A series of 1,2-bis(arylimino) acenaphthylenes (L1-L5) was synthesized and reacted with CoCl2 to afford the corresponding cobalt complexes LCoCl2 (C1-C5). All cobalt complexes have been fully characterized and in the case of C1 by single crystal X-ray diffraction; its molecular structure reveals a distorted tetrahedral geometry. On activation with AlEtCl2, C1-C5 efficiently polymerize isoprene to give polyisoprenes (PIs) with high contents of cis-1,4 units (between 90% and 94%). The influence of reaction temperature and [Al]/[Co] molar ratio on both catalytic performance and the microstructural properties of the PIs is investigated. (C) 2016 Wiley Periodicals, Inc.