Solvent dependence of the stereochemistry of base-catalysed solvolysis of trans-[Co(NH3)4(15NH3)X]3+/2+ ions in dipolar aprotic solvents

Abstract

The preparation is described of trans-[Co(NH₃)₄(¹⁵NH₃)(OSO₂CF₃)][ClO₄]₂ as a precursor for the synthesis of ¹⁵NH₃-labelled complexes trans-[Co(NH₃)₄(¹⁵NH₃)X]³⁺ with weakly co-ordinating neutral ligands X. The availability of these compounds makes it possible to study the stereochemistry of base-catalysed solvolysis of penta-amminecobalt(III) complexes in weakly co-ordinating dipolar aprotic solvents. For a number of cases the observed sterochemistry differs significantly from the results reported earlier for more strongly co-ordinating and protic solvents (around 50% rentention). This difference in sterochemistry cannot be exclusively explained by sovational effects. Specific effects of the entering and leaving groups are snown to be important. The results are compatible with a mechanistic model involving a five-co-ordinate intermediate.