Electronically variable imino-phenanthrolinyl-cobalt complexes; synthesis, structures and ethylene oligomerisation studies

Abstract

The 2-imino-1,10-phenanthroline ligands, 1,10-C 12H 7N 2-2-CR N(2,6- i-Pr 2-4-R 1-C 6H 2) [R = R 1 = H ( L1); R = H, R 1 = Br ( L2); R = H, R 1 = CN ( L3); R = H, R 1 = i-Pr ( L4); R = Me, R 1 = H ( L5); R = Me, R 1 = i-Pr ( L6)], have been prepared in high yield from the condensation reaction of 1,10-C 12H 7N 2-2-CR O (R = H, Me) with one equivalent of the corresponding 4-substituted 2,6-diisopropylaniline. The molecular structures of L2, L5 and L6 reveal the imino nitrogen atoms to adopt a transoid configuration with respect to the phenanthrolinyl nitrogen atoms. Treatment of Lx with one equivalent of CoCl 2 in n-BuOH at 90 °C gives the high spin complexes, ( Lx)CoCl 2 [ Lx = L1 ( 1a), L2 ( 1b), L3 ( 1c), L4 ( 1d), L5 ( 1e), L6 ( 1f)], in which the metal centres exhibit distorted square pyramidal geometries. Activation of 1a–1f with excess methylaluminoxane (MAO) gives catalysts that are modestly active for the oligomerisation of ethylene affording mainly linear α-olefins along with some degree of internal olefins. While the donor capability of the 4-position of the N-aryl group does not appear to affect the activity of the catalyst, it does have an influence on the ratio of α-olefins to internal olefins. Single crystal X-ray diffraction studies have been performed on L2, L5, L6, 1a, 1c and 1f.