ACID DISSOCIATION KINETICS OF THE COPPER(II) COMPLEX OF A 15-MEMBEREDMIXED N3O2 DONOR MACROCYCLE

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 mangane se(II) template followed by reduction of the two imine linkages with N aBH4] was studied over an acidity range (0.01 - 0.5 mol dm(-3) [H+]) a t 25 degrees C and I = 1.0 mol dm(-3) by stopped-flow methods. A bipha sic reaction was observed at 752 nm, the first reaction being complete within 20 ms at 25 degrees C and too rapid to study in detail. The se cond reaction shows a good first order dependence on the hydrogen ion concentration over the whole acidity range and kobs = k(0) + k(H)[H+], where k(0) = 0.52 s(-1) and k(H) = 40.2 dm(3) mol(-1) s(-1) at 25 deg rees C. The k(0) term represents a small but significant solvolytic re action. The mechanism of the acid-catalysed dissociation is discussed.