Oligomerisation of Ethylene to Linear a-Olefins by New Cs- and C1-Symmetric [2,6-Bis(imino)pyridyl]iron and Cobalt Dichloride Complexes

A new family of Cs- and C1-symmetric 2,6-bis(imino)pyridyl ligands has been synthesized. These ligands, which differ from the known ones for the contemporaneous presence of alkyl and aryl substituent at the ketimine nitrogens, form stable five-coordinate complexes with FeCl2 and CoCl2. In combination with methyl aluminoxane (MAO), both iron and cobalt form effective and selective (>99%) catalysts for the oligomerisation of ethylene to Schulz-Flory distribution of a-olefins with the a factor ranging from 0.61 to 0.91. The iron catalysts exhibit TOF as high as 7 x 105 mol of C2H4 (mol of cat x h)-1, and are much more active than the cobalt analogues. Experiments at different ethylene pressures with the iron catalysts showed that both the propagation rate and the chain transfer rate are first order in ethylene pressure.