Benzenedicarbonyl and benzenetricarbonyl linker pyrazolyl complexes of palladium(II): synthesis, Xray structures and evaluation as ethylene polymerisation catalysts

A series of novel compounds with pyrazolyl rings (pz) linked by benzenedicarbonyl (L1–L4) and benzenetricarbonyl (L5, L6) have been prepared and structurally characterized. The mutual orientation of their rings was studied by molecular mechanics. These polydentate species react with PdCl2(NCMe)2 to yield dinuclear complexes in which the Pd centers coordinate to one or two pz units, a terminal chloride and two bridging chloride ligands. In complex [{(3,5-tBu2pzCO)3-1,3,5-C6H4}Pd2Cl2(µ-Cl)2]4 the pyrazolyl ligand L5 acts as a bidentate donor despite the presence of the third pz group. These Pd complexes, when activated with methylaluminoxide (MAO), exhibit activity in ethylene polymerization.