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-R-2-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 x 10(5) g mol(-1)(Co) h(-1)) affording short chain oligomers (C-4-C-30) with good -olefin selectivity. By contrast, Fe1-Fe4, in the presence of MMAO, displayed moderate activities (up 10.9 x 10(4) g(PE) mol(-1)(Fe) h(-1)) for ethylene polymerization forming low-molecular-weight linear polymers (up to 13.0kgmol(-1)) incorporating saturated n-propyl and i-butyl chain ends. For both cobalt and iron, the precatalysts incorporating the more electron withdrawing 4-R-2-substituents [Cl (Co3/Fe3), F (Co4/Fe4)] deliver the best catalytic activities, while with cobalt, these types of substituents additionally broaden the oligomeric distribution. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3980-3989