Acid dissociation kinetics of the copper(II) complex of a 15-membered mixed N3O2 donor macrocycle

Abstract

The kinetics of the acid dissociation of the copper(II) complex of the 15-membered N3O2 donor macrocycle [prepared by reaction of 2,6-bis(2-aminophenoxymethyl)-pyridine with glyoxal in the presence of a manganese(II) template followed by reduction of the two imine linkages with NaBH4] was studied over an acidity range (0.01–0.5 mol dm-3 [H+]) at 25 °C and I = 1.0 mol dm-3 by stopped-flow methods. A biphasic reaction was observed at 752 nm, the first reaction being complete within 20 ms at 25 °C and too rapid to study in detail. The second reaction shows a good first order dependence on the hydrogen ion concentration over the whole acidity range and kobs=k0+kH[H+], where k0 = 0.52 s-1 and kH = 40.2 dm3 mol-1 s-1 at 25 °C. The k0 term represents a small but significant solvolytic reaction. The mechanism of the acid-catalysed dissociation is discussed.