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 ,′-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 -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.