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

Abstract

Phosphine exchange at square-planar trans-Pt(SnPh₃)₂(PMe₂Ph)₂ has been studied by ³¹P 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_ex²⁹⁸ = 33.1 ± 3 dm³ mol⁻¹ s⁻¹, ΔH^‡ = 24.4 ± 7 kJ mol⁻¹ and ΔS^‡ = −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 π-acidic stannyl ligands.