Unsymmetrical 11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-dione, incorporating a para-phenyl substituted pyridine unit fused by both 6- and 7-membered carbocyclic rings, has been prepared on the gram-scale via a multi-step procedure involving cyclization, hydrogenation and oxidation. Templating this diketone, in the presence of cobalt(II) chloride hexahydrate, with the corresponding aniline afforded in good yield five examples of doubly fused bis(arylimino)pyridine-cobalt(II) chlorides, Co1 (aryl = 2,6-dimethylphenyl), Co2 (2,6-diethylphenyl), Co3 (2,6-diisopropylphenyl), Co4 (2,4,6-trimethylphenyl) and Co5 (2,6-diethyl-4-methylphenyl). Structural characterization of Co1, Co2 and Co3 highlights the flexible nature of the inequivalent fused rings on the NNN’-ligand and the skewed disposition of the para-phenyl group. On activation with MAO, Co1–Co5 exhibited high activity for ethylene polymerization at 30 °C (up to 5.66 × 10⁶ g (PE) mol⁻¹ (Co) h⁻¹) with the relative order being as follows: Co4 > Co1 > Co5 > Co3 > Co2. All polyethylenes were strictly linear, while their molecular weights and dispersities showed some notable variations. For Co1, Co2, Co4 and Co5, all polymerizations were well controlled as evidenced by the narrow dispersities of their polymers (M_w/M_n range: 1.8–2.7), while their molecular weights (M_w range: 2.9–10.9 kg mol⁻¹) steadily increased in line with the greater steric properties of the N-aryl ortho-substituents. By contrast, the most hindered 2,6-diisopropyl counterpart Co3 displayed a broad distribution with bimodal characteristics (M_w/M_n = 10.3) and gave noticeably higher molecular weight polymer (M_w = 75.5 kg mol⁻¹). By comparison, the MMAO-activated catalysts were generally less active, but showed similar trends in molecular weight and polymer dispersity. End group analysis of selected polymers via ¹³C and ¹H NMR spectroscopy revealed the presence of both saturated and unsaturated polyethylenes in accordance with competing chain transfer pathways. Notably, when comparing Co3/MAO with its non-phenyl substituted analogue (E_2,6-iPr2Ph)CoCl₂/MAO, the former, though less controlled, displayed higher activity and molecular weight, a finding that points towards a role played by the remote para-phenyl group.

Through the implementation of a one-pot strategy, five examples of non-symmetrical [N,N-diaryl-11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-diimine]iron(II) chloride complexes (aryl = 2,6-Me₂Ph Fe1, 2,6-Et₂Ph Fe2, 2,6-i-Pr₂Ph Fe3, 2,4,6-Me₃Ph Fe4, and 2,6-Et₂-4-MePh Fe5), incorporating fused six- and seven-membered carbocyclic rings and appended with a remote para-phenyl group, were readily prepared. The molecular structures of Fe2 and Fe3 emphasize the variation in fused ring size and the skewed disposition of the para-phenyl group present in the N′,N,N″-ligand support. Upon activation with MAO or MMAO, Fe1–Fe5 all showed high catalytic activity for ethylene polymerization, with an exceptional level of 35.92 × 10⁶ g (PE) mol⁻¹ (Fe) h⁻¹ seen for mesityl-substituted Fe4/MMAO operating at 60 °C. All catalysts generated highly linear polyethylene with good control of the polymer molecular weight achievable via straightforward manipulation of run temperature. Typically, low molecular weight polymers with narrow dispersity (M_w/M_n = 1.5) were produced at 80 °C (MMAO: 3.7 kg mol⁻¹ and MAO: 4.9 kg mol⁻¹), while at temperatures between 40 °C and 50 °C, moderate molecular weight polymers were obtained (MMAO: 35.6–51.6 kg mol⁻¹ and MAO: 72.4–95.5 kg mol⁻¹). Moreover, analysis of these polyethylenes by ¹H and ¹³C NMR spectroscopy highlighted the role played by both β-H elimination and chain transfer to aluminum during chain termination, with the highest rate of β-H elimination seen at 60 °C for the MMAO-activated system and 70 °C for the MAO system.