Article pubs.acs.org/Organometallics
Alternating α‑Olefin Distributions via Single and Double Insertions in Chromium-Catalyzed Ethylene Oligomerization Atanas K. Tomov,† James D. Nobbs,† Juan J. Chirinos,† Prabhjot K. Saini,† Robert Malinowski,† Sarah K. Y. Ho,† Craig T. Young,† David S. McGuinness,‡ Andrew J. P. White,† Mark R. J. Elsegood,§ and George J. P. Britovsek*,† †
Department of Chemistry, Imperial College London, Exhibition Road, London, SW7 2AZ, U.K. School of Physical Sciences−Chemistry, University of Tasmania, Private Bag 75, Hobart 7001, Australia § Chemistry Department, Loughborough University, Loughborough, LE11 3TU, U.K. ‡
S Supporting Information *
ABSTRACT: The catalytic oligomerization of ethylene with chromium-based complexes containing bis(benzimidazolemethyl)amine (BIMA) ligands results in alternating distributions of linear α-olefins (LAOs). Extremely high activities are obtained (>100 000 g mmol−1 h−1 bar−1) with N-alkyl-substituted BIMA ligands, whereas bulky groups on the central nitrogen or alternative central donors result in much lower activities. Variations in the ligand backbone, as well as methylation of the benzimidazole units, lead to reduction in activity. The alternating LAO distributions have been mathematically analyzed using second-order recurrence relations. The shape of the distributions is affected by ethylene pressure (1−4 bar) and by the cocatalyst to some degree. On the basis of the results and analysis presented herein, we propose that the alternating behavior originates from the ability of these chromium BIMA catalysts to undergo single as well as double ethylene insertion reactions. A minor second distribution (
