Three different palladium(II) complexes Pd(NN')Cl-2 and two different palladium(0) complexes Pd(NN')(dmfu) (dmfu = dimethylfumarate) containing NN' pyridyl-imine ligands, have been prepared and used as pre-catalysts for the coupling between iodobenzene and methyl acrylate (Meac) (Heck reaction). All the reactions have been conducted in DMF at 80degreesC, using Et3N as base and a Pd:Ph1: Meac:Et3N = 1:1000:1100:1000 molar ratio. In all cases the complete conversion of iodobenzene into trans-methylcynnamate has been observed within 2.5 h of reaction, with the highest TOF value (1253) obtained with a palladium(II) complex. At the end of the catalytic reactions the dimeric species [Pd2I6][Et3NH](2) has been recovered, pointing out a partial palladium loss from the starting complex species. A poisoning Hg(0) test has shown a heterogeneous nature of the catalytic reactions and this indicates that the Pd(NN') complexes act as metallic palladium reservoirs. The dimer [Pd2I6][Et3NH](2) probably forms from soluble palladium(0) particles arising from the complex decomposition once the substrates have been totally consumed. Interestingly, the dimer [Pd2I6][DMFH](2) has been obtained by reacting PdCl2 and Meac in DMF at 80degreesC. (C) 2004 Elsevier B.V. All rights reserved.