Macrocyclic Trinuclear Nickel Phenoxyimine Catalysts for High-Temperature Polymerization of Ethylene and Isospecific Polymerization of Propylene

A series of macrocyclic multinucleating phenoxyimine ligands and the corresponding neutral binuclear (2-Ni2) and trinuclear (3-Ni3) nickel catalysts have been efficiently synthesized. The trinuclear nickel complex 3-Ni3 showed high activity, high thermal stability, and slow chain transfer in ethylene polymerization, thus producing polyethylene with high molecular weight and low branch density. Highly regiospecific and isospecific polymerization of propylene was also achieved with 3-Ni3, generating regioregular and highly isotactic propylene with high Tm and crystallinity. This is the first example of regio- and stereocontrolled propylene polymerization promoted by nickel phenoxyimine catalysts. Statistical analysis suggested selective 1,2-insertion and enantiomorphic site control mechanism in the chain propagation step, likely caused by the unique steric effect of macrocyclic ligands and the potential cooperative effect.