Six examples of alpha,alpha'-bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridine-cobalt(11) chlorides, [2,3:5,6{C4H8C(NAr)}(2)C5HN]CoCl2 (Ar = 2-(C5H9)-6-MeC6H3 Col, 2-(C6FI11)-6-MeC6H3 Co2, 2-(C8H15)-6-MeC6H3 Co3, 2-(C5H9)-4,6-Me2C6H2 Co4, 2-(C6FI11)-4,6-Me2C6H2 Co5, 2-(C8H15)-4,6-Me2C6H2 Co6), containing N-aryl groups that differ in either the ring size of the ortho-cycloalkyl substituents or the para-R group (R=H, Me), have been synthesized using a one-pot template approach. The molecular structure of Col highlights the ring puckering of both the ortho-cyclopentyl substituents and the two pyridine -fused seven-membered rings; a square-based pyramidal geometry is conferred about the metal center. On activation with either methylaluminoxane (MAO) or modified MAO (MMAO), all six complexes afforded strictly linear polyethylene (all Tm's > 130 degrees C) with high molecular weight (Mw up to 64.3 kg mol(-1)). Furthermore, all precatalysts displayed high activities (up to 2 x 10(6)g PE mot(-1) (Co) h(-1)) at temperatures between 20 and 60 degrees C with the catalytic activities correlating with the type of ortho-cycloalkyl substituent: cyclohexyl (Co2, Co5) > cyclopentyl (Col, Co4) > cyclooctyl (Co6, Co3) for either R = H or Me. The narrow unimodal distributions of the resulting polymers are consistent with single-site active species for the catalysts. (C) 2018 Elsevier Ltd. All rights reserved.