The mechanism of cleavage of a series of seven O,O-dimethyl O-aryl phosphorothioates (6a-g) promoted by a C,N-palladacycle, (2-[N,N-dimethylamino-(methyl)phenynl]-C-1,N)(pyridine) palladium(II) triflate (5:OTf) in methanol at 25 degrees C was investigated with the aim of identifying catalytically important intermediates. Complete (s)(s)pH/rate profiles (in methanol) were conducted for the cleavage of 6a-g in the presence of 0.08 mM 5. The log k(obs) for the catalyzed methanolysis of 6a increases linearly with (s)(s)pH with a plateau above the (s)(s)pK(a)(1) of 11.16 for formation of 5:-OCH3. The profiles for 6b-g are bell-shaped, depending on the apparent ionizations of two acidic groups, with the rate constant maximum of the bell and the (s)(s)pK(a)(1) values shifting to higher (s)(s)pH values as the :(s)(s)pK(a)(HOAr) of the leaving group phenol increases. A Bronsted plot of the log k(obs)(max) (the maximum rate constants for cleavage of 6a-g) vs (s)(s)pK(a)(HOAr) exhibits a downward break at similar to (s)(s)pK(a)(HOAr) 13, with the two wings having beta(1g) values of 0.01 and -0.96. A model describing the kinetically important species involves a complex series of equilibria: 5:(HOCH3):pyr reversible arrow 5:(-OCH3):pyr + H+ (6 reversible arrow)5:(-OCH3):6 + pyr (reversible arrow)phosphorane 7 -> product, where the rate limiting steps change from formation of 5:(-OCH3):6 to formation of thiophosphorane 7 and then to product formation as the aryloxy leaving groups of 6 get progressively worse. Kinetic experiments indicate that the reaction of 5 with 6e, having a 4-chlorophenoxy leaving group, rapidly produces a transient intermediate, postulated to be the palladacycle-bound 5-coordinate thiophosphorane (7e) that exists long enough to obtain its UV/vis spectrum by stopped-flow spectrophotometry. Detailed analysis of the data sheds light on the origins of a previously reported anomalously large beta(1g), of -1.93 for the descending wing of a Bronsted plot (J. Am. Chem. Soc. 2010, 132, 16599). Finally, energetics analysis indicates that the binding of palladacycle to the transition state comprising attack of methoxide on 6e, [MeO- + 6e](double dagger), stabilizes the latter by 34.9 kcal/mol, converting that transition state into an observable intermediate.