Structural and reactivity comparison of analogous organometallic Pd(III) and Pd(IV) complexes.

The tetradentate ligands (R)N4 ((R)N4 = N,N'-di-alkyl-2,11-diaza[3,3](2,6)pyridinophane, R = Me or iPr) were found to stabilize cationic ((R)N4)PdMe(2) and ((R)N4)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 d(7) 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.