Abstract
Specifically deuteriated complexes have been prepared by stereospecific oxidative addition of CD3I to cis-[PtMe2(L)2](L = PMe2Ph or AsMe2Ph) and of MeX (X = Cl, Br, or I) to cis-[Pt(CD3)2(PMe2Ph)2]. These complexes undergo intramolecular scrambling of Me and CD3 groups in solution at room temperature (L = AsMe2Ph) or above (L = PMe2Ph), and decompose by intramolecular reductive elimination of ethane. Kinetic studies of the decomposition of fac-[PtX(Me)3L2](I: X = Cl or Br, L = PMe2Ph; X = I, L = PMe3, PMe2Ph, or PMePh2) indicate that ethane is eliminated from a five-co-ordinate intermediate formed by dissociation of a phosphine ligand, but when L2= 1,2-bis(diphenylphosphino)ethane (dppe) ethane is eliminated without prior phosphine dissociation. In his case the activation energy (69 kJ mol–1) for ethane elimination is considerably lower than the estimated methyl–platinum bond energy (144 kJ mol–1) for (I; X = I, L = PMe2Ph) obtained from a study of the ethane elimination by differential-scanning calorimetry. Methyl groups are eliminated from the platinum(IV) complexes more readily than [2H3]methyl groups, with a mean secondary kinetic-isotope effect k(H)/k(D) of 1·07. The results are interpreted in terms of concerted reductive elimination, with the transition state resembling an ethane complex of platinum(II).
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