Kinetic study of the oxidative addition of methyl iodide to Vaska’s complex in ionic liquids

Oxidative addition of methyl iodide to Vaska’s complex in the ionic liquids 1-butyl-3-methylimidazolium triflate [C4mim][OTf], [C4mim] bis(trifluormethylsulfonyl)imide [Tf2N], and N-hexylpyridinium [C6pyr][Tf2N] occurred cleanly to give the expected Ir(III) oxidative addition product. Pseudo-first order rate constants were determined for the oxidative addition reaction in each solvent ([Vaska’s] = 0.25 mM, [CH3I] = 37.5 mM). The observed rate constants under these conditions were 5–10 times slower than the rate seen in DMF. At high methyl iodide concentrations (>23 mM), the expected first order dependence on methyl iodide was not observed. In each ionic liquid, there was no change in the reaction rates within experimental error over the methyl iodide concentration range of 23–75 mM. At lower methyl iodide concentration, a decrease in rate was observed in [C4mim][Tf2N] with decreasing concentration of methyl iodide.

Graphical abstractOxidative addition of methyl iodide to Vaska’s complex in the ionic liquids gave rates that were 5–10 times slower than the rate seen in DMF. Saturation in the methyl iodide dependence was observed in the ILs. A ligand-promoted mechanism is proposed to account for the saturation kinetics.Figure optionsDownload full-size imageDownload as PowerPoint slide