Unraveling Organoboron/Nickel Ion-Pair Interactions via Benchtop-Stable Carbyl Iminopyridyl NiII Complexes for Olefin Polymerization

Abstract

Abstract While current research on Ni-catalyzed olefin polymerization predominantly focuses on ligand design, ion-pair interactions remain largely unexplored. We report the development of air-stable carbyl iminopyridyl NiII precatalysts to enable an investigation of inner- and outersphere Ni ion-pairs. The use of innersphere organoboron counterions allows the Ni complexes to access higher molecular weight homo/co-polymers and regulate the density and distribution of polyethylene branches. Moreover, implementing a phenyl group on the tether carbon functioned as a rotational barrier, producing higher molecular weight polymers compared to methylsubstituted analogs. A controlled incorporation of shortchain branches was achieved under high ethylene pressure, circumventing the need for elaborate ligand design, low monomer pressures, and the copolymerization with α-olefins. DFT calculations further elucidated the ion-pair interactions and controlled chain-walking mechanism. Here, we provide a new perspective to manipulate the iminopyridyl NiII system leveraging both ion-pair interactions and ligand design to govern polyolefin molecular weights and microstructures.