Dedicated to Prof. Dr. S. Fullub on the occasion of his 60th birthday (14.VI.85)The kinetics of the reaction ( I ) between 1,4,8,1l-tetraazacyclotetradecane (Cy) and a series of Cu(I1) complexes CuL (L = glycolate, malonate, succinate, picolinate, glycinate, iminodiacetate, nitrilotriacetate, N-(2-hydroxyethyl)ethylenediaminetriacetate, ethylenediamine, 1,3-diaminopropane, diethylenetriamine and N,N-bis(3-aminopropylamine) were studied spectrophotometrically at 25" and Z = 0.5 (KNO,). From the analysis of the log kOb,/log [L] profiles obtained at different pH values the resolved bimolecular rate constants k:,",!$ (Table 3) were obtained by a nonlinear curve-fitting procedure. For nearly all systems studied, the rate constant k$k, describing the reaction between the 1 :1 complex CuL and the monoprotonated form of the macrocycle CyH, was obtained. The nonlinear relationship between log k,!$ and log KCuL and its nature is discussed. It is shown that the inverse relationship between reactivity and stability described by others is only a special case of the more general Eqn. 3 described here.Introduction. -Ligand-ligand replacement reactions have been studied in detail and many aspects of the reaction mechanism are well-understood [2]. In general, these reactions proceed through intermediates in which the incoming ligand is partially coordinated and the expelled ligand is partially dissociated. From the detailed analysis of such mechanisms, one can predict the rate of a ligand-ligand exchange process, if one knows the stability of the intermediate. Another possibility to predict rates comes from the observation that an inverse relationship between the stability of the starting complex and its reactivity exists. This has been found for open-chain ligands [3] as well as for cyclic polyamines [4].During our studies on the kinetics of complexation reactions with tetraazamacrocycles in the absence [5] and presence [l] of additional ligands, we became interested whether this rule applies to a large number of chelators with different donor atoms. For such a study the complexation of 1,4,8,ll-tetraazacyclotetradecane (Cy) with a large variety of Cu" complexes seemed ideal, because the reaction can easely be followed, and the rates are accessible to measurements.