Cycloheptyl-fused NNO-ligands as electronically modifiable supports for M(II) (M=Co, Fe) chloride precatalysts; probing performance in ethylene oligo-/polymerization

The N,N,O‐cobalt(II), [2,3‐{C4H8C(NAr)}:5,6‐{C4H8C(O)}C5HN]CoCl2 (Ar = 2,6‐(CHPh2)2‐4‐MeC6H2 Co1, 2,6‐(CHPh2)2‐4‐EtC6H2 Co2, 2,6‐(CHPh2)2‐4‐ClC6H2 Co3, 2,6‐(CHPh2)2‐4‐FC6H2 Co4) and N,N,O‐iron(II) complexes, [2,3‐{C4H8C(NAr)}:5,6‐{C4H8C(O)}C5HN]FeCl2 (Ar = 2,6‐(CHPh2)2‐4‐MeC6H2 Fe1, 2,6‐(CHPh2)2‐4‐EtC6H2 Fe2, 2,6‐(CHPh2)2‐4‐ClC6H2 Fe3, 2,6‐(CHPh2)2‐4‐FC6H2 Fe4), each containing one sterically enhanced but electronically modifiable N‐2,6‐dibenzhydryl‐4‐R2‐phenyl group, have been prepared by a one‐pot template approach using α,α′‐dioxo‐2,3:5,6‐bis(pentamethylene)pyridine, the corresponding aniline along with the respective cobalt or iron salt in acetic acid. Distorted square pyramidal geometries are a feature of the molecular structures of Co1–Co4. Upon activation with MAO or MMAO, Co1–Co4 show good activities (up to 2.2 × 105 g mol−1(Co) h−1) affording short chain oligomers (C4–C30) with good α‐olefin selectivity. By contrast, Fe1–Fe4, in the presence of MMAO, displayed moderate activities (up 10.9 × 104 g(PE) mol−1(Fe) h−1) for ethylene polymerization forming low‐molecular‐weight linear polymers (up to 13.0 kg mol−1) incorporating saturated n‐propyl and i‐butyl chain ends. For both cobalt and iron, the precatalysts incorporating the more electron withdrawing 4‐R2‐substituents [Cl (Co3/Fe3), F (Co4/Fe4)] deliver the best catalytic activities, while with cobalt, these types of substituents additionally broaden the oligomeric distribution.