The di-Zn(II) complex of 1,3-bis[N-1,N-1'-(1,5,9-triazacyclododecyl)] propane with an associated methoxide (3:Zn(II)(2):-OCH3) was prepared and its catalysis of the methanolysis of a series of fourteen methyl aryl phosphate diesters (6) was studied at (s)(s)pH 9.8 in methanol at 25.0 +/- 0.1 degrees C. Plots of k(obs) VS [3:Zn(II)(2):-OCH3](free) for all members of 6 show saturation behavior from which K-M and k(cat)(max) were determined. The second order rate constants for the catalyzed reactions (k(cat)(max)/K-M) for each substrate are larger than the corresponding methoxide catalyzed reaction (k(2)(-OMe)) by 1.4 x 10(8) to 3 x 10(9)-fold. The values of kcatmax for all members of 6 are between 4 x 10(11) and 3 x 10(13) times larger than the solution reaction at (s)(s)pH 9.8, with the largest accelerations being given for substrates where the departing aryloxy unit contains ortho-NO2 or C(= O)OCH3 groups. Based on the linear Bronsted plots of k(cat)(max) VS (s)(s)pK(a)of the phenol, beta(Ig) values of -0.57 and -0.34 are determined respectively for the catalyzed methanolysis of "regular' substrates that do not contain the ortho-NO2 or C(= O)OCH3 groups, and those substrates that do. The data are consistent with a two step mechanism for the catalyzed reaction with rate limiting formation of a catalyst-coordinated phosphorane intermediate, followed by fast loss of the aryloxy leaving group. A detailed energetics calculation indicates that the catalyst binds the transition state comprising [CH3O-:6]double dagger, giving a hypothetical [3:Zn(II)(2):CH3O-:6]double dagger complex, by -21.4 to -24.5 kcal/mol, with the strongest binding being for those substrates having the ortho-NO2 or C(= O)OCH3 groups.