Multidentate ligand kinetics. V. Copper(II) and cyclohexylenediaminetetraacetatonickelate(II)

Article abstract of DOI:10.1021/ic50008a003

The kinetics of the substitution reaction between the hydrated copper(II) ion and the cyclohexylenediaminetetraacetatonickelate(II) ion are studied from pH 1.5 to 3.5. In contrast to the dominant role of copper ion attack in the similar reaction with ethylenediaminetetraacetatonickelate(II), there is no copper ion attack of cyclohexylenediaminetetraacetatonickelate(II). The reaction is first order in the complex and independent of copper concentration but it is highly pH dependent. The acid dissociation rate constants are resolved. The absence of any copper dependence is attributed to the inability of the ion to form dinuclear iminodiacetate intermediates because of hindered rotation and steric blocking due to the hydrocarbon ring. The proposed mechanism indicates that nickel-nitrogen bond dissociation must be a rate-determining step in these multidentate ligand exchange reactions.