Kinetics of the ligand exchange reaction between tetrakis(acetylacetonato)-thorium(IV) and free acetylacetone in CD3CN and CDCl3.

Kinetics of the ligand exchange reaction between tetrakis(acetylacetonato)thorium(IV) and free acetylacetone in CD3CN and CDCl3 was studied by 1H NMR. The rate law was written as rate =k[Th(acac)4][Hacac]enol, where k=(1.0±0.1)×102 s−1 mol−1 kg at 0 °C in CD3CN and (1.7±0.1)×102 s−1 mol−1 kg at −16 °C in CDCl3. The rates were retarded by addition of bases and the retardation effect well correlated with the donor number of the bases. Under the conditions studied, the activation entropies gave large negative values. A ligand exchange mechanism passing through a nine-coordinate intermediate is proposed to interpret the kinetic law.

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