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

The 2-imino-1,10-phenanthroline ligands, 1,10-C12H7N2-2-CRN(2,6-i-Pr2-4-R1-C6H2) [R = R1 = H (L1); R = H, R1 = Br (L2); R = H, R1 = CN (L3); R = H, R1 = i-Pr (L4); R = Me, R1 = H (L5); R = Me, R1 = i-Pr (L6)], have been prepared in high yield from the condensation reaction of 1,10-C12H7N2-2-CRO (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 CoCl2 in n-BuOH at 90 °C gives the high spin complexes, (Lx)CoCl2 [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.

A series of arylimino-phenanthroline-cobalt(II) chloride complexes have been synthesised in which the 4-position of the 2,6-diisopropyl-substituted aryl group has been systematically modified to include electron donating and electron withdrawing substituents; the performance of the complexes as precatalysts for ethylene oligomerisation has been probed.Figure optionsDownload as PowerPoint slide