Bis( oxamato) palladate( II) complexes: synthesis, crystal structure and application to catalytic Suzuki

摘要

New bis(oxamato)palladate(II) complexes, [Pd(H2O)(4)][Pd(2,6-Me(2)pma)(2)]2H(2)O (1), (n-Bu4N)(2)[Pd(2,6-Me(2)pma)(2)]2H(2)O (2a), and (n-Bu4N)(2)[Pd(2,6-Me(2)pma)(2)]2CHCl(3) (2b) (2,6-Me(2)pma=N-2,6-dimethylphenyoxamate and n-Bu4N+ =tetra-n-butylammonium), have been synthesized and the structures of 1 and 2b characterized by single-crystal X-ray diffraction. Complex 1 is a double salt constituted by tetraaquapalladium(II) cations and bis(oxamato)palladate(II) anions interlinked by hydrogen bonds. The palladium(II) ions in 1 are four-coordinate with two oxygens and two nitrogens from two fully deprotonated oxamate ligands (anion), and four water molecules (cation) building centrosymmetric square-planar surroundings. Centrosymmetric bis(oxamato)palladate(II) anions occur in 2b as in 1, the charge balance in this compound being ensured by the bulky n-Bu4N+. The catalytic role of 1 and 2a for the Suzuki reaction has been investigated by using a series of aryl iodide/bromide derivatives in the conventional organic medium dimethylformamide. The tetraaquapalladium(II) unit in 1 appears to be active in the catalytic Suzuki cross-coupling reactions, but it readily decomposes to inactive palladium black.