Kinetics of ligand-displacement reactions of copper(II) complexes of deprotonated linear and macrocyclic dioxotetra-amines. Comparative studies with glycylglycylglycine and glycylglycylhistidine

The kinetics of displacement of doubly deprotonated linear (X1) and 13–15-membered macrocyclic dioxotetra-amines (X2–X4), compared with glycylglycylglycine (X5) and glycylglycylhistidine (X6), from their copper(II) complexes (all commonly expressed as [CuH–2X]) have been studied with ligands of various degrees of nucleophilicity including a linear tetra-amine (L1), macrocyclic tetra-amines (L2 and L3), or ethylenediaminetetra-acetate (edta) in borate (pH 8–9.5) or lutidine buffers (pH 6–7.5). The proposed mechanisms for X1–X4 are analogous to that reported for X6, where proton assistance is needed to aid cleavage of the non-terminal copper–imide bonds and provide open sites for nucleophilic attack. The effects of cyclization of the X ligands and ring size on the relative stability of the [CuH–2X] complexes are well manifested in the ligand-replacement kinetics. Thus, the 14-membered X3 which forms the most stable complex among X1–X6 is the most inert to the substitution reactions.