Structural and reactivity comparison of analogous organometallic Pd(iii) and Pd(iv) complexes

The tetradentate ligands ^RN4 (^RN4 = N,N′-di-alkyl-2,11-diaza[3,3](2,6)pyridinophane, R = Me or iPr) were found to stabilize cationic (^RN4)PdMe₂ and ( ^RN4)PdMeCl complexes in both Pd^III and Pd^IV oxidation states. This allows for the first time a direct structural and reactivity comparison of the two Pd oxidation states in an identical ligand environment. The Pd^III complexes exhibit a distorted octahedral geometry, as expected for a d⁷ metal center, and display unselective C-C and C-Cl bond formation reactivity. By contrast, the Pd^IV complexes have a pseudo-octahedral geometry and undergo selective non-radical C-C or C-Cl bond formation that is controlled by the ability of the complex to access a five-coordinate intermediate.