Pyridine linker pyrazolyl palladium complexes: Synthesis, characterization and ethylene polymerization activity

A series of pyrazolyl compounds with 2,6-pyridinedicarbonyl linker, {RR′pz(CO)}₂py, R = R′ = ^tBu (L1); R = R′ = Me (L2); R = R′ = H (L3), R = H, R′ = Me (L4) has been prepared from the reaction of 2,6-pyridinedicarbonyl chloride with the appropriate pyrazole and a mild base. Ligands L1-L3 reacted with Pd(NCMe) ₂Cl₂ to form mononuclear complexes while the reaction with L4 produced an intractable product. Complexes 1 and 2 were tested for their catalytic activities for the polymerization of ethylene after activation with methylaluminoxane (MAO). Active polymerization catalysts were formed in situ with MAO and that catalyzed the polymerization of ethylene to high-density linear polyethylene. The effects of co-catalyst concentration and temperature are reported. The optimum co-catalyst to catalyst ratio is 3000:1 and catalyst activity decreases above 40 °C due to catalyst deactivation.