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

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posted on 25.04.2011, 00:00 authored by Dirk Penno, Francisco Estevan, Elena Fernández, Pipsa Hirva, Pascual Lahuerta, Mercedes Sanaú, M Úbeda
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.