The mechanism of the reductive activation of PdII pre-catalysts has been extensively studied, but remains poorly understood. Herein, a combined computational and experimental approach is employed to clearly identify a PdII reduction process that has not been considered thus far. Pivalate, assumed to be a general base, was found to decarboxylate and act as a reductant, suggesting an alternative explanation for the superior performance of pivalic acid as an additive in Pd-catalyzed direct C-H arylation reactions.