Cobalt and nickel complexes supported by 2,6-bis(imidate)pyridyl ligands: Synthesis, characterization, and 1,3-butadiene polymerization studies

A series of 2,6-bis(imidate) pyridine ligated Co(II) and Ni(II) complexes with general formula of [2,6-(2,6-(Pr2C6H3N)-Pr-i = COR)(2)C5H3N]MX2 R = Me, M = Co, X = Cl (1a); R = Me, M = Ni, X = Br (2a); R = Et, M = Co, X = Cl (1b); R = Et, M = Ni, X = Br (2b); R = Pr-i, M = Co, X = Cl (1c); R = Pr-i, M = Ni, X = Br (2c); R = CH2CF3, M = Co, X = Cl (1d); R = CH2CF3, M = Ni, X = Br (2d); R = Ph, M = Co, X = Cl (1e); R = Ph, M = Ni, X = Br (2e); R = CH2Ph, M = Co, X = Cl (1f); R = CH2Ph, M = Ni, X = Br (2f)) were synthesized. Determined by single crystal X-ray analysis, complexes 1e and 2c with NNN tridentate ligands adopted approximate distorted square pyramidal configurations whereas complex 1f with tridentate NNO ligand displayed a distorted square pyramidal configuration. Activated by methylaluminoxane (MAO), these complexes exhibited high cis-1,4 selectivity towards 1,3-butadiene polymerization. The structure of substituent and polymerization conditions significantly influenced the catalytic behaviors of the complexes. The addition of PPh3 to the Co(II)-based systems enhanced the catalytic activity and switched the selectivity from cis-1,4 to 1,2 manner. (C) 2015 Elsevier B.V. All rights reserved.