The First Crystal and Molecular Structure of asyn-Acetato-Bridged Dinuclear Cyclometallated Complex [Pd{2,3,4-(MeO)3C6HC(H)=NCH2CH2OH}(μ-OAc)

Abstract

Treatment of the Schiff base ligands 2,3,4-(MeO)3C6H2C(H)=NR (R = CH2CH2OH, 1; R = Me, 17; R = Et, 18; R = Pr, 19; R = tBu, 20) with palladium(II) acetate in toluene gave the dinuclear cyclometallated complexes [Pd{2,3,4-(MeO)3C6HC(H)=NR}(μ-O2CMe)]2 (R = CH2CH2OH, 2; R = Me, 21; R = Et, 22; R = Pr, 23; R = tBu, 24), with the ligand bonded to the palladium atom through the imine nitrogen and the C6 carbon atoms. The 1H and 13C{1H} NMR spectra of the complexes showed the presence of the anti and syn isomers in solution. The anti/syn ratio varies with the solvent and the nature of the imine nitrogen substituent R. Complex 24 with the bulky tBu group showed a 28:1 ratio in chloroform whilst the less bulky substituted complexes showed lower ratios. The X-ray crystal structure of the syn isomer of complex 2 is described. Reaction of the acetato-bridged complex 2 with PPh3 gave the mononuclear complex 4, in a bridge-splitting reaction. Reaction of 2 with the diphosphanes dppm, dppp and dppb in a 1:1 molar ratio gave the dinuclear cyclometallated complexes 5, 6 and 7, respectively. Treatment of 2 with an aqueous solution of sodium chloride gave the chloro-bridged complex 3. Treatment of the cyclometallated chloro-bridged complex 3 with PPh3 in acetone yielded the mononuclear complex 8, and reaction of 3 with silver triflate gave the cyclometallated complex 9, with the palladium atom bonded to four different atoms C, N, O and P. Treatment of 3 with the tertiary diphosphanes dppp, dppb and dppf, in a 1:1 molar ratio gave the dinuclear complexes 10, 11 and 12, respectively, with terminal chloride ligands. However, reaction of 3 with the small “bite” diphosphane dppm gave 13, with a bridging chloride ligand. Reaction of 11 with silver triflate in acetone gave the new dinuclear complex 14, with the Schiff base ligand as [C,N,O] terdentate. Reaction of 3 with the diphosphane dppe in a 1:2 molar ratio, and silver perchlorate, gave the mononuclear complex 15. Treatment of 3 with the triphosphane bis(2-diphenylphosphanylethyl)phenylphosphane in a 1:2 molar ratio, followed by treatment with sodium perchlorate, gave 16, in which the palladium atom was bonded to the triphosphane through the three phosphorus atoms. The X-ray crystal structures of complexes 8, 9, 15 and 16 are also reported. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)