Thioethercarboxylates in palladium chemistry: First proof of hemilabile properties of S–O ligands

Abstract

The reaction of trans-[PdCl(Ph)(PPh 3) 2] with the thallium salts 2-RS-C 6H 4-COOTl (R=Me, Et, i-Pr or t-Bu) yields the compounds trans-[Pd(OOC-C 6H 4-2-SR- κ 1-O)Ph(PPh 3) 2] ( 1a–d). The solid state structure of the compound with R=Et has been confirmed by X-ray analysis. In solution, however, an equilibrium is established between certain complexes in which one PPh 3 ligand is replaced by the sulphur atom of the S–O ligand to afford chelates. The position of the equilibrium depends on both the electron density on the sulphur and the polarity of the solvent used. The standard free energy and activation energy of the mentioned equilibrium are Δ G 0=22 kJ/mol and E A=25–30 kJ/mol for the complex with R= i-Pr ( 1c).