Phosphine exchange at trans-Pt(SnPh3)2(PMe2Ph)2

Phosphine exchange at square-planar trans-Pt(SnPh3)(2)(PMe2Ph)(2) has been studied by P-31 NMR spectroscopy as a function of ligand concentration and temperature in C6D6 using magnetisation transfer techniques. Exchange of a specific phosphine takes place according to a second order rate law with k(ex)(298) = 33.1 +/- 3 dm(3) mol(-1) s(-1), DeltaH double dagger = 24.4 +/- 7 kJ mol(-1) and DeltaS double dagger = -131 +/- 23 J K-1 mol(-1). The highly negative activation entropy and the rate law indicate an associative mode of activation. In spite of the overall large steric requirements of the four tertiary ligands the activation parameters indicate a fairly closed transition state, possibly due to an electronic stabilisation of the transition state by the pi -acidic stannyl ligands.