Oligomerisation of ethylene by bis(imino)pyridyliron and cobalt complexes

A series of bis(imino)pyridyliron and -cobalt complexes[{2,6-(CR=NAr)(2)C5H 3N}MX2] (R = H, Me; M = Fe, Co; X = Cl, Br) 8-16 containing imino-aryl ring s (Ar) with at least one small ortho substituent, as well as Ar = biphenyl and Ar = naphthyl, has been synthesised. Crystallographic analyses of compl exes 9 (Ar = 2,3-dimethylphenyl), 13 and 14 (Ar = biphenyl; X = Cl or Br, r espectively) reveal a distorted trigonal-bipyramidal geometry in the solid state, These complexes, in combination with methyl aluminoxane (MAO), are a ctive catalysts for the oligomerisation of ethylene, yielding >99% linear a lpha-olefin mixtures that follow a Schulz - Flory distribution. Iron ketimi ne (R = Me) precatalysts give the highest activities and a greater a-value than their aldimine (R = H) analogues. Cobalt precatalysts follow a similar trend, though their activities are almost two orders of magnitude lower th an those of the corresponding iron catalysts. Ethylene pressure studies on cobalt precatalyst 15 reveal a first-order dependence on ethylene for both the rate of propagation and the rate of chain transfer, and a pressure inde pendence of a the a value.