to (alkyl)Pt-IV during alkan e functionalization. Pt-195 isotopic labeling demonstrates that the ox idation is not accompanied by transfer of the beta-hydroxyethyl group from one Pt center to another.