The methanolytic cleavage of a series of O,O-dimethyl O-aryl phosphorothioates (1a-g) catalyzed by a C,N-palladacycle, (2-[N,N-dimethylamino(methyl)phenyl]-C-1,N)(pyridine) palladium(II) triflate (3), at 25 degrees C and (s)(s)pH 11.7 in methanol is reported, along with data for the methanolytic cleavage of 1a-g. The methoxide reaction gives a linear log k(2)(-Ome) vs (s)(s)pKa (phenol leaving group) Bronsted plot having a gradient of beta(lg) = -0.47 +/-0.03, suggesting about 34% cleavage of the P-OAr bond in the transition state. On the other hand, the 3-catalyzed cleavage of 1 gives a Bronsted plot with a downward break at (s)(s)pK(a) (phenol) similar to 13, signifying a change in the rate-limiting step in the catalyzed reaction, with the two wings having beta(lg) values of 0.0 +/- 0.03 and 1.93 +/- 0.06. The rate-limiting step for good substrates with low leaving group (s)(s)pK(a) values is proposed to be substrate/pyridine exchange on the palladacycle, while for substrates with poor leaving groups, the rate-limiting step is a chemical one with extensive cleavage of the P-OAr bond. DFT calculations support this process and also identify two intermediates, namely, one where substrate/pyridine interchange has occurred to give the palladacycle coordinated to substrate through the S=P linkage and to methoxide (6) and another where intramolecular methoxide attack has occurred on the P=S unit to give a five-coordinate phosphorane (7) doubly coordinated to Pd via the S- and through a bridging methoxide linked to P and Pd. Attempts to identify the existence of the phosphorane by P-31 NMR in a d(4)-methanol solution containing 10 mM each of 3, trimethyl phosphorothioate (a very slow cleaving substrate), and methoxide proved unsuccessful, instead showing that the phosphorothioate was slowly converted to trimethyl phosphate, with he palladacycle decomposing to Pd-0 and free pyridine. These results provide the first reported example where a palladacycle-promoted solvolysis reaction exhibits a break in the Bronsted plot signifying at least one intermediate, while the DFT calculations provide further insight into a more complex mechanism involving two intermediates.