Methanol solutions containing Cd(II), Mn(II), and a palladacycle, (dimethanol bis(N,N-dimethylbenzylamine-2C, N)palladium(II) (3), are shown to promote the methanolytic transesterification of O-methyl O-4-nitrophenyl phosphorothioate (2b) at 25 degrees C with impressive rate accelerations of 10(6)-10(11) over the background methoxide promoted reaction. A detailed mechanistic investigation of the methanolytic cleavage of 2a-d having various leaving group aryl substitutions, and particularly the 4-nitrophenyl derivative (2b), catalyzed by Pd-complex 3 is presented. Plots of k(obs) versus palladacycle [3] demonstrate strong saturation binding to form 2b:3. Numerical fits of the kinetic data to a universal binding equation provide binding constants, K-b, and first order catalytic rate constants for the methanolysis reaction of the 2b:3 complex (k(cat)) which, when corrected for buffer effects, give corrected (K-cat(corr)) rate constants. A sigmoidal shaped plot of log(K-cat(corr)) versus. (s)(s)pH (in methanol) for the cleavage of 2b displays a broad (s)(s)pH independent region from 5.6 <= (s)(s)pH <= similar to 10 with a k(minimum) = (1.45 +/- 0.24) x 10(-2) s(-1) and a [lyoxide] dependent wing plateauing above a kinetically determined (s)(s)pK(a) of 12.71 +/-0.17 to give a k(maximum) = 7.1 +/- 1.7 s(-1). Bronsted plots were constructed for reaction of 2a-d at (s)(s)pH 8.7 and 14.1, corresponding to reaction in the midpoints of the low and high (s)(s)pH plateaus. The Bronsted coefficients (beta(LG)) are computed as -0.01 +/- 0.03 and -0.86 +/- 0.004 at low and high (s)(s)pH, respectively. In the low (s)(s)pH plateau, and under conditions of saturating 3, a solvent deuterium kinetic isotope effect of k(H)/k(D) = 1.17 +/- 0.08 is observed; activation parameters (Delta H double dagger(Pd) = 14.0 +/- 0.6 kcal/mol and Delta S double dagger(Pd) = -20 +/- 2 cal/mol.K) were obtained for the 3-catalyzed cleavage reaction of 2b. Possible mechanisms are discussed for the reactions catalyzed by 3 at low and high (s)(s)pH. This catalytic system is shown to promote the methanolytic cleavage of O,O-dimethyl phosphorothioate in CD3OD, producing (CD3O)(2)P=O(S-) with a half time for reaction of 34 min.