Analysis of the electronic structure of PdO complexes is reported utilizing multiconfigurational self-consistent field (MCSCF) theory. Models include hard (N) and soft (Cl) donors to mimic proposed Pd oxo intermediates. Calculations argue against formulation of a Pd IV oxo intermediate as posited in earlier experimental studies of Pd II -mediated oxy insertion: i.e., a square-pyramidal complex with a basal oxo ligand. However, low-energy structures with other coordination geometries (trigonal bipyramidal) and isomerism (basal O) were identified. The supporting ligand plays a role in stabilization of the PdO bond as indicated by calculations on the PdOCl 2 fragment and LPdOCl 2 (L = model diimine ligand). P alladium oxo complexes have been proposed as key intermediates for several important transformations. 1,2 For example, oxy insertion into Pd−carbon bonds to form Pd−OR moieties was proposed to go via Pd IV oxo intermediates (Scheme 1). 3,4 Oxy insertion is a key step in catalytic hydrocarbon oxidation, and little precedent exists for selective MR + YO → MOR + Y (YO = oxidant) transformations. Mechanisms of Pd-mediated oxy insertions were never fully elucidated, and proposed Pd IV oxo intermediates were not isolated. Earlier proposals of Pd oxo entities 5 were revisited in light of newer experimental data. 6 A recent DFT study of the reaction of Ni II alkyls with N 2 O producing Ni II alkoxides suggested the intermediacy of a Ni III oxyl (i.e., O −