A Proton Magnetic Resonance Study of Ligand Exchange on the Hexakis-(N, N-dimethylformamide)magnesium(II) Ion

Abstract

The rate of ligand exchange on the hexakis(N, N-dimethylformamide) magnesium(II) ion, [Mg(dmf)₆]²⁺, in CD₂Cl₂ and (CD₃)₂CO diluents is found to be virtually independent of the concentration of free dmf. This is consistent with a reaction mechanism in which bond rupture is the major factor in the rate-determining step for the exchange process. For a solution in which [Mg(dmf)₆²⁺],[dmf] and [CD₂Cl_,] are 0.0768, 0.397 and 13.9 mol dm^-3 respectively, k_ex(215 K) = 23.5 ± 3.2 s^-1, ΔH^‡ = 77.8 + 3.0 kJ mol^-1 and ΔS^‡ = l46 ± 14 J K^-1 mol^-1, and similar kinetic parameters characterize other CD₂Cl₂ solutions. In (CD₃)₂CO diluent the ligand-exchange process is characterized by smaller ΔH^‡ and ΔS^‡ values. These data are discussed in conjunction with kinetic data reported for other magnesium(II) systems.