Seeking new metalloligands: Synthesis and reactivity of palladacycles with pyridine and pyrimidine rings

Treatment of the Schiff base ligands 4-(NC5H4)C6H4C(H)N[2′-(OH)C6H4] (a), 3,5-(N2C4H3)C6H4C(H)N[2′-(OH)-C6H4] (b) and 3,5-(N2C4H3)C6H4C(H) N[2′-(OH)-5′-tBuC6H3] (c) with palladium (II) acetate in toluene gave the poly-nuclear cyclometallated complexes [Pd{4-(NC5H4)C6H3C(H)N[2′-(O)C6H4]}]4(1a), [Pd{3,5-(N2C4H3)C6H3C(H)N[2′-(O)-C6H4]}]4(1b) and [Pd{3,5-(N2C4H3)C6H3C(H)N[2′-(O)-5′-tBuC6H3]}]4(1c) respectively, as air stable solids, with the ligand acting as a terdentate [C,N,O] moiety after deprotonation of the –OH group. Reaction of the cyclometallated complexes with triphenylphosphine gave the mononuclear species [Pd{4-(NC5H4)C6H3C(H) N[2′-(O)C6H4]}(PPh3)], (2a), [Pd{3,5-(N2C4H3)C6H3C(H) N[2′-(O)C6H4]}(PPh3)], (2b) and [Pd{3,5-(N2C4H3)C6H3C(H)N[2′-(O)-5′-tBuC6H3)}(PPh3)], (2c) in which the polynuclear structure has been cleaved and the coordination of the ligand has not changed [C,N,O]. When the cyclometallated complexes 1b and 1c were treated with the diphosphines Ph2P(CH2)4PPh2 (dppb), Ph2PC5H4FeC5H4PPh2 (dppf) and Ph2P(CH2)2PPh2 (t-dppe) in a 1:2 molar ratio the dinuclear cyclometallated complexes [{Pd[3,5-(N2C4H3)C6H3C(H)N{2′-(O)C6H4}]}2(μ-Ph2P(CH2)4PPh2)], (3b), [{Pd[3,5-(N2C4H3)C6H3C(H) N{2′-(O)-5′-tBuC6H3}]}2(μ-Ph2P(CH2)4PPh2)], (3c), [{Pd[3,5-(N2C4H3)C6H3C(H)N{2′-(O)C6H4}]}2(μ-Ph2P(η5-C5H4)Fe(η5-C5H4)PPh2)], (4b), [{Pd[3,5-(N2C4H3)C6H3C(H) N{2′-(O)-5′-tBuC6H3}]}2(μ-Ph2P(η5C5H4)Fe(η5C5H4)P-Ph2)], (4c) and [{Pd[3,5-(N2C4H3)C6H3C(H)N{2′-(O)-5′-tBuC6H3}]}2(μ-Ph2P(CHCH)PPh2)], (5c) were obtained as air stable solids.

Terdentate [C,N,O] Schiff bases with pyridine or pyrimidine rings yield new mono- and polynuclear palladacycles bearing non-coordinated heterocyclic nitrogen donors.Figure optionsDownload as PowerPoint slide