“Coordinatively Open” Binuclear α-Diiminonickel Complexes: Polyethylene Branch Control via Cocatalyst

Polyethylene properties are profoundly determined by branching architecture, necessitating precise control during polymerization. Using 2-[bis(4-fluorophenyl)methyl]-4-chloro-6-methylphenyl-modified α-diimines to establish an open coordination structure while preserving the steric/electronic modulation around the nickel core, a series of binuclear nickel complexes (Ni1–Ni6) was synthesized. These complexes exhibit distinct open coordination environments, confirmed by binuclear motifs and calculated burial volumes. Upon activation with EtAlCl2 or EASC (Et3Al2Cl3), all complexes demonstrate high activities toward ethylene polymerization up to 14.8 × 106 g(PE) mol–1(Ni) h–1 and remarkable thermal stability exemplified by the activity of 3.8 × 106 g(PE) mol–1(Ni) h–1 at 70 °C. Notably, the resulting polyethylene products have tunable crystallinities from plastic to elastomeric due to their distinct branching properties. Cocatalyst choice (EtAlCl2 or EASC), with distinct Lewis acidities, leads to markedly different structural and property profiles. Use of EtAlCl2 as a cocatalyst affords higher molecular weight, low branching density, and elevated crystallinity. In contrast, EASC gives increased branching density, lower molecular weight, depressed melting temperatures, good elongation at break, and enhanced elastic recovery. These findings reveal a robust strategy for controlling branching architecture via cocatalyst selection, enabling tailored microstructures.