Reactions of nickel(II) diphenolate diamide complexes with polydentate ligands

Abstract

(N,N′-ethylenedisalicylamidato)nickelate(II), [NiL]^2–, reacted with ethylenediamine-N,N,N′,N′-tetraacetate (edta) and trans-cyclohexane-1,2-diamine-N,N,N′,N′-tetraacetate (cdta) in borate buffer with first-order rate constants of 3.39 × 10^–4 and 3.44 × 10^–4 s^–1 respectively at pH 9.34. Both the reactions are pH dependent. Kinetic information suggests that the protonated species of [NiL]^2– are the reactive species, the reactivity order being [Ni(H₂L)] > [Ni(HL)]^– > [NiL]^2–. For the edta reaction direct substitution is evident while with cdta steric factors necessitate the formation of an intermediate complex, the decomposition of which in a rate limiting step yields the substituted products. Comparative data for similar reactions involving (N,N′-ethylenedisalicylamidato)cuprate(II) are discussed.