Cyclopalladated compounds derived from [C,N,O] terdentate ligands:: synthesis, characterization and reactivity

Treatment of the Schiff base ligands 2-ClC6H4C(H)=NCH2(C4H7O) (a) and 3,4-(MeO)(2)C6H3C(H) NCH2(C4H7O) (b) with palladium(II) acetate in toluene or glacial acetic acid gave the dinuclear cyclometallated complexes [Pd{2-ClC6H3C(H)-NCH2(C4H7O)}(mu-OAc)](2) (1a) and [Pd{3,4-(MeO)(2)C6H2C(H) NCH2(C4H7O)}(mu-OAc)](2) (1b) with the ligand bonded to the palladium atom through the imine nitrogen and the C6 carbon atom. The H-1 and C-13-{H-1} NMR spectra of the complexes show the occurrence in solution of three pairs of enantiomers. The acetato-bridged cyclometallated complex [Pd{3,4(MeO)(2)C6H3C(H)=NCH2(C4H7O)}(mu-OAc)](2) (1c) was prepared from the enantiopure ligand (R)-3,4-(MeO)(2)C6H3(H)-NCH2(C4H7O) (c). The NMR spectra of 1c showed the existence of only two diastereomers in the solution. The reaction of 1a and 1b with aqueous sodium chloride gave the chloro-bridged complexes [Pd{2-ClC6H3C(H) NCH2(C4H7O)}(mu-Cl)](2) (2a) and [Pd{3,4-(MeO)(2)C6H2C(H)-NCH2(C4H7O)}(mu-Cl)](2) (2b) after a metathesis reaction. The reaction of 2a with PPh3 in acetone gave the mononuclear cyclometallated complex [Pd{2-ClC6H3C(H) NCH2(C4H7O)}(Cl)(PPh3)] (3a) in a bridge-splitting reaction. Treatment of 3a with silver triflate gave the cyclometallated complex [Pd{2-ClC6H3C(H) NCH2(C4H7O);(PPh3)][CF3SO3] (4a) in which the palladium atom is bonded to four different atoms C. N. O and P. When complex 2a was reacted with silver triflate in acetone complex [Pd{2-ClC6H3C(H)-NCH2(C4H7O)}((CH3)(2)CO)][CF3SO3] (5a) was obtained with the ligand as [C,N,O] coordinated. The reaction of complexes 2a and 2b with the diphosphine dppp in a complex-phosphine 1:1 molar ratio gave the dinuclear cyclometallated complexes [{Pd[2-ClC6H3C(H)=NCH2(C4H7O)](Cl)}(2)(mu-Ph2P(CH2)(3)PPh2)] (8a) and [{Pd[3,4-(MeO)(2)C6H2C(H)=NCH2(C4H7O)](Cl)}(2)(mu-Ph2P(CH2)(3)PPh2)] (5b) with the diphosphine bridging the two palladium atoms. Reaction of complexes 2a and 2b with the phosphines dppp and cis-dppe in a 1:2 molar ratio gave the mononuclear complexes [Pd{2-ClC6H3C(H) -NCH2(C4H7O)}{Ph2P(CH2)(3)Ph-2-P,P}][ClO4] (6a), [Pd{3,4-(MeO)(2)C6H2C(H) NCH2(C4H7O)}{Ph2P(Ch(2))(3)Ph-2-P,P}][ClO4] (3b) and [Pd{2-ClC6H2C(H)-NCH2(C4H7O)}(cis-Ph2PCH=CHPh2-P,P)][Cl] (4b). The treatment of 2a with the triphosphine bis(2-diphenylphosphinoethyl)phenylphosphine in 1:2 molar ratio, followed, by treatment with sodium perchlorate gave [Pd{3,4-(MeO)(2)ClC6H3C(H)=NCH2(C4H7O)}{(PPh2CH2CH2)(2)PPh-P,P,P}][ClO4] (7a) in which the palladium atom is bonded to the triphosphine through the three phosphorus atoms and to the Schiff base ligand through one carbon atom and the imine nitrogen. (C) 2002 Elsevier Science Ltd. All rights reserved.