Influencing α-Olefin Selectivity and PE-Wax Suppression Using Cyclohexyl-Fused 2-Imino-1,10-phenanthroline-iron Ethylene Oligomerization Catalysts

A one-pot strategy has been applied to access the cyclohexyl-fused 2-arylimino-1,10-phenanthroline-iron(II) complexes, [(LPh)2Fe][FeCl4] (Fe1) and (Laryl)FeCl2 (aryl = 2,6-F2Ph Fe2, 4-FPh Fe3, 4-MePh Fe4, 2,6-Me2Ph Fe5, 2,6-Et2Ph Fe6, 2,6-i-Pr2Ph Fe7, 2-FPh Fe8, 2-MePh Fe9), that differ in the steric/electronic profile of their N-aryl groups and the number of N,N,N-chelating ligands per iron. Structural characterization of Fe3, Fe5, Fe6, and Fe9, along with the ligand-oxidized species Fe5′ and Fe6′, highlights the distorted square pyramidal geometry about the iron centers and the flexibility/sensitivity of the fused carbocyclic ring. While bis(chelate) Fe1/MAO proved almost inactive for ethylene oligomerization, the majority of the mono(chelate) iron complexes exhibited high to moderate levels of activity under MAO activation. Indeed, the most active system, ortho-methyl Fe9/MAO, attained a level of 3.78 × 106 g oligomer mol–1 (Fe) h–1 displaying >99% selectivity for linear α-olefins (C4–C14+) that follow a Schulz–Flory distribution. When compared to the prototypical 2-imino-1,10-phenanthroline-iron oligomerization catalysts, the current fused systems are less active but are capable of suppressing the formation of polyethylene wax. We attribute this finding to the more open space displayed by the active iron center when compared to that seen in the parent system, leading to more facile β-H elimination.