Ethylene (Co)polymerization by Binuclear Nickel Phenoxyiminato Catalysts with Cofacial Orientation

A series of neutral binuclear nickel phenoxyiminato catalysts connected by rigid skeletons of different lengths have been efficiently synthesized. The rigid skeleton and bulky <i>tert</i>-butyl groups together force two nickel coordination planes to get close and stack in an <i>anti</i> cofacial fashion. With reduced nickel–nickel distances, these binuclear nickel complexes displayed higher catalytic activity, produced polymers with higher molecular weight, and showed less inhibition by the presence of additional polar monomers in ethylene polymerization and copolymerization. We attributed these effects to a favorable consequence of the enhanced bimetallic effect and steric hindrance due to the cofacial orientation

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 (<b>2-Ni</b>_<b>2</b>) and trinuclear (<b>3-Ni</b>_<b>3</b>) nickel catalysts have been efficiently synthesized. The trinuclear nickel complex <b>3-Ni</b>_<b>3</b> 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 <b>3-Ni</b>_<b>3</b>, generating regioregular and highly isotactic propylene with high <i>T</i>_m 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