Oxidative addition reaction of diarylplatinum(ii) complexes with MeI in ionic liquid media: a kinetic study

Abstract

A kinetic study of the oxidative addition reaction of diarylplatinum(II) complexes [Pt(p-MeC₆H₄)₂(NN)] (1a: NN = 1,10-phenanthroline (phen) and 1b: NN = 4,4′-di-tert-butyl-2,2′-bipyridine (^tBu₂bpy)) with MeI in ionic liquids 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([bmim][bta]) or 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) is described. The reactions were investigated as a function of MeI concentration and temperature under pseudo-first-order conditions using UV-vis spectroscopy techniques. In general, the oxidative addition reactions in ionic liquids followed an S_N2 mechanism, similar to that reported for the related reactions in conventional solvents, e.g. benzene or acetone. The reaction rates in different solvents followed the order acetone > ionic liquids > benzene. The trend in the values of k₂ clearly indicated that ionic liquids behave like conventional solvents and that no particular ‘ionic liquid effect’ was detected in this kind of reaction. The effect of solvent on the reactions was examined using a linear solvation energy relationship (LSER) based on the Kamlet–Taft solvent scale. The activation parameters, ΔH^‡ and ΔS^‡, were obtained for the reactions in each solvent and the investigation of enthalpy-entropy compensation confirmed that the mechanism operated in all solvents is similar.