Synthesis and reactivity of novel cyclometallated complexes derived from [C,N,O] terdentate ligands. Crystal structure of [Pd{2,3,4-(MeO)3C6HC(H)N[2-(O)C6H4]}(PPh3)]

Abstract

Treatment of the Schiff base ligands 2,3,4-(MeO)₃C₆H₂C(H)N[2-(OH)C₆H₄], a, and 2,3,4-(MeO)₃C₆H₂C(H)N[2-(OH)-4-MeC₆H₄], b, with palladium(II) acetate in toluene gave the cyclometallated complexes [Pd{2,3,4-(MeO)₃C₆HC(H)N[2-(O)C₆H₄]}]_n, 1a, and [Pd{2,3,4-(MeO)₃C₆HC(H)N[2-(O)-4-MeC₆H₄]}]_n, 1b, respectively, as air stable solids, with the [C,N,O] ligand terdentate after deprotonation of the –OH group. Reaction of the cyclometallated complexes with triphenylphosphine gave the mononuclear species [Pd{2,3,4-(MeO)₃C₆HC(H)N[2-(O)C₆H₄]}(PPh₃)], 2a, and [Pd{2,3,4-(MeO)₃C₆HC(H)N[2-(O)-4-MeC₆H₄]}(PPh₃)], 2b, with cleavage of the polynuclear structure. The molecular structure of 2a has been determined by X-ray crystallography. Treatment of 1a and 1b with the diphosphines dppm, dppp, dppb, dpppe and dppf in a 1∶2 molar ratio afforded the dinuclear cyclometallated complexes [(Pd{2,3,4-(MeO)₃C₆HC(H)N[2-(O)C₆H₄]})₂{μ-PPh₂(CH₂)_nPPh₂}] (3a: n = 1; 4a: n = 3; 5a: n = 4; 6a: n = 5), [(Pd{2,3,4-(MeO)₃C₆HC(H)N[2-(O)C₆H₄]})₂(μ-PPh₂C₅H₄FeC₅H₄PPh₂)], 7a, [(Pd{2,3,4-(MeO)₃C₆HC(H)N[2-(O)-4-MeC₆H₄]})₂{μ-PPh₂(CH₂)_nPPh₂}] (3b: n = 3; 4b: n = 4) and [(Pd{2,3,4-(MeO)₃C₆HC(H)N[2-(O)-4-MeC₆H₄]})₂(μ-PPh₂C₅H₄FeC₅H₄PPh₂)], 5b, as air stable solids. Treatment of 1a and 1b with an excess of mono- or diphosphine did not produce cleavage of the Pd–O_chelating bond.