Selectivity Effects on N,N,N′-Cobalt Catalyzed Ethylene Dimerization/Trimerization Dictated through Choice of Aluminoxane Cocatalyst

The cobalt(II) chloride complexes, [2-(C7H4N2H)-8-(ArN)C10H8N]CoCl2 (Ar = 2,6-Me2C6H3 Co1; 2,6-Et2C6H3 Co2; 2,6-i-Pr2C6H3 Co3; 2,4,6-Me3C6H2 Co4; 2,6-Et2-4-MeC6H2 Co5; 2,4,6-t-Bu3C6H2 Co6), have each been prepared by a one-pot template reaction of 2-benzoimidazolyl-5,6,7-trihydroquinolin-8-one with the corresponding aniline in the presence of cobalt dichloride. The molecular structures of the methanol adducts, Co1(HOMe) and Co4(HOMe), reveal distorted octahedral geometries that self-assemble to form networks based on NH···Cl and OH···Cl intermolecular hydrogen bonding interactions. On activation with methylaluminoxane (MAO), all six cobalt complexes catalyzed ethylene dimerization with a high selectivity for 1-butene. By marked contrast, with modified methylaluminoxane (MMAO), products the result of ethylene dimerization and trimerization were observed with a bias toward the C6 products (up to 49% 1-hexene). In general, the MMAO-promoted oligomerizations display higher catalytic activities with mesityl-containing Co4 the stand-out performer [7.60 × 105 g·mol–1(Co) h–1 at 50 °C].