The methanolysis of various aryl and aliphatic carboxylate esters promoted by methoxide, 1,5,9-triazacyclododecane : Zn²⁺(^âOCH3) and La³⁺(^âOCH3), were studied and the derived rate constants (kOCH3, kcat^3:Zn(OCH3) and kcat^La(OCH3)) correlated in various ways. The metal ion catalyzed reactions are very much faster than the background reactions in some cases reaching up to 7 à 10⁶-fold acceleration when present at concentrations of 5 mmol dm^{â 3}. The data for both metals exhibit non-linear Brønsted correlations with the pKa of the leaving group which are analyzed in terms of a change in rate limiting step from formation to breakdown of a metal-coordinated tetrahedral intermediate as the pKa increases above values of â ¼14.7. Plots of the log kOCH3 reaction vs. the log kcat values for each metal ion indicate low sensitivity for aryl esters and a higher sensitivity for the aliphatic esters. A mechanistic rationale for the observations is presented.