PROTON MAGNETIC-RESONANCE STUDY OF LIGAND-EXCHANGE ON THE HEXAKIS(N,N-DIMETHYLFORMAMIDE)MAGNESIUM(II) ION

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 [CD2Cl2] are 0 · 0768, 0 · 397 and 13 · 9mol dm-3 respectively, kex(215 K) = 23·5 ± 3·2 s-1, △H ‡ = 77·8 ± 3·0 kJ mol-1 and △S ‡ = 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 △H ‡ and △S ‡values. These data are discussed in conjunction with kinetic data reported for other magnesium(ii) systems. © 1979, CSIRO. All rights reserved.