Mechanistic studies of the hydrogen isotope exchange reaction catalysed by homogeneous platinum salts

Abstract

Deuterium exchange between D₂O–CH₃CO₂D solvent and a variety of aromatic compounds is catalysed by tetrachloroplatinate(II) ions. Rhodium and iridium salts are also shown to be homogeneous catalysts for these reactions. Multiple exchange is a consistent phenomenon of all systems. Conditions influencing the stability of platinum(II) in solution are discussed in detail and the basis for the very careful distinction between homogeneous catalysed exchange and the possibility of accompanying heterogeneous exchange by colloidal Pt⁰ is delineated. The exchange kinetics with benzene show inverse first-order dependence on Cl^–. A complicated acid dependence on the reaction is found and interpreted in terms of the effect of acid on the stability of the platinum(II) in solution. These kinetic results are shown to be consistent with the predominant participation of a dissociative π-complex mechanism for the exchange process. The possible relevance of reaction intermediates proposed by other workers is also discussed.