The trans effect and trans influence of triphenyl arsine in platinum(ii) complexes. A comparative mechanistic and structural study

Abstract

The kinetics and mechanism of the reaction between [PtI₃(AsPh₃)]⁻ and pyridine in acetonitrile solvent has been studied by use of stopped-flow spectrophotometry. Substitution of iodide trans to arsine is irreversible under the conditions used and takes place via parallel direct and solvolytic pathways. By comparing the rate constants of the direct pathway with literature values of the corresponding phosphine and stibine complexes the following trans effect series can be obtained: Ph₃Sb > Ph₃P > Ph₃As. The crystal and molecular structures of reactant and product have been determined. Based on Pt–I distances for the investigated arsine complex and literature data for the corresponding phosphine and stibine complexes the following trans influence series was derived: Ph₃P ≥ Ph₃As > Ph₃Sb. To the best of our knowledge this is the first comparison of all the three heavier pnictogens as donor atoms using strictly analogous complexes with identical cis-ligands.