Sterically demanding Fe- and Co-based olefin polymerization catalysts 2-Fe and 2-Co bearing 2,6-bis(biphenylmethyl)-4-methylaniline substituted bis(imino)pyridine ligands were synthesized and evaluated for ethylene polymerization. The late-transition metal complexes were characterized by X-ray diffraction, NMR spectroscopy, and HRMS, while their resultant polymers were characterized by size-exclusion chromatography and H-1 NMR spectroscopy. While catalyst 2-Fe was inactive, catalyst 2-Co was found to polymerize ethylene and avoid any detectable chain-transfer to aluminum events that are known to plague other Fe- and Co-based catalyst systems and to limit molecular weight. Furthermore, 2-Co displays virtually perfect thermal stability up to 80 degrees C and shows greatly enhanced thermal stability at 90 degrees C as compared to previously reported analogues. These observations are attributed to the extreme steric demand imposed by the ligand which mitigates catalyst transfer, deactivation, and decomposition reactions. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3990-3995