Kinetics of acid-catalyzed dissociation of nickel (II) N-alkyl-substituted diamino diamide complexes

The dissociation kinetics of the nickel (11) complexes of 4-methyl-4,7-diazadecanediamide (4-Me-L-2,2,2), 4,7-dimethyl-4,7-diazadecanediamide (4,7-N,N'-Me-2-L-2,2,2), 4-ethyl-4,7-diazadecanediamide (4-Et-L-2,2,2), and 4-methyl-4,8-diazaundecanediamide (4-Me-L-2,3,2) have been studied at 25.0 degreesC and mu = 4.0 M (NaClO4 + HClO4) by the stopped-flow method. These reactions are specific-acid catalyzed; however, the rate constants of these reactions do not depend on the concentrations of acetic, chloroacetic, and dichloroacetic acids. At pH values below 1.0, both the proton-assisted and the direct protonation pathways make contributions to the rates. The ratios of the rate constant of dissociation by the direct protonation pathway to the rate constant by the proton-assisted pathway for the complexes in aqueous solution were measured and discussed.