ENERGETICS AND MECHANISMS OF CARBON-CARBON AND CARBON-IODIDE REDUCTIVE ELIMINATION FROM A PT(IV) CENTER

Thermolysis of dppePtMe(3)I (1, dppe = Ph(2)PCH(2)CH(2)PPh(2)) in both solid state and solution (acetone-d(6)) results in competitive methyl iodide and ethane production. The expected Pt(II) products of these reductive elimination reactions, dppePtMe(2) (2) and dppePtMeI (3), are also observed. In the presence of added iodide (in acetone-d(6)), the carbon-carbon bond forming reductive elimination reaction is substantially inhibited, and an equilibrium is established between 1 and the carbon-iodide reductive elimination products, 2/MeI. Thermodynamic and kinetic parameters for the reductive elimination of methyl iodide from 1 were measured under these conditions (Delta H = 66 +/- 3 kJ/mol, Delta S = 153 +/- 7J/(mol . K); Delta(re)(double dagger) = 104 +/- 1 kJ/mol, Delta S-re(double dagger) = -12 +/- 1 J/(mol . K)). Estimates of the enthalpy of the carbon-carbon reductive elimination reaction (Delta H = -105 kJ/mol) and of Pt-IV-C and Pt-IV-I bond strengths (132 and 196 kJ/mol, respectively) were. made from DSC data. Mechanistic studies of the solution thermolysis support the involvement of a common five-coordinate cationic intermediate (formed by dissociation of iodide), from which both carbon-carbon and carbon-iodide elimination products result. Exclusive production of methyl iodide br ethane can be achieved by the addition or removal of iodide, respectively, from the reaction.