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 r eductive 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 substant ially inhibited, and an equilibrium is established between 1 and the c arbon-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, De lta 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 (Delt a 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 studie s 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 r esult. Exclusive production of methyl iodide br ethane can be achieved by the addition or removal of iodide, respectively, from the reaction .