Mechanistic aspects of the oxidative functionalization of ethane and ethanol by platinum(II) salts in aqueous medium. Role of platinum(II)-olefin and platinum(IV) - alkyl intermediates

Article abstract of DOI:10.1016/0022-328X(95)05568-A

The relative rate of C-H bond activation by the Pt(II) ion decreased in the order H-CH2CH3 > H-CH2CH2OH > H-CH(OH)CH3.The platinum(II)-ethylene complex, ^-, 1, was the key intermediate in the oxidation of ethane, ethanol, and diethyl ether to 1,2-ethanediol by platinum(II) in aqueous medium.In particular, the intermediacy of 1 in the oxidation of ethanol to 1,2-ethanediol and 2-chloroethanol was verified through labeling studies.In D2O, 1, upon oxidation with one of a number of oxidants, converted to ^2-, 2. 2 in turn decomposed to a mixture of 1,2-ethanediol and 2-chloroethanol on heating.The rate conversion of 1 was a function of pH, the anions present, and the oxidant used.While the conversion of 1 to 2 involved a nucleophilic attack by water (or hydroxide ion), such a step was not observed in the absence of an oxidant.In basic D2O, the sequential replacement of Cl^- by OD^- in 1 occurred to successively form ^-, ^- and ^-.The process was reversed upon acidification.The species ^2-, 3, appeared to be the source for the small quantities of hydroxy- and/or chloroacetaldehyde formed during the oxidation of 1. 3 was synthesized independently by the reaction of acetaldehyde with a mixture of PtCl4^2-, and PtCl6^2- in aqueous medium.When 1 was oxidized by Cl2 in CD3OD solution, the principal product was ^2- 4, when a small amount of water was present, and CD3OCH2CH2OCD3 in the absence of water. Keywords: Platinum complex; C-H activation; Oxidation; Ethane; Ethylene; Ethanol