Dinuclear Ortho-Metalated Palladium(II) Compounds with N,N- and N,O-Donor Bridging Ligands. Synthesis of New Palladium(III) Complexes

New dinuclear ortho-metalated palladium(II) compounds with N,N′-diarylformamidinates, Pd₂[(C₆H₄)PPh₂]₂[R′NC(H)NR′]₂ (R′ = C₆H₅, 3a; R′ = p-CH₃C₆H₄, 3b; R′ = p-CH₃OC₆H₄, 3c) and N,O-donor ligands, Pd₂[(C₆H₄)PPh₂]₂[N,O]₂ (N,O = succinimidate (5), phtalimidate (6), 2-hydroxypyridinate (7), acetanilidate (8)) have been synthesized and characterized by NMR spectroscopy and X-ray diffraction methods. The oxidation with iodobenzene dichloride gave new and rare Pd₂⁶⁺ compounds, Pd₂[(C₆H₄)PPh₂]₂[R′NC(H)NR′]₂Cl₂ (R′ = C₆H₅, 4a; R′ = p-CH₃C₆H₄, 4b). DFT calculations on the Pd₂⁴⁺ → Pd₂⁶⁺ oxidation reaction show that the substituents on the amidinate N atoms have a greater effect on the reaction energy than the substituents on the C atom. DFT calculations also confirm that for Pd₂[(C₆H₄)PPh₂]₂[N,O]₂ compounds the symmetric isomers with N atoms trans to O atoms are the most stable complexes. The palladium dimers were tested as precursors of catalysts in tandem diboration/arylation/oxidation reactions.