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

The cobalt(II) chloride complexes, [2-(C 7 H 4 N 2 H)-8-(ArN)C 10 H 8 N]CoCl 2 (Ar = 2,6-Me 2 C 6 H 3 Co1; 2,6-Et 2 C 6 H 3 Co2; 2,6-i-Pr 2 C 6 H 3 Co3; 2,4,6-Me 3 C 6 H 2 Co4; 2,6-Et 2 -4-MeC 6 H 2 Co5; 2,4,6-t-Bu 3 C 6 H 2 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 C 6 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 × 10 5 g·mol -1 (Co) h -1 at 50 °C].